BBA - Molecular Cell Research (v.1833, #12)
Editorial Board (i).
A C-terminal di-leucine motif controls plasma membrane expression of PMCA4b by Géza Antalffy; Katalin Pászty; Karolina Varga; Luca Hegedűs; Ágnes Enyedi; Rita Padányi (2561-2572).
Recent evidences show that the localization of different plasma membrane Ca2 + ATPases (PMCAs) is regulated in various complex, cell type-specific ways. Here we show that in low-density epithelial and endothelial cells PMCA4b localized mostly in intracellular compartments and its plasma membrane localization was enhanced upon increasing density of cells. In good correlation with the enhanced plasma membrane localization a significantly more efficient Ca2 + clearance was observed in confluent versus non-confluent HeLa cell cultures expressing mCherry-PMCA4b. We analyzed the subcellular localization and function of various C-terminally truncated PMCA4b variants and found that a truncated mutant PMCA4b-ct24 was mostly intracellular while another mutant, PMCA4b-ct48, localized more to the plasma membrane, indicating that a protein sequence corresponding to amino acid residues 1158–1181 contained a signal responsible for the intracellular retention of PMCA4b in non-confluent cultures. Alteration of three leucines to alanines at positions 1167–1169 resulted in enhanced cell surface expression and an appropriate Ca2 + transport activity of both wild type and truncated pumps, suggesting that the di-leucine-like motif 1167LLL was crucial in targeting PMCA4b. Furthermore, upon loss of cell–cell contact by extracellular Ca2 + removal, the wild-type pump was translocated to the early endosomal compartment. Targeting PMCA4b to early endosomes was diminished by the L1167–69A mutation, and the mutant pump accumulated in long tubular cytosolic structures. In summary, we report a di-leucine-like internalization signal at the C-tail of PMCA4b and suggest an internalization-mediated loss of function of the pump upon low degree of cell–cell contact.
Keywords: PMCA4b; Di-leucine motif; C-terminal tail; Endocytosis; Plasma membrane expression;
Ca2 + spiking activity caused by the activation of store-operated Ca2 + channels mediates TNF-α release from microglial cells under chronic purinergic stimulation by Masayuki Ikeda; Saki Tsuno; Takashi Sugiyama; Ayami Hashimoto; Kurumi Yamoto; Kouhei Takeuchi; Hiroyuki Kishi; Hiroyuki Mizuguchi; Shin-ichi Kohsaka; Tohru Yoshioka (2573-2585).
Cytokines released from microglia mediate defensive responses in the brain, but the underlying mechanisms are obscure. One proposed process is that nucleotide leakage or release from surrounding cells is sensed by metabotropic (P2Y) and ionotropic (P2X) purinergic receptors, which may trigger long-term intracellular Ca2 + flux and tumor necrosis factor α (TNF-α) release. Indeed, 3 h of exposure to ATP was required to evoke TNF-α release from a murine microglial cell line (MG5). A Ca2 + chelator, ethylene glycol tetraacetic acid (EGTA), reduced ATP-induced TNF-α release, suggesting that intracellular Ca2 + is important in this response. Therefore, Ca2 + sensor genes (YC3.6) were transfected into MG5 cells to investigate the Ca2 + dynamics underlying ATP-induced TNF-α release. The results demonstrated ATP-induced biphasic Ca2 + mobilization mediated by P2Y (~ 5 min) and P2X7 receptors (5–30 min). Moreover, Ca2 + spiking activity in cell processes progressively increased with a reduction in P2X7 receptor-mediated Ca2 + elevation during 3-h ATP stimulation. Increased Ca2 + spiking activity paralleled the reduction in thapsigargin-sensitive internal Ca2 + stores, dendrite extension, and expression of macrophage scavenger receptors with collagenous structure. The Ca2 + spiking activity was enhanced by a P2X7 receptor antagonist (A438079), but inhibited by a store-operated channel antagonist (SKF96365) or by co-transfection of small interference ribonucleic acid (siRNA) targeted on the channel component (Orai1). Furthermore, ATP-induced TNF-α release was enhanced by A438079 but was inhibited by SKF96365. Because store-operated channels (Stim1/Orai1) were expressed both in MG5 and primary microglial cultures, we suggest that P2X7 receptor signaling inhibits store-operated channels during ATP stimulation, and disinhibition of this process gates TNF-α release from microglial cells.
Keywords: Calcium oscillation; Cytokine release; Macrophage; Microglia; Yellow Cameleon;
Role of PTEN in modulation of ADP-dependent signaling pathways in vascular endothelial cells by Rosa Bretón-Romero; Hermann Kalwa; Santiago Lamas; Thomas Michel (2586-2595).
ADP plays critical signaling roles in the vascular endothelium. ADP receptors are targeted by several cardiovascular drugs, yet the intracellular pathways modulated by ADP are incompletely understood. These studies have identified important roles for the phosphatase PTEN in ADP-dependent modulation of the endothelial isoform of nitric oxide synthase (eNOS) as well as of lipid and protein kinase pathways in endothelial cells. We find that ADP-promoted eNOS activation as well as phosphorylation of p38 MAPK are enhanced by siRNA-mediated PTEN knockdown. However, the increase in ADP-dependent eNOS activation promoted by PTEN knockdown is abrogated by siRNA-mediated knockdown of p38 MAPK. These findings indicate that PTEN tonically suppresses both p38 phosphorylation as well as ADP-stimulated eNOS activity. A key enzymatic activity of PTEN is its role as a lipid phosphatase, catalyzing the dephosphorylation of phosphoinositol-3,4,5-trisphosphate (PIP3) to phosphoinositol-4,5-bisphosphate (PIP2). We performed biochemical analyses of cellular phospholipids in endothelial cells to show that siRNA-mediated PTEN knockdown leads to a marked increase in PIP3. Because these complex lipids activate the small GTPase Rac1, we explored the role of PTEN in ADP-modulated Rac1 activation. We used a FRET biosensor for Rac1 to show that ADP-dependent Rac1 activation is blocked by siRNA-mediated PTEN knockdown. We then exploited a FRET biosensor for PIP3 to show that the striking ADP-dependent increase in intracellular PIP3 is entirely blocked by PTEN knockdown. These studies identify a key role for PTEN in the modulation of lipid mediators involved in ADP receptor-regulated endothelial signaling pathways involving eNOS activation in vascular endothelial cells.
Keywords: ADP; Endothelium; Nitric oxide; Phosphoinositides;
Cyclical strain modulates metalloprotease and matrix gene expression in human tenocytes via activation of TGFβ by Eleanor R. Jones; Gavin C. Jones; Kirsten Legerlotz; Graham P. Riley (2596-2607).
Tendinopathies are a range of diseases characterised by degeneration and chronic tendon pain and represent a significant cause of morbidity. Relatively little is known about the underlying mechanisms; however onset is often associated with physical activity. A number of molecular changes have been documented in tendinopathy such as a decrease in overall collagen content, increased extracellular matrix turnover and protease activity. Metalloproteinases are involved in the homeostasis of the extracellular matrix and expression is regulated by mechanical strain. The aims of this study were to determine the effects of strain upon matrix turnover by measuring metalloproteinase and matrix gene expression and to elucidate the mechanism of action. Primary Human Achilles tenocytes were seeded in type I rat tail collagen gels in a Flexcell™ tissue train system and subjected to 5% cyclic uniaxial strain at 1 Hz for 48 h. TGFβ1 and TGFβRI inhibitor were added to selected cultures. RNA was measured using qRT-PCR and TGFβ protein levels were determined using a cell based luciferase assay. We observed that mechanical strain regulated the mRNA levels of multiple protease and matrix genes anabolically, and this regulation mirrored that seen with TGFβ stimulation alone. We have also demonstrated that the inhibition of the TGFβ signalling pathway abrogated the strain induced changes in mRNA and that TGFβ activation, rather than gene expression, was increased with mechanical strain. We concluded that TGFβ activation plays an important role in mechanotransduction. Targeting this pathway may have its place in the treatment of tendinopathy.
Keywords: Strain; Mechanotransduction; Transforming Growth Factor β; Metalloproteinase; Tendon;
IL-6 is produced by adipose-derived stromal cells and promotes osteogenesis by Jeong-Eun Huh; Soo Young Lee (2608-2616).
Although Toll-like receptors (TLRs) have been implicated in the regulation of stem cell functions, their role in osteogenic differentiation of adipose-derived stromal cells (ASCs) has not been reported. We found that ASCs express a restricted subset of TLRs, including TLR1–TLR5, and that TLR agonists such as Pam3CSK4 (TLR1/2 agonist), polyinosinic:polycytidylic acid (TLR3 agonist), lipopolysaccharide (TLR4 agonist), and flagellin (TLR5 agonist), but not R848 (TLR7/8 agonist), consistently induced osteogenic differentiation in murine-derived ASCs, which coincided with the TLR expression pattern of ASCs. Cytokine expression profiles induced by TLR agonists and results from subsequent functional assays indicated that interleukin-6 (IL-6) together with soluble IL-6 receptor (sIL-6R) enhanced osteogenic differentiation of ASCs by activating STAT3. Small interfering RNA (siRNA)-mediated STAT3-silencing blunted osteogenesis and the expression of osteogenic markers, whereas STAT3 overexpression resulted in an increase in osteogenesis. Consistently, STAT3 inhibitor treatment reduced osteogenesis, STAT3 phosphorylation, and expression of osteogenic markers including osterix. Chromatin immunoprecipitation (ChIP) assays indicated that STAT3 binding to the STAT3-binding sites on the osterix promoter increased during IL-6-stimulated osteogenesis. Our results thus establish TLRs as novel regulators of ASCs which signal through IL-6/STAT3 pathway and induce osterix expression as a part of the osteogenesis.
Keywords: TLR; IL-6; STAT3; Osterix; Osteogenesis; Adipose-derived stromal cell;
Hyperosmolarity-induced up-regulation of claudin-4 mediated by NADPH oxidase-dependent H2O2 production and Sp1/c-Jun cooperation by Akira Ikari; Kosuke Atomi; Yasuhiro Yamazaki; Hideki Sakai; Hisayoshi Hayashi; Masahiko Yamaguchi; Junko Sugatani (2617-2627).
Claudin-4 is exclusively localized in the tight collecting ducts in the renal tubule. We examined what molecular mechanism is involved in the regulation of claudin-4 expression. In Madin–Darby canine kidney cells, hyperosmolarity increased the expression level of claudin-4 and the production of reactive oxygen species, which were inhibited by diphenyleneiodonium (DPI), an NADPH oxidase inhibitor, and manganese (III) tetrakis (4-benzoic acid)porphyrin (MnTBAP), a scavenger of H2O2. Both hyperosmolarity and H2O2 increased p-ERK1/2 and p-JNK, which were inhibited by U0126, a MEK inhibitor, and SP600125, a JNK inhibitor, respectively. Immunoprecipitation assay showed that hyperosmolarity increased the association of nuclear Sp1 with c-Jun, which was inhibited by U0126 and SP600125. In mouse inner medullary collecting duct cells and rat kidney slices, hyperosmolarity increased the expression level of claudin-4, which was inhibited by DPI, MnTBAP, U0126, and SP600125. Hyperosmolarity increased luciferase reporter activity of claudin-4, which was inhibited by U0126, SP600125, Sp1 siRNA, and c-Jun siRNA. The activity was inhibited by the mutation in the Sp1 binding site. Chromatin immunoprecipitation assay and avidin–biotin conjugated DNA assay showed that Sp1 and c-Jun are associated with the Sp1 binding site. These results suggest that hyperosmolarity increases nuclear Sp1/c-Jun complex and the association of the complex with the Sp1 binding site, resulting in the segment-specific expression of claudin-4 in the kidney.
Keywords: Claudin-4; Hyperosmolarity; Sp1; c-Jun;
The giardial VPS35 retromer subunit is necessary for multimeric complex assembly and interaction with the vacuolar protein sorting receptor by Silvana L. Miras; María C. Merino; Natalia Gottig; Andrea S. Rópolo; María C. Touz (2628-2638).
The retromer is a pentameric protein complex that mediates the retrograde transport of acid hydrolase receptors between endosomes and the trans-Golgi network and is conserved across all eukaryotes. Unlike other eukaryotes, the endomembrane system of Giardia trophozoite is simple and is composed only of the endoplasmic reticulum and peripheral vesicles (PVs), which may represent an ancient organellar system converging compartments such as early and late endosomes and lysosomes. Sorting and trafficking of membrane proteins and soluble hydrolases from the endoplasmic reticulum to the PVs have been described as specific and conserved but whether the giardial retromer participates in receptor recycling remains elusive. Homologs of the retromer Vacuolar Protein Sorting (Vps35p, Vps26p, and Vps29p) have been identified in this parasite. Cloning the GlVPS35 subunit and antisera production enabled the localization of this protein in the PVs as well as in the cytosol. Tagged expression of the subunits was used to demonstrate their association with membranes, and immunofluorescence confocal laser scanning revealed high degrees of colabeling between the retromer subunits and also with the endoplasmic reticulum and PV compartment markers. Protein–protein interaction data revealed interaction between the subunits of GlVPS35 and the cytosolic domain of the hydrolase receptor GlVps. Altogether our data provide original information on the molecular interactions that mediate assembly of the cargo-selective retromer subcomplex and its involvement in the recycling of the acid hydrolase receptor in this parasite.
Keywords: Giardia lamblia; Retromer; Soluble hydrolase receptor; Endosome; Vacuolar protein sorting;
E3 ubiquitin ligase Fbw7 negatively regulates granulocytic differentiation by targeting G-CSFR for degradation by Savita Lochab; Pooja Pal; Isha Kapoor; Jitendra Kumar Kanaujiya; Sabyasachi Sanyal; Gerhard Behre; Arun Kumar Trivedi (2639-2652).
Tight control between activation and attenuation of granulocyte colony stimulating factor receptor (G-CSFR) signaling is essential to regulate survival, proliferation and differentiation of myeloid progenitor cells. Previous studies demonstrated negative regulation of G-CSFR through endosomal–lysosomal routing and ubiquitin–proteasome mediated degradation. However, very few E3 ubiquitin ligases are known to target G-CSFR for ubiquitin–proteasome pathway. Here we identified F-box and WD repeat domain-containing 7 (Fbw7), a substrate recognizing component of Skp–Cullin–F box (SCF) E3 ubiquitin Ligase physically associates with G-CSFR and promotes its ubiquitin-mediated proteasomal degradation. Our data shows that Fbw7 also interacts with and degrades G-CSFR-T718 (a truncated mutant of G-CSFR found in severe congenital neutropenia/acute myeloid leukemia (SCN/AML patients)) though at a quite slower rate compared to G-CSFR. We further show that glycogen synthase kinase 3 beta (GSK3β), like Fbw7 also targets G-CSFR and G-CSFR-T718 for degradation; however, Fbw7 and GSK3β are interdependent in targeting G-CSFR/G-CSFR-T718 for degradation because they are unable to degrade G-CSFR individually when either of them is knocked down. We further show that Fbw7 mediated downregulation of G-CSFR inhibits signal transducer and activator of transcription 3 (STAT3) phosphorylation which is required for G-CSF dependent granulocytic differentiation. In addition, our data also shows that inhibition of Fbw7 restores G-CSFR signaling leading to enhanced STAT3 activity resulting in massive granulocytic differentiation. These data indicate that Fbw7 together with GSK3β negatively regulates G-CSFR expression and its downstream signaling.
Keywords: Fbw7; G-CSFR; GSK3β; Ubiquitin–proteasome degradation;
Expression of metastasin S100A4 is essential for bone resorption and regulates osteoclast function by Malin C. Erlandsson; Mattias D. Svensson; Ing-Marie Jonsson; Li Bian; Noona Ambartsumian; Sofia Andersson; ZhiQi Peng; Jukka Vääräniemi; Claes Ohlsson; Karin M.E. Andersson; Maria I. Bokarewa (2653-2663).
S100A4 is a Ca-binding protein that regulates cell growth, survival, and motility. The abundant expression of S100A4 in rheumatiod arthritis contributes to the invasive growth of joint tissue and to bone damage. In the present study, we analysed the role of S100A4 in bone homeostasis.Peripheral quantitative computed tomography and histomorphometric analysis were performed in mice lacking the entire S100A4 protein (S100A4KO) and in wild-type (WT) counterparts treated with shRNA-lentiviral constructs targeting S100A4 (S100A4-shRNA). Control groups consisted of sex-matched WT counterparts and WT mice treated with a non-targeting RNA construct.S100A4 deficiency was associated with higher trabecular and cortical bone mass, increased number and thickness of trabeculi combined with larger periosteal circumference and higher predicted bone strength. S100A4 inhibition by shRNA led to an increase in cortical bone in WT mice. S100A4-deficieny was associated with a reduced number of functional osteoclasts. S100A4KO and S100A4-shRNA-treated bone marrow progenitors gave rise to a large number of small TRAP + cells with few nuclei and few pseudopodial processes. Poor osteoclastogenesis and the low resorptive capacity in S100A4Ko mice may be linked to low levels of surface integrins, impaired adhesion capacity, and poor multinucleation in S100A4-deficient osteoclasts, as well as a low content of proteolytic enzymes cathepsin K and MMP3 and MMP9 to break down the organic matrix.S100A4 emerges as a negative regulator of bone metabolism potentially responsible for the excessive bone turnover in conditions marked by high levels of S100A4 protein, such as inflammation and rheumatoid arthritis.
Keywords: S100A4; Osteopetrosis; Bone; Osteoclasts; Cathepsin K; Adhesion molecules;
cAMP inhibits migration, ruffling and paxillin accumulation in focal adhesions of pancreatic ductal adenocarcinoma cells: Effects of PKA and EPAC by Alex Burdyga; Alan Conant; Lee Haynes; Jin Zhang; Kees Jalink; Robert Sutton; John Neoptolemos; Eithne Costello; Alexei Tepikin (2664-2672).
We demonstrated that increasing intracellular cAMP concentrations result in the inhibition of migration of PANC-1 and other pancreatic ductal adenocarcinoma (PDAC) cell types. The rise of cAMP was accompanied by rapid and reversible cessation of ruffling, by inhibition of focal adhesion turnover and by prominent loss of paxillin from focal adhesions. All these phenomena develop rapidly suggesting that cAMP effectors have a direct influence on the cellular migratory apparatus. The role of two primary cAMP effectors, exchange protein activated by cAMP (EPAC) and protein kinase A (PKA), in cAMP-mediated inhibition of PDAC cell migration and migration-associated processes was investigated. Experiments with selective activators of EPAC and PKA demonstrated that the inhibitory effect of cAMP on migration, ruffling, focal adhesion dynamics and paxillin localisation is mediated by PKA, whilst EPAC potentiates migration.
Keywords: cAMP; PKA; EPAC; Cell migration; Paxillin; Pancreatic ductal adenocarcinoma;
Regulation of RNA interference by Hsp90 is an evolutionarily conserved process by Yang Wang; Rebecca Mercier; Tom C. Hobman; Paul LaPointe (2673-2681).
RNAi is a highly conserved mechanism in almost every eukaryote with a few exceptions including the model organism Saccharomyces cerevisiae. A recent study showed that the introduction of the two core components of canonical RNAi systems, Argonaute and Dicer, from another budding yeast, Saccharomyces castellii, restores RNAi in S. cerevisiae. We report here that a functional RNAi system can be reconstituted in yeast with the introduction of only S. castellii Dicer and human Argonaute2. Interestingly, whether or not TRBP2 was present, human Dicer was unable to restore RNAi with either S. castellii or human Argonaute. Contrary to previous reports, we find that human Dicer, TRBP2 and Argonaute2 are not sufficient to reconstitute RNAi in yeast when bona fide RNAi precursors are co-expressed. We and others have previously reported that Hsp90 regulates conformational changes in human and Drosophila Argonautes required to accommodate the loading of dsRNA duplexes. Here we show that the activities of both human and S. castellii Argonaute are subject to Hsp90 regulation in S. cerevisiae. In summary, our results suggest that regulation of the RNAi machinery by Hsp90 may have evolved at the same time as ancestral RNAi.
Keywords: Hsp90; RNAi; Argonaute; Dicer; Yeast;
Quantitative regulation of nuclear pore complex proteins by O-GlcNAcylation by Chiaki Mizuguchi-Hata; Yutaka Ogawa; Masahiro Oka; Yoshihiro Yoneda (2682-2689).
The nuclear pore complex (NPC) is a macromolecular assembly consisting of approximately 30 different proteins called nucleoporins. Several nucleoporins are O-GlcNAcylated, which is a post-translational modification in which the monosaccharide β-N-acetylglucosamine (GlcNAc) is attached to serine or threonine residues within proteins. However, the biological significance of this modification on nucleoporins remains obscure. Here we found that Nup62 and Nup88 protein levels were significantly decreased upon knockdown of O-GlcNAc transferase (OGT), which catalyzes the O-GlcNAcylation of intracellular proteins. Although Nup88, unlike Nup62, was not recognized by an anti-O-GlcNAc antibody or WGA–HRP, knockdown of Nup62 caused a reduction in Nup88 protein levels, suggesting that the observed decrease in Nup88 in OGT knocked-down cells is due to a decrease in Nup62. Furthermore, we found that Nup88 was preferentially associated with O-GlcNAcylated Nup62 compared with non-O-GlcNAcylated Nup62. These results indicate that Nup62 protein levels are primarily maintained by O-GlcNAcylation and that Nup88 is quantitatively regulated through its interaction with O-GlcNAcylated Nup62.
Keywords: Nuclear pore complex; O-GlcNAcylation; Nup62; Nup88; siRNA;
ErbB4 is an upstream regulator of TTF-1 fetal mouse lung type II cell development in vitro by Katja Zscheppang; Ulrike Giese; Stefan Hoenzke; Dorothea Wiegel; Christiane E.L. Dammann (2690-2702).
TTF-1 is an important transcription factor in lung development and lung disease and is essential for lung cell differentiation, specifically surfactant protein (Sftp) expression. The molecular mechanisms that drive the expression and transcriptional control of TTF-1 are not fully understood. In the fetal lung, ErbB4 functions as a transcriptional co-factor and regulates the timely onset of fetal Sftp expression. We speculate that ErbB4 is an upstream regulator of TTF-1 and regulates Sftpb expression via this pathway in alveolar type II cells. Neuregulin-induced ErbB4 and TTF-1 signaling interactions were studied by co-immunoprecipitation and confocal microscopy. Overexpression of ErbB4 and TTF-1 was analyzed in its effect on cell viability, Sftpb expression, TTF-1 expression, and Sftpb and TTF-1 promoter activity. The effect of ErbB4 deletion and ErbB4 nuclear translocation on TTF-1 expression was studied in primary fetal type II epithelial cells, isolated from transgenic HER4heart(−/−) mice. ErbB4 ligand neuregulin induces ErbB4 and TTF-1 co-precipitation and nuclear colocalization. Combined ErbB4 and TTF-1 overexpression inhibits cell viability, while promoting Sftpb expression more than single overexpression of each protein. NRG stimulates TTF-1 expression in ErbB4-overexpressing epithelial cells, while this effect is absent in ErbB4-depleted cells. In primary fetal type II cells, ErbB4 nuclear translocation is critical for its regulation of TTF-1-induced Sftpb upregulation. TTF-1 overexpression did not overcome this important requirement. We conclude that ErbB4 is a critical upstream regulator of TTF-1 in type II epithelial cells and that this interaction is important for Sftpb regulation.
Keywords: Lung development; Neuregulin; Surfactant; Type II cell;
Ca 2 +-binding protein expression in primary human thyrocytes by S. Lorenz; G. Aust; K. Krohn (2703-2713).
We recently identified several Ca2 +-binding proteins (CaBP) from the S100 and annexin family to be regulated by TSH in FRTL-5 cells. Here, we study the regulation of S100A4, S100A6 and ANXA2 in primary human thyrocytes (PHT) derived from surrounding tissues (ST), cold benign thyroid nodules (CTN) and autonomously functioning thyroid nodules (AFTN). We investigated the expression and regulation of CaBP and the effect of their expression on Ca2 + and TSHR signaling. We used an approach that accounts for the potential of an individual PHT culture to proliferate or to express thyroid differentiation features by assessing the expression of FOS and TPO. We found a strong correlation between the regulation of CaBP and the proliferation-associated transcription factor gene FOS. PKA and MEK1/2 were regulators of ANXA2 expression, while PI3-K and triiodothyronine were additionally involved in S100 regulation. The modulated expression of CaBP was reflected by changes in ATP-elicited Ca2 + signaling in PHT. S100A4 increased the ratio of subsequent Ca2 + responses and showed a Ca2 + buffering effect, while ANXA2 affected the first Ca2 + response to ATP. Overexpression of S100A4 led to a reduced activation of NFAT by TSH. Using S100A4 E33Q, D63N, F72Q and Y75K mutants we found that the effects of S100A4 expression on Ca2 + signaling are mediated by protein interaction. We present evidence that TSH has the ability to fine-tune Ca2 + signals through the regulation of CaBP expression. This represents a novel putative cross-regulating mechanism in thyrocytes that could affect thyrocyte signaling and physiology.
Keywords: Thyroid signal transduction; Thyroid physiology; Thyroid cancer; Calcium-binding protein; S100 protein; Annexin;
Protein aggregation propensity is a crucial determinant of intracellular inclusion formation and quality control degradation by Anna Villar-Piqué; Salvador Ventura (2714-2724).
Protein aggregation is linked to many pathological conditions, including several neurodegenerative diseases. The aggregation propensities of proteins are thought to be controlled to a large extent by the physicochemical properties encoded in the primary sequence. We have previously exploited a set of amyloid β peptide (Aβ42) variants exhibiting a continuous gradient of intrinsic aggregation propensities to demonstrate that this rule applies in vivo in bacteria. In the present work we have characterized the behavior of these Aβ42 mutants when expressed in yeast. In contrast to bacteria, the intrinsic aggregation propensity is gated by yeast, in such a way that this property correlates with the formation of intracellular inclusions only above a specific aggregation threshold. Proteins displaying solubility levels above this threshold escape the inclusion formation pathway. In addition, the most aggregation-prone variants are selectively cleared by the yeast quality control degradation machinery. Thus, both inclusion formation and proteolysis target the same aggregation-prone variants and cooperate to minimize the presence of these potentially dangerous species in the cytosol. The demonstration that sorting to these pathways in eukaryotes is strongly influenced by protein primary sequence should facilitate the development of rational approaches to predict and hopefully prevent in vivo protein deposition.
Keywords: Protein aggregation; Protein folding; Amyloid peptide; Fluorescent reporter; Protein degradation; Yeast;
Sumoylation regulates nuclear localization and function of zinc finger transcription factor ZIC3 by Li Chen; Yanlin Ma; Ling Qian; Jun Wang (2725-2733).
ZIC3, an X-linked zinc finger transcription factor, was the first identified gene involved in establishing normal left–right patterning in humans. Mutations in the Zic3 gene in patients cause heterotaxy, which includes congenital heart defects. However, very little is known about how the function of the ZIC3 protein is regulated. Sumoylation is a posttranslational modification process in which a group of small ubiquitin-like modifier (SUMO) proteins is covalently attached to targets via a series of enzymatic reactions. Here, we report for the first time that sumoylation targets human ZIC3 primarily on the consensus lysine residue K248, which is critical for the nuclear retention of ZIC3. Consequently, SUMO modification potentiates the repressive activity of ZIC3 on the promoter of its target gene cardiac α-actin, and the mutation of lysine 248 to arginine (K248R) abolishes its repressive function. We further revealed that ZIC3 variants with mutations found in human patients with congenital anomalies exhibit aberrant sumoylation activity, which at least partially accounts for their cytoplasmic diffusion. Improved sumoylation of human disease-associated ZIC3 variants reestablishes their nuclear occupancy in the presence of SUMO E3 ligase and SUMO-1. Thus, the altered sumoylation status of ZIC3 underpins the developmental abnormalities associated with these ZIC3 mutants. The SUMO targeting consensus sequence in ZIC3 is highly conserved in its paralogs and orthologs, pointing to sumoylation as a general mechanism underlying the functional control of ZIC proteins. This study provides a potential therapeutic strategy to regain the normal subcellular distribution and function of ZIC3 mutants by restoring SUMO conjugation.
Keywords: ZIC3; SUMO; PIAS; Nuclear import/export;
The small GTPase N-Ras regulates extracellular matrix synthesis, proliferation and migration in fibroblasts by Isabel Fuentes-Calvo; Piero Crespo; Eugenio Santos; José M. López-Novoa; Carlos Martínez-Salgado (2734-2744).
In addition to their role as oncogenes, Ras GTPases are key regulators of cell function. There is a proven relationship between the signaling pathways of transforming growth factor-β1 (TGF- β1) and Ras GTPases. Each of the Ras isoforms (H, N and K) exhibits specific modulatory activity on different cellular pathways. Our purpose has been to study some of the mechanisms involved in the development of renal fibrosis, assessing the individual role of N-Ras in basal and TGF-β1-mediated extracellular matrix (ECM) synthesis, proliferation, and migration in immortalized N-Ras deficient fibroblasts (N-ras −/−). Compared to normal counterparts, fibroblasts deficient for N-Ras exhibited higher basal activity levels of phosphatidylinositol-3-kinase (PI3K)/Akt and MEK/Erk, accompanied by upregulated collagen synthesis and diminished proliferation and migration rates. We found that the absence of N-Ras did not affect TGF-β1-induced proliferation and migration, which required PI3K/Akt but not Erk1/2 activation. Similar effector pathway dependence was found for fibronectin and collagen type I expression.Our results indicate that N-Ras might contribute to renal fibrosis through the down-regulation of ECM synthesis and up-regulation proliferation and migration modulating Akt activation. N-Ras also regulates TGF-β1-induced collagen I and fibronectin expression through Erk-independent pathways.
Keywords: Ras proteins; PI3K/Akt; MEK/ERK 1/2; Transforming growth factor-β1; Renal fibrosis;
Specificity protein 4 functionally regulates the transcription of NMDA receptor subunits GluN1, GluN2A, and GluN2B by Anusha Priya; Kaid Johar; Margaret T.T. Wong-Riley (2745-2756).
N-Methyl-d-aspartate (NMDA) receptors are major glutamatergic receptors involved in most excitatory neurotransmission in the brain. The transcriptional regulation of NMDA receptors is not fully understood. Previously, we found that the GluN1 and GluN2B subunits of the NMDA receptor are regulated by nuclear respiratory factors 1 and 2 (NRF-1 and NRF-2). NRF-1 and NRF-2 also regulate all 13 subunits of cytochrome c oxidase (COX), a critical energy-generating enzyme, thereby coupling neuronal activity and energy metabolism at the transcriptional level. Specificity protein (Sp) is a family of transcription factors that bind to GC-rich regions, with Sp1, Sp3, and Sp4 all binding to the same cis- motifs. Sp1 and Sp3 are ubiquitously expressed, whereas Sp4 expression is restricted to neurons and testicular cells. Recently, we found that the Sp1 factor regulates all subunits of COX. The goal of the present study was to test our hypothesis that the Sp factors also regulate specific subunits of NMDA receptors, and that they function with NRF-1 and NRF-2 via one of three mechanisms: complementary, concurrent and parallel, or a combination of complementary and concurrent/parallel. By means of multiple approaches we found that Sp4 functionally regulated GluN1, GluN2A, and GluN2B, but not GluN2C. On the other hand, Sp1 and Sp3 did not regulate these subunits as previously thought. Our data suggest that Sp4 operates in a complementary and concurrent/parallel manner with NRF-1 and NRF-2 to mediate the tight coupling between energy metabolism and neuronal activity at the molecular level.
Keywords: Sp4; GluN1; GluN2A; GluN2B; NMDA; Gene regulation;
A new mechanism of RhoA ubiquitination and degradation: Roles of SCFFBXL19 E3 ligase and Erk2 by Jianxin Wei; Rachel K. Mialki; Su Dong; Andrew Khoo; Rama K. Mallampalli; Yutong Zhao; Jing Zhao (2757-2764).
RhoA is a small GTPase multifunctional protein that regulates cell proliferation and cytoskeletal reorganization. Regulation of its protein stability plays an important role in its biological functions. We have shown that a Skp1-Cul1-F-box (SCF) FBXL19 E3 ubiquitin ligase targets Rac1, a related member of the Rho family for ubiquitination and degradation. Here, SCFFBXL19 mediates RhoA ubiquitination and proteasomal degradation in lung epithelial cells. Ectopically expressed FBXL19 decreased RhoA wild type, active, and inactive forms. Cellular depletion of FBXL19 increased RhoA protein levels and extended its half-life. FBXL19 bound the small GTPase in the cytoplasm leading to RhoA ubiquitination at Lys135. A RhoAK135R mutant protein was resistant to SCFFBXL19-mediated ubiquitination and degradation and exhibited a longer lifespan. Protein kinase Erk2-mediated phosphorylation of RhoA was both sufficient and required for SCFFBXL19-mediated RhoA ubiquitination and degradation. Thus, SCFFBXL19 targets RhoA for its disposal, a process regulated by Erk2. Ectopically expressed FBXL19 reduced phosphorylation of p27 and cell proliferation, a process mediated by RhoA. Further, FBXL19 cellular expression diminished lysophosphatidic acid (LPA)-induced phosphorylation of myosin light chain (MLC) and stress fiber formation. Hence, SCFFBXL19 functions as a RhoA antagonist during cell proliferation and cytoskeleton rearrangement. These results provide the first evidence of an F-box protein targeting RhoA thereby modulating its cellular lifespan that impacts cell proliferation and cytoskeleton rearrangement.
Keywords: Small GTPase protein; Protein stability; Ubiquitin-proteasome system; Phosphorylation; Cell proliferation; Stress fiber;
Yeast growth in raffinose results in resistance to acetic-acid induced programmed cell death mostly due to the activation of the mitochondrial retrograde pathway by Nicoletta Guaragnella; Maša Ždralević; Paolo Lattanzio; Domenico Marzulli; Tammy Pracheil; Zhengchang Liu; Salvatore Passarella; Ersilia Marra; Sergio Giannattasio (2765-2774).
In order to investigate whether and how a modification of mitochondrial metabolism can affect yeast sensitivity to programmed cell death (PCD) induced by acetic acid (AA-PCD), yeast cells were grown on raffinose, as a sole carbon source, which, differently from glucose, favours mitochondrial respiration. We found that, differently from glucose-grown cells, raffinose-grown cells were mostly resistant to AA-PCD and that this was due to the activation of mitochondrial retrograde (RTG) response, which increased with time, as revealed by the up-regulation of the peroxisomal isoform of citrate synthase and isocitrate dehydrogenase isoform 1, RTG pathway target genes. Accordingly, the deletion of RTG2 and RTG3, a positive regulator and a transcription factor of the RTG pathway, resulted in AA-PCD, as shown by TUNEL assay. Neither deletion in raffinose-grown cells of HAP4, encoding the positive regulatory subunit of the Hap2,3,4,5 complex nor constitutive activation of the RTG pathway in glucose-grown cells due to deletion of MKS1, a negative regulator of RTG pathway, had effect on yeast AA-PCD. The RTG pathway was found to be activated in yeast cells containing mitochondria, in which membrane potential was measured, capable to consume oxygen in a manner stimulated by the uncoupler CCCP and inhibited by the respiratory chain inhibitor antimycin A. AA-PCD resistance in raffinose-grown cells occurs with a decrease in both ROS production and cytochrome c release as compared to glucose-grown cells en route to AA-PCD.
Keywords: Mitochondria; Programmed cell death; Retrograde pathway; Yeast; Raffinose; Acetic acid;
A low temperature-inducible protein AtSRC2 enhances the ROS-producing activity of NADPH oxidase AtRbohF by Tomoko Kawarazaki; Sachie Kimura; Ayako Iizuka; Shigeru Hanamata; Hitomi Nibori; Masataka Michikawa; Aya Imai; Mitsutomo Abe; Hidetaka Kaya; Kazuyuki Kuchitsu (2775-2780).
Reactive oxygen species (ROS) produced by NADPH oxidases play critical roles in plant environmental responses. Arabidopsis thaliana NADPH oxidase AtRbohF-mediated ROS-production is involved in abiotic stress responses. Because overproduction of ROS is highly toxic to cells, the activity of AtRbohF needs to be tightly regulated in response to diverse stimuli. The ROS-producing activity of AtRbohF is activated by Ca2 + and protein phosphorylation, but other regulatory factors for AtRbohF are mostly unknown. In this study, we screened for proteins that interact with the N-terminal cytosolic region of AtRbohF by a yeast two-hybrid screen, and isolated AtSRC2, an A. thaliana homolog of SRC2 (soybean gene regulated by cold-2). A co-immunoprecipitation assay revealed that AtSRC2 interacts with the N-terminal region of AtRbohF in plant cells. Intracellular localization of GFP-tagged AtSRC2 was partially overlapped with that of GFP-tagged AtRbohF at the cell periphery. Co-expression of AtSRC2 enhanced the Ca2 +-dependent ROS-producing activity of AtRbohF in HEK293T cells, but did not affect its phosphorylation-dependent activation. Low-temperature treatment induced expression of the AtSRC2 gene in Arabidopsis roots in proportion to levels of ROS production that was partially dependent on AtRbohF. Our findings suggest that AtSRC2 is a novel activator of Ca2 +-dependent AtRbohF-mediated ROS production and may play a role in cold responses.
Keywords: Arabidopsis thaliana; AtRbohF; Cold stress; NADPH oxidase (NOX); Reactive oxygen species (ROS); Respiratory burst oxidase homologue (Rboh);
Post-translational membrane insertion of an endogenous YidC substrate by Philip J. Robinson; Cheryl A. Woolhead (2781-2788).
Membrane protein insertion is controlled by proteinaceous factors embedded in the lipid bilayer. Bacterial inner membrane proteins utilise the Sec translocon as the major facilitator of insertion; however some proteins are Sec independent and instead require only YidC. A common feature of YidC substrates is the exposure of a signal anchor sequence when translation is close to completion; this allows minimal time for targeting and favours a post-translational insertion mechanism. Despite this there is little evidence of YidC's post-translational activity. Here we develop an experimental system that uncouples translation and insertion of the endogenous YidC substrate F0c (subunit c of the F0F1 ATP synthase). In this process we (i) develop a novel one step purification method for YidC, including an on column membrane reconstitution, (ii) isolate a soluble form of F0c and (iii) show that incubation of F0c with YidC proteoliposomes results in a high level of membrane integration. Conformational analyses of inserted F0c through Blue Native PAGE and fluorescence quenching reveal a native, oligomerised structure. These data show that YidC can act as a post-translational insertase, a finding which could explain the absence of a ribosome binding domain on YidC. This correlates with the post-translational activity of other YidC family members lacking the ribosome binding domain.Display Omitted
Keywords: YidC; Membrane insertion; Reconstitution; Targeting; F0c;
GDNF family ligand dependent STAT3 activation is mediated by specific alternatively spliced isoforms of GFRα2 and RET by Lihan Zhou; Heng-Phon Too (2789-2802).
Neurturin (NRTN), a member of the GDNF family of ligands (GFL), is currently investigated in a series of clinical trials for Parkinson's disease. NRTN signals through its cognate receptor GFRα2 and co-receptor RET to induce neurite outgrowth, but the underlying mechanism remains to be better understood. STAT3 was previously shown to be activated by oncogenic RET, independent of ligand and GFRα. In this study, we demonstrated that NRTN induced serine727 but not tyrosine705 phosphorylation of STAT3 in primary cortical neuron and neuronal cell lines. Remarkably, STAT3 phosphorylation was found to be mediated specifically by GFRα2c and RET9 isoforms. Furthermore, serine but not tyrosine dominant negative mutant of STAT3 impaired NRTN induced neurite outgrowth, indicative of the role of STAT3 as a downstream mediator of NRTN function. Similar to NGF, the NRTN induced P-Ser-STAT3 was localized to the mitochondria but not to the nucleus. Mitochondrial STAT3 was further found to be intimately involved in NRTN induced neurite outgrowth. Collectively, these findings demonstrated the hitherto unrecognized and novel role of specific GFRα2 and RET isoforms in mediating NRTN activation of STAT3 and the transcription independent mechanism whereby the mitochondria localized P-Ser-STAT3 mediated NRTN induced neurite outgrowth.
Keywords: GDNF; NRTN; GFRα2; RET; Receptor isoform; Mitochondrial STAT3;
The Akt substrate Girdin is a regulator of insulin signaling in myoblast cells by Angelika Hartung; Anna-Maria Ordelheide; Harald Staiger; Martina Melzer; Hans-Ulrich Häring; Reiner Lammers (2803-2811).
Akt kinases are important mediators of the insulin signal, and some Akt substrates are directly involved in glucose homeostasis. Recently, Girdin has been described as an Akt substrate that is expressed ubiquitously in mammals. Cells overexpressing Girdin show an enhanced Akt activity. However, not much is known about Girdin's role in insulin signaling. We therefore analyzed the role of Girdin in primary human myotubes and found a correlation between Girdin expression and insulin sensitivity of the muscle biopsy donors, as measured by a hyperinsulinemic–euglycemic clamp. To understand this finding on a cellular level, we then investigated the function of Girdin in C2C12 mouse myoblasts. Girdin knock-down reduced Akt and insulin receptor substrate-1 phosphorylation. In contrast, stable overexpression of Girdin in C2C12 cells strikingly increased insulin sensitivity through a massive upregulation of the insulin receptor and enhanced tyrosine phosphorylation of insulin receptor substrate-1. Furthermore, Akt and c-Abl kinases were constitutively activated. To investigate medium-term insulin responses we measured glucose incorporation into glycogen. The Girdin overexpressing cells showed a high basal glycogen synthesis that peaked already at 1 nM insulin. Taken together, we characterized Girdin as a new and major regulator of the insulin signal in myoblasts and skeletal muscle.
Keywords: Girdin; C2C12; Insulin sensitivity; Akt; Abl;
Nuclear localization of aldolase A correlates with cell proliferation by Piotr Mamczur; Andrzej Gamian; Jerzy Kolodziej; Piotr Dziegiel; Dariusz Rakus (2812-2822).
Muscle fructose 1,6-bisphosphate aldolase (ALDA) is a glycolytic enzyme which may localize both in nuclei and cytoplasm of cells, however its role in the nuclei is unclear. Here, we demonstrate the links between subcellular localization of ALDA and the cell cycle progression as well as the availability of energetic substrates. Results of our studies indicate that nuclear localization of ALDA correlates with the proliferative activity of the cells and with the expression of Ki-67, a marker of proliferation, both in the KLN-205 (mouse lung cancer cells) and human squamous cell lung cancer cells (hSCC). Chemically-induced block of cell cycle entry in S phase and the inhibition of transcription stimulate removal of ALDA from cells nuclei suggesting that nuclear ALDA is involved in cells proliferation. On the other hand, subcellular distribution of the enzyme also depends on the stress and pro-survival signals mediated by the Akt and the p38 pathways and, in non-proliferating cells, on the availability of glucose and lactate. The results presented here point to ALDA as a factor involved in the regulation of cells proliferation.
Keywords: Aldolase; KLN-205; Ki-67; Squamous cell lung cancer;
Connective tissue growth factor induces collagen I expression in human lung fibroblasts through the Rac1/MLK3/JNK/AP-1 pathway by Chien-Huang Lin; Ming-Chih Yu; Wan-Hsuan Tung; Tzu-Ting Chen; Chung-Chi Yu; Chih-Ming Weng; Yan-Jyu Tsai; Kua-Jen Bai; Chuang-Ye Hong; Ming-Hsien Chien; Bing-Chang Chen (2823-2833).
Connective tissue growth factor (CTGF) plays an important role in lung fibrosis. In this study, we investigated the role of Rac1, mixed-lineage kinase 3 (MLK3), c-Jun N-terminal kinase (JNK), and activator protein-1 (AP-1) in CTGF-induced collagen I expression in human lung fibroblasts. CTGF caused concentration- and time-dependent increases in collagen I expression. CTGF-induced collagen I expression was inhibited by the dominant negative mutant (DN) of Rac1 (RacN17), MLK3DN, MLK3 inhibitor (K252a), JNK1DN, JNK2DN, a JNK inhibitor (SP600125), and an AP-1 inhibitor (curcumin). Treatment of cells with CTGF caused activation of Rac1, MLK3, JNK, and AP-1. The CTGF-induced increase in MLK3 phosphorylation was inhibited by RacN17. Treatment with RacN17 and the MLK3DN inhibited CTGF-induced JNK phosphorylation. CTGF caused increases in c-Jun phosphorylation and the recruitment of c-Jun and c-Fos to the collagen I promoter. Furthermore, stimulation of cells with the CTGF resulted in increases in AP-1-luciferase activity; this effect was inhibited by Rac1N17, MLK3DN, JNK1DN, and JNK2DN. Moreover, CTGF-induced α-smooth muscle actin (α-SMA) expression was inhibited by the procollagen I small interfering RNA (siRNA). These results suggest for the first time that CTGF acting through Rac1 activates the MLK3/JNK signaling pathway, which in turn initiates AP-1 activation and recruitment of c-Jun and c-Fos to the collagen I promoter and ultimately induces collagen I expression in human lung fibroblasts.Display Omitted
Keywords: Connective tissue growth factor; Collagen I; Signal transduction; Lung fibrosis; Fibroblasts;
Role of PTHrP in human intestinal Caco-2 cell response to oxidative stress by Virginia Lezcano; Claudia Gentili; Ana Russo de Boland (2834-2843).
We have previously demonstrated that parathyroid hormone (PTH) induces apoptosis in human colon adenocarcinoma Caco-2 cells but the effects of its tumoral analog PTH-related peptide (PTHrP) in this cell line are still unknown. In the present work we investigated whether PTHrP, as PTH, is able to induce Caco-2 cell apoptosis or if it exerts protective effects under apoptotic conditions. Using Caco-2 cells cultured under serum deprivation in the presence or absence of PTHrP we demonstrated that, differently to PTH, its analog employed at the same concentration (10− 8 M) is not a pro-apoptotic hormone. Cells were exposed to an oxidative insult in the form of hydrogen peroxide to induce apoptosis, which leads to a 50% loss of cell viability determined by MTS assay, morphological changes observed under fluorescence microscopy and Western blot analysis. Herein we demonstrate, for the first time, that pre-treatment with PTHrP prior to H2O2 incubation, prevents cell death induced by the apoptotic inductor; and using specific inhibitors we evidenced that protein kinase B (AKT), extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase 1/2 (JNK1/2) and p38 mitogen-activated protein kinase (MAPK) mediate this anti-apoptotic effect. Also, we found that PTHrP decreases the pro-apoptotic protein BAX levels and increases the protein expression of the anti-apoptotic HSP27. Immunoblot analysis revealed that H2O2 increases the phosphorylation levels of AKT and MAPKs, exhibiting a cellular defense response; and consequently increases phospho-BAD levels. The H2O2-induced activation of protein kinases is reverted when cells are pre-treated with PTHrP. Altogether these results evidence a protective effect of PTHrP under apoptotic conditions in intestinal cells, which may be mediated by AKT and MAPKs.
Keywords: PTHrP; Caco-2 cell; Apoptosis; MAPK; AKT;
Reconstitution of CKMT1 expression fails to rescue cells from mitochondrial membrane potential dissipation: Implications for controlling RNAi experiments by Christoph Datler; Stefan Grimm (2844-2855).
RNA interference (RNAi) is an essential method in molecular biology to reduce the expression of target genes and thereby determine their function. Since this tool is known to also have unspecific effects, control experiments are needed, chiefly among them the exclusion of off-target effects and the reconstitution of the genes' expression for the rescue of the cellular RNAi effects. We show here that the knock-down of the mitochondrial creatine kinase-1 (CKMT1) by RNA interference causes the dissipation of the mitochondrial membrane potential ΔΨm. This was accomplished with 11 different RNAi constructs designed to target 7 distinct exons as well as exon/intron junctions making unspecific off-target effects unlikely. However, all our attempts failed to rescue human cells from ΔΨm dissipation by the expression of CKMT1 alleles not targeted by RNAi. This included the transient and stable expression of the murine CKMT1 homologue, the expression of human codon usage-modified alleles, the transfection of a novel splice-isoform of CKMT1, and even the introduction of a human genomic clone for CKMT1 with codon usage changes. Our results indicate that while off-target effects of RNA interference can easily be addressed, the rescue of the knock-down phenotype is not necessarily achievable.
Keywords: RNA interference; Phenotype rescue; Creatine kinase-1;
Calixarene bypasses human pancreatic cancer aggressiveness: Downregulation of receptor tyrosine kinases and induction of cell death by reticulum stress and autophagy by Karin Juliane Pelizzaro-Rocha; Marcelo Bispo de Jesus; Roberta Regina Ruela-de-Sousa; Celso Vataru Nakamura; Fabiano Souza Reis; Angelo de Fátima; Carmen Veríssima Ferreira-Halder (2856-2865).
Pancreatic cancer ranks fourth among cancer-related causes of death in North America. Minimal progress has been made in the diagnosis and treatment of patients with late-stage tumors. Moreover, pancreatic cancer aggressiveness is closely related to high levels of pro-survival mediators, which can ultimately lead to rapid disease progression, resistance and metastasis. The main goal of this study was to define the mechanisms by which calixarene, but not other calixarenes, efficiently decreases the aggressiveness of a drug resistant human pancreas carcinoma cell line (Panc-1). Calixarene was more potent in reducing Panc-1 cell viability than gemcitabine and 5-fluorouracil. In relation to the underlying mechanisms of cytotoxic effects, it led to cell cycle arrest in the G0/G1 phase through downregulation of PIM1, CDK2, CDK4 and retinoblastoma proteins. Importantly, calixarene abolished signal transduction of Mer and AXL tyrosine kinase receptors, both of which are usually overexpressed in pancreatic cancer. Accordingly, inhibition of PI3K and mTOR was also observed, and these proteins are positively modulated by Mer and AXL. Despite decreasing the phosphorylation of AKT at Thr308, calixarene caused an increase in phosphorylation at Ser473. These findings in conjunction with increased BiP and IRE1-α provide a molecular basis explaining the capacity of calixarene to trigger endoplasmic reticulum stress and autophagic cell death. Our findings highlight calixarene as a potential candidate for overcoming pancreatic cancer aggressiveness. Importantly, we provide evidence that calixarene affects a broad array of key targets that are usually dysfunctional in pancreatic cancer, a highly desirable characteristic for chemotherapeutics.
Keywords: Calixarene; Pancreatic cancer; Receptor tyrosine kinase; Endoplasmic reticulum stress; Autophagy;
1,8-Cineol inhibits nuclear translocation of NF-κB p65 and NF-κB-dependent transcriptional activity by Johannes F.-W. Greiner; Janine Müller; Marie-Theres Zeuner; Stefan Hauser; Thorsten Seidel; Christin Klenke; Lena-Marie Grunwald; Timo Schomann; Darius Widera; Holger Sudhoff; Barbara Kaltschmidt; Christian Kaltschmidt (2866-2878).
Natural plant-derived products are commonly applied to treat a broad range of human diseases, including cancer as well as chronic and acute airway inflammation. In this regard, the monoterpene oxide 1,8-cineol, the active ingredient of the clinically approved drug Soledum®, is well-established for the therapy of airway diseases, such as chronic sinusitis and bronchitis, chronic obstructive pulmonary disease and bronchial asthma. Although clinical trials underline the beneficial effects of 1,8-cineol in treating inflammatory diseases, the molecular mode of action still remains unclear.Here, we demonstrate for the first time a 1,8-cineol-depending reduction of NF-κB-activity in human cell lines U373 and HeLa upon stimulation using lipopolysaccharides (LPS). Immunocytochemistry further revealed a reduced nuclear translocation of NF-κB p65, while qPCR and western blot analyses showed strongly attenuated expression of NF-κB target genes. Treatment with 1,8-cineol further led to increased protein levels of IκBα in an IKK-independent matter, while FRET-analyses showed restoring of LPS-associated loss of interaction between NF-κB p65 and IκBα. We likewise observed reduced amounts of phosphorylated c-Jun N-terminal kinase 1/2 protein in U373 cells after exposure to 1,8-cineol. In addition, 1,8-cineol led to decreased amount of nuclear NF-κB p65 and reduction of its target gene IκBα at protein level in human peripheral blood mononuclear cells.Our findings suggest a novel mode of action of 1,8-cineol through inhibition of nuclear NF-κB p65 translocation via IκBα resulting in decreased levels of proinflammatory NF-κB target genes and may therefore broaden the field of clinical application of this natural drug for treating inflammatory diseases.Display Omitted
Keywords: 1,8-Cineol; NF-κB; Human cell lines; PBMCs; Inflammation; Inflammatory diseases;
A role for EIIANtr in controlling fluxes in the central metabolism of E. coli K12 by Susan Jahn; Bart R. Haverkorn van Rijsewijk; Uwe Sauer; Katja Bettenbrock (2879-2889).
To investigate a possible role of the nitrogen-PTS (PTSNtr) in controlling carbon metabolism, we determined the growth of Escherichia coli LJ110 and of isogenic derivatives, mutated in components of the PTSNtr, on different carbon sources. The PTSNtr is a set of proteins homologous to the PEP-dependent phosphotransferase system (C-PTS) that transfers a phosphate group from PEP over EINtr (encoded by ptsP) and NPr (encoded by ptsO) to EIIANtr (encoded by ptsN). Strains deleted in ptsN were characterized by a high acetate production coupled to slow growth on glycolytic substrates. The ΔptsP and the ΔptsO strain showed the same behavior as the parent strain. As the phosphorylation level of EIIANtr in these mutants differed significantly from that of the parent strain, phosphorylation of EIIANtr obviously is not important for its function. During growth in minimal medium with defined carbon sources, EIIANtr was always completely phosphorylated in LJ110. Significant amounts of dephosphorylated EIIANtr were only visible in strains lacking EINtr or NPr. mRNA expression studies on glucose revealed a downregulation of genes encoding TCA cycle enzymes when EIIANtr was absent. 13C-flux analyses confirmed higher fluxes towards acetate and lower fluxes in the TCA cycle in the ptsN mutants but additionally hinted to a slightly but significantly increased flux through the pyruvate dehydrogenase complex (PDH). During growth on succinate the ΔptsN strain accumulated mutations in rpoS, while no rpoS mutants were observed for the ΔptsN-O strain. This hints to an additional function of NPr during growth with succinate.
Keywords: Phosphotransferase system; Metabolic control; Overflow metabolism; Nitrogen PTS;
A novel mechanism of XIAP degradation induced by timosaponin AIII in hepatocellular carcinoma by Ning Wang; Yibin Feng; Meifen Zhu; Fung-Ming Siu; Kwan-Ming Ng; Chi-Ming Che (2890-2899).
Inducing tumor cell death is one of the major therapeutic strategies in treating cancer. The aim of this study is to investigate the mechanism underlying the involvement of autophagy in cell death induced by timosaponin AIII (TAIII). Cell viability was determined by MTT and cologenic assay; apoptosis was determined by flow cytometry and TUNEL assay; autophagy was examined by immunoblotting and immunofluorescence; ubiquitination was detected by co-immunoprecipitation; mRNA expression was detected by real-time PCR; and determination of necrotic cell death was approached with LDH assay. The in vivo tumor growth inhibition was determined by xenograft model. TAIII exhibits potent cytotoxicity on human hepatocellular carcinoma (HCC) cells without severe hepatic toxicity. TAIII induced caspase-dependent apoptosis in HCC, and the induction of apoptosis was attributed to the inhibition of TAIII on XIAP expression. Repressing XIAP expression allowed cell tolerance toward the treatment with TAIII. The suppression of XIAP by TAIII is under post-transcriptional control and independent of proteasomal-driven proteolysis. Instead, TAIII-induced AMPKα/mTOR-dependent autophagy was responsible for XIAP suppression and triggered the XIAP heading lysosomal degradation pathway. Ubiquitination of IAPs is required for the autophagic degradation induced by TAIII. Blockade of autophagy turns on the switch of necrotic cell death in TAIII-treated cells. Timosaponin AIII induces HCC cell apoptosis through a p53-independent mechanism involving XIAP degradation through autophagy–lysosomal pathway. The possibility of developing TAIII as a new anti-tumor agent is worth considering.Display Omitted
Keywords: Timosaponin AIII; Apoptosis; Autophagy; XIAP; Lysosomal proteolysis;
Inhibition of LRRK2 kinase activity stimulates macroautophagy by Claudia Manzoni; Adamantios Mamais; Sybille Dihanich; Rosella Abeti; Marc P.M. Soutar; Helene Plun-Favreau; Paola Giunti; Sharon A. Tooze; Rina Bandopadhyay; Patrick A. Lewis (2900-2910).
Leucine Rich Repeat Kinase 2 (LRRK2) is one of the most important genetic contributors to Parkinson's disease. LRRK2 has been implicated in a number of cellular processes, including macroautophagy. To test whether LRRK2 has a role in regulating autophagy, a specific inhibitor of the kinase activity of LRRK2 was applied to human neuroglioma cells and downstream readouts of autophagy examined. The resulting data demonstrate that inhibition of LRRK2 kinase activity stimulates macroautophagy in the absence of any alteration in the translational targets of mTORC1, suggesting that LRRK2 regulates autophagic vesicle formation independent of canonical mTORC1 signaling. This study represents the first pharmacological dissection of the role LRRK2 plays in the autophagy/lysosomal pathway, emphasizing the importance of this pathway as a marker for LRRK2 physiological function. Moreover it highlights the need to dissect autophagy and lysosomal activities in the context of LRRK2 related pathologies with the final aim of understanding their aetiology and identifying specific targets for disease modifying therapies in patients.
Keywords: LRRK2; Macroautophagy; Parkinson's disease; LC3; p62; WIPI2;
Hip2 ubiquitin-conjugating enzyme overcomes radiation-induced G2/M arrest by Yoonhee Bae; Song Hwa Jung; Goo-Young Kim; Hyangshuk Rhim; Seongman Kang (2911-2921).
Radiation induces cell cycle arrest and/or cell death in mammalian cells. In the present study, we show that Hip2, a ubiquitin-conjugating enzyme, can overcome radiation-induced G2/M cell cycle arrest and trigger the entry into mitosis. Ionizing radiation increased the levels of Hip2 by preventing its degradation but not its gene transcription. The stability of Hip2 in irradiated cells was further confirmed using live cell fluorescence imaging. Flow cytometric and molecular analyses revealed that Hip2 abrogated radiation-induced G2/M arrest, promoting entry into mitosis. Bimolecular fluorescence complementation assays and co-immunoprecipitation experiments showed that Hip2 interacted with and targeted p53 for degradation via the ubiquitin proteasome system, resulting in the activation of cdc2-cyclin B1 kinase to promote mitotic entry. These results contribute to our understanding of the mechanisms that regulate cell cycle progression and DNA damage-induced G2/M checkpoint cellular responses.
Keywords: G2/M arrest; Hip2; p53; Radiation; Ubiquitination;
Uptake of advanced glycation end products by proximal tubule epithelial cells via macropinocytosis by Marisa A. Gallicchio; Leon A. Bach (2922-2932).
Chronic hyperglycaemia during diabetes leads to non-enzymatic glycation of proteins to form advanced glycation end products (AGEs) that contribute to nephropathy. We describe AGE uptake in LLC-PK1 and HK2 proximal tubule cell lines by macropinocytosis, a non-specific, endocytic mechanism. AGE–BSA induced dorsal circular actin ruffles and amiloride-sensitive dextran–TRITC uptake, significantly increased AGE–BSA–FITC uptake (167 ± 20% vs BSA control, p < 0.01) and was ezrin-dependent. AGE–BSA–FITC uptake was significantly inhibited by amiloride and inhibitors of Arf6, Rac1, racGEF Tiam1, PAK1 and actin polymerisation. AGE–BSA–FITC, Arf6 and PIP2 co-localised within dorsal circular actin ruffles. AGE–BSA increased PAK1 kinase activity (212 ± 41% vs control, p < 0.05) and protein levels of Tiam1, a Rac1 activator. AGE–BSA significantly increased TGF-β1 protein levels (160 ± 6%, p < 0.001 vs BSA), which were significantly inhibited by inhibitors of Arf6 (82 ± 19%, p < 0.001 vs AGE) and actin polymerisation (107 ± 11%, p < 0.001 vs AGE), suggesting AGEs partially exert their profibrotic effects via macropinocytosis. PAK1 and PIP5Kγ siRNA significantly decreased AGE–BSA–FITC uptake (81 ± 6% and 64 ± 7%, respectively, p < 0.05 vs control for both), and AGE-stimulated TGF-β1 protein release (99 ± 15% and 49 ± 8% of control, p < 0.05 and p < 0.001, respectively). Inhibition of AGE uptake by macropinocytosis inhibitors and a neutralising TGF-β antibody, reversed the AGE-induced decrease in surface Na+K+ATPase, suggesting AGE uptake by macropinocytosis may contribute to diabetic kidney fibrosis and/or EMT by modulating this pump. Understanding methods of cellular uptake and signalling by AGEs may lead to novel therapies for diabetic nephropathy.
Keywords: Macropinocytosis; Nephropathy; TGF-β; Glycation; Diabetes; Na+K+ATPase;
Binding to G-quadruplex RNA activates the mitochondrial GTPase NOA1 by Natalie Al-Furoukh; Steffi Goffart; Marten Szibor; Sjoerd Wanrooij; Thomas Braun (2933-2942).
NOA1 is an evolutionary conserved, nuclear encoded GTPase essential for mitochondrial function and cellular survival. The function of NOA1 for assembly of mitochondrial ribosomes and regulation of OXPHOS activity depends on its GTPase activity, but so far no ligands have been identified that regulate the GTPase activity of NOA1. To identify nucleic acids that bind to the RNA-binding domain of NOA1 we employed SELEX (Systemic Evolution of Ligands by EXponential Enrichment) using recombinant mouse wildtype NOA1 and the GTPase mutant NOA1-K353R. We found that NOA1 binds specifically to oligonucleotides that fold into guanine tetrads (G-quadruplexes). Binding of G-quadruplex oligonucleotides stimulated the GTPase activity of NOA1 suggesting a regulatory link between G-quadruplex containing RNAs, NOA1 function and assembly of mitochondrial ribosomes.
Keywords: NOA1; G-quadruplex; Binding motif; GTPase; Aptamer; SELEX;
Cytoplasmic ribosomal protein S3 (rpS3) plays a pivotal role in mitochondrial DNA damage surveillance by YongJoong Kim; Hag Dong Kim; Joon Kim (2943-2952).
Ribosomal protein S3 (rpS3) is known to play critical roles in ribosome biogenesis and DNA repair. When cellular ROS levels increase, the mitochondrial genes are highly vulnerable to DNA damage. Increased ROS induces rpS3 accumulation in the mitochondria for DNA repair while significantly decreasing the cellular protein synthesis. For the entrance into the mitochondria, the accumulation of rpS3 was regulated by interaction with HSP90, HSP70, and TOM70. Pretreatment with geldanamycin, which binds to the ATP pocket of HSP90, significantly decreased the interaction of rpS3 with HSP90 and stimulated the accumulation of rpS3 in the mitochondria. Furthermore, cellular ROS was decreased and mtDNA damage was rescued when levels of rpS3 were increased in the mitochondria. Therefore, we concluded that when mitochondrial DNA damages accumulate due to increased levels of ROS, rpS3 accumulates in the mitochondria to repair damaged DNA due to the decreased interaction between rpS3 and HSP90 in the cytosol.
Keywords: HSP70; HSP90; Mitochondria; Ribosomal protein S3; ROS;
TRPC3 regulates release of brain-derived neurotrophic factor from human airway smooth muscle by Pawan K. Vohra; Michael A. Thompson; Venkatachalem Sathish; Alexander Kiel; Calvin Jerde; Christina M. Pabelick; Brij B. Singh; Y.S. Prakash (2953-2960).
Exogenous brain-derived neurotrophic factor (BDNF) enhances Ca2 + signaling and cell proliferation in human airway smooth muscle (ASM), especially with inflammation. Human ASM also expresses BDNF, raising the potential for autocrine/paracrine effects. The mechanisms by which ASM BDNF secretion occurs are not known. Transient receptor potential channels (TRPCs) regulate a variety of intracellular processes including store-operated Ca2 + entry (SOCE; including in ASM) and secretion of factors such as cytokines. In human ASM, we tested the hypothesis that TRPC3 regulates BDNF secretion. At baseline, intracellular BDNF was present, and BDNF secretion was detectable by enzyme linked immunosorbent assay (ELISA) of cell supernatants or by real-time fluorescence imaging of cells transfected with GFP–BDNF vector. Exposure to the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFα) (20 ng/ml, 48 h) or a mixture of allergens (ovalbumin, house dust mite, Alternaria, and Aspergillus extracts) significantly enhanced BDNF secretion and increased TRPC3 expression. TRPC3 knockdown (siRNA or inhibitor Pyr3; 10 μM) blunted BDNF secretion, and prevented inflammation effects. Chelation of extracellular Ca2 + (EGTA; 1 mM) or intracellular Ca2 + (BAPTA; 5 μM) significantly reduced secreted BDNF, as did the knockdown of SOCE proteins STIM1 and Orai1 or plasma membrane caveolin-1. Functionally, secreted BDNF had autocrine effects suggested by phosphorylation of high-affinity tropomyosin-related kinase TrkB receptor, prevented by chelating extracellular BDNF with chimeric TrkB-Fc. These data emphasize the role of TRPC3 and Ca2 + influx in the regulation of BDNF secretion by human ASM and the enhancing effects of inflammation. Given the BDNF effects on Ca2 + and cell proliferation, BDNF secretion may contribute to altered airway structure and function in diseases such as asthma.
Keywords: Neurotrophin; Lung; Inflammation; Asthma; Tropomyosin-related kinase; Signaling;
Downregulation of CFTR promotes epithelial-to-mesenchymal transition and is associated with poor prognosis of breast cancer by Jie Ting Zhang; Xiao Hua Jiang; Chen Xie; Hong Cheng; Jian Da Dong; Yan Wang; Kin Lam Fok; Xiao Hu Zhang; Ting Ting Sun; Lai Ling Tsang; Hao Chen; Xiao Juan Sun; Yiu Wa Chung; Zhi Ming Cai; Wen Guo Jiang; Hsiao Chang Chan (2961-2969).
The epithelial-to-mesenchymal transition (EMT), a process involving the breakdown of cell–cell junctions and loss of epithelial polarity, is closely related to cancer development and metastatic progression. While the cystic fibrosis transmembrane conductance regulator (CFTR), a Cl− and HCO3 − conducting anion channel expressed in a wide variety of epithelial cells, has been implicated in the regulation of epithelial polarity, the exact role of CFTR in the pathogenesis of cancer and its possible involvement in EMT process have not been elucidated. Here we report that interfering with CFTR function either by its specific inhibitor or lentiviral miRNA-mediated knockdown mimics TGF-β1-induced EMT and enhances cell migration and invasion in MCF-7. Ectopic overexpression of CFTR in a highly metastatic MDA-231 breast cancer cell line downregulates EMT markers and suppresses cell invasion and migration in vitro, as well as metastasis in vivo. The EMT-suppressing effect of CFTR is found to be associated with its ability to inhibit NFκB targeting urokinase-type plasminogen activator (uPA), known to be involved in the regulation of EMT. More importantly, CFTR expression is found significantly downregulated in primary human breast cancer samples, and is closely associated with poor prognosis in different cohorts of breast cancer patients. Taken together, the present study has demonstrated a previously undefined role of CFTR as an EMT suppressor and its potential as a prognostic indicator in breast cancer.
Keywords: Epithelial-to-mesenchymal transition (EMT); CFTR; Breast cancer; Prognosis; uPA;
Epigenetic upregulation of Bak by ZBP-89 inhibits the growth of hepatocellular carcinoma by Cai Guo Ye; George G. Chen; Rocky L.K. Ho; Juanita L. Merchant; Ming-Liang He; Paul B.S. Lai (2970-2979).
Zinc-binding protein-89 regulates Bak to facilitate apoptosis in cancer cells. This study examined if zinc-binding protein-89 regulates Bak through an epigenetic mechanism in hepatocellular carcinoma. We first demonstrated that the expression of Bak was reduced but the levels of deoxyribonucleic acid methyltransferase 1 and histone deacetylase 3 were increased in hepatocellular carcinoma cancer tissues compared to the corresponding non-cancer tissues. Moreover, there was a negative correlation between Bak expression and deoxyribonucleic acid methyltransferase 1 levels in hepatocellular carcinoma. Administration of zinc-binding protein-89 downregulated histone deacetylase 3 expression and suppressed the activities of histone deacetylase and deoxyribonucleic acid methyltransferase, which led to maintenance of histone acetylation status, inhibited the binding of methyl-CpG-binding protein 2 to genomic deoxyribonucleic acid and demethylated CpG islands in the Bak promoter in hepatocellular carcinoma cells. Using the xenograft mouse tumor model, we demonstrated that zinc-binding protein-89 or inhibitors of either epigenetic enzymes could stimulate Bak expression, induce apoptosis, and arrest tumor growth and that the maximal effort was achieved when zinc-binding protein-89 and the enzyme inhibitors were used in combination. Conclusively, zinc-binding protein-89 upregulates the expression of Bak by targeting multiple components of the epigenetic pathway in hepatocellular carcinoma.
Keywords: Hepatocellular carcinoma; ZBP-89; HDAC; DNMT; Bak;
Simultaneous knock-down of Bcl-xL and Mcl-1 induces apoptosis through Bax activation in pancreatic cancer cells by Hiroki Takahashi; Monica C. Chen; Hung Pham; Yoichi Matsuo; Hideyuki Ishiguro; Howard A. Reber; Hiromitsu Takeyama; Oscar J. Hines; Guido Eibl (2980-2987).
Anti-apoptotic Bcl-2 family proteins have been reported to play an important role in apoptotic cell death of human malignancies. The aim of this study was to delineate the mechanism of anti-apoptotic Bcl-2 family proteins in pancreatic cancer (PaCa) cell survival. We first analyzed the endogenous expression and subcellular localization of anti-apoptotic Bcl-2 family proteins in six PaCa cell lines by Western blot. To delineate the functional role of Bcl-2 family proteins, siRNA-mediated knock-down of protein expression was used. Apoptosis was measured by Cell Death ELISA and Hoechst 33258 staining. In the results, the expression of anti-apoptotic Bcl-2 family proteins varied between PaCa cell lines. Mcl-1 knock-down resulted in marked cleavage of PARP and induction of apoptosis. Down-regulation of Bcl-2 or Bcl-xL had a much weaker effect. Simultaneous knock-down of Bcl-xL and Mcl-1 strongly induced apoptosis, but simultaneous knock-down of Bcl-xL/Bcl-2 or Mcl-1/Bcl-2 had no additive effect. The apoptosis-inducing effect of simultaneous knock-down of Bcl-xL and Mcl-1 was associated with translocation of Bax from the cytosol to the mitochondrial membrane, cytochrome c release, and caspase activation. These results demonstrated that Bcl-xL and Mcl-1 play an important role in pancreatic cancer cell survival. Targeting both Bcl-xL and Mcl-1 may be an intriguing therapeutic strategy in PaCa.
Keywords: Mcl-1; Bcl-xL; Bax; Pancreatic cancer; Apoptosis;
Prevention of Reg I-induced β-cell apoptosis by IL-6/dexamethasone through activation of HGF gene regulation by Kei Nakagawa; Shin Takasawa; Koji Nata; Akiyo Yamauchi; Asako Itaya-Hironaka; Hiroyo Ota; Kiyomi Yoshimoto; Sumiyo Sakuramoto-Tsuchida; Tomoko Miyaoka; Maiko Takeda; Michiaki Unno; Hiroshi Okamoto (2988-2995).
Reg (regenerating gene) product, Reg protein, is induced in pancreatic β-cells and acts as autocrine/paracrine growth factor for regeneration via the cell surface Reg receptor. However, high concentrations of Reg I protein induced β-cell apoptosis. In the present study, we found that hepatocyte growth factor (HGF) attenuated the β-cell apoptosis induced by the high concentrations of Reg I protein and that the combined stimulation of interleukin-6 (IL-6) and dexamethasone (Dx) induced the accumulation of HGF mRNA as well as Reg I mRNA in β-cells. The accumulation of the HGF mRNA was caused by the activation of the HGF promoter. Deletion analysis revealed that the region of − 96 to − 92 of the HGF gene was responsible for the promoter activation by IL-6 + Dx. The promoters contain a consensus transcription factor binding sequence for signal transducer and activator of transcription (STAT). Site-directed mutations of STAT-binding motif in the region markedly attenuated the HGF promoter activity. Chromatin immunoprecipitation assay showed that STAT3 is located at the active HGF promoter in response to IL-6 + Dx stimulation. These results strongly suggest that the combined stimulation of IL-6 and glucocorticoids induces the activation of both Reg and HGF genes and that the anti-apoptotic effects of HGF against the Reg I-induced apoptosis may help β-cell regeneration by Reg I protein.
Keywords: Reg protein; HGF gene; Transcriptional control; IL-6; Glucocorticoids; Pancreatic β cell;
Knock-down of glutaminase 2 expression decreases glutathione, NADH, and sensitizes cervical cancer to ionizing radiation by Lisha Xiang; Ganfeng Xie; Chen Liu; Jie Zhou; Jianfang Chen; Songtao Yu; Jianjun Li; Xueli Pang; Hang Shi; Houjie Liang (2996-3005).
Phosphate-activated mitochondrial glutaminase (GLS2) is suggested to be linked with elevated glutamine metabolism. It plays an important role in catalyzing the hydrolysis of glutamine to glutamate. The present study was to investigate the potent effect of GLS2 on radioresistance of cervical carcinoma. GLS2 was examined in 144 cases of human cervical cancer specimens (58 radioresistant specimens, 86 radiosensitive specimens) and 15 adjacent normal cervical specimens with immunohistochemistry. HeLa cells were treated with a cumulative dose of 50 Gy X-rays, over 6 months, yielding the resistant sub-line HeLaR. The expressions of GLS2 were measured by Western blot. Radioresistance was tested by colony survival assay. Apoptosis was determined by flow cytometry. The levels of glutathione (GSH), reactive oxygen species (ROS), NAD+/NADH ratio and NADP+/NADPH ratio were detected by quantization assay kit. Xenografts were used to confirm the effect of GLS2 on radioresistance in vivo. The expressions of GLS2 were significantly enhanced in tumor tissues of radioresistant patients compared with that in radiosensitive patients. In vitro, the radioresistant cell line HeLaR exhibited significantly increased GLS2 levels than its parental cell line HeLa. GLS2 silenced radioresistant cell HeLaR shows substantially enhanced radiosensitivity with lower colony survival and higher apoptosis in response to radiation. In vivo, xenografts with GLS2 silenced HeLaR were more sensitive to radiation. At the molecular level, knock-down of GLS2 increased the intracellular ROS levels of HeLaR exposed to irradiation by decreasing the productions of antioxidant GSH, NADH and NADPH. GLS2 may have an important role in radioresistance in cervical cancer patients.
Keywords: Phosphate-activated mitochondrial glutaminase; Radioresistance; Cervical cancer; Glutathione;
Linking phospholipase C isoforms with differentiation function in human vascular smooth muscle cells by Louise S. Mackenzie; Joanne S. Lymn; Alun D. Hughes (3006-3012).
The phosphoinositol-phospholipase C (PLC) family of enzymes consists of a number of isoforms, each of which has different cellular functions. PLCγ1 is primarily linked to tyrosine kinase transduction pathways, whereas PLCδ1 has been associated with a number of regulatory proteins, including those controlling the cell cycle. Recent studies have shown a central role of PLC in cell organisation and in regulating a wide array of cellular responses. It is of importance to define the precise role of each isoform, and how this changes the functional outcome of the cell. Here we investigated differences in PLC isoform levels and activity in relation to differentiation of human and rat vascular smooth muscle cells. Using Western blotting and PLC activity assay, we show that PLCδ1 and PLCγ1 are the predominant isoforms in randomly cycling human vascular smooth muscle cells (HVSMCs). Growth arrest of HVSMCs for seven days of serum deprivation was consistently associated with increases in PLCδ1 and SM α-actin, whereas there were no changes in PLCγ1 immuno-reactivity. Organ culture of rat mesenteric arteries in serum free media (SFM), a model of de-differentiation, led to a loss of contractility as well as a loss of contractile proteins (SM α-actin and calponin) and PLCδ1, and no change in PLCγ1 immuno-reactivity. Taken together, these data indicate that PLCδ1 is the predominant PLC isoform in vascular smooth muscle, and confirm that PLCδ1 expression is affected by conditions that affect the cell cycle, differentiation status and contractile function.
Keywords: Phosphoinositol-phospholipase C; Actin; Cytoskeleton; Differentiation; Human vascular smooth muscle;
Identification of the kinesin KifC3 as a new player for positioning of peroxisomes and other organelles in mammalian cells by Denise Dietrich; Florian Seiler; Frank Essmann; Gabriele Dodt (3013-3024).
The attachment of organelles to the cytoskeleton and directed organelle transport is essential for cellular morphology and function. In contrast to other cell organelles like the endoplasmic reticulum or the Golgi apparatus, peroxisomes are evenly distributed in the cytoplasm, which is achieved by binding of peroxisomes to microtubules and their bidirectional transport by the microtubule motor proteins kinesin-1 (Kif5) and cytoplasmic dynein. KifC3, belonging to the group of C-terminal kinesins, has been identified to interact with the human peroxin PEX1 in a yeast two-hybrid screen. We investigated the potential involvement of KifC3 in peroxisomal transport. Interaction of KifC3 and the AAA-protein (ATPase associated with various cellular activities) PEX1 was confirmed by in vivo colocalization and by coimmunoprecipitation from cell lysates. Furthermore, knockdown of KifC3 using RNAi resulted in an increase of cells with perinuclear-clustered peroxisomes, indicating enhanced minus-end directed motility of peroxisomes. The occurrence of this peroxisomal phenotype was cell cycle phase independent, while microtubules were essential for phenotype formation. We conclude that KifC3 may play a regulatory role in minus-end directed peroxisomal transport for example by blocking the motor function of dynein at peroxisomes. Knockdown of KifC3 would then lead to increased minus-end directed peroxisomal transport and cause the observed peroxisomal clustering at the microtubule-organizing center.
Keywords: Kinesins; Peroxisomes; Peroxins; Cytoskeleton;
Transient receptor potential ankyrin-1 (TRPA1) modulates store-operated Ca2 + entry by regulation of STIM1-Orai1 association by Letizia Albarrán; Jose J. Lopez; Natalia Dionisio; Tarik Smani; Gines M. Salido; Juan A. Rosado (3025-3034).
TRPA1 is a non-selective Ca2 + permeable channel located in the plasma membrane that functions as a cellular sensor detecting mechanical, chemical and thermal stimuli, being a component of neuronal, epithelial, blood and smooth muscle tissues. TRPA1 has been shown to influence a broad range of physiological processes that involve Ca2 +-dependent signaling pathways. Here we report that TRPA1 is expressed in MEG01 but not in platelets at the protein level. MEG01 cells maturation induced by PMA results in attenuation of TRPA1 protein expression and enhances thapsigargin-evoked Ca2 + entry without altering the release of Ca2 + from intracellular stores. Inhibition of TRPA1 by HC-030031 results in enhancement of both thrombin- and thapsigargin-stimulated Ca2 + entry. Co-immunoprecipitation experiments revealed that TRPA1 associates with STIM1, as well as Orai1, TRPC1 and TRPC6. Downregulation of TRPA1 expression by MEG01 maturation, as well as pharmacological inhibition of TRPA1 by HC-030031, results in enhancement of the association between STIM1 and Orai1. Altogether, these findings provide evidence for a new and interesting function of TRPA1 in cellular function associated to the regulation of agonist-induced Ca2 + entry by the modulation of STIM1/Orai1 interaction.
Keywords: TRPA1; STIM1; Orai1; Ca2 + entry; MEG01 cell; TRP channel;
Destabilization of KLF10, a tumor suppressor, relies on thr93 phosphorylation and isomerase association by Yu-Chyi Hwang; Chien-Hui Yang; Ching-Hui Lin; Hui-Ju Ch'ang; Vincent H.S. Chang; Winston C.Y. Yu (3035-3045).
KLF10 is now classified as a member of the Krüppel-like transcription factor family and acts as a tumor suppressor. Although KLF10 is originally named as TGF-β-inducible early gene-1 and mimicking the anti-proliferative effect of TGF-β in various carcinoma cells, the transcriptional upregulatory function of KLF10 has been described for a variety of cytokines and in many diseases. Through in vivo and in vitro phosphorylation assays, we identified that KLF10 is a phosphorylated protein in cells. Using yeast-two hybrid screening and site direct mutagenesis, we also identified PIN1 as a novel KLF10 associated protein. PIN1 is a peptidyl-prolyl isomerase enzyme belonging to the parvulin family, which specifically recognizes phosphorylated Ser/Thr-Pro containing substrates. Through protein–protein interaction assays, we showed that the Pro-directed Ser/Thr-Pro motif at Thr-93 in the KLF10 N-terminal region is essential for the interaction between KLF10 and PIN1. More importantly, PIN1 interacts with KLF10 in a phosphorylation-dependent manner and this interaction promotes KLF10 protein degradation in cells. Therefore, KLF10 shows shorter protein stability compared with mutant KLF10 that lacks PIN1 binding ability after cycloheximide treatments. The reversely correlated expression profile between KLF10 and PIN1 as observed in cell lines was also shown in clinic pancreatic cancer specimen. Using in vitro kinase assays and depletion assays, we were able to show that RAF-1 phosphorylates the Thr-93 of KLF10 and affects the KLF10 expression level in cells. Thus these findings as a whole indicate that RAF-1 phosphorylation and PIN1 isomerization together regulate KLF10 stability and further affect the role of KLF10 in tumor progression.
Keywords: Krüppel-like factor 10; KLF10; PIN1; RAF-1; TIEG1;
Flow-induced activation of TRPV5 and TRPV6 channels stimulates Ca2 +-activated K+ channel causing membrane hyperpolarization by Seung-Kuy Cha; Ji-Hee Kim; Chou-Long Huang (3046-3053).
TRPV5 and TRPV6 channels are expressed in distal renal tubules and play important roles in the transcellular Ca2 + reabsorption in kidney. They are regulated by multiple intracellular factors including protein kinases A and C, membrane phospholipid PIP2, protons, and divalent ions Ca2 + and Mg2 +. Here, we report that fluid flow that generates shear force within the physiological range of distal tubular fluid flow activated TRPV5 and TRPV6 channels expressed in HEK cells. Flow-induced activation of channel activity was reversible and did not desensitize over 2 min. Fluid flow stimulated TRPV5 and 6-mediated Ca2 + entry and increased intracellular Ca2 + concentration. N-glycosylation-deficient TRPV5 channel was relatively insensitive to fluid flow. In cells coexpressing TRPV5 (or TRPV6) and Slo1-encoded maxi-K channels, fluid flow induced membrane hyperpolarization, which could be prevented by the maxi-K blocker iberiotoxin or TRPV5 and 6 blocker La3 +. In contrast, fluid flow did not cause membrane hyperpolarization in cells coexpressing ROMK1 and TRPV5 or 6 channel. These results reveal a new mechanism for the regulation of TRPV5 and TRPV6 channels. Activation of TRPV5 and TRPV6 by fluid flow may play a role in the regulation of flow-stimulated K+ secretion via maxi-K channels in distal renal tubules and in the mechanism of pathogenesis of thiazide-induced hypocalciuria.
Keywords: TRPV5; TRPV6; Flow-mediated Ca2 + entry; Ca2 +-activated K+ channel; Flow-mediated K+ secretion; ROMK;
Symplekin, a polyadenylation factor, prevents MOZ and MLL activity on HOXA9 in hematopoietic cells by Anne Largeot; Jérôme Paggetti; Julien Broséus; Romain Aucagne; Brice Lagrange; Romain Z. Martin; Jean Berthelet; Ronan Quéré; Géraldine Lucchi; Patrick Ducoroy; Jean-Noël Bastie; Laurent Delva (3054-3063).
MOZ and MLL encoding a histone acetyltransferase and a histone methyltransferase, respectively, are targets for recurrent chromosomal translocations found in acute myeloblastic or lymphoblastic leukemia. We have previously shown that MOZ and MLL cooperate to activate HOXA9 gene expression in hematopoietic stem/progenitors cells. To dissect the mechanism of action of this complex, we decided to identify new proteins interacting with MOZ. We found that the scaffold protein Symplekin that supports the assembly of polyadenylation machinery was identified by mass spectrometry. Symplekin interacts and co-localizes with both MOZ and MLL in immature hematopoietic cells. Its inhibition leads to a decrease of the HOXA9 protein level but not of Hoxa9 mRNA and to an over-recruitment of MOZ and MLL onto the HOXA9 promoter. Altogether, our results highlight the role of Symplekin in transcription repression involving a regulatory network between MOZ, MLL and Symplekin.
Keywords: Symplekin; MOZ; MLL; HOXA9; Transcription regulation;
Dehydroepiandrosterone sulfate mediates activation of transcription factors CREB and ATF-1 via a Gα11-coupled receptor in the spermatogenic cell line GC-2 by Mazen Shihan; Ulrike Kirch; Georgios Scheiner-Bobis (3064-3075).
Dehydroepiandrosterone sulfate (DHEAS) is a circulating steroid produced in the adrenal cortex, brain, and gonads. Whereas a series of investigations attest to neuroprotective effects of the steroid in the brain, surprisingly little is known about the physiological effects of DHEAS on cells of the reproductive system. Here we demonstrate that DHEAS acting on the spermatogenic cell line GC-2 induces a time- and concentration-dependent phosphorylation of c-Src and Erk1/2 and activates the transcription factors activating transforming factor-1 (ATF-1) and cyclic AMP-responsive element binding protein (CREB). These actions are consistent with the non-classical signaling pathway of testosterone and suggest that DHEAS is a pro-androgen that is converted into testosterone in order to exert its biological activity. The fact, however, that steroid sulfatase mRNA was not detected in the GC-2 cells and the clear demonstration of DHEAS-induced activation of Erk1/2, ATF-1 and CREB after silencing the androgen receptor by small interfering RNA (siRNA) clearly contradict this assumption and make it appear unlikely that DHEAS has to be converted in the cytosol into a different steroid in order to activate the kinases and transcription factors mentioned. Instead, it is likely that the DHEAS-induced signaling is mediated through the interaction of the steroid with a membrane-bound G-protein-coupled receptor, since silencing of Guanine nucleotide-binding protein subunit alpha-11 (Gnα11) leads to the abolition of the DHEAS-induced stimulation of Erk1/2, ATF-1, and CREB. The investigation presented here shows a hormone-like activity of DHEAS on a spermatogenic cell line. Since DHEAS is produced in male and female reproductive organs, these findings could help to define new roles for DHEAS in the physiology of reproduction.
Keywords: DHEAS; Signaling; Erk1/2; CREB; ATF-1; Androgen receptor; Gnα11; Spermatogenic cells;
Ubiquitination of the glycosomal matrix protein receptor PEX5 in Trypanosoma brucei by PEX4 displays novel features by Melisa Gualdrón-López; Nathalie Chevalier; Patrick Van Der Smissen; Pierre J. Courtoy; Daniel J. Rigden; Paul A.M. Michels (3076-3092).
Trypanosomatids contain peroxisome-like organelles called glycosomes. Peroxisomal biogenesis involves a cytosolic receptor, PEX5, which, after its insertion into the organellar membrane, delivers proteins to the matrix. In yeasts and mammalian cells, transient PEX5 monoubiquitination at the membrane serves as the signal for its retrieval from the organelle for re-use. When its recycling is impaired, PEX5 is polyubiquitinated for proteasomal degradation. Stably monoubiquitinated TbPEX5 was detected in cytosolic fractions of Trypanosoma brucei, indicative for its role as physiological intermediate in receptor recycling. This modification's resistance to dithiothreitol suggests ubiquitin conjugation of a lysine residue. T. brucei PEX4, the functional homologue of the ubiquitin-conjugating (UBC) enzyme responsible for PEX5 monoubiquitination in yeast, was identified. It is associated with the cytosolic face of the glycosomal membrane, probably anchored by an identified putative TbPEX22. The involvement of TbPEX4 in TbPEX5 ubiquitination was demonstrated using procyclic ∆PEX4 trypanosomes. Surprisingly, glycosomal matrix protein import was only mildly affected in this mutant. Since other UBC homologues were upregulated, it might be possible that these have partially rescued PEX4's function in PEX5 ubiquitination. In addition, the altered expression of UBCs, notably of candidates involved in cell-cycle control, could be responsible for observed morphological and motility defects of the ∆PEX4 mutant.Display Omitted
Keywords: Trypanosoma; Glycosome biogenesis; Ubiquitination; Peroxin; PEX5; PEX4;
DNA damage response (DDR) induced by topoisomerase II poisons requires nuclear function of the small GTPase Rac by Friedrich Wartlick; Anita Bopp; Christian Henninger; Gerhard Fritz (3093-3103).
Here, we investigated the influence of Rac family small GTPases on mechanisms of the DNA damage response (DDR) stimulated by topoisomerase II poisons. To this end, we examined the influence of the Rac-specific small molecule inhibitor EHT1864 on Ser139 phosphorylation of histone H2AX, a widely used marker of the DDR triggered by DNA double-strand breaks. EHT1864 attenuated the doxorubicin-stimulated DDR in a subset of cell lines tested, including HepG2 hepatoma cells. EHT1864 reduced the level of DNA strand breaks and increased viability following treatment of HepG2 cells with topo II poisons. Protection by EHT1864 was observed in both p53 wildtype (HepG2) and p53 deficient (Hep3B) human hepatoma cells and, furthermore, remained unaffected upon pharmacological inhibition of p53 in HepG2. Apparently, the impact of Rac on the DDR is independent of p53. Protection from doxorubicin-induced DNA damage by EHT1864 comprises both S and G2 phase cells. The inhibitory effect of EHT1864 on doxorubicin-stimulated DDR was mimicked by pharmacological inhibition of various protein kinases, including JNK, ERK, PI3K, PAK and CK1. EHT1864 and protein kinase inhibitors also attenuated the formation of the topo II-DNA cleavable complex. Moreover, EHT1864 mitigated the constitutive phosphorylation of topoisomerase IIα at positions S1106, S1213 and S1247. Doxorubicin transport, nuclear import/export of topoisomerase II and Hsp90-related mechanisms are likely not of relevance for doxorubicin-stimulated DDR impaired by EHT1864. We suggest that multiple kinase-dependent but p53- and heat shock protein-independent Rac-regulated nuclear mechanisms are required for activation of the DDR following treatment with topo II poisons.
Keywords: Rac family small GTPase; Topoisomerase II poisons; DNA damage response;
TRAP assists membrane protein topogenesis at the mammalian ER membrane by Nicole Sommer; Tina Junne; Kai-Uwe Kalies; Martin Spiess; Enno Hartmann (3104-3111).
Membrane protein insertion and topogenesis generally occur at the Sec61 translocon in the endoplasmic reticulum membrane. During this process, membrane spanning segments may adopt two distinct orientations with either their N- or C-terminus translocated into the ER lumen. While different topogenic determinants in membrane proteins, such as flanking charges, polypeptide folding, and hydrophobicity, have been identified, it is not well understood how the translocon and/or associated components decode them. Here we present evidence that the translocon-associated protein (TRAP) complex is involved in membrane protein topogenesis in vivo. Small interfering RNA (siRNA)-mediated silencing of the TRAP complex in HeLa cells enhanced the topology effect of mutating the flanking charges of a signal-anchor, but not of increasing signal hydrophobicity. The results suggest a role of the TRAP complex in moderating the ‘positive-inside’ rule.
Keywords: Sec61 complex; Translocon associated proteins; Endoplasmic reticulum; Membrane protein topogenesis; RNA interference;
Ndrg2 is a PGC-1α/ERRα target gene that controls protein synthesis and expression of contractile-type genes in C2C12 myotubes by Victoria C. Foletta; Erin L. Brown; Yoshitake Cho; Rod J. Snow; Anastasia Kralli; Aaron P. Russell (3112-3123).
The stress-responsive, tumor suppressor N-myc downstream-regulated gene 2 (Ndrg2) is highly expressed in striated muscle. In response to anabolic and catabolic signals, Ndrg2 is suppressed and induced, respectively, in mouse C2C12 myotubes. However, little is known about the mechanisms regulating Ndrg2 expression in muscle, as well as the biological role for Ndrg2 in differentiated myotubes. Here, we show that Ndrg2 is a target of a peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) and estrogen-related receptor alpha (ERRα) transcriptional program and is induced in response to endurance exercise, a physiological stress known also to increase PGC-1α/ERRα activity. Analyses of global gene and protein expression profiles in C2C12 myotubes with reduced levels of NDRG2, suggest that NDRG2 affects muscle growth, contractile properties, MAPK signaling, ion and vesicle transport and oxidative phosphorylation. Indeed, suppression of NDRG2 in myotubes increased protein synthesis and the expression of fast glycolytic myosin heavy chain isoforms, while reducing the expression of embryonic myosin Myh3, other contractile-associated genes and the MAPK p90 RSK1. Conversely, enhanced expression of NDRG2 reduced protein synthesis, and furthermore, partially blocked the increased protein synthesis rates elicited by a constitutively active form of ERRα. In contrast, suppressing or increasing levels of NDRG2 did not affect mRNA expression of genes involved in mitochondrial biogenesis that are regulated by PGC-1α or ERRα. This study shows that in C2C12 myotubes Ndrg2 is a novel PGC-1α/ERRα transcriptional target, which influences protein turnover and the regulation of genes involved in muscle contraction and function.
Keywords: N-myc downstream-regulated gene 2 (Ndrg2); Peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α); Estrogen-related receptor alpha (ERRα); C2C12 myotube; Bioinformatics; Protein synthesis;
Mechanical regulation of cancer cell apoptosis and autophagy: Roles of bone morphogenetic protein receptor, Smad1/5, and p38 MAPK by Sheng-Chieh Lien; Shun-Fu Chang; Pei-Ling Lee; Shu-Yi Wei; Margaret Dah-Tsyr Chang; Jang-Yang Chang; Jeng-Jiann Chiu (3124-3133).
Mechanical forces induced by interstitial fluid flow in and surrounding tissues and by blood/lymphatic flow in vessels may modulate cancer cell invasion and metastasis and anticancer drug delivery. Our previous study demonstrated that laminar flow-induced shear stress induces G2/M arrest in tumor cells. However, whether shear stress modulates final cell fate remains unclear. In this study, we investigated the role of flow-induced shear stress in modulating the survival of four human tumor cell lines, i.e., Hep3B hepatocarcinoma cells, MG63 osteosarcoma cells, SCC25 oral squamous carcinoma cells, and A549 carcinomic alveolar basal epithelial cells. Laminar shear stress (LSS) ranging from 0.5 to 12 dyn/cm2 induced death of these four tumor cell lines. In contrast to LSS at 0.5 dyn/cm2, oscillatory shear stress (OSS) at 0.5 ± 4 dyn/cm2 cannot induce cancer cell death. Both LSS and OSS had no effect on human normal hepatocyte, lung epithelial, and endothelial cells. Application of LSS to these four cell lines increased the percentage of cells stained positively for annexin V–FITC, with up-regulations of cleaved caspase-8, -9, and -3, and PARP. In addition, LSS also induced Hep3B cell autophagy, as detected by acidic vesicular organelle formation, LC3B transformation, and p62/SQSTM1 degradation. By transfecting with small interfering RNA, we found that the shear-induced apoptosis and autophagy are mediated by bone morphogenetic protein receptor type (BMPR)-IB, BMPR-specific Smad1 and Smad5, and p38 mitogen-activated protein kinase in Hep3B cells. Our findings provide insights into the molecular mechanisms by which shear stress induces apoptosis and autophagy in tumor cells.
Keywords: Apoptosis; Autophagy; BMP receptor; MAPK; Mechanical force; Smad1/5;
TRIM13 regulates caspase-8 ubiquitination, translocation to autophagosomes and activation during ER stress induced cell death by Dhanendra Tomar; Paresh Prajapati; Lakshmi Sripada; Kritarth Singh; Rochika Singh; Arun Kumar Singh; Rajesh Singh (3134-3144).
The emerging evidences suggest that endoplasmic (ER) stress is involved in onset of many pathological conditions like cancer and neurodegeneration. The persistent ER stress results in misfolded protein aggregates, which are degraded through the process of autophagy or lead to cell death through activation of caspases. The regulation of crosstalk of autophagy and cell death during ER stress is emerging. Ubiquitination plays regulatory role in crosstalk of autophagy and cell death. In the current study, we describe the role of TRIM13, RING E3 ubiquitin ligase, in regulation of ER stress induced cell death. The expression of TRIM13 sensitizes cells to ER stress induced death. TRIM13 induced autophagy is essential for ER stress induced caspase activation and cell death. TRIM13 induces K63 linked poly-ubiquitination of caspase-8, which results in its stabilization and activation during ER stress. TRIM13 regulates translocation of caspase-8 to autophagosome and its fusion with lysosome during ER stress. This study first time demonstrated the role of TRIM13 as novel regulator of caspase-8 activation and cell death during ER stress.Display Omitted
Keywords: Endoplasmic reticulum stress; Autophagy; Cell death; Ubiquitin ligase; TRIM13; Caspase-8;
A novel Gαs-binding protein, Gas-2 like 2, facilitates the signaling of the A2A adenosine receptor by Yi-Chih Wu; Hsing-Lin Lai; Wei-Cheng Chang; Jiun-Tsai Lin; Yu-Ju Liu; Yijuang Chern (3145-3154).
The A2A adenosine receptor (A2AR) is a G-protein-coupled receptor that contains a long cytoplasmic carboxyl terminus (A2AR-C). We report here that Gas-2 like 2 (G2L2) is a new interacting partner of A2AR-C. The interaction between A2AR and G2L2 was verified by GST pull-down, co-immunoprecipitation, immunocytochemical staining, and fluorescence resonance energy transfer. Expression of G2L2 increased the intracellular cAMP content evoked by A2AR in an A2AR-C-dependent manner. Immunoprecipitation and pull-down assays demonstrated that G2L2 selectively bound to A2AR-C and the inactive form of Gαs to facilitate the recruitment of the trimeric G protein complex to the proximal position of A2AR for efficient activation. Collectively, G2L2 is a new effector that controls the action of A2AR by modulating its ability to regulate the Gαs-mediated cAMP contents.
Keywords: A2A adenosine receptor; cAMP; Gαs; Gas-2 like 2;
Different ataxin-3 amyloid aggregates induce intracellular Ca2 + deregulation by different mechanisms in cerebellar granule cells by Francesca Pellistri; Monica Bucciantini; Gaetano Invernizzi; Elena Gatta; Amanda Penco; Anna Maria Frana; Daniele Nosi; Annalisa Relini; Maria Elena Regonesi; Alessandra Gliozzi; Paolo Tortora; Mauro Robello; Massimo Stefani (3155-3165).
This work aims at elucidating the relation between morphological and physicochemical properties of different ataxin-3 (ATX3) aggregates and their cytotoxicity. We investigated a non-pathological ATX3 form (ATX3Q24), a pathological expanded form (ATX3Q55), and an ATX3 variant truncated at residue 291 lacking the polyQ expansion (ATX3/291Δ). Solubility, morphology and hydrophobic exposure of oligomeric aggregates were characterized. Then we monitored the changes in the intracellular Ca2 + levels and the abnormal Ca2 + signaling resulting from aggregate interaction with cultured rat cerebellar granule cells. ATX3Q55, ATX3/291Δ and, to a lesser extent, ATX3Q24 oligomers displayed similar morphological and physicochemical features and induced qualitatively comparable time-dependent intracellular Ca2 + responses. However, only the pre-fibrillar aggregates of expanded ATX3 (the only variant which forms bundles of mature fibrils) triggered a characteristic Ca2 + response at a later stage that correlated with a larger hydrophobic exposure relative to the two other variants. Cell interaction with early oligomers involved glutamatergic receptors, voltage-gated channels and monosialotetrahexosylganglioside (GM1)-rich membrane domains, whereas cell interaction with more aged ATX3Q55 pre-fibrillar aggregates resulted in membrane disassembly by a mechanism involving only GM1-rich areas. Exposure to ATX3Q55 and ATX3/291Δ aggregates resulted in cell apoptosis, while ATX3Q24 was substantially innocuous. Our findings provide insight into the mechanisms of ATX3 aggregation, aggregate cytotoxicity and calcium level modifications in exposed cerebellar cells.
Keywords: Ataxin-3; Amyloid aggregate; Intracellular Ca2 + level; Oligomer toxicity; Fibril toxicity;
Identification of voltage-gated K+ channel beta 2 (Kvβ2) subunit as a novel interaction partner of the pain transducer Transient Receptor Potential Vanilloid 1 channel (TRPV1) by Carlo Bavassano; Letizia Marvaldi; Michiel Langeslag; Bettina Sarg; Herbert Lindner; Lars Klimaschewski; Michaela Kress; Antonio Ferrer-Montiel; Hans-Günther Knaus (3166-3175).
The Transient Receptor Potential Vanilloid 1 (TRPV1, vanilloid receptor 1) ion channel plays a key role in the perception of thermal and inflammatory pain, however, its molecular environment in dorsal root ganglia (DRG) is largely unexplored. Utilizing a panel of sequence-directed antibodies against TRPV1 protein and mouse DRG membranes, the channel complex from mouse DRG was detergent-solubilized, isolated by immunoprecipitation and subsequently analyzed by mass spectrometry. A number of potential TRPV1 interaction partners were identified, among them cytoskeletal proteins, signal transduction molecules, and established ion channel subunits. Based on stringent specificity criteria, the voltage-gated K+ channel beta 2 subunit (Kvβ2), an accessory subunit of voltage-gated K+ channels, was identified of being associated with native TRPV1 channels. Reverse co-immunoprecipitation and antibody co-staining experiments confirmed TRPV1/Kvβ2 association. Biotinylation assays in the presence of Kvβ2 demonstrated increased cell surface expression levels of TRPV1, while patch-clamp experiments resulted in a significant increase of TRPV1 sensitivity to capsaicin. Our work shows, for the first time, the association of a Kvβ subunit with TRPV1 channels, and suggests that such interaction may play a role in TRPV1 channel trafficking to the plasma membrane.
Keywords: Signaling complex; Dorsal root ganglia; Accessory subunit; TRPV1;
Lysine residues of IGF-I are substrates for transglutaminases and modulate downstream IGF-I signalling by Manaswini Sivaramakrishnan; Tristan I. Croll; Rajesh Gupta; Dario Stupar; Derek R. Van Lonkhuyzen; Zee Upton; Gary K. Shooter (3176-3185).
Numerous studies have reported associations between IGF-I and other extra cellular matrix (ECM) proteins, including fibronectin (FN), integrins, IGF-binding proteins (IGFBPs) and through IGFBPs, with vitronectin (VN). Nevertheless, the precise nature and mechanisms of these interactions are still being characterised. In this paper, we discuss transglutaminases (TGases) as a constituent of the ECM and provide evidence for the first time that IGF-I is a lysine (K)-donor substrate to TGases. When IGF-I was incubated with an alpha-2 plasmin inhibitor-derived Q peptide in the presence of tissue transglutaminase (TG2), an IGF-I:Q peptide cross-linked species was detected using Western immunoblotting and confirmed by mass spectrometry. Similar findings were observed in the presence of Factor XIIIa (FXIIIa) TGase. To identify the precise location of this K-donor TGase site/s on IGF-I, all the three IGF-I K-sites, individually and collectively (K27, K65 and K68), were substituted to arginine (R) using site-directed mutagenesis. Incubation of these K→R IGF-I analogues with Q peptide in the presence of TG2 or FXIIIa resulted in the absence of cross-linking in IGF-I analogues bearing arginine substitution at site 68. This established that K68 within the IGF-I D-domain was the principal K-donor site to TGases. We further annotated the functional significance of these K→R IGF-I analogues on IGF-I mediated actions. IGF-I analogues with K→R substitution within the D-domain at K65 and K68 hindered migration of MCF-7 breast carcinoma cells and correspondingly reduced PI3-K/AKT activation. Therefore, this study also provides first insights into a possible functional role of the previously uncharacterised IGF-I D-domain.
Keywords: Insulin-like growth factor-1; IGF-I; D-domain of IGF-I; Transglutaminase; Migration; Viability;
The human septin7 and the yeast CDC10 septin prevent Bax and copper mediated cell death in yeast by Avital Horowitz; Jason F. Lapointe; Rawan Eid; Sara Sheibani; Nada Gharib; Natalie K. Jones; Hojatollah Vali; Craig A. Mandato; Michael T. Greenwood (3186-3194).
The mechanisms of programmed cell death activate genetically encoded intracellular programs in a controlled manner, the most common form being apoptosis. Apoptosis is carried out through a cascade of caspase mediated proteolytic cleavages initiated by the oligomerization of Bax, a cardinal regulator of mitochondrial-mediated apoptosis. Heterologous expression of Bax in yeast causes cell death that shares a number of similarities to processes that occur in mammalian apoptosis. A screen of a cardiac cDNA library for suppressors of Bax-mediated apoptosis identified human septin7, a protein that belongs to the septin superfamily of conserved GTP-binding proteins that share a conserved cdc/septin domain. Analysis of the amino acid sequence deduced from the septin7 clone as well as the corresponding human septin7 gene revealed that a novel alternatively spliced transcript called septin7 variant4 (v4) was uncovered. Yeast cells overexpressing the human septin7 v4 cDNA were also capable of resisting copper-mediated cell death suggesting that it is not only a Bax suppressor but also an anti-apoptotic sequence. Analysis of septin7 function in a MCA1Δ yeast strain suggests that septin7 inhibits apoptosis in a caspase independent pathway. Overexpression of the yeast septin7 ortholog CDC10 also conferred resistance to the negative effects of copper as well as protecting cells from the overexpression of Bax. In contrast, septin7 was unable to prevent the increase in cell size associated with mutants lacking the endogenous yeast CDC10 gene. Taken together, our analysis suggests that anti-apoptosis is a novel yet evolutionarily conserved property of the septin7 sub-family of septins.
Keywords: Apoptosis; Programmed cell death; Anti-apoptosis; Anti-apoptotic; Cell survival; Cell size;
Lipid rafts control human melanoma cell migration by regulating focal adhesion disassembly by Ruifei Wang; Jiajia Bi; Khamal Kwesi Ampah; Xueqing Ba; Wenguang Liu; Xianlu Zeng (3195-3205).
Tumor cell migration is a crucial step in the metastatic cascade, and interruption of this step is considered to be logically effective in preventing tumor metastasis. Lipid rafts, distinct liquid ordered plasma membrane microdomains, have been shown to influence cancer cell migration, but the underlying mechanisms are still not well understood. Here, we report that lipid rafts regulate the dynamics of actin cytoskeleton and focal adhesion in human melanoma cell migration. Disrupting the integrity of lipid rafts with methyl-β cyclodextrin enhances actin stress fiber formation and inhibits focal adhesion disassembly, accompanied with alterations in cell morphology. Furthermore, actin cytoskeleton, rather than microtubules, mediates the lipid raft-dependent focal adhesion disassembly by regulating the dephosphorylation of focal adhesion proteins and the internalization of β3 integrin. We also show that Src–RhoA–Rho kinase signaling pathway is responsible for lipid raft disruption-induced stress fiber formation. Taken together, these observations provide a new mechanism to further explain how lipid rafts regulate the migration of melanoma cell and suggest that lipid rafts may be novel and attractive targets for cancer therapy.
Keywords: Lipid raft; Focal adhesion; Actin cytoskeleton; Melanoma cell migration;
The role of Sp1 and EZH2 in the regulation of LMX1A in cervical cancer cells by Wen-Chi Lin; Ming-De Yan; Pei-Ning Yu; Hsin-Jung Li; Chih-Chi Kuo; Chia-Lin Hsu; Ya-Wen Lin (3206-3217).
We have reported previously that LIM homeobox transcription factor 1α (LMX1A) is hypermethylated and functions as a metastasis suppressor in cervical cancer cells. However, the regulation of LMX1A in carcinogenesis has not been reported. We aim to clarify whether specificity protein 1 (Sp1) and enhancer of zeste homolog 2 (EZH2) are involved in the regulation of LMX1A in cervical cancer. First we characterized the LMX1A promoter and used overexpression, knockdown, and reporter assays to show that Sp1 increased LMX1A promoter activity. Next, we used site-directed mutagenesis and electrophoresis mobility shift assays (EMSAs) to demonstrate that Sp1-binding sites were important for Sp1-mediated activation of the LMX1A promoter. Chromatin immunoprecipitation data demonstrated that Sp1 could bind directly to the LMX1A promoter and activate endogenous LMX1A expression in cells pretreated with 5-aza-2′-deoxycytidine (5-aza-dC). Knockdown of EZH2 decreased H3K27me3 histone modification but was insufficient to restore LMX1A expression. To explore the effect of EZH2 on the endogenous LMX1A promoter, we treated EZH2-knockdown cells with 5-aza-dC and trichostatin A (TSA) and then depleted the cells of drugs for 3 days. H3K14ac was enriched at the LMX1A promoter in EZH2-knockdown cells and LMX1A mRNA was still expressed. Taken together, these data imply that Sp1 may activate LMX1A expression upon oncogenic stress during cervical cancer development. Moreover, suppression of EZH2 may delay resilencing of LMX1A after the removal of 5-aza-dC and TSA.
Keywords: LMX1A; Sp1; EZH2; Histone modification; DNA methylation; Cervical cancer;
Aldehyde dehydrogenase-1a1 induces oncogene suppressor genes in B cell populations by R. Yasmeen; J.M. Meyers; C.E. Alvarez; J.L. Thomas; A. Bonnegarde-Bernard; H. Alder; T.L. Papenfuss; D.M. Benson; P.N. Boyaka; O. Ziouzenkova (3218-3227).
The deregulation of B cell differentiation has been shown to contribute to autoimmune disorders, hematological cancers, and aging. We provide evidence that the retinoic acid-producing enzyme aldehyde dehydrogenase 1a1 (Aldh1a1) is an oncogene suppressor in specific splenic IgG1+/CD19− and IgG1+/CD19+ B cell populations. Aldh1a1 regulated transcription factors during B cell differentiation in a sequential manner: 1) retinoic acid receptor alpha (Rara) in IgG1+/CD19− and 2) zinc finger protein Zfp423 and peroxisome proliferator-activated receptor gamma (Pparg) in IgG1+/CD19+ splenocytes. In Aldh1a1 −/− mice, splenic IgG1+/CD19− and IgG1+/CD19+ B cells acquired expression of proto-oncogenic genes c-Fos, c-Jun, and Hoxa10 that resulted in splenomegaly. Human multiple myeloma B cell lines also lack Aldh1a1 expression; however, ectopic Aldh1a1 expression rescued Rara and Znf423 expressions in these cells. Our data highlight a mechanism by which an enzyme involved in vitamin A metabolism can improve B cell resistance to oncogenesis.
Keywords: Homeobox transcription factor; Nuclear receptor; Retinaldehyde; Raldh1; Vitamin A metabolism; Multiple myeloma;
Regulation of autophagic flux by dynein-mediated autophagosomes trafficking in mouse coronary arterial myocytes by Ming Xu; Xiao-xue Li; Jing Xiong; Min Xia; Erich Gulbins; Yang Zhang; Pin-Lan Li (3228-3236).
Autophagic flux is an important process during autophagy maturation in coronary arterial myocytes (CAMs). Here, we defined the role and molecular mechanism of the motor protein dynein in the regulation of autophagic flux in CAMs. In mouse CAMs, dynein protein is abundantly expressed. Pharmacological or genetic inhibition of dynein activity dramatically enhanced 7-ketocholesterol (7-Ket)-induced expression of the autophagic marker LC3B and increased the cellular levels of p62, a selective substrate for autophagy. Inhibition of dynein activity increased 7-Ket-induced formation of autophagosomes (APs), but reduced the number of autophagolysosomes (APLs) in CAMs. Furthermore, 7-Ket increased the fusion of APs with lysosomes and the velocity of APs movement in mouse CAMs, which was abolished when the dynein activity in these cells was inhibited. Interestingly, 7-Ket increased lysosomal Ca2 + release and stimulated dynein ATPase activity, both of which were abolished by NAADP antagonists, NED-19 and PPADS. Taken together, our data suggest that NAADP-mediated Ca2 + release plays a crucial role in regulating dynein activity, which mediates APs trafficking and fusion with lysosomes to form APLs thus regulating autophagic flux in CAMs under atherogenic stimulation.Working model for dynein regulation of autophagic flux in CAMs.Display Omitted
Keywords: Dynein; Autophagy; 7-Ketocholesterol; NAADP; Lysosome;
DNA loop domain organization as revealed by single-cell gel electrophoresis by Katerina Afanasieva; Marianna Chopei; Marianna Zazhytska; Maria Vikhreva; Andrei Sivolob (3237-3244).
At higher order levels chromatin is organized into loops. This looping, which plays an important role in transcription regulation and other processes, remains poorly understood. We investigated the kinetics of DNA loop migration during single cell gel electrophoresis (the comet assay). The migration of a part of the loops was shown to be reversible after switching off electrophoresis and to be sensitive to intercalation-induced changes in supercoiling. Another group of the loops migrates rapidly, the rate being insensitive to the supercoiling level. The largest part of the loops cannot migrate at all, presumably because of their large size. The loop ends can be detached in the presence of high concentrations of intercalators or protein denaturants, thus increasing the fraction of DNA that cannot migrate in the gel. The distribution of the loop length up to 100 kilobases appears to be consistent with the fractal globule organization.
Keywords: DNA loop; Supercoiling; Fractal globule; Nucleoid; Comet assay;
BAG3 sensitizes cancer cells exposed to DNA damaging agents via direct interaction with GRP78 by De-Hui Kong; Qiang Zhang; Xin Meng; Zhi-Hong Zong; Chao Li; Bao-Qin Liu; Yifu Guan; Hua-Qin Wang (3245-3253).
Bcl-2 associated athanogene 3 (BAG3) has a modular structure that contains a BAG domain, a WW domain, a proline-rich (PxxP) domain to mediate potential interactions with chaperons and other proteins that participate in more than one signal transduction. In search for novel interacting partners, the current study identified that 78 kDa glucose-regulated protein (GRP78) was a novel partner interacting with BAG3. Interaction between GRP78 and BAG3 was confirmed by coimmunoprecipitation and glutathione S-transferase (GST) pulldown. We also identified that the ATPase domain of GRP78 and BAG domain of BAG3 mediated their interaction. Counterintuitive for a prosurvival protein, BAG3 was found to promote the cytotoxicity of breast cancer MCF7, thyroid cancer FRO and glioma U87 cells subjected to genotoxic stress. In addition, the current study demonstrated that BAG3 interfered with the formation of the antiapoptotic GRP78-procaspase-7 complex, which resulted in an increased genotoxic stress-induced cytotoxicity in cancer cells. Furthermore, overexpression of GRP78 significantly blocked the enhancing effects of BAG3 on activation of caspase-7 and induction of apoptosis by genotoxic stress. Overall, these results suggested that through direct interaction BAG3 could prevent the antiapoptotic effect of GRP78 upon genotoxic stress.
Keywords: BAG3; GRP78; Caspase-7; DNA damage;
Snf1/AMPK promotes SBF and MBF-dependent transcription in budding yeast by Sara Busnelli; Farida Tripodi; Raffaele Nicastro; Claudia Cirulli; Gabriella Tedeschi; Roberto Pagliarin; Lilia Alberghina; Paola Coccetti (3254-3264).
Snf1, the yeast AMP-activated kinase homolog, regulates the expression of several genes involved in adaptation to glucose limitation and in response to cellular stresses. We previously demonstrated that Snf1 interacts with Swi6, the regulatory subunit of SBF and MBF complexes, and activates CLB5 transcription. Here we report that, in α-factor synchronized cells in 2% glucose, the loss of the Snf1 catalytic subunit impairs the binding of SBF and MBF complexes and the subsequent recruitment of the FACT complex and RNA Polymerase II to promoters of G1-genes. By using an analog-sensitive allele of SNF1, SNF1as (I132G), encoding a protein whose catalytic activity is selectively inhibited in vivo by 2-naphthylmethyl pyrazolopyrimidine 1, we show that the inhibition of Snf1 catalytic activity affects the expression of G1-genes causing a delayed entrance into S phase in cells synchronized in G1 phase by α-factor treatment or by elutriation. Moreover, Snf1 is detected in immune complexes of Rpb1, the large subunit of RNA Polymerase II, and is present at both promoters and coding regions of SBF- and MBF-regulated genes 20 min after α-factor release, suggesting a direct role for Snf1 in the activation of the G1-regulon transcription.Display Omitted
Keywords: Cell cycle; RNA Polymerase II; Saccharomyces cerevisiae; SBF–MBF complexes; Snf1/AMPK; SNF1as (I132G);
The IC138 and IC140 intermediate chains of the I1 axonemal dynein complex bind directly to tubulin by Triscia W. Hendrickson; Jonathan L. Goss; Charles A. Seaton; Henry W. Rohrs (3265-3271).
Dyneins are minus end directed microtubule motors that play a critical role in ciliary and flagellar movement. Ciliary dyneins, also known as axonemal dyneins, are characterized based on their location on the axoneme, either as outer dynein arms or inner dynein arms. The I1 dynein is the best-characterized subspecies of the inner dynein arms; however the interactions between many of the components of the I1 complex and the axoneme are not well defined. In an effort to elucidate the interactions in which the I1 components are involved, we performed zero-length crosslinking on axonemes and studied the crosslinked products formed by the I1 intermediate chains, IC138 and IC140. Our data indicate that IC138 and IC140 bind directly to microtubules. Mass-spectrometry analysis of the crosslinked product identified both α- and β-tubulin as the IC138 and IC140 binding partners. This was further confirmed by crosslinking experiments carried out on purified I1 fractions bound to Taxol-stabilized microtubules. Furthermore, the interaction between IC140 and tubulin is lost when IC138 is absent. Our studies support previous findings that intermediate chains play critical roles in the assembly, axonemal targeting and regulation of the I1 dynein complex.
Keywords: I1 dynein; cilia; Flagellum; Axoneme; Tubulin;
Specificity of miR-378a-5p targeting rodent fibronectin by Fengqiong Liu; Qing Lv; William W. Du; Haoran Li; Xiangling Yang; Danyang Liu; Zhaoqun Deng; Wenhua Ling; Yaou Zhang; Burton B. Yang (3272-3285).
One criterion for microRNA identification is based on their conservation across species, and prediction of miRNA targets by empirical approaches using computational analysis relies on the presence of conservative mRNA 3′UTR. Because most miRNA target sites identified are highly conserved across different species, it is not clear whether miRNA targeting is species-specific. To predict miRNA targeting, we aligned all available fibronectin 3′UTRs and observed significant conservation of all 20 species. Twelve miRNAs were predicted to target most fibronectin 3′UTRs, but rodent fibronectin showed potential binding sites specific for five different miRNAs. One of them, the miR-378a-5p, contained a complete matching seed-region for all rodent fibronectin, which could not be found in any other species. We designed experiments to test whether the species-specific targeting possessed biological function and found that expression of miR-378a-5p decreased cancer cell proliferation, migration, and invasion, resulting in inhibition of tumor growth. Silencing fibronectin expression produced similar effects as miR-378a-5p, while transfection with a construct targeting miR-378-5p produced opposite results. Tumor formation assay showed that enhanced expression of fibronectin in the stromal tissues as a background environment suppressed tumor growth, while increased fibronectin expression inside the tumor cells promoted tumor growth. This was likely due to the different signaling direction, either inside-out or outside-in signal. Our results demonstrated that species-specific targeting by miRNA could also exert functional effects. Thus, one layer of regulation has been added to the complex network of miRNA signaling.
Keywords: MicroRNA; 3′UTR; Fibronectin; Species specificity; Invasion;
The involvement of the docking protein Gab1 in mitogenic signalling induced by EGF and HGF in rat hepatocytes by Monica Aasrum; John Ødegård; Dagny Sandnes; Thoralf Christoffersen (3286-3294).
Grb2-assosiated binder (Gab) family proteins are docking molecules that can interact with receptor tyrosine kinases (RTKs) and cytokine receptors and bind several downstream signalling proteins. Studies in several cell types have shown that Gab1 may have a role in signalling mediated by the two RTKs epidermal growth factor (EGF) receptor (EGFR) and Met, the receptor for hepatocyte growth factor (HGF), but the involvement of Gab1 in EGFR and Met signalling has not been directly compared in the same cell. We have studied mechanisms of activation and role in mitogenic signalling of Gab1 in response to EGF and HGF in cultured rat hepatocytes. Gab1, but not Gab2, was expressed in the hepatocytes and was phosphorylated upon stimulation with EGF or HGF. Depletion of Gab1, using siRNA, decreased the ERK and Akt activation, cyclin D1 expression, and DNA synthesis in response to both EGF and HGF. Studies of mechanisms of recruitment to the receptors showed that HGF induced co-precipitation of Gab1 and Met while EGF induced binding of Gab1 to Grb2 but not to EGFR. Gab1 activation in response to both EGF and HGF was dependent on PI3K. While EGF activated Gab1 and Shc equally, within the same concentration range, HGF very potently and almost exclusively activated Gab1, having only a minimal effect on Shc. Collectively, our results strongly suggest that although Gab1 interacts differently with EGFR and Met, it is involved in mitogenic signalling mediated by both these growth factor receptors in hepatocytes.
Keywords: Gab1; EGFR; Met; PI3K; Hepatocytes; Proliferation;
Herp depletion protects from protein aggregation by up-regulating autophagy by Clara Quiroga; Damian Gatica; Felipe Paredes; Roberto Bravo; Rodrigo Troncoso; Zully Pedrozo; Andrea E. Rodriguez; Barbra Toro; Mario Chiong; Jose Miguel Vicencio; Claudio Hetz; Sergio Lavandero (3295-3305).
Herp is an endoplasmic reticulum (ER) stress inducible protein that participates in the ER-associated protein degradation (ERAD) pathway. However, the contribution of Herp to other protein degradation pathways like autophagy and its connection to other types of stress responses remain unknown. Here we report that Herp regulates autophagy to clear poly-ubiquitin (poly-Ub) protein aggregates. Proteasome inhibition and glucose starvation (GS) led to a high level of poly-Ub protein aggregation that was drastically reduced by stably knocking down Herp (shHerp cells). The enhanced removal of poly-Ub inclusions protected cells from death caused by glucose starvation. Under basal conditions and increasingly after stress, higher LC3-II levels and GFP-LC3 puncta were observed in shHerp cells compared to control cells. Herp knockout cells displayed basal up-regulation of two essential autophagy regulators—Atg5 and Beclin-1, leading to increased autophagic flux. Beclin-1 up-regulation was due to a reduction in Hrd1 dependent proteasomal degradation, and not at transcriptional level. The consequent higher autophagic flux was necessary for the clearance of aggregates and for cell survival. We conclude that Herp operates as a relevant factor in the defense against glucose starvation by modulating autophagy levels. These data may have important implications due to the known up-regulation of Herp in pathological states such as brain and heart ischemia, both conditions associated to acute nutritional stress.
Keywords: Poly-ubiquitinated protein; Endoplasmic reticulum stress; Autophagy; UPR; Protein aggregation; Beclin-1;
Dexamethasone increases αvβ3 integrin expression and affinity through a calcineurin/NFAT pathway by Jennifer A. Faralli; Debjani Gagen; Mark S. Filla; Tania N. Crotti; Donna M. Peters (3306-3313).
The purpose of this study was to determine how dexamethasone (DEX) regulates the expression and activity of αvβ3 integrin. FACS analysis showed that DEX treatment induced expression of an activated αvβ3 integrin. Its expression remained high as long as DEX was present and continued following DEX removal. FACS analysis showed that the upregulation of αvβ3 integrin was the result of an increase in the expression of the β3 integrin subunit. By real time qPCR, DEX treatment induced a 6.2-fold increase (p < 0.04) in β3 integrin mRNA by day 2 compared to control and remained elevated for 6 days of treatment and then an additional 10 days once the DEX was removed. The increase in β3 integrin mRNA levels required only 1 day of DEX treatment to increase levels for 4 days in the absence of DEX. In contrast, DEX did not alter β1 integrin mRNA or protein levels. The DEX-induced upregulation of β3 integrin mRNA was partly due to an increase in its half-life to 60.7 h from 22.5 h in control cultures (p < 0.05) and could be inhibited by RU486 and cycloheximide, suggesting that DEX-induced de novo protein synthesis of an activation factor was needed. The calcineurin inhibitors cyclosporin A (CsA) and FK506 inhibited the DEX induced increase in β3 integrin mRNA. In summary, the DEX-induced increase in β3 integrin is a secondary glucocorticoid response that results in prolonged expression of αvβ3 integrin and the upregulation of the β3 integrin subunit through the calcineurin/NFAT pathway.
Keywords: Cytoskeleton; Integrin; Calcineurin; Glucocorticoids; Glaucoma; Trabecular meshwork;
Mdm10 is an ancient eukaryotic porin co-occurring with the ERMES complex by Nadine Flinner; Lars Ellenrieder; Sebastian B. Stiller; Thomas Becker; Enrico Schleiff; Oliver Mirus (3314-3325).
Mitochondrial β-barrel proteins fulfill central functions in the outer membrane like metabolite exchange catalyzed by the voltage-dependent anion channel (VDAC) and protein biogenesis by the central components of the preprotein translocase of the outer membrane (Tom40) or of the sorting and assembly machinery (Sam50). The mitochondrial division and morphology protein Mdm10 is another essential outer membrane protein with proposed β-barrel fold, which has so far only been found in Fungi. Mdm10 is part of the endoplasmic reticulum mitochondria encounter structure (ERMES), which tethers the ER to mitochondria and associates with the SAM complex. In here, we provide evidence that Mdm10 phylogenetically belongs to the VDAC/Tom40 superfamily. Contrary to Tom40 and VDAC, Mdm10 exposes long loops towards both sides of the membrane. Analyses of single loop deletion mutants of Mdm10 in the yeast Saccharomyces cerevisiae reveal that the loops are dispensable for Mdm10 function. Sequences similar to fungal Mdm10 can be found in species from Excavates to Fungi, but neither in Metazoa nor in plants. Strikingly, the presence of Mdm10 coincides with the appearance of the other ERMES components. Mdm10's presence in both unikonts and bikonts indicates an introduction at an early time point in eukaryotic evolution.Display Omitted
Keywords: Eukaryotic β-barrel protein; Multiple sequence alignment; Homology modeling; Phylogenetic analysis; ERMES; SAM;
Metabolic remodeling in frataxin-deficient yeast is mediated by Cth2 and Adr1 by Armando Moreno-Cermeño; David Alsina; Elisa Cabiscol; Jordi Tamarit; Joaquim Ros (3326-3337).
Frataxin is a mitochondrial protein involved in iron metabolism whose deficiency in humans causes Friedreich ataxia. We performed transcriptomic and proteomic analyses of conditional Yeast Frataxin Homologue (Yfh1) mutants (tetO7 -YFH1) to investigate metabolic remodeling upon Yfh1 depletion. These studies revealed that Yfh1 depletion leads to downregulation of many glucose-repressed genes. Most of them were Adr1 targets, a key transcription factor required for growth in non-fermentable carbon sources. Using a GFP-tagged Adr1, we observed that Yfh1 depletion promotes the export of Adr1 from the nucleus to the cytosol without affecting its protein levels. This effect was also observed upon H2O2 treatment, but not by iron overload/starvation, indicating the presence of a regulatory pathway involved in Adr1 export and inactivation upon stress conditions. We also observed that CTH2, a gene involved in the mRNA degradation of several iron-containing enzymes, was induced upon Yfh1 depletion. Accordingly, decreased levels of aconitase and succinate dehydrogenase were observed. Nevertheless, their levels were maintained in a Δcth2 mutant even in the absence of Yfh1. From these results we can conclude that, in addition to altering iron homeostasis, frataxin depletion involves drastic metabolic remodeling governed by Adr1 and Cth2 that finally leads to downregulation of iron–sulfur proteins and other proteins involved in respiratory metabolism.
Keywords: Friedreich ataxia; Yeast frataxin; Iron; Oxidative stress;
Werner complex deficiency in cells disrupts the Nuclear Pore Complex and the distribution of lamin B1 by Zhi Li; Yizhou Zhu; Yujia Zhai; Michelle R. Castroagudin; Yifei Bao; Tommy E. White; Joseph S. Glavy (3338-3345).
From the surrounding shell to the inner machinery, nuclear proteins provide the functional plasticity of the nucleus. This study highlights the nuclear association of Pore membrane (POM) protein NDC1 and Werner protein (WRN), a RecQ helicase responsible for the DNA instability progeria disorder, Werner Syndrome. In our previous publication, we connected the DNA damage sensor Werner's Helicase Interacting Protein (WHIP), a binding partner of WRN, to the NPC. Here, we confirm the association of the WRN/WHIP complex and NDC1. In established WRN/WHIP knockout cell lines, we further demonstrate the interdependence of WRN/WHIP and Nucleoporins (Nups). These changes do not completely abrogate the barrier of the Nuclear Envelope (NE) but do affect the distribution of FG Nups and the RAN gradient, which are necessary for nuclear transport. Evidence from WRN/WHIP knockout cell lines demonstrates changes in the processing and nucleolar localization of lamin B1. The appearance of “RAN holes” void of RAN corresponds to regions within the nucleolus filled with condensed pools of lamin B1. From WRN/WHIP knockout cell line extracts, we found three forms of lamin B1 that correspond to mature holoprotein and two potential post-translationally modified forms of the protein. Upon treatment with topoisomerase inhibitors lamin B1 cleavage occurs only in WRN/WHIP knockout cells. Our data suggest the link of the NDC1 and WRN as one facet of the network between the nuclear periphery and genome stability. Loss of WRN complex leads to multiple alterations at the NPC and the nucleolus.
Keywords: Nuclear Envelope; Nucleolus; Lamin B1; Werner; Nucleoporins; NDC1;
BAG3 is upregulated by c-Jun and stabilizes JunD by Chao Li; Si Li; De-Hui Kong; Xin Meng; Zhi-Hong Zong; Bao-Qin Liu; Yifu Guan; Zhen-Xian Du; Hua-Qin Wang (3346-3354).
BAG3 plays a regulatory role in a number of cellular processes, including cell proliferation, apoptosis, adhesion and migration, epithelial–mesenchymal transition (EMT), autophagy activation, and virus infection. The AP-1 transcription factors are implicated in a variety of important biological processes including cell differentiation, proliferation, apoptosis and oncogenesis. Recently, it has been reported that AP-1 protein c-Jun inhibits autophagy and enhances apoptotic cell death mediated by starvation. However, the molecular mechanisms remain unclear. For the first time, the current study demonstrated that serum starvation downregulated BAG3 at the transcriptional level via c-Jun. In addition, the current study reported that BAG3 stabilized JunD mRNA, which was, at least in part, responsible for the promotion of serum starvation mediated-growth inhibition by BAG3.
Keywords: BAG3; c-Jun; Growth inhibition; JunD;
Short-term TNFα shedding is independent of cytoplasmic phosphorylation or furin cleavage of ADAM17 by Jeanette Schwarz; Claudia Broder; Ansgard Helmstetter; Stefanie Schmidt; Isabell Yan; Miryam Müller; Dirk Schmidt-Arras; Christoph Becker-Pauly; Friedrich Koch-Nolte; Hans-Willi Mittrücker; Björn Rabe; Stefan Rose-John; Athena Chalaris (3355-3367).
Proteolysis of transmembrane molecules is an irreversible post-translational modification enabling autocrine, paracrine and endocrine signaling of many cytokines. The pro-inflammatory activities of membrane bound TNFα (pro-TNFα) strongly depend on ectodomain shedding mediated by the A Disintegrin And Metalloprotease family member ADAM17. Despite the well-documented role of ADAM17 in pro-TNFα cleavage during inflammation, little is known about its regulation. Mitogen-activated protein kinase-induced phosphorylation of the ADAM17 cytoplasmic tail has been described to be required for proper activation. To address, if pro-TNFα shedding depends on cytosolic phosphorylation we analyzed ADAM17 mutants lacking the cytoplasmic domain. ADAM17 mediated shedding of pro-TNFα was induced by PMA, Anisomycin and the phosphatase inhibitors Cantharidin and Calyculin A. Deletion of the entire cytoplasmic portion of ADAM17 abolished furin-dependent proteolytic maturation and pro-TNFα cleavage. Interestingly, we could exclude that resistance to proconvertase processing is the reason for the enzymatic inactivity of ADAM17 lacking the cytoplasmic portion as furin-resistant ADAM17 mutants rescued genetic ADAM17 deficiency after mitogen-activated protein kinase activation. Adding only 6 cytoplasmic amino acids completely restored ADAM17 maturation and shedding of pro-TNFα as well as of both TNF-receptors Finally, we showed that a pro-TNFα mutant lacking the cytoplasmic portion was also shed from the cell surface. We conclude that pro-TNFα cleavage by its major sheddase ADAM17 does not depend on cytosolic phosphorylation and/or interaction. These results have general implications on understanding the activation mechanism controlling the activity of ADAM17.Display Omitted
Keywords: ADAM17; TNFα; Phosphorylation; Intracellular domain; Furin; Cell surface trafficking;
Progesterone regulates the expression and activity of two mouse isoforms of the glycoprotein folding sensor UDP-Glc: Glycoprotein glucosyltransferase (UGGT) by María B. Prados; Julio J. Caramelo; Silvia E. Miranda (3368-3374).
UDP-Glucose:glycoprotein glucosyltransferase (UGGT) is a central component of the endoplasmic reticulum (ER) glycoprotein-folding quality control system, which prevents the exit of partially folded species. UGGT activity can be regulated by the accumulation of misfolded proteins in the ER, a stimulus that triggers a complex signaling pathway known as unfolded protein response (UPR) which is closely associated with inflammation and disease. In this work, we investigated the effect of progesterone (P4) on the expression and activity of UGGT in a mouse hybridoma. We detected the expression of two UGGT isoforms, UGGT1 and UGGT2, and demonstrated that both isoforms are active in these cells. Interestingly, the expression of each isoform is regulated by high physiological P4 concentrations. This work provides the first evidence of a hormonal regulation of UGGT isoform expression and activity, which might influence the glycoprotein quality control mechanism. These findings could contribute to the study of pathologies triggered by the accumulation of misfolded proteins.
Keywords: Progesterone; Endoplasmic reticulum quality control; UDP-Glc: glycoprotein glucosyltransferase; UPR; Folding;
NADPH oxidase subunit p22phox-mediated reactive oxygen species contribute to angiogenesis and tumor growth through AKT and ERK1/2 signaling pathways in prostate cancer by Qi Li; Guang-Bo Fu; Ji-Tai Zheng; Jun He; Xiao-Bing Niu; Qiu-Dan Chen; Yu Yin; Xu Qian; Qing Xu; Min Wang; An-Fang Sun; Yongqian Shu; Hallgeir Rui; Ling-Zhi Liu; Bing-Hua Jiang (3375-3385).
Excessive generation of reactive oxygen species (ROS) in cancer cells is associated with cancer development, but the underlying mechanisms and therapeutic significance remain elusive. In this study, we reported that levels of ROS and p22phox expression are greatly increased in human prostate cancer tissues, and knockdown of p22phox by specific small interfering RNA (siRNA) decreased ROS levels in prostate cancer cells. We also showed that stable downregulation of p22phox in prostate cancer cells inhibited cell proliferation and colony formation, which was mediated by AKT and extracellular signal-regulated kinase (ERK)1/2 signaling pathways and their downstream molecules hypoxia-inducible factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF). The NADPH oxidase subunit NOX1 was also elevated in prostate cancer cells, and was involved in activation of AKT/ERK/HIF-1/VEGF pathway and regulation of cell proliferation. Knockdown of p22phox resulted in inhibition of tumor angiogenesis and tumor growth in nude mice. These findings reveal a new function of p22phox in tumor angiogenesis and tumor growth, and suggest that p22phox is a potential novel target for prostate cancer treatment.
Keywords: p22phox; ROS; Prostate cancer; Angiogenesis; Tumor growth;
Lipocalin-2 elicited by advanced glycation end-products promotes the migration of vascular smooth muscle cells by Tae-Wook Chung; Hee-Jung Choi; Cheorl-Ho Kim; Han-Sol Jeong; Ki-Tae Ha (3386-3395).
Advanced glycation end-products (AGEs) play key roles in the development of diabetic vascular complications by activating the proliferation and migration of vascular smooth muscle cells. Here, we identified an increase of the migratory properties of human aortic smooth muscle cells (HASMC) through AGE-induced expression of lipocalin-2 (LCN2). Because the AGE-elicited expression of LCN2 was diminished by an antibody against the AGE receptor (RAGE), diphenylene iodonium (DPI), N-acetyl cysteine, LY294002, and SP600125, we suggest that AGEs enhance the expression of LCN2 via a RAGE-NADPH oxidase-reactive oxygen species pathway, leading to the phosphorylation of PI3K-Akt and JNK in HASMCs. In addition, a chromatin immunoprecipitation assay and promoter assay revealed that CCAAT/enhancer binding protein β is crucial for AGE-induced expression of LCN2. However, any other AGE-related signaling pathway, including ERK1/2, p38, NF-κB, and AP-1, did not affect the AGE- induced expression of LCN2. Knockdown of LCN2 expression by shRNA showed that AGE-elicited LCN2 expression enhanced the invasive and migratory properties of HASMCs, but showed no effect on cell proliferation. Considering the importance of HASMC migration in the development of atherosclerosis, our study provides a novel insight into diabetic vascular complications.
Keywords: Advanced glycation end-products; Lipocalin-2; Human aortic smooth muscle cells; Migration; Invasion;
MiR-134-mediated β1 integrin expression and function in mesenchymal stem cells by David M. Poitz; Friedrich Stölzel; Laleh Arabanian; Jens Friedrichs; Denitsa Docheva; Matthias Schieker; Fernando A. Fierro; Uwe Platzbecker; Rainer Ordemann; Carsten Werner; Martin Bornhäuser; Ruth H. Strasser; Gerhard Ehninger; Thomas Illmer (3396-3404).
The composition of the hematopoietic stem cell (HSC) niche within the bone marrow is highly dynamic, tightly regulated, and of importance for various HSC properties. Integrins are important molecules within this niche that influence those properties through the interactions of HSCs and mesenchymal stem cells (MSCs). Here we investigated the function of miR-134 in integrin regulation in MSCs. In MSCs, miR-134 post-transcriptionally regulated β1 integrin expression. This negative regulation of β1 integrin was mediated by the binding of miR-134 to its 3′ untranslated region, which contains two conserved binding sites for miR-134. The miR-134-mediated silencing of β1 integrin in MSCs was shown by atomic force microscopy to decrease the adhesion of 32D cells to MSCs transfected with miR-134. Furthermore, the adhesion of MSCs to fibronectin was reduced after transfection with miR-134. MSCs from patients with myelodysplastic syndrome (MDS) revealed highly significant miR-134 overexpression compared with MSCs from healthy bone marrow donors. MSCs from MDS patients showed lower β1 integrin protein, but not lower mRNA, expression, suggesting post-transcriptional regulation. The present study demonstrates miR-134-mediated negative regulation of β1 integrin that influences cell adhesion to and of MSCs. These results further contribute to our understanding of the complexity of MDS.
Keywords: Mesenchymal stem cells; microRNA; miR-134; β1 integrin; CD29; SCP-1; MDS; Myelodysplastic Syndrome;
ERK1/2 regulates hepatocyte Trib1 in response to mitochondrial dysfunction by Sébastien Soubeyrand; Thet Naing; Amy Martinuk; Ruth McPherson (3405-3414).
The TRIB1 locus (8q24.13) is a novel locus identified and replicated by several genome-wide association studies for associations with plasma triglycerides, apolipoprotein B and coronary artery disease. The TRIB1 protein product, tribbles-like protein 1 (Trib1), regulates MAPK activity. MAP kinases transduce a large variety of external signals, leading to a wide range of cellular responses, including growth, differentiation, inflammation and apoptosis. Importantly, Trib1 has been shown to regulate hepatic lipogenesis and very low density lipoprotein production. Despite the relevance of hepatocyte Trib1 to lipid metabolism and atherosclerosis, little is known about the mechanisms regulating Trib1 itself. Here, we identify the mitochondria axis as a regulator of Trib1. Treatment of HepG2 cells with a short pulse of a low oligomycin concentration led to a potent and prolonged increase in the Trib1 mRNA, an effect that was shared with other mitochondria stressors. HuH7 cells as well murine hepatocytes were also responsive albeit to a weaker extent. The upregulation appeared largely independent of reactive oxygen species generation or metabolic stress and was mainly under transcriptional control, with ERK1/2 playing an important regulating role in the process. While the presence of the Trib1 protein could be inferred, attempts to correlate the increased mRNA to changes in protein level were unsuccessful due to the lack of recognizable Trib1 signal. Our data enrich the current paradigm of Trib1 as an activator of the MAPK pathway by uncovering a role for MAPK in regulating Trib1.
Keywords: TRIB1; Mitochondria; Hepatocytes; Oligomycin; MAPK; HepG2;
Cell shape-dependent early responses of fibroblasts to cyclic strain by Neha Gadhari; Mirren Charnley; Mattia Marelli; Jürgen Brugger; Matthias Chiquet (3415-3425).
Randomly spread fibroblasts on fibronectin-coated elastomeric membranes respond to cyclic strain by a varying degree of focal adhesion assembly and actin reorganization. We speculated that the individual shape of the cells, which is linked to cytoskeletal structure and pre-stress, might tune these integrin-dependent mechanotransduction events. To this aim, fibronectin circles, squares and rectangles of identical surface area (2000 μm2) were micro-contact printed onto elastomeric substrates. Fibroblasts plated on these patterns occupied the corresponding shapes. Cyclic 10% equibiaxial strain was applied to patterned cells for 30 min, and changes in cytoskeleton and cell-matrix adhesions were quantified after fluorescence staining. After strain, megakaryocytic leukemia-1 protein translocated to the nucleus in most cells, indicating efficient RhoA activation independently of cell shape. However, circular and square cells (with radial symmetry) showed a significantly greater increase in the number of actin stress fibers and vinculin-positive focal adhesions after cyclic strain than rectangular (bipolar) cells of identical size. Conversely, cyclic strain induced larger changes in pY397-FAK positive focal complexes and zyxin relocation from focal adhesions to stress fibers in bipolar compared to symmetric cells. Thus, radially symmetric cells responded to cyclic strain with a larger increase in assembly, whereas bipolar cells reacted with more pronounced reorganization of actin stress fibers and matrix contacts. We conclude that integrin-mediated responses to external mechanical strain are differentially modulated in cells that have the same spreading area but different geometries, and do not only depend on mere cell size.
Keywords: Cell shape; Micro-contact printing; Cyclic strain; Actin cytoskeleton; RhoA; Focal adhesion;
Induction of mitochondrial biogenesis protects against caspase-dependent and caspase-independent apoptosis in L6 myoblasts by Aaron D. Dam; Andrew S. Mitchell; Joe Quadrilatero (3426-3435).
Apoptotic signaling plays an important role in skeletal muscle degradation, atrophy, and dysfunction. Mitochondria are central executers of apoptosis by directly participating in caspase-dependent and caspase-independent cell death signaling. Given the important apoptotic role of mitochondria, altering mitochondrial content could influence apoptosis. Therefore, we examined the direct effect of modest, but physiological increases in mitochondrial biogenesis and content on skeletal muscle apoptosis using a cell culture approach. Treatment of L6 myoblasts with SNAP or AICAR (5 h/day for 5 days) significantly increased PGC-1, AIF, cytochrome c, and MnSOD protein content as well as MitoTracker staining. Following induction of mitochondrial biogenesis, L6 myoblasts displayed decreased sensitivity to apoptotic cell death as well as reduced caspase-3 and caspase-9 activation following exposure to staurosporine (STS) and C2-ceramide. L6 myoblasts with higher mitochondrial content also exhibited reduced apoptosis and AIF release following exposure to hydrogen peroxide (H2O2). Analysis of several key apoptosis regulatory proteins (ARC, Bax, Bcl-2, XIAP), antioxidant proteins (catalase, MnSOD, CuZnSOD), and reactive oxygen species (ROS) measures (DCF and MitoSOX fluorescence) revealed that these mechanisms were not responsible for the observed cellular protection. However, myoblasts with higher mitochondrial content were less sensitive to Ca2 +-induced mitochondrial permeability transition pore formation (mPTP) and mitochondrial membrane depolarization. Collectively, these data demonstrate that increased mitochondrial content at physiological levels provides protection against apoptotic cell death by decreasing caspase-dependent and caspase-independent signaling through influencing mitochondrial Ca2 +-mediated apoptotic events. Therefore, increasing mitochondrial biogenesis/content may represent a potential therapeutic approach in skeletal muscle disorders displaying increased apoptosis.
Keywords: Cell death; Apoptosis inducing factor; Skeletal muscle; Mitochondrium; AICAR; SNAP;
The BRCA1-binding protein BRAP2 can act as a cytoplasmic retention factor for nuclear and nuclear envelope-localizing testicular proteins by Rebecca G. Davies; Kylie M. Wagstaff; Eileen A. McLaughlin; Kate L. Loveland; David A. Jans (3436-3444).
Regulation of nuclear protein import is central to many cellular processes such as development, with a key mechanism being factors that retain cargoes in the cytoplasm that normally localize in the nucleus. The breast cancer antigen BRCA1-binding protein BRAP2 has been reported as a novel negative regulator of nuclear import of various nuclear localization signal (NLS)-containing viral and cellular proteins, but although implicated in differentiation pathways and highly expressed in tissues including testis, the gamut of targets for BRAP2 action in a developmental context is unknown. As a first step towards defining the BRAP2 interactome, we performed a yeast-2-hybrid screen to identify binding partners of BRAP2 in human testis. Here we report characterization for the first time of three of these: the high mobility group (HMG)-box-domain-containing chromatin component HMG20A, nuclear mitotic apparatus protein NuMA1 and synaptic nuclear envelope protein SYNE2. Co-immunoprecipitation experiments indicate association of BRAP2 with HMG20A, NuMA1, and SYNE2 in testis, underlining the physiological relevance of the interactions, with immunohistochemistry showing that where BRAP2 is co-expressed with HMG20A and NuMA1, both are present in the cytoplasm, in contrast to their nuclear localization in other testicular cell types. Importantly, quantitative confocal microscopic analysis of cultured cells indicates that ectopic expression of BRAP2 inhibits nuclear localization of HMG20A and NuMA1, and prevents nuclear envelope accumulation of SYNE2, the first report of BRAP2 altering localization of a non-nuclear protein. These results imply for the first time that BRAP2 may have an important role in modulating subcellular localization during testicular development.
Keywords: BRAP2; Nuclear transport; Cytoplasmic retention factor; HMG20A; NuMA1; SYNE2;
Corrigendum to “Cyclical strain modulates metalloprotease and matrix gene expression in human tenocytes via activation of TGFβ” [Biochim. Biophys. Acta (2013) 2596–2607] by Eleanor R. Jones; Gavin C. Jones; Kirsten Legerlotz; Graham P. Riley (3445-3446).
Cell death pathways by Slaven Stekovic; Frank Madeo (3447).
Crosstalk between apoptosis, necrosis and autophagy by Vassiliki Nikoletopoulou; Maria Markaki; Konstantinos Palikaras; Nektarios Tavernarakis (3448-3459).
Apoptosis and necrosis are the two major modes of cell death, the molecular mechanisms of which have been extensively studied. Although initially thought to constitute mutually exclusive cellular states, recent findings reveal cellular contexts that require a balanced interplay between these two modes of cellular demise. Several death initiator and effector molecules, signaling pathways and subcellular sites have been identified as key mediators in both processes, either by constituting common modules or alternatively by functioning as a switch allowing cells to decide which route to take, depending on the specific situation. Importantly, autophagy, which is a predominantly cytoprotective process, has been linked to both types of cell death, serving either a pro-survival or pro-death function. Here we review the recent literature that highlights the intricate interplay between apoptosis, necrosis and autophagy, focusing on the relevance and impact of this crosstalk in normal development and in pathology. This article is part of a Special Section entitled: Cell Death Pathways. Guest Editors: Frank Madeo and Slaven Stekovic.
Keywords: Apoptosis; Autophagy; Cell death; Mitoptosis; Necroptosis; Necrosis;
ER stress-induced cell death mechanisms by Renata Sano; John C. Reed (3460-3470).
The endoplasmic-reticulum (ER) stress response constitutes a cellular process that is triggered by a variety of conditions that disturb folding of proteins in the ER. Eukaryotic cells have developed an evolutionarily conserved adaptive mechanism, the unfolded protein response (UPR), which aims to clear unfolded proteins and restore ER homeostasis. In cases where ER stress cannot be reversed, cellular functions deteriorate, often leading to cell death. Accumulating evidence implicates ER stress-induced cellular dysfunction and cell death as major contributors to many diseases, making modulators of ER stress pathways potentially attractive targets for therapeutics discovery. Here, we summarize recent advances in understanding the diversity of molecular mechanisms that govern ER stress signaling in health and disease. This article is part of a Special Section entitled: Cell Death Pathways. Guest Editors: Frank Madeo and Slaven Stekovic.
Keywords: ER Stress; Cell death mechanisms; Diseases;
Cell death by cornification by Leopold Eckhart; Saskia Lippens; Erwin Tschachler; Wim Declercq (3471-3480).
Epidermal keratinocytes undergo a unique form of terminal differentiation and programmed cell death known as cornification. Cornification leads to the formation of the outermost skin barrier, i.e. the cornified layer, as well as to the formation of hair and nails. Different genes are expressed in coordinated waves to provide the structural and regulatory components of cornification. Differentiation-associated keratin intermediate filaments form a complex scaffold accumulating in the cytoplasm and, upon removal of cell organelles, fill the entire cell interior mainly to provide mechanical strength. In addition, a defined set of proteins is cross-linked by transglutamination in the cell periphery to form the so-called cornified envelope. Extracellular modifications include degradation of the tight linkages between corneocytes by excreted proteases, which allows corneocyte shedding by desquamation, and stacking and modification of the excreted lipids that fill the intercellular spaces between corneocytes to provide a water-repellant barrier. In hard skin appendages such as hair and nails these tight intercorneocyte connections remain permanent. Various lines of evidence exist for a role of organelle disintegration, proteases, nucleases, and transglutaminases contributing to the actual cell death event. However, many mechanistic aspects of kearatinocyte death during cornification remain elusive. Importantly, it has recently become clear that keratinocytes activate anti-apoptotic and anti-necroptotic pathways to prevent premature cell death during terminal differentiation. This review gives an overview of the current concept of cornification as a mode of programmed cell death and the anti-cell death mechanisms in the epidermis that secure epidermal homeostasis. This article is part of a Special Section entitled: Cell Death Pathways. Guest Editors: Frank Madeo and Slaven Stekovic.
Keywords: Keratinocyte; Cornification; Apoptosis; Necrosis; NF-κB;
Anoikis molecular pathways and its role in cancer progression by Paolo Paoli; Elisa Giannoni; Paola Chiarugi (3481-3498).
Anoikis is a programmed cell death induced upon cell detachment from extracellular matrix, behaving as a critical mechanism in preventing adherent-independent cell growth and attachment to an inappropriate matrix, thus avoiding colonizing of distant organs. As anchorage-independent growth and epithelial–mesenchymal transition, two features associated with anoikis resistance, are vital steps during cancer progression and metastatic colonization, the ability of cancer cells to resist anoikis has now attracted main attention from the scientific community. Cancer cells develop anoikis resistance due to several mechanisms, including change in integrins' repertoire allowing them to grow in different niches, activation of a plethora of inside-out pro-survival signals as over-activation of receptors due to sustained autocrine loops, oncogene activation, growth factor receptor overexpression, or mutation/upregulation of key enzymes involved in integrin or growth factor receptor signaling. In addition, tumor microenvironment has also been acknowledged to contribute to anoikis resistance of bystander cancer cells, by modulating matrix stiffness, enhancing oxidative stress, producing pro-survival soluble factors, triggering epithelial–mesenchymal transition and self-renewal ability, as well as leading to metabolic deregulations of cancer cells. All these events help cancer cells to inhibit the apoptosis machinery and sustain pro-survival signals after detachment, counteracting anoikis and constituting promising targets for anti-metastatic pharmacological therapy. This article is part of a Special Section entitled: Cell Death Pathways. Guest Editors: Frank Madeo and Slaven Stekovic.
Keywords: Anoikis; Cancer; MicroRNA; Metabolism; Reactive oxygen species;
Developmentally programmed cell death in Drosophila by Donna Denton; May T. Aung-Htut; Sharad Kumar (3499-3506).
During the development of metazoans, programmed cell death (PCD) is essential for tissue patterning, removal of unwanted cells and maintaining homeostasis. In the past 20 years Drosophila melanogaster has been one of the systems of choice for studies involving developmental cell death, providing an ideal genetically tractable model of intermediary complexity between Caenorhabditis elegans and mammals. The lessons learned from studies using Drosophila indicate both the conserved nature of the many cell death pathways as well as novel and unexpected mechanisms. In this article we review the understanding of PCD during Drosophila development, highlighting the key mechanisms that are evolutionarily conserved as well as apparently unusual pathways, which indicate divergence, but provide evidence of complexity acquired during organismic evolution. This article is part of a Special Section entitled: Cell Death Pathways. Guest Editors: Frank Madeo and Slaven Stekovic.
Keywords: Apoptosis; Autophagy; Caspases; Development; Drosophila; Programmed cell death;
When ER stress reaches a dead end by Hery Urra; Estefanie Dufey; Fernanda Lisbona; Diego Rojas-Rivera; Claudio Hetz (3507-3517).
Endoplasmic reticulum (ER) stress is a common feature of several physiological and pathological conditions affecting the function of the secretory pathway. To restore ER homeostasis, an orchestrated signaling pathway is engaged that is known as the unfolded protein response (UPR). The UPR has a primary function in stress adaptation and cell survival; however, under irreversible ER stress a switch to pro-apoptotic signaling events induces apoptosis of damaged cells. The mechanisms that initiate ER stress-dependent apoptosis are not fully understood. Several pathways have been described where we highlight the participation of the BCL-2 family of proteins and ER calcium release. In addition, recent findings also suggest that microRNAs and oxidative stress are relevant players on the transition from adaptive to cell death programs. Here we provide a global and integrated overview of the signaling networks that may determine the elimination of a cell under chronic ER stress. This article is part of a Special Section entitled: Cell Death Pathways. Guest Editors: Frank Madeo and Slaven Stekovic.
Keywords: Cell death; ER stress; Unfolded protein response; Adaptation; Apoptosis;