BBA - Molecular Cell Research (v.1853, #1)
Editorial Board (i).
The RNA-binding protein RBPMS1 represses AP-1 signaling and regulates breast cancer cell proliferation and migration by Jie Fu; Long Cheng; Yu Wang; Ping Yuan; Xiaojie Xu; Lihua Ding; Hao Zhang; Kai Jiang; Haifeng Song; Zhongwu Chen; Qinong Ye (1-13).
The activator protein-1 (AP-1) transcription factor complex plays a crucial role in tumor growth and progression. However, how AP-1 transcriptional activity is repressed is not fully understood. Here, we show that RNA-binding protein with multiple splicing 1 (RBPMS1) physically and functionally interacts with AP-1 in vitro and in vivo. The RNA-recognition motif (RRM) and C-terminus of the RBPMS1 isoforms RBPMS1A and RBPMS1C, but not RBPMS1B, interacted with cFos, a member of the AP-1 family that dimerizes with cJun to stimulate AP-1 transcriptional activity. RBPMS1 did not associate with Jun proteins. RBPMS1A and RBPMS1C bound to the basic leucine zipper (bZIP) domain of cFos that mediates dimerization of AP-1 proteins. In addition, RBPMS1A-C interacted with the transcription factor Smad3, which was shown to interact with cJun and increase AP-1 transcriptional activity. RBPMS1 inhibited c-Fos or Smad3-mediated AP-1 transactivation and the expression of AP-1 target genes known to be the key regulators of cancer growth and progression, including vascular endothelial growth factor (VEGF) and cyclin D1. Mechanistically, RBPMS1 blocks the formation of the cFos/cJun or Smad3/cJun complex as well as the recruitment of cFos or Smad3 to the promoters of AP-1 target genes. In cultured cells and a mouse xenograft model, RBPMS1 inhibited the growth and migration of breast cancer cells through c-Fos or Smad3. These data suggest that RBPMS1 is a critical repressor of AP-1 signaling and RBPMS1 activation may be a useful strategy for cancer treatment.
Keywords: AP-1; RBPMS1; Protein–protein interaction; Breast cancer; Cell growth; Cell migration;
Autophagy in acute leukemias: A double-edged sword with important therapeutic implications by Cecilia Evangelisti; Camilla Evangelisti; Francesca Chiarini; Annalisa Lonetti; Francesca Buontempo; Luca M. Neri; James A. McCubrey; Alberto M. Martelli (14-26).
Macroautophagy, usually referred to as autophagy, is a degradative pathway wherein cytoplasmatic components such as aggregated/misfolded proteins and organelles are engulfed within double-membrane vesicles (autophagosomes) and then delivered to lysosomes for degradation. Autophagy plays an important role in the regulation of numerous physiological functions, including hematopoiesis, through elimination of aggregated/misfolded proteins, and damaged/superfluous organelles. The catabolic products of autophagy (amino acids, fatty acids, nucleotides) are released into the cytosol from autophagolysosomes and recycled into bio-energetic pathways. Therefore, autophagy allows cells to survive starvation and other unfavorable conditions, including hypoxia, heat shock, and microbial pathogens. Nevertheless, depending upon the cell context and functional status, autophagy can also serve as a death mechanism. The cohort of proteins that constitute the autophagy machinery function in a complex, multistep biochemical pathway which has been partially identified over the past decade. Dysregulation of autophagy may contribute to the development of several disorders, including acute leukemias. In this kind of hematologic malignancies, autophagy can either act as a chemo-resistance mechanism or have tumor suppressive functions, depending on the context. Therefore, strategies exploiting autophagy, either for activating or inhibiting it, could find a broad application for innovative treatment of acute leukemias and could significantly contribute to improved clinical outcomes. These aspects are discussed here after a brief introduction to the autophagic molecular machinery and its roles in hematopoiesis.
Keywords: Autophagy; Hematopoietic stem cell; Acute leukemia; Cell survival; Cell death; Targeted therapy;
An optical labeling-based proliferation assay system reveals the paracrine effect of interleukin-6 in breast cancer by Junji Itou; Sunao Tanaka; Fumiaki Sato; Ryutaro Akiyama; Yasuhiko Kawakami; Masakazu Toi (27-40).
Proliferation analysis is one of the basic approaches to characterize various cell types. In conventional cell proliferation assays, the same sample cannot be observed over time, nor can a specific group within a heterogeneous population of cells, for example, cancerous cells, be analyzed separately. To overcome these limitations, we established an optical labeling-based proliferation assay system with the Kaede protein, whose fluorescence can be irreversibly photoconverted from green to red by irradiation. After a single non-toxic photoconversion event, the intensity of red fluorescence in each cell is reduced by cell division. From this, we developed a simple method to quantify cell proliferation by monitoring reduction of red fluorescence over time. This study shows that the optical labeling-based proliferation assay is a viable novel method to analyze cell proliferation, and could enhance our understanding of mechanisms regulating cell proliferation machinery. We used this newly established system to analyze the functions of secreted interleukin-6 (IL-6) in cancer cell proliferation, which had not been fully characterized. Reduction in proliferation was observed following IL-6 knockdown. However, after co-culturing with IL-6-expressing cells, the proliferation of Kaede-labeled IL-6-knockdown cells was restored. These data indicate that in basal-like breast cancer cells, IL-6 exhibits a paracrine effect to positively regulate cell proliferation. Our results thus demonstrate that cancer cells can secrete signaling molecules, such as IL-6, to support the proliferation of other cancer cells.Display Omitted
Keywords: Breast cancer; Interleukin-6; Optical labeling; Paracrine effect; Proliferation; The OPA system;
N-linked Glycosylation on the N-terminus of the dopamine D2 and D3 receptors determines receptor association with specific microdomains in the plasma membrane by Chengchun Min; Mei Zheng; Xiaohan Zhang; Shuohan Guo; Kyoung-Ja Kwon; Chan Young Shin; Hyeong-Suk Kim; Seung Hoon Cheon; Kyeong-Man Kim (41-51).
Numerous G protein-coupled receptors (GPCRs) are glycosylated at extracellular regions. The regulatory roles of glycosylation on receptor function vary across receptor types. In this study, we used the dopamine D2 and D3 receptors as an experimental model to understand the underlying principles governing the functional roles of glycosylation. We used the pharmacological inhibitor, tunicamycin, to inhibit glycosylation, generated chimeric D2 and D3 receptors by swapping their respective N-termini, and produced the glycosylation site mutant D2 and D3 receptors to study the roles of glycosylation on receptor functions, including cell surface expression, signaling, and internalization through specific microdomains. Our results demonstrate that glycosylation on the N-terminus of the D3 receptor is involved in the development of desensitization and proper cell surface expression. In addition, glycosylation on the N-terminus mediates the internalization of D2 and D3 receptors within the caveolae and clathrin-coated pit microdomains of the plasma membrane, respectively, by regulating receptor interactions with caveolin-1 and clathrin. In conclusion, this study shows for the first time that glycosylation on the N-terminus of GPCRs is involved in endocytic pathway selection through specific microdomains. These data suggest that changes in the cellular environment that influence posttranslational modification could be an important determinant of intracellular GPCR trafficking.Display Omitted
Keywords: MβCD; PNGaseF; Post-translational modification;
Thermotolerance induced at a mild temperature of 40 °C alleviates heat shock-induced ER stress and apoptosis in HeLa cells by Ahmed Bettaieb; Diana A. Averill-Bates (52-62).
Hyperthermia (39–45 °C) has emerged as an alternate prospect for cancer therapy in combination with radiation and chemotherapy. Despite promising progress in the clinic, molecular mechanisms involved in hyperthermia-induced cell death are not clear. Hyperthermia causes protein denaturation/aggregation, which results in cell death by apoptosis and/or necrosis. Hyperthermia also induces thermotolerance, which renders cells resistant to subsequent exposure to lethal heat shock. This study investigates the role of both lethal (42–43 °C) and mild (40 °C) hyperthermia in regulating ER stress and ER stress-induced apoptosis in HeLa cells. The ability of mild thermotolerance induced at 40 °C to alleviate either or both of these processes is also determined. Hyperthermia (42–43 °C) induced ER stress, revealed by phosphorylation of PERK, eIF2α and IRE1α, cleavage of ATF6 and increased expression of BiP and sXBP1. Real-time PCR revealed that mRNA levels of ATF6, ATF4, BiP, sXBP1 and CHOP increased in cells exposed to hyperthermia. Moreover, hyperthermia caused disruption of calcium homeostasis and activated the calpain-calpastatin proteolytic system and ER resident caspase 4. Pre-exposure to mild hyperthermia (40 °C) alleviated the induction of cytotoxicity and ER stress by hyperthermia (42–43 °C) and protected cells against ER stress-induced apoptosis. ShRNA-mediated depletion of Hsp72 abrogated protective effects of mild thermotolerance (40 °C) against heat-shock induced ER stress and sensitized cells to ER stress-mediated apoptosis. Our findings show that Hsp72 contributes to the protective effects of mild hyperthermia (40 °C) against hyperthermia-induced ER stress and apoptosis.
Keywords: Hyperthermia; ER stress; Apoptosis; Calpain; Caspase; Hsp72;
Corrigendum to “Interaction of the human prostacyclin receptor and the NHERF4 family member intestinal and kidney enriched PDZ protein (IKEPP)” [Biochim. Biophy. Acta 1823 (2012) 1998–2012] by Helen M. Reid; Elizebeth C. Turner; Eamon P. Mulvaney; Paula B. Hyland; Caitriona McLean; B. Therese Kinsella (63-64).
AMPKα1 deficiency promotes cellular proliferation and DNA damage via p21 reduction in mouse embryonic fibroblasts by Hairong Xu; Yanhong Zhou; Kathleen A. Coughlan; Ye Ding; Shaobin Wang; Yue Wu; Ping Song; Ming-Hui Zou (65-73).
Emerging evidence suggests that activation of adenosine monophosphate-activated protein kinase (AMPK), an energy gauge and redox sensor, controls the cell cycle and protects against DNA damage. However, the molecular mechanisms by which AMPKα isoform regulates DNA damage remain largely unknown. The aim of this study was to determine if AMPKα deletion contributes to cellular hyperproliferation by reducing p21WAF1/Cip1 (p21) expression thereby leading to accumulated DNA damage. The markers for DNA damage, cell cycle proteins, and apoptosis were monitored in cultured mouse embryonic fibroblasts (MEFs) isolated from wild type (WT, C57BL/6J), AMPKα1, or AMPKα2 homozygous deficient (AMPKα1−/−, AMPKα2−/−) mice by Western blot, flow cytometry, and cellular immunofluorescence staining. Deletion of AMPKα1, the predominant AMPKα isoform, but not AMPKα2 in immortalized MEFs led to spontaneous DNA double-strand breaks (DSB) which corresponded to repair protein p53-binding protein 1 (53BP1) foci formation and subsequent apoptosis. Furthermore, AMPKα1 localizes to chromatin and AMPKα1 deletion down-regulates cyclin-dependent kinase inhibitor, p21, an important protein that plays a role in decreasing the incidence of spontaneous DSB via inhibition of cell proliferation. In addition, AMPKα1 null cells exhibited enhanced cell proliferation. Finally, p21 overexpression partially blocked the cellular hyperproliferation of AMPKα1-deleted MEFs via the inhibition of cyclin-dependent kinase 2 (CDK2). Taken together, our results suggest that AMPKα1 plays a fundamental role in controlling the cell cycle thereby affecting DNA damage and cellular apoptosis.
Keywords: AMPKα; p21; 53BP1; DNA damage; Cell proliferation; Apoptosis;
Assembly of β-barrel proteins in the mitochondrial outer membrane by Alexandra I.C. Höhr; Sebastian P. Straub; Bettina Warscheid; Thomas Becker; Nils Wiedemann (74-88).
Mitochondria evolved through endosymbiosis of a Gram-negative progenitor with a host cell to generate eukaryotes. Therefore, the outer membrane of mitochondria and Gram-negative bacteria contain pore proteins with β-barrel topology. After synthesis in the cytosol, β-barrel precursor proteins are first transported into the mitochondrial intermembrane space. Folding and membrane integration of β-barrel proteins depend on the mitochondrial sorting and assembly machinery (SAM) located in the outer membrane, which is related to the β-barrel assembly machinery (BAM) in bacteria. The SAM complex recognizes β-barrel proteins by a β-signal in the C-terminal β-strand that is required to initiate β-barrel protein insertion into the outer membrane. In addition, the SAM complex is crucial to form membrane contacts with the inner mitochondrial membrane by interacting with the mitochondrial contact site and cristae organizing system (MICOS) and shares a subunit with the endoplasmic reticulum–mitochondria encounter structure (ERMES) that links the outer mitochondrial membrane to the endoplasmic reticulum (ER).
Keywords: Bacteria; Beta-barrel; Mitochondria; Outer membrane; Protein assembly; Protein import;
Mutant p53 stimulates chemoresistance of pancreatic adenocarcinoma cells to gemcitabine by Claudia Fiorini; Marco Cordani; Chiara Padroni; Giovanni Blandino; Silvia Di Agostino; Massimo Donadelli (89-100).
Pancreatic adenocarcinoma (PDAC) is the fourth leading cause of cancer-related deaths worldwide; PDAC is characterized by poor prognosis, resistance to conventional chemotherapy and high mortality rate. TP53 tumor suppressor gene is frequently mutated in PDAC, resulting in the accumulation of mutated protein with potential gain-of-function (GOF) activities, such as genomic instability, hyperproliferation and chemoresistance. The purpose of this study was to assess the relevance of the p53 status on the PDAC cells response to the standard drug gemcitabine. We also examined the potential therapeutic effect of p53-reactivating molecules to restore the mutant p53 function in GEM treated PDAC cells. We showed that gemcitabine stabilized mutant p53 protein in the nuclei and induced chemoresistance, concurrent with the mutant p53-dependent expression of Cdk1 and CCNB1 genes, resulting in a hyperproliferation effect. Despite the adverse activation of mutant p53 by gemcitabine, simultaneous treatment of PDAC cells with gemcitabine and p53-reactivating molecules (CP-31398 and RITA) reduced growth rate and induced apoptosis. This synergistic effect was observed in both wild-type and mutant p53 cell lines and was absent in p53-null cells. The combination drug treatment induced p53 phosphorylation on Ser15, apoptosis and autophagosome formation. Furthermore, pharmacological inhibition of autophagy further increased apoptosis stimulated by gemcitabine/CP-31398 treatment. Together, our results show that gemcitabine aberrantly stimulates mutant p53 activity in PDAC cells identifying key processes with potential for therapeutic targeting. Our data also support an anti-tumoral strategy based on inhibition of autophagy combined with p53 activation and standard chemotherapy for both wild-type and mutant p53 expressing PDACs.Display Omitted
Keywords: Pancreatic adenocarcinoma; Gemcitabine; Mutant p53; Gain-of-function (GOF); Autophagy; p53-reactivating molecules;
A charge-dependent mechanism is responsible for the dynamic accumulation of proteins inside nucleoli by Yana R. Musinova; Eugenia Y. Kananykhina; Daria M. Potashnikova; Olga M. Lisitsyna; Eugene V. Sheval (101-110).
The majority of known nucleolar proteins are freely exchanged between the nucleolus and the surrounding nucleoplasm. One way proteins are retained in the nucleoli is by the presence of specific amino acid sequences, namely nucleolar localization signals (NoLSs). The mechanism by which NoLSs retain proteins inside the nucleoli is still unclear. Here, we present data showing that the charge-dependent (electrostatic) interactions of NoLSs with nucleolar components lead to nucleolar accumulation as follows: (i) known NoLSs are enriched in positively charged amino acids, but the NoLS structure is highly heterogeneous, and it is not possible to identify a consensus sequence for this type of signal; (ii) in two analyzed proteins (NF-κB-inducing kinase and HIV-1 Tat), the NoLS corresponds to a region that is enriched for positively charged amino acid residues; substituting charged amino acids with non-charged ones reduced the nucleolar accumulation in proportion to the charge reduction, and nucleolar accumulation efficiency was strongly correlated with the predicted charge of the tested sequences; and (iii) sequences containing only lysine or arginine residues (which were referred to as imitative NoLSs, or iNoLSs) are accumulated in the nucleoli in a charge-dependent manner. The results of experiments with iNoLSs suggested that charge-dependent accumulation inside the nucleoli was dependent on interactions with nucleolar RNAs. The results of this work are consistent with the hypothesis that nucleolar protein accumulation by NoLSs can be determined by the electrostatic interaction of positively charged regions with nucleolar RNAs rather than by any sequence-specific mechanism.
Keywords: Nucleolus; Nucleolar localization signal; RNA; B23;
New insights into the peroxisomal protein inventory: Acyl-CoA oxidases and -dehydrogenases are an ancient feature of peroxisomes by Fátima Camões; Markus Islinger; Sofia C. Guimarães; Sreedhar Kilaru; Martin Schuster; Luis F. Godinho; Gero Steinberg; Michael Schrader (111-125).
Peroxisomes are ubiquitous organelles which participate in a variety of essential biochemical pathways. An intimate interrelationship between peroxisomes and mitochondria is emerging in mammals, where both organelles cooperate in fatty acid β-oxidation and cellular lipid homeostasis. As mitochondrial fatty acid β-oxidation is lacking in yeast and plants, suitable genetically accessible model systems to study this interrelationship are scarce. Here, we propose the filamentous fungus Ustilago maydis as a suitable model for those studies. We combined molecular cell biology, bioinformatics and phylogenetic analyses and provide the first comprehensive inventory of U. maydis peroxisomal proteins and pathways. Studies with a peroxisome-deficient Δpex3 mutant revealed the existence of parallel and complex, cooperative β-oxidation pathways in peroxisomes and mitochondria, mimicking the situation in mammals. Furthermore, we provide evidence that acyl-CoA dehydrogenases (ACADs) are bona fide peroxisomal proteins in fungi and mammals and together with acyl-CoA oxidases (ACOX) belong to the basic enzymatic repertoire of peroxisomes. A genome comparison with baker's yeast and human gained new insights into the basic peroxisomal protein inventory shared by humans and fungi and revealed novel peroxisomal proteins and functions in U. maydis. The importance of our findings for the evolution and function of the complex interrelationship between peroxisomes and mitochondria in fatty acid β-oxidation is discussed.
Keywords: Peroxisome; Ustilago maydis; Fatty acid beta-oxidation; Mitochondria; Filamentous fungus; Organelle biogenesis;
Biphasic effects of luteolin on interleukin-1β-induced cyclooxygenase-2 expression in glioblastoma cells by Sylvie Lamy; Paula Liana Moldovan; Aroua Ben Saad; Borhane Annabi (126-135).
Success in developing therapeutic approaches to target brain tumor-associated inflammation in patients has been limited. Given that the inflammatory microenvironment is a hallmark signature of solid tumor development, anti-inflammatory targeting strategies have been envisioned as preventing glioblastoma initiation or progression. Consumption of foods from plant origin is associated with reduced risk of developing cancers, a chemopreventive effect that is, in part, attributed to their high content of phytochemicals with potent anti-inflammatory properties. We explored whether luteolin, a common flavonoid in many types of plants, may inhibit interleukin (IL)-1β function induction of the inflammation biomarker cyclooxygenase (COX)-2. We found that IL-1β triggered COX-2 expression in U-87 glioblastoma cells and synergized with luteolin to potentiate or inhibit that induction in a biphasic manner. Luteolin pretreatment of cells inhibited IL-1β-mediated phosphorylation of inhibitor of κB, nuclear transcription factor-κB (NF-κB) p65, extracellular signal-regulated kinase-1/2, and c-Jun amino-terminal kinase in a concentration-dependent manner. Luteolin also inhibited AKT phosphorylation and survivin expression, while it triggered both caspase-3 cleavage and expression of glucose-regulated protein 78. These effects were all potentiated by IL-1β, in part through increased nuclear translocation of NF-κB p65. Finally, luteolin was able to reduce IL-1 receptor gene expression, and treatment with IL-1 receptor antagonist or gene silencing of IL-1 receptor prevented IL-1β/luteolin-induced COX-2 expression. Our results document a novel adaptive cellular response to luteolin, which triggers anti-survival and anti-inflammatory mechanisms that contribute to the chemopreventive properties of this diet-derived molecule.
Keywords: COX-2; Inflammation; Interleukin-1; Luteolin; NF-κB; Glioblastoma;
SUMO modification of TBK1 at the adaptor-binding C-terminal coiled-coil domain contributes to its antiviral activity by Vera V. Saul; Rainer Niedenthal; Andreas Pich; Friedemann Weber; M. Lienhard Schmitz (136-143).
The non-canonical IKK kinase TBK1 serves as an important signal transmitter of the antiviral interferon response, but is also involved in the regulation of further processes such as autophagy. The activity of TBK1 is regulated by posttranslational modifications comprising phosphorylation and ubiquitination. This study identifies SUMOylation as a novel posttranslational TBK1 modification. TBK1 kinase activity is required to allow the attachment of SUMO1 or SUMO2/3 proteins. Since TBK1 does not bind to the E2 enzyme Ubc9, this modification most likely proceeds via trans-SUMOylation. Mass spectrometry allowed identifying K694 as the SUMO acceptor site, a residue located in the C-terminal coiled-coil domain which is exclusively responsible for the association with the adaptor proteins NAP1, Sintbad and TANK. SUMO modification at K694 contributes to the antiviral function of TBK1 and accordingly the viral protein Gam1 antagonizes this posttranslational modification.Display Omitted
Keywords: SUMO; Rift Valley fever (RVF) virus; Interferon; TBK1; NF-κB;
The yeast Arf-GAP Glo3p is required for the endocytic recycling of cell surface proteins by Daiki Kawada; Hiromu Kobayashi; Tsuyoshi Tomita; Eisuke Nakata; Makoto Nagano; Daria Elisabeth Siekhaus; Junko Y. Toshima; Jiro Toshima (144-156).
Small GTP-binding proteins of the Ras superfamily play diverse roles in intracellular trafficking. Among them, the Rab, Arf, and Rho families function in successive steps of vesicle transport, in forming vesicles from donor membranes, directing vesicle trafficking toward target membranes and docking vesicles onto target membranes. These proteins act as molecular switches that are controlled by a cycle of GTP binding and hydrolysis regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). In this study we explored the role of GAPs in the regulation of the endocytic pathway using fluorescently labeled yeast mating pheromone α-factor. Among 25 non-essential GAP mutants, we found that deletion of the GLO3 gene, encoding Arf-GAP protein, caused defective internalization of fluorescently labeled α-factor. Quantitative analysis revealed that glo3Δ cells show defective α-factor binding to the cell surface. Interestingly, Ste2p, the α-factor receptor, was mis-localized from the plasma membrane to the vacuole in glo3Δ cells. Domain deletion mutants of Glo3p revealed that a GAP-independent function, as well as the GAP activity, of Glo3p is important for both α-factor binding and Ste2p localization at the cell surface. Additionally, we found that deletion of the GLO3 gene affects the size and number of Arf1p-residing Golgi compartments and causes a defect in transport from the TGN to the plasma membrane. Furthermore, we demonstrated that glo3Δ cells were defective in the late endosome-to-TGN transport pathway, but not in the early endosome-to-TGN transport pathway. These findings suggest novel roles for Arf-GAP Glo3p in endocytic recycling of cell surface proteins.
Keywords: Arf-GAP; Small GTPase; Vesicular trafficking; Intracellular trafficking; Endocytosis;
Glaucarubinone inhibits colorectal cancer growth by suppression of hypoxia-inducible factor 1α and β-catenin via a p-21 activated kinase 1-dependent pathway by Nhi Huynh; John A. Beutler; Arthur Shulkes; Graham S. Baldwin; Hong He (157-165).
p-21-Activated kinase 1 (PAK1) enhances colorectal cancer (CRC) progression by stimulating Wnt/β-catenin, ERK and AKT pathways. PAK1 also promotes CRC survival via up-regulation of hypoxia-inducible factor 1α (HIF-1α), a key player in cancer survival. Glaucarubinone, a quassinoid natural product, inhibits pancreatic cancer growth by down-regulation of PAK1. The aim of this study was to investigate the effect of glaucarubinone on CRC growth and metastasis, and the mechanism involved. Cell proliferation was measured in vitro by [3H]-thymidine incorporation and in vivo by volume of tumor xenografts. Protein concentrations were measured by Western blotting of cell extracts. We report here that glaucarubinone inhibited CRC growth both in vitro and in vivo. The potency of glaucarubinone as an inhibitor of cell proliferation was negatively correlated to PAK1 expression in CRC cells. Glaucarubinone suppressed the expression of HIF-1α and β-catenin. Knockdown of PAK1 by shRNA enhanced inhibition by glaucarubinone while constitutively active PAK1 blocked the inhibitory effect. Our findings indicate that glaucarubinone inhibited CRC growth by down-regulation of HIF-1α and β-catenin via a PAK1-dependent pathway.
Keywords: Glaucarubinone; PAK1; HIF-1α; β-Catenin; CRC;
Chemotactic and proangiogenic role of calcium sensing receptor is linked to secretion of multiple cytokines and growth factors in breast cancer MDA-MB-231 cells by Marco Antonio Hernández-Bedolla; Jorge Carretero-Ortega; Margarita Valadez-Sánchez; José Vázquez-Prado; Guadalupe Reyes-Cruz (166-182).
Breast cancer metastasis to the bone, potentially facilitated by chemotactic and angiogenic cytokines, contributes to a dramatic osteolytic effect associated with this invasive behavior. Based on the intrinsic ability of calcium sensing receptor (CaSR) to control hormonal secretion and considering its expression in the breast, we hypothesized that CaSR plays a chemotactic and proangiogenic role in highly invasive MDA-MB-231 breast cancer cells by promoting secretion of multiple cytokines. In this study, we show that MDA-MB-231 cells stimulated with R-568 calcimimetic and extracellular calcium secreted multiple cytokines and growth factors that induced endothelial cell migration and in vitro angiogenesis. These effects were dependent on the activity of CaSR as demonstrated by the inhibitory effect of either anti-CaSR blocking monoclonal antibodies or calcilytic NPS-2143. Moreover, CaSR knockdown prevented the proangiogenic effect of CaSR agonists. Importantly, CaSR promoted secretion of pleiotropic molecules like GM-CSF, EGF, MDC/CCL22, FGF-4 and IGFBP2, all known to be chemotactic mediators with putative angiogenic factor properties. In contrast, constitutive secretion of IL-6 and β-NGF was attenuated by CaSR. In the case of normal mammary cells, secretion of IL-6 was stimulated by CaSR, whereas a constitutive secretion of RANTES, Angiogenin and Oncostatin M was attenuated by this receptor. Taken together, our results indicate that an altered secretion of chemotactic and proangiogenic cytokines in breast cancer cells is modulated by CaSR, which can be considered a potential target in the therapy of metastatic breast cancer.Display Omitted
Keywords: Calcium sensing receptor; Chemotactic; Angiogenesis; Secretion; Breast cancer; G-protein coupled receptor;
Intramitochondrial adenylyl cyclase controls the turnover of nuclear-encoded subunits and activity of mammalian complex I of the respiratory chain by Domenico De Rasmo; Anna Signorile; Arcangela Santeramo; Maria Larizza; Paolo Lattanzio; Giuseppe Capitanio; Sergio Papa (183-191).
In mammalian cells the nuclear-encoded subunits of complex I are imported into mitochondria, where they are assembled with mt-DNA encoded subunits in the complex, or exchanged with pre-existing copies in the complex. The present work shows that in fibroblast cultures inhibition by KH7 of cAMP production in the mitochondrial matrix by soluble adenylyl cyclase (sAC) results in decreased amounts of free non-incorporated nuclear-encoded NDUFS4, NDUFV2 and NDUFA9 subunits of the catalytic moiety and inhibition of the activity of complex I. Addition of permeant 8-Br-cAMP prevents this effect of KH7. KH7 inhibits accumulation in isolated rat-liver mitochondria and incorporation in complex I of “in vitro” produced, radiolabeled NDUFS4 and NDUFV2 subunits. 8-Br-cAMP prevents also this effect of KH7. Use of protease inhibitors shows that intramitochondrial cAMP exerts this positive effect on complex I by preventing digestion of nuclear-encoded subunits by mitochondrial protease(s), whose activity is promoted by KH7 and H89, an inhibitor of PKA.
Keywords: Mitochondria; Respiratory complex I; cAMP/PKA signaling; Soluble adenylyl cyclase; Mitochondrial proteases;
Structural changes of the ligand and of the receptor alters the receptor preference for neutrophil activating peptides starting with a formylmethionyl group by Huamei Forsman; Malene Winther; Michael Gabl; Sarah Line Skovbakke; Francois Boulay; Marie-Josèphe Rabiet; Claes Dahlgren (192-200).
Pathogenic Staphylococcus aureus strains produce N-formylmethionyl containing peptides, of which the tetrapeptide fMIFL is a potent activator of the neutrophil formyl peptide receptor 1 (FPR1) and the PSMα2 peptide is a potent activator of the closely related FPR2. Variants derived from these two peptide activators were used to disclose the structural determinants for receptor interaction. Removal of five amino acids from the C-terminus of PSMα2 gave rise to a peptide that had lost the receptor-independent neutrophil permeabilizing effect, whereas neutrophil activation capacity as well as its preference for FPR2 was retained. Shorter peptides, PSMα21–10 and PSMα21–5, activate neutrophils, but the receptor preference for these peptides was switched to FPR1.The fMIFL-PSM5–16 peptide, in which the N-terminus of PSMα21–16 was replaced by the sequence fMIFL, was a dual agonist for FPR1/FPR2, whereas fMIFL-PSM5–10 preferred FPR1 to FPR2. Further, an Ile residue was identified as a key determinant for interaction with FPR2. A chimeric receptor in which the cytoplasmic tail of FPR1 was replaced by the corresponding part of FPR2 lost the ability to recognize FPR1 agonists, but gained function in relation to FPR2 agonists.Taken together, our data demonstrate that the C-terminus of the PSMα2 peptide plays a critical role for its cytotoxicity, but is not essential for the receptor-mediated pro-inflammatory activity. More importantly, we show that the amino acids present in the C-terminus, which are not supposed to occupy the agonist-binding pocket in the FPRs, are of importance for the choice of receptor.
Keywords: Neutrophil; Inflammation; Formyl peptide; G-protein coupled receptor;
Transglutaminase 2 interacts with syndecan-4 and CD44 at the surface of human macrophages to promote removal of apoptotic cells by Vinod Nadella; Zhuo Wang; Timothy S. Johnson; Martin Griffin; Andrew Devitt (201-212).
Tissue transglutaminase (TG2) is a multifunctional protein cross-linking enzyme that has been implicated in apoptotic cell clearance but is also important in many other cell functions including cell adhesion, migration and monocyte to macrophage differentiation. Cell surface-associated TG2 regulates cell adhesion and migration, via its association with receptors such as syndecan-4 and β1 and β3 integrins. Whilst defective apoptotic cell clearance has been described in TG2-deficient mice, the precise role of TG2 in apoptotic cell clearance remains ill-defined. Our work addresses the role of macrophage extracellular TG2 in apoptotic cell corpse clearance. Here we reveal TG2 expression and activity (cytosolic and cell surface) in human macrophages and demonstrate that inhibitors of protein crosslinking activity reduce macrophage clearance of dying cells. We show also that cell-impermeable TG2 inhibitors significantly inhibit the ability of macrophages to migrate and clear apoptotic cells through reduced macrophage recruitment to, and binding of, apoptotic cells. Association studies reveal TG2–syndecan-4 interaction through heparan sulphate side chains, and knockdown of syndecan-4 reduces cell surface TG2 activity and apoptotic cell clearance. Furthermore, inhibition of TG2 activity reduces crosslinking of CD44, reported to augment AC clearance. Thus our data define a role for TG2 activity at the surface of human macrophages in multiple stages of AC clearance and we propose that TG2, in association with heparan sulphates, may exert its effect on AC clearance via a mechanism involving the crosslinking of CD44.
Keywords: Macrophages; Transglutaminase 2; Syndecan 4; CD44; Apoptotic cell clearance; Heparan sulphate proteoglycan;
The effect of glucose concentration and sodium phenylbutyrate treatment on mitochondrial bioenergetics and ER stress in 3T3-L1 adipocytes by Ross M. Tanis; Gerardo G. Piroli; Stani D. Day; Norma Frizzell (213-221).
While the 3T3-L1 adipocyte model is routinely used for the study of obesity and diabetes, the mitochondrial respiratory profile in normal versus high glucose has not been examined in detail. We matured adipocytes in normal (5 mM) or high (30 mM) glucose and insulin and examined the mitochondrial bioenergetics. We also assessed the requirement for the Unfolded Protein Response (UPR) and ER stress under these conditions. Basal respiration was ~ 1.7-fold greater in adipocytes that had matured in 30 mM glucose; however, their ability to increase oxygen consumption in response to stress was impaired. Adipogenesis proceeded in both normal and high glucose with concomitant activation of the UPR, but only high glucose was associated with increased levels of ER stress and mitochondrial stress as observed by parallel increases in CHOP and protein succination. Treatment of adipocytes with sodium phenylbutyrate relieved mitochondrial stress through a reduction in mitochondrial respiration. Our data suggests that mitochondrial stress, protein succination and ER stress are uniquely linked in adipocytes matured in high glucose.
Keywords: Adipocyte; Diabetes; Fumarate; Phenylbutyrate; Succination; Uncoupler;
Nucleocytoplasmic shuttling of valosin-containing protein (VCP/p97) regulated by its N domain and C-terminal region by Changcheng Song; Qing Wang; Changzheng Song; Stephen J. Lockett; Nancy H. Colburn; Chou-Chi H. Li; Ji Ming Wang; Thomas J. Rogers (222-232).
Valosin-containing protein (VCP or p97), a member of the AAA family (ATPases associated with diverse cellular activities), plays a key role in many important cellular activities. A genetic deficiency of VCP can cause inclusion body myopathy associated with Paget's disease of bone and frontotemporal dementia (IBMPFD). Previous studies showed that the VCP N domain is essential for the regulation of nuclear entry of VCP. Here we report that IBMPFD mutations, which are mainly located in the N domain, suppress the nuclear entry of VCP. Moreover, the peptide sequence G780AGPSQ in the C-terminal region regulates the retention of VCP in the nucleus. A mutant lacking this sequence can increase the nuclear distribution of IBMPFD VCP, suggesting that this sequence is a potential molecular target for correcting the deficient nucleocytoplasmic shuttling of IBMPFD VCP proteins.
Keywords: Valosin containing protein; Nucleocytoplasmic shuttling; Nuclear export signal; Inclusion body myopathy associated with Paget's disease of bone and frontotemporal dementia (IBMPFD);
STIM1 phosphorylation triggered by epidermal growth factor mediates cell migration by Vanessa Casas-Rua; Patricia Tomas-Martin; Aida M. Lopez-Guerrero; Ignacio S. Alvarez; Eulalia Pozo-Guisado; Francisco Javier Martin-Romero (233-243).
STIM1 is a key regulator of store-operated calcium entry (SOCE), and therefore a mediator of Ca2 + entry-dependent cellular events. Phosphorylation of STIM1 at ERK1/2 target sites has been described as enhancing STIM1 activation during intracellular Ca2 + emptying triggered by the inhibition of the sarco(endo)plasmic Ca2 +-ATPase with thapsigargin. However, no physiological function is known for this specific phosphorylation. The present study examined the role of STIM1 phosphorylation in cell signaling triggered by EGF. Using a human endometrial adenocarcinoma cell line (Ishikawa cells) EGF or H-Ras(G12V), an active mutant of H-Ras, was found to trigger STIM1 phosphorylation at residues Ser575, Ser608, and Ser621, and this process was sensitive to PD0325901, an inhibitor of ERK1/2. Both, ERK1/2 activation and STIM1 phosphorylation took place in the absence of extracellular Ca2 +, indicating that both events are upstream steps for Ca2 + entry activation. Also, EGF triggered the dissociation of STIM1 from EB1 (a regulator of microtubule plus-ends) in a manner similar to that reported for the activation of STIM1 by thapsigargin. Migration of the Ishikawa cells was impaired when STIM1 phosphorylation was targeted by Ser-to-Ala substitution mutation of ERK1/2 target sites. This effect was also observed with the Ca2 + channel blocker SKF96365. Phosphomimetic mutation of STIM1 restored the migration to levels similar to that found for STIM1-wild type. Finally, the increased vimentin expression and relocalization of E-cadherin triggered by EGF were largely inhibited by targeting STIM1 phosphorylation, while STIM1-S575E/S608E/S621E normalized the profiles of these two EMT markers.
Keywords: Calcium; EGF; ERK1/2; Migration; Phosphorylation; STIM1;
Indole-3-carbinol inhibits tumorigenicity of hepatocellular carcinoma cells via suppression of microRNA-21 and upregulation of phosphatase and tensin homolog by Xinmei Wang; Hongyan He; Yuanzhi Lu; Wei Ren; Kun-yu Teng; Chi-ling Chiang; Zhaogang Yang; Bo Yu; Shuhao Hsu; Samson T. Jacob; Kalpana Ghoshal; L. James Lee (244-253).
A major obstacle to successful treatment of hepatocellular carcinoma (HCC) is its high resistance to cytotoxic chemotherapy due to overexpression of multidrug resistance genes. Activation of the AKT pathway is known to be involved in chemoresistance in HCC; however, the underlying mechanisms modulating the AKT pathway by chemopreventive agents remain unclear. In the present study, we found that indole-3-carbinol (I3C) treatment for tumor cells repressed the AKT pathway by increasing the expression of phosphatase and tensin homolog (PTEN) in HCC xenograft tumor and HCC cell lines. qRT-PCR data showed that the expression of miR-21 and miR-221&222 was significantly reduced by I3C in HCC cells in vitro and in vivo. Reactivation of the AKT pathway via restoration of miR-21 was reversed by I3C. Ectopic expression of miR-21 mediated-accelerated wound healing was abrogated by I3C. Moreover, reducing the expression of miR-21 by anti-miR decreased the resistance of HCC cells to I3C. These results provide experimental evidences that I3C could function as a miR-21 regulator, leading to repression of the PTEN/AKT pathway and opening a new avenue for eradication of drug-resistant cells, thus potentially helping to improve the therapeutic outcome in patients diagnosed with HCC.
Keywords: Indole-3-carbinol; Hepatocellular carcinoma; PTEN; miR-21; miR-221&222;
Calling in SYK: SYK's dual role as a tumor promoter and tumor suppressor in cancer by Mariya O. Krisenko; Robert L. Geahlen (254-263).
SYK (spleen tyrosine kinase) is well-characterized in the immune system as an essential enzyme required for signaling through multiple classes of immune recognition receptors. As a modulator of tumorigenesis, SYK has a bit of a schizophrenic reputation, acting in some cells as a tumor promoter and in others as a tumor suppressor. In many hematopoietic malignancies, SYK provides an important survival function and its inhibition or silencing frequently leads to apoptosis. In cancers of non-immune cells, SYK provides a pro-survival signal, but can also suppress tumorigenesis by restricting epithelial–mesenchymal transition, enhancing cell–cell interactions and inhibiting migration.Display Omitted
Keywords: SYK; Spleen tyrosine kinase; Epithelial–mesenchymal transition; Protein phosphorylation; Signal transduction; Apoptosis;