BBA - Molecular Cell Research (v.1833, #10)
Editorial Board (i).
WNK4 inhibits Ca2 +-activated big-conductance potassium channels (BK) via mitogen-activated protein kinase-dependent pathway by Peng Yue; Chengbiao Zhang; Dao-Hong Lin; Peng Sun; Wen-Hui Wang (2101-2110).
We used the perforated whole-cell recording technique to examine the effect of with-no-lysine kinase 4 (WNK4) on the Ca2 + activated big-conductance K channels (BK) in HEK293T cells transfected with BK-α subunit (BK-α). Expression of WNK4 inhibited BK channels and decreased the outward K currents. Coexpression of SGK1 abolished the inhibitory effect of WNK4 on BK channels and restored the outward K currents. Expression of WNK4S1169D//1196D, in which both SGK1-phosphorylation sites (serine 1169 and 1196) were mutated to aspartate, had no effect on BK channels. Moreover, coexpression of SGK1 had no additional effect on K currents in the cells transfected with BKα + WNK4S1169D//1196D, suggesting that SGK1 reversed WNK4-induced inhibition of BK channels by stimulating WNK4 phosphorylation. Expression of WNK4 but not WNK4S1169D//1196D increased the phosphorylation of ERK and p38 mitogen-activated protein kinase (MAPK); an effect was abolished by coexpression of SGK1. The role of ERK and p38 MAPK in mediating the effect of WNK4 on BK channels was further suggested by the finding that the inhibition of ERK and P38 MAPK completely abolished the inhibitory effect of WNK4 on BK channels. In contrast, inhibition of MAPK failed to abolish the inhibitory effect of WNK4 on ROMK channels in both HEK cells and Xenopus oocytes. Expression of dominant negative dynaminK44A (DynK44A) or treatment of the cells with dynasore, a dynamin inhibitor, not only increased K currents but also largely abolished the inhibitory effect of WNK4 on BK channels. However, inhibition of MAPK still increased the outward K currents in the cells transfected with BKα + WNK4 and treated with dynasore. Similar results were obtained in experiments performed in the native tissue in which inhibition of ERK and p38 MAPK increased BK channel activity in the cortical collecting duct (CCD) treated with dynasore. We concluded that WNK4 inhibited BK channels by stimulating ERK and p38 MAPK and that activation of MAPK by WNK4 may inhibit BK channels partially via a mechanism other than stimulating endocytosis.
Keywords: ERK; P38 MAPK; ROMK; K secretion; Cortical collecting duct;
Activation of autophagy by globular adiponectin attenuates ethanol-induced apoptosis in HepG2 cells: Involvement of AMPK/FoxO3A axis by Saroj Nepal; Pil-Hoon Park (2111-2125).
Hepatocellular apoptosis is an important pathological entity of alcoholic liver disease. Previously, we have shown that globular adiponectin (gAcrp) protects liver cells from ethanol-induced apoptosis by modulating an array of signaling pathways. In the present study, we investigated the role of autophagy induction by gAcrp in the suppression of ethanol-induced apoptosis and its potential mechanism(s) in liver cells. Here, we demonstrated that gAcrp significantly restores ethanol-induced suppression of autophagy-related genes, including Beclin-1 and microtubule-associated protein light chain (LC3B) both in primary rat hepatocytes and human hepatoma cell line (HepG2). Globular adiponectin also restored autophagosome formation suppressed by ethanol treatment in HepG2. Furthermore, inhibition of gAcrp-induced autophagic process by knock-down of LC3B prevented protection from ethanol-induced apoptosis. In particular, the autophagic process induced by gAcrp was involved in the suppression of ethanol-induced activation of caspase-8 and expression of Bax. Moreover, knock-down of AMPK by small interfering RNA (siRNA) blocked gAcrp-induced expression of genes related to autophagy, which in turn prevented protection from ethanol-induced apoptosis, suggesting that AMPK plays an important role in the induction of autophagy and protection of liver cells by gAcrp. Finally, we also showed that gAcrp treatment induces translocation of the forkhead box O member protein, FoxO3A, into the nucleus, which may play a role in the induction of autophagy-related genes. Taken together, our data demonstrated that gAcrp protects liver cells from ethanol-induced apoptosis via induction of autophagy. Further, the AMPK-FoxO3A axis plays a cardinal role in gAcrp-induced autophagy and subsequent inhibition of ethanol-induced apoptosis.Display Omitted
Keywords: Adiponectin; AMPK; Apoptosis; Autophagy; Ethanol; FoxO3;
Splicing and beyond: The many faces of the Prp19 complex by Sittinan Chanarat; Katja Sträßer (2126-2134).
The conserved Prp19 complex (Prp19C) — also known as NineTeen Complex (NTC) — functions in several processes of paramount importance for cellular homeostasis. NTC/Prp19C was discovered as a complex that functions in splicing and more specifically during the catalytic activation of the spliceosome. More recent work revealed that NTC/Prp19C plays a role in transcription elongation in Saccharomyces cerevisiae and in genome maintenance in higher eukaryotes. In addition, mouse PRP19 might ubiquitylate proteins targeted for degradation and guide them to the proteasome. Furthermore, NTC/Prp19C has been implicated in lipid droplet biogenesis. In the future, the molecular function of NTC/Prp19C in all of these processes needs to be refined or elucidated. Most of NTC/Prp19C's functions have been shown in only one or few organisms. However, since this complex is highly conserved it is likely that it has the same functions across all species. Moreover, one NTC/Prp19C or different subcomplexes could function in the above-mentioned processes. Intriguingly, NTC/Prp19C might link these different processes to ensure an optimal coordination of cellular processes. Thus, many important questions about the functions of this interesting complex remain to be investigated. In this review we discuss the different functions of NTC/Prp19C focusing on the novel and emerging ones as well as open questions.Display Omitted
Keywords: Prp19 splicing complex (Prp19C); NineTeen Complex (NTC); TREX; Transcription; DNA repair; Protein degradation;
Inhibition of 14-3-3 binding to Rictor of mTORC2 for Akt phosphorylation at Ser473 is regulated by selenoprotein W by Yeong Ha Jeon; Yong Hwan Park; Joon Hyun Kwon; Jea Hwang Lee; Ick Young Kim (2135-2142).
14-3-3 reduces cell proliferation by inhibiting the activity of proteins involved in the signaling pathway that includes Akt kinase. Activation of Akt is enhanced by activating the mammalian target of rapamycin complex 2 (mTORC2). 14-3-3 is also a negative regulator of the mTORC2/Akt pathway, by interacting with a component of mTORC2. Recently, we reported that selenoprotein W (SelW) regulated the interaction between 14-3-3 and its target protein, CDC25B. Here, we show that the binding of Rictor, a component of mTORC2, to 14-3-3, is regulated by the interaction of 14-3-3 with SelW. When SelW was down-regulated, mTORC2-dependent phosphorylation of Akt at Ser473 was decreased. However, the phosphorylation of Thr308 was not affected. The interaction of Rictor with 14-3-3 was increased in SelW-knockdown cells, as compared to control cells. SelW-knockdown cells were also more sensitive to DNA damage induced by etoposide, than control cells. This phenomenon was due to the decreased phosphorylation of Akt at Ser473. We also found that ectopic expression of SelW(U13C) reduced the interaction between Rictor and 14-3-3, leading to Akt phosphorylation at Ser473. Taken together, these findings demonstrate that SelW activates the mTORC2/Akt pathway for Akt phosphorylation at Ser473, by interrupting the binding of Rictor to 14-3-3.
Keywords: Akt; mTOR; Rictor; Selenoprotein W; 14-3-3;
Aldosterone regulates Na+, K+ ATPase activity in human renal proximal tubule cells through mineralocorticoid receptor by Sarah A. Salyer; Jason Parks; Michelle T. Barati; Eleanor D. Lederer; Barbara J. Clark; Janet D. Klein; Syed J. Khundmiri (2143-2152).
The mechanisms by which aldosterone increases Na+, K+ ATPase and sodium channel activity in cortical collecting duct and distal nephron have been extensively studied. Recent investigations demonstrate that aldosterone increases Na–H exchanger-3 (NHE-3) activity, bicarbonate transport, and H+ ATPase in proximal tubules. However, the role of aldosterone in regulation of Na+, K+ ATPase in proximal tubules is unknown. We hypothesize that aldosterone increases Na+, K+ ATPase activity in proximal tubules through activation of the mineralocorticoid receptor (MR). Immunohistochemistry of kidney sections from human, rat, and mouse kidneys revealed that the MR is expressed in the cytosol of tubules staining positively for Lotus tetragonolobus agglutinin and type IIa sodium-phosphate cotransporter (NpT2a), confirming proximal tubule localization. Adrenalectomy in Sprague–Dawley rats decreased expression of MR, ENaC α, Na+, K+ ATPase α1, and NHE-1 in all tubules, while supplementation with aldosterone restored expression of above proteins. In human kidney proximal tubule (HKC11) cells, treatment with aldosterone resulted in translocation of MR to the nucleus and phosphorylation of SGK-1. Treatment with aldosterone also increased Na+, K+ ATPase-mediated 86Rb uptake and expression of Na+, K+ ATPase α1 subunits in HKC11 cells. The effects of aldosterone on Na+, K+ ATPase-mediated 86Rb uptake were prevented by spironolactone, a competitive inhibitor of aldosterone for the MR, and partially by Mifepristone, a glucocorticoid receptor (GR) inhibitor. These results suggest that aldosterone regulates Na+, K+ ATPase in renal proximal tubule cells through an MR-dependent mechanism.
Keywords: Na+; K+ ATPase; Aldosterone; Proximal tubule; Mineralocorticoid receptor; Sodium and glucocorticoid-dependent kinase;
Modulation by Syk of Bcl-2, calcium and the calpain–calpastatin proteolytic system in human breast cancer cells by Bei Fei; Shuai Yu; Robert L. Geahlen (2153-2164).
Syk is a 72 kDa non-receptor tyrosine kinase that is best characterized in hematopoietic cells. While Syk is pro-tumorigenic in some cancer cell types, it also has been reported as a negative regulator of metastatic cell growth in others. An examination of the RelA (p65) subunit of NF-κB expressed in MCF7 breast cancer cells indicated that either treatment with pervanadate or stable expression of Syk protected RelA from calpain-mediated proteolysis. Similar results were observed with the tyrosine phosphatase, PTP1B, another sensitive calpain substrate. The activity of calpain in MCF7 cell lysates was inhibited by both treatment with hydrogen peroxide and expression of Syk, the former due to oxidative inactivation of calpain and the latter to enhanced expression of calpastatin (CAST), the endogenous calpain inhibitor. The level of CAST was elevated in the cytosolic fraction of Syk-positive breast cancer cells resulting in more CAST present in complex with calpain in cell lysates. The high levels of CAST coincided with elevated basal levels of calcium–and of intracellular calpain activity–in Syk-expressing cells resulting from decreased levels of Bcl-2, an inhibitor of IP3-receptor-mediated calcium release. The inhibition of cellular calpain stimulated the Syk-mediated enhancement of NF-κB induced by TNF-α, enhanced tyrosine phosphorylation resulting from integrin crosslinking, and increased the localization of Syk to the plasma membrane.
Keywords: Syk; Calpain; Calpastatin; PTP1B; NF-κB; Bcl-2;
Internal ribosome entry site-mediated translational regulation of ATF4 splice variant in mammalian unfolded protein response by Ching-Ping Chan; Kin-Hang Kok; Hei-Man Vincent Tang; Chi-Ming Wong; Dong-Yan Jin (2165-2175).
Activating transcription factor 4 (ATF4) is a master regulator of genes involved in unfolded protein response (UPR) and its translation is regulated through reinitiation at upstream open reading frames. Here, we demonstrate internal ribosome entry site (IRES)-mediated translation of an alternatively spliced variant of human ATF4. This variant that contains four upstream open reading frames in the 5′ leader region was expressed in leukocytes and other tissues. mRNA and protein expression of this variant was activated in the UPR. Its translation was neither inhibited by steric hindrance nor affected by eIF4G1 inactivation, indicating a cap-independent and IRES-dependent mechanism not mediated by ribosome scanning-reinitiation. The IRES activity mapped to a highly structured region that partially overlaps with the third and fourth open reading frames was unlikely attributed to cryptic promoter or splicing, but was activated by PERK-induced eIF2α phosphorylation. Taken together, our findings reveal a new mechanism for translational regulation of ATF4 in mammalian UPR.
Keywords: ATF4; Translation initiation; Unfolded protein response; Internal ribosome entry site (IRES); Upstream open reading frame; eIF2α;
A novel actin cytoskeleton-dependent noncaveolar microdomain composed of homo-oligomeric caveolin-2 for activation of insulin signaling by Hayeong Kwon; Jaewoong Lee; Kyuho Jeong; Donghwan Jang; Yunbae Pak (2176-2189).
The role of caveolin-2 (cav-2), independently of caveolin-1 (cav-1) and caveolae, has remained elusive. Our data show that cav-2 exists in the plasma membrane (PM) in cells lacking cav-1 and forms homo-oligomeric complexes. Cav-2 did not interact with cavin-1 and cavin-2 in the PM. Rab6-GTP was required for the microtubule-dependent exocytic transport of cav-2 from the Golgi to the PM independently of cav-1. The cav-2-oligomerized noncaveolar microdomain was unaffected by cholesterol depletion and protected from shearing of silica-coated PM. Activation of insulin receptor (IR) was processed in the microdomain. Actin depolymerization affected the formation and sustenance of cav-2-oligomerized noncaveolar microdomain and attenuated IR recruitment to the microdomain thereby inhibiting IR signaling activation. Cav-2 shRNA stable cells and the cells ectopically expressing an oligomerization domain truncation mutant, cav-2∆47–86 exhibited retardation of IR signaling activation via the noncaveolar microdomain. Elevation in status of cav-2 expression rendered the noncaveolar activation of IR signaling in cav-1 down-regulated or/and cholesterol-depleted cells. Our findings reveal a novel homo-oligomeric cav-2 microdomain responsible for regulating activation of IR signaling in the PM.
Keywords: Caveolin-2; Insulin receptor; Actin cytoskeleton; Noncaveolar microdomain; Rab6; Microtubules;
Downregulation of Ezh2 methyltransferase by FOXP3: New insight of FOXP3 into chromatin remodeling? by Zhu Shen; Ling Chen; Xiaojun Yang; Yun Zhao; Eric Pier; Xia Zhang; Xichuan Yang; Ya Xiong (2190-2200).
Transcription factor FOXP3 (forkhead box P3) is found initially as a key regulator in regulatory T cells. Recently its expression has been demonstrated in some non-lymphoid normal and cancerous cells. Now FOXP3 has been proven to regulate cancer-related genes, especially suppressor genes in breast cancer. But the mechanisms by which FOXP3 regulates suppressor genes are not fully determined. In this study, we found the inverse correlation between FOXP3 and Ezh2, an enzyme for histone H3K27 trimethylation (H3K27me3) and a central epigenetic regulator in cancer. The overexpression of FOXP3 weakened Ezh2's enhancement on the mammosphere formation, cell proliferation, directional migration, and colony forming ability of T47D cells. We demonstrated that FOXP3 could downregulate Ezh2 protein level and this depended on not only the FOXP3 expression amount, but also the nuclear localization of FOXP3. More importantly, we demonstrated FOXP3 accelerated Ezh2 protein degradation through the polyubiquitination–proteasome pathway by enhancing the transcription of E3 ligase Praja1 directly. These results provided a new mechanism for FOXP3 in histone modifications as an Ezh2 suppressor and supported new evidence for FOXP3 as a tumor suppressor in breast cancer.
Keywords: FOXP3; Ezh2; Praja1; Transcription; Ubiquitination;
Ephrin-A1/EphA4-mediated adhesion of monocytes to endothelial cells by Stefanie Jellinghaus; David M. Poitz; Georg Ende; Antje Augstein; Sönke Weinert; Beryl Stütz; Rüdiger C. Braun-Dullaeus; Elena B. Pasquale; Ruth H. Strasser (2201-2211).
The Eph receptors represent the largest family of receptor tyrosine kinases. Both Eph receptors and their ephrin ligands are cell-surface proteins, and they typically mediate cell-to-cell communication by interacting at sites of intercellular contact.The major aim of the present study was to investigate the involvement of EphA4–ephrin-A1 interaction in monocyte adhesion to endothelial cells, as this process is a crucial step during the initiation and progression of the atherosclerotic plaque.Immunohistochemical analysis of human atherosclerotic plaques revealed expression of EphA4 receptor and ephrin-A1 ligand in major cell types within the plaque. Short-time stimulation of endothelial cells with the soluble ligand ephrin-A1 leads to a fourfold increase in adhesion of human monocytes to endothelial cells. In addition, ephrin-A1 further increases monocyte adhesion to already inflamed endothelial cells. EphrinA1 mediates its effect on monocyte adhesion via the activated receptor EphA4. This ephrinA1/EphA4 induced process involves the activation of the Rho signaling pathway and does not require active transcription. Rho activation downstream of EphA4 leads to increased polymerization of actin filaments in endothelial cells. This process was shown to be crucial for the proadhesive effect of ephrin-A1.The results of the present study show that ephrin-A1-induced EphA4 forward signaling promotes monocyte adhesion to endothelial cells via activation of RhoA and subsequent stress-fiber formation by a non-transcriptional mechanism.
Keywords: Monocytes; Adhesion; Endothelium; Ephrin; Atherosclerosis;
Activation of the nuclear receptor FXR enhances hepatocyte chemoprotection and liver tumor chemoresistance against genotoxic compounds by Javier Vaquero; Oscar Briz; Elisa Herraez; Jordi Muntané; Jose J.G. Marin (2212-2219).
The success of pharmacological treatments in primary liver cancers is limited by the marked efficacy of mechanisms of chemoresistance already present in hepatocytes. The role of the nuclear receptor FXR is unclear. Although, in non-treated liver tumors, its expression is reduced, the refractoriness to anticancer drugs is high. Moreover, the treatment with cisplatin up-regulates FXR. The aim of this study was to investigate whether FXR is involved in stimulating chemoprotection/chemoresistance in healthy and tumor liver cells. In human hepatocytes, the activation of FXR with the agonist GW4064 resulted in a significant protection against cisplatin-induced toxicity. In human hepatoma Alexander cells, with negligible endogenous expression of FXR, GW4064 also protected against cisplatin-induced toxicity, but only if they were previously transfected with FXR/RXR. Investigation of 109 genes potentially involved in chemoresistance revealed that only ABCB4, TCEA2, CCL14, CCL15 and KRT13 were up-regulated by FXR activation both in human hepatocytes and FXR/RXR-expressing hepatoma cells. In both models, cisplatin, even in the absence of FXR agonists, such as bile acids and GW4064, was able to up-regulate FXR targets genes, which was due to FXR-mediated trans-activation of response elements in the promoter region. FXR-dependent chemoprotection was also efficient against other DNA-damaging compounds, such as doxorubicin, mitomycin C and potassium dichromate, but not against non-genotoxic drugs, such as colchicine, paclitaxel, acetaminophen, artesunate and sorafenib. In conclusion, ligand-dependent and independent activation of FXR stimulates mechanisms able to enhance the chemoprotection of hepatocytes against genotoxic compounds and to reduce the response of liver tumor cells to certain pharmacological treatments.Display Omitted
Keywords: Bile acid; Cancer; Chemotherapy; Drug; Liver; Pharmacology;
Prometaphase arrest-dependent phosphorylation of Bcl-2 family proteins and activation of mitochondrial apoptotic pathway are associated with 17α-estradiol-induced apoptosis in human Jurkat T cells by Cho Rong Han; Do Youn Jun; Yoon Hee Kim; Ji Young Lee; Young Ho Kim (2220-2232).
In Jurkat T cell clone (JT/Neo), G2/M arrest, apoptotic sub-G1 peak, mitochondrial membrane potential (Δψm) loss, and TUNEL-positive DNA fragmentation were induced following exposure to 17α-estradiol (17α-E2), whereas none of these events (except for G2/M arrest) were induced in Jurkat cells overexpressing Bcl-2 (JT/Bcl-2). Under these conditions, phosphorylation at Thr161 and dephosphorylation at Tyr15 of Cdk1, upregulation of cyclin B1 level, histone H1 phosphorylation, Cdc25C phosphorylation at Thr-48, Bcl-2 phosphorylation at Thr-56 and Ser-70, Mcl-1 phosphorylation, and Bim phosphorylation were detected in the presence of Bcl-2 overexpression. However, the 17α-E2-induced upregulation of Bak levels, activation of Bak, activation of caspase-3, and PARP degradation were abrogated by Bcl-2 overexpression. In the presence of the G1/S blocking agent hydroxyurea, 17α-E2 failed to induce G2/M arrest and all apoptotic events including Cdk1 activation and phosphorylation of Bcl-2, Mcl-1 and Bim. The 17α-E2-induced phosphorylation of Bcl-2 family proteins and mitochondrial apoptotic events were suppressed by a Cdk1 inhibitor but not by aurora A and aurora B kinase inhibitors. Immunofluorescence microscopic analysis showed that an aberrant bipolar microtubule array, incomplete chromosome congression at the metaphase plate, and prometaphase arrest, which was reversible, were the underlying factors for 17α-E2-induced mitotic arrest. The in vitro microtubule polymerization assay showed that 17α-E2 could directly inhibit microtubule formation. These results show that the apoptogenic activity of 17α-E2 was due to the impaired mitotic spindle assembly causing prometaphase arrest and prolonged Cdk1 activation, the phosphorylation of Bcl-2, Mcl-1 and Bim, and the activation of Bak and mitochondria-dependent caspase cascade.Display Omitted
Keywords: 17α-Estradiol; Prometaphase arrest; Prolonged Cdk1 activation; Phosphorylation of Bcl-2 family protein; Mitochondrial apoptosis;
Nucleoid localization of Hsp40 Mdj1 is important for its function in maintenance of mitochondrial DNA by Grzegorz L. Ciesielski; Magdalena Plotka; Mateusz Manicki; Brenda A. Schilke; Rafal Dutkiewicz; Chandan Sahi; Jaroslaw Marszalek; Elizabeth A. Craig (2233-2243).
Faithful replication and propagation of mitochondrial DNA (mtDNA) is critical for cellular respiration. Molecular chaperones, ubiquitous proteins involved in protein folding and remodeling of protein complexes, have been implicated in mtDNA transactions. In particular, cells lacking Mdj1, an Hsp40 co-chaperone of Hsp70 in the mitochondrial matrix, do not maintain functional mtDNA. Here we report that the great majority of Mdj1 is associated with nucleoids, DNA-protein complexes that are the functional unit of mtDNA transactions. Underscoring the importance of Hsp70 chaperone activity in the maintenance of mtDNA, an Mdj1 variant having an alteration in the Hsp70-interacting J-domain does not maintain mtDNA. However, a J-domain containing fragment expressed at the level that Mdj1 is normally present is not competent to maintain mtDNA, suggesting a function of Mdj1 beyond that carried out by its J-domain. Nevertheless, loss of mtDNA function upon Mdj1 depletion is retarded when the J-domain, is overexpressed. Analysis of Mdj1 variants revealed a correlation between nucleoid association and DNA maintenance activity, suggesting that localization is functionally important. We found that Mdj1 has DNA binding activity and that variants retaining DNA-binding activity also retained nucleoid association. Together, our results are consistent with a model in which Mdj1, tethered to the nucleoid via DNA binding, thus driving a high local concentration of the Hsp70 machinery, is important for faithful DNA maintenance and propagation.
Keywords: J-protein; Molecular chaperone; DNA transactions; Yeast;
Calpain 1 induce lysosomal permeabilization by cleavage of lysosomal associated membrane protein 2 by Gloria E. Villalpando Rodriguez; Alicia Torriglia (2244-2253).
In light induced retinal degeneration (LIRD) photoreceptor cell death is mediated by caspase independent mechanisms. The activation of LEI/L-DNase II pathway in this model, is due to cathepsin D release from lysosomes, although the underlying mechanism remains poorly understood. In this paper we studied the involvement of calpains in lysosomal permeabilization. We investigated, for the first time, the calpain targets at lysosomal membrane level. We found that calpain 1 is responsible for lysosomal permeabilization by cleavage of the lysosomal associated membrane protein 2 (LAMP 2). Moreover, LAMP 2 degradation and lysosomal permeabilization were rescued by calpain inhibition and the use of MEF−/− lamp 2 cells indicates that the cleavage of LAMP 2A is essential for this permeabilization. Finally, we found that LAMP 2 is cleaved in LIRD, suggesting that the mechanism of calpain induced lysosomal permeabilization is not exclusive of a single cell death model. Overall, these data shed new light on understanding the mechanisms of lysosomal and caspase-independent cell death and point to the original targets for development of the new therapeutic protocols.Display Omitted
Keywords: Calpain; Lysosome; Cathepsin D; LAMP 2; Endonuclease; Protease;
N-terminally truncated forms of human cathepsin F accumulate in aggresome-like inclusions by Barbara Jerič; Iztok Dolenc; Marko Mihelič; Martina Klarić; Tina Zavašnik-Bergant; Gregor Gunčar; Boris Turk; Vito Turk; Veronika Stoka (2254-2266).
The contribution of individual cysteine cathepsins as positive mediators of programmed cell death is dependent on several factors, such as the type of stimuli, intensity and duration of the stimulus, and cell type involved. Of the eleven human cysteine cathepsins, cathepsin F is the only cathepsin that exhibits an extended N-terminal proregion, which contains a cystatin-like domain. We predicted that the wild-type human cathepsin F contains three natively disordered regions within the enzyme's propeptide and various amino acid stretches with high fibrillation propensity. Wild-type human cathepsin F and its N-terminally truncated forms, Ala20–Asp484 (Δ19CatF), Pro126–Asp484 (Δ125CatF), and Met147–Asp484 (Δ146CatF) were cloned into the pcDNA3 vector and overexpressed in HEK 293T cells. Wild-type human cathepsin F displayed a clear vesicular labeling and colocalized with the LAMP2 protein, a lysosomal marker. However, all three N-terminally truncated forms of human cathepsin F were recovered as insoluble proteins, suggesting that the deletion of at least the signal peptides (Δ19CatF), results in protein aggregation. Noteworthy, they concentrated large perinuclear–juxtanuclear aggregates that accumulated within aggresome-like inclusions. These inclusions showed p62-positive immunoreactivity and were colocalized with the autophagy marker LC3B, but not with the LAMP2 protein. In addition, an approximately 2–3 fold increase in DEVDase activity was not sufficient to induce apoptotic cell death. These results suggested the clearance of the N-terminally truncated forms of human cathepsin F via the autophagy pathway, underlying its protective and prosurvival mechanisms.
Keywords: Aggregation-prone; Aggresome; Aggresome-like inclusion; Autophagy; Caspase activation; Cathepsin F;
The Bacillus subtilis EfeUOB transporter is essential for high-affinity acquisition of ferrous and ferric iron by Marcus Miethke; Carmine G. Monteferrante; Mohamed A. Marahiel; Jan Maarten van Dijl (2267-2278).
Efficient uptake of iron is of critical importance for growth and viability of microbial cells. Nevertheless, several mechanisms for iron uptake are not yet clearly defined. Here we report that the widely conserved transporter EfeUOB employs an unprecedented dual-mode mechanism for acquisition of ferrous (Fe[II]) and ferric (Fe[III]) iron in the bacterium Bacillus subtilis. We show that the binding protein EfeO and the permease EfeU form a minimal complex for ferric iron uptake. The third component EfeB is a hemoprotein that oxidizes ferrous iron to ferric iron for uptake by EfeUO. Accordingly, EfeB promotes growth under microaerobic conditions where ferrous iron is more abundant. Notably, EfeB also fulfills a vital role in cell envelope stress protection by eliminating reactive oxygen species that accumulate in the presence of ferrous iron. In conclusion, the EfeUOB system contributes to the high-affinity uptake of iron that is available in two different oxidation states.
Keywords: Iron uptake; Oxidative stress; Tat; YwbL; YwbM; YwbN;
Determining the contributions of caspase-2, caspase-8 and effector caspases to intracellular VDVADase activities during apoptosis initiation and execution by M. Eugenia Delgado; Magnus Olsson; Frank A. Lincoln; Boris Zhivotovsky; Markus Rehm (2279-2292).
Apoptosis signaling crucially depends on caspase activities. Caspase-2 shares features of both initiator and effector caspases. Opinions are divided on whether caspase-2 activity is established during apoptosis initiation or execution in response to DNA damage, death receptor stimulation, or heat shock. So far, approaches towards measuring caspase-2 activity were restricted to analyses in cell homogenates and extracts, yielded inconsistent results, and were often limited in sensitivity, thereby contributing to controversies surrounding the role of caspase-2 during apoptosis. Furthermore, caspases overlap in substrate specificities, and caspase-8 as well as effector caspases may cleave the optimal VDVAD recognition motif as well. We therefore generated a highly sensitive Förster resonance energy transfer (FRET) substrate to determine the relative contribution of these caspases to VDVADase activity non-invasively inside living cells. We observed limited proteolysis of the substrate during apoptosis initiation in response to death receptor stimulation by FasL, TNFα and TRAIL. However, this activity was attributable to caspase-8 rather than caspase-2. Likewise, no caspase-2-specific activity was detected during apoptosis initiation in response to genotoxic stress (cisplatin, 5-FU), microtubule destabilization (vincristine), or heat shock. The contribution of caspase-2 to proteolytic activities during apoptosis execution was insignificant. Since even residual, ectopically introduced caspase-2 activity could readily be detected inside living cells in our measurements, we conclude, in contrast to several previous studies, that caspase-2 activity does not contribute to apoptosis in the scenarios investigated, and that instead caspase-8 and effector caspases are the most significant VDVADases during canonical apoptosis signaling.
Keywords: Apoptosis; Förster Resonance Energy Transfer (FRET); Caspase-2; Caspase-8; Single cell analysis;
Detection and quantification of endoplasmic reticulum stress in living cells using the fluorescent compound, Thioflavin T by Daniel R. Beriault; Geoff H. Werstuck (2293-2301).
The endoplasmic reticulum (ER) plays a central role in the co- and post-translational modification of many proteins. Disruption of these processes can lead to the accumulation of misfolded proteins in the endoplasmic reticulum — a condition known as endoplasmic reticulum stress. In recent years, the association of endoplasmic reticulum stress with a number of disease pathologies has increased interest in the study of this condition. Current methods to detect endoplasmic reticulum stress are indirect and retrospective. Here we describe a new method to detect and quantify endoplasmic reticulum stress in live cells using Thioflavin T (ThT), a small molecule that exhibits enhanced fluorescence when it binds to protein aggregates. We show that enhanced ThT-fluorescence correlates directly with established indicators of unfolded protein response activation. Furthermore, enhanced ThT-fluorescence can be detected in living cells within 20 min of application of an endoplasmic reticulum stress-inducing agent. ThT is capable of detecting endoplasmic reticulum stress induced by distinctly different conditions and compounds, in different cultured cell types as well as in mouse tissue samples. Pre-treatment with a potent endoplasmic reticulum stress-reducing agent, 4-phenylbutyric acid, mitigates the enhanced ThT signal. This new tool will be useful in future research investigating the role of protein misfolding in the development and/or progression of human diseases.
Keywords: Thioflavin T; Endoplasmic reticulum stress; Unfolded protein response; Detection;
MAGI-1 acts as a scaffolding molecule for NGF receptor-mediated signaling pathway by Hidenori Ito; Rika Morishita; Ikuko Iwamoto; Makoto Mizuno; Koh-ichi Nagata (2302-2310).
We have recently found that the membrane-associated guanylate kinase with inverted organization-1 (MAGI-1) was enriched in rat nervous tissues such as the glomeruli in olfactory bulb of adult rats and dorsal root entry zone in spinal cord of embryonic rats. In addition, we revealed the localization of MAGI-1 in the growth cone of the primary cultured rat dorsal root ganglion cells. These results point out the possibility that MAGI-1 is involved in the regulation of neurite extension or guidance. In this study, we attempted to reveal the physiological role(s) of MAGI-1 in neurite extension. We found that RNA interference (RNAi)-mediated knockdown of MAGI-1 caused inhibition of nerve growth factor (NGF)-induced neurite outgrowth in PC12 rat pheochromocytoma cells. To clarify the involvement of MAGI-1 in NGF-mediated signal pathway, we tried to identify binding partners for MAGI-1 and identified p75 neurotrophin receptor (p75NTR), a low affinity NGF receptor, and Shc, a phosphotyrosine-binding adaptor. These three proteins formed an immunocomplex in PC12 cells. Knockdown as well as overexpression of MAGI-1 caused suppression of NGF-stimulated activation of the Shc-ERK pathway, which is supposed to play important roles in neurite outgrowth of PC12 cells. These results indicate that MAGI-1 may act as a scaffolding molecule for NGF receptor-mediated signaling pathway.
Keywords: MAGI-1; NGF; PC12; Shc; ERK;
Protein kinase CK2-dependent phosphorylation of the human Regulators of Calcineurin reveals a novel mechanism regulating the calcineurin–NFATc signaling pathway by Sergio Martínez-Høyer; Álvaro Aranguren-Ibáñez; Javier García-García; Eva Serrano-Candelas; Jordi Vilardell; Virginia Nunes; Fernando Aguado; Baldo Oliva; Emilio Itarte; Mercè Pérez-Riba (2311-2321).
Cyclosporine A and FK506 produce immunosuppression by blocking calcineurin phosphatase activity and consequently activation of cytosolic Nuclear Factor of Activated T-cell (NFATc) transcription factor. Due to the chronic toxicity associated with their administration, the development of more specific immunosuppressants is currently an important unmet medical need. In this context, an immunosuppressant peptide derived from the CIC motif of the human Regulators of Calcineurin (RCAN) proteins has been shown to inhibit NFATc signaling without affecting general phosphatase activity of calcineurin. Here we show that protein kinase CK2 phosphorylates a conserved serine residue within the CIC motif of vertebrate RCANs, which increases its affinity for calcineurin and consequently its inhibition of NFATc-dependent gene expression in activated T-cells. Molecular modeling studies have led us to identify a positively charged interaction site on the surface of calcineurin where the phosphorylated serine residue of the CIC motif would normally locate. Finally, we have also identified RCAN3 as a new phosphoprotein with multiple phosphorylation sites. Therefore, our findings reveal for the first time a novel molecular mechanism underlying the regulation of calcineurin–NFATc signaling by means of phosphorylation of the CIC motif of RCAN proteins. The knowledge of how RCAN proteins modulate the calcineurin–NFATc pathway paves the way for the development of potent novel selective immunosuppressant drugs.
Keywords: Calcineurin–NFATc signaling; RCAN; PXIXIT; CK2; Immunosuppression; Phosphorylation;
The three α1-adrenoceptor subtypes show different spatio-temporal mechanisms of internalization and ERK1/2 phosphorylation by M. Perez-Aso; V. Segura; F. Montó; D. Barettino; M.A. Noguera; G. Milligan; P. D'Ocon (2322-2333).
We analyzed the kinetic and spatial patterns characterizing activation of the MAP kinases ERK 1 and 2 (ERK1/2) by the three α1-adrenoceptor (α1-AR) subtypes in HEK293 cells and the contribution of two different pathways to ERK1/2 phosphorylation: protein kinase C (PKC)-dependent ERK1/2 activation and internalization-dependent ERK1/2 activation. The different pathways of phenylephrine induced ERK phosphorylation were determined by western blot, using the PKC inhibitor Ro 31-8425, the receptor internalization inhibitor concanavalin A and the siRNA targeting β-arrestin 2. Receptor internalization properties were studied using CypHer5 technology and VSV-G epitope-tagged receptors. Activation of α1A- and α1B-ARs by phenylephrine elicited rapid ERK1/2 phosphorylation that was directed to the nucleus and inhibited by Ro 31-8425. Concomitant with phenylephrine induced receptor internalization α1A-AR, but not α1B-AR, produced a maintained and PKC-independent ERK phosphorylation, which was restricted to the cytosol and inhibited by β-arrestin 2 knockdown or concanavalin A treatment. α1D-AR displayed constitutive ERK phosphorylation, which was reduced by incubation with prazosin or the selective α1D antagonist BMY7378. Following activation by phenylephrine, α1D-AR elicited rapid, transient ERK1/2 phosphorylation that was restricted to the cytosol and not inhibited by Ro 31-8425. Internalization of the α1D-AR subtype was not observed via CypHer5 technology. The three α1-AR subtypes present different spatio-temporal patterns of receptor internalization, and only α1A-AR stimulation translates to a late, sustained ERK1/2 phosphorylation that is restricted to the cytosol and dependent on β-arrestin 2 mediated internalization.
Keywords: Adrenaline α1 receptors; ERK1/2; PKC; Internalization; Constitutive activity;
Stimulation of in vivo nuclear transport dynamics of actin and its co-factors IQGAP1 and Rac1 in response to DNA replication stress by Michael A. Johnson; Manisha Sharma; Myth T.S. Mok; Beric R. Henderson (2334-2347).
Actin, a constituent of the cytoskeleton, is now recognized to function in the nucleus in gene transcription, chromatin remodeling and DNA replication/repair. Actin shuttles in and out of the nucleus through the action of transport receptors importin-9 and exportin-6. Here we have addressed the impact of cell cycle progression and DNA replication stress on actin nuclear localization, through study of actin dynamics in living cells. First, we showed that thymidine-induced G1/S phase cell cycle arrest increased the nuclear levels of actin and of two factors that stimulate actin polymerization: IQGAP1 and Rac1 GTPase. When cells were exposed to hydroxyurea to induce DNA replication stress, the nuclear localization of actin and its regulators was further enhanced. We employed live cell photobleaching assays and discovered that in response to DNA replication stress, GFP-actin nuclear import and export rates increased by up to 250%. The rate of import was twice as fast as export, accounting for actin nuclear accumulation. The faster shuttling dynamics correlated with reduced cellular retention of actin, and our data implicate actin polymerization in the stress-dependent uptake of nuclear actin. Furthermore, DNA replication stress induced a nuclear shift in IQGAP1 and Rac1 with enhanced import dynamics. Proximity ligation assays revealed that IQGAP1 associates in the nucleus with actin and Rac1, and formation of these complexes increased after hydroxyurea treatment. We propose that the replication stress checkpoint triggers co-ordinated nuclear entry and trafficking of actin, and of factors that regulate actin polymerization.
Keywords: Nuclear actin; IQGAP1; Rac1; Nuclear transport; FRAP;
The nuclear import factor importin α4 can protect against oxidative stress by Julia C. Young; Jennifer D. Ly-Huynh; Helen Lescesen; Yoichi Miyamoto; Cate Browne; Yoshihiro Yoneda; Peter Koopman; Kate L. Loveland; David A. Jans (2348-2356).
The importin (IMP) superfamily of nuclear transport proteins is essential to key developmental pathways, including in the murine testis where expression of the 6 distinct IMPα proteins is highly dynamic. Present predominantly from the spermatocyte stage onwards, IMPα4 is unique in showing a striking nuclear localization, a property we previously found to be linked to maintenance of pluripotency in embryonic stem cells and to the cellular stress response in cultured cells. Here we examine the role of IMPα4 in vivo for the first time using a novel transgenic mouse model in which we overexpress an IMPα4–EGFP fusion protein from the protamine 1 promoter to recapitulate endogenous testicular germ cell IMPα4 expression in spermatids. IMPα4 overexpression did not affect overall fertility, testis morphology/weight or spermatogenic progression under normal conditions, but conferred significantly (> 30%) increased resistance to oxidative stress specifically in the spermatid subpopulation expressing the transgene. Consistent with a cell-specific role for IMPα4 in protecting against oxidative stress, haploid germ cells from IMPα4 null mice were significantly (c. 30%) less resistant to oxidative stress than wild type controls. These results from two unique and complementary mouse models demonstrate a novel protective role for IMPα4 in stress responses specifically within haploid male germline cells, with implications for male fertility and genetic integrity.
Keywords: Spermatogenesis; Oxidative stress; Nuclear transport; Importin/karyopherin;
SUMO1 negatively regulates the transcriptional activity of EVI1 and significantly increases its co-localization with EVI1 after treatment with arsenic trioxide by Sneha Singh; Anjan Kumar Pradhan; Soumen Chakraborty (2357-2368).
Aberrant expression of the proto-oncogene EVI1 (ecotropic virus integration site1) has been implicated not only in myeloid or lymphoid malignancies but also in colon, ovarian and breast cancers. Despite its importance in oncogenesis, the regulatory factors and mechanisms that potentiate the function of EVI1 and its consequences are partially known. Here we demonstrated that EVI1 is post-translationally modified by SUMO1 at lysine residues 533, 698 and 874. Although both EVI1 and SUMO1 were found to co-localize in nuclear speckles, the sumoylation mutant of EVI1 failed to co-localize with SUMO1. Sumoylation abrogated the DNA binding efficiency of EVI1 and also affected EVI1 mediated transactivation. The SUMO ligase PIASy was found to play a bi-directional role on EVI1, PIASy enhanced EVI1 sumoylation and augmented sumoylated EVI1 mediated repression. PIASy was also found to interact with EVI1 and impaired EVI1 transcriptional activity independent of its ligase activity. Arsenic trioxide (ATO) known to act as an antileukemic agent for acute promyelocytic leukemia (APL) not only enhanced EVI1 sumoylation but also enhanced the co-localization of EVI1 and SUMO1 in nuclear bodies distinct from PML nuclear bodies. ATO treatment also affected the Bcl-xL protein expression in EVI1 positive cell line. Thus, the results showed that arsenic treatment enhanced EVI1 sumoylation, deregulated Bcl-xL, which eventually may induce apoptosis in EVI1 positive cancer cells. The study for the first time explores and reports sumoylation of EVI1, which plays an essential role in regulating its function.
Keywords: EVI1; Sumoylation; Bcl-xL; PIASy; SIRT1; Arsenic trioxide (ATO);
Calpastatin is upregulated in non-immune neuronal cells via toll-like receptor 2 (TLR2) pathways by lipid-containing agonists by Taly Vaisid; Nechama S. Kosower (2369-2377).
Calpain (intracellular Ca2 +-dependent protease) and calpastatin (calpain specific endogenous inhibitor) are widely distributed in biological systems, and have been implicated in many cellular physiological and pathological processes. Calpastatin level is of central importance to the control of calpain activity. We demonstrated for the first time that calpastatin is overexpressed in mycoplasma-contaminated cultured cells (SH-SY5Y cells that are infected by a strain of Mycoplasma hyorhinis (NDMh)). We have found that the calpastatin-upregulating activity resides in the mycoplasmal membrane lipoproteins, and is associated with NF-κB activation. Calpain-promoted proteolysis is attenuated in the NDMh lipoprotein-treated cells. Here we show that the NDMh lipoproteins promoted an increase in calpastatin in SH-SY5Y cells via the TLR2/TAK1/NF-κB pathway. The synthetic mycoplasmal lipopeptide MALP-2 and the bacterial lipopeptide PAM3CSK4 (TLR2 agonists) also promoted calpastatin upregulation. LPS (TLR4 agonist) activated NF-κB without calpastatin increase in the cell. In contrast, lipoteichoic acid (TLR2 agonist) upregulated calpastatin not via NF-κB activation, but via the MEK1/ELK1 pathway. Zymosan and peptidoglycan, TLR2 agonists that lack lipids, did not induce calpastatin upregulation. Cell treatment with a calpastatin-upregulating agonist (lipoteichoic acid) led to the attenuation of Ca2 +-promoted calpain activity, whereas agonists that do not upregulate calpastatin (LPS, Zymosan) were ineffective. Overall, the results indicate that in these non-immune cells, calpastatin is upregulated by TLR2-agonists containing lipids, with more than one downstream pathway involved. Such agonists may be useful for studying mechanisms and factors involved in calpastatin regulation. In addition, suitable TLR2 agonists may be of interest in devising treatments for pathological processes involving excessive calpain activation.
Keywords: Calpastatin; Calpain; TLR agonists; Lipid TLR2 agonists; Mycoplasmal lipoproteins;
Multiple FAS1 domains and the RGD motif of TGFBI act cooperatively to bind αvβ3 integrin, leading to anti-angiogenic and anti-tumor effects by Hye-Nam Son; Ju-Ock Nam; Soyoun Kim; In-San Kim (2378-2388).
TGFBI, a transforming growth factor β-induced extracellular matrix protein, circulates at a level of ~ 300 ng/ml in humans and modulates several integrin-mediated cellular functions. The protein contains an N-terminal EMI domain, four consecutive FAS1 domains, and the RGD motif. Each FAS1 domain and the RGD motif have been known to interact with avb3 integrin. Here, we found that the binding affinity (K d) of TGFBI for αvβ3 integrin was approximately 3.8 × 10− 8 M, a value ~ 2300-fold higher than that of a single FAS1 domain, and demonstrated that this greater affinity was due to the cooperative action of the four FAS1 domains and the RGD motif. Moreover, TGFBI exhibited more potent anti-angiogenic and anti-tumorigenic activities, even at a 100-fold lower molar dose than the reported effective dose of the FAS1 domain. Finally, our data showed that TGFBI specifically targeted the tumor vasculature and accumulated at the tumor site. Collectively, our results support the theory that TGFBI acts as a potent endogenous anti-tumor and anti-angiogenic molecule by targeting αvβ3 integrin, and highlights the importance of physiological circulating TGFBI levels in inhibiting tumor growth.
Keywords: TGFBI; Angiogenesis; αvβ3 integrin; Anti-tumor effect; FAS1 domain;