1
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Koumenis C, Naczki C, Koritzinsky M, Rastani S, Diehl A, Sonenberg N, Koromilas A, Wouters BG. Regulation of protein synthesis by hypoxia via activation of the endoplasmic reticulum kinase PERK and phosphorylation of the translation initiation factor eIF2alpha. Mol Cell Biol 2002; 22:7405-16. [PMID: 12370288 PMCID: PMC135664 DOI: 10.1128/mcb.22.21.7405-7416.2002] [Citation(s) in RCA: 532] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2002] [Revised: 05/29/2002] [Accepted: 07/23/2002] [Indexed: 02/08/2023] Open
Abstract
Hypoxia profoundly influences tumor development and response to therapy. While progress has been made in identifying individual gene products whose synthesis is altered under hypoxia, little is known about the mechanism by which hypoxia induces a global downregulation of protein synthesis. A critical step in the regulation of protein synthesis in response to stress is the phosphorylation of translation initiation factor eIF2alpha on Ser51, which leads to inhibition of new protein synthesis. Here we report that exposure of human diploid fibroblasts and transformed cells to hypoxia led to phosphorylation of eIF2alpha, a modification that was readily reversed upon reoxygenation. Expression of a transdominant, nonphosphorylatable mutant allele of eIF2alpha attenuated the repression of protein synthesis under hypoxia. The endoplasmic reticulum (ER)-resident eIF2alpha kinase PERK was hyperphosphorylated upon hypoxic stress, and overexpression of wild-type PERK increased the levels of hypoxia-induced phosphorylation of eIF2alpha. Cells stably expressing a dominant-negative PERK allele and mouse embryonic fibroblasts with a homozygous deletion of PERK exhibited attenuated phosphorylation of eIF2alpha and reduced inhibition of protein synthesis in response to hypoxia. PERK(-/-) mouse embryo fibroblasts failed to phosphorylate eIF2alpha and exhibited lower survival after prolonged exposure to hypoxia than did wild-type fibroblasts. These results indicate that adaptation of cells to hypoxic stress requires activation of PERK and phosphorylation of eIF2alpha and suggest that the mechanism of hypoxia-induced translational attenuation may be linked to ER stress and the unfolded-protein response.
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23 |
532 |
2
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Koromilas AE, Roy S, Barber GN, Katze MG, Sonenberg N. Malignant transformation by a mutant of the IFN-inducible dsRNA-dependent protein kinase. Science 1992; 257:1685-9. [PMID: 1382315 DOI: 10.1126/science.1382315] [Citation(s) in RCA: 466] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The double-stranded RNA-dependent protein kinase (dsRNA-PK) is thought to be a key mediator of the antiviral and antiproliferative effects of interferons (IFNs). Studies examining the physiological function of the kinase suggest that it participates in cell growth and differentiation by regulating protein synthesis. Autophosphorylation and consequent activation of dsRNA-PK in vitro and in vivo result in phosphorylation of the alpha subunit of eukaryotic initiation factor-2 (eIF-2) and inhibition of protein synthesis. Expression of a functionally defective mutant of human dsRNA-PK in NIH 3T3 cells resulted in malignant transformation, suggesting that dsRNA-PK may function as a suppressor of cell proliferation and tumorigenesis.
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33 |
466 |
3
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Koromilas AE, Lazaris-Karatzas A, Sonenberg N. mRNAs containing extensive secondary structure in their 5′ non-coding region translate efficiently in cells overexpressing initiation factor eIF-4E. EMBO J 1992; 11:4153-8. [PMID: 1396596 PMCID: PMC556925 DOI: 10.1002/j.1460-2075.1992.tb05508.x] [Citation(s) in RCA: 296] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Cellular eukaryotic mRNAs (except organellar) contain at the 5' terminus the structure m7(5')Gppp(5')N (where N is any nucleotide), termed cap. Cap recognition by eukaryotic initiation factor eIF-4F plays an important role in regulating the overall rate of translation. eIF-4F is believed to mediate the melting of mRNA 5' end secondary structure and facilitate 43S ribosome binding to capped mRNAs. eIF-4E, the cap-binding subunit of eIF-4F, plays an important role in cell growth; its overexpression results in malignant transformation of rodent cells, and its phosphorylation is implicated in signal transduction pathways of mitogens and growth factors. The molecular mechanism by which eIF-4E transforms cells is not known. Here, we report that overexpression of eIF-4E facilitates the translation of mRNAs containing excessive secondary structure in their 5' non-coding region. This effect may represent one mechanism by which eIF-4E regulates cell growth and transforms cells in culture.
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33 |
296 |
4
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Donzé O, Jagus R, Koromilas AE, Hershey JW, Sonenberg N. Abrogation of translation initiation factor eIF-2 phosphorylation causes malignant transformation of NIH 3T3 cells. EMBO J 1995; 14:3828-34. [PMID: 7641700 PMCID: PMC394457 DOI: 10.1002/j.1460-2075.1995.tb00052.x] [Citation(s) in RCA: 224] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The interferon induced double-stranded RNA-activated kinase, PKR, has been suggested to act as a tumor suppressor since expression of a dominant negative mutant of PKR causes malignant transformation. However, the mechanism of transformation has not been elucidated. PKR phosphorylates translation initiation factor eIF-2 alpha on Ser51, resulting in inhibition of protein synthesis and cell growth arrest. Consequently, it is possible that cell transformation by dominant negative PKR mutants is caused by inhibition of eIF-2 alpha phosphorylation. Here, we demonstrate that in NIH 3T3 cells transformed by the dominant negative PKR mutant (PKR delta 6), eIF-2 alpha phosphorylation is dramatically reduced. Furthermore, expression of a mutant form of eIF-2 alpha, which cannot be phosphorylated on Ser51 also caused malignant transformation of NIH 3T3 cells. These results are consistent with a critical role of phosphorylation of eIF-2 alpha in control of cell proliferation, and indicate that dominant negative PKR mutants transform cells by inhibition of eIF-2 alpha phosphorylation.
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30 |
224 |
5
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Qu L, Huang S, Baltzis D, Rivas-Estilla AM, Pluquet O, Hatzoglou M, Koumenis C, Taya Y, Yoshimura A, Koromilas AE. Endoplasmic reticulum stress induces p53 cytoplasmic localization and prevents p53-dependent apoptosis by a pathway involving glycogen synthase kinase-3beta. Genes Dev 2004; 18:261-77. [PMID: 14744935 PMCID: PMC338280 DOI: 10.1101/gad.1165804] [Citation(s) in RCA: 206] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The tumor suppressor p53, a sensor of multiple forms of cellular stress, is regulated by post-translational mechanisms to induce cell-cycle arrest, senescence, or apoptosis. We demonstrate that endoplasmic reticulum (ER) stress inhibits p53-mediated apoptosis. The mechanism of inhibition involves the increased cytoplasmic localization of p53 due to phosphorylation at serine 315 and serine 376, which is mediated by glycogen synthase kinase-3 beta (GSK-3beta). ER stress induces GSK-3beta binding to p53 in the nucleus and enhances the cytoplasmic localization of the tumor suppressor. Inhibition of apoptosis caused by ER stress requires GSK-3beta and does not occur in cells expressing p53 with mutation(s) of serine 315 and/or serine 376 to alanine(s). As a result of the increased cytoplasmic localization, ER stress prevents p53 stabilization and p53-mediated apoptosis upon DNA damage. It is concluded that inactivation of p53 is a protective mechanism utilized by cells to adapt to ER stress.
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Research Support, Non-U.S. Gov't |
21 |
206 |
6
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Li S, Labrecque S, Gauzzi MC, Cuddihy AR, Wong AH, Pellegrini S, Matlashewski GJ, Koromilas AE. The human papilloma virus (HPV)-18 E6 oncoprotein physically associates with Tyk2 and impairs Jak-STAT activation by interferon-alpha. Oncogene 1999; 18:5727-37. [PMID: 10523853 DOI: 10.1038/sj.onc.1202960] [Citation(s) in RCA: 192] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
We have examined the effects of human papilloma virus (HPV) E6 proteins on interferon (IFN) signaling. Here we show that expression of the 'malignant' HPV-18 E6 in human HT1080 cells results in inhibition of Jak-STAT activation in response to IFN-alpha but not IFN-gamma. This inhibitory effect is not shared by the 'benign' HPV-11 E6. The DNA-binding and transactivation capacities of the transcription factor ISGF3 are diminished in cells expressing HPV-18 E6 after IFN-alpha treatment as a result of decreased tyrosine phosphorylation of Tyk2, STAT2 and STAT1. However, HPV-18 E6 does not affect the induction of tyrosine phosphorylation and DNA-binding of STAT1 by IFN-gamma. In addition, HPV E6 proteins physically interact with Tyk2. This interaction takes place preferably with HPV-18 E6 and to a lesser extent with HPV-11 E6. The E6/Tyk2 interaction requires the JH6-JH7 domains of Tyk2, which are important for Tyk2 binding to the cytoplasmic portion of IFN-alpha receptor 1 (IFNAR1). These findings demonstrate an inhibitory role of HPV-18 E6 in the IFN-alpha-induced Jak-STAT pathway, which may be explained, at least in part, by the ability of E6 to interact with and impair Tyk2 activation.
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26 |
192 |
7
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Abraham N, Stojdl DF, Duncan PI, Méthot N, Ishii T, Dubé M, Vanderhyden BC, Atkins HL, Gray DA, McBurney MW, Koromilas AE, Brown EG, Sonenberg N, Bell JC. Characterization of transgenic mice with targeted disruption of the catalytic domain of the double-stranded RNA-dependent protein kinase, PKR. J Biol Chem 1999; 274:5953-62. [PMID: 10026221 DOI: 10.1074/jbc.274.9.5953] [Citation(s) in RCA: 184] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The interferon-inducible, double-stranded RNA-dependent protein kinase PKR has been implicated in anti-viral, anti-tumor, and apoptotic responses. Others have attempted to examine the requirement of PKR in these roles by targeted disruption at the amino terminal-encoding region of the Pkr gene. By using a strategy that aims at disruption of the catalytic domain of PKR, we have generated mice that are genetically ablated for functional PKR. Similar to the other mouse model of Pkr disruption, we have observed no consequences of loss of PKR on tumor suppression. Anti-viral response to influenza and vaccinia also appeared to be normal in mice and in cells lacking PKR. Cytokine signaling in the type I interferon pathway is normal but may be compromised in the erythropoietin pathway in erythroid bone marrow precursors. Contrary to the amino-terminal targeted Pkr mouse, tumor necrosis factor alpha-induced apoptosis and the anti-viral apoptosis response to influenza is not impaired in catalytic domain-targeted Pkr-null cells. The observation of intact eukaryotic initiation factor-2alpha phosphorylation in these Pkr-null cells provides proof of rescue by another eukaryotic initiation factor-2alpha kinase(s).
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26 |
184 |
8
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Yaman I, Fernandez J, Liu H, Caprara M, Komar AA, Koromilas AE, Zhou L, Snider MD, Scheuner D, Kaufman RJ, Hatzoglou M. The zipper model of translational control: a small upstream ORF is the switch that controls structural remodeling of an mRNA leader. Cell 2003; 113:519-31. [PMID: 12757712 DOI: 10.1016/s0092-8674(03)00345-3] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Transport of the essential amino acids arginine and lysine is critical for the survival of mammalian cells. The adaptive response to nutritional stress involves increased translation of the arginine/lysine transporter (cat-1) mRNA via an internal ribosome entry site (IRES) within the mRNA leader. Induction of cat-1 IRES activity requires both translation of a small upstream open reading frame (uORF) within the IRES and phosphorylation of the translation initiation factor eIF2alpha. We show here that translation of the upstream ORF unfolds an inhibitory structure in the mRNA leader, eliciting a conformational change that yields an active IRES. The IRES, whose activity is induced by amino acid starvation, is created by RNA-RNA interactions between the 5' end of the leader and downstream sequences. This study suggests that the structure of the IRES is dynamic and regulation of this RNA structure is a mechanism of translational control.
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22 |
162 |
9
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Cuddihy AR, Wong AH, Tam NW, Li S, Koromilas AE. The double-stranded RNA activated protein kinase PKR physically associates with the tumor suppressor p53 protein and phosphorylates human p53 on serine 392 in vitro. Oncogene 1999; 18:2690-702. [PMID: 10348343 DOI: 10.1038/sj.onc.1202620] [Citation(s) in RCA: 161] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The tumor suppressor p53 is a multifunctional protein that plays a critical role in modulating cellular responses upon DNA damage or other stresses. These functions of p53 are regulated both by protein-protein interactions and phosphorylation. The double-stranded RNA activated protein kinase PKR is a serine/threonine kinase that modulates protein synthesis through the phosphorylation of translation initiation factor eIF-2alpha. PKR is an interferon (IFN)-inducible protein that is thought to mediate the anti-viral and anti-proliferative effects of IFN via its capacity to inhibit protein synthesis. Here we report that PKR physically associates with p53. The interaction of PKR with p53 is enhanced by IFNs and upon conditions that p53 acquires a wild type conformation. PKR/p53 complex formation in vitro requires the N-terminal regulatory domain of PKR and the last 30 amino acids of the C-terminus of human p53. In addition, p53 may function as a substrate of PKR since phosphorylation of human p53 on serine392 is induced by activated PKR in vitro. These novel findings raise the possibility of a functional interaction between PKR and p53 in vivo, which may account, at least in part, for the ability of each protein to regulate gene expression at both the transcriptional and the translational levels.
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26 |
161 |
10
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Wong AH, Tam NW, Yang YL, Cuddihy AR, Li S, Kirchhoff S, Hauser H, Decker T, Koromilas AE. Physical association between STAT1 and the interferon-inducible protein kinase PKR and implications for interferon and double-stranded RNA signaling pathways. EMBO J 1997; 16:1291-304. [PMID: 9135145 PMCID: PMC1169727 DOI: 10.1093/emboj/16.6.1291] [Citation(s) in RCA: 137] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The interferon-inducible double-stranded RNA protein kinase PKR controls protein synthesis through the phosphorylation of eukaryotic translation initiation factor (eIF)-2. In addition to its demonstrated role in translational control, several reports have suggested a transcriptional role for PKR. Here we report that PKR is involved in IFN- and dsRNA-signaling pathways by modulating the function of the signal transducer and activator of transcription STAT1. We also show that PKR associates with STAT1 in mouse and human cells. The association is not a kinase-substrate interaction since STAT1 phosphorylation is not modified by PKR in vitro or in vivo. In addition, the formation of the PKR-STAT1 complex is not dependent upon the enzymatic activity of PKR but does require the dsRNA-binding domain of PKR. Moreover, there is a concomitant decrease in PKR-STAT1 interaction and increase in STAT1 DNA binding in response to IFNs or dsRNA. These findings suggest that PKR plays an important role in IFN and dsRNA-signaling pathways by modulating the transcriptional function of STAT1.
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research-article |
28 |
137 |
11
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Cuddihy AR, Li S, Tam NW, Wong AH, Taya Y, Abraham N, Bell JC, Koromilas AE. Double-stranded-RNA-activated protein kinase PKR enhances transcriptional activation by tumor suppressor p53. Mol Cell Biol 1999; 19:2475-84. [PMID: 10082513 PMCID: PMC84040 DOI: 10.1128/mcb.19.4.2475] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The tumor suppressor p53 plays a key role in inducing G1 arrest and apoptosis following DNA damage. The double-stranded-RNA-activated protein PKR is a serine/threonine interferon (IFN)-inducible kinase which plays an important role in regulation of gene expression at both transcriptional and translational levels. Since a cross talk between IFN-inducible proteins and p53 had already been established, we investigated whether and how p53 function was modulated by PKR. We analyzed p53 function in several cell lines derived from PKR+/+ and PKR-/- mouse embryonic fibroblasts (MEFs) after transfection with the temperature-sensitive (ts) mutant of mouse p53 [p53(Val135)]. Here we report that transactivation of transcription by p53 and G0/G1 arrest were impaired in PKR-/- cells upon conditions that ts p53 acquired a wild-type conformation. Phosphorylation of mouse p53 on Ser18 was defective in PKR-/- cells, consistent with an impaired transcriptional induction of the p53-inducible genes encoding p21(WAF/Cip1) and Mdm2. In addition, Ser18 phosphorylation and transcriptional activation by mouse p53 were diminished in PKR-/- cells after DNA damage induced by the anticancer drug adriamycin or gamma radiation but not by UV radiation. Furthermore, the specific phosphatidylinositol-3 (PI-3) kinase inhibitor LY294002 inhibited the induction of phosphorylation of Ser18 of p53 by adriamycin to a higher degree in PKR+/+ cells than in PKR-/- cells. These novel findings suggest that PKR enhances p53 transcriptional function and implicate PKR in cell signaling elicited by a specific type of DNA damage that leads to p53 phosphorylation, possibly through a PI-3 kinase pathway.
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research-article |
26 |
115 |
12
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Guan BJ, Krokowski D, Majumder M, Schmotzer CL, Kimball SR, Merrick WC, Koromilas AE, Hatzoglou M. Translational control during endoplasmic reticulum stress beyond phosphorylation of the translation initiation factor eIF2α. J Biol Chem 2014; 289:12593-611. [PMID: 24648524 DOI: 10.1074/jbc.m113.543215] [Citation(s) in RCA: 113] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER) causes stress to which an unfolded protein response is activated to render cell survival or apoptosis (chronic stress). Transcriptional and translational reprogramming is tightly regulated during the unfolded protein response to ensure specific gene expression. The master regulator of this response is the PERK/eIF2α/ATF4 signaling where eIF2α is phosphorylated (eIF2α-P) by the kinase PERK. This signal leads to global translational shutdown, but it also enables translation of the transcription factor ATF4 mRNA. We showed recently that ATF4 induces an anabolic program through the up-regulation of selected amino acid transporters and aminoacyl-tRNA synthetases. Paradoxically, this anabolic program led cells to apoptosis during chronic ER stress in a manner that involved recovery from stress-induced protein synthesis inhibition. By using eIF2α-P-deficient cells as an experimental system, we identified a communicating network of signaling pathways that contribute to the inhibition of protein synthesis during chronic ER stress. This eIF2α-P-independent network includes (i) inhibition of mammalian target of rapamycin kinase protein complex 1 (mTORC1)-targeted protein phosphorylation, (ii) inhibited translation of a selective group of 5'-terminal oligopyrimidine mRNAs (encoding proteins involved in the translation machinery and translationally controlled by mTORC1 signaling), and (iii) inhibited translation of non-5'-terminal oligopyrimidine ribosomal protein mRNAs and ribosomal RNA biogenesis. We propose that the PERK/eIF2α-P/ATF4 signaling acts as a brake in the decline of protein synthesis during chronic ER stress by positively regulating signaling downstream of the mTORC1 activity. These studies advance our knowledge on the complexity of the communicating signaling pathways in controlling protein synthesis rates during chronic stress.
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Research Support, Non-U.S. Gov't |
11 |
113 |
13
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Robert F, Kapp LD, Khan SN, Acker MG, Kolitz S, Kazemi S, Kaufman RJ, Merrick WC, Koromilas AE, Lorsch JR, Pelletier J. Initiation of protein synthesis by hepatitis C virus is refractory to reduced eIF2.GTP.Met-tRNA(i)(Met) ternary complex availability. Mol Biol Cell 2006; 17:4632-44. [PMID: 16928960 PMCID: PMC1635388 DOI: 10.1091/mbc.e06-06-0478] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
A cornerstone of the antiviral interferon response is phosphorylation of eukaryotic initiation factor (eIF)2alpha. This limits the availability of eIF2.GTP.Met-tRNA(i)(Met) ternary complexes, reduces formation of 43S preinitiation complexes, and blocks viral (and most cellular) mRNA translation. However, many viruses have developed counterstrategies that circumvent this cellular response. Herein, we characterize a novel class of translation initiation inhibitors that block ternary complex formation and prevent the assembly of 43S preinitiation complexes. We find that translation driven by the HCV IRES is refractory to inhibition by these compounds at concentrations that effectively block cap-dependent translation in vitro and in vivo. Analysis of initiation complexes formed on the HCV IRES in the presence of inhibitor indicates that eIF2alpha and Met-tRNA(i)(Met) are present, defining a tactic used by HCV to evade part of the antiviral interferon response.
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Research Support, Non-U.S. Gov't |
19 |
102 |
14
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Krokowski D, Han J, Saikia M, Majumder M, Yuan CL, Guan BJ, Bevilacqua E, Bussolati O, Bröer S, Arvan P, Tchórzewski M, Snider MD, Puchowicz M, Croniger CM, Kimball SR, Pan T, Koromilas AE, Kaufman RJ, Hatzoglou M. A self-defeating anabolic program leads to β-cell apoptosis in endoplasmic reticulum stress-induced diabetes via regulation of amino acid flux. J Biol Chem 2013; 288:17202-13. [PMID: 23645676 DOI: 10.1074/jbc.m113.466920] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Endoplasmic reticulum (ER) stress-induced responses are associated with the loss of insulin-producing β-cells in type 2 diabetes mellitus. β-Cell survival during ER stress is believed to depend on decreased protein synthesis rates that are mediated via phosphorylation of the translation initiation factor eIF2α. It is reported here that chronic ER stress correlated with increased islet protein synthesis and apoptosis in β-cells in vivo. Paradoxically, chronic ER stress in β-cells induced an anabolic transcription program to overcome translational repression by eIF2α phosphorylation. This program included expression of amino acid transporter and aminoacyl-tRNA synthetase genes downstream of the stress-induced ATF4-mediated transcription program. The anabolic response was associated with increased amino acid flux and charging of tRNAs for branched chain and aromatic amino acids (e.g. leucine and tryptophan), the levels of which are early serum indicators of diabetes. We conclude that regulation of amino acid transport in β-cells during ER stress involves responses leading to increased protein synthesis, which can be protective during acute stress but can lead to apoptosis during chronic stress. These studies suggest that the increased expression of amino acid transporters in islets can serve as early diagnostic biomarkers for the development of diabetes.
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Research Support, N.I.H., Extramural |
12 |
94 |
15
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Koromilas AE. Roles of the translation initiation factor eIF2α serine 51 phosphorylation in cancer formation and treatment. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1849:871-80. [PMID: 25497381 DOI: 10.1016/j.bbagrm.2014.12.007] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Revised: 12/03/2014] [Accepted: 12/07/2014] [Indexed: 01/12/2023]
Abstract
Cells respond to various forms of stress by activating anti-proliferative pathways, which allow them to correct the damage caused by stress before re-entering proliferation. If the damage, however, is beyond repair, stressed cells are eliminated from the host by undergoing death. The balance between cell survival and death is essential for cancer formation and is determined by several key pathways that impact on different stages of gene expression. In recent years, it has become evident that phosphorylation of the alpha (α) subunit of the translation initiation factor eIF2 at serine 51 (eIF2αS51P) is an important determinant of cell fate in response to stress. Induction of eIF2αS51P is mediated by a family of four kinases namely, HRI, PKR, PERK and GCN2, each of which responds to distinct forms of stress. Increased eIF2αS51P results in a global inhibition of protein synthesis but at the same time enhances the translation of select mRNAs encoding for proteins that control cell adaptation to stress. Short-term induction of eIF2αS51P has been associated with cell survival whereas long-term induction with cell death. Studies in mouse and human models of cancer have provided compelling evidence that eIF2αS51P plays an essential role in stress-induced tumorigenesis. Increased eIF2αS51P exhibits cell autonomous as well as immune regulatory effects, which can influence tumor growth and the efficacy of anti-tumor therapies. The findings suggest that eIF2αS51P may be of prognostic value and a suitable target for the design and implementation of effective anti-tumor therapies. This article is part of a Special Issue entitled: Translation and Cancer.
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Review |
11 |
93 |
16
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Muaddi H, Majumder M, Peidis P, Papadakis AI, Holcik M, Scheuner D, Kaufman RJ, Hatzoglou M, Koromilas AE. Phosphorylation of eIF2α at serine 51 is an important determinant of cell survival and adaptation to glucose deficiency. Mol Biol Cell 2010; 21:3220-31. [PMID: 20660158 PMCID: PMC2938387 DOI: 10.1091/mbc.e10-01-0023] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Glucose deficiency leads to the induction of eIF2α phosphorylation at serine 51, which results in a global inhibition of protein synthesis. Phosphorylation of eIF2α is an adaptive process that establishes a cytoprotective state in glucose-deficient cells, with possible implications in biological responses that interfere with glucose metabolism. Various forms of stress induce pathways that converge on the phosphorylation of the alpha (α) subunit of eukaryotic translation initiation factor eIF2 at serine 51 (S51), a modification that results in a global inhibition of protein synthesis. In many cases eIF2α phosphorylation is a biological response that facilitates cells to cope with stressful environments. Glucose deficiency, an important form of stress, is associated with an induction of apoptosis. Herein, we demonstrate that eIF2α phosphorylation is a key step in maintaining a balance between the life and death of a glucose-deficient cell. That is, eIF2α phosphorylation acts as a molecular switch that shifts cells from a proapoptotic to a cytoprotective state in response to prolonged glucose deficiency. This adaptation process is associated with the timely expression of proteins and activation of pathways with significant contributions to cell survival and adaptation including the X-linked inhibitor of apoptosis protein (XIAP). We also show that among the eIF2α kinases GCN2 plays a proapoptotic role whereas PERK and PKR play a cytoprotective one in response to glucose deficiency. Our data demonstrate that eIF2α phosphorylation is a significant determinant of survival and adaptation of glucose-deficient cells with possible important implications in biological processes that interfere with glucose metabolism.
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Research Support, Non-U.S. Gov't |
15 |
92 |
17
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Baltzis D, Pluquet O, Papadakis AI, Kazemi S, Qu LK, Koromilas AE. The eIF2alpha kinases PERK and PKR activate glycogen synthase kinase 3 to promote the proteasomal degradation of p53. J Biol Chem 2007; 282:31675-87. [PMID: 17785458 DOI: 10.1074/jbc.m704491200] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha) is mediated by a family of kinases that respond to various forms of environmental stress. The eIF2alpha kinases are critical for mRNA translation, cell proliferation, and apoptosis. Activation of the tumor suppressor p53 results in cell cycle arrest and apoptosis in response to various types of stress. We previously showed that, unlike the majority of stress responses that stabilize and activate p53, induction of endoplasmic reticulum stress leads to p53 degradation through an Mdm2-dependent mechanism. Here, we demonstrate that the endoplasmic reticulum-resident eIF2alpha kinase PERK mediates the proteasomal degradation of p53 independently of translational control. This role is not specific for PERK, because the eIF2alpha kinase PKR also promotes p53 degradation in response to double-stranded RNA. We further establish that the eIF2alpha kinases induce glycogen synthase kinase 3 to promote the nuclear export and proteasomal degradation of p53. Our findings reveal a novel cross-talk between the eIF2alpha kinases and p53 with implications in cell proliferation and tumorigenesis.
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Research Support, Non-U.S. Gov't |
18 |
92 |
18
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Mounir Z, Krishnamoorthy JL, Wang S, Papadopoulou B, Campbell S, Muller WJ, Hatzoglou M, Koromilas AE. Akt determines cell fate through inhibition of the PERK-eIF2α phosphorylation pathway. Sci Signal 2012; 4:ra62. [PMID: 21954288 DOI: 10.1126/scisignal.2001630] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Metazoans respond to various forms of environmental stress by inducing the phosphorylation of the α subunit of eukaryotic translation initiation factor 2 (eIF2α) at serine-51, a modification that leads to global inhibition of mRNA translation. We demonstrate induction of the phosphorylation of eIF2α in mammalian cells after either pharmacological inhibition of the phosphoinositide 3-kinase (PI3K)-Akt pathway or genetic or small interfering RNA-mediated ablation of Akt. This increase in the extent of eIF2α phosphorylation also occurred in Drosophila cells and depended on the endoplasmic reticulum (ER)-resident protein kinase PERK, which was inhibited by Akt-dependent phosphorylation at threonine-799. The activity of PERK and the abundance of phosphorylated eIF2α (eIF2αP) were reduced in mouse mammary gland tumors that contained activated Akt, as well as in cells exposed to ER stress or oxidative stress. In unstressed cells, the PERK-eIF2αP pathway mediated survival and facilitated adaptation to the deleterious effects of the inactivation of PI3K or Akt. Inactivation of the PERK-eIF2αP pathway increased the susceptibility of tumor cells to death by pharmacological inhibitors of PI3K or Akt. Thus, we suggest that the PERK-eIF2αP pathway provides a link between Akt signaling and translational control, which has implications for tumor formation and treatment.
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Research Support, Non-U.S. Gov't |
13 |
91 |
19
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Kazemi S, Papadopoulou S, Li S, Su Q, Wang S, Yoshimura A, Matlashewski G, Dever TE, Koromilas AE. Control of alpha subunit of eukaryotic translation initiation factor 2 (eIF2 alpha) phosphorylation by the human papillomavirus type 18 E6 oncoprotein: implications for eIF2 alpha-dependent gene expression and cell death. Mol Cell Biol 2004; 24:3415-29. [PMID: 15060162 PMCID: PMC381675 DOI: 10.1128/mcb.24.8.3415-3429.2004] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Phosphorylation of the alpha subunit of eukaryotic translation initiation factor 2 (eIF2alpha) at serine 51 inhibits protein synthesis in cells subjected to various forms of stress including virus infection. The human papillomavirus (HPV) E6 oncoprotein contributes to virus-induced pathogenicity through multiple mechanisms including the inhibition of apoptosis and the blockade of interferon (IFN) action. We have investigated a possible functional relationship between the E6 oncoprotein and eIF2alpha phosphorylation by an inducible-dimerization form of the IFN-inducible protein kinase PKR. Herein, we demonstrate that HPV type 18 E6 protein synthesis is rapidly repressed upon eIF2alpha phosphorylation caused by the conditional activation of the kinase. The remainder of E6, however, can rescue cells from PKR-mediated inhibition of protein synthesis and induction of apoptosis. E6 physically associates with GADD34/PP1 holophosphatase complex, which mediates translational recovery, and facilitates eIF2alpha dephosphorylation. Inhibition of eIF2alpha phosphorylation by E6 mitigates eIF2alpha-dependent responses to transcription and translation of proapoptotic genes. These findings demonstrate, for the first time, a role of the oncogenic E6 in apoptotic signaling induced by PKR and eIF2alpha phosphorylation. The functional interaction between E6 and the eIF2alpha phosphorylation pathway may have important implications for HPV infection and associated pathogenesis.
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Research Support, Non-U.S. Gov't |
21 |
90 |
20
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Pluquet O, Qu LK, Baltzis D, Koromilas AE. Endoplasmic reticulum stress accelerates p53 degradation by the cooperative actions of Hdm2 and glycogen synthase kinase 3beta. Mol Cell Biol 2005; 25:9392-405. [PMID: 16227590 PMCID: PMC1265800 DOI: 10.1128/mcb.25.21.9392-9405.2005] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Inactivation of the tumor suppressor p53 by degradation is a mechanism utilized by cells to adapt to endoplasmic reticulum (ER) stress. However, the mechanisms of p53 destabilization by ER stress are not known. We demonstrate here that the E3 ubiquitin-ligase Hdm2 is essential for the nucleocytoplasmic transport and proteasome-dependent degradation of p53 in ER-stressed cells. We also demonstrate that p53 phosphorylation at S315 and S376 is required for its nuclear export and degradation by Hdm2 without interfering with the ubiquitylation process. Furthermore, we show that p53 destabilization in unstressed cells utilizes the cooperative action of Hdm2 and glycogen synthase kinase 3beta, a process that is enhanced in cells exposed to ER stress. In contrast to other stress pathways that stabilize p53, our findings further substantiate a negative role of ER stress in p53 activation with important implications for the function of the tumor suppressor in cells with a dysfunctional ER.
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Research Support, Non-U.S. Gov't |
20 |
89 |
21
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Fernandez J, Yaman I, Merrick WC, Koromilas A, Wek RC, Sood R, Hensold J, Hatzoglou M. Regulation of internal ribosome entry site-mediated translation by eukaryotic initiation factor-2alpha phosphorylation and translation of a small upstream open reading frame. J Biol Chem 2002; 277:2050-8. [PMID: 11684693 DOI: 10.1074/jbc.m109199200] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Adaptation to amino acid deficiency is critical for cell survival. In yeast, this adaptation involves phosphorylation of the translation eukaryotic initiation factor (eIF) 2alpha by the kinase GCN2. This leads to the increased translation of the transcription factor GCN4, which in turn increases transcription of amino acid biosynthetic genes, at a time when expression of most genes decreases. Here it is shown that translation of the arginine/lysine transporter cat-1 mRNA increases during amino acid starvation of mammalian cells. This increase requires both GCN2 phosphorylation of eIF2alpha and the translation of a 48-amino acid upstream open reading frame (uORF) present within the 5'-leader of the transporter mRNA. When this 5'-leader was placed in a bicistronic mRNA expression vector, it functioned as an internal ribosomal entry sequence and its regulated activity was dependent on uORF translation. Amino acid starvation also induced translation of monocistronic mRNAs containing the cat-1 5'-leader, in a manner dependent on eIF2alpha phosphorylation and translation of the 48-amino acid uORF. This is the first example of mammalian regulation of internal ribosomal entry sequence-mediated translation by eIF2alpha phosphorylation during amino acid starvation, suggesting that the mechanism of induced Cat-1 protein synthesis is part of the adaptive response of cells to amino acid limitation.
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85 |
22
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Sasaki A, Inagaki-Ohara K, Yoshida T, Yamanaka A, Sasaki M, Yasukawa H, Koromilas AE, Yoshimura A. The N-terminal truncated isoform of SOCS3 translated from an alternative initiation AUG codon under stress conditions is stable due to the lack of a major ubiquitination site, Lys-6. J Biol Chem 2003; 278:2432-6. [PMID: 12459551 DOI: 10.1074/jbc.c200608200] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The suppressor of cytokine signaling-3 (SOCS3/CIS-33/SSI-3) is an important negative regulator of cytokine signaling. Here, we show that an N-terminal truncated isoform (DeltaN-SOCS3) translated from the internal AUG codon 12 was profoundly induced by endoplasmic reticulum (ER) stress- or active double-stranded RNA-activated protein kinase PKR, as a result of induction of eukaryotic initiation factor 2alpha phosphorylation. DeltaN-SOCS3 exhibited a stronger cytokine-inhibitory activity and a higher stability than WT-SOCS3 in Ba/F3 hematopoietic cells. A potential ubiquitination residue, Lys-6, at the N terminus is evolutionary conserved among SOCS3 species. The K6Q-SOCS3 mutant showed a much longer half-life than WT-SOCS3 in Ba/F3 cells. Furthermore, inhibition of the 26 S proteasome pathway increased both ubiquitination and protein levels of WT-SOCS3 but had no effect on K6Q-SOCS3. SOCS3 mutant lacking the carboxyl-terminal SOCS-box exhibited the same stability as K6Q-SOCS3. These observations suggest that the short form of SOCS3 is a naturally occurring stabilized inhibitory protein, whereas WT-SOCS3 is a short-lived protein modulated by Lys-6 ubiquitination and proteasome-dependent degradation. Our findings provide strong evidence for the first time that translational control plays an important role in stabilization and function of SOCS3.
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82 |
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Fillebeen C, Rivas-Estilla AM, Bisaillon M, Ponka P, Muckenthaler M, Hentze MW, Koromilas AE, Pantopoulos K. Iron inactivates the RNA polymerase NS5B and suppresses subgenomic replication of hepatitis C Virus. J Biol Chem 2005; 280:9049-57. [PMID: 15637067 DOI: 10.1074/jbc.m412687200] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Clinical data suggest that iron is a negative factor in chronic hepatitis C; however, the molecular mechanisms by which iron modulates the infectious cycle of hepatitis C virus (HCV) remain elusive. To explore this, we utilized cells expressing a HCV replicon as a well-established model for viral replication. We demonstrate that iron administration dramatically inhibits the expression of viral proteins and RNA, without significantly affecting its translation or stability. Experiments with purified recombinant HCV RNA polymerase (NS5B) revealed that iron binds specifically and with high affinity (apparent Kd: 6 and 60 microM for Fe2+ and Fe3+, respectively) to the protein's Mg2+-binding pocket, thereby inhibiting its enzymatic activity. We propose that iron impairs HCV replication by inactivating NS5B and that its negative effects in chronic hepatitis C may be primarily due to attenuation of antiviral immune responses. Our data provide a direct molecular link between iron and HCV replication.
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Research Support, Non-U.S. Gov't |
20 |
79 |
24
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Abstract
Regulating gene expression is an effective way for cells to deal with various stresses. The outcome of this regulation differs with the type of stress, and can promote either cell survival or cell death depending on the severity of the injury incurred. Gene expression can be controlled at several steps, including transcription, translation and degradation. An extensively studied protein involved in translational control is the eukaryotic translation initiation factor 2 (eIF2). When eIF2 becomes phosphorylated on a specific serine residue located within the alpha (alpha) subunit, global protein synthesis is halted. This phosphorylation occurs following periods of environmental stress, and plays a significant role in the cellular response to these events. The eIF2alpha kinase family consists of four members, which are each activated in response to different stimuli. Our group has recently discovered that two members of this family, the protein kinase activated by double-stranded RNA (PKR) and the PKR-like endoplasmic reticulum (ER) kinase (PERK) can also regulate the expression of specific proteins by promoting their degradation by the 26S proteasome. Specifically, we demonstrated that degradation of the cell cycle regulator cyclin D1, and the tumour suppressor p53 was promoted by PERK and PKR during periods of ER stress. This novel function may allow the eIF2alpha kinases to affect a larger number of cellular processes than previously believed.
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Review |
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25
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Kazemi S, Mounir Z, Baltzis D, Raven JF, Wang S, Krishnamoorthy JL, Pluquet O, Pelletier J, Koromilas AE. A novel function of eIF2alpha kinases as inducers of the phosphoinositide-3 kinase signaling pathway. Mol Biol Cell 2007; 18:3635-44. [PMID: 17596516 PMCID: PMC1951772 DOI: 10.1091/mbc.e07-01-0053] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Phosphoinositide-3 kinase (PI3K) plays an important role in signal transduction in response to a wide range of cellular stimuli involved in cellular processes that promote cell proliferation and survival. Phosphorylation of the alpha subunit of the eukaryotic translation initiation factor eIF2 at Ser51 takes place in response to various types of environmental stress and is essential for regulation of translation initiation. Herein, we show that a conditionally active form of the eIF2alpha kinase PKR acts upstream of PI3K and turns on the Akt/PKB-FRAP/mTOR pathway leading to S6 and 4E-BP1 phosphorylation. Also, induction of PI3K signaling antagonizes the apoptotic and protein synthesis inhibitory effects of the conditionally active PKR. Furthermore, induction of the PI3K pathway is impaired in PKR(-/-) or PERK(-/-) mouse embryonic fibroblasts (MEFs) in response to various stimuli that activate each eIF2alpha kinase. Mechanistically, PI3K signaling activation is indirect and requires the inhibition of protein synthesis by eIF2alpha phosphorylation as demonstrated by the inactivation of endogenous eIF2alpha by small interfering RNA or utilization of MEFs bearing the eIF2alpha Ser51Ala mutation. Our data reveal a novel property of eIF2alpha kinases as activators of PI3K signaling and cell survival.
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Research Support, Non-U.S. Gov't |
18 |
76 |