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Tansley SN, Wong C, Uttam S, Mogil JS, Khoutorsky A. Translation regulation in the spinal dorsal horn - A key mechanism for development of chronic pain. NEUROBIOLOGY OF PAIN 2018; 4:20-26. [PMID: 30906901 PMCID: PMC6428080 DOI: 10.1016/j.ynpai.2018.03.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Spinal sensitization shares molecular mechanisms with hippocampal LTP and memory. Changes in mRNA translation are observed in many chronic pain conditions. Targeting translational control mechanisms is a promising strategy to inhibit pain. Targeting spinal reconsolidation can reverse established hypersensitivity.
Chronic pain is a pathological condition characterized by long-lasting pain after damaged tissue has healed. Chronic pain can be caused and maintained by changes in various components of the pain pathway, including sensory neurons, spinal cord and higher brain centers. Exaggerated sensitivity and responsiveness of spinal nociceptive circuits, representing maladaptive plasticity, play key roles in the amplification of peripheral signals in chronic pain conditions. This spinal amplification mechanism profoundly contributes to the development and maintenance of chronic pain hypersensitivity in response to peripheral injury, and in some cases occurs independently of the peripheral stimulus. Long-lasting changes in the activity of spinal neurons are caused by alterations in their cellular proteome, which relies on de novo gene expression. Recent evidence indicates that translational control of gene expression plays a major role in determining protein levels, and is intricately involved in different forms of intrinsic and synaptic plasticity. In this review, we summarize findings supporting a key role for translational control in spinal cord-dependent mechanisms of chronic pain, and present recent approaches to reverse persistent pain by targeting these mechanisms.
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Affiliation(s)
- Shannon N Tansley
- Department of Anesthesia, McGill University, Montréal, QC H3A 0G1, Canada.,Department of Psychology, McGill University, Montréal, QC H3A 1B1, Canada
| | - Calvin Wong
- Department of Anesthesia, McGill University, Montréal, QC H3A 0G1, Canada
| | - Sonali Uttam
- Department of Anesthesia, McGill University, Montréal, QC H3A 0G1, Canada
| | - Jeffrey S Mogil
- Department of Anesthesia, McGill University, Montréal, QC H3A 0G1, Canada.,Department of Psychology, McGill University, Montréal, QC H3A 1B1, Canada.,Alan Edwards Centre for Research on Pain, McGill University, Montréal, QC H3A 0G1, Canada
| | - Arkady Khoutorsky
- Department of Anesthesia, McGill University, Montréal, QC H3A 0G1, Canada.,Alan Edwards Centre for Research on Pain, McGill University, Montréal, QC H3A 0G1, Canada
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52
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Bogorad AM, Lin KY, Marintchev A. eIF2B Mechanisms of Action and Regulation: A Thermodynamic View. Biochemistry 2018; 57:1426-1435. [PMID: 29425030 DOI: 10.1021/acs.biochem.7b00957] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Eukaryotic translation initiation factor 2B (eIF2B) is the guanine nucleotide exchange factor of the GTPase eIF2, which brings the initiator Met-tRNAi to the ribosome in the form of the eIF2-GTP·Met-tRNAi ternary complex (TC). The activity of eIF2B is inhibited by phosphorylation of its substrate eIF2 by several stress-induced kinases, which triggers the integrated stress response (ISR). The ISR plays a central role in maintaining homeostasis in the cell under various stress conditions, and its dysregulation is a causative factor in the pathology of a number of neurodegenerative disorders. Over the past three decades, virtually every aspect of eIF2B function has been the subject of uncertainty or controversy: from the catalytic mechanism of nucleotide exchange, to whether eIF2B only catalyzes nucleotide exchange on eIF2 or also promotes binding of Met-tRNAi to eIF2-GTP to form the TC. Here, we provide the first complete thermodynamic analysis of the process of recycling of eIF2-GDP to the TC. The available evidence leads to the conclusion that eIF2 is channeled from the ribosome (as an eIF5·eIF2-GDP complex) to eIF2B, converted by eIF2B to the TC, which is then channeled back to eIF5 and the ribosome. The system has evolved to be regulated by multiple factors, including post-translational modifications of eIF2, eIF2B, and eIF5, as well as directly by the energy balance in the cell, through the GTP:GDP ratio.
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Affiliation(s)
- Andrew M Bogorad
- Department of Physiology & Biophysics , Boston University School of Medicine , Boston , Massachusetts 02118 , United States
| | - Kai Ying Lin
- Department of Physiology & Biophysics , Boston University School of Medicine , Boston , Massachusetts 02118 , United States
| | - Assen Marintchev
- Department of Physiology & Biophysics , Boston University School of Medicine , Boston , Massachusetts 02118 , United States
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A presumed homologue of the regulatory subunits of eIF2B functions as ribose-1,5-bisphosphate isomerase in Pyrococcus horikoshii OT3. Sci Rep 2018; 8:1891. [PMID: 29382938 PMCID: PMC5789824 DOI: 10.1038/s41598-018-20418-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Accepted: 01/17/2018] [Indexed: 02/06/2023] Open
Abstract
The homologues of the regulatory subunits of eukaryotic translation initiation factor 2B (eIF2B) are assumed to be present in archaea. Likewise, an ORF, PH0208 in Pyrococcus horikoshii OT3 have been proposed to encode one of the homologues of regulatory subunits of eIF2B. However, PH0208 protein also shares sequence similarity with a functionally non-related enzyme, ribose-1,5-bisphosphate isomerase (R15Pi), involved in conversion of ribose-1,5-bisphosphate (R15P) to ribulose-1,5-bisphosphate (RuBP) in an AMP-dependent manner. Herein, we have determined the crystal structure of PH0208 protein in order to decipher its true function. Although structurally similar to the regulatory subunits of eIF2B, the ability to bind R15P and RuBP suggests that PH0208 would function as R15Pi. Additionally, this study for the first time reports the binding sites of AMP and GMP in R15Pi. The AMP binding site in PH0208 protein clarified the role of AMP in providing structural stability to R15Pi. The binding of GMP to the 'AMP binding site' in addition to its own binding site indicates that GMP might also execute a similar function, though with less specificity. Furthermore, we have utilized the resemblance between PH0208 and the regulatory subunits of eIF2B to propose a model for the regulatory mechanism of eIF2B in eukaryotes.
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Martin-Marcos P, Zhou F, Karunasiri C, Zhang F, Dong J, Nanda J, Kulkarni SD, Sen ND, Tamame M, Zeschnigk M, Lorsch JR, Hinnebusch AG. eIF1A residues implicated in cancer stabilize translation preinitiation complexes and favor suboptimal initiation sites in yeast. eLife 2017; 6:31250. [PMID: 29206102 PMCID: PMC5756025 DOI: 10.7554/elife.31250] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 12/04/2017] [Indexed: 11/13/2022] Open
Abstract
The translation pre-initiation complex (PIC) scans the mRNA for an AUG codon in favorable context, and AUG recognition stabilizes a closed PIC conformation. The unstructured N-terminal tail (NTT) of yeast eIF1A deploys five basic residues to contact tRNAi, mRNA, or 18S rRNA exclusively in the closed state. Interestingly, EIF1AX mutations altering the human eIF1A NTT are associated with uveal melanoma (UM). We found that substituting all five basic residues, and seven UM-associated substitutions, in yeast eIF1A suppresses initiation at near-cognate UUG codons and AUGs in poor context. Ribosome profiling of NTT substitution R13P reveals heightened discrimination against unfavorable AUG context genome-wide. Both R13P and K16D substitutions destabilize the closed complex at UUG codons in reconstituted PICs. Thus, electrostatic interactions involving the eIF1A NTT stabilize the closed conformation and promote utilization of suboptimal start codons. We predict UM-associated mutations alter human gene expression by increasing discrimination against poor initiation sites.
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Affiliation(s)
- Pilar Martin-Marcos
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States.,Instituto de Biología Funcional y Genómica, IBFG-CSIC, Universidad de Salamanca, Salamanca, Spain
| | - Fujun Zhou
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Charm Karunasiri
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Fan Zhang
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Jinsheng Dong
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Jagpreet Nanda
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Shardul D Kulkarni
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Neelam Dabas Sen
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Mercedes Tamame
- Instituto de Biología Funcional y Genómica, IBFG-CSIC, Universidad de Salamanca, Salamanca, Spain
| | - Michael Zeschnigk
- Institute of Human Genetics, University Duisburg-Essen, Essen, Germany.,Eye Cancer Research Group, Faculty of Medicine, University Duisburg-Essen, Essen, Germany
| | - Jon R Lorsch
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
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Costello JL, Kershaw CJ, Castelli LM, Talavera D, Rowe W, Sims PFG, Ashe MP, Grant CM, Hubbard SJ, Pavitt GD. Dynamic changes in eIF4F-mRNA interactions revealed by global analyses of environmental stress responses. Genome Biol 2017; 18:201. [PMID: 29078784 PMCID: PMC5660459 DOI: 10.1186/s13059-017-1338-4] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Accepted: 10/13/2017] [Indexed: 11/29/2022] Open
Abstract
Background Translation factors eIF4E and eIF4G form eIF4F, which interacts with the messenger RNA (mRNA) 5′ cap to promote ribosome recruitment and translation initiation. Variations in the association of eIF4F with individual mRNAs likely contribute to differences in translation initiation frequencies between mRNAs. As translation initiation is globally reprogrammed by environmental stresses, we were interested in determining whether eIF4F interactions with individual mRNAs are reprogrammed and how this may contribute to global environmental stress responses. Results Using a tagged-factor protein capture and RNA-sequencing (RNA-seq) approach, we have assessed how mRNA associations with eIF4E, eIF4G1 and eIF4G2 change globally in response to three defined stresses that each cause a rapid attenuation of protein synthesis: oxidative stress induced by hydrogen peroxide and nutrient stresses caused by amino acid or glucose withdrawal. We find that acute stress leads to dynamic and unexpected changes in eIF4F–mRNA interactions that are shared among each factor and across the stresses imposed. eIF4F–mRNA interactions stabilised by stress are predominantly associated with translational repression, while more actively initiating mRNAs become relatively depleted for eIF4F. Simultaneously, other mRNAs are insulated from these stress-induced changes in eIF4F association. Conclusion Dynamic eIF4F–mRNA interaction changes are part of a coordinated early translational control response shared across environmental stresses. Our data are compatible with a model where multiple mRNA closed-loop complexes form with differing stability. Hence, unexpectedly, in the absence of other stabilising factors, rapid translation initiation on mRNAs correlates with less stable eIF4F interactions. Electronic supplementary material The online version of this article (doi:10.1186/s13059-017-1338-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Joseph L Costello
- Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, M13 9PT, UK.,Present address: Biosciences, College of Life and Environmental Sciences, Geoffrey Pope Building, University of Exeter, Stocker Road, Exeter, EX4 4QD, UK
| | - Christopher J Kershaw
- Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, M13 9PT, UK
| | - Lydia M Castelli
- Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, M13 9PT, UK.,Present address: Sheffield Institute for Translational Neuroscience, The University of Sheffield, 385a Glossop Road, Sheffield, S10 2HQ, UK
| | - David Talavera
- Division of Cardiovascular Sciences, School of Medicine, Faculty of Biology Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, M13 9PT, UK
| | - William Rowe
- Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, M13 9PT, UK.,Present address: Department of Chemistry, Loughborough University, Epinal Way, Loughborough, Leicestershire, LE11 3TU, UK
| | - Paul F G Sims
- Manchester Institute of Biotechnology (MIB), The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK
| | - Mark P Ashe
- Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, M13 9PT, UK
| | - Christopher M Grant
- Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, M13 9PT, UK
| | - Simon J Hubbard
- Division of Evolution and Genomic Sciences, School of Biological Sciences, Faculty of Biology Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, M13 9PT, UK
| | - Graham D Pavitt
- Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, M13 9PT, UK.
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56
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Sharma S, Sourirajan A, Dev K. Role of Saccharomyces cerevisiae TAN1 (tRNA acetyltransferase) in eukaryotic initiation factor 2B (eIF2B)-mediated translation control and stress response. 3 Biotech 2017; 7:223. [PMID: 28677085 DOI: 10.1007/s13205-017-0857-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Accepted: 06/17/2017] [Indexed: 10/19/2022] Open
Abstract
Eukaryotic initiation factor 2B (eIF2B) controls the first step of translation by catalyzing guanine nucleotide exchange on eukaryotic initiation factor 2 (eIF2). Mutations in the genes encoding eIF2B subunits inhibit the nucleotide exchange and eventually slow down the process of translation, causing vanishing white matter disease. We constructed a Saccharomyces cerevisiae genomic DNA library in YEp24 vector and screened it for the identification of extragenic suppressors of eIF2B mutations, corresponding to human eIF2B mutations. We found a suppressor-II (Sup-II) genomic clone, as suppressor of eIF2Bβ (gcd7-201) mutation. Identification of Sup-II reveals the presence of truncated SEC15, full-length TAN1 (tRNA acetyltransferase), full-length EMC4, full-length YGL230C (putative protein) and truncated SAP4 genes. Full-length TAN1 (tRNA acetyltransferase) gene, subcloned into pEG(KG) vector and overexpressed in gcd7-201 gcn2∆ strain, suppresses the slow-growth (Slg-) and general control derepression (Gcd-) phenotype of gcd7-201 gcn2∆ mutation, but YGL230C did not show any effect. A GST-Tan1p fusion protein of 60 kDa was detected by western blotting using α-GST antibodies. Interestingly, Tan1p overexpression also suppresses the temperature-sensitive (Ts-), Slg- and Gcd- phenotype of eIF2Bγ (gcd1-502) mutant. Role of Tan1p protein in eIF2B-mediated translation regulation was also studied. Results revealed that Tan1p overexpression confers resistance to GCD7 GCN2, gcd7-201 gcn2∆, GCD7 gcn2∆ growth defect under ethanol, H2O2 and caffeine stress. No resistance to DMSO-, NaCl- and DTT-mediated growth defect upon GCD7 gcn2∆, GCD7 GCN2, gcd7-201 gcn2∆ was observed by overexpression of TAN1. Hence, we proposed that Tan1p is involved directly or indirectly in regulating eIF2B-mediated translation.
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Affiliation(s)
- Sonum Sharma
- Faculty of Applied Sciences and Biotechnology, Shoolini University, Solan, Himachal Pradesh, India
| | - Anuradha Sourirajan
- Faculty of Applied Sciences and Biotechnology, Shoolini University, Solan, Himachal Pradesh, India
| | - Kamal Dev
- Faculty of Applied Sciences and Biotechnology, Shoolini University, Solan, Himachal Pradesh, India.
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57
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Jennings MD, Kershaw CJ, Adomavicius T, Pavitt GD. Fail-safe control of translation initiation by dissociation of eIF2α phosphorylated ternary complexes. eLife 2017; 6:e24542. [PMID: 28315520 PMCID: PMC5404910 DOI: 10.7554/elife.24542] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 03/16/2017] [Indexed: 01/21/2023] Open
Abstract
Phosphorylation of eIF2α controls translation initiation by restricting the levels of active eIF2-GTP/Met-tRNAi ternary complexes (TC). This modulates the expression of all eukaryotic mRNAs and contributes to the cellular integrated stress response. Key to controlling the activity of eIF2 are translation factors eIF2B and eIF5, thought to primarily function with eIF2-GDP and TC respectively. Using a steady-state kinetics approach with purified proteins we demonstrate that eIF2B binds to eIF2 with equal affinity irrespective of the presence or absence of competing guanine nucleotides. We show that eIF2B can compete with Met-tRNAi for eIF2-GTP and can destabilize TC. When TC is formed with unphosphorylated eIF2, eIF5 can out-compete eIF2B to stabilize TC/eIF5 complexes. However when TC/eIF5 is formed with phosphorylated eIF2, eIF2B outcompetes eIF5 and destabilizes TC. These data uncover competition between eIF2B and eIF5 for TC and identify that phosphorylated eIF2-GTP translation initiation intermediate complexes can be inhibited by eIF2B.
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Affiliation(s)
- Martin D Jennings
- Division of Molecular and Cellular Function, Faculty of Biology Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Manchester Academic Health Science Centre, The University of Manchester, Manchester, United Kingdom
| | - Christopher J Kershaw
- Division of Molecular and Cellular Function, Faculty of Biology Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Manchester Academic Health Science Centre, The University of Manchester, Manchester, United Kingdom
| | - Tomas Adomavicius
- Division of Molecular and Cellular Function, Faculty of Biology Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Manchester Academic Health Science Centre, The University of Manchester, Manchester, United Kingdom
| | - Graham D Pavitt
- Division of Molecular and Cellular Function, Faculty of Biology Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Manchester Academic Health Science Centre, The University of Manchester, Manchester, United Kingdom
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58
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Molecular Determinants of the Regulation of Development and Metabolism by Neuronal eIF2α Phosphorylation in Caenorhabditis elegans. Genetics 2017; 206:251-263. [PMID: 28292919 DOI: 10.1534/genetics.117.200568] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Accepted: 03/09/2017] [Indexed: 11/18/2022] Open
Abstract
Cell-nonautonomous effects of signaling in the nervous system of animals can influence diverse aspects of organismal physiology. We previously showed that phosphorylation of Ser49 of the α-subunit of eukaryotic translation initiation factor 2 (eIF2α) in two chemosensory neurons by PEK-1/PERK promotes entry of Caenorhabditis elegans into dauer diapause. Here, we identified and characterized the molecular determinants that confer sensitivity to effects of neuronal eIF2α phosphorylation on development and physiology of C. elegans Isolation and characterization of mutations in eif-2Ba encoding the α-subunit of eIF2B support a conserved role, previously established by studies in yeast, for eIF2Bα in providing a binding site for phosphorylated eIF2α to inhibit the exchange factor eIF2B catalytic activity that is required for translation initiation. We also identified a mutation in eif-2c, encoding the γ-subunit of eIF2, which confers insensitivity to the effects of phosphorylated eIF2α while also altering the requirement for eIF2Bγ. In addition, we show that constitutive expression of eIF2α carrying a phosphomimetic S49D mutation in the ASI pair of sensory neurons confers dramatic effects on growth, metabolism, and reproduction in adult transgenic animals, phenocopying systemic responses to starvation. Furthermore, we show that constitutive expression of eIF2α carrying a phosphomimetic S49D mutation in the ASI neurons enhances dauer entry through bypassing the requirement for nutritionally deficient conditions. Our data suggest that the state of eIF2α phosphorylation in the ASI sensory neuron pair may modulate internal nutrient sensing and signaling pathways, with corresponding organismal effects on development and metabolism.
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59
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Mechanism and Regulation of Protein Synthesis in Saccharomyces cerevisiae. Genetics 2017; 203:65-107. [PMID: 27183566 DOI: 10.1534/genetics.115.186221] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 02/24/2016] [Indexed: 12/18/2022] Open
Abstract
In this review, we provide an overview of protein synthesis in the yeast Saccharomyces cerevisiae The mechanism of protein synthesis is well conserved between yeast and other eukaryotes, and molecular genetic studies in budding yeast have provided critical insights into the fundamental process of translation as well as its regulation. The review focuses on the initiation and elongation phases of protein synthesis with descriptions of the roles of translation initiation and elongation factors that assist the ribosome in binding the messenger RNA (mRNA), selecting the start codon, and synthesizing the polypeptide. We also examine mechanisms of translational control highlighting the mRNA cap-binding proteins and the regulation of GCN4 and CPA1 mRNAs.
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60
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Biever A, Boubaker-Vitre J, Cutando L, Gracia-Rubio I, Costa-Mattioli M, Puighermanal E, Valjent E. Repeated Exposure to D-Amphetamine Decreases Global Protein Synthesis and Regulates the Translation of a Subset of mRNAs in the Striatum. Front Mol Neurosci 2017; 9:165. [PMID: 28119566 PMCID: PMC5223439 DOI: 10.3389/fnmol.2016.00165] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Accepted: 12/20/2016] [Indexed: 01/21/2023] Open
Abstract
Repeated psychostimulant exposure induces persistent gene expression modifications that contribute to enduring changes in striatal GABAergic spiny projecting neurons (SPNs). However, it remains unclear whether changes in the control of mRNA translation are required for the establishment of these durable modifications. Here we report that repeated exposure to D-amphetamine decreases global striatal mRNA translation. This effect is paralleled by an enhanced phosphorylation of the translation factors, eIF2α and eEF2, and by the concomitant increased translation of a subset of mRNAs, among which the mRNA encoding for the activity regulated cytoskeleton-associated protein, also known as activity regulated gene 3.1 (Arc/Arg3.1). The enrichment of Arc/Arg3.1 mRNA in the polysomal fraction is accompanied by a robust increase of Arc/Arg3.1 protein levels within the striatum. Immunofluorescence analysis revealed that this increase occurred preferentially in D1R-expressing SPNs localized in striosome compartments. Our results suggest that the decreased global protein synthesis following repeated exposure to D-amphetamine favors the translation of a specific subset of mRNAs in the striatum.
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Affiliation(s)
- Anne Biever
- Centre National de la Recherche Scientifique (CNRS), UMR-5203, Institut de Génomique FonctionnelleMontpellier, France; Institut National de la Santé et de la Recherche Médicale (INSERM), U1191Montpellier, France; Université de Montpellier, UMR-5203Montpellier, France
| | - Jihane Boubaker-Vitre
- Centre National de la Recherche Scientifique (CNRS), UMR-5203, Institut de Génomique FonctionnelleMontpellier, France; Institut National de la Santé et de la Recherche Médicale (INSERM), U1191Montpellier, France; Université de Montpellier, UMR-5203Montpellier, France
| | - Laura Cutando
- Centre National de la Recherche Scientifique (CNRS), UMR-5203, Institut de Génomique FonctionnelleMontpellier, France; Institut National de la Santé et de la Recherche Médicale (INSERM), U1191Montpellier, France; Université de Montpellier, UMR-5203Montpellier, France
| | - Irene Gracia-Rubio
- Centre National de la Recherche Scientifique (CNRS), UMR-5203, Institut de Génomique FonctionnelleMontpellier, France; Institut National de la Santé et de la Recherche Médicale (INSERM), U1191Montpellier, France; Université de Montpellier, UMR-5203Montpellier, France
| | - Mauro Costa-Mattioli
- Department of Neuroscience, Memory and Brain Research Center, Baylor College of Medicine, Houston TX, USA
| | - Emma Puighermanal
- Centre National de la Recherche Scientifique (CNRS), UMR-5203, Institut de Génomique FonctionnelleMontpellier, France; Institut National de la Santé et de la Recherche Médicale (INSERM), U1191Montpellier, France; Université de Montpellier, UMR-5203Montpellier, France
| | - Emmanuel Valjent
- Centre National de la Recherche Scientifique (CNRS), UMR-5203, Institut de Génomique FonctionnelleMontpellier, France; Institut National de la Santé et de la Recherche Médicale (INSERM), U1191Montpellier, France; Université de Montpellier, UMR-5203Montpellier, France
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Kashiwagi K, Ito T, Yokoyama S. Crystal structure of eIF2B and insights into eIF2-eIF2B interactions. FEBS J 2016; 284:868-874. [PMID: 27627185 DOI: 10.1111/febs.13896] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Revised: 08/31/2016] [Accepted: 09/12/2016] [Indexed: 12/20/2022]
Abstract
Eukaryotic translation initiation factor 2B (eIF2B), a heterodecameric complex of two sets of the α, β, γ, δ, and ε subunits, is the guanine nucleotide exchange factor (GEF) specific for eIF2, a heterotrimeric G protein consisting of the α, β, and γ subunits. The eIF2 protein binds GTP on the γ subunits and delivers an initiator methionyl-tRNA (Met-tRNAiMet ) to the ribosome. The GEF activity of eIF2B is inhibited by stress-induced phosphorylation of Ser51 in the α subunit of eIF2, which leads to lower amounts of active eIF2 and a limited quantity of Met-tRNAiMet for the ribosome, resulting in global repression of translation. However, the structural mechanism of the GEF activity inhibition remained enigmatic, and therefore the three-dimensional structure of the entire eIF2B molecule had been awaited. Recently, we determined the crystal structure of Schizosaccharomyces pombe eIF2B. In this Structural Snapshot, we present the structural features of eIF2B and the mechanism underlying the GEF activity inhibition by the phosphorylation of eIF2α, elucidated from structure-based in vitro analyses.
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Affiliation(s)
- Kazuhiro Kashiwagi
- Division of Structural and Synthetic Biology, RIKEN Center for Life Science Technologies, Tsurumi-ku, Yokohama, Japan
| | - Takuhiro Ito
- Division of Structural and Synthetic Biology, RIKEN Center for Life Science Technologies, Tsurumi-ku, Yokohama, Japan
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62
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eIF2B: recent structural and functional insights into a key regulator of translation. Biochem Soc Trans 2016; 43:1234-40. [PMID: 26614666 DOI: 10.1042/bst20150164] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The eukaryotic translation initiation factor (eIF) eIF2B is a key regulator of mRNA translation, being the guanine nt exchange factor (GEF) responsible for the recycling of the heterotrimeric G-protein, eIF2, which is required to allow translation initiation to occur. Unusually for a GEF, eIF2B is a multi-subunit protein, comprising five different subunits termed α through ε in order of increasing size. eIF2B is subject to tight regulation in the cell and may also serve additional functions. Here we review recent insights into the subunit organization of the mammalian eIF2B complex, gained both from structural studies of the complex and from studies of mutations of eIF2B that result in the neurological disorder leukoencephalopathy with vanishing white matter (VWM). We will also discuss recent data from yeast demonstrating a novel function of the eIF2B complex key for translational regulation.
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GCN2- and eIF2α-phosphorylation-independent, but ATF4-dependent, induction of CARE-containing genes in methionine-deficient cells. Amino Acids 2016; 48:2831-2842. [PMID: 27613409 DOI: 10.1007/s00726-016-2318-9] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Accepted: 08/17/2016] [Indexed: 12/26/2022]
Abstract
Amino-acid deprivation is sensed by the eIF2α kinase GCN2. Under conditions of essential amino-acid limitation, GCN2 phosphorylates eIF2α, inhibiting the formation of a new ternary complex and hence mRNA translation initiation. While decreasing global mRNA translation, eIF2α phosphorylation also increases the translation of the integrated stress response (ISR) transcription factor ATF4, which increases the expression of many stress response genes that contain a C/EBP-ATF response element (CARE), including Atf4, 4Ebp1, Asns, and Chop. Using wild-type as well as Gcn2 knockout and unphosphorylatable eIF2α mutant MEFs, we characterized a novel GCN2/eIF2α phosphorylation-independent, but ATF4-dependent, pathway that upregulates the expression of CARE-containing genes in MEFs lacking GCN2 or phosphorylatable eIF2α when these cells are exposed to methionine-deficient, and to a lesser extent arginine- or histidine-deficient, medium. Thus, we demonstrate a GCN2/eIF2α phosphorylation-independent pathway that converges with the GCN2/eIF2α kinase-dependent pathway at the level of ATF4 and similarly results in the upregulation of CARE-containing genes. We hypothesize that the essential role of methionine-charged initiator tRNA in forming ternary complex is responsible for the robust ability of methionine deficiency to induce ATF4 and the ISR even in the absence of GCN2 or eIF2α kinase activity.
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Solanki NR, Stadanlick JE, Zhang Y, Duc AC, Lee SY, Lauritsen JPH, Zhang Z, Wiest DL. Rpl22 Loss Selectively Impairs αβ T Cell Development by Dysregulating Endoplasmic Reticulum Stress Signaling. THE JOURNAL OF IMMUNOLOGY 2016; 197:2280-9. [PMID: 27489283 DOI: 10.4049/jimmunol.1600815] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 07/12/2016] [Indexed: 11/19/2022]
Abstract
Although ribosomal proteins (RP) are thought to primarily facilitate biogenesis of the ribosome and its ability to synthesize protein, emerging evidence suggests that individual RP can perform critical regulatory functions that control developmental processes. We showed previously that despite the ubiquitous expression of the RP ribosomal protein L22 (Rpl22), germline ablation of Rpl22 in mice causes a selective, p53-dependent block in the development of αβ, but not γδ, T cell progenitors. Nevertheless, the basis by which Rpl22 loss selectively induces p53 in αβ T cell progenitors remained unclear. We show in this study that Rpl22 regulates the development of αβ T cells by restraining endoplasmic reticulum (ER) stress responses. In the absence of Rpl22, ER stress is exacerbated in αβ, but not γδ, T cell progenitors. The exacerbated ER stress in Rpl22-deficient αβ T lineage progenitors is responsible for selective induction of p53 and their arrest, as pharmacological induction of stress is sufficient to induce p53 and replicate the selective block of αβ T cells, and attenuation of ER stress signaling by knockdown of protein kinase R-like ER kinase, an ER stress sensor, blunts p53 induction and rescues development of Rpl22-deficient αβ T cell progenitors. Rpl22 deficiency appears to exacerbate ER stress by interfering with the ability of ER stress signals to block new protein synthesis. Our finding that Rpl22 deficiency exacerbates ER stress responses and induces p53 in αβ T cell progenitors provides insight into how a ubiquitously expressed RP can perform regulatory functions that are selectively required by some cell lineages but not others.
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Affiliation(s)
- Nehal R Solanki
- Blood Cell Development and Function Program, Fox Chase Cancer Center, Philadelphia, PA 19111; and Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA 19111
| | - Jason E Stadanlick
- Blood Cell Development and Function Program, Fox Chase Cancer Center, Philadelphia, PA 19111; and
| | - Yong Zhang
- Blood Cell Development and Function Program, Fox Chase Cancer Center, Philadelphia, PA 19111; and
| | - Ann-Cecile Duc
- Blood Cell Development and Function Program, Fox Chase Cancer Center, Philadelphia, PA 19111; and
| | - Sang-Yun Lee
- Blood Cell Development and Function Program, Fox Chase Cancer Center, Philadelphia, PA 19111; and
| | | | - Zhiqiang Zhang
- Blood Cell Development and Function Program, Fox Chase Cancer Center, Philadelphia, PA 19111; and
| | - David L Wiest
- Blood Cell Development and Function Program, Fox Chase Cancer Center, Philadelphia, PA 19111; and
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Jennings MD, Kershaw CJ, White C, Hoyle D, Richardson JP, Costello JL, Donaldson IJ, Zhou Y, Pavitt GD. eIF2β is critical for eIF5-mediated GDP-dissociation inhibitor activity and translational control. Nucleic Acids Res 2016; 44:9698-9709. [PMID: 27458202 PMCID: PMC5175340 DOI: 10.1093/nar/gkw657] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Revised: 07/08/2016] [Accepted: 07/12/2016] [Indexed: 01/10/2023] Open
Abstract
In protein synthesis translation factor eIF2 binds initiator tRNA to ribosomes and facilitates start codon selection. eIF2 GDP/GTP status is regulated by eIF5 (GAP and GDI functions) and eIF2B (GEF and GDF activities), while eIF2α phosphorylation in response to diverse signals is a major point of translational control. Here we characterize a growth suppressor mutation in eIF2β that prevents eIF5 GDI and alters cellular responses to reduced eIF2B activity, including control of GCN4 translation. By monitoring the binding of fluorescent nucleotides and initiator tRNA to purified eIF2 we show that the eIF2β mutation does not affect intrinsic eIF2 affinities for these ligands, neither does it interfere with eIF2 binding to 43S pre-initiation complex components. Instead we show that the eIF2β mutation prevents eIF5 GDI stabilizing nucleotide binding to eIF2, thereby altering the off-rate of GDP from eIF2•GDP/eIF5 complexes. This enables cells to grow with reduced eIF2B GEF activity but impairs activation of GCN4 targets in response to amino acid starvation. These findings provide support for the importance of eIF5 GDI activity in vivo and demonstrate that eIF2β acts in concert with eIF5 to prevent premature release of GDP from eIF2γ and thereby ensure tight control of protein synthesis initiation.
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Affiliation(s)
- Martin D Jennings
- Faculty of Biology Medicine and Health, The University of Manchester, Manchester, M13 9PT, UK
| | - Christopher J Kershaw
- Faculty of Biology Medicine and Health, The University of Manchester, Manchester, M13 9PT, UK
| | - Christopher White
- Faculty of Biology Medicine and Health, The University of Manchester, Manchester, M13 9PT, UK
| | - Danielle Hoyle
- Faculty of Biology Medicine and Health, The University of Manchester, Manchester, M13 9PT, UK
| | - Jonathan P Richardson
- Faculty of Biology Medicine and Health, The University of Manchester, Manchester, M13 9PT, UK
| | - Joseph L Costello
- Faculty of Biology Medicine and Health, The University of Manchester, Manchester, M13 9PT, UK
| | - Ian J Donaldson
- Faculty of Biology Medicine and Health, The University of Manchester, Manchester, M13 9PT, UK
| | - Yu Zhou
- Faculty of Biology Medicine and Health, The University of Manchester, Manchester, M13 9PT, UK
| | - Graham D Pavitt
- Faculty of Biology Medicine and Health, The University of Manchester, Manchester, M13 9PT, UK
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66
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Wengrod JC, Gardner LB. Cellular adaptation to nutrient deprivation: crosstalk between the mTORC1 and eIF2α signaling pathways and implications for autophagy. Cell Cycle 2016; 14:2571-7. [PMID: 26039820 DOI: 10.1080/15384101.2015.1056947] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The hostile tumor microenvironment results in the generation of intracellular stresses including hypoxia and nutrient deprivation. In order to adapt to such conditions, the cell utilizes several stress-response mechanisms, including the attenuation of protein synthesis, the inhibition of cellular proliferation, and induction of autophagy. Autophagy leads to the degradation of cellular contents, including damaged organelles and mutant proteins, which the cell can then use as an alternate energy source. Two integral changes to the signaling milieu to promote such a response include inhibition of the mammalian target of rapamycin complex 1 (mTORC1) and phosphorylation of eIF2α. This review will describe how conditions found in the tumor microenvironment regulate mTORC1 as well as eIF2α, the downstream impact of these modifications, and the implications in tumorigenesis. We will then discuss the remarkable similarities and overlapping function of these 2 signaling pathways, focusing on the response to amino acid deprivation, and present a new model involving crosstalk between them based on our recent work.
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Affiliation(s)
- Jordan C Wengrod
- a Department of Biochemistry and Molecular Pharmacology ; New York University School of Medicine , New York , NY USA
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67
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Vincent HA, Ziehr B, Moorman NJ. Human Cytomegalovirus Strategies to Maintain and Promote mRNA Translation. Viruses 2016; 8:97. [PMID: 27089357 PMCID: PMC4848592 DOI: 10.3390/v8040097] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Revised: 03/25/2016] [Accepted: 03/31/2016] [Indexed: 02/02/2023] Open
Abstract
mRNA translation requires the ordered assembly of translation initiation factors and ribosomal subunits on a transcript. Host signaling pathways regulate each step in this process to match levels of protein synthesis to environmental cues. In response to infection, cells activate multiple defenses that limit viral protein synthesis, which viruses must counteract to successfully replicate. Human cytomegalovirus (HCMV) inhibits host defenses that limit viral protein expression and manipulates host signaling pathways to promote the expression of both host and viral proteins necessary for virus replication. Here we review key regulatory steps in mRNA translation, and the strategies used by HCMV to maintain protein synthesis in infected cells.
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Affiliation(s)
- Heather A Vincent
- Department of Microbiology & Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| | - Benjamin Ziehr
- Department of Microbiology & Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| | - Nathaniel J Moorman
- Department of Microbiology & Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
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68
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Schoborg JA, Clark LG, Choudhury A, Hodgman CE, Jewett MC. Yeast knockout library allows for efficient testing of genomic mutations for cell-free protein synthesis. Synth Syst Biotechnol 2016; 1:2-6. [PMID: 29062921 PMCID: PMC5640588 DOI: 10.1016/j.synbio.2016.02.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Revised: 01/27/2016] [Accepted: 02/12/2016] [Indexed: 12/31/2022] Open
Abstract
Cell-free protein synthesis (CFPS) systems from crude lysates have benefitted from modifications to their enzyme composition. For example, functionally deleting enzymes in the source strain that are deleterious to CFPS can improve protein synthesis yields. However, making such modifications can take substantial time. As a proof-of-concept to accelerate prototyping capabilities, we assessed the feasibility of using the yeast knockout collection to identify negative effectors in a Saccharomyces cerevisiae CFPS platform. We analyzed extracts made from six deletion strains that targeted the single deletion of potentially negative effectors (e.g., nucleases). We found a statistically significant increase in luciferase yields upon loss of function of GCN3, PEP4, PPT1, NGL3, and XRN1 with a maximum increase of over 6-fold as compared to the wild type. Our work has implications for yeast CFPS and for rapidly prototyping strains to enable cell-free synthetic biology applications.
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Key Words
- ANOVA, analysis of variance
- ATP, adenosine triphosphate
- CFPS, cell-free protein synthesis
- CRISPR, clustered regularly interspaced short palindromic repeats
- Cell-free biology
- Cell-free protein synthesis
- In vitro translation
- NTP, nucleoside triphosphate
- OD, optical density
- Protein expression
- SC, synthetic complete media
- Saccharomyces cerevisiae
- Synthetic biology
- YKO, yeast knockout
- cAMP, cyclic adenosine monophosphate
- eIF, eukaryotic initiation factor
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Affiliation(s)
- Jennifer A. Schoborg
- Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3120, USA
- Chemistry of Life Processes Institute, 2170 Campus Drive, Evanston, IL 60208-3120, USA
| | - Lauren G. Clark
- Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3120, USA
- Chemistry of Life Processes Institute, 2170 Campus Drive, Evanston, IL 60208-3120, USA
| | - Alaksh Choudhury
- Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3120, USA
- Chemistry of Life Processes Institute, 2170 Campus Drive, Evanston, IL 60208-3120, USA
- Masters in Biotechnology Program, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3120, USA
| | - C. Eric Hodgman
- Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3120, USA
- Chemistry of Life Processes Institute, 2170 Campus Drive, Evanston, IL 60208-3120, USA
| | - Michael C. Jewett
- Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3120, USA
- Chemistry of Life Processes Institute, 2170 Campus Drive, Evanston, IL 60208-3120, USA
- Masters in Biotechnology Program, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3120, USA
- Robert H. Lurie Comprehensive Cancer Center, Northwestern University, 676 N. St Clair St, Suite 1200, Chicago, IL 60611-3068, USA
- Simpson Querrey Institute, Northwestern University, 303 E. Superior St, Suite 11-131, Chicago, IL 60611-2875, USA
- Corresponding author. 2145 Sheridan Road, Tech E-136, Evanston, IL 60208-3120, USA.2145 Sheridan RoadTech E-136EvanstonIL60208-3120USA
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Kashiwagi K, Shigeta T, Imataka H, Ito T, Yokoyama S. Expression, purification, and crystallization of Schizosaccharomyces pombe eIF2B. ACTA ACUST UNITED AC 2016; 17:33-8. [PMID: 27023709 PMCID: PMC4833825 DOI: 10.1007/s10969-016-9203-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 03/16/2016] [Indexed: 11/24/2022]
Abstract
Tight control of protein synthesis is necessary for cells to respond and adapt to environmental changes rapidly. Eukaryotic translation initiation factor (eIF) 2B, the guanine nucleotide exchange factor for eIF2, is a key target of translation control at the initiation step. The nucleotide exchange activity of eIF2B is inhibited by the stress-induced phosphorylation of eIF2. As a result, the level of active GTP-bound eIF2 is lowered, and protein synthesis is attenuated. eIF2B is a large multi-subunit complex composed of five different subunits, and all five of the subunits are the gene products responsible for the neurodegenerative disease, leukoencephalopathy with vanishing white matter. However, the overall structure of eIF2B has remained unresolved, due to the difficulty in preparing a sufficient amount of the eIF2B complex. To overcome this problem, we established the recombinant expression and purification method for eIF2B from the fission yeast Schizosaccharomyces pombe. All five of the eIF2B subunits were co-expressed and reconstructed into the complex in Escherichia coli cells. The complex was successfully purified with a high yield. This recombinant eIF2B complex contains each subunit in an equimolar ratio, and the size exclusion chromatography analysis suggests it forms a heterodecamer, consistent with recent reports. This eIF2B increased protein synthesis in the reconstituted in vitro human translation system. In addition, disease-linked mutations led to subunit dissociation. Furthermore, we crystallized this functional recombinant eIF2B, and the crystals diffracted to 3.0 Å resolution.
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Affiliation(s)
- Kazuhiro Kashiwagi
- Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.,RIKEN Systems and Structural Biology Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, 230-0045, Japan.,RIKEN Center for Life Science Technologies, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, 230-0045, Japan
| | - Tomoaki Shigeta
- Graduate School of Engineering, University of Hyogo, Himeji, 671-2280, Japan
| | - Hiroaki Imataka
- Graduate School of Engineering, University of Hyogo, Himeji, 671-2280, Japan
| | - Takuhiro Ito
- Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan. .,RIKEN Systems and Structural Biology Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, 230-0045, Japan. .,RIKEN Center for Life Science Technologies, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, 230-0045, Japan.
| | - Shigeyuki Yokoyama
- Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan. .,RIKEN Systems and Structural Biology Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, 230-0045, Japan. .,RIKEN Structural Biology Laboratory, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, 230-0045, Japan.
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70
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Crystal structure of eukaryotic translation initiation factor 2B. Nature 2016; 531:122-5. [DOI: 10.1038/nature16991] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Accepted: 01/12/2016] [Indexed: 12/15/2022]
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71
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Stoichiometry of the eIF2B complex is maintained by mutual stabilization of subunits. Biochem J 2015; 473:571-80. [PMID: 26614765 DOI: 10.1042/bj20150828] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Accepted: 11/26/2015] [Indexed: 12/30/2022]
Abstract
The eukaryotic translation initiation factor eIF2B is a multi-subunit complex with a crucial role in the regulation of global protein synthesis in the cell. The complex comprises five subunits, termed α through ε in order of increasing size, arranged as a heterodecamer with two copies of each subunit. Regulation of the co-stoichiometric expression of the eIF2B subunits is crucial for the proper function and regulation of the eIF2B complex in cells. We have investigated the control of stoichiometric eIF2B complexes through mutual stabilization of eIF2B subunits. Our data show that the stable expression of the catalytic eIF2Bε subunit in human cells requires co-expression of eIF2Bγ. Similarly, stable expression of eIF2Bδ requires both eIF2Bβ and eIF2Bγ+ε. The expression of these subunits decreases despite there being no change in either the levels or the translation of their mRNAs. Instead, these subunits are targeted for degradation by the ubiquitin-proteasome system. The data allow us to propose a model for the formation of stoichiometric eIF2B complexes which can ensure their stoichiometric incorporation into the holocomplex.
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72
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Schmidt C, Beilsten-Edmands V, Robinson CV. Insights into Eukaryotic Translation Initiation from Mass Spectrometry of Macromolecular Protein Assemblies. J Mol Biol 2015; 428:344-356. [PMID: 26497764 DOI: 10.1016/j.jmb.2015.10.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Revised: 09/28/2015] [Accepted: 10/14/2015] [Indexed: 02/05/2023]
Abstract
Translation initiation in eukaryotes requires the interplay of at least 10 initiation factors that interact at the different steps of this phase of gene expression. The interactions of initiation factors and related proteins are in general controlled by phosphorylation, which serves as a regulatory switch to turn protein translation on or off. The structures of initiation factors and a complete description of their post-translational modification (PTM) status are therefore required in order to fully understand these processes. In recent years, mass spectrometry has contributed considerably to provide this information and nowadays is proving to be indispensable when studying dynamic heterogeneous protein complexes such as the eukaryotic initiation factors. Herein, we highlight mass spectrometric approaches commonly applied to identify interacting subunits and their PTMs and the structural techniques that allow the architecture of protein complexes to be assessed. We present recent structural investigations of initiation factors and their interactions with other factors and with ribosomes and we assess the models generated. These models allow us to locate PTMs within initiation factor complexes and to highlight possible roles for phosphorylation sites in regulating interaction interfaces.
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Affiliation(s)
- Carla Schmidt
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
| | - Victoria Beilsten-Edmands
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
| | - Carol V Robinson
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
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73
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Kuhle B, Eulig NK, Ficner R. Architecture of the eIF2B regulatory subcomplex and its implications for the regulation of guanine nucleotide exchange on eIF2. Nucleic Acids Res 2015; 43:9994-10014. [PMID: 26384431 PMCID: PMC4787765 DOI: 10.1093/nar/gkv930] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 09/07/2015] [Indexed: 11/14/2022] Open
Abstract
Eukaryal translation initiation factor 2B (eIF2B) acts as guanine nucleotide exchange factor (GEF) for eIF2 and forms a central target for pathways regulating global protein synthesis. eIF2B consists of five non-identical subunits (α-ϵ), which assemble into a catalytic subcomplex (γ, ϵ) responsible for the GEF activity, and a regulatory subcomplex (α, β, δ) which regulates the GEF activity under stress conditions. Here, we provide new structural and functional insight into the regulatory subcomplex of eIF2B (eIF2B(RSC)). We report the crystal structures of eIF2Bβ and eIF2Bδ from Chaetomium thermophilum as well as the crystal structure of their tetrameric eIF2B(βδ)2 complex. Combined with mutational and biochemical data, we show that eIF2B(RSC) exists as a hexamer in solution, consisting of two eIF2Bβδ heterodimers and one eIF2Bα2 homodimer, which is homologous to homohexameric ribose 1,5-bisphosphate isomerases. This homology is further substantiated by the finding that eIF2Bα specifically binds AMP and GMP as ligands. Based on our data, we propose a model for eIF2B(RSC) and its interactions with eIF2 that is consistent with previous biochemical and genetic data and provides a framework to better understand eIF2B function, the molecular basis for Gcn(-), Gcd(-) and VWM/CACH mutations and the evolutionary history of the eIF2B complex.
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Affiliation(s)
- Bernhard Kuhle
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany
| | - Nora K Eulig
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany
| | - Ralf Ficner
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften, Georg-August-Universität Göttingen, D-37077 Göttingen, Germany
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74
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Gogoi P, Srivastava A, Jayaprakash P, Jeyakanthan J, Kanaujia SP. In silico analysis suggests that PH0702 and PH0208 encode for methylthioribose-1-phosphate isomerase and ribose-1,5-bisphosphate isomerase, respectively, rather than aIF2Bβ and aIF2Bδ. Gene 2015; 575:118-26. [PMID: 26318479 DOI: 10.1016/j.gene.2015.08.048] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Revised: 07/02/2015] [Accepted: 08/23/2015] [Indexed: 12/21/2022]
Abstract
The overall process of protein biosynthesis across all domains of life is similar; however, detailed insights reveal a range of differences in the proteins involved. For decades, the process of protein translation in archaea has been considered to be closer to eukaryotes than to bacteria. In archaea, however, several homologues of eukaryotic proteins involved in translation initiation have not yet been identified; one of them being the initiation factor eIF2B consisting of five subunits (α, β, γ, δ and ε). Three open reading frames (PH0440, PH0702 and PH0208) in Pyrococcus horikoshii have been proposed to encode for the α-, β- and δ-subunits of aIF2B, respectively. The crystal structure of PH0440 shows similarity toward the α-subunit of eIF2B. However, the capability of PH0702 and PH0208 to function as the β- and δ-subunits of eIF2B, respectively, remains uncertain. In this study, we have taken up the task of annotating PH0702 and PH0208 using bioinformatics methods. The phylogenetic analysis of protein sequences belonging to IF2B-like family along with PH0702 and PH0208 revealed that PH0702 belonged to methylthioribose-1-phosphate isomerase (MTNA) group of proteins, whereas, PH0208 was found to be clustered in the group of ribose-1,5-bisphosphate isomerase (R15PI) proteins. A careful analysis of protein sequences and structures available for eIF2B, MTNA and R15PI confirms that PH0702 and PH0208 contain residues essential for the enzymatic activity of MTNA and R15PI, respectively. Additionally, the protein PH0208 comprises of the residues required for the dimer formation which is essential for the biological activity of R15PI. This prompted us to examine all eIF2B-like proteins from archaea and to annotate their function. The results reveal that majority of these proteins are homologues of the α-subunit of eIF2B, even though they lack the residues essential for their functional activity. A better understanding of the mechanism of GTP exchange during translation initiation in archaea is henceforth required.
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Affiliation(s)
- Prerana Gogoi
- Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India
| | - Ambuj Srivastava
- Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India
| | - Prajisha Jayaprakash
- Department of Bioinformatics, Alagappa University, Karaikudi 630004, Tamil Nadu, India
| | - Jeyaraman Jeyakanthan
- Department of Bioinformatics, Alagappa University, Karaikudi 630004, Tamil Nadu, India
| | - Shankar Prasad Kanaujia
- Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India.
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Wortham NC, Proud CG. Biochemical effects of mutations in the gene encoding the alpha subunit of eukaryotic initiation factor (eIF) 2B associated with Vanishing White Matter disease. BMC MEDICAL GENETICS 2015; 16:64. [PMID: 26285592 PMCID: PMC4593227 DOI: 10.1186/s12881-015-0204-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 07/14/2015] [Indexed: 11/10/2022]
Abstract
BACKGROUND Leukoencephalopathy with Vanishing White Matter (VWM) is an autosomal recessive disorder caused by germline mutations in the genes EIF2B1-5, which encode the 5 subunits of the eukaryotic translation initiation factor eIF2B. To date, analysis of the biochemical effects of mutations in the EIF2B2-5 genes has been carried out, but no study has been performed on mutations in the EIF2B1 gene. This gene encodes eIF2Bα, the smallest subunit in eIF2B which has an important role in both the structure and regulation of the eIF2B complex. METHODS eIF2B subunits were overexpressed in HEK293 cells and isolated from the resulting cell lysates by affinity chromatography. Formation of the eIF2B complex and binding of its substrate, eIF2, was assessed by western blot. Assays of the guanine nucleotide exchange (GEF) activity were also carried out. RESULTS Of the 5 eIF2Bα mutations studied, we found 3 that showed loss or reduction of binding of eIF2Bα to the rest of the complex, one with increased GEF activity, and one where no effects on activity or complex formation were observed. CONCLUSIONS This is the first study on eIF2Bα VWM mutations. We show that some mutations cause expected decreases in GEF activity or complex formation, similar to a majority of observed VWM mutations. However, we also observe some unexpected changes which hint at other effects of these mutations on as yet undescribed functions of eIF2B.
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Affiliation(s)
- Noel C Wortham
- Centre for Biological Sciences, University of Southampton, Life Sciences Building 85, Highfield Campus, Southampton, SO17 1BJ, UK.
| | - Christopher G Proud
- Centre for Biological Sciences, University of Southampton, Life Sciences Building 85, Highfield Campus, Southampton, SO17 1BJ, UK. .,South Australian Health and Medical Research Institute, PO Box 11060, SA5001, Adelaide, Australia.
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76
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eIF2 interactions with initiator tRNA and eIF2B are regulated by post-translational modifications and conformational dynamics. Cell Discov 2015; 1:15020. [PMID: 27462419 PMCID: PMC4860841 DOI: 10.1038/celldisc.2015.20] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Accepted: 06/12/2015] [Indexed: 12/18/2022] Open
Abstract
Translation of messenger RNA (mRNA) into proteins is key to eukaryotic gene expression and begins when initiation factor-2 (eIF2) delivers methionyl initiator tRNA (Met-tRNAiMet) to ribosomes. This first step is controlled by eIF2B mediating guanine nucleotide exchange on eIF2. We isolated eIF2 from yeast and used mass spectrometry to study the intact complex, and found that eIF2β is the most labile of the three subunits (eIF2α/β/γ). We then compared conformational dynamics of the ternary complex eIF2:GTP:Met-tRNAiMet with apo eIF2 using comparative chemical cross-linking. Results revealed high conformational dynamics for eIF2α in apo eIF2 while in the ternary complex all three subunits are constrained. Novel post-translational modifications identified here in both eIF2 and eIF2B were combined with established sites, and located within protein sequences and homology models. We found clustering at subunit interfaces and highly phosphorylated unstructured regions, at the N-terminus of eIF2β, and also between the eIF2Bε core and catalytic domains. We propose that modifications of these unstructured regions have a key role in regulating interactions between eIF2 and eIF2B, as well as other eIFs.
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77
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Jennings MD, Pavitt GD. A new function and complexity for protein translation initiation factor eIF2B. Cell Cycle 2015; 13:2660-5. [PMID: 25486352 DOI: 10.4161/15384101.2014.948797] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
eIF2B is a multisubunit protein that is critical for protein synthesis initiation and its control. It is a guanine nucleotide exchange factor (GEF) for its GTP-binding protein partner eIF2. eIF2 binds initiator tRNA to ribosomes and promotes mRNA AUG codon recognition. eIF2B is critical for regulation of protein synthesis via a conserved mechanism of phosphorylation of eIF2, which converts eIF2 from a substrate to an inhibitor of eIF2B GEF. In addition, inherited mutations affecting eIF2B subunits cause the fatal disorder leukoencephalopathy with Vanishing White Matter (VWM), also called Childhood Ataxia with Central nervous system Hypomyelination (CACH). Here we review findings which reveal that eIF2B is a decameric protein and also define a new function for the eIF2B. Our results demonstrate that the eIF2Bγ subunit is required for eIF2B to gain access to eIF2•GDP. Specifically it displaces a third translation factor eIF5 (a dual function GAP and GDI) from eIF2•GDP/eIF5 complexes. Thus eIF2B is a GDI displacement factor (or GDF) in addition to its role as a GEF, prompting the redrawing of the eIF2 cycling pathway to incorporate the new steps. In structural studies using mass spectrometry and cross-linking it is shown that eIF2B is a dimer of pentamers and so is twice as large as previously thought. A binding site for GTP on eIF2B was also found, raising further questions concerning the mechanism of nucleotide exchange. The implications of these findings for eIF2B function and for VWM/CACH disease are discussed.
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Affiliation(s)
- Martin D Jennings
- a Faculty of Life Sciences ; The University of Manchester ; Manchester , UK
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78
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Buffington SA, Huang W, Costa-Mattioli M. Translational control in synaptic plasticity and cognitive dysfunction. Annu Rev Neurosci 2015; 37:17-38. [PMID: 25032491 DOI: 10.1146/annurev-neuro-071013-014100] [Citation(s) in RCA: 251] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Activity-dependent changes in the strength of synaptic connections are fundamental to the formation and maintenance of memory. The mechanisms underlying persistent changes in synaptic strength in the hippocampus, specifically long-term potentiation and depression, depend on new protein synthesis. Such changes are thought to be orchestrated by engaging the signaling pathways that regulate mRNA translation in neurons. In this review, we discuss the key regulatory pathways that govern translational control in response to synaptic activity and the mRNA populations that are specifically targeted by these pathways. The critical contribution of regulatory control over new protein synthesis to proper cognitive function is underscored by human disorders associated with either silencing or mutation of genes encoding proteins that directly regulate translation. In light of these clinical implications, we also consider the therapeutic potential of targeting dysregulated translational control to treat cognitive disorders of synaptic dysfunction.
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Affiliation(s)
- Shelly A Buffington
- Department of Neuroscience, Memory and Brain Research Center, Baylor College of Medicine, Houston, Texas 77030; , ,
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79
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Sidrauski C, McGeachy AM, Ingolia NT, Walter P. The small molecule ISRIB reverses the effects of eIF2α phosphorylation on translation and stress granule assembly. eLife 2015; 4:e05033. [PMID: 25719440 PMCID: PMC4341466 DOI: 10.7554/elife.05033] [Citation(s) in RCA: 401] [Impact Index Per Article: 44.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Accepted: 02/04/2015] [Indexed: 12/16/2022] Open
Abstract
Previously, we identified ISRIB as a potent inhibitor of the integrated stress response (ISR) and showed that ISRIB makes cells resistant to the effects of eIF2α phosphorylation and enhances long-term memory in rodents (Sidrauski et al., 2013). Here, we show by genome-wide in vivo ribosome profiling that translation of a restricted subset of mRNAs is induced upon ISR activation. ISRIB substantially reversed the translational effects elicited by phosphorylation of eIF2α and induced no major changes in translation or mRNA levels in unstressed cells. eIF2α phosphorylation-induced stress granule (SG) formation was blocked by ISRIB. Strikingly, ISRIB addition to stressed cells with pre-formed SGs induced their rapid disassembly, liberating mRNAs into the actively translating pool. Restoration of mRNA translation and modulation of SG dynamics may be an effective treatment of neurodegenerative diseases characterized by eIF2α phosphorylation, SG formation, and cognitive loss.
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Affiliation(s)
- Carmela Sidrauski
- Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francis, San Francisco, United States
| | - Anna M McGeachy
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Nicholas T Ingolia
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Peter Walter
- Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francis, San Francisco, United States
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80
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Wei C, Lin M, Jinjun B, Su F, Dan C, Yan C, Jie Y, Jin Z, Zi-Chun H, Wu Y. Involvement of general control nonderepressible kinase 2 in cancer cell apoptosis by posttranslational mechanisms. Mol Biol Cell 2015; 26:1044-57. [PMID: 25589675 PMCID: PMC4357505 DOI: 10.1091/mbc.e14-10-1438] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
GCN2 exerts its proapoptotic function in cancer cell death by posttranslational mechanisms. Modulation of GCN2 expression can be used for molecular targeted cancer therapy and drug development. Na+,K+-ATPase ligands are the first identified small-molecule drugs that can trigger cancer cell death by modulating GCN2 signaling. General control nonderepressible kinase 2 (GCN2) is a promising target for cancer therapy. However, the role of GCN2 in cancer cell survival or death is elusive; further, small molecules targeting GCN2 signaling are not available. By using a GCN2 level-based drug screening assay, we found that GCN2 protein level critically determined the sensitivity of the cancer cells toward Na+,K+-ATPase ligand–induced apoptosis both in vitro and in vivo, and this effect was largely dependent on C/EBP homologous protein (CHOP) induction. Further analysis revealed that GCN2 is a short-lived protein. In A549 lung carcinoma cells, cellular β-arrestin1/2 associated with GCN2 and maintained the GCN2 protein level at a low level by recruiting the E3 ligase NEDD4L and facilitating consequent proteasomal degradation. However, Na+,K+-ATPase ligand treatment triggered the phosphorylation of GCN2 at threonine 899, which increased the GCN2 protein level by disrupting the formation of GCN2–β-arrestin–NEDD4L ternary complex. The enhanced GCN2 level, in turn, aggravated Na+,K+-ATPase ligand–induced cancer cell apoptosis. Our findings reveal that GCN2 can exert its proapoptotic function in cancer cell death by posttranslational mechanisms. Moreover, Na+,K+-ATPase ligands emerge as the first identified small-molecule drugs that can trigger cancer cell death by modulating GCN2 signaling.
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Affiliation(s)
- Chen Wei
- State Key Lab of Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China State Key Lab of Natural Medicines, China Pharmaceutical University, Nanjing 210017, China
| | - Ma Lin
- State Key Lab of Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Bian Jinjun
- Department of Anaesthesiology and Intensive Care Unit, Changhai Hospital, Affiliated Hospital of the Second Military Medical University, Shanghai 200433, China
| | - Feng Su
- State Key Lab of Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Cao Dan
- State Key Lab of Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Chen Yan
- Department of Chinese Medicine, Jiangsu Cancer Hospital, Nanjing 210009, China
| | - Yang Jie
- State Key Lab of Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Zhang Jin
- State Key Lab of Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Hua Zi-Chun
- State Key Lab of Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China State Key Lab of Natural Medicines, China Pharmaceutical University, Nanjing 210017, China
| | - Yin Wu
- State Key Lab of Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China State Key Lab of Natural Medicines, China Pharmaceutical University, Nanjing 210017, China
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Jennings MD, Pavitt GD. eIF5 is a dual function GAP and GDI for eukaryotic translational control. Small GTPases 2014; 1:118-123. [PMID: 21686265 DOI: 10.4161/sgtp.1.2.13783] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Revised: 09/27/2010] [Accepted: 09/28/2010] [Indexed: 11/19/2022] Open
Abstract
We recently showed in a publication in Nature that the eukaryotic translation initiation factor eIF5 has a second regulatory function and is a GDI (GDP dissociation inhibitor) in addition to its previously characterized role as a GAP (GTPase accelerating protein). These findings provide new insight into the mechanism of translation initiation in eukaryotic cells. Additional findings show that the GDI function is critical for the normal regulation of protein synthesis by phosphorylation of eIF2α at ser51. Because eIF2 phosphorylation is a ubiquitous mode of translational control these results are of broad interest. Here we review these and related studies and suggest they offer further evidence of parallels between the functions of regulators of the translation factor eIF 2 and both heterotrimeric and small GTPases.
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Affiliation(s)
- Martin D Jennings
- Faculty of Life Sciences; The University of Manchester; Manchester UK
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82
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Droppelmann CA, Campos-Melo D, Volkening K, Strong MJ. The emerging role of guanine nucleotide exchange factors in ALS and other neurodegenerative diseases. Front Cell Neurosci 2014; 8:282. [PMID: 25309324 PMCID: PMC4159981 DOI: 10.3389/fncel.2014.00282] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Accepted: 08/25/2014] [Indexed: 12/11/2022] Open
Abstract
Small GTPases participate in a broad range of cellular processes such as proliferation, differentiation, and migration. The exchange of GDP for GTP resulting in the activation of these GTPases is catalyzed by a group of enzymes called guanine nucleotide exchange factors (GEFs), of which two classes: Dbl-related exchange factors and the more recently described dedicator of cytokinesis proteins family exchange factors. Increasingly, deregulation of normal GEF activity or function has been associated with a broad range of disease states, including neurodegeneration and neurodevelopmental disorders. In this review, we examine this evidence with special emphasis on the novel role of Rho guanine nucleotide exchange factor (RGNEF/p190RhoGEF) in the pathogenesis of amyotrophic lateral sclerosis. RGNEF is the first neurodegeneration-linked GEF that regulates not only RhoA GTPase activation but also functions as an RNA binding protein that directly acts with low molecular weight neurofilament mRNA 3' untranslated region to regulate its stability. This dual role for RGNEF, coupled with the increasing understanding of the key role for GEFs in modulating the GTPase function in cell survival suggests a prominent role for GEFs in mediating a critical balance between cytotoxicity and neuroprotection which, when disturbed, contributes to neuronal loss.
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Affiliation(s)
- Cristian A Droppelmann
- Molecular Medicine Group, Robarts Research Institute, Western University London, ON, Canada
| | - Danae Campos-Melo
- Molecular Medicine Group, Robarts Research Institute, Western University London, ON, Canada
| | - Kathryn Volkening
- Molecular Medicine Group, Robarts Research Institute, Western University London, ON, Canada ; Department of Clinical Neurological Sciences, Schulich School of Medicine & Dentistry, Western University London, ON, Canada
| | - Michael J Strong
- Molecular Medicine Group, Robarts Research Institute, Western University London, ON, Canada ; Department of Clinical Neurological Sciences, Schulich School of Medicine & Dentistry, Western University London, ON, Canada
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83
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Gordiyenko Y, Schmidt C, Jennings MD, Matak-Vinkovic D, Pavitt GD, Robinson CV. eIF2B is a decameric guanine nucleotide exchange factor with a γ2ε2 tetrameric core. Nat Commun 2014; 5:3902. [PMID: 24852487 PMCID: PMC4046112 DOI: 10.1038/ncomms4902] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Accepted: 04/15/2014] [Indexed: 01/21/2023] Open
Abstract
eIF2B facilitates and controls protein synthesis in eukaryotes by mediating guanine nucleotide exchange on its partner eIF2. We combined mass spectrometry (MS) with chemical cross-linking, surface accessibility measurements and homology modelling to define subunit stoichiometry and interactions within eIF2B and eIF2. Although it is generally accepted that eIF2B is a pentamer of five non-identical subunits (α–ε), here we show that eIF2B is a decamer. MS and cross-linking of eIF2B complexes allows us to propose a model for the subunit arrangements within eIF2B where the subunit assembly occurs through catalytic γ- and ε-subunits, with regulatory subunits arranged in asymmetric trimers associated with the core. Cross-links between eIF2 and eIF2B allow modelling of interactions that contribute to nucleotide exchange and its control by eIF2 phosphorylation. Finally, we identify that GTP binds to eIF2Bγ, prompting us to propose a multi-step mechanism for nucleotide exchange. Eukaryotic Initiation Factor 2 (eIF2) initiates protein synthesis aided by its partner eIF2B, which stimulates guanine nucleotide exchange on eIF2. Here, Gordiyenko et al. show that eIF2B exists as a decamer and propose a model for its subunit arrangement that provides new insight into its function.
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Affiliation(s)
- Yuliya Gordiyenko
- 1] Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK [2] MRC Laboratory of Molecular Biology, University of Cambridge, Francis Crick Avenue, Cambridge CB2 0QH, UK [3]
| | - Carla Schmidt
- 1] Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK [2]
| | - Martin D Jennings
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Dijana Matak-Vinkovic
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
| | - Graham D Pavitt
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Carol V Robinson
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK
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84
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Sundaram A, Grant CM. Oxidant-specific regulation of protein synthesis in Candida albicans. Fungal Genet Biol 2014; 67:15-23. [PMID: 24699161 DOI: 10.1016/j.fgb.2014.03.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Revised: 03/18/2014] [Accepted: 03/19/2014] [Indexed: 10/25/2022]
Abstract
Eukaryotic cells typically respond to stress conditions by inhibiting global protein synthesis. The initiation phase is the main target of regulation and represents a key control point for eukaryotic gene expression. In Saccharomyces cerevisiae and mammalian cells this is achieved by phosphorylation of eukaryotic initiation factor 2 (eIF2α). We have examined how the fungal pathogen Candida albicans responds to oxidative stress conditions and show that oxidants including hydrogen peroxide, the heavy metal cadmium and the thiol oxidant diamide inhibit translation initiation. The inhibition in response to hydrogen peroxide and cadmium largely depends on phosphorylation of eIF2α since minimal inhibition is observed in a gcn2 mutant. In contrast, translation initiation is inhibited in a Gcn2-independent manner in response to diamide. Our data indicate that all three oxidants inhibit growth of C. albicans in a dose-dependent manner, however, loss of GCN2 does not improve growth in the presence of hydrogen peroxide or cadmium. Examination of translational activity indicates that these oxidants inhibit translation at a post-initiation phase which may account for the growth inhibition in a gcn2 mutant. As well as inhibiting global translation initiation, phosphorylation of eIF2α also enhances expression of the GCN4 mRNA in yeast via a well-known translational control mechanism. We show that C. albicans GCN4 is similarly induced in response to oxidative stress conditions and Gcn4 is specifically required for hydrogen peroxide tolerance. Thus, the response of C. albicans to oxidative stress is mediated by oxidant-specific regulation of translation initiation and we discuss our findings in comparison to other eukaryotes including the yeast S. cerevisiae.
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Affiliation(s)
- Arunkumar Sundaram
- The University of Manchester, Faculty of Life Sciences, Manchester M13 9PT, UK; Faculty of Dentistry, Universiti Sains Islam Malaysia, Kuala Lumpur 55100, Malaysia
| | - Chris M Grant
- The University of Manchester, Faculty of Life Sciences, Manchester M13 9PT, UK.
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85
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Sundaram A, Grant CM. A single inhibitory upstream open reading frame (uORF) is sufficient to regulate Candida albicans GCN4 translation in response to amino acid starvation conditions. RNA (NEW YORK, N.Y.) 2014; 20:559-67. [PMID: 24570481 PMCID: PMC3964917 DOI: 10.1261/rna.042267.113] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Candida albicans is a major fungal pathogen that responds to various environmental cues as part of its infection mechanism. We show here that the expression of C. albicans GCN4, which encodes a transcription factor that regulates morphogenetic and metabolic responses, is translationally regulated in response to amino acid starvation induced by exposure to the histidine analog 3-aminotriazole (3AT). However, in contrast to the well-known translational control mechanisms that regulate yeast GCN4 and mammalian ATF4 expression via multiple upstream open reading frames (uORFs) in their 5'-leader sequences, a single inhibitory uORF is necessary and sufficient for C. albicans GCN4 translational control. The 5'-leader sequence of GCN4 contains three uORFs, but uORF3 alone is sufficient for translational regulation. Under nonstress conditions, uORF3 inhibits GCN4 translation. Amino acid starvation conditions promote Gcn2-mediated phosphorylation of eIF2α and leaky ribosomal scanning to bypass uORF3, inducing GCN4 translation. GCN4 expression is also transcriptionally regulated, although maximal induction is observed at higher concentrations of 3AT compared with translational regulation. C. albicans GCN4 expression is therefore highly regulated by both transcriptional and translational control mechanisms. We suggest that it is particularly important that Gcn4 levels are tightly controlled since Gcn4 regulates morphogenetic changes during amino acid starvation conditions, which are important determinants of virulence in this fungus.
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Affiliation(s)
- Arunkumar Sundaram
- Faculty of Life Sciences, The University of Manchester, Manchester M13 9PT, United Kingdom
- Faculty of Dentistry, Universiti Sains Islam Malaysia, Kuala Lumpur 55100, Malaysia
| | - Chris M. Grant
- Faculty of Life Sciences, The University of Manchester, Manchester M13 9PT, United Kingdom
- Corresponding authorE-mail
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86
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Wortham NC, Martinez M, Gordiyenko Y, Robinson CV, Proud CG. Analysis of the subunit organization of the eIF2B complex reveals new insights into its structure and regulation. FASEB J 2014; 28:2225-37. [DOI: 10.1096/fj.13-243329] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Noel C. Wortham
- Centre for Biological SciencesUniversity of SouthamptonSouthamptonUK
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87
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eIF2B promotes eIF5 dissociation from eIF2*GDP to facilitate guanine nucleotide exchange for translation initiation. Genes Dev 2014; 27:2696-707. [PMID: 24352424 PMCID: PMC3877758 DOI: 10.1101/gad.231514.113] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Protein synthesis factor eIF2 delivers initiator tRNA to the ribosome. Two proteins regulate its G-protein cycle: eIF5 has both GTPase-accelerating protein (GAP) and GDP dissociation inhibitor (GDI) functions, and eIF2B is the guanine nucleotide exchange factor (GEF). In this study, we used protein-protein interaction and nucleotide exchange assays to monitor the kinetics of eIF2 release from the eIF2•GDP/eIF5 GDI complex and determine the effect of eIF2B on this release. We demonstrate that eIF2B has a second activity as a GDI displacement factor (GDF) that can recruit eIF2 from the eIF2•GDP/eIF5 GDI complex prior to GEF action. We found that GDF function is dependent on the eIF2Bε and eIF2Bγ subunits and identified a novel eIF2-eIF2Bγ interaction. Furthermore, GDF and GEF activities are shown to be independent. First, eIF2B GDF is insensitive to eIF2α phosphorylation, unlike GEF. Second, we found that eIF2Bγ mutations known to disrupt GCN4 translational control significantly impair GDF activity but not GEF function. Our data therefore define an additional step in the protein synthesis initiation pathway that is important for its proper control. We propose a new model to place eIF2B GDF function in the context of efficient eIF2 recycling and its regulation by eIF2 phosphorylation.
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88
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Martin-Marcos P, Nanda JS, Luna RE, Zhang F, Saini AK, Cherkasova VA, Wagner G, Lorsch JR, Hinnebusch AG. Enhanced eIF1 binding to the 40S ribosome impedes conformational rearrangements of the preinitiation complex and elevates initiation accuracy. RNA (NEW YORK, N.Y.) 2014; 20:150-67. [PMID: 24335188 PMCID: PMC3895268 DOI: 10.1261/rna.042069.113] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Accepted: 10/17/2013] [Indexed: 05/20/2023]
Abstract
In the current model of translation initiation by the scanning mechanism, eIF1 promotes an open conformation of the 40S subunit competent for rapidly loading the eIF2·GTP·Met-tRNAi ternary complex (TC) in a metastable conformation (POUT) capable of sampling triplets entering the P site while blocking accommodation of Met-tRNAi in the PIN state and preventing completion of GTP hydrolysis (Pi release) by the TC. All of these functions should be reversed by eIF1 dissociation from the preinitiation complex (PIC) on AUG recognition. We tested this model by selecting eIF1 Ssu(-) mutations that suppress the elevated UUG initiation and reduced rate of TC loading in vivo conferred by an eIF1 (Sui(-)) substitution that eliminates a direct contact of eIF1 with the 40S subunit. Importantly, several Ssu(-) substitutions increase eIF1 affinity for 40S subunits in vitro, and the strongest-binding variant (D61G), predicted to eliminate ionic repulsion with 18S rRNA, both reduces the rate of eIF1 dissociation and destabilizes the PIN state of TC binding in reconstituted PICs harboring Sui(-) variants of eIF5 or eIF2. These findings establish that eIF1 dissociation from the 40S subunit is required for the PIN mode of TC binding and AUG recognition and that increasing eIF1 affinity for the 40S subunit increases initiation accuracy in vivo. Our results further demonstrate that the GTPase-activating protein eIF5 and β-subunit of eIF2 promote accuracy by controlling eIF1 dissociation and the stability of TC binding to the PIC, beyond their roles in regulating GTP hydrolysis by eIF2.
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Affiliation(s)
- Pilar Martin-Marcos
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Jagpreet S. Nanda
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Rafael E. Luna
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Fan Zhang
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Adesh K. Saini
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
- Department of Biotechnology, Shoolini University of Biotechnology and Management Sciences, Solan, Himachal Pradesh-173212, India
| | - Vera A. Cherkasova
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Gerhard Wagner
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Jon R. Lorsch
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
- Corresponding authorsE-mail E-mail
| | - Alan G. Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
- Corresponding authorsE-mail E-mail
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Weiss CS, Ochs MM, Hagenmueller M, Streit MR, Malekar P, Riffel JH, Buss SJ, Weiss KH, Sadoshima J, Katus HA, Hardt SE. DYRK2 negatively regulates cardiomyocyte growth by mediating repressor function of GSK-3β on eIF2Bε. PLoS One 2013; 8:e70848. [PMID: 24023715 PMCID: PMC3762802 DOI: 10.1371/journal.pone.0070848] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Accepted: 06/26/2013] [Indexed: 01/19/2023] Open
Abstract
BACKGROUND A prerequisite of hypertrophic response of the myocardium is an increase in protein synthesis. A central regulator of translation initiation is Eukaryotic initiation factor 2B (eIF2B). Here we assessed the hypothesis that regulation of protein synthesis via eIF2Bε is essential to cardiac hypertrophic response in vivo. METHODS Two transgenic mouse lines were generated with cardiac restricted overexpression of eIF2Bε or its mutant eIF2Bε-eIFS(535)A, which cannot be inactivated by phosphorylation through GSK-3β. RESULTS (1) Under baseline conditions eIF2Bε transgenic mice showed no difference in cardiac phenotype compared to wild type, whereas in the mutant eIF2Bε-S(535)A an increase in LV/tibia length (7.5 ± 0.4 mg/mm vs. 6.2 ± 0.2 mg/mm, p<0.001) and cardiomyocyte cross sectional area (13004 ± 570 vs. 10843 ± 347 RU, p<0.01) was observed. (2) Cardiac overexpression of eIF2Bε did not change the response of the heart to pathologic stress induced by chronic isoproterenol treatment. (3) Cardiac overexpression of the eIF2Bε transgene was followed by overexpression of DYRK2 which is known to prime the inhibitory action of GSK-3β on eIF2Bε, while DYRK1A and GSK-3β itself were not increased. (4) In C57BL/6 mice after 48 h of isoproterenol-stimulation or aortic banding, eIF2Bε was increased and DYRK2 was concomitantly decreased. (5) In line with these in vivo findings, siRNA knockdown of DYRK2 in cultured cardiomyocytes resulted in decreased levels of p(S535)- eIF2Bε, (6) whereas adenoviral induced overexpression of DYRK2 was accompanied by clearly increased phosphorylation of eIF2Bε, indicating a coordinated response pattern (7) Adenoviral induced overexpression of DYRK2 leads to significantly reduced cardiomyocyte size and diminishes hypertrophic response to adrenergic stimulation. CONCLUSIONS The interaction of GSK-3β and its priming kinase DYRK2 regulate the activity of eIF2Bε in cardiac myocytes. DYRK2 is a novel negative regulator of cardiomyocyte growth. DYRK2 could serve as a therapeutic option to regulate myocardial growth.
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Affiliation(s)
- Celine S. Weiss
- Internal Medicine III, University Hospital Heidelberg and DZHK (German Center for Cardiovascular Research), Heidelberg, Germany
| | - Marco M. Ochs
- Internal Medicine III, University Hospital Heidelberg and DZHK (German Center for Cardiovascular Research), Heidelberg, Germany
| | - Marco Hagenmueller
- Internal Medicine III, University Hospital Heidelberg and DZHK (German Center for Cardiovascular Research), Heidelberg, Germany
| | - Marcus R. Streit
- Internal Medicine III, University Hospital Heidelberg and DZHK (German Center for Cardiovascular Research), Heidelberg, Germany
| | - Pratima Malekar
- Internal Medicine III, University Hospital Heidelberg and DZHK (German Center for Cardiovascular Research), Heidelberg, Germany
| | - Johannes H. Riffel
- Internal Medicine III, University Hospital Heidelberg and DZHK (German Center for Cardiovascular Research), Heidelberg, Germany
| | - Sebastian J. Buss
- Internal Medicine III, University Hospital Heidelberg and DZHK (German Center for Cardiovascular Research), Heidelberg, Germany
| | - Karl H. Weiss
- Internal Medicine IV, University Hospital Heidelberg, Heidelberg, Germany
| | - Junichi Sadoshima
- New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey, United States of America
| | - Hugo A. Katus
- Internal Medicine III, University Hospital Heidelberg and DZHK (German Center for Cardiovascular Research), Heidelberg, Germany
| | - Stefan E. Hardt
- Internal Medicine III, University Hospital Heidelberg and DZHK (German Center for Cardiovascular Research), Heidelberg, Germany
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90
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Templeton PD, Litman ES, Metzner SI, Ahn NG, Sousa MC. Structure of mediator of RhoA-dependent invasion (MRDI) explains its dual function as a metabolic enzyme and a mediator of cell invasion. Biochemistry 2013; 52:5675-84. [PMID: 23859498 DOI: 10.1021/bi400556e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Metastatic melanoma is among the most intractable cancers to treat; patients show resistance to therapy and limited survival time. A critical step in the development of metastatic melanoma is the acquisition of invasion and transition from thin to thick tumors on the skin, followed by invasion to lymph nodes. Prior studies have shown that metastatic melanoma is associated with dysregulation of RhoA and enhanced expression of a protein named "mediator of RhoA-dependent invasion (MRDI)". Importantly, MRDI is a "moonlighting" enzyme, with two distinct functions in melanoma cells. First, MRDI acts as a methylthioribose-1-phosphate (MTR-1-P) isomerase, catalyzing a critical step in methionine salvage. Second, MRDI promotes and is necessary for melanoma cell invasion, independent of its catalytic activity. This paper demonstrates that MtnA, a bacterial MTR-1-P isomerase, rescues the methionine salvage function of MRDI, but is unable to rescue its role in invasion. The crystal structure of MRDI was solved to a resolution of 2.5 Å to identify structural elements important for its invasion activity. This structure and its comparison with other MTR-1-P isomerases are presented, and mutations within a region separate from the MTR-1-P binding site, which interfere with invasion, are identified. Thus, structural elements in MRDI distal from the MTR-1-P catalytic site are responsible for the invasion phenotype.
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Affiliation(s)
- Paul D Templeton
- Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO 80309-0596, USA
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91
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Kunkeaw N, Jeon SH, Lee K, Johnson BH, Tanasanvimon S, Javle M, Pairojkul C, Chamgramol Y, Wongfieng W, Gong B, Leelayuwat C, Lee YS. Cell death/proliferation roles for nc886, a non-coding RNA, in the protein kinase R pathway in cholangiocarcinoma. Oncogene 2013; 32:3722-31. [PMID: 22926522 PMCID: PMC3869796 DOI: 10.1038/onc.2012.382] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2012] [Revised: 07/09/2012] [Accepted: 07/23/2012] [Indexed: 12/25/2022]
Abstract
We have recently identified nc886 (pre-miR-886 or vtRNA2-1) as a novel type of non-coding RNA that inhibits activation of protein kinase R (PKR). PKR's pro-apoptotic role through eukaryotic initiation factor 2 α (eIF2α) phosphorylation is well established in the host defense against viral infection. Paradoxically, some cancer patients have elevated PKR activity; however, its cause and consequence are not understood. Initially, we evaluated the expression of nc886, PKR and eIF2α in non-malignant cholangiocyte and cholangiocarcinoma (CCA) cells. nc886 is repressed in CCA cells and this repression is the cause of PKR's activation therein. nc886 alone is necessary and sufficient for suppression of PKR via direct physical interaction. Consistently, artificial suppression of nc886 in cholangiocyte cells activates the canonical PKR/eIF2α cell death pathway, suggesting a potential significance of the nc886 suppression and the consequent PKR activation in eliminating pre-malignant cells during tumorigenesis. In comparison, active PKR in CCA cells does not induce phospho-eIF2α nor apoptosis, but promotes the pro-survival nuclear factor-κB pathway. Thus, PKR has a dual life or death role during tumorigenesis. Similarly to the CCA cell lines, nc886 tends to be decreased but PKR tends to be activated in our clinical samples from CCA patients. Collectively from our data, we propose a tumor surveillance model for nc886's role in the PKR pathway during tumorigenesis.
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Affiliation(s)
- Nawapol Kunkeaw
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, TX77555-1072, USA
- The Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand
| | - Sung Ho Jeon
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, TX77555-1072, USA
- Department of Life Science, Hallym University, Chuncheon 200-702, Korea
| | - Kwanbok Lee
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, TX77555-1072, USA
| | - Betty H. Johnson
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, TX77555-1072, USA
| | - Suebpong Tanasanvimon
- Department of Medicine, King Chulalongkorn Memorial Hospital, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
- Department of Gastroenterology, Hepatology, and Nutrition, MD Anderson Cancer Center, Houston, TX
| | - Milind Javle
- Gastrointestinal Medical Oncology, MD Anderson Cancer Center, Houston, TX
| | - Chawalit Pairojkul
- Liver Fluke and Cholangiocarcinoma Research Center, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
| | - Yaovalux Chamgramol
- Liver Fluke and Cholangiocarcinoma Research Center, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
| | - Wipaporn Wongfieng
- The Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand
| | - Bin Gong
- Department of Pathology, The University of Texas Medical Branch, Galveston, TX
| | - Chanvit Leelayuwat
- The Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand
- Liver Fluke and Cholangiocarcinoma Research Center, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
| | - Yong Sun Lee
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, TX77555-1072, USA
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92
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Sidrauski C, Acosta-Alvear D, Khoutorsky A, Vedantham P, Hearn BR, Li H, Gamache K, Gallagher CM, Ang KKH, Wilson C, Okreglak V, Ashkenazi A, Hann B, Nader K, Arkin MR, Renslo AR, Sonenberg N, Walter P. Pharmacological brake-release of mRNA translation enhances cognitive memory. eLife 2013; 2:e00498. [PMID: 23741617 PMCID: PMC3667625 DOI: 10.7554/elife.00498] [Citation(s) in RCA: 458] [Impact Index Per Article: 41.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 04/23/2013] [Indexed: 12/13/2022] Open
Abstract
Phosphorylation of the α-subunit of initiation factor 2 (eIF2) controls protein synthesis by a conserved mechanism. In metazoa, distinct stress conditions activate different eIF2α kinases (PERK, PKR, GCN2, and HRI) that converge on phosphorylating a unique serine in eIF2α. This collection of signaling pathways is termed the 'integrated stress response' (ISR). eIF2α phosphorylation diminishes protein synthesis, while allowing preferential translation of some mRNAs. Starting with a cell-based screen for inhibitors of PERK signaling, we identified a small molecule, named ISRIB, that potently (IC50 = 5 nM) reverses the effects of eIF2α phosphorylation. ISRIB reduces the viability of cells subjected to PERK-activation by chronic endoplasmic reticulum stress. eIF2α phosphorylation is implicated in memory consolidation. Remarkably, ISRIB-treated mice display significant enhancement in spatial and fear-associated learning. Thus, memory consolidation is inherently limited by the ISR, and ISRIB releases this brake. As such, ISRIB promises to contribute to our understanding and treatment of cognitive disorders. DOI:http://dx.doi.org/10.7554/eLife.00498.001.
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Affiliation(s)
- Carmela Sidrauski
- Department of Biochemistry and Biophysics , University of California, San Francisco , San Francisco , United States ; Howard Hughes Medical Institute, University of California, San Francisco , San Francisco , United States
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93
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Valásek LS. 'Ribozoomin'--translation initiation from the perspective of the ribosome-bound eukaryotic initiation factors (eIFs). Curr Protein Pept Sci 2013; 13:305-30. [PMID: 22708493 PMCID: PMC3434475 DOI: 10.2174/138920312801619385] [Citation(s) in RCA: 103] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2011] [Revised: 01/16/2012] [Accepted: 02/16/2012] [Indexed: 02/05/2023]
Abstract
Protein synthesis is a fundamental biological mechanism bringing the DNA-encoded genetic information into
life by its translation into molecular effectors - proteins. The initiation phase of translation is one of the key points of gene
regulation in eukaryotes, playing a role in processes from neuronal function to development. Indeed, the importance of the
study of protein synthesis is increasing with the growing list of genetic diseases caused by mutations that affect mRNA
translation. To grasp how this regulation is achieved or altered in the latter case, we must first understand the molecular
details of all underlying processes of the translational cycle with the main focus put on its initiation. In this review I discuss
recent advances in our comprehension of the molecular basis of particular initiation reactions set into the context of
how and where individual eIFs bind to the small ribosomal subunit in the pre-initiation complex. I also summarize our
current knowledge on how eukaryotic initiation factor eIF3 controls gene expression in the gene-specific manner via reinitiation.
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Affiliation(s)
- Leos Shivaya Valásek
- Laboratory of Eukaryotic Gene Regulation, Institute of Microbiology AS CR, Prague, Czech Republic.
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94
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Grousl T, Ivanov P, Malcova I, Pompach P, Frydlova I, Slaba R, Senohrabkova L, Novakova L, Hasek J. Heat shock-induced accumulation of translation elongation and termination factors precedes assembly of stress granules in S. cerevisiae. PLoS One 2013; 8:e57083. [PMID: 23451152 PMCID: PMC3581570 DOI: 10.1371/journal.pone.0057083] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Accepted: 01/17/2013] [Indexed: 12/26/2022] Open
Abstract
In response to severe environmental stresses eukaryotic cells shut down translation and accumulate components of the translational machinery in stress granules (SGs). Since they contain mainly mRNA, translation initiation factors and 40S ribosomal subunits, they have been referred to as dominant accumulations of stalled translation preinitiation complexes. Here we present evidence that the robust heat shock-induced SGs of S. cerevisiae also contain translation elongation factors eEF3 (Yef3p) and eEF1Bγ2 (Tef4p) as well as translation termination factors eRF1 (Sup45p) and eRF3 (Sup35p). Despite the presence of the yeast prion protein Sup35 in heat shock-induced SGs, we found out that its prion-like domain is not involved in the SGs assembly. Factors eEF3, eEF1Bγ2 and eRF1 were accumulated and co-localized with Dcp2 foci even upon a milder heat shock at 42°C independently of P-bodies scaffolding proteins. We also show that eEF3 accumulations at 42°C determine sites of the genuine SGs assembly at 46°C. We suggest that identification of translation elongation and termination factors in SGs might help to understand the mechanism of the eIF2α factor phosphorylation-independent repression of translation and SGs assembly.
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Affiliation(s)
- Tomas Grousl
- Institute of Microbiology of AS CR, v.v.i., Prague, Czech Republic
| | - Pavel Ivanov
- Institute of Microbiology of AS CR, v.v.i., Prague, Czech Republic
| | - Ivana Malcova
- Institute of Microbiology of AS CR, v.v.i., Prague, Czech Republic
| | - Petr Pompach
- Institute of Microbiology of AS CR, v.v.i., Prague, Czech Republic
| | - Ivana Frydlova
- Institute of Microbiology of AS CR, v.v.i., Prague, Czech Republic
| | - Renata Slaba
- Institute of Microbiology of AS CR, v.v.i., Prague, Czech Republic
| | | | - Lenka Novakova
- Institute of Microbiology of AS CR, v.v.i., Prague, Czech Republic
| | - Jiri Hasek
- Institute of Microbiology of AS CR, v.v.i., Prague, Czech Republic
- * E-mail:
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95
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A yeast purification system for human translation initiation factors eIF2 and eIF2Bε and their use in the diagnosis of CACH/VWM disease. PLoS One 2013; 8:e53958. [PMID: 23335982 PMCID: PMC3545922 DOI: 10.1371/journal.pone.0053958] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Accepted: 12/04/2012] [Indexed: 11/19/2022] Open
Abstract
Recessive inherited mutations in any of five subunits of the general protein synthesis factor eIF2B are responsible for a white mater neurodegenerative disease with a large clinical spectrum. The classical form is called Childhood Ataxia with CNS hypomyelination (CACH) or Vanishing White Matter Leukoencephalopathy (VWM). eIF2B-related disorders affect glial cells, despite the fact that eIF2B is a ubiquitous protein that functions as a guanine-nucleotide exchange factor (GEF) for its partner protein eIF2 in the translation initiation process in all eukaryotic cells. Decreased eIF2B activity measured by a GEF assay in patients' immortalised lymphocytic cells provides a biochemical diagnostic assay but is limited by the availability of eIF2 protein, which is classically purified from a mammalian cell source by column chromatography. Here we describe the generation of a recombinant expression system to produce purified human eIF2 from yeast cells. We demonstrate that human eIF2 can function in yeast cells in place of the equivalent yeast factor. We purify human eIF2 and the C-terminal domain of human eIF2Bε using affinity chromatography from engineered yeast cells and find that both function in a GEF assay: the first demonstration that this human eIF2Bε domain has GEF function. We show that CACH/VWM mutations within this domain reduce its activity. Finally we demonstrate that the recombinant eIF2 functions similarly to eIF2 purified from rat liver in GEF assays with CACH/VWM eIF2B-mutated patient derived lymphocytic cells.
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96
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The yeast eukaryotic translation initiation factor 2B translation initiation complex interacts with the fatty acid synthesis enzyme YBR159W and endoplasmic reticulum membranes. Mol Cell Biol 2012; 33:1041-56. [PMID: 23263984 DOI: 10.1128/mcb.00811-12] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Using affinity purifications coupled with mass spectrometry and yeast two-hybrid assays, we show the Saccharomyces cerevisiae translation initiation factor complex eukaryotic translation initiation factor 2B (eIF2B) and the very-long-chain fatty acid (VLCFA) synthesis keto-reductase enzyme YBR159W physically interact. The data show that the interaction is specifically between YBR159W and eIF2B and not between other members of the translation initiation or VLCFA pathways. A ybr159wΔ null strain has a slow-growth phenotype and a reduced translation rate but a normal GCN4 response to amino acid starvation. Although YBR159W localizes to the endoplasmic reticulum membrane, subcellular fractionation experiments show that a fraction of eIF2B cofractionates with lipid membranes in a YBR159W-independent manner. We show that a ybr159wΔ yeast strain and other strains with null mutations in the VLCFA pathway cause eIF2B to appear as numerous foci throughout the cytoplasm.
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97
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Pavitt GD, Ron D. New insights into translational regulation in the endoplasmic reticulum unfolded protein response. Cold Spring Harb Perspect Biol 2012; 4:cshperspect.a012278. [PMID: 22535228 DOI: 10.1101/cshperspect.a012278] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Homeostasis of the protein-folding environment in the endoplasmic reticulum (ER) is maintained by signal transduction pathways that collectively constitute an unfolded protein response (UPR). These affect bulk protein synthesis and thereby the levels of ER stress, but also culminate in regulated expression of specific mRNAs, such as that encoding the transcription factor ATF4. Mechanisms linking eukaryotic initiation factor 2 (eIF2) phosphorylation to control of unfolded protein load in the ER were elucidated more than 10 years ago, but recent work has highlighted the diversity of processes that impinge on eIF2 activity and revealed that there are multiple mechanisms by which changes in eIF2 activity can modulate the translation of individual mRNAs. In addition, the potential for affecting this step of translation initiation pharmacologically is becoming clearer. Furthermore, it is now clear that another strand of the UPR, controlled by the endoribonuclease inositol-requiring enzyme 1 (IRE1), also affects rates of protein synthesis in stressed cells and that its effector function, mediated by the transcription factor X-box-binding protein 1 (XBP1), is subject to important mRNA-specific translational regulation. These new insights into the convergence of translational control and the UPR will be reviewed here.
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Affiliation(s)
- Graham D Pavitt
- Faculty of Life Sciences, University of Manchester, United Kingdom.
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98
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Baird TD, Wek RC. Eukaryotic initiation factor 2 phosphorylation and translational control in metabolism. Adv Nutr 2012; 3:307-21. [PMID: 22585904 PMCID: PMC3649462 DOI: 10.3945/an.112.002113] [Citation(s) in RCA: 338] [Impact Index Per Article: 28.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Regulation of mRNA translation is a rapid and effective means to couple changes in the cellular environment with global rates of protein synthesis. In response to stresses, such as nutrient deprivation and accumulation of misfolded proteins in the endoplasmic reticulum, phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α~P) reduces general translation initiation while facilitating the preferential translation of select transcripts, such as that encoding activating transcription factor 4 (ATF4), a transcriptional activator of genes subject to the integrated stress response (ISR). In this review, we highlight the translational control processes regulated by nutritional stress, with an emphasis on the events triggered by eIF2α~P, and describe the family of eukaryotic initiation factor 2 kinases and the mechanisms by which each sense different stresses. We then address 3 questions. First, what are the mechanisms by which eIF2α~P confers preferential translation on select mRNA and what are the consequences of the gene expression induced by the ISR? Second, what are the molecular processes by which certain stresses can differentially activate eIF2α~P and ATF4 expression? The third question we address is what are the modes of cross-regulation between the ISR and other stress response pathways, such as the unfolded protein response and mammalian target of rapamycin, and how do these regulatory schemes provide for gene expression programs that are tailored for specific stresses? This review highlights recent advances in each of these areas of research, emphasizing how eIF2α~P and the ISR can affect metabolic health and disease.
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99
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Wang X, Wortham NC, Liu R, Proud CG. Identification of residues that underpin interactions within the eukaryotic initiation factor (eIF2) 2B complex. J Biol Chem 2012; 287:8263-74. [PMID: 22238342 DOI: 10.1074/jbc.m111.331553] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic initiation factor 2B (eIF2B) plays a key role in protein synthesis and in its control. It comprises five different subunits, α-ε, of which eIF2Bε contains the catalytic domain. Formation of the complete complex is crucial for full activity and proper control of eIF2B. Mutations in the genes for eIF2B cause an often severe neurological disorder, "vanishing white matter." eIF2Bγ and eIF2Bε contain homologous and conserved domains with sequence similarity to nucleotidyl transferases (NTs) and acyl transferases and can form a binary complex. The latter contain a hexad repeat that mainly comprises isoleucyl residues (hence termed the "I-patch" region). These data reveal that certain residues in the NT domains of eIF2Bγ/ε, which are highly conserved throughout eukaryotes, play key roles in the interactions between subunits in the eIF2B complex. Our data show that the I-patch regions are important in the interactions between the catalytic eIF2Bγε complex and the other subunits. We also studied the functional effects of vanishing white matter mutations in the NT and I-patch domains. Lastly, our data show that eIF2Bγ promotes the expression of eIF2Bε, providing a mechanism for achieving correct stoichiometry of these eIF2B subunits in the cell.
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Affiliation(s)
- Xuemin Wang
- Centre for Biological Sciences, Life Sciences Building, University of Southampton, Southampton SO17 1BJ, United Kingdom
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100
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Reid PJ, Mohammad-Qureshi SS, Pavitt GD. Identification of intersubunit domain interactions within eukaryotic initiation factor (eIF) 2B, the nucleotide exchange factor for translation initiation. J Biol Chem 2012; 287:8275-85. [PMID: 22238343 PMCID: PMC3318697 DOI: 10.1074/jbc.m111.331645] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
In eukaryotic translation initiation, eIF2B is the guanine nucleotide exchange factor (GEF) required for reactivation of the G protein eIF2 between rounds of protein synthesis initiation. eIF2B is unusually complex with five subunits (α–ϵ) necessary for GEF activity and its control by phosphorylation of eIF2α. In addition, inherited mutations in eIF2B cause a fatal leukoencephalopathy. Here we describe experiments examining domains of eIF2Bγ and ϵ that both share sequence and predicted tertiary structure similarity with a family of phospho-hexose sugar nucleotide pyrophosphorylases. Firstly, using a genetic approach, we find no evidence to support a significant role for a potential nucleotide-binding region within the pyrophosphorylase-like domain (PLD) of eIF2Bϵ for nucleotide exchange. These findings are at odds with one mechanism for nucleotide exchange proposed previously. By using a series of constructs and a co-expression and precipitation strategy, we find that the eIF2Bϵ and -γ PLDs and a shared second domain predicted to form a left-handed β helix are all critical for interprotein interactions between eIF2B subunits necessary for eIF2B complex formation. We have identified extensive interactions between the PLDs and left-handed β helix domains that form the eIF2Bγϵ subcomplex and propose a model for domain interactions between eIF2B subunits.
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Affiliation(s)
- Peter J Reid
- Faculty of Life Sciences, The University of Manchester, Oxford Road, Manchester M13 9PT, United Kingdom
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