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Hanson FM, Ribeiro de Oliveira MI, Cross AK, Allen KE, Campbell SG. eIF2B localization and its regulation during the integrated stress response is cell-type specific. iScience 2024; 27:110851. [PMID: 39310746 PMCID: PMC11414691 DOI: 10.1016/j.isci.2024.110851] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2024] [Revised: 04/30/2024] [Accepted: 08/27/2024] [Indexed: 09/25/2024] Open
Abstract
Eukaryotic initiation factor 2B (eIF2B) controls translation initiation by recycling inactive eIF2-GDP to active eIF2-GTP. Under cellular stress, the integrated stress response (ISR) is activated inhibiting eIF2B activity resulting in the translation attenuation and reprogramming of gene expression to overcome the stress. The ISR can dictate cell fate wherein chronic activation has pathological outcomes. Vanishing white matter disease (VWMD) is a chronic ISR-related disorder with mutations in eIF2B targeting astrocyte and oligodendrocyte cells. Regulation of eIF2B localization (eIF2B bodies) has been implicated in the ISR. We present evidence that neuronal and glial cell types possess distinct patterns of eIF2B bodies which change in a manner correlating to acute and chronic ISR activation. We also demonstrate that while neural and glial cell types respond similarly to the acute induction of the ISR a chronic ISR exerts cell-type specific differences. These findings provide key insights into neural cell responses and adaptation to cellular stress.
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Affiliation(s)
- Filipe M. Hanson
- Biomolecular Sciences Research Centre, Industry and Innovation Research Institute (IRI), Sheffield Hallam University, Sheffield S1 1WB, UK
| | - Madalena I. Ribeiro de Oliveira
- Biomolecular Sciences Research Centre, Industry and Innovation Research Institute (IRI), Sheffield Hallam University, Sheffield S1 1WB, UK
| | - Alison K. Cross
- Biomolecular Sciences Research Centre, Industry and Innovation Research Institute (IRI), Sheffield Hallam University, Sheffield S1 1WB, UK
| | - K. Elizabeth Allen
- Biomolecular Sciences Research Centre, Industry and Innovation Research Institute (IRI), Sheffield Hallam University, Sheffield S1 1WB, UK
| | - Susan G. Campbell
- Biomolecular Sciences Research Centre, Industry and Innovation Research Institute (IRI), Sheffield Hallam University, Sheffield S1 1WB, UK
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2
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The role of eIF2 phosphorylation in cell and organismal physiology: new roles for well-known actors. Biochem J 2022; 479:1059-1082. [PMID: 35604373 DOI: 10.1042/bcj20220068] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Revised: 04/21/2022] [Accepted: 04/25/2022] [Indexed: 02/06/2023]
Abstract
Control of protein synthesis (mRNA translation) plays key roles in shaping the proteome and in many physiological, including homeostatic, responses. One long-known translational control mechanism involves phosphorylation of initiation factor, eIF2, which is catalysed by any one of four protein kinases, which are generally activated in response to stresses. They form a key arm of the integrated stress response (ISR). Phosphorylated eIF2 inhibits eIF2B (the protein that promotes exchange of eIF2-bound GDP for GTP) and thus impairs general protein synthesis. However, this mechanism actually promotes translation of certain mRNAs by virtue of specific features they possess. Recent work has uncovered many previously unknown features of this regulatory system. Several studies have yielded crucial insights into the structure and control of eIF2, including that eIF2B is regulated by several metabolites. Recent studies also reveal that control of eIF2 and the ISR helps determine organismal lifespan and surprising roles in sensing mitochondrial stresses and in controlling the mammalian target of rapamycin (mTOR). The latter effect involves an unexpected role for one of the eIF2 kinases, HRI. Phosphoproteomic analysis identified new substrates for another eIF2 kinase, Gcn2, which senses the availability of amino acids. Several genetic disorders arise from mutations in genes for eIF2α kinases or eIF2B (i.e. vanishing white matter disease, VWM and microcephaly, epileptic seizures, microcephaly, hypogenitalism, diabetes and obesity, MEHMO). Furthermore, the eIF2-mediated ISR plays roles in cognitive decline associated with Alzheimer's disease. New findings suggest potential therapeutic value in interfering with the ISR in certain settings, including VWM, for example by using compounds that promote eIF2B activity.
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3
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Regulation and function of elF2B in neurological and metabolic disorders. Biosci Rep 2022; 42:231311. [PMID: 35579296 PMCID: PMC9208314 DOI: 10.1042/bsr20211699] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Revised: 04/28/2022] [Accepted: 05/12/2022] [Indexed: 11/27/2022] Open
Abstract
Eukaryotic initiation factor 2B, eIF2B is a guanine nucleotide exchange, factor with a central role in coordinating the initiation of translation. During stress and disease, the activity of eIF2B is inhibited via the phosphorylation of its substrate eIF2 (p-eIF2α). A number of different kinases respond to various stresses leading to the phosphorylation of the alpha subunit of eIF2, and collectively this regulation is known as the integrated stress response, ISR. This targeting of eIF2B allows the cell to regulate protein synthesis and reprogramme gene expression to restore homeostasis. Advances within structural biology have furthered our understanding of how eIF2B interacts with eIF2 in both the productive GEF active form and the non-productive eIF2α phosphorylated form. Here, current knowledge of the role of eIF2B in the ISR is discussed within the context of normal and disease states focusing particularly on diseases such as vanishing white matter disease (VWMD) and permanent neonatal diabetes mellitus (PNDM), which are directly linked to mutations in eIF2B. The role of eIF2B in synaptic plasticity and memory formation is also discussed. In addition, the cellular localisation of eIF2B is reviewed and considered along with the role of additional in vivo eIF2B binding factors and protein modifications that may play a role in modulating eIF2B activity during health and disease.
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4
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Xu L, Zhong M, Yang Y, Wang M, An N, Xu X, Zhu Y, Li Z, Chen H, Zhao R, Zheng X. Adult-onset vanishing white matter in a patient with EIF2B3 variants misdiagnosed as multiple sclerosis. Neurol Sci 2021; 43:2659-2667. [PMID: 34755279 DOI: 10.1007/s10072-021-05710-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Accepted: 10/29/2021] [Indexed: 11/26/2022]
Abstract
BACKGROUND Vanishing white matter (VWM) is an autosomal recessive disorder characterized by childhood ataxia with central hypomyelination. Adult-onset VWM should be considered as a differential diagnosis for suspected cases of multiple sclerosis (MS). METHODS Targeted region sequencing (TRS) and Sanger sequencing validation were performed to identify and validate the likely pathogenic mutations in a family with VWM. RESULTS The main clinical manifestations of the proband included decreased vision and sleepiness accompanied by atrophy of the corpus callosum, affected inner rim of the corpus callosum, decreased apparent diffusion coefficient value or persistent hyperintensity-diffusion-weighted imaging, atrophied optic nerve, and no recordable visual evoked potentials. Due to the slow development and atypical VWM image features, MS was initially suspected. After prednisone was administered, the patient's condition did not improve significantly, and other diseases were considered. The TRS and Sanger sequencing identified compound heterozygous mutations of EIF2B3 in the proband; c.965C > G /p.Ala322Gly in exon 8 and c.130G > A/p.Glu44Lys in exon 2 were missense mutations inherited from the mother and father, respectively. The proband's oldest brother had the same compound heterozygous mutations but showed no symptoms. CONCLUSION This is the first report of adult-onset VWM in a Chinese family. Initially, MS was suspected, and genetic testing confirmed the diagnosis of VWM. This study may further broaden the clinical spectrum of EIF2B3, thus providing a foundation for further research on the pathogenesis and genetic therapy for VWM.
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Affiliation(s)
- Lulu Xu
- Department of Geriatric Medicine, the Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266000, Shandong, China
| | - Meixiang Zhong
- Department of Geriatric Medicine, the Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266000, Shandong, China
| | - Yuyuan Yang
- Department of Geriatric Medicine, the Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266000, Shandong, China
| | - Meng Wang
- Department of Geriatric Medicine, the Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266000, Shandong, China
| | - Nina An
- Department of Geriatric Medicine, the Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266000, Shandong, China
| | - Xin Xu
- Department of Neurology, the Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266000, Shandong, China
| | - Yufeng Zhu
- Department of Graduate School, Qinghai University, Xining, 810016, Qinghai, China
| | - Zengwen Li
- Department of Radiology, Gaomi Municipal Hospital, Gaomi, 261500, Shandong, China
| | - Huili Chen
- Department of Ophthalmology, Yijishan Hospital of Wannan Medical College, Wuhu, 241000, China
| | - Renliang Zhao
- Department of Neurology, the Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266000, Shandong, China.
| | - Xueping Zheng
- Department of Geriatric Medicine, the Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266000, Shandong, China.
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5
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Slynko I, Nguyen S, Hamilton EMC, Wisse LE, de Esch IJP, de Graaf C, Bruning JB, Proud CG, Abbink TEM, van der Knaap MS. Vanishing white matter: Eukaryotic initiation factor 2B model and the impact of missense mutations. Mol Genet Genomic Med 2021; 9:e1593. [PMID: 33432707 PMCID: PMC8104162 DOI: 10.1002/mgg3.1593] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Revised: 12/12/2020] [Accepted: 12/21/2020] [Indexed: 12/21/2022] Open
Abstract
Background Vanishing white matter (VWM) is a leukodystrophy, caused by recessive mutations in eukaryotic initiation factor 2B (eIF2B)‐subunit genes (EIF2B1–EIF2B5); 80% are missense mutations. Clinical severity is highly variable, with a strong, unexplained genotype–phenotype correlation. Materials and Methods With information from a recent natural history study, we severity‐graded 97 missense mutations. Using in silico modeling, we created a new human eIF2B model structure, onto which we mapped the missense mutations. Mutated residues were assessed for location in subunits, eIF2B complex, and functional domains, and for information on biochemical activity. Results Over 50% of mutations have (ultra‐)severe phenotypic effects. About 60% affect the ε‐subunit, containing the catalytic domain, mostly with (ultra‐)severe effects. About 55% affect subunit cores, with variable clinical severity. About 36% affect subunit interfaces, mostly with severe effects. Very few mutations occur on the external eIf2B surface, perhaps because they have minor functional effects and are tolerated. One external surface mutation affects eIF2B‐substrate interaction and is associated with ultra‐severe phenotype. Conclusion Mutations that lead to (ultra‐)severe disease mostly affect amino acids with pivotal roles in complex formation and function of eIF2B. Therapies for VWM are emerging and reliable mutation‐based phenotype prediction is required for propensity score matching for trials and in the future for individualized therapy decisions.
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Affiliation(s)
- Inna Slynko
- Division of Medicinal Chemistry, Amsterdam Institute for Molecules, Medicines and Systems, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
| | - Stephanie Nguyen
- Institute for Photonics and Advanced Sensing (IPAS), School of Biological Sciences, The University of Adelaide, Adelaide, SA, Australia
| | - Eline M C Hamilton
- Department of Child Neurology, Emma Children's Hospital, Amsterdam University Medical Centers, Vrije Universiteit and Amsterdam Neuroscience, Amsterdam, the Netherlands
| | - Lisanne E Wisse
- Department of Child Neurology, Emma Children's Hospital, Amsterdam University Medical Centers, Vrije Universiteit and Amsterdam Neuroscience, Amsterdam, the Netherlands
| | - Iwan J P de Esch
- Division of Medicinal Chemistry, Amsterdam Institute for Molecules, Medicines and Systems, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
| | - Chris de Graaf
- Division of Medicinal Chemistry, Amsterdam Institute for Molecules, Medicines and Systems, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
| | - John B Bruning
- Institute for Photonics and Advanced Sensing (IPAS), School of Biological Sciences, The University of Adelaide, Adelaide, SA, Australia
| | - Christopher G Proud
- Hopwood Centre for Neurobiology and Lifelong Health Theme, South Australian Health & Medical Research Institute, Adelaide, SA, Australia.,School of Biological Sciences, The University of Adelaide, Adelaide, SA, Australia
| | - Truus E M Abbink
- Department of Child Neurology, Emma Children's Hospital, Amsterdam University Medical Centers, Vrije Universiteit and Amsterdam Neuroscience, Amsterdam, the Netherlands
| | - Marjo S van der Knaap
- Department of Child Neurology, Emma Children's Hospital, Amsterdam University Medical Centers, Vrije Universiteit and Amsterdam Neuroscience, Amsterdam, the Netherlands.,Department of Functional Genomics, Amsterdam Neuroscience, VU University, Amsterdam, the Netherlands
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6
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Han NC, Kelly P, Ibba M. Translational quality control and reprogramming during stress adaptation. Exp Cell Res 2020; 394:112161. [PMID: 32619498 DOI: 10.1016/j.yexcr.2020.112161] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Revised: 06/26/2020] [Accepted: 06/29/2020] [Indexed: 12/18/2022]
Abstract
Organisms encounter stress throughout their lives, and therefore require the ability to respond rapidly to environmental changes. Although transcriptional responses are crucial for controlling changes in gene expression, regulation at the translational level often allows for a faster response at the protein levels which permits immediate adaptation. The fidelity and robustness of protein synthesis are actively regulated under stress. For example, mistranslation can be beneficial to cells upon environmental changes and also alters cellular stress responses. Additionally, stress modulates both global and selective translational regulation through mechanisms including the change of aminoacyl-tRNA activity, tRNA pool reprogramming and ribosome heterogeneity. In this review, we draw on studies from both the prokaryotic and eukaryotic systems to discuss current findings of cellular adaptation at the level of translation, specifically translational fidelity and activity changes in response to a wide array of environmental stressors including oxidative stress, nutrient depletion, temperature variation, antibiotics and host colonization.
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Affiliation(s)
- Nien-Ching Han
- Department of Microbiology, The Ohio State University, Columbus, OH, 43220, USA
| | - Paul Kelly
- The Ohio State University Molecular, Cellular and Developmental Biology Program, The Ohio State University, Columbus, OH, 43220, USA
| | - Michael Ibba
- Department of Microbiology, The Ohio State University, Columbus, OH, 43220, USA.
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7
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Marini G, Nüske E, Leng W, Alberti S, Pigino G. Reorganization of budding yeast cytoplasm upon energy depletion. Mol Biol Cell 2020; 31:1232-1245. [PMID: 32293990 PMCID: PMC7353153 DOI: 10.1091/mbc.e20-02-0125] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Yeast cells, when exposed to stress, can enter a protective state in which cell division, growth, and metabolism are down-regulated. They remain viable in this state until nutrients become available again. How cells enter this protective survival state and what happens at a cellular and subcellular level are largely unknown. In this study, we used electron tomography to investigate stress-induced ultrastructural changes in the cytoplasm of yeast cells. After ATP depletion, we observed significant cytosolic compaction and extensive cytoplasmic reorganization, as well as the emergence of distinct membrane-bound and membraneless organelles. Using correlative light and electron microscopy, we further demonstrated that one of these membraneless organelles was generated by the reversible polymerization of eukaryotic translation initiation factor 2B, an essential enzyme in the initiation of protein synthesis, into large bundles of filaments. The changes we observe are part of a stress-induced survival strategy, allowing yeast cells to save energy, protect proteins from degradation, and inhibit protein functionality by forming assemblies of proteins.
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Affiliation(s)
- Guendalina Marini
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany
| | - Elisabeth Nüske
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany
| | - Weihua Leng
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany
| | - Simon Alberti
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany
| | - Gaia Pigino
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany
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8
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Marintchev A, Ito T. eIF2B and the Integrated Stress Response: A Structural and Mechanistic View. Biochemistry 2020; 59:1299-1308. [PMID: 32200625 DOI: 10.1021/acs.biochem.0c00132] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The eukaryotic translation initiation factor eIF2 is a GTPase, which brings the initiator Met-tRNAi to the ribosome as the eIF2-GTP·Met-tRNAi ternary complex (TC). TC regeneration is catalyzed by the guanine nucleotide exchange factor (GEF) eIF2B. eIF2 phosphorylation by several stress-induced kinases converts it into a competitive inhibitor of eIF2B. Inhibition of eIF2B activity lowers cellular TC concentrations, which in turn triggers the integrated stress response (ISR). Depending on its degree of activation and duration, the ISR protects the cell from the stress or can itself induce apoptosis. ISR dysregulation is a causative factor in the pathology of multiple neurodegenerative disorders, while ISR inhibitors are neuroprotective. The realization that eIF2B is a promising therapeutic target has triggered significant interest in its structure and its mechanisms of action and regulation. Recently, four groups published the cryo-electron microscopy structures of eIF2B with its substrate eIF2 and/or its inhibitor, phosphorylated eIF2 [eIF2(α-P)]. While all three structures of the nonproductive eIF2B·eIF2(α-P) complex are similar to each other, there is a sharp disagreement between the published structures of the productive eIF2B·eIF2 complex. One group reports a structure similar to that of the nonproductive complex, whereas two others observe a vastly different eIF2B·eIF2 complex. Here, we discuss the recent reports on the structure, function, and regulation of eIF2B; the preclinical data on the use of ISR inhibitors for the treatment of neurodegenerative disorders; and how the new structural and biochemical information can inform and influence the use of eIF2B as a therapeutic target.
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Affiliation(s)
- Assen Marintchev
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118, United States
| | - Takuhiro Ito
- RIKEN Center for Biosystems Dynamics Research, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
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9
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Che Y, Fu L. Aberrant expression and regulatory network of splicing factor-SRSF3 in tumors. J Cancer 2020; 11:3502-3511. [PMID: 32284746 PMCID: PMC7150454 DOI: 10.7150/jca.42645] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Accepted: 02/26/2020] [Indexed: 12/14/2022] Open
Abstract
Alternative splicing facilitates the splicing of precursor RNA into different isoforms. Alternatively spliced transcripts often exhibit antagonistic functions or differential temporal or spatial expression patterns. There is increasing evidence that alternative splicing, especially by the serine-arginine rich (SR) protein family, leads to abnormal expression patterns and is closely related to the development of cancer. SRSF3, also known as SRp20, is a splicing factor. Through alternative splicing, it plays important roles in regulating various biological functions, such as cell cycle, cell proliferation, migration and invasion, under pathological and physiological conditions. Deregulation of SRSF3 is an essential feature of cancers. SRSF3 is also considered a candidate therapeutic target. Therefore, the involvement of abnormal splicing in tumorigenesis and the regulation of splicing factors deserve further analysis and discussion. Here, we summarize the function of SRSF3-regulated alternative transcripts in cancer cell biology at different stages of tumor development and the regulation of SRSF3 in tumorigenesis.
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Affiliation(s)
- Yingying Che
- Institute of Chronic Disease, Qingdao Municipal Hospital, Qingdao University, Qingdao 266000, China
| | - Lin Fu
- Institute of Chronic Disease, Qingdao Municipal Hospital, Qingdao University, Qingdao 266000, China
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10
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Kashiwagi K, Yokoyama T, Nishimoto M, Takahashi M, Sakamoto A, Yonemochi M, Shirouzu M, Ito T. Structural basis for eIF2B inhibition in integrated stress response. Science 2019; 364:495-499. [PMID: 31048492 DOI: 10.1126/science.aaw4104] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 04/05/2019] [Indexed: 01/02/2023]
Abstract
A core event in the integrated stress response, an adaptive pathway common to all eukaryotic cells in response to various stress stimuli, is the phosphorylation of eukaryotic translation initiation factor 2 (eIF2). Normally, unphosphorylated eIF2 transfers the methionylated initiator tRNA to the ribosome in a guanosine 5'-triphosphate-dependent manner. By contrast, phosphorylated eIF2 inhibits its specific guanine nucleotide exchange factor, eIF2B. To elucidate how the eIF2 phosphorylation status regulates the eIF2B activity, we determined cryo-electron microscopic and crystallographic structures of eIF2B in complex with unphosphorylated or phosphorylated eIF2. The unphosphorylated and phosphorylated forms of eIF2 bind to eIF2B in completely different manners: the nucleotide exchange-active and -inactive modes, respectively. These structures explain how phosphorylated eIF2 dominantly inhibits the nucleotide exchange activity of eIF2B.
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Affiliation(s)
- Kazuhiro Kashiwagi
- RIKEN Center for Biosystems Dynamics Research, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Takeshi Yokoyama
- RIKEN Center for Biosystems Dynamics Research, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Madoka Nishimoto
- RIKEN Center for Biosystems Dynamics Research, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Mari Takahashi
- RIKEN Center for Biosystems Dynamics Research, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Ayako Sakamoto
- RIKEN Center for Biosystems Dynamics Research, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Mayumi Yonemochi
- RIKEN Center for Biosystems Dynamics Research, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Mikako Shirouzu
- RIKEN Center for Biosystems Dynamics Research, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Takuhiro Ito
- RIKEN Center for Biosystems Dynamics Research, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan.
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11
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Terumitsu-Tsujita M, Kitaura H, Miura I, Kiyama Y, Goto F, Muraki Y, Ominato S, Hara N, Simankova A, Bizen N, Kashiwagi K, Ito T, Toyoshima Y, Kakita A, Manabe T, Wakana S, Takebayashi H, Igarashi H. Glial pathology in a novel spontaneous mutant mouse of the Eif2b5 gene: a vanishing white matter disease model. J Neurochem 2019; 154:25-40. [PMID: 31587290 DOI: 10.1111/jnc.14887] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 05/24/2019] [Accepted: 09/23/2019] [Indexed: 12/12/2022]
Abstract
Vanishing white matter disease (VWM) is an autosomal recessive neurological disorder caused by mutation(s) in any subunit of eukaryotic translation initiation factor 2B (eIF2B), an activator of translation initiation factor eIF2. VWM occurs with mutation of the genes encoding eIF2B subunits (EIF2B1, EIF2B2, EIF2B3, EIF2B4, and EIF2B5). However, little is known regarding the underlying pathogenetic mechanisms or how to treat patients with VWM. Here we describe the identification and detailed analysis of a new spontaneous mutant mouse harboring a point mutation in the Eif2b5 gene (p.Ile98Met). Homozygous Eif2b5I98M mutant mice exhibited a small body, abnormal gait, male and female infertility, epileptic seizures, and a shortened lifespan. Biochemical analyses indicated that the mutant eIF2B protein with the Eif2b5I98M mutation decreased guanine nucleotide exchange activity on eIF2, and the level of the endoplasmic reticulum stress marker activating transcription factor 4 was elevated in the 1-month-old Eif2b5I98M brain. Histological analyses indicated up-regulated glial fibrillary acidic protein immunoreactivity in the astrocytes of the Eif2b5I98M forebrain and translocation of Bergmann glia in the Eif2b5I98M cerebellum, as well as increased mRNA expression of an endoplasmic reticulum stress marker, C/EBP homologous protein. Disruption of myelin and clustering of oligodendrocyte progenitor cells were also indicated in the white matter of the Eif2b5I98M spinal cord at 8 months old. Our data show that Eif2b5I98M mutants are a good model for understanding VWM pathogenesis and therapy development. Cover Image for this issue: doi: 10.1111/jnc.14751.
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Affiliation(s)
- Mika Terumitsu-Tsujita
- Center for Integrated Human Brain Science, Brain Research Institute, Niigata University, Niigata, Japan.,Division of Neuronal Network, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan.,Administrative Section of Radiation Protection, National Center of Neurology and Psychiatry, National Institute of Neuroscience, Kodaira, Tokyo, Japan
| | - Hiroki Kitaura
- Center for Integrated Human Brain Science, Brain Research Institute, Niigata University, Niigata, Japan.,Department of Pathology, Brain Research Institute, Niigata University, Niigata, Japan
| | - Ikuo Miura
- Technology and Development Team for Mouse Phenotype Analysis, The Japan Mouse Clinic, RIKEN BioResource Research Center, Ibaraki, Japan
| | - Yuji Kiyama
- Division of Neuronal Network, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Fumiko Goto
- Division of Neuronal Network, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Yoshiko Muraki
- Center for Integrated Human Brain Science, Brain Research Institute, Niigata University, Niigata, Japan
| | - Shiho Ominato
- Center for Integrated Human Brain Science, Brain Research Institute, Niigata University, Niigata, Japan
| | - Norikazu Hara
- Department of Molecular Genetics, Brain Research Institute, Niigata University, Niigata, Japan
| | - Anna Simankova
- Division of Neurobiology and Anatomy, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan
| | - Norihisa Bizen
- Division of Neurobiology and Anatomy, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan
| | - Kazuhiro Kashiwagi
- Laboratory for Translation Structural Biology, RIKEN Center for Biosystems Dynamics Research, Tsurumi-ku, Yokohama, Japan
| | - Takuhiro Ito
- Laboratory for Translation Structural Biology, RIKEN Center for Biosystems Dynamics Research, Tsurumi-ku, Yokohama, Japan
| | - Yasuko Toyoshima
- Department of Pathology, Brain Research Institute, Niigata University, Niigata, Japan
| | - Akiyoshi Kakita
- Department of Pathology, Brain Research Institute, Niigata University, Niigata, Japan
| | - Toshiya Manabe
- Division of Neuronal Network, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Shigeharu Wakana
- Technology and Development Team for Mouse Phenotype Analysis, The Japan Mouse Clinic, RIKEN BioResource Research Center, Ibaraki, Japan
| | - Hirohide Takebayashi
- Division of Neurobiology and Anatomy, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan.,Center for Coordination of Research Facilities, Niigata University, Niigata, Japan
| | - Hironaka Igarashi
- Center for Integrated Human Brain Science, Brain Research Institute, Niigata University, Niigata, Japan
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12
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Lin Y, Liang A, He Y, Li Z, Li Z, Wang G, Sun F. Proteomic analysis of seminal extracellular vesicle proteins involved in asthenozoospermia by iTRAQ. Mol Reprod Dev 2019; 86:1094-1105. [PMID: 31215738 DOI: 10.1002/mrd.23224] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2018] [Revised: 05/22/2019] [Accepted: 05/24/2019] [Indexed: 12/13/2022]
Affiliation(s)
- Yu Lin
- International Peace Maternity & Child Health Hospital, Shanghai Key laboratory of Embryo Original Diseases, School of MedicineShanghai Jiao Tong UniversityShanghai China
| | - Ajuan Liang
- Shanghai Key Laboratory for Assisted Reproduction and Reproductive Genetics, Center for Reproductive Medicine, Renji Hospital, School of MedicineShanghai Jiao Tong UniversityShanghai China
| | - Yue He
- International Peace Maternity & Child Health Hospital, Shanghai Key laboratory of Embryo Original Diseases, School of MedicineShanghai Jiao Tong UniversityShanghai China
| | - Zhengzheng Li
- International Peace Maternity & Child Health Hospital, Shanghai Key laboratory of Embryo Original Diseases, School of MedicineShanghai Jiao Tong UniversityShanghai China
| | - Zhenhua Li
- International Peace Maternity & Child Health Hospital, Shanghai Key laboratory of Embryo Original Diseases, School of MedicineShanghai Jiao Tong UniversityShanghai China
| | - Guishuan Wang
- Medical School, Institute of Reproductive MedicineNantong UniversityNantong China
| | - Fei Sun
- International Peace Maternity & Child Health Hospital, Shanghai Key laboratory of Embryo Original Diseases, School of MedicineShanghai Jiao Tong UniversityShanghai China
- Medical School, Institute of Reproductive MedicineNantong UniversityNantong China
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Gordiyenko Y, Llácer JL, Ramakrishnan V. Structural basis for the inhibition of translation through eIF2α phosphorylation. Nat Commun 2019; 10:2640. [PMID: 31201334 PMCID: PMC6572841 DOI: 10.1038/s41467-019-10606-1] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Accepted: 05/10/2019] [Indexed: 11/29/2022] Open
Abstract
One of the responses to stress by eukaryotic cells is the down-regulation of protein synthesis by phosphorylation of translation initiation factor eIF2. Phosphorylation results in low availability of the eIF2 ternary complex (eIF2-GTP-tRNAi) by affecting the interaction of eIF2 with its GTP-GDP exchange factor eIF2B. We have determined the cryo-EM structure of yeast eIF2B in complex with phosphorylated eIF2 at an overall resolution of 4.2 Å. Two eIF2 molecules bind opposite sides of an eIF2B hetero-decamer through eIF2α-D1, which contains the phosphorylated Ser51. eIF2α-D1 is mainly inserted between the N-terminal helix bundle domains of δ and α subunits of eIF2B. Phosphorylation of Ser51 enhances binding to eIF2B through direct interactions of phosphate groups with residues in eIF2Bα and indirectly by inducing contacts of eIF2α helix 58–63 with eIF2Bδ leading to a competition with Met-tRNAi. During stress, protein synthesis is inhibited through phosphorylation of the initiation factor eIF2 on its alpha subunit and its interaction with eIF2B. Here the authors describe a structure of the yeast eIF2B in complex with its substrate - the GDP-bound phosphorylated eIF2, providing insights into how phosphorylation results in a tighter interaction with eIF2B.
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Affiliation(s)
- Yuliya Gordiyenko
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK
| | - José Luis Llácer
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK. .,Instituto de Biomedicina de Valencia del Consejo Superior de Investigaciones Científicas and CIBERER-ISCIII, Valencia, 46010, Spain.
| | - V Ramakrishnan
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK
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Analysis of eIF2B bodies and their relationships with stress granules and P-bodies. Sci Rep 2018; 8:12264. [PMID: 30115954 PMCID: PMC6095920 DOI: 10.1038/s41598-018-30805-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Accepted: 08/06/2018] [Indexed: 12/02/2022] Open
Abstract
Eukaryotic cells respond to stress and changes in the environment in part by repressing translation and forming cytoplasmic assemblies called stress granules and P-bodies, which harbor non-translating mRNAs and proteins. A third, but poorly understood, assembly called the eIF2B body can form and contains the eIF2B complex, an essential guanine exchange factor for the translation initiation factor eIF2. Hypomorphic EIF2B alleles can lead to Vanishing White Matter Disease (VWMD), a leukodystrophy that causes progressive white matter loss. An unexplored question is how eIF2B body formation is controlled and whether VWMD alleles in EIF2B alter the formation of eIF2B bodies, stress granules, or P-bodies. To examine these issues, we assessed eIF2B body, stress granule, and P-body induction in wild-type yeast cells and cells carrying VWMD alleles in the EIF2B2 (GCD7) and EIF2B5 (GCD6) subunits of eIF2B. We demonstrate eIF2B bodies are rapidly and reversibly formed independently of stress granules during acute glucose deprivation. VWMD mutations had diverse effects on stress-induced assemblies with some alleles altering eIF2B bodies, and others leading to increased P-body formation. Moreover, some VWMD-causing mutations in GCD7 caused hyper-sensitivity to chronic GCN2 activation, consistent with VWMD mutations causing hyper-sensitivity to eIF2α phosphorylation and thereby impacting VWMD pathogenesis.
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Pavitt GD. Regulation of translation initiation factor eIF2B at the hub of the integrated stress response. WILEY INTERDISCIPLINARY REVIEWS-RNA 2018; 9:e1491. [PMID: 29989343 DOI: 10.1002/wrna.1491] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2018] [Revised: 05/08/2018] [Accepted: 05/22/2018] [Indexed: 12/29/2022]
Abstract
Phosphorylation of the translation initiation factor eIF2 is one of the most widely used and well-studied mechanisms cells use to respond to diverse cellular stresses. Known as the integrated stress response (ISR), the control pathway uses modulation of protein synthesis to reprogram gene expression and restore homeostasis. Here the current knowledge of the molecular mechanisms of eIF2 activation and its control by phosphorylation at a single-conserved phosphorylation site, serine 51 are discussed with a major focus on the regulatory roles of eIF2B and eIF5 where a current molecular view of ISR control of eIF2B activity is presented. How genetic disorders affect eIF2 or eIF2B is discussed, as are syndromes where excess signaling through the ISR is a component. Finally, studies into the action of recently identified compounds that modulate the ISR in experimental systems are discussed; these suggest that eIF2B is a potential therapeutic target for a wide range of conditions. This article is categorized under: Translation > Translation Regulation.
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Affiliation(s)
- Graham D Pavitt
- Division Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, UK
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16
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Roy S, Jagus R, Morse D. Translation and Translational Control in Dinoflagellates. Microorganisms 2018; 6:microorganisms6020030. [PMID: 29642465 PMCID: PMC6027434 DOI: 10.3390/microorganisms6020030] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Revised: 04/03/2018] [Accepted: 04/05/2018] [Indexed: 12/24/2022] Open
Abstract
Dinoflagellates are unicellular protists that feature a multitude of unusual nuclear features, including large genomes, packaging of DNA without histones, and multiple gene copies organized as tandem gene arrays. Furthermore, all dinoflagellate mRNAs experience trans-splicing with a common 22-nucleotide splice leader (SL) sequence. These features challenge some of the concepts and assumptions about the regulation of gene expression derived from work on model eukaryotes such as yeasts and mammals. Translational control in the dinoflagellates, based on extensive study of circadian bioluminescence and by more recent microarray and transcriptome analyses, is now understood to be a crucial element in regulating gene expression. A picture of the translation machinery of dinoflagellates is emerging from the recent availability of transcriptomes of multiple dinoflagellate species and the first complete genome sequences. The components comprising the translational control toolkit of dinoflagellates are beginning to take shape and are outlined here.
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Affiliation(s)
- Sougata Roy
- Institut de Recherche en Biologie Végétale, Département de Sciences Biologiques, Université de Montréal, 4101 Sherbrooke East, Montréal, QC H1X 2B2, Canada.
| | - Rosemary Jagus
- Institute of Marine & Environmental Technology, University of Maryland Center for Environmental Science701 E. Pratt St., Baltimore, MD 21202, USA.
| | - David Morse
- Institut de Recherche en Biologie Végétale, Département de Sciences Biologiques, Université de Montréal, 4101 Sherbrooke East, Montréal, QC H1X 2B2, Canada.
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Brady LK, Wang H, Radens CM, Bi Y, Radovich M, Maity A, Ivan C, Ivan M, Barash Y, Koumenis C. Transcriptome analysis of hypoxic cancer cells uncovers intron retention in EIF2B5 as a mechanism to inhibit translation. PLoS Biol 2017; 15:e2002623. [PMID: 28961236 PMCID: PMC5636171 DOI: 10.1371/journal.pbio.2002623] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Revised: 10/11/2017] [Accepted: 09/07/2017] [Indexed: 01/09/2023] Open
Abstract
Cells adjust to hypoxic stress within the tumor microenvironment by downregulating energy-consuming processes including translation. To delineate mechanisms of cellular adaptation to hypoxia, we performed RNA-Seq of normoxic and hypoxic head and neck cancer cells. These data revealed a significant down regulation of genes known to regulate RNA processing and splicing. Exon-level analyses classified > 1,000 mRNAs as alternatively spliced under hypoxia and uncovered a unique retained intron (RI) in the master regulator of translation initiation, EIF2B5. Notably, this intron was expressed in solid tumors in a stage-dependent manner. We investigated the biological consequence of this RI and demonstrate that its inclusion creates a premature termination codon (PTC), that leads to a 65kDa truncated protein isoform that opposes full-length eIF2Bε to inhibit global translation. Furthermore, expression of 65kDa eIF2Bε led to increased survival of head and neck cancer cells under hypoxia, providing evidence that this isoform enables cells to adapt to conditions of low oxygen. Additional work to uncover -cis and -trans regulators of EIF2B5 splicing identified several factors that influence intron retention in EIF2B5: a weak splicing potential at the RI, hypoxia-induced expression and binding of the splicing factor SRSF3, and increased binding of total and phospho-Ser2 RNA polymerase II specifically at the intron retained under hypoxia. Altogether, these data reveal differential splicing as a previously uncharacterized mode of translational control under hypoxia and are supported by a model in which hypoxia-induced changes to cotranscriptional processing lead to selective retention of a PTC-containing intron in EIF2B5.
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Affiliation(s)
- Lauren K. Brady
- Department of Radiation Oncology Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- Cellular and Molecular Biology Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
| | - Hejia Wang
- Department of Biochemistry and Molecular Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
| | - Caleb M. Radens
- Cellular and Molecular Biology Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
| | - Yue Bi
- Department of Radiation Oncology Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- Oncology Center, Zhujiang Hospital of Southern Medical University, Guangzhou, Guangdong, China
| | - Milan Radovich
- Indiana University Health Precision Genomics Program, Indianapolis, Indiana, United States of America
- Indiana University Melvin and Bren Simon Cancer Center, Indianapolis, Indiana, United States of America
| | - Amit Maity
- Department of Radiation Oncology Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Cristina Ivan
- Center for RNA Interference and Non-coding RNAs, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
| | - Mircea Ivan
- Department of Medicine, Indiana University Melvin and Bren Simon Cancer Center, Indianapolis, Indiana, United States of America
| | - Yoseph Barash
- Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States of America
- Department of Computer and Information Science, University of Pennsylvania, Philadelphia, United States of America
| | - Constantinos Koumenis
- Department of Radiation Oncology Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
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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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19
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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: 93] [Impact Index Per Article: 13.3] [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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20
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Multiple Sclerosis and EIF2B5: A Paradox or a Missing Link. MULTIPLE SCLEROSIS: BENCH TO BEDSIDE 2017; 958:57-64. [DOI: 10.1007/978-3-319-47861-6_5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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21
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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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22
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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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23
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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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OLA1 regulates protein synthesis and integrated stress response by inhibiting eIF2 ternary complex formation. Sci Rep 2015; 5:13241. [PMID: 26283179 PMCID: PMC4539610 DOI: 10.1038/srep13241] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Accepted: 07/10/2015] [Indexed: 01/06/2023] Open
Abstract
Translation is a fundamental cellular process, and its dysregulation can contribute to human diseases such as cancer. During translation initiation the eukaryotic initiation factor 2 (eIF2) forms a ternary complex (TC) with GTP and the initiator methionyl-tRNA (tRNAi), mediating ribosomal recruitment of tRNAi. Limiting TC availability is a central mechanism for triggering the integrated stress response (ISR), which suppresses global translation in response to various cellular stresses, but induces specific proteins such as ATF4. This study shows that OLA1, a member of the ancient Obg family of GTPases, is an eIF2-regulatory protein that inhibits protein synthesis and promotes ISR by binding eIF2, hydrolyzing GTP, and interfering with TC formation. OLA1 thus represents a novel mechanism of translational control affecting de novo TC formation, different from the traditional model in which phosphorylation of eIF2α blocks the regeneration of TC. Depletion of OLA1 caused a hypoactive ISR and greater survival in stressed cells. In vivo, OLA1-knockdown rendered cancer cells deficient in ISR and the downstream proapoptotic effector, CHOP, promoting tumor growth and metastasis. Our work suggests that OLA1 is a novel translational GTPase and plays a suppressive role in translation and cell survival, as well as cancer growth and progression.
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25
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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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26
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Ferreira MC, Dorboz I, Boespflug-Tanguy O. Efficient detection of frequent eIF2B mutations for the rapid molecular diagnosis of CACH/VWM syndrome. Clin Biochem 2015; 48:1317-23. [PMID: 26162493 DOI: 10.1016/j.clinbiochem.2015.07.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2015] [Revised: 06/05/2015] [Accepted: 07/02/2015] [Indexed: 10/23/2022]
Abstract
OBJECTIVES The aim of this study was to develop a reliable, rapid and cost-effective molecular diagnostic assay allowing widespread routine investigation of eIF2B-related disorders (CACH/VWM syndrome). This heterogeneous disease is caused by autosomal recessive mutations in the genes encoding the five subunits of the translation-initiation factor eIF2B. Such a diagnostic method would be particularly adapted to the apparently acute presentation of the disease. DESIGN AND METHODS We developed a multiplex PCR amplification method for 7 genomic regions of the eIF2B genes in a single run. This method targeted the 8 most frequent mutations representing 61.4% of all mutations identified to date in our laboratory. These mutations affected eIF2B2 exon 5, eIF2B3 exon 2, eIF2B4 exons 8 and 11 and eIF2B5 exons 5, 7 and 8. PCR products were then pooled and subjected to a primer-extension assay validated using previously genotyped samples. RESULTS The results were compared to screening and/or direct sequencing methods: 100% agreement between methods confirmed equivalent sensitivity and specificity. The new assay was highly superior in terms of cost, time to results and robustness despite sample heterogeneity. CONCLUSIONS This genotyping strategy allows the detection of all eIF2B mutations targeted. A second multiplex primer-extension assay is in development to detect the 11 next-most frequent mutations, thus raising the global detection rate to 76.8%. Our approach is widely applicable as it involves standard techniques and equipment. Moreover, it can easily be further adapted to the clinical and genetic heterogeneity of eIF2B-related disorders by including or excluding mutations.
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Affiliation(s)
- Marie-Céleste Ferreira
- CHU Clermont-Ferrand, Molecular Biology Laboratory, Biochemistry Department, Clermont-Ferrand, France; GReD, UMR INSERM 931, CNRS 6247, Faculty of Medicine, Clermont-Ferrand, France.
| | - Imen Dorboz
- Inserm U1141, Paris Diderot University, Sorbonne Paris Cité, DHU PROTECT, Robert Debré Hospital, Paris, France.
| | - Odile Boespflug-Tanguy
- Inserm U1141, Paris Diderot University, Sorbonne Paris Cité, DHU PROTECT, Robert Debré Hospital, Paris, France; Reference Center For Leukodystrophies, Department of Neuropediatrics and Metabolic Diseases, Robert Debré Hospital, AP-HP, Paris, France.
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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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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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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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Hinnebusch AG, Lorsch JR. The mechanism of eukaryotic translation initiation: new insights and challenges. Cold Spring Harb Perspect Biol 2012; 4:cshperspect.a011544. [PMID: 22815232 DOI: 10.1101/cshperspect.a011544] [Citation(s) in RCA: 340] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Translation initiation in eukaryotes is a highly regulated and complex stage of gene expression. It requires the action of at least 12 initiation factors, many of which are known to be the targets of regulatory pathways. Here we review our current understanding of the molecular mechanics of eukaryotic translation initiation, focusing on recent breakthroughs from in vitro and in vivo studies. We also identify important unanswered questions that will require new ideas and techniques to solve.
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Affiliation(s)
- Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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Shimada S, Miya K, Oda N, Watanabe Y, Kumada T, Sugawara M, Shimojima K, Yamamoto T. An unmasked mutation of EIF2B2 due to submicroscopic deletion of 14q24.3 in a patient with vanishing white matter disease. Am J Med Genet A 2012; 158A:1771-7. [PMID: 22678813 DOI: 10.1002/ajmg.a.35431] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2011] [Accepted: 03/29/2012] [Indexed: 12/21/2022]
Abstract
Leukodystrophy with vanishing white matter (VWM) is a neurodegenerative disorder with autosomal recessive traits that is caused by alteration of the eukaryotic translation initiation factor-2B (EIF2B). An 11-month-old patient with distinctive features began to exhibit progressive developmental deterioration associated with intractable epilepsy, which was triggered by recurrent acute infectious diseases. Brain magnetic resonance imaging (MRI) revealed abnormal white matter intensity. Chromosomal microarray testing identified a submicroscopic deletion at 14q24.3 that included EIF2B2, the gene encoding one of the subunits of EIF2B. Because the patient's clinical findings were distinctive for VWM, compound heterozygous mutations of EIF2B2 were suspected, and subsequent sequencing analysis of the remaining allele unmasked the existence of a novel missense mutation of EIF2B2 (V85W). Some distinctive features including small palpebral fissures, bushy eyebrows, ear abnormalities, small upturned nose, downturned corners of the mouth, and micrognathia may be the common features of the patients with 14q24.3 deletions.
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Affiliation(s)
- Shino Shimada
- Tokyo Women's Medical University Institute of Integrated Medical Sciences, Tokyo, Japan
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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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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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Singh CR, Watanabe R, Zhou D, Jennings MD, Fukao A, Lee B, Ikeda Y, Chiorini JA, Campbell SG, Ashe MP, Fujiwara T, Wek RC, Pavitt GD, Asano K. Mechanisms of translational regulation by a human eIF5-mimic protein. Nucleic Acids Res 2011; 39:8314-28. [PMID: 21745818 PMCID: PMC3201852 DOI: 10.1093/nar/gkr339] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Revised: 04/22/2011] [Accepted: 04/25/2011] [Indexed: 11/29/2022] Open
Abstract
The translation factor eIF5 is an important partner of eIF2, directly modulating its function in several critical steps. First, eIF5 binds eIF2/GTP/Met-tRNA(i)(Met) ternary complex (TC), promoting its recruitment to 40S ribosomal subunits. Secondly, its GTPase activating function promotes eIF2 dissociation for ribosomal subunit joining. Finally, eIF5 GDP dissociation inhibition (GDI) activity can antagonize eIF2 reactivation by competing with the eIF2 guanine exchange factor (GEF), eIF2B. The C-terminal domain (CTD) of eIF5, a W2-type HEAT domain, mediates its interaction with eIF2. Here, we characterize a related human protein containing MA3- and W2-type HEAT domains, previously termed BZW2 and renamed here as eIF5-mimic protein 1 (5MP1). Human 5MP1 interacts with eIF2 and eIF3 and inhibits general and gene-specific translation in mammalian systems. We further test whether 5MP1 is a mimic or competitor of the GEF catalytic subunit eIF2Bε or eIF5, using yeast as a model. Our results suggest that 5MP1 interacts with yeast eIF2 and promotes TC formation, but inhibits TC binding to the ribosome. Moreover, 5MP1 is not a GEF but a weak GDI for yeast eIF2. We propose that 5MP1 is a partial mimic and competitor of eIF5, interfering with the key steps by which eIF5 regulates eIF2 function.
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Affiliation(s)
- Chingakham Ranjit Singh
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Ryosuke Watanabe
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Donghui Zhou
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Martin D. Jennings
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Akira Fukao
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Bumjun Lee
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Yuka Ikeda
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - John A. Chiorini
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Susan G. Campbell
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Mark P. Ashe
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Toshinobu Fujiwara
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Ronald C. Wek
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Graham D. Pavitt
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
| | - Katsura Asano
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA, Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK, Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan and NIDCR, NIH, Bethesda, MD 20892, USA
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Liu R, van der Lei HD, Wang X, Wortham NC, Tang H, van Berkel CG, Mufunde TA, Huang W, van der Knaap MS, Scheper GC, Proud CG. Severity of vanishing white matter disease does not correlate with deficits in eIF2B activity or the integrity of eIF2B complexes. Hum Mutat 2011; 32:1036-45. [DOI: 10.1002/humu.21535] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2010] [Accepted: 05/02/2011] [Indexed: 01/28/2023]
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Leng X, Wu Y, Wang X, Pan Y, Wang J, Li J, Du L, Dai L, Wu X, Proud CG, Jiang Y. Functional analysis of recently identified mutations in eukaryotic translation initiation factor 2Bɛ (eIF2Bɛ) identified in Chinese patients with vanishing white matter disease. J Hum Genet 2011; 56:300-5. [PMID: 21307862 DOI: 10.1038/jhg.2011.9] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Vanishing white matter disease (VWM) is the first human hereditary disease known to be caused by defects in initiation of protein synthesis. Gene defects in each of the five subunits of eukaryotic translation initiation factor 2B (eIF2B α-ɛ) are responsible for the disease, although the mechanism of the pathogenesis is not well understood. In our previous study, four novel eIF2Bɛ mutations were found in Chinese patients: p.Asp62Val, p.Cys335Ser, p.Asn376Asp and p.Ser610-Asp613del. Functional analysis was performed on these mutations and the recently reported p.Arg269X. Our data showed that all resulted in a decrease in the guanine nucleotide exchange (GEF) activity of the eIF2B complex. p.Arg269X and p.Ser610-Asp613del mutants displayed the lowest activity, followed by p.Cys335Ser, p.Asn376Asp and p.Asp62Val. p.Arg269X and p.Ser610-Asp613del could not produce stable eIF2Bɛ, leading to almost complete loss-of-function. No evidence was obtained for the three missense mutations in changes in eIF2Bɛ protein level or eIF2BɛSer(540) phosphorylation, and disruption of holocomplex assembly, or binding to eIF2. All patients in our study had the classical phenotype. p.Asp62Val and p.Asn376Asp mutations caused only mildly decreased GEF activity, were probably responsible for relatively mild phenotype in cases of classical VWM.
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Affiliation(s)
- Xuerong Leng
- Pediatric Department, Peking University First Hospital, Beijing, China
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The beta/Gcd7 subunit of eukaryotic translation initiation factor 2B (eIF2B), a guanine nucleotide exchange factor, is crucial for binding eIF2 in vivo. Mol Cell Biol 2010; 30:5218-33. [PMID: 20805354 DOI: 10.1128/mcb.00265-10] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Eukaryotic translation initiation factor 2B (eIF2B) is the guanine nucleotide exchange factor (GEF) for eukaryotic translation initiation factor 2, which stimulates formation of the eIF2-GTP-Met-tRNA(i)(Met) ternary complex (TC) in a manner inhibited by phosphorylated eIF2 [eIF2(αP)]. While eIF2B contains five subunits, the ε/Gcd6 subunit is sufficient for GEF activity in vitro. The δ/Gcd2 and β/Gcd7 subunits function with α/Gcn3 in the eIF2B regulatory subcomplex that mediates tight, inhibitory binding of eIF2(αP)-GDP, but the essential functions of δ/Gcd2 and β/Gcd7 are not well understood. We show that the depletion of wild-type β/Gcd7, three lethal β/Gcd7 amino acid substitutions, and a synthetically lethal combination of substitutions in β/Gcd7 and eIF2α all impair eIF2 binding to eIF2B without reducing ε/Gcd6 abundance in the native eIF2B-eIF2 holocomplex. Additionally, β/Gcd7 mutations that impair eIF2B function display extensive allele-specific interactions with mutations in the S1 domain of eIF2α (harboring the phosphorylation site), which binds to eIF2B directly. Consistent with this, β/Gcd7 can overcome the toxicity of eIF2(αP) and rescue native eIF2B function when overexpressed with δ/Gcd2 or γ/Gcd1. In aggregate, these findings provide compelling evidence that β/Gcd7 is crucial for binding of substrate by eIF2B in vivo, beyond its dispensable regulatory role in the inhibition of eIF2B by eIF (αP).
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Tuckow AP, Vary TC, Kimball SR, Jefferson LS. Ectopic expression of eIF2Bepsilon in rat skeletal muscle rescues the sepsis-induced reduction in guanine nucleotide exchange activity and protein synthesis. Am J Physiol Endocrinol Metab 2010; 299:E241-8. [PMID: 20484009 PMCID: PMC2928514 DOI: 10.1152/ajpendo.00151.2010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Eukaryotic initiation factor 2B (eIF2B) is a guanine nucleotide exchange factor (GEF) whose activity is both tightly regulated and rate-controlling with regard to global rates of protein synthesis. Skeletal muscle eIF2B activity and expression of its catalytic epsilon-subunit (eIF2Bepsilon) have been implicated as potential contributors to the altered rates of protein synthesis in a number of physiological conditions and experimental models. The objective of this study was to directly examine the effects of exogenously expressed eIF2Bepsilon in vivo on GEF activity and protein synthetic rates in rat skeletal muscle. A plasmid encoding FLAG-eIF2Bepsilon was transfected into the tibialis anterior (TA) of one leg, while the contralateral TA received a control plasmid. Ectopic expression of eIF2Bepsilon resulted in increased GEF activity in TA homogenates of healthy rats, demonstrating that the expressed protein was catalytically active. In an effort to restore a deficit in eIF2B activity, we utilized an established model of chronic sepsis in which skeletal muscle eIF2B activity is known to be impaired. Ectopic expression of eIF2Bepsilon in the TA rescued the sepsis-induced deficit in GEF activity and muscle protein synthesis. The results demonstrate that modulation of eIF2Bepsilon expression may be sufficient to correct deficits in skeletal muscle protein synthesis associated with sepsis and other muscle-wasting conditions.
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Affiliation(s)
- Alexander P Tuckow
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA
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Eukaryotic initiation factor 2B (eIF2B) GEF activity as a diagnostic tool for EIF2B-related disorders. PLoS One 2009; 4:e8318. [PMID: 20016818 PMCID: PMC2789406 DOI: 10.1371/journal.pone.0008318] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2009] [Accepted: 11/13/2009] [Indexed: 11/20/2022] Open
Abstract
Background In recent years, the phenotypes of leukodystrophies linked to mutations in the eukaryotic initiation factor 2B genes have been extended, classically called CACH/VWM (Childhood ataxia with cntral hypomyélination/vanishing white matter disorder). The large clinical spectrum observed from the more severe antenatal forms responsible for fetal death to milder adult forms with an onset after 16 years old and restricted to slow cognitive impairment have lead to the concept of eIF2B-related disorders. The typical MRI pattern with a diffuse CSF-like aspect of the cerebral white matter can lack particularly in the adult forms whereas an increasing number of patients with clinical and MRI criteria for CACH/VWM disease but without eIF2B mutations are found. Then we propose the use of biochemical markers to help in this difficult diagnosis. The biochemical diagnosis of eIF2B-related disorder is difficult as no marker, except the recently described asialotransferrin/transferrin ratio measured in cerebrospinal fluid, has been proposed and validated until now. Decreased eIF2B GEF activity has been previously reported in lymphoblastoid cell lines from 30 eIF2B-mutated patients. Our objective was to evaluate further the utility of this marker and to validate eIF2B GEF activity in a larger cohort as a specific diagnostic test for eIF2B-related disorders. Methodology/Principal Findings We performed eIF2B GEF activity assays in cells from 63 patients presenting with different clinical forms and eIF2B mutations in comparison to controls but also to patients with defined leukodystrophies or CACH/VWM-like diseases without eIF2B mutations. We found a significant decrease of GEF activity in cells from eIF2B-mutated patients with 100% specificity and 89% sensitivity when the activity threshold was set at ≤77.5%. Conclusion These results validate the measurement of eIF2B GEF activity in patients' transformed-lymphocytes as an important tool for the diagnosis of eIF2B-related disorders.
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Fraser CS. The molecular basis of translational control. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2009; 90:1-51. [PMID: 20374738 DOI: 10.1016/s1877-1173(09)90001-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Our current understanding of eukaryotic protein synthesis has emerged from many years of biochemical, genetic and biophysical approaches. Significant insight into the molecular details of the mechanism has been obtained, although there are clearly many aspects of the process that remain to be resolved. Importantly, our understanding of the mechanism has identified a number of key stages in the pathway that contribute to the regulation of general and gene-specific translation. Not surprisingly, translational control is now widely accepted to play a role in aspects of cell stress, growth, development, synaptic function, aging, and disease. This chapter reviews the mechanism of eukaryotic protein synthesis and its relevance to translational control.
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Affiliation(s)
- Christopher S Fraser
- Department of Molecular and Cellular Biology, University of California at Davis, Davis, California 95616, USA
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Clues to the mechanism of action of eIF2B, the guanine-nucleotide-exchange factor for translation initiation. Biochem Soc Trans 2008; 36:658-64. [PMID: 18631136 DOI: 10.1042/bst0360658] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A variety of cellular processes rely on G-proteins, which cycle through active GTP-bound and inactive GDP-bound forms. The switch between these states is commonly regulated by GEFs (guanine-nucleotide-exchange factors) and GAPs (GTPase-activating proteins). Although G-proteins have structural similarity, GEFs are very diverse proteins. A complex example of this system is seen in eukaryotic translation initiation between eIF (eukaryotic initiation factor) 2, a G-protein, its five-subunit GEF, eIF2B, and its GAP, eIF5. eIF2 delivers Met-tRNA(i) (initiator methionyl-tRNA) to the 40S ribosomal subunit before mRNA binding. Upon AUG recognition, eIF2 hydrolyses GTP, aided by eIF5. eIF2B then re-activates eIF2 by removing GDP, thereby promoting association of GTP. In the present article, we review data from studies of representative G-protein-GEF pairs and compare these with observations from our research on eIF2 and eIF2B to propose a model for how interactions between eIF2B and eIF2 promote guanine nucleotide exchange.
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Maletkovic J, Schiffmann R, Gorospe JR, Gordon ES, Mintz M, Hoffman EP, Alper G, Lynch DR, Singhal BS, Harding C, Amartino H, Brown CM, Chan A, Renaud D, Geraghty M, Jensen L, Senbil N, Kadom N, Nazarian J, Yuanjian Feng, Zuyi Wang, Hartka T, Morizono H, Vanderver A. Genetic and clinical heterogeneity in eIF2B-related disorder. J Child Neurol 2008; 23:205-15. [PMID: 18263758 DOI: 10.1177/0883073807308705] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Eukaryotic initiation factor 2B (eIF2B)-related disorders are heritable white matter disorders with a variable clinical phenotype (including vanishing white matter disease and ovarioleukodystrophy) and an equally heterogeneous genotype. We report 9 novel mutations in the EIF2B genes in our subject population, increasing the number of known mutations to more than 120. Using homology modeling, we have analyzed the impact of novel mutations on the 5 subunits of the eIF2B protein. Although recurrent mutations have been found at CpG dinucleotides in the EIF2B genes, the high incidence of private or low frequency mutations increases the challenge of providing rapid genetic confirmation of this disorder, and limits the application of EIF2B screening in cases of undiagnosed leukodystrophy.
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Affiliation(s)
- Jelena Maletkovic
- Children's National Medical Center, Children's Research Institute, Center for Genetic Medicine, Washington, DC 20010, USA
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A novel mechanism for the control of translation initiation by amino acids, mediated by phosphorylation of eukaryotic initiation factor 2B. Mol Cell Biol 2007; 28:1429-42. [PMID: 18160716 DOI: 10.1128/mcb.01512-07] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Eukaryotic initiation factor 2B (eIF2B) plays a key role in controlling the initiation of mRNA translation. eIF2B is heteropentamer whose catalytic (epsilon) subunit promotes GDP/GTP exchange on eIF2. We show here that depriving human cells of amino acids rapidly results in the inhibition of eIF2B, independently of changes in eIF2 phosphorylation. Although amino acid deprivation also inhibits signaling through the mammalian target of rapamycin complex 1 (mTORC1), the inhibition of eIF2B activity by amino acid starvation is independent of mTORC1. Instead, amino acids repress the phosphorylation of a novel site in eIF2Bepsilon. We identify this site as Ser525, located adjacent to the known phosphoregulatory region in eIF2Bepsilon. Mutation of Ser525 to Ala abolishes the regulation of eIF2B and protein synthesis by amino acids. This indicates that phosphorylation of this site is crucial for the control of eIF2B and protein synthesis by amino acids. These findings identify a new way in which amino acids regulate a key step in translation initiation and indicate that this involves a novel amino acid-sensitive signaling mechanism.
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Mohammad-Qureshi SS, Haddad R, Hemingway EJ, Richardson JP, Pavitt GD. Critical contacts between the eukaryotic initiation factor 2B (eIF2B) catalytic domain and both eIF2beta and -2gamma mediate guanine nucleotide exchange. Mol Cell Biol 2007; 27:5225-34. [PMID: 17526738 PMCID: PMC1951959 DOI: 10.1128/mcb.00495-07] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Diverse guanine nucleotide exchange factors (GEFs) regulate the activity of GTP binding proteins. One of the most complicated pairs is eukaryotic initiation factor 2B (eIF2B) and eIF2, which function during protein synthesis initiation in eukaryotes. We have mutated conserved surface residues within the eIF2B GEF domain, located at the eIF2Bepsilon C terminus. Extensive genetic and biochemical characterization established how these residues contribute to GEF activity. We find that the universally conserved residue E569 is critical for activity and that even a conservative E569D substitution is lethal in vivo. Several mutations within residues close to E569 have no discernible effect on growth or GCN4 expression, but an alanine substitution at the adjacent L568 is cold sensitive and deregulates GCN4 activity at 15 degrees C. The mutation of W699, found on a separate surface approximately 40 A from E569, is also lethal. Binding studies show that W699 is critical for interaction with eIF2beta, while L568 and E569 are not. In contrast, all three residues are critical for interaction with eIF2gamma. These data show that multiple contacts between eIF2gamma and eIF2Bepsilon mediate nucleotide exchange.
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45
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Abstract
This chapter describes phenotypic assays on specific and general aspects of translation using yeast Saccharomyces cerevisiae as a model eukaryote. To study the effect on start codon selection stringency, a his4(-) or his4-lacZ allele altering the first AUG to AUU is employed. Mutations relaxing the stringent selection confer the His(+) phenotype in the his4(-) strain background or increase expression from his4-lacZ compared to that from wild-type HIS4-lacZ (Sui(-) phenotype). Translation of the Gcn4p transcription activator is strictly regulated by amino acid availability depending on upstream ORF (uORF) elements in the GCN4 mRNA leader. Mutations reducing the eIF2/GTP/Met-tRNA(i)(Met) complex level or the rate of its binding to the 40S subunit derepress GCN4 translation by allowing ribosomes to bypass inhibitory uORFs in the absence of the starvation signal (Gcd(-) phenotype). Mutations impairing scanning or AUG recognition generally impair translational GCN4 induction during amino acid starvation (Gcn(-) phenotype). Different amino acid analogs or amino acid enzyme inhibitors are used to study Gcd(-) or Gcn(-) phenotypes. The method of polysome profiling is also described to gain an ultimate "phenotypic" proof for translation defects.
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Affiliation(s)
- Bumjun Lee
- Molecular, Cellular, and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas, USA
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46
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Mohammad-Qureshi SS, Haddad R, Palmer KS, Richardson JP, Gomez E, Pavitt GD. Purification of FLAG-tagged eukaryotic initiation factor 2B complexes, subcomplexes, and fragments from Saccharomyces cerevisiae. Methods Enzymol 2007; 431:1-13. [PMID: 17923227 DOI: 10.1016/s0076-6879(07)31001-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The eukaryotic initiation factor 2B (eIF2B) is a five-subunit guanine nucleotide exchange factor, that functions during translation initiation to catalyze the otherwise slow exchange of GDP for GTP on its substrate eIF2. Assays to measure substrate interaction and guanine nucleotide release ability of eIF2B require the complex to be purified free of interacting proteins. We have also found that a subcomplex of two subunits, gamma and epsilon or the largest one, epsilon alone, promotes this activity. Within eIF2Bepsilon, the catalytic center requires the C-terminal 200 residues only. Here, we describe our protocols for purifying the Saccharomyces cerevisiae eIF2B complexes and the catalytic subunit using FLAG-tagged proteins overexpressed in yeast cells. Using commercially available FLAG-affinity resin and high salt buffer, we are able to purify active eIF2B virtually free of contaminants.
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Singh CR, Lee B, Udagawa T, Mohammad-Qureshi SS, Yamamoto Y, Pavitt GD, Asano K. An eIF5/eIF2 complex antagonizes guanine nucleotide exchange by eIF2B during translation initiation. EMBO J 2006; 25:4537-46. [PMID: 16990799 PMCID: PMC1589998 DOI: 10.1038/sj.emboj.7601339] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2006] [Accepted: 08/18/2006] [Indexed: 11/08/2022] Open
Abstract
In eukaryotic translation initiation, the eIF2.GTP/Met-tRNA(i)(Met) ternary complex (TC) binds the eIF3/eIF1/eIF5 complex to form the multifactor complex (MFC), whereas eIF2.GDP binds the pentameric factor eIF2B for guanine nucleotide exchange. eIF5 and the eIF2Bvarepsilon catalytic subunit possess a conserved eIF2-binding site. Nearly half of cellular eIF2 forms a complex with eIF5 lacking Met-tRNA(i)(Met), and here we investigate its physiological significance. eIF5 overexpression increases the abundance of both eIF2/eIF5 and TC/eIF5 complexes, thereby impeding eIF2B reaction and MFC formation, respectively. eIF2Bvarepsilon mutations, but not other eIF2B mutations, enhance the ability of overexpressed eIF5 to compete for eIF2, indicating that interaction of eIF2Bvarepsilon with eIF2 normally disrupts eIF2/eIF5 interaction. Overexpression of the catalytic eIF2Bvarepsilon segment similarly exacerbates eIF5 mutant phenotypes, supporting the ability of eIF2Bvarepsilon to compete with MFC. Moreover, we show that eIF5 overexpression does not generate aberrant MFC lacking tRNA(i)(Met), suggesting that tRNA(i)(Met) is a vital component promoting MFC assembly. We propose that the eIF2/eIF5 complex represents a cytoplasmic reservoir for eIF2 that antagonizes eIF2B-promoted guanine nucleotide exchange, enabling coordinated regulation of translation initiation.
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Affiliation(s)
- Chingakham Ranjit Singh
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS, USA
| | - Bumjun Lee
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS, USA
| | - Tsuyoshi Udagawa
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS, USA
| | | | - Yasufumi Yamamoto
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS, USA
| | - Graham D Pavitt
- Faculty of Life Sciences, The University of Manchester, Manchester, UK
- Faculty of Life Sciences, The University of Manchester, Manchester M13 9PT, UK. E-mail:
| | - Katsura Asano
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS, USA
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA. Tel.: +1 785 532 0116; Fax: +1 785 532 6653; E-mail:
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48
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Alone PV, Dever TE. Direct binding of translation initiation factor eIF2gamma-G domain to its GTPase-activating and GDP-GTP exchange factors eIF5 and eIF2B epsilon. J Biol Chem 2006; 281:12636-44. [PMID: 16522633 DOI: 10.1074/jbc.m511700200] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The GTP-binding eukaryotic translation initiation factor eIF2 delivers initiator methionyl-tRNA to the 40 S ribosomal subunit. The factor eIF5 stimulates hydrolysis of GTP by eIF2 upon AUG codon recognition, whereas the factor eIF2B promotes guanine nucleotide exchange on eIF2 to recycle the factor for additional rounds of translation initiation. The GTP-binding (G) domain resides in the gamma subunit of the heterotrimeric eIF2; however, only eIF2beta, and not eIF2gamma, has been reported to directly bind to eIF5 or eIF2B. Using proteins expressed in yeast or recombinant systems we show that full-length yeast eIF2gamma, as well as its isolated G domain, binds directly to eIF5 and the epsilon subunit of eIF2B, and we map the interaction sites to the catalytically important regions of these factors. Consistently, an internal deletion of residues 50-100 of yeast eIF5 impairs the interaction with recombinant eIF2gamma-G domain and abolishes the ability of eIF5 to stimulate eIF2 GTPase activity in translation initiation complexes in vitro. Thus, rather than allosterically regulating eIF2gamma-G domain function via eIF2beta, our data support a model in which the GTPase-activating factor eIF5 and the guanine-nucleotide exchange factor eIF2B modulate eIF2 function through direct interactions with the eIF2gamma-G domain.
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Affiliation(s)
- Pankaj V Alone
- Laboratory of Gene Regulation and Development, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA
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49
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Abstract
eIF2B (eukaryotic initiation factor 2B) is a GEF (guanine nucleotide-exchange factor) that plays, with its substrate eIF2, a key regulatory role in the translation initiation phase of protein synthesis. The importance of correct control of eIF2 and eIF2B for normal physiology is underlined by the recent involvement of the five genes that encode the five eIF2B subunits in a severe autosomal recessive neurodegenerative disease, described in young children as CACH (childhood ataxia with central nervous system hypomyelination)/VWM (leukoencephalopathy with vanishing white matter) syndrome. The syndrome is characterized by episodes of rapid deterioration during febrile illnesses or following head trauma and symmetrical demyelination of the brain white matter with cavitation aspects, leading to a progressive vanishing of the white matter replaced by CSF (cerebrospinal fluid). However, a wide clinical spectrum has been observed in the 148 patients presently reported, from congenital forms with rapid death to adult-onset forms with slow mental decline and progressive motor dysfunction, sometimes associated with congenital eye abnormalities or ovariodysgenesis. So far, 77 different mutations in each of the five EIF2B genes (EIF2B1–5), encoding subunits eIF2Bα–ϵ, have been found, with two-thirds affecting the eIF2Bϵ subunit. The correlation found between the level of GEF activity of eIF2B in the mutated white blood cells and the age at disease onset suggests a direct role of the abnormal translation control in the pathophysiology of the disease.
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50
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Abstract
Cells reprogram gene expression in response to environmental changes by mobilizing transcriptional activators. The activator protein Gcn4 of the yeast Saccharomyces cerevisiae is regulated by an intricate translational control mechanism, which is the primary focus of this review, and also by the modulation of its stability in response to nutrient availability. Translation of GCN4 mRNA is derepressed in amino acid-deprived cells, leading to transcriptional induction of nearly all genes encoding amino acid biosynthetic enzymes. The trans-acting proteins that control GCN4 translation have general functions in the initiation of protein synthesis, or regulate the activities of initiation factors, so that the molecular events that induce GCN4 translation also reduce the rate of general protein synthesis. This dual regulatory response enables cells to limit their consumption of amino acids while diverting resources into amino acid biosynthesis in nutrient-poor environments. Remarkably, mammalian cells use the same strategy to downregulate protein synthesis while inducing transcriptional activators of stress-response genes under various stressful conditions, including amino acid starvation.
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Affiliation(s)
- Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
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