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Abstract
eIF2B (eukaryotic initiation factor 2B) is a multisubunit protein that is required for protein synthesis initiation and its regulation in all eukaryotic cells. Mutations in eIF2B have also recently been found to cause a fatal human disease called CACH (childhood ataxia with central nervous system hypomyelination) or VWM (vanishing white matter disease). This review provides a general background to translation initiation and mechanisms known to control eIF2B function, before describing molecular genetic and biochemical analysis of eIF2B structure and function, integrating work from studies of the yeast and mammalian eIF2B proteins.
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52
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Campbell SG, Hoyle NP, Ashe MP. Dynamic cycling of eIF2 through a large eIF2B-containing cytoplasmic body: implications for translation control. J Cell Biol 2005; 170:925-34. [PMID: 16157703 PMCID: PMC2171431 DOI: 10.1083/jcb.200503162] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2005] [Accepted: 08/03/2005] [Indexed: 11/22/2022] Open
Abstract
The eukaryotic translation initiation factor 2B (eIF2B) provides a fundamental controlled point in the pathway of protein synthesis. eIF2B is the heteropentameric guanine nucleotide exchange factor that converts eIF2, from an inactive guanosine diphosphate-bound complex to eIF2-guanosine triphosphate. This reaction is controlled in response to a variety of cellular stresses to allow the rapid reprogramming of cellular gene expression. Here we demonstrate that in contrast to other translation initiation factors, eIF2B and eIF2 colocalize to a specific cytoplasmic locus. The dynamic nature of this locus is revealed through fluorescence recovery after photobleaching analysis. Indeed eIF2 shuttles into these foci whereas eIF2B remains largely resident. Three different strategies to decrease the guanine nucleotide exchange function of eIF2B all inhibit eIF2 shuttling into the foci. These results implicate a defined cytoplasmic center of eIF2B in the exchange of guanine nucleotides on the eIF2 translation initiation factor. A focused core of eIF2B guanine nucleotide exchange might allow either greater activity or control of this elementary conserved step in the translation pathway.
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Affiliation(s)
- Susan G Campbell
- Faculty of Life Science, The University of Manchester, Manchester, M13 9PT, England, UK
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53
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Hollunder J, Beyer A, Wilhelm T. Identification and characterization of protein subcomplexes in yeast. Proteomics 2005; 5:2082-9. [PMID: 15832363 DOI: 10.1002/pmic.200401121] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Protein complexes are major components of cellular organization. Based on large-scale protein complex data, we present the first statistical procedure to find insightful substructures in protein complexes: we identify protein subcomplexes (SCs), i.e., multiprotein assemblies residing in different protein complexes. Four protein complex datasets with different origins and variable reliability are separately analyzed. Our method identifies well-characterized protein assemblies with known functions, thereby confirming the utility of the procedure. In addition, we also identify hitherto unknown functional entities consisting of either functionally unknown proteins or proteins with different functional annotation. We show that SCs represent more reliable protein assemblies than the original complexes. Finally, we demonstrate unique properties of subcomplex proteins that underline the distinct roles of SCs: (i) SCs are functionally and spatially more homogeneous than complete protein complexes (this fact is utilized to predict functional roles and subcellular localizations for so far unannotated proteins); (ii) the abundance of subcomplex proteins is less variable than the abundance of other proteins; (iii) SCs are enriched with essential and synthetic lethal proteins; and (iv) mutations in SC-proteins have higher fitness effects than mutations in other proteins.
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Affiliation(s)
- Jens Hollunder
- Theoretical Systems Biology, Institute of Molecular Biotechnology, Jena, Germany
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54
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Dietrich J, Lacagnina M, Gass D, Richfield E, Mayer-Pröschel M, Noble M, Torres C, Pröschel C. EIF2B5 mutations compromise GFAP+ astrocyte generation in vanishing white matter leukodystrophy. Nat Med 2005; 11:277-83. [PMID: 15723074 DOI: 10.1038/nm1195] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2004] [Accepted: 01/05/2005] [Indexed: 11/08/2022]
Abstract
Vanishing white matter disease (VWM) is a heritable leukodystrophy linked to mutations in translation initiation factor 2B (eIF2B). Although the clinical course of this disease has been relatively well described, the cellular consequences of EIF2B mutations on neural cells are unknown. Here we have established cell cultures from the brain of an individual with VWM carrying mutations in subunit 5 of eIF2B (encoded by EIF2B5). Despite the extensive demyelination apparent in this VWM patient, normal-appearing oligodendrocytes were readily generated in vitro. In contrast, few GFAP-expressing (GFAP+) astrocytes were present in primary cultures, induction of astrocytes was severely compromised, and the few astrocytes generated showed abnormal morphologies and antigenic phenotypes. Lesions in vivo also lacked GFAP+ astrocytes. RNAi targeting of EIF2B5 severely compromised the induction of GFAP+ cells from normal human glial progenitors. This raises the possibility that a deficiency in astrocyte function may contribute to the loss of white matter in VWM leukodystrophy.
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Affiliation(s)
- Jörg Dietrich
- Department of Biomedical Genetics, Aab Institute, University of Rochester School of Medicine and Dentistry, 601 Elmwood Avenue, Rochester, New York 14642, USA
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55
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Fogli A, Schiffmann R, Hugendubler L, Combes P, Bertini E, Rodriguez D, Kimball SR, Boespflug-Tanguy O. Decreased guanine nucleotide exchange factor activity in eIF2B-mutated patients. Eur J Hum Genet 2005; 12:561-6. [PMID: 15054402 DOI: 10.1038/sj.ejhg.5201189] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Mutations in each of the five eucaryotic initiation factor 2B (eIF2B) subunits have been found in leukodystrophies of various severity: Cree leukoencephalopathy, childhood ataxia with central hypomyelination/leukodystrophy with vanishing white matter and ovarioleukodystrophy. A continuum was observed from fatal infantile forms to adult forms without neurological deterioration. Disease severity was found to correlate with the age at disease onset and the specific amino-acid substitution. In order to analyze the functional consequences of eIF2B mutations, we measured the guanine nucleotide exchange factor (GEF) activity of eIF2B in transformed lymphocytes from 30 affected patients carrying mutations in eIF2B compared to 10 unaffected heterozygotes and 22 controls without eIF2B mutations. A significant decrease of 20-70% in GEF activity was observed in all mutated cells. The severity of this decrement of GEF activity correlated with age at onset of the disease. These results suggest that a deficiency in GEF activity underlies the encephalopathy associated eIF2B-related disease. Our study demonstrates that the evaluation of the GEF activity in transformed lymphocytes represents an interesting alternative test to the systematic screening of the five EIF2B genes. This relevant cellular model may also be used to test the functional impact of different molecules on the GEF activity for future therapeutic strategies.
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Affiliation(s)
- Anne Fogli
- INSERM UMR 384, Faculté de Médecine, 28 place Henri Dunant, Clermont-Ferrand, France
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56
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Afjehi-Sadat L, Shin JH, Felizardo M, Lee K, Slavc I, Lubec G. Detection of hypothetical proteins in 10 individual human tumor cell lines. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2004; 1747:67-80. [PMID: 15680240 DOI: 10.1016/j.bbapap.2004.09.024] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2004] [Revised: 09/27/2004] [Accepted: 09/27/2004] [Indexed: 12/20/2022]
Abstract
The search for new structures in tumors by genomics and proteomics methods is a major goal in tumor biology and may lead to the detection of markers or antigens for the generation of tumor vaccines. The aim of this study was to identify proteins that have been predicted so far based upon their nucleic acid sequence only or show poor identity to known proteins in tumor cell lines. Cell lines of neuroblastoma, colorectal, cervix carcinoma, adenocarcinoma of the ovary, lung and breast cancer, promyelocytic leukaemia, rhabdomyosarcoma, osteosarcoma and malignant melanoma were used. Cell lysates were run on 2D gel electrophoresis with subsequent in-gel digestion and MALDI-TOF-TOF analysis. A series of 10 hypothetical proteins (HPs) were observed and three of these proteins, hypothetical protein (Q9BTE6), CGI-83 protein (Q9Y392) and similar to CG11334 (Q9BV20), were so far described in tumors exclusively. The other seven proteins were already detected at the transcriptional level in normal and tumor cell lines or tissues. In conclusion, the three HPs observed in lung cancer and malignant melanoma may be candidates for development of tumor markers and generation of tumor vaccines.
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Affiliation(s)
- Leila Afjehi-Sadat
- Medical University of Vienna, Division of Basic Science, Department of Pediatrics, Währinger Gürtel 18, A-1090 Vienna, Austria
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57
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Fogli A, Schiffmann R, Bertini E, Ughetto S, Combes P, Eymard-Pierre E, Kaneski CR, Pineda M, Troncoso M, Uziel G, Surtees R, Pugin D, Chaunu MP, Rodriguez D, Boespflug-Tanguy O. The effect of genotype on the natural history of eIF2B-related leukodystrophies. Neurology 2004; 62:1509-17. [PMID: 15136673 DOI: 10.1212/01.wnl.0000123259.67815.db] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Recessive mutations in the five eucaryotic initiation factor 2B (eIF2B) subunits have been found in leukodystrophies of variable age at onset and severity. OBJECTIVES To evaluate the clinical spectrum of eIF2B-related disorders and search for a phenotype-genotype correlation. METHODS Ninety-three individuals (78 families) with an undetermined leukodystrophy were selected on MRI-based criteria of childhood ataxia with central hypomyelination/vanishing white matter (CACH/VWM) for EIF2B genes analysis. RESULTS Eighty-nine percent of individuals with MRI criteria of CACH/VWM have a mutation in one of the eIF2B beta to epsilon subunits. For 83 individuals (68 families), 46 distinct mutations (90% missense) in four of the five eIF2B subunits (beta, gamma, delta, epsilon) were identified. Sixty-four percent were in the epsilon subunit, a R113H substitution was found in 71% of eIF2B epsilon-mutated families. A large clinical spectrum was observed from rapidly fatal infantile to asymptomatic adult forms. Disease severity was correlated with age at onset (p < 0.0001) but not with the type of the mutated subunit nor with the position of the mutation within the protein. Mutations R113H in the epsilon subunit and E213G in the beta subunit were significantly associated with milder forms. CONCLUSIONS The degree of eIF2B dysfunction, which is involved in the regulation of protein synthesis during cellular stress, may play a role in the clinical expression of eIF2B-related disorders.
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Affiliation(s)
- A Fogli
- INSERM UMR 384, Faculté de Médecine, Clermont-Ferrand, France
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58
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Ito T, Marintchev A, Wagner G. Solution Structure of Human Initiation Factor eIF2α Reveals Homology to the Elongation Factor eEF1B. Structure 2004; 12:1693-704. [PMID: 15341733 DOI: 10.1016/j.str.2004.07.010] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2004] [Revised: 07/12/2004] [Accepted: 07/13/2004] [Indexed: 10/26/2022]
Abstract
The GTP-bound form of the trimeric eukaryotic translation initiation factor 2 (eIF2) transfers aminoacylated initiator methionyl tRNA onto the 40S ribosome. We have solved with solution NMR the structure of the alpha subunit of human eIF2 (heIF2alpha). The protein consists of two domains that are mobile relative to each other. The N-terminal domain has an S1-type oligonucleotide/oligosaccharide binding-fold subdomain and an alpha-helical subdomain. The C-terminal domain adopts an alphabeta-fold very similar to the C-terminal domain of elongation factor (eEF) 1Balpha, the guanine-nucleotide exchange factor for eEF1A. The structural and functional similarities found between eIF2alpha/eIF2gamma and eEF1Balpha/eEF1A suggest a model for the interaction of eIF2alpha with eIF2gamma, and eIF2 with Met-tRNAiMet. It further indicates a previously unrecognized evolutionary lineage of eIF2alpha/gamma from the functionally related elongation factor eEF1Balpha/eEF1A complex.
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Affiliation(s)
- Takuhiro Ito
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
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59
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Kakuta Y, Tahara M, Maetani S, Yao M, Tanaka I, Kimura M. Crystal structure of the regulatory subunit of archaeal initiation factor 2B (aIF2B) from hyperthermophilic archaeon Pyrococcus horikoshii OT3: a proposed structure of the regulatory subcomplex of eukaryotic IF2B. Biochem Biophys Res Commun 2004; 319:725-32. [PMID: 15184043 DOI: 10.1016/j.bbrc.2004.05.045] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2004] [Indexed: 10/26/2022]
Abstract
Eukaryotic translation initiation factor 2B (eIF2B) is the guanine-nucleotide exchange factor for eukaryotic initiation factor 2 (eIF2). eIF2B is a heteropentameric protein composed of alpha- subunits. The alpha, beta, and delta subunits form a regulatory subcomplex, while the gamma and form a catalytic subcomplex. Archaea possess homologues of alpha, beta, and delta subunits of eIF2B. Here, we report the three-dimensional structure of an archaeal regulatory subunit (aIF2Balpha) from the hyperthermophilic archaeon Pyrococcus horikoshii OT3 determined by X-ray crystallography at 2.2A resolution. aIF2Balpha consists of two subdomains, an N-domain (residues 1-95) and a C-domain (residues 96-276), connected by a long alpha-helix (alpha5: 78-106). The N-domain contains a five helix bundle structure, while the C-domain folds into the alpha/beta structure, thus showing similarity to D-ribose-5-phosphate isomerase structure. The presence of two molecules in the crystallographic asymmetric unit and the gel filtration analysis suggest a dimeric structure of aIF2Balpha in solution, interacting with each other by C-domains. Furthermore, the crystallographic 3-fold symmetry generates a homohexameric structure of aIF2Balpha; the interaction is primarily mediated by the long alpha-helix at the N-domains. This structure suggests an architecture of the three subunits, alpha, beta, and delta, in the regulatory subcomplex within eIF2B.
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Affiliation(s)
- Yoshimitsu Kakuta
- Laboratory of Biochemistry, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University, Fukuoka 812-8581, Japan
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60
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Li W, Wang X, Van Der Knaap MS, Proud CG. Mutations linked to leukoencephalopathy with vanishing white matter impair the function of the eukaryotic initiation factor 2B complex in diverse ways. Mol Cell Biol 2004; 24:3295-306. [PMID: 15060152 PMCID: PMC381664 DOI: 10.1128/mcb.24.8.3295-3306.2004] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Leukoencephalopathy with vanishing white matter (VWM) is a severe inherited human neurodegenerative disorder that is caused by mutations in the genes for the subunits of eukaryotic initiation factor 2B (eIF2B), a heteropentameric guanine nucleotide exchange factor that regulates both global and mRNA-specific translation. Marked variability is evident in the clinical severity and time course of VWM in patients. Here we have studied the effects of VWM mutations on the function of human eIF2B. All the mutations tested cause partial loss of activity. Frameshift mutations in genes for eIF2Bepsilon or eIF2Bbeta lead to truncated polypeptides that fail to form complexes with the other subunits and are effectively null mutations. Certain point mutations also impair the ability of eIF2Bbeta or -epsilon to form eIF2B holocomplexes and also diminish the intrinsic nucleotide exchange activity of eIF2B. A point mutation in the catalytic domain of eIF2Bepsilon impairs its ability to bind the substrate, while two mutations in eIF2Bbeta actually enhance eIF2 binding. We provide evidence that expression of VWM mutant eIF2B may enhance the translation of specific mRNAs. The variability of the clinical phenotype in VWM may reflect the multiple ways in which VWM mutations affect eIF2B function.
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Affiliation(s)
- Wei Li
- Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
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61
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Hardt SE, Tomita H, Katus HA, Sadoshima J. Phosphorylation of Eukaryotic Translation Initiation Factor 2Bε by Glycogen Synthase Kinase-3β Regulates β-Adrenergic Cardiac Myocyte Hypertrophy. Circ Res 2004; 94:926-35. [PMID: 15001529 DOI: 10.1161/01.res.0000124977.59827.80] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Glycogen synthase kinase 3β (GSK-3β) negatively regulates cardiac hypertrophy. A potential target mediating the antihypertrophic effect of GSK-3β is eukaryotic translation initiation factor 2Bε (eIF2Bε). Overexpression of GSK-3β increased the cellular kinase activity toward GST-eIF2Bε in neonatal rat cardiac myocytes, whereas LiCl (10 mmol/L) or isoproterenol (ISO) (10 μmol/L), a treatment known to inhibit GSK-3β, decreased it. Immunoblot analyses using anti-S535 phosphospecific eIF2Bε antibody showed that S535 phosphorylation of endogenous eIF2Bε was decreased by LiCl or ISO, suggesting that GSK-3β is the predominant kinase regulating phosphorylation of eIF2Bε-S535 in cardiac myocytes. Decreases in eIF2Bε-S535 phosphorylation were also observed in a rat model of cardiac hypertrophy in vivo. Overexpression of wild-type eIF2Bε alone moderately increased cell size (+31±11%;
P
<0.05 versus control), whereas treatment of eIF2Bε-transduced myocytes with LiCl (+73±22% versus eIF2Bε only;
P
<0.05) or ISO (+84±33% versus eIF2Bε only;
P
<0.05) enhanced the effect of eIF2Bε. Overexpression of eIF2Bε-S535A, which is not phosphorylated by GSK-3β, increased cell size (+107±35%) as strongly as ISO (+95±25%), and abolished antihypertrophic effects of GSK-3β, indicating that S535 phosphorylation of eIF2Bε critically mediates antihypertrophic effects of GSK-3β. Furthermore, expression of eIF2Bε-F259L, a dominant-negative mutant, inhibited ISO-induced hypertrophy, indicating that eIF2Bε is required for β-adrenergic hypertrophy. Interestingly, expression of eIF2Bε-S535A partially increased cytoskeletal reorganization, whereas it did not increase expression of atrial natriuretic factor gene. These results suggest that GSK-3β is the predominant kinase mediating phosphorylation of eIF2Bε-S535 in cardiac myocytes, which in turn plays an important role in regulating cardiac hypertrophy primarily through protein synthesis.
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Affiliation(s)
- Stefan E Hardt
- Department of Cell Biology and Molecular Medicine, Cardiovascular Research Institute, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, NJ 07103-2714, USA
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62
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Richardson JP, Mohammad SS, Pavitt GD. Mutations causing childhood ataxia with central nervous system hypomyelination reduce eukaryotic initiation factor 2B complex formation and activity. Mol Cell Biol 2004; 24:2352-63. [PMID: 14993275 PMCID: PMC355856 DOI: 10.1128/mcb.24.6.2352-2363.2004] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Childhood ataxia with central nervous system hypomyelination (CACH), or vanishing white matter leukoencephalopathy (VWM), is a fatal brain disorder caused by mutations in eukaryotic initiation factor 2B (eIF2B). eIF2B is essential for protein synthesis and regulates translation in response to cellular stresses. We performed mutagenesis to introduce changes equivalent to 12 human CACH/VWM mutations in three subunits of the equivalent factor from yeast (Saccharomyces cerevisiae) and analyzed effects on cell growth, translation, and gene expression in response to stresses. None of the mutations is lethal or temperature sensitive, but almost all confer some defect in eIF2B function significant enough to alter growth or gene expression under normal or stress conditions. Biochemical analyses indicate that mutations analyzed in eIF2Balpha and -epsilon reduce the steady-state level of the affected subunit, while the most severe mutant tested, eIF2Bbeta(V341D) (human eIF2B(betaV316D)), forms complexes with reduced stability and lower eIF2B activity. eIF2Bdelta is excluded from eIF2Bbeta(V341D) complexes. eIF2B(betav341D) function can be rescued by overexpression of eIF2Bdelta alone. Our findings imply CACH/VWM mutations do not specifically impair responses to eIF2 phosphorylation, but instead cause protein structure defects that impair eIF2B activity. Altered protein folding is characteristic of other diseases, including cystic fibrosis and neurodegenerative disorders such as Huntington, Alzheimer's, and prion diseases.
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Affiliation(s)
- Jonathan P Richardson
- Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, United Kingdom
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63
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Boesen T, Mohammad SS, Pavitt GD, Andersen GR. Structure of the Catalytic Fragment of Translation Initiation Factor 2B and Identification of a Critically Important Catalytic Residue. J Biol Chem 2004; 279:10584-92. [PMID: 14681227 DOI: 10.1074/jbc.m311055200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic initiation factor (eIF) 2B catalyzes the nucleotide activation of eIF2 to its active GTP-bound state. The exchange activity has been mapped to the C terminus of the eIF2Bepsilon subunit. We have determined the crystal structure of residues 544-704 from yeast eIF2Bepsilon at 2.3-A resolution, and this fragment is an all-helical protein built around the conserved aromatic acidic (AA) boxes also found in eIF4G and eIF5. The eight helices are organized in a manner similar to HEAT repeats. The molecule is highly asymmetric with respect to surface charge and conservation. One area in the N terminus is proposed to be directly involved in catalysis. In agreement with this hypothesis, mutation of glutamate 569 is shown to be lethal. An acidic belt and a second area in the C terminus containing residues from the AA boxes are important for binding to eIF2. Two mutations causing the fatal human genetic disease leukoencephalopathy with vanishing white matter are buried and appear to disrupt the structural integrity of the catalytic domain rather than interfering directly with catalysis or binding of eIF2.
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Affiliation(s)
- Thomas Boesen
- Department of Molecular Biology, Aarhus University, Denmark
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64
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Asano K, Phan L, Valásek L, Schoenfeld LW, Shalev A, Clayton J, Nielsen K, Donahue TF, Hinnebusch AG. A multifactor complex of eIF1, eIF2, eIF3, eIF5, and tRNA(i)Met promotes initiation complex assembly and couples GTP hydrolysis to AUG recognition. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2003; 66:403-15. [PMID: 12762043 DOI: 10.1101/sqb.2001.66.403] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Affiliation(s)
- K Asano
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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65
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Fogli A, Rodriguez D, Eymard-Pierre E, Bouhour F, Labauge P, Meaney BF, Zeesman S, Kaneski CR, Schiffmann R, Boespflug-Tanguy O. Ovarian failure related to eukaryotic initiation factor 2B mutations. Am J Hum Genet 2003; 72:1544-50. [PMID: 12707859 PMCID: PMC1180314 DOI: 10.1086/375404] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2003] [Accepted: 03/04/2003] [Indexed: 11/03/2022] Open
Abstract
Ovarian failure (OF) at age <40 years occurs in approximately 1% of all women. Other than karyotype abnormalities, very few genes are known to be associated with this ovarian dysfunction. We studied eight patients who presented with premature OF and white-matter abnormalities on magnetic resonance imaging. Neurological signs may be absent or present after OF. In seven patients, we report for the first time mutations in three of the five EIF2B genes (EIF2B2, -4, and -5) that were recently shown to cause childhood ataxia with central nervous system hypomyelination/vanishing white-matter disease leukodystrophy. The correlation we observed between the age at onset of the neurological deterioration and the severity of OF suggests a common pathophysiological pathway.
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Affiliation(s)
- Anne Fogli
- INSERM Unité Mixte de Recherche 384, Faculté de Médecine, Clermont-Ferrand, France; Service de Neuropédiatrie, Hôpital A. Trousseau, INSERM U546, Paris; Neurologie A, Hôpital Pierre Wertheimer, Lyon, France; Département de Neurologie, Centre Hospitalier Universitaire, Nîmes, France; Department of Pediatrics, McMaster University, and Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Canada; and Developmental and Metabolic Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda
| | - Diana Rodriguez
- INSERM Unité Mixte de Recherche 384, Faculté de Médecine, Clermont-Ferrand, France; Service de Neuropédiatrie, Hôpital A. Trousseau, INSERM U546, Paris; Neurologie A, Hôpital Pierre Wertheimer, Lyon, France; Département de Neurologie, Centre Hospitalier Universitaire, Nîmes, France; Department of Pediatrics, McMaster University, and Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Canada; and Developmental and Metabolic Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda
| | - Eléonore Eymard-Pierre
- INSERM Unité Mixte de Recherche 384, Faculté de Médecine, Clermont-Ferrand, France; Service de Neuropédiatrie, Hôpital A. Trousseau, INSERM U546, Paris; Neurologie A, Hôpital Pierre Wertheimer, Lyon, France; Département de Neurologie, Centre Hospitalier Universitaire, Nîmes, France; Department of Pediatrics, McMaster University, and Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Canada; and Developmental and Metabolic Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda
| | - Françoise Bouhour
- INSERM Unité Mixte de Recherche 384, Faculté de Médecine, Clermont-Ferrand, France; Service de Neuropédiatrie, Hôpital A. Trousseau, INSERM U546, Paris; Neurologie A, Hôpital Pierre Wertheimer, Lyon, France; Département de Neurologie, Centre Hospitalier Universitaire, Nîmes, France; Department of Pediatrics, McMaster University, and Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Canada; and Developmental and Metabolic Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda
| | - Pierre Labauge
- INSERM Unité Mixte de Recherche 384, Faculté de Médecine, Clermont-Ferrand, France; Service de Neuropédiatrie, Hôpital A. Trousseau, INSERM U546, Paris; Neurologie A, Hôpital Pierre Wertheimer, Lyon, France; Département de Neurologie, Centre Hospitalier Universitaire, Nîmes, France; Department of Pediatrics, McMaster University, and Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Canada; and Developmental and Metabolic Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda
| | - Brandon F. Meaney
- INSERM Unité Mixte de Recherche 384, Faculté de Médecine, Clermont-Ferrand, France; Service de Neuropédiatrie, Hôpital A. Trousseau, INSERM U546, Paris; Neurologie A, Hôpital Pierre Wertheimer, Lyon, France; Département de Neurologie, Centre Hospitalier Universitaire, Nîmes, France; Department of Pediatrics, McMaster University, and Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Canada; and Developmental and Metabolic Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda
| | - Susan Zeesman
- INSERM Unité Mixte de Recherche 384, Faculté de Médecine, Clermont-Ferrand, France; Service de Neuropédiatrie, Hôpital A. Trousseau, INSERM U546, Paris; Neurologie A, Hôpital Pierre Wertheimer, Lyon, France; Département de Neurologie, Centre Hospitalier Universitaire, Nîmes, France; Department of Pediatrics, McMaster University, and Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Canada; and Developmental and Metabolic Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda
| | - Christine R. Kaneski
- INSERM Unité Mixte de Recherche 384, Faculté de Médecine, Clermont-Ferrand, France; Service de Neuropédiatrie, Hôpital A. Trousseau, INSERM U546, Paris; Neurologie A, Hôpital Pierre Wertheimer, Lyon, France; Département de Neurologie, Centre Hospitalier Universitaire, Nîmes, France; Department of Pediatrics, McMaster University, and Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Canada; and Developmental and Metabolic Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda
| | - Raphael Schiffmann
- INSERM Unité Mixte de Recherche 384, Faculté de Médecine, Clermont-Ferrand, France; Service de Neuropédiatrie, Hôpital A. Trousseau, INSERM U546, Paris; Neurologie A, Hôpital Pierre Wertheimer, Lyon, France; Département de Neurologie, Centre Hospitalier Universitaire, Nîmes, France; Department of Pediatrics, McMaster University, and Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Canada; and Developmental and Metabolic Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda
| | - Odile Boespflug-Tanguy
- INSERM Unité Mixte de Recherche 384, Faculté de Médecine, Clermont-Ferrand, France; Service de Neuropédiatrie, Hôpital A. Trousseau, INSERM U546, Paris; Neurologie A, Hôpital Pierre Wertheimer, Lyon, France; Département de Neurologie, Centre Hospitalier Universitaire, Nîmes, France; Department of Pediatrics, McMaster University, and Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Canada; and Developmental and Metabolic Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda
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66
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Wang X, Janmaat M, Beugnet A, Paulin FEM, Proud CG. Evidence that the dephosphorylation of Ser(535) in the epsilon-subunit of eukaryotic initiation factor (eIF) 2B is insufficient for the activation of eIF2B by insulin. Biochem J 2002; 367:475-81. [PMID: 12133000 PMCID: PMC1222905 DOI: 10.1042/bj20020677] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2002] [Revised: 06/06/2002] [Accepted: 07/22/2002] [Indexed: 11/17/2022]
Abstract
Eukaryotic initiation factor (eIF) 2B is a guanine-nucleotide exchange factor that plays a key role in the regulation of protein synthesis. It is activated by insulin, serum and other agents that stimulate general protein synthesis. The largest (epsilon) subunit of eIF2B is a substrate for glycogen synthase kinase (GSK)-3 in vitro, and phosphorylation by GSK3 inhibits the activity of eIF2B. The site of phosphorylation has previously been identified as Ser(535). GSK3 is inactivated by phosphorylation in response to insulin or serum. In Chinese-hamster ovary cells, insulin and serum bring about the dephosphorylation of Ser(535) in vivo, concomitantly with the phosphorylation of GSK3, and these effects are mediated through signalling via phosphoinositide 3-kinase. We have made use of inhibitors of GSK3 to determine whether GSK3 is responsible for phosphorylation of Ser(535) in vivo and to explore the role of phosphorylation of Ser(535) in the regulation of eIF2B. Treatment of cells with LiCl or with either of two recently developed GSK3 inhibitors, SB-415286 and SB-216763, brought about the dephosphorylation of Ser(535), which strongly indicates that this site is indeed a target for GSK3 in vivo. However, these compounds did not elicit significant activation of eIF2B, indicating, consistent with conclusions from one of our previous studies, that additional inputs are required for the activation of eIF2B. Our results also show that each of the inhibitors used affects overall protein synthesis and have additional effects on translation factors or signalling pathways apparently unrelated to their effects on GSK3, indicating that caution must be exercised when interpreting data obtained using these compounds.
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Affiliation(s)
- Xuemin Wang
- Division of Molecular Physiology, School of Life Sciences, MSI/WTB Complex, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland, U.K
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67
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Gomez E, Mohammad SS, Pavitt GD. Characterization of the minimal catalytic domain within eIF2B: the guanine-nucleotide exchange factor for translation initiation. EMBO J 2002; 21:5292-301. [PMID: 12356745 PMCID: PMC129037 DOI: 10.1093/emboj/cdf515] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
For protein synthesis initiation in eukaryotes, eIF2B is the guanine-nucleotide exchange factor for eIF2. eIF2B is an essential multi-subunit factor and a major target for translational control in both yeast and mammalian cells. It was shown previously that the largest eIF2B subunit, eIF2Bepsilon, is the only single subunit with catalytic function. Here we report the results of a molecular dissection of the yeast epsilon subunit encoded by GCD6 in which we have identified the catalytic domain. By analysis of a series of N-terminal deletions in vitro we find that the smallest catalytically active fragment contains residues 518-712 (termed Gcd6p(518-712)). Further deletion to position 581 (Gcd6p(581-712)) results in loss of nucleotide exchange function, but eIF2-binding activity is retained. C- terminal deletion of only 61 residues (Gcd6p(1-651)) results in loss of both functions. Thus Gcd6p(518-712) contains two regions that together constitute the catalytic domain of eIF2B. Finally, we show that the catalytic domain can provide eIF2B biological function in vivo when elevated levels eIF2 and tRNA(i)(Met) are also present.
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Affiliation(s)
- Edith Gomez
- Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, UK
Present address: Department of Biochemistry, University of Leicester, Leicester LE1 7RH, UK Corresponding author e-mail:
| | | | - Graham D. Pavitt
- Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, UK
Present address: Department of Biochemistry, University of Leicester, Leicester LE1 7RH, UK Corresponding author e-mail:
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68
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Fogli A, Wong K, Eymard-Pierre E, Wenger J, Bouffard JP, Goldin E, Black DN, Boespflug-Tanguy O, Schiffmann R. Cree leukoencephalopathy and CACH/VWM disease are allelic at the EIF2B5 locus. Ann Neurol 2002; 52:506-10. [PMID: 12325082 DOI: 10.1002/ana.10339] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Cree leukoencephalopathy is a rapidly fatal infantile autosomal recessive leukodystrophy of unknown cause observed in the native North American Cree and Chippewayan indigenous population. We found in the brain of affected individuals the typical foamy cells with the oligodendroglial phenotype described in central hypomyelination syndrome/vanishing white matter, a syndrome related to mutations in the genes encoding the five subunits of the eucaryotic translation initiation factor eIF2B. In three patients of two Cree families, we found a homozygous missense mutation resulting in a histidine substitution at arginine 195 of epsilon-eIF2B.
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Affiliation(s)
- Anne Fogli
- Institut National de la Santé et de la Recherche Médicale UMR 384, Facultéde Médecine, Clermont-Ferrand, France
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69
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Asano K, Phan L, Krishnamoorthy T, Pavitt GD, Gomez E, Hannig EM, Nika J, Donahue TF, Huang HK, Hinnebusch AG. Analysis and reconstitution of translation initiation in vitro. Methods Enzymol 2002; 351:221-47. [PMID: 12073347 DOI: 10.1016/s0076-6879(02)51850-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Katsura Asano
- Department of Biology, Kansas State University, Manhattan, Kansas 66506, USA
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70
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Abstract
Protein synthesis is the ultimate step of gene expression and a key control point for regulation. In particular, it enables cells to rapidly manipulate protein production without new mRNA synthesis, processing, or export. Recent studies have enhanced our understanding of the translation initiation process and helped elucidate how modifications of the general translational machinery regulate gene-specific protein production.
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Affiliation(s)
- Thomas E Dever
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
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71
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Campbell LE, Proud CG. Differing substrate specificities of members of the DYRK family of arginine-directed protein kinases. FEBS Lett 2002; 510:31-6. [PMID: 11755526 DOI: 10.1016/s0014-5793(01)03221-5] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The mammalian DYRK (dual specificity tyrosine phosphorylated and regulated kinase) family of protein kinases comprises a number of related, but poorly understood enzymes. DYRK1A is nuclear while DYRKs 2 and 3 are cytoplasmic. We recently showed that DYRK2 phosphorylates the translation initiation factor eIF2B at Ser539 in its epsilon-subunit and thereby "primes" its phosphorylation by glycogen synthase kinase-3. Here we have used peptides based on the sequence around Ser539 to help define the specificity of DYRK2/3 in comparison with DYRK1A. These kinases require an arginine N-terminal to the target residue for efficient substrate phosphorylation. This cannot be replaced even by lysine. A peptide with arginine at -2 is phosphorylated much less well by all three kinases than one with arginine at -3. Replacement of the +1 proline by alanine almost completely eliminates substrate phosphorylation, but valine here does allow phosphorylation especially by DYRK2. This study reveals both similarities and differences in the specificities of these arginine-dependent protein kinases.
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Affiliation(s)
- Linda E Campbell
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
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72
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Leegwater PA, Vermeulen G, Könst AA, Naidu S, Mulders J, Visser A, Kersbergen P, Mobach D, Fonds D, van Berkel CG, Lemmers RJ, Frants RR, Oudejans CB, Schutgens RB, Pronk JC, van der Knaap MS. Subunits of the translation initiation factor eIF2B are mutant in leukoencephalopathy with vanishing white matter. Nat Genet 2001; 29:383-8. [PMID: 11704758 DOI: 10.1038/ng764] [Citation(s) in RCA: 274] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Leukoencephalopathy with vanishing white matter (VWM) is an inherited brain disease that occurs mainly in children. The course is chronic-progressive with additional episodes of rapid deterioration following febrile infection or minor head trauma. We have identified mutations in EIF2B5 and EIF2B2, encoding the epsilon- and beta-subunits of the translation initiation factor eIF2B and located on chromosomes 3q27 and 14q24, respectively, as causing VWM. We found 16 different mutations in EIF2B5 in 29 patients from 23 families. We also found two distantly related individuals who were homozygous with respect to a missense mutation in EIF2B2, affecting a conserved amino acid. Three other patients also had mutations in EIF2B2. As eIF2B has an essential role in the regulation of translation under different conditions, including stress, this may explain the rapid deterioration of people with VWM under stress. Mutant translation initiation factors have not previously been implicated in disease.
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Affiliation(s)
- P A Leegwater
- Department of Child Neurology, Free University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
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73
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Ashe MP, Slaven JW, De Long SK, Ibrahimo S, Sachs AB. A novel eIF2B-dependent mechanism of translational control in yeast as a response to fusel alcohols. EMBO J 2001; 20:6464-74. [PMID: 11707417 PMCID: PMC125737 DOI: 10.1093/emboj/20.22.6464] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Fusel alcohols are natural products of amino acid catabolism in the yeast Saccharomyces cerevisiae that cause morphological changes similar to those seen during pseudohyphal growth. We have discovered that certain of these alcohols, including butanol and isoamyl alcohol, bring about a rapid inhibition of translation at the initiation step. This inhibition is strain specific and is not explained by previously described translational control pathways. Using genetic mapping, we have identified a proline to serine allelic variation at amino acid 180 of the GCD1 gene product as the genetic locus that allows translational regulation upon butanol addition. Gcd1p forms part of the eIF2B guanine nucleotide complex that is responsible for recycling eIF2-GDP to eIF2-GTP. This represents one of the key limiting steps of translation initiation and we provide evidence that fusel alcohols target eIF2B in order to bring about translational regulation.
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Affiliation(s)
- Mark P. Ashe
- Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, UK and
Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA Corresponding author e-mail:
| | | | - Susan K. De Long
- Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, UK and
Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA Corresponding author e-mail:
| | | | - Alan B. Sachs
- Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, UK and
Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA Corresponding author e-mail:
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74
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Shalev A, Valásek L, Pise-Masison CA, Radonovich M, Phan L, Clayton J, He H, Brady JN, Hinnebusch AG, Asano K. Saccharomyces cerevisiae protein Pci8p and human protein eIF3e/Int-6 interact with the eIF3 core complex by binding to cognate eIF3b subunits. J Biol Chem 2001; 276:34948-57. [PMID: 11457827 DOI: 10.1074/jbc.m102161200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mammalian, plant, and Schizosaccharomyces pombe eukaryotic initiation factor-3 (eIF3) contains a protein homologous to the product of int-6 (eIF3e), a frequent integration site of mouse mammary tumor viruses. By contrast, Saccharomyces cerevisiae does not encode a protein closely related to eIF3e/Int-6. Here, we characterize a novel S. cerevisiae protein (Pci8p, Yil071cp) that contains a PCI (proteasome-COP9 signalosome-eIF3) domain conserved in eIF3e/Int-6. We show that both Pci8p and human eIF3e/Int-6 expressed in budding yeast interact with the yeast eIF3 complex in vivo and in vitro by binding to a discrete segment of its eIF3b subunit Prt1p and that human eIF3e/Int-6 interacts with the human eIF3b segment homologous to the Pci8p-binding site of yeast Prt1p. These results refine our understanding of subunit interactions in the eIF3 complex and suggest structural similarity between human eIF3e/Int-6 and yeast Pci8p. However, deletion of PCI8 had no discernible effect on cell growth or translation initiation as judged by polysome analysis, suggesting that Pci8p is not required for the essential function of eIF3 in translation initiation. Motivated by the involvement of Int-6 in transcriptional control, we investigated the effects of deleting PCI8 on the total mRNA expression profile by oligonucleotide microarray analysis and found reduced mRNA levels for a subset of heat shock proteins in the pci8Delta mutant. We discuss possible dual functions of Pci8p and Int-6 in transcriptional and translational control.
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Affiliation(s)
- A Shalev
- Laboratory of Gene Regulation and Development, NICHD, and the Basic Research Laboratory, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA
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75
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Wang X, Paulin FE, Campbell LE, Gomez E, O’Brien K, Morrice N, Proud CG. Eukaryotic initiation factor 2B: identification of multiple phosphorylation sites in the epsilon-subunit and their functions in vivo. EMBO J 2001; 20:4349-59. [PMID: 11500362 PMCID: PMC125262 DOI: 10.1093/emboj/20.16.4349] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Eukaryotic initiation factor (eIF) 2B is a heteromeric guanine nucleotide exchange factor that plays an important role in regulating mRNA translation. Here we identify multiple phosphorylation sites in the largest, catalytic, subunit (epsilon) of mammalian eIF2B. These sites are phosphorylated by four different protein kinases. Two conserved sites (Ser712/713) are phosphorylated by casein kinase 2. They lie at the extreme C-terminus and are required for the interaction of eIF2Bepsilon with its substrate, eIF2, in vivo and for eIF2B activity in vitro. Glycogen synthase kinase 3 (GSK3) is responsible for phosphorylating Ser535. This regulatory phosphorylation event requires both the fourth site (Ser539) and a distal region, which acts to recruit GSK3 to eIF2Bepsilon in vivo. The fifth site, which lies outside the catalytic domain of eIF2Bepsilon, can be phosphorylated by casein kinase 1. All five sites are phosphorylated in the eIF2B complex in vivo.
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Affiliation(s)
| | | | | | | | | | - Nicholas Morrice
- Division of Molecular Physiology, School of Life Sciences and
MRC Protein Phosphorylation Unit, MSI/WTB Complex, University of Dundee, Dundee DD1 5EH, UK Corresponding author e-mail:
X.Wang and F.E.M.Paulin contributed equally to this work
| | - Christopher G. Proud
- Division of Molecular Physiology, School of Life Sciences and
MRC Protein Phosphorylation Unit, MSI/WTB Complex, University of Dundee, Dundee DD1 5EH, UK Corresponding author e-mail:
X.Wang and F.E.M.Paulin contributed equally to this work
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76
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Williams DD, Price NT, Loughlin AJ, Proud CG. Characterization of the mammalian initiation factor eIF2B complex as a GDP dissociation stimulator protein. J Biol Chem 2001; 276:24697-703. [PMID: 11323413 DOI: 10.1074/jbc.m011788200] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Initiation factor eIF2B mediates a key regulatory step in the initiation of mRNA translation, i.e. the regeneration of active eIF2.GTP complexes. It is composed of five subunits, alpha-epsilon. The largest of these (epsilon) displays catalytic activity in the absence of the others. The catalytic mechanism of eIF2B and the functions of the other subunits remain to be clarified. Here we show that, when present at similar concentrations to eIF2, mammalian eIF2B can mediate release of eIF2-bound GDP even in the absence of free nucleotide, indicating that it acts as a GDP dissociation stimulator protein. Consistent with this, addition of GDP to purified eIF2.eIF2B complexes causes them to dissociate. The alternative sequential mechanism would require that eIF2Bepsilon itself bind GTP. However, we show that it is the beta-subunit of eIF2B that interacts with GTP. This indicates that binding of GTP to eIF2B is not an essential element of its mechanism. eIF2B preparations that lack the alpha-subunit display reduced activity compared with the holocomplex. Supplementation of such preparations with recombinant eIF2Balpha markedly enhances activity, indicating that eIF2Balpha is required for full activity of mammalian eIF2B.
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Affiliation(s)
- D D Williams
- School of Life Sciences, Medical Sciences Institute/Wellcome Trust Biocentre Complex, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland, United Kingdom
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77
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Erickson FL, Nika J, Rippel S, Hannig EM. Minimum requirements for the function of eukaryotic translation initiation factor 2. Genetics 2001; 158:123-32. [PMID: 11333223 PMCID: PMC1461651 DOI: 10.1093/genetics/158.1.123] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Eukaryotic translation initiation factor 2 (eIF2) is a G protein heterotrimer required for GTP-dependent delivery of initiator tRNA to the ribosome. eIF2B, the nucleotide exchange factor for eIF2, is a heteropentamer that, in yeast, is encoded by four essential genes and one nonessential gene. We found that increased levels of wild-type eIF2, in the presence of sufficient levels of initiator tRNA, overcome the requirement for eIF2B in vivo. Consistent with bypassing eIF2B, these conditions also suppress the lethal effect of overexpressing the mammalian tumor suppressor PKR, an eIF2alpha kinase. The effects described are further enhanced in the presence of a mutation in the G protein (gamma) subunit of eIF2, gcd11-K250R, which mimics the function of eIF2B in vitro. Interestingly, the same conditions that bypass eIF2B also overcome the requirement for the normally essential eIF2alpha structural gene (SUI2). Our results suggest that the eIF2betagamma complex is capable of carrying out the essential function(s) of eIF2 in the absence of eIF2alpha and eIF2B and are consistent with the idea that the latter function primarily to regulate the level of eIF2.GTP.Met-tRNA(i)(Met) ternary complexes in vivo.
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Affiliation(s)
- F L Erickson
- Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, TX 75083-0688, USA
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78
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Williams DD, Pavitt GD, Proud CG. Characterization of the initiation factor eIF2B and its regulation in Drosophila melanogaster. J Biol Chem 2001; 276:3733-42. [PMID: 11060303 DOI: 10.1074/jbc.m008041200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic initiation factor (eIF) 2B catalyzes a key regulatory step in the initiation of mRNA translation. eIF2B is well characterized in mammals and in yeast, although little is known about it in other eukaryotes. eIF2B is a hetropentamer which mediates the exchange of GDP for GTP on eIF2. In mammals and yeast, its activity is regulated by phosphorylation of eIF2alpha. Here we have cloned Drosophila melanogaster cDNAs encoding polypeptides showing substantial similarity to eIF2B subunits from yeast and mammals. They also exhibit the other conserved features of these proteins. D. melanogaster eIF2Balpha confers regulation of eIF2B function in yeast, while eIF2Bepsilon shows guanine nucleotide exchange activity. In common with mammalian eIF2Bepsilon, D. melanogaster eIF2Bepsilon is phosphorylated by glycogen synthase kinase-3 and casein kinase II. Phosphorylation of partially purified D. melanogaster eIF2B by glycogen synthase kinase-3 inhibits its activity. Extracts of D. melanogaster S2 Schneider cells display eIF2B activity, which is inhibited by phosphorylation of eIF2alpha, showing the insect factor is regulated similarly to eIF2B from other species. In S2 cells, serum starvation increases eIF2alpha phosphorylation, which correlates with inhibition of eIF2B, and both effects are reversed by serum treatment. This shows that eIF2alpha phosphorylation and eIF2B activity are under dynamic regulation by serum. eIF2alpha phosphorylation is also increased by endoplasmic reticulum stress in S2 cells. These are the first data concerning the structure, function or control of eIF2B from D. melanogaster.
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Affiliation(s)
- D D Williams
- School of Life Sciences, Medical Sciences Institute/Wellcome Trust Biocentre Complex, University of Dundee, Dundee DD1 5EH, United Kingdom
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79
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Nika J, Rippel S, Hannig EM. Biochemical analysis of the eIF2beta gamma complex reveals a structural function for eIF2alpha in catalyzed nucleotide exchange. J Biol Chem 2001; 276:1051-6. [PMID: 11042214 DOI: 10.1074/jbc.m007398200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic translation initiation factor eIF2 is a heterotrimer that binds and delivers Met-tRNA(i)(Met) to the 40 S ribosomal subunit in a GTP-dependent manner. Initiation requires hydrolysis of eIF2-bound GTP, which releases an eIF2.GDP complex that is recycled to the GTP form by the nucleotide exchange factor eIF2B. The alpha-subunit of eIF2 plays a critical role in regulating nucleotide exchange via phosphorylation at serine 51, which converts eIF2 into a competitive inhibitor of the eIF2B-catalyzed exchange reaction. We purified a form of eIF2 (eIF2betagamma) completely devoid of the alpha-subunit to further study the role of eIF2alpha in eIF2 function. These studies utilized a yeast strain genetically altered to bypass a deletion of the normally essential eIF2alpha structural gene (SUI2). Removal of the alpha-subunit did not appear to significantly alter binding of guanine nucleotide or Met-tRNA(i)(Met) ligands by eIF2 in vitro. Qualitative assays to detect 43 S initiation complex formation and eIF5-dependent GTP hydrolysis revealed no differences between eIF2betagamma and the wild-type eIF2 heterotrimer. However, steady-state kinetic analysis of eIF2B-catalyzed nucleotide exchange revealed that the absence of the alpha-subunit increased K(m) for eIF2betagamma.GDP by an order of magnitude, with a smaller increase in V(max). These data indicate that eIF2alpha is required for structural interactions between eIF2 and eIF2B that promote wild-type rates of nucleotide exchange. We suggest that this function contributes to the ability of the alpha-subunit to control the rate of nucleotide exchange through reversible phosphorylation.
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Affiliation(s)
- J Nika
- Department of Molecular and Cell Biology, The University of Texas at Dallas, Richardson, Texas 75083, USA
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