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Gorbatyuk MS, Starr CR, Gorbatyuk OS. Endoplasmic reticulum stress: New insights into the pathogenesis and treatment of retinal degenerative diseases. Prog Retin Eye Res 2020; 79:100860. [PMID: 32272207 DOI: 10.1016/j.preteyeres.2020.100860] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2019] [Revised: 03/08/2020] [Accepted: 03/17/2020] [Indexed: 12/13/2022]
Abstract
Physiological equilibrium in the retina depends on coordinated work between rod and cone photoreceptors and can be compromised by the expression of mutant proteins leading to inherited retinal degeneration (IRD). IRD is a diverse group of retinal dystrophies with multifaceted molecular mechanisms that are not fully understood. In this review, we focus on the contribution of chronically activated unfolded protein response (UPR) to inherited retinal pathogenesis, placing special emphasis on studies employing genetically modified animal models. As constitutively active UPR in degenerating retinas may activate pro-apoptotic programs associated with oxidative stress, pro-inflammatory signaling, dysfunctional autophagy, free cytosolic Ca2+ overload, and altered protein synthesis rate in the retina, we focus on the regulatory mechanisms of translational attenuation and approaches to overcoming translational attenuation in degenerating retinas. We also discuss current research on the role of the UPR mediator PERK and its downstream targets in degenerating retinas and highlight the therapeutic benefits of reprogramming PERK signaling in preclinical animal models of IRD. Finally, we describe pharmacological approaches targeting UPR in ocular diseases and consider their potential applications to IRD.
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Affiliation(s)
- Marina S Gorbatyuk
- The University of Alabama at Birmingham, Department of Optometry and Vision Science, School of Optometry, USA.
| | - Christopher R Starr
- The University of Alabama at Birmingham, Department of Optometry and Vision Science, School of Optometry, USA
| | - Oleg S Gorbatyuk
- The University of Alabama at Birmingham, Department of Optometry and Vision Science, School of Optometry, USA
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2
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Barth-Baus D, Bhasker CR, Zoll W, Merrick WC. Influence of translation factor activities on start site selection in six different mRNAs. ACTA ACUST UNITED AC 2013; 1:e24419. [PMID: 26824019 PMCID: PMC4718060 DOI: 10.4161/trla.24419] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2013] [Revised: 03/21/2013] [Accepted: 03/22/2013] [Indexed: 11/19/2022]
Abstract
Current literature using biochemical assays, structural analyses and genetic manipulations has reported that the key factors associated with the faithful matching of the initiator met-tRNA to the start codon AUG are eIF1, eIF1A and eIF5. However, these findings were in each case based upon the utilization of a single mRNA, perhaps with variations. In an effort to evaluate this general finding, we tested six different mRNAs. Our results confirm that these three proteins are important for start site selection. However, two additional findings would not have been predicted. The first is that eIF1 plays a major role in selecting against start codons that are in close proximity to the 5′ end of the mRNA (i.e., less than 21 nucleotides). Second, the addition of eIF5B had nearly the same affect as the addition of eIF5. This is unexpected given the different roles that eIF5 and eIF5B have been proposed to play in the 80S initiation pathway. Finally, although many of the mRNAs appear to respond qualitatively in a similar manner, the quantitative differences noted suggest that there is still some mRNA specific character to our findings. This character may be the length of the 5′ UTR, involvement of an IRES element, secondary structure either 5′ or 3′ of the start codon or specific sequence/structure elements that interact with RNA binding proteins or the ribosome.
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Affiliation(s)
- Daine Barth-Baus
- Department of Biochemistry; School of Medicine; Case Western Reserve University; Cleveland, OH USA
| | | | - Wendy Zoll
- Biology Department; Montgomery County Community College; Blue Bell, PA USA
| | - William C Merrick
- Department of Biochemistry; School of Medicine; Case Western Reserve University; Cleveland, OH USA
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3
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Grzmil M, Rzymski T, Milani M, Harris AL, Capper RG, Saunders NJ, Salhan A, Ragoussis J, Norbury CJ. An oncogenic role of eIF3e/INT6 in human breast cancer. Oncogene 2010; 29:4080-9. [PMID: 20453879 DOI: 10.1038/onc.2010.152] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Altered expression of the eukaryotic translation initiation factor 3 (eIF3) subunit eIF3e/INT6 has been described in various types of human cancer, but the nature of its involvement in tumorigenesis is not yet clear. Using immunohistochemical analysis of 81 primary breast cancers, we found that high tumor grade correlated significantly with elevated cytoplasmic eIF3e level in epithelial tumor cells. Analysis of protein synthesis after siRNA-mediated knockdown in breast cancer cell lines indicated that eIF3e is not required for bulk translation. Microarray analysis of total and polysomal RNAs nonetheless identified distinct sets of mRNAs regulated either positively or negatively by eIF3e; functional classification of these revealed a marked enrichment of genes involved in cell proliferation, invasion and apoptosis. Validated mRNA targets regulated positively at the translational level by eIF3e included urokinase-type plasminogen activator and apoptotic regulator BCL-XL, whereas synthesis of proteins including the mitotic checkpoint component MAD2L1 was negatively regulated. Finally, eIF3e-depleted breast carcinoma cells showed reduced in vitro invasion and proliferation. Taken together, our study data suggest that eIF3e has a positive role in breast cancer progression. It regulates the translation, and in some cases abundance, of mRNAs involved in key aspects of cancer cell biology.
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Affiliation(s)
- M Grzmil
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
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4
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The SXL-UNR corepressor complex uses a PABP-mediated mechanism to inhibit ribosome recruitment to msl-2 mRNA. Mol Cell 2009; 36:571-82. [PMID: 19941818 DOI: 10.1016/j.molcel.2009.09.042] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2009] [Revised: 07/06/2009] [Accepted: 09/08/2009] [Indexed: 11/22/2022]
Abstract
Drosophila female viability requires translational repression of msl-2 mRNA by the SXL-UNR 3' UTR corepressor complex, which inhibits ribosome recruitment by an unknown mechanism. Here, we reveal a key role for the poly(A)-binding protein (PABP), a translational activator, in this inhibitory mechanism. Efficient msl-2 mRNA silencing via the 3' UTR requires both a poly(A) tail and PABP function, and we find that UNR directly interacts with PABP. To investigate how the repressor complex and PABP affect RNP composition during early steps in translation initiation, we established direct biochemical assays for synergistic recruitment of eIF4F and ribosomes by the cap and poly(A) tail. We find that the repressor complex targets ribosome binding after PABP-mediated recruitment of eIF4E/G. Our results uncover an important regulatory mechanism of Drosophila dosage compensation and provide insight into PABP-dependent translational control by 3' UTR-bound regulatory proteins.
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5
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Easton LE, Locker N, Lukavsky PJ. Conserved functional domains and a novel tertiary interaction near the pseudoknot drive translational activity of hepatitis C virus and hepatitis C virus-like internal ribosome entry sites. Nucleic Acids Res 2009; 37:5537-49. [PMID: 19596815 PMCID: PMC2760816 DOI: 10.1093/nar/gkp588] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The translational activity of the hepatitis C virus (HCV) internal ribosome entry site (IRES) and other HCV-like IRES RNAs depends on structured RNA elements in domains II and III, which serve to recruit the ribosomal 40S subunit, eukaryotic initiation factor (eIF) 3 and the ternary eIF2/Met-tRNAiMet/GTP complex and subsequently domain II assists subunit joining. Porcine teschovirus-1 talfan (PTV-1) is a member of the Picornaviridae family, with a predicted HCV-like secondary structure, but only stem-loops IIId and IIIe in the 40S-binding domain display significant sequence conservation with the HCV IRES. Here, we use chemical probing to show that interaction sites with the 40S subunit and eIF3 are conserved between HCV and HCV-like IRESs. In addition, we reveal the functional role of a strictly conserved co-variation between a purine–purine mismatch near the pseudoknot (A–A/G) and the loop sequence of domain IIIe (GAU/CA). These nucleotides are involved in a tertiary interaction, which serves to stabilize the pseudoknot structure and correlates with translational efficiency in both the PTV-1 and HCV IRES. Our data demonstrate conservation of functional domains in HCV and HCV-like IRESs including a more complex structure surrounding the pseudoknot than previously assumed.
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Affiliation(s)
- Laura E Easton
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK
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6
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Zeenko VV, Wang C, Majumder M, Komar AA, Snider MD, Merrick WC, Kaufman RJ, Hatzoglou M. An efficient in vitro translation system from mammalian cells lacking the translational inhibition caused by eIF2 phosphorylation. RNA (NEW YORK, N.Y.) 2008; 14:593-602. [PMID: 18230759 PMCID: PMC2248251 DOI: 10.1261/rna.825008] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2007] [Accepted: 12/05/2007] [Indexed: 05/25/2023]
Abstract
In vitro translation systems are used to investigate translational mechanisms and to synthesize proteins for characterization. Most available mammalian cell-free systems have reduced efficiency due to decreased translation initiation caused by phosphorylation of the initiation factor eIF2alpha on Ser51. We describe here a novel cell-free protein synthesis system using extracts from cultured mouse embryonic fibroblasts that are homozygous for the Ser51 to- Ala mutation in eIF2alpha (A/A cells). The translation efficiency of a capped and polyadenylated firefly luciferase mRNA in A/A cell extracts was 30-fold higher than in wild-type extracts. Protein synthesis in extracts from A/A cells was active for at least 2 h and generated up to 20 microg/mL of luciferase protein. Additionally, the A/A cell-free system faithfully recapitulated the selectivity of in vivo translation for mRNA features; translation was stimulated by a 5'-end cap (m7GpppN) and a 3'-end poly(A) tail in a synergistic manner. The system also showed similar efficiencies of cap-dependent and IRES-mediated translation (EMCV IRES). Significantly, the A/A cell-free system supported the post-translational modification of proteins, as shown by glycosylation of the HIV type-1 gp120 and cleavage of the signal peptide from beta-lactamase. We propose that cell-free systems from A/A cells can be a useful tool for investigating mechanisms of mammalian mRNA translation and for the production of recombinant proteins for molecular studies. In addition, cell-free systems from differentiated cells with the Ser51Ala mutation should provide a means for investigating cell type-specific features of protein synthesis.
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Affiliation(s)
- Vladimir V Zeenko
- Department of Nutrition, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
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7
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Locker N, Easton LE, Lukavsky PJ. HCV and CSFV IRES domain II mediate eIF2 release during 80S ribosome assembly. EMBO J 2007; 26:795-805. [PMID: 17255934 PMCID: PMC1794401 DOI: 10.1038/sj.emboj.7601549] [Citation(s) in RCA: 123] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2006] [Accepted: 12/15/2006] [Indexed: 01/11/2023] Open
Abstract
Internal ribosome entry site (IRES) RNAs from the hepatitis C virus (HCV) and classical swine fever virus (CSFV) coordinate cap-independent assembly of eukaryotic 48S initiation complexes, consisting of the 40S ribosomal subunit, eukaryotic initiation factor (eIF) 3 and the eIF2/GTP/Met-tRNA(i)(Met) ternary complex. Here, we report that these IRESes also play a functional role during 80S ribosome assembly downstream of 48S complex formation, in promoting eIF5-induced GTP hydrolysis and eIF2/GDP release from the initiation complex. We show that this function is encoded in their independently folded IRES domain II and that it depends both on its characteristic bent conformation and two conserved RNA motifs, an apical hairpin loop and a loop E. Our data suggest a general mode of subunit joining in HCV and HCV-like IRESes.
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Affiliation(s)
- Nicolas Locker
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
| | - Laura E Easton
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
| | - Peter J Lukavsky
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
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8
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Merrick WC, Barth-Baus D. Use of Reticulocyte Lysates for Mechanistic Studies of Eukaryotic Translation Initiation. Methods Enzymol 2007; 429:1-21. [PMID: 17913616 DOI: 10.1016/s0076-6879(07)29001-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/22/2023]
Abstract
This chapter describes how commercially available, nuclease-treated rabbit reticulocyte lysates can be used to study different types of translation initiation (cap-dependent initiation, reinitiation, internal ribosome entry site-mediated initiation) and the influence of different initiation factors on these translation mechanisms. Additionally, with the use of sucrose gradients, it is possible to use nuclease-treated reticulocyte lysates to monitor the formation of ribosomal complexes for their content of mRNA, initiator met-tRNA(i), and initiation factors. The advantage of using nuclease-treated lysates rather than purified initiation factors is that reactions occur at or near the in vivo rate in contrast to rates observed in reactions with purified components, which are generally 10- to 1000-fold lower. The disadvantage is not being able to accurately control the amount of individual initiation factors, although the use of either factor additions or specific inhibitors can be helpful in assessing the role of specific individual initiation factors.
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Affiliation(s)
- William C Merrick
- Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA
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9
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Locker N, Lukavsky PJ. A practical approach to isolate 48S complexes: affinity purification and analyses. Methods Enzymol 2007; 429:83-104. [PMID: 17913620 DOI: 10.1016/s0076-6879(07)29005-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
In vitro assembly of eukaryotic translation initiation complexes requires purification of ribosomal subunits, eukaryotic initiation factors, and initiator tRNA from natural sources and therefore yields only limited material for functional and structural studies. In this chapter, we describe a robust, affinity chromatography-based method for the isolation of eukaryotic 48S initiation complexes from rabbit reticulocyte lysate (RRL). Both canonical and internal ribosome entry site (IRES)-containing mRNAs labeled with a streptomycin aptamer sequence at the 3' end can be used to purify milligram quantities of 48S particles in a simple, two-step procedure. The 48S complexes purified with this method are properly assembled at the initiation codon, contain the expected RNA and protein components in a 1:1 stoichiometry, and are functional intermediates along the initiation pathway.
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Affiliation(s)
- Nicolas Locker
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
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10
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Locker N, Easton LE, Lukavsky PJ. Affinity purification of eukaryotic 48S initiation complexes. RNA (NEW YORK, N.Y.) 2006; 12:683-90. [PMID: 16484374 PMCID: PMC1421092 DOI: 10.1261/rna.2227906] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
In vitro assembly of translation initiation complexes from higher eukaryotes requires purification of ribosomal subunits, eukaryotic initiation factors, and initiator tRNA from natural sources, and therefore yields only limited material for functional and structural studies. Here we describe a robust, affinity chromatography-based purification of eukaryotic 48S initiation complexes from rabbit reticulocyte lysate (RRL), which significantly reduces the number of individual purification steps. Hybrid RNA molecules, consisting of either a canonical 5' UTR or an internal ribosome entry site (IRES) RNA followed by a short open reading frame and a streptomycin aptamer sequence, are incubated in RRL to form 48S complexes. The assembly reaction is then applied to a dihydrostreptomycin-sepharose column; bound complexes are washed and specifically eluted upon addition of streptomycin. The eluted fractions are further purified by centrifugation through a sucrose density gradient to yield pure 48S particles. Using this purification scheme, properly assembled IRES-mediated as well as canonical 48S complexes were purified in milligram quantities.
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Affiliation(s)
- Nicolas Locker
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom
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11
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Merrick WC. Cap-dependent and cap-independent translation in eukaryotic systems. Gene 2004; 332:1-11. [PMID: 15145049 DOI: 10.1016/j.gene.2004.02.051] [Citation(s) in RCA: 194] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2003] [Revised: 02/04/2004] [Accepted: 02/27/2004] [Indexed: 12/21/2022]
Abstract
Unlike bacterial protein synthesis, eukaryotic protein synthesis has several mechanisms to initiate translation including cap-dependent initiation, re-initiation and internal initiation. While there is extensive biochemical characterization of the multiple steps in cap-dependent initiation, most of the information on the other two mechanisms is derived from studies on the nucleic acid sequences that influence their efficiency. However, even in the best of circumstances, both re-initiation and internal initiation are only 25% as efficient as cap-dependent initiation and more commonly, are only 1-10% as efficient. This general lack of efficiency leaves open possibilities for mis-interpretation/artifacts in vivo (cryptic promoters, alternate splicing) or in vitro (nuclease degradation). Two examples are cited from the author's laboratory as background for the development of a general set of guidelines to minimize errors and validate authenticity for internal initiation.
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Affiliation(s)
- William C Merrick
- Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4935, USA.
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12
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Abstract
Great advances have been made in the past three decades in understanding the molecular mechanics underlying protein synthesis in bacteria, but our understanding of the corresponding events in eukaryotic organisms is only beginning to catch up. In this review we describe the current state of our knowledge and ignorance of the molecular mechanics underlying eukaryotic translation. We discuss the mechanisms conserved across the three kingdoms of life as well as the important divergences that have taken place in the pathway.
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Affiliation(s)
- Lee D Kapp
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205-2185, USA.
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13
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Lee JH, Pestova TV, Shin BS, Cao C, Choi SK, Dever TE. Initiation factor eIF5B catalyzes second GTP-dependent step in eukaryotic translation initiation. Proc Natl Acad Sci U S A 2002; 99:16689-94. [PMID: 12471154 PMCID: PMC139205 DOI: 10.1073/pnas.262569399] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Initiation factors IF2 in bacteria and eIF2 in eukaryotes are GTPases that bind Met-tRNA(i)(Met) to the small ribosomal subunit. eIF5B, the eukaryotic ortholog of IF2, is a GTPase that promotes ribosomal subunit joining. Here we show that eIF5B GTPase activity is required for protein synthesis. Mutation of the conserved Asp-759 in human eIF5B GTP-binding domain to Asn converts eIF5B to an XTPase and introduces an XTP requirement for subunit joining and translation initiation. Thus, in contrast to bacteria where the single GTPase IF2 is sufficient to catalyze translation initiation, eukaryotic cells require hydrolysis of GTP by both eIF2 and eIF5B to complete translation initiation.
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Affiliation(s)
- Joon H Lee
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2716, USA
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14
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Zoll WL, Horton LE, Komar AA, Hensold JO, Merrick WC. Characterization of mammalian eIF2A and identification of the yeast homolog. J Biol Chem 2002; 277:37079-87. [PMID: 12133843 DOI: 10.1074/jbc.m207109200] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To begin the physical characterization of eukaryotic initiation factor (eIF) 2A, a translation initiation factor that binds Met-tRNA(i), tryptic peptides from rabbit reticulocyte eIF2A were analyzed to obtain amino acid sequence information. Sequences for 8 peptides were matched to three different expressed sequence tag clones. The sequence predicted for eIF2A is 585 amino acids. Matching of the cDNA sequence to the human genome revealed that the eIF2A mRNA is made up of 15 or 16 exons, and the gene is contained on chromosome 3. A homolog in Saccharomyces cerevisiae was identified, YGR054W, which is a non-essential gene. Hemagglutinin-tagged yeast eIF2A localizes on both 40 S and 80 S ribosomes. A knockout of both eIF2A and eIF5B yielded a "synthetically sick" yeast strain with a severe slow growth phenotype. The phenotype of this double mutant and the biochemical localization suggest that eIF2A participates in translation initiation. eIF2A does not appear to participate in re-initiation as the DeltaeIF2A strain shows the same level of GCN4 induction with amino acid starvation as seen in wild type yeast. The lack of any apparent phenotype in the DeltaeIF2A strain suggests that eIF2A functions in a minor pathway, perhaps internal initiation or in the translation of a small number of specific mRNAs.
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Affiliation(s)
- Wendy L Zoll
- Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4935, USA
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15
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Shaikhin SM, Smailov SK, Lee AV, Kozhanov EV, Iskakov BK. Interaction of wheat germ translation initiation factor 2 with GDP and GTP. Biochimie 1992; 74:447-54. [PMID: 1637870 DOI: 10.1016/0300-9084(92)90085-s] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The wheat germ translation initiation factor 2 (WGeIF-2) was isolated in a homogeneous state by an efficient procedure and characterized. Its molecular mass, as determined by a gel-filtration method is approximately 150,000 Da. According to SDS-PAGE WGeIF-2 consists of four subunits with M(r) 37,000 (alpha), 40,000 (beta), 42,000 (gamma) and 52,000 (delta). The beta- and gamma-subunits (but not the alpha-subunit) of WGeIF-2 can be readily phosphorylated by the double-stranded RNA activated kinase isolated from rabbit reticulocytes. Dissociation constants for WGeIF-2 complexes with GDP and GTP were measured. In our evaluation the WGeIF-2 affinity for GDP (KdGDP = 1.5 x 10(-7) M) was only 10 times higher than for GTP (KdGTP = 1.5 x 10(-6) M), while for rabbit reticulocyte eIF-2 (RReIF-2) the difference has been estimated as as much as two orders of magnitude in accordance with the literature. Close values of dissociation constants for WGeIF-2 complexes with guanine nucleotides suggest that at a sufficiently high [GTP]/[GDP] ratio the nucleotide exchange in wheat cells may take place without the participation of specific factor (eIF-2B) which catalyzes the nucleotide exchange on eIF-2 from mammalian cells.
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Affiliation(s)
- S M Shaikhin
- Ajtkhozhin Institute of Molecular Biology and Biochemistry, Kazakh Academy of Sciences, Alma-Ata, Michurina, Kazakhstan
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16
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Increase in eukaryotic initiation factor 2B activity following fertilization reflects changes in redox potential. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54250-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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17
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London IM, Levin DH, Matts RL, Thomas NSB, Petryshyn R, Chen JJ. 12 Regulation of Protein Synthesis. CONTROL BY PHOSPHORYLATION PART B - SPECIFIC ENZYMES (II) BIOLOGICAL PROCESSES 1987. [DOI: 10.1016/s1874-6047(08)60263-2] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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18
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Thomas NS, Matts RL, London IM. The storage of globin mRNA during the inhibition of protein synthesis by heme deprivation. Biochem Biophys Res Commun 1986; 134:1048-55. [PMID: 3947357 DOI: 10.1016/0006-291x(86)90357-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The inhibition of protein synthesis in reticulocytes and their lysates caused by heme-deprivation is reversible on restoration of an optimal heme concentration. Inhibition is accompanied by the disaggregation of polyribosomes and the accumulation of components of the translational mechanism. By determining the fate of labeled globin 9S mRNA added to an unfractionated reticulocyte lysate cell-free system, we find that normal cellular mRNA accumulates during inhibition in 20S and 48S complexes and in a complex which sediments just ahead of the 80S ribosome dimer OD260 peak (designated as greater than or equal to 80S complex)1. The 20S and greater than 80S complexes are the major pools of stored mRNA which is readily translated if optimal heme conditions are restored. In the 48S complex, however, the mRNA remains non-functional, and the complex is abortive, probably as a result of deacylation of the Met.tRNAf.
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19
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Thomas NS, Matts RL, Levin DH, London IM. The 60 S ribosomal subunit as a carrier of eukaryotic initiation factor 2 and the site of reversing factor activity during protein synthesis. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(17)39316-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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20
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Crouch D, Safer B. The association of eIF-2 with Met-tRNAi or eIF-2B alters the specificity of eIF-2 phosphatase. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(18)90973-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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21
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Goss DJ, Parkhurst LJ, Mehta HB, Woodley CL, Wahba AJ. Studies on the role of eukaryotic nucleotide exchange factor in polypeptide chain initiation. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(17)42798-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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22
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Wahba AJ, Woodley CL. Molecular aspects of development in the brine shrimp Artemia. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1984; 31:221-65. [PMID: 6397772 DOI: 10.1016/s0079-6603(08)60379-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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23
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De Benedetti A, Baglioni C. Phosphorylation of initiation factor eIF-2 alpha, binding of mRNA to 48 S complexes, and its reutilization in initiation of protein synthesis. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(17)43899-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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24
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Pain VM, Clemens MJ. Assembly and breakdown of mammalian protein synthesis initiation complexes: regulation by guanine nucleotides and by phosphorylation of initiation factor eIF-2. Biochemistry 1983; 22:726-33. [PMID: 6551177 DOI: 10.1021/bi00273a003] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Eukaryotic cell polypeptide chain initiation factor eIF-2 forms ternary complexes with GTP and initiator Met-tRNAf. These complexes can be destabilized in vitro by the addition of salt-washed 40S ribosomal subunits. Our evidence suggests that this destabilization is mediated by GDP generated by premature hydrolysis of the GTP molecule present in the ternary complex. With complexes formed by using a partially purified preparation of eIF-2 from Ehrlich ascites tumor cells, it is possible to reverse the 40S subunit induced inhibition by creating conditions which eliminate free GDP from the system. This reversal probably occurs due to exchange of GTP for the GDP bound to the initiation factor, in a reaction catalyzed by another factor present in the eIF-2 preparation. However, if the eIF-2 has previously been phosphorylated by the reticulocyte heme-controlled repressor, the 40S subunit induced inhibition cannot be reversed by elimination of free GDP. The instability of initiation complexes containing eIF-2, together with the impairment of guanine nucleotide exchange after phosphorylation of eIF-2 [Clemens, M.J., Pain, V.M., Wong, S.-T., & Henshaw, E. C. (1982) Nature (London) 296, 93-95], may be an important aspect of the mechanism of the inhibition of translation by the heme-controlled repressor.
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Protein synthesis in brine shrimp embryos and rabbit reticulocytes. The effect of Mg2+ on binary (eukaryotic initiation factor 2 X GDP) and ternary (eukaryotic initiation factor 2 X GTP X met-tRNAf) complex formation. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)32679-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Jagus R, Crouch D, Konieczny A, Safer B. The role of phosphorylation in the regulation of eukaryotic initiation factor 2 activity. CURRENT TOPICS IN CELLULAR REGULATION 1982; 21:35-63. [PMID: 6291856 DOI: 10.1016/b978-0-12-152821-8.50006-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Van Dijk AM, King GB, Schotman P, Gispen WH. GTP-sensitive phosphorylation of proteins in a postmitochondrial supernatant from rat brainstem affected by ACTH1-24. Neurochem Res 1981; 6:847-61. [PMID: 6273759 DOI: 10.1007/bf00965043] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The effect of ACTH1-24 and cyclic nucleotides on the endogenous phosphorylation of proteins from a postmitochondrial supernatant from rat brainstem was investigated in the presence and absence of GTP. Phosphorylation and its modulation by these compounds were studied in vitro by incorporation of labeled phosphate from [gamma-32P]ATP added to the incubation mixture. Phosphoproteins were subsequently analyzed by autoradiography after one- and two-dimensional separation. Eight ACTH-sensitive phosphoproteins of molecular weights 75 (IEP 4.0), 67, 64, 50 (IEP 4.7), 47 (IEP 4.8), 38, 34, and 24K were found. The effects of ACTH on phosphorylation were mainly inhibitory, and the affected protein bands did not coincide with the phosphoproteins sensitive to cyclic AMP and cyclic GMP. Phosphorylation of those phosphoprotein bands and its ACTH sensitivity appeared to be highly sensitive to GTP. It is suggested that the activity of protein kinases involved in hormone-sensitive phosphorylation in a postmitochondrial rat brainstem fraction is regulated by GTP-dependent mechanisms.
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Mobilization of newly synthesized RNAs into polysomes inXenopus laevis embryos. ACTA ACUST UNITED AC 1981; 190:103-110. [DOI: 10.1007/bf00848403] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/1980] [Accepted: 02/26/1981] [Indexed: 11/25/2022]
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Jagus R, Anderson WF, Safer B. The regulation of initiation of mammalian protein synthesis. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1981; 25:127-85. [PMID: 6164076 DOI: 10.1016/s0079-6603(08)60484-5] [Citation(s) in RCA: 228] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Buhl WJ, Sarre TF, Hilse K. Characterization of a native mRNA containing preinitiation complex from rabbit reticulocytes: RNA and protein constituents. Biochem Biophys Res Commun 1980; 93:979-87. [PMID: 7387688 DOI: 10.1016/0006-291x(80)91172-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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Clemens MJ, Echetebu CO, Tilleray VJ, Pain VM. Stimulation of initiation factor eIF-2 by a rat liver protein with GDPase activity. Biochem Biophys Res Commun 1980; 92:60-7. [PMID: 6101948 DOI: 10.1016/0006-291x(80)91519-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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