201
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Gustin KE, Sarnow P. Inhibition of nuclear import and alteration of nuclear pore complex composition by rhinovirus. J Virol 2002; 76:8787-96. [PMID: 12163599 PMCID: PMC136411 DOI: 10.1128/jvi.76.17.8787-8796.2002] [Citation(s) in RCA: 150] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2002] [Accepted: 06/06/2002] [Indexed: 12/18/2022] Open
Abstract
Nucleocytoplasmic trafficking pathways and the status of nuclear pore complex (NPC) components were examined in cells infected with rhinovirus type 14. A variety of shuttling and nonshuttling nuclear proteins, using multiple nuclear import pathways, accumulated in the cytoplasm of cells infected with rhinovirus. An in vitro nuclear import assay with semipermeabilized infected cells confirmed that nuclear import was inhibited and that docking of nuclear import receptor-cargo complexes at the cytoplasmic face of the NPC was prevented in rhinovirus-infected cells. The relocation of cellular proteins and inhibition of nuclear import correlated with the degradation of two NPC components, Nup153 and p62. The degradation of Nup153 and p62 was not due to induction of apoptosis, because p62 was not proteolyzed in apoptotic HeLa cells, and Nup153 was cleaved to produce a 130-kDa cleavage product that was not observed in cells infected with poliovirus or rhinovirus. The finding that both poliovirus and rhinovirus cause inhibition of nuclear import and degradation of NPC components suggests that this may be a common feature of the replicative cycle of picornaviruses. Inhibition of nuclear import is predicted to result in the cytoplasmic accumulation of a large number of nuclear proteins that could have functions in viral translation, RNA synthesis, packaging, or assembly. Additionally, inhibition of nuclear import also presents a novel strategy whereby cytoplasmic RNA viruses can evade host immune defenses by preventing signal transduction into the nucleus.
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Affiliation(s)
- Kurt E Gustin
- Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305, USA
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202
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Abstract
As invading viruses do not harbor functional ribosomes in their virions, successful amplification of the viral genomes requires that viral mRNAs compete with cellular mRNAs for the host cell translation apparatus. Several RNA viruses have evolved remarkable strategies to recruit the host translation initiation factors required for the first steps in translation initiation by host cell mRNAs. This review describes the ways that three families of RNA viruses effectively usurp limiting translation initiation factors from the host.
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Affiliation(s)
- Martin Bushell
- Department of Microbiology and Immunology, Stanford University School of Medicine, CA 94305, USA
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203
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Martínez-Salas E, López de Quinto S, Ramos R, Fernández-Miragall O. IRES elements: features of the RNA structure contributing to their activity. Biochimie 2002; 84:755-63. [PMID: 12457563 DOI: 10.1016/s0300-9084(02)01408-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The activity of internal ribosome entry site (IRES) elements depends on their structural organization. We have addressed here the study of conserved structural motifs in the foot-and-mouth disease virus (FMDV) IRES as an example to understand the relationship between RNA structure and function. The features of the RNA structure known to be functionally relevant are discussed in regards to the capacity to modulate interaction of translation initiation factors with the FMDV IRES element. Additionally, the contribution of non-canonical RNA-binding proteins to FMDV IRES organization as well as stimulation of its activity by other mRNA regions is discussed.
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Affiliation(s)
- Encarnación Martínez-Salas
- Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Cantoblanco 28049, Madrid, Spain.
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204
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Back SH, Shin S, Jang SK. Polypyrimidine tract-binding proteins are cleaved by caspase-3 during apoptosis. J Biol Chem 2002; 277:27200-9. [PMID: 12004072 DOI: 10.1074/jbc.m203887200] [Citation(s) in RCA: 35] [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
The polypyrimidine tract-binding protein (PTB), an RNA-binding protein, is required for efficient translation of some mRNAs containing internal ribosomal entry sites (IRESs). Here we provide evidence that the addition of apoptosis-inducing agents to cells results in the cleavage of PTB isoforms 1, 2, and 4 by caspase-3. This cleavage of PTB separated the N-terminal region, containing NLS-RRM1, from the C-terminal region, containing RRM2-3-4. Our data indicate that there are three noncanonical caspase-3 target sites in PTBs, namely Ile-Val-Pro-Asp(7)Ile, Leu-Tyr-Thr-Asp(139)Ser, and Ala-Ala-Val-Asp(172)Ala. The C-terminal PTB fragments localized to the cytoplasm, as opposed to the nucleus where most intact PTBs are found. Moreover, these C-terminal PTB fragments inhibited translation of polioviral mRNA, which contains an IRES element requiring PTB for its activation. This suggests that translation of some IRES-containing mRNAs is regulated by proteolytic cleavage of PTB during apoptosis.
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Affiliation(s)
- Sung Hoon Back
- National Research Laboratory, Department of Life Science, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San31, Hyoja-Dong, Pohang, Kyungbuk 790-784, Korea
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205
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Liebig HD, Seipelt J, Vassilieva E, Gradi A, Kuechler E. A thermosensitive mutant of HRV2 2A proteinase: evidence for direct cleavage of eIF4GI and eIF4GII. FEBS Lett 2002; 523:53-7. [PMID: 12123803 DOI: 10.1016/s0014-5793(02)02933-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Infection of mammalian cells with picornaviruses like entero-, rhino-, and aphthoviruses leads to an inhibition of cap-dependent cellular protein synthesis by the cleavage of both translation initiation factors, eIF4GI and eIF4GII. In entero- and rhinovirus infection this cleavage process is mediated by the viral 2A proteinase (2A(pro)). In order to discriminate between a direct mode of eIF4G cleavage and an indirect cleavage via activation of a cellular proteinase, a thermosensitive 2A(pro) mutant (ts-2A(pro)) of human rhinovirus 2 was employed. Temperature shift experiments of cytoplasmic HeLa cell extracts incubated with ts-2A(pro) strongly support a direct mode of cleavage of eIF4GI and eIF4GII by the viral 2A(pro).
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Affiliation(s)
- Hans Dieter Liebig
- Institute of Medical Biochemistry, Division of Biochemistry, University of Vienna, Dr. Bohrgasse 9/3, 1030, Vienna, Austria
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206
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Byrd MP, Zamora M, Lloyd RE. Generation of multiple isoforms of eukaryotic translation initiation factor 4GI by use of alternate translation initiation codons. Mol Cell Biol 2002; 22:4499-511. [PMID: 12052860 PMCID: PMC133909 DOI: 10.1128/mcb.22.13.4499-4511.2002] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Eukaryotic translation initiation factor 4GI (eIF4GI) is an essential protein that is the target for translational regulation in many cellular processes and viral systems. It has been shown to function in both cap-dependent and cap-independent translation initiation by recruiting the 40S ribosomal subunit to the mRNA cap structure or internal ribosome entry site (IRES) element, respectively. Interestingly eIF4GI mRNA itself has been reported to contain an IRES element in its 5' end that facilitates eIF4GI protein synthesis via a cap-independent mechanism. In HeLa cells, eIF4GI exists as several isoforms that differ in their migration in sodium dodecyl sulfate (SDS) gels; however, the nature of these isoforms was unclear. Here, we report a new cDNA clone for eIF4GI that extends the 5' sequence 340 nucleotides beyond the previously published sequence. The new extended sequence of eIF4GI is located on chromosome 3, within two additional exons immediately upstream of the previously published eIF4GI sequence. When mRNA transcribed from this cDNA clone was translated in vitro, five eIF4GI polypeptides were generated that comigrated in SDS-polyacrylamide gels with the five isoforms of native eIF4GI. Furthermore, translation of eIF4GI-enhanced green fluorescent protein fusion constructs in vitro or in vivo generated five isoforms of fusion polypeptides, suggesting that multiple isoforms of eIF4GI are generated by alternative translation initiation in vitro and in vivo. Mutation of two of the five in-frame AUG residues in the eIF4GI cDNA sequence resulted in loss of corresponding polypeptides after translation in vitro, confirming alternate use of AUGs as the source of the multiple polypeptides. The 5' untranslated region of eIF4GI mRNA also contains an out-of-frame open reading frame (ORF) that may down-regulate expression of eIF4GI. Further, data are presented to suggest that a proposed IRES embedded in the eIF4GI ORF is able to catalyze synthesis of multiple eIF4GI isoforms as well. Our data suggest that expression of the eIF4GI isoforms is partly controlled by a complex translation strategy involving both cap-dependent and cap-independent mechanisms.
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Affiliation(s)
- Marshall P Byrd
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA
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207
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Gaudernak E, Seipelt J, Triendl A, Grassauer A, Kuechler E. Antiviral effects of pyrrolidine dithiocarbamate on human rhinoviruses. J Virol 2002; 76:6004-15. [PMID: 12021333 PMCID: PMC136215 DOI: 10.1128/jvi.76.12.6004-6015.2002] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Human rhinoviruses (HRVs) are the predominant cause of the common cold. The frequency of HRV infections in industrial countries and the lack of effective therapeutical treatment underline the importance of research for new antiviral substances. As viral infections are often accompanied by the generation of oxidative stress inside the infected cells, several redox-active substances were tested as potential antivirals. In the course of these studies it was discovered that pyrrolidine dithiocarbamate (PDTC) is an extremely potent compound against HRV and poliovirus infection in cell culture. Besides the ability to dramatically reduce HRV production by interfering with viral protein expression, PDTC promotes cell survival and abolishes cytopathic effects in infected cells. PDTC also protects cells against poliovirus infection. These effects were highly specific, as several other antioxidants (vitamin C, Trolox, 2-mercaptoethanol, and N-acetyl-L-cysteine) are inactive against HRV infection. Synthesis of HRV proteins and cleavage of eucaryotic initiation factor 4G responsible for host cell shutoff of cellular protein synthesis are severely inhibited in the presence of PDTC.
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Affiliation(s)
- Elisabeth Gaudernak
- Institute of Medical Biochemistry, University of Vienna, Vienna Biocenter, A-1030 Vienna, Austria
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208
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Ohlmann T, Prévôt D, Décimo D, Roux F, Garin J, Morley SJ, Darlix JL. In vitro cleavage of eIF4GI but not eIF4GII by HIV-1 protease and its effects on translation in the rabbit reticulocyte lysate system. J Mol Biol 2002; 318:9-20. [PMID: 12054764 DOI: 10.1016/s0022-2836(02)00070-0] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In eukaryotic cells, protein synthesis is regulated by a set of initiation factors (eIF) that are required for recruiting the 40 S ribosomal subunit onto the mRNA molecule. Among these proteins, eIF4GI, which is targeted by picornaviral proteases, makes a bridge between the mRNA cap structure (via eIF4E) and the 40 S ribosome (via eIF3). Recently, internal ribosome entry segment (IRES) elements have been characterized in the genomic RNA of both simian immunodeficiency virus (SIV) and human immunodeficiency virus type 1 (HIV-1), suggesting that viral expression of these two viruses can be regulated at the translational level. Thus, by analogy with members of the picornavirus family, we have investigated the action of the HIV-1 protease on initiation factors eIF4GI and eIF4GII using cell extracts and the rabbit reticulocyte lysate system. Our results show that eIF4GI, but not eIF4GII, is substrate for HIV-1 protease and this effect can be prevented by a HIV-1 protease inhibitor, palinavir. However, in contrast to picornaviral proteases, the cleavage of eIF4GI by HIV-1 protease occurs at multiple sites and impairs translation of both cap-dependent and IRES-containing RNAs, except for the HCV IRES, which does not require eIF4GI or eIF4GII for activity.
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Affiliation(s)
- Théophile Ohlmann
- LaboRetro, Inserm U412, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364 Lyon cedex 07, France.
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209
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Kuyumcu-Martinez NM, Joachims M, Lloyd RE. Efficient cleavage of ribosome-associated poly(A)-binding protein by enterovirus 3C protease. J Virol 2002; 76:2062-74. [PMID: 11836384 PMCID: PMC135927 DOI: 10.1128/jvi.76.5.2062-2074.2002] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2001] [Accepted: 12/04/2001] [Indexed: 11/20/2022] Open
Abstract
Poliovirus (PV) causes a rapid and drastic inhibition of host cell cap-dependent protein synthesis during infection while preferentially allowing cap-independent translation of its own genomic RNA via an internal ribosome entry site element. Inhibition of cap-dependent translation is partly mediated by cleavage of an essential translation initiation factor, eIF4GI, during PV infection. In addition to cleavage of eIF4GI, cleavage of eIF4GII and poly(A)-binding protein (PABP) has been recently proposed to contribute to complete host translation shutoff; however, the relative importance of eIF4GII and PABP cleavage has not been determined. At times when cap-dependent translation is first blocked during infection, only 25 to 35% of the total cellular PABP is cleaved; therefore, we hypothesized that the pool of PABP associated with polysomes may be preferentially targeted by viral proteases. We have investigated what cleavage products of PABP are produced in vivo and the substrate determinants for cleavage of PABP by 2A protease (2A(pro)) or 3C protease (3C(pro)). Our results show that PABP in ribosome-enriched fractions is preferentially cleaved in vitro and in vivo compared to PABP in other fractions. Furthermore, we have identified four N-terminal PABP cleavage products produced during PV infection and have shown that viral 3C protease generates three of the four cleavage products. Also, 3C(pro) is more efficient in cleaving PABP in ribosome-enriched fractions than 2A(pro) in vitro. In addition, binding of PABP to poly(A) RNA stimulates 3C(pro)-mediated cleavage and inhibits 2A(pro)-mediated cleavage. These results suggest that 3C(pro) plays a major role in processing PABP during virus infection and that the interaction of PABP with translation initiation factors, ribosomes, or poly(A) RNA may promote its cleavage by viral 2A and 3C proteases.
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Affiliation(s)
- N Muge Kuyumcu-Martinez
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
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210
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Morley SJ. The regulation of eIF4F during cell growth and cell death. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2002; 27:1-37. [PMID: 11575157 DOI: 10.1007/978-3-662-09889-9_1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- S J Morley
- Biochemistry Laboratory, School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK
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211
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Zamora M, Marissen WE, Lloyd RE. Multiple eIF4GI-specific protease activities present in uninfected and poliovirus-infected cells. J Virol 2002; 76:165-77. [PMID: 11739682 PMCID: PMC135685 DOI: 10.1128/jvi.76.1.165-177.2002] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cleavage of eukaryotic translation initiation factor 4GI (eIF4GI) is required for shutoff of host cell translation during poliovirus (PV) infection of HeLa cells. Reports published by several groups have led to confusion whether this cleavage is mediated by viral 2A protease (2A(pro)) or a putative cellular enzyme (termed eIF4Gase) which is activated by 2A(pro) or other aspects of viral infection. Here we have further investigated eIF4Gase activities in PV-infected cells. Column purification of eIF4GI cleavage activity separated two activities which generated N-terminal cleavage products of different lengths. Both activities were detected using either native eIF4G or radiolabeled recombinant eIF4G as the substrate. Analysis of cleavage products formed by each activity on native and mutant substrates suggests that one activity cleaves eIF4G1 at or very near the 2A(pro) cleavage site and the other activity cleaves approximately 40 residues upstream of the 2A(pro) cleavage site. When PV infections in HeLa cells were supplemented with 2 mM guanidine, which indirectly limits expression of 2A(pro), two distinct C-terminal cleavage fragments of eIF4GI were detected. These C-terminal cleavage fragments of eIF4GI were purified from infected cells, and a new eIF4GI cleavage site was mapped to a unique site 43 amino acids upstream of the known 2A(pro) cleavage site. Further, eIF4GI cleavage in vivo could be blocked by addition of zVAD to PV-guanidine infections. zVAD is a broad-spectrum caspase inhibitor which had no effect on 2A(pro) cleavage activity or PV polyprotein processing. Lastly, similar types of eIF4Gase cleavage activities were also detected in uninfected cells under various conditions, including early apoptosis or during cell cycle transit. The data suggest that the same types of eIF4GI cleavage activities which are generated in PV-infected cells can also be generated in the absence of virus. Taken together, the data support a model in which multiple cellular activities process eIF4GI in PV-infected cells, in addition to 2A(pro).
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Affiliation(s)
- Miguel Zamora
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA
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212
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Gallie DR. Cap-independent translation conferred by the 5' leader of tobacco etch virus is eukaryotic initiation factor 4G dependent. J Virol 2001; 75:12141-52. [PMID: 11711605 PMCID: PMC116110 DOI: 10.1128/jvi.75.24.12141-12152.2001] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The 5' leader of tobacco etch virus (TEV) genomic RNA directs efficient translation from the naturally uncapped viral mRNA. Two distinct regions within the TEV 143-nucleotide leader confer cap-independent translation in vivo even when present in the intercistronic region of a discistronic mRNA, indicating that the TEV leader contains an internal ribosome entry site (IRES). In this study, the requirements for TEV IRES activity were investigated. The TEV IRES enhanced translation of monocistronic or dicistronic mRNAs in vitro under competitive conditions, i.e., at high RNA concentration or in lysate partially depleted of eukaryotic initiation factor 4F (eIF4F) and eIFiso4F, the two cap binding complexes in plants. The translational advantage conferred by the TEV IRES under these conditions was lost when the lysate reduced in eIF4F and eIFiso4F was supplemented with eIF4F (or, to a lesser extent, eIFiso4F) but not when supplemented with eIF4E, eIFiso4E, eIF4A, or eIF4B. eIF4G, the large subunit of eIF4F, was responsible for the competitive advantage conferred by the TEV IRES. TEV IRES activity was enhanced moderately by the poly(A)-binding protein. These observations suggest that the TEV IRES directs cap-independent translation through a mechanism that involves eIF4G specifically.
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Affiliation(s)
- D R Gallie
- Department of Biochemistry, University of California, Riverside, California 92521-0129, USA.
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213
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Hinnebusch AG. Unleashing yeast genetics on a factor-independent mechanism of internal translation initiation. Proc Natl Acad Sci U S A 2001; 98:12866-8. [PMID: 11698676 PMCID: PMC60786 DOI: 10.1073/pnas.241517998] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Affiliation(s)
- A G Hinnebusch
- 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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214
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Sakoda Y, Ross-Smith N, Inoue T, Belsham GJ. An attenuating mutation in the 2A protease of swine vesicular disease virus, a picornavirus, regulates cap- and internal ribosome entry site-dependent protein synthesis. J Virol 2001; 75:10643-50. [PMID: 11602706 PMCID: PMC114646 DOI: 10.1128/jvi.75.22.10643-10650.2001] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Virulent and avirulent strains of swine vesicular disease virus (SVDV), a picornavirus, have been characterized previously. The major determinants for attenuation have been mapped to specific residues in the 1D-2A-coding region. The properties of the 2A proteases from the virulent and avirulent strains of SVDV have now been examined. Both proteases efficiently cleaved the 1D/2A junction in vitro and in vivo. However, the 2A protease of the avirulent strain of SVDV was much less effective than the virulent-virus 2A protease at inducing cleavage of translation initiation factor eIF4GI within transfected cells. Hence the virulent-virus 2A protease is much more effective at inhibiting cap-dependent protein synthesis. Furthermore, the virulent-virus 2A protease strongly stimulated the internal ribosome entry sites (IRESs) from coxsackievirus B4 and from SVDV, while the avirulent-virus 2A protease was significantly less active in these assays. Thus, the different properties of the 2A proteases from the virulent and avirulent strains of SVDV in regulating protein synthesis initiation reflect the distinct pathogenic properties of the viruses from which they are derived. A single amino acid substitution, adjacent to His21 of the catalytic triad, is sufficient to confer the characteristics of the virulent-strain 2A protease on the avirulent-strain protease. It is concluded that the efficiency of picornavirus protein synthesis, controlled directly by the IRES or indirectly by the 2A protease, can determine virus virulence.
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Affiliation(s)
- Y Sakoda
- Department of Exotic Disease, National Institute of Animal Health, Kodaira, Tokyo 187-0022, Japan
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215
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Lyons T, Murray KE, Roberts AW, Barton DJ. Poliovirus 5'-terminal cloverleaf RNA is required in cis for VPg uridylylation and the initiation of negative-strand RNA synthesis. J Virol 2001; 75:10696-708. [PMID: 11602711 PMCID: PMC114651 DOI: 10.1128/jvi.75.22.10696-10708.2001] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Chimeric poliovirus RNAs, possessing the 5' nontranslated region (NTR) of hepatitis C virus in place of the 5' NTR of poliovirus, were used to examine the role of the poliovirus 5' NTR in viral replication. The chimeric viral RNAs were incubated in cell-free reaction mixtures capable of supporting the sequential translation and replication of poliovirus RNA. Using preinitiation RNA replication complexes formed in these reactions, we demonstrated that the 3' NTR of poliovirus RNA was insufficient, by itself, to recruit the viral replication proteins required for negative-strand RNA synthesis. The 5'-terminal cloverleaf of poliovirus RNA was required in cis to form functional preinitiation RNA replication complexes capable of uridylylating VPg and initiating the synthesis of negative-strand RNA. These results are consistent with a model in which the 5'-terminal cloverleaf and 3' NTRs of poliovirus RNA interact via temporally dynamic ribonucleoprotein complexes to coordinately mediate and regulate the sequential translation and replication of poliovirus RNA.
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Affiliation(s)
- T Lyons
- Department of Microbiology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA
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216
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Gallie DR, Browning KS. eIF4G functionally differs from eIFiso4G in promoting internal initiation, cap-independent translation, and translation of structured mRNAs. J Biol Chem 2001; 276:36951-60. [PMID: 11483601 DOI: 10.1074/jbc.m103869200] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic initiation factor (eIF) 4G plays an important role in assembling the initiation complex required for ribosome binding to an mRNA. Plants, animals, and yeast each express two eIF4G homologs, which share only 30, 46, and 53% identity, respectively. We have examined the functional differences between plant eIF4G proteins, referred to as eIF4G and eIFiso4G, when present as subunits of eIF4F and eIFiso4F, respectively. The degree to which a 5'-cap stimulated translation was inversely correlated with the concentration of eIF4F or eIFiso4F and required the poly(A)-binding protein for optimal function. Although eIF4F and eIFiso4F directed translation of unstructured mRNAs, eIF4F supported translation of an mRNA containing 5'-proximal secondary structure substantially better than did eIFiso4F. Moreover, eIF4F stimulated translation from uncapped monocistronic or dicistronic mRNAs to a greater extent than did eIFiso4F. These data suggest that at least some functions of plant eIFiso4F and eIF4F have diverged in that eIFiso4F promotes translation preferentially from unstructured mRNAs, whereas eIF4F can promote translation also from mRNAs that contain a structured 5'-leader and that are uncapped or contain multiple cistrons. This ability may also enable eIF4F to promote translation from standard mRNAs under cellular conditions in which cap-dependent translation is inhibited.
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Affiliation(s)
- D R Gallie
- Department of Biochemistry, University of California, Riverside, California 92521-0129, USA.
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217
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Glaser W, Cencic R, Skern T. Foot-and-mouth disease virus leader proteinase: involvement of C-terminal residues in self-processing and cleavage of eIF4GI. J Biol Chem 2001; 276:35473-81. [PMID: 11459842 DOI: 10.1074/jbc.m104192200] [Citation(s) in RCA: 37] [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
The leader proteinase (L(pro)) of foot-and-mouth disease virus frees itself from the nascent polyprotein, cleaving between its own C terminus and the N terminus of VP4 at the sequence Lys-Leu-Lys- downward arrow-Gly-Ala-Gly. Subsequently, the L(pro) impairs protein synthesis from capped mRNAs in the infected cell by processing a host protein, eukaryotic initiation factor 4GI, at the sequence Asn-Leu-Gly- downward arrow-Arg-Thr-Thr. A rabbit reticulocyte lysate system was used to examine the substrate specificity of L(pro) and the relationship of the two cleavage reactions. We show that L(pro) requires a basic residue at one side of the scissile bond to carry out efficient self-processing. This reaction is abrogated when leucine and lysine prior to the cleavage site are substituted by serine and glutamine, respectively. However, the cleavage of eIF4GI is unaffected by the inhibition of self-processing. Removal of the 18-amino acid C-terminal extension of L(pro) slowed eIF4GI cleavage; replacement of the C-terminal extension by unrelated amino acid sequences further delayed this cleavage. Surprisingly, wild-type L(pro) and the C-terminal variants all processed the polyprotein cleavage site in an intermolecular reaction at the same rate. However, when the polyprotein cleavage site was part of the same polypeptide chain as the wild-type Lb(pro), the rate of processing was much more rapid. These experiments strongly suggest that self-processing is an intramolecular reaction.
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Affiliation(s)
- W Glaser
- Institute of Medical Biochemistry, Division of Biochemistry, University of Vienna, Vienna BioCenter, Dr. Bohr-Gasse 9/3, A-1030 Vienna, Austria
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218
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López de Quinto S, Lafuente E, Martínez-Salas E. IRES interaction with translation initiation factors: functional characterization of novel RNA contacts with eIF3, eIF4B, and eIF4GII. RNA (NEW YORK, N.Y.) 2001; 7:1213-26. [PMID: 11565745 PMCID: PMC1370167 DOI: 10.1017/s1355838201010433] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Translation initiation promoted by picornavirus internal ribosome entry site (IRES) elements is dependent on the association of specific IRES sequences to the initiation factor eIF4G. However the RNA determinants interacting with other components of the translational machinery are still unknown. In this study, we have identified novel RNA-protein interactions between the foot-and-mouth disease virus (FMDV) IRES and three translation initiation factors. A doublet of 116/110 kDa that crosslinked to the FMDV IRES is a component of eIF3. We show here that domain 5 holds the preferential binding site for eIF3, although this complex initiation factor can establish multiple contacts with the IRES structure. We have also identified the phylogenetically conserved hairpin of domain 5 as the RNA motif responsible for eIF4B interaction. Mutation of this stem-loop structure abrogated eIF4B, but not eIF3, binding to the IRES. Remarkably, IRES mutants severely affected in their interaction with eIF4B showed a mild reduction in IRES activity when tested in the context of a bicistronic expression vector in transfected cells. Finally, we provide evidence of the interaction of eIF4GII with FMDV IRES, the RNA determinants for this interaction being shared with its functional homolog eIF4GI. The FMDV Lb protease generated a C-terminal fragment of eIF4GII that binds to the IRES as efficiently as the intact protein. Competition experiments showed that titration of eIF4B or p110/116 interaction with the FMDV IRES required a large excess of competitor relative to eIF4G, strongly suggesting that eIF4G-IRES interaction is a limiting factor to titrate the IRES. Comparative analysis of the activity of IRES mutants affected in domains 4 and 5 regarding their pattern of RNA-protein complex formation demonstrates that while binding of eIF4B with the FMDV IRES is dispensable, interaction of eIF4G is a central feature of the activity of this element.
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Affiliation(s)
- S López de Quinto
- Centro de Biología Molecular Severo Ochoa, CSIC-UAM, Cantoblanco, Madrid, Spain
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219
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Abstract
The process of eukaryotic gene expression involves a diverse number of steps including transcription, RNA processing, transport, translation, and mRNA turnover. A critical step in understanding this process will be the development of mathematical models that quantitatively describe and predict the behavior of this complex system. We have simulated eukaryotic mRNA turnover in a linear multicomponent model based on the known mRNA decay pathways in yeast. Using rate constants based on experimental data for the yeast unstable MFA2 and stable PGK1 transcripts, the computational modeling reproduces experimental observations after minor adjustments. Subsequent analysis and a series of in silico experiments led to several conclusions. First, we demonstrate that mRNA half-life as commonly measured underestimates the average life span of an mRNA. Second, due to the properties of the pathways, the measurement of a half-life can predominantly measure different steps in the decay network. A corollary of this fact is that different mRNAs will be affected differentially by changes in specific rate constants. Third, the way to obtain the largest change of levels of mRNA for the smallest changes in rate is by changing the rate of deadenylation, where a large amount of regulation of mRNA decay occurs. Fourth, the 3'-to-5' degradation of mRNA shows mRNA-specific rates of degradation that are dependent on the 5' structure of the mRNA. These programs can be run over the Web, are adaptable to other eukaryotes, and provide outputs as graphs and virtual northern gels, which can be directly compared to experimental data. Therefore, this model constitutes a useful tool for the quantitative analysis of the process and control of mRNA degradation in eukaryotic cells.
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Affiliation(s)
- D Cao
- Howard Hughes Medical Institute and Department of Molecular and Cellular Biology, University of Arizona, Tucson 85721, USA
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220
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Ali IK, McKendrick L, Morley SJ, Jackson RJ. Truncated initiation factor eIF4G lacking an eIF4E binding site can support capped mRNA translation. EMBO J 2001; 20:4233-42. [PMID: 11483526 PMCID: PMC149147 DOI: 10.1093/emboj/20.15.4233] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Picornavirus proteases cleave translation initiation factor eIF4G into a C-terminal two-thirds fragment (hereafter named p100) and an N-terminal one-third fragment, which interacts with the cap-binding factor eIF4E. As the timing of this cleavage correlates broadly with the shut-off of host cell protein synthesis in infected cells, a very widespread presumption has been that p100 cannot support capped mRNA translation. Through the use of an eIF4G-depleted reticulocyte lysate system, we show that this presumption is incorrect. Moreover, recombinant p100 can also reverse the inhibition of capped mRNA translation caused either by m7GpppG cap analogue, by 4E-BP1, which sequesters eIF4E and thus blocks its association with eIF4G, or by cleavage of endogenous eIF4G by picornavirus proteases. The concentration of p100 required for maximum translation of capped mRNAs is approximately 4-fold higher than the endogenous eIF4G concentration in reticulocyte lysates. Our results imply that picornavirus-induced shut-off is not due to an intrinsic inability of p100 to support capped mRNA translation, but to the viral RNA outcompeting host cell mRNA for the limiting concentration of p100.
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Affiliation(s)
| | - Linda McKendrick
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA and
School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK Corresponding author e-mail:
| | - Simon J. Morley
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA and
School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK Corresponding author e-mail:
| | - Richard J. Jackson
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA and
School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK Corresponding author e-mail:
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221
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Saghir AN, Tuxworth WJ, Hagedorn CH, McDermott PJ. Modifications of eukaryotic initiation factor 4F (eIF4F) in adult cardiocytes by adenoviral gene transfer: differential effects on eIF4F activity and total protein synthesis rates. Biochem J 2001; 356:557-66. [PMID: 11368785 PMCID: PMC1221869 DOI: 10.1042/0264-6021:3560557] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In adult feline cardiocytes, increases in eukaryotic initiation factor 4F (eIF4F) activity are correlated with accelerated rates of total protein synthesis produced in response to increased load. Adenoviral gene transfer was employed to increase either eIF4F complex formation or the phosphorylation of eIF4E on Ser-209. To simulate load,cardiocytes were electrically stimulated to contract (2 Hz,5 ms pulses). Non-stimulated cardiocytes were used as controls.Adenovirus-mediated overexpression of wild-type eIF4E increased the total eIF4E pool by 120-140% above endogenous levels after 24 h and produced a corresponding increase in eIF4F content.However, it did not accelerate total protein synthesis rates inquiescent cardiocytes; neither did it potentiate the increase produced by contraction. To modify the affinity of eIF4F, cardiocytes were infected with a mutant (eIF4E/W56F) with a decreased binding affinity for the mRNA cap. Overexpression of eIF4E/W56F increased the quantity of eIF4F but the rate of total protein synthesis was decreased inquiescent and contracting cardiocytes. Overexpression of a mutant that blocked eIF4E phosphorylation (eIF4E/S209A) increased the quantity ofeIF4F without any significant effect on total protein synthesis rates in quiescent or contracting cardiocytes. Overexpression of the eIF4Ekinase Mnk-1 increased eIF4E phosphorylation without a corresponding increase in eIF4F complex formation or in the rate of total protein synthesis. We conclude the following: (1) eIF4F assembly is increased by raising eIF4E levels via adenoviral gene transfer; (2) the capbinding affinity of eIF4F is a rate-limiting determinant for total protein synthesis rates; and (3) increases in the quantity of eIF4Falone or in eIF4E phosphorylation are not sufficient to accelerate total protein synthesis rates.
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Affiliation(s)
- A N Saghir
- Department of Medicine, Strom Thurmond Biomedical ResearchBuilding, Room 303, 114 Doughty Street, Charleston, SC 29403, USA
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222
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Affiliation(s)
- C U Hellen
- Department of Microbiology and Immunology, Morse Institute for Molecular Genetics, State University of New York Health Science Center at Brooklyn, Brooklyn, New York 11203, USA.
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223
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Bushell M, Wood W, Carpenter G, Pain VM, Morley SJ, Clemens MJ. Disruption of the interaction of mammalian protein synthesis eukaryotic initiation factor 4B with the poly(A)-binding protein by caspase- and viral protease-mediated cleavages. J Biol Chem 2001; 276:23922-8. [PMID: 11274152 DOI: 10.1074/jbc.m100384200] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic initiation factor (eIF) 4B interacts with several components of the initiation pathway and is targeted for cleavage during apoptosis. In a cell-free system, cleavage of eIF4B by caspase-3 coincides with a general inhibition of protein synthetic activity. Affinity chromatography demonstrates that mammalian eIF4B interacts with the poly(A)-binding protein and that a region consisting of the N-terminal 80 amino acids of eIF4B is both necessary and sufficient for such binding. This interaction is lost when eIF4B is cleaved by caspase-3, which removes the N-terminal 45 amino acids. Similarly, the association of eIF4B with the poly(A)-binding protein in vivo is reduced when cells are induced to undergo apoptosis. Cleavage of the poly(A)-binding protein itself, using human rhinovirus 3C protease, also eliminates the interaction with eIF4B. Thus, disruption of the association between mammalian eIF4B and the poly(A)-binding protein can occur during both apoptosis and picornaviral infection and is likely to contribute to the inhibition of translation observed under these conditions.
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Affiliation(s)
- M Bushell
- Department of Biochemistry and Immunology, Cellular and Molecular Sciences Group, St. George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, United Kingdom
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224
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Abstract
Although the association remains controversial, enteroviruses have been implicated in the aetiology of several chronic diseases in humans. Investigations in vitro lead to better understanding of virus-cell interactions, and improve our knowledge of the molecular factors that are involved in the establishment and maintenance of these infections. Recent findings suggest that the most important factor in the establishment of a persistent infection is receptor usage. Studies of the mechanisms that are at work in these in-vitro models of viral infection have shown that there is frequently a co-evolution of mutant cells with higher resistance to viral infection and of virus variants with increased virulence (i.e. variants with the ability to utilize other cell-surface molecules as receptors).
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Affiliation(s)
- G Frisk
- Department of Women's and Children's Health, Uppsala University, Akademiska Hospital, Uppsala, Sweden.
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225
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Martínez-Salas E, Ramos R, Lafuente E, López de Quinto S. Functional interactions in internal translation initiation directed by viral and cellular IRES elements. J Gen Virol 2001; 82:973-984. [PMID: 11297672 DOI: 10.1099/0022-1317-82-5-973] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Affiliation(s)
- Encarnación Martínez-Salas
- Centro de Biología Molecular 'Severo Ochoa', Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain1
| | - Ricardo Ramos
- Centro de Biología Molecular 'Severo Ochoa', Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain1
| | - Esther Lafuente
- Centro de Biología Molecular 'Severo Ochoa', Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain1
| | - Sonia López de Quinto
- Centro de Biología Molecular 'Severo Ochoa', Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain1
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226
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Gustin KE, Sarnow P. Effects of poliovirus infection on nucleo-cytoplasmic trafficking and nuclear pore complex composition. EMBO J 2001; 20:240-9. [PMID: 11226174 PMCID: PMC140206 DOI: 10.1093/emboj/20.1.240] [Citation(s) in RCA: 234] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Infection of eukaryotic cells with lytic RNA viruses results in extensive interactions of viral gene products with macromolecular pathways of the host, ultimately leading to death of the infected cells. We show here that infection of cells with poliovirus results in the cytoplasmic accumulation of a variety of shuttling and non-shuttling nuclear proteins that use multiple nuclear import pathways. In vitro nuclear import assays using semi-permeabilized infected cells confirmed that nuclear import was blocked and demonstrated that docking of nuclear import receptor-cargo complexes at the cytoplasmic face of the nuclear pore complex (NPC) was prevented. Analysis of components of the NPC revealed that two proteins, Nup153 and p62, were proteolyzed during poliovirus infection. These results suggest that the cytoplasmic relocalization of numerous cellular proteins is caused by the inhibition of multiple nuclear import pathways via alterations in NPC composition in poliovirus-infected cells. Blocking of nuclear import points to a novel strategy by which cytoplasmic RNA viruses can evade host immune defenses, by preventing signal transduction to the nucleus.
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Affiliation(s)
| | - Peter Sarnow
- Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA
Corresponding author e-mail:
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227
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Abstract
Picornaviruses are small animal viruses with positive-strand genomic RNA, which is translated using cap-independent internal translation initiation. The key role in this is played by ciselements of the 5"-untranslated region (5"-UTR) and, in particular, by the internal ribosome entry site (IRES). The function of translational ciselements requires both canonical translation initiation factors (eIFs) and additional IRES trans-acting factors (ITAFs). All known ITAFs are cell RNA-binding proteins which play a variety of functions in noninfected cells. Specific features of translational ciselements substantially affect the phenotype and, in particular, tissue tropism and pathogenic properties of picornaviruses. It is clear that, in some cases, the molecular mechanism involved is a change in interactions between viral ciselements and ITAFs. The properties and tissue distribution of ITAFs may determine the biological properties of other viruses that also use the IRES-dependent translation initiation. Since this mechanism is also involved in translation of several cell mRNAs, ITAF may contribute to the regulation of the most important aspects of the living activity in noninfected cells.
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Affiliation(s)
- V. I. Agol
- Chumakov Institute of Poliomyelitis and Virus Encephalites, Russian Academy of Medical Sciences, and, Moscow State University, Moscow, Russia
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228
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Abstract
Many viruses interfere with host cell function in ways that are harmful or pathological. This often results in changes in cell morphology referred to as cytopathic effects. However, pathogenesis of virus infections also involves inhibition of host cell gene expression. Thus the term "cytopathogenesis," or pathogenesis at the cellular level, is meant to be broader than the term "cytopathic effects" and includes other cellular changes that contribute to viral pathogenesis in addition to those changes that are visible at the microscopic level. The goal of this review is to place recent work on the inhibition of host gene expression by RNA viruses in the context of the pathogenesis of virus infections. Three different RNA virus families, picornaviruses, influenza viruses, and rhabdoviruses, are used to illustrate common principles involved in cytopathogenesis. These examples were chosen because viral gene products responsible for inhibiting host gene expression have been identified, as have some of the molecular targets of the host. The argument is made that the role of the virus-induced inhibition of host gene expression is to inhibit the host antiviral response, such as the response to double-stranded RNA. Viral cytopathogenesis is presented as a balance between the host antiviral response and the ability of viruses to inhibit that response through the overall inhibition of host gene expression. This balance is a major determinant of viral tissue tropism in infections of intact animals.
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Affiliation(s)
- D S Lyles
- Department of Microbiology and Immunology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1064, USA.
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229
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Marissen WE, Gradi A, Sonenberg N, Lloyd RE. Cleavage of eukaryotic translation initiation factor 4GII correlates with translation inhibition during apoptosis. Cell Death Differ 2000; 7:1234-43. [PMID: 11175261 DOI: 10.1038/sj.cdd.4400750] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Eukaryotic translation initiation factor 4G (eIF4G), which has two homologs known as eIF4GI and eIF4GII, functions in a complex (eIF4F) which binds to the 5' cap structure of cellular mRNAs and facilitates binding of capped mRNA to 40S ribosomal subunits. Disruption of this complex in enterovirus-infected cells through eIF4G cleavage is known to block this step of translation initiation, thus leading to a drastic inhibition of cap-dependent translation. Here, we show that like eIF4GI, the newly identified homolog eIF4GII is cleaved during apoptosis in HeLa cells and can serve as a substrate for caspase 3. Proteolysis of both eIF4GI and eIF4GII occurs with similar kinetics and coincides with the profound translation inhibition observed in cisplatin-treated HeLa cells. Both eIF4GI and eIF4GII can be cleaved by caspase 3 with similar efficiency in vitro, however, eIF4GII is processed into additional fragments which destroy its core central domain and likely contributes to the shutoff of translation observed in apoptosis. Cell Death and Differentiation (2000) 7, 1234 - 1243.
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Affiliation(s)
- W E Marissen
- Department of Microbiology & Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, OK 73104, USA
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230
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Guarné A, Hampoelz B, Glaser W, Carpena X, Tormo J, Fita I, Skern T. Structural and biochemical features distinguish the foot-and-mouth disease virus leader proteinase from other papain-like enzymes. J Mol Biol 2000; 302:1227-40. [PMID: 11183785 DOI: 10.1006/jmbi.2000.4115] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The structures of the two leader protease (Lpro) variants of foot-and-mouth disease virus known to date were solved using crystals in which molecules were organized as molecular fibers. Such crystals diffract to a resolution of only approximately 3 A. This singular, pseudo-polymeric organization is present in a new Lpro crystal form showing a cubic packing. As molecular fiber formation appeared unrelated to crystallization conditions, we mutated the reactive cysteine 133 residue, which makes a disulfide bridge between adjacent monomers in the fibers, to serine. None of the intermolecular contacts found in the molecular fibers was present in crystals of this variant. Analysis of this Lpro structure, refined at 1.9 A resolution, enables a detailed definition of the active center of the enzyme, including the solvent organization. Assay of Lpro activity on a fluorescent hexapeptide substrate showed that Lpro, in contrast to papain, was highly sensitive to increases in the cation concentration and was active only across a narrow pH range. Examination of the Lpro structure revealed that three aspartate residues near the active site, not present in papain-like enzymes, are probably responsible for these properties.
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Affiliation(s)
- A Guarné
- Institut de Biologia Molecular de Barcelona, Barcelona, Spain
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231
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Holcik M, Sonenberg N, Korneluk RG. Internal ribosome initiation of translation and the control of cell death. Trends Genet 2000; 16:469-73. [PMID: 11050335 DOI: 10.1016/s0168-9525(00)02106-5] [Citation(s) in RCA: 185] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The majority of cellular stresses lead to the inhibition of cap-dependent translation. Some mRNAs, however, are translated by a cap-independent mechanism, mediated by ribosome binding to internal ribosome entry site (IRES) elements located in the 5' untranslated region. Interestingly, IRES elements are found in the mRNAs of several survival factors, oncogenes and proteins crucially involved in the control of apoptosis. These mRNAs are translated under a variety of stress conditions, including hypoxia, serum deprivation, irradiation and apoptosis. Thus, IRES-mediated translational control might have evolved to regulate cellular responses in acute but transient stress conditions that would otherwise lead to cell death.
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Affiliation(s)
- M Holcik
- Solange Gauthier Karsh Molecular Genetics Laboratory, Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, ON, K1H 8L1, Ottawa, Canada.
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232
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López de Quinto S, Martínez-Salas E. Interaction of the eIF4G initiation factor with the aphthovirus IRES is essential for internal translation initiation in vivo. RNA (NEW YORK, N.Y.) 2000; 6:1380-92. [PMID: 11073214 PMCID: PMC1370009 DOI: 10.1017/s1355838200000753] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The strategies developed by internal ribosome entry site (IRES) elements to recruit the translational machinery are poorly understood. In this study we show that protein-RNA interaction of the eIF4G translation initiation factor with sequences of the foot-and-mouth disease virus (FMDV) IRES is a key determinant of internal translation initiation in living cells. Moreover, we have identified the nucleotides required for eIF4G-RNA functional interaction, using native proteins from FMDV-susceptible cell extracts. Substitutions in the conserved internal AA loop of the base of domain 4 led to strong impairment of both eIF4G-RNA interaction in vitro and IRES-dependent translation initiation in vivo. Conversely, substitutions in the vicinity of the internal AA loop that did not impair IRES activity retained their ability to interact with eIF4G. Direct UV-crosslinking as well as competition assays indicated that domains 1-2, 3, and 5 of the IRES did not contribute to this interaction. In agreement with this, binding to domain 4 alone was as efficient as to the full-length IRES. The C-terminal fragment of eIF4G, proteolytically processed by the FMDV Lb protease, was sufficient to interact with the IRES or to its domain 4 alone. Additionally, we show here that binding of the eIF4B initiation factor to the IRES required domain 5 sequences. Moreover, eIF4G-IRES interaction was detected in the absence of eIF4B-IRES binding, suggesting that both initiation factors interact with the 3' region of the IRES but use different residues. The strong correlation found between eIF4G-RNA interaction and IRES activity in transfected cells suggests that eIF4G acts as a linker to recruit the translational machinery in IRES-dependent initiation.
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233
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Lomakin IB, Hellen CU, Pestova TV. Physical association of eukaryotic initiation factor 4G (eIF4G) with eIF4A strongly enhances binding of eIF4G to the internal ribosomal entry site of encephalomyocarditis virus and is required for internal initiation of translation. Mol Cell Biol 2000; 20:6019-29. [PMID: 10913184 PMCID: PMC86078 DOI: 10.1128/mcb.20.16.6019-6029.2000] [Citation(s) in RCA: 155] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mammalian eukaryotic initiation factor 4GI (eIF4GI) may be divided into three similarly sized regions. The central region (amino acids [aa] 613 to 1090) binds eIF3, eIF4A, and the encephalomyocarditis virus (EMCV) internal ribosomal entry site (IRES) and mediates initiation on this RNA. We identified the regions of eIF4GI that are responsible for its specific interaction with the IRES and that are required to mediate 48S complex formation on the IRES in vitro. Mutational analysis demarcated the IRES binding fragment of eIF4GI (aa 746 to 949) and indicated that it does not resemble an RNA recognition motif (RRM)-like domain. An additional amino-terminal sequence (aa 722 to 746) was required for binding eIF4A and for 48S complex formation. eIF4GI bound the EMCV IRES and beta-globin mRNA with similar affinities, but association with eIF4A increased its affinity for the EMCV IRES (but not beta-globin RNA) by 2 orders of magnitude. On the other hand, eIF4GI mutants with defects in binding eIF4A were defective in mediating 48S complex formation even if they bound the IRES normally. These data indicate that the eIF4G-eIF4A complex, rather than eIF4G alone, is required for specific high-affinity binding to the EMCV IRES and for internal ribosomal entry on this RNA.
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Affiliation(s)
- I B Lomakin
- Department of Microbiology and Immunology, State University of New York Health Science Center at Brooklyn, Brooklyn, New York 11203, USA
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234
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Thompson SR, Sarnow P. Regulation of host cell translation by viruses and effects on cell function. Curr Opin Microbiol 2000; 3:366-70. [PMID: 10972496 DOI: 10.1016/s1369-5274(00)00106-5] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Viruses have evolved a remarkable variety of strategies to modulate the host cell translation apparatus with the aim of optimizing viral mRNA translation and replication. Recent studies have revealed that modulation of both host and viral mRNA translation can be accomplished by selective alteration of translation factors in virus-infected cells. These findings provide new insights into the functioning of the translational apparatus in both uninfected and infected cells.
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Affiliation(s)
- S R Thompson
- Department of Microbiology and Immunology, Stanford University School of Medicine, CA 94305, USA.
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235
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Morley SJ, Jeffrey I, Bushell M, Pain VM, Clemens MJ. Differential requirements for caspase-8 activity in the mechanism of phosphorylation of eIF2alpha, cleavage of eIF4GI and signaling events associated with the inhibition of protein synthesis in apoptotic Jurkat T cells. FEBS Lett 2000; 477:229-36. [PMID: 10908726 DOI: 10.1016/s0014-5793(00)01805-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Previously we have reported that induction of apoptosis in Jurkat cells results in an inhibition of overall protein synthesis with the selective and rapid cleavage of eukaryotic initiation factor (eIF) 4GI. For the cleavage of eIF4GI, caspase-3 activity is both necessary and sufficient in vivo, in a process which does not require signaling through the p38 MAP kinase pathway. We now show that activation of the Fas/CD95 receptor promotes an early, transient increase in the level of eIF2alpha phosphorylation, which is temporally correlated with the onset of the inhibition of translation. This is associated with a modest increase in the autophosphorylation of the protein kinase activated by double-stranded RNA. Using a Jurkat cell line that is deficient in caspase-8 and resistant to anti-Fas-induced apoptosis, we show that whilst the cleavage of eIF4GI is caspase-8-dependent, the enhancement of eIF2alpha phosphorylation does not require caspase-8 activity and occurs prior to the cleavage of eIF4GI. In addition, activation of the Fas/CD95 receptor results in the caspase-8-dependent dephosphorylation and degradation of p70(S6K), the enhanced binding of 4E-BP1 to eIF4E, and, at later times, the cleavage of eIF2alpha. These data suggest that apoptosis impinges upon the activity of several polypeptides which are central to the regulation of protein synthesis and that multiple signaling pathways are involved in vivo.
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Affiliation(s)
- S J Morley
- Biochemistry Laboratory, School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK.
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236
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Gingras AC, Raught B, Sonenberg N. eIF4 initiation factors: effectors of mRNA recruitment to ribosomes and regulators of translation. Annu Rev Biochem 2000; 68:913-63. [PMID: 10872469 DOI: 10.1146/annurev.biochem.68.1.913] [Citation(s) in RCA: 1630] [Impact Index Per Article: 65.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Eukaryotic translation initiation factor 4F (eIF4F) is a protein complex that mediates recruitment of ribosomes to mRNA. This event is the rate-limiting step for translation under most circumstances and a primary target for translational control. Functions of the constituent proteins of eIF4F include recognition of the mRNA 5' cap structure (eIF4E), delivery of an RNA helicase to the 5' region (eIF4A), bridging of the mRNA and the ribosome (eIF4G), and circularization of the mRNA via interaction with poly(A)-binding protein (eIF4G). eIF4 activity is regulated by transcription, phosphorylation, inhibitory proteins, and proteolytic cleavage. Extracellular stimuli evoke changes in phosphorylation that influence eIF4F activity, especially through the phosphoinositide 3-kinase (PI3K) and Ras signaling pathways. Viral infection and cellular stresses also affect eIF4F function. The recent determination of the structure of eIF4E at atomic resolution has provided insight about how translation is initiated and regulated. Evidence suggests that eIF4F is also implicated in malignancy and apoptosis.
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Affiliation(s)
- A C Gingras
- Department of Biochemistry McGill University, Montréal, Québec, Canada.
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237
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Clemens MJ, Bushell M, Jeffrey IW, Pain VM, Morley SJ. Translation initiation factor modifications and the regulation of protein synthesis in apoptotic cells. Cell Death Differ 2000; 7:603-15. [PMID: 10889505 DOI: 10.1038/sj.cdd.4400695] [Citation(s) in RCA: 182] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
The rate of protein synthesis is rapidly down-regulated in mammalian cells following the induction of apoptosis. Inhibition occurs at the level of polypeptide chain initiation and is accompanied by the phosphorylation of the alpha subunit of initiation factor eIF2 and the caspase-dependent cleavage of initiation factors eIF4G, eIF4B, eIF2alpha and the p35 subunit of eIF3. Proteolytic cleavage of these proteins yields characteristic products which may exert regulatory effects on the translational machinery. Inhibition of caspase activity protects protein synthesis from long-term inhibition in cells treated with some, but not all, inducers of apoptosis. This review describes the initiation factor modifications and the possible signalling pathways by which translation may be regulated during apoptosis. We discuss the significance of the initiation factor cleavages and other changes for protein synthesis, and the implications of these events for our understanding of the cellular changes associated with apoptosis.
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Affiliation(s)
- M J Clemens
- Department of Biochemistry and Immunology, Cellular and Molecular Sciences Group, St George's Hospital Medical School, Cranmer Terrace, London SW17 ORE, UK.
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238
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Abstract
Picornavirus RNA is translated within cells even when cellular cap-dependent protein synthesis is blocked. The efficiency of recognition of the viral RNA by the translational apparatus can determine viral tropism. The roles of cellular translation-initiation factors and other RNA-binding proteins in viral RNA-mediated protein synthesis are discussed.
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Affiliation(s)
- G J Belsham
- BBSRC Institute for Animal Health, Pirbright, Woking, Surrey, UK GU24 0NF.
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239
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Holcik M, Korneluk RG. Functional characterization of the X-linked inhibitor of apoptosis (XIAP) internal ribosome entry site element: role of La autoantigen in XIAP translation. Mol Cell Biol 2000; 20:4648-57. [PMID: 10848591 PMCID: PMC85872 DOI: 10.1128/mcb.20.13.4648-4657.2000] [Citation(s) in RCA: 185] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2000] [Accepted: 04/11/2000] [Indexed: 12/14/2022] Open
Abstract
X-linked inhibitor of apoptosis protein (XIAP) is a key regulator of programmed cell death triggered by various apoptotic triggers. Translation of XIAP is controlled by a 162-nucleotide (nt) internal ribosome entry site (IRES) element located in the 5' untranslated region of XIAP mRNA. XIAP IRES mediates efficient translation of XIAP under physiological stress and enhances cell protection against serum deprivation and radiation-induced apoptosis. In the present report we describe the assembly of a sequence-specific RNA-protein complex consisting of at least four cytosolic proteins on the XIAP IRES element. We determine that the core binding sequence is approximately 28 nt long and is located 34 nt upstream of the initiation site. Moreover, we identify the La autoantigen as a protein that specifically binds XIAP IRES in vivo and in vitro. The biological relevance of this interaction is further demonstrated by the inhibition of XIAP IRES-mediated translation in the absence of functional La protein. The results suggest an important role for the La protein in the regulation of XIAP expression, possibly by facilitating ribosome recruitment to the XIAP IRES.
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Affiliation(s)
- M Holcik
- Apoptogen Inc.; Solange Gauthier Karsh Molecular Genetics Laboratory, Children's Hospital of Eastern Ontario, Ottawa, Canada
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240
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Seipelt J, Liebig HD, Sommergruber W, Gerner C, Kuechler E. 2A proteinase of human rhinovirus cleaves cytokeratin 8 in infected HeLa cells. J Biol Chem 2000; 275:20084-9. [PMID: 10867028 DOI: 10.1074/jbc.275.26.20084] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rhino- and enteroviruses encode two proteinases, 2A and 3C, which are responsible for the processing of the viral polyprotein and for cleavage of several cellular proteins. To identify further targets of the 2A proteinase of human rhinovirus serotype 2 (HRV2), an in vitro cleavage assay followed by two-dimensional electrophoresis was employed. Cytokeratin 8, a member of the intermediate filament group of proteins, was found to be proteolytically cleaved in vitro by the 2A proteinase of HRV2 and of coxsackievirus B4 and in vivo during HRV2 infection of HeLa cells. The cleavage results in removal of 14 amino acids from the N-terminal head domain of cytokeratin 8. However, other intermediate filament proteins (cytokeratins 7 and 18 and vimentin) were not cleaved in the course of the HRV2 infection. Compared with the processing of the eucaryotic translation initiation factors 4GI and 4GII, cleavage of cytokeratin 8 occurs late in the infection cycle at the time of the onset of the cytopathic effect.
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Affiliation(s)
- J Seipelt
- Institute of Medical Biochemistry, Division of Biochemistry, University of Vienna, Dr. Bohrgasse 9/3, A-1030 Vienna, Austria
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241
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Abstract
As obligate intracellular parasites, viruses rely exclusively on the translational machinery of the host cell for the synthesis of viral proteins. This relationship has imposed numerous challenges on both the infecting virus and the host cell. Importantly, viruses must compete with the endogenous transcripts of the host cell for the translation of viral mRNA. Eukaryotic viruses have thus evolved diverse mechanisms to ensure translational efficiency of viral mRNA above and beyond that of cellular mRNA. Mechanisms that facilitate the efficient and selective translation of viral mRNA may be inherent in the structure of the viral nucleic acid itself and can involve the recruitment and/or modification of specific host factors. These processes serve to redirect the translation apparatus to favor viral transcripts, and they often come at the expense of the host cell. Accordingly, eukaryotic cells have developed antiviral countermeasures to target the translational machinery and disrupt protein synthesis during the course of virus infection. Not to be outdone, many viruses have answered these countermeasures with their own mechanisms to disrupt cellular antiviral pathways, thereby ensuring the uncompromised translation of virion proteins. Here we review the varied and complex translational programs employed by eukaryotic viruses. We discuss how these translational strategies have been incorporated into the virus life cycle and examine how such programming contributes to the pathogenesis of the host cell.
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Affiliation(s)
- M Gale
- University of Texas Southwestern Medical Center, Dallas, Texas, USA.
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242
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Maltese E, Bucci M, Macchia S, Latorre P, Pagnotti P, Pierangeli A, Bercoff RP. Inhibition of cap-dependent gene expression induced by protein 2A of hepatitis A virus. J Gen Virol 2000; 81:1373-81. [PMID: 10769081 DOI: 10.1099/0022-1317-81-5-1373] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The viral protein 2A of hepatitis A virus (HAV) lacks the conserved 18 aa sequence found in other picornavirus proteases; hence, it is unclear whether the induction of CPE by culture-adapted HAV strains is due to 2A-mediated activity. Moreover, the cleavage sites and actual borders of HAV 2A are not known. Accordingly, a nested series of cDNA sequences encoding the segment of the HAV polyprotein (aa 760-1087) were linked to the 5'-UTR of poliovirus type 2 (Lansing strain) and inserted downstream of the gene encoding human growth hormone (GH). Following transfection of COS-1 cells, levels of GH (translation of which was entirely cap dependent) were determined in culture supernatants. Expression of HAV peptides extending from aa 764, 776 or 791 to 981 strongly inhibited cap-dependent translation of GH, whereas cap-independent expression of a reporter gene (CAT) directed by the poliovirus RNA 5'-UTR was unaffected. The inhibitory effect was absent in constructs expressing either the short peptide encompassing aa 760-836 or proteins initiated downstream of the putative cleavage site 836-837, suggesting that the boundaries of a functional HAV 2A may extend from the Gln/Ser junction 791-792 to residue 981, while peptides initiated at the Gln/Ala pair 836-837 may result from alternative cleavage. Point mutations that substituted members of the triad Ser(916), His(927) and Asp(931) abolished the inhibitory effect on cap-dependent translation, suggesting that the HAV-induced CPE may be mediated by 2A protein.
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Affiliation(s)
- E Maltese
- Department of Cellular & Developmental Biology, University of Rome 'La Sapienza', Viale di Porta Tiburtina 28, 00185 Rome, Italy
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243
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Badorff C, Berkely N, Mehrotra S, Talhouk JW, Rhoads RE, Knowlton KU. Enteroviral protease 2A directly cleaves dystrophin and is inhibited by a dystrophin-based substrate analogue. J Biol Chem 2000; 275:11191-7. [PMID: 10753926 DOI: 10.1074/jbc.275.15.11191] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Enteroviruses such as Coxsackievirus B3 can cause dilated cardiomyopathy through unknown pathological mechanism(s). Dystrophin is a large extrasarcomeric cytoskeletal protein whose genetic deficiency causes hereditary dilated cardiomyopathy. In addition, we have recently shown that dystrophin is proteolytically cleaved by the Coxsackievirus protease 2A leading to functional impairment and morphological disruption. However, the mechanism of dystrophin cleavage and the exact cleavage site remained to be identified. Antibody epitope mapping of endogenous dystrophin indicated protease 2A-mediated cleavage at the site in the hinge 3 region predicted by a neural network algorithm (human, amino acid 2434; mouse, amino acid 2427). Using site-directed mutagenesis, peptide sequencing, and fluorescence resonance energy transfer assays with recombinant dystrophin, we demonstrate that this putative site in mouse and human dystrophin is a direct substrate for the Coxsackieviral protease 2A both in vitro and in vivo. The substrate analogue protease inhibitor z-LSTT-fmk was designed based on the dystrophin sequence that interacts with the protease 2A and was found to have an IC(50) of 550 nM in vitro. Dystrophin is the first cellular substrate of the enteroviral protease 2A that was identified using by a bioinformatic approach and for which the cleavage site was molecularly mapped within living cells.
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Affiliation(s)
- C Badorff
- Department of Medicine, University of California, San Diego, California 92093, USA
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244
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Rowe A, Ferguson GL, Minor PD, Macadam AJ. Coding changes in the poliovirus protease 2A compensate for 5'NCR domain V disruptions in a cell-specific manner. Virology 2000; 269:284-93. [PMID: 10753707 DOI: 10.1006/viro.2000.0244] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Polioviruses are single-stranded RNA viruses with an unusually long noncoding region (NCR) at the 5' end predicted to have an elaborate secondary structure made up of six domains. Mutations in domain V of the poliovirus 5'NCR that disrupt secondary structure are responsible for attenuation of the virus and a temperature-sensitive (ts) phenotype in vitro. In addition to direct back mutation or compensatory second site mutation in the 5'NCR as previously documented, the ts phenotype was found to be compensated for in monkey kidney cells in vitro by a coding change in the protease 2A. These coding changes were found throughout the protease with no obvious pattern or trend. They were not all found to be equivalent and limited in ability to compensate for the severest domain V disruption. The compensatory effect of the 2A changes was found to be cell specific, having no effect on monkey neurovirulence and in a mouse cell line but a significant effect in two monkey cell lines and a human epithelial line.
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Affiliation(s)
- A Rowe
- Department of Virology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, EN6 3QG, United Kingdom
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245
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Abstract
The eukaryotic mRNA 5' cap structure facilitates translation. However, cap-dependent translation is impaired at mitosis, suggesting a cap-independent mechanism for mRNAs translated during mitosis. Translation of ornithine decarboxylase (ODC), the rate-limiting enzyme in the biosynthesis of polyamines, peaks twice during the cell cycle, at the G1/S transition and at G2/M. Here, we describe a cap-independent internal ribosome entry site (IRES) in the ODC mRNA that functions exclusively at G2/M. This ensures elevated levels of polyamines, which are implicated in mitotic spindle formation and chromatin condensation. c-myc mRNA also contains an IRES that functions during mitosis. Thus, IRES-dependent translation is likely to be a general mechanism to synthesize short-lived proteins even at mitosis, when cap-dependent translation is interdicted.
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Affiliation(s)
- S Pyronnet
- Department of Biochemistry and McGill Cancer Center, McGill University, Montréal, Qúebec, Canada
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246
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Barco A, Feduchi E, Carrasco L. A stable HeLa cell line that inducibly expresses poliovirus 2A(pro): effects on cellular and viral gene expression. J Virol 2000; 74:2383-92. [PMID: 10666269 PMCID: PMC111720 DOI: 10.1128/jvi.74.5.2383-2392.2000] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A HeLa cell clone (2A7d) that inducibly expresses the gene for poliovirus protease 2A (2A(pro)) under the control of tetracycline has been obtained. Synthesis of 2A(pro) induces severe morphological changes in 2A7d cells. One day after tetracycline removal, cells round up and a few hours later die. Poliovirus 2A(pro) cleaves both forms of initiation factor eIF4G, causing extensive inhibition of capped-mRNA translation a few hours after protease induction. Methoxysuccinyl-Ala-Ala-Pro-Val-chloromethylketone, a selective inhibitor of 2A(pro), prevents both eIF4G cleavage and inhibition of translation but not cellular death. Expression of 2A(pro) still allows both the replication of poliovirus and the translation of mRNAs containing a picornavirus leader sequence, while vaccinia virus replication is drastically inhibited. Translation of transfected capped mRNA is blocked in 2A7d-On cells, while luciferase synthesis from a mRNA bearing a picornavirus internal ribosome entry site (IRES) sequence is enhanced by the presence of 2A(pro). Moreover, synthesis of 2A(pro) in 2A7d cells complements the translational defect of a poliovirus 2A(pro)-defective variant. These results show that poliovirus 2A(pro) expression mimics some phenotypical characteristics of poliovirus-infected cells, such as cell rounding, inhibition of protein synthesis and enhancement of IRES-driven translation. This cell line constitutes a useful tool to further analyze 2A(pro) functions, to complement poliovirus 2A(pro) mutants, and to test antiviral compounds.
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Affiliation(s)
- A Barco
- Centro de Biología Molecular, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
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247
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Goldstaub D, Gradi A, Bercovitch Z, Grosmann Z, Nophar Y, Luria S, Sonenberg N, Kahana C. Poliovirus 2A protease induces apoptotic cell death. Mol Cell Biol 2000; 20:1271-7. [PMID: 10648613 PMCID: PMC85262 DOI: 10.1128/mcb.20.4.1271-1277.2000] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A cell line was generated that expresses the poliovirus 2A protease in an inducible manner. Tightly controlled expression was achieved by utilizing the muristerone A-regulated expression system. Upon induction, cleavage of the eukaryotic translation initiation factor 4GI (eIF4GI) and eIF4GII is observed, with the latter being cleaved in a somewhat slower kinetics. eIF4G cleavage was accompanied by a severe inhibition of protein synthesis activity. Upon induction of the poliovirus 2A protease, the cells displayed fragmented nuclei, chromatin condensation, oligonucleosome-size DNA ladder, and positive TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) staining; hence, their death can be characterized as apoptosis. These results indicate that the expression of the 2A protease in mammalian cells is sufficient to induce apoptosis. We suggest that the poliovirus 2A protease induces apoptosis either by arresting cap-dependent translation of some cellular mRNAs that encode proteins required for cell viability, by preferential cap-independent translation of cellular mRNAs encoding apoptosis inducing proteins, or by cleaving other, yet unidentified cellular target proteins.
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Affiliation(s)
- D Goldstaub
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel
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248
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Bushell M, Wood W, Clemens MJ, Morley SJ. Changes in integrity and association of eukaryotic protein synthesis initiation factors during apoptosis. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:1083-91. [PMID: 10672017 DOI: 10.1046/j.1432-1327.2000.01101.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Induction of apoptosis results in inhibition of the rate of overall protein synthesis in a variety of cell types. We have shown previously that polypeptide chain initiation factor eIF4GI is rapidly cleaved by caspase-3, whereas other components of the eIF4F complex are much more stable during apoptosis in BJAB and Jurkat cells. We have now extended our analysis to other factors involved in the initiation of protein synthesis and we report here that eIF4B, the p35 subunit of eIF3, and minor proportions of the alpha subunit of eIF2 and the eIF4E-binding protein 4E-BP1 are also cleaved to give rise to discrete fragments. These cleavages occur with delayed kinetics relative to that seen for eIF4GI, and eIF2beta and eIF2gamma levels also decrease at a relatively late stage of apoptosis. In contrast, the second form of eIF4G described recently, eIF4GII, is cleaved as rapidly as eIF4GI under the same conditions. Purified recombinant caspase-3 is able to degrade eIF4B and eIF3(p35) in vitro, producing fragments of the same sizes as those seen in intact cells. Induction of apoptosis also results in a biphasic change in the association of 4E-BP1 with eIF4E. Thus the progress of apoptosis is characterized by a complex programme of changes in several initiation factors, including the specific fragmentation or complete degradation of some and alterations in the association status of others. These events are likely to contribute to the inhibition of protein synthesis seen under these conditions.
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Affiliation(s)
- M Bushell
- Biochemistry Group, School of Biological Sciences, University of Sussex, Brighton, UK
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249
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Raught B, Gingras AC, Gygi SP, Imataka H, Morino S, Gradi A, Aebersold R, Sonenberg N. Serum-stimulated, rapamycin-sensitive phosphorylation sites in the eukaryotic translation initiation factor 4GI. EMBO J 2000; 19:434-44. [PMID: 10654941 PMCID: PMC305580 DOI: 10.1093/emboj/19.3.434] [Citation(s) in RCA: 217] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The eukaryotic translation initiation factor 4G (eIF4G) proteins play a critical role in the recruitment of the translational machinery to mRNA. The eIF4Gs are phosphoproteins. However, the location of the phosphorylation sites, how phosphorylation of these proteins is modulated and the identity of the intracellular signaling pathways regulating eIF4G phosphorylation have not been established. In this report, two-dimensional phosphopeptide mapping demonstrates that the phosphorylation state of specific eIF4GI residues is altered by serum and mitogens. Phosphopeptides resolved by this method were mapped to the C-terminal one-third of the protein. Mass spectrometry and mutational analyses identified the serum-stimulated phosphorylation sites in this region as serines 1108, 1148 and 1192. Phosphoinositide-3-kinase (PI3K) inhibitors and rapamycin, an inhibitor of the kinase FRAP/mTOR (FKBP12-rapamycin-associated protein/mammalian target of rapamycin), prevent the serum-induced phosphorylation of these residues. Finally, the phosphorylation state of N-terminally truncated eIF4GI proteins acquires resistance to kinase inhibitor treatment. These data suggest that the kinases phosphorylating serines 1108, 1148 and 1192 are not directly downstream of PI3K and FRAP/mTOR, but that the accessibility of the C-terminus to kinases is modulated by this pathway(s).
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Affiliation(s)
- B Raught
- Department of Biochemistry and McGill Cancer Centre, McGill University, 3655 Drummond, Montréal, Québec H3G 1Y6, Canada
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250
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Abstract
This chapter focuses on the history of the discovery of cap and an update of research on viral and cellular-messenger RNA (mRNA) capping. Cap structures of the type m7 GpppN(m)pN(m)p are present at the 5′ ends of nearly all eukaryotic cellular and viral mRNAs. A cap is added to cellular mRNA precursors and to the transcripts of viruses that replicate in the nucleus during the initial phases of transcription and before other processing events, including internal N6A methylation, 3′-poly (A) addition, and exon splicing. Despite the variations on the methylation theme, the important biological consequences of a cap structure appear to correlate with the N7-methyl on the 5′-terminal G and the two pyrophosphoryl bonds that connect m7G in a 5′–5′ configuration to the first nucleotide of mRNA. In addition to elucidating the biochemical mechanisms of capping and the downstream effects of this 5′- modification on gene expression, the advent of gene cloning has made available an ever-increasing amount of information on the proteins responsible for producing caps and the functional effects of other cap-related interactions. Genetic approaches have demonstrated the lethal consequences of cap failure in yeasts, and complementation studies have shown the evolutionary functional conservation of capping from unicellular to metazoan organisms.
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Affiliation(s)
- Y Furuichi
- AGENE Research Institute, Kamakura, Japan
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