title: The regulation of hepatitis C virus (HCV) internal ribosome-entry site-mediated translation by HCV replicons and nonstructural proteins.
abstract: Hepatitis C virus (HCV), the global leading cause of chronic liver disease, has a positive-sense, ssRNA genome that encodes a large polyprotein. HCV polyprotein translation is initiated by an internal ribosome-entry site (IRES) located at the 5' end of the viral genome, in a cap-independent manner, but the regulatory mechanism of this process remains poorly understood. In this study, we characterized the effect of HCV nonstructural proteins on HCV IRES-directed translation in both HCV replicon cells and transiently transfected human liver cells expressing HCV nonstructural proteins. Using bicistronic reporter gene constructs carrying either HCV or other viral IRES sequences, we found that the HCV IRES-mediated translation was specifically upregulated in HCV replicon cells. This enhancement of HCV IRES-mediated translation by the replicon cells was inhibited by treatment with either type I interferon or ribavirin, drugs that perturb HCV genome replication, suggesting that the enhancement is probably due to HCV-encoded protein function(s). Reduced phosphorylation levels of both eIF2alpha and eIF4E were observed in the replicon cells, which is consistent with our previous findings and indicates that the NS5A nonstructural protein may be involved in the regulatory mechanism(s). Indeed, transient expression of NS5A or NS4B in human liver cells stimulated HCV IRES activity. Interestingly, mutation in the ISDR of NS5A perturbed this stimulation of HCV IRES activity. All these results suggest, for the first time, that HCV nonstructural proteins preferentially stimulate the viral cap-independent, IRES-mediated translation.
authors.affiliation: Department of Microbiology, School of Medicine, University of Washington, Seattle, WA, USA.
authors.forename: Yupeng
authors.initials: Y
authors.lastname: He
authors.affiliation: Department of Microbiology, School of Medicine, University of Washington, Seattle, WA, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Yan
authors.affiliation: Department of Microbiology, School of Medicine, University of Washington, Seattle, WA, USA.
authors.forename: Carlos
authors.initials: C
authors.lastname: Coito
authors.affiliation: Department of Microbiology, School of Medicine, University of Washington, Seattle, WA, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Gale
authors.affiliation: Regional Primate Research Center, University of Washington, Seattle, WA, USA.|Department of Microbiology, School of Medicine, University of Washington, Seattle, WA, USA.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Katze
mesh_terms: D000998:Antiviral Agents / Q000494:pharmacology; D002460:Cell Line; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D016679:Genome, Viral; D016174:Hepacivirus / Q000235:genetics*; D006801:Humans; D007370:Interferon Type I / Q000494:pharmacology; D010766:Phosphorylation; D020815:Polyproteins / Q000235:genetics; D014176:Protein Biosynthesis / Q000187:drug effects; D012093:Replicon / Q000502:physiology*; D012254:Ribavirin / Q000494:pharmacology; D014162:Transfection; D015854:Up-Regulation; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000502:physiology*; D014779:Virus Replication / Q000187:drug effects; D012324:RNA-Dependent RNA Polymerase
chemical_list: D000998:Antiviral Agents; D015852:Eukaryotic Initiation Factor-2; D039561:Eukaryotic Initiation Factor-4E; D007370:Interferon Type I; D020815:Polyproteins; D012254:Ribavirin; D017361:Viral Nonstructural Proteins; C093542:NS4 protein, hepatitis C virus; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase