title: Down-regulation of the retinoblastoma tumor suppressor by the hepatitis C virus NS5B RNA-dependent RNA polymerase.
abstract: The retinoblastoma tumor-suppressor protein (Rb) plays a critical role in controlling cellular proliferation and apoptosis by regulating E2F transcription factors. Rb is a key target of oncoproteins expressed by DNA tumor viruses, but RNA viruses are not known to regulate Rb function. Here, we show that Rb abundance is negatively regulated in cells containing replicating genomic RNA from hepatitis C virus, a human virus strongly associated with hepatocellular carcinoma. The viral RNA-dependent RNA polymerase NS5B forms a complex with Rb, targeting it for degradation and resulting in reduction of Rb abundance, activation of E2F-responsive promoters, and cell proliferation. NS5B contains a conserved Leu-x-Cys/Asn-x-Asp motif that is homologous to Rb-binding domains in the oncoproteins of DNA viruses. This domain overlaps the polymerase active site, and mutations within it abrogate Rb binding and reverse the effects of NS5B on E2F promoter activation and cell proliferation. These findings suggest a unique link between an oncogenic RNA virus implicated in the development of liver cancer and a critically important tumor-suppressor protein.
authors.affiliation: Department of Microbiology and Immunology, Institute for Human Infections and Immunity, University of Texas Medical Branch, Galveston, 77555-1019, USA.
authors.forename: Tsubasa
authors.initials: T
authors.lastname: Munakata
authors.forename: Mitsuyasu
authors.initials: M
authors.lastname: Nakamura
authors.forename: Yuqiong
authors.initials: Y
authors.lastname: Liang
authors.forename: Kui
authors.initials: K
authors.lastname: Li
authors.forename: Stanley M
authors.initials: SM
authors.lastname: Lemon
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D002460:Cell Line; D015536:Down-Regulation / Q000235:genetics*; D050684:E2F Transcription Factors / Q000378:metabolism; D016174:Hepacivirus / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008156:Luciferases; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000378:metabolism*; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D050684:E2F Transcription Factors; D016160:Retinoblastoma Protein; D017361:Viral Nonstructural Proteins; D008156:Luciferases; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase