title: Non-structural protein 4A of Hepatitis C virus accumulates on mitochondria and renders the cells prone to undergoing mitochondria-mediated apoptosis.
abstract: Non-structural protein 4A (NS4A) of Hepatitis C virus (HCV) functions as a cofactor for NS3 by forming a complex with it to augment its enzymic activities. NS4A also forms a complex with other HCV proteins, such as NS4B/NS5A, to facilitate the formation of the viral RNA replication complex on the endoplasmic reticulum (ER) membrane. In addition to its essential role in HCV replication, NS4A is thought to be involved in viral pathogenesis by affecting cellular functions. In this study, it was demonstrated that NS4A was localized not only on the ER, but also on mitochondria when expressed either alone or together with NS3 in the form of the NS3/4A polyprotein and in the context of HCV RNA replication in Huh7 cells harbouring an HCV RNA replicon. Moreover, NS4A expression altered the intracellular distribution of mitochondria significantly and caused mitochondrial damage, as evidenced by the collapsed mitochondrial transmembrane potential and release of cytochrome c into the cytoplasm, which led ultimately to induction of apoptosis through activation of caspase-3, but not caspase-8. Consistently, Huh7 cells expressing NS3/4A and those harbouring an HCV RNA replicon were shown to be more prone to undergoing actinomycin D-induced, mitochondria-mediated apoptosis, compared with the control Huh7 cells. Taken together, these results suggest the possibility that HCV exerts cytopathic effect (CPE) on the infected cells under certain conditions and that NS4A is responsible, at least in part, for the conditional CPE in HCV-infected cells.
authors.affiliation: Division of Microbiology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nomura-Takigawa
authors.affiliation: Division of Microbiology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
authors.forename: Motoko
authors.initials: M
authors.lastname: Nagano-Fujii
authors.affiliation: Division of Microbiology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
authors.forename: Lin
authors.initials: L
authors.lastname: Deng
authors.affiliation: Division of Molecular Pathology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
authors.forename: Sohei
authors.initials: S
authors.lastname: Kitazawa
authors.affiliation: Division of Microbiology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ishido
authors.affiliation: Division of Microbiology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
authors.forename: Kiyonao
authors.initials: K
authors.lastname: Sada
authors.affiliation: Division of Microbiology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
authors.forename: Hak
authors.initials: H
authors.lastname: Hotta
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D045304:Cytochromes c / Q000378:metabolism; D003588:Cytopathogenic Effect, Viral; D004721:Endoplasmic Reticulum / Q000821:virology; D004789:Enzyme Activation; D016174:Hepacivirus / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008564:Membrane Potentials; D016253:Microscopy, Immunoelectron; D008928:Mitochondria / Q000502:physiology / Q000821:virology*; D012367:RNA, Viral / Q000096:biosynthesis / Q000235:genetics; D012093:Replicon; D017361:Viral Nonstructural Proteins / Q000502:physiology; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*; D014774:Virulence; D014779:Virus Replication; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases
chemical_list: D002352:Carrier Proteins; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases; D045304:Cytochromes c; D047908:Intracellular Signaling Peptides and Proteins; D012367:RNA, Viral; D017361:Viral Nonstructural Proteins; D014764:Viral Proteins; C084422:NS3 protein, hepatitis C virus; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases; C455041:NS4A cofactor peptide, Hepatitis C virus; C505407:CASP3 protein, human; C505530:CASP8 protein, human