title: Inhibition of protein synthesis by the nonstructural proteins NS4A and NS4B of hepatitis C virus.
abstract: Possible inhibitory effects of hepatitis C virus (HCV) proteins on cellular protein synthesis were analyzed using transient expression system. The core protein, the nonstructural protein 4A (NS4A) and NS4B, but not NS3, NS5A or NS5B, inhibited p21/Waf1 expression post-transcriptionally. Further analysis revealed that the inhibition by NS4A and NS4B was mediated at least partly, if not entirely, at the translation level. NS4A-mediated translational inhibition was counteracted to some extent by NS3 co-expressed either in trans or cis. Co-expression of NS4A and NS4B exerted an additive effect on the translational inhibition. The N-terminal two-thirds of NS4A (amino acids 1-40) was shown to be involved in the translational inhibition. We also tested possible inhibitory effects of NS4A and NS4B on synthesis of other cellular proteins in parallel with p21/Waf1. NS4A and NS4B inhibited p21/Waf1 most strongly, followed by RNase L, p53, a C-terminally truncated form of CREB-RP and 2'-5' oligoadenylate synthetase. p21/Waf1, RNase L and p53 are known to have the PEST (proline-glutamic acid-serine-threonine) motif with relatively high scores in their sequences and considered to be sensitive to intracellular degradation. Taken together, our results suggest that NS4A and NS4B each mediate translational inhibition and, probably, increased degradation of certain cellular proteins.
authors.affiliation: Department of Microbiology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
authors.forename: Ruth H
authors.initials: RH
authors.lastname: Florese
authors.forename: Motoko
authors.initials: M
authors.lastname: Nagano-Fujii
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Iwanaga
authors.forename: Rachmat
authors.initials: R
authors.lastname: Hidajat
authors.forename: Hak
authors.initials: H
authors.lastname: Hotta
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism*; D016174:Hepacivirus / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis / Q000187:drug effects*; D014407:Tumor Cells, Cultured; D017361:Viral Nonstructural Proteins / Q000378:metabolism / Q000494:pharmacology*; D014764:Viral Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism
chemical_list: C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; C093542:NS4 protein, hepatitis C virus; D017361:Viral Nonstructural Proteins; D014764:Viral Proteins