title: Hepatitis C virus NS5A binds to the mRNA cap-binding eukaryotic translation initiation 4F (eIF4F) complex and up-regulates host translation initiation machinery through eIF4E-binding protein 1 inactivation.
abstract: Initiation, a major rate-limiting step of host protein translation, is a critical target in many viral infections. Chronic hepatitis C virus (HCV) infection results in hepatocellular carcinoma. Translation initiation, up-regulated in many cancers, plays a critical role in tumorigenesis. mTOR is a major regulator of host protein translation. Even though activation of PI3K-AKT-mTOR by HCV non-structural protein 5A (NS5A) is known, not much is understood about the regulation of host translation initiation by this virus. Here for the first time we show that HCV up-regulates host cap-dependent translation machinery in Huh7.5 cells through simultaneous activation of mTORC1 and eukaryotic translation initiation factor 4E (eIF4E) by NS5A. NS5A, interestingly, overexpressed and subsequently hyperphosphorylated 4EBP1. NS5A phosphorylated eIF4E through the p38 MAPK-MNK pathway. Both HCV infection and NS5A expression augmented eIF4F complex assembly, an indicator of cap-dependent translation efficiency. Global translation, however, was not altered by HCV NS5A. 4EBP1 phosphorylation, but not that of S6K1, was uniquely resistant to rapamycin in NS5A-Huh7.5 cells, indicative of an alternate phosphorylation mechanism of 4EBP1. Resistance of Ser-473, but not Thr-308, phosphorylation of AKT to PI3K inhibitors suggested an activation of mTORC2 by NS5A. NS5A associated with eIF4F complex and polysomes, suggesting its active involvement in host translation. This is the first report that implicates an HCV protein in the up-regulation of host translation initiation apparatus through concomitant regulation of multiple pathways. Because both mTORC1 activation and eIF4E phosphorylation are involved in tumorigenesis, we propose that their simultaneous activation by NS5A might contribute significantly to the development of hepatocellular carcinoma.
authors.affiliation: Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Hyderabad 500007, India.
authors.forename: Anju
authors.initials: A
authors.lastname: George
authors.forename: Swarupa
authors.initials: S
authors.lastname: Panda
authors.forename: Devika
authors.initials: D
authors.lastname: Kudmulwar
authors.forename: Salma Pathan
authors.initials: SP
authors.lastname: Chhatbar
authors.forename: Sanjeev Chavan
authors.initials: SC
authors.lastname: Nayak
authors.forename: Harinivas Harshan
authors.initials: HH
authors.lastname: Krishnan
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000821:virology; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D002472:Cell Transformation, Viral / Q000235:genetics; D004351:Drug Resistance / Q000187:drug effects / Q000235:genetics; D039561:Eukaryotic Initiation Factor-4E / Q000235:genetics / Q000378:metabolism; D039562:Eukaryotic Initiation Factor-4F / Q000235:genetics / Q000378:metabolism*; D016174:Hepacivirus / Q000235:genetics / Q000378:metabolism*; D006526:Hepatitis C / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000821:virology; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D010442:Peptide Chain Initiation, Translational; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000235:genetics; D011132:Polyribosomes / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors; D015854:Up-Regulation; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000900:Anti-Bacterial Agents; D018797:Cell Cycle Proteins; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D011506:Proteins; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors; D017361:Viral Nonstructural Proteins; C493245:CRTC2 protein, human; C087000:EIF4EBP1 protein, human; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase