The Hepatitis C virus NS5A protein activates a phosphoinositide 3-kinase-dependent survival signaling cascade.
Hepatitis C virus (HCV) establishes a persistent infection, with up to 80% of infected individuals proceeding to chronic hepatitis, which in many cases may result in liver cirrhosis and hepatocellular carcinoma (HCC); indeed HCV infection is increasingly associated with the development of HCC. The long time period (up to 30 years) between primary infection and the onset of HCC implies that HCV is not directly oncogenic but in some way predisposes patients to develop tumors, though the mechanism for this is unclear as yet. We report here that NS5A binds directly to the Src homology 3 domain of the p85 regulatory subunit of phosphoinositide 3-kinase (PI3K), and this interaction is mediated by a novel (non-proline-rich) motif within NS5A. Coimmunoprecipitation analysis revealed that NS5A bound native heterodimeric PI3K and enhanced the phosphotransferase activity of the catalytic (p110) subunit both in vitro and in human cell lines harboring a subgenomic HCV replicon or expressing NS5A alone. NS5A-mediated activation of PI3K resulted in increased phosphorylation and activity of Akt/protein kinase B and concomitantly provided protection against the induction of apoptosis in both replicon-harboring cells and cells stably expressing NS5A alone. These data suggest that stimulation of PI3K by NS5A may represent an indirect mechanism for development of HCC in HCV-infected patients and further suggests potential therapeutic strategies to counteract the occurrence of HCV-related HCC.
Street
Andrew
A
School of Biochemistry and Microbiology, Astbury Centre for Structural Molecular Biology, University of Leeds, Mount Preston Street, Leeds, West Yorkshire LS2 9JT, United Kingdom.
Macdonald
Andrew
A
Crowder
Katherine
K
Harris
Mark
M
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D019556:COS Cells; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002384:Catalysis; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004247:DNA / Q000737:chemistry; D053938:DNA Fragmentation; D019281:Dimerization; D005822:Genetic Vectors; D005982:Glutathione Transferase / Q000378:metabolism; D016174:Hepacivirus / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000473:pathology; D008113:Liver Neoplasms / Q000473:pathology; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D015854:Up-Regulation; D017361:Viral Nonstructural Proteins / Q000378:metabolism*; D018909:src Homology Domains; D012324:RNA-Dependent RNA Polymerase
D053148:Caspase 3; D020169:Caspases; D004247:DNA; D005982:Glutathione Transferase; D019869:Phosphatidylinositol 3-Kinases; D011993:Recombinant Fusion Proteins; D017361:Viral Nonstructural Proteins; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase; C505407:CASP3 protein, human