Activation of the interferon-inducible 2 '-5 '-oligoadenylate synthetase gene by hepatitis C virus core protein

The effects of hepatitis C virus (HCV) proteins on several signal transduct ion pathways in human nonneoplastic hepatocyte PH5CH8 cells were investigat ed using expression vectors encoding HCV proteins derived from HCV-infected human nonneoplastic cultured T-lymphocyte and hepatocyte cells (MT-2C and PH5CH7), which could support HCV replication. The amino acid sequences of H CV proteins obtained from HCV-infected human cells were identical or very c lose to the consensus sequences of the proteins derived from the original i noculum used for HCV infection. During the course of the study, we found th at HCV core protein specifically activated the 40/46-kDa 2'-5'-oligoadenyla te synthetase (2'-5'-OAS) gene promoter in a dose dependent manner in diffe rent human hepatocyte cell lines (PH5CH8, HepG2, and PLC/PRF/5). We also fo und that the activation by core protein was further enhanced in the cells t reated with alpha interferon. The expression of E1 or E2 envelope protein o r nonstructural NS5A protein did not activate the 2'-5'-OAS gene promoter. We demonstrated that the activation by core protein in the hepatocyte cells was suppressed by antisense RNA complementary to core-encoding RNA. Deleti on mutant analysis of core protein and deletion analysis of the 2'-5'-OAS g ene promoter have been performed. Finally, we demonstrated that the activat ion of the 2'-5'-OAS gene occurred at the transcriptional level and further more demonstrated that the endogenous 2'-5'-OAS gene was also activated by core protein. This is the first report to show that a viral protein activat ed the 2'-5'-OAS gene.