| Hepatitis C virus causes chronic hepatitis that can progress to end-stage cirrhosis and hepatocellular carcinoma. Mechanisms of HCV pathogenesis are not well understood. To study HCV-host cell interactions, I have developed a ponA-inducible expression system for a full-length HCV ORF in non-transformed human hepatocyte line HH4 cells using the ecdysone receptor regulatory system. PonA-induced full-length HCV ORF mRNA was detected by Northern analysis using probes for Core or NS5B regions. Immunoblot detection of HCV Core, E1, E2, NS3, NS5A demonstrated tight-regulated and dose-dependent induction and proper processing of HCV proteins in this system. At least 85% of ponA-treated cells expressed HCV proteins detectable by immunostaining. Immuno-fluorescence (IF) staining revealed that Core, NS3 and NS5A co-localized in perinuclear regions and may associate with early endosomal protein EEA1.;HCV proteins are implicated in HCV pathogenesis by perturbing cellular functions such as cell growth, apoptosis response, cytokine signaling, stress response, and innate immune response. Therefore, I examined cellular responses to the conditional expression of full length HCV ORF in my system. BrdU incorporation assay and growth rate assay demonstrated that HCV ORF expression decreased cell growth. HCV ORF expression was not directly cytotoxic. However, sensitization to Fas but not TRAIL induced apoptosis was observed in HH4 cells expressing HCV ORE HCV ORF expression induced ROS accumulation and concomitantly upregulated GCL activity and increased intracellular level of GSH, a vital protective antioxidant. Activation of NFkappaB, a transcription factor involved in regulating genes involved in innate immune response/inflammation, was detected by EMSA in HCV ORF expressing cells. Consistent with the above findings, microarray data indicated that HCV ORF expression in HH4 cells down-regulated cell growth, upregulated innate immune response/inflammation, and activated oxidative stress responses.;Taken together, my results suggest that HCV proteins in non-transformed human hepatocytes sensitize cells to Fas-mediated apoptosis, induce oxidative stress, activate NFkappaB and inflammatory response, and inhibit cell growth. Hepatocellular injuries caused by Fas-mediated apoptosis, chronic inflammation, and oxidative stress are common in hepatitis C. Therefore, my system represents a useful model for studying molecular and cellular mechanisms of HCV pathogenesis. |
