Hepatocellular carcinoma (HCC) occurs in a significant number of patients with hepatitis C virus (HCV) infection. HCV causes double-strand DNA breaks and enhances the mutation frequency of proto-oncogenes and tumor suppressors. However, the underlying mechanisms for these oncogenic events are still elusive. Here, we studied the role of c-Jun, signal transducer and activator of transcription 3 (STAT3), and nitric oxide (NO) in spontaneous and diethylnitrosamine (DEN)-initiated and/or phenobarbital (Pb)-promoted HCC development using HCV core transgenic (Tg) mice. The viral core protein induces hepatocarcinogenesis induction as a tumor initiator under promotion by Pb treatment alone. Conditional knockout of c-jun and stat3 in hepatocytes achieves a nearly complete, additive effect on prevention of core-induced spontaneous HCC or core-enhanced HCC incidence caused by DEN/Pb. Core protein induces hepatocyte proliferation and the expression of inflammatory cytokines (interleukin-6, tumor necrosis factor-alpha, interleukin-1) and inducible NO synthase (iNOS); the former is dependent on c-Jun and STAT3, and the latter on c-Jun. Oxidative DNA damage repair activity is impaired by the HCV core protein due to reduced DNA glycosylase activity for the excision of 8-oxo-2'-deoxyguanosine. This impairment is abrogated by iNOS inhibition or c-Jun deficiency, but aggravated by the NO donor or iNOS-inducing cytokines. The core protein also suppresses apoptosis mediated by Fas ligand because of c-Jun-dependent Fas down-regulation.
Conclusion: These results indicate that the HCV core protein potentiates chemically induced HCC through c-Jun and STAT3 activation, which in turn, enhances cell proliferation, suppresses apoptosis, and impairs oxidative DNA damage repair, leading to hepatocellular transformation.