Induction of high-molecular-weight (HMW) tumor necrosis factor(TNF) alpha by hepatitis C virus (HCV) non-structural protein 3 (NS3) in liver cells is AP-1 and NF-kappaB-dependent activation.

Chronic infection of hepatitis C virus (HCV)-infected patients is associated with the production of serum and interhepatic inflammatory cytokines including tumor necrosis factor alpha (TNF-alpha). In this study, we delineated part of the mechanism whereby HCV induces the synthesis of TNF-alpha in human liver cell lines HepG2 and Huh7. HepG2 transiently transfected with the full-length HCV cDNA expressed high-molecular-weight (HMW) TNF-alpha mRNAs, which were absent in the control cells. In addition tightly regulated expression of HCV NS3 in both HepG2 and Huh7 was found to induce the expression of HMW mRNAs and subsequently the production of biologically active TNF-alpha. Interestingly, the expression of NS3 protein in HepG2-NS3 or in Huh7-NS3 resulted in the activation of kinase (IKK-alpha) of NF-alphaB inhibitor (IalphaB) and in the enhancement of the DNA-binding activity of the nuclear transcription factor NF-kappaB. The inhibition of the transcription of TNF-alpha mRNAs and subsequently TNF-alpha production following the treatment of HepG2-NS3 or Huh7-NS3 transfectants with the inhibitor of NF-kappaB, Bay 11-7082, suggesting the importance of NF-kappaB for the regulation of NS3-mediated TNF-alpha expression in HepG2 and HeLa cells. Interestingly, data obtained from luciferase assays, in liver and in non-liver cells showed the contribution of NS3 protein in the regulation of TNF-alpha promoter through the activation of AP-1 and NF-kappaB. Our data indicate that the intrahepatic TNF-alpha production induced by HCV is transcriptionally up-regulated by HCV NS3. Therefore, HCV NS3 may have a potential role in the induction of intrahepatic inflammatory processes that occur during acute and chronic hepatitis C.