Hepatitis C virus nonstructural 5B protein regulates tumor necrosis factor alpha signaling through effects on cellular IκB kinase

Hepatitis C virus (HCV) NS5B protein is a membrane-associated phosphoprotein that possesses an RNA-dependent RNA polymerase activity. We recently reported that NS5A protein interacts with TRAF2 and modulates tumor necrosis factor alpha (TNF-alpha)-induced NF-kappa B and Jun N-terminal protein kinase (JNK). Since NS5A and NS5B are the essential components of the HCV replication complex, we examined whether NS5B could modulate TNF-alpha-induced NF-kappa B and JNK activation. In this study, we have demonstrated that TNF-alpha-induced NF-kappa B activation is inhibited by NS5B protein in HEK293 and hepatic cells. Furthermore, NS5B protein inhibited both TRAF2- and IKK-induced NF-kappa B activation. Using coirnmunoprecipitation assays, we show that NS5B interacts with IKK alpha. Most importantly, NS5B protein in HCV subgenomic replicon cells interacted with endogenous IKK alpha, and then TNF-alpha-mediated IKK alpha kinase activation was significantly decreased by NS5B. Using in vitro kinase assay, we have further found that NS5B protein synergistically activated TNF-alpha-mediated JNK activity in HEK293 and hepatic cells. These data suggest that NS5B protein modulates TNF-alpha signaling pathways and may contribute to HCV pathogenesis.