Activation of c-Jun NH2-terminal kinase (JNK) signaling pathway is essential for the stimulation of hepatitis C virus (HCV) non-structural protein 3 (NS3)-mediated cell growth

Hepatitis C virus (HCV) non-structural protein 3 (NS3) has been shown to affect cellular functions and is thought to contribute to the development of HCV-related hepatocarcinogenesis. In this study, we delineated part of the mechanisms whereby NS3 protein stimulates cell growth in liver (HepG2) and non-liver (HeLa) cells. The expression of NS3 protein enhanced cell growth, c-jun NH2-terminal kinase (JNK) activation, DNA binding activities of the transcription factors AP-1 and ATF-2, and c-jun expression, but not the activation of extracellular signal-regulated kinase (ERK) or p38MAPK. Whereas co-expression of NS3 with its cofactor NS4A inhibited NS3-mediated cell growth without to influence NS3-mediated JNK activation, or to affect the basal activities of ERK or p38MAPK. Pre-treatment of NS3 protein-expressing cells with JNK inhibitor, SP600125, abolished activation of AP-1 and ATF-2 and inhibited c-jun expression and induced cell growth, suggesting that JNK activation is essential for the stimulation of NS3-mediated cell growth.