Sustained activation of mitogen-activated protein kinases and activator protein 1 by the hepatitis B virus X protein in mouse hepatocytes in vivo

Transcriptional activation of diverse cellular genes by the X protein (HBx) of hepatitis B virus (HBV has been suggested as one of the mechanisms for HBV-associated hepatocellular carcinoma. However, such functions of HBx hav e been studied using transformed cells in culture and have not been examine d in the normal adult hepatocytes, a natural host of HBV. Using an efficien t hepatocyte-specific virus-based gene delivery system developed in our lab oratory earlier, we studied the HBx action in vivo. We demonstrate that fol lowing virosome-mediated, delivery of HBx DNA, a large population (>50%) of hepatocytes express the HBx protein in a dose-dependent manner, which indu ces a significant increase in the activity of extracellular signal-regulate d kinases (ERKs) in the livers of HBx-transfected mice. Inhibition of HBx-i nduced ERK activation following intravenous administration of PD98059, a mi togen-activated protein kinase kinase kinase (MEK) inhibitor, confirmed the requirement for MEK in the activation of ERKs by HBx. Induction of ERK act ivity by HBx was sustained for up to 30 days. Interestingly, sustained acti vation of c-jun N-terminal kinases (JNKs) for up to 30 days was also noted. Such constitutive ERK and JNK activation as a consequence of continued: HB x expression also led to sustained stimulation of further downstream events , such as increased levels of c-Jun and c-Fos proteins along with the persi stent induction of activator protein 1 binding activity. Taken together, ou r data suggest a critical role of these molecules in HBx-mediated cell tran sformation.