Sorafenib overcomes the chemoresistance in HBx-expressing hepatocellular carcinoma cells through down-regulation of HBx protein stability and suppresses HBV gene expression

Previous studies have revealed that HBx expression has anti-apoptotic effects, resulting in increased drug resistance in HCC cells. Thus, we examined if sorafenib efficiently induces apoptosis in HBx-overexpressing HCC cells. Noticeably, sorafenib efficiently induced apoptosis, even in HBx-expressing HepG2 cells, indicating that the HBx protein does not attenuate sorafenib-induced apoptosis. We next investigated if sorafenib modulates autophagy, allowing HCC cells to overcome the chemoresistance conferred by the HBx protein. Although autophagy plays a cytoprotective role against sorafenib-induced lethality, sorafenib was effective irrespective of HBx protein overexpression. We next examined if sorafenib exerts its cytotoxic effect via direct effects on the HBx protein. Importantly, sorafenib decreased HBx protein stability through a proteasome-dependent degradation pathway. Moreover, sorafenib decreased HBV gene expression and viral promoter activity. Taken together, sorafenib efficiently induces apoptotic cell death in HBx-expressing HCC cells via the downregulation of the HBx protein, a key factor in the anti-cancer drug resistance observed in HBV-induced HCC.