HBV X gene is required for maintaining the tumorigenicity of hepatocellular carcinoma cells

Abstract

Hepatitis B virus (HBV) infection is a major cause of human hepatocellular carcinoma (HCC) in Southeast Asia and Hong Kong. Among the four proteins that originate from the HBV genome, HBV X (HBx) is the most potentially oncogenic factor. Despite the extensive studies on the roles of HBx in the development of HCC, the precise mechanism of HBx in tumor formation is still unclear and remains controversial. However, the expression of HBx in the majority of HCC cases strongly suggests that it may play a critical role in maintaining the tumorigenicity of HCC. In this study, we used stably transfected vector-derived short hairpin RNAs (shRNAs) to knock down the expression of HBx in PLC/PRF/5 HCC cell line which constitutively produces HBx. Preliminary data showed that this tool could successfully reduce HBx mRNA levels by 70-95% in PLC/PRF/5 cells. Inhibition of HBx expression in PLC/PRF/5 cells significantly reduced the cell growth rate in low serum medium and the ability of anchorage-independent growth in soft agar. Besides, suppressing the expression of HBx caused decreased expression levels of c-myc and Bcl-XL. Furthermore, by immunofluorenscence microscopy, we found that there was less amount of NF-κB localized in the nuclei of the PLC/PRF/5 cells that exhibited reduced levels of HBx expression due to RNAi. Hence, we propose that HBx might maintain tumorigenicity of HCC cells by inducing NF-κB nuclear translocalization that is associated with the transcriptional activation of the expression of c-myc, Bcl-XL and perhaps of other oncogenes.