Effect of Hepatitis B virus X T118N mutant protein in HepG2 cell cycle and apoptosis regulation

Hepatitis B virus (HBV) belongs to Hepadnaviridae family and caused liver infection. HBV infection can develop into hepatocellular carcinoma, one of which is due to presence of HBV X protein (HBx). Some mutations are known to be associated with development of liver carcinoma, for instance HBx K130M/V131I (HBx_KV). In Indonesia, HBx T118N (HBx_T) has been found at similar frequency as the HBx_KV. This study aims to examine the effect of HBx T118N mutant on cell cycle and apoptosis regulation.

In this study, analysis of CyclinE, p21, Bax, and Bcl-2 gene expression was performed using RT-qPCR. Cell cycle and apoptosis analysis was done using flowcytometry with PI and Annexin V-PI staining, respectively. Caspase 3 activity assay was performed using CaspACE™ Colorimetric Assay Kit. The presence of HBx_T mutant increased CyclinE expression at 72 h post transfection, similarly to HBx_KV. Both Bax and Bcl-2 mRNA level were also increased HepG2 cells expressing HBx_T in comparison to HBx_KV expression at 72 h post transfection. HBx_T expression in HepG2 cells at 48 h post transfection caused increase of AnnexinV+/PI- and AnnexinV+/PI+ cell populations, as compared to HBx_wt expression.

Our data suggests that HBx_T influences cell cycle and apoptosis regulation in slightly different mechanism to HBx_KV. Further investigations are still required to understand HBx_T mutant involvement in development of chronic liver disease and liver cirrhosis.