Article Abstract

HBx deletion-mutant combined with the reverse transcriptase enzyme/s* mutation is involved in HBV mediated liver cell proliferation and apoptosis

Authors: Yi Ouyang, Lei Fu, Shifang Peng, Deming Tan, Xiaoyu Fu


Background: One of the most common cancers worldwide is hepatocellular carcinoma (HCC). Studies have shown that Hepatitis B virus (HBV) X gene (HBx) mutations play a potentially important oncogenic role in the pathogenesis of this disease. However, the molecular mechanisms underlying the malignant transformation of liver cells following HBV infection are poorly understood. We previously identified a novel deletion mutation in HBx (HBx-d382) that is capable of transforming hepatocytes and increasing their tumorigenic capacity. As part of the afore-mentioned study, we also identified reverse transcriptase enzyme (rt)/s* double mutants in nucleoside analogue (NA)-resistant patients. This current study was conducted to determine if HBx-d382 and rt/s* mutations co-exist in HCC patients. The study also aimed to identify the role of these mutations in HCC.
Methods: DNA from serum samples obtained from 152 NA-resistant patients with chronic hepatitis B (CHB) and 33 patients with HCC were sequenced to identify samples harboring both the HBx-d382 mutation and rt/s* double mutations. As part of this study, we also generated lentivirus constructs carrying different HBV mutations including rtA181T/sW172*, rtM204I/sW196*, HBx-d382, rtA181T/sW172*/HBx-d382 and rtM204I/sW196*/HBx-d382. The recombinant viral constructs were used to infect a human hepatocyte cell line (LO2). The LO2 cell line was used to evaluate the effect of the mutations on apoptosis, cellular proliferation and the rate of colony formation in the LO2 cells harboring different mutations.
Results: We identified rt/s*/HBx-d382 mutations in both HBV-related HCC and NA-resistant CHB clinical samples and observed that the rate of occurrence of rt/s*/HBx-d382 mutations in HBV-related HCC is relatively high. The results of this study revealed that the rtA181T/sW172* and rtM204I/sW196* double mutants exhibited enhanced proliferation, reduced apoptosis and an increased rate of colony formation in LO2 cells. Expression of p53 and CyclinD1 were increased and the level of p21 was decreased in the rtA181T/sW172* and rtM204I/sW196* expressing LO2 cells. More importantly, rt/s* double mutations combined with the HBx-d382 mutation resulted in more severe phenotypes compared with rt/s* double mutation alone in LO2 cell lines.
Conclusions: Our data suggest that rt/s*/HBx-d382 triple mutants play a crucial role in HBV-mediated HCC formation.