The Effects and Underlying Mechanisms of Hepatitis B Virus X Gene Mutants on the Development of Hepatocellular Carcinoma

Abstract Background: We aimed to elucidate the mechanism by which hepatitis B virus X (HBx) gene mutations increase the risk of hepatocellular carcinoma (HCC) and identify novel therapeutic targets.Methods: Wild-type and four HBx mutants (M1, A1762T/G1764A; M2, T1674G+T1753C+A1762T/G1764A; M3, C1653T+T1674G+A1762T/G1764A; Ct-HBx, carboxylic acid-terminal truncated HBx) were delivered into the livers of fumarylacetoacetate hydrolase-deficient mice by using the Sleeping Beauty (SB) transposon system, respectively. Seven liver tissues and seven tumor tissues of the SB mouse models were subjected to HBV-capture sequencing. Three liver tissues from WT-HBx mice, three tumor tissues from M3-HBx mice, and three tumor tissues from Ct-HBx mice were subjected to cDNA microarray analysis. HeLa cells stably expressing WT-HBx and the four HBx mutants were also subjected to cDNA microarray assay.Results: The incidence of HCC was higher in the mice injected with M3-HBx or Ct-HBx. M3-HBx had a stronger capacity of upregulating inflammatory cytokines than other HBx variants. HBV-capture sequencing showed that the HBx fragments were mainly integrated into intergenic and intron regions. No significant difference was observed in the number of insertion sites between tumors and liver tissues. Ectopic expression of the HBx mutants, especially M3-HBx and Ct-HBx, significantly increased cell proliferation and the S phase proportion of HepG2 and HeLa cells, compared to WT-HBx. Liver tissues of the SB mice and the transfected cells were subjected to cDNA microarray analysis. Plasminogen activator inhibitor-1 (PAI1) and cell division cycle 20 (CDC20) were identified as novel effectors. M3-HBx and Ct-HBx significantly upregulated the expression of PAI1 and CDC20 in HepG2 and HeLa cells as well as the livers of the SB mice. PAI1 silencing attenuated the effect of M3-HBx and Ct-HBx on the growth of HepG2 cells and greatly decreased the growth of HeLa cells with Ct-HBx. Conclusion: HBx C1653T+T1674G+A1762T/G1764A mutant and Ct-HBx promote carcinogenesis via upregulating PAI1 and CDC20. PAI1, an important player bridging the HBx mutants and HCC, should be a promising candidate as a predictive and prognostic biomarker and therapeutic target in HBV-related HCC.