HBx mutants differentially affect the activation of hypoxia-inducible factor-1α in hepatocellular carcinoma

Background: Mutations in HBx gene are frequently found in HBV-associated hepatocellular carcinoma (HCC). Activation of hypoxia-inducible factor-1 alpha (HIF-1 alpha) contributes to HCC development and progression. Wild-type HBx has been demonstrated to activate HIF-1 alpha, but the effect of HBx mutations on HIF-1 alpha has not been elucidated. Methods: HBx mutations were identified by gene sequencing in 101 HCC tissues. Representative HBx mutants were cloned and transfected into HCC cells. Expression and activation of HIF-1 alpha were analysed by western blot and luciferase assays, respectively. The relationship between HBx mutants and HIF-1 alpha expression in HCC tissues was also evaluated. Results: The dual mutations K130M/V131I enhanced the functionality of HBx as they upregulated the expression and transcriptional activity of HIF-1 alpha. The C-terminal truncations and deletion mutations, however, weakened the ability of HBx to upregulate HIF-1 alpha. Meanwhile, the C-terminus was further found to be essential for the stability and transactivation of HBx. In the HCC tissues, there was a positive association between the HBx mutants and HIF-1 alpha expression. Conclusion: Different mutations of HBx exert differentiated effects on the functionality of HIF-1 alpha, however, the overall activity of HBx mutants appears to increase the expression and transcriptional activity of HIF-1 alpha.