Hepatitis B virus X (HBX) protein upregulates β-catenin in a human hepatic cell line by sequestering SIRT1 deacetylase

Hepatitis B virus X (HBX) protein has been reported to induce upregulation of beta-catenin, a known proto-oncogene, in p53-knockout and p53-mutant hepatic cell lines both in a GSK-3 beta-dependent manner and via interaction with adenomatous polyposis coli, which results in protection from beta-catenin degradation. In this study, we describe a novel mechanism for HBX-mediated upregulation of beta-catenin. We observed that HBX interacts with SIRT1, a class III histone deacetylase. Furthermore, the presence of HBX attenuated the interaction between SIRT1 and beta-catenin, leading to protection of beta-catenin from the inhibitory action of SIRT1. Reduction of SIRT1 with siRNA or suppression of SIRT1 activity with nicotinamide upregulated beta-catenin protein levels. In contrast, enhancement of SIRT1 activity with resveratrol reduced beta-catenin protein levels. Furthermore, in Hep3B cells stably expressing HBX, overexpression of SIRT1 or treatment with resveratrol enhanced sensitivity to doxorubicin-induced apoptosis, indicating that upregulation of SIRT1 could be a therapeutic strategy for HBV-related hepatocellular carcinoma. Based on these results, we propose that HBX upregulates beta-catenin by sequestering SIRT1, which leads to anticancer drug treatment resistance.