HBx Enhances the Nrf2/ARE-dependent Antioxidant Response by Promoting Nuclear Export and Downregulation of Bach1.

Hepatitis B virus (HBV) infection disrupts redox homeostasis in hepatocytes and is associated with the development of liver diseases. We previously reported that HBV activates the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) signaling pathway, a major cellular defense mechanism against oxidative stress. However, it remains unclear whether Bach1, a transcriptional repressor that antagonizes Nrf2, is involved in the HBV-induced activation of Nrf2/ARE pathway. In this study, we aimed to elucidate how HBV affects Bach1 expression and subcellular localization and how these changes contribute to activation of the Nrf2/ARE signaling pathway. ARE reporter assays revealed that Bach1 knockdown significantly enhanced HBx‑induced ARE activity, whereas Bach1 overexpression markedly attenuated it, indicating that Bach1 suppresses the HBx‑mediated antioxidant response. HBV infection and HBx expression reduced endogenous Bach1 protein levels without affecting Bach1 mRNA levels, suggesting post-transcriptional downregulation. Immunofluorescence and subcellular fractionation suggested that HBx contributes to HBV-induced Bach1 nuclear export. Co‑immunoprecipitation and immunofluorescence staining further demonstrated that HBx interacts with Bach1 in both the nucleus and cytoplasm. Notably, HBV infection upregulated the expression of NQO1, an Nrf2 target gene that was previously reported to contribute to HBx stabilization. In addition, Bach1 knockdown increased NQO1 and HBx protein levels. These findings suggest that Bach1 exerts an antiviral function by limiting Nrf2/ARE pathway activation and consequently restricting HBx stabilization. Collectively, our results suggest that HBx promotes nuclear export and downregulation of Bach1, thereby shifting the redox regulatory balance toward Nrf2 dominance, enhancing NQO1 expression, and stabilizing HBx protein.