CUL4B facilitates HBV replication by promoting HBx stabilization.

Objective: Hepatitis B virus (HBV) infection is a major public health problem worldwide. However, the regulatory mechanismsunderlying HBV replication remain unclear. Cullin 4B-RING ubiquitin E3 ligase (CRL4B) is involved in regulating diversephysiological and pathophysiological processes. In our study, we aimed to explain the role of CUL4B in HBV infection. Methods: Cul4b transgenic mice or conditional knockout mice, as well as liver cell lines with CUL4B overexpression or knockdown,were used to assess the role of CUL4B in HBV replication. Immunoprecipitation assays and immunofluorescence staining wereperformed to study the interaction between CUL4B and HBx. Cycloheximide chase assays and in vivo ubiquitination assays wereperformed to evaluate the half-life and the ubiquitination status of HBx. Results: The hydrodynamics-based hepatitis B model in Cul4b transgenic or conditional knockout mice indicated that CUL4Bpromoted HBV replication (P < 0.05). Moreover, the overexpression or knockdown system in human liver cell lines validated thatCUL4B increased HBV replication in an HBx-dependent manner. Importantly, immunoprecipitation assays and immunofluorescencestaining showed an interaction between CUL4B and HBx. Furthermore, CUL4B upregulated HBx protein levels by inhibiting HBxubiquitination and proteasomal degradation (P < 0.05). Finally, a positive correlation between CUL4B expression and HBV pgRNAlevel was observed in liver tissues from HBV-positive patients and HBV transgenic mice. Conclusions: CUL4B enhances HBV replication by interacting with HBx and disrupting its ubiquitin-dependent proteasomaldegradation. CUL4B may therefore be a potential target for anti-HBV therapy.