CUL4B facilitates HBV replication by promoting HBx stabilization

Objective:Hepatitis B virus(HBV)infection is a major public health problem worldwide.However,the regulatory mechanisms underlying HBV replication remain unclear.Cullin 4 B-RING ubiquitin E3 ligase(CRL4 B)is involved in regulating diverse physiological and pathophysiological processes.In our study,we aimed to explain the role of CUL4 B in HBV infection.Methods:Cul4 b transgenic mice or conditional knockout mice,as well as liver cell lines with CUL4 B overexpression or knockdown,were used to assess the role of CUL4 B in HBV replication.Immunoprecipitation assays and immunofluorescence staining were performed to study the interaction between CUL4 B and HBx.Cycloheximide chase assays and in vivo ubiquitination assays were performed to evaluate the half-life and the ubiquitination status of HBx.Results:The hydrodynamics-based hepatitis B model in Cul4 b transgenic or conditional knockout mice indicated that CUL4 B promoted HBV replication(P<0.05).Moreover,the overexpression or knockdown system in human liver cell lines validated that CUL4 B increased HBV replication in an HBx-dependent manner.Importantly,immunoprecipitation assays and immunofluorescence staining showed an interaction between CUL4 B and HBx.Furthermore,CUL4 B upregulated HBx protein levels by inhibiting HBx ubiquitination and proteasomal degradation(P<0.05).Finally,a positive correlation between CUL4 B expression and HBV pg RNA level was observed in liver tissues from HBV-positive patients and HBV transgenic mice.Conclusions:CUL4 B enhances HBV replication by interacting with HBx and disrupting its ubiquitin-dependent proteasomal degradation.CUL4 B may therefore be a potential target for anti-HBV therapy.