Search

Objective: Hepatitis B virus (HBV) infection is a major public health problem worldwide. However, the regulatory mechanisms underlying HBV replication remain unclear. Cullin 4B-RING ubiquitin E3 ligase (CRL4B) is involved in regulating diverse physiological 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 were performed to study the interaction between CUL4B 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 Cul4b transgenic or conditional knockout mice indicated that CUL4B promoted HBV replication (P < 0.05). Moreover, the overexpression or knockdown system in human liver cell lines validated that CUL4B increased HBV replication in an HBx-dependent manner. Importantly, immunoprecipitation assays and immunofluorescence staining showed an interaction between CUL4B and HBx. Furthermore, CUL4B upregulated HBx protein levels by inhibiting HBx ubiquitination and proteasomal degradation (P < 0.05). Finally, a positive correlation between CUL4B expression and HBV pgRNA level 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 proteasomal degradation. CUL4B may therefore be a potential target for anti-HBV therapy.

Objective: The E3 ligase, CRL4, plays diverse roles in different cellular processes, such as DNA damage, transcriptional regulation, cell cycle progression, and cell apoptosis. Our previous study showed that CUL4A and CUL4B had a strong association with tobacco smoking risk in lung squamous cell carcinoma (SCC) and small cell lung carcinoma (SCLC). This study aimed to define the potential mechanism underlying the roles of CUL4A and CUL4B in the development of SCC and SCLC. Methods: We determined the role of CUL4A and CUL4B in the cell cycle and apoptosis of SCC and SCLC, and identified the key apoptosis-related gene involved in the oncogenic activity of CUL4B by Western blot, immunohistochemical staining, flow cytometry, and enzyme inhibition experiments. Results: We found that depletion of CUL4A and CUL4B reduced the proliferation of SCC and SCLC cells. CUL4Aknockdown but not CUL4Bknockdown arrested cells in G1 phase while upregulating P21 and CUL4Bknockdown promoted cell apoptosis through upregulation of FOXO3A. Accordingly, CUL4B decreased FOXO3A expression by activating the ERK signaling pathway and mediating FOXO3A degradation via the ubiquitin-proteasome pathway. Conclusions: These results identified the function of E3 ligase CRL4 in regulating SCC and SCLC cell proliferation, which provides a potential strategy for cancer therapy by targeting FOXO3A and the E3 ligase, CRL4.