TRIM25 inhibits HBV replication by promoting HBx degradation and the RIG-I-mediated pgRNA recognition

BACKGROUND: The hepatitis B virus (HBV) vaccine has been efficiently used for decades. However, hepatocellular carcinoma caused by HBV is still prevalent globally. We previously reported that interferon (IFN)-induced tripartite motif-containing 25 (TRIM25) inhibited HBV replication by increasing the IFN expression, and this study aimed to further clarify the anti-HBV mechanism of TRIM25. METHODS: The TRIM25-mediated degradation of hepatitis B virus X (HBx) protein was determined by detecting the expression of HBx in TRIM25-overexpressed or knocked-out HepG2 or HepG2-NTCP cells via Western blotting. Co-immunoprecipitation was performed to confirm the interaction between TRIM25 and HBx, and colocalization of TRIM25 and HBx was identified via immunofluorescence; HBV e-antigen and HBV surface antigen were qualified by using an enzyme-linked immunosorbent assay (ELISA) kit from Kehua Biotech. TRIM25 mRNA, pregenomic RNA (pgRNA), and HBV DNA were detected by quantitative real-time polymerase chain reaction. The retinoic acid-inducible gene I (RIG-I) and pgRNA interaction was verified by RNA-binding protein immunoprecipitation assay. RESULTS: We found that TRIM25 promoted HBx degradation, and confirmed that TRIM25 could enhance the K90-site ubiquitination of HBx as well as promote HBx degradation by the proteasome pathway. Interestingly, apart from the Really Interesting New Gene (RING) domain, the SPRY domain of TRIM25 was also indispensable for HBx degradation. In addition, we found that the expression of TRIM25 increased the recognition of HBV pgRNA by interacting with RIG-I, which further increased the IFN production, and SPRY, but not the RING domain is critical in this process. CONCLUSIONS: The study found that TRIM25 interacted with HBx and promoted HBx-K90-site ubiquitination, which led to HBx degradation. On the other hand, TRIM25 may function as an adaptor, which enhanced the recognition of pgRNA by RIG-I, thereby further promoting IFN production. Our study can contribute to a better understanding of host-virus interaction.