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

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. 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. 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. 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.

Song H ，Xiao Q ，Xu F ，Wei Q ，Wang F ，Tan G ... -  《-》

Type I IFN augments IL-27-dependent TRIM25 expression to inhibit HBV replication.

Tan G ，Xiao Q ，Song H ，Ma F ，Xu F ，Peng D ，Li N ，Wang X ，Niu J ，Gao P ，Qin FX ，Cheng G ... -  《-》

Human Respiratory Syncytial Virus NS 1 Targets TRIM25 to Suppress RIG-I Ubiquitination and Subsequent RIG-I-Mediated Antiviral Signaling.

Ban J ，Lee NR ，Lee NJ ，Lee JK ，Quan FS ，Inn KS ... -  《Viruses-Basel》

The ubiquitin-specific protease USP15 promotes RIG-I-mediated antiviral signaling by deubiquitylating TRIM25.

Pauli EK ，Chan YK ，Davis ME ，Gableske S ，Wang MK ，Feister KF ，Gack MU ... -  《-》

TRIM38 Induced in Respiratory Syncytial Virus-infected Cells Downregulates Type I Interferon Expression by Competing with TRIM25 to Bind RIG-I.

Innate immune response is the first line of defense for the host against virus invasion. One important response is the synthesis and secretion of type I interferon (IFN-I) in the virus-infected host cells. Here, we found that respiratory syncytial virus (RSV) infection induced high expression of TRIM25, which belongs to the tripartite motif-containing (TRIM) family of proteins. TRIM25 bound and activated retinoic acid-inducible gene I (RIG-I) by K63-linked ubiquitination. Accordingly, RIG-I mediated the production of IFN-I mainly through the nuclear factor kappa-B (NF-κB) pathway in respiratory epithelial cells. Interestingly, IFN-I, in turn, promoted a high expression of TRIM38 which downregulated the expression of IFN-I by reducing the protein level of RIG-I by K48-linked ubiquitination. More importantly, the binding site of TRIM25 to RIG-I was found in the narrow 25th-43rd amino acid (aa) region of RIG-I N-terminus. In contrast, the binding sites of TRIM38 to RIG-I were found in a much wider amino acid region, which included the binding site of TRIM25 on RIG-I. As a result, TRIM38 inhibits the production of IFN-I by competing with TRIM25 for RIG-I binding. Thus, TRIM38 negatively regulates RIG-I activation to, in turn, downregulate IFN-I expression, thus interfering with host immune response. A negative feedback loop effectively "puts the brakes" on the reaction once host immune response is overactivated and homeostasis is unbalanced. We also discovered that TRIM25 bound RIG-I by a new K63-linked ubiquitination located at K-45 of the first caspase recruitment domain (CARD). Collectively, these results confirm an antagonism between TRIM38 and TRIM25 in regulating IFN-I production by affecting RIG-I activity following RNA virus infection.

Sun Q ，Han X ，Meng L ，Li H ，Chen Y ，Yin L ，Wang C ，Wang J ，Li M ，Gao X ，Li W ，Wei L ，Ma C ... -  《-》