TRIM25 promotes antiviral innate immune response by stabilizing IRF7 and its nuclear translocation.

Most avian species lack interferon regulatory factor 3 (IRF3), a key transcription factor that initiates antiviral interferon responses, leaving how they achieve rapid RNA virus defense unclear. Here, we identify duck tripartite motif containing 25 protein (TRIM25) as an unexpected, central activator of IRF7-dependent antiviral signaling that compensates for the absence of IRF3. Viral RNA stimulation strongly induced TRIM25 expression in duck embryonic fibroblasts (DEFs). Overexpression of TRIM25 increased IFN-β production and restricted the replication of multiple RNA viruses in DEFs and in ducklings, whereas TRIM25 knockdown enhanced viral replication (tembusu virus, TMUV, novel duck reovirus, NDRV, vesicular stomatitis virus, VSV). Mechanistically, TRIM25 functioned as an E3 ubiquitin ligase that catalyzed K27-linked polyubiquitination of IRF7 at lysine 46 (K46), thereby promoting IRF7 stability and nuclear translocation. Mutation of TRIM25 catalytic residues or of IRF7 K46 abolished these effects. In addition, TRIM25 stabilized IRF7 independently of its ligase activity by antagonizing suppressor of cytokine signaling 1 (SOCS1)-mediated degradation. Notably, TRIM25-driven signaling occurred independently of retinoic acid-inducible gene I (RIG-I) activation. Together, these findings reveal a dual regulatory mechanism by which avian TRIM25 activates IRF7 to elicit robust type I interferon (IFN-I) responses, providing a molecular explanation for rapid antiviral immunity in species lacking IRF3. IMPORTANCE: Most avian species, including those in the orders