Porcine TRIM45 negatively regulates the RLR signaling pathway by targeting IKKε for protein degradation.

The tripartite motif 45 (TRIM45) protein belongs to the RING-type E3 ubiquitin ligases and exerts multiple biological functions in cell signaling and inflammation regulation by catalyzing ubiquitination of adaptor proteins in the corresponding cascades. In the present work, we obtained the porcine TRIM45 (porTRIM45) coding sequence and examined its contribution to type I IFN induction. The open reading frame (ORF) encodes a 580-amino-acid polypeptide that shares 84.7-89.7% sequence identity with orthologs from human, mouse, and monkey. porTRIM45 harbors a RING domain, two B-box domains, a coiled-coil domain, and a FIL domain, and exhibits broad tissue distribution across porcine tissues. Functional analyses showed that porTRIM45 participates in modulating type I IFN production upon poly(I:C) stimulation. Mechanistically, porTRIM45 associates with porcine IκB kinase epsilon (IKKε) and promotes its K48-linked polyubiquitination for proteasomal degradation, consequently dampening RLRs signaling pathway. Additionally, we verified that the RING and FIL domains are indispensable for the E3 ligase function of porTRIM45. Collectively, our findings underscore the crucial role of porTRIM45 in IKKε-mediated innate immune signaling in pigs.