NLRC3 regulates RIP2, STING, TBK1, and TRAF6 mediated type I IFN signaling and inflammatory response in large yellow croaker Larimichthys crocea

As a member of the NLRs family, NLRC3 has been determined to function in the NF-κB, MAPK, and type I IFN signaling, which are crucial for the host innate immunity and inflammatory response. In this study, an NLRC3 ortholog, named as Lc-NLRC3, was cloned and identified in large yellow croaker (Larimichthys crocea). The gene characteristics analysis revealed that Lc-NLRC3 consists of 18 exons and 17 introns, with a full-length open reading frame (ORF) of 3405 bp, encoding a protein of 1134 amino acids (aa), that containing a N-terminal CARD domain, a central NACHT domain, and a C-terminal LRRs domain. It was shown that Lc-NLRC3 is predominantly found in the cytosol, and was widely distributed across various tissues/organs, with the highest expression detected in the intestine, and could be induced by poly I:C, LPS, PGN, and Pseudomonas plecoglossicida stimulation. Importantly, Lc-NLRC3 overexpression significantly activate NF-κB, TNFα, IL-1β, IRF3, IRF7, and IFN1 promoters, whereas when co-expressed with RIP2, STING, or TBK1, it down-regulated those promoter activation compared to their individual overexpression alone, thereby suppressing downstream antiviral and inflammatory gene expression. Interestingly, Lc-NLRC3 associated with TRAF6 in IRF3/IRF7 promoter activation, and enhanced the expression of IRF7, Mx, ISG15, and TNF-α. Co-immunoprecipitation assays also confirmed interactions of Lc-NLRC3 with RIP2, STING, TBK1, and TRAF6. The above results imply that Lc-NLRC3 is an important regulator in RIP2, STING, TBK1, and TRAF6 mediated type I IFN signaling and inflammatory response.