SARM suppresses TRIF, TRAF3, and IRF3/7 mediated antiviral signaling in large yellow croaker Larimichthys crocea

Abstract

As a TIR domain-containing molecular, sterile α-and armadillo motif-containing protein (SARM) acts as an adaptor in Toll-like receptor (TLR) signaling, and also plays important roles in mediating apoptosis and neuronal injury. In the present study, the ortholog of <i>SARM</i>, named as <i>Lc-SARM</i>, was cloned and identified in large yellow croaker (<i>Larimichthys crocea</i>). The full-length ORF of <i>Lc-SARM</i> consists of 2,154 bp, encoding a protein of 717 amino acids (aa), which is comprised of an N-terminal ARM domain, two SAM domains, and a C-terminal TIR domain. Confocal microscopy revealed that <i>Lc</i>-SARM was mainly distributed in the cytoplasm, and the mRNA expression level of <i>Lc-SARM</i> was broadly distributed in all the detected organs/tissues, with the highest expression level found in the brain. The expression patterns of <i>Lc-SARM</i> could be induced in response to poly I:C, LPS, PGN stimulations, and <i>Pseudomonas plecoglossicida</i> infection. Notably, although the overexpression of <i>Lc</i>-SARM could significantly induce NF-κB, IRF3, IRF7, and type I IFN promoter activation, whereas the co-expression of <i>Lc-</i>SARM with <i>Lc-</i>TRIF, <i>Lc</i>-TRAF3, <i>Lc</i>-IRF3, or <i>Lc</i>-IRF7 significantly down-regulated the induction of NF-κB, IRF3, IRF7, or type I IFN promoter activation, and suppressed the antiviral effects as well as the downstream antiviral-related genes expression compared to the only overexpression of <i>Lc</i>-TRIF, <i>Lc</i>-TRAF3, <i>Lc</i>-IRF3, or <i>Lc</i>-IRF7. Co-immunoprecipitation (Co-IP) assays also demonstrated that <i>Lc-</i>SARM interacts separately with <i>Lc</i>-TRIF, <i>Lc</i>-TRAF3, <i>Lc</i>-IRF3, and <i>Lc</i>-IRF7. It is thus collectively suggested that <i>Lc</i>-SARM functions as a negative regulator in <i>Lc</i>-TRIF, <i>Lc</i>-TRAF3, and <i>Lc</i>-IRF3/7 involved antiviral signaling.