SOX9 negatively regulates the RLR antiviral signaling by targeting MAVS.

Mitochondrial virus-induced signal adaptor (MAVS), also known as VISA, IPS-1, and Cardif, is a crucial adaptor protein in the RIG-I-like receptor (RLR) signaling pathway. Upon viral infection, RIG-I recognizes viral dsRNA and further transfers it to mitochondria, where it binds to MAVS through its CARD domain, generating a series of signal cascades. Transduction through this signaling cascade leads to phosphorylation and nuclear translocation of interferon regulatory factor 3/7 (IRF3/IRF7) and activation of NF-κB, which ultimately produces type I interferon (IFN) and proinflammatory cytokines. Here, our experiments demonstrated that overexpression of SRY-related high-mobility group protein 9 (SOX9) significantly inhibited Sendai virus (SeV)-induced and MAVS-mediated activation of the IFN-β promoter and ISRE. However, knocking out the expression of SOX9 in cells promoted SeV-induced IFN-β promoter and ISRE activation. Further studies have shown that SOX9 interacts with MAVS and targets MAVS to inhibit the association of MAVS-TRAF2, thereby inhibiting MAVS-mediated TRAF2 ubiquitination. Taken together, these results indicate that SOX9 downregulates IFN-β expression and antiviral signal transduction by targeting MAVS.