Palmitoyl-transferase 3 promotes mitochondrial antiviral signaling protein degradation by modulating its ubiquitination.

The innate antiviral immunity of humans serves as their first line of defence against viral and microbial illnesses. The retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) signaling pathway requires the mitochondrial antiviral signaling protein (MAVS) to function properly. ZDHHCs, a family of acyltransferases, regulate diverse biological processes via interactions with numerous mammalian proteins and viral proteins. However, the role of ZDHHCs in antiviral innate immunity against RNA viruses remains largely elusive. Here, we show that ZDHHC3 downregulates the RLR signaling pathway. Ectopic ZDHHC3 expression reduces RIG-IN- and SeV-mediated IFN-β promoter activity, IRF3 nuclear transduction, and transcription of the IFN-β and ISG genes. Furthermore, ectopic expression of ZDHHC3 decreases MAVS stability by promoting proteasomal degradation, which can be reversed by MG132 but not CQ. ZDHHC3 interacts with MAVS and promotes its breakdown by increasing K48-linked ubiquitination rather than K63-linked ubiquitination. ZDHHC3 deletion resulted in increased IFN-β promoter activity and transcription of the IFN-β and ISG genes. ZDHHC3 knockdown promotes subsequent antiviral signaling and reduces viral replication, indicating the role of ZDHHC3 in antiviral innate immunity. In addition, the catalytically inactive mutant ZDHHC3 C157S efficiently reversed the IFN-β promoter activity produced by RIG-IN, which was consistent with the results of 2-BP treatment. Collectively, these data show that ZDHHC3 inhibits the RNA virus-triggered signaling cascade by targeting MAVS and provides new insights into the role of ZDHHC3 in antiviral innate immunity.