PRMT6 inhibits K63-linked ubiquitination and promotes the degradation of IRF3 in the antiviral innate immunity of black carp Mylopharyngodon piceus

Protein arginine methyltransferases (PRMT6) has been shown to negatively regulate interferon (IFN) production in mammals, however, the role of teleost PRMT6 in IFN signaling remains largely unknown. In our previous study, black carp (Mylopharyngodon piceus) PRMT6 (bcPRMT6) has been identified to inhibit bcTBK1/bcIRF3 cascade. In this study, bcIRF3-induced transcription of bcIFNa, bcIFNb, bcp50 and bcIl1 beta in host cells was attenuated by co-expressed bcPRMT6. Accordingly, bcIRF3-mediated antiviral activity against grass carp reovirus (GCRV) and spring viremia of carp virus (SVCV) was obviously dampened by bcPRMT6. Knockdown of bcPRMT6 enhanced the antiviral ability of host cells and improved the transcription of bcIFNa, bcViperin and bcIl1 beta. When co-expressed with bcPRMT6 in either mammalian or fish cells, the protein level of bcIRF3 was decreased, which implied the triggered degradation of bcIRF3 by bcPRMT6. And interestingly, this decreased protein expression of bcIRF3 was rescued by chloroquine but not MG132, indicating the lysosome-dependent degradation of this molecule. The subsequent immunoprecipitation and immunoblot assay demonstrated that K63-linked ubiquitination but not K48-linked of bcIRF3 was obviously attenuated by bcPRMT6. And the immunofluorescent staining data suggested that the nuclear translocation of bcIRF3 was inhibited by bcPRMT6. Taken together, our data concludes that bcPRMT6 promotes the degradation of bcIRF3 through lysosome pathway and inhibits K63-linked ubiquitination of bcIRF3, leading to the dampened antiviral signaling mediated by bcIRF3.