The PB1 protein of H9N2 influenza A virus inhibits antiviral innate immunity by targeting MAVS for TRIM25-mediated autophagic degradation.

The proteins encoded by Influenza A virus (IAV) evade the innate immune system through diverse strategies to facilitate their replication. However, the regulatory mechanisms remain not fully understood. In this study, we identified that the H9N2 PB1 protein suppressed the activities of the IFN-β, ISRE, and NF-κB promoters. Furthermore, H9N2 PB1 inhibited the phosphorylation of IRF3, IκBα, and TBK1 and the secretion of IFN-β. The results demonstrated H9N2 PB1 as a negative regulator of the RIG-I signaling pathway. Subsequent investigations revealed a specific interaction between H9N2 PB1 and MAVS, which disturbed the stability of MAVS. Notably, we discovered that H9N2 PB1 exploited the function of TRIM25, leading to the autophagic degradation of MAVS through K48-linked polyubiquitination. In conclusion, we uncovered a negative regulatory axis consisting of H9N2 PB1-TRIM25-MAVS-IFN-I. These findings provide valuable insights into the molecular interactions involved in the regulation of the host's innate immune antiviral response by IAV.