The viral proteins of influenza A virus competitively bind to TRIM31 with MAVS to fine-tune the antiviral innate immunity.

The influenza A virus (IAV) continues to pose a serious threat to animals and humans, making it urgent to reveal more about IAV-host interactions. Tripartite motif protein 31 (TRIM31), an E3 ubiquitin ligase, has been identified as an agonist of the type-I interferon (IFN-I) response against RNA viruses by targeting mitochondrial antiviral signaling protein (MAVS). Here, we demonstrated that TRIM31 plays critical and novel roles in the life cycle of IAV. TRIM31 promoted the IFN-I signaling induced by IAV; however, it was surprisingly found that TRIM31 does not affect IAV replication. Instead, IAV replication was significantly promoted by TRIM31 in MAVS- or interferon receptor-deficient cells, suggesting TRIM31 may facilitate IAV replication in an interferon-independent manner. Mechanistically, TRIM31 interacted specifically with the basic polymerase 1 (PB1), acidic polymerase (PA), and hemagglutinin (HA) proteins of different subtypes of IAV. The interaction between TRIM31 and the PB1, PA, and HA proteins enhances the stability and polymerase and membrane fusion activities of these viral proteins by catalyzing the K63-linked ubiquitination. Further, the PB1, PA, and HA proteins competitively bind to TRIM31 for IAV replication, leading to the attenuation of the TRIM31-MVAS complex-mediated IFN-I signaling activation. Therefore, the antiviral and proviral effects of TRIM31 reach a balance in IAV-infected cells, resulting in no significant impact on IAV replication. Our novel findings revealed an IAV-specific mechanism that IAV exploits TRIM31 to fine-tune the antiviral innate response and maintain the homeostasis of viral replication. IMPORTANCE: During the long-term symbiosis with the host, IAVs have evolved a series of unique mechanisms to adapt to the host and support their own replication. The MAVS-mediated IFN-I signaling pathway is crucial for host cells to defend against RNA virus invasion, with TRIM31 functioning as a specific agonist for the activation of IFN-I antiviral response. In the present study, we demonstrated that IAV exploits TRIM31 to promote the stability and activity of viral proteins and reduces the positive effect of TRIM31 on the IFN-I response, thereby preventing TRIM31 from inhibiting IAV replication. Therefore, our results revealed a novel mechanism employed by IAV to adapt to host antiviral response and expanded our understanding of virus-host interactions.