APPV NS5A employs PKR activation to redirect IRF3 phosphorylation from Ser396 to Ser386, ultimately resulting in the inhibition of IFN production.

Atypical porcine pestivirus (APPV) is an emerging pathogen that poses a significant threat to the global swine industry. The nonstructural protein 5 A (NS5A) of Flavivirus is a known immunomodulator; however, its precise role in APPV pathogenesis, particularly its interaction with host interferon (IFN) responses, remains poorly understood. This study elucidates a novel molecular mechanism by which APPV NS5A manipulates host IFN production. We demonstrate that APPV NS5A exerts a dual effect on the phosphorylation of interferon regulatory factor 3 (IRF3): it inhibits the phosphorylation of IRF3 at Ser396 by disrupting the formation of the TBK1-IKKε-IRF3 complex, while simultaneously promoting the interaction between PKR and IRF3 by inducing PKR activation, ultimately resulting in the phosphorylation of IRF3 at Ser386. This phosphorylation switch consequently inhibits the production of IFN. Our research provides critical insights into the immune evasion strategies and pathogenic mechanisms of APPV, identifying the NS5A-PKR-IRF3 axis as a potential therapeutic target for developing novel antiviral interventions.