Abstract
African swine fever (ASF) is an acute transmissible disease caused by the African swine fever virus (ASFV), which has evolved multiple mechanisms to circumvent the host immune response. This research reveals that ASFV pI73R (I73R protein) downregulates cGAS-STING-mediated interferon beta (IFN-β) activation. ASFV pI73R binds to TBK1 and IRF3 mRNAs, promoting their nuclear retention and attenuating IFN-β production. Furthermore, silencing I73R enhances IFN-β mRNA levels and increases TBK1 and IRF3 protein levels in primary porcine alveolar macrophages (PAMs) exposed to ASFV. Unlike other reported mechanisms of inhibition of IFN-β by other ASFV proteins, pI73R inhibits IFN-β through its RNA binding function. Using structure-based virtual screening, we identified a small-molecule compound, STL527159, which disrupts the pI73R-RNA interaction, thereby restoring nuclear export and translation of the target TBK1 and IRF3 mRNAs. This compound markedly reduced ASFV infection in vitro. These findings provide new perspectives on the immune evasion strategies used by ASFV and offer a novel theoretical foundation for the development of antiviral drugs and novel vaccine candidates against ASFV.