Seneca Valley Virus 3C protease negatively regulates the type I interferon pathway by acting as a viral...

The mechanisms that enable Seneca Valley Virus (SVV) to escape the host innate immune response are not well known. Previous studies demonstrated that SVV 3C^pro suppresses innate immune responses by cleavage of host proteins and degradation of IRF3 and IRF7 protein expression. Here, we showed that SVV 3C protease (3C^pro) has deubiquitinating activity. Overexpressed 3C^pro inhibits the ubiquitination of cellular substrates, acting on both lysine-48- and lysine-63-linked polyubiquitin chains. SVV infection also possessed deubiquitinating activity. The ubiquitin-proteasome system was significantly involved in SVV replication. Furthermore, 3C^pro inhibited the ubiquitination of retinoic acid-inducible gene I (RIG-I), TANK-binding kinase 1 (TBK1), and TNF receptor-associated factor 3 (TRAF3), thereby blocking the expression of interferon (IFN)-β and IFN stimulated gene 54 (ISG54) mRNAs. A detailed analysis revealed that mutations (H48A, C160A, or H48A/C160A) that ablate the Cys and His residues of 3C^pro abrogated its deubiquitinating activity and the ability of 3C^pro to block IFN-β induction. Together, our results demonstrate a novel mechanism developed by SVV 3C^pro to promote viral replication, and may also provide a novel strategy for improving ubiquitination-based therapy.