EMCV Non-Structural Protein 2C Antagonizes cGAS-STING-Mediated Type I Interferon Signaling via Promoting K48-Linked Polyubiquitination and Degradation of STING.

The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway serves as a central innate immune signaling axis in host defense against DNA virus infections, and RNA viruses have also evolved diverse strategies to counteract this pathway. Encephalomyocarditis virus (EMCV), a zoonotic RNA virus, utilizes its 2C protein to antagonize RIG-I-like receptor-mediated type I interferon signaling and induce autophagic degradation of calcium binding and coiled-coil domain 2, thereby evading host antiviral immunity. However, the precise molecular mechanism by which EMCV 2C protein modulates the cGAS-STING pathway remains incompletely understood. Herein, we show that EMCV infection reduces the expression of cGAS and STING proteins, and its 2C protein significantly suppresses the production of IFN-β triggered by poly(dA:dT) or viral infection, as well as the mRNA expression of interferon-stimulated genes. Mechanistically, 2C protein binds to STING via its ATPase domain and facilitates K48-linked polyubiquitination and proteasomal degradation of STING, while dominantly interfering STING translocation to the Golgi apparatus and the formation of STING-TBK1-IRF3 complex, thereby blocking STING-mediated IFN-β signal transduction at multiple levels. This study reveals a novel mechanism by which the EMCV 2C protein suppresses the host antiviral response by targeting STING and promoting its ubiquitination and degradation. This finding deepens understanding of the immune evasion mechanism of EMCV and provides a theoretical foundation for the development of antiviral therapies targeting the 2C protein of picornaviruses.