Porcine Rotavirus NSP4 Inhibits Type I Interferon Production via NRBF2-Mediated Autophagic Degradation of MDA-5.

The type I interferon (IFN-I) signaling pathway plays a pivotal role in orchestrating antiviral innate immune defenses, particularly during the clearance of invading pathogens. Rotaviruses have evolved a repertoire of viral proteins to counteract host immune surveillance. While certain functions of rotavirus nonstructural proteins in antagonizing IFN-I signaling have been characterized, the precise molecular mechanism by which nonstructural protein 4 (NSP4) impairs host immunity remains elusive. Here, we demonstrated that the porcine rotavirus (PoRV) nonstructural protein NSP4 potently suppresses the transcriptional activation of interferon-stimulated genes (ISGs), IFN-β promoters, and interferon-sensitive response elements (ISREs) while abrogating the phosphorylation of interferon regulatory factor 3 (IRF3). Mechanistically, NSP4 promotes the degradation of melanoma differentiation-associated gene 5 (MDA-5) via nuclear receptor binding factor 2 (NRBF2)-dependent autophagy, thereby subverting IFN-I production. The validity of this mechanism in primary epithelial cells was also verified by constructing an intestinal organoid model in piglets. Collectively, our findings elucidate a previously unrecognized immune evasion mechanism by which NSP4 antagonizes the IFN-I-mediated antiviral response, providing novel molecular insights for developing therapeutic strategies against rotavirus infections.