African Swine Fever Virus MGF-505-7R Negatively Regulates cGAS-STING-Mediated Signaling Pathway.

African swine fever virus (ASFV) is a devastating infectious disease in pigs, severely threatening the global pig industry. To efficiently infect animals, ASFV must evade or inhibit fundamental elements of the innate immune system, namely the type I IFN response. In this study, we identified that ASFV MGF-505-7R protein exerts a negative regulatory effect on STING-dependent antiviral responses. MGF-505-7R interacted with STING and inhibited the cGAS-STING signaling pathway at STING level. MGF-505-7R overexpression either degraded STING or STING expression was reduced in ASFV-infected cells via autophagy, whereas STING expression was elevated in MGF-505-7R-deficient ASFV-infected cells. We further found that MGF-505-7R promoted the expression of the autophagy-related protein ULK1 to degrade STING, whereas ULK1 was elevated in MGF-505-7R-deficient ASFV-infected cells. Moreover, MGF-505-7R-deficient ASFV induced more IFN-β production than wild-type ASFV and was attenuated in replication compared with wild-type ASFV. The replicative ability of MGF-505-7R-deficient ASFV was also attenuated compared with wild-type. Importantly, MGF-505-7R-deficient ASFV was fully attenuated in pigs. Our results showed for the first time, to our knowledge, a relationship involving the cGAS-STING pathway and ASFV MGF-505-7R, contributing to uncover the molecular mechanisms of ASFV virulence and to the rational development of ASFV vaccines.