African swine fever virus E120R inhibited cGAS-STING-mediated IFN-β and NF-κB pathways

African swine fever (ASF) is an acute and severe contagious disease triggered by the African swine fever virus (ASFV), which severely threatens the global swine industry. At present, no safe and efficacious vaccine has been provided to prevent and control this disease. The pathogenesis and immune evasion mechanism of ASFV are still unknown, which seriously hinders the development of safe and effective ASF vaccines. Certain proteins of ASFV involved in immunosuppression helped to evade the host innate immune response. The cGAS-STING signaling pathway is important to the innate immune system. It induces the production of type I interferons (IFNs) and other cytokines by recognizing cytoplasmic DNA, mediating antimicrobial innate immunity through type I IFN, and nuclear factor-κB (NF-κB) pathways. In the present study, E120R, a late-phase expression protein and a key virulent factor of ASFV inhibited cGAS-STING mediated promoter activities of IFN-β and NF-κB in HEK293T cells. The ectopic expression of E120R down-regulated IFN-β pathway by targeting interferon regulatory factor 3 (IRF3) and p65, inhibited the phosphorylation of STING, and further inhibited the phosphorylation of TANK-binding kinase 1 (TBK1) and IRF3, with no significant effects on p65 phosphorylation. Additionally, E120R also inhibited the NF-κB pathways by inhibiting the nuclear translocation of p50 and p65, which was mediated by Sendai virus (SeV). Further, the study showed that the 61–80 amino acids sites in the C-terminal domain of E120R were crucial for these functions. In conclusion, our work preliminarily elucidated a novel mechanism of inhibiting host innate immune response by ASFV E120R, which will provide a new target for the ASFV live gene deletion vaccine development and the theoretical basis for ASFV prevention.