The MGF300-2R protein of African swine fever virus is associated with viral pathogenicity by promoting the autophagic degradation of IKK & alpha; and IKK & beta; through the recruitment of TOLLIP

Author summaryThe left variable region in the genome of African swine fever virus (ASFV) contains a large number of multigene family genes (MGFs), but the impact of individual MGFs on viral replication and pathogenicity is largely unknown. In this study, we identified MGF300-2R as a new virulence factor, which is critical for viral replication in vivo and in vitro. Furthermore, we showed that MGF300-2R promotes the K27-linked ubiquitination of IKK & alpha; and IKK & beta; for TOLLIP-dependent autophagic degradation, serving as a suppressor to prevent the activation of the NF-& kappa;B signaling pathway. Our findings highlight the relevance of the inflammatory response in the virulence of ASFV and imply MGF300-2R as a candidate target for the rational design of vaccines against ASFV infections. The multigene family genes (MGFs) in the left variable region (LVR) of the African swine fever virus (ASFV) genome have been reported to be involved in viral replication in primary porcine alveolar macrophages (PAMs) and virulence in pigs. However, the exact functions of key MGFs in the LVR that regulate the replication and virulence of ASFV remains unclear. In this study, we identified the MGF300-2R gene to be critical for viral replication in PAMs by deleting different sets of MGFs in the LVR from the highly virulent strain ASFV HLJ/18 (ASFV-WT). The ASFV mutant lacking the MGF300-2R gene (Del2R) showed a 1-log reduction in viral titer, and induced higher IL-1 & beta; and TNF-& alpha; production in PAMs than did ASFV-WT. Mechanistically, the MGF300-2R protein was found to interact with and degrade IKK & alpha; and IKK & beta; via the selective autophagy pathway. Furthermore, we showed that MGF300-2R promoted the K27-linked polyubiquitination of IKK & alpha; and IKK & beta;, which subsequently served as a recognition signal for the cargo receptor TOLLIP-mediated selective autophagic degradation. Importantly, Del2R exhibited a significant reduction in both replication and virulence compared with ASFV-WT in pigs, likely due to the increased IL-1 & beta; and TNF-& alpha;, indicating that MGF300-2R is a virulence determinant. These findings reveal that MGF300-2R suppresses host innate immune responses by mediating the degradation of IKK & alpha; and IKK & beta;, which provides clues to paving the way for the rational design of live attenuated vaccines to control ASF.