African swine fever (ASF), caused by the African swine fever virus (ASFV), is characterized by high mortality in infected pigs. ASFV infection triggers severe inflammatory response in the host, which is a crucial contributor to the high lethality of this disease. However, the underlying mechanism by which ASFV infection induces inflammatory response is still poorly understood. In this study, we found that UV-inactivated ASFV induces interleukin-1β (IL-1β) production, suggesting that certain structural proteins incorporated in the virion possess the ability to trigger inflammatory response. Further investigations demonstrated that deletion of the ASFV A137R gene significantly inhibited the ASFV-induced upregulation of the mRNA transcription of various proinflammatory genes and phosphorylation of p65 and IκBα. Furthermore, the purified pA137R protein promoted the mRNA transcription of these proinflammatory genes and phosphorylation of p65 and IκBα. Additionally, pA137R protein interacted with the NACHT and LRR domains of NLRP3 through its N terminal 1-99 amino acid (aa) domain, thereby promoting the oligomerization of NLRP3 and ASC and subsequently facilitating NLRP3 inflammasome assembly. Collectively, our findings identify ASFV pA137R protein as a key proinflammatory determinant of ASFV, which not only advances our understanding of the molecular mechanisms underlying ASFV-induced inflammatory response but also provides new insights into ASFV pathogenesis.

Keywords: African swine fever virus (ASFV); NF-κB pathway; NLRP3 inflammasome; pA137R protein.