pMGF505-7R determines pathogenicity of African swine fever virus infection by inhibiting IL-1β and type I IFN production

Abstract

Inflammatory factors and type I interferons (IFNs) are key components of host antiviral innate immune responses, which can be released from the pathogen-infected macrophages. African swine fever virus (ASFV) has developed various strategies to evade host antiviral innate immune responses, including alteration of inflammatory responses and IFNs production. However, the molecular mechanism underlying inhibition of inflammatory responses and IFNs production by ASFV-encoded proteins has not been fully understood. Here we report that ASFV infection only induced low levels of IL-1β and type I IFNs in porcine alveolar macrophages (PAMs), even in the presence of strong inducers such as LPS and poly(dA:dT). Through further exploration, we found that several members of the multigene family 360 (MGF360) and MGF505 strongly inhibited IL-1β maturation and IFN-β promoter activation. Among them, pMGF505-7R had the strongest inhibitory effect. To verify the function of pMGF505-7R in vivo, a recombinant ASFV with deletion of the MGF505-7R gene (ASFV-Δ7R) was constructed and assessed. As we expected, ASFV-Δ7R infection induced higher levels of IL-1β and IFN-β compared with its parental ASFV HLJ/18 strain. ASFV infection-induced IL-1β production was then found to be dependent on TLRs/NF-κB signaling pathway and NLRP3 inflammasome. Furthermore, we demonstrated that pMGF505-7R interacted with IKKα in the IKK complex to inhibit NF-κB activation and bound to NLRP3 to inhibit inflammasome formation, leading to decreased IL-1β production. Moreover, we found that pMGF505-7R interacted with and inhibited the nuclear translocation of IRF3 to block type I IFN production. Importantly, the virulence of ASFV-Δ7R is reduced in piglets compared with its parental ASFV HLJ/18 strain, which may due to induction of higher IL-1β and type I IFN production in vivo. Our findings provide a new clue to understand the functions of ASFV-encoded pMGF505-7R and its role in viral infection-induced pathogenesis, which might help design antiviral agents or live attenuated vaccines to control ASF.

African Swine Fever Virus A528R Inhibits TLR8 Mediated NF-κB Activity by Targeting p65 Activation and Nuclear Translocation

“…Specifically, in terms of IFN response, A528R promotes the expression of the autophagyrelated protein ULK1 to degrade STING and suppress IFN induction [15]. A528R also interacts with IRF3 to inhibit its nuclear translocation and block type I IFN production [14]. In terms of inflammation, A528R interacts with IKKα to inhibit IL-1β gene transcription and with NLRP3 to block proIL-1β maturation and secretion [14].…”

“…A528R also interacts with IRF3 to inhibit its nuclear translocation and block type I IFN production [14]. In terms of inflammation, A528R interacts with IKKα to inhibit IL-1β gene transcription and with NLRP3 to block proIL-1β maturation and secretion [14]. In our study, we found A528R interacts with NF-κB p65 to inhibit NF-κB activation, but we did not exclude other signaling proteins upstream p65, such as IKKα/β/γ complex, which may be modulated by A528R.…”

“…It was initially identified as the inhibitor of poly I:C mediated IRF3 and NF-κB signaling, as well as type I IFN mediated signaling [13]. Recent reports showed that A528 inhibited cGAS-STING-IFN signaling as well as NLRP3 inflammasome signaling [14,15]. Although the inhibitory effect of A528R on NF-κB signaling has been reported for a long time, the mechanism by which A528R inhibits the NF-κB signaling pathway is not clear [16].…”

African Swine Fever Virus MGF360-14L Negatively Regulates Type I Interferon Signaling by Targeting IRF3

“…ASFV has been reported to inhibit signaling in the cGAS-STING pathway and downregulate IFN-β levels when porcine macrophages are infected with the ASFV Armenia/07 virulent strain ( García-Belmonte et al., 2019 ). MGF-505-7R and MGF-505-11R interact with STING, inhibit the cGAS-STING signaling pathway and subvert type I IFN production ( Li et al., 2021a ; Yang K. et al., 2021 ). DP96R of the ASFV China 2018/1 strain is reported to negatively regulate type I IFN expression and NF-κB signaling by inhibiting both TBK1 and IKKβ ( Wang et al., 2018 ).…”

“…For instance, DP96R of ASFV China 2018/1 was reported to negatively regulate IFN-I expression and NF-kB signaling by inhibiting both TBK1 and IKKb (Wang et al, 2018). MGF-505-7R interacts with IKKa, STING, and IRF3 and inhibits the cGAS-STING signaling pathway to block IFN-b and inhibit pro-inflammatory IFN-gmediated JAK-STAT1 signaling (Li J. et al, 2021;Li et al, 2021a;Li et al, 2021b). E120R interacts with IRF3 and interferes with recruitment of IRF3 to TBK1, which in turn suppresses IRF3 phosphorylation, decreasing IFN production (Liu H. et al, 2021).…”