The Mechanism For The Inhibition Of G3BP1-mediated RIG-I Signaling Pathway By FMDV

The innate immune system is the first line of host to defense against pathogenic microorganism infection.The host pattern-recognition receptors(PRRs)can recognize nucleic acids generated by pathogens,which induces the expression of type I interferons,inflammatory factors,and effector proteins of anti-pathogenic microorganisms.RNA viruses are a class of major pathogens that cause severe infectious and immunological diseases.Upon virus infection,viral RNAs are detected by cytoplasmic sensors including RIG-I and MDA5.Binding of viral RNAs to RIG-I and MDA5 induces their conformational changes,and then they are recruited to the mitochondrial membrane-located adaptor protein VISA.This triggers the formation of large prion-like VISA polymers,which in turn serve as platforms for recruitment of TRAF2/3/5/6 through its TRAF-binding motifs.The TRAF proteins further recruit TBK1 and the IKK complex to phosphorylate IRF3 and I?B? respectively,leading to activation of IRF3 and NF-?B,which work corporately to induce type I interferons and inflammatory cytokines production.During RNA virus infection,the recognition of viral nucleic acids by PRRs is the key events to induce innate immune response,but how to recognize nucleic acids by RIG-I and MDA5 needs to further study.In this study,we identified Ras-GTPase activating protein SH3 domain binding protein 1(G3BP1)as a positive regulator of SeV-induced interferon production signaling pathway.In contrast,knockdown or knockout of G3BP1 had opposite effects.We further found that G3BP1 interacted specifically with RIG-I but not MDA5.Mechanistically,overexpression of G3BP1 inhibited the RNF125-mediated ubiquification of RIG-I to maintain stability of RIG-I.In addition,G3BP1 could bind 5?pppRNA and promote the binding of RIG-I to 5?pppRNA.These results suggest that G3BP1 is a co-activator of RIG-I and the study provides a new perspective on the regulation mechanism of RLRs-mediated antiviral innate immunity.Previous reports suggested that foot-and-mouth disease virus(FMDV)3C and L could cleave porcine G3BP1,but FMDV 3C and L do not interact with G3BP1 and the mechanism is unclear.Whether G3BP1 interacts with other FMDV proteins and regulates picornavirus replication such as FMDV by mediating innate immunity needs to be further studies.In the study,we found that porcine G3BP1 also increased SeV-triggered interferon production.The porcine G3BP1 interacted with FMDV 3A both in vitro and in vivo with FMDV infection.To examine how did FMDV 3A regulate procine G3BP1-mediated RIG-I signaling pathway,we contransfected FMDV 3A and other indicated expression plasmids and found that overexpression of FMDV 3A degraded G3BP1 proteins and inhibited G3BP1-mediated RIG-I signaling pathway by upregulating the expression of autophagy ralated protein LRRC25.In addition,other picornaviruses 3A proteins,such SVV 3A,EV71 3A,and EMCV 3A also degraded G3BP1 protein by upregulating LRRC25 expression.Overall,the study showed that both human and procine G3BP1 increased SeV-induced interferon production and human G3BP1 inhibited E3 ubiquitin-protein ligase RNF125-mediated RIG-I ubiquification but other picornaviruses 3A proteins including FMDV 3A degraded procine G3BP1 by upregulating LRRC25 to reduce the expression of RIG-I.The study provides a new molecular mechanism for RIG-I-mediated signal transduction and also reveals a new molecular mechanism for FMDV to evade host immune response,which provides a new theoretical basis for the development of a new vaccine against FMD.