Effect Of Gene Type 3 Porcine Circovirus Cap And ORF3 Encoding Protein On Host Type ? Interferon Signaling Pathway And Its Mechanism Research

Porcine circovirus type 3(PCV3),the smallest DNA virus currently reported and the causative agent of porcine circovirus-related diseases,is widely distributed in swine farms in China.It is closely related to porcine respiratory diseases and reproductive disorders,which results in severe immunosuppression and clinical symptoms in pigs,causing substantial economic losses.[Objective] To investigate the role of Porcine circovirus 3 in regulation of host innate immune response,and investigate the involved antagonistic mechanism to provide a theoretical basis for clarification of the molecular mechanisms for PCV3-mediated immune suppression,and provide a new perspective for PCV3 prevention and control.[Methods] The expression of PCV3 viral proteins was verified by Western blotting and indirect immunofluorescence.The Real-time quantification PCR,Dual luciferase gene reporting system and ELSA assay were performed to investigate the effect of PCV3 viral proteins on type I interferon pathway activation,and the Co-immunoprecipitation was carried out to investigate the involved antagonistic mechanism.Western blotting and co-immunoprecipitation were performed to investigate the antagonistic mechanism of PCV3-Cap on the adaptor protein of type I interferon pathway,and to analyze the mechanism of PCV3-Cap inhibition of type I interferon pathway.Western blotting,indirect immunofluorescence,real-time PCR and co-immunoprecipitation were performed to investigate the mechanism of inhibition of type I interferon pathway by PCV3-ORF3.[Results] The expression of PCV3 viral proteins was verified,and PCV3-Cap and PCV3-ORF3 inhibited the activation of type I interferon signaling pathway and the secretion of IFN-? stimulated by Poly(dA:dT).The interaction of PCV3-Cap with the adaptor protein MITA of innate immune signaling pathway was identified.PCV3-ORF3 down-regulated cGAS expression through caspase pathway.PCV3-ORF3 interacted with MITA and IRF7,and inhibited the formation of theMITA-TBK1-IRF7 complex and the MITA-TRAP?-iRhom2 transport complex.The study first demonstrate that both the PCV3 Cap and ORF3 encoding protein blocked the activation of the IFNs pathway by acting on MITA,thereby evading the host's antiviral innate immune response.