Molecular Mechanism Of Inhibition Of Host Type ? Interferon Response By Nonstructural Protein Of Feline Diseases Virus

The number of pet cats has reached more than 70 million in China by 2019,and the prevention and control of pet cat epidemic diseases is facing great challenges.Clinically,feline panleukopenia caused by feline panleukopenia virus(FPV)and feline infectious rhinoconjunctivitis caused by feline calicivirus(FCV)are the most prevalent.Although the etiology of the two viruses has been studied for decades.However,there are few studies on its effect on host innate immune response.In the present study,we used the Feline interferon signaling pathway research platform to demonstrate that infection with the FPV strain Philips-Roxane failed to activate the interferon ?(IFN-?)pathway but could antagonize the induction of IFN stimulated by Sendai virus(SeV)in F81 cells.Subsequently,by screening FPV nonstructural and structural proteins,we found that only nonstructural protein 2(NS2)significantly suppressed IFN expression.We demonstrated that the inhibition of SeV-induced IFN-?production by FPV NS2 depended on the obstruction of the IFN regulatory factor 3(IRF3)signaling pathway.Further,we verified that NS2 was able to target the serine/threonine-protein kinase TBK1 and prevent it from being recruited by stimulator of interferon genes(STING)protein,which disrupted the phosphorylation of the downstream protein IRF3.In this study,we found FCV strain 2280 to be relatively resistant to treatment with IFN-?.FCV 2280 infection inhibited IFN-induced activation of the ISRE promoter and transcription of ISGs.The mechanistic analysis showed that the expression of IFNAR1 was markedly reduced in FCV 2280-infected cells by inducing the degradation of IFNAR1 mRNA,which inhibited the phosphorylation of downstream adaptors.Further,overexpression of the FCV 2280 nonstructural protein p30 downregulated the expression of IFNAR1 mRNA.His-p30 fusion proteins were produced in Escherichia coli and purified,and an in vitro digestion assay was performed.The results showed that 2280 His-p30 could directly degrade IFNAR1 RNA.Next,we constructed two chimeric viruses:rFCV 2280-F9 p30 and rFCV F9-2280 p30.Compared to infection with the parental virus,rFCV 2280-F9 p30 infection displayed attenuated activities in reducing the level of IFNAR1 and inhibiting the phosphorylation of STAT1 and STAT2,whereas rFCV F9-2280 p30 displayed enhanced activities.Animal.experiments showed that the virulence of rFCV 2280-F9 p30 infection was attenuated but that the virulence of rFCV F9-2280 p30 was increased compared to that of the parental viruses.Collectively,these data show that FCV 2280 p30 could directly and selectively degrade IFNAR1 mRNA,thus blocking the type I interferon-induced activation of the JAK-STAT signaling pathway.which may contribute to the pathogenesis of FCV infection.This study demonstrated the molecular mechanism of immune escape of FPV and FCV through their non-structural proteins to inhibit the host type I interferon response.The results will contribute to the study on the pathogenesis of the two viruses and the development of antiviral drugs and vaccines,and provide scientific support for the prevention and control of feline viral infectious diseases.