Study On The Molecular Mechanism Of Mink Enteritis Virus Inhibiting The Induction Of Type ? Interferon

Mink enteritis virus(MEV)is an acute highly contagious infectious pathogen,causing severe disease in minks and resulting in great economic losses worldwide.In innate immunity,type ? interferon(IFN-?),the most important antiviral cytokines,can induce hundreds of interferon-stimulated genes(ISGs)to against viral infections,and regulate the adaptive immunity.Many kinds of viruses can induce the production of IFN-?,but MEV can not.While the molecular mechanism is not clear.In order to further understand the interaction between MEV and its host,we studied the mechanism of MEV inhibiting the induction of type ?interferon.Previous studies found that MEV was inefficient to induce IFN-?.In this study,we detected the mRNA levels of IFN?,IFN? and ISGs in CRFK cells.The results showed that the expression of IFN?,IFN? and ISGs was downregulated by MEV.Moreover,MEV also inhibit the expression of IFN? induced by poly(I:C)in CRFK cells.By pre-exposing of exogenous interferon(IFNa)for 6 h to CRFK cells,we found that the infection and replication of MEV were not influenced.Further studies found that nonstructural protein NS1 could inhibit the transcription of IFN? with or without stimulation of poly(I:C),and the DNA binding domain of NS1 played an important role in this process.Subsequently,we showed that NS1 could directly bind to IFN? promoter to inhibit its transcription.IRF3 and NF-?B signaling pathway play an important role in the induction of IFN-I.Further studies found that NS1 inhibited the activation of IRF3 and NF-?B induced by signaling molecules,including STING,MAVS,TBK1 and IKK?.By Western blotting and confocal microscopy experiments,it was found that NS1 could block the activation of IRF3 signaling pathway by inhibiting the phosphorylation of IRF3 and TBK1,but did not affect the nuclear translocation of IRF3.In addition,we demonstrated that NS1 reduced the phosphorylation and degradation of I?B? and the phosphorylation of p65 and its translocation into the nucleus.The immunoprecipitation and confocal microscopy experiments further demonstrated that NS1 associates with IKK? to disrupt IKK?-IKK? or IKK?-NEMO interaction,which decreased the formation of IKK complex.Kinase domain of IKK? is important for phosphorylation of I?B?.The truncated fragment analysis of IKK? domains confirmed that NS1 could bind to kinase domain of IKK?.All results indicated that,post infection of MEV,IFN-? was not produced in CRFK cells.And the proliferation of MEV was nonsensitive to exogenous interferon.NS1 could directly bind to IFN? promoter to inhibit its transcription.Moreover,NS1 could also target IRF3 and IKK? to inhibit the phosphorylation of IRF3 and interfere with the formation of IKK complex,blocking the IRF3 and NF-?B signaling pathways,respectively.The mechanism of MEV inhibiting the induction of IFN-I was studied deeply in this paper.These data may provide a new theoretical basis and thought for us to understand the pathogenesis of MEV and the development of new attenuated vaccine.