| As the first defense line o f human body,innate immunit y plays important ro le in defending against viral infect ion.The virus can be recognized by different pattern-recognit ion receptors to activate the adpter protein MAVS or STING leading to a signaling cascade that activates the transcript ion factors IR F3 and NF-κB,and inducing the production o f interferons(IFNs)and inflammatory factors.Interferon can be recognized by the interferon receptors on cell surface to activate the JAK-STAT signaling pathway and induces the expression of ISGs,which can play the ant iviral funct ion.The level o f IFNs induced by virus is very important for the body to play an ant iviral role.Low level of IFN can lead to persistent viral infect ion.However,the excessive expression of IFN can cause excessive immunit y and aut oimmunit y disease.To maintain the balance o f the expression o f IFN,both virus and host factors regulat e the IFN signaling pathway.Recent ly,more and more studies show that host factors play an important role in regulat ing the expression of IFN.Therefore,it is ver y valuable to explore the funct ion and mechanism of host factors on IFN signaling pathway.In this study,we found that the level of IRF1 m RNA and protein was upregulated by poly(I: C),RNA viruses(NDV and VSV)or HSV.Similarly,IRF1 was induced by IFNα.When IFNAR1 was silenced,IRF1 could not be induced by viruses,indicating that the induction of IRF1 by viral infect ion relies on the IFN-JAK-STAT signal pathway.To explore the ro le of IRF1 in IFN signal pathway,we delivered or silenced IRF1 in different kinds of cells.We found that IRF1 pro moted the induction of type I IFN and type III IFN induced by DNA or RNA viruses,thereby inhibit ing viral replication.To exclude that IRF1 exerts antiviral effect by direct ly affect ing the expression of ISGs.First,we tested the effect of IRF1 on the production of ISGs and found that IRF1 can only enhance the product ion of ISGs induced by the virus,but has no significant effect on the expression of ISGs induced by interferon.Secondly,we found that in IFNAR1 silenced cell lines,IRF1 lost its pro motion of poly(I:C)-induced ISGs.Finally,we tested the effect of IRF1 on the JAK-STAT signaling pathway activated by IFNα and found that IRF1 has no significant effect on the phosphorylation of STATs.In order to determine the key targets of IRF1 act ing on the interferon signal pathway,the western blot data showed that IRF1 promoted the phosphorylation and dimerizat ion of IRF3 as well as the trans location of p-IRF3 fro m cytoplasm to nucleus.IRF1 localizes in the cytoplasm and nucleus during rest ing state and IRF3 localizes in the cytoplasm.Immunofluorescence data showed that IRF1 co-localized with IRF3 in cytoplasm.And viral infection pro moted the trans location of IRF3 from the cytoplasm to the nucleus and co-localized with IRF1 in the nucleus.IP analysis demonstrated the interaction between IRF1 and IRF3.And further studies showed that IRF1 interacted with the IAD do main of IRF3 through its DBD domain and the DBD domain of IRF1 was also the key funct ional domain for its interact ion with IRF3.Finally,we explored the mechanism of how IRF1 promotes IRF3 phosphorylation.We found that IRF1 inhibited the interact ion between IRF3 and its phosphatase PP2 A,while the delet ion of DBD of IRF1 could not blocked IRF3 and PP2 A interact ion.Further funct ional verificat ion,we found that co-overexpressed IRF1 and PP2 A could reverse the inhibit ion of virus-induced IRF3 phosphorylat ion and interferon product ion by PP2 A.All these data suggested that IRF1 promotes the innate immune response to viral infect ion by enhancing the activat ion of IRF3,thereby inhibit ing viral infection.Collectively,the results of our study provide new insight into the regulator y mechanism o f IFN signaling and uncover the role of IRF1 in the posit iv e regulation o f the innate immune response to viral infect ion.Supplements the regulat ion mode o f IRF3,a key protein in the production of interferon and provides new target for the development of ant iviral drugs. |
