Protein Tyrosine Phosphorylation In Innate Immune Sensing Of Cytosolic Nucleic Acids

Cytosolic nucleic acids sensing elicits innate antiviral immunity,which acts as the first line of defence against viral infection.When host cells are invaded and infected by virus,pattern recognition receptors(PRRs)in the cytoplasm detect viral RNA or DNA and then signal to the nucleus to induce the transcription and translation of type ?/?interferons(IFNs)and hundreds of interferon-stimulated genes(ISGs),which play crucial roles in inhibition of viral replication and clearance of viral particle.TANK-binding kinase 1(TBK1)is the key component of innate antiviral pathway.When activated by upstream adaptor proteins MAYS and STING,TBK1 phosphorylates and activates the dovnstream transcription factor,interferon regulatory factor 3(IRF3),to induce its dimerization and translocation into the nucleus,where it binds to the target sequences to drive genes transcription.Notably,aberrant activation of TBKI induces excessive IFN products,proinflaunatory cytokines and chemokines,which is one of major causes of autoimmune and auto inflammatory diseases.Therefore,the intrinsical equilibrium of TBK1 activation is critical and subjected to complex regulation.Previous reports regarding the post-translational regulation of TBK1 have focused on the Ser/Thr phosphorylation and ubiquitination.It remains totally unclear whether tyrosine phosphorylation and tyrosine kinases also directly participate in the regulation of TBK1 and nucleic acid immune sensing.Here,we revealed that Lck,Hck,and Fgr,members of the Src family kinases(SFKs),directly phosphorylate TBK1 at Tyr354/394 to prevent TBK1 dimerization and thus activation.Intriguingly,activation of antiviral responses directly induces the expression of Lck/Hck/Fgr through IRF3-mediated transcription.In accordance,Lck/Hck/Fgr triple knockout(tKO)cells exhibit enhanced TBK1 activation and antiviral responses,and adiministration of Lck inhibitors in zebrafish and mice protects animals from viral attack and extends their survivals.Therefore,our results unveil the function and underlying mechanism of tyrosine phosphorylation in integration of irnate antiviral immunity,and identify tyrosine kianses Lck/Hck/Fgr as the negative and physiological regulator of TBK1 and innate immune responses.Our study thus suggests new therapeutic targets for antiviral treatment,and indicates that small molecule inhibitors of SFKs may be valuable in prevention and cure of viral infecious diseases.