Lck/Hck/Fgr-Mediated Tyrosine Phosphorylation Negatively Regulates TBK1 to Restrain Innate Antiviral Responses.

Cytosolic nucleic acid sensing elicits interferon production for primary antiviral defense through cascades controlled by protein ubiquitination and Ser/Thr phosphorylation. Here we show that TBK1, a core kinase of antiviral pathways, is inhibited by tyrosine phosphorylation. The Src family kinases (SFKs) Lck, Hck, and Fgr directly phosphorylate TBK1 at Tyr354/394, to prevent TBK1 dimerization and activation. Accordingly, antiviral sensing and resistance were substantially enhanced in Lck/Hck/Fgr triple knockout cells and ectopic expression of Lck/Hck/Fgr dampened the antiviral defense in cells and zebrafish. Small-molecule inhibitors of SFKs, which are conventional anti-tumor therapeutics, enhanced antiviral responses and protected zebrafish and mice from viral attack. Viral infection induced the expression of Lck/Hck/Fgr through TBK1-mediated mobilization of IRF3, thus constituting a negative feedback loop. These findings unveil the negative regulation of TBK1 via tyrosine phosphorylation and the functional integration of SFKs into innate antiviral immunity.