New Kinases In Regulating Cytosolic RNA Sensing And Innate Antiviral Immunity

Innate immune sensing recognizes conserved pathogen-associated molecular patterns(PAMPs)via pattern recognition receptors(PRRs)to initiate the downstream immune signal pathway.As an essential component of vertebrate innate immune recognition,cytosolic nucleic acid sensing plays a pivotal role in host defense against virus invasion.Cytosolic RIG-1-like receptors(RLRs)sense viral RNA,while cytosolic DNA is recognized by cGAS,and this signaling is facilitated either via mitochondria-associated MAVS(also known as VISA,IPS-1,Cardif)or via endoplasmic reticulum-located STING(also known as MITA),resulting in the activation of TBK1 and/or IKKs.TBK1/IKKs phosphorylate and mobilize the transcription factor IRF3 or IRF7,which then dimerizes and translocates to the nucleus to drive Type Ⅰ/Ⅲ interferons(IFNs)transcription,in cooperation with NF-κB.IFNs then induce hundreds of IFNs-stimulated genes(ISGs)expression and regulate adaptive immunity to establish antiviral status in host and neighboring cells.Cytosolic nucleic acid sensing also plays an important role in regulating chronic inflammation,autoimmune diseases,cancer immunity and neurodegenerative diseases.Protein post-translational modification plays a pivotal role in regulating cytosolic nucleic acid sensing.Tyrosine phosphorylation is one of the most fundamental parts of post-translational modification which involved in regulation of every aspect of cellular physiology.On the other hand,nucleoside-diphosphate(NDP)kinases are essential in maintaining the intracellular nucleotide homeostasis,and thus control a variety of intracellular physiological activities.Our current research focused on kinases that play a crucial role in the cytosolic nucleic acid sensing,especially tyrosine kinases and nucleoside-diphosphate kinases that have no reported roles in innate immunity.Here we find that TBK1,the core kinase of antiviral pathways,is inhibited by tyrosine phosphorylation caused by Src family tyrosine kinases(SFKs)Lck,Hck and Fgr.These SFKs directly phosphorylate TBK1 at Tyr 354/394 to suppress TBK1 dimerization and subsequent activation.Accordingly,deletion of Lck/Hck/Fgr dramatically improve cytosolic nucleic acid sensing and antiviral host defense,while small molecule inhibitors of Lck strengthen antiviral responses and protect zebrafish and mice from viral infection.Thus,we identify new protein kinases which directly modify TBK1 at tyrosine residues,regulate TBK1 activity,and govern host antiviral defense,which unveils a negative feedback regulation of cytosolic RNA sensing.In addition,we identified a mitochondrial NDP kinase NME4 that significantly enhances the cytosolic RNA sensing.NME4 controls mitochondrial dynamics through the mitochondrial fusion regulator OPA1,which drives MAVS aggregation to facilitate the activation of TBK1 and transcription factor IRF3.This study proposed a crucial regulatory role of NDP kinase in cytosolic RNA recognition and antiviral defense and verified a key role of mitochondrial dynamics in MAVS amyloid aggregation.It provides new theoretical and experimental basis for understanding the activation of cytosolic RNA sensing and the regulation of host antiviral defense.