KAT5 Acetylates CGAS To Promote Innate Immune Response To DNA Virus

After pathogenic invasion,the germline-encoded pattern-recognition receptors(PRRs)detect pathogen-associated molecular patterns(PAMPs),which triggers a series of immune signaling cascades for ultimate elimination of the pathogens and clearance of infected cells.Upon DNA virus infection,viral DNA acts as a major PAMP to trigger antiviral innate immune response.In mammalian cells,the most widely expressed and utilized cytosolic viral DNA sensor is cyclic GMP-AMP(c GAMP)synthase(cGAS),which forms “cGAS-DNA” liquid droplet upon viral infection and mediates synthesis of a unique dinucleotide called cyclic GMP-AMP(c GAMP).c GAMP in turn binds to the endoplasmic reticulum(ER)-associated protein MITA(also called MITA),which then translocates from the ER via ER-Golgi intermediate complex(ERGIC)to perinuclear punctate structures.During these processes,the kinase TBK1 and the transcriptional factor IRF3 are recruited to the MITA-associated complex,leading to phosphorylation of IRF3 by TBK1 and its activation to induce transcription of hundreds of downstream antiviral genes.The lysine acetyltransferase 5(KAT5)is a catalytic subunit of the highly conserved Nu A4 acetyltransferase complex,which plays critical roles in DNA damage repair,p53-mediated apoptosis,HIV-1 transcription and autophagy.Although KAT5 has been investigated mainly as a transcriptional regulator,increasing evidences show that KAT5 also acts as a key regulator in signal transduction pathways by targeting non-histone proteins such as ULK1,PRAK,LIPIN1 for acetylation.cGAS is consisted of two domains,the unstructured N-terminal domain(aa1-160)and the C-terminal catalytic domain(aa161-521)which binds to its substrates GTP and ATP.The activation of cGAS is regulated by various post-translational modifications.However,whether the activation of cGAS is regulated by acetylation remains unclear.In this study,we reveal a critical role of the acetyltransferase KAT5 in innate antiviral response by mediating acetylation of the N-terminal domain of cGAS.In an expression screen,KAT5 was identified as a positive regulator of cGAS-mediated signaling.Overexpression of KAT5 promoted cGAS-mediated transcription of downstream antiviral genes,whereas knockdown of KAT5 or treatment of cells with KAT5 specific inhibitor had opposite effects.In vivo experiments indicated that KAT5-inactive mice produced less serum cytokines,had higher viral titres in the brain and were more susceptible to inflammatory death following HSV-1 infection.These results suggest that KAT5 plays an important role in efficient innate immune response to DNA virus.Several experiments suggest that KAT5 functions by targeting cGAS for acetylation.Knockdown of KAT5 inhibited viral DNA-induced c GAMP production,but had no marked effects on c GAMP-induced transcription of downstream antiviral genes.KAT5 was constitutively associated with cGAS,and their association was increased following viral infection.Furthermore,KAT5 catalyzed acetylation of cGAS.Mass spectrometry and mutagenesis indicated that KAT5 catalyzed the acetylation at multiple lysine residues including K47,K52,K62 and K83 in the N-terminal domain of cGAS.DNA pulldown and MST assays indicated that acetylated cGAS by KAT5 had a higher affinity to DNA.These results suggest that KAT5 promotes innate immune response to DNA virus by mediating the acetylation of cGAS.Our findings suggest that KAT5-mediated cGAS acetylation at its N-terminus is important for efficient innate immune response to DNA virus.This study reveals a mechanism on cGAS-mediated innate immune response to DNA virus,which may provide a target for the development of drugs or vaccines against DNA virus infection.