Herpes Simplex Virus 1 Tegument Protein VP22 And UL46 Abrogate CGAS/STING-mediated Antiviral Innate Immunity

The innate immune system,the first line of host defense against invading pathogens,is very important for host to defend virus infection,which depends on various pathogen recognition receptors(PRRs).The PRRs detect structurally conserved pathogen-associated molecular patterns(PAMPs)generated during the pathogen life cycle and trigger the production of type-I interferon(IFN-I)and other antiviral factors.cGAS,which is a nucleotidyltransferase,is an important cytoplasmic sensor that recognizes various DNA ligands in different cell types.Upon binding to cytosolic double-stranded DNA,cGAS would be activated and utilizes ATP and GTP to produce cyclic GMP-AMP(c GAMP)through its enzymatic activity.The cGAMP produced by cGAS activates stimulator of interferon gene(STING),which then recruits TANK-binding kinase 1(TBK1),leading to the activation of interferon regulatory factor 3(IRF3)and inducing the production of IFN-?.Herpes simplex virus type 1(HSV-1),a typical human-restricted DN A virus,is well known for its ability to cause a lifelong latent infection in neurons and trigger reactivation and lytic infection mainly epithelial or mucosal.However,HSV-1 has developed multiple mechanisms to attenuate host antiviral machinery.A systematic screening for viral proteins involved in the inhibition of cGAS/STING mediated signal pathway,and revealing the underlying mechanism will provide new insights into the host-virus interaction and help develop novel antiviral approaches.Part 1: In the present study,a systematic screening for HSV-1 proteins involved in the inhibition of cGAS/STING mediated signal pathway was performed through dual-luciferase reporter(DLR)assays.our redults showed that HSV-1 tegument protein VP22 acted as an inhibitor of c GAS/STING-mediated production of IFN and its downstream antiviral genes.O ur results showed that ectopic expression of VP22 decreased cGAS/STING-mediated IFN-? promoter activation and IFN-? production.We generated VP22-deficient virus((35)VP22)by C RISPR-Cas9 gene knockout technology.The infection of wild-type HSV-1(WT),but not(35)VP22,inhibited immunostimulatory DNA(ISD)induced activation of IFN signaling pathway.Further study showed that VP22 interacted with c GAS and inhibited enzymatic activity of cGAS.In addition,stably knockdown of cGAS facilitated the replication of(35)VP22,but not WT.In summary,our findings indicated that HSV-1 VP22 acted as an antagonist of IFN signaling to persistently evade host innate antiviral responses.Part 2: In the present study,we found that HSV-1 tegument protein UL46 acted as an inhibitor of cGAS/STING-mediated production of IFN and its downstream antiviral genes.O ur results showed that ectopic expression of UL46 decreased cGAS/STING-mediated IFN-? promoter activation and IFN-? production.The infection of WT,but not UL46-deficient virus,inhibited ISD induced activation of IFN signaling pathway.Further study showed that UL46 interacted with STING and TBK1.The underlying molecular mechanism is that UL46 abrogates the phosphorylation of STING.In the present study,we demonstrated that VP22 inhibited enzymatic activity of cGAS and UL46 abrogated the interaction between STING and TBK1,thus evaded cGAS/STING mediated signal pathway.