Herpes Simplex Virus 1 Tegument Protein VP22 Abrogates cGAS/STING-Mediated Antiviral Innate Immunity.

Cytosolic DNA arising from intracellular pathogens is sensed by cyclic GMP-AMP synthase (cGAS) and triggers a powerful innate immune response. However, herpes simplex virus 1 (HSV-1), a double-stranded DNA virus, has developed multiple mechanisms to attenuate host antiviral machinery and facilitate viral infection and replication. In the present study, we found that HSV-1 tegument protein VP22 acts as an inhibitor of cGAS/stimulator of interferon genes (cGAS/STING)-mediated production of interferon (IFN) and its downstream antiviral genes. Our results showed that ectopic expression of VP22 decreased cGAS/STING-mediated IFN-β promoter activation and IFN-β production. Infection with wild-type (WT) HSV-1, but not VP22-deficient virus (ΔVP22), inhibited immunostimulatory DNA (ISD)-induced activation of the IFN signaling pathway. Further study showed that VP22 interacted with cGAS and inhibited the enzymatic activity of cGAS. In addition, stable knockdown of cGAS facilitated the replication of ΔVP22 virus but not the WT. In summary, our findings indicate that HSV-1 VP22 acts as an antagonist of IFN signaling to persistently evade host innate antiviral responses.IMPORTANCE cGAS is very important for host defense against viral infection, and many viruses have evolved ways to target cGAS and successfully evade the attack by the immune system of their susceptible host. This study demonstrated that HSV-1 tegument protein VP22 counteracts the cGAS/STING-mediated DNA-sensing antiviral innate immunity signaling pathway by inhibiting the enzymatic activity of cGAS. The findings in this study will expand our understanding of the interaction between HSV-1 replication and the host DNA-sensing signaling pathway.

Huang J ，You H ，Su C ，Li Y ，Chen S ，Zheng C ... -  《-》

Herpes Simplex Virus 1 Abrogates the cGAS/STING-Mediated Cytosolic DNA-Sensing Pathway via Its Virion Host Shutoff Protein, UL41.

Cyclic GMP-AMP synthase (cGAS) is a key DNA sensor capable of detecting microbial DNA and activating the adaptor protein stimulator of interferon genes (STING), leading to interferon (IFN) production and host antiviral responses. Cells exhibited reduced type I IFN production in response to cytosolic DNA in the absence of cGAS. Although the cGAS/STING-mediated DNA-sensing signal is crucial for host defense against many viruses, especially for DNA viruses, few viral components have been identified to specifically target this signaling pathway. Herpes simplex virus 1 (HSV-1) is a DNA virus that has evolved multiple strategies to evade host immune responses. In the present study, we found that HSV-1 tegument protein UL41 was involved in counteracting the cGAS/STING-mediated DNA-sensing pathway. Our results showed that wild-type (WT) HSV-1 infection could inhibit immunostimulatory DNA-induced activation of the IFN signaling pathway compared with the UL41-null mutant virus (R2621), and ectopic expression of UL41 decreased cGAS/STING-mediated IFN-β promoter activation and IFN-β production. Further study indicated that UL41 reduced the accumulation of cGAS to abrogate host recognition of viral DNA. In addition, stable knockdown of cGAS facilitated the replication of R2621 but not WT HSV-1. For the first time, HSV-1 UL41 was demonstrated to evade the cGAS/STING-mediated DNA-sensing pathway by degrading cGAS via its RNase activity.IMPORTANCE HSV-1 is well known for its ability to evade host antiviral responses and establish a lifelong latent infection while triggering reactivation and lytic infection under stress. Currently, whether HSV-1 evades the cytosolic DNA sensing and signaling is still poorly understood. In the present study, we found that tegument protein UL41 targeted the cGAS/STING-mediated cellular DNA-sensing pathway by selectively degrading cGAS mRNA. Knockdown of endogenous cGAS could facilitate the replication of R2621 but not WT HSV-1. Furthermore, UL41 was shown for the first time to act directly on cGAS. Findings in this study could provide new insights into the host-virus interaction and help develop new approaches against HSV-1.

Su C ，Zheng C 《-》

β-Catenin Is Required for the cGAS/STING Signaling Pathway but Antagonized by the Herpes Simplex Virus 1 US3 Protein.

The cGAS/STING-mediated DNA-sensing signaling pathway is crucial for interferon (IFN) production and host antiviral responses. Herpes simplex virus I (HSV-1) is a DNA virus that has evolved multiple strategies to evade host immune responses. Here, we demonstrate that the highly conserved β-catenin protein in the Wnt signaling pathway is an important factor to enhance the transcription of type I interferon (IFN-I) in the cGAS/STING signaling pathway, and the production of IFN-I mediated by β-catenin was antagonized by HSV-1 US3 protein via its kinase activity. Infection by US3-deficienct HSV-1 and its kinase-dead variants failed to downregulate IFN-I and IFN-stimulated gene (ISG) production induced by β-catenin. Consistent with this, absence of β-catenin enhanced the replication of US3-deficienct HSV-1, but not wild-type HSV-1. The underlying mechanism was the interaction of US3 with β-catenin and its hyperphosphorylation of β-catenin at Thr556 to block its nuclear translocation. For the first time, HSV-1 US3 has been shown to inhibit IFN-I production through hyperphosphorylation of β-catenin and to subvert host antiviral innate immunity.IMPORTANCE Although increasing evidence has demonstrated that HSV-1 subverts host immune responses and establishes lifelong latent infection, the molecular mechanisms by which HSV-1 interrupts antiviral innate immunity, especially the cGAS/STING-mediated cellular DNA-sensing signaling pathway, have not been fully explored. Here, we show that β-catenin promotes cGAS/STING-mediated activation of the IFN pathway, which is important for cellular innate immune responses and intrinsic resistance to DNA virus infection. The protein kinase US3 antagonizes the production of IFN by targeting β-catenin via its kinase activity. The findings in this study reveal a novel mechanism for HSV-1 to evade host antiviral immunity and add new knowledge to help in understanding the interaction between the host and HSV-1 infection.

You H ，Lin Y ，Lin F ，Yang M ，Li J ，Zhang R ，Huang Z ，Shen Q ，Tang R ，Zheng C ... -  《-》

Herpes Simplex Virus 1 Serine Protease VP24 Blocks the DNA-Sensing Signal Pathway by Abrogating Activation of Interferon Regulatory Factor 3.

The interferon (IFN)-mediated antiviral response is a central aspect of host defense; however, viruses have evolved multiple strategies to counteract IFN-mediated responses in order to successfully infect the host. Herpes simplex virus 1 (HSV-1), a typical human-restricted DNA virus, is capable of counteracting host immune responses via several distinct viral proteins, thus establishing a lifelong latent infection. In this study, we demonstrate that the VP24 protein, a serine protease of HSV-1 essential for the formation and maturation of capsids, is a novel antagonist of the beta interferon (IFN-β) pathway. Here, VP24 was shown for the first time to dampen interferon stimulatory DNA (ISD)-triggered IFN-β production and inhibit IFN-β promoter activation induced by cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) and by STING, respectively. Further study demonstrated that ectopic expression of VP24 selectively blocked IFN regulatory factor 3 (IRF3) but not NF-κB promoter activation. In addition, VP24 was demonstrated to downregulate ISD-induced phosphorylation and dimerization of IRF3 during HSV-1 infection with a VP24 stable knockdown human foreskin fibroblast cell line. The underlying molecular mechanism is that VP24 abrogates the interaction between TANK-binding kinase 1 (TBK1) and IRF3, hence impairing IRF3 activation. These results illustrate that VP24 is able to block the production of IFN-β by inhibiting IRF3 activation, which may represent a critical adaptation to enable viral effective replication within the host. This study demonstrated that HSV-1 protein VP24 could inhibit IFN-β production and promoter activation triggered by ISD, cGAS and STING and by STING, respectively. VP24 selectively blocked IRF3 promoter activation and ISD-induced phosphorylation and dimerization of IRF3 without affecting the NF-κB promoter activation during viral infection. VP24 also inhibited IRF3 activation by impeding the interaction between TBK1 and IRF3 during viral infection. This study provides new insights into the immune evasion mediated by HSV-1 and identifies VP24 as a crucial effector for HSV-1 to evade the host DNA-sensing signal pathway.

Zhang D ，Su C ，Zheng C 《-》

Duck Enteritis Virus Inhibits the cGAS-STING DNA-Sensing Pathway To Evade the Innate Immune Response.

Gao L ，Liu R ，Yang F ，Li X ，Liu C ，Qi X ，Cui H ，Zhang Y ，Wang S ，Wang X ，Gao Y ，Li K ... -  《-》