The cGas-Sting Signaling Pathway Is Required for the Innate Immune Response Against Ectromelia Virus.

Wen-Yu Cheng,Zhi-Zhong Jing,Huai-Jie Jia,Zhao-Lin Long,Xiao-Bing He,Qi-Wang Jin,Guo-Hua Chen

doi:10.3389/fimmu.2018.01297

Abstract

Activation of the DNA-dependent innate immune pathway plays a pivotal role in the host defense against poxvirus. Cyclic GMP-AMP synthase (cGAS) is a key cytosolic DNA sensor that produces the cyclic dinucleotide cGMP-AMP (cGAMP) upon activation, which triggers stimulator of interferon genes (STING), leading to type I Interferons (IFNs) production and an antiviral response. Ectromelia virus (ECTV) has emerged as a valuable model for investigating the host–Orthopoxvirus relationship. However, the role of cGas–Sting pathway in response to ECTV is not clearly understood. Here, we showed that murine cells (L929 and RAW264.7) mount type I IFN responses to ECTV that are dependent upon cGas, Sting, TANK binding kinase 1 (Tbk1), and interferon regulatory factor 3 (Irf3) signaling. Disruption of cGas or Sting expression in mouse macrophages blocked the type I IFN production and facilitated ECTV replication. Consistently, mice deficient in cGas or Sting exhibited lower type I IFN levels and higher viral loads, and are more susceptible to mousepox. Collectively, our study indicates that the cGas–Sting pathway is critical for sensing of ECTV infection, inducing the type I IFN production, and controlling ECTV replication.

Highlights

Innate immune responses to pathogen infection are initiated with the recognition of microbial pathogen-associated molecular patterns (PAMPs) through a limited number of germline-encoded receptors called pattern-recognition receptors (PRRs) [1,2,3]
We showed that murine L929 and RAW264.7 cells, but not NIH3T3 cells, mount type I IFN responses against Ectromelia virus (ECTV) infection via the cGas–Sting pathway
The phosphorylation of TANK binding kinase 1 (TBK1) or interferon regulatory factor 3 (IRF3) induced by ECTV were severely impaired in all these gene knockout peritoneal macrophages (Figures 5C,D). These results definitively show that ECTV infection is capable of activating the cGas–Sting–TANK binding kinase 1 (Tbk1)–interferon regulatory factor 3 (Irf3) axis and Tlr9, leading to the transcription of type I IFNs

Summary

Introduction

Innate immune responses to pathogen infection are initiated with the recognition of microbial pathogen-associated molecular patterns (PAMPs) through a limited number of germline-encoded receptors called pattern-recognition receptors (PRRs) [1,2,3]. PRRs exist in the plasma or endosomal membranes, cytoplasm, and nucleus of some cell types to sense both extracellular and intracellular infections [5,6,7]. Nucleic acid-sensing PRRs are one of the major subsets of PRRs that sense DNA and RNA [7,8,9] Some members of these membrane-bound PRRs, such as Toll-like receptors (TLR3, 7, 8, and 9), are located in the endosomes that detect environmental RNA or DNA, while others, such as the DNA sensors AIM2-like receptors (AIM2, IFI16, and IFIX) and cyclic GMP-AMP synthase (cGAS), and the RNA sensors RIG-I-like receptors (RIG-I, MDA5, and LPG2), recognize microbial nucleic acid in the cytosol and/or nucleus [10,11,12,13]. Following the recognition of microbial RNA or DNA, the PRRs are activated through conformational changes or specific modifications that drive the induction of type I interferon (IFN) and pro-inflammatory cytokines to protect the host from the invading pathogens [14,15,16]

Methods

Results

Conclusion