cGAS and CD-NTase enzymes: structure, mechanism, and evolution

Kranzusch, Philip J.

doi:10.1016/j.sbi.2019.08.003

Cited by 70 publications

(70 citation statements)

References 69 publications

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“…However, the upstream signaling machinery that activates STING in insects remains poorly understood. Insects encode enzymes like Drosophila melanogaster CG7194 and CG12970 that are part of the cGAS/DncV-like nucleotidyltransferase (CD-NTase) family ( Kranzusch, 2019 ; Whiteley et al, 2019 ), but these enzymes are significantly divergent from mammalian cGAS and it is unclear if insect CD-NTases synthesize 2′3′-cGAMP or respond to cytosolic DNA. Our results show that nearly all poxin representatives from across all groups retain specificity for 2′3′-cGAMP and fail to cleave 3′3′-cGAMP.…”

Section: Discussionmentioning

confidence: 99%

Structures of diverse poxin cGAMP nucleases reveal a widespread role for cGAS-STING evasion in host–pathogen conflict

Eaglesham

McCarty

Kranzusch

2020

eLife

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DNA viruses in the family Poxviridae encode poxin enzymes that degrade the immune second messenger 2′3′-cGAMP to inhibit cGAS-STING immunity in mammalian cells. The closest homologs of poxin exist in the genomes of insect viruses suggesting a key mechanism of cGAS-STING evasion may have evolved outside of mammalian biology. Here we use a biochemical and structural approach to discover a broad family of 369 poxins encoded in diverse viral and animal genomes and define a prominent role for 2′3′-cGAMP cleavage in metazoan host-pathogen conflict. Structures of insect poxins reveal unexpected homology to flavivirus proteases and enable identification of functional self-cleaving poxins in RNA-virus polyproteins. Our data suggest widespread 2′3′-cGAMP signaling in insect antiviral immunity and explain how a family of cGAS-STING evasion enzymes evolved from viral proteases through gain of secondary nuclease activity. Poxin acquisition by poxviruses demonstrates the importance of environmental connections in shaping evolution of mammalian pathogens.

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Section: Discussionmentioning

confidence: 99%

Structures of diverse poxin cGAMP nucleases reveal a widespread role for cGAS-STING evasion in host–pathogen conflict

Eaglesham

McCarty

Kranzusch

2020

eLife

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“…Upon binding DNA, cGAS synthesizes 2’3’-cGAMP, a cyclic dinucleotide (CDN) secondary messenger that binds to and activates STING 7–10 . Bacteria also synthesize CDNs such as c-di-AMP, c-di-GMP and 3’3’-cGAMP, which can be sensed by STING (reviewed in 11 ). Upon activation, STING recruits through its C-terminal tail (CTT) region the kinase TBK1, which phosphorylates and activates the transcription factor Interferon Regulatory Factor (IRF) 3 to trigger interferon (IFN) production 12 .…”

Section: Introductionmentioning

confidence: 99%

2’3’-cGAMP triggers a STING and NF-κB dependent broad antiviral response in Drosophila

Cai

Holleufer

Simonsen

et al. 2019

Preprint

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28We recently reported that an orthologue of STING regulates infection by picorna-like 29 viruses in drosophila. In mammals, STING is activated by the cyclic dinucleotide 2'3'-30 cGAMP produced by cGAS, which acts as a receptor for cytosolic DNA. Here, we 31show that injection of flies with 2'3'-cGAMP can induce expression of dSTING-32 regulated genes. Co-injection of 2'3'-cGAMP with a panel of RNA or DNA viruses 33 results in significant reduction of viral replication. This 2'3'-cGAMP-mediated 34 protection is still observed in flies mutant for the genes Atg7 and AGO2, which 35encode key components of the autophagy and small interfering RNA pathways, 36 respectively. By contrast, it is abrogated in flies mutant for the NF-κB transcription 37 factor Relish. Analysis of the transcriptome of 2'3'-cGAMP injected flies reveals a 38 complex pattern of response, with early and late induced genes. Our results reveal 39 that dSTING regulates an NF-κB -dependent antiviral program, which predates the 40 emergence of Interferon Regulatory Factors and interferons in vertebrates. 41 42 43 44 45 46 47 48 49 50 51 52 Introduction 53Insects, like all animals, are plagued by viral infections, which they oppose 54 through their innate immune system. Induction of transcription of antiviral genes upon 55 sensing of infection is a common antiviral response observed across kingdoms. In 56 insects, inducible responses contribute to defense against viruses, together with RNA 57 interference (RNAi) and constitutively expressed restriction factors (reviewed in 1 ). 58Apart from RNAi, these mechanisms are still poorly characterized and appear to be 59 largely virus-specific 2-4 . Combining genetics and transcriptomic analysis, we recently 60 showed that the evolutionarily conserved factor dSTING participates together with the 61 kinase IKKβ and the NF-κB transcription factor Relish in a novel pathway controlling 62 infection by the picorna-like viruses Drosophila C virus (DCV) and Cricket Paralysis 63Virus (CrPV) in the model organism Drosophila melanogaster 5 . 64In mammals, STING is a central component of the mammalian cytosolic DNA 65 sensing pathway, where it acts downstream of the receptor cyclic GMP-AMP 66 synthase (cGAS) 6 . Upon binding DNA, cGAS synthesizes 2'3'-cGAMP, a cyclic 67 dinucleotide (CDN) secondary messenger that binds to and activates STING 7-10 . 68Bacteria also synthesize CDNs such as c-di-AMP, c-di-GMP and 3'3'-cGAMP, which 69 can be sensed by STING (reviewed in 11 ). Upon activation, STING recruits through its 70 C-terminal tail (CTT) region the kinase TBK1, which phosphorylates and activates the 71 transcription factor Interferon Regulatory Factor (IRF) 3 to trigger interferon (IFN) 72 production 12 . STING can also activate NF-κB and autophagy independently from its 73 CTT domain in mammalian cells [13][14][15] . 74The identification of STING in animals devoid of interferons, such as insects, 75 raises the question of the ancestral function of this molecule. Since most 76 invertebrates lack the IRF family of tran...

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“…This family of enzymes is present in metazoans and bacteria and synthesises a wide array of linear and cyclic dinucleotides, trinucleotides and oligonucleotides. The 2 0 -5 0 -oligoadenylate synthetase (OAS) enzymes are part of this group and share striking structural similarity with cGAS (Hornung et al, 2014;Kranzusch, 2019). Through an oligoadenylate second messenger, their stimulation by dsRNA leads to activation of RNase L, which degrades cellular and viral RNAs and thus exerts antiviral activity (Choi et al, 2015).…”

Section: The Cgas-sting Signalling Axismentioning

confidence: 99%

Regulation and inhibition of the DNA sensor cGAS

Hertzog

Rehwinkel

2020

EMBO Reports

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Cell-autonomous sensing of nucleic acids is essential for host defence against invading pathogens by inducing antiviral and inflammatory cytokines. cGAS has emerged in recent years as a non-redundant DNA sensor important for detection of many viruses and bacteria. Upon binding to DNA, cGAS synthesises the cyclic dinucleotide 2 0 3 0-cGAMP that binds to the adaptor protein STING and thereby triggers IRF3-and NFjB-dependent transcription. In addition to infection, the pathophysiology of an everincreasing number of sterile inflammatory conditions in humans involves the recognition of DNA through cGAS. Consequently, the cGAS/STING signalling axis has emerged as an attractive target for pharmacological modulation. However, the development of cGAS and STING inhibitors has just begun and a need for specific and effective compounds persists. In this review, we focus on cGAS and explore how its activation by immunostimulatory DNA is regulated by cellular mechanisms, viral immune modulators and small molecules. We further use our knowledge of cGAS modulation by cells and viruses to conceptualise potential new ways of pharmacological cGAS targeting.

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cGAS and CD-NTase enzymes: structure, mechanism, and evolution

Cited by 70 publications

References 69 publications

Structures of diverse poxin cGAMP nucleases reveal a widespread role for cGAS-STING evasion in host–pathogen conflict

Structures of diverse poxin cGAMP nucleases reveal a widespread role for cGAS-STING evasion in host–pathogen conflict

2’3’-cGAMP triggers a STING and NF-κB dependent broad antiviral response in Drosophila

Regulation and inhibition of the DNA sensor cGAS

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