Cyclic GMP-AMP Is an Endogenous Second Messenger in Innate Immune Signaling by Cytosolic DNA

Abstract

Cytosolic DNA induces type-I interferons and other cytokines that are important for antimicrobial defense but can also result in autoimmunity. This DNA signaling pathway requires the adaptor protein STING and the transcription factor IRF3, but the mechanism of DNA sensing is unclear. Here we showed that mammalian cytosolic extracts synthesized cyclic-GMP-AMP (cGAMP) in vitro from ATP and GTP in the presence of DNA but not RNA. DNA transfection or DNA virus infection of mammalian cells also triggered cGAMP production. cGAMP bound to STING, leading to the activation of IRF3 and induction of interferon-β. Thus, cGAMP represents the first cyclic di-nucleotide in metazoa and it functions as an endogenous second messenger that triggers interferon production in response to cytosolic DNA.

Cutting Edge: Antimalarial Drugs Inhibit IFN-β Production through Blockade of Cyclic GMP-AMP Synthase–DNA Interaction

“…As demonstrated previously, cGAS is the key cytosolic DNA sensor required for IFN-b production in THP1 cells in response to DNA (12,15). Therefore, we transfected THP1 cells with dsDNA in the presence or absence of different AMDs and quantified IFN-b expression by quantitative PCR.…”

“…Following binding to dsDNA, cGAS undergoes a conformational change, revealing a catalytic active site that synthesizes the cyclic dinucleotide, cyclic dinucleotide GMP-AMP (cGAMP) (14). cGAMP binds to the adapter protein, stimulator of IFN genes (STING), which triggers activation of TANK-binding kinase 1 and phosphorylation of IFN regulatory factor 3, with resulting transcription of IFN-b (12,15).…”

Cellular and molecular regulation of innate inflammatory responses

“…RIG-I 11 and melanoma differentiation-associated protein 5 (MDA5) 12 can recognize viral dsRNA and recruit the CARD containing adaptor protein MAVS (also known as IPS-1, CARDIF or VISA), leading to IRF activation and the production of type I IFN. In addition to RLRs, a group of cytosolic DNA sensors such as cyclic GMP-AMP synthase (cGAS), [13][14][15] absent in melanoma 2 (AIM2), 16,17 DDX41, 18,19 Rad50, 20,21 LRRFIP1, 22 DNA-dependent activator of IRFs (DAI), 23 as well as various RNA sensors such as IFN-induced protein with tetratricopeptide repeats 1 (IFIT1) 24 also play potent roles in inducing antiviral immune response, respectively via the adaptor protein stimulator of interferon genes (STING, also known as MITA, ERIS or MPYS) or the MAVS pathway. cGAS, which was previously thought to recognize cytoplasmic dsDNA over 40 bp in a sequence-independent manner, is recently shown to recognize unpaired guanosines flanking short (12-20 bp) dsDNA (Y-form DNA) found in human immunodeficiency virus type 1 to induce type I IFN production.…”

TREX1 Deficiency Triggers Cell-Autonomous Immunity in a cGAS-Dependent Manner

“…Intracellular dsDNA arising during viral or bacterial infection constitutes a very potent danger signal that stimulates innate immune responses characterized by the production of proinflammatory cytokines and type I IFNs (1). Cyclic GMP-AMP synthase (cGAS) has been identified as a cytosolic DNA receptor responsible for the induction of an antiviral and proinflammatory gene expression profile (2)(3)(4). Upon dsDNA binding, cGAS catalyzes the production of the second messenger molecule cGAMP(29-59), a unique cyclic dinucleotide molecule containing one 29-59 phosphodiester linkage in addition to a canonical 39-59 linkage (5)(6)(7)(8).…”