cGAS is activated by DNA in a length‐dependent manner

Abstract

Cytosolic DNA stimulates innate immune responses, including type I interferons (IFN), which have antiviral and immunomodulatory activities. Cyclic GMP-AMP synthase (cGAS) recognizes cytoplasmic DNA and signals via STING to induce IFN production. Despite the importance of DNA in innate immunity, the nature of the DNA that stimulates IFN production is not well described. Using low DNA concentrations, we show that dsDNA induces IFN in a length-dependent manner. This is observed over a wide length-span of DNA, ranging from the minimal stimulatory length to several kilobases, and is fully dependent on cGAS irrespective of DNA length. Importantly, studies reveal that long DNA activates recombinant human cGAS more efficiently than short DNA, showing that length-dependent DNA recognition is an intrinsic property of cGAS independent of accessory proteins. Collectively, this work identifies long DNA as the molecular entity stimulating the cGAS pathway upon cytosolic DNA challenge such as viral infections.

STING pathway agonism as a cancer therapeutic

“…cGAS binding to DNA does not depend on the DNA sequence but does have a minimum length requirement for optimal activation. This ranges from 45 to 70 base pairs at 1 mg/mL to 800‐2000 bp at lower, more physiological DNA concentrations . The binding of cGAS to DNA is cooperative in that when a cGAS dimer binds two strands of DNA, it orients them in such a way that favors binding of subsequent cGAS dimers.…”

“…This ranges from 45 to 70 base pairs at 1 mg/mL to 800-2000 bp at lower, more physiological DNA concentrations. 33 The binding of cGAS to DNA is cooperative in that when a cGAS dimer binds two strands of DNA, it orients them in such a way that favors binding of subsequent cGAS dimers. The resulting structure resembles a ladder, with cGAS dimers forming rungs between adjacent DNA strands.…”

Innate immunity in allergy

“…Recent studies have revealed the existence of a new intracellular DNA sensing system. Cyclic GMP‐AMP synthase (cGAS), a member of nucleotidyltransferase family, binds dsDNA in a sequence‐independent manner but is activated in a length‐dependent manner (longer than 94‐bp DNA) . cGAS undergoes a conformational change of its catalytic center and then produces the cyclic GMP‐AMP (cGAMP) from ATP and GTP (Figure ) .…”

Length does matter for cGAS

“…Finally, the work by Luecke et al (2017) underlines the need for a better definition of the antagonistic activities of cytoplasmic DNA nucleases on cGAS sensing of ssDNA, dsDNA and DNA:RNA hybrids in homeostasis and during infections (Fig 1). (1) Different types of DNAs are presented, ordered according to the predicted sensitivity of cGAS to these molecules [1,3,8] (note: a concurrent analysis of these DNA forms has not been performed to date). Short dsDNAs are~45-70 bp long [1], with the 45-bp ISD (interferon stimulatory DNA) being the prototypical sequence used as cGAS ligand (although not representing a physiological DNA produced by the cell).…”

“…(1) Different types of DNAs are presented, ordered according to the predicted sensitivity of cGAS to these molecules [1,3,8] (note: a concurrent analysis of these DNA forms has not been performed to date). Short dsDNAs are~45-70 bp long [1], with the 45-bp ISD (interferon stimulatory DNA) being the prototypical sequence used as cGAS ligand (although not representing a physiological DNA produced by the cell). (2) Endogenous nucleases limit the cytoplasmic accumulation of DNAs from (1) (note: the type of endogenous DNA processed by SAMHD1 is unknown) [2,6,9,10].…”