Small cytosolic dsDNAs repress cGAS activation and induce autophagy

Cyclic GMP-AMP (cGAMP) synthase (cGAS), a major cytosolic DNA sensor, activates innate immune responses by producing cGAMP, which activates stimulator of interferon genes (STING)1. Cytosolic DNA induces autophagy in a cGAS-dependent manner to avoid persistent immune stimulation. Although dsDNAs 45 bp 2-4. However, whether cytosolic dsDNAs < 45 bp exist in mammalian cells remains unclear. Here, we identified a class of small cytosolic DNAs (scDNAs) of [~]20-40 bp in human and mouse cell lines. scDNAs competed with herring testis DNA (HT-DNA, [~]200-1500 bp) for binding to cGAS, and repressing HT-DNA-induced cGAS activation and the associated interferon {beta} (IFN{beta}) production. Moreover, scDNAs promoted cGAS and Beclin-1 interaction, triggering the release of Rubicon, a negative regulator of phosphatidylinositol 3-kinase class III (PI3KC3)5,6, from the Beclin-1-PI3KC3 complex, activating PI3KC3 and inducing autophagy. DNA damage decreased and autophagy inducers increased scDNA levels. scDNA transfection or autophagy induction attenuated DNA damage-induced cGAS-STING activation and IFN{beta} expression. Thus, scDNAs acted as molecular brakes of cGAS activation, preventing excessive inflammatory cytokine production following DNA damage. Our findings lay foundations for understanding the physiological and pathological functions of scDNAs.