cGAS suppresses genomic instability as a decelerator of replication forks

Abstract

The cyclic GMP-AMP synthase (cGAS), a sensor of cytosolic DNA, is critical for the innate immune response. Here, we show that loss of cGAS in untransformed and cancer cells results in uncontrolled DNA replication, hyperproliferation, and genomic instability. While the majority of cGAS is cytoplasmic, a fraction of cGAS associates with chromatin. cGAS interacts with replication fork proteins in a DNA binding–dependent manner, suggesting that cGAS encounters replication forks in DNA. Independent of cGAMP and STING, cGAS slows replication forks by binding to DNA in the nucleus. In the absence of cGAS, replication forks are accelerated, but fork stability is compromised. Consequently, cGAS-deficient cells are exposed to replication stress and become increasingly sensitive to radiation and chemotherapy. Thus, by acting as a decelerator of DNA replication forks, cGAS controls replication dynamics and suppresses replication-associated DNA damage, suggesting that cGAS is an attractive target for exploiting the genomic instability of cancer cells.

Enhanced cGAS-STING-dependent interferon signaling associated with mutations in ATAD3A

“…In trying to assess the functional effect of the p.(Gly355Asp) and p.(Arg528Trp) substitutions in the context of interferon signaling, we observed that overexpression of ATAD3A (wild-type or mutant) significantly compromised cell survival in THP-1 cells, U2OS cells and primary healthy fibroblasts (data not shown), consistent with previous reports of defects induced by overexpression of wild-type AAA ATPases (Evans et al, 2005;Harel et al, 2016). To circumvent this problem, we expressed these mutations in U2OS cells stably expressing STING and endogenous cGAS (Chen et al, 2020), and treated the cells with the caspase inhibitor Q-VD-OPh so as to block caspase-mediated apoptosis (Rongvaux et al, 2014). In this way we were able to avoid cell death secondary to ATAD3A overexpression, and observed increased ISG expression with both mutations (Fig.…”

STING enhances cell death through regulation of reactive oxygen species and DNA damage

“…The magnitude of this effect following radiation treatment (a reduction by 2-3-fold) is remarkable, predicts significant reduction in DNA damage, and is borne out by measurements of reduced γH2AX foci, comet tail moment, and markers of mitotic catastrophe in STING KO cells. Several studies have implicated components of the cGAS-STING signaling pathway in the control of DNA repair directly but with varying effect on cell survival [49][50][51] . In contrast our data show that rather than a direct effect on DNA repair, STING controls ROS homeostasis thus regulating the susceptibility for subsequent DNA damage.…”

The Trinity of cGAS, TLR9, and ALRs Guardians of the Cellular Galaxy Against Host-Derived Self-DNA

“…These patients also show the altered cGAS distribution and activation in response to the chromatin lacking linker histone. However, cGAS in the nucleus interacts with the replication fork proteins in a DNA-binding manner and slows it down independent of STING to prevent the replication stress ( 84 ). Thus cGAS-deficient cells are highly sensitive to radiation and cancer therapeutics.…”

“…Hence, cGAS targeting may serve as a potential target for anticancer therapies. Thus via acting as a decelerator of DNA replication forks, the nuclear cGAS suppresses replication-associated DNA damage that can efficiently target to exploit genomic instability of cancer cells ( 84 ). In addition to STING-independent genomic stability, the cGAS-dependent activation of STING/TBK1/IRF3 promotes p21 or cyclin-dependent kinase inhibitor (CDKI) in the nucleus reduces micronucleus formation, delays G2/M transition, and maintains chromosomal stability ( 87 ).…”