Dynamic phosphorylation of cGAS by DNA-PKcs and PPP1CC balances DNA repair and innate immunity.

Cyclic GMP-AMP synthase (cGAS) is a DNA sensor that localizes to both the cytosol and the nucleus, with dynamic nucleocytoplasmic shuttling. In the cytosol, it drives innate immune signaling upon detecting misplaced self-DNA or foreign DNA. In the nucleus, cGAS is normally tethered to chromatin and catalytically silent, but upon genotoxic stress it is reactivated and engages in DNA damage repair.How cGAS temporally coordinates these dual functions during genotoxic stress remains unresolved. In this study, we identified a context-dependent phosphorylation timer in cells with detectable nuclear cGAS that balances cGAS effects on immune signaling and DNA repair. In G1 phase, cGAS is rapidly phosphorylated by DNA-PKcs after irradiation. This modification suppresses cGAS catalytic activity and delays downstream immune signaling without affecting non-homologous end joining (NHEJ) repair, thereby prioritizing DNA repair over immune activation. Subsequent dephosphorylation by PPP1CC, occurring 8-12 h later, releases cGAS from damage sites and reactivates the cGAS-STING pathway.In S phase, phosphorylated cGAS selectively blocks homologous recombination(HR) while preserving NHEJ. This prevents pathway competition and favors rapid and efficient repair.Later, PPP1CC-mediated dephosphorylation inhibits NHEJ, restores HR competence, and reactivates cGAS catalytic activity. These findings reveal a spatiotemporal mechanism that couples DNA repair progression to immune activation, suggesting that the phosphorylation status of cGAS may inform the therapeutic timing of combined radiotherapy and immunotherapy.