As the major DNA sensor that activates the STING-TBK1 signaling cascade, cGAS is mainly present in the cytosol. A number of recent reports have indicated that cGAS also plays critical roles in the nucleus. Our previous work demonstrated for the first time that cGAS is translocated to the nucleus upon the occurrence of DNA damage and inhibits homologous recombination (HR), one of the two major pathways of DNA double strand break (DSB) repair. However, whether nuclear cGAS regulates the other DSB repair pathway, nonhomologous end joining (NHEJ), which can be further divided into the less error-prone canonical NHEJ (c-NHEJ) and more mutagenic alternative NHEJ (alt-NHEJ) subpathways, has not been characterized. Here, we demonstrated that cGAS tipped the balance of the two NHEJ subpathways toward c-NHEJ. Mechanistically, the cGAS-Ku80 complex enhanced the interaction between DNA-PKcs and the deubiquitinase USP7 to improve DNA-PKcs protein stability, thereby promoting c-NHEJ. In contrast, the cGAS-Ku80 complex suppressed alt-NHEJ by directly binding to the promoter of Polθ to suppress its transcription. Together, these findings reveal a novel function of nuclear cGAS in regulating DSB repair, suggesting that the presence of cGAS in the nucleus is also important in the maintenance of genome integrity.

作为激活 STING-TBK1 信号级联的主要 DNA 传感器，cGAS 主要存在于细胞质中。最近的一些报告表明，cGAS 在细胞核中也发挥着关键作用。我们之前的工作首次证明，cGAS 在 DNA 损伤发生时易位到细胞核并抑制同源重组（HR），这是 DNA 双链断裂（DSB）修复的两个主要途径之一。然而，核cGAS是否调节另一个DSB修复途径，即非同源末端连接（NHEJ），它可以进一步分为不易出错的规范NHEJ（c-NHEJ）和更具诱变性的替代NHEJ（alt-NHEJ）子途径，目前尚不清楚。没有被表征。在这里，我们证明 cGAS 使两条 NHEJ 子通路的平衡向 c-NHEJ 倾斜。从机制上讲，cGAS-Ku80复合物增强了DNA-PKcs和去泛素酶USP7之间的相互作用，从而提高了DNA-PKcs蛋白的稳定性，从而促进了c-NHEJ。相比之下，cGAS-Ku80复合物通过直接结合到Polθ的启动子来抑制其转录，从而抑制alt-NHEJ。总之，这些发现揭示了核 cGAS 在调节 DSB 修复中的新功能，表明核中 cGAS 的存在对于维持基因组完整性也很重要。