ER-Directed TREX1 Limits cGAS Recognition of Micronuclei

TLDR: A novel method for the purification of micronuclei and live-cell imaging is used to show that the ER-associated nuclease TREX1 inhibits cGAS sensing of micronsuclei by stably associating with and degrading micronuclear DNA upon micronsuclear envelope rupture, establishing ER-directed resection of micRONuclear DNA by TREX 1 as a critical regulator of cytosolic DNA sensing in chromosomally unstable cells.

Abstract: Chromosomal instability in cancer results in the formation of nuclear aberrations termed micronuclei. Spontaneous loss of micronuclear envelope integrity exposes DNA to the cytoplasm, leading to chromosome fragmentation and innate immune activation. Despite connections to cancer genome evolution and anti-tumor immunity, the mechanisms underlying damage and immune sensing of micronuclear DNA are poorly understood. Here, we use a novel method for the purification of micronuclei and live-cell imaging to show that the ER-associated nuclease TREX1 inhibits cGAS sensing of micronuclei by stably associating with and degrading micronuclear DNA upon micronuclear envelope rupture. We identify a TREX1 mutation, previously associated with autoimmune disease, that untethers TREX1 from the ER, disrupts TREX1 localization to micronuclei, alleviates micronuclear DNA damage, and enhances cGAS recognition of micronuclei. Together, these results establish ER-directed resection of micronuclear DNA by TREX1 as a critical regulator of cytosolic DNA sensing in chromosomally unstable cells and provide a mechanistic basis for the importance of TREX1 ER-tethering in preventing autoimmunity.