ER-directed TREX1 limits cGAS activation at micronuclei

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.

Genotoxic stress and viral infection induce transient expression of APOBEC3A and pro-inflammatory genes through two distinct pathways

“…Twenty-four hours after transfection, mCherry-expressing cells were single cell-sorted into 96-well plates. MCF10A IRF3 KO and MCF10A p53 KO cell lines was created as previously described 66 , 84 . For every target, three or more independent clones were generated.…”

Nuclear cGAS: guard or prisoner?

“…One reason for the activation of cGAS by micronuclear chromatin might be that the limited amount of accessible nucleosome acidic patches they contain are insufficient to sequester the whole cytosolic pool of cGAS, allowing free cGAS activation by nearby free chromosomal DNA. In this context, the DNA 3′‐5′ exonuclease TREX1 was found as a critical regulator of cytosolic DNA sensing in chromosomally unstable cells, degrading micronuclear DNA when bound to the endoplasmic reticulum (ER) (Mohr et al , 2021). In contrast to the degradation of micronuclear DNA by ER‐associated TREX1, cytosolic immunostimulatory DNA bound to cGAS forms phase‐separated liquid–liquid droplets that limit its degradation by TREX1 (Zhou et al , 2021).…”

Chromosome length and gene density contribute to micronuclear membrane stability

“…1D), and this could have significant effects on DNA damage and the extent of genome instability. Generation of double-stranded DNA breaks in MN both pre-and postrupture depends on replication initiation (Crasta et al, 2012;Hatch et al, 2013;Umbreit et al, 2020;Zhang et al, 2015), whereas the cytoplasmic nuclease TREX1 (three prime repair exonuclease 1) likely acts on ruptured MN throughout the cell cycle to generate ssDNA (Mohr et al, 2021). Currently, only MN that remain intact until NE disassembly or rupture after initiating DNA replication have been shown to undergo chromothripsis (Ly et al, 2019(Ly et al, , 2016Umbreit et al, 2020;Zhang et al, 2015).…”

“…In contrast, early MN rupture causes whole chromosome aneuploidy in interphase and the next cell cycle. In addition, TREX1 inhibits cGAS-STING activation, suggesting that rupture timing could affect innate immune signaling as well (Harding et al, 2017; Mackenzie et al, 2017; Mohr et al, 2021). How these two pathways of DNA damage, and chromosome-specific differences in transcription, replication timing, and NE assembly interact to determine the consequences of micronucleation and MN rupture remains to be determined.…”