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Aberrant replication causes cells lacking BRCA2 to enter mitosis with under-replicated DNA, which activates a repair mechanism known as mitotic DNA synthesis (MiDAS). Here, we identify genome-wide the sites where MiDAS reactions occur when BRCA2 is abrogated. High-resolution profiling revealed that these sites are different from MiDAS at aphidicolin-induced common fragile sites in that they map to genomic regions replicating in the early S-phase, which are close to early-firing replication origins, are highly transcribed, and display R-loop-forming potential. Both transcription inhibition in early S-phase and RNaseH1 overexpression reduced MiDAS in BRCA2-deficient cells, indicating that transcription-replication conflicts (TRCs) and R-loops are the source of MiDAS. Importantly, the MiDAS sites identified in BRCA2-deficient cells also represent hotspots for genomic rearrangements in BRCA2-mutated breast tumors. Thus, our work provides a mechanism for how tumor-predisposing BRCA2 inactivation links transcription-induced DNA damage with mitotic DNA repair to fuel the genomic instability characteristic of cancer cells.

Original publication

DOI

10.1016/j.molcel.2022.07.011

Type

Journal article

Journal

Mol Cell

Publication Date

15/09/2022

Volume

82

Pages

3382 - 3397.e7

Keywords

BRCA2, MiDAS, R-loops, TRCs, genome stability, mitotic DNA synthesis, transcription-replication conflicts, Aphidicolin, BRCA2 Protein, Chromosome Fragile Sites, DNA, DNA Damage, DNA Replication, Genomic Instability, Humans, Mitosis