FIGNL1 inhibits homologous recombination in BRCA2 deficient cells by dissociating RAD51 filaments

Homologous recombination (HR) deficiency upon BRCA2 loss arises from defects in the formation of RAD51 nucleoprotein filaments. Here, we demonstrate that loss of the anti-recombinase FIGNL1 retains RAD51 loading at DNA double-stranded breaks (DSBs) in BRCA2-deficient cells, leading to genome stability, HR proficiency, and viability of BRCA2-deficient mouse embryonic stem cells. Mechanistically, we directly show that strand invasion and subsequent HR defects upon BRCA2 loss primarily arises from the unrestricted removal of RAD51 from DSB sites by FIGNL1, rather than from defective RAD51 loading. Furthermore, we identify that the MMS22L-TONSL complex interacts with FIGNL1 and is critical for HR in BRCA2/FIGNL1 double-deficient cells. These findings identify a pathway for tightly regulating RAD51 activity to promote efficient HR, offering insights into mechanisms of chemoresistance in BRCA2-deficient tumors.