A genome-wide inducible CRISPR screen to identify novel PARPi resistance genes

Proper repair of DNA damage lesions is essential to maintaining genome integrity and preventing the development of a multitude of human diseases including cancer. Increasing evidence suggests the importance of the nuclear envelope in the spatial regulation of DNA repair, although both the players and mechanisms of such regulatory processes remain poorly defined. Through a genome-wide synthetic viability screen for PARP inhibitor (PARPi) resistance using an inducible CRISPR/Cas9 platform and BRCA1-deficient breast cancer cells, we identified a transmembrane nuclease (renamed NUMEN) that could facilitate compartmentalized and NHEJ-dependent repair of DNA double-strand breaks at the nuclear periphery. Collectively, our data demonstrate that NUMEN generates short 5' overhangs through its endonuclease and 3' to 5' exonuclease activities, promotes the repair of DNA lesions including heterochromatic LAD breaks as well as deprotected telomeres, and functions as a downstream effector of DNA-PKcs. These findings underline NUMEN's role as a key player in DNA repair pathway choice and genome stability maintenance and have implications for ongoing research into the development and treatment of genome instability disorders and diseases.