Hygromycin b selection

Mouse embryonic fibroblasts proficient for PARP-1 (WT), or deficient for PARP-1 (PARP-1 (−/−)) were cultured in Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% fetal bovine serum (FBS) (Hyclone-ThermoFisher Scientific, Ottawa, Canada). U2OS, HeLa, and HeLa PARP-1 SilenciX control (Tebu-bio) were cultured in DMEM with 10% FBS. PARP-1 HeLa SilenciX is a cell line engineered to stably knock down PARP-1 via RNA interference. Cells were maintained under hygromycin B selection (250 μg/mL; Invitrogen). U2OS-PARP-1 (−/−) cells were cultured in DMEM supplemented with 10% FBS and 2 μg/mL puromycin. U2OS cells stably expressing GFP-RPA2 were maintained in DMEM through continuous G418 selection (500 μg/mL; Invitrogen). The ER-AsiSI U2OS cell line was maintained in phenol red-free DMEM media supplemented with 10% charcoal-stripped FBS (Sigma) and 1 μg/mL puromycin. In order to induce DNA damage, AsiS1 U2OS cells were treated with 300 nM 4-OHT for 3 h. U2OS cells stably expressing an mCherry-LacI-FokI construct containing an integrated reporter transgene were maintained in DMEM by puromycin (2 μg/mL) and hygromycin B (100 μg/mL) selection. To induce DNA DSBs, cell lines were treated with both 0.5 mM Shield-1 and 1 mM 4-OHT for 1 h. Human embryonic kidney 293 cells (HEK 293), HEK 293T, or HEK 293T-PARP-1 (−/−) cells were cultured in DMEM supplemented with 10% FBS.