Hypoxia decreases homologous recombination independent of PARP activity. (A) RAD51 protein expression is decreased in RKO cells following 16 h × 0.02% O2 and remains suppressed for at least after 8 h of reoxygenation with or without ABT-888. (B) RAD51 protein expression is decreased in H1299, DU145, RKO, HCT116, and MCF7 cancer cells as well as HIF-1α-isogenic MEFs following 72 h × 0.2% O2 with or without ABT-888. (C) Functional HR (as assessed by the DR-GFP assay) is decreased following 72 h × 0.2% O2 but is unaffected by ABT-888 in H1299 cells. Representative dot plots are shown. Columns, mean of 3 experiments; bars, SE; *, P<0.05.