Fig. 4: BRCA1-I15 promotes PARPi resistance.

a BRCA1 and RAD51 foci formation was assessed by immunofluorescence (IF) with or without 10 Gy IR. See Supplementary Fig. 3b for representative images as well as γ-H2AX and 53BP1 controls. b HR repair capacity assessed by DR-GFP assay. **p < 0.01 compared to 293T cells. See Supplementary Fig. 3c−d for representative histograms and summary. c MDA-MB-231 and SNU-251-RR cells were treated with scrambled (Sc), BRCA1 exon 11 (E11) or intron 15 (I15)-targeting siRNA and BRCA1 protein expression assessed by Western blotting. d Cells were treated as in panel (c) and examined by IF for BRCA1 and RAD51 foci post 10 Gy IR. ***p < 0.001 compared to Sc-treated cells. See Supplementary Fig. 3e for representative images. e Cells were treated as in panel (c) and subject to increasing concentrations of rucaparib and colony formation assessed. Data are the mean ± SD of n = 3 biological replicates. Statistical significance was assessed by unpaired, two-tailed t tests.