Pin1 and BRCA1 colocalize in DNA damage repair foci and Pin1 ablation disrupts HR. A, BRCA1-proficient MCF10A cells were irradiated (5 Gy) and fixed 2 hours later for immunofluorescence with Pin1 and BRCA1. B, Quantification of data in A. Bars correspond to means ± SD of experimental triplicates. C and D, MCF10A cells were transduced with either shRNA control or shPin1, irradiated followed by immunostaining for BRCA1 and γH2AX 2 hours later. BRCA1 and γH2AX foci after irradiation in the presence (C) or absence of Pin1 (D). E, Immunoblotting of Pin1. F, Quantification of γH2AX and BRCA1 foci. Bars represent means ± SD of experimental triplicate experiments. Five cells were counted per experiment. G, Silencing Pin1 disrupts HR as assessed by short tract conversion in ES cells of the BRCA1f/Δmut genotype (left), similar to what is seen in ES cells of the BRCA1mut/Δmut genotype (right). Bars, means ± SD of experimental triplicates. *, P < 0.05.