Figure 2

Rac1 inhibition attenuates IR-induced G ₂ /M arrest. (A) Upper panel: MCF-7 cells were incubated for 1 hour with increasing doses of the Rac1 inhibitor NSC23766 and then exposed to 20-Gy IR. After 15-minute incubation at 37°C, Rac1 activity was determined. As a positive control, MCF-7 cells were serum-starved for 24 hours in the medium containing 0.3% fetal bovine serum, treated with 1 μM phorbol 12-myristate 13-acetate for 5 minutes, and analyzed for Rac1 activity (PMA). Lower panel: MCF-7 cells were preincubated for 1 hour with NSC23766 at the indicated doses and treated with/without 20-Gy IR. After 24-hour incubation after IR, the cells were analyzed for DNA content with fluorescence-activated cell sorting (FACS). Graph depicts the percentage of cells with 4N-DNA content and represents the mean ± SD of quadruplicate samples. (B) MCF-7 cells were exposed to IR at the indicated doses in the presence or absence of 100 μM NSC23766. After IR, the cells were incubated for 8 or 24 hours and analyzed for DNA content. Results depict the percentage of cells with 4N-DNA content and represent the mean ± SD of two separate experiments with duplicate samples. (C) Human breast cancer cells (MDA-MB-231, T47D, ZR-75-1) were treated with or without 10-Gy IR in the presence or absence of 100 μM NSC23766, incubated for 24 hours, and analyzed for DNA content. Results depict the percentage of cells with 4N-DNA content and represent the mean ± SD of two sets of experiments in duplicate samples.