fig5

Figure 5. Deprivation of estrogen sensitizes ER-positive cells to DNA damage. (A, B) MCF7 cells were deprived of E2 for 72 h. E2 (+ E2) or EtOH (- E2) was added to cells for 24 h, and then the indicated amounts of the DNA-damaging agent Neocarzinostatin (NCS) were added. Ten days after seeding, the cells were stained with crystal violet and colonies of ≥ 50 cells were counted. (A) Average number of colonies obtained from cells not treated with NCS. (B) Clonogenic survival assay, analyzing the ratio of colonies compared with treatment control. The results from three experiments are shown. *A significant change compared to control; P-value < 0.05. (C) A model depicting the interplay among estrogen, HRR factors, and DNA damage in ER-positive cells. In E2-deprived cells, there is a basal level of mRNA encoding HRR factors. Upon supplementation of E2, the level of these mRNAs is elevated. Induction of DNA damage in E2-cells deprived cells also results in augmentation of mRNA levels of HRR genes. On the contrary, induction of DNA damage in cells that were grown in the presence of E2 did not result in increased levels of HRR genes mRNAs. HRR: Homologous recombination repair.