2012 Volume 34 Issue 3 Pages 129-135
17β-Estradiol (E2) is crucial for various physiological functions, such as in the development of the uterus and the mammary gland. However, prolonged exposure to E2 is a risk factor for breast cancer. E2 is metabolized to carcinogenic 4-hydroxyestradiol (4-OHE2) and non-carcinogenic 2-hydroxyestradiol (2-OHE2) by CYP1A1 and CYP1B1 in the breast tissue, respectively. These two catechol estrogens are converted to methylated metabolites by catechol-O-methyltransferase (COMT). 4-OHE2 has been reported to be further oxidized to quinone intermediates which react with purine bases in DNA to form depurinating adducts, which generate highly mutagenic apurinic (AP) sites. Recently, phosphorylation of histone H2AX (γ-H2AX) has emerged as a sensitive marker for not only DNA double-strand breaks but also various types of DNA damage. 4-OHE2-induced γ-H2AX in MCF-7 cells has never been reported yet. In this study, we investigated whether 4-OHE2 induces γ-H2AX in response to DNA damage in the presence or absence of Ro 41-0960, an inhibitor of COMT, in human breast cancer MCF-7 cells. AP sites and γ-H2AX were induced 1-2 h after treatment with 4-OHE2 and Ro 41-0960. The generation of intracellular reactive oxygen species (ROS) was also observed, as determined by 2′-7′-dichlorodihydrofluorescein diacetate fluorescence. By comparison, 2-OHE2 and Ro 41-0960 had no effect on AP sites, γ-H2AX or the generation of ROS. KU-55933, an inhibitor of ataxia telangiectasia mutated (ATM), decreased the formation of γ-H2AX in conjunction with 4-OHE2 and Ro 41-0960. These results demonstrate that 4-OHE2, in the presence of Ro 41-0960, induces ATM-dependent γ-H2AX in MCF-7 cells.