Catecholestrogens induce oxidative stress and malignant transformation in human endometrial glandular cells: Protective effect of catechol-O- methyltransferase

Prolonged exposure to unopposed estrogens is a major risk factor for the development of endometrial cancer. Oxidative metabolism of estradiol (E ₂) into the catecholestrogens (CEs), 4-hydroxyestradiol (4-OHE ₂) and 2-hydroxyestradiol (2-OHE₂), may play an important role in estrogen carcinogenicity. CEs can be oxidized to the corresponding ortho-quinone derivatives with concomitant formation of the reactive oxygen species (ROS). Catechol-O-methyltransferase (COMT) is the major enzyme involved in the detoxification of CEs in extrahepatic tissues. We investigated the potential of E₂, 2-OHE₂ and 4-OHE₂ to induce microsatellite instability (MSI) and neoplastic transformation of immortalized human endometrial glandular (EM) cells. We also investigated the functional significance of COMT gene expression on modulating the effects of E₂ and CEs in EM cells. Our data indicated that E₂ and 4-OHE₂ induce MSI, ROS and neoplastic transformation in EM cells. The capacity of E₂ and its catechol metabolites to induce MSI, ROS and neoplastic transformation in EM cells is ranked as follows: 4-OHE₂ > E ₂ > 2-OHE₂. Knockdown of COMT expression in EM cells resulted in increased estrogenic milieu and increased estrogen-induced cell proliferation. More importantly, knockdown of COMT increased the propensity of E₂ or CEs to induce ROS, MSI and neoplastic transformation of EM cells. In contrast, overexpression of COMT in EM cells significantly reduced the cellular estrogenic milieu and protected against E₂- or CEs-induced, ROS, MSI and neoplastic transformation. The capacity of E₂ or CEs to induce neoplastic transformation of human endometrial glandular cells in vitro may suggest that E₂-induced endometrial cancer is mediated by its metabolism into CEs. Our study clearly indicates that COMT gene expression plays a critical role in modulating the hormonal and carcinogenic effects of E ₂ and CEs and, consequently, modifies the risk for E ₂-induced endometrial cancer. To the best of our knowledge, this is the first study to (i) demonstrate the potential capacity of estrogen and its catechol metabolites to induce neoplastic transformation of immortalized human endometrial glandular cells; and (ii) illustrate the important role of COMT gene expression in protecting against E₂-induced endometrial cancer.