Phytoestrogens Modulate the Expression of 17α-Estradiol Metabolizing Enzymes in Cultured MCF-7 Cells

Abstract

The activation of 17beta-estradiol (E2) to 2-hydroxyestradiol (2-HO-E2), the more genotoxic 4-hydroxyestradiol (4-HO-E2), and the oxidation to the respective quinones constitutes a risk factor in hormonal carcinogenesis. 2-HO-E2 is formed by cytochrome P450 CYP1A1, and 4-HO-E2 is formed by CYP1B1. Both are detoxified by catechol-O-methyltransferase (COMT), whereas their quinones are inactivated by NADPH-quinone-oxidoreductase (QR). Since the soy isoflavones genistein (GEN) and daidzein (DAI) are widely consumed due to their putative protective function in breast carcinogenesis, we examined the influence of E2, GEN, and DAI on CYP1A1/1B1, COMT, and QR expression in MCF-7 cells by reverse transcription/competitive PCR. CYP1A1 and COMT enzyme activity were determined using ethoxyresorufin and quercetin as substrates. Furthermore, estrogen receptor (ER)-regulated cell proliferation was determined by E-screen. E2, GEN, and DAI inhibited the expression of CYP1A1, COMT, and QR. The maximum effect (reduction by 40-80%, depending on the gene product and compound) was obtained at 100 pM E2, 1 microM GEN, and 10 microM DAI, which also induced the most pronounced cell proliferation in the E-screen. In contrast, expression of CYP1B1 was only slightly affected. CYP1A1 and COMT mRNA levels correlated with enzyme activities. The ER antagonist ICI 182,780 reversed the E2- and isoflavone-mediated effects. Thus, GEN and DAI at estrogen-active concentrations stimulate the formation of the more E2 genotoxic metabolites and inhibit the detoxification of catechol and quinone estrogens in estrogen-responsive tumor cells.

Cadmium modulates expression of aryl hydrocarbon receptor-associated genes in rat uterus by interaction with the estrogen receptor

“…This suggests an ER-mediated mechanism and cross-talk between the ER and AhR pathways. A down-regulation of CYP1A1 enzyme activity and mRNA expression by E 2 has been also demonstrated in MCF-7 breast cancer cells (Wagner et al 2008) and was antagonized by the anti-estrogen fulvestrant (ICI 182.780).…”

“…For instance, estrogenic concentrations of E 2 and the phytoestrogens daidzein and genistein decreased CYP1A1 expression and activity in MCF-7 cells, and these effects were reversed by an ER antagonist (Wagner et al 2008). In the human endometrium, AhR protein levels were found to vary within the menstrual cycle and peak at ovulation (Küchenhoff et al 1999) suggesting that AhR expression is modulated by sex steroids.…”

Gene Expression Profiling of Breast Cancer Cell Lines in Response to Soy Isoflavones Using a Pangenomic Microarray Approach

“…However, in a recent study, Wagner et al (2008) examined the influence of E 2 , genistein, and daidzein on CYP1A1=1B1, COMT, and QR expression in MCF-7 cells by reverse-transcription polymerase chain reaction (PCR). They showed an insignificant change in CYP1B1 mRNA levels.…”

Dietary intake of isoflavones and breast cancer risk by estrogen and progesterone receptor status

“…Soy isoflavones can act as an estrogenic agonist or antagonist depending on the estrogen concentration [11] and reduce levels of ovarian steroids in normal women [12]. Some experimental data even suggest that soy constituents can be estrogenic and potentially risk enhancing [27], and that soy increased the expression of alpha estrogen receptors in the rat mammary gland [28].…”