Metabolic activation of 17beta-estradiol (E2) to
catechols and
quinones together with lack of deactivation constitute risk factors in human breast
carcinogenesis. E2-catchols are generated by
cytochrome P450-dependent
monooxygenases (CYPs). Deactivation of E2, E2-catechols, and E2-quinones is mediated by
UDP-glucuronosyltransferase (UGT),
sulfotransferase (SULT),
catechol-O-methyltransferase (COMT),
glutathione-S-transferase (GST), and
NADPH-
quinone-
oxidoreductase (QR)
isozymes, respectively. The aim of the present study was to quantify
mRNA levels of E2-metabolizing
isozymes expressed in MCF-7 cells cultured in the presence/absence of
steroids by reverse transcription/competitive PCR in relation to the housekeeping gene
hypoxanthine-guanine phosphoribosyltransferase and compare them with expression levels in normal human mammary gland (MG) and liver tissue.
CYP1A1, 1B1, SULT1A1, 1A2, membrane-bound and soluble COMT, GSTT1, QR1, and UGT2B7 were detected in both tissues and MCF-7 cells; however, most
enzymes were expressed at least tenfold higher in liver. Yet, CYP1B1 was expressed as high in breast as in liver and UGTs were not detected in MCF-7 cells cultured with
steroids. MCF-7 cells cultured
steroid-free additionally expressed
CYP1A2 as well as UGT1A4, 1A8, and 1A9. Normal human liver but not MG expressed
CYP1A2, 3A4, UGT1A1, 1A3, 1A4, 1A9, and SULT2A1.
UGT1A8 was only detected in MCF7 cells but was not found in human liver. Thus, our study provides a comprehensive overview of expression levels of E2-metabolizing
enzymes in a popular in vitro model and in human tissues, which will contribute to the interpretation of in vitro studies concerning the activation/deactivation of E2.