Prolonged exposure to high level of
estrogen is a known risk factor for breast
carcinogenesis. In cells,
estrogens, in particular
estrone (E1) and
17 beta-estradiol (E2), can be converted to
catecholestrogens (CEs) which may be oxidized to form CE-semiquinones and CE-
quinones that are capable of binding to
DNA to induce mutations, followed by
carcinogenesis. Whether the body is equipped with protective mechanisms against potentially harmful CEs, therefore, is an important issue. The present study was designed to examine the role of sulfation in the metabolism of CEs. MCF-7
breast cancer cells and MCF 10A human mammary epithelial cells were metabolically labeled with [35S]
sulfate in the presence of individual CEs. Analysis of the labeling media showed the generation and release of exclusively [35S]sulfated 2-methoxy-E1 or [35S]sulfated 2- or 4-methoxy-E2 by cells labeled in the presence of 2-OH-E1 or 2- or 4-OH-E2. Whereas both [35S]sulfated 4-methoxy-E1 and [35S]sulfated 4-OH-E1 were detected in the labeling media of cells labeled in the presence of 4-OH-E1. These results indicated a concerted action of
catechol-O-methyltransferase (COMT) and the cytosolic
sulfotransferase (SULT)
enzyme(s) in the metabolism of CEs. Enzymatic assays revealed that, five (SULT1A1, SULT1A2,
SULT1A3, SULT1C4, and SULT1E1) of eleven known human SULTs tested could use CEs and methoxyestrogens (MEs) as substrates, with SULT1E1 displaying the strongest sulfating activity.