TOXI 37 |
| Estrogen sulfotransferase (SULT1E1) sulfonates estrogens to biologically inactive estrogen-sulfates and represents an estrogen-inactivation pathway. A number of pharmaceuticals and environmental contaminants which are known inhibitors of SULT1E1 may dysregulate this estrogen-inactivation pathway and cause potential estradiol-dependent proliferation, genotoxicity, or aneuploidy. The aim of this research is to understand the effect of estrogen sulfotransferase inhibitors on estradiol metabolism in human mammary epithelial cells. Our hypothesis is that SULT1E1 is responsible for the sulfonation of estradiol in human mammary epithelial cells, and that reduced estradiol-sulfonation due to SULT1E1 inhibition is a mechanism for increasing estrogen-dependent toxicity. We used both transformed (MCF-7) and non-transformed (human mammary epithelial, HME) cells as models. We found that cultured HME cells efficiently metabolized estradiol to estradiol-3-sulfate, and that this sulfonation was effectively inhibited by addition of SULT1E1 inhibitor to the culture media at concentration similar to the Ki determined with recombinant SULT1E1. It is noteworthy that while this inhibition of estradiol sulfonation initially increased estradiol concentration in HME cultures, the increase was not sustained. Rather, estradiol was subsequently converted to estrone, resulting in higher estrone concentration in HME culture. We found that cultured MCF-7 cells (ER?+) were capable of limited estradiol sulfonation, yet even this limited sulfonation was inhibited in the presence of SULT1E1 inhibitor. A well-known characteristic of MCF-7 cells is that they have about 2-fold increase in proliferation rate in the presence of exogenous estradiol (10-12 – 10-6 M, culture media). We found that, without adding exogenous estradiol, SULT1E1 inhibitor was able to mimic the 2-fold MCF-7 cell proliferation effect in a dose-dependent manner. This MCF-7 cell proliferation is consistent with the conclusion that reduced estradiol-sulfonation due to SULT1E1 inhibition is a mechanism for increasing estrogen-dependent toxicity. Further studies are ongoing. (Supported by NIH/NCRR grant #P20RR016457 and by NSF/SBE grant #0245039.) |
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Poster Session and Awards
6:00 PM-10:00 PM, Tuesday, August 21, 2007 BCEC -- 204 A/B, Poster
Division of Chemical Toxicology |