Rapid yeast estrogen bioassays stably expressing human estrogen receptors α and β, and green fluorescent protein:: a comparison of different compounds with both receptor types

Previously, we described the construction of a rapid yeast bioassay stably expressing human estrogen receptor alpha (hERalpha) and yeast enhanced green fluorescent protein (yEGFP) in response to estrogens. In the present study, the properties of this assay were further studied by testing a series of estrogenic compounds. Furthermore, a similar assay was developed based on the stable expression of human estrogen receptor beta (hERbeta). When exposed to 17beta-estradiol, the maximum transcriptional activity of the ERbeta cytosensor was only about 40% of the activity observed with ERalpha, but the concentration where half-maximal activation is reached (EC50), was about five times lower. The relative estrogenic potencies (REP), defined as the ratio between the EC50 of 17beta-estradiol and the EC50 of the compound, of the synthetic hormones dienestrol, hexestrol and especially mestranol were higher with ERalpha, while DES was slightly more potent with ERbeta. The gestagens progesterone and medroxyprogesterone- acetate showed no response, whereas the androgen testosterone showed a very weak response. The anabolic agent, 19-nortestosterone showed a clear dose-related response with estrogen receptor alpha but not beta. The phytoestrogens coumestrol, genistein, genistin, daidzein, daidzin and naringenin were relatively more potent with ERP. Ranking of the estrogenic potency with ERalpha was: 17beta-estradiol much greater than 8-prenylnaringenin > coumestrol > zearalenone much greater than genistein much greater than genistin > naringenin. The ranking with the ERp was: 17beta-estradiol much greater than cournestrol > genistein > zearalenone > 8-prenylnaringen much greater than daidzein > naringenin > genistin much greater than daidzin. The hop estrogen 8-prenylnaringenin is relatively more potent with ERalpha. These data show that the newly developed bioassays are valuable tools for the rapid and high-throughput screening for estrogenic activity. (C) 2004 Elsevier Ltd. All rights reserved.