Validation of a new yeast-based reporter assay consisting of human estrogen receptors alpha/beta and coactivator SRC-1: application for detection of estrogenic activity in environmental samples.

Endocrine disruptors are exogenous substances that act like hormones in the endocrine system and disrupt the physiologic function of endogenous hormones. In the present study, we established reporter yeast strains (Saccharomyces cerevisiae) expressing human estrogen receptors, ERL alpha or ER beta. These strains contain a reporter plasmid carrying an estrogen responsive element (ERE) upstream of the beta-galactosiclase gene, and a plasmid expressing a steroid receptor coactivator, SRC-1e. Using these reporter strains, we demonstrated dose-dependent estrogenic activities of different categories of ligands, a natural hormone, 17 beta-estradiol (E2); a synthetic drug, diethylstilbestrol (DES); phytoestrogens, genistein, daizein and emodin; and an environmental endocrine disrupter, bisphenol A. EC50 values of E2 for ER alpha and ER beta are 5.31 x 10(-10) and 5.85 x 10(-10) M, respectively. We also demonstrated that these yeasts were applicable for measuring estrogenic activities of environmental water samples. Most downstream sites of a river showed similar activity in both ER alpha and ER beta assays. These yeast strains are useful and convenient for detecting and comparing the estrogenic ligand activities of environmental samples in response to ER alpha and ER beta. (C) 2009 Wiley Periodicals, Inc. Environ Toxicol 24: 513-521, 2009.