Assaying estrogenicity by quantitating the expression levels of endogenous estrogen-regulated genes

Scientific evidence suggests that humans and wildlife species may experience adverse health consequences from exposure to environmental chemicals that interact with the endocrine system. Reliable short-term assays are needed to identify hormone-disrupting chemicals. In this study we demonstrate that the estrogenic activity of a chemical can be evaluated by assaying induction or repression of endogenous estrogen-regulated "marker genes" in human breast cancer MCF-7 cells. We included four marker genes in the assay-pS2, transforming growth factor beta 3 (TGF beta 3), monoamine oxidase A, and alpha 1-antichymotrypsin-and we evaluated estrogenic activity for 17 beta-estradiol (E-2), diethylstilbestrol, alpha-zearalanol, nonylphenol, genistein, methoxychlor, endosulphan, o,p-DDE, bisphenol A, dibutylphthalate, 4-hydroxy tamoxifen, and ICI 182.780. All four marker genes responded strongly to the three high-potency estrogens (E-2, diethylstilbestrol, and alpha-zearalanol), whereas the potency of the other chemicals was 10(3)- to 10(6)-fold lower than that of E-2. There were some marker gene-dependent differences in the relative potencies of the tested chemicals. TGF beta 3 was equally sensitive to the three high-potency estrogens, whereas the sensitivig to alpha-zearalanol was approximately 10-fold lower than the sensitivity to E-2 and diethylstilbestrol when assayed with the other three marker genes. The potency of nonylphenol was equal to that of genistein when assayed with pS2 and TGF beta 3, but 10- to 100-fold higher/lower with monoamine oxidase A and alpha 1-antichymotrypsin, respectively. The results are in agreement with results obtained by other methods and suggest that an assay based on endogenous gene expression may offer an attractive alternative to other E-SCREEN methods.