Differential Responses of Various Pharmaceuticals to Human Estrogen Receptors α and β in Newly-constructed Yeast Reporter Assays

We examined the agonistic and antagonistic activities of three categories of pharmaceuticals, including selective estrogen receptor modulators (SERM), tamoxifen (Tam), raloxifene (Ral) and clomiphene citrate (CC); a “pure” ER antagonist, ICI 182,780 (ICI); and a subtype (ERα)-selective agonist, propyl pyrazole triol (PPT), using our newly established reporter yeast strains (Saccharomyces cerevisiae), which express human ERα or ERα. These strains also contain a reporter plasmid carrying one copy of estrogen responsive element (ERE) upstream of the α-galactosidase gene, and a plasmid expressing a steroid receptor coactivator, SRC-1e. In the ERa assay, none of the tested pharmaceuticals demonstrated antagonistic activity, whereas all showed weak agonistic activity at concentrations higher than 1X10-7M. In the ERβ assay, Tam, CC and ICI showed antagonistic activity, whereas only Ral showed agonistic activity at concentrations higher than 1 X 10-8 M. The distinct estrogenic response in the ERα and ERβ assays was mainly due to their differences in ligand affinity and interaction with coactivators. PPT showed an agonistic effect in the ERα assay, but not in the ERβ assay. This study showed that our ERα and ERβ reporter yeasts have different responses to the test pharmaceuticals and are able to distinguish subtype-selective ligands. These reporter yeasts are applicable for exploring ER subtype-specific therapeutic agents and for detecting leaked pharmaceuticals that may act as environmental endocrine disruptors. Key words: yeast reporter assay, hERα, hERβ, SERM.