Transcriptional regulation of the estrogen-inducible pS2 breast cancer marker gene by the ERR family of orphan nuclear receptors

The estrogen-receptor- related receptors (ERRS) alpha, beta, and gamma are orphan nuclear hormone receptors that share significant homology with the e strogen receptors (ERs) but are not activated by natural estrogens. In cont rast, the ERRs display constitutive transcriptional activity in the absence of exogenously added ligand. However, the ERRs bind to the estrogen respon se element and to the extended half-sites of which a subset can also be rec ognized by ER alpha, suggesting that ERRs and ERs may control overlapping r egulatory pathways. To test this hypothesis, we explored the possibility th at ERRs could regulate the expression of the estrogen- inducible pS2 gene, a human breast cancer prognostic marker. Transfection studies show that all of the ERR isoforms can activate the pS2 promoter in a variety of cell typ es, including breast cancer cell lines. Surprisingly, sequence analysis com bined with mutational studies revealed that, in addition to the well-charac terized estrogen response element, the presence of a functional extended ha lf-site within the pS2 promoter is also required for complete response to b oth ER and ERR pathways. We show that ERR transcriptional activity on the p S2 promoter is considerably enhanced in the presence of all three members o f the steroid receptor coactivator family but is completely abolished on tr eatment with the synthetic estrogen diethylstilbestrol, a recently describe d inhibitor of ERR function. Finally, we demonstrate that ERR alpha is the major isoform expressed in human breast cancer cell lines and that diethyls tilbestrol can inhibit the growth of both ER-positive and -negative cell li nes. Taken together, these results demonstrate that estrogen-inducible gene s such as pS2 can be ERR targets and suggest that pharmacological modulatio n of ERRa activity may have therapeutic value in the treatment of breast ca ncer.