Cell proliferation and modulation of interaction of estrogen receptors with coregulators induced by ERa and ERB agonists

The aim of the present study was to investigate modulation of the interaction of the ERa and ERß with coregulators in the ligand responses induced by estrogenic compounds. To this end, selective ERa and ERß agonists were characterized for intrinsic relative potency reflected by EC50 and maximal efficacy towards ERa and ERß mediated response in ER selective reporter gene assays, and subsequently tested for induction of cell proliferation in T47D-ERß cells with variable ERa/ERß ratio, and finally for ligand dependent modulation of the interaction of ERa and ERß with coregulators using the MARCoNI assay, with 154 unique nuclear receptor coregulator peptides derived from 66 different coregulators. Results obtained reveal an important influence of the ERa/ERß ratio and receptor selectivity of the compounds tested on induction of cell proliferation. ERa agonists activate cell proliferation whereas ERß suppresses ERa mediated cell proliferation. The responses in the MARCoNI assay reveal that upon ERa or ERß activation by a specific agonist, the modulation of the interaction of the ERs with coregulators is very similar indicating only a limited number of differences upon ERa or ERß activation by a specific ligand. Differences in the modulation of the interaction of the ERs with coregulators between the different agonists were more pronounced. Based on ligand dependent differences in the modulation of the interaction of the ERs with coregulators, the MARCoNI assay was shown to be able to classify the ER agonists discriminating between different agonists for the same receptor, a characteristic not defined by the ER selective reporter gene or proliferation assays. It is concluded that the ultimate effect of the model compounds on proliferation of estrogen responsive cells depends on the intrinsic relative potency of the agonist towards ERa and ERß and the cellular ERa/ERß ratio whereas differences in the modulation of the interaction of the ERa and ERß with coregulators contribute to the ligand dependent responses induced by estrogenic compounds