Cell proliferation and modulation of interaction of estrogen receptors with coregulators induced by ERα and ERβ agonists

The aim of the present study was to investigate modulation of the interaction of the ER alpha and ER beta with coregulators in the ligand responses induced by estrogenic compounds. To this end, selective ER alpha and ER beta agonists were characterized for intrinsic relative potency reflected by EC50 and maximal efficacy towards ER alpha and ER beta mediated response in ER selective reporter gene assays, and subsequently tested for induction of cell proliferation in T47D-ER beta cells with variable ER alpha/ER beta ratio, and finally for ligand dependent modulation of the interaction of ER alpha and ER beta 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 ER alpha/ER beta ratio and receptor selectivity of the compounds tested on induction of cell proliferation. ER alpha agonists activate cell proliferation whereas ER beta suppresses ER alpha mediated cell proliferation. The responses in the MARCoNI assay reveal that upon ER alpha or ER beta 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 ER alpha or ER beta 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 ER alpha and ER beta and the cellular ER alpha/ER beta ratio whereas differences in the modulation of the interaction of the ER alpha and ER beta with coregulators contribute to the ligand dependent responses induced by estrogenic compounds. (C) 2014 Elsevier Ltd. All rights reserved.