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Estrogen receptors: selective ligands, partners, and distinctive pharmacology
B S Katzenellenbogen1, M M Montano, T R Ediger
1Department of Molecular and Integrative Physiology, University of Illinois and College of Medicine, Urbana 6180, USA.
Abstract:
The action of nuclear hormone receptors is tripartite, involving the receptor, its ligands, and its co-regulator proteins. The estrogen receptor (ER), a member of this superfamily, is a hormone-regulated transcription factor that mediates the effects of estrogens and anti-estrogens (e.g., tamoxifen) in breast cancer and other estrogen target cells. This chapter presents our recent work on several aspects of estrogen action and the function of the ER: 1) elucidation of ER structure-function relationships and development of ligands that are selective for one of the two ER subtypes, ERalpha or ERbeta; 2) identification of ER-selective co-regulators that potentiate the inhibitory effectiveness of anti-estrogens and dominant-negative ERs and modulate the activity of estrogens; 3) characterization of genes that are regulated by the anti-estrogen-ER versus the estrogen-ER complex; and 4) elucidation of the intriguing pharmacology of these ER complexes at different gene regulatory sites. These findings indicate that different residues of the ER hormone-binding domain are involved in the recognition of structurally distinct estrogens and anti-estrogens and highlight the exquisite precision of the regulation of ER activities by ligands, with small changes in ligand structure resulting in major changes in receptor character. Studies also explore the biology and distinct pharmacology mediated by ERalpha and ERbeta complexed with different ligands through different target genes. The upregulation of the anti-oxidant detoxifying phase II enzyme, quinone reductase, by the anti-estrogen-occupied ER, mediated via the electrophile response element in the QR gene, may contribute to the beneficial antioxidant effects of anti-estrogens in breast cancer and illustrates the activation of some genes by ER via non-estrogen response element sequences. The intriguing biology of estrogen in its diverse target cells is thus determined by the structure of the ligand, the ER subtype involved, the nature of the hormone-responsive gene promoter, and the character and balance of co-activators and co-repressors that modulate the cellular response to the ER-ligand complex. The continuing development of novel ligands and the study of how they function as selective agonists or antagonists through ERalpha or ERbeta should allow optimized tissue selectivity of these agents for hormone replacement therapy and treatment and prevention of breast cancer.
Insights
Researchers explored estrogen receptor (ER) function, developing selective ligands and identifying co-regulators. This work clarifies how ER subtypes and ligands regulate gene expression, impacting breast cancer treatment and hormone therapy.
Area of Science:
- Molecular Endocrinology
- Cancer Biology
- Pharmacology
Background:
- Nuclear hormone receptors, including the estrogen receptor (ER), are crucial transcription factors mediating hormonal effects.
- ER plays a key role in estrogen-sensitive cells, including breast cancer, by responding to estrogens and anti-estrogens like tamoxifen.
Purpose of the Study:
- To elucidate ER structure-function relationships and develop subtype-selective ligands (ERalpha and ERbeta).
- To identify ER-selective co-regulators that modulate anti-estrogen and estrogen activity.
- To characterize gene regulation by ER complexes and explore their pharmacology at gene regulatory sites.
Main Methods:
- Investigated ER structure-function relationships and ligand selectivity for ERalpha/ERbeta.
- Identified and characterized ER-selective co-regulators.
- Analyzed gene regulation by ER-ligand complexes and their interactions with gene promoters.
Main Results:
- Demonstrated that distinct ER hormone-binding domain residues recognize different estrogens and anti-estrogens.
- Showcased how ligand structure precisely dictates ER activity and receptor character.
- Revealed ERalpha and ERbeta mediate distinct pharmacology through different target genes, including anti-estrogen-induced quinone reductase upregulation.
Conclusions:
- Estrogen biology is complex, determined by ligand structure, ER subtype, gene promoter, and co-regulator balance.
- Development of novel selective ER ligands offers potential for optimized tissue selectivity in hormone replacement and breast cancer therapy.