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Antiestrogens: mechanisms and actions in target cells
B S Katzenellenbogen1, M M Montano, P Le Goff
1Department of Physiology and Biophysics, University of Illinois, Urbana 61801, USA.
Summary
Estrogen receptor (ER) activity is complex, influenced by antiestrogens, cell type, and signaling pathways. Phosphorylation and cAMP modify ER function, impacting gene expression and cell growth.
Area of Science:
- Molecular Endocrinology
- Cell Signaling
- Receptor Biology
Background:
- Antiestrogens modulate estrogen receptor (ER) activity by inducing conformational changes and inhibiting estrogen effects.
- ER ligand binding involves competitive interactions, but distinct binding sites for estrogens and antiestrogens exist, as shown by ER mutants.
- Mutations in the ER hormone-binding domain can lead to ligand discrimination mutants, altering the receptor's response to estrogens versus antiestrogens.
Purpose of the Study:
- To investigate the complex mechanisms regulating estrogen receptor (ER) activity by estrogens and antiestrogens.
- To explore the role of cell context, promoter elements, and signaling pathways (e.g., cAMP, phosphorylation) in ER-mediated gene expression.
- To understand how variant ERs and external stimuli modulate the agonist/antagonist balance of antiestrogens.
Main Methods:
- Utilized estrogen receptor (ER) mutants with altered hormone-binding domains and C-terminal regions.
- Conducted studies across various cell lines and with different promoter constructs.
- Investigated the effects of protein kinase activators (e.g., cAMP) and growth factors on ER activity and phosphorylation.
Main Results:
- Demonstrated significant cell context- and promoter-dependent actions of antiestrogens and variant ERs.
- Showed that cAMP can synergize with estrogens to enhance ER transcriptional activity and alter the agonist/antagonist balance of antiestrogens.
- Confirmed that phosphorylation of the ER and associated proteins, influenced by estrogens, antiestrogens, and other signaling molecules, modulates ER biological effectiveness.
Conclusions:
- ER-mediated signaling is highly complex, involving intricate crosstalk between different cellular signal transduction pathways.
- The cellular environment and specific promoter sequences critically influence the biological outcomes of ER activation by estrogens and antiestrogens.
- Understanding these regulatory mechanisms is crucial for deciphering cell proliferation and gene expression control by the ER pathway.