Estrogens, acting via estrogen receptor (ER) play key roles in growth, differentiation, and gene regulation in the reproductive, central nervous, and skeletal systems. ER-mediated gene transcription contributes to the development and spread of breast, uterine, and liver cancer. Steroid receptor coactivator-1a (SRC1a) belongs to the P160 family of coactivators, which is the best known of the many coactivators implicated in ER-mediated transactivation. Binding of full-length P160 coactivators to steroid receptors has been difficult to investigate in vitro. This chapter details how to investigate the interaction of SRC1a with ER using the fluorescence anisotropy/polarization microplate assay (FAMA).
[Show abstract][Hide abstract] ABSTRACT: Analyses of steroid receptors are important for understanding molecular details of transcriptional control, as well as providing
insight as to how an individual transacting factor contributes to cell identity and function. These studies have led to the
identification of a superfamily of regulatory proteins that include receptors for thyroid hormone and the vertebrate morphogen
retinoic acid. Although animals employ complex and often distinct ways to control their physiology and development, the discovery
of receptor-related molecules in a wide range of species suggests that mechanisms underlying morphogenesis and homeostasis
may be more ubiquitous than previously expected.
[Show abstract][Hide abstract] ABSTRACT: Estrogen receptor (ER) toxicity has hampered the development of vertebrate cell lines stably expressing substantial levels of recombinant wild-type ER. To isolate clonal lines of HeLa cells stably expressing epitope-tagged ER, we used a construction encoding a single bicistronic mRNA, in which FLAG-epitope-tagged human ERα (fER) was translated from a 5'-translation initiation site and fused to the neomycin resistance gene, which was translated from an internal ribosome entry site. One stable HeLa-ER-positive cell line (HeLa-ER1) produces 1,300,000 molecules of fER/cell (~20-fold more ER than MCF-7 cells). The HeLa fER is biologically active in vivo, as judged by rapid death of the cells in the presence of either 17β-estradiol or trans-hydroxytamoxifen and the ability of the cell line to activate a transfected estrogen response element (ERE)-containing reporter gene. The FLAG-tagged ER was purified to near homogeneity in a single step by immunoaffinity chromatography with anti-FLAG monoclonal antibody. Purified fER exhibited a distribution constant (K(D)) for 17β-estradiol of 0.45 nM. Purified HeLa fER and HeLa fER in crude nuclear extracts exhibit similar K(D) values for the ERE (0.8 nM and I nM, respectively), which are approximately 10 times lower than the K(D) of 10 nM we determined for purified ER expressed using the baculovirus system. HMG-1 strongly stimulated binding of both crude and purified HeLa fER to the ERE (K(D) of 0.25 nM). In transfected HeLa cells, HMG-1 exhibited a dose-dependent stimulation of 17β-estradiol-dependent transactivation. At high levels of transfected HMG-1 expression plasmid, transactivation by ER became partially ligand-independent, and transactivation by trans-hydroxytamoxifen was increased by more than 25-fold. These data describe a system in which ER, stably expressed in HeLa cells and easily purified, exhibits extremely high affinity for the ERE, and suggest that intracellular levels of HMG-1 may be limiting for ER action.
[Show abstract][Hide abstract] ABSTRACT: Estrogens display intriguing tissue-selective action that is of great biomedical importance in the development of optimal therapeutics for the prevention and treatment of breast cancer, for menopausal hormone replacement, and for fertility regulation. Certain compounds that act through the estrogen receptor (ER), now referred to as selective estrogen receptor modulators (SERMs), can demonstrate remarkable differences in activity in the various estrogen target tissues, functioning as agonists in some tissues but as antagonists in others. Recent advances elucidating the tripartite nature of the biochemical and molecular actions of estrogens provide a good basis for understanding these tissue-selective actions. As discussed in this thematic review, the development of optimal SERMs should now be viewed in the context of two estrogen receptor subtypes, ERalpha and ERbeta, that have differing affinities and responsiveness to various SERMs, and differing tissue distribution and effectiveness at various gene regulatory sites. Cellular, biochemical, and structural approaches have also shown that the nature of the ligand affects the conformation assumed by the ER-ligand complex, thereby regulating its state of phosphorylation and the recruitment of different coregulator proteins. Growth factors and protein kinases that control the phosphorylation state of the complex also regulate the bioactivity of the ER. These interactions and changes determine the magnitude of the transcriptional response and the potency of different SERMs. As these critical components are becoming increasingly well defined, they provide a sound basis for the development of novel SERMs with optimal profiles of tissue selectivity as medical therapeutic agents.
Breast Cancer Research 02/2000; 2(5):335-44. DOI:10.1186/bcr78 · 5.49 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.