Estrogen receptor beta

Abstract: We have cloned a novel member of the nuclear receptor superfamily. The cDNA of clone 29 was isolated from a rat prostate cDNA library and it encodes a protein of 485 amino acid residues with a calculated molecular weight of 54.2 kDa. Clone 29 protein is unique in that it is highly homologous to the rat estrogen receptor (ER) protein, particularly in the DNA-binding domain (95%) and in the C-terminal ligand-binding domain (55%). Expression of clone 29 in rat tissues was investigated by in situ hybridization and prominent expression was found in prostate and ovary. In the prostate clone 29 is expressed in the epithelial cells of the secretory alveoli, whereas in the ovary the granuloma cells in primary, secondary, and mature follicles showed expression of clone 29. Saturation ligand-binding analysis of in vitro synthesized clone 29 protein revealed a single binding component for 17beta-estradiol (E2) with high affinity (Kd= 0.6 nM). In ligand-competition experiments the binding affinity decreased in the order E2 > diethylstilbestrol > estriol > estrone > 5alpha-androstane-3beta,17beta-diol >> testosterone = progesterone = corticosterone = 5alpha-androstane-3alpha,17beta-diol. In cotransfection experiments of Chinese hamster ovary cells with a clone 29 expression vector and an estrogen-regulated reporter gene, maximal stimulation (about 3-fold) of reporter gene activity was found during incubation with 10 nM of E2. Neither progesterone, testosterone, dexamethasone, thyroid hormone, all-trans-retinoic acid, nor 5alpha-androstane-3alpha,I7beta-diol could stimulate reporter gene activity, whereas estrone and 5alpha-androstane-3beta,17beta-diol did. We conclude that clone 29 cDNA encodes a novel rat ER, which we suggest be named rat ERbeta to distinguish it from the previously cloned ER (ERalpha) from rat uterus.

Abstract: The rat estrogen receptor (ER) exists as two subtypes, ER alpha and ER beta, which differ in the C-terminal ligand binding domain and in the N-terminal transactivation domain. In this study we investigated the messenger RNA expression of both ER subtypes in rat tissues by RT-PCR and compared the ligand binding specificity of the ER subtypes. Saturation ligand binding analysis of in vitro synthesized human ER alpha and rat ER beta protein revealed a single binding component for 16 alpha-iodo-17 beta-estradiol with high affinity [dissociation constant (Kd) = 0.1 nM for ER alpha protein and 0.4 nM for ER beta protein]. Most estrogenic substances or estrogenic antagonists compete with 16 alpha-[125I]iodo-17 beta-estradiol for binding to both ER subtypes in a very similar preference and degree; that is, diethylstilbestrol > hexestrol > dienestrol > 4-OH-tamoxifen > 17 beta-estradiol > coumestrol, ICI-164384 > estrone, 17 alpha-estradiol > nafoxidine, moxestrol > clomifene > estriol, 4-OH-estradiol > tamoxifen, 2-OH-estradiol, 5-androstene-3 beta, 17 beta-diol, genistein for the ER alpha protein and dienestrol > 4-OH-tamoxifen > diethylstilbestrol > hexestrol > coumestrol, ICI-164384 > 17 beta-estradiol > estrone, genistein > estriol > nafoxidine, 5-androstene-3 beta, 17 beta-diol > 17 alpha-estradiol, clomifene, 2-OH-estradiol > 4-OH-estradiol, tamoxifen, moxestrol for the ER beta protein. The rat tissue distribution and/or the relative level of ER alpha and ER beta expression seems to be quite different, i.e. moderate to high expression in uterus, testis, pituitary, ovary, kidney, epididymis, and adrenal for ER alpha and prostate, ovary, lung, bladder, brain, uterus, and testis for ER beta. The described differences between the ER subtypes in relative ligand binding affinity and tissue distribution could contribute to the selective action of ER agonists and antagonists in different tissues.

Abstract: Ligand-dependent activation of transcription by nuclear receptors (NRs) is mediated by interactions with coactivators. Receptor agonists promote coactivator binding, and antagonists block coactivator binding. Here we report the crystal structure of the human estrogen receptor alpha (hER alpha) ligand-binding domain (LBD) bound to both the agonist diethylstilbestrol (DES) and a peptide derived from the NR box II region of the coactivator GRIP1 and the crystal structure of the hER alpha LBD bound to the selective antagonist 4-hydroxytamoxifen (OHT). In the DES-LBD-peptide complex, the peptide binds as a short alpha helix to a hydrophobic groove on the surface of the LBD. In the OHT-LBD complex, helix 12 occludes the coactivator recognition groove by mimicking the interactions of the NR box peptide with the LBD. These structures reveal the two distinct mechanisms by which structural features of OHT promote this "autoinhibitory" helix 12 conformation.

Abstract: A novel estrogen receptor (hereinafter referred to as ER beta) was cloned using degenerate PCR primers. A comparison of the amino acid sequence of ER beta with the "classical' ER (ER alpha) shows a high degree of conservation of the DNA-binding domain (96%), and of the ligand-binding domain (58%). In contrast, the A/B domain, the hinge region and the F-domain are not conserved. Northern blot analysis revealed that ER beta is expressed in human thymus, spleen, ovary and testis. Transient transfections of an ER beta expression construct together with an ERE-based reporter construct in CHO cells clearly demonstrated transactivation of ER beta by 17 beta-estradiol. In addition, the ER alpha antagonist ICI-164384 is a potent antagonist for ER beta as well. Interestingly, the level of transactivation by 17 beta-estradiol is higher for ER alpha than for ER beta, which may reflect suboptimal conditions for ER beta at the level of the ligand, responsive element or cellular context.

Abstract: This invention provides methods of screening test compounds for the ability to activate or inhibit estrogen receptor beta (ER beta ) mediated gene activation at an AP1 site. In particular, the methods involve providing a cell comprising an estrogen receptor beta (ER beta ), AP1 proteins, and a construct comprising a promoter comprising an AP1 site which regulates expression of a first reporter gene. The cell is contacted with the test compound and changes in expression levels of the reporter gene are detected indicating whether the test compounds activate transcription, inactivate transcription or have no effect at the AP1 site.