Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P67775 (alpha isoform)
 797 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have modeled the ligand-binding domain (LBD) of the human estrogen receptor protein (hER) by homology to the known crystal structure of the LBD of the alpha isoform of human retinoate-X receptor (hRX). Alignment of hER with members of the nuclear receptor superfamily defined probable secondary structures which we used to constrain backbone torsion angles and hydrogen bonds. From published studies we identified key interactions between hER and estradiol to use to dock the hormone in its ligand-binding pocket. Since the hRX crystal structure corresponds to the unliganded form of the LBD, we adopted the "mousetrap" mechanism proposed by Renaud et al to predict the structure of the E2-bound hER. Refinement by molecular dynamics and energy minimization gave a model which matches well the known facts about the estradiol phamacophore. It also provides a possible explanation for how hER discriminates between estradiol and testosterone.
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PMID:Homology model for the ligand-binding domain of the human estrogen receptor. 961 7

Nitric oxide (NO) is an important mediator of physiologic processes in the airway. Levels of exhaled NO are greatest and asthma symptoms are least in menstruating women during midcycle, when estrogen levels are highest. To better understand the role of estrogen in airway function, we tested the hypothesis that estrogen stimulates endothelial NO synthase (eNOS) in NCI-H441 human bronchiolar epithelial cells. eNOS activation was assessed by measuring conversion of [3H]L-arginine to [3H]L-citrulline in intact cells. eNOS activity rose in the presence of estradiol-17beta (E2beta), with a maximum stimulation of 243% at 10(-8) M E2beta. This response was comparable to the 201% increase elicited by the calcium (Ca2+) ionophore A23187 (10(-5) M), and was evident as early as 5 min after such treatment. Actinomycin D had no effect on the response to E2beta, and eNOS abundance was similar in control and E2beta-treated cells. E2beta-stimulated eNOS activity was dependent on the influx of extracellular Ca2+, and was completely inhibited by the estrogen receptor (ER) antagonist ICI182,780. Messenger RNA and protein for the alpha isoform of ER (ERalpha) were evident in the H441 cells, and freshly isolated ovine airway epithelial cells also coexpressed eNOS and ERalpha. These findings indicate that estrogen acutely activates existing eNOS in H441 airway epithelial cells, through a process that involves the stimulation of epithelial ER and Ca2+ influx. This process may play a role in the hormonal modulation of airway function.
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PMID:Estrogen acutely stimulates endothelial nitric oxide synthase in H441 human airway epithelial cells. 1010 Sep 97

To determine the origin and evolutionary significance of a recently discovered isoform of the estrogen receptor (ERbeta), we examined the phylogenetic relationship of ERbeta to the well-known alpha isoform (ERalpha) and other steroid receptors. Our phylogenetic analyses traced the origin of ERbeta to a single duplication event at least 450 million years ago. Since this duplication, the evolution of both ER isoforms has apparently been constrained such that 80% of the amino acid positions in the DNA binding domain (DBD) and 53% of the ligand binding domain (LBD) have remained unchanged. Using the phylogenetic tree, we determined the amount of evolutionary change that had occurred in two ER isoforms. The DBD and the LBD had lower rates of evolutionary change compared to the NH(2) terminal domain. However, even with strong selective constraints on the DBD and LBD, our phylogenetic analyses demonstrate two clearly separate phylogenetic histories for ERalpha and ERbeta dating back several hundred million years. The ancient duplication of ER and the parallel evolution of the two ER isoforms suggest that, although ERalpha and ERbeta share a substantial degree of sequence identity, they play unique roles in vertebrate physiology and reproduction.
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PMID:Phylogenetic analyses reveal ancient duplication of estrogen receptor isoforms. 1055 42

Estrogen may mediate some of its effects on hippocampal function through the alpha isoform of the estrogen receptor (ERalpha). By light microscopy, ERalpha-immunoreactivity (-I) is found in the nuclei of scattered inhibitory gamma-aminobutyric acid (GABA)ergic interneurons. However, several lines of evidence indicate that estrogen also may exert some of its effects through rapid nongenomic mechanisms, possibly by binding to plasma membranes. Thus, to determine whether ERalpha is found in extranuclear sites in the hippocampal formation (HF), four different antibodies to ERalpha were localized by immunoelectron microscopy in proestrous rats. Ultrastructural analysis revealed that in addition to interneuronal nuclei, ERalpha-I was affiliated with the cytoplasmic plasmalemma of select interneurons and with endosomes of a subset of principal (pyramidal and granule) cells. Moreover, ERalpha labeling was found in profiles dispersed throughout the HF, but slightly more numerous in CA1 stratum radiatum. Approximately 50% of the ERalpha-labeled profiles were unmyelinated axons and axon terminals that contained numerous small, synaptic vesicles. ERalpha-labeled terminals formed both asymmetric and symmetric synapses on dendritic shafts and spines, suggesting that ERalphas arise from sources in addition to inhibitory interneurons. About 25% of the ERalpha-I was found in dendritic spines, many originating from principal cells. Within spines, ERalpha-I often was associated with spine apparati and/or polyribosomes, suggesting that estrogen might act locally through the ERalpha to influence calcium availability, protein translation, or synaptic growth. The remaining 25% of ERalpha-labeled profiles were astrocytes, often located near the spines of principal cells. Collectively, these results suggest that ERalpha may serve as both a genomic and nongenomic transducer of estrogen action in the HF.
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PMID:Ultrastructural evidence that hippocampal alpha estrogen receptors are located at extranuclear sites. 1111 25

The classical alpha isoform of the estrogen receptor (ER) has been reported to localize almost exclusively in the nucleus. However, studies on non-genomic steroid effects have also suggested the existence of ERs residing at the cell surface. In this work, we present immunological data supporting extra-nuclear ERalpha localization in uterine (SHM) and mammary (MCF-7) cell lines. Immunocytological studies performed on SHM cells revealed that native ERs mainly localize as a perinuclear cytoplasmic ring. The receptors were rapidly translocated to the nucleus by 17beta-estradiol. In addition to nuclear ERs, a peripheral reservoir of ERalpha immunoreactivity, most probably associated with the plasma membrane, was detected in MCF-7 cells. These results were confirmed by the detection of membrane estrogen binding sites using fluorescent estrogen-BSA derivatives and ligand binding assays to intact cells, where [3H]-estradiol could be partly displaced by impeded estrogen conjugates. Partial inhibition of radioligand binding by an antibody against the steroid binding domain of the ERalpha suggests that the isoform faces the extracellular media in MCF-7 cells. Moreover, ERalpha-like proteins ( approximately 67 kDa) were found to be associated in isolated membrane subfractions from the cells. However, immunocytology of COS-1 (ER-negative) and SHM cells transfected with the complete cDNA coding for the cloned ERalpha and beta isoforms showed exclusive nuclear localization of the overexpressed ERs. The non-classical distribution of native ERalpha-like proteins in each cell line, suggests an alternative mode of ERalpha cellular localization/function. Cell type-dependent processing may account for the differential localization shown by native and expressed receptors in the systems considered.
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PMID:Differential cellular localization of estrogen receptor alpha in uterine and mammary cells. 1147 46

The synthesis of mammalian steroid hormones by plants has been reported. However, their physiological role in plants is controversial. The existence of receptor molecules as those of animal cells could provide clues into a possible steroid mechanism of action. Solanum glaucophyllum callus cultures were found to contain not only 17beta-estradiol and estrone but also abundant estrogen binding sites. These sites were specific for 17beta-estradiol ( approximately 550 fmol/mg protein) and could also be competed by the known estrogen receptor (ER) agonist diethylstilbestrol. Antibodies directed against specific sequences of the classical ER alpha isoform, labelled a approximately 67 kDa band which comigrated with the mammalian ER alpha antigen. ER alpha-like proteins were tested positive as estrogen binders in Ligand blot experiments using 17beta-estradiol macromolecular derivatives as ligands. Our results provide first evidences on the existence of estrogen binding proteins structurally related to the mammalian ER alpha subtype in a higher plant system.
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PMID:Presence of estrogens and estrogen receptor-like proteins in Solanum glaucophyllum. 1174 16

The contamination of bivalve molluscs by lipophylic toxins is mainly detected by the use of unfractionated extracts from contaminated material in mouse bioassays. The development of alternate detection methods based on the use of cultured cells is hampered by difficulties related to the complexity of matrices including toxic compounds obtained from contaminated material. In this paper we have used unfractionated lipid extracts prepared from the digestive gland of mussels, which gave a negative response by the mouse bioassay, and have investigated their effects on functioning of MCF-7 cells. We show that altered growth was induced after addition of lipid extracts corresponding to less than 1mg of digestive gland per ml of culture medium. The cytotoxic effect was also confirmed by the analysis of the effect of the unfractionated extracts on four selected proteins, which were used as markers of general (actin), regulatory (mitogen activated protein kinase isoforms ERK1 and ERK2), as well as differentiative (alpha isoform of estrogen receptor) functions of the MCF-7 human breast cancer cell line.
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PMID:Cytotoxic responses to unfractionated extracts from digestive glands of mussels. 1182 Nov 30

Studies from our laboratory have demonstrated rapid ( < 1 min) non-genomic activation of Na(+)-H(+) exchange, K(+) recycling, PKC activity and a PKC-dependent Ca(2+) entry through L-type Ca(2+) channels specifically by mineralocorticoids in distal colon. Aldosterone directly stimulates the activity of the PKC alpha isoform (but not PKC delta, PKC epsilon and PKC zeta) in a cell-free assay system containing only purified commercially available enzyme, appropriate substrate peptide, co-factors and lipid vesicles. The primary ion transport target of the non-genomic signal transduction cascade elicited by aldosterone in epithelia is the Na(+)-H(+) exchanger. In isolated colonic crypts, aldosterone produced a PKC alpha sensitive intracellular alkalinisation within 1 min of hormone addition. Intracellular alkalinisation upregulates an ATP-dependent K(+) channel, which is involved in K(+) recycling to maintain the electrical driving force for Na(+) absorption, while inhibiting a Ca(2+) -dependent K(+) channel, which generates the charge balance for Cl(-) secretion. The non-genomic response to aldosterone in distal colon appears to enhance the capacity for absorption while down-regulating the potential for secretion. We have also demonstrated rapid (< 1 min) non-genomic activation of Na(+)-H(+) exchange, K(+) recycling, PKC alpha activity, and a PKC delta- and PKA-dependent Ca(2+) entry through di-hydropyridine-blockable Ca(2+) channels specifically by 17beta-estradiol in distal colon. These rapid effects are female gender specific and are insensitive to inhibitors of the classical estrogen receptor (ER). 17 beta-Estradiol directly stimulated the activity of both PKC delta and PKC alpha (but not PKC epsilon or PKC zeta) in a cell-free assay system. E2 rapidly inhibited basolateral K(Ca) channel activity which would be expected to result in an acute inhibition of Cl(-) secretion. Physiological concentrations of E2 (0.1-10 nM) reduced both basal and secretagogue-induced Cl(-) secretion. This anti-secretory effect of E2 is sensitive to PKC inhibition, intracellular Ca(2+) chelation, and is female gender specific and insensitive to inhibitors of the classical ER. These observations link rapid non-genomic activation of second messengers with a rapid gender-specific physiological effect in the whole tissue. Aldosterone and E2 differ in their protein kinase signal transduction and both hormones stimulate specific PKC isoforms indicating both common and divergent signalling systems for salt-retaining steroid hormones. The physiological function of non-genomic effects of aldosterone and estradiol is to shift the balance from net secretion to net absorption in a pluripotential epithelium.
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PMID:Non-genomic convergent and divergent signalling of rapid responses to aldosterone and estradiol in mammalian colon. 1196 Jun 25

We examined whether estrogen receptor (ER)alpha is required for estrogen to stimulate cancellous bone formation in long bones of male mice. 17 beta-Estradiol (E(2)) was administered to ER alpha(-/-) male mice or wild-type (WT) littermate controls at 40, 400, or 4000 microg/kg by daily sc injection for 28 d and histomorphometric analysis performed at the distal femoral metaphysis. In WT mice, treatment with E(2) (40 microg/kg per d) increased the proportion of cancellous bone surfaces undergoing mineralization and stimulated mineral apposition rate. In addition, higher doses of E(2) induced the formation of new cancellous bone formation surfaces in WT mice. In contrast, E(2) had little effect on any of these parameters in ER alpha(-/-) mice. Immunohistochemistry was subsequently performed using an ER alpha-specific C-terminal polyclonal antibody. In WT mice, ER alpha was expressed both by cancellous osteoblasts and a significant proportion of mononuclear bone marrow cells. Immunoreactivity was also observed in cancellous osteoblasts of ER alpha(-/-) mice, resulting from expression of the activation function-1-deficient 46-kDa ER alpha isoform previously reported to be expressed in normal osteoblasts and bones of ER alpha(-/-) mice. Taken together, our results suggest that estrogen stimulates bone formation in mouse long bones via a mechanism that requires the presence of full-length ER alpha possessing activation function-1.
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PMID:Estrogen receptor-alpha dependency of estrogen's stimulatory action on cancellous bone formation in male mice. 1269 7

Estrogen receptors (alpha and beta) are members of the steroid/thyroid nuclear receptors superfamily of ligand-dependent transcription factors. Impact of the alpha isoform of estrogen receptor (ER) on breast cancer etiology and progression is now well established. Current therapeutic strategy to treat ER-positive breast cancer relies on the blockade of ER trancriptional activity by antiestrogens. Data accumulated during the last five years on the mechanism of action of ER enable one to foresee new strategies. These data indeed reveal that ER is not statically bound to DNA at promoter sites of genes regulating cell proliferation and/or differentiation, but rather behaves as a very mobile protein continuously shuttling between targets located within various cellular compartments (i.e. membrane, microsomes, nucleus...). This allows the receptor to generate both non-genomic and genomic responses. Ligands, growth factors and second messengers produced downstream of activated membrane receptors modulate ER-mediated responses by interfering with the traffic patterns of the receptor, as well as by locally blocking its transient anchorage. Changes in ER turnover rate associated with these regulatory processes seem also to strongly influence the ability of the receptor to mediate gene transactivation. The present paper surveys these biological data and analyzes how they may be integrated into new drug design programs aimed at expanding our therapeutic armamentarium against breast cancer.
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PMID:Estrogen receptor alpha: impact of ligands on intracellular shuttling and turnover rate in breast cancer cells. 1647 75


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