Estrogen binding in the rat and human

Endogenous estrogen, testosterone and progesterone levels in relation to breast cancer risk

Multiple lines of evidence support a central role of hormones in the etiology of breast cancer. In epidemiologic studies, considerable effort has focused on delineating the role of endogenous hormones in risk of breast cancer among postmenopausal women. Recently, substantial additional data has accrued from prospective studies where endogenous hormones are measured in study subjects prior to disease diagnosis. In this review, the epidemiologic evidence linking sex steroids--estrogens, testosterone, and progesterone, specifically--with subsequent risk of breast cancer in both premenopausal and postmenopausal women is summarized. Overall, a strong positive association between breast cancer risk and circulating levels of both estrogens and testosterone has now been well confirmed among postmenopausal women; women with hormone levels in the top 20% of the distribution (versus bottom 20%) have a two- to three-fold higher risk of breast cancer. Evidence among premenopausal women is more limited, though increased risk associated with higher levels of testosterone is consistent. However, both positive and null associations have been observed with estrogens and progesterone and clearly more evaluation is needed.

Effect of dextran-coated charcoal treatment on 17 beta-estradiol receptor in human benign prostatic hyperplasia

Using glycerol density gradient centrifugation technique, single saturation dose assay, and Scatchard plot, the effect of dextran-coated charcoal (DCC) treatment of homogenate or crude cytosol on estradiol binding protein in human benign prostatic hyperplasia was investigated. Receptor binding is increased after thirty minutes DCC treatment of homogenate or cytosol. Increase in estradiol binding is accompanied by loss in cytosolic protein. A 75 per cent increase in binding of estradiol to its receptor was observed after two hours incubation of DCC with homogenate. The concomitant increase in estradiol binding and decrease in protein concentration in both homogenate or cytosol after DCC treatment indicate the possible removal of some protein(s) which inactivate(s) the estradiol receptor. Removal of cofactors required for activation of proteases and removal of endogenous steroids which could be occupying the estradiol sites also are possible. This simple experimental procedure has improved significantly the methodology for the measurement and characterization of estrogen receptor in human BPH.

Remodeling the estrogen receptor model

The estrogen receptor model has revised to make it compatible with new data on subcellular localization of the receptor and physical characteristics of solubilized versus immobilized receptors. Our current model suggests that receptors, with or without bound estrogen, are present in the nuclear fraction. Furthermore, the receptor behaves as if it were immobilized or bound to some nuclear constituent at all times. Thus, the association of the estrogen-free receptor (unbound receptor) to a target site in the nucleus is considered to be the critical event in defining the nature of the response to estrogenic hormones.

Estrogen and progesterone receptors in meningiomas

Two-thirds of all meningiomas and four-fifths of intraspinal and sphenoidal meningiomas occur in women. Meningiomas frequently enlarge or become symptomatic during pregnancy or during the luteal phase of the menstrual cycle. There is an increased incidence of meningiomas in women with breast carcinoma. In a series of 23 patients with meningiomas, the authors assayed biopsy specimens of the tumor for the presence of estrogen (ER) and progesterone (PR) receptors, using glycerol density gradient centrifugation and dextran-coated charcoal techniques. Significant levels of ER were found in only 17% of the patients, while significant PR levels were detected in 39%. Only one of the 16 tumors from female patients had significant ER levels, whereas three of the seven tumors from men had significant ER levels. Eight of the 16 tumors in women had significant PR levels, whereas only one of the seven tumors in men had a significant PR level. Thus, three out of four tumors with definite ER were from men, whereas eight of nine tumors with definite PR were from women. Of the eight women whose tumors contained PR, three were premenopausal and five postmenopausal. The single tumor with high levels of PR in the male patient was histologically atypical. The results of this series were compared with six published series of sex steroid assays in meningiomas. These seven series were divided into two groups: one group included two reports from the same laboratories in France, and the other the remaining five reports. Much higher percentages of both ER- and PR-positive tumors were reported from the French group. The authors suggest that this discrepancy may be due to the use of preoperative glucocorticoid therapy in the series from the United States. Since meningiomas are known to enlarge during periods when levels of circulating progestins are high, the presence of significant quantities of PR in a high percentage of tumors may have therapeutic implications for recurrent, malignant, or incompletely excised tumors, or for medically fragile patients. Conversely, since meningiomas are not known to enlarge during the proliferative phase of the menstrual cycle or with exogenous estrogen therapy, the small number of tumors positive for ER may indicate that ER lacks clinical significance. High levels of PR found in a small group of histologically aggressive tumors in several series may indicate that hormonal therapy may be especially useful in this difficult subset of patients.

Estriol and estradiol interactions with the estrogen receptor in vivo and in vitro

The cytosolic estrogen receptor (calf uterus) bound to estradiol (E2) at 0 degrees C changes from a state with fast into a state with slow E2 dissociation rates when placed at 28 degrees C. This temperature accelerated transition in receptor affinity for its ligand takes place within 10 min at 28 degrees C. Similarly, receptor bound to estriol (E3) at 0 degrees C changes, when heated, from a state with fast into a state with slow E3 dissociation. The main difference between RE2 and RE3 was that E3 dissociates from unheated 8S RE3 and heat-transformed 5S RE3 at a much faster rate than E2 from RE2 . In the mature ovariectomized rat a slow dissociating 5S receptor estrogen complex is found in nuclei 1 h after injection of [3H]E2 or [3H]E3. In vitro dissociation of these 2 estrogens from this nuclear bound receptor formed in vivo takes place at rates similar to those from heat-transformed cytosolic RE2 or RE3 complexes. Addition of pyridoxal 5'-phosphate (PLP) to the slow-dissociating heat-transformed 5S estrogen receptor complexes causes rapid dissociation of E2 or E3; this effect is dose-dependent and is not due to disruption of 5S dimers, since after PLP addition RE2 and RE3 sediment unchanged as 5S dimers. The presence of a large excess of non-radioactive 4S RE3 does not interfere with the temperature induced rapid transition of 4S R[3H]E2 complexes from the state with fast into a state with slow E2 dissociation kinetics. A model is presented to explain the temperature induced biphasic estrogen dissociation from the receptor. It is proposed that the low affinity 4S RE2 monomer undergoes a temperature and estrogen dependent conformation change, such that the ligand is "locked" into the receptor's binding site. This conformational change results in the formation of a high affinity 4S monomer from which estrogen dissociates at a slower rate. This reaction is independent from subsequent 4S to 5S dimerization (transformation). The different rates of ligand dissociation from the low and high affinity 4S receptors reflect the different interactions (hydrophobic and hydrogen bonding) of E2 and E3 with the estrogen binding domain.

Nuclear localization of unoccupied oestrogen receptors

According to the current model of steroid hormone action oestrogen is thought to bind to its receptor in the cytoplasm of target cells and the oestrogen-receptor complex is then translocated into the nucleus. This model is based on evidence obtained in homogenized cell preparations in which free receptor is associated with the cytosol, whereas steroid-bound receptor is associated with the nuclear fraction. Some data suggest, however, that the unfilled receptor may reside in the nucleus, and that cytosolic localization represents an extraction artefact. We have now reinvestigated the subcellular distribution of unfilled oestrogen receptor using cytochalasin B-induced enucleation to obtain cytoplast and nucleoplast fractions from receptor-containing GH3 cells derived from rat pituitary tumours. We found that cytoplasts prepared from GH3 cells contain little oestrogen-binding activity and that most of the unfilled oestrogen receptors are associated with the nuclear fraction. We therefore suggest that the standard model is in error and that the unoccupied receptor is nuclear in the intact cell.

Distribution of specific binding of [3H]promegestone in benign prostatic hypertrophy in regard to age, race and histological differences

Progesterone receptors were measured in BPH tissues obtained via open prostatectomy on over thirty [30] patients. Specific receptor concentration was determined by computation of the suppressible binding from the 8S region of the glycerol density gradient (centrifuged in a vertical rotor) as described by McGuire and his colleagues. Measurable progesterone receptor concentrations were obtained from all thirty specimens. These patients were subsequently categorized on the basis of several parameters including age, race, and histology of the hyperplasia. Age and race groupings demonstrated no specific distribution pattern, however, there was a marked difference in mean receptor concentration between the histological classifications.

Role of estrogens and progesterone in the etiology and prevention of endometrial cancer: review

Our present knowledge of the role of sex steroids in the development as well as the prevention of endometrial cancer is reviewed. Factors which increase the exposure of the uterus to unopposed estrogens, either exogenous or endogenous, are associated with increased risk of endometrial adenocarcinoma. However, there is increasing evidence that progestogens can reverse endometrial hyperplasia and protect against the development of endometrial cancer. The mechanisms to explain the antiestrogenic effects of progestogens include changes in enzyme activity and steroid receptors in endometrial tissue. Postmenopausal women treated with combined estrogen and progestogen have the lowest incidence of endometrial carcinoma. Oral contraceptives containing both estrogen and progestogen in each tablet are protective against adenocarcinoma of the endometrium, while the sequential oral contraceptive pills afforded less protection. The risks and benefits of these hormone therapies are discussed in relation to the etiology and prevention of endometrial cancer.

Characterization and stabilization of progesterone receptors in human benign prostatic hypertrophy

Experimental conditions for the optimum detection and measurement of the cytosolic progestogen receptor in human prostatic hyperplasia and neoplasia are described. In presence of 20 mM molybdate ion and a reaction time of 0.5-2 h at 0-2 degrees C, we are able to detect the appearance of a [6.7-3H]-17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione ([3H]-R5020) and [3H]-progesterone binding moiety in human prostatic cytosol. The [3H]-R5020 binding protein sediments at approximately 8-11S in a glycerol density gradient centrifuged in a Sorvall TV865 rotor (vertical rotor). Maximal binding of [3H]-R5020 occurs at 30 min at 25 degrees C and 1 h at 0 degree C. Considerable overall improvement in receptor detection and measurement was made when gradient centrifugation was carried out in a vertical rotor instead of swing bucket rotor. The specifically bound [3H]-R5020 is displaced by progesterone, triamcinolone acetonide and R5020, but not by cortisol, dihydrotestosterone, 17 beta-estradiol, or diethylstilbestrol. High affinity was demonstrated by Scatchard analysis on binding of [3H]-5020 to receptors from cytosol of benign prostatic hypertrophy (BPH) giving a KD of 2.4 X 10(-10)M and a binding site concentration of 50 fmol/mg protein. Molybdate ion maintains the hormone receptor complex in 8-11S form which is totally converted to the 4-5S form in the presence of 0.6 M K Cl. The optimum concentration of fluoride ion for enhancing the specific binding of [3H]-R5020 was determined to be between 20 and 50 mM. Cytosol from human BPH in the presence of 25 mM sodium fluoride contains [3H]-R5020 receptors which sedimented mostly in the 4-5S region of glycerol density gradient. Sodium-molybdate and sodium fluoride stabilize and stimulate the specific [3H]-R5020 receptor complex at 25 and 0 degree C. The loss of specific receptor hormone binding capacity can be reversed by fluoride and, to a lesser extent, by molybdate.

Intranuclear transformation of the estrogen receptor in adulthood: tissue and species similarities

Previous studies in immature rodents have demonstrated the presence of two forms (4S, 5S) of salt extractable estrogen receptor in uterine nuclear preparations. The link between these binding forms appears to be that of hormone dependence and time in a precursor-product relationship. In the present study, this relationship has been observed in nuclear extracts of the uterus and anterior pituitary of intact and gonadectomized adult rats. Both forms of the estrogen receptor have also been isolated from purified nuclei of endometrial cell preparations of the adult dog. As a result of these studies, the phenomenon of intranuclear receptor transformation in estrogen action may now be extended to include (a) the physiologic state of adulthood, (b) persist in the absence of endogenous estrogens and (c) be a feature of estrogen target tissues in animal species other than rodents.

Equilibrium: the intracellular distribution of steroid receptors

Data are presented which suggest that there are unbound receptors for oestrogen in nuclei of the smooth muscle cells of the myometrium. A new model for the distribution of unbound receptors is proposed in which unbound receptor is in equilibrium, partitioned between nucleus and cytoplasm according to the free water content of these intracellular compartments.

Factors influencing association of glucocorticoid receptor-steroid complexes with nuclei, chromatin, and DNA: interpretation of binding data

Attempts to reconstruct, in a test tube, the steroid-hormone system of a responsive cell are fraught with enumerable difficulties. In this chapter I have attempted to point out some of the factors that affect receptor-steroid complexes and their interactions with acceptors. In most cases there is a quantitative influence of these factors on the level of steroid complex binding to acceptors. In some cases, selected experimental designs that neglect these factors and methods of presenting the observed data may lead to artifactual conclusions. Several of these problems should disappear when the prospect of pure receptor-steroid complexes [127, 147, 150, 181, 247, 248] becomes a common occurrence. Nevertheless much has already been learned about the interactions of complexes with acceptors, which in turn have been used to help formulate models of steroid-hormone action.

Association of estrone with the development of endometrial carcinoma

Although few clinicians suspect estrogen as the prime cause of endometrial carcinoma, a retrospective study showed the following among postmenopausal women: 70 per cent of those with endometrial carcinoma and only 23 per cent of matched control subjects used estrogen systemically. Endometrial cancer developed an average of five years earlier in those taking than in those not receiving estrogen. Forty-two per cent of those with endometrial cancer had received estrogen three years or more. Most significantly, conjugated estrogens were used by 89 per cent of postmenopausal cancer patients who had received any estrogenic substance. The increased risk of endometrial cancer for all patients receiving conjugated estrogen (the risk ratio) was 7.4. This risk ratio increased with duration of conjugated estrogen exposure, from 4.6 in patients with less than three years' exposure to 9.2 in patients with three or more years' exposure.

Increased risk of endometrial carcinoma among users of conjugated estrogens

The possibility that the use of conjugated estrogens increases the risk of endometrial carcinoma was investigated in patients and a twofold age-matched control series from the same population. Conjugated estrogens (principally sodium estrone sulfate) use was recorded for 57 per cent of 94 patients with endometrial carcinoma, and for 15 per cent of controls. The corresponding point estimate of the (instantaneous) risk ratio was 7.6 with a one-sided 95 per cent lower confidence limit of 4.7. The risk-ratio estimate increased with duration of exposure: from 5.6 for 1 to 4.9 years exposure to 13.9 for seven or more years. The estimated proportion of cases related to conjugated estrogens, the etiologic fraction, was 50 per cent with a one-sided 95 per cent lower confidence limit of 41 per cent. These data suggest that conjugated estrogens have an etiologic role in endometrial carcinoma.