Uterine receptor-estradiol complexes and their interaction with nuclear binding sites

Characterization of uterine sex steroid receptors in the pig and their variation during the oestrous cycle

The present study establishes and validates an in vitro binding and exchange assay for tissue receptors for oestradiol (E) and progesterone (P) in pig uterus. Both hormones bound to specific cytoplasmic (Rc) and nuclear (Rn) receptor proteins with high affinity. The relative concentrations of the receptors were measured in dissected samples from endometrium and myometrium obtained at late prooestrus, oestrus, and luteal phases of the oestrous cycle. The Scatchard analysis of the oestradiol and R 5020-receptor complex displayed linearity and indicated a single class of high affinity, low capacity binding sites. Significant variations were seen in the binding of E and P to their cytosolic and nuclear receptors, following the changes in the circulating levels of the hormones in blood plasma during the oestrous cycle. Both tissue components, i.e. endometrium and myometrium followed a similar pattern when related to the stage of the oestrous cycle considered. The ERc increased from prooestrus, reaching a maximum at standing oestrus, thereafter decreasing. The concentration of ERn increased from prooestrus towards the early luteal phase, with a significant reduction by day 8 of the cycle. The amounts of PRc were maximal at standing oestrus, remaining high during the early luteal phase, while the PRn showed a linear increase from oestrus onwards throughout the luteal phase.

Oestradiol and progesterone receptors in the pig oviduct during the oestrous cycle

The concentrations of the tissue receptors for oestradiol (E) and progesterone (P) in the porcine oviduct at different stages on the oestrous cycle have been investigated by in vitro binding and exchange methods. Both hormones bound to specific cytoplasmic (Rc) and nuclear (Rn) receptor proteins with high affinity. The concentrations of ERc and ERn were two-fold higher in the ampulla as compared to the isthmus. The amount of ERc in the isthmic portion of the oviduct did not vary throughout the oestrous cycle. However, the ampullar ERc concentrations increased during prooestrus, showed a maximum at standing oestrus, thereafter decreasing. Significant variations in the amount of oviductal ERn were observed. Despite the differences in ERn amounts between segments, the concentration of ERn increased significantly during late prooestrus, attaining a three-fold elevation and remaining elevated during the period of standing oestrous and early luteal phase (days 3-4), thereafter returning to basal levels. No significant variations in the amount of isthmic PRc were found throughout the period studied. The ampulla, however, showed a significant increase in PRc concentrations during standing oestrus, thereafter decreasing. The concentrations of PRn in isthmus and ampulla were of about the same magnitude and varied significantly during the oestrous cycle, increasing in concentration from standing oestrous onwards. The temporal relationships between the variations in levels of oestradiol and progesterone receptors in oviductal tissues and those of the circulating plasma levels were established. The data obtained in this study suggest a relationship between the changes in the levels of oestradiol and progesterone oviductal binding during the first days of the oestrous cycle, and the gamete and embryo transport throughout the oviduct in the porcine species.

The binding of [3H]oestradiol-receptor complex to hypothalamic chromatin of male and female mice

Histones and masking acidic proteins were removed from hypothalamic chromatin in order to evaluate/measure the number of available acceptor sites for the [3H]oestradiol-receptor complex. This number increases after dehistonizing and unmasking and is lower than published values for comparable preparations. No sex-related difference in [3H]oestradiol-receptor binding to hypothalamic chromatin in vitro was observed. Failure to observe such a difference suggests that sexual differentiation and steroid sensitivity cannot be attributed to marked differences in the degree of chromatin masking.

Binding of the estradiol-receptor complex to reconstituted nucleoacidic protein from calf uterus

Non-histone protein-DNA complexes with acceptor activity for estradiol-receptor complexes were reconstituted from fractionated calf uterine chromatin. Acceptor activity had tissue specificity with target tissue binding exceeding non-target tissue binding. The binding of estradiol-receptor complexes to acceptor sites was dependent on intact non-histone protein-DNA complexes, reconstituted select non-histone proteins, and protein equivalent: DNA reconstitution ratios. [3H]Estradiol-receptor complexes were bound to reconstituted non-histone protein-DNA complexes (i.e., nucleoacidic protein) with a high affinity and with a limited number of binding sites. Fractionation of uterine chromatin non-histone proteins identified two major sets of non-histone proteins which had acceptor activity when reconstituted with DNA. Thus, it seems possible to reconstitute nucleoacidic protein fractions with specific acceptor activity for the calf uterine estrogen receptor.

Receptors for estrogens and progesterone in the porcine cervix

In vitro binding and exchange methods were used to determine the levels of estradiol and progesterone receptors in cytosolic and nuclear fractions of cells obtained from the porcine cervix at different stages of the estrous cycle. The concentration of estradiol cytosolic receptors was about 4500 sites/cell during the luteal phase and increased to a maximum of approximately 7600 sites/cell on day 1 of the cycle, decreasing to a level of 2700 sites/cell on days 3-4. The estradiol nuclear receptor level increased between the end of the luteal phase and the onset of heat from 300 to 1200 sites/cell. No reduction in the number of nuclear sites was seen between day 1 and 3-4. The level of the progesterone cytosolic receptor and its cycle profile was very similar to that of the estradiol receptor. The nuclear receptor, however, reached its lowest level of 760 sites/cell on day 1 of the cycle, increased to a value of 4700 sites on days 3-4 and showed a steady level of about 1000 sites/cell during the luteal phase. The data obtained agree with present theories on the endocrine mechanisms regulating receptor levels in the uterus. Furthermore, these data support a concept in which the constriction of the cervix occurring in response to increased concentrations of circulating estradiol is mediated via steroid receptors.

Electrocautery: effects on steroid receptors in human breast cancer

The determination of steroid receptors in human breast cancers has assumed increasing importance over the past several decades. Improper handling of the specimens could affect results obtained. This study details the effects excessive levels of heat that occur with the use of electrocautery can have on steroid receptor quantities and localization. Twelve resected primary and metastatic human breast cancers were analyzed for cytoplasmic and nuclear receptors by biochemical analysis. In addition, steroid binding was determined by direct fluorescent histochemical techniques. To a portion of each resected specimen a Boviec was applied to simulate electrocautery resection. Analysis of the different portions of the same tumor revealed that there was a decrease in measurable cytoplasmic receptor in all cauterized specimens and a concomitant increase in the nuclear receptor. A similar shift in steroid binding was noted in all the specimens analyzed by fluorescent histochemical techniques. The results of this study show that the application of excessive heat to human breast cancers will lead to false negative biochemical steroid receptor determination by shifting the receptors intranuclear.

Effects of progesterone on uptake and metabolism of 17 beta-estradiol by mouse uterine luminal epithelium

The influence of progesterone (P4) pretreatment on the uptake and retention of [3H]estradiol-17 beta ([3H]E2) in whole uterus and luminal epithelium was examined in ovariectomized mice. After s.c. injection of 50 ng [3H]E2 uterine, epithelial and epithelial nuclear levels of radioactivity were maximal 3 h post-injection: maximum epithelial levels were sustained from 3 to 6 h in Pa-treated, but not control tissue. P4 treatment did not significantly alter the proportion of epithelial or uterine radioactivity recovered as [3H]E2, or the intracellular distribution of the hormone. Preparation of epithelial suspensions in buffer containing excess 17 beta-estradiol (E2) did not significantly alter their [3H]E2 content. After intraluminal injection of 100 pg [3H]E2 rates of loss from uterine, epithelial and epithelial nuclear preparations did not differ significantly between control and P4-treated tissues. We conclude that P4 does not inhibit E2-induced luminal epithelial mitosis by preventing E2 reaching the epithelial cells and nuclei, by changing its distribution in the tissue, or by increasing its rate of loss from the tissue or its metabolism to less active estrogens like estrone.

The estrogen-induced vitellogenin synthesis in chicken liver after estrogen withdrawal or antiestrogen treatment

(1) The induction of vitellogenin synthesis in chicken liver by an estrogen implant as well as the decline of vitellogenin synthesis and nuclear receptor concentration after withdrawal of the implant were studied. For the detection of vitellogenin the SAC immunoprecipitation technique was used. The nuclear receptor decreases very rapidly and somewhat earlier than the capacity of the liver to synthesize vitellogenin. (2) The inhibition by antiestrogens of the estrogen-induced vitellogenin synthesis as well as of the accumulation of the estrogen-receptor complex in the nucleus was investigated. Tamoxifen as well as the recently described 1,1,2,2-tetramethyl-1,2-bis(4'-hydroxyphenyl)ethane were found to be true antiestrogens in the chicken liver, i.e. they inhibit estrogen-induced vitellogenin synthesis but themselves cause no induction.

The binding of [3H]oestradiol-receptor complexes to calf uterine chromatin

Various aspects of the interaction of oestrogen-receptor complexes with calf uterine chromatin covalently coupled to cellulose were analysed. Partially purified [3H]oestradiol-receptor complexes were bound to intact, or partially deproteinized, chromatin resins. Proteins were removed from the chromatin-cellulose resins by extraction with high molarities of salt, including NaCl/urea, guanidine hydrochloride and guanidine thiocyanate. After extensive washing to remove the salt, [3H]oestradiol-receptor-complex solutions were added to the resins and the degree of binding was determined. The extent of [3H]oestradiol-receptor-complex binding to chromatin was enhanced by extraction of chromosomal proteins. By varying the molarity of the salt, and consequently the extent of protein removal, it was possible to resolve [3H]oestradiol-receptor-complex binding to guanidine thiocyanate-extracted chromatin into two components. Similarly, [3H]oestradiol-receptor-complex binding to guanidine hydrochloride-treated chromatin included three regions of enhanced binding capacity. The [3H]oestradiol-receptor-chromatin interaction was saturable with respect to both intact and salt-extracted resins. Thus uterine chromatin may contain three or more specific classes of acceptors for the oestrogen-receptor complex.

The role of progesterone receptors in the management of advanced breast cancer

The identification of steroid receptors in human breast cancer tissues has provided biochemical markers to predict hormone responsiveness. Analysis of tumors from 328 patients for the estrogen receptor protein (ERP) revealed significant levels in 225 patients (68%). Fifty-five patients with advanced disease were subjected to hormonal manipulation. Thirty patients underwent ablative surgery consisting of adrenalectomy or adrenalectomy and oophorectomy. Twenty-five patients were treated with additive therapy utilizing the new antiestrogen Tamoxifen. The ECOG criteria for an objective response were applied to all patients. Fifteen of the 24 estrogen receptor-positive patients (63%) subjected to endocrine ablation responded. Eleven of twenty (55%) ERP-positive patients responded to Tamoxifen therapy. Only one ERP-negative patient responded in the total group. Simultaneous analysis of these same specimens for the progesterone receptor protein (PgRP) revealed that 151 patients were ERP and PgRP positive (46%); 74 (23%) were ERP positive and PgRP negative; 90 (27%) were ERP and PgRP negative, and 13 (4%) were ERP negative and PgRP positive. In the two treatment groups the overall response rate when both receptors were positive was 77% with a higher percentage of responders in the endocrine ablative group (88% vs. 64%). In addition, a greater duration of response was achieved in those patients treated with endocrine ablation.

Replenishment and nuclear retention of oestradiol-17 beta receptors in rat uteri during postnatal development

1. Uteri of 6--10-day-old rats do not show a late growth response to oestrogen (increase in rate of DNA synthesis and cell division) exhibited by fully competent (20 days or older) uteri. We posed the question whether the lack of the late growth response is due to an inability to replenish the cytoplasmic pool of oestrogen receptors or to curtailed retention of oestrogen binding in the nucleus. Uterine nuclear and cytoplasmic receptors were measured by a [3H]oestradiol-17 beta exchange assay, at 1, 3, 6, 14 and 24 h after oestrogen injection. 2. The replenishment of cytoplasmic oestrogen receptors showed a similar pattern in the uteri of 6 and 10-day-old (partially responsive) and in 20-day-old (fully responsive) rats. 3. Oestrogen was retained longer in uterine nuclei obtained from 5 and 10-day-old rats than in uterine nuclei of 20 and 25-day-old rats. 4. Oestrogen receptors resistant to 0.4 M KCl extraction (residual receptors) were found in uterine nuclei of 6 and 25-day-old rats after oestrogen injection at all the times tested. The concentration of these residual receptors during the late period (6--24 h after injection) was not significantly different in uterine nuclei of 6-day-old and 25-day-old rats. 5. We conclude that neither lack of oestrogen receptor replenishment nor curtailed retention of oestrogen binding in the nucleus is the factor which limits the complete responsiveness to oestrogen in uteri of rats during postnatal development.

The specific binding of estradiol to the nuclear matrix

Recent studies on the eukaryotic nucleus have described the presence of a structural component termed the nuclear matrix, that appears to be involved in nucleic acid synthesis. This study will present evidence that the nuclear matrix of both the rat uterus and chick liver contains specific, high affinity, saturable estradiol binding sites.

The binding of 3H-labelled oestradiol- and progesterone-receptor complexes to hypothalamic chromatin of male and female sheep

Chromatin isolated from hypothalamic nuclei of sexually mature entire male and female sheep was linked to cellulose in u.v. light. The saturation binding of 3H-labelled oestrogen- and progesterone-receptor complexes, prepared by (NH4)2SO4 precipitation from the 105000g supernatant of hypothalamic cytosol, was then measured in vitro in 0.15m-KCl. Saturation binding was also measured after extraction of histones and masking acidic proteins. Salt + urea was observed to be more effective than guanidine hydrochloride in unmasking receptor acceptor sites, and the binding of labelled receptor complexes to dehistonized unmasked chromatin was shown to be largely resistant to 0.4m-KCl extraction. Whereas extents of receptor-complex binding were similar to published values for comparable preparations of hen oviduct chromatin, no sex-related difference was observed. However, binding of progesterone-receptor to chromatin was greater than that of oestradiol-receptor. Binding also increased more after removal of histones and masking acidic proteins, suggesting the presence of a greater number of progesterone-receptor acceptor sites in hypothalamic chromatin than of estradiol-receptor acceptor sites. The failure to demonstrate a sex-related difference in oestradiol-receptor binding to hypothalamic chromatin in vitro is discussed.

Progesterone-regulated changes in transcriptional events in rabbit uterus

The role of steroid receptors in the early events of progesterone action was elucidated by examining the temporal relationship between the nuclear accumulation of progestin receptor and changes in activities of RNA polymerases I and II, as well as that of chromatin template in rabbit uterus. Following a 5-day estrogen pretreatment, the animals received an intravenous injection of progesterone (10 mg), after which they were killed at timed intervals. Nuclear progestin receptor level, as measured by an exchange assay, reached the peak value 30 min after hormone administration (11 600 to 46 600 sites/nucleus) and declined to the control levels by 4 h. Changes in the activities of RNA polymerase I and II did not follow identical time courses: polymerase I rose at 30 min and remained elevated for 2 h and then declined to about 75% of the pretreatment activity, whereas RNA polymerase II activity increased more rapidly (at 15 min), and was followed by a sharp decrease to about 50% of the initial value. Thereafter, the latter enzyme activity rose slowly and reached the pretreatment level within 12 h of progesterone administration. Early changes in chromatin template activity were similar to those in RNA polymerase I with a second rise by 8--10 h. The early inhibition of transcriptional events by progesterone may result from antiestrogenic properties of this steroid. Accumulation of nuclear progestin receptor occurs at a similar time to early changes in the transcriptional events suggesting a regulatory role for the hormone receptor complexes.