Nuclear binding of progesterone in chick oviduct. Multiple binding sites in vivo and transcriptional response.

1. Varied doses of labelled or unlabelled progesterone were injected into immature chicks which had previously been stimulated with oestrogen. The concentrations of nuclear bound [3H]progesterone were correlated with the effects of the hormone on endogenous RNA polymerase I and II activities in isolated oviduct nuclei. 2. The extent of nuclear localization of [3H]progesterone in oviduct (a progesterone target tissue) was shown to be much greater than in lung (non-target tissue). The conccentration of bivalent cations in solvents used in the nuclei isolations has a marked effect on the amount of bound hormone in the nuclei. 3. Evidence for the existence of several classes of binding sites for progesterone in the oviduct nuclei is given. These classes represent about 1000) 10000 and 100000 molecules of the hormone per cell nucleus and are saturated by injecting approx. 10, 100 and 1000 mug of progesterone respectively. 4. When saturation of the first (highest affinity) class of nuclear sites occurs, a marked inhibition in RNA polymerase II (but not RNA polymerase I) activity was observed. When the second class of sites was saturated, alterations in both RNA polymerase I and II activities were observed. Binding to the third class of nuclear binding sites was not accompained by further changes in polymerase activity. It is suggested that the first two classes of nuclear binding sites may represent functional sites for progesterone action in the chick oviduct.     

Isolation of estrogen receptor in complex with a discrete nuclear subfraction from hen oviduct.

A nuclear subfraction containing bound estrogen receptor in presumed complex with its nuclear acceptor site has been partially purified from hen oviduct. Sucrose density gradient ultracentrifugation was used to separate mechanically sheared chromatin (i.e. lysed nuclei) into several fractions which differed in protein to DNA ratio as well as in vitro template activity. Gradient fractions were then examined for the presence of bound estrogen receptors. Care was taken to use physiological ionic strength buffers when preparing nuclei since the number of estrogen receptors per nucleus decreased from 5600 to 1600 when nuclei prepared in low ionic strength (mu = 0.013 M) were compared with nuclei prepared in physiological ionic strength (mu = 0.2 M). [3H]Estradiol was introduced into nuclear estrogen receptors by exposing minced oviduct to labeled hormone in tissue culture or by exchanging nuclear estrogen receptor complexes formed in vivo with labeled hormone. In all cases, receptor was found in a fast sedimenting nuclear subfraction of low in vitro template activity. Sodium dodecyl sulfate-gel electrophoresis revealed no differences between proteins from receptor-containing and slower sedimenting fractions. Hybrdization experiments using a cDNA probe made from ovalbumin mRNA indicated no enrichment of this gene in DNA from receptor-containing nuclear material. Salt-extracted nuclear estrogen receptor was shown to partially aggregate to fast sedimenting species of heterogeneous size when sedimented in gradients containing low salt concentrations. Bound receptors were distinguished from such receptor aggregates using a novel electrophoresis technique. In addition, receptor aggregates could be disrupted in high salt, while bound receptors were resistant to this treatment. The number of exchangeable nuclear estrogen receptors in immature chicks given secondary estrogen stimulation was compared with birds that had been withdrawn from hormone. The number of receptors per nucleus was shown to be higher in animals given secondary stimulation, and these receptors were associated exclusively with fast sedimenting nuclear material.     

The chick oviduct in tissue culture. I. Initial characterization of growing primary oviduct tissue cultures

A simple three-enzyme treatment of collagenase, dispase and hyaluronidase on finely minced chick oviduct yields clumps of 50-150 cells. These cells attach to collagen-treated dishes and survive in culture for at least 2 weeks without subculturing. Oviduct cell cultures can also be induced to grow. Estradiol or epidermal growth factor (EGF) induce a 40% increase in cells in 4 days when cultures are grown in serum levels that do not support growth. Serum from estrogen-stimulated chicks promotes rapid cellular proliferation (doubling times of 1-2 days). Sera from estrogen withdrawn chicks, laying hen or horse do not support as rapid proliferation. The oviduct growth-promoting factors in serum from estrogen-stimulated chicks are not steroids or fibroblast growth factors (FGF). Removal of steroids from these sera by charcoal treatment or delipidization does not decrease the rate of growth. The addition of 1-100 nM estradiol does not increase a serum's ability to promote growth. Purified FGF or platelet-derived growth factor (PDGF) do not induce oviduct proliferation. These results were reproduced in oviduct cell cultures started from estrogen-stimulated and withdrawn chicks as well as laying hens. Thus the factors in serum from estrogen-stimulated chicks that promote rapid oviduct growth are induced by estrogen treatments in vivo, but do not seem to be only steroids.     

Expression of the avian c-erb B (EGF receptor) protooncogene during estrogen-promoted oviduct growth

Expression of cellular erb B protooncogene messenger RNAs has been analyzed in the oviducts of immature chicks during estrogen-promoted growth. Hybridization of oviduct total cellular RNA with viral-derived erb B oncogene probes demonstrated significant expression of c-erb B mRNA in oviduct cells of untreated chicks. Daily administration of estrogen (diethylstilbestrol) to chicks results in marked oviduct growth but did not appreciably affect expression levels of c-erb B messenger RNA in oviducts after 2, 4 or 6 days of treatment. Withdrawal of chicks from estrogen treatment resulted in termination of oviduct growth. However, c-erb B messenger RNAs were detectable in the nonproliferative tissue at 5 days after hormone withdrawal. Readministration of diethylstilbestrol, progesterone or diethylstilbestrol plus progesterone to hormone-withdrawn birds (secondary stimulation) also did not affect c-erb B messenger RNA levels in the oviduct. These results demonstrate significant expression of the cellular erb B (epidermal growth factor receptor) gene in the avian oviduct. However, EGF receptor messenger RNA synthesis is not modulated in the oviduct by steroid hormones.     

Kinetics of the appearance of nuclear estrogen binding sites in chicken liver

A single injection of estradiol to immature male chickens results in a very rapid increase in the number of both soluble and tightly bound nuclear estrogen binding sites. After an intermediate levelling off, a second longer lasting increase in binding sites is observed. Whereas the first rapid increase seems to be independent of RNA and protein synthesis, the second one obviously requires intact RNA and protein synthesis. From these results we conclude that there is a pool of cytoplasmic estrogen binding sites, which supplies the precursor for the nuclear binding sites. After this pool is exhausted, it is replenished by new synthesis of binding sites. However, although several laboratories have attempted to demonstrate directly the existence of such a cytoplasmic estrogen receptor in the chicken liver, all have so far been unsuccessful.     

Regulation of nuclear binding of the avian oviduct progesterone receptor. Changes during estrogen-induced oviduct development, withdrawal, and secondary stimulation

The progesterone receptors from various stages of estrogen induced oviduct development, estrogen withdrawal, and secondary stimulation with estrogen were examined. The progesterone receptors were characterized for their biological function (i.e. capacity for nuclear translocation, nuclear binding, and effects on RNA polymerase II activity) as well as certain physical properties. The progesterone receptors from the undeveloped or partially developed oviducts (0 to 8 days of estrogen treatment) displayed little or no nuclear translocation and binding in vivo or in vitro. Similarly, progesterone showed little or no effect in vivo on RNA polymerase II activity at the early stages of development. As development progressed from 8 to 12 days of estrogen treatment, the above parameters rapidly increased to maximal levels and plateaued through day 23 of estrogen treatment. A marked decrease in these parameters occurred within 1 day of estrogen withdrawal. The reverse series of events occurred during secondary estrogen stimulation of 10-day-old withdrawn chicks. While the receptor concentrations increased rapidly to maximum values by 2 days of restimulation, receptor function did not return until day 4. Similarly, the effects of progesterone on RNA polymerase II activity reached maximal values by day 4. The progesterone receptor isolated from oviducts during development, estrogen withdrawal, and restimulation, displayed similar patterns of cell-free binding to chromatin and nucleoacidic protein as that observed in vivo supporting the nativeness of the in vitro binding assay. In contrast, the cell-free binding of these same progesterone receptor to pure DNA were not similar to the in vivo binding, i.e. no patterns (differences) in progesterone receptor binding were observed. These data support that protein DNA complexes and not pure DNA represent the native acceptor sites for oviduct progesterone receptor. Comparison of the progesterone receptor between the functional and nonfunctional states revealed no differences in the steroid affinity for the receptor, in the apparent pI of the species, or in the sedimentation of the receptor under high salt conditions. However, the nonfunctional receptors consistently displayed a deficiency in one of the two monomer molecular species (the B species) as determined by isoelectric focusing. These results suggest that both monomer species of progesterone receptor are required for biological activity. Interestingly, the 7S "aggregate" species of the progesterone receptor was constantly detected even when only one of the monomer species was present.(ABSTRACT TRUNCATED AT 400 WORDS)     

Diethylstilbestrol metabolites and analogs. Biochemical probes for differential stimulation of uterine estrogen responses

Diethylstilbestrol (DES) and certain chemically structural derivatives and analogs, indenestrol A (IA), indenestrol B (IB), indanestrol (IN), and pseudo-DES (PD), have been used as probes to examine various estrogenic responses previously considered interrelated and obligatory to the stimulation of uterine growth. All the analogs had poor uterotropic activity in vivo which ranged from 10-200 times less than that of estradiol or DES. The poor uterotropic activity was not due to poor binding affinity for the receptor. All compounds except IN interacted with the mouse uterine estrogen receptor with high affinity (approximately Ka 1.5-2.2 X 10(10) M-1). In addition, the compounds were able to translocate similar levels of receptor to the nucleus in vivo. Nuclear retention and occupancy of the estrogen receptor by the compounds was comparable to the patterns produced by DES or estradiol. The activity of uterine tissue responses was investigated during treatment with the compounds. Only IA stimulated uterine glucose-6-phosphate dehydrogenase to significant levels similar to DES or estradiol. Uterine progesterone receptor was induced to varying degrees by all compounds; the indenestrol isomers (IA and IB) were the most active. Uterine DNA synthesis was marginally stimulated by the derivatives and analogs except for IB which showed a response increase comparable to DES or estradiol. Because of the differential stimulation, these data suggest that in uterine tissue estrogen receptor stimulates certain biochemical responses independently and not in concert. The ability of a particular response to be increased may depend on the chemical nature of the ligand receptor complex and its interaction at genomic sites.     

The relative binding affinity of diethylstilbestrol to uterine nuclear estrogen receptor: effect of serum and serum albumin

The relative binding affinity (RBA) of diethylstilbestrol (DES) was determined in nuclear fractions of the rat uterus. DES displayed a two- to threefold greater affinity (RBA = 245 +/- 36) than estradiol (RBA = 100) for nuclear E receptor. The RBA of DES to nuclear E receptor was lowered significantly in the presence of rat serum (43 +/- 1) or human serum (52 +/- 7). Dilution of human serum resulted in a progressive increase in the RBA of DES which approached that observed in the absence of serum. Addition of purified human serum albumin mimicked the decrease in RBA of DES that was observed with serum. The IC50 of estradiol was not changed in the presence of either rat serum or albumin. These data show that DES possesses a greater affinity for nuclear E receptor than estradiol and that serum albumin can modulate DES binding to uterine E receptor.     

Oestrogen receptors in chick oviduct. Characterization and subcellular distribution.

Macromolecular components with properties of oestrogen receptors have been identified in the 0.5 M KCl nuclear soluble, the nuclear insoluble and the cytosol fractions of laying hen and immature (2--4 weeks, untreated by hormone) chicken oviduct. 7n the 0.5 M KCl extract of laying hen oviduct nuclei, a receptor, of protein nature according to the effects of enzymic treatments, has been identified. It exhibits high affinity for oestradiol with an apparent equilibrium association constant KA = 4 - 109 M-1 at 4 degrees C. The binding of [3H] oestradiol is abolished by 1 muM oestriol, oestrone and diethylstilboestrol, but not by the same concentration of progesterone, testosterone, and cortisol. Sucrose gradient ultracentrifugation studies in the presence of 0.5 M KCl indicate a sedimentation coefficient of 4.3 S, and there is partial aggregation in low-ionic-strength medium. The estimated number of binding sites per nucleus is about 5000, as calculated from DNA content of chick diploid genome. Most of the binding sites were found to be occupied by endogenous oestrogen(s). Oestradiol dissociates from the receptor according to an apparent two-step mechanism. The half-life time for the faster dissociation step is 18 h at 0 degrees C, 25 min at 20 degrees C and 10 min at 30 degrees C, and for the slower one is 180 h, 115 min and 60 min, respectively. In the 0.5 M KCl extract of immature chicken oviduct nuclei, there are approximately 500 receptor sites per nucleus; their affinity for oestradiol is the same as in the case of laying hen soluble nuclear receptor. After repeated extractions of nuclei with 0.5 M KCl medium, a substantial quantity of oestrogen binding sites remains in the residual fraction. Binding characteristics of this insoluble nuclear receptor resemble those of the soluble nuclear receptor: high affinity for oestradiol (KA = 7 - 10(8) M-1 at 37 degrees C) and specificity for oestrogens. The estimated number of binding sites are approximately 2000/cell for laying hen, and approximately 1000/cell for immature chicken. In the high-speed supernatant fraction of laying hen oviduct homogenates, an oestrogen receptor is also present, but its concentration is low (less than or equal to 100 sites/cell) and at the limits of sensitivity of the methods used. In the cytosol of immature chicken oviduct, there are approximately 2500 oestradiol receptor sites per cell.     

Interaction of the calf uterine estrogen receptor with acceptor sites in heterologous chicken target cell nuclei

Estrogen receptor (ER) from chicken liver and calf uterus were used to study the capacity and the characteristics of the receptor binding sites (acceptor sites) in chicken target cell nuclei. Binding studies were performed at a physiological salt concentration of 0.15 M KCl. Binding of liver ER to liver nuclei was temperature-dependent, showing a 9-fold increase between 0 and 28 degrees C. The maximal number of acceptor sites measured in this cell-free system (280 sites/nucleus) was considerably lower than measured in nuclei after in vivo administration of estrogen (820 sites/nucleus). Moreover incubation of nuclei with the liver ER preparation resulted in a substantial breakdown of nuclear DNA, making this ER less suitable for DNA binding studies. The temperature-activated calf uterine receptor bound to liver nuclei at 0 degrees C, at which temperature no DNA degradation was measured. To all chicken cell nuclei tested, the receptor bound with a high affinity (Kd = 0.4-1.0 nM). Nuclear binding displayed tissue specificity: oviduct greater than heart, liver greater than spleen greater than erythrocytes and was salt dependent. Calf uterine ER binding in liver nuclei ranged from 3000-6000 acceptor sites per nucleus when assayed under conditions of a constant protein or a constant DNA concentration. Nuclei isolated from estrogen-treated cockerels bound a 2-fold lower number of calf uterine ER complexes when compared to control nuclei. Incubation of nuclei with a fixed concentration of [3H]ER from liver and increasing concentrations of uterine non-radioactive-ER also resulted in a reduced binding of the liver receptor. Both types of experiments suggest that liver and uterine ER compete for a common nuclear acceptor site. Our data demonstrate that the ER from calf uterus is very useful as a probe to examine the nature of the acceptor sites in heterologous chicken target cell nuclei. The assay system functions at 0 degrees C, a temperature at which no DNA degradation occurs.     

Estrogen causes a rapid, large and prolonged rise in the level of nuclear estrogen receptor in Xenopus laevis liver.

In male $\text{Xenopus laevis}$, a single large injection of estradiol causes a large rise in the level of estradiol receptor in liver nuclei. The rise is almost certainly due to synthesis, and the newly-synthesized receptor is indistinguishable from pre-existing receptor. The high level of receptor induced by estradiol persists for over 30 days, well after the vitellogenin synthesis that is also induced has disappeared.     

Androgen-induced nuclear accumulation of the estrogen receptor.

The effect of androgens on the nuclear uptake of both tritiated estradiol (3H-E2) and the estrogen receptor was studied in immature rat uteri. It was demonstrated that in vitro preincubation of immature rat uteri with various androgens (1 muM to 50 muM) followed by incubation with 3H-E2 (20 nM) resulted in a greatly decreased specific nuclear uptake of 3H-E2. Non-androgenic steroids had no effect. It was also confirmed that 5alpha-dihydrotestosterone (DHT) causes the accumulation of the estrogen receptor in the nuclei of uterine tissue. In vitro incubations of rat uteri with DHT (1muM and 50muM) were found to cause maximal nuclear estrogen receptor accumulation to the same degree as caused by estradiol, i.e. the nuclear uptake of approximately 100% of the estrogen receptor. Antiandrogens, which block the binding of androgens to the testosterone receptor in various tissues, did not inhibit the DHT - induced decrease in the 3H-E2 uptake by the uterine nuclei or the DHT - caused accumulation of the estrogen receptor in nuclei. These results seem to indicate that the uterine testosterone receptor has no role in the androgen - induced nuclear uptake of the estrogen receptor. However, the non-steroidal antiestrogens inhibited the DHT - induced nuclear accumulation of the estrogen receptor. This would seem to indicate that the estrogen - and androgen - induced nuclear accumulation of the estrogen receptor share a common mechanism.     

Isolation of a nuclear ribonucleoprotein fraction from chick oviduct containing ovalbumin messenger RNA sequences

A method was developed for the isolation of a ribonucleoprotein fraction from chick oviduct nuclei that contains 70% of the pulse-labeled RNA. These fractions also contain about 1% of the nuclear DNA and have an average RNA to DNA ratio of about 4:1. The major nuclear RNP proteins of 32,000 M_r are present along with many additional proteins including histories. However, polysomal proteins and major oviduct cytoplasmic proteins are absent. Nuclei from fully stimulated chick oviduct contain about 3000 copies of ovalbumin messenger RNA sequences of which about 200 are in the RNP complexes: these complexes have sedimentation coefficients of 30 to 350 S and are resistant to disruption by EDTA.The level of ovalbumin mRNA sequences in these complexes reflects the overall rate of synthesis of this RNA. Withdrawal of estrogen leads to a parallel decline of nuclear estrogen receptors and ovalbumin mRNA sequences in the RNP complexes and a subsequent loss of cytoplasmic ovalbumin mRNA about three hours later. The 300-fold decrease in the level of ovalbumin mRNA sequences in these complexes and the eightfold decrease in stability of cytoplasmic ovalbumin mRNA account for the 2500-fold decrease in the level of cytoplasmic ovalbumin mRNA observed during withdrawal. Upon stimulation with estrogen, the kinetics of reappearance of ovalbumin mRNA sequences in the RNP complexes apparently accounts for the accumulation of cytoplasmic ovalbumin mRNA. Thus the nuclear RNP has some of the properties expected of nascent RNP complexes.The levels of ovalbumin and conalbumin mRNA sequences increase in the nuclear RNP with markedly different kinetics: conalbumin mRNA sequences reach half maximum by 1.5 hours, whereas ovalbumin mRNA sequences in these complexes reach half maximum at about eight hours. In the analysis in the accompanying Appendix, we show that the immediate increase of conalbumin mRNA sequences in the nuclear RNP may be accounted for by interaction of the hormone receptor complex with a single regulatory site, whereas the delayed increase of ovalbumin mRNA sequences in the RNP may be due to a requirement for interaction of the hormone receptor complex with multiple regulatory sites.