Human progesterone receptors: synthesis, structure, and phosphorylation.
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The androgen receptor does not mediate progestin regulation of progesterone biosynthesis in cultured rat granulosa cells.
In the present investigation the influence of androgens and progestins on the FSH modulation of progesterone biosynthesis was studied in cultured rat granulosa cells. Cells obtained from the ovaries of immature estrogen treated rats were cultured for three days in serum free medium or in medium supplemented with FSH or CPA, with or without reduced androgen DHT or the synthetic progestin R5020 alone or in combination with the anti-androgen CPA. Treatment with FSH increased pregnenolone, progesterone and 20 alpha-OHP accumulation in the culture medium 20-, 14- and 7-fold, respectively. Furthermore FSH increased the activity of the enzyme 3 beta-HSD. Concurrent treatment with DHT or R5020 augmented the FSH stimulated steroidogenesis of cultured cells. The androgen enhancement of FSH stimulated steroidogenesis of cultured granulosa cells was blocked by concomitant treatment with CPA, whereas treatment of cultures with anti-androgen did not affect the stimulatory effect of the synthetic progestin R5020.
20-alpha-Dihydroprogesterone↗
Simultaneous measurement of progesterone receptors and DNA indices by flow cytometry: analysis of breast cancer cell mixtures and genetic instability of the T47D line.
A flow cytometry assay that can simultaneously measure progesterone receptors (PR) and DNA indices in breast cancers would be a valuable clinical tool. We have developed a prototype assay that has proven useful in studies of the cell biology of breast cancer cell lines. The assay uses PR-specific monoclonal primary antibodies and fluorescein-conjugated secondary antibodies to measure PR, and propidium iodide to measure DNA. We find that the specific PR fluorescence generated by labeling PR-rich T47D human breast cancer cells is located predominantly in nuclei. The flow cytometry assay can quantitatively measure large fluctuations in intracellular PR levels: an apparent increase in PR following acute progestin treatment that cannot be documented by ligand binding assays; and the receptor down-regulation that follows chronic progestin treatment. The assay can identify fewer than 10% PR-positive cells in a population of PR-negative cells having the same DNA content, and it can sort PR-positive and PR-negative cells from cell mixtures having different DNA indices. Gating allows quantitative analysis of these mixed cell populations by ploidy, cell-cycle phase, and PR content. Finally, the assay has allowed us to monitor the gradual emergence of a stable hypertetraploid cell population, designated T47Dv, from the wild-type hyperdiploid T47Dco stocks. The new cells have unchanged estrogen receptors but even higher PR levels than the parental cells. They have five to ten copies of chromosome 11, site of the PR gene and other genes of interest in breast cancer.
Biomarkers, Tumor↗
Synthesis of human progesterone receptors in T47D cells. Nascent A- and B-receptors are active without a phosphorylation-dependent post-translational maturation step.
Human progesterone receptors (PR) are structurally complex. At basal states there are two forms: A-receptors of approximately 94 kDa and B-receptors which are triplets of approximately 114, 117, and 120 kDa. All the proteins bind hormone and are phosphorylated. By using PR-rich T47Dco human breast cancer cells, pulse-labeling with [35S]methionine, and receptor immunopurification with anti-PR monoclonal antibodies, we show that PR are synthesized as single B-proteins of 114 kDa and single A-proteins of 94 kDa. The mature B-triplets form 6-10 h later by post-translational phosphorylation at sites restricted to the B-proteins. This slow maturation is not required for PR activation to hormone binding states, however, since A- and B-receptors that are less than 15 min old respond to progestins by undergoing transformation and nuclear binding accompanied by a rapid secondary phosphorylation common to both proteins. These studies explain the complex structure of the mature human B-receptors and the transformed A- and B-receptors, and address issues dealing with A- and B-proreceptor synthesis and receptor activation rates.
Cell Nucleus↗
Simultaneous measurement of progesterone receptors and DNA indices by flow cytometry: characterization of an assay in breast cancer cell lines.
Progesterone receptors (PR) are the strongest predictors of response to hormone therapy in metastatic breast cancer, while PR and the DNA indices of cell ploidy and percentage of S phase are useful prognostic indicators in early stage breast cancer. We have developed a flow cytometry method to measure PR and DNA indices simultaneously using two aneuploid breast cancer cell lines--PR-positive T47D cells and PR-negative MDA-231 cells. Cells were pretreated with the progestin 17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione, harvested, counted, fixed with paraformaldehyde, and permeabilized with Triton X-100. To measure total PR, cells were first exposed to a mixture of the mouse anti-PR monoclonal antibody AB-52, which binds both Protein A and Protein B of human PR, and to monoclonal antibody B-30 or B-64, which bind only Protein B. Then the cells were treated with fluorescein isothiocyanate-conjugated goat anti-mouse second antibody to produce a green fluorescence signal corresponding to PR. To measure nonspecific binding, cells were treated with mouse IgG1 as the first antibody in a parallel incubation. Specific immunoassayable PR is the difference between total and nonspecific binding. Following the antibodies, the cells were treated with RNase A and propidium iodide to give a red fluorescence signal corresponding to DNA content. Red and green fluorescence per cell was then quantified by flow cytometry. This method gives a strong specific signal for PR in several T47D cell sublines but no specific binding in MDA-231 cells. Progestin treatment led to apparent increases in PR. The proportion of cells in the G0-G1, S, and G2-M phases of the cell cycle was determined from DNA histograms and showed that both cell lines were hyperdiploid. The simultaneous flow cytometry method allowed assignment of relative PR levels in subsets of cells segregated by their DNA content. In T47D cells, PR were present throughout the cell cycle, and levels doubled in G2 and mitosis.
Antibodies, Monoclonal↗
Comparison of an immunocytochemical assay for progesterone receptor with a biochemical method of measurement and immunocytochemical examination of the relationship between progesterone and estrogen receptors.
Using a rat monoclonal antibody raised against human progesterone receptor (PR) we have developed an immunocytochemical technique to detect PR in human normal and malignant breast tissue and have compared the distribution of this with that obtained by the conventional dextran-coated charcoal steroid-binding assay. Immunoreactive PR was detected exclusively in the nuclei of epithelial cells in 29/51 (56.9%) of breast cancers studied. There was an excellent correlation between the immunocytochemical and dextran-coated charcoal techniques, with concordance in 43/51 (84.3%) cases [regression coefficient (Spearman) = 0.78; P less than 0.001]. The relationship between PR and estrogen receptor (ER) was also examined immunocytochemically using a monoclonal antiserum to ER. Twenty-eight out of 51 (54.9%) tumors were positive for both receptors and 13/51 (25.5%) negative for both. ER-positive, PR-negative tumors were found in 9/51 (17.6%) cases whereas only one case (2%) was PR-positive, ER-negative.
Antibodies, Monoclonal↗
Effect of ether or ketamine anesthesia on rat uterine estrogen and progesterone receptors.
Rat uterine estrogen receptors (ER) and progesterone receptors (PR) have been used as controls in ER and PR assays of breast tumors. Stunning or decapitation of experimental animals without prior anesthesia is no longer acceptable as a method of killing. Thus, we compared the effects of two anesthetics on the concentration of rat uterine ER and PR. Rats were killed by one of three methods: (a) stunning, (b) ether anesthesia followed by decapitation, or (c) ketamine anesthesia followed by decapitation. ER and PR concentrations were determined by titration assay, with dextran-coated charcoal separation, and quantified by Scatchard analysis. No significant differences were found in mean receptor concentrations or dissociation constants for the three groups. The results indicate that there is no residual effect of diethyl ether or ketamine hydrochloride on the binding of either estrogen or progestin to their respective receptors. The use of decapitation after either ether or ketamine anesthesia is appropriate for measuring ER and PR receptors in rat uteri.
Anesthesia↗
Mammalian progesterone receptor shows differential sensitivity to sulfhydryl group modifying agents when bound to agonist and antagonist ligands.
Modulation of calf uterine progesterone receptor (PR), in relation to its binding to synthetic steroids with known agonist (R5020) and antagonist (RU486) properties, was studied in the presence of iodoacetamide (IA), N-ethylmaleimide (NEM), beta-mercaptoethanol (MER), and dithiothreitol (DTT). Pretreatment of uterine cytosol at 4 degrees C with NEM (4-10 mM) reduced the binding of [3H]RU486 to PR by 40%, but [3H] R5020 binding was completely abolished. Whereas IA (2-10 mM) treatment did not affect [3H]RU486 binding, [3H]R5020 binding was totally eliminated. DTT or MER increased the binding of both steroids slightly (15%). [3H]R5020- or [3H]RU486-receptor complexes (Rc) migrated in the 8 S region and were eliminated upon pretreatment with NEM. At 23 degrees C, DTT increased the amount of 4 S [3H]R5020-Rc, but had no effect on the [3H]RU486-Rc. In the control, [3H]RU486 binding to the 8 S PR could be competed with radioinert R5020 or RU486, but R5020 failed to compete in the presence of IA. The heat-treated [3H]R5020- and [3H]RU486-Rc showed reduced binding to DNA-cellulose in the presence of NEM and IA. The results of our study suggest that SH group modifications differentially influence the properties of mammalian PR complexed with either R5020 or RU486. In the presence of IA, the [3H]RU486-Rc remained in the 8 S form when incubated at 23 degrees C, indicating that RU486 binding causes conformational changes in PR which are distinct from those that result upon R5020 binding.
Animals↗
Establishment of pharmacological doses of estrogen-dependent mammary tumors with estrogen and progesterone receptors.
A new mammary carcinoma (TF15) which was derived from ovary-dependent mammary carcinoma (TF4) and which was dependent on pharmacological doses of estrogen was established. TF15 grew well in ovariectomized rats given injections of 1mg 17 beta-estradiol but not in intact or ovariectomized rats with injections of 0,1, 10 or 100 micrograms 17 beta-estradiol. TF15 was found to be a secretory carcinoma and contained estrogen and progesterone receptors. In general, pharmacological doses of estrogen inhibit the growth of mammary carcinomas with estrogen receptors (ER) and progesterone receptors (PgR) in humans and animals whether they are ovary-dependent or not (1-10). Recently, we obtained mammary carcinomas which are dependent on pharmacological doses of estrogen by subcutaneous implantation of explants from ovary-dependent mammary carcinomas (TF4) in female rats after ovariectomy and injections of low doses of estrogen. In the present paper, the biological, biochemical and morphological characteristics of these carcinomas are reported.
Animals↗
Decreased progesterone binding and attenuated progesterone action in cultured human breast carcinoma cells treated with epidermal growth factor.
Specific progesterone binding by cultured human breast carcinoma T47D, MCF-7, and ZR75-1 cells was decreased 25-40% by epidermal growth factor (EGF), with a 50% effective dose of 0.1 nM EGF. Studies with the soluble and particulate fractions prepared after homogenization of T47D cells grown in glass roller bottles revealed equivalent EGF-induced decreases in progesterone binding to receptors in both fractions. Equilibrium progesterone binding studies with these soluble and particulate fractions revealed that EGF decreased the receptor number, but had no effect on affinity. With cells grown adherent to plastic dishes, EGF treatment induced a greater decrease in binding to receptors recovered in the particulate fraction, than to receptors recovered in the soluble fraction. The decrease in progesterone binding induced by 20 nM EGF was maximal after 2 min of cellular EGF treatment for receptors recovered in the soluble fraction, but was only half-maximal after 15 min for receptors recovered in the particulate fraction. Decreased progesterone binding persisted for at least 8 days in cells cultured with 1 nM EGF. Either insulin or EGF stimulated T47D cell proliferation by two- to threefold with a 50% effective dose of 100 nM for insulin and 0.1 nM for EGF. The progestin, R5020, decreased T47D cell growth by 30% with a 50% effective dose of 1 nM. Either EGF or insulin antagonized the inhibitory effect of R5020 on cell reproduction, but progestins did not antagonize the growth stimulatory response of cells to EGF. Progestins increased the number of EGF receptors within 12 h of their addition to T47D cells, but this response was lost after 6 days. These data show that EGF or progesterone can regulate the receptor number of the other, but for cell reproduction, the effect of EGF is dominant over that of progestins.
Animals↗
Progesterone receptor: stability studies and correlation between steroid binding assay and enzyme immunoassay.
We evaluated and compared Abbott Laboratories' newly developed enzyme immunoassay (EIA) for measuring progesterone receptors (PgR) with that of DuPont's steroid-binding assay (SBA). We also used both methods to study the stability of PgR under various conditions. THere were excellent correlations for all 59 cytosols compared (r = 0.94) and for the 44 cytosols containing PgR greater than 10 fmol per milligram of protein (r = 0.93), but the correlation for cytosols containing less than 10 fmol of PgR per milligram was poor. We found PgR to be more stable as assayed by EIA than by SBA. The biological half-lives of PgR at 30, 4, and -60 degrees C were approximately 3 h, 6 days, and 19 days, respectively. The effect of molybdate on PgR is complex. Its presence during tissue homogenization leads to analytical recovery of more PgR and may stabilize PgR during storage. Its presence during enzyme immunoassay is less critical. Unlike estrogen receptor, PgR is not protected by its ligand, R5020.
Half-Life↗
Effects of progestins on growth of experimental breast cancer in culture: interaction with estradiol and prolactin and involvement of the polyamine pathway.
The role of progesterone either alone or in combination with other hormones in breast cancer growth is not well established. In these experiments, using the hormone-responsive N-nitrosomethylurea-induced rat mammary tumor grown in the soft agar clonogenic assay, we tested the colony-stimulating effect of progesterone and the synthetic progestin R5020 over a wide range of physiological and pharmacological concentrations (from 0.1 nM to 10 microM). Both progesterone and R5020 were found to have a significant colony-stimulating effect which was more pronounced in the absence of serum. The action of progesterone appeared to plateau at concentrations of 10 or 100 nM, whereas R5020 was maximally effective at lower concentrations (approximately 1 nM). A biphasic dose-dependent effect was occasionally seen both with progesterone and R5020 with a loss of colony-stimulating effect at high concentrations. The combined administration of varying doses of progesterone (0.1, 1, 10, and 100 nM) and estradiol (10(-10) M and 10(-9) M) was found at times to potentiate and at times to decrease colony formation over that observed with the individual treatments. The former effect, when present, was usually seen with low doses of progesterone, while the latter was frequently observed with high concentrations (100 nM). No major potentiation or suppression of colony formation over individual treatments was observed when varying doses of progesterone (1, 10, and 100 nM) were added together with prolactin (50 ng/ml). The administration of the polyamine biosynthesis inhibitor alpha-difluoromethylornithine completely blocked the colony-stimulating effect of progesterone. The inhibitory effect of alpha-difluoromethylornithine was completely reversed in a dose-dependent fashion by exogenous administration of spermidine, thus implying a critical involvement of the polyamine pathway in progesterone action.
Animals↗
Immunocytochemical localization of progesterone receptors in breast cancer with anti-human receptor monoclonal antibodies.
Monoclonal antibodies (MAbs), recently produced against human progesterone receptors (PR), were used for immunocytochemical localization of PR. The specificity of the immunocytochemical assay for PR was demonstrated by incubation with control MAbs, preabsorption of MAbs with highly purified human PR, and by the cell and tissue distribution of the immunostaining reaction. With human breast cancer cell lines, immunoreactivity was confined to cells that contain PR by steroid-binding assay. Moreover, immunostaining was induced by estradiol in estrogen-responsive cells, MCF-7 and ZR-75-1. In a preliminary study with 33 breast carcinomas, a good correspondence was obtained between immunocytochemical staining and PR content assessed by conventional steroid-binding assay. Immunoperoxidase localization was also obtained with other human target tissues. In normal breast and benign breast disease, immunoreactivity was observed with nuclei of ductal epithelial cells and hyperplastic epithelium. In uterus, immunostaining of endometrium was localized to nuclei of stromal and glandular epithelial cells and in myometrium to nuclei of smooth muscle cells. The effect of the progestin agonist, R5020, and antagonist, RU 486, on PR localization was investigated with the PR-rich T47D human breast cancer cell line. In the absence of hormone, immunostaining was exclusively nuclear. This was true under a number of cell culture conditions designed to eliminate endogenous progestins from the culture medium. Exclusive nuclear localization of PR was not due to a failure of the MAbs to recognize unoccupied PR, since each MAb bound equally well in vitro with different receptor forms. These included liganded and unliganded cytosol PR, molybdate stabilized PR, and nuclear-transformed receptors. Nor was failure to detect cytoplasmic staining due to a selective destruction or loss of unoccupied PR from the cytoplasmic compartment as a result of cell fixation. This was assessed by dot blot immunoassay of PR antigen distribution in subcellular fractions of fixed and unfixed cells. Continuous exposure of cells to R5020 resulted in a transient (30-60 min) increase in nuclear staining intensity (without change in cytoplasmic reactivity), followed by a progressive decline in immunoreactivity. By 24 h of R5020 treatment, the vast majority of cells displayed no immunostaining reaction. These immunocytochemical data are consistent with progestins down regulating their own receptors due to a loss in cellular PR content and not to inactivation of receptors.(ABSTRACT TRUNCATED AT 400 WORDS)
Antibodies, Monoclonal↗
Microassay for nuclear binding of steroid receptors with use of intact cells from small samples of avian and human tissue.
A micro version of a nuclear binding assay to assess the biological activity of receptors for steroid hormones was developed for application to small (needle) biopsies of human tumors for the purpose of predicting responses to steroid therapy. This easier assay requires 10-fold less tissue than the original nuclear binding assay described for progesterone receptors in the avian oviduct, endometrium, and endometrial carcinomas (Spelsberg TC, et al., Endocrinology 1987;121:631). We describe the application of this micro assay to normal avian oviduct and cancers of the human breast, and we demonstrate a tissue specificity and saturation of nuclear binding. The micro assay reliably measured as little as 0.5 mg equivalents of tissue per assay tube. Results for breast tumors determined to be estrogen-receptor-positive by the standard dextran-coated charcoal method were also determined with this nuclear binding assay. As described previously for progesterone receptors in endometrial carcinomas, some receptor-positive breast biopsies displayed negligible capacity for nuclear binding. Therefore, with the present assay we have identified nonfunctional receptors in these biopsies, which may be useful for accurate prediction of patients' responses to therapy with hormones.
Animals↗
Resolution of high and low affinity progesterone receptors from human breast carcinoma T47D cells.
Each of four independent experimental approaches showed that human breast carcinoma T47D cells contain both high and low affinity progesterone receptors. (i) Equilibrium-specific [3H]progesterone binding to adherent cultured cells revealed dissociation constants (Kd) of 1.5 and 60 nM and 0.33 and 2.4 X 10(6) sites/cell, respectively. Both the high and low affinity receptors were specific for progestins as demonstrated by steroid binding competition studies conducted at 5 and 50 nM [3H]progesterone. (ii) Equilibrium [3H]progesterone binding to the resolved soluble and particulate fractions from a cell homogenate sedimented at 40,000 X g.min revealed Kd = 1.4 nM high affinity binding sites exclusively in the supernatant fraction and Kd = 24 nM low affinity sites exclusively in the particulate fraction. Extraction of the particulate fraction with a high ionic strength buffer solubilized the low affinity receptors stoichiometrically; but once solubilized, they displayed Kd = 2.4 nM high affinity progesterone binding. Characterizations of 3H-ligand bound specifically to progesterone receptors in intact cells or resolved subcellular fractions revealed no [3H]progesterone metabolites that could account for the low affinity binding. (iii) Calculations based on the rate constants of [3H] progesterone association with or dissociation from adherent cells revealed the same dissociation constants for both high and low affinity binding as those determined by equilibrium measurements. (iv) Nonionic detergent extraction of cells incubated with a wide range of [3H]progesterone concentrations revealed high affinity progesterone binding to receptors in the detergent-soluble fraction and low affinity binding associated primarily with the particulate residue, consistent with the data on equilibrium progesterone binding to resolved cell homogenate fractions. The rate of extraction of the high affinity receptor-progesterone complex with nonionic detergent (t1/2 = 1 min at 0 degrees C) equaled the rate of extraction of a representative lysosomal enzyme, beta-acetylglucosaminidase.
Binding, Competitive↗
Sex steroid receptors in normal and malignant endometrium.
Estradiol and progesterone receptor concentrations have been measured and their hormonal regulation extensively studied in normal human endometrium. However, in endometrial cancer, the biochemical assays presently used face the complex problem of tumor and tissue heterogeneity. This problem may be circumvented by immunocytochemistry on tissue sections proven to be histologically malignant. The in vivo experimental model developed in our laboratory is an ideal source of tissue necessary for purification of the progesterone receptor and antibody production. Hopefully, the physiology of the receptor may be studied under ideal conditions in this experimental system.
Affinity Labels↗
Intracellular localization of steroid hormone receptors. A challenging problem. Autoradiographic and biochemical study.
The classical model for the mechanism of action of steroids holds that unbound receptors for steroids reside exclusively in the cytoplasmic compartment and that they undergo translocation to the nucleus when bound to steroids in a process which is temperature sensitive. In the present study we looked at the localization of the estradiol receptor using autoradiography and biochemical procedure. Uteri from ovariectomized and/or ovariectomized-adrenalectomized rats, as well as several cell lines (with estrogen receptor (ER+) were incubated with [3H]-estradiol or [3H]-R2858 (methoxy-17-ethinylestradiol) for 5 min to 2 h at different concentrations of ligands (0.1-10 nM) at 4 degrees C. When the tissue or cells were processed for autoradiography the localization of steroid was nuclear and cytoplasmic. In contrast when the tissue or cells were processed using the usual biochemical procedures, all binding activity appeared in the cytosolic fraction. In addition, when concentrated preparations of homogenized uteri as well as several nuclear preparations from cell lines were made, free receptor could be demonstrated in the crude nuclear preparations. In the present study, data are presented which suggest that there are unbound receptors for estrogen in nuclei of the smooth muscle cells of myometrium as well as in nuclei of the several cell lines (ER+). We propose a new model for the distribution of estrogen receptors in which unbound receptors are in equilibrium, partitioned between nucleus and cytoplasm according to the free water content of these intracellular compartments.
Adrenalectomy↗
Identification and androgen regulation of two proteins released by T47D human breast cancer cells.
Three [35S]methionine-labeled polypeptides released by T47D human breast cancer cells have been identified as corresponding to two proteins previously described in breast gross cystic disease fluid. A Mr 43,000 protein was immunoprecipitated by polyclonal antibodies to the Zn-alpha 2-glycoprotein. A Mr 18,000 and a Mr 13,000 polypeptide were both immunoprecipitated by four monoclonal antibodies directed against four separate epitopes of Mr 15,000 gross cystic disease fluid protein, a major protein that is characteristic of apocrine gland secretions. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, purified Mr 15,000 gross cystic disease fluid protein migrated at the level of the Mr 18,000 protein of T47D cells. The proteins were regulated by androgens and progestins. In addition to a general stimulation of protein secretion, 5 alpha-dihydrotestosterone (DHT) specifically increased, by 2- to 20-fold, the release of the Mr 43,000 and Mr 18,000 proteins into the medium. DHT also increased the cellular level of the Mr 18,000 protein, as shown by immunoprecipitation with a Mr 15,000 gross cystic disease fluid protein antibody, which suggests a stimulation of protein synthesis. The progestin 17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione also increased the release in the medium of the Mr 43,000 and Mr 18,000 proteins, but higher molar concentrations were required than in the case of DHT. The induction of these proteins by DHT and 17,21-dimethyl-19nor,4,9-pregnadiene-3,20-dione was specifically inhibited by the antiandrogen flutamide which has no effect on other progestin-regulated proteins. This suggests an effect mediated by the androgen receptor. This is the first report on the identification of two proteins induced by androgens in a human breast cancer cell line. These proteins should be useful in studying the role of androgens in human mammary tumors and their mechanism of action in cell culture.
Androgens↗