Aromatase activity in human ovarian cancer

Eighty-four tumor samples from 70 women with primary ovarian cancer were assayed for cytosol estrogen (ERc) and progestin (PRc) receptor concentrations and aromatase activity. In addition, 22 of the tumors were studied for their response to the aromatase inhibitor, 4-OH-androstenedione, in a soft agar clonogenic cell assay system. Although aromatase activity was detected in almost all of the primary tumors, this enzyme was barely detectable in the majority of metastatic tumor samples. There was no significant correlation between aromatase activity and either the ERc or PRc content of the tumors, or tumor grade. Of 12 tumors grown successfully in the soft agar culture system, only 1 showed a substantial (>50%) reduction in colony-forming efficiency after exposure to the aromatase inhibitor. These results suggest that local estrogen biosynthesis probably does not play an important role in the majority of epithelial ovarian tumors. However, there may be a small subset of estrogen receptor-positive tumors in which aromatase could provide a local growth stimulus.     

Analysis of rat uterine estrogen receptors by high-pressure liquid chromatography methods

Cytosolic (ERc) and nuclear (ERn) estrogen receptors prepared from rat uteri were characterized by size-exclusion and ion-exchange HPLC. The oligomeric ERc eluted as a single, sharp peak near the exclusion volume of the gel column; ERn eluted as a broad peak. When salt-extracted ERn was partially purified sequentially by Sephadex G-200, DEAE-cellulose chromatography and polyacrylamide gel electrophoresis, the partially purified receptor moieties were not distinguishable by the sucrose gradient method, but showed characteristic retention times in the size-exclusion HPLC column. Further distinction in net surface charges was observed between ERc and ERn moieties by ion-exchange high-pressure liquid chromatography (HPLC). Molybdate-stabilized ERc was eluted as sharp peak at 0.27 M salt gradient. In contrast, fresh extracts of ERn emerged as a broad peak in the region of 0.1-0.2 M salt gradient. In the absence of molybdate, ERc dissociated into several 4-5 S molecules, which were well resolved in the DEAE column. This report, therefore, demonstrates the usefulness of size-exclusion and ion-exchange HPLC for steroid receptor analysis.     

A study of cytoplasmic and nuclear estrogen and progestin receptors in gynecologic neoplasms

A rapid method for simultaneous preparation of cytosol and nuclear estrogen (E) and progestin (P) receptors and their in vitro determination is described. The method was applied to several uterine or ovarian surgical specimens to evaluate their steroid hormone "dependence". The results suggest that low cytoplasmic E receptor levels (ERc) are associated with higher nuclear E receptor (ERn) levels but no apparent correlation was observed between PRc and ERn levels. The method appeared to be suitable for screening steroid hormone receptor content in tumor tissues and may provide better estimation of steroid dependence since both cytoplasmic and nuclear compartments can be studied simultaneously.     

Transformation of calf uterine progesterone receptor: analysis of the process when receptor is bound to progesterone and RU38486

Effects of different transforming agents were examined on the sedimentation characteristics of calf uterine progesterone receptor (PR) bound to the synthetic progestin [3H]R5020 or the known progesterone antagonist [3H]RU38486 (RU486). [3H]R5020-receptor complexes [progesterone-receptor complexes (PRc)] sedimented as fast migrating 8S moieties in 8-30% linear glycerol gradients containing 0.15 M KCl and 20 mM Na2MoO4. Incubation of cytosol containing [3H]PRc at 23 degrees C for 10-60 min, or at 0 degrees C with 0.15-0.3 M KCl or 1-10 mM ATP, caused a gradual transformation of PRc to a slow sedimenting 4S form. This 8S to 4S transformation was molybdate sensitive. In contrast, the [3H]RU486-receptor complex exhibited only the 8S form. Treatment with all three activation agents caused a decrease in the 8S form but no concomitant transformation of the [3H]RU486-receptor complex into the 4S form. PR in the calf uterine cytosol incubated at 23 or at 0 degrees C with 0.3 M KCl or 10 mM ATP could be subsequently complexed with [3H]R5020 to yield the 4S form of PR. However, the cytosol PR transformed in the absence of any added ligand failed to bind [3H]RU486. Heat treatment of both [3H]R5020- and [3H]RU486-receptor complexes caused an increase in DNA-cellulose binding, although the extent of this binding was lower when RU486 was bound to receptors. An aqueous two-phase partitioning analysis revealed a significant change in the surface properties of PR following both binding to ligand and subsequent transformation. The partition coefficient (Kobsd) of the heat-transformed [3H]R5020-receptor complex increased about 5-fold over that observed with PR at 0 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Neonatal castration of male and female rats affects hypothalamic and pituitary estrogen nuclear and progestin cytosol receptors

We compared the effects of neonatal or adult castration (7 days) and 2 or 7 days of estrogen treatment on the concentrations of estradiol cystolic (ERc) and nuclear (ERn), and progestin cytosolic receptors (PRc) in the hypothalamus, amygdala and pituitaries of adult rats. Two days of estradiol (E2) treatment greatly increased ERn levels, but no further concentration changes occurred by Day 7 in any of the tissues. Long- and short-term castrated males and females had comparable ERn concentrations on Day 2 versus Day 7. Tissue ERn levels were significantly lower in short-term males compared to short-term females or neonatally castrated males and females. In a second study, ERn levels were compared in E2-treated short-term castrated males and females on Day 2. A sex difference was observed, with females having greater ERn levels in most areas. Estrogen significantly increased PRc levels in pituitary (PIT) and hypothalamus, and these levels were comparable in Day 2 and Day 7 animals. Thus, the ability of estrogen to induce PRc synthesis is somewhat refractory in long-term castrated rats.     

Flow cytometric analysis of human breast tumors and assessment of in vitro chemosensitivity by clonogenic assays

We report a double-agar clonogenic system adapted to human breast cancer. We optimized the conditions for cell growth and clonogenicity with respect to hormones (insulin, estradiol, progesterone) and components of the extracellular matrix (collagen, laminin and fibronectin). Using our experimental improvements, 67% of the breast tumor samples received were grown successfully. Tests on 21 tumors with three agents: Doxorubicin, Methotrexate and 5-Fluorouracil permit objective discrimination of the in vitro pharmacosensitivity of human breast tumors. Flow cytometric analysis reveal that 64% of the tumors were diploid and 36% were aneuploid. The aneuploid tumors grew better in the double agar layer system used for the clonogenic assay. The diploid tumors were especially rich in estrogen (ER⁺) and progesterone (PR⁺) receptors whereas the aneuploid tumors were mostly estrogen and progesterone receptors negative (ER^–/PR^–). Finally, we noted no difference in drug responsiveness depending on the tumor ploidy and steroid receptor content.Abbreviations DCC dextran coated charcoal - DI DNA index - DXB Doxorubicin - ECM extracellular matrix component - ER estrogen receptors - FCM flow cytometry - 5-FU 5-Fluorouracil - HTSCA human tumor stem cell assay - MTX Methotrexate - PBC primary breast carcinoma - PI proliferative index - PR progesterone receptors - SPF S phase fraction     

Steroid receptors analysis in human mammary tumors by isoelectric focusing in agarose

A high resolution and quantitative method for isoelectric focusing has been developed to separate the isoforms of estrogen and progesterone receptors in human mammary tumor cytosols stabilized by sodium molybdate. Agarose gels (0.5%) were used. Six samples can be analyzed on one gel in about 2 h, and 35-microliters samples are sufficient to determine the estrogen receptor isoform pattern. The constant yields and the reproducibility of data allow a quantitative analysis of these receptors. Four estrogen receptor isoforms have been observed (pI 4.7, 5.5, 6, and 6.5), isoforms with pI 4.7 and 6.5 being present in all tumors. After incubation at 28 degrees C in high ionic strength, the comparison of isoelectric focusing and high-performance size exclusion chromatography patterns of estrogen receptor confirms the oligomeric structure of the pI 4.7 isoform and suggests a monomeric structure for the pI 6.5 isoform. Under the same conditions of analysis, only one progesterone receptor isoform has been detected with pI 4.7.     

Sodium molybdate increases the amount of progesterone and estrogen receptor detected in certain human breast cancer cytosols

When sodium molybdate is added at a final concentration of 20 mM, additional 85 and 4S progesterone (³ H-R5020) receptor can be detected in the cytosols from a number of human breast cancers. Additional estrogen receptor also could be measured in some cytosols, and a quantitative temperaturedependent conversion of 8S to 4S binding molecules achieved. Sodium molybdate also prevented the loss of binding activity that occurred when cytosols were incubated at 30° in the absence of added estradiol. In addition to increasing the amount of progesterone receptor, and to a lesser extent estrogen receptor that may be detected, elucidation of the mechanism by which this salt stabilized receptors should contribute to further understanding of how cytosol steroid receptor content and function is regulated.     

Metabolism of pregnenolone by human breast cancer. Evidence for 17 alpha-hydroxylase and 17,20-lyase.

The metabolism of 7-(3)H-pregnenolone was studied in vitro using 16 human breast carcinomas. All mammary tumors transformed pregnenolone to progesterone. All estrogen receptor poor tumors and 4 out of 8 estrogen receptor rich tumors converted pregnenolone to 17-hydroxypregnenolone. Five estrogen receptor poor tumors showed the presence of 17,20-lyase as evidenced by formation of dehydroepiandrosterone and androstenedione. In two estrogen receptor poor tumors, conversions of pregnenolone to progesterone, 17-hydroxy pregnenolone, dehydroepiandrosterone, androstenedione and finally to estradiol was documented, providing a hypothetical pathway for steroid metabolism in human breast cancer. The conversion of pregnenolone to 17-hydroxypregnenolone was significantly less in receptor rich tumors and was totally absent in 4 receptor rich tumors with estrogen receptors of over 45 fmol/mg protein.     

Characterization of steroid hormone receptors with ion-exchange fast protein liquid chromatography

Androgen, estrogen and progesterone receptors have been characterized with anion exchange Fast Protein Liquid Chromatography (FPLC) on a Mono Q column (Pharmacia). In the presence of sodium molybdate androgen receptors in cytosols from rat prostate, rat epididymis and calf uterus eluted as a single sharp peak at 0.32 M NaCl with recoveries of approx 90%. The molybdate-stabilized form of the androgen receptor from rat prostate was purified about 75-fold. The receptor containing FPLC-peak fractions sedimented in high salt (0.4 M KCl) linear sucrose gradients at 3.6 S (prostate) and at 4.6 S (epididymis and calf uterus) respectively. Multiple forms of the androgen receptor were present in cytosols from rat prostate prepared in the absence of sodium molybdate, probably due to proteolytic breakdown of the native form. Calf uterine estradiol and progesterone receptors prepared in the presence of sodium molybdate (20 mM) eluted from the Mono Q column at 0.32 M NaCl. The molybdate-stabilized forms of the oestradiol and progesterone receptors were purified approx 70-fold and 30-fold respectively. In the absence of molybdate the estradiol receptor dissociated into two major forms eluting at 0.23 M NaCl and 0.37 M NaCl. After heat induced transformation (30 min at 25 degrees C) of the estradiol receptor one major peak was eluted at 0.42 M NaCl, indicating a change in the surface charge of the estradiol receptor as a result of the 4 S to 5 S transformation. It is concluded that the FPLC anion exchange system is a powerful, fast tool for characterization and partial purification of steroid receptors. In addition this technique could be applied as a rapid procedure for the quantitative estimation of steroid receptors in small biological samples.     

Physicochemical analysis of reversible molybdate effects on different molecular forms of glucocorticoid receptor

Several distinct molecular forms of glucocorticoid receptor have been identified in a melanoma model system. We have used velocity sedimentation to monitor molybdate dependent alterations in receptor size and heterogeneity. In the absence of molybdate, native glucocorticoid receptor from dexamethasone-sensitive tumors sediments at 7–8 S and 12–13 S. Under identical conditions, receptor isolated from dexamethasone-resistant tumors sediments at 7–8 S only. However, when molybdate is introduced, either during homogenization or immediately prior to centrifugation, glucocorticoid receptors from both dexamethasone-sensitive and -resistant tumors sediment sharply at 9–10 S. These molybdate induced phenomena are reversible. The activated forms of glucocorticoid receptor isolated from both dexamethasone-sensitive and -resistant tumors by DEAE-cellulose chromatography have similar sedimentation coefficients (4–5 S) which are unaffected by molybdate.     

Interaction of antiprogestins with progesterone receptors in rat uterus

Cytosolic and nuclear progesterone receptors (PRc and PRn) under antiprogestin treatment were measured in rat deciduoma and compared with values for contralateral (nondeciduomatous) rat uterine tissue. Uterine PRc and PRn of the progesterone treated group were 101 +/- 8.7 and 4770 +/- 590 fmol/mg DNA respectively. After treatment with antiprogestins STS-557, 5 alpha-DNE, (5 alpha-dihydronorethisterone), 5 alpha-DNG (5 alpha-dihydronorgestrel), RU-22092 and RU-16556, PRc in the nondeciduomatous control horn ranged from 127 to 377 fmol/mg DNA and PRn from 2785 to 17925 fmol/mg DNA. In the decidual tissue, PRc decreased significantly (4.6 +/- 0.8 fmol/mg DNA) on 5 alpha-DNG treatment as compared with the progesterone alone treatment group (147 +/- 3.8). PRn in decidual tissue also decreased maximally on 5 alpha-DNG treatment. These results suggest that the interaction of antiprogestins may not be identical in control uterine tissue and in deciduoma.     

Effects of molybdate on steroid receptors in intact GH1 cells. Evidence for dissociation of an intracellular 10 S receptor oligomer prior to nuclear accumulation

Treatment of intact GH1 cells with sodium molybdate inhibits the subsequent rate of nuclear accumulation of hormone-occupied glucocorticoid and estrogen receptors. Cells were incubated at 23 degrees C for 1 h with 30 mM molybdate and then for up to 30 min with [3H]triamcinolone acetonide or [3H]estradiol in the continued presence of molybdate. Although molybdate did not affect the rate of receptor occupancy with either steroid, cells treated with molybdate had more occupied cytosolic and fewer occupied nuclear receptors than control cells. For the glucocorticoid receptor, cells treated with molybdate had more 10 S and fewer 4 S cytosolic receptors than control cells. In low salt cytosol molybdate inhibits the temperature-mediated subunit dissociation of occupied 10 S glucocorticoid receptor. These results suggest that a hormone-mediated dissociation of an intracellular 10 S oligomeric glucocorticoid receptor form to its 4 S subunits is required prior to accumulation of occupied receptors in the nuclear fraction. In cells incubated at 37 degrees C for 1 h or longer with [3H]triamcinolone acetonide, molybdate shifts the steady state intracellular distribution of receptor toward the 10 S cytosolic receptor form, consistent with the interpretation that molybdate affects the rapidly exchanging subunit equilibrium between the 10 S and 4 S cytosolic forms by slowing the rate of 10 S receptor dissociation. Molybdate prevents loss of glucocorticoid-occupied 10 S but not 4 S receptors in heated cytosol by stabilizing the relatively protease-resistant 10 S receptor. Since molybdate stabilizes 10 S oligomeric steroid receptors in vitro, the effects of molybdate on nuclear accumulation of occupied receptors in intact cells support the intracellular existence and physiological relevance of 10 S glucocorticoid and estrogen receptors. These results support a general model for steroid receptor activation in which binding of hormone promotes dissociation of intracellular 8-10 S oligomeric receptors to their DNA-binding subunits.     

Spatial and molecular aspects of estrogen and progesterone receptor expression in human uteri and uterine carcinomas

The expression of steroid hormone receptors as molecules reflecting processes of development and differentiation in the human uterine tissue was analysed in a spatial distinct fashion: tissue samples were excised at the fundus and at different, spatially distinct positions of the uterus. They were analysed for concentrations of cytosolic estrogen and progesterone receptors in supernatants from frozen sections using an isoelectric focusing technique. The spatial and molecular distinct, qualitative and quantitative pattern of their expression in the human uterus and uterine adenocarcinomas were studied by sectioning tissue sample from the functionalis through the basalis of the endometrium until reaching deep myometrial parts of the tissue: (1) Specific spatial patterns of estrogen and progesterone receptor levels were detectable throughout the menstrual cycle. (2) For proliferative endometrium from the functionalis to the basalis of the endometrium, the content of both cytosolic receptor species increased up to 6-fold. (3) Differences detectable were less pronounced in the myometrial part of the tissue. (4) Differences of steroid receptor concentrations measured in the endometrium at different uterine positions were highest between fundus and corpus of the endometrium. (5) Maximal differences were detectable around ovulation. (6) After secretory transformation of the organ, specific patterns were still detectable, however quantitative differences were less pronounced. (7) Additionally, quantitative differences measurable were accompanied by variations of molecular properties of the progesterone receptor as demonstrated in an isoelectric focusing gel. (8) In endometrial adenocarcinomas, not only significant quantitative alterations in steroid receptor content were measured, but also a significantly changed spatial pattern of receptor concentrations, also a change of the molecular properties of the progesterone receptor was resolved if these tumor parameters were compared to those detected in the normal tissue of the same organ surrounding the tumor.     

An Exchange Assay for the Measurement of Cell Nuclear Estrogen Receptors in Microdissected Brain Regions

An exchange assay is described for the measurement of nuclear estrogen receptors (ERn) in microdissected brain regions. The distribution of ERn in the hypothalamus and amygdala of the rat 1 h after an injection of estradiol (E) is presented. Combining the exchange assay with a previously described method for measurement of cytosol estrogen receptors (ERc) in microdissected brain samples, gonadectomized male and female rats were compared for ERc and ERn. While ERc concentrations tended to be higher in females than in males in all regions of the hypothalamus, with a significant sex difference in the arcuate-median eminence, no sex difference in ERn concentrations was observed after E injection. These results suggest that ERc measurements alone are not sufficient to establish the capacity of the E receptor system: ERn measurements are also necessary to establish the relationship between receptor levels and physiologic estrogen responsiveness.     

Effects of Temperature,Nucleotides and Sodium Molybdate on Activation and DNA Binding of Estrogen,Glucocorticoid, Progesterone and Androgen Receptors In MCF-7 Human Cancer Cells

Abstract

We studied the effects of temperature, ribonucleotides and sodium molybdate on the activation and DNA cellulose binding of estrogen, glucocorticoid, progesterone and androgen receptor complexes in MCF-7 cells. Using DNA cellulose binding as a measure of receptor activation, we found that ribonucleotides activated all four of these receptor complexes. Temperature also activated glucocorticoid receptor complexes efficiently but activated progesterone and androgen receptor complexes less well. Temperature did not activate estrogen receptor complexes. Sodium molybdate blocked either ATP or temperature induced activation of glucocorticoid, progesterone and androgen receptor complexes but only partially blocked estrogen activation. Sodium molybdate also prevented the formation of multiple forms of estrogen and glucocorticoid receptor complexes seen on DEAE cellulose and hydroxylapatite chromatography of crude cytosol. The mechanism by which ribonucleotide enhances and molybdate inhibits activation are discussed.     

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)     

A multidrug-resistant MCF-7 human breast cancer cell line which exhibits cross-resistance to antiestrogens and hormone-independent tumor growth in vivo

MCF-7 human breast cancer cells provide a useful in vitro model system to study hormone-responsive breast cancer as they contain receptors for estrogen and progesterone, and estrogen both induces the synthesis of specific proteins in these cells and increases their rate of proliferation. An MCF-7 cell line which was selected for resistance to adriamycin (MCF-7/AdrR) exhibits the phenotype of multidrug resistance (MDR), and displays multiple biochemical changes. MDR in MCF-7/AdrR is also associated with a loss of mitogenic response to estrogen and the development of cross-resistance to the antiestrogen 4-hydroxytamoxifen. In addition, while the parental MCF-7 cell line responds to estrogen with increased levels of progesterone receptors and the secretion of specific proteins, these estrogen responses are lost in MCF-7/AdrR. Furthermore, while the formation of tumors in nude mice by wild-type MCF-7 cells is dependent upon the presence of estrogen, MCF-7/AdrR cells form tumors in the absence of exogenous estrogen administration. These changes in hormonal sensitivity and estrogen-independent tumorigenicity of the multidrug-resistant MCF-7 cell line are associated with a loss of the estrogen receptor and a concomitant increase in the level of receptors for epidermal growth factor. Thus, in MCF-7/AdrR cells, the development of MDR is associated with alterations in the expression of both cytosolic and membrane receptors, resulting in resistance to hormonal agents and the expression of hormone-independent tumor formation.     

MCF-7; a human breast cancer cell line with estrogen, androgen, progesterone, and glucocorticoid receptors.

We have identified receptors for glucocorticoids, progestins, and androgens in a human breast tumor cell line (MCF-7) known to have estrogen receptor. Sucrose density gradients show that MCF-7 cytosol contains approximately 100 fm/mg protein estradiol (E2-3H) receptor, more than 300 fm/mg protein progesterone receptor (measured with R5020-3H), about 40 fm/mg protein 5alpha-dihydrotestosterone (5alpha-DHT-3H) receptor, and 800 fm/mg glucocorticoid receptor (measured with dexamethasone-3H). Dissociation constants obtained by Scatchard analyses were approximately 0.6 x 10(-10)M (E2), 1 x 10(-9)M (R5020), 2.8 x 10(-10)M (5alpha-DHT) and 8 x 10(-9)M (dexamethasone). No cross competition was found for estrogen receptor, but progestins competed for androgen and glucocorticoid binding. The androgen, but not the glucocorticoid, partially competed for R5020 binding to progesterone receptor. This first demonstration of 4 classes of steroid receptors in human breast cancer means that MCF-7 may be an excellent in vitro model for studying the mechanism of tumor response to endocrine therapy as well as the complex relationships between binding and biological actions of these hormones.