Binding of mibolerone to androgen receptor of benign hypertrophic human prostate. Comparison with R1881

The binding nature of mibolerone in cytosols and nuclear extracts from hypertrophic human prostate was examined in comparison with that of R 1881. The binding of mibolerone in the cytosol and nuclear extract was single and of high affinity when evaluated by the method of Scatchard (1949). Binding of mibolerone with testosterone-binding globulin was not detected. The sedimentation coefficients of the binder for mibolerone in the cytosol and nuclear extract were 10.6 S and 3.6 S, respectively. When triamcinolone acetonide was induced in the binding medium, inhibition of mibolerone binding in the cytosol by testosterone and dihydrotestosterone was potentiated and this may imply that the binding observed in the presence of triamcinolone acetonide was responsible for the binding of the androgen receptor. In the nuclear extract, the binding was attributable mainly to the androgen receptor irrespective of the presence or absence of triamcinolone acetonide. These properties of the binding observed in the hypertrophic human prostate were almost same as those of the binding with R 1881. Although maximum binding sites measured using mibolerone were correlated with those using R 1881 in the cytosols as well as in the nuclear extracts, the values obtained with mibolerone were slightly greater than those with R 1881. Thus, mibolerone seems to be a suitable ligand for measuring the androgen receptor, but when compared with R 1881 no special merits in using mibolerone were detected.     

Characterization of a [3H]methyltrienolone (R1881) binding protein in rat liver cytosol

The binding of radiolabelled methyltrienolone 17 beta-hydroxy-17 alpha-methyl-estra-4,9,11-trien-3-one (R1881) to adult male rat liver cytosol has been characterized in the presence of Na-molybdate to stabilize steroid-hormone receptors, and triamcinolone acetonide to block progestin receptors. Using sucrose density gradient analysis, male liver cytosol contains a [3H] R1881 macromolecular complex which sediments in the 8-9S region. 8S binding of R1881 to male rat serum, female liver cytosol or cytosol from a tfm rat cannot be demonstrated. Further metabolism of [3H] R1881 following 20h incubation with male rat liver cytosol was excluded: In the 8S region 97% of [3H] R1881 was recovered by thin layer chromatography. Characteristics of this [3H] R1881-8S binding protein include high affinity (Kd = 2.3 +/- 41 nM) and low binding capacity (18.8 +/- 3.3 fmol/mg cytosol protein), precipitability in 0-33% ammonium sulfate, and translocation to isolated nuclei following in vivo R1881 treatment. Whereas, the cytosol R1881-receptor is competed for by dihydrotestosterone, testosterone, and estradiol, [3H] estradiol binding in the 8S region is not competitive with androgens but does compete with diethylstilbestrol. The nuclear androgen binding site has a Kd = 2.8 nM for [3H] R1881, and is androgen specific (testosterone greater than 5 alpha-dihydrotestosterone greater than estradiol greater than progesterone greater than cyproterone acetate greater than diethylstilbestrol greater than dexamethasone greater than triamcinolone). Since a number of liver proteins including the drug and steroid metabolizing enzymes are, in part, influenced by the sex-hormone milieu, the presence of a specific androgen receptor in male rat liver may provide valuable insight into the regulation of these proteins.     

Binding of [3H]methyltrienolone to androgen receptor in rat liver

The synthetic androgen methyltrienolone is superior to testosterone and androstenedione for the measurement of androgen receptor in tissues where the native ligands are metabolized into inactive derivatives. [3H]Methyltrienolone binds with a high affinity to androgen receptor in cytosol prepared from male rat livers, as the Scatchard analysis revealed that the Kd value was 3.3 X 10(-8) M and the number of binding sites was 35.5 fmol/mg protein. Since methyltrienolone also binds glucocorticoid receptor which exists in rat liver, the apparent binding of androgen receptor is faulty when measured in the presence of glucocorticoid receptor. The binding of methyltrienolone to glucocorticoid receptor can be blocked by the presence of a 100-fold molar excess of unlabeled synthetic glucocorticoid, triamcinolone acetonide, without interfering in its binding to androgen receptor, because triamcinolone does not bind to androgen receptor. Triamcinolone-blocked cytosol exhibited that the Kd value was 2.5 X 10(-8) M and the number of binding sites was 26.3 fmol/mg protein, indicating a reduction to 3/4 of that in the untreated cytosol. The profile of glycerol gradient centrifugation indicated that [3H]methyltrienolone-bound receptor migrated in the 8-9 S region in both untreated and triamcinolone-blocked cytosols, but the 8-9 S peak in triamcinolone-blocked cytosol was reduced to about 3/4 of that of untreated cytosol.     

Quantification of cytosolic steroid receptors in secretory and non-secretory epithelial cells of the canine prostate

Radiolabelled methyltrienolone, dihydrotestosterone and estradiol were used as ligands to identify and quantify androgen and estrogen receptors in freshly dispersed cells from the canine prostate. Soluble extracts (cytosols) were obtained from secretory and non-secretory epithelial cells separated on the basis of their density in Percoll gradients. For both cell types, as well as for the whole prostate, Scatchard plot analyses were linear and showed a single class of high affinity binding sites: Kd values of 3.6 +/- 2.2 X 10(-9) M and 3.0 +/- 1.2 X 10(-10) M were measured for the androgen and estrogen receptors, respectively. The number of binding sites for the cytosolic androgen receptor, expressed per mg of protein or per mg of DNA, was 2.4- to 6.7-fold higher in the non-secretory cells compared to the secretory cells. However, these two cell types contained a similar number of specific sites for the estrogens. The specificities of the androgen and estrogen receptors were shown to be identical for the two cell types: the binding of [3H]R1881 was strongly inhibited by unlabelled R1881, 5 alpha-androstane-3 alpha, 17 beta-diol and dihydrotestosterone, while 5 alpha-androstane-3 beta, 17 beta-diol, estradiol and estrone did not displace bound R1881. The addition of triamcinolone acetonide did not alter the binding of R1881 in extracts of either cell type or in the whole prostate. The binding of [3H]estradiol to the estrogen receptor was highly specific since a strong displacement was only observed with estradiol (83%).     

A microassay for the measurement of androgen receptors in human prostatic tissue.

A microassay utilizing R 1881 (methyltrienolone) has been developed for the measurement of androgen receptor sites in the cytosol and nuclear extract of human prostatic tissue. Binding of R 1881 to the progesterone binding molecule in cytosol was eliminated by the addition of triamcinolone acetonide. Utilizing a six tube, single point assay, the number of binding sites estimated in nuclear extract averaged 95% of the number measured by a full 7 point Scatchard analysis; the number estimated by the microassay in cytosol averaged 91%. When the single point assay was applied to needle biopsy specimens (200 mg of tissue), the estimated number of binding sites in nuclei averageed 83% of the number measured in bulk tissue (2 grams) utilizing a 7 point Scatchard analysis; the number in cytosol estimated by the microassay on needle biopsy specimens averaged 73%. It is hoped that this technique may be useful in correlating receptor content with hormonal responsiveness in men with metastatic carcinoma of the prostate.     

Up-regulation of androgen receptor binding in male rat fat pad adipose precursor cells exposed to testosterone: study in a whole cell assay system

Binding of androgens to adipocytes has previously been evaluated using cytosol fractions without taking into account nuclear binding, although the latter is suggested to be close to the physiological site of action. In the present study, performed in differentiated fat pad adipose precursor cells, we describe a simple, reliable and reproducible androgen binding assay in a system with intact cells. Tritiated and unlabeled methyltrienolone (R1881) were used to define specific and unspecific androgen binding. Triamcinolone acetonide was added to prevent the binding of R1881 to other types of receptors. Differentiated adipose precursor cells contain a homogeneous class of high affinity androgen binding sites, and binding is saturable and reversible. Binding apparently occurs at one site, with a Kd in the range of physiological androgen concentration (about 4 nM). Competition studies indicate that the receptor is specific for R1881, testosterone and dihydrotestosterone, which have approximately the same affinity, while progesterone, estradiol and dexamethasone show much lower affinity. Androgen binding was markedly enhanced after cellular exposure to R1881 and testosterone but not dihydrotestosterone, and this increase was dependent on protein synthesis, suggesting the formation of new receptors by these androgens. In conclusion, fully differentiated adipocytes contain a specific, high affinity receptor, the density of which is dependent on androgens.     

Characterization of unoccupied (R) and occupied (RA) androgen binding components of the hyperplastic human prostate.

Saturation protocols were developed for measurement of unoccupied (R) and steroid-occupied (RA) androgen binding components of human hyperplastic prostate. The concentration of unoccupied cytoplasmic binding sites (2 hr incubation at 2 degrees C) for the synthetic androgen R1881 (17beta-hydroxy-17alpha-methyl-estra-4,9,11-trien-3-one) and the synthetic progestin R5020 (17alpha,21-dimethyl-19-norpregna-4,9-diene-3,20-dione) respectively was 10.7 +/- 1.4 and 14.3 +/- 3.2 fmoles per mg cytosol protein and the apparent steroid affinity respectively was 9.6 +/- 0.8 and 1.6 +/- 0.4 x 10(8) M-1. Steroid specificity of the unoccupied cytoplasmic R1881 and R5020 binding sites was similar. When R1881 and R5020 were employed as probes of total, R plus RA, cytoplasmic binding components (20-24 hr incubation at 15 degrees C) saturable binding of R5020 was not detectable. Total cytoplasmic R1881 binding site concentration and apparent affinity for R1881 were 51.7 +/- 3.3 fmoles per mg cytosol protein and 2.7 +/- 0.6 x 10(7) M-1. R5020 was a poor inhibitor of R1881 binding to total cytoplasmic R1881 binding components.     

Assay of androgen binding sites by exchange with methyltrienolone (R 1881).

Methyltrienolone (R 1881 - 17beta-hydroxy-17alpha-methyl-estra-4,9,11-trien-3-one) binds specifically to androgen receptor in rat prostate cytosol where, unlike androstanolone, it is not metabolized. By exchanging bound endogenous hormone in rat prostate cytosol with labelled R 1881, it is possible to measure total (free anc occupied) binding sites. This assay method has also been applied to the measurement of androgen receptor sites in human benign prostatic hypertrophy where R 1881 has the added advantage of not being bound by any contaminating plasma protein (sex hormone binding protein).     

Human placenta contains a high affinity R1881 binding site that is not the androgen receptor

Human placental cytosol was shown to contain a species that binds the synthetic androgen, methyltrienolone (R1881) with high affinity (Kd 6.5 nM). Major differences were found between this placental androgen binding species and the classical androgen receptor found in human foreskin cytosol. Competitive binding assays in the placental cytosol using [3H]R1881 as tracer showed a 200-fold excess of testosterone to compete poorly, while dihydrotestosterone and the synthetic androgen mibolerone did not compete at all. The placental R1881 binding component was found not to bind to hydroxylapatite, although all classes of steroid receptors are reported to do so. Temperature studies showed that the placental binding site is stable at elevated temperatures with no loss of binding after 4 h at 45 degrees C. Ion exchange chromatography showed that the placental R1881 binding site eluted from DEAE cellulose at a lower salt concentration than foreskin androgen receptors. These results show that R1881 is not entirely specific for androgen receptors and that human placenta contains an androgen binding site that is not the classical androgen receptor.     

Comparison of glucocorticoid-binding proteins in normal and neoplastic mammary tissues of the rat.

Kinetic and molecular properties of components binding [3H]triamcinolone acetonide were studied using 105,000g supernatants of lactating mammary gland, R3230AC, and dimethylbenz[a]anthracene (DMBA) induced mammary tumors of the rat. Using a dextran-coated charcoal adsorption procedure, the relationship between specific glucocorticoid binding and protein concentration was linear in the range of 0.5-4.0 mg/reaction. These cytoplasmic macromolecules bound [3H]triamcinolone acetonide with limited capacity (50-400 fmol/mg of cytosol protein) and high affinity, Kd approximately 10(-8)-10(-9) M. Optimal binding was obtained when homogenizations were made in Tris buffers, at pH 7.4, containing monothioglycerol. Time course of association of [3H]triamcinolone acetonide and its binding sites showed maximal binding by 6-8 hr at 3 degrees which remained unchanged up to 24 hr. The rate constant of association at 3 degrees was in the range of 2-4 x 10(5) M-1 min-1. The rate constant of dissociation of bound [3H]triamcinolone acetonide could not be calculated accurately since the reaction was essentially irreversible for 5 hr at 3 degrees. Estimation of the half-life of the steroid-binding protein complexes from the Kd and the rate constant for association gave a value of 11-12 hr. From ligand specificity studies, the glucocorticoids, triamcinolone acetonide, corticosterone, cortisol, and dexamethasone competed well for [3H]triamcinolone acetonide binding sites. Progesterone, aldosterone, and the anti-glucocorticoid, cortexolone, were also good competitors while androgens and estrogens were weak inhibitors of binding. The binding compenents sedimented at 7-8 S in sucrose gradients of low ionic strength and dissociated into lower molecular weight components sedimenting at 4-5S in high ionic strength gradients. Studies in vivo using animals bearing the DMBA-induced tumor demonstrated that [3H]triamcinolone acetonide binding complexes were present in cytoplasmic and nuclear compartments. Sedimentation coefficients of the cytoplasmic and nuclear forms of these receptors labeled in vivo were 7-8S and 4-5S, respectively. These studies suggest that the molecular and kinetic binding properties of glucocorticoid receptors in neoplastic mammary tissues are similar to those of the normal mammary gland.     

Androgen receptor in human placental villi

In studies with a synthetic androgen, R 1881, an androgen-binding component was found in the cytosol of human placental villi. Kinetic analysis indicated that the Kd value of this component was 1.4 nM at 0-4 degrees C and that binding of R 1881 amounted to 277 +/- 73 fmol/mg protein. glycerol density gradient ultracentrifugation showed a peak of binding activity in the 8S region in a medium of low ionic strength, but in the 4.5S region in a medium containing 9.5 M KCl. The R 1881-binding component was inactivated by mild heat- or trypsin-treatment, but not by treatment with DNase or RNase. Most of the R 1881-binding activity was sedimented at 20 to 40% saturation of ammonium sulfate. These findings indicate that the R 1881-binding component in human placental cytosol is quite similar in its characteristics to androgen receptors, which are present in various androgen-responsive organs. Testosterone was a more potent competitor of R 1881-binding than DHT or cyproterone acetate. Scatchard plots indicated that the binding site of testosterone was identical with that of R 1881. These findings suggest that the androgen receptor in placental cytosol is specific for testosterone. The Kd value for testosterone was calculated to be 3.2 nM.     

Cytosol glucocorticoid receptor in the neoplastic epithelial duct cell line from human salivary gland (HSG)

Neoplastic epithelial duct cell line from human salivary gland (HSG cell) contained cytosol glucocorticoid receptor. Scatchard analysis of cytosol indicated that the dissociation constant (Kd) was 5.6-6.5 nmol/l and the number of binding sites was 83-92 fmol/mg protein. A competitive assay showed that the binding sites for [3H]triamcinolone acetonide were specific to glucocorticoid. Glycerol density gradient centrifugation displayed that the [3H]triamcinolone acetonide receptor complexes sedimented in the 8.5 S region under low salt conditions and in the 4.2 S region under high salt condition (0.4 M KCl). The same high salt conditions induced an increased binding of [3H]triamcinolone acetonide complexes for DNA-cellulose.     

Androgen receptors in ventral prostate glands of zinc deficient rats

Androgen binding has been studied in the prostate cytosol of zinc deficient rats by charcoal assays. Rats were housed individually in plastic cages and maintained on a zinc deficient diet for 3 months. The cytosol fraction of prostate gland was incubated with various concentrations of tritiated methyltrienolone (3H-R1881, a synthetic androgen) alone or in the presence of 500-fold excess of radioinert R1881. Scatchard analysis of the data revealed that the number of androgen binding sites in the cytosol fraction of the zinc deficient rat prostate was 31 +/- 5.2 fmol/mg cytosol protein. This was significantly lower than that (84 +/- 11.5 fmol/mg protein) of the controls. Their dissociation constant (Kd = 1.6 +/- 0.6 nM) on the other hand was not different from that (1.7 +/- 0.7 nM) of control animals. This decrease in the concentration of cytosol receptor sites in the zinc deficient state suggests that this metal is involved in the androgen-binding process in the target cells.     

A hybrid ligand method for androgen receptor measurement

Existing techniques for androgen receptor (AR) assay are complicated by cross-reactivity of ligand binding affinities that can lead to incorrect estimation of receptor concentration. Two most frequently used ligands are [3H]dihydrotestosterone [( 3H]DHT) and [3H]methyltrienolone [( 3H]R1881), which in addition to binding to AR also bind to sex hormone binding globulin (SHBG; Kd = 1.5 nM) and progesterone receptors (PgR; Human Kd = 1 nM, rat Kd = 6 nM) respectively. Triamcinolone acetonide (TMA) is commonly used to block binding of [3H]R1881 to PgR, however at high concentrations TMA itself will bind AR (Kd = 7 microM). We have developed a hybrid ligand method for the measurement of AR in the presence of SHBG and PgR. This method used [3H]R1881 as the high specific activity labelled tracer and DHT as the unlabelled competitor of specific AR binding. Using this assay, 20% of human colorectal carcinomas were found to contain AR.     

Androgen receptors in brain and pituitary of female rats: cyclic changes and comparisons with the male

The in vitro binding of a synthetic androgen, methyltrienolone ([3H]-R1881), to brain and pituitary (PIT) cytosol and nuclear extracts was determined in male and female rats. Purified cytosol was prepared from PIT or hypothalamic-preoptic area-amygdala (HPA) and incubated in the presence of 0.1 to 10 nM [3H]-R1881. Scatchard analysis revealed the presence of a single, saturable, high-affinity binding site in PIT cytosol with a dissociation constant (Kd) of 0.42 X 10(-10) M in females and 0.95 X 10(-10) M in intact males. The Kd of HPA cytosol was much less in castrated males [0.47 +/- 0.05 (SEM) X 10(-10)M, n = 7] and females (0.63 +/- 0.1 X 10(-10) M, n = 4) than in intact males (5.8 +/- 1.1 X 10(-10) M, n = 8). Treatment of castrated males with dihydrotestosterone (DHT) for 24 h (250 micrograms/100 g of body weight) increased the Kd of HPA cytosol only slightly (1.6 X 10(-10) M, mean of two replicates). Scatchard analysis of salt-extracted nuclear androgen receptor (ARn) showed a single, high-affinity binding site with similar Kd values in PIT and HPA of intact and castrated, DHT-treated male rats (PIT Kd = 7.3 X 10(-10) M, 9.3 X 10(-10) M; HPA Kd = 1.5 X 10(-9) M, 1.3 X 10(-9) M, respectively). Competition studies involving a range of several radioinert steroids revealed that the binding of [3H]-R1881 to cytosol (ARc) and nuclear extract was specific for androgen receptor when triamcinolone acetonide (10 microM) was added. The ARc and ARn levels were quantified in PIT, preoptic area (POA), hypothalamus (HT), amygdala, hippocampus, and cortex by single point estimation. Significantly (p less than 0.01) greater amounts of ARc were detected in PIT of ovariectomized females (32.7 +/- 2.9 fmol/mg of protein) than in that of orchidectomized males (22.33 +/- 1.6 fmol/mg of protein). The highest levels in the brain were seen in HT and POA. Pituitary ARc in females varied throughout the estrous cycle. Significantly (p less than 0.01) greater amounts were detected on estrus (45.8 +/- 2.2 fmol/mg of protein) and proestrus (39.0 +/- 1.9 fmol/mg of protein) than on diestrus (29.2 +/- 1.5 fmol/mg of protein). These data confirm the existence of specific receptors for androgen in male and female brain and PIT, and suggest an important role for androgen in the control of PIT hormone secretion in the female.     

The Mr 90,000 heat shock protein-free androgen receptor has a high affinity for steroid, in contrast to the glucocorticoid receptor

Transformed and bacterially expressed glucocorticoid receptors free from Mr 90,000 heat shock protein (hsp90) have a 100-fold lower steroid-binding affinity than the hsp90-bound nontransformed receptor, suggesting that hsp90 is needed for high-affinity steroid binding [Nemoto, T., Ohara-Nemoto, Y., Denis, M., & Gustafsson, J.-A. (1990) Biochemistry 29, 1880-1886]. To investigate whether or not this phenomenon is common to all steroid receptors, we investigated the steroid-binding affinities of bacterially expressed and transformed androgen receptors. The C-terminal portion of the rat androgen receptor containing the putative steroid-binding domain was expressed as a fusion protein of protein A in Escherichia coli. The recombinant protein bound a synthetic androgen, [3H]R1881, with high affinity (Kd = 0.8 +/- 0.3 nM). Glycerol gradient analysis revealed that the recombinant protein sedimented at around the 3S region irrespective of the presence of molybdate, indicating that the receptor is present in monomeric form. The steroid-free transformed androgen receptor was obtained by exposure of rat submandibular gland cytosol to 0.4 M NaCl in the absence of steroid. High-performance ion-exchange liquid chromatography analysis showed that the transformed androgen receptor bound to [3H]R1881 with high affinity. Thus these observations indicate that, in contrast to the glucocorticoid receptor, hsp90 is not required for the high-affinity steroid binding of the androgen receptor. In addition, the hsp90-free androgen receptor prebound with radioinert R1881 was efficiently relabeled with [3H]R1881, while the triamcinolone acetonide-bound, transformed glucocorticoid receptor failed in ligand exchange. The inability to achieve ligand exchange probably reflects the low steroid-binding affinity of this entity.     

Androgen binding as evidenced by a whole cell assay system using cultured canine prostatic epithelial cells

The androgen receptor content in the prostate has been usually evaluated using subcellular fractions without taking into account cellular and functional heterogeneity of the gland. Using enriched populations of immature canine prostatic epithelial cells cultured in primary monolayers, a whole cell assay system was developed to measure androgen receptors. Tritiated dihydrotestosterone (DHT) and/or methyltrienolone (R1881) in serum-free medium were used as ligands and Triamcinolone acetonide (0.5 microM) was added to prevent the binding of R1881 to other types of receptors. The amount of radiolabelled ligand specifically bound to the cells was determined at equilibrium. Specific binding was proportional to the number of cells seeded. Scatchard analysis revealed the presence of at least two types of binding sites. The Kd for the high affinity binding site was 2 x 10(-9) M. Competition studies indicated that this component was specific for androgens; Methyltrienolone, Mibolerone and the antiandrogen RU 23908 were the most efficient competitors. They were followed by DHT, 5 alpha-androstane-3 alpha, 17 beta-diol, testosterone, estradiol and estrone. Progesterone, 5 alpha-androstane-3 beta, 17 beta-diol and epitestosterone were not inhibitors. The level of specific binding was 11.0 +/- 7.6 fmol of bound R1881 per 10(6) cells (n = 34) or 2075 +/- 1434 fmol per mg of DNA; these values correspond to an average of 6624 +/- 4577 sites per cell. Thus, using this whole cell assay system, specific and androgen receptors were detected in immature prostatic epithelial cells in culture. This assay will therefore be useful to study the interrelationship between androgen binding activity and specific cell functions.     

Binding of methyltrienolone to various androgen-dependent and androgen-responsive tissues in four animal species.

Comparative sucrose gradient studies of the in vitro binding of dihydrotestosterone (DHT) and of a synthetic androgen, methyltrienolone (R 1881), have been done with the cytosols of various tissues of the rat, mouse, cock and man. With rat prostate cytosol, the amount of R 1881 and DHT binding in the 8-9S region of the gradient was found to be comparable. Specific 8-9S peaks of R 1881 were also found in rat levator ani/bulbocavernosus and skeletal muscles and in the mouse kidney. Only 4-5S peaks could be demonstrated in the cock's comb while DHT under the same conditions showed both 8-9S and 4-5S binding. Binding of R 1881 to the cytosol of the hyperplastic prostate was polydispersed, and showed evidence of the presence of aggregates. Evidence was also found that R 1881 could bind to the progesterone receptor in rat uterus. Our study supports the theory that in a given species the androgen receptors are similar if not identical in all the tissues. The synthetic androgen R 1881 appears to be a useful tool for androgen receptor studies in various animal species provided that the tissue under study contains no progesterone receptor.     

The presence of a hitherto undefined high-capacity androgen binding macromolecule in human ovarian cancer tissue

Sex hormone binding globulin (SHBG) is known to interfere in the quantitation of androgen receptors (AR) if dihydrotestosterone (DHT) is used. We used a monoclonal antibody to remove SHBG from cytosol. In cytosol of benign prostatic hyperplastic (BPH) tissue low capacity binding for DHT, but not for R1881, was found after removal of SHBG. AR were detected in 18 of 20 ovarian cancer cytosols. In the two AR-negative cases, non-saturable binding for DHT, testosterone and R1881 was observed. Incubation with anti-SHBG did not change this. An hitherto undefined androgen binding macromolecule(s), with high-capacity binding for natural and synthetic androgens, but not for estrogen and progesterone, seems to be present in these ovarian cancer tissues. The functionality of these androgen binding macromolecules in ovarian cancer is yet to be demonstrated.     

Corticosterone binding in AtT-20 pituitary tumor cell cytosol: evidence for one class of binding site for both natural and synthetic glucocorticoids.

The AtT-20 mouse pituitary cell is an established, cloned cell line which produced adrenocorticotrophic hormone in a glucocorticoid-suppressible manner. A receptor for glucocorticoids was identified in cytosol prepared from these cells using the natural mouse glucocorticoid, corticosterone, as the labeled ligand. The question of whether this binding component is identical to the one detectable using labeled triamcinolone acetonide was addressed by comparing their physicochemical characteristics and by detailed studied of binding specificity using both ligands. The corticosterone and triamcinolone acetonide binding components behaved similarly on sucrose density gradient analysis and DEAE-cellulose ion-exchange chromatography. Scatchard analysis with corticosterone detected 30% fewer binding sites than a similar analysis with triamcinolone acetonide, probably because corticosterone binding was of lower affinity (Kd = 8.6 . 10(-9)M vs. 1.4 . 10(-9)M) and hence less stable. The relative glucocorticoid binding affinities of thirteen unlabeled steroids were obtained using either labeled steroid as ligand. Both ligands yielded similar results, suggesting that they both detected a similar binding site. The results suggest that AtT-20 cell cytosol contains a single class of binding site which detects both natural and synthetic glucocorticoids.