An androgen binding protein in the testis cytosol fraction of adult rats. Comparison with the androgen binding protein in the epididymis

The cytosol fraction of rat testicular homogenates contained a specific androgen binding protein (t-ABP), indistinguishable from, the androgen binding protean in. the epididymis(e-ABP) in terms of its chromatographic behaviour by gel filtration, sedimentation rate, mobility on polyacrylamide electrophoresis and steroid specificity(5α-diaydrotestosterone(DHT) > testosterone > estradiol-17β > parogesterone and estradiol-17α).The stability of t-ABP as well was similar to that of e-ABP. The aBP-DHT complexes were stable between pH 6.5–10, exhibiting the highest degree of binding between pH 8–9. The binding activity persisted after heating at 50°C for 30 min., whereas heating at 60°C for 30 min. completely destroyed the binding. DHT did not significantly increase the stability towards pH and temperature denaturation. Binding activity was not reduced by 1 mM p-chloro-mercuri-phenyl-sulphonate (PCMPS), whereas similar treatment with 1 nM N-ethyl-maleimide(NEM) or 1 mM Ellman's reagent reduced it by some 10–50 per cent. Exposure to 10 mM β-mercaptoethanol(βME) reduced the binding by 60–70 per cent. These studies strongly indicate that t-ABP and e-ABP are identical proteins.Hemicastration for 4 weeks eliminated the ABP from the epididymal cytosol fraction on the castrated side, indicating that this protein is produced by the testis.     

Androgen binding to cytosol prepared from epididymides of sexually mature castrated rabbits: evidence for a cytoplasmic receptor.

The presence of androgen-binding activity in cytosol prepared from the major anatomical segments (caput, corpus, and cauda) of the epididymis of castrated sexually mature rabbits has been demonstrated. A portion of this binding activity is likely to be the epididymal androgen receptor. When epididymal cytosol from adult castrated rabbits is analyzed on low-ionic strength (0.01 MKCl) sucrose gradients, two peaks of macromolecular binding could be detected, one congruent to 4.6S and one congruent to 8S. On gradients containing 1.0 M KCl, only one sedimenting form congruent to 4.6S could be demonstrated, suggesting that the 8S component is composed of aggregates. If cytosol was preincubated with labeled androgen, followed by an incubation with unlabeled androgen, and subsequently analyzed for binding on low-ionic strength gradients, only the congruent to 8S peak could be detected, indicating that most of the binding in the congruent to 4.6S region was rapidly dissociable. This suggests that binding in this region was to moieties other than receptor. Since androgen binding proteins (ABP) of testicular origin would have been cleared from the epididymis at the timepoints that we concentrated on for most of these studies, the 4.6S binding probably represents the association of androgen with plasma testosterone binding globulin (TeBG). The binding of androgen to the receptor can be inhibited by cyproterone, while this antiandrogen does not inhibit binding to either ABP or TeBG at the concentration used.     

Testosterone-induced responsiveness to androgen in Shionogi mouse carcinoma cells

Primary cell cultures from an androgen-dependent mouse mammary carcinoma, the Shionogi-SC 115 tumor, were cultured in the presence or absence of testosterone (50 nM). Characteristic changes in cellular morphology and cell growth were observed according to the presence or absence of the androgen. In testosterone-containing medium, cells formed individual clones, piling up one over another and showed no contact inhibition, whereas in the absence of the androgen, cells had a flattened morphology, they grew in a monolayer and cell multiplication was reduced. The testosterone-dependent changes were observed in culture as long as cells were maintained in androgen-containing medium. Only a few (3-5) days of culture in the absence of testosterone rendered cells irreversibly unresponsive to the androgen, and they could no longer produce tumours after inoculation in the host animal. Cellular proteins were analysed after culture in the presence or absence of testosterone. After [35S]methionine labelling of cells and SDS-PAGE of the cytosol, several proteins were specifically synthesized in the presence of testosterone, predominantly a 45 kD protein, which was not seen in the absence of the androgen. Conversely, a protein of 35 kD present in absence of the hormone disappeared in the presence of testosterone. The anti-androgen cyproterone acetate inhibited the characteristic cellular morphology, cell proliferation and protein synthesis observed in the presence of the the androgen. The antiprogestin and anti-glucocorticosteroid RU 486 also showed limited anti-androgen activity. The concentration of specific androgen receptor-binding sites did not change significantly after 3 months of culture with or without testosterone, i.e., in responsive and unresponsive cells.     

Medroxyprogesterone acetate has opposite effects on the androgen binding protein concentrations in serum and epididymis

In the rat, the effects of progestin and androgen administration on serum, testicular and epididymal androgen binding protein (rABP) concentrations were determined and related to the organ weight and morphology. Adult rats were treated with medroxyprogesterone acetate (MPA; 17 alpha-acetoxy-6 alpha-methylprogesterone), testosterone propionate (TP) and mibolerone (MB; 7 alpha, 17 alpha-dimethyl-19-nortestosterone). MPA reduced testicular and epididymal weights and the concentrations of serum follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone. During MPA treatment testicular and epididymal ABP content declined in parallel with organ weights and hormone concentrations, whereas serum ABP concentrations increased. Combinations of MPA and TP reduced testicular and epididymal ABP, but the reductions were less than with MPA alone; this combined treatment also elevated serum AMP. Both MB and TP reduced ABP in the male reproductive tract, but unlike MPA did not increase the concentration of this protein in serum. The results suggest that MPA acts directly on Sertoli cells resulting in increased ABP release into the blood. The comparison was made of steady state polyacrylamide gel electrophoresis (SS-PAGE) and radioimmunoassay (RIA) methods of estimating rABP. The potency ratio of testicular ABP estimated by the two methods (RIA:SS-PAGE) was three times higher than this ratio in the epididymis in normal and hormonally treated animals. Due to differences in end points, these observations imply that these assays do not quantify the molecules in the same way in one or both of these tissues. The results indicate, however, that both assays are suitable for following rABP concentration in animals with altered hormonal states.     

Evidence for an androgen binding protein in the testis of a teleost fish (Salmo gairdneri R.): a potential marker of Sertoli cell function

A factor binding tritiated testosterone was detected using "steady-state" polyacrylamide-gel electrophoresis, in rainbow trout genital tract. It migrated with a Rf identical to that of rat ABP. This binding was thermolabile, and was competitively inhibited by unlabelled testosterone. The steroid binding protein was found in cytosols from trout testes which had been previously perfused to avoid blood contamination, trout seminal plasma and in testicular explants incubation media. Using a quantitative assay and a Scatchard analysis, 25-50 pmol binding sites per gram gonad were found in testis cytosol. Binding affinity constant for testosterone in the various samples was close to 4 x 10(8) M(-1). The dissociation of steroid-protein complex was rapid (t 1/2 approximately 1.5 min). Hormonal specificity was studied by the competition of 3H-T binding with several concentrations of unlabelled competitors and the following order for affinities was obtained: dihydrotestosterone approximately androstenedione greater than testosterone greater than oestradiol greater than 17 alpha, 20 beta DHP greater than 11KT greater than cyproterone acetate greater than cortisol. High testicular cytosol and seminal plasma concentrations and apparent in vitro production indicate that the testis may synthesize an ABP-like protein in the trout. Such a factor would provide a unique marker of Sertoli cell activity and regulation in various physiological or experimental situations.     

Evidence for an androgen receptor in the seminiferous tubules of the human testis

Androgen receptors (AR) were studied in seminiferous tubule cytosol and testicular nuclear extracts prepared from testes of previously untreated elderly men undergoing orchiectomy as therapy for prostatic carcinoma. Cytosol exhibited high affinity (Kd = 0.8 nM), saturable binding of [3H]methyltrienolone; however, the synthetic progestin, promegestone was a stronger competitor for MT binding sites than were 5 alpha-dihydrotestosterone (DHT) or testosterone (T), suggesting the presence of progesterone-like binding sites. Addition of triamcinolone acetonide (TA) produced the usual relative steroid specificity for AR binding and reduced the measured AR binding capacity by 19 +/- 8% (Mean +/- SD, n = 3). The umber of MT binding sites was 30-40 fmol/mg protein, or an average of 65 fmol/g testis, and the equilibrium dissociation constant at 0 degrees C was 0.6-1.4 nM. In the presence of sodium molybdate, binding was stable for 40 h at 0 degrees C and the half-time of dissociation of the MT-AR complex was 12-16 h. The binding of salt extractable (600 mM KCl) nuclear sites to MT was saturable and was specific for androgens. The number of binding sites in nuclear extracts was 170 fmol/g testis and the apparent equilibrium dissociation constant was 4.2 nM. Thus, the binding of MT to human seminiferous tubule cytosol and testicular nuclear extract exhibits properties which are nearly identical to those of the prostate AR. Further study of this androphilic protein may provide insight into the role of androgen in normal and abnormal spermatogenesis in man.     

Physiological role for androgen binding protein-steroid complex in testis?

The concentration of $\text{unbound}$ androgens in the lumen of rat testis seminiferous tubules is not dependent on the presence of the extra-cellular androgen binding protein (ABP); other parameters such as permeability properties, fluid dynamics and metabolic activities in different testicular compartments appear to have a much greater influence. It has been shown that in other target tissues the metabolic effects of steroids on cells depend on the concentration of the steroids which are not bound to extra-cellular proteins. It is therefore unlikely that the physiological function of ABP is related to the accumulation of androgens around germinal cells.     

Effects of steroidal and non-steroidal antiandrogens on the androgen binding properties of the rat ventral prostate androgen receptor

Steroidal (cyproterone acetate) and non-steroidal (RU23908 and hydroxyflutamide) antiandrogens are able to block testosterone-induced increases in nuclear androgen receptor (AR) in the prostate of 1-day orchidectomized rats, but when given alone, RU23908 and hydroxyflutamide increase nuclear AR (RU23908 greater than hydroxyflutamide) in the same animal model. The increases in nuclear AR induced by antiandrogen alone or with testosterone alone are blocked by cycloheximide 1 h after administration, suggesting that androgen or antiandrogens induce de novo AR synthesis. Concomitant to nuclear AR accumulation, testosterone is able to induce depletion of cytosol and microsomal AR. Blockade of testosterone-induced depletion of microsomal AR, but not of cytosol AR, occurs in the presence of antiandrogens. Cyproterone acetate has a higher relative binding affinity (RBA) for microsomal AR and cytosol AR than RU23908 or hydroxyflutamide. This phenomenon is in good agreement with the degree of inhibition by these compounds of the association rate of androgen for the microsomal AR. This correlation between RBA and inhibition of the initial rate of hormone binding to the receptor is not found for cytosol AR. The results show that antiandrogens are not 'pure' antagonists of androgen action and they are potent agonists in the absence of testosterone. Furthermore, testosterone alone or antiandrogens per se regulate AR levels acutely by protein-synthesis dependent mechanisms of action, in rat ventral prostate.     

Regulation by FSH and dibutyryl cyclic AMP of the formation of androgen-binding protein in Sertoli cell-enriched cultures.

Sertoli cell-enriched preparations from testes of 20-day-old rats were cultured in a defined medium in the presence and absence of FSH or dibutyryl cyclic AMP (dcAMP). Androgen-binding activity was assayed in the culture medium, and related to testicular androgen-binding protein (ABP). The production and secretion of ABP by the Sertoli cell-enriched preparation was increased after FSH or dcAMP treatment of the primary culture. It is concluded that ABP is produced by Sertoli cells. The possibility of involvement of other cell types in the testis in ABP production is discussed.     

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.     

Characterization of an androgen binding protein (ABP) in rat testis and epididymis

An androgen binding protein (ABP) was demonstrated in the 105,000 g supernatant of rat testis homogenate after charcoal extraction of endogenous steroids. Testis ABP proved to be identical to an ABP previously described in rat epididymis. It contained saturable high-affinity sites which exhibited binding specificity for dihydrotestosterone (6) and testosterone when measured by polyacrylamide gel electrophoresis or by competitive binding using charcoal adsorption. Binding to ABP was not affected by ribonuclease or neuraminidase but was decreased by the disulfide reducing agent, dithiothreitol and the sulfhydryl reagent, N-ethylmaleimide. Binding was abolished by treatment with proteolytic enzyme. The mean molecular radius of ABP was 2.92 nm as determined by the retardation of electrophoretic mobility in polyacrylamide gels of decreasing pore size. Assuming a partial specific volume of 0.66–0.74 the molecular weight was 86,000–91,000 for a spherical molecule. ABP binding was stable after treating at 45° C for 20 min. but was destroyed at 60° C. Binding was maximal between pH 7.5 and 9.0 and decreased at pH below 7.0.     

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.     

Androgen binding protein, sperm production, semen output and LH and testosterone profiles in young postpubertal bulls

An androgen binding protein (ABP), which binds 5alpha-dihydrotestosterone with high affinity (Ka = 0.3 x 10(9) M(-1)), has been demonstrated in testicular and epididymal cytosols of 5 young post pubertal bulls (15-17 months old) of the Montbeliarde dairy breed. Simultaneously, daily sperm production (DSP), semen output and plasma LH and testosterone concentrations (from frequent samplings) were determined. ABP levels were 21 fmoles/mg protein in testis and 59, 22 and 43 fmoles/mg, respectively, in caput, corpus and cauda epididymis. Mean DSP, per gram of testis, was 16.6 x 10(6) spermatozoa, and the mean sperm output was approximately 1.5 x 10(9) spermatozoa per ejaculate. Mean LH and testosterone levels were 1.5 ng/ml and 2.1 ng/ml, respectively. One bull (882) was clearly distinguishable from the others, in showing higher ABP and testosterone levels together with a lower daily sperm production. Results of this study may (1) suggest a physiological role of ABP in sperm epididymal maturation and (2) give a new parameter in the evaluation of individual bulls testicular function.     

Androgenic regulation of luteinizing hormone secretion: relationship to androgen binding in sheep pituitary

Castrated ram lambs (wethers) were investigated for sensitivity to androgen feedback and to determine whether this feedback inhibition of luteinizing hormone (LH) was associated with changes in pituitary androgen receptors. Administration of Silastic capsules containing either dihydrotestosterone or testosterone was found to produce dose-dependent inhibitory effects on serum LH levels in wethers. Physiological dosages of these androgens (i.e., those that produce serum levels of dihydrotestosterone [0.24 ng/ml] or testosterone [2.1 ng/ml] similar to those of intact rams) resulted in differential inhibition of serum LH and LH content of the anterior pituitary. Whereas the inhibitory effect of dihydrotestosterone on pituitary LH content was much more dramatic than that seen with testosterone, the high dosage of testosterone also produced a substantial decrease in pituitary LH content. Responses of the pituitary to changes in serum androgen were compared to responses of the seminal vesicle, which served as a control androgen target organ. Androgen levels were positively correlated with seminal vesicle weights, but pituitary weights were unaffected by castration and/or androgen replacement. Treatments with dihydrotestosterone were associated with decreased cytosol androgen binding activity (i.e., receptors) in pituitary and seminal vesicle, suggesting that both of these tissues were sites of androgen action. Although testosterone inhibited serum LH levels, pituitary cytosol androgen receptors were not affected by changes in serum testosterone. We conclude from these data that dihydrotestosterone is a physiological regulator of pituitary LH secretion in the ram and that further study is needed to investigate the complex actions of testosterone and its metabolites on pituitary function.     

Steroid metabolism and binding activity in a murine renal tumor cell line

The purpose of this study was to partially characterize the steroid binding activity of murine renal tumor cells in continuous culture. The steroid receptor content of a cloned renal tumor cell line (RAG) and a subline RAG-2 was examined by sucrose gradient analysis, hydroxylapatite and dextran-coated charcoal methods. The RAG cells lacked estrogen- and progestin-binding activity, whereas specific 5 alpha-dihydrotestosterone (DHT) and dexamethasone (Dx) binding activities were detected as 8S peaks on low salt gradients. The specificity of DHT binding was examined by sucrose gradient analysis: DHT, R1881 and ORG2058 all completely inhibited [3H]DHT binding whereas diethylstilbestrol and Dx were ineffective. The androgen receptor content of the RAG cells was approx. 15 fmol/mg cytosol protein by the hydroxylapatite-filter assay, with an estimated Kd for methyltrienolone (R1881) of 5 nM at 0 degrees C. Scatchard analysis of [3H]Dx binding by RAG cytosol showed a Kd of 6 nM for Dx and 44 nM for corticosterone at 0 degrees C. Glucocorticoid receptor levels were estimated to be 182 fmol/mg cytosol protein by dextran-coated charcoal assay. Metabolism of [3H]testosterone and [3H]DHT by RAG cells was examined 1, 4 and 6 h after exposure to labeled hormone. Radioactive DHT was the primary intracellular metabolite recovered after exposure to [3H]testosterone. There was little conversion of DHT to androstanediol.     

Intracellular Ca2+ stimulates the binding to androgen receptors in platelets

In this study, we demonstrated that ADP-induced platelet aggregation activates the binding of testosterone (T) to its receptor. It is well known that binding of ADP to its receptors induced the release of Ca2+ ions from dense bodies into the cytosol of platelets. In this work, we compared the binding of testosterone or dihydrotestosterone to their receptors using cytosol obtained from ADP-treated and non-treated platelets. These experiments were repeated using EGTA (a calcium chelator) or U73122 (a phospholipase C enzymatic activity inhibitor) to the ADP-treated platelets. In addition, we also developed a competition analysis for the androgen receptors (AR) using [3H]DHT, non-radioactive T, DHT or cyproterone acetate from ADP-treated platelets cytosol. The results from this study indicate that the cytosol obtained from non-ADP-treated platelets did not show any binding to [3H]T or [3H]DHT, whereas cytosol from ADP-treated platelets binds to the radio-labeled androgens. Furthermore cytosol from ADP plus U73122-treated platelets did not show binding to [3H]T or [3H]DHT. These data suggest that intracellular Ca2+ ions stimulates the binding of androgens to their receptors in platelets cytosol. The competition analysis shows that T and DHT have high affinities for the androgen receptors with similar IC50 values, whereas cyproterone acetate shows a lower affinity. The results from these data clearly indicate the presence of androgen receptors in platelets.     

Androgen binding protein (ABP) in rabbit testis and epididymis

ABP has been measured in 105,000 g supernatants of testis and epididymls from rabbits of different ages and compared with a similar androgen binding protein (TeBG) in rabbit serum. Whereas the concentration of ABP in the caput epididymidis increased markedly from immaturity to adulthood, serum TeBG decreased, indicating that ABP and TeBG are regulated by different hormonal mechanisms.The concentration of ABP (pmoles/mg protein) in sexually mature rabbits was much higher in the epididymis than in the testis. Within the epididymis most of the ABP was concentrated within the caput, and very low amounts were found in the cauda, indicating that binding activity of ABP is destroyed as it passes through the epididymis.In addition to ABP (R_f ~0.7), rabbit epididymal supernatant contains a larger binding protein for 5α-dihydrotestosterone (DHT; 17β-hydroxy-5α-androstan-3-one) with slower electrophoretic mobility (R_f ~0.4) and a more rapid sedimentation rate on sucrose gradients (7S). This component is most probably the intracellular androgen receptor in the rabbit e pididymis.     

Estradiol-17 beta inhibition of androgen uptake, metabolism and binding in epididymis of adult male rats in vivo: a comparison with cyproterone acetate

The effects of estradiol-17 beta on androgen uptake, metabolism and binding were studied in rat epididymis in vivo in comparison with cyproterone acetate. Steroids (250 ug/100 g body weight) were injected 5 min prior to 3H-testosterone in castrate rats. Estradiol-17 beta inhibited 3H-testosterone uptake into epididymal cytosol by 58% as compared to 38% by cyproterone acetate. 3H-Testosterone uptake into epididymal nuclei was inhibited 95% by estradiol-17 beta and 83% by cyproterone acetate. Total bound radioactivity in cytosol fractions was reduced to a greater extent by estradiol-17 beta than cyproterone acetate when either 3H-testosterone or 3H-dihydrotestosterone was injected. Binding of 3H-dihydrotestosterone to nuclear receptors was completely abolished by estradiol-17 beta; whereas approximately 20% binding remained in the nuclear extract after cyproterone acetate treatment. Metabolism of 3H-testosterone in vivo was also altered by estradiol-17 beta, resulting in diminished conversion to 3H-dihydrotestosterone. Cyproterone acetate, on the other hand, did not affect 3H-testosterone metabolism. Estradiol-17 beta and cyproterone acetate inhibited in vitro binding of 3H-dihydrotestosterone to the intracellular cytoplasmic receptor, but not the intraluminal androgen binding protein (ABP). These data suggest that estradiol-17 beta may have a more potent antiandrogenic effect on the epididymis than cyproterone acetate due to inhibition of 5 alpha reduction of testosterone as well as binding to the androgen receptor.     

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.     

Effects of dicyclohexane derivatives on androgen metabolism in the rat prostate

Dicyclohexane derivatives, which inhibit the binding of testosterone and dihydrotestosterone (DHT) to the androgen-binding protein (ABP) of rat epididymis without interfering with their binding to the androgen receptor, show a similar selectivity in their effects on androgen metabolism. Their ability to inhibit the aromatization of testosterone has been reported previously. This paper demonstrates that they are potent inhibitors of 3 alpha(beta)-hydroxysteroid:NAD(P)+ oxidoreductase activity (3-HSD) in the particulate fraction from rat prostate gland; the values of Ki for their inhibition of this enzyme are similar to that of the Km for DHT as substrate. The dicyclohexane derivatives are markedly less effective against the cytosolic NADPH-dependent 3-HSD, and they do not appear to inhibit testosterone 5 alpha-reductase activity. These characteristics are likely to complicate the proposed use of the dicyclohexane derivatives as probes for the role of ABP in vivo. However, they may be of interest in the study of structure-activity relationships in androgen-metabolizing enzymes, particularly in the examination of the different forms of 3-HSD.