Receptor-proteims for androgens and the mode of action of androgens on gene transcription in ventral prostate

Therapeutic Rationales, Progresses, Failures, and Future Directions for Advanced Prostate Cancer

Patients with localized prostate cancer (PCa) have several therapeutic options with good prognosis. However, survival of patients with high-risk, advanced PCa is significantly less than patients with early-stage, organ-confined disease. Testosterone and other androgens have been directly linked to PCa progression since 1941. In this review, we chronicle the discoveries that led to modern therapeutic strategies for PCa. Specifically highlighted is the biology of androgen receptor (AR), the nuclear receptor transcription factor largely responsible for androgen-stimulated and castrate-recurrent (CR) PCa. Current PCa treatment paradigms can be classified into three distinct but interrelated categories: targeting AR at pre-receptor, receptor, or post-receptor signaling. The continuing challenge of disease relapse as CR and/or metastatic tumors, destined to occur within three years of the initial treatment, is also discussed. We conclude that the success of PCa therapies in the future depends on targeting molecular mechanisms underlying tumor recurrence that still may affect AR at pre-receptor, receptor, and post-receptor levels.

Protein B23/nucleophosmin/numatrin nuclear dynamics in relation to protein kinase CK2 and apoptotic activity in prostate cells

Protein B23/nucleophosmin/numatrin (B23) is a key nucleolar/nuclear matrix-associated protein required for cell growth-related functions, such as rRNA synthesis. Protein kinase CK2 (CK2) (formerly casein kinase 2, a protein Ser/Thr kinase signal that is involved in cell growth and cell death) mediates phosphorylation of B23, thereby influencing its functional activity. Here we have delineated the dynamics of B23 and its link to CK2 status in response to altered growth stimuli and induction of apoptosis in cultured prostate cells and in rat prostate cells in vivo. Our studies employing PC-3 and ALVA-41 prostate cancer cells demonstrated colocalization of CK2 and B23 in the nucleus. Further, CK2 and B23 underwent coordinate modulation in the nucleus related to their nucleocytoplasmic shuttling in response to induction of apoptotic activity in cells caused by downregulation of CK2 or by treatment with other apoptosis-inducing agents. These alterations in nuclear association of B23 occurred in the absence of a significant change in the level of cytoplasmic B23. Similar studies in the in vivo model of rat prostate epithelial cells subjected to androgen deprivation (that resulted in loss of nuclear CK2 and induction of apoptosis) demonstrated dynamic modulation of nuclear matrix-associated B23 without a significant change in its cytoplasmic level. These changes were reversed by androgen-mediated growth response in the prostate. Our results suggest that CK2-mediated phosphorylation of B23 is essential for its retention in the nucleus and that coordinated nuclear localization of B23 and CK2 is dynamically regulated in response to altered growth status in the cell.

Molecular signaling pathways that regulate prostate gland development

Prostate gland development is a complex process that involves coordination of multiple signaling pathways including endocrine, paracrine, autocrine, juxtacrine and transcription factors. To put this into proper context, the present manuscript will begin with a brief overview of the stages of prostate development and a summary of androgenic signaling in the developing prostate, which is essential for prostate formation. This will be followed by a detailed description of other transcription factors and secreted morphogens directly involved in prostate formation and branching morphogenesis. Except where otherwise indicated, results from rodent models will be presented since studies that examine molecular signaling in the developing human prostate gland are sparse at the present time.

Androgen increases AT1a receptor expression in abdominal aortas to promote angiotensin II-induced AAAs in apolipoprotein E-deficient mice

OBJECTIVE

Castration of male apolipoprotein E-deficient (apoE-/-) mice reduces angiotensin II (Ang II)-induced abdominal aorta aneurysms (AAAs) to that of female mice. The purpose of this study was to determine whether this reduction is attributable to androgen-mediated regulation of aortic Ang II type 1A receptors (AT1aR).

METHODS AND RESULTS

AT1aR mRNA abundance in the AAA-prone region of abdominal aortas was 8-fold greater compared to thoracic aortas of male but not female mice. AT1aR mRNA abundance decreased after castration in abdominal but not thoracic aortas of male mice. Dihydrotestosterone (DHT, 0.16 mg/d) administration to castrated male mice restored AT1aR mRNA abundance in abdominal aortas but had no effect in thoracic aortas. DHT also increased AT1aR mRNA abundance in abdominal aortas from female mice. Castrated male or female apoE-/- mice were administered DHT during infusion of saline or Ang II (1000 ng/kg/min for 28 days). DHT administration did not alter serum cholesterol concentrations, lipoprotein distributions, or atherosclerotic lesion areas in either male or female mice. However, administration of DHT increased AAA incidence in male (27% placebo versus 75% DHT) and female mice (28% placebo versus 64% DHT).

CONCLUSIONS

Androgen promotes AT1aR mRNA abundance in abdominal aortas associated with increased Ang II-induced AAAs.

Designer androgens in sport: when too much is never enough

The recent identification of tetrahydrogestrinone (THG), the first true "designer androgen," as a sports doping agent reflects both an alarmingly sophisticated illicit manufacturing facility and an underground network of androgen abusers in elite sports, as well as the still untapped potential for designer androgens in medicine. Never marketed, THG was apparently developed as a potent androgen that was undetectable by conventional International Olympic Committee-mandated urinary sports doping tests. As a potent androgen and progestin with unspecified contaminants, its distribution for use at high doses without any prior biological or toxicological evaluation poses significant health risks. Yet this diversion of science also highlights the prospect of designer androgens for use in human medicine. Designer androgens also offer the possibility of tissue-specific effects enhancing the beneficial effects of androgens while mitigating the undesirable ones. Further developments require better understanding of the postreceptor tissue selectivity of androgens, comparable to the mechanism underlying that of partial estrogen agonists (SERMs). This experience highlights the ongoing need for vigilance to detect novel drug doping strategies in order to maintain fairness and safety in elite sports. This will require the deployment of generic catch-all tests, such as sensitive and specific in vitro androgen bioassays, coupled with the development of mass spectrometry-based tests for specific doping agents.

Molecular mechanism of androgen action

Androgens affect the growth and development of a wide variety of cell types in both males and females and produce their effects by binding to androgen receptors, which modulate the transcription of specific genes. Testosterone is the major active androgen circulating in blood, but in many tissues it is metabolized by 5alpha-reductase to 5alpha-dihydrotestosterone, which binds to and activates the androgen receptor. Androgen receptors are members of the nuclear receptor family of transcription factors, and these nuclear receptors control transcription by recruitment of a variety of co-activators and co-repressors. Mutations in the androgen receptor and 5alpha-reductase can affect male sexual development. 5alpha-Reductase is also critical for parturition and fetal survival in mice. Inhibitors of 5alpha-reductase are being used increasingly to treat some androgen-dependent disorders. Because androgens also suppress the growth of certain cancer cells, they might also have a role in treating prostate cancer.

Dihydrotestosterone prevents spontaneous adenocarcinomas in the prostate-seminal vesicle in aging L-W rats

BACKGROUND

Gene-regulated mechanisms govern tumor development, but the actual development of tumors can be suppressed or promoted by epigenetic factors. Lobund-Wistar (L-W) rats are genetically predisposed to development of spontaneous and induced metastasizing moderately differentiated adenocarcinomas in the prostate-seminal vesicle (P-SV) complex. In L-W rats with one slow-release subcutaneous implant of dihydrotestosterone (DHT) (5alpha-Androstan-17beta-ol-3-one), the development of induced P-SV tumors 14 months later was significantly suppressed, with involution of testes, aspermia, and absence of detectable serum testosterone. The tumor-suppressive effect of DHT was confirmed. Spontaneous P-SV tumors developed in 57 of 220 control L-W rats (26%) at an average age 20 months.

METHODS

At age 12 months, 70 L-W rats were administered an implant of 40 mg of DHT, and 75 untreated rats served as controls. All rats that developed palpable P-SV tumors were autopsied, and surviving rats were autopsied at age 24 months.

RESULTS

At age 24 months, 9 of 70 DHT-treated rats (12.8%) and 20 of 75 DHT-free control rats (26.6%) had developed P-SV tumors spontaneously at average age 20.5 and 20 months, respectively.

CONCLUSIONS

Slow-release implants of DHT administered to L-W rats at age 12 months reduced by 50% the development of spontaneous P-SV tumors by age 24 months.

Prostate gland: structure, functions and regulation

The prostate gland plays an important role in male reproduction. It secretes enzymes, lipids, amines and metal ions essential for the normal function of spermatozoa. Development, differentiation and maintenance of the prostate gland depend on steroid and peptide hormones. Beside hormones growth factors also regulate the prostate gland. This review will focus on the structure, functions and mode of regulation of the prostate gland.

Autoregulation of androgen receptor expression in rodent prostate: immunohistochemical and in situ hybridization analysis

Autoregulation of androgen receptor mRNA and protein was investigated by immunohistochemical and in situ hybridization techniques. In both mouse and rat prostate, the epithelial cell nuclei were stained with the monoclonal or polyclonal antibodies raised against human androgen receptor. It was observed that 3 days after castration, nuclear staining of the epithelium was greatly reduced, while androgen treatment restored the staining intensity to a normal level. In situ hybridization using an androgen receptor cDNA fragment as probe demonstrated that the change in androgen receptor mRNA level correlated with the change in antibody staining intensity. These data suggested an up-regulation of androgen receptor expression by androgen.

Prostate plasma membrane receptor: a hypothesis

Based on 50 years of emerging knowledge about and changing views of prostate biochemistry and physiology and especially on the belief that there is an underlying mechanism of androgen control, the hypothesis is developed and tested that the rates of proliferation, biosynthesis, metabolism, and secretion are modulated through the hormone-sensitive Na, K-ATPase of the plasma membrane. These preliminary experiments, constituting a novel synthesis of technologies from endocrinology, intermediary metabolism, and membrane transport, attempt to explain the extraordinary production and secretion of citrate and how this may be coupled to sustaining prostate cell number and function. Attention is focused on learning where androgen is bound and how it interacts with the Na,K-ATPase. Both the dissimilar properties of epithelial and stromal cells in the separate regions of the acinus and the changing environment of growth factors in which these cells are bathed help account for their unlike reactivities during development and ongoing mature function. Little wonder that one hormone can have so many effects!

Steroid hormone receptors

In the three decades since the original discovery of receptors for steroid hormones, much has been learned about the biochemical processes by which these regulatory agents exert their effects in target tissues. The intracellular receptor proteins are potential transcription factors, needed for optimal gene expression in hormone-dependent cells. They are present in an inactive form until association with the hormone converts them to a functional state that can react with target genes. Transformation of the receptor protein to the nuclear binding form appears to involve the removal of both macromolecular and micromolecular factors that act to keep the receptor form reacting with DNA. Much of the native receptor is present in the nucleus, loosely bound and readily extractable, but for some and possibly all steroid hormones, some receptor is in the cytoplasm, perhaps in equilibrium with a nuclear pool. Methods have been developed for the stabilization, purification, and characterization of receptor proteins, and through cloning and sequencing of their cDNAs, primary structures for these receptors are now known. This has led to the recognition of structural similarities among the family of receptors for the different steroid hormones and to the identification of regions in the protein molecule responsible for the various aspects of their function. Monoclonal antibodies recognizing specific molecular domains are available for most receptors. Despite the knowledge that has been acquired, many important questions remain unsolved. How does association with the steroid remove factors keeping the receptor protein in its native state, and how does binding of the transformed receptor to the response element in the promoter region enhance gene transcription? Once it has converted the receptor to the nuclear binding state, is there a further role for the steroid in modulating transcription? Still not entirely clear is the involvement of phosphorylation and/or dephosphorylation in hormone binding, receptor transformation, and transcriptional activation. Less vital to basic understanding but important in the overall picture is whether the native receptors for gonadal hormones are entirely confined to the nucleus or whether there is an intracellular distribution equilibrium. With the effort now being devoted to this field, and with the application of new experimental techniques, especially those of molecular biology, our understanding of receptor function is progressing rapidly. The precise mechanism of steroid hormone action should soon be completely established.

A comparative study of the selectivity and efficiency of target tissue uptake of five tritium-labeled androgens in the rat

A comparative study of the tissue distribution of five tritium-labeled androgens was done in rats to determine the efficiency and selectivity of their uptake by target tissue. Testosterone (T), 5 alpha-dihydrotestosterone (DHT), 19-nortestosterone (nor-T), mibolerone (Mib) and methyltrienolone (R1881) all showed selective uptake by the ventral prostate in one-day castrated rats (250 g) that was 61-90% displaceable by co-injection of an excess of unlabeled steroid. The greatest uptake was with R1881 (0.69% injected dose per gram prostate tissue (%ID/g) at 1 h), and Mib (0.56% ID/g); the other three showed lower uptake (approx. 0.4% ID/g). The target tissue activity remained high for all compounds up to 4 h after injection, and at 2-4 h the prostate to blood ratio for Mib and R1881 exceeded 10 and 20, respectively. The uptake efficiency and selectivity of these five androgens appear to be related to their affinity for the androgen receptor and their resistance to metabolism. Mib and R1881 have substantial affinity for other steroid receptors, which might account for some of their prostate uptake. However, co-administration of triamcinolone acetonide, which has high affinity for progesterone and corticosteroid receptors but not for the androgen receptor, failed to block their uptake significantly, whereas co-administration of DHT, the most selective ligand for the androgen receptor, blocked their uptake as completely as the unlabeled tracer itself. The prostate uptake of Mib and R1881 in intact animals was significantly lower than in castrated animals, but treatment of the intact animals with diethylstilbestrol restored their uptake nearly to the level seen in castrated animals. These uptake patterns are consistent with earlier studies of in vivo androgen uptake and with known changes in androgen receptor content and occupancy as a result of castration or diethylstilbestrol treatment. They further suggest that high affinity androgens labeled with suitable radionuclides--particularly derivatives of mibolerone (Mib) or methyltrienolone (R1881)--may be effective receptor-based imaging agents for androgen target tissues and tumors, even when patients are already receiving hormonal therapy.

The synthesis and testing of E-17 alpha-(2-iodovinyl)-5 alpha-dihydrotestosterone and Z-17 alpha-(2-iodovinyl)-5 alpha-dihydrotestosterone as gamma-emitting ligands for the androgen receptor

Two iodinated steroids, E-17 alpha-(2-iodovinyl)-5 alpha-dihydrotestosterone and Z-17 alpha-(2-iodovinyl)-5 alpha-dihydrotestosterone were synthesized in a search for a gamma-emitting androgen that binds with high affinity to the androgen receptor. Such compounds would be extremely useful research tools for studies of androgen responsive tissues and as in vivo probes of androgen responsive tumors such as prostate cancer. These 17 alpha-iodovinyl steroids were synthesized because many 17 alpha-substituents do not interfere markedly with binding to the androgen receptor and because similar analogs of other steroids, estrogens and progestins, have been shown to have the requisite properties for ligands to those receptors. Both of these potential ligands were tested for their ability to compete with [3H]R1881 for binding to the androgen receptor in cytosols from prostate, hypothalamus and pituitary. The relative binding affinities ranged between 5 and 20%, depending upon the tissue and steroid. In order to test the two ligands directly, they were both synthesized labelled with 125I and tested for binding to the androgen receptor in prostatic cytosol and in vivo for specific concentration in androgen responsive tissues. While there was considerable binding in the prostatic cytosol, it was not specific because 5 alpha-dihydrotestosterone did not compete. Likewise in the in vivo experiment there was no evidence for androgen receptor mediated concentration of the tracers. While on the basis of relative binding affinity, these 2 steroids appeared to be good candidates for androgen receptor ligands, neither were useful for this purpose. These results contribute new information which will be valuable in the design of other gamma-emitting androgens and emphasises that, in this process, other factors such as metabolism and nonspecific binding must be considered.

Glucocorticoid-receptor complexes are associated with small RNA in vitro

Identification of RNA associated with soluble glucocorticoid-receptor complexes of HeLa cells was performed by immunoprecipitation of receptor complexes with a monoclonal antibody raised against rat liver glucocorticoid receptor. Polyacrylamide gel electrophoresis of RNA extracted from immunoprecipitates of cytosolic complexes revealed the presence of eight RNA bands, consisting of 28S, 18S, and small RNAs, including 5.8S, 5S and tRNA. A comparison of RNA species immunoprecipitated by monoclonal anti-glucocorticoid receptor antibody and IgG purified from normal mouse serum showed that four small RNAs were preferentially recovered after immunoprecipitation with anti-glucocorticoid receptor antibody. When these species were analyzed on sequencing gels, their nucleotide lengths coincided with those of 7-3, 7S, U2, and U1 RNA. Immunoprecipitation of nuclear extracts containing glucocorticoid-receptor-RNA complexes showed that the same set of small RNAs was preferentially immunoprecipitated by anti-glucocorticoid receptor antibody. The four small RNAs we detected represented minor species in whole extracts, and their preferential immunoprecipitation by anti-glucocorticoid receptor antibody was prevented by removal of glucocorticoid-receptor complexes from HeLa cell extracts. We conclude that 7-3, 7S, U2, and U1 RNA are associated with glucocorticoid-receptor complexes in vitro, and hypothesize that post-transcriptional effects of glucocorticoids may in part be mediated through interaction of receptor complexes with these small RNAs.

Androgen receptors: structures, mutations, antibodies and cellular dynamics

An overview of recent studies from this and other laboratories on the structures and intracellular dynamics of androgen receptors is presented. Human and rat androgen receptors are unique in that, aside from their DNA and androgen binding domains, they have amino terminal regions rich in oligo- and poly(amino acids) motifs as in some regulatory and homeotic genes. Point mutations that cause sequence changes or deletion of regions of androgen receptors appear to be responsible for some cases of androgen-insensitivity. Monoclonal antibodies produced against specific regions of the androgen receptor bind to androgen receptors but not other major steroid receptors. Androgen receptors in the human and rat prostate, and monkey seminal vesicle were localized to the nucleus of target cells in these tissues with these antibodies; androgen receptors also were found in the cytoplasm of some target cells. Actinomycin D and 3'-deoxyadenosine, inhibitors of transcription, RNA processing and nucleo-cytoplasmic transport of RNA, interfere with the intracellular dynamics of androgen receptors, suggesting as we have proposed previously that androgen receptors may function not only at the site of transcription but also are involved in posttranscriptional regulation of mRNA stability and utilization.

Stereochemical complementary of DNA and steroid agonists and antagonists

Modelling studies in our laboratories over the past decade have demonstrated that a variety of natural products exhibit stereochemical complementarity with nucleic acids. In the case of steroid hormones, the basic cyclopentanophenanthrene skeleton fits between base pairs in partially unwound double stranded DNA; heteroatoms on the steroids form stereospecific donor/acceptor linkages to hydrogen bonding heteroatoms on the DNA. Each of the hormones appears to fit best in the site, i.e. 5'-dTdG-3'.5'dCdA-3'; the pattern of donor/acceptor linkages is unique for each type of hormonal activity. Steroid hormone agonists fit into the same site as the parent hormone; degree of fit correlates with degree of hormonal activity. Steroid hormone antagonists (e.g. RU 486; tamoxifen; anandron) fit into the same site as the agonists but possess different donor/acceptor linkages than the parent hormone; these linkages occur within the site between the base pairs or along the outside surface of the DNA helix in the major or minor grooves. A chronological review of the underlying concepts and observations leading to these discoveries is presented. Work in progress and some potential implications of the emerging technology are also discussed.

Effects of alcohol feeding on androgen receptors in the rat pituitary gland

Specific binding of testosterone-1 beta, 2 beta-3H by cytosol from anterior pituitary gland of alcohol-fed, isocaloric control, and castrated control and alcohol-fed rats with or without testosterone treatment has been investigated by charcoal assay. The number of androgen binding sites was significantly reduced in alcohol-fed rats (8 +/- 1.0 fmoles/mg cytosol protein), when compared to the isocaloric control value (13.2 +/- 2.1 fmoles/mg protein), with no significant change in Kd (0.7 +/- 0.14 nM). Castration significantly increased the number of receptor sites in control rats and when castrated control animals were treated with testosterone the binding sites were decreased to the intact control level. In contrast, castration or testosterone given to castrated alcohol-fed rats did not alter alcohol-induced reduction of the receptor sites. The binding affinity (Kd) is identical in all groups. The concentration of serum luteinizing hormone (LH) was significantly lower in alcohol-fed rats when compared to that of normal controls. An increased serum LH level with a decreased testosterone level was noted in castrated control rats. However, castration of alcohol-fed rats had little or no effects on the concentrations of LH and testosterone. Administration of testosterone suppressed castration-induced high LH in control rats but alcohol-induced reduction of LH level was not altered by this treatment. These findings indicate that alcohol exerts a suppressive effect on the content of androgen receptors and secretory functions of gonadotropins in the pituitary gland.

Production, clearance, and metabolism of testosterone in men with prostatic cancer

It was previously unknown whether the production and metabolism of testosterone was altered in men with prostatic cancer. We recently observed a familial influence on the plasma concentration of sex steroids in men with the cancer. We have now determined, by isotope dilution techniques, the blood testosterone production and clearance rates and testosterone metabolism to potent androgen metabolites in men with prostatic cancer, their brothers, and unrelated controls. Nineteen men had a diagnosis of prostatic cancer before age 63 (probands), 23 were brothers of these index cases, and nine controls matched for age were selected randomly from the general population. None had received endocrine therapy. The plasma content of testosterone, dihydrotestosterone, sex hormone binding globulin, apparent free testosterone concentration, follicle-stimulating hormone, and luteinizing hormone were not significantly different between the groups. The metabolic clearance rate of testosterone was significantly (P = .04) higher in probands (458 liters/day/body surface area, median) than in controls (306 liters/day/body surface area). The conversion ratios of both testosterone (1.8%) and dihydrotestosterone (16.9%) to 3 alpha-androstanediol were significantly greater (P = .04 and P = .004, respectively) in probands than in controls (0.95%, 7.8%). These results indicate that men with prostatic cancer have elevated clearance rates of testosterone and an increased conversion ratio of testosterone to its potent 5 alpha-reduced metabolites.

Dihydrotestosterone does not induce prostate adenocarcinoma in L-W rats

It has been postulated that dihydrotestosterone (DHT) is the active trophic androgen in initiating pathogenic changes in the prostate gland. Groups of prostate cancer-susceptible male L-W rats (age 3 months) were treated with subcutaneous depots of testosterone or of DHT. After 14 months, prostate adenocarcinomas had developed in 24% of the testosterone-treated rats but not in the DHT-treated rats. In the latter rats, the testes were significantly reduced in weight, there was no evidence of spermatogenesis, and serum testosterone levels were not detectable. It appears that DHT as administered to L-W rats had an antiandrogenic effect.

Androgen interactions with intact nuclear envelopes from the rat ventral prostate

Intact nuclear envelopes containing nuclear pore complexes have been prepared from the rat ventral prostate. The polypeptide profile of the nuclear envelopes from the rat prostate resembled that of nuclear envelopes prepared from the male rat liver. Isolation of the nuclear envelopes after incubation of purified nuclei with radioactive dihydrotestosterone results in labelling of the membrane. More dihydrotestosterone is bound after incubations at 22 degrees C for 18 h than at 2 degrees C for 18 h or 22 degrees C for 2 h. Scatchard analysis revealed a class of binding sites with an apparent Kd of 46 nM. Dihydrotestosterone, testosterone, cyproterone acetate and methyltrienolone were effective as competitors of labelled dihydrotestosterone binding to the nuclear envelopes, while estradiol did not compete. Castration of the rats 24, 48 and 96 h prior to preparation of nuclei resulted in loss of androgen binding to the membranes. Extraction with 0.6 M NaCl resulted in the loss of 72% of the androgen binding.

Interaction of cyproterone acetate with rat prostatic androgen receptors

We have investigated the binding of cyproterone acetate (CA) to cytosolic androgen receptors (RC) and translocation of the RCCA complex into the nucleus. In a cell-free system (3H)CA binds to cytosolic androgen receptors with high affinity (KD = 11.6 nM) and limited capacity (180-200 femtomoles/mg protein). (3H)CA, however, dissociates very rapidly from the cytosolic and nuclear androgen receptors (Rn) at 0 degree C. Incubation of RC (3H)CA at 20 degrees C increased its ability to bind to nuclei. Translocation of RC (3H)CA to nuclei of intact cells was demonstrated after incubation of prostatic tissue with (3H)CA in tissue culture medium at 37 degrees C. In vivo administration of CA to castrated rats promoted RCCA translocation but did not induce androgen receptor replenishment. These data demonstrate that CA binds to and translocates androgen receptors to nuclei without concomitant receptor replenishment.

Studies on the role of the sex-hormone-binding globulin (SHBG) in prostatic gland hypertrophy in men. II. In vitro research

The effect of SHBG, stilbestrol and cyproterone acetate on the amount of 3H-DHT in the cell nuclei of hypertrophic prostatic glands was studied in vitro. It was found the SHBG lowers the DHT content, whereas stilbestrol and cyproterone acetate in the presence of SHBG tends to increase the amount of 3H-DHT in the nuclei.

RNA-containing nuclear binding sites for glucocorticoid-receptor complexes

RNase A treatment of HeLa cell nuclei causes a time- and concentration-dependent release of dexamethasone-receptor complexes. If nuclei are incubated in the absence of enzyme, only 60% of RNase-releasable complexes can be detected. Sucrose density gradient analysis of nuclear extracts shows that receptor complexes released by RNase treatment sediment at 3.6 S, whereas complexes obtained from untreated nuclei sediment between 7 and 3.6 S. Our results show that a fraction of dexamethasone-receptor complexes retained by HeLa cell nuclei is located in binding sites involving RNA.

Remodeling the estrogen receptor model

The estrogen receptor model has revised to make it compatible with new data on subcellular localization of the receptor and physical characteristics of solubilized versus immobilized receptors. Our current model suggests that receptors, with or without bound estrogen, are present in the nuclear fraction. Furthermore, the receptor behaves as if it were immobilized or bound to some nuclear constituent at all times. Thus, the association of the estrogen-free receptor (unbound receptor) to a target site in the nucleus is considered to be the critical event in defining the nature of the response to estrogenic hormones.

Steroid receptor recycling and its possible role in the modulation of steroid hormone action

The fate of steroid-receptor complexes after their nuclear retention in target cells is not firmly established. Nuclear glucocorticoid- and androgen-receptor complexes could be recycled back to the cytosol in their responsive tissues, whereas this has not been clearly established for the case of progesterone and estrogen receptors. The models of steroid receptor recycling proposed so far involve release of chromatin-bound complexes into the cytosol, loss of steroid, and receptor inactivation. These receptors, however, can eventually be reactivated to a steroid binding form to reinitiate a cycle of steroid binding and further nuclear translocation. We propose that this model can represent a general aspect of steroid hormone action, provided that inactivation/reactivation processes occur in every steroid responsive system. A process involving a reversible receptor inactivation could play a major role in the control of steroid receptor recycling. It is proposed that a control on the extent of receptor available to steroid binding could result in a modulation of cellular responses to steroid hormones.

Testosterone and tolerance in rat vas deferens

Testosterone is able to inhibit the development of tolerance in the smooth muscle of the rat vas deferens. Cycloheximide and actinomycin D also inhibit the tolerance to morphine and ethanol in smooth muscle of rat vas deferens. The toxic effect of cycloheximide and actinomycin D do not play roles in the inhibition of tolerance. The physiological responses of vas deferens to norepinephrine are not altered by cycloheximide and actinomycin D.

The use of a hydroxylapatite-filter steroid receptor assay method in the study of the modulation of androgen receptor interaction

Receptors for androgen, estrogen, and glucocorticoid can be assayed by hydroxylapatite adsorption of the radioactive steroid-receptor complex and washing of the adducts on membrane filters mounted on a multiple filter holder. The method is economical, very rapid and sensitive. This new receptor assay method was used to study the modulation of androgen receptor of rat ventral prostate by metal ions, thiols, and ligand structure. The interaction of androgen with the naked receptor is inhibited by 10 microM ZnCl2, CdSO4, or CuSO4 but this inhibition is competed by androgen and is reversed by DTT. The androgen-receptor complex is less sensitive to divalent metal ions but Zn2+, at 3 mM, appears to alter the conformation of the receptor and promote the release of androgen. Certain phenanthrene derivatives exhibited striking structural specificities in their ability to compete with radioactive androgen for binding to the prostate receptor. The results suggest that the receptor has binding preference toward individual ring structure in the steroid.

Present concept of the relevance of steroid receptors for prostatic cancer

Suitable assays for nuclear androgen-receptors in human prostatic cancer tissue have been presented. Correlations between NAR-content and response to hormonal therapy are demonstrated. The methods are time consuming and require expensive equipment as well as experience. Individual laboratory standards seem to determine response rates. The earlier methodological difficulties are replaced by a new set of problems for which as yet no single solution is available. As there is a tendency to use aspiration cytology more and more for diagnosis as well as follow-up of prostatic cancer, a cytochemical method would be extremely valuable. Research in that direction should be pursued.

In vitro metabolism of (3H)-androstenedione in the rat epididymis and vas deferens

The in vitro metabolism of (3H)-androstenedione in the epididymis and vas deferens of intact and castrated rats was investigated and the metabolites formed were identified by radio gas chromatography. Incubation of slices of caput epididymidis for 2 hr at 34 degrees C metabolised 90% androstenedione. Similar incubations of tissue samples from cauda epididymidis and vas deferens metabolized 60 and 25% of androstenedione respectively. The major metabolites formed in the epididymis were androstanedione (caput: 48%; cauda: 33%) and androsterone (caput: 35%; cauda: 13%). These metabolites appeared in much less concentration in the incubations with vas deferens (about 8% each). In general, conversion to testosterone and dihydrotesterone was low in all the three organs examined. Castration did not significantly alter the metabolic pattern in the caput epididymidis and vas deferens but promoted the formation of androsterone (38%) in the cauda epididymidis. The conversion of androstenedione, a weak androgen to testosterone, dihydrotestosterone and 3 alpha/3 beta-diols in the epididymidis and vas deferens of castrated rats may be of physiological significance. In addition, androsterone appears to be an important androgenic metabolite in the epididymis.

RNase-sensitive glucocorticoid-receptor complexes from HELA cell nuclei

Dexamethasone-receptor complexes can be extracted from HeLa cell nuclei by mild sonication. These complexes can account for 800-1000 binding sites/cell, and are indistinguishable from salt-extractable ones as judged by sucrose gradient centrifugation in the presence of 0.3 M KCl, showing a sedimentation coefficient of 3.6 S. These complexes, however, broadly sediment in the 7 to 3.6 S region of low salt sucrose gradients. Enzymatic treatment of soluble extracts from nuclear sonicates shows that RNA is associated to dexamethasone-receptor complexes.

Androgen receptors in the brain of neonatal normal male and androgen insensitive rats

Androgen binding was investigated in the cytosol of brains from neonatal normal and tfm rats using sucrose gradient and charcoal assay. The neonatal normal rat brain contains androgen receptors which sediment at 8S in a sucrose gradient at low ionic strength and at 4S in the presence of 0.5M KC1. These receptors have a high affinity (Kd = 1.2 X 10(-9)M) for dihydrotestosterone (DHT), with a binding capacity of 7.3 X 10(-15) moles/mg cytosol protein. By contrast, there is very little, if any, high affinity androgen receptors in the neonatal tfm rat brain. Apparently, metabolism of testosterone does not affect androgen binding in the neonatal rat brain. The presence of these receptors and the occurrence of aromatization in the brain of neonatal rats are discussed in relation to their possible roles in sexual differentiation of the brain.

Intracellular inactivation, reactivation and dynamic status of prostate androgen receptors

The dynamic status of the androgen receptor in prostate cells was studied by incubation of rat ventral prostate with radioactive 17beta-hydroxy-5alpha-androstan-3-one (5alpha-dihydrotestosterone) in the presence and absence of respiratory poisons and inhibitors of protein and RNA synthesis and also by isotope chasing of the radioactive androgen-receptor complexes. The androgen receptor in the prostate appears to go through a dynamic process of recycling between the cytoplasm and the nucleus as well as an inactivation process. The radioactive androgen-receptor complex, however, is maintained at a constant level for at least 2h during incubation at 37 degrees C, even in the absence of new protein synthesis, suggesting that early androgen actions may not require a depletion of a major portion of cellular receptor. In the presence of 2,4-dinitrophenol, the androgen receptor is rapidly deactivated (half life, 2min). The inactive receptor can be reactivated efficiently by an energy-dependent process, even in the absence of protein synthesis. Receptor binding of androgen and nuclear chromatin binding of the androgen-receptor complex are fast processes; half-maximum binding can be achieved within 1 and 10min respectively. On the contrary, the overall process of the release of the receptor complex from nuclear chromatin and its reappearance in the cytosol fraction has a long half life of about 70min. This slow process may reflect the involvement of the steroid-receptor complex in a time-consuming mechanism that is essential for hormone responses. Actinomycin D can increase the nuclear receptor level by 50% or more. This increase is not due to a decrease in the rate of receptor release from nuclei or to inhibition of DNA degradation by the antibiotic.

Characterization and partial purification of androgen receptors from ram seminal vesicles

An androgen receptor has been demonstrated in the cytosol and in the nuclear fraction of ram seminal vesicles. The cytosol receptor was stabilized by sodium molybdate and 2 distinct [3H]methyltrienolone-binding proteins, one sedimenting at 9S and one sedimenting at 3S, could be demonstrated by sucrose-gradient centrifugation in the presence of 50 mM molybdate. The slower sedimenting form could be partially purified by ADP-sepharose chromatography. The purified receptor still sedimented at 3S after centrifugation on sucrose gradients containing either 0.6 M KCl or 50 mM molybdate. The receptor was destroyed by heating at 50 degrees C for 30 min and its complex with [3H]methyltrienolone dissociated slowly at low temperatures. The apparent equilibrium-dissociation constant (KD) for the purified receptor was: 3.8 x 10(-10) M. The relative affinities for different steroids decreased in the following sequence: 5 alpha-dihydrotestosterone greater than or equal to methyltrienolone greater than testosterone much greater than estradiol greater than R5020 greater than progesterone greater than diethylstilbestrol. The nuclear androgen receptor sedimented at 3S on sucrose gradients containing 0.6 M KCl. At pH 7.4 it behaved as an acidic protein with an electrophoretic mobility towards the anodic region of the agar gel. Because of the relatively large content of cytoplasmic and nuclear androgen receptors and the availability of large amounts of tissue the ram seminal vesicles could be a suitable source for large-scale purification of these receptors.

Inhibition of androgen binding in human foreskin fibroblasts by antiandrogens

Antiandrogen effects on androgen receptor binding and androgen metabolism were studied in cultured human newborn foreskin fibroblasts. Three different antiandrogens were tested in this system: (a) cyproterone acetate (CA); (b) RU23908; and (c) R2956. CA and R2956 were equipotent inhibitors of androgen binding to its intracellular receptor. The magnitude of this action was nearly twice as great against the endogenous androgen ligands, dihydrotestosterone (DHT) or testosterone (T), than with the synthetic ligand, methyltrienolone (R1881). Whereas the relative binding affinities of CA and R2956 were approximately 5-10 times less than T or DHT, RU23908 was another order of magnitude less effective as an inhibitor of androgen binding. The lower relative binding affinity determined for RU23908 could not be explained on the basis of a requirement for metabolic activation. Subcellular fractionation studies and sucrose density gradient analysis further confirmed the rank order of antiandrogenic potency. None of the antiandrogens influenced the rate or profile of metabolites from cellular metabolism of T or DHT. We propose that cultured human genital skin fibroblasts may serve as a valuable system for the future evaluation of antiandrogens in intact ells under physiologic conditions.

Binding of androgens to a nuclear-envelope fraction from the rat ventral prostate

A nuclear-envelope fraction was isolated from the rat ventral prostate which is virtually free of DNA and contains little RNA or plasma membrane. Isolation of this nuclear-envelope fraction after incubation of purified nuclei with radioactive dihydrotestosterone results in labelling of the membrane. More binding of dihydrotestosterone is observed after incubations at 22 degrees C for 17 h than at 4 degrees C for 17 h or at 22 degrees C for 60 min. Scatchard analysis revealed a class of binding sites with KD 8.4 nM. Dihydrotesterone and testosterone were almost equally effective as competitors of labelled dihydrotestosterone binding on the purified nuclear-envelope fraction, whereas diethylstilboestrol was less effective and dexamethasone did not compete well. When the outer membrane of the nuclei was removed with Triton X-100, a 24% decrease in specific binding of androgens was observed. Castration 24 h before preparation of nuclei resulted in loss of the androgen binding to the membrane.