Structure and function of the androgen receptor

Integration of androgen hormones in endometrial cancer biology

Endometrial cancer (EC) is a gynecological pathology that affects the uterine inner lining. In recent years, genomic studies revealed continually evolving mutational landscapes of endometrial tumors that hold great potential for tailoring therapeutic strategies. This review aims to broaden our knowledge of EC biology by focusing on the role of androgen hormones. First, we discuss epidemiological evidence implicating androgens with EC pathogenesis and cover their biosynthesis and metabolism to bioactive 11-oxyandrogens. Next, we explore the endometrial tumor tissue and the altered microbiota as alternative sources of androgens and their 11-oxymetabolites in EC patients. Finally, we discuss the biological significance of androgens' genomic and nongenomic signaling as part of a medley of pathways ultimately deciding the fate of cells.

Computational Analysis of Residue-Specific Binding Free Energies of Androgen Receptor to Ligands

Androgen receptor (AR) is an important therapeutic target for the treatment of diseases such as prostate cancer, hypogonadism, muscle wasting, etc. In this study, the complex structures of the AR ligand-binding domain (LBD) with fifteen ligands were analyzed by molecular dynamics simulations combined with the alanine-scanning-interaction-entropy method (ASIE). The quantitative free energy contributions of the pocket residues were obtained and hotspot residues are quantitatively identified. Our calculation shows that that these hotspot residues are predominantly hydrophobic and their interactions with binding ligands are mainly van der Waals interactions. The total binding free energies obtained by summing over binding contributions by individual residues are in good correlation with the experimental binding data. The current quantitative analysis of binding mechanism of AR to ligands provides important insight on the design of future inhibitors.

The role of gonadotropins in testicular and adrenal androgen biosynthesis pathways-Insights from males with congenital hypogonadotropic hypogonadism on hCG/rFSH and on testosterone replacement

OBJECTIVE

To delineate the role of gonadotropins in male androgen biosynthesis pathways.

DESIGN

Case-control study.

PATIENTS AND MEASUREMENTS

Twenty five males with congenital hypogonadotropic hypogonadism (CHH) underwent hCG/rFSH and testosterone treatment sequentially. Serum steroid hormone profiles (testosterone precursors and metabolites) on both replacement regimens were analysed, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and compared to those of healthy controls, matched by age, BMI and serum testosterone.

RESULTS

On testosterone replacement, serum concentrations of the classic Δ4 pathway hormones progesterone and 17-hydroxy-progesterone (17-OHP), and the marker steroid of an alternative pathway of testosterone synthesis (androstenediol) were decreased, compared to controls. Androstanediol, a marker of the backdoor pathway of dihydrotestosterone (DHT) synthesis, was increased. 17-OH-pregnenolone, androstenedione and DHEAS (Δ5 pathway), three 11-oxygenated C19 androgens (11-keto-A4, 11-keto-T and 11-keto-DHT) and the testosterone (T) metabolites DHT and 17ß-oestradiol (E2) were similar to controls. On gonadotropin replacement, 17-OHP, 17-OH-pregnenolone, DHEAS and androstenedione, as well as DHT, androstenediol, and all 11-oxygenated C19 androgens were normal. Progesterone (Δ4 pathway) was slightly decreased, and androstanediol (backdoor DHT pathway) and E2 (T metabolite) were increased.

CONCLUSIONS

In males with CHH, serum steroid hormone profiles resemble those of healthy men, if hCG/rFSH is used for substitution. Gonadotropins contribute to steroid hormone production along the classic Δ4 pathway and co-activate an alternative pathway of testosterone biosynthesis via androstenediol. Backdoor DHT biosynthesis, Δ5 17-OH-pregnenolone, DHEA(S) and androstenedione synthesis and 11-oxygenated C19 androgen production are activated independently of gonadotropins. The androgen replacement modality used for treatment of hypogonadal males with absent or reduced endogenous LH/FSH secretion may impact on long-term health and quality of life.

In vitro effects of androgen on testicular development by the AR-foxl3-rec8/fbxo47 axis in orange-spotted grouper (Epinephelus coioides)

In orange-spotted grouper, androgen can promote the development of testis and spermatogenesis, but the effect of androgen on testis development is unclear. Forkhead box L 3 (Foxl3) is important in the development of fish testis. Rec8 and fbxo47 are involved in meiosis, which impacts spermatogenesis. The present study investigated the plausible role of testis development through the Foxl3 transcriptional regulation of rec8 and fbxo47. The results of tissue distribution showed that rec8 and fbxo47 are highly expressed in gonad. In addition, the highest expression of foxl3, rec8, and fbxo47 was in the testis and intersex compared with the other stages of gonadal development, suggesting that foxl3, rec8, and fbxo47 are important in testis development. In addition, by using dual-luciferase assays, we found that the androgen can increase foxl3 promoter activity and Foxl3 can upregulate rec8 and fbxo47 promoter activity. Furthermore, the addition of β-testosterone significantly increased foxl3, rec8, and fbxo47 promoter activity. Together, these results suggest that foxl3 plays a decisive role in testis development by regulating the expression of rec8 or fbxo47 and imply that AR-foxl3-rec8/fbxo47 affects the testis development pathway.

Therapeutic targeting of the androgen receptor (AR) and AR variants in prostate cancer

Prostate cancer (PCa) accounted for over 300 000 deaths world-wide in 2018. Most of the PCa deaths occurred due to the aggressive castration-resistant PCa (CRPC). Since the androgen receptor (AR) and its ligands contribute to the continued growth of androgen-dependent PCa (ADPCa) and CRPC, AR has become a well-characterized and pivotal therapeutic-target. Although AR signaling was identified as therapeutic-target in PCa over five-decades ago, there remains several practical issues such as lack of antagonist-bound AR crystal structure, stabilization of the AR in the presence of agonists due to N-terminus and C-terminus interaction, unfavorable large-molecule accommodation of the ligand-binding domain (LBD), and generation of AR splice variants that lack the LBD that impede the discovery of highly potent fail-safe drugs. This review summarizes the AR-signaling pathway targeted therapeutics currently used in PCa and the approaches that could be used in future AR-targeted drug development of potent next-generation molecules. The review also outlines the discovery of molecules that bind to domains other than the LBD and those that inhibit both the full length and splice variant of ARs.

Androgen Receptor Gene Variants in New Cases of Equine Androgen Insensitivity Syndrome

In the domestic horse; failure of normal masculinization and virilization due to deficiency of androgenic action leads to a specific disorder of sexual development known as equine androgen insensitivity syndrome (AIS). Affected individuals appear to demonstrate an incoherency between their genetic sex and sexual phenotype; i.e., XY-sex chromosome constitution and female phenotypic appearance. AIS is well documented in humans. Here we report the finding of two novel genetic variants for the AR-gene identified in a Tennessee Walking Horse and a Thoroughbred horse mare; each in individual clinical cases of horse AIS syndrome.

Steroid receptor/coactivator binding inhibitors: An update

The purpose of this review is to highlight recent developments in small molecules and peptides that block the binding of coactivators to steroid receptors. These coactivator binding inhibitors bind at the coregulator binding groove, also known as Activation Function-2, rather than at the ligand-binding site of steroid receptors. Steroid receptors that have been targeted with coactivator binding inhibitors include the androgen receptor, estrogen receptor and progesterone receptor. Coactivator binding inhibitors may be useful in some cases of resistance to currently prescribed therapeutics. The scope of the review includes small-molecule and peptide coactivator binding inhibitors for steroid receptors, with a particular focus on recent compounds that have been assayed in cell-based models.

PC-1 works in conjunction with E3 ligase CHIP to regulate androgen receptor stability and activity

The androgen receptor (AR) is not only a ligand-dependent transcription factor, but also functions as a licensing factor, a component of DNA replication, which is degraded during mitosis. Furthermore, the deregulation of AR activity is involved in the initiation of prostate cancer and contributes to castration resistant prostate cancer (CRPC). While AR degradation is known to occur primarily through a proteasome-mediated pathway, very little is known about how this process is regulated, especially in M phase. PC-1 is an androgen-responsive factor and expresses specificity in prostate cancer, with higher expression noted at G2/M. In this study, PC-1 was shown to interact with AR and E3 ligase CHIP (Carboxy-terminus of Hsc70 Interacting Protein) and to enhance AR/CHIP interactions, thereby decreasing AR stability. Moreover, PC-1 was found to act in conjunction with CHIP in the decreasing of AR via ubiquitination, with the subsequent degradation predominantly occurring during M phase. PC-1 was also found to repress AR transcriptional activity in androgen-dependent and androgen-independent prostate cancer cells and attenuate the growth inhibition of AR. In conclusion, these findings should provide new clues regarding the modulation of AR turnover and activity via PC-1 and reveals an essential role of PC-1 in AR signaling.

Nuclear Androgen Receptor Regulates Testes Organization and Oocyte Maturation in Zebrafish

Androgens act through the nuclear androgen receptor (AR) to regulate gonad differentiation and development. In mice, AR is necessary for spermatogenesis, testis development, and formation of external genitalia in males and oocyte maturation in females. However, the extent to which these phenotypes are conserved in nonmammalian vertebrates is not well understood. Here, we generate zebrafish with a mutation in the ar gene (aruab105/105) and examine the role of AR in sexual determination and gonad development. We found that zebrafish AR regulates male sexual determination, because the majority of aruab105/105 mutant embryos developed ovaries and displayed female secondary sexual characteristics. The small percentage of mutants that developed testes displayed female secondary sexual characteristics, exhibited structurally disorganized testes, and were unable to release or produce normal levels of sperm, demonstrating that AR is necessary for zebrafish testis development and fertility. In females, we found that AR regulates oocyte maturation and fecundity. The aruab105/105 mutant females developed ovaries filled primarily with immature stage I oocytes and few mature stage III oocytes. Two genes whose expression is enriched in wild-type ovaries compared with testes (cyp19a1a, foxl2a) were upregulated in ar mutant testes, and two genes enriched in testes (amh, dmrt1) were upregulated in ar mutant ovaries. These findings demonstrate that AR regulates sexual determination, testis development, and oocyte maturation and suggest that AR regulates sexually dimorphic gene expression. The ar mutant we developed will be useful for modeling human endocrine function in zebrafish.

An androgen response element driven reporter assay for the detection of androgen receptor activity in prostate cells

The androgen receptor (AR) transcription factor plays a key role in the development and progression of prostate cancer, as is evident from the efficacy of androgen-deprivation therapy, AR is also the most frequently mutated gene, in castration resistant prostate cancer (CRPC). AR has therefore become an even more attractive therapeutic target in aggressive and disseminated prostate cancer. To investigate mechanisms of AR and AR target gene activation in different subpopulations of prostate cancer cells, a toolkit of AR expressor and androgen response element (ARE) reporter vectors were developed. Three ARE reporter vectors were constructed with different ARE consensus sequences in promoters linked to either fluorescence or luciferase reporter genes in lentiviral vector backbones. Cell lines transduced with the different vectors expressed the reporters in an androgen-dependent way according to fluorescence microscopy, flow cytometry and multi-well fluorescent and luminescence assays. Interestingly, the background reporter activity in androgen-depleted medium was significantly higher in LNCaP cells compared to the prostate transit amplifying epithelial cell lines, EP156T-AR and 957E/hTERT-AR with exogenous AR. The androgen-induced signal to background was much higher in the latter benign prostate cells than in LNCaP cells. Androgen-independent nuclear localization of AR was seen in LNCaP cells and reduced ARE-signaling was seen following treatment with abiraterone, an androgen synthesis inhibitor. The ARE reporter activity was significantly stronger when stimulated by androgens than by β-estradiol, progesterone and dexamethasone in all tested cell types. Finally, no androgen-induced ARE reporter activity was observed in tumorigenic mesenchymal progeny cells of EP156T cells following epithelial to mesenchymal transition. This underscores the observation that expression of the classical luminal differentiation transcriptome is restricted in mesenchymal type cells with or without AR expression, and presence of androgen.

Gender Specificity of a Genetic Variant of Androgen Receptor and Risk of Coronary Artery Disease

BACKGROUND

Androgens are known to influence the risk of developing cardiovascular diseases. This study aims at investigating the possible association between G1733A polymorphism in the coding region of androgen receptor (AR) gene and premature coronary artery disease (CAD).

METHODS

A total of 460 Greek subjects were investigated for the G1733A polymorphism. The patient group consisted of 250 CAD individuals, aged less than 58 years, while 210 healthy individuals served as controls. Genotyping was performed using the PCR-RFLP method.

RESULTS

Significant differences in genotype distribution (P = 0.0067) and allele frequencies (P = 0.0060) have been observed between patients and controls in the women's subgroup. Conversely, the genotype/allele frequencies were similar between patients and controls in the subgroup of men.

CONCLUSION

We may conclude that the G1733A polymorphism of AR gene could be a useful genetic marker for the assessment of a woman's risk for CAD in our Caucasian Greek population.

Seasonal and sexual dimorphisms in expression of androgen receptor and its coactivators in brain and peripheral copulatory tissues of the green anole

Green anoles are seasonally breeding lizards, with an annual rise in testosterone (T) being the primary activator of male sexual behaviors. Responsiveness to T is decreased in the non-breeding season (NBS) compared to breeding season (BS) on a variety of levels, including displays of reproductive behavior and the morphology and biochemistry of associated tissues. To evaluate the possibility that seasonal changes in responsiveness to T are regulated by androgen receptors (AR) and/or two of its coactivators, CREB binding protein (CBP) and steroid receptor coactivator-1 (SRC-1), we tested whether they differ in expression across season in brains of both sexes and in peripheral copulatory tissues of males (hemipenis and retractor penis magnus muscle). AR mRNA was increased in the brains of males compared to females and in copulatory muscle in the BS compared to NBS. In the hemipenis, transcriptional activity appeared generally diminished in the NBS. T-treatment increased AR mRNA in the copulatory muscle and AR protein in the hemipenis, the latter to a greater extent in the BS than the NBS. T also decreased SRC-1 protein in hemipenis. Interpretations are complicated, in part because levels of mRNA and protein expression were not correlated and multiple sizes of the AR and CBP proteins were detected, with some tissue specificity. However, the results are consistent with the idea that differences in receptor and coactivator expression at central and peripheral levels may play roles in regulating sex and seasonal differences in the motivation or physical ability to engage in sexual behavior.

Numerical framework to model temporally resolved multi-stage dynamic systems

Numerical modeling of steroid hormone signaling presents an exciting challenge involving spatiotemporal coordination of multiple events. Ligand binding in cytoplasm triggers dissociation and/or association of coregulators which subsequently regulate DNA binding and transcriptional activity in nucleus. In order to develop a comprehensive multi-stage model, it is imperative to follow not only the transcriptional outcomes but also the intermediate protein complexes. Accordingly, we developed a software toolkit for simulating complex biochemical pathways as a set of non-linear differential equations in LabVIEW (Laboratory Virtual Instrumentation and Engineering Workbench, National Instruments, Austin, TX) environment. The toolkit is visual, highly modular, loosely coupled with the rest of LabVIEW, scalable and extensible. The toolkit can be used to develop and validate biochemical models and estimate model parameters from existing experimental data. We illustrate the application of the toolkit for simulation of steroid hormone response in cells, and demonstrate how the toolkit can be employed for other biological and chemical systems as well. The software module presented here can be used stand-alone as well as built into data collection and analysis applications.

GTG mutation in the start codon of the androgen receptor gene in a family of horses with 64,XY disorder of sex development

Genetic sex in mammals is determined by the sex chromosomal composition of the zygote. The X and Y chromosomes are responsible for numerous factors that must work in close concert for the proper development of a healthy sexual phenotype. The role of androgens in case of XY chromosomal constitution is crucial for normal male sex differentiation. The intracellular androgenic action is mediated by the androgen receptor (AR), and its impaired function leads to a myriad of syndromes with severe clinical consequences, most notably androgen insensitivity syndrome and prostate cancer. In this paper, we investigated the possibility that an alteration of the equine AR gene explains a recently described familial XY, SRY + disorder of sex development. We uncovered a transition in the first nucleotide of the AR start codon (c.1A>G). To our knowledge, this represents the first causative AR mutation described in domestic animals. It is also a rarely observed mutation in eukaryotes and is unique among the >750 entries of the human androgen receptor mutation database. In addition, we found another quiet missense mutation in exon 1 (c.322C>T). Transcription of AR was confirmed by RT-PCR amplification of several exons. Translation of the full-length AR protein from the initiating GTG start codon was confirmed by Western blot using N- and C-terminal-specific antibodies. Two smaller peptides (25 and 14 amino acids long) were identified from the middle of exon 1 and across exons 5 and 6 by mass spectrometry. Based upon our experimental data and the supporting literature, it appears that the AR is expressed as a full-length protein and in a functional form, and the observed phenotype is the result of reduced AR protein expression levels.

FUS/TLS is a co-activator of androgen receptor in prostate cancer cells

Androgen receptor (AR) is a member of the nuclear receptor family of transcription factors. Upon binding to androgens, AR becomes transcriptionally active to regulate the expression of target genes that harbor androgen response elements (AREs) in their promoters and/or enhancers. AR is essential for the growth and survival of prostate cancer cells and is therefore a target for current and next-generation therapeutic modalities against prostate cancer. Pathophysiologically relevant protein-protein interaction networks involving AR are, however, poorly understood. In this study, we identified the protein FUsed/Translocated in LipoSarcoma (FUS/TLS) as an AR-interacting protein by co-immunoprecipitation of endogenous proteins in LNCaP human prostate cancer cells. The hormonal response of FUS expression in LNCaP cells was shown to resemble that of other AR co-activators. FUS displayed a strong intrinsic transactivation capacity in prostate cancer cells when tethered to basal promoters using the GAL4 system. Chromatin immunoprecipitation experiments showed that FUS was recruited to ARE III of the enhancer region of the PSA gene. Data from ectopic overexpression and “knock-down” approaches demonstrated that AR transcriptional activity was enhanced by FUS. Depletion of FUS reduced androgen-dependent proliferation of LNCaP cells. Thus, FUS is a novel co-activator of AR in prostate cancer cells.

Dynamics of coregulator-induced conformational perturbations in androgen receptor ligand binding domain

Androgen receptor (AR) coregulators modulate ligand-induced gene expression in a tissue specific manner. The molecular events that follow coactivator binding to AR and the mechanisms that govern the sequence-specific effects of AR coregulators are poorly understood. Using consensus coactivator sequence D11-FxxLF and biophysical techniques, we show that coactivator association is followed by conformational rearrangement in AR ligand binding domain (AR-LBD) that is enthalpically and entropically favorable with activation energy of 29.8±4.2 kJ/mol. Further characterization of ARA70 and SRC3-1 based consensus sequences reveal that each coactivator induces a distinct conformational state in the dihydrotestosterone:AR-LBD:coactivator complex. Complementary computational modeling revealed that coactivator induced specific alterations in the backbone flexibility of AR-LBD distant from the site of coactivator binding and that the intramolecular rearrangements in AR-LBD backbone induced by the two coactivator peptides were different. These data suggest that coactivators may impart specificity in the transcriptional machinery by changing the steady-state conformation of AR-LBD. These data provide direct evidence that even in the presence of same ligand, AR-LBD can occupy distinct conformational states depending on its interactions with specific coactivators in the tissues. We posit that this coactivator-specific conformational gating may then dictate subsequent binding partners and interaction/affinity for the DNA-response elements.

Kinetic and thermodynamic characterization of dihydrotestosterone-induced conformational perturbations in androgen receptor ligand-binding domain

Ligand-induced conformational perturbations in androgen receptor (AR) are important in coactivator recruitment and transactivation. However, molecular rearrangements in AR ligand-binding domain (AR-LBD) associated with agonist binding and their kinetic and thermodynamic parameters are poorly understood. We used steady-state second-derivative absorption and emission spectroscopy, pressure and temperature perturbations, and 4,4'-bis-anilinonaphthalene 8-sulfonate (bis-ANS) partitioning to determine the kinetics and thermodynamics of the conformational changes in AR-LBD after dihydrotestosterone (DHT) binding. In presence of DHT, the second-derivative absorption spectrum showed a red shift and a change in peak-to-peak distance. Emission intensity increased upon DHT binding, and center of spectral mass was blue shifted, denoting conformational changes resulting in more hydrophobic environment for tyrosines and tryptophans within a more compact DHT-bound receptor. In pressure perturbation calorimetry, DHT-induced energetic stabilization increased the Gibbs free energy of unfolding to 8.4 +/- 1.3 kcal/mol from 3.5 +/- 1.6 kcal/mol. Bis-ANS partitioning studies revealed that upon DHT binding, AR-LBD underwent biphasic rearrangement with a high activation energy (13.4 kcal/mol). An initial, molten globule-like burst phase (k approximately 30 sec(-1)) with greater solvent accessibility was followed by rearrangement (k approximately 0.01 sec(-1)), leading to a more compact conformation than apo-AR-LBD. Molecular simulations demonstrated unique sensitivity of tyrosine and tryptophan residues during pressure unfolding with rearrangement of residues in the coactivator recruitment surfaces distant from the ligand-binding pocket. In conclusion, DHT binding leads to energetic stabilization of AR-LBD domain and substantial rearrangement of residues distant from the ligand-binding pocket. DHT binding to AR-LBD involves biphasic receptor rearrangement including population of a molten globule-like intermediate state.

Care of women with XY karyotype: a clinical practice guideline

OBJECTIVE

To provide an evidence-based guideline for professionals working with XY women.

DESIGN

Review including patient cases from a Danish fertility clinic.

SETTING

University-associated scientific unit and fertility clinic.

PATIENT(S)

Three selected cases.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Evaluation of etiology, diagnosis, treatment, and associated disorders in XY women.

RESULT(S)

Many gene mutations can cause abnormal fetal development leading to androgen insensitivity syndrome or gonadal dysgenesis disorders. Females with these disorders have an XY karyotype but look like girls. They are mostly diagnosed at puberty, and the condition will often lead to serious psychological problems. Increased risk of malignancies and problems with pregnancy and infertility are other aspects that should be considered. This guideline will aid doctors in caring for XY females.

CONCLUSION(S)

A precise diagnosis is important, because the treatment possibilities (e.g., use of allogenic oocytes) depend on the subgroup to which the XY female belongs.

Progesterone receptor requires a co-chaperone for signalling in uterine biology and implantation

Embryo implantation is absolutely dependent on the preparation of the uterus to the receptive stage and attainment by the blastocyst of implantation competency. Co-ordinated effects of progesterone and oestrogen are essential for these processes and determine the window of implantation. In rodents, a generalized stromal edema occurs before blastocyst attachment followed by uterine luminal closure. This leads to apposition of the blastocyst trophectoderm against the luminal epithelium and ultimately attachment. Progesterone is essential for luminal closure, which must occur for successful implantation. More importantly, progesterone is critical for almost every stage of pregnancy, including ovulation, fertilization, implantation, decidualization and pregnancy maintenance. Progesterone exerts its effects on target tissues primarily via nuclear progesterone receptor (PR) whose optimal activity is potentiated by an immunophilin co-chaperone, FK-506 binding protein 4 (FKBP52). While mice lacking PR are infertile due to complete failure of ovulation, fertilization, and implantation, female mice with targeted deletion of the Fkbp52 gene are infertile specifically because of implantation failure resulting from compromised uterine receptivity. This review highlights the evolution of knowledge about progesterone signalling during early pregnancy. Future studies are likely to provide a better understanding of FKBP52-PR signalling in promoting uterine receptivity for implantation and may reveal new targets for improving infertility.

Cloning and characterization of androgen receptor from bullfrog, Rana catesbeiana

We have cloned and characterized a full-length cDNA of androgen receptor (AR) from the testis of bullfrog, Rana catesbeiana. The cDNA contains an open reading frame of 2328 nucleotides encoding a protein of 776 amino acid residues. The bullfrog AR shows high homology with ARs from other species in its amino acid sequence. Its overall homology with those of African clawed frog, Japanese eel and human is 70, 53, and 63%, respectively. As expected, the N-terminal domain shows much less homology (30-59%) than both DNA-binding domain (85-92%) and ligand binding domain (80-89%). Northern blot analysis detected the bullfrog AR message as a single transcript of around 9 kb only in the testis. However, RT-PCR analysis revealed that AR mRNA is also expressed in other tissues although the levels are very low compared to that in the testis. Western blot analysis of whole tissue extracts showed the presence of AR protein in fore brain, heart, and testis. The AR gene is present as a single copy in bullfrog based on Southern blot analysis of genomic DNA. Altogether, the results suggest that the bullfrog AR is evolutionary conserved and may have functions similar to those shown in other species.

Cyclin D1: mechanism and consequence of androgen receptor co-repressor activity

Androgen receptor regulation is pivotal for prostate growth and development. Activation of the receptor is dictated by association with androgen (ligand) and through interaction with co-activators and co-repressors. We have shown previously that cyclin D1 functions as a co-repressor to inhibit ligand-dependent androgen receptor activation. We demonstrate that cyclin D1 directly binds the N terminus of the androgen receptor and that this interaction is independent of ligand. Furthermore, we show that the interaction occurs in the nucleus and does not require the LXXLL motif of cyclin D1. Although two distinct transactivation domains exist in the N terminus (AF-1 and AF-5), the data shown support the hypothesis that cyclin D1 targets the AF-1 transactivation function. The constitutively active AF-5 domain was refractory to cyclin D1 inhibition. By contrast, cyclin D1 completely abolished androgen receptor activity, even in the presence of potent androgen receptor co-activators. This action of cyclin D1 at least partially required de-acetylase activity. Finally, we show that transient, ectopic expression of cyclin D1 results in reduced cell cycle progression in androgen-dependent LNCaP cells independent of CDK4 association. Collectively, our data support a model wherein cyclin D1 has a mitogenic (CDK4-dependent) function and an anti-mitogenic function (dependent on regulation of the AF-1 domain) that can collectively control the rate of androgen-dependent cellular proliferation. These findings provide insight into the non-cell cycle functions of cyclin D1 and provide the impetus to study its pleiotropic effects in androgen-dependent cells, especially prostatic adenocarcinomas.

Androgen receptor in the harderian glands of the golden hamster: characterization and the effects of androgen deprivation, the pituitary, and gender

The harderian glands of the golden hamster were found, by a competitive binding assay using [3H]mibolerone as the ligand, to have a high affinity androgen receptor. In intact male hamsters, this receptor was present in both cytosolic and nuclear KCl-extractable fractions. Castration or hypophysectomy led to 3- to 5-fold increases in the concentrations of cytosolic receptor with decreased dissociation constants. Hypophysectomy with maintenance of prolactin levels (by removal of pituitaries and their implantation either in the sella turcica or under the kidney capsule) had no effect on androgen receptor binding, compared to hypophysectomy alone. Female hamsters had androgen receptor levels which were 2 to 4 times higher than those of intact males. Hypophysectomy led to elevated receptor binding in ovariectomized female hamsters and this rise was prevented by maintaining prolactin levels. Binding of [3H]mibolerone in male glands was effectively inhibited by 5 alpha-dihydrotestosterone, whereas the parent molecule, testosterone, required approximately a 10-fold greater molar excess to achieve the same amount of inhibition. Estradiol and progesterone were relatively poor inhibitors of the observed binding of [3H]mibolerone, while dexamethasone was ineffective. Sucrose gradient studies indicated that the harderian androgen receptor migrated to the 8S region, as expected for this receptor in molybdate-containing gradients. These results indicate that the androgen receptor in the hamster harderian gland is a 5 alpha-dihydrotestosterone receptor.

Molecular mechanisms of androgen action

Androgens directly regulate a vast number of physiological events. These direct androgen effects are mediated by a nuclear receptor that exhibits four major functions or activities: steroid binding, DNA binding, transactivation, and nuclear localization. The SBD consists of a hydrophobic pocket of amino acids that exhibits high-affinity, androgen-specific binding. Based on studies of mutant AR, it appears that a number of different amino acids contribute to the steroid binding characteristics of the AR. The DNA binding domain confers sequence-specific binding to structures called androgen-responsive elements. The specificity of steroid binding and DNA binding provides a crucial basis for androgen-specific regulation of target genes. The nuclear localization signal shares homology with known nuclear localization signals and, coupled with the presence of androgens, is responsible for localizing the AR to the nucleus. The transactivation functions reside mostly in the NH2 terminus but the responsible domains are as yet poorly defined. Though the different domains can act as independent moieties, one domain can clearly alter the behavior of another domain. For instance, the SBD appears to inhibit the transactivating functions until steroid is bound and the amino terminus prevents DNA binding activity until steroid is bound. The relative ease of introducing mutations with polymerase chain reaction technology will facilitate further delineation of critical amino acids and domains responsible for the various activities of the AR. The recent cloning and characterization of AR promoters revealed that the AR genes are driven by a TATA-less promoter characteristics of housekeeping genes. Analysis of transcription rates, mRNA levels, and protein levels indicates that androgens and pkA and pkC pathways modulate expression of AR mRNA and protein. This indicates that the same signal pathways that interact to regulate androgen target genes also regulate the levels of AR in the target tissues. Surprisingly few androgen-regulated genes have been well characterized for the mechanisms by which androgen regulates the gene. The C(3), Slp, probasin, PSA, and hKLK2 genes have provided examples where androgens regulate transcription. Posttranscriptional regulation by androgens has been demonstrated for the SVP1, 2, 3, and 4 and AR genes. The mechanisms underlying posttranscriptional regulation are poorly defined but substantial progress has been made in defining the critical elements that mediate transcriptional effects of androgens. Transcriptional effects are mediated through binding of androgen-AR complexes to specific DNA sequences called AREs. Simple AREs such as those found in C(3) and kallikrein genes tend to be permissive in that GR and PR can also act through the same element.(ABSTRACT TRUNCATED AT 400 WORDS)

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!

The prostate plasma membrane as an androgen receptor

The pivotal role of the cell nucleus in androgenic control of target organs, such as the prostate, has become increasingly suspect. Equally qualified receptor activities have been found in the cytosol, endoplasmic reticulum, and plasma membrane. It is presently difficult to explain how a sex steroid can manage proliferation, metabolism, biosynthesis and secretion, all through chromatin-directed signals. In my search for a more satisfactory mediator of androgen action, I discovered that the sodium-potassium-dependent ATPase of the prostate plasma membrane binds androgen, and is activated by the hormone's presence to serve as a metabolic pacemaker. This paper is my terminal status report on one aspect of this hypothesis; namely, the nature and site of androgen binding, with clues as to the mode of action. SDS-PAGE indicates that androgen can be bound to the beta-subunit of prostatic Na,K-ATPase. Selective enrichment of the enzyme by reversible coupling to either concanavalin A or a DHT-affinity column support this conclusion. Several studies show the dynamic effect of androgen binding: increased ouabain binding; enhancement of this binding by facilitated phosphorylation; spectroscopic evidence of conformational shifts, possibly consequences of these suggested activities for regulation, especially of metabolism, are examined.