Androgen receptors: structures, mutations, antibodies and cellular dynamics

Crosstalk between the Androgen Receptor and PPAR Gamma Signaling Pathways in the Prostate

Nuclear receptors are a superfamily of ligand-activated transcription factors that play critical roles in the regulation of normal biological processes and several disease states. Of the nuclear receptors expressed within the prostate, the androgen receptor (AR) promotes the differentiation of prostatic epithelial cells and stimulates production of enzymes needed for liquefaction of semen. Multiple forms of AR also promote the growth of both early and late stage prostate cancers. As a result, drugs that target the AR signaling pathway are routinely used to treat patients with advanced forms of prostate cancer. Data also suggest that a second member of the nuclear receptor superfamily, the peroxisome proliferator activated receptor gamma (PPARγ), is a tumor suppressor that regulates growth of normal prostate and prostate cancers. Recent studies indicate there is a bidirectional interaction between AR and PPARγ, with each receptor influencing the expression and/or activity of the other within prostatic tissues. In this review, we examine how AR and PPARγ each regulate the growth and development of normal prostatic epithelial cells and prostate cancers. We also discuss interactions between the AR and PPARγ signaling pathways and how those interactions may influence prostate biology.

Proteasomal degradation unleashes the pro-death activity of androgen receptor

Androgen receptor (AR) is able to promote stress-induced cell death independently of its transcription activity in androgen-independent prostate cancer cells. Yet, the underlying mechanism is incompletely understood. Here, we report that stress-induced proteasomal degradation of AR contributes to its pro-death activity. Upon exposure to ultraviolet light and staurosporine, AR underwent proteasomal degradation. Blockade of AR degradation significantly suppressed stress-induced apoptosis in androgen-independent prostate cancer cells. Ectopic expression of the AR N-terminal (AR-N) domain, which lacks DNA- and ligand-binding abilities, led to cell death without any additional death stimuli. Truncation analysis revealed that AR-N domain contains several sub-domains that regulate the pro-death activity of AR, specifically the first 105 amino acids, which function as a minimal pro-death domain acting upstream of caspases. The pro-apoptotic activity of AR N-terminal fragments was suppressed by ectopic expression of Bcl-2 or selected caspase inhibitors. Thus, our results reveal a novel mechanism by which AR promotes stress-induced cell death in androgen-independent prostate cancer cells.

Non-genomic mechanisms of action of steroid hormones

Sex steroid hormones are known to act through intracellular receptors and their cognate hormone response elements, located in the promoters of hormone-regulated genes. However, this classical mechanism of action cannot account for a variety of rapid effects of steroids (within seconds or minutes). In this review, non-genomic modes of target cell responses to sex steroids are described. The prototypical example is the resumption of meiosis in amphibian oocytes, triggered by progesterone at the plasma membrane level. Membrane effects of progesterone may also account for sperm maturation. Other membrane-mediated effects of steroids are reviewed. Whether a steroid hormone might elicit responses from a single cell through both genomic and membrane mechanisms remains an open question.

Androgen and its receptor promote Bax-mediated apoptosis

Androgen and its receptor (AR) have been reported to have pro- or antiapoptotic functions. However, the underlying molecular mechanism is incompletely understood. We report here that androgen and AR promote Bax-mediated apoptosis in prostate cancer cells. UV irradiation and ectopic expression of Bax induce apoptosis in AR-positive, but not AR-negative prostate cancer cells. UV- and Bax-induced apoptosis is abrogated in AR-positive cells that express small interference RNA (siRNA) of AR and is sensitized by reintroduction of AR into AR-negative cells. Although AR is able to promote Bax-mediated apoptosis independently of androgen, the promotion by AR can be further potentiated by androgen via AR-dependent transcription activation. AR is essential for the translocation of Bax to mitochondria in UV- or Bax-induced apoptosis. Inhibition of Bax expression by Bax siRNA suppresses UV-induced apoptosis in AR-positive cells. In addition, introduction of AR into AR-negative prostate cancer cells upregulates expression levels of the BH3-only protein Noxa, whereas inhibition of Noxa expression reduces the promotion by AR on UV-induced apoptosis. Thus, our results reveal a novel cross talk between the androgen/AR hormonal signaling pathway and the intrinsic apoptotic death pathway that determines the sensitivity of stress-induced apoptosis in prostate cancer cells.

Androgen receptor mRNA is inversely regulated by testosterone and estradiol in adult mouse brain

Androgen receptor (AR) is expressed in different tissues including the brain and is under regulation by sex steroid hormones. It mediates the action of androgen which plays a key role in learning, memory, and other brain functions that deteriorate with increasing age. We have correlated the expression of AR mRNA with its promoter methylation and their regulation by testosterone and estradiol in the brain cortex of adult and old male and female mice. Results revealed that (i) AR mRNA expression was significantly higher in male than in female mice. (ii) In both sexes, AR mRNA level was down-regulated by testosterone in adult and old, but up-regulated by estradiol only in adult mice. (iii) Methylation of AR core promoter was increased by testosterone, but decreased by estradiol. These findings show that AR mRNA expression and its core promoter methylation are inversely regulated by testosterone and estradiol in the adult mice brain cortex. Such regulation of AR expression might influence androgen action during aging of the mice brain.

The extract of Thujae occidentalis semen inhibited 5alpha-reductase and androchronogenetic alopecia of B6CBAF1/j hybrid mouse

BACKGROUND

The conversion of testosterone to dihydrotestosterone; 5alpha-androstan-17beta-ol-3-one by 5alpha-reductase plays a crucial role in hair baldness and prostatomegaly. Recent approach showed specific inhibitors for 5alpha-reductase type 2 such as finasteride promoted hair growth in male pattern alopecia.

OBJECTIVE

In order to search for effective medicinal plant extracts applied topically for androgenetic alopecia, we screened natural plant extracts having inhibitory activities of 5alpha-reductase type 2 and demonstrated its biological function in androgen-related animal models.

METHODS

We evaluated the inhibition activities of numerous plant extracts by contact cell based metabolic method using a stable HEK 293 cell line expressing human 5alpha-reductase (type 2). To elucidate the biological activity in vivo, the Thujae occidentalis semen (TOS) extract was topically applied to fuzzy rat and androchronogenetic alopecia (AGA) mouse, respectively. The secreted sebum and the size of sebaceous glands of fuzzy rat were measured after 6 weeks. Also, after the topical treatment with TOS extract and androgen receptor antagonist (cyproterone acetate) simultaneously with subcutaneous injection of testosterone (1 mg/mice/day), hair loss patterns of female B6CBAF1/j hybrid mouse were observed.

RESULTS

TOS extract showed higher inhibition activity of 5alpha-reductase type 2(IC(50) value=2.6 microg/ml) than that of gamma-linolenic acid, but lower than that of finasteride. When applied to fuzzy rat, the amount of sebum and sebaceous gland size decreased remarkably. In AGA model, alopecia degrees of two groups, treated with TOS extract (P<0.015) or cyproterone acetate (P<0.01), were lower than that of vehicle (propylene glycol:ethanol=7:3) and there was no difference between above two groups.

CONCLUSION

We have demonstrated the inhibitory activity of TOS extract for 5alpha-reductase type 2 and its biological action in two animal models, suggesting that TOS extract would be used as an effective agent for male pattern baldness by modifying androgen conversion.

Selective intranuclear redistribution of PPAR isoforms by RXR alpha

The intracellular localization of transcriptionally active green fluorescent protein (GFP) chimeras linked to PPARs for human PPAR alpha (GFP-PPARh alpha) and mouse PPAR alpha, beta, and gamma 1 (GFP-PPARm alpha, GFP-PPARm beta, and GFP-PPARm gamma, respectively) was examined in the mouse hepatoma cell line, Hepa-1, using fluorescence microscopy. A predominantly nuclear and diffuse distribution of each isoform was found in both the presence and absence of specific ligands for each receptor. GFP-PPARm alpha-G (containing a Glu282Gly substitution of PPARm alpha) and a phosphorylation mutant, GFP-PPARm gamma-A (containing a Ser82Ala substitution of PPARm gamma), exhibited altered transcriptional activities, but displayed similar intracellular localization patterns compared with their respective wild-type receptors. Coexpression of nuclear receptor corepressor suppressed, whereas steroid receptor coactivator-1 enhanced the transcriptional activity of each of the GFP-PPAR isoforms, but did not discernibly alter their intracellular distributions, both in the presence and absence of PPAR ligands. Interestingly, coexpression of the obligate heterodimeric partner of PPARs, RXR alpha, resulted in an intranuclear redistribution of the GFP-PPARm gamma isoform characterized by a reticulated pattern of the green fluorescent label for PPAR gamma within the nucleus, but not in nucleoli, and a heightened concentration of the fluorescent label surrounding nucleolar structures and at the nuclear membrane. Conversely, coexpression of yellow fluorescent protein-RXR alpha and native PPARm gamma resulted in a similar distribution of the yellow fluorescent tag. This localization pattern was not discernibly altered by PPAR gamma or RXR alpha-specific ligands. These results implicate RXR alpha in the nuclear reorganization of PPAR gamma and suggest that PPAR gamma colocalizes with RXR alpha at specific locations within the nucleus independent of added ligand.

Androgen receptor: structural domains and functional dynamics after ligand-receptor interaction

Androgens are C-19 steroids secreted primarily from the testes and adrenals that play a critical role in reproduction. Reproductive functions of androgens are mediated through coordination of diverse physiological processes ranging from brain functions to specific cell proliferation and apoptosis. At the molecular level, most of these regulatory influences are exerted by altered expression of appropriate genes by the androgen receptor (AR), a member of the nuclear receptor (NR) superfamily. The unliganded AR is a cytoplasmic protein and, upon ligand binding, it translocates into the nucleus. Thereafter, in conjunction with other transcription factors and coactivators, the AR influences transcription of target genes through a multistep process that includes its clustering in a subnuclear compartment. Here, we describe the genomic organization of the AR, the role of individual structural domains in specific AR function, and the influence of agonistic/antagonistic ligands in the intracellular movement of the receptor. We also show that the AR is capable of undergoing multiple rounds of nucleocytoplasmic recycling after ligand binding and dissociation. Xenobiotic ligands, considered as selective androgen receptor modulators (SARMs), can modulate AR activity by inhibiting either its nuclear translocation or its subnuclear clustering and subsequent transactivation function.

Sebocytes are the Key Regulators of Androgen Homeostasis in Human Skin

The mRNA expression patterns of the androgen receptor and the androgen metabolizing enzymes 3beta-hydroxysteroid dehydrogenase/Delta(5-4)-isomerase, 17beta-hydroxysteroid dehydrogenase, 5alpha-reductase, and 3alpha-hydroxysteroid dehydrogenase were investigated in three different cell populations originating from human skin, SZ95 sebocytes, HaCaT keratinocytes, and MeWo melanoma cells, by means of reverse transcription polymerase chain reaction. Restriction analysis of cDNA fragments was performed to identify isozymes of 3beta-hydroxysteroid dehydrogenase/Delta(5-4)-isomerase and 3alpha-hydroxysteroid dehydrogenase. In addition, 3H-dihydroepiandrosterone and 3H-testosterone were used as substrates to determine the metabolic activity of these enzymes in SZ95 sebocytes, primary sebocyte cultures, and HaCaT keratinocytes. Furthermore, the effects of the selective 5alpha-reductase type 1 and 2 inhibitors, 4,7beta-dimethyl-4-aza-5alpha-cholestan-3-one and dihydrofinasteride, respectively, and of the 3beta-hydroxysteroid dehydrogenase/Delta(5-4)-isomerase inhibitor cyproterone acetate on androgen metabolism were investigated. Androgen receptor mRNA was detected in SZ95 sebocytes and HaCaT keratinocytes but not in MeWo melanoma cells, whereas 3beta-hydroxysteroid dehydrogenase/Delta(5-4)-isomerase isotype 1 mRNA and metabolic activity were only found in SZ95 sebocytes. The enzyme activity could be inhibited by cyproterone acetate. Type 2 17beta-hydroxysteroid dehydrogenase, type 1 5alpha-reductase, and 3alpha-hydroxysteroid dehydrogenase mRNA were expressed in all three cell populations tested, whereas type 3 17beta-hydroxysteroid dehydrogenase mRNA could only be detected in SZ95 sebocytes. The major metabolic steps of testosterone in SZ95 sebocytes, primary sebocyte cultures, and HaCaT keratinocytes were its conversion to androstenedione by 17beta-hydroxysteroid dehydrogenase and further to 5alpha-androstanedione by 5alpha-reductase. The type 1 5alpha-reductase selective inhibitor 4,7beta-dimethyl-4-aza-5alpha-cholestan-3-one, but not the type 2 selective inhibitor dihydrofinasteride, inhibited 5alpha-reductase at low concentrations in SZ95 sebocytes and HaCaT keratinocytes. 5alpha-androstanedione was degraded to androsterone by 3alpha-hydroxysteroid dehydrogenase, which exhibited a stronger activity in HaCaT keratinocytes than in SZ95 sebocytes and in primary sebocyte cultures. Lower levels of 5alpha-dihydrotestosterone and 5alpha-androstanediol were also detected in all cells tested. Our investigations show that specific enzyme expression and activity in cultured sebocytes and keratinocytes seem to allocate different duties to these cells in vitro. Sebocytes are able to synthesize testosterone from adrenal precursors and to inactivate it in order to maintain androgen homeostasis, whereas keratinocytes are responsible for androgen degradation.

Influence of anti-androgens on the anterior horn cells of rat spinal cord: morphometric and in-situ hybridization studies

To examine the roles of the androgens for growth and maintenance of anterior horn cells (AHCs) of the spinal cord, one of the two anti-androgen agents, flutamide or cyproterone, was injected into young rats. Morphometric analysis of the spinal cords after the injections showed that the average area occupied by an AHC was significantly smaller in the rats treated with the anti-androgens than in the controls. By contrast, neurons in the posterior horns did not show significant difference in their size. Moreover, an in-situ hybridization of choline acetyltransferase (CAT) messenger RNA revealed a significant reduction in the signal density in AHCs in the treated rats. These results show that androgens play an important role in the growth and maintenance of AHCs, and influence a wide range of protein synthesis, including that of CAT.

Dynamics of protein kinase CK2 association with nucleosomes in relation to transcriptional activity

Protein kinase CK2 has been implicated in control of cell growth and proliferation. Since growth stimuli evoke its preferential association with chromatin and nuclear matrix, we examined the dynamics of CK2 in nucleosomes fractionated on the basis of their transcriptional activity in the rat prostate. In this model, androgens induce expression of androgen-dependent genes but inhibit the androgen-repressed genes, whereas absence of androgens has the reverse effect. The level of CK2 was higher in the active than in inactive nucleosomes from normal prostate. Differential alterations in the levels of CK2 activity in the transcriptionally active versus inactive nucleosomes were evoked by androgen deprivation or administration. Comparison of the distribution of CK2 in active and inactive nucleosomes under varying androgenic conditions showed that the relative CK2 activity intrinsic to the transcriptionally active nucleosomes remained fairly stable, concordant with gene activity specific to the androgenic status. However, CK2 associated with inactive nucleosomes declined to a minimal level on androgen deprivation but increased rapidly on androgen administration (reflecting expression of multiple androgen-dependent genes). We suggest a role for CK2 in promoting the conformational transition of inactive nucleosomes to the active form and in the function of transcriptionally active nucleosomes.

One additional mutation at exon A amplifies thermolability of androgen receptor in a case with complete androgen insensitivity syndrome

We have previously demonstrated a substitutional mutation (glycine to alanine at position 820) of the androgen receptor (AR) gene in a patient with complete androgen insensitivity syndrome (CAIS). We first examined whether the mutation could lead to a disorder in AR binding activity in in vitro expression experiments. In a luciferase assay, the effect of the mutant AR on a target's gene was definitely impaired. However, the mutant AR had less thermal instability compared to that of the patient's fibroblast cell lines established in a whole-cell binding assay. In order to analyze the cause of the thermal instability, a further analysis of exon A in the AR gene was performed because the previous study had been performed only between exon B and H encoding the DNA-binding domain and the hormone-binding domain. The second mutation (leucine to proline at position 257) was newly identified. In in vitro expression experiments, the AR with both mutations showed marked thermal instability, whereas the AR with a mutation in exon A had no effect on thermal stability. The results show that the N-terminal domain might also play an important role in amplifying or modifying the AR binding activity.

Physiology and pathophysiology of androgen action

Knowledge of the physiology of male sexual differentiation and the clinical presentation of androgen insensitivity syndromes (AIS) has led to an increasing understanding of the mechanisms of androgen action. Androgens induce their specific response via the androgen receptor (AR), which in turn regulates the transcription of androgen-responsive target genes. The androgen-dependent development of male genital structures and the induction of the normal male phenotype depends on the presence of an intact AR. Structural alterations leading to malfunction of the AR are associated with variable inhibition of virilization despite normal or even supranormal serum levels of androgens. The mapping, cloning and sequencing of the AR gene have facilitated new insights into the study of androgen action. Functional investigation of the normal and the mutant AR in vivo as well as in vitro has led to the characterization of the distinct molecular steps involved in the normal androgen action pathways that are inhibited in the androgen insensitivity syndrome.

Shortage of glutamine (CAG) homopolymeric repeats suppresses the expression of the androgen receptor in familial cases with complete androgen insensitivity syndrome

The androgen receptor gene of two familial cases with complete androgen insensitivity syndrome was analyzed. The shortage of glutamine homopolymeric repeats (13 repeats) in the N-terminal domain of the androgen receptor of the patients was identified by DNA sequence analysis. In vitro transfection experiments with the patients' androgen receptor gene indicated that the expression of the androgen receptor in transfected COS-7 cells was decreased by 10% as compared to that of the wild type androgen receptor gene. The thermal stability of the 5 alpha-dihydrotestosterone-androgen receptor complex was also partially impaired. The capacity of the androgen receptor to activate target gene transcription was partially disturbed in a luciferase assay. The shortened glutamine homopolymeric repeats might therefore be related to the pathogenesis of complete androgen insensitivity syndrome.

Effect of turosteride, a 5 alpha-reductase inhibitor, on the Dunning R3327 rat prostatic carcinoma

BACKGROUND

Turosteride (FCE 26073) is a new, potent, and selective 5 alpha-reductase inhibitor. We have investigated its effect on tumor growth, organ weight, and serum hormone levels in rats bearing the androgen sensitive Dunning R3327 prostatic carcinoma.

METHODS

Animals with tumor diameters of 0.5-1.5 cm were treated for 9 weeks with turosteride (50 and 200 mg/kg/day, 6 days a week, orally), flutamide (25 mg/kg/day, 6 days a week, orally), and leuprolide (300 micrograms/rat, every 3 weeks, subcutaneously) or they were castrated.

RESULTS

Turosteride was ineffective at the dose of 50 mg/kg/day, whereas at 200 mg/kg/ day it significantly decreased tumor growth by 45%. Flutamide and leuprolide were highly effective in reducing tumor growth (70 and 77%), although their effect was slightly lower than that of castration (85%). A significant reduction of ventral prostate weight occurred in rats treated with turosteride at 50 and 200 mg/kg/day (53% and 60%). In contrast to leuprolide and castration, the inhibitory effect of turosteride on tumor growth and prostate weight was not associated to any decrease in serum testosterone.

CONCLUSIONS

Turosteride has antitumor activity on Dunning prostatic tumor growth and its role in prostatic cancer treatment is worthy of further investigation.

Nuclear matrix as an anchor for protein kinase CK2 nuclear signalling

Nuclear matrix (NM) is not only the structural basis for nuclear shape but also is intimately involved in nuclear functional activities. Among the modulatory factors that may affect these diverse activities are the signals that may influence the state or composition of the NM proteins. One such mechanism for altering the functional activity of at least some NM proteins may be the extent of their phosphorylation. Protein kinase CK2 appears to associate with NM and to phosphorylate a number of NM-associated proteins. Chromatin- and NM-associated CK2 is rapidly modulated by mitogenic signals. We propose that NM serves as a physiological anchor for nuclear signalling of protein kinase CK2 which may influence functions of NM such as transcription of active genes and growth.

Differential display RT PCR of total RNA from human foreskin fibroblasts for investigation of androgen-dependent gene expression

Male sexual differentiation is a process that involves androgen action via the androgen receptor. Defects in the androgen receptor, many resulting from point mutations in the androgen receptor gene, lead to varying degrees of impaired masculinization in chromosomally male individuals. To date no specific androgen regulated morphogens involved in this process have been identified and no marker genes are known that would help to predict further virilization in infants with partial androgen insensitivity. In the present study we first show data on androgen regulated gene expression investigated by differential display reverse transcription PCR (dd RT PCR) on total RNA from human neonatal genital skin fibroblasts cultured in the presence or absence of 100 nM testosterone. Using three different primer combinations, 54 cDNAs appeared to be regulated by androgens. Most of these sequences show the characteristics of expressed mRNAs but showed no homology to sequences in the database. However 15 clones with significant homology to previously cloned sequences were identified. Seven cDNAs appear to be induced by androgen withdrawal. Of these, five are similar to ETS (expression tagged sequences) from unknown genes; the other two show significant homology to the cDNAs of ubiquitin and human guanylate binding protein 2 (GBP-2). In addition, we have identified 8 cDNA clones which show homologies to other sequences in the database and appear to be upregulated in the presence of testosterone. Four of these clones again are similar to ETS from unknown genes. Three differential expressed sequences that appear to be upregulated in the presence of testosterone show significant homology to the cDNAs of L-plastin and one to the cDNA of testican. This latter gene codes for a proteoglycan involved in cell social behavior and therefore of special interest in this context. The results of this study are of interest in further investigation of normal and disturbed androgen-dependent gene expression.

Characterization of rat 5alpha-reductases type 1 and type 2 expressed in Saccharomyces cerevisiae

Two isoforms of the rat 5alpha-reductase (5alpha-R), the enzyme that converts testosterone into dihydrotestosterone (DHT), and other delta4-3-keto steroids (e.g. progesterone and corticoids) into their 5alpha-reduced metabolites, have been cloned. In this study, a convenient and efficient system was developed to overexpress the two isoenzymes in Saccharomyces cerevisiae by using the ubiquitin-fusion expression system. Two yeast expression vectors have been prepared, YEpR1 and YEpR2, which code for 5alpha-R type 1 and 5alpha-R type 2 respectively; they contain the copper-responsive yeast metallothionein promoter (CUP1) upstream of the ubiquitin coding sequence, and the full-length rat 5alpha-R type 1 or 5alpha-R type 2 cDNAs in frame to the 3' end of the ubiquitin cDNA. The activity of the two isoenzymes produced in yeast was determined in cell lysates at the enzyme pH optima (type 1, pH 7.5; type 2, pH 5.5) and a possible differential intracellular distribution was also evaluated. The kinetic parameters were: type 1, Km 4.6 microM, Vmax.100.6 micrograms/h per mg of protein; type 2, Km 68.6 nM, Vmax. 0.84 micrograms/h per mg of protein. Yeast cell lysates were fractionated by differential centrifugation and the 5alpha-R type 1 activity was maximal in fractions containing nuclei (1000 g and 2500 g), whereas the maximal activity of 5alpha-R type 2 was present in subcellular fractions sedimenting at higher speeds (20000g). The data indicate that yeasts overexpress the two 5alpha-R isoenzymes, maintaining their native biochemical properties, and that the two isoforms are probably differentially localized within the yeast cell.

Roles of estrogen and SHBG in prostate physiology

Heretofore, the function of estrogen in the prostate, other than as an antiandrogen, has been unclear. In this review of a growing fund of knowledge about both estrogen and the plasma protein, sex hormone-binding globulin (SHBG), or testosterone-estradiol binding globulin (TeBG), the hypothesis is proposed that estrogen, mediated by SHBG, participates with androgen in setting the pace of prostatic growth and function. It is suggested that the estrogen not only directs stromal proliferation and secretion, but also, through IGF-I, conditions the response of the epithelium to androgen.

Androgen and glucocorticoid regulation of androgen receptor cDNA expression

Androgen receptor (AR) levels are regulated by androgens, other steroids and non-steroidal hormones via complex, tissue-specific processes. Since alterations in receptor levels may influence cellular sensitivity to androgens, understanding AR regulation is of fundamental and potentially therapeutic significance. In most target tissues and AR-containing cell lines, AR mRNA is down-regulated in response to androgens. We have reconstituted this androgen-mediated down-regulation of AR mRNA in COS 1 cells transfected with a human AR cDNA under the control of the cytomegalovirus (CMV) promoter. The sequences mediating receptor mRNA down-regulation are represented within the AR cDNA and not within the CMV promoter. Androgenic down-regulation of AR cDNA expression was time- and dose-dependent, resembling native AR mRNA down-regulation. In addition, androgenic regulation of the receptor cDNA was not dependent on protein synthesis suggesting that AR and/or another pre-existing protein(s) is involved in this process. In COS 1 cells co-transfected with androgen and glucocorticoid receptor cDNAs, dexamethasone mimicked the action of androgen in down-regulating AR mRNA. This response depended on glucocorticoid receptors. Androgen had little effect on steady-state levels of AR protein consistent with reports that androgen down-regulates AR mRNA but increases AR protein half-life (Kemppainen et al. (1992) J. Biol. Chem. 267, 968-974; Zhou et al. (1995) Mol. Endocrinol. 9, 208-218). However, glucocorticoids decreased AR protein levels in cells that co-expressed androgen and glucocorticoid receptors. These results indicate that sequences represented in the AR cDNA mediate AR mRNA down-regulation by both androgens and glucocorticoids. Inhibition of AR mRNA and protein by glucocorticoids suggests that these steroids may modulate androgen action in tissues, such as mammary gland and prostate, which express both androgen and glucocorticoid receptors.

In vitro labeling of gonadal steroid hormone receptors in brain tissue sections

Autoradiographic methods have been developed for measurement of gonadal steroid receptors in situ in brain tissue sections. Based on principles established previously for estrogen receptors in the rat brain using a 125I-labeled ligand, procedures have been developed for in vitro labeling of estrogen, androgen, and progestin receptors with commercially available tritiated ligands. Addition of protamine sulfate to the incubation buffer precipitates the receptors in situ in the tissue sections, allowing them to be detected autoradiographically after incubation with labeled steroid and subsequent washing to remove unbound and nonspecifically bound ligand. Occupied and unoccupied estrogen receptors can be measured selectively using appropriately modified incubation conditions. In the case of androgen and progestin receptors, unoccupied receptors are readily detected by in vitro labeling of tissue sections, but occupied receptors do not appear to label efficiently. Preliminary data suggest that these methods should be equally applicable to a variety of laboratory animals, including the rat, mouse, guinea pig, and monkey.

Novel expression of luteinizing hormone/chorionic gonadotropin receptor gene in rat prostates

The reverse transcription-polymerase chain reaction (RT-PCR) amplified an expected 255 bp luteinizing hormone/chorionic gonadotropin (LH/CG) receptor sequence from rat prostates. Northern blotting demonstrated that prostates contain 4.3, 3.3, 2.6, 1.8, 0.8 and 0.2 kb LH/CG receptor transcripts. Western immunoblotting and ligand blotting demonstrated that prostates also contain an 80 kDa receptor protein which can bind 125I-labeled hCG and this binding was inhibited by excess unlabeled hCG. In situ hybridization and immunocytochemistry revealed that while the receptors are most abundant in epithelial cells, they are scarcely found in the stroma. The ventral lobe contained more receptors than the lateral lobe and the receptors in peripheral acini of the ventral lobe are higher which progressively decreased towards central acini. In summary, prostate glands express LH/CG receptor gene. The cellular, topographical and lobular distribution of receptors suggest that LH may directly regulate prostate functions.

Cell type specific expression of steroid 5 alpha-reductase 2

Isozymes of steroid 5 alpha-reductase (5 alpha-reductase) have crucial roles in androgen physiology by synthesizing the potent hormone dihydrotestosterone. The expression pattern of the 5 alpha-reductase type 2 isozyme was determined in genital and extragenital tissues by developing an immunohistochemical assay using formalin-fixed tissue and affinity purified polyclonal antibodies that specifically recognize this isozyme. Expression was detected in basal epithelial and stromal cells of the normal prostate but not in luminal epithelial cells. Stromal cells of the seminal vesicle also expressed the type 2 isozyme. In contrast, staining was detected in epithelial cells of the epididymis but not in the surrounding stroma. Myofibroblasts in foreskin samples of normal and hypospadiac individuals expressed antigen and were distributed in bands throughout the prepuce, suggesting a clonal origin. In most cells the type 2 isozyme exhibited a perinuclear subcellular distribution. However, in liver hepatocytes the protein was distributed throughout the intracellular membrane compartment.

Molecular prenatal diagnosis of partial androgen insensitivity syndrome based on the Hind III polymorphism of the androgen receptor gene

OBJECTIVE

Partial androgen insensitivity syndromes are the cause of genital ambiguity that is at times quite severe; there is, therefore, a high demand for prenatal diagnosis in families already afflicted with this syndrome. When the mutation has not been identified, the diagnosis can be made by the study of the polymorphisms of the androgen receptor gene. To perform molecular prenatal diagnosis in a family with partial androgen insensitivity syndrome, we studied the Hind III polymorphism of the androgen receptor gene on the trophoblastic DNA. The use of this restriction fragment length polymorphism tracked maternal X chromosome segregation and established prenatal diagnosis although the mutation had not yet been identified in this family. FAMILY: The mother had been previously described as heterozygous for the Hind III polymorphism and chromosomal segregation analysis showed that the affected allele was associated with the 6.7-kb Hind III fragment.

MEASUREMENTS

Hind III RFLP with an androgen receptor gene cDNA probe was realized on the trophoblastic DNA, along with measurement of androgen binding activity on the trophoblastic cells.

RESULTS

We detected the presence of the 6.7-kb fragment in the DNA of the trophoblastic cells suggesting the fetus was affected. Partial androgen insensitivity syndrome was confirmed by a considerable decrease in androgen binding activity on the trophoblastic cells and by sonography of the fetus. After a therapeutic abortion requested by the parents, the diagnosis was confirmed by clinical examination of the fetus, biochemical analyses of the fetal androgen receptor, and molecular studies of the fetal DNA.

CONCLUSIONS

When the mutation of the androgen receptor gene has not been identified, Hind III polymorphism of the trophoblastic DNA is useful in the prenatal diagnosis of androgen insensitivity syndrome in high-risk families.

Expression of 5 alpha-reductase in bacteria as a trp E fusion protein and its use in the production of antibodies for immunocytochemical localization of 5 alpha-reductase

A cDNA encoding a full-length rat 5 alpha-reductase was isolated using female rat liver mRNA and the polymerase chain reaction, and fused to the Escherichia coli trp E gene in a pATH expression vector. The trp E-5 alpha-reductase fusion protein expressed in bacteria and a synthetic oligopeptide corresponding to the C-terminus of rat 5 alpha-reductase were used as antigens to produce rabbit polyclonal antibodies to 5 alpha-reductase. Antibodies to the 5 alpha-reductase portion of the fusion protein and to the peptide were purified by affinity chromatography. Antibodies against the 5 alpha-reductase fusion protein reacted with a single component of rat liver microsomes with M(r) 26,000 on Western blots, consistent with the size of 5 alpha-reductase predicted from its cDNA, and with a M(r) 23,000 component on Western blots of detergent extracts of rat ventral prostate nuclei; other rat ventral prostate cellular fractions (mitochondrial, microsomal, cytosol) bound little or no antibody. Antibody against the synthetic peptide reacted with a M(r) 26,000 component of rat liver microsomes as well as with several components in various cellular fractions of rat ventral prostate. With anti-5 alpha-reductase fusion protein antibodies, specific immunocytochemical staining was observed in the epithelial cell nuclei of the rat ventral prostate, seminal vesicle, epididymis and other accessory sex glands. This nuclear staining was specific, since antibodies from non-immunized rabbits did not give nuclear staining and preincubation of the anti-5 alpha-reductase fusion protein antibodies with the trp E-5 alpha-reductase fusion protein eliminated nuclear staining. Incubation of antibodies with trp E (without the 5 alpha-reductase fusion) had no effect on nuclear staining. Specific staining was not detected in the cytoplasm of these epithelial cells. Little or no specific staining was observed in stromal cells in these rat tissues. Human prostate was also immunocytochemically stained with this antibody. Specific staining was found in both epithelial and stromal cell nuclei.

Immunocytochemical localization of androgen receptors in human skin using monoclonal antibodies against the androgen receptor

Androgen receptors were localized in cryostat sections of human skin using monoclonal antibodies to the human androgen receptor. Bound antibodies were detected using biotinylated rabbit anti-rat IgG, peroxidase-conjugated streptavidin, and diaminobenzidine as chromogen. In the neonatal foreskin, antibody to androgen receptor bound to keratinocytes in the epidermis and to fibroblasts and vascular endothelial cells in the dermis. Immunohistochemical staining was stronger in nuclei than in cytoplasm. This staining was specific, because there was no significant staining when antibody to the androgen receptor was replaced with IgG from nonimmunized rats or with buffer, or when antibody to androgen receptor was incubated, prior to immunostaining, with a trp E-human androgen-receptor fusion protein used as immunogen. Incubation of androgen receptor antibody with trp E alone did not affect staining. Androgen-receptor antibody also bound to keratinocytes, fibroblasts, and endothelial cells in skin from adult men and women. Skin from the scalp, nose, lip, back, and chest gave positive staining for androgen receptor. Antibody to androgen receptor also bound to the coil and ductal cells of eccrine glands, external root sheath of hair follicles, epithelium in the hair bulb, dermal papilla cells, and sebocytes. There was no significant binding to adipocytes, collagen, or stratum corneum. These results show that androgen receptor is present in cells that are known to be targets for androgens and also in cells in which the biologic effects of androgens are yet to be characterized.

Complete androgen insensitivity syndrome associated with a de novo mutation of the androgen receptor gene detected by single strand conformation polymorphism

In a French child with complete androgen insensitivity syndrome and negative receptor-binding, no gross deletion has been found. Using single-strand conformation polymorphism assay, a useful screening method for rapid detection of DNA sequence alterations, and direct DNA sequencing, a G-T nucleotide substitution in exon 5 of the androgen receptor gene at nucleotide 2590 was found. This changed codon 743, glycine to valine, in the hormone-binding domain and created a new recognition sequence for the restriction endonuclease Asp HI. Amplification of exon 5 by polymerase chain reaction followed by digestion with Asp HI enabled easy recognition of the described mutation. Since the mother's exon 5 was undigested, we suspected the de novo nature of this nucleotide substitution. This was confirmed by direct sequencing of the mother's DNA which only showed the canonical sequence. To our knowledge, there has been no previous report of a de novo mutation described within the androgen receptor gene in patients with androgen insensitivity syndrome.

Exon skipping gives rise to alternatively spliced forms of the estrogen receptor in breast tumor cells

We have previously described three messenger RNA variants coding for the human estrogen receptor (ER) [1]. These variants were identified using the polymerase chain reaction to perform directed cloning of ER cDNAs synthesized from polyadenylated RNA extracted from the human breast cancer cell line T47D. Each of the variants is characterized by the precise deletion of a single exon within the protein coding region of this message and was presumably derived by inaccurate or promiscuous splicing of primary estrogen receptor transcripts. We report here the results of RNAse protection experiments which independently confirm the existence of these splicing variants in T47D cells. Similar analysis of RNA from MCF-7 cells also revealed the presence of variant ER transcripts, suggesting that they may be a common finding in tumor cell lines which express the estrogen receptor. However, attempts to identify splicing variants in a number of nominally ER-negative cell lines using either RNAse protection or PCR amplification were without success.

Interaction of the 90-kDa heat shock protein with native and in vitro translated androgen receptor and receptor fragments

Androgen receptor (AR) from rat ventral prostate and AR synthesized in vitro by translation in rabbit reticulocyte lysate of AR mRNA, transcribed from a pGEM-4Z DNA template were compared by gel permeation chromatography and by sucrose gradient ultracentrifugation. Under non-activating conditions the AR from rat prostate migrated as an 8-9 S complex of approx. 300 kDa. The addition of chicken antibodies against HSP90 shifted this complex to the void volume of the column or to the bottom of the ultracentrifugation gradient. Under activating conditions, on the other hand, the AR migrated as a 110 kDa, 5.2 S protein and was no longer displaced by HSP90 antibodies. Under all these conditions, the behaviour of in vitro synthesized AR was very similar to that of AR from rat prostate. By selective use of restriction enzymes on the template of transcription AR mutants could be prepared from which an increasing part was deleted at their carboxy terminal end. The interaction with HSP90 was conserved for AR1-758 missing the last 145 amino acids, but was lost in AR1-703. Furthermore, a large internal deletion (ARd41-469) of the major part of the amino terminal half of the AR did not result in the loss of HSP90 binding. These results indicate that a specific subregion (amino acids 704-758) of the carboxy terminal half of the AR is required for the interaction with HSP90.

Inhibition of steroid 5 alpha-reductase by specific aliphatic unsaturated fatty acids

Human or rat microsomal 5 alpha-reductase activity, as measured by enzymic conversion of testosterone into 5 alpha-dihydrotestosterone or by binding of a competitive inhibitor, [3H]17 beta-NN-diethulcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one ([3H]4-MA) to the reductase, is inhibited by low concentrations (less than 10 microM) of certain polyunsaturated fatty acids. The relative inhibitory potencies of unsaturated fatty acids are, in decreasing order: gamma-linolenic acid greater than cis-4,7,10,13,16,19-docosahexaenoic acid = cis-6,9,12,15-octatetraenoic acid = arachidonic acid = alpha-linolenic acid greater than linoleic acid greater than palmitoleic acid greater than oleic acid greater than myristoleic acid. Other unsaturated fatty acids such as undecylenic acid, erucic acid and nervonic acid, are inactive. The methyl esters and alcohol analogues of these compounds, glycerols, phospholipids, saturated fatty acids, retinoids and carotenes were inactive even at 0.2 mM. The results of the binding assay and the enzymic assay correlated well except for elaidic acid and linolelaidic acid, the trans isomers of oleic acid and linoleic acid respectively, which were much less active than their cis isomers in the binding assay but were as potent in the enzymic assay. gamma-Linolenic acid had no effect on the activities of two other rat liver microsomal enzymes: NADH:menadione reductase and glucuronosyl transferase. gamma-Linolenic acid, the most potent inhibitor tested, decreased the Vmax. and increased Km values of substrates, NADPH and testosterone, and promoted dissociation of [3H]4-MA from the microsomal reductase. gamma-Linolenic acid, but not the corresponding saturated fatty acid (stearic acid), inhibited the 5 alpha-reductase activity, but not the 17 beta-dehydrogenase activity, of human prostate cancer cells in culture. These results suggest that unsaturated fatty acids may play an important role in regulating androgen action in target cells.

Neural androgen receptors and scent marking of male gerbils: modulation by females

The involvement of brain cytosolic androgen receptors in the female-induced increase in scent-marking behavior of male Mongolian gerbils was studied. Scent-marking activities and serum testosterone concentrations were measured in low-marking control males and in males with increased scent-marking activities, stimulated by the presence of conspecific females in the same room. For every individual male the concentrations and affinities of androgen receptors were determined in four parts of the brain, which contained the hippocampus, septum, corpus striatum, amygdala, stria terminalis, and the hypothalamus. Compared to the basal unstimulated period, the marking activities of male gerbils significantly increased 58% during the presence of female conspecifics in their housing room. The serum testosterone concentrations did not change significantly during female presence. The association constants of the cytosolic androgen receptors were higher in the female-stimulated males compared to isolated control males. In contrast, the cytosolic receptor concentration was reduced. The difference reached significance in one of the brain parts. Individual levels in scent-marking activities could not be explained by correlation with individual androgen receptor parameters. The present results suggest that increased androgen binding in the brain may be involved in the elevation of scent-marking activities in male gerbils, caused by urinary chemical signals of female conspecifics.

Estradiol increases the duration of nuclear androgen receptor occupation in the preoptic area of the male rat treated with dihydrotestosterone

Androgens and estrogens interact in neural tissues to regulate behavioral and neuroendocrine responses. As an initial attempt to identify the cellular level at which these steroids interact, we characterized the time course of nuclear androgen receptor (ARn) occupation in the preoptic area of the hypothalamus (POA) after chronic dihydrotestosterone (DHT) administration and determined whether it was modified by concurrent treatment with estradiol benzoate (EB). We found that ARn levels peaked (47.1 +/- 12.6 fmol/mg DNA) by 12 h after castrated rats were treated with Silastic capsules filled with crystalline DHT and remained significantly elevated for at least an additional 12 h. When EB was injected (2 micrograms/rat) at the same time the DHT capsules were inserted, peak levels of ARn in POA were reached sooner (6 h) and retained longer (48 h). Comparisons with other central and peripheral tissues suggested that this response was unique to the POA. These results suggest that estrogens may modify the response of POA neurons to androgens by altering the duration of ARn occupation.

Differentiation of mesenchymal tissues during phallic morphogenesis with emphasis on the os penis: roles of androgens and other regulatory agents

This article reviews various aspects of differentiation and growth of phallic mesodermal tissues with special reference to the os penis. In many species of certain mammalian orders the penile interior contains an os penis or baculum with bona fide bone. Mechanisms of phenotypic sex differentiation and the androgenic regulation of morphogenesis of genitourinary tracts of both sexes are first overviewed. Thereafter the various mesodermal tissues in fully developed penes and clitorides are discussed. The developmental fate of mesenchymal cells in the fetal genital tubercles is then considered in detail, including considerations of epithelial-mesenchymal interactions. The review concludes with a discussion of the possible roles of certain polypeptide growth factors acting in concert with androgenic steroids. Special emphasis is placed on the potential role of bone morphogenetic proteins in formation of the os penis in a restricted number of eutherian mammalian taxa.

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.

Immunohistochemical study of androgen receptor in benign hyperplastic and cancerous human prostates

Androgen receptor was detected immunohistochemically in benign as well as malignant prostatic tissues by using a monoclonal rat anti-human androgen receptor antibody (AN 1-15). In both benign and malignant cells, the androgen receptor was exclusively localized in nuclei. In hyperplastic prostate, the androgen receptor was stained in the glandular and the stromal cells. In the gland, cells facing the lumen were stained more intensively than those adjacent to the basal membrane. In cancer tissue, receptor-positive and -negative cancer cells were intermingled. The percent of strongly positive cancer cells was correlated inversely with grade. Relapsed cells showed a low population of strongly positive cells irrespective of grade.