The human androgen receptor: complementary deoxyribonucleic acid cloning, sequence analysis and gene expression in prostate

A and B forms of the androgen receptor are present in human genital skin fibroblasts

Two forms of the androgen receptor (AR) protein (apparent molecular masses, approximately 110 kDa and approximately 87 kDa) are present in human genital skin fibroblasts. The 87-kDa isoform (AR-A) contains an intact C terminus but lacks the normal N terminus found in the 110-kDa isoform (AR-B). AR-A is the same size as the mutant form of AR produced in fibroblasts from an androgen-resistant individual (R776) by initiation of AR synthesis at the internal Met-188 residue of AR-B. The ratio of AR-B to AR-A in fibroblasts derived from normal individuals is approximately 10:1. The AR isoforms detected in these experiments resemble the A and B forms of the human progesterone receptor, which also are encoded by a single gene and differ by the absence or presence of an N-terminal segment. The A and B forms of the human progesterone receptor differ in their ability to activate target genes and are regulated differently in various types of cells. The identification of similar forms of human AR raises the possibility that AR-A and AR-B also subserve different functions.

Androgens regulate expression of the gene coding for a mouse vas deferens protein related to the aldo-keto reductase superfamily in epithelial cell subcultures

Mouse vas deferens protein (MVDP), a member of the aldo-keto reductase superfamily, is exclusively produced in the vas deferens. To better understand androgen-regulated MVDP gene expression we have used RNA hybridization to study the effects of androgens on the steady-state levels of MVDP mRNA in vas deferens epithelial cell subcultures. Northern blot analysis revealed that these cells only express MVDP mRNA in the presence of androgens. There was a close relationship between MVDP mRNA levels and dihydrotestosterone concentrations. MVDP mRNA is induced over a period of 24h and maximal induction is about 25-fold. Treatment of cells with cycloheximide completely abolished the observed androgen effect suggesting that the induction of the MVDP gene by androgens depends on continuous protein synthesis. Transient transfection of vas deferens epithelial cells with MMTV-CAT vector showed that these cells contained functional androgen receptors and that they are a suitable system to study androgen effect on MVDP gene regulatory elements.

Androgen receptor gene mutations in human prostate cancer

To investigate the structural abnormality of the androgen receptor (AR) in human prostate cancers, exons B-H encoding DNA- and hormone-binding domains were examined by single-strand conformation polymorphism analysis of polymerase chain reaction products using originally designed oligoprimers. Tissues from 7 cases of untreated stage B prostate cancer surgically removed and from 8 cases of endocrine therapy-resistant cancers obtained at autopsy were used in the study. Two different mutations were identified in exons D and H in the different cancer foci of the same cancer death patient. One mutation in exon D (at codon 701, Leu to His) was detected in the prostate, and the other in exon H (at codon 877, Thr to Ala) was found in metastatic tissues. In untreated cancer tissues and the other autopsy samples, no mutations were detected. The mutation in exon H was identical to that reported in LNCaP cells. These results indicate that AR gene mutations occur in relation to endocrine therapy-resistance, although the mutation was found in 1 out of 8 resistant cases (12.5%) at autopsy.

A new mutation within the deoxyribonucleic acid-binding domain of the androgen receptor gene in a family with complete androgen insensitivity syndrome

OBJECTIVE

To study the androgen receptor gene in a large kindred with complete androgen insensitivity syndrome and positive receptor-binding activity.

DESIGN

Enzymatic amplification coupled with single strand conformation polymorphism and DNA sequencing were used.

RESULTS

In all the affected members, single strand conformation polymorphism showed a mobility shift in exon 2, suggesting a sequence alteration. Sequencing identified a valine into phenylalanine substitution at position 581 in the first zinc finger of the DNA-binding domain.

CONCLUSIONS

This valine 581 is conserved in all nuclear receptors and has an important role for the recognition of the androgen response elements by the activated androgen receptor. This amino acid substitution has not been previously described in the androgen receptor in patients with androgen insensitivity syndrome. Moreover, single strand conformation polymorphism allowed determination of the generation in which the mutation appeared and performance of carrier diagnosis in this family.

Mutations of androgen receptor gene in androgen insensitivity syndromes

The androgen receptor belongs to the family of steroid-thyroid hormone-retinoid nuclear receptors. It contains 3 major domains: a hormone-binding region, a DNA-binding region and an amino-terminal region. Cloning of the cDNA encoding the androgen receptor and elucidation of the androgen receptor gene structure enabled the characterization of the molecular defects associated with androgen insensitivity. Mutations of the androgen receptor in 46,XY individuals cause a spectrum of androgen insensitivity syndromes, ranging from female phenotype (testicular feminization) to minor degrees of undervirilization or infertility. Reports on androgen receptor gene structure in patients with complete or partial forms of androgen insensitivity demonstrate that gene deletions are very rare. Several categories of mutations have been reported and are reviewed in this paper. Nucleotide substitutions in the androgen-binding domain or the N-terminal region that cause insertion of premature termination codons result in failure to form a functional protein. Missense mutations within the androgen-binding domain are responsible for a decrease or absence of receptor-binding activity. Mutations within the DNA-binding domain are associated with a positive receptor-binding form of androgen insensitivity. Analysis of described mutations indicates that they are spread throughout the gene, either associated with partial or complete androgen insensitivity. Furthermore, the same point mutation was reported to be associated with variable phenotypic expression of androgen insensitivity syndrome. It is thus difficult to define a genotype/phenotype relationship. However, mutations causing androgen insensitivity will certainly yield important new insights into the molecular basis of androgen action.

Two polymorphic microsatellites in a coding segment of the canine androgen receptor gene

A 0.6-kb segment of exon 1 of the canine androgen receptor gene contains two polymorphic CAG tandem repeats which encode strings of glutamine homopolymers. The number of CAGs in each tandem repeat was determined by (1) polymerase chain reaction (PCR) amplification of a gene segment containing both repeats, (2) cleavage between repeats with restriction enzyme EcoO109I and (3) fractionation of the restriction fragments containing individual CAG repeats by denaturing polyacrylamide gel electrophoresis (PAGE). Individual genomic DNA samples from 80 unrelated dogs (53 males plus 27 females for a total of 107 X chromosomes) contained 10-12 CAGs in the 5' repeats and 10-13 CAGs in the 3' repeats. Thirteen distinct androgen receptor genotypes were identified. Eleven (or 41%) of the 27 unrelated females were heterozygous in one or both repeat regions, whereas all male samples produced single bands as expected for X chromosome markers. A total of seven distinct haplotypes contributed to the 13 genotypes. The 'polymorphism information content' or 'PIC' for this seven-allele X chromosome marker was 0.67.

Identification of androgen receptor in the rat spinal motoneurons. Immunohistochemical and immunoblotting analyses with monoclonal antibody

Androgens play an important role in motoneuron growth, development and regeneration. We proved the existence of androgen receptor (AR) in the motoneurons of the rat spinal cord by the immunohistochemical stain and Western blotting. The possibility that AR protein in spinal cord is expressed in tissue-specific form is proposed, being different from other androgen-dependent tissues. AR abnormality in X-linked spinal and bulbar muscular atrophy (SBMA) among a variety of motor neuron diseases were reported recently. Our study may give some clue to the AR abnormality leading to the degeneration of motoneurons.

Hormonal regulation of androgen receptor mRNA in the brain and anterior pituitary gland of the male rat

To determine possible cellular mechanisms governing androgen action in the brain, we examined the hormonal regulation of androgen receptor (AR) mRNA in neural tissues by Northern blot hybridization and RNase protection analysis. While a single hybridizable species of AR mRNA of approximately 11 kb was found in the anterior pituitary gland (AP) and ventral prostate gland (VP), an additional species of AR mRNA, approximately 2 kb smaller, was revealed in neural tissues. Furthermore, in these neural tissues, hormonal regulation of the two species of mRNA was coordinated; long-term castration increased levels of both forms, while testosterone replacement reduced them. The same pattern of regulation was observed for the single 11 kb form in the AP. An RNase protection assay was validated and utilized to quantitatively analyze the hormonal regulation of AR mRNA. Castration (4 days) resulted in significantly increased AR mRNA in the AP and hypothalamic-preoptic area, but not the amygdala, which subsequent administration of dihydrotestosterone (DHT; 1 day; 2 mg/animal) significantly decreased. In the AP, administration of estradiol benzoate (EB) for 1 or 5 days also reversed this effect. However, EB treatment increased the amount of total RNA isolated per gland. Consequently, when the data are normalized to RNA content per gland, 5 days of EB treatment resulted in a significant increase in AR mRNA content. These findings suggest that in contrast to the AP and VP, two forms of androgen receptor mRNA exist in the brain. In addition, there appears to be tissue and hormone specific regulation of AR mRNA.

Immunohistochemistry of the androgen receptor in human benign and malignant prostate tissue

The role of the androgen receptor in the development and progression of prostatic carcinoma has not been defined. The development of androgen receptor antibodies has provided new opportunities for direct immunohistochemical analysis. We compared the androgen receptor staining characteristics of fresh human prostatic carcinoma with benign prostatic hyperplasia (BPH) using an avidin-biotin complex method. Cancer and BPH obtained from the same radical retropubic prostatectomy specimen in 10 prostate cancer patients (68.5 +/- 7.3 years old standard deviation) and BPH from 10 noncancer patients (71.5 +/- 7.7 years old) were incubated with AR52, a rabbit polyclonal antibody against a synthetic androgen receptor peptide. Nuclei within each section were graded for intensity of androgen receptor staining (0-absent, 1-weak, 2-moderate or 3-strong) and the percentage (0 to 100%) of nuclei sampled staining at each of these intensity levels was determined. A total intensity score (0 to 300) was the summation of the products of each intensity score (0 to 3) and their corresponding percentages. Cancer sections (166 +/- 69) stained less intensely and more heterogeneously than BPH in cancer patients (246 +/- 41, Student's t test p < 0.05) and noncancer patients (225 +/- 39, p < 0.05). The decreased intensity and greater heterogeneity of androgen receptor staining in cancer tissue may implicate a quantitative or functional difference in androgen receptor between prostatic carcinoma and BPH.

Androgen biology as a basis for the diagnosis and treatment of androgenic disorders in women. I

Disorders of androgen excess in women are common in the practice of dermatology. The literature regarding the evaluation and treatment of women with cutaneous hyperandrogenism (acne, hirsutism, and alopecia) is vast and is contained in numerous subspecialty journals. At first glance, the basic science knowledge required to understand androgen biology appears exceedingly complex. However, an understanding of androgen physiology and a familiarity with the relevant literature are the basis of appropriate evaluations and treatment recommendations. In the first of this two-part series, we review the basic science of androgen biology and pathophysiology in women. The second part of this series will cover the evaluation of suspected hyperandrogenic women and the therapeutic modalities that are available.

Image analysis of androgen receptor immunostaining in metastatic prostate cancer. Heterogeneity as a predictor of response to hormonal therapy

BACKGROUND

Reliable predictors of the response of prostate cancer to androgen ablation therapy are lacking. The goals of this study were to determine whether nuclear androgen receptor (AR) concentrations in metastatic prostate cancer varied within and between specimens and to correlate this information with the response to therapy.

METHODS

AR concentration was evaluated by computer-assisted image analysis of immunohistochemical staining intensity in 200 malignant epithelial nuclei of each of 17 specimens of Stage D2 prostate cancer obtained before hormonal therapy. The data were correlated with the time to tumor progression (relapse) after hormonal therapy.

RESULTS

AR staining intensity varied within specimens, and the variance of staining intensity was significantly greater (P = 0.03) in the poor responders (n = 8; time to progression, < 20 months) than in the good responders (n = 9; time to progression, > or = 20 months). The kurtosis was significantly lower in poor responders (P = 0.04). However, the mean AR staining intensity was not significantly different among patients. The frequency distribution plots of good responders were generally uniform and unimodal, but those of poor responders were flattened (more platykurtic), dispersed, and highly variable. Thus, the AR concentration per cell was significantly more heterogeneous in poor responders. Variance was a significant predictor of response. Five of 6 patients with a high variance (defined as variance greater than the mean) were poor responders, whereas 8 of 11 patients with a low variance were good responders (an overall classification accuracy of 13 of 17, 76%).

CONCLUSIONS

The greater AR heterogeneity in poor responders may reflect a greater genetic instability in tumors that have progressed further toward androgen independence and may be a valuable predictor of progression.

Related individuals with different androgen receptor gene deletions

We have identified different members of one family affected by androgen insensitivity syndrome who have deletions of different exons of the X-linked androgen receptor (AR) gene. Two affected (XY) siblings have a deletion of exon E of the AR gene and their affected (XY) aunt has a normal exon E, but a deletion of exons F and G of the same gene. The mother and maternal grandmother of the children both carry the exon E deletion, but not the exon F, G deletion. Both deletions are 5 kb in length and have one breakpoint within a 200-bp region in intron 5; however, they extend in opposite directions. The probability that these two different deletions have arisen at random is extremely low, but the cause of this intriguing phenomenon remains to be found.

Expression of androgen and progesterone receptors in primary human meningiomas

Meningiomas are common brain tumors that show a predilection for females and become more aggressive during pregnancy and menses. The existence of gender-specific hormone receptors in meningiomas has long been a matter of controversy; the recent cloning of androgen, estrogen, and progesterone receptors has facilitated their direct evaluation. The authors have demonstrated the expression of androgen and progesterone receptor messenger ribonucleic acid and protein product in nine primary human meningiomas by Northern blot analysis. Cellular localization was achieved by in situ hybridization analysis. Estrogen receptor expression was not detected. Normal adult meninges were shown to express very low levels of both androgen and progesterone receptors.

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.

Androgen receptor and mechanism of androgen action

Androgen receptor is the intracellular protein that mediates biological actions of physiological androgens (testosterone and 5 alpha-dihydrotestosterone). Androgen receptor belongs to a large family of ligand-dependent proteins whose function is to modulate expression of genes and gene networks in a cell- and tissue-specific manner. The present overview describes the structurally important domains of the receptor protein, and discusses several aspects in the structure-function relationship, using naturally occurring receptor mutants in androgen insensitivity patients or experimental animals as examples. In addition, characteristics of androgen receptor expressed in a heterologous system are described, and their potential usefulness in specific molecular studies discussed.

FTZ-F1 beta, a novel member of the Drosophila nuclear receptor family

The Drosophila melanogaster gene FTZ-F1 beta, encoding a novel member of the steroid/thyroid hormone receptor gene superfamily, was isolated by cross-hybridization with a complementary DNA for the Drosophila nuclear receptor, FTZ-F1 (Lavorgna et al., 1991). The cDNA deduced protein sequence for FTZ-F1 beta displays significant amino acid identity with other vertebrate and invertebrate nuclear receptors, most notably with FTZ-F1. Also, bacterially expressed FTZ-F1 beta protein binds to a FTZ-F1 binding site found in the zebra stripe promoter element of the segmentation gene fushi tarazu (ftz). Northern blot analysis detected FTZ-F1 beta expression at all stages of the Drosophila life cycle including a possible maternal component. In situ hybridization in whole-mounted embryos localized transcripts for FTZ-F1 beta evenly expressed throughout the blastodermal layer in early embryos. At later stages of development strong FTZ-F1 beta expression is observed in both the brain and ventral chord structures as well as in the hindgut. Temporal and spatial expression patterns of the FTZ-F1 beta gene suggest that it may have multiple roles in early embryogenesis, neurogenesis, and in the adult. Furthermore, the identification of FTZ-F1 beta as a nuclear receptor family member suggests that an as yet undiscovered FTZ-F1 beta specific ligand is involved in Drosophila development.

Molecular genetics of human androgen insensitivity

Androgen insensitivity syndromes represent one cause of human male pseudohermaphroditism related to defects in the androgen receptor. The formation of a biologically active androgen receptor complex with testosterone and 5 alpha-dihydrotestosterone is required for normal androgen action during fetal development and differentiation of the internal accessory sex glands and external genitalia. Cloning of the human androgen receptor complementary DNA and genetic screening of human subjects with the clinical and biochemical features of androgen insensitivity using the polymerase chain reaction, denaturing gradient gel electrophoresis and nucleotide sequencing techniques have led to the identification of molecular defects in the androgen receptor. The complexity of phenotypic presentation by affected subjects with the complete or partial forms of androgen insensitivity is represented by the heterogeneity of androgen receptor gene mutations which include deletions and point mutations, with the latter causing inappropriate splicing of RNA, premature termination of transcription and amino acid substitutions. The naturally occurring mutations in the androgen receptor of subjects with androgen insensitivity represent a base upon which we can increase our understanding of the structure and function of the androgen receptor in normal physiology and disease.

Telomere-associated chromosome fragmentation: applications in genome manipulation and analysis

Telomere-associated chromosome fragmentation (TACF) is a new approach for chromosome mapping based on the non-targeted introduction of cloned telomeres into mammalian cells. TACF has been used to generate a panel of somatic cell hybrids with nested terminal deletions of the long arm of the human X chromosome, extending from Xq26 to the centromere. This panel has been characterized using a series of X chromosome loci. Recovery of the end clones by plasmid rescue produces a telomeric marker for each cell line and partial sequencing will allow the generation of sequence tagged sites (STSs). TACF provides a powerful and widely applicable method for genome analysis, a general way of manipulating mammalian chromosomes and a first step towards constructing artificial mammalian chromosomes.

Regulation of androgen receptor mRNA and protein level by steroid hormones in human mammary cancer cells

The regulation of the human androgen receptor (AR) by steroid hormones in human mammary cancer cells was investigated using immunocytochemical and ligand binding assays for its protein and Northern blot analyses for the corresponding mRNA. MFM-223 cells contain high levels of ARs and are growth-inhibited by dihydrotestosterone (DHT). The AR protein is down-regulated to 57% of the control by 10 nM DHT after 24 h, and the corresponding mRNA is also reduced. The nonsteroidal antiandrogen hydroxyflutamide had no effect on the AR level, whereas after incubation with 1 microM cyproterone acetate a slight down-regulation was observed. The AR level was restored completely after release from a 7 day treatment with DHT. However, only 60% of the control level was restored, if the cells wer grown in the presence of DHT for 6 weeks. In androgen-pretreated cells the proliferation rate remained decreased even after the withdrawal of DHT. Concomitantly the distinct growth inhibition was lost. Transfection experiments demonstrated a reduced activity of the residual androgen receptor in these pretreated cells. In addition to the AR, EFM-19 cells also contain significant amounts of estrogen and progesterone receptors. EFM-19 cells are not growth inhibited by physiological concentrations of DHT. Autoregulation of AR was also found in this cell line. Additionally, reduced levels of AR protein and mRNA were found in EFM-19 cells after treatment with the synthetic progestin R5020. The maximum effect of R5020 was observed at the high concentration of 1 microM. Estrogen treatment with 10 nM 17 beta-estradiol for 3 days reduced the AR level only by 25%.

Prenatal prediction of androgen insensitivity syndrome using exon 1 polymorphism of the androgen receptor gene

Exon 1 polymorphism of the androgen receptor (AR) gene is characterized by a (CAG)n(CAA) repeat at position 172 following the translation start codon. The aim of this study was to determine whether AR gene exon 1 polymorphism could be used to perform prenatal diagnosis in high risk families with complete or partial androgen insensitivity syndrome. After enzymatic amplification of a 1 kilobase exon 1 fragment, each DNA was simultaneously digested by MspI and PstI restriction enzymes. After electrophoresis on a 15% electrophoresis on a 15% acrylamide gel or a 6% Nusieve gel, we measured the size of the obtained fragments and determined the number of CAG repeats since a 282 basepair fragment corresponds to 21 CAG. We previously showed that the number of CAG repeats within the AR gene exon 1 in 23 families with complete or partial androgen insensitivity syndrome was 19 +/- 4. By this method, we detected heterozygosity in 50% of the mothers. We present here 2 exclusion prenatal diagnoses using exon 1 polymorphism of the AR gene. Family A presented a boy with a severe form of partial androgen insensitivity syndrome. The mother had 2 uncles with ambiguous genitalia. In family B, the affected child had a complete androgen insensitivity syndrome. In both families, analysis of the AR gene exon 1 polymorphism of the trophoblastic DNA showed the presence of the normal maternal X chromosome. The parents decided to carry on the gestation. In family A, the newborn had normal male external genitalia. In family B, sonography confirmed the presence of normal male external genitalia. These data suggest that exon 1 polymorphism of the AR gene could be prenatally used to predict androgen insensitivity syndrome.

Androgen receptor immunoreactivity in intact and castrate guinea pig using antipeptide antibodies

We developed and used antibodies to an androgen receptor (AR)-specific synthetic peptide (amino acids 201-222 of the human androgen receptor) to localize AR in the brain and peripheral tissues of intact and castrate adult male guinea pigs. Immunoreactivity was localized to the nucleus of epithelial and stromal cells in the prostate of intact animals. Immunostaining was abolished in the prostate 4 days following castration. Androgen receptor immunoreactivity was found in brain nuclei known to be involved in reproductive and other androgen-dependent behaviors, including the preoptic area, medial basal hypothalamus, and anterior pituitary gland. Castration had no effect on the distribution or intensity of AR immunostaining in the brain. These data indicate a differential regulation of AR in the brain compared to peripheral tissues.

Mutations in the ligand-binding domain of the androgen receptor gene cluster in two regions of the gene

We have analyzed the nucleotide sequence of the androgen receptor from 22 unrelated subjects with substitution mutations of the hormone-binding domain. Eleven had the phenotype of complete testicular feminization, four had incomplete testicular feminization, and seven had Reifenstein syndrome. The underlying functional defect in cultured skin fibroblasts included individuals with absent, qualitative, or quantitative defects in ligand binding. 19 of the 21 substitution mutations (90%) cluster in two regions that account for approximately 35% of the hormone-binding domain, namely, between amino acids 726 and 772 and between amino acids 826 and 864. The fact that one of these regions is homologous to a region of the human thyroid hormone receptor (hTR-beta) which is a known cluster site for mutations that cause thyroid hormone resistance implies that this localization of mutations is not a coincidence. These regions of the androgen receptor may be of particular importance for the formation and function of the hormone-receptor complex.

Genomic organization of the human retinoic acid receptor beta 2

Recently three isoforms of the mouse retinoic acid receptor (mRAR beta 1, mRAR beta 2, mRAR beta 3) have been described, generated from the same gene (Zelent et al., 1991). The isoforms differ in their 5'-untranslated (5'-UTR) and A region, but have identical B to F regions. The N-terminal variability of mRAR beta 1/beta 3 is encoded in the first two exons (E1 and E2), while exon E3 includes N-terminal sequences of the mRAR beta 2 isoform. We have determined the structure of the human RAR beta 2 gene, using a genomic library from K562 cells. The open reading frame is split into eight exons: E3 contains sequences for the N-terminal A region and E4 to E10 encode the common part of the receptor, including the DNA-binding domain and ligand-binding domain. Corresponding to other nuclear receptors, both 'zinc-fingers' of the DNA-binding domain are encoded separately in two exons and the ligand-binding domain is assembled from five exons.

A unique point mutation in the androgen receptor gene in a family with complete androgen insensitivity syndrome

OBJECTIVE

To further delineate the diversity of genetic alterations in the gene coding for the androgen receptor in individuals with the androgen insensitivity syndrome and to increase our understanding of the disease at the molecular level.

DESIGN

This was a prospective study in which genomic deoxyribonucleic acid (DNA) from individuals with androgen insensitivity were examined through the polymerase chain reaction and DNA sequencing analysis.

PATIENTS

Eleven complete and four individuals with partial androgen insensitivity syndrome were examined.

RESULTS

Exons two through eight were grossly intact in all study subjects. Nucleotide sequence analysis revealed that three of three related family members with complete androgen insensitivity had the same guanine to adenine base substitution in exon five of the steroid-binding domain.

CONCLUSION

The subsequent alanine to threonine amino acid conversion may have resulted in a configurational change of the androgen receptor protein leading to complete androgen insensitivity. This precise alteration has not been previously identified in the human androgen receptor gene in patients with the androgen insensitivity syndrome.

Transcriptional regulation of androgen receptor gene expression in Sertoli cells and other cell types

Regulation of androgen receptor (AR) mRNA expression was studied in Sertoli cells and peritubular myoid cells isolated from immature rat testis, and in the lymph node carcinoma cell line derived from a human prostate (LNCaP). Addition of dibutyryl-cyclic AMP (dbcAMP) to Sertoli cell cultures resulted in a rapid transient decrease in AR mRNA expression (5 h), which was followed by a gradual increase in AR mRNA expression (24-72 h). This effect of dbcAMP mimicked follicle-stimulating hormone (FSH) action. In peritubular myoid cells, there was only a moderate but prolonged decrease during incubation in the presence of dbcAMP, and in LNCaP cells no effect of dbcAMP on AR mRNA expression was observed. When Sertoli cells or peritubular myoid cells were cultured in the presence of androgens, AR mRNA expression in these cell types did not change. This is in contrast to LNCaP cells, that showed a marked reduction of AR mRNA expression during androgen treatment. In the present experiments, transcriptional regulation of AR gene expression in Sertoli cells and LNCaP cells was also examined. Freshly isolated Sertoli cell clusters were transfected with a series of luciferase reporter gene constructs, driven by the AR promoter. It was found that addition of dbcAMP to the transfected Sertoli cells resulted in a small but consistent increase in reporter gene expression (which was interpreted as resulting from AR promoter activity); a construct that only contained the AR 5' untranslated region of the cDNA sequence did not show such a regulation. The same constructs, transfected into LNCaP cells, did not show any transcriptional down-regulation when the synthetic androgen R1881 was added to the cell cultures. A nuclear transcription elongation experiment (run-on), however, demonstrated that androgen-induced AR mRNA down-regulation in LNCaP cells resulted from an inhibition of AR gene transcription. The present results indicate that in Sertoli cells and LNCaP cells, hormonal effects on AR gene transcription play a role in regulation of AR expression. However, AR gene transcription in these cells is differentially regulated.

Analysis of the CAG repeat region of the androgen receptor gene in a kindred with X-linked spinal and bulbar muscular atrophy

Herein we describe a family with X-linked spinal and bulbar muscular atrophy (SBMA or Kennedy's disease), an adult onset neuromuscular disease characterized by slow progression, predominant proximal and bulbar muscle weakness. One frequent association is the appearance of gynecomastia. This disorder was previously shown to be linked to the locus DXYS1 on the proximal long arm of the X chromosome. Recently, a report implicated a mutation at the N-terminus of the androgen receptor gene involving amplification of CAG repeats as the cause of X-linked SBMA. We studied this region of the androgen receptor in a kindred clinically suspected but not confirmed of having X-linked SBMA by the polymerase chain reaction (PCR) followed by Southern analysis and DNA sequencing. The mutated allele was found to have an increased number of 51 CAG repeats confirming the clinical diagnosis of SBMA. Normal individuals revealed 23 repeat numbers within the normal range, while another unrelated X-linked SBMA patient had an enlarged CAG repeat region. The carrier or disease status could be established or confirmed in 12 individuals of this family on the basis of detecting normal and disease alleles reflected by the number of CAG repeats.

Domain functions of the androgen receptor

Molecular cloning of the androgen receptor cDNA has facilitated analysis of structure/function relationships of this ligand activated transcription factor. Amplification of mutant androgen receptor DNA using the polymerase chain reaction has revealed single base and deletion mutations in the androgen receptor gene that cause the androgen insensitivity syndrome in rats and humans. Site directed mutagenesis of the NH2-terminal and hinge regions indicates specific sequences required for full transcriptional activation and nuclear targeting of the androgen receptor. Finally, transient transfection systems have shown that the antiandrogen cyproterone acetate is both an agonist and antagonist, while hydroxyflutamide acts only as an antagonist and thus is a pure antiandrogen.

Androgen receptor gene mutations in human prostate cancer

We screened human prostate cancer tissues for the presence of somatic mutations in the hormone binding domain of the androgen receptor (AR) gene. Exons E-H were amplified from genomic DNA using the polymerase chain reaction and analyzed by denaturing gradient gel electrophoresis (DGGE), which separates DNA fragments that differ by only a single base. We detected a mutation in exon E of the hormone binding domain in 1 of 26 specimens of untreated organ-confined stage B prostate cancer. The mutation was not detectable in peripheral blood lymphocyte DNA. Lymphocyte DNA (wild-type AR) migrated in DGGE as a single band. The tumor DNA migrated in DGGE as four bands, consistent with the presence of cells with mutant AR plus cells with wild-type AR and indicating that the tumor contained a somatic mutation. To our knowledge, a somatic AR gene mutation has not been reported previously. Sequencing revealed a G----A substitution in codon 730, changing valine to methionine. Codon 730 is in a region highly conserved among all steroid receptors. The abundance of the mutated fragment (about 50% of the DNA in the specimen) indicates its presence in cells with a growth advantage. A somatic mutation could be detected by DGGE if it represented at least 10% of the sample. Failure to detect mutations in other specimens analyzed may be due to this limit of sensitivity, the presence of mutations in other parts of the AR, or a low frequency of mutations in early stage disease.

Molecular defects in the androgen receptor causing androgen resistance

Patients with androgen resistance exhibit a spectrum of abnormalities of male sexual development ranging from 46,XY phenotypic women (complete testicular feminization) to undervirilized fertile men. The definition of the androgen receptor gene structure has permitted the identification of the defects causing androgen resistance in a number of patients. In some individuals androgen resistance is caused by large-scale structural alterations in the androgen receptor gene. In most patients, however, the androgen receptor mutation is the result of single nucleotide substitutions, which cause premature termination or amino acid replacement that result in the synthesis of defective androgen receptor proteins. These amino acid substitutions identify residues crucial to the normal function of the androgen receptor protein.

Nuclear localization of androgen receptor in heterogeneous samples of normal, hyperplastic and neoplastic human prostate

To facilitate an understanding of how androgens participate in the genesis of human benign hyperplasia and carcinoma we assayed androgen receptor in the epithelium and stroma of human prostatic tissue from 57 patients. Immunohistochemical staining of human androgen receptor was performed on 106 sections of normal prostate, benign prostatic hyperplasia (BPH) and prostate cancer. To determine variability of androgen receptor staining sections taken from different portions of the gland were studied. Frozen tissue sections were incubated with monoclonal antiandrogen receptor antibodies and staining was completed by the indirect avidin-biotin peroxidase method. Antibody staining was found mainly in the nucleus of prostatic epithelial cells, although some stromal cells also showed positive staining. Unlike normal prostate, there was a heterogeneous distribution of androgen receptor in BPH and prostate cancer. The androgen receptor content in well differentiated adenocarcinoma epithelium was significantly higher compared to moderately (p less than 0.05) and poorly (p less than 0.05) differentiated adenocarcinoma. Regardless of the origin of stromal tissue, some staining was observed. In each specimen studied the androgen receptor staining was consistent qualitatively and quantitatively for each pathological component throughout the specimen. These data confirm that androgen receptor is a nuclear receptor protein. Furthermore, they show the ability of monoclonal antibodies to reveal cellular/subcellular distribution of androgen receptor, and demonstrate a correlation between the degree of tumor differentiation and androgen receptor content in epithelial but not in stromal cells. These observations may have important implications for understanding the variable tumor response to hormone therapy.

Loss of the 17p chromosomal region in a metastatic carcinoma of the prostate

Genetic alterations of multiple loci that serve as markers for the induction and progression of disease have been identified in several adenocarcinomas, but not in adenocarcinoma of the prostate. To determine if similar genetic alterations occur in prostate carcinoma and could serve as markers for the extent of clinical disease, we have examined 23 predominantly moderately-differentiated, localized prostate carcinomas and one prostatic dysplasia for changes in the structure and copy number of ten selected genes. These genes include 1) those important to androgen metabolism in the prostate, the androgen receptor and steroid 5 alpha reductase genes; 2) those that map to the 10q (PLAU) and 7q (MET) chromosomal regions found deleted in some prostate carcinomas, and 3) proto-oncogenes (ERBB2, INT2, and MYC) and tumor suppressor gene loci (RB1, TP53 and D17S5) found altered in adenocarcinomas of the breast, colon and lung. Gene alterations were detected in one specimen, a lymph node metastasis from a poorly differentiated tumor. This specimen exhibited loss of heterozygosity for two loci putatively active in tumor suppression, TP53 and D17S5, on the short arm of chromosome 17. This study indicates that gross genetic alterations were not evident and could not be used as markers of tumor development in well- or moderately-differentiated, localized lesions, but that loss of the 17p region may be a useful marker for advanced carcinomas in the prostate.

Immunocytochemical localization of androgen receptors in the male songbird and quail brain

The distribution of androgen receptors was studied in the brain of the Japanese quail (Coturnix japonica), the zebra finch (Taeniopygia guttata), and the canary (Serinus canaria) by immunocytochemistry with a polyclonal antibody (AR32) raised in rabbit against a synthetic peptide corresponding to a sequence located at the N-terminus of the androgen receptor molecule. In quail, androgen receptor-immunoreactive cells were observed in the nucleus intercollicularis and in various nuclei of the preoptic-hypothalamic complex, namely, the nucleus preopticus medialis, the ventral part of the nucleus anterior medialis hypothalami, the nucleus paraventricularis magnocellularis, the nucleus ventromedialis hypothalami, and the tuberal hypothalamus. In the two songbird species, labeled cells were also observed in various nuclei in the preoptic-hypothalamic region, in the nucleus taeniae, and in the nucleus intercollicularis. Additional androgen receptor-immunoreactive cells were present in the androgen-sensitive telencephalic nuclei that are part of the song control system. These immunoreactive cells filled and outlined the boundaries of the hyperstriatum ventrale, pars caudalis, nucleus magnocellularis neostriatalis anterioris (both in the lateral and medial subdivisions), and nucleus robustus archistriatalis. The immunoreactive material was primarily present in cell nuclei but a low level of immunoreactivity was also clearly detected in cytoplasm in some brain areas. These studies demonstrate, for the first time, that androgen receptors can be detected by immunocytochemistry in the avian brain and the results are in general agreement with the binding data obtained by autoradiography with tritiated dihydrotestosterone. Immunocytochemical methods offer several advantages over autoradiography and their use for the study of the androgen receptor will greatly facilitate the analysis of steroid-sensitive systems in the avian brain.

Expression and characterization of full-length and partial human androgen receptor fusion proteins. Implications for the production and applications of soluble steroid receptors in Escherichia coli

We have expressed fusion proteins encoding defined segments of the coding segment of the human androgen receptor (hAR) in Escherichia coli using the pGEX-2T expression vector. Large quantities of fusion proteins containing glutathione-S-transferase (GST) linked to the amino or carboxy terminal region of the receptor and a fusion protein containing the complete amino acid sequence of the androgen receptor were produced in soluble form. The GST hAR fusion proteins containing the hormone-binding domain of the androgen receptor exhibit high affinity specific binding for a variety of natural and synthetic androgens. Analysis of the binding properties of the complete and truncated androgen receptor fusion proteins revealed that the amino terminus affects the Kd of the fusion proteins for mibolerone (0.89 vs. 3.43 nM for the truncated and complete fusion proteins, respectively). Despite these differences, both the truncated and complete hAR fusion proteins exhibit a higher affinity for dihydrotestosterone than for testosterone, implying that the preferential affinity for dihydrotestosterone observed in androgen receptor prepared from native sources is a measure of the inherent structure of the hormone-binding domain. Furthermore, the ligand-receptor complex is stable, as the ligand is not easily displaced with unlabelled competitor and is stable to mild heat denaturation. Fusion proteins containing the DNA-binding domain demonstrate specific DNA binding, as evidenced by studies using segments of the mouse mammary tumor virus long terminal repeat (MMTV-LTR) and synthetic glucocorticoid response elements. These studies establish that GST hAR fusion proteins exhibit physical properties similar to those of native androgen receptor. Affinity purification using a glutathione affinity resin and cleavage of the fusion proteins at a thrombin cleavage site permits a marked enrichment using a two-step purification. The use of such methods will facilitate the study of the normal and mutant receptor proteins.

The human androgen receptor: structure/function relationship in normal and pathological situations

Discrete functions have been attributed to precise regions of the human androgen receptor (hAR) by expression of deletion mutants in COS and HeLa cells. A large C-terminal domain constitutes the hormone-binding region and a central basis, cysteine-rich domain is responsible for DNA binding. In addition, separate domains responsible for transactivation and nuclear translocation have been identified. In LNCaP cells (a prostate tumor cell line) the hAR is a heterogeneous protein which is synthesized as a single 110 kDa protein, but becomes rapidly phosphorylated to a 112 kDa protein. Metabolic labeling experiments using radioactive orthophosphate also indicated that the hAR is a phosphoprotein. Structural analysis of the AR gene in LNCaP cells and in 46, XY-individuals displaying androgen insensitivity (AIS) has revealed several different point mutations. In LNCaP cells the mutation affects both binding specificity and transactivation by different steroids. In a person with complete AIS a point mutation was identified in the splice donor site of intron 4, which prevents normal splicing and activates a cryptic splice donor site in exon 4. The consequence is a functionally inactive AR protein due to an in-frame deletion in the steroid-binding domain. In two unrelated individuals with complete AIS, two different single nucleotide alterations in codon 686 (Asp) were found. Both mutations resulted in functionally inactive ARs due to rapidly dissociating hormone-AR complexes. It is concluded that the hAR is a heterogeneous phosphoprotein in which functional errors have a dramatic impact on phenotype and fertility of 46, XY-individuals.

Immunohistochemistry and biochemistry in detection of androgen, progesterone, and estrogen receptors in benign and malignant human prostatic tissue

The relative distribution of androgen (AR), progesterone (PR), and estrogen receptors (ER) was localized and estimated in human prostate tissue by immunohistochemistry in five normal tissue samples, in eight benign hyperplastic (BPH) samples, in nine primary cancers, and in seven prostate cancer metastases. Moreover, three prostatic cancer cell lines (LNCaP, DU 145, and PC 3) were analyzed. A comparison between the results obtained by radioligand binding assays and immunohistochemistry was performed for the AR and PR. Using immunohistochemistry, the AR was exclusively detected in the nuclei of both benign and malignant prostatic epithelial cells. The highest proportion of AR-positive cells was found in BPH and in prostate cancer metastases as compared with normal prostatic tissue. In a majority of the cases, the PR was only present in the nuclei of stromal cells. Benign hyperplastic prostates contained higher proportions of PR-positive cells as compared with primary carcinoma. PR was sparse in epithelial cells. ER-positive stromal cell nuclei were only detected in carcinomatous prostates. A few ER-positive epithelial cell nuclei were found in one sample each of a BPH and normal prostate. All cells from the androgen-dependent, LNCaP, cell line and a majority of the cells from the androgen-independent, DU 145, cell line were AR-positive. In contrast, the cells from the androgen-independent, PC 3, cell line were all AR-negative. All three cell lines were PR- and ER-negative. The radioligand binding technique detected the AR in extracts from both the cytosol and the nucleus. Again BPH contained higher amounts of AR as compared with normal prostatic tissue. The LNCaP cells contained high amounts of cytosolic AR while cells from the DU 145 and PC 3 cell lines lacked detectable AR as estimated by biochemical techniques. There seemed to be a discrepancy between biochemically measured and immunohistochemically estimated receptor content.