A novel missense mutation in the amino-terminal domain of the human androgen receptor gene in a family with partial androgen insensitivity syndrome causes reduced efficiency of protein translation

The role of the androgen receptor (AR) in male sexual differentiation is revealed in part by the analysis of naturally occurring mutations in families with androgen insensitivity syndrome (AIS). We have investigated a family with partial AIS affecting three generations and have identified a G to A substitution in the AR gene at the fourth position 3' from the A of the ATG initiation codon changing the second amino acid residue from glutamic acid to lysine (EK2). Transient expression of the mutant EK2-pCMVhAR expression vector in COS cells revealed decreased translation with a 20-50% reduction in mutant protein relative to wild type AR by immunoblot analysis. The rate of dissociation of [3H]methyltrienolone from the EK2 mutant (half-time [t1/2] = 1.7 +/- 0.08 SE h) was increased compared with wild type AR (t1/2 = 2.4 +/- 0.11 h). Cotransfection studies using an androgen responsive luciferase reporter vector demonstrated a 50% reduction in transcriptional activation by EK2. These functional alterations are consistent with the partial AIS phenotype in affected males, corroborate the AR amino-terminal domain effect on kinetics of androgen binding, and provide physiological evidence for earlier translation experiments identifying the nucleotide sequence for optimal translation initiation.

Androgen and glucocorticoid receptors in the stroma and epithelium of prostatic hyperplasia and carcinoma

Differences in stromal and epithelial cell staining for androgen and glucocorticoid receptors (ARs and GRs) were investigated in 20 patients with clinically localized prostatic carcinoma treated by radical prostatectomy. Sections of benign prostatic hyperplasia and prostatic carcinoma from each patient were stained with antibodies to AR and GR using an avidin-biotin peroxidase technique. The specificity of the GR immunoreactivity was established in benign prostatic hyperplasia and prostatic carcinoma by immunohistochemistry using the GR antibody absorbed with synthetic peptide and Western blotting. Nuclear staining intensity and percentage of nuclei stained were summed to obtain AR and GR immunostaining scores. AR staining of prostatic carcinoma epithelial [103 +/- 58 (SD)] and stromal (126 +/- 48) nuclei was less than in benign prostatic hyperplasia (142 +/- 47 and 169 +/- 56; paired Student's t tests, P = 0.02 and P = 0.01); however, no difference in staining intensity occurred between stroma and epithelium in either tissue type. GR stained intensely in stromal cells from benign prostatic hyperplasia (189 +/- 50) and prostatic carcinoma (163 +/- 60). However, prostatic carcinoma epithelial cells (34 +/- 57) had low levels of glucocorticoid receptor staining (P < 10(-7)), and benign prostatic hyperplasia epithelium (74 +/- 51) was intermediate. In most patients, GR could not be detected in nuclei of prostatic carcinoma epithelial cells but was undiminished in stromal cell nuclei. There was no relationship by multivariate regression analysis between AR or GR staining and age, serum prostate-specific antigen, Gleason grade, or pathological stage. In comparison with AR, the greater variability of GR staining in epithelium versus stroma of prostatic carcinoma warrants further study of GR, particularly in the area of stromal-epithelial interaction.

Evidence for an anti-parallel orientation of the ligand-activated human androgen receptor dimer

Domain interactions of the human androgen receptor (AR) dimer were investigated using a protein-protein interaction assay in which the NH2- and carboxyl-terminal regions of human AR were fused to the Saccharomyces cerevisiae GAL4 DNA-binding domain and herpes simplex virus VP16 transactivation domain to produce chimeric proteins. Transcriptional activation of a GAL4 luciferase reporter vector up to 100-fold was greater than Fos/Jun leucine zipper binding, indicating stable AR interaction between AR NH2-terminal residues 1-503 and steroid-binding domain residues 624-919 that was specific for and dependent on androgen binding to the steroid-binding domain and was inhibited by anti-androgen binding. Deletion mutagenesis within the NH2-terminal region indicated transactivation domain residues 142-337 were not required for dimerization, whereas deletions near the NH2 terminus (delta 14-150) or NH2-terminal to the DNA-binding domain (delta 339-499) reduced or eliminated the AR interaction, respectively. An NH2-/NH2-terminal interaction was also observed, but no interaction was detected between ligand-free or bound steroid-binding domains. The results indicate that high affinity androgen binding promotes interactions between the NH2-terminal and steroid-binding domains of human AR, raising the possibility of an androgen-induced anti-parallel AR dimer.

Specificity of simple hormone response elements in androgen regulated genes

Androgen (AR) and glucocorticoid (GR) receptors recognize a family of 15 base pair partial palindromic hormone response elements (HRE). We have studied receptor interactions with several HREs from androgen regulated genes to determine their potential to mediate a selective androgen response. Synthetic oligonucleotides corresponding to the elements were analysed for receptor binding and steroid dependent transcriptional enhancer activities. Each HRE contained the 3' half-site sequence (5'-TGTNCT-3') of the glucocorticoid response element (GRE) consensus sequence. HREs that countained the 5' half-site GRE consensus sequence (5'-A/GGNACA/G-3') had the strongest and-rogen response element (ARE) and GRE activities. In methylation interference assays, AR and GR interacted with identical base contact sites in the response elements. Two elements that deviated from the GRE consensus sequence by a single optimal base in the 5' half, had reduced ARE activity with no significant change in GRE activity and displayed lower binding of AR than GR in mobility shift assays using purified DNA binding domain peptides. Transfections with AR/GR and GR/AR chimeras containing the N-terminal domain of one receptor linked to the DNA-binding and C-terminal domains of the other suggested that N-terminal domain functions of GR also contributed to the greater GRE than ARE activities of the response elements.

Androgen receptor antagonist versus agonist activities of the fungicide vinclozolin relative to hydroxyflutamide

The mechanism of antiandrogenic activity of vinclozolin (3-(3,5-dichlorophenyl)-5-methyl-5-vinyloxazolidine-2,4-dione), a dicarboximide fungicide under investigation for its potential adverse effects on human male reproduction, was investigated using recombinant human androgen receptor (AR). The two primary metabolites of vinclozolin in plants and mammals are M1 (2-[[3,5-dichlorophenyl)-carbamoyl]oxy]-2-methyl-3-butenoic acid) and M2 (3',5'-dichloro-2-hydroxy-2-methylbut-3-enanilide). Both metabolites, in a dose-dependent manner, target AR to the nucleus and inhibit androgen-induced transactivation mediated by the mouse mammary tumor virus promoter. M2 is a 50-fold more potent inhibitor than M1 and only 2-fold less than hydroxyflutamide. In the presence of dihydrotestosterone (50 nM), M2 (0.2-10 microM) inhibits androgen-induced AR binding to androgen response element DNA. In the absence of dihydrotestosterone, concentrations of 10 microM M2 or hydroxyflutamide promote AR binding to androgen response element DNA and activation of transcription. Agonist activities of M2 and hydroxyflutamide occur at 10-fold lower concentrations with the mutant AR (Thr877 to Ala) endogenous to LNCaP human prostate cancer cells. The results indicate that androgen antagonists can act as agonists, depending on ligand binding affinity, concentration, and the presence of competing natural ligands.

Persistent DDT metabolite p,p'-DDE is a potent androgen receptor antagonist

The increase in the number of reports of abnormalities in male sex development in wildlife and humans coincided with the introduction of 'oestrogenic' chemicals such as DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) into the environment. Although these phenotypic alterations are thought to be mediated by the oestrogen receptor, they are also consistent with inhibition of androgen receptor-mediated events. Here we report that the major and persistent DDT metabolite, p,p'-DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene), has little ability to bind the oestrogen receptor, but inhibits androgen binding to the androgen receptor, androgen-induced transcriptional activity, and androgen action in developing, pubertal and adult male rats. The results suggest that abnormalities in male sex development induced by p,p'-DDE and related environmental chemicals may be mediated at the level of the androgen receptor.

Identification of three proline-directed phosphorylation sites in the human androgen receptor

Full-length wild type and deletion mutant human androgen receptors (AR) were transiently expressed in monkey kidney COS cells to identify the phosphorylated amino acid residues. Phosphoamino acid analysis indicated serine (Ser) and threonine (Thr) residues as the major sites of phosphorylation. Both NH2- and carboxyl-terminal fragments containing the DNA-binding domain were highly phosphorylated, suggesting the presence of phosphorylation sites throughout the protein. Site-directed mutagenesis of wild type and deletion mutant AR at proline-directed consensus phosphorylation sites replaced Ser or Thr residues with Ala; wild type and mutant ARs were expressed in the presence of [32P]orthophosphate and isolated by immunoprecipitation using AR-specific antipeptide antibodies. Three proline-directed phosphorylation sites were identified: Ser 81 and 94 in the NH2-terminal region and Ser 650 in the hinge region. Expression of a series of NH2-terminal AR fragments provided evidence for additional sites in the NH2-terminal region. The effect of loss of each phosphorylation site on receptor function was determined by introducing the Ser to Ala mutations into full-length AR. Substituting Ser 81 and 94 with Ala had little effect on transcriptional activity when assayed by transient cotransfection. Substituting Ser 650 with Ala in the hinge region reduced transcriptional activity up to 30%. The results suggest at least three proline-directed phosphorylation sites in AR, one of which, serine 650, contributes to optimal gene activation by AR.

Identification of sequences mediating guanylyl cyclase dimerization

Deletion mutagenesis was used to identify sequences required for dimerization and enzymatic activity of the intracellular domain of the membrane guanylyl cyclase, GC-A. The intracellular domain of GC-A contains a protein kinase-like domain near its amino terminus, a guanylyl cyclase catalytic domain near its carboxyl terminus, and, between these domains, a region of unknown function predicted to form an amphipathic alpha-helix. Gel filtration analysis of deletion mutants of the GC-A intracellular domain suggested that a 43 amino acid sequence within the interdomain region was both necessary and sufficient for dimerization and was required for guanylyl cyclase catalytic activity. The ability of this sequence to mediate protein dimerization was confirmed in the yeast two-hybrid system, in which its fusion to the lexA DNA-binding domain and to the VP16 transcriptional activation domain led to their dimerization and consequent activation of a lexA-HIS3 gene. Thus, we have identified sequences responsible for dimerization of the intracellular domain of a guanylyl cyclase and shown that they are required for enzyme activity. Modulation of their interaction may be important in guanylyl cyclase activation.

Hormone-dependent transactivation by the human androgen receptor is regulated by a dnaJ protein

Genetic studies were performed to examine the role of eukaryotic dnaJ protein, Ydj1p, in the regulated activation of human androgen receptor (hAR) after heterologous expression in Saccharomyces cerevisiae. Hormone-dependent activation of hAR was measured as a function of lacZ reporter gene expression, which was defective in ydj1-151 and ydj1-2 delta null mutant strains compared to the wild type. This defect was not due to receptor misfolding, since hAR in both wild type and mutant strains had a similar capacity to bind hormone. The target for Ydj1p action was determined to be the hAR hormone binding domain since an N-terminal fragment lacking this region was constitutively active in both wild type and ydj1-151 mutant strains. These data correlate hormone dependence of hAR activation with a requirement for Ydj1p function and are consistent with a role for dnaJ proteins in signal transduction by steroid hormone receptors.

Androgen receptor expression in meningiomas

The predominance of meningiomas in females, the accelerated growth of these tumors during the luteal phase of the menstrual cycle and during pregnancy, and the association between meningiomas and breast cancer have led to a number of studies examining the potential role of steroids in the growth of meningiomas. The possibility that androgens play a role in meningioma proliferation has been suggested by a small number of investigators. The aim of this study was to examine the expression of androgen receptor messenger ribonucleic acid (mRNA) and correlate it using immunochemistry with the nuclear localization of androgen receptor in a large number of meningiomas. Thirty-nine meningiomas were examined by Northern blot analysis for the presence of measurable amounts of androgen receptor mRNA and eight of these were analyzed by immunohistochemistry for receptor protein. Sixty-seven percent of the meningiomas expressed androgen receptor mRNA. There was a marked predominance of women among the patients whose tumors expressed androgen receptor; 69% were women and 31% were men. The immunohistochemical data correlated with Northern blot analysis of mRNA. The staining was predominantly nuclear, suggesting that the androgen receptor resides in a location that can activate gene expression.

Stability of an expanded trinucleotide repeat in the androgen receptor gene in transgenic mice

The expansion of trinucleotide repeat sequences underlies a number of hereditary neurological disorders. To study the stability of a trinucleotide repeat and to develop an animal model of one of these disorders, spinal and bulbar muscular atrophy (SBMA), we have generated transgenic mice carrying either the normal or expanded repeat human androgen receptor (AR) gene. Unlike the disease allele in humans, the AR cDNA containing the expanded repeat in transgenic mice showed no change in repeat length with transmission. Expression of the SBMA AR was found in transgenic mice, but at a lower level than normal endogenous expression. The lack of a physiological pattern of expression may explain why no phenotypic effects of the transgene were observed.

Specificity of ligand-dependent androgen receptor stabilization: receptor domain interactions influence ligand dissociation and receptor stability

The molecular basis for the different physiological effects of testosterone (T) and dihydrotestosterone (DHT) was investigated using recombinantly expressed wild-type and mutant androgen receptor (AR). Rates of androgen dissociation from nuclear and cytoplasmic AR were compared with hormone- and concentration-dependent receptor degradation rates. T dissociates from AR 3 times faster than DHT or methyltrienolone (R1881) and is less effective in stabilizing the receptor. Analysis of AR deletion mutants and AR/glucocorticoid receptor chimeras indicates that the AR NH2-terminal domain has a specific role in stabilizing the receptor by slowing the rate of ligand dissociation and AR degradation. Amino acid mutations that abolish receptor dimerization, nuclear localization, or DNA-binding activity have no significant effect on androgen dissociation or AR degradation. A naturally occurring steroid-binding domain mutation (Val889 to Met) that causes androgen insensitivity, but does not alter equilibrium androgen binding affinity, lowered the androgen-binding capacity as a result of increased rates of androgen dissociation and AR degradation. Thus, AR stabilization and function require prolonged receptor occupancy with androgen, with a similar extent of stabilization observed at higher concentrations of faster dissociating androgens and lower concentrations of slower dissociating androgens. Retention of receptor-bound androgen is enhanced by an interaction between the AR NH2-terminal and steroid-binding domains. The ligand specificity and concentration dependence of receptor stabilization provide an explanation for physiological differences in the actions of T and DHT.

Androgen and glucocorticoid receptors interact with insulin degrading enzyme

We recently identified a protein, designated receptor accessory factor (RAF), that interacts directly with and enhances the DNA binding of androgen (AR) and glucocorticoid (GR) receptor peptide fragments. To determine its identity, RAF was purified from HeLa cell extracts by anion-exchange and DNA affinity chromatography. RAF activity co-purified with a 110-kDa protein, the partial amino acid sequence of which shares 97.5% identity with insulin degrading enzyme (IDE), a metalloendoprotease implicated in the intracellular degradation of insulin. The identity of RAF was confirmed in gel shift assays by demonstrating that AR.RAF and GR.RAF DNA complexes shifted to a slower mobility in the presence of an IDE antibody. Purified preparations of RAF had insulin degrading activity, and this activity was inhibited by AR. In addition, the interaction of AR or GR with RAF was competed by insulin and bacitracin, a competitive inhibitor of IDE. The interactions of AR and GR with IDE may have important implications for both insulin- and steroid-mediated signaling.

A ligand-dependent bipartite nuclear targeting signal in the human androgen receptor. Requirement for the DNA-binding domain and modulation by NH2-terminal and carboxyl-terminal sequences

The amino acid sequence requirements for androgen-dependent androgen receptor nuclear import were determined by immunostaining transiently expressed full-length wild type and mutant human androgen receptors (AR) in monkey kidney COS cells and measuring transcriptional activity by cotransfection with a luciferase reporter vector in monkey kidney CV1 cells. Mutagenesis studies revealed a bipartite nuclear targeting sequence in the DNA binding and hinge regions at amino acids 617-633, consisting of two clusters of basic amino acids separated by 10 amino acids, (sequence: see text). In a series of deletion mutants, AR NH2-terminal fragments (residues 1-639 through 1-723) displayed constitutive nuclear import, and transcriptional activity was similar to that of the ligand-activated full-length wild type AR. In contrast, nuclear import and transcriptional activation were inhibited by sequence extensions into the steroid-binding domain (1-771). Constitutive nuclear import was regained in part by NH2-terminal deletions of full-length AR. Expression of AR/pyruvate kinase chimeras defined a sequence required for pre-dominant nuclear localization as residues 580-661, comprised of the second zinc finger region of the DNA-binding domain, the 17-amino-acid putative targeting sequence, and 28 residues of flanking carboxyl-terminal sequence. These studies suggest that the bipartite nuclear targeting sequence of AR includes flanking sequence and is modulated by interactions between the NH2-and carboxyl-terminal regions.

Characterization of mutant androgen receptors causing partial androgen insensitivity syndrome

The androgen insensitivity syndrome (AIS) is an X-linked disorder caused by mutations of the androgen receptor (AR) gene resulting in a spectrum of sex phenotypes that ranges from complete female (complete AIS) to nearly complete male (partial AIS). Using the polymerase chain reaction and denaturing gradient gel electrophoresis, we have analyzed the AR gene in three 46,XY individuals with partial AIS. In one subject whose androgen insensitivity was manifest at birth by clitoromegaly, posterior labial fusion, and a urogenital sinus, androgen-binding affinity in genital skin fibroblasts was similar to that of the control. In this subject, a mutation was identified in exon C encoding the second zinc finger of the androgen receptor. The mutation converted a leucine residue at position 616 to arginine, causing greatly reduced binding of receptor to an androgen-response element DNA sequence. However, the mutant AR retained a low level of transcriptional activity at physiological androgen concentrations in keeping with the subject's phenotype of partial AIS. In the second subject, who also had an ambiguous external genital phenotype, a single base mutation was identified in exon G, converting arginine at position 840 to histidine. Androgen-binding affinity in genital skin fibroblasts of this subject was 7-fold lower than control, and the mutant receptor had reduced transcriptional activity. In the third subject, who had a female phenotype with normal pubic hair reflecting a low degree of androgen responsiveness, the valine residue at position 889 was replaced by methionine. This mutant receptor had apparent normal androgen-binding affinity but reduced androgen-binding capacity when examined by expression of the recreated mutant AR in COS 7 cells. These results demonstrate the clinical, functional, and molecular heterogeneity in the syndrome of partial androgen insensitivity.

Suppression of sodium channel function in differentiating C2 muscle cells stably overexpressing rat androgen receptors

Differentiation of skeletal muscle and the formation of the neuromuscular junction are regulated by steroid hormones. The effects of androgens on ion channel proteins central to neuromuscular signalling have been investigated in differentiating mouse muscle C2 cells and in C2 cells that stably overexpress the rat androgen receptor (AR) cDNA. Neither the expression nor function of ACh receptors was regulated by androgenic actions in these cells. However, voltage-dependent sodium (Na) current density was decreased by androgen treatment of C2 cells and was abolished, even in the absence of androgens, in C2 cells that overexpress the AR. The decrease in functional Na current was not accompanied by concomitant decreases in Na channel mRNA, suggesting that AR influence posttranscriptional processing of Na channels in differentiating C2 cells.

A complex response element in intron 1 of the androgen-regulated 20-kDa protein gene displays cell type-dependent androgen receptor specificity

The androgen-regulated 20-kDa protein gene consists of four exons that code for a major secretory protein of rat ventral prostate. Analysis of its potential cis-acting transcriptional regulatory elements revealed that a large intron 1 region (In-1) had stronger androgen response element (ARE) activity than did the 5'-flanking DNA. In cotransfected CV1 cells, In-1 and its most active subfragment In-1c functioned as AREs but not glucocorticoid response elements (GRE). Nevertheless several ARE/GRE-like partial palindromic sequences are present in In-1c, and it bound both androgen receptors and glucocorticoid receptors in mobility shift assays. A cluster of three ARE/GRE-like sequences contained within a 39-base pair sequence of In-1c had both ARE and GRE activities when analyzed as an isolated oligonucleotide, suggesting that other elements within In-1c determined its ARE specificity. In addition to ARE/GRE-like sequences, In-1c contains putative response elements for the transcription factors AP1, CREB, AP2, OCT-1, C/EBP, and a number of inverted and direct repeats. The ARE specificity of In-1c observed in CV1 cells was diminished in PC3 and HeLa cells transiently cotransfected with an androgen receptor or glucocorticoid receptor expression vector together with an In-1c reporter vector; however, the ARE activity of In-1c was greater than its GRE activity in these cell lines. Interestingly, a 131-base pair subfragment of In-1c retained ARE specificity in all three cell lines.

Isolation and analysis of vaccinia virus previrions

Vaccinia virus (VV) virion morphogenesis is a complex sequence of events that occurs late in viral infection that is essential for the production of mature progeny. Electron microscopy studies have identified multiple morphogenic forms of virus particles, apparently assembled in a sequence from immature to mature particles that correlates with distinct physical changes. This assembly process is, however, rather poorly understood at the molecular level. To better characterize the multiple forms of VV previrions, sucrose log gradient fractionation of VV-infected cells was used to separate radiolabeled immature and mature forms of the virus. Depending on time postinfection that the infected cells were harvested, four distinct peaks of acid-precipitable counts could be detected that displayed different rates of sedimentation. Using pulse-chase analysis procedures, the labeled peaks were shown to have precursor-product relationships as slower sedimenting entities chased to faster sedimenting ones with time. These peaks were referred to as A, B, C, and V particles, with A being the initial precursor form found near the top of the gradient and V being the fastest sedimenting product. As the previrions mature, they migrated faster in the gradient and became infectious and resistant to treatment with DNase I. The core protein composition of the A particles was predominantly uncleaved precursors, with only small amounts of the mature core proteins 4a, 4b, 25K, and 23K evident. However, as the sedimentation rate of the particles increased, proteolytic maturation proceeded such that C particles were composed almost exclusively of mature core proteins. Together these results indicate that several distinct and separable forms of VV previrions exist, that VV core protein precursors are associated with the previrions prior to cleavage, and that maturation of the core proteins is coordinately linked to the conversion from noninfectious previrions to infectious viral particles.