Dehydroepiandrosterone activates mutant androgen receptors expressed in the androgen-dependent human prostate cancer xenograft CWR22 and LNCaP cells

An androgen receptor (AR) gene mutation identified in the androgen-dependent human prostate cancer xenograft, CWR22, changed codon 874 in the ligand-binding domain (exon H) from CAT for histidine to TAT for tyrosine and abolished a restriction site for the endonuclease SfaNI. SfaNI digestion of AR exon H DNA from normal but not from prostate cancer tissue indicated H874Y is a somatic mutation that occurred before the initial tumor transplant. CWR22, an epithelial cell tumor, expresses a 9.6-kb AR mRNA similar in size to the AR mRNA in human benign prostatic hyperplasia. AR protein is present in cell nuclei by immunostaining as in other androgen-responsive tissues. Transcriptional activity of recombinant H874Y transiently expressed in CV1 cells in the presence of testosterone or dihydrotestosterone was similar to that of wild type AR. With dihydrotestosterone at a near physiological concentration (0.01 nM), H874Y and wild type AR induced 2-fold greater luciferase activity than did the LNCaP mutant AR T877A. The adrenal androgen, dehydroepiandrosterone (10 and 100 nM) with H874Y stimulated a 3- to 8-fold greater response than with wild type AR and at 100 nM the response was similar with the LNCaP mutant. H874Y, like the LNCaP cell mutant, was more responsive to estradiol and progesterone than was wild type AR. The antiandrogen hydroxyflutamide (10 nM) had greater agonist activity (4- to 7-fold) with both mutant ARs than with wild type AR. AR mutations that alter ligand specificity may influence tumor progression subsequent to androgen withdrawal by making the AR more responsive to adrenal androgens or antiandrogens.

Generation and characterization of an IGFBP-7 antibody: identification of 31kD IGFBP-7 in human biological fluids and Hs578T human breast cancer conditioned media

The cDNA encoding mac25 (IGFBP-7) was firsr derived from mRNA isolated from leptomeningial and senescent human mammary epithelial cells (1,2). The open reading frame was shown to predict a protein with homology to the amino terminus of the IGF binding proteins, (IGFBP)1-6. Studies in our laboratory have shown that baculovirus generated mac25 binds IGF-I and-II in a specific manner, leading to the renaming of mac25 as IGFBP-7 (3). Further studies at the cellular level, to identify the involvement of IGFBP-7 in IGF regulation and cell growth, require a specific antibody against the protein, which has yet to be identified in either cultured cells or in vivo. We have now generated three polyclonal antibodies against the purified baculovirus peptide and, by western immunoblots and immunoprecipitation, demonstrated the existence of a specific 31,000 dalton protein. It is a secreted protein, and can be identified in the conditioned media of Hs578T breast cancer cells, as well as in normal human urine, cerebrospinal fluid and amniotic fluid. Subsequent studies with these antibodies should help elucidate the physiological role(s) of this protein.

Environmental antiandrogens: developmental effects, molecular mechanisms, and clinical implications

Industrial chemicals and environmental pollutants can disrupt reproductive development in wildlife and humans by mimicking or inhibiting the action of the gonadal steroid hormones, estradiol and testosterone. The toxicity of these so-called environmental endocrine disruptors is especially insidious during sex differentiation and development due to the crucial role of gonadal steroid hormones in regulating these processes. This review describes the mechanism of toxicity and clinical implications of a new class of environmental chemicals that inhibit androgen-mediated sex development. For several of these chemicals, including the agricultural fungicide vinclozolin and the ubiquitous and persistent 1,1,1-trichloro-2,2-bis (p-chlorophenyl)ethane metabolite, 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene, the molecular mechanism of action and the adverse developmental effects on male sex differentiation have been elucidated and are used as examples. Environmental chemicals with antiandrogenic activity offer profound implications with regard to recent clinical observations that suggest an increasing incidence of human male genital tract malformations, male infertility, and female breast cancer. Finally, in light of increasing concern over the potential endocrine disrupting effects of environmental pollutants, an in vitro/in vivo investigational strategy is presented which has proved useful in identifying chemicals with antiandrogen activity and their mechanism of action.

Characterization of an expanded glutamine repeat androgen receptor in a neuronal cell culture system

Spinal and bulbar muscular atrophy (SBMA) is an inherited form of lower motor neuron degeneration caused by expansion of a CAG repeat in the androgen receptor (AR) gene. To study the mechanism by which this mutation causes neuronal pathology, we stably transfected a motor neuron hybrid cell line with human AR cDNAs containing either 24 or 65 repeats (AR24 and AR65, respectively). Both forms of receptor were able to bind ligand and activate transcription of a reporter construct equally well. Likewise, the subcellular localizations of AR24 and AR65 were similar, in both the presence and the absence of ligand. AR24- and AR65-expressing clones were phenotypically indistinguishable. They survived equally well after differentiation and were equally susceptible to damage by oxidative stress. Our studies thus demonstrate that, in a neuronal system, the expanded repeat AR functions like the normal repeat AR in several important ways. Because levels of AR65 expression were consistently lower than levels of AR24 expression, we propose that the loss of function of AR seen in SBMA may be due to decreased levels of receptor expression rather than to a difference in intrinsic properties. The postulated gain of function responsible for neuronal degeneration remains to be determined.

Reduced androgen receptor gene expression with first exon CAG repeat expansion

The molecular basis for partial androgen insensitivity associated with adult onset spinal/bulbar muscular atrophy was investigated by transient transfection of human androgen receptor (AR) expression vectors containing increasing CAG repeat lengths in the first exon. An inverse relationship was observed between CAG repeat length and AR mRNA and protein levels. Trinucleotide repeat lengths of 43 and 65 associated with spinal/bulbar muscular atrophy decreased AR mRNA and protein levels but did not alter equilibrium binding affinity for [3H]R1881 or inherent transcriptional activity of AR, expressed as androgen-dependent fold induction of a mouse mammary tumor virus promoter-luciferase reporter vector. The findings indicate that glutamine expansion up to 66 residues in the NH2-terminal domain of AR does not alter AR functional activity. Rather, CAG repeat expansion in the region of the first exon reduces AR mRNA and protein expression. The study reveals a previously unrecognized effect of CAG repeat length on AR mRNA expression and a novel molecular mechanism for androgen resistance.

Growth inhibition of human prostate cells in vitro by novel inhibitors of androgen synthesis

The long-standing strategy for the treatment of metastatic prostate cancer has been to reduce androgenic stimulation of tumor growth by removal of the testes, the primary site of testosterone synthesis. However, a low level of androgenic stimulation may continue, even after castration, by the conversion of adrenal androgens to 5alpha-dihydrotestosterone (DHT) in the prostate tumor cells. Two important enzymes of the androgen biosynthetic pathway are 17alpha-hydroxylase/C17,20-lyase, which regulates an early step in the synthesis of testosterone and other androgens in both the testes and adrenal glands, and 5alpha-reductase, which converts testosterone to the more potent androgen, DHT, in the prostate. We have identified new inhibitors of these enzymes that may be of use in achieving a more complete ablation of androgens in the treatment of metastatic prostate cancer. Three derivatives of androstene were shown to inhibit 17alpha-hydroxylase/C17,20-lyase with potencies 2-20-fold greater than that of ketoconazole, a previously established inhibitor of this enzyme. Derivatives of pregnane and pregnene displayed activities against 5alpha-reductase that were comparable to that of N-(1,1-dimethyl-ethyl)-3-oxo-4-aza-5alpha-androst-1-ene-17beta-car boxamide. All of the 5alpha-reductase inhibitors were able to at least partially inhibit the mitogenic effect of testosterone in either histocultures of human benign prostatic hypertrophic tissue or in cultures of the LNCaP human prostatic tumor cell line. For these compounds, it appears that this inhibition can be attributed to a reduction of DHT synthesis in these cultures, because no inhibitory effect was observed in DHT-treated cultures, and none of the compounds had a cytotoxic effect. Surprisingly, one of the inhibitors of 17alpha-hydroxylase/C17,20-lyase, 17beta-(4-imidazolyl)-5-pregnen-3beta-ol, was also able to inhibit the mitogenic effect of testosterone in both the histoculture and cell culture assays and had an effect against DHT as well. In transcriptional activation assays, it was found that this compound is an antagonist of both the wild-type androgen receptor and the mutant androgen receptor, which is present in LNCaP cells. In conclusion, the abilities of these compounds to inhibit androgen synthesis and, in some cases, to exert antiandrogen activity, did in fact translate to an inhibitory effect on the growth of human prostatic tissue in vitro, suggesting their potential utility in the treatment of prostatic cancer.

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.