A new mutation of the androgen receptor, P817A, causing partial androgen insensitivity syndrome: in vitro and structural analysis

Androgen insensitivity syndrome (AIS) is an X-linked disease caused by mutations in the androgen receptor (AR) resulting in various degrees of defective masculinization in 46,XY individuals. In the present study, we describe a novel mutation in exon 7 of the AR gene in an Egyptian patient with partial AIS (PAIS). Sequencing analysis of the AR gene revealed a novel missense mutation, P817A, within the ligand-binding domain (LBD). This is the first report of a mutation within the short amino acid motif (codons 815-817) of the beta-strand lying between helices H8 and H9 of the AR LBD. The functional defects of the mutated protein were characterized by in vitro study and included significantly decreased ligand-binding affinity and impaired transactivation potential. Limited proteolysis assays performed with the wild-type and mutant AR receptors incubated with the synthetic agonist R1881 revealed that the P817A mutation resulted in a reduced stabilization of the AR active conformation. Structural analyses showed that this mutation is likely to perturb the beta-sheet interaction between residues 815-817 and 911-913. This structural alteration destabilizes the position of the C-terminal extension, which contains residues critical for androgen function.

[The androgen receptor: molecular pathology]

Androgens play a crucial role in the development, maintenance and regulation of male phenotype and reproductive physiology through the androgen receptor, a transcription factor. Testosterone or dihydrotestosterone binding induces a trans-conformation of the androgen receptor and allows its translocation into the nucleus, where it recognizes specific DNA sequences. Recent developments in molecular genetics, as well as structural analysis of the androgen receptor, allow a better understanding of the structure/function relationship of this nuclear receptor. Molecular analyses of androgen insensitivity syndrome, as well as hormone-resistant prostate cancer, Kennedy's disease and isolated male infertility, have been proved useful as privileged models for this purpose. In the absence of identified AR receptor mutations in androgen insensitivity syndromes, abnormalities of transcriptional cofactor should be considered. Finally, identification of androgen-dependent genes will be helpful for evaluating the degree of the molecular defect of androgen action within target cells.

Disorders of androgen action

Disorders of androgen action are the main cause of male pseudohermaphroditism and include 5alphaR deficiency and androgen receptor defects. 5alphaR deficiency is characterized by female genitalia with some degree of masculinization, clitoromegaly, and severely bifid scrotum corresponding to the so-called pseudovaginal perineoscrotal hypospadias. At the onset of puberty, increased muscle mass, development of pubic hair, and phallic growth are associated with the acquisition of male gender identity. Normal or increased levels of testosterone and an elevated testosterone-to-dihydrotestosterone ratio after human chorionic gonadotropin stimulation testing suggest 5alphareductase deficiency, and the diagnosis can be ascertained by identifying the mutation in the 5alphaR-2 gene. Whatever the patient's age at diagnosis, psychological evaluation with 5alphaRD is vital. Androgen receptor defects encompass two clinical expressions: the complete and partial androgen insensitivity syndromes. Complete androgen insensitivity syndrome should be suspected at birth in the presence of inguinal hernia in a girl without genital ambiguity. At puberty, the sign of alert is primary amenorrhea with normal female phenotype and harmonious mammary development but no pubic hair growth. Partial androgen insensitivity syndrome covers a wide spectrum of undervirilized phenotypes ranging from clitoromegaly at birth to infertile men. In all cases, complementary investigations should include plasma testosterone and luteinizing hormone as well as androgen-binding capacity in cultured genital skin fibroblasts. Diagnosis is confirmed by identification of the androgen receptor gene mutation. Although patients with complete androgen insensitivity syndrome are raised as females, patients with partial androgen insensitivity syndrome should be managed according to age at diagnosis, response to treatment with exogenous androgens, and the presence of an androgen gene mutation. Gonadectomy in complete androgen insensitivity syndrome should be performed before puberty, and androgen substitution may improve the development of external genitalia in some patients with partial androgen insensitivity syndrome. Psychological follow-up is necessary.

Mutant luteinizing hormone receptors in a compound heterozygous patient with complete Leydig cell hypoplasia: abnormal processing causes signaling deficiency

Over the past 5 yr several inactivating mutations in the LH receptor gene have been demonstrated to cause Leydig cell hypoplasia, a rare autosomal recessive form of male pseudohermaphroditism. Here, we report the identification of two new LH receptor mutations in a compound heterozygous case of complete Leydig hypoplasia and determine the cause of the signaling deficiency at a molecular level. On the paternal allele of the patient we identified in codon 343 a T to A transversion that changes a conserved cysteine in the hinge region of the receptor to serine (C343S); on the maternal allele a T to C transition causes another conserved cysteine at codon 543 in trans-membrane segment 5 to be altered to arginine (C543R). Both of these mutant receptors are completely devoid of hormone-induced cAMP reporter gene activation. Using Western blotting of expressed LH receptor protein with a hemagglutinin tag, we further show that despite complete absence of total and cell surface hormone binding, protein levels of both mutant LH receptors are only moderately affected. The expression and study of enhanced green fluorescent protein-tagged receptors confirmed this view and further indicated that initial translocation to the endoplasmic reticulum of these mutant receptors is normal. After that, however, translocation is halted or misrouted, and as a result, neither mutant ever reaches the cell surface, and they cannot bind hormone. This lack of processing is also indicated by reduced presence of an 80-kDa protein, the only N-linked glycosylated protein in the LH receptor protein profile. Thus, complete lack of signaling by the identified mutant LH receptors is caused by insufficient processing from the endoplasmic reticulum to the cell surface and results in complete Leydig cell hypoplasia in this patient.

Human prostatic cell line PNT1A, a useful tool for studying androgen receptor transcriptional activity and its differential subnuclear localization in the presence of androgens and antiandrogens

The human immortalized prostatic cell line PNT1A has been proved to be a good model for analysis of cellular processes such as the prostatic epithelium proliferation in response to androgens and growth factors. Here we used this cell line for studying the transcriptional activity and trafficking of the androgen receptor (AR) by analyzing several actions of antiandrogens. Transient transfection experiments with PNT1A cells were performed with wild type human AR and an androgen-responsive gene reporter. We demonstrated that the transcription of reporter gene could be triggered by natural androgens (testosterone and dihydrotestosterone) in PNT1A cells as well as in the prostatic carcinoma cell line DU-145. With competitive experiments in the two cell lines, we observed no difference between the antagonistic capacity of cyproterone acetate (CPA) and hydroxyflutamide at 10(-7) M. At this concentration, bicalutamide antagonist activity was lower. In parallel, we compared the subcellular localization of the modified green fluorescent protein (EGFP)-AR in COS-7, PNT1A and DU-145 cell lines under fluorescence microscopy: we found different distributions between nucleus and cytoplasm, depending on the cell line and the culture medium. Androgen induced cluster formation within the nucleus of the PNT1A and DU-145 cells. However, the cytonuclear trafficking of androgen bound EGFP-AR in the same living cell and nuclear foci were easier to examine in the PNT1A cells. The antiandrogen capacity of bicalutamide was manifested by a slower androgen-dependent nuclear transfer of EGFP-AR and a homogeneous nuclear localization. A delayed advent of nuclear clusters was observed in presence of CPA. We conclude that the PNT1A cell line is a better model than the DU-145 cell line to analyze the trafficking of AR and the association of AR on the nuclear matrix, as well as to observe the action of antiandrogens on these critical steps in prostate cells.

Environmental xenoestrogens, antiandrogens and disorders of male sexual differentiation

Over the past 20 years, the documented increase in the disorders of male sexual differentiation, such as hypospadias, cryptorchidism, and micropenis, has led to the suspicion that environmental chemicals are detrimental to normal male genital development in utero. Male sexual differentiation is critically dependent on the normal action of androgens, and unbalanced androgen/estrogen ratios can disturb it. Environmental xenoestrogens (such as herbicides, pesticides, PCBs, plasticizers, and polystyrenes) that mimic estrogens or environmental antiandrogens (such as polyaromatic hydrocarbons, linuron, vinclozolin, and pp'DDE) that disturb endocrine balance, cause demasculinizing effects in the male foetus. These environmental chemicals are often referred to as endocrine disruptors: they are thought to mimic endogenous estrogens by entering the cell, binding to the receptor and activating transcription, they may also antagonize normal androgen action. We have established numerous cell lines to assess the estrogenicity and antiandrogenicity of compounds found in the environment and to identify new products present in wastewater effluents that are able to disrupt endocrine functions. Several cell lines responding to estrogens have been obtained in our group, including cells with different enzymatic equipment and cells expressing chimeric receptor or natural estrogen receptors alpha and beta. These cell lines have proved to be useful for assessing the biological activity of pesticides, fungicides, and chemicals found in plastic or discarded in the environment. In order to generate a powerful tool for the investigation of androgen action and the rapid screening of potential antagonists, we developed a new stable prostatic cell line. The PALM cell line is an original cellular model to characterize the response of hAR, and it provides an easy and rapid bioluminescent test to identify new antagonists. We also developed a model based on a fusion protein between the androgen receptor (AR) and the green fluorescent protein (GFP) to study the intracellular dynamics of AR. The GFP-AR model was applied to define the ability of several xenoestrogens and antiandrogens to inhibit the nuclear transfer of AR. The ubiquitous presence of endocrine disruptors in the environment and the increased incidence of neonatal genital malformation support the hypothesis that disturbed male sexual differentiation may in some cases be caused by increased exposure to environmental xenoestrogens and/or antiandrogens.

Disorders linked to insufficient androgen action in male children

Virilization of the external genitalia in the male fetus requires testosterone and dihydrotestosterone (DHT), which is formed from testosterone by the action of the enzyme, 5alpha-reductase type 2 (5alphaR-2). Mediation of the effects of both testosterone and DHT requires a functional androgen receptor (AR) located in the cytoplasmic compartment of target cells. DHT (or testosterone) binding induces a conformational change which facilitates AR nuclear transport, phosphorylation and dimerization, ultimately regulating of the rate of transcription of androgen-dependent genes. Any event which impairs DHT formation (mutation within the 5alphaR-2 gene or 5alphaR-2 inhibitors) or normal function of the AR (mutation in the AR gene, antiandrogens) may result in insufficient androgen action in the male fetus and in subsequent undervirilization in the newborn. Hypospadias may be due to a defect in androgen action due to mutation of the 5alphaR-2 or of the AR gene. Mutation of unidentified genes is likely to underlie this displacement of the urethral meatus from the tip to the ventral side of the phallus. An aetiological role for environmental chemical products has been postulated, since ethnic as well as geographical differences in the incidence of hypospadias have been noted. Increasing evidence has been gathered indicating that widely used industrial and agricultural chemicals have deleterious effects on normal male sexual differentiation. Cryptorchidism and micropenis may represent an intersex phenotype, even if they are isolated. Aetiological factors include 5alphaR-2 gene mutation, AR gene mutation or environmental hormonal disruptors. In conclusion, several phenotypes have been attributed to insufficient androgen action during fetal life. Whereas mutations in the 5alphaR-2 gene and AR gene are natural, attention should be focused on environmental endocrine disruptors that are able to mimic steroid 5alpha-reductase deficiency or partial androgen insensitivity syndrome.

A stable prostatic bioluminescent cell line to investigate androgen and antiandrogen effects

We developed a new stable prostatic cell line expressing the human androgen receptor (AR) and the AR-responsive reporter gene to generate a powerful tool for investigating androgen action and for rapid screening of agonists and antagonists. The AR-deficient PC-3 cells were stably transfected with pSG(5)-puro-hAR and pMMTV-neo-Luc. After selection with puromycin and neomycin, one highly inducible clone was isolated and named PALM, for PC-3-Androgen receptor-Luciferase-MMTV. The expression of hAR was confirmed by western blot and steroid-binding assays on the whole cells. The transcriptional activity of the clone was measured after incubation of cells with increasing concentrations of synthetic R1881 or natural androgens (DHT and testosterone). The three agonists had the same maximal activity at 0.1 microM and the fold induction was equal to 20. The agonist and antagonist activities of the steroidal antiandrogens (cyproterone acetate and RU2956) and the non-steroidal antiandrogens (nilutamide, bicalutamide, inocoterone and hydroxyflutamide) measured with the PALM cells were in good correlation with the results obtained with transiently transfected cells. The selectivity in steroid transactivation was demonstrated with estradiol, progesterone, cortisol, dexamethasone and aldosterone. Spironolactone and RU486 showed partial agonist and antagonist activities, whereas R5020 presented only a partial antagonist activity. We here demonstrate that this stable transfectant provides an accurate tool for studying wild-type human AR activation and its regulation by androgens and antiandrogens in a human prostatic epithelial cell, which is routinely available and remains androgen-responsive in vitro.

Transcriptional interferences between normal or mutant androgen receptors and the activator protein 1--dissection of the androgen receptor functional domains

We investigated the interferences of the normal or mutated androgen receptor with the activator protein-1 (AP-1) by assessing their effects on transcriptional activity in CV-1 cells. A luciferase reporter gene was constructed downstream from either a promoter for the mouse vas deferens protein, or a trimerized 12-O-tetradecanoyl phorbol-13-acetate-response element site whose transcriptions are activated by androgen and 12-O-tetradecanoyl phorbol-13-acetate, a potent AP-1 activator. The blockade of dephosphorylation by protein phosphatases identifies the protein phosphatases that modulate the AP-1/androgen receptor cross-talk. Using engineered or naturally occurring androgen receptor mutants that are responsible for complete or partial androgen insensitivity syndromes, we defined the subregions involved in the cross-talk of the androgen receptor with the AP-1 factors. First, it appears that the 188 first amino acids of the N-terminal domain of the androgen receptor are necessary to obtain a full transrepression. Second, a functional and intact ligand binding domain is critical for the modulation of androgen/AP-1 pathway interactions. Third, normal DNA binding capacity of the androgen receptor is not required. Two mutants at positions 568 and 581 of the DNA binding domain demonstrate that the transactivation and transrepression functions of the androgen receptor can be dissociated. Collectively, these data indicate that several segments of the androgen receptor are involved in cross-talk with the AP-1 pathway. Mutations within the DNA binding domain of the androgen receptor highly impair these interferences.

Trafficking of androgen receptor mutants fused to green fluorescent protein: a new investigation of partial androgen insensitivity syndrome

The naturally occurring mutations of the androgen receptor (AR), detected in patients with androgen insensitivity syndrome (AIS), are currently analyzed by in vitro assays. Unfortunately, these assays do not always permit the demonstration of a direct relationship between the in vitro activity of the receptor and the severity of the phenotype (in particular, for mutations detected in patients with partial AIS). We recently studied the trafficking of wild-type AR, fused to the green fluorescent protein (GFP) in living cells. In the present study, we applied this method for the analysis of AR mutants to find out whether it could be a complementary method of investigation of AIS. After construction of the GFP-AR mutant fusion proteins, the androgen-binding characteristics, nuclear transfer capacities, and transcriptional activities were evaluated. The nuclear transfer was quantified in the presence of various concentrations of dihydrotestosterone (DHT). We studied two mutants associated with partial AIS: G743V and R840C. The androgen-binding characteristics of both mutants were affected, in comparison with normal AR. Although the affinities were similar, the dissociation rate of GFP-AR-G743V was twice that of GFP-AR-R840C. In transcriptional assay, both mutants were active only at high concentrations of androgen. The nuclear trafficking of the mutants was evaluated by two parameters: 1) the rate of nuclear transfer; and 2) the maximal amount of receptors imported into the nucleus. At 10(-6) mol/L DHT, the GFP-AR mutants entered into the nucleus in a fashion similar to that of GFP-AR-wt. At 10(-7) mol/L DHT, the rate and maximal degree of nuclear import were both reduced, even more, for GFP-AR-G743V. The difference between mutants was more pronounced at 10(-9) mol/L DHT, because GFP-AR-G743V entered into the nucleus with even slower kinetics. Though the androgen-binding affinity and transcriptional activity assays did not reveal major differences between mutants, the dissociation rate and the trafficking capacity measurements permitted the activity of the mutants to be differentiated. We observed that the nuclear transfer capacities of these mutants are in correlation with the severity of the phenotype. The GFP-AR model provides an opportunity both to observe the dynamics of the hormone/receptor complex in living cells and to study the impact of the ligand-binding domain mutation, as opposed to certain in vitro techniques. Because the nuclear import capacity correlates well with the degree of androgen insensitivity, the GFP-AR is a useful complementary tool to understanding the phenotype/genotype relationship of AR function in patients with AIS.

Quantitation of androgen receptor messenger RNA from genital skin fibroblasts by reverse transcription--competitive polymerase chain reaction

To gain further information concerning the regulation by androgen of AR mRNA expression in cultured genital skin fibroblasts (GSF), we first developed a quantitative reverse transcription-competitive polymerase chain reaction (RT-PCR). This method used an ethidium bromide stain analysis of the PCR products for the accurate quantitation of low levels of human androgen receptor (hAR) mRNA in GSF. To control for variations due to sample preparation, and to minimize the disparity of the reverse transcriptase efficiency between samples after the RT procedure, we produced an initial PCR for the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene, and then adjusted the amount of cDNA to that of this housekeeping gene. Competitive PCR for hAR was then immediately performed on normalized cDNA with a competitor DNA that exhibited a 13 bp deletion as compared to the 163 bp for the target fragment, and the PCR products were easily separated by 3.5% agarose gel electrophoresis. This quantitation procedure involved no additional steps, such as enzymatic cleavage of the PCR products, nor the use of radioactivity. In GSF from individuals, we found that the normal amount of AR mRNA was 5.6 attomoles/microg RNA, (+/-1.0, s.e.m.) with an intra- and an inter-assay of 8.4 and 14.7%, respectively. We observed a biphasic pattern of AR mRNA expression in normal human GSF in the presence of physiological concentration of androgen. Quantitative RT-PCR of AR mRNA may be useful for studying AR mRNA expression in experimental or clinical conditions.

Trafficking of the androgen receptor in living cells with fused green fluorescent protein-androgen receptor

The trafficking of the androgen receptor (AR) in transfected cells was studied using a green fluorescent protein (GFP)-AR chimera. The reporter molecule GFP enabled the localization of AR in living cells with a good spatial and temporal resolution. After the construction of GFP-AR and verification of the size of the fusion protein produced, we demonstrated that GFP-AR conserves the functional properties of the AR: GFP-AR had the same androgen-binding affinity as AR, and GFP-AR efficiently transactivated an androgen-responsive gene in response to synthetic androgen at 30 degrees C. The fusion protein was first detected throughout the cytoplasm without hormone, fluorescence becoming nuclear rapidly after androgen incubation. This hormone dependence of AR trafficking was confirmed by the use of the mutant GFP-AR-del4, which lacked the androgen-binding function. The mutant was localized in the cytoplasm in the absence of hormone, but the distribution was not modified by androgen incubation. An ACAS 570 scanning laser cytometer was used to quantify fluorescence in a single living cell, first without and then with hormone. Different hormones and antihormones were tested to determine the dynamics of GFP-AR translocation into the nucleus. All the drugs used were able to induce nuclear translocation, and steady state level was rapidly attained within 1 h. The ratio of receptors in cytoplasmic and nuclear compartments was related to both affinity and concentration of ligand. The data from this follow-up study demonstrated for the first time the intracellular dynamics of the hormone-dependent trafficking of AR in a single living cell.

A novel substitution (Leu707Arg) in exon 4 of the androgen receptor gene causes complete androgen resistance

A wide spectrum of androgen receptor (AR) gene mutations has been reported in complete androgen insensitivity syndromes. The molecular basis of androgen resistance was investigated in a female newborn with complete testicular feminization. Sequencing identified a point mutation in exon 4 responsible for a leucine (CTG) to arginine (CGG) replacement at codon 707. This novel mutation is located in the amino-terminal part of the ligand-binding domain of the AR. To determine the functional properties of the mutated AR and to establish the correlation with the clinical phenotype of androgen resistance, the mutation was reproduced in AR wild-type complementary DNA, and the plasmid was transfected into AR-free mammalian cells. In vitro studies showed that the mutant AR was functionally defective as an androgen-binding molecule. Electrophoretic mobility shift assay revealed that the binding of mutated AR to DNA was reduced. Finally, the mutant was unable to induce the transcriptional activation of androgen-responsive reporter gene. This amino acid defect in the primary sequence probably involves the rupture of hydropathicity in a region that is conserved among members of the steroid receptor subfamily. Our data substantiate the major contribution of leucine 707 to normal AR function and demonstrate that its substitution by an arginine caused the complete androgen insensitivity in this patient. Our findings also contribute to the elaboration of the structure-function map of the AR based on naturally occurring mutations.

Immunohistochemical localization and immunoblotting of androgen receptor in spinal neurons of male and female rats

Androgen activity in the central nervous system, as in other tissues, is mediated by the androgen receptor. We performed the precise localization of the androgen receptor in spinal cord of male and female adult rats by immunohistochemistry using polyclonal antibodies. Light microscopy indicated immunoreactivity in the anterior horn with a strong staining in motoneurons, but staining was also observed in the posterior horn. Electron microscopy showed a predominant nuclear immunostaining. A weaker but significant immunoreactive androgen receptor was also noted in the perinuclear/ intracysternal position. Moreover, no differences were found between male and female rats. Immunoblotting demonstrated that the androgen receptor is expressed in both ventral and dorsal spinal cord, with an apparent molecular mass identical to that noted in other androgen-dependent tissues. The expression of androgen receptor in motoneurons corroborates the role of androgens in motoneuron growth, development and regeneration and underlies the possibility that androgen receptor abnormality leads to the motoneuron degeneration observed in X-linked spinal and bulbar muscular atrophy.

Complete androgen insensitivity syndrome due to a new frameshift deletion in exon 4 of the androgen receptor gene: functional analysis of the mutant receptor

We studied the androgen receptor gene in a large kindred with complete androgen insensitivity syndrome and negative receptor-binding activity, single-strand conformation polymorphism (SSCP) analysis and sequencing identified a 13 base pair deletion within exon 4. This was responsible for a predictive frameshift in the open reading frame and introduction of a premature stop codon at position 783 instead of 919. The deletion was reproduced in androgen receptor wildtype cDNA and transfected into mammalian cells. Western blot showed a smaller androgen receptor of 94 kDa for the transfected mutated cDNA instead of 110 kDa. Androgen-binding assay of the mutated transfected cells assessed the lack of androgen-binding. Gel retardation assay demonstrated the ability of the mutant to bind target DNA; however, the mutant was unable to transactivate a reporter gene. Although the role of the partial deletion in the lack of androgen action was expected, in vitro analyses highlight the role of the abnormal C-terminal portion in the inhibition of the receptor transregulatory activity of the protein causing androgen resistance in this family.