The androgen receptor gene mutations database (ARDB): 2004 update

Genomic biomarkers, androgen pathway and prostate cancer

Prostate cancer is the most frequent male malignancy diagnosed in western countries and the second leading cause of cancer-related deaths. The growth and function of the prostate gland depends on androgens. Owing to the importance of androgens in prostate development, genes involved in androgen biosynthesis and metabolism have been extensively studied. In this review, we address recent progress toward the use of inherited and acquired genetic variants to predict susceptibility and clinical outcomes of prostate cancer patients. Many of these genetic variants involve several genes related to the biosynthesis and metabolism of androgens, such as steroid-5-α-reductase, α polypeptide 2 (SRD5A2), cytochrome P450 (CYP)19A1, CYP17A1, hydroxy-δ-5-steroid dehydrogenase, 3 β- and steroid δ-isomerase 2 (HSD3B2) and androgen receptor (AR). With increasing knowledge, it may be possible to distinguish indolent from aggressive prostate tumors by molecular fingerprinting. Furthermore, with the emergence of new investigative tools, such as microarray platforms and comparative genomic hybridization (CGH) array, a variety of new genomic biomarkers will be available in the future to provide accurate prognostic and monitoring solutions for individualized patient care.

Phenotypic heterogeneity of mutations in androgen receptor gene

Androgen receptor (AR) gene has been extensively studied in diverse clinical conditions. In addition to the point mutations, trinucleotide repeat (CAG and GGN) length polymorphisms have been an additional subject of interest and controversy among geneticists. The polymorphic variations in triplet repeats have been associated with a number of disorders, but at the same time contradictory findings have also been reported. Further, studies on the same disorder in different populations have generated different results. Therefore, combined analysis or review of the published studies has been of much value to extract information on the significance of variations in the gene in various clinical conditions. AR genetics has been reviewed extensively but until now review articles have focused on individual clinical categories such as androgen insensitivity, male infertility, prostate cancer, and so on. We have made the first effort to review most the aspects of AR genetics. The impact of androgens in various disorders and polymorphic variations in the AR gene is the main focus of this review. Additionally, the correlations observed in various studies have been discussed in the light of in vitro evidences available for the effect of AR gene variations on the action of androgens.

Somatic mutations at the trinucleotide repeats of androgen receptor gene in male hepatocellular carcinoma

Androgen and androgen receptor (AR) have long been implicated in liver carcinogenesis, especially for the male dominance feature. However, whether AR gene could occur in somatic mutations that might contribute to this process has not yet been studied. DNA sequencing and genotyping were conducted for detecting the genetic aberrations of AR gene in 257 primary hepatocellular carcinomas (HCCs) and also the dysplastic nodules (DN) from another 11 patients. Twenty-one AR somatic mutations causing amino acid changes were identified in HCC and even in the precancerous DN. The missense somatic mutations of AR were rare in HCC (2 cases) but the trinucleotide repeat (TNR) changes, both at (CAG)n and (GGC)n, was a more common one (19 cases). Notably, all these mutations occurred in male patients and most TNR changes belonged to the contraction type (15 out of 19 cases, 78.9%), which has been reported to associate with increased AR transcriptional activity. Most samples with TNR changes did not show microsatellite instability, suggesting a different cause for these TNR mutations. Although no significant correlation was identified between AR mutations and the clinicopathologic parameters, we found the (CAG)n length significantly shorter in hepatitis B virus (HBV)(+) HCCs than in HBV(-) HCCs and the (GGC)n length significantly correlates with the overall survival. In conclusion, the mis-sense somatic mutations of AR were rare in HCC but the TNR change was a more common one, which exclusively occurred in males. Moreover, the length of TNR carried clinical significance in special HCC group.

Drug Insight: role of the androgen receptor in the development and progression of prostate cancer

Functional androgen receptor (AR) signaling is necessary for the development of prostate cancer. The therapeutic effect of androgen deprivation therapy for prostate cancer was described over 60 years ago and this treatment remains the mainstay of systemic therapy despite its transient response duration. It has become clear that AR expression and signaling remains intact as the disease evolves from androgen-sensitive cancer to classically (but perhaps inaccurately) termed hormone refractory prostate cancer. Through several genetic and epigenetic adaptations, prostate tumors continue to rely on AR growth signaling and they thus remain targets of 'hormonal' therapy. The development of new strategies and drugs that can abrogate AR signaling will probably result in important clinical benefits. The biology of androgen independence and the development of new approaches targeting AR signaling are reviewed herein.

Uncoupling of hormone-dependence from chaperone-dependence in the L701H mutation of the androgen receptor

The mechanisms underlying androgen receptor (AR)-mediated progression of prostate cancer following androgen ablation have yet to be fully determined. On this basis we screened naturally occurring mutants of human AR for hormone-independent activity using a yeast model system. An initial screen of 43 different mutants revealed that ARs having a Leu701His mutation (AR(L701H)) exhibited hormone-independent activation of a lacZ reporter gene. The AR(L701H) mutant bound dihydrotestosterone to a similar extent as did wild type AR, although its ability to be induced by hormone for transactivation was reduced substantially. Subsequent studies focused on the dependence of AR(L701H) on molecular chaperones for folding to the active state. We found that AR(L701H) was highly dependent on Hsp90 for its hormone-independent activation, suggesting that this chaperone functions in AR(L701H) folding. However, the mutant did not respond specifically to increased levels of FKBP52, suggesting that this chaperone functions at the hormone-dependent activation stage in the folding process. Further studies of AR(L701H) in PC3 cells suggested that this mutant is prohibited from hormone-independent transactivation in mammalian cells. However, basal expression of a reporter gene by AR(L701H) was not impaired by the presence of 17-allylamino-17-demethoxygeldanamycin as was wild type AR, suggesting differential interactions of these receptors with molecular chaperones in animal cells.

A differential ligand-mediated response of green fluorescent protein-tagged androgen receptor in living prostate cancer and non-prostate cancer cell lines

Androgen has been shown to promote the proliferation of prostate cancer through the action of the androgen receptor (AR). Mutation (T877A) of the AR gene found in an androgen-sensitive prostate cancer cell line, LNCaP, has been postulated to be involved in hypersensitivity and loss of specificity for androgen. In the present study, trafficking of AR and AR (T877A) in living prostate and non-prostate cancer cell lines under high and low concentrations of androgen and antiandrogen was investigated by tagging green fluorescent protein (GFP) to the receptors. In the presence of a high concentration of androgen, AR-GFP localized in the nucleus by forming discrete clusters in all cell lines. AR (T877A)-GFP was also translocated to the nucleus in LNCaP and COS-1 cells by the addition of a high concentration of androgen. In contrast, in the presence of a low concentration of androgen, the translocation of AR-GFP and AR (T877A)-GFP was observed in LNCaP cells, but not in COS-1 cells. Upon the addition of antiandrogen, AR-GFP was translocated to the nucleus but did not form subnuclear foci in both COS-1 and LNCaP cells, whereas AR (T877A)-GFP in both cells was translocated to the nucleus with subnuclear foci. The present study demonstrates the differential response of nuclear trafficking of AR and its mutant in prostate cancer cell lines and COS cells, and the subcellular and subnuclear compartmentalization provide important information on the sensitivity of the AR mutation.

The androgen receptor DNA-binding domain determines androgen selectivity of transcriptional response

The AR (androgen receptor) is a hormone-dependent transcription factor that translates circulating androgen hormone levels into a physiological cellular response by directly regulating the expression of its target genes. It is the key molecule in e.g. the development and maintenance of the male sexual characteristics, spermatocyte production and prostate gland development and growth. It is also a major factor in the onset and maintenance of prostate cancer and a first target for pharmaceutical action against the further proliferation of prostate cancer cells. The AR is a member of the steroid hormone receptors, a group of steroid-inducible transcription factors sharing an identical consensus DNA-binding motif. The problem of how specificity in gene activation is achieved among the different members of this nuclear receptor subfamily is still unclear. In this report, we describe our investigations on how the AR can specifically activate its target genes, while the other steroid hormone receptors do not, despite having the same consensus monomeric DNA-binding motif. In this respect, we describe how the AR interacts with a newly identified class of steroid-response elements to which only the AR and not, for example, the glucocorticoid receptor can bind.

Identification of Putative Androgen Receptor Interaction Protein Modules

We have developed a novel androgen receptor (AR) expression system in the 293 human embryonic kidney cell line that recapitulates AR biochemical activity as a steroid hormone receptor in prostate cancer cells. We used this system to identify putative AR-binding proteins in the cytosolic and nuclear compartments of mammalian cells using a large scale co-immunoprecipitation strategy coupled to quantitative mass spectrometry. For example, the heat shock 70 and 90 chaperones, which are known regulators of steroid hormone receptor, were identified as AR-binding proteins. AR purification enriched for proteins involved in RNA processing, protein transport, and cytoskeletal organization, suggesting a functional link between AR and these protein modules in mammalian cells. For example, AR purification in the nuclear compartment led to the specific enrichment of alpha-actinin-4, clathrin heavy chain, and serine-threonine protein kinase C delta. Short interfering RNA knockdown studies and co-transcriptional reporter assays revealed that clathrin heavy chain possessed co-activator activity during AR-mediated transcription, whereas alpha-actinin-4 and protein kinase C delta displayed both co-activator and co-repressor activity during AR-mediated transcription that was dependent upon their relative expression levels. Lastly immunohistochemical staining of prostate tissue showed that alpha-actinin-4 levels decreased in the nucleus of high grade cancerous prostate samples, suggesting its possible deregulation in advanced prostate cancers as previously observed in late stage metastatic breast cancers. Taken together, these findings suggest AR binds to specific protein modules in mammalian cells and that these protein modules may provide a molecular framework for interrogating AR function in normal and cancerous prostate epithelial cells.

Prostate cancer: Re-focusing on androgen receptor signaling

Prostate cancer is the most common, non-dermatologic cancer in men. Since prostate cancer is highly associated with increased age, the incidence of this disease is expected to increase as the population ages. In its initial stages prostate cancer depends upon the actions of androgen, and androgen deprivation therapy induces tumor regression. Currently, androgen deprivation is achieved by either surgical or chemical androgen blockade. Unfortunately, nearly all prostate cancer patients develop tumors that grow despite androgen blockade and ultimately relapse. Many alterations in prostate cancer cells contribute to this state. Although chemotherapy induces short remissions in some patients, there are no curative therapies for metastatic disease. This review summarizes our current understanding in androgen signaling and the mechanisms that allow tumor cells to bypass androgen manipulation therapy. The identification of novel survival pathways and effector molecules that drive androgen independent growth is necessary to develop effective therapies for advanced prostate cancers.

A naturally occurring mutation in the human androgen receptor of a subject with complete androgen insensitivity confers binding and transactivation by estradiol

The clinical phenotype of complete androgen insensitivity (CAIS) was associated with a mutation in the human androgen receptor (hAR) gene encoding the amino acid substitution, M745I, in the hAR protein. Transcriptional activation of hAR(M745I) by the synthetic androgen, methyltrienolone (R1881), was reduced compared to wild-type (wt) hAR. The transcriptional co-activator, androgen receptor associated protein 70 (ARA70), failed to enhance transactivation of hAR(M745I) at lower concentrations of R1881 (0.01-0.1 nM), whereas the p160 co-activators, SRC-1 and TIF2, stimulated activity. Transcriptional activity of hAR(M745I) was stimulated by 1 or 10 nM R1881 and activity was further enhanced by co-expression of ARA70 similar to that of the hAR(wt). Transcriptional activity of hAR(wt) was minimally stimulated by estradiol (E2) without or with co-expression of ARA70, whereas 10 or 100 nM E2 increased transactivation by hAR(M745I) of the androgen-responsive MMTV-luciferase reporter gene by 10-fold and activity was further enhanced by ARA70. Increasing concentrations of E2 competed more effectively for binding of R1881 to hAR(M745I) than to hAR(wt), indicative of the preferential binding of E2 to the mutant hAR. Partial tryptic digestion of hAR wt and M745I revealed that activation of the mutant protein was reduced in the presence of R1881. By contrast, tryptic digestion showed that the mutant hAR was activated by the binding of E2. In conclusion, the clinical phenotype of CAIS resulted from a hAR gene mutation encoding hAR(M745I) with reduced binding and transactivation by androgens, but the novel properties of enhanced affinity for and increased transactivation by estradiol.

Unexpected paracrine action of prostate cancer cells harboring a new class of androgen receptor mutation—A new paradigm for cooperation among prostate tumor cells

The emergence of mutations in the androgen receptor (AR) gene is a recurrent event during progression of prostate cancer (PCa) on androgen ablation therapy. In this study, we show that nonsense mutations that lead to carboxyl-terminal end truncated ARs are found at high frequency in metastatic PCas. Transcriptional activities of the Q640X mutant AR in the androgen-sensitive LNCaP cell line differ to those of the wild-type AR. Indeed, this mutant AR exhibits strong and ligand-independent transcriptional activities from an artificial promoter construct containing two repeats of androgen-responsive elements, but is inactive on the human PSA gene promoter. Nevertheless, the expression of the Q640X mutant AR in LNCaP cells is accompanied by an increase in the level of PSA protein, and by an increase in the expression of the endogenous AR gene. This enhanced expression of the endogenous AR gene is not limited to the sole transfected cells, but is observed in non-transfected neighboring cells. Additionally, in co-cultures of transfected and non-transfected LNCaP cells, the Q640X mutant AR leads to an unpredicted nuclear localization of the endogenous AR protein in the two cellular populations and this, in the absence of androgen. These data indicate that cells expressing the Q640X mutant AR acquire the property to emit a signal that activates the AR in neighboring cells by a paracrine mechanism and in a ligand-independent manner. Our data strongly support the notion of cooperation among tumor cells in PCa and could be of relevance for the understanding of progression on androgen ablation therapy.

Bisphenol A facilitates bypass of androgen ablation therapy in prostate cancer

Prostatic adenocarcinomas depend on androgen for growth and survival. First line treatment of disseminated disease exploits this dependence by specifically targeting androgen receptor function. Clinical evidence has shown that androgen receptor is reactivated in recurrent tumors despite the continuance of androgen deprivation therapy. Several factors have been shown to restore androgen receptor activity under these conditions, including somatic mutation of the androgen receptor ligand-binding domain. We have shown previously that select tumor-derived mutants of the androgen receptor are receptive to activation by bisphenol A (BPA), an endocrine-disrupting compound that is leached from polycarbonate plastics and epoxy resins into the human food supply. Moreover, we have shown that BPA can promote cell cycle progression in cultured prostate cancer cells under conditions of androgen deprivation. Here, we challenged the effect of BPA on the therapeutic response in a xenograft model system of prostate cancer containing the endogenous BPA-responsive AR-T877A mutant protein. We show that after androgen deprivation, BPA enhanced both cellular proliferation rates and tumor growth. These effects were mediated, at least in part, through androgen receptor activity, as prostate-specific antigen levels rose with accelerated kinetics in BPA-exposed animals. Thus, at levels relevant to human exposure, BPA can modulate tumor cell growth and advance biochemical recurrence in tumors expressing the AR-T877A mutation.

Androgen resistance

Androgen resistance causes the androgen insensitivity syndrome in its variant forms and is a paradigm of clinical syndromes associated with hormone resistance. In its complete form, the syndrome causes XY sex reversal and a female phenotype. Partial resistance to androgens is a common cause of ambiguous genitalia of the newborn, but a similar phenotype may result from several other conditions, including defects in testis determination and androgen biosynthesis. The biological actions of androgens are mediated by a single intracellular androgen receptor encoded by a gene on the long arm of the X chromosome. Mutations in this gene result in varying degrees of androgen receptor dysfunction and phenotypes that often show poor concordance with the genotype. Functional characterization and three-dimensional modelling of novel mutant receptors has been informative in understanding the mechanism of androgen action. Management issues in syndromes of androgen insensitivity include decisions on sex assignment, timing of gonadectomy in relation to tumour risk, and genetic and psychological counselling.

Mutation screening of the androgen receptor promoter and untranslated regions in prostate cancer

BACKGROUND

Mechanisms, other than gene amplification, leading to overexpression of AR in androgen ablation-resistant prostate cancer remain unknown and could include genetic alterations in the promoter or untranslated regions (UTR) of the AR gene.

MATERIALS AND METHODS

DNAs from five prostate cancer cell lines, 19 LuCaP xenografts, 44 clinical tumors, and 36 non-malignant controls were used for screening mutations in the upstream regulatory region, promoter and the 5'- and 3'-UTRs of the AR gene with denaturating high performance liquid chromatography (DHPLC) and sequencing.

RESULTS

Ten different sequence variations were found in prostate cancer cell lines and xenografts. However, none of them were recurrent or were found in clinical prostate cancer specimens or in normal controls.

CONCLUSIONS

Recurrent mutations in the promoter or UTRs of AR seem to be rare, and thus not likely mechanisms for the increased expression of the gene in the androgen ablation-resistant prostate cancer.

Male infertility and androgen receptor gene mutations: clinical features and identification of seven novel mutations

OBJECTIVE

Androgens and a functioning androgen receptor (AR) are essential for development and maintenance of the male phenotype and spermatogenesis. Consistent with this, mutations in the AR gene cause a variety of defects related to androgen insensitivity, ranging from complete feminization to phenotypic males with infertility. The aim of his study was to analyse the prevalence of AR gene mutations in male infertility and to clarify the genotype-phenotype relation.

DESIGN

Males with infertility were recruited consecutively at the Centre for Male Gamete Cryopreservation at the University of Padova from January 1996 to January 2005.

PATIENTS

One thousand five hundred and seventeen men with < 10 million sperm/ml and 310 age-matched normozoospermic controls.

METHODS

Screening for AR gene mutation was done by DHPLC and sequencing, and reproductive hormone concentrations were measured.

RESULTS

We found 20 mutations in 26 of 1517 patients (1.7%) and no mutations in controls. A high number of mutations localized in exon 1 of the AR gene coding for the transactivation domain of the protein. Of 20 mutations, 7 represent novel mutations. With respect to men without AR mutations, subjects with AR mutations have lower ejaculate volume, higher testosterone levels, higher oestradiol levels, and higher androgen sensitivity index. However, the ranges for these variables were highly overlapping between men with and without AR gene mutations. Also clinical manifestations of AR mutations are not unique and 22 men had only spermatogenic impairment.

CONCLUSIONS

AR gene mutations are quite frequent in unselected infertile men but no specific hormonal or clinical data could be used to preselect patients at risk of mutations.

An automated procedure to identify biomedical articles that contain cancer-associated gene variants

The proliferation of biomedical literature makes it increasingly difficult for researchers to find and manage relevant information. However, identifying research articles containing mutation data, a requisite first step in integrating large and complex mutation data sets, is currently tedious, time-consuming and imprecise. More effective mechanisms for identifying articles containing mutation information would be beneficial both for the curation of mutation databases and for individual researchers. We developed an automated method that uses information extraction, classifier, and relevance ranking techniques to determine the likelihood of MEDLINE abstracts containing information regarding genomic variation data suitable for inclusion in mutation databases. We targeted the CDKN2A (p16) gene and the procedure for document identification currently used by CDKN2A Database curators as a measure of feasibility. A set of abstracts was manually identified from a MEDLINE search as potentially containing specific CDKN2A mutation events. A subset of these abstracts was used as a training set for a maximum entropy classifier to identify text features distinguishing "relevant" from "not relevant" abstracts. Each document was represented as a set of indicative word, word pair, and entity tagger-derived genomic variation features. When applied to a test set of 200 candidate abstracts, the classifier predicted 88 articles as being relevant; of these, 29 of 32 manuscripts in which manual curation found CDKN2A sequence variants were positively predicted. Thus, the set of potentially useful articles that a manual curator would have to review was reduced by 56%, maintaining 91% recall (sensitivity) and more than doubling precision (positive predictive value). Subsequent expansion of the training set to 494 articles yielded similar precision and recall rates, and comparison of the original and expanded trials demonstrated that the average precision improved with the larger data set. Our results show that automated systems can effectively identify article subsets relevant to a given task and may prove to be powerful tools for the broader research community. This procedure can be readily adapted to any or all genes, organisms, or sets of documents.

Androgen receptor gene mutations in androgen insensitivity syndrome cause distinct patterns of reduced activation of androgen-responsive promoter constructs

Assessment of quantitative impairment of reporter gene activation is an important strategy proving pathogenetic relevance of androgen receptor (AR)-gene mutations in androgen insensitivity syndrome (AIS). We hypothesized the additional existence of mutation-specific patterns of reduced target gene activation. Four AR-gene mutations causing AIS, L712F, M780I, R855H, and V866M, respectively, were recreated in an AR-expression plasmid. Activation of three structurally different androgen-dependent promoters (MMTV, (ARE)2TATA, and GRE-OCT) was measured in transfected CHO-cells in response to dihydrotestosterone (DHT), testosterone, androstenedione and stanozolol (S). V866M showed the lowest activity across all conditions. R855H exhibited strikingly high activation of MMTV in response to DHT. M780I showed markedly low activation of (ARE)2TATA by S. L712F demonstrated high activation of GRE-OCT. In essence, each mutation was characterized in this model by a specific pattern of reduced reporter gene activation. Our AR crystal structure analyses showed that L712 and M780 may cause distinct alterations of AR-ligand- and AR-coregulator interaction interfaces supporting the experimental observations. Our data support the hypothesis that mutations of the AR-gene in AIS induce mutation-specific patterns of reduced promoter activation in vitro. Considering the diversity of natural androgen-regulated promoters, mutation-specific differences of androgen response patterns may be of relevance in vivo and consequently may influence the AIS-phenotype. Assessment of transactivation patterns in vitro may be an interesting concept to extend functional description of AR-gene mutations in AIS.

Cell-line and tissue-specific signatures of androgen receptor-coregulator transcription

Normal genital skin fibroblasts (GSF) and the human prostate carcinoma cell line LNCaP have been used widely as cell culture models of genital origin to study androgen receptor (AR) signaling. We demonstrate that LNCaP shows a reproducible response to androgens as assessed using cDNA-microarrays representing approximately 32,000 unique human genes, whereas several independent GSF strains are virtually unresponsive. We show that LNCaP cells express markedly higher AR protein levels likely contributing to the observed differences of androgen responsiveness. However, previous data suggested that AR-expression levels alone do not determine androgen responsiveness of human GSF compared to LNCaP. We hypothesized that cell-specific differences in expression levels of AR coregulators might contribute to differences in androgen responsiveness and might be found by comparing LNCaP and GSFs. Using the Canadian McGill-database of AR coregulators ( http://www.mcgill.ca/androgendb ), we identified 61 AR-coregulator genes represented by 282 transcripts on our microarray platform that was used to measure transcript profiles of LNCaP and GSF cells. Baseline expression levels of 48 AR-coregulator transcripts representing 33 distinct genes showed significant differences between GSF and LNCaP, four of which we confirmed by reverse transcriptase polymerase chain reaction. Compared to LNCaP, GSFs displayed significant upregulation of AR coregulators that can function as repressors of AR-transactivation, such as caveolin 1. Analysis of a recently published comprehensive dataset of 115 microarrays representing 35 different human tissues revealed tissue-specific signatures of AR coregulators that segregated with ontogenetically related groups of tissues (e.g., lymphatic system and genital tissues, brain). Our data demonstrate the existence of cell-line and tissue-specific expression patterns of molecules with documented AR coregulatory functions. Therefore, differential expression patterns of AR coregulators could modify tissue-specificity and diversity of androgen actions in development, physiology, and disease.

Sexualmedizinische Aspekte bei Intersexsyndromen

Disorders of somatosexual development that lead to ambiguous genitalia occur in one from 3,000-5,000 newborns. Parents and health care professionals are confronted with a number of crucial questions: to what sex should the child be assigned, what is the appropriate treatment in terms of hormonal and surgical interventions, when and how should these take place, and what impact do they have on the development of gender identity (GI), psychosexual well-being and fertility? This paper reviews the etiology, treatment and outcome in terms of GI and sexual health for the following syndromes: congenital adrenal hyperplasia (CAH), complete and partial androgen insensitivity (cAIS, pAIS), and pure and mixed gonadal dysgenesis (pGD, mGD). Emphasis is focussed on the current discussion involving the timing and extent of genital surgery. Finally, a procedure is introduced that covers the sexual-medical needs of patients, parents and health care professionals.

Mechanisms leading to the development of hormone-resistant prostate cancer

Advanced and metastatic prostate cancers remain potentially lethal tumors. Although androgen deprivation therapy remains the most effective treatment, patients who progress to androgen independence die of their disease. This article focuses on the mechanisms by which hormone resistance develops, including the reactivation of androgen receptor during androgen deprivation therapy, the role of cancer stem cells, and the emergence of epithelial-mesenchymal transition cells, which have increased metastatic potential. It is through an enhanced understanding of these mechanisms that new therapies can be developed to combat this disease.

Predicting the oncogenicity of missense mutations reported in the International Agency for Cancer Research (IARC) mutation database on p53

Many mutation databases, comprising thousands of reported mutations, are available. Often the clinical significance of the reported mutations is unknown. In this study we developed an algorithm that allows prediction of the clinical significance of missense mutations reported in a mutation database. Nonsense mutations are used as a referent group for this assessment. We used the International Association for Research on Cancer (IARC) mutation database on TP53 to implement the algorithm. First, on the basis of published data [Nachman MW, Crowell SL. 2000. Genetics 156:297-304], we ascribed mutation rates to every single nucleotide substitution (SNS) in the core domain of the TP53 gene. Second, for every possible SNS we computed the expected number of missense mutations, under the assumption that missense mutations are as oncogenic as nonsense ones. The natural logarithm of the ratio of the observed to the expected number of missense mutations (LR) was used as a quantitative measure of oncogenicity (i.e., the ability of a mutation to produce cancer). We estimated the relative oncogenicity of all missense mutations reported in the IARC p53 mutation database, and constructed a profile of oncogenicity of the missense mutations along the DNA-binding region of p53.

Androgen receptor as a therapeutic target for androgen independent prostate cancer

Prostate cancer is the leading cause of nonskin malignancy and the second leading cause of cancer death in men. Androgen deprivation therapy is the first-line of systemic therapy against advanced prostate cancer. All advanced prostate cancers eventually grow despite castrate levels of testosterone. We review the evidence that androgen independent prostate cancer continues to require androgen receptor activity for growth, the mechanisms of androgen receptor activation in the castrate setting, and possible points of intervention for novel therapies targeting the androgen receptor and prostate cancer.

Novel FXXFF and FXXMF motifs in androgen receptor cofactors mediate high affinity and specific interactions with the ligand-binding domain

Upon hormone binding, a hydrophobic coactivator binding groove is induced in the androgen receptor (AR) ligand-binding domain (LBD). This groove serves as high affinity docking site for alpha-helical FXXLF motifs present in the AR N-terminal domain and in AR cofactors. Study of the amino acid requirements at position +4 of the AR FXXLF motif revealed that most amino acid substitutions strongly reduced or completely abrogated AR LBD interaction. Strong interactions were still observed following substitution of Leu+4 by Phe or Met residues. Leu+4 to Met or Phe substitutions in the FXXLF motifs of AR cofactors ARA54 and ARA70 were also compatible with strong AR LBD binding. Like the corresponding FXXLF motifs, interactions of FXXFF and FXXMF variants of AR and ARA54 motifs were AR specific, whereas variants of the less AR-selective ARA70 motif displayed increased AR specificity. A survey of currently known AR-binding proteins revealed the presence of an FXXFF motif in gelsolin and an FXXMF motif in PAK6. In vivo fluorescence resonance energy transfer and functional protein-protein interaction assays showed direct, efficient, and specific interactions of both motifs with AR LBD. Mutation of these motifs abrogated interaction of gelsolin and PAK6 proteins with AR. In conclusion, we have demonstrated strong interaction of FXXFF and FXXMF motifs to the AR coactivator binding groove, thereby mediating specific binding of a subgroup of cofactors to the AR LBD.

Targeting the androgen receptor in hormone-refractory prostate cancer--new concepts

The androgen receptor (AR) plays a key regulatory role in hormone-naive, as well as in advanced, therapy-resistant prostate cancer. Therefore, the development of novel treatment strategies using new means for targeting AR function in prostate tumors aims at providing better options for control of progression and progressive disease. This review summarizes recent attempts in this field with a critical view on their clinical usefulness. In addition to classic endocrine therapy by surgical and/or chemical castration, there are concepts to inhibit the AR directly through anti-androgens, selective AR modulators, naturally occurring AR inhibitors, neutralizing antibodies and dominant-negative peptides. A unique possibility to prevent AR expression at the transcriptional level represents the use of antisense technology. The advantage of this method is that AR expression, and thus any aberrant route of its activation is prevented. Furthermore, there are several approaches by which AR signaling is inactivated indirectly. Degradation of heat-shock proteins, which direct appropriate AR protein folding, or modulation of various growth factor signaling cascades, which are thought to contribute to AR activation in the androgen-deprived patient, have been investigated.

An uncommon large deletion in the androgen-receptor gene in a XY female with complete androgen insensitivity syndrome

Androgen insensitivity is a disorder characterized by an abnormal male sexual development, in which the androgen action is impaired due to structural defects in the androgen receptor gene. We report a case of a 46,XY subject with female phenotype (normal breast and external genitalia) lacking sexual hair, affected with primary amenorrhea. In this patient, we found a deletion of a large region of the androgen receptor gene encoding the steroid-binding domain of the protein, causing a complete inability to bind the androgens. This uncommon molecular defect impaired the expression of androgen-dependent genes inducing the female phenotype.

Metastasis-associated protein 2 is a repressor of estrogen receptor alpha whose overexpression leads to estrogen-independent growth of human breast cancer cells

Estrogen receptor (ER)alpha activity is controlled by the balance of coactivators and corepressors contained within cells that are recruited into transcriptional complexes. The metastasis-associated protein (MTA) family has been demonstrated to be associated with breast tumor cell progression and ERalpha activity. We demonstrate that MTA2 expression is correlated with ERalpha protein expression in invasive breast tumors. We show that the MTA2 family member can bind to ERalpha and repress its activity in human breast cancer cells. Furthermore, it can inhibit ERalpha-mediated colony formation and render breast cancer cells resistant to estradiol and the growth-inhibitory effects of the antiestrogen tamoxifen. MTA2 participates in the deacetylation of ERalpha protein, potentially through its associated histone deacetylase complex 1 activity. We hypothesize that MTA2 is a repressor of ERalpha activity and that it could represent a new therapeutic target of ERalpha action in human breast tumors.

Probing the Functional Link between Androgen Receptor Coactivator and Ligand-binding Sites in Prostate Cancer and Androgen Insensitivity

The androgen receptor (AR) is a ligand-activated transcription factor required for male sex development and virilization and contributes to prostate cancer initiation and progression. High affinity androgen binding triggers conformational changes required for AR transactivation. Here we characterized naturally occurring AR gene mutations in the region of activation function 2 (AF2) that decrease or increase AR transcriptional activity by altering the region bounded by AF2 and the ligand binding pocket without affecting equilibrium androgen binding affinity. In the androgen insensitivity syndrome, germ line AR mutations increase the androgen dissociation rate and reduce AR FXXLF motif binding and the recruitment of steroid receptor coactivator (SRC)/p160 coactivator LXXLL motifs. In prostate cancer, somatic AR mutations in AF2 or near the bound ligand slow androgen dissociation and increase AR stabilization and coactivator recruitment. Crystal structures of the AR ligand binding domain bound to R1881 and FXXLF or LXXLL motif peptide indicate the mutations are proximal to the AF2 bound peptide, adjacent to the ligand pocket, or in a putative ligand gateway. The results suggest a bidirectional structural relay between bound ligand and coactivator that establishes AR functional potency in vivo.

Regulation of androgen receptor signaling in prostate cancer

Prostate cancer is a significant cause of morbidity and mortality worldwide. Normal prostate tissue is regulated by androgens, which activate the androgen receptor, a nuclear receptor transcription factor. Most prostate tumors retain androgen dependence, therefore, current therapies for advanced prostate cancer either reduce androgen levels or prevent binding to the androgen receptor. Despite this regimen, prostate cancer invariably progresses to a fatal, androgen-refractory state. Although these relapsed tumors are androgen independent, they are still dependent on the androgen receptor for their growth and survival. The focus of this review will be to highlight our current understanding of the mechanisms of androgen receptor activation in androgen-refractory prostate cancer. How these mechanisms of androgen receptor activation could be targeted in this advanced stage of the disease is also discussed.

Impaired helix 12 dynamics due to proline 892 substitutions in the androgen receptor are associated with complete androgen insensitivity

Structural studies of the ligand-binding domain (LBD) of several steroid receptors have revealed that the dynamic properties of the C-terminal helix 12 (H12) are the major determinant of the activation mode of these receptors. H12 exhibits high mobility and different conformations in the absence of ligand. Upon ligand binding, H12 is stabilized in a precise position to seal the ligand-binding pocket and finalize the assembly of the activation function (AF-2) domain. In this study, we investigated the role of the conserved proline 892 of the androgen receptor (AR) in directing the dynamic location and orientation of the AR-H12. We used a combined approach including kinetic and biochemical assays with molecular dynamic simulations to analyze two substitutions (P892A and P892L) identified in individuals with complete androgen insensitivity syndrome. Our analyses revealed distinct mechanisms by which these substitutions impair H12 function resulting in severely defective receptors. The AR-P892A receptor exhibited reduced ligand binding and transactivational potential because of an increased flexibility in H12. The AR-P892L substitution renders the receptor inactive due to a distorted, unstructured and misplaced H12. To confirm the mutants' inability to stabilize H12 in an active position, we have developed a novel in vivo assay to evaluate the accessibility of the H12-docking site on the AR-LBD surface. An extrinsic AR-H12 peptide was able to interact with wild-type and mutant LBDs in the absence of ligand. Ligand-induced proper positioning of the intrinsic H12 of wild-type AR prevented these interactions, whereas the misplacement of the mutants' H12 did not. Proline at this position may be critical for H12 dynamics not only in the AR, but also in other nuclear receptors where this proline is conserved.

Prevalent mutations in prostate cancer

Quantitative and structural genetic alterations cause the development and progression of prostate cancer. A number of genes have been implicated in prostate cancer by genetic alterations and functional consequences of the genetic alterations. These include the ELAC2 (HPC2), MSR1, and RNASEL (HPC1) genes that have germline mutations in familial prostate cancer; AR, ATBF1, EPHB2 (ERK), KLF6, mitochondria DNA, p53, PTEN, and RAS that have somatic mutations in sporadic prostate cancer; AR, BRCA1, BRCA2, CHEK2 (RAD53), CYP17, CYP1B1, CYP3A4, GSTM1, GSTP1, GSTT1, PON1, SRD5A2, and VDR that have germline genetic variants associated with either hereditary and/or sporadic prostate cancer; and ANXA7 (ANX7), KLF5, NKX3-1 (NKX3.1), CDKN1B (p27), and MYC that have genomic copy number changes affecting gene function. More genes relevant to prostate cancer remain to be identified in each of these gene groups. For the genes that have been identified, most need additional genetic, functional, and/or biochemical examination. Identification and characterization of these genes will be a key step for improving the detection and treatment of prostate cancer.

Biology of progressive, castration-resistant prostate cancer: directed therapies targeting the androgen-receptor signaling axis

Prostate cancers that are progressing on medical and surgical therapies designed to ablate the action of androgens continue to express androgen receptor (AR) and to depend on signaling through the receptor for growth. A more clinically relevant classification of castration-resistant disease focuses on the mechanisms of receptor activation, which include (1) changes in the level of ligand(s) in tumor tissue; (2) increased levels of the protein due to gene amplification or altered mRNA expression; (3) activating mutations in the receptor that affect structure and function; (4) changes in coregulatory molecules including coactivators and corepressors; and (5) factors that lead to activation of the receptor independent of the level of ligand or receptor allowing kinase cross talk. From an AR perspective, the term "hormone refractory" is inappropriate. On the basis of this schema, we discuss strategies that are focused on the AR either directly or indirectly, as single agents or in combination, that are in clinical development.

Endocrine disrupting compounds and prostate cancer

Prostate cancer is a major health concern and is treated based on its hormone dependence. Agents that alter hormone action can have substantial biological effects on prostate cancer development and progression. As such, there is significant interest in uncovering the potential effects of endocrine disrupting compound (EDC) exposure on prostate cancer. The present review is focused on agents that alter hormone action in the prostate and how they may impact cancer growth or treatment.

Androgen receptor in prostate cancer: cause or cure?

Growth of prostate tumours is dependent on androgens. Hence, therapy involves removing androgens and opposing their effects using antiandrogens. This is initially successful but inevitably fails and tumours recur. The cause of this transition to hormone-independence, and the precise role of the androgen receptor in this, is a matter of considerable debate. A recent study used a mouse model to assess the effects of increased androgen receptor expression in the prostate and found that, whereas increased expression of wild-type receptor had no effect, a mutation of the androgen receptor caused it to have oncogenic properties. This goes some way to elucidating how the androgen receptor affects tumour growth, and provides an exciting model for further study of androgen receptor mutations in prostate cancer.

Decreased Androgen Receptor Levels and Receptor Function in Breast Cancer Contribute to the Failure of Response to Medroxyprogesterone Acetate

Previously, we reported that androgen receptor (AR), but not estrogen receptor (ER) or progesterone receptor (PR), is predictive of response to the synthetic progestin, medroxyprogesterone acetate (MPA), in a cohort of 83 patients with metastatic breast cancer. To further investigate the role of AR in determining response to MPA in this cohort, we analyzed AR levels by immunohistochemistry with two discrete antisera directed at either the NH2 or the COOH termini of the receptor. Compared with tumors that responded to MPA (n = 31), there was a significant decrease in the intensity and extent of AR immunoreactivity with both AR antisera in tumors from nonresponders (n = 52). Whereas only a single AR immunostaining pattern was detected in responders to MPA, reflecting concordance of immunoreactivity with the two AR antisera, tumors from nonresponders exhibited four distinct AR immunostaining patterns: (a) concordance with the two antibodies (31%), (b) staining only with the COOH-terminal antibody (33%), (c) staining only with the NH2-terminal antibody (22%), or (d) no immunoreactivity with either NH2- or COOH-terminal antibody (14%). DNA sequencing and functional analysis identified inactivating missense gene mutations in the ligand-binding domain of the AR in tumors from two of nine nonresponders positive with the NH2-terminal AR antisera but negative for COOH-terminal immunoreactivity and lacking specific, high-affinity dihydrotestosterone binding in tumor cytosol fractions. Tumors with more AR than the median level (37 fmol/mg protein) had significantly lower levels of PR (30 fmol/mg protein) than tumors with low AR (PR; 127 fmol/mg protein) despite comparable levels of ER. Ligand-dependent activation of the AR in human T47D and MCF-7 breast cancer cells resulted in inhibition of estradiol-stimulated cell proliferation and a reduction in the capacity of the ER to induce expression of the PR. These effects could be reversed using a specific AR antisense oligonucleotide. Increasing the ratio of AR to ER resulted in a greater androgen-dependent inhibition of ER function. Collectively, these data suggest that reduced levels of AR or impaired AR function contribute to the failure of MPA therapy potentially due to abrogation of the inhibitory effect of AR on ER signaling.

Current thoughts on the role of the androgen receptor and prostate cancer progression

Androgens play a central role in the development and maintenance of prostate tissue. Treatment of prostate cancer by androgen ablation either surgically or biochemically results in massive cell death and tumor regression. However, this is often followed by the onset of aggressive disease, which is fatal. Various studies have been conducted to understand the mechanism leading to the establishment of aggressive disease following treatment. An interesting comprehensive study recently conducted by Chen et al shows the increase in androgen receptor (AR) transcript to be the key factor in disease recurrence following treatment. This up-regulation in the AR levels is shown to increase sensitivity to low levels of androgen, leading to ligand-dependent downstream gene expression and tumor recurrence. A "mass action" model has been proposed to explain this phenomenon. Moreover, the increase in mRNA levels has been shown to facilitate conversion of classic antagonists to agonists of hormones action by the recruitment of a subset of co-activators to the promoters of AR-responsive genes. This study underscores the importance of ARs in the establishment of prostate cancer and offers several insights into the mechanism by which tumors recur following androgen ablation. The study also prompts several questions about the reason behind the observed up-regulation and also the mechanism by which classic antagonists are rendered agonistic. The need for the design of novel therapeutic analogues is also emphasized.

Structural basis for accommodation of nonsteroidal ligands in the androgen receptor

The mechanism by which the androgen receptor (AR) distinguishes between agonist and antagonist ligands is poorly understood. AR antagonists are currently used to treat prostate cancer. However, mutations commonly develop in patients that convert these compounds to agonists. Recently, our laboratory discovered selective androgen receptor modulators, which structurally resemble the nonsteroidal AR antagonists bicalutamide and hydroxyflutamide but act as agonists for the androgen receptor in a tissue-selective manner. To investigate why subtle structural changes to both the ligand and the receptor (i.e. mutations) result in drastic changes in activity, we studied structure-activity relationships for nonsteroidal AR ligands through crystallography and site-directed mutagenesis, comparing bound conformations of R-bicalutamide, hydroxyflutamide, and two previously reported nonsteroidal androgens, S-1 and R-3. These studies provide the first crystallographic evidence of the mechanism by which nonsteroidal ligands interact with the wild type AR. We have shown that changes induced to the positions of Trp-741, Thr-877, and Met-895 allow for ligand accommodation within the AR binding pocket and that a water-mediated hydrogen bond to the backbone oxygen of Leu-873 and the ketone of hydroxyflutamide is present when bound to the T877A AR variant. Additionally, we demonstrated that R-bicalutamide stimulates transcriptional activation in AR harboring the M895T point mutation. As a whole, these studies provide critical new insight for receptor-based drug design of nonsteroidal AR agonists and antagonists.

The structural basis of androgen receptor activation: intramolecular and intermolecular amino-carboxy interactions

Nuclear receptors (NRs) are ligand-regulated transcription factors important in human physiology and disease. In certain NRs, including the androgen receptor (AR), ligand binding to the carboxy-terminal domain (LBD) regulates transcriptional activation functions in the LBD and amino-terminal domain (NTD). The basis for NTD-LBD communication is unknown but may involve NTD-LBD interactions either within a single receptor or between different members of an AR dimer. Here, measurement of FRET between fluorophores attached to the NTD and LBD of the AR established that agonist binding initiated an intramolecular NTD-LBD interaction in the nucleus and cytoplasm. This intramolecular folding was followed by AR self-association, which occurred preferentially in the nucleus. Rapid, ligand-induced intramolecular folding and delayed association also were observed for estrogen receptor-alpha but not for peroxisome proliferator activated receptor-gamma2. An antagonist ligand, hydroxyflutamide, blocked the NTD-LBD association within AR. NTD-LBD association also closely correlated with the transcriptional activation by heterologous ligands of AR mutants isolated from hormone-refractory prostate tumors. Intramolecular folding, but not AR-AR affinity, was disrupted by mutation of an alpha-helical ((23)FQNLF(27)) motif in the AR NTD previously described to interact with the AR LBD in vitro. This work establishes an intramolecular NTD-LBD conformational change as an initial component of ligand-regulated NR function.

Roles of steroid receptor coactivator (SRC)-1 and transcriptional intermediary factor (TIF) 2 in androgen receptor activity in mice

Genetic disruption of the steroid receptor coactivator (SRC)-1 and transcriptional intermediary factor (TIF)2/SRC-2 in mouse resulted in distinctive mutant phenotypes. To quantify their roles in the function of androgen receptor (AR) transcriptional activity in vivo, we generated a unique transgenic AR-reporter mouse and analyzed the cell-specific contributions of SRC-1 and TIF2 to the activity of AR in mouse testis. Transgenic AR-luciferase and transgenic AR-lacZ mice harbor a recombinant mouse AR gene, AR(GAL4DBD), which is functionally coupled with a upstream activation sequence-mediated reporter gene (AR activity indicator). After characterization of these mice in terms of AR function, we further derived bigenic mice by crossing AR activity indicator mice with the SRC-1-/- or TIF2+/- mutant mice. Analyses of the resultant bigenic mice by in vivo imaging and luciferase assays showed that testicular AR activity was decreased significantly in those with the TIF2+/- mutation but not in the SRC-1+/- background, suggesting that TIF2 serves as the preferential coactivator for AR in testis. Immunohistological analysis confirmed that AR and TIF2 coexist in mouse testicular Sertoli cell nuclei under normal conditions. Although SRC-1 concentrates in Sertoli cell nuclei in the absence of TIF2, nuclear SRC-1 is not able to rescue AR activity in the TIF2 mutant background. Interestingly, SRC-1 appears to negatively influence AR activity, thereby counterbalancing the TIF2-stimulated AR activity. Our results provide unique in vivo insights to the multidimensional cell-type-specific interactions between AR and coregulators.

Androgen receptor mutants detected in recurrent prostate cancer exhibit diverse functional characteristics

BACKGROUND

Alterations in the function of androgen receptor (AR) and its signaling pathway may be responsible for the progression of prostate cancer. The goal of the present study was to investigate the potential roles of AR structural and functional alterations in the progression of prostate cancer, and the relationship between the structure and function of the AR.

METHODS

AR gene in 58 prostate cancer samples was examined for mutations using PCR-single strand conformation polymorphism (SSCP) analysis and DNA sequencing. Effects of mutations on the structure and function of AR were investigated by androgen-binding assays and transactivation assays, respectively.

RESULTS

Four novel somatic mutations (G142V, D221H, E872Q, and M886I) were identified from recurrent prostate cancer samples. None of the AR mutants differed from wild-type AR (wtAR) in their abilities to bind the synthetic androgen methyltrienolone. However, these mutated AR exhibited diverse functional characteristics as compared with wtAR. G142V and D221H showed increased responses to DHT. E872Q could be abnormally activated by 17beta-estradiol, progesterone, and cyproterone acetate (CPA). Furthermore, E872Q and M886I presented increased responses to DHT in the presence of coactivators TIF-2 and CBP, but not p300. On the other hand, although overexpression of corepressors N-CoR and SMRT could result in evident inhibition on DHT- or CPA-induced transactivity of wtAR and the AR mutants, N-CoR displayed stronger inhibitory effects on DHT-induced transactivity of the AR mutants (especially for E872Q and M886I) than that of wtAR. To our knowledge, this is the first characterization of enhanced inhibitory effects of corepressors on the transactivity of the AR mutants found in prostate cancer.

CONCLUSIONS

The data presented here demonstrate that AR mutants found in prostate cancer had different functional alterations, which might play an important role in the progression of prostate cancer.

The E211 G>A Androgen Receptor Polymorphism Is Associated with a Decreased Risk of Metastatic Prostate Cancer and Androgenetic Alopecia

The androgen receptor (AR) gene encodes a transcription factor, which mediates androgen action in target tissues, including the prostate. Prostate cancer is androgen dependent, implicating AR in susceptibility to this male condition. Male pattern balding, androgenetic alopecia, has recently been associated with prostate cancer, suggesting shared androgen pathways. The CAG and GGC repeats in the AR have been studied extensively as markers of prostate cancer susceptibility, with inconclusive findings, whereas the AR-E211 G>A polymorphism has been associated with androgenetic alopecia. We assessed the repeat linked single nucleotide polymorphism as a marker of risk association in prostate cancer, including androgenetic alopecia, in an Australian population-based case-control study. In 815 prostate cancer cases and 719 controls, the proportion of A-allele carriers was the same in each group. Overall, there was no evidence for an association between the A allele and risk of prostate cancer, however, the proportion of A-allele carriers in metastatic prostate cancer (5%) was lower than in less advanced disease (16%, P = 0.03). The proportion of A-allele carriers was 24% in nonbald men but it was lower in men with vertex alopecia alone (13%, P = 0.001) or in combination with frontal alopecia (7%, P < 0.0001). This inverse association between the A allele and baldness was independent of prostate cancer status (P for interaction = 0.2). These results suggest that the AR-E211 A allele, in linkage with the functional repeat sequences, is associated with a lower risk of metastatic prostate cancer and a lower risk of alopecia.

Mechanisms of Disease: polymorphisms of androgen regulatory genes in the development of prostate cancer

Androgens are of primary importance in the etiology of prostate cancer, and binding of the androgen dihydrotestosterone to the androgen receptor is thought to stimulate prostate growth. It has been proposed that polymorphisms within key androgen regulatory genes may contribute to an individual's risk of developing prostate cancer. Attributing single polymorphisms to complex, late-onset, chronic diseases such as prostate cancer is probably not feasible, but identification of genes that increase risk will contribute to larger-scale multigenic risk assessment. Here, we review the current status of our knowledge of associations between important androgen regulatory gene polymorphisms and prostate cancer risk.

Mutation of the androgen receptor causes oncogenic transformation of the prostate

Recent evidence demonstrates that the androgen receptor (AR) continues to influence prostate cancer growth despite medical therapies that reduce circulating androgen ligands to castrate levels and/or block ligand binding. Whereas the mutation, amplification, overexpression of AR, or cross-talk between AR and other growth factor pathways may explain the failure of androgen ablation therapies in some cases, there is little evidence supporting a causal role between AR and prostate cancer. In this study, we functionally and directly address the role whereby AR contributes to spontaneous cancer progression by generating transgenic mice expressing (i) AR-WT to recapitulate increased AR levels and ligand sensitivity, (ii) AR-T857A to represent a promiscuous AR ligand response, and (iii) AR-E231G to model altered AR function. Whereas transgenes encoding either AR-WT or AR-T857A did not cause prostate cancer when expressed at equivalent levels, expression of AR-E231G, which carries a mutation in the most highly conserved signature motif of the NH2-terminal domain that also influences interactions with cellular coregulators, caused rapid development of prostatic intraepithelial neoplasia that progressed to invasive and metastatic disease in 100% of mice examined. Taken together, our data now demonstrate the oncogenic potential of steroid receptors and implicate altered AR function and receptor coregulator interaction as critical determinants of prostate cancer initiation, invasion, and metastasis.

Androgen receptor modifications in prostate cancer cells upon long-termandrogen ablation and antiandrogen treatment

To study the mechanisms whereby androgen-dependent tumors relapse in patients undergoing androgen blockade, we developed a novel progression model for prostate cancer. The PC346C cell line, established from a transurethral resection of a primary tumor, expresses wild-type (wt) androgen receptor (AR) and secretes prostate-specific antigen (PSA). Optimal proliferation of PC346C requires androgens and is inhibited by the antiandrogen hydroxyflutamide. Orthotopic injection in the dorsal-lateral prostate of castrated athymic nude mice did not produce tumors, whereas fast tumor growth occurred in sham-operated males. Three androgen-independent sublines were derived from PC346C upon long-term in vitro androgen deprivation: PC346DCC, PC346Flu1 and PC346Flu2. PC346DCC exhibited androgen-insensitive growth, which was not inhibited by flutamide. AR and PSA were detected at very low levels, coinciding with background AR activity in a reporter assay, which suggests that these cells have bypassed the AR pathway. PC346Flu1 and PC346Flu2 were derived by culture in steroid-stripped medium supplemented with hydroxyflutamide. PC346Flu1 strongly upregulated AR expression and showed 10-fold higher AR activation than the parental PC346C. PC346Flu1 proliferation was inhibited in vitro by R1881 at 0.1 nM concentration, consistent with a slower tumor growth rate in intact males than in castrated mice. PC346Flu2 carries the well-known T877A AR mutation, causing the receptor to become activated by diverse nonandrogenic ligands including hydroxyflutamide. Array-based comparative genomic hybridization revealed little change between the various PC346 lines. The common alterations include gain of chromosomes 1, 7 and 8q and loss of 13q, which are frequently found in prostate cancer. In conclusion, by in vitro hormone manipulations of a unique androgen-dependent cell line expressing wtAR, we successfully reproduced common AR modifications observed in hormone-refractory prostate cancer: downregulation, overexpression and mutation.

C19‐5‐ene Steroids in Nature

Dehydroepiandrosterone (DHEA), produced from cholesterol in the adrenals, is the most abundant steroid in our circulation. It is present almost entirely as the sulfate ester, but the free steroid is the form that serves as a precursor of estrogens and androgens, as well as 7- and 16-oxygenated derivatives. Mammalian tissues reduce the 17-keto Group of DHEA to produce androstenediol-a weak estrogen and full-fledged androgen. Its androgen activity is not inhibited by the anti-androgens commonly used to treat prostate cancer. It is probably responsible for the growth of therapy-resistant prostate cancer. DHEA is hydroxylated at the 7 alpha position, and this derivative is oxidized by 11 beta-hydroxysteroid dehydrogenase to form 7-keto DHEA. The latter is reduced by the same dehydrogenase to form 7 beta-hydroxy DHEA. When fed to rats, each of the latter three steroids induce the formation of two thermogenic enzymes in the liver. The late-term human fetus produces relatively large amounts of 16 alphahydroxy DHEA, which serves the mother as a precursor of estriol.

Molecular pathology of the androgen receptor in male (in)fertility

Idiopathic male infertility, accounting for 40% of all male infertility cases, is postulated to have a genetic basis. The androgen receptor (AR) plays a crucial post-meiotic role during male germ cell differentiation, which includes terminal differentiation of spermatids and their release from the seminiferous epithelium. Mutations in the AR gene result in a condition known as androgen insensitivity syndrome (AIS) affecting normal male morphogenesis. Depending on the severity of the syndrome, the external phenotype can range from normal female to normal male. In almost all cases affected individuals are infertile. In seven reported cases individuals appeared to suffer primarily or solely from male infertility, suggesting these AR mutations specifically cause male infertility. Three of these mutations are possibly population specific. Longer CAG repeats present in exon 1 of the AR have been studied as a possible risk factor for male infertility. Results are contradictory, with a trend to significance (Asian populations) and non-significance (European populations). Recent advances in protein modelling techniques may result in a much better understanding of the mechanism of action of the known infertility mutations. The determination of the significance of longer CAG repeats is likely to require studies that examine CAG repeat lengths in spermatozoa as well as patients' blood.

Gene Regulation in Spermatogenesis

Mammalian spermatogenesis is a complex hormone-dependent developmental program in which a myriad of events must take place to ensure that germ cells reach their proper stage of development at the proper time. Many of these events are controlled by cell type- and stage-specific transcription factors. The regulatory mechanisms involved provide an intriguing paradigm for the field of developmental biology and may lead to the development of new contraceptives an and innovative routs to treat male infertility. In this review, we address three aspects of the genetic regulatory mechanism that drive spermatogenesis. First, we detail what is known about how steroid hormones (both androgens and estrogens) and their cognate receptors initiate and maintain mammalian spermatogenesis. Steroids act through three mechanistic routes: (i) direct activation of genes through hormone-dependent promoter elements, (ii) secondary transcriptional responses through activation of hormone-dependent transcription factors, and (iii) rapid, transcription-independent (nonclassical) events induced by steroid hormones. Second, we provide a survey of transcription factors that function in mammalian spermatogenesis, including homeobox, zinc-finger, heat-shock, and cAMP-response family members. Our survey is not intended to cover all examples but to give a flavor for the gamut of biological roles conferred by transcription factors in the testis, particularly those defined in knockout mice. Third, we address how testis-specific transcription is achieved. In particular, we cover the evidence for and against the idea that some testis-specific genes are transcriptionally silent in somatic tissues as a result of DNA methylation.

Intranuclear organization and function of the androgen receptor

We have entered an exciting era for androgen-receptor (AR) research that should provide a detailed description of how the AR functions as a ligand-regulated transcription factor. That AR activity is regulated by subcellular compartmentalization was first established a decade ago with the finding that binding of androgen to the AR induces its translocation from the cytoplasm to the nucleus. The contribution of compartmentalization to AR activity is, however, likely to extend beyond simple delivery to the nucleus. Defects in AR and coregulator compartmentalization in the nucleus have been demonstrated in prostate cancer, androgen-insensitivity syndrome, and spinal and bulbar muscular atrophy. A complete understanding of AR function and dysfunction in disease requires integrating transcription with the spatial and temporal regulation imposed by subnuclear organization and nuclear transport.