Differential modulation of androgen receptor action by deoxyribonucleic acid response elements

The relationship between sexual dimorphism and androgen response element proliferation in primate genomes

In the males of many vertebrate species, sexual selection has led to the evolution of sexually dimorphic traits, which often are developmentally controlled by androgen signaling involving androgen response elements (AREs). Evolutionary changes in the number and genomic locations of AREs can modify patterns of receptor regulation and potentially alter gene expression. Here, we use recently sequenced primate genomes to evaluate the hypothesis that the strength of sexual selection is related to the genome-wide number of AREs in a diversifying lineage. In humans, we find a higher incidence of AREs near male-biased genes and androgen-responsive genes when compared to randomly selected genes from the genome. In a set of primates, we find that gains or losses of AREs proximal to genes are correlated with changes in male expression levels and the degree of sex-biased expression of those genes. In a larger set of primates, we find that increases in indicators of sexual selection are correlated with genome-wide ARE counts. Our results suggest that the responsiveness of the genome to androgens in humans and their close relatives has been shaped by sexual selection that arises from competition among males for mating access to females.

Molecular Dynamics Simulations of a Chimeric Androgen Receptor Protein (SPARKI) Confirm the Importance of the Dimerization Domain on DNA Binding Specificity

The DNA binding domains of Androgen/Glucocorticoid receptors (AR/GR), members of class I steroid receptors, bind as a homo-dimer to a cis-regulatory element. These response elements are arranged as inverted repeat (IR) of hexamer “AGAACA”, separated with a 3 base pairs spacer. DNA binding domains of the Androgen receptor, AR-DBDs, in addition, selectively recognize a direct-like repeat (DR) arrangement of this hexamer. A chimeric AR protein, termed SPARKI, in which the second zinc-binding motif of AR is swapped with that of GR, however, fails to recognize DR-like elements. By molecular dynamic simulations, we identify how the DNA binding domains of the wild type AR/GR, and also the chimeric SPARKI model, distinctly interact with both IR and DR response elements. AR binds more strongly to DR than GR binds to IR elements. A SPARKI model built from the structure of the AR (SPARKI-AR) shows significantly fewer hydrogen bond interactions in complex with a DR sequence than with an IR sequence. Moreover, a SPARKI model based on the structure of the GR (SPARKI-GR) shows a considerable distortion in its dimerization domain when complexed to a DR-DNA whereas it remains in a stable conformation in a complex with an IR-DNA. The diminished interaction of SPARKI-AR with and the instability of SPARKI-GR on DR response elements agree with SPARKI's lack of affinity for these sequences. The more GR-like binding specificity of the chimeric SPARKI protein is further emphasized by both SPARKI models binding even more strongly to IR elements than observed for the DNA binding domain of the GR.

Androgen receptor co-regulation in prostate cancer

Prostate cancer (PCa) progression relies on androgen receptor (AR) action. Preventing AR's ligand-activation is the frontline treatment for metastatic PCa. Androgen deprivation therapy (ADT) that inhibits AR ligand-binding initially induces remission but eventually fails, mainly because of adaptive PCa responses that restore AR action. The vast majority of castration-resistant PCa (CRPC) continues to rely on AR activity. Novel therapeutic strategies are being explored that involve targeting other critical AR domains such as those that mediate its constitutively active transactivation function, its DNA binding ability, or its interaction with co-operating transcriptional regulators. Considerable molecular and clinical variability has been found in AR's interaction with its ligands, DNA binding motifs, and its associated coregulators and transcription factors. Here, we review evidence that each of these levels of AR regulation can individually and differentially impact transcription by AR. In addition, we examine emerging insights suggesting that each can also impact the other, and that all three may collaborate to induce gene-specific AR target gene expression, likely via AR allosteric effects. For the purpose of this review, we refer to the modulating influence of these differential and/or interdependent contributions of ligands, cognate DNA-binding motifs and critical regulatory protein interactions on AR's transcriptional output, which may influence the efficiency of the novel PCa therapeutic approaches under consideration, as co-regulation of AR activity.

An Approach to Greater Specificity for Glucocorticoids

Glucocorticoid steroids are among the most prescribed drugs each year. Nonetheless, the many undesirable side effects, and lack of selectivity, restrict their greater usage. Research to increase glucocorticoid specificity has spanned many years. These efforts have been hampered by the ability of glucocorticoids to both induce and repress gene transcription and also by the lack of success in defining any predictable properties that control glucocorticoid specificity. Correlations of transcriptional specificity have been observed with changes in steroid structure, receptor and chromatin conformation, DNA sequence for receptor binding, and associated cofactors. However, none of these studies have progressed to the point of being able to offer guidance for increased specificity. We summarize here a mathematical theory that allows a novel and quantifiable approach to increase selectivity. The theory applies to all three major actions of glucocorticoid receptors: induction by agonists, induction by antagonists, and repression by agonists. Simple graphical analysis of competition assays involving any two factors (steroid, chemical, peptide, protein, DNA, etc.) yields information (1) about the kinetically described mechanism of action for each factor at that step where the factor acts in the overall reaction sequence and (2) about the relative position of that step where each factor acts. These two pieces of information uniquely provide direction for increasing the specificity of glucocorticoid action. Consideration of all three modes of action indicate that the most promising approach for increased specificity is to vary the concentrations of those cofactors/pharmaceuticals that act closest to the observed end point. The potential for selectivity is even greater when varying cofactors/pharmaceuticals in conjunction with a select class of antagonists.

Structure of the homodimeric androgen receptor ligand-binding domain

The androgen receptor (AR) plays a crucial role in normal physiology, development and metabolism as well as in the aetiology and treatment of diverse pathologies such as androgen insensitivity syndromes (AIS), male infertility and prostate cancer (PCa). Here we show that dimerization of AR ligand-binding domain (LBD) is induced by receptor agonists but not by antagonists. The 2.15-Šcrystal structure of homodimeric, agonist- and coactivator peptide-bound AR-LBD unveils a 1,000-Ų large dimerization surface, which harbours over 40 previously unexplained AIS- and PCa-associated point mutations. An AIS mutation in the self-association interface (P767A) disrupts dimer formation in vivo, and has a detrimental effect on the transactivating properties of full-length AR, despite retained hormone-binding capacity. The conservation of essential residues suggests that the unveiled dimerization mechanism might be shared by other nuclear receptors. Our work defines AR-LBD homodimerization as an essential step in the proper functioning of this important transcription factor.

The androgen receptor is crucial for the development and physiology of reproductive organs. Here the authors present the structure of the androgen receptor ligand-binding domain bound to dihydrotestosterone, identifying a homodimerization interface that is crucial for receptor activity in vivo.

Role of Nuclear Receptors in Central Nervous System Development and Associated Diseases

The nuclear hormone receptor (NHR) superfamily is composed of a wide range of receptors involved in a myriad of important biological processes, including development, growth, metabolism, and maintenance. Regulation of such wide variety of functions requires a complex system of gene regulation that includes interaction with transcription factors, chromatin-modifying complex, and the proper recognition of ligands. NHRs are able to coordinate the expression of genes in numerous pathways simultaneously. This review focuses on the role of nuclear receptors in the central nervous system and, in particular, their role in regulating the proper development and function of the brain and the eye. In addition, the review highlights the impact of mutations in NHRs on a spectrum of human diseases from autism to retinal degeneration.

BAY 1024767 blocks androgen receptor mutants found in castration-resistant prostate cancer patients

Androgen receptor (AR) mutations arise in patients developing resistance to hormone deprivation therapies. Here we describe BAY 1024767, a thiohydantoin derivative with strong antagonistic activity against nine AR variants with mutations located in the AR ligand-binding domain (LBD), and against wild-type AR. Antagonism was maintained, though reduced, at increased androgen levels. Anti-tumor efficacy was evidenced in vivo in the KuCaP-1 prostate cancer model which bears the W741C bicalutamide resistance mutation and in the syngeneic prostate cancer rat model Dunning R3327-G. The prevalence of six selected AR mutations was determined in plasma DNA originating from 100 resistant patients and found to be at least 12%. Altogether the results show BAY 1024767 to be a strong antagonist for several AR mutants linked to therapy resistance, which opens the door for next-generation compounds that can benefit patients based on their mutation profile.

Mouse Spermatogenesis Requires Classical and Nonclassical Testosterone Signaling

Testosterone acts though the androgen receptor in Sertoli cells to support germ cell development (spermatogenesis) and male fertility, but the molecular and cellular mechanisms by which testosterone acts are not well understood. Previously, we found that in addition to acting through androgen receptor to directly regulate gene expression (classical testosterone signaling pathway), testosterone acts through a nonclassical pathway via the androgen receptor to rapidly activate kinases that are known to regulate spermatogenesis. In this study, we provide the first evidence that nonclassical testosterone signaling occurs in vivo as the MAP kinase cascade is rapidly activated in Sertoli cells within the testis by increasing testosterone levels in the rat. We find that either classical or nonclassical signaling regulates testosterone-mediated Rhox5 gene expression in Sertoli cells within testis explants. The selective activation of classical or nonclassical signaling pathways in Sertoli cells within testis explants also resulted in the differential activation of the Zbtb16 and c-Kit genes in adjacent spermatogonia germ cells. Delivery of an inhibitor of either pathway to Sertoli cells of mouse testes disrupted the blood-testis barrier that is essential for spermatogenesis. Furthermore, an inhibitor of nonclassical testosterone signaling blocked meiosis in pubertal mice and caused the loss of meiotic and postmeiotic germ cells in adult mouse testes. An inhibitor of the classical pathway caused the premature release of immature germ cells. Collectively, these observations indicate that classical and nonclassical testosterone signaling regulate overlapping and distinct functions that are required for the maintenance of spermatogenesis and male fertility.

Recent developments in antiandrogens and selective androgen receptor modulators

The androgens testosterone and dihydrotestosterone play an essential role in the development and maintenance of primary and secondary male characteristics. Androgens bind to a specific androgen receptor (AR), a ligand-dependent transcription factor which controls the expression of a large number of downstream target genes. The AR is an essential player in early and late prostate cancer, and may also be involved in some forms of breast cancer. It also represents a drug target for the treatment of hypogonadism. Recent studies furthermore indicate that targeting the AR in pathologies such as frailty syndrome, cachexia or polycystic ovary syndrome may have clinical benefit. Numerous AR ligands with very different pharmacological properties have been identified in the last 40 years and helped to treat several of these diseases. However, progress still needs to be made in order to find compounds with an improved profile with regard to efficacy, differentiation and side-effects. This will only be achieved through a better understanding of the mechanisms involved in normal and aberrant AR signaling.

Interactions of the mineralocorticoid receptor--within and without

The mineralocortoid receptor (MR) regulates salt homeostasis in the kidneys and plays a range of other roles in the heart, vasculature, brain and adipose tissue. It interacts with both mineralocorticoids and glucocorticoids to mediate transcription of target genes. The ability of the MR to exert tissue- and ligand-specific effects relies on its interactions with a range of binding partners, including the chaperone proteins, coregulators, other transcription factors, DNA and modifying proteins. Interactions within the domains of the MR also modulate the overall transcriptional complex. This review will discuss the current understanding of interactions involving the MR and highlight their relevance to ligand- or tissue-specificity as well as their suitability as therapeutic targets.

The Rhox genes

Homeobox genes encode transcription factors that have crucial roles in embryogenesis. A recently discovered set of homeobox genes--the Rhox genes--are expressed during both embryogenesis and in adult reproductive tissues. The 33 known mouse Rhox genes are clustered together in a single region on the X chromosome, while likely descendents of the primodial Rhox cluster, Arx and Esx1, have moved to other positions on the X chromosome. Here, we summarize what is known about the regulation and function of Rhox cluster and Rhox-related genes during embryogenesis and gametogenesis. The founding member of the Rhox gene cluster--Rhox5 (previously known as Pem)--has been studied in the most depth and thus is the focus of this review. We also discuss the unusually rapid evolution of the Rhox gene cluster.

Paired hormone response elements predict caveolin-1 as a glucocorticoid target gene

Glucocorticoids act in part via glucocortocoid receptor binding to hormone response elements (HREs), but their direct target genes in vivo are still largely unknown. We developed the criterion that genomic occurrence of paired HREs at an inter-HRE distance less than 200 bp predicts hormone responsiveness, based on synergy of multiple HREs, and HRE information from known target genes. This criterion predicts a substantial number of novel responsive genes, when applied to genomic regions 10 kb upstream of genes. Multiple-tissue in situ hybridization showed that mRNA expression of 6 out of 10 selected genes was induced in a tissue-specific manner in mice treated with a single dose of corticosterone, with the spleen being the most responsive organ. Caveolin-1 was strongly responsive in several organs, and the HRE pair in its upstream region showed increased occupancy by glucocorticoid receptor in response to corticosterone. Our approach allowed for discovery of novel tissue specific glucocorticoid target genes, which may exemplify responses underlying the permissive actions of glucocorticoids.

Intronic DNA elements regulate androgen-dependent expression of the murine Nkx3.1 gene

Nkx3.1 is a well-conserved homeobox gene that is involved in development, differentiation and maintenance of prostate epithelial cells. Nkx3.1 expression is induced by androgen in prostate epithelia and, as such, our interest is to understand the mechanism(s) for this androgen-dependent expression in normal epithelial cells. In this report, we show that the region of DNA sequence 2.7 kilobases in front of the mouse Nkx3.1 gene drives enhanced transcription in prostate epithelia cells; however, this segment was not capable of androgen-directed regulation. Among the multiple, potential androgen response elements (AREs) identified by scanning sequences near and within the gene, two sequences within the intron of the murine Nkx3.1 gene were demonstrated to confer androgen-dependent transcription in reporter gene transfection experiments. Each of the elements, termed ARE A and ARE B, contained a 6-base pair core sequence, TGTTCT, that has been described as an androgen receptor half-site binding sequence, separated by 498 base pairs of DNA. Both of the intronic half-sites bind activated androgen receptor from a variety of sources, albeit with different apparent affinities. This region of the Nkx3.1 gene demonstrates a high degree of conservation among diverse species and mutagenesis experiments demonstrated that both elements are required for androgen stimulation. Taken together, our study shows that androgen-dependent transcription of the mouse Nkx3.1 gene is conferred through a noncanonical element within the intron of the gene.

DNA dependent recruitment of DDX17 and other interacting proteins by the human androgen receptor

An oligonucleotide-based assay (OBA) was used to identify novel co-factors that can be recruited by the deoxyribonucleic acid (DNA)-bound androgen receptor (AR). Nuclear extracts obtained from LNCaP cells, after incubation with R1881, were incubated with biotinylated oligonucleotides bound to streptavidin coated beads. The oligonucleotides contain 3 copies in tandem of the androgen responsive element ARE1 from the prostate specific antigen (PSA) gene promoter. As control incubation, a scrambled version of the tandem ARE1 was used. Immunoblots of the eluents revealed that the AR was bound to the ARE1 oligonucleotide and to a much lesser extent to the scrambled oligonucleotide. Proteins eluted from the oligonucleotides, were separated on a 5-15% sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) gradient gel, followed by identification using mass spectrometry. Identified proteins were scored for having one or more of the following known properties: nuclear localization, involved in transcription regulation, involvement in steroid hormone receptor (SHR) function, or specifical involvement in AR function. A total number of 85 nuclear proteins were found in two separate OBAs. Based on peptide counting, we found enrichment of 7 proteins eluted from the ARE1 oligonucleotide, compared to the scrambled oligonucleotide. Taken together with the obtained scores, these proteins are considered putative AR co-factors. One of these proteins, DDX17, is known to be a co-factor for estrogen receptor alpha (ERalpha), but has never been associated with AR function. The results indicate that the ARE oligonucleotide-based assay may allow enrichment of new candidate DNA-bound AR interacting proteins.

Epigenetic regulation and downstream targets of the Rhox5 homeobox gene

The discovery of the Rhox homeobox gene cluster on the X chromosome opens up new vistas in the regulation of reproductive processes in mammals. In mice, this cluster comprises more than 30 genes that are selectively expressed in reproductive tissues. A subset of Rhox genes are androgen and AR regulated in postnatal and adult Sertoli cells, making them candidates to mediate androgen-dependent steps during spermatogenesis. The best characterized of these androgen/AR-regulated genes is Rhox5 (Pem), the founding member of the Rhox gene cluster. Targeted deletion of Rhox5 in mice causes male subfertility marked by increased germ-cell apoptosis and decreased sperm count and motility. Microarray analyses identified a wide variety of genes regulated by Rhox5 in Sertoli cells. One of them is the tumour suppressor UNC5C, a pro-apoptotic molecule previously only known to be involved in brain development. Targeted deletion of Unc5c causes decreased germ-cell apoptosis in postnatal and adult testes, indicating that it also has a role in spermatogenesis and supporting a model in which Rhox5 promotes germ-cell survival by downregulating Unc5c. Rhox5 has two independently regulated promoters that have distinct expression patterns. The unique tissue-specific and developmentally regulated transcription pattern of these two promoters appear to be controlled by DNA methylation. Both promoters are methylated in tissues in which they are not expressed, suggesting that DNA methylation serves to repress Rhox5 expression in inappropriate cell types and tissues. In summary, the Rhox gene cluster is an epigenetically regulated set of genes encoding a large number of transcription factors that are strong candidates to regulate gametogenesis and other aspects of reproduction.

A role for androgens in regulating circadian behavior and the suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) of the hypothalamus is the locus of a master circadian clock controlling behavioral and physiological rhythms, including rhythmic secretion of gonadal hormones. Gonadectomy results in marked alteration of circadian behaviors, including lengthened free-running period, decreased precision of daily onset of running, and elimination of early-evening but not late-night activity bouts. Androgen replacement restores these responses. These aspects of rhythmicity are thought to be regulated by the brain clock, although the site of androgen action remains unknown. Anatomically, the rodent SCN is composed of a ventrolateral core and a dorsomedial shell, and the present studies show that androgen receptors (AR) are localized to the ventrolateral core SCN. Using a transgenic mouse bearing dual reporter molecules driven by the AR targeted to both membrane and nucleus, we find that projections of AR-containing cells form a dense plexus in the core, with their fibers appearing to exit the SCN dorsally. In a second transgenic strain, in which the retinorecipient gastrin-releasing peptide cells express a green fluorescent protein reporter, we show that gastrin-releasing peptide cells contain AR. Through immunocytochemistry, we also show that SCN AR cells express FOS after a light pulse. Importantly, gonadectomy reduces the FOS response after a phase-shifting light pulse, whereas androgen replacement restores levels to those in intact animals. Taken together, the results support previous findings of a hypothalamic neuroendocrine feedback loop. As such, the SCN regulates circadian rhythms in gonadal hormone secretion, and in turn, androgens act on their receptors within the SCN to alter circadian function.

Multiple androgen response elements cooperate in androgen regulated activity of the type 1 neutral endopeptidase promoter

The neutral endopeptidase (NEP) gene is transcriptionally regulated by androgen in prostate cancer cells. We previously identified in the NEP gene an androgen responsive element (NEP-ARE) and an androgen responsive region (NEP-ARR) that together conveyed only moderate androgen-inducibility [Mol. Cell. Endocrinol. 170 (2000) 131]. Therefore, we characterized the entire genomic structure of the NEP gene and identified ARE1 (ACTCAACAttgTGTCCTTT) and ARE2 (CAGGACAtttTGTCCC), which are located in the 3'-untranslated region and in intron 17, respectively. Steroid-dependent enhancement of transcription was assayed by transfecting the pGL-3-luciferase reporter plasmid containing three copies of ARE1 or ARE2 into PC-3 cells. Luciferase activities were increased 3.6-fold (ARE1) and 5-fold (ARE2) by androgen (AR), 4.2-fold (ARE1) and 8.2-fold (ARE2) by dexamethasone, and 3-fold (ARE1) and 4.1-fold (ARE2) by progesterone. Mutation of the ARE1 and ARE2 sequences completely abrogated androgen-inducibility. We next showed that both ARE1 and ARE2 are involved in the transcriptional regulation of the NEP gene, demonstrating in vitro and in vivo binding with AR as determined by electrophoretic mobility gel shift and chromatin immunoprecipitation (ChIP) assays, Furthermore, ARE1 and ARE2 mediate coordinated androgen-inducibility in both an SV40 promoter and the native NEP type 1 promoter. These data indicate the newly identified ARE1 and ARE2 together with the previously identified NEP-ARE function as androgen response elements, and that androgen regulation of the NEP gene is regulated by the coordinated action of multiple AREs in prostate cancer cells.

Post-translational modifications of steroid receptors

The multiple physiological functions of steroid hormones have been known for many years. The cloning of the steroid receptors in the mid-1980s led to the concept of ligand-activated transcription factors and to the identification of specific DNA response elements in the regulatory regions of target genes. The next main development was the identification of cofactors with activating or repressing functions, of which several act by modifying histones and locally affecting the chromatin structure. Work from several groups shows that the steroid receptors themselves can also be modified at various positions. Besides the long-known phosphorylation at tyrosines and serine/threonine residues, other covalent additions such as acetylation, ubiquitylation and sumoylation have been evidenced for steroid receptors in recent years. These modifications affect receptor stability and activity, and provide potential mechanisms for cell- or gene-specific regulation. A better understanding of the impact of these post-translational modifications (PTMs) on steroid receptor function should help in the identification of novel ligands with improved clinical profiles.

Structure and function of steroid receptor AF1 transactivation domains: induction of active conformations

Steroid hormones are important endocrine signalling molecules controlling reproduction, development, metabolism, salt balance and specialized cellular responses, such as inflammation and immunity. They are lipophilic in character and act by binding to intracellular receptor proteins. These receptors function as ligand-activated transcription factors, switching on or off networks of genes in response to a specific hormone signal. The receptor proteins have a conserved domain organization, comprising a C-terminal LBD (ligand-binding domain), a hinge region, a central DBD (DNA-binding domain) and a highly variable NTD (N-terminal domain). The NTD is structurally flexible and contains surfaces for both activation and repression of gene transcription, and the strength of the transactivation response has been correlated with protein length. Recent evidence supports a structural and functional model for the NTD that involves induced folding, possibly involving alpha-helix structure, in response to protein-protein interactions and structure-stabilizing solutes.

The ubiquitin-specific protease USP10 modulates androgen receptor function

The role of the ubiquitin/proteasome system in degrading nuclear hormone receptors and regulating their transcriptional function has emerged in the last few years. We identified the ubiquitin-specific protease USP10 as part of DNA-bound androgen receptor (AR) complexes purified from nuclear extracts of PC-3 cells stably expressing the AR. The interaction between USP10 and the AR was confirmed by GST pull-down assays. Fluorescence microscopy documented that USP10 was localised in the nucleus and the cytoplasm. Cell-based transactivation assays in PC-3/AR cells revealed that overexpression of wild-type USP10, but not of an enzymatically inactive form, stimulated AR activity mediated by reporter constructs harbouring selective androgen response elements (AREs), non-selective steroid response elements (SREs) or the mouse mammary tumour virus (MMTV) promoter. Conversely, USP10 expression knock-down by siRNAs impaired the MMTV response to androgen. In summary, the data indicate that USP10 is a new cofactor that binds to the AR and stimulates the androgen response of target promoters. This finding underlines the role of the ubiquitin/proteasome system in modulating the AR function.

Regulation of the Rhox5 Homeobox Gene in Primary Granulosa Cells: Preovulatory Expression and Dependence on SP1/SP3 and GABP1

Homeobox genes encode transcription factors that regulate embryonic development and postnatal events. Rhox5 (previously called Pem), the founding member of a homeobox gene cluster that we recently identified on the X chromosome, is selectively expressed in granulosa cells in the ovary and other somatic-cell types in other reproductive organs. In this report, we investigate its regulation in granulosa cells in the rat ovary. We found that Rhox5 expression in the ovary is governed by the Rhox5 distal promoter and is expressed at least as early as Day 5 postpartum. Rhox5 mRNA levels are regulated during the ovarian cycle, peaking before ovulation. Deletion analysis revealed a 25-nt element essential for distal promoter transcription in primary granulosa cells. This distal promoter element contains two ETS and one SP1 transcription-factor family binding sites that mutagenesis analysis indicated were essential for high-level transcription. This element was both necessary and sufficient for transcription, because it activated transcription when placed upstream of a heterologous minimal promoter. Cold competition and electrophoretic mobility shift assay studies demonstrated that SP1, SP3, and the ETS family transcription factor GABP bound this element. Dominant-negative forms of GABP and SP3 repressed distal promoter expression in primary rat granulosa, showing that these factors are crucial for Rhox5 expression. Cotransfection of dominant-negative mutants indicated that Rhox5 expression in granulosa cells is regulated by the c-Jun N-terminal protein kinase (JNK, MAPK8) and RAS pathways, which are known to be upstream of ETS family transcription factors. The discovery that Rhox5 expression in granulosa cells is regulated by MAPK pathways and ETS and SP1 family members provides an opportunity to understand how these regulatory pathways and factors collaborate to regulate gene expression during the ovarian cycle.

The role of DNA response elements as allosteric modulators of steroid receptor function

Steroid receptors are ligand-activated transcription factors which control the expression of their target genes by binding to specific DNA elements. Consensus response elements have been delineated for the glucocorticoid, androgen, progesterone and mineralocorticoid receptors on one hand (steroid response element, SRE) and for the estrogen receptor on the other hand (estrogen response element, ERE). Small variations in these sequences not only affect the binding but may also have a dramatic impact on the transcriptional activity of steroid receptors. It has now become obvious that DNA response elements do not merely tether regulatory proteins to control regions of target genes but may additionally impart conformational changes onto the DNA-binding domain as well as to neighbouring domains of steroid receptors. This in turn will create unique platforms for selective recruitment of cofactors and possibly for induction of modifications in local chromatin architecture. An additional level of complexity is added by the frequent presence of multiple response elements in gene promoter regions. The allosteric effects of DNA response elements on steroid receptors may be essential for differential gene expression and this offers interesting perspectives for the identification of selective modulators.

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.

Novel molecular aspects of prostate carcinogenesis

Prostate adenocarcinoma is one of the most frequently diagnosed forms of cancer in the male population of the Western world. The pivotal role of androgen and its receptor in this disease has been abundantly documented and indeed, chemical castration and treatment with antiandrogens are now standard therapies. However, relapse is often observed after 18-24 months, due to the remarkable ability of prostate tumour cells to adapt to low or undetectable androgen levels. Amplification and mutations of the androgen receptor (AR) gene have been described as well as alterations in cofactor expression and crosstalk with other signalling pathways. Another recent line of research focused on the re-programming of gene expression taking place in prostate tumours. Global expression profiling of normal and cancerous prostate tissues led to the identification of tumour-distinctive patterns. Validation studies are currently underway to identify novel drug targets as well as diagnostic and outcome prediction markers.

Structural basis of androgen receptor binding to selective androgen response elements

Steroid receptors bind as dimers to a degenerate set of response elements containing inverted repeats of a hexameric half-site separated by 3 bp of spacer (IR3). Naturally occurring selective androgen response elements have recently been identified that resemble direct repeats of the hexameric half-site (ADR3). The 3D crystal structure of the androgen receptor (AR) DNA-binding domain bound to a selective ADR3 reveals an unexpected head-to-head arrangement of the two protomers rather than the expected head-to-tail arrangement seen in nuclear receptors bound to response elements of similar geometry. Compared with the glucocorticoid receptor, the DNA-binding domain dimer interface of the AR has additional interactions that stabilize the AR dimer and increase the affinity for nonconsensus response elements. This increased interfacial stability compared with the other steroid receptors may account for the selective binding of AR to ADR3 response elements.