Androgen receptor corepressors: an overview

Androgen receptor (AR) coregulators: a diversity of functions converging on and regulating the AR transcriptional complex

Androgens, acting through the androgen receptor (AR), are responsible for the development of the male phenotype during embryogenesis, the achievement of sexual maturation at puberty, and the maintenance of male reproductive function and behavior in adulthood. In addition, androgens affect a wide variety of nonreproductive tissues. Moreover, aberrant androgen action plays a critical role in multiple pathologies, including prostate cancer and androgen insensitivity syndromes. The formation of a productive AR transcriptional complex requires the functional and structural interaction of the AR with its coregulators. In the last decade, an overwhelming and ever increasing number of proteins have been proposed to possess AR coactivating or corepressing characteristics. Intriguingly, a vast diversity of functions has been ascribed to these proteins, indicating that a multitude of cellular functions and signals converge on the AR to regulate its function. The current review aims to provide an overview of the AR coregulator proteins identified to date and to propose a classification of these AR coregulator proteins according to the function(s) ascribed to them. Taken together, this approach will increase our understanding of the cellular pathways that converge on the AR to ensure an appropriate transcriptional response to androgens.

Influence of nucleophosmin/B23 on DNA binding and transcriptional activity of the androgen receptor in prostate cancer cell

The promotion and progression of prostate cancer (PCa) are associated with androgen receptor (AR) signalling. AR functions are modulated by a variety of co-factors amongst which we identified the nucleophosmin (NPM/B23), a member of the histone chaperone family. Here, we show that NPM is overexpressed in PCa compared to normal adjacent tissues. AR and NPM interact in vitro and in vivo, and NPM is critical for androgen-dependent transcriptional activation in LNCaP cells as an anti-NPM siRNA downregulates transcription of a transfected androgen response element (ARE)-containing reporter promoter as well as expression of the endogenous androgen responsive prostate-specific antigen (PSA) gene. By investigating the effect of NPM on AR, we have also observed that NPM enhances AR binding to an ARE in vitro in electrophoretic gel mobility-shift assay experiments. Chromatin immunoprecipitation studies further demonstrated that both AR and NPM associate with AREs of the PSA gene in vivo. Altogether, our data suggest that the molecular histone chaperone NPM could regulate AR functions by promoting assembly of AR-containing regulatory complexes and that high levels of NPM might alter AR functions in PCa.

The evolving biology and treatment of prostate cancer

Since the effectiveness of androgen deprivation for treatment of advanced prostate cancer was first demonstrated, prevention strategies and medical therapies for prostate cancer have been based on understanding the biologic underpinnings of the disease. Prostate cancer treatment is one of the best examples of a systematic therapeutic approach to target not only the cancer cells themselves, but the microenvironment in which they are proliferating. As the population ages and prostate cancer prevalence increases, challenges remain in the diagnosis of clinically relevant prostate cancer as well as the management of the metastatic and androgen-independent metastatic disease states.

A splicing variant of the androgen receptor detected in a metastatic prostate cancer exhibits exclusively cytoplasmic actions

The androgen receptor (AR) is a ligand-activated transcription factor that displays genomic actions characterized by binding to androgen-response elements in the promoter of target genes as well as nongenomic actions that do not require nuclear translocation and DNA binding. In this study, we report exclusive cytoplasmic actions of a splicing variant of the AR detected in a metastatic prostate cancer. This AR variant, named AR23, results from an aberrant splicing of intron 2, wherein the last 69 nucleotides of the intronic sequence are retained, leading to the insertion of 23 amino acids between the two zinc fingers in the DNA-binding domain. We show that the nuclear entry of AR23 upon dihydrotestosterone (DHT) stimulation is impaired. Alternatively, DHT-activated AR23 forms cytoplasmic and perinuclear aggregates that partially colocalize with the endoplasmic reticulum and are devoid of genomic actions. However, in LNCaP cells, this cytoplasmic DHT-activated AR23 remains partially active as evidenced by the activation of transcription from androgen-responsive promoters, the stimulation of NF-kappaB transcriptional activity and by the decrease of AP-1 transcriptional activity. Our data reveal novel cytoplasmic actions for this splicing AR variant, suggesting a contribution in prostate cancer progression.

Subcellular Localization Modulates Activation Function 1 Domain Phosphorylation in the Androgen Receptor

Although the steady-state distribution of the androgen receptor (AR) is predominantly nuclear in androgen-treated cells, androgen-bound AR shuttles between the nucleus and the cytoplasm. In the present study we have addressed how nucleocytoplasmic shuttling contributes to the regulation of AR. Nuclear transport signal fusions were used to force AR localization to the nucleus or cytoplasm of prostate cancer cells, and the effect of localization on shuttling, transcription, androgen binding, and phosphorylation was determined. Fusing the simian virus 40 nuclear localization signal or c-Abl nuclear export signal to AR resulted in androgen-independent localization to the nucleus or cytoplasm, respectively. AR forced to the nucleus was transcriptionally active on prostate-specific antigen and mouse mammary tumor virus promoters driving reporter genes. AR forced to the cytoplasm was largely inactive on the prostate-specific antigen promoter, but, surprisingly, AR was active on the mouse mammary tumor virus promoter and on two endogenous genes examined. Thus, highly transient nuclear localization of AR is sufficient to activate transcription. Androgen dissociation rates and the dissociation constant (KD) of AR for androgen were similar whether AR was localized to the cytoplasm or the nucleus, suggesting the ligand-binding cycle of AR is not strictly linked to its compartmentalization. Using phosphosite antibodies, we found that compartmentalization influences the phosphorylation state of AR. We show there is a bias for androgen-dependent phosphorylation of Ser81, Ser256, and Ser308 in the nucleus and androgen-independent phosphorylation of Ser94 in the cytoplasm. We propose that one function of nucleocytoplasmic shuttling is to integrate the signaling environment in the cytoplasm with AR activity in the nucleus.

Cyclin D3/CDK11p58 complex is involved in the repression of androgen receptor

Androgen receptor (AR) is essential for the maintenance of the male reproductive systems and is critical for the carcinogenesis of human prostate cancers (PCas). D-type cyclins are closely related to the repression of AR function. It has been well documented that cyclin D1 inhibits AR function through multiple mechanisms, but the mechanism of how cyclin D3 exerts its repressive role in the AR signaling pathway remains to be identified. In the present investigation, we demonstrate that cyclin D3 and the 58-kDa isoform of cyclin-dependent kinase 11 (CDK11p58) repressed AR transcriptional activity as measured by reporter assays of transformed cells and prostate-specific antigen expression in PCa cells. AR, cyclin D3, and CDK11p58 formed a ternary complex in cells and were colocalized in the luminal epithelial layer of the prostate. AR activity is controlled by phosphorylation at specific sites. We found that AR was phosphorylated at Ser-308 by cyclin D3/CDK11p58 in vitro and in vivo, leading to the repressed activity of AR transcriptional activation unit 1 (TAU1). Furthermore, androgen-dependent proliferation of PCa cells was inhibited by cyclin D3/CDK11p58 through AR repression. These data suggest that cyclin D3/CDK11p58 signaling is involved in the negative regulation of AR function.

Sirtuin 1 is required for antagonist-induced transcriptional repression of androgen-responsive genes by the androgen receptor

Androgen antagonists or androgen deprivation is a primary therapeutic modality for the treatment of prostate cancer. Invariably, however, the disease becomes progressive and unresponsive to androgen ablation therapy (hormone refractory). The molecular mechanisms by which the androgen antagonists inhibit prostate cancer proliferation are not fully defined. In this report, we demonstrate that sirtuin 1 (SIRT1), a nicotinamide adenosine dinucleotide-dependent histone deacetylase (HDAC) linked to the regulation of longevity, is required for androgen antagonist-mediated transcriptional repression and growth suppression. Androgen antagonist-bound androgen receptor (AR) recruits SIRT1 and nuclear receptor corepressor to AR-responsive promoters and deacetylates histone H3 locally at the prostate-specific antigen promoter. Furthermore, SIRT1 down-regulation by small interfering RNA or by pharmacological means increased the sensitivity of androgen-responsive genes to androgen stimulation, enhanced the sensitivity of prostate cancer cell proliferative responses to androgens, and decreased the sensitivity of prostate cancer cells to androgen antagonists. In this study, we demonstrate the ligand-dependent recruitment of a class III HDAC into a corepressor transcriptional complex and a necessary functional role for a class III HDAC as a transcriptional corepressor in AR antagonist-induced transcriptional repression. Collectively, these findings identify SIRT1 as a corepressor of AR and elucidate a new molecular pathway relevant to prostate cancer growth and approaches to therapy.

Alien interacts with the human androgen receptor and inhibits prostate cancer cell growth

Prostate cancer cell growth is initially androgen dependent. Androgen antagonists are used in prostate cancer therapy to inactivate the transcriptional activity of the human androgen receptor (hAR) and to inhibit the proliferation of prostate cancer. Here, we have characterized Alien with characteristics of a corepressor as a novel interacting factor for the antagonist bound hAR. Alien is recruited to hAR in the presence of the AR antagonist cyproterone acetate (CPA). The interaction of Alien with hAR is verified in vivo and in vitro by a modified mammalian two-hybrid system, coimmunoprecipitation, chromatin immunoprecipitation, and in vitro binding assays. In contrast to other nuclear receptors, Alien binds to the amino-terminus of hAR with the receptor SUMOylation (small ubiquitin modifier) sites being involved. Furthermore, cellular localization of Alien is changed towards a predominant nuclear localization upon treatment of prostate cancer cells with CPA. Notably, stable expression of Alien in LNCaP cells inhibits both endogenous prostate-specific antigen expression and proliferation of these cells in the presence of CPA but not in the presence of an AR agonist. These findings underline the importance of corepressors for inhibition of prostate cancer cell growth by androgen antagonists.

Ligand-specific dynamics of the androgen receptor at its response element in living cells

Androgens have key roles in normal physiology and in male sexual differentiation as well as in pathological conditions such as prostate cancer. Androgens act through the androgen receptor (AR), which is a ligand-modulated transcription factor. Antiandrogens block AR function and are widely used in disease states, but little is known about their mechanism of action in vivo. Here, we describe a rapid differential interaction of AR with target genomic sites in living cells in the presence of agonists which coincides with the recruitment of BRM ATPase complex and chromatin remodeling, resulting in transcriptional activation. In contrast, the interaction of antagonist-bound or mutant AR with its target was found to be kinetically different: it was dramatically faster, occurred without chromatin remodeling, and resulted in the lack of transcriptional inhibition. Fluorescent resonance energy transfer analysis of wild-type AR and a transcriptionally compromised mutant at the hormone response element showed that intramolecular interactions between the N and C termini of AR play a key functional role in vivo compared to intermolecular interactions between two neighboring ARs. These data provide a kinetic and mechanistic basis for regulation of gene expression by androgens and antiandrogens in living cells.

Proline-, glutamic acid-, and leucine-rich protein-1/modulator of nongenomic activity of estrogen receptor enhances androgen receptor functions through LIM-only coactivator, four-and-a-half LIM-only protein 2

Proline-, glutamic acid-, and leucine-rich protein-1 (PELP1) is a coregulator of multiple nuclear receptors. Molecular mechanisms of PELP1 function are not completely understood, but its expression is up-regulated in hormonal-dependent cancers. Using a yeast two-hybrid screen, we found that four-and-a-half LIM-only protein 2 (FHL2) interacted with PELP1. FHL2 is a transcriptional regulator that associates with nuclear cofactors, including androgen receptors (ARs), and contains an intrinsic activation domain. PELP1 and FHL2 interact in vitro and in vivo and colocalize in the nuclear compartment. PELP1 interacts with FHL2 via LIM domains 3 and 4 and synergistically enhances the transcriptional activity of FHL2. Src kinase is required for PELP1-mediated enhancement of FHL2 functions because knockdown of Src kinase expression or function abolished PELP1-mediated FHL2 activation functions. PELP1 interacted with AR and enhanced FHL2-mediated AR transactivation functions. PELP1 knockdown by small interfering RNA or PELP1 mutant, which lacks an activation domain, reduced FHL2-mediated AR transactivation. Biochemical analyses revealed a complex consisting of PELP1, FHL2, and AR in prostate cancer cells. PELP1/MNAR expression was elevated in high-grade prostate tumors. Our results suggest that PELP1 functions as a molecular adaptor, coupling FHL2 with nuclear receptors, and PELP1-FHL2 interactions may have a role in prostate cancer progression.

A novel function of caspase-8 in the regulation of androgen-receptor-driven gene expression

Transcriptional regulation by the androgen receptor (AR) is critical for male sexual development and prostate cancer. In this study, we used an expression cloning strategy to identify molecules that regulate AR-driven transcription. Screening of a human cDNA library resulted in isolation of caspase-8 (Casp8), an initiator caspase that mediates death-receptor-induced apoptosis. Casp8 repressed AR-dependent gene expression independently of its apoptotic protease activity by disrupting AR amino-terminal and carboxy-terminal (N/C) interaction and inhibiting androgen-induced AR nuclear localization. Protein-protein interaction analysis revealed that three motifs in Casp8 specifically interacted with the motifs that are known to be involved in AR N/C interaction. Substitutions of the amino-acid residues critical for AR-Casp8 interactions abolished the Casp8-mediated inhibition of AR transactivation. In addition, knockdown of Casp8 by RNA interference specifically affected the androgen-dependent expression of AR-targeting genes in LNCaP cells. These results indicate that Casp8 has a novel function beyond its known role in the mediation of apoptosis.

Hormonal control of androgen receptor function through SIRT1

The NAD-dependent histone deacetylase Sir2 plays a key role in connecting cellular metabolism with gene silencing and aging. The androgen receptor (AR) is a ligand-regulated modular nuclear receptor governing prostate cancer cellular proliferation, differentiation, and apoptosis in response to androgens, including dihydrotestosterone (DHT). Here, SIRT1 antagonists induce endogenous AR expression and enhance DHT-mediated AR expression. SIRT1 binds and deacetylates the AR at a conserved lysine motif. Human SIRT1 (hSIRT1) repression of DHT-induced AR signaling requires the NAD-dependent catalytic function of hSIRT1 and the AR lysine residues deacetylated by SIRT1. SIRT1 inhibited coactivator-induced interactions between the AR amino and carboxyl termini. DHT-induced prostate cancer cellular contact-independent growth is also blocked by SIRT1, providing a direct functional link between the AR, which is a critical determinant of progression of human prostate cancer, and the sirtuins.

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.

SP1 and SP3 mediate progesterone-dependent induction of the 17beta hydroxysteroid dehydrogenase type 2 gene in human endometrium

The opposing actions of estrogen and progesterone during the menstrual cycle regulate the cyclical and predictable endometrial proliferation and differentiation that is required for implantation. Progesterone indirectly stimulates the expression of 17beta hydroxysteroid dehydrogenase type 2 (HSD17B2), which catalyzes the conversion of biologically potent estradiol to weakly estrogenic estrone in the endometrial epithelium. We previously demonstrated upregulation of the HSD17B2 gene in human endometrial epithelial cells by factors secreted from endometrial stromal cells in response to progesterone. We investigated the underlying mechanism by which these stroma-derived, progesterone-induced paracrine factors stimulate HSD17B2 expression. Here, we show that transcription factors SP1 and SP3 interact with specific motifs in HSD17B2 promoter to upregulate enzyme expression in human endometrial epithelial cell lines. Conditioned medium (CM) from progestin-treated stromal cells increased levels of SP1 and SP3 in endometrial epithelial cells and induced HSD17B2 mRNA expression. Mithramycin A, an inhibitor of SP1-DNA interaction, reduced epithelial HSD17B2 promoter activity in a dose-dependent manner. Serial deletion and site-directed mutants of the HSD17B2 promoter demonstrated that two overlapping SP1 motifs (nt -82/-65) are essential for induction of promoter activity by CM or overexpression of SP1/SP3. CM markedly enhanced, whereas anti-SP1/SP3 antibodies inhibited, binding of nuclear proteins to this region of the HSD17B2 promoter. In vivo, we demonstrated a significant spatiotemporal association between epithelial SP1/SP3 and HSD17B2 levels in human endometrial biopsies. Taken together, these data suggest that HSD17B2 expression in endometrial epithelial cells, and, therefore, estrogen inactivation, is regulated by SP1 and SP3, which are downstream targets of progesterone-dependent paracrine signals originating from endometrial stromal cells.

PSPC1, NONO, and SFPQ are expressed in mouse Sertoli cells and may function as coregulators of androgen receptor-mediated transcription

In Sertoli cells of testis, androgen receptor-regulated gene transcription plays an indispensable role in maintaining spermatogenesis. Androgen receptor activity is modulated by a number of coregulators which are associated with the androgen receptor. Non-POU-domain-containing, octamer binding protein (NONO), a member of the DBHS-containing proteins, complexes with androgen receptor and functions as a coactivator for the receptor. Paraspeckle protein 1 alpha isoform (PSPC1, previously known as PSP1) and Splicing factor, proline- and glutamine-rich (SFPQ, previously known as PSF), other members of the DBHS-containing proteins, are also found in androgen receptor complexes, suggesting that these DBHS-containing proteins may cooperatively regulate androgen receptor-mediated gene transcription. We demonstrated that PSPC1, NONO, and SFPQ are coexpressed in Sertoli cell line TTE3 and interact reciprocally. The effect of the DBHS-containing proteins on the transcriptional activity was assessed using the construct containing androgen-responsive elements followed by a luciferase gene. The results showed that all the DBHS-containing proteins activate androgen receptor-mediated transcription, and PSPC1 is the most effective coactivator among them. Furthermore, we confirmed the presence of PSPC1, NONO, and SFPQ proteins in Sertoli cells of adult mouse testis sections. These observations suggest that PSPC1, NONO, and SFPQ form complexes with each other in Sertoli cells and may regulate androgen receptor-mediated transcriptional activity.

A Role of the Amino-Terminal (N) and Carboxyl-Terminal (C) Interaction in Binding of Androgen Receptor to Chromatin

The N-terminal domain of AR is known to engage a hormone-dependent interaction with its C-terminal ligand-binding domain, and this N/C interaction is known to modulate AR transcriptional activity. Using Xenopus oocytes as a model system to study transcriptional regulation in chromatin, we found that two previously reported N/C interaction-defective AR mutants, one with deletion of 23FQNLF27(ARDeltaF) and one with a Gly 21 to Glu mutation (ARG21E), were surprisingly inactive in activating transcription from various reporters assembled into chromatin. Further study using chromatin immunoprecipitation assay revealed that these mutants failed to bind both mouse mammary tumor virus-long terminal repeat and prostate-specific antigen enhancer assembled into chromatin. This defect is specific to chromatin because both mutants could bind to a consensus AR response element in vitro and activate transcription driven by mouse mammary tumor virus-long terminal repeat in transient transfection as effective as the wild-type AR. To further substantiate this novel finding, we established 293 cell lines that stably expressed either AR or ARDeltaF mutant in an inducible manner. Using these cell lines, we confirmed by using chromatin immunoprecipitation assay that AR but not ARDeltaF could bind to the endogenous prostate-specific antigen enhancer. Furthermore, we found that the ARDeltaF mutant interacts poorly with Brg1, the ATPase subunit of the chromatin-remodeling factor SWI/SNF. Taken together, our study reveals a novel role of AR N/C interaction in control of AR chromatin binding and suggests a working model that the proper N/C interaction is required for AR to recruit SWI/SNF complex, which in turn remodels chromatin to allow AR to bind to AR response elements in chromatin.

Receptor-interacting protein 140 is a repressor of the androgen receptor activity

The androgen receptor (AR) is a ligand-activated transcription factor that controls growth and survival of prostate cancer cells. In the present study, we investigated the regulation of AR activity by the receptor-interacting protein 140 (RIP140). We first showed that RIP140 could be coimmunoprecipitated with the receptor when coexpressed in 293T cells. This interaction appeared physiologically relevant because chromatin immunoprecipitation assays revealed that, under R1881 treatment, RIP140 could be recruited to the prostate-specific antigen encoding gene in LNCaP cells. In vitro glutathione S-transferase pull-down assays provided evidence that the carboxy-terminal domain of AR could interact with different regions of RIP140. By means of fluorescent proteins, we demonstrated that ligand-activated AR was not only able to translocate to the nucleus but also to relocate RIP140 from very structured nuclear foci to a diffuse pattern. Overexpression of RIP140 strongly repressed AR-dependent transactivation by preferentially targeting the ligand binding domain-dependent activity. Moreover, disruption of RIP140 expression induced AR overactivation, thus revealing RIP140 as a strong AR repressor. We analyzed its mechanism of transrepression and first demonstrated that different regions of RIP140 could mediate AR-dependent repression. We then showed that the carboxy-terminal end of RIP140 could reverse transcriptional intermediary factor 2-dependent overactivation of AR. The use of mutants of RIP140 allowed us to suggest that C-terminal binding protein played no role in RIP140-dependent inhibition of AR activity, whereas histone deacetylases partly regulated that transrepression. Finally, we provided evidence for a stimulation of RIP140 mRNA expression in LNCaP cells under androgen treatment, further emphasizing the role of RIP140 in androgen signaling.

Gonadal steroids in critical illness

Gonadal steroids are metabolized in target cells and then interact with specific receptors to exert genomic and nongenomic effects. Complex feedback loops that involve the immune-neuroendocrine axis, limbic system, and gonadal steroids play a vital role in the adaptation to critical illness. Preclinical studies demonstrate adverse physiological effects of androgens on the cardiovascular and immune systems despite its purported anabolic effects. Similar models also demonstrate salutary effects of estrogens on these systems. Thus, during the catabolic phases of acute and chronic critical illness, estrogen, and not androgen, therapy may prove to be a valuable intervention. However, during the post-critical illness recovery phase, when anabolism is critical, androgen therapy may still be useful and safe.

Androgen activation of the sterol regulatory element-binding protein pathway: Current insights

The cellular effects of androgens are mediated by a cognate receptor, the androgen receptor. Typically, the androgen receptor is viewed to exert its activity by binding to androgen response elements located in or near the promoter region of target genes, thereby directly affecting the expression of these genes. However, increasing evidence indicates that androgens may also indirectly influence the expression of genes that do not contain androgen response elements by modulating the activity of secondary transcription factors, mediating the expression of growth factors acting in a paracrine or autocrine fashion, or by inducing changes in the production of other hormones. These indirect effects of androgens can induce cascade-like actions and may play an important role in more complex processes involving coordinated responses of genes, cells, and organs. Previously, our laboratory has identified and characterized a novel indirect mechanism of androgen action involving proteolytical activation of the key lipogenic transcription factor sterol regulatory element-binding protein (SREBP), resulting in the coordinate up-regulation of entire cellular lipogenic pathways. Interestingly, activation of SREBPs by androgens occurs not only under normal physiological conditions but has also been observed in a growing number of pathologies, and more in particular in the setting of steroid-regulated cancers, where increased lipogenesis has been shown to have remarkable diagnostic and prognostic potential and is considered a prime target for novel therapeutic approaches. This review aims to analyze current insights into the molecular mechanism(s) underlying androgen activation of the SREBP pathway and to ascertain the extent to which this phenomenon can be generalized to androgen-responsive cell systems.

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.

Microarray profiling of gene expression patterns in adult male rat brain following acute progesterone treatment

Progesterone can influence various behaviors in adult male rats, however, little is known about which particular genes are regulated by progesterone in the male rat brain. Using focused microarray technology, we where able to define a subset of genes that are responsive to progesterone. Nylon membrane-based cDNA microarrays were used to profile gene expression patterns in the preoptic area/mediobasal hypothalamus (POA/MBH) of male rat brain 7 h following a single injection of progesterone. RNA was isolated from the brains of 6 male rats injected with progesterone and 6 male rats injected with sesame oil. Next, we hybridized the RNA from each animal to individual cDNA microarrays that contained more than 100 target genes, all of which are involved in cAMP and or calcium signaling pathways. Direct side-by-side comparison of all 12 arrays revealed differences in the expression patterns of 12 different genes. We confirmed the data gathered from the arrays on 4 different genes using Real-Time PCR. These data begin to outline the important role played by progesterone in mediating changes in gene expression within the male brain.

Modulation of Androgen Receptor Transactivation by FoxH1

Androgen signaling plays key roles in the development and progression of prostate cancer, and numerous ongoing studies focus on the regulation of androgen receptor (AR) transactivity to develop novel therapies for the treatment of androgen-independent prostate cancer. FoxH1, a member of the Forkhead-box (FOX) gene family of transcription factors, takes part in mediating transforming growth factor-beta/activin signaling through its interaction with the Smad2.Smad4 complex. Using a series of experiments, we found that FoxH1 repressed both ligand-dependent and -independent transactivation of the AR on androgen-induced promoters. This action of FoxH1 was independent of its transactivation capacity and activin A but relieved by Smad2.Smad4. In addition, the repression of the AR by FoxH1 did not require deacetylase activity. A protein-protein interaction was identified between the AR and FoxH1 independently of dihydrotestosterone. Furthermore, a confocal microscopic analysis of LNCaP cells revealed that the interaction between the AR and FoxH1 occurred in the nucleus and that FoxH1 specifically blocked the foci formation of dihydrotestosterone-activated AR, which has been shown to be correlated with the AR transactivation potential. Taken together, our results indicate that FoxH1 functions as a new corepressor of the AR. Our observations not only strengthen the role of FoxH1 in AR-mediated transactivation but also suggest that therapeutic interventions based on AR-coregulator interactions could be designed to block both androgen-dependent and -independent growth of prostate cancer.