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

Mechanistic Insights into Bisphenol A-Mediated Male Infertility: Potential Role of Panax Ginseng Extract

Male infertility is identified by the inability of a man to successfully impregnate his fertile female partner, even following a year of regular unprotected sexual intercourse. About half of all infertility cases are attributed to what is known as "male factor" infertility. The escalating prevalence of male infertility in the contemporary era across the globe can be largely attributed to environmental pollution, which is the common etiological factor due to the ubiquitous presence of the environmental contaminants. Bisphenol A is recognized as an endocrine-disrupting chemical that has adverse effects on both male and female reproductive systems. On the other hand, numerous studies have demonstrated that Panax ginseng possessed the potential to improve male infertility parameters; promote spermatogenesis, recover the quality and motility of sperm and enhance testicular functions as it acted as a natural androgen supplement. The objective of this review is to offer a summary of the findings obtained from the current research data on the insult of bisphenol A (BPA) on male infertility and its supposed mode of action, as well as shed light on the potent ameliorative role of Panax ginseng extract, with a special focus on the mechanism behind its action. This review delivers a clear understanding of BPA mechanism of action on male infertility and the presumed risks deriving from its exposure. Also, this review provides evidence for the functional role of Panax ginseng extract in restoring male fertility.

Androgen Receptor in Hormone Receptor-Positive Breast Cancer

Breast cancer subtypes expressing hormone receptors (HR+ BCa) have a good prognosis and respond to first-line endocrine therapy (ET). However, the majority of HR+ BCa patients exhibit intrinsic or acquired ET resistance (ET-R) and rapid onset of incurable metastatic BCa. With the failure of conventional ET, limited targeted therapy exists for ET-R HR+ BCa patients. The androgen receptor (AR) in HR-negative BCa subtypes is emerging as an attractive alternative target for therapy. The AR drives Luminal AR (LAR) triple-negative breast cancer progression, and LAR patients consistently exhibit positive clinical benefits with AR antagonists in clinical trials. In contrast, the function of the AR in HR+ BCa is more conflicting. AR in HR+ BCa correlates with a favorable prognosis, and yet, the AR supports the development of ET-R BCa. While AR antagonists were ineffective, ongoing clinical trials with a selective AR modulator have shown promise for HR+ BCa patients. To understand the incongruent actions of ARs in HR+ BCa, the current review discusses how the structure and post-translational modification impact AR function. Additionally, completed and ongoing clinical trials with FDA-approved AR-targeting agents for BCa are presented. Finally, we identify promising investigational small molecules and chimera drugs for future HR+ BCa therapy.

Newly Developed Targeted Therapies Against the Androgen Receptor in Triple-Negative Breast Cancer: A Review

Among different types of breast cancers (BC), triple-negative BC (TNBC) amounts to 15% to 20% of breast malignancies. Three principal characteristics of TNBC cells are (i) extreme aggressiveness, (ii) absence of hormones, and (iii) growth factor receptors. Due to the lack or poor expression of the estrogen receptor, human epidermal growth factor receptor 2, and progesterone receptor, TNBC is resistant to hormones and endocrine therapies. Consequently, chemotherapy is currently used as the primary approach against TNBC. Expression of androgen receptor (AR) in carcinoma cells has been observed in a subset of patients with TNBC; therefore, inhibiting androgen signaling pathways holds promise for TNBC targeting. The new AR inhibitors have opened up new therapy possibilities for BC patients carrying AR-positive TNBC cells. Our group provides a comprehensive review of the structure and function of the AR and clinical evidence for targeting the cell's nuclear receptor in TNBC. We updated AR agonists, inhibitors, and antagonists. We also presented a new era of genetic manipulating CRISPR/Cas9 and nanotechnology as state-of-the-art approaches against AR to promote the efficiency of targeted therapy in TNBC. SIGNIFICANCE STATEMENT: The lack of effective treatment for triple-negative breast cancer is a health challenge. The main disadvantages of existing treatments are their side effects, due to their nonspecific targeting. Molecular targeting of cellular receptors, such as androgen receptors, increased expression in malignant tissues, significantly improving the survival rate of breast cancer patients.

Differential DNA-binding and cofactor recruitment are possible determinants of the synthetic steroid YK11-dependent gene expression by androgen receptor in breast cancer MDA-MB 453 cells

Recently, selective androgen receptor modulators (SARMs), which bind to AR and act in a tissue/effect-specific manner, have been developed, but the selective mechanism is not well understood. In this study, we investigated the selective mechanism using the synthetic steroid YK11, which showed AR-mediated gene-selective transactivation. In the AR-positive human breast cancer MDA-MB-453 cells, different patterns of AR-mediated target gene expression and AR recruitment to their enhancer regions were observed between DHT and YK11. A docking study suggested the helices 11 and 12 was moved by the sterically hindered C17-group of YK11. Furthermore, the mutational studies of AR Gln902 and mammalian two-hybrid assays suggested different cofactor recruitment between DHT and YK11. The results of this study suggest that gene selective regulation by SARMs results from differential DNA-binding and/or cofactor recruitment by ligands. These results provide novel insights into the mechanism of action of SARMs.

The androgen receptor depends on ligand-binding domain dimerization for transcriptional activation

Whereas dimerization of the DNA-binding domain of the androgen receptor (AR) plays an evident role in recognizing bipartite response elements, the contribution of the dimerization of the ligand-binding domain (LBD) to the correct functioning of the AR remains unclear. Here, we describe a mouse model with disrupted dimerization of the AR LBD (AR^Lmon/Y ). The disruptive effect of the mutation is demonstrated by the feminized phenotype, absence of male accessory sex glands, and strongly affected spermatogenesis, despite high circulating levels of testosterone. Testosterone replacement studies in orchidectomized mice demonstrate that androgen-regulated transcriptomes in AR^Lmon/Y mice are completely lost. The mutated AR still translocates to the nucleus and binds chromatin, but does not bind to specific AR binding sites. In vitro studies reveal that the mutation in the LBD dimer interface also affects other AR functions such as DNA binding, ligand binding, and co-regulator binding. In conclusion, LBD dimerization is crucial for the development of AR-dependent tissues through its role in transcriptional regulation in vivo. Our findings identify AR LBD dimerization as a possible target for AR inhibition.

Steroid receptor-coregulator transcriptional complexes: new insights from CryoEM

Steroid receptors activate gene transcription through recruitment of a number of coregulators to facilitate histone modification, chromatin remodeling, and general transcription machinery stabilization. Understanding the structures of full-length steroid receptor and coregulatory complexes has been difficult due to their large molecular sizes and dynamic structural conformations. Recent developments in cryo-electron microscopy (cryoEM) technology and proteomics have advanced the structural studies of steroid receptor complexes. Here, we will review the insights we learned from cryoEM studies of the estrogen and androgen receptor transcriptional complexes. Despite similar domain organizations, the two receptors have different coregulator interaction modes. The cryoEM structures now have revealed the fundamental differences between the two receptors and their functional mechanisms.

Glucocorticoid receptor Thr524 phosphorylation by MINK1 induces interactions with 14-3-3 protein regulators

The glucocorticoid receptor (GR) is a ligand-dependent transcription factor that plays a central role in inflammation. The GR activity is also modulated via protein–protein interactions, including binding of 14-3-3 proteins induced by GR phosphorylation. However, the specific phosphorylation sites on the GR that trigger these interactions and their functional consequences are less clear. Hence, we sought to examine this system in more detail. We used phosphorylated GR peptides, biophysical studies, and X-ray crystallography to identify key residues within the ligand-binding domain of the GR, T524 and S617, whose phosphorylation results in binding of the representative 14-3-3 protein 14-3-3ζ. A kinase screen identified misshapen-like kinase 1 (MINK1) as responsible for phosphorylating T524 and Rho-associated protein kinase 1 for phosphorylating S617; cell-based approaches confirmed the importance of both GR phosphosites and MINK1 but not Rho-associated protein kinase 1 alone in inducing GR–14-3-3 binding. Together our results provide molecular-level insight into 14-3-3-mediated regulation of the GR and highlight both MINK1 and the GR–14-3-3 axis as potential targets for future therapeutic intervention.

Structural Insights of Transcriptionally Active, Full-Length Androgen Receptor Coactivator Complexes

Steroid receptors activate gene transcription by recruiting coactivators to initiate transcription of their target genes. For most nuclear receptors, the ligand-dependent activation function domain-2 (AF-2) is a primary contributor to the nuclear receptor (NR) transcriptional activity. In contrast to other steroid receptors, such as ERα, the activation function of androgen receptor (AR) is largely dependent on its ligand-independent AF-1 located in its N-terminal domain (NTD). It remains unclear why AR utilizes a different AF domain from other receptors despite that NRs share similar domain organizations. Here, we present cryoelectron microscopy (cryo-EM) structures of DNA-bound full-length AR and its complex structure with key coactivators, SRC-3 and p300. AR dimerization follows a unique head-to-head and tail-to-tail manner. Unlike ERα, AR directly contacts a single SRC-3 and p300. The AR NTD is the primary site for coactivator recruitment. The structures provide a basis for understanding assembly of the AR:coactivator complex and its domain contributions for coactivator assembly and transcriptional regulation.

Effects and mechanisms of pyrethroids on male reproductive system

Synthetic pyrethroids are used as insecticides in agriculture and a variety of household applications worldwide. Pyrethroids are widely distributed in all environmental compartments and the general populations are exposed to pyrethroids through various routes. Pyrethroids have been identified as endocrine-disrupting chemicals (EDCs) which are responsible for the male reproductive impairments. The data confirm pyrethroids cause male reproductive damages. The insecticides exert the toxic effects on male reproductive system through various complex mechanisms including antagonizing androgen receptor (AR), inhibiting steroid synthesis, affecting the hypothalamic-pituitary-gonadal (HPG) axis, acting as estrogen receptor (ER) modulators and inducing oxidative stress. The mechanisms of male reproductive toxicity of pyrethroids involve multiple targets and pathways. The review will provide further insight into pyrethroid-induced male reproductive toxicity and mechanisms, which is crucial to preserve male reproductive health.

Ligand induced dissociation of the AR homodimer precedes AR monomer translocation to the nucleus

The androgen receptor (AR) regulates male sexual development. We have now investigated AR homodimerization, hormone-dependent monomerization and nuclear translocation in PC-3 and COS-1 cells, by utilizing mutations associated with the androgen insensitivity syndrome: Pro767Ala, Phe765Leu, Met743Val and Trp742Arg. AR wild type (WT) was expressed as a homodimer in the cytoplasm, while none of these mutants formed homodimers. Unlike AR WT which responded to 1 nM dihydrotestosterone (DHT) to dissociate and translocate into the nucleus, AR Pro767Ala and Phe765Leu mutants remain as the monomer in the cytoplasm. In the crystal structure of the AR LBD homodimer, Pro767 and Phe765 reside closely on a loop that constitutes the dimer interface; their sidechains interact with the Pro767 of the other monomer and with the DHT molecule in the ligand-binding pocket. These observations place Phe765 at a position to facilitate DHT binding to Pro767 and lead to dissociation of the AR homodimer in the cytoplasm. This Pro-Phe Met relay may constitute a structural switch that mediates androgen signaling and is conserved in other steroid hormone receptors.

A magic drug target: Androgen receptor

Androgen receptor (AR) is closely associated with a group of hormone-related diseases including the cancers of prostate, breast, ovary, pancreas, etc and anabolic deficiencies such as muscle atrophy and osteoporosis. Depending on the specific type and stage of the diseases, AR ligands including not only antagonists but also agonists and modulators are considered as potential therapeutics, which makes AR an extremely interesting drug target. Here, we at first review the current understandings on the structural characteristics of AR, and then address why and how AR is investigated as a drug target for the relevant diseases and summarize the representative antagonists and agonists targeting five prospective small molecule binding sites at AR, including ligand-binding pocket, activation function-2 site, binding function-3 site, DNA-binding domain, and N-terminal domain, providing recent insights from a target and drug development view. Further comprehensive studies on AR and AR ligands would bring fruitful information and push the therapy of AR relevant diseases forward.

GR Utilizes a Co-Chaperone Cytoplasmic CAR Retention Protein to Form an N/C Interaction

The N-terminal domain (NTD) of nuclear receptor superfamily members has been recently reported to regulate functions of the receptor through the interaction between the NTD and the C-terminal ligand binding domain (LBD), so-called an N/C interaction. Although this N/C interaction has been demonstrated in various nuclear receptors, eg, androgen receptor, this concept has not been observed in glucocorticoid receptor (GR). We hypothesized that GR requires its co-chaperone CCRP (cytoplasmic constitutive active/androstane receptor retention protein) to form a stable N/C interaction. This hypothesis was examined by co-immunoprecipitation assays using GR fragments overexpressing COS-1 cell lysate. Here, we demonstrated that GR undergoes the N/C interaction between the ²⁶VMDFY³⁰ motif in the NTD and the LBD. More importantly, co-chaperone CCRP is now found to induce this interaction. By the fact that a negative charge at Y30 disrupts this interaction, this residue, a potential phosphorylation site, was indicated to regulate the GR N/C interaction critically. Utilizing Y30F and Y30E mutants as N/C interacting and noninteracting forms of GR, respectively, a 2-dimensional blue native/sodium dodecyl sulfate-polyacrylamide gel electrophoresis was performed to examine whether or not the N/C interaction regulated formation of GR complexes. A cDNA microarray analysis was performed with COS-1 cells expressing Y30F or Y30E. We will present experimental data to demonstrate that CCRP is essential for GR to form the N/C interaction and will discuss its implications in GR functions.

Novel Selective Agents for the Degradation of Androgen Receptor Variants to Treat Castration-Resistant Prostate Cancer

Androgen receptor (AR) mediates the growth of prostate cancer throughout its course of development, including in abnormal splice variants (AR-SV)-driven advanced stage castration-resistant disease. AR stabilization by androgens makes it distinct from other steroid receptors, which are typically ubiquitinated and degraded by proteasomes after ligand binding. Thus, targeting AR in advanced prostate cancer requires the development of agents that can sustainably degrade variant isoforms for effective therapy. Here we report the discovery and characterization of potent selective AR degraders (SARD) that markedly reduce the activity of wild-type and splice variant isoforms of AR at submicromolar doses. Three SARDs (UT-69, UT-155, and (R)-UT-155) bind the amino-terminal transcriptional activation domain AF-1, which has not been targeted for degradation previously, with two of these SARD (UT-69 and UT-155) also binding the carboxy-terminal ligand binding domain. Despite different mechanisms of action, all three SARDs degraded wild-type AR and inhibited AR function, exhibiting greater inhibitory potency than the approved AR antagonists. Collectively, our results introduce a new candidate class of next-generation therapeutics to manage advanced prostate cancer. Cancer Res; 77(22); 6282-98. ©2017 AACR.

AKT1 has dual actions on the glucocorticoid receptor by cooperating with 14-3-3

Glucocorticoids are important therapeutic compounds for acute lymphoblastic leukemia (ALL). AKT1 or the protein kinase B is frequently activated in ALL, and contributes to the development of glucocorticoid resistance. We examined impact of AKT1 on glucocorticoid receptor (GR)-induced transcriptional activity in cooperation with phospho-serine/threonine-binding protein 14-3-3. AKT1 has two distinct actions on GR transcriptional activity, one through segregation of GR in the cytoplasm by phosphorylating GR at Ser-134 and subsequent association of 14-3-3, and the other through direct modulation of GR transcriptional activity in the nucleus. For the latter, AKT1 and 14-3-3 are attracted to DNA-bound GR, accompanied by AKT1-dependent p300 phosphorylation, H3S10 phosphorylation and H3K14 acetylation at the DNA site. These two actions of AKT1 regulate distinct sets of glucocorticoid-responsive genes. Our results suggest that specific inhibition of the AKT1/14-3-3 activity on the cytoplasmic retention of GR may be a promising target for treating glucocorticoid resistance observed in ALL.

Therapeutic Rationales, Progresses, Failures, and Future Directions for Advanced Prostate Cancer

Patients with localized prostate cancer (PCa) have several therapeutic options with good prognosis. However, survival of patients with high-risk, advanced PCa is significantly less than patients with early-stage, organ-confined disease. Testosterone and other androgens have been directly linked to PCa progression since 1941. In this review, we chronicle the discoveries that led to modern therapeutic strategies for PCa. Specifically highlighted is the biology of androgen receptor (AR), the nuclear receptor transcription factor largely responsible for androgen-stimulated and castrate-recurrent (CR) PCa. Current PCa treatment paradigms can be classified into three distinct but interrelated categories: targeting AR at pre-receptor, receptor, or post-receptor signaling. The continuing challenge of disease relapse as CR and/or metastatic tumors, destined to occur within three years of the initial treatment, is also discussed. We conclude that the success of PCa therapies in the future depends on targeting molecular mechanisms underlying tumor recurrence that still may affect AR at pre-receptor, receptor, and post-receptor levels.

Quantification of transcription factor-DNA binding affinity in a living cell

The apparent dissociation constant (K_d) for specific binding of glucocorticoid receptor (GR) and androgen receptor (AR) to DNA was determined in vivo in Xenopus oocytes. The total nuclear receptor concentration was quantified as specifically retained [³H]-hormone in manually isolated oocyte nuclei. DNA was introduced by nuclear microinjection of single stranded phagemid DNA, chromatin is then formed during second strand synthesis. The fraction of DNA sites occupied by the expressed receptor was determined by dimethylsulphate in vivo footprinting and used for calculation of the receptor-DNA binding affinity. The forkhead transcription factor FoxA1 enhanced the DNA binding by GR with an apparent K_d of ∼1 μM and dramatically stimulated DNA binding by AR with an apparent K_d of ∼0.13 μM at a composite androgen responsive DNA element containing one FoxA1 binding site and one palindromic hormone receptor binding site known to bind one receptor homodimer. FoxA1 exerted a weak constitutive- and strongly cooperative DNA binding together with AR but had a less prominent effect with GR, the difference reflecting the licensing function of FoxA1 at this androgen responsive DNA element.

Chromosome Y genetic variants: impact in animal models and on human disease

Chromosome Y (chrY) variation has been associated with many complex diseases ranging from cancer to cardiovascular disorders. Functional roles of chrY genes outside of testes are suggested by the fact that they are broadly expressed in many other tissues and correspond to regulators of basic cellular functions (such as transcription, translation, and protein stability). However, the unique genetic properties of chrY (including the lack of meiotic crossover and the presence of numerous highly repetitive sequences) have made the identification of causal variants very difficult. Despite the prior lack of reliable sequences and/or data on genetic polymorphisms, earlier studies with animal chrY consomic strains have made it possible to narrow down the phenotypic contributions of chrY. Some of the evidence so far indicates that chrY gene variants associate with regulatory changes in the expression of other autosomal genes, in part via epigenetic effects. In humans, a limited number of studies have shown associations between chrY haplotypes and disease traits. However, recent sequencing efforts have made it possible to greatly increase the identification of genetic variants on chrY, which promises that future association of chrY with disease traits will be further refined. Continuing studies (both in humans and in animal models) will be critical to help explain the many sex-biased disease states in human that are contributed to not only by the classical sex steroid hormones, but also by chrY genetics.

The polyglutamine-expanded androgen receptor has increased DNA binding and reduced transcriptional activity

Expansion of a polyglutamine-encoding trinucleotide CAG repeat in the androgen receptor (AR) to more than 37 repeats is responsible for the X-linked neuromuscular disease spinal and bulbar muscular atrophy (SBMA). Here we evaluated the effect of polyglutamine length on AR function in Xenopus oocytes. This allowed us to correlate the nuclear AR concentration to its capacity for specific DNA binding and transcription activation in vivo. AR variants with polyglutamine tracts containing either 25 or 64 residues were expressed in Xenopus oocytes by cytoplasmic injection of the corresponding mRNAs. The intranuclear AR concentration was monitored in isolated nuclei and related to specific DNA binding as well as transcriptional induction from the hormone response element in the mouse mammary tumor virus (MMTV) promoter. The expanded AR with 64 glutamines had increased capacity for specific DNA binding and a reduced capacity for transcriptional induction as related to its DNA binding activity. The possible mechanism behind these polyglutamine-induced alterations in AR function is discussed.

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Spinal bulbular muscular atrophy is caused by a polyQ expanded androgen receptor.

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Function of AR with expanded polyQ tract was analyzed in Xenopus oocytes.

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AR with expanded polyQ tract has increased DNA binding but reduced gene activation.

Chromatin remodeler mutations in human cancers: epigenetic implications

Chromatin remodeler complexes exhibit the ability to alter nucleosome composition and positions, with seemingly divergent roles in the regulation of chromatin architecture and gene expression. The outcome is directed by subunit variation and interactions with accessory factors. Recent studies have revealed that subunits of chromatin remodelers display an unexpectedly high mutation rate and/or are inactivated in a number of cancers. Consequently, a repertoire of epigenetic processes are likely to be affected, including interactions with histone modifying factors, as well as the ability to precisely modulate nucleosome positions, DNA methylation patterns and potentially, higher-order genome structure. However, the true significance of chromatin remodeler genetic aberrations in promoting a cascade of epigenetic changes, particularly during initiation and progression of cancer, remains largely unknown.

Glucocorticoid Receptor Transcriptional Activation via the BRG1-Dependent Recruitment of TOP2β and Ku70/86

BRG1, the central ATPase of the human SWI/SNF complex, is critical for biological functions, including nuclear receptor (NR)-regulated transcription. Analysis of BRG1 mutants demonstrated that functional motifs outside the ATPase domain are important for transcriptional activity. In the course of experiments examining protein interactions mediated through these domains, Ku70 (XRCC6) was found to associate with a BRG1 fragment encompassing the conserved helicase-SANT-associated (HSA) and BRK domains of BRG1. Subsequent transcriptional activation assays and chromatin immunoprecipitation studies showed that Ku70/86 and components of the topoisomerase IIβ (TOP2β)/poly(ADP ribose) polymerase 1 (PARP1) complex are necessary for NR-mediated SWI/SNF-dependent transcriptional activation from endogenous promoters. In addition to establishing Ku-BRG1 binding and TOP2β/PARP1 recruitment by nuclear receptor transactivation, we demonstrate that the transient appearance of glucocorticoid receptor (GR)/BRG1-dependent, TOP2β-mediated double-strand DNA breaks is required for efficient GR-stimulated transcription. Taken together, these results suggest that a direct interaction between Ku70/86 and BRG1 brings together SWI/SNF remodeling capabilities and TOP2β activity to enhance the transcriptional response to hormone stimulation.

A comparative study of the androgenic properties of progesterone and the progestins, medroxyprogesterone acetate (MPA) and norethisterone acetate (NET-A)

The importance of investigating the molecular mechanism of action of medroxyprogesterone acetate (MPA) and norethisterone acetate (NET-A), two clinically important progestins used in hormone therapy (HT), has been highlighted by clinical evidence showing that MPA and norethisterone (NET) increase the risk of the development of breast cancer in HRT users, and that MPA may increase susceptibility to- and transmission of HIV-1. The aim of this study was to compare the molecular mechanisms of action of MPA, NET-A and progesterone (Prog) via the androgen receptor (AR) in a cell line model that can minimize confounding factors such as the presence of other steroid receptors. This study is the first to determine accurate apparent Ki values for Prog, MPA and NET-A toward the human AR in COS-1 cells. The results reveal that these ligands have a similar binding affinity for the AR to that of the natural androgen 5α-dihydrotestosterone (DHT) (Ki's for DHT, Prog, MPA and NET-A are 29.4, 36.6, 19.4 and 21.9 nM, respectively). Moreover, in both transactivation and transrepression transcriptional assays we demonstrate that, unlike Prog, MPA and NET-A are efficacious AR agonists, with activities comparable to DHT. One of the most novel findings of our study is that NET-A, like DHT, induces the ligand-dependent interaction between the NH2- and COOH-terminal domains (N/C-interaction) of the AR independent of promoter-context, while MPA does not induce the N/C interaction on a classical ARE and does so only weakly on an AR-selective ARE. This suggests that MPA and NET-A may exert differential promoter-specific actions via the AR in vivo. Consistent with this, molecular modeling suggests that MPA and NET-A induce subtle differences in the structure of the AR ligand binding domain. Taken together, the results from this study suggest that unlike Prog, both MPA and NET-A used in hormonal therapy are likely to compete with DHT and exert significant and promoter-specific off-target transcriptional effects via the AR, possibly contributing to some of the observed side-effects with the clinical use of MPA and NET-A.

Mechanism of androgen receptor corepression by CKβBP2/CRIF1, a multifunctional transcription factor coregulator expressed in prostate cancer

The transcription factor coregulator Casein kinase IIβ-binding protein 2 or CR6-interacting factor 1 (CKβBP2/CRIF1) binds the androgen receptor (AR) in prostate cancer cells and in response to dihydrotestosterone localizes with AR on the prostate-specific antigen gene enhancer, but does not bind DNA suggesting CKβBP2/CRIF1 localization in chromatin is determined by AR. In this study we show also that CKβBP2/CRIF1 inhibits wild-type AR and AR N-terminal transcriptional activity, binds to the AR C-terminal region, inhibits interaction of the AR N- and C-terminal domains (N/C interaction) and competes with p160 coactivator binding to the AR C-terminal domain, suggesting CKβBP2/CRIF1 interferes with AR activation functions 1 and 2. CKβBP2/CRIF1 is expressed mainly in stromal cells of benign prostatic hyperplasia and in stroma and epithelium of prostate cancer. CKβBP2/CRIF1 protein is increased in epithelium of androgen-dependent prostate cancer compared to benign prostatic hyperplasia and decreased slightly in castration recurrent epithelium compared to androgen-dependent prostate cancer. The multifunctional CKβBP2/CRIF1 is a STAT3 interacting protein and reported to be a coactivator of STAT3. CKβBP2/CRIF1 is expressed with STAT3 in prostate cancer where STAT3 may help to offset the AR repressor effect of CKβBP2/CRIF1 and allow AR regulation of prostate cancer growth.

Sex hormone receptor repertoire in breast cancer

Classification of breast cancer as endocrine sensitive, hormone dependent, or estrogen receptor (ER) positive refers singularly to ER α . One of the oldest recognized tumor targets, disruption of ER α -mediated signaling, is believed to be the mechanistic mode of action for all hormonal interventions used in treating this disease. Whereas ER α is widely accepted as the single most important predictive factor (for response to endocrine therapy), the presence of the receptor in tumor cells is also of prognostic value. Even though the clinical relevance of the two other sex hormone receptors, namely, ER β and the androgen receptor remains unclear, two discordant phenomena observed in hormone-dependent breast cancers could be causally related to ER β -mediated effects and androgenic actions. Nonetheless, our understanding of regulatory molecules and resistance mechanisms remains incomplete, further compromising our ability to develop novel therapeutic strategies that could improve disease outcomes. This review focuses on the receptor-mediated actions of the sex hormones in breast cancer.

ARF represses androgen receptor transactivation in prostate cancer

Androgen receptor (AR) signaling is essential for prostate cancer (PCa) development in humans. The initiation of prostate malignancy and progression to a castration-resistant stage are largely contributed by the modulation of AR activity through its coregulatory proteins. We and others previously reported that p14 alternative reading frame (ARF) expression is positively correlated with the disease progression and severity of PCa. Here, we provide evidence that p14ARF physically interacts with AR and functions as an AR corespressor in both an androgen-dependent and androgen-independent manner. Endogenous ARF (p14ARF in human and p19ARF in mouse) and AR colocalize in both human PCa cells in vitro and PCa tissues of mouse and human in vivo. Overexpression of p14ARF in PCa cells significantly attenuates the activities of androgen response region (ARR2)-probasin and prostate-specific antigen (PSA) promoters. The forced expression of p14ARF in cells resulted in a suppression of PSA and NK transcription factor locus 1 (NKX3.1) expression. Conversely, knockdown of endogenous p14ARF in human PCa cells with short hairpin RNA enhanced AR transactivation activities in a dose-dependent and p53-independent manner. Furthermore, we demonstrated that p14ARF binds to both the N-terminal domain and the ligand-binding domain of AR, and the human double minute 2 (HDM2)-binding motif of p14ARF is required for the interaction of p14ARF and AR proteins. p14ARF perturbs the androgen-induced interaction between the N terminus and C terminus of AR. Most importantly, we observed that the expression of PSA is reversely correlated with p14ARF in human prostate tissues. Taken together, our results reveal a novel function of ARF in modulation of AR transactivation in PCa.

FoxA1 corrupts the antiandrogenic effect of bicalutamide but only weakly attenuates the effect of MDV3100 (Enzalutamide™)

Prostate cancer growth depends on androgens. Synthetic antiandrogens are used in the cancer treatment. However, antiandrogens, such as bicalutamide (BIC), have a mixed agonist/antagonist activity. Here we compare the antiandrogenic capacity of BIC to a new antiandrogen, MDV3100 (MDV) or Enzalutamide™. By reconstitution of a hormone-regulated enhancer in Xenopus oocytes we show that both antagonists trigger the androgen receptor (AR) translocation to the nucleus, albeit with a reduced efficiency for MDV. Once in the nucleus, both AR-antagonist complexes can bind sequence specifically to DNA in vivo. The forkhead box transcription factor A (FoxA1) is a negative prognostic indicator for prostate cancer disease. FoxA1 expression presets the enhancer chromatin and makes the DNA more accessible for AR binding. In this context the BIC-AR antiandrogenic effect is seriously compromised as demonstrated by a significant chromatin remodeling and induction of a robust MMTV transcription whereas the MDV-AR complex displays a more persistent antagonistic character.

Prostaglandin 15d-PGJ(2) inhibits androgen receptor signaling in prostate cancer cells

Androgen signaling, in particular overexpression of the androgen receptor (AR), is critical for the growth and progression of prostate cancer. Because the AR is amenable to targeting by small-molecule inhibitors, it remains the major druggable target for the advanced disease. Inflammation has also been implicated in the cancerous growth in the prostate. Here we show that 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), an endogenously produced antiinflammatory prostaglandin, targets the AR and acts as a potent AR inhibitor, rapidly repressing AR target genes, such as FKBP51 and TMPRSS2 in prostate cancer cells. However, exposure of prostate cancer cells to 15d-PGJ(2) does not simply evoke a general inhibition of nuclear receptor activity or transcription because under the same conditions, peroxisome proliferator-activated receptor-γ is activated by 15d-PGJ(2). Moreover, 15d-PGJ(2) rapidly triggers modifications of AR by small ubiquitin-related modifier-2/3 (SUMO-2/3), which may modulate the repressing effect of 15d-PGJ(2) on AR-dependent transcription. Chromatin immunoprecipitation assays indicate that the inhibitory effect of 15d-PGJ(2) on FKBP51 and TMPRSS2 expression occurs in parallel with the inhibition of the AR binding to the regulatory regions of these genes. However, the DNA-binding activity is not the only AR function targeted by 15d-PGJ(2) because the prostaglandin also blunted the androgen-dependent interaction between the AR amino and carboxy termini. In conclusion, our results identify 15d-PGJ(2) as a potent and direct inhibitor of androgen signaling, suggesting novel possibilities in restricting the AR activity in prostate cancer cells.

Coordinated action of hypoxia-inducible factor-1α and β-catenin in androgen receptor signaling

The androgen receptor (AR) acts as a ligand-dependent transcriptional factor and plays a critical role in the development and progression of androgen-dependent and castration-resistant prostate cancer. Castration results in hypoxia in prostate cancer cells, and hypoxia enhances transcriptional activity of AR through hypoxia-inducible factor (HIF)-1α at low serum androgen levels mimicking the castration-resistant stage. However, HIF-1α is necessary but not sufficient for hypoxia-activated AR transactivation, and the molecular mechanism that regulates AR function in castration-resistant prostate cancer remains unclear. Here, we report that β-catenin is required for HIF-1α-mediated AR transactivation in hypoxic LNCaP prostate cancer cells under low androgen conditions. HIF-1α and β-catenin coordinately enhanced AR N-terminal and C-terminal interaction. β-Catenin accumulated in the nucleus in the HIF-1α protein-positive cells of LNCaP xenografts in castrated mice. In LNCaP cells, when HIF-1α was knocked down or was exogenously expressed in the cytoplasm, hypoxia-induced nuclear localization of β-catenin was inhibited. β-Catenin formed a complex with HIF-1α both in the nucleus and in the cytoplasm. Hypoxia increased the amount of a complex composed of AR and β-catenin, and knockdown of HIF-1α attenuated the recruitment of AR and β-catenin to the androgen response elements (AREs) of androgen-responsive genes. Furthermore, together with β-catenin, HIF-1α bound to the AREs in the presence of androgen. These results demonstrate that (i) HIF-1α and β-catenin coordinately enhance AR transactivation by accelerating N-terminal and C-terminal interaction; (ii) HIF-1α promotes nuclear translocation of β-catenin in hypoxia; and (iii) AR, HIF-1α, and β-catenin form a ternary complex on AREs.

The stress response mediator ATF3 represses androgen signaling by binding the androgen receptor

Activating transcription factor 3 (ATF3) is a common mediator of cellular stress response signaling and is often aberrantly expressed in prostate cancer. We report here that ATF3 can directly bind the androgen receptor (AR) and consequently repress AR-mediated gene expression. The ATF3-AR interaction requires the leucine zipper domain of ATF3 that independently binds the DNA-binding and ligand-binding domains of AR, and the interaction prevents AR from binding to cis-acting elements required for expression of androgen-dependent genes while inhibiting the AR N- and C-terminal interaction. The functional consequences of the loss of ATF3 expression include increased transcription of androgen-dependent genes in prostate cancer cells that correlates with increased ability to grow in low-androgen-containing medium and increased proliferative activity of the prostate epithelium in ATF3 knockout mice that is associated with prostatic hyperplasia. Our results thus demonstrate that ATF3 is a novel repressor of androgen signaling that can inhibit AR functions, allowing prostate cells to restore homeostasis and maintain integrity in the face of a broad spectrum of intrinsic and environmental insults.

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.

Chromatin remodeling during glucocorticoid receptor regulated transactivation

Steroid hormone receptor (SR) signaling leads to widespread changes in gene expression, and aberrant SR signaling can lead to malignancies including breast, prostate, and lung cancers. Chromatin remodeling is an essential component of SR signaling, and defining the process of chromatin and nucleosome remodeling during signaling is critical to the continued development of related therapies. The glucocorticoid receptor (GR) is a key SR that activates numerous promoters including the well defined MMTV promoter. The activation of MMTV by GR provides an excellent model for teasing apart the sequence of events between hormone treatment and changes in gene expression. Comparing hormone-induced transcription from stably integrated promoters with defined nucleosomal structure to that from transiently expressed, unstructured promoters permits key distinctions between interactions that require remodeling and those that do not. The importance of co-activators and histone modifications prior to remodeling and the formation of the preinitiation complex that follows can also be clarified by defining key transition points in the propagation of hormonal signals. Combined with detailed mapping of proteins along the promoter, a temporal and spatial understanding of the signaling and remodeling processes begins to emerge. In this review, we examine SR signaling with a focus on GR activation of the MMTV promoter. We also discuss the ATP-dependent remodeling complex SWI/SNF, which provides the necessary remodeling activity during GR signaling and interacts with several SRs. BRG1, the central ATPase of SWI/SNF, also interacts with a set of BAF proteins that help determine the specialized function and fine-tuned regulation of BRG1 remodeling activity. BRG1 regulation comes from its own subdomains as well as its interactive partners. In particular, the HSA domain region of BRG1 and unique features of its ATPase homology appear to play key roles in regulating remodeling function. Details of the inter-workings of this chromatin remodeling protein continue to be revealed and promise to improve our understanding of the mechanism of chromatin remodeling during steroid hormone signaling. This article is part of a Special Issue entitled: Chromatin in time and space.

Androgen receptor serine 81 phosphorylation mediates chromatin binding and transcriptional activation

Our previous findings indicated that androgen receptor (AR) phosphorylation at serine 81 is stimulated by the mitotic cyclin-dependent kinase 1 (CDK1). In this report, we extended our previous study and confirmed that Ser-81 phosphorylation increases during mitosis, coincident with CDK1 activation. We further showed blocking cell cycle at G(1) or S phase did not disrupt androgen-induced Ser-81 phosphorylation and AR-dependent transcription, consistent with a recent report that AR was phosphorylated at Ser-81 and activated by the transcriptional CDK9. To assess the function of Ser-81 phosphorylation in prostate cancer (PCa) cells expressing endogenous AR, we developed a ligand switch strategy using a ligand-binding domain mutation (W741C) that renders AR responsive to the antagonist bicalutamide. An S81A/W741C double mutant AR stably expressed in PCa cells failed to transactivate the endogenous AR-regulated PSA or TMPRSS2 genes. ChIP showed that the S81A mutation prevented ligand-induced AR recruitment to these genes, and cellular fractionation revealed that the S81A mutation globally abrogated chromatin binding. Conversely, the AR fraction rapidly recruited to chromatin after androgen stimulation was highly enriched for Ser-81 phosphorylation. Finally, inhibition of CDK1 and CDK9 decreased AR Ser-81 phosphorylation, chromatin binding, and transcriptional activity. These findings indicate that Ser-81 phosphorylation by CDK9 stabilizes AR chromatin binding for transcription and suggest that CDK1-mediated Ser-81 phosphorylation during mitosis provides a pool of Ser-81 phosphorylation AR that can be readily recruited to chromatin for gene reactivation and may enhance AR activity in PCa.

Regulation of androgen receptor-dependent transcription by coactivator MED1 is mediated through a newly discovered noncanonical binding motif

Nuclear receptor (NR) activation by cognate ligand generally involves allosteric realignment of C-terminal α-helices thus generating a binding surface for coactivators containing canonical LXXLL α-helical motifs. The androgen receptor (AR) is uncommon among NRs in that ligand triggers an intramolecular interaction between its N- and C-terminal domains (termed the N/C interaction) and that coactivators can alternatively bind to surfaces in the AR N-terminal or hinge regions. The evolutionary conserved Mediator complex plays a key coregulatory role in steroid hormone-dependent transcription and is chiefly targeted to NRs via the LXXLL-containing MED1 subunit. Whereas MED1 has been demonstrated to serve as a key transcriptional coactivator for AR, the mechanisms by which AR recruits MED1 have remained unclear. Here we show that MED1 binds to a distinct AR N-terminal region termed transactivation unit-1 (Tau-1) via two newly discovered noncanonical α-helical motifs located between MED1 residues 505 and 537. Neither of the two MED1 LXXLL motifs is required for AR binding, whereas loss of the intramolecular AR N/C interaction decreases MED1 binding. We further demonstrate that mitogen-activated protein kinase phosphorylation of MED1 enhances the AR-MED1 interaction in prostate cancer cells. In sum, our findings reveal a novel AR-coactivator binding mechanism that may have clinical implications for AR activity in prostate cancer.

Mechanisms of prostate cancer initiation and progression

Prostate cancer is a major health problem as it continues to be the most frequently diagnosed cancer in men in the Western world. While improved early detection significantly decreased mortality, prostate cancer still remains the second leading cause of cancer-related death in Western men. Understanding the mechanisms of prostate cancer initiation and progression should have a significant impact on development of novel therapeutic approaches that can help to combat this disease. The recent explosion of novel high-throughput genetic technologies together with studies in animal models and human tissues allowed a comprehensive analysis and functional validation of the molecular changes. This chapter will summarize and discuss recently identified critical genetic and epigenetic changes that drive prostate cancer initiation and progression. These discoveries should help concentrate the efforts of drug development on key pathways and molecules, and finally translate the knowledge that is gained from mechanistic studies into effective treatments.

Regulation of androgen-responsive transcription by the chromatin remodeling factor CHD8

The androgen receptor (AR) mediates the effect of androgens through its transcriptional function during both normal prostate development and in the emergence and progression of prostate cancer. AR is known to assemble coactivator complexes at target promoters to facilitate transcriptional activation in response to androgens. Here we identify the ATP-dependent chromatin remodeling factor chromodomain helicase DNA-binding protein 8 (CHD8) as a novel coregulator of androgen-responsive transcription. We demonstrate that CHD8 directly associates with AR and that CHD8 and AR simultaneously localize to the TMPRSS2 enhancer after androgen treatment. In the LNCaP cell line, reduction of CHD8 levels by small interfering RNA treatment severely diminishes androgen-dependent activation of the TMPRSS2 gene. We demonstrate that the recruitment of AR to the TMPRSS2 promoter in response to androgen treatment requires CHD8. Finally, CHD8 facilitates androgen-stimulated proliferation of LNCaP cells, emphasizing the physiological importance of CHD8. Taken together, we present evidence of a functional role for CHD8 in AR-mediated transcriptional regulation of target genes.

Identification of SRC3/AIB1 as a preferred coactivator for hormone-activated androgen receptor

Transcription activation by androgen receptor (AR), which depends on recruitment of coactivators, is required for the initiation and progression of prostate cancer, yet the mechanisms of how hormone-activated AR interacts with coactivators remain unclear. This is because AR, unlike any other nuclear receptor, prefers its own N-terminal FXXLF motif to the canonical LXXLL motifs of coactivators. Through biochemical and crystallographic studies, we identify that steroid receptor coactivator-3 (SRC3) (also named as amplified in breast cancer-1 or AIB1) interacts strongly with AR via synergistic binding of its first and third LXXLL motifs. Mutagenesis and functional studies confirm that SRC3 is a preferred coactivator for hormone-activated AR. Importantly, AR mutations found in prostate cancer patients correlate with their binding potency to SRC3, corroborating with the emerging role of SRC3 as a prostate cancer oncogene. These results provide a molecular mechanism for the selective utilization of SRC3 by hormone-activated AR, and they link the functional relationship between AR and SRC3 to the development and growth of prostate cancer.

Involvement of three glutamine tracts in human androgen receptor transactivation

The androgen receptor (AR) possesses a polymorphic polyglutamine tract (polyQ), whose length is inversely correlated with its transcriptional activity. Here, we investigated whether 6 and 5 repetitive glutamine tracts (Q6 and Q5, respectively) in the N-terminal domain of AR also have effects on AR transactivation. In a reporter gene assay using two-tandem repeats of an androgen response element, deletion of glutamine tracts significantly increased AR transactivation in the following order: wild-type<a single deletion of polyQ or Q5<double deletion of polyQ and Q6<double deletion of polyQ and Q5<triple deletion. Deletion of polyQ alone or combined deletion of polyQ and Q5 from an AR mutant lacking the ligand-binding domain, which is constitutively active due to activation function-1, increased AR transactivation. However, the glutamine tracts had no influence on activation function-1 activity, suggesting that the glutamine tracts modulate the binding of AR to DNA. Q5, like polyQ, was found to be involved in the interaction between the NH(2)- and COOH-terminal regions of AR (N-C interaction). These results indicate that the inhibitory effects of polyQ and Q5 on AR transactivation are the due, at least in part, to their negative regulation of N-C interaction.

Peroxisome proliferator-activated receptor gamma coactivator-1alpha interacts with the androgen receptor (AR) and promotes prostate cancer cell growth by activating the AR

There are currently few successful therapies for castration-resistant prostate cancer (CRPC). CRPC is thought to result from augmented activation of the androgen/androgen receptor (AR) signaling pathway, which could be enhanced by AR cofactors. In this study, peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) was found to be an AR cofactor. PGC-1alpha interacted with the N-terminal domain of AR, was involved in the N- and C-terminal interaction of AR, and enhanced the DNA-binding ability of AR to androgen-responsive elements in the prostate-specific antigen enhancer and promoter regions to increase the transcription of AR target genes. Silencing of PGC-1alpha suppressed cell growth of AR-expressing prostate cancer (PCa) cells by inducing cell-cycle arrest at the G(1) phase, similar to inhibition of androgen/AR signaling. Furthermore, PGC-1alpha knock-down also suppressed cell growth in the castration-resistant LNCaP-derivatives. These findings indicate that PGC-1alpha is involved in the proliferation of AR-expressing PCa cells by acting as an AR coactivator. Modulation of PGC-1alpha expression or function may offer a useful strategy for developing novel therapeutics for PCa, including CRPC, which depends on AR signaling by overexpressing AR and its coactivators.

A novel androgen receptor amino terminal region reveals two classes of amino/carboxyl interaction-deficient variants with divergent capacity to activate responsive sites in chromatin

The androgen receptor (AR) is an important signaling molecule in multiple tissues, yet its mode of action and cell-specific activities remain enigmatic. AR function has been best studied in the prostate, in which it is essential for growth and homeostasis of the normal organ as well as each stage of cancer development. Investigation of mechanisms responsible for continued AR action that evolve during prostate cancer progression or after hormonal management of the disease have been instructive in defining AR signaling pathways. In the current paper, we use sequence similarity and the collocation of somatic mutations in prostate cancer to define residues 501-535 of the AR amino-terminal domain as an important mediator of receptor function. Specifically, the 501-535 region is required for optimal interaction of the amino-terminal domain with both the p160 coactivator, nuclear receptor coactivator-2, and the AR-ligand binding domain in the amino/carboxyl (N/C) interaction. The N/C interaction is decreased by deletion of the 501-535 region but is distinct from deletion of the (23)FQNLF(27) peptide in that it does not affect the capacity of the AR to activate transcription from a chromatin integrated reporter or recruitment of the receptor to androgen-responsive loci in vivo. Collectively, we have been able to outline two classes of N/C-deficient AR variant that are divergent in their capacity to act in a chromatin context, thereby further defining the interplay between N/C interaction and coregulator recruitment via multiple receptor domains. These mechanisms are likely to be key determinants of the cell and promoter specific activities of the AR.

Deleted in breast cancer 1, a novel androgen receptor (AR) coactivator that promotes AR DNA-binding activity

Androgen receptor (AR) plays a critical role in development and maintenance of male reproductive functions and the etiology of prostate cancer. As a ligand-regulated transcription factor, identification and characterization of AR coregulators are essential for understanding the molecular mechanisms underlying its diverse biological functions. Here we reported the identification of a novel AR coactivator, deleted in breast cancer 1 (DBC1), through a biochemical approach. DBC1 interacts with AR in a ligand-stimulated manner and facilitates AR transcriptional activation in transfected cells as well as in Xenopus oocytes. In in vitro gel shift experiments, recombinant DBC1 drastically enhanced AR DNA-binding activity. Expression of DBC1 also enhanced the binding of AR to chromatinized template in vivo, whereas knockdown of DBC1 impaired the binding of AR to endogenous prostate-specific antigen (PSA) gene in the prostate cancer cell line LNCaP. Thus, our data identify DBC1 as a novel AR coactivator.

Inhibition of androgen receptor transcriptional activity as a novel mechanism of action of arsenic

Environmental sodium arsenite is a toxin that is associated with male infertility due to decreased and abnormal sperm production. Arsenic trioxide (ATO), another inorganic trivalent semimetal, is an effective therapy for acute promyelocytic leukemia, and there is investigation of its possible efficacy in prostate cancer. However, the mechanism of arsenic action in male urogenital tract tissues is not clear. Because the androgen receptor (AR) plays an important role in spermatogenesis and prostate cancer, we explored the possibility that trivalent arsenic regulates AR function. We found that arsenic inhibited AR transcriptional activity in prostate cancer and Sertoli cells using reporter gene assays testing several androgen response element-containing regions and by assessing native target gene expression. Arsenic inhibition of AR activity was not due to down-regulation of AR protein levels, decreased hormone binding to AR, disruption of AR nuclear translocation, or interference with AR-DNA binding in vitro. However, chromatin immunoprecipitation studies revealed that arsenic inhibited AR recruitment to an AR target gene enhancer in vivo. Consistent with a deficiency in AR-chromatin binding, arsenic disrupted AR amino and carboxyl termini interaction. Furthermore, ATO caused a significant decrease in prostate cancer cell proliferation that was more pronounced in cells expressing AR compared with cells depleted of AR. In addition, inhibition of AR activity by ATO and by the AR antagonist, bicalutamide, was additive. Thus, arsenic-induced male infertility may be due to inhibition of AR activity. Further, because AR is an important target in prostate cancer therapy, arsenic may serve as an effective therapeutic option.

Cyclin D1 repressor domain mediates proliferation and survival in prostate cancer

Regulation of the androgen receptor (AR) is critical to prostate cancer (PCa) development; therefore, AR is the first line therapeutic target for disseminated tumors. Cell cycle dependent accumulation of cyclin D1 negatively modulates the transcriptional regulation of the AR through discrete, CDK4-independent mechanisms. The transcriptional co-repressor function of cyclin D1 resides within a defined motif termed ther repressor domain (RD), and it was hypothesized that this motif could be utilized as a platform to develop new strategies for blocking AR function. Here, we demonstrate that expression of the RD peptide is sufficient to disrupt AR transcriptional activation of multiple, prostate-specific AR target genes. Importantly, these actions are sufficient to specifically inhibit S-phase progression in AR-positive PCa cells, but not in AR-negative cells or tested AR-positive cells of other lineages. As expected, impaired cell cycle progression resulted in a suppression of cell doubling. Additionally, cell death was observed in AR-positive cells that maintain androgen dependence and in a subset of castrate-resistant PCa cells, dependent on Akt activation status. Lastly, the ability of RD to cooperate with existing hormone therapies was examined, which revealed that RD enhanced the cellular response to an AR antagonist. Together, these data demonstrate that RD is sufficient to disrupt AR-dependent transcriptional and proliferative responses in PCa, and can enhance efficacy of AR antagonists, thus establishing the impetus for development of RD-based mimetics.