Androgen receptor phosphorylation, turnover, nuclear transport, and transcriptional activation. Specificity for steroids and antihormones

A molecular switch from tumor suppressor to oncogene in ER+ve breast cancer: Role of androgen receptor, JAK-STAT, and lineage plasticity

Cancers develop resistance to inhibitors of oncogenes mainly due to target-centric mechanisms such as mutations and splicing. While inhibitors or antagonists force targets to unnatural conformation contributing to protein instability and resistance, activating tumor suppressors may maintain the protein in an agonistic conformation to elicit sustainable growth inhibition. Due to the lack of tumor suppressor agonists, this hypothesis and the mechanisms underlying resistance are not understood. In estrogen receptor (ER)-positive breast cancer (BC), androgen receptor (AR) is a druggable tumor suppressor offering a promising avenue for this investigation. Spatial genomics suggests that the molecular portrait of AR-expressing BC cells in tumor microenvironment corresponds to better overall patient survival, clinically confirming AR's role as a tumor suppressor. Ligand activation of AR in ER-positive BC xenografts reprograms cistromes, inhibits oncogenic pathways, and promotes cellular elasticity toward a more differentiated state. Sustained AR activation results in cistrome rearrangement toward transcription factor PROP paired-like homeobox 1, transformation of AR into oncogene, and activation of the Janus kinase/signal transducer (JAK/STAT) pathway, all culminating in lineage plasticity to an aggressive resistant subtype. While the molecular profile of AR agonist-sensitive tumors corresponds to better patient survival, the profile represented in the resistant phenotype corresponds to shorter survival. Inhibition of activated oncogenes in resistant tumors reduces growth and resensitizes them to AR agonists. These findings indicate that persistent activation of a context-dependent tumor suppressor may lead to resistance through lineage plasticity-driven tumor metamorphosis. Our work provides a framework to explore the above phenomenon across multiple cancer types and underscores the importance of factoring sensitization of tumor suppressor targets while developing agonist-like drugs.

Effects of Taraxaci Herba (Dandelion) on Testosterone Propionate-Induced Benign Prostatic Hyperplasia in Rats

Benign prostatic hyperplasia (BPH) is the non-malignant enlargement of the prostate, associated with lower urinary tract symptoms (LUTSs). Taraxaci Herba (TH), commonly known as dandelion, has traditionally been utilized in East Asia to treat symptoms related to LUTSs. Based on this traditional use, our study aimed to explore the inhibitory effects of TH on BPH progression using a testosterone propionate-induced rat model. To induce BPH, male Sprague Dawley rats were castrated and injected subcutaneously with testosterone propionate (3 mg/kg/day) for 28 days. Concurrently, TH extract was administered orally at doses of 100 and 300 mg/kg/day throughout the four-week period of testosterone propionate injections. The TH extract significantly reduced both the absolute and relative weights of the prostate, along with histopathological changes in the gland. Moreover, it lowered serum levels of testosterone and dihydrotestosterone and reduced the expression of the androgen receptor in the prostate. Additionally, the TH extract modulated the protein expressions of Bax and Bcl-2, which are key regulators of apoptosis in prostate cells. Collectively, our findings suggest that TH inhibits BPH development partially by modulating androgen signaling and inducing apoptosis within the prostate.

Therapeutic Potential of Bipolar Androgen Therapy for Castration-Resistant Prostate Cancer: In Vitro and In Vivo Studies

Androgen deprivation therapy (ADT) is a primary treatment for advanced prostate cancer (PCa), but resistance often leads to castration-resistant PCa (CRPC). CRPC remains androgen receptor (AR)-dependent, and AR overexpression causes vulnerability to high doses of androgen in CRPC. Bipolar androgen therapy (BAT) refers to the periodic administration of testosterone, resulting in oscillation between supraphysiologic and near-castrate serum testosterone levels. In this study, we evaluated the efficacy of BAT against CRPC in a preclinical setting. To emulate CRPC characteristics, PCa cell lines (LNCaP, VCaP, and 22Rv1) were cultured in phenol red-free RPMI-1640 medium supplemented with 10% dextran-coated charcoal treated FBS (A- cell line). Cell viability, AR, and AR-V7 expression were evaluated using the Cell Counting Kit-8 and Western blotting. In vivo studies involved 12 castrated NOG mice injected with LNCaP/A- cells, treated with testosterone pellets or controls in 2-week cycles. Tumor sizes were measured post a 6-week treatment cycle. Bicalutamide inhibited PCa cell viability but not in the adapted cell lines. Supraphysiologic androgen levels suppressed AR-expressing PCa cell growth in vitro. In vivo, high AR-expressing LNCaP cells proliferated under castrate conditions, while BAT-treated xenografts exhibited significant growth inhibition with low Ki-67 and mitotic indexes and a high cell death index. This study provides preliminary evidence that BAT is effective for the treatment of CRPC through rapid cycling between supraphysiologic and near-castrate serum testosterone levels, inducing an anti-tumor effect.

A phenotypically robust model of spinal and bulbar muscular atrophy in Drosophila

Spinal and bulbar muscular atrophy (SBMA) is an X-linked disorder that affects males who inherit the androgen receptor (AR) gene with an abnormal CAG triplet repeat expansion. The resulting protein contains an elongated polyglutamine (polyQ) tract and causes motor neuron degeneration in an androgen-dependent manner. The precise molecular sequelae of SBMA are unclear. To assist with its investigation and the identification of therapeutic options, we report here a new model of SBMA in Drosophila melanogaster. We generated transgenic flies that express the full-length, human AR with a wild-type or pathogenic polyQ repeat. Each transgene is inserted into the same safe harbor site on the third chromosome of the fly as a single copy and in the same orientation. Expression of pathogenic AR, but not of its wild-type variant, in neurons or muscles leads to consistent, progressive defects in longevity and motility that are concomitant with polyQ-expanded AR protein aggregation and reduced complexity in neuromuscular junctions. Additional assays show adult fly eye abnormalities associated with the pathogenic AR species. The detrimental effects of pathogenic AR are accentuated by feeding flies the androgen, dihydrotestosterone. This new, robust SBMA model can be a valuable tool toward future investigations of this incurable disease.

Clostridium scindens metabolites trigger prostate cancer progression through androgen receptor signaling

Prostate cancer (PCa) is one of the most common malignancies in men; recently, PCa-related mortality has increased worldwide. Although androgen deprivation therapy (ADT) is the standard treatment for PCa, patients often develop aggressive castration-resistant PCa (CRPC), indicating the presence of an alternative source of androgen. Clostridium scindens is a member of the gut microbiota and can convert cortisol to 11β-hydroxyandrostenedione (11β-OHA), which is a potent androgen precursor. However, the effect of C. scindens on PCa progression has not been determined. In this study, androgen-dependent PCa cells (LNCaP) were employed to investigate whether C. scindens-derived metabolites activate androgen receptor (AR), which is a pivotal step in the development of PCa. Results showed that cortisol metabolites derived from C. scindens-conditioned medium promoted proliferation and enhanced migration of PCa cells. Furthermore, cells treated with these metabolites presented activated AR and stimulated AR-regulated genes. These findings reveal that C. scindens has the potential to promote PCa progression via the activation of AR signaling. Further studies on the gut-prostate axis may help unravel an alternative source of androgen that triggers CRPC exacerbation.

The role of ubiquitination in spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is a neurodegenerative and neuromuscular genetic disease caused by the expansion of a polyglutamine-encoding CAG tract in the androgen receptor (AR) gene. The AR is an important transcriptional regulator of the nuclear hormone receptor superfamily; its levels are regulated in many ways including by ubiquitin-dependent degradation. Ubiquitination is a post-translational modification (PTM) which plays a key role in both AR transcriptional activity and its degradation. Moreover, the ubiquitin-proteasome system (UPS) is a fundamental component of cellular functioning and has been implicated in diseases of protein misfolding and aggregation, including polyglutamine (polyQ) repeat expansion diseases such as Huntington's disease and SBMA. In this review, we discuss the details of the UPS system, its functions and regulation, and the role of AR ubiquitination and UPS components in SBMA. We also discuss aspects of the UPS that may be manipulated for therapeutic effect in SBMA.

The androgen receptor is a therapeutic target in desmoplastic small round cell sarcoma

Desmoplastic small round cell tumor (DSRCT) is an aggressive, usually incurable sarcoma subtype that predominantly occurs in post-pubertal young males. Recent evidence suggests that the androgen receptor (AR) can promote tumor progression in DSRCTs. However, the mechanism of AR-induced oncogenic stimulation remains undetermined. Herein, we demonstrate that enzalutamide and AR-directed antisense oligonucleotides (AR-ASO) block 5α-dihydrotestosterone (DHT)-induced DSRCT cell proliferation and reduce xenograft tumor burden. Gene expression analysis and chromatin immunoprecipitation sequencing (ChIP-seq) were performed to elucidate how AR signaling regulates cellular epigenetic programs. Remarkably, ChIP-seq revealed novel DSRCT-specific AR DNA binding sites adjacent to key oncogenic regulators, including WT1 (the C-terminal partner of the pathognomonic fusion protein) and FOXF1. Additionally, AR occupied enhancer sites that regulate the Wnt pathway, neural differentiation, and embryonic organ development, implicating AR in dysfunctional cell lineage commitment. Our findings have direct clinical implications given the widespread availability of FDA-approved androgen-targeted agents used for prostate cancer.

Androgen receptor can promote tumour progression in desmoplastic small round cell tumour (DSRCT), an aggressive paediatric malignancy that predominantly affects young males. Here, the authors show that DSRCT is an AR-driven malignancy and sensitive to androgen deprivation therapy

Targeting androgen signaling in ILC2s protects from IL-33-driven lung inflammation, independently of KLRG1

BACKGROUND

Allergic asthma is more severe and frequent in women than in men. In male mice, androgens negatively control group 2 innate lymphoid cell (ILC2) development and function by yet unknown mechanisms.

OBJECTIVES

We sought to investigate the impact of androgen on ILC2 homeostasis and IL-33-mediated inflammation in female lungs. We evaluated the role of androgen receptor (AR) signaling and the contribution of the putative inhibitory receptor killer cell lectin-like receptor G1 (KLRG1).

METHODS

Subcutaneous pellets mimicking physiological levels of androgen were used to treat female mice together with mice expressing a reporter enzyme under the control of androgen response elements and mixed bone marrow chimeras to assess the cell-intrinsic role of AR activation within ILC2s. We generated KLRG1-deficient mice.

RESULTS

We established that lung ILC2s express a functionally active AR that can be in vivo targeted with exogenous androgens to negatively control ILC2 homeostasis, proliferation, and function. Androgen signaling upregulated KLRG1 on ILC2s, which inhibited their proliferation on E-cadherin interaction. Despite evidence that KLRG1 impaired the competitive fitness of lung ILC2s during inflammation, KLRG1 deficiency neither alters in vivo ILC2 numbers and functions, nor did it lead to hyperactive ILC2s in either sexes.

CONCLUSIONS

AR agonists can be used in vivo to inhibit ILC2 homeostatic numbers and ILC2-dependent lung inflammation through cell-intrinsic AR activation. Although androgen signals in ILC2s to upregulate KLRG1, we demonstrate that KLRG1 is dispensable for androgen-mediated inhibition of pulmonary ILC2s.

Mapping Motor Neuron Vulnerability in the Neuraxis of Male SOD1G93A Mice Reveals Widespread Loss of Androgen Receptor Occurring Early in Spinal Motor Neurons

Sex steroid hormones have been implicated as disease modifiers in the neurodegenerative disorder amyotrophic lateral sclerosis (ALS). Androgens, signalling via the androgen receptor (AR), predominate in males, and have widespread actions in the periphery and the central nervous system (CNS). AR translocates to the cell nucleus when activated upon binding androgens, whereby it regulates transcription of target genes via the classical genomic signalling pathway. We previously reported that AR protein is decreased in the lumbar spinal cord tissue of symptomatic male SOD1^G93A mice. Here, we further explored the changes in AR within motor neurons (MN) of the CNS, assessing their nuclear AR content and propensity to degenerate by endstage disease in male SOD1^G93A mice. We observed that almost all motor neuron populations had undergone significant loss in nuclear AR in SOD1^G93A mice. Interestingly, loss of nuclear AR was evident in lumbar spinal MNs as early as the pre-symptomatic age of 60 days. Several MN populations with high AR content were identified which did not degenerate in SOD1^G93A mice. These included the brainstem ambiguus and vagus nuclei, and the sexually dimorphic spinal MNs: cremaster, dorsolateral nucleus (DLN) and spinal nucleus of bulbocavernosus (SNB). In conclusion, we demonstrate that AR loss directly associates with MN vulnerability and disease progression in the SOD1^G93A mouse model of ALS.

Supraphysiologic Testosterone Induces Ferroptosis and Activates Immune Pathways through Nucleophagy in Prostate Cancer

The discovery that androgens play an important role in the progression of prostate cancer led to the development of androgen deprivation therapy (ADT) as a first line of treatment. However, paradoxical growth inhibition has been observed in a subset of prostate cancer upon administration of supraphysiologic levels of testosterone (SupraT), both experimentally and clinically. Here we report that SupraT activates cytoplasmic nucleic acid sensors and induces growth inhibition of SupraT-sensitive prostate cancer cells. This was initiated by the induction of two parallel autophagy-mediated processes, namely, ferritinophagy and nucleophagy. Consequently, autophagosomal DNA activated nucleic acid sensors converge on NFκB to drive immune signaling pathways. Chemokines and cytokines secreted by the tumor cells in response to SupraT resulted in increased migration of cytotoxic immune cells to tumor beds in xenograft models and patient tumors. Collectively, these findings indicate that SupraT may inhibit a subset of prostate cancer by activating nucleic acid sensors and downstream immune signaling. SIGNIFICANCE: This study demonstrates that supraphysiologic testosterone induces two parallel autophagy-mediated processes, ferritinophagy and nucleophagy, which then activate nucleic acid sensors to drive immune signaling pathways in prostate cancer.

Sex-specific Difference of Hippocampal Synaptic Plasticity in Response to Sex Neurosteroids

Numerous studies provide increasing evidence, which supports the ideas that every cell in the brain of males may differ from those in females due to differences in sex chromosome complement as well as in response to hormonal effects. In this study, we address the question as to whether actions of neurosteroids, thus steroids, which are synthesized and function within the brain, contribute to sex-specific hippocampal synaptic plasticity. We have previously shown that predominantly in the female hippocampus, does inhibition of the conversion of testosterone to estradiol affect synaptic transmission. In this study, we show that testosterone and its metabolite dihydrotestosterone are essential for hippocampal synaptic transmission specifically in males. This also holds true for the density of mushroom spines and of spine synapses. We obtained similar sex-dependent results using primary hippocampal cultures of male and female animals. Since these cultures originated from perinatal animals, our findings argue for sex-dependent differentiation of hippocampal neurons regarding their responsiveness to sex neurosteroids up to birth, which persist during adulthood. Hence, our in vitro findings may point to a developmental effect either directly induced by sex chromosomes or indirectly by fetal testosterone secretion during the perinatal critical period, when developmental sexual priming takes place.

Hormone-Dependent Prostate Cancers are Dependent on Rac Signaling for Growth and Survival

Prostate cancer remains a common cause of cancer mortality in men. Initially, cancers are dependent of androgens for growth and survival. First line therapies reduce levels of circulating androgens or target the androgen receptor (AR) directly. Although most patients show durable responses, many patients eventually progress to castration-resistant prostate cancer (CRPC) creating a need for alternative treatment options. The Rac1 signaling pathway has previously been implicated as a driver of cancer initiation and disease progression. We investigated the role of HACE1, the E3 ubiquitin ligase for Rac1, in prostate cancer and found that HACE1 is commonly lost resulting in hyperactive Rac signaling leading to enhanced cellular proliferation, motility and viability. Importantly, we show that a Rac inhibitor can attenuate the growth and survival of prostate cancer cells. Rac signaling was also found to be critical in prostate cancers that express the AR. Rac inhibition in androgen dependent cells resulted in reduction of AR target gene expression suggesting that targeting Rac1 may be an alternative method for blocking the AR signaling axis. Finally, when used in combination with AR antagonists, Rac inhibition enhanced the suppression of AR target gene expression. Therefore, targeting Rac in prostate cancer has the potential to enhance the efficacy of approved AR therapies.

Disruption of classical estrogenic targets in brown trout primary hepatocytes by the model androgens testosterone and dihydrotestosterone

Estrogenic effects triggered by androgens have been previously shown in a few studies. Aromatization and direct binding to estrogen receptors (ERs) are the most proposed mechanisms. For example, previously, a modulation of vitellogenin A (VtgA) by testosterone (T), an aromatizable androgen, was reported in brown trout primary hepatocytes. The effect was reversed by an ER antagonist. In this study, using the same model the disruption caused by T and by the non-aromatizable androgen - dihydrotestosterone (DHT), was assessed in selected estrogenic targets. Hepatocytes were exposed (96 h) to six concentrations of each androgen. The estrogenic targets were VtgA, ERα, ERβ1 and two zona pellucida genes, ZP2.5 and ZP3a.2. The aromatase CYP19a1 gene and the androgen receptor (AR) were also included. Modulation of estrogenic targets was studied by quantitative real-time PCR and immunohistochemistry, using an HScore system. VtgA and ERα were up-regulated by DHT (1, 10, 100 μM) and T (10, 100 μM). In contrast, ERβ1 was down-regulated by DHT (10, 100 μM), and T (100 μM). ZP2.5 mRNA levels were increased by DHT and T (1, 10, 100 μM), while ZP3a.2 was up-regulated by DHT (100 μM) and T (10, 100 μM). Positive correlations were found between VtgA and ERα mRNA levels and ZPs and ERα, after exposure to both androgens. The mRNA levels of CYP19a1 were not changed, while AR expression tended to increase after micromolar DHT exposures. HScores for Vtg and ZPs corroborated the molecular findings. Both androgens triggered estrogen signaling through direct binding to ERs, most probably ERα.

Dysregulation of Steroid Hormone Receptors in Motor Neurons and Glia Associates with Disease Progression in ALS Mice

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease targeting motor neurons which shows sexual dimorphism in its incidence, age of onset, and progression rate. All steroid hormones, including androgens, estrogens, and progestogens, have been implicated in modulating ALS. Increasing evidence suggests that steroid hormones provide neuroprotective and neurotrophic support to motor neurons, either directly or via surrounding glial cell interactions, by activating their respective nuclear hormone receptors and initiating transcriptional regulatory responses. The SOD1G93A transgenic mouse also shows sex-specific differences in age of onset and progression, and remains the most widely used model in ALS research. To provide a more comprehensive understanding of the influences of steroid hormone signaling in ALS, we systemically characterized sex hormone receptor expression at transcript and protein levels, cellular localization, and the impact of disease course in lumbar spinal cords of male and female SOD1G93A mice. We found that spinal motor neurons highly express nuclear androgen receptor (AR), estrogen receptor (ER)α, ERβ, and progesterone receptor with variations in glial cell expression. AR showed the most robust sex-specific difference in expression and was downregulated in male SOD1G93A mouse spinal cord, in association with depletion in 5α-reductase type 2 isoform, which primarily metabolizes testosterone to 5α-dihydrotestosterone. ERα was highly enriched in reactive astrocytes of SOD1G93A mice and ERβ was strongly upregulated. The 5α-reductase type 1 isoform was upregulated with disease progression and may influence local spinal cord hormone levels. In conclusion, steroid hormone receptor expression is dynamic and cell-type specific in SOD1G93A mice which may provide targets to modulate progression in ALS.

Exploring germline recombination in Nestin-Cre transgenic mice using floxed androgen receptor

The Cre-loxP strategy for tissue selective gene deletion has become a widely employed tool in neuroscience research. The validity of these models is largely underpinned by the temporal and spatial selectivity of recombinase expression under the promoter of the Cre driver line. Ectopic Cre-recombinase expression gives rise to off-target effects which can confound results and is especially detrimental if this occurs in germline cells. The Nestin-Cre transgenic mouse is broadly used for selective gene deletion in neurons of the central and peripheral nervous systems. Here we have crossed this mouse with a floxed androgen receptor (AR) transgenic to generate double transgenic neuronal ARKO mice (AR^flox ::NesCre) to study germline deletion in male and female transgenic breeders. In male AR^flox ::NesCre breeders, a null AR allele was passed on to 86% of progeny regardless of the inheritance of the NesCre transgene. In female AR^flox/wt ::NesCre breeders, a null AR allele was passed on to 100% of progeny where AR^flox was expected to be transmitted. This surprisingly high incidence of germline recombination in the Nestin-Cre driver line warrants caution in devising suitable breeding strategies, consideration of accurate genotyping approaches and highlights the need for thorough characterization of tissue-specific gene deletion in this model.

The role of the androgen receptor in prostate development and benign prostatic hyperplasia: A review

Benign prostatic hyperplasia (BPH) is a benign enlargement of the prostate in which incidence increases linearly with age, beginning at about 50 years old. BPH is a significant source of morbidity in aging men by causing lower urinary tract symptoms and acute urinary retention. Unfortunately, the etiology of BPH incidence and progression is not clear. This review highlights the role of the androgen receptor (AR) in prostate development and the evidence for its involvement in BPH. The AR is essential for normal prostate development, and individuals with defective AR signaling, such as after castration, do not experience prostate enlargement with age. Furthermore, decreasing dihydrotestosterone availability through therapeutic targeting with 5α-reductase inhibitors diminishes AR activity and results in reduced prostate size and symptoms in some BPH patients. While there is some evidence that AR expression is elevated in certain cellular compartments, how exactly AR is involved in BPH progression has yet to be elucidated. It is possible that AR signaling within stromal cells alters intercellular signaling and a "reawakening" of the embryonic mesenchyme, loss of epithelial AR leads to changes in paracrine signaling interactions, and/or chronic inflammation aids in stromal or epithelial proliferation evident in BPH. Unfortunately, a subset of patients fails to respond to current medical approaches, forcing surgical treatment even though age or associated co-morbidities make surgery less attractive. Fundamentally, new therapeutic approaches to treat BPH are not currently forthcoming, so a more complete molecular understanding of BPH etiology is necessary to identify new treatment options.

Anti-proliferative transcriptional effects of medroxyprogesterone acetate in estrogen receptor positive breast cancer cells are predominantly mediated by the progesterone receptor

Medroxyprogesterone acetate (MPA) is a first generation progestin that has been in clinical use for various hormonal conditions in women since the 1960s. Although developed as a progesterone receptor (PR) agonist, MPA also has strong binding affinity for other steroid receptors. This promiscuity confounds the mechanistic action of MPA in target cells that express multiple steroid receptors. This study is the first to assess the relative contribution of progesterone, androgen and glucocorticoid receptors in mediating the transcriptional activity of MPA on endogenous targets in breast cancer cells that endogenously express all three receptors at comparable levels. Gene expression profiling in estrogen receptor positive (ER+) ZR-75-1 breast cancer cells demonstrated that although the MPA-regulated transcriptome strongly overlapped with that of Progesterone (PROG), 5α-dihydrotestosterone (DHT) and Dexamethasone (DEX), it clustered most strongly with that of PROG, suggesting that MPA predominantly acts via the progesterone receptor (PR) rather than androgen receptor (AR) or glucocorticoid receptor (GR). Subsequent experiments manipulating levels of these receptors, either through specific culture conditions or with lentiviral shRNAs targeting individual receptors, also revealed a stronger contribution of PR compared to AR and GR on the expression of endogenous target genes that are either commonly regulated by all ligands or specifically regulated only by MPA. A predominant contribution of PR to MPA action in ER+ T-47D breast cancer cells was also observed, although a stronger role for AR was evident in T-47D compared to that observed in ZR-75-1 cells. Network analysis of ligand-specific and commonly regulated genes demonstrated that MPA utilises different transcription factors and signalling pathways to inhibit proliferation compared with PROG. This study reaffirms the importance of PR in mediating MPA action in an endogenous breast cancer context where multiple steroid receptors are co-expressed and has potential implications for PR-targeting therapeutic strategies in ER+ breast cancer.

Therapeutic targeting of the androgen receptor (AR) and AR variants in prostate cancer

Prostate cancer (PCa) accounted for over 300 000 deaths world-wide in 2018. Most of the PCa deaths occurred due to the aggressive castration-resistant PCa (CRPC). Since the androgen receptor (AR) and its ligands contribute to the continued growth of androgen-dependent PCa (ADPCa) and CRPC, AR has become a well-characterized and pivotal therapeutic-target. Although AR signaling was identified as therapeutic-target in PCa over five-decades ago, there remains several practical issues such as lack of antagonist-bound AR crystal structure, stabilization of the AR in the presence of agonists due to N-terminus and C-terminus interaction, unfavorable large-molecule accommodation of the ligand-binding domain (LBD), and generation of AR splice variants that lack the LBD that impede the discovery of highly potent fail-safe drugs. This review summarizes the AR-signaling pathway targeted therapeutics currently used in PCa and the approaches that could be used in future AR-targeted drug development of potent next-generation molecules. The review also outlines the discovery of molecules that bind to domains other than the LBD and those that inhibit both the full length and splice variant of ARs.

Overcoming resistance to anabolic SARM therapy in experimental cancer cachexia with an HDAC inhibitor

No approved therapy exists for cancer-associated cachexia. The colon-26 mouse model of cancer cachexia mimics recent late-stage clinical failures of anabolic anti-cachexia therapy and was unresponsive to anabolic doses of diverse androgens, including the selective androgen receptor modulator (SARM) GTx-024. The histone deacetylase inhibitor (HDACi) AR-42 exhibited anti-cachectic activity in this model. We explored combined SARM/AR-42 therapy as an improved anti-cachectic treatment paradigm. A reduced dose of AR-42 provided limited anti-cachectic benefits, but, in combination with GTx-024, significantly improved body weight, hindlimb muscle mass, and grip strength versus controls. AR-42 suppressed the IL-6/GP130/STAT3 signaling axis in muscle without impacting circulating cytokines. GTx-024-mediated β-catenin target gene regulation was apparent in cachectic mice only when combined with AR-42. Our data suggest cachectic signaling in this model involves catabolic signaling insensitive to anabolic GTx-024 therapy and a blockade of GTx-024-mediated anabolic signaling. AR-42 mitigates catabolic gene activation and restores anabolic responsiveness to GTx-024. Combining GTx-024, a clinically established anabolic therapy, with AR-42, a clinically evaluated HDACi, represents a promising approach to improve anabolic response in cachectic patients.

Androgen Receptor Is a Non-canonical Inhibitor of Wild-Type and Mutant Estrogen Receptors in Hormone Receptor-Positive Breast Cancers

Sustained treatment of estrogen receptor (ER)-positive breast cancer with ER-targeting drugs results in ER mutations and refractory unresponsive cancers. Androgen receptor (AR), which is expressed in 80%-95% of ER-positive breast cancers, could serve as an alternate therapeutic target. Although AR agonists were used in the past to treat breast cancer, their use is currently infrequent due to virilizing side effects. Discovery of tissue-selective AR modulators (SARMs) has renewed interest in using AR agonists to treat breast cancer. Using translational models, we show that AR agonist and SARM, but not antagonist, inhibit the proliferation and growth of ER-positive breast cancer cells, patient-derived tissues, and patient-derived xenografts (PDX). Ligand-activated AR inhibits wild-type and mutant ER activity by reprogramming the ER and FOXA1 cistrome and rendering tumor growth inhibition. These findings suggest that ligand-activated AR may function as a non-canonical inhibitor of ER and that AR agonists may offer a safe and effective treatment for ER-positive breast cancer.

AIB1 sequestration by androgen receptor inhibits estrogen-dependent cyclin D1 expression in breast cancer cells

Background

Androgens, through their own receptor, play a protective role on breast tumor development and progression and counterbalance estrogen-dependent growth stimuli which are intimately linked to breast carcinogenesis.

Methods

Cell counting by trypan blu exclusion was used to study androgen effect on estrogen-dependent breast tumor growth. Quantitative Real Time RT–PCR, western blotting, transient transfection, protein immunoprecipitation and chromatin immunoprecipitation assays were carried out to investigate how androgen treatment and/or androgen receptor overexpression influences the functional interaction between the steroid receptor coactivator AIB1 and the estrogen- or androgen receptor which, in turn affects the estrogen-induced cyclin D1 gene expression in MCF-7 breast cancer cells. Data were analyzed by ANOVA.

Results

Here we demonstrated, in estrogen receptor α (ERα)-positive breast cancer cells, an androgen-dependent mechanism through which ligand-activated androgen receptor (AR) decreases estradiol-induced cyclin D1 protein, mRNA and gene promoter activity. These effects involve the competition between AR and ERα for the interaction with the steroid receptor coactivator AIB1, a limiting factor in the functional coupling of the ERα with the cyclin D1 promoter. Indeed, AIB1 overexpression is able to reverse the down-regulatory effects exerted by AR on ERα-mediated induction of cyclin D1 promoter activity. Co-immunoprecipitation studies indicated that the preferential interaction of AIB1 with ERα or AR depends on the intracellular expression levels of the two steroid receptors. In addition, ChIP analysis evidenced that androgen administration decreased E₂-induced recruitment of AIB1 on the AP-1 site containing region of the cyclin D1 gene promoter.

Conclusions

Taken together all these data support the hypothesis that AIB1 sequestration by AR may be an effective mechanism to explain the reduction of estrogen-induced cyclin D1 gene activity. In estrogen-dependent breast cancer cell proliferation, these findings reinforce the possibility that targeting AR signalling may potentiate the effectiveness of anti-estrogen adjuvant therapies.

Molecular Mechanisms and Therapeutics for SBMA/Kennedy's Disease

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease caused by a polyglutamine (polyQ) expansion in the androgen receptor (AR). Despite the fact that the monogenic cause of SBMA has been known for nearly 3 decades, there is no effective treatment for this disease, underscoring the complexity of the pathogenic mechanisms that lead to a loss of motor neurons and muscle in SBMA patients. In the current review, we provide an overview of the system-wide clinical features of SBMA, summarize the structure and function of the AR, discuss both gain-of-function and loss-of-function mechanisms of toxicity caused by polyQ-expanded AR, and describe the cell and animal models utilized in the study of SBMA. Additionally, we summarize previously conducted clinical trials which, despite being based on positive results from preclinical studies, proved to be largely ineffective in the treatment of SBMA; nonetheless, these studies provide important insights as researchers develop the next generation of therapies.

Supraphysiological androgens suppress prostate cancer growth through androgen receptor-mediated DNA damage

Prostate cancer (PC) is initially dependent on androgen receptor (AR) signaling for survival and growth. Therapeutics designed to suppress AR activity serve as the primary intervention for advanced disease. However, supraphysiological androgen (SPA) concentrations can produce paradoxical responses leading to PC growth inhibition. We sought to discern the mechanisms by which SPA inhibits PC and to determine if molecular context associates with anti-tumor activity. SPA produced an AR-mediated, dose-dependent induction of DNA double-strand breaks (DSBs), G0/G1 cell cycle arrest and cellular senescence. SPA repressed genes involved in DNA repair and delayed the restoration of damaged DNA which was augmented by PARP1 inhibition. SPA-induced DSBs were accentuated in BRCA2-deficient PCs, and combining SPA with PARP or DNA-PKcs inhibition further repressed growth. Next-generation sequencing was performed on biospecimens from PC patients receiving SPA as part of ongoing Phase II clinical trials. Patients with mutations in genes mediating homology-directed DNA repair were more likely to exhibit clinical responses to SPA. These results provide a mechanistic rationale for directing SPA therapy to PCs with AR amplification or DNA repair deficiency, and for combining SPA therapy with PARP inhibition.

Targeting the turnover of oncoproteins as a new avenue for therapeutics development in castration-resistant prostate cancer

The current therapeutic armamentarium for castration-resistant prostate cancer (CRPC) includes second-generation agents such as the Androgen Receptor (AR) inhibitor enzalutamide and the androgen synthesis inhibitor abiraterone acetate, immunotherapies like sipuleucel-T, chemotherapies including docetaxel and cabazitaxel and the radiopharmaceutical radium 223 dichloride. However, relapse of CRPC resistant to these therapeutic modalities occur rapidly. The mechanisms of resistance to these treatments are complex, including specific mutations or alternative splicing of oncogenic proteins. An alternative approach to treating CRPC may be to target the turnover of these molecular drivers of CRPC. In this review, the mechanisms by which protein stability of several oncoproteins such as AR, ERG, GR, CYP17A1 and MYC, will be discussed, as well as how these findings could be translated into novel therapeutic agents.

Intergenerational response to the endocrine disruptor vinclozolin is influenced by maternal genotype and crossing scheme

In utero exposure to vinclozolin (VIN), an antiandrogenic fungicide, is linked to multigenerational phenotypic and epigenetic effects. Mechanisms remain unclear. We assessed the role of antiandrogenic activity and DNA sequence context by comparing effects of VIN vs. M2 (metabolite with greater antiandrogenic activity) and wild-type C57BL/6 (B6) mice vs. mice carrying mutations at the previously reported VIN-responsive H19/Igf2 locus. First generation offspring from VIN-treated 8nrCG mutant dams exhibited increased body weight and decreased sperm ICR methylation. Second generation pups sired by affected males exhibited decreased neonatal body weight but only when dam was unexposed. Offspring from M2 treatments, B6 dams, 8nrCG sires or additional mutant lines were not similarly affected. Therefore, pup response to VIN over two generations detected here was an 8nrCG-specific maternal effect, independent of antiandrogenic activity. These findings demonstrate that maternal effects and crossing scheme play a major role in multigenerational response to in utero exposures.

Targeting AR Variant-Coactivator Interactions to Exploit Prostate Cancer Vulnerabilities

Castration-resistant prostate cancer (CRPC) progresses rapidly and is incurable. Constitutively active androgen receptor splice variants (AR-Vs) represent a well-established mechanism of therapeutic resistance and disease progression. These variants lack the AR ligand-binding domain and, as such, are not inhibited by androgen deprivation therapy (ADT), which is the standard systemic approach for advanced prostate cancer. Signaling by AR-Vs, including the clinically relevant AR-V7, is augmented by Vav3, an established AR coactivator in CRPC. Using mutational and biochemical studies, we demonstrated that the Vav3 Diffuse B-cell lymphoma homology (DH) domain interacted with the N-terminal region of AR-V7 (and full length AR). Expression of the Vav3 DH domain disrupted Vav3 interaction with and enhancement of AR-V7 activity. The Vav3 DH domain also disrupted AR-V7 interaction with other AR coactivators: Src1 and Vav2, which are overexpressed in PC. This Vav3 domain was used in proof-of-concept studies to evaluate the effects of disrupting the interaction between AR-V7 and its coactivators on CRPC cells. This disruption decreased CRPC cell proliferation and anchorage-independent growth, caused increased apoptosis, decreased migration, and resulted in the acquisition of morphological changes associated with a less aggressive phenotype. While disrupting the interaction between FL-AR and its coactivators decreased N-C terminal interaction, disrupting the interaction of AR-V7 with its coactivators decreased AR-V7 nuclear levels.Implications: This study demonstrates the potential therapeutic utility of inhibiting constitutively active AR-V signaling by disrupting coactivator binding. Such an approach is significant, as AR-Vs are emerging as important drivers of CRPC that are particularly recalcitrant to current therapies. Mol Cancer Res; 15(11); 1469-80. ©2017 AACR.

The combined effect of USP7 inhibitors and PARP inhibitors in hormone-sensitive and castration-resistant prostate cancer cells

PURPOSE OF THE STUDY

Reduced levels of the tumor suppressor protein CCDC6 sensitize cancer cells to the treatment with PARP-inhibitors. The turnover of CCDC6 protein is regulated by the de-ubiquitinase USP7, which also controls the androgen receptor (AR) stability. Here, we correlated the expression levels of CCDC6 and USP7 proteins in primary prostate cancers (PC). Moreover, we tested the efficacy of the USP7 inhibitors, in combination with PARP-inhibitors as a novel therapeutic option in advanced prostate cancer.Experimental techniques: PC cells were exposed to USP7 inhibitor, P5091, together with cycloheximide, to investigate the turnover of the USP7 substrates, AR and CCDC6. As outcome of the AR downregulation, transcription targets of AR and its variant V7 were examined by qPCR. As a result of CCDC6 degradation, the induction of PARP inhibitors sensitivity was evaluated by analyzing PC cells viability and foci formation. We scored and correlated CCDC6 and USP7 expression levels in a prostate cancer tissue microarray (TMA).

RESULTS

P5091 accelerated the degradation of AR and V7 isoform affecting PSA, UBE2C, CDC20 transcription and PC cells proliferation. Moreover, P5091 accelerated the degradation of CCDC6 sensitizing the cells to PARP-inhibitors, that acted sinergistically with genotoxic agents. The immunohistochemical analysis of both CCDC6 and USP7 proteins exhibited significant correlation for the intensity of staining (p ≤ 0.05).Data interpretation: Thus, CCDC6 and USP7 represent predictive markers for the combined treatment of the USP7-inhibitors and PARP-inhibitors in advanced prostate cancer.

Up-Regulation of Follistatin-Like 1 By the Androgen Receptor and Melanoma Antigen-A11 in Prostate Cancer

BACKGROUND

High affinity androgen binding to the androgen receptor (AR) activates genes required for male sex differentiation and promotes the development and progression of prostate cancer. Human AR transcriptional activity involves interactions with coregulatory proteins that include primate-specific melanoma antigen-A11 (MAGE-A11), a coactivator that increases AR transcriptional activity during prostate cancer progression to castration-resistant/recurrent prostate cancer (CRPC).

METHODS

Microarray analysis and quantitative RT-PCR were performed to identify androgen-regulated MAGE-A11-dependent genes in LAPC-4 prostate cancer cells after lentivirus shRNA knockdown of MAGE-A11. Chromatin immunoprecipitation was used to assess androgen-dependent AR recruitment, and immunocytochemistry to localize an androgen-dependent protein in prostate cancer cells and tissue and in the CWR22 human prostate cancer xenograft.

RESULTS

Microarray analysis of androgen-treated LAPC-4 prostate cancer cells indicated follistatin-like 1 (FSTL1) is up-regulated by MAGE-A11. Androgen-dependent up-regulation of FSTL1 was inhibited in LAPC-4 cells by lentivirus shRNA knockdown of AR or MAGE-A11. Chromatin immunoprecipitation demonstrated AR recruitment to intron 10 of the FSTL1 gene that contains a classical consensus androgen response element. Increased levels of FSTL1 protein in LAPC-4 cells correlated with higher levels of MAGE-A11 relative to other prostate cancer cells. FSTL1 mRNA levels increased in CRPC and castration-recurrent CWR22 xenografts in association with predominantly nuclear FSTL1. Increased nuclear localization of FSTL1 in prostate cancer was suggested by predominantly cytoplasmic FSTL1 in benign prostate epithelial cells and predominantly nuclear FSTL1 in epithelial cells in CRPC tissue and the castration-recurrent CWR22 xenograft. AR expression studies showed nuclear colocalization of AR and endogenous FSTL1 in response to androgen.

CONCLUSION

AR and MAGE-A11 cooperate in the up-regulation of FSTL1 to promote growth and progression of CRPC. Prostate 77:505-516, 2017. © 2016 Wiley Periodicals, Inc.

Androgens Upregulate Endometrial Epithelial Progesterone Receptor Expression: Potential Implications for Endometriosis

BACKGROUND

Androgenic compounds have been implicated in induction of endometrial atrophy yet the mechanisms of androgen effects on human endometrium have not been well studied. We hypothesized that androgens may promote their endometrial effects via modulation of progesterone receptor (PR) expression.

METHODS

Proliferative phase endometrial samples were collected at the time of hysterectomy. We evaluated the effect of the potent androgen 5α-dihydrotestosterone (DHT) on endometrial PR expression by treating human endometrial explants, endometrial stromal cells, and Ishikawa cells with DHT. Ishikawa cells were also treated with DHT ± the androgen receptor (AR) blocker flutamide. The PR-B, total PR messenger RNA (mRNA), and PR protein expression were assessed. Expression of cyclin D1 and D2 was checked as markers of cell proliferation.

RESULTS

As expected, estradiol induced PR expression in isolated stromal cells, endometrial epithelial cells, and tissue explants. The DHT treatment also resulted in increased PR expression in endometrial explants and Ishikawa cells but not in stromal cells. Further, protein levels of both nuclear PR isoforms (PR-A and PR-B) were induced with the DHT treatment. Although flutamide treatment alone did not affect PR expression, flutamide diminished androgen-induced upregulation of PR in both endometrial explants and Ishikawa cells. Although estradiol induced both cyclin D1 and cyclin D2 mRNA, DHT did not induce these markers of cell proliferation.

CONCLUSION

Androgens may mediate endometrial effects through upregulation of PR gene and protein expression. Endometrial PR upregulation by androgens is mediated, at least in part, through AR.

Growth Inhibition by Testosterone in an Androgen Receptor Splice Variant-Driven Prostate Cancer Model

BACKGROUND

Castration resistance creates a significant problem in the treatment of prostate cancer. Constitutively active splice variants of androgen receptor (AR) have emerged as drivers for resistance to androgen deprivation therapy, including the next-generation androgen-AR axis inhibitors abiraterone and enzalutamide. In this study, we describe the characteristics of a novel castration-resistant prostate cancer (CRPC) model, designated JDCaP-hr (hormone refractory).

METHODS

JDCaP-hr was established from an androgen-dependent JDCaP xenograft model after surgical castration. The expression of AR and its splice variants in JDCaP-hr was evaluated by immunoblotting and quantitative reverse transcription-polymerase chain reaction. The effects of AR antagonists and testosterone on JDCaP-hr were evaluated in vivo and in vitro. The roles of full-length AR (AR-FL) and AR-V7 in JDCaP-hr cell growth were evaluated using RNA interference.

RESULTS

JDCaP-hr acquired a C-terminally truncated AR protein during progression from the parental JDCaP. The expression of AR-FL and AR-V7 mRNA was upregulated by 10-fold in JDCaP-hr compared with that in JDCaP, indicating that the JDCaP and JDCaP-hr models simulate castration resistance with some clinical features, such as overexpression of AR and its splice variants. The AR antagonist bicalutamide did not affect JDCaP-hr xenograft growth, and importantly, testosterone induced tumor regression. In vitro analysis demonstrated that androgen-independent prostate-specific antigen secretion and cell proliferation of JDCaP-hr were predominantly mediated by AR-V7. JDCaP-hr cell growth displayed a bell-shaped dependence on testosterone, and it was suppressed by physiological concentrations of testosterone. Testosterone induced rapid downregulation of both AR-FL and AR-V7 expression at physiological concentrations and suppressed expression of the AR target gene KLK3.

CONCLUSIONS

Our findings support the clinical value of testosterone therapy, including bipolar androgen therapy, in the treatment of AR-overexpressed CRPC driven by AR splice variants that are not clinically actionable at present. Prostate 76:1536-1545, 2016. © 2016 Wiley Periodicals, Inc.

The Efflux Transporter ABCG2 Maintains Prostate Stem Cells

Prostate stem cells (PSC) are characterized by their intrinsic resistance to androgen deprivation therapy (ADT), possibly due to the lack of androgen receptor (AR) expression. PSCs resistance to ADT and PSC expansion in castration resistant prostate cancer (CRPC) has sparked great interest in using differentiation therapy as an adjuvant to ADT. Understanding the mechanisms, by which PSCs maintain their undifferentiated phenotype, thus has important implications in differentiation therapy. In the prostate, the ATP binding cassette sub-family G member 2 (ABCG2) transporters, which enrich for AR-positive, ADT-resistant PSCs, play an important role in regulating the intracellular androgen levels by effluxing androgens. We hypothesized that the ABCG2-mediated androgen efflux is responsible for maintaining PSCs in an undifferentiated state. Using the HPr-1-AR (nontumorigenic) and CWR-R1 (tumorigenic) prostate cell lines, it was demonstrated that inhibiting the ABCG2-mediated androgen efflux, with Ko143 (ABCG2 inhibitor), increased the nuclear AR expression due to elevated intracellular androgen levels. Increased nuclear translocation of AR is followed by increased expression of AR regulated genes, a delayed cell growth response, and increased luminal differentiation. Furthermore, Ko143 reduced tumor growth rates in mice implanted with ABCG2-expressing CWR-R1 cells. In addition, Ko143-treated mice had more differentiated tumors as evidenced by an increased percentage of CK8⁺/AR⁺ luminal cells and decreased percentage of ABCG2-expressing cells. Thus, inhibiting ABCG2-mediated androgen efflux forces the PSCs to undergo an AR-modulated differentiation to an ADT-sensitive luminal phenotype.

IMPLICATIONS

This study identifies the mechanism by which the prostate stem cell marker, ABCG2, plays a role in prostate stem cell maintenance and provides a rationale for targeting ABCG2 for differentiation therapy in prostate cancer. Mol Cancer Res; 15(2); 128-40. ©2016 AACR.

Transcriptomic and physiological changes in Eastern Mosquitofish (Gambusia holbrooki) after exposure to progestins and anti-progestagens

Endocrine active compounds (EACs) remain an important group of chemicals that require additional evaluation to determine their environmental impacts. While estrogens and androgens were previously demonstrated to impact organisms during environmental exposures, progestagens have recently been shown to have strong impacts on aquatic organisms. To gain an understanding of the impacts of these types of chemicals on aquatic species, experiments evaluating the mechanisms of action of progestagen exposure were conducted with the Eastern Mosquitofish (Gambusia holbrooki). The objective of this study was to conduct hepatic microarray analysis of male and female G. holbrooki exposed to progestins and anti-progestagens. In addition, we evaluated the ability of levonorgestrel, a synthetic progesterone (progestin), to induce anal fin elongation and to determine how anal fin growth is modulated during co-exposures with progesterone and androgen receptor antagonists. Gene expression analyses were conducted on male and female G. holbrooki exposed for 48h to the agonist levonorgestrel, the antagonist mifepristone, or a mixture of the two chemicals. Microarray analysis revealed that mifepristone does not act as an anti-progestagen in G. holbrooki in liver tissues, and that levonorgestrel elicits strong effects on the processes of embryo development and lipid transport. Levonorgestrel was also demonstrated to induce male secondary sexual characteristic formation in females, and co-exposure of either an androgen or levonorgestrel in the presence of the anti-androgen flutamide prevented anal fin elongation. These results provide indications as to the potential impacts of progestins, including non-target effects such as secondary sexual characteristic formation, and demonstrate the importance of this class of chemicals on aquatic organisms.

The expression of thyroid hormone receptors (THR) is regulated by the progesterone receptor system in first trimester placental tissue and in BeWo cells in vitro

BACKGROUND

Thyroid hormones are essential for the maintenance of pregnancy and a deficiency in maternal thyroid hormones has been associated with early pregnancy losses. The aim of this study was a systematic investigation of the influence of mifepristone (RU 486) on the expression of the thyroid hormone receptor (THR) isoforms THRα1, THRα2, THRβ1 and THRβ2 on protein and mRNA-level.

METHODS

Samples of placental tissue were obtained from patients with mifepristone induced termination of pregnancy (n=13) or mechanical induced termination of normal pregnancy (n=20), each from the 4th to 13th week of pregnancy. Expression of THRα1, THRα2, THRβ1 and THRβ2 was analysed on protein level by immunohistochemistry and on mRNA level by real time RT-PCR (TaqMan). The influence of progesterone on THR gene expression was analysed in the trophoblast tumour cell line BeWo by real time RT-PCR (TaqMan).

RESULTS

Nuclear expression of THRα1, THRα2 and THRβ1 is downregulated on protein level in mifepristone (RU 486) treated villous trophoblast tissue. In decidual tissue, we found a significant downregulation only for THRα1 in mifepristone treated tissue. On mRNA level, we also found a significantly reduced expression of THRA but no significant downregulation for THRB in placental tissue. The gene THRA encodes the isoform THRα and the gene THRB encodes the isoform THRβ. The majority of cells expressing the thyroid hormone receptors in the decidua are decidual stromal cells. In addition, in vitro experiments with trophoblast tumour cells showed that progesterone significantly induced THRA but not THRB expression.

CONCLUSIONS

Termination of pregnancy with mifepristone (RU 486) leads to a downregulation of THRα1, THRα2 and THRβ1 in villous trophoblasts and in addition to a decreased expression of THRA in placental tissue. Decreased expression of THRα1 induced by RU486 could also be found in the decidua. Therefore inhibition of the progesterone receptor may be responsible for this downregulation. This assumption is supported by the finding, that stimulation of the progesterone receptor by progesterone itself up-regulated THRA in trophoblast cells in vitro.

Sex steroids stimulate leptin gene expression in Atlantic salmon parr hepatocytes in vitro

In mammals, leptin plays an important role in puberty and reproduction and leptin is regulated by sex steroids. Elevated leptin levels have been associated with sexual maturation in some teleosts such as Atlantic salmon. In the present study, primary cultures of Atlantic salmon hepatocytes were used to investigate the direct effects of different sex steroids on expression of the two salmon leptin-a genes, lepa1 and lepa2. Testosterone (T) stimulated both lepa1 and lepa2 in a dose dependent manner after four days of incubation. The stimulatory effect of T on leptin expression was not prevented by co-incubation with the aromatase inhibitor fadrozole, indicating a direct androgen effect on transcription. The non-aromatizable androgen 11-ketotestosterone (11-KT), which is the main androgen in fish, was generally slightly less potent than T in stimulating lepa1 and lepa2. The strongest stimulatory response was seen for 17β-estradiol (E2). E2 treatment significantly up-regulated lepa1 and lepa2 gene expression at doses of 10nM and 1nM for each gene, respectively. Lepa1, but not lepa2, was stimulated by T and 11-KT in immature male and immature female parr, while E2 stimulated expression of both genes. The sensitivity to sex steroid stimulation differed in maturing males compared to immature. In maturing males, the androgens and E2 stimulated lepa2 but not lepa1, while in immature males, the androgens and E2 stimulated lepa1, but only E2 stimulated lepa2. The differential response of the two leptin paralogues to the sex steroids suggests differences in regulation of the two leptin genes during maturation. Altogether, these results indicate that leptin expression in Atlantic salmon hepatocytes is directly regulated at the transcriptional level by the main teleost androgens and an estrogen, and that the response might depend on the developmental stage of the fish.

Downregulation of Critical Oncogenes by the Selective SK2 Inhibitor ABC294640 Hinders Prostate Cancer Progression

The bioactive sphingolipid sphingosine-1-phosphate (S1P) drives several hallmark processes of cancer, making the enzymes that synthesize S1P, that is, sphingosine kinase 1 and 2 (SK1 and SK2), important molecular targets for cancer drug development. ABC294640 is a first-in-class SK2 small-molecule inhibitor that effectively inhibits cancer cell growth in vitro and in vivo. Given that AR and Myc are two of the most widely implicated oncogenes in prostate cancer, and that sphingolipids affect signaling by both proteins, the therapeutic potential for using ABC294640 in the treatment of prostate cancer was evaluated. This study demonstrates that ABC294640 abrogates signaling pathways requisite for prostate cancer growth and proliferation. Key findings validate that ABC294640 treatment of early-stage and advanced prostate cancer models downregulate Myc and AR expression and activity. This corresponds with significant inhibition of growth, proliferation, and cell-cycle progression. Finally, oral administration of ABC294640 was found to dramatically impede xenograft tumor growth. Together, these pre-clinical findings support the hypotheses that SK2 activity is required for prostate cancer function and that ABC294640 represents a new pharmacological agent for treatment of early stage and aggressive prostate cancer.

IMPLICATIONS

Sphingosine kinase inhibition disrupts multiple oncogenic signaling pathways that are deregulated in prostate cancer.

The Deubiquitinating Enzyme USP7 Regulates Androgen Receptor Activity by Modulating Its Binding to Chromatin

The androgen receptor (AR), a nuclear receptor superfamily transcription factor, plays a key role in prostate cancer. AR signaling is the principal target for prostate cancer treatment, but current androgen-deprivation therapies cannot completely abolish AR signaling because of the heterogeneity of prostate cancers. Therefore, unraveling the mechanism of AR reactivation in androgen-depleted conditions can identify effective prostate cancer therapeutic targets. Increasing evidence indicates that AR activity is mediated by the interplay of modifying/demodifying enzymatic co-regulators. To better understand the mechanism of AR transcriptional activity regulation, we used antibodies against AR for affinity purification and identified the deubiquitinating enzyme ubiquitin-specific protease 7, USP7 as a novel AR co-regulator in prostate cancer cells. We showed that USP7 associates with AR in an androgen-dependent manner and mediates AR deubiquitination. Sequential ChIP assays indicated that USP7 forms a complex with AR on androgen-responsive elements of target genes upon stimulation with the androgen 5α-dihydrotestosterone. Further investigation indicated that USP7 is necessary to facilitate androgen-activated AR binding to chromatin. Transcriptome profile analysis of USP7-knockdown LNCaP cells also revealed the essential role of USP7 in the expression of a subset of androgen-responsive genes. Hence, inhibition of USP7 represents a compelling therapeutic strategy for the treatment of prostate cancer.

Antiandrogens act as selective androgen receptor modulators at the proteome level in prostate cancer cells

Current therapies for prostate cancer include antiandrogens, inhibitory ligands of the androgen receptor, which repress androgen-stimulated growth. These include the selective androgen receptor modulators cyproterone acetate and hydroxyflutamide and the complete antagonist bicalutamide. Their activity is partly dictated by the presence of androgen receptor mutations, which are commonly detected in patients who relapse while receiving antiandrogens, i.e. in castrate-resistant prostate cancer. To characterize the early proteomic response to these antiandrogens we used the LNCaP prostate cancer cell line, which harbors the androgen receptor mutation most commonly detected in castrate-resistant tumors (T877A), analyzing alterations in the proteome, and comparing these to the effect of these therapeutics upon androgen receptor activity and cell proliferation. The majority are regulated post-transcriptionally, possibly via nongenomic androgen receptor signaling. Differences detected between the exposure groups demonstrate subtle changes in the biological response to each specific ligand, suggesting a spectrum of agonistic and antagonistic effects dependent on the ligand used. Analysis of the crystal structures of the AR in the presence of cyproterone acetate, hydroxyflutamide, and DHT identified important differences in the orientation of key residues located in the AF-2 and BF-3 protein interaction surfaces. This further implies that although there is commonality in the growth responses between androgens and those antiandrogens that stimulate growth in the presence of a mutation, there may also be influential differences in the growth pathways stimulated by the different ligands. This therefore has implications for prostate cancer treatment because tumors may respond differently dependent upon which mutation is present and which ligand is activating growth, also for the design of selective androgen receptor modulators, which aim to elicit differential proteomic responses dependent upon cellular context.

Age- and Sex-Dependent Changes in Androgen Receptor Expression in the Developing Mouse Cortex and Hippocampus

During the perinatal period, male mice are exposed to higher levels of testosterone (T) than females, which promotes sexual dimorphism in their brain structures and behaviors. In addition to acting via estrogen receptors after being locally converted into estradiol by aromatase, T also acts directly through androgen receptor (AR) in the brain. Therefore, we hypothesized that AR expression in the developing mouse cortex and hippocampus was sexually dimorphic. To test our hypothesis, we measured and determined AR mRNA and protein levels in mouse cortex/hippocampus collected on the day of birth (PN0) and 7 (PN7), 14 (PN14), and 21 (PN21) days after birth. We demonstrated that, as age advanced, AR mRNA levels increased in the cortex/hippocampus of both sexes but showed no sex difference. Two AR proteins, the full-length (110 kDa) and a smaller isoform (70 kDa), were detected in the developing mouse cortex/hippocampus with an age-dependent increase in protein levels of both AR isoforms at PN21 and a transient masculine increase in expression of the full-length AR protein on PN7. Thus, we conclude that the postnatal age and sex differences in AR protein expression in combination with the sex differences in circulating T may cause sexual differentiation of the mouse cortex/hippocampus.

Sexually-motivated song is predicted by androgen-and opioid-related gene expression in the medial preoptic nucleus of male European starlings (Sturnus vulgaris)

Across vertebrates, communication conveys information about an individual's motivational state, yet little is known about the neuroendocrine regulation of motivational aspects of communication. For seasonally breeding songbirds, increases in testosterone in spring stimulate high rates of sexually-motivated courtship song, though not all birds sing at high rates. It is generally assumed that testosterone or its metabolites act within the medial preoptic nucleus (POM) to stimulate the motivation to sing. In addition to androgen receptors (ARs) and testosterone, opioid neuropeptides in the POM influence sexually-motivated song production, and it has been proposed that testosterone may in part regulate song by modifying opioid systems. To gain insight into a possible role for androgen-opioid interactions in the regulation of communication we examined associations between sexually-motivated song and relative expression of ARs, mu opioid receptors (muORs), and preproenkephalin (PENK) in the POM (and other regions) of male European starlings using qPCR. Both AR and PENK expression in POM correlated positively with singing behavior, whereas muOR in POM correlated negatively with song. Furthermore, the ratio of PENK/muOR expression correlated negatively with AR expression in POM. Finally, in the ventral tegmental area (VTA), PENK expression correlated negatively with singing behavior. Results support the hypothesis that ARs may alter opioid gene expression in POM to fine-tune singing to reflect a male's motivational state. Data also suggest that bidirectional relationships may exist between opioids and ARs in POM and song, and additionally support a role for opioids in the VTA, independent of AR activity in this region.

Inhibition of Stat5a/b Enhances Proteasomal Degradation of Androgen Receptor Liganded by Antiandrogens in Prostate Cancer

Although poorly understood, androgen receptor (AR) signaling is sustained despite treatment of prostate cancer with antiandrogens and potentially underlies development of incurable castrate-resistant prostate cancer. However, therapies targeting the AR signaling axis eventually fail when prostate cancer progresses to the castrate-resistant stage. Stat5a/b, a candidate therapeutic target protein in prostate cancer, synergizes with AR to reciprocally enhance the signaling of both proteins. In this work, we demonstrate that Stat5a/b sequesters antiandrogen-liganded (MDV3100, bicalutamide, flutamide) AR in prostate cancer cells and protects it against proteasomal degradation in prostate cancer. Active Stat5a/b increased nuclear levels of both unliganded and antiandrogen-liganded AR, as demonstrated in prostate cancer cell lines, xenograft tumors, and clinical patient-derived prostate cancer samples. Physical interaction between Stat5a/b and AR in prostate cancer cells was mediated by the DNA-binding domain of Stat5a/b and the N-terminal domain of AR. Moreover, active Stat5a/b increased AR occupancy of the prostate-specific antigen promoter and AR-regulated gene expression in prostate cancer cells. Mechanistically, both Stat5a/b genetic knockdown and antiandrogen treatment induced proteasomal degradation of AR in prostate cancer cells, with combined inhibition of Stat5a/b and AR leading to maximal loss of AR protein and prostate cancer cell viability. Our results indicate that therapeutic targeting of AR in prostate cancer using antiandrogens may be substantially improved by targeting of Stat5a/b.

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.

Androgen receptor and its splice variant, AR-V7, differentially regulate FOXA1 sensitive genes in LNCaP prostate cancer cells

Prostate cancer (PCa) is an androgen-dependent disease, and tumors that are resistant to androgen ablation therapy often remain androgen receptor (AR) dependent. Among the contributors to castration-resistant PCa are AR splice variants that lack the ligand-binding domain (LBD). Instead, they have small amounts of unique sequence derived from cryptic exons or from out of frame translation. The AR-V7 (or AR3) variant is constitutively active and is expressed under conditions consistent with CRPC. AR-V7 is reported to regulate a transcriptional program that is similar but not identical to that of AR. However, it is unknown whether these differences are due to the unique sequence in AR-V7, or simply to loss of the LBD. To examine transcriptional regulation by AR-V7, we have used lentiviruses encoding AR-V7 (amino acids 1-627 of AR with the 16 amino acids unique to the variant) to prepare a derivative of the androgen-dependent LNCaP cells with inducible expression of AR-V7. An additional cell line was generated with regulated expression of AR-NTD (amino acids 1-660 of AR); this mutant lacks the LBD but does not have the AR-V7 specific sequence. We find that AR and AR-V7 have distinct activities on target genes that are co-regulated by FOXA1. Transcripts regulated by AR-V7 were similarly regulated by AR-NTD, indicating that loss of the LBD is sufficient for the observed differences. Differential regulation of target genes correlates with preferential recruitment of AR or AR-V7 to specific cis-regulatory DNA sequences providing an explanation for some of the observed differences in target gene regulation.

Antiandrogen flutamide protects male mice from androgen-dependent toxicity in three models of spinal bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is a late-onset, progressive neurodegenerative disease linked to a polyglutamine (polyQ) expansion in the androgen receptor (AR). Men affected by SBMA show marked muscle weakness and atrophy, typically emerging midlife. Given the androgen-dependent nature of this disease, one might expect AR antagonists to have therapeutic value for treating SBMA. However, current work from animal models suggests otherwise, raising questions about whether polyQ-expanded AR exerts androgen-dependent toxicity through mechanisms distinct from normal AR function. In this study, we asked whether the nonsteroidal AR antagonist flutamide, delivered via a time-release pellet, could reverse or prevent androgen-dependent AR toxicity in three different mouse models of SBMA: the AR97Q transgenic (Tg) model, a knock-in (KI) model, and a myogenic Tg model. We find that flutamide protects mice from androgen-dependent AR toxicity in all three SBMA models, preventing or reversing motor dysfunction in the Tg models and significantly extending the life span in KI males. Given that flutamide effectively protects against androgen-dependent disease in three different mouse models of SBMA, our data are proof of principle that AR antagonists have therapeutic potential for treating SBMA in humans and support the notion that toxicity caused by polyQ-expanded AR uses at least some of the same mechanisms as normal AR before diverging to produce disease and muscle atrophy.

Galeterone prevents androgen receptor binding to chromatin and enhances degradation of mutant androgen receptor

PURPOSE

Galeterone inhibits the enzyme CYP17A1 and is currently in phase II clinical trials for castration-resistant prostate cancer (CRPC). Galeterone is also a direct androgen receptor (AR) antagonist and may enhance AR degradation. This study was undertaken to determine the molecular basis for AR effects and their therapeutic potential.

EXPERIMENTAL DESIGN

Effects of galeterone on AR expression and activities were examined in prostate cancer cell lines.

RESULTS

Similar to the AR antagonist enzalutamide, but in contrast to bicalutamide, galeterone did not induce binding of a constitutively active VP16-AR fusion protein to reporter genes and did not induce AR recruitment to endogenous androgen-regulated genes based on chromatin immunoprecipitation. Galeterone at low micromolar concentrations that did not induce cellular stress responses enhanced AR protein degradation in LNCaP and C4-2 cells, which express a T878A mutant AR, but not in prostate cancer cells expressing wild-type AR. Further transfection studies using stable LNCaP and PC3 cell lines ectopically expressing wild-type or T878A-mutant ARs confirmed that galeterone selectively enhances degradation of the T878A-mutant AR.

CONCLUSIONS

Similar to enzalutamide, galeterone may be effective as a direct AR antagonist in CRPC. It may be particularly effective against prostate cancer cells with the T878A AR mutation but may also enhance degradation of wild-type AR in vivo through a combination of direct and indirect mechanisms. Finally, these findings show that conformational changes in AR can markedly enhance its degradation and thereby support efforts to develop further antagonists that enhance AR degradation.

Status-appropriate singing behavior, testosterone and androgen receptor immunolabeling in male European starlings (Sturnus vulgaris)

Vocalizations convey information about an individual's motivational, internal, and social status. As circumstances change, individuals respond by adjusting vocal behavior accordingly. In European starlings, a male that acquires a nest site socially dominates other males and dramatically increases courtship song. Although circulating testosterone is associated with social status and vocal production it is possible that steroid receptors fine-tune status-appropriate changes in behavior. Here we explored a possible role for androgen receptors. Male starlings that acquired nest sites produced high rates of courtship song. For a subset of males this occurred even in the absence of elevated circulating testosterone. Immunolabeling for androgen receptors (ARir) was highest in the medial preoptic nucleus (POM) in males with both a nest site and elevated testosterone. For HVC, ARir was higher in dominant males with high testosterone (males that sang longer songs) than dominant males with low testosterone (males that sang shorter songs). ARir in the dorsal medial portion of the nucleus intercollicularis (DM) was elevated in males with high testosterone irrespective of dominance status. Song bout length related positively to ARir in POM, HVC and DM, and testosterone concentrations related positively to ARir in POM and DM. Results suggest that the role of testosterone in vocal behavior differs across brain regions and support the hypothesis that testosterone in POM underlies motivation, testosterone in HVC relates to song quality, and testosterone in DM stimulates vocalizations. Our data also suggest that singing may influence AR independent of testosterone and that alternative androgen-independent pathways regulate status-appropriate singing behavior.