Recruitment of beta-catenin by wild-type or mutant androgen receptors correlates with ligand-stimulated growth of prostate cancer cells

Nuclear receptor NURR1 functions to promote stemness and epithelial-mesenchymal transition in prostate cancer via its targeting of Wnt/β-catenin signaling pathway

Dysregulated activation of Wnt/β-catenin signaling pathway is a frequent or common event during advanced progression of multiple cancers. With this signaling activation, it enhances their tumorigenic growth and facilitates metastasis and therapy resistance. Advances show that this signaling pathway can play dual regulatory roles in the control of cellular processes epithelial-mesenchymal transition (EMT) and cancer stemness in cancer progression. Aberrant activation of Wnt/β-catenin signaling pathway is shown to be common in prostate cancer and also castration-resistant prostate cancer (CRPC). However, the transcriptional regulators of this pathway in prostate cancer are still not well characterized. NURR1 (NR4A2) is an orphan nuclear receptor and plays an important role in the development of dopaminergic neurons. Previously, we have shown that NURR1 exhibits an upregulation in isolated prostate cancer stem-like cells (PCSCs) and a xenograft model of CRPC. In this study, we further confirmed that NURR1 exhibited an upregulation in prostate cancer and also enhanced expression in prostate cancer cell lines. Functional and molecular analyses showed that NURR1 could act to promote both in vitro (cancer stemness and EMT) and also in vivo oncogenic growth of prostate cancer cells (metastasis and castration resistance) via its direct transactivation of CTNNB1 (β-catenin) and activation of β-catenin to mediate the activation of Wnt/β-catenin signaling pathway. Moreover, we also demonstrated that NURR1 activity in prostate cancer cells could be modulated by small molecules, implicating that NURR1 could be a potential therapeutic target for advanced prostate cancer management.

Modulation of the canonical Wnt activity by androgen signaling in prostate epithelial basal stem cells

Both the canonical Wnt and androgen receptor (AR) signaling pathways are important for prostate organogenesis and homeostasis. How they crosstalk to regulate prostate stem cell behaviors remains unclear. Here, we show in lineage-tracing mouse models that although Wnt is essential for basal stem cell multipotency, ectopic Wnt activity promotes basal cell over-proliferation and squamous phenotypes, which are counteracted by elevated levels of androgen. In prostate basal cell organoids, dihydrotestosterone (DHT) antagonizes R-spondin-stimulated growth in a concentration-dependent manner. DHT down-regulates the expressions of a Wnt reporter and target genes, and RNA sequencing (RNA-seq) analyses identify Wnt signaling as a key altered pathway. Mechanistically, DHT enhances AR and β-catenin protein binding, and CUT&RUN analyses reveal that ectopic AR sequesters β-catenin away from its Wnt-related cistrome. Our results suggest that an intermediate level of Wnt activity in prostate basal stem cells, achieved via AR-β-catenin interaction, is essential for normal prostate homeostasis.

Nuclear Receptor Coregulators in Hormone-Dependent Cancers

Nuclear receptors (NRs) function collectively as a transcriptional signaling network that mediates gene regulatory actions to either maintain cellular homeostasis in response to hormonal, dietary and other environmental factors, or act as orphan receptors with no known ligand. NR complexes are large and interact with multiple protein partners, collectively termed coregulators. Coregulators are essential for regulating NR activity and can dictate whether a target gene is activated or repressed by a variety of mechanisms including the regulation of chromatin accessibility. Altered expression of coregulators contributes to a variety of hormone-dependent cancers including breast and prostate cancers. Therefore, understanding the mechanisms by which coregulators interact with and modulate the activity of NRs provides opportunities to develop better prognostic and diagnostic approaches, as well as novel therapeutic targets. This review aims to gather and summarize recent studies, techniques and bioinformatics methods used to identify distorted NR coregulator interactions that contribute as cancer drivers in hormone-dependent cancers.

Endocrine Disruptors and Prostate Cancer

The role of endocrine disruptors (EDs) in the human prostate gland is an overlooked issue even though the prostate is essential for male fertility. From experimental models, it is known that EDs can influence several molecular mechanisms involved in prostate homeostasis and diseases, including prostate cancer (PCa), one of the most common cancers in the male, whose onset and progression is characterized by the deregulation of several cellular pathways including androgen receptor (AR) signaling. The prostate gland essentiality relies on its function to produce and secrete the prostatic fluid, a component of the seminal fluid, needed to keep alive and functional sperms upon ejaculation. In physiological condition, in the prostate epithelium the more-active androgen, the 5α-dihydrotestosterone (DHT), formed from testosterone (T) by the 5α-reductase enzyme (SRD5A), binds to AR and, upon homodimerization and nuclear translocation, recognizes the promoter of target genes modulating them. In pathological conditions, AR mutations and/or less specific AR binding by ligands modulate differently targeted genes leading to an altered regulation of cell proliferation and triggering PCa onset and development. EDs acting on the AR-dependent signaling within the prostate gland can contribute to the PCa onset and to exacerbating its development.

Lajis N, Abas F, Othman I, Naidu R. Mechanism of Anti-Cancer Activity of Curcumin on Androgen-Dependent and Androgen-Independent Prostate Cancer

Prostate cancer (PCa) is a heterogeneous disease and ranked as the second leading cause of cancer-related deaths in males worldwide. The global burden of PCa keeps rising regardless of the emerging cutting-edge technologies for treatment and drug designation. There are a number of treatment options which are effectively treating localised and androgen-dependent PCa (ADPC) through hormonal and surgery treatments. However, over time, these cancerous cells progress to androgen-independent PCa (AIPC) which continuously grow despite hormone depletion. At this particular stage, androgen depletion therapy (ADT) is no longer effective as these cancerous cells are rendered hormone-insensitive and capable of growing in the absence of androgen. AIPC is a lethal type of disease which leads to poor prognosis and is a major contributor to PCa death rates. A natural product-derived compound, curcumin has been identified as a pleiotropic compound which capable of influencing and modulating a diverse range of molecular targets and signalling pathways in order to exhibit its medicinal properties. Due to such multi-targeted behaviour, its benefits are paramount in combating a wide range of diseases including inflammation and cancer disease. Curcumin exhibits anti-cancer properties by suppressing cancer cells growth and survival, inflammation, invasion, cell proliferation as well as possesses the ability to induce apoptosis in malignant cells. In this review, we investigate the mechanism of curcumin by modulating multiple signalling pathways such as androgen receptor (AR) signalling, activating protein-1 (AP-1), phosphatidylinositol 3-kinases/the serine/threonine kinase (PI3K/Akt/mTOR), wingless (Wnt)/ß-catenin signalling, and molecular targets including nuclear factor kappa-B (NF-κB), B-cell lymphoma 2 (Bcl-2) and cyclin D1 which are implicated in the development and progression of both types of PCa, ADPC and AIPC. In addition, the role of microRNAs and clinical trials on the anti-cancer effects of curcumin in PCa patients were also reviewed.

Interplay Between SOX9, Wnt/β-Catenin and Androgen Receptor Signaling in Castration-Resistant Prostate Cancer

Androgen receptor (AR) signaling plays a key role not only in the initiation of prostate cancer (PCa) but also in its transition to aggressive and invasive castration-resistant prostate cancer (CRPC). However, the crosstalk of AR with other signaling pathways contributes significantly to the emergence and growth of CRPC. Wnt/β-catenin signaling facilitates ductal morphogenesis in fetal prostate and its anomalous expression has been linked with PCa. β-catenin has also been reported to form complex with AR and thus augment AR signaling in PCa. The transcription factor SOX9 has been shown to be the driving force of aggressive and invasive PCa cells and regulate AR expression in PCa cells. Furthermore, SOX9 has also been shown to propel PCa by the reactivation of Wnt/β-catenin signaling. In this review, we discuss the critical role of SOX9/AR/Wnt/β-catenin signaling axis in the development and progression of CRPC. The phytochemicals like sulforaphane and curcumin that can concurrently target SOX9, AR and Wnt/β-catenin signaling pathways in PCa may thus be beneficial in the chemoprevention of PCa.

Molecular and functional characterization of Arabidopsis thaliana VPNB1 gene involved in plant vascular development

Armadillo (ARM) repeat containing proteins constitute a large family in plants and are involved in diverse cellular functions, like signal transduction, proliferation and differentiation. In animals, ARM repeat proteins have been implicated in cancer development. In this study, we aimed in characterizing the VPNB1 gene from Arabidopsis thaliana and its role in plant development, by implementing a number of genetic and molecular approaches. AtVPNB1 encodes for an ARM repeat protein of unknown function, exclusively expressed in the cambium as well as in the differentiating xylem and phloem cells of the vascular system. Subcellular localization experiments showed that VPNB is confined in nucleoplasmic speckle-like structures unrelated to cajal bodies. Transgenic VPNB-impaired plants exhibit a slower growing phenotype and a non-canonical pattern of xylem tissue. On the contrary, VPNB overexpression lines display an inverted phenotype of increased growth, accompanied by an increased deposition of phloem and xylem cell layers. In line with the above data, qPCR analysis revealed a deregulation of several key master genes of secondary wall biosynthesis, underlining the involvement of VPNB1 in the regulation and differentiation of the root and shoot vascular tissue.

The effects of flutamide on cell-cell junctions in the testis, epididymis, and prostate

In this review, we summarize recent findings on the effect of the anti-androgen flutamide on cell-cell junctions in the male reproductive system. We outline developmental aspects of flutamide action on the testis, epididymis, and prostate, and describe changes in junction protein expression and organization of junctional complexes in the adult boar following prenatal and postnatal exposure. We also discuss findings on the mechanisms by which flutamide induces alterations in cell-cell junctions in reproductive tissues of adult males, with special emphasis on cytoplasmic effects. Based on the results from in vivo and in vitro studies in the rat, we propose that flutamide affects the expression of junction proteins and junction complex structure not only by inhibiting androgen receptor activity, but equally important by modulating protein kinase-dependent signaling in testicular cells. Additionally, results from studies on prostate cancer cell lines point to a role for the cellular molecular outfit in response to flutamide.

Aberrant TGF-β Signaling Drives Castration-Resistant Prostate Cancer in a Male Mouse Model of Prostate Tumorigenesis

The androgen receptor (AR) plays a critical role as a driver of castration-resistant prostate cancer (CRPC). Our previous studies demonstrated that disruption of transforming growth factor-β (TGF-β) signaling via introduction of dominant-negative transforming growth factor-β type II receptor (DNTGFβRII) in the prostate epithelium of transgenic adenocarcinoma of the prostate mice accelerated tumor. This study investigated the consequences of disrupted TGF-β signaling on prostate tumor growth under conditions of castration-induced androgen deprivation in the preclinical model of DNTGFβRII. Our results indicate that in response to androgen deprivation therapy (ADT) the proliferative index in prostate tumors from DNTGFβRII mice was higher compared with prostate tumors from TGFβRII wild-type (WT) mice, whereas there was a reduced incidence of apoptosis in tumors from DNTGFβRII. Protein and gene expression profiling revealed that tumors from DNTGFβRII mice exhibit a strong nuclear AR localization among the prostate tumor epithelial cells and increased AR messenger RNA after ADT. In contrast, TGFβRII WT mice exhibited a marked loss in nuclear AR in prostate tumor acini (20 weeks), followed by a downregulation of AR and transmembrane protease serine 2 messenger RNA. There was a significant increase in nuclear AR and activity in prostate tumors from castrate DNTGFβRII compared with TGFβRII WT mice. Consequential to aberrant TGF-β signaling, ADT enhanced expression and nuclear localization of Smad4 and β-catenin. Our findings support that under castrate conditions, aberrant TGF-β signaling leads to AR activation and β-catenin nuclear localization, an adaptation mechanism contributing to emergence of CRPC. The work defines a potentially significant new targeting platform for overcoming therapeutic resistance in CRPC.

A Tale of Two Signals: AR and WNT in Development and Tumorigenesis of Prostate and Mammary Gland

Prostate cancer (PCa) is one of the most common cancers and among the leading causes of cancer deaths for men in industrialized countries. It has long been recognized that the prostate is an androgen-dependent organ and PCa is an androgen-dependent disease. Androgen action is mediated by the androgen receptor (AR). Androgen deprivation therapy (ADT) is the standard treatment for metastatic PCa. However, almost all advanced PCa cases progress to castration-resistant prostate cancer (CRPC) after a period of ADT. A variety of mechanisms of progression from androgen-dependent PCa to CRPC under ADT have been postulated, but it remains largely unclear as to when and how castration resistance arises within prostate tumors. In addition, AR signaling may be modulated by extracellular factors among which are the cysteine-rich glycoproteins WNTs. The WNTs are capable of signaling through several pathways, the best-characterized being the canonical WNT/β-catenin/TCF-mediated canonical pathway. Recent studies from sequencing PCa genomes revealed that CRPC cells frequently harbor mutations in major components of the WNT/β-catenin pathway. Moreover, the finding of an interaction between β-catenin and AR suggests a possible mechanism of cross talk between WNT and androgen/AR signaling pathways. In this review, we discuss the current knowledge of both AR and WNT pathways in prostate development and tumorigenesis, and their interaction during development of CRPC. We also review the possible therapeutic application of drugs that target both AR and WNT/β-catenin pathways. Finally, we extend our review of AR and WNT signaling to the mammary gland system and breast cancer. We highlight that the role of AR signaling and its interaction with WNT signaling in these two hormone-related cancer types are highly context-dependent.

The promise and perils of HDAC inhibitors in neurodegeneration

Histone deacetylases (HDACs) represent emerging therapeutic targets in the context of neurodegeneration. Indeed, pharmacologic inhibition of HDACs activity in the nervous system has shown beneficial effects in several preclinical models of neurological disorders. However, the translation of such therapeutic approach to clinics has been only marginally successful, mainly due to our still limited knowledge about HDACs physiological role particularly in neurons. Here, we review the potential benefits along with the risks of targeting HDACs in light of what we currently know about HDAC activity in the brain.

Molecular pathways and targets in prostate cancer

Prostate cancer co-opts a unique set of cellular pathways in its initiation and progression. The heterogeneity of prostate cancers is evident at earlier stages, and has led to rigorous efforts to stratify the localized prostate cancers, so that progression to advanced stages could be predicted based upon salient features of the early disease. The deregulated androgen receptor signaling is undeniably most important in the progression of the majority of prostate tumors. It is perhaps because of the primacy of the androgen receptor governed transcriptional program in prostate epithelium cells that once this program is corrupted, the consequences of the ensuing changes in activity are pleotropic and could contribute to malignancy in multiple ways. Following localized surgical and radiation therapies, 20-40% of patients will relapse and progress, and will be treated with androgen deprivation therapies. The successful development of the new agents that inhibit androgen signaling has changed the progression free survival in hormone resistant disease, but this has not changed the almost ubiquitous development of truly resistant phenotypes in advanced prostate cancer. This review summarizes the current understanding of the molecular pathways involved in localized and metastatic prostate cancer, with an emphasis on the clinical implications of the new knowledge.

Beyond androgen deprivation: ancillary integrative strategies for targeting the androgen receptor addiction of prostate cancer

The large majority of clinical prostate cancers remain dependent on androgen receptor (AR) activity for proliferation even as they lose their responsiveness to androgen deprivation or antagonism. AR activity can be maintained in these circumstances by increased AR synthesis--often reflecting increased NF-κB activation; upregulation of signaling pathways that promote AR activity in the absence of androgens; and by emergence of AR mutations or splice variants lacking the ligand-binding domain, which render the AR constitutively active. Drugs targeting the N-terminal transactivating domain of the AR, some of which are now in preclinical development, can be expected to inhibit the activity not only of unmutated ARs but also of the mutant forms and splice variants selected for by androgen deprivation. Concurrent measures that suppress AR synthesis or boost AR turnover could be expected to complement the efficacy of such drugs. A number of nutraceuticals that show efficacy in prostate cancer xenograft models--including polyphenols from pomegranate, grape seed, and green tea, the crucifera metabolite diindolylmethane, and the hormone melatonin--have the potential to suppress AR synthesis via downregulation of NF-κB activity; clinical doses of salicylate may have analogous efficacy. The proteasomal turnover of the AR is abetted by diets with a high ratio of long-chain omega-3 to omega-6 fatty acids, which are beneficial in prostate cancer xenograft models; berberine and sulforaphane, by inhibiting AR's interaction with its chaperone Hsp90, likewise promote AR proteasomal degradation and retard growth of human prostate cancer in nude mice. Hinge region acetylation of the AR is required for optimal transactivational activity, and low micromolar concentrations of the catechin epigallocatechin-3-gallate (EGCG) can inhibit such acetylation--possibly explaining the ability of EGCG administration to suppress androgenic activity and cell proliferation in prostate cancer xenografts. Hence, it is proposed that regimens featuring an N-terminal domain-targeting drug, various nutraceuticals/drugs that downregulate NF-κB activity, and/or supplemental intakes of fish oil, berberine, sulforaphane, and EGCG have potential for blocking proliferation of prostate cancer by targeting its characteristic addiction to androgen receptor activity.

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.

Prostate cancer bone metastases acquire resistance to androgen deprivation via WNT5A-mediated BMP-6 induction

Background:

Androgen ablation is the first-line therapy for patients with metastatic prostate cancer (CaP). However, castration resistance will eventually emerge. In the present study, we have investigated the role of bone morphogenetic protein-6 (BMP-6) in the development of castration-resistant prostate cancer (CRPC) in the context of bone metastases.

Methods:

We initially investigated the clinical course of 158 men with advanced CaP who were treated with primary androgen deprivation therapy. To elucidate the underlying mechanism of CRPC in the context of bone metastases, we examined the impact of bone stromal cells on CaP in the absence of androgens using a co-culture model.

Results:

In the 158 patients, we found that the median time to prostate-specific antigen progression was significantly shorter when bone metastases were present (14 months (95% CI, 10.2–17.8 months) vs 57 months (95% CI, 19.4–94.6 months)). These results suggest that bone–tumour interactions may accelerate castration resistance. Consistent with this hypothesis, in vitro co-cultures demonstrated that CaP cells proliferated under an androgen-depleted condition when incubated with bone stromal cells. Mechanistically, gene expression analysis using quantitative polymerase chain reaction arrays showed a dramatic induction of BMP-6 by CaP cell lines in the presence of bone stromal cells. Further studies revealed that WNT5A derived from bone stromal cells induced the expression of BMP-6 by CaP cells; BMP-6 in turn stimulated cellular proliferation of CaP cells in an androgen-deprived media via a physical interaction between Smad5 and β-catenin. Intracellularly, WNT5A increased BMP-6 expression via protein kinase C/NF-κB pathway in CaP cell lines.

Conclusions:

These observations suggest that bone–CaP interaction leads to castration resistance via WNT5A/BMP-6 loop.

Androgen receptor activity is affected by both nuclear matrix localization and the phosphorylation status of the heterogeneous nuclear ribonucleoprotein K in anti-androgen-treated LNCaP cells

The androgen receptor (AR) plays a central role in the development and progression of prostate cancer (PCa) and anti-androgen therapy is a standard treatment. Unfortunately, after a few years, the majority of patients progress, developing androgen-independent PCa. AR-driven gene transcription recruits a large number of co-activator/co-repressor complexes; among these, the heterogeneous nuclear ribonucleoprotein K (hnRNP K) directly interacts with and regulates the AR translational apparatus. Here we examined AR and hnRNP K expression in response to the treatment of LNCaP cells with anti-androgen cyproterone acetate (CPA) or bicalutamide (BIC). AR and hnRNP K modulation and compartmentalization were studied by Western blot and confocal microscopy. Phosphate-affinity gel electrophoresis was employed to examine how anti-androgens modified hnRNP K phosphorylation. 10(-6) M CPA significantly stimulated LNCaP proliferation, whereas for 10(-4) M CPA or 10(-5) M BIC an antagonistic effect was observed. After anti-androgen treatment, AR expression was remarkably down-regulated within both the cytoplasm and the nucleus; however, when CPA had an agonist activity, the AR associated with the nuclear matrix (NM) increased approximately 2.5 times. This increase was synchronous with a higher PSA expression, indicating that the NM-associated AR represents the active complex. After BIC treatment, hnRNP K expression was significantly lower in the NM, the protein was hypophosphorylated and the co-localization of AR and hnRNP K decreased. In contrast, CPA as an agonist caused hnRNP K hyperphosphorylation and an increase in the co-localization of two proteins. These findings demonstrate that, in vitro, there is a strong relationship between NM-associated AR and both cell viability and PSA levels, indicating that AR transcriptional activity is critically dependent on its subnuclear localization. Moreover, the agonistic/antagonistic activity of anti-androgens is associated with modifications in hnRNP K phosphorylation, indicating an involvement of this protein in the AR transcriptional activity and likely in the onset of the androgen-independent phenotype.

Enzalutamide, an androgen receptor signaling inhibitor, induces tumor regression in a mouse model of castration-resistant prostate cancer

BACKGROUND

Enzalutamide (formerly MDV3100 and available commercially as Xtandi), a novel androgen receptor (AR) signaling inhibitor, blocks the growth of castration-resistant prostate cancer (CRPC) in cellular model systems and was shown in a clinical study to increase survival in patients with metastatic CRPC. Enzalutamide inhibits multiple steps of AR signaling: binding of androgens to AR, AR nuclear translocation, and association of AR with DNA. Here, we investigate the effects of enzalutamide on AR signaling, AR-dependent gene expression and cell apoptosis.

METHODS

The expression of AR target gene prostate-specific antigen (PSA) was measured in LnCaP and C4-2 cells. AR nuclear translocation was assessed in HEK-293 cells stably transfected with AR-yellow fluorescent protein. The in vivo effects of enzalutamide were determined in a mouse xenograft model of CRPC. Differential gene expression in LNCaP cells was measured using Affymetrix human genome microarray technology.

RESULTS

We found that unlike bicalutamide, enzalutamide lacked AR agonistic activity at effective doses and did not induce PSA expression or AR nuclear translocation. Additionally, it is more effective than bicalutamide at inhibiting agonist-induced AR nuclear translocation. Enzalutamide induced the regression of tumor volume in a CRPC xenograft model and apoptosis in AR-over-expressing prostate cancer cells. Finally, gene expression profiling in LNCaP cells indicated that enzalutamide opposes agonist-induced changes in genes involved in processes such as cell adhesion, angiogenesis, and apoptosis.

CONCLUSIONS

These results indicate that enzalutamide efficiently inhibits AR signaling, and we suggest that its lack of AR agonist activity may be important for these effects.

Effects of platelet-activating factor and its differential regulation by androgens and steroid hormones in prostate cancers

Background:

Platelet-activating factor (PAF) is an arachidonic acid metabolite that plays an important role in cell proliferation, migration and neoangiogenesis, but whether it is involved in the progression of prostate cancer remains undiscovered.

Methods:

Clinical prostate specimens were investigated with immunohistochemistry method and in vitro cell experiments referred to MTS cell proliferation assay, invasion and migration experiment, quantitative real-time RT–PCR assay, western blotting analysis and ELISA assay.

Results:

Platelet-activating factor synthetase, lyso-PAF acetyl transferase (LPCAT1), increased significantly in castration-resistant prostate cancer (CRPC) specimens and CRPC PC-3 cells than that in controls. Intriguingly, PAF induced invasion and migration of PC-3 cells but not LNCaP cells. The PAF receptor antagonist inhibited proliferation of LNCaP and PC-3 cells. Dihydrotestosterone (DHT) treatment caused a decrease in LPCAT1 expression and PAF release in LNCaP cells, which could be blocked by androgen receptor antagonists. Finally, DHT increased LPCAT1 expression and PAF release in PC-3 cells in a Wnt/β-catenin-dependent manner.

Conclusion:

For the first time, our data supported that PAF might play pivotal roles in the progression of prostate cancer, which might throw a new light on the treatment of prostate cancer and the prevention of the emergence of CRPC.

Role of WNT7B-induced noncanonical pathway in advanced prostate cancer

Advanced prostate cancer is characterized by incurable castration-resistant progression and osteoblastic bone metastasis. While androgen deprivation therapy remains the primary treatment for advanced prostate cancer, resistance inevitably develops. Importantly, mounting evidence indicates that androgen receptor (AR) signaling continues to play a critical role in the growth of advanced prostate cancer despite androgen deprivation. While the mechanisms of aberrant AR activation in advanced prostate cancer have been extensively studied, the downstream AR target genes involved in the progression of castration resistance are largely unknown. Here, we identify WNT7B as a direct AR target gene highly expressed in castration-resistant prostate cancer (CRPC) cells. Our results show that expression of WNT7B is necessary for the growth of prostate cancer cells and that this effect is enhanced under androgen-deprived conditions. Further analyses reveal that WNT7B promotes androgen-independent growth of CRPC cells likely through the activation of protein kinase C isozymes. Our results also show that prostate cancer-produced WNT7B induces osteoblast differentiation in vitro through a direct cell-cell interaction, and that WNT7B is upregulated in human prostate cancer xenografts that cause an osteoblastic reaction when grown in bone. Taken together, these results suggest that AR-regulated WNT7B signaling is critical for the growth of CRPC and development of the osteoblastic bone response characteristic of advanced prostate cancer.

β-catenin is required for prostate development and cooperates with Pten loss to drive invasive carcinoma

Prostate cancer is a major cause of male death in the Western world, but few frequent genetic alterations that drive prostate cancer initiation and progression have been identified. β-Catenin is essential for many developmental processes and has been implicated in tumorigenesis in many tissues, including prostate cancer. However, expression studies on human prostate cancer samples are unclear on the role this protein plays in this disease. We have used in vivo genetic studies in the embryo and adult to extend our understanding of the role of β-Catenin in the normal and neoplastic prostate. Our gene deletion analysis revealed that prostate epithelial β-Catenin is required for embryonic prostate growth and branching but is dispensable in the normal adult organ. During development, β-Catenin controls the number of progenitors in the epithelial buds and regulates a discrete network of genes, including c-Myc and Nkx3.1. Deletion of β-Catenin in a Pten deleted model of castration-resistant prostate cancer demonstrated it is dispensable for disease progression in this setting. Complementary overexpression experiments, through in vivo protein stabilization, showed that β-Catenin promotes the formation of squamous epithelia during prostate development, even in the absence of androgens. β-Catenin overexpression in combination with Pten loss was able to drive progression to invasive carcinoma together with squamous metaplasia. These studies demonstrate that β-Catenin is essential for prostate development and that an inherent property of high levels of this protein in prostate epithelia is to drive squamous fate differentiation. In addition, they show that β-Catenin overexpression can promote invasive prostate cancer in a clinically relevant model of this disease. These data provide novel information on cancer progression pathways that give rise to lethal prostate disease in humans.

Prostate cancer is a major cause of male death in the Western world, but few genes involved in this disease have been identified. We have undertaken an in-depth in vivo analysis in the prostate of the β-Catenin protein, which has been shown to be important in many processes during embryogenesis and has been implicated in tumorigenesis. Our studies demonstrate that β-Catenin is essential for prostate development but is dispensable in the normal adult organ. Analysis of a mouse model of a frequently mutated human prostate tumour suppressor, Pten loss, revealed that β-Catenin is not required for neoplastic formation in this model, even in castrated conditions. However, increased β-Catenin levels can cooperate with Pten loss to promote the progression of aggressive invasive prostate cancer together with squamous metaplasia. These data uncover the role of β-Catenin in the prostate and provide new insights on how pathways interact to drive human prostate cancer.

TCF/LEFs and Wnt signaling in the nucleus

T-cell factor/lymphoid enhancer factor (TCF/LEF) transcription factors are the major end point mediators of Wnt/Wingless signaling throughout metazoans. TCF/LEFs are multifunctional proteins that use their sequence-specific DNA-binding and context-dependent interactions to specify which genes will be regulated by Wnts. Much of the work to define their actions has focused on their ability to repress target gene expression when Wnt signals are absent and to recruit β-catenin to target genes for activation when Wnts are present. Recent advances have highlighted how these on/off actions are regulated by Wnt signals and stabilized β-catenin. In contrast to invertebrates, which typically contain one TCF/LEF protein that can both activate and repress Wnt targets, gene duplication and isoform complexity of the family in vertebrates have led to specialization, in which individual TCF/LEF isoforms have distinct activities.

Role of androgen receptor polyQ chain elongation in Kennedy's disease and use of natural osmolytes as potential therapeutic targets

Instability of CAG triplet repeat encoding polyglutamine (polyQ) stretches in the gene for target protein has been implicated as a putative mechanism in several inherited neurodegenerative diseases. Expansion of polyQ chain length in the androgen receptor (AR) causes spinal and bulbar muscular atrophy (SBMA) or Kennedy's disease. Although the mechanisms underlying gain-of-neurotoxic function are not completely understood, suggested pathological mechanisms of SBMA involve the formation of AR nuclear and cytoplasmic aggregates, a characteristic feature of patients with SBMA. The fact that certain AR coactivators are sequestered into the nuclear inclusions in SBMA possibly through protein-protein interactions supports the notion that AR transcriptional dysregulation may be a potential pathological mechanism leading to SBMA. AR conformational states associated with aberrant polyQ tract also modulate the interaction of AR with several coactivators. In many cases, such diseases can be treated through protein replacement therapy; however, because recombinant proteins do not cross the blood-brain barrier, the effectiveness of such therapies is limited in case of neurodegenerative diseases that warrant alternative therapeutic approaches. Among different approaches, inhibiting protein aggregation with small molecules that can stimulate protein folding and reverse aggregation are the most promising ones. Thus, naturally occurring osmolytes or "chemical chaperones" that can easily cross the blood-brain barrier and stabilize the functional form of a mutated protein by shifting the folding equilibrium away from degradation and/or aggregation is a useful therapeutic approach. In this review, we discuss the role of polyQ chain length extension in the pathophysiology of SBMA and the use of osmolytes as potential therapeutic tool.

Wnt/β-catenin signalling in prostate cancer

The Wnts are secreted cysteine-rich glycoproteins that have important roles in the developing embryo as well as in tissue homeostasis in adults. Dysregulation of Wnt signalling can lead to several types of cancer, including prostate cancer. A hallmark of the signalling pathway is the stabilization of the transcriptional co-activator β-catenin, which not only regulates expression of many genes implicated in cancer but is also an essential component of cadherin cell adhesion complexes. β-catenin regulates gene expression by binding members of the T-cell-specific transcription factor/lymphoid enhancer-binding factor 1 (TCF/LEF-1) family of transcription factors. In addition, β-catenin associates with the androgen receptor, a key regulator of prostate growth that drives prostate cancer progression. Wnt/β-catenin signalling can be controlled by secreted Wnt antagonists, many of which are downregulated in cancer. Activation of the Wnt/β-catenin pathway has effects on prostate cell proliferation, differentiation and the epithelial-mesenchymal transition, which is thought to regulate the invasive behaviour of tumour cells. However, whether targeting Wnt/β-catenin signalling is a good therapeutic option for prostate cancer remains unclear.

Androgen-induced PSA expression requires not only activation of AR but also endogenous IGF-I or IGF-I/PI3K/Akt signaling in human prostate cancer epithelial cells

BACKGROUND

Prostate cancer (PrCa) risk is positively associated with levels of insulin-like growth factor I (IGF-I) and prostate specific antigen (PSA), both androgen receptor (AR) signaling target genes in PrCa cells. Although activated AR is required for androgen-induction of expression of both genes, effects of the IGF-I signaling pathways on the androgen-induction of PSA have not been studied.

METHODS

Human prostate stromal and epithelial cancer cells were treated alone or in coculture with steroid hormone and/or inhibitors. Gene or protein expression was analyzed by real time RT-PCR or Western blotting of lysates, nuclear extracts, or immunoprecipitated products.

RESULTS

In PrCa epithelial cells, endogenous IGF-I, significantly induced by R1881, was required for R1881-induction of PSA. Increased IGF-I correlated with accumulation of cytoplasmic dephospho β-catenin (CPDP β-catenin), a co-activator of AR signaling. Exogenous IGF-I enhanced R1881-induced PSA and accumulation of CPDP β-catenin in LAPC-4 cells. Functional depletion of IGF-I or IGF-I receptor diminished PSA induction. Induction of IGF-I reached a plateau while PSA consecutively increased. Inhibiting PI3K abolished R1881-induced Akt phosphorylation, CPDP and nuclear β-catenin and nuclear association of AR/β-catenin, consequently abrogating R1881-induced expression of IGF-I and/or PSA.

CONCLUSIONS

By integrating androgen, IGF-I and β-catenin signaling pathways, these data reveal that androgen-induced PSA expression requires activation of AR and endogenous IGF-I or IGF-I/PI3K/Akt signaling, suggesting a positive feedback cycle for increased production of PSA associated with PrCa.

Role of the androgen receptor CAG repeat polymorphism in prostate cancer, and spinal and bulbar muscular atrophy

Androgens are involved in the development of several tissues, including prostate, skeletal muscle, bone marrow, hair follicles, and brain. Most of the biological effects of the androgens are mediated through an intracellular transcription factor, the androgen receptor (AR) at the level of gene regulation. Several types of mutations in the AR gene have been linked to endocrine dysfunctions. The expansion of CAG codon repeat, coding for a polyglutamine (PolyQ) tract in the N-terminal domain is one such mutation. The polyQ chain length impacts AR's ability to interact with critical coregulators, which in turn modulates its transcriptional efficacy. Pathologic manifestations of variations in polyQ chain length have been associated with prostate cancer susceptibility, and the Spinal and Bulbar Muscular Atrophy (SBMA), a neurodegenerative disease. In this review article, we discuss multiple aspects of the role of polyQ chain length in the actions of the AR, their importance in prostate cancer development and progression, and SBMA with an aim to understand the underlying mechanisms involved in these diseases, which can be targeted for future therapeutic approaches.

Cross-regulation of signaling pathways: an example of nuclear hormone receptors and the canonical Wnt pathway

Predicting the potential physiological outcome(s) of any given molecular pathway is complex because of cross-talk with other pathways. This is particularly evident in the case of the nuclear hormone receptor and canonical Wnt pathways, which regulate cell growth and proliferation, differentiation, apoptosis, and metastatic potential in numerous tissues. These pathways are known to intersect at many levels: in the intracellular space, at the membrane, in the cytoplasm, and within the nucleus. The outcomes of these interactions are important in the control of stem cell differentiation and maintenance, feedback loops, and regulating oncogenic potential. The aim of this review is to demonstrate the importance of considering pathway cross-talk when predicting functional outcomes of signaling, using nuclear hormone receptor/canonical Wnt pathway cross-talk as an example.

Dehydroepiandrosterone administration or G{alpha}q overexpression induces {beta}-catenin/T-Cell factor signaling and growth via increasing association of estrogen receptor-{beta}/Dishevelled2 in androgen-independent prostate cancer cells

beta-Catenin/T-cell factor signaling (beta-CTS) plays multiple critical roles in carcinogenesis and is blocked by androgens in androgen receptor (AR)-responsive prostate cancer (PrCa) cells, primarily via AR sequestration of beta-catenin from T-cell factor. Dehydroepiandrosterone (DHEA), often used as an over-the-counter nutritional supplement, is metabolized to androgens and estrogens in humans. The efficacy and safety of unregulated use of DHEA are unclear. We now report that DHEA induces beta-CTS via increasing association of estrogen receptor (ER)-beta with Dishevelled2 (Dvl2) in AR nonresponsive human PrCa DU145 cells, a line of androgen-independent PrCa (AiPC) cells. The induction is temporal, as assessed by measuring kinetics of the association of ERbeta/Dvl2, protein expression of the beta-CTS targeted genes, c-Myc and cyclin D1, and cell growth. However, in PC-3 cells, another human AiPC cell line, DHEA exerts no detectible effects, partly due to their lower expression of Galpha-subunits and DHEA down-regulation of ERbeta/Dvl2 association. When Galphaq is overexpressed in PC-3 cells, beta-CTS is constitutively induced, including increasing c-Myc and cyclin D1 protein expression. This effect involved increasing associations of Galphaq/Dvl2 and ERbeta/Dvl2 and promoted cell growth. These activities require ERbeta in DU-145 and PC-3 cells because they are blocked by ICI 182-780 treatment inactivating ERbeta, small interfering RNA administration depleting ERbeta, or AR overexpression arresting ERbeta. These data suggest that novel pathways activating beta-CTS play roles in the progression of AiPC. Although DHEA may enhance PrCa cell growth via androgenic or estrogenic pathways, the effects of DHEA administration on clinical prostate function remain to be determined.

Selective androgen receptor modulators as function promoting therapies

PURPOSE OF REVIEW

The past decade has witnessed an unprecedented discovery effort to develop selective androgen receptor modulators (SARMs) that improve physical function and bone health without adversely affecting the prostate and cardiovascular outcomes. This review describes the historical evolution, the rationale for SARM development, and the mechanisms of testosterone action and SARM selectivity.

RECENT FINDINGS

Although steroidal SARMs have been around since the 1940s, a number of nonsteroidal SARMs that do not serve as substrates for CYP19 aromatase or 5alpha-reductase, act as full agonists in muscle and bone and as partial agonists in prostate are in development. The differing interactions of steroidal and nonsteroidal compounds with androgen receptor (AR) contribute to their unique pharmacologic actions. Ligand binding induces specific conformational changes in the ligand-binding domain, which could modulate surface topology and protein-protein interactions between AR and coregulators, resulting in tissue-specific gene regulation. Preclinical studies have demonstrated the ability of SARMs to increase muscle and bone mass in preclinical rodent models with varying degree of prostate sparing. Phase I trials of SARMs in humans have reported modest increments in fat-free mass.

SUMMARY

SARMs hold promise as a new class of function promoting anabolic therapies for a number of clinical indications, including functional limitations associated with aging and chronic disease, frailty, cancer cachexia, and osteoporosis.

5alpha-dihydrotestosterone (DHT) retards wound closure by inhibiting re-epithelialization

The ongoing search for explanations as to why elderly males heal acute skin wounds more slowly than do their female counterparts (and are more strongly disposed to conditions of chronic ulceration) has identified endogenous oestrogens and androgens as being respectively enhancers and inhibitors of repair. We previously demonstrated that blocking the conversion of testosterone to 5alpha-dihydrotestosterone (DHT) limits its ability to impair healing, suggesting that DHT is a more potent inhibitor of repair than is testosterone. The present study aimed to delineate the central mechanisms by which androgens delay repair. Whilst the contractile properties of neither rat wounds in vivo nor fibroblast-impregnated collagenous discs in vitro appeared to be influenced by androgen manipulations, the global blockade of DHT biosynthesis markedly accelerated re-epithelialization of incisional and excisional wounds and reduced local expression of beta-catenin, a key inhibitor of repair. Moreover, DHT retarded the in vitro migration of epidermal keratinocytes following scratch wounding. By contrast, it failed to influence the migratory and proliferative properties of dermal fibroblasts, suggesting that its primary inhibitory effect is upon re-epithelialization. These novel findings may be of particular significance in the context of chronic ulceration, for which being male is a key risk factor.

Crosstalk between the androgen receptor and beta-catenin in castrate-resistant prostate cancer

The androgen-signaling pathway plays an important role in the development and hormonal progression of prostate cancer to the castrate-resistant stage (also called androgen-independent or hormone refractory). The Wnt pathway and beta-catenin contribute to prostate biology and pathology. Here application of Affymetrix GeneChip analysis revealed the genomic similarity of the LNCaP hollow fiber model to clinical samples and identified genes with differential expression during hormonal progression. The fiber model samples clustered according to the expression profile of androgen-regulated genes to provide genomic evidence for the reactivation of the AR signaling pathway in castrate-resistant prostate cancer. Pathway-based characterization of gene expression identified activation of the Wnt pathway. Together with the increased expression of AR and beta-catenin, there was increased nuclear colocalization and interaction of endogenous AR and beta-catenin in castrate-resistant prostate cancer from castrated mice. Surprisingly, no interaction or colocalization of AR and beta-catenin could be detected in xenografts from noncastrated mice. These studies provide the first in vivo evidence to support aberrant activation of the AR through the Wnt/beta-catenin signaling pathway during progression of prostate cancer to the terminal castrate-resistant stage.

Structural basis for nuclear receptor corepressor recruitment by antagonist-liganded androgen receptor

Androgen receptor (AR) recruitment of transcriptional corepressors NCoR and SMRT can be enhanced by antagonists such as mifepristone. This study shows that enhanced NCoR binding to the mifepristone-liganded AR is mediated by the NCoR COOH-terminal N1 CoRNR box and that this selectivity is due to charged residues unique to the COOH-terminal CoRNR boxes of NCoR and SMRT. Significantly, these residues are on a helical face adjacent to oppositely charged residues in helix 4 of the AR ligand-binding domain. Mutagenesis of these AR residues in helix 4, as well as mutation of lysine 720 in helix 3 (predicted to interact with the CoRNR box), markedly impaired AR recruitment of NCoR, indicating that N1 CoRNR box binding is being stabilized by these ionic interactions in the AR ligand-binding domain coactivator/corepressor binding site. Finally, results using a helix 12-deleted AR indicate that mifepristone induces allosteric changes in addition to helix 12 displacement that are critical for NCoR binding. These findings show that AR antagonists can enhance corepressor recruitment by stabilizing a distinct antagonist conformation of the AR coactivator/corepressor binding site and support the development of additional antagonists that may be able to further enhance AR recruitment of corepressors.

Wnt signaling: the good and the bad

Since the first Wnt gene was identified in 1982, the functions and mechanisms of Wnt signaling have been extensively studied. Wnt signaling is conserved from invertebrates to vertebrates and regulates early embryonic development as well as the homeostasis of adult tissues. In addition, both embryonic stem cells and adult stem cells are regulated by Wnt signaling. Deregulation of Wnt signaling is associated with many human diseases, particularly cancers. In this review, we will discuss in detail the functions of many components involved in the Wnt signal transduction pathway. Then, we will explore what is known about the role of Wnt signaling in stem cells and cancers.

Evaluation of a variant in the transcription factor 7-like 2 (TCF7L2) gene and prostate cancer risk in a population-based study

BACKGROUND

Transcription factor 7-like 2 (TCF7L2) is a high mobility group-box containing protein that is a critical member of the Wnt/beta-catenin canonical signaling pathway. In addition to its recently recognized role in diabetes, aberrant TCF7L2 expression has been implicated in cancer through regulation of cell proliferation and apoptosis by c-MYC and cyclin D. It has been hypothesized that germline variants within the TCF7L2 gene previously associated with diabetes may affect cancer risk through the Wnt/beta-catenin signaling pathway. Specifically, the same risk allele of single nucleotide polymorphism (SNP) rs12255372 that is associated with diabetes (T allele) has recently been associated with an increased risk of breast cancer.

METHODS

Here, we investigated associations between rs12255372 and prostate cancer risk among 1,457 cases and 1,351 controls from a population-based study.

RESULTS

The variant TT genotype was not associated with overall prostate cancer risk. However, there was evidence that men homozygous for the variant T allele had an elevated relative risk of more aggressive prostate cancer, as defined by high Gleason score (OR = 1.7, 95% CI = 1.0-2.8) or regional/distant stage (OR = 1.7, 95% CI = 1.1-2.6) disease.

CONCLUSIONS

Our findings suggest that this variant in the TCF7L2 gene may be associated with risk of developing more clinically significant disease. These results need to be confirmed, but provide initial evidence that the TCF7L2 gene may alter risk of developing more aggressive prostate cancer.

Activity of androgen receptor antagonist bicalutamide in prostate cancer cells is independent of NCoR and SMRT corepressors

The mechanisms by which androgen receptor (AR) antagonists inhibit AR activity, and how their antagonist activity may be abrogated in prostate cancer that progresses after androgen deprivation therapy, are not clear. Recent studies show that AR antagonists (including the clinically used drug bicalutamide) can enhance AR recruitment of corepressor proteins [nuclear receptor corepressor (NCoR) and silencing mediator of retinoid and thyroid receptors (SMRT)] and that loss of corepressors may enhance agonist activity and be a mechanism of antagonist failure. We first show that the agonist activities of weak androgens and an AR antagonist (cyproterone acetate) are still dependent on the AR NH(2)/COOH-terminal interaction and are enhanced by steroid receptor coactivator (SRC)-1, whereas the bicalutamide-liganded AR did not undergo a detectable NH(2)/COOH-terminal interaction and was not coactivated by SRC-1. However, both the isolated AR NH(2) terminus and the bicalutamide-liganded AR could interact with the SRC-1 glutamine-rich domain that mediates AR NH(2)-terminal binding. To determine whether bicalutamide agonist activity was being suppressed by NCoR recruitment, we used small interfering RNA to deplete NCoR in CV1 cells and both NCoR and SMRT in LNCaP prostate cancer cells. Depletion of these corepressors enhanced dihydrotestosterone-stimulated AR activity on a reporter gene and on the endogenous AR-regulated PSA gene in LNCaP cells but did not reveal any detectable bicalutamide agonist activity. Taken together, these results indicate that bicalutamide lacks agonist activity and functions as an AR antagonist due to ineffective recruitment of coactivator proteins and that enhanced coactivator recruitment, rather than loss of corepressors, may be a mechanism contributing to bicalutamide resistance.

Gene therapy approach in prostate cancer cells using an active Wnt signal

BACKGROUND

Functional activation of beta-catenin/T-cell factor (Tcf) signaling plays an important role in the early events of carcinogenesis. In past recent years accumulated evidence has demonstrated a significant role for the Wnt pathway in the development and progression of human prostate cancer. The objective of the current study was to use a gene-targeting approach to selectively kill human prostate cancer cells with activated beta-catenin/Tcf signaling.

METHODS

A recombinant adenovirus that carries a lethal gene (PUMA) under the control of a beta-catenin/T-cell factor (Tcf)-responsive promoter (Ad-TOP-PUMA), was used to selectively target human prostate cancer cells (PC-3) in which the beta-catenin/Tcf pathway is activated, and compared its killing efficiency in cancer cells in which this pathway is inactive (DU145 cells). Ad-FOP-PUMA, carrying a mutant Tcf binding site, was used as a control virus. Cell viability was measured by methylene blue assay, and the level of beta-catenin/Tcf activity was measured by luciferase assay.

RESULTS

The Ad-TOP-PUMA adenovirus inhibited PC-3 cell growth in a dose and time-dependent fashion, but did not had any effect on DU145 cell growth.

CONCLUSIONS

Selective targeting of prostate cancer cells with the activated beta-catenin pathway may be a novel and effective therapy in prostate cancer.

Glyceraldehyde-3-phosphate Dehydrogenase Enhances Transcriptional Activity of Androgen Receptor in Prostate Cancer Cells

Androgen receptor (AR) functions as a transcriptional factor for genes involved in proliferation and differentiation of normal and cancerous prostate cells. Coactivators that bind to AR are required for maximal androgen action. Here we report that increasing the expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in a prostate cancer cell line by as little as 1.8-fold enhances transcriptional activity of AR (but not the transcriptional activity of glucocorticoid receptor or estrogen receptor alpha) in a ligand-dependent manner and results in an increased expression of prostate-specific antigen. Small interference RNA-mediated knockdown of GAPDH significantly attenuated ligand-activated AR transactivation. Immunoprecipitation analysis revealed the presence of an endogenous protein complex containing GAPDH and AR in both the cytoplasm and nucleus. Addition of a nuclear localization signal (NLS) to GAPDH (GAPDH-NLS) completely abolished the ability of GAPDH to transactivate AR. Neither wild-type GAPDH nor GAPDH-NLS enhanced transcriptional activity of mutant AR (AR Delta C-Nuc) that is a constitutively active form of AR in the nucleus, even though GAPDH-NLS formed a complex with wild-type AR or AR Delta C-Nuc. AR transactivation was enhanced by a mutant GAPDH lacking dehydrogenase activity. GAPDH enhanced the transcriptional activity of AR(T875A) activated by an antagonist such as hydroxyflutamide or cyproterone acetate. These results indicate that GAPDH functions as a coactivator with high selectivity for AR and enhances AR transactivation independent of its glycolytic activity. Further, these data suggest that formation of a GAPDH.AR complex in the cytoplasm rather than nucleus is essential for GAPDH to enhance AR transactivation.

Wnt/beta-catenin signaling is a component of osteoblastic bone cell early responses to load-bearing and requires estrogen receptor alpha

The Wnt/beta-catenin pathway has been implicated in bone cell response to their mechanical environment. This response is the origin of the mechanism by which bone cells adjust bone architecture to maintain bone strength. Osteoporosis is the most widespread failure of this mechanism. The degree of osteoporotic bone loss in men and women is related to bio-available estrogen. Here we report that in osteoblastic ROS 17/2.8 cells and primary osteoblast cultures, a single short period of dynamic mechanical strain, as well as the glycogen synthase kinase-3beta (GSK-3beta) inhibitor LiCl, increased nuclear accumulation of activated beta-catenin and stimulated TCF/LEF reporter activity. This effect was blocked by the estrogen receptor (ER) modulators ICI 182,780 and tamoxifen and was absent in primary osteoblast cultures from mice lacking ERalpha. Microarray expression data for 25,000 genes from total RNA extracted from tibiae of wild-type mice within 24 h of being loaded in vivo showed differential gene regulation between loaded and contralateral non-loaded bones of 10 genes established to be involved in the Wnt pathway. Only 2 genes were involved in loaded tibiae from mice lacking ERalpha (ERalpha(-/-)). Together these data suggest that Wnt/beta-catenin signaling contributes to bone cell early responses to mechanical strain and that its effectiveness requires ERalpha. Reduced effectiveness of bone cell responses to bone loading, associated with estrogen-related decline in ERalpha, may contribute to the failure to maintain structurally appropriate bone mass in osteoporosis in both men and women.

Androgen receptor coregulators and their involvement in the development and progression of prostate cancer

The androgen receptor signaling axis plays an essential role in the development, function and homeostasis of male urogenital structures including the prostate gland although the mechanism by which the AR axis contributes to the initiation, progression and metastatic spread of prostate cancer remains somewhat enigmatic. A number of molecular events have been proposed to act at the level of the AR and associated coregulators to influence the natural history of prostate cancer including deregulated expression, somatic mutation, and post-translational modification. The purpose of this article is to review the evidence for deregulated expression and function of the AR and associated coactivators and corepressors and how such events might contribute to the progression of prostate cancer by controlling the selection and expression of AR targets.

Inactivation of Apc in the mouse prostate causes prostate carcinoma

Alterations of the Wnt/beta-catenin signaling pathway are positively associated with the development and progression of human cancer, including carcinoma of the prostate. To determine the role of activated Wnt/beta-catenin signaling in mouse prostate carcinogenesis, we created a mouse prostate tumor model using probasin-Cre-mediated deletion of Apc. Prostate tumors induced by the deletion of Apc have elevated levels of beta-catenin protein and are highly proliferative. Tumor formation is fully penetrant and follows a consistent pattern of progression. Hyperplasia is observed as early as 4.5 weeks of age, and adenocarcinoma is observed by 7 months. Continued tumor growth usually necessitated sacrifice between 12 and 15 months of age. Despite the high proliferation rate, we have not observed metastasis of these tumors to the lymph nodes or other organs. Surgical castration of 6-week-old mice inhibited tumor formation, and castration of mice with more advanced tumors resulted in the partial regression of specific prostate glands. However, significant areas of carcinoma remained 2 months postcastration, suggesting that tumors induced by Apc loss of function are capable of growth under conditions of androgen depletion. We conclude that the prostate-specific deletion of Apc and the increased expression of beta-catenin associated with prostate carcinoma suggests a role for beta-catenin in prostate cancer and offers an appropriate animal model to investigate the interaction of Wnt signaling with other genetic and epigenetic signals in prostate carcinogenesis.

Multifaceted interaction between the androgen and Wnt signaling pathways and the implication for prostate cancer

Androgen action in prostate and prostate cancer cells is dependent upon the androgen receptor (AR) protein that transcriptionally regulates the expression of androgen-dependent genes in the presence of a steroid ligand. Whereas the overall schema of androgen action mediated by this receptor protein appears to be relatively simple, androgen signaling is now known to be influenced by several other cell signal transduction pathways and here we review the evidence that the canonical Wnt signaling pathway also modulates androgen signaling at multiple levels. Wnt is a complex signaling pathway whose endpoint involves activation of transcription from LEF-1/TCF transcription factors and it is known to be involved in the development and progression of numerous human epithelial tumors including prostate cancer. beta-catenin protein, a particularly critical molecular component of canonical Wnt signaling is now known to promote androgen signaling through its ability to bind to the AR protein in a ligand-dependent fashion and to enhance the ability of liganded AR to activate transcription of androgen-regulated genes. Under certain conditions, glycogen synthase kinase-3beta (GSK-3beta), a protein serine/threonine kinase that regulates beta-catenin degradation within the Wnt signaling pathway, can also phosphorylate AR and suppress its ability to activate transcription. Finally, it was recently found that the human AR gene itself is a target of LEF-1/TCF-mediated transcription and that AR mRNA is highly upregulated by activation of Wnt signaling in prostate cancer cells. Paradoxically, Wnt activation also appears to stimulate Akt activity promoting an MDM-2-mediated degradation process that reduces AR protein levels in Wnt-stimulated prostate cancer cells. Collectively, this information indicates that the multifaceted nature of the interaction between the Wnt and the androgen signaling pathways likely has numerous consequences for the development, growth, and progression of prostate cancer.

Androgen receptor regulates nuclear trafficking and nuclear domain residency of corepressor HDAC7 in a ligand-dependent fashion

In addition to chromosomal proteins, histone deacetylases (HDACs) target transcription factors in transcriptional repression. Here, we show that the class II HDAC family member HDAC7 is an efficient corepressor of the androgen receptor (AR). HDAC7 resided in the cytoplasm in the absence of AR or a cognate ligand, but hormone-occupancy of AR induced nuclear transfer of HDAC7. Nuclear colocalization pattern of AR and HDAC7 was dependent on the nature of the ligand. In the presence of testosterone, a portion of HDAC7 localized to pearl-like nuclear domains, whereas AR occupied with antagonistic ligands cyproterone acetate- or casodex (bicalutamide) recruited HDAC7 from these domains to colocalize with the receptor in speckles and nucleoplasm in a more complete fashion. Ectopic expression of PML-3 relieved the repressive effect of HDAC7 on AR function by sequestering HDAC7 to PML-3 domains. AR acetylation at Lys630/632/633 was not the target of HDAC7 repression, since repression of AR function was independent of these acetylation sites. Moreover, the deacetylase activity of HDAC7 was in part dispensable in the repression of AR function. In sum, our results identify HDAC7 as a novel AR corepressor whose subcellular and subnuclear compartmentalization can be regulated in an androgen-selective manner.

Epigenetics of prostate cancer: beyond DNA methylation

Epigenetic mechanisms permit the stable inheritance of cellular properties without changes in DNA sequence or amount. In prostate carcinoma, epigenetic mechanisms are essential for development and progression, complementing, amplifying and diversifying genetic alterations. DNA hypermethylation affects at least 30 individual genes, while repetitive sequences including retrotransposons and selected genes become hypomethylated. Hypermethylation of several genes occurs in a coordinate manner early in carcinogenesis and can be exploited for cancer detection, whereas hypomethylation and further hypermethylation events are associated with progression. DNA methylation alterations interact with changes in chromatin proteins. Prominent alterations at this level include altered patterns of histone modification, increased expression of the EZH2 polycomb histone methyltransferase, and changes in transcriptional corepressors and coactivators. These changes may make prostate carcinoma particularly susceptible to drugs targeting chromatin and DNA modifications. They relate to crucial alterations in a network of transcription factors comprising ETS family proteins, the androgen receptor, NKX3.1, KLF, and HOXB13 homeobox proteins. This network controls differentiation and proliferation of prostate epithelial cells integrating signals from hormones, growth factors and cell adhesion proteins that are likewise distorted in prostate cancer. As a consequence, prostate carcinoma cells appear to be locked into an aberrant state, characterized by continued proliferation of largely differentiated cells. Accordingly, stem cell characteristics of prostate cancer cells appear to be secondarily acquired. The aberrant differentiation state of prostate carcinoma cells also results in distorted mutual interactions between epithelial and stromal cells in the tumor that promote tumor growth, invasion, and metastasis.

The Glucocorticoid Receptor Represses Cyclin D1 by Targeting the Tcf-β-Catenin Complex

The ability of glucocorticoids (GCs) to regulate cell proliferation plays an important role in their therapeutic use. The canonical Wnt pathway, which promotes the proliferation of many cancers and differentiated tissues, is an emerging target for the actions of GCs, albeit existing links between these signaling pathways are indirect. By screening known Wnt target genes for their ability to respond differently to GCs in cells whose proliferation is either positively or negatively regulated by GCs, we identified c-myc, c-jun, and cyclin D1, which encode rate-limiting factors for G(1) progression of the cell cycle. Here we show that in U2OS/GR cells, which are growth-arrested by GCs, the glucocorticoid receptor (GR) represses cyclin D1 via Tcf-beta-catenin, the transcriptional effector of the canonical Wnt pathway. We demonstrate that GR can bind beta-catenin in vitro, suggesting that GC and Wnt signaling pathways are linked directly through their effectors. Down-regulation of beta-catenin by RNA interference impeded the expression of cyclin D1 but not of c-myc or c-jun and had no significant effect on the proliferation of U2OS/GR cells. Although these results revealed that beta-catenin and cyclin D1 are not essential for the regulation of U2OS/GR cell proliferation, considering the importance of the Wnt pathway for proliferation and differentiation of other cells, the repression of Tcf-beta-catenin activity by GR could open new possibilities for tissue-selective GC therapies.

PTEN and GSK3beta: key regulators of progression to androgen-independent prostate cancer

Prostate cancer (PrCa) is characterized by progression from an androgen-dependent phenotype to one that is inevitably androgen independent (AI) and lethal. Recent evidence strongly suggests that the phosphatidylinositol-3-kinase/Akt (PI3K/Akt) and androgen receptor (AR) signalling pathways provide prostatic epithelium with the necessary signalling events to escape the apoptotic response associated with androgen withdrawal therapy. Silencing of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and glycogen synthase kinase beta (GSK3beta) are frequently associated with advanced PrCa systems and likely serve critical roles in promoting AR and PI3K/Akt gain-of-function. That PTEN negatively regulates AR and is sufficient to promote metastatic PrCa in murine models strongly implies its role as a gatekeeper of progressive PrCa. In human PrCa, PTEN loss is correlated with substantial increases in Akt(Ser473) and integrin-linked kinase expression, both of which promote Ser(9) phospho-inhibition of GSK3beta and inactivation of apoptotic factors. Sufficient evidence also suggests that GSK3beta is not only a critical regulator of proproliferative signalling but also a promiscuous one as PI3K/Akt pools of GSK3beta are, at least in part, functionally interchangeable with those of the Wnt/beta-catenin pathway. Thus, GSK3beta may serve not only as a mediator of PI3K/Akt activation but may also regulate the potent transactivation and proproliferative effects that Wnt3a and beta-catenin confer upon AR. These data suggest that prostate-specific activation of GSK3beta may serve as a viable pharmacological option. Thus, in this review, we emphasize that temporal changes in GSK3beta and PTEN expression during progression to AI PrCa are important factors when considering the potential for therapies targeting the oncogenic contributions of PI3K/Akt and AR signalling pathways.

Activation of beta-catenin signaling in prostate cancer by peptidyl-prolyl isomerase Pin1-mediated abrogation of the androgen receptor-beta-catenin interaction

Androgen receptor (AR) interacts with beta-catenin and can suppress its coactivation of T cell factor 4 (Tcf4) in prostate cancer (PCa) cells. Pin1 is a peptidyl-prolyl cis/trans isomerase that stabilizes beta-catenin by inhibiting its binding to the adenomatous polyposis coli gene product and subsequent glycogen synthase kinase 3beta (GSK-3beta)-dependent degradation. Higher Pin1 expression in primary PCa is correlated with disease recurrence, and this study found that Pin1 expression was markedly increased in metastatic PCa. Consistent with this result, increased expression of Pin1 in transfected LNCaP PCa cells strongly accelerated tumor growth in vivo in immunodeficient mice. Pin1 expression in LNCaP cells enhanced beta-catenin/Tcf4 transcriptional activity, as assessed using Tcf4-regulated reporter genes, and increased expression of endogenous Tcf4 and c-myc. However, in contrast to results in cells with intact PTEN and active GSK-3beta, Pin1 expression in LNCaP PCa cells, which are PTEN deficient, did not increase beta-catenin. Instead, Pin1 expression markedly inhibited the beta-catenin interaction with AR, and Pin1 abrogated the ability of AR to antagonize beta-catenin/Tcf4 binding and transcriptional activity. These findings demonstrate that AR can suppress beta-catenin signaling, that the AR-beta-catenin interaction can be regulated by Pin1, and that abrogation of this interaction can enhance beta-catenin/Tcf4 signaling and contribute to aggressive biological behavior in PCa.

Interaction of nuclear receptors with the Wnt/beta-catenin/Tcf signaling axis: Wnt you like to know?

The cross-regulation of Wnt/beta-catenin/Tcf ligands, kinases, and transcription factors with members of the nuclear receptor (NR) family has emerged as a clinically and developmentally important area of endocrine cell biology. Interactions between these signaling pathways result in a diverse array of cellular effects including altered cellular adhesion, tissue morphogenesis, and oncogenesis. Analyses of NR interactions with canonical Wnt signaling reveal two broad themes: Wnt/beta-catenin modulation of NRs (theme I), and ligand-dependent NR inhibition of the Wnt/beta-catenin/Tcf cascade (theme II). Beta-catenin, a promiscuous Wnt signaling member, has been studied intensively in relation to the androgen receptor (AR). Beta-catenin acts as a coactivator of AR transcription and is also involved in co-trafficking, increasing cell proliferation, and prostate pathogenesis. T cell factor, a transcriptional mediator of beta-catenin and AR, engages in a dynamic reciprocity of nuclear beta-catenin, p300/CREB binding protein, and transcriptional initiation factor 2/GC receptor-interaction protein, thereby facilitating hormone-dependent coactivation and transrepression. Beta-catenin responds in an equally dynamic manner with other NRs, including the retinoic acid (RA) receptor (RAR), vitamin D receptor (VDR), glucocorticoid receptor (GR), progesterone receptor, thyroid receptor (TR), estrogen receptor (ER), and peroxisome proliferator-activated receptor (PPAR). The NR ligands, vitamin D(3), trans/cis RA, glucocorticoids, and thiazolidines, induce dramatic changes in the physiology of cells harboring high Wnt/beta-catenin/Tcf activity. Wnt signaling regulates, directly or indirectly, developmental processes such as ductal branching and adipogenesis, two processes dependent on NR function. Beta-catenin has been intensively studied in colorectal cancer; however, it is now evident that beta-catenin may be important in cancers of the breast, prostate, and thyroid. This review will focus on the cross-regulation of AR and Wnt/beta-catenin/Tcf but will also consider the dynamic manner in which RAR/RXR, GR, TR, VDR, ER, and PPAR modulate canonical Wnt signaling. Although many commonalities exist by which NRs interact with the Wnt/beta-catenin signaling pathway, striking cell line and tissue-specific differences require deciphering and application to endocrine pathology.

Involvement of {beta}-catenin and unusual behavior of CBP and p300 in glucocorticosteroid signaling in Schwann cells

In the nervous system, glucocorticosteroid hormones play a major role during development and adult life. Myelin-forming cells are among the targets of glucocorticosteroids, which have been shown to promote myelination both in the central and peripheral nervous system. Glucocorticosteroid-stimulated gene transcription is mediated by the glucocorticosteroid receptor (GR) that recruits coactivators of the p160 family, forming a docking platform for secondary coactivators, such as cAMP-response element binding protein (CREB)-binding protein (CBP) or its close homologue, p300. Here, we investigated the role of CBP and p300 in mouse Schwann cells (MSC80). We show that, although the CBP/p300 binding domain of steroid receptor coactivator-1 is crucial for GR transactivation, neither CBP nor p300 enhanced GR transcriptional activation, as shown by overexpression and small interfering RNA (siRNA) knocking-down experiments. Unexpectedly, overexpression of p300, considered as a coactivator of the GR, resulted in inhibition of GR transcriptional activity. Studies with p300 deletion mutants demonstrated that p300-dependent repression is related to its acetyltransferase activity. Functional and pull-down assays showed that beta-catenin may be the coactivator replacing CBP in the GR transcriptional complex. Our results suggest the formation of a GR-coactivator complex within Schwann cells, indicating that glucocorticosteroids may act by means of unusual partners in the nervous system, and we show a repressive effect of p300 on nuclear receptors.