The androgen receptor in hormone-refractory prostate cancer: relevance of different mechanisms of androgen receptor signaling (Review)

The Yin Yang Role of Nitric Oxide in Prostate Cancer

Nitric oxide (NO) is a ubiquitous signaling molecule in the human body with well-known roles in many different processes and organ systems. In cancer, the two-concentrations hypothesis of NO has dictated that low levels of NO are cancer promoting, while high levels of NO are protective against cancer. Although prostate cancer is a hormonally driven malignancy, research has been shifting away from androgen-responsive epithelial cells and evolving to focus on NO therapies, the tumor microenvironment (TME), and inflammation. NO is reported to be able to inhibit activity of the androgen receptor. This may prevent prostate growth, but low levels of NO could conversely select for castration-resistant prostate cells, creating an aggressive cancer phenotype. At high levels, nitrosative stress created from NO overproduction can be protective against prostate neoplasia. In this review, we discuss development and possibilities of NO-based therapies for prostate cancer.

Role of androgen receptor splice variants, their clinical relevance and treatment options

PURPOSE

In this review, we summarize the importance of AR variants with a particular focus on clinically relevant members of this family.

METHODS

A non-systematic literature review was performed based on Medline and PubMed.

RESULTS

Endocrine therapy represents the central paradigm for the management of prostate cancer. Eventually, in response to androgen ablation therapy, several resistance mechanisms against the endocrine therapy might develop that can circumvent the therapy approaches. One specific resistance mechanism that has gained increasing attention is the generation of alternatively spliced variants of the androgen receptor, with AR-V7 being the most prominent. More broadly, AR-V7 is one member of a group of alternatively spliced AR variants that share a common feature, the missing ligand-binding domain. These ΔLBD androgen receptor variants have shown the capability to induce androgen receptor-mediated gene transcription even under conditions of androgen deprivation and to drive cancer progression.

CONCLUSION

The methods used for detecting AR-Vs, at least on the mRNA level, are well-advanced and harbor the potential to be introduced into clinical diagnostics. It is important to note, that the testing, especially of AR-V7 has its limitations in predicting treatment response. More promising is the great number of active clinical trials aimed at reducing the AR-Vs, and using this to re-sensitize CRPC towards endocrine treatment might provide additional treatment options for CRPC patients in the future.

Design, synthesis, and evaluation of the antiproliferative activity of hydantoin-derived antiandrogen-genistein conjugates

Androgen receptor (AR) signaling is vital to the viability of all forms of prostate cancer (PCa). With the goal of investigating the effect of simultaneous inhibition and depletion of AR on viability of PCa cells, we designed, synthesized and characterized the bioactivities of bifunctional agents which incorporate the independent cancer killing properties of an antiandrogen and genistein, and the AR downregulation effect of genistein within a single molecular template. We observed that a representative conjugate, 9b, is much more cytotoxic to both LNCaP and DU145 cells relative to the antiandrogen and genistein building blocks as single agents or their combination. Moreover, conjugate 9b more effectively down regulates cellular AR protein levels relative to genistein and induces S phase cell cycle arrest. The promising bioactivities of these conjugates warrant further investigation.

A review on the strategies for oral delivery of proteins and peptides and their clinical perspectives

In the modern world, a number of therapeutic proteins such as vaccines, antigens, and hormones are being developed utilizing different sophisticated biotechnological techniques like recombinant DNA technology and protein purification. However, the major glitches in the optimal utilization of therapeutic proteins and peptides by the oral route are their extensive hepatic first-pass metabolism, degradation in the gastrointestinal tract (presence of enzymes and pH-dependent factors), large molecular size and poor permeation. These problems can be overcome by adopting techniques such as chemical transformation of protein structures, enzyme inhibitors, mucoadhesive polymers and permeation enhancers. Being invasive, parenteral route is inconvenient for the administration of protein and peptides, several research endeavors have been undertaken to formulate a better delivery system for proteins and peptides with major emphasis on non-invasive routes such as oral, transdermal, vaginal, rectal, pulmonary and intrauterine. This review article emphasizes on the recent advancements made in the delivery of protein and peptides by a non-invasive (peroral) route into the body.

Adaptive responses of androgen receptor signaling in castration-resistant prostate cancer

Prostate Cancer (PCa) is an important age-related disease being the most common cancer malignancy and the second leading cause of cancer mortality in men in Western countries. Initially, PCa progression is androgen receptor (AR)- and androgen-dependent. Eventually advanced PCa reaches the stage of Castration-Resistant Prostate Cancer (CRPC), but remains dependent on AR, which indicates the importance of AR activity also for CRPC. Here, we discuss various pathways that influence the AR activity in CRPC, which indicates an adaptation of the AR signaling in PCa to overcome the treatment of PCa. The adaptation pathways include interferences of the normal regulation of the AR protein level, the expression of AR variants, the crosstalk of the AR with cytokine tyrosine kinases, the Src-Akt-, the MAPK-signaling pathways and AR corepressors. Furthermore, we summarize the current treatment options with regard to the underlying molecular basis of the common adaptation processes of AR signaling that may arise after the treatment with AR antagonists, androgen deprivation therapy (ADT) as well as for CRPC, and point towards novel therapeutic strategies. The understanding of individualized adaptation processes in PCa will lead to individualized treatment options in the future.

Role of p38 MAP Kinase Signal Transduction in Solid Tumors

Mitogen-activated protein kinases (MAPKs) mediate a wide variety of cellular behaviors in response to extracellular stimuli. One of the main subgroups, the p38 MAP kinases, has been implicated in a wide range of complex biologic processes, such as cell proliferation, cell differentiation, cell death, cell migration, and invasion. Dysregulation of p38 MAPK levels in patients are associated with advanced stages and short survival in cancer patients (e.g., prostate, breast, bladder, liver, and lung cancer). p38 MAPK plays a dual role as a regulator of cell death, and it can either mediate cell survival or cell death depending not only on the type of stimulus but also in a cell type specific manner. In addition to modulating cell survival, an essential role of p38 MAPK in modulation of cell migration and invasion offers a distinct opportunity to target this pathway with respect to tumor metastasis. The specific function of p38 MAPK appears to depend not only on the cell type but also on the stimuli and/or the isoform that is activated. p38 MAPK signaling pathway is activated in response to diverse stimuli and mediates its function by components downstream of p38. Extrapolation of the knowledge gained from laboratory findings is essential to address the clinical significance of p38 MAPK signaling pathways. The goal of this review is to provide an overview on recent progress made in defining the functions of p38 MAPK pathways with respect to solid tumor biology and generate testable hypothesis with respect to the role of p38 MAPK as an attractive target for intervention of solid tumors.

The CXCL12/CXCR4 axis promotes ligand-independent activation of the androgen receptor

The molecular mechanisms responsible for the transition of some prostate cancers from androgen ligand-dependent to androgen ligand-independent are incompletely established. Molecules that are ligands for G protein coupled receptors (GPCRs) have been implicated in ligand-independent androgen receptor (AR) activation. The purpose of this study was to examine whether CXCL12, the ligand for the GPCR, CXCR4, might mediate prostate cancer cell proliferation through AR-dependent mechanisms involving functional transactivation of the AR in the absence of androgen. The results of these studies showed that activation of the CXCL12/CXCR4 axis promoted: The nuclear accumulation of both wild-type and mutant AR in several prostate epithelial cell lines; AR-dependent proliferative responses; nuclear accumulation of the AR co-regulator SRC-1 protein; SRC-1:AR protein:protein association; co-localization of AR and SRC-1 on the promoters of AR-regulated genes; AR- and SRC-1 dependent transcription of AR-regulated genes; AR-dependent secretion of the AR-regulated PSA protein; P13K-dependent phosphorylation of AR; MAPK-dependent phosphorylation of SRC-1, and both MAPK- and P13K-dependent secretion of the PSA protein, in the absence of androgen. Taken together, these studies identify CXCL12 as a novel, non-steroidal growth factor that promotes the growth of prostate epithelial cells through AR-dependent mechanisms in the absence of steroid hormones. These findings support the development of novel therapeutics targeting the CXCL12/CXCR4 axis as an ancillary to those targeting the androgen/AR axis to effectively treat castration resistant/recurrent prostate tumors.

JS-K, a glutathione/glutathione S-transferase-activated nitric oxide releasing prodrug inhibits androgen receptor and WNT-signaling in prostate cancer cells

BACKGROUND

Nitric oxide (NO) and its oxidative reaction products have been repeatedly shown to block steroid receptor function via nitrosation of zinc finger structures in the DNA-binding domain (DBD). In consequence NO-donors could be of special interest for the treatment of deregulated androgen receptor(AR)-signaling in castration resistant prostate cancer (CRPC).

METHODS

Prostate cancer (PCa) cells were treated with JS-K, a diazeniumdiolate derivate capable of generating large amounts of intracellular NO following activation by glutathione S-transferase. Generation of NO was determined indirectly by the detection of nitrate in tissue culture medium or by immunodetection of nitrotyrosine in the cytoplasm. Effects of JS-K on intracellular AR-levels were determined by western blotting. AR-dimerization was analyzed by mammalian two hybrid assay, nuclear translocation of the AR was visualized in PCa cells transfected with a green fluorescent AR-Eos fusion protein using fluorescence microscopy. Modulation of AR- and WNT-signalling by JS-K was investigated using reporter gene assays. Tumor cell proliferation following JS-K treatment was measured by MTT-Assay.

RESULTS

The NO-releasing compound JS-K was shown to inhibit AR-mediated reporter gene activity in 22Rv1 CRPC cells. Inhibition of AR signaling was neither due to an inhibition of nuclear import nor to a reduction in AR-dimerization. In contrast to previously tested NO-donors, JS-K was able to reduce the intracellular concentration of functional AR. This could be attributed to the generation of extremely high intracellular levels of the free radical NO as demonstrated indirectly by high levels of nitrotyrosine in JS-K treated cells. Moreover, JS-K diminished WNT-signaling in AR-positive 22Rv1 cells. In line with these observations, castration resistant 22Rv1 cells were found to be more susceptible to the growth inhibitory effects of JS-K than the androgen dependent LNCaP which do not exhibit an active WNT-signaling pathway.

CONCLUSIONS

Our results suggest that small molecules able to inhibit WNT- and AR-signaling via NO-release represent a promising platform for the development of new compounds for the treatment of CRPC.

AR-Q640X, a model to study the effects of constitutively active C-terminally truncated AR variants in prostate cancer cells

PURPOSE

A recently identified mechanism allowing prostate cancer (PCa) cells to grow in the absence of androgens is the expression of constitutively active, C-terminally truncated androgen receptor (AR) variants lacking vast parts of the ligand-binding domain. These AR variants termed ARΔLBD are either products of alternative splicing, point mutations leading to premature stop codons or proteolytic cleavage of the AR. Some controversies exist about the requirement of additional full-length AR for the full transcriptional activity of the ARΔLBD. On basis of a mutated, C-terminally truncated AR termed Q640X, we developed an experimental model for the study of ARΔLBD in PCa cells.

METHODS

Activation of AR-dependent promoters was analyzed by reporter gene assays. Dimerization studies were conducted using a mammalian two-hybrid system.

RESULTS

Although Q640X/Q640X homodimers were able to induce the expression of certain AR target genes, Q640X/AR heterodimers were necessary to activate the full panel of androgen-dependent genes under androgen-deprived conditions.

CONCLUSIONS

The following study supports the hypothesis that castration-resistant prostate cancer (CRPC) cells are able to activate specific androgen-dependent genes by selective modulation of the ratio between ARΔLBD and their putative dimerization partners like the full-length AR or other ARΔLBD in the absence of androgens. The present data suggest that AR-mutant Q640X is a powerful experimental tool for the functional analysis of ARΔLBD in CRPC.

The nrf1 and nrf2 balance in oxidative stress regulation and androgen signaling in prostate cancer cells

Reactive oxygen species (ROS) signaling has recently sparked a surge of interest as being the molecular underpinning for cancer cell survival, but the precise mechanisms involved have not been completely elucidated. This review covers the possible roles of two ROS-induced transcription factors, Nrf1 and Nrf2, and the antioxidant proteins peroxiredoxin-1 (Prx-1) and Thioredoxin-1 (Txn-1) in modulating AR expression and signaling in aggressive prostate cancer (PCa) cells. In androgen independent (AI) C4-2B cells, in comparison to the parental androgen dependent (AD) LNCaP cells, we present evidence of high Nrf1 and Prx-1 expression and low Nrf2 expression in these aggressive PCa cells. Furthermore, in DHT treated C4-2B cells, increased expression of the p65 (active) isoform of Nrf1 correlated with enhanced AR transactivation. Our findings implicate a crucial balance of Nrf1 and Nrf2 signaling in regulating AR activity in AI-PCa cells. Here we will discuss how understanding the mechanisms by which oxidative stress may affect AR signaling may aid in developing novel therapies for AI-PCa.

Snail transcription factor regulates neuroendocrine differentiation in LNCaP prostate cancer cells

BACKGROUND

Snail transcription factor induces epithelial-mesenchymal transition (EMT) via decreased cell adhesion-associated molecules like E-cadherin, and increased mesenchymal markers like vimentin. We previously established Snail-mediated EMT model utilizing androgen-dependent LNCaP cells. These cells express increased vimentin protein and relocalization of E-cadherin from the cell membrane to the cytosol. Interestingly, Snail transfection in LNCaP cells resulted in cells acquiring a neuroendocrine (NE)-like morphology with long neurite-like processes.

METHODS

We tested for expression of NE markers neuron-specific enolase (NSE) and chromogranin A (CgA) by Western blot analysis, and performed proliferation assays to test for paracrine cell proliferation.

RESULTS

LNCaP cells transfected with Snail displayed increase in the NE markers, NSE and CgA as well as translocation of androgen receptor (AR) to the nucleus. LNCaP C-33 cells that have been previously published as a neuroendocrine differentiation (NED) model exhibited increased expression levels of Snail protein as compared to LNCaP parental cells. Functionally, conditioned medium from the LNCaP-Snail transfected cells increased proliferation of parental LNCaP and PC-3 cells, which could be abrogated by NSE/CgA siRNA. Additionally, NED in LNCaP-C33 cells or that induced in parental LNCaP cells by serum starvation could be inhibited by knockdown of Snail with siRNA.

CONCLUSION

Overall our data provide evidence that Snail transcription factor may promote tumor aggressiveness in the LNCaP cells through multiple processes; induction of EMT may be required to promote migration, while NED may promote tumor proliferation by a paracrine mechanism. Therefore, therapeutic targeting of Snail may prove beneficial in not only abrogating EMT but also NED.

Chemosensitization of prostate cancer by modulating Bcl-2 family proteins

A major challenge in oncology is the development of chemoresistance. This often occurs as cancer progresses and malignant cells acquire mechanisms to resist insults that would normally induce apoptosis. The onset of androgen independence in advanced prostate cancer is a prime example of this phenomenon. Overexpression of the pro-survival/anti-apoptotic proteins Bcl-2, Bcl-xL, and Mcl-1 are hallmarks of this transition. Here we outline the evolution of therapeutics designed to either limit the source or disrupt the interactions of these pro-survival proteins. By either lessening the stoichiometric abundance of Bcl-2/xL/Mcl-1 in reference to their pro-apoptotic foils or freeing these pro-apoptotic proteins from their grip, these treatments aim to sensitize cells to chemotherapy by priming cells for death. DNA anti-sense and RNA interference have been effectively employed to decrease Bcl-2 family mRNA and protein levels in cell culture models of advanced prostate cancer. However, clinical studies are lagging due to in vivo delivery challenges. The burgeoning field of nanoparticle delivery holds great promise in helping to overcome the challenge of administering highly labile nucleic acid based therapeutics. On another front, small molecule inhibitors that block the hetero-dimerization of pro-survival with pro-apoptotic proteins have significant clinical advantages and have advanced farther in clinical trials with promising early results. Most recently, a peptide has been discovered that can convert Bcl-2 from a pro-survival to a pro-apoptotic protein. The future may lie in targeting multiple steps of the apoptotic pathway, including Bcl-2/xL/Mcl-1, to debilitate the survival capacity of cancer cells and make chemotherapy induced death their only option.

Secreted Frizzled-related protein-1 is a negative regulator of androgen receptor activity in prostate cancer

Secreted Frizzled-related protein-1 (sFRP1) associates with Wnt proteins and its loss can lead to activation of Wnt/beta-catenin signalling. It is frequently downregulated in cancer, including prostate cancer, but its function in prostate cancer is unclear because it can increase proliferation of prostate epithelial cells. We investigated the function of sFRP1 in androgen-dependent prostate cancer and found that sFRP1 inhibited androgen receptor (AR) transcriptional activity. In addition, sFRP1 inhibited the proliferation of androgen-dependent LNCaP cells but not of an androgen-independent subline LNCaP-r, suggesting a role in androgen-dependent growth. The inhibition of AR by sFRP1 was unaffected by co-expression of Wnt3a, stabilised beta-catenin or beta-catenin shRNA, suggesting it does not involve Wnt/beta-catenin signalling. Wnt5a also inhibited AR and expression of Wnt5a and sFRP1 together did not further inhibit AR, suggesting that Wnt5a and sFRP1 activate the same signal(s) to inhibit AR. However, sFRP1 inhibition of AR was unaffected by inhibitors of kinases involved in Wnt/Ca(2+) and Wnt/planar cell polarity non-canonical Wnt signalling. Interestingly, the cysteine-rich domain of sFRP1 interacted with Frizzled receptors expressed in prostate cancer cells, suggesting that sFRP1/Frizzled complexes activate a signal that leads to repression of AR. Taken together, these observations highlight the function of beta-catenin-independent Wnt signalling in the control of AR activity and provide one explanation for sFRP1 downregulation in prostate cancer.

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

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

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.

Imaging androgen receptor function during flutamide treatment in the LAPC9 xenograft model

The current understanding of the response of androgen receptor to pharmacologic inhibitors in prostate cancer is derived primarily from serum prostate-specific antigen (PSA) levels. In this study, we test whether a novel androgen receptor-specific molecular imaging system is able to detect the action of the antiandrogen flutamide on androgen receptor function in xenograft models of prostate cancer. Adenoviruses bearing an optical imaging cassette containing an androgen receptor-responsive two-step transcriptional amplification system were injected into androgen-dependent and hormone-refractory tumors of animals undergoing systemic time-controlled release of the antiandrogen flutamide. Imaging of tumors with a cooled charge-coupled device camera revealed that the response of AdTSTA to flutamide is more sensitive and robust than serum PSA measurements. Flutamide inhibits the androgen signaling pathway in androgen-dependent but not refractory tumors. Analysis of androgen receptor and RNA polymerase II binding to the endogenous PSA gene by chromatin immunoprecipitation revealed that flutamide treatment and androgen withdrawal have different molecular mechanisms. The application of imaging technology to study animal models of cancer provides mechanistic insight into antiandrogen targeting of androgen receptor during disease progression.

In vivo effects of the human type I insulin-like growth factor receptor antibody A12 on androgen-dependent and androgen-independent xenograft human prostate tumors

PURPOSE

The type I insulin-like growth factor receptor (IGF-IR) and its ligands have been shown to play a critical role in prostate carcinoma development, growth, and metastasis. Targeting the IGF-IR may be a potential treatment for prostate cancer. A fully human monoclonal antibody, A12, specific to IGF-IR, has shown potent antitumor effects in breast, colon, and pancreatic cancers in vitro and in vivo. In this study, we tested the in vivo effects of A12 on androgen-dependent and androgen-independent prostate tumor growth.

EXPERIMENTAL DESIGN

Androgen-dependent LuCaP 35 and androgen-independent LuCaP 35V prostate tumors were implanted s.c. into intact and castrated severe combined immunodeficient mice, respectively. When tumor volume reached about 150 to 200 mm(3), A12 was injected at 40 mg/kg body weight thrice a week for up to 5 weeks.

RESULTS

We find that A12 significantly inhibits growth of androgen-dependent LuCaP 35 and androgen-independent LuCaP 35V prostate xenografts, however, by different mechanisms. In LuCaP 35 xenografts, A12 treatment induces tumor cell apoptosis or G(1) cycle arrest. In LuCaP 35V xenografts, A12 treatment induces tumor cell G(2)-M cycle arrest. Moreover, we find that blocking the function of IGF-IR down-regulates androgen-regulated gene expression in androgen-independent LuCaP 35V tumor cells.

CONCLUSIONS

Our findings suggest that A12 is a therapeutic candidate for both androgen-dependent and androgen-independent prostate cancer. Our findings also suggest an IGF-IR-dependent activity of the androgen receptor in androgen-independent prostate cancer cells.

A human- and male-specific protocadherin that acts through the wnt signaling pathway to induce neuroendocrine transdifferentiation of prostate cancer cells

Protocadherin-PC (PCDH-PC) is a gene on the human Y chromosome that is selectively expressed in apoptosis- and hormone-resistant human prostate cancer cells. The protein encoded by PCDH-PC is cytoplasmically localized and has a small serine-rich domain in its COOH terminus that is homologous to the beta-catenin binding site of classical cadherins. Variants of prostate cancer cells that express PCDH-PC have high levels of nuclear beta-catenin protein and increased wnt-signaling. In this study, we show that transfection of human prostate cancer cells (LNCaP) with PCDH-PC or culture of these cells in androgen-free medium (a condition that up-regulates PCDH-PC expression) activates wnt signaling as assessed by nuclear accumulation of beta-catenin, increased expression of luciferase from a reporter vector promoted by Tcf binding elements and increased expression of wnt target genes. Moreover, LNCaP cells transfected with PCDH-PC or grown in androgen-free medium transdifferentiate to neuroendocrine-like cells marked by elevated expression of neuron-specific enolase and chromogranin-A. Neuroendocrine transdifferentiation was also observed when LNCaP cells were transfected by stabilized beta-catenin. Increased wnt signaling and neuroendocrine transdifferentiation of LNCaP cells induced by culture in androgen-free medium was suppressed by short interfering RNAs that target PCDH-PC as well as by dominant-negative Tcf or short interfering RNA against beta-catenin, supporting the hypothesis that increased expression of PCDH-PC is driving neuroendocrine transdifferentiation by activating wnt signaling. These findings have significant implications for the process through which prostate cancers progress to hormone resistance in humans.