Androgen Induction of Prostate Cancer Cell Invasion Is Mediated by Ezrin

The miRNAs 203a/210-3p/5001-5p regulate the androgen/androgen receptor/YAP-induced migration in prostate cancer cells

BACKGROUND

Prostate cancer (PCa) patients with elevated level of androgen receptor (AR) correlate with higher metastatic incidence. Protein expression of AR and its target gene prostate-specific antigen (PSA) are elevated in metastatic prostate tumors as compared to organ-confined tumors. Androgen treatment or elevation of AR promotes metastasis of PCa in cell culture and murine model. However, under androgen depleted condition, AR suppressed cell mobility and invasiveness of PCa cells. Androgen deprivation therapy in PCa patients is associated with higher risk of cancer metastasis. We therefore investigated the dual roles of AR and miRNAs on PCa metastasis.

METHODS

The PC-3AR (PC-3 cells re-expressing AR) and LNCaP cells were used as PCa cell model. Transwell migration and invasion assay, wound-healing assay, zebrafish xenotransplantation assay, and zebrafish vascular exit assay were used to investigate the role of AR and androgen on PCa metastasis. Micro-Western Array, co-immunoprecipitation and Immunofluorescence were applied to dissect the molecular mechanism lying underneath. The miRNA array, miRNA inhibitors or plasmid, and chromatin immunoprecipitation assay were used to study the role of miRNAs on PCa metastasis.

RESULTS

In the absence of androgen, AR repressed the migration and invasion of PCa cells. When androgen was present, AR stimulated the migration and invasion of PCa cells both in vitro and in zebrafish xenotransplantation model. Androgen increased phospho-AR Ser81 and yes-associated protein 1 (YAP), decreased phospho-YAP Ser217, and altered epithelial-mesenchymal transition (EMT) proteins in PCa cells. Co-IP assay demonstrated that androgen augmented the interaction between YAP and AR in nucleus. Knockdown of YAP or treatment with YAP inhibitor abolished the androgen-induced migration and invasion of PCa cells, while overexpression of YAP showed opposite effects. The miRNA array revealed that androgen decreased hsa-miR-5001-5p but increased hsa-miR-203a and hsa-miR-210-3p in PC-3AR cells but not PC-3 cells. Treatment with inhibitors targeting hsa-miR-203a/hsa-miR-210-3p, or overexpression of hsa-miR-5001-5p decreased YAP expression as well as suppressed the androgen-induced migration and invasion of PCa cells. Chromatin immunoprecipitation (ChIP) assay demonstrated that AR binds with promoter region of has-miR-210-3p in the presence of androgen.

CONCLUSIONS

Our observations indicated that miRNAs 203a/210-3p/5001-5p regulate the androgen/AR/YAP-induced PCa metastasis.

Role of actin-binding proteins in prostate cancer

The molecular mechanisms driving the onset and metastasis of prostate cancer remain poorly understood. Actin, under the control of actin-binding proteins (ABPs), plays a crucial role in shaping the cellular cytoskeleton, which in turn supports the morphological alterations in normal cells, as well as the invasive spread of tumor cells. Previous research indicates that ABPs of various types serve distinct functions, and any disruptions in their activities could predispose individuals to prostate cancer. These ABPs are intricately implicated in the initiation and advancement of prostate cancer through a complex array of intracellular processes, such as severing, linking, nucleating, inducing branching, assembling, facilitating actin filament elongation, terminating elongation, and promoting actin molecule aggregation. As such, this review synthesizes existing literature on several ABPs linked to prostate cancer, including cofilin, filamin A, and fascin, with the aim of shedding light on the molecular mechanisms through which ABPs influence prostate cancer development and identifying potential therapeutic targets. Ultimately, this comprehensive examination seeks to contribute to the understanding and management of prostate diseases.

Cancer Stem Cells and Androgen Receptor Signaling: Partners in Disease Progression

Cancer stem cells exhibit self-renewal, tumorigenesis, and a high differentiation potential. These cells have been detected in every type of cancer, and different signaling pathways can regulate their maintenance and proliferation. Androgen receptor signaling plays a relevant role in the pathophysiology of prostate cancer, promoting cell growth and differentiation processes. However, in the case of prostate cancer stem cells, the androgen receptor negatively regulates their maintenance and self-renewal. On the other hand, there is evidence that androgen receptor activity positively regulates the generation of cancer stem cells in other types of neoplasia, such as breast cancer or glioblastoma. Thus, the androgen receptor role in cancer stem cells depends on the cellular context. We aimed to analyze androgen receptor signaling in the maintenance and self-renewal of different types of cancer stem cells and its action on the expression of transcription factors and surface markers associated with stemness.

Ez-Metastasizing: The Crucial Roles of Ezrin in Metastasis

Ezrin is the cytoskeletal organizer and functions in the modulation of membrane-cytoskeleton interaction, maintenance of cell shape and structure, and regulation of cell-cell adhesion and movement, as well as cell survival. Ezrin plays a critical role in regulating tumor metastasis through interaction with other binding proteins. Notably, Ezrin has been reported to interact with immune cells, allowing tumor cells to escape immune attack in metastasis. Here, we review the main functions of Ezrin, the mechanisms through which it acts, its role in tumor metastasis, and its potential as a therapeutic target.

The testosterone paradox of advanced prostate cancer: mechanistic insights and clinical implications

The discovery of the benefits of castration for prostate cancer treatment in 1941 led to androgen deprivation therapy, which remains a mainstay of the treatment of men with advanced prostate cancer. However, as early as this original publication, the inevitable development of castration-resistant prostate cancer was recognized. Resistance first manifests as a sustained rise in the androgen-responsive gene, PSA, consistent with reactivation of the androgen receptor axis. Evaluation of clinical specimens demonstrates that castration-resistant prostate cancer cells remain addicted to androgen signalling and adapt to chronic low-testosterone states. Paradoxically, results of several studies have suggested that treatment with supraphysiological levels of testosterone can retard prostate cancer growth. Insights from these studies have been used to investigate administration of supraphysiological testosterone to patients with prostate cancer for clinical benefits, a strategy that is termed bipolar androgen therapy (BAT). BAT involves rapid cycling from supraphysiological back to near-castration testosterone levels over a 4-week cycle. Understanding how BAT works at the molecular and cellular levels might help to rationalize combining BAT with other agents to achieve increased efficacy and tumour responses.

Ezrin gone rogue in cancer progression and metastasis: An enticing therapeutic target

Cancer metastasis is the primary cause of morbidity and mortality in cancer as it remains the most complicated, devastating, and enigmatic aspect of cancer. Several decades of extensive research have identified several key players closely associated with metastasis. Among these players, cytoskeletal linker Ezrin (the founding member of the ERM (Ezrin-Radixin-Moesin) family) was identified as a critical promoter of metastasis in pediatric cancers in the early 21st century. Ezrin was discovered 40 years ago as a aminor component of intestinal epithelial microvillus core protein, which is enriched in actin-containing cell surface structures. It controls gastric acid secretion and plays diverse physiological roles including maintaining cell polarity, regulating cell adhesion, cell motility and morphogenesis. Extensive research for more than two decades evinces that Ezrin is frequently dysregulated in several human cancers. Overexpression, altered subcellular localization and/or aberrant activation of Ezrin are closely associated with higher metastatic incidence and patient mortality, thereby justifying Ezrin as a valuable prognostic biomarker in cancer. Ezrin plays multifaceted role in multiple aspects of cancer, with its significant contribution in the complex metastatic cascade, through reorganizing the cytoskeleton and deregulating various cellular signaling pathways. Current preclinical studies using genetic and/or pharmacological approaches reveal that inactivation of Ezrin results in significant inhibition of Ezrin-mediated tumor growth and metastasis as well as increase in the sensitivity of cancer cells to various chemotherapeutic drugs. In this review, we discuss the recent advances illuminating the molecular mechanisms responsible for Ezrin dysregulation in cancer and its pleiotropic role in cancer progression and metastasis. We also highlight its potential as a prognostic biomarker and therapeutic target in various cancers. More importantly, we put forward some potential questions, which we strongly believe, will stimulate both basic and translational research to better understand Ezrin-mediated malignancy, ultimately leading to the development of Ezrin-targeted cancer therapy for the betterment of human life.

Proteogenomic Characterization of Patient-Derived Xenografts Highlights the Role of REST in Neuroendocrine Differentiation of Castration-Resistant Prostate Cancer

PURPOSE

An increasing number of castration-resistant prostate cancer (CRPC) tumors exhibit neuroendocrine (NE) features. NE prostate cancer (NEPC) has poor prognosis, and its development is poorly understood.Experimental Design: We applied mass spectrometry-based proteomics to a unique set of 17 prostate cancer patient-derived xenografts (PDX) to characterize the effects of castration in vivo, and the proteome differences between NEPC and prostate adenocarcinomas. Genome-wide profiling of REST-occupied regions in prostate cancer cells was correlated to the expression changes in vivo to investigate the role of the transcriptional repressor REST in castration-induced NEPC differentiation.

RESULTS

An average of 4,881 proteins were identified and quantified from each PDX. Proteins related to neurogenesis, cell-cycle regulation, and DNA repair were found upregulated and elevated in NEPC, while the reduced levels of proteins involved in mitochondrial functions suggested a prevalent glycolytic metabolism of NEPC tumors. Integration of the REST chromatin bound regions with expression changes indicated a direct role of REST in regulating neuronal gene expression in prostate cancer cells. Mechanistically, depletion of REST led to cell-cycle arrest in G₁, which could be rescued by p53 knockdown. Finally, the expression of the REST-regulated gene secretagogin (SCGN) correlated with an increased risk of suffering disease relapse after radical prostatectomy.

CONCLUSIONS

This study presents the first deep characterization of the proteome of NEPC and suggests that concomitant inhibition of REST and the p53 pathway would promote NEPC. We also identify SCGN as a novel prognostic marker in prostate cancer.

Ezrin mediates both HGF/Met autocrine and non-autocrine signaling-induced metastasis in melanoma

Aberrant HGF/Met signaling promotes tumor migration, invasion, and metastasis through both autocrine and non-autocrine mechanisms; however, the molecular downstream signaling mechanisms by which HGF/Met induces metastasis are incompletely understood. We here report that Ezrin expression is stimulated by HGF and correlates with activated HGF/Met, indicating that HGF/Met signaling regulates the expression of Ezrin. We show that HGF/Met signaling activates the transcription factor Sp1 through the MAPK pathway, and activated Sp1 can in turn directly bind to the promoter of Ezrin gene and regulate its transcription. Notably, knockdown of Ezrin expression by shRNAs inhibits the metastasis induced by either HGF/Met autocrine or non-autocrine signaling in syngeneic wildtype and HGF transgenic mouse hosts. We also used small molecule drugs in preclinical mouse models to confirm that Ezrin is one of the downstream molecules mediating HGF/Met signaling-induced metastasis in melanoma. We conclude that Ezrin is a key downstream factor involved in the regulation of HGF/Met signaling-induced metastasis and demonstrate a link between Ezrin and HGF/Met/MAPK/Sp1 activation in the metastatic process. Our data indicate that Ezrin represents a promising therapeutic target for patients bearing tumors with activated HGF/Met signaling.

Connexins, important players in the dissemination of prostate cancer cells

Over the past 50years, increasing experimental evidences have established that connexins (Cxs) and gap junctional intercellular communication (GJIC) ensure an important role in both the onset and development of cancerous processes. In the present review, we focus on the impact of Cxs and GJIC during the development of prostate cancer (PCa), from the primary growth mainly localized in acinar glands and ducts to the distant metastasis mainly concentrated in bone. As observed in several other types of solid tumours, Cxs and especially Cx43 exhibit an ambivalent role with a tumour suppressor effect in the early stages and, conversely, a rather pro-tumoural profile for most of invasion and dissemination steps to secondary sites. We report here the current knowledge on the function of Cxs during PCa cells migration, cytoskeletal dynamics, proteinases activities and the cross talk with the surrounding stromal cells in the microenvironment of the tumour and the bones. In addition, we discuss the role of Cxs in the bone tropism even if the prostate model is rarely used to study the complete sequence of cancer dissemination compared to breast cancer or melanoma. Even if not yet fully understood, these recent findings on Cxs provide new insights into their molecular mechanisms associated with progression and bone targeted behaviour of PCa. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

A Novel Invasive-Related Biomarker in Three Subtypes of Nonfunctioning Pituitary Adenomas

OBJECTIVE

To identify biomarkers key to invasiveness of the 3 subtypes of nonfunctioning pituitary adenomas (NFPAs) and provide a guidance for therapeutic decision making and identification of potential adjuvant drugs.

METHODS

Fifty NFPA tumor tissues obtained from transsphenoidal surgery were used in the study. Three invasive NFPAs and 4 noninvasive NFPAs were used for gene expression microarray analyses. In addition, there are 5 invasive NFPAs and 4 noninvasive NFPAs used for proteomic analyses. Invasive-related biomarkers were identified by bioinformatics analysis by integrating the transcriptomics and proteomics data sets. All 3 subtypes of NFPAs (null cell adenomas, oncocytomas, and gonadotroph adenomas) were used to validate differentially expressed candidate biomarkers by means of quantitative real-time reverse transcription polymerase chain reaction and Western blot. The level of EZR was downregulated in pituitary adenoma cell line GH3 to investigate the invasive effect of EZR on GH3 cells by using the RNA interference technique.

RESULTS

Eight genes involved in the invasion function were found by bioinformatics analysis, and the EZR gene was identified as a novel invasive-related biomarker in the 3 subtypes of NFPAs. The expression level of EZR was found higher in terms of invasiveness than the noninvasive ones of the 3 subtypes of NFPAs. Moreover, the knockdown of EZR inhibited the invasion of GH3 cells in vitro.

CONCLUSIONS

EZR is a novel biomarker in terms of invasion among the 3 subtypes of NFPAs, and it is a promising guide for therapeutic decision making as well.

CXCR6-CXCL16 axis promotes prostate cancer by mediating cytoskeleton rearrangement via Ezrin activation and αvβ3 integrin clustering

Cytoskeletal rearrangement is required for migration and invasion, which are the key steps of cancer metastasis. Ezrin and integrin co-ordinate these processes by regulating cellular adhesion and cytoskeletal polymerization-depolymerization. It is also well established that chemokine-chemokine receptor axis plays a crucial role in regulating cancer cell migration and invasion. In this study, we show involvement of CXC chemokine receptor 6 (CXCR6) and its only natural ligand CXCL16 in pathobiology of prostate cancer (PCa). CXCR6 is highly expressed in PCa tissues and cell lines (LNCaP and PC3), relative to normal tissue and cells. CXCR6 expression in PCa tissues correlated with higher Gleason score. Similarly, aggressive PCa cells (PC3) show high CXCR6 compared to less aggressive LNCaP. Besides, PC3 cells show higher MMPs expression compared to LNCaP cells following CXCL16 stimulation. Intriguingly, CXCR6-CXCL16 interaction in PCa cells promotes Ezrin activation, α_vβ₃ integrin clustering and capping at the leading edge in FAK/PI3K/PKC dependent manner, thereby modifying cellular adhesion as well as motility. Together these results demonstrate that CXCL16 stimulation changes cytoskeletal dynamics resulting in enhanced migration, invasion and adhesion to endothelial cells, ultimately enabling PCa cells to achieve their metastatic goal.

Resistin, a fat-derived secretory factor, promotes metastasis of MDA-MB-231 human breast cancer cells through ERM activation

Resistin, an adipocyte-secreted factor, is known to be elevated in breast cancer patients. However, the molecular mechanism by which resistin acts is not fully understood. The aim of this study was to investigate whether resistin could stimulate invasion and migration of breast cancer cells. Here, we report that resistin stimulated invasion and migration of breast cancer cells as well as phosphorylation of c-Src. Inhibition of c-Src blocked resistin-induced breast cancer cell invasion. Resistin increased intracellular calcium concentration, and chelation of intracellular calcium blocked resistin-mediated activation of Src. Resistin also induced phosphorylation of protein phosphatase 2A (PP2A). Inhibition of c-Src blocked resistin-mediated PP2A phosphorylation. In addition, resistin increased phosphorylation of PKCα. Inhibition of PP2A enhanced resistin-induced PKCα phosphorylation, demonstrating that PP2A activity is critical for PKCα phosphorylation. Resistin also increased phosphorylation of ezrin, radixin, and moesin (ERM). Additionally, ezrin interacted with PKCα, and resistin promoted co-localization of ezrin and PKCα. Either inhibition of c-Src and PKCα or knock-down of ezrin blocked resistin-induced breast cancer cells invasion. Moreover, resistin increased expression of vimentin, a key molecule for cancer cell invasion. Knock-down of ezrin abrogated resistin-induced vimentin expression. These results suggest that resistin play as a critical regulator of breast cancer metastasis.

Plasmodium vivax inhibits erythroid cell growth through altered phosphorylation of the cytoskeletal protein ezrin

BACKGROUND

The underlying causes of severe malarial anaemia are multifactorial. In previously reports, Plasmodium vivax was found to be able to directly inhibited erythroid cell proliferation and differentiation. The molecular mechanisms underlying the suppression of erythropoiesis by P. vivax are remarkably complex and remain unclear. In this study, a phosphoproteomic approach was performed to dissect the molecular mechanism of phosphoprotein regulation, which is involved in the inhibitory effect of parasites on erythroid cell development.

METHODS

This study describes the first comparative phosphoproteome analysis of growing erythroid cells (gECs), derived from human haematopoietic stem cells, exposed to lysates of infected erythrocytes (IE)/uninfected erythrocytes (UE) for 24, 48 and 72 h. This study utilized IMAC phosphoprotein isolation directly coupled with LC MS/MS analysis.

RESULTS

Lysed IE significantly inhibited gEC growth at 48 and 72 h and cell division resulting in the accumulation of cells in G0 phase. The relative levels of forty four phosphoproteins were determined from gECs exposed to IE/UE for 24-72 h and compared with the media control using the label-free quantitation technique. Interestingly, the levels of three phosphoproteins: ezrin, alpha actinin-1, and Rho kinase were significantly (p < 0.05) altered. These proteins display interactions and are involved in the regulation of the cellular cytoskeleton. Particularly affected was ezrin (phosphorylated at Thr567), which is normally localized to gEC cell extension peripheral processes. Following exposure to IE, for 48-72 h, the ezrin signal intensity was weak or absent. This result suggests that phospho-ezrin is important for actin cytoskeleton regulation during erythroid cell growth and division.

CONCLUSIONS

These findings suggest that parasite proteins are able to inhibit erythroid cell growth by down-regulation of ezrin phosphorylation, leading to ineffective erythropoiesis ultimately resulting in severe malarial anaemia. A better understanding of the mechanisms of ineffective erythropoiesis may be beneficial in the development of therapeutic strategies to prevent severe malarial anaemia.

Androgen receptor signaling in prostate cancer

The androgen receptor (AR), ligand-induced transcription factor, is expressed in primary prostate cancer and in metastases. AR regulates multiple cellular events, proliferation, apoptosis, migration, invasion, and differentiation. Its expression in prostate cancer cells is regulated by steroid and peptide hormones. AR downregulation by various compounds which are contained in fruits and vegetables is considered a chemopreventive strategy for prostate cancer. There is a bidirectional interaction between the AR and micro-RNA (miRNA) in prostate cancer; androgens may upregulate or downregulate the selected miRNA, whereas the AR itself is a target of miRNA. AR mutations have been discovered in prostate cancer, and their incidence may increase with tumor progression. AR mutations and increased expression of selected coactivators contribute to the acquisition of agonistic properties of anti-androgens. Expression of some of the coactivators is enhanced during androgen ablation. AR activity is regulated by peptides such as cytokines or growth factors which reduce the concentration of androgen required for maximal stimulation of the receptor. In prostate cancer, variant ARs which exhibit constitutive activity were detected. Novel therapies which interfere with intracrine synthesis of androgens or inhibit nuclear translocation of the AR have been introduced in the clinic.

Inactivation of Src-to-ezrin pathway: a possible mechanism in the ouabain-mediated inhibition of A549 cell migration

Ouabain, a cardiac glycoside found in plants, is primarily used in the treatment of congestive heart failure and arrhythmia because of its ability to inhibit Na⁺/K⁺-ATPase pump. Recently ouabain has been shown to exert anticancer effects but the underlying mechanism is not clear. Here, we explored the molecular mechanism by which ouabain exerts anticancer effects in human lung adenocarcinoma. Employing proteomic techniques, we found 7 proteins downregulated by ouabain in A549 including p-ezrin, a protein associated with pulmonary cancer metastasis in a dose-dependent manner. In addition, when the relative phosphorylation levels of 39 intracellular proteins were compared between control and ouabain-treated A549 cells, p-Src (Y416) was also found to be downregulated by ouabain. Furthermore, western blot revealed the ouabain-mediated downregulation of p-FAK (Y925), p-paxillin (Y118), p130CAS, and Na⁺/K⁺-ATPase subunits that have been shown to be involved in the migration of cancer cells. The inhibitory effect of ouabain and Src inhibitor PP2 on the migration of A549 cells was confirmed by Boyden chamber assay. Anticancer effects of ouabain in A549 cells appear to be related to its ability to regulate and inactivate Src-to-ezrin signaling, and proteins involved in focal adhesion such as Src, FAK, and p130CAS axis are proposed here.

OTUB1 de-ubiquitinating enzyme promotes prostate cancer cell invasion in vitro and tumorigenesis in vivo

Background

Ubiquitination is a highly dynamic and reversible process with a central role in cell homeostasis. Deregulation of several deubiquitinating enzymes has been linked to tumor development but their specific role in prostate cancer progression remains unexplored.

Methods

RNAi screening was used to investigate the role of the ovarian tumor proteases (OTU) family of deubiquitinating enzymes on the proliferation and invasion capacity of prostate cancer cells. RhoA activity was measured in relation with OTUB1 effects on prostate cancer cell invasion. Tumor xenograft mouse model with stable OTUB1 knockdown was used to investigate OTUB1 influence in tumor growth.

Results

Our RNAi screening identified OTUB1 as an important regulator of prostate cancer cell invasion through the modulation of RhoA activation. The effect of OTUB1 on RhoA activation is important for androgen-induced repression of p53 expression in prostate cancer cells. In localized prostate cancer tumors OTUB1 was found overexpressed as compared to normal prostatic epithelial cells. Prostate cancer xenografts expressing reduced levels of OTUB1 exhibit reduced tumor growth and reduced metastatic dissemination in vivo.

Conclusions

OTUB1 mediates prostate cancer cell invasion through RhoA activation and promotes tumorigenesis in vivo. Our results suggest that drugs targeting the catalytic activity of OTUB1 could potentially be used as therapeutics for metastatic prostate cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-014-0280-2) contains supplementary material, which is available to authorized users.

Desmoglein 3: a help or a hindrance in cancer progression?

Desmoglein 3 is one of seven desmosomal cadherins that mediate cell-cell adhesion in desmosomes. Desmosomes are the intercellular junctional complexes that anchor the intermediate filaments of adjacent cells and confer strong cell adhesion thus are essential in the maintenance of tissue architecture and structural integrity. Like adherens junctions, desmosomes function as tumour suppressors and are down regulated in the process of epithelial-mesenchymal transition and in tumour cell invasion and metastasis. However, recently several studies have shown that various desmosomal components, including desmoglein 3, are up-regulated in cancer with increased levels of expression correlating with the clinical stage of malignancy, implicating their potentiality to serve as a diagnostic and prognostic marker. Furthermore, in vitro studies have demonstrated that overexpression of desmoglein 3 in cancer cell lines activates several signal pathways that have an impact on cell morphology, adhesion and locomotion. These additional signalling roles of desmoglein 3 may not be associated to its adhesive function in desmosomes but rather function outside of the junctions, acting as a key regulator in the control of actin based cellular processes. This review will discuss recent advances which support the role of desmoglein 3 in cancer progression.

The evaluation of involvement of angiotensin II, its receptors, and androgen receptor in endometrial cancer

Endometrial cancer (EC) is the most common gynecological malignancy. Alterations of angiogenic factors including angiotensin (AngII) or VEGF are observed in EC. Expression of angiotensin receptor 1 (AT1) is correlated with EC. Moreover, the expression of VEGF is up-regulated by AngII. Androgens are involved in the pathogenesis of EC. Genetic variations in androgen receptor (AR) gene may increase EC risk. This review proved strong correlation among EC, AngII, its receptors and AR, where AT influence on AR and, as a result, induce the expression of genes related to carcinogenesis.

Dinitrosopiperazine-mediated phosphorylated-proteins are involved in nasopharyngeal carcinoma metastasis

N,N'-dinitrosopiperazine (DNP) with organ specificity for nasopharyngeal epithelium, is involved in nasopharyngeal carcinoma (NPC) metastasis, though its mechanism is unclear. To reveal the pathogenesis of DNP-induced metastasis, immunoprecipitation was used to identify DNP-mediated phosphoproteins. DNP-mediated NPC cell line (6-10B) motility and invasion was confirmed. Twenty-six phosphoproteins were increased at least 1.5-fold following DNP exposure. Changes in the expression levels of selected phosphoproteins were verified by Western-blotting analysis. DNP treatment altered the phosphorylation of ezrin (threonine 567), vimentin (serine 55), stathmin (serine 25) and STAT3 (serine 727). Furthermore, it was shown that DNP-dependent metastasis is mediated in part through ezrin at threonine 567, as DNP-mediated metastasis was decreased when threonine 567 of ezrin was mutated. Strikingly, NPC metastatic tumors exhibited a higher expression of phosphorylated-ezrin at threonine 567 than the primary tumors. These findings provide novel insight into DNP-induced NPC metastasis and may contribute to a better understanding of the metastatic mechanisms of NPC tumors.

ERM proteins in cancer progression

Members of the ezrin-radixin-moesin (ERM) family of proteins are involved in multiple aspects of cell migration by acting both as crosslinkers between the membrane, receptors and the actin cytoskeleton, and as regulators of signalling molecules that are implicated in cell adhesion, cell polarity and migration. Increasing evidence suggests that the regulation of cell signalling and the cytoskeleton by ERM proteins is crucial during cancer progression. Thus, both their expression levels and subcellular localisation would affect tumour progression. High expression of ERM proteins has been shown in a variety of cancers. Mislocalisation of ERM proteins reduces the ability of cells to form cell-cell contacts and, therefore, promotes an invasive phenotype. Similarly, mislocalisation of ERM proteins impairs the formation of receptor complexes and alters the transmission of signals in response to growth factors, thereby facilitating tumour progression. In this Commentary, we address the structure, function and regulation of ERM proteins under normal physiological conditions as well as in cancer progression, with particular emphasis on cancers of epithelial origin, such as those from breast, lung and prostate. We also discuss any recent developments that have added to the understanding of the underlying molecular mechanisms and signalling pathways these proteins are involved in during cancer progression.

REST mediates androgen receptor actions on gene repression and predicts early recurrence of prostate cancer

The androgen receptor (AR) is a key regulator of prostate tumorgenesis through actions that are not fully understood. We identified the repressor element (RE)-1 silencing transcription factor (REST) as a mediator of AR actions on gene repression. Chromatin immunoprecipitation showed that AR binds chromatin regions containing well-characterized cis-elements known to mediate REST transcriptional repression, while cell imaging studies confirmed that REST and AR closely co-localize in vivo. Androgen-induced gene repression also involves modulation of REST protein turnover through actions on the ubiquitin ligase β-TRCP. Androgen deprivation or AR blockage with inhibitor MDV3100 (Enzalutamide) leads to neuroendocrine (NE) differentiation, a phenomenon that is mimicked by REST inactivation. Gene expression profiling revealed that REST not only acts to repress neuronal genes but also genes involved in cell cycle progression, including Aurora Kinase A, that has previously been implicated in the growth of NE-like castration-resistant tumors. The analysis of prostate cancer tissue microarrays revealed that tumors with reduced expression of REST have higher probability of early recurrence, independently of their Gleason score. The demonstration that REST modulates AR actions in prostate epithelia and that REST expression is negatively correlated with disease recurrence after prostatectomy, invite a deeper characterization of its role in prostate carcinogenesis.

SOCS2 mediates the cross talk between androgen and growth hormone signaling in prostate cancer

Anabolic signals such as androgens and the growth hormone/insulin-like growth factor 1 (GH/IGF-1) axis play an essential role in the normal development of the prostate but also in its malignant transformation. In this study, we investigated the role of suppressor of cytokine signaling 2 (SOCS2) as mediator of the cross talk between androgens and GH signals in the prostate and its potential role as tumor suppressor in prostate cancer (PCa). We observed that SOCS2 protein levels assayed by immunohistochemistry are elevated in hormone therapy-naive localized prostatic adenocarcinoma in comparison with benign tissue. In contrast, however, castration-resistant bone metastases exhibit reduced levels of SOCS2 in comparison with localized or hormone naive, untreated metastatic tumors. In PCa cells, SOCS2 expression is induced by androgens through a mechanism that requires signal transducer and activator of transcription 5 protein (STAT5) and androgen receptor-dependent transcription. Consequentially, SOCS2 inhibits GH activation of Janus kinase 2, Src and STAT5 as well as both cell invasion and cell proliferation in vitro. In vivo, SOCS2 limits proliferation and production of IGF-1 in the prostate in response to GH. Our results suggest that the use of GH-signaling inhibitors could be of value as a complementary treatment for castration-resistant PCa.

SUMMARY

Androgen induced SOCS2 ubiquitin ligase expression and inhibited GH signaling as well as cell proliferation and invasion in PCa, whereas reduced SOCS2 was present in castration-resistant cases. GH-signaling inhibitors might be a complementary therapeutic option for advanced PCa.

Sphingolipid regulation of ezrin, radixin, and moesin proteins family: implications for cell dynamics

A key but poorly studied domain of sphingolipid functions encompasses endocytosis, exocytosis, cellular trafficking, and cell movement. Recently, the ezrin, radixin and moesin (ERM) family of proteins emerged as novel potent targets regulated by sphingolipids. ERMs are structural proteins linking the actin cytoskeleton to the plasma membrane, also forming a scaffold for signaling pathways that are used for cell proliferation, migration and invasion, and cell division. Opposing functions of the bioactive sphingolipid ceramide and sphingosine-1-phosphate (S1P), contribute to ERM regulation. S1P robustly activates whereas ceramide potently deactivates ERM via phosphorylation/dephosphorylation, respectively. This recent dimension of cytoskeletal regulation by sphingolipids opens up new avenues to target cell dynamics, and provides further understanding of some of the unexplained biological effects mediated by sphingolipids. In addition, these studies are providing novel inroads into defining basic mechanisms of regulation and action of bioactive sphingolipids. This review describes the current understanding of sphingolipid regulation of the cytoskeleton, it also describes the biologies in which ERM proteins have been involved, and finally how these two large fields have started to converge. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

Desmoglein 3 promotes cancer cell migration and invasion by regulating activator protein 1 and protein kinase C-dependent-Ezrin activation

Desmoglein 3 (Dsg3), the pemphigus vulgaris antigen, has recently been shown to be upregulated in squamous cell carcinoma (SCC) and has been identified as a good tumor-specific marker for clinical staging of cervical sentinel lymph nodes in head and neck SCC. However, little is known about its biological function in cancer. The actin-binding protein Ezrin and the activator protein 1 (AP-1) transcription factor are implicated in cancer progression and metastasis. Here, we report that Dsg3 regulates the activity of c-Jun/AP-1 as well as protein kinase C (PKC)-mediated phosphorylation of Ezrin-Thr567, which contributes to the accelerated motility of cancer cells. Ectopic expression of Dsg3 in cancer cell lines caused enhanced phosphorylation at Ezrin-Thr567 with concomitant augmented membrane protrusions, cell spreading and invasive phenotype. We showed that Dsg3 formed a complex with Ezrin at the plasma membrane that was required for its proper function of interacting with F-actin and CD44 as Dsg3 knockdown impaired these associations. The increased Ezrin phosphorylation in Dsg3-overexpressing cells could be abrogated substantially by various pharmacological inhibitors for Ser/Thr kinases, including PKC and Rho kinase that are known to activate Ezrin. Furthermore, a marked increase in c-Jun S63 phosphorylation, among others, was found in Dsg3-overexpressing cells and the activation of c-Jun/AP-1 was further supported by a luciferase reporter assay. Taken together, our study identifies a novel Dsg3-mediated c-Jun/AP-1 regulatory mechanism and PKC-dependent Ezrin phosphorylation that could be responsible for Dsg3-associated cancer metastasis.

Cyr61 is regulated by cAMP-dependent protein kinase with serum levels correlating with prostate cancer aggressiveness

BACKGROUND

Cysteine-rich angiogenic inducer 61 (Cyr61) is an extracellular matrix protein involved in the transduction of growth factor and hormone signaling. Previously, we demonstrated that Cyr61 was highly expressed in prostate cancer (PCa) but that the expression levels were associated with a lower risk of PCa recurrence. In the present study, we demonstrate that serum Cyr61 is a potential biomarker that correlates with PCa aggressiveness. Furthermore, we also explore the potential mechanism underlying the changes in Cyr61 expression during PCa progression.

METHODS

Cyr61 concentrations in the medium from PCa cell lines and in serum samples obtained from PCa patients were measured by sandwich ELISA. Serum Cyr61 levels were correlated with disease characteristics and the association between Cyr61 expression changes by several types of stimulation or stress and cAMP/cAMP-dependent protein kinase (PKA) pathway were examined.

RESULTS

There was a positive correlation between Cyr61 levels in cell supernatants and mRNA expression in these cell lines. Serum Cyr61 levels were significantly higher in non-organ-confined PCa patients (116.3 ± 140.2 ng/ml) than in organ-confined PCa patients (79.7 ± 56.1 ng/ml) (P = 0.031). Cyr61 expression was up-regulated in response to both lysophosphatidic acid and androgen treatments which promoted PCa cell invasion. Serum starvation and phosphoinositide-3-kinase inhibition also resulted in Cyr61 up-regulation; however, they suppressed cell proliferation. Cyr61 up-regulation was correlated with an increase in cAMP and suppressed by PKA inhibition.

CONCLUSIONS

These findings suggest that Cyr61 expression in PCa is regulated by the cAMP/PKA pathway and that circulating Cyr61 levels are a potential serum-based biomarker for characterizing PCa.

Cryptotanshinone suppresses androgen receptor-mediated growth in androgen dependent and castration resistant prostate cancer cells

Androgen receptor (AR) is the major therapeutic target for the treatment of prostate cancer (PCa). Anti-androgens to reduce or prevent androgens binding to AR are widely used to suppress AR-mediated PCa growth; however, the androgen depletion therapy is only effective for a short period of time. Here we found a natural product/Chinese herbal medicine cryptotanshinone (CTS), with a structure similar to dihydrotestosterone (DHT), can effectively inhibit the DHT-induced AR transactivation and prostate cancer cell growth. Our results indicated that 0.5 μM CTS effectively suppresses the growth of AR-positive PCa cells, but has little effect on AR negative PC-3 cells and non-malignant prostate epithelial cells. Furthermore, our data indicated that CTS could modulate AR transactivation and suppress the DHT-mediated AR target genes (PSA, TMPRSS2, and TMEPA1) expression in both androgen responsive PCa LNCaP cells and castration resistant CWR22rv1 cells. Importantly, CTS selectively inhibits AR without repressing the activities of other nuclear receptors, including ERα, GR, and PR. The mechanistic studies indicate that CTS functions as an AR inhibitor to suppress androgen/AR-mediated cell growth and PSA expression by blocking AR dimerization and the AR-coregulator complex formation. Furthermore, we showed that CTS effectively inhibits CWR22Rv1 cell growth and expressions of AR target genes in the xenograft animal model. The previously un-described mechanisms of CTS may explain how CTS inhibits the growth of PCa cells and help us to establish new therapeutic concepts for the treatment of PCa.

Protein phosphatase 1α mediates ceramide-induced ERM protein dephosphorylation: a novel mechanism independent of phosphatidylinositol 4, 5-biphosphate (PIP2) and myosin/ERM phosphatase

ERM (ezrin, radixin, and moesin) proteins are cytoskeletal interacting proteins that bind cortical actin, the plasma membrane, and membrane proteins, which are found in specialized plasma membrane structures such as microvilli and filopodia. ERM proteins are regulated by phosphatidylinositol 4, 5-biphosphate (PIP(2)) and by phosphorylation of a C-terminal threonine, and its inactivation involves PIP(2) hydrolysis and/or myosin phosphatase (MP). Recently, we demonstrated that ERM proteins are also subject to counter regulation by the bioactive sphingolipids ceramide and sphingosine 1-phosphate. Plasma membrane ceramide induces ERM dephosphorylation whereas sphingosine 1-phosphate induces their phosphorylation. In this work, we pursue the mechanisms by which ceramide regulates dephosphorylation. We found that this dephosphorylation was independent of hydrolysis and localization of PIP(2) and MP. However, the results show that ERM dephosphorylation was blocked by treatment with protein phosphatase 1 (PP1) pharmacological inhibitors and specifically by siRNA to PP1α, whereas okadaic acid, a PP2A inhibitor, failed. Moreover, a catalytic inactive mutant of PP1α acted as dominant negative of the endogenous PP1α. Additional results showed that the ceramide mechanism of PP1α activation is largely independent of PIP(2) hydrolysis and MP. Taken together, these results demonstrate a novel, acute mechanism of ERM regulation dependent on PP1α and plasma membrane ceramide.

Radixin regulates cell migration and cell-cell adhesion through Rac1

The ERM proteins ezrin, radixin and moesin are adaptor proteins that link plasma membrane receptors to the actin cytoskeleton. Ezrin and moesin have been implicated in cell polarization and cell migration, but little is known about the involvement of radixin in these processes. Here we show that radixin is required for migration of PC3 prostate cancer cells, and that radixin, but not ezrin or moesin, depletion by RNAi increases cell spread area and cell-cell adhesion mediated by adherens junctions. Radixin depletion also alters actin organization and distribution of active phosphorylated ezrin and moesin. Similar effects were observed in MDA-MB-231 breast cancer cells. The phenotype of radixin-depleted cells is similar to that induced by constitutively active Rac1, and Rac1 is required for the radixin knockdown phenotype. Radixin depletion also increases the activity of Rac1 but not Cdc42 or RhoA. Analysis of Rac guanine nucleotide exchange factors (GEFs) suggests that radixin affects the activity of Vav GEFs. Indeed, Vav GEF depletion reverts the phenotype of radixin knockdown and reduces the effect of radixin knockdown on Rac1 activity. Our results indicate that radixin plays an important role in promoting cell migration by regulating Rac1-mediated epithelial polarity and formation of adherens junctions through Vav GEFs.

Macrophage binding to receptor VCAM-1 transmits survival signals in breast cancer cells that invade the lungs

Aberrant expression of vascular cell adhesion molecule-1 (VCAM-1) in breast cancer cells is associated with lung relapse, but the role of VCAM-1 as a mediator of metastasis has remained unknown. We report that VCAM-1 provides a survival advantage to breast cancer cells that infiltrate leukocyte-rich microenvironments such as the lungs. VCAM-1 tethers metastasis-associated macrophages to cancer cells via counter-receptor α4-integrins. Clustering of cell surface VCAM-1, acting through Ezrin, triggers Akt activation and protects cancer cells from proapoptotic cytokines such as TRAIL. This prosurvival function of VCAM-1 can be blocked by antibodies against α4-integrins. Thus, newly disseminated cancer cells expressing VCAM-1 can thrive in leukocyte-rich microenvironments through juxtacrine activation of a VCAM-1-Ezrin-PI3K/Akt survival pathway.

N,N'-dinitrosopiperazine-mediated ezrin protein phosphorylation via activation of Rho kinase and protein kinase C is involved in metastasis of nasopharyngeal carcinoma 6-10B cells

N,N'-Dinitrosopiperazine (DNP) is a carcinogen for nasopharyngeal carcinoma (NPC), which shows organ specificity to nasopharyngeal epithelium. Herein, we demonstrate that DNP induces fiber formation of NPC cells (6-10B) and also increases invasion and motility of 6-10B cells. DNP-mediated NPC metastasis also was confirmed in nude mice. Importantly, DNP induced the expression of phosphorylated ezrin (phos-ezrin) at threonine 567 (Thr-567) dose- and time-dependently but had no effect on the total ezrin expression at these concentrations. Furthermore, DNP-induced phos-ezrin expression was dependent on increased Rho kinase and protein kinase C (PKC) activity. DNP may activate Rho kinase through binding to its pleckstrin homology and may activate PKC through promoting its translocation to the plasma membrane in vivo. DNP-induced phos-ezrin was associated with induction of fiber growth in 6-10B cells. However, DNP could not induce motility and invasion of NPC cells containing ezrin mutated at Thr-567. Similarly, DNP could not induce motility and invasion of the cells containing siRNAs against Rho or PKC. These results indicate that DNP induces ezrin phosphorylation at Thr-567, increases motility and invasion of cells, and promotes tumor metastasis. DNP may be involved in NPC metastasis through regulation of ezrin phosphorylation at Thr-567.

Decreased ezrin and paxillin expression in human urothelial bladder tumors correlate with tumor progression

OBJECTIVES

F-actin binding proteins ezrin and paxillin are involved in cell adhesion and cell migration/invasion. The aim of the study was to investigate their role in urothelial bladder carcinogenesis.

MATERIALS AND METHODS

Expression of ezrin and paxillin was studied by immunohistochemistry in 104 and 96 cases of urothelial bladder tumors, respectively. Correlations with clinicopathologic data and expression of p53, E-cadherin, and β-catenin were examined.

RESULTS

Positive ezrin and paxillin protein expression was found in 99% and 93.7% of cases, respectively. Membranous expression of ezrin was significantly lower in high grade tumors and correlated with invasion. Multivariate analysis showed that ezrin is an independent predictor of muscularis propria invasion. Paxillin expression was significantly decreased in urothelial carcinomas compared with tumors of low malignant potential and low paxillin levels also correlated with advancing tumor stage and invasion. A statistically significant correlation was found between membranous ezrin and E-cadherin as well as between ezrin and paxillin expression in urothelial tumors.

CONCLUSIONS

Down-regulation of ezrin and paxillin in urothelial bladder tumors is associated with aggressive tumor features and invasiveness.

Differential involvement of ezrin/radixin/moesin proteins in sphingosine 1-phosphate-induced human pulmonary endothelial cell barrier enhancement

Endothelial cell (EC) barrier dysfunction induced by inflammatory agonists is a frequent pathophysiologic event in multiple diseases. The platelet-derived phospholipid sphingosine-1 phosphate (S1P) reverses this dysfunction by potently enhancing the EC barrier through a process involving Rac GTPase-dependent cortical actin rearrangement as an integral step. In this study we explored the role of the ezrin, radixin, and moesin (ERM) family of actin-binding linker protein in modulating S1P-induced human pulmonary EC barrier enhancement. S1P induces ERM translocation to the EC periphery and promotes ERM phosphorylation on a critical threonine residue (Ezrin-567, Radixin-564, Moesin-558). This phosphorylation is dependent on activation of PKC isoforms and Rac1. The majority of ERM phosphorylation on these critical threonine residues after S1P occurs in moesin and ezrin. Baseline radixin phosphorylation is higher than in the other two ERM proteins but does not increase after S1P. S1P-induced moesin and ezrin threonine phosphorylation is not mediated by the barrier enhancing receptor S1PR1 because siRNA downregulation of S1PR1 fails to inhibit these phosphorylation events, while stimulation of EC with the S1PR1-specific agonist SEW2871 fails to induce these phosphorylation events. Silencing of either all ERM proteins or radixin alone (but not moesin alone) reduced S1P-induced Rac1 activation and phosphorylation of the downstream Rac1 effector PAK1. Radixin siRNA alone, or combined siRNA for all three ERM proteins, dramatically attenuates S1P-induced EC barrier enhancement (measured by transendothelial electrical resistance (TER), peripheral accumulation of di-phospho-MLC, and cortical cytoskeletal rearrangement. In contrast, moesin depletion has the opposite effects on these parameters. Ezrin silencing partially attenuates S1P-induced EC barrier enhancement and cytoskeletal changes. Thus, despite structural similarities and reported functional redundancy, the ERM proteins differentially modulate S1P-induced alterations in lung EC cytoskeleton and permeability. These results suggest that ERM activation is an important regulatory event in EC barrier responses to S1P.

17β-Estradiol enhances breast cancer cell motility and invasion via extra-nuclear activation of actin-binding protein ezrin

Estrogen promotes breast cancer metastasis. However, the detailed mechanism remains largely unknown. The actin binding protein ezrin is a key component in tumor metastasis and its over-expression is positively correlated to the poor outcome of breast cancer. In this study, we investigate the effects of 17β-estradiol (E2) on the activation of ezrin and its role in estrogen-dependent breast cancer cell movement. In T47-D breast cancer cells, E2 rapidly enhances ezrin phosphorylation at Thr⁵⁶⁷ in a time- and concentration-dependent manner. The signalling cascade implicated in this action involves estrogen receptor (ER) interaction with the non-receptor tyrosine kinase c-Src, which activates the phosphatidylinositol-3 kinase/Akt pathway and the small GTPase RhoA/Rho-associated kinase (ROCK-2) complex. E2 enhances the horizontal cell migration and invasion of T47-D breast cancer cells in three-dimensional matrices, which is reversed by transfection of cells with specific ezrin siRNAs. In conclusion, E2 promotes breast cancer cell movement and invasion by the activation of ezrin. These results provide novel insights into the effects of estrogen on breast cancer progression and highlight potential targets to treat endocrine-sensitive breast cancers.

Enforcing host cell polarity: an apicomplexan parasite strategy towards dissemination

The propagation of apicomplexan parasites through transmitting vectors is dependent on effective dissemination of parasites inside the mammalian host. Intracellular Toxoplasma and Theileria parasites face the challenge that their spread inside the host depends in part on the motile capacities of their host cells. In response, these parasites influence the efficiency of dissemination by altering adhesive and/or motile properties of their host cells. Theileria parasites do so by targeting signalling pathways that control host cell actin dynamics. The resulting enforced polar host cell morphology facilitates motility and invasiveness, by establishing focal adhesion and invasion structures at the leading edge of the infected cell. This parasite strategy highlights mechanisms of motility regulation that are also likely relevant for immune or cancer cell motility.

Activins and cell migration

Activins are the members of transforming growth factor β superfamily and act as secreted proteins; they were originally identified with a reproductive function, acting as endocrine-derived regulators of pituitary follicular stimulating hormone. In recent years, additional functions of activins have been discovered, including a regulatory role during crucial phases of growth, differentiation, and development such as wound healing, tissue repair, and regulation of branching morphogenesis. The functions of activins through activin receptors are pleiotrophic, while involving in the etiology and pathogenesis of a variety of diseases and being cell type-specific, they have been identified as important players in cancer metastasis, immune responses, inflammation, and are most likely involved in cell migration. In this chapter, we highlight the current knowledge of activin signaling and discuss the potential physiological and pathological roles of activins acting on the migration of various cell types.

The natural compounds atraric acid and N-butylbenzene-sulfonamide as antagonists of the human androgen receptor and inhibitors of prostate cancer cell growth

Extracts from the plant Pygeum africanum are widely used in the therapy of benign prostate hyperplasia (BPH) and in combinational therapy for prostate cancer, the second leading cause of cancer death and the mostly diagnosed form of cancer in men. The androgen receptor (AR) plays a crucial role in the development of the prostate as well as in prostate diseases. Even though the extracts from P. africanum are considered as beneficial for prostate diseases in clinical trials, and some active compounds for treatment of BPH could be identified, compounds responsible for AR inhibition and the molecular mechanism for inhibition of prostatitis need to be identified. Recently, atraric acid and N-butylbenzene-sulfonamide were isolated from a selective dichlormethane extract of P. africanum as two novel AR antagonistic compounds. The molecular mechanisms of AR inhibition were analyzed and are summarized here. Both compounds are the first known natural, complete and specific AR antagonist.

Changes in cortical cytoskeletal and extracellular matrix gene expression in prostate cancer are related to oncogenic ERG deregulation

Background

The cortical cytoskeleton network connects the actin cytoskeleton to various membrane proteins, influencing cell adhesion, polarity, migration and response to extracellular signals. Previous studies have suggested changes in the expression of specific components in prostate cancer, especially of 4.1 proteins (encoded by EPB41 genes) which form nodes in this network.

Methods

Expression of EPB41L1, EPB41L2, EPB41L3 (protein: 4.1B), EPB41L4B (EHM2), EPB41L5, EPB49 (dematin), VIL2 (ezrin), and DLG1 (summarized as „cortical cytoskeleton" genes) as well as ERG was measured by quantitative RT-PCR in a well-characterized set of 45 M0 prostate adenocarcinoma and 13 benign tissues. Hypermethylation of EPB41L3 and GSTP1 was compared in 93 cancer tissues by methylation-specific PCR. Expression of 4.1B was further studied by immunohistochemistry.

Results

EPB41L1 and EPB41L3 were significantly downregulated and EPB41L4B was upregulated in cancer tissues. Low EPB41L1 or high EPB41L4B expression were associated with earlier biochemical recurrence. None of the other cortical cytoskeleton genes displayed expression changes, in particular EPB49 and VIL2, despite hints from previous studies. EPB41L3 downregulation was significantly associated with hypermethylation of its promoter and strongly correlated with GSTP1 hypermethylation. Protein 4.1B was detected most strongly in the basal cells of normal prostate epithelia. Its expression in carcinoma cells was similar to the weaker one in normal luminal cells. EPB41L3 downregulation and EPB41L4B upregulation were essentially restricted to the 22 cases with ERG overexpression. Expression changes in EPB41L3 and EPB41L4B closely paralleled those previously observed for the extracellular matrix genes FBLN1 and SPOCK1, respectively.

Conclusions

Specific changes in the cortical cytoskeleton were observed during prostate cancer progression. They parallel changes in the expression of extracellular matrix components and all together appear to be associated with oncogenic ERG overexpression. We hypothesize that these alterations may contribute to the increased invasivity conferred to prostate cancer cells by ERG deregulation.

Epigenetic drugs can stimulate metastasis through enhanced expression of the pro-metastatic Ezrin gene

Ezrin has been reported to be upregulated in many tumors and to participate in metastatic progression. No study has addressed epigenetic modification in the regulation of Ezrin gene expression, the importance of which is unknown. Here, we report that highly metastatic rhabdomyosarcoma (RMS) cells with high levels of Ezrin have elevated acetyl-H3-K9 and tri-methyl-H3-K4 as well as reduced DNA methylation at the Ezrin gene promoter. Conversely, poorly metastatic RMS cells with low levels of Ezrin have reduced acetyl-H3-K9 and elevated methylation. Thus epigenetic covalent modifications to histones within nucleosomes of the Ezrin gene promoter are linked to Ezrin expression, which in fact can be regulated by epigenetic mechanisms. Notably, treatment with histone deacetylase (HDAC) inhibitors or DNA demethylating agents could restore Ezrin expression and stimulate the metastatic potential of poorly metastatic RMS cells characterized by low Ezrin levels. However, the ability of epigenetic drugs to stimulate metastasis in RMS cells was inhibited by expression of an Ezrin-specific shRNA. Our data demonstrate the potential risk associated with clinical application of broadly acting covalent epigenetic modifiers, and highlight the value of combination therapies that include agents specifically targeting potent pro-metastatic genes.

Differential effects of ceramide and sphingosine 1-phosphate on ERM phosphorylation: probing sphingolipid signaling at the outer plasma membrane

ERM proteins are regulated by phosphorylation of the most C-terminal threonine residue, switching them from an activated to an inactivated form. However, little is known about the control of this regulation. Previous work in our group demonstrated that secretion of acid sphingomyelinase acts upstream of ERM dephosphorylation, suggesting the involvement of sphingomyelin (SM) hydrolysis in ERM regulation. To define the role of specific lipids, we employed recombinant bacterial sphingomyelinase (bSMase) as a direct probe of SM metabolism at the plasma membrane. bSMase induced a rapid dose- and time-dependent decrease in ERM dephosphorylation. ERM dephosphorylation was driven by ceramide generation and not by sphingomyelin depletion, as shown using recombinant sphingomyelinase D. The generation of ceramide at the plasma membrane was sufficient for ERM regulation, and no intracellular SM hydrolysis was required, as was visualized using Venus-tagged lysenin probe, which specifically binds SM. Interestingly, hydrolysis of plasma membrane bSMase-induced ceramide using bacterial ceramidase caused ERM hyperphosphorylation and formation of cell surface protrusions. The effects of plasma membrane ceramide hydrolysis were due to sphingosine 1-phosphate formation, as ERM phosphorylation was blocked by an inhibitor of sphingosine kinase and induced by sphingosine 1-phosphate. Taken together, these results demonstrate a new regulatory mechanism of ERM phosphorylation by sphingolipids with opposing actions of ceramide and sphingosine 1-phosphate. The approach also defines a tool kit to probe sphingolipid signaling at the plasma membrane.

The natural compound atraric acid is an antagonist of the human androgen receptor inhibiting cellular invasiveness and prostate cancer cell growth

Extracts from Pygeum africanum are used in the treatment of prostatitis, benign prostatic hyperplasia and prostate cancer (Pca), major health problems of men in Western countries. The ligand-activated human androgen receptor (AR) supports the growth of the prostate gland. Inhibition of human AR by androgen ablation therapy and by applying synthetic anti-androgens is therefore the primary goal in treatment of patients. Here, we show that atraric acid (AA) isolated from bark material of Pygeum africanum has anti-androgenic activity, inhibiting the transactivation mediated by the ligand-activated human AR. This androgen antagonistic activity is receptor specific and does not inhibit the closely related glucocorticoid or progesterone receptors. Mechanistically, AA inhibits nuclear transport of AR. Importantly, AA is able to efficiently repress the growth of both the androgen-dependent LNCaP and also the androgen-independent C4-2 Pca cells but not that of PC3 or CV1 cells lacking AR. In line with this, AA inhibits the expression of the endogenous prostate specific antigen gene in both LNCaP und C4-2 cells. Analyses of cell invasion revealed that AA inhibits the invasiveness of LNCaP cells through extracellular matrix. Thus, this study provides a molecular insight for AA as a natural anti-androgenic compound and may serve as a basis for AA derivatives as a new chemical lead structure for novel therapeutic compounds as AR antagonists, that can be used for prophylaxis or treatment of prostatic diseases.

Profiling protein markers associated with lymph node metastasis in prostate cancer by DIGE-based proteomics analysis

Current predictive tools and imaging modalities are not accurate enough for preoperative diagnosis of lymph node metastatic prostate cancer (LNM PCa). Proteomic analysis is introduced to screen potential biomarkers for early detection of LNM PCa. In our initial study, protein samples from localized and LNM PCa as well as benign prostatic hyperplasia tissues were analyzed using two-dimensional fluorescence difference in gel electrophoresis (2-D DIGE) coupled with MALDI-TOF/TOF MS. We identified 58 proteins that were differentially expressed in the LNM PCa group relative to the localized PCa group. Six of these proteins, e-FABP5, MCCC2, PPA2, Ezrin, SLP2, and SM22, are functionally relevant to cancer metastasis. Expression of these proteins was therefore further validated in tissue samples from the original cohort and also from a larger, independent cohort of patients using real time PCR, Western blotting, and immunohistochemistry staining. In addition, the serum levels of e-FABP5 were also examined by ELISA. Relative to localized PCa tissues, LNM PCa tissues had increased expression of e-FABP5, MCCC2, PPA2, Ezrin, and SLP2 and decreased expression of SM22. Patients with LNM PCa had significantly higher levels of serum e-FABP5. This study presents evidence that increased expression of e-FABP5, MCCC2, PPA2, Ezrin, and SLP2 and decreased expression of SM22 are useful diagnostic markers for the existence of LNM PCa.

Ezrin mediates c-Myc actions in prostate cancer cell invasion

The forced overexpression of c-Myc in mouse prostate and in normal human prostate epithelial cells results in tumor transformation with an invasive phenotype. How c-Myc regulates cell invasion is poorly understood. In this study, we have investigated the interplay of c-Myc and androgens in the regulation of prostate cancer cell invasion. We found that c-Myc induces cell invasion and anchorage-independent growth by regulating ezrin protein expression in the presence of androgens. The activity of the ezrin promoter is controlled by androgens through c-Myc, which binds to a phylogenetically conserved E-Box located in the proximal promoter region. Besides, we also show that ezrin is an important regulator of c-Myc protein levels. These effects are achieved through androgen-induced changes in ezrin phosphorylation, which results in the regulation of downstream signals. These downstream signals involve the modulation of Akt and GSK-3beta activity resulting in increased c-Myc protein synthesis and inhibition of its degradation. In summary, we have shown a key role for ezrin as a mediator of c-Myc-induced tumorigenesis in prostate cancer cells.

Berberine inhibits metastasis of nasopharyngeal carcinoma 5-8F cells by targeting Rho kinase-mediated Ezrin phosphorylation at threonine 567

Ezrin is highly expressed in metastatic tumors and is involved in filopodia formation as well as promotion of tumor metastasis. Thus, Ezrin may serve as a potential target for anti-metastatic therapy. This study demonstrates that berberine reduces filopodia formation of a nasopharyngeal carcinoma (NPC) cell line, 5-8F, at non-cytotoxic concentrations. Furthermore, invasion and motility of 5-8F cells are decreased in a dose- and time-dependent manner, resulting in 73.0% invasion and 67.0% motility inhibition at 20 mum. The inhibitory effects of berberine on 5-8F cell metastasis were further confirmed in a mouse model of metastasis. Berberine treatment in vivo resulted in a 51.1% inhibition of tumor metastasis to the lymph nodes and decreased Ezrin phosphorylation at threonine 567 in metastatic samples. Berberine suppressed the presence of phosphorylated Ezrin (phospho-Ezrin) in a dose- and time-dependent manner but had no effect on total Ezrin protein expression at non-cytotoxic concentrations. Furthermore, the inhibitory effects of berberine on phospho-Ezrin were dependent on the suppression of Rho kinase activity. Reduction of Ezrin phosphorylation at Thr(567) by berberine was associated with its inhibitory effect on filopodia formation in 5-8F cells. However, berberine did not effectively inhibit the motility and invasion of NPC cells containing Ezrin Thr(567) mutants. These results confirm that berberine inhibits Ezrin phosphorylation at Thr(567). Nonetheless, berberine reduces motility and invasion of cells and inhibits tumor metastasis. The reduction of Rho kinase-mediated Ezrin phosphorylation mediated by berberine may be a novel anti-metastatic pathway in NPC 5-8F cells.