Notch1-expressing cells are indispensable for prostatic branching morphogenesis during development and re-growth following castration and androgen replacement

Notch Signaling and PD-1/PD-L1 Interaction in Hepatocellular Carcinoma: Potentialities of Combined Therapies

Immunotherapy has shown significant improvement in the survival of patients with hepatocellular carcinoma (HCC) compared to TKIs as first-line treatment. Unfortunately, approximately 30% of HCC exhibits intrinsic resistance to ICIs, making new therapeutic combinations urgently needed. The dysregulation of the Notch signaling pathway observed in HCC can affect immune cell response, reducing the efficacy of cancer immunotherapy. Here, we provide an overview of how Notch signaling regulates immune responses and present the therapeutic rationale for combining Notch signaling inhibition with ICIs to improve HCC treatment. Moreover, we propose using exosomes as non-invasive tools to assess Notch signaling activation in hepatic cancer cells, enabling accurate stratification of patients who can benefit from combined strategies.

Prostate Cancer Stem Cells: Biology and Treatment Implications

Stem cells differentiate into mature organ/tissue-specific cells at a steady pace under normal conditions, but their growth can be accelerated during the process of tissue healing or in the context of certain diseases. It is postulated that the proliferation and growth of carcinomas are sustained by the presence of a vital cellular compartment resembling stem cells residing in normal tissues: 'stem-like cancer cells' or cancer stem cells (CSCs). Mutations in prostate stem cells can lead to the formation of prostate cancer. Prostate CSCs (PCSCs) have been identified and partially characterized. These express surface markers include CD44, CD133, integrin α2β1, and pluripotency factors like OCT4, NANOG, and SOX2. Several signaling pathways are also over-activated, including Notch, PTEN/Akt/PI3K, RAS-RAF-MEK-ERK and HH. Moreover, PCSCs appear to induce resistance to radiotherapy and chemotherapy, while their presence has been linked to aggressive cancer behavior and higher relapse rates. The development of treatment policies to target PCSCs in tumors is appealing as radiotherapy and chemotherapy, through cancer cell killing, trigger tumor repopulation via activated stem cells. Thus, blocking this reactive stem cell mobilization may facilitate a positive outcome through cytotoxic treatment.

Fringe family genes and their modulation of Notch signaling in cancer

Fringes are glycosyltransferases that transfer N-acetylglucosamine to the O-linked fucose of Notch receptors. They regulate the Notch signaling activity that drives tumor formation and progression, resulting in poor prognosis. However, the specific tumor-promoting role of Fringes differs depending on the type of cancer. Although a particular Fringe member could act as a tumor suppressor in one cancer type, it may act as an oncogene in another. This review discusses the tumorigenic role of the Fringe family (lunatic fringe, manic fringe, and radical fringe) in modulating Notch signaling in various cancers. Although the crucial functions of Fringes continue to emerge as more mechanistic studies are being pursued, further translational research is needed to explore their roles and therapeutic benefits in various malignancies.

Recent Progress on Biodegradable Tissue Engineering Scaffolds Prepared by Thermally-Induced Phase Separation (TIPS)

Porous biodegradable scaffolds provide a physical substrate for cells allowing them to attach, proliferate and guide the formation of new tissues. A variety of techniques have been developed to fabricate tissue engineering (TE) scaffolds, among them the most relevant is the thermally-induced phase separation (TIPS). This technique has been widely used in recent years to fabricate three-dimensional (3D) TE scaffolds. Low production cost, simple experimental procedure and easy processability together with the capability to produce highly porous scaffolds with controllable architecture justify the popularity of TIPS. This paper provides a general overview of the TIPS methodology applied for the preparation of 3D porous TE scaffolds. The recent advances in the fabrication of porous scaffolds through this technique, in terms of technology and material selection, have been reviewed. In addition, how properties can be effectively modified to serve as ideal substrates for specific target cells has been specifically addressed. Additionally, examples are offered with respect to changes of TIPS procedure parameters, the combination of TIPS with other techniques and innovations in polymer or filler selection.

Notch Signaling Pathway in Cancer-Review with Bioinformatic Analysis

Simple Summary

The Notch signaling pathway, which controls multiple cell differentiation processes during the embryonic stage and adult life, is associated with carcinogenesis and disease progression. The aim of the present study was to highlight cancer heterogeneity with respect to the Notch pathway. Our analysis concerns the effects of the Notch signaling at different levels, including core components and downstream target genes. We also demonstrate overall and disease-free survival results, pointing out the characteristics of particular Notch components. Depending on tissue context, Notch members can be either oncogenic or suppressive. We observed different expression profile core components and target genes that could be associated with distinct survival of patients. Advances in our understanding of the Notch signaling in cancer are very promising for the development of new treatment strategies for the benefit of patients.

Abstract

Notch signaling is an evolutionarily conserved pathway regulating normal embryonic development and homeostasis in a wide variety of tissues. It is also critically involved in carcinogenesis, as well as cancer progression. Activation of the Notch pathway members can be either oncogenic or suppressive, depending on tissue context. The present study is a comprehensive overview, extended with a bioinformatics analysis of TCGA cohorts, including breast, bladder, cervical, colon, kidney, lung, ovary, prostate and rectum carcinomas. We performed global expression profiling of the Notch pathway core components and downstream targets. For this purpose, we implemented the Uniform Manifold Approximation and Projection algorithm to reduce the dimensions. Furthermore, we determined the optimal cutpoint using Evaluate Cutpoint software to established disease-free and overall survival with respect to particular Notch members. Our results demonstrated separation between tumors and their corresponding normal tissue, as well as between tumors in general. The differentiation of the Notch pathway, at its various stages, in terms of expression and survival resulted in distinct profiles of biological processes such as proliferation, adhesion, apoptosis and epithelial to mesenchymal transition. In conclusion, whether oncogenic or suppressive, Notch signaling is proven to be associated with various types of malignancies, and thus may be of interest as a potential therapeutic target.

Notch3 promotes prostate cancer-induced bone lesion development via MMP-3

Prostate cancer metastases primarily localize in the bone where they induce a unique osteoblastic response. Elevated Notch activity is associated with high-grade disease and metastasis. To address how Notch affects prostate cancer bone lesions, we manipulated Notch expression in mouse tibia xenografts and monitored tumor growth, lesion phenotype, and the bone microenvironment. Prostate cancer cell lines that induce mixed osteoblastic lesions in bone expressed 5–6 times more Notch3, than tumor cells that produce osteolytic lesions. Expression of active Notch3 (NICD3) in osteolytic tumors reduced osteolytic lesion area and enhanced osteoblastogenesis, while loss of Notch3 in osteoblastic tumors enhanced osteolytic lesion area and decreased osteoblastogensis. This was accompanied by a respective decrease and increase in the number of active osteoclasts and osteoblasts at the tumor-bone interface, without any effect on tumor proliferation. Conditioned medium from NICD3-expressing cells enhanced osteoblast differentiation and proliferation in vitro, while simultaneously inhibiting osteoclastogenesis. MMP-3 was specifically elevated and secreted by NICD3-expressing tumors, and inhibition of MMP-3 rescued the NICD3-induced osteoblastic phenotypes. Clinical osteoblastic bone metastasis samples had higher levels of Notch3 and MMP-3 compared to patient matched visceral metastases or osteolytic metastasis samples. We identified a Notch3-MMP-3 axis in human prostate cancer bone metastases that contributes to osteoblastic lesion formation by blocking osteoclast differentiation, while also contributing to osteoblastogenesis. These studies define a new role for Notch3 in manipulating the tumor microenvironment in bone metastases.

Transcriptional Reprogramming and Novel Therapeutic Approaches for Targeting Prostate Cancer Stem Cells

Prostate cancer is the most common malignancy in men and the second cause of cancer-related deaths in western countries. Despite the progress in the treatment of localized prostate cancer, there is still lack of effective therapies for the advanced forms of the disease. Most patients with advanced prostate cancer become resistant to androgen deprivation therapy (ADT), which remains the main therapeutic option in this setting, and progress to lethal metastatic castration-resistant prostate cancer (mCRPC). Current therapies for prostate cancer preferentially target proliferating, partially differentiated, and AR-dependent cancer cells that constitute the bulk of the tumor mass. However, the subpopulation of tumor-initiating or tumor-propagating stem-like cancer cells is virtually resistant to the standard treatments causing tumor relapse at the primary or metastatic sites. Understanding the pathways controlling the establishment, expansion and maintenance of the cancer stem cell (CSC) subpopulation is an important step toward the development of more effective treatment for prostate cancer, which might enable ablation or exhaustion of CSCs and prevent treatment resistance and disease recurrence. In this review, we focus on the impact of transcriptional regulators on phenotypic reprogramming of prostate CSCs and provide examples supporting the possibility of inhibiting maintenance and expansion of the CSC pool in human prostate cancer along with the currently available methodological approaches. Transcription factors are key elements for instructing specific transcriptional programs and inducing CSC-associated phenotypic changes implicated in disease progression and treatment resistance. Recent studies have shown that interfering with these processes causes exhaustion of CSCs with loss of self-renewal and tumorigenic capability in prostate cancer models. Targeting key transcriptional regulators in prostate CSCs is a valid therapeutic strategy waiting to be tested in clinical trials.

A pivotal role of androgen signaling in Notch-responsive cells in prostate development, maturation, and regeneration

Androgen signaling is essential for prostate development, morphogenesis, and regeneration. Emerging evidence also indicates a regulatory role of Notch signaling in prostate development, differentiation, and growth. However, the collaborative regulatory mechanisms of androgen and Notch signaling during prostate development, growth, and regeneration are largely unknown. Hairy and Enhancer of Split 1 (Hes1) is a transcriptional regulator of Notch signaling pathways, and its expression is responsive to Notch signaling. Hes1-expressing cells have been shown to possess the regenerative capability to repopulate a variety of adult tissues. In this study, we developed new mouse models to directly assess the role of the androgen receptor in prostatic Hes1-expressing cells. Selective deletion of AR expression in embryonic Hes1-expressing cells impeded early prostate development both in vivo and in tissue xenograft experiments. Prepubescent deletion of AR expression in Hes1-expressing cells resulted in prostate glands containing abnormalities in cell morphology and gland architecture. A population of castration-resistant Hes1-expressing cells was revealed in the adult prostate, with the ability to repopulate prostate epithelium following androgen supplementation. Deletion of AR in Hes1-expressing cells diminishes their regenerative ability. These lines of evidence demonstrate a critical role for the AR in Notch-responsive cells during the course of prostate development, morphogenesis, and regeneration, and implicate a mechanism underlying interaction between the androgen and Notch signaling pathways in the mouse prostate.

I-Optimal Design of Hierarchical 3D Scaffolds Produced by Combining Additive Manufacturing and Thermally Induced Phase Separation

The limitations in the transport of oxygen, nutrients, and metabolic waste products pose a challenge to the development of bioengineered bone of clinically relevant size. This paper reports the design and characterization of hierarchical macro/microporous scaffolds made of poly(lactic-co-glycolic) acid and nanohydroxyapatite (PLGA/nHA). These scaffolds were produced by combining additive manufacturing (AM) and thermally induced phase separation (TIPS) techniques. Macrochannels with diameters of ~300 μm, ~380 μm, and ~460 μm were generated by embedding porous 3D-plotted polyethylene glycol (PEG) inside PLGA/nHA/1,4-dioxane or PLGA/1,4-dioxane solutions, followed by PEG extraction using deionized (DI) water. We have used an I-optimal design of experiments (DoE) and the response surface analysis (JMP® software) to relate three responses (scaffold thickness, porosity, and modulus) to the four experimental factors affecting the scaffold macro/microstructures (e.g., PEG strand diameter, PLGA concentration, nHA content, and TIPS temperature). Our results indicated that a PEG strand diameter of ~380 μm, a PLGA concentration of ~10% w/v, a nHA content of ~10% w/w, and a TIPS temperature around -10°C could generate scaffolds with a porosity of ~90% and a modulus exceeding 4 MPa. This paper presents the steps for the I-optimal design of these scaffolds and reports on their macro/microstructures, characterized using scanning electron microscopy (SEM) and micro-computed tomography (micro-CT).

Dual tumor suppressing and promoting function of Notch1 signaling in human prostate cancer

Adenocarcinomas of the prostate arise as multifocal heterogeneous lesions as the likely result of genetic and epigenetic alterations and deranged cell-cell communication. Notch signaling is an important form of intercellular communication with a role in growth/differentiation control and tumorigenesis. Contrasting reports exist in the literature on the role of this pathway in prostate cancer (PCa) development. We show here that i) compared to normal prostate tissue, Notch1 expression is significantly reduced in a substantial fraction of human PCas while it is unaffected or even increased in others; ii) acute Notch activation both inhibits and induces process networks associated with prostatic neoplasms; iii) down-modulation of Notch1 expression and activity in immortalized normal prostate epithelial cells increases their proliferation potential, while increased Notch1 activity in PCa cells suppresses growth and tumorigenicity through a Smad3-dependent mechanism involving p21^WAF1/CIP1; iv) prostate cancer cells resistant to Notch growth inhibitory effects retain Notch1-induced upregulation of pro-oncogenic genes, like EPAS1 and CXCL6, also overexpressed in human PCas with high Notch1 levels. Taken together, these results reconcile conflicting data on the role of Notch1 in prostate cancer.

Morphoregulatory pathways in prostate ductal development

The mouse prostate is a male sex-accessory gland comprised of a branched ductal network arranged into three separate bilateral lobes: the anterior, dorsolateral, and ventral lobes. Prostate ductal development is the primary morphogenetic event in prostate development and requires a complex regulation of spatiotemporal factors. This review provides an overview of prostate development and the major genetic regulators and signaling pathways involved. To identify new areas for further study, we briefly highlight the likely important, but relatively understudied, role of the extracellular matrix (ECM). Finally, we point out the potential importance of the ECM in influencing the behavior and prognosis of prostate cancer. Developmental Dynamics 246:89-99, 2017. © 2016 Wiley Periodicals, Inc.

Prostate organogenesis: tissue induction, hormonal regulation and cell type specification

Prostate organogenesis is a complex process that is primarily mediated by the presence of androgens and subsequent mesenchyme-epithelial interactions. The investigation of prostate development is partly driven by its potential relevance to prostate cancer, in particular the apparent re-awakening of key developmental programs that occur during tumorigenesis. However, our current knowledge of the mechanisms that drive prostate organogenesis is far from complete. Here, we provide a comprehensive overview of prostate development, focusing on recent findings regarding sexual dimorphism, bud induction, branching morphogenesis and cellular differentiation.

The Notch-1 receptor in prostate tumorigenesis

The Notch signalling pathway plays a fundamental role in tissue development due to its involvement in cell fate determination and postnatal tissue differentiation. Its capacity to regulate cell growth and development has been linked to the occurrence of several cancers including that of the prostate. The transmembrane receptor Notch-1 of this pathway has been linked to the oncogenic role of Notch signalling in prostate adenocarcinoma. Other studies have suggested a tumour suppressive function for Notch-1. This review focuses on the role of Notch-1 in prostate cancer development and maintenance and relates this to the fundamental role of Notch in normal prostate development. The current understanding of the aberrant Notch signalling characteristic of prostate cancer is discussed, and recent therapeutic advances in this field are presented.

Notch signaling in the prostate: critical roles during development and in the hallmarks of prostate cancer biology

PURPOSE

This review aims to summarize the evidence that Notch signaling is associated with prostate development, tumorigenesis and prostate tumor progression.

METHODS

Studies in PubMed database were searched using the keywords of Notch signaling, prostate development and prostate cancer. Relevant literatures were identified and summarized.

RESULTS

The Notch pathway plays an important role in determining cell fate, proliferation, differentiation and apoptosis. Recent findings have highlighted the involvement of Notch signaling in prostate development and in the maintenance of adult prostate homeostasis. Aberrant Notch expression in tissues leads to dysregulation of Notch functions and promotes various neoplasms, including prostate cancer. High expression of Notch has been implicated in prostate cancer, and its expression increases with higher cancer grade. However, the precise role of Notch in prostate cancer has yet to be clearly defined. The roles of Notch either as an oncogene or tumor suppressor in prostate cancer hallmarks such as cell proliferation, apoptosis and anoikis, hypoxia, migration and invasion, angiogenesis as well as the correlation with metastasis are therefore discussed.

CONCLUSIONS

Notch signaling is a complicated signaling pathway in modulating prostate development and prostate cancer. Understanding and manipulating Notch signaling could therefore be of potential therapeutic value in combating prostate cancer.

Ornithine Decarboxylase Activity Is Required for Prostatic Budding in the Developing Mouse Prostate

The prostate is a male accessory sex gland that produces secretions in seminal fluid to facilitate fertilization. Prostate secretory function is dependent on androgens, although the mechanism by which androgens exert their effects is still unclear. Polyamines are small cationic molecules that play pivotal roles in DNA transcription, translation and gene regulation. The rate-limiting enzyme in polyamine biosynthesis is ornithine decarboxylase, which is encoded by the gene Odc1. Ornithine decarboxylase mRNA decreases in the prostate upon castration and increases upon administration of androgens. Furthermore, testosterone administered to castrated male mice restores prostate secretory activity, whereas administering testosterone and the ornithine decarboxylase inhibitor D,L-α-difluromethylornithine (DFMO) to castrated males does not restore prostate secretory activity, suggesting that polyamines are required for androgens to exert their effects. To date, no one has examined polyamines in prostate development, which is also androgen dependent. In this study, we showed that ornithine decarboxylase protein was expressed in the epithelium of the ventral, dorsolateral and anterior lobes of the adult mouse prostate. Ornithine decarboxylase protein was also expressed in the urogenital sinus (UGS) epithelium of the male and female embryo prior to prostate development, and expression continued in prostatic epithelial buds as they emerged from the UGS. Inhibiting ornithine decarboxylase using DFMO in UGS organ culture blocked the induction of prostatic buds by androgens, and significantly decreased expression of key prostate transcription factor, Nkx3.1, by androgens. DFMO also significantly decreased the expression of developmental regulatory gene Notch1. Other genes implicated in prostatic development including Sox9, Wif1 and Srd5a2 were unaffected by DFMO. Together these results indicate that Odc1 and polyamines are required for androgens to exert their effect in mediating prostatic bud induction, and are required for the expression of a subset of prostatic developmental regulatory genes including Notch1 and Nkx3.1.

HES6 promotes prostate cancer aggressiveness independently of Notch signalling

Notch signalling is implicated in the pathogenesis of a variety of cancers, but its role in prostate cancer is poorly understood. However, selected Notch pathway members are overrepresented in high-grade prostate cancers. We comprehensively profiled Notch pathway components in prostate cells and found prostate cancer-specific up-regulation of NOTCH3 and HES6. Their expression was particularly high in androgen responsive lines. Up- and down-regulating Notch in these cells modulated expression of canonical Notch targets, HES1 and HEY1, which could also be induced by androgen. Surprisingly, androgen treatment also suppressed Notch receptor expression, suggesting that androgens can activate Notch target genes in a receptor-independent manner. Using a Notch-sensitive Recombination signal binding protein for immunoglobulin kappa J region (RBPJ) reporter assay, we found that basal levels of Notch signalling were significantly lower in prostate cancer cells compared to benign cells. Accordingly pharmacological Notch pathway blockade did not inhibit cancer cell growth or viability. In contrast to canonical Notch targets, HES6, a HES family member known to antagonize Notch signalling, was not regulated by Notch signalling, but relied instead on androgen levels, both in cultured cells and in human cancer tissues. When engineered into prostate cancer cells, reduced levels of HES6 resulted in reduced cancer cell invasion and clonogenic growth. By molecular profiling, we identified potential roles for HES6 in regulating hedgehog signalling, apoptosis and cell migration. Our results did not reveal any cell-autonomous roles for canonical Notch signalling in prostate cancer. However, the results do implicate HES6 as a promoter of prostate cancer progression.

Tumor-suppressive activity of Lunatic Fringe in prostate through differential modulation of Notch receptor activation

Elevated Notch ligand and receptor expression has been associated with aggressive forms of prostate cancer, suggesting a role for Notch signaling in regulation of prostate tumor initiation and progression. Here, we report a critical role for Lunatic Fringe (Lfng), which encodes an O-fucosylpeptide 3-ß-N-acetylglucosaminyltransferase known to modify epidermal growth factor repeats of Notch receptor proteins, in regulation of prostate epithelial differentiation and proliferation, as well as in prostate tumor suppression. Deletion of Lfng in mice caused altered Notch activation in the prostate, associated with elevated accumulation of Notch1, Notch2, and Notch4 intracellular domains, decreased levels of the putative Notch3 intracellular fragment, as well as increased expression of Hes1, Hes5, and Hey2. Loss of Lfng resulted in expansion of the basal layer, increased proliferation of both luminal and basal cells, and ultimately, prostatic intraepithelial neoplasia. The Lfng-null prostate showed down-regulation of prostatic tumor suppressor gene NKX3.1 and increased androgen receptor expression. Interestingly, expression of LFNG and NKX3.1 were positively correlated in publically available human prostate cancer data sets. Knockdown of LFNG in DU-145 prostate cancer cells led to expansion of CD44(+)CD24(-) and CD49f(+)CD24(-) stem/progenitor-like cell population associated with enhanced prostatosphere-forming capacity. Taken together, these data revealed a tumor-suppressive role for Lfng in the prostate through differential regulation of Notch signaling.

Lgr4 is a key regulator of prostate development and prostate stem cell differentiation

Mechanisms modulating prostate cell fate determination remain unexplored. The leucine-rich repeat containing G-protein-coupled receptors (Lgr) have been identified as important stem cell markers in various tissues. Here, we investigated the roles of Lgr4/Gpr48 in prostate stem cells (PSCs) and development. Lgr4 was ubiquitously expressed during early prostate development prior to lineage specification, with adult expression restricted to a few basal cells (principally Lin(-)Sca1(+)CD49f(+)). Lgr4(-/-) mice had compromised branching morphogenesis and delayed epithelial differentiation, leading to decreased prostate size and impaired luminal cell function. In vitro prostate sphere culture revealed that Lgr4(-/-) Lin(-)/Sca1(+)/CD49f(+) cells failed to generate p63(low) cells, indicating a differentiation deficiency. Furthermore, Lgr4 ablation arrested PSC differentiation of in vivo kidney capsule prostate grafts, suggesting that Lgr4 modulates PSC properties independent of hormonal and mesenchymal effects. Analysis of neonatal prostates and prostate spheres revealed a decrease in Wnt, Sonic Hedgehog, and Notch1 expression in Lgr4(-/-) cells. Lgr4 loss blocked differentiation of prostate sphere p63(hi) cells to p63(low). Treatment with exogenous Sonic Hedgehog partially restored the differentiation of p63(hi) cells in Lgr4(-/-) spheres. Taken together, our data revealed the roles of Lgr4 in early prostate development and in stem cell differentiation through regulation of the Wnt, Notch, and Sonic Hedgehog signaling pathways.

Notch signaling in prostate cancer: a moving target

INTRODUCTION

By regulating cell fate, proliferation, and survival, Notch pathway signaling provides critical input into differentiation, organization, and function of multiple tissues. Notch signaling is also becoming an increasingly recognized feature in malignancy, including prostate cancer, where it may play oncogenic or tumor suppressive roles.

METHODS

Based on an electronic literature search from 2000 to 2013 we identified, summarized, and integrated published research on Notch signaling dynamics in prostate homeostasis and prostate cancer.

RESULTS

In benign prostate, Notch controls the differentiation state and architecture of the gland. In prostate cancer, similar features correlate with lethal potential and may be influenced by Notch. Increased Notch1 can confer a survival advantage on prostate cancer cells, and levels of Notch family members, such as Jagged2, Notch3, and Hes6 increase with higher cancer grade. However, Notch signaling can also antagonize growth and survival of both benign and malignant prostate cells, possibly through antagonistic effects of the Notch target HEY1 on androgen receptor function.

DISCUSSION

Notch signaling can dramatically influence prostate development and disease. Determining the cellular contexts where Notch promotes or suppresses prostate growth could open opportunities for diagnostic and therapeutic interventions.

NOTCH and PTEN in prostate cancer

Over the past decade, our understanding of the role that Notch-signaling has in tumorigenesis has shifted from leukemogenesis into cancers of solid tumors. Emerging data suggests that in addition to direct effects mediated through the canonical Notch pathway, Notch may participate in epithelial tumor development through regulation of pathways such as PTEN/PI3K/Akt. Prostate cancer is a disease for which PTEN gene expression is especially essential. This review will summarize a role for Notch in prostate development and cancer with an emphasis on how the Notch pathway may intersect with PTEN/PI3K/Akt and mTOR signaling.

Prostate tumor OVerexpressed-1 (PTOV1) down-regulates HES1 and HEY1 notch targets genes and promotes prostate cancer progression

BACKGROUND

PTOV1 is an adaptor protein with functions in diverse processes, including gene transcription and protein translation, whose overexpression is associated with a higher proliferation index and tumor grade in prostate cancer (PC) and other neoplasms. Here we report its interaction with the Notch pathway and its involvement in PC progression.

METHODS

Stable PTOV1 knockdown or overexpression were performed by lentiviral transduction. Protein interactions were analyzed by co-immunoprecipitation, pull-down and/or immunofluorescence. Endogenous gene expression was analyzed by real time RT-PCR and/or Western blotting. Exogenous promoter activities were studied by luciferase assays. Gene promoter interactions were analyzed by chromatin immunoprecipitation assays (ChIP). In vivo studies were performed in the Drosophila melanogaster wing, the SCID-Beige mouse model, and human prostate cancer tissues and metastasis. The Excel package was used for statistical analysis.

RESULTS

Knockdown of PTOV1 in prostate epithelial cells and HaCaT skin keratinocytes caused the upregulation, and overexpression of PTOV1 the downregulation, of the Notch target genes HEY1 and HES1, suggesting that PTOV1 counteracts Notch signaling. Under conditions of inactive Notch signaling, endogenous PTOV1 associated with the HEY1 and HES1 promoters, together with components of the Notch repressor complex. Conversely, expression of active Notch1 provoked the dismissal of PTOV1 from these promoters. The antagonist role of PTOV1 on Notch activity was corroborated in the Drosophila melanogaster wing, where human PTOV1 exacerbated Notch deletion mutant phenotypes and suppressed the effects of constitutively active Notch. PTOV1 was required for optimal in vitro invasiveness and anchorage-independent growth of PC-3 cells, activities counteracted by Notch, and for their efficient growth and metastatic spread in vivo. In prostate tumors, the overexpression of PTOV1 was associated with decreased expression of HEY1 and HES1, and this correlation was significant in metastatic lesions.

CONCLUSIONS

High levels of the adaptor protein PTOV1 counteract the transcriptional activity of Notch. Our evidences link the pro-oncogenic and pro-metastatic effects of PTOV1 in prostate cancer to its inhibitory activity on Notch signaling and are supportive of a tumor suppressor role of Notch in prostate cancer progression.

Androgen receptor promotes the oncogenic function of overexpressed Jagged1 in prostate cancer by enhancing cyclin B1 expression via Akt phosphorylation

The Jagged1, a Notch signaling pathway ligand, had been shown to have a positive correlation with prostate cancer development. Our study for Jagged1 expression in 218 prostate cancer tissue samples also supports this conclusion. However, the detailed molecular mechanism of Jagged1 in promoting the progression of prostate cancer is still unclear. Through cell proliferation examination, androgen receptor (AR) was found to promote the oncogenic function of Jagged1 to enhance the cell proliferation rate by comparing four prostate cancer cell lines, LNCaP, LAPC4, DU145, and PC3, which was further validated through analyzing the survival of 118 patients treated with androgen-deprivation therapy (ADT) with different expression levels of Jagged1 and AR. More importantly, our data showed that Jagged1 combined with AR could increase the phosphorylation level of Akt and, in turn, phosphorylated Akt plays an important role in regulating the expression level of cyclin B1 by interacting with AR and increasing the transcriptional activity of AR. These data indicate that prostate cancer progression regulated by Jagged1 can be dramatically enhanced by combining with AR through promoting Akt activity.

IMPLICATIONS

This study could benefit our clinical treatments for patients with prostate cancer with overexpressed Jagged1 by targeting AR and Akt.

Genetic cell ablation

Targeted cell ablation has proven to be a valuable approach to study in vivo cell functions during organogenesis, tissue homeostasis, and regeneration. Over the last two decades, various approaches have been developed to refine the control of cell ablation. In this review, we give an overview of the distinct genetic tools available for targeted cell ablation, with a particular emphasis on their respective specificity.

Disruption of prostate epithelial differentiation pathways and prostate cancer development

One of the foremost problems in the prostate cancer (PCa) field is the inability to distinguish aggressive from indolent disease, which leads to difficult prognoses and thousands of unnecessary surgeries. This limitation stems from the fact that the mechanisms of tumorigenesis in the prostate are poorly understood. Some genetic alterations are commonly reported in prostate tumors, including upregulation of Myc, fusion of Ets genes to androgen-regulated promoters, and loss of Pten. However, the specific roles of these aberrations in tumor initiation and progression are poorly understood. Likewise, the cell of origin for PCa remains controversial and may be linked to the aggressive potential of the tumor. One important clue is that prostate tumors co-express basal and luminal protein markers that are restricted to their distinct cell types in normal tissue. Prostate epithelium contains layer-specific stem cells as well as rare bipotent cells, which can differentiate into basal or luminal cells. We hypothesize that the primary oncogenic cell of origin is a transient-differentiating bipotent cell. Such a cell must maintain tight temporal and spatial control of differentiation pathways, thus increasing its susceptibility for oncogenic disruption. In support of this hypothesis, many of the pathways known to be involved in prostate differentiation can be linked to genes commonly altered in PCa. In this article, we review what is known about important differentiation pathways (Myc, p38MAPK, Notch, PI3K/Pten) in the prostate and how their misregulation could lead to oncogenesis. Better understanding of normal differentiation will offer new insights into tumor initiation and may help explain the functional significance of common genetic alterations seen in PCa. Additionally, this understanding could lead to new methods for classifying prostate tumors based on their differentiation status and may aid in identifying more aggressive tumors.

Notch and TGFβ form a reciprocal positive regulatory loop that suppresses murine prostate basal stem/progenitor cell activity

The role of Notch signaling in the maintenance of adult murine prostate epithelial homeostasis remains unclear. We found that Notch ligands are mainly expressed within the basal cell lineage, while active Notch signaling is detected in both the prostate basal and luminal cell lineages. Disrupting the canonical Notch effector Rbp-j impairs the differentiation of prostate basal stem cells and increases their proliferation in vitro and in vivo, but does not affect luminal cell biology. Conversely, ectopic Notch activation in adult prostates results in a decrease in basal cell number and luminal cell hyperproliferation. TGFβ dominates over Notch signaling and overrides Notch ablation-induced proliferation of prostate basal cells. However, Notch confers sensitivity and positive feedback by upregulating a plethora of TGFβ signaling components including TgfβR1. These findings reveal crucial roles of the self-enforced positive reciprocal regulatory loop between TGFβ and Notch in maintaining prostate basal stem cell dormancy.

Specific changes in the expression of imprinted genes in prostate cancer--implications for cancer progression and epigenetic regulation

Epigenetic dysregulation comprising DNA hypermethylation and hypomethylation, enhancer of zeste homologue 2 (EZH2) overexpression and altered patterns of histone modifications is associated with the progression of prostate cancer. DNA methylation, EZH2 and histone modifications also ensure the parental-specific monoallelic expression of at least 62 imprinted genes. Although it is therefore tempting to speculate that epigenetic dysregulation may extend to imprinted genes, expression changes in cancerous prostates are only well documented for insulin-like growth factor 2 (IGF2). A literature and database survey on imprinted genes in prostate cancer suggests that the expression of most imprinted genes remains unchanged despite global disturbances in epigenetic mechanisms. Instead, selective genetic and epigenetic changes appear to lead to the inactivation of a sub-network of imprinted genes, which might function in the prostate to limit cell growth induced via the PI3K/Akt pathway, modulate androgen responses and regulate differentiation. Whereas dysregulation of IGF2 may constitute an early change in prostate carcinogenesis, inactivation of this imprinted gene network is rather associated with cancer progression.

Wnt and Notch pathways have interrelated opposing roles on prostate progenitor cell proliferation and differentiation

Tissue stem cells are capable of both self-renewal and differentiation to maintain a constant stem cell population and give rise to the plurality of cells within a tissue. Wnt signaling has been previously identified as a key mediator for the maintenance of tissue stem cells; however, possible cross-regulation with other developmentally critical signaling pathways involved in adult tissue homeostasis, such as Notch, is not well understood. By using an in vitro prostate stem cell colony ("prostasphere") formation assay and in vivo prostate reconstitution experiments, we demonstrate that Wnt pathway induction on Sca-1(+) CD49f(+) basal/stem cells (B/SCs) promotes expansion of the basal epithelial compartment with noticeable increases in "triple positive" (cytokeratin [CK] 5(+), CK8(+), p63(+)) prostate progenitor cells, concomitant with upregulation of known Wnt target genes involved in cell-cycle induction. Moreover, Wnt induction affects expression of epithelial-to-mesenchymal transition signature genes, suggesting a possible mechanism for priming B/SC to act as potential tumor-initiating cells. Interestingly, induction of Wnt signaling in B/SCs results in downregulation of Notch1 transcripts, consistent with its postulated antiproliferative role in prostate cells. In contrast, induction of Notch signaling in prostate progenitors inhibits their proliferation and disrupts prostasphere formation. In vivo prostate reconstitution assays further demonstrate that induction of Notch in B/SCs disrupts proper acini formation in cells expressing the activated Notch1 allele, Notch-1 intracellular domain. These data emphasize the importance of Wnt/Notch cross-regulation in adult stem cell biology and suggest that Wnt signaling controls the proliferation and/or maintenance of epithelial progenitors via modulation of Notch signaling.

Notch signaling: simplicity in design, versatility in function

Notch signaling is evolutionarily conserved and operates in many cell types and at various stages during development. Notch signaling must therefore be able to generate appropriate signaling outputs in a variety of cellular contexts. This need for versatility in Notch signaling is in apparent contrast to the simple molecular design of the core pathway. Here, we review recent studies in nematodes, Drosophila and vertebrate systems that begin to shed light on how versatility in Notch signaling output is generated, how signal strength is modulated, and how cross-talk between the Notch pathway and other intracellular signaling systems, such as the Wnt, hypoxia and BMP pathways, contributes to signaling diversity.

Down regulation of CSL activity inhibits cell proliferation in prostate and breast cancer cells

The Notch receptor pathway provides a paradigm for juxtacrine signaling pathways and controls stem cell function, developmental cell fate decisions, and cellular differentiation. The Notch pathway is constitutively activated in human cancers by chromosomal rearrangements, activating point mutations, or altered expression patterns. Therefore, the Notch pathway is the subject of chemotherapeutic intervention in a variety of human cancers. Notch receptor activation results in the gamma-secretase dependent proteolytic cleavage of the receptor to liberate the Notch intracellular domain that acts to mediate co-activator recruitment to the DNA binding transcription factor, CSL (CBF-1/RBP-Jκ, Su(H), Lag-1). Therapeutic targeting of the Notch pathway by gamma-secretase inhibitors prevents NICD production and regulates CSL-dependent transcriptional activity. To interrogate the loss of CSL activity in breast and prostate cancer cells, we used lentiviral-based shRNA knockdown of CSL. Knockdown of CSL expression was assessed by decreased DNA binding activity and resulted in decreased cell proliferation. In contrast, gamma-secretase inhibitor (GSI) treatment of these prostate and breast cancer cell lines resulted in minimal growth effects. PCR profiling of Notch pathway genes identified expression changes in few genes (Delta-like-1, Deltex-1, LMO2, and SH2D1A) after CSL knockdown. Consistent with differential effects of GSI on cell survival, GSI treatment failed to recapitulate the gene expression changes observed after CSL knockdown. Thus, CSL inhibition may provide a more effective mechanism to inhibit Notch-pathway dependent cancer cell proliferation as compared to GSI treatment.

Effects of cadmium on proliferation and self-renewal activity of prostate stem/progenitor cells

Cadmium (Cd) is an occupational and environmental pollutant that induces numerous pathological effects, including injuries to prostate. The aim of the present study was to investigate the effects of Cd on self-renewal and proliferation of prostate stem/progenitor cells (PSPC) and its possible mechanisms. Prostate epithelial cells were prepared from mice to form sphere in Matrigel/PrEGM supplemented with cadmium chloride (CdCl(2)). The data showed that CdCl(2) inhibits sphere-forming ability and proliferation of PSPC in a concentration dependent manner. Primary spheres were then passaged to form daughter spheres and we found that CdCl(2) suppressed PSPC self-renewal activity, which recovered after further passaging. We also detected the protein level of androgen receptor (AR) in the spheres of each passage. The results showed that AR in primary spheres is suppressed by CdCl(2) in a concentration dependent manner. However, no obvious change of AR was found in subsequent passages. The in vivo toxicity of CdCl(2) on PSPC was detected by giving mice drinking water with CdCl(2). Our results demonstrated in vivo inhibition effect of CdCl(2) on self-renewal activity of PSPC. Consistent with in vitro results, self-renewal activity of PSPC was recovered after CdCl(2) withdrawal. In addition, CdCl(2) also in vivo suppressed PSPC proliferation as indicated by Ki67 immunostaining. Our finding suggested that Cd may inhibit proliferation and self-renewal activity of PSPC by suppressing AR, which could be important to further understanding the complex mechanism of Cd toxicity in prostate.

Differentiation of the ductal epithelium and smooth muscle in the prostate gland are regulated by the Notch/PTEN-dependent mechanism

We have shown previously that during branching morphogenesis of the mouse prostate gland, Bone morphogenetic protein 7 functions to restrict Notch1-positive progenitor cells to the tips of the prostate buds. Here, we employed prostate-specific murine bi-genic systems to investigate the effects of gain and loss of Notch function during prostate development. We show that Nkx3.1(Cre) and Probasin(Cre) alleles drive expression of Cre recombinase to the prostate epithelium and periepithelial stroma. We investigated the effects of gain of Notch function using the Rosa(NI1C) conditional allele, which carries a constitutively active intracellular domain of Notch1 receptor. We carried out the analysis of loss of Notch function in Nkx3.1(Cre/+);RBP-J(flox/flox) prostates, where RBP-J is a ubiquitous transcriptional mediator of Notch signaling. We found that gain of Notch function resulted in inhibition of the tumor suppressor PTEN, and increase in cell proliferation and progenitor cells in the basal epithelium and smooth muscle compartments. In turn, loss of Notch/RBP-J function resulted in decreased cell proliferation and loss of epithelial and smooth muscle progenitors. Gain of Notch function resulted in an early onset of benign prostate hyperplasia by three months of age. Loss of Notch function also resulted in abnormal differentiation of the prostate epithelium and stroma. In particular, loss of Notch signaling and increase in PTEN promoted a switch from myoblast to fibroblast lineage, and a loss of smooth muscle. In summary, we show that Notch signaling is necessary for terminal differentiation of the prostate epithelium and smooth muscle, and that during normal prostate development Notch/PTEN pathway functions to maintain patterned progenitors in the epithelial and smooth muscle compartments. In addition, we found that both positive and negative modulation of Notch signaling results in abnormal organization of the prostate tissue, and can contribute to prostate disease in the adult organ.

LEF1 identifies androgen-independent epithelium in the developing prostate

Lymphoid enhancer-binding factor (LEF)1 is a major mediator and a target in canonical Wnt/β-catenin pathway. Interactions between the androgen receptor (AR) and canonical Wnt pathways have been implicated in the development of the genitourinary organs. Here, we investigated the localization and role of LEF1-positive cells during development of the prostate gland in human and in the murine model. We show that during human prostate development, LEF1 is restricted to the basal epithelial layer of the urogenital sinus. During mouse development, Lef1 is also present in the urogenital mesenchyme in addition to the basal epithelial layer of the urogenital sinus. In the course of elongation and branching of the prostatic ducts, Lef1 is localized to the proliferating epithelium at the distal tips of the buds. Notably, during branching morphogenesis, domains of Lef1 and AR are mutually exclusive. We further employed the TOPGAL reporter strain to examine the dynamics of Wnt signaling in the context of prostate regression upon a 7-d treatment with a competitive AR inhibitor, bicalutamide. We found that Wnt/Lef1-positive basal cells are not dependent upon androgen for survival. Furthermore, upon bicalutamide treatment, Wnt/Lef1-positive basal progenitors repopulated the luminal compartment. We conclude that Wnt/Lef1 activity identifies an androgen-independent population of prostate progenitors, which is important for embryonic development and organ maintenance and regeneration in the adult.

When NRF2 talks, who's listening?

Activation of the KEAP1-NRF2 signaling pathway is an adaptive response to environmental and endogenous stresses and serves to render animals resistant to chemical carcinogenesis and other forms of toxicity, whereas disruption of the pathway exacerbates these outcomes. This pathway, which can be activated by sulfhydryl-reactive, small-molecule pharmacologic agents, regulates the inducible expression of an extended battery of cytoprotective genes, often by direct binding of the transcription factor to antioxidant response elements in the promoter regions of target genes. However, it is becoming evident that some of the protective effects may be mediated indirectly through cross talk with additional pathways affecting cell survival and other aspects of cell fate. These interactions provide a multi-tiered, integrated response to chemical stresses. This review highlights recent observations on the molecular interactions and their functional consequences between NRF2 and the arylhydrocarbon receptor (AhR), NF-κB, p53, and Notch1 signaling pathways.

Molecular signatures of the primitive prostate stem cell niche reveal novel mesenchymal-epithelial signaling pathways

Background

Signals between stem cells and stroma are important in establishing the stem cell niche. However, very little is known about the regulation of any mammalian stem cell niche as pure isolates of stem cells and their adjacent mesenchyme are not readily available. The prostate offers a unique model to study signals between stem cells and their adjacent stroma as in the embryonic prostate stem cell niche, the urogenital sinus mesenchyme is easily separated from the epithelial stem cells. Here we investigate the distinctive molecular signals of these two stem cell compartments in a mammalian system.

Methodology/Principal Findings

We isolated fetal murine urogenital sinus epithelium and urogenital sinus mesenchyme and determined their differentially expressed genes. To distinguish transcripts that are shared by other developing epithelial/mesenchymal compartments from those that pertain to the prostate stem cell niche, we also determined the global gene expression of epidermis and dermis of the same embryos. Our analysis indicates that several of the key transcriptional components that are predicted to be active in the embryonic prostate stem cell niche regulate processes such as self-renewal (e.g., E2f and Ap2), lipid metabolism (e.g., Srebp1) and cell migration (e.g., Areb6 and Rreb1). Several of the enriched promoter binding motifs are shared between the prostate epithelial/mesenchymal compartments and their epidermis/dermis counterparts, indicating their likely relevance in epithelial/mesenchymal signaling in primitive cellular compartments. Based on differential gene expression we also defined ligand-receptor interactions that may be part of the molecular interplay of the embryonic prostate stem cell niche.

Conclusions/Significance

We provide a comprehensive description of the transcriptional program of the major regulators that are likely to control the cellular interactions in the embryonic prostatic stem cell niche, many of which may be common to mammalian niches in general. This study provides a comprehensive source for further studies of mesenchymal/epithelial interactions in the prostate stem cell niche. The elucidation of pathways in the normal primitive niche may provide greater insight into mechanisms subverted during abnormal proliferative and oncogenic processes. Understanding these events may result in the development of specific targeted therapies for prostatic diseases such as benign prostatic hypertrophy and carcinomas.

Regulation of notch1 signaling by nrf2: implications for tissue regeneration

The Keap1-Nrf2-ARE signaling pathway elicits an adaptive response for cell survival after endogenous and exogenous stresses, such as inflammation and carcinogens, respectively. Keap1 inhibits the transcriptional activation activity of Nrf2 (p45 nuclear factor erythroid-derived 2-related factor 2) in unstressed cells by facilitating its degradation. Through transcriptional analyses in Keap1- or Nrf2-disrupted mice, we identified interactions between the Keap1-Nrf2-ARE and the Notch1 signaling pathways. We found that Nrf2 recognized a functional antioxidant response element (ARE) in the promoter of Notch1. Notch1 regulates processes such as proliferation and cell fate decisions. We report a functional role for this cross talk between the two pathways and show that disruption of Nrf2 impeded liver regeneration after partial hepatectomy and was rescued by reestablishment of Notch1 signaling.

Notch-1 signaling is lost in prostate adenocarcinoma and promotes PTEN gene expression

Prostate tumorigenesis is associated with loss of PTEN gene expression. We and others have recently reported that PTEN is regulated by Notch-1 signaling. Herein, we tested the hypothesis that alterations of the Notch-1 signaling pathway are present in human prostate adenocarcinoma and that Notch-1 signaling regulates PTEN gene expression in prostate cells. Prostate adenocarcinoma cases were examined by immunohistochemistry for ligand cleaved (activated) Notch-1 protein. Tumor foci exhibited little cleaved Notch-1 protein, but expression was observed in benign tissue. Both tumor and benign tissue expressed total (uncleaved) Notch-1. Reduced Hey-1 expression was seen in tumor foci but not in benign tissue, confirming loss of Notch-1 signaling in prostate adenocarcinoma. Retroviral expression of constitutively active Notch-1 in human prostate tumor cell lines resulted in increased PTEN gene expression. Incubation of prostate cell lines with the Notch-1 ligand, Delta, resulted in increased PTEN expression indicating that endogenous Notch-1 regulates PTEN gene expression. Chromatin immunoprecipitation demonstrated that CBF-1 was bound to the PTEN promoter. These data collectively indicate that defects in Notch-1 signaling may play a role in human prostate tumor formation in part via a mechanism that involves regulation of the PTEN tumor suppressor gene.

Targeted knockdown of Notch1 inhibits invasion of human prostate cancer cells concomitant with inhibition of matrix metalloproteinase-9 and urokinase plasminogen activator

PURPOSE

Notch, a type 1 transmembrane protein, plays a key role in the development of many tissues and organ types. Aberrant Notch signaling, found in a wide variety of human cancers, contributes to tumor development. Because Notch1 was found to be overexpressed in prostate cancer (PCa) cells and human PCa tissue, we therefore tested our hypothesis that overexpression of Notch1 in PCa promotes tumor invasion.

EXPERIMENTAL DESIGN

Notch1 expression was evaluated in human PCa cells and human PCa tissues. PCa cells were transiently transfected with Notch1-specific small interfering RNAs in concentrations ranging from 30 to 120 nmol/L and subsequently evaluated for effects on invasion and expression analysis for molecules involved in invasion.

RESULTS

Small interfering RNA-mediated knockdown of Notch1 in PC3 and 22Rnu1 PCa cells dramatically decreased their invasion. Focused cDNA array revealed that Notch1 knockdown resulted in significant reduction in the expression of urokinase plasminogen activator (uPA) and matrix metalloproteinase-9 (MMP9) gene transcripts. These data were further verified by reverse transcription-PCR, real-time reverse transcription-PCR, and immunoblot analysis. Knockdown of Notch1 was also observed to significantly reduce the mRNA expression and protein levels of uPA and its receptor uPAR. A significant reduction in MMP9 expression in Notch1 knockdown cells suggested a role for Notch1 in augmenting MMP9 transcription.

CONCLUSIONS

Our data show the involvement of Notch1 in human PCa invasion and that silencing of Notch1 inhibits invasion of human PCa cells by inhibiting the expression of MMP9 and uPA. Thus, targeting of Notch1 could be an effective therapeutic approach against PCa.

A role for notch signaling in stromal survival and differentiation during prostate development

Notch1 signaling is involved in epithelial growth and differentiation of prostate epithelia, and we have examined the role that notch signaling plays in the stroma of the developing prostate. We initially observed expression of delta-like 1 (Dlk1) and Notch2 in gene profiling studies of prostatic mesenchyme, and anticipated that they might be expressed in a key subset of inductive mesenchyme. Using quantitative RT-PCR, Northern blotting, and whole mount in situ hybridization, we confirmed that both Dlk1 and Notch2 mRNAs showed a restricted expression pattern within subsets of the stroma during prostate development. Localization of Dlk1 and Notch2 proteins mirrored the transcript expression, and showed both distinct and overlapping expression patterns within the stroma. Dlk1 and Notch2 were coexpressed in condensed inductive mesenchyme of the ventral mesenchymal pad (VMP), and were partially colocalized in the smooth muscle (SM) layer of the urethral stroma. In addition, Dlk1 was not expressed in SM adjacent to the VMP in female urethra. The function of notch signaling was examined using organ cultures of prostate rudiments and a small molecule inhibitor of notch receptor activity. Inhibition of notch signaling led to a loss of stromal tissue in both prostate and female VMP cultures, suggesting that this pathway was required for stromal survival. Inhibition of notch signaling also led to changes in both epithelial and stromal differentiation, which was evident in altered distributions of SM alpha-actin and p63 in prostates grown in vitro. The effects of notch signaling upon the stroma were only evident in the presence of testosterone, in contrast to effects upon epithelial differentiation.

Nitroreductase-mediated cell ablation in transgenic zebrafish embryos

Prodrug dependent cell ablation is a method that allows inducible and spatially restricted cell destruction. We describe transgenic methods to express the Escherichia coli nfsB in a tissue restricted manner in the zebrafish. This bacterial gene encodes a nitroreductase (NTR) enzyme that can render prodrugs such as metronidazole (Met) cytotoxic. Using the expression of NTR fused to a fluorescent protein, one can simultaneously make cells susceptible to prodrug treatment and visualize cell ablation as it occurs.

Molecular signaling pathways that regulate prostate gland development

Prostate gland development is a complex process that involves coordination of multiple signaling pathways including endocrine, paracrine, autocrine, juxtacrine and transcription factors. To put this into proper context, the present manuscript will begin with a brief overview of the stages of prostate development and a summary of androgenic signaling in the developing prostate, which is essential for prostate formation. This will be followed by a detailed description of other transcription factors and secreted morphogens directly involved in prostate formation and branching morphogenesis. Except where otherwise indicated, results from rodent models will be presented since studies that examine molecular signaling in the developing human prostate gland are sparse at the present time.

The Notch pathway in prostate development and cancer

The Notch family of transmembrane receptors are important mediators of cell fate determination. Accordingly, Notch signaling is intimately involved in the development of numerous tissues. Recent findings have highlighted a critical role for Notch signaling in normal prostate development. Notch signaling is required for embryonic and postnatal prostatic growth and development, for proper cell lineage specification within the prostate, as well as for adult prostate maintenance and regeneration following castration and hormone replacement. Evidence for Notch as a regulator of prostate cancer development, progression, and metastasis has also emerged. This review summarizes our current understanding of the role of Notch pathway elements, including members of the Jagged, Delta-like, hairy/enhancer-of-split, and hairy/enhancer-of-split related with YRPW motif families, in prostate development and tumorigenesis. Data supporting Notch pathway elements as oncogenes and tumor suppressors in prostate tumors, as well as data implicating Notch receptors and ligands as potential markers of normal prostate stem/progenitor cells and prostate cancer stem/initiating cells, are also presented.

Prostate epithelial cell fate

Androgen receptor (AR) within prostatic mesenchymal cells, with the absence of AR in the epithelium, is still sufficient to induce prostate development. AR in the luminal epithelium is required to express the secretory markers associated with differentiation. Nkx3.1 is expressed in the epithelium in early prostatic embryonic development and expression is maintained in the adult. Induction of the mouse prostate gland by the embryonic mesenchymal cells results in the organization of a sparse basal layer below the luminal epithelium with rare neuroendocrine cells that are interdispersed within this basal layer. The human prostate shows similar glandular organization; however, the basal layer is continuous. The strong inductive nature of embryonic prostatic and bladder mesenchymal cells is demonstrated in grafts where embryonic stem (ES) cells are induced to differentiate and organize as a prostate and bladder, respectively. Further, the ES cells can be driven by the correct embryonic mesenchymal cells to form epithelium that differentiates into secretory prostate glands and differentiated bladders that produce uroplakin. This requires the ES cells to mature into endoderm that gives rise to differentiated epithelium. This process is control by transcription factors in both the inductive mesenchymal cells (AR) and the responding epithelium (FoxA1 and Nkx3.1) that allows for organ development and differentiation. In this review, we explore a molecular mechanism where the pattern of transcription factor expression controls cell determination, where the cell is assigned a developmental fate and subsequently cell differentiation, and where the assigned cell now emerges with it's own unique character.

Functions of normal and malignant prostatic stem/progenitor cells in tissue regeneration and cancer progression and novel targeting therapies

This review summarizes the recent advancements that have improved our understanding of the functions of prostatic stem/progenitor cells in maintaining homeostasis of the prostate gland. We also describe the oncogenic events that may contribute to their malignant transformation into prostatic cancer stem/progenitor cells during cancer initiation and progression to metastatic disease stages. The molecular mechanisms that may contribute to the intrinsic or the acquisition of a resistant phenotype by the prostatic cancer stem/progenitor cells and their differentiated progenies with a luminal phenotype to the current therapies and disease relapse are also reviewed. The emphasis is on the critical functions of distinct tumorigenic signaling cascades induced through the epidermal growth factor system, hedgehog, Wnt/beta-catenin, and/or stromal cell-derived factor-1/CXC chemokine receptor-4 pathways as well as the deregulated apoptotic signaling elements and ATP-binding cassette multidrug transporter. Of particular therapeutic interest, we also discuss the potential beneficial effects associated with the targeting of these signaling elements to overcome the resistance to current treatments and prostate cancer recurrence. The combined targeted strategies toward distinct oncogenic signaling cascades in prostatic cancer stem/progenitor cells and their progenies as well as their local microenvironment, which could improve the efficacy of current clinical chemotherapeutic treatments against incurable, androgen-independent, and metastatic prostate cancers, are also described.

Rbp-j regulates expansion of pancreatic epithelial cells and their differentiation into exocrine cells during mouse development

Notch signaling regulates cell fate determination in various tissues. We have reported the generation of mice with a pancreas-specific knockout of Rbp-j using Pdx.cre mice. Those mice exhibited premature endocrine and ductal differentiation. We now generated mice in which the Rbp-j gene was inactivated in Ptf1a-expressing cells using Ptf1a.cre mice. The timing of the Cre-mediated deletion in Rbp-j(f/f) Ptf1a.cre mice is 1 day later than that in Rbp-j(f/f) Pdx.cre mice. In Rbp-j(f/f) Ptf1a.cre mouse pancreases, at E13.5, the reduced Hes1 expression was accompanied by reduced epithelial growth, but premature endocrine cell differentiation was minimal. At E15.5, Pdx1 expression was repressed and acinar cell differentiation was reduced, but an increase in acinar cell proliferation was observed during the perinatal period. Our study indicates that, in addition to its role in preventing premature differentiation of early endocrine cells, Rbp-j regulates epithelial growth, Pdx1 expression, and acinar cell differentiation during mid-pancreatic development.

Noggin is required for normal lobe patterning and ductal budding in the mouse prostate

Mesenchymal expression of the BMP antagonist NOGGIN during prostate development plays a critical role in pre-natal ventral prostate development and opposes BMP4-mediated inhibition of cell proliferation during postnatal ductal development. Morphologic examination of newborn Noggin-/- male fetuses revealed genitourinary anomalies including cryptorchidism, incomplete separation of the hindgut from the urogenital sinus (UGS), absence of the ventral mesenchymal pad, and a complete loss of ventral prostate (VP) budding. Examination of lobe-specific marker expression in the E14 Noggin-/- UGS rescued by transplantation under the renal capsule of a male nude mouse confirmed a complete loss of VP determination. More modest effects were observed in the other lobes, including decreased number of ductal buds in the dorsal and lateral prostates of newborn Noggin-/- males. BMP4 and BMP7 have been shown to inhibit ductal budding and outgrowth by negatively regulating epithelial cell proliferation. We show here that NOGGIN can neutralize budding inhibition by BMP4 and rescues branching morphogenesis of BMP4-exposed UGS in organ culture and show that the effects of BMP4 and NOGGIN activities converge on P63+ epithelial cells located at nascent duct tips. Together, these studies show that the BMP-NOGGIN axis regulates patterning of the ventral prostate, regulates ductal budding, and controls proliferation of P63+ epithelial cells in the nascent ducts of developing mouse prostate.

Estrogen receptors: how do they signal and what are their targets

During the past decade there has been a substantial advance in our understanding of estrogen signaling both from a clinical as well as a preclinical perspective. Estrogen signaling is a balance between two opposing forces in the form of two distinct receptors (ER alpha and ER beta) and their splice variants. The prospect that these two pathways can be selectively stimulated or inhibited with subtype-selective drugs constitutes new and promising therapeutic opportunities in clinical areas as diverse as hormone replacement, autoimmune diseases, prostate and breast cancer, and depression. Molecular biological, biochemical, and structural studies have generated information which is invaluable for the development of more selective and effective ER ligands. We have also become aware that ERs do not function by themselves but require a number of coregulatory proteins whose cell-specific expression explains some of the distinct cellular actions of estrogen. Estrogen is an important morphogen, and many of its proliferative effects on the epithelial compartment of glands are mediated by growth factors secreted from the stromal compartment. Thus understanding the cross-talk between growth factor and estrogen signaling is essential for understanding both normal and malignant growth. In this review we focus on several of the interesting recent discoveries concerning estrogen receptors, on estrogen as a morphogen, and on the molecular mechanisms of anti-estrogen signaling.

Self-renewal and multilineage differentiation in vitro from murine prostate stem cells

Murine prostate stem cells express integrin alpha 6, which modulates survival, proliferation, and differentiation signaling through its interaction with the extracellular protein laminin. When plated in vitro in laminin containing Matrigel medium, 1 of 500-1,000 murine prostate cells can grow and form clonogenic spheroid structures that we term prostate spheres. Prostate spheres can be serially passaged individually or in bulk to generate daughter spheres with similar composition, demonstrating that sphere-forming cells are capable of self-renewal. Spheres spontaneously undergo lineage specification for basal and transit-amplifying cell types. P63-expressing cells localized to the outer layers of prostate spheres possess higher self-renewal capacity, whereas cells toward the center display a more differentiated transit-amplifying phenotype, as demonstrated by the expression of the prostate stem cell antigen. When dihydrotestosterone is added to the medium, the androgen receptor is stabilized, is imported to the nucleus, and drives differentiation to a luminal cell-like phenotype. A fraction of sphere cells returned to an in vivo environment can undergo differentiation and morphogenesis to form prostate tubular structures with defined basal and luminal layers accompanied by prostatic secretions. This study demonstrates self-renewal and multilineage differentiation from single adult prostate stem/progenitor cells in a specific in vitro microenvironment.

Increased expression and differential phosphorylation of stathmin may promote prostate cancer progression

BACKGROUND

Proteins which regulate normal development may promote tumorigenesis, tumor progression, or metastasis through dysregulation of these functions. We postulate that proteins, which regulate prostate growth also promote prostate cancer (PCa) progression.

METHODS

Two Dimensional Gel Electrophoresis was utilized to compare patterns of protein expression in 12T-7f prostates (LPB-Tag mouse model for PCa) during tumor development and progression with those of normal developing and adult wild type CD-1 prostates. Stathmin expression and phosphorylation patterns were analyzed in mouse and human PCa cell lines as well as in human PCa tissue arrays.

RESULTS

Stathmin was identified by two-dimensional gel electrophoresis and mass spectrometry. Stathmin levels increase early during normal mouse prostate development and again during prostate tumor development and progression. In human prostate adenocarcinoma, stathmin increases in Gleason pattern 5. Further, stathmin is differentially phosphorylated in androgen-dependent LNCaP cells compared to androgen-independent PC-3 and DU145 cells. This differential phosphorylation is modulated by androgen and anti-androgen treatment.

CONCLUSION

Stathmin expression is highest when the prostate is undergoing morphogenesis or tumorigenesis and these processes may be regulated through differential phosphorylation. Furthermore, modulation of stathmin phosphorylation may correlate with the development of androgen-independent PCa.

Prostatic stem cell marker identified by cDNA microarray in mouse

PURPOSE

Identifying prostatic stem cells is important to elucidate the mechanisms by which the prostate develops and control prostate cancer. We recently reported that the proximal region of the mouse prostate contains a population of stem cells. However, to our knowledge the specific marker of stem cells in the proximal region remains unknown.

MATERIALS AND METHODS

We performed cDNA microarray analysis of cells obtained from the proximal region and from the remaining regions in dorsal prostates to identify several candidate stem cell markers. After we focused on 1 candidate among them we confirmed the expression of this candidate gene by reverse transcriptase-polymerase chain reaction analysis and immunohistochemistry. We also investigated the relation between positive cells for this marker and those for telomerase reverse transcriptase. Finally, we investigated the functional potential of prominin positive cells in 3-dimensional culture.

RESULTS

Seven of 4,800 genes analyzed showed proximal/remaining ratios greater than 20. Of these genes we focused on prominin because it is a cell surface marker widely used to identify and isolate stem cells from various organs. We found a prominin positive cell population enriched in the basal cell layer in the proximal region, and the coincidence of prominin and telomerase reverse transcriptase immunostaining. We also found that prominin positive cells gave rise to numerous and large-branched ducts, whereas prominin negative cells formed far fewer such structures in 3-dimensional culture.

CONCLUSIONS

A small population of prominin positive cells in the mouse prostate basal layer of the proximal region represents a stem cell population.