Does the microenvironment influence the cell types of origin for prostate cancer?

Novel insights in cell cycle dysregulation during prostate cancer progression

Prostate cancer (CaP) remains the second leading cause of cancer deaths in Western men. These deaths occur because metastatic CaP acquires resistance to available treatments. The novel and functionally diverse treatment options that have been introduced in the clinic over the past decade each eventually induce resistance for which the molecular basis is diverse. Both initiation and progression of CaP have been associated with enhanced cell proliferation and cell cycle dysregulation. A better understanding of the specific pro-proliferative molecular shifts that control cell division and proliferation during CaP progression may ultimately overcome treatment resistance. Here, we examine literature for support of this possibility. We start by reviewing recently renewed insights in prostate cell types and their proliferative and oncogenic potential. We then provide an overview of the basic knowledge on the molecular machinery in charge of cell cycle progression and its regulation by well-recognized drivers of CaP progression such as androgen receptor and retinoblastoma protein. In this respect, we pay particular attention to interactions and reciprocal interplay between cell cycle regulators and androgen receptor. Somatic alterations that impact the cell cycle-associated and -regulated genes encoding p53, PTEN and MYC during progression from treatment-naïve, to castration-recurrent, and in some cases, neuroendocrine CaP are discussed. We considered also non-genomic events that impact cell cycle determinants, including transcriptional, epigenetic and micro-environmental switches that occur during CaP progression. Finally, we evaluate the therapeutic potential of cell cycle regulators and address challenges and limitations in the approaches modulating their action for CaP treatment.

Mast Cell-Derived SAMD14 Is a Novel Regulator of the Human Prostate Tumor Microenvironment

Mast cells (MCs) are important cellular components of the tumor microenvironment and are significantly associated with poor patient outcomes in prostate cancer and other solid cancers. The promotion of tumor progression partly involves heterotypic interactions between MCs and cancer-associated fibroblasts (CAFs), which combine to potentiate a pro-tumor extracellular matrix and promote epithelial cell invasion and migration. Thus far, the interactions between MCs and CAFs remain poorly understood. To identify molecular changes that may alter resident MC function in the prostate tumor microenvironment, we profiled the transcriptome of human prostate MCs isolated from patient-matched non-tumor and tumor-associated regions of fresh radical prostatectomy tissue. Transcriptomic profiling revealed a distinct gene expression profile of MCs isolated from prostate tumor regions, including the downregulation of SAMD14, a putative tumor suppressor gene. Proteomic profiling revealed that overexpression of SAMD14 in HMC-1 altered the secretion of proteins associated with immune regulation and extracellular matrix processes. To assess MC biological function within a model of the prostate tumor microenvironment, HMC-1-SAMD14+ conditioned media was added to co-cultures of primary prostatic CAFs and prostate epithelium. HMC-1-SAMD14+ secretions were shown to reduce the deposition and alignment of matrix produced by CAFs and suppress pro-tumorigenic prostate epithelial morphology. Overall, our data present the first profile of human MCs derived from prostate cancer patient specimens and identifies MC-derived SAMD14 as an important mediator of MC phenotype and function within the prostate tumor microenvironment.

Its written all over your face: The molecular and physiological consequences of aging skin

Perhaps the most recognizable consequences of tissue aging are manifested in the skin. Hair graying and loss, telltale wrinkles, and age spots are indicative of physiological aging symptoms, many of which are analogous to processes in other tissues as well with less visible outcomes. While the study of skin aging has been conducted for decades, more recent work has illuminated many of the fundamental molecular and physiological causes of aging in the skin. Recent technological advances have allowed for the detection and quantification of a variety of physiological triggers that lead to aging in the skin and molecular methods have begun to determine the etiology of these phenotypic features. This review will attempt to summarize recent work in this area and provide some speculation about the next wave of studies.

Tumor-Associated Macrophages (TAM) are recruited to the aging prostate epithelial lesions and become intermingled with basal cells

BACKGROUND

Prostate cancer remains one of the most common cancers in men. Macrophages are thought to be important regulators in cancers, and their potential involvement in prostate cancer should not be overlooked. Therefore, the association between macrophages and the pre-tumorous changes in prostate epithelium during aging deserves further investigation.

OBJECTIVES

We sought to investigate whether macrophages would be recruited into the prostate epithelium that display pathological lesions commonly found during aging.

MATERIALS AND METHODS

Prostates of aging rats, with and without treatment with a combination of testosterone and estradiol, were examined for premalignant and malignant epithelial lesions. For comparison, prostates of castrated rats were also investigated.

RESULTS

Intraepithelial macrophages were found restricted to areas of premalignant and malignant lesions. An unprecedented interaction between macrophages and basal cells was observed in the aging pathological lesions. The intraepithelial macrophages were associated with autophagy, in contrast to those found after castration. In prostate lesions, the intraepithelial macrophages had TAM phenotype (CD68+/iNOS+/CD206+/ARG+), denoting a possible involvement in cancer progression. However, M2 macrophages (CD68+/CD163+) were recruited into the epithelium after castration, possibly to phagocytize cells undergoing apoptosis.

DISCUSSION AND CONCLUSION

In conclusion, macrophages were recruited into the prostate epithelium and presented diverse phenotypes and morphology, consistent with changes reflected in the hormonal environment. Macrophages with the TAM phenotype were found restricted to areas of premalignant and malignant lesions in aging prostates, denoting a possible involvement in cancer progression. In contrast, M2 macrophages were found in the regressed epithelium after castration.

Hypoxia induced cancer stem cell enrichment promotes resistance to androgen deprivation therapy in prostate cancer

Androgen deprivation therapy (ADT) is the main treatment to prolong survival in advance stage prostate cancer (PCa) but associated resistance leads to the development of terminal castrate resistant PCa (CRPC). Current research demonstrates that prostate cancer stem cells (PCSC) play a critical role in the development of treatment resistance and subsequent disease progression. Despite uncertainty surrounding the origin of these cells, studies clearly show they are associated with poorer outcomes and that ADT significantly enhances their numbers. Here in we highlight how activation of HIF signalling, in response to hypoxic conditions within the tumour microenvironment, results in the expression of genes associated with stemness and EMT promoting PCSC emergence which ultimately drives tumour relapse to CRPC. Hypoxic conditions are not only enhanced by ADT but the associated decrease in AR activation also promotes PI3K/AKT signalling which actively enhances HIF and its effects on PCSC's. Furthermore, emerging evidence now indicates that HIF-2α, rather than the commonly considered HIF-1α, is the main family member that drives PCSC emergence. Taken together this clearly identifies HIF and associated pathways as key targets for new therapeutic strategies that could potentially prevent or slow PCSC promoted resistance to ADT, thus holding potential to prolong patient survival.

Proteomic Profiling of Human Prostate Cancer-associated Fibroblasts (CAF) Reveals LOXL2-dependent Regulation of the Tumor Microenvironment

In prostate cancer, cancer-associated fibroblasts (CAF) exhibit contrasting biological properties to non-malignant prostate fibroblasts (NPF) and promote tumorigenesis. Resolving intercellular signaling pathways between CAF and prostate tumor epithelium may offer novel opportunities for research translation. To this end, the proteome and phosphoproteome of four pairs of patient-matched CAF and NPF were characterized to identify discriminating proteomic signatures. Samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with a hyper reaction monitoring data-independent acquisition (HRM-DIA) workflow. Proteins that exhibited a significant increase in CAF versus NPF were enriched for the functional categories "cell adhesion" and the "extracellular matrix." The CAF phosphoproteome exhibited enhanced phosphorylation of proteins associated with the "spliceosome" and "actin binding." STRING analysis of the CAF proteome revealed a prominent interaction hub associated with collagen synthesis, modification, and signaling. It contained multiple collagens, including the fibrillar types COL1A1/2 and COL5A1; the receptor tyrosine kinase discoidin domain-containing receptor 2 (DDR2), a receptor for fibrillar collagens; and lysyl oxidase-like 2 (LOXL2), an enzyme that promotes collagen crosslinking. Increased activity and/or expression of LOXL2 and DDR2 in CAF were confirmed by enzymatic assays and Western blotting analyses. Pharmacological inhibition of CAF-derived LOXL2 perturbed extracellular matrix (ECM) organization and decreased CAF migration in a wound healing assay. Further, it significantly impaired the motility of co-cultured RWPE-2 prostate tumor epithelial cells. These results indicate that CAF-derived LOXL2 is an important mediator of intercellular communication within the prostate tumor microenvironment and is a potential therapeutic target.

Cells of Origin for Prostate Cancer

Comprehensive knowledge of the normal prostate epithelial lineage hierarchy is a prerequisite to investigate the identity of the cells of origin for prostate cancer. The basal and luminal cells constitute most of the prostate epithelium and have been the major focuses of the study on the cells of origin for prostate cancer. Much progress has been made during the past few decades, mainly using mouse models, to understand the inter-lineage relationship and intra-lineage heterogeneity in adults as well as the lineage plasticity during conditions of stress. These studies have concluded that the adult mouse prostate basal and luminal cells are largely independently sustained under physiological conditions, but both types of cells possess the capacity for bipotent differentiation under stress or artificial experimental conditions. However, the existence or the identity of the putative progenitors within each lineage warrants further investigation. Whether the human prostate lineage hierarchy is completely the same as that of the mouse remains uncertain. Experiments from independent groups have demonstrated that both types of cells in mice and humans can serve as targets for transformation. But controversies remain whether the disease from distinct cells of origin display different clinical behaviors. Further investigation of the intra-lineage heterogeneity will provide new insights into this issue. Understanding the identity of the cells of origin for prostate cancer will help identify novel prognostic markers for early detection of aggressive prostate cancers, provide insights into the therapeutic vulnerability of these tumors, and inspire novel therapeutic strategies.

The adaptive immune system promotes initiation of prostate carcinogenesis in a human c-Myc transgenic mouse model

Increasing evidence from epidemiological and pathological studies suggests a role of the immune system in the initiation and progression of multiple cancers, including prostate cancer. Reports on the contribution of the adaptive immune system are contradictive, since both suppression and acceleration of disease development have been reported. This study addresses the functional role of lymphocytes in prostate cancer development using a genetically engineered mouse model (GEMM) of human c-Myc driven prostate cancer (Hi-Myc mice) combined with B and T cell deficiency (RAG1^-/- mice). From a pre-cancerous stage on, Hi-Myc mice showed higher accumulation of immune cells in their prostates then wild-type mice, of which macrophages were the most abundant. The onset of invasive adenocarcinoma was delayed in Hi-MycRAG1^-/- compared to Hi-Myc mice and associated with decreased infiltration of leukocytes into the prostate. In addition, lower levels of the cytokines CXCL2, CCL5 and TGF-β1 were detected in Hi-MycRAG1^-/- compared to Hi-Myc mouse prostates. These results from a GEMM of prostate cancer provide new insights into the promoting role of the adaptive immune system in prostate cancer development. Our findings indicate that the endogenous adaptive immune system does not protect against de novo prostate carcinogenesis in Hi-Myc transgenic mice, but rather accelerates the formation of invasive adenocarcinomas. This may have implications for the development of novel treatment strategies.

v-Src Oncogene Induces Trop2 Proteolytic Activation via Cyclin D1

Proteomic analysis of castration-resistant prostate cancer demonstrated the enrichment of Src tyrosine kinase activity in approximately 90% of patients. Src is known to induce cyclin D1, and a cyclin D1-regulated gene expression module predicts poor outcome in human prostate cancer. The tumor-associated calcium signal transducer 2 (TACSTD2/Trop2/M1S1) is enriched in the prostate, promoting prostate stem cell self-renewal upon proteolytic activation via a γ-secretase cleavage complex (PS1, PS2) and TACE (ADAM17), which releases the Trop2 intracellular domain (Trop2 ICD). Herein, v-Src transformation of primary murine prostate epithelial cells increased the proportion of prostate cancer stem cells as characterized by gene expression, epitope characteristics, and prostatosphere formation. Cyclin D1 was induced by v-Src, and Src kinase induction of Trop2 ICD nuclear accumulation required cyclin D1. Cyclin D1 induced abundance of the Trop2 proteolytic cleavage activation components (PS2, TACE) and restrained expression of the inhibitory component of the Trop2 proteolytic complex (Numb). Patients with prostate cancer with increased nuclear Trop2 ICD and cyclin D1, and reduced Numb, had reduced recurrence-free survival probability (HR = 4.35). Cyclin D1, therefore, serves as a transducer of v-Src-mediated induction of Trop2 ICD by enhancing abundance of the Trop2 proteolytic activation complex. Cancer Res; 76(22); 6723-34. ©2016 AACR.

Current status and perspectives in atomic force microscopy-based identification of cellular transformation

Understanding the complex interplay between cells and their biomechanics and how the interplay is influenced by the extracellular microenvironment, as well as how the transforming potential of a tissue from a benign to a cancerous one is related to the dynamics of both the cell and its surroundings, holds promise for the development of targeted translational therapies. This review provides a comprehensive overview of atomic force microscopy-based technology and its applications for identification of cellular progression to a cancerous phenotype. The review also offers insights into the advancements that are required for the next user-controlled tool to allow for the identification of early cell transformation and thus potentially lead to improved therapeutic outcomes.

Prostate cancer metastasis: roles of recruitment and reprogramming, cell signal network and three-dimensional growth characteristics

Prostate cancer (PCa) metastasizes to bone and soft tissues, greatly decreasing quality of life, causing bone pain, skeletal complications, and mortality in PCa patients. While new treatment strategies are being developed, the molecular and cellular basis of PCa metastasis and the “cross-talk” between cancer cells and their microenvironment and crucial cell signaling pathways need to be successfully dissected for intervention. In this review, we introduce a new concept of the mechanism of PCa metastasis, the recruitment and reprogramming of bystander and dormant cells (DCs) by a population of metastasis-initiating cells (MICs). We provide evidence that recruited and reprogrammed DCs gain MICs phenotypes and can subsequently metastasize to bone and soft tissues. We show that MICs can also recruit and reprogram circulating tumor cells (CTCs) and this could contribute to cancer cell evolution and the acquisition of therapeutic resistance. We summarize relevant molecular signaling pathways, including androgen receptors (ARs) and their variants and growth factors (GFs) and cytokines that could contribute to the predilection of PCa for homing to bone and soft tissues. To understand the etiology and the biology of PCa and the effectiveness of therapeutic targeting, we briefly summarize the animal and cell models that have been employed. We also report our experience in the use of three-dimensional (3-D) culture and co-culture models to understand cell signaling networks and the use of these attractive tools to conduct drug screening exercises against already-identified molecular targets. Further research into PCa growth and metastasis will improve our ability to target cancer metastasis more effectively and provide better rationales for personalized oncology.

The many ways to make a luminal cell and a prostate cancer cell

Research in the area of stem/progenitor cells has led to the identification of multiple stem-like cell populations implicated in prostate homeostasis and cancer initiation. Given that there are multiple cells that can regenerate prostatic tissue and give rise to prostate cancer, our focus should shift to defining the signaling mechanisms that drive differentiation and progenitor self-renewal. In this article, we will review the literature, present the evidence and raise important unanswered questions that will help guide the field forward in dissecting critical mechanisms regulating stem-cell differentiation and tumor initiation.

An in vitro system to characterize prostate cancer progression identified signaling required for self-renewal

Mutations in RB and PTEN are linked to castration resistance and poor prognosis in prostate cancer. Identification of genes that are regulated by these tumor suppressors in a context that recapitulates cancer progression may be beneficial for discovering novel therapeutic targets. Although various genetically engineered mice thus far provided tumor models with various pathological stages, they are not ideal for detecting dynamic changes in gene transcription. Additionally, it is difficult to achieve an effect specific to tumor progression via gain of functions of these genes. In this study, we developed an in vitro model to help identify RB- and PTEN-loss signatures during the malignant progression of prostate cancers. Trp53^-/- ; Rb^f/f , Trp53^-/- ; Pten^f/f , and Trp53^-/- ; Rb^f/f ; Pten^f/f prostate epithelial cells were infected with AD-LacZ or AD-Cre. We found that deletion of Rb, Pten or both stimulated prostasphere formation and tumor development in immune-compromised mice. The GO analysis of genes affected by the deletion of Rb or Pten in Trp53^-/- prostate epithelial cells identified a number of genes encoding cytokines, chemokines and extracellular matrix remodeling factors, but only few genes related to cell cycle progression. Two genes (Il-6 and Lox) were further analyzed. Blockade of Il-6 signaling and depletion of Lox significantly attenuated prostasphere formation in 3D culture, and in the case of IL-6, strongly suppressed tumor growth in vivo. These findings suggest that our in vitro model may be instrumental in identifying novel therapeutic targets of prostate cancer progression, and further underscore IL-6 and LOX as promising therapeutic targets. © 2015 Wiley Periodicals, Inc.

Cell types of origin for prostate cancer

Analyses of cell types of origin for prostate cancer should result in new insights into mechanisms of tumor initiation, and may lead to improved prognosis and selection of appropriate therapies. Here, we review studies using a range of methodologies to investigate the cell of origin for mouse and human prostate cancer. Notably, analyses using tissue recombination assays support basal epithelial cells as a cell of origin, whereas in vivo lineage-tracing studies in genetically-engineered mice implicate luminal cells. We describe how these results can be potentially reconciled by a conceptual distinction between cells of origin and cells of mutation, and outline how new experimental approaches can address the potential relationship between cell types of origin and disease outcome.

Loss of ATF3 promotes hormone-induced prostate carcinogenesis and the emergence of CK5(+)CK8(+) epithelial cells

Steroid sex hormones can induce prostate carcinogenesis, and are thought to contribute to the development of prostate cancer during aging. However, the mechanism for hormone-induced prostate carcinogenesis remains elusive. Here we report that activating transcription factor 3 (ATF3) – a broad stress sensor – suppressed hormone-induced prostate carcinogenesis in mice. While implantation of testosterone and estradiol (T+E₂) pellets for 2 months in wild-type mice rarely induced prostatic intraepithelial neoplasia (PIN) in dorsal prostates (1 out of 8 mice), loss of ATF3 led to the appearance of not only PIN but also invasive lesions in almost all examined animals. The enhanced carcinogenic effects of hormones on ATF3-deficient prostates did not appear to be caused by a change in estrogen signaling, but were more likely a consequence of elevated androgen signaling that stimulated differentiation of prostatic basal cells into transformation-preferable luminal cells. Indeed, we found that hormone-induced lesions in ATF3-knockout mice often contained cells with both basal and luminal characteristics, such as p63⁺ cells (a basal cell marker) showing luminal-like morphology, or cells double-stained with basal (CK5⁺) and luminal (CK8⁺) markers. Consistent with these findings, low ATF3 expression was found to be a poor prognostic marker for prostate cancer in a cohort of 245 patients. Our results thus support that ATF3 is a tumor suppressor in prostate cancer.

Cellular Mechanisms Underlying Intertumoral Heterogeneity

Intertumoral heterogeneity is driven by a combination of intrinsic and extrinsic mechanisms. Intrinsic mechanisms include the genetic/epigenetic mutational profile of cells and the nature of the 'cell of origin'. There is accumulating evidence that distinct 'cells of origin' within an organ can give rise to different subtypes of cancer. Tissue-specific stem and progenitor cells are the predominant targets exploited for tumor initiation. Extrinsic factors imposed by the microenvironment may also directly influence the cell of origin by eliciting dedifferentiation. Identification of these target cell populations is important for earlier diagnosis, the detection of premalignant clones during relapse, and the design of prevention therapies for high-risk cancer families. Here we review recent developments in deciphering the cellular origins of solid cancers.

Inflammation and prostate cancer: friends or foe?

INTRODUCTION

Prostate cancer is the most common non-cutaneous malignancy diagnosed in men. Moving from histological observations since a long time, it has been recognized that innate and adaptive immunity actively participates in the pathogenesis, surveillance, and progression of prostate cancer.

MATERIALS AND METHODS

A PubMed and Web of Science databases search was performed for studies providing evidence on the roles of the innate and adaptive immunity during the development and progression of prostate cancer.

CONCLUSIONS

There are growing evidences that chronic inflammation is involved in the regulation of cellular events in prostate carcinogenesis, including disruption of the immune response and regulation of the tumor microenvironment. This review discusses the role played by the innate and adaptive immune system in the local progression of prostate cancer, and the prognostic information that we can currently understand and exploit.

Different Growth Patterns of Canine Prostatic Carcinoma Suggests Different Models of Tumor-Initiating Cells

Controversies remain regarding the cell type from which human prostate cancer originates, and many attempts have been made to identify the cellular origin of canine prostate cancer but without definitive proof. This study aims to evaluate the expression of luminal (androgen receptor [AR], cytokeratin [CK]8/18) and basal (CK14, CK5) cell markers in different histologic subtypes of canine prostatic carcinoma (PC) and to suggest the most likely tumor-initiating cells. Normal prostates (n = 8) were characterized by AR+CK8/18+ luminal cells and few CK5+ basal cells, while CK14 was absent. Similar pattern was observed in all 35 prostates with benign prostatic hyperplasia, except few scattered CK14+ basal cells in 13 samples (37.14%). AR was localized in the nucleus of both normal and hyperplastic cells. In 34 samples of PC, the following growth patterns were identified: cribriform (44.12%), solid (32.35%), small acinar/ductal (20.59%), and micropapillary (2.94%). Most PCs expressed AR and CK8/18, while CK5 and CK14 expression was observed in 25% and 20% of cases, respectively. AR revealed a variable intracellular distribution, both nuclear and cytoplasmic. Solid PC was characterized by an undifferentiated or aberrant phenotype with a reduced expression of AR and CK8/18, increased number of CK14+ cells, and 7 antigen expression patterns. This study demonstrated a predominance of differentiated luminal cell types in canine prostatic tumors, although the role of basal cells in prostate carcinogenesis should also be considered. Moreover, few scattered CK5+ cells in AR+CK8/18+ tumors identified the existence of intermediate cells, from which neoplastic transformation may alternatively commence.

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.

Klf5 deletion promotes Pten deletion-initiated luminal-type mouse prostate tumors through multiple oncogenic signaling pathways

Krüppel-like factor 5 (KLF5) regulates multiple biologic processes. Its function in tumorigenesis appears contradictory though, showing both tumor suppressor and tumor promoting activities. In this study, we examined whether and how Klf5 functions in prostatic tumorigenesis using mice with prostate-specific deletion of Klf5 and phosphatase and tensin homolog (Pten), both of which are frequently inactivated in human prostate cancer. Histologic analysis demonstrated that when one Pten allele was deleted, which causes mouse prostatic intraepithelial neoplasia (mPIN), Klf5 deletion accelerated the emergence and progression of mPIN. When both Pten alleles were deleted, which causes prostate cancer, Klf5 deletion promoted tumor growth, increased cell proliferation, and caused more severe morphologic and molecular alterations. Homozygous deletion of Klf5 was more effective than hemizygous deletion. Unexpectedly, while Pten deletion alone expanded basal cell population in a tumor as reported, Klf5 deletion in the Pten-null background clearly reduced basal cell population while expanding luminal cell population. Global gene expression profiling, pathway analysis, and experimental validation indicate that multiple mechanisms could mediate the tumor-promoting effect of Klf5 deletion, including the up-regulation of epidermal growth factor and its downstream signaling molecules AKT and ERK and the inactivation of the p15 cell cycle inhibitor. KLF5 also appears to cooperate with several transcription factors, including CREB1, Sp1, Myc, ER and AR, to regulate gene expression. These findings validate the tumor suppressor function of KLF5. They also yield a mouse model that shares two common genetic alterations with human prostate cancer—mutation/deletion of Pten and deletion of Klf5.

Prostate epithelial stem and progenitor cells

The classic androgen ablation and replacement experiment demonstrates that prostate epithelia possess extensive regenerative capacities and implies the existence of the prostate stem/progenitor cells. These cells may serve as the cells of origin for prostate cancer and their intrinsic property may dictate the clinical behaviors of the resulting diseases. Therefore, detailed characterization of these cells will potentially benefit disease prevention, diagnosis and prognosis. In this review, we describe several major in vitro and in vivo approaches that have been employed in the studies of the prostate stem cell activities, summarize the major progress that has been made during the last two decades regarding the identity of prostate stem/progenitor cells and their niches, and discuss some remaining outstanding questions in the field.

Luminal cells are favored as the cell of origin for prostate cancer

The identification of cell types of origin for cancer has important implications for tumor stratification and personalized treatment. For prostate cancer, the cell of origin has been intensively studied, but it has remained unclear whether basal or luminal epithelial cells, or both, represent cells of origin under physiological conditions in vivo. Here, we use a novel lineage-tracing strategy to assess the cell of origin in a diverse range of mouse models, including Nkx3.1(+/-); Pten(+/-), Pten(+/-), Hi-Myc, and TRAMP mice, as well as a hormonal carcinogenesis model. Our results show that luminal cells are consistently the observed cell of origin for each model in situ; however, explanted basal cells from these mice can generate tumors in grafts. Consequently, we propose that luminal cells are favored as cells of origin in many contexts, whereas basal cells only give rise to tumors after differentiation into luminal cells.

Distinct phases of human prostate cancer initiation and progression can be driven by different cell-types

The cells that initiate and propagate cancer are important therapeutic targets. However, the progression from cells of origin to tumor-propagating cells is poorly defined for most human cancers. Mouse models indicate that both basal and luminal cells can initiate prostate cancer, while studies with human prostate tissue have demonstrated a role for basal cells in transformation. Our recent study provides evidence that a common cell of origin can produce alternative variants of human epithelial cancer. Our findings also reveal that the cell of origin that initiates cancer is not continuously required to maintain and propagate the disease. Importantly, the cells responsible for initiating human prostate cancer can have a distinct cellular phenotype from the cells needed to maintain it.

Cancer stem cells: constantly evolving and functionally heterogeneous therapeutic targets

Elucidating the origin of and dynamic interrelationship between intratumoral cell subpopulations has clear clinical significance in helping to understand the cellular basis of treatment response, therapeutic resistance, and tumor relapse. Cancer stem cells (CSC), together with clonal evolution driven by genetic alterations, generate cancer cell heterogeneity commonly observed in clinical samples. The 2013 Shanghai International Symposium on Cancer Stem Cells brought together leaders in the field to highlight the most recent progress in phenotyping, characterizing, and targeting CSCs and in elucidating the relationship between the cell-of-origin of cancer and CSCs. Discussions from the symposium emphasize the urgent need in developing novel therapeutics to target the constantly evolving CSCs.

Senescent remodeling of the innate and adaptive immune system in the elderly men with prostate cancer

Despite years of intensive investigation that has been made in understanding prostate cancer, it remains a major cause of death in men worldwide. Prostate cancer emerges from multiple alterations that induce changes in expression patterns of genes and proteins that function in networks controlling critical cellular events. Based on the exponential aging of the population and the increasing life expectancy in industrialized Western countries, prostate cancer in the elderly men is becoming a disease of increasing significance. Aging is a progressive degenerative process strictly integrated with inflammation. Several theories have been proposed that attempt to define the role of chronic inflammation in aging including redox stress, mitochondrial damage, immunosenescence, and epigenetic modifications. Here, we review the innate and adaptive immune systems and their senescent remodeling in elderly men with prostate cancer.

Beyond the androgen receptor: new approaches to treating metastatic prostate cancer. Report of the 2013 Prouts Neck Prostate Cancer Meeting

INTRODUCTION

The Prouts Neck Meetings on Prostate Cancer began in 1985 through the efforts of the Organ Systems Branch of the National Cancer Institute to stimulate new research and focused around specific questions in prostate tumorigenesis and therapy.

METHODS

These meetings were think tanks, composed of around 75 individuals, and divided equally between young investigators and senior investigators. Over the years, many new concepts related to prostate cancer resulted from these meetings and the prostate cancer community has sorely missed them since the last one in 2007.

RESULTS

We report here the first of a new series of meetings. The 2013 meeting focused on defining how the field of treatment for metastatic prostate cancer needs to evolve to impact survival and was entitled: "Beyond AR: New Approaches to Treating Metastatic Prostate Cancer." As castrate resistant prostate cancers escape second generation anti-androgen agents, three phenotypes/genotypes of CRPC appear to be increasing in prevalence and remain resistant to treatment: NeuroEndocrine Prostate Cancer, Persistent AR-Dependent Prostate Cancer, and Androgen Receptor Pathway Independent Prostate Cancer.

DISCUSSION

It is clear that new treatment paradigms need to be developed for this diverse group of diseases. The Prouts Neck 2013 Meeting on Prostate Cancer helped to frame the current state of the field and jumpstart ideas for new avenues of treatment.