Sca-1 expression identifies stem cells in the proximal region of prostatic ducts with high capacity to reconstitute prostatic tissue

JAK/STAT signaling maintains an intermediate cell population during prostate basal cell fate determination

Unipotent basal and luminal stem cells maintain prostate homeostasis, with an intermediate cell population emerging during prostate inflammation or cancer. However, the identities of basal stem cell and intermediate cell population remain unclear. Here we identified a rare intermediate cell population expressing luminal markers (termed Basal-B) with enhanced organoid formation capacity, and a larger basal population (termed Basal-A). Genetic lineage tracing revealed Basal-B cells represented a transient basal stem cell state during prostate homeostasis and androgen-mediated regeneration. Activated JAK/STAT signaling was identified in Basal-B cells, and its inhibition significantly reduced Basal-B markers expression. Inflammation increased Basal-B-to-luminal cell transdifferentiation, but JAK/STAT inhibition notably attenuated this effect. Pten gene deletion increased Nkx3.1-expressing Basal-B-like cell population and led to neoplasia. In humans, h-Basal-B cells were more prevalent in benign prostate hyperplasia. This study reveals the identities of intermediate Basal-B cells and underscores the role of JAK/STAT signaling in prostate cell fate determination.

Integrated single-cell analysis defines the epigenetic basis of castration-resistant prostate luminal cells

Understanding prostate response to castration and androgen receptor signaling inhibitors (ARSI) is critical to improving long-term prostate cancer (PCa) patient survival. Here, we use a multi-omics approach on 229,794 single cells to create a mouse single-cell reference atlas for interpreting mouse prostate biology and castration response. Our reference atlas refines single-cell annotations and provides a chromatin context, which, when coupled with mouse lineage tracing, demonstrates that castration-resistant luminal cells are distinct from the pre-existent urethra-proximal stem/progenitor cells. Molecular pathway analysis and therapeutic studies further implicate AP1 (JUN/FOS), WNT/β-catenin, FOXQ1, NF-κB, and JAK/STAT pathways as major drivers of castration-resistant luminal populations with relevance to human PCa. Our datasets, which can be explored through an interactive portal (https://visportal.roswellpark.org/data/tang/), can aid in developing combination treatments with ARSI for advanced PCa patients.

Cancer stem cell in prostate cancer progression, metastasis and therapy resistance

Prostate cancer (PCa) is the most diagnosed malignancy in the men worldwide. Cancer stem cells (CSCs) are the sub-population of cells present in the tumor which possess unique properties of self-renewal and multilineage differentiation thus thought to be major cause of therapy resistance, disease relapse, and mortality in several malignancies including PCa. CSCs have also been shown positive for the common stem cells markers such as ALDH EZH2, OCT4, SOX2, c-MYC, Nanog etc. Therefore, isolation and characterization of CSCs specific markers which may discriminate CSCs and normal stem cells are critical to selectively eliminate CSCs. Rapid advances in the field offers a theoretical explanation for many of the enduring uncertainties encompassing the etiology and an optimism for the identification of new stem-cell targets, development of reliable and efficient therapies in the future. The emerging reports have also provided unprecedented insights into CSCs plasticity, quiescence, renewal, and therapeutic response. In this review, we discuss the identification of PCa stem cells, their unique properties, stemness-driving pathways, new diagnostics, and therapeutic interventions.

Emerging organoid models to study the epididymis in male reproductive toxicology

The importance of the epididymis on sperm maturation and consequently male fertility has been well documented. The pseudostratified epithelium of the epididymis is comprised of multiple cell types, including principal cells, which are the most abundant, and basal cells. The role of basal cells has been unclear and has been a source of discussion in the literature. However, the recent demonstration that these cells are multipotent or adult stem cells has opened new areas of research in epididymal biology. One such avenue is to understand the regulation of these stem cells, and to exploit their properties to develop tools for toxicological studies to elucidate the effects of chemicals on cell differentiation and epididymal function in vitro. Studies in both rat and mouse have shown that purified single epididymal basal cells cultured under 3D conditions can proliferate and differentiate to form organoids, or mini organs. Furthermore, these epididymal basal stem cells can self-renew and differentiate into other epididymal cell types. It is known that during epididymal development, basal cells are derived from undifferentiated columnar cells, which have been reported to share common properties to stem cells. Like basal cells, these undifferentiated columnar cells can also form organoids under 3D culture conditions and can differentiate into basal, principal and clear cells. Organoids derived from either basal cells or columnar cells offer unique models for toxicology studies and represent an exciting and emerging approach to understand the epididymis.

Heterogeneity and complexity of the prostate epithelium: New findings from single-cell RNA sequencing studies

The recent advent of single-cell RNA-sequencing technology has provided new fundamental insights into the heterogeneity of the prostate epithelium. Several independent studies have described extensive heterogeneity of the luminal epithelial compartment, including a major division between a novel population of luminal cells located in the proximal region of the prostate ducts versus luminal cells located more distally. Proximal luminal cells as well as novel periurethral cells display increased progenitor potential in organoid culture and tissue reconstitution assays, but not in lineage-tracing analyses during prostate homeostasis, suggesting context-dependent plasticity of these populations. Here we describe and synthesize recent findings regarding the epithelial cell populations in the mouse prostate, draw comparisons to the human prostate, and address the relevance of these findings to prostate diseases and cancer.

Recent advances in tissue stem cells

Stem cells are undifferentiated cells capable of self-renewal and differentiation, giving rise to specialized functional cells. Stem cells are of pivotal importance for organ and tissue development, homeostasis, and injury and disease repair. Tissue-specific stem cells are a rare population residing in specific tissues and present powerful potential for regeneration when required. They are usually named based on the resident tissue, such as hematopoietic stem cells and germline stem cells. This review discusses the recent advances in stem cells of various tissues, including neural stem cells, muscle stem cells, liver progenitors, pancreatic islet stem/progenitor cells, intestinal stem cells, and prostate stem cells, and the future perspectives for tissue stem cell research.

Natural Products Targeting Cancer Stem Cells for Augmenting Cancer Therapeutics

Cancer stem cells (CSC) have been identified in several types of solid tumors. In some cases, CSC may be the source of all the tumor cells, the cause of the tumor's resistance to chemotherapeutic agents, and the source of metastatic cells. Thus, a combination therapy targeting non-CSC tumor cells as well as specifically targeting CSCs holds the potential to be highly effective. Natural products (NPs) have been a historically rich source of biologically active compounds and are known for their ability to influence multiple signaling pathways simultaneously with negligible side effects. In this review, we discuss the potential of NPs in targeting multiple signaling pathways in CSC and their potential to augment the efficacy of standard cancer therapy. Specifically, we focus on the anti-CSC activities of flavonoids, FDA-approved drugs originating from natural sources. Additionally, we emphasize the potential of NPs in targeting microRNA-mediated signaling, given the roles of microRNA in the maintenance of the CSC phenotype.

NEK2 plays an active role in Tumorigenesis and Tumor Microenvironment in Non-Small Cell Lung Cancer

Abnormal expression and dysfunction of Never-in-mitosis-A-related kinase 2 (NEK2) result in tumorigenesis. High levels of NEK2 are related to malignant progression, drug resistance, and poor prognosis. However, the relationship between NEK2 levels and the occurrence of non-small cell lung cancer (NSCLC) remains unknown. This study aimed to explore the impacts of NEK2 on the oncogenesis of NSCLC and the tumor microenvironment. Downregulation of NEK2 inhibited A549 and H1299 cell proliferation, migration, and invasion, blocking cell cycle at the G0/G1 phase. Loss of NEK2 inhibited the release of IL-10 from tumor cells, M2-like polarization of macrophages, angiogenesis, and vascular endothelial cell migration. Furthermore, NEK2 deficiency inhibited tumor growth in vivo. Taken together, NEK2 knockdown inhibited the occurrence and development of NSCLC, M2 polarization of macrophages, and angiogenesis. The abnormal expression of NEK2 might not only indicate tumor progression and patient prognosis but also serve as a potential molecular therapeutic target with great development prospects.

Aberrant CREB1 activation in prostate cancer disrupts normal prostate luminal cell differentiation

The molecular mechanisms of luminal cell differentiation are not understood well enough to determine how differentiation goes awry during oncogenesis. Using RNA-Seq analysis, we discovered that CREB1 plays a central role in maintaining new luminal cell survival and that oncogenesis dramatically changes the CREB1-induced transcriptome. CREB1 is active in luminal cells, but not basal cells. We identified ING4 and its E3 ligase, JFK, as CREB1 transcriptional targets in luminal cells. During luminal cell differentiation, transient induction of ING4 expression is followed by a peak in CREB1 activity, while JFK increases concomitantly with CREB1 activation. Transient expression of ING4 is required for luminal cell induction; however, failure to properly down-regulate ING4 leads to luminal cell death. Consequently, blocking CREB1 increased ING4 expression, suppressed JFK, and led to luminal cell death. Thus, CREB1 is responsible for the suppression of ING4 required for luminal cell survival and maintenance. Oncogenic transformation by suppressing PTEN resulted in constitutive activation of CREB1. However, the tumor cells could no longer fully differentiate into luminal cells, failed to express ING4, and displayed a unique CREB1 transcriptome. Blocking CREB1 in tumorigenic cells suppressed tumor growth in vivo, rescued ING4 expression, and restored luminal cell formation, but ultimately induced luminal cell death. IHC of primary prostate tumors demonstrated a strong correlation between loss of ING4 and loss of PTEN. This is the first study to define a molecular mechanism whereby oncogenic loss of PTEN, leading to aberrant CREB1 activation, suppresses ING4 expression causing disruption of luminal cell differentiation.

Exosomes and Cancer Stem Cells in Cancer Immunity: Current Reports and Future Directions

Cancer stem cells (CSCs), which have the capacity to self-renew and differentiate into various types of cells, are notorious for their roles in tumor initiation, metastasis, and therapy resistance. Thus, underlying mechanisms for their survival provide key insights into developing effective therapeutic strategies. A more recent focus has been on exosomes that play a role in transmitting information between CSCs and non-CSCs, resulting in activating CSCs for cancer progression and modulating their surrounding microenvironment. The field of CSC-derived exosomes (CSCEXs) for different types of cancer is still under exploration. A deeper understanding and further investigation into CSCEXs’ roles in tumorigenicity and the identification of novel exosomal components are necessary for engineering exosomes for the treatment of cancer. Here, we review the features of CSCEXs, including surface markers, cargo, and biological or physiological functions. Further, reports on the immunomodulatory effects of CSCEXs are summarized, and exosome engineering for CSC-targeting is also discussed.

Progenitors in prostate development and disease

The prostate develops by epithelial budding and branching processes that occur during fetal and postnatal stages. The adult prostate demonstrates remarkable regenerative capacity, with the ability to regrow to its original size over multiple cycles of castration and androgen administration. This capacity for controlled regeneration prompted the search for an androgen-independent epithelial progenitor in benign prostatic hyperplasia (BPH) and prostate cancer (PCa). BPH is hypothesized to be a reawakening of ductal branching, resulting in the formation of new proximal glands, all while androgen levels are decreasing in the aging male. Advanced prostate cancer can be slowed with androgen deprivation, but resistance eventually occurs, suggesting the existence of an androgen-independent progenitor. Recent studies indicate that there are multiple castration-insensitive epithelial cell types in the proximal area of the prostate, but not all act as progenitors during prostate development or regeneration. This review highlights how recent cellular and anatomical studies are changing our perspective on the identity of the prostate progenitor.

Olfactomedin 4 mediation of prostate stem/progenitor-like cell proliferation and differentiation via MYC

Olfactomedin 4 (OLFM4) is expressed in normal prostate epithelial cells and immortalized normal human prostate epithelial cells (RWPE1), but the identity of OLFM4-expressing cells within these populations and OLFM4's physiological functions in these cells have not been elucidated. Using single-cell RNA sequencing analysis, we found here that OLFM4 was expressed in multiple stem/progenitor-like cell populations in both the normal prostate epithelium and RWPE1 cells and was frequently co-expressed with KRT13 and LY6D in RWPE1 cells. Functionally, OLFM4-knockout RWPE1 cells exhibited enhanced proliferation of the stem/progenitor-like cell population, shifts stem/progenitor-like cell division to favor symmetric division and differentiated into higher levels PSA expression cells in organoid assays compared with OLFM4-wild RWPE1 cells. Bulk-cell RNA sequencing analysis pinpointed that cMYC expression were enhanced in the OLFM4-knockout RWPE1 cells compared with OLFM4-wild cells. Molecular and signaling pathway studies revealed an increase in the WNT/APC/MYC signaling pathway gene signature, as well as that of MYC target genes that regulate multiple biological processes, in OLFM4-knockout RWPE1 cells. These findings indicated that OLFM4 is co-expressed with multiple stem/progenitor cell marker genes in prostate epithelial cells and acts as a novel mediator in prostate stem/progenitor cell proliferation and differentiation.

RUNX1 marks a luminal castration-resistant lineage established at the onset of prostate development

The characterization of prostate epithelial hierarchy and lineage heterogeneity is critical to understand its regenerative properties and malignancies. Here, we report that the transcription factor RUNX1 marks a specific subpopulation of proximal luminal cells (PLCs), enriched in the periurethral region of the developing and adult mouse prostate, and distinct from the previously identified NKX3.1+ luminal castration-resistant cells. Using scRNA-seq profiling and genetic lineage tracing, we show that RUNX1+ PLCs are unaffected by androgen deprivation, and do not contribute to the regeneration of the distal luminal compartments. Furthermore, we demonstrate that a transcriptionally similar RUNX1+ population emerges at the onset of embryonic prostate specification to populate the proximal region of the ducts. Collectively, our results reveal that RUNX1+ PLCs is an intrinsic castration-resistant and self-sustained lineage that emerges early during prostate development and provide new insights into the lineage relationships of the prostate epithelium.

A single-cell atlas of the mouse and human prostate reveals heterogeneity and conservation of epithelial progenitors

Understanding the cellular constituents of the prostate is essential for identifying the cell of origin for prostate adenocarcinoma. Here, we describe a comprehensive single-cell atlas of the adult mouse prostate epithelium, which displays extensive heterogeneity. We observe distal lobe-specific luminal epithelial populations (LumA, LumD, LumL, and LumV), a proximally enriched luminal population (LumP) that is not lobe-specific, and a periurethral population (PrU) that shares both basal and luminal features. Functional analyses suggest that LumP and PrU cells have multipotent progenitor activity in organoid formation and tissue reconstitution assays. Furthermore, we show that mouse distal and proximal luminal cells are most similar to human acinar and ductal populations, that a PrU-like population is conserved between species, and that the mouse lateral prostate is most similar to the human peripheral zone. Our findings elucidate new prostate epithelial progenitors, and help resolve long-standing questions about anatomical relationships between the mouse and human prostate.

Single-cell transcriptomics identifies a distinct luminal progenitor cell type in distal prostate invagination tips

The identification of prostate stem/progenitor cells and characterization of the prostate epithelial cell lineage hierarchy are critical for understanding prostate cancer initiation. Here, we characterized 35,129 cells from mouse prostates, and identified a unique luminal cell type (termed type C luminal cell (Luminal-C)) marked by Tacstd2, Ck4 and Psca expression. Luminal-C cells located at the distal prostate invagination tips (termed Dist-Luminal-C) exhibited greater capacity for organoid formation in vitro and prostate epithelial duct regeneration in vivo. Lineage tracing of Luminal-C cells indicated that Dist-Luminal-C cells reconstituted distal prostate luminal lineages through self-renewal and differentiation. Deletion of Pten in Dist-Luminal-C cells resulted in prostatic intraepithelial neoplasia. We further characterized 11,374 human prostate cells and confirmed the existence of h-Luminal-C cells. Our study provides insights into the prostate lineage hierarchy, identifies Dist-Luminal-C cells as the luminal progenitor cell population in invagination tips and suggests one of the potential cellular origins of prostate cancer.

Urethral luminal epithelia are castration-insensitive cells of the proximal prostate

BACKGROUND

Castration-insensitive epithelial progenitors capable of regenerating the prostate have been proposed to be concentrated in the proximal region based on facultative assays. Functional characterization of prostate epithelial populations isolated with individual cell surface markers has failed to provide a consensus on the anatomical and transcriptional identity of proximal prostate progenitors.

METHODS

Here, we use single-cell RNA sequencing to obtain a complete transcriptomic profile of all epithelial cells in the mouse prostate and urethra to objectively identify cellular subtypes. Pan-transcriptomic comparison to human prostate cell types identified a mouse equivalent of human urethral luminal cells, which highly expressed putative prostate progenitor markers. Validation of the urethral luminal cell cluster was performed using immunostaining and flow cytometry.

RESULTS

Our data reveal that previously identified facultative progenitors marked by Trop2, Sca-1, KRT4, and PSCA are actually luminal epithelial cells of the urethra that extend into the proximal region of the prostate, and are resistant to castration-induced androgen deprivation. Mouse urethral luminal cells were identified to be the equivalent of previously identified human club and hillock cells that similarly extend into proximal prostate ducts. Benign prostatic hyperplasia (BPH) has long been considered an "embryonic reawakening," but the cellular origin of the hyperplastic growth concentrated in the periurethral region is unclear. We demonstrate an increase in urethral luminal cells within glandular nodules from BPH patients. Urethral luminal cells are further increased in patients treated with a 5-α reductase inhibitor.

CONCLUSIONS

Our data demonstrate that cells of the proximal prostate that express putative progenitor markers, and are enriched by castration in the proximal prostate, are urethral luminal cells and that these cells may play an important role in the etiology of human BPH.

The regulatory pathways leading to stem-like cells underlie prostate cancer progression

Prostate cancer (PCa) is the most common cause of malignancy in males and the third leading cause of cancer mortality in the United States. The standard care for primary PCa with local invasive disease mainly is surgery and radiation. For patients with distant metastases, androgen deprivation therapy (ADT) is a gold standard. Regardless of a favorable outcome of ADT, patients inevitably relapse to an end-stage castration-resistant prostate cancer (CRPC) leading to mortality. Therefore, revealing the mechanism and identifying cellular components driving aggressive PCa is critical for prognosis and therapeutic intervention. Cancer stem cell (CSC) phenotypes characterized as poor differentiation, cancer initiation with self-renewal capabilities, and therapeutic resistance are proposed to contribute to the onset of CRPC. In this review, we discuss the role of CSC in CRPC with the evidence of CSC phenotypes and the possible underlying mechanisms.

KLF4, A Gene Regulating Prostate Stem Cell Homeostasis, Is a Barrier to Malignant Progression and Predictor of Good Prognosis in Prostate Cancer

There is a considerable need to identify those individuals with prostate cancer who have indolent disease. We propose that genes that control adult stem cell homeostasis in organs with slow turnover, such as the prostate, control cancer fate. One such gene, KLF4, overexpressed in murine prostate stem cells, regulates their homeostasis, blocks malignant transformation, and controls the self-renewal of tumor-initiating cells. KLF4 loss induces the molecular features of aggressive cancer and converts PIN lesions to invasive sarcomatoid carcinomas; its re-expression in vivo reverses this process. Bioinformatic analysis links these changes to human cancer. KLF4 and its downstream targets make up a gene signature that identifies indolent tumors and predicts recurrence-free survival. This approach may improve prognosis and identify therapeutic targets for advanced cancer.

Available criteria for segregating prostate cancer patients into those requiring therapeutic intervention and those who can be followed are inadequate. Xiong et al. show that KLF4 and its downstream targets make up a gene signature that identifies indolent tumors. This approach may improve prognosis and identify therapeutic targets for advanced cancer.

Tumor Dormancy and Slow-Cycling Cancer Cells

Cancer cell heterogeneity is a universal feature of human tumors and represents a significant barrier to the efficacy and duration of anticancer therapies, especially targeted therapeutics. Among the heterogeneous cancer cell populations is a subpopulation of relatively quiescent cancer cells, which are in the G0/G1 cell-cycle phase and refractory to anti-mitotic drugs that target proliferative cells. These slow-cycling cells (SCCs) preexist in untreated tumors and frequently become enriched in treatment-failed tumors, raising the possibility that these cells may mediate therapy resistance and tumor relapse. Here we review several general concepts on tumor cell heterogeneity, quiescence, and tumor dormancy. We discuss the potential relationship between SCCs and cancer stem cells (CSCs). We also present our current understanding of how SCCs and cancer dormancy might be regulated. Increasing knowledge of SCCs and tumor dormancy should lead to identification of novel molecular regulators and therapeutic targets of tumor relapse, residual diseases, and metastasis.

Smooth Muscle Differentiation of Penile Stem/Progenitor Cells Induced by Microenergy Acoustic Pulses In Vitro

INTRODUCTION

Modulating tissue-resident stem and progenitor cells with a non-invasive, mechanobiological intervention is an optimal approach for tissue regeneration. Stem cell antigen-1 (Sca-1) has been identified as a stem cell marker within many organs but never within the penis.

AIM

To localize and isolate penile stem/progenitor cells (PSPCs) and to evaluate cellular differentiation after exposure to induction medium and microenergy acoustic pulse (MAP) therapy.

METHODS

Six male Sprague-Dawley rats were used to isolate PSPCs. Isolation was followed by stem cell characterization and differentiation assays. The PSPCs were then treated with MAP (0.033 mJ/mm², 1 Hz) at various dosages (25, 50, 100, and 200 pulses) and for different durations (1, 2, 4, 6, or 8 hours) in vitro.

MAIN OUTCOME MEASURE

The PSPCs (Sca-1-positive cells) were isolated using the magnetic-activated cell sorting system. PSPC cellular differentiation was assessed after induction with induction medium and with MAP in vitro. Wnt/β-catenin signaling was also assayed.

RESULTS

The PSPCs were successfully localized within the penile subtunic and perisinusoidal spaces, and they were successfully isolated using magnetic-activated cell sorting. The stemness of the cells was confirmed by stem cell marker characterization and by multiple differentiation into smooth muscle cells, endothelial cells, adipocytes, and neurons. MAP-induced PSPCs differentiated into smooth muscle cells by activating the Wnt/β-catenin signaling pathway in a time- and dosage-dependent manner.

CLINICAL IMPLICATIONS

By modulating resident PSPCs, MAP may have utility in the treatment of erectile dysfunction (ED).

STRENGTHS & LIMITATIONS

This study provides solid evidence in support of microenergy therapies, including both MAP and low-intensity extracorporeal shock wave therapy, for the treatment of ED. Additional studies are needed and should include additional stem cells markers. Furthermore, studies exploring the underling mechanisms for PSPC activation and differentiation are required.

CONCLUSION

PSPCs were successfully identified, localized, and isolated. Additionally, MAP provoked PSPCs to differentiate into smooth muscle cells via the Wnt/β-catenin signaling pathway. As such, MAP provides a novel method for activating endogenous tissue-resident stem/progenitor cells and might facilitate stem cell regenerative therapy targeting ED. Peng D, Yuan H, Liu T, et al. Smooth Muscle Differentiation of Penile Stem/Progenitor Cells Induced by Microenergy Acoustic Pulses In Vitro. J Sex Med 2019; 16:1874-1884.

Prostate Stem Cells and Cancer Stem Cells

Stem/progenitor cells play central roles in processes of organogenesis and tissue maintenance, whereas cancer stem cells (CSCs) are thought to drive tumor malignancy. Here, we review recent progress in the identification and analysis of normal prostate stem/progenitor cells as well as putative CSCs in both genetically engineered mouse models as well as in human tissue. We also discuss studies that have investigated the cell type of origin for prostate cancer. In addition, we provide a critical assessment of methodologies used in stem cell analyses and outline directions for future research.

Tissue regeneration and the epididymal stem cell

BACKGROUND

In most pseudostratified epithelia, basal cells represent a multipotent adult stem cell population. These cells generally remain in a quiescent state, until they are stimulated to respond to tissue damage by initiating epithelial regeneration. In the epididymis, cell proliferation occurs at a relatively slow rate under normal physiological conditions. Epididymal basal cells have been shown to share common properties with multipotent adult stem cells. The development of organoids from stem cells represents a novel approach for understanding cellular differentiation and characterization of stem cells.

OBJECTIVE

To review the literature on tissue regeneration in the epididymis and demonstrate the presence of an epididymal stem cell population.

METHODS

PubMed database was searched for studies reporting on cell proliferation, regeneration, and stem cells in the epididymis. Three-dimensional cell culture of epididymal cells was used to determine whether these can develop into organoids in a similar fashion to stem cells from other tissues.

RESULTS

The epididymal epithelium can rapidly regenerate following orchidectomy or efferent duct ligation, in order to maintain epithelial integrity. Studies have isolated a highly purified fraction of rat epididymal basal cells and reported that these cells displayed properties similar to those of multipotent adult stem cells. In two-dimensional cell culture conditions, these cells differentiated into cells which expressed connexin 26, a marker of columnar cells, and cytokeratin 8. Furthermore, three-dimensional cell culture of epididymal cells resulted in the formation of organoids, a phenomenon associated with the proliferation and differentiation of stem cells in vitro.

CONCLUSIONS

The rapid proliferation and tissue regeneration of the epididymal epithelium to preserve its integrity following tissue damage as well as the ability of cells to differentiate into organoids in vitro support the notion of a resident progenitor/stem cell population in the adult epididymis.

Spatially Restricted Stromal Wnt Signaling Restrains Prostate Epithelial Progenitor Growth through Direct and Indirect Mechanisms

Cell-autonomous Wnt signaling has well-characterized functions in controlling stem cell activity, including in the prostate. While niche cells secrete Wnt ligands, the effects of Wnt signaling in niche cells per se are less understood. Here, we show that stromal cells in the proximal prostatic duct near the urethra, a mouse prostate stem cell niche, not only produce multiple Wnt ligands but also exhibit strong Wnt/β-catenin activity. The non-canonical Wnt ligand Wnt5a, secreted by proximal stromal cells, directly inhibits proliefration of prostate epithelial stem or progenitor cells whereas stromal cell-autonomous canonical Wnt/β-catenin signaling indirectly suppresses prostate stem or progenitor activity via the transforming growth factor β (TGFβ) pathway. Collectively, these pathways restrain the proliferative potential of epithelial cells in the proximal prostatic ducts. Human prostate likewise exhibits spatially restricted distribution of stromal Wnt/β-catenin activity, suggesting a conserved mechanism for tissue patterning. Thus, this study shows how distinct stromal signaling mechanisms within the prostate cooperate to regulate tissue homeostasis.

The Contributions of Prostate Cancer Stem Cells in Prostate Cancer Initiation and Metastasis

Research in the last decade has clearly revealed a critical role of prostate cancer stem cells (PCSCs) in prostate cancer (PC). Prostate stem cells (PSCs) reside in both basal and luminal layers, and are the target cells of oncogenic transformation, suggesting a role of PCSCs in PC initiation. Mutations in PTEN, TP53, and RB1 commonly occur in PC, particularly in metastasis and castration-resistant PC. The loss of PTEN together with Ras activation induces partial epithelial–mesenchymal transition (EMT), which is a major mechanism that confers plasticity to cancer stem cells (CSCs) and PCSCs, which contributes to metastasis. While PTEN inactivation leads to PC, it is not sufficient for metastasis, the loss of PTEN concurrently with the inactivation of both TP53 and RB1 empower lineage plasticity in PC cells, which substantially promotes PC metastasis and the conversion to PC adenocarcinoma to neuroendocrine PC (NEPC), demonstrating the essential function of TP53 and RB1 in the suppression of PCSCs. TP53 and RB1 suppress lineage plasticity through the inhibition of SOX2 expression. In this review, we will discuss the current evidence supporting a major role of PCSCs in PC initiation and metastasis, as well as the underlying mechanisms regulating PCSCs. These discussions will be developed along with the cancer stem cell (CSC) knowledge in other cancer types.

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.

Sphere-Formation Assay: Three-Dimensional in vitro Culturing of Prostate Cancer Stem/Progenitor Sphere-Forming Cells

Cancer Stem Cells (CSCs) are a sub-population of cells, identified in most tumors, responsible for the initiation, recurrence, metastatic potential, and resistance of different malignancies. In prostate cancer (PCa), CSCs were identified and thought to be responsible for the generation of the lethal subtype, commonly known as Castration-Resistant Prostate Cancer (CRPC). In vitro models to investigate the properties of CSCs in PCa are highly required. Sphere-formation assay is an in vitro method commonly used to identify CSCs and study their properties. Here, we report the detailed methodology on how to generate and propagate spheres from PCa cell lines and from murine prostate tissue. This model is based on the ability of stem cells to grow in non-adherent serum-free gel matrix. We also describe how to use these spheres in histological and immuno-fluorescent staining assays to assess the differentiation potential of the CSCs. Our results show the sphere-formation Assay (SFA) as a reliable in vitro assay to assess the presence and self-renewal ability of CSCs in different PCa models. This platform presents a useful tool to evaluate the effect of conventional or novel agents on the initiation and self-renewing properties of different tumors. The effects can be directly evaluated through assessment of the sphere-forming efficiency (SFE) over five generations or other downstream assays such as immuno-histochemical analysis of the generated spheres.

EMT, stemness and tumor plasticity in aggressive variant neuroendocrine prostate cancers

Neuroendocrine/Aggressive Variant Prostate Cancers are lethal variants of the disease, with an aggressive clinical course and very short responses to conventional therapy. The age-adjusted incidence rate for this tumor sub-type has steadily increased over the past 20 years in the United States, with no reduction in the associated mortality rate. The molecular networks fueling its emergence and sustenance are still obscure; however, many factors have been associated with the onset and progression of neuroendocrine differentiation in clinically typical adenocarcinomas including loss of androgen-receptor expression and/or signaling, conventional therapy, and dysregulated cytokine function. "Tumor-plasticity" and the ability to dedifferentiate into alternate cell lineages are central to this process. Epithelial-to-mesenchymal (EMT) signaling pathways are major promoters of stem-cell properties in prostate tumor cells. In this review, we examine the contributions of EMT-induced cellular-plasticity and stem-cell signaling pathways to the progression of Neuroendocrine/Aggressive Variant Prostate Cancers in the light of potential therapeutic opportunities.

Monoamine Oxidase Deficiency Causes Prostate Atrophy and Reduces Prostate Progenitor Cell Activity

Monoamine oxidases (MAOs) degrade a number of biogenic and dietary amines, including monoamine neurotransmitters, and play an essential role in many biological processes. Neurotransmitters and related neural events have been shown to participate in the development, differentiation, and maintenance of diverse tissues and organs by regulating the specialized cellular function and morphological structures of innervated organs such as the prostate. Here we show that mice lacking both MAO isoforms, MAOA and MAOB, exhibit smaller prostate mass and develop epithelial atrophy in the ventral and dorsolateral prostates. The cellular composition of prostate epithelium showed reduced CK5⁺ or p63⁺ basal cells, accompanied by lower Sca-1 expression in p63⁺ basal cells, but intact differentiated CK8⁺ luminal cells in MAOA/B-deficient mouse prostates. MAOA/B ablation also decreased epithelial cell proliferation without affecting cell apoptosis in mouse prostates. Using a human prostate epithelial cell line, we found that stable knockdown of MAOA and MAOB impaired the capacity of prostate stem cells to form spheres, coinciding with a reduced CD133⁺ /CD44⁺ /CD24^- stem cell population and less expression of CK5 and select stem cell markers, including ALDH1A1, TROP2, and CD166. Alternative pharmacological inhibition of MAOs also repressed prostate cell stemness. In addition, we found elevated expression of MAOA and MAOB in epithelial and/or stromal components of human prostate hyperplasia samples compared with normal prostate tissues. Taken together, our findings reveal critical roles for MAOs in the regulation of prostate basal progenitor cells and prostate maintenance. Stem Cells 2018;36:1249-1258.

s-SHIP expression identifies a subset of murine basal prostate cells as neonatal stem cells

Isolation of prostate stem cells (PSCs) is crucial for understanding their biology during normal development and tumorigenesis. In this aim, we used a transgenic mouse model expressing GFP from the stem cell-specific s-SHIP promoter to mark putative stem cells during postnatal prostate development. Here we show that cells identified by GFP expression are present transiently during early prostate development and localize to the basal cell layer of the epithelium. These prostate GFP+ cells are a subpopulation of the Lin- CD24+ Sca-1+ CD49f+ cells and are capable of self-renewal together with enhanced growth potential in sphere-forming assay in vitro, a phenotype consistent with that of a PSC population. Transplantation assays of prostate GFP+ cells demonstrate reconstitution of prostate ducts containing both basal and luminal cells in renal grafts. Altogether, these results demonstrate that s-SHIP promoter expression is a new marker for neonatal basal prostate cells exhibiting stem cell properties that enables PSCs in situ identification and isolation via a single consistent parameter. Transcriptional profiling of these GFP+ neonatal stem cells showed an increased expression of several components of the Wnt signaling pathway. It also identified stem cell regulators with potential applications for further analyses of normal and cancer stem cells.

Linneg Sca-1high CD49fhigh prostate cancer cells derived from the Hi-Myc mouse model are tumor-initiating cells with basal-epithelial characteristics and differentiation potential in vitro and in vivo

A cell line was established from ventral prostate (VP) tumors of one-year-old Hi-Myc mice. These cells, called HMVP2 cells, are Lin^negSca-1^highCD49f^high with high CD44 and CD29 expression and express CK14, Sca-1 and CD49f (but not CK8), suggesting basal-epithelial characteristics. Furthermore, HMVP2 cells form spheroids and both the cells and spheroids produce tumors in syngeneic mice. After four days of culture, HMVP2 spheroids underwent a gradual transition from Lin^negSca-1^highCD49f^high expression to Lin^negSca-1^lowCD49f^low while a subpopulation of the cells retained the original Lin^negSca-1^highCD49f^high expression pattern. Additional cell subpopulations expressing Lin positive markers were also present suggesting further differentiation of HMVP2 spheroids. Two additional highly tumorigenic cell lines (HMVP2A1 and HMVP2A2) were isolated from HMVP2 cells after subsequent tumor formation in FVB/N mice. Concurrently, we also established cell lines from the VP of 6 months old Hi-Myc mice (named as HMVP1) and FVB/N mice (called NMVP) having less aggressive growth properties compared to the other three cell lines. AR expression was reduced in HMVP2 cells compared to NMVP and HMVP1 cells and almost absent in HMVP2A1 and HMVP2A2 cells. These cell lines will provide valuable tools for further mechanistic studies as well as preclinical studies to evaluate preventive and/or therapeutic agents for prostate cancer.

Histone 2B-GFP Label-Retaining Prostate Luminal Cells Possess Progenitor Cell Properties and Are Intrinsically Resistant to Castration

The existence of slow-cycling luminal cells in the prostate has been suggested, but their identity and functional properties remain unknown. Using a bigenic mouse model to earmark, isolate, and characterize the quiescent stem-like cells, we identify a label-retaining cell (LRC) population in the luminal cell layer as luminal progenitors. Molecular and biological characterizations show that these luminal LRCs are significantly enriched in the mouse proximal prostate, exhibit relative dormancy, display bipotency in both in vitro and in vivo assays, and express a stem/progenitor gene signature with resemblance to aggressive prostate cancer. Importantly, these LRCs, compared with bulk luminal cells, maintain a lower level of androgen receptor (AR) expression and are less androgen dependent and also castration resistant in vivo. Finally, analysis of phenotypic markers reveals heterogeneity within the luminal progenitor cell pool. Our study establishes luminal LRCs as progenitors that may serve as a cellular origin for castration-resistant prostate cancer.

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A bigenic mouse model to study prostatic slow-cycling luminal epithelial cells

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Prostate label-retaining cells (LRCs) exhibit stem/progenitor cell activities

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Luminal LRCs are developmentally bipotent and display a progenitor gene signature

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Luminal LRCs resist castration and molecularly resemble aggressive prostate cancer

Stem Cell Pathology

Rapid advances in stem cell biology and regenerative medicine have opened new opportunities for better understanding disease pathogenesis and the development of new diagnostic, prognostic, and treatment approaches. Many stem cell niches are well defined anatomically, thereby allowing their routine pathological evaluation during disease initiation and progression. Evaluation of the consequences of genetic manipulations in stem cells and investigation of the roles of stem cells in regenerative medicine and pathogenesis of various diseases such as cancer require significant expertise in pathology for accurate interpretation of novel findings. Therefore, there is an urgent need for developing stem cell pathology as a discipline to facilitate stem cell research and regenerative medicine. This review provides examples of anatomically defined niches suitable for evaluation by diagnostic pathologists, describes neoplastic lesions associated with them, and discusses further directions of stem cell pathology.

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 Adaptability of Somatic Stem Cells: A Review

Cell and tissue specific somatic stem cells develop as dynamic populations of precursor cells to discrete tissue and organ differentiation during embryonic and fetal stages and their potential evolves with development. Some of their progeny are sequestered into separate cell niches of tissues as adult somatic stem cells at various times during organ development and differentiation These are diverse cell populations of stem and progenitor cells that respond to homeostatic needs for cell and tissue maintenance and the cycling of differentiated cells for physiological/ endocrinological changes. Nominally, multipotent stem cells in one or more niches follow specific lineages of differentiation that can be followed by diverse markers of differentiation. The activation of precursors appears to be stochastic and results in a population of heterogeneous progenitor cells. When variations in the functional need of the tissue or organ occurs, the progenitor cells exhibit flexibility in their differentiation capacity. Regulation of the progenitors is the result of signals from the stem cell niche that can cause adaptive changes in the behavior or function of the stem -progenitor cell lineage. A possible mechanism may be alteration in the differentiation capacity of the resident or introduced cells. Certain quiescent stem cells also serve as a potential cell reservoir for trauma induced cell regeneration through adaptive changes in differentiation of stem cells, progenitor cells and differentiated cells. If the stem-progenitor cell population is normally depleted or destroyed by trauma, differentiated cells from the niche microenvironment can restore the specific stem potency which suggests the process of dedifferentiation.

An Adult Mouse Thyroid Side Population Cell Line that Exhibits Enriched Epithelial-Mesenchymal Transition

BACKGROUND

Studies of thyroid stem/progenitor cells have been hampered due to the small organ size and lack of tissue, which limits the yield of these cells. A continuous source that allows the study and characterization of thyroid stem/progenitor cells is desired to push the field forward.

METHOD

A cell line was established from Hoechst-resistant side population cells derived from mouse thyroid that were previously shown to contain stem/progenitor-like cells. Characterization of these cells were carried out by using in vitro two- and three-dimensional cultures and in vivo reconstitution of mice after orthotopic or intravenous injection, in conjunction with quantitative reverse transcription polymerase chain reaction, Western blotting, immunohisto(cyto)chemistry/immunofluorescence, and RNA seq analysis.

RESULTS

These cells were named SPTL (side population cell-derived thyroid cell line). Under low serum culturing conditions, SPTL cells expressed the thyroid differentiation marker NKX2-1, a transcription factor critical for thyroid differentiation and function, while no expression of other thyroid differentiation marker genes were observed. SPTL cells formed follicle-like structures in Matrigel^® cultures, which did not express thyroid differentiation marker genes. In mouse models of orthotopic and intravenous injection, the latter following partial thyroidectomy, a few SPTL cells were found in part of the follicles, most of which expressed NKX2-1. SPTL cells highly express genes involved in epithelial-mesenchymal transition, as demonstrated by RNA seq analysis, and exhibit a gene-expression pattern similar to anaplastic thyroid carcinoma.

CONCLUSION

These results demonstrate that SPTL cells have the capacity to differentiate into thyroid to a limited degree. SPTL cells may provide an excellent tool to study stem cells, including cancer stem cells of the thyroid.

Young Bone-Marrow Sca-1+ Stem Cells Rejuvenate the Aged Heart and Improve Function after Injury through PDGFRβ-Akt pathway

Bone marrow (BM) reconstitution with young BM cells in aged recipients restores the functionality of cardiac resident BM-derived progenitors. This study investigated the cell type primarily responsible for this effect. We reconstituted old mice with BM cells from young or old mice and found that the number of stem cell antigen 1 (Sca-1) cells homing to the heart was significantly greater in young than old chimeras. We then reconstituted old mice with young BM Sca-1⁺ or Sca-1⁻ cells. We found that Sca-1 cells repopulated the recipient BM and homed to the heart. The number of BM-derived cells in the aged myocardium co-expressing PDGFRβ was 3 times greater in Sca-1⁺ than Sca-1⁻ chimeric mice. Sca-1⁺ chimeras had more active cell proliferation in the infarcted heart and improved ventricular function after MI. The improved regeneration involved activation of the PDGFRβ/Akt/p27^Kip1 pathway. Sca-1⁺ stem cells rejuvenated cardiac tissue in aged mice. Restoration of the Sca-1⁺ subset of stem cells by BM reconstitution improved cardiac tissue regeneration after injury in aged mice.

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

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

SCA-1 Labels a Subset of Estrogen-Responsive Bipotential Repopulating Cells within the CD24+ CD49fhi Mammary Stem Cell-Enriched Compartment

Estrogen stimulates breast development during puberty and mammary tumors in adulthood through estrogen receptor-α (ERα). These effects are proposed to occur via ERα⁺ luminal cells and not the mammary stem cells (MaSCs) that are ERα^neg. Since ERα⁺ luminal cells express stem cell antigen-1 (SCA-1), we sought to determine if SCA-1 could define an ERα⁺ subset of EpCAM⁺/CD24⁺/CD49f^hi MaSCs. We show that the MaSC population has a distinct SCA-1⁺ population that is abundant in pre-pubertal mammary glands. The SCA-1⁺ MaSCs have less stem cell markers and less in vivo repopulating activity than their SCA-1^neg counterparts. However, they express ERα and specifically enter the cell cycle at puberty. Using estrogen-deficient aromatase knockouts (ArKO), we showed that the SCA-1⁺ MaSC could be directly modulated by estrogen supplementation. Thus, SCA-1 enriches for an ERα⁺, estrogen-sensitive subpopulation within the CD24⁺/CD49f^hi MaSC population that may be responsible for the hormonal sensitivity of the developing mammary gland.

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SCA-1⁺ delineates ER-positive cells in the CD24⁺ CD49f^hi mammary stem population

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SCA-1⁺ cells have lower repopulation activity

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SCA-1⁺ cells are estrogen responsive

Inducible Mouse Models for Cancer Drug Target Validation

Genetically-engineered mouse (GEM) models have provided significant contributions to our understanding of cancer biology and developing anticancer therapeutic strategies. The development of GEM models that faithfully recapitulate histopathological and clinical features of human cancers is one of the most pressing needs to successfully conquer cancer. In particular, doxycycline-inducible transgenic mouse models allow us to regulate (induce or suppress) the expression of a specific gene of interest within a specific tissue in a temporal manner. Leveraging this mouse model system, we can determine whether the transgene expression is required for tumor maintenance, thereby validating the transgene product as a target for anticancer drug development (target validation study). In addition, there is always a risk of tumor recurrence with cancer therapy. By analyzing recurrent tumors derived from fully regressed tumors after turning off transgene expression in tumor-bearing mice, we can gain an insight into the molecular basis of how tumor cells escape from their dependence on the transgene (tumor recurrence study). Results from such studies will ultimately allow us to predict therapeutic responses in clinical settings and develop new therapeutic strategies against recurrent tumors. The aim of this review is to highlight the significance of doxycycline-inducible transgenic mouse models in studying target validation and tumor recurrence.

Keratin 13 Is Enriched in Prostate Tubule-Initiating Cells and May Identify Primary Prostate Tumors that Metastasize to the Bone

Background

Benign human prostate tubule-initiating cells (TIC) and aggressive prostate cancer display common traits, including tolerance of low androgen levels, resistance to apoptosis, and microenvironment interactions that drive epithelial budding and outgrowth. TIC can be distinguished from epithelial and stromal cells that comprise prostate tissue via cell sorting based upon Epcam, CD44, and CD49f antigenic profiles. Fetal prostate epithelial cells (FC) possess a similar antigenic profile to adult TIC and are capable of inducing tubule formation. To identify the TIC niche in human prostate tissue, differential keratin (KRT) expression was evaluated.

Results

Gene expression data generated from Affymetrix Gene Chip human U133 Plus 2.0 array of sorted adult and fetal epithelial cells revealed KRT13 to be significantly enriched in FC and TIC compared to basal cells (BC) and luminal cells (LC) (p<0.001). Enriched KRT13 expression was confirmed by RT-PCR and cytospin immunostaining. Immunohistochemical analysis of KRT13 expression revealed rare KRT13⁺ epithelia throughout prostatic ducts/acini in adult tissue specimens and differentiated tubules in 24-week recombinant grafts, In contrast, abundant KRT13 expression was observed in developing ducts/acini in fetal prostate and cord-like structures composing 8-week recombinant grafts. Immunostaining of a prostate tissue microarray revealed KRT13⁺ tumor foci in approximately 9% of cases, and this subset displayed significantly shorter time to recurrence (p = 0.031), metastases (p = 0.032), and decreased overall survival (p = 0.004). Diagnostic prostate needle biopsies (PNBX) from untreated patients with concurrent bone metastases (clinical stage M1) displayed KRT13⁺ tumor foci, as did bone metastatic foci.

Conclusions

The expression profile of KRT13 in benign fetal and adult prostate tissue and in recombinant grafts, as well as the frequency of KRT13 expression in primary and metastatic prostate cancer indicates that it may be a marker of a stem/progenitor-like cell state that is co-opted in aggressive tumor cells. KRT13 is enriched in benign stem-like cells that display androgen-resistance, apoptosis-resistance, and branching morphogenesis properties. Collectively our data demonstrate that KRT13 expression is associated with poor prognosis at multiple stages of disease progression and may represent an important biomarker of adverse outcome in patients with prostate cancer.

Bmi1 marks distinct castration-resistant luminal progenitor cells competent for prostate regeneration and tumour initiation

Identification of defined cell populations with stem/progenitor properties is key for understanding prostate development and tumorigenesis. Here we show that the polycomb repressor protein Bmi1 marks a population of castration-resistant luminal epithelial cells enriched in the mouse proximal prostate. We employ lineage tracing to show that these castration-resistant Bmi1-expressing cells (or CARBs) are capable of tissue regeneration and self-renewal. Notably, CARBs are distinct from the previously described luminal castration-resistant Nkx3.1-expressing cells (CARNs). CARBs can serve as a prostate cancer cell-of-origin upon Pten deletion, yielding luminal prostate tumours. Clonal analysis using the R26R-confetti allele indicates preferential tumour initiation from CARBs localized to the proximal prostate. These studies identify Bmi1 as a marker for a distinct population of castration-resistant luminal epithelial cells enriched in the proximal prostate that can serve as a cell of origin for prostate cancer.

The polycomb repressor protein Bmi1 has a role in self-renewal and tumorigenesis. Here, the authors use lineage tracing to show that Bmi-expressing cells are a distinct population of cells, primarily found in the luminal compartment, which is castration resistant, can initiate cancer and regenerate prostate.

Basal Progenitors Contribute to Repair of the Prostate Epithelium Following Induced Luminal Anoikis

Contact with the extracellular matrix is essential for maintenance of epithelial cells in many tissues, while in its absence epithelial cells can detach and undergo anoikis. Here, we show that anoikis of luminal cells in the prostate epithelium is followed by a program of tissue repair that is mediated in part by differentiation of basal epithelial cells to luminal cells. We describe a mouse model in which inducible deletion of E-cadherin in prostate luminal cells results in their apoptotic cell death by anoikis, in the absence of phenotypic effects in the surrounding stroma. Quantitative assessments of proliferation and cell death in the luminal and basal compartments indicate that basal cells can rapidly generate luminal cells. Thus, our findings identify a role for basal-to-luminal differentiation in prostate epithelial repair, and provide a normal context to analogous processes that may occur during prostate cancer initiation.

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Induced deletion of E-cadherin results in anoikis of prostate luminal cells

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Luminal anoikis and tissue repair take place in the absence of stromal phenotypes

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Basal cells proliferate and differentiate to produce luminal cells during repair

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These findings suggest a conserved role for basal cells in epithelial tissue repair

Ly6E/K Signaling to TGFβ Promotes Breast Cancer Progression, Immune Escape, and Drug Resistance

Stem cell antigen Sca-1 is implicated in murine cancer stem cell biology and breast cancer models, but the role of its human homologs Ly6K and Ly6E in breast cancer are not established. Here we report increased expression of Ly6K/E in human breast cancer specimens correlates with poor overall survival, with an additional specific role for Ly6E in poor therapeutic outcomes. Increased expression of Ly6K/E also correlated with increased expression of the immune checkpoint molecules PDL1 and CTLA4, increased tumor-infiltrating T regulatory cells, and decreased natural killer (NK) cell activation. Mechanistically, Ly6K/E was required for TGFβ signaling and proliferation in breast cancer cells, where they contributed to phosphorylation of Smad1/5 and Smad2/3. Furthermore, Ly6K/E promoted cytokine-induced PDL1 expression and activation and binding of NK cells to cancer cells. Finally, we found that Ly6K/E promoted drug resistance and facilitated immune escape in this setting. Overall, our results establish a pivotal role for a Ly6K/E signaling axis involving TGFβ in breast cancer pathophysiology and drug response, and highlight this signaling axis as a compelling realm for therapeutic invention. Cancer Res; 76(11); 3376-86. ©2016 AACR.

Actions of Estrogenic Endocrine Disrupting Chemicals on Human Prostate Stem/Progenitor Cells and Prostate Carcinogenesis

Substantial evidences from epidemiological and animal-based studies indicate that early exposure to endocrine disrupting chemicals (EDCs) during the developmental stage results in a variety of disorders including cancer. Previous studies have demonstrated that early estrogen exposure results in life-long reprogramming of the prostate gland that leads to an increased incidence of prostatic lesions with aging. We have recently documented that bisphenol A (BPA), one of the most studied EDCs with estrogenic activity has similar effects in increasing prostate carcinogenic potential, supporting the connection between EDCs exposure and prostate cancer risk. It is well accepted that stem cells play a crucial role in development and cancer. Accumulating evidence suggest that stem cells are regulated by extrinsic factors and may be the potential target of hormonal carcinogenesis. Estrogenic EDCs which interfere with normal hormonal signaling may perturb prostate stem cell fate by directly reprogramming stem cells or breaking down the stem cell niche. Transformation of stem cells into cancer stem cells may underlie cancer initiation accounting for cancer recurrence, which becomes a critical therapeutic target of cancer management. We therefore propose that estrogenic EDCs may influence the development and progression of prostate cancer through reprogramming and transforming the prostate stem and early stage progenitor cells. In this review, we summarize our current studies and have updated recent advances highlighting estrogenic EDCs on prostate carcinogenesis by possible targeting prostate stem/progenitor cells. Using novel stem cell assays we have demonstrated that human prostate stem/progenitor cells express estrogen receptors (ER) and are directly modulated by estrogenic EDCs. Moreover, employing anin vivohumanized chimeric prostate model, we further demonstrated that estrogenic EDCs initiate and promote prostatic carcinogenesis in an androgen-supported environment. These findings support our hypothesis that prostate stem/progenitor cells may be the direct targets of estrogenic EDCs as a consequence of developmental exposure which carry permanent reprogrammed epigenetic and oncogenic events and subsequently deposit into cancer initiation and progression in adulthood.

Stem cell and neurogenic gene-expression profiles link prostate basal cells to aggressive prostate cancer

The prostate gland mainly contains basal and luminal cells constructed as a pseudostratified epithelium. Annotation of prostate epithelial transcriptomes provides a foundation for discoveries that can impact disease understanding and treatment. Here we describe a genome-wide transcriptome analysis of human benign prostatic basal and luminal epithelial populations using deep RNA sequencing. Through molecular and biological characterizations, we show that the differential gene-expression profiles account for their distinct functional properties. Strikingly, basal cells preferentially express gene categories associated with stem cells, neurogenesis and ribosomal RNA (rRNA) biogenesis. Consistent with this profile, basal cells functionally exhibit intrinsic stem-like and neurogenic properties with enhanced rRNA transcription activity. Of clinical relevance, the basal cell gene-expression profile is enriched in advanced, anaplastic, castration-resistant and metastatic prostate cancers. Therefore, we link the cell-type-specific gene signatures to aggressive subtypes of prostate cancer and identify gene signatures associated with adverse clinical features.

Gene-expression profiles can be used to predict the prognosis of cancer patients. Here, the authors describe gene expression profiles of human prostate epithelial lineages and show that basal cells have intrinsic stem and neurogenic properties, and molecularly resemble aggressive prostate cancer.

Prostate cancer stem cells: deciphering the origins and pathways involved in prostate tumorigenesis and aggression

The cells of the prostate gland are dependent on cell signaling pathways to regulate their growth, maintenance and function. However, perturbations in key signaling pathways, resulting in neoplastic transformation of cells in the prostate epithelium, are likely to generate subtypes of prostate cancer which may subsequently require different treatment regimes. Accumulating evidence supports multiple sources of stem cells in the prostate epithelium with distinct cellular origins for prostate tumorigenesis documented in animal models, while human prostate cancer stem-like cells (PCSCs) are typically enriched by cell culture, surface marker expression and functional activity assays. As future therapies will require a deeper understanding of its cellular origins as well as the pathways that drive PCSC maintenance and tumorigenesis, we review the molecular and functional evidence supporting dysregulation of PI3K/AKT, RAS/MAPK and STAT3 signaling in PCSCs, the development of castration resistance, and as a novel treatment approach for individual men with prostate cancer.

Stem cells in genetically-engineered mouse models of prostate cancer

The cancer stem cell model proposes that tumors have a hierarchical organization in which tumorigenic cells give rise to non-tumorigenic cells, with only a subset of stem-like cells able to propagate the tumor. In the case of prostate cancer, recent analyses of genetically engineered mouse (GEM) models have provided evidence supporting the existence of cancer stem cells in vivo. These studies suggest that cancer stem cells capable of tumor propagation exist at various stages of tumor progression from prostatic intraepithelial neoplasia (PIN) to advanced metastatic and castration-resistant disease. However, studies of stem cells in prostate cancer have been limited by available approaches for evaluating their functional properties in cell culture and transplantation assays. Given the role of the tumor microenvironment and the putative cancer stem cell niche, future studies using GEM models to analyze cancer stem cells in their native tissue microenvironment are likely to be highly informative.

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.

Stem Cell Antigen-1 Identifies a Distinct Androgen-Independent Murine Prostatic Luminal Cell Lineage with Bipotent Potential

Recent lineage tracing studies support the existence of prostate luminal progenitors that possess extensive regenerative capacity, but their identity remains unknown. We show that Sca-1 (stem cell antigen-1) identifies a small population of murine prostate luminal cells that reside in the proximal prostatic ducts adjacent to the urethra. Sca-1(+) luminal cells do not express Nkx3.1. They do not carry the secretory function, although they express the androgen receptor. These cells are enriched in the prostates of castrated mice. In the in vitro prostate organoid assay, a small fraction of the Sca-1(+) luminal cells are capable of generating budding organoids that are morphologically distinct from those derived from other cell lineages. Histologically, this type of organoid is composed of multiple inner layers of luminal cells surrounded by multiple outer layers of basal cells. When passaged, these organoids retain their morphological and histological features. Finally, the Sca-1(+) luminal cells are capable of forming small prostate glands containing both basal and luminal cells in an in vivo prostate regeneration assay. Collectively, our study establishes the androgen-independent and bipotent organoid-forming Sca-1(+) luminal cells as a functionally distinct cellular entity. These cells may represent a putative luminal progenitor population and serve as a cellular origin for castration resistant prostate cancer.