Symmetrical and asymmetrical division analysis provides evidence for a hierarchy of prostate epithelial cell lineages

Single-cell RNA sequencing of human prostate basal epithelial cells reveals zone-specific cellular populations and gene expression signatures

Despite evidence of genetic signatures in normal tissue correlating with disease risk, prospectively identifying genetic drivers and cell types that underlie subsequent pathologies has historically been challenging. The human prostate is an ideal model to investigate this phenomenon because it is anatomically segregated into three glandular zones (central, peripheral, and transition) that develop differential pathologies: prostate cancer in the peripheral zone (PZ) and benign prostatic hyperplasia (BPH) in the transition zone (TZ), with the central zone (CZ) rarely developing disease. More specifically, prostatic basal cells have been implicated in differentiation and proliferation during prostate development and regeneration; however, the contribution of zonal variation and the critical role of basal cells in prostatic disease etiology are not well understood. Using single-cell RNA sequencing of primary prostate epithelial cultures, we elucidated organ-specific, zone-specific, and cluster-specific gene expression differences in basal cells isolated from human prostate and seminal vesicle (SV). Aggregated analysis identified ten distinct basal clusters by Uniform Manifold Approximation and Projection. Organ specificity compared gene expression in SV with the prostate. As expected, SV cells were distinct from prostate cells by clustering, gene expression, and pathway analysis. For prostate zone specificity, we identified two CZ-specific clusters, while the TZ and PZ populations clustered together. Despite these similarities, differential gene expression was identified between PZ and TZ samples that correlated with gene expression profiles in prostate cancer and BPH, respectively. Zone-specific profiles and cell type-specific markers were validated using immunostaining and bioinformatic analyses of publicly available RNA-seq datasets. Understanding the baseline differences at the organ, zonal, and cellular level provides important insight into the potential drivers of prostatic disease and guides the investigation of novel preventive or curative treatments. Importantly, this study identifies multiple prostate basal cell populations and cell type-specific gene signatures within prostate basal epithelial cells that have potential critical roles in driving prostatic diseases. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Prostate lineage-specific metabolism governs luminal differentiation and response to antiandrogen treatment

Lineage transitions are a central feature of prostate development, tumourigenesis and treatment resistance. While epigenetic changes are well known to drive prostate lineage transitions, it remains unclear how upstream metabolic signalling contributes to the regulation of prostate epithelial identity. To fill this gap, we developed an approach to perform metabolomics on primary prostate epithelial cells. Using this approach, we discovered that the basal and luminal cells of the prostate exhibit distinct metabolomes and nutrient utilization patterns. Furthermore, basal-to-luminal differentiation is accompanied by increased pyruvate oxidation. We establish the mitochondrial pyruvate carrier and subsequent lactate accumulation as regulators of prostate luminal identity. Inhibition of the mitochondrial pyruvate carrier or supplementation with exogenous lactate results in large-scale chromatin remodelling, influencing both lineage-specific transcription factors and response to antiandrogen treatment. These results establish reciprocal regulation of metabolism and prostate epithelial lineage identity.

Instant processing of large-scale image data with FACT, a real-time cell segmentation and tracking algorithm

Quantifying cellular characteristics from a large heterogeneous population is essential to identify rare, disease-driving cells. A recent development in the combination of high-throughput screening microscopy with single-cell profiling provides an unprecedented opportunity to decipher disease-driving phenotypes. Accurately and instantly processing large amounts of image data, however, remains a technical challenge when an analysis output is required minutes after data acquisition. Here, we present fast and accurate real-time cell tracking (FACT). FACT can segment ∼20,000 cells in an average of 2.5 s (1.9-93.5 times faster than the state of the art). It can export quantifiable features minutes after data acquisition (independent of the number of acquired image frames) with an average of 90%-96% precision. We apply FACT to identify directionally migrating glioblastoma cells with 96% precision and irregular cell lineages from a 24 h movie with an average F1 score of 0.91.

Role of brahma-related gene 1/brahma-associated factor subunits in neural stem/progenitor cells and related neural developmental disorders

Different fates of neural stem/progenitor cells (NSPCs) and their progeny are determined by the gene regulatory network, where a chromatin-remodeling complex affects synergy with other regulators. Here, we review recent research progress indicating that the BRG1/BRM-associated factor (BAF) complex plays an important role in NSPCs during neural development and neural developmental disorders. Several studies based on animal models have shown that mutations in the BAF complex may cause abnormal neural differentiation, which can also lead to various diseases in humans. We discussed BAF complex subunits and their main characteristics in NSPCs. With advances in studies of human pluripotent stem cells and the feasibility of driving their differentiation into NSPCs, we can now investigate the role of the BAF complex in regulating the balance between self-renewal and differentiation of NSPCs. Considering recent progress in these research areas, we suggest that three approaches should be used in investigations in the near future. Sequencing of whole human exome and genome-wide association studies suggest that mutations in the subunits of the BAF complex are related to neurodevelopmental disorders. More insight into the mechanism of BAF complex regulation in NSPCs during neural cell fate decisions and neurodevelopment may help in exploiting new methods for clinical applications.

Lineage Tracing and Molecular Real-Time Imaging of Cancer Stem Cells

The cancer stem cells (CSC) are the roots of cancer. The CSC hypothesis may provide a model to explain the tumor cell heterogeneity. Understand the biological mechanism of CSC will help the early detection and cure of cancer. The discovery of the dynamic changes in CSC will be possible by the using of bio-engineering techniques-lineage tracing. However, it is difficult to obtain real-time, continuous, and dynamic live-imaging information using the traditional approaches that take snapshots of time points from different animals. The goal of molecular imaging is to monitor the in situ, continuous molecular changes of cells in vivo. Therefore, the most advanced bioengineering lineage tracing approach, while using a variety of molecular detection methods, will maximize the presentation of CSC. In this review, we first introduce the method of lineage tracing, and then introduce the various components of molecular images to dynamic detect the CSC. Finally, we analyze the current situation and look forward the future of CSC detection.

Keratin Profiling by Single-Cell RNA-Sequencing Identifies Human Prostate Stem Cell Lineage Hierarchy and Cancer Stem-Like Cells

Single prostate stem cells can generate stem and progenitor cells to form prostaspheres in 3D culture. Using a prostasphere-based label retention assay, we recently identified keratin 13 (KRT13)-enriched prostate stem cells at single-cell resolution, distinguishing them from daughter progenitors. Herein, we characterized the epithelial cell lineage hierarchy in prostaspheres using single-cell RNA-seq analysis. Keratin profiling revealed three clusters of label-retaining prostate stem cells; cluster I represents quiescent stem cells (PSCA, CD36, SPINK1, and KRT13/23/80/78/4 enriched), while clusters II and III represent active stem and bipotent progenitor cells (KRT16/17/6 enriched). Gene set enrichment analysis revealed enrichment of stem and cancer-related pathways in cluster I. In non-label-retaining daughter progenitor cells, three clusters were identified; cluster IV represents basal progenitors (KRT5/14/6/16 enriched), while clusters V and VI represent early and late-stage luminal progenitors, respectively (KRT8/18/10 enriched). Furthermore, MetaCore analysis showed enrichment of the “cytoskeleton remodeling–keratin filaments” pathway in cancer stem-like cells from human prostate cancer specimens. Along with common keratins (KRT13/23/80/78/4) in normal stem cells, unique keratins (KRT10/19/6C/16) were enriched in cancer stem-like cells. Clarification of these keratin profiles in human prostate stem cell lineage hierarchy and cancer stem-like cells can facilitate the identification and therapeutic targeting of prostate cancer stem-like cells.

Resistance to androgen receptor signaling inhibition does not necessitate development of neuroendocrine prostate cancer

Resistance to AR signaling inhibitors (ARSis) in a subset of metastatic castration-resistant prostate cancers (mCRPCs) occurs with the emergence of AR^– neuroendocrine prostate cancer (NEPC) coupled with mutations/deletions in PTEN, TP53, and RB1 and the overexpression of DNMTs, EZH2, and/or SOX2. To resolve whether the lack of AR is the driving factor for the emergence of the NE phenotype, molecular, cell, and tumor biology analyses were performed on 23 xenografts derived from patients with PC, recapitulating the full spectrum of genetic alterations proposed to drive NE differentiation. Additionally, phenotypic response to CRISPR/Cas9-mediated AR KO in AR⁺ CRPC cells was evaluated. These analyses document that (a) ARSi-resistant NEPC developed without androgen deprivation treatment; (b) ARS in ARSi-resistant AR⁺/NE⁺ double-positive “amphicrine” mCRPCs did not suppress NE differentiation; (c) the lack of AR expression did not necessitate acquiring a NE phenotype, despite concomitant mutations/deletions in PTEN and TP53, and the loss of RB1 but occurred via emergence of an AR^–/NE^– double-negative PC (DNPC); (d) despite DNPC cells having homogeneous genetic driver mutations, they were phenotypically heterogeneous, expressing basal lineage markers alone or in combination with luminal lineage markers; and (e) AR loss was associated with AR promoter hypermethylation in NEPCs but not in DNPCs.

Regulation of Formation, Stemness and Therapeutic Resistance of Cancer Stem Cells

Over the past 20 years cancer stem cells (CSCs) have been proposed as key players in the tumorigenesis and progression, which are closely related to the initiation, metastasis and therapeutic resistance of cancer. Evidences have been provided that both genetic and epigenetic factors contribute to the regulation of the formation and stemness maintenance as well as the therapeutic resistance of CSCs via affecting various signal pathways. In addition, the interaction between CSCs and tumor microenvironment has also been revealed to be involved in the above-described processes. With the aim of targeting CSCs to improve treatment outcome, we herein discuss the mechanisms that orchestrate the characteristic of CSCs by the three elements and potential therapeutic strategies. We also summarize how several key regulatory factors function in the regulation of not only the formation and stemness maintenance, but also the therapeutic resistance of CSCs. Thus, future studies focusing on these key factors would be helpful for the development of novel drugs targeting CSCs.

Regulation of stem/progenitor cell maintenance by BMP5 in prostate homeostasis and cancer initiation

Tissue homeostasis relies on the fine regulation between stem and progenitor cell maintenance and lineage commitment. In the adult prostate, stem cells have been identified in both basal and luminal cell compartments. However, basal stem/progenitor cell homeostasis is still poorly understood. We show that basal stem/progenitor cell maintenance is regulated by a balance between BMP5 self-renewal signal and GATA3 dampening activity. Deleting Gata3 enhances adult prostate stem/progenitor cells self-renewal capacity in both organoid and allograft assays. This phenotype results from a local increase in BMP5 activity in basal cells as shown by the impaired self-renewal capacity of Bmp5-deficient stem/progenitor cells. Strikingly, Bmp5 gene inactivation or BMP signaling inhibition with a small molecule inhibitor are also sufficient to delay prostate and skin cancer initiation of Pten-deficient mice. Together, these results establish BMP5 as a key regulator of basal prostate stem cell homeostasis and identifies a potential therapeutic approach against Pten-deficient cancers.

CXCL12γ induces human prostate and mammary gland development

BACKGROUND

Epithelial stem cells (ESCs) demonstrate a capacity to maintain normal tissues homeostasis and ESCs with a deregulated behavior can contribute to cancer development. The ability to reprogram normal tissue epithelial cells into prostate or mammary stem-like cells holds great promise to help understand cell of origin and lineage plasticity in prostate and breast cancers in addition to understanding normal gland development. We previously showed that an intracellular chemokine, CXCL12γ induced cancer stem cells and neuroendocrine characteristics in both prostate and breast adenocarcinoma cell lines. However, its role in normal prostate or mammary epithelial cell fate and development remains unknown. Therefore, we sought to elucidate the functional role of CXCL12γ in the regulation of ESCs and tissue development.

METHODS

Prostate epithelial cells (PNT2) or mammary epithelial cells (MCF10A) with overexpressed CXCL12γ was characterized by quantitative real-time polymerase chain reaction, Western blots, and immunofluorescence for lineage marker expression, and fluorescence activated cell sorting analyses and sphere formation assays to examine stem cell surface phenotype and function. Xenotransplantation animal models were used to evaluate gland or acini formation in vivo.

RESULTS

Overexpression of CXCL12γ promotes the reprogramming of cells with a differentiated luminal phenotype to a nonluminal phenotype in both prostate (PNT2) and mammary (MCF10A) epithelial cells. The CXCL12γ-mediated nonluminal type cells results in an increase of epithelial stem-like phenotype including the subpopulation of EPCAM^Lo /CD49f^Hi /CD24^Lo /CD44^Hi cells capable of sphere formation. Critically, overexpression of CXCL12γ promotes the generation of robust gland-like structures from both prostate and mammary epithelial cells in in vivo xenograft animal models.

CONCLUSIONS

CXCL12γ supports the reprogramming of epithelial cells into nonluminal cell-derived stem cells, which facilitates gland development.

The Sca-1+ and Sca-1- mouse prostatic luminal cell lineages are independently sustained

The phenotypic and functional heterogeneity of the mouse prostate epithelial cell lineages remains incompletely characterized. We show that the Sca-1⁺ luminal cells at the mouse proximal prostate express Sox2. These cells are replicative quiescent, castration resistant, and do not possess secretory function. We use the Probasin-CreER^T2 and Sox2-CreER^T2 models in concert with a fluorescent reporter line to label the Sca-1^- and Sca-1⁺ luminal cells, respectively. By a lineage tracing approach, we show that the two luminal cell populations are independently sustained. Sox2 is dispensable for the maintenance of the Sca-1⁺ luminal cells but is essential for their facultative bipotent differentiation capacity. The Sca-1⁺ luminal cells share molecular features with the human TACSTD2⁺ luminal cells. This study corroborates the heterogeneity of the mouse prostate luminal cell lineage and shows that the adult mouse prostate luminal cell lineage is maintained by distinct cellular entities rather than a single progenitor population.

Klf5 acetylation regulates luminal differentiation of basal progenitors in prostate development and regeneration

Prostate development depends on balanced cell proliferation and differentiation, and acetylated KLF5 is known to alter epithelial proliferation. It remains elusive whether post-translational modifications of transcription factors can differentially determine adult stem/progenitor cell fate. Here we report that, in human and mouse prostates, Klf5 is expressed in both basal and luminal cells, with basal cells preferentially expressing acetylated Klf5. Functionally, Klf5 is indispensable for maintaining basal progenitors, their luminal differentiation, and the proliferation of their basal and luminal progenies. Acetylated Klf5 is also essential for basal progenitors' maintenance and proper luminal differentiation, as deacetylation of Klf5 causes excess basal-to-luminal differentiation; attenuates androgen-mediated organoid organization; and retards postnatal prostate development. In basal progenitor-derived luminal cells, Klf5 deacetylation increases their proliferation and attenuates their survival and regeneration following castration and subsequent androgen restoration. Mechanistically, Klf5 deacetylation activates Notch signaling. Klf5 and its acetylation thus contribute to postnatal prostate development and regeneration by controlling basal progenitor cell fate.

Identification of a Zeb1 expressing basal stem cell subpopulation in the prostate

The basal cell compartment in many epithelial tissues is generally believed to serve as an important pool of stem cells. However, basal cells are heterogenous and the stem cell subpopulation within basal cells is not well elucidated. Here we uncover that the core epithelial-to-mesenchymal transition (EMT) inducer Zeb1 is expressed in a prostate basal cell subpopulation. The Zeb1⁺ prostate epithelial cells are multipotent prostate basal stem cells (PBSCs) that can self-renew and generate functional prostatic glandular structures at the single-cell level. Genetic ablation studies reveal an indispensable role for Zeb1 in prostate basal cell development. Utilizing unbiased single-cell transcriptomic analysis of over 9000 mouse prostate basal cells, we confirm the existence of the Zeb1⁺ basal cell subset. Moreover, Zeb1⁺ epithelial cells can be detected in mouse and human prostate tumors. Identification of the PBSC and its transcriptome profile is crucial to advance our understanding of prostate development and tumorigenesis.

Evaluating the Differentiation Capacity of Mouse Prostate Epithelial Cells Using Organoid Culture

The prostate epithelium is comprised predominantly of basal and luminal cells. In vivo lineage tracing has been utilized to define the differentiation capacity of mouse prostate basal and luminal cells during development, tissue-regeneration and transformation. However, evaluating cell-intrinsic and extrinsic regulators of prostate epithelial differentiation capacity using a lineage tracing approach often requires extensive breeding and can be cost-prohibitive. In the prostate organoid assay, basal and luminal cells generate prostatic epithelium ex vivo. Importantly, primary epithelial cells can be isolated from mice of any genetic background or mice treated with any number of small molecules prior to, or after, plating into three-dimensional (3D) culture. Sufficient material for evaluation of differentiation capacity is generated after 7-10 days. Collection of basal-derived and luminal-derived organoids for (1) protein analysis by Western blot and (2) immunohistochemical analysis of intact organoids by whole-mount confocal microscopy enables researchers to evaluate the ex vivo differentiation capacity of prostate epithelial cells. When used in combination, these two approaches provide complementary information about the differentiation capacity of prostate basal and luminal cells in response to genetic or pharmacological manipulation.

Luminal-contact-inhibition of epithelial basal stem cell multipotency in prostate organogenesis and homeostasis

Prostate epithelial basal cells are highly plastic in their luminal differentiation capability. Basal stem cells actively produce luminal cells during organogenesis, but become restricted in the adult prostate unless receiving oncogenic or inflammatory stimuli. Given that the number of luminal cells increases relative to basal cells through development and that equilibrium is reached in the adulthood, we hypothesize that a negative-feedback mechanism exists to inhibit basal-to-luminal differentiation. We provide evidence supporting this hypothesis by comparing murine prostatic growth in a tissue reconstitution assay with cell recombinants of different basal-to-luminal ratios. Additionally, in organoid culture, hybrid organoids derived from adjacent basal and luminal cells showed reduced basal stem cell activities, suggesting contact inhibition. Importantly, removal of adult luminal cells in vivo via either an inducible Cre/loxP-Dre/rox dual-lineage-tracing system or orthotopic trypsin injection led to robust reactivation of basal stem cell activities, which acts independent of androgen. These data illustrate the prostate organ as a distinctive paradigm where cell contact from differentiated daughter cells restricts adult stem cell multipotency to maintain the steady-state epithelial architecture.

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.

Transcriptional repression by androgen receptor: roles in castration-resistant prostate cancer

Androgen receptor (AR), a hormonal transcription factor, plays important roles during prostate cancer progression and is a key target for therapeutic interventions. While androgen-deprivation therapies are initially successful in regressing prostate tumors, the disease ultimately comes back as castration-resistant prostate cancer (CRPC) or at the late stage as neuroendocrine prostate cancer (NEPC). CRPC remains largely dependent on hyperactive AR signaling in the milieu of low androgen, while NEPC is negative of AR expression but positive of many AR-repressed genes. Recent technological advances in genome-wide analysis of transcription factor binding sites have revealed an unprecedented set of AR target genes. In addition to its well-known function in activating gene expression, AR is increasingly known to also act as a transcriptional repressor. Here, we review the molecular mechanisms by which AR represses gene expression. We also summarize AR-repressed genes that are aberrantly upregulated in CRPC and NEPC and represent promising targets for therapeutic intervention.

Lineage plasticity-mediated therapy resistance in prostate cancer

Therapy resistance is a significant challenge for prostate cancer treatment in clinic. Although targeted therapies such as androgen deprivation and androgen receptor (AR) inhibition are effective initially, tumor cells eventually evade these strategies through multiple mechanisms. Lineage reprogramming in response to hormone therapy represents a key mechanism that is increasingly observed. The studies in this area have revealed specific combinations of alterations present in adenocarcinomas that provide cells with the ability to transdifferentiate and perpetuate AR-independent tumor growth after androgen-based therapies. Interestingly, several master regulators have been identified that drive plasticity, some of which also play key roles during development and differentiation of the cell lineages in the normal prostate. Thus, further study of each AR-independent tumor type and understanding underlying mechanisms are warranted to develop combinational therapies that combat lineage plasticity in prostate cancer.

Sox2 Expression Marks Castration-Resistant Progenitor Cells in the Adult Murine Prostate

Identification of defined epithelial cell populations with progenitor properties is critical for understanding prostatic development and disease. Here, we demonstrate that Sox2 expression is enriched in the epithelial cells of the proximal prostate adjacent to the urethra. We use lineage tracing of Sox2-positive cells during prostatic development, homeostasis, and regeneration to show that the Sox2 lineage is capable of self-renewal and contributes to prostatic regeneration. Persisting luminal cells express Sox2 after castration, highlighting a potential role for Sox2 in cell survival and castration-resistance. In addition to revealing a novel progenitor population in the prostate, these data implicate Sox2 as a regulatory factor of adult prostate epithelial stem cells. Stem Cells 2019;37:690-700.

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.

Loss of Par3 promotes prostatic tumorigenesis by enhancing cell growth and changing cell division modes

Although cell polarity plays an important role in epithelial tumorigenesis, the consequence of polarity protein loss in prostatic tumorigenesis and the underlying mechanisms remain unclear. Using conditional knockout mouse models, we found in the current study that loss of polarity protein Par3 increases prostatic epithelial cell growth, elevates symmetrical cell divisions in basal cells, and randomizes spindle orientation in luminal cells, causing the development of high-grade prostatic intraepithelial neoplasia (PIN). Mechanistically, loss of Par3 dissociates the Par3/merlin/Lats1 complex, consequently inhibiting phosphorylation of Lats1 to attenuate the Hippo pathway. Furthermore, attenuated Hippo pathway enhances nuclear translocation of Yes-associated protein (YAP), which promotes cell proliferation and symmetrical cell divisions through transcriptional activation of Ki-67 and Sox2. In addition, Lats1 dephosphorylation impairs its interaction with G protein signaling modulator 2 (GPSM2, which is also known as LGN) that causes randomization of spindle orientation in luminal cells. Interestingly, co-deletion of Par3 and Lats1 for complete blockade of the Hippo pathway in mice results in prostate tumor initiation, whereas co-deletion of Par3 and YAP for disrupting YAP nuclear translocation reverses the phenotypes to a relatively normal state. Therefore, our findings highlight combination of Par3 loss and blockade of the Hippo pathway as a novel mechanism for prostatic tumorigenesis.

Diverse progenitor cells preserve salivary gland ductal architecture after radiation-induced damage

The ductal system of the salivary gland has long been postulated to be resistant to radiation-induced damage, a common side effect incurred by head and neck cancer patients receiving radiotherapy. Yet, whether the ducts are capable of regenerating after genotoxic injury, or whether damage to ductal cells induces lineage plasticity, as has been reported in other organ systems, remains unknown. Here, using the murine salivary gland, we show that two ductal progenitor populations, marked exclusively by KRT14 and KIT, maintain non-overlapping ductal compartments after radiation exposure but do so through distinct cellular mechanisms. KRT14⁺ progenitor cells are fast-cycling cells that proliferate in response to radiation-induced damage in a sustained manner and divide asymmetrically to produce differentiated cells of the larger granulated ducts. Conversely, KIT⁺ intercalated duct cells are long-lived progenitors for the intercalated ducts that undergo few cell divisions either during homeostasis or after gamma radiation, thus maintaining ductal architecture with slow rates of cell turnover. Together, these data illustrate the regenerative capacity of the salivary ducts and highlight the heterogeneity in the damage responses used by salivary progenitor cells to maintain tissue architecture.

Prostate Luminal Progenitor Cells in Development and Cancer

Prostate cancer (PCa) has a predominantly luminal phenotype. Basal cells were previously identified as a cell of origin for PCa, but increasing evidence implicates luminal cells as a preferred cell of origin for PCa, as well as key drivers of tumor development and progression. Prostate luminal cells are understudied compared with basal cells. In this review, we describe the contribution of prostate luminal progenitor (LP) cells to luminal cell development and their role in prostate development, androgen-mediated regeneration of castrated prostate, and tumorigenesis. We also discuss the potential value of LP transcriptomics to identify new targets and therapies to treat aggressive PCa. Finally, we propose future research directions focusing on molecular mechanisms underlying LP cell biology and heterogeneity in normal and diseased prostate.

E-cadherin bridges cell polarity and spindle orientation to ensure prostate epithelial integrity and prevent carcinogenesis in vivo

Cell polarity and correct mitotic spindle positioning are essential for the maintenance of a proper prostate epithelial architecture, and disruption of the two biological features occurs at early stages in prostate tumorigenesis. However, whether and how these two epithelial attributes are connected in vivo is largely unknown. We herein report that conditional genetic deletion of E-cadherin, a key component of adherens junctions, in a mouse model results in loss of prostate luminal cell polarity and randomization of spindle orientations. Critically, E-cadherin ablation causes prostatic hyperplasia which progresses to invasive adenocarcinoma. Mechanistically, E-cadherin and the spindle positioning determinant LGN interacts with the PDZ domain of cell polarity protein SCRIB and form a ternary protein complex to bridge cell polarity and cell division orientation. These findings provide a novel mechanism by which E-cadherin acts an anchor to maintain prostate epithelial integrity and to prevent carcinogenesis in vivo.

Luminal cells are the most abundant type of the prostate epithelial cells. Most prostate cancers also display a luminal phenotype. Horizontal cell division of luminal cells allows the surface expansion of the secretory prostate lumen and meanwhile maintains the monolayer and polarized epithelial architecture. Disruption of the epithelial integrity and appearance of multilayer epithelia are early events in prostate adenocarcinoma development. However, the molecular mechanism that ensures the horizontal division in luminal cells remains largely unknown. Here, we generated a genetically engineered mouse model in which E-cadherin, a key component of the adherens junction that serves to connect the lateral plasma membrane of neighboring epithelial cells, was knocked out in the prostate luminal cells. E-cadherin deletion leads to loss of cell polarity and disoriented cell division, which subsequently causes dysregulated cell proliferation and strongly predisposes mice for prostate tumorigenesis. Importantly, we revealed that E-cadherin acts as an anchor to recruit cell polarity protein SCRIB and spindle positioning determinant LGN to the lateral cell membrane, thereby ensure a proper alignment of the cell division plane. All these findings uncover a novel mechanism by which E-cadherin links cell polarity and spindle orientation to keep prostate epithelial integrity and prevent carcinogenesis.

Transcriptional regulation of P63 on the apoptosis of male germ cells and three stages of spermatogenesis in mice

Infertility affects 10-15% of couples worldwide, and male factors account for 50%. Spermatogenesis is precisely regulated by genetic factors, and the mutations of genes result in abnormal spermatogenesis and eventual male infertility. The aim of this study was to explore the role and transcriptional regulation of P63 in the apoptosis and mouse spermatogenesis. P63 protein was decreased in male germ cells of P63^(+/-) mice compared with wild-type mice. There was no obvious difference in testis weight, sperm motility, and fecundity between P63^(+/-) and wild-type mice. However, abnormal germ cells were frequently observed in P63^(+/-) mice at 2 months old. Notably, apoptotic male germ cells and the percentage of abnormal sperm were significantly enhanced in P63^(+/-) mice compared to wild-type mice. Spermatogonia, pachytene spermatocytes and round spermatids were isolated from P63^(+/-) and wild-type mice using STA-PUT velocity sedimentation, and they were identified phenotypically with high purities. RNA sequencing demonstrated distinct transcription profiles in spermatogonia, pachytene spermatocytes, and round spermatids between P63^(+/-) mice and wild-type mice. In total, there were 645 differentially expressed genes (DEGs) in spermatogonia, 106 DEGs in pachytene spermatocytes, and 1152 in round spermatids between P63^(+/-) mice and wild-type mice. Real time PCR verified a number of DEGs identified by RNA sequencing. Gene ontology annotation and pathway analyzes further indicated that certain key genes, e.g., Ccnd2, Tgfa, Hes5, Insl3, Kit, Lef1, and Jun were involved in apoptosis, while Dazl, Kit, Pld6, Cdkn2d, Stra8, and Ubr2 were associated with regulating spermatogenesis. Collectively, these results implicate that P63 mediates the apoptosis of male germ cells and regulates three stages of spermatogenesis transcriptionally. This study could provide novel targets for the diagnosis and treatment of male infertility.

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

Zinc transporter 2 interacts with vacuolar ATPase and is required for polarization, vesicle acidification, and secretion in mammary epithelial cells

An important feature of the mammary gland is its ability to undergo profound morphological, physiological, and intracellular changes to establish and maintain secretory function. During this process, key polarity proteins and receptors are recruited to the surface of mammary epithelial cells (MECs), and the vesicle transport system develops and matures. However, the intracellular mechanisms responsible for the development of secretory function in these cells are unclear. The vesicular zinc (Zn²⁺) transporter ZnT2 is critical for appropriate mammary gland architecture, and ZnT2 deletion is associated with cytoplasmic Zn²⁺ accumulation, loss of secretory function and lactation failure. The underlying mechanisms are important to understand as numerous mutations and non-synonymous genetic variation in ZnT2 have been detected in women that result in severe Zn²⁺ deficiency in exclusively breastfed infants. Here we found that ZnT2 deletion in lactating mice and cultured MECs resulted in Zn²⁺-mediated degradation of phosphatase and tensin homolog (PTEN), which impaired intercellular junction formation, prolactin receptor trafficking, and alveolar lumen development. Moreover, ZnT2 directly interacted with vacuolar H⁺-ATPase (V-ATPase), and ZnT2 deletion impaired vesicle biogenesis, acidification, trafficking, and secretion. In summary, our findings indicate that ZnT2 and V-ATPase interact and that this interaction critically mediates polarity establishment, alveolar development, and secretory function in the lactating mammary gland. Our observations implicate disruption in ZnT2 function as a modifier of secretory capacity and lactation performance.

Inactivation of STAT3 Signaling Impairs Hair Cell Differentiation in the Developing Mouse Cochlea

Although STAT3 signaling is demonstrated to regulate sensory cell differentiation and regeneration in the zebrafish, its exact role is still unclear in mammalian cochleae. Here, we report that STAT3 and its activated form are specifically expressed in hair cells during mouse cochlear development. Importantly, conditional cochlear deletion of Stat3 leads to an inhibition on hair cell differentiation in mice in vivo and in vitro. By cell fate analysis, inactivation of STAT3 signaling shifts the cell division modes from asymmetric to symmetric divisions from supporting cells. Moreover, inhibition of Notch signaling stimulates STAT3 phosphorylation, and inactivation of STAT3 signaling attenuates production of supernumerary hair cells induced by a Notch pathway inhibitor. Our findings highlight an important role of the STAT3 signaling during mouse cochlear hair cell differentiation and may have clinical implications for the recovery of hair cell loss-induced hearing impairment.

Isolation and functional interrogation of adult human prostate epithelial stem cells at single cell resolution

Using primary cultures of normal human prostate epithelial cells, we developed a novel prostasphere-based, label-retention assay that permits identification and isolation of stem cells at a single cell level. Their bona fide stem cell nature was corroborated using in vitro and in vivo regenerative assays and documentation of symmetric/asymmetric division. Robust WNT10B and KRT13 levels without E-cadherin or KRT14 staining distinguished individual stem cells from daughter progenitors in spheroids. Following FACS to isolate label-retaining stem cells from label-free progenitors, RNA-seq identified unique gene signatures for the separate populations which may serve as useful biomarkers. Knockdown of KRT13 or PRAC1 reduced sphere formation and symmetric self-renewal highlighting their role in stem cell maintenance. Pathways analysis identified ribosome biogenesis and membrane estrogen-receptor signaling enriched in stem cells with NF-ĸB signaling enriched in progenitors; activities that were biologically confirmed. Further, bioassays identified heightened autophagy flux and reduced metabolism in stem cells relative to progenitors. These approaches similarly identified stem-like cells from prostate cancer specimens and prostate, breast and colon cancer cell lines suggesting wide applicability. Together, the present studies isolate and identify unique characteristics of normal human prostate stem cells and uncover processes that maintain stem cell homeostasis in the prostate gland.

The drebrin/EB3 pathway drives invasive activity in prostate cancer

Prostate cancer is the most common cancer in men and the metastatic form of the disease is incurable. We show here that the drebrin/EB3 pathway, which co-ordinates dynamic microtubule/actin filament interactions underlying cell shape changes in response to guidance cues, plays a role in prostate cancer cell invasion. Drebrin expression is restricted to basal epithelial cells in benign human prostate but is upregulated in luminal epithelial cells in foci of prostatic malignancy. Drebrin is also upregulated in human prostate cancer cell lines and co-localizes with actin filaments and dynamic microtubules in filopodia of pseudopods of invading cells under a chemotactic gradient of the chemokine CXCL12. Disruption of the drebrin/EB3 pathway using BTP2, a small molecule inhibitor of drebrin binding to actin filaments, reduced the invasion of prostate cancer cell lines in 3D in vitro assays. Furthermore, gain- or loss-of-function of drebrin or EB3 by over-expression or siRNA-mediated knockdown increases or decreases invasion of prostate cancer cell lines in 3D in vitro assays, respectively. Finally, expression of a dominant-negative construct that competes with EB3 binding to drebrin, also inhibited invasion of prostate cancer cell lines in 3D in vitro assays. Our findings show that co-ordination of dynamic microtubules and actin filaments by the drebrin/EB3 pathway drives prostate cancer cell invasion and is therefore implicated in disease progression.

Lineage Specification from Prostate Progenitor Cells Requires Gata3-Dependent Mitotic Spindle Orientation

During prostate development, basal and luminal cell lineages are generated through symmetric and asymmetric divisions of bipotent basal cells. However, the extent to which spindle orientation controls division symmetry or cell fate, and the upstream factors regulating this process, are still elusive. We report that GATA3 is expressed in both prostate basal progenitor and luminal cells and that loss of GATA3 leads to a mislocalization of PRKCZ, resulting in mitotic spindle randomization during progenitor cell division. Inherently proliferative intermediate progenitor cells accumulate, leading to an expansion of the luminal compartment. These defects ultimately result in a loss of tissue polarity and defective branching morphogenesis. We further show that disrupting the interaction between PRKCZ and PARD6B is sufficient to recapitulate the spindle and cell lineage phenotypes. Collectively, these results identify a critical role for GATA3 in prostate lineage specification, and further highlight the importance of regulating spindle orientation for hierarchical cell lineage organization.

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Gata3 regulates prostate lineage specification and tissue architecture

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Loss of Gata3 causes aPKC mislocalization and mitotic spindle randomization

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aPKC-Par6 decoupling randomizes the spindle and perturbs lineage specification

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Spindle regulation prevents progenitor cell accumulation and tissue hyperplasia

Dissecting cell-type-specific roles of androgen receptor in prostate homeostasis and regeneration through lineage tracing

Androgen signals through androgen receptor (AR) to influence prostate development and cancer. How stromal and epithelial AR regulate prostate homeostasis remains unclear. Using genetic lineage tracing, we systematically investigated the role of cell-autonomous AR in different prostate epithelial cell types. Here we show that AR is dispensable for basal cell maintenance, but is cell-autonomously required for the luminal differentiation of rare basal stem cells. In contrast, AR deletion in luminal cells alters cell morphology and induces transient over-proliferation, without affecting androgen-mediated luminal cell survival or regeneration. However, AR is selectively required for the maintenance of daughter cells produced by castration-resistant Nkx3.1-expressing luminal stem cells (CARNs). Notably, Pten loss can override AR-loss effects in both basal and luminal compartments to initiate tumours. Our data reveal distinct cell-type-specific roles of epithelial AR in orchestrating prostate homeostasis, and question the notion that epithelial AR serves as a tumour suppressor in early cancer initiation.

Androgen receptor is an important regulator of prostate development and cancer. In this study, the authors use genetic lineage tracing in mice to clarify the role of AR in different prostate epithelial cells.

Highly durable organic electrode for sodium-ion batteries via a stabilized α-C radical intermediate

It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized α-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the α-radical demonstrates reversible transformation between three states: C=C; α-C·radical; and α-C- anion. Such transformation provides additional Na+ storage equal to more than 0.83 Na+ insertion per α-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.

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.

Systematic dissection of phenotypic, functional, and tumorigenic heterogeneity of human prostate cancer cells

Human cancers are heterogeneous containing stem-like cancer cells operationally defined as cancer stem cells (CSCs) that possess great tumor-initiating and long-term tumor-propagating properties. In this study, we systematically dissect the phenotypic, functional and tumorigenic heterogeneity in human prostate cancer (PCa) using xenograft models and >70 patient tumor samples. In the first part, we further investigate the PSA^−/lo PCa cell population, which we have recently shown to harbor self-renewing long-term tumor-propagating cells and present several novel findings. We show that discordant AR and PSA expression in both untreated and castration-resistant PCa (CRPC) results in AR⁺PSA⁺, AR⁺PSA⁻, AR⁻PSA⁻, and AR⁻PSA⁺ subtypes of PCa cells that manifest differential sensitivities to therapeutics. We further demonstrate that castration leads to a great enrichment of PSA^−/lo PCa cells in both xenograft tumors and CRPC samples and systemic androgen levels dynamically regulate the relative abundance of PSA⁺ versus PSA^−/lo PCa cells that impacts the kinetics of tumor growth. We also present evidence that the PSA^−/lo PCa cells possess distinct epigenetic profiles. As the PSA^−/lo PCa cell population is heterogeneous, in the second part, we employ two PSA⁻ (Du145 and PC3) and two PSA⁺ (LAPC9 and LAPC4) PCa models as well as patient tumor cells to further dissect the clonogenic and tumorigenic subsets. We report that different PCa models possess distinct tumorigenic subpopulations that both commonly and uniquely express important signaling pathways that could represent therapeutic targets. Our results have important implications in understanding PCa cell heterogeneity, response to clinical therapeutics, and cellular mechanisms underlying CRPC.

Quantitative lineage tracing strategies to resolve multipotency in tissue-specific stem cells

Here, Wuidart et al. present a rigorous new method for assessing the lineage relationship and stem cell fate in different organs and tissues. The authors developed two novel methods for determining lineage relationships: the first one based on statistical analysis of multicolor lineage tracing, and the second one based on lineage tracing at saturation to assess the fate of all stem cells within a given lineage and the “flux” of cells between different lineages.

Lineage tracing has become the method of choice to study the fate and dynamics of stem cells (SCs) during development, homeostasis, and regeneration. However, transgenic and knock-in Cre drivers used to perform lineage tracing experiments are often dynamically, temporally, and heterogeneously expressed, leading to the initial labeling of different cell types and thereby complicating their interpretation. Here, we developed two methods: the first one based on statistical analysis of multicolor lineage tracing, allowing the definition of multipotency potential to be achieved with high confidence, and the second one based on lineage tracing at saturation to assess the fate of all SCs within a given lineage and the “flux” of cells between different lineages. Our analysis clearly shows that, whereas the prostate develops from multipotent SCs, only unipotent SCs mediate mammary gland (MG) development and adult tissue remodeling. These methods offer a rigorous framework to assess the lineage relationship and SC fate in different organs and tissues.

Regulation of Prostate Development and Benign Prostatic Hyperplasia by Autocrine Cholinergic Signaling via Maintaining the Epithelial Progenitor Cells in Proliferating Status

Regulation of prostate epithelial progenitor cells is important in prostate development and prostate diseases. Our previous study demonstrated a function of autocrine cholinergic signaling (ACS) in promoting prostate cancer growth and castration resistance. However, whether or not such ACS also plays a role in prostate development is unknown. Here, we report that ACS promoted the proliferation and inhibited the differentiation of prostate epithelial progenitor cells in organotypic cultures. These results were confirmed by ex vivo lineage tracing assays and in vivo renal capsule recombination assays. Moreover, we found that M3 cholinergic receptor (CHRM3) was upregulated in a large subset of benign prostatic hyperplasia (BPH) tissues compared with normal tissues. Activation of CHRM3 also promoted the proliferation of BPH cells. Together, our findings identify a role of ACS in maintaining prostate epithelial progenitor cells in the proliferating state, and blockade of ACS may have clinical implications for the management of BPH.

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

Isolation and analysis of discreet human prostate cellular populations

The use of lineage tracing in transgenic mouse models has revealed an abundance of subcellular phenotypes responsible for maintaining prostate homeostasis. The ability to use fresh human tissues to examine the hypotheses generated by these mouse experiments has been greatly enhanced by technical advances in tissue processing, flow cytometry and cell culture. We describe in detail the optimization of protocols for each of these areas to facilitate research on solving human prostate diseases through the analysis of human tissue.

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.

Cancer Stem Cells

The cancer stem cell model in solid tumors has evolved significantly from the early paradigm shifting work highlighting parallels between the stem cell hierarchy in hematologic malignancies and solid tumors. Putative stem cells can dedifferentiated, be induced by context, and be the result of accumulated genetic mutations. The simple hypothesis that stem cell therapies will overcome the minority of cells that lead to recurrence has evolved with it. Nevertheless, the body of evidence that this field is clinically relevant in patients and patient care has grown with the complexity of the hypotheses, and numerous clinical strategies to target these cells have been identified. Herein we review this progress and highlight the work still outstanding.

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.

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.

Prostate Cancer Stem-like Cells Contribute to the Development of Castration-Resistant Prostate Cancer

Androgen deprivation therapy (ADT) has been the standard care for patients with advanced prostate cancer (PC) since the 1940s. Although ADT shows clear benefits for many patients, castration-resistant prostate cancer (CRPC) inevitably occurs. In fact, with the two recent FDA-approved second-generation anti-androgens abiraterone and enzalutamide, resistance develops rapidly in patients with CRPC, despite their initial effectiveness. The lack of effective therapeutic solutions towards CRPC largely reflects our limited understanding of the underlying mechanisms responsible for CRPC development. While persistent androgen receptor (AR) signaling under castration levels of serum testosterone (<50 ng/mL) contributes to resistance to ADT, it is also clear that CRPC evolves via complex mechanisms. Nevertheless, the physiological impact of individual mechanisms and whether these mechanisms function in a cohesive manner in promoting CRPC are elusive. In spite of these uncertainties, emerging evidence supports a critical role of prostate cancer stem-like cells (PCSLCs) in stimulating CRPC evolution and resistance to abiraterone and enzalutamide. In this review, we will discuss the recent evidence supporting the involvement of PCSLC in CRPC acquisition as well as the pathways and factors contributing to PCSLC expansion in response to ADT.

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.

PTEN is required to maintain luminal epithelial homeostasis and integrity in the adult mammary gland

In the mammary gland, PTEN loss in luminal and basal epithelial cells results in differentiation defects and enhanced proliferation, leading to the formation of tumors with basal epithelial characteristics. In breast cancer, PTEN loss is associated with a hormone receptor-negative, basal-like subtype that is thought to originate in a luminal epithelial cell. Here, we show that luminal-specific PTEN loss results in distinct effects on epithelial homeostasis and mammary tumor formation. Luminal PTEN loss increased proliferation of hormone receptor-negative cells, thereby decreasing the percentage of hormone receptor-positive cells. Moreover, luminal PTEN loss led to misoriented cell divisions and mislocalization of cells to the intraluminal space of mammary ducts. Despite their elevated levels of activated AKT, Pten-null intraluminal cells showed increased levels of apoptosis. One year after Pten deletion, the ducts had cleared and no palpable mammary tumors were detected. These data establish PTEN as a critical regulator of luminal epithelial homeostasis and integrity in the adult mammary gland, and further show that luminal PTEN loss alone is not sufficient to promote the progression of mammary tumorigenesis.

Characterization of autoimmune inflammation induced prostate stem cell expansion

BACKGROUND

The presence of inflammation in prostate cancer (PCa) and benign prostate hyperplasia (BPH) has been well described but the cellular mechanisms by which inflammation modulates the prostate are currently unclear. Prostate stem cells (PSC) not only maintain prostate homeostasis but also are considered to be the cell of origin of PCa and an important contributor to BPH. However, the impact of inflammation on PSC is not well understood. Therefore, we initiated studies to evaluate the effect of inflammation on PSC.

METHOD

Ovalbumin specific CD8(+) T cells were intravenously delivered to intact and castrated prostate ovalbumin expressing transgenic-3 (POET-3) mice to induce inflammation. Lin (CD45/CD31)(-) Sca1(+) CD49f(+) cells (LSC) and progenitor cells within LSC were determined by flow cytometry. Sorted LSC were subjected to a prostate sphere forming assay to evaluate PSC clonal propagation, proliferation, immediate differentiation, and self-renewal ability. Density of individual spheres was measured by a cantilever-based resonator weighing system. Morphology and characterization of prostate spheres was determined by hematoxylin and eosin (H&E) staining and immunohistochemistry (IHC). Finally, immediate PSC differentiation in sphere formation was determined by immunofluorescence for epithelial cytokeratin markers cytokeratin (CK) 5 and CK8.

RESULT

Data presented here demonstrate a significant expansion of the proliferative (BrdU(+) ) LSC population, including CK5(+) , p63(+) , CK18(+) cells, as well as intermediate cells (CK5(+) /CK8(+) ) in inflamed prostates. Histological images reveal that PSC from inflamed prostates produce significantly larger spheres, indicating that the enhanced proliferation observed in LSC is sustained in vitro in the absence of inflammatory mediators. In addition, cultures from inflamed PSC yielded increased number of tubule-like spheres. These tube-like spheres grown from PSCs isolated from inflamed mice exhibited stratification of a CK8(+) luminal-like layer and a CK5(+) basal-like layer. Notably, the numbers of spheres formed by inflamed and non-inflamed PSC were equal, suggesting that even though proliferation is enhanced by inflammation, the homeostatic level of PSC is maintained.

CONCLUSION

Induction of inflammation promotes PSC expansion and immediate differentiation through highly proliferative progenitor cells while the homeostasis of PSC is maintained.