Paul A. Berry

Prospective Identification of Tumorigenic Prostate Cancer Stem Cells

Existing therapies for prostate cancer eradicates the bulk of cells within a tumor. However, most patients go on to develop androgen-independent disease that remains incurable by current treatment strategies. There is now increasing evidence in some malignancies that the tumor cells are organized as a hierarchy originating from rare stem cells that are responsible for maintaining the tumor. We report here the identification and characterization of a cancer stem cell population from human prostate tumors, which possess a significant capacity for self-renewal. These cells are also able to regenerate the phenotypically mixed populations of nonclonogenic cells, which express differentiated cell products, such as androgen receptor and prostatic acid phosphatase. The cancer stem cells have a CD44+/alpha2beta1hi/CD133+ phenotype, and we have exploited these markers to isolate cells from a series of prostate tumors with differing Gleason grade and metastatic states. Approximately 0.1% of cells in any tumor expressed this phenotype, and there was no correlation between the number of CD44+/alpha2beta1hi/CD133+ cells and tumor grade. The identification of a prostate cancer stem cell provides a powerful tool to investigate the tumorigenic process and to develop therapies targeted to the stem cell.

Gene expression profiling of human prostate cancer stem cells reveals a pro-inflammatory phenotype and the importance of extracellular matrix interactions.

BackgroundThe tumor-initiating capacity of many cancers is considered to reside in a small subpopulation of cells (cancer stem cells). We have previously shown that rare prostate epithelial cells with a CD133+/α2β1hi phenotype have the properties of prostate cancer stem cells. We have compared gene expression in these cells relative to their normal and differentiated (CD133-/α2β1low) counterparts, resulting in an informative cancer stem cell gene-expression signature.ResultsCell cultures were generated from specimens of human prostate cancers (n = 12) and non-malignant control tissues (n = 7). Affymetrix gene-expression arrays were used to analyze total cell RNA from sorted cell populations, and expression changes were selectively validated by quantitative RT-PCR, flow cytometry and immunocytochemistry. Differential expression of multiple genes associated with inflammation, cellular adhesion, and metastasis was observed. Functional studies, using an inhibitor of nuclear factor κB (NF-κB), revealed preferential targeting of the cancer stem cell and progenitor population for apoptosis whilst sparing normal stem cells. NF-κB is a major factor controlling the ability of tumor cells to resist apoptosis and provides an attractive target for new chemopreventative and chemotherapeutic approaches.ConclusionWe describe an expression signature of 581 genes whose levels are significantly different in prostate cancer stem cells. Functional annotation of this signature identified the JAK-STAT pathway and focal adhesion signaling as key processes in the biology of cancer stem cells.

JAK-STAT Blockade Inhibits Tumor Initiation and Clonogenic Recovery of Prostate Cancer Stem-like Cells

Interleukin (IL)-6 overexpression and constitutive STAT3 activation occur in many cancers, including prostate cancer. However, their contribution to prostate stem and progenitor cells has not been explored. In this study, we show that stem-like cells from patients with prostate cancer secrete higher levels of IL-6 than their counterparts in non-neoplastic prostate. Tumor grade did not influence the levels of expression or secretion. Stem-like and progenitor cells expressed the IL-6 receptor gp80 with concomitant expression of pSTAT3. Blockade of activated STAT3, by either anti-IL-6 antibody siltuximab (CNTO 328) or LLL12, a specific pSTAT3 inhibitor, suppressed the clonogenicity of the stem-like cells in patients with high-grade disease. In a murine xenograft model used to determine the in vivo effects of pSTAT3 suppression, LLL12 treatment effectively abolished outgrowth of a patient-derived castrate-resistant tumor. Our results indicate that the most primitive cells in prostate cancer require pSTAT3 for survival, rationalizing STAT3 as a therapeutic target to treat advanced prostate cancer.

Androgen receptor signalling in prostate: effects of stromal factors on normal and cancer stem cells.

The prostate gland is the most common site for cancer in males within the developed world. Androgens play a vital role in prostate development, maintenance of tissue function and pathogenesis of prostate disease. The androgen receptor signalling pathway facilitates that role in both the epithelial compartment and in the underlying stroma. Stroma is a key mediator of androgenic effects upon the epithelium and can regulate both the fate of the epithelial stem cell and potentially the initiation and progression of prostate cancer. Different groups of growth factors are expressed by stroma, which control proliferation, and differentiation of prostate epithelium demonstrating a critical role for stroma in epithelial growth and homeostasis. Paracrine stromal proteins may offer the possibility to control tumour stem cell growth and could permit prostate specific targeting of both therapies and of androgen responsive proteins. The effect of 5alpha-dihydrotestosterone, the more potent metabolite of testosterone, on expression of androgen-regulated genes in stroma from benign prostatic hyperplasia is a key mediator of epithelial cell fate. Global gene expression arrays have recently identified new candidate genes in androgen responsive stroma, some of which have androgen receptor binding sites in their promoter regions. Some of these genes have direct androgen receptor binding ability.

Regulation of the stem cell marker CD133 is independent of promoter hypermethylation in human epithelial differentiation and cancer

BackgroundEpigenetic control is essential for maintenance of tissue hierarchy and correct differentiation. In cancer, this hierarchical structure is altered and epigenetic control deregulated, but the relationship between these two phenomena is still unclear. CD133 is a marker for adult stem cells in various tissues and tumour types. Stem cell specificity is maintained by tight regulation of CD133 expression at both transcriptional and post-translational levels. In this study we investigated the role of epigenetic regulation of CD133 in epithelial differentiation and cancer.MethodsDNA methylation analysis of the CD133 promoter was done by pyrosequencing and methylation specific PCR; qRT-PCR was used to measure CD133 expression and chromatin structure was determined by ChIP. Cells were treated with DNA demethylating agents and HDAC inhibitors. All the experiments were carried out in both cell lines and primary samples.ResultsWe found that CD133 expression is repressed by DNA methylation in the majority of prostate epithelial cell lines examined, where the promoter is heavily CpG hypermethylated, whereas in primary prostate cancer and benign prostatic hyperplasia, low levels of DNA methylation, accompanied by low levels of mRNA, were found. Moreover, differential methylation of CD133 was absent from both benign or malignant CD133+/α2β1integrinhi prostate (stem) cells, when compared to CD133-/α2β1integrinhi (transit amplifying) cells or CD133-/α2β1integrinlow (basal committed) cells, selected from primary epithelial cultures. Condensed chromatin was associated with CD133 downregulation in all of the cell lines, and treatment with HDAC inhibitors resulted in CD133 re-expression in both cell lines and primary samples.ConclusionsCD133 is tightly regulated by DNA methylation only in cell lines, where promoter methylation and gene expression inversely correlate. This highlights the crucial choice of cell model systems when studying epigenetic control in cancer biology and stem cell biology. Significantly, in both benign and malignant prostate primary tissues, regulation of CD133 is independent of DNA methylation, but is under the dynamic control of chromatin condensation. This indicates that CD133 expression is not altered in prostate cancer and it is consistent with an important role for CD133 in the maintenance of the hierarchical cell differentiation patterns in cancer.

The calcium sensor STIM1 is regulated by androgens in prostate stromal cells

Prostate development and maintenance in the adult results from an interaction of stromal and glandular components. Androgens can drive this process by direct action on the stroma. We investigated whether there was a direct link between androgens and another key regulator of stromal cells, intracellular Ca2+ ([Ca2+]i).

Expression and localization of endothelin-converting enzyme-1 in human prostate cancer.

Endothelin (ET)-1 can influence cancer invasion and metastasis by exerting an autocrine (epithelial) or paracrine (stromal) influence on growth. ET-1 is generated from big ET-1 by endothelin-converting enzyme (ECE)-1, which has four recognized isoforms, ECE-1a, ECE-1b, ECE-1c, and ECE-1d, differing only in their amino-terminal regions. This study investigated the expression and localization of the ECE-1 isoforms in prostate cancer (PC). The epithelial cell lines used were androgen-sensitive LNCaP, androgen-independent PC-3 and Du145, and nonmalignant transformed PNT1-a, PNT2-C2, and P4E6 prostate cells. Primary cells derived from malignant and benign tissue from radical prostatectomies were also exploited. Previously, we reported increased ECE-1 expression in androgen-independent PC cell lines, as compared with androgen-sensitive cells. Our present data show that transcripts for all ECE-1 isoforms were present in all epithelial cell lines analyzed. However, only the ECE-1c protein was detectable in PC-3, Du145, PNT2-C2, and PNT1-a cells. ECE-1c localized to both the cell surface and intracellular compartments in individual cell lines. In primary stromal cells, all individual ECE-1 isoforms were expressed at the mRNA level, with the exception of ECE-1a. ECE-1b and ECE-1c protein levels were higher in malignant stromal cells, as compared with benign cells. In stroma, ECE-1c protein was localized to the cell surface, with filamentous immunoreactivity throughout the cell, whereas ECE-1b immunoreactivity was punctate throughout the cytoplasm. The upregulation of the ECE-1c isoform in PC cell lines is being investigated further.

Phorbol ester stimulates ethanolamine release from the metastatic basal prostate cancer cell line PC3 but not from prostate epithelial cell lines LNCaP and P4E6.

Background:Malignancy alters cellular complex lipid metabolism and membrane lipid composition and turnover. Here, we investigated whether tumorigenesis in cancer-derived prostate epithelial cell lines influences protein kinase C-linked turnover of ethanolamine phosphoglycerides (EtnPGs) and alters the pattern of ethanolamine (Etn) metabolites released to the medium.Methods:Prostate epithelial cell lines P4E6, LNCaP and PC3 were models of prostate cancer (PCa). PNT2C2 and PNT1A were models of benign prostate epithelia. Cellular EtnPGs were labelled with [1-3H]-Etn hydrochloride. PKC was activated with phorbol ester (TPA) and inhibited with Ro31-8220 and GF109203X. D609 was used to inhibit PLD (phospholipase D). [3H]-labelled Etn metabolites were resolved by ion-exchange chromatography. Sodium oleate and mastoparan were tested as activators of PLD2. Phospholipase D activity was measured by a transphosphatidylation reaction. Cells were treated with ionomycin to raise intracellular Ca2+ levels.Results:Unstimulated cell lines release mainly Etn and glycerylphosphorylEtn (GPEtn) to the medium. Phorbol ester treatment over 3h increased Etn metabolite release from the metastatic PC3 cell line and the benign cell lines PNT2C2 and PNT1A but not from the tumour-derived cell lines P4E6 and LNCaP; this effect was blocked by Ro31-8220 and GF109203X as well as by D609, which inhibited PLD in a transphosphatidylation reaction. Only metastatic PC3 cells specifically upregulated Etn release in response to TPA treatment. Oleate and mastoparan increased GPEtn release from all cell lines at the expense of Etn. Ionomycin stimulated GPEtn release from benign PNT2C2 cells but not from cancer-derived cell lines P4E6 or PC3. Ethanolamine did not stimulate the proliferation of LNCaP or PC3 cell lines but decreased the uptake of choline (Cho).Conclusions:Only the metastatic basal PC3 cell line specifically increased the release of Etn on TPA treatment most probably by PKC activation of PLD1 and increased turnover of EtnPGs. The phosphatidic acid formed will maintain a cancer phenotype through the regulation of mTOR. Ethanolamine released from cells may reduce Cho uptake, regulating the membrane PtdEtn:PtdCho ratio and influencing the action of PtdEtn-binding proteins such as RKIP and the anti-apoptotic hPEBP4. The work highlights a difference between LNCaP cells used as a model of androgen-dependent early stage PCa and androgen-independent PC3 cells used to model later refractory stage disease.

Abstract B25: DNA hypermethylation in prostate cancer is a consequence of aberrant epithelial differentiation and hyperproliferation

Prostate cancer (CaP) is mostly composed of differentiated luminal cells, but contains a small subpopulation of undifferentiated basal cells (including stem-like cells), which is thought to be the driving force of CaP. In cancers, CpG island hypermethylation has been associated with gene downregulation, but the causal relationship between the two phenomena is still debated. This study aimed to understand the function and origin of CpG island hypermethylation in CaP, in the context of cancer hierarchy and differentiation. We have analyzed separately primary prostate basal and luminal cells derived from BPH and CaP. This allowed us to dissect the intra-tumor heterogeneity, and to understand the origin of gene downregulation and hypermethylation in CaP. We report that a set of genes commonly hypermethylated in CaP (including GSTP1) is: (i) downregulated as a result of prostate-specific epithelial differentiation in both CaP and benign prostatic hyperplasia (BPH); (ii) selectively hypermethylated in differentiated (luminal) cancer cells, process promoted by the hyperproliferating phenotype of these cells; (iii) actively expressed and methylation free in undifferentiated (basal) CaP cells. Downregulation and hypermethylation of these genes is not essential for tumor development or tumor expansion. Moreover, for all these genes, downregulation induced by prostate-specific differentiation, is independent of DNA hypermethylation, and is associated with detachment of RNA PolII from their promoter and reduction in histone marks associated with active transcription. Citation Format: Davide Pellacani, Dimitra Kestoras, Alastair P. Droop, Fiona M. Frame, Paul A. Berry, Mitchell G. Lawrence, Michael J. Stower, Matthew S. Simms, Vincent M. Mann, Anne T. Collins, Gail P. Risbridger, Norman J. Maitland. DNA hypermethylation in prostate cancer is a consequence of aberrant epithelial differentiation and hyperproliferation. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr B25.

Abstract 5209: Prostate cancer progenitor cells have distinct DNA methylation profile which changes upon differentiation

Prostate cancer is phenotypically, genetically and epigenetically heterogeneous. In the present study we have dissected the epigenetic heterogeneity of prostate cancer by analyzing DNA methylation patterns in pure subpopulations of primary cancer cells, on the basis of their differentiation status. GSTP1, an enzyme involved in intracellular detoxification, is highly expressed in prostate basal epithelial cells but is down-regulated in luminal cells by a mechanism independent of DNA methylation. The GSTP1 promoter becomes frequently hypermethylated in prostate cancer, where the majority of cells bear a luminal-like phenotype. However, a small subpopulation of basal cells ( − /CD31 − /CD24 + cells from prostate primary tissues highly enriched for AR + /KRT8 + /GSTP1 low cells bearing a luminal-like phenotype, while generation of prostate primary epithelial cultures gave rise to cells with basal phenotype. In luminal-like cells, GSTP1 was hypermethylated in cancer samples compared to benign controls. However, no significant hypermethylation of GSTP1 was found in the basal-like cells, where the gene was actively expressed in both benign and cancer samples. Lack of GSTP1 promoter methylation was also found in tumor xenografts generated in Rag2 −/+ gammaC −/+ mice from primary prostate cancer tissues. These xenografts do not undergo complete differentiation and show an intermediate phenotype expressing both basal and luminal markers. Moreover, in BPH-1 cells, a fast cycling immortalized cell line, expression and promoter methylation of GSTP1 correlated with the differentiation status of the cells, being hypermethylated in more differentiated cells. Our results strongly indicate that within prostate cancer there is a subpopulation of undifferentiated basal-like cells that do not hypermethylate the GSTP1 promoter. We hypothesize that these cells can differentiate into luminal-like cancer cells, which down-regulate GSTP1 and hypermethylate its promoter as a consequence of aberrant proliferation. Future work will include determination of the mechanism of GSTP1 down-regulation in normal and malignant prostate epithelial differentiation, and whether this mechanism is shared with other genes frequently hypermethylated in prostate cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5209. doi:1538-7445.AM2012-5209