- Open Access
Polycomb-mediated silencing in neuroendocrine prostate cancer
© Clermont et al.; licensee Biomed Central. 2015
- Received: 12 November 2014
- Accepted: 13 March 2015
- Published: 3 April 2015
Neuroendocrine prostate cancer (NEPC) is a highly aggressive subtype of prostate cancer (PCa) for which the median survival remains less than a year. Current treatments are only palliative in nature, and the lack of suitable pre-clinical models has hampered previous efforts to develop novel therapeutic strategies. Addressing this need, we have recently established the first in vivo model of complete neuroendocrine transdifferentiation using patient-derived xenografts. Few genetic differences were observed between parental PCa and relapsed NEPC, suggesting that NEPC likely results from alterations that are epigenetic in nature. Thus, we sought to identify targetable epigenetic regulators whose expression was elevated in NEPC using genome-wide profiling of patient-derived xenografts and clinical samples.
Our data indicate that multiple members of the polycomb group (PcG) family of transcriptional repressors were selectively upregulated in NEPC. Notably, CBX2 and EZH2 were consistently the most highly overexpressed epigenetic regulators across multiple datasets from clinical and xenograft tumor tissues. Given the striking upregulation of PcG genes and other transcriptional repressors, we derived a 185-gene list termed ‘neuroendocrine-associated repression signature’ (NEARS) by overlapping transcripts downregulated across multiple in vivo NEPC models. In line with the striking upregulation of PcG family members, NEARS was preferentially enriched with PcG target genes, suggesting a driving role for PcG silencing in NEPC. Importantly, NEARS was significantly associated with high-grade tumors, metastatic progression, and poor outcome in multiple clinical datasets, consistent with extensive literature linking PcG genes and aggressive disease progression.
We have explored the epigenetic landscape of NEPC and provided evidence of increased PcG-mediated silencing associated with aberrant transcriptional regulation of key differentiation genes. Our results position CBX2 and EZH2 as potential therapeutic targets in NEPC, providing opportunities to explore novel strategies aimed at reversing epigenetic alterations driving this lethal disease.
- Neuroendocrine prostate cancer
- Patient-derived xenografts
With a median survival of less than a year, neuroendocrine prostate cancer (NEPC) represents the most aggressive prostate malignancy and only a small fraction of NEPC patients benefit from current treatments . While NEPC may arise de novo, most cases result from the transdifferentiation of a typical prostate adenocarcinoma (PCa) into NEPC following androgen-deprivation therapy (ADT) [2,3]. Histologically, NEPC is characterized by the presence of small round cells with a prominent nucleus and scant cytoplasm. Typically arranged in a monomorphic pattern, NEPC cells stain positive for neuroendocrine markers such as chromogranin A (CHGA) and synaptophysin (SYP) but negative for PCa markers like androgen receptor (AR) and prostate-specific antigen (PSA) . Since NEPC cells lack AR expression, they probably arise by positive selection following AR suppression, thus providing an adaptive mechanism to achieve castration resistance . Accordingly, due to the recent FDA approval of potent AR-targeting drugs in patients receiving ADT, NEPC incidence is expected to dramatically rise in the near future, creating an urgent need for improved therapeutics . Emerging evidence suggests that epigenetic alterations may be involved in neuroendocrine transdifferentiation (NETD) [6,7], providing unexplored opportunities to identify novel drug targets for this invariably lethal disease.
Epigenetics is a broad term that encompasses all mitotically and meiotically heritable changes in chromatin structure and gene expression that do not result from alterations in DNA sequence . Epigenetic regulation is conferred by covalent modifications on DNA and histones, which define the transcriptional activity of surrounding genomic regions . Historically, the first epigenetic modification discovered was DNA methylation at CpG dinucleotides, a mark typically correlating with transcriptional silencing [10,11]. On histones, numerous chemical modifications can be enzymatically added and removed from N-terminal tails by a large network of epigenetic regulators (EpRs), giving rise to a highly complex ‘histone code’ . Examples of post-translational modifications include methylation, acetylation, ubiquitination, phosphorylation, and many others that are starting to gain recognition . The transcriptional effect conferred by these modifications depends on the particular chemical mark as well as the residue on which it is deposited . Three main types of EpRs dynamically control chromatin: 1) writers, which catalyze the addition of covalent modifications; 2) erasers, which remove these marks; and 3) readers, which directly bind epigenetic modifications . Readers can simultaneously interact with chromatin-remodeling factors, thereby reshaping the epigenome in a reversible fashion . Importantly, almost all EpRs lie downstream of signal transduction pathways, allowing for dynamic chromatin modulation in response to external cues . Accordingly, epigenetic regulation plays a key role in fundamental processes that involve changes in phenotypic identity such as development and cancer [17,18]. Since epigenetic modifications are reversible, EpRs can be pharmacologically targeted by small molecule inhibitors, and a rapidly growing number of ‘epi-drugs’ are receiving FDA approval .
Given the growing interest in identifying clinically relevant epigenetic alterations, considerable attention has been given to the polycomb group (PcG) gene family in the context of human cancer . PcG proteins represent important epigenetic silencers that have been strongly linked to cellular de-differentiation and malignant progression . Assembling into two main polycomb repressive complexes (PRC1 and PRC2), these proteins regulate hundreds of genes involved in major cell fate decisions . In the classical PcG silencing model, PRC2 trimethylates histone H3 at lysine 27 (H3K27me3), through its catalytic subunit EZH2 . This repressive chromatin mark can be directly recognized by the N-terminal chromodomain of chromobox proteins (CBX2,4,6,7,8) , which then recruit PRC1 members to chromatin via a C-terminal domain . At genomic sites, PRC1 can then monoubiquitylate histone H2A (H2AK119ub) through its catalytic components RING1A or RING1B, which further represses PcG target loci . To date, dysregulation of PcG-mediated silencing has been observed in many aggressive tumor types but has not been studied in NEPC. Interestingly, PcG genes are required for neurogenesis and neural stem cell survival [27-29], implying that they may regulate differentiation into neuronal lineages. In line with this idea, we and others have recently shown that EZH2 mRNA levels are upregulated in NEPC , suggesting that alterations in PcG-mediated repression may be involved in NEPC pathogenesis.
Given the lack of xenograft and cell line models to study NEPC, we established the first in vivo model of ADT-induced NEPC using patient-derived xenografts implanted in the mouse subrenal capsule at the Living Tumor Laboratory . Our initial analysis revealed that the original PCa (LTL331) and the relapsed NEPC (LTL331R) tumor lines share a remarkably similar genetic profile, suggesting that epigenetic alterations were likely to drive NEPC . We therefore conducted comparative gene expression analysis between LTL331R and LTL331, as well as in a clinical NEPC cohort, to identify EpRs that were differentially expressed in NEPC. Our data demonstrate that multiple PcG family members are overexpressed in NEPC, notably CBX2 and EZH2. Consistent with these results, we derived a neuroendocrine-associated repression signature (NEARS) that predicted aggressive disease progression and was enriched in PcG targets. Overall, our results support a clinically relevant function for PcG-mediated silencing, revealing novel targets for development of epigenetic therapies in the context of lethal NEPC.
Expression profiling of epigenetic regulators in NEPC
Distribution of 147 investigated epigenetic regulators across different epigenetic modifications, activities, and transcriptional effects
Epigenetic regulator distribution
To further characterize these epigenetic alterations, we focused on individual genes that were aberrantly regulated in both the clinical NEPC cohort and in LTL331R. An important finding was that the PcG H3K27me3 reader CBX2 was the most highly overexpressed transcript in both datasets (Figure 1E, FC 331R/331 = 8.2, FC NEPC/PCa = 10.2). Interestingly, the H3K27me3 writer EZH2 was the second most highly upregulated transcript (Figure 1E, FC 331R/331 = 3.4, FC NEPC/PCa = 9.2), implying that H3K27me3 and its downstream epigenetic effects may be potentiated in the molecular context of NEPC. Of note, the selected gene list also included two other PRC1-containing CBX proteins, CBX6 and CBX8 (Figure 1E), further supporting a role for dysregulated PcG-mediated silencing during neuroendocrine transdifferentiation. In addition to the increase in PcG genes themselves, we also observed that 73% of non-PcG repressors in our list of upregulated EpRs have been reported to directly interact with at least one PcG member (Additional file 3: Table S3). These PcG-interacting proteins were mainly involved in DNA methylation (DNMT1, DNMT3A, DNMT3B, MBD1) and histone methylation (SUV39H1, DOT1L, CHD5, CBX3), suggesting that the upregulation of other EpRs may contribute to the effect of altered PcG-mediated silencing in NEPC [32,33].
PcG gene expression in LTL patient-derived xenografts
Another similarity between NEPC and SCLC is that both malignancies were reported to have frequent RB1 inactivation, which contributes to their high proliferative rate [38,39]. Thus, we investigated the RB1 status in our patient-derived xenograft models. As expected, RB1 expression was relatively high in almost all PCa xenografts while the expression of CBX2 and EZH2 was considerably lower (Additional file 6: Figure S1). Conversely, the expression of RB1 was undetectable in the NEPC tumor lines LTL352 and LTL370 while LTL331R exhibited a modest increase (Additional file 6: Figure S1). Genomic characterization of these models revealed that both LTL352 and LTL had homozygous RB1 deletion while LTL331R had a monoallelic loss and a hemyzygous mutation in RB1 (Wyatt et al. unpublished). Taken together, these data suggest that aberrant PcG-mediated silencing may cooperate with RB1 inactivation to sustain the high proliferative rate of NEPC.
Polycomb silencing and neuroendocrine-associated repression signature
List of top 12 literature-derived concepts most significantly associated with NEARS
NEARS literature-defined Oncomine concept analysis
CBX8 target genes in human embryonic fibroblasts
Upregulated genes in neutrophils compared to other blood cells
Downregulated in human embryonic stem cells vs differentiated counterparts
Downregulated genes in prostate cancer after androgen ablation therapy
SUZ12 target genes in human embryonic stem cells
Trimethylated H3K27 target genes in human embryonic stem cells
DrugBank targets - FDA approved
Upregulated genes in weakly invasive colon cancer cells
Polycomb group target genes in human embryonic stem cells
Upregulated genes in prostate cancer cells in response to synthetic androgen R1881
EED target genes in human embryonic fibroblasts
Trimethylated H3K27 target genes in human embryonic fibroblasts
Correlations between downregulation of NEARS and poor prognostic factors in clinical prostate tumors
Clinical parameters associated with NEARS
1° vs Met
Taylor Prostate 3
Advanced Gleason Score
Advanced Gleason Score
Advanced Gleason Score
Advanced Gleason Score
Advanced Gleason Score
Taylor Prostate 3
Advanced Gleason Score
Advanced Gleason Score
Dead at 3 years
Recurrence at 5 years
Taylor Prostate 3
Recurrence at 3 years
Taylor Prostate 3
Recurrence at 5 years
Dead at 5 years
Recurrence at 3 years
NEPC is an incurable malignancy which is expected to become more prevalent given the widespread use of potent AR-targeting drugs, which positively select for AR-negative NEPC cells . However, the lack of suitable pre-clinical NEPC models has limited investigations into the molecular underpinnings of NEPC, therefore hampering therapeutic development of novel agents to treat this deadly disease. To circumvent this issue, we established a high fidelity, patient-derived xenograft model retaining classical NEPC features observed in the clinic  that allows us to investigate the molecular mechanisms involved in NEPC transdifferentiation. Using this model, we identified many PcG genes that are dysregulated in NEPC, a finding that was also observed in a clinical cohort and in additional patient-derived NEPC xenografts from the Living Tumor Laboratory. Moreover, we derived a NEARS that was predictive of PcG gain of function and aggressive disease progression. Based on these results, we propose that aberrant PcG-mediated silencing contributes to NEPC pathogenesis and that disrupting PcG activity may emerge as a valuable therapeutic strategy in NEPC.
Within the epigenetic landscape of NEPC, there was a global upregulation of repressive EpRs, and more than 70% of them were reported to directly interact with PcG complexes. Notably, all three genes encoding DNMTs were overexpressed in NEPC, suggesting that aberrant DNA methylation may synergize with alterations in PcG-mediated repression. In line with those results, increasing evidence supports the idea that PcG activity dictates DNMT recruitment to chromatin at target loci, implying a central role for PcG complexes in DNA methylation and its resulting epigenetic effects [42,43]. Aberrant DNA methylation has previously been reported in PCa, and the question of how DNA methylation patterns vary between PCa and NEPC remains unanswered . Since cell fate transitions involve differential DNA methylation at enhancer regions , an attractive hypothesis is that PcG complexes and DNMTs synergize to regulate key enhancers relevant to neuroendocrine transdifferentiation. Consequently, future experiments should explore the distribution of DNA methylation in the context of genome-wide PRC1 and PRC2 chromatin binding in NEPC cells.
In line with the upregulation of PcG genes observed in NEPC, we derived a list of genes recurrently silenced in multiple NEPC models (NEARS) that was strongly associated with PcG-mediated repression. Moreover, silencing of NEARS in localized PCa tissue predicts an aggressive clinical course, consistent with the notion that certain PCas may be predisposed to acquire neuroendocrine-like features in a PcG-dependent manner. Interestingly, NEARS contained many PcG target genes in embryonic stem cells, implying that PcG activity in NEPC may suppress epithelial differentiation through silencing of genes specifying specialization into prostatic tissues, particularly since NEARS included some AR-regulated genes. In line with this idea, epigenetic reprogramming of a similar nature has been repeatedly observed in many aggressive tumor types featuring aberrant PcG-mediated repression . In addition, neurogenesis is PcG-dependent [29,46], thus it seems likely that the activation of neuroendocrine-specific transcriptional programs may also be facilitated by increased PcG activity. Supporting this idea, we observed preferential overexpression of PcG genes CBX2 and EZH2 in SCLC, which represents a lung cancer subtype with neuroendocrine differentiation. Taken together, these results suggest that gene expression profiles regulated by PcG genes during normal embryogenesis are re-established in NEPC and possibly other neuroendocrine malignancies.
Despite playing imperative roles during embryonic development , CBX2 has been overlooked for many years in the cancer literature. Genetic inactivation of CBX2 (M33 in mice) causes lethality in 50% of subjects and the remaining progeny exhibit gonadal, adrenal, and splenic defects, reflecting a critical function for CBX2 in cellular differentiation [47,48]. In this paper, we report that CBX2 was consistently the most upregulated EpR in NEPC compared to PCa in our analyzed datasets. These findings support our recent discovery that CBX2 confers a genomic and transcriptomic profile consistent with that of an oncogene . We have shown that high CBX2 expression correlates with poor patient outcome and more aggressive tumor phenotypes , in line with the clinical features of NEPC.
From a molecular standpoint, it is important to note that CBX2 upregulation observed in NEPC occurs in the context of overexpressed EZH2 and other PRC2 members, which likely alters the genomic distribution of the H3K27me3 mark. This has considerable mechanistic implications since CBX2 can directly bind H3K27me3 and recruit PRC1 to H3K27me3 sites, which solidifies transcriptional repression at target loci . Thus, CBX2 overexpression might represent an alteration necessary to mediate the downstream epigenetic effect of PRC2 gain of function. Biochemical evidence supports this hypothesis since, although PRC1 composition varies in a context-dependent manner, PRC1 complexes found at H3K27me3 sites are preferentially enriched in CBX2 and not other CBX proteins . While the relative contribution of CBX2 compared to other CBX members remains under investigation, the strong upregulation of CBX2 in NEPC, in addition to its critical role in cellular differentiation, suggest that CBX2 is functionally involved in the progression of NEPC.
Finally, we believe that the reported aberrations in PcG-mediated silencing have clear therapeutic implications, particularly given the emerging improvements in targeting the cancer epigenome [50,51]. In particular, we believe the interaction between CBX2 and H3K27me3 bridges the function of PRC2 and PRC1, thus representing a critical junction in this altered epigenetic pathway . A few strategies can be put forward to therapeutically target this axis in the context of NEPC. First, small molecule inhibitors interfering with the methyltransferase activity of EZH2 have already been developed and warrant further investigation in NEPC . Second, antagonists of the CBX2 chromodomain represent another promising path, as they would disrupt the binding between CBX2 and H3K27me3. At present, there are no small molecules directly targeting CBX2, although the development of CBX7 antagonists hints that a similar strategy could also be employed for CBX2 [54,55]. Third, antisense oligonucleotides (ASOs) may be used to reduce the expression of key PcG genes such as CBX2 and EZH2. An exponentially increasing number of ASOs have entered clinical testing, highlighting the potential of ASOs as therapeutic agents . Taken together, our results highlight relevant alterations in Polycomb-mediated silencing that may be clinically targetable in lethal NEPC, thereby adding to the growing landscape of cancer epigenetics.
Given the sparsity of adequate pre-clinical NEPC models, we investigated the epigenetic underpinnings of NEPC using innovative patient-derived xenograft models available at the Living Tumor Laboratory. Data obtained using this model was further validated in a clinical NEPC cohort. Using an integrative approach, we identified a striking upregulation of many key PcG genes, notably CBX2 and EZH2. In addition, we reported a clinically relevant dysregulation of PcG target genes in multiple NEPC models, consistent with a driving role for PcG complexes. Thus, our study reveals novel insights into NEPC pathogenesis and provides the rationale to establish therapeutic strategies aimed at disrupting altered PcG-mediated silencing.
Clinical expression datasets
Originating from the work of Beltran et al. the clinical NEPC cohort contained 7 NEPC tumors and 30 PCas which contained less than 10% stroma, as confirmed by a certified pathologist . Prognostic analysis of NEARS, as well as the selected list of EpRs, was conducted using PCa datasets available from the Oncomine resource (www.oncomine.com) , which encompassed more than 3,800 patients. Clinical parameters assessed for differential gene expression included grade, metastasis, outcome, and stage. Analysis of literature-derived concepts correlated with NEARS was also done through the Oncomine resource, and the final list was unbiasedly determined using the lowest P values of associated concepts. Expression profiles of lung malignancies were generated by The Clinical Lung Cancer Genome Project (CLCGP) and Network Genomic Medicine (NGM)  (http://www.uni-koeln.de/med-fak/clcgp/).
We established a list of targetable EpRs based on the following inclusion criteria: 1) being involved either in DNA methylation, histone acetylation, or histone methylation and 2) function as a writer, eraser, or reader of the epigenetic code. EpRs regulating DNA methylation were also subdivided into the same functional categories as those established for histone modifications (that is, writer = DNA methyltransferase (DNMT), eraser = ten eleven translocation (TET), reader = methyl CpG-binding domain (MBD)). Analysis of relevant literature [57-65] was conducted to identify such candidates, which were subsequently assessed in our NEPC datasets. In a similar way, a list of PcG genes was also derived from the literature using recent review papers written by authorities in the field [52,66,67]. We also derived a list of repressors that directly interact with PcG proteins based on literature findings (Additional file 3: Table S3). Finally, NEARS was established by combining the 185 genes downregulated in all three of the following datasets: 1) LTL331R/LTL331, 2) Clinical NEPC/PCa, and 3) LTL331/all LTL PCa .
Establishment of paraffin-embedded tissue sections and immunostaining were conducted as previously described [6,68]. Detection was done using primary antibodies specific to PSA (rabbit polyclonal, Dako, Glostrup, Denmark), SYP (mouse monoclonal, Dako), CBX2 (rabbit polyclonal, Pierce, Rockford, USA), and EZH2 (rabbit monoclonal, Cell Signaling, Danvers, USA), as well as a goat anti-rabbit secondary antibody (Vector Laboratory, Peterborough, UK).
As previously described , the Living Tumor Lab (www.livingtumorlab.com) has established a bank of high-fidelity patient-derived xenografts. Tumor tissues were obtained from patients through a protocol approved by the Clinical Research Ethics Board of the University of British Columbia (UBC) and the BC Cancer Agency (BCCA). All patients signed a consent form approved by the Ethics Board (UBC Ethics Board #: H09-01628 and H04-60131; VCHRI #: V09-0320 and V07-0058). In this study, we used microarray data derived from ten PCa and three NEPC tumor lines, all of which retain the classical histological features of their respective subtype. The microarray gene expression data for these tumor lines have been previously deposited in the NCBI Gene Expression Omnibus (GEO) and are freely available under the accession number GSE41193.
All statistical analyses were carried out with the Graphpad Prism software (version 6.0) using a statistical threshold of P ≤ 0.05 unless otherwise stated.
This work was supported by the Canadian Cancer Society Research Institute (CCSRI, CDH), Canadian Institutes of Health Research (YW), Terry Fox Research Institute (YW), Prostate Cancer Canada (CC, YW), BC Cancer Foundation (YW), Michael Smith Foundation for Health Research (FC), and CCSRI (YW). The authors thank past and current lab members for insightful discussions.
- Palmgren JS, Karavadia SS, Wakefield MR. Unusual and underappreciated: small cell carcinoma of the prostate. Semin Oncol. 2007;34:22–9.View ArticlePubMedGoogle Scholar
- Yuan TC, Veeramani S, Lin MF. Neuroendocrine-like prostate cancer cells: neuroendocrine transdifferentiation of prostate adenocarcinoma cells. Endocr Relat Cancer. 2007;14:531–47.View ArticlePubMedGoogle Scholar
- Lotan TL, Gupta NS, Wang W, Toubaji A, Haffner MC, Chaux A, et al. ERG gene rearrangements are common in prostatic small cell carcinomas. Mod Pathol. 2011;24:820–8.View ArticlePubMed CentralPubMedGoogle Scholar
- Furtado P, Lima MV, Nogueira C, Franco M, Tavora F. Review of small cell carcinomas of the prostate. Prostate Cancer. 2011;2011:543272.View ArticlePubMed CentralPubMedGoogle Scholar
- Beltran H, Tomlins S, Aparicio A, Arora V, Rickman D, Ayala G, et al. Aggressive variants of castration-resistant prostate cancer. Clin Cancer Res. 2014;20:2846–50.View ArticlePubMedGoogle Scholar
- Lin D, Wyatt AW, Xue H, Wang Y, Dong X, Haegert A, et al. High fidelity patient-derived xenografts for accelerating prostate cancer discovery and drug development. Cancer Res. 2014;74:1272–83.View ArticlePubMedGoogle Scholar
- Beltran H, Rickman DS, Park K, Chae SS, Sboner A, MacDonald TY, et al. Molecular characterization of neuroendocrine prostate cancer and identification of new drug targets. Cancer Discov. 2011;1:487–95.View ArticlePubMed CentralPubMedGoogle Scholar
- Berger SL, Kouzarides T, Shiekhattar R, Shilatifard A. An operational definition of epigenetics. Genes Dev. 2009;23:781–3.View ArticlePubMed CentralPubMedGoogle Scholar
- Goldberg AD, Allis CD, Bernstein E. Epigenetics: a landscape takes shape. Cell. 2007;128:635–8.View ArticlePubMedGoogle Scholar
- Holliday R, Pugh JE. DNA modification mechanisms and gene activity during development. Science. 1975;187:226–32.View ArticlePubMedGoogle Scholar
- Riggs AD. X inactivation, differentiation, and DNA methylation. Cytogenet Cell Genet. 1975;14:9–25.View ArticlePubMedGoogle Scholar
- Allfrey VG, Faulkner R, Mirsky AE. Acetylation and methylation of histones and their possible role in the regulation of RNA synthesis. Proc Natl Acad Sci U S A. 1964;51:786–94.View ArticlePubMed CentralPubMedGoogle Scholar
- Arnaudo AM, Garcia BA. Proteomic characterization of novel histone post-translational modifications. Epigenetics Chromatin. 2013;6:24.View ArticlePubMed CentralPubMedGoogle Scholar
- Bannister AJ, Kouzarides T. Regulation of chromatin by histone modifications. Cell Res. 2011;21:381–95.View ArticlePubMed CentralPubMedGoogle Scholar
- Jenuwein T, Allis CD. Translating the histone code. Science. 2001;293:1074–80.View ArticlePubMedGoogle Scholar
- Lu C, Thompson CB. Metabolic regulation of epigenetics. Cell Metab. 2012;16:9–17.View ArticlePubMed CentralPubMedGoogle Scholar
- Cantone I, Fisher AG. Epigenetic programming and reprogramming during development. Nat Struct Mol Biol. 2013;20:282–9.View ArticlePubMedGoogle Scholar
- Esteller M. Epigenetics in cancer. N Engl J Med. 2008;358:1148–59.View ArticlePubMedGoogle Scholar
- Nebbioso A, Carafa V, Benedetti R, Altucci L. Trials with 'epigenetic' drugs: an update. Mol Oncol. 2012;6:657–82.View ArticlePubMedGoogle Scholar
- Richly H, Aloia L, Di Croce L. Roles of the polycomb group proteins in stem cells and cancer. Cell Death Dis. 2011;2:e204.View ArticlePubMed CentralPubMedGoogle Scholar
- Bracken AP, Helin K. Polycomb group proteins: navigators of lineage pathways led astray in cancer. Nat Rev Cancer. 2009;9:773–84.View ArticlePubMedGoogle Scholar
- Lee TI, Jenner RG, Boyer LA, Guenther MG, Levine SS, Kumar RM, et al. Control of developmental regulators by polycomb in human embryonic stem cells. Cell. 2006;125:301–13.View ArticlePubMed CentralPubMedGoogle Scholar
- Margueron R, Reinberg D. The polycomb complex PRC2 and its mark in life. Nature. 2011;469:343–9.View ArticlePubMed CentralPubMedGoogle Scholar
- Kaustov L, Ouyang H, Amaya M, Lemak A, Nady N, Duan S, et al. Recognition and specificity determinants of the human cbx chromodomains. J Biol Chem. 2011;286:521–9.View ArticlePubMed CentralPubMedGoogle Scholar
- Senthilkumar R, Mishra RK. Novel motifs distinguish multiple homologues of polycomb in vertebrates: expansion and diversification of the epigenetic toolkit. BMC Genomics. 2009;10:549.View ArticlePubMed CentralPubMedGoogle Scholar
- Levine SS, Weiss A, Erdjument-Bromage H, Shao Z, Tempst P, Kingston RE. The core of the polycomb repressive complex is compositionally and functionally conserved in flies and humans. Mol Cell Biol. 2002;22:6070–8.View ArticlePubMed CentralPubMedGoogle Scholar
- Pereira JD, Sansom SN, Smith J, Dobenecker MW, Tarakhovsky A, Livesey FJ. Ezh2, the histone methyltransferase of PRC2, regulates the balance between self-renewal and differentiation in the cerebral cortex. Proc Natl Acad Sci U S A. 2010;107:15957–62.View ArticlePubMed CentralPubMedGoogle Scholar
- Egan CM, Nyman U, Skotte J, Streubel G, Turner S, O'Connell DJ, et al. CHD5 is required for neurogenesis and has a dual role in facilitating gene expression and polycomb gene repression. Dev Cell. 2013;26:223–36.View ArticlePubMedGoogle Scholar
- Bello B, Holbro N, Reichert H. Polycomb group genes are required for neural stem cell survival in postembryonic neurogenesis of Drosophila. Development. 2007;134:1091–9.View ArticlePubMedGoogle Scholar
- Kouzarides T. Chromatin modifications and their function. Cell. 2007;128:693–705.View ArticlePubMedGoogle Scholar
- Rhodes DR, Yu J, Shanker K, Deshpande N, Varambally R, Ghosh D, et al. ONCOMINE: a cancer microarray database and integrated data-mining platform. Neoplasia. 2004;6:1–6.View ArticlePubMed CentralPubMedGoogle Scholar
- Viré E, Brenner C, Deplus R, Blanchon L, Fraga M, Didelot C, et al. The polycomb group protein EZH2 directly controls DNA methylation. Nature. 2006;439:871–4.View ArticlePubMedGoogle Scholar
- Gao Z, Zhang J, Bonasio R, Strino F, Sawai A, Parisi F, et al. PCGF homologs, CBX proteins, and RYBP define functionally distinct PRC1 family complexes. Mol Cell. 2012;45:344–56.View ArticlePubMed CentralPubMedGoogle Scholar
- Oesterling JE, Hauzeur CG, Farrow GM. Small cell anaplastic carcinoma of the prostate: a clinical, pathological and immunohistological study of 27 patients. J Urol. 1992;147:804–7.PubMedGoogle Scholar
- Shah RB, Mehra R, Chinnaiyan AM, Shen R, Ghosh D, Zhou M, et al. Androgen-independent prostate cancer is a heterogeneous group of diseases: lessons from a rapid autopsy program. Cancer Res. 2004;64:9209–16.View ArticlePubMedGoogle Scholar
- Molina JR, Yang P, Cassivi SD, Schild SE, Adjei AA. Non-small cell lung cancer: epidemiology, risk factors, treatment, and survivorship. Mayo Clin Proc. 2008;83:584–94.View ArticlePubMed CentralPubMedGoogle Scholar
- (CLCGP) CLCGP, (NGM) NGM. A genomics-based classification of human lung tumors. Sci Transl Med. 2013;5:209ra153.Google Scholar
- Tan HL, Sood A, Rahimi HA, Wang W, Gupta N, Hicks J, et al. Rb loss is characteristic of prostatic small cell neuroendocrine carcinoma. Clin Cancer Res. 2014;20:890–903.View ArticlePubMed CentralPubMedGoogle Scholar
- Sutherland KD, Proost N, Brouns I, Adriaensen D, Song JY, Berns A. Cell of origin of small cell lung cancer: inactivation of Trp53 and Rb1 in distinct cell types of adult mouse lung. Cancer Cell. 2011;19:754–64.View ArticlePubMedGoogle Scholar
- Bolton EC, So AY, Chaivorapol C, Haqq CM, Li H, Yamamoto KR. Cell- and gene-specific regulation of primary target genes by the androgen receptor. Genes Dev. 2007;21:2005–17.View ArticlePubMed CentralPubMedGoogle Scholar
- Terry S, Beltran H. The many faces of neuroendocrine differentiation in prostate cancer progression. Front Oncol. 2014;4:60.View ArticlePubMed CentralPubMedGoogle Scholar
- Schlesinger Y, Straussman R, Keshet I, Farkash S, Hecht M, Zimmerman J, et al. Polycomb-mediated methylation on Lys27 of histone H3 pre-marks genes for de novo methylation in cancer. Nat Genet. 2007;39:232–6.View ArticlePubMedGoogle Scholar
- Ohm JE, McGarvey KM, Yu X, Cheng L, Schuebel KE, Cope L, et al. A stem cell-like chromatin pattern may predispose tumor suppressor genes to DNA hypermethylation and heritable silencing. Nat Genet. 2007;39:237–42.View ArticlePubMed CentralPubMedGoogle Scholar
- Kron K, Trudel D, Pethe V, Briollais L, Fleshner N, van der Kwast T, et al. Altered DNA methylation landscapes of polycomb-repressed loci are associated with prostate cancer progression and ERG oncogene expression in prostate cancer. Clin Cancer Res. 2013;19:3450–61.View ArticlePubMedGoogle Scholar
- Ziller MJ, Gu H, Müller F, Donaghey J, Tsai LT, Kohlbacher O, et al. Charting a dynamic DNA methylation landscape of the human genome. Nature. 2013;500:477–81.View ArticlePubMedGoogle Scholar
- Testa G. The time of timing: how polycomb proteins regulate neurogenesis. Bioessays. 2011;33:519–28.View ArticlePubMedGoogle Scholar
- Katoh-Fukui Y, Tsuchiya R, Shiroishi T, Nakahara Y, Hashimoto N, Noguchi K, et al. Male-to-female sex reversal in M33 mutant mice. Nature. 1998;393:688–92.View ArticlePubMedGoogle Scholar
- Katoh-Fukui Y, Owaki A, Toyama Y, Kusaka M, Shinohara Y, Maekawa M, et al. Mouse polycomb M33 is required for splenic vascular and adrenal gland formation through regulating Ad4BP/SF1 expression. Blood. 2005;106:1612–20.View ArticlePubMedGoogle Scholar
- Clermont PL, Sun L, Crea F, Thu KL, Zhang A, Parolia A, et al. Genotranscriptomic meta-analysis of the polycomb gene CBX2 in human cancers: initial evidence of an oncogenic role. Br J Cancer. 2014;111(8):1663–72.View ArticlePubMedGoogle Scholar
- Filippakopoulos P, Qi J, Picaud S, Shen Y, Smith WB, Fedorov O, et al. Selective inhibition of BET bromodomains. Nature. 2010;468:1067–73.View ArticlePubMed CentralPubMedGoogle Scholar
- Dawson MA, Kouzarides T. Cancer epigenetics: from mechanism to therapy. Cell. 2012;150:12–27.View ArticlePubMedGoogle Scholar
- Di Croce L, Helin K. Transcriptional regulation by polycomb group proteins. Nat Struct Mol Biol. 2013;20:1147–55.View ArticlePubMedGoogle Scholar
- Crea F, Hurt EM, Mathews LA, Cabarcas SM, Sun L, Marquez VE, et al. Pharmacologic disruption of polycomb repressive complex 2 inhibits tumorigenicity and tumor progression in prostate cancer. Mol Cancer. 2011;10:40.View ArticlePubMed CentralPubMedGoogle Scholar
- Tabet S, Douglas SF, Daze KD, Garnett GA, Allen KJ, Abrioux EM, et al. Synthetic trimethyllysine receptors that bind histone 3, trimethyllysine 27 (H3K27me3) and disrupt its interaction with the epigenetic reader protein CBX7. Bioorg Med Chem. 2013;21:7004–10.View ArticlePubMedGoogle Scholar
- Simhadri C, Daze KD, Douglas SF, Quon TT, Dev A, Gignac MC, et al. Chromodomain antagonists that target the polycomb-group methyllysine reader protein chromobox homolog 7 (CBX7). J Med Chem. 2014;57:2874–83.View ArticlePubMedGoogle Scholar
- Dean NM, Bennett CF. Antisense oligonucleotide-based therapeutics for cancer. Oncogene. 2003;22:9087–96.View ArticlePubMedGoogle Scholar
- Bestor TH. The DNA, methyltransferases of mammals. Hum Mol Genet. 2000;9:2395–402.View ArticlePubMedGoogle Scholar
- Allis CD, Berger SL, Cote J, Dent S, Jenuwien T, Kouzarides T, et al. New nomenclature for chromatin-modifying enzymes. Cell. 2007;131:633–6.View ArticlePubMedGoogle Scholar
- Kinney SR, Pradhan S. Ten eleven translocation enzymes and 5-hydroxymethylation in mammalian development and cancer. Adv Exp Med Biol. 2013;754:57–79.View ArticlePubMedGoogle Scholar
- Kohli RM, Zhang Y. TET enzymes, TDG and the dynamics of DNA demethylation. Nature. 2013;502:472–9.View ArticlePubMed CentralPubMedGoogle Scholar
- Dokmanovic M, Clarke C, Marks PA. Histone deacetylase inhibitors: overview and perspectives. Mol Cancer Res. 2007;5:981–9.View ArticlePubMedGoogle Scholar
- North BJ, Verdin E. Sirtuins: Sir2-related NAD-dependent protein deacetylases. Genome Biol. 2004;5:224.View ArticlePubMed CentralPubMedGoogle Scholar
- Parry L, Clarke AR. The roles of the methyl-CpG binding proteins in cancer. Genes Cancer. 2011;2:618–30.View ArticlePubMed CentralPubMedGoogle Scholar
- Filippakopoulos P, Knapp S. The bromodomain interaction module. FEBS Lett. 2012;586:2692–704.View ArticlePubMedGoogle Scholar
- Tajul-Arifin K, Teasdale R, Ravasi T, Hume DA, Mattick JS, Group RG, et al. Identification and analysis of chromodomain-containing proteins encoded in the mouse transcriptome. Genome Res. 2003;13:1416–29.View ArticlePubMed CentralPubMedGoogle Scholar
- Schwartz YB, Pirrotta V. A new world of polycombs: unexpected partnerships and emerging functions. Nat Rev Genet. 2013;14:853–64.View ArticlePubMedGoogle Scholar
- Simon JA, Kingston RE. Occupying chromatin: polycomb mechanisms for getting to genomic targets, stopping transcriptional traffic, and staying put. Mol Cell. 2013;49:808–24.View ArticlePubMed CentralPubMedGoogle Scholar
- Lin D, Watahiki A, Bayani J, Zhang F, Liu L, Ling V, et al. ASAP1, a gene at 8q24, is associated with prostate cancer metastasis. Cancer Res. 2008;68:4352–9.View ArticlePubMedGoogle Scholar
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