Role Of Polycomb Repressive Complex 2 Research Articles

EZH2 represses mesenchymal genes and upholds the epithelial state of breast carcinoma cells

Emerging studies support that the polycomb repressive complex 2 (PRC2) regulates phenotypic changes of carcinoma cells by modulating their shifts among metastable states within the epithelial and mesenchymal spectrum. This new role of PRC2 in cancer has been recently proposed to stem from the ability of its catalytic subunit EZH2 to bind and modulate the transcription of mesenchymal genes during epithelial-mesenchymal transition (EMT) in lung cancer cells. Here, we asked whether this mechanism is conserved in other types of carcinomas. By combining TGF-β-mediated reversible induction of epithelial to mesenchymal transition and inhibition of EZH2 methyltransferase activity, we demonstrate that EZH2 represses a large set of mesenchymal genes and favours the residence of breast cancer cells towards the more epithelial spectrum during EMT. In agreement, analysis of human patient samples supports that EZH2 is required to efficiently repress mesenchymal genes in breast cancer tumours. Our results indicate that PRC2 operates through similar mechanisms in breast and lung cancer cells. We propose that PRC2-mediated direct transcriptional modulation of the mesenchymal gene expression programme is a conserved molecular mechanism underlying cell dissemination across human carcinomas.

A novel interplay between PRC2 and miR-3189 regulates epithelial-mesenchymal transition (EMT) via modulating COL6A2 in glioblastoma.

Recent studies have shed light on disrupted collagen signaling in Gliomas, yet the regulatory landscape remains largely unexplored. This study enquired into the role of polycomb repressive complex-2 (PRC2)-mediated H3K27me3 modification, a key epigenetic factor in glioma. Using in-house data, we identified miRNAs downregulated in glioblastoma (GBM) with the potential to regulate Collagen VI family genes. Notably, miR-3189 emerged as a prime PRC2 target. Its expression was significantly downregulated in Indian GBM patients as well as other glioma cohorts. Mechanistic insights, involving Luciferase assays, mutagenesis, and Western blot analysis, confirmed direct targeting of Collagen VI member COL6A2 by miR-3189-3p. Functional assays demonstrated that miR-3189-3p restrained GBM malignancy by inhibiting proliferation, migration, and epithelial-mesenchymal transition (EMT). Conversely, COL6A2 overexpressed in GBM patients, countered miR-3189, and promoted the malignant phenotype. Gene set enrichment analysis highlighted EMT enrichment in GBM patients with elevated COL6A2 expression, carrying prognostic implications. This study uncovers intricate interactions between two epigenetic regulators-H3K27me3 and miR-3189-working synergistically to modulate Collagen VI gene; thus, influencing the malignancy of GBM. Targeting this H3K27me3|miR-3189-3p|COL6A2 axis presents a potential therapeutic avenue against GBM.

The Polycomb group protein MEDEA controls cell proliferation and embryonic patterning in Arabidopsis.

SummaryEstablishing the embryonic body plan of multicellular organisms relies on precisely orchestrated cell divisions coupled with pattern formation, which, in animals, are regulated by Polycomb group (PcG) proteins. The conserved Polycomb Repressive Complex 2 (PRC2) mediates H3K27 trimethylation and comes in different flavors in Arabidopsis. The PRC2 catalytic subunit MEDEA is required for seed development; however, a role for PRC2 in embryonic patterning has been dismissed. Here, we demonstrate that embryos derived from medea eggs abort because MEDEA is required for patterning and cell lineage determination in the early embryo. Similar to PcG proteins in mammals, MEDEA regulates embryonic patterning and growth by controlling cell-cycle progression through repression of CYCD1;1, which encodes a core cell-cycle component. Thus, Arabidopsis embryogenesis is epigenetically regulated by PcG proteins, revealing that the PRC2-dependent modulation of cell-cycle progression was independently recruited to control embryonic cell proliferation and patterning in animals and plants.

Genetic Impairments of PRC2 Activity in Oncology: Problems and Prospects

PRC2 (Polycomb repressive complex 2) is a conserved protein complex in multicellular organisms that is required to maintain gene repression. The catalytic subunit of PRC2, the EZH2 protein, provides the methylation of histone H3K27 (H3K27me1/2/3). It was demonstrated that a number of human cancers were associated with overexpression of PRC2 subunits, as well as with mutations that enhanced the EZH2 catalytic activity. At the same time, a group of cancers correlate with mutations that inhibit PRC2. A number of small molecule inhibitors to the PRC2 subunits have been developed, primarily to EZH2. One of these, tazemetostat, received approval in January 2020 in the United States for the treatment of epithelioid sarcoma. This review focuses on the role of PRC2 in cancer development and summarizes information on the designed PRC2 inhibitors.

Memory of Divisional History Directs the Continuous Process of Primitive Hematopoietic Lineage Commitment.

SummaryHematopoietic stem cells (HSCs) exist in a dormant state and progressively lose regenerative potency as they undergo successive divisions. Why this functional decline occurs and how this information is encoded is unclear. To better understand how this information is stored, we performed RNA sequencing on HSC populations differing only in their divisional history. Comparative analysis revealed that genes upregulated with divisions are enriched for lineage genes and regulated by cell-cycle-associated transcription factors, suggesting that proliferation itself drives lineage priming. Downregulated genes are, however, associated with an HSC signature and targeted by the Polycomb Repressive Complex 2 (PRC2). The PRC2 catalytic subunits Ezh1 and Ezh2 promote and suppress the HSC state, respectively, and successive divisions cause a switch from Ezh1 to Ezh2 dominance. We propose that cell divisions drive lineage priming and Ezh2 accumulation, which represses HSC signature genes to consolidate information on divisional history into memory.

Abstract 5188: Epigenetic changes mediated by polycomb repressive complex 2 are associated with cisplatin acquired resistance in testicular germ cell tumor

Abstract Testicular germ cell tumors (TGCTs) represent the most common carcinoma affecting young men. TGCTs serve as a paradigm of chemo-sensitive tumors as more than 80% of metastatic disease can be cured with cisplatin-based chemotherapy. However, therapy resistance can occur, which results in poor patient outcomes. The mechanisms of cisplatin resistant in these tumors remain largely undefined. To study the mechanism of cisplatin acquired resistance we generated several independent, acquired resistant clones of parental NT2/D1, 833K and 2102EP testicular cancer cells employing an in vitro protocol designed to mimic the standard-of-care cisplatin regimen used to treat TGCT patients. We further characterized 10 of these clonal lines and confirmed stable cisplatin resistance ranging from 5- to 30-fold. After confirming the cisplatin resistance, we performed RNA seq transcriptomic profiling, differential gene expression analysis, DAVID and GSEA. Remarkably, RNA-seq based transcriptional profiling revealed highly significant alterations shared between the majority of the resistant cells regardless of their parental cell of origin. This includes apparent amplification of chromosomal region 17q21-25 in 8 of 10 lines. Unexpectedly, 7 of 10 lines had a highly significant enrichment of genes regulated by H3K27 methylation and polycomb repressive complex 2 (PRC2). Transcription factor prediction analysis of genes differentially expressed between resistant and parental cells revealed that polycomb complex members were among the most highly ranked predicted transcription factors responsible for the gene expression changes. These include EZH2, SUZ12, JARID2 and BMI1. We will present our ongoing studies investigating the role of PRC2 and H3K27 methylation in mediating cisplatin resistance in these cells and in patient samples. Together our data suggests that repression of H3K27 methylation may be a mechanism of cisplatin acquired resistance in TGCTs and that restoration of PRC2 function could be a viable approach to overcome treatment failure. Citation Format: Ratnakar Singh, Zeeshan Fazal, Emmanuel Bikorimana, Andrea Corbet, Jennifer Rodriguez, Alyssa Steege, Sarah J. Freemantle, Michael J. Spinella. Epigenetic changes mediated by polycomb repressive complex 2 are associated with cisplatin acquired resistance in testicular germ cell tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5188.

1342 Polycomb repressive complex 2 controls differentiation program in human epidermal progenitor cells

Polycomb repressive complex 2 (PRC2) catalyses methylation of Lys-27 of histone H3 leading to transcriptional repression of target genes. In mouse skin, Ezh2, a catalytic subunit of PRC2, prevents premature differentiation of epidermal progenitor cells and their ectopic differentiation into Merkel cells. However, the role of PRC2 in human skin homeostasis remains unclear. Here, we show an increased EZH2 and H2K27me3 expression in differentiated suprabasal keratinocytes in human epidermis. Similarly, Ca2+-induced differentiation markedly up-regulated EZH2 expression in primary human epidermal keratinocytes (NHEK). Interestingly, knockdown of PRC2 subunits EZH1, EZH2 and EED using siRNA and small molecule inhibitors GSK126 and UNC1999 up-regulated expression of KRT1, LOR and FLG genes and suppressed cell proliferation in NHEKs cultured in low Ca2+ condition. However, disruption of the PRC2 function in already differentiated keratinocytes did not affect expression of the terminal differentiation genes. Bioinformatic analysis of genome-wide EZH2 and H3K27me3 distribution identified distinct sets of PRC2 targets in undifferentiated progenitor cells and their differentiated progeny. Taken together, these results highlight a critical role for PRC2 in human epithelial progenitor cells proliferation and differentiation.

Depletion of polycomb repressive complex 2 core component EED impairs fetal hematopoiesis

Polycomb repressive complex 2 (PRC2), a H3K27me3 methyltransferase complex, promotes the development of many organs by silencing ectopic transcription program. However, currently little is known about the role of PRC2 in blood and vascular development. In this study, we interrogated the function of embryonic ectoderm development (EED), a core PRC2 component, in both endothelial and hematopoietic tissues by inactivating a floxed murine EED allele with Tie2Cre, which catalyzes recombination in endothelial and hematopoietic lineages. Murine EEDfl/fl;Tie2Cre (EEDCKO) embryos died at embryonic day (E) 13.5. We did not observe structural abnormalities of blood vessels or cardiac valves, suggesting that EED is dispensable in endothelial cells for initial steps of vascular development. EEDCKO embryos were pale and had abnormal livers. Flow cytometry of fetal liver cells showed that EED depletion significantly impeded erythroid maturation. There was a corresponding increase in myeloid progenitors and granulocytes and macrophages, suggesting an attenuated differentiation path in myeloid lineages. Moreover, EED depletion impaired the generation of hematopoietic stem cells. Collectively, our study demonstrates that within Tie2Cre-recombined embryonic cells, EED is required for proper erythropoiesis and for formation of hematopoietic progenitor and stem cells, but is dispensable for endothelial lineage commitment and early vascular patterning.

Abstract 3551: Non-coding RNA HOTAIR connects DNA damage signaling to NF-κB activation in cisplatin resistant ovarian cancer

Abstract The Polycomb Repressive Complex 2 (PRC2) has been implicated in cancer and a role for PRC2 during DNA damage response (DDR) has recently been reported. To examine changes in gene expression with DDR in cisplatin (cddp)-resistant ovarian cancer (OC), we performed whole transcriptome RNA-seq analysis of isogenic cddp-sensitive and -resistant OC cell lines (A2780 and A2780-cp). Differential expression of PRC components (SUZ12, EZH1, SIRT1, PHC1 &2) (P<0.05), NF-κB pathway members (NCAM, ABCB9, RAGE, IL4R, IL6R, BCL2L11) (P<0.05), and long non-coding RNAs (lncRNAs) known to associate with PRC2 (P<0.05), including Hox transcript antisense intergenic RNA or HOTAIR, was observed. In tumors from patients with high grade serous OC at diagnosis, basal expression of HOTAIR was greater (P<0.01) compared to normal ovarian surface epithelium and marked overexpression of HOTAIR was observed in tumors obtained from patients who had developed platinum-resistant OC. Ablation of HOTAIR using dsiRNA resensitized A2780-cp to cddp, while ectopic over-expression of HOTAIR increased (P<0.05) A2780 cell survival after cddp treatment (3-fold vs. control). To further examine HOTAIR regulation, we conducted a promoter analysis using bioinformatics tools and luciferase assays. We identified a putative p65-NF-κB binding site (906-GGGACACCCC-915) 906 bp upstream of the HOTAIR transcription start site. Treatment of A2780 cells with the NF-κB activator TNF-α induced HOTAIR (16-fold vs. control) and NF-κB enrichment (3-fold assessed by ChIP assays) at the HOTAIR promoter. Furthermore, in A2780-cp compared to A2780, total Iκ-Bα levels were reduced (P<0.05) and nuclear p65 levels were increased, indicating that endogenous activation of NF-κB contributes to cddp resistance and DDR. Consistent with this observation, cddp treatment (20μM for 0-24hrs) of A2780 cells increased (P<0.05) HOTAIR expression by 5- and 16-fold at 8 and 24 hrs and decreased (P<0.05) Iκ-Bα protein levels at similar time points. Furthermore, inhibiting NF-κB by either gliotoxin (5μM) or Bay-11 (3μM) completely abolished cddp-induced HOTAIR expression in A2780 cells, demonstrating that NF-κB is a HOTAIR transcriptional activator during cddp-induced DDR. Importantly, EZH2 and histone H3 lysine-27 trimethylation (H3K27me3) levels were enriched (6- and 17-fold) in the Iκ-Bα promoter at 24 and 48 hours post cddp treatment, and HOTAIR depletion using dsiRNA reduced the observed EZH2-H3K27me3 enrichment at the Iκ-Bα promoter, demonstrating that HOTAIR recruits PRC2 complex to the Iκ-Bα promoter to prolong NF-κB activation during cddp-induced genotoxic stress. Mouse xenograft studies with A2780 cells overexpressing HOTAIR are ongoing. The results of this study support a role for HOTAIR as a positive regulator of the NF-κB pathway and PRC2 during cisplatin-induced DNA damage. We further suggest that HOTAIR may serve as a therapeutic target in cisplatin-resistant OC. Citation Format: Ali R. Ozes, Dave F. Miller, Yunlong Liu, Kenneth P. Nephew. Non-coding RNA HOTAIR connects DNA damage signaling to NF-κB activation in cisplatin resistant ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3551. doi:10.1158/1538-7445.AM2014-3551

Origin of the polycomb repressive complex 2 and gene silencing by an E(z) homolog in the unicellular alga Chlamydomonas

Polycomb group proteins play an essential role in the maintenance of cell identity and the regulation of development in both animals and plants. The Polycomb Repressive Complex 2 (PRC2) is involved in the establishment of transcriptionally silent chromatin states, in part through its ability to methylate lysine 27 of histone H3 by the Enhancer of zeste [E(z)] subunit. The absence of PRC2 in unicellular model fungi and its function in the repression of genes vital for the development of higher eukaryotes led to the proposal that this complex may have evolved together with the emergence of multicellularity. However, we report here on the widespread presence of PRC2 core subunits in unicellular eukaryotes from the Opisthokonta, Chromalveolata and Archaeplastida supergroups. To gain insight on the role of PRC2 in single celled organisms, we characterized an E(z) homolog, EZH, in the green alga Chlamydomonas reinhardtii. RNAi-mediated suppression of EZH led to defects in the silencing of transgenes and retrotransposons as well as to a global increase in histone post-translational modifications associated with transcriptional activity, such as trimethylation of histone H3 lysine 4 and acetylation of histone H4. On the basis of the parsimony principle, our findings suggest that PRC2 appeared early in eukaryotic evolution, even perhaps in the last unicellular common ancestor of eukaryotes. One of the ancestral roles of PCR2 may have been in defense responses against intragenomic parasites such as transposable elements, prior to being co-opted for lineage specific functions like developmental regulation in multicellular eukaryotes.

Targeting of EZH2 to a defined genomic site is sufficient for recruitment of Dnmt3a but not de novo DNA methylation

Polycomb-mediated gene silencing and DNA methylation underlie many epigenetic processes important in normal development as well as in cancer. An interaction between EZH2 of the Polycomb repressive complex 2 (PRC2), which trimethylates lysine 27 on Histone 3 (H3K27me3), and all three DNA methyltransferases (DNMTs) has been demonstrated, implicating a role for PRC2 in directing DNA methylation. Interestingly, however, the majority of H3K27me3 marked genes lack DNA methylation in ES cells, indicating that EZH2 recruitment may not be sufficient to promote DNA methylation. Here, we employed a Gal4DBD/gal4UAS-based system to directly test if EZH2 binding at a defined genomic site is sufficient to promote de novo DNA methylation in a murine erythroleukaemia cell line. Targeting of a Gal4DBD-EZH2 fusion to an intergenic transgene bearing a gal4 binding-site array promoted localized recruitment of SUZ12 and BMI1, subunits of PRC2 and PRC1, respectively, and deposition of H3K27me3. Further analysis of the H3K27me3-marked site revealed the persistence of H3K4me2, a mark inversely correlated with DNA methylation. Strikingly, while DNMT3a was also recruited in an EZH2-dependent manner, de novo DNA methylation of the transgene was not observed. Thus, while targeting of EZH2 to a specific genomic site is sufficient for recruitment of DNMT3a, additional events are required for de novo DNA methylation.