Maintenance of Transcriptional Repression by Polycomb Proteins

Team Publications

Year of publication 2019

Sabrina Bondu, Anne-Sophie Alary, Carine Lefèvre, Alexandre Houy, Grace Jung, Thibaud Lefebvre, David Rombaut, Ismael Boussaid, Abderrahmane Bousta, François Guillonneau, Prunelle Perrier, Samar Alsafadi, Michel Wassef, Raphaël Margueron, Alice Rousseau, Nathalie Droin, Nicolas Cagnard, Sophie Kaltenbach, Susann Winter, Anne-Sophie Kubasch, Didier Bouscary, Valeria Santini, Andrea Toma, Mathilde Hunault, Aspasia Stamatoullas, Emmanuel Gyan, Thomas Cluzeau, Uwe Platzbecker, Lionel Adès, Hervé Puy, Marc-Henri Stern, Zoubida Karim, Patrick Mayeux, Elizabeta Nemeth, Sophie Park, Tomas Ganz, Léon Kautz, Olivier Kosmider, Michaëla Fontenay (2019 Jul 12)

A variant erythroferrone disrupts iron homeostasis in -mutated myelodysplastic syndrome.

Science translational medicine : DOI : eaav5467 Learn more
Summary

Myelodysplastic syndromes (MDS) with ring sideroblasts are hematopoietic stem cell disorders with erythroid dysplasia and mutations in the splicing factor gene. Patients with MDS with mutations often accumulate excessive tissue iron, even in the absence of transfusions, but the mechanisms that are responsible for their parenchymal iron overload are unknown. Body iron content, tissue distribution, and the supply of iron for erythropoiesis are controlled by the hormone hepcidin, which is regulated by erythroblasts through secretion of the erythroid hormone erythroferrone (ERFE). Here, we identified an alternative transcript in patients with MDS with the mutation. Induction of this transcript in primary -mutated bone marrow erythroblasts generated a variant protein that maintained the capacity to suppress hepcidin transcription. Plasma concentrations of ERFE were higher in patients with MDS with an gene mutation than in patients with wild-type MDS. Thus, hepcidin suppression by a variant ERFE is likely responsible for the increased iron loading in patients with -mutated MDS, suggesting that ERFE could be targeted to prevent iron-mediated toxicity. The expression of the variant transcript that was restricted to -mutated erythroblasts decreased in lenalidomide-responsive anemic patients, identifying variant ERFE as a specific biomarker of clonal erythropoiesis.

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Andrea Frapporti, Caridad Miró Pina, Olivier Arnaiz, Daniel Holoch, Takayuki Kawaguchi, Adeline Humbert, Evangelia Eleftheriou, Bérangère Lombard, Damarys Loew, Linda Sperling, Karine Guitot, Raphaël Margueron, Sandra Duharcourt (2019 Jun 22)

The Polycomb protein Ezl1 mediates H3K9 and H3K27 methylation to repress transposable elements in Paramecium.

Nature communications : 2710 : DOI : 10.1038/s41467-019-10648-5 Learn more
Summary

In animals and plants, the H3K9me3 and H3K27me3 chromatin silencing marks are deposited by different protein machineries. H3K9me3 is catalyzed by the SET-domain SU(VAR)3-9 enzymes, while H3K27me3 is catalyzed by the SET-domain Enhancer-of-zeste enzymes, which are the catalytic subunits of Polycomb Repressive Complex 2 (PRC2). Here, we show that the Enhancer-of-zeste-like protein Ezl1 from the unicellular eukaryote Paramecium tetraurelia, which exhibits significant sequence and structural similarities with human EZH2, catalyzes methylation of histone H3 in vitro and in vivo with an apparent specificity toward K9 and K27. We find that H3K9me3 and H3K27me3 co-occur at multiple families of transposable elements in an Ezl1-dependent manner. We demonstrate that loss of these histone marks results in global transcriptional hyperactivation of transposable elements with modest effects on protein-coding gene expression. Our study suggests that although often considered functionally distinct, H3K9me3 and H3K27me3 may share a common evolutionary history as well as a common ancestral role in silencing transposable elements.

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CAMPAGNE Antoine, LEE Ming-Kang, ZIELINSKI Dina, MICHAUD Audrey, LE CORRE Stéphanie, DINGLI Florent, CHEN Hong, SHAHIDIAN Lara Z, SERVANT Nicolas, LOEW Damarys, PASMANT Eric, PISTEL-VINAY Sophie, WASSEF Michel, MARGUERON Raphaël (2019 Jan 21)

BAP1 complex promotes transcription by opposing PRC1-mediated H2A ubiquitylation

Nature Communications : DOI : 10.1038/s41467-018-08255-x Learn more
Summary

In Drosophila, a complex consisting of Calypso and ASX catalyzes H2A deubiquitination and has been reported to act as part of the Polycomb machinery in transcriptional silencing. The mammalian homologs of these proteins (BAP1 and ASXL1/2/3, respectively), are frequently mutated in various cancer types, yet their precise functions remain unclear. Using an integrative approach based on isogenic cell lines generated with CRISPR/Cas9, we uncover an unanticipated role for BAP1 in gene activation. This function requires the assembly of an enzymatically active BAP1-associated core complex (BAP1.com) containing one of the redundant ASXL proteins. We investigate the mechanism underlying BAP1.com-mediated transcriptional regulation and show that it does not participate in Polycomb-mediated silencing. Instead, our results establish that the function of BAP1.com is to safeguard transcriptionally active genes against silencing by the Polycomb Repressive Complex 1.

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Year of publication 2018

Yan Wang, Haizhen Long, Juan Yu, Liping Dong, Michel Wassef, Baowen Zhuo, Xia Li, Jicheng Zhao, Min Wang, Cuifang Liu, Zengqi Wen, Luyuan Chang, Ping Chen, Qian-Fei Wang, Xueqing Xu, Raphael Margueron, Guohong Li (2018 Sep 26)

Histone variants H2A.Z and H3.3 coordinately regulate PRC2-dependent H3K27me3 deposition and gene expression regulation in mES cells.

BMC biology : 107 : DOI : 10.1186/s12915-018-0568-6 Learn more
Summary

The hierarchical organization of eukaryotic chromatin plays a central role in gene regulation, by controlling the extent to which the transcription machinery can access DNA. The histone variants H3.3 and H2A.Z have recently been identified as key regulatory players in this process, but the underlying molecular mechanisms by which they permit or restrict gene expression remain unclear. Here, we investigated the regulatory function of H3.3 and H2A.Z on chromatin dynamics and Polycomb-mediated gene silencing.

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Eric Conway, Emilia Jerman, Evan Healy, Shinsuke Ito, Daniel Holoch, Giorgio Oliviero, Orla Deevy, Eleanor Glancy, Darren J Fitzpatrick, Marlena Mucha, Ariane Watson, Alan M Rice, Paul Chammas, Christine Huang, Indigo Pratt-Kelly, Yoko Koseki, Manabu Nakayama, Tomoyuki Ishikura, Gundula Streubel, Kieran Wynne, Karsten Hokamp, Aoife McLysaght, Claudio Ciferri, Luciano Di Croce, Gerard Cagney, Raphaël Margueron, Haruhiko Koseki, Adrian P Bracken (2018 Apr 10)

A Family of Vertebrate-Specific Polycombs Encoded by the LCOR/LCORL Genes Balance PRC2 Subtype Activities.

Molecular cell : 408-421.e8 : DOI : S1097-2765(18)30186-2 Learn more
Summary

The polycomb repressive complex 2 (PRC2) consists of core subunits SUZ12, EED, RBBP4/7, and EZH1/2 and is responsible for mono-, di-, and tri-methylation of lysine 27 on histone H3. Whereas two distinct forms exist, PRC2.1 (containing one polycomb-like protein) and PRC2.2 (containing AEBP2 and JARID2), little is known about their differential functions. Here, we report the discovery of a family of vertebrate-specific PRC2.1 proteins, “PRC2 associated LCOR isoform 1” (PALI1) and PALI2, encoded by the LCOR and LCORL gene loci, respectively. PALI1 promotes PRC2 methyltransferase activity in vitro and in vivo and is essential for mouse development. Pali1 and Aebp2 define mutually exclusive, antagonistic PRC2 subtypes that exhibit divergent H3K27-tri-methylation activities. The balance of these PRC2.1/PRC2.2 activities is required for the appropriate regulation of polycomb target genes during differentiation. PALI1/2 potentially link polycombs with transcriptional co-repressors in the regulation of cellular identity during development and in cancer.

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Year of publication 2017

Lucie Hebert, Dorine Bellanger, Chloé Guillas, Antoine Campagne, Florent Dingli, Damarys Loew, Alice Fievet, Virginie Jacquemin, Tatiana Popova, Didier Jean, Fatima Mechta-Grigoriou, Raphaël Margueron, Marc-Henri Stern (2017 Oct 27)

Modulating BAP1 expression affects ROS homeostasis, cell motility and mitochondrial function.

Oncotarget : 72513-72527 : DOI : 10.18632/oncotarget.19872 Learn more
Summary

The tumor suppressor BAP1 associates with ASXL1/2 to form the core Polycomb complex PR-DUB, which catalyzes the removal of mono-ubiquitin from several substrates including histone H2A. This complex also mediates the poly-deubiquitination of HCFC1, OGT and PCG1-α, preventing them from proteasomal degradation. Surprisingly, considering its role in a Polycomb complex, no transcriptional signature was consistently found among BAP1-inactivated tumor types. It was hypothesized that BAP1 tumor suppressor activity could reside, at least in part, in stabilizing proteins through its poly-deubiquitinase activity. Quantitative mass spectrometry and gene expression arrays were used to investigate the consequences of BAP1 expression modulation in the NCI-H226 mesothelioma cell line. Analysis of differentially expressed proteins revealed enrichment in cytoskeleton organization, mitochondrial activity and ROS management, while gene expression analysis revealed enrichment in the epithelial-to-mesenchymal transition pathway. Functional assessments in BAP1 inactivated, BAP1 wild-type and BAP1 catalytically dead-expressing NCI-H226 and QR mesothelioma cell lines confirmed alteration of these pathways and demonstrated that BAP1 deubiquitinase activity was mandatory to maintain these phenotypes. Interestingly, monitoring intracellular ROS levels partly restored the morphology and the mitochondrial activity. Finally, the study suggests new tumorigenic and cellular functions of BAP1 and shows for the first time the interest of studying the proteome as readout of BAP1 inactivation.

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M Wassef, A Luscan, A Battistella, S Le Corre, H Li, M R Wallace, M Vidaud, R Margueron (2017 May 14)

Versatile and precise gene-targeting strategies for functional studies in mammalian cell lines.

Methods (San Diego, Calif.) : DOI : S1046-2023(16)30269-9 Learn more
Summary

The advent of programmable nucleases such as ZFNs, TALENs and CRISPR/Cas9 has brought the power of genetic manipulation to widely used model systems. In mammalian cells, nuclease-mediated DNA double strand break is mainly repaired through the error-prone non-homologous end-joining (NHEJ) repair pathway, eventually leading to accumulation of small deletions or insertions (indels) that can inactivate gene function. However, due to the variable size of the indels and the polyploid status of many cell lines (e.g., cancer-derived cells), obtaining a knockout usually requires lengthy screening and characterization procedures. Given the more precise type of modifications that can be introduced upon homology-directed repair (HDR), we have developed HDR-based gene-targeting strategies that greatly facilitate the process of knockout generation in cell lines. To generate reversible knockouts (R-KO), a selectable promoter-less STOP cassette is inserted in an intron, interrupting transcription. Loss-of-function can be validated by RT-qPCR and is removable, enabling subsequent restoration of gene function. A variant of the R-KO procedure can be used to introduce point mutations. To generate constitutive knockouts (C-KO), an exon is targeted, which makes use of HDR-based gene disruption together with NHEJ-induced indels on non-HDR targeted allele(s). Hence the C-KO procedure greatly facilitates simultaneous inactivation of multiple alleles. Overall these genome-editing tools offer superior precision and efficiency for functional genetic approaches. We provide detailed protocols guiding in the design of targeting vectors and in the analysis and validation of gene targeting experiments.

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Daniel Holoch, Raphaël Margueron (2017 May 10)

Mechanisms Regulating PRC2 Recruitment and Enzymatic Activity.

Trends in biochemical sciences : DOI : S0968-0004(17)30072-5 Learn more
Summary

Polycomb repressive complex 2 (PRC2) and its histone H3 lysine-27 methylation activity are crucial for multicellular development by virtue of their role in maintaining transcriptional repression patterns. The recruitment and enzymatic activity of PRC2 are controlled by a series of intricate mechanisms whose molecular details have been emerging at a rapid pace. Recent studies have uncovered intriguing modes of PRC2 regulation by facultative PRC2 subunits, PRC1, and specific features of the chromatin environment. Together, these findings have produced a rich and fast-evolving picture of the biochemical signals that govern PRC2 function, with many exciting questions still remaining.

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Manuela Portoso, Roberta Ragazzini, Živa Brenčič, Arianna Moiani, Audrey Michaud, Ivaylo Vassilev, Michel Wassef, Nicolas Servant, Bruno Sargueil, Raphaël Margueron (2017 Feb 8)

PRC2 is dispensable for HOTAIR-mediated transcriptional repression.

The EMBO journal : DOI : e201695335 Learn more
Summary

Long non-coding RNAs (lncRNAs) play diverse roles in physiological and pathological processes. Several lncRNAs have been suggested to modulate gene expression by guiding chromatin-modifying complexes to specific sites in the genome. However, besides the example of Xist, clear-cut evidence demonstrating this novel mode of regulation remains sparse. Here, we focus on HOTAIR, a lncRNA that is overexpressed in several tumor types and previously proposed to play a key role in gene silencing through direct recruitment of Polycomb Repressive Complex 2 (PRC2) to defined genomic loci. Using genetic tools and a novel RNA-tethering system, we investigated the interplay between HOTAIR and PRC2 in gene silencing. Surprisingly, we observed that forced overexpression of HOTAIR in breast cancer cells leads to subtle transcriptomic changes that appear to be independent of PRC2. Mechanistically, we found that artificial tethering of HOTAIR to chromatin causes transcriptional repression, but that this effect does not require PRC2. Instead, PRC2 recruitment appears to be a consequence of gene silencing. We propose that PRC2 binding to RNA might serve functions other than chromatin targeting.

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Daniel Holoch, Raphaël Margueron (2017 Jan 31)

Chromatin biology: Breaking into the PRC2 cage.

Nature chemical biology : DOI : 10.1038/nchembio.2313 Learn more
Summary

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Year of publication 2016

M Wassef, R Margueron (2016 Oct 16)

The multiple facets of PRC2 alterations in cancers.

Journal of molecular biology : DOI : S0022-2836(16)30427-2 Learn more
Summary

Genome sequencing of large cohorts of tumors has revealed that mutations in genes encoding chromatin regulators are frequent in cancer. However, the precise contribution of these mutations to tumor development often remains elusive. Here, we review the current knowledge concerning alterations of the Polycomb machinery in cancer, with a particular focus on the Polycomb Repressive Complex 2 (PRC2), a key chromatin modifier involved in the maintenance of transcriptional silencing. A broad variety of alterations can impair PRC2 activity yet, overall, only one type of alteration is found in a given class of tumor. We discuss the potential impact of the various types of PRC2 alterations on gene expression. We propose that the distinct set of genes regulated by PRC2 depending on tumor etiology constrain the type of alteration of PRC2 that can fuel tumor development. Beyond this specificity, we propose that PRC2 and more generally chromatin regulators act as gatekeepers of transcriptional integrity, a role that often confers a tumor-suppressive function.

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M Wassef, A Michaud, R Margueron (2016 Jul 16)

Association between EZH2 expression, silencing of tumor suppressors and disease outcome in solid tumors.

Cell cycle (Georgetown, Tex.) : 0 Learn more
Summary

EZH2, the main catalytic component of the Polycomb Repressive Complex 2 (PRC2) is apparently upregulated in most solid tumors. Furthermore its expression generally associates with poor prognosis. It was proposed that this correlation reflects a causal event, EZH2 mediating the silencing of key tumor suppressor loci. In contrast, we recently showed that EZH2 is dispensable for solid tumor development and that its elevated expression reflects the abnormally high proliferation rate of cancer cells. Here, we investigate the functional association between EZH2 expression and silencing of key tumor suppressor loci and further illustrate the confounding effect of proliferation on EZH2’s association to outcome.

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Marie Schoumacher, Stéphanie Le Corre, Alexandre Houy, Eskeatnaf Mulugeta, Marc-Henri Stern, Sergio Roman-Roman, Raphaël Margueron (2016 Jun 9)

Uveal melanoma cells are resistant to EZH2 inhibition regardless of BAP1 status.

Nature medicine : 577-8 : DOI : 10.1038/nm.4098 Learn more
Summary

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Year of publication 2015

Michel Wassef, Veronica Rodilla, Aurélie Teissandier, Bruno Zeitouni, Nadege Gruel, Benjamin Sadacca, Marie Irondelle, Margaux Charruel, Bertrand Ducos, Audrey Michaud, Matthieu Caron, Elisabetta Marangoni, Philippe Chavrier, Christophe Le Tourneau, Maud Kamal, Eric Pasmant, Michel Vidaud, Nicolas Servant, Fabien Reyal, Dider Meseure, Anne Vincent-Salomon, Silvia Fre, Raphaël Margueron (2015 Dec 6)

Impaired PRC2 activity promotes transcriptional instability and favors breast tumorigenesis.

Genes & development : 2547-62 : DOI : 10.1101/gad.269522.115 Learn more
Summary

Alterations of chromatin modifiers are frequent in cancer, but their functional consequences often remain unclear. Focusing on the Polycomb protein EZH2 that deposits the H3K27me3 (trimethylation of Lys27 of histone H3) mark, we showed that its high expression in solid tumors is a consequence, not a cause, of tumorigenesis. In mouse and human models, EZH2 is dispensable for prostate cancer development and restrains breast tumorigenesis. High EZH2 expression in tumors results from a tight coupling to proliferation to ensure H3K27me3 homeostasis. However, this process malfunctions in breast cancer. Low EZH2 expression relative to proliferation and mutations in Polycomb genes actually indicate poor prognosis and occur in metastases. We show that while altered EZH2 activity consistently modulates a subset of its target genes, it promotes a wider transcriptional instability. Importantly, transcriptional changes that are consequences of EZH2 loss are predominantly irreversible. Our study provides an unexpected understanding of EZH2’s contribution to solid tumors with important therapeutic implications.

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Wassef M1, Rodilla V1, Teissandier A2, Zeitouni B2, Gruel N3, Sadacca B3, Irondelle M3, Charruel M1, Ducos B4, Michaud A1, Caron M1, Marangoni E3, Chavrier P3, Le Tourneau C5, Kamal M6, Pasmant E7, Vidaud M7, Servant N2, Reyal F3, Meseure D8, Vincent-Salomon A3, Fre S1, Margueron R1. (2015 Dec 4)

Impaired PRC2 activity promotes transcriptional instability and favors breast tumorigenesis.

Genes & DevelopmentImpaired PRC2 activity promotes transcriptional instability and favors breast tumorigenesis. : DOI : 10.1101/gad.269522.115 Learn more
Summary

Abstract

Alterations of chromatin modifiers are frequent in cancer, but their functional consequences often remain unclear. Focusing on the Polycomb protein EZH2 that deposits the H3K27me3 (trimethylation of Lys27 of histone H3) mark, we showed that its high expression in solid tumors is a consequence, not a cause, of tumorigenesis. In mouse and human models, EZH2 is dispensable for prostate cancer development and restrains breast tumorigenesis. High EZH2 expression in tumors results from a tight coupling to proliferation to ensure H3K27me3 homeostasis. However, this process malfunctions in breast cancer. Low EZH2 expression relative to proliferation and mutations in Polycomb genes actually indicate poor prognosis and occur in metastases. We show that while altered EZH2 activity consistently modulates a subset of its target genes, it promotes a wider transcriptional instability. Importantly, transcriptional changes that are consequences of EZH2 loss are predominantly irreversible. Our study provides an unexpected understanding of EZH2’s contribution to solid tumors with important therapeutic implications.

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