Mécanisme de répression par les protéines polycomb

Publications de l’équipe

Année de publication : 2010

Syuzo Kaneko, Gang Li, Jinsook Son, Chong-Feng Xu, Raphael Margueron, Thomas A Neubert, Danny Reinberg (2010 Dec 3)

Phosphorylation of the PRC2 component Ezh2 is cell cycle-regulated and up-regulates its binding to ncRNA.

Genes & development : 2615-20 : DOI : 10.1101/gad.1983810 En savoir plus
Résumé

Ezh2 functions as a histone H3 Lys 27 (H3K27) methyltransferase when comprising the Polycomb-Repressive Complex 2 (PRC2). Trimethylation of H3K27 (H3K27me3) correlates with transcriptionally repressed chromatin. The means by which PRC2 targets specific chromatin regions is currently unclear, but noncoding RNAs (ncRNAs) have been shown to interact with PRC2 and may facilitate its recruitment to some target genes. Here we show that Ezh2 interacts with HOTAIR and Xist. Ezh2 is phosphorylated by cyclin-dependent kinase 1 (CDK1) at threonine residues 345 and 487 in a cell cycle-dependent manner. A phospho-mimic at residue 345 increased HOTAIR ncRNA binding to Ezh2, while the phospho-mimic at residue 487 was ineffectual. An Ezh2 domain comprising T345 was found to be important for binding to HOTAIR and the 5′ end of Xist.

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Guohong Li, Raphael Margueron, Guobin Hu, David Stokes, Yuh-Hwa Wang, Danny Reinberg (2010 Apr 14)

Highly compacted chromatin formed in vitro reflects the dynamics of transcription activation in vivo.

Molecular cell : 41-53 : DOI : 10.1016/j.molcel.2010.01.042 En savoir plus
Résumé

High-order chromatin was reconstituted in vitro. This species reflects the criteria associated with transcriptional regulation in vivo. Histone H1 was determinant to formation of condensed structures, with deacetylated histones giving rise to highly compacted chromatin that approximated 30 nm fibers as evidenced by electron microscopy. Using the PEPCK promoter, we validated the integrity of these templates that were refractory to transcription by attaining transcription through the progressive action of the pertinent factors. The retinoic acid receptor binds to highly compacted chromatin, but the NF1 transcription factor binds only after histone acetylation by p300 and SWI/SNF-mediated nucleosome mobilization, reflecting the in vivo case. Mapping studies revealed the same pattern of nucleosomal repositioning on the PEPCK promoter in vitro and in vivo, correlating with NF1 binding and transcription. The reconstitution of such highly compacted « 30 nm » chromatin that mimics in vivo characteristics should advance studies of its conversion to a transcriptionally active form.

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Raphaël Margueron, Danny Reinberg (2010 Mar 20)

Chromatin structure and the inheritance of epigenetic information.

Nature reviews. Genetics : 285-96 : DOI : 10.1038/nrg2752 En savoir plus
Résumé

Although it is widely accepted that the regulation of the chromatin landscape is pivotal to conveying the epigenetic program, it is still unclear how a defined chromatin domain is reproduced following DNA replication and transmitted from one cell generation to the next. Here, we review the multiple mechanisms that potentially affect the inheritance of epigenetic information in somatic cells. We consider models of how histones might be recycled following replication, and discuss the importance of positive-feedback loops, long-range gene interactions and the complex network of trans-acting factors in the transmission of chromatin states.

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Gang Li, Raphael Margueron, Manching Ku, Pierre Chambon, Bradley E Bernstein, Danny Reinberg (2010 Feb 4)

Jarid2 and PRC2, partners in regulating gene expression.

Genes & development : 368-80 : DOI : 10.1101/gad.1886410 En savoir plus
Résumé

The Polycomb group proteins foster gene repression profiles required for proper development and unimpaired adulthood, and comprise the components of the Polycomb-Repressive Complex 2 (PRC2) including the histone H3 Lys 27 (H3K27) methyltransferase Ezh2. How mammalian PRC2 accesses chromatin is unclear. We found that Jarid2 associates with PRC2 and stimulates its enzymatic activity in vitro. Jarid2 contains a Jumonji C domain, but is devoid of detectable histone demethylase activity. Instead, its artificial recruitment to a promoter in vivo resulted in corecruitment of PRC2 with resultant increased levels of di- and trimethylation of H3K27 (H3K27me2/3). Jarid2 colocalizes with Ezh2 and MTF2, a homolog of Drosophila Pcl, at endogenous genes in embryonic stem (ES) cells. Jarid2 can bind DNA and its recruitment in ES cells is interdependent with that of PRC2, as Jarid2 knockdown reduced PRC2 at its target promoters, and ES cells devoid of the PRC2 component EED are deficient in Jarid2 promoter access. In addition to the well-documented defects in embryonic viability upon down-regulation of Jarid2, ES cell differentiation is impaired, as is Oct4 silencing.

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Année de publication : 2009

Raphael Margueron, Neil Justin, Katsuhito Ohno, Miriam L Sharpe, Jinsook Son, William J Drury, Philipp Voigt, Stephen R Martin, William R Taylor, Valeria De Marco, Vincenzo Pirrotta, Danny Reinberg, Steven J Gamblin (2009 Sep 22)

Role of the polycomb protein EED in the propagation of repressive histone marks.

Nature : 762-7 : DOI : 10.1038/nature08398 En savoir plus
Résumé

Polycomb group proteins have an essential role in the epigenetic maintenance of repressive chromatin states. The gene-silencing activity of the Polycomb repressive complex 2 (PRC2) depends on its ability to trimethylate lysine 27 of histone H3 (H3K27) by the catalytic SET domain of the EZH2 subunit, and at least two other subunits of the complex: SUZ12 and EED. Here we show that the carboxy-terminal domain of EED specifically binds to histone tails carrying trimethyl-lysine residues associated with repressive chromatin marks, and that this leads to the allosteric activation of the methyltransferase activity of PRC2. Mutations in EED that prevent it from recognizing repressive trimethyl-lysine marks abolish the activation of PRC2 in vitro and, in Drosophila, reduce global methylation and disrupt development. These findings suggest a model for the propagation of the H3K27me3 mark that accounts for the maintenance of repressive chromatin domains and for the transmission of a histone modification from mother to daughter cells.

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Année de publication : 2008

Raphael Margueron, Guohong Li, Kavitha Sarma, Alexandre Blais, Jiri Zavadil, Christopher L Woodcock, Brian D Dynlacht, Danny Reinberg (2008 Nov 26)

Ezh1 and Ezh2 maintain repressive chromatin through different mechanisms.

Molecular cell : 503-18 : DOI : 10.1016/j.molcel.2008.11.004 En savoir plus
Résumé

Polycomb group proteins are critical to maintaining gene repression established during Drosophila development. Part of this group forms the PRC2 complex containing Ez that catalyzes di- and trimethylation of histone H3 lysine 27 (H3K37me2/3), marks repressive to transcription. We report that the mammalian homologs Ezh1 and Ezh2 form similar PRC2 complexes but exhibit contrasting repressive roles. While PRC2-Ezh2 catalyzes H3K27me2/3 and its knockdown affects global H3K27me2/3 levels, PRC2-Ezh1 performs this function weakly. In accordance, Ezh1 knockdown was ineffectual on global H3K27me2/3 levels. Instead, PRC2-Ezh1 directly and robustly represses transcription from chromatinized templates and compacts chromatin in the absence of the methyltransferase cofactor SAM, as evidenced by electron microscopy. Ezh1 targets a subset of Ezh2 genes, yet Ezh1 is more abundant in nonproliferative adult organs while Ezh2 expression is tightly associated with proliferation, as evidenced when analyzing aging mouse kidney. These results might reflect subfunctionalization of a PcG protein during evolution.

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Kavitha Sarma, Raphael Margueron, Alexey Ivanov, Vincenzo Pirrotta, Danny Reinberg (2008 Feb 21)

Ezh2 requires PHF1 to efficiently catalyze H3 lysine 27 trimethylation in vivo.

Molecular and cellular biology : 2718-31 : DOI : 10.1128/MCB.02017-07 En savoir plus
Résumé

The mammalian Polycomblike protein PHF1 was previously shown to interact with the Polycomb group (PcG) protein Ezh2, a histone methyltransferase whose activity is pivotal in sustaining gene repression during development and in adulthood. As Ezh2 is active only when part of the Polycomb Repressive Complexes (PRC2-PRC4), we examined the functional role of its interaction with PHF1. Chromatin immunoprecipitation experiments revealed that PHF1 resides along with Ezh2 at Ezh2-regulated genes such as the HoxA loci and the non-Hox MYT1 and WNT1 genes. Knockdown of PHF1 or of Ezh2 led to up-regulated HoxA gene expression. Interestingly, depletion of PHF1 did correlate with reduced occupancy of Bmi-1, a PRC1 component. As expected, knockdown of Ezh2 led to reduced levels of its catalytic products H3K27me2/H3K27me3. However, reduced levels of PHF1 also led to decreased global levels of H3K27me3. Notably, the levels of H3K27me3 decreased while those of H3K27me2 increased at the up-regulated HoxA loci tested. Consistent with this, the addition of PHF1 specifically stimulated the ability of Ezh2 to catalyze H3K27me3 but not H3K27me1/H3K27me2 in vitro. We conclude that PHF1 modulates the activity of Ezh2 in favor of the repressive H3K27me3 mark. Thus, we propose that PHF1 is a determinant in PcG-mediated gene repression.

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