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Alternative splicing decouples local from global PRC2 activity

ABSTRACT: PRC2 mediates epigenetic maintenance of gene silencing in eukaryotes via methylation of H3K27. This complex interacts with sets of accessory factors forming two distinct subtypes (PRC2.1 and PRC2.2) that differ in their action and chromatin targeting mechanisms. However, the underlying molecular mechanisms orchestrating PRC2 assembly are not yet understood. Here, we report the identification of an alternative splicing event involving that alternative splicing of the PRC2 core component SUZ12 exon 4 which generates two isoforms coexisting in the same cell in virtually all tissues and developmental stages. Skipping this exon generates a previously uncharacterized isoform (SUZ12S) that forces the formation of the PRC2.1 subtype and favors PRC2 dimerization. Our results suggest that while SUZ12L is needed for maintenance of global H3K27 methylation levels, While SUZ12S is necessary and sufficient to ensure correct repression of Polycomb target genes via promoter-proximal H3K27me3 deposition, the full-length SUZ12L isoform is needed for maintenance of global H3K27 methylation levels. Lastly, we show that mouse embryonic stem cells lacking either of the two isoforms display impaired exit from pluripotency upon differentiation stimulus. Our findings thus reveal evidence for the existence of a physiological mechanism regulating PRC2 assembly and higher order interactions, with an impact on H3K27 methylation and gene repression.

ORGANISM(S): Mus musculus

PROVIDER: GSE223666 | GEO | 2024/03/18

REPOSITORIES: GEO

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EZH2 Variants Differentially Regulate Polycomb Repressive Complex 2 in Histone Methylation and Cell Differentiation

Project description:Background: Polycomb repressive complex 2 (PRC2) is responsible for establishing and maintaining histone H3K27 methylation during cell differentiation and proliferation. H3K27 can be mono-, di-, or tri-methylated, resulting in differential gene regulation. However, it remains unknown how PRC2 specifies the degree and biological effects of H3K27 methylation within a given cellular context. One way to determine PRC2 specificity may be through alternative splicing of Ezh2, PRC2’s catalytic subunit, during cell differentiation and tissue maturation. Results: We fully characterized the alternative splicing of Ezh2 in somatic cells and male germ cells and found that Ezh’s exon 14 was differentially regulated during mitosis and meiosis. The Ezh2 isoform containing exon 14 (ex14-Ezh2) is upregulated during cell cycle progression, consistent with a role in maintaining H3K27 methylation during chromatin replication. In contrast, the isoform lacking exon 14 (ex14D-Ezh2) was almost exclusively present in spermatocytes when new H3K27me2 is established during meiotic differentiation. Moreover, Ezh2’s transcript is normally controlled by E2F transcription activators, but in spermatocytes, Ezh2’s transcription is controlled by the meiotic regulator MYBL1. Compared to ex14-EZH2, ex14D-EZH2 has a diminished efficiency for catalyzing H3K27me3 and promotes embryonic stem cell differentiation. Conclusions: Ezh2’s expression is regulated at transcriptional and post-transcriptional levels in a cellular context-dependent manner. EZH2 variants determine functional specificity of PRC2 in histone methylation during cell proliferation and differentiation.

2018-12-01 | GSE123174 | GEO

Cxorf67-FLAG co-immunoprecipitation analysis from 293T cells

Project description:The regulation of gene expression is controlled in part by post-translational modifications to histone proteins. Methylation at histone H3, lysine 27 (H3K27), which is catalyzed by Polycomb repressive complex 2 (PRC2), is associated with silenced chromatin. Previous studies have identified dysregulation of H3K27 methylation in pediatric diffuse intrinsic pontine gliomas (DIPGs), the majority of which feature mutation of lysine 27 to methionine. This “oncohistone” potently inhibits PRC2 activity and leads to a global reduction in H3K27 methylation. Similar to DIPG, posterior fossa type A (PFA) ependymomas also show low levels of H3K27 methylation. Although PFAs do not possess the H3K27M oncohistone mutation, they do show increased expression of Cxorf67. Interestingly, Cxorf67 contains a C-terminal sequence that resembles the sequence surrounding H3K27, and we find that this portion of Cxorf67 inhibits PRC2 activity to an even greater extent than the H3K27M oncohistone. Thus, we suggest re-naming Cxorf67 as EZHIP (Enhancer of Zeste Homologs Inhibitory Protein). Furthermore, when expressed in 293T cells, Cxorf67 interacts with several members of PRC2 and induces changes in H3K27 methylation patterns that mirror the changes in H3K27 methylation induced by expression of H3K27M. We propose that PFAs have dysregulated H3K27 methylation by a mechanism that involves inhibition of PRC2 by Cxorf67, which could drive tumorigenesis.

2019-04-09 | PXD013390 | Pride

Accurate H3K27 methylation patterns can be established de novo by SUZ12-directed PRC2

Project description:The Polycomb repressive complex 2 (PRC2) catalyzes H3K27 methylation and is required for maintaining transcriptional patterns and cellular identity, but the specification and maintenance of genomic PRC2 binding and H3K27 methylation patterns remain incompletely understood. Epigenetic mechanisms have been proposed, wherein pre-existing H3K27 methylation directs recruitment and regulates the catalytic activity of PRC2 to support its own maintenance. Here we investigate if such mechanisms are required for specifying H3K27 methylation patterns in mouse embryonic stem cells. Through genetic knockouts of subunits, we find that PRC2 is responsible for all levels of H3K27 methylation, and that methylation patterns can be accurately established de novo, when a subunit is reintroduced in the absence of pre-existing H3K27 methylation and PRC2 chromatin binding. Furthermore, we find that the core-subunit SUZ12 directs genomic binding of PRC2, which is essential for establishing correct methylation patterns.

2018-01-12 | GSE103685 | GEO

Histone post translational modification mass sprectrometry SUZ12 exon 4 cell lines

Project description:We investigate the contribution of each SUZ12 isoform on PRC2 activity on chromatin using our different ESC lines. As an additional comparison for ∆ex4 cells (SUZ12-S), we included an ESC clone in which an unsuccessful CRISPR editing event resulted in a mutant allele with nearly constitutive splicing of exon 4 (herein, CSex4) and normal Suz12 expression levels (expressing only SUZ12-L). First, we profiled H3K27 bulk PTMs by WB and observed that, while CSex4 cells showed no major differences to control cells, ∆ex4 cells displayed lower levels of H3K27me2 and -me3, with higher levels of mono-methylation and acetylation. Similar results were obtained when comparing SUZ12-L and SUZ12-S ESC rescue lines. To validate these findings with an antibody-independent technique, and to additionally profile other histone PTMs, we analysed these cells with histone-MS. In line with the previous estimates26, WT cells displayed approximately 85% of H3K27 methylation. This proportion was largely similar in CSex4 cells, while it dropped to ~50% in ∆ex4 cells, with H3K27me2 and -me3 being the most affected modifications. Notably, H3K27me2/3 loss in ∆ex4 cells occurred at histone peptides regardless of their H3K36 methylation status. Moreover, the global H3K36 methylation rates were not affected in either CSex4 or ∆ex4 cells (Figure S4C), and no major changes in methylation or acetylation levels were observed at other residues. Importantly, reintroduction of SUZ12-L in KO cells rescued a higher degree of methylation compared to SUZ12-S. Overall, these results indicate that SUZ12-S alone is unable to maintain global physiological levels of H3K27 methylation; rather SUZ12-L is also necessary for this task.

2024-03-18 | PXD046640 | Pride

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2018-04-05 | GSE100679 | GEO

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2018-04-05 | GSE108302 | GEO

SUZ12 immunoprecipitation followed by protein indentification via mass spectrometry (SUZ12 IP-MS) in mESCs of SUZ12 WT, delta exon 4, KO, and KO rescues with SUZ12-L and SUZ12-S

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2024-03-18 | PXD046660 | Pride

Physical and functional screening of Polycomb Repressor Complex 2 highlights novel regulators of histone H3 lysine 27 methylation status

Project description:Polycomb Repressor Complex 2 (PRC2) is a multi-protein epigenetic regulator complex that plays critical roles in early development and tissue differentiation. The complex catalyzes the methylation of histone H3 lysine 27 (H3K27). The tri-methyl state (H3K27me3) is well studied as an agent of gene repression, but more recently distinct roles for the mono- and di-methyl states have been discovered. In order to more fully understand how PRC2-associated factors might influence H3K27 status, we screened for physical associations of PRC2 subunits. Knockdown of these factors was used to produce functional interaction maps focused on H3K27 methylation, including proteins that have positive and negative effects on the levels each histone mark.

2018-04-05 | PXD005381 | Pride

Two distinct functional axes of positive feedback-enforced PRC2 recruitment in mouse embryonic stem cells

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2020-08-07 | PXD014290 | Pride

Two distinct functional axes of positive feedback-enforced PRC2 recruitment in mouse embryonic stem cells

2021-09-22 | PXD020684 | Pride

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