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Characterization of an antagonistic switch between histone H3 lysine 27 methylation and acetylation in the transcriptional regulation of Polycomb group target genes.

Pasini D, Malatesta M, Jung HR, Walfridsson J, Willer A, Olsson L, Skotte J, Wutz A, Porse B, Jensen ON, Helin K - Nucleic Acids Res. (2010)

Bottom Line: We show that loss of PRC2 activity results in a global increase in H3K27 acetylation.Moreover, we provide evidence that the acetylation of H3K27 is catalyzed by the acetyltransferases p300 and CBP.Based on these data, we propose that the PcG proteins in part repress transcription by preventing the binding of acetyltransferases to PcG target genes.

View Article: PubMed Central - PubMed

Affiliation: Biotech Research and Innovation Centre (BRIC), University of Copenhagen, Copenhagen, Denmark.

ABSTRACT
Polycomb group (PcG) proteins are transcriptional repressors, which regulate proliferation and cell fate decisions during development, and their deregulated expression is a frequent event in human tumours. The Polycomb repressive complex 2 (PRC2) catalyzes trimethylation (me3) of histone H3 lysine 27 (K27), and it is believed that this activity mediates transcriptional repression. Despite the recent progress in understanding PcG function, the molecular mechanisms by which the PcG proteins repress transcription, as well as the mechanisms that lead to the activation of PcG target genes are poorly understood. To gain insight into these mechanisms, we have determined the global changes in histone modifications in embryonic stem (ES) cells lacking the PcG protein Suz12 that is essential for PRC2 activity. We show that loss of PRC2 activity results in a global increase in H3K27 acetylation. The methylation to acetylation switch correlates with the transcriptional activation of PcG target genes, both during ES cell differentiation and in MLL-AF9-transduced hematopoietic stem cells. Moreover, we provide evidence that the acetylation of H3K27 is catalyzed by the acetyltransferases p300 and CBP. Based on these data, we propose that the PcG proteins in part repress transcription by preventing the binding of acetyltransferases to PcG target genes.

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Regulation of H3K27me3 and H3K27Ac target gene binding in MLL-AF9 HSPCs and FDCP-mix cells. (A) β-Globin, Lipocalin and Hoxa9 qPCR expression analyses in FDCP-mix cells before and after granulocytic differentiation and in MLL-AF9-expressing HSPC. (B) ChIP analyses of Hoxa9 and Olig1 promoters in FDCP-mix cells and MLL-AF9-expressing HSPCs using the indicated antibodies. H3K27Ac, H3K9Ac and H3K27me3 signals are normalized to histone density using an H3-specific antibody.
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Figure 4: Regulation of H3K27me3 and H3K27Ac target gene binding in MLL-AF9 HSPCs and FDCP-mix cells. (A) β-Globin, Lipocalin and Hoxa9 qPCR expression analyses in FDCP-mix cells before and after granulocytic differentiation and in MLL-AF9-expressing HSPC. (B) ChIP analyses of Hoxa9 and Olig1 promoters in FDCP-mix cells and MLL-AF9-expressing HSPCs using the indicated antibodies. H3K27Ac, H3K9Ac and H3K27me3 signals are normalized to histone density using an H3-specific antibody.

Mentions: Homeotic genes (HOX) are the best-characterized PcG target genes. HOX genes play an essential role in the regulation of normal development (36). Moreover, deregulation of HOX expression has been linked to the development of different forms of human cancer (37). For example, HOXA9 overexpression in HSPC is important for HSPC immortalization (38), and the specific activation of HOXA9 expression is a feature of several leukemic fusion proteins including MLL-AF9 (39–41). To investigate if the increased expression of Hoxa9 in immortalized HSPC involves transcriptional mechanism similar to the one described above for ES cell differentiation, we compared MLL-AF9 immortalized c-kit+ HSPC with a multipotent hematopoietic progenitor cell line FDCP-mix [the FDCP-mix cells were chosen to allow the expansion in TC of normal hematopoietic progenitors (31)]. As previously reported (28,42), MLL-AF9 immortalized HSPCs are blocked at the progenitor stage of the granulocytic differentiation pathways as confirmed by the expression of the granulocytic marker Lipocalin (Figure 4A). Lipocalin expression is silenced in the FDCP-mix cells and is activated to similar levels as in MLL-AF9 expressing cells when induced to differentiate into granulocytes (Figure 4A). Importantly, Hoxa9 expression was specifically detected in the MLL-AF9 expressing cells, but not in the differentiating FDCP-mix cells demonstrating the direct role of MLL-AF9 in Hoxa9 transcriptional activation (Figure 4A).Figure 4.


Characterization of an antagonistic switch between histone H3 lysine 27 methylation and acetylation in the transcriptional regulation of Polycomb group target genes.

Pasini D, Malatesta M, Jung HR, Walfridsson J, Willer A, Olsson L, Skotte J, Wutz A, Porse B, Jensen ON, Helin K - Nucleic Acids Res. (2010)

Regulation of H3K27me3 and H3K27Ac target gene binding in MLL-AF9 HSPCs and FDCP-mix cells. (A) β-Globin, Lipocalin and Hoxa9 qPCR expression analyses in FDCP-mix cells before and after granulocytic differentiation and in MLL-AF9-expressing HSPC. (B) ChIP analyses of Hoxa9 and Olig1 promoters in FDCP-mix cells and MLL-AF9-expressing HSPCs using the indicated antibodies. H3K27Ac, H3K9Ac and H3K27me3 signals are normalized to histone density using an H3-specific antibody.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2926606&req=5

Figure 4: Regulation of H3K27me3 and H3K27Ac target gene binding in MLL-AF9 HSPCs and FDCP-mix cells. (A) β-Globin, Lipocalin and Hoxa9 qPCR expression analyses in FDCP-mix cells before and after granulocytic differentiation and in MLL-AF9-expressing HSPC. (B) ChIP analyses of Hoxa9 and Olig1 promoters in FDCP-mix cells and MLL-AF9-expressing HSPCs using the indicated antibodies. H3K27Ac, H3K9Ac and H3K27me3 signals are normalized to histone density using an H3-specific antibody.
Mentions: Homeotic genes (HOX) are the best-characterized PcG target genes. HOX genes play an essential role in the regulation of normal development (36). Moreover, deregulation of HOX expression has been linked to the development of different forms of human cancer (37). For example, HOXA9 overexpression in HSPC is important for HSPC immortalization (38), and the specific activation of HOXA9 expression is a feature of several leukemic fusion proteins including MLL-AF9 (39–41). To investigate if the increased expression of Hoxa9 in immortalized HSPC involves transcriptional mechanism similar to the one described above for ES cell differentiation, we compared MLL-AF9 immortalized c-kit+ HSPC with a multipotent hematopoietic progenitor cell line FDCP-mix [the FDCP-mix cells were chosen to allow the expansion in TC of normal hematopoietic progenitors (31)]. As previously reported (28,42), MLL-AF9 immortalized HSPCs are blocked at the progenitor stage of the granulocytic differentiation pathways as confirmed by the expression of the granulocytic marker Lipocalin (Figure 4A). Lipocalin expression is silenced in the FDCP-mix cells and is activated to similar levels as in MLL-AF9 expressing cells when induced to differentiate into granulocytes (Figure 4A). Importantly, Hoxa9 expression was specifically detected in the MLL-AF9 expressing cells, but not in the differentiating FDCP-mix cells demonstrating the direct role of MLL-AF9 in Hoxa9 transcriptional activation (Figure 4A).Figure 4.

Bottom Line: We show that loss of PRC2 activity results in a global increase in H3K27 acetylation.Moreover, we provide evidence that the acetylation of H3K27 is catalyzed by the acetyltransferases p300 and CBP.Based on these data, we propose that the PcG proteins in part repress transcription by preventing the binding of acetyltransferases to PcG target genes.

View Article: PubMed Central - PubMed

Affiliation: Biotech Research and Innovation Centre (BRIC), University of Copenhagen, Copenhagen, Denmark.

ABSTRACT
Polycomb group (PcG) proteins are transcriptional repressors, which regulate proliferation and cell fate decisions during development, and their deregulated expression is a frequent event in human tumours. The Polycomb repressive complex 2 (PRC2) catalyzes trimethylation (me3) of histone H3 lysine 27 (K27), and it is believed that this activity mediates transcriptional repression. Despite the recent progress in understanding PcG function, the molecular mechanisms by which the PcG proteins repress transcription, as well as the mechanisms that lead to the activation of PcG target genes are poorly understood. To gain insight into these mechanisms, we have determined the global changes in histone modifications in embryonic stem (ES) cells lacking the PcG protein Suz12 that is essential for PRC2 activity. We show that loss of PRC2 activity results in a global increase in H3K27 acetylation. The methylation to acetylation switch correlates with the transcriptional activation of PcG target genes, both during ES cell differentiation and in MLL-AF9-transduced hematopoietic stem cells. Moreover, we provide evidence that the acetylation of H3K27 is catalyzed by the acetyltransferases p300 and CBP. Based on these data, we propose that the PcG proteins in part repress transcription by preventing the binding of acetyltransferases to PcG target genes.

Show MeSH
Related in: MedlinePlus