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      Therapeutic targeting of polycomb and BET bromodomain proteins in diffuse intrinsic pontine gliomas

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          Abstract

          Nucleosomes containing mutant K27M histones in diffuse intrinsic pediatric gliomas (DIPG) exclude PRC2 binding and recruit BET bromodomain proteins; however, residual PRC2-dependent repression of specific loci, is required for DIPG oncogenesis. These results provide a rationale for targeting these epigenetic regulators in patients.

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          Driver mutations in histone H3.3 and chromatin remodelling genes in paediatric glioblastoma.

          Glioblastoma multiforme (GBM) is a lethal brain tumour in adults and children. However, DNA copy number and gene expression signatures indicate differences between adult and paediatric cases. To explore the genetic events underlying this distinction, we sequenced the exomes of 48 paediatric GBM samples. Somatic mutations in the H3.3-ATRX-DAXX chromatin remodelling pathway were identified in 44% of tumours (21/48). Recurrent mutations in H3F3A, which encodes the replication-independent histone 3 variant H3.3, were observed in 31% of tumours, and led to amino acid substitutions at two critical positions within the histone tail (K27M, G34R/G34V) involved in key regulatory post-translational modifications. Mutations in ATRX (α-thalassaemia/mental retardation syndrome X-linked) and DAXX (death-domain associated protein), encoding two subunits of a chromatin remodelling complex required for H3.3 incorporation at pericentric heterochromatin and telomeres, were identified in 31% of samples overall, and in 100% of tumours harbouring a G34R or G34V H3.3 mutation. Somatic TP53 mutations were identified in 54% of all cases, and in 86% of samples with H3F3A and/or ATRX mutations. Screening of a large cohort of gliomas of various grades and histologies (n = 784) showed H3F3A mutations to be specific to GBM and highly prevalent in children and young adults. Furthermore, the presence of H3F3A/ATRX-DAXX/TP53 mutations was strongly associated with alternative lengthening of telomeres and specific gene expression profiles. This is, to our knowledge, the first report to highlight recurrent mutations in a regulatory histone in humans, and our data suggest that defects of the chromatin architecture underlie paediatric and young adult GBM pathogenesis.
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            Somatic Histone H3 Alterations in Paediatric Diffuse Intrinsic Pontine Gliomas and Non-Brainstem Glioblastomas

            To identify somatic mutations in paediatric diffuse intrinsic pontine gliomas (DIPGs), we performed whole genome sequencing of 7 DIPGs and matched germline DNA, and targeted sequencing of an additional 43 DIPGs and 36 non-brainstem paediatric glioblastomas (non-BS-PGs). 78% of DIPGs and 22% of non-BS-PGs contained p.K27M mutation in H3F3A, encoding histone H3.3, or the related HIST1H3B, encoding histone H3.1. An additional 14% of non-BS-PGs had somatic p.G34R H3F3A mutations.
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              The histone H3.3K27M mutation in pediatric glioma reprograms H3K27 methylation and gene expression.

              Recent studies have identified a Lys 27-to-methionine (K27M) mutation at one allele of H3F3A, one of the two genes encoding histone H3 variant H3.3, in 60% of high-grade pediatric glioma cases. The median survival of this group of patients after diagnosis is ∼1 yr. Here we show that the levels of H3K27 di- and trimethylation (H3K27me2 and H3K27me3) are reduced globally in H3.3K27M patient samples due to the expression of the H3.3K27M mutant allele. Remarkably, we also observed that H3K27me3 and Ezh2 (the catalytic subunit of H3K27 methyltransferase) at chromatin are dramatically increased locally at hundreds of gene loci in H3.3K27M patient cells. Moreover, the gain of H3K27me3 and Ezh2 at gene promoters alters the expression of genes that are associated with various cancer pathways. These results indicate that H3.3K27M mutation reprograms epigenetic landscape and gene expression, which may drive tumorigenesis.
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                Author and article information

                Journal
                Nature Medicine
                Nat Med
                Springer Nature
                1078-8956
                1546-170X
                February 27 2017
                February 27 2017
                :
                :
                Article
                10.1038/nm.4296
                5667640
                28263307
                ca3b7ecc-cb36-4963-9472-a4d20bd180c6
                © 2017
                History

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