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ATRX loss in glioma results in epigenetic dysregulation of cell cycle phase transition [RNA-seq]

ABSTRACT: ATRX, a chromatin remodeler protein, is recurrently mutated in H3F3A-mutant pediatric glioblastoma (GBM) and IDH-mutant grade 2/3 adult glioma. Previous work has shown that ATRX-deficient GBM cells show enhanced sensitivity to irradiation, but the etiology remains unclear. We found that ATRX binds regulatory elements of cell cycle phase transition genes in GBM cells, and there is a marked reduction in Checkpoint Kinase 1 (CHEK1) expression with ATRX loss, leading to early release of G2/M entry after irradiation. ATRX-deficient cells exhibit enhanced activation of master cell cycle regulator ATM with irradiation. Mice intra-cranially implanted with ATRX-deficient GBM cells demonstrate doubling of median survival compared to the ATRX-Wild Type controls when treated with ATM inhibitor AZD0156 and radiation. This study demonstrates that ATRX-deficient high-grade gliomas (HGGs) display epigenetic dysregulation of cell cycle phase transitions, which opens a new window for therapies targeting this unique phenotype.

ORGANISM(S): Mus musculus

PROVIDER: GSE178113 | GEO | 2022/01/18

REPOSITORIES: GEO

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Project description:The outcome for children with high-grade gliomas (HGG) remains dismal, with a two-year survival rate of only 10-30%. Approximately half of pediatric HGGs are diffuse intrinsic pontine glioma (DIPG), a brainstem tumor that arises almost exclusively in children. Genome-wide analyses of copy number imbalances previously showed that platelet derived growth factor receptor alpha (PDGFRA) is the most frequent target of focal amplification in pediatric HGGs. To determine whether the PDGFRA is also targeted by more subtle mutations not detected by copy number analysis, we sequenced all PDGFRA coding exons from a cohort of pediatric HGGs. Somatic activating mutations were identified in 14.4% (13/90) of non-brainstem pediatric HGGs and 4.7% (2/43) of DIPGs, including missense mutations and in-frame deletions and insertions not previously described. 40% of tumors with mutation showed concurrent amplification, while 60% carried heterozygous mutations. Six different mutations impacting different domains all resulted in ligand-independent receptor activation that was blocked by small molecule inhibitors of PDGFR. Expression of mutants in p53-null primary mouse astrocytes conferred a proliferative advantage in vitro, and generated HGGs in vivo with complete penetrance when implanted into brain. The gene expression signatures reflected the spectrum of human diffuse HGGs. PDGFRA intragenic deletion of exons 8 and 9 were previously shown in adult HGG, but were not detected in 83 non-brainstem pediatric HGG and 57 DIPGs. Thus, a distinct spectrum of mutations confers constitutive receptor activation and oncogenic activity to PDGFR in childhood HGG. To better understand the consequence of PDGFRα mutation in pediatric gliomagenesis, retroviral constructs expressing wild-type PDGFRα or six selected PDGFRα mutants that affect different regions of the receptor were generated for functional studies. p53-null primary mouse astrocyte (PMA) cultures were chosen as a relevant cellular background to assess PDGFRα function.

Project description:Ataxia telangiectasia (AT) is an autosomal recessive disorder characterized by neuronal degeneration, telangiectasias, acute cancer predisposition, and hypersensitivity to ionizing radiation (IR). The gene defective in AT, ATM (for AT-mutated), encodes a protein, pATM that has been found to have IR-inducible kinase activity. Cells from individuals with AT exhibit severely attenuated cell cycle checkpoints in response to gamma radiation exposure. pATM has been hypothesized to act as part of a complex that senses DNA damage, in particular, DNA double strand breaks. We are studying the pATM-dependent gene expression responses to a dose of 1.5 Gy radiation in lymphoblastoid cell lines from multiple individuals with either wild type or mutated ATM. The gene expression analyses were performed on Agilent Human 1A Oligo chips containing approximately 16,000 60mer probes. We identified a set of genes whose gene expression changes are ATM-dependent following exposure to 1.5 Gy IR. This set of genes was tested by real time quantitative PCR analysis. The study consists of one dose group - 1.5 Gray gamma radiation. Samples were collected 6 hr following irradiation (treated) or mock irradiation (controls) for each culture. Each culture has a treated sample and a control sample. There are cultures from 6 wild-type ATM individuals and cultures from 6 individuals that are ATM-deficient, for a total of 12 cultures. Hybridizations compared RNA extracted from each individual culture's treated sample against its corresponding control sample, and were performed as dye-flip duplicates (1 replicate in each direction). Hybridizations were performed on the Human 1A Oligo Chips using low input, direct labeling at Paradigm Genetics Laboratory. Microarray scanning was performed with the Agilent G2565AA Scanner. Paradigm Standard Operating Procedures were followed for quality analysis, sample labeling, microarray hybridization and washing, scanning, image analysis and initial data analysis.

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ATRX loss in glioma results in epigenetic dysregulation of cell cycle phase transition [RNA-seq]

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