EPCO-08. ATRX DEFICIENCY INDUCES DYSFUNCTIONAL HETEROCHROMATIN ARCHITECTURE IN GLIOMAS AND ESTABLISHES DISEASE-DEFINING TRANSCRIPTIONAL NETWORKS

Abstract

Abstract Loss of ATRX (Alpha Thalassemia/Mental Retardation Syndrome X, a member of SWI/SNF family chromatin regulator is altered in diffuse gliomas and defines molecular subtypes with aggressive behavior. Mechanistically, ATRX regulates incorporation of histone H3.3 into chromatin sites across the genome, maintains alternative lengthening of telomeres and establishes genomic distribution of polycomb responsive genes. We have recently reported Atrx deficiency induces glioma oncogenic features via widespread alterations in chromatin accessibility using mouse Neural Progenitor Cells (mNPCs- Tp53 -/-,Atrx -/-). Surprisingly, Atrx was found to be associated with transcription start site and enhancer regions, suggesting their strong association with epigenome architecture. In this background, we have recently performed ChIP-seq for histone marks that define active transcription, enhancers, repressors and gene bodies and Cohesion molecules on Atrx intact and deficient mNPCs. Our integrated analysis reports depletion of H3K9me3 loci’s with enrichment of H3K27me3 marks that coincidently enriched with Atrx binding sites and Lamina-Associated Domains (LADs). GSEA confirmed that the genes corresponding to “newly formed LADs” in mNPC-to-astrocyte differentiation are significantly enriched for genes down-regulated in Atrx deficient mNPCs and belongs to Gene Ontology categories such as cell cycle, chromosome organization and DNA damage. Alternatively, genes corresponding to decreased LAD association are enriched for up-regulated genes in Atrx deficient mNPCs and for regulation of differentiation, adhesion and cell death. Additionally, whole-genome bisulphite sequencing further demonstrated loss of methylation marks at H3K9me3 sites in Atrx deficient mNPCs, suggesting perturbations of heterochromatin regions leading to activation of canonical signals that define glioma phenotype and disease-state. To summarize, our data establishes tangible links between Atrx deficiency and dysregulated chromatin and heterochromatin architecture in gliomas and suggests the role of Atrx in establishing global chromatin features and transcriptional networks. Further, our data unravel novel therapeutic molecules/pathways for engineering potential.