GENT-21. ATRX DEFICIENCY PROMOTES INVASION AND ALTERS THE DIFFERENTIATION CAPACITY OF GLIOMA CELLS OF ORIGIN BY DYSREGULATING GENOME-WIDE CHROMATIN ACCESSIBILITY AND MODULATING TRANSCRIPTIONAL PROGRAMS

Abstract

Comprehensive genomic profiling in cancer continues to reveal frequent alterations in epigenetic regulators, firmly implicating chromatin biology in the oncogenic process. Inactivating mutations in the SWI/SNF family member ATRX invariably pair with mutations in TP53 and IDH1/2 and represent defining molecular alterations in diffusely infiltrating gliomas. So far, ATRX deficiency has been linked to a wide spectrum of physiological dysfunction, including aberrant gene regulation, abnormal telomere maintenance, genomic instability, and aneuploidy, but the molecular mechanism(s) by which ATRX deficiency promotes oncogenesis are still largely unknown. To understand the role of Atrx loss-of-function mutations in gliomagenesis, we inactivated Atrx in Tp53-/- murine neuroepithelial progenitor cells (NPCs), which have been implicated as potential glioma cells of origin by several prior studies. Interestingly, Atrx loss induced NPCs to stop growing as neurospheres and adopt an adherent phenotype, while also exhibiting significantly increased cellular motility by transwell migration assay, the latter an established pathogenic feature of diffusely infiltrating gliomas. Moreover, when cultured in differentiation conditions, Atrx deficient cells displayed upregulation of astrocyte markers and downregulation of neuronal and oligodendrocyte markers, suggesting that Atrx directly regulates NPCs differentiation state and potential. Notably, the observed phenotypes correlated with altered gene expression profiles involving molecular networks implicated in development, regulation of signal transduction and cellular motility and invasion. Integrating these transcriptional changes with shifts in chromatin accessibility occurring with Atrx deficiency and genome-wide Atrx distribution, as determined by ChIP-seq, revealed highly significant spatial correlations between differentially expressed genes, regions of altered chromatin compaction, and genomic sites normally occupied by Atrx. Taken together, these findings demonstrate that Atrx deficiency induces widespread disruptions in chromatin organization, which in turn lead to dramatic shifts in gene expression and acquisition of disease-relevant phenotypes in putative glioma cells of origin.