Gene-15. Targeting of Ependymoma as Informed by Oncogenic 3d Genome Organization

Abstract

By profiling enhancers in primary ependymoma tumors, we have recently identified putative oncogenes, molecular targets, and functional pathways. Inhibition of selected targets diminished the proliferation of patient-derived neurospheres and increased survival in mouse models of ependymoma. While enhancers frequently regulate the nearest gene, unambiguous identification of enhancer target genes remains to be a challenge in the absence of chromosome conformation information. Consequently, we have now used HiC to map the 3-dimensional organization of tumor chromatin in the two most common and aggressive ependymoma subgroups: posterior fossa group A (PF-EPN-A) and supratentorial ependymomas with gene fusions involving the NF-κB subunit gene RELA (ST-EPN-RELA). By an integrative analysis of enhancer and gene expression in the context of the newly derived HiC data, we find that a large amount of the previously predicted enhancer target genes can be confirmed by physical interactions. Importantly, we also identify many new putative tumor-dependency genes activated by long-range promoter-enhancer interactions. Complementary to the analysis of gene-enhancer interactions, we have also leveraged the HiC data for resolving structural rearrangements underlying copy number alterations frequently observed in PF-EPN-A tumors. Especially copy number gains of the 1q arm of chromosome 1 are associated with poor survival. Our preliminary results reveal complex structural variants that underlie 1q gains, which lead to inter-chromosomal rearrangements and affect several genes that potentially contribute to poor survival. We now aim to test the relevance of the novel candidate tumor-dependency genes for tumor cell growth and proliferation in patient derived ependymoma models.