EWS-FLI1 utilizes divergent chromatin remodeling mechanisms to directly activate or repress enhancer elements in Ewing sarcoma

The aberrant transcription factor EWS FLI1 drives Ewing sarcoma but its molecular function is not completely understood. We find that EWS FLI1 reprograms gene regulatory circuits in Ewing sarcoma by directly inducing or repressing enhancers. At GGAA repeat elements which lack evolutionary conservation and regulatory potential in other cell types EWS FLI1 multimers induce chromatin opening and create de novo enhancers that physically interact with target promoters. Conversely EWS FLI1 inactivates conserved enhancers containing canonical ETS motifs by displacing wild type ETS transcription factors. These divergent chromatin remodeling patterns repress tumor suppressors and mesenchymal lineage regulators while activating oncogenes and potential therapeutic targets such as the kinase VRK1. Our findings demonstrate how EWS FLI1 establishes an oncogenic regulatory program governing both tumor survival and differentiation.