Downstream EWS/FLI1-upstream Ewing's sarcoma

Ewing's sarcoma family tumors are a good example of how genome research has advanced our understanding of the molecular pathogenesis of an otherwise enigmatic disease. This group of embryonal bone tumors is characterized by the expression of a chimeric ETS-family oncogene, predominantly EWS/FLI1. There is now convincing evidence for a mesenchymal descent from an early pluripotent progenitor. EWS/FLI1 has been shown to drive proliferation of Ewing's sarcoma cells and block most of the differentiation potential except for a partial neural gene expression program. The EWS/FLI1 fusion protein acts mainly as a gene activator, directly interacting with chromatin at two kinds of binding site: distant enhancers enriched in GGAA microsatellites, and proximal promoters containing classical ETS-binding motifs and recognition motifs for other transcription factors. EWS/FLI1 also represses a large number of genes, mainly indirectly, presumably by altering microRNA expression and epigenetic mechanisms, and potentially affecting post-transcriptional gene regulation. Modulation of EWS/FLI1 expression is not only a desirable therapeutic goal, but may also occur under physiological conditions and influence the course of the disease.