Abstract 2009: A new repressive network module in Ewing's Sarcoma

Abstract

Abstract The EWS-FLI1 chimeric transcription factor characteristic of Ewing's sarcoma family tumors (ESFT) constitutes the prototype of an aberrant ETS transcription factor causally involved in oncogenesis. However, the mechanisms of transcriptional regulation leading to ETS driven tumorigensis are poorly understood. Previously, we have successfully established and tested a research plan that proceeds from genomics data production, via bioinformatic generation of specific hypotheses to functional elucidation of EWS-FLI1 associated transcription network modules. In-silico analysis of time-resolved expression data revealed enrichment of ETS binding motifs in early EWS-FLI1 activated target genes, while EWS-FLI1 repressed genes showed most prominently enrichment of recognition motifs for forkhead box (FOX) proteins. Other motifs significantly co-occurring in the same promoter with FOX motifs were mainly containing homeobox domains (POU, SOX, NKX, CDP, TGIF). Concentrating on the EWS-FLI1 repressed transcriptional network most FOX proteins (FOXO1, FOXO3, FOXD1 and FOXN3) in the data set were found to be EWS-FLI1 repressed. Promoters of two of these genes, FOXO1 and FOXO3, were directly bound by EWS-FLI1 in a ChIP-seq experiment, and were also expressed at lower levels in ESFT than in mesenchymal progenitor cells which constitute a likely cell of origin for ESFT. Furthermore, bioinformatic analysis showed that FOX motifs were significantly co-enriched with ETS motifs in promoters of the same gene for ∼4% of all genes. Thus, we hypothesize that EWS-FLI1 exerts a major part of its repressive effect via inhibition of FOX proteins and may also directly (co-)repress a subset of these genes. In depth dissection of this newly identified repressive module of the EWS-FLI1 transcription network is performed by ectopic expression, RNA interference (RNAi) and reporter gene technologies combined with mutation analysis, and chromatin immunoprecipitation and protein co-immunoprecipitation. This study was funded by: “European Embryonal Tumor Pipeline” 6th framework program of the European Commission, (STREP “E.E.T. Pipeline” contract LSHC-CT-2006-037260), and by funds from the Austrian Research Fund FWF. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2009.