Abstract 1407: The influence of EWS-FLI1 on the Rho/Actin/MRTF circuit in Ewing sarcoma

Abstract

Abstract Ewing sarcoma (ES) is the second most common bone tumor in children and adolescents. The disease is characterized by the expression of the aberrant transcription factor EWS-FLI1, which is a fusion gene product originating from the chromosomal translocation t(11;22)(q24;q12). Despite good treatment outcomes for patients with localized ES, about 25% of patients already harbor metastatic disease upon presentation and are prevalently faced with poor overall survival. The metastatic cascade is a complex process. Remodeling of the actin cytoskeleton is the first step for a cell in order to acquire a migratory phenotype. The major regulator of the actin cytoskeleton is the Rho family of GTPases, which upon G-protein coupled receptor (GPCR) signaling gets activated and promotes the polymerization of monomeric G-actin into stress fibers. Concurrently G-actin releases the myocardin-related transcription factor family (MRTF) of transcriptional coactivators. MRTFs translocate into the nucleus where they, together with the transcription factor serum response factor (SRF), bind to serum response elements (SRE) in the promoter of genes involved in cell adhesion, migration and motility. However, the ternary complex factor (TCF) family, a class of transcriptional coactivators activated through Ras signaling, can compete with MRTFs for SRF complexing and binds to ets-motifs on SRE. The ets-transcription factor EWS-FLI1 has been shown to substitute for TCFs, potentially interfering with SRF target gene expression. We therefore hypothesize that EWS-FLI1 interferes with GPCR downstream signaling by competition with MRTFs. By gene expression profiling, we show that several putative MRTF target genes are repressed in the presence of EWS-FLI1 in ES cell lines and are strongly induced upon EWS-FLI1 knockdown. Using the MRTFA target gene transgelin (TAGLN) as an example, we show that knockdown of MRTFA can only reduce its serum inducibility in the absence but not in the presence of EWS-FLI1 supporting our hypothesis of EWS-FLI1 perturbing GPCR signaling in ES. With this study we want to elucidate the role of EWS-FLI1 in the regulation of early steps of the metastatic process in ES. Supported by the Liddy Shriver Sarcoma Initiative. Citation Format: Anna M. Katschnig, Raphaela Schwentner, Stephan Niedan, Maximilian O. Kauer, Elizabeth R. Lawlor, Dave N.T. Aryee, Heinrich Kovar. The influence of EWS-FLI1 on the Rho/Actin/MRTF circuit in Ewing sarcoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1407. doi:10.1158/1538-7445.AM2014-1407