Abstract B36: The Ewing's sarcoma fusion oncogene EWS-FLI1 induces tumors and developmental phenotypes in zebrafish

Abstract

Ewing's sarcoma, a member of the small round blue cell family of tumors, is an aggressive and malignant bone tumor of children and young adults. The cells are generally poorly differentiated, although can also have characteristics of neuroectodermal cells. Ewing's tumors are characterized by a t(11:22) that generates a fusion of the EWS protein and the FLI1 transcription factor. This fusion oncoprotein, EWS-FLI1, represents a potential therapeutic target for treatment of Ewing's sarcoma. However, the molecular mechanisms by which EWS-FLI1 mediates tumorigenesis remain unknown. Few animal models exist in which to study the function of EWS-FLI1. Here, we report the use of zebrafish as a new vertebrate model of EWS-FLI1 function and tumorigenesis. Using the zebrafish Tol2 transposon system, we have developed several transgenic models to study the function of EWS-FLI1 in a vertebrate model organism. First, we have injected zebrafish with transposons containing human EWS-FLI1 driven by either the heat shock or the β-actin promoter. A subset of the injected fish developed tumors when raised to adulthood. These tumors strongly resemble Ewing's sarcoma. This finding demonstrates that the functional targets of EWS-FLI1 that mediate tumor development are conserved from zebrafish to human. We observe an increased incidence of tumors in a p53 mutant background, suggesting that the p53 pathway may suppress EWS-FLI1 driven tumorigenesis. We are performing microarray analysis to identify candidate downstream effector genes and to compare to previously identified EWS-FLI1 target genes. In addition to these tumors, we identified transgenic lines that transmit the EWS-FLI1 transgene to their progeny. The embryos that express EWS-FLI1 exhibit abnormal embryonic development. This result suggests that EWS-FLI1 may regulate conserved developmental pathways. These transgenic lines represent a novel physiological context in which to study the cellular function of EWS-FLI1. From these two models of EWS-FLI1 expression in the zebrafish, we conclude that human EWS-FLI1 functions in zebrafish and that these models provide a novel context in which to study the function of this fusion oncogene. Additionally, the rapid development and small size of the zebrafish will allow us to utilize these models for genetic and chemical screens for specific EWS-FLI1 inhibitors for the treatment of Ewing's sarcoma. Citation Information: Cancer Res 2009;69(23 Suppl):B36.