DNA-BINDING AND TRANSCRIPTIONAL ACTIVATION PROPERTIES OF THE EWS-FLI-1 FUSION PROTEIN RESULTING FROM THE T(1122) TRANSLOCATION IN EWING SARCOMA

The 5' half of the EWS gene has recently been described to be fused to the 3' regions of genes encoding the DNA-binding domain of several tr anscriptional regulators, including ATF1, FLI-1, and ERG, in several h uman tumors. The most frequent occurrence of this situation results fr om the t(11;22)(q24;q12) chromosome translocation specific for Ewing s arcoma (ES) and related tumors which joins EWS sequences to the 3' hal f of FLI-1, which encodes a member of the Ets family of transcriptiona l regulators. We show here that this chimeric gene encodes an EWS-FLI- 1 nuclear protein which binds DNA with the same Sequence specificity a s the wild-type parental FLI-1 protein. We further show that EWS-FLI-1 is an efficient sequence-specific transcriptional activator of model promoters containing FLI-1 (Ets)-binding sites, a property which is st rictly dependent on the presence of its EWS domain. Comparison of the properties of the N-terminal activation domain of FLI-1 to those of th e EWS domain of the fusion protein indicates that EWS-FLI-1 has altere d transcriptional activation properties compared with FLI-1. These res ults suggest that EWS-FLI-1. contributes to the transformed phenotype of ES tumor cells by inducing the deregulated and/or unscheduled activ ation of genes normally responsive to FLI-1 or to other close members of the Ets family. ES and related tumors are characterized by an eleva ted level of c-myc expression. We show that EWS-FLI-1 is a transactiva tor of the c-myc promoter, suggesting that upregulation of c-myc expre ssion is under control of EWS-FLI-1.