EWS FLI-1 CHIMERIC PROTEIN IS A TRANSCRIPTIONAL ACTIVATOR/

Fli-1, an ets related gene, was found to be rearranged in 75% of eryth roleukemias induced by Friend murine leukemia virus. We have shown pre viously that the Fli-1 gene codes fora sequence specific transcription al activator which contains two autonomous transcriptional activation domains, one at the amino terminal region and the other at the carboxy terminal region. Recently human Fli-1 gene was shown to be involved i n Ewing's sarcoma and related subtypes of primitive neuroectodermal tu mors which share t(11;22) (q24;q12) chromosome translocation. In these tumors the carboxyl terminal region of Fli-1 was found to be fused wi th the amino terminal region of a putative RNA binding protein, EWS. B ecause part of the amino terminal transcriptional activation domain of Fli-1 was replaced with the amino terminal domain of the EWS (NTD-EWS ) which shares homology with RNA polymerase II, it was speculated that NTD-EWS may interfere with RNA pol II function. Alternatively, NTD-EW S could also contribute to the transcriptional activation function of EWS/Fli-1 chimeric protein by providing either a modulatory/regulatory domain or a novel transcriptional activation domain. Here we show tha t EWS/Fli-1 chimeric protein functions as a transcriptional activator. Deletion analysis reveals that the EWS domain functions as a modulato ry/regulatory domain for the transcriptional activation properties of the carboxy terminal transcriptional activation domain of EWS/Fli-1. W e therefore propose that replacement of the amino terminal transcripti onal activation domain of the Fli-1 protein with the regulatory domain of NTD-EWS results in the activation of the carboxy terminal transcri ptional activation domain of Fli-1 which may be the molecular mechanis m involved in these human tumors.