THE FLI-1 AND CHIMERIC EWS-FLI-1 ONCOPROTEINS DISPLAY SIMILAR DNA-BINDING SPECIFICITIES

Although recent data have demonstrated that the chimeric EWS-FLI-1 cDN A isolated from cases of Ewing's sarcoma can transform NIH 3T3 cells, little is known about the basis for this transformation. Since FLI-1 a nd EWS-FLI-1 contain an Ets domain, both proteins may act as sequence- specific transcription factors. Here the DNA binding properties of FLI -1 and EWS-FLI-1 have been examined. An epitope-tagging strategy was d eveloped to determine the optimum DNA-binding sequence of FLI-1. The a lignment of cloned binding sequences showed a consensus DNA-binding si te of ACCGGAAG/aT/c. This consensus sequence shows greater specificity for sequence 5' of the GGAA core site than those of other Ets protein s. Using several truncated forms of FLI-1, we show that the Ets domain is necessary and sufficient for the DNA binding specificity of FLI-1. The EWS-FLI-1 protein displayed the same DNA binding specificity and affinity as FLI-1 did. Despite their DNA binding similarities, the EWS -FLI-1 translocation product is likely to have a distinct pattern of e xpression from that of FLI-1 since the translocation results in the re placement of the 5' regulatory region of Fli-1 with that of EWS. Consi stent with this we found that Fli-1 mRNA expression in lymphocytes was high in quiescent cells and disappeared upon activation while EWS mRN A expression was low in resting cells and increased in activated T cel ls. In summary, our data suggest that EWS-FLI-1 might act through the same target genes normally regulated by FLI-1, and EWS-FLI-1-induced t ransformation may result from dysregulation of FLI-1 target genes duri ng cell proliferation and differentiation.