EWS center dot Fli-1 fusion protein interacts with hyperphosphorylated RNApolymerase II and interferes with serine-arginine protein-mediated RNA splicing

Ewing's sarcoma displays a characteristic chromosomal translocation that re sults in fusion of the N-terminal domain of the Ewing's sarcoma protein (EW S) to the C-terminal DNA-binding domain of the ETS family transcription fac tor Fli-1 (Friend leukemia integration-1). EWS possesses structural motifs suggesting a role in transactivation as well as RNA binding. We demonstrate that wild-type EWS protein functions as an adapter molecule coupling trans cription to RNA splicing by binding to hyperphosphorylated RNA polymerase I I through the N-terminal domain of EWS and recruiting serine-arginine (SR) splicing factors through the C-terminal domain of EWS. The oncogenic EWS Fl i-1 fusion protein retains the ability to bind to hyperphosphorylated RNA p olymerase II but lacks the ability to recruit SR proteins because of replac ement of the C-terminal domain of EWS by Fli-1. In an in vivo splicing assa y, the EWS.Fli-1 fusion protein inhibits SR protein-mediated E1A pre-mRNA s plicing in a dominant-negative manner. These results indicate that EWS Fli- 1 interferes with the normal function of EWS and implicate uncoupling of ge ne transcription from RNA splicing in the pathogenesis of Ewing's sarcoma.