A FUNCTIONAL ETS DNA-BINDING DOMAIN IS REQUIRED TO MAINTAIN MULTIPOTENCY OF HEMATOPOIETIC PROGENITORS TRANSFORMED BY MYB-ETS

Earlier work demonstrated that the Myb-Ets fusion protein of E26 avian leukemia virus induces the proliferation of multipotent hematopoietic progenitors (MEPs). These progenitors differentiate spontaneously at low frequencies along the erythroid lineage, and following the introdu ction of kinase/ras-type oncogenes or treatment with TPA, they are ind uced to differentiate along the myelomonocytic and eosinophilic lineag es. Here, we show that the ts1.1 mutant of E26 encodes an Ets DNA-bind ing domain that is both defective and thermolabile for binding of spec ific DNA sequences. Correlating with this, ts1.1 MEP colonies transfor med at the permissive temperature exhibit elevated levels of erythroid cells and eosinophils, whereas at the nonpermissive temperature they are induced to differentiate along the erythroid and myelomonocytic li neages and, to a lesser extent, along the eosinophil lineage. Inductio n of the former two lineages cannot be separated by pulse shift experi ments and is essentially completed 2.5 days after temperature shift. O ur results indicate that the Ets portion of the Myb-Ets fusion protein inhibits the lineage commitment of multipotent hematopoietic progenit ors, probably via binding to regulatory DNA sequences of specific targ et genes.