REGULATION OF EOSINOPHIL-SPECIFIC GENE-EXPRESSION BY A C EBP-ETS COMPLEX AND GATA-1/

The EOS47 antigen is an early and specific marker of eosinophil differ entiation in the chicken haematopoietic system. To elucidate the trans ciptional events controlling commitment to the eosinophil lineage, we studied the regulation of the eosinophil-specific EOS47 promoter. This promoter is TATA-less, and binds trancription factors of the Ets, C/E BP, GATA and Myb families. These sites are contained within a 309 bp p romoter fragment which is sufficient for specific high level transcrip tion in an eosinophil cell line, Co-transfection experiments in Q2bn f ibroblasts showed cooperative activation of the EOS47 proximal promote r by c-Myb, Ets-1/Fli-1, GATA-1 and C/EBP alpha, The Ets-1/Fli-1 and C /EBP alpha proteins were the most potent activators, and acted with hi gh synergy through juxtaposed binding sites located similar to 60 bp u pstream of the transcription start site, The Ets-1 and C/EBP alpha pro teins were found to associate physically via their DNA-binding domains and to bind their combined binding site cooperatively. GATA-1 showed biphasic regulation of the EOS47 promoter, activating at low and repre ssing at high protein concentrations. These results demonstrate combin atorial activation of an eosinophil-specific promoter by ubiquitous an d lineage-restricted haematopoietic transcription factors, They also i ndicate that direct interactions between C/EBPs and specific Ets famil y members, together with GATA-1, are important for eosinophil lineage determination.