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 differentiation in the chicken haematopoietic system. To elucidate the transciptional 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/EBP, GATA and Myb families. These sites are contained within a 309 bp promoter fragment which is sufficient for specific high level transcription in an eosinophil cell line. Co‐transfection experiments in Q2bn fibroblasts showed cooperative activation of the EOS47 proximal promoter by c‐Myb, Ets‐1/Fli‐1, GATA‐1 and C/EBPα. The Ets‐1/Fli‐1 and C/EBPα proteins were the most potent activators, and acted with high synergy through juxtaposed binding sites located ∼60 bp upstream of the transcription start site. The Ets‐1 and C/EBPα proteins 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 repressing at high protein concentrations. These results demonstrate combinatorial activation of an eosinophil‐specific promoter by ubiquitous and lineage‐restricted haematopoietic transcription factors. They also indicate that direct interactions between C/EBPs and specific Ets family members, together with GATA‐1, are important for eosinophil lineage determination.