Identification of the major positive regulators of c-myb expression in hematopoietic cells of different lineages

Abstract

The c-myb gene is primarily expressed in hematopoietic cells, and it is overexpressed in many leukemias. The regulation of its expression is of critical importance in hematopoietic cells. We identified the major positive regulatory sites in the 5'-flanking sequence of the human c-myb gene, and we found that the positive regulators differed in cells of different lineages. In the Molt-4 T-cell line, two Ets-like binding sites were required for the expression of c-myb. The 5' site played a minor role in the regulation of c- myb expression, and we demonstrated that a protein of 67 kDa bound to this site. Antibodies against Ets proteins showed no cross-reactivity with this protein. We showed that Ets-1 bound to the 3'-regulatory site in the c-myb promoter by electrophoretic mobility shift assay and antibody studies. Both of these Ets-like binding sites were nonfunctional in the DHL-9 B-cell line and the K562 myeloid cell line. We identified a novel transcription factor of 50.5 kDa that was required for expression of c-myb in these cell lines.