Volume 272, Number 3,
Issue of January 17, 1997
pp. 1943-1949
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
Identification of the Major Positive Regulators of
c-myb Expression in Hematopoietic Cells of Different
Lineages
(Received for publication, July 30, 1996, and in revised form, October 25, 1996)
Janet
Sullivan
,
Brian
Feeley
,
Juan
Guerra
and
Linda M.
Boxer
From the Center for Molecular Biology in Medicine, Palo Alto
Veterans Affairs Medical Center and the Department of Medicine,
Stanford University School of Medicine,
Stanford, California 94305
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.