Mol Cell Biol, July 1998, p. 3915-3925, Vol. 18, No. 7
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Synergize with Different Regions of AML1
Division of Hematology/Oncology, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts1; Department of Biochemistry, Vanderbilt Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee2; and Division of Pediatric Oncology, Johns Hopkins Oncology Center, Baltimore, Maryland3
Received 11 February 1998/Returned for modification 23 March 1998/Accepted 13 April 1998
Control elements of many genes are regulated by multiple activators
working in concert to confer the maximal level of expression, but the
mechanism of such synergy is not completely understood. The promoter of
the human macrophage colony-stimulating factor (M-CSF) receptor
presents an excellent model with which we can study synergistic,
tissue-specific activation for two reasons. First, myeloid-specific
expression of the M-CSF receptor is regulated transcriptionally by
three factors which are crucial for normal hematopoiesis: PU.1, AML1,
and C/EBP
. Second, these proteins interact in such a way as to
demonstrate at least two examples of synergistic activation. We have
shown that AML1 and C/EBP
activate the M-CSF receptor promoter in a
synergistic manner. As we report here, AML1 also synergizes, and
interacts physically, with PU.1. Detailed analysis of the physical and
functional interaction of AML1 with PU.1 and C/EBP
has revealed that
the proteins contact one another through their DNA-binding domains and
that AML1 exhibits cooperative DNA binding with C/EBP
but not with
PU.1. This difference in DNA-binding abilities may explain, in part,
the differences observed in synergistic activation. Furthermore, the
activation domains of all three factors are required for synergistic
activation, and the region of AML1 required for synergy with PU.1 is
distinct from that required for synergy with C/EBP
. These
observations present the possibility that synergistic activation is
mediated by secondary proteins contacted through the activation domains of AML1, C/EBP
, and PU.1.
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