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Mol. Cell. Biol., 03 1996, 1231-1240, Vol 16, No. 3
DE Zhang, CJ Hetherington, S Meyers, KL Rhoades, CJ Larson, HM Chen, SW Hiebert and DG Tenen
Transcription factors play a key role in the development and
differentiation of specific lineages from multipotential progenitors.
Identification of these regulators and determining the mechanism of how
they activate their target genes are important for understanding normal
development of monocytes and macrophages and the pathogenesis of a common
form of adult acute leukemia, in which the differentiation of monocytic
cells is blocked. Our previous work has shown that the monocyte-specific
expression of the macrophage colony-stimulating factor (M-CSF) receptor is
regulated by three transcription factors interacting with critical regions
of the M-CSF receptor promoter, including PU.1 and AML1.PU.1 is essential
for myeloid cell development, while the AML1 gene is involved in several
common leukemia-related chromosome translocations, although its role in
hematopoiesis has not been fully identified. Along with AML1, a third
factor, Mono A, interacts with a small region of the promoter which can
function as a monocyte-specific enhancer when multimerized and linked to a
heterologous basal promoter. Here, we demonstrate by electrophoretic
mobility shift assays with monocytic nuclear extracts, COS-7 cell-
transfected factors, and specific antibodies that the monocyte-enriched
factor Mono A is CCAAT enhancer-binding protein (C/EBP). C/EBP has been
shown previously to be an important transcription factor involved in
hepatocyte and adipocyte differentiation; in hematopoietic cells, C/EBP is
specifically expressed in myeloid cells. In vitro binding analysis reveals
a physical interaction between C/EBP and AML1. Further transfection studies
show that C/EBP and AML1 in concert with the AML1 heterodimer partner CBF
beta synergistically activate M-CSF receptor by more then 60 fold. These
results demonstrate that C/EBP and AML1 are important factors for
regulating a critical hematopoietic growth factor receptor, the M-CSF
receptor, suggesting a mechanism of how the AML1 fusion protein could
contribute to acute myeloid leukemia. Furthermore, they demonstrate
physical and functional interactions between AML1 and C/EBP transcription
factor family members.
Copyright © 1996, American Society for Microbiology
CCAAT enhancer-binding protein (C/EBP) and AML1 (CBF alpha2) synergistically activate the macrophage colony-stimulating factor receptor promoter
Department of Medicine, Beth Israel Hospital and Harvard Medical School, Boston, Massachusetts 02215, USA.
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