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Mol. Cell. Biol., 11 1995, 6100-6108, Vol 15, No. 11
C McCoy, DE Smith and MM Cornwell
P-glycoprotein, the product of the MDR1 gene (multidrug resistance gene 1),
is an energy-dependent efflux pump associated with treatment failure in
some hematopoietic malignancies. Its expression is regulated during normal
hematopoietic differentiation, although its function in normal
hematopoietic cells is unknown. To identify cellular factors that regulate
the expression of MDR1 in hematopoietic cells, we characterized the cis-
and trans-acting factors mediating 12-O- tetradecanoylphorbol-13-acetate
(TPA) activation of the MDR1 promoter in K562 cells. Transient-transfection
assays demonstrated that an MDR1 promoter construct containing nucleotides
-69 to +20 conferred a TPA response equal to that of a construct containing
nucleotides -434 to +105. TPA induced EGR1 binding to the -69/+20 promoter
sequences over a time course which correlated with increased MDR1 promoter
activity and increased steady-state MDR1 RNA levels. The -69/+20 promoter
region contains an overlapping SP1/EGR site. The TPA-responsive element was
localized to the overlapping SP1/EGR site by using a synthetic reporter
construct. A mutation in this site that inhibited EGR protein binding
blocked the -69/+20 MDR1 promoter response to TPA. The expression of a
dominant negative EGR protein also blocked the TPA response of the - 69/+20
promoter construct. Finally, the expression of EGR1 was sufficient to
activate a construct containing tandem MDR1 promoter SP1/EGR sites. These
data suggest a role for EGR1 in modulating MDR1 promoter activity in
hematopoietic cells.
Copyright © 1995, American Society for Microbiology
12-O-tetradecanoylphorbol-13-acetate activation of the MDR1 promoter is mediated by EGR1
Clinical Division, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104, USA.
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