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Division of Digestive Diseases, Veterans Affairs Medical Center and University of Cincinnati College of Medicine, Cincinnati, Ohio 45267
We have investigated the regulation of gene
transcription in the intestine using the guanylyl cyclase C
(GCC) gene as a model. GCC is expressed in crypts and
villi in the small intestine and in crypts and surface epithelium of
the colon. DNase I footprint, electrophoretic mobility shift assay
(EMSA), transient transfection assays, and mutagenesis experiments
demonstrated that GCC transcription is regulated by a critical
hepatocyte nuclear factor-4 (HNF-4) binding site between bp
46 and
29 and that bp
38 to
36 were essential for binding. Binding of
HNF-4 to the GCC promoter was confirmed by competition EMSA and by
supershift EMSA. In Caco-2 and T84 cells, which express both GCC and
HNF-4, the activity of GCC promoter and/or luciferase reporter
plasmids containing 128 or 1973 bp of 5'-flanking sequence was
dependent on the HNF-4 binding site in the proximal promoter. In
COLO-DM cells, which express neither GCC nor HNF-4, cotransfection of
GCC promoter/luciferase reporter plasmids with an HNF-4 expression
vector resulted in 23-fold stimulation of the GCC promoter. Mutation of
the HNF-4 binding site abolished this transactivation. Transfection of
COLO-DM cells with the HNF-4 expression vector stimulated transcription of the endogenous GCC gene as well. These results indicate that HNF-4
is a key regulator of GCC expression in the intestine.
Escherichia coli heat-stable enterotoxin; gene transcription
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