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Section of Digestive and Liver Diseases, Department of Medicine, University of Illinois at Chicago and Westside Veterans Affairs Medical Center, Chicago, Illinois 60612
The
Na+/H+ exchanger (NHE) 2 belongs to a family of
plasma membrane transporters involved in intracellular pH and cell
volume regulation. We recently reported cloning of human
NHE2 (hNHE2) from a colonic cDNA library.
Northern blot analysis has identified NHE2 mRNA only in
small intestine, prostate, kidney, colon, and skeletal muscle. In this
study, we describe the structure and 5'-regulatory region of the
hNHE2 gene. The hNHE2 gene spans >90 kb
and is organized in 12 exons intervened by 11 introns. All introns
contain the conserved GT and AG dinucleotides at the donor and acceptor
sites, respectively. The hNHE2 gene was mapped to chromosome
2q11.2. Primer extension analysis revealed a single transcription
initiation site in human colonic adenocarcinoma cell lines. Analysis of
the DNA nucleotide sequences of a 1.4-kb fragment of the 5'-flanking
region shows no canonical TATA or CAAT boxes. However, the promoter
region contains several potential cis-regulatory elements
such as Sp1, early growth response-1, activator protein-2, MyoD, p300,
nuclear factor-
B, myeloid zinc finger protein-1, caudal-related
homeobox (Cdx) gene A, and Cdx protein-2 binding sites. In
transient transfection studies, a reporter construct containing the
1.4-kb promoter region exhibited low luciferase activity levels.
However, after deletion upstream of
664, its activity increased
approximately threefold. Thus our data suggest that an inhibitory
element may exist in the NHE2 promoter 5'-upstream region.
exon-intron junction; chromosome 2q11.2; transcription factor; C2BBe1; transfection
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