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-subunit gene expression by Helicobacter
pylori
Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425
Clinical studies and in vitro data from isolated parietal
cells suggest that acute Helicobacter pylori infection inhibits acid secretion. Gastric acidification is mediated by
H+-K+-ATPase, an integral protein of parietal
cell apical membranes. To test the hypothesis that H. pylori
downregulates H+-K+-ATPase 
-subunit (HK)
gene expression and to identify potential intracellular signaling
pathways mediating such regulation, we transfected human gastric
adenocarcinoma (AGS) cells with human and rat HK 5'-flanking
DNA fused to a luciferase reporter plasmid. Histamine caused
dose-dependent, cimetidine-sensitive (10
4
M) increases in cAMP, free intracellular Ca2+, and
HK promoter activation in AGS cells. H. pylori infection of
transfected AGS cells dose dependently inhibited basal and histamine-stimulated HK promoter activity by 80% and 66%,
respectively. H. pylori dose dependently inhibited phorbol
myristate acetate-induced (107 M) and staurosporine-
(107 M) and calphostin C-sensitive (5 × 108 M) activation of HK promoter. Also, H. pylori inhibited epidermal growth factor (EGF)
(108 M), genistein-sensitive (5 × 105 M) activation of HK promoter, reducing
activity to 60% of basal level. These data suggest that H. pylori
inhibits HK gene expression via intracellular pathways involving
protein kinases A and C and protein tyrosine kinase, AGS cells have
functional histamine H2 and EGF receptors, and transiently
transfected AGS cells are a useful model for studying regulation of
HK gene expression.
gastric adenocarcinoma cells; luciferase; promoter regulation; acid secretion; H2 receptor
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