Inhibition of human gastric H+-K+-ATPase α-subunit gene expression by Helicobacter pylori

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 alpha-subunit (HK alpha) gene expression and to identify potential intracellular signaling pathways mediating such regulation, we transfected human gastric adenocarcinoma (AGS) cells with human and rat HK alpha 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 alpha promoter activation in AGS cells. H. pylori infection of transfected AGS cells dose dependently inhibited basal and histamine-stimulated HK alpha promoter activity by 80% and 66%, respectively. H. pylori dose dependently inhibited phorbol myristate acetate-induced (10(-7) M) and staurosporine( 10(-7) M) and calphostin C-sensitive (5 x 10(-8) M) activation of HK alpha promoter. Also, H. pylori inhibited epidermal growth factor (EGF) (10(-8) M), genistein-sensitive (5 x 10(-5) M) activation of HK alpha promoter, reducing activity to 60% of basal level. These data suggest that H. pylori inhibits HK alpha gene expression via intracellular pathways involving protein kinases A and C and protein tyrosine kinase, AGS cells have functional histamine H-2 and EGF receptors, and transiently transfected AGS cells are a useful model for studying regulation of HK alpha gene expression.