title: Inhibition of human gastric H(+)-K(+)-ATPase alpha-subunit gene expression by Helicobacter pylori.
abstract: 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 (HKalpha) gene expression and to identify potential intracellular signaling pathways mediating such regulation, we transfected human gastric adenocarcinoma (AGS) cells with human and rat HKalpha 5'-flanking DNA fused to a luciferase reporter plasmid. Histamine caused dose-dependent, cimetidine-sensitive (10(-4) M) increases in cAMP, free intracellular Ca(2+), and HKalpha promoter activation in AGS cells. H. pylori infection of transfected AGS cells dose dependently inhibited basal and histamine-stimulated HKalpha 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 HKalpha promoter. Also, H. pylori inhibited epidermal growth factor (EGF) (10(-8) M), genistein-sensitive (5 x 10(-5) M) activation of HKalpha promoter, reducing activity to 60% of basal level. These data suggest that H. pylori inhibits HKalpha 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 HKalpha gene expression.
authors.affiliation: Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
authors.forename: M
authors.initials: M
authors.lastname: Göõz
authors.forename: C E
authors.initials: CE
authors.lastname: Hammond
authors.forename: K
authors.initials: K
authors.lastname: Larsen
authors.forename: Y V
authors.initials: YV
authors.lastname: Mukhin
authors.forename: A J
authors.initials: AJ
authors.lastname: Smolka
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002927:Cimetidine / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D015536:Down-Regulation; D015870:Gene Expression / Q000502:physiology*; D017506:H(+)-K(+)-Exchanging ATPase / Q000235:genetics*; D016481:Helicobacter Infections / Q000235:genetics; D016480:Helicobacter pylori / Q000502:physiology*; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000502:physiology; D051381:Rats; D013270:Stomach / Q000201:enzymology*; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D007527:Isoenzymes; D002927:Cimetidine; D006632:Histamine; D000242:Cyclic AMP; D017506:H(+)-K(+)-Exchanging ATPase; D002118:Calcium