Helicobacter pylori-induced H,K-ATPase alpha-subunit gene repression is mediated by NF-kappaB p50 homodimer promoter binding.

Infection of human gastric body mucosa by the gram-negative, microaerophilic bacterium Helicobacter pylori induces an inflammatory response and a transitory hypochlorhydria that progresses in approximately 2% of patients to atrophic gastritis, dysplasia, and gastric adenocarcinoma. We have previously shown that H. pylori infection of cultured gastric epithelial cells (AGS) represses the activity of the transfected alpha-subunit (HKalpha) promoter of H,K-ATPase, the parietal cell enzyme mediating acid secretion. However, the mechanistic details of H. pylori-mediated repression of HKalpha and ensuing hypochlorhydria are unknown. H. pylori is known to upregulate the transcription factor NF-kappaB through the ERK1/2 MAPK pathway. We identified NF-kappaB-binding regions in the HKalpha promoter and found that H. pylori inoculation of AGS cells increased NF-kappaB p50 binding to the transfected HKalpha promoter and repressed its transcriptional activity. Immunoblot and DNA-protein interaction studies showed that although active phosphorylated NF-kappaB p65 is present in H. pylori-infected AGS cells, an NF-kappaB p50/p65 heterodimeric complex fails to bind to the HKalpha promoter. Point mutations at -159 and -161 bp in the HKalpha promoter NF-kappaB binding sequence prevented binding of NF-kappaB p50 and prevented H. pylori repression of point-mutated HKalpha promoter activity in transfected AGS cells. Small interfering RNA-mediated knockdown of NF-kappaB p50 in H. pylori-infected AGS cells also abrogated H. pylori-induced HKalpha repression, whereas NF-kappaB p65 knockdown did not. We conclude that H. pylori inhibits HKalpha gene expression by ERK1/2-mediated NF-kappaB p50 homodimer binding to the HKalpha promoter. This study identifies a novel pathogen-dependent mechanism of H,K-ATPase inhibition and contributes to understanding of H. pylori pathophysiology.