calpain and Helicobacter-Infections

Helicobacter pylori is a risk factor for the development of gastritis, gastroduodenal ulcers, and gastric adenocarcinoma. H. pylori-induced disruption of epithelial adherens junctions (AJs) is thought to promote the development of severe disease; however, the mechanisms whereby H. pylori alters AJ structure remain incompletely understood. The present study demonstrates that H. pylori infection in human patients is associated with elevated serum levels of an 80-kDa E-cadherin ectodomain, whose presence is independent of the presence of serum antibodies against CagA. In vitro, a heat-labile H. pylori surface component activates the host protease calpain in human gastric MKN45 cells independently of the virulence factors CagA and VacA. H. pylori-induced calpain activation results in cleavage of E-cadherin to produce a 100-kDa truncated form and induce relocalization of E-cadherin and β-catenin. Stimulation of MKN45 cells with the toll-like receptor 2 (TLR2) ligand P3C activated calpain and disrupted E-cadherin and β-catenin in a pattern similar to that induced by H. pylori. Inhibition of TLR2 prevented H. pylori-induced calpain activation and AJ disassembly. Together, these findings identify a novel pathway whereby H. pylori activates calpain via TLR2 to disrupt gastric epithelial AJ structure.

Topics: Adherens Junctions; beta Catenin; Cadherins; Calpain; Cell Line; Cell Line, Tumor; Enzyme Activation; Epithelial Cells; Gastric Mucosa; Helicobacter Infections; Helicobacter pylori; Host-Pathogen Interactions; Humans; Toll-Like Receptor 2

Helicobacter pylori persistently colonize the human stomach and have been linked to atrophic gastritis and gastric carcinoma. Although it is well known that H. pylori infection can result in hypochlorhydria, the molecular mechanisms underlying this phenomenon remain poorly understood. Here we show that VacA permeabilizes the apical membrane of gastric parietal cells and induces hypochlorhydria. The functional consequences of VacA infection on parietal cell physiology were studied using freshly isolated rabbit gastric glands and cultured parietal cells. Secretory activity of parietal cells was judged by an aminopyrine uptake assay and confocal microscopic examination. VacA permeabilization induces an influx of extracellular calcium, followed by activation of calpain and subsequent proteolysis of ezrin at Met(469)-Thr(470), which results in the liberation of ezrin from the apical membrane of the parietal cells. VacA treatment inhibits acid secretion by preventing the recruitment of H,K-ATPase-containing tubulovesicles to the apical membrane of gastric parietal cells. Electron microscopic examination revealed that VacA treatment disrupts the radial arrangement of actin filaments in apical microvilli due to the loss of ezrin integrity in parietal cells. Significantly, expression of calpain-resistant ezrin restored the functional activity of parietal cells in the presence of VacA. Proteolysis of ezrin in VacA-infected parietal cells is a novel mechanism underlying H. pylori-induced inhibition of acid secretion. Our results indicate that VacA disrupts the apical membrane-cytoskeletal interactions in gastric parietal cells and thereby causes hypochlorhydria.

Topics: Achlorhydria; Actin Cytoskeleton; Animals; Bacterial Proteins; Calcium; Calpain; Cell Membrane; Cell Membrane Permeability; Cells, Cultured; Cytoskeletal Proteins; Gastritis, Atrophic; Helicobacter Infections; Helicobacter pylori; Humans; Parietal Cells, Gastric; Rabbits; Stomach Neoplasms