How H. pylori Leads Cells Astray

Abstract

The gastric bacterium Helicobacter pylori is associated with gastritis, gastroduodenal ulcers, gastric adenocarcinoma, and gastric lymphoma. The cytotoxin-associated gene A antigen (CagA) is translocated into gastric epithelial cells, where it undergoes tyrosine phosphorylation and triggers cell scattering and morphological changes, and it has been implicated in H. pylori 's pathogenic effects. The mechanism by which CagA affects cell behavior and morphology, however, remainsunclear. Mimuro et al. determined that CagA interacted with the adaptor protein Grb2 (growth factor receptor-binding protein 2) in AGS gastric adenocarcinoma cells independently of having undergone tyrosine phosphorylation, which leads to activation of the mitogen-associated protein kinase pathway and to cell scattering and proliferation. Using CagA mutants expressed in H. pylori that lacked endogenous CagA, the authors determined that substituting phenylalanine for tyrosine in the phosphorylated region of CagA (PY region) did not interfere with CagA-evoked scattering in infected cells, whereas deletion of the PY region abolished cell scattering. Western analysis using fusion proteins containing Grb2 domains indicated that both phosphorylated and nonphosphorylated CagA bound to Grb2, as did the phenylalanine-substituted CagA mutant, but not the mutant lacking the PY region. A dominant-negative Grb2 mutant that interfered with Ras activation by Grb2 inhibited H. pylori -induced cell scattering. Consistent with Ras pathway implication in the response, a sustained late phase of mitogen-activated and extracellular signal-regulated kinase kinase (MEK) activation in response to H. pylori infection depended on CagA expression. Analysis of the effects of various CagA constructs stably transfected into MDCK cells implicated the PY region in CagA-induced MEK phosphorylation, as well as scattering and proliferation. H. Mimuro, T. Suzuki, J. Tanaka, M. Asahi, R. Haas, C. Sasakawa, Grb2 is a key mediator of Helicobacter pylori CagA protein activities. Mol. Cell 10 , 745-755 (2002). [Online Journal]