Activation of intercellular adhesion molecule 1 expression by Helicobacter pylori is regulated by NF-kappaB in gastric epithelial cancer cells

Interactions between leukocytes and epithelial cells may play a key role in Helicobacter pylori-associated gastric mucosal inflammation. This process is mediated by various cell adhesion molecules. The present study examined the molecular mechanisms leading to H. pylori-induced epithelial cell intercellular adhesion molecule-1 (ICAM-1; also called CD54) expression. Coculture of epithelial cells with cytotoxin-associated gene pathogenicity island-positive (cag PAI(+)) H. pylori strains, but not with a cag PAI(-) strain or H. pylori culture supernatants, resulted in upregulation of steady-state mRNA levels and cell surface expression of ICAM-1. Coculture with H. pylori induced an increase in luciferase activity in cells which were transfected with a luciferase reporter gene linked to the 5'-flanking region of the ICAM-1 gene. H. pylori activated the ICAM-1 promoter via the NF-kappaB binding site. An inducible nuclear protein complex bound to the ICAM-1 NF-kappaB site and was identified as the NF-kappaB p50-p65 heterodimer. H. pylori induced the degradation of IkappaB-alpha, a major cytoplasmic inhibitor of NF-kappaB, and stimulated the expression of IkappaB-alpha mRNA. Pretreatment of epithelial cells with pyrrolidine dithiocarbamate, which blocks NF-kappaB activation, inhibited H. pylori-induced ICAM-1 expression. THP-1 macrophagic cells, peripheral blood mononuclear cells, and purified neutrophils adhered to H. pylori-infected epithelial cells to a greater extent than to uninfected cells. These results show that H. pylori directly induces expression of ICAM-1 on gastric epithelial cells in an NF-kappaB-dependent manner that may support leukocyte attachment during inflammation.     

Effect of inhibition of extracellular signal-regulated kinase 1 and 2 pathway on apoptosis and bcl-2 expression in Helicobacter pylori-infected AGS cells

Helicobacter pylori induces activation of mitogen-activated protein kinases (MAPKs). However, its effect on H. pylori-induced apoptosis has not been evaluated. Thus, we examined whether H. pylori-induced extracellular signal-regulated kinase 1 and 2 (ERK1/2) and p38 MAPK activation affects gastric epithelial cell apoptosis and bcl-2 family gene expression, especially in relation to the cagA status of an H. pylori strain. In flow cytometric and oligonucleosome-bound DNA enzyme-linked immunosorbent assay analyses, infection with cagA(+) H. pylori strains induced gastric cancer cell apoptosis in AGS cells more prominently than infection with cagA mutants. Activation of ERK1/2 and p38 MAPKs was also more prominent in cagA(+) strains. Pretreatment with a MEK inhibitor (PD98059) inhibited ERK1/2 activation and increased H. pylori-induced apoptosis significantly. This increased apoptosis was accompanied by decreased antiapoptotic bcl-2 mRNA expression among bcl-2-related genes (bcl-2, bax, bak, mcl-1, and bcl-X(L/S)), and the effect was also more prominent in the cagA(+) strains. However, the alteration of bcl-2 gene expression was not accompanied by protein level changes. Inhibition of p38 using specific inhibitor SB203580 decreased H. pylori-induced apoptosis but resulted in little alteration of bcl-2-related gene expression. In conclusion, H. pylori-induced ERK1/2 activation, especially by the cagA(+) H. pylori strain, may play a protective role against gastric epithelial cell apoptosis partially through maintenance of bcl-2 gene expression.