Strains of Helicobacter pylori which carry the cag (cytotoxin-associated gene) region upregulate production of the neutrophil-activating chemokine IL-8 in gastric epithelial cells. cag+ strains are more frequently isolated from patients with peptic ulceration and gastric adenocarcinoma. Cag strains are less potent in up-regulating IL-8 production and are more frequently isolated from asymptomatic subjects. Thus activation of an inflammatory response in gastric epithelial cells by cag+ H. pylori may be a critical step in the pathogenesis of H.pylori-associated gastroduodenal disease. This proposal examines the hypothesis that differences in the virulence of H.pylori strains are correlated to their ability to induce epithelial cell activation and differentially regulate epithelial cell chemokine production. Infection with cag+ H.pylori activate the transcription factors NF- kappaB and AP-1 in gastric epithelial cells. These factors then up- regulate IL-8 gene transcription. ENA-78 is an epithelial cell-derived chemokine structurally and functionally similar to IL-8. Cag+ H. Pylori block cytokine-stimulated ENA-78 production in the gastric epithelial cell. The ability of H. pylori to inhibit ENA-78 release may be a virulence mechanism which allows the bacterium to balance immune activation with immune evasion and thereby achieve chronic indolent infection of its host.
Aim 1 will define the molecular mechanisms whereby cag+ H.pylori up- regulate IL-8 gene expression in AGS gastric epithelial cells using IL-8 reporter gene transfections and electrophoretic mobility shift analysis of transcription factor activation. It will also test the importance of NF-kappaB activation in the pathogenesis of H.pylori gastritis in mice treated with p65 NF-kappaB antisense oligonucleotides.
Aim 2 will identify specific genes in the H.pylori cag region which participate in up- regulating IL-8 expression by the host epithelial cell using isogenic cag gene mutants.
Aim 3 will determine the molecular mechanisms whereby cag+ H.pylori block ENA-78 expression in IL-1beta- stimulated AGS cells and will examine the contribution of specific H. Pylori cag region genes to this effect. It will also attempt to isolate and characterize the H.pylori-derived factor responsible for ENA-78 repression. Identifying H.pylori virulence factors which modulate host immune and inflammatory responses and determining their mechanisms of action are key to targeting new management strategies for this highly prevalent pathogen.
