Analysis ofHelicobacter pylori cagAPromoter Elements Required for Salt-Induced Upregulation of CagA Expression

Abstract

ABSTRACTHelicobacter pyloriinfection and consumption of a high-salt diet are each associated with an increased risk for the development of gastric cancer. To investigate potential synergism between these factors, we used a global proteomic approach to analyzeH. pyloristrains cultured in media containing varying salt concentrations. Among the differentially expressed proteins identified, CagA exhibited the greatest increase in expression in response to high salt concentrations. Analysis of 36H. pyloristrains isolated from patients in two regions of Colombia with differing incidences of gastric cancer revealed marked differences among strains in salt-responsive CagA expression. Sequence analysis of thecagApromoter region in these strains revealed a DNA motif (TAATGA) that was present in either one or two copies. Salt-induced upregulation of CagA expression was detected more commonly in strains containing two copies of the TAATGA motif than in strains containing one copy. Mutagenesis experiments confirmed that two copies of the TAATGA motif are required for salt-induced upregulation of CagA expression. In summary, there is considerable heterogeneity amongH. pyloristrains in salt-regulated CagA expression, and these differences are attributable to variation in a specific DNA motif upstream of thecagAtranscriptional start site.