Importance of Helicobacter pylori CagA and VacA natural variants upon the regulation of AGS cell cycle phase progression in vitro

H. pylori infection is the principal cofactor for gastric cancer (GC) development. Both GC cells and colonized gastric epithelium show alterations of cell cycle progression; nonetheless, the role played by the main virulence determinants of such species, CagA and VacA, in cell turnover perturbation is not clear. Four cagA and VacA natural variants of H. pylori were examined. They were characterized for cagA, and vacA genes, CagA and VacA proteins and cytotoxicity. All strains possessed vacA. The other strain characteristics are: CCUG 17874, cagA+/CagA+/VacA+/cytotoxic; G50, cagA-/CagA-/VacA-/non-cytotoxic; G12, cagA+/CagA-/VacA+/non-cytotoxic; Ba142, cagA-/CagA-/VacA-/cytotoxic. Semiconfluent AGS cells in culture were infected in vitro with cell/organism ratios of 1:100. Uninoculated medium was the negative control. Flasks were incubated overnight; cell proliferation was evaluated by a FACS scan flow cytometer (Beckton and Dickinson, USA). Tests were performed in duplicate and results are expressed as means of the two assays. The mean percentages of cells in phase S+G2-M and infected by strains CCUG 17874, G50, G12 and Ba142, as well as uninfected cells, were respectively 24.19, 32.42, 34.63, 34.88 and 35.58 (P < 0.05, CCUG 17874 vs. the other strains and negative control). These in vitro findings suggest that only CCUG 17874 strain was able to disturb cell proliferation and that, in order to inhibit cell cycle progression in vitro, the infecting H. pylori organisms have to possess cagA, express its product, produce VacA immune reacting with an anti-VacA serum and be cytotoxic. These results may help understanding the pathogenesis of GC development.