H. pylori infection of the gastric mucosa is associated with increased epithelial cell apoptosis. In vitro, interferon-gamma and TNF-alpha have been shown to increase the sensitivity of cells to apoptosis induced by H. pylori. The p53 tumor suppressor gene is frequently mutated in many cancers, including gastric cancer. Since p53 protein can induce apoptosis, we sought to determine whether or not p53 increases the ability of gastric epithelial cells to undergo apoptosis in response to H. pylori-induced cell injury. Human gastric epithelial cell lines, AGS (p53 wild-type) cells and AGS cells infected with HPV E6 gene (AGS-E6) to inactivate p53 were exposed to H. pylori. The p53, p21, and p14ARF proteins were measured in gastric epithelial cells by immunoelectrophoresis. Gastric epithelial cell apoptosis was measured by DNA end-labeling assay (TUNEL) and subG0 cell fractions using flow cytometry, and by agarose gel electrophoresis of DNA. Exposure to H. pylori increased the levels of p53, p21, and p14ARF proteins two fold in AGS cells. Gastric AGS cells with fragmented DNA increased from 1.1% to 68% in after exposure to H. pylori for 24 hr. However, AGS-E6 cells were relatively resistant to apoptosis induced by H. pylori (only 15% of cells underwent apoptosis). In additional experiments, mouse embryonic fibroblasts (MEFs) were used to further investigate the role of ARF in stabilizing p53 after exposure to H. pylori. Wild-type and p19ARF-/- MEFs were exposed to H. pylori and evaluated for activation of p53, p19ARF, and apoptosis. As with AGS cells, H. pylori stimulated a 2-fold increase in p53 and p19ARF in wild-type MEFs; however, there was no increase in p53 in ARF-null MEFs. H. pylori easily stimulated apoptosis in wild-type MEFs, although, the absence of p19ARF significantly reduced the ability of H. pylori to induce apoptosis in these cells. Activation of ARF by H. pylori is important in stabilizing p53 resulting in increased apoptosis. Thus, inactivation of either ARF or p53 in gastric cells may reduce their ability to undergo apoptosis in response to injury induced by H. pylori.