The discovery of Helicobacter pylori (H. pylori) infection has greatly changed our understanding of upper G.I. tract diseases, including peptic ulcer disease and stomach cancer. The world health organization has classified H. pylori as a group one carcinogen. Reactive oxygen species (ROS) are known carcinogens and have been shown to play a role in gastric cancer. Our studies have shown that H. pylori stimulates the generation of ROS within gastric cells. By placing gastric cells into a pro-oxidant state, H. pylori increases the risk of DNA damage from ROS and the development of cancer. Epithelial cells protect themselves from DNA damage by undergoing apoptosis. H. pylori induce apoptosis is associated with activation of both NF-kappaB and p53. Also H. pylori induced apoptosis is associated with stimulation of the CD95/Fas pathway. Our preliminary studies show that the increase in p53 protein after exposure of gastric cells to H. pylori is associated with increased expression of p14 ARF and down regulation of mdm2. The studies planned in this proposal will identify any interactions between p53 mediated apoptosis and CD95/Fas-mediated apoptosis in response to H. pylori We hypothesize that stimulation of intracellular reactive oxygen species within eukaryotic cells is a major mediator of H. pylori induced cellular injury resulting in oxidant associated DNA damage and apoptosis. We further hypothesize that transcription factors p53 and NF-KappaB are important downstream mediators of ROS induced cellular injury from exposure to H. pylori. Our more recent studies show that the rise in p53 after exposure to H. pylori is secondary to stimulation of ARF which stabilizes p53 by preventing Mdm2 inhibition of p53 activity and Mdm2 mediated degradation of p53. Therefore, ROS may be responsible for stimulation of ARF resulting in increased p53.
The specific aims of this proposal are: (1) to determine whether or not ROS leads to activation of NF-KappaB which may sensitize gastric cells to apoptosis, dependent or independent of p53; (2) To elucidate mediators of ARF activation by H. pylori leading to increased p53 protein and apoptosis; (3) To determine the involvement of the CD95 (Fas/Apo-1) receptor/ligand system in p53 sensitization of gastric cells to apoptosis induced by H. pylori. Identification of transcription factors activated by this bacterium and elucidation of apoptotic pathways involved will assist us to develop better treatment strategies to prevent serious disease from this infection. By protecting gastric cells from ROS, one may be able to negate the carcinogenic properties of this bacterium.
