Induction of spermine oxidase by enterotoxigenic Bacteroides fragilis in colon models results in DNA damage

AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA 3131 It is estimated that the etiology of 20-30% of epithelial cancers is directly associated with inflammation, though the molecular events linking inflammation and the necessary carcinogenic mutations remain to be clarified. In the context of gastrointestinal disease, bacterial infection by Helicobacter pylori and enterotoxigenic Bacteroides fragilis (ETBF) are significant sources of chronic inflammation and have been identified as risk factors for the development of gastric and colon cancer, respectively. We have previously demonstrated that H. pylori and the cytokine tumor necrosis factor-α (TNF-α) rapidly induce spermine oxidase (SMO), resulting in increased cellular reactive oxygen species (ROS) and DNA damage, in gastric and lung epithelial cells. To test the hypothesis that ETBF-induced SMO expression may be a source of oxidative damage in the colon, HT29/c1 and T84 human colon epithelial cell lines were treated with purified recombinant B. fragilis toxin (BFT). BFT treatment resulted in a rapid induction of SMO expression as measured by quantitative real-time PCR and western blotting, increased ROS detected by flow cytometry utilizing a H2DCFDA probe, and increased formation of 8-oxodeoxyguanosine measured by mass spectrometry. BFT treatment resulted in increased phosphorylated c-Jun N-terminal kinase (JNK) by western blotting and pre-treatment of HT29/c1 cells with the selective JNK inhibitor SP600125 abrogated SMO induction, suggesting a role for the activator protein-1 (AP-1) signaling pathway in the ETBF-mediated induction of SMO. These results are consistent with a recent report demonstrating the importance of AP-1 in ETBF-induced enteritis and our previous studies in gastric and lung epithelial cells. Our studies suggest that induction of SMO by inflammatory stimuli occurs in multiple epithelial systems and results in oxidative DNA damage, suggesting that SMO may represent one molecular link between chronic inflammation and epithelial carcinogenesis.