40-to 100-kD protein(s) of Helicobacter pylori stimulate DNA synthesis in epithelial cell lines without affecting apoptosis

Background: Previous in vitro studies have demonstrated that water extracts and sonicates of Helicobacter pylori increase DNA synthesis in a small int estinal epithelial cell line. The aim of this study was to identify mitogen ic factor(s) in a water extract of a H. pylori strain and to examine their effects on DNA synthesis and apoptosis in vitro, Methods: IEC-6 and FHs 74 cells were incubated for 24 h with different dilutions of a water extract o f H. pylori (cytotoxic strain 88-23) or with 6 protein fractions obtained b y gel filtration. Cells were labeled with tritiated thymidine and processed for autoradiography. DNA synthesis was evaluated by the labeling index (LI %). The proportion of IEC-6 cells undergoing apoptosis and/or necrosis was evaluated by flow cytometry using fluorescein isothiocyanate (FITC)-labeled annexin-V and propidium iodide. In vitro caspase activity was also determi ned as an alternative method for detection of apoptosis. Results: The water extract of H. pylori 88-23 markedly increased DNA synthesis in both epithe lial cell lines (p < 0.01). A marked stimulation of DNA synthesis was also observed in IEC-6 cells incubated with fraction II-containing proteins of a molecular weight ranging between 40 and 100 kD (p < 0.01). A lesser stimul ation of DNA synthesis was observed in cells incubated with higher concentr ations of the other protein fractions (p < 0.01). Neither the water extract of H. pylori 88-23 nor the protein fraction II (40-100 kD) induced apoptos is in IEC-6 cells. Conclusion: A water extract of H. pylori 88-23 and a pro tein fraction containing proteins with molecular weights of 40-100 kD stimu late DNA synthesis in a rat and human small intestinal cell line, Apoptosis was unaffected by the water extract and by protein fraction II, which indi cate that the H, pylori-derived mitogen(s) have the capacity to directly en hance epithelial cell proliferation in vitro. Copyright (C) 2000 S. Karger AG, Basel.