The unique carcinogenic factor Tipα in cancer microenvironment of H. pylori infection Free

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To investigate the carcinogenic process of H. pylori infection in the stomach, we first identified TNF-α inducing protein gene (Tipα), which is cloned from genomic DNA of H. pylori strain 26695. Tipα protein is a potent inducer of TNF-α gene expression and tumor promoting activity in Bhas 42 (v-H-ras transfected BALB3T3) cells. Furthermore, we found that Tipα strongly induced expression of chemokine genes, such as Ccl2, Ccl7, Ccl20, Cxcl1, Cxcl5, Cxcl10 and Cxcl12, as determined by comprehensive DNA microarray analysis and quantitative real-time RT-PCR. Thus, Tipα released from H. pylori is a potent inducer of chemokines as well as cytokines. Next, we determined the amounts of Tipα in culture mediums secreted from various H. pylori strains isolated from patients with gastritis and gastric cancer, by Western blotting using anti-Tipα antibody. It is of interest to note that the H. pylori clinical isolates obtained from gastric cancer patients released Tipα significantly more than did those from patients with gastritis, suggesting that Tipα is an important factor in cancer development during the process of H. pylori infection in the human stomach. To clarify precisely how Tipα induces NF-κB activation in the gastric epithelial cells, we studied whether Tipα would bind to a receptor of stomach cancer cells, MGT-40, using fluorescently labeled Tipα: We found that fluorescent-Tipα specifically bound to the cells and then entered the cells, in a dose- and temperature-dependent manner, whereas, an inactive mutant del-Tipα neither bound to, nor entered the cells, indicating the presence of a specific receptor for Tipα. Immunoprecipitation of Tipα after labeling of cell surface proteins with biotin indicated that Tipα bound to 160 kDa biotin-labeled proteins, but that inactive del-Tipα did not, suggesting that 160 kDa protein is the receptor of Tipα. All the results showed that Tipα induces NF-κB activation, and that gene expression of TNF-α and chemokines - mediated through a receptor, 160 kDa membrane protein in the gastric epithelial cells - causes inflammation and cancer in the stomach. Tipα is a unique carcinogenic factor of H. pylori, and its mechanism of action is completely different from that of CagA.