TNF-α-inducing protein (Tipα), a unique carcinogenic factor secreted from H. pylori, as a new molecular target for gastric cancer prevention

A92

Japan has the highest incidence rates of gastric cancer in the world, and the prevalence rate of Helicobacter pylori (H. pylori) is especially high over the age of 40. Therefore, development of an effective cancer prevention strategy is an essential task for cancer research, based on understanding the carcinogenic mechanisms of H. pylori. Using our evidence that TNF-α is the essential cytokine for tumor promotion, and that inhibition of TNF-α production is the common mechanism of cancer preventive agents, we hypothesized that a gene product of H. pylori, which induces TNF-α, is directly involved in cancer development and would be a suitable molecular target for gastric cancer prevention. We then cloned TNF-α-inducing protein (Tipα) gene from the genome of H. pylori strain 26695. Tipα is a strong inducer of TNF-α and chemokine genes mediated through NF-κB activation in a cagPAI-independent manner; it demonstrates transforming activity in Bhas 42 (v-H-ras transfected BALB/3T3) cells. Tipα protein is secreted from H. pylori as a homodimer form, and mutagenesis analysis revealed that one cysteine residue is the essential for formation of both the homodimer and the biological activities of Tipα. Using 28 clinical isolates of H. pylori from patients with chronic gastritis and gastric cancer in Saitama Cancer Center, we next examined Tipα secretion. We found that H. pylori clinical isolates obtained from gastric cancer patients secreted significantly larger amounts of Tipα into culture broth than did those from chronic gastritis patients. Therefore, we think that Tipα is a suitable marker to determine high risk groups for gastric cancer. To reveal the molecular mechanism of Tipα, flow cytometry and immunocytochemical analyses were conducted: rTipα bound to cell surface molecules specifically, and penetrated the cytosol; some rTipα was found localized in the nuclei of gastric cancer cells MGT-40; but rdel-Tipα, an inactive mutant which lacks six amino acids including two cysteine residues, showed negligible penetration into cytosol and nuclei. Recently, we found that Tipα has DNA bonding activity by Biacore. Thus Tipα is a new carcinogenic factor of H. pylori, with a mechanism of action completely different from that of CagA. All results indicate that Tipα is a suitable molecular target for gastric cancer prevention.