TNF-alpha-inducing protein, a carcinogenic factor secreted from H. pylori, enters gastric cancer cells.

TNF-alpha inducing protein (Tip alpha) is secreted from Helicobacter pylori (H. pylori): it is a potent inducer of TNF-alpha and chemokine genes, mediated through NF-kappaB activation, and it also induces tumor-promoting activity in Bhas 42 cells. To investigate the carcinogenic mechanisms of H. pylori with Tip alpha, we first examined how Tip alpha acts on gastric epithelial cells. We found that fluorescent-Tip alpha specifically bound to, and then entered, the cells in a dose- and temperature-dependent manner, whereas deletion mutant of Tip alpha (del-Tip alpha), an inactive form, neither bound to nor entered the cells, suggesting the presence of a specific binding molecule. Mutagenesis analysis of Tip alpha revealed that a dimer formation of Tip alpha with a disulfide bond is required for both specific binding and induction of TNF-alpha gene expression. A confocal laser scanning microscope revealed some Tip alpha in the nuclei, but del-Tip alpha was not present, which indicated that an active form of Tip alpha can penetrate the nucleus and may be involved in the induction of TNF-alpha gene expression. Examination of Tip alpha production and secretion in 28 clinical isolates revealed that H. pylori obtained from gastric cancer patients secreted Tip alpha in significantly higher amounts than did H. pylori from patients with chronic gastritis, suggesting that Tip alpha is an essential factor in H. pylori inflammation and cancer microenvironment in the human stomach. Tip alpha is thus a new carcinogenic factor of H. pylori that can enter the nucleus through a specific binding molecule, and its mechanism of action is completely different from that of CagA.