| Research Abstract |
Stomach cancer has a high mortality rate in East Asia, and is strongly associated with Helicobacter pylori (H.pylori) infection. H.pylori is known to express chemokine genes in the gastric mucosa, chemokines that are important host immune factors facilitating inflammation and tumor growth. To investigate the mechanism of carcinogenesis in the stomach, it is essential to determine which molecule of H.pylori is involved in induction of chemokines, but this has remained unclear. We previously reported that a tumor necrosis factor-α (TNF-α) inducing protein (Tipα) secreted from H.pylori acts as a tumor promoter in stomach cancer development, and thus started to investigate whether Tipα is involved in induction of chemokine genes. Comprehensive gene expression analysis was conducted using DNA microarray and KeyMolnet analyses. The gene expression was quantitatively analyzed by real-time RT-PCR. Comprehensive and quantitative gene expression analyses revealed that Tipα induces gene expressio
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n of the chemokines Cc12, Cc17, Cc120, Cxc11, Cxc12, Cxc15 and Cxc110 extensively and simultaneously in mouse stomach cancer cells, MGT-40. Tipα induced high levels of chemokine gene expression, whereas inactive deleted Tipα, del-Tipα, showed only marginal expression, suggesting a correlation between tumor promotion and chemokine gene expression by Tipα. MG-132, a proteasome inhibitor which represses NF-κB-activation, inhibited chemokine gene expressions. We report here that Tipα of H.pylori gene product is a strong inducer of chemokine gene expressions, providing a new model for stomach cancer development.
The significance of catechins, the main constituents of green tea, is being increasingly recognized with regard to cancer prevention. Catechins have been studied for interactions with various proteins, but the mechanisms of the various catechins are not yet elucidated. Based on our previous observation that nucleic acids extracted from catechin-treated cells are colored, we studied whether catechins directly interact with nucleic acids using surface plasmon resonance assay (Biacore) and cold spray ionization (CSI) mass spectrometry (MS). These two methods clearly showed that (-)-epigallocatechin gallate (EGCG) binds to both DNA and RNA molecules: the Biacore assay indicated that four catechins bound to DNA oligomers, and CSI-MS analysis showed one to three EGCG molecules bound to single strand 18 mers of DNA and RNA. Moreover, one or two molecules of EGCG bound to double-stranded AG: CT oligomers of various nucleotide lengths. These results suggest that multiple binding sites of EGCG are present in DNA and RNA oligomers. Double-stranded DNA oligomers were detected only as EGCG-bound forms at high temperature, whereas at low temperature both the free and bound forms were detected, suggesting that EGCG protects dsDNA oligomers from dsDNA-melting to ssDNA. Since both galloyl and catechol groups of EGCG are essential for DNA binding, both groups seem to hold strands of DNA via their branching structure. These findings reveal for the first time the link between catechins and polynucleotide, and will intensify our understanding the effects of catechins on DNA in terms of cancer prevention. Less
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