Disturbance of intracellular SHP-2 activity and cell growth regulation by Helicobacter pylori CagA

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1.We established AGS human gastric epithelial cells that conditionally express CagA by employing Tet-On system. The cells expressing CagA exhibited the growth factor-like morphological change as in the case of cagA-positive H.pylori infection. Using the cells, we investigated the CagA effect on Ras/MAPK pathway. As results, we revealed that the morphological change induced by CagA was dependent on MAPK activity but not on Ras activity. On the other hand, we observed that tyrosine phosphorylation levels of tyrosine kinase FAK decreased in CagA-expressing cells. SHP-2 directly dephosphorylates FAK phosphorylation sites which associate with FAK activation, and thereby inactivates FAK. From these results, we clarified that CagA disrupt intracellular signaling by in activation of FAK through SHP-2 activation as well as activation of Ras-independent MAPK cascade.2.We analyzed changes in gene expression caused by ectopic expression of the cagA gene in gastric epithelial cells using a DNA microarray, and accordingly found multiple cagA-responsive genes. Analyzing putative promoter sequences of the cagA-responsive genes, binding sites for particular transcription factors were significantly over-represented in the promoter regions of CagA-activated genes. Furthermore, we found that CagA is capable of activating gene transcription which is dependent on a specific transcriptional factor in the cells. It is suggested that CagA biological activity causes dysregulation of intracellular gene-expression profile.3.We constructed cagA transgenic mouse to investigate CagA biological activity and the mechanism of CagA mediated-development of gastric cancer in vivo. We have established several transgenic lines which show expression of cagA gene.