The effects of H. pylori CagA on DNA amplification and protein expression status of the HER2 gene in gastric cancer.

Abstract

67 Background: We investigated whether Cag A contributes to the DNA copy change and expression of the HER2 gene mRNA transcript and, consequently, affects HER2 protein expression to evaluate the significance of H. pylori Cag A and HER2 amplification in gastric cancer. Methods: We used the AGS gastric cancer and HFE-145 immortalized non-neoplastic gastric mucosa cell lines to investigate whether Cag A regulates DNA copy number and HER2 expression. We also confirmed the effects of Cag A on gastric cancer tissues. Immunohistochemistry with or without fluorescence in situ hybridization (FISH) was conducted to determine the level of HER2 protein expression based on the revised criteria in the HER2 test guidelines. Results: H. pylori CagA transfected AGS cells showed a significant increase in HER2 gene copy number and expression. In addition, Cag A expression was detected in 17 (56.7%) of 30 gastric cancer (GC) tissues, and eight (47%) showed HER2 DNA amplification of more than two-fold (P = 0.013). A positive correlation was observed among DNA copy number, the mRNA transcript, and HER2 gene protein expression (p < 0.05). HER2 overexpression was detected in 12 (40%) of 30 gastric cancers by Hoffman’s criteria. Conclusions: These results suggest that H. pylori CagA may induce overexpression of the HER2 gene protein by increasing HER2 DNA and mRNA copy number. To overcome the weakness of the current HER2 assessment criteria, we propose to test HER2 DNA copy number changes with immunohistochemistry, instead of FISH.