sequences difference of CagA between East Asian strain and Western strain of Helicobacter pylori and its impact on the proliferation and apoptosis of gastric cancer cells

Abstract:

[Background] Helicobacter pylori (H. pylori) has been described as a main pathogenic factor for gastric cancer. Protein product of the cytotoxin associated gene A (CagA) has been known as the only oncoprotein that is secreted and injected into gastric epithelial cells by the bacteria, thus mediating the development of gastric cancer. [Objective] To compare the sequence difference of CagA between the East Asian strain and Western strain of H. pylori, and explore the effects of H. pylori-CagA on the proliferation and apoptosis of gastric cancer cells. [Methods] DNA and amino acid sequences of CagA in East Asian strain and Western strain were analyzed. A eukaryotic expression vector containing the cagA gene from each strain was constructed and transferred into AGS gastric cancer cells. The CagA protein was assessed using Western blot. Cell growth curve and apoptosis were determined using CCK8 and flow cytometry, respectively. [Results] Comparison of the DNA and amino acid sequences in the CagA between the two strains revealed some characteristic differences. The expression vectors of H. pylori-cagA gene were constructed successfully and named as GZ7/cagA (East Asian strain) and 26695/cagA (Western strain). Compared with cells transfected with the empty vector, the cells transfected with the East Asian strain and the Western strain derived cagA expressed CagA proteins, but there is no difference in protein levels between the two groups. The cells transfected with the East Asian strain and the Western strain derived cagA grew significantly fast or slower, respectively (P<0.05). The apoptotic rates of cells expressing the East Asian strain derived CagA and the Western strain derived CagA were 7.23±0.96 and 9.17±1.40, respectively, both being higher than that of the cells expressing the empty vector (5.03±0.63) (P<0.05). [Conclusion] There are structural and functional differences in the CagA between the East Asian and Western strains of H. pylori. While the one in the East Asian strain promotes the proliferation, Western CagA inhibits the proliferation of gastric cancer cells. However, the CagA in the both strains promotes apoptosis of the cells.