619 The Helicobacter pylori Bacterial Oncoprotein CagA is Upregulated Following Adherence to Gastric Epithelial Cells

Abstract

expressing MKN28 cells. The participation of p53 in autophagy was assessed using a p53 expression plasmid, and the effect of a p53 mutation on CagA degradation was assessed using p53-/KATOIII cells. Results: The expression of p53 protein was significantly attenuated to 58% at 24 h after AGS cells infected with wild-type H. pylori and conversion of LC3 I to LC3 II, which shows autophagy, was clearly detected. The level of phosphorylation of HDM2 (pHDM2) was significantly increased by 2.0-fold in these cells, suggesting that p53 was degraded by the proteasome-mediated pathway through activation of HDM2. However, in AGS cells after infection with VacA-negative H. pylori, the expression of p53 did not decrease, and conversion of LC3 I to LC3 II was repressed. The intracellular CagA of VacA-negative H. pylori was significantly increased by 2.2-fold as compared with that of wild-type H. pylori. In p53-/KATOIII cells after infection with wild-type H. pylori, the conversion of LC3 I to LC3 II was clearly detected, and the degradation of intracellular CagA was enhanced. On the other hand, in p53-/KATOIII cells transfected with wild-type p53 (p53WT) expression plasmid, the conversion of LC3 I to LC3 II was repressed, and the degradation of CagA was repressed. In contrast, at 24 h after H. pylori infection of the p53-/KATOIII cells transfected with R273H mutation of p53 (p53R273H) expression plasmid, the intracellular CagA level was significantly increased by 1.8-fold as compared with those transfected with p53WT expression plasmid. The conversion of LC3 I to LC3 II in p53-/KATOIII cells transfected with p53R273H expression plasmid was also repressed. Conclusion: Our findings indicate that down-regulation of p53 accelerates the degradation of CagA by promoting autophagy induction and a specific p53 mutation increased the stability of CagA by inhibiting its autophagic degradation.