Disturbance of cell signaling by H. pylori CagA

1. CagA的膜结合对胃上皮细胞中CagA的致病作用很重要，它需要EPIYA基序，但不依赖于EPIYA酪氨酸磷酸化。CagA激活的SHP-2直接使FAK的磷酸化酪氨酸残基去磷酸化，这是活化磷酸化位点。因此，FAK的激活在细胞中被取消，SHP-2对FAK的抑制在CagA.3的形态发生活性中起着至关重要的作用。CagA诱导细胞形态变化是由于ras不依赖于Erk信号的修饰。通过DNA芯片筛选caga应答基因，我们鉴定出了NFAT。CagA通过calcalineurin /PLCg通路诱导NFAT的核易位和转录活性。此外，幽门螺杆菌VacA毒素抵消了CagA激活nfat的能力。利用一系列代表幽门螺杆菌临床分离株的epya -repeat变异，我们发现epya -repeat多态性（由于EPIYA片段的数量和顺序的差异）影响磷酸化依赖性CagA的生物活性。我们发现了由16个氨基酸残基组成的CagA多聚基序，并介导了CagA分子间的相互作用。CagA的多聚是表达与细胞形态发生活性和细胞运动刺激有关的CagA生物活性的必要条件。

1. Membrane association of CagA is important for the pathogenic action of CagA in gastric epithelial cells and requires the EPIYA motif but is independent of EPIYA tyrosine phosphorylation.2. The activated SHP-2 with CagA directly dephosphorylates phospho-tyrosine residues of FAK, which are the activating phosphorylation sites. Accordingly, FAK activation is abolished in cells, and the inhibition of FAK by SHP-2 plays a crucial role in the morphogenetic activity of CagA.3. Induction of cell morphological change with CagA is due to the Ras-independent modification of Erk signals.4. By screening of CagA-responsive genes using DNA microarray, we identified NFAT. CagA induced nuclear translocation and transcriptional activity of NFAT depending on calcineurin/PLCg pathway. Furthermore, H. pylori VacA toxin counteracted the ability of CagA to activate NFAT.5. Using a series of EPIYA-repeat variants of CagA that represent reported variations in clinical isolates of H. pylori, we show that EPIYA-repeat polymorphism, which is due to differences of both number and order of EPIYA segment, influences the phosphorylation-dependent CagA biological activity.6. We identified CagA multimerization motif that is composed of 16 amino acid residues and mediates an intermolecular interaction between CagA molecules. The CagA multimerization is necessary to express CagA biological activity that relates with cell morphogenetic activity and stimulation of cell motility.