Function analysis of Helicobacter pylori cag pathogenicity island

CagA磷酸化位点的多样性决定了CagA与SHP-2的结合亲和力，被认为是决定幽门螺杆菌感染临床结局的重要变量。在这项工作中，我们调查了来自日本两个不同地区(福井和冲绳)的分离株中CagA的多样性，这两个地区的胃癌风险不同，并研究了多样性与临床结果的关系。对158株临床分离株(92株福井株和66株冲绳株)的cagA基因进行了序列分析。我们还研究了CagA的组织学特征与多样性之间的关系。体外感染人胃上皮AGS细胞，检测CagA的磷酸化及CagA与SHP-2的结合亲和力。几乎所有(98.9%)福井株和68.2%的冲绳株都有东亚CagA阳性株。感染东亚CagA阳性菌株的胃炎患者的炎症分级、胃炎活动性和萎缩程度显著高于感染cagA阴性或西方CagA阳性菌株的胃炎患者。此外，所有胃癌菌株均为东亚CagA阳性。在生化方面，东亚CagA蛋白表现出比西方CagA蛋白更强的SHP-2结合活性。提示东亚CagA阳性幽门螺杆菌感染与萎缩性胃炎和胃癌密切相关，东亚CagA阳性菌株具有比西方型更强的SHP-2结合活性，其诱导的持续活动性炎症可能在萎缩性胃炎和胃癌的发病机制中起作用。

The diversity of the CagA phosphorylation site, which determines the binding affinity of CagA to SHP-2, is suspected to be an important variable in determining the clinical outcome of Helicobacter pylori infection. In this work, we investigated the diversity of CagA in isolates from two different areas in Japan (Fukui and Okinawa), where gastric cancer risk is different, and examined the relationship between the diversity and clinical outcome. A total of 158 clinical isolates (92 Fukui strains and 66 Okinawa strains) was subjected to sequence analysis of the cagA gene. We also examined the relationship between histological features and diversity of CagA. The CagA phosphorylation and the binding affinity of CagA to SHP-2 were also examined by in vitro infection using human gastric epithelial AGS cells. Almost all (98.9%) Fukui and 68.2% of Okinawa strains possessed East Asian CagA-positive strains. The grades of inflammation, activity of gastritis, and atrophy were significantly higher in gastritis patients infected with the East Asian CagA-positive strain than in gastritis patients infected with cagA-negative or Western CagA-positive strains. Furthermore, all gastric cancer strains were East Asian CagA-positive. Biochemically, the East Asian CagA protein exhibited stronger SHP-2 binding activity than the Western CagA did. These findings suggest that infection of East Asian CagA-positive H. pylori infection is substantially associated with atrophic gastritis and gastric cancer, and that persistent active inflammation induced by the East Asian CagA-positive strain, which possesses stronger SHP-2 binding activity than the Western type, may play a role in the pathogenesis of atrophic gastritis and gastric cancer.