胃幽門螺旋桿菌 (Helicobacter pylori)在近年來的研究中,被認為與人類胃部疾病相關,長期的感染會造成人類胃部發炎、胃潰瘍、十二指腸潰瘍,甚至腸胃道癌症及淋巴相關淋巴癌。胃幽門螺旋桿菌的毒力因子主要分為兩大類,第一類與細菌的黏附能力相關,如: 鞭毛;第二類則造成胃部組織的受損,如: Vacuolating toxin A (VacA), Cytotoxin-associated gene A (CagA)等。研究指出,長期感染胃幽門螺旋桿菌,會使胃部細胞nuclear factor (NF)-kB 活化,進一步促進細胞分泌IL-8,產生發炎反應,而長期的胃部發炎就是導致胃部疾病的主要原因。
CagA 毒素是被幽門螺旋桿菌送入細胞體中的毒素之ㄧ,幽門螺旋桿菌中的cag PAI gene 能夠製造第四型分泌系統 (Type IV Secretion System),與CagA 蛋白。當CagA 蛋白透過第四型分泌系統進入細胞後,會與Src family kinase 作用,造成CagA 上C 端的EPIYA motif (Glu-Pro-Ile-Tyr-Ala) 被磷酸化,隨著訊息傳遞路徑,導致細胞型態改變,形成hummingbird phenotypes。在我們的研究中發現,CagA 促使細胞分泌IL-8,需要activator protein-1 (AP-1) promoter 及 NF-kB promoter 兩個共同作用才能誘發,並且CagA 所造成的訊息傳遞路徑,需要cholesterol 的參與。另外,我們使用了CagA 的缺失序列,進一步探討位於CagA上EPIYA motif 所扮演的角色,研究結果也指出,CagA 上的EPIYA motif 的存在對於細胞內CagA 趨向細胞膜上的lipid rafts 區域是重要的,並且EPIYA motif對於CagA 誘發細胞分泌IL-8 是必須存在的。因此,在我們的研究成果中,說明了CagA 上的EPIYA motifs 能夠促使細胞中的CagA 與細胞膜上的lipid rafts 作用,進一步促使訊息傳遞,造成細胞的變形及發炎反應。
The infection of Helicobacter pylori was thought to be related with human gastric diseases including peptic ulcer, lymphoma, gastric atrophy, and adenocaecinoma. Upon infection of gastric epithelial cells, Helicobacter pylori
cytotoxin-associated gene A (CagA) is injected into epithelial cells via the type IV secretion system, which is dependent on cholesterol. Translocated CagA then co-localizes with the lipid raft marker GM1 and interacts with c-Src in which a tyrosine residue in the CagA Glu-Pro-Ile-Tyr-Ala (EPIYA) repeat region can be phosphorylated. In the present study, we found that CagA induction of IL-8 promoter activity in gastric epithelial cells was dependent on both of the presence of activator protein-1 (AP-1) and nuclear factor (NF)-kB binding sites, and cholesterol plays a crucial role in the pathway. Additionally, the EPIYA repeat region in the C-terminal domain was indispensable for CagA-induced interleukin (IL)-8 promoter activity, and this activity was dependent on cholesterol. Using multiple CagA truncation constructs, we showed that the C-terminal domain containing the EPIYA repeats was responsible for CagA-induced IL-8 promoter activity and for raft association. Our results suggest the importance of the EPIYA repeat region for interaction of CagA with lipid rafts and for CagA-induced pathogenesis.