Department of Medicine, University of California, San Diego, San Diego, California, USA.
Gastroenterology. 2010 Jul;139(1):239-48. doi: 10.1053/j.gastro.2010.03.036. Epub 2010 Mar 18.
BACKGROUND & AIMS: Infection with Helicobacter pylori represses expression of the gastric H, K-adenosine triphosphatase alpha-subunit (HKalpha), which could contribute to transient hypochlorhydria. CagL, a pilus protein component of the H pylori type IV secretion system, binds to the integrin alpha(5)beta1 to mediate translocation of virulence factors into the host cell and initiate signaling. alpha(5)beta1 binds a disintegrin and metalloprotease (ADAM) 17, a metalloenzyme that catalyzes ectodomain shedding of receptor tyrosine kinase ligands. We investigated whether H pylori-induced repression of HKalpha is mediated by CagL activation of ADAM17 and release of heparin-binding epidermal growth factor (HB-EGF).
HKalpha promoter and ADAM17 activity were measured in AGS gastric epithelial cells transfected with HKalpha promoter-reporter constructs or ADAM17-specific small interfering RNAs and infected with H pylori. HB-EGF secretion was measured by enzyme-linked immunosorbent assay analysis, and ADAM17 interaction with integrins was investigated by coimmunoprecipitation analyses.
Infection of AGS cells with wild-type H pylori or an H pylori cagL-deficient isogenic mutant that also contained a wild-type version of cagL (P12DeltacagL/cagL) repressed HKalpha promoter-Luc reporter activity and stimulated ADAM17 activity. Both responses were inhibited by point mutations in the nuclear factor-kappaB binding site of HKalpha or by infection with P12DeltacagL. Small interfering RNA-mediated silencing of ADAM17 in AGS cells inhibited the repression of wild-type HKalpha promoter and reduced ADAM17 activity and HB-EGF production, compared to controls. Coimmunoprecipitation studies of AGS lysates showed that wild-type H pylori disrupted ADAM17-alpha5beta1 complexes.
During acute H pylori infection, CagL dissociates ADAM17 from the integrin alpha(5)beta1 and activates ADAM17-dependent, nuclear factor-kappaB-mediated repression of HKalpha. This might contribute to transient hypochlorhydria in patients with H pylori infection.
幽门螺杆菌（H. pylori）感染会抑制胃 H、K-三磷酸腺苷酶α亚基（HKalpha）的表达，这可能导致短暂性低胃酸。CagL 是 H. pylori Ⅳ型分泌系统的菌毛蛋白成分，与整合素 α5β1 结合，介导毒力因子向宿主细胞的转运，并启动信号转导。α5β1 结合解整合素金属蛋白酶 17（ADAM17），ADAM17 是一种金属蛋白酶，可催化受体酪氨酸激酶配体的细胞外结构域脱落。我们研究了 H. pylori 是否通过 CagL 激活 ADAM17 和释放肝素结合表皮生长因子（HB-EGF）来介导 HKalpha 的抑制。
AGS 胃上皮细胞转染 HKalpha 启动子报告构建体或 ADAM17 特异性小干扰 RNA 后，用 H. pylori 感染，检测 HKalpha 启动子和 ADAM17 活性。通过酶联免疫吸附分析检测 HB-EGF 分泌，通过共免疫沉淀分析研究 ADAM17 与整合素的相互作用。
AGS 细胞感染野生型 H. pylori 或含有野生型 cagL（P12DeltacagL/cagL）的 cagL 缺陷型同源突变体均抑制 HKalpha 启动子-Luc 报告活性并刺激 ADAM17 活性。HKalpha 核因子-κB 结合位点的点突变或感染 P12DeltacagL 均可抑制这两种反应。AGS 细胞中 ADAM17 的小干扰 RNA 沉默抑制了野生型 HKalpha 启动子的抑制，并降低了 ADAM17 活性和 HB-EGF 产生，与对照组相比。AGS 细胞裂解物的共免疫沉淀研究表明，野生型 H. pylori 破坏了 ADAM17-α5β1 复合物。
在急性 H. pylori 感染期间，CagL 将 ADAM17 从整合素 α5β1 上解离，并激活 ADAM17 依赖性、核因子-κB 介导的 HKalpha 抑制。这可能导致 H. pylori 感染患者的短暂性低胃酸。
