Nakayama Masaaki, Hisatsune Junzo, Yamasaki Eiki, Isomoto Hajime, Kurazono Hisao, Hatakeyama Masanori, Azuma Takeshi, Yamaoka Yoshio, Yahiro Kinnosuke, Moss Joel, Hirayama Toshiya
Department of Bacteriology, Institute of Tropical Medicine, Nagasaki University, Nagasaki 8528523, Japan.
J Biol Chem. 2009 Jan 16;284(3):1612-9. doi: 10.1074/jbc.M806981200. Epub 2008 Nov 7.
Helicobacter pylori VacA toxin contributes to the pathogenesis and severity of gastric injury. We found that incubation of AZ-521 cells with VacA resulted in phosphorylation of protein kinase B (Akt) and glycogen synthase kinase-3beta (GSK3beta) through a PI3K-dependent pathway. Following phosphorylation and inhibition of GSK3beta,beta-catenin was released from a GSK3beta/beta-catenin complex, with subsequent nuclear translocation. Methyl-beta-cyclodextrin (MCD) and phosphatidylinositol-specific phospholipase C (PI-PLC), but not 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) and bafilomycin A1, inhibited VacA-induced phosphorylation of Akt, indicating that it does not require VacA internalization and is independent of vacuolation. VacA treatment of AZ-521 cells transfected with TOPtkLuciferase reporter plasmid or control FOPtkLucifease reporter plasmid resulted in activation of TOPtkLuciferase, but not FOPtkLucifease. In addition, VacA transactivated the beta-catenin-dependent cyclin D1 promoter in a luciferase reporter assay. Infection of AZ-521 cells by a vacA mutant strain of H. pylori failed to induce phosphorylation of Akt and GSK3beta, or release of beta-catenin from a GSK3beta/beta-catenin complex. Taken together, these results support the conclusion that VacA activates the PI3K/Akt signaling pathway, resulting in phosphorylation and inhibition of GSK3beta, and subsequent translocation ofbeta-catenin to the nucleus, consistent with effects of VacA on beta-catenin-regulated transcriptional activity. These data introduce the possibility that Wnt-dependent signaling might play a role in the pathogenesis of H. pylori infection, including the development of gastric cancer.
幽门螺杆菌空泡毒素（VacA）会导致胃损伤的发病机制及严重程度。我们发现，用VacA孵育AZ - 521细胞会通过磷脂酰肌醇 - 3激酶（PI3K）依赖性途径导致蛋白激酶B（Akt）和糖原合酶激酶 - 3β（GSK3β）磷酸化。GSK3β磷酸化并被抑制后，β - 连环蛋白从GSK3β/β - 连环蛋白复合物中释放出来，随后发生核转位。甲基 - β - 环糊精（MCD）和磷脂酰肌醇特异性磷脂酶C（PI - PLC），而非5 - 硝基 - 2 -（3 - 苯基丙基氨基） - 苯甲酸（NPPB）和巴弗洛霉素A1，抑制了VacA诱导的Akt磷酸化，表明这不需要VacA内化且与空泡形成无关。用TOPtk荧光素酶报告质粒或对照FOPtk荧光素酶报告质粒转染的AZ - 521细胞经VacA处理后，TOPtk荧光素酶被激活，但FOPtk荧光素酶未被激活。此外，在荧光素酶报告基因检测中，VacA反式激活了β - 连环蛋白依赖性细胞周期蛋白D1启动子。幽门螺杆菌的vacA突变株感染AZ - 521细胞未能诱导Akt和GSK3β磷酸化，也未能使β - 连环蛋白从GSK3β/β - 连环蛋白复合物中释放出来。综上所述，这些结果支持以下结论：VacA激活PI3K/Akt信号通路，导致GSK3β磷酸化并被抑制，随后β - 连环蛋白转位至细胞核，这与VacA对β - 连环蛋白调节的转录活性的影响一致。这些数据提示Wnt依赖性信号通路可能在幽门螺杆菌感染的发病机制中起作用，包括胃癌的发生。
