Liu Lijun, Zhao Xiaochen, Pierre Sandrine V, Askari Amir
Department of Physiology, Pharmacology, Metabolism, and Cardiovascular Sciences, The University of Toledo College of Medicine, Toledo, Ohio 43614-2598, USA.
Am J Physiol Cell Physiol. 2007 Nov;293(5):C1489-97. doi: 10.1152/ajpcell.00158.2007. Epub 2007 Aug 29.
Our previous studies on cardiac myocytes showed that positive inotropic concentrations of the digitalis drug ouabain activated signaling pathways linked to Na(+)-K(+)-ATPase through Src and epidermal growth factor receptor (EGFR) and led to myocyte hypertrophy. In view of the known involvement of phosphatidylinositol 3-kinase (PI3K)-Akt pathways in cardiac hypertrophy, the aim of the present study was to determine whether these pathways are also linked to cardiac Na(+)-K(+)-ATPase and, if so, to assess their role in ouabain-induced myocyte growth. In a dose- and time-dependent manner, ouabain activated Akt and phosphorylation of its substrates mammalian target of rapamycin and glycogen synthase kinase in neonatal rat cardiac myocytes. Akt activation by ouabain was sensitive to PI3K inhibitors and was also noted in adult myocytes and isolated hearts. Ouabain caused a transient increase of phosphatidylinositol 3,4,5-trisphosphate content of neonatal myocytes, activated class IA, but not class IB, PI3K, and increased coimmunoprecipitation of the alpha-subunit of Na(+)-K(+)-ATPase with the p85 subunit of class IA PI3K. Ouabain-induced activation of ERK1/2 was prevented by Src, EGFR, and MEK inhibitors, but not by PI3K inhibitors. Activation of Akt by ouabain, however, was sensitive to inhibitors of PI3K and Src, but not to inhibitors of EGFR and MEK. Similarly, ouabain-induced myocyte hypertrophy was prevented by PI3K and Src inhibitors, but not by an EGFR inhibitor. These findings 1) establish the linkage of the class IA PI3K-Akt pathway to Na(+)-K(+)-ATPase and the essential role of this linkage to ouabain-induced myocyte hypertrophy and 2) suggest cross talk between these PI3K-Akt pathways and the signaling cascades previously identified to be associated with cardiac Na(+)-K(+)-ATPase.
我们之前对心肌细胞的研究表明，洋地黄药物哇巴因的正性肌力浓度通过Src和表皮生长因子受体（EGFR）激活与Na(+)-K(+)-ATP酶相关的信号通路，并导致心肌细胞肥大。鉴于已知磷脂酰肌醇3激酶（PI3K）-Akt通路参与心肌肥大，本研究的目的是确定这些通路是否也与心脏Na(+)-K(+)-ATP酶相关，如果相关，则评估它们在哇巴因诱导的心肌细胞生长中的作用。哇巴因以剂量和时间依赖性方式激活新生大鼠心肌细胞中的Akt及其底物雷帕霉素哺乳动物靶蛋白和糖原合酶激酶的磷酸化。哇巴因对Akt的激活对PI3K抑制剂敏感，在成年心肌细胞和离体心脏中也有发现。哇巴因导致新生心肌细胞中磷脂酰肌醇3,4,5-三磷酸含量短暂增加，激活IA类而非IB类PI3K，并增加Na(+)-K(+)-ATP酶α亚基与IA类PI3K的p85亚基的共免疫沉淀。哇巴因诱导的ERK1/2激活被Src、EGFR和MEK抑制剂阻断，但未被PI3K抑制剂阻断。然而，哇巴因对Akt的激活对PI3K和Src抑制剂敏感，但对EGFR和MEK抑制剂不敏感。同样，哇巴因诱导的心肌细胞肥大被PI3K和Src抑制剂阻断，但未被EGFR抑制剂阻断。这些发现1）确立了IA类PI3K-Akt通路与Na(+)-K(+)-ATP酶的联系以及该联系对哇巴因诱导的心肌细胞肥大的重要作用，2）提示这些PI3K-Akt通路与先前确定的与心脏Na(+)-K(+)-ATP酶相关的信号级联之间存在相互作用。
