Liu Shi Jie, Zhang Jia Yu, Li Hong Lian, Fang Zheng Yu, Wang Qun, Deng Heng Mei, Gong Cheng Xin, Grundke-Iqbal Inge, Iqbal Khalid, Wang Jian Zhi
Pathophysiology Department, Neuroscience Institute, Tongji Medical College, Hua-Zhong University of Science and Technology, Wuhan 430030, People's Republic of China.
J Biol Chem. 2004 Nov 26;279(48):50078-88. doi: 10.1074/jbc.M406109200. Epub 2004 Sep 15.
Microtubule-associated protein tau is abnormally hyperphosphorylated in Alzheimer's disease (AD) and other tauopathies and is believed to lead to neurodegeneration in this family of diseases. Here we show that infusion of forskolin, a specific cAMP-dependent protein kinase A (PKA) activator, into the lateral ventricle of brain in adult rats induced activation of PKA by severalfold and concurrently enhanced the phosphorylation of tau at Ser-214, Ser-198, Ser-199, and or Ser-202 (Tau-1 site) and Ser-396 and or Ser-404 (PHF-1 site), which are among the major abnormally hyperphosphorylated sites seen in AD. PKA activation positively correlated to the extent of tau phosphorylation at these sites. Infusion of forskolin together with PKA inhibitor or glycogen synthase kinase-3 (GSK-3) inhibitor revealed that the phosphorylation of tau at Ser-214 was catalyzed by PKA and that the phosphorylation at both the Tau-1 and the PHF-1 sites is induced by basal level of GSK-3, because forskolin activated PKA and not GSK-3 and inhibition of the latter inhibited the phosphorylation at Tau-1 and PHF-1 sites. Inhibition of cdc2, cdk5, or MAPK had no significant effect on the forskolin-induced hyperphosphorylation of tau. Forskolin inhibited spatial memory in a dose-dependent manner in the absence but not in the presence of R(p)-adenosine 3',5'-cyclic monophosphorothioate triethyl ammonium salt, a PKA inhibitor. These results demonstrate for the first time that phosphorylation of tau by PKA primes it for phosphorylation by GSK-3 at the Tau-1 and the PHF-1 sites and that an associated loss in spatial memory is inhibited by inhibition of the hyperphosphorylation of tau. These data provide a novel mechanism of the hyperphosphorylation of tau and identify both PKA and GSK-3 as promising therapeutic targets for AD and other tauopathies.
微管相关蛋白tau在阿尔茨海默病（AD）和其他tau蛋白病中异常过度磷酸化，并且被认为在这类疾病中导致神经退行性变。在此我们表明，向成年大鼠脑侧脑室内注入毛喉素（一种特异性的环磷酸腺苷（cAMP）依赖性蛋白激酶A（PKA）激活剂）可使PKA激活数倍，并同时增强tau蛋白在Ser-214、Ser-198、Ser-199和/或Ser-202（Tau-1位点）以及Ser-396和/或Ser-404（PHF-1位点）的磷酸化，这些位点是AD中主要的异常过度磷酸化位点。PKA激活与这些位点tau蛋白的磷酸化程度呈正相关。同时注入毛喉素与PKA抑制剂或糖原合酶激酶-3（GSK-3）抑制剂表明，Ser-214位点tau蛋白的磷酸化由PKA催化，而Tau-1和PHF-1位点的磷酸化由基础水平的GSK-3诱导，因为毛喉素激活的是PKA而非GSK-3，抑制后者可抑制Tau-1和PHF-1位点的磷酸化。抑制细胞周期蛋白依赖性激酶2（cdc2）、细胞周期蛋白依赖性激酶5（cdk5）或丝裂原活化蛋白激酶（MAPK）对毛喉素诱导的tau蛋白过度磷酸化无显著影响。在不存在PKA抑制剂R(p)-腺苷3',5'-环磷酸硫代三乙铵盐的情况下，毛喉素以剂量依赖性方式抑制空间记忆，但在其存在时则不然。这些结果首次证明，PKA介导的tau蛋白磷酸化使其在Tau-1和PHF-1位点易于被GSK-3磷酸化，并且tau蛋白过度磷酸化的抑制可防止相关的空间记忆丧失。这些数据提供了一种tau蛋白过度磷酸化的新机制，并确定PKA和GSK-3均为AD和其他tau蛋白病有前景的治疗靶点。
