Chow Hei-Man, Guo Dong, Zhou Jie-Chao, Zhang Guan-Yun, Li Hui-Fang, Herrup Karl, Zhang Jie
Division of Life Science and the State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Kowloon, Hong Kong;
Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Institute of Neuroscience, College of Medicine, Xiamen University, Xiamen, Fujian 361102, People's Republic of China; and.
Proc Natl Acad Sci U S A. 2014 Nov 11;111(45):E4887-95. doi: 10.1073/pnas.1402627111. Epub 2014 Oct 20.
Glycogen synthase kinase 3β (GSK3β) and cyclin-dependent kinase 5 (CDK5) are tau kinases and have been proposed to contribute to the pathogenesis of Alzheimer's disease. The 3D structures of these kinases are remarkably similar, which led us to hypothesize that both might be capable of binding cyclin proteins--the activating cofactors of all CDKs. CDK5 is normally activated by the cyclin-like proteins p35 and p39. By contrast, we show that GSK3β does not bind to p35 but unexpectedly binds to p25, the calpain cleavage product of p35. Indeed, overexpressed GSK3β outcompetes CDK5 for p25, whereas CDK5 is the preferred p35 partner. FRET analysis reveals nanometer apposition of GSK3β:p25 in cell soma as well as in synaptic regions. Interaction with p25 also alters GSK3β substrate specificity. The GSK3β:p25 interaction leads to enhanced phosphorylation of tau, but decreased phosphorylation of β-catenin. A partial explanation for this situation comes from in silico modeling, which predicts that the docking site for p25 on GSK3β is the AXIN-binding domain; because of this, p25 inhibits the formation of the GSK3β/AXIN/APC destruction complex, thus preventing GSK3β from binding to and phosphorylating β-catenin. Coexpression of GSK3β and p25 in cultured neurons results in a neurodegeneration phenotype that exceeds that observed with CDK5 and p25. When p25 is transfected alone, the resulting neuronal damage is blocked more effectively with a specific siRNA against Gsk3β than with one against Cdk5. We propose that the effects of p25, although normally attributed to activate CDK5, may be mediated in part by elevated GSK3β activity.
糖原合酶激酶3β（GSK3β）和细胞周期蛋白依赖性激酶5（CDK5）是tau蛋白激酶，有人提出它们在阿尔茨海默病的发病机制中起作用。这些激酶的三维结构非常相似，这使我们推测它们可能都能够结合细胞周期蛋白——所有CDK的激活辅因子。CDK5通常由类细胞周期蛋白p35和p39激活。相比之下，我们发现GSK3β不与p35结合，但意外地与p25结合，p25是p35的钙蛋白酶解产物。实际上，过表达的GSK3β与CDK5竞争结合p25，而CDK5是p35的首选结合伙伴。荧光共振能量转移分析显示，在细胞体以及突触区域，GSK3β与p25在纳米尺度上相互靠近。与p25的相互作用也改变了GSK3β的底物特异性。GSK3β与p25的相互作用导致tau蛋白磷酸化增强，但β-连环蛋白磷酸化减少。这种情况的部分原因来自计算机模拟，该模拟预测p25在GSK3β上的对接位点是AXIN结合域；因此，p25抑制了GSK3β/AXIN/APC破坏复合物的形成，从而阻止GSK3β与β-连环蛋白结合并使其磷酸化。在培养的神经元中共表达GSK3β和p25会导致神经退行性表型，其程度超过CDK5与p25共表达时观察到的情况。当单独转染p25时，针对Gsk3β的特异性siRNA比针对Cdk5的siRNA更有效地阻断由此产生的神经元损伤。我们提出，p25的作用虽然通常归因于激活CDK5，但可能部分是由GSK3β活性升高介导的。
