Free PKC catalytic subunits (PKM) phosphorylate tau via a pathway distinct from that utilized by intact PKC
Free PKC catalytic subunits (PKM) phosphorylate tau via a pathway distinct from that utilized by intact PKC
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DOI：
10.1016/s0006-8993(99)02146-0
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发表时间：
1999-12-11
期刊：
影响因子：
2.9
通讯作者：
Shea, TB
中科院分区：
文献类型：
--
作者：
Ekinci, FJ;Shea, TB
蛋白激酶C(PKC)在细胞膜上被可逆地激活：通过产生二酰基甘油(DAG)和细胞内储存的钙离子释放。PKC也被Calain介导的PKC调节亚基和催化亚基的PKC裂解不可逆转地激活；由此产生的游离PKC催化亚基被称为PKM。与PKC不同，PKM是辅因子不依赖的，在膜外扩散后保持活性，理论上可以磷酸化PKC无法接触到的和不适合PKC的靶标。我们研究了佛波酯TPA和离子载体A23187介导的钙内流(实验上分别对应于DAG介导和Calain介导的激活)对微管相关蛋白tau磷酸化的下游影响。这两种方法都增强了磷酸化tau的免疫反应性，但锂和olomoucin(分别是tan kinaseGSK-3β和CDK5的抑制剂)都不能抑制这种反应。TPA介导的增加，而不是离子载体介导的增加，可通过与丝裂原激活蛋白(MAP)激酶抑制剂PD98059共同处理而被阻断。这些发现表明，PKC通过MAP激酶途径磷酸化tau，但PKM可以绕过这一要求，从而表明不同的细胞内途径可以由PKC和PKM介导。因此，在不适当的钙内流后，PKM的产生可能会触发一个或多个额外的途径，促进tau的磷酸化。(C)1999 Elsevier Science B.V.保留所有权利。
Protein kinase C (PKC) is reversibly activated at the plasma membrane: by the generation of diacylglycerol (DAG) coupled with the release of Ca2+ from intracellular stores. PKC is also irreversibly activated by calpain-mediated PKC cleavage of the regulatory and catalytic subunits; resultant free PKC catalytic subunits are termed "PKM''. Unlike PKC, PKM is co-factor-independent, remains active following diffusion away from the membrane, and can theoretically phosphorylate targets inaccessible to, and inappropriate for, PKC. We examined the downstream consequences of PKC activation by the phorbol ester TPA and by ionophore A23187-mediated calcium influx (which experimentally correspond to DAG-mediated and calpain-mediated activation, respectively) on phosphorylation of the microtubule-associated protein tau. Both methods increased phospho-tau immunoreactivity, and neither was inhibited by lithium or olomoucin (inhibitors of tan kinases GSK-3 beta and cdk5, respectively). The TPA-mediated increase, and not the ionophore-mediated increase, was blocked by co-treatment with the mitogen-activated protein (MAP) kinase kinase inhibitor PD98059. These findings indicate that PKC phosphorylates tau via the MAP kinase pathway, but that PKM can bypass this requirement, therefore demonstrating that distinct intracellular pathways can be mediated by PKC and PKM. PKM generation may therefore trigger one or more additional pathways contributing to tau phosphorylation following inappropriate calcium influx. (C) 1999 Elsevier Science B.V. All rights reserved.