Litersky J M, Johnson G V
Department of Psychiatry, University of Alabama, Birmingham 35294.
J Biol Chem. 1992 Jan 25;267(3):1563-8.
The effects of cAMP-dependent protein kinase (cAMP-PK) phosphorylation on the degradation of the microtubule-associated protein tau by calpain were studied. Purified bovine brain tau that had been phosphorylated by cAMP-PK had a slower migration pattern on sodium dodecyl sulfate-polyacrylamide gels and a more acidic, less heterogeneous pattern on two-dimensional, nonequilibrium pH gradient electrophoresis (NEPHGE) gels compared with untreated tau. Phosphorylation of tau by cAMP-PK significantly inhibited its proteolysis by calpain compared with untreated tau. To our knowledge this is the first demonstration that phosphorylation of tau by a specific kinase results in increased resistance to hydrolysis by calpain. Tau dephosphorylated by alkaline phosphatase migrated more rapidly on sodium dodecyl sulfate-polyacrylamide gels and also showed an altered two-dimensional NEPHGE pattern. Dephosphorylation of tau had no effect on its susceptibility to calpain proteolysis, indicating that regulation of the susceptibility to calpain hydrolysis is due to the phosphorylation of a specific site(s). These results suggest a role for phosphorylation in regulating the degradation of tau. Abnormal phosphorylation could result in a protease-resistant tau population which may contribute to the formation of paired helical filaments in Alzheimer's disease.
研究了环磷酸腺苷依赖性蛋白激酶（cAMP-PK）磷酸化对钙蛋白酶介导的微管相关蛋白tau降解的影响。与未处理的tau相比，经cAMP-PK磷酸化的纯化牛脑tau在十二烷基硫酸钠-聚丙烯酰胺凝胶上的迁移模式较慢，在二维非平衡pH梯度电泳（NEPHGE）凝胶上呈现出更酸性、异质性更低的模式。与未处理的tau相比，cAMP-PK对tau的磷酸化显著抑制了钙蛋白酶对其的蛋白水解作用。据我们所知，这是首次证明特定激酶对tau的磷酸化会导致其对钙蛋白酶水解的抗性增加。经碱性磷酸酶去磷酸化的tau在十二烷基硫酸钠-聚丙烯酰胺凝胶上迁移更快，并且二维NEPHGE模式也发生了改变。tau的去磷酸化对其对钙蛋白酶蛋白水解的敏感性没有影响，表明对钙蛋白酶水解敏感性的调节是由于特定位点的磷酸化。这些结果表明磷酸化在调节tau降解中起作用。异常磷酸化可能导致形成对蛋白酶有抗性的tau群体，这可能有助于阿尔茨海默病中双螺旋丝的形成。
