Kerokoski Petri, Suuronen Tiina, Salminen Antero, Soininen Hilkka, Pirttilä Tuula
Department of Neuroscience and Neurology, University of Kuopio, Finland.
Biochem Biophys Res Commun. 2002 Nov 15;298(5):693-8. doi: 10.1016/s0006-291x(02)02543-3.
Hyperphosphorylated tau protein is the primary component of neurofibrillary tangles observed in several neurodegenerative disorders. It has been hypothesized that in certain pathological conditions, the calcium activated protease, calpain, would cleave the cyclin-dependent kinase 5 (cdk5) activator p35 to a p25 fragment, which would lead to augmented cdk5 activity, and cdk5-mediated tau hyperphosphorylation. To test this hypothesis, we induced calpain-mediated p35 cleavage in rat hippocampal neuronal cultures and studied the relationship between p25 production, cdk5 activity, and tau phosphorylation. In glutamate-treated cells p35 was cleaved to p25 and this was associated with elevated cdk5 activity. However, tau phosphorylation was concomitantly decreased at multiple sites. The calpain inhibitor MDL28170 prevented the cleavage of p35 but had no effect on tau phosphorylation, suggesting that calpain-mediated processes, i.e., the cleavage of p35 to p25 and cdk5 activation, do not contribute to tau phosphorylation in these conditions. Treatment of the neuronal cultures with N-methyl-D-aspartic acid or with calcium ionophores resulted in an outcome highly similar to that of glutamate. We conclude that, in neuronal cells, the cleavage of p35 to p25 is associated with increased activity of cdk5 but not with tau hyperphosphorylation.
过度磷酸化的tau蛋白是在几种神经退行性疾病中观察到的神经原纤维缠结的主要成分。据推测，在某些病理条件下，钙激活蛋白酶钙蛋白酶会将细胞周期蛋白依赖性激酶5（cdk5）激活剂p35切割成p25片段，这将导致cdk5活性增强，以及cdk5介导的tau过度磷酸化。为了验证这一假设，我们在大鼠海马神经元培养物中诱导了钙蛋白酶介导的p35切割，并研究了p25产生、cdk5活性和tau磷酸化之间的关系。在谷氨酸处理的细胞中，p35被切割成p25，这与cdk5活性升高有关。然而，tau在多个位点的磷酸化同时减少。钙蛋白酶抑制剂MDL28170可阻止p35的切割，但对tau磷酸化没有影响，这表明在这些条件下，钙蛋白酶介导的过程，即p35切割成p25和cdk5激活，与tau磷酸化无关。用N-甲基-D-天冬氨酸或钙离子载体处理神经元培养物，其结果与谷氨酸处理的结果高度相似。我们得出结论，在神经元细胞中，p35切割成p25与cdk5活性增加有关，但与tau过度磷酸化无关。
