Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University, Minami-Osawa 1-1, Hachioji, Tokyo 192-0397, Japan.
Biochemistry. 2010 Jul 6;49(26):5482-93. doi: 10.1021/bi100631f.
Cyclin-dependent kinase 5 (Cdk5) is activated by binding to its activators, p35 and p39. The level of Cdk5 activity is determined by the amount of p35 and p39, which is regulated not only by transcription but also via proteasomal degradation. Alternatively, calpain-induced cleavage of p35 to p25 can induce aberrant Cdk5 activation. As the regulation of p35 and p39 proteolysis is not well understood, we have studied here the mechanisms governing their degradation and cleavage. We find that p35 and p39 undergo proteasomal degradation in neurons, with p39 showing a slower degradation rate than p35. Degradation of the activators is dependent on their respective N-terminal p10 region, as indicated by experiments in which cognate p10 regions were swapped between p35 and p39. The effect of the p10 region on degradation and cleavage could be assigned to its membrane binding properties, mediated predominantly by myristoylation. Together, these results indicate that both proteasomal degradation and calpain cleavage of p35 and p39 are stimulated by membrane association, which is in turn mediated via myristoylation of their p10 regions. However, p35 and p39 show differences in degradation and cleavage rates, which may in fact underlie the distinct physiological and pathological functions of these two Cdk5 activators.
周期蛋白依赖性激酶 5（Cdk5）通过与它的激活剂 p35 和 p39 结合而被激活。Cdk5 活性的水平取决于 p35 和 p39 的量，其水平不仅受转录调控，还受蛋白酶体降解的调控。另外，钙蛋白酶诱导的 p35 切割为 p25 可以诱导异常的 Cdk5 激活。由于对 p35 和 p39 蛋白水解的调节机制尚未完全了解，我们在此研究了控制其降解和切割的机制。我们发现 p35 和 p39 在神经元中经历蛋白酶体降解，p39 的降解速度比 p35 慢。激活剂的降解依赖于它们各自的 N 端 p10 区，这可以通过在 p35 和 p39 之间交换同源 p10 区的实验来证明。p10 区对降解和切割的影响可以归因于其膜结合特性，主要通过豆蔻酰化介导。总之，这些结果表明，p35 和 p39 的蛋白酶体降解和钙蛋白酶切割均受膜结合的刺激，而这反过来又通过它们的 p10 区的豆蔻酰化来介导。然而，p35 和 p39 在降解和切割速率上存在差异，这实际上可能是这两种 Cdk5 激活剂具有不同生理和病理功能的基础。
