Regulation of Cdk5 activity and function in neurons

CDK5是一种在有丝分裂后神经元中表达的CDC2相关蛋白激酶，通过与脑特异性激活物p35或p39结合而被激活。在科学研究助学金的支持下，我们分析了CDK5在小鼠和大鼠脑神经元中的激活机制。P35是一种被蛋白酶体降解的短寿命蛋白。目前尚不清楚p35的降解是如何在神经元中触发的。我们发现，当神经元被谷氨酸(一种兴奋性神经递质)处理时，p35被降解。降解发生在谷氨酸受体丰富的突触后区域。伴随着p35降解的CDK5活性的失活刺激了钙-钙调蛋白激酶II的激活，这参与了长时程增强的诱导，这是记忆形成的基本机制。P35通过第二个甘氨酸的肉豆蔻酰化作用与膜结合。此外，p35与细胞膜的结合抑制了CDK5的激酶活性。膜结合的CDKs/p35在用非离子去污剂处理后被激活。P35被钙激活的半胱氨酸蛋白酶--钙激活的半胱氨酸蛋白酶切割成p25，导致神经细胞死亡。当神经元受到内质网应激时，Thapsigardin可诱导其分裂。Thapsigardin治疗后2~4d可诱导神经细胞死亡，CDK5抑制剂罗斯科维汀可抑制细胞死亡。产生的P25被移位到细胞核内，并增加了细胞核内CDK5的激酶活性。我们认为，CDK5//p25通过激活有丝分裂后神经元的细胞周期机制来诱导神经细胞死亡。

Cdk5, a cdc2-related protein kinase expressed in postmitotic neurons, is activated by association with brain specific activator p35 or p39. By support from the Grant-in-Aid for Scientific Research, we have analyzed the activation mechanism of Cdk5 in neurons of mouse or rat brains. p35 is a short life protein degraded by proteasome. It was unknown how degradation of p35 is triggered in neurons. We found that p35 was degraded when neurons were treated with glutamate, an excitatory neurotransmitter. Degradation occurred in postsynaptic regions where glutamate receptors are rich. Inactivation of Cdk5 activity accompanied by degradation of p35 stimulated the activation of Ca-calmodulin kinase II, which is involved in induction of long term potentiation, a basic mechanism of memory formation. p35 was shown to associate with membranes through its myristoylation at the second Gly. Further, association of p35 with membranes suppressed the kinase activity of Cdk5. Membrane bound CdkS/p35 was activated when they were released from membranes by treatment with nonionic detergent. p35 is cleaved to p25 by calpain, a Ca-activated cysteine protease, resulting in induction of neuronal cell death. The cleavage was induced when neurons were suffered with endoplasmic reticulum-stress by Thapsigardin. Thapsigardin tretment induced neuronal cell death 2 -4 days after treatment and the cell death was suppressed by Cdk5 inhibitor Roscovitine. p25 generated was translocated into nucleus and increased the kinase activity of Cdk5 in the nucleus. We think that Cdk5//p25 induce neuronal cell death by activating cell cycle machinery in post-mitotic neurons.