Nguyen Minh Dang, Boudreau Mathieu, Kriz Jasna, Couillard-Després Sebastien, Kaplan David R, Julien Jean-Pierre
Research Institute of the McGill University Health Center, Centre for Research in Neuroscience, Montreal, Quebec, Canada H3G 1A4.
J Neurosci. 2003 Mar 15;23(6):2131-40. doi: 10.1523/JNEUROSCI.23-06-02131.2003.
There is growing evidence for involvement of members of the cyclin-dependent kinase (Cdk) family in neurodegenerative disorders and in apoptotic death of neurons subjected to various insults. After our recent report that a deregulation of Cdk5 activity by p25 may contribute to pathogenesis of amyotrophic lateral sclerosis (ALS), we further examined the possible involvement of other Cdks in mice expressing a mutant form of superoxide dismutase (SOD1(G37R)) linked to ALS. No substantial changes in Cdk2 or Cdk6 distribution and kinase activities were detected in spinal motor neurons from SOD1(G37R) mice when compared with normal mice. Of particular interest was the upregulation and mislocalization of Cdk4, a regulator of the G1-S checkpoint of the cell cycle, in motor neurons of SOD1(G37R) mice. The increase of Cdk4 activity in SOD1(G37R) mice was associated with an increase in nuclear Cdk4, cyclin D1, its coactivator, and with the abnormal phosphorylation of the retinoblastoma (Rb) protein at Cdk phosphorylation sites. Pharmacological treatment of SOD1(G37R) mice with minocycline, a compound that attenuates microgliosis and slows down disease, lessened the dysregulation of Cdk5/Cdk4 and the phosphorylation of Rb. Interestingly, phospho-Rb was immunoprecipitated with anti-Cdk4 but not with anti-Cdk5 antibodies, suggesting a key role for Cdk4 in the phosphorylation of Rb. Remarkably, the overexpression of a transgene coding for human neurofilament H, a phosphorylation sink for deregulated Cdk5 activity by p25, resulted in a reduction in levels of nuclear Cdk4 and Rb phosphorylation. These results indicate that a cell cycle signaling at the neuronal G1-S checkpoint subsequent to Cdk5 deregulation may constitute a critical step of the neuronal death pathway in ALS caused by mutant SOD1.
越来越多的证据表明，细胞周期蛋白依赖性激酶（Cdk）家族成员参与神经退行性疾病以及遭受各种损伤的神经元的凋亡死亡。在我们最近报道p25对Cdk5活性的失调可能导致肌萎缩侧索硬化症（ALS）的发病机制之后，我们进一步研究了其他Cdk在表达与ALS相关的突变形式超氧化物歧化酶（SOD1(G37R)）的小鼠中的可能作用。与正常小鼠相比，在SOD1(G37R)小鼠的脊髓运动神经元中未检测到Cdk2或Cdk6分布及激酶活性的实质性变化。特别有趣的是，细胞周期G1-S期检查点的调节因子Cdk4在SOD1(G37R)小鼠的运动神经元中上调且定位错误。SOD1(G37R)小鼠中Cdk4活性的增加与细胞核中Cdk4、细胞周期蛋白D1及其共激活因子的增加以及视网膜母细胞瘤（Rb）蛋白在Cdk磷酸化位点的异常磷酸化有关。用米诺环素对SOD1(G37R)小鼠进行药物治疗，米诺环素是一种可减轻小胶质细胞增生并减缓疾病进程的化合物，可减轻Cdk5/Cdk4的失调和Rb的磷酸化。有趣的是，磷酸化的Rb可与抗Cdk4抗体免疫沉淀，但不能与抗Cdk5抗体免疫沉淀，这表明Cdk4在Rb的磷酸化中起关键作用。值得注意的是，编码人神经丝H的转基因的过表达，人神经丝H是p25对失调的Cdk5活性的磷酸化底物，导致细胞核中Cdk4水平和Rb磷酸化降低。这些结果表明，Cdk5失调后神经元G1-S期检查点的细胞周期信号传导可能是突变型SOD1引起的ALS中神经元死亡途径的关键步骤。
