Zhang Yi, Qu Dianbo, Morris Erick J, O'Hare Michael J, Callaghan Steven M, Slack Ruth S, Geller Herbert M, Park David S
Ottawa Health Research Institute, Neuroscience Group, University of Ottawa, Ottawa, Ontario, Canada, K1H 8M5.
J Neurosci. 2006 Aug 23;26(34):8819-28. doi: 10.1523/JNEUROSCI.2593-06.2006.
Cell cycle regulators appear to play a paradoxical role in neuronal death. We have shown previously that cyclin-dependent kinases (CDKs), along with their downstream effectors, Rb (retinoblastoma) and E2F/DP1 (E2 promoter binding factor/deleted in polyposis 1), regulate neuronal death evoked by the DNA damaging agent camptothecin. However, the mechanism by which CDKs are activated in this model is unclear. The cell division cycle 25A (Cdc25A) phosphatase is a critical regulator of cell cycle CDKs in proliferating cells. In cortical neurons, we presently show that expression of Cdc25A promotes death even in the absence of DNA damage. Importantly, Cdc25A activity is rapidly increased during DNA damage treatment. Inhibition of Cdc25A blocks death and reduces cyclin D1-associated kinase activity and Rb phosphorylation. This indicates that endogenous Cdc25A activity is important for regulation of cell cycle-mediated neuronal death. We also examined how Cdc25A activity is regulated after DNA damage. Cultured embryonic cortical neurons have a significant basal activity of checkpoint kinase 1 (Chk1), a kinase that regulates cell cycle arrest. During camptothecin treatment of neurons, this activity is rapidly downregulated with a concomitant increase in Cdc25A activity. Importantly, expression of wild-type Chk1, but not kinase-dead Chk1, inhibits the camptothecin-induced increase in Cdc25A activity. In addition, Chk1 expression also promotes survival in the presence of the DNA-damaging agent. Together, our data suggest that a Chk1/Cdc25A activity participates in activation of a cell cycle pathway-mediated death signal in neurons. These data also define how a proliferative signal may be abnormally activated in a postmitotic environment.
细胞周期调节因子在神经元死亡过程中似乎发挥着矛盾的作用。我们之前已经表明，细胞周期蛋白依赖性激酶（CDK）及其下游效应分子Rb（视网膜母细胞瘤）和E2F/DP1（E2启动子结合因子/息肉病1中缺失），调节由DNA损伤剂喜树碱诱发的神经元死亡。然而，在该模型中CDK被激活的机制尚不清楚。细胞分裂周期25A（Cdc25A）磷酸酶是增殖细胞中细胞周期CDK的关键调节因子。在皮质神经元中，我们目前发现，即使在没有DNA损伤的情况下，Cdc25A的表达也会促进细胞死亡。重要的是，在DNA损伤处理过程中，Cdc25A的活性迅速增加。抑制Cdc25A可阻断细胞死亡，并降低细胞周期蛋白D1相关激酶活性和Rb磷酸化。这表明内源性Cdc25A活性对于调节细胞周期介导的神经元死亡很重要。我们还研究了DNA损伤后Cdc25A活性是如何被调节的。培养的胚胎皮质神经元具有显著的基础检查点激酶1（Chk1）活性，Chk1是一种调节细胞周期停滞的激酶。在喜树碱处理神经元的过程中，这种活性迅速下调，同时Cdc25A活性增加。重要的是，野生型Chk1的表达，而不是激酶失活的Chk1的表达，抑制了喜树碱诱导的Cdc25A活性增加。此外，Chk1的表达在存在DNA损伤剂的情况下也能促进细胞存活。总之，我们的数据表明Chk1/Cdc25A活性参与了神经元中细胞周期途径介导的死亡信号的激活。这些数据还定义了在有丝分裂后环境中增殖信号可能如何被异常激活。
