The E2F–Cdc2 Cell-Cycle Pathway Specifically Mediates Activity Deprivation-Induced Apoptosis of Postmitotic Neurons
The E2F–Cdc2 Cell-Cycle Pathway Specifically Mediates Activity Deprivation-Induced Apoptosis of Postmitotic Neurons
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DOI：
10.1523/jneurosci.23-05-01649.2003
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发表时间：
2003-03
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影响因子：
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通讯作者：
Y. Konishi;A. Bonni
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文献类型：
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作者：
Y. Konishi;A. Bonni
神经元凋亡在哺乳动物脑的正常发育中起着关键作用，并被认为是导致几种神经系统疾病的发病机制。然而，神经元凋亡的细胞内机制仍不完全清楚。在本研究中，我们的特点是细胞周期为基础的机制，神经元活性剥夺诱导有丝分裂后神经元凋亡。活动剥夺，而不是生长因子的撤退，被发现诱导Cdc2的表达和随后Cdc2介导的细胞凋亡的颗粒神经元的发育大鼠小脑。我们发现，活动剥夺诱导cdc2的转录在神经元中通过的cdc2启动子内的E2F结合元件（EBE）。在DNA结合试验中发现在颗粒神经元中表达的转录因子E2F1与cdc2基因的EBE结合。在染色质免疫沉淀分析中，内源性E2F1与颗粒神经元中的内源性cdc2基因的启动子形成复合物，表明内源性E2F1准备激活神经元中的内源性cdc2基因的转录。与这一结论一致，当在颗粒神经元中表达时，E2 F的一种主要干扰形式会阻断活性剥夺诱导的cdc 2转录。在其他实验中，我们发现E2F1在颗粒神经元中的表达诱导Cdc2的表达，并通过激活Cdc2促进神经元凋亡。值得注意的是，与诱导颗粒神经元中E2F介导的Cdc2表达和激活相反，活动剥夺未能刺激触发DNA合成和复制的E2F靶基因的表达。总之，我们的研究结果定义了一种新的凋亡机制，E2F选择性地耦合的活动剥夺诱导的信号cdc2转录的刺激DNA合成的情况下，从而最终在Cdc2介导的有丝分裂后神经元凋亡。
Neuronal apoptosis plays a critical role in the normal development of the mammalian brain and is thought to contribute to the pathogenesis of several neurologic disorders. However, the intracellular mechanisms underlying apoptosis of neurons remain incompletely understood. In the present study, we characterized a cell-cycle-based mechanism by which neuronal activity deprivation induces apoptosis of postmitotic neurons. Activity deprivation, but not growth factor withdrawal, was found to induce Cdc2 expression and consequent Cdc2-mediated apoptosis in granule neurons of the developing rat cerebellum. We found that activity deprivation induces cdc2 transcription in neurons via an E2F-binding element (EBE) within the cdc2 promoter. The transcription factor E2F1 that is expressed in granule neurons was found in DNA binding assays to bind to the EBE of the cdc2gene. In chromatin immunoprecipitation analysis, endogenous E2F1 forms a complex with the promoter of the endogenous cdc2 gene in granule neurons, indicating that endogenous E2F1 is poised to activate transcription of the endogenous cdc2 gene in neurons. Consistent with this conclusion, a dominant interfering form of E2F, when expressed in granule neurons, blocked activity deprivation-inducedcdc2 transcription. In other experiments, we found that the expression of E2F1 in granule neurons induces Cdc2 expression and promotes neuronal apoptosis via the activation of Cdc2. Remarkably, in contrast to inducing the E2F-mediated expression and activation of Cdc2 in granule neurons, activity deprivation fails to stimulate the expression of E2F-target genes that trigger DNA synthesis and replication. Together, our findings define a novel apoptotic mechanism whereby E2F selectively couples an activity deprivation-induced signal to cdc2 transcription in the absence of stimulating DNA synthesis and thus culminating in Cdc2-mediated apoptosis of postmitotic neurons.