DGKζ is degraded through the cytoplasmic ubiquitin-proteasome system under excitotoxic conditions, which causes neuronal apoptosis because of aberrant cell cycle reentry
DGKζ is degraded through the cytoplasmic ubiquitin-proteasome system under excitotoxic conditions, which causes neuronal apoptosis because of aberrant cell cycle reentry
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DGK z 在兴奋性毒性条件下通过细胞质泛素-蛋白酶体系统降解，由于异常的细胞周期折返而导致神经元凋亡
DOI：
10.1016/j.cellsig.2012.03.021
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发表时间：
2012
期刊：
影响因子：
4.8
通讯作者：
Goto K.
中科院分区：
文献类型：
--
作者：
Okada M;Hozumi Y;Tanaka T;Suzuki Y;Yanagida M;Araki Y;Evangelisti C;Yagisawa H;Topham MK;Martelli AM;Goto K.
最近的报道描述了二酰基甘油激酶（DGK）家族在各种病理条件下的参与。在动物短暂缺血模型中，含有核定位信号（NLS）的DGKζ在海马神经元中迅速从细胞核转移到细胞质，并在再灌注后逐渐消失。这些神经元因谷氨酸兴奋性毒性而延迟死亡。本研究探讨DGKζ与神经元死亡的分子机制和功能关系。在原代培养的神经元中，短暂暴露于兴奋毒性浓度的谷氨酸导致DGKζ的细胞质积累，随后下调。结果表明，DGKζ下调是通过泛素-蛋白酶体系统（UPS）的蛋白水解降解引起的，而不是转录抑制。核输出抑制剂leptomycin b的存在抑制了DGKζ的泛素化。此外，nls缺失的突变体DGKζΔNLS主要定位于细胞质，其泛素化程度比野生型DGKζ更严重。从功能的角度来看，通过特异性siRNA对DGKζ进行体外基因沉默，增强了谷氨酸暴露后培养神经元的DNA片段化。在机体水平上，dgk - ζ缺陷小鼠的海马神经元易受盐酸盐诱导的癫痫发作的影响。此外，dgk - ζ缺陷海马表现出Ser807/811磷酸化的视网膜母细胞瘤蛋白水平的显著增加，同时D型和E型细胞周期蛋白的表达上调，表明细胞周期再进入。总的来说，这些结果表明1)谷氨酸兴奋毒性诱导DGKζ的核胞质易位，随后通过海马神经元的胞质UPS降解；2)DGKζ缺陷神经元不会直接死亡，尽管它们由于异常的细胞周期再进入而更容易受到兴奋毒性的影响。
Recent reports have described the involvement of the diacylglycerol kinase (DGK) family in various pathological conditions. In an animal model of transient ischemia, DGKζ containing a nuclear localization signal (NLS) is shown to translocate quickly from the nucleus to the cytoplasm in hippocampal neurons and to disappear gradually after reperfusion. Those neurons die a delayed neuronal death because of glutamate excitotoxicity. This study investigated the molecular mechanism and functional relation linking DGKζ and neuronal death. In primary cultured neurons, transient exposure to excitotoxic concentration of glutamate led to cytoplasmic accumulation of DGKζ followed by its down-regulation. Results showed that DGKζ down-regulation was caused by proteolytic degradation through the ubiquitin–proteasome system (UPS) rather than transcriptional inhibition. DGKζ polyubiquitination was inhibited in the presence of nuclear export inhibitor leptomycin B. Furthermore, NLS-deleted mutant DGKζΔNLS, which mainly localizes to the cytoplasm, was ubiquitinated more heavily than wild-type DGKζ. From a functional perspective, in vitro gene silencing of DGKζ via specific siRNA enhanced DNA fragmentation in cultured neurons after glutamate exposure. At the organismal level, hippocampal neurons of DGKζ-deficient mice showed vulnerability to kainate-induced seizures. In addition, DGKζ-deficient hippocampus exhibited a significant increase in Ser807/811 phosphorylated retinoblastoma protein levels together with up-regulation of the expression of type D and E cyclins, indicative of cell cycle reentry. Collectively, these results suggest that 1) glutamate excitotoxicity induces nucleocytoplasmic translocation of DGKζ followed by its degradation through the cytoplasmic UPS in hippocampal neurons and that 2) DGKζ-deficient neurons do not succumb directly to apoptosis, although they are more vulnerable to excitotoxicity because of aberrant cell cycle reentry.