DGK味 is degraded through the cytoplasmic ubiquitin-proteasome system under excitotoxic conditions, which causes neuronal apoptosis because of aberrant cell cycle reentry

详细信息	查看全文 | 推荐本文 |

• 作者：Masashi Okada^a ; Yasukazu Hozumi^a ; Toshiaki Tanaka^a ; Yusuke Suzuki^a ; Mitsuaki Yanagida^b ; Yoshihiko Araki^b ; Camilla Evangelisti^c ; ¹ ; Hitoshi Yagisawa^d ; Matthew K. Topham^e ; Alberto M. Martelli^c ; Kaoru Goto^a ; ^{kgoto@med.id.yamagata-u.ac.jp}
• 关键词：Diacylglycerol kinase ; Excitotoxicity ; Ubiquitin&ndash ; proteasome system ; Cell cycle reentry
• 刊名：Cellular Signalling
• 出版年：2012
• 期刊代码：42_08986568
• 类别：bio
• 出版时间：August, 2012
• 卷：24
• 期：8
• 页码：1573-1582
• 文件大小：1294 K

摘要

Recent reports have described the involvement of the diacylglycerol kinase (DGK) family in various pathological conditions. In an animal model of transient ischemia, DGK味 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 DGK味 and neuronal death. In primary cultured neurons, transient exposure to excitotoxic concentration of glutamate led to cytoplasmic accumulation of DGK味 followed by its down-regulation. Results showed that DGK味 down-regulation was caused by proteolytic degradation through the ubiquitin-proteasome system (UPS) rather than transcriptional inhibition. DGK味 polyubiquitination was inhibited in the presence of nuclear export inhibitor leptomycin B. Furthermore, NLS-deleted mutant DGK味螖NLS, which mainly localizes to the cytoplasm, was ubiquitinated more heavily than wild-type DGK味. From a functional perspective, in vitro gene silencing of DGK味 via specific siRNA enhanced DNA fragmentation in cultured neurons after glutamate exposure. At the organismal level, hippocampal neurons of DGK味-deficient mice showed vulnerability to kainate-induced seizures. In addition, DGK味-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 DGK味 followed by its degradation through the cytoplasmic UPS in hippocampal neurons and that 2) DGK味-deficient neurons do not succumb directly to apoptosis, although they are more vulnerable to excitotoxicity because of aberrant cell cycle reentry.