DGK¦Æ 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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• 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
• 出版时间：August, 2012
• 年：2012
• 卷：24
• 期：8
• 页码：1573-1582
• 全文大小：1294 K

文摘

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