Recent reports have described the involvement of the diacylglycerol kinase (DGK) family in various pathological conditions. In an animal model of transient ischemia, DGK zeta 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 zeta and neuronal death. In primary cultured neurons, transient exposure to excitotoxic concentration of glutamate led to cytoplasmic accumulation of DGK zeta followed by its down-regulation. Results showed that DGK zeta down-regulation was caused by proteolytic degradation through the ubiquitin-proteasome system (UPS) rather than transcriptional inhibition. DGK zeta polyubiquitination was inhibited in the presence of nuclear export inhibitor leptomycin B. Furthermore, NLS-deleted mutant DGK zeta Delta NLS, which mainly localizes to the cytoplasm, was ubiquitinated more heavily than wild-type DGK zeta. From a functional perspective, in vitro gene silencing of DGK zeta via specific siRNA enhanced DNA fragmentation in cultured neurons after glutamate exposure. At the organismal level, hippocampal neurons of DGK zeta-deficient mice showed vulnerability to kainate-induced seizures. In addition, DGK zeta-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 zeta followed by its degradation through the cytoplasmic UPS in hippocampal neurons and that 2) DGK zeta-deficient neurons do not succumb directly to apoptosis, although they are more vulnerable to excitotoxicity because of aberrant cell cycle reentry.
M. Okada, Y. Hozumi, T. Tanaka, Y. Suzuki, M. Yanagida, Y. Araki, et al. (2012). DGKζ is degraded through the cytoplasmic ubiquitin-proteasome system under excitotoxic conditions, which causes neuronal apoptosis because of aberrant cell cycle reentry. CELLULAR SIGNALLING, 24, 1573-1582 [10.1016/j.cellsig.2012.03.021].
DGKζ is degraded through the cytoplasmic ubiquitin-proteasome system under excitotoxic conditions, which causes neuronal apoptosis because of aberrant cell cycle reentry.
C. Evangelisti;MARTELLI, ALBERTO MARIA;
2012
Abstract
Recent reports have described the involvement of the diacylglycerol kinase (DGK) family in various pathological conditions. In an animal model of transient ischemia, DGK zeta 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 zeta and neuronal death. In primary cultured neurons, transient exposure to excitotoxic concentration of glutamate led to cytoplasmic accumulation of DGK zeta followed by its down-regulation. Results showed that DGK zeta down-regulation was caused by proteolytic degradation through the ubiquitin-proteasome system (UPS) rather than transcriptional inhibition. DGK zeta polyubiquitination was inhibited in the presence of nuclear export inhibitor leptomycin B. Furthermore, NLS-deleted mutant DGK zeta Delta NLS, which mainly localizes to the cytoplasm, was ubiquitinated more heavily than wild-type DGK zeta. From a functional perspective, in vitro gene silencing of DGK zeta via specific siRNA enhanced DNA fragmentation in cultured neurons after glutamate exposure. At the organismal level, hippocampal neurons of DGK zeta-deficient mice showed vulnerability to kainate-induced seizures. In addition, DGK zeta-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 zeta followed by its degradation through the cytoplasmic UPS in hippocampal neurons and that 2) DGK zeta-deficient neurons do not succumb directly to apoptosis, although they are more vulnerable to excitotoxicity because of aberrant cell cycle reentry.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
