Regulatory mechanisms of neuronal differentiation and death by necdin

Necdin在终末分化的神经元中表达，这种蛋白的强制表达抑制了细胞的生长。Necdin结合转录因子E2F1和P53，这两个转录因子都参与神经元凋亡，并抑制它们的活性。最近，Necdin被认为是Prader-Willi综合征的候选基因，Prader-Willi综合征是一种与基因组印记相关的神经行为综合征。因此，Necdin可能是控制神经元终末分化和凋亡的关键因子。在这项研究中，我们分析了Necdin与其靶蛋白之间的分子相互作用，以深入了解神经元终末分化和凋亡背后的分子背景。获得的结果如下：1)利用酵母双杂交技术分离到两个编码与Necdin相互作用的蛋白的cDNA。一种是细胞质钙结合蛋白NEFA，另一种是核基质蛋白hnRNP U。2)NEFA定位于细胞质和内质网，与Necdin协同调节钙代谢。3)Necdin和hnRNP U均定位于核基质，形成抑制细胞生长的复合体。4)分化神经元胞浆中含有丰富的Necdin。5)Necdin与特定的富含G基序结合，并作为转录抑制因子发挥作用。这些结果表明，Necdin通过与存在于神经元胞核和胞浆中的各种蛋白质相互作用，参与神经元的终末分化和存活。

Necdin is expressed in terminally differentiated neurons, and enforced expression of this protein suppresses cell growth. Necdin binds to the transcription factors E2F1 and p53, both of which are involved in neuronal apoptosis, and suppresses their activities. Recently necdin is thought to be a candidate gene for Prader-Willi syndrome, a genomic imprinting-associated neurobehavioral syndrome. Therefore, necdin may be a pivotal factor that controls terminal differentiation and apoptosis in neurons. In this study, we analyzed the molecular interactions between necdin and its target proteins to gain insights into molecular background behind neuronal terminal differentiation and apoptosis. The results obtained are : 1) We isolated two cDNAs encoding proteins that interacts with necdin by yeast two-hybrid assay. One is the cytoplasmic calcium binding protein NEFA, and the other is the nuclear matrix protein hnRNP U. 2) NEFA is localized to the cytoplasm and endoplasmic reticulum, and regulates calcium metabolism in cooperation with necdin. 3) Both necdin and hnRNP U are localized to nuclear matrix and form a complex to suppress cell growth. 4) Necdin is abundant in the cytosol in differentiated neurons. 5) Necdin binds to specific G-rich motif and functions as a transcription repressor. These results suggest that necdin is involved in neuronal terminal differentiation and survival by interacting with various protein present in neuronal nucleus and cytoplasm.