Elucidation of molecular signaling mechanism of axonal guidance

信号素作为排斥因子在轴突引导中发挥重要作用，CRMP家族蛋白被认为参与信号素信号转导。我们已经鉴定出一个新的GTP酶CRAG，它含有一个核定位信号序列(NLS)，是崩溃蛋白反应介体蛋白(CRMP)相关分子(CRAM ICRMP-51)的结合蛋白。在神经元中，CRAG在活性氧(ROS)介导的应激反应中发挥着重要作用，其中包括信号素3A信号。有趣的是，在刺激信号素3A后，CRAG形成了与PML小体相关的独特的核包涵体。这一结果支持信号素利用氧化还原信号，并提供了信号素可能通过激活CRAG来调节裸鼠转录调控的新概念。另一方面，CRAG被发现参与了聚谷氨酰胺病的分子机制。实际上，CRAG与PML伴生，导致PML小体大的Ling样结构，泛素化，这是聚谷氨酰胺病的特征。重要的是，CRAG通过泛素-蛋白酶体途径促进核包涵体中错误折叠的聚谷氨酰胺蛋白的快速降解，并减轻其细胞毒性。最近，我们发现慢载体介导的CRAG在小脑神经元中的表达清除了多聚Q聚集体，并显著改善了聚谷氨酰胺病小鼠的严重共济失调。在不久的将来，靶向表达CRAG将成为治疗人类聚谷氨酰胺病的一种潜在的基因治疗方法。

Semaphorins play a critical role in axon guidance as repulsive factors and CRMP family proteins are believed to be involved in semaphorin signaling. We have identified a novel GTPase named CRAG containing a nuclear localization signal sequence (NLS) as a binding protein of collapsin response mediator protein (CRMP) -associated molecule (CRAM ICRMP-51) . In neurons, CRAG plays an important role for reactive oxygen species (ROS) -mediated stress response including semaphorin3A signaling. Interestingly, CRAG forms unique nuclear inclusion associated with PML bodies after stimulation of semaphorin3A. This result supports that semaphorins utilize redox signaling and provides new concept that semaphorins may regulate transcriptional regulation in nudes by activation of CRAG.On the other hand, CRAG was found to be involved in the molecular mechanism of polyglutamine disease. Actually, CRAG associates with and PML, leading to a large ling-like stnicture of PML body with ubiquitination which is characteristic of polyglutamine diseases. Importantly, CRAG promoted a rapid degradation of misfolded polyglutamine proteins in the nuclear inclusions through ubiquitin-proteasome pathway and attenuated their cell toxicity. Most recently, we showed that lentivector-mediated CRAG expression in cerebellar neurons cleared PolyQ aggregates and strikingly ameliorated severe ataxia in model mice of polyglutamine disease.In the near future, targeted expression of CRAG is a potential gene therapy for human polyglutamine diseases.