Regulation of Neuronal Survival by the Rit GTPase

描述(由申请人提供)：导致细胞死亡/存活的信号通路影响包括癌症和许多神经退行性疾病在内的疾病。因此，阐明调控这些过程的信号转导机制对于理解基础生物学和治疗干预非常重要。神经营养因子部分地通过激活小的GTP结合蛋白RAS来刺激神经元存活，RAS通过将神经营养因子启动的信号转化为包括PI-3激酶/Akt和MEK/ERK在内的多个信号通路来促进存活。在最初的资助阶段，有人提出一组新的、进化上保守的与RAS相关的GTP酶，包括两个哺乳动物蛋白(Rit和Rin)和一个果蝇直系同源基因(Ric)，在调节细胞凋亡信号中发挥关键作用。从这项工作中，现在很清楚Rit和Ric都以一种不同于RAS的方式促进神经元存活。最初的假说现在被扩展到解决这些抗凋亡信号级联是如何被调控的。这一建议的中心假设是RIT GTPase在神经元中作为一个分子开关，对凋亡应激和神经营养素启动的信号做出反应，激活依赖于p38 MAP激酶信号的独特的促生存信号级联反应。提出了三个具体的目标：目标1将表征激活的RIT促进神经元存活的能力。特别是，我们将评估RIT信号在营养因子撤除介导的神经元凋亡中的保护作用。使用来自两个转基因小鼠模型的原代神经元，或者在神经元中特异地表达激活的RIT，或者使用纯合子RIT基因敲除小鼠(在之前的时期培育)，现在可以分析这些关键问题。此外，微阵列分析将用于分类RIT信号调节的神经元转录程序。目的2将确定NGF刺激的TrkA与RIT激活偶联的调节机制，以及p38 MAP激酶级联的RIT依赖调节的性质。目的3将探索RIT抗细胞凋亡信号的关键信号通路。特别是，RIT介导的p38-MSK1/2激酶级联和CREB转录通路的激活似乎发挥了核心作用，并将使用细胞模型系统和原代神经元的组合进行测试。重要的是，自上一篇综述以来发展的数据表明，第二个新的RIT-p38-HSP27-MK2通路可能刺激AKT信号提供神经元保护。总之，这些研究将确立RIT在神经元存活中的作用。调节这种新的RAS相关的G蛋白可能会对神经元生理学产生显著的影响，并使RIT及其效应器成为开发新的治疗策略的潜在靶点。公共卫生相关性：神经元的死亡导致或促成了各种神经退行性疾病，包括中风、癫痫、帕金森病、亨廷顿病和阿尔茨海默病。重要的是，我们发现了一种促进神经元存活的蛋白质，保护神经元免受潜在致命刺激的影响。了解促进神经元存活的机制对于制定这些疾病的治疗策略是至关重要的。因此，这项研究的目标是加快这种蛋白质在神经退行性疾病中的治疗利用进展。

DESCRIPTION (provided by applicant): Signaling pathways that contribute to cell death/survival influence diseases including cancer and many neurodegenerative conditions. Elaborating signal transduction mechanisms that regulate these processes are thus important for understanding basic biology and for therapeutic intervention. Neurotrophins potently stimulate neuronal survival in part by activating the small GTP-binding protein Ras, which functions by translating neurotrophin-initiated signals into multiple signaling pathways, including PI-3 kinase/Akt and MEK/ERK, to promote survival. In the initial funding period it was proposed that a novel, and evolutionarily conserved group of Ras-related GTPases, including two mammalian proteins (Rit and Rin) and a single Drosophila ortholog (Ric), play critical roles in regulating apoptotic signaling. From this work, it is now clear that both Rit and Ric promote neuronal survival in a manner distinct from that of Ras. The original hypothesis is now expanded to address how these anti-apoptotic signaling cascades are regulated. The central hypothesis of this proposal is that the Rit GTPase functions as a molecular switch in neurons, responding to both apoptotic stresses and neurotrophin-initiated signals, to activate a distinct pro-survival signaling cascade that relies upon p38 MAP kinase signaling. Three specific aims are proposed: Aim 1 will characterize the ability of activated Rit to promote neuronal survival. In particular, we will assess the ability of Rit signaling to protect neurons from trophic factor-withdrawal mediated apoptosis. Using primary neurons from two transgenic mouse models either expressing activated Rit specifically in neurons or a homozygous Rit knockout mouse (developed during the previous period) it is now possible to analyze these critical issues. In addition, microarray analysis will be used to catalog the neuronal transcriptional program regulated by Rit signaling. Aim 2 will determine the regulatory mechanism that couples NGF-stimulated TrkA to Rit activation and the nature of Rit-dependent regulation of the p38 MAP kinase cascade. Aim 3 will explore the critical signaling pathways utilized for Rit anti-apoptotic signaling. In particular, Rit-mediated activation of both the p38- MSK1/2 kinase cascade and CREB transcriptional pathways appear to play central roles and will be tested using a combination of both cell model systems and primary neurons. Importantly, data developed since the previous review suggests that a second novel Rit-p38-HSP27-MK2 pathway may stimulate AKT signaling to afford neuronal protection. In summary, these studies will establish a role for Rit in neuronal survival. Regulation of this novel Ras-related G-protein may have a pronounced impact on neuronal physiology and would make Rit and its effectors, potential targets for the development of new therapeutic strategies. PUBLIC HEALTH RELEVANCE: The death of neurons causes or contributes to various neurodegenerative disorders including stroke, epilepsy, Parkinson's disease, Huntington's disease, and Alzheimer's disease. Importantly, we have discovered a protein that promotes neuronal survival, protecting neurons from potentially lethal stimuli. Understanding the mechanism that foster neuronal survival is of fundamental importance to the development of treatment strategies for these disorders. Thus, the goal of this research is to speed progress toward therapeutic exploitation of this protein in neurodegenerative disease.