Regulation of Neuronal Survival by Ras-like GTPase

Ras 样 GTP 酶对神经元存活的调节

基本信息

批准号：
7068618
负责人：
Douglas Allen Andres
金额：
$ 34.16万
依托单位：
UNIVERSITY OF KENTUCKY
依托单位国家：
美国
项目类别：
财政年份：
2003
资助国家：
美国
起止时间：
2003-07-01 至 2008-04-30
项目状态：
已结题

项目摘要

DESCRIPTION (provided by applicant): Aberrant apoptosis contributes to various neurodegenerative disorders. Elaborating the signal transduction mechanisms that regulate neuronal survival is thus important for understanding both 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 and directing neurotrophin-initiated signals into multiple signaling pathways. Recent data indicate that the Ras-dependent signaling pathways, PI-3 kinase/Akt and MEK/ERK, and the Ras-independent MEK5/ERK5 signaling cascade, are the primary mediators of neurotrophin-dependent survival. We have discovered a novel, evolutionarily conserved group of Ras-related proteins. There are at least two highly related human genes (Rit and Rin), while Drosophila express only one family member (Ric). These proteins represent a gene family that functions to regulate signaling networks that have been conserved from flies to man. Overexpression of a constitutively active mutant of Rit in pheochromocytoma cells induces neurite outgrowth and survival by activating a MEK-dependent, but PI-3 kinase/Akt-independent, signaling pathway. In addition, activated Rit expression in primary neurons inhibits trophic factor-withdrawal induced apoptosis and promotes axonal outgrowth. Thus, Rit controls survival pathway(s) in a manner distinct from that of Ras, likely functioning to control MEK5/ERK5 signaling, or regulating a novel signaling pathway, which activates ERK kinases. We hypothesize that Rit functions to translate and direct neurotrophin-initiated signals to pro-survival signaling cascades in a manner distinct from Ras. Three specific aims are described to evaluate this hypothesis. Specific Aim 1 will determine if activation of Rit signaling pathways promotes the survival of primary cultured neurons and if Rit function is essential for neuronal cell survival. Specific Aim 2 will examine the extracellular stimuli that regulate Rit function, via neurotrophin-associated or neurotrophin-independent pathways. Specific Aim 3 will examine the mechanism of Rit-mediated ERK activation and determine if established ERK-dependent pro-survival signaling pathways are important for Rit-mediated neuronal survival. Preliminary studies have demonstrated that Drosophila is sensitive to altered Ric activity, resulting in developmental defects in the wing and eye. We will undertake a genetic screening approach to identify genes that interact with Ric, and vertebrate homologues will be analyzed for their ability to contribute to Rit function in neuronal cells. Through the combined use of biochemistry, molecular biology, and genetics, these studies will form the foundation for understanding the function of this unique regulator of neuronal survival.

描述（由申请人提供）：异常细胞凋亡导致各种神经退行性疾病。因此，阐明调节神经元存活的信号转导机制对于理解基础生物学和治疗干预都很重要。神经营养蛋白部分通过激活小 GTP 结合蛋白 Ras 来有效刺激神经元存活，Ras 通过将神经营养蛋白启动的信号翻译并引导到多个信号通路中发挥作用。最近的数据表明，Ras 依赖性信号通路、PI-3 激酶/Akt 和 MEK/ERK 以及 Ras 独立性 MEK5/ERK5 信号级联是神经营养蛋白依赖性生存的主要介质。我们发现了一组新颖的、进化上保守的 Ras 相关蛋白。人类至少有两种高度相关的基因（Rit 和 Rin），而果蝇仅表达一种家族成员（Ric）。这些蛋白质代表了一个基因家族，其功能是调节从果蝇到人类都保守的信号网络。在嗜铬细胞瘤细胞中过度表达 Rit 组成型活性突变体，通过激活 MEK 依赖性但 PI-3 激酶/Akt 独立的信号通路来诱导神经突生长和存活。此外，原代神经元中激活的 Rit 表达可抑制营养因子撤除诱导的细胞凋亡并促进轴突生长。因此，Rit 以与 Ras 不同的方式控制生存途径，可能起到控制 MEK5/ERK5 信号传导的作用，或调节激活 ERK 激酶的新信号传导途径。我们假设 Rit 的功能是以与 Ras 不同的方式将神经营养蛋白启动的信号翻译并引导至促生存信号级联。描述了三个具体目标来评估这一假设。具体目标 1 将确定 Rit 信号通路的激活是否会促进原代培养神经元的存活，以及 Rit 功能是否对于神经元细胞的存活至关重要。具体目标 2 将检查通过神经营养蛋白相关或神经营养蛋白独立途径调节 Rit 功能的细胞外刺激。具体目标 3 将检查 Rit 介导的 ERK 激活机制，并确定已建立的 ERK 依赖性促生存信号通路是否对 Rit 介导的神经元存活很重要。初步研究表明，果蝇对 Ric 活性的改变敏感，导致翅膀和眼睛的发育缺陷。我们将采用遗传筛选方法来识别与 Ric 相互作用的基因，并分析脊椎动物同源物对神经元细胞中 Rit 功能的贡献能力。通过生物化学、分子生物学和遗传学的结合使用，这些研究将为理解这种独特的神经元存活调节剂的功能奠定基础。