Function of the Ras Related Ral Proteins

描述(由申请人提供)：本提案的总体目标是更好地了解RAS相关的Ral-GTP酶家族的功能。Rala和RalB参与多种细胞功能，包括控制囊泡分选、基因表达和细胞增殖。作为GTP酶，Ral蛋白作为分子开关将细胞外信号传递到特定的细胞内信号级联。在细胞中，RAL蛋白通过与一类RAL特异性鸟嘌呤核苷酸交换因子(RAL-GEF)相互作用而达到活性GTP结合状态。有一类Ral-GEF与GTP结合的RAS结合并被激活，越来越多的证据支持这样的观点，即升高的Ral-Global/Ral信号具有促进人类肿瘤发生的潜力。这项提案将试图揭示两个新确定的过程背后的机制，通过这两个过程对全球环境基金和全球DS进行监管。其中一个过程通过与PDK1蛋白激酶的相互作用正向调节ral-gef的活性，另一个过程通过蛋白激酶D介导的磷酸化负向调节ral-gef的活性。 活性GTP结合的Ral蛋白结合并改变一组下游“效应器”蛋白的活性，从而影响细胞过程。这项建议的研究将在我们最近发现的基础上展开，Rala而不是RalB通过其新发现的效应器--外囊，并可能通过一种不依赖于外囊的机制，提高膜蛋白向上皮细胞基侧表面的递送速度，从而在维持细胞极性方面发挥作用。因此，一组目标是确定这两个密切相关的AL家族成员活动差异的生化基础。另一个目标是确定参与基底侧膜递送的额外的Rala“效应器”。我们还计划确定Rala与外囊或其他RAL效应器结合如何促进MDCK上皮细胞的膜转运。了解ral在这一过程中的功能非常重要，因为膜蛋白的错误传递和极化可能会导致严重的疾病，包括囊性纤维化、I细胞疾病、家族性、多囊肾病，甚至可能是癌症。 最后，人们越来越认识到，Ral-GEF通过独立于其激活GTP酶的能力的机制来促进GTP酶的下游信号传递。因此，这项建议的另一个目的是评估Ral-环境基金结合蛋白在细胞过程中贡献功能的能力，这些功能补充了由Ral-环境基金/Ral信号级联介导的细胞过程中活跃的Ral的功能。

DESCRIPTION (provided by applicant): The overall goal of this proposal is to gain a better understanding of the functions of the Ras related Ral- GTPase family. RalA and RalB have been implicated in diverse cell functions including the control of vesicle sorting, gene expression and cell proliferation. As GTPases, Ral proteins function as molecular switches to transmit extracellular signals to specific intracellular signaling cascades. Ral proteins reach the active GTP bound state in cells by interacting with one of a family of Ral-specific guanine nucleotide exchange factors (Ral-GEFs). One class of Ral-GEFs binds to and is activated by GTP-bound Ras, and a growing body of evidence supports the idea that elevated Ral-GEF/Ral signaling has the potential to contribute to human oncogenesis. This proposal will attempt to reveal the mechanisms underlying two newly identified processes by which the Ral-GEF, Ral-GDS, is regulated. One process positively regulates Ral-GEF activity through interaction with the PDK1 protein kinase, and the other negatively regulates Ral-GEF activity through protein kinase D-mediated phosphorylation. Active GTP-bound Ral proteins bind to and alter the activity of a set of downstream "effector" proteins to influence cellular processes. Studies in this proposal will expand upon our recent finding that RalA but not RalB functions in the maintenance of cellular polarity by enhancing the rate of delivery of membrane proteins to the basolateral surface of epithelial cells through its newly identified effector, the exocyst, and possibly through an exocyst-independent mechanism. Thus, one set of goals is to define the biochemical basis for the difference in activities of these two closely related Ral family members. Another goal is to identify the additional RalA "effector" that participates in basolateral membrane delivery. We also plan to define how RalA binding to the exocyst or other Ral effectors promotes membrane delivery in MDCK epithelial cells. Understanding how Ral functions in this process is important because faulty delivery and polarization of membrane proteins can lead to serious diseases including cystic fibrosis, I cell disease, familial, polycystic kidney disease and possibly cancer. Finally, there is a growing appreciation that Ral-GEFs contribute to downstream signaling from GTPases by mechanisms that are independent from their ability to activate GTPases. Therefore, another aim of this proposal is to evaluate the contribution of Ral-GEF binding proteins for their ability to contribute functions that complement those of active Ral in cell processes mediated by the Ral-GEF/Ral signaling cascade.