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- GTPase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。Ral蛋白通过与Ral特异性鸟嘌呤核苷酸交换因子（Ral- gef）家族中的一个相互作用，在细胞中达到活性GTP结合状态。一类al- gef与gtp结合的Ras结合并被其激活，越来越多的证据支持这一观点，即升高的al- gef /Ral信号传导有可能促进人类肿瘤的发生。本提案将试图揭示两个新发现的过程背后的机制，这些过程是对Ral-GEF和Ral-GDS进行监管的。一个过程通过与PDK1蛋白激酶相互作用正向调节Ral-GEF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活性。

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.