Coordination of membrane traffic on the exocytic pathway through rab GEF and rab

描述(申请人提供)：膜交通是一系列基本的细胞功能所必需的，例如控制细胞表面受体的可及性、葡萄糖转运体对胰岛素的反应、抗原递呈、神经元传递以及上皮细胞极性的建立和维持。因此，膜交通的调节与包括癌症、糖尿病和神经变性在内的广泛的人类疾病直接相关。Rab GTP酶是膜交通的关键调节因子。通过招募和激活一组功能不同的效应器，单个Rab GTP酶可以协调给定的膜运输阶段的各种亚反应，包括囊泡萌发、传递、系留和融合。此外，我们的结果表明，相邻的运输阶段也可以通过协调的RAB调节来耦合。我们最近定义了一个Rab鸟嘌呤核苷酸交换因子级联，在这个级联中，一个Rab处于GTP结合的状态，招募沿着胞外途径激活下一个Rab的Gab。我们也有初步证据表明Rab GTPase激活蛋白(GAP)级联以逆流方式运行。在这里，下游的RAB招募了使上游RAB失活的缺口。净效应是Rab转换，其中给定的膜片开始标记一个Rab，但随着时间的推移，变得标记另一个Rab。由于每个RAB招募并激活一组不同的效应器，这导致膜的功能成熟。我们将更详细地探索这两个级联机制，并测试分离相邻的膜交通阶段的生理后果。我们将测试Sec4P效应器在陷阱组装中的作用，并探索几个新的假定的Sec4P效应器的作用。通过这些研究，我们将开始将胞外途径定义为一个完全协调的系统，而不是一个孤立的子反应的集合。膜运输是物质在细胞内不同隔室之间转移的机制，膜运输的调节与包括癌症、糖尿病和神经变性在内的一系列人类疾病直接相关。这项研究探讨了膜运输的不同阶段被协调调节的分子机制。

DESCRIPTION (provided by applicant): Membrane traffic is required for a broad range of essential cellular functions, such as controlling the accessibility of cell surface receptors, the translocation of glucose transporters in response to insulin, antigen presentation, neuronal transmission and the establishment and maintenance of epithelial cell polarity. Therefore, the regulation of membrane traffic is directly relevant to a broad range of human diseases including cancer, diabetes and neural degeneration. Rab GTPases are key regulators of membrane traffic. By recruiting and activating a functionally diverse set of effectors, a single Rab GTPase can coordinate the various sub- reactions within a given stage of membrane traffic, including vesicle budding, delivery, tethering and fusion. Furthermore, our results indicate that adjacent stages of transport can also be coupled through coordinated rab regulation. We recently defined a rab guanine nucleotide exchange factor (GEF) cascade in which one rab, in its GTP-bound state, recruits the GEF that activates the next rab along the exocytic pathway. We also have preliminary evidence for a rab GTPase activating protein (GAP) cascade operating in a counter current fashion. Here the downstream rab recruits the GAP that inactivates the upstream rab. The net effect is rab conversion in which a given patch of membrane starts out labeled with one rab, but over time becomes labeled with another rab. Since each rab recruits and activates a distinct set of effectors, this leads to a functional maturation of the membrane. We will explore these two cascade mechanisms in further detail and test the physiological consequences of uncoupling adjacent stages of membrane traffic. We will test the role of a Sec4p effector in SNARE assembly and explore the roles of several new putative Sec4p effectors. Through these studies we will begin to define the exocytic pathway as a fully coordinated system, rather than as a collection of isolated sub-reactions. Membrane traffic is the mechanism by which material is transferred between different compartments within the cell and the regulation of membrane traffic is directly relevant to a broad range of human diseases including cancer, diabetes and neural degeneration. This study addresses the molecular mechanisms by which different stages of membrane traffic are coordinately regulated.