Temporal and spatial regulation of signal transduction by Rab family small G proteins

Rab家族小G蛋白在哺乳动物细胞中由60多个不同的成员组成，是膜运输的关键调节因子。由于每个成员识别细胞内膜上的不同子集，因此该家族可能有助于各种细胞功能中信号转导的时间和空间调节。在这个项目中，我们分析了Rab蛋白在神经传递，细胞-细胞粘附和细胞生长中的功能。在神经传递方面，我们重点研究了Rab 3A及其相关蛋白对神经递质释放的调节作用。我们产生Rab 3 GAP p130缺陷小鼠，并使用小鼠表明，这种蛋白质通过调节Rab 3A在神经末梢的活性和易位在神经递质释放和突触可塑性中起着重要作用。在细胞间粘附方面，我们着重研究了粘附蛋白在上皮细胞间粘附位点的转运。我们先前发现Rabl 3调节整合粘附蛋白claudins和occludin向紧密连接的转运。在本项目中，我们鉴定了JRAB/MICAL-L2作为一种新的Rab 13效应蛋白，其定位于紧密连接，并发现Rab 13-JRAB系统的功能是建立紧密连接的形成。我们还发现，另一个Rab家族成员Rab 8也与JRAB相互作用，这种相互作用有助于通过调节E-钙粘蛋白（一种整合的粘附连接蛋白）的转运来组装粘附连接。至于细胞生长，我们表明，Rabring 7，我们已经确定为一种新的Rab 7效应蛋白，具有E3连接酶活性，这种蛋白质是参与EGF受体通过其E3连接酶活性的内吞运输。

The Rab family small G proteins, which consist of more than 60 different members in mammalian cells, are key regulators in membrane trafficking. Since each member recognizes distinct subsets on intracellular membranes, this family may contribute to temporal and spatial regulation of signal transduction in various cellular functions. In this project, we analyzed the functions of Rab proteins in neurotransmission, cell-cell adhesion, and cell growth. As to neurotransmission, we focused on the process of neurotransmitter release, which Rab3A and its related proteins regulate. We generated Rab3 GAP p130-deficient mice and showed using the mice that this protein plays important roles in neurotransmitter release and synaptic plasticity through regulation of the activity and translocation of Rab3A at the nerve endings. As to the cell-cell adhesion, we focused on the transport of the adhesion proteins to the cell-cell adhesion sites of the epithelial cells. We had previously found that Rabl3 regulates the transport of the integral adhesion proteins, claudins and occludin, to the tight junctions. In this project, we identified JRAB/MICAL-L2 as a novel Rabl3 effector protein, which localized to the tight junctions and found that the Rab13-JRAB system functions to establish the formation of the tight junctions. We moreover found that another Rab family member Rab8 also interacts with JRAB and that this interaction contributes to the assembly of adherens junctions through regulation of the transport of E-cadherin, an integral adherens junction protein. As to the cell growth, we showed that Rabring7, which we had identified as a novel Rab7 effector protein, has E3 ligase activity and that this protein is involved in the endocytic trafficking of EGF receptor through its E3 ligase activity.