G protein-dependent vectorial transportation of receptors, ion channels, and transporters

G蛋白偶联或酪氨酸激酶连接的受体参与许多信号转导的调节。在这些膜受体的刺激下，不仅受体分子本身，而且离子通道或转运体也通过内吞途径内化到细胞内。因此，在膜运输中存在着媒介运输。在本研究中，我们研究了这些受体调节载体转运的分子机制。主要研究结果如下：1)不同类型的膜受体，如G蛋白偶联受体和酪氨酸激酶连接受体，协同激活脂蛋白激酶磷脂酰肌醇(PI)3-OH激酶。我们发现I类(p110β亚型)PI3-OH激酶负责协同刺激，其接头Gab2通过Src酪氨酸激酶和ERK的双重磷酸化参与信号转导。2)小G蛋白转运酶Rab家族参与膜转运途径。我们已经确定RIN家族的新成员是Rab5的鸟嘌呤核苷酸交换因子(GEF)。RIN家族包含许多功能结构域，如SH2、Pro富集区(与SH3结合)、Vps9(环境基金)和RA(RAS结合)，在内吞途径的早期阶段似乎扮演着接头或支架蛋白的角色。3)我们还发现了一个新的Ras样小GTP酶家族Di-Ras、Rheb，它们可能参与了膜转运途径。Rheb在培养细胞中的表达诱导了细胞质大空泡的形成，这些大空泡的特征是晚内吞(晚内吞体样和溶酶体样)成分。Rheb似乎调节神经胶质细胞中谷氨酸转运体的内化。

G protein-coupled or tyrosine kinase-linked receptors are involved in the regulations of many signal transductions. After the stimulation of these membrane receptors, not only the receptor molecules themselves but also ion channels or transporters are internalized into the cells through endocytic pathways. Thus, there is vectorial transportation in the membrane trafficking. In this study, we investigated the molecular mechanisms whereby these receptors regulate the vectorial transportation.The major findings obtained in this study are summarized as follows.1) The lipid kinase phosphatidylinositol (PI) 3-OH kinase is synergistically stimulated by different types of membrane receptors, such as G protein-coupled and tyrosine kinase-linked receptors. We have found that the class I (p110beta subtype) PI 3-OH kinase is responsible for the synergistic stimulation and that its adaptor, Gab2, is involved in the signaling through its dual phosphorylation by Src tyrosine kinase and ERK. 2) The small GTPase Rab family are involved in membrane trafficking pathways. We have identified novel members of the RIN family as guanine nucleotide-exchange factors (GEFs) for Rab5. The RIN family, which contains many functional domains, such as SH2, Pro-rich region (binding to SH3), Vps9 (GEF), and RA (Ras-association), appear to act as adaptors or scaffold proteins in early steps of the endocytic pathway. 3) We have also identified novel family of Ras-like small GTPases, Di-Ras, Rheb, which might be involved in membrane trafficking pathways. Rheb expression in culture cells induced formation of the cytoplasmic large vacuoles, which are characterized as late endocytic (late endosome-and lysosome-like) components. Rheb appears to regulate the internalization of glutamate transporter in glial cells.