INSULIN RECEPTORS AND MOLECULAR MECHANISMS OF INSULIN ACTION

胰岛素与细胞表面的受体结合。 靶细胞，从而激活胰岛素受体酪氨酸激酶。 激活的受体磷酸化酪氨酸残基 胞内蛋白质。我们已经对下游进行了调查 GLUT4葡萄糖转位的最终途径 分离的大鼠脂肪细胞的质膜转运蛋白 胰岛素作用的重要生理靶细胞。使用 在大鼠脂肪细胞中瞬时表达的技术，我们有 此前证明，IRS-1是一种底物 参与了胰岛素对GLUT4移位的调节作用， 以及磷脂酰肌醇3-激酶(PI-3-Kinase)的激活 活动也在调解这一行动中发挥了必要的作用 胰岛素。最近，我们从几个方面扩展了这些研究： (1)克隆小鼠IRS-3的编码基因 胰岛素受体底物家族；(2)证明小鼠 IRS-2、小鼠IRS-3和人IRS-4可以替代IRS-1 介导GLUT4的易位；(3)证明 蛋白激酶B(也称为Akt)参与了这一途径 在PI3-激酶下游。在单独的研究中，我们有 发现了一组与胰岛素相关的新蛋白质家族 受体，也与其他受体酪氨酸激酶。分选 Nexin 1(Snx1)最初是在吉尔的实验室克隆的， 据报道，结合到细胞质尾部的表皮生长 因子受体。我们通过以下方式扩展了这一观察 展示了当Snx1与其他几种受体结合时 在哺乳动物细胞中共表达，包括受体 胰岛素、血小板衍生生长因子、瘦素和转铁蛋白。在……里面 此外，我们已经克隆并鉴定了另外三个 同源基因：Snx2、Snx3和Snx4。如Snx1、Snx2和Snx4 与受体酪氨酸激酶相关，而Snx3不与之相关。 我们目前正在完成编码两个 额外的分类连接：Snx5和Snx6。所有六个排序连接项 包含一个保守的Px(NADPH氧化酶同源)结构域 大约100个氨基酸。此外，他们的关系很密切 几种蛋白质(Vps5p、Grd19p和Mvp1p)的同源物 参与酵母中的蛋白质运输。我们正在调查这个角色 哺乳动物细胞中的分类连接蛋白，重点是 可能与胰岛素受体的功能有关。

Insulin binds to its receptor on the surface of the target cell, thereby activating the insulin receptor tyrosine kinase. The activated receptor phosphorylates tyrosine residues in multiple intracellular proteins. We have investigated the downstream pathway that eventuates in translocation of GLUT4 glucose transporters to the plasma membrane in isolated rat adipocytes, a physiologically important target cell for insulin action. Using an technique involving transient expression in rat adipocytes, we have previously demonstrated that IRS-1 is one of the substrates which participates in mediating the effect of insulin to translocate GLUT4, and that activation of phosphatidyl inositol 3-kinase (PI 3-kinase) activity also plays a necessary role in mediating this action of insulin. Recently, we have extended these studies in several ways: (1) cloning the cDNA encoding murine IRS-3, another member of the insulin receptor substrate family; (2) demonstrating that murine IRS-2, murine IRS-3, and human IRS-4 can substitute for IRS-1 in mediating the translocation of GLUT4; (3) demonstrating that protein kinase B (also known as Akt) participates in this pathway downstream from PI 3-kinase. In separate studies, we have identified a family of novel proteins that associate with the insulin receptor, and also with other receptor tyrosine kinases. Sorting nexin 1 (Snx1) was originally cloned in Gill's laboratory and reported to bind to the cytoplasmic tail of the epidermal growth factor receptor. We have extended this observation by demonstrating the Snx1 also binds to several other receptors when co-expressed in mammalian cells, including the receptors for insulin, platelet-derived growth factor, leptin, and transferrin. In addition, we have cloned and characterized three additional homologs: Snx2, Snx3, and Snx4. Like Snx1, Snx2 and Snx4 associate with receptor tyrosine kinases although Snx3 does not. We are currently completing the cloning of cDNA's encoding two additional sorting nexins: Snx5 and Snx6. All six sorting nexins contain a conserved PX (NADPH oxidase homology) domain of approximately 100 amino acids. In addition, they are close homologs of several proteins (Vps5p, Grd19p, and Mvp1p) that are involved in protein trafficking in yeast. We are investigating the role of the sorting nexins in mammalian cells, with emphasis upon possible relationships to the function of insulin receptors.