INSULIN RECEPTORS AND MOLECULAR MECHANISMS OF INSULIN ACTION

胰岛素与其表面的受体结合， 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， 细胞内蛋白质我们调查了下游 导致GLUT 4葡萄糖转运的途径 在离体大鼠脂肪细胞中， 生理上重要的胰岛素作用靶细胞。使用 技术涉及大鼠脂肪细胞瞬时表达，我们有 以前证明IRS-1是一种底物， 参与介导胰岛素转运GLUT 4的作用， 磷脂酰肌醇3-激酶（PI 3-kinase） 活动也发挥了必要的作用，在调解这一行动， 胰岛素最近，我们以几种方式扩展了这些研究： (1)克隆编码鼠IRS-3的cDNA，IRS-3是 胰岛素受体底物家族;（2）证明小鼠 IRS-2、鼠IRS-3和人IRS-4可以在细胞内替代IRS-1， 介导GLUT 4的易位;（3）证明， 蛋白激酶B（也称为Akt）参与该途径 PI 3-激酶的下游。 在不同的研究中，我们有 发现了一个新的蛋白质家族， 受体，也与其他受体酪氨酸激酶。分选 连接蛋白1（Snx 1）最初是在吉尔的实验室克隆的， 据报道与表皮生长的细胞质尾部结合 因子受体我们将这一观察延伸到 这表明Snx 1也与几种其他受体结合， 在哺乳动物细胞中共表达，包括 胰岛素、血小板衍生生长因子、瘦素和转铁蛋白。在 此外，我们还克隆和表征了三个额外的 同源物：Snx 2、Snx 3和Snx 4。例如Snx 1、Snx 2和Snx 4 与受体酪氨酸激酶相关，但Snx 3不相关。 我们目前正在完成编码两个 其他分类连接蛋白：Snx 5和Snx 6。所有六个排序连接 含有一个保守的PX（NADPH氧化酶同源性）结构域， 大约100个氨基酸。此外，他们还接近 几种蛋白质（Vps 5 p，Grd 19 p和Mvp 1 p）的同源物， 参与酵母中蛋白质的运输。我们正在调查 在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.