MECHANISM OF INSULIN SIGNAL ON GLUCOSE TRANSPORT IN KNOCKOUT MICE

在胰岛素诱导的葡萄糖转运的主要靶点脂肪和肌肉组织中，已知葡萄糖转运蛋白同种型GLUT 4响应于胰岛素从大的细胞内池易位到细胞表面，尽管调节该过程的信号传导机制尚未完全理解。胰岛素可增强多种内源性底物的酪氨酸磷酸化，如胰岛素受体底物（IRS）-1，IRS-2，Grb 2相关结合物-1（GRB 1）和Shc。磷脂酰肌醇（PI）3-激酶在葡萄糖转运的胰岛素信号转导中起重要作用。胰岛素被认为通过与含磷酸酪氨酸的蛋白质如IRS-1和IRS-2以及pp 60结合来激活这种酶。为了研究脂肪细胞中内源性底物与葡萄糖转运之间的关系，我们分析了靶向破坏内源性底物基因IRS-1的小鼠。抗磷酸酪氨酸免疫沉淀中胰岛素刺激的PI 3-激酶活性是小鼠脂肪细胞中野生型PI 3-激酶活性的54.3%。Pp 60是主要的酪氨酸磷酸化蛋白，主要与PI 3-激酶相关，而IRS-2的酪氨酸磷酸化及其与该酶的相关性非常低。在这些细胞中，葡萄糖转运、葡萄糖转运和GLUT 4易位分别降低至野生型的52%和67.9%，胰岛素刺激葡萄糖转运的敏感性也受损。这些数据表明，1）IRS-1在胰岛素诱导的野生型小鼠脂肪细胞中GLUT 4易位中起主要作用，2）在IRS-1不存在的情况下，pp 60通过PI 3-激酶的活化参与该过程。

In adipose and muscle tissue, the major targets of insulin-induced glucose transport, it is known that glucose transporter isoform GLUT4 translocates from a large intracellular pool to the cell surface in response to insulin, although the signaling mechanism regulating this process is not fully understood. Insulin enhances tyrosine phosphorylation of several endogenous substrates such as insulin receptor substrate (IRS)-1, IRS-2, Grb2-associated binder-1 (GRB1) and Shc. Phosphatidylinositol (PI) 3-kinase play the important role for insulin signal transduction on glucose transport. Insulin is thought to activated this enzyme via binding to phosphotyrosine-containing proteins such as IRS-1 and IRS-2 and pp60. To investigate the relationship between endogenous substrates and glucose transport in adipose cells, we analyzed mice with targeted disruption of the endogenous substrate gene, IRS-1. Insulin-stimulated PI 3-kinase activity in the antiphosphotyrosine immnoprecipitates is 54.3 % of wild type in adipose cells from the mice. Pp60 was the major tyrosine phosphorylated protein and predominantly associated with PI 3-kinase, whereas tyrosine phosphorylation of IRS-2 and its association with this enzyme are very low. In these cells, glucose transport, glucose transport and GLUT4 translocation are decreased to 52 % and 67.9 % of those from wild-type, respectively, sensitivity of insulin to stimulate glucose transport was also impaired. These data suggested that 1) IRS-1 plays a major role in insuln-induced translocation of GLUT4 in adipose cells from wild-type mice, and 2) pp60 takes in this process via activation of PI 3-kinase in the absence of IRS-1.