Kristiansen S, Ramlal T, Klip A
Copenhagen Muscle Research Centre, August Krogh Institute, 13 Universitetsparken, DK-2100 Copenhagen, Denmark.
Biochem J. 1998 Oct 15;335 ( Pt 2)(Pt 2):351-6. doi: 10.1042/bj3350351.
Insulin stimulates the rate of glucose transport into muscle and adipose cells by translocation of glucose transporter (GLUT4)-containing vesicles from an intracellular storage pool to the surface membrane. This event is mediated through the insulin receptor substrates (IRSs), which in turn activate phosphatidylinositol (PI) 3-kinase isoforms. It has been suggested that insulin causes attachment of PI 3-kinases to the intracellular GLUT4-containing vesicles in rat adipose cells. Furthermore, it has also been shown that GLUT4-containing vesicles in adipose cells contain a PI 4-kinase. In the present study we investigate whether GLUT4-containing vesicles isolated from rat skeletal muscle display PI 3-kinase and/or PI 4-kinase activities. Insulin stimulation caused a rapid increase (5-15-fold increase compared with control) in the intracellular cytosolic IRS-1-associated PI-3 kinase activity. This PI 3-kinase activity was also present in a membrane preparation containing the insulin-regulatable pool of GLUT4 transporters. However, when GLUT4-containing vesicles were isolated by immunoprecipitation from basal and insulin-stimulated (3 min) skeletal muscle, the vesicles displayed PI 4-kinase, but not PI 3-kinase, activity. Insulin did not regulate the PI 4-kinase activity in the GLUT4-containing vesicles. In conclusion, GLUT4-containing vesicles from rat skeletal muscle contain a PI 4-kinase, but not a PI 3-kinase. It is suggested that, in skeletal muscle, insulin causes activation of the IRS/PI 3-kinase complex in an intracellular membrane compartment associated closely with the GLUT4-containing vesicles, but not in the GLUT4-containing vesicles themselves.
胰岛素通过将含葡萄糖转运蛋白4（GLUT4）的囊泡从细胞内储存池转运至表面膜，刺激葡萄糖转运到肌肉和脂肪细胞的速率。这一过程由胰岛素受体底物（IRSs）介导，而胰岛素受体底物又会激活磷脂酰肌醇（PI）3-激酶同工型。有人提出胰岛素可使PI 3-激酶附着于大鼠脂肪细胞内含有GLUT4的囊泡上。此外，也已表明脂肪细胞中含GLUT4的囊泡含有一种PI 4-激酶。在本研究中，我们探究从大鼠骨骼肌分离出的含GLUT4的囊泡是否具有PI 3-激酶和/或PI 4-激酶活性。胰岛素刺激导致细胞内胞质中与IRS-1相关的PI-3激酶活性迅速增加（与对照组相比增加了5至15倍）。这种PI 3-激酶活性也存在于含有可被胰岛素调节的GLUT4转运蛋白池的膜制剂中。然而，当通过免疫沉淀从基础状态和胰岛素刺激（3分钟）的骨骼肌中分离出含GLUT4的囊泡时，这些囊泡显示出PI 4-激酶活性，但没有PI 3-激酶活性。胰岛素并未调节含GLUT4的囊泡中的PI 4-激酶活性。总之，大鼠骨骼肌中含GLUT4的囊泡含有一种PI 4-激酶，但不含PI 3-激酶。有人提出，在骨骼肌中，胰岛素会使IRS/PI 3-激酶复合物在与含GLUT4的囊泡紧密相关的细胞内膜区室中被激活，而不是在含GLUT4的囊泡本身中被激活。
