Dissection of the Mechanism of Obesity-induced Insullin Resistance

胰岛素受体亚基-1（IRS-1）是胰岛素受体和IGF-1受体酪氨酸激酶的主要底物。酪氨酸磷酸化的IRS-1与参与葡萄糖转运蛋白转位的磷脂酰肌醇3-激酶85 K亚基和参与p2 l * 和MAP激酶级联反应的src同源蛋白（ASH）/Grb 2结合。为了阐明IRS-1在体内的生理作用，我们制作了具有IRS-1基因位点靶向破坏的小鼠。IRS-I基因靶向破坏的纯合子小鼠出生时存活，但胚胎和出生后生长迟缓。他们也对胰岛素的降糖作用有抵抗力。这些数据表明胰岛素和IGF_s的信号转导存在IRS-1依赖性和IRS-1非依赖性途径（Tmemoto等人，Nature 372：182-186，1994）。我们检测了野生型和IRS-1缺陷型小鼠肝脏中胰岛素刺激的酪氨酸磷酸化蛋白， 关于我们 ce.在IRS-1缺陷小鼠的肝脏中，胰岛素对190-kDa蛋白质（ppl 90）的酪氨酸磷酸化显著刺激，这在野生型小鼠中除了IRS-1外观察到微弱。我们还证明pp 190在免疫学上与IRS-1不同，并且与磷脂酰肌醇3-激酶的85-kDa亚基和IRS-1的Grb 2/Ash分子相关。我们确定pp 190作为胰岛素受体激酶（IRS-2）的一种新型底物，它可以结合PI 3-激酶和Ash/Grb 2，并且其酪氨酸磷酸化在IRS-1缺陷小鼠中特异性诱导。这些数据表明，pp 19 O可能在胰岛素的信号转导中发挥某些生理作用;此外，pp 19 O的酪氨酸磷酸化的诱导可能是IRS-1缺陷小鼠中替代IRS-1的代偿机制之一（Tobe et al.，270：5698-5701，1995）。我们进一步研究了IRS-1和IRS-2在胰岛素生理靶器官的生物学作用中的作用，通过比较胰岛素在野生型和IRS-1缺陷小鼠中的作用。在IRS-1缺陷小鼠的肌肉中，对胰岛素诱导的P13激酶激活、葡萄糖转运、p70 S6激酶和MAP激酶激活的反应。与野生型小鼠相比，mRNA翻译和蛋白质合成显著受损。在野生型和IRS-I缺陷小鼠中，胰岛素诱导的蛋白质合成对渥曼青霉素既敏感又不敏感。然而，在另一个靶器官，肝脏，胰岛素诱导的P13激酶和MAP激酶激活的反应没有显着降低。在肝脏中，酪氨酸磷酸化的IRS-2（IRS-1缺陷小鼠）的量与IRS-1（野生型小鼠）的量大致相等，而肌肉中的IRS-2的量仅为IRS-1的20%至30%。结论：（i）IRS-1在胰岛素在肌肉中的两个主要生物学作用，即葡萄糖转运和蛋白质合成中起着中心作用;（ii）胰岛素抵抗

Insulin receptor subustrate-1(IRS-1) is the major substrate of insulin receptor and IGF-l receptor tyrosine kinases. Tyrosine-phosphorylated IRS-1 binds the 85K subunit of phosphatidylinositol 3-kinase which may be involved in the translocation of glucose transporters and the abundant src homology protein (ASH) / Grb2 which may be involved in activationn of p2l* and MAP kinase cascade. To clarify the physiological roles of IRS-1 in vivo, we made mice with a targeted disruption of the IRS-1 gene locus. Mice homozygous for targeted disruption of the IRS-I gene were born alive but were retarded in embryonal and postnatal growth. They also had resistance to the glucose-lowering effects of insulin. These data suggest the existence of both IRS-1-dependent and IRS-1-independent pathways for signal transduction of insulin and IGF_s (Tmemoto et al., Nature 372 : 182-186, 1994). We have examined the insulin-stimulated tyrosine-phosphorylated proteins in livers of wild type and IRS-1-deficient mi … More ce. Tyrosine phosphorylation of an 190-kDa protein (ppl9O) by insulin was significantly stimulated in livers of IRS-1-deftcient mice, which was weakly observed in wild type mice in addition to IRS-1. We also demonstrated that pp190 was immunologically distinct from IRS-1 and was associated with both the 85-kDa subunit of phosphatidylinositol 3-kinase and the Grb2/Ash molecule as IRS-1. We identified pp190 as a novel substrate for insulin receptor kinase (IRS-2), which can bind both PI3-kinase and Ash/Grb2, and whose tyrosine phosphorylation is specifically induced in IRS-1-deficient mice. These data suggested that pp19O may play some physiological roles in insulin's signal transduction ; furthermore, induction of tyrosine phosphorylation of pp19O may be one of the compensatory mechanisms that substitute for IRS-1 in IRS-1-deficient mice (Tobe et al., I.Biob Chem. 270 : 5698-5701, 1995). We further investigated the roles of IRS-1 and IRS-2 in the biological actions in the physiological target organs of insulin by comparing the effects of insulin in wild-type and IRS-1-deficient mice. In muscles from IRS-1-deficient mice, the responses to insulin-induced P13-kinase activation, glucose transport, p70 S6 kinase and MAP kinase activation. mRNA translation, and protein synthesis were significantly impaired compared with those in wild-type mice. Insulin-induced protein synthesis was both wortmannin sensitive and insensitive in wild-type and IRS-I-deficient mice. However, in another target organ, the liver, the responses to insulin-induced P13-kinase and MAP kinase activation were not significantly reduced. The amount of tyrosine-phosphorylated IRS-2 (in IRS-1-deficient mice) was roughly equal to that of IRS-1 (in wild-type mice) in the liver, whereas it was only 20 to 30% of that of IRS-1 in the muscles. In counclusion, (i) IRS-1 plays central roles in two major biological actions of insulin in muscles, glucose transport and protein synthesis ; (ii) the insulin resistance Less