Solow B T, Harada S, Goldstein B J, Smith J A, White M F, Jarett L
Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
Mol Endocrinol. 1999 Oct;13(10):1784-98. doi: 10.1210/mend.13.10.0361.
In response to insulin, tyrosine kinase activity of the insulin receptor is stimulated, leading to autophosphorylation and tyrosine phosphorylation of proteins including insulin receptor subunit (IRS)-1, IRS-2, and Shc. Phosphorylation of these proteins leads to activation of downstream events that mediate insulin action. Insulin receptor kinase activity is requisite for the biological effects of insulin, and understanding regulation of insulin receptor phosphorylation and kinase activity is essential to understanding insulin action. Receptor tyrosine kinase activity may be altered by direct changes in tyrosine kinase activity, itself, or by dephosphorylation of the insulin receptor by protein-tyrosine phosphatases. After 1 min of insulin stimulation, the insulin receptor was tyrosine phosphorylated 8-fold more and Shc was phosphorylated 50% less in 32D cells containing both IRS-1 and insulin receptors (32D/IR+IRS-1) than in 32D cells containing only insulin receptors (32D/IR), insulin receptors and IRS-2 (32D/IR+IRS-2), or insulin receptors and a form of IRS-1 that cannot be phosphorylated on tyrosine residues (32D/IR+IRS-1F18). Therefore, IRS-1 and IRS-2 appeared to have different effects on insulin receptor phosphorylation and downstream signaling. Preincubation of cells with pervanadate greatly decreased protein-tyrosine phosphatase activity in all four cell lines. After pervanadate treatment, tyrosine phosphorylation of insulin receptors in insulin-treated 32D/IR, 32D/ IR+IRS-2, and 32D/IR+IRS-1F18 cells was markedly increased, but pervanadate had no effect on insulin receptor phosphorylation in 32D/IR+IRS-1 cells. The presence of tyrosine-phosphorylated IRS-1 appears to increase insulin receptor tyrosine phosphorylation and potentially tyrosine kinase activity via inhibition of protein-tyrosine phosphatase(s). This effect of IRS-1 on insulin receptor phosphorylation is unique to IRS-1, as IRS-2 had no effect on insulin receptor tyrosine phosphorylation. Therefore, IRS-1 and IRS-2 appear to function differently in their effects on signaling downstream of the insulin receptor. IRS-1 may play a major role in regulating insulin receptor phosphorylation and enhancing downstream signaling after insulin stimulation.
胰岛素作用下，胰岛素受体的酪氨酸激酶活性被激活，导致自身磷酸化以及包括胰岛素受体底物（IRS）-1、IRS-2和Shc在内的蛋白质的酪氨酸磷酸化。这些蛋白质的磷酸化会引发下游事件的激活，从而介导胰岛素的作用。胰岛素受体激酶活性对于胰岛素的生物学效应是必需的，理解胰岛素受体磷酸化和激酶活性的调节对于理解胰岛素作用至关重要。受体酪氨酸激酶活性可能通过酪氨酸激酶活性本身的直接变化，或通过蛋白酪氨酸磷酸酶对胰岛素受体的去磷酸化而改变。胰岛素刺激1分钟后，同时含有IRS-1和胰岛素受体的32D细胞（32D/IR+IRS-1）中，胰岛素受体的酪氨酸磷酸化程度比仅含有胰岛素受体的32D细胞（32D/IR）、含有胰岛素受体和IRS-2的32D细胞（32D/IR+IRS-2）或含有胰岛素受体和一种酪氨酸残基不能被磷酸化的IRS-1形式的32D细胞（32D/IR+IRS-1F18）高8倍，而Shc的磷酸化程度低50%。因此，IRS-1和IRS-2对胰岛素受体磷酸化和下游信号传导似乎有不同的影响。用过钒酸钠对细胞进行预孵育可大大降低所有四种细胞系中的蛋白酪氨酸磷酸酶活性。用过钒酸钠处理后，胰岛素处理的32D/IR、32D/IR+IRS-2和32D/IR+IRS-1F18细胞中胰岛素受体的酪氨酸磷酸化显著增加，但过钒酸钠对32D/IR+IRS-1细胞中的胰岛素受体磷酸化没有影响。酪氨酸磷酸化的IRS-1的存在似乎通过抑制蛋白酪氨酸磷酸酶来增加胰岛素受体酪氨酸磷酸化，并可能增加酪氨酸激酶活性。IRS-1对胰岛素受体磷酸化的这种作用是IRS-1特有的，因为IRS-2对胰岛素受体酪氨酸磷酸化没有影响。因此，IRS-1和IRS-2在对胰岛素受体下游信号传导的影响上似乎发挥着不同的作用。IRS-1可能在胰岛素刺激后调节胰岛素受体磷酸化和增强下游信号传导中起主要作用。
