Brüning J C, Winnay J, Cheatham B, Kahn C R
Joslin Diabetes Center, Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA.
Mol Cell Biol. 1997 Mar;17(3):1513-21. doi: 10.1128/MCB.17.3.1513.
Mice made insulin receptor substrate 1 (IRS-1) deficient by targeted gene knockout exhibit growth retardation and abnormal glucose metabolism due to resistance to the actions of insulin-like growth factor 1 (IGF-1) and insulin (E. Araki et al., Nature 372:186-190, 1994; H. Tamemoto et al., Nature 372:182-186, 1994). Embryonic fibroblasts and 3T3 cell lines derived from IRS-1-deficient embryos exhibit no IGF-1-stimulated IRS-1 phosphorylation or IRS-1-associated phosphatidylinositol 3-kinase (PI 3-kinase) activity but exhibit normal phosphorylation of IRS-2 and Shc and normal IRS-2-associated PI 3-kinase activity. IRS-1 deficiency results in a 70 to 80% reduction in IGF-1-stimulated cell growth and parallel decreases in IGF-1-stimulated S-phase entry, PI 3-kinase activity, and induction of the immediate-early genes c-fos and egr-1 but unaltered activation of the mitogen-activated protein kinases ERK 1 and ERK 2. Expression of IRS-1 in IRS-1-deficient cells by retroviral gene transduction restores IGF-1-stimulated mitogenesis, PI 3-kinase activation, and c-fos and egr-1 induction in proportion to the level of reconstitution. Increasing the level of IRS-2 in these cells by using a retrovirus reconstitutes IGF-1 activation of PI 3-kinase and immediate-early gene expression to the same degree as expression of IRS-1; however, IRS-2 overexpression has only a minor effect on IGF-1 stimulation of cell cycle progression. These results indicate that IRS-1 is not necessary for activation of ERK 1 and ERK 2 and that activation of ERK 1 and ERK 2 is not sufficient for IGF-1-stimulated activation of c-fos and egr-1. These data also provide evidence that IRS-1 and IRS-2 are not functionally interchangeable signaling intermediates for stimulation of mitogenesis despite their highly conserved structure and many common functions such as activating PI 3-kinase and early gene expression.
通过靶向基因敲除使胰岛素受体底物1（IRS-1）缺失的小鼠，由于对胰岛素样生长因子1（IGF-1）和胰岛素的作用产生抵抗，表现出生长迟缓以及葡萄糖代谢异常（E. 荒木等人，《自然》372:186 - 190，1994；H. 为元本等人，《自然》372:182 - 186，1994）。源自IRS-1缺陷胚胎的胚胎成纤维细胞和3T3细胞系，未表现出IGF-1刺激的IRS-1磷酸化或与IRS-1相关的磷脂酰肌醇3激酶（PI 3激酶）活性，但IRS-2和Shc的磷酸化正常，且与IRS-2相关的PI 3激酶活性正常。IRS-1缺陷导致IGF-1刺激的细胞生长减少70%至80%，同时IGF-1刺激的S期进入、PI 3激酶活性以及即刻早期基因c-fos和egr-1的诱导也相应减少，但丝裂原活化蛋白激酶ERK 1和ERK 2的激活未改变。通过逆转录病毒基因转导在IRS-1缺陷细胞中表达IRS-1，可恢复IGF-1刺激的有丝分裂、PI 3激酶激活以及c-fos和egr-1诱导，且与重组水平成比例。通过使用逆转录病毒增加这些细胞中IRS-2的水平，可使PI 3激酶的IGF-1激活和即刻早期基因表达恢复到与IRS-1表达相同的程度；然而，IRS-2的过表达对IGF-1刺激的细胞周期进程仅有轻微影响。这些结果表明，IRS-1对于ERK 1和ERK 2的激活并非必需，且ERK 1和ERK 2的激活不足以实现IGF-1刺激的c-fos和egr-1激活。这些数据还提供了证据，表明尽管IRS-1和IRS-2结构高度保守且具有许多共同功能，如激活PI 3激酶和早期基因表达，但它们在刺激有丝分裂方面并非功能上可互换的信号中间体。
