Differential signaling by insulin receptor substrate 1 (IRS-1) and IRS-2 in IRS-1-deficient cells.
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.
Brüning
J C
JC
Joslin Diabetes Center, Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA.
Winnay
J
J
Cheatham
B
B
Kahn
C R
CR
D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics; D051766:Early Growth Response Protein 1; D004789:Enzyme Activation; D005347:Fibroblasts; D051380:GRB2 Adaptor Protein; D005786:Gene Expression Regulation; D018014:Gene Transfer Techniques; D017781:Genes, Immediate-Early; D016762:Genes, fos / Q000235:genetics; D006801:Humans; D017874:Immediate-Early Proteins; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D018345:Mice, Knockout; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D016196:S Phase; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; C495949:Grb2 protein, mouse; C526292:IRS1 protein, human; C526297:IRS2 protein, human; D017874:Immediate-Early Proteins; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; D010750:Phosphoproteins; D011506:Proteins; D014157:Transcription Factors; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017871:Calcium-Calmodulin-Dependent Protein Kinases