Comparison of the insulin and insulin-like growth factor 1 mitogenic intracellular signaling pathways

Endocrinology. 1996 Oct;137(10):4427-34. doi: 10.1210/endo.137.10.8828504.


We compared the intracellular insulin-like growth factor-1 (IGF-1) and insulin signaling pathways in Rat1 fibroblasts expressing the equivalent number of insulin receptors and endogenous IGF-1 receptors. Insulin and IGF-1 stimulated tyrosine phosphorylation of IRS-1 and Shc in a similar dose- and time-dependent manner. The time course of Shc phosphorylation by both IGF-1 and insulin was slower than that of IRS-1. Both phosphorylated IRS-1 and Shc associated with Grb2.Sos complexes, leading to p21ras activation. To compare the functional importance of p21ras for IGF-1-and insulin-induced DNA synthesis, single cell microinjection studies were performed. BrdU incorporation into newly synthesized DNA was measured by immunofluorescence microscopy to assess the functional importance of p21ras. Both IGF-1 and insulin stimulated BrdU incorporation, but the effect of IGF-1 was greater. Microinjection of anti-p21ras antibody completely inhibited both IGF-1-and insulin-induced DNA synthesis, indicating the central role of p21ras in signaling by both hormones. Signal transduction from these receptors to Grb2.Sos complexes can occur through IRS-1 and/or Shc. To assess these two possible pathways, we performed Western blots for Grb2 in anti-Shc and anti-IRS-1 immunoprecipitates and found that 5-fold more Grb2 was associated with Shc than with IRS-1 after either IGF-1 or insulin stimulation. Microinjection of anti-Shc antibody inhibited IGF-1 and insulin stimulation of DNA synthesis by 78% and 74%, respectively. By microinjecting Shc subdomains of GST fusion proteins, we found that Shc N-terminus, but not the Shc SH2, was the functionally important domain through which Shc interacts with IGF-1 and insulin receptors. Insulin stimulation caused hyperphosphorylation and decreased electrophoretic mobility of Sos, and a similar effect was seen with IGF-1, although the time course was delayed compared with insulin. Finally, IGF-1 activated mitogen-activated proten kinase activity more effectively than insulin. These data indicate that Shc, rather than IRS-1, appears to be the predominant functional link to Grb2.Sos complexes from the IGF-1 receptor, as it is from the insulin receptor. Although IGF-1 and insulin stimulate cell cycle progression with similar coupling mechanisms from the receptor to Shc, to Grb2.Sos, to p21ras, the delayed IGF-1 induced mobility shift of Sos could lead to, at least in part, more efficient coupling to mitogen-activated protein kinase. These findings might explain the greater mitogenic activity of IGF-1 compared with insulin.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing*
  • Adaptor Proteins, Vesicular Transport*
  • Animals
  • Antibodies / immunology
  • Fibroblasts / metabolism
  • GRB2 Adaptor Protein
  • Glutathione Transferase / genetics
  • Humans
  • Insulin / physiology*
  • Insulin Receptor Substrate Proteins
  • Insulin-Like Growth Factor I / physiology*
  • Intracellular Membranes / metabolism*
  • Microinjections
  • Mitogens / physiology*
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Proteins / genetics
  • Proteins / immunology
  • Proteins / metabolism
  • Proto-Oncogene Proteins p21(ras) / immunology
  • Rats
  • Recombinant Fusion Proteins / pharmacology
  • Shc Signaling Adaptor Proteins
  • Signal Transduction*
  • Src Homology 2 Domain-Containing, Transforming Protein 1
  • Swine


  • Adaptor Proteins, Signal Transducing
  • Adaptor Proteins, Vesicular Transport
  • Antibodies
  • GRB2 Adaptor Protein
  • GRB2 protein, human
  • Grb2 protein, rat
  • IRS1 protein, human
  • Insulin
  • Insulin Receptor Substrate Proteins
  • Irs1 protein, rat
  • Mitogens
  • Phosphoproteins
  • Proteins
  • Recombinant Fusion Proteins
  • SHC1 protein, human
  • Shc Signaling Adaptor Proteins
  • Shc1 protein, rat
  • Src Homology 2 Domain-Containing, Transforming Protein 1
  • Insulin-Like Growth Factor I
  • Glutathione Transferase
  • HRAS protein, human
  • Proto-Oncogene Proteins p21(ras)