Shc is the predominant signaling molecule coupling insulin receptors to activation of guanine nucleotide releasing factor and p21ras-GTP formation.
Insulin stimulates tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and She in Rat1 fibroblasts overexpressing wild type insulin receptors. We investigated the relative role of IRS-1 and She in insulin activation of guanine nucleotide releasing factor (GNRF) and p21ras-GTP formation. The time course of insulin-stimulated tyrosine phosphorylation of IRS-1 was rapid, whereas Shc phosphorylation was relatively slow. Growth factor receptor bound protein-2 (Grb2) associated with IRS-1 rapidly and gradually dissociated after 5 min, whereas Grb2 association with Shc was slower and reached a maximum at 10 min after insulin stimulation. Thus, the kinetics of Grb2 association with IRS-1 and She corresponded closely to the time course of tyrosine phosphorylation of IRS-1 and Shc, respectively. Importantly, 3-13-fold more Grb2 was associated with Shc than with IRS-1. In addition, the kinetics of insulin-stimulated GNRF activity and p21ras-GTP formation corresponded more closely to the time course of Shc phosphorylation than to the kinetics of IRS-1 phosphorylation. Furthermore, immunoprecipitation of Shc proteins from cell lysates of insulin-stimulated cells removed 67% of the GNRF activity, whereas precipitation of IRS-1 had a negligible effect on GNRF activity. Thus, although both IRS-1 and Shc associate with Grb2, the current results indicate that Shc plays a more important role than IRS-1 in insulin stimulation of GNRF activity and subsequent p21ras-GTP formation.
Sasaoka
T
T
Department of Medicine, University of California, San Diego, La Jolla 92093.
Draznin
B
B
Leitner
J W
JW
Langlois
W J
WJ
Olefsky
J M
JM
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D002478:Cells, Cultured; D051380:GRB2 Adaptor Protein; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D007700:Kinetics; D015689:Oncogene Protein p21(ras) / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism*; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D020663:ras Guanine Nucleotide Exchange Factors
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D051380:GRB2 Adaptor Protein; C495950:Grb2 protein, rat; D020662:Guanine Nucleotide Exchange Factors; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D010750:Phosphoproteins; D011506:Proteins; D055765:Shc Signaling Adaptor Proteins; C528035:Shc1 protein, rat; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D020663:ras Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate; D011972:Receptor, Insulin; D015689:Oncogene Protein p21(ras)