FIG. 3.

βIRKO cells exhibit a compensatory increase in expression of IGF-1 receptors. (a) To determine the presence and cross-reactivity of insulin and IGF-1 receptors we treated control β-cells with IGF-I (100 nM) and performed immunoprecipitation and blotting for either the insulin receptor or the IGF-1 receptor. For experiments in panels b to d, cells were treated with IGF-I (100 nM) for 0, 1, 5 or 15 min. (b) Tyrosine phosphorylation of insulin receptor (right panel) and IGF-1 receptor (left panel). (c) Tyrosine phosphorylation of IRS-1 and IRS-2. The immunoprecipitates (IP) with anti-IRS-1 or anti-IRS-2 from the indicated cell lysates with or without IGF-1 stimulation were immunoblotted (IB) with anti-PY (top panels) or the p85 antibody (bottom panels). (d) PI3K activity associated with the phosphotyrosine complex. PI3K activity was measured in the immunoprecipitation reaction with anti-PY from the indicated cell lysates. (e) Phosphorylation of Akt and ERK. The cell lysates were immunoblotted with the indicated antibodies. Representative blots are shown from three independent experiments.