Abstract
Fibroblasts cultured from an infant with leprechaunism and insulin resistance have been reported to exhibit profound, selective defect in insulin binding. We now examine the effect of this defect on two acute metabolic actions of insulin thought to be mediated by the insulin receptor, glucose incorporation and N-methyl-alpha-aminoisobutyric acid (Me-AiBu) uptake. In the patient's fibroblasts, maximal insulin-stimulated glucose incorporation was less than 25% of that in control fibroblasts, whereas stimulation by hydrogen peroxide, an insulinomimetic agent that acts distal to the insulin receptor, was normal. By contrast, insulin stimulated Me-AiBu uptake to the same extent in patient's and control fibroblasts. Impaired glucose incorporation and relatively normal Me-AiBu uptake also were observed in the patient's cells with multiplication-stimulating activity, an insulin-like growth factor, despite the fact that multiplication-stimulating activity appeared to stimulate both responses in normal fibroblasts via an insulin-like growth factor receptor. The divergent effects on two hormone-stimulated functions in the patient's cells suggests differences in the coupling of a receptor to different effectors. The same coupling mechanisms appear to be used by insulin receptors and receptors for insulin-like growth factors.