Insulin receptor function in fibroblasts from patients with leprechaunism. Differential alterations in binding, autophosphorylation, kinase activity, and receptor-mediated internalization.
Insulin receptor function was examined in cultured skin fibroblasts from three patients with leprechaunism (Ark-1, Minn-1, and Can-1), a rare syndrome of severe insulin resistance and neonatal growth retardation. All three patients cell lines demonstrated insulin binding less than 15% of control. This was primarily due to reduced affinity of the receptor in Can-1 and due to reduced number of receptors in the other two cell lines (Ark-1 and Minn-1). When expressed as a fraction of total insulin bound, the percentage of cell-associated insulin internalized and degraded did not differ between the patient cell lines and the controls. However, chloroquine, which inhibited degradation by 50% in the control cells, had no effect in the cells from the patients. When normalized to insulin binding, insulin receptor autophosphorylation was normal in cells from Can-1, but reduced in those of Ark-1 and Minn-1. In contrast, the receptor-associated tyrosine kinase activity toward exogenous substrates was decreased in all three patient cell lines. These results suggest that leprechaunism is a biochemically heterogenous disease associated with a variety of alterations in receptor function. Cells from Ark-1 and Minn-1 exhibit parallel alterations in receptor autophosphorylation and kinase activity. Cells from Can-1 demonstrate normal receptor autophosphorylation but reduced kinase activity, thus displaying a unique form of a mutant insulin receptor. Despite reduced kinase activity, all three cell lines exhibit normal rates of insulin internalization, but decreased lysosomal-mediated degradation. Our data imply that receptor autophosphorylation and kinase activity may be regulated separately and that kinase activity may be linked to insulin degradation, but not necessarily internalization.
D004700:Endocrine System Diseases / Q000201:enzymology / Q000378:metabolism*; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism*; D006130:Growth Disorders / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011972:Receptor, Insulin / Q000032:analysis / Q000502:physiology*; D013577:Syndrome
D007328:Insulin; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin