Cell Culture Studies on Patients with Extreme Insulin Resistance. I. Receptor Defects on Cultured Fibroblasts*

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Abstract
Insulin binding has been characterized on fibroblasts cultured from two patients with the type A syndrome of insulin resistance and acanthosis nigricans (A-l and A-3) and from one infant with insulin resistance associated with leprechaunism. [125I]Insulin binding was markedly decreased in cells from all three patients. The defect in insulin receptors appeared specific; binding of insulin-like growth factor I was normal. Assuming a cooperative model for the insulin receptor, the decrease in insulin binding in the cells of the leprechaun infant and of patient A-l appears to be due to a decrease in receptor affinity. In both cases, this decrease in affinity was associated with an accelerated dissociation of bound [125I]insulin and a loss of negative cooperativity, i.e. dissociation was not accelerated by the addition of unlabeled hormone. In contrast, cells from patient A-3 showed no change in affinity, but demonstrated a reduction in apparent receptor number. Multiple other abnormalities of insulin receptor interactions were present on the patients' cell lines. All three cell lines had lost the normal pH optimum for [125I]insulin binding. Furthermore, all showed abnormal behavior with regard to specificity. Multiplication-stimulating activity, an insulin-like growth factor that is about 1% as potent as insulin in displacing [125I]insulin from normal human fibroblasts, was about 60-100% as potent as insulin in A-l and leprechaun cells and about 10% as potent as insulin in A-3 cells. In addition, antibody to the insulin receptor showed little or no cross-reactivity with cells from patient A-l and the leprechaun, whereas the inhibitory effect in fibroblasts from patient A-3 was essentially normal. Insulin analogs, such as guinea pig insulin, desoctapeptide insulin, and porcine proinsulin, competed for insulin binding in a normal fashion. These data as well as the results of other studies suggest that in some insulin-resistant states, such as leprechaunism and the type A syndrome of insulin resistance and acanthosis nigricans, there are genetic defects in the insulin receptor which are expressed on the cultured fibroblasts of these patients. The defects observed are heterogeneous and include alterations not only in receptor affinity or number but also differences in pH sensitivity, multiplication-stimulating activity competition, and defects at the postreceptor level. These data suggest that these cells possess both quantitative and qualitative (structural) abnormalities in the receptor which may be further elucidated by structural studies. These cells should provide useful model systems to aid in our understanding of insulin action. (JClin Endocrinol Metab54: 261, 1982)