Cell Culture Studies on Patients with Extreme Insulin Resistance. II. Abnormal Biological Responses in Cultured Fibroblasts*

Abstract

Insulin stimulation of glycogen synthase and of thymidine incorporation into DNA has been examined in fibroblasts derived from three insulin-resistant patients: two with the type A syndrome of insulin resistance and acanthosis nigricans and one with the syndrome of leprechaunism. All three cell lines were previously shown to exhibit abnormal insulin-binding properties with alterations in receptor number or affinity. In the basal state, fibroblasts from all three patients contained normal levels of total glycogen synthase activity. Two of the cell lines, those of type A patient A-l and those of the leprechaun infant, had an abnormally high percentage of the enzyme in its glucose-6-phosphate-independent or dephosphorylated form and lower than normal cellular glycogen stores, consistent with an inverse correlation between percent I activity and glycogen content observed with other cells. Cells from patient A-3 had normal levels of glycogen and a low percentage of enzyme in the independent form. Insulin activated glycogen synthase in all three cell lines. In both type A patients, however, the dose-response curve was shifted 5-fold to the right. With fibroblasts from the leprechaun infant, glycogen synthase stimulation was normal or supranormal. The ability of insulin to stimulate thymidine incorporation into DNA in all three cell lines was also impaired. This defect was most marked in cells from patient A-l and the leprechaun. Fibroblasts from the leprechaun infant and from patient A-3 also responded poorly to serum stimulation of DNA synthesis. These data demonstrate that defects in either receptor number, as with the cells of patient A-3, or in receptor affinity, as with the cells of patient A-l, can be associated with abnormal insulin stimulation of a metabolic event, such as activation of glycogen synthase. Interestingly, the cells of the leprechaun infant, with an affinity defect qualitatively identical to that found in patient A-l cells, respond normally to insulin in this assay system. This suggests a complex coupling of insulin binding and response and raises the possibility that insulin stimulation of glycogen synthase in fibroblasts might be mediated through a receptor other than the insulin receptor, at least in these cells. In addition, the abnormal mitogenic effect of insulin in all three cell lines suggests that either functionally intact insulin receptors are needed to help mediate this event or that other receptor or postreceptor defects are also present in these cell lines.