Abstract
In order to investigate the mechanism of insulin resistance, lymphocytes from various patients were transformed by Epstein-Barr virus. These cells were able to bind insulin. Decreased insulin binding was shown in three different types of cells from a 6-year-old boy with insulin resistance (JRM 1-a): erythrocytes (37.4% of normal), transformed lymphocytes (9.8% of normal) and fibroblasts (53.3% of normal). In addition to lymphocytes from JRM 1-a, those from patients with non-insulin dependent diabetes mellitus (NIDDM) and a patient with Type B insulin receptor disease were transformed. Although insulin binding was decreased in the erythrocytes from these subjects, insulin binding to the transformed lymphocytes was not altered. For further evaluation of the defect of insulin binding in the patient JRM1-a, two subunits of insulin receptor on transformed lymphocytes were studied. First, the alpha-subunit of insulin receptor was labeled with 125I-insulin by a chemical cross linker. Second, the beta-subunit of lectin-purified insulin receptor was labeled with 32P-ATP in the absence or presence of insulin (autophosphorylation). Both alpha-subunits and beta-subunits of insulin receptor from JRM 1-a showed normal molecular size on the autoradiographs of sodium dodecyl sulfate poly acrylamide gels, but their contents of labeled materials were decreased compared with those of the controls. But insulin (500 ng/ml) stimulated 32P-ATP incorporation into the beta-subunit of transformed lymphocytes from JRM 1-a to the same extent as in the control (630% and 550% over basal, respectively). In spite of decreased insulin binding to fibroblasts from JRM 1-a, the maximally insulin-stimulated glucose incorporation into his fibroblasts was not altered. However, the insulin dose-response curve of JRM 1-a cells was shifted to the right. These results indicated that the defects resided in insulin bindng but not in the post-receptor steps in the patient JRM 1-a, and that investigation of transformed lymphocytes and fibroblasts is useful for the clarification of insulin receptor abnormalities.
