Binding of insulin and insulin-like growth factor I (IGF-I) to HepG2 cells was analysed with regard to competition by both insulin and IGF-I. At concentrations of insulin that caused maximal phosphorylation of the insulin receptor, virtually no displacement of IGF-I binding was observed. Similarly, at concentrations of IGF-I that caused maximal phosphorylation of the IGF-I receptor, no displacement of insulin binding was observed. 2. When the phosphorylation of both receptors was examined individually by using specific monoclonal antibodies to immunoprecipitate the receptors, phosphorylation of the insulin receptor was found to increase on both serine and tyrosine residues in cells treated with 100 ng of IGF-I/ml. In contrast, no increased phosphorylation of IGF-I receptor was observed in cells treated with 100 ng of insulin/ml. 3. The increase in phosphorylation of insulin receptor in response to IGF-I correlated with the dose-response of IGF-I-stimulated phosphorylation of the IGF-I receptor. 4. The IGF-I-stimulated phosphorylation of the insulin receptor could be blocked by preincubation with a monoclonal antibody that blocks IGF-I binding to the IGF-I receptor.
摘要
就胰岛素和胰岛素样生长因子I（IGF-I）两者的竞争性而言，分析了胰岛素和IGF-I与HepG2细胞的结合情况。在导致胰岛素受体最大磷酸化的胰岛素浓度下，几乎未观察到IGF-I结合的置换。同样，在导致IGF-I受体最大磷酸化的IGF-I浓度下，也未观察到胰岛素结合的置换。2. 当通过使用特异性单克隆抗体免疫沉淀受体来单独检测两种受体的磷酸化时，发现在用100 ng IGF-I/ml处理的细胞中，胰岛素受体的丝氨酸和酪氨酸残基的磷酸化均增加。相比之下，在用100 ng胰岛素/ml处理的细胞中，未观察到IGF-I受体磷酸化增加。3. 胰岛素受体对IGF-I的磷酸化增加与IGF-I刺激的IGF-I受体磷酸化的剂量反应相关。4. IGF-I刺激的胰岛素受体磷酸化可通过与阻断IGF-I与IGF-I受体结合的单克隆抗体预孵育来阻断。
