| Abstract: | In the present study, we investigated the ability of a monoclonal antibody to the insulin receptor to regulate the expression of the insulin receptor of IM-9 lymphocytes. Previously, this antibody was shown to be a competitive antagonist of insulin action on severe metabolic functions. In the present study, we report that preincubation of IM-9 cells with the monoclonal antibody caused a dose- and time-dependent decrease in the subsequent ability of these cells to bind 125I-insulin, a phenomenon termed down regulation. The antibody was approximately 100 times more potent than insulin at down regulating the receptor. In contrast, the antibody was 5 times less potent than insulin in competing for binding to insulin receptors and dissociated 4 times more rapidly than insulin from IM-9 cells. Three lines of evidence suggested that the mechanism of down regulation by the antibody was the same as the one used by insulin. First, both agents caused a rapid initial decrease in insulin binding to cells followed by a slower, gradual decrease in binding. Second, the down regulation caused by both was reversible, and this reversibility required new protein synthesis. Third, the antibody, like insulin, accelerated receptor degradation. Since the antibody does not mimic the other effects of insulin on metabolic processes, these results suggest that the mechanism of insulin receptor down regulation is different from the mechanism of insulin action on other cellular functions. |
