Direct Demonstration of Separate Receptors for Growth and Metabolic Activities of Insulin and Multiplication-stimulating Activity (an Insulinlike Growth Factor) Using Antibodies to the Insulin Receptor

Authors:
  • GKGeorge L. King
    George L. King
  • CKC. Ronald Kahn
    C. Ronald Kahn
  • MRMatthew M. Rechler
    Matthew M. Rechler
  • SNS. Peter Nissley
    S. Peter Nissley
Open Access
Publisher website
Google Scholar
Abstract
Insulin and such insulinlike growth factors as multiplication stimulating activity (MSA) are related polypeptides that have common biological activities. Both insulin and MSA produce acute metabolic responses (stimulation of glucose oxidation in isolated fat cells) as well as growth effects (stimulation of [3H]thymidine incorporation into DNA in cultured fibroblasts). In addition, most cells have separate receptors for insulin and insulinlike growth factors, and both peptides have weaker affinity for each other's specific receptors than for their own. To determine, therefore, whether these effects are mediated by receptors for insulin, insulinlike growth factors, or both, we have selectively blocked insulin receptors with a specific antagonist, namely Fab fragments derived from naturally occurring antibodies to the insulin receptor. In rat adipocytes, 10 μg/ml of antireceptor Fab inhibited insulin binding by 90%, whereas it inhibited MSA binding 5 and spermine, agents that stimulate glucose oxidation through noninsulin receptor pathways, were not affected by the blockade of insulin receptors with Fab antibody fragments. These data suggest that this acute metabolic effect of both insulin and MSA is mediated via the insulin receptor. In cultured human fibroblasts, 10 μg/ml of Fab inhibited insulin binding by 90% and MSA binding by 15%. In fibroblasts, however, blockade of the insulin receptor did not alter the dose response for stimulation of thymidine incorporation into DNA by either insulin or MSA. Furthermore, intact antireceptor antibody immunoglobulin (Ig)G, which produces multiple other insulinlike effects, and Fab fragments of antireceptor antibody did not stimulate thymidine incorporation. These data demonstrate directly that the insulin receptor mediates the metabolic effects of insulin and MSA, whereas the growth-promoting action of both peptides is mediated by the MSA receptor or other growth factors.

This publication has 34 references indexed in Scilit: