Regulation of biological functions by an insulin receptor monoclonal antibody in insulin receptor .beta.-subunit mutants

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Abstract
We investigated the effects of MA-5, a human-specific monoclonal antibody to the insulin receptor alpha-subunit, on transmembrane signaling in cell lines transfected with and expressing both normal human insulin receptors and receptors mutated in their beta-subunit tyrosine kinase domains. In cell lines expressing normal human insulin receptors, MA-5 stimulated three biological functions: aminoisobutyric acid (AIB) uptake, thymidine incorporation, and S6 kinase activation. Under conditions where these biological functions were stimulated, there was no detectable stimulation of receptor tyrosine kinase. We then combined the use of this monoclonal antibody with cells expressing insulin receptors with mutations in the beta-subunit tyrosine kinase domain; two of ATP binding site mutants V1008 (Gly----Val) and M1030 (Lys----Met) and one triple-tyrosine autophosphorylation site mutant F3 (Tyr----Phe at 1158, 1162, and 1163). In cells expressing V1008 receptors, none of the three biological functions of insulin was stimulated. In cells expressing M1030 receptors, AIB uptake was stimulated to a small, but significant, extent whereas the other two functions were not. In cells expressing F3 receptors, AIB uptake and S6 kinase activation, but not thymidine incorporation, were fully stimulated. The data suggest, therefore, that (1) activation of insulin receptor tyrosine kinase may not be a prerequisite for signaling of all the actions of insulin and (2) there may be multiple signal transduction pathways to account for the biological actions of insulin.