THE DOMINANT-NEGATIVE EFFECT OF A KINASE-DEFECTIVE INSULIN-RECEPTOR ON INSULIN-LIKE GROWTH FACTOR-I-STIMULATED SIGNALING IN RAT-1 FIBROBLASTS

To study the interaction between insulin receptor (IR) and insulin-lik e growth factor-I (IGF-I) receptor (IGF-IR) tyrosine kinases, we exami ned IGF-I action in Rat-1 cells expressing a naturally occurring tyros ine kinase-deficient mutant IR(Asp 1048 IR). IGF-I normally stimulated receptor autophosphorylation, IRS-I phosphorylation, and glycogen syn thesis in cells expressing Asp 1048 IR. However, the Asp 1048 IR inhib ited IGF-I-stimulated thymidine uptake by 45% to 52% and amino acid up take (aminoisobutyric acid [AIB]) by 58% in Asp 1048 IR cells. Further more, IGF-I-stimulated tyrosine kinase activity toward synthetic polym ers, She phosphorylation, and mitogen-activated protein (MAP) kinase a ctivity was inhibited. The inhibition of mitogenesis and AIB uptake wa s restored with the amelioration of the impaired tyrosine kinase activ ity and Shc phosphorylation by the introduction of abundant wild-type IGF-IR in Asp 1048 IR cells. These results suggest that the Asp 1048 I R causes a dominant negative effect on IGF-IR in transmitting signals to She and MAP kinase activation, which leads to decreased IGF-I-stimu lated DNA synthesis, and that the kinase-defective insulin receptor do es not affect IGF-I-stimulated IRS-I phosphorylation, which leads to t he normal IGF-I-stimulated glycogen synthesis. Copyright (C) 1996 by W .B. Saunders Company