IMPAIRED INSULIN SIGNALING IN SKELETAL-MUSCLES FROM TRANSGENIC MICE EXPRESSING KINASE-DEFICIENT INSULIN-RECEPTORS

Transgenic mice which overexpress kinase-deficient human insulin recep tors in muscle were used to study the relationship between insulin rec eptor tyrosine kinase and the in vivo activation of several downstream signaling pathways. Intravenous insulin stimulated insulin receptor t yrosine kinase activity by 7-fold in control muscle versus less than o r equal to 1.5-fold in muscle from transgenic mice. Similarly, insulin failed to stimulate tyrosyl phosphorylation of receptor beta-subunits or insulin receptor substrate 1 (IRS-1) in transgenic muscle, Insulin substantially stimulated IRS-1 associated phosphatidylinositol (PI) 3 -kinase in control versus absent stimulation in transgenic muscles. In contrast, insulin-like growth factor 1 modestly stimulated PI 3-kinas e in both control and transgenic muscle, The effects of insulin to sti mulate p42 mitogen activated protein kinase and c-fos mRNA expression were also markedly impaired in transgenic muscle. Specific immunopreci pitation of human receptors followed by measurement of residual insuli n receptors suggested the presence of hybrid mouse-human heterodimers, In contrast, negligible hybrid formation involving insulin-like growt h factor 1 receptors was evident, We conclude that (i) transgenic expr ession of kinase-defective insulin receptors exerts dominant-negative effects at the level of receptor autophosphorylation and kinase activa tion; (ii) insulin receptor tyrosine kinase activity is required for i n vivo insulin-stimulated IRS-1 phosphorylation, IRS-1-associated PI 3 -kinase activation, phosphorylation of mitogen-activated protein kinas e, and c-fos gene induction in skeletal muscle; (iii) hybrid receptor formation is likely to contribute to the in vivo dominant-negative eff ects of kinase-defective receptor expression.