Domain-Dependent Effects of Insulin and IGF-1 Receptors on Preadipocyte Gene Expression

Despite a high degree of homology, insulin and IGF-1 receptors (IR/IGF1R) mediate distinct cellular and physiological functions. Here, using chimeric and site-mutated receptors, we demonstrate how domain differences between IR and IGF1R contribute the distinct functions of these receptors. Receptors with the intracellular domain of IGF1R show increased activation of Shc and Gab-1 and more potent regulation of genes involved in proliferation, corresponding to its higher mitogenic activity. Conversely, receptors with the intracellular domain of IR display higher IRS-1 phosphorylation, stronger regulation of genes in metabolic pathways and more dramatic glycolytic responses to hormonal stimulation. We generated mouse brown preadipocytes in which both insulin and IGF-1 receptors (IR and IGF1R) had been genetically inactivated using Cre-lox recombination. These IR and IGF1R DKO cells were then reconstituted with wild-type mouse IR, IGF1R, or one of two chimeric receptors: IR/IGF1R with the IR extracellular domain (ECD) fused to the IGF1R transmembrane and intracellular domains (ICD) and IGF1R/IR with the ECD of IGF1R fused to the ICD domains of IR. Three independent clones for each line were used for the study. For expression analysis, we serum-starved the preadipocytes clones overnight and stimulated cells with 100 nM insulin, IGF-1 or vehicle for 6 h, and subjected the cellular RNA to analysis using Affymetrix Mouse Gene 2.0 ST arrays.