Insulin and insulin-like growth factor I binding to cultured rat glomerular mesangial cells.
The potential effects of insulin and insulin-like growth factor I (IGF-I) on mesangial cell (MC) metabolism and growth were examined. Radiolabeled insulin or IGF-I were incubated with cell membranes from rapidly proliferating (subconfluent) or nonproliferating (confluent) MC in the presence of increasing concentrations of unlabeled heterologous and homologous ligands (0-10(-6) M). Insulin binding to MC was specific and saturable, with Scatchard analysis of binding data showing the characteristic curvilinear plot. The predicted insulin binding maximum of 4.2 X 10(-12) M/100 micrograms protein for a theoretical high affinity site was consistent with a relatively low density of receptors, which were the same in proliferating and nonproliferating cell preparations. Specific binding of IGF-I to MC was also demonstrated. Binding data for membranes from proliferating cultures generated a linear Scatchard plot, which predicted a binding maximum of 3.5-9.7 X 10(-11) M/100 micrograms protein and a Kd of 2.0-3.2 X 10(-9) M. In contrast, membranes from nonproliferating cultures had no demonstrable specific binding of IGF-I. Covalent cross-linking of radiolabeled IGF-I to membranes from subconfluent cells demonstrated specific binding to a 145K membrane protein. A 95K membrane protein from a partially purified receptor preparation demonstrated autophosphorylation when incubated with 5 X 10(-9) M IGF-I. Incubation of MC with 10(-9) M IGF-I doubled cellular growth rates, an effect that could be duplicated only with high concentrations (10(-6) M) of insulin. These observations indicate that MC express predominantly receptors for IGF-I, and that growth stimulatory effects of physiological concentrations of IGF-I and pharmacological concentrations of insulin are probably mediated through the IGF-I receptor.
D000345:Affinity Labels; D000818:Animals; D002455:Cell Division; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003432:Cross-Linking Reagents; D005920:Glomerular Mesangium / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains; D013002:Somatomedins / Q000378:metabolism*; D013388:Succinimides
D000345:Affinity Labels; D003432:Cross-Linking Reagents; D007328:Insulin; D013002:Somatomedins; D013388:Succinimides; D007334:Insulin-Like Growth Factor I; C019358:disuccinimidyl suberate