Interactions of insulin-like growth factors I and II and multiplication-stimulating activity with receptors and serum carrier proteins.
Insulin-like growth factors (IGFs) I and II, purified from human plasma, and multiplication-stimulating activity (MSA), purified from media conditioned by the BRL 3A rat liver cell line, are polypeptides with similar biological and biochemical properties. We have compared the interaction of 125I-labeled and unlabeled MSA, IGF-I, and IGF-II with four intact cell or cell membrane preparations previously shown to possess MSA receptors: rat liver plasma membranes, chick embryo fibroblasts, human fibroblasts, and BRL 3A2 cells. In each case, specific binding of 125I-labeled IGF-I and IGF-II was demonstrated. With each 125I-labeled peptide, significant inhibition of binding and parallel dose-response curves were observed with unlabeled IGF-I, IGF-II, and MSA. Striking differences were noted, however, in the relative potencies of the unlabeled peptides as competitive inhibitors of binding. We conclude that the different specificities of binding inhibition reflect a significant heterogeneity among IGF receptors. A similar heterogeneity appears to occur among somatomedin carrier proteins in rat and human sera.
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002642:Chick Embryo; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D018969:Insulin-Like Growth Factor Binding Proteins; D007335:Insulin-Like Growth Factor II; D008099:Liver / Q000378:metabolism; D010455:Peptides / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011955:Receptors, Drug / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*
D002352:Carrier Proteins; D007328:Insulin; D018969:Insulin-Like Growth Factor Binding Proteins; D010455:Peptides; D011956:Receptors, Cell Surface; D011955:Receptors, Drug; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007335:Insulin-Like Growth Factor II