Expression of a type I insulin-like growth factor receptor with low affinity for insulin-like growth factor II

E. L. Germain-Lee, M. Janicot, R. Lammers, A. Ullrich, S. J. Casella

Research output: Contribution to journalArticlepeer-review


We investigated the binding properties of the type I insulin-like growth factor (IGF) receptor expressed in NIH-3T3 fibroblasts transfected with a human type I receptor cDNA. Cell surface receptors bound IGF-I with K(D) = 1 nM as predicted. Although recent studies have suggested that IGF-I and IGF-II bind to type I receptors with near-equal affinity, the receptors in this system bound IGF-II with much lower affinity (K(D)) = 15-20 nM). When type I receptors from the transfected cells were solubilized and immunopurified, however, both 125I-1GF-I and 125I-1GF-II bound to the purified receptors with extremely high and relatively similar affinities (K(D) = 8 and 17 pM respectively). Thus the immunopurified receptors had higher affinity but lower specificity for the two ligands. The monoclonal antibody αIR-3 effectively inhibited IGF-I binding to cell surface receptors (75±10 %), but did not inhibit IGF-II binding. In the purified receptor assay, αIR-3 also inhibited IGF-I binding more effectively than IGF-II binding (38±7 % versus 10±4 %). We conclude that the products of this cDNA can account for the binding patterns that we previously observed in receptors immunopurified from human placenta. The differential effect of αIR-3 on IGF-I versus IGF-II raises the possibility that these homologous growth factors bind to immunologically distinct epitopes on the type I receptor.

Original languageEnglish (US)
Pages (from-to)413-417
Number of pages5
JournalBiochemical Journal
Issue number2
StatePublished - 1992

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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