Functional and immunological distinction between insulin-like growth factor I receptor subtypes in KB cells.
Subtypes of insulin-growth factor I (IGF-I) receptors, including hybrid receptors containing insulin receptor alpha beta dimers associated with IGF-I receptor alpha beta dimers, have been described in a number of systems. The molecular basis of the multiple subtypes and their functional significance is not understood. Ligand-dependent phosphorylation of insulin and IGF-I receptors and immunoprecipitation with antipeptide and monoclonal antibodies have been used to characterize the subpopulations of these receptors in the human KB cell line. IGF-I receptors exhibit beta subunits of 95 and 102 kDa in these cells. IGF-I receptors containing 102-kDa beta subunits are immunoprecipitated by the IGF-I receptor-specific antibody alpha-IR3. Antibody alpha-IR3 does not appear to recognize a hybrid receptor in these cells. However, an antipeptide antibody against the carboxyl-terminal domain of the insulin receptor (AbP5) immunoprecipitates a population of receptors phosphorylated in response to IGF-I (1 nM) which contains both 95- and 102-kDa beta subunits. These receptors must be hybrid complexes because AbP5 does not recognize the 102-kDa beta subunit directly. The inability of antibody alpha-IR3 to recognize these complexes suggests that their IGF-I receptor alpha subunits must differ from typical IGF-I receptor alpha subunits either in primary sequence or conformation. Therefore, KB cells may contain more than one type of IGF-I receptor alpha subunit. Hybrid IGF-I receptors can also be distinguished from homotypic IGF-I receptors by their responsiveness to IGF-II. Stimulation of autophosphorylation in hybrid IGF-I receptors by IGF-I is 3-4-fold greater than that seen in response to IGF-II. In contrast, IGF-I and IGF-II are nearly equipotent in stimulating autophosphorylation in the alpha-IR3-reactive receptor population. This suggests the existence of functionally distinct receptor subtypes which may differ in their ability to mediate the biological effects of IGF-II.
Garofalo
R S
RS
Department of Anatomy and Cell Biology, State University of New York Health Science Center, Brooklyn 11203.
Barenton
B
B
D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D003432:Cross-Linking Reagents; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011956:Receptors, Cell Surface / Q000276:immunology / Q000378:metabolism*; D017451:Receptors, Somatomedin; D014407:Tumor Cells, Cultured
D003432:Cross-Linking Reagents; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II