Preferential binding of insulin-like growth factors to a binding protein rather than to receptors on chicken hepatoma cell (LMH) membranes.
[125I]IGF-I binding to chicken hepatoma cell (LMH) membranes was displaced by unlabelled IGF-I or IGF-II, but not by insulin. Cross-linking revealed specific binding sites of 128 and 28-31 kDa, which following solubilization could be separated by wheat germ agglutinin (WGA) chromatography. [125I]IGF-I binding to the WGA eluate (128 kDa) could be displaced by insulin although with a 30-fold lower potency than IGF-I. Binding to the WGA flow-through (28-31 kDa) was not inhibited by insulin. This suggested that IGF binding to LMH was due mainly to membrane bound IGFBP rather than to type 1 IGF receptors. A reverse proportion was observed in normal chicken liver. A predominant 28 kDa IGFBP was synthesized and secreted by LMH cells, together with an unusual 60 kDa IGF binding entity which only bound [125I]IGF-II (with weak affinity). This process was not affected by the presence or absence of glucose, dexamethasone, glucagon, insulin or IGF-I.
Duclos
M J
MJ
Endocrinologie de La Croissance et du Métabolisme, Station de Recherches Avicoles, Institut National de la Recherche Agronomique, Nouzilly, France.
Chevalier
B
B
Simon
J
J
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002645:Chickens; D003432:Cross-Linking Reagents; D007328:Insulin / Q000378:metabolism; D018970:Insulin-Like Growth Factor Binding Protein 1; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D007457:Iodine Radioisotopes; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D011485:Protein Binding; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D013002:Somatomedins / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014909:Wheat Germ Agglutinins
D002352:Carrier Proteins; D003432:Cross-Linking Reagents; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D007457:Iodine Radioisotopes; D013002:Somatomedins; D014909:Wheat Germ Agglutinins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1