Antipeptide antibody to the insulin-like growth factor-I receptor sequence 1232-1246 inhibits the receptor kinase activity.
To approach the question of why insulin-like growth factor-I (IGF-I) and insulin have different physiological actions, we developed antibodies directed against cytoplasmic regions of the IGF-I receptor exhibiting a low degree of homology with the corresponding sequences of the insulin receptor. We found that an antipeptide antibody directed against the beta-subunit carboxyl-terminal sequence (1232-1246) of the IGF-I receptor significantly reduced the in vitro receptor autophosphorylation. The ability of the synthetic peptide corresponding to the IGF-I receptor sequence 1232-1246 to abolish this inhibitory effect reflects the specific nature of the antibody interaction with the targeted domain in the receptor. Antipeptide antibody to IGF-I receptor sequence 1232-1246 also decreased receptor phosphorylation activity toward the exogenous substrate poly(Glu/Tyr). The reduction in poly(Glu/Tyr) phosphorylation was seen even when the antibody was incubated with a receptor previously activated and phosphorylated. Therefore, the inhibitory action on substrate phosphorylation is likely to be unrelated to the antibody reduction of receptor autophosphorylation but rather results from a global decrease in receptor enzymatic activity. The effect of the antipeptide antibody on receptor tyrosine kinase cannot be accounted for by a lowering of the receptor Km for ATP or of its affinity for the substrate poly(Glu/Tyr). Moreover, the interaction of the antibody with the receptor had no repercussion on the ligand binding site as shown by the unaltered IGF-I binding. Taken together our data suggest that the beta-subunit carboxyl-terminal domain of the IGF-I receptor plays a key role in regulating its kinase activity and that the particular sequence recognized by our antipeptide antibody could be involved in negative regulation of receptor functioning.
Kaliman
P
P
Institut National de la Santé et de la Recherche Médicale, Unité 145, Faculté de Médecine, Nice, France.
Baron
V
V
Gautier
N
N
Van Obberghen
E
E
D016475:3T3 Cells; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000906:Antibodies / Q000276:immunology; D015153:Blotting, Western; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000276:immunology; D017451:Receptors, Somatomedin; D013379:Substrate Specificity
D000906:Antibodies; D036341:Intercellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D010455:Peptides; D047428:Protein Kinase Inhibitors; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; C027606:L-glutamic acid-L-tyrosine copolymer; D007334:Insulin-Like Growth Factor I; D000255:Adenosine Triphosphate