Activation of the insulin-like growth factor type 1 receptor by deletion of amino acids 870-905.
We have created a deletion mutant of the insulin-like growth factor type 1 receptor (IGF-1 R) which lacks the 36 amino acids (aa) immediately N-terminal to the transmembrane domain (Delta870-905 IGF-1 R). This region has been reported to have a negative effect on the transforming potential of an avian sarcoma virus gag-IGF-1 R fusion protein. We have sought to determine whether this region plays a similar role in the intact IGF-1 R. Analysis of the tyrosine kinase activity of the Delta870-905 IGF-1 R shows that the mutant receptor is autophosphorylated without IGF-1 stimulation, indicating that the tyrosine kinase domain is constitutively active. In addition, processing of the receptor is decreased, resulting in accumulation of a high molecular weight proreceptor containing both alpha and beta-subunits. A well-characterized substrate of the IGF-1 R, IRS-1, is constitutively phosphorylated by the Delta870-905 IGF-1 R and phosphoinositide (PI) 3-kinase activity, which is normally activated by the phosphorylation of IRS-1 following IGF-1 stimulation, is increased even in the absence of IGF-1. A second intracellular signal pathway normally activated by IGF-1, the MAP kinase pathway, showed no increase in activity in the absence of IGF-1. The Delta870-905 IGF-1 R promoted cell proliferation only in the presence of IGF-1. We conclude that this deletion increases the basal activity of the IGF-1 receptor tyrosine kinase and activates PI 3-kinase, but is unable to stimulate MAP kinase in the absence of ligand. These results confirm those seen in the gag-IGF-1 R fusion protein and indicate that aa 870-905 exert a negative effect on the tyrosine kinase domain of the beta-subunit of the IGF-1 R.
Li
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S
Department of Pathology and Laboratory Medicine, MCP-Hahnemann School of Medicine, Allegheny University, 2900 Queen Lane, Philadelphia, Pennsylvania 19129, USA.
Zhang
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Hoff
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Sell
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C
D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D004789:Enzyme Activation; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion
D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; D017526:Receptor, IGF Type 1; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases