Phosphotyrosine-containing proteins in bovine chromaffin cells: effects of insulin-like growth factor I (IGF-I).
1. Antiphosphotyrosine antibodies were used to detect phosphotyrosine-containing proteins in immunoblots of bovine chromaffin cell proteins. 2. Unstimulated cells exhibited two major phosphotyrosine-containing proteins, which had Mr's of 121,000 and 70,000. Insulin-like growth factor I (IGF-I) had little effect on the phosphotyrosine content of these two proteins but greatly increased the phosphotyrosine content of three other proteins of Mr 185,000, 170,000, and 96,000. These proteins were found predominantly in the particulate fraction of cell homogenates. 3. The effects of the IGF-I were time and concentration dependent, with maximal increases in phosphorylation occurring after 1 min of treatment with 10 nM IGF-I. Na3VO4, an inhibitor of phosphotyrosine phosphatases, potentiated the effects of IGF-I. 4. Thus, the IGF-I receptor appears to function as an IGF-I-activated protein tyrosine kinase in chromaffin cells. The tyrosine kinase activity of the IGF-I receptor presumably mediates the effects of IGF-I on chromaffin cell function.
Cahill
A L
AL
Department of Pediatrics, University of Chicago, Illinois 60637.
Perlman
R L
RL
D000313:Adrenal Medulla / Q000737:chemistry* / Q000166:cytology; D000818:Animals; D002417:Cattle; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008970:Molecular Weight; D010750:Phosphoproteins / Q000032:analysis*; D010766:Phosphorylation / Q000187:drug effects; D019000:Phosphotyrosine; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000502:physiology*; D017451:Receptors, Somatomedin; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000032:analysis
D010750:Phosphoproteins; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D019000:Phosphotyrosine; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D011505:Protein-Tyrosine Kinases