title: C-kinase phosphorylates the epidermal growth factor receptor and reduces its epidermal growth factor-stimulated tyrosine protein kinase activity.
abstract: The Ca2+- and phospholipid-dependent protein kinase (C-kinase) binds tightly in the presence of Ca2+ to purified membranes of A431 human epidermoid carcinoma cells. The major membrane substrate for C-kinase is the epidermal growth factor (EGF) receptor. Phosphorylation of the EGF receptor is Ca2+-dependent and occurs at threonine and serine residues. After tryptic digestion of the receptor, three major phosphothreonine-containing peptides were identified. These are identical with three new phosphopeptides present in the EGF receptor isolated from A431 cells treated with either of the tumor promoters 12-O-tetradecanoylphorbol 13-acetate or teleocidin. C-kinase catalyzes phosphorylation at these same sites in purified EGF receptor protein. These results indicate that, in A431 cells exposed to tumor promoters, C-kinase catalyzes phosphorylation of a significant population of EGF receptor molecules. This phosphorylation of EGF receptors results in decreased self-phosphorylation of the EGF receptor at tyrosine residues both in vivo and in vitro and in decreased EGF-stimulated tyrosine kinase activity in vivo.
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology*; D002118:Calcium / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D010766:Phosphorylation; D011493:Protein Kinase C; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*
chemical_list: D010446:Peptide Fragments; D011956:Receptors, Cell Surface; D004815:Epidermal Growth Factor; D011494:Protein Kinases; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D002118:Calcium