TPA inhibits the tyrosine kinase activity of the neu protein in vivo and in vitro.
P185 is a receptor-like protein encoded by the neu/erbB-2 proto-oncogene. A point mutation in the transmembrane domain renders this protein oncogenic. We report here that incubation of cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulates the phosphorylation of the normal neu protein (p185) and the oncogenic neu protein (p185*). The increased phosphorylation occurs mainly on serine and threonine residues. Phosphate labeling experiments showed that TPA causes a reduction of basal phosphotyrosine in p185 but not p185*. Immunoblotting with antiphosphotyrosine antibody yielded similar results. TPA also inhibited tyrosine phosphorylation of p185* in an in vitro immune complex kinase assay. These data suggest that protein kinase C, the receptor for TPA, regulates p185 function through serine or threonine phosphorylation.
Cao
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Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06510.
Decker
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Stern
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D000596:Amino Acids / Q000032:analysis; D000818:Animals; D000911:Antibodies, Monoclonal; D002460:Cell Line; D007700:Kinetics; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D018719:Erb-b2 Receptor Tyrosine Kinases; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D000596:Amino Acids; D000911:Antibodies, Monoclonal; D010761:Phosphorus Radioisotopes; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases; D013755:Tetradecanoylphorbol Acetate; D013762:Tetrahydrofolate Dehydrogenase