title: Tumor promoters block tyrosine-specific phosphorylation of the epidermal growth factor receptor.
abstract: Tyrosine-specific phosphorylation of the epidermal growth factor (EGF) receptor in hormonally stimulated A431 cells is blocked by three chemically distinct classes of tumor promoters. Tumor-promoting esters of the diterpene phorbol (phorbol 12-myristate 13-acetate, beta-phorbol 12,13-dibutyrate, and beta-phorbol 12,13-didecanoate), indole alkaloids (teleocidin and lyngbyatoxin A), and polyacetates ( aplysiatoxin and debromoaplysiatoxin ) all inhibited EGF-stimulated phosphorylation of the receptor. Non-tumor-promoting analogs (beta-phorbol, alpha-phorbol 12,13-didecanoate, and hydrolyzed teleocidin) had no effect on the levels of receptor phosphorylation. The ED50 values of the inhibitory effect (0.1-3 ng/ml) reflected the relative tumor-promoting abilities of these compounds in vivo. None of the tumor promoters tested significantly decreased the overall specific binding of 125I-labeled EGF to A431 cells. Scatchard analysis, however, revealed two apparent EGF receptors in this cell type. The dose-responses for tumor-promoter inhibition of EGF receptor tyrosine phosphorylation and high-affinity EGF binding were similar, suggesting that the same initial event is responsible for both effects. This demonstrates a correlation between modulation of EGF receptor binding and phosphorylation of tyrosine by tumor promoters. The data suggest a possible role for protein kinase C, the putative cellular receptor for these tumor promoters, in the mechanism of action.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D002273:Carcinogens / Q000494:pharmacology*; D002294:Carcinoma, Squamous Cell; D002460:Cell Line; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors; D006801:Humans; D007700:Kinetics; D010703:Phorbol Esters / Q000494:pharmacology*; D010704:Phorbols / Q000494:pharmacology*; D010766:Phosphorylation; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D014443:Tyrosine
chemical_list: D000596:Amino Acids; D002273:Carcinogens; D010703:Phorbol Esters; D010704:Phorbols; D011956:Receptors, Cell Surface; D014443:Tyrosine; D004815:Epidermal Growth Factor; D011494:Protein Kinases; D066246:ErbB Receptors; D011493:Protein Kinase C