title: cAMP-dependent protein kinase stimulates epidermal growth factor-dependent phosphorylation of epidermal growth factor receptors.
abstract: Epidermal growth factor (EGF)-dependent transfer of radiolabeled phosphate from [gamma-32P]ATP to 160-kDa EGF receptor solubilized from human epidermoid carcinoma A431 cell surface membranes was stimulated up to 3-fold by addition of 3',5'-cAMP and purified cAMP-dependent protein kinase. Phosphorylation of EGF receptors was stimulated to the same extent when cAMP-dependent protein kinase catalytic subunit was substituted for 3',5'-cAMP and cAMP-dependent protein kinase. Phosphoamino acid analysis revealed that the extent of phosphorylation of EGF receptor at tyrosine residues was the same regardless of whether cAMP-dependent protein kinase catalytic subunit was present in or omitted from the system. Increased EGF receptor phosphorylation occurring in response to cAMP-dependent protein kinase catalytic subunit was accounted for by phosphorylation at serine or threonine residues. In samples phosphorylated in the presence of cAMP-dependent protein kinase catalytic subunit, phosphate was present in tyrosine, serine, and threonine in a ratio of 32:60:8. Two-dimensional mapping of radiolabeled phosphopeptides produced from EGF receptors by digestion with trypsin revealed the generation of one additional major phosphoserine-containing peptide when cAMP-dependent protein kinase was present with EGF in the EGF receptor kinase system. Degradation of 160-kDa EGF receptors to a 145-kDa form by purified Ca2+-activated neutral protease produced a 145-kDa fragment with phosphoserine content increased over that present initially in the 160-kDa precursor.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002294:Carcinoma, Squamous Cell; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D004815:Epidermal Growth Factor / Q000378:metabolism* / Q000494:pharmacology; D066246:ErbB Receptors; D006801:Humans; D008970:Molecular Weight; D010748:Phosphopeptides / Q000032:analysis; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D010748:Phosphopeptides; D011956:Receptors, Cell Surface; D004815:Epidermal Growth Factor; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D066246:ErbB Receptors