Epidermal growth factor stimulates phosphorylation of RAF-1 independently of receptor autophosphorylation and internalization.
Phosphorylation of the RAF-1 protooncogene product and activation of its associated serine/threonine kinase are common features of the response of cells to peptide growth factors. We have used wild-type and mutant epidermal growth factor (EGF) receptors to investigate mechanisms of RAF-1 phosphorylation. In vivo EGF treatment rapidly stimulated phosphorylation of RAF-1 exclusively on serine residues. Stimulation of RAF-1 phosphorylation occurred at 37 degrees C but not at 4 degrees C and persisted after dissociation of EGF from its receptor. EGF-induced RAF-1 serine phosphorylation required the intrinsic tyrosine kinase activity of the EGF receptor but was independent of EGF receptor self-phosphorylation and of ligand-induced receptor internalization. Down-regulation of protein kinase C did not affect the EGF-induced increase in RAF-1 phosphorylation. These data suggest that the activated tyrosine kinase activity of the EGF receptor enhances serine phosphorylation of RAF-1 via an intermediary molecule(s).
Baccarini
M
M
Department of Developmental Biology and Cancer, Albert Einstein College of Medicine, New York, New York 10461.
Gill
G N
GN
Stanley
E R
ER
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D007739:L Cells / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000302:isolation & purification / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D014162:Transfection
D000596:Amino Acids; D011518:Proto-Oncogene Proteins; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D019908:Proto-Oncogene Proteins c-raf