Direct activation of the serine/threonine kinase activity of Raf-1 through tyrosine phosphorylation by the PDGF beta-receptor.
We have examined the interaction between the serine/threonine kinase proto-oncogene product Raf-1 and the tyrosine kinase PDGF beta-receptor. Raf-1 tyrosine phosphorylation and kinase activity were increased by PDGF treatment of 3T3 cells or CHO cells expressing wild-type PDGF receptors but not mutant receptors defective in transmitting mitogenic signals, suggesting that the increase in Raf-1 kinase activity is a significant event in PDGF-induced mitogenesis. Concurrent with these increases, Raf-1 associated with the ligand-activated PDGF receptor. Furthermore, both mammalian Raf-1 and Raf-1 expressed using a recombinant baculoviral vector, associated in vitro with baculoviral-expressed PDGF receptor. This association was markedly decreased by prior phosphatase treatment of the receptor. Following incubation of partially purified baculoviral-expressed PDGF receptor with partially purified Raf-1, Raf-1 became phosphorylated on tyrosine and its serine/threonine kinase activity increased 4- to 6-fold. This is the first demonstration of the direct modulation of a protein activity by a growth factor receptor tyrosine kinase.
Morrison
D K
DK
Department of Medicine, Howard Hughes Medical Institute, University of California, San Francisco 94143.
Kaplan
D R
DR
Escobedo
J A
JA
Rapp
U R
UR
Roberts
T M
TM
Williams
L T
LT
D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation; D066298:In Vitro Techniques; D007304:Insect Viruses / Q000235:genetics; D051379:Mice; D010766:Phosphorylation; D019000:Phosphotyrosine; D010982:Platelet-Derived Growth Factor / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D011956:Receptors, Cell Surface / Q000502:physiology*; D017479:Receptors, Platelet-Derived Growth Factor; D013329:Structure-Activity Relationship; D014162:Transfection; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D010982:Platelet-Derived Growth Factor; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D019000:Phosphotyrosine; D014443:Tyrosine; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D017479:Receptors, Platelet-Derived Growth Factor; D019908:Proto-Oncogene Proteins c-raf