Ras controls coupling of growth factor receptors and protein kinase C in the membrane to Raf-1 and B-Raf protein serine kinases in the cytosol.
A dominant negative mutant of Ras, M17 Ras, was used to study the role of Ras in receptor coupling of Raf-1 and B-Raf protein serine/threonine kinases (PSKs). We found that mutant Ras blocks serum- and 12-O-tetradecanoyl phorbol 13-acetate-induced activation of Raf-1 kinase in NIH3T3 cells and Raf-1 as well as B-Raf PSK stimulation by nerve growth factor (NGF) in PC12 pheochromocytoma cells. Mitogen stimulation of Raf kinase was measured by determination of Raf hyperphosphorylation and activity towards exogenous substrates and both of these events were inhibited in cells expressing M17 Ras. In contrast, tyrosine phosphorylation of a direct substrate of activated tyrosine kinase receptors, phospholipase C-gamma 1 (PLC-gamma 1), was unaffected. These data indicate that tyrosine phosphorylation of PLC-gamma 1 is not sufficient for growth induction in NIH3T3 cells and that Ras mediates signal transfer from activated membrane receptors to Raf kinases in the cytosol. As activated Raf induced differentiation in PC12 cells expressing M17 Ras we conclude that Raf kinase activation may be sufficient to account for this aspect of NGF function.
Troppmair
J
J
Viral Pathology Section, National Cancer Institute, Frederick, Maryland 21702-1201.
Bruder
J T
JT
App
H
H
Cai
H
H
Liptak
L
L
Szeberényi
J
J
Cooper
G M
GM
Rapp
U R
UR
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001790:Blood Physiological Phenomena; D003600:Cytosol / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D066246:ErbB Receptors / Q000502:physiology; D011905:Genes, ras; D051379:Mice; D008969:Molecular Sequence Data; D009414:Nerve Growth Factors / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000502:physiology*; D011494:Protein Kinases / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D019908:Proto-Oncogene Proteins c-raf; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D009414:Nerve Growth Factors; D011518:Proto-Oncogene Proteins; D003907:Dexamethasone; D011494:Protein Kinases; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D016186:Receptor, Macrophage Colony-Stimulating Factor; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate