Role of diacylglycerol-regulated protein kinase C isotypes in growth factor activation of the Raf-1 protein kinase.

TitleRole of diacylglycerol-regulated protein kinase C isotypes in growth factor activation of the Raf-1 protein kinase.
Publication TypeJournal Article
Year of Publication1997
AuthorsCai H, Smola U, Wixler V, Eisenmann-Tappe I, Diaz-Meco MT, Moscat J, Rapp U, Cooper GM
JournalMol Cell Biol
Date Published1997 Feb
Keywords3T3 Cells, Animals, Cell Division, Cell Line, COS Cells, Diglycerides, Enzyme Activation, Epidermal Growth Factor, Isoenzymes, Mice, Mitogens, Mutation, Protein Kinase C, Protein Kinase C-alpha, Protein Kinase C-epsilon, Protein-Serine-Threonine Kinases, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-raf, Recombinant Fusion Proteins, Signal Transduction, Spodoptera, Tetradecanoylphorbol Acetate, Transfection

The Raf protein kinases function downstream of Ras guanine nucleotide-binding proteins to transduce intracellular signals from growth factor receptors. Interaction with Ras recruits Raf to the plasma membrane, but the subsequent mechanism of Raf activation has not been established. Previous studies implicated hydrolysis of phosphatidylcholine (PC) in Raf activation; therefore, we investigated the role of the epsilon isotype of protein kinase C (PKC), which is stimulated by PC-derived diacylglycerol, as a Raf activator. A dominant negative mutant of PKC epsilon inhibited both proliferation of NIH 3T3 cells and activation of Raf in COS cells. Conversely, overexpression of active PKC epsilon stimulated Raf kinase activity in COS cells and overcame the inhibitory effects of dominant negative Ras in NIH 3T3 cells. PKC epsilon also stimulated Raf kinase in baculovirus-infected Spodoptera frugiperda Sf9 cells and was able to directly activate Raf in vitro. Consistent with its previously reported activity as a Raf activator in vitro, PKC alpha functioned similarly to PKC epsilon in both NIH 3T3 and COS cell assays. In addition, constitutively active mutants of both PKC alpha and PKC epsilon overcame the inhibitory effects of dominant negative mutants of the other PKC isotype, indicating that these diacylglycerol-regulated PKCs function as redundant activators of Raf-1 in vivo.

Alternate JournalMol Cell Biol
PubMed ID9001227
PubMed Central IDPMC231799
Grant ListR01 CA18689 / CA / NCI NIH HHS / United States
Related Faculty: 
Jorge Moscat, Ph.D. Maria Diaz-Meco Conde, Ph.D.

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