Evidence for a bifurcation of the mitogenic signaling pathway activated by Ras and phosphatidylcholine-hydrolyzing phospholipase C.

TitleEvidence for a bifurcation of the mitogenic signaling pathway activated by Ras and phosphatidylcholine-hydrolyzing phospholipase C.
Publication TypeJournal Article
Year of Publication1995
AuthorsBjørkøy G, Overvatn A, Diaz-Meco MT, Moscat J, Johansen T
JournalJ Biol Chem
Date Published1995 Sep 08
Keywords3T3 Cells, Animals, Cell Transformation, Neoplastic, DNA Replication, Genes, Dominant, Hydrolysis, Mice, Mitogens, Mutation, Oncogene Protein p21(ras), Phenotype, Phorbol Esters, Phosphatidylcholines, Protein Kinases, Protein-Serine-Threonine Kinases, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-raf, Signal Transduction, Type C Phospholipases

NIH 3T3 cells stably transfected with the gene encoding phosphatidylcholine-hydrolyzing phospholipase C (PC-PLC) from Bacillus cereus display a chronic elevation of intracellular diacylglycerol levels and a transformed phenotype. We have used such PC-PLC-transformed cells to evaluate the roles of the cytoplasmic serine/threonine kinases Raf-1, zeta protein kinase C (zeta PKC) and protein kinase A (PKA) in oncogenesis and mitogenic signal transduction elicited by phosphatidylcholine hydrolysis. We demonstrate here that stable expression of dominant negative mutants of both zeta PKC and Raf-1 lead to reversion of PC-PLC-transformed cells. Interestingly, expression of kinase defective zeta PKC also reverted NIH 3T3 cells transformed by the v-Ha-ras oncogene. Activation of PKA in response to elevation of cAMP levels also lead to reversion of PC-PLC-induced transformation, implicating PKA as a negative regulator acting downstream of PC-PLC. On the other hand, inhibition or depletion of phorbol ester responsive PKCs attenuated but did not block the ability of PC-PLC-transformed cells to induce DNA synthesis in the absence of growth factors. These results clearly implicate both Raf-1 and zeta PKC as necessary downstream components for transduction of the mitogenic/oncogenic signal generated by PLC-mediated hydrolysis of phosphatidylcholine and suggest, together with other recent evidence, a bifurcation in the signaling pathway downstream of PC-PLC.

Alternate JournalJ Biol Chem
PubMed ID7673165
Related Faculty: 
Jorge Moscat, Ph.D. Maria Diaz-Meco Conde, Ph.D.

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