Hydrolysis of phosphatidylcholine couples Ras to activation of Raf protein kinase during mitogenic signal transduction.
We have investigated the relationship between hydrolysis of phosphatidylcholine (PC) and activation of the Raf-1 protein kinase in Ras-mediated transduction of mitogenic signals. As previously reported, cotransfection of a PC-specific phospholipase C (PC-PLC) expression plasmid bypassed the block to cell proliferation resulting from expression of the dominant inhibitory mutant Ras N-17. In contrast, PC-PLC failed to bypass the inhibitory effect of dominant negative Raf mutants, suggesting that PC-PLC functions downstream of Ras but upstream of Raf. Consistent with this hypothesis, treatment of quiescent cells with exogenous PC-PLC induced Raf activation, even when normal Ras function was blocked by Ras N-17 expression. Further, activation of Raf in response to mitogenic growth factors was blocked by inhibition of endogenous PC-PLC. Taken together, these results indicate that hydrolysis of PC mediates Raf activation in response to mitogenic growth factors.
Cai
H
H
Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115.
Erhardt
P
P
Troppmair
J
J
Diaz-Meco
M T
MT
Sithanandam
G
G
Rapp
U R
UR
Moscat
J
J
Cooper
G M
GM
D016475:3T3 Cells; D000818:Animals; D002455:Cell Division; D004789:Enzyme Activation; D011905:Genes, ras; D006868:Hydrolysis; D051379:Mice; D009154:Mutation; D010713:Phosphatidylcholines / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D015398:Signal Transduction; D014162:Transfection; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
D010713:Phosphatidylcholines; D011518:Proto-Oncogene Proteins; D019908:Proto-Oncogene Proteins c-raf; D010738:Type C Phospholipases