Ral and Rho-dependent activation of phospholipase D in v-Raf-transformed cells.
Phospholipase D (PLD) activity is commonly elevated in response to mitogenic signals. We reported previously that although the transformed phenotype induced by v-Src was dependent upon Raf-1, the PLD activity induced by v-Src was independent of Raf-1. This observation suggested to us that Raf would not likely be an activator of PLD. However, upon examination of PLD activity in v-Raf-transformed cells, surprisingly, we found that PLD activity is elevated to levels that were even higher than that observed in v-Src-transformed cells. To characterize the mechanism of v-Raf-induced PLD activity, we examined the dependence of v-Raf-induced PLD activity upon protein kinase C (PKC) the small GTPases Ral and Rho, which have all been implicated in the activation of PLD. The v-Raf-induced PLD activity was inhibited by dominant negative mutants for both Ral and Rho. The dependence upon Ral was particularly surprising since Ral is a downstream target of Ras, which is an upstream activator of Raf. Depleting cells of PKC by long term phorbol ester treatment actually increased PLD activity in v-Raf-transformed cells, indicating that v-Raf-induced PLD activity is not dependent on PKC. These data describe a novel mechanism for PLD activation by v-Raf that is independent of PKC, but dependent upon both Ral and Rho GTPases.
Frankel
P
P
Department of Biological Sciences, Hunter College of the City University of New York 10021, USA.
Ramos
M
M
Flom
J
J
Bychenok
S
S
Joseph
T
T
Kerkhoff
E
E
Rapp
U R
UR
Feig
L A
LA
Foster
D A
DA
D016475:3T3 Cells; D000818:Animals; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000502:physiology; D019204:GTP-Binding Proteins / Q000502:physiology*; D051379:Mice; D027384:Oncogene Proteins v-raf; D010739:Phospholipase D / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D015682:Retroviridae Proteins, Oncogenic / Q000502:physiology*; D012234:Rho Factor / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D020725:ral GTP-Binding Proteins
D015682:Retroviridae Proteins, Oncogenic; D012234:Rho Factor; D027384:Oncogene Proteins v-raf; D011493:Protein Kinase C; D010739:Phospholipase D; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020725:ral GTP-Binding Proteins