Involvement of phosphatidylcholine-specific phospholipase C in platelet-derived growth factor-induced activation of the mitogen-activated protein kinase pathway in Rat-1 fibroblasts.
The role of phosphatidylcholine (PC) hydrolysis in activation of the mitogen-activated protein kinase (MAPK) pathway by platelet-derived growth factor (PDGF) was studied in Rat-1 fibroblasts. PDGF induced the transient formation of phosphatidic acid, choline, diacylglycerol (DG), and phosphocholine, the respective products of phospholipase D (PLD) and phospholipase C (PC-PLC) activity, with peak levels at 5-10 min. PLD-catalyzed transphosphatidylation (with n-butyl alcohol) diminished DG formation at 5 min but not at later stages of PDGF stimulation. Phorbol ester-induced down-regulation of protein kinase C (PKC) completely blocked PLD activation but not the formation of DG and phosphocholine at 10 min of PDGF stimulation. Collectively, these data indicate that PDGF activates both PLD and PC-PLC. In contrast, epidermal growth factor did not activate PC-PLC in these cells, and it activated PLD only weakly. DG formation by itself, through Bacillus cereus PC-PLC treatment of cells, was sufficient to mimic PDGF in activation of MAPK independent of phorbol ester-sensitive PKC. Since PKC down-regulation blocked PDGF-induced PLD but not MAPK activation, we conclude that PLD is not involved in MAPK signaling. In contrast, MAPK activation by exogenous (bacterial) PLD was not affected by PKC down-regulation, indicating that signals evoked by exogenous PLD differ from endogenous PLD. D609 (2-10 microg/ml), an inhibitor of PC-PLC, blocked PDGF- but not epidermal growth factor-induced MAPK activation. However, D609 should be used with caution since it also affects PLD activity. The results suggest that PC-PLC rather than PLD plays a critical role in the PDGF-activated MAPK pathway.
van Dijk
M C
MC
Division of Cellular Biochemistry, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Muriana
F J
FJ
de Widt
J
J
Hilkmann
H
H
van Blitterswijk
W J
WJ
D000818:Animals; D001952:Bridged-Ring Compounds / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D004075:Diglycerides / Q000378:metabolism; D015536:Down-Regulation; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects; D006868:Hydrolysis; D009636:Norbornanes; D010713:Phosphatidylcholines / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010739:Phospholipase D / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D051381:Rats; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D015398:Signal Transduction; D013859:Thiocarbamates; D013871:Thiones / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D001952:Bridged-Ring Compounds; D004075:Diglycerides; D009636:Norbornanes; D010713:Phosphatidylcholines; D010726:Phosphodiesterase Inhibitors; D010982:Platelet-Derived Growth Factor; D013859:Thiocarbamates; D013871:Thiones; C046498:tricyclodecane-9-yl-xanthogenate; D004815:Epidermal Growth Factor; D017479:Receptors, Platelet-Derived Growth Factor; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010738:Type C Phospholipases; C105598:phosphatidylcholine-specific phospholipase C; D010739:Phospholipase D