The role of phosphatidic acid in platelet-derived growth factor-induced proliferation of rat hepatic stellate cells.
Platelet-derived growth factor (PDGF) is the most potent mitogen for hepatic stellate cells (HSCs) in vitro. The aim of this study was to investigate the role of the lipid-derived second messenger phosphatidic acid (PA) in mediating this effect and, in particular, to determine its interaction with the extracellular signal-regulated kinase (ERK) cascade. HSCs were isolated from rat livers. PA production was determined by lipid extraction and thin-layer chromatography (TLC) after prelabeling cells with [(3)H]myristate. ERK activity was measured by an in vitro kinase assay after immunoprecipitation. Mitogenic concentrations of PDGF, but not those of the relatively less potent mitogen, transforming growth factor alpha (TGF-alpha), stimulated the sustained production of PA from HSCs. Exogenous PA stimulated HSC proliferation and a sustained increase in ERK activity, and proliferation was completely blocked by the inhibition of ERK activation with PD98059. The stimulation of ERK by PDGF was of a similar magnitude but more sustained than that caused by TGF-alpha. These results suggest that the potent mitogenic effect of PDGF in HSCs may be caused, in part, by the generation of PA and subsequently by a more sustained activation of ERK than occurs with less potent mitogens that do not induce the production of this lipid second messenger.
Reeves
H L
HL
Center for Liver Research, University of Newcastle-upon-Tyne, Newcastle upon Tyne, United Kingdom.
Thompson
M G
MG
Dack
C L
CL
Burt
A D
AD
Day
C P
CP
D000818:Animals; D002455:Cell Division; D004075:Diglycerides / Q000096:biosynthesis; D004789:Enzyme Activation; D008099:Liver / Q000166:cytology*; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D010712:Phosphatidic Acids / Q000096:biosynthesis / Q000494:pharmacology / Q000502:physiology*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D015290:Second Messenger Systems; D016211:Transforming Growth Factor alpha / Q000494:pharmacology
D004075:Diglycerides; D010712:Phosphatidic Acids; D010982:Platelet-Derived Growth Factor; D016211:Transforming Growth Factor alpha; D019950:Mitogen-Activated Protein Kinase 1