title: Phospholipase D and extracellular signal-regulated kinase in hepatic stellate cells: effects of platelet-derived growth factor and extracellular nucleotides.
abstract: We have previously provided evidence suggesting that phosphatidic acid, possibly derived from the hydrolysis of phosphatidylcholine by phospholipase D (PLD), is involved in platelet-derived growth factor (PDGF)-mediated increases in extracellular signal-regulated kinase (ERK) activity and DNA synthesis in rat hepatic stellate cells (HSC), the primary fibrogenic cells of the liver. A recent study has shown the presence of P2Y nucleotide receptors on HSC that are coupled to contraction and synthesis of the matrix component, alpha1-procollagen, leading to the suggestion that they may represent a new therapeutic target in the treatment of liver fibrosis. However, although extracellular nucleotides have been shown to stimulate both PLD and ERK, and to elicit proliferation of fibrogenic cells outside the liver, their effect on these parameters in HSC have not yet been investigated. PLD activity was determined by [3H]choline release and [3H]phosphatidylbutanol production, ERK activity by Western blotting, and DNA synthesis by [3H]thymidine incorporation. We report here, for the first time in HSC, that extracellular nucleotides stimulate PLD activity and a sustained activation of ERK. However, in contrast to PDGF, nucleotides had negligible effects on DNA synthesis. Moreover, the effects of PDGF and nucleotides on PLD and ERK were not additive, suggesting activation of the same PLD isoform and pool of ERK. The data demonstrate that nucleotide-stimulated PLD and ERK activities are not coupled to DNA synthesis in HSC. Instead, these responses may be linked to other phenotypic changes associated with activated HSC such as increases in contraction, motility, or extracellular matrix deposition.
authors.affiliation: Centre for Liver Research, The Medical School, University of Newcastle upon Tyne, United Kingdom.
authors.forename: Joaquin
authors.initials: J
authors.lastname: Benitez-Rajal
authors.forename: Maria-Jose
authors.initials: MJ
authors.lastname: Lorite
authors.forename: Alastair D
authors.initials: AD
authors.lastname: Burt
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Day
authors.forename: Michael G
authors.initials: MG
authors.lastname: Thompson
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002794:Choline / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D020404:Glycerophospholipids / Q000378:metabolism; D008099:Liver / Q000166:cytology* / Q000378:metabolism*; D008297:Male; D009711:Nucleotides / Q000494:pharmacology*; D010739:Phospholipase D / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014544:Uridine Triphosphate / Q000494:pharmacology
chemical_list: D020404:Glycerophospholipids; D009711:Nucleotides; D010982:Platelet-Derived Growth Factor; D012333:RNA, Messenger; C051521:phosphatidylethanol; D000255:Adenosine Triphosphate; D004247:DNA; D048049:Extracellular Signal-Regulated MAP Kinases; D010739:Phospholipase D; D002794:Choline; D014544:Uridine Triphosphate