Very low density lipoprotein-mediated signal transduction and plasminogen activator inhibitor type 1 in cultured HepG2 cells.
In normal subjects and in patients with cardiovascular disease, plasma triglycerides are positively correlated with plasminogen activator inhibitor type 1 (PAI-1) levels. Moreover, in vitro studies indicate that VLDLs induce PAI-1 synthesis in cultured cells, ie, endothelial and HepG2 cells. However, the signaling pathways involved in the effect of VLDL on PAI-1 synthesis have not yet been investigated. We report that VLDLs induce a signaling cascade that leads to an enhanced secretion of PAI-1 by HepG2 cells. In myo-[(3)H]inositol-labeled HepG2 cells, VLDL (100 microg/mL) caused a time-dependent increase in [(3)H]inositol phosphates, the temporal sequence being tris>bis>monophosphate. VLDL brought about a time-dependent stimulation of membrane-associated protein kinase C (PKC) activity and arachidonate release. Finally, VLDL stimulated mitogen-activated protein (MAP) kinase, and this effect was reduced by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), which suggests that PKC plays a pivotal role in MAP kinase phosphorylation. VLDL-induced PAI-1 secretion was completely prevented by U73122, a specific inhibitor of phosphatidylinositol-specific phospholipase C, by H7 or by PKC downregulation, and by mepacrine (all P<0.01 versus VLDL-treated cells). 3,4,5-Trimethoxybenzoic acid 8-(diethylamino)-octyl ester, which prevents Ca2+ release from intracellular stores, inhibited VLDL-induced PAI-1 secretion by 60% (P<0.05), and the MAP kinase/extracellular signal-regulated kinase kinase (MEK) inhibitor PD98059 completely suppressed both basal and VLDL-induced PAI-1 secretion. These data demonstrate that VLDL-induced PAI-1 biosynthesis results from a principal signaling pathway involving PKC-mediated MAP kinase activation.
Institute of Pharmacological Sciences, University of Milan, Italy.
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Banfi
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Mussoni
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Risé
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Cattaneo
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Vicentini
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Battaini
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Galli
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Tremoli
D000975:Antioxidants / Q000494:pharmacology; D016718:Arachidonic Acid / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D006528:Carcinoma, Hepatocellular; D015243:Cholesterol, VLDL / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D005342:Fibrinolysis; D005419:Flavonoids / Q000494:pharmacology; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010739:Phospholipase D / Q000378:metabolism; D010766:Phosphorylation; D017395:Plasminogen Activator Inhibitor 1 / Q000096:biosynthesis* / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D011760:Pyrrolidinones / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology; D014316:Tritium; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
D000975:Antioxidants; D002121:Calcium Channel Blockers; D015243:Cholesterol, VLDL; D004791:Enzyme Inhibitors; D004963:Estrenes; D005419:Flavonoids; D010716:Phosphatidylinositols; D010726:Phosphodiesterase Inhibitors; D017395:Plasminogen Activator Inhibitor 1; D011760:Pyrrolidinones; D014316:Tritium; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D016718:Arachidonic Acid; D014443:Tyrosine; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D019284:Thapsigargin; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010739:Phospholipase D; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one