title: Selective hydrolysis of plasmalogens in endothelial cells following thrombin stimulation.
abstract: The present study was performed to characterize thrombin-stimulated phospholipase A2 (PLA2) activity and the resultant release of lysophospholipids from endothelial cells. The majority of PLA2 activity in endothelial cells was membrane associated, Ca2+ independent, and arachidonate selective. Incubation with thrombin increased membrane-associated PLA2 activity using both plasmenylcholine and alkylacyl glycerophosphocholine substrates in the absence of Ca2+, with no increase in activity observed with phosphatidylcholine substrate. The increased PLA2 activity was accompanied by arachidonic acid and lysoplasmenylcholine (LPlasC) release from endothelial cells into the surrounding medium. Thrombin-induced changes were duplicated by stimulation with the thrombin-receptor-directed peptide SFLLRNPNDKYEPF. Pretreatment with the Ca2+-independent PLA2 inhibitor bromoenol lactone blocked thrombin-stimulated increases in PLA2 activity, arachidonic acid, and LPlasC release. Stimulation of protein kinase C (PKC) increased basal PLA2 activity and LPlasC production. Thrombin-stimulated PLA2 activity and LPlasC production were enhanced with PKC activation and completely prevented with PKC downregulation. Thus thrombin treatment of endothelial cells activates a PKC-activated, membrane-associated, Ca2+-independent PLA2 that selectively hydrolyzes arachidonylated, ether-linked phospholipid substrates, resulting in LPlasC and arachidonic acid release.
authors.affiliation: Department of Pathology, St. Louis University School of Medicine, St. Louis, Missouri 63104, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Creer
authors.forename: J
authors.initials: J
authors.lastname: McHowat
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D006868:Hydrolysis / Q000187:drug effects; D008246:Lysophospholipids / Q000378:metabolism; D009281:Naphthalenes / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D010955:Plasmalogens / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D011753:Pyrones / Q000494:pharmacology; D013552:Swine; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000494:pharmacology*
chemical_list: D008246:Lysophospholipids; D009281:Naphthalenes; D010446:Peptide Fragments; D010726:Phosphodiesterase Inhibitors; D010955:Plasmalogens; D011753:Pyrones; C021215:lysoplasmalogens; C072032:thrombin receptor peptide (42-55); D016718:Arachidonic Acid; C068314:6-(bromomethylene)tetrahydro-3-(1-naphthaleneyl)-2H-pyran-2-one; D011493:Protein Kinase C; D010741:Phospholipases A; D054467:Phospholipases A2; D013917:Thrombin