TAILIEUCHUNG - Báo cáo khóa học: Stimulation-dependent recruitment of cytosolic phospholipase A2-a to EA.hy.926 endothelial cell membranes leads to calcium-independent association

Cytosolic phospholipase A2 -a (cPLA2 -a) is a calcium-activated enzyme involved in agonist-induced arachidonic acid release. In endothelial cells, free arachidonic acid is predominantly converted into prostacyclin, a potent vaso-dilator and inhibitor of platelet activation. As the rate-lim-iting step in prostacyclin production is the generation of free arachidonic acid by cPLA2-a, this enzyme has become an attractive pharmacological target and the focus of many studies. Following stimulation with calcium-mobilizing agonists, cPLA2 -atranslocates to intracellular phospholipid membranes via its C2 domain | Eur. J. Biochem. 271 69-77 2004 FEBS 2003 doi Stimulation-dependent recruitment of cytosolic phospholipase A2-a to endothelial cell membranes leads to calcium-independent association Seema Grewal Jennifer Smith Sreenivasan Ponnambalam and John Walker School of Biochemistry and Molecular Biology University of Leeds UK Cytosolic phospholipase A2-a cPLA2-a is a calcium-activated enzyme involved in agonist-induced arachidonic acid release. In endothelial cells free arachidonic acid is predominantly converted into prostacyclin a potent vasodilator and inhibitor of platelet activation. As the rate-limiting step in prostacyclin production is the generation of free arachidonic acid by cPLA2-a this enzyme has become an attractive pharmacological target and the focus of many studies. Following stimulation with calcium-mobilizing agonists cPLA2-a translocates to intracellular phospholipid membranes via its C2 domain. In this study the calcium-induced association of cPLA2-a with endothelial cell membranes was investigated. Subcellular fractionation and immunofluorescence studies showed that following stimulation with histamine thrombin or the calcium ionophore A23187 cPLA2-a relocated to intracellular membranes. Treatment of A23187-stimulated cells with EGTA or BAPTA-AM demonstrated that a substantial pool of cPLA2-a remained associated with membrane frac tions in a calcium-independent manner. Furthermore immunofluorescence microscopy studies revealed that cells stimulated for periods of greater than 10 min showed a high proportion of calcium-independent membrane-associated cPLA2-a. Calcium-independent membrane association of cPLA2-a was not due to hydrophobic or cytoskeletal interactions. Finally the recombinant C2 domain of cPLA2-a exhibited calcium-independent membrane binding to membranes isolated from A23187-stimulated cells but not those isolated from nonstimulated cells. These findings suggest that novel mechanisms .

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