Interactions of 12‐lipoxygenase with phospholipase A₂isoforms following platelet activation through the glycoprotein VI collagen receptor

Abstract

Recent studies implicate the collagen receptor, glycoprotein VI (GPVI) in activation of platelet 12-lipoxygenase (p12-LOX). Herein, we show that GPVI-stimulated 12-hydro(peroxy)eicosatetraenoic acid (H(P)ETE) synthesis is inhibited by palmityl trifluromethyl ketone or oleyloxyethylphosphocholine , but not bromoenol lactone, implicating secretory and cytosolic, but not calcium-independent phospholipase A 2 (PLA 2 ) isoforms. Also, following GPVI activation, 12-LOX co-immunoprecipitates with both cytosolic and secretory PLA 2 (sPLA 2 ). Finally, venoms containing sPLA 2 acutely activate p12-LOX in a dose-dependent manner. This study shows that platelet 12-H(P)ETE generation utilizes arachidonate substrate from both c-and sPLA 2 and that 12-LOX functionally associates with both PLA 2 isoforms.

Phospholipid-esterified Eicosanoids Are Generated in Agonist-activated Human Platelets and Enhance Tissue Factor-dependent Thrombin Generation

“…A previous study showed that cPLA2 is required for generation of free 12 S -HETE; however, this was not the case for 12-HETE-PLs because PACOCF3 was without effect (Fig. 4) (33). Inhibition by MAFP suggests that AA destined for HETE-PL generation is hydrolyzed by a PLA2 that could include platelet-activating factor-acetylhydrolase, fatty acid amylhydrolase, cPLA2, or iPLA2; however, the latter two enzymes were excluded by the use of PACOCF3 and BEL.…”

Protease-Activated Receptor Signaling in Platelets Activates Cytosolic Phospholipase A 2α Differently for Cyclooxygenase-1 and 12-Lipoxygenase Catalysis

“…Platelet COX-1 is localized to the intracellular membrane complex with characteristics of the endoplasmic reticulum that is referred to as the dense tubular system 32. On the other hand, the 12-LOX is predominantly localized in the cytosol of rat platelets that have been isolated so as to minimize ex vivo activation, and it undergoes calcium- and thrombin-dependent translocation to a membrane fraction,33,34 from which it can be coimmunoprecipitated with cPLA 2 α 17. Thus, the differences between PAR-induced signaling to the cPLA 2 α providing substrate to COX-1 and that coupled to 12-LOX may occur in the context of localization of the 2 oxygenases at separate sites in the platelet.…”

“…As is the case with TxA 2 biosynthesis, virtually all of the AA substrate for platelet 12-LOX is derived from activation of cPLA 2 α 7. 12-HETE is released by collagen and also by higher concentrations of thrombin 12,17. To better understand the effect of thrombin on 12-HETE release, we have characterized and compared signaling of its 2 receptors, PAR1 and PAR4, with the activation of cPLA 2 α coupled to 12-LOX.…”

Ganglioside GM3 is involved in neuronal cell death

“…GEM acts as a "glycosignaling domain" either by recruiting molecules that are involved in signaling pathways, allowing their molecular interaction, or by modulating signaling function (53). Activated 12-LOX was reported to be translocated to the plasma membrane (41) and to functionally associate with phospholipase A2 isoforms (54). It has not been reported that 12-LOX exists, at least temporarily, in GEM.…”