Protease-activated receptor signaling in platelets activates cytosolic phospholipase A2α differently for cyclooxygenase-1 and 12-lipoxygenase catalysis.
OBJECTIVE
The rate-limiting step in the biosynthesis of thromboxane A(2) (TxA(2)) and 12-hydroxyeicosatetraenoic acid (12-HETE) by platelets is activation of cytosolic phospholipase A(2α) (cPLA(2α)), which releases arachidonic acid, which is the substrate for cyclooxygenase-1 (COX-1) and 12-lipoxygenase. We evaluated signaling via the human platelet thrombin receptors, protease-activated receptor (PAR) 1 and PAR4, to the activation of cPLA(2α), which provides a substrate for the biosynthesis of TxA(2) and 12-HETE.


RESULTS
Stimulating washed human platelets resulted in delayed biosynthesis of 12-HETE, which continues after maximal formation of TxA(2) is completed, suggesting that 12-HETE is not formed by the same pool of arachidonic acid that provides a substrate to COX-1. PAR1-induced formation of TxA(2) was inhibited by the phosphatidylinositol kinase inhibitor LY294002, whereas this inhibitor did not block 12-HETE biosynthesis. Both 1-butanol and propranolol also blocked TxA(2) biosynthesis but did not inhibit 12-HETE formation.


CONCLUSIONS
The concerted evidence indicates that the platelet thrombin receptors signal activation of cPLA(2α) coupled to COX-1 by a pathway different from that signaling activation of the cPLA(2α) coupled to 12-lipoxygenase.
Cardeza Foundation for Hematologic Research, Department of Medicine, Thomas Jefferson University, 1015 Walnut Street, Philadelphia, PA 19107, USA. michael.holinstat@jefferson.edu
Michael
M
Holinstat
Olivier
O
Boutaud
Patrick L
PL
Apopa
Joanne
J
Vesci
Manju
M
Bala
John A
JA
Oates
Heidi E
HE
Hamm
D020001:1-Butanol / Q000494:pharmacology; D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid / Q000378:metabolism; D001092:Arachidonate 12-Lipoxygenase / Q000378:metabolism*; D016718:Arachidonic Acid / Q000378:metabolism; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D051545:Cyclooxygenase 1 / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D015777:Eicosanoids / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D054513:Group IV Phospholipases A2 / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D009025:Morpholines / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D044462:Receptors, Proteinase-Activated / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013928:Thromboxane A2 / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D002867:Chromones; D015777:Eicosanoids; D004791:Enzyme Inhibitors; D009025:Morpholines; D044462:Receptors, Proteinase-Activated; D016718:Arachidonic Acid; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D013928:Thromboxane A2; D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; D020001:1-Butanol; D011433:Propranolol; D001092:Arachidonate 12-Lipoxygenase; D051545:Cyclooxygenase 1; D011493:Protein Kinase C; D048051:p38 Mitogen-Activated Protein Kinases; D054513:Group IV Phospholipases A2; D002118:Calcium