Involvement of MAP kinases in the control of cPLA2 and arachidonic acid release in endothelial cells

Cytosolic Phospholipase A2 (cPLA2) has been implicated in receptor-mediated release of arachidonic acid from membrane phospholipids, the limiting step in prostacyclin and other eicosanoid production. Its activity is controlled by Ca++ levels and enzymatically regulated phosphorylation. The purpose of this study was to assess the importance of phosphorylation of cPLA2 in human umbilical vein endothelial cells and to identify the kinases involved. Inhibitors were used to study the pathways leading to phosphorylation and activation of mitogen activated protein kinases (MAP-kinases) and cPLA2, as well as release of arachidonic acid and prostacyclin production after stimulation with different agonists. We have found that agonists that release arachidonic acid, including histamine, thrombin, AlF4−, and pervanadate, all activate the MAP kinases ERK, p38 and JNK and cause phosphorylation of cPLA2. Agonist specific differences in the signal transduction pathways included variable contribution of tyrosine phosphorylation, protein kinase C and ERK activity, and different effects of pertussis toxin. Treatment with PD98059 (inhibitor of ERK-activation) or SB203580 (inhibitor of p38) caused partial decrease in arachidonic acid release and cPLA2 activity. In contrast the nonspecific protein kinase inhibitor staurosporin completely inhibited cPLA2 activity. We conclude that in endothelial cells arachidonic acid release is largely mediated by cPLA2 through agonist-specific pathways. The MAP kinases ERK and p38 both have demonstrable but not major effect on agonist stimulated arachidonic acid release and the data suggest that an additional unidentified kinase also has a role.