Involvement of MAP kinases in the control of cPLA(2) and arachidonic acid release in endothelial cells

Cytosolic Phospholipase A(2) (cPLA(2)) has been implicated in receptor-medi ated release of arachidonic acid from membrane phospholipids, the limiting step in prostacyclin and other eicosanoid production. Its activity is contr olled by Ca++ levels and enzymatically regulated phosphorylation. The purpo se of this study was to assess the importance of phosphorylation of cPLA(2) in human umbilical vein endothelial cells and to identify the kinases invo lved. inhibitors were used to study the pathways leading to phosphorylation and activation of mitogen activated protein kinases (MAP-kinases) and cPLA (2), as well as release of arachidonic acid and prostacyclin production aft er stimulation with different agonists. We have found that agonists that re lease arachidonic acid, including histamine, thrombin, AlF4-. and pervanada te, all activate the MAP kinases ERK, p38 and JNK and cause phosphorylation of cPLA(2). Agonist specific differences in the signal transduction pathwa ys included variable contribution of tyrosine phosphorylation, protein kina se C and ERK activity, and different effects of pertussis toxin. Treatment with PD98059 (inhibitor of ERK-activation) or SB203580 (inhibitor of p38) c aused partial decrease in arachidonic acid release and cPLA(2) activity. In contrast the nonspecific protein kinase inhibitor staurosporin completely inhibited cPLA(2) activity. We conclude that in endothelial cells arachidon ic acid release is largely mediated by cPLA(2) through agonist-specific pat hways. The MAP kinases ERK and p38 both have demonstrable but not major eff ect on agonist stimulated arachidonic acid release and the data suggest tha t an additional unidentified kinase also has a role. (C) 2001 Elsevier Scie nce Ireland Ltd. All rights reserved.