Arachidonic acid regulates the translocation of 5-lipoxygenase to the nuclear membranes in human neutrophils

Elevation of the intracellular cAMP concentration in agonist- activated human neutrophils ( PMN) leads to the concomitant inhibitions of arachidonic acid ( AA) release, 5- lipoxygenase ( 5- LO) translocation, and leukotriene ( LT) biosynthesis. We report herein that exogenous AA completely prevents cAMP- dependent inhibition of 5- LO translocation and LT biosynthesis in agonist- activated PMN. Moreover, the group IVA phospholipase A(2) inhibitor pyrrophenone and the MEK inhibitor U- 0126 inhibited AA release and 5- LO translocation in activated PMN, and these effects were also prevented by exogenous AA, demonstrating a functional link between AA release and 5- LO translocation. Polyunsaturated fatty acids of the C18 and C20 series containing at least three double bonds located from carbon 9 ( or closer to the carboxyl group) were equally effective as AA in restoring 5- LO translocation in pyrrophenone- treated agonist- activated PMN. Importantly, experiments with the 5- LO- activating protein inhibitor MK- 0591 and the intracellular Ca2+ chelator BAPTA- AM demonstrated that the AA- regulated 5- LO translocation is FLAP- and Ca2+ dependent. Finally, the redox and competitive 5- LO inhibitors L- 685,015, L- 739,010, and L- 702,539 ( but not cyclooxygenase inhibitors) efficiently substituted for AA to reverse the pyrrophenone inhibition of 5-LO translocation, indicating that the site of regulation of 5- LO translocation by AA is at or in the vicinity of the catalytic site. This report demonstrates that AA regulates the translocation of 5- LO in human PMN and unravels a novel mechanism of the cAMP- mediated inhibition of LT biosynthesis.