Phosphorylation- and stimulus-dependent inhibition of cellular 5-lipoxygenase activity by nonredox-type inhibitors.

Nonredox-type 5-lipoxygenase (5-LO) inhibitors such as ZM230487 or L-739.010 potently suppress leukotriene biosynthesis at low cellular peroxide tone. Here, we show that inhibition of 5-LO product formation by nonredox-type 5-LO inhibitors in human isolated polymorphonuclear leukocytes (PMNL) depends on the activation pathway of 5-LO. Thus, compared with 5-LO product synthesis induced by the Ca2+-mobilizing agent ionophore A23187, cell stress-induced 5-LO product formation involving 5-LO kinase pathways required ~10- to 100-fold higher concentrations of ZM230487 or L-739.010 for comparable 5-LO inhibition. No such differences were observed for the iron ligand-type 5-LO inhibitor BWA4C or the novel-type 5-LO inhibitors hyperforin and 3-O-acetyl-11-keto-boswellic acid. Experiments using purified 5-LO revealed that Ca2+ is no prerequisite for potent enzyme inhibition by ZM230487, and exposure of PMNL to the combination of ionophore and cell stress did not restore potent 5-LO suppression. Intriguingly, a significant difference in the potency of nonredox-type inhibitors (but not of BWA4C) was determined between wild-type 5-LO and the mutant S271A/S663A-5-LO (lacking phosphorylation sites for ERK1/2 and MAPKAPK-2) in HeLa cells. Collectively, our data suggest that compared with Ca2+-mediated 5-LO product formation, enzyme activation involving 5-LO phosphorylation events specifically and strongly alters the susceptibility of 5-LO toward nonredox-type inhibitors in intact cells.