Phorbol ester up-regulates capacities for nuclear translocation and phosphorylation of 5-lipoxygenase in Mono Mac 6 cells and human polymorphonuclearleukocytes

The leukotrienes are inflammatory mediators derived from arachidonic acid. It was demonstrated that the priming of leukocytes with phorbol-12-myristat e-13-acetate (PMA) leads to the increased formation of 5-lipoxygenase (5-LO ) products in parallel with the increased association of 5-LO with the nucl eus and the activation of kinases that can phosphorylate 5-LO in vitro. Sti mulation of the monocytic cell line Mono Mac 6 with calcium ionophore gave low 5-LO product formation and no detectable redistribution of 5-LO. Howeve r, after priming of Mono Mac 6 cells with phorbol esters, ionophore led to the association of 45% to 75% of cellular 5-LO with the nuclear membrane, t o 5-LO kinase activation, to enhanced release of arachidonate, and to subst antial leukotriene synthesis. Similar results were obtained for human polym orphonuclear leukocytes stimulated with low-dose ionophore, In addition, fo r each cell type, PMA priming up-regulated leukotriene biosynthesis in the presence of exogenous arachidonic acid. A protein kinase inhibitor, calphos tin C, reduced the association of 5-LO with the nucleus and 5-LO kinase act ivity, and the formation of 5-LO products was inhibited. These results sugg est that PMA up-regulates leukotriene biosynthesis not only by increasing t he release of endogenous arachidonate, but also by increasing the capacity for 5-LO phosphorylation and for the translocation of 5-LO to the nucleus i n leukocytes, (Blood. 2001;97:2487-2495) (C) 2001 by The American Society o f Hematology.