5-lipoxygenase is phosphorylated by p38 kinase-dependent MAPKAP kinases

5-lipoxygenase (5-LO) catalyzes the initial steps in the formation of leuko trienes, a group of inflammatory mediators derived from arachidonic: acid ( AA). Here we describe that activation of p38 mitogen-activated protein kina se in human polymorphonuclear leukocytes and in Mono Mac 6 cells leads to a ctivation of downstream kinases, which can subsequently phosphorylate 5-LO in vitro. Different agents activated the 5-LO kinase activities, including stimuli for cellular leukotriene biosynthesis (A23187, thapsigargin, N-form yl-leucyl-phenylalanine), compounds that up-regulate the capacity for leuko triene biosynthesis (phorbol 12-myristate 13-acetate, tumor necrosis factor alpha, granulocyte/macrophage colony-stimulating factor), and well known p 38 stimuli as sodium arsenite and sorbitol. For all stimuli, 5-LO kinase ac tivation was counteracted by SB203580 (3 mu M or less), an inhibitor of p38 kinase. At least two p38-dependent 5-LO kinase activities were found. Base d on migration properties in in-gel kinase assays and immunoreactivity, one of these was identified as mitogen-activated protein kinase-activated prot ein kinase 2 (MAPKAP kinase 2). The other appeared to be MAPKAP kinase 3; h owever, it could not be excluded that also other p38-dependent kinases cont ributed. When polymorphonuclear leukocytes were incubated with sodium arsen ite (strong activator of 5-LO kinases), platelet-activating factor and exog enous AA, there was a 4-fold increase in 5-LO activity as compared with inc ubations with only platelet-activating factor and AA. This indicates that 5 -LO phosphorylation can be one factor determining cellular 5-LO activity.