Primate Monocytes - CD14, CD16 - Ziegler-Heitbrock

Monocyte-derived soluble protein confers 5-lipoxygenase activity Ca²⁺-dependent

Abstract

5-Lipoxygenase (5-LO) is a Ca(2+)-stimulated enzyme that initializes the formation of proinflammatory leukotrienes from arachidonic acid (AA). In this report, we demonstrate that a soluble protein of the monocytic cell line Mono Mac 6 confers 5-LO activity Ca(2+)-dependent in vitro. Thus, in broken cell preparations of human polymorphonuclear leukocytes (PMNL) and rat basophilic leukemia (RBL)-1 cells, 5-LO converted AA (>20&mgr;M) in the absence of Ca(2+), whereas Ca(2+) was absolutely required for 5-LO activity in broken cell preparations of MM6 cells. 5-LO partially purified from MM6 cells was substantially active in the absence of Ca(2+). Recombination experiments revealed that the cytosolic fraction of MM6 cells contains a factor that suppresses the activity of partially purified 5-LO from PMNL, RBL-1, and MM6 cells in the absence but not in the presence of Ca(2+). Further characterization showed that this factor is a 80-100kDa heat-sensitive protein.