Rapid induction of arachidonic acid release by monocyte chemotactic protein-1 and related chemokines: Role of Ca2+ influx, synergism with platelet-activating factor and significance for chemotaxis

Monocyte Chemotactic Protein-1 (MCP-1), a member of the Cys-Cys branch of the chemokine superfamily, induced a mepacrine- and manoalide-sensitive increase in the release of [³H]arachidonic acid from prelabeled human monocytes and monocytic THP-1 leukemic cells. The effect was rapid (3H]arachidonic acid release was observed in the absence of Ca²⁺ influx (5 mM EGTA or 5 mM Ni²⁺) or in monocytes loaded with a Ca²⁺-buffering agent. However, using ionophore-permeabilized monocytes and controlled intracellular Ca²⁺ concentration it was possible to dissociate MCP-1-induced Ca²⁺ influx from [³H]arachidonic acid release. Thus, the MCP-1-induced increase in [Ca²⁺]_i is necessary but not sufficient for arachidonic acid accumulation. Phospholipase A₂ inhibitors (mepacrine, p-bromophenacyl bromide, and manoalide) blocked monocyte polarization and chemotaxis induced by MCP-1. The related Cys-Cys chemokines RANTES and LD78/MIP1α also induced a rapid release of [³H]arachidonic acid, and their chemotactic activity was blocked by phospholipase A₂ inhibitors. Brief (5 min) pretreatment of monocytes with platelet-activating factor amplified MCP-1-induced arachidonic acid release and, at MCP-1 suboptimal concentrations, synergized in inducing monocyte migration. Since MCP-1 and platelet-activating factor are induced concomitantly by inflammatory cytokines in monocytes and endothelial cells, we speculate that the observed synergism may have in vivo relevance. The results presented here show that the Cys-Cys chemokines MCP-1, LD78/MIP1α, and RANTES cause rapid release of arachidonic acid in monocytes and that this may be important in inducing monocyte chemotaxis.