Novel translocation responses of cytosolic phospholipase A2α fluorescent proteins

Cytosolic phospholipase A2 (cPLA(2))alpha responds to the rise in cytosolic Ca2+ ([Ca2+](i)) attending cell stimulation by moving to intracellular membranes, releasing arachidonic acid (AA) from these membranes, and thereby initiating the synthesis of various lipid mediators. Under some conditions, however, cPLA(2)alpha translocation occurs without any corresponding changes in [Ca2+](i). The signal for such responses has not been identified. Using confocal microscopy to track fluorescent proteins fused to cPLA(2)alpha or cPLA(2)alpha's C2 domain, we find that AA mimics Ca2+ ionophores in stimulating cPLA(2)alpha translocations to the perinuclear ER and to a novel site, the lipid body. Unlike the ionophores, AA acted independently of [Ca2+](i) rises and did not translocate the proteins to the Golgi. AA's action did not involve its metabolism to eicosanoids or acylation into cellular lipids. Receptor agonists also stimulated translocations targeting lipid bodies. We propose that AA is a signal for Ca2+-independent cPLA2a translocation and that lipid bodies are common targets of cPLA(2)alpha and contributors to stimulus-induced lipid mediator synthesis. (C) 2008 Elsevier B.V. All rights reserved.