Phosphatidylinositol 4,5-Bisphosphate Anchors Cytosolic Group IVA Phospholipase A2 to Perinuclear Membranes and Decreases Its Calcium Requirement for Translocation in Live Cells

摘要

The eicosanoids are centrally involved in the onset and resolution of inflammatory processes. A key enzyme in eicosanoid biosynthesis during inflammation is group IVA phospholipase A₂ (also known as cytosolic phospholipase A_2α, cPLA₂α). This enzyme is responsible for generating free arachidonic acid from membrane phospholipids. cPLA₂α translocates to perinuclear membranes shortly after cell activation, in a process that is governed by the increased availability of intracellular Ca2+. However, cPLA₂α also catalyzes membrane phospholipid hydrolysis in response to agonists that do not mobilize intracellular Ca2+. How cPLA₂α interacts with membranes under these conditions is a major, still unresolved issue. Here, we report that phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P₂] promotes translocation of cPLA₂α to perinuclear membranes of intact cells in a manner that is independent of rises in the intracellular Ca2+ concentration. PtdIns(4,5)P₂ anchors the enzyme to perinuclear membranes and allows for a proper interaction with its phospholipid substrate to release arachidonic acid.