Role of sphingolipids in arachidonic acid metabolism

The arachidonic acid (AA) cascade is regulated mainly by the actions of two rate-limiting enzymes, phospholipase A₂ (PLA₂) and inducible cyclooxygenase-2 (COX-2). PLA₂ acts to generate AA, which serves as the precursor substrate for COX-2 in the metabolic pathway leading to prostaglandin production. Amongst more than 30 members of the PLA₂ family, cytosolic PLA₂α (cPLA₂α, group IVA) plays a major role in releasing AA from cellular membranes. Sphingolipids are a novel class of bioactive lipids that play key roles in the regulation of several cellular processes including growth, differentiation, inflammatory responses, and apoptosis. Recent studies implicated a regulatory function of sphingolipids in prostaglandin production. Whereas ceramide-1-phosphate and lactosylceramide activate cPLA₂α directly, sphingosine-1-phosphate induces COX-2 expression. Sphingomyelin has been shown to inhibit the activity of cPLA₂α. In addition, several sphingolipid analogs including a therapeutic agent currently used clinically are also reported to be inhibitors of cPLA₂α. This review explores the role of sphingolipids in the regulation of cPLA₂α and COX-2.