Phosphorylation of cPLA(2)alpha at Ser(505) Is Necessary for Its Translocation to PtdInsP(2)-Enriched Membranes

Group IVA cytosolic phospholipase A(2)alpha (cPLA(2)alpha) is a key enzyme in physiology and pathophysiology because it constitutes a rate-limiting step in the pathway for the generation of pro- and anti-inflammatory eicosanoid lipid mediators. cPLA(2)alpha activity is tightly regulated by multiple factors, including the intracellular Ca2+ concentration, phosphorylation reactions, and cellular phosphatidylinositol (4,5) bisphosphate levels (PtdInsP(2)). In the present work, we demonstrate that phosphorylation of the enzyme at Ser(505) is an important step for the translocation of the enzyme to PtdInsP(2)-enriched membranes in human cells. Constructs of eGFP-cPLA(2) mutated in Ser(505) to Ala (S505A) exhibit a delayed translocation in response to elevated intracellular Ca2+, and also in response to increases in intracellular PtdInsP(2) levels. Conversely, translocation of a phosphorylation mimic mutant (S505E) is fully observed in response to cellular increases in PtdInsP(2) levels. Collectively, these results suggest that phosphorylation of cPLA(2)alpha at Ser(505) is necessary for the enzyme to translocate to internal membranes and mobilize arachidonic acid for eicosanoid synthesis.