Phosphorylation of cPLA 2 α at Ser 505 Is Necessary for Its Translocation to PtdInsP 2 -Enriched Membranes.

Group IVA cytosolic phospholipase A 2 α (cPLA 2 α) 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 α activity is tightly regulated by multiple factors, including the intracellular Ca 2+ 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 Ca 2+ , 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 α at Ser 505 is necessary for the enzyme to translocate to internal membranes and mobilize arachidonic acid for eicosanoid synthesis.