Role of phosphatidylinositol 4,5-bisphosphate in the activation of cytosolic phospholipase A2-α

Cytosolic phospholipase A2-α (cPLA2) plays an important role in the release of arachidonic acid and in cell injury. Activation of cPLA2 is dependent on a rise in cytosolic Ca2+ concentration, membrane association via the Ca2+-dependent lipid binding (CaLB) domain, and phosphorylation. This study addresses the activation of cPLA2 via potential association with membrane phosphatidylinositol 4,5-bisphosphate (PIP2), including the role of a “pleckstrin homology (PH)-like” region of cPLA2 (amino acids 263-354). In cells incubated with complement, phorbol myristate acetate + the Ca2+ ionophore, A23187, or epidermal growth factor + A23187, expression of the PH domain of phospholipase C-δ1 (which sequesters membrane PIP2) attenuated cPLA2 activity. Stimulated cPLA2 activity was also attenuated by the expression of cPLA2 135-366, or cPLA2 2-366, and expression of a PIP2-specific 5′-phosphatase. However, in a yeast-based assay that tests the ability of proteins to bind to membrane lipids, including PIP2, with high affinity, only cPLA2 1-200 (CaLB domain) was able to interact with membrane lipids, whereas cPLA2s 135-366, 2-366, 201-648, and 1-648 were unable to do so. Therefore, cPLA2 activity can be modulated by sequestration or depletion of cellular PIP2, although the interaction of cPLA2 with membrane PIP2 appears to be indirect, or of weak affinity.