Association with actin mediates the EGTA‐resistant binding of cytosolic phospholipase A 2 ‐α to the plasma membrane of activated platelets

The association of cytosolic phospholipase A 2 ‐α (cPLA 2 α) with intracellular membranes is central to the generation of free arachidonic acid and thromboxane A 2 in activated platelets. Despite this, the site and nature of this membrane association has not been fully characterised upon platelet activation. High resolution imaging showed that cPLA 2 α was distributed in a partly structured manner throughout the resting platelet. Upon glass activation or thrombin stimulation, cPLA 2 α relocated to a peripheral region corresponding to the platelet plasma membrane. Upon thrombin stimulation of platelets a major pool of cPLA 2 α was associated with the plasma membrane in an EGTA‐resistant manner. EGTA‐resistant membrane binding was abolished upon de‐polymerisation of actin filaments by DNase I and furthermore, cPLA 2 α co‐immunoprecipitated with actin upon thrombin stimulation of platelets. Immunofluorescence microscopy studies revealed that, upon platelet activation, cPLA 2 α and actin co‐localised at the plasma membrane. Thus we have identified a novel mechanism for the interaction of cPLA 2 α with its membrane substrate via interaction with actin.