Association with actin mediates the EGTA-resistant binding of cytosolic phospholipase A2-α to the plasma membrane of activated platelets

The association of cytosolic phospholipase A2-α (cPLA2α) with intracellular membranes is central to the generation of free arachidonic acid and thromboxane A2 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 cPLA2α was distributed in a partly structured manner throughout the resting platelet. Upon glass activation or thrombin stimulation, cPLA2α relocated to a peripheral region corresponding to the platelet plasma membrane. Upon thrombin stimulation of platelets a major pool of cPLA2α 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, cPLA2α co-immunoprecipitated with actin upon thrombin stimulation of platelets. Immunofluorescence microscopy studies revealed that, upon platelet activation, cPLA2α and actin co-localised at the plasma membrane. Thus we have identified a novel mechanism for the interaction of cPLA2α with its membrane substrate via interaction with actin.