Hydrolysis of cytoskeletal proteins by the Ca2+-dependent protease during platelet activation

During platelet stimulation, the cytosolic Ca2+ concentration increases to micromolar levels. One consequence of this increase is that the Ca2+-dependent protease within platelets is activated. Activation of the Ca2+-dependent protease results in hydrolysis of actin-binding protein and P235. Actin-binding protein and P235 can both affect the organization of actin, thus activation of the Ca2+-dependent protease may provide a regulatory mechanism by which stimulus-induced changes in the organization of actin filaments could be directed. Although both actin-binding protein and P235 affect actin polymerization, stimulus-induced actin polymerization occurs before hydrolysis of actin-binding protein or P235 can be detected, thus it seems unlikely that hydrolysis of these proteins affects actin polymerization. Actin-binding protein also cross-links actin filaments into networks, a function that is lost when it is hydrolyzed by the Ca2+-dependent protease. Thus, hydrolysis of actin-binding protein may result in disruption of the actin filament networks that form early during platelet activation and permit the reorganization of filaments into the bundles present at later stages of platelet activation.