Regulation of phospholipid scramblase activity during apoptosis and cell activation by protein kinase C delta

Phospholipid scramblase induces nonspecific bidirectional movement of phosp holipids across the membrane during cell activation and has been proposed t o mediate the appearance of phosphatidylserine (PS) in the plasma membrane outer leaflet during apoptosis, a cell surface change that is critical for apoptotic cell removal. We report here that protein kinase C (PKC) delta pl ays an important role in activated transbilayer movement of phospholipids a nd surface PS exposure by directly enhancing the activity of phospholipid s crambIase, Specific inhibition of PKC delta by rottlerin prevented both apo ptosis- and activation-induced scrambIase activity. PKC delta was either se lectively cleaved and activated in a caspase 3-dependent manner (during apo ptosis) or translocated to the plasma membrane (in stimulated cells) and co uld directly phosphorylate scramblase immunoprecipitated from Jurkat cells. Furthermore, reconstitution of PKC delta and scramblase, but not scramblas e or PKC delta alone in Chinese hamster ovary cells demonstrated enhanced s cramblase activity.