Loss of Plasma Membrane Phospholipid Asymmetry Requires Raft Integrity

Abstract

Cholesterol-rich membrane microdomains, also termed lipid rafts, are implicated in the recruitment of essential proteins for intracellular signal transduction. In nonstimulated cells, phosphatidylserine, an anionic aminophospholipid essential for the hemostatic response, is mostly sequestered in the inner leaflet of the plasma membrane. Cell stimulation by Ca2+-mobilizing or apoptogenic agents induces the migration of phosphatidylserine to the exoplasmic leaflet, allowing the assembly and activation of several key enzyme complexes of the coagulation cascade and phagocyte recognition of stimulated or senescent cells. We have recently proposed that store-operated Ca2+ entry regulates externalization of phosphatidylserine at the cell surface (Kunzelmann-Marche, C., Freyssinet, J.-M., and Martı́nez, M. C. (2001)J. Biol. Chem. 276, 5134–5139). Here, we show that store-operated Ca2+ entry and phosphatidylserine exposure are dramatically reduced after raft disruption by methyl-β-cyclodextrin. In addition, transient receptor potential channel 1-specific antibody was able to significantly decrease Ca2+-induced redistribution of phosphatidylserine. Furthermore, store-operated Ca2+ entry and phosphatidylserine exposure were dependent in part on the extracellular signal-regulated kinase pathway associated with rafts. Hence, raft integrity and store-operated Ca2+ entry involving transient receptor potential channel 1 channels are essential for completion of the phosphatidylserine transmembrane redistribution process.