Lipid rafts are essential for the regulation of SOCE by plasma membrane resident STIM1 in human platelets

Abstract

STIM1 is a transmembrane protein essential for the activation of store-operated Ca²+ entry (SOCE), a major Ca²+ influx mechanism. STIM1 is either located in the endoplasmic reticulum, communicating the Ca²+ concentration in the stores to plasma membrane channels or in the plasma membrane, where it might sense the extracellular Ca²+ concentration. Plasma membrane-located STIM1 has been reported to mediate the SOCE sensitivity to extracellular Ca²+ through its interaction with Orai1. Here we show that plasma membrane lipid raft domains are essential for the regulation of SOCE by extracellular Ca²+. Treatment of platelets with the SERCA inhibitor thapsigargin (TG) induced Mn²+ entry, which was inhibited by increasing concentrations of extracellular Ca²+. Platelet treatment with methyl-β-cyclodextrin, which removes cholesterol and disrupts the lipid raft domains, impaired the inactivation of Ca²+ entry induced by extracellular Ca²+. Methyl-β-cyclodextrin also abolished translocation of STIM1 to the plasma membrane stimulated by treatment with TG and prevented TG-evoked co-immunoprecipitation between plasma membrane-located STIM1 and the Ca²+ permeable channel Orai1. These findings suggest that lipid raft domains are essential for the inactivation of SOCE by extracellular Ca²+ mediated by the interaction between plasma membrane-located STIM1 and Orai1.