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

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.

Research Highlights
► STIM1 located in the plasma membrane is involved in the regulation of SOCE.
► Lipid rafts are involved in the regulation of SOCE by plasma membrane-STIM1.
► Lipid rafts are necessary for the translocation of STIM1 to the plasma membrane.
► Lipid rafts support the association between plasma membrane-STIM1 and Orai1.