STIM1 regulates acidic Ca2+ store refilling by interaction with SERCA3 in human platelets

Ca2+ mobilization regulates a wide variety of cellular functions. Platelets posses agonist-releasable Ca2+ stores in acidic organelles where sarcoendoplasmic reticulum Ca2+-ATPase-3 (SERCA) pump is involved in store refilling. Stromal interaction molecule 1 (STIM1), which has been presented as a central regulator of platelet function, is a Ca2+ sensor of the intracellular Ca2+ stores. Here we present that STIM1 is required for acidic store refilling. Electrotransjection of cells with anti-STIM1 (Y231–K243) antibody, directed towards a cytoplasmic sequence of STIM1, significantly reduced acidic store refilling, which was tested by remobilizing Ca2+ from the acidic stores using 2,5-di-(t-butyl)-1,4-hydroquinone (TBHQ) after a brief refilling period that followed thrombin stimulation. Platelet treatment with thrombin or thapsigargin in combination with ionomycin, to induce extensive Ca2+ store depletion, resulted in a transient increase in the interaction between STIM1 and SERCA3, reaching a maximum 30 s after stimulation. The coupling between STIM1 and SERCA3 was abolished by electrotransjection with anti-STIM1 antibody. The interaction between STIM1 and SERCA3 induced by thrombin or by treatment with thapsigargin plus ionomycin is reduced in platelets from type 2 diabetic patients, as well as Ca2+ reuptake into the acidic Ca2+ stores. These findings provide evidence for a role of STIM1 in acidic store refilling in platelets probably acting as a Ca2+ sensor and regulating the activity of SERCA3. This action is impaired in platelets from type 2 diabetics, which might lead to the enhanced cytosolic Ca2+ concentration observed and, therefore, in platelet hyperactivity.