Blood Journal
Leading the way in experimental and clinical research in hematology

The serum- and glucocorticoid-inducible kinase 1 (SGK1) influences platelet calcium signaling and function by regulation of Orai1 expression in megakaryocytes

  1. Oliver Borst1,2,
  2. Eva-Maria Schmidt1,
  3. Patrick Münzer1,
  4. Tanja Schönberger2,
  5. Syeda T. Towhid1,
  6. Margitta Elvers2,
  7. Christina Leibrock1,
  8. Evi Schmid1,
  9. Anja Eylenstein1,
  10. Dietmar Kuhl3,
  11. Andreas E. May2,
  12. Meinrad Gawaz2, and
  13. Florian Lang1
  1. 1Department of Physiology, University of Tübingen, Tübingen, Germany;
  2. 2Innere Medizin III, Department of Cardiology and Cardiovascular Medicine, University of Tübingen, Tübingen, Germany; and
  3. 3Center for Molecular Neurobiology, Institute for Molecular and Cellular Cognition, University Medical Center Hamburg-Eppendorf, Hamburg, Germany

Abstract

Platelets are activated on increase of cytosolic Ca2+ activity ([Ca2+]i), accomplished by store-operated Ca2+ entry (SOCE) involving the pore-forming ion channel subunit Orai1. Here, we show, for the first time, that the serum- and glucocorticoid-inducible kinase 1 (SGK1) is expressed in platelets and megakaryocytes. SOCE and agonist-induced [Ca2+]i increase are significantly blunted in platelets from SGK1 knockout mice (sgk1−/−). Similarly, Ca2+-dependent degranulation, integrin αIIbβ3 activation, phosphatidylserine exposure, aggregation, and in vitro thrombus formation were significantly impaired in sgk1−/− platelets, whereas tail bleeding time was not significantly enhanced. Platelet and megakaryocyte Orai1 transcript levels and membrane protein abundance were significantly reduced in sgk1−/− mice. In human megakaryoblastic cells (MEG-01), transfection with constitutively active S422DSGK1 but not with inactive K127NSGK1 significantly enhanced Orai1 expression and SOCE, while effects reversed by the SGK1 inhibitor GSK650394 (1μM). Transfection of MEG-01 cells with S422DSGK1 significantly increased phosphorylation of IκB kinase α/β and IκBα resulting in nuclear translocation of NF-κB subunit p65. Treatment of S422DSGK1-transfected MEG-01 cells with the IκB kinase inhibitor BMS-345541 (10μM) abolished SGK1-induced increase of Orai1 expression and SOCE. The present observations unravel SGK1 as novel regulator of platelet function, effective at least in part by NF-κB–dependent transcriptional up-regulation of Orai1 in megakaryocytes and increasing platelet SOCE.

  • Submitted June 9, 2011.
  • Accepted August 28, 2011.
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