title: Impact of the serum- and glucocorticoid-inducible kinase 1 on platelet dense granule biogenesis and secretion.
abstract: BACKGROUND
  Platelet secretion is critical to development of acute thrombotic occlusion. Platelet dense granules contain a variety of important hemostatically active substances. Nevertheless, biogenesis of platelet granules is poorly understood.
  
  
  OBJECTIVE
  Serum- and glucocorticoid-inducible kinase 1 (SGK1) has been shown to be highly expressed in platelets and megakaryocytes, but its role in the regulation of platelet granule biogenesis and its impact on thrombosis has not been investigated so far.
  
  
  RESULTS
  Electron microscopy analysis of the platelet ultrastructure revealed a significant reduction in the number and packing of dense granules in platelets lacking SGK1 (sgk1(-/-) ). In sgk1(-/-) platelets serotonin content was significantly reduced and activation-dependent secretion of ATP, serotonin and CD63 significantly impaired. In vivo adhesion after carotis ligation was significantly decreased in platelets lacking SGK1 and occlusive thrombus formation after FeCl3 -induced vascular injury was significantly diminished in sgk1(-/-) mice. Transcript levels and protein abundance of dense granule biogenesis regulating GTPase Rab27b were significantly reduced in sgk1(-/-) platelets without affecting Rab27b mRNA stability. In MEG-01 cells transfection with constitutively active (S422) (D) SGK1 but not with inactive (K127) (N) SGK1 significantly enhanced Rab27b mRNA levels. Sgk1(-/-) megakaryocytes show significantly reduced expression of Rab27b and serotonin/CD63 levels compared with sgk1(+/+) megakaryocytes. Proteome analysis identified nine further vesicular transport proteins regulated by SGK1, which may have an impact on impaired platelet granule biogenesis in sgk1(-/-) platelets independent of Rab27b.
  
  
  CONCLUSIONS
  The present observations identify SGK1 as a novel powerful regulator of platelet dense granule biogenesis, platelet secretion and thrombus formation. SGK1 is at least partially effective because it regulates transcription of Rab27b in megakaryocytes.
authors.affiliation: Department of Cardiology and Cardiovascular Medicine, University of Tübingen, Tübingen, Germany.|Department of Physiology, University of Tübingen, Tübingen, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Walker
authors.affiliation: Department of Pediatric Surgery and Pediatric Urology, University Children's Hospital Tübingen, Tübingen, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Schmid
authors.affiliation: Department of Physiology, University of Tübingen, Tübingen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Russo
authors.affiliation: Department of Physiology, University of Tübingen, Tübingen, Germany.
authors.forename: E-M
authors.initials: EM
authors.lastname: Schmidt
authors.affiliation: Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany.
authors.forename: O
authors.initials: O
authors.lastname: Burk
authors.affiliation: Department of Cardiology and Cardiovascular Medicine, University of Tübingen, Tübingen, Germany.|Department of Physiology, University of Tübingen, Tübingen, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Münzer
authors.affiliation: Proteom Center Tübingen, University of Tübingen, Tübingen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Velic
authors.affiliation: Proteom Center Tübingen, University of Tübingen, Tübingen, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Macek
authors.affiliation: Department of Dermatology, University Hospital Tübingen, Tübingen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Schaller
authors.affiliation: Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany.|Department of Clinical Pharmacology, University Hospital, Tübingen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Schwab
authors.affiliation: Molecular Medicine, National Heart and Lung Institute, Imperial College London, London, UK.
authors.forename: M C
authors.initials: MC
authors.lastname: Seabra
authors.affiliation: Department of Cardiology and Cardiovascular Medicine, University of Tübingen, Tübingen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Gawaz
authors.affiliation: Department of Physiology, University of Tübingen, Tübingen, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Lang
authors.affiliation: Department of Cardiology and Cardiovascular Medicine, University of Tübingen, Tübingen, Germany.|Department of Physiology, University of Tübingen, Tübingen, Germany.
authors.forename: O
authors.initials: O
authors.lastname: Borst
mesh_terms: D000255:Adenosine Triphosphate / Q000097:blood / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000201:enzymology* / Q000378:metabolism / Q000648:ultrastructure; D020212:Carotid Artery Injuries / Q000097:blood / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000201:enzymology* / Q000378:metabolism / Q000648:ultrastructure; D004195:Disease Models, Animal; D005260:Female; D005838:Genotype; D017874:Immediate-Early Proteins / Q000097:blood* / Q000172:deficiency / Q000235:genetics; D008297:Male; D008533:Megakaryocytes / Q000201:enzymology / Q000378:metabolism; D018345:Mice, Knockout; D010641:Phenotype; D015539:Platelet Activation; D010974:Platelet Aggregation; D017346:Protein Serine-Threonine Kinases / Q000097:blood* / Q000172:deficiency / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D022142:Secretory Vesicles / Q000201:enzymology* / Q000378:metabolism / Q000648:ultrastructure; D012701:Serotonin / Q000097:blood / Q000378:metabolism; D015398:Signal Transduction; D060149:Tetraspanin 30 / Q000097:blood / Q000378:metabolism; D013927:Thrombosis / Q000097:blood / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D000255:Adenosine Triphosphate; D017874:Immediate-Early Proteins; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D012701:Serotonin; D060149:Tetraspanin 30; D020691:rab GTP-Binding Proteins; D000099184:Serum-Glucocorticoid Regulated Kinases; C554587:Cd63 protein, mouse; C512958:Rab27b protein, mouse
keywords: Rab27b protein, mouse; Sgk1 protein, mouse; biogenesis; blood platelets; secretory granules