title: A role for glycosphingolipid-enriched microdomains in platelet glycoprotein Ib-mediated platelet activation.
abstract: BACKGROUND
  Glycoprotein (GP) Ib, a platelet von Willebrand factor (VWF) receptor, plays a crucial role in thrombosis and hemostasis. As recent reports have suggested that GPIb partially locates in a particular region, designated as glycosphingolipid-enriched microdomains (GEMs), we hypothesized that GEMs play a central role in GPIb-mediated platelet activation.
  
  
  METHODS
  Platelets were stimulated by VWF/botrocetin to activate platelets through GPIb. GEMs and non-GEMs were isolated by sucrose density gradient ultracentrifugation and the location of signaling molecules characterized. The role of GEMs-mediated signaling in platelet behavior was tested by platelet aggregation and by platelet interaction with immobilized VWF under flow conditions when GEMs were disrupted by methyl-beta-cyclodextrin (MbetaCD).
  
  
  RESULTS
  GPIb was partially translocated to GEMs upon VWF/botrocetin stimulation. Immunoprecipitation of GPIb in GEMs and non-GEMs revealed that the tyrosine kinases, Src and Lyn, were associated with GPIb only in GEMs after GPIb-stimulation, and not in non-GEMs. Activation of PLCgamma2 was more intense in GEMs than non-GEMs. Disruption of GEMs by MbetaCD strongly inhibited tyrosine phosphorylation of Syk and PLCgamma2. Functional studies revealed that stable adhesion of platelets to a VWF-coated surface under flow was impaired by GEM disruption by MbetaCD.
  
  
  CONCLUSIONS
  The combined results suggest that GEMs play an important role in GPIb-mediated platelet activation.
authors.affiliation: Department of Laboratory and Clinical Medicine, University of Yamanashi, Yamanashi, Japan.
authors.forename: W
authors.initials: W
authors.lastname: Jin
authors.forename: O
authors.initials: O
authors.lastname: Inoue
authors.forename: N
authors.initials: N
authors.lastname: Tamura
authors.forename: K
authors.initials: K
authors.lastname: Suzuki-Inoue
authors.forename: K
authors.initials: K
authors.lastname: Satoh
authors.forename: M C
authors.initials: MC
authors.lastname: Berndt
authors.forename: M
authors.initials: M
authors.lastname: Handa
authors.forename: S
authors.initials: S
authors.lastname: Goto
authors.forename: Y
authors.initials: Y
authors.lastname: Ozaki
mesh_terms: D002448:Cell Adhesion; D006028:Glycosphingolipids / Q000378:metabolism*; D006801:Humans; D015539:Platelet Activation / Q000502:physiology*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000502:physiology*; D011485:Protein Binding; D015398:Signal Transduction; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D006028:Glycosphingolipids; D019038:Platelet Glycoprotein GPIb-IX Complex; D019061:src-Family Kinases