title: Dextran sulfate triggers platelet aggregation via direct activation of PEAR1.
abstract: Dextran sulfate (DxS; Mr 500 kD) induces fibrinogen receptor (αIIbβ3) activation via CLEC-2/Syk signaling and via a Syk-independent SFK/PI3K/Akt-dependent tyrosine kinase pathway in human and murine platelets. The platelet surface receptor, responsible for the DxS-induced Syk-independent Akt-activation, has hitherto not been identified. We found that DxS elicited a concentration-dependent aggregation of human platelets resulting from direct PEAR1 activation by DxS. Blocking the PEAR1 receptor, in combination with a selective Syk-inhibitor, completely abrogated the DxS-driven platelet aggregation. The DxS-induced Syk-phosphorylation was not affected in Pear1(-/-) platelets, but Akt-phosphorylation was largely abolished. As a result, the aggregation of Pear1(-/-) platelets was reduced and reversible, i.e. aggregates were less stable compared to wild-type platelet aggregates. Moreover, DxS-induced Pear1(-/-) platelet aggregation was fully abrogated by Syk inhibition, indicating that the remaining platelet aggregation of Pear1(-/-) platelets was Syk dependent. Hence, the Pear1/c-Src/PI3K/Akt- and CLEC-2/Syk-signaling pathways are independently and additively activated during platelet aggregation by DxS.
  
  
  CONCLUSIONS
  The DxS-induced aggregation of human and murine platelets is the result of activation of PI3K/Akt through direct PEAR1 phosphorylation and parallel Syk-signaling through CLEC-2.
authors.affiliation: a Center for Molecular and Vascular Biology , Department of Cardiovascular Sciences , KU Leuven , Leuven , Belgium.
authors.forename: Christophe
authors.initials: C
authors.lastname: Vandenbriele
authors.affiliation: b Cell Surface Signalling Laboratory , Wellcome Trust Sanger Institute, Cambridge CB10 1HH , UK.
authors.forename: Yi
authors.initials: Y
authors.lastname: Sun
authors.affiliation: a Center for Molecular and Vascular Biology , Department of Cardiovascular Sciences , KU Leuven , Leuven , Belgium.
authors.forename: Maarten
authors.initials: M
authors.lastname: Criel
authors.affiliation: a Center for Molecular and Vascular Biology , Department of Cardiovascular Sciences , KU Leuven , Leuven , Belgium.
authors.forename: Katrien
authors.initials: K
authors.lastname: Cludts
authors.affiliation: a Center for Molecular and Vascular Biology , Department of Cardiovascular Sciences , KU Leuven , Leuven , Belgium.
authors.forename: Soetkin
authors.initials: S
authors.lastname: Van Kerckhoven
authors.affiliation: a Center for Molecular and Vascular Biology , Department of Cardiovascular Sciences , KU Leuven , Leuven , Belgium.
authors.forename: Benedetta
authors.initials: B
authors.lastname: Izzi
authors.affiliation: a Center for Molecular and Vascular Biology , Department of Cardiovascular Sciences , KU Leuven , Leuven , Belgium.
authors.forename: Thomas
authors.initials: T
authors.lastname: Vanassche
authors.affiliation: a Center for Molecular and Vascular Biology , Department of Cardiovascular Sciences , KU Leuven , Leuven , Belgium.
authors.forename: Peter
authors.initials: P
authors.lastname: Verhamme
authors.affiliation: a Center for Molecular and Vascular Biology , Department of Cardiovascular Sciences , KU Leuven , Leuven , Belgium.
authors.forename: Marc F
authors.initials: MF
authors.lastname: Hoylaerts
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism*; D002460:Cell Line; D016264:Dextran Sulfate / Q000494:pharmacology*; D006801:Humans; D037181:Lectins, C-Type / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects*; D010979:Platelet Function Tests; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase / Q000378:metabolism
chemical_list: C104778:CLEC2B protein, human; D037181:Lectins, C-Type; D008562:Membrane Glycoproteins; C502809:PEAR1 protein, human; D011956:Receptors, Cell Surface; D016264:Dextran Sulfate; D000072377:Syk Kinase
keywords: Basic research—platelet signaling; PEAR1; Pear1−/− platelets; Syk; dextran sulfate; platelets; signaling