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PAR1‐mediated stable platelet aggregation requires temporal regulation of Rap1 activity by phosphatidylinositol phosphates (PIPns).
Author(s) -
Holinstat Michael,
Hudson W. James,
Preininger Anita M.,
Milne Stephen B.,
Brown H. Alex,
Hamm Heidi E.
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.646.3
Subject(s) - rap1 , platelet activation , phosphatidylinositol , chemistry , platelet , microbiology and biotechnology , activator (genetics) , thrombin , signal transduction , pi3k/akt/mtor pathway , biochemistry , receptor , biology , immunology
Thrombin is the most potent activator of platelets through reversible and then irreversible aggregation and it mediates a diverse range of vascular effects which may result in acute coronary syndrome and stroke. We demonstrate that PAR1, but not PAR4, signals human platelet activation through generation of a phosphatidylinositol phosphate (PIPn) signaling pathway which mediates Rap1 regulation of stable platelet activation. To investigate this signaling requirement for PIP n s, we examined the activation kinetics of Rap1, platelet aggregation, protein complex formation and proteomics. Treatment with PI‐kinase inhibitors significantly altered the kinetics of PAR1‐, but not PAR4‐mediated Rap1 activation and platelet aggregation. Additionally, PI5K and PI3Kγ were required for stable PAR1‐mediated platelet aggregation and Rap1 was found to form a protein complex with both PI3K and PI5K following PAR1 stimulation. Although stable platelet activation is sensitive to perturbation of the PI‐kinase pathway, early Rap1 activation and platelet aggregation are insensitive to perturbations along the PI‐kinase pathway. Hence, this novel lipid signaling pathway is a potential target for anti‐platelet therapy. This study was supported in part by grants P50 HL081009 (to H.E.H.) and K99 HL089457 (to M.H.) from the National Institutes of Health.