title: Tyrosine kinases activate store-mediated Ca2+ entry in human platelets through the reorganization of the actin cytoskeleton.
abstract: We have recently reported that store-mediated Ca(2+) entry in platelets is likely to be mediated by a reversible trafficking and coupling of the endoplasmic reticulum with the plasma membrane, a model termed 'secretion-like coupling'. In this model the actin cytoskeleton plays a key regulatory role. Since tyrosine kinases have been shown to be important for Ca(2+) entry in platelets and other cells, we have now investigated the possible involvement of tyrosine kinases in the secretion-like-coupling model. Treatment of platelets with thrombin or thapsigargin induced actin polymerization by a calcium-independent pathway. Methyl 2,5-dihydroxycinnamate, a tyrosine kinase inhibitor, prevented thrombin- or thapsigargin-induced actin polymerization. The effects of tyrosine kinases in store-mediated Ca(2+) entry were found to be entirely dependent on the actin cytoskeleton. PP1, an inhibitor of the Src family of proteins, partially inhibited store-mediated Ca(2+) entry. In addition, depletion of intracellular Ca(2+) stores stimulated cytoskeletal association of the cytoplasmic tyrosine kinase pp60(src), a process that was sensitive to treatment with cytochalasin D and PP1, but not to inhibition of Ras proteins using prenylcysteine analogues. Finally, combined inhibition of both Ras proteins and tyrosine kinases resulted in complete inhibition of Ca(2+) entry, suggesting that these two families of proteins have independent effects in the activation of store-mediated Ca(2+) entry in human platelets.
authors.affiliation: Department of Physiology, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK.
authors.forename: J A
authors.initials: JA
authors.lastname: Rosado
authors.forename: D
authors.initials: D
authors.lastname: Graves
authors.forename: S O
authors.initials: SO
authors.lastname: Sage
mesh_terms: D000199:Actins / Q000378:metabolism*; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002934:Cinnamates / Q000494:pharmacology; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007477:Ions; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D011506:Proteins / Q000494:pharmacology; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
chemical_list: D000199:Actins; D002934:Cinnamates; D004791:Enzyme Inhibitors; D007477:Ions; D019384:Nucleic Acid Synthesis Inhibitors; D011506:Proteins; C073882:phosphoprotein phosphatase inhibitor 1; D015638:Cytochalasin D; D014443:Tyrosine; D004533:Egtazic Acid; C067472:methyl 2,5-dihydroxycinnamate; D019284:Thapsigargin; D011505:Protein-Tyrosine Kinases; D016392:Proto-Oncogene Proteins pp60(c-src); D013917:Thrombin; D018631:ras Proteins; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium