title: Thrombopoietin potentiates activation of human platelets in association with JAK2 and TYK2 phosphorylation.
abstract: Thrombopoietin (TPO), also known as the c-mpl ligand, stimulates rapid tyrosine phosphorylation of multiple proteins in human platelets including the Janus family kinases JAK2 and TYK2. On its own, TPO has no effect on platelet aggregation and dense-granule secretion but induces a general potentiation of these responses by other stimuli. The most dramatic effect is observed against threshold concentrations of agonists for aggregation. Shape change or weak reversible aggregation induced by low concentrations of thrombin, collagen and the thromboxane mimetic, U46619, are converted into irreversible aggregation in the presence of TPO. A similar result is obtained in the presence of the ADP scavenger apyrase and cyclo-oxygenase inhibitor indomethacin. TPO also induces potentiation of dense-granule secretion measured through release of 5-hydroxy[3H]-tryptamine. This effect is most striking against low concentrations of stimuli and is independent of aggregation as it is observed in the presence of chelation of extracellular Ca2+ with EGTA. TPO potentiates activation of phospholipase C and elevation of intracellular Ca2+, providing a molecular explanation for potentiation of functional responses. TPO may have an important physiological role in priming platelet activation in thrombocytopenia, an action that may help to compensate for the reduced platelet density.
authors.affiliation: Department of Pharmacology, University of Oxford, U.K.
authors.forename: B
authors.initials: B
authors.lastname: Rodríguez-Liñares
authors.forename: S P
authors.initials: SP
authors.lastname: Watson
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D001081:Apyrase / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology*; D002118:Calcium / Q000097:blood; D003094:Collagen / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology; D004533:Egtazic Acid / Q000494:pharmacology; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D007295:Inositol Phosphates / Q000097:blood; D053614:Janus Kinase 2; D007700:Kinetics; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000097:blood*; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins / Q000494:pharmacology; D053634:TYK2 Kinase; D013917:Thrombin / Q000494:pharmacology; D013926:Thrombopoietin / Q000494:pharmacology*; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
chemical_list: D007295:Inositol Phosphates; D011450:Prostaglandin Endoperoxides, Synthetic; D011506:Proteins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D014662:Vasoconstrictor Agents; D015240:Phorbol 12,13-Dibutyrate; D004533:Egtazic Acid; D013928:Thromboxane A2; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D003094:Collagen; D013926:Thrombopoietin; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D053634:TYK2 Kinase; C070139:TYK2 protein, human; D013917:Thrombin; D001081:Apyrase; D002118:Calcium; D007213:Indomethacin