title: Negative feedback regulation of human platelets via autocrine activation of the platelet-derived growth factor alpha-receptor.
abstract: Human platelets contain platelet-derived growth factor (PDGF) in their alpha-granules which is released during platelet exocytosis. We show by immunoprecipitation and 125I-PDGF binding experiments that human platelets have functionally active PDGF alpha-receptors, but not beta-receptors. The PDGF alpha-receptor (PDGFR-alpha) was identified as a 170-kDa glycosylated protein-tyrosine kinase as found in other cell types. Stimulation of platelets with 0.1 unit/ml thrombin resulted in a significant increase (2-5-fold) of the tyrosine phosphorylation of the PDGFR-alpha, as determined by immunoprecipitation with phosphotyrosine antiserum as well as with PDGFR-alpha antiserum. The observed thrombin-induced autophosphorylation of the PDGFR-alpha was inhibited by the addition of a neutralizing monoclonal PDGF antibody. Thus, our results suggest that the platelet PDGFR-alpha is stimulated in an autocrine manner by PDGF secreted during platelet activation. Preincubation of platelets with PDGF inhibited thrombin-induced platelet aggregation and secretion of ATP + ADP and beta-hexosaminidase. Thrombin-induced platelet aggregation was also reversed when PDGF was added 30 s after thrombin stimulation. Inhibition of the autocrine PDGF pathway during platelet activation by the PDGF antibody led to a potentiation of thrombin-induced beta-hexosaminidase secretion. Thus, the PDGFR-alpha takes part in a negative feedback regulation during platelet activation. Our demonstration of PDGF alpha-receptors on human platelets and its inhibitory function during platelet activation identifies a new possible role of PDGF in the regulation of thrombosis.
authors.affiliation: Ludwig Institute for Cancer Research, Biomedical Center, Uppsala, Sweden.
authors.forename: F S
authors.initials: FS
authors.lastname: Vassbotn
authors.forename: O K
authors.initials: OK
authors.lastname: Havnen
authors.forename: C H
authors.initials: CH
authors.lastname: Heldin
authors.forename: H
authors.initials: H
authors.lastname: Holmsen
mesh_terms: D000077214:Becaplermin; D001792:Blood Platelets / Q000201:enzymology / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005246:Feedback; D006801:Humans; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology; D020574:Proto-Oncogene Proteins c-sis; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D013917:Thrombin / Q000037:antagonists & inhibitors; D014443:Tyrosine / Q000378:metabolism; D001619:beta-N-Acetylhexosaminidases / Q000378:metabolism
chemical_list: D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D011994:Recombinant Proteins; D000077214:Becaplermin; D014443:Tyrosine; D017479:Receptors, Platelet-Derived Growth Factor; D001619:beta-N-Acetylhexosaminidases; D013917:Thrombin