title: Thrombospondin-1 induces platelet activation through CD36-dependent inhibition of the cAMP/protein kinase A signaling cascade.
abstract: Cyclic adenosine monophosphate (cAMP)-dependent signaling modulates platelet function at sites of vascular injury. Here we show that thrombospondin-1 (TSP-1) prevents cAMP/protein kinase A (PKA) signaling through a CD36-dependent mechanism. Prostaglandin E₁ (PGE₁) induced a robust inhibition of both platelet aggregation and platelet arrest under physiologic conditions of flow. Exogenous TSP-1 reduced significantly PGE₁-mediated inhibition of both platelet aggregation and platelet arrest. TSP-1 prevented PGE₁-stimulated cAMP accrual and phosphorylation of PKA substrates, through a mechanism requiring phosphodiesterase3A. TSP-1 also inhibited VASP phosphorylation stimulated by the nonhydrolyzable cAMP analog, 8-bromo-cAMP, indicating that it may regulate cAMP-mediated activation of PKA. The inhibitory effect of TSP-1 on cAMP signaling could be reproduced with a peptide possessing a CD36 binding sequence of TSP-1, while the effects of TSP-1 were prevented by a CD36 blocking antibody. TSP-1 and the CD36 binding peptide induced phosphorylation of Src kinases, p38 and JNK. Moreover, inhibition of Src kinases blocked TSP-1-mediated regulation of cAMP concentrations and the phosphorylation of VASP, indicating that TSP-1 modulated the cAMP/PKA signaling events through a tyrosine kinase-dependent pathway downstream of CD36. These data reveal a new role for TSP-1 in promoting platelet aggregation through modulation of the cAMP-PKA signaling pathway.
authors.affiliation: Hull-York Medical School, University of Hull, Castle Hill Hospital, Cottingham, UK.
authors.forename: Wayne
authors.initials: W
authors.lastname: Roberts
authors.forename: Simbarashe
authors.initials: S
authors.lastname: Magwenzi
authors.forename: Ahmed
authors.initials: A
authors.lastname: Aburima
authors.forename: Khalid M
authors.initials: KM
authors.lastname: Naseem
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000527:Alprostadil / Q000494:pharmacology; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D018955:CD36 Antigens / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D018056:Hemorheology / Q000187:drug effects; D006801:Humans; D010455:Peptides / Q000494:pharmacology; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects*; D019700:Thrombospondin 1 / Q000494:pharmacology*; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D018955:CD36 Antigens; D010455:Peptides; D019700:Thrombospondin 1; D000242:Cyclic AMP; D019061:src-Family Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D000527:Alprostadil