title: Exposure of ligand-binding sites on platelet integrin alpha IIB/beta 3 by phosphorylation of the beta 3 subunit.
abstract: The exposure of ligand-binding sites for adhesive proteins on platelet integrin alpha IIB/beta 3 (glycoprotein IIB/IIIA) by platelet-activating (PAF) is transient, whereas sites exposed by alpha-thrombin remain accessible. The same difference is seen in the phosphorylation of the beta 3 subunit. Inhibition of protein kinases (1 microM staurosporine) and protein kinase C (10 microM bisindolylmaleimide) closes binding sites exposed by both agonists and induces dephosphorylation of beta 3. Inhibition of Tyr-kinases (20 microM Herbimycin A) has only a slight effect. Inhibition of Ser/Thr-phosphatases (1 microM okadaic acid, 30 s preincubation) changes the transient exposure and beta phosphorylation by PAF into the 'permanent' patterns induced by alpha-thrombin. Inhibition of Tyr-phosphatases (100 microM vanadate) has little effect. Preincubation with okadaic acid makes exposed binding sites and phosphorylated beta 3 insensitive to staurosporine, resulting in exposed alpha IIB/beta 3 independent of concurrent phosphorylation/dephosphorylation. The stoichiometry of beta 3 phosphorylation by alpha-thrombin is 0.80+/-0.10. Thus, one of the mechanisms that regulates exposure and closure of ligand-binding sites on the alpha IIb/beta 3 is phosphorylation/dephosphorylation of a Ser/Thr-residue in the beta 3 subunit.
authors.affiliation: Department of Haematology, University Hospital Utrecht, The Netherlands.
authors.forename: G
authors.initials: G
authors.lastname: van Willigen
authors.forename: I
authors.initials: I
authors.lastname: Hers
authors.forename: G
authors.initials: G
authors.lastname: Gorter
authors.forename: J W
authors.initials: JW
authors.lastname: Akkerman
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D016227:Benzoquinones; D001665:Binding Sites; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005340:Fibrinogen / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D047029:Lactams, Macrocyclic; D008024:Ligands; D008301:Maleimides / Q000494:pharmacology; D010766:Phosphorylation; D010972:Platelet Activating Factor / Q000494:pharmacology; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000187:drug effects / Q000502:physiology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000097:blood; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000097:blood; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000097:blood; D011809:Quinones / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives; D019311:Staurosporine
chemical_list: D000470:Alkaloids; D016227:Benzoquinones; D004791:Enzyme Inhibitors; D005353:Fibronectins; D007211:Indoles; D047029:Lactams, Macrocyclic; D008024:Ligands; D008301:Maleimides; D010972:Platelet Activating Factor; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D047428:Protein Kinase Inhibitors; D011809:Quinones; D017828:Rifabutin; C020754:herbimycin; D005340:Fibrinogen; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D019311:Staurosporine; C088060:bisindolylmaleimide