title: Inhibition of ADP-induced platelet activation by 7-chloro-4-nitrobenz-2-oxa-1,3-diazole: covalent modification of aggregin, a putative ADP receptor.
abstract: ADP-induced platelet responses play an important role in the maintenance of hemostasis. There has been disagreement concerning the identity of an ADP receptor on the platelet surface. The chemical structure of 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD-CI) shows considerable resemblance to that of the adenine moiety of adenine-based nucleotides. The reagent has been previously used by other investigators as an affinity label for adenine nucleotide-requiring enzymes, such as mitochondrial ATPase and the catalytic subunit of cAMP-dependent protein kinase. Since ADP-induced platelet responses depend on the binding of ADP to its receptor, we investigated the effect on ADP-induced platelet responses and the nature of ADP-binding protein modified by NBD-CI. NBD-CI inhibited ADP-induced shape change and aggregation of platelets in platelet-rich plasma in a concentration- and time-dependent manner. NBD-CI also inhibited ADP-induced shape change, aggregation, exposure of fibrinogen binding sites, secretion, and calcium mobilization in washed platelets. NBD-CI did not act as an agonist for platelet shape change and aggregation. Covalent modification of platelets by NBD-CI blocked the ability of ADP to antagonize the increase in intracellular levels of cAMP mediated by iloprost (a stable analogue of prostaglandin I2). NBD-CI was quite specific in inhibiting platelet aggregation by those agonists, e.g., ADP, collagen, and U44619 (a thromboxane mimetic), that completely or partially depend on the binding of ADP to its receptor. Autoradiogram of the gel obtained by SDS-PAGE of solubilized platelets modified by [14C]-NBD-CI showed the presence of a predominant radiolabeled protein band at 100 kDa corresponding to aggregin, a putative ADP receptor. The intensity of this band was considerably decreased when platelets were either preincubated with ADP and ATP or covalently modified by a sulfhydryl group modifying reagent before modification by [14C]-NBD-CI. These results (1) indicate that covalent modification of aggregin by NBD-CI contributed to loss of the ADP-induced platelet responses, and (2) suggest that there is a sulfhydryl group in the ADP-binding domain of aggregin.
authors.affiliation: Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: R N
authors.initials: RN
authors.lastname: Puri
authors.forename: R W
authors.initials: RW
authors.lastname: Colman
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D009327:4-Chloro-7-nitrobenzofurazan / Q000494:pharmacology*; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000032:analysis; D002449:Cell Aggregation / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D003094:Collagen / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D005340:Fibrinogen / Q000032:analysis; D006801:Humans; D015539:Platelet Activation / Q000187:drug effects*; D010980:Platelet Membrane Glycoproteins / Q000187:drug effects*; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000494:pharmacology; D013997:Time Factors
chemical_list: D010980:Platelet Membrane Glycoproteins; D011450:Prostaglandin Endoperoxides, Synthetic; C055422:aggregin; D000001:Calcimycin; D013928:Thromboxane A2; D000244:Adenosine Diphosphate; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; C010959:5'-(4-fluorosulfonylbenzoyl)adenosine; D005340:Fibrinogen; D003094:Collagen; D000242:Cyclic AMP; D013917:Thrombin; D009327:4-Chloro-7-nitrobenzofurazan; D000241:Adenosine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium