15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and arginyl-glycyl-aspartyl-serine

The effect of platelet stimulation on the subcellular localization of CD38, a membrane glycoprotein that catalyses the synthesis of cyclic ADP-ribose from beta-NAD+ was investigated. Treatment of human platelets with thrombin caused the association of about 40% of the total ADP-ribosyl cyclase activity with the cytoskeleton, through the translocation of the CD38 molecule from the Triton X-100-soluble to the insoluble fraction. The interaction of CD38 with the cytoskeleton was a specific and reversible process, mediated by the binding to the actin-rich filaments and was inhibited by treatment of platelets with cytochalasin D. This event was regulated by integrin alphaIIb beta3 and platelet aggregation as it was prevented by the inhibition of fibrinogen binding and was not observed in platelets from a patient affected by Glanzmann thrombasthenia. These results demonstrate that the subcellular localization of CD38 can be influenced by platelet stimulation with physiological agonists, and that membrane CD38 can interact with intracellular proteins.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Actins; Adenosine Diphosphate Ribose; ADP-ribosyl Cyclase; ADP-ribosyl Cyclase 1; Antigens, CD; Antigens, Differentiation; Blood Platelets; Collagen; Cyclic ADP-Ribose; Cytoskeleton; Humans; In Vitro Techniques; Membrane Glycoproteins; Multienzyme Complexes; NAD+ Nucleosidase; Oligopeptides; Platelet Aggregation; Protein Binding; Thrombin

The effects of the fibrinogen-derived tetrapeptide, Arg-Gly-Asp-Ser (RGDS), on platelet activation processes was studied. At concentrations of 100-300 microM, RGDS completely prevented platelet aggregation induced by all the common platelet agonists, 'weak' and 'strong'. In agreement with earlier views on the aggregation-dependency of weak agonist-induced thromboxane synthesis and 5-hydroxytryptamine (5HT) secretion, RGDS (100-300 microM) inhibited these events induced by ADP, adrenaline and low concentrations of thrombin and collagen but not that induced by high concentrations of thrombin and collagen. 5HT secretion induced by the protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), was also not affected by RGDS, but proteolytic degradation of the translocated membrane-bound enzyme in PMA-treated platelets, due to the actions of the Ca2+-dependent protease (Ca-DP), was completely prevented such that in the presence of RGDS, sustained increases in membrane-bound PKC activity were observed. PMA alone caused only transient increases in membrane-bound PKC. This effect of RGDS was similar to the effect of E64-d, a recently described inhibitor of Ca-DP in platelets, or the effects seen with PMA in unstirred non-aggregating platelets. It is concluded that RGDS inhibits the actions of Ca-DP in platelets via inhibition of aggregation.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Amino Acid Sequence; Blood Platelets; Collagen; Fibrinogen; Humans; In Vitro Techniques; Kinetics; Molecular Sequence Data; Oligopeptides; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Protein Kinase C; Serotonin; Tetradecanoylphorbol Acetate; Thrombin