Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recent studies propose the existence of two distinct Ca2+ compartments in human platelets based on the expression of different SERCA isoforms with distinct sensitivity to thapsigargin and 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ). Using fura-2-loaded human platelets we have found that depletion of the TBHQ sensitive store reduces thrombin--but not ADP--or vasopressin (AVP)-induced Ca2+ release. Redistribution of cytosolic Ca2+ after thrombin stimulation resulted in overloading of the TBHQ-sensitive store. This phenomenon was not observed with ADP or AVP. We found that NAADP decreases the Ca2+ concentration into the stores in permeabilized platelets, which is prevented by depletion of the TBHQ-sensitive store. Nimodipine, an inhibitor of the NAADP receptor, reduced thrombin-induced Ca2+ release from the TBHQ-sensitive stores, without having any effect on the responses elicited by ADP or AVP. Finally, the phospholipase C inhibitor, U-73122, abolished ADP- and AVP-induced Ca2+ release, suggesting that their responses are entirely dependent on IP3 generation. In contrast, treatment with both U-73122 and nimodipine was required to abolish thrombin-induced Ca2+ release. We suggest that thrombin evokes Ca2+ release from TBHQ-sensitive and insensitive stores, which requires both NAADP and IP3, respectively, while ADP and AVP exert an IP3-dependent release of Ca2+ from the TBHQ-insensitive compartment in human platelets.
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PMID:Two distinct Ca2+ compartments show differential sensitivity to thrombin, ADP and vasopressin in human platelets. 1609 82

Accumulating evidence implicates nicotinic acid adenine dinucleotide phosphate (NAADP) in the control of Ca(2+)-dependent functions. Little, however, is known concerning its role in the vascular endothelium, a major regulator of blood pressure. Here, we show that NAADP acetoxymethyl ester (NAADP-AM), a cell-permeant NAADP analog, increases cytosolic Ca(2+) concentration in aortic endothelial cells. We demonstrate that these signals and those evoked by acetylcholine are blocked by disrupting acidic organelles with bafilomycin A1. In contrast, Ca(2+) signals in response to thrombin are only partially inhibited by bafilomycin A1 treatment, and those to ATP were insensitive, suggesting that recruitment of acidic stores is agonist-specific. We further show that NAADP-evoked Ca(2+) signals hyperpolarize endothelial cells and generate NO. Additionally, we demonstrate that NAADP dilates aortic rings in an endothelium- and NO-dependent manner. Finally, we show that intravenous administration of NAADP-AM into anesthetized rats decreases mean arterial pressure. Our data extend the actions of NAADP to the endothelium both in vitro and in vivo, pointing to a previously unrecognized role for this messenger in controlling blood pressure.
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PMID:Acidic NAADP-sensitive calcium stores in the endothelium: agonist-specific recruitment and role in regulating blood pressure. 2087 34

CD38, a multifunctional enzyme that catalyzes the synthesis of intracellular Ca(2+) messengers, cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP), is known to be expressed on platelets. However, the role of CD38 in platelets remains unclear. Our present results show that treatment of platelets with thrombin results in a rapid and sustained Ca(2+) signal, resulting from a coordinated interplay of Ca(2+)-mobilizing messengers, inositol 1,4,5-trisphosphate, cADPR, and NAADP. By dissecting the signaling pathway using various agents, we delineated that cADPR and NAADP are sequentially produced through CD38 internalization by protein kinase C via myosin heavy chain IIA following phospholipase C activation in thrombin-induced platelets. An inositol 1,4,5-trisphosphate receptor antagonist blocked the thrombin-induced formation of cADPR and NAADP as well as Ca(2+) signals. An indispensable response of platelets relying on cytosolic calcium is the surface exposure of phosphatidylserine (PS), which implicates platelet procoagulant activity. Scrutinizing this parameter reveals that CD38(+/+) platelets fully express PS on the surface when stimulated with thrombin, whereas this response was decreased on CD38(-/-) platelets. Similarly, PS exposure and Ca(2+) signals were attenuated when platelets were incubated with 8-bromo-cADPR, bafilomycin A1, and a PKC inhibitor. Furthermore, in vivo, CD38-deficient mice exhibited longer bleeding times and unstable formation of thrombus than wild type mice. These results demonstrate that CD38 plays an essential role in thrombin-induced procoagulant activity of platelets and hemostasis via Ca(2+) signaling mediated by its products, cADPR and NAADP.
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PMID:Critical role for CD38-mediated Ca2+ signaling in thrombin-induced procoagulant activity of mouse platelets and hemostasis. 2133 89

A variety of endothelial agonist-induced responses are mediated by rises in intracellular Ca(2+), suggesting that different Ca(2+) signatures could fine-tune specific inflammatory and thrombotic activities. In search of new intracellular mechanisms modulating endothelial effector functions, we identified nicotinic acid adenine dinucleotide phosphate (NAADP) as a crucial second messenger in histamine-induced Ca(2+) release via H1 receptors (H1R). NAADP is a potent intracellular messenger mobilizing Ca(2+) from lysosome-like acidic compartments, functionally coupled to the endoplasmic reticulum. Using the human EA.hy926 endothelial cell line and primary human umbilical vein endothelial cells, we show that selective H1R activation increases intracellular NAADP levels and that H1R-induced calcium release involves both acidic organelles and the endoplasmic reticulum. To assess that NAADP links H1R to Ca(2+)-signaling we used both microinjection of self-inactivating concentrations of NAADP and the specific NAADP receptor antagonist, Ned-19, both of which completely abolished H1R-induced but not thrombin-induced Ca(2+) mobilization. Interestingly, H1R-mediated von Willebrand factor (VWF) secretion was completely inhibited by treatment with Ned-19 and by siRNA knockdown of 2-pore channel NAADP receptors, whereas thrombin-induced VWF secretion failed to be affected. These findings demonstrate a novel and specific Ca(2+)-signaling mechanism activated through H1R in human endothelial cells, which reveals an obligatory role of NAADP in the control of VWF secretion.
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PMID:NAADP links histamine H1 receptors to secretion of von Willebrand factor in human endothelial cells. 2136 92

Platelets play a vital role in maintaining haemostasis. Human platelet activation depends on Ca2+ release, leading to cell activation, granule secretion and aggregation. NAADP (nicotinic acid-adenine dinucleotide phosphate) is a Ca2+-releasing second messenger that acts on acidic Ca2+ stores and is used by a number of mammalian systems. In human platelets, NAADP has been shown to release Ca2+ in permeabilized human platelets and contribute to thrombin-mediated platelet activation. In the present study, we have further characterized NAADP-mediated Ca2+ release in human platelets in response to both thrombin and the GPVI (glycoprotein VI)-specific agonist CRP (collagen-related peptide). Using a radioligand-binding assay, we reveal an NAADP-binding site in human platelets, indicative of a platelet NAADP receptor. We also found that NAADP releases loaded 45Ca2+ from intracellular stores and that total platelet Ca2+ release is inhibited by the proton ionophore nigericin. Ned-19, a novel cell-permeant NAADP receptor antagonist, competes for the NAADP-binding site in platelets and can inhibit both thrombin- and CRP-induced Ca2+ release in human platelets. Ned-19 has an inhibitory effect on platelet aggregation, secretion and spreading. In addition, Ned-19 extends the clotting time in whole-blood samples. We conclude that NAADP plays an important role in human platelet function. Furthermore, the development of Ned-19 as an NAADP receptor antagonist provides a potential avenue for platelet-targeted therapy and the regulation of thrombosis.
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PMID:NAADP regulates human platelet function. 2196 41

Two-pore channels (TCPS) are NAADP-sensitive receptor channels that conduct Ca(2+) efflux from the intracellular stores. Discharge of the internal Ca(2+) pools results in the activation of store-operated Ca(2+) entry (SOCE); however, the role of TPCs in the modulation of SOCE remains unexplored. Mammalian cells express three TPCs: TPC1, TPC2 and TPC3, a pseudogene in humans. Here we report that MEG01 and HEK293 cells endogenously express TPC1 and TPC2. Silencing TPC2 expression results in attenuation of the rate and extent of thapsigargin (TG)-evoked SOCE both in MEG01 and HEK293 cells, without having any effect on the ability of cells to accumulate Ca(2+) into the TG-sensitive stores. Similarly, silencing of native TPC2 expression reduced thrombin-induced Ca(2+) entry both in MEG01 and HEK293 cells. Biotinylation analysis revealed that TPC1 and TPC2 are expressed in internal membranes. Finally, co-immunoprecipitation experiments indicated that endogenously expressed TPC2, but not TPC1, assoicates STIM1 and Orai1, but not with TRPC1, in MEG01 cells with depleted intracellular Ca(2+) stores, but not in resting cells. These results provide strong evidence for modulation of SOCE by TPC2 involving de novo association between TPC2 and STIM1, as well as Orai1, in human cells.
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PMID:Two-pore channel 2 (TPC2) modulates store-operated Ca(2+) entry. 2307 36