Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Quite apart from their ability to generate active polypeptides from hormone precursors and to function as digestive enzymes, proteinases are now known to play a hormone-like role by triggering signal transduction pathways in target cells. The best understood example of proteinase-mediated signaling can be seen in the action of thrombin, which in addition to triggering the coagulation cascade, regulates platelet and endothelial cell function via its serine proteinase activity. The discovery of the G-protein-coupled 'receptor' responsible for these cellular actions of thrombin (Proteinase-activated Receptor-1, or PAR(1)) represents one of the more intriguing signal transduction stories elucidated over past decade or so. It is the objective of this brief review to provide an overview of the discovery and molecular pharmacology of the PAR family and to indicate the widespread roles these receptor systems can play in a variety of tissues. Further, the article (1) illustrates the utility of employing receptor-selective PAR-activating peptides to determine the potential physiological roles these receptors play in vivo and (2) describes how these agonists have identified receptors other than the PARs. Finally, the mechanisms other than via the PARs by which proteinases can generate cellular signals are summarized.
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PMID:Proteinase-mediated signaling: proteinase-activated receptors (PARs) and much more. 1460 51

Protease activated receptor-1 (PAR-1) is a key mediator of the cellular actions of alpha-thrombin. Thus, antagonism of this unique G-protein coupled receptor with a small molecule represents a means of selectively inhibiting thrombin's cellular actions without inhibiting its proteolytic activity. RWJ-58259 (alphaS)-N-[(1S)-3-amino-1-[[(phenylmethyl)- amino]carbonyl]propyl]-alpha-[[[[[1-(2,6-dichlorophenyl)methyl]-3-(1-pyrrolidinylmethyl)-1H-indazol-6-yl]amino]carbonyl]amino]-3,4-difluorobenzenepropanamide) is a potent and selective inhibitor of PAR-1 identified as part of a synthetic chemistry program based upon a de novo design approach. RWJ-58259 inhibited thrombin-induced platelet aggregation in human platelets with an IC50 of 0.37 microM without inhibiting thrombin's proteolytic activity or aggregation induced by other agonists. RWJ-58259 was not effective in guinea pig models of thrombosis. This reflected the presence of a second thrombin-sensitive receptor system in guinea pigs (PAR-3/4) and the selectivity of RWJ-58259 for PAR-1. However, RWJ-58259 was effective in a non-human primate model of thrombosis. Because human platelets have a PAR expression profile similar to the non-human primate, PAR-1 antagonism has the potential to be antithrombotic in humans. RWJ-58259 also inhibited thrombin-induced intracellular calcium signaling and proliferation in rat vascular smooth muscle cells. Perivascular application of RWJ-58259 in vivo significantly inhibited arterial injury-induced stenosis in a rat model of balloon angioplasty. These preclinical results suggest a potential clinical utility of RWJ-58259 for treatment of thrombotic disorders and vascular injury associated with acute coronary interventions and atherosclerosis. Given the potential role of PAR-1 in thrombin's actions in other cell types and disease states, RWJ-58259 provides a means for assessing additional clinical utilities of PAR-1 antagonism in disease conditions such as inflammation, cancer and neurodegeneration.
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PMID:RWJ-58259: a selective antagonist of protease activated receptor-1. 1464 34

Protease-activated G protein-coupled receptors (PAR1-4) are tethered-ligand receptors that are activated by proteolytic cleavage of the extracellular domain (exodomain) of the receptor. PAR1, the prototypic member of the PAR family, is the high-affinity thrombin receptor of platelets and vascular endothelium and plays a critical role in blood coagulation, thrombosis, and inflammation. Here, we describe the solution structure of the thrombin-cleaved exodomain of PAR1. The side chains of a hydrophobic hirudin-like (Hir) sequence and adjacent anionic motif project into solution. Docking of the exodomain Hir sequence to exosite I of thrombin reveals that the tethered ligand in the cleaved exodomain bends away from thrombin, leaving its active site available to another large macromolecular substrate. The N-terminal ligand is longer than anticipated and forms an intramolecular complex with a region located in the C terminus of the exodomain. Mutational analysis confirmed that this C-terminal region is a ligand binding site for both intra- and intermolecular ligands. A lipidated-ligand binding site peptide was found to be an effective inhibitor of thrombin-induced platelet aggregation.
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PMID:Structural basis for thrombin activation of a protease-activated receptor: inhibition of intramolecular liganding. 1465 70

In fibroblasts, thrombin induces collagen deposition through activation of a G-protein-coupled receptor, proteinase-activated receptor 1 (PAR(1)). In the current study, we examined whether PAR(1) antagonism inhibits hepatic stellate cell (HSC) activation in vitro and whether it protects against fibrosis development in a rodent model of cirrhosis. A rat HSC line was used for in vitro studies whereas cirrhosis was induced by bile duct ligation (BDL). The current results demonstrated that HSCs express PAR(1), as well as proteinase-activated receptors 2 (PAR(2)) and 4 (PAR(4)), and that all three PARs were up-regulated in response to exposure to growth factor in vitro. Exposure to thrombin and to SFLLRN-(SF)-NH(2), a PAR(1) agonist, and GYPGKF (GY)-NH(2), a PAR(4) agonist, triggered HSC proliferation and contraction, as well as monocyte chemotactic protein-1 (MCP-1) production and collagen I synthesis and release. These effects were inhibited by the PAR(1) antagonist. Administration of this antagonist, 1.5 mg/kg/d, to BDL rats reduced liver type I collagen messenger RNA (mRNA) expression and surface collagen by 63%, as measured by quantitative morphometric analysis. Similarly, hepatic and urinary excretion of hydroxyproline was reduced significantly by the PAR(1) antagonist. In conclusion, PAR(s) regulates HSC activity; development of PAR antagonists might be a feasible therapeutic strategy for protecting against fibrosis in patients with chronic liver diseases.
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PMID:PAR1 antagonism protects against experimental liver fibrosis. Role of proteinase receptors in stellate cell activation. 1476 89

Strong agonists cause platelets to expose a procoagulant surface supporting the assembly of two important coagulation enzyme complexes. Equilibrium binding has determined the density of high affinity saturable factor IXa binding sites to be 500-600 sites/platelet. We have now used flow cytometry to visualize the binding of factor IX and IXa to thrombin- or SFLLRN-activated platelets. Concentrations of these agonists that are half-maximal or maximal in kinetic studies resulted in only a small subpopulation (4-20%) of platelets binding factor IX or IXa with the density of binding sites for factor IX being about half of that for factor IXa, consistent with previous equilibrium binding studies. A small subpopulation (5 +/- 1.5%) of platelets stimulated with either agonist also exposed annexin V binding sites, and this subpopulation of platelets also bound factor IXa. Annexin V decreased factor IXa binding in the presence or absence of factor VIIIa, and factor IXa could also decrease annexin V binding on some platelets indicating a common binding site in agreement with previous studies. All platelets binding factor IXa were positive for glycoprotein IX, at the same glycoprotein IX surface density as seen in platelets negative for factor IXa binding. These studies refine the results from equilibrium binding studies and suggest that, on average, only a small subpopulation (approximately 10%) of PAR 1-stimulated platelets expose approximately 6000 factor IXa binding sites/platelet.
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PMID:A subpopulation of platelets responds to thrombin- or SFLLRN-stimulation with binding sites for factor IXa. 1501 Apr 76

When tissues are injured and bleeding occurs, blood clotting is immediately activated and fibrin clots are formed by thrombin. Afterwards, antithrombin III promptly inactivates thrombin, which restricts the clotting to the bleeding site. In inflamed sites, tissue factor is expressed on cells in the lesion by stimulation from cytokines, and produces thrombin. In this case, thrombin may survive longer because of inefficient inactivation by antithrombin III due to dilution and less perturbation in the interstitial fluid, and therefore, has a greater chance to activate thrombin receptors (protease-activated receptors: PARs) on the cells, which induces various cellular events including proliferation, migration, and shape change. Recent studies have suggested a pathophysiological association of the PAR pathway with crescentic glomerulonephritis. However, the role of thrombin in human diseases has not been fully studied, probably because of a lack of simple and reliable methods for measuring thrombin in clinical samples. To solve this problem, we developed an ELISA system for human alpha-thrombin and applied it to the measurement of thrombin in the urine of patients with glomerulonephritis. Thrombin in urine was detected in glomerulonephritic patients but not in healthy volunteers or disseminated intravascular coagulation patients, which suggests that thrombin in urine may reflect thrombin generation by clotting activation in the glomerular lesion.
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PMID:[Evaluation of thrombin in urine as a real-time indicator of clotting activation in glomerulonephritis]. 1516 4

Airway remodelling is a feature of chronic asthma comprising smooth muscle hypertrophy and deposition of extracellular matrix (ECM) proteins. Matrix metalloproteinases (MMPs) breakdown ECM, are involved in tissue remodelling and have been implicated in airway remodelling. Although mesenchymal cells are an important source of MMPs, little data are available on airway smooth muscle (ASM) derived MMPs. We therefore investigated MMP and tissue inhibitor of metalloproteinase (TIMP) production and activity in human ASM cells. MMPs and TIMPs were examined using quantitative real-time RT-PCR, Western blotting, zymography and a quench fluorescence (QF) assay of total MMP activity. The most abundant MMPs were pro-MMP-2, pro- MMP-3, active MMP-3 and MT1-MMP. TIMP-1 and TIMP-2 expression was low in cell lysates but high in conditioned medium. High TIMP secretion was confirmed by the ability of ASM-conditioned medium to inhibit recombinant MMP-2 in a QF assay. Thrombin increased MMP activity by activation of pro-MMP-2 independent of the conventional smooth muscle thrombin receptors PAR 1 and 4. In conclusion, ASM cells express pro-MMP-2, pro and active MMP-3, MMP-9 and MT1-MMP. Unstimulated cells secrete excess TIMP 1 and 2, preventing proteolytic activity. MMP-2 can be activated by thrombin which may contribute to airway remodelling.
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PMID:Matrix metalloproteinase expression and activity in human airway smooth muscle cells. 1526 5

Active thrombin is found in the airways of patients with a variety of inflammatory lung diseases. However, whether thrombin contributes to the pathologies of these diseases is unknown, although thrombin is a potent inflammatory mediator in other organ systems. In the present study we have assessed the acute inflammatory effect of inhaled thrombin and investigated the possible receptors mediating any effects in mice. Thrombin (200-2000 U kg(-1) intranasally), induced the recruitment of a small, but significant, number of neutrophils into the airways as assessed by differential counts of cells retrieved by bronchoalveolar lavage (BAL). This small response was mimicked by peptide agonists of proteinase-activated receptor-4 (PAR(4); GYPGKF, AYPGKF; 2-20 mg kg(-1)), but not PAR(1) (SFLLRN; 2-20 mg kg(-1)). By contrast, trypsin (200-2000 U kg(-1)) caused profound inflammation and lung damage. Concentrations of tumour necrosis factor-alpha (TNF-alpha) were elevated in BAL fluid from thrombin-treated mice, and a TNF-alpha-neutralising antibody inhibited the influx of neutrophils in response to thrombin. Although isolated alveolar macrophages appeared to express PAR(1)- and PAR(4)-immunoreactivity, these cells failed to release TNF-alpha above baseline levels in response to thrombin, trypsin or any of the peptide PAR agonists. Neither thrombin (2000 U kg(-1)) nor trypsin (200 U kg(-1)) modified the airway neutrophilia in response to intranasal bacterial lipopolysaccharide (LPS; 100 micrograms kg(-1)). In conclusion, exogenous thrombin has only a modest acute inflammatory action in the lung that appears to be mediated by PAR(4) and involve release of TNF-alpha from an unknown source.
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PMID:Effects of inhaled thrombin receptor agonists in mice. 1530 75

The vascular hypothesis for the pathogenesis of systemic sclerosis was perhaps Professor LeRoy's most important scientific contribution. One early and important consequence of vascular injury is the release of activated thrombin. In this manuscript we present our data and review the current understanding of the role played by thrombin in the process of fibrosis, particularly as it relates to scleroderma lung disease. Thrombin's cellular effects are intimately involved in promoting myofibroblast differentiation, endothelial cell activation, extracellular matrix protein deposition, and the induction of important profibrotic factors. Such studies confirm that thrombin is one of the major mediators in the development and progression of pulmonary fibrosis. Therefore, targeting the major receptor of thrombin, PAR-I, and its downstream signaling molecules may lead to novel therapeutic approaches for the management of scleroderma lung fibrosis. We are indebted to Dr LeRoy for his many contributions to the field of scleroderma, and for all that he did to stimulate our interest in these studies.
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PMID:Thrombin-mediated cellular events in pulmonary fibrosis associated with systemic sclerosis (scleroderma). 1534 97

There are considered the characteristic features of thrombin functional activity in central and peripheral nervous system. A family of specialized membrane receptors--so called PARs (Proteinase Activated Receptors) and their presence in several parts of CNS is described. The concentration- and PAR-dependent neuroprotecting and injuring effects of thrombin in CNS are compared. The literature and original authors data are presented demonstrating the presence of PARs in peripheral nervous system and the ability of endogenous and exogenous thrombin to influence the regeneration of peripheral nerves. The perspectives of experimental approach are discussed, when the exogenous thrombin or peptide-agonists of PARs are used to accelerate the nerve regeneration in vivo.
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PMID:[Characteristic properties of thrombin neurotropic activity]. 1545 52


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