Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.69 (APC)
 16,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombomodulin (TM) is a transmembrane glycoprotein that interacts with thrombin, thereby serving as a cofactor in the activation of protein C, a major physiologically relevant natural anticoagulant. Although initially described as a vascular endothelial cell receptor, TM has also been reported to be synthesized by several cells, including megakaryocytes, platelets, monocytes, neutrophils (PMN), mesothelial cells, and synovial lining cells. A prominent feature of rheumatoid arthritis (RA) is infiltration of PMN into the joint space. To determine whether TM might play a role in the inflammatory process, we examined synovial fluid for the presence of TM in 10 patients with RA and five patients with osteoarthritis (OA). We determined that the mean synovial fluid and plasma TM levels in the OA group were 23.5 ng/mL and 24.2 ng/mL, respectively, whereas those with RA had a significantly elevated mean synovial fluid TM level of 136.2 ng/mL as compared with the plasma TM concentration of 43.9 ng/mL (P < .05). Synovial fluid TM levels did not correlate with PMN counts (r = .261). Purified TM from synovial fluid was identical in molecular weight to plasma-derived TM and was biologically functional with respect to protein C cofactor activity. Using direct immunofluorescence, we determined that adherent cultured synovial fluid cells that are not monocytoid in origin express surface and cytoplasmic TM, thereby providing an alternative source of the protein. Biologic activity of the cell-surface TM was confirmed by acceleration of thrombin-dependent protein C activation. Northern analysis of RNA extracted from the cultured cells indicated that TM messenger RNA was present, suggesting local synthesis. Our results indicate that in RA-associated synovial effusions, biologically active TM is increased, the source of which may be from plasma, PMN, and/or synovial lining cells. TM may play a regulatory role either in fibrin deposition in the inflamed joint and/or in the progression of the inflammatory process.
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PMID:Biologically active thrombomodulin is synthesized by adherent synovial fluid cells and is elevated in synovial fluid of patients with rheumatoid arthritis. 767 98

Recently, we identified and cloned a human endothelial cell protein C/activated protein C receptor (EPCR). EPCR was predicted to be a type 1 transmembrane glycoprotein and a novel member of the CD1/major histocompatibility complex superfamily with 28% identity with CD1d. Even greater homology (62% identity) was detected with the murine protein, CCD41, which was previously characterized as a centrosome-associated, cell cycle-dependent protein. This raised the possibility that CCD41 was the murine homologue of EPCR. To address this possibility, to better understand structure-function relationships, and to facilitate physiological experiments on EPCR function, we cloned and sequenced murine and bovine EPCR from endothelial cell cDNA libraries. The nucleotide sequence of murine EPCR and CCD41 exhibited five differences corresponding to one base change, three single-base insertions, and one base deletion in the protein coding region. As a result, the predicted structures of EPCR and CCD41 differed in their amino and carboxyl termini but were identical in the central portion of the coding sequence. Based on comparison of the murine, bovine, and human EPCR sequences and the regions where discrepancies between murine EPCR and CCD41 were detected, we believe that CCD41 is probably identical to murine EPCR and that the reported sequence differences are likely the result of compression on the sequencing gel. Compared with human EPCR, the murine and bovine sequences were 69 and 73% identical, respectively, and 57% of the residues were identical between all three species. Both bovine and murine EPCR could bind human activated protein C when the cDNA clones were transfected into 293T cells. Like human EPCR, of the cell lines tested, the murine EPCR message was restricted to endothelium. Cloning of the murine and bovine homologue of EPCR will facilitate in vivo and in vitro studies of the role of EPCR in the protein C pathway.
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PMID:Molecular cloning and expression of murine and bovine endothelial cell protein C/activated protein C receptor (EPCR). The structural and functional conservation in human, bovine, and murine EPCR. 789 Jun 76

Human protein C and activated protein C are shown to bind to endothelium specifically, selectively and saturably (Kd = 30 nM, 7000 sites per cell) in a Ca(2+)-dependent fashion. Expression cloning revealed a 1.3-kilobase pair cDNA that coded for a novel type 1 transmembrane glycoprotein capable of binding protein C. This protein appears to be a member of the CD1/major histocompatibility complex superfamily. Like thrombomodulin, the receptor involved in protein C activation, the endothelial cell protein C receptor function and message are both down-regulated by exposure of endothelium to tumor necrosis factor. Identification of endothelial cell protein C receptor as a member of the CD1/major histocompatibility complex superfamily provides insights into the role of protein C in regulating the inflammatory response.
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PMID:Identification, cloning, and regulation of a novel endothelial cell protein C/activated protein C receptor. 792 70

We have previously shown that protein S, a vitamin K-dependent protein, is a bone matrix component synthesized and secreted by osteoblasts. Because protein S is a cofactor of protein C in inhibiting factor Va and VIIIa, we have looked for the presence of the proteins related to the anticoagulant protein C system in human MG 63 osteosarcoma cells and in human adult osteoblast-like cells. Using immunoblotting, we have shown that protein C, factor V, and C4b binding protein are not secreted by these cells. We have shown by enzyme-linked immunoassay, immunocytochemistry, and immunoprecipitation of labeled proteins that thrombomodulin, a transmembrane glycoprotein involved with thrombin in the activation of protein C, is present at the cell surface of osteoblasts. Moreover, using a protein C activation system where thrombin and protein C are added to the cells, we have shown that protein C could be activated at the osteoblast cell surface. This activation of exogenous protein C, reflecting the activity of thrombomodulin, as well as the expression of the thrombomodulin antigen, is regulated by some bone resorption-enhancing factors. 1,25-dihydroxyvitamin D3 and retinoic acid increase thrombomodulin expression and activity in a dose-dependent manner whereas tumor necrosis factor alpha and interleukin 1 decrease these parameters. Because thrombomodulin is known to inhibit single-chain urokinase-type plasminogen activator, a molecule present in the osteoblast microenvironment, these findings suggest that thrombomodulin could play a role in the regulation of bone resorption by modulating the plasmin system.
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PMID:Thrombomodulin is synthesized by osteoblasts, stimulated by 1,25-(OH)2D3 and activates protein C at their cell membrane. 839 72

Hemodynamic forces modulate various endothelial cell functions even in the presence of cytokines under gene regulation. We have investigated the effect of shear stress on the coagulation and fibrinolysis systems in cultured human umbilical vein endothelial cells (HUVECs) perturbed by cytokines, using modified cone-plate viscometer. Thrombomodulin (TM), a surface glycoprotein receptor for thrombin that catalyzes the activation of the protein C anticoagulant pathway, and tissue factor (TF), a transmembrane glycoprotein that plays a central role in blood coagulation, are important regulators for coagulation in endothelium. Shear stress of 18 dynes/cm2 increased the expression of TM either in the presence or absence of TNF alpha (100 U/ml). In contrast, shear stresses of 6 approximately 24 dynes/cm2 decreased the expression of TNF alpha-induced TF in a shear intensity- and exposure time- dependent manner Tissue plasminogen activator(t-PA), which converts plasminogen to plasmin to degrade fibrin clot, and plasminogen activator inhibitor-1 (PAI-1), which inhibits t-PA function, play central roles in fibrinolysis in the endothelium. Treatment of the cells with IL-1 beta or TNF-alpha under static conditions had no effect on t-PA secretion, while release of PAI-1 increased. When cells were exposed to increasing shear stress up to 24 dynes/cm2, levels of t-PA significantly increased relative to shear stress, while PAI-1 secretion decreased gradually. In the presence of IL-1 beta or TNF-alpha, the increased production of t-PA was further augmented. These results clearly indicate that shear forces act as an important regulators of the coagulation and fibrinolysis systems in endothelium, to maintain antithrombogenicity of blood vessels.
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PMID:[Regulation of antithrombogenicity in endothelium by hemodynamic forces]. 913 94

We have used our previously described ex vivo mesothelial cell (MC)-mediated gene therapy strategy (Gene Ther. 2:393-401, 1995) to modify the functional properties of the rat parietal peritoneal mesothelium in vivo by expression of a membrane-bound recombinant protein on the MC surface. Rat primary MCs were stably transfected (using strontium phosphate DNA coprecipitation) with a plasmid containing the gene for rat thrombomodulin (TM), a transmembrane glycoprotein that functions as an essential cofactor for the physiological activation of the anticoagulant protein C by the enzyme thrombin. As demonstrated by immunohistochemistry and by direct equilibrium binding with radiolabeled thrombin, genetically modified MCs expressed high levels of TM antigen on their surface in vitro. As judged by a thrombin-dependent protein C activation assay, such MC membrane-bound TM was biologically active. Once reseeded on the denuded parietal peritoneal surface of syngeneic recipients, these TM-transfected MCs continued to express TM antigen in vivo for at least 90 days. Moreover, the recombinant TM expressed on the reconstituted parietal mesothelium retained its ability to activate protein C in a thrombin-dependent manner. Our data indicate that MC-mediated expression of TM can be used to augment the anticoagulant properties of the parietal peritoneal surface. In general, our results suggest that ex vivo MC-mediated gene therapy can be used to deliver other therapeutic transmembrane proteins to the MC surface to enhance the functional repertoire of the parietal mesothelium in vivo.
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PMID:Enhancement of the functional repertoire of the rat parietal peritoneal mesothelium in vivo: directed expression of the anticoagulant and antiinflammatory molecule thrombomodulin. 960 18

The anticoagulant transmembrane glycoprotein thrombomodulin (TM) is expressed at the luminal surface of vascular endothelial cells. Recently, we showed that TM antigen and TM mRNA are expressed in brain microvessels in several species and that brain capillaries have the capability to activate protein C. The activation of protein C in brain microcirculation was greatly impaired by major stroke risk factors in rats due to downregulation of TM. In this study, a partial sequence of TM was determined from TM mRNA from brain capillaries examined in brain capillaries of the rat, a species that provides a useful model to investigate stroke mechanisms in relation to brain hemostasis. The predicted deduced amino acid sequences for rat TM were compared with other TM sequences. Particularly high homology (77-100%) among functional domains of the protein, i.e., the epidermal growth factor repeats (EGFRs) 1-6 and the transmembrane region, was observed between mice and rats. Somewhat less degree of homology was observed for bovine and human EGFRs 1-6, while the homology of the transmembrane region was 92-96%. All cysteine residues were conserved among the TM sequences, and specific amino acids previously suggested to be essential for activation of protein C by thrombin TM were highly conserved. We conclude that the highly conserved mRNA and protein sequences may reflect a similar anticoagulant role of TM in brain endothelial and systemic vascular endothelial cells across different species.
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PMID:Rat brain capillary thrombomodulin: structure and function. 985 12

The endothelial cell receptor (EPCR) for protein C (PC)/activated protein C (APC) is a 221 amino-acid residues long transmembrane glycoprotein with unclear physiological function. To facilitate future studies and to rationalize recently reported experimental data about this protein, we have constructed three-dimensional models of human, bovine and mouse EPCR using threading and comparative model building. EPCR is homologous to CD1/MHC class I molecules. It consists of two domains, which are similar to the alpha1 and alpha2 domains of MHC class I molecules, whereas the alpha3 domain of MHC is replaced in EPCR by a transmembrane region followed by a short cytosolic tail. The alpha1 and alpha2 domains of CD1/MHC proteins form a groove, which binds short peptides. These domains are composed of an eight-stranded antiparallel beta-pleated sheet with two long antiparallel alpha-helices. The distance between the helical segments dictates the width of the groove. The cleft in EPCR appears to be relatively narrow and it is lined with hydrophobic/aromatic and polar residues with a few charged amino acids. Analysis of the human EPCR model predicts that (a) the protein does not contain any calcium binding pockets; (b) C101 and C169 form a buried disulphide bridge, while C97 is free, and buried in the core of the molecule; and (c) four potential glycosylation sites are solvent exposed.
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PMID:Structural prediction and analysis of endothelial cell protein C/activated protein C receptor. 1055 43

Cancer is a genetic disease. The unstable genome of cancer cells causes tumour progression through multiple alterations in suppressor and promoter genes, leading to loss of homeostatic and gain of oncogenic functions. Invasion is the critical step in the acquisition of malignancy. It implicates a continuous molecular conversation of the cancer cells with other cells and with the extracellular matrix in which adhesion molecules are crucial. One of these, E-cadherin, is discussed in the present review. E-cadherin is a transmembrane glycoprotein that forms a complex with cytoplasmic proteins, termed catenins because they link E-cadherin to the actin cytoskeleton. E-cadherin/catenin-mediated intercellular adhesion and communication is mainly homophylic homotypic. There is compelling evidence from experiments in vitro as well as in vivo to accept that the E-cadherin/catenin complex acts as an invasion suppressor. The mechanism of this action is not only through cell-cell adhesion but also through transduction of signals to the cell's motility system. In the replication error positive human colon cancer cell line HCT-8, the alpha E-catenin gene CTNNA1 is an invasion suppressor gene. Here, the transition from the non-invasive to the invasive state was prevented by introduction into the unstable non-invasive cells of either an extra CTNNA1 or a wild type hMSH6 mismatch repair gene. beta-catenin also participates at a complex which comprises the adenomatous polyposis cancer protein APC. In colorectal cancer, mutation of either APC or beta-catenin is oncogenic. Downregulation of the E-cadherin/catenin complex may occur in several ways amongst which are gene mutations, methylation of 5'CpG dinucleotides within the promotor region of E-cadherin, tyrosine phosphorylation of beta-catenin, cell surface expression of proteoglycans sterically hindering E-cadherin and proteolytic release of fragments from the extracellular part of E-cadherin. Upregulation of the E-cadherin/catenin complex has been realized with a series of agents, some of which can be used therapeutically. In most human gastrointestinal cancers the E-cadherin/catenin or related complexes are disturbed and this underscores their pivotal role in the progression of these tumours. Mutations of the E-cadherin gene, including germline mutations, occur in diffuse gastric carcinoma, CpG methylation around the promotor region of E-cadherin in hepatocellular carcinomas and mutations of the APC tumour suppressor gene or in the beta-catenin oncogene in most colorectal cancers. The literature agrees about the disturbance of immunohistochemical patterns of E-cadherin and catenin expression in gastrointestinal cancers. Conflicting opinions do, however, exist about the prognostic value of such immunohistochemical aberrations. We doubt that immunohistochemistry of E-cadherin or catenins add prognostic value to the already used histological grading systems. In our opinion the major benefit from understanding of the E-cadherin/catenin-mediated pathways of invasion will be the development of new anti-invasive treatment strategies.
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PMID:The role of the E-cadherin/catenin complex in gastrointestinal cancer. 1069 69

The objective of this study was to review the mechanisms by which thrombomodulin (TM) may modulate inflammation. The data were taken from published research performed by other laboratories and our own experimental results. TM is a transmembrane glycoprotein receptor and cofactor for thrombin in the protein C anticoagulant system. Recent studies have revealed that TM has activities, both dependent and independent of either protein C or thrombin, that affect biological systems beyond the coagulation pathway. This review highlights recent insights, provided by in vitro and in vivo analyses, into how the unique structural domains of TM effectively modify coagulation, fibrinolysis, and inflammation in health and disease. A paradigm is presented to describe how these apparently distinct functions are integrated to maintain homeostasis under stress conditions. Finally, we explore the potential diagnostic and therapeutic utility of dissecting out the structure-function correlates of TM. We conclude that TM plays a central role in regulating not only hemostasis but also inflammation, thus providing a close link between these processes. Elucidation of the molecular mechanisms by which TM functions will likely provide novel targets for therapeutic intervention.
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PMID:Novel functions of thrombomodulin in inflammation. 1511 27


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