Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.73 (urokinase-type plasminogen activator)
 10,685 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The very low density lipoprotein (VLDL) receptor binds apolipoprotein E-rich lipoproteins as well as the 39-kDa receptor-associated protein (RAP). Ligand blotting experiments using RAP and immunoblotting experiments using an anti-VLDL receptor IgG detected the VLDL receptor in detergent extracts of human aortic endothelial cells, human umbilical vein endothelial cells, and human aortic smooth muscle cells. To gain insight into the role of the VLDL receptor in the vascular endothelium, its ligand binding properties were further characterized. In vitro binding experiments documented that lipoprotein lipase (LpL), a key enzyme in lipoprotein catabolism, binds with high affinity to purified VLDL receptor. In addition, urokinase complexed with plasminogen activator-inhibitor type I (uPA.PAI-1) also bound to the purified VLDL receptor with high affinity. To assess the capacity of the VLDL receptor to mediate the cellular internalization of ligands, an adenoviral vector was used to introduce the VLDL receptor gene into a murine embryonic fibroblast cell line deficient in the VLDL receptor and the LDL receptor-related protein, another endocytic receptor known to bind LpL and uPA.PAI-1 complexes. Infected fibroblasts that express the VLDL receptor mediate the cellular internalization of 125I-labeled LpL and uPA.PAI-1 complexes, leading to their degradation. Non-infected fibroblasts or fibroblasts infected with the lacZ gene did not internalize these ligands. These studies confirm that the VLDL receptor binds to and mediates the catabolism of LpL and uPA.PAI-1 complexes. Thus, the VLDL receptor may play a unique role on the vascular endothelium in lipoprotein catabolism by regulating levels of LpL and in the regulation of fibrinolysis by facilitating the removal of urokinase complexed with its inhibitor.
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PMID:The very low density lipoprotein receptor mediates the cellular catabolism of lipoprotein lipase and urokinase-plasminogen activator inhibitor type I complexes. 759 75

The accumulation of excessive cholesterol-rich lipoproteins within vascular cells, the proliferation of vascular cells, and fibrin deposition are hallmark features of atherosclerosis. Evidence accumulated over the past few years supports the hypothesis that one member of the LDL receptor family, the low density lipoprotein receptor-related protein (LRP), affects the dynamics of each of these processes. LRP is expressed in several vascular cell types, including smooth muscle cells, and in macrophages, and is also expressed in these cells in atherosclerotic lesions. This receptor is a large endocytotic receptor that mediates the catabolism of a number of molecules known to be important in vascular biology, including apolipoprotein E- and lipoprotein lipase-enriched lipoproteins, thrombospondin, and plasminogen activators. The capacity of LRP to mediate lipoprotein catabolism may be a factor in the development of the lesion by contributing to the formation of foam cells. LRP has recently been shown to mediate the catabolism of thrombospondin, a molecule that has potent biological effects on cells of the vasculature. The regulation of its extracellular accumulation by LRP might modulate the dynamic processes of tissue remodeling associated with the response to vascular injury. In addition, LRP regulates the expression of plasmin activity by directly binding and mediating the cellular internalization of urokinase- and tissue-type plasminogen activators. The cellular removal of these two enzymes decreases the local profibrinolytic potential, possibly leading to a thrombotic state at lesion sites.
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PMID:LDL receptor-related protein: a multiligand receptor for lipoprotein and proteinase catabolism. 761 59

The role of plasminogen activator inhibitor type 1 (PAI-1) in the clearance of tissue-type plasminogen activator (t-PA) by hepatocyte-like cells was studied. Rat (Novikoff) hepatoma cells were able to bind and degrade t-PA in a PAI-1 independent fashion, but PAI-1 markedly increased the rate of degradation and t-PA/PAI-1 was a more efficient inhibitor of 125I-t-PA or of 125I-t-PA/PAI-1 degradation than free t-PA. Competition studies revealed that the effect of PAI-1 is unlikely to involve determinants located on the PAI-1 part of the complex: 1) an excess of free PAI had no effect on the rate of degradation of 125I-t-PA/PAI-1.2) Complexes of PAI-1 with urokinase-type PA or with a t-PA mutant lacking the finger and growth factor domains were unable to compete for the binding and degradation of free or PAI-1-complexed 125I-t-PA.3) t-PA KHRR296-299AAAA, a mutant which reacts 2 orders of magnitude slower with PAI-1 than wild type t-PA, behaved similar to wild type t-PA. The clearance via both the PAI-1-dependent and the PAI-1-independent mechanisms was inhibited by the receptor-associated protein, a general inhibitor of clearance mediated by the LDL receptor-related protein. We conclude that t-PA can be cleared by rat hepatoma cells in a PAI-1 independent fashion, but after complex formation with PAI-1, binding of t-PA to the cells is increased and clearance accelerated. Both mechanisms seem to involve the same receptor.
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PMID:The role of plasminogen activator inhibitor type 1 in the clearance of tissue-type plasminogen activator by rat hepatoma cells. 811 17

Binding of urokinase-type plasminogen activator (uPA) to its glycosylphosphatidylinositol-anchored receptor (uPAR) initiates signal transduction, adhesion, and migration in certain cell types. To determine whether some of these activities may be mediated by associations between the uPA/uPAR complex and other cell surface proteins, we studied the binding of complexes composed of recombinant, soluble uPA receptor (suPAR) and single chain uPA (scuPA) to a cell line (LM-TK- fibroblasts) that does not express glycosylphosphatidylinositol (GPI)-anchored proteins to eliminate potential competition by endogenous uPA receptors. scuPA induced the binding of suPAR to LM-TK- cells. Binding of labeled suPAR/scuPA was inhibited by unlabeled complex, but not by scuPA or suPAR added separately, indicating cellular binding sites had been formed that are not present in either component. Binding of the complex was inhibited by low molecular weight uPA (LMW-uPA) indicating exposure of an epitope found normally in the isolated B chain of two chain uPA (tcuPA), but hidden in soluble scuPA. Binding of LMW-uPA was independent of its catalytic site and was associated with retention of its enzymatic activity. Additional cell binding epitopes were generated within suPAR itself by the aminoterminal fragment of scuPA, which itself does not bind to LM-TK- cells. When scuPA bound to suPAR, a binding site for alpha 2-macroglobulin receptor/LDL receptor-related protein (alpha 2 MR/LRP) was lost, while binding sites for cell-associated vitronectin and thrombospondin were induced. In accord with this, the internalization and degradation of cell-associated tcuPA and tcuPA-PAI-1 complexes proceeded less efficiently in the presence of suPAR. Further, little degradation of suPAR was detected, suggesting that cell-bound complex dissociated during the initial stages of endocytosis. Thus, the interaction of scuPA with its receptor causes multiple functional changes within the complex including the dis-appearance of an epitope in scuPA involved in its clearance from the cell surface and the generation of novel epitopes that promote its binding to proteins involved in cell adhesion and signal transduction.
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PMID:Interaction of single-chain urokinase with its receptor induces the appearance and disappearance of binding epitopes within the resultant complex for other cell surface proteins. 869 2

The mouse is the most commonly used species for in vivo studies on angiogenesis related to tumor development. Yet, to the best of our knowledge, very few reports on the in vitro interaction of the angiogenic basic fibroblast growth factor (bFGF) with mouse endothelial cells are available. Three mouse endothelial cell lines originated from aorta (MAECs), brain capillaries (MBECs), and heart capillaries (MHECs) were characterized for endothelial phenotypic markers, in vivo tumorigenic activity, and the capacity to respond in vitro to bFGF. These cells express angiotensin-converting enzyme, acetylated LDL receptor, constitutive endothelial nitric oxide synthase, and vascular cell adhesion molecule-1 and bind Griffonia simplicifolia-I lectin. When injected subcutaneously in nude mice, MAECs induced the appearance of slow-growing vascular lesions reminiscent of epithelioid hemangioendothelioma, whereas MBEC xenografts grew rapidly, showing Kaposi's sarcoma-like morphological features. No lesions were induced by injection of MHECs. MAECs, MBECs, and MHECs expressed both low-affinity heparan sulfate bFGF-binding sites and high-affinity tyrosine kinase receptors (FGFRs) on their surfaces. In particular, MAECs expressed FGFR-2/bek mRNA, whereas microvascular MBECs and MHECs expressed FGFR-1/flg mRNA. Accordingly, bFGF induced a mitogenic response and the phosphorylation of extracellular signal-regulated kinase-2 in all the cell lines. In contrast, upregulation of urokinase-type plasminogen activator expression was observed in bFGF-treated microvascular MBECs and MHECs but not in MAECs. Also, bFGF-treated MBECs and MHECs but not MAECs invaded a three-dimensional fibrin gel and formed hollow, capillary-like structures. The relevance of the modifications of the fibrinolytic balance of mouse microvascular endothelium in bFGF-induced angiogenesis was validated in vivo by a gelatin-sponge assay in which the plasmin inhibitors tranexamic acid and epsilon-aminocaproic acid given to mice in the drinking water inhibited neovascularization induced by the growth factor. In conclusion, differences in response to bFGF exist between large-vessel MAECs and microvascular MBECs and MHECs. Both in vitro and in vivo data point to a role of the profibrinolytic phenotype induced by bFGF in microvascular endothelial cells during mouse angiogenesis. Our observations make these endothelial cell lines suitable for further studies on mouse endothelium during angiogenesis and in angioproliferative diseases.
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PMID:Basic fibroblast growth factor-induced angiogenic phenotype in mouse endothelium. A study of aortic and microvascular endothelial cell lines. 910 63

The plasminogen activation system is thought to be important in cell migration processes. A role for this system during smooth muscle cell migration after vascular injury has been suggested from several animal studies. However, not much is known about its involvement in human vascular remodelling. We studied the involvement of the plasminogen activation system in human smooth muscle cell migration in more detail using an in vitro wound assay and a matrix invasion assay. Inhibition of plasmin activity or inhibition of urokinase-type plasminogen activator (u-PA) activity resulted in approximately 40% reduction of migration after 24 h in the wound assay and an even stronger reduction (70-80%) in the matrix invasion assay. Migration of smooth muscle cells in the presence of inhibitory antibodies against tissue-type plasminogen activator (t-PA) was not significantly reduced after 24 h, but after 48 h a 30% reduction of migration was observed, whereas in the matrix invasion assay a 50% reduction in invasion was observed already after 24 h. Prevention of the interaction of u-PA with cell surface receptors by addition of soluble u-PA receptor or alpha2-macroglobulin receptor associated protein (RAP) to the culture medium, resulted in a similar inhibition of migration and invasion. From these results it can be concluded that both u-PA and t-PA mediated plasminogen activation can contribute to in vitro human smooth muscle cell migration and invasion. Furthermore, the interaction between u-PA and its cell surface receptor appears also to be involved in this migration and invasion process. The inhibitory effects on migration and invasion by the addition of RAP suggests an involvement of a RAP sensitive receptor of the LDL receptor family, possibly the LDL-receptor related protein (LRP) and/or the VLDL receptor.
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PMID:The migration of human smooth muscle cells in vitro is mediated by plasminogen activation and can be inhibited by alpha2-macroglobulin receptor associated protein. 926 89

The initial step in atherosclerosis is the rapid targeting of monocytes to the sites of inflammation and endothelial injury. Serum levels of intercellular adhesion molecule-1 were found to be increased in ischaemic heart disease patients and polymorphisms in the E-selectin gene were associated with accelerated atherosclerosis in young (age < 40 years) patients, further suggesting a role of inflammation in atherosclerosis. Cholesterol loading in macrophages was found to induce interleukin-8 expression, suggesting an association between foam cell formation and beta 2-integrin-dependent adhesion of leukocytes. Enhanced endothelium-platelet interaction induced by hypercholesterolaemia is mediated by von Willebrand factor, whereas platelet adhesion to subendothelial matrix is mediated by fibulin-fibrinogen complexes. Activated platelets mediate the homing of leukocytes by interaction with the subendothelial matrix under shear stresses that do not allow neutrophil adhesion. They may also contribute to the oxidative modification of LDL, provide a source of lipids for foam cell generation and contribute to smooth muscle cell proliferation. Oxidized LDL induces tissue factor in macrophages that also provide sites for fibrin polymerization and decreases the anticoagulant activity of endothelium by interfering with thrombomodulin expression and inactivating tissue factor pathway inhibitor. Intravascular fibrinolysis induced by tissue-type plasminogen activator or urokinase may contribute to the initiation of atherosclerosis by inducing P-selectin and platelet activating factor as well as to plaque rupture, either directly or indirectly, by activating metalloproteinases. Plasminogen activator inhibitor-1 inhibits smooth muscle cell migration and, in the presence of vitronectin, promotes the clearance of thrombin by LDL receptor-related protein at sites of endothelial injury.
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PMID:Thrombosis and atherosclerosis. 933 57

Primary cultures of human endometrial stromal cells expressed a single class of specific high-affinity binding sites for urokinase plasminogen activator (UPA) with a dissociation constant KD 1.0 nmol/l and saturation at 2.0 nmol/l. Similar binding data and number of free binding sites, about 200 fmol/mg protein, were found for UPA in complex with its inhibitor plasminogen activator inhibitor-1 (PAI-1). These binding data agree with those reported for the specific cell surface receptor for UPA, and stromal cell expression of UPA receptor mRNA was identified in Northern blots. Cell surface-bound UPA was degraded at 37 degrees C. Degradation of complexed UPA was more efficient than that of free UPA. Degradation of free UPA did not require prior binding to endogenous PAI-1. Degradation of both free and complexed UPA was reduced by 70% by colchicine, chloroquine and methylamine, indicating that degradation involved both internalization and lysosomal enzymes. Furthermore, degradation was independently inhibited by about 70% with anti-UPA receptor antibodies and receptor-associated protein, indicating that the UPA receptor as well as one or more receptors of the low-density lipoprotein (LDL) receptor supergene family were involved in the degradation process. Receptor-associated protein ligand blotting demonstrated a major band co-migrating with the LDL receptor-related protein or glycoprotein 330/megalin, and a minor band co-migrating with the very low-density lipoprotein receptor. Immunoblotting positively demonstrated expression of LDL receptor-related protein, but not glycoprotein 330.
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PMID:Degradation of urokinase plasminogen activator (UPA) in endometrial stromal cells requires both the UPA receptor and the low-density lipoprotein receptor-related protein/alpha2-macroglobulin receptor. 966 42

Mouse midlate placental development involves extensive tissue remodeling and cell invasion, processes which could be mediated by extracellular proteolytic enzymes. We have performed in situ expression analysis of urokinase type plasminogen activator (uPA), as well as functionally related molecules (uPA receptor, low density lipoprotein receptor-related protein, plasminogen activator inhibitor type-1) in day 10.5 to 18.5 post coitum (p.c.) murine placentas. In situ hybridization demonstrated the presence of uPA transcripts in the invasive trophoblast cells, in particular in glycogen-rich trophoblasts, a cell population that between embryonic days 12.5 and 15.5 infiltrates the maternal decidual tissue. In addition, we observed high uPA expression in the cells of uterine epithelium. Enzymatically active uPA was detected in both sites of uPA mRNA expression by in situ zymography. Expression and activity data suggest a role for this protease in the processes of cell invasion and uterine epithelial remodeling. Only low levels of uPA receptor (uPAR) transcripts were found in trophoblasts and decidual tissue at days 10.5 and 11.5 p.c. At the same stages, a prominent expression of plasminogen activator inhibitor type-1 (PAI-1) by spongiotrophoblasts and giant trophoblasts, as well as of LDL receptor-related protein (LRP) by spongiotrophoblasts and decidual cells could be detected, suggesting a role in regulating extracellular proteolysis in the area of fetomaternal interface. Analysis of uPA null placentas showed the presence of decidual extravascular fibrin deposits, which were not detected in wild type placentas. At the same time, the extent of infiltration of trophoblast cells in maternal decidual tissue, evaluated by anti-cytokeratin immunostaining, was similar in wild type and uPA null placentas. Our studies show that in murine hemochorial placentation, uPA has an essential role in the maintenance of the fibrinogenic/fibrinolytic balance in the decidua. The function of uPA in trophoblast invasion appears not to be indispensable, and its absence can be overcome by redundant or compensatory mechanisms.
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PMID:Expression and function of the urokinase type plasminogen activator during mouse hemochorial placental development. 973 98

The LDL receptor family members are endocytic receptors composed of repeated protein modules, including clusters of ligand binding LDL receptor class A (LA) repeats. The large (approximately 600 kDa) members LRP and megalin bind numerous structurally unrelated and often complex ligands at different combinations of sites. LRP is expressed in a wide but restricted set of cell types including hepatocytes, macrophages, smooth muscle cells, and neurons of the CNS. Megalin is expressed in various epithelia including proximal kidney tubules, intestine, and ependymal cells. The two receptors share a multitude of ligands, and their function in vivo is therefore to a large extent determined by their expression pattern. For example, both receptors can endocytose lipoproteins, but this function appears mainly relevant for LRP. In addition, LRP helps regulating urokinase receptor expression on the cell surface via ligand-mediated internalization followed by return of the naked urokinase receptor to the cell surface. Both receptors also have specialist functions. LRP is specific for binding of alpha2-macroglobulin-proteinase complexes and provides clearance of the complexes and of peptides, e.g. cytokines, associated with the complex. Megalin has important functions in vitamin B12 homeostasis since it specifically mediates uptake of the vitamin B12-transcobalamin complex and helps building a storage pool for the vitamin in the kidneys. Moreover, megalin binds cubilin, the recently identified receptor for B12-intrinsic factor complex, thus providing a mechanism for uptake of dietary vitamin B12. Finally, megalin specifically mediates uptake of apolipoprotein J/clusterin, a binding protein for the Abeta peptide implicated in Alzheimer's disease. The binding of multiple complex ligands that belong to distinct physiological systems provides a challenge in future studies aiming at elucidating the role of LRP and megalin in disease mechanisms.
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PMID:Receptors of the low density lipoprotein (LDL) receptor family in man. Multiple functions of the large family members via interaction with complex ligands. 979 28


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