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 cellular receptor for human urokinase-type plasminogen activator (u-PAR) is shown by several independent criteria to be a true member of a family of integral membrane proteins, anchored to the plasma membrane exclusively by a COOH-terminal glycosyl-phosphatidylinositol moiety. 1) Amino acid analysis of u-PAR after micropurification by affinity chromatography and N-[2-hydroxy-1,1-bis(hydroxymethyl)-ethyl]glycine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the presence of 2-3 mol of ethanolamine/mol protein. 2) Membrane-bound u-PAR is efficiently released from the surface of human U937 cells by trace amounts of purified bacterial phosphatidylinositol-specific phospholipase C. This soluble form of u-PAR retains the binding specificity toward both u-PA and its amino-terminal fragment holding the receptor-binding domain. 3) Treatment of purified u-PAR with phosphatidylinositol-specific phospholipase C or mild alkali completely alters the hydrophobic properties of the receptor as judged by temperature-induced detergent-phase separation and charge-shift electrophoresis. 4) Biosynthetic labeling of u-PAR was obtained with [3H]ethanolamine and myo-[3H]inositol. 5) Finally, comparison of amino acid compositions derived from cDNA sequence and amino acid analysis shows that a polypeptide of medium hydrophobicity is excised from the COOH terminus of the nascent u-PAR. A similar proteolytic processing has been reported for other proteins that are linked to the plasma membrane by a glycosyl-phosphatidylinositol membrane anchor.
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PMID:Cellular receptor for urokinase plasminogen activator. Carboxyl-terminal processing and membrane anchoring by glycosyl-phosphatidylinositol. 184 68

Human glomerular epithelial cells (GECs) in culture synthesize single-chain, urokinase-type plasminogen activator (SC-uPA), tissue-type plasminogen activator (t-PA), and plasminogen activator inhibitor 1 (PAI-1) and possess specific membrane-binding sites for u-PA. Using purified 125I-alpha thrombin, we demonstrate here the presence of two populations of specific binding sites for thrombin on GECs (1.Kd = 4.3 +/- 1.0 x 10(-10) M, 5.4 +/- 1.4 x 10(4) M sites per cell, 2. Kd = 1.6 +/- 0.5 x 10(-8) M, 7.9 +/- 1.8 x 10(5) sites per cell). Purified human alpha thrombin promoted the proliferation of GECs and induced a time- and dose-dependent increase of SC-uPA, t-PA, and PAI-1 antigens released by GECs. Thrombin-mediated increase in antigen was paralleled by an increase in the levels of corresponding u-PA and PAI-1 messenger RNA. In contrast, thrombin decreased u-PA activity in conditioned medium. This discrepancy between u-PA antigen and u-PA activity was explained by a limited proteolysis of SC-uPA by thrombin, leading to a two-chain form detected by immunoblotting and that could not be activated by plasmin. Thrombin also decreased the number of u-PA binding sites on GECs (p less than 0.05) without changing receptor affinity. Hirudin inhibited the binding and the cellular effects of thrombin, whereas thrombin inactivated by diisopropylfluorophosphate had no effect, indicating that both membrane binding and catalytic activity of thrombin were required. We conclude that thrombin, through specific membrane receptors, stimulates proliferation of GECs and decreases the fibrinolytic activity of GECs both at the cell surface and in the conditioned medium. These results suggest that thrombin could be involved in the pathogenesis of extracapillary proliferation and persistency of fibrin deposits in crescentic glomerulonephritis.
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PMID:Thrombin increases proliferation and decreases fibrinolytic activity of kidney glomerular epithelial cells. 184 34

The binding of t-PA-PAI-1 to human hepatocytes at 4 degrees C reached a maximum at 2 h. Scatchard analysis indicated 74,000 +/- 11,000 high-affinity binding sites for complex per human hepatocyte, with a Kd of 0.87 +/- 0.09 nM. Almost identical results were achieved with the human hepatoma cell line Hep G2. Binding of [125I]t-PA-PAI-1 complex was unaffected by high concentrations of unlabelled t-PA, PAI-1, u-PA or u-PA-PAI-1 complex; only t-PA-PAI-1 complex competed for binding. Hepatocyte-bound t-PA-PAI-1 was internalized and degraded at 37 degrees C. Thus, hepatocytes have a specific t-PA-PAI-1 receptor that participates in clearance of this complex.
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PMID:The receptor for tissue plasminogen activator (t-PA) in complex with its inhibitor, PAI-1, on human hepatocytes. 184 16

Degradation of cartilage matrix macromolecules depends on the increase of metalloprotease activity. It has been suggested that interleukin 1 (IL-1) contributes to cartilage break-down by modulating the synthesis of the elements favoring an activation of these metalloenzymes. We analyzed the effect of IL-1 on the synthesis of collagenase, stromelysin, and tissue inhibitor of metalloproteases (TIMP) in human cartilage explants and culture chondrocytes, as well as its effect on the secretion of plasminogen activators (t-PA, u-PA) and inhibitors (PAI-1, PAI-2) in cartilage explants. Messenger RNA levels of collagenase and TIMP were also analyzed following chondrocyte incubation in the presence or absence of IL-1. We demonstrate that IL-1 stimulates the secretion of metalloproteases and t-PA in a dose dependent manner. At a relatively low concentration (5 pg/ml), IL-1 induced collagenase and stromelysin synthesis in parallel with a decline in TIMP secretion. While IL-1 induced collagenase gene expression, no change in the TIMP mRNA level was noted. The increase in t-PA synthesis was accompanied by a decreased PAI-1 level, while the PAI-2 level remained unchanged. u-PA could not be detected in the culture medium. This study gives insight into the ways that the synthesis, activation and inhibition of metalloproteases are modulated by IL-1. These results support the importance of IL-1 in the etiology of cartilage degeneration.
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PMID:In vitro effects of interleukin 1 on the synthesis of metalloproteases, TIMP, plasminogen activators and inhibitors in human articular cartilage. 185 Dec 31

Kidneys have long been recognized as a major source of plasminogen activators (PAs). However, neither the sites of synthesis of the enzymes nor their role in renal function have been elucidated. By the combined use of zymographies on tissue sections and in situ hybridizations, we have explored the cellular distribution of urokinase-type (u-PA) and tissue-type (t-PA) plasminogen activators and of their mRNAs in developing and adult mouse kidneys. In 17.5-d old embryos, renal tubules synthesize u-PA, while S-shaped bodies produce t-PA. In the adult kidney, u-PA is synthesized and released in urine by the epithelial cells lining the straight parts of both proximal and distal tubules. In contrast, t-PA is produced by glomerular cells and by epithelial cells lining the distal part of collecting ducts. The precise segmental distribution of PAs suggests that both enzymes may be implicated in the maintenance of tubular patency, by catalyzing extracellular proteolysis to prevent or circumvent protein precipitation.
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PMID:Sites of synthesis of urokinase and tissue-type plasminogen activators in the murine kidney. 190 Mar 11

Fifty cases of colorectal adenocarcinoma were immunohistochemically examined for the relationship between distribution of plasminogen activators (PAs) and the degree of differentiation of cancer cells as reflected by carcinoembryonic antigen (CEA) expression as well as tumor cell kinetics. The A chain of urokinase-type PA (u-PA-A) was mainly observed in the apical portions of highly differentiated cancer cells. Increased expression and change in localization to the cytoplasm were found with progressive dedifferentiation. The numbers of DNA polymerase alpha (pol. alpha) positive cancer cells also increased in line with u-PA-A expression. The B chain of u-PA (u-PA-B), and the A and B chains of tissue-type PA (t-PA-A and -B) did not show similar alteration. The present findings suggest that the distribution of u-PA-A in colorectal carcinoma tissues, the degree of tumor differentiation, and the proliferation kinetics of cancer cells are closely related.
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PMID:Immunohistochemical analysis of plasminogen activator expression in human colorectal carcinomas: correlation with CEA distribution and tumor cell kinetics. 190 Nov 19

Plasminogen activators (PA), particularly the lower Mr urokinase (u-PA) type, have been associated with tumor cell invasion and metastasis. We have examined the expression of PA by two human prostate cancer cell lines (PC-3 and DU-145) using functional and immunologic techniques. The culture media and cell extracts of the more aggressive PC-3 cell line contained more than two-fold greater PA activity than the relatively indolent DU-145 cell line. Zymographic studies identified the PA expressed as u-PA. PC-3 cells expressed an additional lower molecular weight form of u-PA not noted in DU-145 cells. Heterogeneity in u-PA expression was shown by the fibrin lysis assay, immunohistochemistry, and dual parameter flow cytometry indicating the presence of phenotypically divergent cell populations. Increased u-PA expression may identify those tumor cells that possess aggressive biological potential.
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PMID:Heterogeneity in plasminogen activator (PA) levels in human prostate cancer cell lines: increased PA activity correlates with biologically aggressive behavior. 190 92

The content of PAI-I was measured in carcinoma tissues from the stomach and colorectum divided macroscopically into 3 portions: the central part of the carcinoma, the marginal part of the carcinoma containing some normal mucosa, and the normal mucosa. Among these tissues, the highest levels of PAI-I antigen were found in the central part of the carcinoma. On the other hand, no PAI-I antigen or activity was observed in the normal mucosae. The PAI-I produced in the stomach and colorectal carcinoma tissues showed a non-lytic zone with a molecular weight of 54 kDa by reverse fibrin autography, and this 54-kDa band reacted with anti-PAI-I IgG on an immunoblotted nitrocellulose membrane by the avidin-biotin complex method. The contents of PAI-2 in the carcinoma tissues were not significantly different from those in the normal mucosa of the stomach and colorectum. In both the stomach and colorectal carcinomas, the highest value of u-PA/total PA (sum of u-PA and t-PA) was observed in the central part of the carcinoma, followed by the marginal part of the carcinoma, and was lowest in the normal mucosa. We conclude that increased levels of PAI-I in malignant tissue of the stomach and colorectal tract may serve to modulate extra-cellular proteolysis by u-PA.
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PMID:Plasminogen activator inhibitor 1 in human carcinoma tissues. 190 4

An analysis was made of the various possible activators of single-chain urokinase-type plasminogen activator (scu-PA) in the dextran sulphate euglobulin fraction (DEF) of human plasma. scu-PA activators were detected in an assay system in which the substrate scu-PA, in physiological concentration (50 pM), was immuno-immobilized. After activation of the immobilized scu-PA for a certain period of time the activity of the generated amount of immuno-immobilized two-chain u-PA was determined with plasminogen and the chromogenic substrate S-2251. The scu-PA activator activity (scuPA-AA) in the DEF of plasmas deficient in factor XII or prekallikrein was about half of that in the DEF of normal plasma. Separation of scuPA-AA in the DEF by gel chromatography showed to major peaks, one eluting with an apparent Mr of 500,000 and the other around Mr 100,000. The former peak, which coincided with the activity peak of the kallikrein-kininogen complex, was absent in the DEF of plasma depleted of prekallikrein and therefore was identified as kallikrein. The latter peak was still present in the depleted plasma and most likely represents plasmin, because its scuPA-AA coincided with the activity peak of plasmin and could be fully inhibited by antibodies raised against human plasminogen. It is concluded that plasmin and the contact-activation factor kallikrein each contribute for about 50% to the scuPA-AA in the DEF. Compared on a molar basis, however, plasmin was found to be almost 1,000 times more effective than kallikrein, and we conclude, therefore, that in vivo plasmin is the primary activator of scu-PA and the role of the contact system is of secondary importance.
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PMID:An analysis of the activators of single-chain urokinase-type plasminogen activator (scu-PA) in the dextran sulphate euglobulin fraction of normal plasma and of plasmas deficient in factor XII and prekallikrein. 190 69

The localization of tissue plasminogen activator (t-PA) on microthrombi in various organs of disseminated intravascular coagulation rats (DIC rats) was investigated by using microautoradiographic technique. After the injection of [125I]fibrinogen, experimental DIC rats induced by the infusion of thrombin for 1 h were submitted to microautoradiograms (MARGMs) of some major organs. The radioactivity of [125I]fibrin thrombi, which were observed as silver grains, was localized in the glomeruli and parts of small vessels in the kidney. In the liver, microthrombi were seen in sinusoid vessels and on Kupffer cells. In addition, many microthrombi were noted in small vessels in the lung and marginal zones in the spleen. Two min after the intravenous administration of [125I]t-PA to DIC rats, many silver grains were observed on each MARGM of the kidney, lung, liver and spleen showing the formation of microthrombi. From the identical results with the observations of MARGMs after the injection of [125I]fibrinogen, we confirmed that t-PA was highly accumulated to microthrombi formed in small vessels of the organs. The scattered silver grains were widely observed on the hepatocytes. This result suggested that t-PA bound to the parenchymal cell surface might be transported into the hepatocytes by receptor-mediated endocytosis. On the other hand, when [125I]urokinase plasminogen activator [( 125I]u-PA) was administered intravenously to DIC rats, many silver grains were observed on MARGM of the proximal tubules in the kidney but not seen on MARGMs of the glomeruli in the kidney, nor in the lung, liver, and spleen. This observation suggested that u-PA might not have a characteristic to accumulate to thrombi.
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PMID:Localization of tissue plasminogen activator on experimental microthrombi in rats. Microautoradiographic observations. 190 22


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