Surface receptors for urokinase plasminogen activator

Secretion of urokinase and plasminogen activator inhibitor-1 by normal colonic epithelium in vitro

Urokinase is a neutral protease whose major site of action is the external surface of the plasma membrane of cells and whose major function seems to be modulation of cell adhesion, such as that which occurs during cell migration. This study aimed to determine whether colonic epithelium is involved with the urokinase system. The contents of urokinase and one of its specific inhibitors, plasminogen activator inhibitor-1, were measured in culture supernatant and cell homogenates of isolated human colonic crypt cells. The amounts of both factors increased in supernatants over 24 hours, and approximately twice the amount was found in supernatants than in autologous cell homogenates. The secretion of both factors was similar in serum free and serum containing media. Northern blot analysis showed that messenger ribonucleic acid specific for urokinase and plasminogen activator inhibitor-1 was present in colonic crypt cells and that expression over 18 hours of culture was increased 12 fold for urokinase type plasminogen activator and two to fourfold for the inhibitor compared with values found in autologous freshly isolated cells. Urokinase activity was detected in crypt cell homogenates and supernatants indicating that it was present in excess of its inhibitors. Control experiments indicated that the epithelial cells themselves were responsible for the observations and excluded artefactual effects of the isolation procedure. In conclusion, isolated human colonic epithelial cells secrete urokinase and at least one of its specific inhibitors. Further investigation of the role of urokinase in the physiology and pathophysiology of colonic epithelium is indicated.

The plasminogen activation system in bovine milk: differential localization of tissue-type plasminogen activator and urokinase in milk fractions is caused by binding to casein and urokinase receptor

We have analyzed the occurrence of components of the plasminogen activation system in bovine milk. Zymographic analyses showed that tissue-type plasminogen activator (t-PA) occurred in association with casein micelles, partially as a complex with type-1 plasminogen activator inhibitor (PAI-1), whereas urokinase-type plasminogen activator (u-PA) was confined to milk leukocytes. Whey contained a component with a plasminogen dependent proteolytic activity which was shown to be plasma prekallikrein (PPK). The u-PA in the milk leukocytes was shown to be bound to urokinase receptor (u-PAR). A purification to near-homogeneity of the bovine u-PAR was undertaken. Investigating the novel t-PA binding to casein micelles by ligand blotting and Sepharose immobilized casein, multimeric forms of kappa-casein and dimeric alpha s2-casein were identified as t-PA binding components. The kappa-casein gene and the fibrinogen gene are believed to have evolved from a common ancestor. Thus, the recent finding that casein enhances t-PA catalyzed plasminogen activation (Marcus, G., Hitt, S., Harvey, S.R. and Tritsch, G.L. (1993) Fibrinolysis 7, 229-236), and the observed t-PA/casein binding suggests that the casein micelle, which also contains plasminogen, may serve as a matrix for t-PA-catalyzed plasminogen activation in milk.

Structural aspects of serpin inhibition

The essential roles of proteins of the serpin family in many physiological processes, along with new discoveries of their unique folding properties, have attracted intense interest in recent years. Many serpins display unusual mobile behavior attributed to rearrangements of alpha-helical or beta-sheet domains, whereby large scale transitions accompany a variety of functions, including inactivation. This unusual behavior was first recognized with the X-ray structure of modified alpha 1-proteinase inhibitor. Subsequent experiments, including new X-ray structures, have revealed a surprising variety of conformations which are functionally important but only partially understood. We review here experimental evidence for conformations relevant to the serpin inhibitory mechanism.

Immunoelectron microscopy of the receptor for urokinase plasminogen activator and cathepsin D in the human breast cancer cell line MDA-MB-231

Receptors for urokinase-type plasminogen activator (uPAR) are present on the surface of many cell types and appear to be the key determinant controlling extracellular proteolysis catalyzed by the urokinase-type plasminogen activator (uPA). Receptor-bound uPA may be inhibited by the specific inhibitors PAI-1 and PAI-2, and the complex thus formed may subsequently be internalized and degraded in lysosomes. Biochemical evidence has recently indicated that also uPAR is internalized with the uPA/uPAI complex. We report here the subcellular localization of uPAR and cathepsin D in the MDA-MB-231 human breast cancer cell line studied by immuno-electron microscopy of ultrathin cryosections using single or double immunostaining techniques. Cell surface uPAR was preferentially localized at cell-cell junctions; cytoplasmic uPAR was inside large vesicles of different morphology and in flat Golgi saccules. A number of vesicles also contained cathepsin D. The uPAR was exclusively membrane-bound at the cell surface and in cytoplasmic vesicles without cathepsin D. In lysosomal vesicles with both cathepsin D and u-PAR, uPAR was probably degraded as it was observed in the luminal contents.

Receptor-mediated endocytosis of plasminogen activators and activator/inhibitor complexes

Recent findings have elucidated the mechanism for clearance from the extracellular space of the two types of plasminogen activators, urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA), and their type-1 inhibitor (PAI-1). Activator/PAI-1 complexes and uncomplexed t-PA bind to the multi-ligand receptors alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2MR) and epithelial glycoprotein 330 (gp330). These receptors mediate endocytosis and degradation of u-PA/PAI-1 complex bound to the glycosyl phosphatidyl inositol-anchored urokinase receptor (u-PAR) on cell surfaces, and participate, in cooperation with other receptors, in hepatic clearance of activator/PAI-1 complexes and uncomplexed t-PA from blood plasma. The alpha 2MR- and gp330-mediated endocytosis of a ligand (u-PA/PAI-1 complex) initially bound to another receptor (u-PAR) is a novel kind of interaction between membrane receptors. Binding to alpha 2MR and gp330 is a novel kind of molecular recognition of serine proteinases and serpins.

Quantitation of the receptor for urokinase plasminogen activator by enzyme-linked immunosorbent assay

Binding of the urokinase plasminogen activator (uPA) to a specific cell surface receptor (uPAR) plays a crucial role in proteolysis during tissue remodelling and cancer invasion. An immunosorbent assay for the quantitation of uPAR has now been developed. This assay is based on two monoclonal antibodies recognizing the non-ligand binding part of this receptor, and it detects both free and occupied uPAR, in contrast to ligand-binding assays used previously. In a variant of the assay, the occupied fraction of uPAR is selectively detected with a uPA antibody. To be used as a standard, a soluble variant of uPAR, suPAR, has been constructed by recombinant technique and the protein content of a purified suPAR standard preparation was determined by amino acid composition analysis. The sensitivity of the assay (0.6 ng uPAR/ml) is strong enough to measure uPAR in extracts of cultured cells and cancer tissue. Recent studies have shown that a high uPA level in tumor extracts is in some cancers associated with poor prognosis. The present assay will now allow similar prognostic studies of uPAR levels.

Overview on fibrinolysis: plasminogen activation pathways on fibrin and cell surfaces

Plasminogen activation at the surface of fibrin or of cell membranes is a sophisticated specialized system for localized extracellular proteolysis implicated in a large variety of biological functions (fibrinolysis, cell migration and extracellular matrix degradation). Assembly of plasminogen and/or activators at specific binding sites induces conformational changes that make accessible the scissile peptide bond of plasminogen and exposes the active centre of the tissue-type plasminogen activator. The mechanism of activation by pro-urokinase, a second type of activator that binds to cell membrane but not to fibrin, is far from being understood. It may be able, however, in contrast to urokinase, to specifically activate plasminogen bound to partially degraded fibrin. An extremely low Km and high catalytic rate are characteristic of the process of activation at surfaces. In contrast, activation in liquid phase by tissue-type plasminogen activator proceeds at an extremely low catalytic rate. The initiation and amplification of plasminogen activation depend on specific interactions between the modular constitutive units of these proteins and binding sites present on cell or fibrin surfaces. Thus, the most important mechanism for the acceleration of fibrinolysis and pericellular proteolysis is the unveiling of carboxy-terminal lysine residues on these surfaces, to which plasminogen may bind. Since plasminogen bound to carboxy-terminal lysines of progressively degraded fibrin or membranes is readily transformed into plasmin by fibrin-bound t-PA, this mechanism represents the most important pathway for the acceleration and amplification of fibrinolysis. Alpha-2-antiplasmin, by inhibiting plasmin release from surfaces, regulates the extent and rate of this process but has no effect on fibrin-bound or membrane-bound plasmin. Lipoprotein(a), a particle possessing a plasminogen-like apolipoprotein, apo(a), may interfere with this mechanism by inhibiting the specific binding of plasminogen to lysine residues in membrane or fibrin surfaces.

Expression and localization of elements of the plasminogen activation system in benign breast disease and breast cancers

The malignant potential of solid tumors is related to the ability to invade adjacent tissue and to metastasize. These properties of cancer cells depend on the synthesis of proteolytic enzymes which are able to digest adjacent connective tissue and basement membranes. We hypothesized that all elements of the plasminogen activation system might be overexpressed in malignant human breast tumors, functioning as an essential element in tumor invasion and metastasis. As determined by histopathological methods, the malignant tumors showed statistically significantly higher expression of urokinase plasminogen activator (uPA), type-1 plasminogen activator inhibitor (PAI-1), and especially urokinase plasminogen activator receptor (uPAR) than benign tissues. All those elements were present in higher amounts in the cancer cells than in the cells of benign or normal breast tissues. High exhibition of tissue plasminogen activator (tPA) found in cancer seems to be random and not related to the malignant or benign state, since benign and malignant tumors show overexpression of tissue plasminogen activator with similar frequency. When the tumors express high amounts of uPA, they express a high amount of uPAR in 50% of cases and PAI-1 in 57.3% of cases. When urokinase is expressed in low amount, the receptor is low in 28.6% and inhibitor in 21.4% of malignant breast tumors. This statistically significant consensus, 78.6% in the case of urokinase and its receptor and 78.6% in case of urokinase and its inhibitor, suggests that these activities may be the result of a unique mechanism of control, activated in the last steps of malignant transformation.

Urokinase (uPA) and its inhibitor PAI-1 are strong and independent prognostic factors in node-negative breast cancer

Evidence has accumulated that invasion and metastasis in solid tumors require the action of tumor-associated proteases, which promote the dissolution of the surrounding tumor matrix and the basement membranes. The serine protease urokinase-type plasminogen activator (uPA), which is elevated in solid tumors, appears to play a key role in these processes. We used enzyme-linked immunoassays (ELISA) to test for uPA antigen and its inhibitor PAI-1 in tumor tissue extracts of 247 breast cancer patients who were enrolled in a prospective study. The relation of these data to known prognostic factors and to other variables such as DNA analysis and cathepsin D was studied. Disease-free and overall survival were analyzed according to Cox's proportional hazard model. The major new finding is that breast cancer patients with either high uPA (> 2.97 ng/mg protein) or high content of the uPA inhibitor PAI-1 (> 2.18 ng/mg protein) in their primary tumors have an increased risk of relapse and death. Multivariate analyses revealed uPA to be an independent and strong prognostic factor. The impact of uPA is as high as that of the lymph node status. In node-negative patients the impact of uPA is closely followed by that of PAI-1. Since uPA and PAI-1 are independent prognostic factors, the node-negative patients could be subdivided further by combining these two variables. In this refined analysis, patients whose primary tumors have lower levels of both antigens evidently have a very low risk of relapse (93% disease-free survival at three years) in contrast to patients with high uPA and high PAI-1 (55% disease-free survival at three years). The combination of uPA and PAI-1 in our group of patients with axillary node-negative breast cancer allows us to identify the 45 percent of patients having an increased risk of relapse. Consequently, more than half of the patients had less than a 10% probability of relapse and thus would possibly be candidates for being spared the necessity of adjuvant therapy.

Tumoral invasion in the central nervous system

During growth, migration and differentiation, cells closely interact with the extracellular matrix (ECM). The harmony between cells and their environment is a key factor that maintains the normal architecture of tissues. Loss of growth control is not the only characteristic of oncogenesis, loss of control by the ECM is an important event that allows malignant cells to further progress toward invasion and metastasis. Changes in cell adhesion, proteolytic degradation of the ECM and cell migration have all been described during invasion of most tissues by tumor cells. However little is known of these changes in tumors of the central nervous system (CNS). Although brain tumor cells may share some of the invasive characteristics of tumors that arise outside the CNS, the particular structure and composition of the brain ECM suggest the existence of unique invasive mechanisms in these tumors. Furthermore, the interaction between brain tumor cells and their ECM may explain the intriguing observation that despite their highly invasive behavior, these cells remain poorly metastatic. This review focuses on biochemical mechanisms essential for tumor invasion and how they relate to invasion of tumors that arise in the CNS.

Comparative study of fibrinolytic activity on 937 line after stimulation by interferon gamma, 1,25 dihydroxyvitamin D3 and their combination

Previous study showed that the secretion of urokinase (UK) by monoblastic cell line U 937 and the number of binding sites for urokinase and for plasminogen (Plg) on the cell surfaces were augmented by interferon gamma (INF tau). This induction led to an increase in fibrinolytic activity on cell surfaces. A similar increase was also observed when treating the U 937 cells with 1,25-dihydroxyvitamin D3 (1,25 (OH)2D3. Here we report that the combination of these two agents induced a 2.7 fold increase in the plasminogen activator activity on U 937 cell surfaces in comparison with 1 fold increase induced by INF tau and 1.3 fold increase by 1,25(OH)2D3. As evaluated by a flow cytometer, the increased fibrinolytic activity induced by the combination of INF tau and 1,25(OH)2D3 could be attributed to the increase of the number of binding sites both for UK (3.7 x 10(4) vs 1.2 x 10(4) per cell) and for Plg (16.2 x 10(4) vs 3.6 x 10(4) per cell), accompanied by an increased expression of CD 14, which is an antigen of differentiation on cell surfaces. These results suggest that the expression of urokinase receptors and plasminogen receptors may be coupled together by unknown intracellular mechanisms during cell differentiation, and support the idea that the concomitant regulation of these two receptors for UK and Plg is an important aspect in cell associated-fibrinolytic activity.

Regulation of the endothelial cell urokinase-type plasminogen activator receptor. Evidence for cyclic AMP-dependent and protein kinase C-dependent pathways

Binding of urokinase-type plasminogen activator (u-PA) to specific receptors (u-PAR) on the surface of endothelial cells contributes to the regulation of plasmin-dependent processes such as fibrinolysis and angiogenesis. We studied the effect of raising intracellular levels of cyclic AMP (cAMP) and/or activating protein kinase C on the expression of u-PAR in cultured human umbilical vein endothelial cells (HUVEC). Incubation of HUVEC with forskolin stimulated a time- and concentration-dependent increase in the expression of u-PAR, measured both by an increase in the specific binding of radiolabeled single-chain u-PA (scu-PA) and by increased binding of anti-u-PAR antibodies. Maximal increase in u-PAR expression (81 +/- 11% above control, n = 11) was not associated with a change in receptor affinity for scu-PA when HUVEC were incubated for 20 hours at 37 degrees C with 50 microM forskolin. Receptor induction by forskolin was inhibited when HUVEC were preincubated with deoxyadenosine monophosphate (DAM), an inhibitor of adenylyl cyclase. A similar increase in receptor expression (128 +/- 27% above control, n = 3) was induced by the cAMP analogue 8-bromoadenosine 3':5'-cyclic monophosphate (50 mM). Forskolin induced an approximately twofold increase in the expression of a single approximately 1.4-kb u-PAR messenger RNA (mRNA) transcript within 2 hours. Phorbol myristate acetate (PMA) also stimulated a time- and concentration-dependent increase in specific scu-PA binding. The maximal increase in u-PAR expression (254 +/- 27% above control, n = 11) was observed when HUVEC were preincubated with 10 nM PMA for 20 hours. Induction of u-PAR by PMA was inhibited when HUVEC were preincubated with either cycloheximide or H7 but was unaffected by DAM. u-PAR induced by PMA showed a reduced affinity for scu-PA (Kd, 14 +/- 2 nM versus 3.6 +/- 0.6 nM, p < 0.001; n = 8). PMA stimulation for 20 hours resulted in a sixfold increase in a single approximately 1.4-kb u-PAR mRNA transcript, with increased levels detectable within 30 minutes. Coincubation of HUVEC with optimal concentrations of forskolin and PMA for 20 hours produced a fully additive increase in u-PAR expression at both the mRNA and protein levels. These data suggest that both cAMP-dependent and protein kinase C-dependent protein kinase pathways may independently regulate u-PAR expression in human endothelial cells.

Urokinase and urokinase receptor: a paracrine/autocrine system regulating cell migration and invasiveness

Urokinase and its receptor are essential components of the cell migration machinery, providing an inducible, transient and localized cell surface proteolytic activity. This activity has been shown to be required in normal and pathological forms of cellular invasiveness (i.e. in several embryonic developmental processes, during inflammatory responses and cancer metastasis and spreading). It represents one of the best known of the proteolytic systems which are currently under investigation in this field. The urokinase receptor allows a continuous regulation of the proteolytic activity at cell contacts, utilizing the different localization of urokinase and its inhibitors. The receptor, in fact, in addition to focusing the enzymatic activity at focal and cell-cell contacts, also regulates it by internalizing and degrading only the inhibited form of urokinase. Internalized receptor releases the ligands to the lysosomes and recycles back to surface. In this way, the proteolytically active areas of the cell surface can be continuously monitored for their activity and their location modified. The cell can thus coordinate its migration efforts with a step-wise modification of the proteolytic activity-map of the cell surface. The urokinase cycle can be supported by one individual cell (autocrine) or by two or more cells. In the latter case, complementation and synergism of urokinase and its receptor are found.

Persistence of plasmin-mediated pro-urokinase activation on the surface of human monocytoid leukemia cells in vitro

Human leukemia cell lines, unlike those from adherent tumors, have been shown to continuously activate the pro-urokinase (pro-u-PA) they produce. In the present study we found that, in normal cell-culture conditions in 10% FCS the plasminogen activation cascade works continuously on monocytoid leukemia cells, which expressed plasmin activity and active u-PA on their cell surface. This plasmin catalyzed the conversion of the produced pro-u-PA to active 2-chain urokinase (tcu-PA), and was derived from bovine serum plasminogen by the activity of cell-bound tcu-PA. Plasmin generation was abolished and pro-u-PA accumulated in cell cultures that were grown for several days, either in the presence of serum thoroughly depleted of plasminogen, or in the presence of 1 mM tranexamic acid. Plasmin generated on the cell surface was found to be present in 2 enzymatically active fragments, of M(r) 85,000 and M(r) 50,000, which were slowly released into the growth medium. These fragments could activate pro-u-PA in serum-free growth medium. Most of the bound plasmin could be washed off cells with 10 mM tranexamic acid, but complete removal of plasmin from the cell surface required washing of the cells with acid-glycine pH 3.0.

Plasminogen activators in normal tissue and carcinomas of the human oesophagus and stomach

Carcinogenesis in the human colon is associated with a marked increase of urokinase type plasminogen activator and a decrease of tissue type plasminogen activator. This study was performed to determine the concentrations of urokinase type plasminogen activator and tissue type plasminogen activator in normal tissue and carcinomas along the upper part of the gastrointestinal tract. Activity and antigen levels of both activators were determined in homogenates of endoscopically obtained biopsies from normal and carcinomatous tissues. Although the concentrations of tissue type plasminogen activator and urokinase type plasminogen activator in normal squamous epithelium of the oesophagus were low compared with those in columnar epithelium from the stomach, the urokinase type plasminogen activator/tissue type plasminogen activator antigen ratio of the different locations showed hardly any difference. Significant but heterogeneous increases were found in urokinase type plasminogen activator concentrations of biopsy specimens originating from carcinomas of both epithelial cell types. A decrease in tissue type plasminogen activator concentrations, as found in human colon carcinomas, could only be shown in carcinomas of columnar epithelium origin but not in squamous cell carcinomas of the oesophagus. The increase of urokinase type plasminogen activator and urokinase type plasminogen activator/tissue type plasminogen activator antigen ratio and the decrease of tissue type plasminogen activator in the carcinomas did not show a significant correlation with known prognostic determinants as differentiation grade, TNM classification, intestinal metaplasia, inflammation, and ulceration. The heterogeneous increase of urokinase type plasminogen activator in oesophageal and stomach carcinomas, together with the recently described association of urokinase type plasminogen activator in tissue extracts of breast carcinomas with aggressiveness and prognosis, may be relevance to prognostic studies, may be of relevance to prognostic studies in oesophageal and gastric cancer.

The plasminogen-plasmin system in malignancy

The study of the plasminogen-plasmin system has, in the past, contributed much to the understanding of fibrinolysis and thrombolysis. Attention is now focused on the role of the components of this system in many biologic functions. Findings of uPA, its receptor and its inhibitor in many tumor tissues and tumor cell lines, strongly implicate their involvement in tumor invasion, tumor cell proliferation and metastasis. The characteristics of the plasminogen activators, the uPA receptor and the plasminogen activator inhibitors as well as their expression and regulation in tumors and tumor cell lines are reviewed.

The plasminogen activator urokinase and its inhibitor PAI-2 in endometrial cancer

Invasion and metastasis of malignant cells require the disruption of the extracellular matrix, degradation of basement membranes, and intrusion into connective tissue and vascular and lymphatic spaces. Several studies have indicated a role for urokinase (u-PA) in proteolysis of the extracellular matrix and hence in stromal invasion and metastasis. Many malignant cells are known to secrete u-PA. Plasminogen activator inhibitor-type 2 (PAI-2) is an inhibitor of u-PA and is present in several neoplastic cell lines and malignant ascites. We measured u-PA and PAI-2 antigen in tissue homogenates of normal and malignant endometrium from 21 postmenopausal patients. Enzyme-linked immunoassays which measure the bound and unbound, single-and two-chain form of the activator and bound and unbound form of the inhibitor were used. Urokinase was present in four of seven normal (range, 0.15-0.5; median, 0.15 ng/mg protein) and in significantly higher concentrations in all malignant endometrial homogenates (range, 0.41-9.2; median, 3.4 ng/mg protein), P < 0.001. PAI-2 was detectable in four of seven normal endometrial homogenates at low concentrations (range, 1.1-3.1; median, 1.1 ng/mg protein) and in all malignant tissue homogenates at significantly higher levels (range, 1.6-27.3; median, 4.9 ng/mg protein), P < 0.01. Levels of endometrial PAI-2 were higher in stages IC or greater compared to those in stages IA and 1B cancers (P < 0.05). PAI-2 may be useful as a prognostic marker in endometrial cancer.

A soluble form of the glycolipid-anchored receptor for urokinase-type plasminogen activator is secreted from peripheral blood leukocytes from patients with paroxysmal nocturnal hemoglobinuria

The cellular urokinase-type plasminogen-activator (uPA) receptor (uPAR) is a glycolipid-anchored membrane protein thought to be involved in pericellular proteolysis during cell migration and tumor invasion. In the present study, we have identified and characterized two soluble forms of uPAR which have retained their ligand-binding capability. One variant was generated in vitro by treatment of intact normal cells with either a phosphatidylinositol-specific phospholipase C (PLC) or endoproteinase Asp-N. The other soluble uPAR variant was secreted in vivo from peripheral blood leukocytes affected by the stem-cell disorder paroxysmal nocturnal hemoglobinuria (PNH), and was found in the plasma from these PNH patients as well as in the conditioned medium from cultured PNH leukocytes. Under normal conditions, we find no evidence for any shedding or secretion of a soluble uPA-binding counterpart to human uPAR in plasma. Unlike normal leukocytes, the PNH-affected cells do not express uPAR on the cell surface, although they do contain apparently normal levels of uPAR-specific mRNA. The secreted uPAR derived from PNH cells has a mobility in SDS/PAGE that is slightly higher than that of uPAR solubilized by PtdIns-specific PLC or detergent, but resembles that of a truncated, recombinant uPAR variant, which has its C-terminus close to the proposed glycolipid-attachment site, suggesting that the secreted protein has been proteolytically processed for glycolipid attachment. The presence in plasma from PNH patients of such a secreted, hydrophilic form of uPAR lends support to the hypothesis that the lesion underlying the PNH disorder resides either in glycolipid biosynthesis or in the function of an as-yet-unidentified transamidating enzyme assumed to cleave and assemble the truncated uPAR with the preformed glycolipid moiety.

Urokinase binding to laminin-nidogen. Structural requirements and interactions with heparin

Recently we have shown that heparin and related sulfated polyanions are low-affinity ligands of the kringle domain in the amino-terminal region (ATF) of human urokinase (u-PA), and proposed that this may facilitate loading of u-PA onto its receptor at the focal contacts between adherent cells and their matrix. We have now tested other components of the cell matrix (fibronectin, vitronectin, thrombospondin and laminin-nidogen) for u-PA binding, and found that laminin-nidogen is also a ligand of the u-PA ATF. Direct binding assays and competition binding assays with defined fragments of laminin-nidogen showed that there are u-PA binding sites in fragment E4 of laminin as well as in nidogen. The long-arm terminal domain of laminin (fragment E3), which contains a heparin-binding site, competed for binding of u-PA to immobilised heparin. However nidogen, which does not bind to heparin, also inhibited binding of u-PA to heparin, and this effect was also observed with recombinant nidogen and with a fragment of nidogen lacking the carboxy-terminal domain. Direct binding assays confirmed that u-PA binds to nidogen through a site in the u-PA ATF. We conclude that u-PA binds to laminin-nidogen by interactions involving the ATF region of u-PA, the E4 domain of laminin and the rod or amino-terminal regions of nidogen. Since nidogen is suggested to be an important bridging molecule in the maintenance of the supramolecular organization in basement membranes, the presence of a binding site for u-PA in nidogen indicates a role for plasminogen activation in basement membrane remodelling.

Tumor necrosis factor regulation of endothelial cell extracellular proteolysis: the role of urokinase plasminogen activator

Morphological and functional changes in the endothelial cell phenotype which may be central to proinflammatory processes can be elicited by tumor necrosis factor alpha (TNF). Recent observations have indicated that TNF can promote the expression, synthesis and secretion of urokinase plasminogen activator (uPA) in low passage human umbilical vein endothelial cells which normally synthesize little uPA. To further address this issue, we evaluated the ability of TNF to regulate: 1) PA and plasminogen activator inhibitor (PAI-1) mRNA expression and 2) endothelial cell surface associated PA and PAI-1. TNF (100 U/ml) treatment of endothelial cultures induced steady state levels of uPA and PAI-1 mRNA following a 18 hr treatment both 6-fold and 2-fold, respectively utilizing northern analysis. In accord with Northern analyses, TNF stimulated a time and dose dependent increase in cell surface associated uPA antigen as determined by a cell based ELISA assay and immunofluorescence in conjunction with flow cytometry. Treatment of endothelial cell cultures with 100 U/ml of TNF resulted in a 3-fold increase in cell surface uPA antigen levels which peaked at 8 hr. In contrast, no changes in tissue-PA (tPA) and PAI-1 cell surface antigen expression were evident under analogous conditions over a 24 hr period. The TNF mediated increase in both uPA mRNA and cell surface uPA expression correlated with the increased ability of endothelial cells to invade matrix and organize into tube-like structures when cultured on Matrigel.(ABSTRACT TRUNCATED AT 250 WORDS)

Tumor-associated urokinase-type plasminogen activator: biological and clinical significance

Evidence has accumulated that invasion and metastasis in solid tumors require the action of tumor-associated proteases, which promote the dissolution of the surrounding tumor matrix and the basement membranes. Receptor-bound urokinase-type plasminogen activator (uPA) appears to play a key role in these events. uPA converts plasminogen into plasmin and thus mediates pericellular proteolysis during cell migration and tissue remodeling under physiological and pathophysiological conditions. uPA is secreted as an enzymatically inactive proenzyme (pro-uPA) by tumor cells and stroma cells. uPA exerts its proteolytic function on normal cells and tumor cells as an ectoenzyme after having bound to a high-affinity cell surface receptor. After binding, pro-uPA is activated by serine proteases (e.g. plasmin, trypsin or plasma kallikrein) and by the cysteine proteases cathepsin B or L, resp. Receptor-bound enzymatically active uPA converts plasminogen to plasmin which is bound to a different low-affinity receptor on tumor cells. Plasmin then degrades components of the tumor stroma (e.g. fibrin, fibronectin, proteoglycans, laminin) and may activate procollagenase type IV which degrades collagen type IV, a major part of the basement membrane. Hence receptor-bound uPA will promote plasminogen activation and thus the dissolution of the tumor matrix and the basement membrane which is a prerequisite for invasion and metastasis. Tissues of primary cancer and/or metastases of the breast, ovary, prostate, cervix uteri, bladder, lung and of the gastrointestinal tract contain elevated levels of uPA compared to benign tissues. In breast cancer uPA and PAI-1 antigen in tumor tissue extracts are independent prognostic factors for relapse-free and overall survival.

Assembly of plasmin-generating proteins on the surface of human endothelial cells

Traditionally, plasmin generation has been conceptualized as a process oriented on the surface of a fibrin-containing thrombus. Recent work, however, indicated that plasminogen and its activators, tissue plasminogen activator (t-PA) and urokinase, can assemble on the surface of cultured human umbilical vein endothelial cells (HUVECs). On binding to HUVECs, plasminogen is activated by t-PA approximately 12-fold more efficiently than fluid-phase plasminogen, and is converted to a plasmin-modified form, possibly unique to cell surfaces. In addition, t-PA interacts with HUVECs at two sites. The major binding site preserves its activity and represents a true (relative molecular weight 40,000) membrane-associated exoreceptor. The low-density lipoprotein (LDL)-like lipoprotein, lipoprotein(a), is highly associated with atherosclerosis, bears striking sequence homology to plasminogen, and competes with plasminogen for cell surface binding. In summary, functional assembly of plasminogen and t-PA may represent an important thromboregulatory system.

A hybrid protein of urokinase growth-factor domain and plasminogen-activator inhibitor type 2 inhibits urokinase activity and binds to the urokinase receptor

The binding of urokinase-type plasminogen activator (uPA) to its specific cell-surface receptor (uPAR) localises the proteolytic cascade initiated by uPA to the pericellular environment. Inhibition of uPA activity or prevention of uPA binding to uPAR might have a beneficial effect on disease states wherein this activity is deregulated, e.g. cancer and some inflammatory diseases. To this end, a bifunctional hybrid molecule consisting of the uPAR-binding growth-factor domain of uPA (amino acids 1-47; GFuPA) at the N-terminus of plasminogen-activator inhibitor type 2 (PAI-2) was produced in Saccharomyces cerevisiae. The purified protein inhibited uPA with kinetics similar to placental or recombinant PAI-2 and was also found to bind to U937 cells and to FL amnion cells. GFuPA-PAI-2 competed with uPA, the N-terminal fragment of uPA and a proteolytic fragment of uPA (amino acids 4-43) in cell binding experiments, indicating that the molecule bound to the cells via uPAR. Hence, both the uPA-inhibitory and uPAR-binding domains of the hybrid molecule were functional, demonstrating the feasibility of the novel concept of introducing an unrelated, functional domain onto a member of the serine-protease-inhibitor superfamily.

Tissue-type plasminogen activator is involved in skeletal metastasis from human breast cancer

This study was undertaken to determine if primary breast tumor plasminogen activator expression correlates with skeletal metastasis in breast cancer. Total plasminogen activator activity was significantly lower in tumors of patients with recurrence than in recurrence-free patients. Similarly, the primary tumors of patients with skeletal metastasis contained considerably less enzyme activity compared with those of patients surviving without skeletal metastasis. When patients with skeletal metastasis were categorized in terms of their recurrence pattern, those who had skeletal metastasis without other organ metastasis had significantly less tissue-type plasminogen activator antigen in their primary breast tumors than did those who had metastasis to other organs. Furthermore, a significantly lower level of tissue-type plasminogen activator antigen was found in primary tumors associated with axial bone metastasis than in those associated with appendicular bone metastasis. These results suggest that tissue-type plasminogen activator is involved in skeletal metastasis formation by its effects through the vertebral venous plexus.

D-dimer and CA 125 levels in patients with ovarian cancer during antineoplastic therapy. Prognostic significance for the success of anti-cancer treatment

In patients with ovarian cancer before they receive chemotherapy, the level of fibrin degradation products (D-dimer), is correlated with the tumor load. In this study, the evolution of D-dimer was compared in patients receiving antineoplastic therapy with the evolution of the disease. The patients could be classified into three groups. In Group 1 (nine patients), both plasma CA 125 (a tumor-associated antigen) and D-dimer remained elevated; the prognosis was always poor. In Group 2 (eight patients), CA 125 and D-dimer decreased simultaneously, complete remission was observed in two patients, and significant residual tumor was observed in the others. In Group 3 (nine patients), despite an important decrease in CA 125, D-dimer remained elevated during therapy. In this group, complete remission was observed in six patients, and three others showed a large decrease in their tumor load. The combination of a decrease in CA 125 levels with a continuous enhanced level of D-dimer during chemotherapy identified a subgroup of patients with a favorable prognosis.

Modulation of activities and RNA level of the components of the plasminogen activation system during fusion of human myogenic satellite cells in vitro

Primary cultures of human myogenic stem cells (satellite cells) mimic myogenic differentiation. During this process, the expression of the components of the plasminogen activation system underwent modulation. Activities and mRNA levels of tissue-type and urokinase-type plasminogen activator were increased in a reproducible pattern during differentiation. A modulation of the mRNA level of PAI-2 was also observed. Human satellite cells expressed a urokinase receptor and also the mRNA level of this component underwent modulation. With the exception of PAI-1 mRNA, the level of all mRNAs increased from Day 4 to Day 8, i.e., just before myoblasts fusion, and then remained high at later stages. The modulation of the plasminogen activating activity indicates that this system is directly involved in the fusion process of myogenic differentiation.

The effect of tissue type plasminogen activator (tPA) on osteoclastic resorption in embryonic mouse long bone explants: a possible role for the growth factor domain of tPA

Osteoblasts produce proteolytic enzymes and their production is regulated by osteotropic agents. It has been suggested that these proteases play a role in bone resorption by removing the superficial collagenous layer from the bone matrix and indirectly inducing migration of osteoclast precursors towards the bone matrix. We examined the effect of the plasminogen activator tPA on osteoclastic resorption using 17-day-old mouse embryonic long bone explants representing different stages of osteoclast development, that is, radii containing already mature osteoclasts and metacarpals containing no mature osteoclasts but only osteoclast precursors/progenitors which are still confined to the periosteum. Tissue type PA stimulated osteoclastic resorption (measured as 45Ca-release) in 17-day-old fetal metacarpals but not in radii of the same animal. Blocking the enzymatic activity of tPA did not inhibit its effect on osteoclastic resorption. Plasmin, the direct product of PA enzymatic activity, did not induce osteoclastic resorption. However, a tPA-mutant missing the growth-factor-like domain of the molecule, failed to stimulate 45Ca-release from the metacarpals. In addition, in both systems tPA and transforming growth factor alpha had similar effects on osteoclastic resorption. The finding that tPA stimulated 45Ca-release only in the metacarpals suggests that tPA has an effect on osteoclast formation rather than on the activity of already mature osteoclasts. Under the experimental conditions used this effect seems to be mediated by the growth factor domain of tPA rather than by the enzymatic activity of the molecule.

Demonstration of a possible link between high grade malignancy in dimethylbenz[a]anthracene-induced rat mammary carcinoma and increased urokinase plasminogen activator content

Recent reports have suggested that tissue-type plasminogen activator activity is regulated by estrogen in 7,12-dimethylbenz[a]anthracene-induced rat mammary carcinoma type I cells but is not necessarily regulated by estrogen in type II mammary carcinoma cells. We have compared the biological features of these two types of mammary carcinoma cells and have found that, although there is no difference in estrogen receptor content between these two cell types, the plasminogen activator activity markedly differs. Tissue-type plasminogen activator activity is significantly higher in type I carcinoma than in type II carcinoma, urokinase-type activity is significantly higher in type II carcinoma than in type I carcinoma. When these two types were compared in terms of rate of tumor growth, type II carcinomas clearly showed more rapid growth than type I carcinomas. Survival studies showed significantly shorter survival of type II tumor-bearing rats compared with type I tumor-bearing rats. Furthermore, type II carcinomas contained a greater proportion of aneuploid cells than type I carcinomas. These results suggest that type II carcinoma cells, in which estrogen is unable to regulate tissue-type plasminogen activator activity, are considered to be of a higher grade of malignancy than type I carcinoma cells.

A chromogenic enzymatic assay capable of detecting prourokinase-like material in plasma

We report a functional assay capable of quantifying prourokinase (ProUK)- like material in plasma where urokinase (UK) is also present. The assay involves inactivation of urokinase with a specific, active site directed irreversible inhibitor, dansyl-glutamyl glycyl arginine chloromethylketone (dansyl- GGACK). Excess inhibitor is subsequently quenched with dithiothreitol (DTT). The ProUK-like material in plasma is then converted to active urokinase with thermolysin, a proteolytic enzyme of bacterial origin. Alpha 2-macroglobulin in plasma inhibits thermolysin; however alpha 2-macroglobulin is inactivated with methylamine. The assay can detect as little as 20 ng of ProUK and is linear from 20 to 120 ng. The assay was applied to quantify the amount of ProUK-like material in plasma obtained from dog at various times after i.v. administration of 100,000 or 75,000 U/kg, of pro-urokinase.

Changes in the coagulation-fibrinolysis balance of endothelial cells and mononuclear phagocytes: role in disseminated intravascular coagulation associated with infectious diseases

Over the last few years, evidence has accumulated that the pathogenetic mechanism of disseminated intravascular coagulation encountered in patients with infectious diseases is extraordinarily complex and involves multiple interactions between the microorganism itself and/or a number of mediators, both microorganism derived and host manufactured, and multifunctional cellular systems, namely endothelial cells and mononuclear phagocytes. In particular, infectious agents and mediators shift the coagulation-fibrinolysis equilibrium of these cells towards fibrin formation and accumulation, via enhancement of procoagulant properties and reduction of both anticoagulant and fibrinolytic capacities. New insights into the pathogenetic mechanism may have important implications for the management of infected patients with disseminated intravascular coagulation.

Extracellular and cell-associated localizations of plasminogen activators and plasminogen activator inhibitor-1 in cultured endothelium

The extracellular localizations of urokinase-type plasminogen activator (uPA), tissue-type plasminogen activator (tPA), and plasminogen activator inhibitor-1 (PAI-1) were examined in cultured bovine capillary endothelial cells (BCEs) by an immunofluorescence method using BCEs treated with or without saponin and focal contact preparations. The specific immunofluorescence of cell surface uPA showed a patchy or strand-like distribution and was colocalized with vinculin strands indicating that uPA secreted from BCEs was mainly deposited at the cell surface of focal contacts. BCEs at a subconfluent density showed a higher intensity of specific immunofluorescence for uPA than when they were at a confluent density. tPA was observed over the dorsal surface of cultured BCEs and accentuated at their margins, suggesting that tPA was diffusely distributed on the luminal surface of BCEs in vivo. PAI-1 was distributed in the extracellular matrix under cultured BCEs. These findings suggest that uPA and PAI-1 are located under BCEs participating in the regulation of proteolytic activities provoked by plasminogen-PAs-plasmin system in vivo. The localization of tPA appears to be consistent with its function, which is to maintain the fluidity of the blood and to initiate thrombolysis in vivo.

Factor XIII of blood coagulation inhibits the oxidative phagocyte metabolism and suppresses the immune response in vivo

Factor XIII of blood coagulation (F XIII) belongs to the family of transglutaminases and is a major cell product of certain subsets of macrophages. The gene for F XIIIA is coupled to the immune response genes of the HLA-region on chromosome 6. F XIII dose- dependently inhibits the in vitro chemiluminescence response of human phagocytes. About 0.1 units of F XIII/ml (final) decreased the chemiluminescence response to about 50%. In addition, about 0.6 units of F XIII/ml inhibits 50% of the release of the lysosomal hydrolase N-acetyl-beta glucosaminidase in both immune complex stimulated and unstimulated monocytes. Intraperitoneal application of F XIII reduced the activity of phagocytes in a F XIII dose dependent manner. 0.25 units of F XIII reduced the chemiluminescence reaction of murine peritoneal M phi to about 50% of the activity of PBS treated animals after 2 or 24 hours of in vivo incubation. In the Fisher/Lewis rats skin transplantation model, injections of 5 units of F XIII/animal on days 1-7 or on days 10-17 increased the survival times of the transplants from the control value of 17.0 +/- 1.4 to 26.0 +/- 2.0 and 23.0 +/- 2.4 days, respectively. F XIII may represent a novel and physiological immune suppressive agent for a broad range of human diseases of autoimmune character.