Directed plasminogen activation at the surface of normal and malignant cells

Plasminogen activator inhibitor type 1 in cancer: therapeutic and prognostic implications

Degradation of the extracellular matrix plays a crucial role in cancer invasion. This degradation is accomplished by the concerted action of several enzyme systems, including generation of the serine protease plasmin by the urokinase pathway of plasminogen activation, different types of collagenases and other metalloproteinases, and other extracellular enzymes. The degradative enzymes are involved also in tissue remodelling under non-malignant conditions, and the main difference appears to be that mechanisms which regulates these processes under normal conditions are defective in cancer. Specific inhibitors have been identified for most of the proteolytic enzymes, e.g. plasminogen activator inhibitors (PAI's) and tissue inhibitors of metalloproteinases (TIMP's). It has been contemplated that these inhibitors counteracted the proteolytic activity of the enzymes, thereby inhibiting extracellular tissue degradation which in turn should prevent tumor cell invasion. This review focuses on plasminogen inhibitor type 1 (PAI-1). It is described that PAI-1 is not produced by the epithelial cancer cell but by the stromal cells in the tumors, suggesting a concerted action between stroma and tumor cells in the processes controlling proteolysis in cancer. The specific localization of PAI-1 to the tumor stroma and in many cases to areas surrounding the tumor vessels has lead us to suggest that PAI-1 serves to protect the tumor stroma from the ongoing uPA-mediated proteolysis. This hypothesis is supported by recent clinical data showing increased levels of PAI-1 in metastases as compared to the primary tumor as well as data demonstrating that high levels of PAI-1 in tumor extracts from breast, lung, gastric and ovarian cancer is associated with a shorter overall survival.(ABSTRACT TRUNCATED AT 250 WORDS)

Urokinase receptor mediates mechanical force transfer across the cell surface

The tripartite complex formed by the urokinase receptor, urokinase, and its inhibitor is an enzymatic system that controls plasmin formation involved in degradation of extracellular matrix proteins. With the use of magnetic twisting cytometry with urokinase-coated ferromagnetic beads, we applied mechanical stress directly to the urokinase receptor on the surface of human myogenic cells in culture. The stiffness and the stiffening response measured through the urokinase receptor resembled those of integrins, which are linked mechanically to the cytoskeleton. Furthermore, stiffness decreased with disruption of actin microfilaments. These results demonstrate that the urokinase receptor is coupled mechanically to the cytoskeleton. Inhibition of the tripartite complex formation with antibodies led to a twofold increase in cytoskeletal stiffness. A stiffened cytoskeleton might impede cytoskeletal remodeling and reorganization and thus impede cell motility. Our results demonstrate that the urokinase receptor mediates mechanical force transfer across the cell surface. As such, it is a novel pathway to regulate cytoskeletal stiffness and, thereby, possibly to modulate motility of normal and abnormal adherent cells.

The plasminogen activation system and its role in lung cancer. A review

The urokinase pathway of the plasminogen activation is involved in proteolytic degradation of various tissues, including dissolution of the extracellular matrix and basement membranes during the process of cancer cell invasion. Recent studies have demonstrated that components of the plasminogen activation system have a prognostic impact in breast-, lung-, colorectal, bladder and gastric cancer. A number of studies, reviewed here, have focused on the role of the plasminogen activation system in different lung cancer types. There seems to be an obvious difference between the expression, localization and prognostic impact of the components of the plasminogen activation system in different lung cancer types. The differences seen could be helpful in understanding the biology of different lung cancer types, and components of the plasminogen activation system may have prognostic relevance and clinical implications in some lung cancer types, even though confirmatory studies are needed.

Analysis of the interaction of group A streptococci with fibrinogen, streptokinase and plasminogen

Group A streptococci demonstrate a number of distinct ways to interact with the human fibrinolytic system to acquire unregulatable cell-surface enzymatic activity. Interactions between bacteria, fibrinogen, streptokinase and plasminogen resulted in acquisition of cell-associated enzymatic activity that can lyse fibrin clots despite the presence of the major physiological plasmin inhibitor, alpha 2-antiplasmin. Western blot analysis of extracted streptococcal surface proteins suggested that binding of fibrinogen to M or M-related proteins mediated the capture of streptokinase-plasminogen complexes to the bacteria. The enzymatic complex formed by reaction of bacteria with fibrinogen, streptokinase and plasminogen was found to be more stable in human plasma than pre-formed plasmin bound directly to the same bacteria strain.

Characterization of plasminogen system on rat yolk sac carcinoma (L2) cells

The plasminogen (Plg) system on rat yolk sac carcinoma (L2) cells was characterized by zymography, Western and immunoprecipitation analysis, reverse-transcriptase polymerase chain reaction, binding, and activity assays. The L2 cells produced tissue Plg activator but not urokinase Plg activator and contained RNA for Plg activator inhibitor 1, but Plg activator inhibitor 1 was not detectable by zymography or Western analysis and contained the receptor for urokinase Plg activator. Plg bound to the cells in a saturable manner when plasmin inhibitors were present with a dissociation constant of 1.34 +/- 0.18 x 10(-6) M and 1.54 +/- 0.25 x 10(7) sites/cell. Immunoprecipitation analysis showed that Plg was binding to gp330, a known Plg receptor. Once bound to the L2 cells, Plg was activated by tissue Plg activator to plasmin in a time- and concentration-dependent manner. Under saturating Plg conditions, most of the plasmin produced was released into the medium. Inhibition of plasmin activation occurred when Plg activator inhibitor 1, anticatalytic tissue Plg activator antibody, or Heymann nephritis autoantibody was present.

Components of the plasminogen activation system in uveal melanoma--a clinico-pathological study

In tumour development, proteases such as plasminogen activators (PAs) play a role in degradation of the extracellular matrix and other tissue barriers. Recently, we demonstrated that plasminogen activators, their inhibitors, and urokinase receptor emerge in late stages of cutaneous melanocytic tumour progression. In this study we investigated the expression and distribution of the various components of the PA system and the presence of PA enzyme activity in 45 freshly frozen primary uveal melanoma with known follow-up (14 spindle and 31 non-spindle type) and in metastases (n = 5). Tissue-type PA (t-PA) was found in endothelium of blood vessels and in tumour cells in almost all lesions, and was markedly present at the invasive front (towards the sclera and Bruch's membrane), but no correlation with tumour-related death could be established. Urokinase PA (u-PA) was expressed focally, by only five non-spindle cell melanomas but in all metastases. u-PA expression correlated with occurrence of metastasis. u-PA receptor (u-PAR) was present in one-third of all the tumours examined. Plasminogen activator inhibitors (PAI-1 and PAI-2) were found only focally in approximately 10 per cent of the lesions. Staining of t-PA, u-PA, and PAI was observed in all the metastases. We conclude that in uveal melanoma, u-PA expression may be associated with metastatic disease and accordingly with a poor prognosis. Further research on a larger group of tumours with known follow-up is needed to establish whether u-PA positivity is of additional prognostic value in uveal melanoma.

Properties of metastasizing and nonmetastasizing human melanoma cells

Dissemination of tumor cells includes several steps, such as: (a) detachment of tumor cells from the primary tumor, (b) traversement of the basement membrane, and (c) migration into the extracellular matrix. In these processes, at least two important categories of proteins are involved: proteases and adhesion molecules. In this contribution we describe the expression and function of components of the plasminogen activator (PA) system (proteases) and of integrins (cell-matrix adhesion molecules) in a panel of four human melanoma cell lines with different invasive and metastatic capacity. Regarding the components of the PA system, we found differences in expression of urokinase-type PA (uPA) and type 1 and 2 PA inhibitors (PAI-1 and -2) between metastasizing and nonmetastasizing cell lines. Both components were exclusively expressed in the highly invasive and metastatic cell lines. Interestingly, studies on the expression of PA components in fresh human melanocytic lesions, showed expression of these components exclusively in advanced primary melanomas and melanoma metastases. Regarding integrin expression we found elevated levels of VLA-2 and VLA-6 in the highly invasive and metastatic cell lines compared with normal cultured melanocytes and nonmetastatic melanoma cell lines. In addition, increased adhesion of the highly metastatic cell lines to laminin (LM) and collagen (COLL) was observed. Furthermore, reduced adhesion of normal melanocytes and nonmetastatic melanoma cells to LM and CO was mainly due to the fact that the integrins involved in adhesion to these matrix components were present in an inactive state. Finally, differences were observed in expression of integrins involved in adhesion to fibronectin.

RNA synthesis inhibition stabilises urokinase mRNA in macrophages

Urokinase-type plasminogen activator (uPA) mRNA is induced in macrophages by the lineage specific growth factor CSF-1. Upon removal of CSF-1 from bone marrow-derived macrophages (BMM), uPA mRNA decayed with a half-life of 2 h. If RNA synthesis inhibitors actinomycin D, 5,6-dichloro-1-beta-ribofuranosyl benzimidazole (DRB) or alpha-amanitin were added at the time as CSF-1 removal, the uPA message was stabilised. This was not a general effect on CSF-1 responsive mRNAs, as c-myc mRNA decayed with normal kinetics in the presence of inhibitors. The requirement for ongoing RNA synthesis for the degradation of uPA mRNA in BMM suggests that a component of the degradative pathway may be induced following removal of CSF-1.

Impact of age and sex on survival after curative resection for carcinoma of the esophagus

BACKGROUND

The impact of age and sex-related changes in the endogenous hormonal milieu on survival after curative resection for esophageal epithelial cancer is explored. Adami et al. have suggested that the event of puberty has a favorable impact on survival after treatment of epithelial cancers.

METHODS

The database consisted of 469 patients with esophageal cancer treated surgically with an intent to cure (without any gross residual disease at the end of the primary treatment) at Tata Memorial Hospital between 1980 and 1989.

RESULTS

Life-stable analysis revealed a significantly better 5-year survival for women younger than 49 years (35%, CI 24-48) compared with men of the same age (16%, CI 8-27) (P < 0.008). There was no difference in survival between men (17%, CI 12-23) and women (26%, CI 16-37) older than 49 years (P = 0.08). A Cox proportional hazard model showed sex to be the second most significant determinant of survival (P = 0.002) after lymph node metastasis (P < 0.0001).

CONCLUSION

The finding that the survival benefit is confined to women younger than 49 years is consistent with the hypothesis that the endocrine milieu in premenopausal women may prevent the establishment of micrometastases and thus improve the prognosis for esophageal epithelial cancer.

Human Co115 colon carcinoma cells potentiate the degradation of laminin mediated by tissue-type plasminogen activator

The plasminogen activation (PA) system of human Co115 colon carcinoma cells was investigated. Analysis at the levels of protein and mRNA of cultured cells and of histozymography of tumor xenografts in nude mice showed that Co115 cells produce only tissue type PA (t-PA) and no urokinase (u-PA). Also, mRNA for the u-PA receptor and for PA inhibitor type 2 (PAI-2), but not for PAI-1, were detected. We developed a quantitative degradation assay using glutaraldehyde-immobilized 125I-laminin to investigate the capacity of Co115 cells to degrade laminin. Laminin degradation by Co115 cells was completely inhibited by 100 micrograms/ml of polyclonal anti-t-PA IgG, by the plasmin inhibitors aprotinin (100 micrograms/ml) or epsilon-aminocaproic acid (EACA; at 0.3 M), but not by antibodies against u-PA or u-PAR nor by nonimmune IgG. Cycloheximide-treated Co115 cells were unable to degrade laminin but increased laminin degradation induced by conditioned medium of Co115 cells or recombinant t-PA. No potentiation was observed when Co115 cells and laminin were kept separated by Transwell inserts. Our results suggest that Co115 human colon carcinoma cells degrade laminin by potentiating t-PA-mediated plasminogen activation at the cell surface which requires close contact between tumor cells and laminin substrate.

Inactive urokinase and increased levels of its inhibitor type 1 in colorectal cancer liver metastasis

BACKGROUND/AIMS

Human colorectal carcinogenesis was previously found to be associated with an increased urokinase-type plasminogen activator expression, both in antigen and activity, accompanied by simultaneously enhanced levels of plasminogen activator inhibitors type 1 and type 2. This increased proteolytic activity may contribute to invasive growth and metastasis of the tumors.

METHODS

In the present study, homogenates of liver metastases, primary colorectal carcinomas, and adjacent normal tissues were evaluated regarding the level and composition of urokinase, tissue-type plasminogen activator, and plasminogen activator inhibitors.

RESULTS

Concentrations of urokinase were significantly increased in primary carcinomas and liver metastases compared with normal tissues, whereas tissue-type plasminogen activator levels were significantly decreased. Liver metastases showed, in contrast to the carcinomas, hardly any activity of plasminogen activators, which could be attributed to the enhanced presence of the inactive proenzyme form of urokinase in combination with more complexes of plasminogen activators with inhibitors. Furthermore, liver metastases had an eightfold higher content of inhibitor type 1 compared with the primary carcinomas. The excess of inhibitors was confirmed by addition of plasminogen activators to metastasis homogenates, which resulted in increased complex formation.

CONCLUSIONS

Colorectal cancer metastasis in the liver is associated with an inactivation of the enhanced urokinase cascade, which might allow tumor cells to settle in the liver.

Lipofectin-aided cell delivery of ribozyme targeted to human urokinase receptor mRNA

A 37-mer hammerhead ribozyme has been designed to efficiently cleave the 1.4 kb mRNA of the urokinase plasminogen activator receptor (uPAR). Under in vitro conditions, the chemically synthesized ribozyme cleaved uPAR mRNA and inhibited its translation in a concentration-dependent fashion. The ribozymes were 5'-[35S]thiophosphorylated and used as a model to analyze conditions for RNA delivery in a cultured human osteosarcoma cell system. Ribozymes degraded immediately in cell-conditioned medium but ribozymes complexed with lipofectin were protected from RNases for up to 22 h. Lipofectin rapidly transported ribozyme into the cell, where it accumulated almost exclusively in the cytoplasm. Thus, lipofectin dramatically enhances stability and cytoplasmic delivery of ribozymes, potentially enabling targeting of mRNA in vivo.

Relationship of the plasminogen activator/plasmin cascade to osteoclast invasion and mineral resorption in explanted fetal metatarsal bones

An attempt was made to establish whether the activation of plasminogen into plasmin is necessary either for the preparatory phases to bone resorption, involving the recruitment of osteoclast precursors, their migration toward mineralized surfaces, and their final differentiation, or for the subsequent osteoclastic resorption phase. 45Ca-labeled fetal (17 day) mouse metatarsals were cultured under conditions in which they pursue their modeling for a few days. In this model, the resorption phase, monitored by the release of 45Ca into the medium, is entirely dependent on the preparatory phases affecting osteoclast precursors. It was, as expected, stimulated by parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D3 and inhibited by calcitonin. PTH also enhanced the activity of tissue-type plasminogen activator (PA) in extracts of metatarsals but not that of urokinase (which is, however, the main PA present in the mouse fetal metatarsal culture model). The resorption processes were not dependent on the presence of plasminogen in the media, even when the rudiments were precultured with tranexamic acid to remove their endogenous plasminogen. Moreover, they were not influenced by inhibitors of plasmin, either the plasma inhibitors alpha 2-antiplasmin, alpha 2-macroglobulin, and alpha 1-antitrypsin, or aprotinin, which was tested under a variety of conditions. Aprotinin also did not influence the resorption (loss of calcium and hydroxyproline) of 19 day fetal mouse calvariae cultured with PTH in a medium devoid of plasminogen. It is concluded that the various steps implicated in the bone resorption processes that occur in the metatarsals and in the calvariae culture models are not dependent on the activity of plasmin. The function of PAs in bone, however, could be exerted through direct proteolysis of extracellular proteins other than plasminogen or be mediated by a molecular structural domain distinct from their catalytic domain.

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.

Secretion of plasminogen activators by cells cultured from subretinal fluid

Secretion of plasminogen activators was examined in 11 cells cultures from subretinal fluid of patients with retinal detachment. The plasminogen activator production was compared to 4 retinal pigment epithelial cell cultures from post-mortem donors with no known retinal pathology. Plasminogen activator activity was evaluated by zymography and was corrected for the total cell protein in the cultures. Cells from subretinal fluid had more proteolytic activity and secreted more active urokinase-type plasminogen activator than retinal pigment epithelial cells of donor origin. It is possible that cells from subretinal fluid are modulated by the conditions in subretinal fluid to secrete more urokinase-type plasminogen activator, generally considered to be a sign of invasive growth or that the subretinal fluid cultures contain other cell types than solely retinal pigment epithelial cells, such as pigmented macrophages, with an active plasminogen activator production. Alternatively, retinal pigment epithelial cells detached into the subretinal fluid may represent a selected population of retinal pigment epithelial cells with a more active extracellular proteolysis.

Extracellular matrix-degrading proteinases in the nervous system

The proteolytic activities of matrix metalloproteinases and plasminogen activators as well as their inhibitors are important in maintaining the integrity of the extracellular matrix (ECM). Cell-ECM interactions influence cell proliferation, differentiation, adhesion and migration. In the nervous system, proteolysis of the ECM is involved in neuronal cell migration in the developing cerebellum and in neurite outgrowth. Likewise, in pathological conditions such as brain tumour growth and invasion, leukocyte infiltration into brain tumours, leukocyte trafficking in the central nervous system in inflammatory diseases such as multiple sclerosis and viral encephalitis, and in nerve demyelination, matrix-degrading proteinases and their inhibitors have been implicated. An understanding of cell-ECM interactions and ECM degradation in diseases of the nervous system would provide new insight for drug design and other forms of therapy.

Confocal fluorescence microscopy of urokinase plasminogen activator receptor and cathepsin D in human MDA-MB-231 breast cancer cells migrating in reconstituted basement membrane

Using confocal fluorescence microscopy with a monoclonal antibody, we have localized the receptor for urokinase plasminogen activator (uPAR) in MDA-MB-231 human breast cancer cells migrating into a reconstituted basement membrane. Patchy and polarized uPAR immunoreactivity was found at the cell membrane, and strong staining was found both in the ruffled border or leading edge of the cells and at pseudopodia penetrating into the membrane. Intracellular uPAR staining was localized in the paranuclear region and in rounded granule-like structures; some of these were identified as lysosomes by double staining for uPAR and the lysosomal enzyme cathepsin D. Urokinase plasminogen activator (uPA) activity has previously been shown to play a role in migration of cells into basement membranes, and it has been proposed that uPAR also is involved in this process. uPA is known to be internalized and degraded after complex formation with the inhibitor PAI-1. Lysosomal uPAR immunoreactivity may result from concomitant internalization of the receptor.

A common response element mediates differential effects of phorbol esters and forskolin on type-1 plasminogen activator inhibitor gene expression in human breast carcinoma cells

We have characterized regulation of type-1 plasminogen activator inhibitor (PAI-1) gene expression by phorbol 12-myristate 13-acetate (PMA) and the cAMP-inducing agent forskolin in the human breast carcinoma cell line MCF-7. PMA caused a strong induction of PAI-1, while forskolin suppressed the PMA response. Transfection experiments with fusion genes showed that sequences mediating PMA induction as well as forskolin suppression were present between base pairs -100 and -30 of the 5'-flanking region of the PAI-1 gene. The region was found to contain two Sp1 binding sites. A proximal sequence in the region, TGAGTTCA (P box), with sequence similarity to phorbol ester response elements (TRE) as well as to cAMP response elements (CRE), bound a low-abundance, as yet unidentified nuclear protein in MCF-7 cells. This sequence had a higher affinity to purified c-jun homodimer than to c-jun/c-fos heterodimer in MCF-7 nuclear extracts; it had no affinity to the proteins binding to CRE consensus sequences in these extracts. A distal TRE-like sequence, TGAGTGG (D box), had a weak affinity to c-jun/c-fos heterodimer and c-jun homodimer; binding of proteins to this sequence was facilitated by binding of proteins to the P box. Both the P box and the D box were necessary for PMA responsiveness, suggesting a cooperativity between the two binding sites. A mutation of the P box removing the CRE similarity abolished the forskolin suppression of the PMA response. We propose that the protein kinase C and the protein kinase A signal-transduction pathways, with opposite effects on PAI-1 gene expression converge by modulating differently P-box-binding proteins.

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.

Expression of plasminogen activator inhibitor type 2 in normal and psoriatic epidermis

The plasminogen activator (PA) proteolytic cascade has been implicated in the regulation of cell activities, including proliferation and differentiation, both of which occur continuously in normal human epidermis and are aberrant in psoriatic epidermis. To elucidate further the mechanisms by which PA is regulated in epidermis, we evaluated the levels of PA inhibitors type 1 (PAI-1) and type 2 (PAI-2) in normal and psoriatic epidermis. PAI-2, but not PAI-1, was detectable by mRNA, antigen, and activity assays, indicating that PAI-2 is the predominant epidermal PA inhibitor. In situ hybridization revealed that PAI-2 mRNA occurred throughout normal epidermis, although the signal was most intense in the granular layers. Similarly, PAI-2 antigen was most prominent in the granular layers; its distribution in these differential layers was along the cell periphery. Diffuse, fainter staining for PAI-2 was also detected in the basal cells and in some spinous layers of normal epidermis. Extracts of normal epidermis contained PA inhibitory activity identified as PAI-2 by immunoprecipitation with specific antibody. In psoriatic epidermis, PAI-2 mRNA and antigen were most prominent in the more superficial layers beneath the cornified cells. As with normal epidermis, PAI-2 assumed a pericellular distribution in the psoriatic cells. These data demonstrate that PAI-2 is constitutively expressed in vivo by keratinocytes in human epidermis and indicate that this protein is the predominant inhibitor of PA activity in normal and psoriatic human epidermis.

Activities, localizations, and roles of serine proteases and their inhibitors in human brain tumor progression

The plasminogen activation system consists of plasminogen activators and their inhibitors, serine proteases, and serpins. The proteases and inhibitors regulate a variety of processes in tissue morphogenesis, differentiation, cell migration, and cancer cell invasiveness and metastasis. One of the plasminogen activators, urokinase-type plasminogen activator (uPA), binds to a specific surface and provides a localized cell surface proteolytic activity required for the destruction of extracellular matrix, which is a vital step in tumor cell invasion. The proteolytic activity of uPA is modulated by its cell surface receptor, as well as by plasminogen activator inhibitor type-1 (PAI-1) and, to a lesser degree, by other inhibitors. The role of plasminogen activators and their inhibitors in cancer invasion can be demonstrated in the development and progression of malignant brain tumors. Our findings indicate that uPA and PAI-1 expression are dramatically upregulated in malignant brain tumors in parallel with the histological progression of the tumors. The results suggest that these molecules may contribute to tumor invasion in addition to their significant role in angiogenesis. An evaluation of the plasminogen activation system could add diagnostic and prognostic significance to the evaluation of individual patients.

Proteolysis and invasiveness of brain tumors: role of urokinase-type plasminogen activator receptor

The cellular receptor for urokinase-type plasminogen activator (uPAR) in glioblastoma cell lines has been identified and found to be similar to the uPAR expressed by other tumor cell lines. Increased levels of uPAR have been found in primary malignant brain tumor tissues, especially highly malignant glioblastoma, and, to a lesser degree, in malignant astrocytomas, suggesting that this receptor might be involved in efficient activation of pro-uPA and confinement of uPA activity on the cell surface of invading brain tumors. The cell surface uPARs in gliomas could constitute an optimum environment for the generation and activity of plasmin, which is known to play a crucial role in the dissolution of the extracellular matrix during tumor cell invasion. In situ hybridization studies have shown that uPAR mRNA is expressed abundantly in tumor cells and is consistently present at the invasive edges of malignant gliomas. These results imply that uPAR is involved in plasmin-catalyzed proteolysis during glioma invasion and that interference with the uPA:uPAR interactions could constitute a novel approach for developing therapeutic strategies to counteract invasion of brain tumors.

A novel, specific pro-urokinase complex on monocyte-like cells, detected by transglutaminase-catalyzed cross-linking

Radiolabeled pro-urokinase plasminogen activator (pro-uPA) was cross-linked to a specific protein on the surface of human monocyte-like U937 cells in a reaction catalyzed by tissue transglutaminase. The conjugate formed with this unknown component had a much higher molecular weight (apparent M(r) 250,000-300,000) than the complex of pro-uPA and the urokinase plasminogen activator receptor (uPAR). There was a strong preference for the pro-form of uPA. The conjugate was recognized by antibodies against uPA but not by anti-uPAR antibodies. Nevertheless, the blocking of uPAR with a monoclonal antibody abolished the formation of the conjugate, thus showing a role of uPAR in this process.

Structural analysis of a new highly metastatic cell line PaTu 8902 from a primary human pancreatic adenocarcinoma

The new cell line PaTu 8902 was established from a human pancreatic grade II adenocarcinoma of ductal origin. In early passages, cultured cells showed a high degree of heterogeneity in terms of their morphology and the number of chromosomes per cell. When transplanted subcutaneously into nude mice, these cells grew as tumors with a similar morphology and differentiation (grade II) to the primary tumor. In contrast, after prolonged cultivation, cells were more homogenous in terms of their morphology and number of chromosomes per cell, and the corresponding nude mouse xenografts were less differentiated (grade III). When cells from late passages were injected intravenously into nude mice, lung metastases occurred after 3-4 weeks. In addition, tumor cells were found in the wall of the esophagus and in the pleural cavity, indicating a high metastatic potential for PaTu 8902 cells in nude mice.

Enzyme-linked immunosorbent assay of urokinase-type plasminogen activator (uPA) in cytosolic extracts of human breast cancer tissue

The enzyme urokinase-type plasminogen activator (uPA) plays a role in cancer invasion, and high levels of uPA in detergent extracts of mammary cancer tissue have been reported to be associated with a poor prognosis. We have explored the possibility of using mammary cancer cytosol extracts routinely prepared for steroid receptor analysis for retrospective prognostic studies of uPA. A sandwich enzyme-linked immunosorbent assay (ELISA) for uPA was developed, using polyclonal catching antibodies and a mixture of three biotinylated monoclonal detecting antibodies, that were selected to recognize free uPA, inhibitor-bound uPA, and uPA bound to its cell surface receptor. The assay detects active uPA and its inactive proenzyme form, pro-uPA, equally well. The limit of detection is approximately 1 pg of pro-uPA in a volume of 100 microliters, and there is a linear dose-response up to 100 pg pro-uPA. The efficiency in extracting uPA of a neutral non-detergent buffer used to prepare cytosol extracts was compared with that of 4 other buffers. There was a pronounced difference in the efficiency, the most efficient being a pH 4.2 buffer containing the non-ionic detergent Triton X-100, while the least efficient was the buffer used to prepare cytosols. Nevertheless, uPA immunoreactivity was readily measurable in the cytosols, and there was a close correlation between the amounts of uPA extracted under optimal conditions and those routinely used for steroid hormone receptor analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Interconversions between active, inert and substrate forms of denatured/refolded type-1 plasminogen activator inhibitor

The latent form of type-1 plasminogen activator inhibitor (PAI-1) acquires inhibitory activity by denaturation followed by refolding. We show here that the reactions of denatured/refolded PAI-1 with plasminogen activators are affected by low concentrations of SDS, which may remain after using SDS for denaturation. Without SDS, the active fraction of denatured/refolded PAI-1 comprised around 60%. Increasing SDS concentrations led to conversions to an inert form without inhibitory activity; then to a substrate form, that is being cleaved proteolytically in the reactive centre by the activators without complex formation, and finally to a second inert form. The first two conversions were associated with changes of the reactivity with monoclonal antibodies and of the thermal stability, respectively. Our results define clearly different interconvertible forms of denatured/refolded PAI-1, distinguish these from the latent and the reactive-centre-cleaved forms, and provide conditions for reproducibly producing reactive-centre-cleaved PAI-1 and PAI-1/activator complexes.

Differential expression of plasminogen activators and their inhibitors in an organotypic skin coculture system

Using immunohistochemistry and in situ hybridization, we have characterized the expression and localization of components of the plasminogen activator proteolytic cascade in an organotypic coculture system which consists of a “dermal” portion (human dermal fibroblasts throughout a collagen matrix) and a stratified, well-differentiated epidermal portion. Specifically, the following components were examined: the enzymes urokinase-type plasminogen activator and tissue-type plasminogen activator and their type 1 and type 2 inhibitors. Urokinase plasminogen activator mRNA and antigen were found predominantly in the least differentiated, basal keratinocytes; in some fields there was also faint deposition of antigen beneath the basal cells. The distribution of plasminogen activator inhibitor type 1 was similar to that of urokinase, except that inhibitor type 1 antigen deposition beneath the basal cells appeared more intense and uniform. In contrast to the results with urokinase plasminogen activator and inhibitor type 1, tissue plasminogen activator mRNA and antigen were localized focally in the suprabasal, i.e. more differentiated, keratinocytes. Plasminogen activator inhibitor type 2 mRNA and antigen were detected in most epidermal layers, but were more intense suprabasally and often spared the basal layer. These studies demonstrate that the same type of cell, i.e. the keratinocyte, can express different components of the plasminogen activator cascade depending on its state of differentiation. The change in expression of plasminogen activator cascade components with keratinocyte differentiation suggests distinct epidermal functions for these components, related to cell-matrix interaction and epidermal differentiation.

The role of the urokinase receptor in extracellular matrix degradation by HT29 human colon carcinoma cells

Urokinase (u-PA) and the urokinase receptor (u-PAR), are thought to play a critical role in the invasive and metastatic properties of cancer cells. The HT29 human colon-carcinoma cell line was selected to evaluate these aspects. HT29 cells express u-PA receptors (100,000 sites/cell, KD = 1.5 nM), but no PA activity and therefore are unable to generate plasmin in the presence of plasminogen. These cells have been transfected with a human u-PA cDNA to investigate whether secreted u-PA would enhance in vitro extracellular matrix degradation, and whether the binding of u-PA to the cell surface is determinant. Five clones were selected for stable expression of high PA activity. These clones were capable of marked plasminogen-dependent degradation of R22 smooth-muscle-cell-derived extracellular matrix, whereas the parental cell line contributed to an insignificant breakdown only. Aprotinin, polyclonal anti-u-PA IgG, recombinant PAI-2, and co-culture with human PAI-I-producing mouse L cells significantly inhibited this degradation. Furthermore, a peptide displacing u-PA from its receptor as well as 2 different polyclonal anti-u-PA receptor IgGs decreased the breakdown after 24 hr by as much as 70% and 81%, respectively. These results show that the binding of u-PA to its receptor plays an important role in in vitro matrix breakdown by HT29 u-PA transfectants.

Proteolytic activity in leg ulcer exudate

Twenty-five leg ulcer exudate samples from 17 patients with chronic non-healing venous leg ulcer were analyzed for proteolytic activity using radial caseinolysis procedures and zymographic analysis, and for fibronectin fragmentation using immunoblotting technology. Caseinolytic activity was detected in 21 of the 25 samples. A minority of them were inhibited (3 were totally, 6 partially inhibited) by aprotinin, a serine proteinase inhibitor, suggesting that proteinase(s) other than plasmin were also responsible for the caseinolysis. In zymographic analysis, 23 of the 25 samples showed positive reactions for enzyme activities comigrating with plasmin and urokinase-type plasminogen activator. Fibronectin fragmentation, another sign of proteolytic activity, was seen in all but 2 ulcers. No correlation was seen between bacterial infection or inflammatory cells and the above parameters in the wound fluid. Acute wound fluid collected from the donor sites of patients undergoing split skin grafting was used as a control. In the control specimens no proteolytic activity was found during the days following operation. These results show that there is proteolytic activity in the chronic ulcer exudate and support the possibility that the proteolytic activity and consequent fibronectin fragmentation may be related to the retarded epithelization and ulcer healing.

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.

Selective localization of receptors for urokinase amino-terminal fragment at substratum contact sites of an in vitro-established line of human epidermal cells

We have shown the presence of surface receptors for the amino-terminal fragment (ATF) of human urokinase-type plasminogen activator (u-PA) on an in vitro-established cell line of human epidermal origin by both radio-binding assays with human 125I-u-PA-ATF and transmission electron microscopy of a gold-u-PA complex. On the basis of cross-linking experiments with 125I-u-PA-ATF and subsequent autoradiography of the gels we have observed that such receptors are not spontaneously released into the culture medium. The treatment with phosphatidylinositol-specific phospholipase C induces the release of the receptor, which behaves as a glycosyl phosphatidyl inositol(GPI)-anchored protein. Phase-partitioning experiments on cell lysates have shown that the receptor partitions into the detergent phase. By detaching cell monolayers with the chelating agent EDTA we have prepared the cell-substratum contact sites of these cells, which represent only the 3.5% of the surface membrane of monolayered cells. Such plasma membrane remnants are highly selected since they contain about 43% of total u-PA-ATF binding sites. Such binding sites show the same biochemical and morphological characteristics of u-PA-ATF receptors observed in the monolayered cells, thus indicating that u-PA is selectively concentrated at the level of cell-substratum contacts. This is likely to enable directional proteolysis for cell migration and invasion.

Membrane proteases: roles in tissue remodeling and tumour invasion

The coordinated control of extracellular matrix degradation on the cell surface involves three crucial elements: secreted proteases and their inhibitors, surface protease receptors and integral membrane proteases. The roles that each of these elements play in cell surface proteolysis are described. The localization of proteases to the cell surface, protease activation, and regulation of cell surface proteolysis by protease inhibitors are key issues for elucidating the role of membrane proteases in tissue remodeling and tumour invasion.

Regulation of urokinase plasminogen activator localization in keratinocytes by calcium ion and E-cadherin

In keratinocyte culture, the cellular distribution of many adhesion markers and the organization of intercellular junctions are controlled by the calcium ion concentration of the medium. We show in the present study that urokinase plasminogen activator (uPA) localization in the human keratinocyte is similarly dependent upon calcium concentration. At 30 microM calcium, uPA is present throughout the cell, often with a perinuclear concentration. Upon calcium elevation to 1.0 mM, uPA is concentrated along the cell-cell borders, where it colocalizes (at the light microscope level) with E-cadherin. Blocking antibody to E-cadherin delays the calcium-induced redistribution of uPA, in a manner very similar to the previously observed delay in redistribution of several adhesion-related markers, including vinculin, desmoplakin, and beta 1 integrin. These data suggest a link between the redistribution of uPA to the cell-cell borders and the calcium-induced organization of intercellular junctions in the human keratinocyte. The presence of uPA along the intercellular borders suggests that this enzyme may be involved in regulation of epidermal adhesion through proteolysis.

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.

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.