Addition Of Plasminogen Research Articles

Minor Role of Plasminogen in Complement Activation on Cell Surfaces.

Atypical hemolytic uremic syndrome (aHUS) is a rare, but severe thrombotic microangiopathy. In roughly two thirds of the patients, mutations in complement genes lead to uncontrolled activation of the complement system against self cells. Recently, aHUS patients were described with deficiency of the fibrinolytic protein plasminogen. This zymogen and its protease form plasmin have both been shown to interact with complement proteins in the fluid phase. In this work we studied the potential of plasminogen to restrict complement propagation. In hemolytic assays, plasminogen inhibited complement activation, but only when it had been exogenously activated to plasmin and when it was used at disproportionately high concentrations compared to serum. Addition of only the zymogen plasminogen into serum did not hinder complement-mediated lysis of erythrocytes. Plasminogen could not restrict deposition of complement activation products on endothelial cells either, as was shown with flow cytometry. With platelets, a very weak inhibitory effect on deposition of C3 fragments was observed, but it was considered too weak to be significant for disease pathogenesis. Thus it was concluded that plasminogen is not an important regulator of complement on self cells. Instead, addition of plasminogen was shown to clearly hinder platelet aggregation in serum. This was attributed to plasmin causing disintegration of formed platelet aggregates. We propose that reduced proteolytic activity of plasmin on structures of growing thrombi, rather than on complement activation fragments, explains the association of plasminogen deficiency with aHUS. This adds to the emerging view that factors unrelated to the complement system can also be central to aHUS pathogenesis and suggests that future research on the mechanism of the disease should expand beyond complement dysregulation.

Factors influencing the cell adhesion and invasion capacity of Mycoplasma gallisepticum

BackgroundThe cell invasiveness of Mycoplasma gallisepticum, the causative agent of respiratory disease in chickens and infectious sinusitis in turkeys, may be a substantial factor in the well-known chronicity of these diseases and in the systemic spread of infection. To date, not much is known about the host factors and mechanisms involved in promotion or obstruction of M. gallisepticum adherence and/or cell invasion.In the current study, the influence of extracellular matrix (ECM) proteins such as fibronectin, collagen type IV and heparin, as well as plasminogen/plasmin, on the adhesion and cell invasion levels of M. gallisepticum to chicken erythrocytes and HeLa cells was investigated in vitro. Two strains, Rhigh and Rlow, which differ in their adhesion and invasion capacity, were analyzed by applying a modified gentamicin invasion assay. Binding of selected ECM molecules to M. gallisepticum was proven by Western blot analysis.ResultsCollagen type IV, fibronectin, and plasminogen exerted positive effects on adhesion and cell invasion of M. gallisepticum, with varying degrees, depending on the strain used. Especially strain Rhigh, with its highly reduced cell adhesion and invasion capabilities seemed to profit from the addition of plasminogen. Western and dot blot analyses showed that Rhigh as well as Rlow are able to adsorb horse fibronectin and plasminogen present in the growth medium. Depletion of HeLa cell membranes from cholesterol resulted in increased adhesion, but decreased cell invasion.ConclusionECM molecules seem to play a supportive role in the adhesion/cell invasion process of M. gallisepticum. Cholesterol depletion known to affect lipid rafts on the host cell surface had contrary effects on cell adherence and cell invasion of M. gallisepticum.

Plasminogen stimulates propagation of protease-resistant prion proteinin vitro

To clarify the role of plasminogen as a cofactor for prion propagation, we conducted functional assays using a cell-free prion protein (PrP) conversion assay termed protein misfolding cyclic amplification (PMCA) and prion-infected cell lines. Here, we report that plasminogen stimulates propagation of the protease-resistant scrapie PrP (PrP(Sc)). Compared to control PMCA conducted without plasminogen, addition of plasminogen in PMCA using wild-type brain material significantly increased PrP conversion, with an EC(50) = ∼56 nM. PrP conversion in PMCA was substantially less efficient with plasminogen-deficient brain material than with wild-type material. The activity stimulating PrP conversion was specific for plasminogen and conserved in its kringle domains. Such activity was abrogated by modification of plasminogen structure and interference of PrP-plasminogen interaction. Kinetic analysis of PrP(Sc) generation demonstrated that the presence of plasminogen in PMCA enhanced the PrP(Sc) production rate to ∼0.97 U/μl/h and reduced turnover time to ∼1 h compared to those (∼0.4 U/μl/h and ∼2.5 h) obtained without supplementation. Furthermore, as observed in PMCA, plasminogen and kringles promoted PrP(Sc) propagation in ScN2a and Elk 21(+) cells. Our results demonstrate that plasminogen functions in stimulating conversion processes and represents the first cellular protein cofactor that enhances the hypothetical mechanism of prion propagation.

Inhibition of uPAR and uPA reduces invasion in papillary thyroid carcinoma cells

We analyzed the expression of urokinase plasminogen activator (uPA) and its receptor (uPAR) in papillary thyroid carcinoma (PTC) and normal thyroid tissue and examined in vitro how uPA and uPAR contribute to an invasive/metastatic phenotype, and the functional consequences of inhibiting this system. Retrospective chart review of PTC patients, followed by prospective study using previously obtained patient tissue and PTC cellular models. uPA and uPAR RNA and protein levels were analyzed in PTC patient tissue samples, PTC and normal thyroid tissue culture cells, and conditioned media (CM) using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and/or Western blotting. The plasminogen-activating ability of CM was examined using dark-quenched casein fluorimetry and casein-plasminogen gel zymography. The invasive potentials of the PTC and normal thyroid epithelial cell lines were assessed using an in vitro cellular invasion/migration system. uPA and uPAR RNA and protein levels were increased in PTC patient samples and PTC cells relative to controls. uPA and uPAR RNA were also significantly higher in patients with metastatic disease. Casein-plasminogen zymography and Western blotting demonstrated increased active uPA secreted by PTC cells compared with normal thyroid cells. Fluorimetric assays revealed that the PTC cells' CM was able to activate plasminogen, resulting in measurable casein hydrolysis. This casein hydrolysis was prevented by the addition of several specific uPA inhibitors. Finally, the in vitro invasion phenotypes of PTC cells were augmented by the addition of plasminogen, and this augmentation was reversed by inhibitory anti-uPA and anti-uPAR antibodies. These data provide new functional evidence of the uPA/uPAR system's role in PTC invasion/metastasis and demonstrate the attractiveness of uPA and uPAR as molecular biomarkers and therapeutic targets.

Abstract 520: Inhibition of uPAR and uPA reduces invasion and degradative potential in papillary thyroid carcinoma cells

Abstract Papillary thyroid cancer (PTC) is the most prevalent endocrine and thyroid malignancy. The ability of PTC to invade and migrate great distances contributes to distant metastases, which represent the most common cause of PTC-related death. The urokinase plasminogen activator (uPA) and the urokinase plasminogen receptor (uPAR) are key mediators of tumor invasion. Upon binding to uPAR, pro-uPA is converted to its active form, which is then capable of cleaving plasminogen to plasmin. Plasmin can then degrade components of the basement membrane and extracellular matrix, a prerequisite for tumor cell invasion and metastasis. The binding of uPA by uPAR also seems to mediate several signaling events that contribute to a migratory phenotype, as well as various growth signals. In this study, we analyzed uPA and uPAR expression in PTC and normal thyroid tissue, and examined in vitro how uPA and uPAR contribute to an invasive/metastatic phenotype, as well as the functional consequences of inhibiting this system. uPA and uPAR RNA were also significantly higher in patients with metastatic disease. Casein-plasminogen zymography and western blotting demonstrated increased active uPA secreted by BCPAP cells compared to NTHY-Ori-3-1. Fluorimetric assays revealed that BCPAP CM was able to activate plasminogen, resulting in measureable casein hydrolysis. This casein hydrolysis was prevented by the addition of several specific uPA inhibitors. The in vitro invasion phenotype of BCPAP cells was augmented by the addition of plasminogen, and this augmentation was reversed by inhibitory anti-uPA and anti-uPAR antibodies. Cells transfected with siRNA against uPAR demonstrated decreased migratory and invasive potentials as measured by Matrigel invasion assays. Finally, uPAR-knockdown cells exhibited decreased proliferation when compared to non-targeting siRNA transfectant cells. These data provide new functional evidence of the uPA/uPAR system's role in PTC invasion/metastasis and demonstrate the attractiveness of uPA and uPAR as molecular biomarkers and therapeutic targets. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 520.

Role of plasminogen activation in neuronal organization and survival

We characterized the interactions between plasminogen and neurons and investigated the associated effects on extracellular matrix proteolysis, cell morphology, adhesion, signaling and survival. Upon binding of plasminogen to neurons, the plasmin formed by constitutively expressed tissue plasminogen activator (tPA) degrades extracellular matrix proteins, leading to retraction of the neuron monolayer that detaches from the matrix. This sequence of events required both interaction of plasminogen with carboxy-terminal lysine residues and the proteolytic activity of plasmin. Surprisingly, 24 h after plasminogen addition, plasmin-detached neurons survived and remained associated in clusters maintaining focal adhesion kinase phosphorylation contrasting with other adherent cell types fully dissociated by plasmin. However, long-term incubation (72 h) with plasminogen was associated with an increased rate of apoptosis, suggesting that prolonged exposure to plasmin may cause neurotoxicity. Regulation of neuronal organization and survival by plasminogen may be of pathophysiological relevance, as plasminogen is expressed in the brain and/or extravasate during vascular accidents or inflammatory processes.

Impact of plasminogen on an in vitro wound healing model based on a perfusion cell culture system

Vascular reorganization in wound healing is a complex process, which involves coagulation, endothelial cell proliferation and migration, basement membrane regeneration, and fibrinolysis. During this healing process, the hemostatic system and the angiogenic system are intimately interconnected. To elucidate the contribution of plasminogen in the process of wound healing, we have established a perfusion cell culture system. Using this novel cell culture system, we found that addition of plasminogen in the perfusion medium allowed the "scratch-wounded" endothelial cells to recover completely, while mini-plasminogen only affected the migration but not the proliferation of the endothelial cells. In the process of recovery with the addition of plasminogen, significant plasmin activity could only be detected when the growth of the endothelial cells have almost reached confluence. This finding indicates that wound healing is triggered and promoted during the absence of the proteolytic activity of plasmin. In addition, we could not detect any matrix metalloproteinase activity in the perfusion culture medium throughout the whole culture period. However, we did found that the circulating medium collected from the perfusion system at the early phase of the healing process has stimulatory activity on the growth of endothelial cells, but the proliferative activity decreased back to the basal level when the cells reached confluence. Thus, by using the perfusion cell culture system, we found that proliferation of endothelial cells is regulated by plasminogen and the wound healing process is controlled by a temporal interaction between the endothelial cells and plasminogen.

Effect of plasmin, plasminogen activators and a plasmin inhibitor on bovine in vitro embryo production

In the present study, four experiments were conducted to investigate the possible effects of plasminogen activators (urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA)), plasmin, and a plasmin inhibitor (epsilon-aminocaproic acid (epsilon-ACA)) on different stages of bovine in vitro embryo production (IVP). The concentrations of these modifiers in IVP media were conditioned according to the plasminogen activator activity of bovine preovulatory follicular fluid. Media were modified in a single phase of IVP with an 18 h or 24 h incubation for in vitro maturation (IVM) and a 24 h or 48 h incubation for the IVF or in vitro culture (IVC), respectively. After IVM the oocytes were either fixed and stained or underwent IVF and IVC. The main findings were: (1) plasmin added to the 18 h IVM medium increased maturation rate without affecting fertilisation or embryo development rates; (2) t-PA added to the IVF medium significantly increased cleavage; (3) u-PA added to the IVC medium significantly increased embryo development rates; (4) the efficiency of all phases of IVP was reduced after the addition of epsilon-ACA; and (5) plasminogen addition had no effect in any IVP phase tested. We conclude that the members of the plasminogen activator-plasmin system contribute in different ways to bovine IVM, IVF and IVC.

Cell Surface-Bound Plasminogen Regulates Hepatocyte Proliferation Through a uPA-Dependent Mechanism

Plasminogen and plasminogen activators play important roles in liver regeneration. Previously, we found that plasminogen potentiates hepatocyte proliferation in the primary culture of rat hepatocytes. Here, we examined how exogenous plasminogen affects the downstream events leading to cell proliferation. The addition of plasminogen to hepatocytes increased urokinase-type plasminogen activator (uPA) activity, but did not affect matrix metalloproteinase (MMP)-9 or MMP-2 activities. To increase uPA activity, plasminogen was required to bind the hepatocyte surface through the lysine-binding site of plasminogen molecule, but neither uPA mRNA nor uPA receptor (uPAR) mRNA was affected by the exogenous plasminogen. In addition, treatment of hepatocytes with an uPA inhibitor, p-aminobenzamidine, inhibited the plasminogen-induced and even EGF-induced hepatocyte proliferation. These results suggest that plasminogen-related control of hepatocyte proliferation is exerted topically by producing a hyperfibrinolytic state on the cellular surface involving the activation of uPA.

Insulin-like Growth Factor-binding Protein-5 Activates Plasminogen by Interaction with Tissue Plasminogen Activator, Independently of Its Ability to Bind to Plasminogen Activator Inhibitor-1, Insulin-like Growth Factor-I, or Heparin

Transgenic mice expressing IGFBP-5 in the mammary gland exhibit increased cell death and plasmin generation. Because IGFBP-5 has been reported to bind to plasminogen activator inhibitor-1 (PAI-1), we determined the effects of this interaction in HC11 cells. PAI-1 prevented plasmin generation from plasminogen and inhibited cleavage of focal adhesions, expression of caspase 3, and cell death. IGFBP-5 could in turn prevent the effects of PAI-1. IGFBP-5 mutants with reduced affinity for IGF-I (N-term) or deficient in heparin binding (HEP- and C-term E and F) were also effective. This was surprising because IGFBP-5 reportedly interacts with PAI-1 via its heparin-binding domain. Biosensor analysis confirmed that, although wild-type IGFBP-5 and N-term both bound to PAI-1, the C-term E had greatly decreased interaction with PAI-1. This suggests that IGFBP-5 does not antagonize the actions of PAI-1 by a direct molecular interaction. In a cell-free system, using tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA) to activate plasminogen, PAI-1 inhibited plasmin generation induced by both activators, whereas IGFBP-5 prevented the effects of PAI-1 on tPA but not uPA. Furthermore, we noted that IGFBP-5 activated plasminogen to a greater extent than could be explained solely by inhibition of PAI-1, suggesting that IGFBP-5 could directly activate tPA. Indeed, IGFBP-5 and the C-term E and F were all able to enhance the activity of tPA but not uPA. These data demonstrate that IGFBP-5 can enhance the activity of tPA and that this can result in cell death induced by cleavage of focal adhesions. Thus IGFBP-5 can induce cell death by both sequestering IGF-I and enhancing plasmin generation.

Plasminogen activator inhibitor-1 impairs plasminogen activationmediated vascular smooth muscle cell apoptosis

The role of plasminogen activator inhibitor-1 (PAI-1) in vascular smooth muscle cell (VSMC) apoptosis mediated by plasminogen activation was studied with the use of aorticVSMC derived from mice with deficiency of PAI-1 (PAI-1 (-/-) ), tissue-type (t-PA (-/-) ) or urokinase-type (u-PA (-/-) ) plasminogen activator or from wildtype (WT) mice with corresponding genetic background. Plasminogen incubated with confluent VSMC was activated in a concentration-dependent and saturable manner for all four cell types, with maximal activation rates that were comparable for WT, u-PA (-/-) and t-PA (-/-) cells, but about two-fold higher for PAI-1 (-/-) cells. Plasminogen activation was impaired by addition of the lysine analogue 6-aminohexanoic acid, and by addition of t-PA and u-PA neutralizing antibodies, suggesting that it depends on binding to cell surface COOH-terminal lysine residues, and on plasminogen activator activity. Morphological alterations consistent with apoptosis were observed much earlier in PAI-1 (-/-) than in WT VSMC. Without addition of plasminogen, the apoptotic index was similar for all four cell types, whereas after incubation with physiological plasminogen concentrations, it was greater in PAI-1 (-/-) VSMC, as compared to WT, t-PA (-/-) or u-PA (-/-) VSMC. Furthermore, the apoptotic rate paralleled the release of plasmin. Thus, plasmin-mediated apoptosis of VSMC occurs via plasminogen activation by either t-PA or u-PA and is impaired by PAI-1.

In Vitro Models for Assessing Transcranial Ultrasound-Enhanced Thrombolysis

To the Editor: Contrary to the promising results of recent clinical studies, Pfaffenberger et al conclude from in vitro data that diagnostic ultrasound (US) is not suitable for transcranial enhancement of tissue plasminogen activator (tPA) thrombolysis.1 Their contention is based on surprising control data showing significant clot lysis without tPA and plasminogen and relatively modest increases in clot dissolution with tPA. Interestingly, their reported clot weight loss of 21.8% after 1 hour of incubation in saline alone is much higher than that which they recently reported in another journal using the same methods (2.8%±1.8%2 and 11.0%±3.8%3). Likewise, the effect of tPA alone (27.4%) also differs with earlier results of 19.9%±4.3%3 and 22.7%±9.0%.2 These discrepancies seem important, because a 19.9% effect of tPA alone would have been lower than combined US and recombinant tPA through the skull (26.2%), thus encouraging the authors to positively assess transcranial US thrombolysis. Because clot dissolution is dependent on the amount of plasminogen present and on the amount of tPA available for activation of the plasminogen, little clot lysis should occur during the first 60 minutes of incubation in saline, with or without tPA. To study our hypothesis, we used experimental conditions similar to those of Pfaffenberger et al. 1.5 mL of citrated …

295 RELATIONSHIP BETWEEN PLASMINOGEN ACTIVATOR/PLASMIN SYSTEM AND IN VITRO FERTILIZATION ABILITY IN THE PIG

Plasminogen activators (PAs) are serine proteases, known to be secreted by a large number of cell types, that convert plasminogen into plasmin. The present study was undertaken to identify PAs in porcine gametes and to investigate a possible role of plasminogen in fertilization in vitro in the pig. The oocyte maturation medium used was North Carolina State University-23 (NCSU-23) medium supplemented with 10% (v/v) porcine follicular fluid (pFF), 0.6 mM cysteine, 10 IU/mL human chorionic gonadotropin (hCG), and 10 IU/mL pregnant mare's serum gonadotropin (PMSG). To determine the changes of PA activities in porcine oocytes during maturation, the cumulus-oocyte complexes (COCs) were incubated in NCSU-33 in an atmosphere of 5% CO2 in air at 39�C for 0, 24, or 48 h. On the other hand, to investigate the release of PAs by boar spermatozoa, fresh spermatozoa were pre-incubated in fertilization medium (mTBM) for 0, 2, 4, or 6 h. After culture, 40 COCs, 40 cumulus-free oocytes, and 40 � 106 spermatozoa were separately put into microtubes containing 20 �L of sample buffer [5.0% (w:v) sodium dodecyl sulfate (SDS), 20% (v:v) glycerol, and 0.0025% (w:v) bromophenol blue in 0.125 M Tris-HCl buffer] and frozen at -80�C until used for analysis. PA activities in porcine oocytes and spermatozoa were quantified using SDS-PAGE, casein-agar zymography, and densitometry. Data were analyzed by ANOVA and Duncan's multiple-range test using the Statistical Analysis System (SAS Institute, Inc., Cary, NC, USA). In the COCs cultured for 24-18 h, tissue-type plasminogen activator (tPA), urokinase-type PA (uPA), and tPA-PA inhibitor (tPA-PAI) were observed. Also, PA activities increased as duration of culture increased. However, no uPA activity was detected in cumulus-free oocytes. In procine fresh spermatozoa, tPA, uPA, and tPA-PAI were observed. When spermatozoa were incubated for 2, 4, or 6 h in fertilization medium, the rate of acrosome reaction (AR) in spermatozoa increased as the duration of culture increased, but PA activities decreased gradually. However, PA activities in sperm-conditioned medium increased as duration of culture increased. On the other hand, to determine the effect of plasminogen on fertilization ability of porcine oocyte and spermatozoa, plasminogen (50 �g/mL) was added in fertilization medium. Addition of plasminogen to fertilization medium increased (P < 0.05) AR in spermatozoa and sperm binding to the zona pellucida (ZP), compared with control group. The ZP solubility (zona digestion time) was higher in medium with than that without plasminogen. When porcine oocytes and spermatozoa were co-incubated in fertilization medium with plasminogen, the polyspermic rate was lower in medium with than that without plasminogen. Also, plasminogen significantly (P < 0.05) increased formation rate of the male pronucleus in oocytes penetrated by spermatozoa. These results suggest that supplementing of plasminogen in fertilization medium may play a positive role in improving of fertilization ability in vitro in the pig.

Indications of neutralising anti-idiotypic antibodies and selective proteolytic fragmentation in polyclonal anti-D IgG preparations

Proteolytic fragmentation is the only suggested cause of potency losses during storage of liquid human polyclonal anti-D Ig. Besides the effect of fragmentation, we have investigated the potential contribution of neutralising anti-idiotypic antibodies (anti-Ids). Potency changes during storage and/or upon pH reduction in anti-D IgG batches with or without addition of plasminogen and urokinase were quantitatively analysed by the autoanalyser (AA) method or by a special procedure of flow cytometry (FC). Moreover, simultaneous changes of the molecular size distribution pattern have been determined by size exclusion chromatography. In contrast to the AA procedure, the particular FC methodology was found to be almost insensitive to proteolysis comprising up to 30% of total IgG. Data interpretation was based on the assumption that both assays cannot detect Ids with neutralised paratopes. In the absence of detectable neutralisation (functional absence of anti-Ids), it could be demonstrated that the anti-D IgG subpopulation is more sensitive to fragmentation by endogenous protease as compared to the unrelated bulk. However, both methods detected batch- and assay-dependently variable potency losses during storage. Moreover, the increase of potency induced by pH reduction correlated with the increase of monomeric IgG, essentially on the expense of dimers. This finding was interpreted to indirectly indicate the neutralising action of anti-Ids known to be the major driving force of dimer formation in polyclonal IgG. A more or less pronounced pH-dependent potency increase was also detectable in three arbitrarily selected batches of two other manufacturers. The data allows to assume that anti-Id-mediated neutralisation can significantly contribute to losses of anti-D potency. In addition, it turned out that anti-D plasma itself can be the source of anti-Ids.

Eotaxin promotes eosinophil transmigration via the activation of the plasminogen-plasmin system

The effect of eotaxin, a potent eosinophil chemotactic factor, on eosinophil transmigration through a reconstituted basal membrane (Matrigel) was evaluated. Eotaxin induced significant eosinophil transmigration in the presence of 10% fetal bovine serum (FBS) and interleukin-5. Its effect was optimal at 0.01 microM, and it plateaued at 18 h. Eotaxin's effect was greater with eosinophils from asthmatic subjects (61.1 +/- 3.4%) than with eosinophils from normal subjects (38.7 +/- 4.2%) (P < 0.001). Inhibition of metalloproteinases decreased eotaxin-induced transmigration by < or = 10.4%, whereas inhibition of the plasminogen-plasmin system decreased eotaxin's effect by < or = 44.4% (P = 0.0002). Moreover, eotaxin-induced transmigration was largely diminished in medium with low concentrations of serum [0.5% FBS: 6.1 +/- 2.4%; 10% FBS: 40.2 +/- 5.8% (P = 0.0001)] but returned to its initial level with the addition of plasminogen (2 U/mL) to 0.5% FBS (43.1 +/- 6.5%). These data show that eotaxin is an efficient promoter of eosinophil transmigration in vitro, that it is more potent with cells from asthmatics than with normal cells, and that its effect depends predominantly on the activation of the plasminogen-plasmin system.

Stimulation of Plasminogen Activator Activity and Matrix Metalloproteinases of Human Dental Pulp–Derived Cells by Tumor Necrosis Factor–α

The effects of tumor necrosis factor (TNF)-alpha on the plasminogen activator (PA)/plasmin system in human dental pulp (HDP) cells were examined. TNF-alpha treatment induced a significantly high level of PA activity in the conditioned medium of HDP cells in a time- and dose-dependent manner, compared with untreated control cells. Western-blot analysis revealed that tissue type (t)PA protein in conditioned medium was increased by TNF-alpha when compared with control medium. Furthermore the tPA mRNA level had increased in HDP cells treated with TNF-alpha, as determined by reverse transcription-polymerase chain reaction, but urokinase PA and PA inhibitor-1 mRNA levels did not increase. We examined the effects of TNF-alpha against activities of matrix metalloproteinases (MMPs) using zymography. TNF-alpha stimulated MMP-2 activity in conditioned medium and stimulated MMP-9 activity with addition of plasminogen into conditioned medium. The present results suggested that TNF-alpha stimulates PA activity via an enhancement of tPA gene expression in HDP cells and MMP-2 activity, and further that tPA-activated TNF-alpha stimulated MMP-9.

Host metalloproteinases in Lyme arthritis.

To assess the role of matrix metalloproteinases (MMPs) in cartilage and bone erosions in Lyme arthritis We examined synovial fluid from 10 patients with Lyme arthritis for the presence of MMP-2, MMP-3, MMP-9, and "aggrecanase" activity using gelatinolytic zymography and immunoblot analysis. We developed an in vitro model of Lyme arthritis using cartilage explants and observed changes in cartilage degradation in the presence of Borrelia burgdorferi and/or various protease inhibitors. Synovial fluid from patients with Lyme arthritis was found to contain at least 3 MMPs: gelatinase A (MMP-2), stromelysin (MMP-3), and gelatinase B (MMP-9). In addition, there was evidence in 2 patients of "aggrecanase" activity not accounted for by the above enzymes. Infection of cartilage explants with B. burgdorferi resulted in induction of MMP-3, MMP-9, and "aggrecanase" activity. Increased induction of these enzymes by B. burgdorferi alone was not sufficient to cause cartilage destruction in the explants as measured by glycosaminoglycan (GAG) and hydroxyproline release. However, addition of plasminogen, which can act as an MMP activator, to cultures resulted in significant GAG and hydroxyproline release in the presence of B. burgdorferi. The MMP inhibitor batimastat significantly reduced the GAG release and completely inhibited the collagen degradation. MMPs are found in synovial fluids from patients with Lyme arthritis and are induced from cartilage tissue by the presence of B. burgdorferi. Inhibition of MMP activity prevents B. burgdorferi-induced cartilage degradation in vitro.

Contribution of the Plasmin/Matrix Metalloproteinase Cascade to the Retraction of Human Fibroblast Populated Collagen Lattices

To assess the contribution of the plasmin/matrix metalloproteinase cascade in lattices retraction, human gingival fibroblast-populated collagen lattices were supplemented with plasminogen. The rate of lattice retraction was enhanced by addition of plasminogen. This effect was concomitant to plasmin generation, prostromelysin-1 and procollagenase activation. Plasminogen-mediated initiation of that proteolytic cascade was accompanied by conspicuous changes in cell morphology and collagen fibers organization. At day 1 of culture fibroblasts shifted from a rounded (control) to an elongated (in presence of plgn) shape. At the latest stage of retraction, intense vacuolization around fibroblasts was noticed in plgn-supplemented lattices which paralleled the increased collagen degradation. Plgn-enhancing influence on the initial phase of lattice retraction could be totally annihilated by either aprotinin or Batimastat. Those data emphasize the crucial importance of the plasmin–MMP proteolytic cascade in granulation tissue retraction in a healing wound.

Autocrine regulation of growth stimulation in human epithelial ovarian carcinoma by serine-proteinase-catalysed release of the urinary-type-plasminogen-activator N-terminal fragment

Ovarian carcinomas secrete single-chain urinary-type plasminogen activator (scuPA) and expression of uPA is up-regulated relative to normal ovarian epithelium, leading to an enhanced proteolytic capacity which may facilitate invasion. Furthermore, the uPA receptor (uPAR) is present on ovarian carcinoma cells and is occupied in tumour tissues. In the present study, incubation of scuPA with serum-free conditioned medium from ovarian carcinoma cells resulted in release of a 14 kDa polypeptide. N-terminal sequence analysis identified this fragment as the uPA N-terminal fragment (NTF), which contains a growth-factor and a kringle domain. NTF generation was abolished by serine-proteinase inhibitors, but not inhibitors of matrix metalloproteinases, and was not enhanced by the addition of plasminogen or plasmin. To determine whether ovarian carcinoma-cell growth is altered by uPA, the effect of exogenous scuPA or NTF on proliferation was analysed. Both NTF and scuPA induced a dose-dependent increase in proliferation, with maximal stimulation obtained at 10-20 nM. Furthermore, blocking the interaction of endogenous uPA with uPAR using anti-NTF antibodies significantly inhibited proliferation. Together these data indicate that, in addition to enhancing the invasive activity of ovarian carcinoma cells via increased pericellular proteolysis, uPA also acts as a mitogen for ovarian carcinoma cells, suggesting a biochemical mechanism whereby uPA may contribute to ovarian carcinoma progression by modulating both cell invasion and proliferation.

Endothelial cell surface actin serves as a binding site for plasminogen, tissue plasminogen activator and lipoprotein(a).

One of the mechanisms by which endothelial cells (ECs) regulate fibrinolysis is through the regulated assembly of proteins such as plasminogen, tissue plasminogen activator (tPA) and urokinase (uPA) on their membrane surface. Receptors for many of these fibrinolytic factors have been isolated and characterized. A unique 45 kD plasminogen receptor present on ECs derived from vein vasculature has been identified and resolved into two plasminogen binding components. One component consists of the unique 45 kD plasminogen receptor (pI = 6.3) whereas the other component (pI = 5.1) is identified as the cytoskeletal protein, actin. Immunofluorescent studies of isolated ECs confirm the presence of actin on their extracellular surface. This observation is consistent with a number of other recent reports of actin externally localized on other cell types. In vitro studies using purified actin confirm that plasminogen binds to actin both saturably and with relatively high affinity. Competition studies with lysine indicated that the binding was largely kringle-dependent, and when binding of tPA to actin was assessed, it also bound to actin with 70-80% of binding inhibited by lysine. Lipoprotein (a), which shows homology with plasminogen, also interacted with actin. Addition of plasminogen and low-density lipoproteins inhibited Lp(a) binding to actin in a dose-dependent fashion. Moreover, in competition with tPA, partial inhibition of plasminogen binding to actin was also observed. In experiments using anti-actin antibodies added in excess to cultured ECs, binding of plasminogen was inhibited by 45%, tPA binding was inhibited by 46% and Lp(a) binding was reduced by 56%, confirming actin as a binding site for these various ligands whilst attesting to the presence of other EC receptors for these proteins. Collectively, the data presented are consistent with actin playing a major role in localizing binding not only of plasminogen, but also of tissue plasminogen activator and Lp(a) to the surface of human endothelial cells.