Urokinase inhibitor in human placenta

Fibrinogen and Antifibrinolytic Proteins: Interactions and Future Therapeutics

Thrombus formation remains a major cause of morbidity and mortality worldwide. Current antiplatelet and anticoagulant therapies have been effective at reducing vascular events, but at the expense of increased bleeding risk. Targeting proteins that interact with fibrinogen and which are involved in hypofibrinolysis represents a more specific approach for the development of effective and safe therapeutic agents. The antifibrinolytic proteins alpha-2 antiplasmin (α2AP), thrombin activatable fibrinolysis inhibitor (TAFI), complement C3 and plasminogen activator inhibitor-2 (PAI-2), can be incorporated into the fibrin clot by FXIIIa and affect fibrinolysis by different mechanisms. Therefore, these antifibrinolytic proteins are attractive targets for the development of novel therapeutics, both for the modulation of thrombosis risk, but also for potentially improving clot instability in bleeding disorders. This review summarises the main properties of fibrinogen-bound antifibrinolytic proteins, their effect on clot lysis and association with thrombotic or bleeding conditions. The role of these proteins in therapeutic strategies targeting the fibrinolytic system for thrombotic diseases or bleeding disorders is also discussed.

The role of endogenous tissue-type plasminogen activator in neuronal survival after ischemic stroke: friend or foe?

Endogenous protease tissue-type plasminogen activator (tPA) has highly efficient fibrinolytic activity and its recombinant variants alteplase and tenecteplase are established as highly effective thrombolytic drugs for ischemic stroke. Endogenous tPA is constituted of five functional domains through which it interacts with a variety of substrates, binding proteins and receptors, thus having enzymatic and cytokine-like effects to act on all cell types of the brain. In the past 2 decades, numerous studies have explored the clinical relevance of endogenous tPA in neurological diseases, especially in ischemic stroke. tPA is released from many cells within the brain parenchyma exposed to ischemia conditions in vitro and in vivo, which is believed to control neuronal fate. Some studies proved that tPA could induce blood-brain barrier disruption, neural excitotoxicity and inflammation, while others indicated that tPA also has anti-excitotoxic, neurotrophic and anti-apoptotic effects on neurons. Therefore, more work is needed to elucidate how tPA mediates such opposing functions that may amplify tPA from a therapeutic means into a key therapeutic target in endogenous neuroprotection after stroke. In this review, we summarize the biological characteristics and pleiotropic functions of tPA in the brain. Then we focus on possible hypotheses about why and how endogenous tPA mediates ischemic neuronal death and survival. Finally, we analyze how endogenous tPA affects neuron fate in ischemic stroke in a comprehensive view.

Probable Roles of Coagulation Cascade and Fibrinolysis System in the Development of Allergic Rhinitis

BACKGROUND

Dysregulation of the coagulation cascade and fibrinolysis system may play an etiologic role in many diseases. Allergic diseases such as bronchial asthma, atopic dermatitis, and conjunctivitis are also associated with fibrin accumulation caused by a change in hemostasis. However, only a few studies have dealt with the relationship between allergic rhinitis (AR) and the coagulation system.

OBJECTIVE

We investigated the difference of coagulation and fibrinolysis cascade components between an AR mouse model and a control mice.

METHODS

BALB/c mice were sensitized and challenged with ovalbumin. Multiple parameters of coagulation cascade and fibrinolysis system such as factors II, V, VII, X, and XIII; tissue-type plasminogen activator; urokinase-type plasminogen activator (u-PA); plasminogen activator inhibitor-1 (PAI-1); and fibrin were compared between the AR model group and the control group.

RESULTS

The symptom scores and eosinophil counts were higher in the AR group than in the control group ( P < .01). The mRNA expression level of u-PA ( P = .040) was significantly lower, and the expression levels of factor II ( P = .038) and factor X ( P = .036) were significantly higher, in the AR group. Immunohistochemical staining revealed that most of the fibrinolysis system and coagulation cascade components were localized to the epithelium, endothelium, and submucosal glands of the nasal mucosa. u-PA was downregulated in the AR group, whereas fibrin deposition was more prominent in the AR group than in the control group.

CONCLUSION

In AR, particular components of the coagulation cascade were increased and fibrinolysis system was decreased compared to normal control. This difference may be associated with the fibrin deposition in the mucosa of AR mouse model.

Regulation of the human plasminogen activator inhibitor type 2 gene: cooperation of an upstream silencer and transactivator

Transcriptional up-regulation of the plasminogen activator inhibitor type-2 (PAI-2) gene is a major response to cellular stress. The expression of PAI-2 is induced by a variety of cytokines and growth factors that act in a cell type- and differentiation stage-dependent manner. We previously reported that the human SERPINB2 gene promoter is controlled by three major transcription regulatory domains: an inducible proximal promoter, an upstream silencer (PAUSE-1), and a distal transactivator region between -5100 and -3300, which appears to overcome inhibition mediated by the silencer. The distal transactivator region is inducible by the phorbol ester PMA, a potent activator of the protein kinase C (PKC) pathway that is a powerful inducer of PAI-2 gene expression in monocytes, macrophages, and myelomonocytic cells as well as in epidermal keratinocytes. Here we show that a 21-bp region (-4952/-4932), containing an AP-1 element, is both necessary and sufficient for PMA-induced transactivator activity in PAI-2-expressing U937 cells. This site specifically binds FosB in PAI-2-expressing U937 cells but not in HeLa cells that do not express PAI-2, and overexpression of FosB, c-Fos, or c-Jun in HeLa cells is sufficient to cause derepression of transcription from the SERPINB2 promoter. Although FosB is likely to be involved in transactivator-mediated derepression of PAI-2 transcription in macrophage-like cells, as exemplified by the U937 cell line, c-Jun may be functional in other cell types. These data suggest a model for the transcriptional control of the human PAI-2 gene and further our understanding of the molecular basis for its tissue-specific expression.

The Expression of Fibrinolytic Components in Chronic Paranasal Sinus Disease

Background

Fibrinolytic components, their receptors, and inhibitors are considered to play an important role in inflammation and tissue remodeling including chronic rhinosinusitis (CRS). To clarify the relationship between these components and the pathology of CRS, we analyzed fibrinolytic components in sinonasal mucosa of CRS.

Methods

Sinonasal mucosa samples from 12 patients with CRS without nasal polyp (CRSsNP), 14 patients with CRS with nasal polyp (CRSwNP), and 12 control patients were prepared. By immunohistochemistry and ELISA, samples were studied with respect to urokinase-type plasminogen activator (uPA), uPA receptor (uPAR), plasminogen activator inhibitor-1 (PAI-1) and key mediators in sinus disease, TGF-beta1 and eosinophil cationic protein (ECP).

Results

uPA- or uPAR-positive inflammatory cells were increased in CRSwNP compared to controls and CRSsNP, whereas PAI-1-positive cells were increased in CRSsNP compared to CRSwNP and controls. ELISA measurements revealed that uPAR concentrations were increased in both CRSsNP (16.1 ng/mL; 10.4–22.9; p < 0.05) and CRSwNP (20.8 ng/mL; 9.62–25.9; p < 0.01) compared to controls (8.7 ng/mL; 7.9–12.9), and PAI-1 concentrations were increased in CRSsNP (198.8 ng/mL; 147.4–234.1) compared to controls (107.3 ng/mL; 92.6–175.3; p < 0.01) and CRSwNP (113.5 ng/mL; 105.1–193.5; p < 0.05). Moreover, the concentrations of TGF-beta1 correlated with PAI-1 in CRSsNP, and ECP correlated with uPAR protein in CRSwNP.

Conclusion

Fibrinolytic components were highly expressed in CRSwNP compared to normal controls, whereas the inhibiting protein was up-regulated in CRSsNP. Furthermore, correlations between the expressions of fibrinolytic components and key mediators in CRS were found.

Transition of pathophysiological significance of plasminogen activator inhibitor-From a chief player in antiinflammation, antifibrinolysis to that in the development of insulin resistance

In the early phase of research, plasminogen activator inhibitor (PAI) was regarded as a negative regulator of fibrinolytic system, but the later study clarified that the changes in PAI level is closely related to risk factors of various pathologic processes of the lifestyle-related diseases. It is accepted that PAI-1 is a risk factor of the cardiovascular event in lifestyle-related diseases by recent researches analyzing the detailed function of PAI-1. In this review paper, we described the transition of pathophysiological significance of PAI based on many research papers especially from ours, which clarified the mechanism on protein expression of PAI, especially PAI-1.

Protection of plasminogen activator inhibitor-1-deficient mice from nasal allergy

This study was performed to clarify the relationship between fibrinolytic components and the pathology of allergy, particularly that during the development of nasal allergy and nasal tissue changes. Intranasal OVA challenge after sensitization by i.p. administration of OVA induced a higher level of excess subepithelial collagen deposition in wild-type (WT) C57BL/6J mice than in plasminogen activator inhibitor (PAI)-1-deficient (PAI-1(-/-)) mice. The excess PAI-1 induction in the nasal mucosa and higher level of active PAI-1 in the nasal lavage fluid of WT-OVA mice compared with those in WT-control mice suggested that the decrease of proteolytic activity inhibits the removal of subepithelial collagen. The frequency of sneezing, nasal rubbing, nasal hyperresponsiveness, production of specific IgG1 and IgE in the serum, and production of IL-4 and IL-5 in splenocyte culture supernatant increased significantly in WT-OVA mice. In PAI-1(-/-) mice, these reactions were absent, and specific IgG2a in serum and IFN-gamma in splenocyte culture medium increased significantly. Histopathologically, there were marked goblet cell hyperplasia and eosinophil infiltration into the nasal mucosa in WT-OVA mice, but these were absent in PAI-1(-/-) mice. These results indicate that the immune response in WT-OVA mice can be classified as a dominant Th2 response, which would promote collagen deposition. In contrast, the Th2 response in PAI-1(-/-) mice was down-regulated, and the immune response shifted from Th2-dominant reaction to a Th1-dominant one. Taken together, these findings suggest that PAI-1 plays an important role not only in thrombolysis but also in immune response.

Modification by the tissue plasminogen activator-plasmin system of morphine-induced dopamine release and hyperlocomotion, but not anti-nociceptive effect in mice

The extracellular serine protease tissue plasminogen activator (tPA) that converts plasminogen into plasmin is abundantly expressed throughout the central nervous system. We have recently demonstrated that the tPA-plasmin system participates in the rewarding and locomotor-stimulating effects of morphine by acutely regulating morphine-induced dopamine release in the nucleus accumbens (NAc). In the present study, we examined the effects of microinjections of plasminogen activator inhibitor-1 (PAI-1), tPA or plasmin into the NAc on morphine-induced dopamine release, hyperlocomotion and anti-nociceptive effects in ICR mice. A single morphine treatment resulted in an increase in protein levels of PAI-1 in the NAc. Microinjection of PAI-1 into the NAc dose-dependently reduced morphine-induced dopamine release and hyperlocomotion. In contrast, microinjection of tPA into the NAc significantly potentiated morphine-induced dopamine release and hyperlocomotion without affecting basal levels. Furthermore, microinjection of plasmin enhanced morphine-induced dopamine release, but did not modify the hyperlocomotion induced by morphine. The intracerebroventricular injection of PAI-1, tPA and plasmin at high doses had no effect on the anti-nociceptive effects of morphine. These results suggest that the tPA-plasmin system is involved in the regulation of morphine-induced dopamine release and dopamine-dependent behaviors but not the anti-nociceptive effects of morphine.

Expression of urokinase, plasminogen activator inhibitors and urokinase receptor in pregnant rhesus monkey uterus during early placentation

We have investigated plasmin mediated proteolysis associated with trophoblast invasion during early stages of pregnancy in the rhesus monkey. In situ hybridization and immunocytochemical localization were used to define the cellular and tissue distribution of urokinase plasminogen activator (uPA), plasminogen activator inhibitor type 1 (PAI-1) and 2 (PAI-2) and urokinase receptor in early monkey placenta and uterus. Our results indicate: (1) uPA is expressed in proliferating and invasive cytotrophoblast located in chorionic villi as well as in extravillous trophoblast associated with uterine arterioles. This raises the possibility that urokinase may play an important role in trophoblast invasion. (2) PAI-1 mRNA is specifically localized in two areas where invasive trophoblast cells encounter maternal tissue directly. The extravillous cytotrophoblast cells at the maternofetal junction express PAI-1 mRNA. The invasive endovascular trophoblast cells within the uterine arterioles also express PAI-1 mRNA. The location sensitive expression of PAI-1 mRNA at the maternofetal junction may imply a protective function of this protease inhibitor that might be induced through interaction with decidual cells. (3) Urokinase receptor antigen has also been found at the maternofetal junction and in endovascular trophoblast cells of the invaded maternal blood vessel. (4) PAI-2 immunoreactivity is found in association with cytotrophoblast cells in anchoring choronic villi suggesting its association with early placentation. In conclusion, we propose that the plasmin/plasminogen activator system may not only regulate extracellular matrix degradation, but also modify migration and invasive behaviour of extravillous trophoblast cells, during early placentation.

Evidence for intracellular cleavage of plasminogen activator inhibitor type 2 (PAI-2) in normal epidermal keratinocytes

Plasminogen activator inhibitor type 2 (PAI-2) is a serine proteinase inhibitor (serpin), present in high quantities in stratified squamous epithelia. Detergent extracts of human epidermis or cultured keratinocytes contain primarily active, nonglycosylated PAI-2. In keratinocytes, the vast majority of PAI-2 is retained within the cell, supporting the hypothesis that PAI-2 may serve specific intracellular function(s) through interaction with an unknown cytoplasmic proteinase. During interaction with the target proteinase, cleavage of PAI-2 within its reactive site loop leads to the formation of a more stable, "relaxed" conformation (PAI-2r). Using a monoclonal antibody specific for PAI-2r, we demonstrate here that PAI-2r is present in keratinocytes of the granular and basal layers of normal human epidermis. In addition, PAI-2r is detectable in cultured human epidermal keratinocytes, where it is concentrated in a detergent-insoluble fraction within differentiating cells. These data provide evidence for the presence of an endogenous, keratinocyte-derived proteinase that constitutively cleaves intracellular PAI-2 in normal human epidermal keratinocytes. Cleavage of PAI-2 by this proteinase may reflect specific intracellular action of PAI-2 in normal cells. Finally, we demonstrate that a commercially available anti-PAI-2 monoclonal antibody (#3750, American Diagnostica, Greenwich, CT), under native experimental conditions, preferentially recognizes the uncleaved, active form of PAI-2 and does not efficiently detect PAI-2r.

Expression of tissue type and urokinase type plasminogen activators as well as plasminogen activator inhibitor type-1 and type-2 in human and rhesus monkey placenta

The distribution of mRNAs and antigens of tissue type (t) and urokinase type (u) plasminogen activators (PA) plus their corresponding inhibitors, type-1 (PAI-1) and type-2 (PAI-2) were studied in human and rhesus monkey placentae by in situ hybridisation and immunocytochemistry. Specific monkey cRNA and antibodies against human tPA, uPA, PAI-1 and PAI-2 were used as probes. The following results were obtained. (1) All the molecules tPA, uPA, PAI-1 and PAI-2 and their mRNAs were identified in the majority of the extravillous cytotrophoblast cells of the decidual layer between Rohr's and Nitabuch's striae and in cytotrophoblast cells of the chorionic plate, basal plate, intercotyledonary septae and cytotrophoblast cells of the chorionic villous tree. (2) Expression of uPA and PAI-2 was noted in villous trophoblast whereas tPA and PAI-1 were mainly concentrated where detachment from maternal tissue occurs. (3) No expression of tPA, uPA, PAI-1 and PAI-2 was observed in the basal plate endometrial stromal cells, chorionic plate connective tissue cells, septal endometrial stromal cells or villous core mesenchyme. (4) The distribution of probes observed following in situ hybridisation is generally consistent with the immunofluorescence pattern of the corresponding antigens and no significant interspecies differences were noted. It is possible that both decidual and extravillous trophoblast cells of placentae of human and rhesus monkey are capable of producing tPA, uPA, PAI-1 and PAI-2 to differing extents. Coordinated expression of these genes in the tissue may play an essential role in the maintenance of normal placentation and parturition. The differences in distribution we observed are consistent with the suggestion that coordinated expression of tPA and its inhibitor PAI-1 may play a key role in fibrinolytic activity in the early stages of placentation and separation of placenta from maternal tissue at term. On the other hand, uPA with its inhibitor PAI-2 appears mainly to play a role in degradation of trophoblast cell-associated extracellular matrix, and thus may be of greatest importance during early stages of placentation.

The plasminogen activator inhibitor-2 gene is not required for normal murine development or survival

Plasminogen activator inhibitor-2 (PAI-2), a member of the serpin gene family, is thought to serve as a primary regulator of plasminogen activation in the extravascular compartment. High levels of PAI-2 are found in keratinocytes, monocytes, and the human trophoblast, the latter suggesting a role in placental maintenance or embryo development. The primarily intracellular distribution of PAI-2 also may indicate a unique regulatory role in a protease-dependent cellular process such as apoptosis. To examine the potential functions of PAI-2 in vivo, we generated PAI-2-deficient mice by gene targeting in embryonic stem cells. Homozygous PAI-2-deficient mice exhibited normal development, survival, and fertility and were also indistinguishable from normal controls in response to a bacterial infectious challenge or endotoxin infusion. No differences in monocyte recruitment into the peritoneum were observed after thioglycollate injection. Epidermal wound healing was equivalent among PAI-2 -/- null and control mice. Finally, crossing PAI-2 -/- with PAI-1 -/- mice to generate animals deficient in both plasminogen activator inhibitors failed to uncover an overlap in function between these two related proteins.

Suppression of keratinocyte proliferation by plasminogen activator inhibitor-2

We have previously shown that urokinase plasminogen activator (uPA) stimulates the growth of human keratinocytes in culture. For this effect, uPA activity is essential to generate the active amino terminal fragment, by an autolytic process. Our findings indicated further that inhibition of uPA may result in the suppression of growth of keratinoytes. Here, we provide evidence that plasminogen activator inhibitor (PAI)-2 has an anti-proliferative effect on keratinocytes. The uPA activity in cultured keratinocytes increased in parallel with cell proliferation, reaching a maximum level at confluency and decreasing gradually thereafter. The analysis of synchronized cells showed that the peak uPA activity in the medium occured just prior to S-phase, suggesting that the production and secretion of uPA is related to cell proliferation. In contrast, PAI-2 levels showed a steady increase, even after confluency. When PAI-2, purified from human cornified cells, was added to synchronized keratinocytes, S-phase was no longer evident and the peak uPA activity was eliminated. In experiments with a bacterially expressed PAI-2 fusion protein, [3H]thymidine incorporation by keratinocytes was significantly suppressed, confirming an anti-proliferative effect of PAI-2. These results strongly suggest that PAI-2 is involved in the regulation of keratinocyte proliferation and differentiation.

The binding of biotin analogues by streptavidin: a Raman spectroscopic study

Raman spectra of anhydrous complexes of streptavidin (Strep) with biotin (Bio) and some Bio analogues [Biotin methyl ester (MEBio), desthiobiotin (DEBio), 2'-iminobiotin (IMBio), and diaminobiotin (DABio)] were recorded. The vibrational results indicate that the interaction with some of these ligands is able to modify the overall structure of the protein and this binding results in a decrease in the beta-sheet content and an increase in the alpha-helix content. To further confirm the conformational changes of the protein structure due to Bio analogue binding, the curve-fitting analysis of the amide I Raman band of neat Strep and of the complexes were performed. The intensity ratio of the components due to the beta-sheet and alpha-helix conformations decreased in the Strep-MEBio, Strep-IMBio (pH 11), and Strep-Bio systems, whereas in all the other systems the changes were not significant. This behavior differs from that of Avi bound to the same ligands and suggests that Strep and Avi differ in their binding selectivity. A good correlation was found between the secondary structure percentages of the Avi and of the Strep complexes and deltaG(o). On the basis of this linear relationship, the vibrational results allow for an acceptable evaluation of the dissociation constants of the Strep complexes, not previously reported in the literature. The present results indicate a correlation between the type of interaction and the effects of the protein-substrate bonding on the overall structure of the proteins. The amino acid residues in the binding site appear to be positioned in a such a way as to provide a precise fit of Bio. Even slight change in the substrate structure causes a weakness in the strength of the binding. The vibrational results confirm that both the imidazolidinone and the thiophan rings are important in the Strep-Bio interactions, but the former is more responsible for the high affinity of the binding. One of the Tyr residues is hydrogen bound with the ureido ring and another Tyr could be involved in the binding pocket. Trp residues do not directly bind the ligand and probably stabilize other binding site residues which in turn interact directly with Bio.

Localization and distribution of tissue type and urokinase type plasminogen activators and their inhibitors Type 1 and 2 in human and rhesus monkey fetal membranes

Fetal membranes consist of 10 distinct layers including components of amnion, chorion and decidua, the latter being of maternal origin. They form mechanically integrated sheets capable of retaining amniotic fluid and play an essential role in protecting fetal growth and development in the pregnant uterus. The extracellular matrix, substrate for plasminogen activators (PAs), is an important supportive framework of the fetal membranes. Fetal membranes from women with preterm premature rupture of membranes may differ in their protease activity compared with normal membranes. To identify the presence of PAs and their inhibitors (PAI) and their possible role in the process of fetal membrane rupture, this study investigated the distribution and localization of both protein and mRNA for tissue (t) and urokinase (u) PA and their inhibitors type 1 (PAI-1) and type 2 (PAI-2) in amniochorion of human and rhesus monkey using conventional and confocal immunofluorescence microscopy. In situ hybridization analysis showed that the distribution and localization of mRNAs for tPA, uPA, PAI-1 and PAI-2 were similar in the fetal membranes of human and rhesus monkey; no obvious species difference was observed. Evidence of tPA mRNA was detected in amniotic epithelium, trophoblast cells and nearly all cells of the decidual layer. Strong expression of uPA mRNA was noted in the decidual cells which increased in intensity as the abscission point was approached. Weak staining in chorion laeve trophoblast was also detected. In situ hybridization experiments showed PAI-1 mRNA to be concentrated mainly in the decidual cells, some of which were interposed into the maternal-facing edge of the chorion laeve. Maximal labelling of the decidua occurred towards the zone of abscission. Weak expression of PAI-1 mRNA was also noted in some cells of the chorion laeve. The distribution of PAI-2 mRNA in amniochorion was also concentrated in the cells of the decidual layer, maximum expression of the mRNA was in the level of abscission. No detectable amount of mRNAs for tPA, uPA, PAI-1 and PAI-2 was found in the fibroblast, reticular and spongy layers. Distribution of the proteins of tPA, uPA and PAI-1 in the fetal membranes of these two species was consistent with the distribution of their mRNA. Anti-PAI-2 immunofluorescence was found to be strongly concentrated in the amniotic epithelium, but PAI-2 mRNA was negative in this layer, suggesting that the epithelium-associated PAI-2 is not of epithelial origin. These findings suggest that a local fibrinolysis in fetal membranes generated by precisely balanced expression of PAs and their inhibitors via paracrine or autocrine mechanisms may play an essential role in fetal membrane development, maturation and in membrane rupture. Following an analysis of the distribution and synthesis of activators and inhibitors it was found that they may play a role in abscission during the third stage of labour.

Intracellular polymerization of the serpin plasminogen activator inhibitor type 2

Plasminogen activator inhibitor type 2 (PAI-2) is synthesized in two molecular forms: an intracellular, nonglycosylated form and an extracellular, glycosylated form. The bitopological distribution of PAI-2 is caused by an inefficient internal secretion signal. In addition, the secretion efficiency of PAI-2 seems to differ, depending on the cell type, differentiation state, and culture conditions. In recombinant cell clones designed for the synthesis of the secreted form of PAI-2, the fraction of secreted PAI-2 decreased with increasing expression levels. Subcellular fractionation of cell clones with higher expression levels revealed that PAI-2 accumulating in the cell was mainly associated with the organelles of the secretory pathway. Electrophoresis under nondenaturating conditions revealed that the PAI-2 retained at higher expression levels was mainly polymerized. Polymers of PAI-2 were also detected in cytosolic extracts prepared from human placenta and phorbol ester-stimulated U 937 cells, indicating that intracellular polymerization of PAI-2 may occur in the cytosols of cells that normally express PAI-2 under physiological conditions. When purified PAI-2 or cellular extracts were incubated at 37 degrees C for 24 h most of the PAI-2 protein was found to polymerize. Polymer formation was prevented by the addition of synthetic peptides with sequences corresponding to residues P2 to P14 in the reactive center loop of PAI-2 and antithrombin. These synthetic peptides also caused dissociation of prepolymerized purified PAI-2 and PAI-2 polymers in cellular extracts. Incubation with unrelated peptides of the same size had no effect on polymer formation or dissociation of preformed polymers, indicating that polymerization of PAI-2 occurs by the loop-sheet mechanism. Taken together, our data suggest that the wild-type form of PAI-2, like some natural pathological genetic variants of alpha1-antitrypsin, antithrombin, and C1 inhibitor readily polymerizes intracellularly and that polymerization may lead to a reduced secretion efficiency.

Prostaglandin E2 regulates production of plasminogen activator isoenzymes, urokinase receptor, and plasminogen activator inhibitor-1 in primary cultures of rat calvarial osteoblasts

The bone resorbing agent, prostaglandin E2 (PGE2), was found to alter several components of the plasminogen activator (PA)/plasmin pathway in primary cultures of rat neonatal osteoblast-like cells. The mRNA and activities of both urokinase-type PA (uPA) and tissue-type PA (tPA) were enhanced by PGE2 treatment. The presence of mRNA for the uPA receptor (uPAR) has been demonstrated in these cells and steady-state levels shown to be greatly enhanced, the response being rapid and sustained for at least 24 hours. mRNA for plasminogen activator inhibitor 1 (PAI-1) was modulated in a biphasic manner, with inhibition of the constitutive level apparent at 4 hours of treatment and stimulation apparent at 12 hours and longer, while PAI-1 protein, measured by an ELISA assay for rat PAI-1, was diminished over this period. Neither PAI-2 mRNA nor mRNA for the broad spectrum protease inhibitor, protease nexin-1 (PN-1), was found to be modulated by PGE2. Therefore, PGE2 is likely to stimulate cell surface proteolytic activity, since uPA mRNA and cell-associated activity were elevated, as was mRNA for the cellular receptor for uPA. Although it was not possible to measure uPAR number and affinity it seems likely that elevated uPAR mRNA would translate into increased uPARs which would localize the increased uPA activity to the pericellular region. tPA mRNA and activity were also increased transiently with the activity inhibited with prolonged incubations, apparently by PAI-1. Elevation of tPA mRNA and activity may result in elevated activity within the extracellular matrix as tPA has been reported to associate with several matrix proteins. Thus the early effect of PGE2 would be to promote proteolysis, both pericellularly and in the extracellular matrix. The inhibition of PAI-1 mRNA and protein, which would contribute to the elevation of activity, is due to PGE2, but the later stimulatory effect on PAI-1 mRNA may be due to feedback regulation by transforming growth factor beta (TGF beta), secreted by osteoblasts and activated by elevated levels of PA.

Cathepsin D-like aspartyl protease activity mediates the degradation of tissue-type plasminogen activator/plasminogen activator inhibitor-1 complexes in human monocytes

Plasminogen activator inhibitor-1 (PAI-1) is the most important inhibitor of tissue-type plasminogen activator (t-PA) in plasma and plays a major role in the regulation of fibrinolysis. Plasma t-PA/PAI-1 complexes are cleared via a receptor-dependent mechanism in hepatocytes, while the fate of complexes formed in the extracellular matrix and in thrombi is less well understood. In this study, the degradation of t-PA/PAI-1 complexes by monocytes was examined. THP-1 monocytoid cells and freshly isolated human monocytes internalize and degrade [125I]t-PA/PAI-1 complexes at rates of 11.4 +/- 5.9 (mean +/- S.D.) and 44.6 +/- 6.3 ng/10(6) cells/h, respectively. Degradation is blocked by receptor-associated protein (RAP), indicating a member of the low density lipoprotein (LDL) receptor family is involved in the uptake/degradation of t-PA/PAI-1 complexes by monocytes. Degradation of t-PA/PAI-1 complexes is also inhibited by chloroquine and by pepstatin A, suggesting that a lysosomal aspartyl protease is likely involved. SDS-PAGE and Western blotting demonstrated that the purified lysosomal aspartyl protease, cathepsin D, is capable of digesting t-PA (t1/2 15 min), active PAI-1 (t1/2 2 h), and t-PA/PAI-1 complex (t1/2 30 min). Cathepsin D sequentially cleaves PAI-1 after hydrophobic amino acids, yielding lower molecular weight fragments. PAI-1 conformation influences the degradative efficiency of cathepsin D, with vitronectin-bound PAI-1 and latent PAI-1 exhibiting resistance to proteolysis and > 10-fold prolongation in t1/2. These data provide evidence that t-PA/PAI-1 complexes are internalized by human monocytes via a member of the low density lipoprotein (LDL) receptor family, and identifies cathepsin D-like aspartyl protease activity as largely responsible for the degradation of these complexes. Furthermore, vitronectin-bound PAI-1 and latent PAI-1 are relatively resistant to degradation by cathepsin D, which may be of importance in complex physiological environments.

Pathophysiology of fibrinolysis

The observed association between abnormal fibrinolysis and a tendency toward bleeding or thrombosis demonstrates the (patho)physiological importance of the fibrinolytic system. Deficient fibrinolysis represents an important haemostatic abnormality associated with thrombosis. A decreased fibrinolytic activity may be due to a defective synthesis and/or release of tissue-type plasminogen activator (t-PA) from the vessel wall, to a deficiency or functional defect in the plasminogen or fibrinogen molecule or more frequently to increased levels of t-PA inhibitor. Alternatively, excessive fibrinolysis due to increased levels of t-PA, to alpha 2-antiplasmin deficiency or to plasminogen activator inhibitor-1 (PAI-1) deficiency, may result in bleeding tendency.

Plasminogen activators and plasminogen activator inhibitors: biochemical aspects

Although this chapter does not represent a historical review, it will be clear how the biochemistry of t-PA, u-PA, PAI-1 and PAI-2 has evolved and where we stand in 1994. While the functional activities of the proteins were recognized at least three to four decades ago, highly purified preparations became available around 1980. In the mid-eighties the cDNAs of the proteins were cloned, representing a major breakthrough in the biochemistry of the four proteins. Amino acid sequences were derived from the nucleotide sequences, homologies with other proteins were recognized and larger amounts of (recombinant) proteins became available for research. In addition, mutant proteins were prepared by recombinant DNA technology, enabling investigation of structure-function relationships. This report is mainly based on the latter studies. Detailed information about three-dimensional structures of the proteins and the mode of interaction with other macromolecules is still lacking. To obtain this information will be the goal for biochemists in the coming years.

A qualitative and quantitative protein database approach identifies individual and groups of functionally related proteins that are differentially regulated in simian virus 40 (SV40) transformed human keratinocytes: an overview of the functional changes associated with the transformed phenotype

A qualitative and quantitative two-dimensional (2-D) gel database approach has been used to identify individual and groups of proteins that are differentially regulated in simian virus 40 (SV40) transformed human keratinocytes (K14). Five hundred and sixty [35S]methionine-labeled proteins (462 isoelectric focusing, IEF; 98 nonequilibrium pH gradient electrophoresis, NEPHGE), out of the 3038 recorded in the master keratinocyte database, were excised from dry, silver-stained gels of normal proliferating primary keratinocytes and K14 cells and the radioactivity was determined by liquid scintillation counting. Two hundred and thirty five proteins were found to be either up- (177) or down-regulated (58) in the transformed cells by 50% or more, and of these, 115 corresponded to known proteins in the keratinocyte database (J.E. Celis et al., Electrophoresis 1993, 14, 1091-1198). The lowest abundance acidic protein quantitated was present in about 60,000 molecules per cell, assuming a value of 10(8) molecules per cell for total actin. The results identified individual, and groups of functionally related proteins that are differentially regulated in K14 keratinocytes and that play a role in a variety of cellular activities that include general metabolism, the cytoskeleton, DNA replication and cell proliferation, transcription and translation, protein folding, assembly, repair and turnover, membrane traffic, signal transduction, and differentiation. In addition, the results revealed several transformation sensitive proteins of unknown identity in the database as well as known proteins of yet undefined functions. Within the latter group, members of the S100 protein family--whose genes are clustered on human chromosome 1q21--were among the highest down-regulated proteins in K14 keratinocytes. Visual inspection of films exposed for different periods of time revealed only one new protein in the transformed K14 keratinocytes and this corresponded to keratin 18, a cytokeratin expressed mainly by simple epithelia. Besides providing with the first global overview of the functional changes associated with the transformed phenotype of human keratinocytes, the data strengthened previous evidence indicating that transformation results in the abnormal expression of normal genes rather than in the expression of new ones.

Microglia express the type 2 plasminogen activator inhibitor in the brain of control subjects and patients with Alzheimer's disease

Localization of type 2 plasminogen activator inhibitor (PAI-2) was investigated immunohistochemically in postmortem brain tissue of control subjects and patients with Alzheimer's disease (AD). Both the mouse monoclonal and the goat polyclonal antibodies to PAI-2 stained microglia. Reactive microglia were stained more intensely than resting microglia. PAI-2 may regulate the plasminogen activators and plasmin system in lesions of AD. It is suggested that PAI-2 plays a role for cell migration and matrix breakdown as well as for aberrant neurite outgrowth in senile plaques where persistent microglial activation is observed.

Plasminogen-activator inhibitor type 2 (PAI-2) is a spontaneously polymerising SERPIN. Biochemical characterisation of the recombinant intracellular and extracellular forms

Plasminogen-activator inhibitor type 2 (PAI-2) is a specific inhibitor of plasminogen activators (PA) that exists in an intracellular, low-molecular-mass form and a secreted, high-molecular-mass form that varies with respect to glycosylation. Here we have developed expression systems for both forms of PAI-2 and biochemically characterised the purified proteins. In order to obtain efficient secretion, we constructed an artificial signal sequence and fused it to the coding region of PAI-2. With this construct, more than 90% of PAI-2 was secreted as a glycosylated, 60-kDa molecular-mass form, but the level of expression was low and unstable. To obtain higher expression of secreted PAI-2, a novel expression vector based on the Semliki-forest-virus replicon was used. Secreted PAI-2 was purified to homogeneity and N-terminal sequence analysis showed that the artificial signal peptide was correctly removed. The intracellular, non-glycosylated form of PAI-2 was expressed in Escherichia coli and purified to homogeneity. Both the secreted and the intracellular forms of PAI-2 were found to inhibit plasminogen activators by forming SDS-resistant complexes and the second-order rate constants were similar for both forms, ranging over 2.4-2.7 x 10(6) M-1s-1 for urokinase-type PA, 2.5-2.7 x 10(5) M-1s-1 for two-chain tissue-type PA and 0.8-1.2 x 10(4) M-1s-1 for single-chain tissue-type PA. None of the purified PAI-2 forms bound to vitronectin. Circular-dichroism spectral analysis revealed that PAI-2 has a CD spectrum that resembles ovalbumin more than PA-inhibitor type 1, confirming the greater similarity between these two members of the serine-protease inhibitor family. Similar to what has been described for the Z-form of alpha 1-antitrypsin, purified PAI-2 was found to spontaneously form polymers during incubation at room temperature. Attempts to convert PAI-2 to a stable locked conformation resembling the conformation of latent PAI-1 by treatment with diluted guanidinium chloride were unsuccessful. Instead, this treatment enhanced the formation of PAI-2 polymers, possibly by the loop-sheet polymerisation mechanism described for alpha 1-antitrypsin.

Inhibition of the effects of rheumatoid synovial fluid cells on chondrogenesis and cartilage breakdown in vitro: possible therapeutical conclusions. A morphological--biochemical study

Short-term co-cultivation of blastemal cells from 12-day-old mouse limb buds and human rheumatoid synovial fluid cells in high density cultures (Trowell culture system) resulted, depending on when co-cultivation started, either in (1) an inhibition of chondrogenesis (co-cultivation right from the start) or in (2) an extensive breakdown of cartilaginous matrix (co-cultivation after formation of embryonic cartilage). These synovial effects were markedly impeded if Avarol (a dioxygenase inhibitor) was applied singly or in combination with PAI-2 (a u-PA-inhibitor). PAI-2 alone, however, had no effect on the synovial-induced inhibition of chondrogenesis, but produced a pronounced inhibitory effect on matrix breakdown. The effects of both inhibitors were studied electron microscopically and biochemically (determination of sulfated-glycosaminoglycans in the high density cultures by Alcian Blue binding assay). The results of this study are consistent with the presumption that rheumatoid synovial cells are capable of inhibiting chondrogenesis and enhancing the breakdown of the cartilaginous matrix. Amongst others, the possible mediators involved are prostaglandins and plasminogen activators. The response to the inhibitors Avarol and PAI-2 is compatible with their mode of action. The chondroprotective action of these substances may be useful in developing potential antirheumatic drugs.

Processing of complex between urokinase and its type-2 inhibitor on the cell surface. A possible regulatory mechanism of urokinase activity

Complexes between the urokinase-type plasminogen activator (uPA) and its type-2 inhibitor (PAI-2) are bound by a cell-surface receptor for uPA and rapidly cleaved into two fragments of 70 and 22 kDa. The 70-kDa fragment contains the active site of uPA and PAI-2, while the 22-kDa species was identified as the amino terminal fragment of uPA, that binds specifically to the receptor. When the experiment is performed at 4 degrees C, both fragments remain bound to the cell surface and can be eluted by acid treatment. We therefore postulate that after the binding of the uPA-PAI-2 complex, a new binding site for the 70-kDa species becomes available. This additional binding favours the cleavage of the complex into the 70-and 22-kDa fragments; the 70-kDa species is endocytosed or released, while the 22-kDa fragment remains on the cell surface to prevent the binding of intact uPA.

Plasminogen activators and their inhibitors in leukemic cell homogenates

Plasminogen activator (PA) and PA inhibitor (PAI) were measured in homogenates of leukemia cells. Both PA and PAI levels were higher in non-lymphoblastic leukemia than in lymphoblastic leukemia. The levels were below the sensitivity of determination in chronic myelocytic leukemia (CML) but showed significant increases in blast crisis (CML,bc). The level of the tissue type PA (t-PA) antigen was highest in acute myeloblastic leukemia (AML) and that of the urokinase type PA (u-PA) was highest in acute promyelocytic leukemia (APL). The PAI-I antigen showed no marked cell specificity, but the PAI-II antigen was markedly increased in myelomonocytic leukemia and acute monocytic leukemia (AMoL). From these findings, various PAs and PAIs are considered to be present in leukemia cells and to be involved in hemostatic disorders, thus they are of diagnostic value in leukemia.

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.

Occupancy of the cancer cell urokinase receptor (uPAR): effects of acid elution and exogenous uPA on cell surface urokinase (uPA)

The development of a simple, sensitive fluorimetric assay for the measurement of cell surface-associated urokinase plasminogen activator (uPA) on viable, adherent HCT116 cells in microtitre plates, after a preincubation with purified human plasminogen is described. The assay determines plasmin activity by the cleavage of H-D-Val-Leu-Lys 4-aminomethyl coumarin under near physiological pH and ionic conditions with a sensitivity in the range of 5-100 mIU uPA/well at excitation 355 nm and emission 460 nm. Plasmin generated during the assay converted all cell-surface sc-uPA to tc-uPA, allowing the determination of total uPA activity. Inhibitor studies (PAI-2, amiloride or Glu-Gly-Arg chloromethylketone) confirmed the specificity of the uPA assay. Removal of these agents prior to assay allowed determination of the cell surface sc-uPA:tc-uPA ratio. Cell surface activity was only partially removed by acid elution. This corresponded with the loss of a number of proteins and uPA-containing species as detected by SDS-PAGE, gelatin enzymography and Western blotting. Although the major protein species eluted had a M(r) of 55 kDa, reacted with a commercial anti-human uPA mAb and correlated with the main lytic zone, other higher M(r) species were also eluted from HCT116 cells. Exogenous uPA increased cell-surface activity markedly on cells previously treated with acid. Following acid elution, cell surface uPA activity was restored after 30h in culture suggesting either de novo synthesis or release of pre-formed uPA with subsequent secretion and binding to uPAR. The assay has enabled studies on adherent cells to address questions about the regulation and expression of cell-surface uPA.

Synergistic stimulating effect between cyclic AMP and phorbol ester on plasminogen activator inhibitor type 2 production in human promyelocytic leukemia cell line PL-21

We investigated the effect of agents which raise intracellular cyclic AMP (cAMP) and protein kinase C activators on the production of plasminogen activator inhibitor type-2 (PAI-2) by cultured human promyelocytic leukemia cell line, PL-21. As previously reported, PMA, a protein kinase C activator, showed a strong stimulating effect on the PAI-2 production. 1-oleoyl-2-acetyl-sn-glycerol (OAG), another synthetic protein kinase C activator, also showed a stimulating effect, which was, however, much less than that of PMA. The agents which raise intracellular cAMP, dibutyryl cAMP, 8-bromo cAMP, prostaglandin E1, and 3-isobutyl-1-methyl-xanthine, little increased the PAI-2 production when tested alone, but showed significant synergistic effects with PMA or OAG. The synergistic effect between PMA and dibutyryl cAMP was further verified by SDS-PAGE followed by immunoblotting using a monoclonal antibody against the PAI-2. It is interesting that the up-regulation of PAI-2 by cAMP and the synergistic effect with PKC activators forms a contrast to the previous reported bi-directional regulation of endothelial PAI-1 secretion by PKC activator and cAMP.

Possible role of plasminogen activator inhibitor 2 in the prevention of the metastasis of gastric cancer tissues

The concentrations of urinary type plasminogen activator (u-PA), plasminogen activator inhibitor 1 (PAI-1), and PAI-2 were measured in gastric cancer tissues and adjacent healthy mucosal tissues. Levels of u-PA, PAI-1 and PAI-2 were higher in cancer than in control tissues. PAI-1 levels were higher together with the progression of cancer however there were no differences in u-PA or PAI-2 levels. Tumors with higher PAI-1 and lower PAI-2 levels tend to metastasize to remote lymph nodes. When the numbers of involved lymph nodes were analyzed, tumors with the large number of metastatic lymph nodes showed higher PAI-1 and lower PAI-2 level. No difference was shown in u-PA levels among these groups. These tendencies were more significant in patients with progressed gastric cancer. These results suggest that tumor with higher PAI-2 levels tend to localize or have less tendency to metastasize to lymph nodes. On the other hand PAI-1 was generally higher in tumor with invasion into nearby tissue or with nodal metastasis.

Purification and characterisation of plasminogen activator inhibitor 2 produced in Saccharomyces cerevisiae

Expression of plasminogen activator inhibitor 2 (PAI-2) under the control of the protease B gene promoter in a mutant strain of Saccharomyces cerevisiae, DS569, resulted in its accumulation intracellularly at up to 20% of the soluble cell protein. Provision of an N-terminal signal sequence resulted in the secretion of a hyperglycosylated molecule. The intracellularly produced PAI-2 was purified by copper-chelate and anion-exchange chromatography to greater than 95% pure and was fully active. The recombinant PAI-2 formed SDS-stable complexes with urokinase and tissue-type plasminogen activator and inhibited the proteases with similar reaction kinetics to placental PAI-2 (second-order rate constant for uPA, 2.4 x 10(6) M-1 s-1, and for two-chain tPA, 0.7 x 10(5) M-1 s-1). As is the case for placental PAI-2, the N-terminus of the yeast-derived recombinant PAI-2 was blocked. The high productivity and consequent ease of purification mean that S. cerevisiae provides an excellent source of recombinant PAI-2 for investigation of its therapeutic potential in the treatment of neoplastic and inflammatory diseases.