Detection of both type 1 and type 2 plasminogen activator inhibitors in human cells

PCR-RFLP Detection of PAI-2 Variants in Myocardial Infarction

PAI-2 is one of the regulators of the fibrinolytic system. The importance of the fibrinolytic cascades in the pathogenesis of myocardial infarction has been demonstrated by many investigators. Recently, some investigators have shown that two variants of PAI-2, designated A and B, are associated with the formation of large molecular PAI-2 complexes. This polymorphism is therefore present a genetic predisposition for the development of coronary artery disease and multiple sclerosis. Therefore, the prevalence of this polymorphism among 45 patients with MI and 20 control subjects was investigated. The AA genotype of the PAI-2 gene was found to be more frequent among those subjects with MI. These data provide evidence that a polymorphism of the PAI-2 gene is associated with an increased risk of MI.

Co-localization of fibrinolytic activators and inhibitors with macrophages in atherosclerotic vessels

The plasmin system is involved in hemostasis and tissue remodelling. The accumulation of plasminogen activators and their inhibitors in atherosclerotic lesions may be due to invasion of inflammatory cells in the vessel wall. High concentrations of macrophages are associated with increased risk of atherosclerotic plaque rupture. By immunohistochemistry on circumferential serial sections of atherosclerotic and healthy vessels the morphological association of plasminogen activators and inhibitors with macrophages was studied. Urokinase plasminogen activator (u-PA), plasminogen activator inhibitor type 2 (PAI-2), and macrophages were mainly expressed within plaques while tissue plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAI-1) were also expressed outside plaque lesions. Computer assisted image analysis on diseased vessels showed that regulatory proteins of the fibrinolytic system were found more often in areas positive for macrophages than in other parts of the sections (p < 0.001). u-PA was significantly more defined to areas positive for macrophages than tissue plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAI-1) (p < 0.05). Similarly, PAI-2 expression was more associated with macrophage distribution than PAI-1 (p < 0.05). Tumor necrosis factor α (TNFα), an inflammatoric mediator of macrophages, had the same levels of co-localization with macrophages as u-PA and PAI-2. These results suggest that u-PA and PAI-2 might be key factors for inflammatory regulation of plasmin mediated proteolysis in the vessel walls.

Tumor cell-expressed SerpinB2 is present on microparticles and inhibits metastasis

Expression of SerpinB2 (plasminogen activator inhibitor type 2/PAI-2) by certain cancers is associated with a favorable prognosis. Although tumor-associated host tissues can express SerpinB2, no significant differences in the growth of a panel of different tumors in SerpinB2(-/-) and SerpinB2(+/+) mice were observed. SerpinB2 expression by cancer cells (via lentiviral transduction) also had no significant effect on the growth of panel of mouse and human tumor lines in vivo or in vitro. SerpinB2 expression by cancer cells did, however, significantly reduce the number of metastases in a B16 metastasis model. SerpinB2-expressing B16 cells also showed reduced migration and increased length of invadopodia-like structures, supporting the classical view that that tumor-derived SerpinB2 is inhibiting extracellular urokinase. Importantly, although SerpinB2 is usually poorly secreted, we found that SerpinB2 effectively reaches the extracellular milieu on the surface of 0.5-1 μm microparticles (MPs), where it was able to inhibit urokinase. We also provide evidence that annexins mediate the binding of SerpinB2 to phosphatidylserine, a lipid characteristically exposed on the surface of MPs. The presence of SerpinB2 on the surface of MPs provides a physiological mechanism whereby cancer cell SerpinB2 can reach the extracellular milieu and access urokinase plasminogen activator (uPA). This may then lead to inhibition of metastasis and a favorable prognosis.

Cytokines and Growth Factors in Implantation

Implantation failure is the most important rate limiting factor in the success of assisted reproductive techniques like In vitro fertilization–embryo transfer (IVF-ET). Cytokines are multifunctional signaling molecules having an implicit role in the human implantation process. This review focuses on the redundant roles of cytokines during the various stages of implantation. It also indicates that levels of cytokines in biological fluids like serum and follicular fluid obtained during oocyte retrieval might act as determinants of implantation potential of the blastocyst. Thus a holistic, metabolomic approach of analyzing biological fluids may provide a simpler approach to study the hitherto enigmatic process rather than the proteomic and genomic approach.

Human papilloma virus transformed CaSki cells constitutively express high levels of functional SerpinB2

Many malignant tissues, including human papilloma virus (HPV)-associated cancers, express SerpinB2, also known as plasminogen activator inhibitor type-2 (PAI-2). Whether SerpinB2 is expressed by the HPV-transformed cancer cells, and if so, whether SerpinB2 is mutated or behaves aberrantly remains unclear. Here we show that HPV-transformed CaSki cells express high levels of constitutive wild-type SerpinB2, with cellular distribution, glycosylation, secretion, cleavage, induction and urokinase binding similar to that reported for primary cells. Neutralization of secreted SerpinB2 failed to affect CaSki cell migration or growth. Lentivirus-based over-expression of SerpinB2 also had no effect on growth, and we were unable to confirm a role for SerpinB2 in binding or regulating expression of the retinoblastoma protein. CaSki cells thus emerge as a useful tool for studying SerpinB2, with the physiological function of SerpinB2 expression by tumor cells remaining controversial. Using CaSki cells as a source of endogenous SerpinB2, we confirmed that SerpinB2 efficiently binds the proteasomal subunit member β1.

Cytokine regulation during the formation of the fetal-maternal interface: focus on cell-cell adhesion and remodelling of the extra-cellular matrix

The establishment of human pregnancy requires the orchestration of substantial cell differentiation and tissue remodelling processes in the context of a complex dialogue between the receptive endometrium and the implanting blastocyst, and is therefore dependent upon a complex sequence of signalling events. Cytokines play an important role in each step of implantation, modulating expression of adhesion molecules on both the fetal and maternal surfaces, regulating expression of the proteases that remodel the extra-cellular matrix, and promoting invasion and differentiation of trophoblasts. Here we review the role of cytokines in regulating the establishment of the fetal-maternal interface, with a particular focus on regulation of the functional expression of CAMs, the ECM and of the proteinases that modulate their function.

Nafamostat Attenuated the Impairment of Fibrinolysis in Animal Sepsis Model by Suppressing the Increase of Plasminogen Activator Inhibitor Type 1

BACKGROUND

In endotoxemia, plasminogen activator inhibitor-1 (PAI-1) increases and develops clinical symptoms by suppressing fibrinolysis. We analyzed therapeutic advantage of nafamostat, a broad-range protease inhibitor, on fibrinolysis in an animal sepsis model.

METHODS

Male Wister rats infused with lipopolysaccharide (LPS) (50 mg/kg) alone or together with nafamostat (0.1 mg/kg/hr) for 4 hours were analyzed.

RESULTS

Plasma PAI-1 (4.2: 4.0-5.0 ng/mL, median and interquartile range) increased after LPS infusion (3700: 3400-4000), which was attenuated by nafamostat (2300: 2100-2600, p < 0.05). Fibrin(ogen) degradation products after LPS injection (173: 152-182 microg/mL) were further elevated by nafamostat (205: 205-228, p < 0.05), Nafamostat attenuated polymorphonuclear neutrophils infiltration in the liver, and tended to suppress plasma tumor necrosis factor-alpha levels. Nafamostat did not affect thrombin generation, platelet count, markers of liver and kidney function, and overall mortality.

CONCLUSIONS

Nafamostat appeared to improve impaired fibrinolysis by suppressing the increase of PAI-1 in plasma, though it did not largely improve clinical parameters.

Influence of monocyte-like cells on the fibrinolytic activity of peritoneal mesothelial cells and the effect of sodium hyaluronate

OBJECTIVE

To determine whether the presence of cells of the monocyte-macrophage system affects the fibrinolytic response of peritoneal mesothelial cells to lipopolysaccharide (LPS) in the presence and absence of sodium hyaluronate.

DESIGN

Controlled laboratory experiment.

SETTING

Cell cultures in an academic laboratory research environment.

PATIENT(S)

Human peritoneal mesothelial cells were harvested from patients undergoing a laparotomy for noninfectious reasons and were cultured in vitro. Co-cultures were formed by adding U-937 human monocyte-like cells to a monolayer of mesothelial cells.

INTERVENTION(S)

After 24 hours, cultures were treated with 10 ng/mL of LPS, and sodium hyaluronate was added in a final concentration of 0.2%. Controls received medium without sodium hyaluronate.

MAIN OUTCOME MEASURE(S)

After 24 hours' incubation, tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), and plasminogen activator inhibitor-1 (PAI-1) levels were determined in medium and cell lysates by using ELISA techniques.

RESULT(S)

In medium of co-cultures, tPA and PAI-1 concentrations were statistically significantly increased compared with the case of monocultures, whereas uPA concentration was statistically significantly decreased. In cell lysates of co-cultures, PAI-1 concentration was statistically significantly increased compared with the case of monocultures, whereas tPA and uPA were unaffected. Treatment with sodium hyaluronate statistically significantly decreased PAI-1 and uPA concentrations in medium of monocultures but decreased uPA concentration only in medium of co-cultures, compared with the case of controls.

CONCLUSION(S)

Cells of the monocyte-macrophage system modulate the fibrinolytic capacity of LPS treated human peritoneal mesothelial cells and interfere in the hyaluronan-associated changes in mesothelial fibrinolytic capacity.

Plasminogen activator inhibitor type 2 (PAI-2) is present in normal human conjunctiva

The purpose was to characterize plasminogen activator inhibitor type 2 (PAI-2) expression in normal human conjunctiva in vivo and in vitro. PAI-2 antigen was assayed by immunostaining and immunoblotting of extracts from normal human conjunctival epithelial lysates and conditioned media (CM) of cultured human conjunctival keratinocytes. Immunostaining of normal human conjunctival epithelia revealed that PAI-2 was found consistently in the superficial keratinocytes and, in some biopsies, also in the lower keratinocyte layers. In all cases, PAI-2 was concentrated around the cell periphery. In extracts of conjunctival epithelia and cultured conjunctival keratinocytes, PAI-2 had an apparent molecular weight of 45 kDa, consistent with the non-glycosylated form. The majority of PAI-2, approximately 90%, was cell associated, however, a small percentage of PAI-2 was released into the CM in a linear manner with time. PAI-2 in the conditioned medium had a higher molecular weight, consistent with a glycosylated form. Conjunctival PAI-2 was active, as shown by its ability to complex with a target enzyme, urokinase plasminogen activator (uPA). Although PAI-2 was detectable both in monolayer (i.e., relatively undifferentiated) conjunctival keratinocyte cultures as well as in stratified (i.e., more differentiated) cultures, steady state levels of PAI-2 were greater in the latter. PAI-2 is constitutively expressed by normal human conjunctival epithelial cells. The expression of PAI-2 throughout all epithelial layers in some biopsies of conjunctiva in vivo contrasts with the previously established distribution of PAI-2 in corneal epithelia, where it is present exclusively in the most superficial (i.e. most highly differentiated) cells. The role of PAI-2 in either tissue is unclear. However, we speculate that its distinct distribution in conjunctival versus corneal epithelia underscores inherent differences between these tissues, and may reflect specific functions of this proteinase inhibitor in both conjunctival and corneal epithelial cells.

Alterations in endothelial cell proteinase and inhibitor polarized secretion following treatment with interleukin-1, phorbol ester, and human melanoma cell conditioned medium

Polarized secretion of matrix metalloproteinases and plasminogen activators by monkey aortic endothelial cells was studied in vitro, using transwell inserts. The endothelial cells constitutively expressed matrix metalloproteinase-2, tissue inhibitors of metalloproteinases 1 and 2, urokinase, and tissue plasminogen activator, all with basal preference. Matrix metalloproteinase-9 activity was induced by phorbol 12-myristate 13-acetate (apical), interleukin-1 alpha (basal), and by conditioned medium from DX3 human melanoma cells (basal). The DX3 melanoma conditioned medium also stimulated basal secretion of matrix metalloproteinase-2, urokinase, tissue plasminogen activator, and tissue inhibitors of metalloproteinases. The rise in proteolytic activity in the basal direction was reflected by increased capacity to degrade subendothelial basement membrane type IV collagen, shown immunohistologically, using monkey kidney tissue sections and basement membrane deposited by endothelial cells into the transwell membrane. Thus, IL-1 alpha and DX3 melanoma conditioned medium can stimulate endothelial cells in vitro to concentrate secretion of proteinases spatially onto the underlying basement membrane. We suggest that the stimulation of endothelial cell proteinase activity by tumor cells may facilitate tumor cell extravasation.

Retinoic acid enhances plasminogen activation on the cell surface

The importance of cell-associated plasminogen activation in the extracellular matrix degradation processes is becoming increasingly evident. To elucidate the modulators of net plasminogen activation on the cell surface, we have recently established an assay system. Using this system, we examined the effects of several candidate modulators on cell surface plasminogen activator in the human fibrosarcoma cell line HT-1080 and the SV40-transformed human lung fibroblast cell line WI-38 VA 13 2RA. Although the majority of the candidates had no effect or a selective effect on either cell line, only retinoic acid markedly enhanced cell surface plasminogen activator activity in both HT-1080 and WI-38 VA13 2RA cells in a time-dependent manner. The effect of retinoic acid was neutralized by actinomycin D. The enhanced activity was inhibited by anti-uPA IgG and by pretreatment with phosphatidylinositol-specific phospholipase C. These findings suggest that retinoic acid increases the amount of receptor-bound uPA via de novo synthesis, and that it plays an important role in modulating cell-associated plasminogen activation.

Plasminogen activator inhibitor-2 expression in inflamed appendix

Plasminogen activator inhibitors are thought to be responsible for the abolition of fibrinolytic activity in inflamed peritoneum. This reduction in the fibrin clearing capacity of the peritoneum promotes the formation of intra-abdominal adhesions. High concentrations of plasminogen activator inhibitor-2 (PAI-2) have been previously found in inflamed peritoneal tissue using immunoassays, but it is undetectable in normal peritoneum. The aim of this study was to localize plasminogen activator inhibitor-2 production in tissue by in situ mRNA hybridisation. Sections of normal and inflamed human appendix were hybridised with a digoxigenin labelled cDNA probe. In normal appendix staining was confined to macrophages in the mucosa. Macrophage staining was also seen in inflamed tissue but with a wider distribution throughout the appendix wall. PAI-2 was also localized to mesothelial cells of inflamed but not normal appendix. Cell identities were confirmed using immunohistochemistry directed against cell specific markers. Staining was absent from control slides incubated with plasmid DNA or PAI-2 probe following ribonuclease digestion. The identification of the cells expressing the PAI-2 gene in peritoneum increases our understanding of the pathophysiological process leading to fibrin deposition within the abdomen during peritonitis.

Gene regulation of interleukin-1 beta, interleukin-1 receptor type I, and plasminogen activator inhibitor-1 and -2 in human granulosa-luteal cells

OBJECTIVE

To investigate the regulation of messenger ribonucleic acid (mRNA) levels of interleukin-1 beta (IL-1 beta), interleukin-1 (IL-1) receptor type 1, and plasminogen activator (PA) inhibitor-1 and -2 in cumulus cells, granulosa-luteal cells, and macrophage-depleted granulosa-luteal cells obtained from human preovulatory follicles.

DESIGN

Prospective longitudinal study.

SETTING, PATIENTS

Patients undergoing assisted reproductive technologies (ART) in the Department of Gynecology and Obstetrics, Stanford University, Stanford, California.

INTERVENTIONS

Cumulus cells and granulosa-luteal cells were collected by ultrasound-guided transvaginal aspiration at the time of ART.

MAIN OUTCOME MEASURES

Northern blot analysis of mRNA levels of IL-1 beta, IL-1 receptor type 1, PA inhibitor-1 and -2 in cumulus cells, granulosa-luteal cells and macrophage-depleted granulosa-luteal cells, and indirect immunocytochemical analysis of the IL-1 system and macrophages in granulosa-luteal cell preparations were performed.

RESULTS

Interleukin-1 beta mRNA levels in uncultured cumulus cells were less than those of uncultured granulosa-luteal cells with no differences in IL-1 receptor type 1 mRNA levels between these two cell types. Granulosa-luteal cell IL-1 receptor type 1 mRNA levels were expressed constitutively throughout 24 hours of culture with no effect by hCG, whereas IL-1 beta mRNA levels increased within 6 hours, and then remained elevated for 24 hours with no effect by hCG. Interleukin-1 beta significantly increased granulosa-luteal cell mRNA levels of IL-1 beta (over twofold), IL-1 receptor type 1 (over twofold), PA inhibitor-1 (approximately 1.4-fold), and PA inhibitor-2 (approximately 1.6-fold). In contrast, IL-1 beta had no effect on IL-1 beta and IL-1 receptor type 1 mRNA levels in macrophage-depleted granulosa-luteal cells. Granulosa-luteal cells, not macrophages, account for the majority of the immunocytochemical staining for IL-1 beta and IL-1 receptor type 1 in follicular aspirates.

CONCLUSIONS

These studies suggest that the IL-1 system is regulated in human granulosa-luteal cells during the periovulatory period. Furthermore, the augmentation of PA inhibitor-1 and -2 mRNA levels by IL-1 beta suggests a potential role for IL-1 beta in remodeling of the human ovary during the periovulatory period.

Cytokine modulation of plasminogen activator inhibitor-1 (PAI-1) production by human articular cartilage and chondrocytes. Down-regulation by tumor necrosis factor alpha and up-regulation by transforming growth factor-B basic fibroblast growth factor

Recombinant human cytokines were examined for their effects on plasminogen activator inhibitor-1 (PAI-1) production by human articular cartilage and chondrocyte monolayer cultures. Cartilage and chondrocytes were cultured with and without added cytokines and the conditioned media assayed for PAI-1 by a specific enzyme-linked immunosorbent assay, and mRNA levels determined by Northern blot analysis. Tumor necrosis factor alpha (TNF alpha) reduced, and transforming growth factor-beta (TGF-beta) and basic fibroblast growth factor (bFGF) increased, the levels of PAI-1 antigen and mRNA in the culture fluids and cell extracts, respectively. The effects of TNF alpha and TGF-beta on PAI-1 antigen levels were both time- and concentration-dependent; optimum doses being 10-100 pM TNF alpha and 0.4-0.8 nM TGF-beta, with each cytokine exerting its effect on PAI-1 antigen levels within 8 h of addition to culture. TNF alpha (and interleukin-1 alpha) also countered the effects of TGF-beta and bFGF. The anti-inflammatory drugs, indomethacin and dexamethasone, did not appear to modulate PAI-1 levels in cultures of cartilage tissue. The inhibition of PAI-1 levels by cytokines and reagents which stimulate cartilage resorption (i.e., TNF alpha, interleukin-1 alpha, retinoic acid) and enhancement by cytokines which counter it (i.e., TGF-beta, bFGF) further implicate plasminogen activator in the mechanism(s) of cartilage degradation in diseases such as arthritis.

Cytokine-mediated regulation of rat ovarian function: interleukin-1 inhibits plasminogen activator activity through the induction of plasminogen activator inhibitor-1 (PAI-1)

Intraovarian IL-1 has recently been implicated as a mediator in the ovulatory process. Since PA activation is an established component of the ovulatory cascade, consideration was given in this report to the possibility that IL-1 may modulate ovarian PA economy. Whole ovarian dispersates from immature rats (25-27-days-old) were cultured under serum-free conditions for 48 h in the absence or presence of IL-1beta. Cellular PA activity was measured by plasminogen-dependent cleavage of 14C-labeled globin. Cells grown in the absence of IL-1 exhibited appreciable PA activity, as assessed by the cleavage of 0.074 +/- 0.026 mg [14C]-globin/5 x 10(5) cells (mean +/- SD). Exposure to IL-1 (10 ng/ml) led to a 30% reduction in cell-associated PA activity (p < 0.001). The IL-1-mediated inhibition occurred concurrently with a 10-fold increase in the ability of the corresponding conditioned media to inhibit exogenous urokinase activity. At similar cell densities of 5 x 10(5) cells/well, isolated cultures of theca and granulosa cells exhibited comparable PA activity in the absence of IL-1. However, only theca cells responded to IL-1 with inhibition of plasminogen activation and enhancement of urokinase inhibitory activity. Granulosa cells in turn failed to respond to IL-1. Both the inhibition of PA activity and the increase in urokinase inhibitory activity proved cell-density- and IL-1 dose-dependent. The IL-1-induced inhibition of urokinase was abolished by the administration of a polyclonal anti-rat PAI-1 IgG. Both effects of IL-1 were counteracted in a dose-dependent fashion by the soluble IL-1 receptor (which specifically complexes with IL-1), and by a highly-specific IL-1 receptor antagonist suggesting that the IL-1 effects are receptor-mediated. The present observations indicate that ovarian PA activity is subject to inhibition by IL-1 probably by way of PAI-1 of theca-interstitial origin. Inasmuch as IL-1 may be involved in initiating and maintaining the preovulatory cascade, the periovulatory activation of plasminogen must be accomplished by agents other than IL-1.

Inhibition of tissue plasminogen activators and urokinase by human saliva

The fibrinolytic activity found in body fluids is mediated through the generation of plasmin from plasminogen by plasminogen activator. Mixed fresh human saliva was found to have plasminogen activator inhibitory activity that has not yet been characterized. In the present study, mixed fresh human saliva was found to contain an inhibitor for tissue plasminogen activator and for urokinase. The plasminogen activator inhibitory activity was mainly found in the mixed fresh human saliva cellular pellet containing buccal epithelial cells and not in the supernatant salivary fluid. Saliva collected by Stenson's duct cannulation does not have any PA-inhibitor activity, although saliva collected from submandibular glands contains small amounts of such activity. The salivary plasminogen activator inhibitor is unstable, and its activity is lost during storage.

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.

Plasminogen activator inhibitor 2 reduces peritoneal fibrinolytic activity in inflammation

Fibrinolysis in peritoneal tissue may play a role in the development of intra-abdominal adhesions. The plasminogen-activating capacity of human peritoneum results largely from the presence of tissue plasminogen activator (tPA). Inflammation reduces peritoneal plasminogen-activating activity and leads to the appearance of plasminogen activator inhibitor (PAI) type 1. The role of PAI-2 in the inhibition of peritoneal fibrinolysis during inflammation was investigated in this study. The plasminogen-activating activity of peritoneal biopsy homogenates (seven inflamed, seven normal), measured using a fibrin plate technique, was reduced in inflamed compared with normal tissue (median < 0.07 versus 13.9 units/cm2, P < 0.01); tPA antigen levels were not significantly different (median 1.02 versus 1.34 ng/ml). PAI-1 and PAI-2 antigens were not detected in normal human peritoneum but were present in inflamed peritoneum (median concentration 8.8 ng/ml for PAI-1, 26.7 ng/ml for PAI-2). These inhibitors may be important factors in adhesion formation by contributing to the abolition of peritoneal plasminogen-activating activity.

Independent regulation of plasminogen activator inhibitor 2 and plasminogen activator inhibitor 1 in human synovial fibroblasts

OBJECTIVE

To study the plasminogen activator inhibitor(s) (PAI) produced in vitro by human synovial fibroblast-like cells.

METHODS

Human synovial cell explant cultures were established using cells from nonrheumatoid donors. PAI-2 and PAI-1 antigens were measured by enzyme-linked immunosorbent assay, and messenger RNA (mRNA) levels were determined by Northern blot.

RESULTS

The synovial fibroblasts produced both PAI-2 and PAI-1. Interleukin-1 (IL-1) increased PAI-2 but decreased PAI-1 formation, both at the protein and the mRNA levels. Using cyclooxygenase inhibitors, evidence was obtained that an endogenous cyclooxygenase product(s) in the IL-1-treated cultures inhibited formation of both PAIs; exogenous prostaglandin E2 (10(-7) M) reversed the effect of cyclooxygenase inhibition. The glucocorticoid dexamethasone (10(-6) to 10(-7) M) inhibited IL-1-stimulated PAI-2 formation but reversed the suppressive effect of IL-1 on PAI-1 production.

CONCLUSION

PAI-2 formation and PAI-1 formation can be regulated independently in human synoviocytes, illustrating the complexity of the modulation of the net PA activity expressed by these cells.

Relationship between cathepsin D, urokinase, and plasminogen activator inhibitors in malignant vs benign breast tumours

The concentrations of cathepsin D (Cath D), urokinase (uPA) and two plasminogen activator inhibitors (PAI-1 and PAI-2) were analysed in the cytosols of 130 human mammary tumours (43 benign tumours and 87 primary and unilateral breast carcinomas). uPA, PAI-1 and PAI-2 levels were measured by antigenic immunoassays and Cath D by immunoradiometric assay. The median levels of the four parameters were significantly higher in the malignant tumours than in the benign ones. Cath D and uPA increases were 4-fold and 5-fold respectively. PAI-1 and PAI-2 increases were much more important, 74-fold and 29-fold respectively. In malignant tumours, median levels of Cath D and uPA did not vary according to classical prognostic factors (histologic grade, presence or absence of axillary lymph nodes, steroid receptors, UICC stage, tumour size, age, and menopausal status). However, PAI-1 decreased in ER+ and PR+ tumours and PAI-2 increased in menopausal women's tumours. When Cath D, uPA, PAI-1 and PAI-2 levels in malignant tumours were compared, positive correlations were found for all combinations. The implication of plasminogen activator inhibitors in the phenomenon was surprising and merits further investigation using tools other than global antigen measurements in tumours.

Plasminogen activator inhibitors in human tears

Plasminogen activator inhibitor activity was demonstrated in tears of patients suffering from various corneal and conjunctival diseases. Active plasminogen activator inhibitor was also detected by reverse fibrin zymography in tears of a patient suffering from Sjögren's syndrome and in those who underwent eye surgery. Immunoblotting revealed that both type 1 and type 2 plasminogen activator inhibitors may be present in human tears when the epithelial cells of the cornea and conjunctiva are affected and/or the permeability of the conjunctival blood vessels is increased. The molecular weight of inhibitors suggested the simultaneous presence of both free and activator-complexed inhibitors. However, no plasminogen activator inhibitor was detectable in normal human tears, suggesting that the presence of plasminogen activator inhibitors in tears may be associated with the pathological events at the ocular surface.

Modulation of plasminogen activators and plasminogen activator inhibitors by TGF-beta, IL-1 alpha and EGF in fetal rat calvaria cells at different times of culture

Fetal rat calvaria cells (RC cells) grown in long term culture in the presence of ascorbic acid and organic phosphate proliferate and differentiate to form mineralized nodules of bone. Since transforming growth factor beta (TGF-beta), interleukin 1-alpha (IL-1 alpha) and epidermal growth factor (EGF) affect both bone resorption and bone formation, we have studied the ability of these growth factors to affect plasminogen activators and plasminogen activator inhibitors release by RC cells at different times throughout this proliferation/differentiation sequence. Cultures in log phase growth (day 4), when first multilayering (day 7) and when bone nodules were forming (day 13) were exposed to either TGF-beta, IL-1 alpha, EGF or vehicle. Conditioned medium was collected after 6 and 24 h and plasminogen activators and plasminogen activator inhibitors were analysed by fibrin autography and reverse fibrin autography. TGF-beta-mediated changes in plasminogen activator were apparent at day 4. By day 7 two molecular weight species of plasminogen activator were noted; a 65 kDa species, prominent at 24 h exposure was blocked by anti-tPA antibody, and a 38 kDa plasminogen activator, prominent after 6 h of stimulation was not blocked by anti-tPA antibody. Plasminogen activator-plasminogen activator inhibitor complexes are also increased. IL-1 alpha caused similar increases in plasminogen activator and plasminogen activator inhibitor with maximal activity measured at day 13, coincident with the time when bone nodules were forming. EGF-mediated changes were less by comparison. TGF-beta significantly decreased bone nodule formation after both a 6 and 24 h serum-free exposure, whereas IL-1 alpha and EGF decreased nodule number only after the 24 h exposure. The data suggest that the three factors influence the expression of plasminogen activator and plasminogen activator inhibitor by RC cells and their effect is different at different times of culture.

Recombinant human interleukin-1 inhibits plasminogen activator inhibitor-1 (PAI-1) production by human articular cartilage and chondrocytes

Human articular cartilage and chondrocyte monolayers in culture constitutively produced plasminogen activator inhibitor-1 (PAI-1) protein and mRNA, as assessed by a specific enzyme-linked immunosorbent assay and Northern blotting analysis, respectively. Recombinant human interleukin-1 (IL-1) invoked a dose-dependent inhibition of PAI-1 production in both cartilage and chondrocyte cultures. The inhibitory effect of IL-1 was observed between 2-8h after addition of the cytokine, while the optimal dose was between 10-100U/ml IL-1 alpha (57-570pM IL-1 alpha). Results obtained by Northern analysis of chondrocyte total RNA reflected those found for the PAI-1 antigen, namely, that nontreated chondrocytes showed PAI-1 mRNA which was reduced by IL-1 treatment. To our knowledge, this is the first report where IL-1 has been found to inhibit PAI-1 expression. Since IL-1 has been shown before to cause human cartilage destruction and a correlated change in plasminogen activator activity, it could be that a concomitant reduction in PAI-1 levels by IL-1 may be significant in the control of these changes in cartilage.

Transforming growth factor-beta modulates plasminogen activator activity and plasminogen activator inhibitor type-1 expression in human keratinocytes in vitro

Transforming growth factor beta (TGF-beta) is a multifunctional mediator with effects on cellular growth, differentiation, and extracellular matrix (ECM) metabolism. Because TGF-beta stimulates fibronectin expression in cultured human keratinocytes, we wished to determine whether it might also affect ECM degradation through the plasminogen activator (PA)-plasminogen activator inhibitor (PAI) system. Immunofluorescence of human keratinocytes using a monospecific antiserum to type 1 PAI (PAI-1) showed enhanced cellular and ECM staining when they were cultured in the presence of TGF-beta. The antiserum also identified an Mr 50,000 protein in conditioned media that was markedly enhanced by TGF-beta. A corresponding stimulation of PAI-1 mRNA was demonstrated by quantitative RNA blot analysis. Total plasminogen activating activity of conditioned medium was markedly decreased by TGF-beta. Zymography showed this to be at least partially due to decreased secreted urokinase activity. TGF-beta may play an important role in stabilizing the provisional matrix synthesized by keratinocytes in healing wounds.

Increased proteolytic activity is responsible for the aberrant morphogenetic behavior of endothelial cells expressing the middle T oncogene

Expression of the polyoma virus middle T (mT) oncogene in vivo is associated with a profound subversion of normal vascular development, which results in the formation of endothelial tumors (hemangiomas). In an attempt to understand the molecular mechanisms responsible for this phenomenon, we have investigated, in an in vitro system, the morphogenetic properties of endothelial cells expressing this oncogene. mT-expressing endothelioma (End) cells grown within fibrin gels formed large hemangioma-like cystic structures. All End cell lines examined expressed high levels of fibrinolytic activity resulting from increased production of urokinase-type plasminogen activator and decreased production of plasminogen activator inhibitors. Neutralization of excess proteolytic activity by exogenously added serine protease inhibitors corrected the aberrant in vitro behavior of End cells and allowed the formation of capillary-like tubules. These results suggest that tightly controlled proteolytic activity is essential for vascular morphogenesis and that physiological protease inhibitors play an important regulatory role in angiogenesis.

Production of plasminogen activator and plasminogen activator inhibitor by bovine lymphatic endothelial cells: modulation by TNF-alpha

We have investigated whether lymphatic endothelial cells in culture produce plasminogen activators (PAs) and their inhibitors (PAIs) and if these activities can be modulated by the inflammatory cytokine Tumor Necrosis Factor alpha (TNF-alpha). Examination by reverse fibrin autography of the conditioned medium from these cells revealed a PAI of Mr 50 kDa. Also evident by fibrin autography were two species of PAs, of Mr 110 kDa and Mr 60 kDa. The 110 kDa protein co-migrated with the PA-PAI complexes and the 60 kDa protein co-migrated with tissue Plasminogen Activator (tPA). Functional and immunological assays indicated the human TNF-alpha increased the type 1 plasminogen activator inhibitor (PAI-1) in a time dependent manner. Treatment of the cells with recombinant human TNF-alpha for 24 hours resulted in a 3 to 7 fold increase in the amount of PAI released into the conditioned media. Immunoblot analysis identified the PAI in the TNF-alpha treated cell conditioned media, as PAI-1. Deposition of PAI-1 in the extracellular matrix then became apparent. TNF-alpha increased 4 fold the amount of tPA-PAI-1 complexes (Mr 110 kDa) detected in the conditioned media. Free tPA (Mr 60 kDa) decreased to 1/5 of control. Net fibrinolytic activity, as determined by a chromogenic substrate assay, decreased after TNF-alpha treatment. No urokinase type Plasminogen Activator (uPA) activity was detected in control or treated cells. This fibrinolytic activity may be important in maintaining free fluid movement in the interstitium and lymphatic vessels and in inflammatory states this potential may be decreased by the increase in PAI-1.

Modulation of plasminogen activator production by interleukin 1: differential responses of fibroblasts derived from human skin and rheumatoid and non-rheumatoid synovium

Rheumatoid synovial fibroblasts were treated with purified porcine interleukin 1 alpha and recombinant human interleukin 1B, and the production of secreted and cell-associated plasminogen activator activity was measured. No stimulation of plasminogen activator activity was seen in response to either preparation of interleukin 1, and in more than half of the cell cultures interleukin 1 caused a significant decrease in the secreted levels of PA activity. Increased levels of prostaglandin E were produced in the same experiments, indicating that the cells were responsive to the interleukin 1 preparations. Both retinoic acid and unfractionated monocyte conditioned medium were able to stimulate the production of PA activity by the rheumatoid synovial fibroblast cultures. The rheumatoid synovial fibroblasts produced two species of plasminogen activator as indicated by SDS polyacrylamide gel electrophoresis, with apparent Mr of approx. 50,000 and 100,000. The Mr = 50,000 species co-migrates with urokinase-type plasminogen activator. No species is produced which co-migrates with tissue type plasminogen activator. Studies with antibodies also indicate that the activity produced is urokinase-type plasminogen activator. The Mr = 100,000 species may be an enzyme-inhibitor complex. Two non-rheumatoid synovial fibroblast cultures and two out of six human skin fibroblast cultures did produce elevated levels of plasminogen activator activity in response to recombinant human interleukin 1B. The results suggest that fibroblast populations may differ in their response to interleukin 1, in terms of production of plasminogen activator activity.

Dexamethasone increases the release of three 44 kD proteins immunologically related to plasminogen activator inhibitor-1 from human umbilical vein endothelial and rabbit coronary microvessel endothelial cells

Endothelial cells synthesize and release different proteins involved in their function, and some of these proteins may play important roles in the cellular response to injury, infection, or glucocorticoids. We have examined the profile of proteins released from rabbit coronary microvascular endothelial (RCME) and human umbilical vein endothelial (HUVE) cells using two-dimensional polyacrylamide gel electrophoresis. The production of three anionic 44kD proteins was increased in RCME and HUVE-cell conditioned medium after treatment with dexamethasone, endotoxin or hypoxia-reoxygenation. The three 44 kD proteins were recognized by antisera raised against endothelial type plasminogen activator inhibitor (PAI-1). Dexamethasone treatment of HUVE and RCME cells reduced cellular and secreted plasminogen activator activity, but no significant effect of dexamethasone on PAI-1 activity in conditioned media could be demonstrated. These observations suggest that although the 44Kd proteins exhibit immunoreactivity with PAI-1 antisera, these proteins are most likely inactive forms of PAI-1.

The majority of type 1 plasminogen activator inhibitor associated with cultured human endothelial cells is located under the cells and is accessible to solution-phase tissue-type plasminogen activator

The interactions between exogenously added tissue-type plasminogen activator (t-PA) and the active form of type 1 plasminogen activator inhibitor (PAI-1) produced by and present in cultured human umbilical vein endothelial cells (HUVECs) were investigated. Immunoblotting analysis of the conditioned media obtained from monolayers of HUVECs treated with increasing concentrations of t-PA (less than or equal to 10 micrograms/ml) revealed a dose-dependent formation of both t-PA/PAI-1 complexes, and of a 42,000-Mr cleaved or modified form of the inhibitor. Immunoradiometric assays indicated that t-PA treatment resulted in a fourfold increase in PAI-1 antigen present in the conditioned media. This increase did not result from the release of PAI-1 from intracellular stores, but rather reflected a t-PA-dependent decrease in the PAI-1 content of the Triton X-100 insoluble extracellular matrix (ECM). Although the rate of t-PA-mediated release of PAI-1 was increased by the removal of the monolayer, similar quantities of PAI-1 were removed in the presence or absence of the cells. These results suggest that the cells only represent a semipermeable barrier between ECM-associated PAI-1 and exogenous t-PA. Treatment of HUVECs with t-PA (1 microgram/ml, 2 h) to deplete the ECM of PAI-1 did not affect the subsequent rate of PAI-1 production and deposition into the ECM. Immunogold electron microscopy of HUVECs not only confirmed the location of PAI-1 primarily in the region between the culture substratum and ventral cell surface but failed to demonstrate significant (less than 1%) PAI-1 on the cell surface. Thus, the majority of PAI-1 associated with cultured HUVEC monolayers is present under the cells in the ECM and is accessible to solution-phase t-PA.

Retinal pigment epithelial cells produce a latent fibrinolytic inhibitor that is antigenically and biochemically related to type 1 plasminogen activator inhibitor produced by vascular endothelial cells

Conditioned media from retinal pigment epithelial (RPE) cells in culture contain active and latent plasminogen activator inhibitors (PAIs). Latent activity is unmasked by denaturants and accounts for the vast majority of total inhibitor activity. Activation by denaturants is an unusual characteristic previously described for PAI-1, the inhibitor produced by vascular endothelial cells. This property is not shared by PAI-2 or protease nexin. Reverse fibrin autography demonstrates that the PAI activity in RPE-conditioned media (RPE-CM) comigrates with purified endothelial cell-derived PAI-1 and has an apparent Mr of 50,000. Immunoblotting with a monospecific antiserum directed against endothelial cell-derived PAI-1 demonstrates a cross-reacting protein in RPE-CM at 50 kDa, and this same antiserum is able to immunoprecipitate a 50 kDa protein from [35S]methionine-labeled RPE-CM. These data suggest that RPE cells produce a PAI that is biochemically and immunologically related to PAI-1.

Characterization of keratinocyte plasminogen activator inhibitors and demonstration of the prevention of pemphigus IgG-induced acantholysis by a purified plasminogen activator inhibitor

To investigate the mechanisms by which cutaneous plasminogen activator (PA) may be regulated, we have tested cultured keratinocytes for the presence of PA inhibitors. Using biosynthetic labeling experiments with 35S-methionine in conjunction with specific antibody precipitation, we have shown that human keratinocytes in culture synthesized and secreted both PA inhibitor 1 and PA inhibitor 2. PA inhibitor 1 was present in conditioned media in the inactive form, but it could be detected with reverse phase autography. PA inhibitor 2 was detected by its ability to form complexes with 125I-uPA. Potential therapeutic relevance for cutaneous PA inhibitor 2 was suggested in skin organ culture experiments which demonstrated that purified PA inhibitor 2 from human placenta was able to prevent the acantholytic changes induced by pemphigus IgG.