cDNA cloning and expression in E. coli of a plasminogen activator inhibitor (PAI) related to a PAI produced by Hep G2 hepatoma cell

The plasminogen activator inhibitor-1 paradox in cancer: a mechanistic understanding

The paradoxical pro-tumorigenic function of plasminogen activator inhibitor 1 (PAI-1, aka Serpin E1) in cancer progression and metastasis has been the subject of an abundant scientific literature that has pointed to a pro-angiogenic role, a growth and migration stimulatory function, and an anti-apoptotic activity, all directed toward promoting tumor growth, cancer cell survival, and metastasis. With uPA, PAI-1 is among the most reliable biomarkers and prognosticators in many cancer types. More recently, a novel pro-tumorigenic function of PAI-1 in cancer-related inflammation has been demonstrated. These multifaceted activities of PAI-1 in cancer progression are explained by the complex structure of PAI-1 and its multiple functions that go beyond its anti-fibrinolytic and anti-plasminogen activation activities. However, despite the multiple evidences supporting a pro-tumorigenic role of PAI-1 in cancer, and the development of several inhibitors, targeting PAI-1, has remained elusive. In this article, the various mechanisms responsible for the pro-tumorigenic functions of PAI-1 are reviewed with emphasis on its more recently described contribution to cancer inflammation. The challenges of targeting PAI-1 in cancer therapy are then discussed.

The role of bradykinin in the antifibrotic actions of perindoprilat on human mesangial cells

BACKGROUND

Angiotensin-converting enzyme inhibitors (ACE-I) protect against the development of glomerulosclerosis using mechanisms partly dissociated from their systemic antihypertensive action. The aim of the current study was to delineate the mechanism of action underlying the antifibrotic effects of the ACE-I perindoprilat in the context of macrophage-mediated scarring in human mesangial cells.

METHODS

Mesangial cells were treated with macrophage-conditioned medium (MPCM) in the presence or absence of the ACE-I perindoprilat.

RESULTS

Forty micromol/L perindoprilat reduced MPCM-induced mesangial cell fibronectin levels by 19.4 +/- 0.6% (P < 0.001). Immunoprecipitation of 35S-methionine biosynthetically labeled fibronectin and Northern analysis suggested that the decrease in fibronectin levels was not caused by reduced synthesis. MPCM stimulated the production of matrix metalloproteinases (MMP) 2, 3, and 9 in mesangial cells; however, these were not significantly altered by ACE-I treatment, and neither was production of their tissue inhibitor of metalloproteinases (TIMP-1). Addition of exogenous bradykinin to MPCM-treated mesangial cells resulted in a 22.5 +/- 1.4% (P < 0.02) reduction in secreted fibronectin levels, while semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and Southern blotting demonstrated that bradykinin B2 receptor expression was up regulated by 71 +/- 30% in MPCM-stimulated mesangial cells in response to ACE-I treatment (P= 0.032). Moreover, the bradykinin B2 receptor antagonist HOE 140 attenuated the beneficial effects of perindoprilat. MPCM-stimulated mesangial cell protein expression levels of plasminogen activator system components tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) were altered after treatment with ACE-I.

CONCLUSION

These results suggest that ACE-I-induced renoprotection, in the context of macrophage-stimulated mesangial cell scarring, is mediated, at least in part, via the actions of bradykinin.

Protein-bound polysaccharide PSK inhibits tumor invasiveness by down-regulation of TGF-beta1 and MMPs

Transforming growth factor beta1 (TGF-beta1) and matrix metalloproteinases (MMPs) produced by tumor cells play important roles in tumor invasion. PSK, a protein-bound polysaccharide, is widely used in Japan as an immunopotentiating biological response modifier for cancer patients. In this study, we focused on the effects of PSK on invasiveness, TGF-beta1 production, and MMPs expression in two human tumor cell lines, pancreatic cancer cell line (NOR-P1) and gastric cancer cell line (MK-1P3). PSK significantly decreased the invasiveness of both cell lines through Matrigel-coated filters but did not affect cell viability, proliferation, or adhesion. Decreased invasion was associated with the inhibition of TGF-beta1, MMP-2, and MMP-9 at both mRNA and protein levels as assessed by reverse transcriptase-polymerase chain reaction, gelatin zymography, and enzyme-linked immunosorbent assay. Antibody against TGF-beta1 neutralized the MMP activities of both cell lines. PSK also suppressed the expression of urokinase plasminogen activator (uPA) and uPA receptor but did not change plasminogen activator inhibitor-1 (PAI-1) expression. Western blot analysis showed that PSK reduced uPA protein expression but not PAI-1 expression in the both cell lines. These results indicate that PSK suppresses tumor cell invasiveness through down-regulation of several invasion-related factors including TGF-beta1, uPA, MMP-2, and MMP-9.

Expression of calcium-binding protein S100A2 in breast lesions

A suppression subtraction cDNA library representing mRNAs expressed at a higher level in a benign breast tumour-derived cell line relative to the malignant MCF-7A cell line contained cDNAs corresponding to mRNAs for plasminogen activator inhibitor I, annexin VIII and the EF-hand protein S100A2. S100A2 protein has previously been shown to be expressed in normal human breast epithelium, but not in human breast carcinoma cell lines. Using a PCR-based assay and in situ hybridization on histological sections of human breast specimens, the mRNA for S100A2 was shown to be present in all benign breast lesions examined as well as in normal epithelium. S100A2 mRNA was detectable in 37% of specimens of carcinoma in situ, but in less than 15% of carcinoma specimens. The results suggest that the loss of S100A2 is associated with the development of malignant cells and is not associated with early tumour development.

TGF-beta induces fibronectin synthesis through a c-Jun N-terminal kinase-dependent, Smad4-independent pathway

Transforming growth factor-beta (TGF-beta) exerts its effects on cell proliferation, differentiation and migration in part through its modulation of extracellular matrix components, such as fibronectin and plasminogen activator inhibitor-1 (PAI-1). Although the SMAD family of proteins recently has been shown to be a key participant in TGF-beta signaling, other signaling pathways have also been shown to be activated by TGF-beta. We report here that c-Jun N-terminal kinase (JNK), a member of the MAP kinase family, is activated in response to TGF-beta in the human fibrosarcoma HT1080-derived cell line BAHgpt. Stable expression of dominant-negative forms of JNK1 and MKK4, an upstream activator of JNK, results in loss of TGF-beta-stimulated fibronectin mRNA and protein induction, while having little effect on TGF-beta-induced levels of PAI-1. The human fibronectin promoter contains three CRE elements, one of which has been shown to bind a c-Jun-ATF-2 heterodimer. Utilizing a GAL4 fusion trans-reporting system, we demonstrate a decrease in transactivating potential of GAL4-c-Jun and GAL4-ATF-2 in dominant-negative JNK1- and MKK4-expressing cells. Finally, we show that TGF-beta-induced fibronectin synthesis is independent of Smad4. These results demonstrate that TGF-beta-mediated fibronectin induction requires activation of JNK which in turn modulates the activity of c-Jun and ATF-2 in a Smad4independent manner.

Influence of glycation on LDL-induced generation of fibrinolytic regulators in vascular endothelial cells

Hyperglycemia and dyslipidemia are two biochemical markers of diabetes mellitus. Increased incidence of cardiovascular disease and impaired fibrinolytic activity have been found in diabetic subjects. Previous studies have demonstrated that low density lipoproteins (LDLs) stimulate the production of plasminogen activator inhibitor-1 (PAI-1) and reduce the generation of tissue plasminogen activator (tPA) in vascular endothelial cells (ECs). The present study investigated the effect of glycated LDL on the production of PAI-1 and tPA in cultured human umbilical vein ECs (HUVECs). Glycation increased the abundance of glucitollysine and conjugated dienes in LDL and amplified the overproduction of PAI-1 and the reduction in tPA generation from HUVECs induced by LDL. The steady-state levels of PAI-1 mRNA in glycated LDL-treated ECs were significantly higher than those in native LDL-treated cells. Actinomycin D blocked the increase in PAI-1 generation induced by glycated LDL. Glycated LDL did not significantly reduce the levels of tPA mRNA but attenuated de novo synthesis of tPA in ECs. Treatment with 25 mmol/L aminoguanidine, an antioxidant and inhibitor of the formation of advanced glycation end products, during glycation normalized glycated LDL-induced generation of PAI-1 and tPA in ECs. The results of the present study indicate that glycation enhances the production of PAI-1 and attenuates tPA synthesis in ECs induced by LDL, which may contribute to the increased incidence of cardiovascular complications in diabetes. Formation of advanced glycation end products or peroxidation may be involved in glycated LDL-induced alterations in the generation of fibrinolytic regulators from ECs.

Inhibition by hirulog-1 of generation of plasminogen activator inhibitor-1 from vascular smooth-muscle cells induced by thrombin

Hirulog-1 effectively prevents thrombosis in coronary artery disease and is associated with a low incidence of bleeding complications. Our study characterized the effect of Hirulog-1 on thrombin-induced production of plasminogen activator inhibitor-1 (PAI-1) in cultured baboon aortic smooth-muscle cells (BASMCs). Thrombin increased the steady-state levels of PAI-1 messenger RNA (mRNA) and the release of PAI-1 antigen from BASMCs. Treatments with 10-20 mg/L of Hirulog-1 inhibited >80% of thrombin-induced PAI-1 generation from BASMCs. Hirulog-1 alone did not significantly alter PAI-1 production in the absence of thrombin. Significant reduction of thrombin-induced PAI-1 release was observed in cultures treated with Hirulog-1 for 1 h. The maximal effect of Hirulog-1 on thrombin-induced PAI-1 release was achieved in cultures treated with thrombin plus Hirulog-1 for 3 to 6 h, associated with the normalization of PAI-1 mRNA levels induced by thrombin treatment. Strong inhibition by Hirulog-1 on thrombin-induced PAI-1 release remained in cultures with 8 h of the treatment, but the effect was attenuated 16 h after a single addition of the inhibitor. Our study demonstrates that Hirulog-1 effectively inhibited thrombin-induced PAI-1 production in cultured vascular SMCs at mRNA and protein levels. Vascular SMCs may be exposed to high concentrations of thrombin when endothelium is injured. The information generated from this study suggests that Hirulog-1 potentially prevents intravascular thrombogenesis through inhibiting thrombin-induced PAI-1 production in vascular SMCs, especially when hypercoagulation and endothelial injury occurs.

ECM degradation by cultured human mesangial cells is mediated by a PA/plasmin/MMP-2 cascade

We examined the role of the plasminogen activator/plasmin system in extracellular matrix (ECM) degradation by human mesangial cells cultured on thin films of 125I-labeled ECM (Matrigel). ECM degradation (release of 125I into the medium) was dependent on exogenous plasminogen, proportional to the number of mesangial cells and amount of plasminogen added, and coincident with the appearance of plasmin in the medium. ECM degradation was completely blocked (P < 0.001) by two plasmin inhibitors, alpha-2-antiplasmin (40 micrograms/ml) and aprotinin (216 KIU/ml), and partially reduced (-33 +/- 1.8%, P < 0.01) by TIMP-1 (40 micrograms/ml), a specific inhibitor of matrix metalloproteinases. Zymography of medium obtained from cells cultured in the absence of plasminogen revealed the presence of latent matrix metalloproteinase-2 (MMP-2) which was converted to a lower molecular weight, active form in the presence of mesangial cells and plasminogen. Northern analysis of poly A+RNA prepared from cultured human mesangial cells revealed mRNA for tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA), plasminogen activator inhibitor-1 (PAI-1), and uPA receptor (uPAR). The presence of uPA protein in medium obtained from cultured human mesangial cells was demonstrated by Western blotting and ELISA which revealed a large molar excess of PAI-1 (1.2 +/- 0.1 x 10(-9) M) over uPA (1.2 +/- 0.1 x 10(-12) M) and tPA (0.19 +/- 0.04 x 10(-9) M). ECM degradation was reduced by a monoclonal antibody (MAb) against human tPA (-54 +/- 8.6%) or human uPA (-39 +/- 5.2%) compared to cells treated with identical amounts of non-specific monoclonal IgG (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Co-expression of urokinase, urokinase receptor and PAI-1 is necessary for optimum invasiveness of cultured lung cancer cells

We investigated the importance of the urokinase (uPA)-plasmin system in fostering invasion of human lung cancer cells through artificial basement membranes composed of Matrigel. Eight cell lines (including 1 small cell and 7 non-small cell lines) were examined. One cell line did not express any components of the urokinase system. Four cell lines had substantial levels of endogenous uPA detectable on their surfaces. Three of these cell lines co-expressed the plasminogen activator inhibitor PAI-1 in addition to uPA. Assays for invasiveness revealed 4 cell lines capable of traversing a Matrigel barrier, including the 3 which co-expressed uPA, PAI-1 and uPA receptor. Surprisingly, the cell line expressing only uPA and uPA receptor displayed no invasive capacity despite levels of secreted uPA more than 20-fold higher than the other cell lines studied. Based on these observations, we hypothesized that both uPA and PAI-1 might be important for invasion by lung tumor cells, at least in vitro. We therefore tested polyclonal antibodies which inhibit uPA and PAI-1 activity for their effects on the highly invasive H292 cell line. After 3 days, invasive capacity was inhibited by antibodies to both uPA and PAI-1 in a dose-dependent manner. The plasmin inhibitor aprotinin reduced H292 cell invasion by 70%. Taken together, our data demonstrate that in cultured human lung cancer cells the uPA-plasmin system is important in promoting invasion into basement membranes and suggest that a critical balance between uPA and PAI-1 is necessary for optimal invasiveness. Our data are consistent with results from recent clinical studies showing that PAI-1 expression in tumor tissue is an adverse prognostic feature.

Effect of thrombin on release of plasminogen activator inhibitor-1 from cultured primate arterial smooth muscle cells

Plasminogen activator inhibitor-1 (PAI-1) is the major inhibitor for plasmin formation promoted by tissue and urokinase plasminogen activators. The present study demonstrates that thrombin increase PAI-1 antigen, biological activity, and gene expression in cultured baboon aortic smooth muscle cells (BASMC). Thrombin elevates PAI-1 antigen in conditioned medium of BASMC within 10 min of the treatment, with the peak increase after 30 min of the treatment. Overexpression of PAI-1 gene was detected in the cultures exposed to thrombin for at least 60 min. PAI activity in conditioned medium increased in the cultures treated with thrombin for at least 4 h. The thrombin-induced early increase of PAI-1 antigen (up to 30 min of the stimulation) was blocked by hirudin (a specific inhibitor of thrombin), mimicked by trypsin and not suppressed by cycloheximide (a protein synthesis inhibitor). The majority of metabolically labeled PAI-1 associated with BASMC was present in extracellular matrix. The level of extracellular matrix-associated PAI-1 was reduced 40% by 30 min of thrombin treatment. Our results suggest that thrombin not only increases PAI-1 transcription but also proteolytically cleaves PAI-1 from the extracellular matrix of vascular SMC. PAI-1 released by thrombin from the extracellular matrix may not alter PAI activity in extracellular fluid but may reduce the storage of PAI-1 in the extracellular matrix of vascular smooth muscle cells.

Increased intramural expression of plasminogen activator inhibitor type 1 after balloon injury: a potential progenitor of restenosis

OBJECTIVES

This study was performed to determine whether altered gene expression of plasminogen activator inhibitor type 1 (PAI-1) occurs within the arterial wall after experimentally induced balloon injury.

BACKGROUND

PAI-1, known to inhibit fibrinolysis in the circulation and to be present within atherosclerotic vessels, may influence proteolysis in the arterial wall and neointimal formation after angioplasty.

METHODS

In rabbit carotid arteries subjected to balloon injury, both PAI-1 gene and protein expression were assayed sequentially with the use of Northern blotting, in situ hybridization and immunohistochemical studies.

RESULTS

In uninjured, normal vessels PAI-1 messenger ribonucleic acid (mRNA) was not detectable by Northern blotting or in situ hybridization. However, injury was followed within 3 h by increases in PAI-1 mRNA (3.2 kb) of 5.9-fold compared with that in contralateral control carotid arteries (Northern blots). PAI-1 mRNA was detectable by in situ hybridization early after injury first in adventitia; after 24 h it was particularly prominent in the media. From 1 to 4 weeks after injury it was consistently detectable and was localized in neointimal vascular smooth muscle and endothelial cells at a time when neointimal thickening was marked. Cells of both types exhibited PAI-1 protein detected immunohistochemically. In vessels maintained in organ culture after balloon injury in vivo, sustained increases in PAI-1 activity appeared in conditioned media as well.

CONCLUSIONS

Our results indicate that balloon injury simulating angioplasty in patients induces intramural expression of PAI-1 in vascular smooth muscle and endothelial cells. The decreased cell surface fibrinolytic activity likely to result from the increased PAI-1 expression may initiate or exacerbate mural thrombosis. Accordingly, excessive stimulation with clot-associated mitogens may stimulate vascular smooth muscle cell proliferation, which, coupled with increased accumulation of extracellular matrix attributable to decreased plasmin-mediated degradation, may contribute to restenosis.

Modulation of expression of monocyte/macrophage plasminogen activator activity and its implications for attenuation of vasculopathy

BACKGROUND

The binding of urokinase-type plasminogen activator (uPA) to its receptor (uPAR) on cell surfaces has the potential to influence degradation of extracellular matrix (ECM). Thus, uPA bound to monocyte/macrophages and its interactions with plasminogen activator inhibitors types 1 and 2 (PAI-1 and PAI-2) may modify atherogenesis by altering cell-associated proteolytic activity, degradation of ECM, and neointimal formation at sites of vascular injury.

METHODS AND RESULTS

To determine whether the expression of proteins on the surface of cells involved in fibrinolysis changes in human cells in response to mediators implicated in atherogenesis, we exposed U937 cells (an immortal human monocyte-like cell line) to transforming growth factor-beta (TGF-beta) and to thrombin. Induction of uPAR mRNA occurred with TGF-beta (5 ng/mL) in a time-dependent fashion (P = .05; n = 4). Thrombin (5 National Institutes of Health [NIH] U/mL) increased uPAR mRNA by 2.8-fold above control (n = 4) without altering PAI-1 mRNA or protein synthesis (n = 4). The increase in uPAR gene expression in cells exposed to either TGF-beta or thrombin translated into a functional increase in cell-surface proteolytic activity. Under control conditions, U937 cells expressed PAI-2 but not PAI-1 mRNA. PAI-2 mRNA expression increased (P < .05; n = 4) with thrombin (5 NIH U/mL) but was suppressed by TGF-beta (5 ng/mL). TGF-beta induced PAI-1 mRNA within 6 hours accompanied by a 9-fold increase in PAI-1 protein from 6 hours (2.9 +/- 1.9 ng/mL) to 24 hours (20.0 +/- 9.6 ng/mL, P = .005; n = 3) paralleled by increased synthesis as shown in metabolic labeling experiments with 35S-methionine and immunoprecipitation of labeled PAI-1. PAI-1 mRNA and protein expression were seen in human coronary artery atherectomy specimens as well and were localized to analogous monocyte/macrophages and to smooth muscle cells as judged from results of in situ hybridization and immunocytochemistry studies.

CONCLUSIONS

The results indicate that there is induction of PAI-1 and uPAR in U937 cells exposed to TGF-beta and thrombin. In atheroma, analogous processes may modulate early migration of luminal monocytes into the subintimal space and proteolysis of ECM. Thus, cell surface, monocyte-directed fibrinolysis may influence atherosclerosis, restenosis, or both.

Purification and characterization of active and stable recombinant plasminogen-activator inhibitor accumulated at high levels in Escherichia coli

Plasminogen-activator inhibitor type 1 (PAI-1), the primary physiological inhibitor of tissue-type plasminogen activator, is an unusual member of the serine protease inhibitor (serpin) superfamily in that it spontaneously converts to a latent form lacking activity. This latent form can be reactivated by denaturation and refolding, but the activation is usually incomplete and often leads to aggregation of the protein. In this study we have developed a high-level expression system that leads to the accumulation of PAI-1 at 30-50% total microbial protein. We have developed a single-step purification protocol which can be completed in a few hours, yielding approximately 20 mg purified recombinant PAI-1/litre culture. The purified PAI-1 was 80-100% active and was stable upon incubation at 37 degrees C with a half-life of approximately 48 h. At 20 degrees C, PAI-1 activity was stable for a week and at 4 degrees C it retained its activity completely for up to two months. Freezing caused significant loss of activity. The stability of PAI-1 activity was found to be dependent on pH and ionic strength, being most stable at pH 5.6 and at an ionic strength of 1 M salt. We show that by a combination of high-level expression and rapid purification under optimum conditions, it is possible to produce active and stable PAI-1 in high yield.

Potentiation by hypercholesterolemia of the induction of aortic intramural synthesis of plasminogen activator inhibitor type 1 by endothelial injury

Accumulation of plasminogen activator inhibitor type 1 (PAI-1) in the arterial wall may accelerate atherogenesis by inhibiting fibrinolysis, diminishing proteolysis of extracellular matrix proteins, or modifying migration of vascular smooth muscle cells. Increased intramural expression of the PAI-1 gene is induced by thrombosis. To determine whether it occurs also in response to a sustained mechanical insult to endothelium, hypercholesterolemia, or both, rabbits were subjected to sustained aortic injury induced by implantation of indwelling polyethylene tubing, to hyperlipidemia induced by cholesterol and peanut oil feeding over a period of 8 weeks, or both. Sustained vascular injury alone did not increase plasma PAI-1. However, hypercholesterolemia with or without mechanically induced vascular injury increased plasma PAI-1 twofold. The expression of PAI-1 mRNA in aorta (Northern blots) was significantly increased when vascular injury was combined with hyperlipidemia. In situ hybridization showed that the increase with mechanical injury alone occurred in endothelial cells covering the neointima (positive for factor VIII and thrombomodulin), in abnormally differentiated vascular smooth muscle cells (positive for embryonic myosin heavy chain), and in macrophages (positive for the RAM-11 anti-macrophage antibody). Qualitatively similar but much more marked increases in PAI-1 gene expression were seen when arterial injury was accompanied by hypercholesterolemia. Neither vitronectin, known to stabilize PAI-1, nor vitronectin mRNA increased in liver. However, immunocytochemistry and Western blots demonstrated marked aortic accumulation of vitronectin protein with hyperlipidemia, particularly in subendothelial fibrotic regions, accompanied by increased neointimal vitronectin mRNA as shown by in situ hybridization. These results suggest that increased synthesis and stabilization of vascular PAI-1 may potentiate accumulation of extracellular matrix, thereby accelerating atherosclerosis.

Species-specific differential cleavage and polyadenylation of plasminogen activator inhibitor type 1 hnRNA

Plasminogen activator inhibitor type 1 (PAI-1) is the primary physiologic inhibitor of the naturally occurring plasminogen activators. In higher primates two forms of mature PAI-1 mRNA (3.2 kb and 2.2 kb) arise by alternative cleavage and polyadenylation of PAI-1 hnRNA which is regulated in a tissue-specific fashion in humans. In other mammals only the 3.2 kb mRNA has been detected. The putative downstream polyadenylation site in humans that gives rise to the 3.2 kb PAI-1 mRNA consists of three overlapping copies of the consensus polyadenylation sequence while no consensus polyadenylation sequence is found upstream at a position that could generate the shorter mRNA species. To determine whether differential cleavage and polyadenylation of PAI-1 mRNA is due to species-specific differences in trans-acting factors that process PAI-1 mRNA or to the presence of a nonconsensus polyadenylation site acquired recently during primate evolution we prepared plasmids in which the 3' nontranslated region of the human PAI-1 gene or the mouse PAI-1 cDNA was inserted downstream of the neomycin gene in the plasmid pSV2neo. We show that the 3'-nontranslated region of the human PAI-1 gene but not the mouse PAI-1 cDNA conferred alternative cleavage and polyadenylation to the neomycin gene in transfected human Hep G2 cells as well as mouse NIH3T3 and rat L6 cells.

Induction of endothelial cell expression of the plasminogen activator inhibitor type 1 gene by thrombosis in vivo

BACKGROUND

We have shown previously that products from activated platelets can augment synthesis of plasminogen activator inhibitor type 1 (PAI-1) in cultured endothelial and hepatoma (Hep G2) cells in vitro and increase plasma PAI-1 activity in vivo in rabbits. Accordingly, the effects of activation of platelets associated with thrombosis and thrombolysis in vivo on plasma PAI-1 activity and expression of the PAI-1 gene in endothelium, liver, and other organs were characterized.

METHODS AND RESULTS

Endothelial injury giving rise to platelet-rich thrombi was induced with electrical stimulation in carotid arteries in rabbits. Clot lysis and recanalization were induced subsequently with intravenous tissue-type plasminogen activator (t-PA) and verified with Doppler flow probes. Plasma PAI-1 activity (mean +/- SD) increased from 6 +/- 2 arbitrary units (AU)/ml to 129 +/- 48 AU/ml (n = 15) within several hours after recanalization. When t-PA had failed to induce recanalization, the increase was much less (from 7 +/- 2 to 42 +/- 23 AU/ml, n = 11). To define mechanisms responsible for these changes, PAI-1 messenger RNA (mRNA) was evaluated by Northern blot analysis and localized in tissues by in situ hybridization. Strong and consistent induction of PAI-1 mRNA was evident in aorta, heart, and liver of animals subjected to thrombosis (twofold to threefold increases compared with values in controls), particularly in those in which thrombolysis had been induced (fourfold to sixfold). After thrombolysis, an intense, PAI-1 mRNA-specific signal was detected in endothelium of aorta, liver, and heart, with less intense signals in endothelium of lung, adrenals, and kidneys.

CONCLUSIONS

The increases in plasma PAI-1 activity follow a preceding increase in endothelial cell expression of the PAI-1 gene as reflected by PAI-1 mRNA levels. Thus, increased synthesis of endothelial cell PAI-1 after thrombosis and thrombolysis may attenuate endogenous fibrinolysis early after coronary thrombolysis, thereby potentiating early, thrombotic reocclusion.

Augmented arterial wall expression of type-1 plasminogen activator inhibitor induced by thrombosis

Type-1 plasminogen activator inhibitor (PAI-1), the primary physiological inhibitor of endogenous plasminogen activators, modulates fibrinolysis, cell migration, and tissue repair. To determine whether genetic expression of PAI-1 is augmented in the walls of vessels exposed to thrombi but not to a direct physical insult such as electrical injury, we induced arterial thrombosis in rabbit carotid arteries with intraluminal surgical silk sutures and performed in situ hybridization for PAI-1 messenger RNA (mRNA) and immunohistochemistry for PAI-1 antigen at selected intervals. PAI-1 activity in plasma remained virtually constant. In contrast, PAI-1 mRNA increased in endothelial cells juxtaposed to thrombi, in smooth muscle cells adjacent to the neointima, and in macrophages surrounding the suture material. PAI-1 protein was detected in regions in which PAI-1 mRNA was expressed. The increased expression of PAI-1 mRNA colocalized with PAI-1 protein in the endothelium juxtaposed to thrombi may potentiate thrombosis by shifting the local balance between fibrinolysis and thrombosis toward thrombosis. Furthermore, it may alter vascular remodeling and predispose to stenosis after interventions such as angioplasty, in which local thrombosis cannot be avoided.

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.

Direct effects of gemfibrozil on the fibrinolytic system. Diminution of synthesis of plasminogen activator inhibitor type 1

BACKGROUND

Platelet-associated epidermal growth factor (EGF) and transforming growth factor-beta (TGF-beta) can augment synthesis of plasminogen activator inhibitor type 1 (PAI-1). Accordingly, exacerbation of atherogenesis may accompany release of platelet-associated growth factors (or mitogens) occurring in association with occult, repetitive thrombosis and thrombolysis. In the Helsinki primary prevention trial, gemfibrozil decreased coronary events but did so essentially only in initially hypertriglyceridemic subjects. Such subjects are known to exhibit high concentrations of PAI-1 in plasma.

METHODS AND RESULTS

To determine whether pharmacological concentrations of gemfibrozil directly affect PAI-1 synthesis, we characterized its effects on a human hepatoma cell line (Hep G2) in vitro. Gemfibrozil decreased basal PAI-1 secretion by 43% and attenuated the augmentation of PAI-1 synthesis over 24 hours induced by EGF and TGF-beta by 37% and 39% without altering overall protein synthesis. Furthermore, it blocked the EGF and TGF-beta-induced increases in PAI-1 mRNA over 6 hours by 65% and 60%. Increases in plasma PAI activity induced by infusion of purified growth factors or by autologous platelet lysates in rabbits were inhibited by gemfibrozil by more than 50%.

CONCLUSIONS

Beneficial effects of gemfibrozil in reducing coronary events in hypertriglyceridemic patients may depend, in part, on potentiation of fibrinolysis by direct diminution of synthesis of endogenous PAI-1.

Mechanisms contributing to increased synthesis of plasminogen activator inhibitor type 1 in endothelial cells by constituents of platelets and their implications for thrombolysis

We recently hypothesized that after pharmacologically induced coronary thrombolysis, increased activity of plasminogen activator inhibitor type 1 (PAI-1) retards recanalization, contributes to early reocclusion, or both. This hypothesis was based on the increased elaboration of PAI-1 that we observed in cultured liver cells exposed to growth factors releasable from platelets activated at sites of thrombosis in vivo. PAI-1 released locally is particularly likely to attenuate lysis of thrombi that are targets of thrombolytic drugs. Accordingly, the present study was performed to determine whether synthesis of PAI-1 by endothelial cells is augmented by products of platelets. Lysates from platelets (0.5-8.0 x 10(4)/mm3 media, i.e. less than 10% of the concentration of platelets in blood) increased synthesis and release of PAI-1 into both the extracellular matrix and conditioned media (by 2.8-fold and 3.3-fold within 6 and 24 hours, respectively). Synthesis of neither tissue-type plasminogen activator nor overall protein increased. Increased synthesis of PAI-1 was confirmed by immunoprecipitation of [35S]PAI-1 after metabolic labeling of cells. The increased elaboration of PAI-1 was consistent with increased transcription as reflected by the observed increase in PAI-1 mRNA of 2.2-fold in 4 hours. Effects of platelet lysates were simulated by transforming growth factor beta (TGF-beta), known to be present in platelet alpha-granules and released with platelet activation. Antibody to TGF-beta reduced the stimulation of PAI-1 synthesis by TGF-beta, as expected, by 82%.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of plasminogen activator inhibitor by products released from platelets

Activation of platelets and augmentation of plasma plasminogen activator inhibitor (PAI) type I activity accompany acute myocardial infarction. To determine whether the two may be related, platelet compounds including epidermal growth factor and transforming growth factor beta as well as platelet lysates were studied in rabbits in vivo. After intravenous infusion of epidermal growth factor (1 and 5 micrograms/kg), plasma PAI activity increased sevenfold and 20-fold, peaking at 2 hours. After infusions of transforming growth factor beta (0.2 and 0.5 microgram/kg), plasma PAI activity increased sevenfold and 12-fold but peaked more slowly (at 5 hours). After infusion of platelet lysates (lysates from 2.8 and 5.6 X 10(8) platelets/kg), the increase was 19-fold and 35-fold, with a peak at 4 hours. Platelet lysates induced a pronounced increase of plasma PAI type 1 messenger RNA (Northern blots) in aorta, liver, and myocardium. Anti-transforming growth factor beta neutralizing antibody markedly attenuated the plasma PAI increase. Concentrations in plasma of fibrinogen and alpha 2-antiplasmin were virtually unaffected under all conditions. Thus, platelet-associated growth factors and platelet lysates, shown previously to increase plasma PAI type 1 messenger RNA expression and protein production in cultured hepatocytes and vascular endothelial cells in vitro, augment plasma PAI in vivo as well. Accordingly, activation of platelets and release of platelet-associated growth factors appear to contribute to the increased plasma PAI seen after myocardial infarction.

Expression of human plasminogen activator inhibitor type-1 (PAI-1) in Escherichia coli as a soluble protein comprised of active and latent forms. Isolation and crystallization of latent PAI-1

Expression of human recombinant plasminogen activator inhibitor type-1 (PAI-1) in Escherichia coli has led to crystallization of 'latent' PAI-1. Cleavage with restriction endonucleases of a cDNA clone encoding PAI-1 yielded an 1127 base pair fragment encoding residues 2-376 of the 379 amino acid serpin. Synthetic DNA linkers were ligated to the 5' and 3' ends of the subclone to add an initiation codon and restore the full coding sequence, and the resulting semisynthetic gene was incorporated into an expression plasmid, pPAIST-7, under the control of the E. coli trp promoter. Transformation of E. coli GE81 with pPAIST-7 led to expression of unglycosylated PAI-1. Lysates of expression cultures contained PAI-1 activity and PAI-1 protein with the predicted Mr. Unglycosylated PAI-1 from E. coli exhibited characteristic properties of authentic PAI-1: (1) it was recovered in both active and inactive (latent) forms; (2) its activity declined during incubation at 37 degrees C; (3) latent PAI-1 was activated by treatment with 4 M guanidine hydrochloride; (4) reactivated PAI-1 formed a detergent-stable complex with tissue plasminogen activator. Latent PAI-1 accounted for more than 85% of PAI-1 in cell lysates and was purified by ammonium sulfate fractionation, anion-exchange chromatography and hydrophobic interaction chromatography. The purified latent PAI-1 was crystallized.

Low molecular weight fibrinolytic inhibitor from Guerin epithelioma

Antifibrinolytic activity of the extract from Guerin epithelioma, a highly metastatic tumour implanted to rats, was determined by fibrinolytic and zymographic methods. The extract exhibits antifibrinolytic activity which is thermostable (60-100 degrees C) and pH-stable (pH 2.7-12). It contains a fibrinolytic inhibitor, with Mr about 7000, with antiplasmin properties, bound to lys-Sepharose and heparin-Sepharose. The molecular weight, physicochemical properties and antiplasmin action of the epithelioma inhibitor prove its identity with the low molecular weight antifibrinolytic factor appearing in the plasma of rats during the development of this tumour.

Interaction between plasminogen activator inhibitor type 1 (PAI-1) bound to fibrin and either tissue-type plasminogen activator (t-PA) or urokinase-type plasminogen activator (u-PA). Binding of t-PA/PAI-1 complexes to fibrin mediated by both the finger and the kringle-2 domain of t-PA

Plasminogen activation is catalyzed both by tissue-type-(t-PA) and by urokinase-type plasminogen activator (u-PA). This reaction is controlled by plasminogen activator inhibitor type 1 (PAI-1) that is either present in plasma or bound to fibrin, present in a thrombus. We studied the mechanism of in vitro inhibition of both t-PA and u-PA activity by PAI-1 bound to fibrin. It is shown that activation of latent PAI-1 unmasks a specific fibrin-binding site that is distinct from its reactive site. This reactive site of activated PAI-1 bound to fibrin is fully exposed to form complexes with t-PA and u-PA, that are unable to activate plasminogen. Upon complex formation with either one of the plasminogen activators, PAI-1 apparently undergoes a conformational change and loses its affinity for fibrin. Consequently, complexes of u-PA and PAI-1 dissociate from the fibrin matrix and are encountered in the fluid phase. In contrast, t-PA/PAI-1 complexes remain bound to fibrin. By employing recombinant t-PA deletion-mutant proteins, that precisely lack domains involved in fibrin binding, we demonstrate that binding of t-PA/PAI-1 complexes is mediated by both the "finger" (F) and the "kringle-2" (K2) domain of t-PA. A model is proposed that explains inhibition of the fibrinolytic process, at the level of plasminogen activation by t-PA, directed by PAI-1 bound to fibrin. An implication of the proposed model is that t-PA/PAI-1 complexes and free t-PA compete for the same binding sites on fibrin.

Recombinant plasminogen activator inhibitor-1 reverses the bleeding tendency associated with the combined administration of tissue-type plasminogen activator and aspirin in rabbits

The major side effect of thrombolytic therapy is bleeding; however, the pathogenesis of this potential complication is not well understood. Accordingly, we examined the effects of aspirin and recombinant human tissue-type plasminogen activator (rt-PA) on serial template bleeding times and on hemostasis parameters in rabbits. The administration of intravenous aspirin (15 mg/kg) produced a slight prolongation in bleeding times, from 2.1 +/- 0.5 to 2.6 +/- 0.5 min (mean +/- SD, n = 26, P less than 0.01), whereas rt-PA (1 mg/kg per h for 2 h) lengthened the bleeding time from 2.4 +/- 0.3 to 3.2 +/- 0.6 min (n = 5, P = NS). Combination of aspirin with 0.5 mg/kg per h of rt-PA for 2 h prolonged the bleeding time from 2.5 +/- 0.4 to 6.2 +/- 0.9 min (n = 10, P less than 0.01), with an associated fibrinogen decrease of approximately 15%. The combination of aspirin with 1 mg/kg per h of rt-PA for 2 h prolonged the bleeding time from 3.0 +/- 0.3 to 8.3 +/- 1.4 min (n = 8, P less than 0.01) and simultaneously induced a decrease of plasma fibrinogen by approximately 40%. Virtually all animals treated with rt-PA and aspirin manifested a bleeding tendency, as evidenced by spontaneous rebleeding at sites of previously performed template bleeding times or oozing at the femoral venous catheterization site. Intravenous bolus injection of 1 mg/kg of guanidine hydrochloride-reactivated recombinant human plasminogen activator inhibitor-1 (rPAI-1) at the end of the rt-PA infusion resulted in complete reversal, within 5 min, of the prolongation of the bleeding time, and in a disappearance of the bleeding tendency. Nonreactivated rPAI-1 and tranexamic acid were significantly less potent in reversing the bleeding time prolongation. These findings indicate that aspirin and rt-PA given separately do not markedly affect the template bleeding time, but in combination induce a marked prolongation associated with a significant bleeding tendency. This bleeding time prolongation can be rapidly normalized by the administration of reactivated rPAI-1.

Potential attenuation of fibrinolysis by growth factors released from platelets and their pharmacologic implications

Increased concentrations of the fast-acting tissue-type plasminogen activator (t-PA) inhibitor attenuate the fibrinolytic activity of pharmacologically administered activators of the fibrinolytic system such as t-PA. Accordingly, it was hypothesized that augmentation of synthesis and elaboration of inhibitor from the liver, leading to increased concentrations of inhibitor in plasma, or from endothelial cells in the vicinity of thrombi undergoing lysis, leading to increased concentrations locally, may contribute to failure of pharmacologically induced thrombolysis or to early reocclusion. Because platelets are rich in transforming growth factor beta and epidermal growth factor-like activity, it was thought that release of growth factors from platelets activated in vivo could mediate increases of the inhibitor in plasma by stimulating its formation in the liver and its local release from endothelial cells in the vicinity of thrombi. If so, fibrinolysis might be rendered more effective by concomitant prevention of platelet growth factor release. Transforming growth factor beta, a major constituent of platelets, increased concentrations of the t-PA inhibitor messenger ribonucleic acid (mRNA) in human hepatoma cells in a specific and dose-dependent manner. A peak effect was seen with 5 ng/ml and a 10-fold increase in 6 hours. Release of inhibitor protein into conditioned media increased as well. Induction of the inhibitor mRNA increase was elicited by exposure as brief as 30 minutes. Cycloheximide, an inhibitor of protein synthesis, was not inhibitory. The mechanisms responsible differed from those seen with epidermal growth factor, shown previously in the laboratory to increase inhibitor mRNA. In addition, the 2 factors were synergistic. Platelet lysates elicited effects simulating those of the purified growth factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibrinolytic inhibitors from the experimental rat epithelioma

Guerin epithelioma, a highly metastatic tumour implanted to Wistar rats contains two inhibitors of fibrinolysis which can be detected with the use of zymographic techniques. The first one--with Mr about 48000 forms SDS-stable complex with urokinase. The second--with Mr about 7000 inhibits fibrinolytic and amidolytic activity of plasmin.

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.

Cloning and sequencing of cDNA for the rat plasminogen activator inhibitor-1

A cDNA encoding rat plasminogen activator-inhibitor (PAI-1) has been isolated from an HTC rat hepatoma cell cDNA library constructed in phage lambda gt10. The cDNA contains 118 bp of 5'-untranslated sequence, 1206 bp encoding a 402-amino acid (aa) protein and 1747 bp of 3'-untranslated sequence. The protein-coding sequence and the derived amino acid sequence share 82% and 81% identity, respectively, with human PAI-1 cDNA and protein. The rat cDNA encodes a preprotein with a 23-aa leader peptide and a predicted N-terminal serine for the mature protein. Three of four potential N-glycosylation acceptor sites as well as the active site of rat PAI-1 are identical to the human protein. The 3'-untranslated region contains a number of unusual regions, including 80 bp of tandemly repeated GpA dinucleotides, a 115-bp stretch which shares greater than 90% sequence identity with a region within the 3'-untranslated cDNA of human PAI-1, and two 70-bp stretches of highly T-rich sequence located close to the 3'-terminus of the cDNA.

Plasminogen activator inhibitor type 1: cell-specific and differentiation-induced expression and regulation in human cell lines, as determined by enzyme-linked immunosorbent assay

We have performed a comparative study of the regulation by glucocorticoids and phorbol 12-myristate 13-acetate (PMA) of the production of type 1 plasminogen activator inhibitor (PAI-1) by 12 human cell lines. A sandwich-type enzyme-linked immunosorbent assay (ELISA) for PAI-1 that measures free PAI-1 as well as complexes between PAI-1 and both types of plasminogen activators has been used. Basal PAI-1 accumulation varied more than 5000-fold between the cell lines. No correlation was found between the PAI-1 level and other characteristics of the cell lines, except that three lines of SV40-transformed fibroblasts produced more PAI-1 than two non-transformed fibroblast cell lines. Three out of the 12 cell lines responded to glucocorticoids by an increased PAI-1 production. Four cell lines responded to PMA by an increased PAI-1 production. In addition, PMA-induced differentiation of the monocyte cell line U937 and the promyelocytic cell line HL-60 into macrophage-like cells was found to be correlated with an up to 100-fold increase in PAI-1 accumulation. The PMA-dependent differentiation of HL-60 cells led to acquisition of glucocorticoid inducibility of PAI-1. These findings provide information for future studies of the molecular mechanism of cell-specific expression and regulation of PAI-1.

Bovine endothelial cell plasminogen activator inhibitor. Purification and heat activation

A plasminogen activator inhibitor (PAI) was purified from bovine endothelial cell conditioned medium by a simple procedure in the absence of protein denaturant. The yield was 2.2 mg from 1.61 conditioned medium in a typical experiment. The purified inhibitor showed a single band on sodium dodecyl sulfate/polyacrylamide gel electrophoresis and reverse fibrin autography with an apparent molecular mass of 45 kDa. The amino-terminal 40-amino-acid sequence was determined and found to be 70% similar to the reported corresponding sequence of human PAI-1. The amino acid composition also revealed a close relationship between bovine PAI and human PAI-1. The purified PAI was substantially inactive (570 U/mg) but it could be activated by treatment with protein denaturants such as 1% SDS (1.8 X 10(5) U/mg) and 4 M guanidine-HCl (1.5 X 10(5) U/mg). A more effective activation of this latent PAI was achieved by heat treatment at 100 degrees C for 2.5 min, generating the specific activity of 1.0 X 10(6) U/mg. The heat-activated PAI lost its activity during incubation at 56 degrees C for 30 min, but repeated heat at 100 degrees C for 2.5 min could regenerate about 70% of the initial activity. Treatment at 37 degrees C, 56 degrees C and 80 degrees C, however, failed to activate the latent PAI at all. These findings suggest that the buried reactive site of the latent PAI is exposed as a result of a heat-induced, specific conformational change, but tends to be masked again during renaturation under mild conditions, i.e. the PAI protein takes on preferentially a latent form.

The regulatory region of the human plasminogen activator inhibitor type-1 (PAI-1) gene

The human gene for plasminogen activator inhibitor type-1 (PAI-1) has been isolated and its promoter region characterized. PAI-1 regulation by glucocorticoids, transforming growth factor-beta (TGF-beta) and the phorbol ester PMA is shown to be exerted at the promoter level. A fragment spanning 805 nucleotides of the 5' flanking and 72 of the 5' untranslated region contain information enough to promote transcription and to respond to glucocorticoids when fused to a reporter gene and transfected into human fibrosarcoma cells. A moderately repetitive DNA sequence, containing a TATA box, a GRE consensus, a Z-DNA forming sequence and two imperfect direct repeats at the extremities, is present a few nucleotides 5' of the human PAI-1 gene transcription start site, raising the possibility that this gene could have been activated by DNA insertion during evolution.