Plasminogen activator inhibitor type 1 biosynthesis and mRNA level are increased by dexamethasone in human fibrosarcoma cells

Post-transcriptional regulation of plasminogen activator inhibitor type-1 expression in human pleural mesothelial cells

The plasminogen activator inhibitor type-1 (PAI-1) effectively blocks the activities of free and receptor-bound urokinase-type plasminogen activator. Incubation of cultured human pleural mesothelial (Met5A) cells with TGF-beta increased PAI-1 protein. TGF-beta, phorbol myristate acetate, and the translation inhibitor cycloheximide induced PAI-1 mRNA and slowed its degradation, suggesting that PAI-1 mRNA could be regulated by interaction of a PAI-1 binding protein (PAI-1 mRNABp) with PAI-1 mRNA. We found that an approximately 60 kD cytoplasmic PAI-1 mRNABp is detectable in cytoplasmic extracts of MeT5A human pleural mesothelial and malignant mesothelioma cells. The PAI-1 mRNABp specifically binds to a 33-nt sequence in the 3' untranslated region of PAI-1 mRNA. Insertion of this 33-nt sequence destabilizes otherwise stable beta-globin mRNA, indicating that the binding sequence accelerates decay of endogenous PAI-1 mRNA. Competitive inhibition by overexpression of the 33-nt binding sequence in MeT5A cells reduced PAI-1 mRNA decay and increased PAI-1 protein and mRNA expression, indicating that the PAI-1 mRNABp destabilizes PAI-1 mRNA by its interaction with the endogenous 33-nt binding sequence. Incubation of Met5A cells with TGF-beta attenuated the interaction of the PAI-1 mRNABp with the 33-nt sequence. By conventional and affinity purification, we isolated the PAI-1 mRNABp and confirmed its identity as 6-phospho-d-gluconate-NADP oxidoreductase, which specifically interacts with the full-length and the 33-nt sequence of the PAI-1 mRNA 3' untranslated region. This newly recognized pathway could influence expression of PAI-1 by mesothelial or mesothelioma cells at the level of mRNA stability in the context of pleural inflammation or malignancy.

Plasminogen activator inhibitor-1 polymers, induced by inactivating amphipathic organochemical ligands

Negatively charged organochemical inactivators of the anti-proteolytic activity of plasminogen activator inhibitor-1 (PAI-1) convert it to inactive polymers. As investigated by native gel electrophoresis, the size of the PAI-1 polymers ranged from dimers to multimers of more than 20 units. As compared with native PAI-1, the polymers exhibited an increased resistance to temperature-induced unfolding. Polymerization was associated with specific changes in patterns of digestion with non-target proteases. During incubation with urokinase-type plasminogen activator, the polymers were slowly converted to reactive centre-cleaved monomers, indicating substrate behaviour of the terminal PAI-1 molecules in the polymers. A quadruple mutant of PAI-1 with a retarded rate of latency transition also had a retarded rate of polymerization. Studying a number of serpins by native gel electrophoresis, ligand-induced polymerization was observed only with PAI-1 and heparin cofactor II, which were also able to copolymerize. On the basis of these results, we suggest that the binding of ligands in a specific region of PAI-1 leads to so-called loop-sheet polymerization, in which the reactive centre loop of one molecule binds to beta-sheet A in another molecule. Induction of serpin polymerization by small organochemical ligands is a novel finding and is of protein chemical interest in relation to pathological protein polymerization in general.

P52PAI-1 gene expression in butyrate-induced flat revertants of v-ras-transformed rat kidney cells: mechanism of induction and involvement in the morphological response

Sodium n-butyrate-induced flat reversion in v-K-ras oncogene-transformed rat kidney (KNRK) cells is associated with transcriptional activation of the p52PAI-1 gene (which encodes the type-1 inhibitor of plasminogen activator). Butyrate-initiated expression of p52PAI-1 mRNA and protein correlated with induced cell spreading and preceded development of cell-to-substrate focal adhesions. Such undersurface matrix contact structures, which are absent from parental KNRK cells, require proximal PAI-1 deposition for their stabilization. Stimulated p52PAI-1 expression by flat revertants (approximating 25-fold that of control cells) and the accompanying cytoarchitectural reorganization appeared to be programmed responses to butyrate as both events required de novo RNA and protein synthesis, metabolic characteristics consistent with a secondary pathway of gene regulation. To assess the relevance of p52PAI-1 induction to the process of flat reversion more critically, a molecular genetic approach was designed to maintain high-level constitutive p52PAI-1 synthesis in the absence of butyrate. KNRK cells transfected with a Rc/CMVPAI plasmid construct, in which expression of a p52PAI-1 cDNA insert was driven by enhancer-promoter sequences from the immediate-early gene of human cytomegalovirus, formed colonies comprised of flat-revertant-like cells with a greater frequency than did cells transfected with the Rc/CMV vector alone (24.8% and 1.7% respectively). Comparative analysis of randomly selected Rc/ CMVPAI clones indicated that a 10-fold increase in immunoreactive p52PAI-1 protein, relative to Rc/CMV isolates, correlated with generation of the flat phenotype. These data suggest that induced p52PAI-1 expression probably functions in the development of morphological revertants in the KNRK cell system.

Postoperative changes in plasma tissue-type plasminogen activator and type 1 plasminogen activator inhibitor

To clarify the changes which occur postoperatively in intravascular fibrinolysis, plasma levels of tissue-type plasminogen activator (t-PA) antigen, the total plasminogen activator inhibitor type-1 (PAI-1) antigen, and the t-PA-PAI-1 complexes were assayed in this study. Blood samples were taken the morning before surgery, then at 0, 12, 24, 36, 60, 108, and 156 h postoperatively in ten patients who underwent radical surgery for thoracic esophageal cancer. The plasma levels of the t-PA and total PAI-1 antigens, and the t-PA-PAI-1 complexes were then measured by enzyme immunoassay. The plasma t-PA and total PAI-1 levels increased significantly in the immediate postoperative period, the percent increase of the latter being much greater than that of the former. Moreover, the calculated free t-PA antigen level was decreased throughout the postoperative period, suggesting postoperative hypofibrinolysis. The platelet count and neutrophil elastase level were significantly correlated with the free t-PA antigen level at r = 0.630, P < 0.001, and r = -0.447, P < 0.01, respectively. The results of this study indicated that post-operative hypofibrinolysis caused by the increased synthesis of PAI-1 may enhance postoperative hypercoagulability, and this may lead to the development of organ damage. Thus, the concentration of the PAI-1 antigen may be a potentially important index for the prediction of postoperative illness.

Opposite and independent actions of cyclic AMP and transforming growth factor beta in the regulation of type 1 plasminogen activator inhibitor expression

We have investigated the mechanisms by which type 1 plasminogen activator inhibitor (PAI-1) is regulated by transforming growth factor beta (TGF-beta) and by epidermal growth factor (EGF) in CCL64 mink lung epithelial cells, BSC-1 monkey kidney epithelial cells, mouse embryo fibroblast (AKR-2B 84A) cells and normal rat kidney fibroblasts (NRK). TGF-beta increases PAI-1 expression in all four cell lines, and EGF acts synergistically with TGF-beta to increase PAI-1 expression in CCL64 cells but not in the other three cell lines. Here we show that PAI-1 expression can be regulated independently through two different signal transduction pathways. One pathway involves protein kinase C and is stimulated by the tumour promoter phorbol myristate acetate (PMA). Whereas preincubation with PMA completely eliminated PMA-induced PAI-1 synthesis and secretion in both CCL64 and BSC-1 cells, this treatment had no effect on TGF-beta- and EGF-induced PAI-1 levels. Therefore we conclude that protein kinase C does not mediate the effects of either EGF or TGF-beta on PAI-1 expression. The expression of PAI-1 was decreased by agents increasing intracellular cyclic AMP: (cAMP) cholera toxin, forskolin and dibutyryl cAMP lowered both the basal level and the TGF-beta- and PMA-induced levels of PAI-1 expression. These effects of cAMP-elevating agents and of TGF-beta on PAI-1 protein synthesis were also reflected in changes in TGF-beta-induced PAI-1 gene transcription, as measured by nuclear run-on. These results show that PAI-1 gene expression is sensitive to high levels of intracellular cAMP and that this effect occurs at the transcriptional level. Although increased intracellular cAMP concentrations decrease the absolute level of PAI-1 expression, the ability of TGF-beta and EGF to induce PAI-1 gene expression is unchanged. These results are discussed in relation to the observation that sensitivity to cAMP is a common feature of TGF-beta-regulated genes.

Transcriptional regulation of plasminogen activator inhibitor type-1 mRNA in Hep G2 cells by epidermal growth factor

Secretion of plasminogen activator inhibitor type-1 (PAI-1) by cultured cells is increased after exposure to specific cytokines and growth factors. We have shown previously that incubation of Hep G2 cells with epidermal growth factor (EGF) results in a marked increase in steady state levels of PAI-1 mRNA (Lucore, C.L., et al. (1988) J. Biol. Chem. 263, 15845-15848). The present study was undertaken to determine whether the regulation of expression of PAI-1 mRNA by EGF is mediated at the level of transcription and/or by post-transcriptional mechanisms. The rate of transcription of the PAI-1 gene measured by nuclear run-on assays was found to be increased within 2 h after stimulation of the cells with EGF (5 ng/ml) (3.2 fold increase relative to control, n = 2, range 3.0-3.4). It reached a maximum in 3 h, (9.2 fold increase relative to control, n = 2, range 8.8-9.6) and returned to baseline in 5 h. Exposure of the cells to EGF did not increase the rate of transcription of the glyceraldehyde-3-phosphate dehydrogenase gene. The half life of PAI-1 mRNA in Hep G2 cells was 120 min as determined by RNA blot analysis after exposure of the cells to actinomycin D to inhibit transcription. Stimulation of the cells with EGF did not result in significant change in the half life of PAI-1 mRNA. The results demonstrate that exposure of Hep G2 cells to EGF increases PAI-1 gene transcription.

Plasminogen activator inhibitor type I stabilizes vitronectin-dependent adhesions in HT-1080 cells

Polyclonal antibodies against plasminogen activator inhibitor type-I (PAI-1) caused rapid retraction and rounding of substrate-attached HT-1080 cells. The kinetics and extent of antibody-mediated cell rounding were not dependent on either urokinase or plasmin activity. Cells adherent to vitronectin-coated substrates detached within 2 h of antibody addition. Cells adherent to fibronectin were unaffected by the antibodies. Immunoblotting of substrate-attached material indicated that HT-1080 cells deposited PAI-1 into vitronectin, but not fibronectin, dependent contacts. These data suggest that the antibody-mediated cell rounding resulted from a steric disruption of vitronectin-dependent adhesions, indicating that the binding site on vitronectin for PAI-1 is near, but does not overlap, the binding site for vitronectin receptor. The accumulation of PAI-1 into vitronectin-dependent adhesion sites correlated temporally with the preferential degradation of fibronectin from the substrate. HT-1080 cells adherent to either fibronectin or vitronectin were able to activate exogenous plasminogen to plasmin. Plasmin levels were increased 200% on cells adherent to fibronectin and 100% on cells adherent to vitronectin. In the presence of a neutralizing antibody against PAI-1, vitronectin adherent cells activated plasminogen to the same extent as fibronectin adherent cells. Plasmin levels of 200% above baseline were associated with retraction of cells from the substrate. The ability of vitronectin adherent cells to activate exogenous plasmin was completely blocked in the presence of neutralizing antibodies against urokinase. These data represent the first demonstration that vitronectin-associated PAI-1 regulates urokinase in focal contact areas.

Dexamethasone-induced plasminogen activator inhibitor: characterization, purification, and preparation of monoclonal antibodies

The effects of dexamethasone on protein synthesis were studied in human fibrosarcoma (HT-1080) cells. Dexamethasone induced a new protein of 46 kD which was rapidly secreted into the medium, while neither progesterone nor estradiol would induce the synthesis of this protein and only a small increase in its amount could be seen in the presence of testosterone. The 46 kD protein was partially purified by ammonium sulfate precipitation and gel filtration and mouse monoclonal antibodies to it were produced in mouse hybrid cells. Altogether 13 positive clones were found, of which six reacted only with native and seven reacted with the unreduced 46 kD protein in Western blotting. It was possible by using polyclonal antibodies to plasminogen activator inhibitor type I (PAI-1) and purified plasminogen activator inhibitor type I to confirm that the 46 kD protein purified and characterized here was PAI-1. In addition, the 46 kD protein clearly inhibited plasminogen activation, thus further confirming that protein isolated was an inhibitor of plasminogen activator. Since the induction of PAI-1 by dexamethasone was very extensive, it is possible that glucocorticoids regulate proteolysis and fibrinolysis in vivo by increasing the amount of the inhibitor of plasminogen activator and thus preventing the activation of plasminogen to plasmin. The reduction of activation of plasminogen to plasmin by glucocorticoid-induced inhibitor could be of great importance, e.g., in various blistering diseases, in metastases from malignant cells, and in the migration of inflammatory cells.

Urokinase-dependent adhesion loss and shape change after cyclic adenosine monophosphate elevation in cultured rat mesangial cells

Mesangial cells in culture change shape and become less adhesive in response to cAMP elevation (e.g., treatment with isoproterenol plus isobutylmethylxanthine (IM). Inhibitors of serine proteases inhibit cellular shape change in response to IM. To further examine the role of cell surface proteases in shape change, adhesion plaque proteins (i.e., preparations of ventral membranes and extracellular matrix) were separated in SDS-polyacrylamide gels containing gelatin with and without plasminogen. Four discrete zones of lysis were evident in plasminogen gels (indicative of activation of plasminogen) from control adhesion plaques: one inconspicuous zone with a Mr approximately 150 kD, another at approximately 115 kD, and a doublet at approximately 35-32 kD. Another diffuse zone of lysis centered around Mr approximately 70 kD and contained a defined band of approximately 56 kD. Adhesion plaques contained most of the plasminogen activators (PA). 5 min after IM treatment, the Mr approximately 150- and approximately 115-kD PA were increased in activity. Vasopressin (VP), which prevented shape change and adhesion loss when added along with IM, inhibited the increase in these PA. Preincubation with monoclonal or polyclonal antibodies to urokinase-type plasminogen activator (uPA) totally inhibited the IM-inducible shape change and adhesion loss. Activation of plasminogen throughout the gels revealed multiple protease resistant bands that markedly increased with IM treatment (maximal at 45 min). These may represent focal control mechanisms. uPA thus may mediate focal proteolysis, which results in shape change and decreased adhesion.

Type 1 plasminogen activator inhibitor gene: functional analysis and glucocorticoid regulation of its promoter

Plasminogen activator inhibitor type 1 is an important component of the fibrinolytic system and its biosynthesis is subject to complex regulation. To study this regulation at the level of transcription, we have identified and sequenced the promoter of the human plasminogen activator inhibitor type 1 gene. Nuclease protection experiments were performed by using endothelial cell mRNA and the transcription initiation (cap) site was established. Sequence analysis of the 5' flanking region of the gene revealed a perfect "TATA box" at position -28 to position -23, the conserved distance from the cap site. Comparative functional studies with the firefly luciferase gene as a reporter gene showed that fragments derived from this 5' flanking region exhibited high promoter activity when transfected into bovine aortic endothelial cells and mouse Ltk- fibroblasts but were inactive when introduced into HeLa cells. These studies indicate that the fragments contain the plasminogen activator inhibitor type 1 promoter and that it is expressed in a tissue-specific manner. Although the fragments were also silent in rat FTO2B hepatoma cells, their promoter activity could be induced up to 40-fold with the synthetic glucocorticoid dexamethasone. Promoter deletion mapping experiments and studies involving the fusion of promoter fragments to a heterologous gene indicated that dexamethasone induction is mediated by a glucocorticoid responsive element with enhancer-like properties located within the region between nucleotides -305 and +75 of the plasminogen activator inhibitor type 1 gene.

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.

Glucocorticoid-modulated gene expression of tissue- and urinary-type plasminogen activator and plasminogen activator inhibitor 1 and 2

Constitutive gene expression of four components of plasminogen activating enzyme system, urinary and tissue-type plasminogen activator (u-PA and t-PA), plasminogen activator inhibitor 1 (PAI-1) and PAI-2 in HT-1080 human fibrosarcoma cells, was modulated by the synthetic glucocorticoid dexamethasone (Dex, 10(-7) M). More than 90% of u-PA, t-PA and PAI-1 antigen was found in conditioned medium, whereas PAI-2 was mainly cell associated. In 48-h culture supernatants (expressed per 10(6) cells) PAI-1 antigen increased from 350 to 3,300 ng and t-PA from 19 to 38 ng. u-PA and PAI-2 in the same samples decreased from 380 to 46 ng and from 3.5 to 1.8 ng, respectively. Northern blot hybridization and nuclear "Run-on" transcription assays demonstrated that the increase of t-PA and PAI-1 and the decrease of u-PA were associated with equivalent changes of gene template activity. Modulation of u-PA, t-PA and PAI-1 gene expression by Dex was completely blocked by the glucocorticoid antagonist RU 38486, suggesting that all effects were mediated through the glucocorticoid receptor. Cycloheximide, an inhibitor of protein biosynthesis induced a rapid transient increase of t-PA, u-PA and PAI-1 mRNA and a sustained increase of PAI-2 mRNA, but blocked the more long term effects of Dex, suggesting that both constitutive and hormonally regulated maintenance of mRNA steady state levels required protein biosynthesis.