Activators and inhibitors of the plasminogen system in Alzheimer's disease

Accumulation and deposition of Aβ is one of the main neuropathological hallmarks of Alzheimer's disease (AD) and impaired Aβ degradation may be one mechanism of accumulation. Plasmin is the key protease of the plasminogen system and can cleave Aβ. Plasmin is activated from plasminogen by tissue plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). The activators are regulated by inhibitors which include plasminogen activator inhibitor-1 (PAI-1) and neuroserpin. Plasmin is also regulated by inhibitors including α2-antiplasmin and α2-macroglobulin. Here, we investigate the mRNA levels of the activators and inhibitors of the plasminogen system and the protein levels of tPA, neuroserpin and α2-antiplasmin in post-mortem AD and control brain tissue. Distribution of the activators and inhibitors in human brain sections was assessed by immunoperoxidase staining. mRNA measurements were made in 20 AD and 20 control brains by real-time PCR. In an expanded cohort of 38 AD and 38 control brains tPA, neuroserpin and α2-antiplasmin protein levels were measured by ELISA. The activators and inhibitors were present mainly in neurons and α2-antiplasmin was also associated with Aβ plaques in AD brain tissue. tPA, uPA, PAI-1 and α2-antiplasmin mRNA were all significantly increased in AD compared to controls, as were tPA and α2-antiplasmin protein, whereas neuroserpin mRNA and protein were significantly reduced. α2-macroglobulin mRNA was not significantly altered in AD. The increases in tPA, uPA, PAI-1 and α2-antiplasmin may counteract each other so that plasmin activity is not significantly altered in AD, but increased tPA may also affect synaptic plasticity, excitotoxic neuronal death and apoptosis.     

Plasminogen activation: biochemistry, physiology, and therapeutics

The mammalian serine protease zymogen, plasminogen, can be converted into the active enzyme plasmin by vertebrate plasminogen activators urokinase (uPA), tissue plasminogen activator (tPA), factor XII-dependent components, or by bacterial streptokinase. The biochemical properties of the major components of the system, plasminogen/plasmin, plasminogen activators, and inhibitors of the plasminogen activators, are reviewed. The plasmin system has been implicated in a variety of physiological and pathological processes such as fibrinolysis, tissue remodeling, cell migration, inflammation, and tumor invasion and metastasis. A defective plasminogen activator/inhibitor system also has been linked to some thromboembolic complications. Recent studies of the mechanism of fibrinolysis in human plasma suggest that tPA may be the primary initiator and that overall fibrinolytic activity is strongly regulated at the tPA level. A simple model for the initiation and regulation of plasma fibrinolysis based on these studies has been formulated. The plasminogen activators have been used for thrombolytic therapy. Three new thrombolytic agents--tPA, pro-uPA, and acylated streptokinase-plasminogen complex--have been found to possess better properties over their predecessors, urokinase and streptokinase. Further improvements of these molecules using genetic and protein engineering tactics are being pursued.     

Lysine 156 promotes the anomalous proenzyme activity of tPA: X-ray crystal structure of single-chain human tPA.

Tissue type plasminogen activator (tPA) is the physiological initiator of fibrinolysis, activating plasminogen via highly specific proteolysis; plasmin then degrades fibrin with relatively broad specificity. Unlike other chymotrypsin family serine proteinases, tPA is proteolytically active in a single-chain form. This form is also preferred for therapeutic administration of tPA in cases of acute myocardial infarction. The proteolytic cleavage which activates most other chymotrypsin family serine proteinases increases the catalytic efficiency of tPA only 5- to 10-fold. The X-ray crystal structure of the catalytic domain of recombinant human single-chain tPA shows that Lys156 forms a salt bridge with Asp194, promoting an active conformation in the single-chain form. Comparisons with the structures of other serine proteinases that also possess Lys156, such as trypsin, factor Xa and human urokinase plasminogen activator (uPA), identify a set of secondary interactions which are required for Lys156 to fulfil this activating role. These findings help explain the anomalous single-chain activity of tPA and may suggest strategies for design of new therapeutic plasminogen activators.     

Kinetics of the inhibition of plasminogen activators by the plasminogen-activator inhibitor. Evidence for ''second-site'' interactions.

The reactions between plasminogen-activator inhibitor (PAI) and different plasminogen activators were studied in the presence of chromogenic peptide substrates for the enzymes. Our findings suggest that the rate constants for the reactions of PAI with single-chain tissue plasminogen activator (tPA), two-chain tPA, high-Mr urokinase and low-Mr urokinase are high and quite similar (1.6 X 10(7)-3.9 X 10(7) M-1.s-1). A free active site in the enzymes seems to be necessary for their reaction with PAI. Amino acids with antifibrinolytic properties did not interfere with the reactions. However, di-isopropyl phosphorofluoridate-inactivated tPA inhibited the reaction between PAI and all plasminogen activators in a similar way. These findings clearly demonstrated that a 'second-site' interaction, in addition to that between the enzyme active site and the inhibitor 'bait' peptide bond, is of importance for the high reaction rate. The reaction rate between PAI and single-chain tPA in the presence of an activator substrate (D-Ile-Pro-Arg p-nitroanilide) was decreased in the presence of fibrin. Fibrin caused a decrease in the Km for the single-chain tPA-substrate reaction. As a consequence, the 'free' concentration of single-chain tPA in the system decreased in the presence of fibrin, affecting the reaction rate between PAI and single-chain tPA. The phenomenon might be of physiological relevance, in the sense that single-chain tPA bound to fibrin in the presence of plasminogen would be protected against inactivation by PAI.     

Regulation of tissue-type plasminogen activator and plasminogen activator inhibitor type-1 in cultured rat Sertoli and Leydig cells

New data are provided to show that (i) rat Sertoli cells produce two types of plasminogen activators, tissue type (tPA) and urokinase type (uPA), and a plasminogen activator inhibitor type-1 (PAI-1); (ii) both tPA (but not uPA) and PAI-1 secretion in the culture are modified by FSH, forskolin, dbcAMP, GnRH, PMA and growth factors (EGF and FGF), but not by hCG and androstenedione (△4); (iii) in vitro secretion of tPA and PA-PAI-1 complexes of Sertoli cells are greatly enhanced by presence of Leydig cells which produce negligible tPA but measurable PAI-1 activity;(iv) combination culture of Sertoli and Leydig cells remarkably increases FSH-induced PAI-1 activity and decreases hCG- and forskolin-induced inhibitor activity as compared with that of two cell types cultured alone. These data suggest that rat Sertoli cells, similar to ovarian granulosa cells, are capable of secreting both tPA and uPA, as well as PAI-1. The interaction of Sertoli cells and Leydig cells is essential for the cells to response to     

Plasminogen activator expression in F9 teratocarcinoma embryoid bodies and their endoderm derivatives

Plasminogen activators are believed to play an important role in tissue remodeling and cell migration. During mouse embryogenesis, visceral endoderm secretes urokinase-type plasminogen activator (uPA) whereas parietal endoderm secretes tissue-type plasminogen activator (tPA). Visceral endoderm from F9 embryoid bodies can transdifferentiate into parietal endoderm under the appropriate culture conditions. We have examined at the protein and mRNA levels the type of plasminogen activator expressed in whole embryoid bodies, visceral endoderm and its parietal endoderm derivatives. Our experiments show that the visceral endoderm on F9 embryoid bodies synthesizes and secretes substantial amounts of both tPA and uPA. In contrast, the parietal endoderm derived directly from the visceral endoderm secretes dramatically increased levels of tPA and decreases production of uPA to low or below detectable levels. These data support the finding that visceral endoderm can transdifferentiate to parietal endoderm. In addition, this transition provides an excellent model for studying the molecular basis of the coincident down- and upregulation of the two plasminogen activators as well as their potential function during embryogenesis.     

Molecular basis of specific inhibition of urokinase plasminogen activator by amiloride

The urokinase plasminogen activator (uPA) and tissue plasminogen activator (tPA) are very similar serine proteases with the same physiological function, the activation of plasminogen. An increased amount or activity of uPA but not tPA has been detected in human cancers. The PAs are weak proteolytic enzymes, but they activate plasminogen to plasmin, a strong proteolytic enzyme largely responsible for the malignant properties of cancers. It has been shown recently that the administration of uPA inhibitors can reduce tumor size. Inhibitors of uPA could therefore be used as anti-cancer and anti-angiogenesis agents. It has been found that amiloride competitively inhibits the catalytic activity of uPA but not tPA. Modification of this chemical could therefore produce a new class of uPA specific inhibitors and a new class of anti-cancer agents. The X-ray structure of the uPA complex with amiloride is not known. There are structural differences in the specificity pocket of uPA and tPA. However, the potential energy of binding amiloride is lower outside this cavity in the case of tPA. A region responsible for binding amiloride to tPA has been proposed as the loop B93-B101, reached in negatively charged amino acids present in tPA but not uPA.     

Expression of a Novel Chimeric-Truncated tPA in Pichia pastoris with Improved Biochemical Properties

Thrombolytic therapy by plasminogen activators (PAs) has been a main goal in the treatment of acute myocardial infarction. Despite improved outcomes of currently available thrombolytic therapies, all these agents have different drawbacks that may result in less than optimal outcomes. In order to make tissue plasminogen activator (tPA) more potent, while being more resistant to plasminogen activator inhibitor-1 (PAI-1) and having a higher affinity to fibrin, a new chimeric-truncated form of tPA (CT tPA) was designed and expressed in Pichia pastoris. This novel variant consists of a finger domain of Desmoteplase, an epidermal growth factor (EGF) domain, a kringle 1 (K1) domain, a kringle 2 (K2) domain, in which the lysine binding site (LBS) was deleted, and a protease domain, where the four amino acids lysine 296, arginine 298, arginine 299, and arginine 304 were substituted by aspartic acid. The chimera CT tPA showed 14-fold increase in its activity in the presence of fibrin compared to the absence of fibrin. Furthermore, CT tPA showed about 10-fold more potency than commercially available full-length tPA (Actylase^®) and provided 1.2-fold greater affinity to fibrin. A residual activity of only 68 % was observed after incubation of Actylase^® with PAI-1, however, 91 % activity remained for CT tPA. These promising findings suggest that the novel CT tPA variant might be an acceptable PA with superior characteristics and properties.     

A spectrophotometric solid-phase fibrin-tissue plasminogen activator activity assay (SOFIA-tPA) for high-fibrin-affinity tissue plasminogen activators

A new spectrophotometric solid-phase fibrin-tissue plasminogen activator activity assay (SOFIA-tPA), specific for the quantitation of tissue plasminogen activators, is described. The method is based on (1) the high-affinity binding (Kp = 1.4 +/- 2 nM) of tPA to a solid-phase fibrin network constructed by thrombin proteolysis of fibrinogen covalently coupled to polyglutaraldehyde-activated polyvinyl chloride microtiter plates, and (2) the subsequent development of PA activity by the fibrin-tPA complex and its measurement with a coupled assay using a chromogenic substrate highly selective for plasmin. Conditions were chosen such that the rate of para-nitroaniline release from the substrate is directly proportional to the concentration of tPA. The support is able to isolate tPA from the bulk of proteins present in any biological fluid allowing the assay to specifically detect tPA activity (range: 0.01 to 50 IU/ml) even in the presence of other activators, proteases, and inhibitors. Since the assay is done in a well-defined reaction mixture (the fibrin-tPA complex, plasminogen, and the synthetic substrate), kinetics studies using pure or crude tPA can be performed. Standard curves (rate measurement and endpoint methods) were made using the international standard (preparation 83/517) for tPA.     

Conjugation to an antifibrin monoclonal antibody enhances the fibrinolytic potency of tissue plasminogen activator in vitro

Tissue plasminogen activator (tPA) was covalently linked by disulfide bonds to a monoclonal antibody specific for the amino terminus of the beta chain of fibrin (antibody 59D8). The activity of the tPA-59D8 conjugate was compared with that of tPA, urokinase (UK), and a UK-59D8 conjugate. For lysis of fibrin monomer, tPA was 10 times as potent as UK, whereas both UK-59D8 and tPA-59D8 conjugates were 100 times as potent as UK and 10 times as potent as tPA. Conjugation of tPA or UK to antibody 59D8 produced a 3.2-4.5-fold enhancement in clot lysis in human plasma over that of the respective unconjugated plasminogen activator. However, the UK-59D8 conjugate was only as potent as tPA alone. Antibody-conjugated tPA or UK consumed less fibrinogen, alpha 2-antiplasmin, and plasminogen than did the unconjugated activators, at equipotent fibrinolytic concentrations. Antibody targeting thus appears to increase the concentration of tPA in the vicinity of a fibrin deposit, which thereby leads to enhanced fibrinolysis.     

Highly Effective Fibrinolysis by a Sequential Synergistic Combination of Mini-Dose tPA plus Low-Dose Mutant proUK

Results of thrombolysis by monotherapy with either tPA or proUK have not lived up to expectations. Since these natural activators are inherently complementary, this property can be utilized to a synergistic advantage; and yet, this has undergone little evaluation. ProUK is no longer available because at pharmacological concentrations it converts to UK in plasma. Therefore, a single site proUK mutant, M5, was developed to address this problem and was used in this study. Fibrinolysis was measured using preformed fluoresceinated 24 h old clots in a plasma milieu rather than by the standard automated method, because proUK/M5 is sensitive to inactivation by thrombin and activation by plasmin. The shortest 50% clot lysis time that could be achieved by tPA or M5 alone was determined: mean times were 55 and 48 minutes respectively. These bench marks were matched by 6% of the tPA monotherapy dose combined with 40% that of M5: mean lysis time 47 minutes with less associated fibrinogenolysis. Results showed that the tPA effect was limited to initiating fibrinolysis which was completed by M5 and then tcM5. Plasma C1-inhibitor inhibited fibrinogenolysis by M5, providing protection from side effects not available for proUK. In conclusion, by utilizing the complementary properties and sequential modes of action of each activator, more efficient fibrinolysis with less non-specific effects can be achieved than with traditional monotherapy. In vivo validation is needed, but in a previous clinical trial using a similar combination of tPA and proUK (5% and 50% monotherapy doses) very promising results have already been obtained.     

The Role of Tissue-type Plasminogen Activator in Rat Corpus Luteum

It is here reported for the first time that luteal cells are capable of secreting plasminogen activators(PA),(both tissue-type,tPA,and urokinase-type,uPA),and plasminogen activator inhibitor type-1(PAl-1).Using organ culture model,we have demonstrated that tPA,but not uPA,showed markedchange during luteolytic period in rat corpus luteum.A great amount oftPA was secreted in corpusluteum on D 14 and D 17 while very low level of tPA activity was detected before D 12.Correspondingly,the progesterone production in the corpus luteum increased gradually in a time-dependent manner from D 1 to D 12 but dropped abruptly to a very low level on D 14.Additionof exogenous tPA to the CL culture caused considerable decrease in progesterone secretion whileinclusion of purified monoclone tPA antibodies in the culture augmented progesterone productionof CL.It is therefore suggested that tPA may play an important role in luteolytic process.     

A peptide mimicking the C-terminal part of the reactive center loop induces the transition to the latent form of plasminogen activator inhibitor type-1

Plasminogen activator inhibitor-1 (PAI-1) is the primary inhibitor of plasminogen activators (uPA and tPA) and thus plays a central role in fibrinolysis. The spontaneous insertion of its reactive centre loop (RCL) into β-sheet A is responsible for its irreversible conversion into the inactive latent form. In this study, we used two peptides mimicking residues P14-P9 and P8-P3 of the RCL so as to understand this dynamic process. We show that both peptides inhibit the formation of PAI-1/uPA and PAI-1/tPA complexes via two different mechanisms. Targeting the N-terminal part of the loop induces the cleavage of PAI-1 by the proteases uPA/tPA while targeting its C-terminal part greatly favors the irreversible formation of latent PAI-1.     

Overexpression of plasminogen activators in the nucleus accumbens enhances cocaine-, amphetamine- and morphine-induced reward and behavioral sensitization

Urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA) are extracellular proteases that play a role in synaptic plasticity and remodeling. Psychostimulants induce both tPA and uPA in acute and chronic drug delivery, but cocaine induces preferentially uPA, whereas morphine and amphetamine induce preferentially tPA. Specific doxycline-regulatable lentiviruses expressing these extracellular proteases have been prepared and stereotaxically injected into the nucleus accumbens. We show that tPA-overexpressing animals show greater locomotor activity and behavioral sensitization upon morphine and amphetamine treatments. These effects could be fully suppressed by doxycycline or when tPA had been silenced using small interfering RNAs (siRNAs)-expressing lentiviruses. Furthermore, animals infected with lentiviruses expressing uPA show enhanced conditional place preference for cocaine compared with tPA-overexpressing animals. In contrast, tPA-overexpressing animals when administered amphetamine or morphine showed greater place preference compared with uPA-overexpressing animals. The effects are suppressed when tPA has been silenced using specific siRNAs-expressing vectors. Tissue-type plasminogen activator and uPA possibly induce distinct behaviors, which may be interpreted according to their differential pattern of activation and downstream targets. Taken together, these data add further evidence for a significant function of extracellular proteases tPA and uPA in addiction and suggest a differential role of plasminogen activators in this context.     

Plasminogen activators augment endothelial cell organization in vitro by two distinct pathways

Endothelial cell differentiation into capillary structures is a complex process that requires the concerted effects of several extracellular matrix proteases, including plasminogen activators. Here, the role of tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) was evaluated in an in vitro model of endothelial morphogenesis involving organization of human umbilical vein endothelial cells into tubular structures when they are cultured on the basement membrane preparation, Matrigel. Both uPA and tPA were detected in HUVEC cultures on Matrigel, and inhibitors of plasminogen activators or of serine proteases decreased the extent of the tube network formed by the cells. The decrease resulting from serine protease inhibitors was additive to that from matrix metalloproteinase inhibitors which have previously been shown to decrease tube formation in this model, suggesting that the two classes of proteases modulate tube formation by distinct mechanisms. Plasminogen activator inhibitor (PAl)-1 decreased tube formation by 50% when added up to 4.5 h after the initiation of an 18 h assay and caused 25% inhibition when added 9.5 h after culture initiation, indicating that the effects of plasminogen activators are not limited to an early event in the differentiation process. Steady-state expression of mRNA for uPA increased during the first several hours of culture on Matrigel, further supporting a role for PA activity throughout the process of tube formation. These findings suggested that PAs may affect multiple events during tube-forming activity. A fucosylated peptide comprising the amino-terminal domain of uPA that binds to the uPA receptor (uPAR) but lacking proteolytic activity enhanced tube formation. In contrast, a defucosylated form of the same peptide had no effect. Since fucosylation of this fragment has been shown to be essential in other models of cell stimulation by uPA-uPAR interaction, these data support the hypothesis that uPA enhances endothelial morphogenesis both through proteolytic activity and via uPAR occupancy. Plasminogen activators could facilitate angiogenesis in vivo. © 1995 Wiley-Liss Inc.     

The multifaceted role of plasminogen in inflammation

A fine-tuned activation and deactivation of proteases and their inhibitors are involved in the execution of the inflammatory response. The zymogen/proenzyme plasminogen is converted to the serine protease plasmin, a key fibrinolytic factor by plasminogen activators including tissue-type plasminogen activator (tPA). Plasmin is part of an intricate protease network controlling proteins of initial hemostasis/coagulation, fibrinolytic and complement system. Activation of these protease cascades is required to mount a proper inflammatory response. Although best known for its ability to dissolve clots and cleave fibrin, recent studies point to the importance of fibrin-independent functions of plasmin during acute inflammation and inflammation resolution. In this review, we provide an up-to-date overview of the current knowledge of the enzymatic and cytokine-like effects of tPA and describe the role of tPA and plasminogen receptors in the regulation of the inflammatory response with emphasis on the cytokine storm syndrome such as observed during coronavirus disease 2019 or macrophage activation syndrome. We discuss tPA as a modulator of Toll like receptor signaling, plasmin as an activator of NFkB signaling, and summarize recent studies on the role of plasminogen receptors as controllers of the macrophage conversion into the M2 type and as mediators of efferocytosis during inflammation resolution.     

Inhibitory effect of angiostatins on activity of the plasminogen/plasminogen activator system

Angiostatins, kringle-containing fragments of plasminogen, are potent inhibitors of angiogenesis. Effects of three angiostatin forms, K1–3, K1–4, and K1-4.5 (0–2 μM), on the rate of native Glu-plasminogen activation by its physiological activators in the absence or presence of soluble fibrin were investigated in vitro. Angiostatins did not affect the intrinsic amidolytic activities of plasmin and plasminogen activators of tissue type (tPA) and urokinase type (single-chain scuPA and two-chain tcuPA), but inhibited conversion of plasminogen to plasmin in a dose-dependent manner. All three angiostatins suppressed Glu-plasminogen activation by tcuPA independently of the presence of fibrin, and the inhibitory effect increased in the order: K1-3 < K1-4 < K1-4.5. The inhibitory effects of angiostatins on the scuPA activator activity were lower and further decreased in the presence of fibrin. Angiostatin K1-3 (up to 2 μM) had no effect, while 2 μM angiostatins K1-4 and K1-4.5 inhibited the fibrin-stimulated Glu-plasminogen activation by tPA by 50 and 100%, respectively. The difference in effects of the three angiostatins on the Glu-plasminogen activation by scuPA, tcuPA, and tPA in the absence or presence of fibrin is due to the differences in angiostatin structures, mechanisms of action, and fibrin-specificity of plasminogen activators, as well as due to the influence of fibrin on the Glu-plasminogen conformation. Angiostatins in vivo, which mimic plasminogen-binding activity, can inhibit plasminogen activation stimulated by various proteins (including fibrin) of extracellular matrix, thereby blocking cell migration and angiogenesis. The data of this work indicate that the inhibition of Glu-plasminogen activation under the action of physiological plasminogen activators by angiostatins can be implicated in the complex mechanism of their antiangiogenic and antitumor action.     

The low density lipoprotein receptor-related protein modulates protease activity in the brain by mediating the cellular internalization of both neuroserpin and neuroserpin-tissue-type plasminogen activator complexes

Proteases contribute to a variety of processes in the brain; consequently, their activity is carefully regulated by protease inhibitors, such as neuroserpin. This inhibitor is thought to be secreted by axons at synaptic regions where it controls tissue-type plasminogen activator (tPA) activity. Mechanisms regulating neuroserpin are not known, and the current studies were undertaken to define the cellular pathways involved in neuroserpin catabolism. We found that both active neuroserpin and neuroserpin.tPA complexes were internalized by mouse cortical cultures and embryonic fibroblasts in a process mediated by the low density lipoprotein receptor-related protein (LRP). Surprisingly, despite the fact that active neuroserpin is internalized by LRP, this form of the molecule does not directly bind to LRP on its own, indicating the requirement of a cofactor for neuroserpin internalization. Our studies ruled out the possibility that endogenously produced plasminogen activators (i.e. tPA and urokinase-type plasminogen activator) are responsible for the LRP-mediated internalization of active neuroserpin, but could not rule out the possibility that another cell-associated proteases capable of binding active neuroserpin functions in this capacity. In summary, neuroserpin levels appear to be carefully regulated by LRP and an unidentified cofactor, and this pathway may be critical for maintaining the balance between proteases and inhibitors.     

A study of tissue plasminogen activator forms from human small intestine

At least two forms of plasminogen activators which crossreacted with antiserum against tissue plasminogen activator (tPA) have been found in human small intestine homogenates. One of these activities has very slow mobility on Sephadex G-200 and is presumably a degraded form of tPA. The other moved very fast and was dispersed on gel filtration matrices, and probably represents aggregates of tPA with some other materials. Whereas 1 M NaCl, 1% Triton X-100 or 1 M potassium thiocyanate was unable to break up these aggregates, the high molecular weight components co-migrating with tPA could be separated from tPA by 4 M guanidine-HCl.     

Different mechanisms contribute to simultaneous inhibition of urokinase and tissue-type plasminogen activators by glucocorticoids in human ovarian carcinoma cells

Previous studies from our laboratory have demonstrated that OVCA 433 human ovarian carcinoma cells are glucocorticoid responsive by several criteria and contain high affinity, saturable, steroid-specific glucocorticoid receptors. These cells secrete both mammalian plasminogen activators (PAs), urokinase (uPA) and tissue-type PA (tPA). Treatment of OVCA 433 cells with 1 x 10(-7) M dexamethasone (Dex) for 4 days led to 77% and 83% reductions in the extracellular activities of uPA and tPA, respectively, released into serum-free conditioned medium during a 1-h period. Dex treatment led to a 71% decrease in the rate of extracellular uPA antigen accumulation, as determined by enzyme-linked immunosorbent assay, as well as a 73% reduction in steady state uPA mRNA levels. In contrast, Dex treatment led to only a 42% decrease in the rate of extracellular tPA antigen accumulation and a 48% decrease in tPA mRNA levels; such decreases were insufficient to account for the 83% reduction in tPA activity. Thus, while Dex-induced decreases in uPA antigen and mRNA levels accounted for all but 6% of the decrease in uPA activity, a large discrepancy existed between the magnitudes of decreased tPA activity and decreased tPA antigen and mRNA levels. OVCA 433 cells produce both PAI-1 and PAI-2, two specific PA inhibitors. Treatment of cells with 1 x 10(-7) M Dex for 4 days led to a 3.3-fold increase in the rate of extracellular PAI-1 accumulation, with little or no effect on PAI-2 accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)