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

Contribution of fibrinolytic tests to the differential diagnosis of veno-occlusive disease complicating pediatric hematopoietic stem cell transplantation

BACKGROUND

Veno-occlusive disease (VOD) is a major complication following hematopoietic stem cell transplantation (HSCT). Its diagnosis is based on clinical criteria, which have a limited sensitivity. Increased plasminogen activator inhibitor-1 (PAI-1) levels have been suggested as a marker of VOD. We aimed to prospectively evaluate how the fibrinolytic parameters behaved to discriminate VOD from other liver disorders occurring after HSCT in a pediatric population.

PROCEDURES

A total of 195 HSCT were performed on 161 children and VOD complicated 11 cases (6.8%). Alanine aminotransferase, total bilirubin, PAI-1 antigen (PAI-1:Ag) and activity, t-PA antigen, D-dimer, prothrombin time, activated partial thromboplastin time, antithrombin, fibrinogen, and platelet counts were measured in 105 HSCT before and then weekly for 1 month after HSCT.

RESULTS

An early, significant increase in the fibrinolytic parameters was seen in patients who developed VOD, even before VOD was diagnosed clinically, by comparison with patients without complications or those with non-VOD liver disorders. The combined increase in bilirubin, D-dimer, and PAI-1:Ag levels beyond the normal range distinguished VOD cases from other liver complications with a high sensitivity and specificity.

CONCLUSIONS

Our study demonstrates that fibrinolytic tests can help diagnose VOD after HSCT in the pediatric population.

Failure to lyse venous thrombi because of elevated plasminogen activator Inhibitor 1 (PAI-1) and 4G polymorphism of its promotor genome (The PAI-1/4G Syndrome)

Plasminogen activator Inhibitor 1 (PAI-1) inhibits plasminogen activators leading to decreased fibrinolysis and increased risk of thromboembolic disease (TED). Shifts in PAI-1 promoter genome from normal 5G>5G to 4G>5G or 4G>4G alleles are associated with overexpression of PAI-1. In this study patients with residual venous thrombi were observed to have increased PAI-1 levels and more frequent shifts to 4G alleles. Of the 26, 20 (76.9%) patients with unresolved thrombus had elevated PAI-1 values. 4G genomic shifts were found in 92.9% patients studied. Normal PAI-1 levels were found in 5 patients with 4G polymorphisms. Thus, PAI-1 is often elevated among patients with residual thrombus, with an unexpectedly high prevalence of the 4G polymorphism of the promoter genome. Patients with persistent thrombus should be considered at risk of having constituently increased PAI-1 due to genomic changes in the PAI-1 promoter genome. Hypotheses are proposed to explain those with normal PAI-1, despite having 4G polymorphisms.

EGF regulates plasminogen activator inhibitor-1 (PAI-1) by a pathway involving c-Src, PKCdelta, and sphingosine kinase 1 in glioblastoma cells

Patients with gliomas expressing high levels of epidermal growth factor receptor (EGFR) and plasminogen activator inhibitor-1 (PAI-1) have a shorter overall survival prognosis. Moreover, EGF enhances PAI-1 expression in glioma cells. Although multiple known signaling cascades are activated by EGF in glioma cells, we show for the first time that EGF enhances expression of PAI-1 via sequential activation of c-Src, protein kinase C delta (PKCdelta), and sphingosine kinase 1 (SphK1), the enzyme that produces sphingosine-1-phosphate. EGF induced rapid phosphorylation of c-Src and PKCdelta and concomitant translocation of PKCdelta as well as SphK1 to the plasma membrane. Down-regulation of PKCdelta abolished EGF-induced SphK1 translocation and up-regulation of PAI-1 by EGF; whereas, down-regulation of PKCalpha had no effect on the EGF-induced PAI-1 activation but enhanced its basal expression. Similarly, inhibition of c-Src activity by PP2 blocked both EGF-induced translocation of SphK1 and PKCdelta to the plasma membrane and up-regulation of PAI-1 expression. Furthermore, SphK1 was indispensable for both EGF-induced c-Jun phosphorylation and PAI-1 expression. Collectively, our results provide a functional link between three critical downstream targets of EGF, c-Src, PKCdelta, and SphK1 that have all been implicated in regulating motility and invasion of glioma cells.

Fibrinolysis, inflammation, and regulation of the plasminogen activating system

The maintenance of a given physiological process demands a coordinated and spatially regulated pattern of gene regulation. This applies to genes encoding components of enzyme cascades, including those of the plasminogen activating system. This family of proteases is vital to fibrinolysis and dysregulation of the expression pattern of one or more of these proteins in response to inflammatory events can impact on hemostasis. Gene regulation occurs on many levels, and it is apparent that the genes encoding the plasminogen activator (fibrinolytic) proteins are subject to both direct transcriptional control and significant post-transcriptional mechanisms. It is now clear that perturbation of these genes at either of these levels can dramatically alter expression levels and have a direct impact on the host's response to a variety of physiological and pharmacological challenges. Inflammatory processes are well known to impact on the fibrinolytic system and to promote thrombosis, cancer and diabetes. This review discusses how inflammatory and other signals affect the transcriptional and post-transcriptional expression patterns of this system, and how this modulates fibrinolysis in vivo.

Adrenal gland-dependent augmentation of plasminogen activator inhibitor-1 expression in streptozotocin-induced diabetic mice

BACKGROUND

Diabetes is associated with an excess risk of cardiac events, and one risk factor for infarction is an elevated level of plasminogen activator inhibitor-1 (PAI-1).

OBJECTIVES AND METHODS

To evaluate whether the glucocorticoid hormones are involved in the diabetes-induced PAI-1 production, we examined expression profiles of PAI-1 mRNA in adrenalectomized (ADX) mice with streptozotocin (STZ)-induced diabetes.

RESULTS

The diabetes-induced augmentation of plasma PAI-1 levels and PAI-1 mRNA expression in the heart and lungs was completely normalized in diabetic ADX mice. The glucocorticoid receptor antagonist RU486 significantly, but only partly suppressed PAI-1 induction in STZ-induced diabetic mice, suggesting that factors other than glucocorticoids are also involved in PAI-1 induction provoked by diabetes.

CONCLUSION

Our results suggested that the adrenal gland plays a critical role in the progression of thrombosis in diabetic patients by inducing expression of the PAI-1 gene.

Aldosterone increases plasminogen activator inhibitor-1 synthesis in rat cardiomyocytes

Plasminogen activator inhibitor-1 (PAI-1) is an anti-thrombolytic factor that also promotes tissue fibrosis. Under certain conditions, exposure to aldosterone can result in cardiac fibrosis by an unknown mechanism. In the current study, we tested the hypothesis that PAI-1 is a mediator of aldosterone's fibrotic effects. Aldosterone increased levels of PAI-1 mRNA and protein in the H9c2 rat cardiac cell line, responses that could be blocked by the mineralocorticoid receptor (MR) antagonist spironolactone. Confocal microscopy confirmed an effect of aldosterone to increase PAI-1 expression with reversal by spironolactone. Aldosterone also increased PAI-1 expression in neonatal rat cardiomyocytes, which was again blocked by spironolactone. In the neonatal cardiomyocytes (but not the H9c2 cells), anti-transforming growth factor-beta1 antibody inhibited the PAI-1 response to aldosterone. In summary, aldosterone directly increased PAI-1 expression in two different cardiac muscle cell types, an effect that was dependent on MR. In the neonatal cells, there appeared to be a requirement for transforming growth factor-beta1.

Effect of plasminogen activator inhibitor-1 in diabetes mellitus and cardiovascular disease

Concentrations of plasminogen activator inhibitor-1 (PAI-1) are elevated beginning at the stage of impaired glucose tolerance and continuing through the development of diabetes mellitus and the metabolic syndrome. Evolving evidence of the central role of PAI-1 in mediating fibrosis and thrombosis increasingly supports the theory that it is a significant risk factor for macrovascular complications and cardiovascular disease, particularly in patients with diabetes. Several clinical studies have demonstrated a strong correlation between circulating PAI-1 levels and cardiovascular events and mortality. With the potentially severe effects of elevated PAI-1 levels becoming evident, there is increased interest in developing therapies targeted at reducing PAI-1 expression or circulating concentrations. Thus far, weight loss, inhibitors of the renin-angiotensin system, and insulin sensitization through use of thiazolidinediones (TZDs) appear to be the most promising strategies for managing elevated PAI-1 levels. Of these, TZD therapy is the only one that provides the benefits of both long-term glycemic control and improved cardiovascular risk profile. This article reviews the regulation of PAI-1, its activity in various disease states, and available treatment options.

Plasminogen activator inhibitor-1 and the kidney

Plasminogen activator inhibitor-1 (PAI-1) is a serine protease inhibitor that was isolated 20 years ago. First recognized as an inhibitor of intravascular fibrinolysis, it is now evident that PAI-1 is a multifunctional protein with actions that may be dependent on or independent of its protease inhibitory effects. The latter often involve interactions between PAI-1 and vitronectin or the urokinase receptor. The protease-inhibitory actions of PAI-1 extend beyond fibrinolysis and include extracellular matrix turnover and activation of several proenzymes and latent growth factors. PAI-1 has been implicated in several renal pathogenetic processes, including thrombotic microangiopathies and proliferative and/or crescentic glomerulopathies. Most recently, it has become clear that PAI-1 also plays a pivotal role in progressive renal disease, both glomerulosclerosis and tubulointerstitial fibrosis. An active area of present research interest, untold stories are likely to be uncovered soon.

Cell adhesion regulates the plasminogen activator inhibitor-1 gene expression in anchorage-dependent cells

Plasminogen activator inhibitor-1 (PAI-1) is the primary inhibitor of both tissue- and urokinase-type plasminogen activators (t-PA, u-PA). PAI-1 also regulates the attachment of cells to the adhesive glycoprotein vitronectin (VN). PAI-1 gene expression has been observed in various cell types, and many regulatory factors have been identified to play a role in PAI-1 gene transcription. The complete picture of how the PAI-1 gene is expressed when cells adhere to a culture plate has not been fully elucidated. We found that in anchorage-dependent cells, PAI-1 gene was up-regulated when cells were beginning to attach to a culture dish and was down-regulated when cells had attached completely. The PAI-1 gene expression was induced only in adhered cells but not in non-adhered cells. The regulation of PAI-1 protein was also found in both culture medium and cell lysate when cells were attached to a culture dish. Our experiment indicates that vitronectin and fibronectin, as components of ECM, may be the factors involved in the regulation of PAI-1 gene expression. PAI-1, as an inhibitor of the interaction between vitronectin and integrin alphavbeta3, may also be a regulator of its own expression.

Increased transcription and modified growth state-dependent expression of the plasminogen activator inhibitor type-1 gene characterize the senescent phenotype in human diploid fibroblasts

The type-1 inhibitor of plasminogen activator (PAI-1) is a major physiologic regulator of pericellular proteolytic activity and, as such, influences matrix integrity, cell-to-substrate adhesion, and cellular proliferation. Excessive accumulation of both PAI-1 mRNA and protein correlates with the progressive acquisition of morphological and growth traits characteristic of the senescent phenotype (Mu and Higgins, 1995, J. Cell. Physiol., 165:647-657). Compared to early-passage IMR-90 human diploid fibroblasts, a late-passage senescence-associated 11-fold elevation in steady-state PAI-1 mRNA content reflected a 15-fold increase in constitutive PAI-1 gene transcription. Differential mRNA stability was not a factor in age-associated PAI-1 overexpression in IMR-90 cells. Upon removal of serum, early-passage human fibroblasts enter into a state of growth arrest with marked down-regulation of PAI-1 synthesis. Rapid induction of both the 3.0- and 2.2-kb PAI-1 mRNA species was evident upon serum-induced "activation" of quiescent early-passage fibroblasts; induced PAI-1 transcripts were maximal at 2 hr post-serum stimulation and declined in late G1 prior to entry into S phase. In contrast, late-passage (p32) fibroblasts maintained a significant level of PAI-1 expression under serum-free culture conditions. Although the PAI-1 gene was further responsive to serum in senescent cells, transcript abundance remained elevated and actually increased over the 12 to 16 hr post-serum addition period (a time when early-passage fibroblasts down-regulate PAI-1 mRNA content). Development of the senescent phenotype in human fibroblasts is associated, therefore, with significant changes in PAI-1 gene regulation. Such reprogramming involves predominantly transcriptional events and results in a marked increase in steady-state PAI-1 transcript abundance involving both the 3.0- and 2.2-kb mRNA species.

Complex regulation of plasminogen activator inhibitor type-1 (PAI-1) gene expression by serum and substrate adhesion

Expression of plasminogen activator inhibitor type-1 (PAI-1), a member of the serine protease inhibitor (SERPIN) superfamily that functions to negatively regulate the plasmin-based pericellular proteolytic cascade, was induced early after exposure of growth-arrested normal rat kidney (NRK) cells to serum-containing medium. Increased PAI-1 transcription was rapid (evident within 10 min of serum addition) and involved immediate-early response kinetics. [3H]Thymidine autoradiography was used to map the time frame of PAI-1 expression during a synchronous growth cycle. PAI-1 transcript accumulation peaked in mid-G1 phase (approx. 4-6 h post-stimulation) and declined prior to, or concomitant with, the onset of DNA synthetic phase. Serum increased PAI-1 expression in NRK cells in agarose suspension, as well as monolayer, culture; induction in suspended cells (similar to monolayer culture conditions) also occurred in the presence of cyclohexamide or puromycin. The serum-inductive pathway leading to PAI-1 gene activation is thus functional regardless of adhesive conditions or capacity for de novo protein synthesis. The amplitude of induction and maintenance of expression in later stages of G1, however, were subject to adhesive influences. PAI-1 transcript accumulation at 4 and 8 h post-stimulation in newly adherent cells, moreover, was blocked by puromycin, indicating that both immediate-early and secondary mechanisms regulate PAI-1 mRNA levels during progression of NRK cells through an 'activated' G1 growth phase.

Plasminogen activator inhibitor type-1 synthesis and mRNA expression in HepG2 cells are regulated by VLDL

The effect of VLDL on plasminogen activator inhibitor type 1 biosynthesis in HepG2 cells was investigated. Exposure of HepG2 cells to VLDL (range, 10 to 100 micrograms protein per milliliter) for 16 hours resulted in an enhanced release of PAI-1 antigen and PAI activity into conditioned medium, accompanied by the accumulation of intracellular triglycerides. By using a monoclonal antibody (IgG C7) specific to the LDL receptor, we showed that the effect of VLDL is mediated by its interaction with the LDL receptor. Enhanced PAI-1 release was due to increased biosynthesis: PAI-1 mRNA was doubled, mainly because of the effect on the 2.2-kb PAI-1 mRNA rather than the 3.2-kb transcript. Addition of insulin with the VLDL further enhanced PAI-1 antigen release and PAI-1 mRNA accumulation. The effect of VLDL on steady state levels of PAI-1 mRNA was apparently not due to an increase of gene transcription but to stabilization of both PAI-1 mRNA transcripts. The enhancing effect of VLDL on PAI-1 biosynthesis in HepG2 cells may raise PAI-1 antigen levels not only in hypertriglyceridemic states but also in those conditions in which both insulin and VLDL are elevated.

Differential growth state-dependent regulation of plasminogen activator inhibitor type-1 expression in senescent IMR-90 human diploid fibroblasts

The type-1 inhibitor of plasminogen activator (PAI-1) regulates pericellular proteolytic activity functioning, thereby to control matrix integrity, cell growth, and morphology. Subconfluent late-passage IMR-90 human fibroblasts and normal rat kidney (NRK) cells, both at the stage of replicative senescence accumulated 15- to 30-fold more undersurface PAI-1 protein compared to early-passage, actively-proliferating, cultures. Senescence-associated elevations in PAI-1 expression by IMR-90 cells reflected corresponding 11-fold increases in the 3.0- and 2.2-kb PAI-1 mRNA species. The 2.2-kb transcript exhibited a greater age-dependent increase (7.2-fold) compared to the 3.0-kb mRNA (3.7-fold). Since PAI-1 expression is coupled to growth activation in serum-deprived cultures (Ryan and Higgins, 1993, J. Cell. Physiol., 155:376-384), it was important to determine if PAI-1 gene regulation was altered as a function of cellular aging. In contrast to early-passage cultures, senescent IMR-90 fibroblasts did not down-regulate either PAI-1 protein expression or steady-state levels of PAI-1 mRNA transcripts upon serum-deprivation. Late-passage human fibroblasts at their proliferative end-stage, thus, appear to regulate PAI-1 mRNA levels through different mechanisms than do young, actively-proliferating, cells. PAI-1 overexpression during in vitro cellular aging, therefore, may contribute to the acquisition of specific senescence-associated phenotypic traits (e.g., enlarged cell morphology; increased adhesivity) by altering the pericellular proteolytic balance influencing, in turn, the formation or stability of cell-to-substrate attachment complexes.

Butyrate regulates gene expression of the plasminogen activating system in colon cancer cells

Butyrate is a potent differentiating agent present in high concentrations in colonic lumen as a result of metabolic breakdown of dietary fibre and, as such, may directly influence colonic cancer progression. We have investigated the effects of butyrate on an enzyme system important in colonic tumour progression, the plasminogen-activating system, in a poorly differentiated colon cancer cell. Butyrate was found to induce a rapid and transient increase in plasminogen activator inhibitor type 1 (PAI-1) mRNA while concomitantly suppressing the constitutive production of both urokinase-type plasminogen activator (uPA) and uPA receptor (uPAR) mRNA transcripts. We have investigated the mechanisms involved in mediating these effects by run-on transcription and RNA stability analyses. Our data show that PAI-1 mRNA induction occurs through both regulation of the stability of the alternately spliced 3.3 kb PAI-1 mRNA transcript and induction of the 2.4 kb PAI-1 mRNA transcript. Studies using modulators of signal transduction pathways demonstrate that induction of PAI-1 mRNA synthesis is independent of protein kinase C but dependent on the activation of protein kinase A. Suppression of uPA mRNA by butyrate was found to occur by down-regulation of gene transcription through a process independent of de novo protein synthesis. The transcription rate of the uPAR gene was not modulated by butyrate, but rapid turnover of the uPAR gene by butyrate was dependent on ongoing protein synthesis. Our results demonstrate that butyrate can effect rapid changes in the expression of genes of the plasminogen-activating system through several different mechanisms in a gene-specific manner.

Cell-shape-dependent modulation of p52(PAI-1) gene expression involves a secondary response pathway

Expression of the rat p52(PAI-1) gene is positively regulated by agents that influence cellular microfilament organization and/or cell-to-substrate adhesion [e.g. cytochalasin D (CD) and sodium n-butyrate (NaB)] [Higgins, Chaudhari and Ryan (1991) Biochem. J. 273, 651-658; Higgins, Ryan and Providence (1994) J. Cell. Physiol. 159, 187-195]. As shape-responsive genes may be subject to inducer-specific controls, the biochemical mechanisms underlying the shape-dependent pathway of p52(PAI-1) gene regulation were examined in v-ras-transformed rat kidney (KNRK) cells. NaB and/or CD effectively stimulated p52(PAI-1) run-off transcription and augmented de novo p52(PAI-1) mRNA and protein synthesis in KNRK cells; induction at both the mRNA and protein levels was inhibited by actinomycin D. Pretreatment with cycloheximide (CX) markedly attenuated NaB- and/or CD-stimulated p52(PAI-1) expression. CX alone, however, induced low levels of p52(PAI-1) mRNA; increased p52(PAI-1) protein synthesis was evident after release of KNRK cells from CX blockade. Such CX-mediated induction was also sensitive to actinomycin D. Full stimulation of p52(PAI-1) expression in KNRK cells in response to the shape modulators NaB and/or CD involves transcriptional activation of the p52(PAI-1) gene, requires de novo RNA synthesis and occurs through a secondary-response (i.e. protein-synthesis-dependent) pathway.

Degradation of matrix proteins in liver fibrosis

Hepatic fibrosis occurs as a consequence of net accumulation of matrix proteins (particularly collagen types I and III) in liver. Current concepts of the pathogenesis of liver fibrosis place major emphasis on the activation of hepatic lipocytes (fat-storing or Ito cells) to a myofibroblast-like phenotype with a consequent increase in their synthesis of matrix proteins. While this is an important factor, there is increasing evidence to indicate that liver fibrosis is a dynamic pathologic process in which altered matrix degradation may also play a significant role. Extracellular degradation of matrix proteins is regulated by a family of enzymes called the matrix metalloproteinases, which is subdivided into three groups; collagenases which degrade interstitial collagens (types I, II and III), type IV collagenases/gelatinases which degrade basement membrane (type IV) collagen and gelatins and stromelysins which degrade a broad range of substrates including proteoglycans, laminin, gelatins and fibronectin. The extracellular activity of these enzymes is regulated by several mechanisms which include alterations in gene transcription and proenzyme synthesis, cleavage of secreted proenzymes to active forms, and specific inhibition of activated forms by tissue inhibitor(s) of metalloproteinases (TIMPs). In liver, current evidence indicates that activated hepatic lipocytes and Kupffer cells play a central role in synthesis of matrix metalloproteinases. Under defined conditions they synthesize interstitial collagenase, 72 kDa and 95 kDa type IV collagenase/gelatinase and possibly stromelysin. Moreover, lipocytes also contribute to regulation of the extracellular activity of these enzymes by secretion of TIMP-1 and alpha 2-macroglobulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Down-regulation of Drosophila Egf-r mRNA levels following hyperactivated receptor signaling

Internalization of ligand-receptor complexes is a well-documented mechanism for limiting the duration and magnitude of a signaling event. In the case of the EGF-Receptor (EGF-R), exposure to EGF or TGF-alpha results in internalization of up to 95% of the surface receptor pool within 5 minutes of exposure to ligand. In this report, we show that levels of Drosophila Egf-r mRNA are strongly down-regulated in epidermal cells likely to have recently undergone high levels of EGF-R signaling. The cells in which Egf-r mRNA levels are down-regulated express the rhomboid gene, which is thought to locally amplify EGF-R signaling. Widespread Egf-r mRNA down-regulation can be induced by ubiquitous expression of rhomboid or by eliminating the Gap1 gene. These results suggest that cells engaged in intense EGF-R/RAS signaling limit the duration of the signal through a combination of short-acting negative feedback mechanisms such as receptor internalization followed by a longer lasting reduction in receptor transcript levels. Control of Egf-r mRNA levels by altering transcription or mRNA stability is a new tier of regulation to be considered in analysis of EGF-R signaling during development.

Transcriptional regulation of plasminogen activator inhibitor-1 expression in human synovial fibroblasts by prostaglandin E2: mediation by protein kinase A and role of interleukin-1

Differential expression of PAI-1 in connective tissues has been associated etiologically with some forms of arthritis. Our objective was to delineate the mechanisms by which PGE2 and IL-1 beta, inflammatory mediators commonly found at sites of inflammation, regulate the expression and synthesis of PAI-1 in human synoviocytes. PGE2 (and PGE1) inhibited PAI-1 mRNA expression and secretion in a dose-dependent manner with an IC50 (for antigen secretion) of 4.6 x 10(-10) M and 8.7 x 10(-10) M, respectively. Cyclic AMP agonists forskolin, Sp-cAMP, and IBMX mimic the effects of the PGEs. rhIL-1 beta stimulated the secretion of PAI-1 in a dose-dependent fashion under basal culture conditions; the effect was reversed by actinomycin D and the protein kinase inhibitors H7 and staurosporine but not KT-5720. PMA, an activator of protein kinase C, transiently increased (maximum 3 h) the expression of PAI-1 mRNA by approximately 10-fold, especially the 3.2 kb species. However, there was no significant increase in PAI-1 antigen secreted into the culture medium after PMA (100-300 nM) treatment. The half-life (t1/2) of PAI-1 mRNA, both the 3.2 and 2.2 transcripts was about 9.6 h (mean n = 3) and PGE2 has no affect on the stability of both messages. PGE2 reduced the rate of PAI-1 gene transcription as judged by run-off assays. The NSAID naproxen (30 micrograms/ml) induced the expression of PAI-1 mRNA over basal levels and super-induced the inhibitor's expression above rhIL-1 beta stimulated levels. Our results suggest that PGE2 suppresses PAI-1 expression and synthesis by activation of the cAMP/PKA system and inhibition of the rate of gene transcription. Data concerning the activation of PKC suggest that the expression, synthesis and release of the PAI-1 may be differentially regulated in normal human synoviocytes.

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.

The EGF-inducible protein EIP-1 of migrating normal and malignant rat liver epithelial cells is identical to plasminogen activator inhibitor 1 and is a component of the ECM migration tracks

Induction of rat liver epithelial cell migration by epidermal growth factor (EGF) changes the expression pattern of secreted proteins. The expression of the early induced glycoprotein EGF-inducible protein No. 1 (EIP-1) correlates with the migratory behavior of both normal and Ha-ras-transformed, tumorigenic cells and is deposited into the ECM migration tracks. The sequence of two clones from a cDNA library of EGF-induced cells and the amino terminal sequence of the purified protein revealed that EIP-1 is identical to rat plasminogen activator inhibitor 1 (PAI-1). Based on the migration-linked expression pattern of EIP-1/PAI-1 it is proposed that the inhibitor is required for the migration of these cells, but not sufficient to stimulate it.

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.

Augmentation of synthesis of plasminogen activator inhibitor type 1 by insulin and insulin-like growth factor type I: implications for vascular disease in hyperinsulinemic states

Accelerated atherosclerosis accompanying diabetes mellitus, obesity, and some types of hypertension has been associated with hyperinsulinemia, augmented plasma plasminogen activator inhibitor type 1 (PAI-1), or both. We hypothesized that insulin and insulin-like growth factor type I (IGF-I) can influence synthesis of PAI-1, thereby potentially attenuating fibrinolysis. In HepG2 cells used as a model system, concentrations of insulin and IGF-I consistent with those seen in plasma independently stimulated PAI-1 synthesis. Accumulation of PAI-1 protein in conditioned medium over 24 hr was stimulated more with insulin alone than with the combination. Synergistic increases were evident, however, in the accumulation of PAI-1 protein over 48 hr with a concomitant increase in PAI-1 mRNA. A 10- to 20-fold increase in IGF binding protein I mRNA was seen 16-48 hr after exposure of the HepG2 cells to insulin and IGF-I, an increase abolished by cycloheximide. The results obtained are consistent with the hypothesis that hyperinsulinemia coupled with physiologic concentrations of IGF-I may attenuate fibrinolytic activity in vivo, thereby contributing to accelerated atherosclerosis.