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

Cyclic AMP enhances TGFβ responses of breast cancer cells by upregulating TGFβ receptor I expression

Cellular functions are regulated by complex networks of many different signaling pathways. The TGFβ and cAMP pathways are of particular importance in tumor progression. We analyzed the cross-talk between these pathways in breast cancer cells in 2D and 3D cultures. We found that cAMP potentiated TGFβ-dependent gene expression by enhancing Smad3 phosphorylation. Higher levels of total Smad3, as observed in 3D-cultured cells, blocked this effect. Two Smad3 regulating proteins, YAP (Yes-associated protein) and TβRI (TGFβ receptor 1), were responsive to cAMP. While YAP had little effect on TGFβ-dependent expression and Smad3 phosphorylation, a constitutively active form of TβRI mimicked the cAMP effect on TGFβ signaling. In 3D-cultured cells, which show much higher levels of TβRI and cAMP, TβRI was unresponsive to cAMP. Upregulation of TβRI expression by cAMP was dependent on transcription. A proximal TβRI promoter fragment was moderately, but significantly activated by cAMP suggesting that cAMP increases TβRI expression at least partially by activating TβRI transcription. Neither the cAMP-responsive element binding protein (CREB) nor the TβRI-regulating transcription factor Six1 was required for the cAMP effect. An inhibitor of histone deacetylases alone or together with cAMP increased TβRI expression by a similar extent as cAMP alone suggesting that cAMP may exert its effect by interfering with histone acetylation. Along with an additive stimulatory effect of cAMP and TGFβ on p21 expression an additive inhibitory effect of these agents on proliferation was observed. Finally, we show that mesenchymal stem cells that interact with breast cancer cells can simultaneously activate the cAMP and TGFβ pathways. In summary, these data suggest that combined effects of cAMP and TGFβ, as e.g. induced by mesenchymal stem cells, involve the upregulation of TβRI expression on the transcriptional level, likely due to changes in histone acetylation. As a consequence, cancer cell functions such as proliferation are affected.

Synergistic and multidimensional regulation of plasminogen activator inhibitor type 1 expression by transforming growth factor type β and epidermal growth factor

The major physiological inhibitor of plasminogen activator, type I plasminogen activator inhibitor (PAI-1), controls blood clotting and tissue remodeling events that involve cell migration. Transforming growth factor type β (TGFβ) and epidermal growth factor (EGF) interact synergistically to increase PAI-1 mRNA and protein levels in human HepG2 and mink Mv1Lu cells. Other growth factors that activate tyrosine kinase receptors can substitute for EGF. EGF and TGFβ regulate PAI-1 by synergistically activating transcription, which is further amplified by a decrease in the rate of mRNA degradation, the latter being regulated only by EGF. The combined effect of transcriptional activation and mRNA stabilization results in a rapid 2-order of magnitude increase in the level of PAI-1. TGFβ also increases the sensitivity of the cells to EGF, thereby recruiting the cooperation of EGF at lower than normally effective concentrations. The contribution of EGF to the regulation of PAI-1 involves the MAPK pathway, and the synergistic interface with the TGFβ pathway is downstream of MEK1/2 and involves phosphorylation of neither ERK1/2 nor Smad2/3. Synergism requires the presence of both Smad and AP-1 recognition sites in the promoter. This work demonstrates the existence of a multidimensional cellular mechanism by which EGF and TGFβ are able to promote large and rapid changes in PAI-1 expression.

Role of hypoxia and cAMP in the transdifferentiation of human fetal cardiac fibroblasts: implications for progression to scarring in autoimmune-associated congenital heart block

OBJECTIVE

Identification of isolated congenital heart block (CHB) predicts, with near certainty, the presence of maternal anti-SSA/Ro antibodies; however, the 2% incidence of CHB in first offspring of anti-SSA/Ro+ mothers, 20% recurrence in subsequent pregnancies, and discordance in identical twins suggest that an environmental factor amplifies the effect of the antibody. Accordingly, this study was carried out to explore the hypothesis that hypoxia potentiates a profibrosing phenotype of the fetal cardiac fibroblast.

METHODS

Evidence of an effect of hypoxia was sought by immunohistologic evaluation of CHB-affected fetal heart tissue and by determination of erythropoietin levels in cord blood. The in vitro effect of hypoxia on gene expression and phenotype in fibroblasts derived from fetal hearts and lungs was investigated by Affymetrix arrays, quantitative polymerase chain reaction (PCR), immunofluorescence, and immunoblotting.

RESULTS

In vivo hypoxic exposure was supported by the prominent intracellular fibroblast expression of hypoxia-inducible factor 1alpha in conduction tissue from 2 fetuses in whom CHB led to death. The possibility that hypoxia was sustained was suggested by significantly elevated erythropoietin levels in cord blood from CHB-affected, as compared with unaffected, anti-SSA/Ro-exposed neonates. In vitro exposure of cardiac fibroblasts to hypoxia resulted in transdifferentiation to myofibroblasts (a scarring phenotype), as demonstrated on immunoblots and immunofluorescence by increased expression of smooth muscle actin (SMA), an effect not seen in lung fibroblasts. Hypoxia-exposed cardiac fibroblasts expressed adrenomedullin at 4-fold increased levels, as determined by Affymetrix array, quantitative PCR, and immunofluorescence, thus focusing attention on cAMP as a modulator of fibrosis. MDL12,330A, an adenylate cyclase inhibitor that lowers the levels of cAMP, increased expression of fibrosis-related proteins (mammalian target of rapamycin, SMA, plasminogen activator inhibitor type 1, and type I collagen), while the cAMP activator forskolin attenuated transforming growth factor beta-elicited fibrosing end points in the cardiac fibroblasts.

CONCLUSION

These findings provide evidence that hypoxia may amplify the injurious effects of anti-SSA/Ro antibodies. Modulation of cAMP may be a key component in the scarring phenotype. Further assessment of the susceptibility of cardiac fibroblasts to cAMP modulation offers a new research direction in CHB.

C-phycocyanin transcriptionally regulates uPA mRNA through cAMP mediated PKA pathway in human fibroblast WI-38 cells

We have previously demonstrated the efficacy of c-phycocyanin in up-regulation of urokinase-type plasminogen activator (uPA) in bovine endothelial cell line. However, the mechanism of action and pathway elucidation in uPA regulation is unclear. In experiments reported here, we have investigated the mechanism of action of c-phycocyanin (c-pc) induced uPA gene modulation in human fibroblast (WI-38) cell line. ELISA test confirmed that c-pc increased the uPA antigen whereas PAI-1 antigen level was unaffected. Treatment of cells with c-pc significantly (P<0.05) enhanced the uPA mRNA level in a dose (50 microg/ml) and time dependent (up to 4 h) manner. This effect of c-pc was abolished by treatment with dichloro-1-beta-D-ribofuranosyl benzamidazole (DRB) (10 microg/ml). Co-treatment of c-pc with 200 microg/ml cycloheximide (CHX), translation inhibitor, resulted in over accumulation of uPA mRNA. These results suggest that uPA induction by c-pc is transcriptionally regulated and does not require de novo protein synthesis. We also provide evidence that c-pc stimulates uPA gene through cAMP dependent pathway as adenylyl cyclase (AC) inhibitor, dideoxyadenosine (DDA) significantly inhibited the uPA mRNA expression and co-treatment with adenylyl cyclase analogue, dBcAMP recovered the effect of c-pc on gene activity. Furthermore, the present investigation provides evidence on the regulatory pathway involved in the c-pc stimulus. C-pc induced uPA expression was completely inhibited by PKA inhibitor (KT 5200), indicating the regulation is dependent on PKA pathway. Elimination of PKC pathway components by prolonged incubation with excess amount of phorbol 12-myristate 13-acetate (PMA) failed to abolish the c-pc effect on uPA expression indicating the regulation is independent of PKC pathway. Taken together, our data indicate that uPA gene regulation by c-pc is transcriptionally controlled through cAMP mediated PKA pathway.

Transcriptional regulation of plasminogen activator inhibitor-1 by transforming growth factor-β, activin A and microphthalmia-associated transcription factor

Plasminogen activator inhibitor-1 (PAI-1) is a key molecule that regulates turnover of the extracellular matrix. In the present study, we characterized PAI-1 gene expression in mast cells and melanocytes. In bone marrow-derived cultured mast cells, up-regulation of the PAI-1 gene was observed upon treatment with TGF-beta1, and was regulated at the transcriptional level. Microphthalmia-associated transcription factor (MITF), a member of the basic helix-loop-helix leucine zipper family of tissue-specific transcription factors predominantly expressed in mast cells, melanocytes and osteoclasts, also stimulated PAI-1 gene transcription, and TGF-beta1 did not increase PAI-1 mRNA levels in mast cells from mi/mi mice expressing dominant-negative MITF. MITF isoforms regulated TGF-beta1-induced transcription of PAI-1 differently; MITF-E-mediated transcription was further increased by TGF-beta1, whereas transcriptional activation by TGF-beta1 was blocked by MITF-M or MITF-mc expression. In contrast, activin A, another member of the TGF-beta family, enhanced transcription induced by MITF-M, as well as by MITF-E, although MITF-mc blocked activin A-induced transcription of PAI-1. Different regulation of PAI-1 gene expression upon TGF-beta1 and activin A treatment was also detected in B16 melanocytes; TGF-beta1 transiently increased the PAI-1 mRNA level, whereas activin A had prolonged effects on up-regulation of PAI-1. Our results on the control of PAI-1 gene expression by MITF isoforms, TGF-beta1 and activin A suggest that discrete regulation of the plasminogen activator system occurs in a cell type-specific manner.

Pentoxifylline Attenuates Tubulointerstitial Fibrosis by Blocking Smad3/4-Activated Transcription and Profibrogenic Effects of Connective Tissue Growth Factor

Pentoxifylline (PTX) is a potent inhibitor of connective tissue growth factor (CTGF), but its underlying mechanism is poorly understood. Here, it was demonstrated that PTX inhibited not only TGF-beta1-induced CTGF expression but also CTGF-induced collagen I (alpha1) [Col I (alpha1)] expression in normal rat kidney fibroblasts (NRK-49F) and alpha-smooth muscle actin expression in normal rat kidney proximal tubular epithelial cells (NRK-52E). Furthermore, PTX attenuated tubulointerstitial fibrosis, myofibroblasts accumulation, and expression of CTGF and Col I (alpha1) in unilateral ureteral obstruction kidneys. The mechanism by which PTX reduced CTGF in NRK-49F and NRK-52E was investigated. Activation of Smad3/4 was essential for TGF-beta1-induced CTGF transcription, but PTX did not interfere with TGF-beta1 signaling to Smad2/3 activation and association with Smad4 and their nuclear translocation. However, PTX was capable of blocking activation of TGF-beta1-induced Smad3/4-dependent reporter as well as CTGF promoter, suggesting that PTX affects a factor that acts cooperatively with Smad3/4 to execute transcriptional activation. It was found that PTX increased intracellular cAMP and caused cAMP response element binding protein phosphorylation. The protein kinase A antagonist H89 abolished the inhibitory effect of PTX on Smad3/4-dependent CTGF transcription, whereas dibutyryl cAMP and forskolin recapitulated the inhibitory effect. In conclusion, these results indicate that PTX inhibits CTGF expression by interfering with Smad3/4-dependent CTGF transcription through protein kinase A and blocks the profibrogenic effects of CTGF on renal cells. Because of the dual blockade, PTX potently attenuates the tubulointerstitial fibrosis in unilateral ureteral obstruction kidneys.

Transforming growth factor-beta and its role in asthma

Transforming growth factor-beta (TGF-beta) is an important fibrogenic and immunomodulatory factor that may play a role in the structural changes observed in the asthmatic airways. In vitro as well as in vivo studies have evidenced a dual role for TGF-beta: it can either function as a pro- or anti-inflammatory cytokine on inflammatory cells, participating into the initiation and resultion of inflammatory and immune responses in the airways. TGF-beta is also involved in the remodelling of the airway wall, and has in particular been related to the subepithelial fibrosis. TGF-beta is produced in the airways by inflammatory cells infiltrated in the bronchial mucosa, as well as by structural cells of the airway wall including fibroblasts, epithelial, endothelial and smooth muscle cells. By releasing TGF-beta, these different cell types may then participate into the increased levels of TGF-beta observed in bronchoalveolar lavage fluid from asthmatic patients. Taken together, these results suggest that TGF-beta may play a role in inflammation in asthma. However, as its role is dual in the modulation of inflammation, further studies are needed to elucidate the precise role of TGF-beta in the airways.

Thrombospondin-1 expression in human myometrium before and during pregnancy, before and during labor, and in human myometrial cells in culture

The activation of latent transforming growth factor beta (L-TGFbeta) is essential for the action of TGFbeta, which, in turn, is involved in the regulation of expression of some progesterone-responsive genes. One mechanism by which TGFbeta is activated involves thrombospondin (TSP), a protein that binds extracellular proteins. Immunoreactive TSP (irTSP) protein and TSP-1 mRNA in myometrial tissues of ovulatory and pregnant women were localized by immunohistochemistry and in situ hybridization. IrTSP and TSP-1 mRNA were randomly distributed in myometrial smooth muscle cells of some, but not all, tissues of pregnant women at term before labor; but in some areas of most of these tissues, irTSP was intense and commonly localized extracellularly. Intense irTSP and TSP-1 mRNA in myocytes were more common in myometrium during labor. In myometrium from ovulatory women (n = 26), irTSP was localized primarily in vascular smooth muscle cells and was detected occasionally in scattered myocytes. Little TSP-1 mRNA was demonstrable by in situ hybridization in vessels or myocytes of myometrial tissue from ovulatory women (n = 7). By Northern analysis of total RNA, TSP-1 mRNA was detected in myometrial tissue of pregnant women and in human myometrial smooth muscle cells in culture. The levels of TSP-1 mRNA in myometrial tissues of pregnant women during labor (n = 18) were greater than those in myometrium at > 37 wk gestation before labor began (n = 25, p < 0.001). The ratios of TSP-1 to glyceraldehyde 3-phosphate dehydrogenase mRNAs in 3 myometrial tissues during oxytocin-induced labor were not statistically different from those in myometrium during spontaneous labor but were greater than those in myometrium before labor (p < 0.05). The level of TSP-1 mRNA in confluent human myometrial cells in culture was relatively high, was increased by treatment with fetal bovine serum, and was decreased by treatment with platelet-derived growth factor or activators of adenylyl cyclase or protein kinase C. Myometrial cells in culture constitute a useful model for studying the regulation of TSP-1 gene expression in human myometrium.

Inhibition of TGF-beta-stimulated CTGF gene expression and anchorage-independent growth by cAMP identifies a CTGF-dependent restriction point in the cell cycle

CTGF is a 38 kDa cysteine-rich peptide whose synthesis and secretion are selectively induced by transforming growth factor beta (TGF-beta) in connective tissue cells. We have investigated the signaling pathways controlling the TGF-beta induction of connective tissue growth factor (CTGF) gene expression. Our studies indicate that inhibitors of tyrosine kinases and protein kinase C do not block the signaling pathway used by TGF-beta to induce CTGF gene expression. In contrast, elevation of cAMP levels within the target cells by a variety of methods blocked the induction of CTGF by TGF-beta. Furthermore, agents that elevate cAMP blocked the induction of anchorage-independent growth (AIG) by TGF-beta. Inhibition of AIG could be overcome by the addition of CTGF, indicating that it was not a general inhibition of growth but a selective inhibition of CTGF synthesis that is responsible for the inhibition of TGF-beta-induced AIG by cAMP. Kinetic studies of the induction of DNA synthesis by CTGF in cells arrested by cAMP indicate that the block occurs in very late G1. These and other studies in monolayer cultures suggest that the CTGF restriction point in the cell cycle is distinct from the adhesion-dependent arrest point.

Cyclic nucleotide regulation of type-1 plasminogen activator-inhibitor mRNA stability in rat hepatoma cells. Identification of cis-acting sequences

Type-1 plasminogen activator-inhibitor (PAI-1) is a major physiologic inhibitor of plasminogen activation. Incubation of HTC rat hepatoma cells with the cyclic nucleotide analogue, 8-bromo-cAMP, causes a dramatic increase in tissue-type plasminogen activator activity secondary to a 90% decrease in PAI-1 mRNA. Although 8-bromo-cAMP causes a modest decrease in PAI-1 transcription, regulation is primarily the result of a 3-fold increase in the rate of PAI-1 mRNA degradation. To determine the cis-acting sequences required for cyclic nucleotide regulation, we have stably transfected HTC cells with chimeric genes containing sequences from the rat PAI-1 cDNA and the mouse beta-globin gene and examined the effect of cyclic nucleotides on the decay rate of these transcripts. The mRNA transcribed from the beta-globin gene is stable and not cyclic nucleotide-regulated, whereas the transcript from a construct containing the beta-globin coding region and the PAI-1 3'-untranslated region (UTR) is destabilized in the presence of 8-bromo-cAMP, suggesting that this response is mediated by sequences in the PAI-1 3'-UTR. Analyses by deletion of sequences from this chimeric construct indicate that, whereas more than one region of the PAI-1 3'-UTR can confer cyclic nucleotide responsiveness, the 3'-most 134-nucleotide sequence alone is sufficient to do so. Insertion of PAI-1 sequences within the beta-globin 3'-UTR confirms that the 3'-most 134 nucleotides of PAI-1 mRNA can confer cyclic nucleotide regulation of stability on a heterologous transcript, suggesting that this sequence may play a major role in hormonal regulation of PAI-1 mRNA stability.

Genotype-specific transcriptional regulation of PAI-1 expression by hypertriglyceridemic VLDL and Lp(a) in cultured human endothelial cells

The hypothesized relationships between plasminogen activator inhibitor (PAI-1) genotypes, PAI-1 levels, and their potential regulation by hypertriglyceridemic (HTG) very low density lipoprotein (VLDL) and lipoprotein(a) [Lp(a)] was examined in a PAI-1 genotyped human umbilical vein endothelial cell (HUVEC) culture model system. Individual human umbilical veins were used to obtain cultured ECs and were genotyped for PAI-1 by using the HindIII restriction fragment length polymorphism (RFLP) as a marker for genetic variation. Digested genomic DNA, examined by Southern blot analysis and probed with an [alpha-32P]dCTP-labeled 2.2-kb PAI-1 cDNA, yielded three RFLPs designated 1/1 (22-kb band only), 1/2 (22-plus 18-kb bands), and 2/2 (18-kb band only). Individual PAI-1 genotyped HUVEC cultures were incubated in the absence or presence of HTG-VLDL (0 to 50 micrograms/mL) or Lp(a) (0 to 50 micrograms/mL) at 37 degrees C for various times (4 to 24 hours), followed by analyses of PAI-1 antigen (by ELISA) and mRNA (by ribonuclease protection assay) levels, EC surface-localized plasmin generation assays, and nuclear run-on transcription assays. Secreted PAI-1 antigen levels were increased approximately 2- to 3-fold by HTG-VLDL and approximately 1.6 to 2-fold by Lp(a); mRNA levels were increased approximately 3- to 4.5-fold by HTG-VLDL and approximately 2.5- to 3.2-fold by Lp(a) compared with medium-incubated controls, primarily in the 2/2 PAI-1 genotype HUVEC cultures. Increases in PAI-1 mRNA induced by HTG-VLDL or Lp(a) could be abolished by coincubation with actinomycin D (2 x 10(-6) mol/mL) or puromycin (1 microgram/mL). In addition, nuclear transcription run-on assays typically demonstrated that HTG-VLDL increased PAI-1 gene transcription rates by approximately 5- to 6-fold and approximately 4- to 5-fold, respectively, primarily in the 2/2 PAI-1 genotype HUVEC cultures compared with 1/1 PAI-1 genotype HUVEC cultures or medium-incubated controls. The positive control interleukin-1 increased both 2/2 and 1/1 PAI-1 mRNA levels by approximately 5- to 6-fold. Increased PAI-1 antigen and mRNA expression were associated with a concomitant 50% to 60% decrease in plasmin generation. These combined results demonstrate the genotype-specific regulation of PAI-1 expression by HTG-VLDL and Lp(a) and further indicate that these risk factor-associated components regulate PAI-1 gene expression at the transcriptional level in cultured HUVECs. Results from these studies further suggest that individuals with this responsive 2/2 PAI-1 genotype may reflect the additional inherent potential for later HTG-VLDL- or Lp(a)-induced fibrinolytic dysfunction, resulting in the early initiation of thrombosis, atherogenesis, and coronary artery disease.

Up-regulation of type 1 plasminogen activator inhibitor messenger RNA with thrombotic changes in renal grafts

Small vessel thrombosis is a prominent feature in kidneys undergoing vascular rejection. Type I and type 2 plasminogen activator inhibitors (PAI-1 and PAI-2, respectively) are known to mediate thrombosis. To examine the potential role of PAI-1 and PAI-2 in the mediation of vascular injury, the relationship and the time course of gene expression of PAI-1 and PAI-2 with the thrombotic changes in renal grafts were investigated in an unmodified rejection model in rats. Orthotopic renal transplantation was performed from Lewis to dark agouti (DA) rats and from DA to DA isografts; untreated normal rat kidneys were used as controls. The rats were killed on days 1-9 posttransplantation (n=18 in each allograft and isograft group). The grafts were analyzed by histopathology, in situ mRNA hybridization and Northern blot methods. The results show that PAM mRNA was first detected at day 4, when the thrombotic changes in the grafts were first seen, and that this relationship persisted during the time course observed to day 9. There was no detectable PAI-1 mRNA in the control groups and no PAI-2 in either group. In situ hybridization showed that PAI-1 positive cells were predominantly located in the cortical interstitium, consistent with the distribution of interstitial microthrombi. These results provide experimental evidence that the thrombotic changes in rejecting allografts are associated with the up-regulation of PAI-1 in the donor tissue, whereas PAI-2, from our results, does not seem to influence these changes. The data are consistent with a role for PAI-1 in the pathogenesis of vascular rejection.

Cloning of the mink plasminogen activator inhibitor type-1 messenger RNA: an mRNA with a short half life

In mink lung CCL64 epithelial cells the rate of synthesis of plasminogen activator inhibitor type I (PAI-1) increases 10-100-fold within 3 h in response to 12-O-tetradecanoyl phorbol-13-acetate (PMA). The PAI-1 gene is regulated transcriptionally. Parallel studies of the time-courses of PAI-1 synthesis and secretion and of mRNA accumulation indicate that the amount of secreted PAI-1 produced by the cells is tightly coupled to the level of its transcript. The half-life of the PAI-1 mRNA was found to be 25 min which is much shorter than previously reported for PAI-1 in other cells. Actinomycin D, which is commonly used to determine mRNA half-life, stabilized the PAI-1 mRNA. Cycloheximide also stabilized the mRNA. The short half-life and the superinducibility of PAI mRNA are properties shared with rapidly degraded mRNAs encoding protooncoproteins. A 2.97-kb cDNA clone containing the entire coding sequence of PAI-1 was isolated from a cDNA library made from mink lung CCL64 epithelial cells stimulated with PMA. The PAI-1 cDNA contains a long 3'-untranslated region (UTR) of 1720 bp whose sequence is highly conserved among PAI-1 mRNAs from different species. The PAI-1 mRNA also contains several AUUUA pentamer sequences which are the features of an A+U-rich regulatory element such as is found on the fos protooncogene mRNA. Upstream of one of these AUUUA pentamers are several highly conserved sequences that are also found in the 3' UTR of the fos and integrin receptor alpha-subunit mRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

A common response element mediates differential effects of phorbol esters and forskolin on type-1 plasminogen activator inhibitor gene expression in human breast carcinoma cells

We have characterized regulation of type-1 plasminogen activator inhibitor (PAI-1) gene expression by phorbol 12-myristate 13-acetate (PMA) and the cAMP-inducing agent forskolin in the human breast carcinoma cell line MCF-7. PMA caused a strong induction of PAI-1, while forskolin suppressed the PMA response. Transfection experiments with fusion genes showed that sequences mediating PMA induction as well as forskolin suppression were present between base pairs -100 and -30 of the 5'-flanking region of the PAI-1 gene. The region was found to contain two Sp1 binding sites. A proximal sequence in the region, TGAGTTCA (P box), with sequence similarity to phorbol ester response elements (TRE) as well as to cAMP response elements (CRE), bound a low-abundance, as yet unidentified nuclear protein in MCF-7 cells. This sequence had a higher affinity to purified c-jun homodimer than to c-jun/c-fos heterodimer in MCF-7 nuclear extracts; it had no affinity to the proteins binding to CRE consensus sequences in these extracts. A distal TRE-like sequence, TGAGTGG (D box), had a weak affinity to c-jun/c-fos heterodimer and c-jun homodimer; binding of proteins to this sequence was facilitated by binding of proteins to the P box. Both the P box and the D box were necessary for PMA responsiveness, suggesting a cooperativity between the two binding sites. A mutation of the P box removing the CRE similarity abolished the forskolin suppression of the PMA response. We propose that the protein kinase C and the protein kinase A signal-transduction pathways, with opposite effects on PAI-1 gene expression converge by modulating differently P-box-binding proteins.