Control of plasminogen-activator inhibitor type 2 gene expression in the differentiation of monocytic cells

SerpinB2 inhibits migration and promotes a resolution phase signature in large peritoneal macrophages

SerpinB2 (plasminogen activator inhibitor type 2) has been called the "undecided serpin" with no clear consensus on its physiological role, although it is well described as an inhibitor of urokinase plasminogen activator (uPA). In macrophages, pro-inflammatory stimuli usually induce SerpinB2; however, expression is constitutive in Gata6+ large peritoneal macrophages (LPM). Interrogation of expression data from human macrophages treated with a range of stimuli using a new bioinformatics tool, CEMiTool, suggested that SerpinB2 is most tightly co- and counter-regulated with genes associated with cell movement. Using LPM from SerpinB2-/- and SerpinB2R380A (active site mutant) mice, we show that migration on Matrigel was faster than for their wild-type controls. Confocal microscopy illustrated that SerpinB2 and F-actin staining overlapped in focal adhesions and lamellipodia. Genes associated with migration and extracellular matrix interactions were also identified by RNA-Seq analysis of migrating RPM from wild-type and SerpinB2R380A mice. Subsequent gene set enrichment analyses (GSEA) suggested SerpinB2 counter-regulates many Gata6-regulated genes associated with migration. These data argue that the role of SerpinB2 in macrophages is inhibition of uPA-mediated plasmin generation during cell migration. GSEA also suggested that SerpinB2 expression (likely via ensuing modulation of uPA-receptor/integrin signaling) promotes the adoption of a resolution phase signature.

The transcription factor C/EBP-β mediates constitutive and LPS-inducible transcription of murine SerpinB2

SerpinB2 or plasminogen activator inhibitor type 2 (PAI-2) is highly induced in macrophages in response to inflammatory stimuli and is linked to the modulation of innate immunity, macrophage survival, and inhibition of plasminogen activators. Lipopolysaccharide (LPS), a potent bacterial endotoxin, can induce SerpinB2 expression via the toll-like receptor 4 (TLR4) by ∼1000-fold over a period of 24 hrs in murine macrophages. To map the LPS-regulated SerpinB2 promoter regions, we transfected reporter constructs driven by the ∼5 kb 5'-flanking region of the murine SerpinB2 gene and several deletion mutants into murine macrophages. In addition, we compared the DNA sequence of the murine 5′ flanking sequence with the sequence of the human gene for homologous functional regulatory elements and identified several regulatory cis-acting elements in the human SERPINB2 promoter conserved in the mouse. Mutation analyses revealed that a CCAAT enhancer binding (C/EBP) element, a cyclic AMP response element (CRE) and two activator protein 1 (AP-1) response elements in the murine SerpinB2 proximal promoter are essential for optimal LPS-inducibility. Electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays demonstrated that LPS induces the formation of C/EBP-β containing complexes with the SerpinB2 promoter. Importantly, both constitutive and LPS-induced SerpinB2 expression was severely abrogated in C/EBP-β-null mouse embryonic fibroblasts (MEFs) and primary C/EBP-β-deficient peritoneal macrophages. Together, these data provide new insight into C/EBP-β-dependent regulation of inflammation-associated SerpinB2 expression.

Plasminogen activator inhibitor type 2: still an enigmatic serpin but a model for gene regulation

Plasminogen activator inhibitor type-2 (PAI-2; SERPINB2) is an atypical member of the Ov-serpin family of serine protease inhibitors. While it is an undisputed inhibitor of urokinase and tissue-type plasminogen activator in the extracellular space and on the cell surface, the weight of circumstantial evidence suggests that PAI-2 also fulfills an intracellular role which is independent of plasminogen activator inhibition and indeed may not even involve protease inhibition at all. More and more data continue to implicate a role for PAI-2 in many settings, the most recent associating it as a modulator of the innate immune response. Further to the debates concerning its physiological role, there are few genes, if any, that display the regulation profile of the PAI-2 gene: PAI-2 protein and mRNA levels can be induced in the order of, not hundred-, but thousand-folds in a process that is controlled at many levels including gene transcription and mRNA stability while an epigenetic component is also likely. The ability of some cells, including monocytes, fibroblasts, and neurons to have the capacity to increase PAI-2 synthesis to such high levels is intriguing enough. So why do these cells have the capacity to synthesize so much of this protein? While tantalizing clues continue to be revealed to the field, an understanding of how this gene is regulated so profoundly has provided insights into the broader mechanics of gene expression and regulation.

The plasminogen activator inhibitor 2 transcript is destabilized via a multi-component 3' UTR localized adenylate and uridylate-rich instability element in an analogous manner to cytokines and oncogenes

Plasminogen activator inhibitor type 2 (PAI-2; SERPINB2) is a highly-regulated gene that is subject to both transcriptional and post-transcriptional control. For the latter case, inherent PAI-2 mRNA instability was previously shown to require a nonameric adenylate-uridylate element in the 3' UTR. However, mutation of this site was only partially effective at restoring complete mRNA stabilization. In the present study, we have identified additional regulatory motifs within the 3' UTR that cooperate with the nonameric adenylate-uridylate element to promote mRNA destabilization. These elements are located within a 74 nucleotide U-rich stretch (58%) of the 3' UTR that flanks the nonameric motif; deletion or substitution of this entire region results in complete mRNA stabilization. These new elements are conserved between species and optimize the destabilizing capacity with the nonameric element to ensure complete mRNA instability in a manner analogous to some class I and II adenylate-uridylate elements present in transcripts encoding oncogenes and cytokines. Hence, post-transcriptional regulation of the PAI-2 mRNA transcript involves an interaction between closely spaced adenylate-uridylate elements in a manner analogous to the post-transcriptional regulation of oncogenes and cytokines.

Identification of proteins cleaved downstream of caspase activation in monocytes undergoing macrophage differentiation

We have shown previously that caspases were specifically involved in the differentiation of peripheral blood monocytes into macrophages while not required for monocyte differentiation into dendritic cells. To identify caspase targets in monocytes undergoing macrophagic differentiation, we used the human monocytic leukemic cell line U937, whose macrophagic differentiation induced by exposure to 12-O-tetradecanoylphorbol 13-acetate (TPA) can be prevented by expression of the baculovirus caspase-inhibitory protein p35. A comparative two-dimensional gel proteomic analysis of empty vector- and p35-transfected cells after 12 h of exposure to 20 nm TPA, followed by mass spectrometry analysis, identified 38 differentially expressed proteins. Those overexpressed in p35-expressing cells (n = 16) were all full-length, whereas half of those overexpressed in control cells (n = 22) were N- or C-terminal cleavage fragments. The cleavage or degradation of seven of these proteins was confirmed in peripheral blood monocytes undergoing macrophage colony-stimulating factor-induced macrophagic differentiation. In U937 cells exposed to TPA, these proteolytic events can be inhibited by expression of a caspase-8 dominant negative mutant or the cowpox virus CrmA caspase inhibitor. These cleavages provide new insights to analyze the role of caspases in this specific differentiation program.

Characterisation of PAUSE-1, a powerful silencer in the human plasminogen activator inhibitor type 2 gene promoter

Plasminogen activator inhibitor type 2 (PAI-2) is a serine protease inhibitor traditionally regarded as a regulator of fibrinolysis and extracellular matrix degradation. More recently, PAI-2 has been implicated in diverse processes such as keratinocyte differentiation, cell death and viral pathogenesis. The PAI-2 promoter tightly regulates PAI-2 gene expression in a cell-specific manner and this control is mediated, in part, by the upstream silencer element, PAUSE-1. Here we have defined PAUSE-1 and investigated its activity as a silencer. A series of mutations were generated within the PAUSE-1 element and analysed for transcription factor binding and transcriptional silencing activity. These studies have defined the minimal functional PAUSE-1 element as TCTN(x)AGAN(3)T(4), where x = 0, 2 or 4. Examination of related elements present in other promoters, such as the human IFNbeta promoter, suggests that PAUSE-1 is a member of a family of universal silencers with the consensus sequence TCTN(x)AGA. UV crosslinking analyses determined that the PAUSE-1 binding protein was approximately 67 kDa. Insertion of PAUSE-1 into the heterologous (SV40) or the minimal PAI-2 promoters silenced transcription by 2.5-fold. These data show that PAUSE-1 acts as a powerful silencer of PAI-2 gene transcription and is likely to be important in the silencing of other genes as well.

No evidence of a role for activating CDK2 mutations in melanoma

Inactivation of p16INK4a and/or activation of cyclin-dependent kinase-4 (CDK4) are strongly associated with both susceptibility and progression in melanoma. Activating CDK4 mutations prevent the binding and inhibition of CDK4 by p16INK4a. A second, more indirect role for CDK4 is in late G1, where it may sequester the inhibitors p27KIP1 or p21CIP1 away from CDK2, and in doing so upregulate the CDK2 activity necessary for cells to proceed completely through G1 into S phase. As the pivotal residues around the most predominant R24C activating CDK4 mutation are invariant between CDK2 and CDK4, we speculated that the pivotal arginine (position 22 in CDK2), or a nearby residue, may be mutated in some melanomas, resulting in the diminution of its binding and inhibition by p27KIP1 or p21CIP1. However, except for a silent polymorphism, we detected no variants within this region of the CDK2 gene in 60 melanoma cell lines. Thus, if CDK2 activity is dysregulated in melanoma it is likely to occur by a means other than mutations causing loss of direct inhibition. We also examined the expression of the CDK2 gene in melanoma cell lines, to assess its possible co-regulation with the gene for the melanocyte-lineage antigen pmel17, which maps less than 1 kb away in head to head orientation with CDK2 and may be transcribed off the same bidirectional promoter. However, expression of the genes is not co-regulated.

Localization of the mosaic transmembrane serine protease corin to heart myocytes

Corin cDNA encodes an unusual mosaic type II transmembrane serine protease, which possesses, in addition to a trypsin-like serine protease domain, two frizzled domains, eight low-density lipoprotein (LDL) receptor domains, a scavenger receptor domain, as well as an intracellular cytoplasmic domain. In in vitro experiments, recombinant human corin has recently been shown to activate pro-atrial natriuretic peptide (ANP), a cardiac hormone essential for the regulation of blood pressure. Here we report the first characterization of corin protein expression in heart tissue. We generated antibodies to two different peptides derived from unique regions of the corin polypeptide, which detected immunoreactive corin protein of approximately 125-135 kDa in lysates from human heart tissues. Immunostaining of sections of human heart showed corin expression was specifically localized to the cross striations of cardiac myocytes, with a pattern of expression consistent with an integral membrane localization. Corin was not detected in sections of skeletal or smooth muscle. Corin has been suggested to be a candidate gene for the rare congenital heart disease, total anomalous pulmonary venous return (TAPVR) as the corin gene colocalizes to the TAPVR locus on human chromosome 4. However examination of corin protein expression in TAPVR heart tissue did not show evidence of abnormal corin expression. The demonstrated corin protein expression by heart myocytes supports its proposed role as the pro-ANP convertase, and thus a potentially critical mediator of major cardiovascular diseases including hypertension and congestive heart failure.

Localization, expression and genomic structure of the gene encoding the human serine protease testisin

Testisin is a recently identified human serine protease expressed by premeiotic testicular germ cells and is a candidate tumor suppressor for testicular cancer. Here, we report the characterization of the gene encoding testisin, designated PRSS21, and its localization on the short arm of human chromosome 16 (16p13.3) between the microsatellite marker D16S246 and the radiation hybrid breakpoint CY23HA. We have further refined the localization to cosmid 406D6 in this interval and have established that the gene is approximately 4. 5 kb in length, and contains six exons and five intervening introns. The structure of PRSS21 is very similar to the human prostasin gene (PRSS8) which maps nearby on 16p11.2, suggesting that these genes may have evolved through gene duplication. Sequence analysis showed that the two known isoforms of testisin are generated by alternative pre-mRNA splicing. A major transcription initiation site was identified 97 nucleotides upstream of the testisin translation start and conforms to a consensus initiator element. The region surrounding the transcription initiation site lacks a TATA consensus sequence, but contains a CCAAT sequence and includes a CpG island. The 5'-flanking region contains several consensus response elements including Sp1, AP1 and several testis-specific elements. Analysis of testisin gene expression in tumor cell lines shows that testisin is not expressed in testicular tumor cells but is aberrantly expressed in some tumor cell lines of non-testis origin. These data provide the basis for identifying potential genetic alterations of PRSS21 that may underlie both testicular abnormalities and tumorigenesis.

Picornavirus receptor down-regulation by plasminogen activator inhibitor type 2

Therapeutic interference with virus-cell surface receptor interactions represents a viable antiviral strategy. Here we demonstrate that cytoplasmic expression of the serine protease inhibitor (serpin), plasminogen activator inhibitor type 2 (PAI-2), affords a high level of protection from lytic infection by multiple human picornaviruses. The antiviral action of PAI-2 was mediated primarily through transcriptional down-regulation of the following virus receptors: intercellular adhesion molecule 1 (ICAM-1, a cellular receptor for the major group of rhinoviruses), decay-accelerating factor (a cellular receptor for echoviruses and coxsackieviruses), and to a lesser extent the coxsackie-adenovirus receptor protein (a cellular receptor for group B coxsackieviruses and group C adenoviruses). Expression of related cell surface receptors, including membrane cofactor protein and the poliovirus receptor, remained unaffected. These findings suggest that PAI-2 and/or related serpins may form the basis of novel antiviral strategies against picornavirus infections and also therapeutic interventions against ICAM-1-mediated respiratory inflammation.

Plasminogen activator inhibitor type-2 (PAI-2) gene transcription requires a novel NF-kappaB-like transcriptional regulatory motif

Induction of human plasminogen activator inhibitor type-2 (PAI-2) gene transcription is the response of macrophages to inflammatory stimuli, such as the pleiotropic cytokine, tumour necrosis factor-alpha (TNFalpha). Here we have examined whether PAI-2 gene transcription in response to TNFalpha may be mediated through a regulatory pathway involving the transcription factor, NF-kappaB. We have tested the function of two potential NF-kappaB-like sites present in the PAI-2 proximal promoter for responsiveness to TNFalpha using chloramphenicol acetyl transferase reporter gene deletion and mutation analyses. While no evidence was found for TNFalpha regulation of the PAI-2 gene through either of these two sites, one of the NF-kappaB-like motifs, transcriptional regulatory motif (TRM), present at position -400 was found to be essential for constitutive PAI-2 transcription, as mutation of this motif abolished basal PAI-2 promoter activity in both monocyte-like U937 cells and HT1080 fibrosarcoma cells. Competition electrophoretic mobility shift assays identified four TRM-binding proteins present in U937, HT1080 and HeLa cell extracts, which bound to this motif but were not components of the NF-kappaB regulatory complex. Expression screening of a HeLa cell cDNA library using the -400 TRM as a probe identified two cDNAs encoding partial peptides which specifically bound the TRM motif. DNA sequence analysis revealed that one cDNA was novel, and the second cDNA encoded exon 5 of the nephroblastoma overexpressed (novH) proto-oncogene, suggesting a new role for this peptide in gene regulation. Taken together, these findings identify a new regulatory element required for constitutive PAI-2 transcription, and identify potential DNA-binding proteins associated with this element that may play a role in PAI-2 gene regulation.

Expression of dioxin-responsive genes in human endometrial cells in culture

To investigate expression of dioxin-responsive genes in human endometrial cells with exposure to 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD), human endometrial stromal cells immortalized with temperature-sensitive SV40 T antigen were used for the experiments. Cells were treated with 0.1% DMSO or 0.1, 1, 10, or 100 nM TCDD for 24 h. Induction of interleukin-1beta (IL-1beta) and plasminogen activator inhibitor-2 (PAI-2) mRNAs was analyzed by reverse-transcription polymerase chain reaction. Expression of IL-1beta or PAI-2 mRNA in response to TCDD was increased in a dose-dependent fashion. The maximum increases of PAI-2 and IL-1beta mRNAs were observed at 100 and 10 nM TCDD, respectively. While cycloheximide treatment did not show a significant difference of PAI-2 mRNA levels between control and TCDD-treated cells, mRNA stability assay using actinomycin D showed that PAI-2 mRNA in TCDD-treated cells was about twofold more stable than the control cells. While expression of CYP1A1 mRNA was not detected and levels of ARNT mRNA were not altered by TCDD exposure, the amount of AhR mRNA was decreased dose dependently. The present study represents an initial attempt to determine the responses of dioxin-responsive genes in human endometrial cells following TCDD exposure. The results demonstrated that IL-1beta and PAI-2 genes are induced dose dependently in human endometrial cells with exposure to TCDD and expression of PAI-2 mRNA is controlled at the posttranscriptional level.

Regulation of the level and glycosylation state of plasminogen activator inhibitor type 2 during human keratinocyte differentiation

Plasminogen activator inhibitor type 2 (PAI-2) is an unusual member of the serine proteinase inhibitor (serpin) family which has been implicated in the protection of cells from programmed cell death. Human epidermal keratinocytes synthesize large amounts of PAI-2 in two active forms: glycosylated and non-glycosylated. Calcium (Ca2+), a well-known inducer of numerous aspects of keratinocyte terminal differentiation, increases the steady-state levels of PAI-2 mRNA and protein. As the cultures become more differentiated due to longer incubation with Ca2+, the glycosylated form is preferentially elevated. Surprisingly, glycosylated as well as non-glycosylated PAI-2 remains predominantly cell-associated, in a trypsin-inaccessible form and thus most likely inside the cell. Tumor necrosis factor-alpha (TNF-alpha), an inflammatory mediator that induces some markers of keratinocyte differentiation, also increases PAI-2 mRNA and protein levels. Experiments using cultures in which protein kinase C has been downregulated suggest that Ca2+, but not TNF-alpha, acts at least partially through one or more isozymes of this kinase for induction of PAI-2. This is consistent with the finding that the effect of simultaneous addition of Ca2+ plus TNF-alpha is at least additive, compared with addition of either stimulant alone. These data demonstrate that the keratinocyte maintains multiple regulatory pathways for control of PAI-2 expression, at least one of which is related to terminal differentiation.

The serine proteinase inhibitor (serpin) plasminogen activation inhibitor type 2 protects against viral cytopathic effects by constitutive interferon alpha/beta priming

The serine proteinase inhibitor (serpin) plasminogen activator inhibitor type 2 (PAI-2) is well characterized as an inhibitor of extracellular urokinase-type plasminogen activator. Here we show that intracellular, but not extracellular, PAI-2 protected cells from the rapid cytopathic effects of alphavirus infection. This protection did not appear to be related to an effect on apoptosis but was associated with a PAI-2-mediated induction of constitutive low-level interferon (IFN)-alpha/beta production and IFN-stimulated gene factor 3 (ISGF3) activation, which primed the cells for rapid induction of antiviral genes. This primed phenotype was associated with a rapid development of resistance to infection by the PAI-2 transfected cells and the establishment of a persistent productive infection. PAI-2 was also induced in macrophages in response to viral RNA suggesting that PAI-2 is a virus response gene. These observations, together with the recently demonstrated PAI-2-mediated inhibition of tumor necrosis factor-alpha induced apoptosis, (a) illustrate that PAI-2 has an additional and distinct function as an intracellular regulator of signal transduction pathway(s) and (b) demonstrate a novel activity for a eukaryotic serpin.

Phorbol ester-induced down-regulation of topoisomerase II alpha mRNA in a human erythroleukemia cell line. Evidence for a post-transcriptional mechanism

Tumor-promoting phorbol esters such as phorbol 12-myristate 13-acetate (PMA) are reported to induce megakaryocyte terminal differentiation of the erythroleukemia cell line K562. This differentiation is accompanied by the regulation of various gene products such as gamma-globin (Lumelsky and Forget, Mol Cell Biol 11: 3528-3536, 1991) and platelet-derived growth factor-beta (PDGF-beta) (Mäkelä et al., Mol Cell Biol 7: 3656-3662, 1987). PMA has also been found to regulate topoisomerase (topo) II alpha in other myeloid leukemia lines. The purpose of this study was to investigate whether PMA regulates topo II alpha in K562 cells and, if so, to identify the mechanisms responsible for this regulation. Northern blot analysis revealed that topo II alpha mRNA is down-regulated as is gamma-globin. This activity was not due to a generalized decrease in mRNA, as PDGF-beta message actually increased in response to PMA treatment. RNase protection assays confirmed the decline in the topo II alpha message. Transfection experiments with various topo II promoter CAT constructs extending to 2200 bp upstream of the ATG start site revealed regions that enhance and regions that inhibit CAT expression in the absence of PMA However, PMA did not affect this CAT expression. Run-on experiments using 5' and 3' human topo II cDNA probes confirmed that transcriptional initiation of the topo II gene was not affected by PMA, whereas that of c-myc did decrease. Therefore, the apparent decrease in topo II alpha mRNA in K562 cells upon their treatment with PMA appeared to be the result of a post-transcriptional mechanism.

Alternatively spliced variants of the cell adhesion molecule CD44 and tumour progression in colorectal cancer

Increased expression of alternatively spliced variants of the CD44 family of cell adhesion molecules has been associated with tumour metastasis. In the present study, expression of alternatively spliced variants of CD44 and their cellular distribution have been investigated in human colonic tumours and in the corresponding normal mucosa, in addition to benign adenomatous polyps. The expression of CD44 alternatively spliced variants has been correlated with tumour progression according to Dukes' histological stage. CD44 variant expression was determined by immunohistochemisty using monoclonal antibodies directed against specific CD44 variant domains together with RT-PCR analysis of CD44 variant mRNA expression in the same tissue specimens. We demonstrate that as well as being expressed in colonic tumour cells, the full range of CD44 variants, CD44v2-v10, are widely expressed in normal colonic crypt epithelium, predominantly in the crypt base. CD44v6, the epitope which is most commonly associated with tumour progression and metastasis, was not only expressed by many benign colonic tumours, but was expressed as frequently in normal basal crypt epithelium as in malignant colonic tumour cells, and surprisingly, was even absent from some metastatic colorectal tumours. Expression of none of the CD44 variant epitopes was found to be positively correlated with tumour progression or with colorectal tumour metastasis to the liver, results which are inconsistent with a role for CD44 variants as indicators of colonic cancer progression.

Tissue plasminogen activator and plasminogen activator inhibitors of type 1 and type 2 in the plasma of parturient women

Changes in the fibrinolytic system of parturient women have so far been only partially documented. Our main questions were whether and how the concentration of tissue plasminogen activator (tPA) and plasminogen activator inhibitors of type 1 (PAI-1) and type 2 (PAI-2) change in the plasma throughout normal labor. The study group consisted of 38 women with normal pregnancy, delivering at term. The concentration of antigens tPA, PAI-1 and PAI-2 in plasma was tested by enzyme-linked immuno-sorbent assay method, and the activity of PAI-1 by plasmin method. Results were analysed statistically. During labor the level of tPA antigen increases over two times: from 9.3 +/- 4.3 ng/ml before labor, to 23.3 +/- 9.6 ng/ml in the second stage of labor. Changes of PAI-1 antigen as well as its activity though noticeable, were not statistically significant. PAI-2 antigen level increased significantly in the third stage (146.3 +/- 58.7 ng/ml before labor, and 212.2 +/- 75.0 ng/ml after placenta expulsion). In summary the more significant change in the fibrinolytic system during labor is an increase of the level of tPA and PAI-2 antigens, but their peaks appear in different stages of labor. The predominance of PAIs over tPA is maintained throughout the whole labor, though on a lower level as can be inferred from the tPA/PAIs ratio.

Plasminogen activator inhibitor type 2 inhibits tumor necrosis factor alpha-induced apoptosis. Evidence for an alternate biological function

Plasminogen activator inhibitor type 2 (PAI-2) is a serine proteinase inhibitor or serpin that is a major product of macrophages in response to endotoxin and inflammatory cytokines. We have explored the role of PAI-2 in apoptotic cell death initiated by tumor necrosis factor alpha (TNF). HeLa cells stably transfected with PAI-2 cDNA were protected from TNF-induced apoptosis, whereas cells transfected with antisense PAI-2 cDNA, a control gene, or the plasmid vector alone remained susceptible. The level of PAI-2 expressed by different HeLa cell clones was inversely correlated with their sensitivity to TNF. Loss of TNF sensitivity was not a result of loss of TNF receptor binding. In contrast, PAI-2 expression did not confer protection against apoptosis induced by ultraviolet or ionizing radiation. The serine proteinase urokinase-type plasminogen activator was not demonstrated to be the target of PAI-2 action. The P1-Arg amino acid residue of PAI-2 was determined to be required for protection, because cells expressing PAI-2 with an Ala in this position were not protected from TNF-mediated cell death. The results suggest that intracellular PAI-2 might be an important factor in regulating cell death in TNF-mediated inflammatory processes through inhibition of a proteinase involved in TNF-induced apoptosis.

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.

Expression of plasminogen activator inhibitor type 2 in normal and psoriatic epidermis

The plasminogen activator (PA) proteolytic cascade has been implicated in the regulation of cell activities, including proliferation and differentiation, both of which occur continuously in normal human epidermis and are aberrant in psoriatic epidermis. To elucidate further the mechanisms by which PA is regulated in epidermis, we evaluated the levels of PA inhibitors type 1 (PAI-1) and type 2 (PAI-2) in normal and psoriatic epidermis. PAI-2, but not PAI-1, was detectable by mRNA, antigen, and activity assays, indicating that PAI-2 is the predominant epidermal PA inhibitor. In situ hybridization revealed that PAI-2 mRNA occurred throughout normal epidermis, although the signal was most intense in the granular layers. Similarly, PAI-2 antigen was most prominent in the granular layers; its distribution in these differential layers was along the cell periphery. Diffuse, fainter staining for PAI-2 was also detected in the basal cells and in some spinous layers of normal epidermis. Extracts of normal epidermis contained PA inhibitory activity identified as PAI-2 by immunoprecipitation with specific antibody. In psoriatic epidermis, PAI-2 mRNA and antigen were most prominent in the more superficial layers beneath the cornified cells. As with normal epidermis, PAI-2 assumed a pericellular distribution in the psoriatic cells. These data demonstrate that PAI-2 is constitutively expressed in vivo by keratinocytes in human epidermis and indicate that this protein is the predominant inhibitor of PA activity in normal and psoriatic human epidermis.

Southwestern blot mapping of potential regulatory proteins binding to the DNA encoding plasminogen activator inhibitor type 2

In order to investigate the molecular basis for the regulated expression of plasminogen activator inhibitor type 2 (PAI-2), we sought to identify monocyte-derived nuclear factors which interact with the PAI-2 gene. We have explored the application of Southwestern blot mapping as an approach for identifying specific DNA-protein interactions and targeting potential regulatory DNA elements. The procedure involves an initial global screening of a crude preparation of nuclear proteins with radiolabelled DNA fragments (200-300 bp) derived from a large region (8.8 kb) of PAI-2. The bound DNA fragments are eluted and their location within PAI-2 mapped by Southern blot hybridization analysis. We have used this procedure to examine the differential binding of nuclear factors from the U937 monocytic cell in the absence and in the presence of the differentiating agent, 12-phorbol 13-myristate acetate (PMA), in order to identify proteins that bind specifically to the 5' flanking promoter region and first intron of PAI-2. Eleven DNA-binding proteins ranging in molecular mass from 27 to 92 kDa were identified, and the results define three regions of the gene which contain DNA-binding sites which may be involved in the transcriptional regulation of PAI-2. Deletion analysis using a series of 5' deletion mutants spanning PAI-2 fused to a chloramphenicol acetyltransferase-encoding reporter gene (cat) demonstrates that two of the regions identified by Southwestern blot mapping contain elements which can function to modulate PAI-2 expression in transient transfections of U937 cells.

Sodium butyrate differentially modulates plasminogen activator inhibitor type-1, urokinase plasminogen activator, and its receptor in a human colon carcinoma cell

Human colonic epithelium is exposed to varying levels of sodium butyrate, which is derived from the bacterial fermentation of dietary carbohydrate. Sodium butyrate has several effects on colonic tumor cells in vitro, including arrest of cell growth and differentiation. In the present study we have found that, in addition to a reduction in cellular proliferation, sodium butyrate induces the transient expression of plasminogen activator inhibitor type-1 (PAI-1) in the LIM 2405 human colonic tumor cell. Approximately 40% of the PAI-1 secreted is biologically active as judged by the formation of higher molecular weight, SDS-resistant complexes with urokinase plasminogen activator (uPA). The enhanced PAI-1 biosynthesis was accompanied by an increase in PAI-1 mRNA levels. During the same time period, the amount of secreted uPA remained relatively constant, but the level of cell associated uPA decreased slowly and was accompanied by a decrease in uPA mRNA levels. The uPA receptor is synthesized constitutively by these cells, and was down-regulated at both the protein and mRNA levels in response to sodium butyrate. The results demonstrate that sodium butyrate can alter the balance of components of the plasminogen activator system in a manner which favours net decreased plasminogen activator activity and suggests a role for sodium butyrate in the regulation of extracellular proteolysis.