Involvement of Sp1 in basal and retinoic acid induced transcription of the human tissue-type plasminogen activator gene

Retinoic acid triggers c-kit gene expression in spermatogonial stem cells through an enhanceosome constituted between transcription factor binding sites for retinoic acid response element (RARE), spleen focus forming virus proviral integration oncogene (SPFI1) (PU.1) and E26 transformation-specific (ETS)

Restricted availability of retinoic acid (RA) in the testicular milieu regulates transcriptional activity of c-kit (KIT, CD117), which aids in the determination of spermatogonial stem-cell differentiation. The effect of RA on c-kit has been reported previously, but its mode of genomic action remains unresolved. We studied the molecular machinery guiding RA responsiveness to the c-kit gene using spermatogonial stem-cell line C18-4 and primary spermatogonial cells. A novel retinoic acid response element (RARE) positioned at -989 nucleotides upstream of the transcription start site (TSS) was identified, providing a binding site for a dimeric RA receptor (i.e. retinoic acid receptor gamma (RARγ) and retinoic X receptor). RA treatment influenced c-kit promoter activity, along with endogenous c-kit expression in C18-4 cells. A comprehensive promoter deletion assay using the pGL3B reporter system characterised the region spanning -271bp and -1011bp upstream of the TSS, which function as minimal promoter and maximal promoter, respectively. In silico analysis predicted that the region -1011 to +58bp comprised the distal enhancer RARE and activators such as spleen focus forming virus proviral integration oncogene (SPFI1) (PU.1), specificity protein 1 (SP1) and four E26 transformation-specific (ETS) tandem binding sites at the proximal region. Gel retardation and chromatin immunoprecipitation (ChIP) assays showed binding for RARγ, PU.1 and SP1 to the predicted consensus binding sequences, whereas GABPα occupied only two out of four ETS binding sites within the c-kit promoter region. We propose that for RA response, an enhanceosome is orchestrated through scaffolding of a CREB-binding protein (CBP)/p300 molecule between RARE and elements in the proximal promoter region, controlling germ-line expression of the c-kit gene. This study outlines the fundamental role played by RARγ, along with other non-RAR transcription factors (PU.1, SP1 and GABPα), in the regulation of c-kit expression in spermatogonial stem cells in response to RA.

Allelic imbalance of tissue-type plasminogen activator (t-PA) gene expression in human brain tissue

We have identified a single-nucleotide polymorphism (SNP) in the t-PA enhancer (-7351C>T), which is associated with endothelial t-PA release in vivo. In vitro studies demonstrated that this SNP is functional at the level of transcription. In the brain, t-PA has been implicated in both physiologic and pathophysiologic processes. The aim of the present study was to examine the effect of the t-PA –7351C>T SNP on t-PA gene expression in human brain tissue. Allelic mRNA expression was measured in heterozygous post-mortem brain tissues using quantitative TaqMan genotyping assay. Protein-DNA interactions were assessed using electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP). Significantly higher levels of t-PA mRNA were generated from chromosomes that harboured the wild-type –7351C allele, as compared to those generated from the mutant T allele (for the hippocampus, C to T allelic ratio of ~1.3, p=0.010, n=12; and for the cortex, C to T allelic ratio of ~1.2, p=0.017, n=12). EMSA showed reduced neuronal and astrocytic nuclear protein binding affinity to the T allele, and identified Sp1 and Sp3 as the major transcription factors that bound to the –7351 site. ChIP analyses confirmed that Sp1 recognises this site in intact cells. In conclusion, the t-PA –7351C>T SNP affects t-PA gene expression in human brain tissue. This finding might have clinical implications for neurological conditions associated with enhanced t-PA levels, such as in the acute phase of cerebral ischaemia, and also for stroke recovery.

Dependence of Proximal GC Boxes and Binding Transcription Factors in the Regulation of Basal and Valproic Acid-Induced Expression of t-PA

Objective. Endothelial tissue-type plasminogen activator (t-PA) release is a pivotal response to protect the circulation from occluding thrombosis. We have shown that the t-PA gene is epigenetically regulated and greatly induced by the histone deacetylase (HDAC) inhibitor valproic acid (VPA). We now investigated involvement of known t-PA promoter regulatory elements and evaluated dependence of potential interacting transcription factors/cofactors. Methods. A reporter vector with an insert, separately mutated at either the t-PA promoter CRE or GC box II or GC box III elements, was transfected into HT-1080 and HUVECs and challenged with VPA. HUVECs were targeted with siRNA against histone acetyl transferases (HAT) and selected transcription factors from the Sp/KLF family. Results. An intact VPA-response was observed with CRE mutated constructs, whereas mutation of GC boxes II and III reduced the magnitude of the induction by 54 and 79% in HT-1080 and 49 and 50% in HUVECs, respectively. An attenuated induction of t-PA mRNA was observed after Sp2, Sp4, and KLF5 depletion. KLF2 and p300 (HAT) were identified as positive regulators of basal t-PA expression and Sp4 and KLF9 as repressors. Conclusion. VPA-induced t-PA expression is dependent on the proximal GC boxes in the t-PA promoter and may involve interactions with Sp2, Sp4, and KLF5.

Human tissue-type plasminogen activator

Tissue-type plasminogen activator (t-PA ) plays an important role in the removal of intravascular fibrin deposits and has several physiological roles and pathological activities in the brain. Its production by many other cell types suggests that t-PA has additional functions outside the vascular and central nervous system. Activity of t-PA is regulated at the level of its gene transcription, its mRNA stability and translation, its storage and regulated release, its interaction with cofactors that enhance its activity, its inhibition by inhibitors such as plasminogen activator inhibitor type 1 or neuroserpin, and its removal by clearance receptors. Gene transcription of t-PA is modulated by a large number of hormones, growth factors, cytokines or drugs and t-PA gene responses may be tissue-specific. The aim of this review is to summarise current knowledge on t-PA function and regulation of its pericellular activity, with an emphasis on regulation of its gene expression.

Retinoic acid induces expression of the thyroid hormone transporter, monocarboxylate transporter 8 (Mct8)

Retinoic acid (RA) and thyroid hormone are critical for differentiation and organogenesis in the embryo. Mct8 (monocarboxylate transporter 8), expressed predominantly in the brain and placenta, mediates thyroid hormone uptake from the circulation and is required for normal neural development. RA induces differentiation of F9 mouse teratocarcinoma cells toward neurons as well as extraembryonal endoderm. We hypothesized that Mct8 is functionally expressed in F9 cells and induced by RA. All-trans-RA (tRA) and other RA receptor (RAR) agonists dramatically (>300-fold) induced Mct8. tRA treatment significantly increased uptake of triiodothyronine and thyroxine (4.1- and 4.3-fold, respectively), which was abolished by a selective Mct8 inhibitor, bromosulfophthalein. Sequence inspection of the Mct8 promoter region and 5'-rapid amplification of cDNA ends PCR analysis in F9 cells identified 11 transcription start sites and a proximal Sp1 site but no TATA box. tRA significantly enhanced Mct8 promoter activity through a consensus RA-responsive element located 6.6 kilobases upstream of the coding region. A chromatin immunoprecipitation assay demonstrated binding of RAR and retinoid X receptor to the RA response element. The promotion of thyroid hormone uptake through the transcriptional up-regulation of Mct8 by RAR is likely to be important for extraembryonic endoderm development and neural differentiation. This finding demonstrates cross-talk between RA signaling and thyroid hormone signaling in early development at the level of the thyroid hormone transporter.

Retinoids regulate human amniotic tissue-type plasminogen activator gene by a two-step mechanism

The collagenolytic effects of the tissue-type plasminogen activator (t-PA) leading to extracellular matrix degradation are clearly involved in the physiopathology of human foetal membranes rupture. Nevertheless, the regulation of t-PA gene expression in extraembryonic developmental contexts remains unknown. The aim of our study is to propose the retinoic acids (RAs) as molecular regulators of t-PA expression in foetal membranes. RA induced t-PA mRNA and proteins in a time-dependent manner in amniotic membrane explants and Wistar Institute Susan Hayflick (WISH) cells. Furthermore, the use of cycloheximide revealed a two-step regulation of t-PA gene. Gene reporter assays confirmed that the RA-induced t-PA gene expression occurred through interactions of retinoid receptors (RARs and RXRs) with a DR5 response element located at –7 kb from the transcription site. Site-directed mutagenesis of this region of the t-PA promoter showed that SP1 factor was also retinoid-mediated induction, and immunoprecipitation assays revealed that SP1 and RAR/RXR interacted physically. Chromatin immunoprecipitation demonstrated that interactions between RARs, RXRs and t-PA promoter were time dependent: RAR-α/RXR-α bound DR5 motif before and up to 12 hrs of RA exposure, and RAR-β/RXR-α bound DR5 response element after 12 hrs of RA treatment. Finally, experiments using shRNA and RAR-β-specific antagonist revealed that reducing RAR-β induction decreased t-PA induction. Altogether, our results established that the RA-mediated regulation of t-PA in human foetal membranes occurred through two steps, with a major role played by RAR-β.

Retinoids and activation of PKC induce tissue-type plasminogen activator expression and storage in human astrocytes

BACKGROUND

Emerging data demonstrate important roles for tissue-type plasminogen activator (t-PA) in the central nervous system (CNS). In contrast to endothelial cells, little is known about the regulation of t-PA gene expression and secretion in astrocytes.

OBJECTIVES

The aims of the present study were to investigate whether t-PA gene expression is regulated by retinoids and the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) in human astrocytes, and to study whether t-PA is stored and subject to regulated release from these cells, as with endothelial cells.

METHODS

Native human astrocytes were treated with RA and/or PMA. mRNA was quantified by real-time RT-PCR and protein secretion determined by ELISA. Intracellular t-PA immunoreactivity in astrocytes was examined by immunocyto- and histochemistry.

RESULTS

RA and/or PMA induced a time-dependent increase in t-PA mRNA and protein levels in astrocytes, reaching 10-fold after combined treatment. This was associated with increased amounts of t-PA storage in intracellular granular structures. Both forskolin and histamine induced regulated release of t-PA. The presence of t-PA in reactive astrocytes was confirmed in human brain tissue.

CONCLUSIONS

These data show that RA and PKC activation induce a strong up-regulation of t-PA expression in astrocytes, and increased intracellular storage pools. Moreover, a regulated release of t-PA can be induced from these cells. This raises the possibility that astrocytes contribute to the regulation of extracellular t-PA levels in the CNS.

Quercetin induced tissue-type plasminogen activator expression is mediated through Sp1 and p38 mitogen-activated protein kinase in human endothelial cells

BACKGROUND

Wine polyphenol quercetin upregulates tissue-type plasminogen activator (t-PA) transcription in cultured human umbilical cord vein endothelial cells (HUVECs). However, the regulatory elements and signaling pathways involved in this regulation are unknown.

OBJECTIVES

We aimed to localize quercetin-responsive t-PA promoter elements, identify the proteins that bind these elements, and decipher signaling pathways involved in the regulation of t-PA.

METHODS

To localize quercetin-responsive elements, HUVECs were transiently transfected with various t-PA promoter-reporter constructs. Element functionality was evaluated by mutational analysis. Nuclear protein-t-PA element interactions were evaluated by electrophoretic mobility shift assays (EMSAs) and chromatin immunoprecipitation (ChIP) analysis. Mitogen-activated protein kinase (MAPK) inhibitors were used to determine the signaling pathways involved in t-PA regulation. MAPK inhibition effects were evaluated by real-time PCR, immunoblotting analysis, and transfections. Coimmunoprecipitation was used to evaluate MAPK and transcription factor interaction.

RESULTS

Deletion of the t-PA promoter region - 288 to - 250 resulted in loss of quercetin responsiveness. This region contains putative Sp1-binding elements, which we termed Sp1a and Sp1b. Sp1b mutation abolished the quercetin-inducible response, whereas Sp1a mutation had no effect. EMSA and ChIP analysis demonstrated quercetin-enhanced Sp1 binding to Sp1b. Inhibition of p38 MAPK abrogated basal and quercetin-induced t-PA expression and promoter activity, as well as quercetin-induced Sp1 binding to Sp1b. Quercetin enhanced p38 MAPK and Sp1 physical association, which was similarly diminished by p38 MAPK inhibition.

CONCLUSIONS

We showed, for the first time, the presence of a functional Sp1-binding element in the t-PA promoter controlling quercetin induction via the p38 MAPK pathway. Understanding these mechanisms may provide new insights into polyphenol cardioprotective effects.

Differences in the expression of cathepsin B in B16 melanoma metastatic variants depend on transcription factor Sp1

Cathepsin B contributes to the invasiveness of B16 melanoma cells in mice, with the highly metastatic B16a melanoma producing six- to eightfold more cathepsin B mRNA and protein than the less metastatic B16F1 variant. The proximal promoter region of the cathepsin B (Ctsb) gene (-149 to +94) was previously found to be capable of reproducing this pattern of differential gene activation in B16 melanoma variants. The binding of B16 melanoma nuclear proteins to this promoter region has now been mapped to three GC-boxes (Sp1 transcription factor binding sites) and a potential X-box [tax response element (TRE)/c-AMP responsive element (CRE) site]. Mutation of the GC-boxes at -55 and -37 independently decreased the expression of a luciferase reporter gene in B16a cells to the level observed in B16F1 cells. Promoter activity was also attenuated by mutations within the GC-rich segment between +6 and +16, but not by mutation of the putative X-box. Both Sp1 and Sp3 bound the GC-boxes in the Ctsb promoter, and western blotting showed the level of Sp1 to be greater in B16a compared to B16F1 cells. B16F1 cells that were made to express Sp1 at levels observed in B16a cells produced corresponding increased amounts of endogenous cathepsin B mRNA and enzyme activity. Thus, the difference in cathepsin B expression between high and low metastatic B16 melanoma variants is largely due to different levels of Sp1.

Common Genetic Variation in Five Thrombosis Genes and Relations to Plasma Hemostatic Protein Level and Cardiovascular Disease Risk

OBJECTIVE

We undertook a linkage disequilibrium (LD)-based genetic approach to investigate the hypothesis that common sequence variants in 5 thrombosis genes influence plasma hemostatic protein levels or risk of cardiovascular disease (CVD).

METHODS AND RESULTS

In a reference panel, we characterized LD structure at the fibrinogen gene cluster (fibrinogen-beta[FGB], FGA, and FGG), factor VII (F7), and tissue plasminogen activator (PLAT) loci. Forty-one tag single nucleotide polymorphisms (SNPs) were genotyped in 1811 unrelated Framingham Heart Study participants. There were significant associations of 9 FGB SNPs with fibrinogen level (minimum P=0.002) and of 7 F7 SNPs and factor VII level (minimum P<0.0001). SNPs at the PLAT locus were not associated with PLAT level. In stepwise analysis, a single FGB variant explained 1% of the residual variance in fibrinogen level, and 2 F7 SNPs together explained 10% of the residual variance in factor VII level. Two PLAT haplotypes were associated with CVD (multivariable-adjusted global P=0.0004).

CONCLUSIONS

A comprehensive survey of common sequence variation demonstrates that cis-regulatory SNPs explain a modest proportion of the residual variance in circulating fibrinogen and factor VII level and PLAT haplotypes increase the risk of CVD. Additional studies are warranted to confirm the association of PLAT sequence variation and risk of CVD.

GA-binding protein and p300 are essential components of a retinoic acid-induced enhanceosome in myeloid cells

Expression of CD18, the beta chain of the leukocyte integrins, is transcriptionally regulated by retinoic acid (RA) in myeloid cells. Full RA responsiveness of the CD18 gene requires its proximal promoter, which lacks a retinoic acid response element (RARE). Rather, RA responsiveness of the CD18 proximal promoter requires ets sites that are bound by GA-binding protein (GABP). The transcriptional coactivator, p300, further increases CD18 RA responsiveness. We demonstrate that GABPalpha, the ets DNA-binding subunit of GABP, physically interacts with p300 in myeloid cells. This interaction involves the GABPalpha pointed domain (PNT) and identifies p300 as the first known interaction partner of GABPalpha PNT. Expression of the PNT domain, alone, disrupts the GABPalpha-p300 interaction and decreases the RA responsiveness of the CD18 proximal promoter. Chromatin immunoprecipitation and chromosome conformation capture demonstrate that, in the presence of RA, GABPalpha and p300 at the proximal promoter recruit retinoic acid receptor/retinoid X receptor from a distal RARE to form an enhanceosome. A dominant negative p300 construct disrupts enhanceosome formation and reduces the RA responsiveness of CD18. Thus, proteins on the CD18 proximal promoter recruit the distal RARE in the presence of RA. This is the first description of an RA-induced enhanceosome and demonstrates that GABP and p300 are essential components of CD18 RA responsiveness in myeloid cells.

The promoter of brain-specific angiogenesis inhibitor 1-associated protein 4 drives developmentally targeted transgene expression mainly in adult cerebral cortex and hippocampus

Restricting transgene expression to specific cell types and maintaining long-term expression are major goals for gene therapy. Previously, we cloned brain-specific angiogenesis inhibitor 1-associated protein 4 (BAI1-AP4), a novel brain-specific protein that interacts with BAI1, and found that it was developmentally upregulated in the adult brain. In this report, we isolated 5 kb of the 5' upstream sequence of the mouse BAI1-AP4 gene and analyzed its promoter activity. Functional analyses demonstrated that an Sp1 site was the enhancer, and the region containing the transcription initiation site and an AP2-binding site was the basal promoter. We examined the ability of the BAI1-AP4 promoter to drive adult brain-specific expression by using it to drive lacZ expression in transgenic (TG) mice. Northern blot analyses showed a unique pattern of beta-galactosidase expression in TG brain, peaking at 1 month after birth, like endogenous BAI1-AP4. Histological analyses demonstrated the same localization and developmental expression of beta-galactosidase and BAI1-AP4 in most neurons of the cerebral cortex and hippocampus. Our data indicate that TG mice carrying the BAI1-AP4 promoter could be a valuable model system for region-specific brain diseases.

Stimulation of vascular endothelial growth factor gene transcription by all trans retinoic acid through Sp1 and Sp3 sites in human bronchioloalveolar carcinoma cells

In this study, we examined the effects of all trans-retinoic acid (at-RA) on the vascular endothelial growth factor (VEGF) expression in human bronchioloalveolar carcinoma NCI-H322 cells to evaluate the potential of at-RA to affect tumor progression. Northern blot and enzyme-linked immunosorbent assay analyses indicate that VEGF production is significantly increased by 1 microM of at-RA. A series of 5'-deletion and site-directed mutation analyses indicated that G+C-rich sequence located at -81 and -52 was required for at-RA- and retinoic acid receptor alpha-mediated induction of VEGF promoter. Electrophoretic mobility shift and supershift assays showed that major constituents of nuclear factors binding to G+C-rich sequences are Sp1 and Sp3. Pretreatment with cycloheximide, a protein synthesis inhibitor, prevented the at-RA-mediated induction of VEGF mRNA expression. Likewise, at-RA-mediated VEGF expression was completely blocked in the presence of genistein, an inhibitor for tyrosine kinases. These results suggest that an increase in transcription of the VEGF promoter by at-RA is mediated through Sp1 site, and both new protein synthesis and tyrosine kinase activation are necessary for this induction. Because VEGF can promote neovascularization in cancer cells, an induction of VEGF by at-RA may preclude the therapeutic application of at-RA to cancer patients.

Sodium butyrate induces transcription from the G alpha(i2) gene promoter through multiple Sp1 sites in the promoter and by activating the MEK-ERK signal transduction pathway

Sodium butyrate, an erythroid differentiation inducer and a histone deacetylase inhibitor, increases G alpha(i2) levels in differentiating K562 cells. Here we show that sodium butyrate induces G alpha(i2) gene transcription via sequences at -50/-36 and -92/-85 in the G alpha(i2) gene promoter. Both sequences contain core sequence motif for Sp1 binding; electrophoretic mobility shift as well as supershift assays confirmed binding to Sp1. Transcription from the G alpha(i2) gene promoter was also activated by two other histone deacetylase inhibitors, trichostatin A and Helminthsporium carbonium toxin (HC toxin), which also induce erythroblastic differentiation in K562 cells. However, hydroxyurea, a potent erythroid differentiation inducer in these cells, did not activate transcription from this gene promoter, indicating that promoter activation is inducer-specific. Mutations within the Sp1 sites at -50/-36 and -92/-85 in the G alpha(i2) gene promoter substantially decreased transcriptional activation by sodium butyrate, trichostatin A, or HC toxin. Transfection with constitutively activated ERKs indicated that this promoter can be activated through the MEK-ERK signal transduction pathway. Inhibition of the MEK-ERK pathway with U0126 or reduction in the expression of endogenous ERK with an antisense oligonucleotide to ERK significantly inhibited sodium butyrate- and HC toxin-induced transcription but had no effect on trichostatin A-induced transcription. Inhibition of the JNK and p38 MAPKs, using selective inhibitors, had no effect on sodium butyrate-induced transcription. In cells in which sodium butyrate induction of promoter activation had been inhibited by various concentrations of U0126, constitutively activated ERK2 reversed this inhibition. These results show that the MEK-ERK signal transduction pathway is important in butyrate signaling, which eventually converges in the cell nucleus.