Role of the liver-enriched transcription factor hepatocyte nuclear factor 1 in transcriptional regulation of the factor V111 gene

Heterogeneity and reciprocity of FVIII and VWF expression, and the response to shear stress in cultured human endothelial cells

BACKGROUND

Substantial phenotypic heterogeneity exists in endothelial cells and while much of this heterogeneity results from local microenvironments, epigenetic modifications also contribute.

METHODS

Cultured human umbilical vein endothelial cells, human pulmonary microvascular endothelial cells, human hepatic sinusoidal endothelial cells, human lymphatic endothelial cells (hLECs), and two different isolations of endothelial colony forming cells (ECFCs) were assessed for levels of factor VIII (FVIII) and von Willebrand factor (VWF) RNA and protein. The intracellular location and co-localization of both proteins was evaluated with immunofluorescence microscopy and stimulated release toof FVIII and VWF from Weibel-Palade bodies (WPBs) was evaluated. Changes in expression of FVIII and VWF RNA after hLECs and ECFCs were exposed to 2 or 15 dynes/cm2 of laminar shear stress were also assessed.

RESULTS

We observed considerable heterogeneity in FVIII and VWF expression among the endothelial cells. With the exception of hLECs, FVIII RNA and protein were barely detectable in any of the endothelial cells and a reciprocal relationship between levels of FVIII and VWF appears to exist. When FVIII and VWF are co-expressed, they do not consistently co-localize in the cytoplasm. However, in hLECs where significantly higher levels of FVIII are expressed, FVIII and VWF co-localize in WPBs and are released together when stimulated. Expression of both FVIII and VWF is markedly reduced when hLECs are exposed to higher or lower levels of laminar shear stress, while in ECFCs there is a minimal response for both proteins.

CONCLUSIONS

Variable levels of FVIII and VWF RNA and protein exist in a subset of cultured human endothelial cells. Higher levels of FVIII present in hLECs co-localize with VWF and are released together when exposed to a secretagogue.

Factor VIII as a potential player in cancer pathophysiology

BACKGROUND

Trousseau sign was the first demonstration of a close relationship between cancer and thrombosis. Currently, venous thromboembolism (VTE) is five to six times more likely to occur in cancer patients, whereas there is a greater risk of cancer diagnoses following thromboses. In considering novel players, factor VIII (FVIII), an essential coagulation cofactor with emerging extracoagulative functions, has been identified as an independent VTE risk factor in cancer; however, the basis of this increase is unknown.

OBJECTIVE

To investigate the possible direct expression and secretion of FVIII by cancer cells.

METHODS

Bladder cancer, with a high VTE risk, and normal bladder tissue and epithelium, were used to investigate FVIII. Factor VIII protein and secretion were examined in bladder cancer cell lines. Expanding to other cancers, the Cancer Cell line Encyclopedia database was used to analyze FVIII, tissue factor, FV, FVII, FIX, FX, and von Willebrand factor (VWF) mRNA in 811 cell lines subdivided according to origin. Factor VIII protein synthesis, secretion, and bioactivity were investigated in a profile of cancer cell lines of differing origins.

RESULTS AND CONCLUSIONS

Although expressed in the normal bladder epithelium, FVIII mRNA and protein were higher in matched bladder neoplasms, with synthesis and secretion of bioactive FVIII evident in bladder cancer cells. This can be extended to other cancer cell lines, with a pattern reflecting the tumor origin, and that is independent of VWF and other relevant players in the coagulation cascade. Here, evidence is provided of a possible independent role for FVIII in cancer-related pathophysiology.

Deciphering the Ets-1/2-mediated transcriptional regulation of F8 gene identifies a minimal F8 promoter for hemophilia A gene therapy

Amajor challenge in the development of a gene therapy for hemophilia A is the selection of cell type- or tissue-specific promoters to ensure factor VIII (FVIII) expression without eliciting an immune response. As liver sinusoidal endothelial cells are the major FVIII source, understanding the transcriptional F8 regulation in these cells would help to optimize the minimal F8 promoter (pF8) to efficiently drive FVIII expression. In silico analyses predicted several binding sites (BS) for the E26 transformation-specific (Ets) transcription factors Ets-1 and Ets-2 in the pF8. Reporter assays demonstrated a significant up-regulation of pF8 activity by Ets-1 or Ets- 1/Est-2 combination, while Ets-2 alone was ineffective. Moreover, Ets-1/Ets- 2-DNA binding domain mutants (DBD) abolished promoter activation only when the Ets-1 DBD was removed, suggesting that pF8 up-regulation may occur through Ets-1/Ets-2 interaction with Ets-1 bound to DNA. pF8 carrying Ets-BS deletions unveiled two Ets-BS essential for pF8 activity and response to Ets overexpression. Lentivirus-mediated delivery of green fluorescent protein (GFP) or FVIII cassettes driven by the shortened promoters, led to GFP expression mainly in endothelial cells in the liver and to longterm FVIII activity without inhibitor formation in HA mice. These data strongly support the potential application of these promoters in hemophilia A gene therapy.

FVIII expression by its native promoter sustains long-term correction avoiding immune response in hemophilic mice

Here we describe a successful gene therapy approach for hemophilia A (HA), using the natural F8 promoter (pF8) to direct gene replacement to factor VIII (FVIII)-secreting cells. The promoter sequence and the regulatory elements involved in the modulation of F8 expression are still poorly characterized and biased by the historical assumption that FVIII expression is mainly in hepatocytes. Bioinformatic analyses have highlighted an underestimated complexity in gene expression at this locus, suggesting an activation of pF8 in more cell types than those previously expected. C57Bl/6 mice injected with a lentiviral vector expressing green fluorescent protein (GFP) under the pF8 (lentiviral vector [LV].pF8.GFP) confirm the predominant GFP expression in liver sinusoidal endothelial cells, with a few positive cells detectable also in hematopoietic organs. Therapeutic gene delivery (LV.pF8.FVIII) in hemophilic C57/Bl6 and 129-Bl6 mice successfully corrected the bleeding phenotype, rescuing up to 25% FVIII activity, using a codon-optimized FVIII, with sustained activity for the duration of the experiment (1 year) without inhibitor formation. Of note, LV.pF8.FVIII delivery in FVIII-immunized HA mice resulted in the complete reversion of the inhibitor titer with the recovery of therapeutic FVIII activity. Depletion of regulatory T cells (Tregs) in LV-treated mice allowed the formation of anti-FVIII antibodies, indicating a role for Tregs in immune tolerance induction. The significant blood loss reduction observed in all LV.pF8.FVIII-treated mice 1 year after injection confirmed the achievement of a long-term phenotypic correction. Altogether, our results highlight the potency of pF8-driven transgene expression to correct the bleeding phenotype in HA, as well as potentially in other diseases in which an endothelial-specific expression is required.

Production of coagulation factor VII in human cell lines Sk-Hep-1 and HKB-11

Recombinant factor VII (rFVII) is the main therapeutic choice for hemophilia patients who have developed inhibitory antibodies against conventional treatments (FVIII and FIX). Because of the post-translational modifications, rFVII needs to be produced in mammalian cell lines. In this study, for the first time, we have shown efficient rFVII production in HepG2, Sk-Hep-1, and HKB-11 cell lines. Experiments in static conditions for a period of 96 h showed that HepG2-FVII produced the highest amounts of rhFVII, with an average of 1843 ng/mL. Sk-hep-1-FVII cells reached a maximum protein production of 1432 ng/mL and HKB-11-FVII cells reached 1468 ng/mL. Sk-Hep-1-rFVII and HKB-11-rFVII were selected for the first step of scale-up. Over 10 days of spinner flask culture, HKB-11 and SK-Hep-1 cells showed a cumulative production of rFVII of 152 μg and 202.6 μg in 50 mL, respectively. Thus, these human cell lines can be used for an efficient production of recombinant FVII. With more investment in basic research, human cell lines can be optimized for the commercial production of different bio therapeutic proteins.

Forced expression of Nanog in human bone marrow-derived endothelial cells activates other six pluripotent genes

Human endothelial cells (ECs) have the ability to make up the lining of blood vessels. These cells are also capable of neovascularization and revascularization and have been applied in various clinical situations. With the aim of understanding the effect of NANOG superexpression on ECs, we transduced the Nanog gene into the ECs. Nanog is highly expressed in embryonic stem cells (ESCs) and is essential for pluripotency and self-renewal. However, Nanog can also be expressed in somatic stem cells, and this gene is related to great expansion capacity in vitro. We found that ECs expressing Nanog showed expression of other stemness genes, such as Sox2, FoxD3, Oct4, Klf4, c-myc, and β-catenin, that are not normally expressed or are expressed at very low levels in ECs. Nanog is one of the stemness genes that can activate other stemness genes, and the upregulation of the Nanog gene seems to be critical for reprogramming cells. In this study, the introduction of Nanog was sufficient to alter the expression of key genes of the pluripotent pathway. The functional importance of Nanog for altering the cell expression profile and morphology was clearly demonstrated by our results.

Pluripotent reprogramming of fibroblasts by lentiviral mediated insertion of SOX2, C-MYC, and TCL-1A

Reprogramming of somatic cells to pluripotency promises to boost cellular therapy. Most instances of direct reprogramming have been achieved by forced expression of defined exogenous factors using multiple viral vectors. The most used 4 transcription factors, octamer-binding transcription factor 4 (OCT4), (sex determining region Y)-box 2 (SOX2), Kruppel-like factor 4 (KLF4), and v-myc myelocytomatosis viral oncogene homolog (C-MYC), can induce pluripotency in mouse and human fibroblasts. Here, we report that forced expression of a new combination of transcription factors (T-cell leukemia/lymphoma protein 1A [TCL-1A], C-MYC, and SOX2) is sufficient to promote the reprogramming of human fibroblasts into pluripotent cells. These 3-factor pluripotent cells are similar to human embryonic stem cells in morphology, in the ability to differentiate into cells of the 3 embryonic layers, and at the level of global gene expression. Induced pluripotent human cells generated by a combination of other factors will be of great help for the understanding of reprogramming pathways. This, in turn, will allow us to better control cell-fate and apply this knowledge to cell therapy.

Endothelial cell processing and alternatively spliced transcripts of factor VIII: potential implications for coagulation cascades and pulmonary hypertension

Background

Coagulation factor VIII (FVIII) deficiency leads to haemophilia A. Conversely, elevated plasma levels are a strong predictor of recurrent venous thromboemboli and pulmonary hypertension phenotypes in which in situ thromboses are implicated. Extrahepatic sources of plasma FVIII are implicated, but have remained elusive.

Methodology/Principal Findings

Immunohistochemistry of normal human lung tissue, and confocal microscopy, flow cytometry, and ELISA quantification of conditioned media from normal primary endothelial cells were used to examine endothelial expression of FVIII and coexpression with von Willebrand Factor (vWF), which protects secreted FVIII heavy chain from rapid proteloysis. FVIII transcripts predicted from database mining were identified by rt-PCR and sequencing. FVIII mAb-reactive material was demonstrated in CD31+ endothelial cells in normal human lung tissue, and in primary pulmonary artery, pulmonary microvascular, and dermal microvascular endothelial cells. In pulmonary endothelial cells, this protein occasionally colocalized with vWF, centered on Weibel Palade bodies. Pulmonary artery and pulmonary microvascular endothelial cells secreted low levels of FVIII and vWF to conditioned media, and demonstrated cell surface expression of FVIII and vWF Ab–reacting proteins compared to an isotype control. Four endothelial splice isoforms were identified. Two utilize transcription start sites in alternate 5′ exons within the int22h-1 repeat responsible for intron 22 inversions in 40% of severe haemophiliacs. A reciprocal relationship between the presence of short isoforms and full-length FVIII transcript suggested potential splice-switching mechanisms.

Conclusions/Significance

The pulmonary endothelium is confirmed as a site of FVIII secretion, with evidence of synthesis, cell surface expression, and coexpression with vWF. There is complex alternate transcription initiation from the FVIII gene. These findings provide a framework for future research on the regulation and perturbation of FVIII synthesis, and of potential relevance to haemophilia, thromboses, and pulmonary hypertensive states.

Recombinant expression of coagulation factor VIII in hepatic and non-hepatic cell lines stably transduced with third generation lentiviral vectors comprising the minimal factor VIII promoter

BACKGROUND

Lentiviral vectors have the capacity to transduce stably non-dividing, differentiated and undifferentiated cells of various tissues, including liver. To obtain high-level expression of transgenes, vectors often rely on viral promoters. However, recent data suggest that the supraphysiologic expression from ubiquitous viral promoters may not be beneficial and harbor the risk of oncogene activation. Therefore this study explored the lentiviral-mediated expression of human coagulation factor VIII (FVIII) driven by the physiologic FVIII gene promoter (FVIII-p), the liver-specific human alpha-1-antitrypsin gene promoter (hAAT-p), the ubiquitous but non-viral EF1alpha promoter (EF1alpha-p) and the viral CMV promoter.

METHODS

Hepatic and non-hepatic cell lines were stably transduced with lentiviral vectors encoding FVIIIdelB and EGFP. To compare the different promoters, lentiviral vectors were cloned to drive FVIII expression from FVIII-p, EF1alpha-p, hAAT-p and CMV-p.

RESULTS

As expected, the strong viral CMV-p and the ubiquitous EF1alpha-p resulted in the highest FVIII expression in all cell lines tested (CMV-p 1.85 IU/mL/10(6) cells for 293T, 3.15 for HepG2, 5.03 for SK-Hep, 0.91 for Hepa1-6; EF1-alpha promoter 0.30 IU/mL/10(6) cells for 293T, 0.04 for HepG2, 2.75 for SK-Hep, 0.46 for Hepa1-6). While the hAAT-p resulted in low FVIII levels (0.10 IU/mL/10(6)cells in HepG2 and 0.04 in Hepa1-6), the FVIII promoter gave reasonable expression levels in hepatic cells (0.47 IU/mL/10(6)cells in Hepa1-6 and 0.44 in SK-Hep).

DISCUSSION

These results indicate the potential usefulness of the FVIII-p for hemophilia A gene therapy.

The chimeric cytokine Hyper-IL-6 enhances the efficiency of lentiviral gene transfer in hepatocytes both in vitro and in vivo

Lentiviral vectors have been used for gene transfer into the liver but their ability to efficiently transduce quiescent hepatocytes remains controversial. Lentivirus-mediated gene transfer is more efficient in cycling cells. We determine the effect of H-IL6 in the lentiviral transduction. The lentiviral vector was used to transduce HepG2 cells and mice liver cells, previously treated with H-IL6. The highest transduction level was observed in HepG2 cells treated with 30 ng/mL H-IL6 and in the mice that received 4 microg H-IL6. Our results suggest that H-IL6 is an inducer of lentiviral gene transfer into the liver cells without any toxicity.

CCAAT/enhancer-binding protein-beta participates in insulin-responsive expression of the factor VII gene

Expression of the human coagulation factor VII (FVII) gene by hepatoma cells was modulated in concert with levels of glucose and insulin in the culture medium. In low glucose medium without insulin, amounts of both FVII mRNA and secreted FVII protein were coordinately increased; in the presence of glucose with insulin, both were decreased. Analysis of the FVII promoter showed that these effects could be reproduced in a reporter-gene system, and a small promoter element immediately upstream of the translation start site of the gene, which mediated these effects, was identified. Mutation of this element largely abrogated the glucose/insulin-responsive change in expression of the reporter gene. Several members of the CCAAT/enhancer-binding protein family were found to be capable of binding the identified sequence element but not the mutated element. The expression of a FVII minigene directed by a segment of the native FVII promoter responded to co-expressed activating and inhibiting forms of CCAAT/enhancer-binding protein beta.

A sequence variation scan of the coagulation factor VIII (FVIII) structural gene and associations with plasma FVIII activity levels

Plasma factor VIII coagulant activity (FVIII:C) level is a highly heritable quantitative trait that is strongly correlated with thrombosis risk. Polymorphisms within only 1 gene, the ABO blood-group locus, have been unequivocally demonstrated to contribute to the broad population variability observed for this trait. Because less than 2.5% of the structural FVIII gene (F8) has been examined previously, we resequenced all known functional regions in 222 potentially distinct alleles from 137 unrelated nonhemophilic individuals representing 7 racial groups. Eighteen of the 47 variants identified, including 17 single-nucleotide polymorphisms (SNPs), were previously unknown. As the degree of linkage disequilibrium across F8 was weak overall, we used measured-genotype association analysis to evaluate the influence of each polymorphism on the FVIII:C levels in 398 subjects from 21 pedigrees known as the Genetic Analysis of Idiopathic Thrombophilia project (GAIT). Our results suggested that 92714C>G, a nonsynonymous SNP encoding the B-domain substitution D1241E, was significantly associated with FVIII:C level. After accounting for important covariates, including age and ABO genotype, the association persisted with each C-allele additively increasing the FVIII:C level by 14.3 IU dL(-1) (P = .016). Nevertheless, because the alleles of 56010G>A, a SNP within the 3' splice junction of intron 7, are strongly associated with 92714C>G in GAIT, additional studies are required to determine whether D1241E is itself a functional variant.

Spectrum of molecular defects and mutation detection rate in patients with mild and moderate hemophilia A

The amount of residual F8 (FVIII:C) determines the clinical severity of hemophilia A. Recently, we showed that the mutation detection rate in severely affected male patients (FVIII:C<1% of normal) is virtually 100% when testing for the common intron 22-/intron 1- inversions and big deletions, followed by genomic sequencing of the F8 gene. Here we report on the spectrum of mutations and their distribution throughout the F8 gene sequence in 135 patients with moderate (n=23) or mild (n=112) hemophilia A. In contrast to the severe form of the disorder, analysis on the genomic level failed to detect the molecular defect in approximately 4% of the moderately and in approximately 12% of the mildly affected patients. A total of 36 of the mutations identified in this study are novel. The vast majority of the detected changes were missense. The newly detected amino acid substitutions were scored for potential distant or local conformational changes and influence on molecular stability for every single F8 domain with available structures, using homology modeling. Two molecular changes in the promoter region of the factor VIII gene (c.-112G>A and -219C>T), affecting the core segment (minimal promoter) were detected in two patients with mild hemophilia A. To our knowledge this is the first report on promoter mutations in the F8 gene.

New insight into the molecular basis of hemophilia A

Since publication of the sequence of the factor VIII gene (F8) in 1984, a large number of mutations that cause hemophilia A (HA) have been identified. With the technical advances associated with mutation screenings, it is now possible to identify a putative F8 sequence alteration in the great majority of HA patients. The mutation spectrum includes 2 inversion hot spots (intron 1 and intron 22 inversions) mediated by intrachromosomal recombination between 2 copies of long inverted repeats, one of which lies within the F8 gene whereas the other is extragenic. Point mutations are distributed over all of the exons, and deletions or insertions of different sizes and mutations affecting splice sites account for the rest of the known mutations. In a small number of cases, however, we are unable to find any disease-determining DNA changes in the coding regions of the F8 gene. This fact points to possibilities of unknown gene rearrangements that disrupt the F8 gene or mutations in other genes that play a role in the processing/secretion of the factor VIII protein. Moreover, the proof of an absence of F8 messenger RNA (mRNA) in one patient points to either a defect in the expression of F8 mRNA or its rapid degradation, which may represent a novel mechanism leading to HA.

Haemophilia A: from mutation analysis to new therapies

Haemophilia is caused by hundreds of different mutations and manifests itself in clinical conditions of varying severity. Despite being inherited in monogenic form, the clinical features of haemophilia can be influenced by other genetic factors, thereby confounding the boundary between monogenic and multifactorial disease. Unlike sufferers of other genetic diseases, haemophiliacs can be treated successfully by intravenous substitution of coagulation factors. Haemophilia is also the most attractive model for developing gene-therapy protocols, as the normal life expectancy of haemophiliacs allows the side effects of gene therapy, as well as its efficiency, to be monitored over long periods.

Cloning and characterization of the human beta2-glycoprotein I (beta2-GPI) gene promoter: roles of the atypical TATA box and hepatic nuclear factor-1alpha in regulating beta2-GPI promoter activity

Beta2-glycoprotein I (beta2-GPI) is a plasma glycoprotein primarily synthesized in the liver. The interindividual variability of beta2-GPI expression in subjects with various metabolic syndromes and disease states suggests that it may have clinical importance. However, the regulation of beta2-GPI gene expression has not been clarified. To gain more insight into the control of beta2-GPI gene expression, we cloned the 4.1-kb 5'-flanking region and characterized the proximal promoter of the beta2- GPI gene in this study. Cis -acting elements required for beta2-GPI promoter activity were identified with transient transfection assays in the hepatoma cell lines HepG2 and Huh7 and in non-hepatic HeLa cells. Serial deletion analyses of the beta2-GPI 5'-flanking sequence revealed that the region from -197 to +7 had strong promoter activity in hepatoma cells but not in HeLa cells. Truncation and site-directed mutagenesis of putative cis -elements within this region showing an atypical TATA box and a HNF-1 (hepatic nuclear factor-1) element were both essential for the beta2-GPI promoter activity. Subsequent gel mobility shift assays confirmed the interaction of HNF-1alpha with the HNF-1 site residing downstream of the TATA box. Co-transfection of beta2-GPI promoter-luciferase vector with HNF-1alpha expression vector in Huh7 and HNF-1-deficient HeLa cells demonstrated the transactivation effect of HNF-1alpha on beta2-GPI promoter activity. In addition, overexpression of HNF-1alpha enhanced the endogenous beta2-GPI expression. These results suggest that the atypical TATA box and HNF-1 cis-element are critical for beta2-GPI transcription and HNF-1alpha may play an important role in cell-specific regulation of beta2-GPI gene expression.

Identification of functional regulatory regions of the connexin32 gene promoter

Connexin32 (Cx32) is the predominant gap junction protein expressed in adult rat hepatocytes. This study investigated transcriptional regulation of the rat Cx32 gene in MH(1)C(1) rat hepatoma cells using transient expression assays in conjunction with promoter mutagenesis and 5' nested deletion analysis. Site-directed mutagenesis of the -736 and -187 hepatocyte nuclear factor-1 (HNF-1) sites, the -196 and -116 Sp1 sites, and the -729 and -329 Yin Yang 1 (YY1) sites all significantly reduced promoter activity. We have defined the contribution of each individual site to promoter activity in the intact cell. A novel upstream region of the Cx32 promoter (-1042 to -758) was cloned and shown to contain negative regulatory elements. The transcription factors HNF-1 and Sp1 have important functional roles in the transcriptional regulation of basal and cell-specific Cx32 expression. The multifunctional transcription factor YY1 is also implicated.

The canine factor VIII 3'-untranslated region and a concatemeric hepatocyte nuclear factor 1 regulatory element enhance factor VIII transgene expression in vivo

If gene therapy is to be an effective treatment modality for hemophilia A, therapeutic levels and tissue-restricted expression of factor VIII (FVIII) must be achieved through optimization of transgene expression. To this end, we incorporated three types of sequence elements into a canine B domain-deleted FVIII transgene cassette and individually evaluated their effect on FVIII transgene expression. Functional FVIII activity was initially assessed in vitro and hydrodynamic injection of the different transgene constructs into mice was subsequently used as a model to compare in vivo expression of the various modified transgenes. Our results demonstrate that in vitro transgene expression is, in these studies, not a good predictor of in vivo transgene performance. In vivo analysis of a hybrid tissue-restricted promoter element, consisting of a concatemer of five hepatocyte nuclear factor 1 (HNF-1) consensus-binding motifs juxtaposed to the human FVIII proximal promoter, indicates that it is as efficient at mediating expression of the FVIII protein as the cytomegalovirus promoter. Addition of the full-length canine FVIII 3'-UTR also enhances transgene expression of FVIII in vivo. Sequence analysis of the canine FVIII 3'-UTR and human FVIII 3'-UTR indicates that the former lacks instability sequences and may therefore be more effective in stabilizing FVIII mRNA. Subsequent inclusion of FVIII introns 16 and 17 into the natural locations of the transgene disrupted mRNA processing and abolished expression of the FVIII protein. Introduction of intron 17 proximal to the FVIII cDNA did not enhance in vivo expression of canine FVIII from the transgene.

A role for CCAAT/enhancer-binding protein in hepatic expression of thrombin-activable fibrinolysis inhibitor

Thrombin-activable fibrinolysis inhibitor (TAFI) is a procarboxypeptidase B-like zymogen that upon activation by thrombin, thrombin-thrombomodulin, or plasmin attenuates fibrin clot lysis by inhibiting positive feedback in the fibrinolytic cascade. The concentration of TAFI in plasma varies in the human population and thus may constitute a risk factor for thrombotic disorders. In addition, TAFI has been reported to be a positive acute phase reactant in mice. We have initiated molecular analysis of the human TAFI promoter to understand the mechanisms underlying regulation of TAFI gene expression. We identified a putative C/EBP-binding site between -53 and -40 of the promoter. Mutations in this site that abolish C/EBP binding decrease TAFI promoter activity in human hepatoma (HepG2) cells by approximately 80%. Gel mobility shift analyses indicated that C/EBP-beta present in HepG2 nuclear extracts and C/EBP-alpha and -beta present in adult rat liver nuclear extracts bind to the C/EBP site. C/EBP-alpha, -beta, and -delta isoforms are all capable of binding to the C/EBP site and activating the TAFI promoter. The identification of a functional C/EBP-binding site in the human TAFI promoter may have important implications for the regulation of expression of this gene during development and in response to inflammatory stimuli.

The human and mouse GATA-6 genes utilize two promoters and two initiation codons

GATA-6 has been implicated in the regulation of myocardial differentiation during cardiogenesis. To determine how its expression is controlled, we have characterized the human and mouse genes. We have mapped their transcriptional start sites and demonstrate that two alternative promoters and 5' noncoding exons are utilized. Both transcript isoforms are expressed in the same tissue-specific and developmental stage-specific pattern, and their ratio appears similar wherever examined. The more upstream noncoding exon showed a substantial degree of homology between the two mammalian species, suggesting a conserved regulatory function. Moreover, in transfection assays we show that elements within this exon act to promote its transcription. Positive regulatory elements that effect transcription from the more downstream exon were not apparent in this assay, revealing a regulatory distinction between the two promoters. We also demonstrate alternative initiator codon usage in both the human and mouse GATA-6 genes. Both isoforms of the protein are synthesized in vitro regardless of which 5' noncoding exon is present in the RNA, although the larger protein has greater transcriptional activation potential in transfection assays. Thus, GATA-6 function in the cell is controlled by a complex interplay of transcriptional and translational regulation.

Down-regulation of the rat hepatic sterol 27-hydroxylase gene by bile acids in transfected primary hepatocytes: possible role of hepatic nuclear factor 1alpha

In vitro and in vivo studies have shown that the sterol 27-hydroxylase (CYP27) gene is transcriptionally repressed by hydrophobic bile acids. The molecular mechanism(s) of repression of CYP27 by bile acids is unknown. To identify the bile acid responsive element (BARE) and transcription factor(s) that mediate the repression of CYP27 by bile acids, constructs of the CYP27 5'-flanking DNA were linked to either the CAT or luciferase reporter gene and transiently transfected into primary rat hepatocytes. Taurocholate (TCA), taurodeoxycholate (TDCA) and taurochenodeoxycholate (TCDCA) significantly reduced CAT activities of the -840/+23, -329/+23, and -195/+23 mCAT constructs. A -76/+23 construct showed no regulation by bile acids. When a DNA fragment (-110/-86) from this region was cloned in front of an SV 40 promoter it showed down-regulation by TDCA. 'Super'-electrophoretic mobility shift assays (EMSA) indicated that both HNF1alpha and C/EBP bind to the -110 to -86 bp DNA fragment. Recombinant rat HNF1alpha and C/EBPalpha competitively bound to this DNA fragment. 'Super'-EMSA showed that TDCA addition to hepatocytes in culture decreased HNF1alpha, but not C/EBP, binding to the -110/-86 bp DNA fragment. A four base pair substitution mutation (-103 to -99) in this sequence eliminated TCA and TDCA regulation of the (-840/+23) construct. The substitution mutation also eliminated (>95%) HNF1alpha, but not C/EBP, binding to this DNA fragment. We conclude that bile acids repress CYP27 transcription through a putative BARE located between -110 and -86 bp of the CYP27 promoter. The data suggest that bile acids repress CYP27 transcriptional activity by decreasing HNF1alpha binding to the CYP27 promoter.

Enhanced binding of HLF/DBP heterodimers represents one mechanism of PAR protein transactivation of the factor VIII and factor IX genes

The regulatory regions of the genes for coagulation Factors VIII and IX contain binding sites for both liver-enriched and ubiquitous transcriptional regulators. We investigated the role of the liver-enriched protein, hepatic leukemia factor (HLF), in mediating transcriptional regulation of the Factor VIII and IX genes. Using transient transfection assays in HepG2 hepatoma cells, we demonstrated the ability of HLF alone and in synergistic combination with the D-box binding protein (DBP), another proline and acidic-rich (PAR) protein family member, to transactivate these promoters. HLF is capable of binding to multiple sites in both the Factor VIII and Factor IX promoters. At least some of the synergistic activation of the Factor VIII promoter seen with HLF and DBP cotransfection can be attributed to increased binding of HLF-DBP heterodimers to two Factor VIII promoter sites. We have also demonstrated that an E2A-HLF chimera, derived from a t(17;19) translocation in pre-B acute lymphoblastic leukemia (ALL) cells, is capable of mediating expression from the Factor VIII and Factor IX promoters in both hepatoma cells and pre-B ALL cells. These observations indicate that the PAR family of transcription factors plays an important and complex role in regulating expression of the Factor VIII and Factor IX genes, involving the binding of both homodimeric and heterodimeric complexes of HLF and DBP to several sites in the promoters. Finally, these studies reaffirm the potential role of dimeric transcription factor complexes in mediating interactions with specific promoter elements, which, in the case of the Factor VIII promoter, results in dramatically enhanced binding of HLF-DBP heterodimers to two cis-acting sequences. These observations further our understanding of the role played by members of the PAR family of transcription factors in regulating expression of the Factor VIII and Factor IX genes.

Exon-I is involved in positive as well as negative regulation of human angiotensinogen gene expression

Angiotensinogen is the glycoprotein precursor of one of the most potent vasoactive hormones, angiotensin-II. Angiotensinogen gene is primarily expressed in the liver, and this gene locus is linked with human essential hypertension. We show here that a mutation in exon-I reduces the basal expression of the human angiotensinogen gene in liver cells. We also show that a nucleotide sequence in exon-I binds to liver-enriched transcription factor HNF-3 and a ubiquitous factor AP4. Our studies also show that transient transfection of an expression vector containing AP4 coding sequence downregulates the expression of reporter constructs containing human angiotensinogen gene promoter. By contrast, co-transfection of an expression vector containing HNF-3beta coding sequence increases the expression of these reporter constructs. The human angiotensinogen gene has a C/A polymorphism located at -20, and we have shown that estrogen receptor-alpha binds to this sequence when nucleoside A is present at this site. We show here that co-transfection of an expression vector containing AP4 coding sequence reduces estrogen-induced promoter activity of reporter constructs containing human angiotensinogen gene promoter (with nucleoside A at -20) attached to the CAT gene. These studies partly explain the molecular mechanisms involved in tissue-specific expression of the human angiotensinogen gene.

A survey of 178 NF-Y binding CCAAT boxes

The CCAAT box is one of the most common elements in eukaryotic promoters, found in the forward or reverse orientation. Among the various DNA binding proteins that interact with this sequence, only NF-Y (CBF, HAP2/3/4/5) has been shown to absolutely require all 5 nt. Analysis of a database with 178 bona fide NF-Y binding sites in 96 unrelated promoters confirms this need and points to specific additional flanking nucleotides (C, Pu, Pu on the 5'-side and C/G, A/G, G,A/C, G on the 3'-side) required for efficient binding. The frequency of CCAAT boxes appears to be relatively higher in TATA-less promoters, particularly in the reverse ATTGG orientation. In TATA-containing promoters the CCAAT box is preferentially located in the -80/-100 region (mean position -89) and is not found nearer to the Start site than -50. In TATA-less promoters it is usually closer to the +1 signal (at -66 on average) and is sometimes present in proximity to the Cap site. The consensus and location of NF-Y binding sites parallel almost perfectly a previous general statistical study on CCAAT boxes in 502 unrelated promoters. This is an indication that NF-Y is the major, if not the sole, CCAAT box recognizing protein and that it might serve different roles in TATA-containing and TATA-less promoters.

Characterization of the bovine prion protein gene: the expression requires interaction between the promoter and intron

We cloned the part of the bovine PrP gene which contains the 5'-flanking region, exon 1, exon 2 and intron 1 to analyze its promoter region. The 5' non-coding region of the bovine PrP gene consisted of three exons and two introns, and its organization was similar to that of the mouse, rat and sheep PrP genes. The 5'-flanking region of the bovine PrP gene from the transcription start site to nucleotide position -88 was (G + C)-rich (78%) and contained three potential binding sites for the transcription factor Sp1, but no CCAAT-box or TATA-box. This region showed high homology (89%) with that of the sheep PrP gene, but relatively low homology (approximately 46-62%) with the same region of the mouse, rat, hamster and human PrP genes. The position from -88 to -30 within the 5'-flanking region of the bovine PrP gene showed major promoter activity. However, this region was able to function properly only in collaboration with the region at +123 to +891 of intron 1 of the bovine PrP gene.