A Nuclear Factor Y (NFY) Site Positively Regulates the Human CD34 Stem Cell Gene

Reduction of Cell Proliferation by Acute C2H6O Exposure

Simple Summary

Alcoholic beverages and acetaldehyde formed during their metabolism are carcinogenic to humans. Alcohol drinking may affect bone marrow stem cell niche, suppressing physiological hematopoiesis and ultimately reducing the organism’s capacity to fight against cancer, infections, and to promote tissue regeneration. To elucidate in vivo the cellular mechanisms associated with alcohol intake toxicity, we used a mouse model in which proliferating cells produce the firefly’s light-emitting protein. In this animal, alcohol exposure transiently “turns off the light”, indicating a negative effect on cell proliferation in the bone marrow and spleen. Pharmacological treatment with substances interfering with ethanol metabolism, reducing acetaldehyde production, partially restores the physiological cell proliferation rate. Over 560 million people worldwide have increased susceptibility to acetaldehyde toxicity and 4% of cancer deaths are attributable to alcohol. Our model might provide a suitable tool to further investigate in vivo the effects of alcohol metabolism and aldehydes production on carcinogenesis.

Abstract

Endogenous acetaldehyde production from the metabolism of ingested alcohol exposes hematopoietic progenitor cells to increased genotoxic risk. To develop possible therapeutic strategies to prevent or reverse alcohol abuse effects, it would be critical to determine the temporal progression of acute ethanol toxicity on progenitor cell numbers and proliferative status. We followed the variation of the cell proliferation rate in bone marrow and spleen in response to acute ethanol intoxication in the MITO-Luc mouse, in which NF-Y-dependent cell proliferation can be assessed in vivo by non-invasive bioluminescent imaging. One week after ethanol administration, bioluminescent signals in bone marrow and spleen decreased below the level corresponding to physiological proliferation, and they progressively resumed to pre-treatment values in approximately 4 weeks. Boosting acetaldehyde catabolism by administration of an aldehyde dehydrogenase activity activator or administration of polyphenols with antioxidant activity partially restored bone marrow cells’ physiological proliferation. These results indicate that in this mouse model, bioluminescent alteration reflects the reduction of the physiological proliferation rate of bone marrow progenitor cells due to the toxic effect of aldehydes generated by alcohol oxidation. In summary, this study presents a novel view of the impact of acute alcohol intake on bone marrow cell proliferation in vivo.

In vivo assessment of a single adenine mutation in 5'UTR of Endothelin-1 gene in paediatric cases with severe pulmonary hypertension: an observational study

Objective

Endothelin-1 plays an important role in the pathogenesis of severe pulmonary hypertension. The + 139 ‘A’, adenine insertion variant in 5′UTR of edn1 gene has been reported to be associated with increased expression of Endothelin-1 in vitro. The aim of present study was to explore the association of this variant with the circulating levels of Endothelin-1 in vivo using archived DNA and plasma samples from 38 paediatric congenital heart disease (cyanotic and acyanotic) patients with severe pulmonary hypertension.

Results

The plasma Endothelin-1 levels were highly varied ranging from 1.63 to75.16 pg/ml. The + 139 ‘A’ insertion variant in 5′UTR of edn1 was seen in 8 out of 38 cases with only one acyanotic sample demonstrating homozygosity of inserted ‘A’ allele at + 139 site (4A/4A genotype). The plasma Endothelin-1 levels in children with homozygous variant 3A/3A genotype were comparable in cyanotic and acyanotic groups. Lone 4A/4A acyanotic sample had ET-1 levels similar to the median value of ET-1 associated with 3A/3A genotype and was absent in cyanotic group presumably due to deleterious higher ET-1 levels. The discussed observations, limited by the small sample size, are suggestive of homozygous adenine insertion variant posing a risk in cyanotic babies with Severe Pulmonary Hypertension.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05609-5.

CD34 cells in somatic, regenerative and cancer stem cells: Developmental biology, cell therapy, and omics big data perspective

The transmembrane phosphoglycoprotein protein CD34 has conventionally been regarded as a marker for hematopoietic progenitors. Its expression on these cells has been leveraged for cell therapy applications in various hematological disorders. More recently, the expression of CD34 has also been reported on cells of nonhematopoietic origin. The list includes somatic cells such as endothelial cells, fibrocytes and interstitial cells and regenerative stem cells such as corneal keratocytes, muscle satellite cells, and muscle-derived stem cells. Furthermore, its expression on some cancer stem cells (CSCs) has also been reported. Till date, the functional roles of this molecule have been implicated in a multitude of cellular processes including cell adhesion, signal transduction, and maintenance of progenitor phenotype. However, the complete understanding about this molecule including its developmental origins, its embryonic connection, and associated functions is far from complete. Here, we review our present understanding of the structure and putative functions of the CD34 molecule based upon our literature survey. We also probed various biological databases to retrieve data related to the expression and associated molecular functions of CD34. Such information, upon synthesis, is hence likely to provide the suitability of such cells for cell therapy. Moreover, we have also covered the existing cell therapy and speculated cell therapy applications of CD34⁺ cells isolated from various lineages. We have also attempted here to speculate the role(s) of CD34 on CSCs. Finally, we discuss number of large-scale proteomics and transcriptomics studies that have been performed using CD34⁺ cells.

Contextual Refinement of Regulatory Targets Reveals Effects on Breast Cancer Prognosis of the Regulome

Gene expression regulators, such as transcription factors (TFs) and microRNAs (miRNAs), have varying regulatory targets based on the tissue and physiological state (context) within which they are expressed. While the emergence of regulator-characterizing experiments has inferred the target genes of many regulators across many contexts, methods for transferring regulator target genes across contexts are lacking. Further, regulator target gene lists frequently are not curated or have permissive inclusion criteria, impairing their use. Here, we present a method called iterative Contextual Transcriptional Activity Inference of Regulators (icTAIR) to resolve these issues. icTAIR takes a regulator’s previously-identified target gene list and combines it with gene expression data from a context, quantifying that regulator’s activity for that context. It then calculates the correlation between each listed target gene’s expression and the quantitative score of regulatory activity, removes the uncorrelated genes from the list, and iterates the process until it derives a stable list of refined target genes. To validate and demonstrate icTAIR’s power, we use it to refine the MSigDB c3 database of TF, miRNA and unclassified motif target gene lists for breast cancer. We then use its output for survival analysis with clinicopathological multivariable adjustment in 7 independent breast cancer datasets covering 3,430 patients. We uncover many novel prognostic regulators that were obscured prior to refinement, in particular NFY, and offer a detailed look at the composition and relationships among the breast cancer prognostic regulome. We anticipate icTAIR will be of general use in contextually refining regulator target genes for discoveries across many contexts. The icTAIR algorithm can be downloaded from https://github.com/icTAIR.

Gene expression regulators, such as transcription factors and microRNAs, are critical actors in cellular physiology and pathophysiology and act by modulating the expression levels of sets of target genes. Given their significance, numerous experiments have sought to characterize the specific target genes of specific regulators, which in turn has led to regulator target gene list databases. Unfortunately, these lists are plagued by poor curation and validation. Further, all lists suffer from the fundamental issue that regulator targets vary across tissue type and physiological state, or “context”, making them poor for conducting downstream, context-specific analyses. To address this issue, here we present a method called icTAIR that contextually-refines regulator target gene lists. To demonstrate its value, we use icTAIR to take the largest-available database of regulator target gene lists, refine it for the breast cancer context, and use both the pre-refined and refined lists for downstream survival analyses in over 3,400 tumors. We find that icTAIR improves the statistical power of the analyses by multiple orders of magnitude. This in turn lets us map the relational network of breast cancer regulators and identify regulators with prognostic effects even after clinicopathological adjustment. We anticipate icTAIR will be broadly useful in regulator studies.

Nitric oxide has contrasting age-dependent effects on the functionality of murine hematopoietic stem cells

Background

The success of hematopoietic stem cell (HSC) transplantation is dependent on the quality of the donor HSCs. Some sources of HSCs display reduced engraftment efficiency either because of inadequate number (e.g., fetal liver and cord blood), or age-related dysfunction (e.g. in older individuals). Therefore, use of pharmacological compounds to improve functionality of HSCs is a forefront research area in hematology.

Methods

Lineage negative (Lin⁻) cells isolated from murine bone marrow or sort-purified Lin⁻Sca-1⁺c-Kit⁺CD34⁻ (LSK-CD34⁻) were treated with a nitric oxide donor, sodium nitroprusside (SNP). The cells were subjected to various phenotypic and functional assays.

Results

We found that SNP treatment of Lin⁻ cells leads to an increase in the numbers of LSK-CD34⁺ cells in them. Using sort-purified LSK CD34⁻ HSCs, we show that this is related to acquisition of CD34 expression by LSK-CD34⁻ cells, rather than proliferation of LSK-CD34⁺ cells. Most importantly, this upregulated expression of CD34 had age-dependent contrasting effects on HSC functionality. Increased CD34 expression significantly improved the engraftment of juvenile HSCs (6–8 weeks); in sharp contrast, it reduced the engraftment of adult HSCs (10–12 weeks). The molecular mechanism behind this phenomenon involved nitric oxide (NO)-mediated differential induction of various transcription factors involved in commitment with regard to self-renewal in adult and juvenile HSCs, respectively. Preliminary experiments performed on cord blood-derived and mobilized peripheral blood-derived cells revealed that NO exerts age-dependent contrasting effects on human HSCs as well.

Conclusions

This study demonstrates novel age-dependent contrasting effects of NO on HSC functionality and suggests that HSC age may be an important parameter in screening of various compounds for their use in manipulation of HSCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0433-x) contains supplementary material, which is available to authorized users.

CpG methylation at the USF-binding site mediates cell-specific transcription of human ascorbate transporter SVCT2 exon 1a

SVCT2 (sodium-vitamin C co-transporter 2) is the major transporter mediating vitamin C uptake in most organs. Its expression is driven by two promoters (CpG-poor exon 1a promoter and CpG-rich exon 1b promoter). In the present study, we mapped discrete elements within the proximal CpG-poor promoter responsible for exon 1a transcription. We identified two E boxes for USF (upstream stimulating factor) binding and one Y box for NF-Y (nuclear factor Y) binding. We show further that NF-Y and USF bind to the exon 1a promoter in a co-operative manner, amplifying the binding of each to the promoter, and is absolutely required for the full activity of the exon 1a promoter. The analysis of the CpG site located at the upstream USF-binding site in the promoter showed a strong correlation between expression and demethylation. It was also shown that exon 1a transcription was induced in cell culture treated with the demethylating agent decitabine. The specific methylation of this CpG site impaired both the binding of USF and the formation of the functional NF-Y-USF complex as well as promoter activity, suggesting its importance for cell-specific transcription. Thus CpG methylation at the upstream USF-binding site functions in establishing and maintaining cell-specific transcription from the CpG-poor SVCT2 exon 1a promoter.

NF-Y is necessary for hematopoietic stem cell proliferation and survival

HSC function depends on the tight control of proliferation and the balance between self-renewal and differentiation. Here, we report that the trimeric transcription factor NF-Y is critical for the survival of cycling, but not quiescent HSCs. With the use of a conditional knockout mouse model, we demonstrate that NF-Ya deletion creates an accumulation of HSCs in G(2)/M and prompts apoptosis, causing hematopoietic failure and death of the animal. These defects are accompanied by the dysregulation of multiple genes that influence cell cycle control (cyclin b1 and p21), apoptosis (Bcl-2), and self-renewal (HoxB4, Notch1, Bmi-1) and are independent of p53. Our results identify NF-Y as a pivotal upstream participant in a regulatory network necessary for the preservation of cycling HSCs.

RUNX1 regulates the CD34 gene in haematopoietic stem cells by mediating interactions with a distal regulatory element

The transcription factor RUNX1 is essential to establish the haematopoietic gene expression programme; however, the mechanism of how it activates transcription of haematopoietic stem cell (HSC) genes is still elusive. Here, we obtained novel insights into RUNX1 function by studying regulation of the human CD34 gene, which is expressed in HSCs. Using transgenic mice carrying human CD34 PAC constructs, we identified a novel downstream regulatory element (DRE), which is bound by RUNX1 and is necessary for human CD34 expression in long-term (LT)-HSCs. Conditional deletion of Runx1 in mice harbouring human CD34 promoter-DRE constructs abrogates human CD34 expression. We demonstrate by chromosome conformation capture assays in LT-HSCs that the DRE physically interacts with the human CD34 promoter. Targeted mutagenesis of RUNX binding sites leads to perturbation of this interaction and decreased human CD34 expression in LT-HSCs. Overall, our in vivo data provide novel evidence about the role of RUNX1 in mediating interactions between distal and proximal elements of the HSC gene CD34.

Cellular iron depletion and the mechanisms involved in the iron-dependent regulation of the growth arrest and DNA damage family of genes

Iron plays a crucial part in proliferation while iron deficiency results in G(1)/S arrest, DNA damage, and apoptosis. However, the precise role of iron in cell cycle control remains unclear. We showed that iron depletion using the iron chelators, desferrioxamine (DFO), or 2-hydroxy-1-napthylaldehyde isonicotinoyl hydrazone (311), increased the mRNA levels of the growth arrest and DNA damage 45α gene, GADD45α (Darnell, G. and Richardson, D. R. (1999) Blood 94, 781-792). In this study, we examined the effect of iron depletion on up-regulating GADD family members involved in growth control, including cell cycle arrest, apoptosis, and DNA repair, making them therapeutic targets for tumor suppression. We showed the GADD family members were up-regulated by cellular iron depletion. Further, up-regulation of GADD45α after iron deprivation was independent of hypoxia-inducible factor-1α (HIF-1α), octamer-1 (Oct-1), p53 and early growth response 1 (Egr1). We then analyzed the regulatory elements responsible for iron depletion-mediated regulation of GADD45α and identified the specific transcription factor/s involved. This region was within -117 bp and -81 bp relative to the start codon where the consensus sequences of three transcription factors are located: the CCAAT-binding factor/nuclear factor-Y (NF-Y), the stabilizing molecule v-MYB and the enhancer, CCAAT enhancer-binding protein (CEBPα). Mutation analysis, shRNA studies, Western blotting, and electrophoretic mobility shift assays led to the identification of NF-Y in the transcriptional up-regulation of GADD45α after iron depletion. Furthermore, like GADD45α, NF-YA was up-regulated after iron chelation and down-regulated by iron supplementation. These results are important for understanding the mechanisms of iron depletion-mediated cell cycle arrest, DNA damage repair, and apoptosis.

Rb and nucleolin antagonize in controlling human CD34 gene expression

Retinoblastoma protein (Rb) controls cell proliferation, differentiation, survival and gene expression and it has a central role in the signaling network that provides a cell cycle checkpoint in the G1 phase of the cell cycle. Studies in mice have shown that Rb regulates interactions between hematopoietic stem cells and their bone marrow microenvironment and it acts as a critical regulator of hematopoietic stem and progenitor cells under stress. In human hematopoiesis, the CD34 protein is expressed on a subset of progenitor cells capable of self-renewal, multilineage differentiation, and hematopoietic reconstitution, and CD34 has a role in the differentiation of hematopoietic cells. Here we find that, in CD34-positive hematopoietic cells, Rb controls the human CD34 promoter region by antagonizing the CD34 promoter factor nucleolin to provide a mechanism that links expression of endogenous CD34 to cell cycle progression. Our study suggests a direct involvement of Rb in the transcriptional program of human CD34-positive hematopoietic stem/progenitor cells, thus providing further insights into the molecular network relevant to the features of these cells.

Regulation of SOX3 gene expression is driven by multiple NF-Y binding elements

The presented results demonstrate that human SOX3 promoter possesses three CCAAT box control elements involved in the regulation of SOX3 gene expression in NT2/D1 cells. By mutational analysis we have shown that all three elements are of functional relevance for constitutive SOX3 expression. Electrophoretic mobility shift assays indicate that the active complexes at three sites involve the ubiquitously expressed CCAAT binding protein NF-Y. The involvement of NF-Y in the up-regulation of SOX3 expression in NT2/D1 cells was demonstrated in vivo by Northern and Western blot analyses. Furthermore, in co-transfection experiments we have shown that NF-Y mediates transcriptional activation of SOX3 promoter. Our data indicate that multiple CCAAT control elements are involved in the regulation of the SOX3 promoter, suggesting that NF-Y functions as a key regulator of SOX3 gene expression. Further, our results indicate that these elements can be recognized as modulators of retinoic acid induced activation of SOX3 expression.

Nucleolin regulates gene expression in CD34-positive hematopoietic cells

CD34 glycoprotein in human hematopoiesis is expressed on a subset of progenitor cells capable of self-renewal, multilineage differentiation, and hematopoietic reconstitution. Nucleolin is an abundant multifunctional phosphoprotein of growing eukaryotic cells, involved in regulation of gene transcription, chromatin remodeling, and RNA metabolism, whose transcripts are enriched in murine hematopoietic stem cells, as opposed to differentiated tissue. Here we show that, in human CD34-positive hematopoietic cells, nucleolin activates endogenous CD34 and Bcl-2 gene expression, and cell surface CD34 protein expression is thereby enhanced by nucleolin. Nucleolin-mediated activation of CD34 gene transcription results from direct sequence-specific interactions with the CD34 promoter region. Nucleolin expression prevails in CD34-positive cells mobilized into peripheral blood (PB), as opposed to CD34-negative peripheral blood mononuclear cells (PBMCs). Therefore, in intact CD34-positive mobilized PB cells, a recruitment of nucleolin to the CD34 promoter region takes place, accompanied by nucleosomal determinants of gene activity, which are absent from the CD34 promoter region in CD34-negative PBMCs. Our data show that nucleolin acts as a component of the gene regulation program of CD34-positive hematopoietic cells and provide further insights into processes by which human CD34-positive hematopoietic stem/progenitor cells are maintained.

Molecular Mechanisms for Transcriptional Regulation of Human High-Affinity IgE Receptor β-Chain Gene Induced by GM-CSF

The beta-chain of the high-affinity receptor for IgE (FcepsilonRI) plays an important role in regulating activation of FcepsilonRI-expressing cells such as mast cells in allergic reactions. We already reported that the transcription factor myeloid zinc finger (MZF) 1 which formed a high m.w. complex including four and a half LIM-only protein (FHL)3 in the nucleus repressed human beta-chain gene expression through an element in the fourth intron. We also found that GM-CSF induced expression of MZF-1 and nuclear translocation of FHL3. We screened a human cDNA library and identified NFY which was reported to bind histone deacetylases (HDACs) as a constituent of the complex. The C-subunit of NFY was demonstrated to form a ternary complex with MZF-1/FHL3 and interact with a beta-chain gene region including the element in the fourth intron. HDAC1 and HDAC2 were also shown to interact with the fourth intron region of the beta-chain gene. In a human mast cell line HMC-1 cultured with GM-CSF, both beta-chain expression and acetylation of histones interacting with the fourth intron region of the beta-chain gene were decreased. Collectively, these results indicated that HDACs, which were recruited to the beta-chain gene through the element in the fourth intron by MZF-1/FHL3/NFY, repressed beta-chain gene transcription by deacetylation of histones in the presence of GM-CSF. These mechanisms will be involved in not only the cell type-specific repression of beta-chain gene expression in differentiating hemopoietic cells but also the repression of beta-chain gene expression in the peripheral cells under specific circumstances.

Transcriptional regulation of the mouse PNRC2 promoter by the nuclear factor Y (NFY) and E2F1

PNRC2 (Proline-rich Nuclear Receptor Coactivator 2) was previously identified through its interaction with SF1 (steroidogenic factor 1) and has been demonstrated to be a novel coactivator for multiple nuclear receptors. In this study, PNRC2 was found to be widely expressed in mouse tissues with a strong expression in lung, spleen, ovary, thymus, and colon. Alignment of mouse genomic sequence with mouse cDNA sequence (BC006598), using mouse genome browser, defines that PNRC2 gene, located on chromosome 4, contains 3 exons: 166 bp-exon I, 205 bp-exon II, and 1526 bp-exon III. The translational start site is located in exon III. The first two exons are not translated. The 420 bp coding sequence in exon III encodes a 140 amino acid protein. To understand the molecular mechanisms that regulate the expression of PNRC2 gene, we have cloned and characterized the 5'-flanking region of the gene. Potential transcriptional start sites were determined by 5' RACE analysis. Functional analysis of the 5' flanking region of the mPNRC2 gene by deletion mutagenesis, transient transfection and luciferase assays revealed that the -67/+53 region is the minimal promoter of the mouse PNRC2 gene in HeLa cells. Within this sequence we identified two putative binding sites (inverted CCAAT box) for the transcription factor NFY (nuclear factor Y), a factor mediating cell type-specific and cell-cycle regulated expression of genes, and one binding site for E2F1, a founding member of the E2F family that displays the properties of both an oncogene and a tumor suppressor gene. Mutating each individual CCAAT site or changing the orientation of the CAATT box led to a 5-fold decrease in PNRC2 promoter activity in transient transfection experiments. Gel shift, supershift assay, and ChIP analysis demonstrated the specific binding of NFY and E2F1 proteins to the mouse PNRC2 promoter. Transient transfections and luciferase assays further revealed that overexpression of NFY enhanced-promoter activity of PNRC2 gene in a dose-dependent manner while overexpression of E2F1 strongly repressed the activity of the PNRC2 promoter. Since most genes regulated by E2F1 or NFY play a regulatory role in the cell cycle, the finding that the PNRC2 promoter is activated by NFY and repressed by E2F1 indicates that in addition to functioning as nuclear receptor coactivator, PNRC2 may also play a role in the cell cycle.

Characterization of the human P-type 6-phosphofructo-1-kinase gene promoter in neural cell lines

In humans three isoforms of 6-phosphofructo-1-kinase (PFK) exist. Among them platelet-type PFK (PFKP) is highly abundant in the brain. With its distinct allosteric properties PFKP is regarded to be the key enzyme for the regulation of glycolysis in this organ. We cloned 1.7 kb of the 5' upstream promoter of the human PFKP gene and analyzed the promoter activity by deletion and mutation analysis using a luciferase reporter. The transcription start point was determined at 48 bp upstream of the start codon. In deletion studies the region -65 to +48 turned out to be sufficient for promoter activity while fragment -153 to +48 showed the highest promoter activity. Sequence analysis of the region from -153 to +48 revealed a stretch of eight adjacent putative transcription factor binding sites, seven of which are Sp-family specific sites. Sp1 and Sp3 were shown to bind to most if not all of them. Additionally, an NF-Y binding site was identified. Results of deletion and mutation analysis suggest that all of these transcription factors contribute positively to promoter activity. The methylation status of the promoter region was analyzed in different neural tumor cell lines and compared with that in human leukocytes and muscle.

Regulation of the Cell Type-specific dentin sialophosphoprotein gene expression in mouse odontoblasts by a novel transcription repressor and an activator CCAAT-binding factor

Dentin sialophosphoprotein (DSPP) is an extracellular matrix protein that is cleaved into dentin sialoprotein (DSP) and dentin phosphoprotein (DPP) with a highly restricted expression pattern in tooth and bone. Mutations of the DSPP gene are associated with dentin genetic diseases. Regulation of tissue-specific DSPP expression has not been described. To define the molecular basis of this cell-specific expression, we characterized the promoter responsible for the cell-specific expression of the DSPP gene in odontoblasts. Within this region, DNase I footprinting and electrophoretic mobility shift assays delineated one element that contains an inverted CCAAT-binding factor site and a protein-DNA binding site using nuclear extracts from odontoblasts. A series of competitive electrophoretic mobility shift assay analyses showed that the protein-DNA binding core sequence, ACCCCCA, is a novel site sufficient for protein binding. These two protein-DNA binding sequences are conserved at the same proximal position in the mouse, rat, and human DSPP gene promoters and are ubiquitously present in the promoters of other tooth/bone genes. Mutations of the CCAAT-binding factor binding site resulted in a 5-fold decrease in promoter activity, whereas abolishment of the novel protein-DNA binding site increased promoter activity by about 4.6-fold. In contrast to DSPP, expression levels of the novel protein were significantly reduced during odontoblastic differentiation and dentin mineralization. The novel protein was shown to have a molecular mass of 72 kDa. This study shows that expression of the cell type-specific DSPP gene is mediated by the combination of inhibitory and activating mechanisms.

The amino terminal and E2F interaction domains are critical for C/EBP alpha-mediated induction of granulopoietic development of hematopoietic cells

The transcription factor C/EBP alpha (CCAAT/enhancer binding protein alpha) is critical for granulopoiesis. Gene disruption in mice blocks early granulocyte differentiation and disruption of C/EBP alpha function has been implicated in human acute myeloid leukemia (AML), but no systematic structure-function analysis has been undertaken to identify the mechanisms involved in C/EBP alpha-mediated granulocyte differentiation. Here we demonstrate that loss of either of 2 key regions results in disruption of C/EBP alpha granulocytic development: the amino terminus and specific residues residing on the non-DNA binding face of the basic region. Mutation of either results in loss of C/EBP alpha inhibition of E2F and down-regulation of c-Myc, but only mutation of the basic region results in loss of physical interaction with E2F. In contrast, while the amino terminal mutant retains the ability to interact with E2F, this mutant fails to bind a C/EBP alpha site efficiently, fails to activate C/EBP alpha target genes, and is also defective in inhibition of E2F activity. These results further emphasize the importance of inhibition of proliferative pathways in granulopoiesis and demonstrate that several regions of the C/EBP alpha protein are involved in this mechanism.

NF-Y cooperates with USF1/2 to induce the hematopoietic expression of HOXB4

The transcription factor homeobox B4 (HOXB4) is preferentially expressed in immature hematopoietic cells and implicated in the transition from primitive hematopoiesis to definitive hematopoiesis as well as in immature hematopoietic cell proliferation and differentiation. We previously identified Hox response element 1 (HxRE-1) and HxRE-2/E-box as 2 critical DNA-binding sites of the HOXB4 promoter active in hematopoietic cells and demonstrated that upstream stimulating factor 1 and 2 (USF1/2) activate HOXB4 transcription through their binding to the E-box site. Here we report that the trimeric regulatory complex nuclear factor Y (NF-Y) is the factor that recognizes HxRE-1 and activates the HOXB4 promoter in hematopoietic cells. We further show that NF-Y interacts biochemically with USF1/2 on the HOXB4 promoter, and that the formation of this NF-Y/USF1/2 complex is required for the full activity of the HOXB4 promoter. Most important, NF-Ya subunit protein levels are found to be lower in c-Kit-Gr-1+ granulocytic bone marrow (BM) cells than in c-Kit+ immature BM cells, in parallel with a reduction of NF-Y occupancy on the HOXB4 promoter as shown by chromatin immunoprecipitation (ChIP) assay. These results suggest that NF-Y is a developmentally regulated inducer of the HOXB4 gene in hematopoietic cells.

Functional significance of a hereditary adenine insertion variant in the 5'-UTR of the endothelin-1 gene

Endothelin-1 (ET-1) is known as a potent vasoconstrictor peptide and stimulator of cell proliferation. The human preproendothelin-1 mRNA contains a frequent adenine insertion polymorphism (allele frequency = 0.28) within the 5'-untranslated region (5'-UTR), 138 bp downstream of the transcription start site, which was assumed to be related to hypertension. This 5'-UTR variant could putatively influence the mRNA secondary structure and stability, efficacy of translation initiation, or binding of sequence-specific mRNA-binding proteins. By cloning the entire ET-1 gene 5'-UTR in a pGL3 vector and transfection of two cell lines, we studied the effects on luciferase expression in vitro. Luciferase activity was significantly increased in the insertion variant (I) compared to the wild-type (D) variant for both COS1 (2.97 +/- 0.12 versus 2.17 +/- 0.10; P = 0.002) and HepG2 cells (5.42 +/- 0.90 versus 3.68 +/- 0.37; P = 0.002). Investigations performed ex vivo using human umbilical vein endothelial cells were performed to examine the influence of genotypes on the formation of mRNA and protein. Preproendothelin-1-mRNA was quantified in relation to GAPDH by a realtime polymerase chain reaction. Homozygous I-carriers showed significant elevated mRNA levels compared to I/D and I/I-carriers (I/I 9.03 +/- 1.86, I/D 2.07 +/- 1.15, D/D 2.33 +/- 0.99; P = 0.001). ET-1 protein expression, determined by enzyme-linked immunosorbent assay, was increased among I-carriers (I/I 814 +/- 144, I/D 528 +/- 103, D/D 556 +/- 75 pg/ml; P = 0.001). The observed effects may be due to an enhanced mRNA stability because the half-life of mRNA consisting of the I-variant was prolonged (35.4 +/- 7.9 versus 19.9 +/- 4.5 min). We were able to show that the +138 I/D polymorphism is of functional importance for ET-1 expression, and this may have consequences for vessel tonus regulation.

Reversibility of CD34 expression on human hematopoietic stem cells that retain the capacity for secondary reconstitution

The cell surface protein CD34 is frequently used as a marker for positive selection of human hematopoietic stem/progenitor cells in research and in transplantation. However, populations of reconstituting human and murine stem cells that lack cell surface CD34 protein have been identified. In the current studies, we demonstrate that CD34 expression is reversible on human hematopoietic stem/progenitor cells. We identified and functionally characterized a population of human CD45(+)/CD34(-) cells that was recovered from the bone marrow of immunodeficient beige/nude/xid (bnx) mice 8 to 12 months after transplantation of highly purified human bone marrow-derived CD34(+)/CD38(-) stem/progenitor cells. The human CD45(+) cells were devoid of CD34 protein and mRNA when isolated from the mice. However, significantly higher numbers of human colony-forming units and long-term culture-initiating cells per engrafted human CD45(+) cell were recovered from the marrow of bnx mice than from the marrow of human stem cell-engrafted nonobese diabetic/severe combined immunodeficient mice, where 24% of the human graft maintained CD34 expression. In addition to their capacity for extensive in vitro generative capacity, the human CD45(+)/CD34(-) cells recovered from the bnx bone marrow were determined to have secondary reconstitution capacity and to produce CD34(+) progeny following retransplantation. These studies demonstrate that the human CD34(+) population can act as a reservoir for generation of CD34(-) cells. In the current studies we demonstrate that human CD34(+)/CD38(-) cells can generate CD45(+)/CD34(-) progeny in a long-term xenograft model and that those CD45(+)/CD34(-) cells can regenerate CD34(+) progeny following secondary transplantation. Therefore, expression of CD34 can be reversible on reconstituting human hematopoietic stem cells.

Distal elements are critical for human CD34 expression in vivo

The elements regulating gene expression in hematopoietic stem cells are still poorly understood. We previously reported that a 141-kilobase (kb) human CD34 transgene confers properly regulated human CD34 expression in transgenic mice. A construct with only the human CD34 promoter and 3' enhancer region is not sufficient, suggesting that critical distal elements are necessary for expression of the human CD34 gene. To further localize such elements, we analyzed deletion constructs of the human CD34 gene and evaluated their function in transgenic mice. Constructs harboring as little as 18 kb of 5' and 26 kb of 3' human CD34 flanking sequence conferred human expression in tissues of transgenic mice with a pattern similar to that of the 141-kb human transgene. In contrast, a construct harboring 10 kb of 5' and 17 kb of 3' human CD34 flanking sequence gave no expression. These data demonstrate that regions between 10 to 18 kb upstream and/or 17 to 26 kb downstream of the human CD34 gene contain critical elements for human CD34 expression in vivo. Further functional analysis of these regions in transgenic mice will be crucial for understanding CD34 gene expression in hematopoietic stem and progenitor cells.

Transgenic targeting with regulatory elements of the human CD34 gene

The human CD34 gene is expressed on early progenitor and stem cells in the bone marrow. Here we report the isolation of the human CD34 locus from a human P1 artificial chromosome (PAC) library and the characterization and evaluation of this genomic fragment for expression of reporter genes in stable cell lines and transgenic mice. We show that a 160-kb fragment spanning 110 kb of the 5' flanking region and 26 kb of the 3' flanking region of the CD34 gene directs expression of the human CD34 gene in the bone marrow of transgenic mice. The expression of human CD34 transgenic RNA in tissues was found to be similar to that of the endogenous murine CD34 gene. Colony-forming cell assays showed that bone marrow cells staining positive for human CD34 consist of early progenitor cells in which expression of CD34 decreased with cell maturation. In order to test the construct for its ability to express heterologous genes in vivo, we used homologous recombination in bacteria to insert the tetracycline-responsive transactivator protein tTA. Analysis of transgenic human CD34-tTA mice by cross breeding with a strain carrying Cre recombinase under control of a tetracycline-responsive element demonstrated induction of Cre expression in mice in a pattern consistent with the expression of the human CD34 transgene.

Transforming growth factor-beta1 causes transcriptional activation of CD34 and preserves haematopoietic stem/progenitor cell activity

Stem/progenitor cells endowed with in vitro and in vivo haematopoietic activity express the surface protein CD34. Transforming growth factor beta1 (TGF-beta1) is one of the soluble molecules that regulate cell cycle and differentiation of haematopoietic cells, but has pleiotropic activities depending on the state of responsiveness of the target cells. It has previously been shown that TGF-beta1 maintains human CD34+ haematopoietic progenitors in an undifferentiated state, independently of any cell cycle effect. Here, we have shown that TGF-beta1 upregulates the human CD34, an effect that was evident in primary stem/progenitor cells (CD34+lin-) both at the transcriptional and protein levels, and was not associated with any relevant effect on cell growth. The presence of TGF-beta1 influenced differentiation, maintaining primary CD34+/Lin- in an undifferentiated state. This effect was associated with Smad activation and with a dramatic decrease in p38 phosphorylation. Moreover, blocking p38 phosphorylation by the SB202190 inhibitor increased CD34 RNA levels but did not enhance CD34 protein expression in CD34+/Lin- cells, suggesting that modulation of multiple signalling pathways is necessary to reproduce TGF-beta1 effects. These data establish the role that TGF-beta1 has in the modulation of the CD34 stem/progenitor protein and stem/progenitor functions, providing important clues for understanding haematopoietic development and a potential tool for the modulation of human haematopoiesis.

Transforming growth factor-beta1 transcriptionally activates CD34 and prevents induced differentiation of TF-1 cells in the absence of any cell-cycle effects

A number of cytokines modulate self-renewal and differentiation of hematopoietic elements. Among these is transforming growth factor beta1 (TGF-beta1), which regulates cell cycle and differentiation of hematopoietic cells, but has pleiotropic activities depending on the state of responsiveness of the target cells. It has been previously shown by us and other authors that TGF-beta1 maintains human CD34(+) hematopoietic progenitors in an undifferentiated state, independently of any cell cycle effects, and that depletion of TGF-beta1 triggers differentiation accompanied by a decrease in CD34 antigen expression. In the present work, we show that exogenous TGF-beta1 upregulates the human CD34 antigen in the CD34(+) cell lines TF-1 and KG-1a, but not in the more differentiated CD34(-) cell lines HL-60 and K-562. We further studied this effect in the pluripotent erythroleukemia cell line TF-1. Here, TGF-beta1 did not effect cell growth, but induced transcriptional activation of full-length CD34 and prevented differentiation induced by differentiating agents. This effect was associated with nuclear translocation of Smad-2, activation of TAK-1, and with a dramatic decrease in p38 phosphorylation. In other systems TGF-beta1 has been shown to activate a TGF-beta-activated kinase 1 (TAK1), which in turn, activates p38. The specific inhibitor of p38 phosphorylation, SB202190, also increased CD34 RNA expression, indicating the existence of a link between p-38 inhibition by TGF-beta1 and CD34 overexpression. Our data demonstrate that TGF-beta1 transcriptionally activates CD34 and prevents differentiation of TF-1 cells by acting independently through the Smad, TAK1 and p38 pathways, and thus provide important clues for the understanding of hematopoietic development and a potential tool to modify response of hematopoietic cells to mitogens or differentiating agents.

Inhibitory effect of the mi transcription factor encoded by the mutant mi allele on GA binding protein-mediated transcript expression in mouse mast cells

The mi transcription factor (MITF) is a basic-helix-loop-helix leucine zipper (bHLH-Zip) transcription factor that is important for the development of mast cells. Mast cells of mi/mi genotype express normal amounts of abnormal MITF (mi-MITF), whereas mast cells of tg/tg genotype do not express any MITFs. The synthesis of heparin is abnormal in the skin mast cells of mi/mi mice. Because N-deacetylase/N-sulfotransferase 2 (NDST-2) is essential for the synthesis of heparin, the amount of NDST-2 messenger RNA (mRNA) was compared among cultured mast cells (CMCs) of +/+, mi/mi, and tg/tg genotypes. The NDST-2 mRNA was detected by in situ hybridization in the skin mast cells of +/+ and tg/tg mice, but not in the skin mast cells of mi/mi mice. The amount of NDST-2 mRNA decreased significantly in CMCs derived from mi/mi mice when compared to the values of +/+ and tg/tg mice, suggesting that the defective form of MITF inhibited the expression of the NDST-2 transcript. The expression of NDST-2 transcript was mediated by the GGAA motif located in the 5'-untranslated region. GA binding protein (GABP) bound the GGAA motif and increased the amount of NDST-2 transcript. The mi-MITF appeared to inhibit the ability of GABP to express NDST-2 transcript by disturbing its nuclear localization. This is the first study to show that expression of an abnormal form of a bHLH-Zip transcription factor can dramatically alter the intracellular location of another DNA/RNA binding factor, which in turn brings about profound and unexpected consequences on transcript expression.

Structural characterization and chromosomal localization of the mouse cDNA and gene encoding the bone tyrosine phosphatase, mOST-PTP

Tyrosine kinases and phosphatases are regulators of the steady-state levels of phosphotyrosine proteins and, in this way, are key players in determining the functional state of the cell. As a unique member of the protein tyrosine phosphatase (PTP) superfamily, osteotesticular PTP (OST-PTP) is a receptor protein whose expression is highly regulated during osteoblast differentiation and in response to modulators of bone remodeling such as parathyroid hormone and vitamin D3. To explore the molecular mechanisms and signaling pathways important in the regulation of this gene, we characterized the structural organization of the mouse OST-PTP cDNA and gene and determined its chromosomal localization. The mouse cDNA is approximately 5.5 kb including 5.1 kb of coding sequence, 315 bp 5' UTR and 102 bp 3' UTR. It is expressed as a single approximately 5.8 kb transcript in day 8 differentiated MC3T3 osteoblasts. Although highly homologous to the rat OST-PTP cDNA, the mouse cDNA possesses a 74 bp insert in the 5' UTR which contains several potential transcription factor binding sites such as AP-2 and NFkappaB. The mouse OST-PTP (mOST-PTP) gene is a single copy gene encompassing 35 exons and spanning only 20.65 kb. As such, it is the smallest gene of the characterized receptor PTP genes. This is due to the lack of large introns and the conserved spatial organization of exons which encode specific protein motifs in the mOST-PTP molecule. Sequence analysis of the putative mOST-PTP promoter revealed basal elements as well as many potential cis-acting regulatory elements with relevance to gene regulation in bone. Of particular interest is the single osteoblast specific element known as osteocalcin specific element 2 (OSE2) found at position -1867, as well as numerous VDRE and NFkappaB sites found throughout the promoter and the 5' UTR. Fluorescence in situ hybridization studies have shown that mOST-PTP localizes to mouse chromosome 1, region F-G which is syntenic to the segment of human chromosome 1q32-33. This characterization of the mOST-PTP cDNA and gene will facilitate future experiments exploring the mechanisms of regulation of this phosphatase during osteogenesis.

Regulation of CD34 transcription by Sp1 requires sites upstream and downstream of the transcription start site

CD34 is a cell surface glycoprotein expressed on hematopoietic stem and progenitor cells, but not on fully differentiated cells in the peripheral blood. To better understand the molecular regulation of early hematopoiesis, we are elucidating the mechanisms of CD34 transcriptional regulation. By deletion analysis we identify a 39-bp element in the proximal region of murine CD34 promoter that is critical for promoter activity. Electromobility shift assays indicate that nuclear proteins of hematopoietic cells bind to this domain; however, the presence of this binding activity does not correlate directly with CD34 expression.Using methylation interference, the DNA binding site for this activity was localized to four guanine residues within the GGGGTCGG sequence from -48 to -54 bp. When the four contact guanines were mutated, both protein binding and promoter activity were abolished. Although this sequence does not contain a standard consensus for Sp1, this transcription factor binds specifically to the 39-bp region and stimulates promoter activity in both hematopoietic cells and in Sp1 null Drosophila S2 cells. In addition, Ku binds to this domain in a sequence-specific manner. Activation of the CD34 promoter by Sp1 requires the presence of a binding domain at -48 bp as well as the 5' untranslated region, which also binds Sp1.A functional interaction between regulatory regions upstream and downstream of the transcription start site is required for CD34 gene expression.