Human GATA-1 Research Articles

Spectroscopic determination of the thermodynamics of cobalt and zinc binding to GATA proteins.

Vertebrate GATA proteins regulate processes that are vital to development, and each possesses two tandem GATA finger domains: an N-terminal GATA finger and a C-terminal GATA finger. These GATA fingers require Zn(2+) to fold, to bind DNA recognition elements, and to regulate transcription. While the GATA-1 C-terminal finger is necessary and sufficient to bind to single GATA DNA sites, the N-terminal finger interacts with DNA such that the double finger unit (DF domain) has a binding and transactivation profile that is tuned by the DNA-binding site. Co(2+) was used as a spectroscopic probe in a series of competition titrations to determine the affinity of Co(2+) and Zn(2+) for the C-terminal finger from chicken GATA-1 and the double finger from human GATA-1 (referred to in this report as CF and DF). For CF, these experiments yielded K(b)(Co) = 1.0 (+/-1.3) x 10(7) M(-1) and K(b)(Zn) = 2.0 (+/-1.3) x 10(10) M(-1). For DF, these experiments yielded equilibrium constants for the process of two M(2+) binding to form M(2+)(2)-DF of beta(2)(Co) = 2.5 (+/-1.6) x 10(14) M(-2) and beta(2)(Zn) = 6.3 (+/-2.5) x 10(20) M(-2). The ZnS(4) coordination environment of Zn(2+)-bound CF was confirmed with X-ray absorption spectroscopy. A detailed analysis of these data suggests that the N-terminal and C-terminal fingers of DF act as independent and identical Zn(2+)-binding sites and each finger binds Zn(2+) with an affinity equivalent to that of CF.

A unique role of an amino terminal 16-residue region of long-type GATA-6.

Human GATA-6 mRNA utilizes two Met-codons in frame as translational initiation codons in cultured mammalian cells. An internal ribosome entry site (IRES) is not present in front of the coding region for short-type GATA-6. The 5'-upstream sequence with a short upstream open reading frame (uORF) did not affect the production of either long- or short-type GATA-6. Introduction of a canonical Kozak sequence around the upstream Met-codon resulted in predominant synthesis of long-type GATA-6, suggesting that the translation of short-type GATA-6 could be due to leaky scanning of the Met-codon by ribosomes. We found that at least the sequence comprising the 90th to 139th nucleotide bases from the first letter of the upstream Met-codon plays a positive role in the expression of long-type GATA-6. This was confirmed by insertion of the corresponding sequence in frame at the site of deletion (the 38th to 304th nucleotide residues). However, insertion of the sequence comprising the 92nd to 141st bases did not suppress the negative effect of the deletion. These results suggest that the translation of this region (Glu-31-Cys-46) could be critical for the apparent production of long-type GATA-6. We also demonstrated that long-type GATA-6 is potentially more active than the short-type.

Sp and GATA factors are critical for Apolipoprotein AI downstream enhancer activity in human HepG2 cells

The factors that bind to the hepatic-specific human apolipoprotein AI ( apoAI) 48-bp downstream enhancer (DSE) were identified and characterized by electrophoretic mobility shift assays. A significant homology was shown between the histone 4 ( H4) promoters and the hepatic-specific human apoAI DSE at Sp1 and H4TF2 binding sites. Human HepG2 nuclear extracts were used to form four specific complexes with the DSE (referred to as apoAI DSE-1, -2, -3, and -4). The apoAI DSE-1 and -2 complexes showed similar binding specificity to the Sp/H4TF1 consensus site within the apoAI DSE. The apoAI DSE-1 complex was predominantly recognized by anti-Sp1 and Sp3 sera in gel shift assays, indicating that the DSE was recognized by multiple Sp family members. Nuclear extracts that were prepared from retinoic acid treated HepG2 cells showed increased levels of Sp factors in gel shift and Western blot assays. The apoAI DSE-2 complex was identified as H4TF1 and formed in the absence of magnesium chloride. The apoAI DSE-3 complex bound to a consensus GATA element within the DSE that was recognized by recombinant human GATA-6 as well. The apoAI DSE-3 complex was completely disrupted by a GATA-4 antibody in EMSA. GATA-4 and -6 were detected in nuclear extracts prepared from retinoic acid treated HepG2 cells using Western blot assays. The highest apoAI DSE-3 levels were observed with retinoic acid treated HepG2 cell nuclear extracts in EMSA. ApoAI DSE-4 is a multi-factor complex that includes an Sp/H4TF1 factor and either H4TF2 or apoAI DSE-3. Because apoAI DSE mutations revealed transcription defects in transient transfection assays, we conclude that the entire DSE sequence is required for full apoAI transcriptional activity in HepG2 cells.

Purification of human recombinant GATA-1 from bacteria: implication for protein-protein interaction studies.

GATA-1 is a key regulator of terminal erythroid differentiation in mammals and birds. The structural and biochemical studies of human GATA-1 (hGATA-1) are limited by the difficulty of its purification in a sufficient amount. Here we describe the procedure for obtaining pure bacterial recombinant hGATA-1 in an active functional state. We demonstrate that this protein may be successfully used for preparing an affinity column, producing GATA-1-specific rabbit polyclonal antibodies, and studying DNA-protein and protein-protein interactions.

Transcriptional regulation of the KEL gene and Kell protein expression in erythroid and non-erythroid cells

The Kell blood-group antigen was originally reported to be a protein expressed in erythroid tissue only. Transcriptional analysis of the KEL promoter activity in human erythroleukaemia K562 and epithelial HeLa cells by electrophoretic mobility-shift and supershift assays, chloramphenicol acetyltransferase assays, co-transfection studies and site-directed mutagenesis provided the following results: (i) the KEL promoter exhibits a strong transcriptional activity in K562 cells and, unexpectedly, a basal non-erythroid activity in HeLa cells, (ii) up-regulation of the 5′ distal promoter activity occurs only in the erythroid context, and (iii) two motifs localized in the exon 1 region, which bind the Sp1/Sp3 and the human GATA-1/Ku70/80 factors, were required for down-regulation of the promoter activity, but inhibition of the promoter activity by the repressing factors in HeLa cells was incomplete. KEL expression in HeLa cells was performed further by primer-extension analysis, which revealed the presence of a low amount of Kell transcript correlating with basal expression of the Kell protein in these cells, as shown by immunopurification and Western-blot analysis. DNA sequencing of the transcript revealed a sequence identical to that obtained from erythroid tissue. In human tissues, KEL expression was investigated by dot-blot analysis and revealed high levels of Kell mRNAs, particularly in brain tissues, testis and lymphoid tissues. Moreover, most tissues analysed exhibited low levels of Kell transcripts. The Kell protein was also detected by immunohistochemistry in the Sertoli cells of the testis and in lymphoid tissues like spleen and tonsil, specifically localized in the follicular dendritic cells. Altogether, the results indicated that KEL expression is not restricted to erythroid tissue.

Stimulation of GATA-2 as a mechanism of hydrogen peroxide suppression in hypoxia-induced erythropoietin gene expression.

Hydrogen peroxide (H2O2) has previously been shown to inhibit the DNA binding activity of hypoxia inducible factor-1 (HIF-1), the accumulation of HIF-1alpha protein and erythropoietin (Epo) gene expression. Epo gene expression has been previously shown to be down-regulated through a GATA binding site at its promoter region. In this study, the effect of H2O2 on Epo gene expression under hypoxic conditions through a GATA transcription factor was investigated. Hypoxic induction was found to be inhibited upon the addition of H2O2, and this effect could be reversed through the addition of catalase. Hypoxic induction was found to be suppressed by co-transfection with a human GATA-2 cDNA expression plasmid. Transfection of Hep3B cells with a reporter gene bearing a mutation at the promoter GATA binding site was found to be only mildly affected by the addition of H2O2. Electrophoretic gel mobility shift assays (EMSAs), using the Epo promoter GATA site as a probe and the GATA-2 protein extracted from Hep3B cells, showed that addition of H2O2 enhanced the binding of GATA-2 while addition of catalase inhibited this binding. From these results, we conclude that H2O2 increases the binding activity of GATA-2 in a specific manner, thereby suppressing the activity of the Epo promoter and thus inhibiting Epo gene expression.

Identification of a GATA-overlapping sequence within the enhancer of the murine GPIIb promoter that induces transcriptional deregulation in human K562 cells

AbstractThe human and the murine glycoprotein platelet IIb (GPIIb) promoters are megakaryocyte specific in human and murine cell systems, respectively. Here we show that the murine promoter is, however, highly active when transfected in K562 human cells in which the human promoter is almost inactive. A murine promoter, in which the enhancer element was replaced by the human, retrieves its megakaryocytic specificity in human cell lines. The human and murine GATA-binding sites located in the enhancer region display slight sequence divergence next to the consensus GATA core sequence. Gel shift experiments show that, although the murine and the human GATA sequences both bind GATA-1, the murine sequence alone forms an additional complex (B) not detected with the human sequence. When the murine GATA-containing region is replaced by the human in the context of the murine GPIIb promoter, megakaryocyte specificity is restored in the human cell lines. A G nucleotide 3′ to GATA appears crucial because its substitution abrogates B but not GATA-1 binding and restores megakaryocyte specificity to the murine promoter. Conversely, substitution of the human GATA-1 binding sequence by its murine homologue that binds both GATA-1 and complex B induces an abnormal activity for the human promoter in K562 cells. Altogether, our data suggest that limited changes in the GATA-containing enhancer of the GPIIb promoter can induce the recruitment of accessory proteins that could be involved in alteration of a megakaryocyte-restricted gene activation program.

Identification of a GATA-overlapping sequence within the enhancer of the murine GPIIb promoter that induces transcriptional deregulation in human K562 cells

The human and the murine glycoprotein platelet IIb (GPIIb) promoters are megakaryocyte specific in human and murine cell systems, respectively. Here we show that the murine promoter is, however, highly active when transfected in K562 human cells in which the human promoter is almost inactive. A murine promoter, in which the enhancer element was replaced by the human, retrieves its megakaryocytic specificity in human cell lines. The human and murine GATA-binding sites located in the enhancer region display slight sequence divergence next to the consensus GATA core sequence. Gel shift experiments show that, although the murine and the human GATA sequences both bind GATA-1, the murine sequence alone forms an additional complex (B) not detected with the human sequence. When the murine GATA-containing region is replaced by the human in the context of the murine GPIIb promoter, megakaryocyte specificity is restored in the human cell lines. A G nucleotide 3′ to GATA appears crucial because its substitution abrogates B but not GATA-1 binding and restores megakaryocyte specificity to the murine promoter. Conversely, substitution of the human GATA-1 binding sequence by its murine homologue that binds both GATA-1 and complex B induces an abnormal activity for the human promoter in K562 cells. Altogether, our data suggest that limited changes in the GATA-containing enhancer of the GPIIb promoter can induce the recruitment of accessory proteins that could be involved in alteration of a megakaryocyte-restricted gene activation program.

Transcription Factor GATA-2 Gene Is Located Near 3q21 Breakpoints in Myeloid Leukemia

Rearrangements affecting chromosome band 3q21 are observed in a subgroup of patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS). However, little is known about the molecular consequences of such aberrations. We therefore established a PAC contig in the 3q21 breakpoint region and identified potential protein coding sequences by exon trapping. One of the exons isolated was from the human GATA-2 gene, which we showed to be transcribed from telomere to centromere. The majority of 3q21 breakpoints are located telomeric to the transcribed portion of this gene in a region that in mice appears to be necessary for proper promoter function. Results of GATA-2 expression analyses in leukemic cell lines as well as primary patient samples are compatible with the hypothesis that 3q21 aberrations contribute to leukemogenesis through deregulation of the hematopoietic transcription factor GATA-2.

Identification of human GATA-2 gene distal IS exon and its expression in hematopoietic stem cell fractions.

Transcription factor GATA-2 is essential for the proper function of hematopoietic stem cells and progenitors. Two first exons/promoters have been found in the mouse GATA-2 gene, and a distal IS promoter shows activity specific to hematopoietic progenitors and neural tissues. To ascertain whether the two-promoter system is also utilized in the human GATA-2 gene, we isolated and analyzed a P1 phage clone containing this gene. The nucleotide sequence of the human GATA-2 gene 5' flanking region was determined over 10 kbp, and a human IS exon was identified in the locus through sequence comparison analysis with that of the mouse GATA-2 IS exon. RNA blotting and reverse-transcribed PCR analyses identified a transcript that starts from the IS exon in human leukemia-derived cell lines. The IS-originated transcript was also identified in CD34-positive bone marrow and cord blood mononuclear cells, which are recognized as clinically important hematopoietic stem cell-enriched fractions. Phylogenic comparison of the human and mouse GATA-2 gene sequences revealed several regions in the locus that exhibit high sequence similarity. These results demonstrate that the GATA-2 gene regulatory machinery is conserved among vertebrates. The fact that the human IS promoter is active in the hematopoietic stem cell/progenitor fraction may be an important clue for the design of a vector system that can specifically express various genes in hematopoietic stem cells and progenitors.

C/EBPβ and GATA-1 Synergistically Regulate Activity of the Eosinophil Granule Major Basic Protein Promoter: Implication for C/EBPβ Activity in Eosinophil Gene Expression

AbstractEosinophil granule major basic protein (MBP) is expressed exclusively in eosinophils and basophils in hematopoietic cells. In our previous study, we demonstrated a major positive regulatory role for GATA-1 and a negative regulatory role for GATA-2 in MBP gene transcription. Further analysis of the MBP promoter region identified a C/EBP (CCAAT/enhancer-binding protein) consensus binding site 6 bp upstream of the functional GATA-binding site in the MBP gene. In the cell line HT93A, which is capable of differentiating towards both the eosinophil and neutrophil lineages in response to retinoic acid (RA), C/EBPα mRNA expression decreased significantly concomitant with eosinophilic and neutrophilic differentiation, whereas C/EBPβ expression was markedly increased. Electrophoretic mobility shift assays (EMSAs) showed that recombinant C/EBPβ protein could bind to the potential C/EBP-binding site (bp −90 to −82) in the MBP promoter. Furthermore, we have demonstrated that both C/EBPβ and GATA-1 can bind simultaneously to the C/EBP- and GATA-binding sites in the MBP promoter. To determine the functionality of both the C/EBP- and GATA-binding sites, we analyzed whether C/EBPβ and GATA-1 can stimulate the MBP promoter in the C/EBPβ and GATA-1 negative Jurkat T-cell line. Cotransfection with C/EBPβ and GATA-1 expression vectors produced a 5-fold increase compared with cotransfection with the C/EBPβ or GATA-1 expression vectors individually. In addition, GST pull-down experiments demonstrated a physical interaction between human GATA-1 and C/EBPβ. Expression of FOG (F̲riendo̲fG̲ATA), which binds to GATA-1 and acts as a cofactor for GATA-binding proteins, decreased transactivation activity of GATA-1 for the MBP promoter in a dose-dependent manner. Our results provide the first evidence that both GATA-1 and C/EBPβ synergistically transactivate the promoter of an eosinophil-specific granule protein gene and that FOG may act as a negative cofactor for the eosinophil lineage, unlike its positively regulatory function for the erythroid and megakaryocyte lineages.

C/EBPβ and GATA-1 Synergistically Regulate Activity of the Eosinophil Granule Major Basic Protein Promoter: Implication for C/EBPβ Activity in Eosinophil Gene Expression

Eosinophil granule major basic protein (MBP) is expressed exclusively in eosinophils and basophils in hematopoietic cells. In our previous study, we demonstrated a major positive regulatory role for GATA-1 and a negative regulatory role for GATA-2 in MBP gene transcription. Further analysis of the MBP promoter region identified a C/EBP (CCAAT/enhancer-binding protein) consensus binding site 6 bp upstream of the functional GATA-binding site in the MBP gene. In the cell line HT93A, which is capable of differentiating towards both the eosinophil and neutrophil lineages in response to retinoic acid (RA), C/EBP mRNA expression decreased significantly concomitant with eosinophilic and neutrophilic differentiation, whereas C/EBPβ expression was markedly increased. Electrophoretic mobility shift assays (EMSAs) showed that recombinant C/EBPβ protein could bind to the potential C/EBP-binding site (bp −90 to −82) in the MBP promoter. Furthermore, we have demonstrated that both C/EBPβ and GATA-1 can bind simultaneously to the C/EBP- and GATA-binding sites in the MBP promoter. To determine the functionality of both the C/EBP- and GATA-binding sites, we analyzed whether C/EBPβ and GATA-1 can stimulate the MBP promoter in the C/EBPβ and GATA-1 negative Jurkat T-cell line. Cotransfection with C/EBPβ and GATA-1 expression vectors produced a 5-fold increase compared with cotransfection with the C/EBPβ or GATA-1 expression vectors individually. In addition, GST pull-down experiments demonstrated a physical interaction between human GATA-1 and C/EBPβ. Expression of FOG (F̲riendo̲fG̲ATA), which binds to GATA-1 and acts as a cofactor for GATA-binding proteins, decreased transactivation activity of GATA-1 for the MBP promoter in a dose-dependent manner. Our results provide the first evidence that both GATA-1 and C/EBPβ synergistically transactivate the promoter of an eosinophil-specific granule protein gene and that FOG may act as a negative cofactor for the eosinophil lineage, unlike its positively regulatory function for the erythroid and megakaryocyte lineages.

Selection of DNA Binding Sites for Human Transcriptional Regulator GATA-6

The DNA-binding sites for transcriptional regulator GATA-6 were selected and amplified by means of a PCR-mediated random-site selection method involving filter binding and gel-mobility shift analysis using the zinc finger region of human GATA-6 fused with GST. Sequencing and comparison of the selected clones suggested that (A/T/C)GAT(A/T)(A) is the consensus binding sequence, which is similar to the GATA motif (A/T)GATA(A/G) and the gastric motif (G/C)PuPu(G/C)NGAT(A/T)PuPy. GATA-6 also binds to a similar sequence containing the GATC but not the GATG sequence. These results indicated that GATA-6 shows broader sequence specificity as to DNA binding. However, adenine is favored on both sides of the core for strong binding [AGAT(A/T)A], and the order of binding is GATA > GATT > GATC. Full-length human GATA-6 expressed in COS-1 cells showed essentially the same binding specificity, suggesting that the zinc finger region of GATA-6 mainly contributes to the selection of the binding sequence. Furthermore, the non-RI method presented in this paper is convenient for determination of the binding sites of other DNA-binding proteins.

Molecular cloning of gaf1, a Schizosaccharomyces pombe GATA factor, which can function as a transcriptional activator.

As a first step to elucidate the functions of Schizosaccharomyces pombe (S. pombe) GATA factors, we have isolated the gaf1+ gene (GATA-factor like gene) in S. pombe. The predicted amino acid (aa) sequence of Gaf1 reveals a single zinc finger domain typical of fungal GATA factors, and the zinc finger exhibits 60% aa identity to that of human GATA-1. The open reading frame of Gaf1 predicts a protein of Mr 32 kDa consisting of 290 intronless amino acids. Disruption of this gene has no effect on cell viability and growth rate. The GST-Gaf1 fusion protein binds specifically to GATA motifs of its own promoter as well as DAL7 UAS, a canonical GATA motif of Saccharomyces cerevisiae (S. cerevisiae) The specific DNA-binding activity resides within the N-terminal half of Gaf1 (Gaf1N; aa 1-120) containing the zinc finger, whereas the C-terminal half (Gaf1C; aa 121-290) contains transactivation sequences that induce the expression of the lacZ reporter when fused to the GAL4 DNA binding domain. These results demonstrate that Gaf1 may function as a transcriptional activator consisting of DNA-binding and transactivation domains.

Alternative Promoters Regulate Transcription of the Mouse GATA-2 Gene

Transcription factor GATA-2 has been shown to be a key regulator in hematopoietic progenitor cells. To elucidate how the expression of the GATA-2 gene is controlled, we isolated the mouse GATA-2 (mGATA-2) gene. Transcription of mGATA-2 mRNAs was found to initiate from two distinct first exons, both of which encode entirely untranslated regions, while the remaining five exons are shared by each of the two divergent mRNAs. Reverse transcriptase-polymerase chain reaction analysis revealed that GATA-2 mRNA initiated at the upstream first exon (IS) in Sca-1+/c-kit+ hematopoietic progenitor cells, whereas mRNA that initiates at the downstream first exon (IG) is expressed in all tissues and cell lines that express GATA-2. While the structure of the IG exon/promoter shows high similarity to those of the Xenopus and human GATA-2 genes, the IS exon/promoter has not been described previously. When we examined the regulation contributing to IS transcription using transient transfection assays, we found that sequences lying between -79 and -61 are critical for the cell type-specific activity of the IS promoter. DNase I footprinting experiments and electrophoretic mobility shift assays demonstrated the binding of transcription factors to this region. These data indicate that the proximal 80 base pair region of IS promoter is important for the generation of cell type-specific expression of mGATA-2 from the IS exon.

GATA-6 DNA binding protein expressed in human gastric adenocarcinoma MKN45 cells

A cDNA for the GATA-6 (GATA-GT1) DNA binding protein was cloned from a library of the human gastric adenocarcinoma cell line MKN45. The deduced amino acid sequence (449 residues) indicates that the primary structure of human GATA-6 is highly homologous to that of the rat protein. The potential phosphorylation site for protein kinases (A and C), and histidine and alanine clusters are conserved. Whereas the rat H +/K +-ATPase α and β subunit genes have two and three GATA protein binding sites in their promoter regions, respectively, the human α subunit gene has only one binding site [Maeda, M., Kubo, K., Nishi, T. and Futai, M. (1996) J. Exp. Biol. 199, 513–520]. We cloned the 5′-upstream region of the human H +/K +-ATPase β subunit gene by genome walking and found that it also has a single GATA protein binding site near the TATA ☐. The GATA sites of the human α and β subunit genes are recognized by the zinc finger domain of human GATA-6. The conservation of the GATA protein binding sites suggests that they are important for the gene regulation of the human and rat H +/K +-ATPase.

Molecular cloning of human GATA-6 DNA binding protein: high levels of expression in heart and gut

Human GATA-6 has been cloned from foetal heart by a combination of PCR-based methods and cDNA library screening. The 3.8 kbp cDNA has a coding sequence of 1347 bp the 449 aa protein is virtually identical in the two zinc-finger binding domains to other human GATA sequences, but varies considerably in the amino and carboxy terminal regions. The sequence shows greatest similarity to GATA-6-like sequences from rat, mouse, chicken and Xenopus. Northern analysis and in situ hybridisation show that GATA-6 is expressed at high levels in human adult and foetal heart as well as in gut derivatives. It is postulated that GATA-6, in concert with GATA-4, plays a crucial role in the regulation of cardiac differentiation.

Regulation of Aquaporin-2 Gene Transcription by GATA-3

To evaluate the functional role of GATA motifs in the 5′-flanking region of a kidney-specific AQP-2 water channel gene, we sought to isolate a GATA factor(s) expressed in collecting ducts and determined the role on the AQP-2 promoter. Two cDNAs encoding GATA factors were isolated from rat kidney, whose sequences were highly homologous with human GATA-2 and -3. Reverse-transcription PCR using dissected nephron segments revealed that rat GATA-3 but not GATA-2 was expressed in collecting ducts, thus indicating that GATA-3 could interact with GATA motifs in the AQP-2 promoter. Transactivation experiments utilizing the rat GATA-3 expression vector indicated that rat GATA-3 increased the AQP-2 promoter activity about fourfold. These results indicated that GATA motifs in the 5′-flanking region of the hAQP-2 gene were functional cis-elements and that GATA-3 in collecting ducts may be one of the important regulators of AQP-2 expressioninvivo.

Negative Regulation of the Erythropoietin Gene Expression by the GATA Transcription Factors

AbstractWe examined regulation of the human erythropoietin (Epo) gene through the GATA sequence in the Epo promoter and showed that Hep3B and HepG2 cells express human GATA-2 (hGATA-2) mRNA and protein. Nuclear extracts of QT6 cells transfected with hGATA-1, 2, or 3 transcription factors showed specific binding to the GATA element in the human Epo gene promoter by gel mobility shift assay. Transient transfection of Hep3B cells with hGATA-1, 2, or 3 showed that each of these transcription factors significantly decreased the level of expression of Epo mRNA as assessed by a competitive polymerase chain reaction. Transient transfection of Hep3B cells with hGATA-1, 2, and 3 and an Epo-reporter gene (growth hormone [GH]) construct showed significant inhibition of the Epo promoter. Antisense oligonucleotide for hGATA-2 transcription factor significantly increased the Epo protein in Hep3B cells under 1% O2 for 24 hours incubation. Furthermore, transient transfection of Hep3B cells with hGATA-1, 2, and 3 and an Epo-reporter gene (luciferase) construct also showed significant inhibition of the Epo promoter. However, transfection of the mutated GATA sequence of the Epo-luciferase gene with hGATA-1, 2, and 3 interfere with the inhibition of the Epo promoter. We conclude that the hGATA-1, 2, and 3 transcription factors specifically bind to the GATA element in the human Epo gene promoter and negatively regulate Epo gene expression.

Constitutive Expression of GATA-1 Interferes With the Cell-Cycle Regulation

GATA-1, mainly expressed during erythroid differentiation, has been shown to regulate the genes specifically expressed in the late stages of erythropoiesis and to protect erythroid cells from apoptosis, suggesting that it might interfere with the cell cycle. By expressing the retrovirally transduced human GATA-1 cDNA in NIH3T3 fibroblasts, we have shown that GATA-1 alone was unable to transactivate its erythroid-specific target genes in these nonerythroid cells. However, GATA-1 expression had a dramatic effect on the proliferation of these fibroblasts. The cloning efficiency of the GATA-1-expressing fibroblasts was maintained but their S phase was greatly elongated and their G1 and G2/M phases were reduced, impairing substantially their proliferation. When cultured at low serum concentrations for 48 hours, GATA-1-expressing fibroblasts failed to accumulate in the G0/G1 phases but did not become serum independent. GATA-1-expressing fibroblasts expressed D1, A, and B1 cyclin mRNAs under conditions of serum starvation or at confluence, whereas these cyclin mRNAs were downregulated in the parental NIH3T3 cells cultured under the same conditions. Moreover, these effects of GATA-1 expression on proliferation were not limited to NIH3T3 cells, since different clones of hGATA-1 virus-infected FDCP-1 cells, a murine interleukin-3-dependent hematopoietic cell line, had a slower growth rate than control cells. Based on these data, we hypothesize that GATA-1 plays a role in the regulation of the cell cycle during terminal erythroid differentiation.