DNA-binding specificities of the GATA transcription factor family

Identification and Characterization of the Hematopoietic Cell-Specific Enhancer-Like Element of the Mouse Hex Gene

Hex is one of the homeobox genes suggested to be important for hematopoietic cell differentiation. However, its biological function and mechanism of transcriptional regulation in hematopoietic cells remain elusive. We have identified the regulatory region necessary for transcription of the mouse Hex gene in K562 leukemia cells through transient reporter assays involving various deletion mutants. This region, comprising +775 to +1177 in the first intron, had enhancer-like properties and showed high activity in other hematopoietic cell lines such as U937, HEL, and RAW264.7, but little activity in other Hex-expressing cell lines such as MH(1)C(1) and H4IIE hepatoma cells, suggesting that this region functions as a hematopoietic cell-specific enhancer-like element. Binding site mutation of hematopoietic transcription factors, such as GATAs and c-Myb present in the enhancer-like element, significantly decreased the luciferase reporter gene expression in K562 cells. Electrophoretic mobility shift assays showed that GATA-1, GATA-2, or c-Myb actually binds to three of these putative binding sites, and also suggested that several unidentified factors might interact with the enhancer-like element. Overexpression of GATA-1, GATA-2, or c-Myb stimulated the enhancer-like activity via these three binding sites. Thus, we conclude that Hex expression in hematopoietic cells is mainly regulated by GATA-1, GATA-2, and c-Myb via this intronic enhancer-like element.

GATA-4 regulates cardiac morphogenesis through transactivation of the N-cadherin gene

Cardia bifida is known to occur in animal models lacking the cardiogenic transcriptional factor GATA-4. The downstream target genes responsible for this cardiac deformity remain unknown, however. Treatment with small interfering RNAs (siRNA) specifically targeting GATA-4 into cardiac mesodermal cells led to the development of cardia bifida in chick embryos. RT-PCR using mRNAs extracted from cardiac tubes revealed that the GATA-4-specific siRNA selectively suppresses expression of N-cadherin mRNA, one of the genes essential for the single heart formation, without affecting other cardiac marker mRNAs. Analysis of the N-cadherin gene promoter activity using a luciferase reporter gene system and electrophoretic mobility shift assays revealed that GATA-4 binds directly to the N-cadherin gene promoter region, thereby transactivating its expression. We therefore concluded that the cardia bifida observed in the GATA-4-deleted model is caused by the transcriptional down-regulation of N-cadherin expression.

The atypical GATA protein TRPS1 represses androgen-induced prostate-specific antigen expression in LNCaP prostate cancer cells

Prostate-specific antigen (PSA) is considered as an important marker for prostate cancer. Regulation of PSA gene expression is mediated by androgens bound to androgen receptors via androgen response elements (AREs) in its promoter and far upstream enhancer regions. In addition, GATA proteins contribute to PSA gene transcription by interacting with GATA motifs present in the PSA enhancer sequence. The TRPS1 gene contains a single GATA zinc finger domain and not only binds to forward consensus GATA motifs but also to an inverse GATA motif overlapping the ARE III in the far upstream enhancer of the PSA gene. Overexpression of TRPS1 in androgen-dependent human LNCaP prostate cancer cells inhibited the transcription of a transiently transfected PSA enhancer/promoter-driven luciferase reporter construct. Furthermore, overexpression of TRPS1 reduced the androgen-induced endogenous PSA levels secreted in culture medium of LNCaP cells. Our results suggest a role of TRPS1 in androgen regulation of PSA gene expression.

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.

Transcriptional regulation of the cardiac-specificMLC2gene duringXenopusembryonic development

The mechanisms by which transcription factors, which are not themselves tissue restricted, establish cardiomyocyte-specific patterns of transcription in vivo are unknown. Nor do we understand how positional cues are integrated to provide regionally distinct domains of gene expression within the developing heart. We describe regulation of the Xenopus XMLC2 gene,which encodes a regulatory myosin light chain of the contractile apparatus in cardiac muscle. This gene is expressed from the onset of cardiac differentiation in the frog embryo and is expressed throughout all the myocardium, both before and after heart chamber formation. Using transgenesis in frog embryos, we have identified an 82 bp enhancer within the proximal promoter region of the gene that is necessary and sufficient for heart-specific expression of an XMLC2 transgene. This enhancer is composed of two GATA sites and a composite YY1/CArG-like site. We show that the low-affinity SRF site is essential for transgene expression and that cardiac-specific expression also requires the presence of at least one adjacent GATA site. The overlapping YY1 site within the enhancer appears to act primarily as a repressor of ectopic expression, although it may also have a positive role. Finally, we show that the frog MLC2 promoter drives pan myocardial expression of a transgene in mice, despite the more restricted patterns of expression of murine MLC2 genes. We speculate that a common regulatory mechanism may be responsible for pan-myocardial expression of XMLC2 in both the frog and mouse, modulation of which could have given rise to more restricted patterns of expression within the heart of higher vertebrates.

Regulation of human microsomal epoxide hydrolase gene (EPHX1) expression by the transcription factor GATA-4

Microsomal epoxide hydrolase (mEH) is a bifunctional protein that plays a crucial role in the metabolism of numerous xenobiotics as well as in mediating the hepatic sodium-dependent uptake of bile acids that are involved in numerous physiological processes including the regulation of cholesterol metabolism. The transcription factors and nuclear receptors that control the constitutive and inducible expression of the mEH gene (EPHX1), however, have not been described. To characterize these factors, a series of 5'-deletion constructs have been transfected into human liver-derived HepG2 cells as well as non-hepatic HeLa cells. Promoter activity analysis indicated the presence of a positive regulatory element in the -80/-70 bp region. Sequence analysis revealed a putative GATA site at -79/-74 bp as well as an additional site at -31/-26 bp. Electrophoretic mobility shift assays with an anti-GATA-4 antibody confirmed that GATA-4 bound to these two sites with a dissociation constant of 1.56 nM (-79 site) and 0.65 nM (-31 site). Coexpression of GATA-4 stimulated EPHX1 promoter activity up to 7.5-fold in a dose-dependent manner. Endogenous EPHX1 message in HepG2 cells was also significantly increased by overexpression of GATA-4. Mutating the -79 element resulted in a 65% loss of promoter activity, while mutating the -31 element had no effect on basal activity but greatly reduced the response to additional GATA-4. In HeLa cells, which do not express GATA-4, EPHX1 activity was negligible; however, activity could be reconstituted by the addition of exogenous GATA-4. These results demonstrate that GATA-4 plays a critical role in regulating EPHX1 expression.

Multiple GATA sites: protein binding and physiological relevance for the regulation of the proline transporter gene of Aspergillus nidulans

In Aspergillus nidulans, proline can serve both as a carbon and a nitrogen source. The transcription of the prnB gene, encoding the proline transporter, is efficiently repressed only by the simultaneous presence of ammonium and glucose. Thus, repression of this gene demands the activation of the CreA repressor and the inactivation of the positive-acting GATA factor AreA. Repression of all other prn structural genes results largely from inducer exclusion. In an areA null mutation background, prnB is repressible by the sole presence of glucose. We have determined by EMSA and missing-base interference experiments that there are 15 AreA-binding sites in the prnD-prnB intergenic region. Only sites 13/14, in the proximity of the prnB TATA box, are clearly involved in transcriptional activation and regulation. Mutation of these sites mimics qualitatively the regulatory effect of an areA null mutation. The deletion of the TATA box has a measurable effect on the maximal level of prnB transcription but does not alter the regulation pattern of this gene.

Determinants of GATA-1 binding to DNA: the role of non-finger residues

Mammalian GATA transcription factors are expressed in various tissues in a temporally regulated manner. The prototypic member, GATA-1, is required for normal erythroid, megakaryocytic, and mast cell development. This family of DNA-binding proteins recognizes a consensus (A/T)GATA(A/G) motif and possesses homologous DNA binding domains consisting of two zinc fingers. The C-terminal finger of GATA-1 recognizes the consensus motif with nanomolar affinities, whereas the N-terminal finger shows a binding preference for a GATC motif, albeit with much reduced affinity (Kd approximately microm). The N-terminal finger of GATA-2 also shows a preference for an AGATCT binding site, with an increased affinity attributed to N- and C-terminal flanking basic residues (Kd approximately nm). To understand the differences in the binding specificities of the N- and C-terminal zinc fingers of GATA-1, we have constructed a series of swapped domain peptides. We show that the specificity for AGATAA over AGATCT arises from the C-terminal non-finger basic domain. Thus, the N-terminal finger binds preferentially to AGATAA once appended to the C-terminal arm of the C-terminal finger. We further show that this specificity arises from the highly conserved QTRNRK residues. The converse is, however, untrue in the case of the C-terminal finger; swapping of QTRNRK with the corresponding LVSKRA does not switch the DNA binding specificity from AGATAA to AGATCT. These results highlight the important role of residues adjacent to the CXXCX17CNAC zinc finger motif (i.e. non-finger residues) in the specific recognition of DNA residues.

Structure of the murine tenascin-R gene and functional characterisation of the promoter

The tenascin-R (TN-R) gene encodes a multidomain extracellular matrix glycoprotein belonging to the tenascin family. It is detectable mainly in oligodendrocytes and neuronal subpopulations of the central nervous system. In this report, we describe the structure of the 5'-region of the mouse TN-R gene and characterise the activity of its promoter. By in silico cloning and genome walking, we have deduced the organisation of the gene and identified the promoter sequence by 5'-RACE technology. TN-R transcripts in adult mouse brain contain non-coding exons 1 and 2 as demonstrated by the reverse transcriptase-polymerase chain reaction. The promoter displays its activity in cultured cells of neural origin, but not in a fibroblast-like cell line or an undifferentiated teratocarcimoma cell line. As for the human and rat genes, the elements required for the full and cell type-specific activity of the promoter are contained in exon 1 and 167 bp upstream of this exon. The mouse TN-R promoter sequence is similar to that of rat and human in that it displays similarly unusual features: it lacks any classical TATA-box or CAAT-box, GC-rich regions or initiator elements. The promoter contains consensus sequences for binding of a variety of transcription factors, notably p53/p73 and glucocorticoid receptors.

A GATA-specific inhibitor (K-7174) rescues anemia induced by IL-1beta, TNF-alpha, or L-NMMA

Interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), or N(G)-monomethyl-L-arginine (L-NMMA) are increased in patients with chronic disease-related anemia. They increase the binding activity of GATA and inhibit erythropoietin (Epo) promoter activity. In this study, we examined the ability of K-7174 (a GATA-specific inhibitor) to improve Epo production when inhibited by treatment with IL-1beta, TNF-alpha, or L-NMMA. Epo protein production and promoter activity were induced in Hep3B cells with 1% O2. However, 15 U/ml IL-1beta, 220 U/ml TNF-alpha, or 10(-3) M L-NMMA inhibited Epo protein production and promoter activity, respectively. Addition of 10 microM K-7174 rescued these inhibitions of Epo protein production and promoter activity induced by IL-1beta, TNF-alpha, or L-NMMA, respectively. Electrophoretic mobility shift assays revealed that addition of K-7174 decreased GATA binding activity, which was increased with the addition of IL-1beta, TNF-alpha, or L-NMMA. Furthermore, intraperitoneal injection of mice with IL-1beta or TNF-alpha decreased the hemoglobin concentrations and reticulocyte counts. However, the addition of K-7174 reversed these effects. These results raise the possibility of using K-7174 as therapy to treat anemia.

Novel roles for GATA transcription factors in the regulation of steroidogenesis

Steroidogenesis is a tightly regulated process that is dependent on pituitary hormones. In steroidogenic tissues, hormonal stimulation triggers activation of an intracellular signalling pathway that typically involves cAMP production, activation of PKA, and phosphorylation of target transcription factors. In the classic cAMP signalling pathway, phosphorylation of CREB (cAMP response element (CRE)-binding protein) and its subsequent binding to cAMP-response elements (CREs) in the regulatory regions of target genes play a key role in mediating cAMP responsiveness. However, the cAMP responsive regions of several genes expressed in steroidogenic tissues do not contain consensus CREs indicating that other transcription factors are also involved. We have been studying the role played by the GATA family of transcription factors. GATA factors are expressed in a variety of tissues including the adrenals and gonads. Since the regulatory regions of several steroidogenic genes contain GATA elements, we have proposed that GATA factors, particularly GATA-4 and GATA-6, might represent novel downstream effectors of hormonal signalling in steroidogenic tissues. In vitro experiments have revealed that GATA-4 is indeed phosphorylated in steroidogenic cells and that phosphorylation levels are rapidly induced by cAMP. GATA-4 phosphorylation is mediated by PKA. Phosphorylation increases GATA-4 DNA-binding activity and enhances its transcriptional properties on multiple steroidogenic promoters. We now define a new molecular mechanism whereby phospho-GATA factors contribute to increased transcription of steroidogenic genes in response to hormonal stimulation.

High-level activation by a duodenum-specific enhancer requires functional GATA binding sites

The purine metabolic gene adenosine deaminase (ADA) is expressed at high levels in a well-defined spatiotemporal pattern in the villous epithelium of proximal small intestine. A duodenum-specific enhancer module responsible for this expression pattern has been identified in the second intron of the human ADA gene. It has previously been shown that binding of the factor PDX-1 is essential for function of this enhancer. The studies presented here examine the proposed roles of GATA factors in the enhancer. Site-directed mutagenesis of the enhancer's GATA binding sites crippled enhancer function in 10 lines of transgenic mice, with 9 of the lines demonstrating <1% of normal activity. Detailed studies along the longitudinal axis of mouse small intestine indicate that GATA-4 and GATA-5 mRNA levels display a reciprocal pattern, with low levels of GATA-6 throughout. Interestingly, gel shift studies with duodenal nuclear extracts showed binding only by GATA-4.

Structural and functional characterisation of the DNA binding domain of the Aspergillus nidulans gene regulatory protein AreA

The 876-aa protein AreA regulates the expression of numerous genes involved in nitrogen metabolism in Aspergillus nidulans, and interacts with GATA sequences upstream of the relevant genes. We have carried out limited proteolysis of the C-terminal domain of the AreA protein in order to identify possible structural domains within the protein. A stable 156-amino-acid fragment was identified that contained the zinc finger region, and this sequence was cloned and expressed in E. coli. Fluorescence spectroscopy of the purified protein showed that the proteolytic domain was folded and could be denatured by high concentrations of urea (approximately 4 M), exhibiting a sharp transition. Fluorescence spectroscopy was also used to monitor binding to a DNA duplex containing the AreA recognition site, demonstrating tight binding of the domain to its DNA recognition sequence. The DNA binding affinity of the domain is comparable with that of the native AreA protein and much higher than that of the minimal zinc finger region of AreA.

GATA-1 and c-myb crosstalk during red blood cell differentiation through GATA-1 binding sites in the c-myb promoter

GATA-1 and c-Myb transcription factors represent key regulators of red blood cell development. GATA-1 is upregulated and c-myb proto-oncogene expression is downregulated when red cell progenitors differentiate into erythrocytes. Here we have employed a culture system, that faithfully recapitulates red blood cell differentiation in vitro, to follow the kinetics of GATA-1 and c-myb expression. We show that c-myb proto-oncogene expression is high in progenitors and effectively downregulated at the time when nuclear GATA-1 accumulates and cells differentiate into erythrocytes. Additionally, we identified two GATA-1 binding sites within the c-myb promoter and demonstrate that GATA-1 protein binds to these sites in vitro. Furthermore, GATA-1 represses c-myb expression through one of the GATA-1 binding sites in transient transfection experiments and this requires FOG-1. Thus, our study provides evidence for a direct molecular link between GATA-1 activity and c-myb proto-oncogene expression during terminal red cell differentiation.

Characterization of an alpha-L-arabinofuranosidase gene (abf1) from Penicillium purpurogenum and its expression

An alpha-L-arabinofuranosidase gene (abf1) from Penicillium purpurogenum was identified and sequenced. abf1 has an open reading frame of 1518 bp, does not contain introns and codes for a protein of 506 amino acids. The deduced mature protein has a molecular mass of 49.6 KDa, and its sequence is homologous to arabinofuranosidases of glycosyl hydrolase family 54. Southern blots suggest that abf1 is a single copy gene. Putative sequences for the binding of the transcriptional regulators XlnR, CreA, PacC, AlcR and AreA are present in the promoter. Northern-blot analysis shows that abf1 is expressed at neutral but not at alkaline or acidic pH values. The presence of binding sites for regulatory elements in the promoter region has been compared to the genes of other fungal enzymes belonging to the same family. This is the first characterization of an abf gene from a Penicillium species.

Molecular cloning of the mouse AMY-1 gene and identification of the synergistic activation of the AMY-1 promoter by GATA-1 and Sp1

We have reported that a novel c-Myc binding protein, AMY-1, stimulated the transcription activity of c-Myc and was translocated from the cytoplasm to the nucleus in a c-Myc-dependent manner. AMY-1 works as an inducer of human K562 cell differentiation upon induction of AraC. To characterize the expression or functional importance of AMY-1, the genomic DNA of mouse AMY-1 was cloned and characterized. Both mouse and human genomic DNAs, the latter of which was retrieved from a human DNA database, comprise five exons spanning about 11 kb. To characterize the promoter of the mouse AMY-1 gene, a series of deletion constructs of the region upstream of the first ATG was linked to the luciferase gene, and their luciferase activities were measured in human HeLa and K562 cells. The results showed that Sp1 was essential for AMY-1 expression in both cell lines and that GATA-1 is also necessary in K562 cells. Sp1 in both cell lines and GATA-1 only in K562 cells were identified as proteins binding to these sites by a mobility shift assay. Furthermore, it was found that GATA-1 stimulated AMY-1 expression synergistically with Sp1 in ectopically expressed insect cells and that both proteins were associated in K562 cells.

The promoter of the classical MHC class I locus in rainbow trout (Oncorhynchus mykiss)

In rainbow trout only a single classical major histocompatibility complex (MHC) class I locus has been identified. In previous studies it was shown that this locus, Onmy-UBA, is characterised by extensive polymorphism and ubiquitous expression. In the present study the sequence of the promoter region of Onmy-UBA was analysed. Within this region several fragments for transcription regulation could be detected, including interferon-sensitive enhancer elements. The promoter region is very similar to that of classical MHC class I in higher vertebrates. In agreement with the interferon sensitive elements identified in its promoter, Onmy-UBA expression in rainbow trout gonad cells (RTG-2 cell line) was up-regulated after infection with infectious haematopoietic necrosis virus (IHNV).

Cloning and characterization of porcine common gamma chain gene

The common gamma chain, which was originally identified as a component of interleukin-2 receptors (IL-2R), plays a key role in differentiation of T lymphocytes and natural killer (NK) cells. In the present study, cDNA of the porcine common gamma chain gene and its genomic DNA were molecularly cloned and characterized. The porcine common gamma chain gene was found to consist of 8 exons, spanning approximately 3.7 kb, and to encode a 368-amino acid polypeptide. The amino acid sequence showed 82.4%, 71.1%, 86.1%, and 84.8% similarities with that of human, murine, bovine, and canine chains, respectively. The common gamma chain gene was assigned to swine chromosome Xq13 by FISH analysis and was consistent with the result of radiation hybrid (RH) mapping. When various porcine tissues were examined for the expression of this gene, the expression was observed in lymphocytes and lymphocyte-related tissues. Since GATA, T cell factor-1 (TCF-1), Ets-1, activated protein2 (AP-2), and Ikaros2 binding motifs were demonstrated in the 5' upstream region of this gene, promoter activity was investigated using luciferase gene as a reporter. The results indicate that the Ets-1 binding motif in the segment from -95 to -59 (major transcription initiation site: +1) was an essential cis-acting regulatory element for the common gamma chain gene in lymphoid cells.

Interaction of a GATA factor with cis-acting elements involved in light regulation of nuclear genes encoding chloroplast glyceraldehyde-3-phosphate dehydrogenase in Arabidopsis

We have previously identified a cis-acting element, named the XXIII box, that is essential for light-regulated expression of the nuclear gene GAPB, which encodes the B subunit of chloroplast glyceraldehyde-3-phosphate dehydrogenase from Arabidopsis thaliana. Examination of the sequences indicated that there are two GATA motifs within the XXIII box. Based on the degree of the amino-acid sequence identity in the DNA binding domains, we divided the 25 GATA factors encoded in the Arabidopsis genome into three classes. We chose GATA-1 and GATA-20 from Class I and Class II, which include the majority of GATA factors, for overexpression in an Escherichia coli expression system. Gel mobility shift assays showed that GATA-1, but not GATA-20, binds specifically to the two GATA motifs within the XXIII fragment. In addition, we showed that GATA-1 could also bind specifically to a cis-acting element in the promoter of the GAPA gene, which is coordinately regulated by light with the GAPB gene. Based on these results, we propose that light controls the expression of GAPA and GAPB genes in part by regulating the binding of the same transcription factor at their GATA motifs.

Regulation of cell type-specific mouse Fc epsilon RI beta-chain gene expression by GATA-1 via four GATA motifs in the promoter

The FcR beta-chain, a subunit of two related multisubunit receptor complexes, the FcepsilonRI and FcgammaRIII, amplifies the mast cell response and is necessary for the cell surface expression of FcepsilonRI in mouse. The transient reporter assay indicated that -69/+4 region is required for cell type-specific transcriptional regulation of mouse beta-chain gene. EMSA using Abs against transcription factors or competitive oligonucleotides demonstrated that -58/-40 region (containing overlapping three GATA-1 sites, -53/-48, -46/-51, and -42/-47) and -31/-26 region (containing one GATA-1 site) are recognized by GATA-1. The promoter activity of beta-chain was decreased by nucleotide replacements of the GATA-1 sites in mouse mast cell line PT18. Furthermore, exogenously produced GATA-1 up-regulated the promoter activity in CV-1 cells, which are negative in the beta-chain production and the up-regulation was apparently suppressed by GATA-1 site mutations. These results indicate that cell type-specific transcription of mouse beta-chain gene is regulated by GATA-1.

A novel muscle-specific enhancer identified within the deletion overlap region of two XLDC patients lacking muscle exon 1 of the human dystrophin gene

Previous studies point to the involvement of several discrete transcriptional enhancers in the modulation of dystrophin gene expression in skeletal and cardiac muscle. Analysis of deletion breakpoints in two X-linked dilated cardiomyopathy patients with mutations that remove muscle exon 1 identified a 3.2-kb deletion overlap region (XLDC3.2) between -1199 and +2057 bp predicted to contain regulatory elements essential for dystrophin gene expression in cardiac muscle. A novel-sequence-based search strategy was used to identify a 543-bp region downstream of muscle exon 1 rich in cardiac-specific transcriptional elements. Designated dystrophin muscle enhancer 2 (DME2), this candidate enhancer was seen to function in a position- and orientation-independent manner in muscle cell lines but not in fibroblasts. As only modest activity was observed in primary neonatal rat cardiomyocytes, DME2 is thought to play a role in dystrophin gene regulation at later stages of cardiac muscle development.

Transcription factors in cardiogenesis: the combinations that unlock the mysteries of the heart

Heart formation is one of the first signs of organogenesis within the developing embryo and this process is conserved from flies to man. Completing the genetic roadmap of the molecular mechanisms that control the cell specification and differentiation of cells that form the developing heart has been an exciting and fast-moving area of research in the fields of molecular and developmental biology. At the core of these studies is an interest in the transcription factors that are responsible for initiation of a pluripotent cell to become programmed to the cardiac lineage and the subsequent transcription factors that implement the instructions set up by the cells commitment decision. To gain a better understanding of these pathways, cardiac-expressed transcription factors have been identified, cloned, overexpressed, and mutated to try to determine function. Although results vary depending on the gene in question, it is clear that there is a striking evolutionary conservation of the cardiogenic program among species. As we move up the evolutionary ladder toward man, we encounter cases of functional redundancy and combinatorial interactions that reflect the complex networks of gene expression that orchestrate heart development. This review focuses on what is known about the transcription factors implicated in heart formation and the role they play in this intricate genetic program.

Domains of Pit-1 required for transcriptional synergy with GATA-2 on the TSH beta gene

Previous studies showed that Pit-1 functionally cooperates with GATA-2 to stimulate transcription of the TSH beta gene. Pit-1 and GATA-2 are uniquely coexpressed in pituitary thyrotropes and activate transcription by binding to a composite promoter element. To define the domains of Pit-1 important for functional cooperativity with GATA-2, we cotransfected a set of Pit-1 deletions with an mTSH beta-luciferase reporter. Plasmids were titrated to express equivalent amounts of protein. A mutant containing a deletion of the hinge region between the POU and homeodomains retained the ability to fully synergize with GATA-2. In contrast, mutants containing deletions of amino acids 2-80 or 72-125 demonstrated 56 or 34% of the synergy found with the full-length protein, suggesting that these regions contributed to cooperativity. Mutants with deletions of the POU-specific or homeodomain further reduced the effect signifying the requirement for DNA binding. GST interaction studies demonstrated that only the homeodomain of Pit-1 interacted with GATA-2. Finally, several mutations between the Pit-1 and GATA-2 sites on the TSH beta promoter reduced binding for each factor and greatly reduced ternary complex formation. Thus multiple domains of Pit-1 are required for full synergy with GATA-2 and sequences between the two binding sites contribute to co-occupancy with both factors on the proximal TSH beta promoter.

Chromatin structure and control of beta-like globin gene switching

The human beta-globin locus is a complex genetic system widely used for analysis of eukaryotic gene expression. The locus consists of five functional beta-like globin genes, epsilon, (G)gamma, (A)gamma, delta, and beta, arrayed on the chromosome in the order that they are expressed during ontogeny. Globin gene expression is regulated, in part, by the locus control region, which physically consists of five DNaseI-hypersensitive sites located 6-22 Kb upstream of the epsilon -globin gene. During ontogeny two switches occur in beta-globin gene expression that reflect the changing oxygen requirements of the fetus. The first switch from embryonic epsilon - to fetal gamma-globin occurs at six weeks of gestation. The second switch from gamma- to adult delta- and beta-globin occurs shortly after birth. Throughout the locus, cis-acting elements exist that are dynamically bound by trans-acting proteins, including transcription factors, co-activators, repressors, and chromatin modifiers. Discovery of novel erythroid-specific transcription factors and a role for chromatin structure in gene expression have enhanced our understanding of the mechanism of globin gene switching. However, the hierarchy of events regulating gene expression during development, from extracellular signaling to transcriptional activation or repression, is complex. In this review we attempt to unify the current knowledge regarding the interplay of cis-acting elements, transcription factors, and chromatin modifiers into a comprehensive overview of globin gene switching.

Arabidopsis thaliana GATA factors: organisation, expression and DNA-binding characteristics

Many light-responsive promoters contain GATA motifs and a number of nuclear proteins have been defined that interact with these elements. Type-IV zinc-finger proteins have been extensively characterised in animals and fungi and are referred to as GATA factors by virtue of their affinity for promoter elements containing this sequence. We previously identified cDNA sequences representing four Arabidopsis thaliana type-TV zinc-finger proteins. Here we define the organisation and expression of GATA-1, GATA-2, GATA-3 and GATA-4 as well as DNA-binding characteristics of their encoded proteins. Transcripts from all four genes can be detected in all tissues examined suggesting that they are not developmentally regulated at the level of transcription. In vitro binding experiments with Escherichia coli-derived recombinant proteins were performed using motifs previously defined as targets for nuclear GATA-binding proteins. These studies reveal differences in DNA binding specificity of GATA-1 as compared to the other three proteins. In vivo protein-DNA interactions monitored by yeast one-hybrid assays reveal different binding characteristics as compared to those defined with E. coli-derived recombinant protein. Trans-activation of gene expression by the four Arabidopsis proteins via some, but not all, DNA elements tested indicates that the Arabidopsis proteins can form functional interactions with previously defined promoter elements containing GATA motifs. We conclude that the Arabidopsis type-IV zinc-finger proteins may represent the previously defined family of nuclear GATA-binding proteins implicated in light-responsive transcription.

The human IL-3 locus is regulated cooperatively by two NFAT-dependent enhancers that have distinct tissue-specific activities

The human IL-3 gene is expressed by activated T cells, mast cells, and eosinophils. We previously identified an enhancer 14 kb upstream of the IL-3 gene, but this element only functioned in a subset of T cells and not in mast cells. To identify additional mechanisms governing IL-3 gene expression, we mapped DNase I hypersensitive (DH) sites and evolutionarily conserved DNA sequences in the IL-3 locus. The most conserved sequence lies 4.5 kb upstream of the IL-3 gene and it encompassed an inducible cyclosporin A-sensitive DH site. A 245-bp fragment spanning this DH site functioned as a cyclosporin A-sensitive enhancer, and was induced by calcium and kinase signaling pathways in both T cells and mast cells via an array of three NFAT sites. The enhancer also encompassed AML1, AP-1, and Sp1 binding sites that potentially mediate function in both T and myeloid lineage cells, but these sites were not required for in vitro enhancer function in T cells. In stably transfected T cells, the -4.5-kb enhancer cooperated with the -14-kb enhancer to activate the IL-3 promoter. Hence, the IL-3 gene is regulated by two enhancers that have distinct but overlapping tissue specificities. We also identified a prominent constitutive DH site at -4.1 kb in T cells, mast cells, and CD34(+) myeloid cells. This element lacked in vitro enhancer function, but may have a developmental role because it appears to be the first DH site to exist upstream of the IL-3 gene during hemopoietic development before IL-3 expression.

Cooperative interaction of Xvent-2 and GATA-2 in the activation of the ventral homeobox gene Xvent-1B

The Xvent family of homeobox transcription factors is essential for the establishment of the dorsal-ventral body axis during Xenopus embryogenesis. In contrast to Xvent-2B and other members of the Xvent-2 subfamily, Xvent-1B is not a direct response gene of bone morphogenetic protein-4 signaling. Xvent-1B is activated by Xvent-2, but CHX experiments revealed the requirement of additional factors. In this study, we report on the cooperative effect of Xvent-2 and the zinc finger transcription factor GATA-2 on the promoter of the Xvent-1B gene. We show that GATA-2 is a direct target gene of bone morphogenetic protein-4 and that GATA-2 interacts with Xvent-2 to activate transcription of Xvent-1B. Both transcription factors bind to distinct elements within the Xvent-1B promoter, and GATA-2 physically interacts with the C-terminal domain of Xvent-2. Promoter/reporter studies in Xenopus embryos revealed that full activation of Xvent-1B requires both Xvent-2 and GATA-2. Moreover, the two factors are sufficient to direct transcription of Xvent-1B in the presence of CHX at the ventral side of the embryo. The failure of both factors to activate Xvent-1B on the dorsal side suggests the existence of a dorsal inhibitor. This inhibitor is likely a component of the dorsal Wnt signaling pathway because nuclear translocation of beta-catenin before midblastula transition results in a suppression of Xvent-1B transcription.

Down-regulation of GATA-3 expression during human papillomavirus-mediated immortalization and cervical carcinogenesis

To identify cellular genes that may be involved in human papillomavirus (HPV)-mediated immortalization mRNA differential display analysis was performed on preimmortal and subsequent immortal stages of four human keratinocyte cell lines transformed by HPV type 16 or 18 DNA. This yielded a cDNA fragment encoding the transcription factor GATA-3 that was strongly reduced in intensity in all immortal stages of the four cell lines. A marked reduction in both GATA-3 mRNA and protein expression in HPV-immortalized cell lines was confirmed by reverse transcriptase-polymerase chain reaction, Western blot analysis, and immunohistochemistry and was also shown to be apparent in cervical carcinoma cell lines. Immunohistochemical analysis of cervical tissue specimens showed a clear nuclear staining for GATA-3 in normal cervical squamous epithelium (n = 14) and all cervical intraepithelial neoplasia (CIN) I (n = 6) and CIN II lesions (n = 2). In contrast, 11% (1 of 9) of CIN III lesions and 67% (8 of 12) of cervical squamous cell carcinomas revealed a complete absence of GATA-3 immunostaining. Hence, complete down-regulation of GATA-3 expression represents a rather late event during cervical carcinogenesis. Whether GATA-3 down-regulation is etiologically involved in HPV-mediated immortalization and cervical carcinogenesis remains to be examined.

Interleukin-13 gene expression is regulated by GATA-3 in T cells: role of a critical association of a GATA and two GATG motifs

Using a transgenic approach, we studied the role of GATA-3 in T cells. As previously shown, enforced GATA-3 expression in transgenic mice inhibits Th1 differentiation of CD4 T cells, but unexpectedly, both type 1 (interferon gamma) and type 2 (interleukin (IL)-4 and IL-13) cytokine genes were activated in the transgenic CD8 T cells. Because IL-13 gene expression was highly enhanced in vivo by GATA-3 expression, we studied the human and the mouse IL-13 gene promoters and found an evolutionary-conserved association of a consensus GATA binding site and two GATG motifs. We showed that efficient GATA-3 binding to this regulatory sequence required these three motifs and that the affinity of the GATA zinc fingers for this association was five times higher than for the consensus GATA binding site alone. Transfections in a T cell line or transactivation by GATA-3 showed that the combination of the three sites was required for full transcriptional activity of the IL-13 gene promoter. Finally we showed that this association of binding sites causes a very high sensitivity of the IL-13 gene promoter to small variations in the level of GATA-3 protein. Altogether, these results indicate an important role of GATA-3 in CD8 cytokine gene expression and demonstrate that a critical network of GATA binding sites highly modulates GATA-3 activity.

Friend of GATA is expressed in naive Th cells and functions as a repressor of GATA-3-mediated Th2 cell development

The commitment of naive T cells to polarized Th cells requires specific changes in their transcription factors. Retrovirally overexpressed GATA-3 has been reported to induce the Th2 cytokine profile in developing Th1 cells. In this study, we examined the role of the N-terminal finger (Nf) of GATA-3 in Th2 cell development. The Nf, as well as the C-terminal finger and the transactivation domain, is critical for the induction of the Th2 phenotype. Using the GATA-3-Nf as a bait, our yeast two-hybrid screening identified friend of GATA (FOG) in the Th2 cell-specific library. Naive T cells express significant levels of FOG mRNA, which was rapidly down-regulated upon commitment to both Th1 and Th2 lineages. In reporter assays, FOG blocked the GATA-3-mediated activation of several cytokine promoters. Finally, retroviral expression of FOG in developing Th2 cells suppressed both IL-4 and IL-5 and allowed for IFN-gamma production, which was accompanied by a significant level of T-bet mRNA expression. Serial deletion mutation analysis indicated that the N-terminal region, but not the consensus C-terminal binding protein-binding motif, of FOG is critical for the effects. Our results clearly indicate that 1) FOG is a repressor of GATA-3 in naive T cells and 2) the down-regulation of FOG induces Th2 cell differentiation by releasing GATA-3 from its repression.

Identification of a candidate regulatory region in the human CD8 gene complex by colocalization of DNase I hypersensitive sites and matrix attachment regions which bind SATB1 and GATA-3

To locate elements regulating the human CD8 gene complex, we mapped nuclear matrix attachment regions (MARs) and DNase I hypersensitive (HS) sites over a 100-kb region that included the CD8B gene, the intergenic region, and the CD8A gene. MARs facilitate long-range chromatin remodeling required for enhancer activity and have been found closely linked to several lymphoid enhancers. Within the human CD8 gene complex, we identified six DNase HS clusters, four strong MARs, and several weaker MARs. Three of the strong MARs were closely linked to two tissue-specific DNase HS clusters (III and IV) at the 3' end of the CD8B gene. To further establish the importance of this region, we obtained 19 kb of sequence and screened for potential binding sites for the MAR-binding protein, SATB1, and for GATA-3, both of which are critical for T cell development. By gel shift analysis we identified two strong SATB1 binding sites, located 4.5 kb apart, in strong MARs. We also detected strong GATA-3 binding to an oligonucleotide containing two GATA-3 motifs located at an HS site in cluster IV. This clustering of DNase HS sites and MARs capable of binding SATB1 and GATA-3 at the 3' end of the CD8B gene suggests that this region is an epigenetic regulator of CD8 expression.

AP-2 gamma and the homeodomain protein distal-less 3 are required for placental-specific expression of the murine 3 beta-hydroxysteroid dehydrogenase VI gene, Hsd3b6

The enzyme 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD) is essential for the biosynthesis of all active steroid hormones. It exists as multiple isoforms in humans and rodents, each the product of a distinct gene. Human 3 beta-HSD I in placenta is essential for placental progesterone biosynthesis and thus is essential for the maintenance of pregnancy. The murine ortholog, 3 beta-HSD VI, is the only isoform expressed in giant trophoblast cells during the first half of mouse pregnancy. This study was designed to identify the cis-acting element(s) and the associated transcription factors required for trophoblast-specific expression of 3 beta-HSD VI. Transfection studies in placental and nonplacental cells identified a novel 66-bp trophoblast-specific enhancer element located between -2896 and -2831 of the 3 beta-HSD VI promoter. DNase protection analysis of the enhancer element identified three trophoblast-specific binding sites, FPI, FPII, and FPIII. Electrophoretic mobility shift assays with oligonucleotides representing the protected sequences, FPI and FPIII, and nuclear extracts isolated from human JEG-3 cells and from mouse trophoblast cells, demonstrated the same binding pattern that was distinct from the binding pattern with mouse Leydig cell nuclear proteins. Further electrophoretic mobility shift assays identified AP-2 gamma and the homeodomain protein, Dlx 3, as the transcription factors that specifically bind to FPI and FPIII, respectively. Site-specific mutations in each of the binding sites eliminated enhancer activity indicating that AP-2 gamma and Dlx 3, together with an additional transcription factor(s) that are conserved between humans and mice, are required for trophoblast-specific expression of 3 beta-HSD VI.

Analysis of the promoters for the beta-esterase genes associated with insecticide resistance in the mosquito Culex quinquefasciatus

Resistance to organophosphorus (OP) insecticides in the mosquito Culex quinquefasciatus is primarily due to the amplification and over-expression of non-specific esterases. Co-amplification of two esterase genes, estalpha2(1) and estbeta2(1), is the most common resistance genotype. In both resistant and susceptible mosquitoes the alpha- and beta-esterase genes are oriented in a head-to-head arrangement, the intergenic sequences containing promoter elements for the divergent transcription of both esterases. Transient transfection of luciferase reporter gene constructs into a C. quinquefasciatus cell line was used to study these promoters. A control vector was constructed with the strong Drosophila actin 5c promoter driving expression of beta-galactosidase. The beta-esterase promoters from both insecticide resistant and -susceptible insects were highly active in directing luciferase expression. Transfections with panels of deletions revealed several regions where binding sites for positive and negative regulatory elements are located, and candidate transcription factor sites have been identified. Gel shift assays have identified one DNA-protein interaction that is stronger with the resistant than with the equivalent but slightly altered susceptible sequence. The arthropod initiator site TCAGT 135bp upstream of the ATG in both beta-esterase promoters is essential for transcription initiation, but a putative TATA box is not involved.

Erythropoietin receptor signalling is required for normal brain development

Erythropoietin, known for its role in erythroid differentiation, has been shown to be neuroprotective during brain ischaemia in adult animal models. Although high levels of erythropoietin receptor are produced in embryonic brain, the role of erythropoietin during brain development is uncertain. We now provide evidence that erythropoietin acts to stimulate neural progenitor cells and to prevent apoptosis in the embryonic brain. Mice lacking the erythropoietin receptor exhibit severe anaemia and defective cardiac development, and die at embryonic day 13.5 (E13.5). By E12.5, in addition to apoptosis in foetal liver, endocardium and myocardium, the erythropoietin receptor null mouse shows extensive apoptosis in foetal brain. Lack of erythropoietin receptor affects brain development as early as E10.5, resulting in a reduction in the number of neural progenitor cells and increased apoptosis. Corresponding in vitro cultures of cortical cells from Epor–/– mice also exhibited decreases in neuron generation compared with normal controls and increased sensitivity to low oxygen tension with no surviving neurons in Epor–/– cortical cultures after 24 hour exposure to hypoxia. The viability of primary Epor+/+ rodent embryonic cortical neurons was further increased by erythropoietin stimulation. Exposure of these cultures to hypoxia induced erythropoietin expression and a tenfold increase in erythropoietin receptor expression, increased cell survival and decreased apoptosis. Cultures of neuronal progenitor cells also exhibited a proliferative response to erythropoietin stimulation. These data demonstrate that the neuroprotective activity of erythropoietin is observed as early as E10.5 in the developing brain, and that induction of erythropoietin and its receptor by hypoxia may contribute to selective cell survival in the brain.

Hypodermal expression of Caenorhabditis elegans TGF-beta type I receptor SMA-6 is essential for the growth and maintenance of body length

There are several transforming growth factor-beta (TGF-beta) pathways in the nematode Caenorhabditis elegans. One of these pathways regulates body length and is composed of the ligand DBL-1, serine/threonine protein kinase receptors SMA-6 and DAF-4, and cytoplasmic signaling components SMA-2, SMA-3, and SMA-4. To further examine the molecular mechanisms of body-length regulation in the nematode by the TGF-beta pathway, we examined the regional requirement for the type-I receptor SMA-6. Using a SMA-6::GFP (green fluorescent protein) reporter gene, sma-6 was highly expressed in the hypodermis, unlike the type-II receptor DAF-4, which is reported to be ubiquitously expressed. We then examined the ability of SMA-6 expression in different regions of the C. elegans body to rescue the sma-6 phenotype (small) and found that hypodermal expression of SMA-6 is necessary and sufficient for the growth and maintenance of body length. We also demonstrate that GATA sequences in the sma-6 promoter contribute to the hypodermal expression of sma-6.

The N-terminal zinc finger of the erythroid transcription factor GATA-1 binds GATC motifs in DNA

The mammalian transcription factor GATA-1 is required for normal erythroid and megakaryocytic development. GATA-1 contains two zinc fingers, the C-terminal finger, which is known to bind (A/T)GATA(A/G) motifs in DNA and the N-finger, which is important for interacting with co-regulatory proteins such as Friend of GATA (FOG). We now show that, like the C-finger, the N-finger of GATA-1 is also capable of binding DNA but recognizes distinct sequences with the core GATC. We demonstrate that the GATA-1 N-finger can bind these sequences in vitro and that in cellular assays, GATA-1 can activate promoters containing GATC motifs. Experiments with mutant GATA-1 proteins confirm the importance of the N-finger, as the C-finger is not required for transactivation from GATC sites. Recently four naturally occurring mutations in GATA-1 have been shown to be associated with familial blood disorders. These mutations all map to the N-finger domain. We have investigated the effect of these mutations on the recognition of GATC sites by the N-finger and show that one mutation R216Q abolishes DNA binding, whereas the others have only minor effects.

A region upstream of the human delta-globin gene shows a stage-specific interaction with globin promoters in erythroid cell lines

We previously showed that the 651-bp DNA fragment, located 3 kb upstream from the human delta-globin gene (fragment F5), is able to inhibit adult, not fetal, globin promoter in mouse erythroleukemia cell lines (MEL) expressing adult globin genes. Here we show in transient analysis that fragment F5 has a strong inhibitory effect on fetal gamma-globin promoter in human erythroleukemia cell lines (HEL) expressing fetal globin genes. Since the beta-promoter constructs were poorly expressed in fetal cells, new plasmids containing an HPFH promoter (Ggamma(-175), T to C), which is strongly expressed in both fetal and adult cell lines, were made. Here we report that fragment F5 in HEL cells has a strong inhibitory effect on wild-type gamma-promoter only; no effect was evident on gamma(-175)-promoter in either MEL or HEL cell lines. Altogether these results show a stage-specific interaction between fragment F5 and globin promoters during development. We also report the presence of several bindings for erythroid GATA family factors by electrophoretic mobility shift assay, using nuclear extracts from erythroid cell lines.

Modulation of endogenous GATA-4 activity reveals its dual contribution to Müllerian inhibiting substance gene transcription in Sertoli cells

Secretion of Müllerian inhibiting substance by fetal Sertoli cells is essential for normal male sex differentiation since it induces regression of the Müllerian ducts in the developing male embryo. Proper spatiotemporal expression of the MIS gene requires a specific combination of transcription factors, including the zinc finger factor GATA-4 and the nuclear receptor steroidogenic factor-1, which both colocalize with Müllerian inhibiting substance in Sertoli cells. To establish the molecular mechanisms through which GATA-4 contributes to MIS transcription, we have generated and characterized novel GATA-4 dominant negative competitors. The first one, which consisted solely of the GATA-4 zinc finger DNA-binding domain, was an efficient competitor of GATA transcription mediated both by direct GATA binding to DNA and protein-protein interactions involving GATA factors. The second type of competitor consisted of the same GATA-4 zinc finger DNA-binding domain but harboring mutations that prevented DNA binding. This second class of competitors repressed GATA-dependent transactivation by specifically competing for GATA protein-protein interactions without affecting the DNA-binding activity of endogenous GATA factors. These competitors, along with the GATA-4 cofactor FOG-2 (friend of GATA-2), were used to specifically modulate endogenous GATA-4 activity in Sertoli cells. Our results indicate that GATA-4 contributes to MIS promoter activity through two distinct mechanisms. Moreover, the GATA competitors described here should provide invaluable in vitro and in vivo tools for the study of GATA- dependent transcription and the identification of new target genes.

Differential activation of intestinal gene promoters: functional interactions between GATA-5 and HNF-1 alpha

The effects of GATA-4, -5, and -6, hepatocyte nuclear factor-1 alpha (HNF-1 alpha) and -beta, and Cdx-2 on the rat and human lactase-phlorizin hydrolase (LPH) and human sucrase-isomaltase (SI) promoters were studied using transient cotransfection assays in Caco-2 cells. GATA factors and HNF-1 alpha were strong activators of the LPH promoters, whereas HNF-1 alpha and Cdx-2 were strong activators of the SI promoter, although GATA factors were also necessary for maximal activation of the SI gene. Cotransfection of GATA-5 and HNF-1 alpha together resulted in a higher activation of all three promoters than the sum of the activation by either factor alone, demonstrating functional cooperativity. In the human LPH promoter, an intact HNF-1 binding site was required for functional synergy. This study is the first to demonstrate 1) differential activation of the LPH and SI promoters by multiple transcription factors cotransfected singly and in combination and 2) that GATA and HNF-1 transcription factors cooperatively activate intestinal gene promoters. Synergistic activation is a mechanism by which higher levels of tissue-specific expression might be attained by overlapping expression of specific transcription factors.

Function of GATA transcription factors in induction of endothelial vascular cell adhesion molecule-1 by tumor necrosis factor-alpha

Endothelial vascular cell adhesion molecule-1 (VCAM-1) is expressed in response to cytokine stimulation and plays a critical role in inflammatory reactions. Previously, we developed a novel VCAM-1 inhibitor that acts through a mechanism independent of nuclear factor-kappaB activity. It suppresses the binding activity of GATA proteins in cytokine-stimulated endothelial cells, which may be related to the anti-VCAM-1 induction effect of this drug. In this study, we investigated the role of GATA proteins in the induction of VCAM-1 by tumor necrosis factor-alpha (TNF-alpha) in human endothelial cells. The mRNA expression of GATA-6 was increased, whereas GATA-3 mRNA was decreased by TNF-alpha stimulation. Electrophoretic mobility shift assay showed that TNF-alpha stimulation increased the DNA binding of GATA-6 but decreased that of GATA-3. Experiments using protein overexpression or antisense oligonucleotides revealed that GATA-6 potently acts as a positive regulator of VCAM-1 gene transcription. In contrast, overexpression of GATA-3 was able to suppress TNF-alpha-induced VCAM-1 expression. Our results provide evidence of the importance of GATA proteins in the induction of VCAM-1 by TNF-alpha in vascular endothelial cells. The switch from GATA-3 to GATA-6 is taken to be an important transcriptional control event in TNF-alpha induction of VCAM-1.

Role of the multifunctional CDP/Cut/Cux homeodomain transcription factor in regulating differentiation, cell growth and development

CDP/Cux/Cut proteins are an evolutionarily conserved family of proteins containing several DNA binding domains: one Cut homeodomain and one, two or three Cut repeats. In Drosophila melanogaster, genetic studies indicated that Cut functions as a determinant of cell-type specification in several tissues, notably in the peripheral nervous system, the wing margin and the Malpighian tubule. Moreover, Cut was found to be a target and an effector of the Notch signaling pathway. In vertebrates, the same functions appear to be fulfilled by two cut-related genes with distinct patterns of expression. Cloning of the cDNA for the CCAAT-displacement protein (CDP) revealed that it was the human homologue of Drosophila Cut. CDP was later found be the DNA binding protein of the previously characterized histone nuclear factor D (HiNF-D). CDP and its mouse counterpart, Cux, were also reported to interact with regulatory elements from a large number of genes, including matrix attachment regions (MARs). CDP/Cut proteins were found generally to function as transcriptional repressors, although a participation in transcriptional activation is suggested by some data. Repression by CDP/Cut involves competition for binding site occupancy and active repression via the recruitment of a histone deacetylase activity. Various combinations of Cut repeats and the Cut homeodomains can generate distinct DNA binding activities. These activities are elevated in proliferating cells and decrease during terminal differentiation. One activity, involving the Cut homeodomain, is upregulated in S phase. CDP/Cut function is regulated by several post-translational modification events including phosphorylation, dephosphorylation, and acetylation. The CUTL1 gene in human was mapped to 7q22, a chromosomal region that is frequently rearranged in various cancers.

Characterization of the bi-directional transcriptional control region between the human UFD1L and CDC45L genes

The human UFD1L and CDC45L genes, adjacently located in the head-to-head direction on chromosome 22q11, are separated by a 884 base-pair (bp) segment constituting the putative transcriptional control region. In this region we mapped one transcription start site at 69 bp upstream of UFD1L gene, and one major and one minor start sites at 76 bp and 503 bp upstream of CDC45L gene, which are to center in the putative core promoters designated as P(UFD1L), P(CDC45L/major), and P(CDC45L/minor), respectively. The three core promoters lacked a TATA-motif and had a high GC-content. To determine the approximate ranges for the regulatory promoters, the 884-bp fragment or those with a series of deletions were placed between firefly and renilla luciferase genes present in the head-to-head direction in a single plasmid, and the resulting plasmids were assayed for the two transiently induced enzyme activities. The P(UFD1L) and P(CDC45L/major) regulatory promoters were within 418 and 454 bp upstream of the respective start sites and their greater parts were not overlapping. The activity of P(CDC45L/minor) regulatory promoter was markedly enhanced when P(CDC45L/major) and its regulatory promoter were deleted. The deletion analyses revealed the basal activities of the three core promoters, which were enhanced by approximately twofold by the respective regulatory promoters, on the transfected DNA templates.

Transcriptional Control of T Lymphocyte Differentiation

Initiation of gene transcription by transcription factors (TFs) is an important regulatory step in many developmental processes. The differentiation of T cell progenitors in the thymus is tightly controlled by signaling molecules, ultimately activating nuclear TFs that regulate the expression of T lineage-specific genes. During the last 2 years, significant progress has been made in our understanding of the signaling routes and TFs operating during the earliest stages of thymic differentiation at the CD4(-)CD8(-) double negative stage. Here we will review the TF families that play an important role in differentiation of thymocytes, particularly focusing on recent new information with respect to the Tcf, bHLH, GATA, and CBF/HES TF families.

GATA factors differentially activate multiple gonadal promoters through conserved GATA regulatory elements

The GATA factors are a group of transcriptional regulators that play essential roles in cell differentiation, organ morphogenesis, and tissue-specific gene expression during development. The six vertebrate GATA factors are expressed in a broad spectrum of tissues, including the hemopoietic system, heart, gut, brain, placenta, pituitary, and gonads. Interestingly, GATA-like DNA-binding proteins are found in the gonads of several species, ranging from lower invertebrates to humans, thus supporting an evolutionary conserved and crucial role for these factors in gonadal development and function. Indeed, GATA factors are expressed from the onset of gonadal development and are later found in multiple cell lineages of both the testis and ovary. We now report that GATA-4 differentially activates transcription of several genes expressed in the gonads that encode either steroidogenic enzymes (steroidogenic acute regulatory protein and aromatase), hormones (inhibin alpha and Müllerian inhibiting substance) and a transcription factor (SF-1) known to be essential for gonadal development and function. Thus, our results identify GATA-4 as an important regulator of gonadal gene transcription where its specificity of action is mediated through synergistic interactions with other transcription factors such as SF-1.

Enhancer regions of ovine interferon-tau gene that confer PMA response or cell type specific transcription

Interferon-tau (IFNtau), produced by the trophectoderm of peri-implantation conceptuses in ruminant ungulates, attenuates the uterine production of a luteolytic factor, prostaglandin F(2alpha), resulting in the maintenance of corpus luteum function. However, molecular mechanisms regulating the temporal/spatial expression of IFNtau gene are not clearly understood. The 5'-upstream region of the sheep IFNtau (oIFNtau) gene was examined for its transcriptional regulation in two different cell types; JEG3 cells supported the transactivation of oIFNtau-reporter construct, but HeLa cells did not. In a heterologous SV40 enhancer-oIFNtau promoter or oIFNtau enhancer-SV40 promoter systems, elements required for such cell specific transactivation were localized between -654 and -555 bases, the enhancer, but not the basal promoter region of the oIFNtau gene. In these combinations, high degrees of transactivation were observed in JEG3 cells and the activity was further enhanced by the addition of phorbol 12-myristate 13-acetate (PMA), while those responses were absent in HeLa cells. To identify nucleotide sequences responsible for cell specific expression, transient transfection studies with sequential point mutations in the enhancer elements were executed. Transactivation of oIFNtau enhancer-reporter constructs was primarily regulated by three regions containing AP-1 site, GATA like sequence and site(s) unidentified. In gel mobility shift assays (GMSAs), the AP-1 site located in the enhancer region was recognized by nuclear extracts from both cell types. However, one of the GMSA probes containing GATA-like sequence exhibited different DNA-protein complex patterns in JEG3 and HeLa cells. Observations, in which the same upstream sequence behaved differently due possibly to kinds of nuclear factors available in these cell lines, suggest that such a sequence may be involved in cell specific transactivation of the oIFNtau gene. Furthermore, the same enhancer sequences were also recognized by nuclear extracts from sheep trophoblasts, suggesting that the enhancer sequences between -654 and -555 bases of oIFNtau gene may be functioning in vivo.

Hairless is translocated to the nucleus via a novel bipartite nuclear localization signal and is associated with the nuclear matrix

Hair follicle cycling is an exquisitely regulated and dynamic process consisting of phases of growth, regression and quiescence. The transitions between the phases are governed by a growing number of regulatory proteins, including transcription factors. The hairless (hr) gene encodes a putative transcription factor that is highly expressed in the skin, where it appears to be an essential regulator during the regression of the catagen hair follicle. In hairless mice, as well as humans with congenital atrichia, the absence of hr gene function initiates a premature and abnormal catagen due to a dysregulation of apoptosis and cell adhesion, and defects in the signaling required for hair follicle remodeling. Here, we report structure-function studies of the hairless gene product, in which we identify a novel bipartite nuclear localization signal (NLS) of the form KRA(X13) PKR. Deletion analysis of the mouse hr gene mapped the NLS to amino acid residues 409–427. Indirect immunofluorescence microscopy of cells transiently transfected with hairless-green fluorescent fusion proteins demonstrated that these amino acid residues are necessary and sufficient for nuclear localization. Furthermore, nuclear fractionation analysis revealed that the hr protein is associated with components of the nuclear matrix.

GATA family transcription factors activate lactase gene promoter in intestinal Caco-2 cells

The GATA family of transcription factors regulate tissue-specific patterns of gene expression during development. We have characterized the interaction between GATA proteins and the lactase gene promoter. Nuclear protein bound to the lactase gene GATA region cis element (-97 to -73) was analyzed by electrophoretic mobility shift assays (EMSA) and supershift assays with GATA antibodies. Lactase promoter activities were assayed in Caco-2 cells transfected with wild-type and mutated luciferase promoter-reporter constructs and GATA-4/5/6 expression constructs. EMSA with the GATA region probe yields a specific DNA-protein complex that requires the GATA factor binding site WGATAR. The complex is recognized by GATA-4- and GATA-6-specific antibodies. GATA-4/5/6 expression constructs are able to activate transcription driven by the wild-type promoter, but not by a promoter in which the GATA binding site is mutated, in Caco-2 and nonintestinal QT6 cells. GATA factor binding to the lactase cis element correlates with functional promoter activation. We conclude that each of the GATA family zinc finger proteins expressed in the intestine, GATA-4, -5, and -6, can interact with the lactase promoter GATA element and can function to activate the promoter in Caco-2 cells.

A GATA-dependent right ventricular enhancer controls dHAND transcription in the developing heart

Heart formation in vertebrates is believed to occur in a segmental fashion, with discreet populations of cardiac progenitors giving rise to different chambers of the heart. However, the mechanisms involved in specification of different chamber lineages are unclear. The basic helix-loop-helix transcription factor dHAND is expressed in cardiac precursors throughout the cardiac crescent and the linear heart tube, before becoming restricted to the right ventricular chamber at the onset of looping morphogenesis. dHAND is also expressed in the branchial arch neural crest, which contributes to craniofacial structures and the aortic arch arteries. Using a series of dHAND-lacZ reporter genes in transgenic mice, we show that cardiac and neural crest expression of dHAND are controlled by separate upstream enhancers and we describe a composite cardiac-specific enhancer that directs lacZ expression in a pattern that mimics that of the endogenous dHAND gene throughout heart development. Deletion analysis reduced this enhancer to a 1.5 kb region and identified subregions responsible for expression in the right ventricle and cardiac outflow tract. Comparison of mouse regulatory elements required for right ventricular expression to the human dHAND upstream sequence revealed two conserved consensus sites for binding of GATA transcription factors. Mutation of these sites abolished transgene expression in the right ventricle, identifying dHAND as a direct transcriptional target of GATA factors during right ventricle development. Since GATA factors are not chamber-restricted, these findings suggest the existence of positive and/or negative coregulators that cooperate with GATA factors to control right ventricular-specific gene expression in the developing heart.