GATAAG; a cis-control region binding an erythroid-specific nuclear factor with a role in globin and non-globin gene expression

X-linked sideroblastic anemia due to ALAS2 intron 1 enhancer element GATA-binding site mutations

X-linked sideroblastic anemia (XLSA) is the most common form of congenital sideroblastic anemia. In affected males, it is uniformly associated with partial loss-of-function missense mutations in the erythroid-specific heme biosynthesis protein 5-aminolevulinate synthase 2 (ALAS2). Here, we report five families with XLSA owing to mutations in a GATA transcription factor binding site located in a transcriptional enhancer element in intron 1 of the ALAS2 gene. As such, this study defines a new class of mutations that should be evaluated in patients undergoing genetic testing for a suspected diagnosis of XLSA.

Direct and indirect gene regulation by a life-extending FOXO protein in C. elegans: roles for GATA factors and lipid gene regulators

In long-lived C. elegans insulin/IGF-1 pathway mutants, the life-extending FOXO transcription factor DAF-16 is present throughout the animal, but we find that its activity in a single tissue can delay the aging of other tissues and extend the animal's life span. To better understand the topography of DAF-16 action among the tissues, we analyzed a collection of DAF-16-regulated genes. DAF-16 regulated most of these genes in a cell-autonomous fashion, often using tissue-specific GATA factors to direct their expression to specific tissues. DAF-16 could also act cell nonautonomously to influence gene expression. DAF-16 affected gene expression in other cells, at least in part, via the lipid-gene regulator MDT-15. DAF-16, and probably MDT-15, could act cell nonautonomously in the endoderm to ameliorate the paralysis caused by expressing Alzheimer's Aβ protein in muscles. These findings suggest that MDT-15-dependent intercellular signals, possibly lipid signals, can help to coordinate tissue physiology, enhance proteostasis, and extend life in response to DAF-16/FOXO activity.

Experimental validation of predicted mammalian erythroid cis-regulatory modules

Multiple alignments of genome sequences are helpful guides to functional analysis, but predicting cis-regulatory modules (CRMs) accurately from such alignments remains an elusive goal. We predict CRMs for mammalian genes expressed in red blood cells by combining two properties gleaned from aligned, noncoding genome sequences: a positive regulatory potential (RP) score, which detects similarity to patterns in alignments distinctive for regulatory regions, and conservation of a binding site motif for the essential erythroid transcription factor GATA-1. Within eight target loci, we tested 75 noncoding segments by reporter gene assays in transiently transfected human K562 cells and/or after site-directed integration into murine erythroleukemia cells. Segments with a high RP score and a conserved exact match to the binding site consensus are validated at a good rate (50%-100%, with rates increasing at higher RP), whereas segments with lower RP scores or nonconsensus binding motifs tend to be inactive. Active DNA segments were shown to be occupied by GATA-1 protein by chromatin immunoprecipitation, whereas sites predicted to be inactive were not occupied. We verify four previously known erythroid CRMs and identify 28 novel ones. Thus, high RP in combination with another feature of a CRM, such as a conserved transcription factor binding site, is a good predictor of functional CRMs. Genome-wide predictions based on RP and a large set of well-defined transcription factor binding sites are available through servers at http://www.bx.psu.edu/.

Differential effects of GATA-1 on proliferation and differentiation of erythroid lineage cells

The zinc finger transcription factor GATA-1 is essential for both primitive (embryonic) and definitive (adult) erythropoiesis. To define the roles of GATA-1 in the production and differentiation of primitive and definitive erythrocytes, we established GATA-1-null embryonic stem cell lines in which GATA-1 was able to be conditionally expressed by using the tetracycline conditional gene expression system. The cells were subjected to hematopoietic differentiation by coculturing on OP9 stroma cells. We expressed GATA-1 in the course of primitive and definitive erythropoiesis and analyzed the ability of GATA-1 to rescue the defective erythropoiesis caused by the GATA-1 null mutation. Our results show that GATA-1 functions in the proliferation and maturation of erythrocytes in a distinctive manner. The early-stage expression of GATA-1 during both primitive and definitive erythropoiesis was sufficient to promote the proliferation of red blood cells. In contrast, the late-stage expression of GATA-1 was indispensable to the terminal differentiation of primitive and definitive erythrocytes. Thus, GATA-1 affects the proliferation and differentiation of erythrocytes by different mechanisms.

GATA-1: friends, brothers, and coworkers

GATA-1 is the founding member of the GATA family of transcription factors. GATA-1 and GATA family member GATA-2 are expressed in erythroid and megakaryocytic lineages, in which they play a crucial role in cell maturation and differentiation. GATA-1 regulates the transcription of many specific and nonspecific erythroid genes by binding to DNA at the consensus sequence WGATAR, which is recognized by all of the GATA family of transcription factors. However, it was identified in eosinophilic cells and also in Sertoli cells in testis. Its activity depends on close cooperation with a functional network of cofactors, among them Friend of GATA, PU.1, and CBP/p300. The GATA-1 protein structure has been well described and includes two zinc fingers that are directly involved in the interaction with DNA and other proteins in vivo. GATA-1 mutations in the zinc fingers can cause deregulation of required interactions and lead to severe dysfunction in the hematopoietic system.

Association between angiotensin II type 1 receptor gene polymorphism and essential hypertension: the Ohasama Study

Gene targeting approaches have suggested that the angiotensin II type 1 receptor (AT1R) is involved in blood pressure (BP) regulation and modulation of the effect of angiotensin II. The A1166C polymorphism of the AT1 receptor gene (AT1R/A1166C) is associated with hypertension in Caucasians, but not in Japanese. The goal of this study, the Ohasama Study, was to examine the association between AT1R/A1166C and hypertension, especially home BP, in the Japanese general population. The Ohasama Study was a cohort study based on Japanese rural residents of Ohasama Town in the northern part of Japan. Subjects who gave informed consent to the study protocol and genetic analysis were recruited. Home BP was measured twice in the morning within 1 h of waking up and in the evening just before going to bed. The TaqMan polimerase chain reaction (PCR) method clearly determined AT1R/A1166C genotypes (n =1,207). The genotype distribution of AT1R/A1166C was as follows: AA 84%; AC 15%; CC 1%. There was almost no difference in baseline characteristics among the AT1R genotypes (AA, AC, CC). In the subjects not receiving antihypertensive medication (n =817), both casual BP and home BP were not different among the AT1R genotypes after adjusting for confounding factors (age, sex, body mass index, current smoking habit and current alcohol consumption). The frequency of hypertension showed no difference among AT1R genotypes after adjusting for confounding factors, though the AC and CC genotypes were more frequent in hypertensives than in normotensives. Our data suggested that the AT1R/A1166C polymorphism is not a major genetic predisposing factor for hypertension in Japanese.

F2-Isoprostane level is associated with the angiotensin II type 1 receptor -153A/G gene polymorphism

Recent studies have shown that F2-isoprostane levels-a marker for lipid peroxidation-are increased in human renovascular hypertension but not in essential hypertension. Angiotensin II specifically stimulates F2-isoprostane production through activation of the AT1 receptor. The objective was to determine whether there is a relationship between the level of oxidative stress evaluated by measuring urinary F2-isoprostanes levels and polymorphisms of genes involved in the renine angiotensin aldosterone system (RAAS) regulation. The population studied included 100 subjects, 65 of whom were healthy normotensives; the other 35 were suffering from untreated, essential hypertension. The polymorphisms studied concern the genes encoding angiotensin I-converting enzyme (ACE/in16del/ins), angiotensin II receptor type I (AGTR1/A+39C[A+1166C] and AGTR1/A-153G), angiotensinogen (AGT/M235T), and aldosterone synthase (CYP11B2/T344C). Oxidative stress was evaluated by measuring urinary F2-isoprostanes levels. The characteristics of the population were as follows: men/women = 46/56; age = 50 +/- 10 years; BMI = 24 +/- 3 kg/m2; SBP = 131.7 +/- 17.2 mm Hg; DBP = 84.6 +/- 10.4 mm Hg. In univariate analysis, urinary F2-isoprostane levels were significantly lower in the presence of the G allele of AGTR1/A-153G (56 +/- 17 vs 76 +/- 39 pmol/mmol creatinine; P < 0.001, and P < 0.01 after Bonferroni correction for 10 tests). In multivariate analysis, taking into account BP, age, gender, BMI, plasma glucose, and total cholesterol, the G allele of AGTR1/A-153G is linked independently to urinary F2-isoprostanes level (P < 0.01). Our data suggest that F2-isoprostane level depends at least in part on the A-153G polymorphism of the angiotensin II AT1 receptor gene. The clinical and prognostic relevance of this polymorphism requires further investigation.

GATA-1 and NF-Y cooperate to mediate erythroid-specific transcription of Gfi-1B gene

Expression of Gfi (growth factor-independence)-1B, a Gfi-1-related transcriptional repressor, is restricted to erythroid lineage cells and is essential for erythropoiesis. We have determined the transcription start site of the human Gfi-1B gene and located its first non-coding exon approximately 7.82 kb upstream of the first coding exon. The genomic sequence preceding this first non-coding exon has been identified to be its erythroid-specific promoter region in K562 cells. Using gel-shift and chromatin immunoprecipitation (ChIP) assays, we have demonstrated that NF-Y and GATA-1 directly participate in transcriptional activation of the Gfi-1B gene in K562 cells. Ectopic expression of GATA-1 markedly stimulates the activity of the Gfi-1B promoter in a non-erythroid cell line U937. Interestingly, our results have indicated that this GATA-1-mediated trans-activation is dependent on NF-Y binding to the CCAAT site. Here we conclude that functional cooperation between GATA-1 and NF-Y contributes to erythroid-specific transcriptional activation of Gfi-1B promoter.

Renin-angiotensin system polymorphisms in Taiwanese primary vesicoureteral reflux

We studied the angiotensin-converting enzyme (ACE), angiotensinogen (AGT), and angiotensin II type 1 receptor (AT1R) gene polymorphisms for association with susceptibility to primary vesicoureteral reflux (VUR) and disease progression in 74 Taiwanese children, including 16 with end-stage renal disease (ESRD), and 117 normal controls. Polymerase chain reaction-amplified products containing the ACE gene T-5491C, A-5466C, T-3892C, A-3692C, A-240T, Alu I/D, the AGT gene C-532T, G-217A, G-152A, A-20C, A-6G, T174M, T235M, and the AT1R gene A-1138T, T-810A, T-713G, C-521T, AG-214CC, A-153G, A1166C polymorphisms were analyzed by restriction enzyme digestion, gel electrophoresis, or single-strand conformation polymorphism analysis. All the polymorphisms examined were in Hardy-Weinberg equilibrium. The strong non-random association within the ACE, AGT, and AT1R genes suggests low levels of intragenic recombination. None of these polymorphisms showed association with VUR susceptibility. However, the allele frequency distribution of the six ACE polymorphisms among primary VUR patients with or without ESRD was statistically different. The linked ACE T-A-T-A-A-I allele was observed significantly more frequently in VUR children with ESRD (P<0.001). A significant increase of left ventricular mass index was also found in the linked ACE T-A-T-A-A-I allele group compared with the non-ACE T-A-T-A-A-I allele group of patients aged 18 years with renal progression. The AGT A-6G genotype frequencies were significantly different when the analysis was stratified by genotype of the ACE polymorphisms. The data showed that ACE gene polymorphisms were associated with progressive renal deterioration in Taiwanese children with VUR and might act synergistically with the -6 G allele of the AGT gene.

FLI-1 is a suppressor of erythroid differentiation in human hematopoietic cells

The FLI-1 oncogene, a member of the ETS family of transcription factors, is associated with both normal and abnormal hematopoietic cell growth and lineage-specific differentiation. We have previously shown that overexpression of FLI-1 in pluripotent human hematopoietic cells leads to the induction of a megakaryocytic phenotype. In this report we show that FLI-1 also acts as an inhibitor of erythroid differentiation. Following the induction of erythroid differentiation, pluripotent cells express reduced levels of FLI-1. In contrast, when FLI-1 is overexpressed in these cells, the levels of erythroid markers are reduced. The ability of FLI-1 overexpressing cells to respond to erythroid-specific inducers such as hemin and Ara-C is also inhibited, and the uninduced cells show a reduced level of the erythroid-associated GATA-1 transcription factor mRNA. Furthermore, expression of a GATA-1 promoter-driven reporter construct in K562 cells is inhibited by co-transfection with a construct expressing FLI-1. Our results support the hypothesis that FLI-1 can act both positively and negatively in the regulation of hematopoietic cell differentiation, and that inhibition of GATA-1 expression may contribute to FLI-1-mediated inhibition of erythroid differentiation.

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

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

Factor binding to the human gamma-globin gene distal CCAAT site: candidates for repression of the normal gene or activation of HPFH mutants

We have examined factor binding to the distal human gamma-globin CCAAT site and three naturally occurring hereditary persistence of fetal haemoglobin (HPFH) mutations of this site. Factor binding was examined using nuclear extracts from the erythroleukaemic cell lines K562 and MEL, and from A4 cells, a non-transformed mouse bone marrow stem cell line, using the electrophoretic mobility shift assay. Under standard binding conditions, in addition to the previously reported binding by a CCAAT factor (CP1) and GATA-1, the wild-type (wt) sequence bound high mobility factors which appeared to be GATA-2 isoforms. However, when the non-specific competitor conditions were varied, the binding profile with K562, but not MEL nuclear extract, was substantially altered. CP1 and GATA-1 were absent, and two new factors were detected, one of which bound preferentially to the Greek and Japanese non-deletion HPFH mutants. However, binding by the GATA-2 isoforms to the wt sequence was maintained with both cell types, as it was using the A4 cell line. With modified binding conditions, in A4 cells the two non-deletion and the Black deletion HPFH mutants each had a different protein binding profile which was lost on erythroid induction of the cells. We discuss the possibility that the GATA-2 isoforms bound to the wt sequence may function to suppress wt gamma gene expression in the bone marrow. Additionally, those factors which bind preferentially either to the deletion or non-deletion HPFH mutants may play positive roles in establishing an active chromatin structure.

Molecular regulation of insulin-like growth factor-I and its principal binding protein, IGFBP-3

The insulin-like growth factors (IGFs) have diverse anabolic cellular functions, and structure similar to that of proinsulin. The distribution of IGFs and their receptors in a wide variety of organs and tissues enables the IGFs to exert endocrine, paracrine, and autocrine effects on cell proliferation and differentiation, caloric storage, and skeletal elongation. IGF-I exhibits particular metabolic responsiveness, and circulating IGF-I originates predominantly in the liver. Hepatic IGF-I production is controlled at the level of gene transcription, and transcripts are initiated largely in exon 1. Hepatic IGF-I gene transcription is reduced in conditions of protein malnutrition and diabetes mellitus, and our laboratory has used in vitro transcription to study mechanisms related to diabetes. We find that the presence of sequences downstream from the major transcription initiation sites in exon 1 is necessary for the diabetes-induced decrease in IGF-I transcription. Six nuclear factor binding sites have been identified within the exon 1 downstream region, and footprint sites III and V appear to be necessary for metabolic regulation; region V probes exhibit a decrease in nuclear factor binding with hepatic nuclear extracts from diabetic animals. IGFs in biological fluids are associated with IGF binding proteins, and IGFs circulate as a 150-kDa complex that consists of an IGF, an IGFBP-3, and an acid-labile subunit. Circulating IGFBP-3 originates mainly in hepatic nonparenchymal cells, where IGF-I increases IGFBP-3 mRNA stability, but insulin increases IGFBP-3 gene transcription. Regulation of IGFBP-3 gene transcription by insulin appears to be mediated by an insulin-responsive element, which recognizes insulin-responsive nuclear factors in both gel mobility shift assays and southwestern blots. Studies of mechanisms underlying the modulation of IGF-I and IGFBP-3 gene transcription, and identification of critical nuclear proteins involved, should lead to new understanding of the role and regulation of these important growth factors in diabetes mellitus and other metabolic disorders.

Transcriptional activity of pannier is regulated negatively by heterodimerization of the GATA DNA-binding domain with a cofactor encoded by the u-shaped gene of Drosophila

The genes pannier (pnr) and u-shaped (ush) are required for the regulation of achaete-scute during establishment of the bristle pattern in Drosophila. pnr encodes a protein belonging to the GATA family of transcription factors, whereas ush encodes a novel zinc finger protein. Genetic interactions between dominant pnr mutants bearing lesions situated in the amino-terminal zinc finger of the GATA domain and ush mutants have been described. We show here that both wild-type Pannier and the dominant mutant form activate transcription from the heterologous alpha globin promoter when transfected into chicken embryonic fibroblasts. Furthermore, Pnr and Ush are found to heterodimerize through the amino-terminal zinc finger of Pnr and when associated with Ush, the transcriptional activity of Pnr is lost. In contrast, the mutant pnr protein with lesions in this finger associates only poorly with Ush and activates transcription even when cotransfected with Ush. These interactions have been investigated in vivo by overexpression of the mutant and wild-type proteins. The results suggest an antagonistic effect of Ush on Pnr function and reveal a new mode of regulation of GATA factors during development.

Involvement of the transcriptional factor GATA-1 in regulation of expression of coproporphyrinogen oxidase in mouse erythroleukemia cells

Coproporphyrinogen oxidase (CPO; EC 1.3.3.3), the sixth enzyme of heme biosynthesis, transcribed from a single promoter is markedly induced during erythroid differentiation. CPO is ubiquitously expressed in all cells. To determine cis-acting elements of the human CPO gene, the promoter region of the gene was isolated, and three potential GATA-1 motifs and four GC boxes were found within this fragment. In a functional analysis of various deletion mutants, we found that the GATA-1 binding site at -143 to -138 was essential for basic and inducible expressions of the CPO gene in mouse erythroleukemia (MEL) cells. Gel mobility shift assay revealed that GATA-1 bound to the region is required for the expression and this was confirmed by observations that the nuclear protein bound to the GATA-1 motif was supershifted with anti GATA-1 antibody, by gel mobility shift assay. Furthermore, co-expression of mouse GATA-1 in MEL cells led to an increase in the promoter activity, which was markedly increased by dimethyl sulfoxide-treatment. These results indicate that GATA-1 plays an important role in regulation of transcription of the CPO gene in erythroid cells.

Over-expression of GATA-6 in Xenopus embryos blocks differentiation of heart precursors

Xenopus GATA-6 transcripts are first detected at the beginning of gastrulation in the mesoderm, and subsequent domains of expression include the field of cells shown to have heart-forming potential. In this region, GATA-6 expression continues only in those cells that go on to form the heart; however, a decrease occurs prior to terminal differentiation. Artificial elevation of GATA-6, but not GATA-1, prevents expression of both cardiac actin and heart-specific myosin light chain. This effect is heart-specific because cardiac actin expression is unaffected in somites. Expression of the earlier marker XNkx-2.5 was unaffected and morphological development of the heart was initiated independently of the establishment of the contractile machinery. We conclude that a reduction in the level of GATA-6 is important for the progression of the cardiomyogenic differentiation programme and that GATA-6 may act to maintain heart cells in the precursor state. At later stages, when the elevated GATA-6 levels had decayed, differentiation ensued but the number of cells contributing to the myocardium had increased, suggesting either that the blocked cells had proliferated or that additional cells had been recruited.

Oxidative stress is involved in the UV activation of p53

In many vertebrate cells exposure to ultraviolet light lead to a dramatic increase in the cellular levels of the tumour suppressor protein p53, followed by a biological response of either growth arrest or programmed cell death. Ultraviolet light can be absorbed directly by cellular macromolecules, leading to photochemical modification of DNA and proteins. Additionally, it also causes free radical formation, resulting in oxidative stress. Whereas ultraviolet light and ionizing radiation both induce DNA lesions which trigger an activation of the p53 pathway, the magnitude of the p53 response elicited by ionizing radiation is comparatively low. Following irradiation with ultraviolet light two populations of p53-reactive cells are induced: a population accumulating high levels of p53 protein and a population with comparatively low levels of p53, similar in magnitude to the p53 response following ionizing radiation. Pretreatment of cells with N-acetylcysteine, an agent known to counteract oxidative stress, attenuates the cellular p53 response to ultraviolet light by reducing the number of cells with high p53 levels but does not affect the response to ionizing radiation. We demonstrate that N-acetylcysteine pretreatment does not prevent the inflicted DNA damage and therefore conclude that oxidative stress is a causative agent in the ultraviolet light activation of the p53 pathway.

Cell-type-specific expression of the platelet-derived growth factor alpha receptor: a role for GATA-binding protein

Platelet-derived growth factor alpha receptor (PDGF alpha R) is a transmembrane tyrosine kinase receptor for all three existing PDGF isoforms, AA, AB, and BB. Transcripts of PDGF alpha R are detected as early as in fertilized mouse eggs and throughout adulthood in a time- and space-specific manner, thereby suggesting an important role of PDGFs in mammalian development. In this study, we have investigated the mechanism involved in cell-type-specific PDGF alpha R gene expression during early embryonic development. Using F9 embryonic carcinoma cells as an in vitro study model, we identified a differentiation-dependent enhancer element within the PDGF alpha R promoter that controlled receptor expression during parietal endoderm cell differentiation induced by retinoic acid and dibutyryl cyclic AMP treatment. The differentiation-dependent enhancer element sequence bore no resemblance to consensus DNA-binding sites of either the retinoic acid receptor family or the cyclic AMP-responsive element-binding protein family. It was composed of two identical 12-bp direct repeats separated by a 17-bp insert sequence enriched in C and A nucleotides. Although only a single repeat was needed to form specific DNA-protein complexes with factors present in F9 parietal endoderm cell extracts, both repeats together were necessary to display cell-type-specific enhancing activity. Mutational analysis revealed that the protein-binding sites within the repeat sequences were identical to GATA-binding sites. In this study, we provided evidence to suggest that a member of the GATA transcription factor family (GATA-4) is responsible for parietal endoderm-specific PDGF alpha R expression.

Zinc fingers 1-7 of EVI1 fail to bind to the GATA motif by itself but require the core site GACAAGATA for binding

EVI1 is a zinc finger oncoprotein that binds via fingers 1-7 to the sequence GACAAGATAA. The target genes on which EVI1 acts are unknown. This binding motif overlaps with that for the GATA transcription factors, (T/A)GATA(A/G), and GATA-1 can bind to and activate transcription via a GACAAGATAA motif. The possibility has been raised that, when overexpressed in leukemogenesis, EVI1 may function by interfering with the differentiation-promoting action of GATA factors. To explore this, we have assessed the affinity of EVI1 for the GATA binding sites derived from erythroid-specific GATA-1 target genes, and found only low affinity interactions. We examined the contacts between EVI1 and DNA by methylation interference studies, which revealed extensive contacts between EVI1 and its binding site. The importance of the contacts for high affinity binding was shown by in vitro quantitative gel shift studies and in vivo cotransfection studies. To examine what types of sequences from mouse genomic DNA bind to EVI1, we isolated and sequenced five EVI1-binding fragments, and each showed the GACAAGATA site. The data presented contribute to our knowledge of the binding specificity of EVI1, and yield a clearer picture of what sequences can, and cannot, act as targets for EVI1 action.

Molecular analysis of Evi1, a zinc finger oncogene involved in myeloid leukemia

Through chromosomal rearrangements and/or proviral insertions, a number of genes encoding nuclear transcription factors have been identified that play key roles in leukemogenesis. One of these is Evi1, which plays a role in both murine and human myeloid leukemia. The exact mechanism by which Evi1 exerts its leukemogenic effect is not clear, but it may involve the inhibition of terminal differentiation, through the abnormal repression of genes necessary for cellular maturation. Our analysis of the DNA binding characteristics of EVI1 indicate a high degree of specificity, which likely indicates that the protein acts on a tightly defined number of targets in the cell. We are beginning to characterize candidate target genes located in the mouse genome near EVI1 binding sites with the expectation that these will yield insight into EVI1 function both in normal cells and in leukemogenesis.

Structural and functional analysis of the promoter of the murine V gamma 1.1 T cell receptor gene

The expression of the germ-line gene V gamma 1.1-C gamma 4 of the T cell receptor (TcR) gamma chain depends on interleukin (IL)-3 induction in hematopoietic cells, while in T cells, the rearranged gene is expressed constitutively. To understand the mechanism that controls TcR gamma gene expression, we cloned and characterized the structure and function of the V gamma 1.1-C gamma 4 TcR promoter. IL-3-dependent cell lines and T cell lines utilized the same transcriptional start sites. In chloramphenicol acetyltransferase (CAT) assays, the minimal 70-bp promoter confers strong transcriptional activity which is 50-60% of the Moloney long terminal repeat promoter activity. The 500-bp promoter region linked to the CAT gene exhibits IL-3 dependency similar to the endogenous TcR gamma gene. The immediate 3' and 5' flanking sequences inhibit the promoter activity two- to fourfold. The promoter lacks an obvious TATA box or CAAT box sequences, but contains a GC box in the untranslated region 3' to the promoter. The GC box is the core sequence of the element which binds Sp1-like proteins. Cloning of this Sp1 binding element in front of the thymidine kinase (TK) promoter and mutations generated in this site demonstrate its function as a silencer. Ultraviolet cross-linking analysis with the Sp1 binding site from the TcR gamma promoter revealed binding of a 90-100-kDa protein in a T cell line (EL-4) and 40-50 and 90-100-kDa proteins in FDC-P1 cells. The possible function of the Sp1-like protein in silencing the minimal promoter activity is discussed.

Transcriptional regulation of the rat insulin-like growth factor-I gene involves metabolism-dependent binding of nuclear proteins to a downstream region

Insulin-like growth factor-I (IGF-I) gene transcription is mediated largely via exon 1. In an initial search for regulatory regions, rat hepatocytes were transfected with IGF-I constructs. Since omission of downstream sequences led to reduced expression, we then used in vitro transcription to evaluate potential metabolic regulation via downstream regions. With templates including 219 base pairs of downstream sequence, transcriptional activity was reduced 70-90% with hepatic nuclear extracts from diabetic versus normal rats. However, activity was comparable with templates lacking downstream sequences. The downstream region contained six DNase I footprints, and templates with deletion of either region III or V no longer provided reduced transcriptional activity with nuclear extracts from diabetic rats. Nuclear protein binding to regions III and V appeared to be metabolically regulated, as shown by reduced DNase I protection and activity in gel mobility shift assays with nuclear extracts from diabetic rats. Southwestern blotting probes corresponding to regions III and V recognized a approximately 65-kDa nuclear factor present at reduced levels in diabetic rats. These findings indicate that a downstream region in exon 1 may be important for both IGF-I expression and metabolic regulation. Altered concentration or activity of a transcription factor(s) binding to this region may contribute to reduced IGF-I gene transcription associated with diabetes mellitus.

Tissue-specific regulation of the rabbit 15-lipoxygenase gene in erythroid cells by a transcriptional silencer

The 15-lipoxygenase (lox) gene is expressed in a tissue-specific manner, predominantly in erythroid cells but also in airway epithelial cells and eosinophils. We demonstrate in this report that the 5' flanking DNA of the 15-lox gene contains sequences which down-regulate its activity in a variety of non-erythroid cell lines but not in two erythroid cell lines. The element has characteristics of a transcriptional 'silencer' since it functions in both orientations. The main activity of the silencer has been mapped to the first 900 bp of 5' flanking DNA, which contains nine binding sites for a nuclear factor present in non-erythroid cells but not in erythroid cells. These binding sites have similar sequences and multiple copies of the binding sites confer tissue-specific down-regulation when attached to a minimal lox promoter fragment. The 5' flanking DNA also contains a cluster of three binding sites for the GATA family of transcription factors.

A new approach to isolate genomic control regions. Application to the GATA transcription factor family

We have designed a new strategy to isolate unknown DNA regions interacting with one or several related regulatory proteins. It involves trapping such DNAs by their cognate binding proteins followed by PCR amplification, as described previously [Kinzler, K. & Vogelstein, B. (1989) Nucleic Acids Res. 17, 3645-3653]. To overcome the inability of such a procedure to discriminate between functional and non-functional binding sites as well as to specifically trap short DNA motifs from the whole higher eukaryotic genome, we have used as starting material DNA isolated from transcriptionally competent chromatin fractions, instead of total genomic DNA. To test our strategy, we selected human DNA sequences that bind members of the GATA family, known to recognize similar WGATAR motifs. These proteins are expressed in different cell types in which they regulate the transcription of different sets of genes; thus, transcriptionally active chromatin containing GATA motifs should differ according to the cell type. We have trapped and analyzed DNA fragments isolated from an active chromatin fraction, from erythroid cells and lymphoid cells, using GATA-1 and GATA-3 proteins, respectively. We show that regulatory GATA sequences known to be in open chromatin in erythroid cells (typified by the HSIII fragment of the beta-globin locus control region) or in lymphoid cells (typified by a fragment of the CD2 locus control region) are dramatically enriched in a cell-specific manner, demonstrating the potency of the method. The sequences of the erythroid or lymphoid DNA fragments isolated through the procedure described here were determined and display subset-site preference for GATA-1 and GATA-3.

Nuclear proteins that interact with the beta maj globin promoter start to accumulate in MEL cells within 12 hours of induction and RNA copies of the promoter successfully compete their binding in vitro

The induction of differentiation in mouse erythroleukemia (MEL) cells by dimethylsulfoxide (DMSO) is characterized by increased transcription of globin genes. We have determined that DMSO treated cells increase the levels of nuclear factors capable of overall interactions with the beta maj globin promoter during the initial 24 h post induction, as measured by gel mobility analysis. Two unprocessed beta maj globin mRNA precursors, which are present in MEL cell nuclei early in differentiation, were previously shown to contain the 5' promoter flanking region, and thereby provided the nucleus with a pool of regulatory sequences in multiple RNA copies. We have studied the effect of RNA copies of the promoter region on binding interactions between DNA sequences of the beta maj globin promoter and nuclear factors that interact with these sequences. The promoter region RNA transcripts competed effectively for DNA binding proteins in vitro, while the antisense RNA from the same region did not. The most pronounced competition was observed with proteins from 12 h after DMSO induction, when the concentration of the DNA binding proteins was still increasing. Since the 'upstream' transcripts predominate at 12 h after DMSO induction, these results indicate that the promoter region transcripts may influence the equilibrium of binding between the beta maj globin promoter and the nuclear factors that bind to this region during DMSO induction.

cAMP-dependent protein kinase is necessary for increased NF-E2.DNA complex formation during erythroleukemia cell differentiation

When murine erythroleukemia (MEL) cells are induced to differentiate by hexamethylene bisacetamide (HMBA), erythroid-specific genes are transcriptionally activated; however, transcriptional activation of these genes is severely impaired in cAMP-dependent protein kinase (protein kinase A)-deficient MEL cells. The transcription factor NF-E2, composed of a 45-kDa (p45) and an 18-kDa (p18) subunit, is essential for enhancer activity of the globin locus control regions (LCRs). DNA binding of NF-E2 and alpha-globin LCR enhancer activity was significantly less in HMBA-treated protein kinase A-deficient cells compared to cells containing normal protein kinase A activity; DNA binding of several other transcription factors was the same in both cell types. In parental cells, HMBA treatment and/or prolonged activation of protein kinase A increased the amount of NF-E2.DNA complexes without change in DNA binding affinity; the expression of p45 and p18 was the same under all conditions. p45 and p18 were phosphorylated by protein kinase A in vitro, but the phosphorylation did not affect NF-E2.DNA complexes, suggesting that protein kinase A regulates NF-E2.DNA complex formation indirectly, e.g. by altering expression of a regulatory factor(s). Thus, protein kinase A appears to be necessary for increased NF-E2.DNA complex formation during differentiation of MEL cells and may influence erythroid-specific gene expression through this mechanism.

Regulation of J6 gene expression by transcription factor GATA-4

Retinoic acid-induced differentiation of mouse F9 embryonal carcinoma cells into primitive endoderm is accompanied by increased transcription of the gene for J6, a heat shock protein implicated in collagen biosynthesis. In this paper we present evidence that transcription factor GATA-4, a retinoic acid-inducible GATA-binding protein, is involved in the regulation of J6 gene expression in F9 cells. Northern-blot analysis indicates that transcripts encoding GATA-4 and J6 increase in parallel during retinoic acid-induced differentiation of F9 cells. Gel-shift experiments and antibody binding studies demonstrate that: (1) GATA-4 is the major GATA-binding protein activity in differentiated F9 cells, and (2) GATA-4 binds to consensus GATA motifs in the retinoic acid-responsive portion of the J6 promoter. Co-transfection studies using NIH 3T3 cells show that GATA-4 is a potent trans-activator of the J6 promoter. These lines of evidence suggest that expression of J6 in F9 cells is regulated by GATA-4. We speculate that transcription factor GATA-4 may also control other genes involved in extracellular matrix formation in the yolk sac.

Erythropoietin-induced transcription at the murine beta maj-globin promoter. A central role for GATA-1

Using J2E cells and the murine beta maj-globin promoter as a model, we have performed the first direct analyses of erythropoietin (EPO)-activated transcription from defined templates. The -346 to +26 beta maj promoter was shown to comprise a target for maximal activation. This included a positive role for a -346 to -107-base pair (bp) domain in J2E cells, but not in F-MEL cells. Mutagenesis of a -215-bp AGATAA element within this domain showed that this effect did not require GATA-1 binding. In contrast, a critical role for GATA-1 at a -60-bp (G)GATAG element was defined by mutagenesis (GGg-TAG and TGATAG), complementation with a synthetic TGATAA element, and the demonstrated specific binding of GATA-1. Proximal CCAAT (-75) and CACCC (-90) elements also were shown to contribute to transcriptional activation in J2E cells, yet exerted quantitatively distinct effects in the F-MEL system. Based on these results, minimal [TGATAA]4-TATA and TGATAA-CACCC-TATA promoters were constructed and assayed in each system. Remarkably, the [TGATAA]4-TATA promoter, but not the TGATAA-CACCC-TATA promoter, was induced efficiently by EPO in J2E cells, whereas the TGATAA-CACCC-TATA promoter was highly induced by Me2SO in F-MEL cells. These findings suggest that mechanisms of EPO-induced transcription in J2E cells involve GATA-1 and differ from chemically activated mechanisms studied previously in F-MEL cells. Globin induction in J2E cells was not associated with effects of EPO on levels or nuclear translocation of GATA-1. However, hemoglobinization was induced by okadaic acid, 8-Br-cAMP, and forskolin, a finding consistent with induction mechanisms that may involve modulated serine/threonine phosphorylation.

Regulatory elements in the first intron of the mouse Ha-ras gene

The Ha-ras gene is one of the three oncogenes (Ha-ras, Ki-ras, and N-ras) of the ras superfamily of small G proteins. The p21ras proteins encoded by the ras genes are key proteins involved in the transduction of signals from membrane receptor-tyrosine kinases to downstream targets. The ras genes seem to play a ubiquitous role in the control of cell proliferation and cell differentiation. At the same time, ras genes may perform specific differentiated functions in certain cell types. Little is known about the regulation of expression of the Ha-ras gene. The first intron of the Ha-ras gene has been reported to be highly conserved between human and rodent. We investigated the role that this intron may play in the regulation of expression of Ha-ras. The promoter region of the Ha-ras gene exhibits characteristics of a housekeeping gene. Deletion analysis shows the existence of an enhancer-type element in the 5' region of the first intron (intron 0). DNase 1 footprinting experiments reveal five sites that interact with nuclear proteins from fibroblast and epithelial cell lines. Deletion and site-directed mutagenesis of three of these sites show that two are involved in a positive effect and one in a negative effect on the regulation of expression of the mouse Ha-ras gene.

Transcriptional and posttranslational regulation of the general amino acid permease of Saccharomyces cerevisiae

The cellular level and activity of the general amino acid permease, the product of the GAP1 gene of Saccharomyces cerevisiae, are regulated at the level of transcription by two systems, the products of URE2/GLN3 and NIL1 in response to the nitrogen sources of the growth medium and inactivation in response to the presence of glutamine or glutamate. Active permease is phosphorylated. The addition of glutamine causes rapid dephosphorylation and inactivation of the permease with the same kinetics, which is followed by slower disappearance of the protein. These results suggest that inactivation of the permease results from its dephosphorylation.

The GATA-4 transcription factor transactivates the cardiac muscle-specific troponin C promoter-enhancer in nonmuscle cells

The unique contractile phenotype of cardiac myocytes is determined by the expression of a set of cardiac muscle-specific genes. By analogy to other mammalian developmental systems, it is likely that the coordinate expression of cardiac genes is controlled by lineage-specific transcription factors that interact with promoter and enhancer elements in the transcriptional regulatory regions of these genes. Although previous reports have identified several cardiac muscle-specific transcriptional elements, relatively little is known about the lineage-specific transcription factors that regulate these elements. In this report, we demonstrate that the slow/cardiac muscle-specific troponin C (cTnC) enhancer contains a specific binding site for the lineage-restricted zinc finger transcription factor GATA-4. This GATA-4-binding site is required for enhancer activity in primary cardiac myocytes. Moreover, the cTnC enhancer can be transactivated by overexpression of GATA-4 in non-cardiac muscle cells such as NIH 3T3 cells. In situ hybridization studies demonstrate that GATA-4 and cTnC have overlapping patterns of expression in the hearts of postimplantation mouse embryos and that GATA-4 gene expression precedes cTnC expression. Indirect immunofluorescence reveals GATA-4 expression in cultured cardiac myocytes from neonatal rats. Taken together, these results are consistent with a model in which GATA-4 functions to direct tissue-specific gene expression during mammalian cardiac development.

The GATA-4 transcription factor transactivates the cardiac muscle-specific troponin C promoter-enhancer in nonmuscle cells

The unique contractile phenotype of cardiac myocytes is determined by the expression of a set of cardiac muscle-specific genes. By analogy to other mammalian developmental systems, it is likely that the coordinate expression of cardiac genes is controlled by lineage-specific transcription factors that interact with promoter and enhancer elements in the transcriptional regulatory regions of these genes. Although previous reports have identified several cardiac muscle-specific transcriptional elements, relatively little is known about the lineage-specific transcription factors that regulate these elements. In this report, we demonstrate that the slow/cardiac muscle-specific troponin C (cTnC) enhancer contains a specific binding site for the lineage-restricted zinc finger transcription factor GATA-4. This GATA-4-binding site is required for enhancer activity in primary cardiac myocytes. Moreover, the cTnC enhancer can be transactivated by overexpression of GATA-4 in non-cardiac muscle cells such as NIH 3T3 cells. In situ hybridization studies demonstrate that GATA-4 and cTnC have overlapping patterns of expression in the hearts of postimplantation mouse embryos and that GATA-4 gene expression precedes cTnC expression. Indirect immunofluorescence reveals GATA-4 expression in cultured cardiac myocytes from neonatal rats. Taken together, these results are consistent with a model in which GATA-4 functions to direct tissue-specific gene expression during mammalian cardiac development.

A hormone-encoding gene identifies a pathway for cardiac but not skeletal muscle gene transcription

In contrast to skeletal muscle, the mechanisms responsible for activation and maintenance of tissue-specific transcription in cardiac muscle remain poorly understood. A family of hormone-encoding genes is expressed in a highly specific manner in cardiac but not skeletal myocytes. This includes the A- and B-type natriuretic peptide (ANP and BNP) genes, which encode peptide hormones with crucial roles in the regulation of blood volume and pressure. Since these genes are markers of cardiac cells, we have used them to probe the mechanisms for cardiac muscle-specific transcription. Cloning and functional analysis of the rat BNP upstream sequences revealed unexpected structural resemblance to erythroid but not to muscle-specific promoters and enhancers, including a requirement for regulatory elements containing GATA motifs. A cDNA clone corresponding to a member of the GATA family of transcription factors was isolated from a cardiomyocyte cDNA library. Transcription of this GATA gene is restricted mostly to the heart and is undetectable in skeletal muscle. Within the heart, GATA transcripts are localized in ANP- and BNP-expressing myocytes, and forced expression of the GATA protein in heterologous cells markedly activates transcription from the natural cardiac muscle-specific ANP and BNP promoters. This GATA-dependent pathway defines the first mechanism for cardiac muscle-specific transcription. Moreover, the present findings reveal striking similarities between the mechanisms controlling gene expression in hematopoietic and cardiac cells and may have important implications for studies of cardiogenesis.

Novel insights into erythroid development revealed through in vitro differentiation of GATA-1 embryonic stem cells

Mouse embryonic stem (ES) cells lacking the transcription factor GATA-1 do not produce mature red blood cells either in vivo or in vitro. To define the consequences of GATA-1 loss more precisely, we used an in vitro ES cell differentiation assay that permits enumeration of primitive (EryP) and definitive (EryD) erythroid precursors and recovery of pure erythroid colonies. In contrast to normal ES cells, GATA-1- ES cells fail to generate EryP precursors. EryD precursors, however, are normal in number but undergo developmental arrest and death at the proerythroblast stage. Contrary to initial expectations, arrested GATA-1(-)-definitive proerythroblasts express GATA target genes at normal levels. Transcripts of the related factor GATA-2 are remarkably elevated in GATA-1- proerythroblasts. These findings imply substantial interchangeability of GATA factors in vivo and suggest that GATA-1 normally serves to repress GATA-2 during erythropoiesis. The approach used here is a paradigm for the phenotypic analysis of targeted mutations affecting hematopoietic development.

A hormone-encoding gene identifies a pathway for cardiac but not skeletal muscle gene transcription

In contrast to skeletal muscle, the mechanisms responsible for activation and maintenance of tissue-specific transcription in cardiac muscle remain poorly understood. A family of hormone-encoding genes is expressed in a highly specific manner in cardiac but not skeletal myocytes. This includes the A- and B-type natriuretic peptide (ANP and BNP) genes, which encode peptide hormones with crucial roles in the regulation of blood volume and pressure. Since these genes are markers of cardiac cells, we have used them to probe the mechanisms for cardiac muscle-specific transcription. Cloning and functional analysis of the rat BNP upstream sequences revealed unexpected structural resemblance to erythroid but not to muscle-specific promoters and enhancers, including a requirement for regulatory elements containing GATA motifs. A cDNA clone corresponding to a member of the GATA family of transcription factors was isolated from a cardiomyocyte cDNA library. Transcription of this GATA gene is restricted mostly to the heart and is undetectable in skeletal muscle. Within the heart, GATA transcripts are localized in ANP- and BNP-expressing myocytes, and forced expression of the GATA protein in heterologous cells markedly activates transcription from the natural cardiac muscle-specific ANP and BNP promoters. This GATA-dependent pathway defines the first mechanism for cardiac muscle-specific transcription. Moreover, the present findings reveal striking similarities between the mechanisms controlling gene expression in hematopoietic and cardiac cells and may have important implications for studies of cardiogenesis.

Transcription factor GATA-1-multiprotein complexes and chicken erythroid development

The chicken erythrocyte transcription factor, GATA-1, is associated with several non-DNA binding proteins. We show that GATA-1 multiprotein complexes exist in primitive and definitive erythrocytes. These complexes bind to GATA motifs of the rho-globin promoter and histone H5 enhancer with high affinity, and to the chicken beta-globin promoter specialized TATA element and enhancer GATA with low affinity. The low affinity beta-globin TATA element would allow basal transcription factors to displace the GATA-1 multiprotein complex. Further, our results suggest that rho-globin promoter's low affinity Sp1 binding site and reduced levels of Sp1 in definitive cells prevent its expression in these cells.

Human GATA-3 trans-activation, DNA-binding, and nuclear localization activities are organized into distinct structural domains

GATA-3 is a zinc finger transcription factor which is expressed in a highly restricted and strongly conserved tissue distribution pattern in vertebrate organisms, specifically, in a subset of hematopoietic cells, in cells within the central and peripheral nervous systems, in the kidney, and in placental trophoblasts. Tissue-specific cellular genes regulated by GATA-3 have been identified in T lymphocytes and the placenta, while GATA-3-regulated genes in the nervous system and kidney have not yet been defined. We prepared monoclonal antibodies with which we could dissect the biochemical and functional properties of human GATA-3. The results of these experiments show some anticipated phenotypes, for example, the definition of discrete domains required for specific DNA-binding site recognition (amino acids 303 to 348) and trans activation (amino acids 30 to 74). The signaling sequence for nuclear localization of human GATA-3 is a property conferred by sequences within and surrounding the amino finger (amino acids 249 to 311) of the protein, thereby assigning a function to this domain and thus explaining the curious observation that this zinc finger is dispensable for DNA binding by the GATA family of transcription factors.

Human GATA-3 trans-activation, DNA-binding, and nuclear localization activities are organized into distinct structural domains

GATA-3 is a zinc finger transcription factor which is expressed in a highly restricted and strongly conserved tissue distribution pattern in vertebrate organisms, specifically, in a subset of hematopoietic cells, in cells within the central and peripheral nervous systems, in the kidney, and in placental trophoblasts. Tissue-specific cellular genes regulated by GATA-3 have been identified in T lymphocytes and the placenta, while GATA-3-regulated genes in the nervous system and kidney have not yet been defined. We prepared monoclonal antibodies with which we could dissect the biochemical and functional properties of human GATA-3. The results of these experiments show some anticipated phenotypes, for example, the definition of discrete domains required for specific DNA-binding site recognition (amino acids 303 to 348) and trans activation (amino acids 30 to 74). The signaling sequence for nuclear localization of human GATA-3 is a property conferred by sequences within and surrounding the amino finger (amino acids 249 to 311) of the protein, thereby assigning a function to this domain and thus explaining the curious observation that this zinc finger is dispensable for DNA binding by the GATA family of transcription factors.

Endothelial-cell-specific regulation of von Willebrand factor gene expression

In both tissue sections and cell culture, the endothelial nature of a cell is most commonly determined by demonstration of its expression of von Willebrand factor (vWf) protein and/or mRNA. Thus, the mechanism of cell-type-specific transcriptional regulation of the vWf gene is central to studying the basis of endothelial-cell-specific gene expression. In this study, deletion analyses were carried out to identify the region of the vWf gene which regulates its endothelial-cell-specific expression. A 734-bp fragment which spans the sequence from -487 to +247 relative to the transcription start site was identified as the cell-type-specific promoter. It consists of a minimal core promoter located between -90 and +22, a strong negative regulatory element located upstream of the core promoter (ca. -500 to -300), and a positive regulatory region located downstream of the core promoter in the first exon. The activity of the core promoter is not cell type specific, and the negative regulatory region is required to inhibit its activity in all cell types. The positive regulatory region relieves this inhibition only in endothelial cells and results in endothelial-cell-specific gene expression. The positive regulatory region contains sequences predicting possible SP1, GATA, and octamer binding sites. Mutations in either the SP1 or octamer sequence have no effect on transcriptional activity, while mutation in the GATA binding element totally abolishes the promoter activity. Evidence that a GATA factor is involved in this interaction is presented. Thus, the positive regulatory region with an intact GATA binding site is required to overcome the inhibitory effect of the negative regulatory element and activate vWf gene expression in an endothelial-cell-specific manner.

Endothelial-cell-specific regulation of von Willebrand factor gene expression

In both tissue sections and cell culture, the endothelial nature of a cell is most commonly determined by demonstration of its expression of von Willebrand factor (vWf) protein and/or mRNA. Thus, the mechanism of cell-type-specific transcriptional regulation of the vWf gene is central to studying the basis of endothelial-cell-specific gene expression. In this study, deletion analyses were carried out to identify the region of the vWf gene which regulates its endothelial-cell-specific expression. A 734-bp fragment which spans the sequence from -487 to +247 relative to the transcription start site was identified as the cell-type-specific promoter. It consists of a minimal core promoter located between -90 and +22, a strong negative regulatory element located upstream of the core promoter (ca. -500 to -300), and a positive regulatory region located downstream of the core promoter in the first exon. The activity of the core promoter is not cell type specific, and the negative regulatory region is required to inhibit its activity in all cell types. The positive regulatory region relieves this inhibition only in endothelial cells and results in endothelial-cell-specific gene expression. The positive regulatory region contains sequences predicting possible SP1, GATA, and octamer binding sites. Mutations in either the SP1 or octamer sequence have no effect on transcriptional activity, while mutation in the GATA binding element totally abolishes the promoter activity. Evidence that a GATA factor is involved in this interaction is presented. Thus, the positive regulatory region with an intact GATA binding site is required to overcome the inhibitory effect of the negative regulatory element and activate vWf gene expression in an endothelial-cell-specific manner.

Activation of the beta-globin promoter by the locus control region correlates with binding of a novel factor to the CAAT box in murine erythroleukemia cells but not in K562 cells

Four distinct factors in extracts from murine erythroleukemia (MEL) cells interacted with the human beta-globin gene promoter CAAT box: CP1, GATA-1, and two novel factors, denoted a and b, one of which is highly inducible in the MEL system. GATA-1 binding to the CAAT element was very unstable (half-life < 1 min), whereas bindings of a, b, and CP1 were comparatively stable, with half-lives of 18, 19, and 3.5 min, respectively. Stable transfections of MEL cells showed that in the presence of the beta-globin locus control region (LCR), the wild-type CAAT box, a mutant which bound to GATA-1 with increased stability over the normal sequences, and a mutant which bound a, b, and CP1 specifically could all stimulate transcription greater than ninefold over that induced by a null CAAT mutation in both uninduced and terminally differentiated MEL cells. A mutant which bound the a and b factors specifically gave only a twofold stimulation of promoter activity, and this lower activity correlated with a decrease in the stability of binding of the b protein. On the other hand, CP1 binding alone did not stimulate transcription. Taken together, these results suggest that in the context of the wild-type beta-globin CAAT element the b factor stimulates transcription directed by the LCR in MEL cells, although the LCR can also function through more stable GATA-1-binding sequences. However, in K562 cells, the wild-type beta-globin CAAT box alone was unable to stimulate gene expression directed by the LCR and high levels of transcription were obtained only upon inclusion of more upstream beta-globin promoter sequences. In contrast, a construct containing only the A gamma-globin CAAT box region did give high expression levels in K562 cells. Thus, there is a fundamental difference in the way the LCR functions in these two model systems in terms of its requirements at the promoter level.

Activation of the beta-globin promoter by the locus control region correlates with binding of a novel factor to the CAAT box in murine erythroleukemia cells but not in K562 cells

Four distinct factors in extracts from murine erythroleukemia (MEL) cells interacted with the human beta-globin gene promoter CAAT box: CP1, GATA-1, and two novel factors, denoted a and b, one of which is highly inducible in the MEL system. GATA-1 binding to the CAAT element was very unstable (half-life < 1 min), whereas bindings of a, b, and CP1 were comparatively stable, with half-lives of 18, 19, and 3.5 min, respectively. Stable transfections of MEL cells showed that in the presence of the beta-globin locus control region (LCR), the wild-type CAAT box, a mutant which bound to GATA-1 with increased stability over the normal sequences, and a mutant which bound a, b, and CP1 specifically could all stimulate transcription greater than ninefold over that induced by a null CAAT mutation in both uninduced and terminally differentiated MEL cells. A mutant which bound the a and b factors specifically gave only a twofold stimulation of promoter activity, and this lower activity correlated with a decrease in the stability of binding of the b protein. On the other hand, CP1 binding alone did not stimulate transcription. Taken together, these results suggest that in the context of the wild-type beta-globin CAAT element the b factor stimulates transcription directed by the LCR in MEL cells, although the LCR can also function through more stable GATA-1-binding sequences. However, in K562 cells, the wild-type beta-globin CAAT box alone was unable to stimulate gene expression directed by the LCR and high levels of transcription were obtained only upon inclusion of more upstream beta-globin promoter sequences. In contrast, a construct containing only the A gamma-globin CAAT box region did give high expression levels in K562 cells. Thus, there is a fundamental difference in the way the LCR functions in these two model systems in terms of its requirements at the promoter level.