A common protein binds to two silencers 5' to the human beta-globin gene

Developmental regulation of the vertebrate globin multigene family

"Hemoglobin switching," or the sequential expression of globin genes in erythroid cells during development, has provided an important paradigm for tissue- and stage-specific gene regulation. Over the past decade, regulatory DNA sequences and transcription factors involved in controlling the expression of individual globin genes in erythroid cells have been identified. The picture that has emerged indicates that gene proximal control elements collaborate with a "locus control region" located far upstream - probably via a DNA looping mechanism - to ensure that each gene is turned on only in erythroid cells and at the appropriate time during development. Interactions among the various regulatory sequences are thought to be mediated and stabilized by an array of tissue-specific and ubiquitous proteins. Chromatin structure plays a critical but still poorly understood role in this process.

A Potent Conformation-Constrained Synthetic Peptide Mimic of a Homeodomain Selectively Regulates Target Genes in Cells

DNA, as a target for therapeutic intervention, remains largely unexplored. DLX-4, a homeodomain containing transcription factor, and its spliced isoforms play crucial roles in many aspects of cellular biochemistry and important roles in many diseases. A smaller peptide mimicking the homeodomain of the transcription factor DLX-4 was designed and synthesized by suitable conjoining of its modified DNA-binding elements. The peptide binds to DLX-4 target sites on the regulatory region of the globin gene cluster with native-like affinity and specificity in vitro. When conjugated to cell penetrating and nuclear localization sequences, it upregulated some of the genes repressed by DLX-4 or its isoforms, such as β- and γ-globin genes in erythropoietin-induced differentiating CD34⁺ human hematopoietic stem/progenitor cells with high specificity by competing with the respective binding sites. Engineered peptides mimicking DNA-binding domains of transcription factors offer the potential for creating synthetic molecules for directly targeting DNA sites with high specificity.

A conserved regulatory element in the mammalian β-globin promoters

We provide here evidence for a conserved regulatory element for transcription of the β-family globin genes based on a comparative study of 32 genes from 16 mammals. The element is characterized by the appearance of AA or TT dinucleotides in the A + T-rich region located 200-400 bp upstream of the cap sites. G-tracts 3-5 nucleotides long exist between the A + T-rich region and the conserved transcription factor binding sites (GATA-1 site and the CACCC, CCAAT, and ATA boxes) apparently dividing the regions. The average periodicity of AA or TT dinucleotides in the region from a total of 18 β-family globin genes from four species was approximately 10 bp, suggesting that the DNA in these regions shows right-handed superhelicity. The proposed biological function of this element is to adjust the spatial positions for the first interaction of the transcription factor(s) which can recognize specific DNA sequences in the presence of packed chromatin.

Association of α globin gene quadruplication and heterozygous β thalassemia in patients with thalassemia intermedia

Ten patients with thalassemia intermedia with variable severity and apparent simple heterozygosis for beta0 39 C>T nonsense mutation were submitted to clinical, hematologic and molecular studies. The presence of an unknown molecular defect (silent beta-thalassemia) unlinked to the beta cluster interacting with the heterozygous beta thalassemia, was previously postulated in these families. Analysis of the alpha globin gene cluster with PCR-based methods (MLPA, GAP-PCR, digestion with restriction enzymes) detected complex rearrangements in the alpha cluster. A duplication of the alpha globin gene locus, including the upstream regulatory region, was present in all the patients, associated in some of them with deletion or non-deletion alpha thalassemia. The variability of the clinical phenotype correlates with the degree of the globin chain imbalance. The presence of alpha globin cluster duplication should be considered in patients heterozygote for beta-thalassemia with thalassemia intermedia phenotype and in the carriers of suspected silent beta thalassemia.

Association of polymorphic pattern of the (AT) × (T)y motif of β-globin gene in North Indian thalassemia patients with variable clinical expression

Among the polymorphic genetic markers of the β-globin gene cluster, the (AT) × (T)y motif and a common C→T variation at -158 of the Gγ globin gene were investigate din 20 β-thalassemia IVSI-5 (G→C) homozygous patients with variable clinical manifestation and 10 normal subjects from north India to deduce any association with the co-inherited genetic polymorphism. We found (AT)(7)(T)(7) repeat motif in all the 20 chromosomes of normal subjects and two different sequence configuration(AT)(8)(T)(5), (AT)(9)(T)(5) in the patient group whereas the presence of -158(C→T) Gγ was quite polymorphic. We conclude that polymorphism -158(C→T) Gγ and (AT) × (T)y sequence variation other than (AT)(7)(T)(7) could influence the phenotype by increasing Hb F expression.

BP1 motif in the human beta-globin promoter affects beta-globin expression during embryonic/fetal erythropoiesis in transgenic mice bearing the human beta-globin gene

The binding of the transcription factor BP1 (beta protein 1) to its site on the promoter of the adult beta-globin gene has a silencing effect on beta-globin transcription in vitro. To better understand the mechanism of BP1's negative regulation of beta-globin expression, we developed transgenic mice bearing a human beta-globin locus-containing cosmid. Specifically, we introduced a mutated BP1 binding site (mtBP1) into the promoter of the beta-globin gene sequence of this cosmid construct. In the mtBP1 mice, we detected a more than a 20-fold increase in human beta-globin expression in the yolk sac-derived blood at E10.5, a 3-fold increase in fetal livers at E13.5, and an approximately 1.4-fold increase in adult reticulocytes compared with control mice bearing the human beta-globin gene with the wild-type BP1 binding site sequence (wtBP1). Our in vivo observations support the contention that the BP1 binding site of the beta-globin promoter plays an important role in the regulation of transcription of the adult beta-globin gene.

The study of sequence configuration and functional impact of the (AC)n(AT)xTy motif in human beta-globin gene promoter

In this report we examine the (AC)n(AT)xTy motif residing -530 bp 5' upstream of the beta-globin gene in Chinese thalassaemic patients. This motif is a putative binding site for a repressor protein, termed beta protein 1 (BP1) (Berg et al., Nucleic Acids Res 1989;17:8833-8852). Variations in the (AC)n(AT)xTy repeats affect the binding affinity of BP1, thereby altering the expression of the beta-globin gene. Eight different configurations of this repeat motif are identified in our population of Chinese beta-thalassaemia patients. A (AC)3(AT)7T5 motif was identified among these thalassaemia patients and its influence in beta-globin gene expression was studied using stable transfection assay in murine erythroleukemia (MEL) cells. Our data demonstrated that the (AC)3(AT)7T5 motif has a moderately strong repressor effect on the expression of the cis-linked beta-globin gene. The high affinity of BP1 for this motif may result in the suppression of the transcription of the beta-globin gene (Berg et al., Am J Hematol 1991;36:42-47). We postulate that silencer elements in the beta-globin promoter play an important role in modifying the clinical presentation of the disease.

Molecular therapies in beta-thalassaemia

The beta-thalassaemias have a major global impact on health and mortality. Allogeneic haemopoietic stem cell transplantation is the only approach that may lead to a cure but this approach is not available to most patients. The mainstay treatment for the majority remains life-long blood transfusion in combination with a rigorous regime of iron chelation. Improved understanding of the pathophysiology and molecular basis of the disease has provided clues for more effective strategies that aim to correct the defect in beta-globin chain synthesis at the primary level or redress the alpha/beta-globin chain imbalance at the secondary level. Improved understanding of the molecular basis of the disease complications, such as iron overloading, has also provided clues for potential molecular targets at the tertiary level.

BP1 is a negative modulator of definitive erythropoiesis

Beta protein 1 (BP1), a human homeotic transcription factor, is expressed during hematopoeisis in the erythroid lineage. To determine the in vivo role of BP1 in erythropoiesis, we have undertaken two complementary approaches using enforced BP1 expression in both transgenic mice and embryonic stem (ES) cells. Despite repeated attempts, only one adult transgenic BP1 founder mouse among 121 mice was obtained. This mouse presumably survived due to transgene mosaicism because the transgene could not be transmitted. This mouse expressed BP1 and displayed splenomegaly, extramedullary erythropoiesis and severe amyloidosis A in the kidney, a phenotype compatible with thalassemia. Consistently, the presence of BP1 transgene in fetuses was associated with paleness and lethality. In ES cells, BP1 expression in primary differentiation appeared to antagonize adult β-globin expression. In secondary differentiation, BP1 expression reduced significantly β-globin gene expression in both primitive and definitive erythroid cells, whereas it impaired only the definitive erythroid cell differentiation. These studies showed that BP1 can negatively modulate adult β-globin gene expression and definitive erythroid cell differentiation, and suggest that BP1 could play a role in thalassemia.

Polymorphisms in the HBB gene relate to individual cardiorespiratory adaptation in response to endurance training

OBJECTIVE

The crucial role of haemoglobin in endurance performance has been well documented. We examined whether polymorphisms in the HBB gene modified aerobic capacity.

METHODS

102 recruits were trained by running 5000 m three times per week for 18 weeks. Exercise intensity progressively increased from an initial heart rate corresponding to 95% of the individual baseline ventilatory threshold during the first 10 weeks to 105% during the last 8 weeks. The phenotypes measured were running economy and VO(2)max. Running economy was determined by measuring submaximal VO(2) for 5 min at a constant running speed of 12 km.h(-1) and VO(2)max was obtained during an incremental test to exhaustion. Genomic DNA was extracted from white cells of peripheral blood and the -551C/T, intron2,+16C/G and +340 A/T genotypes were examined relative to the TAA site variants by PCR-RFLP.

RESULTS

Genotype distributions were in Hardy-Weinberg equilibrium at three loci. None of the running economy and VO(2)max-related traits were associated with the three polymorphisms or haplotypes at baseline, while the training response of running economy was associated with -551C/T and intron2,+16C/G polymorphisms. Subjects homozygous for intron2,+16C/C or -551C/C had decreased oxygen cost of running compared to the other individuals.

DISCUSSION

It was concluded that the -551C/C or intron2,+16C/C genotype might explain part of the individual variation in the cardiorespiratory adaptation to endurance training.

Strong linkage disequilibrium of a HbE variant with the (AT)9(T)5 repeat in the BP1 binding site upstream of the beta-globin gene in the Thai population

A binding site for the repressor protein BP1, which contains a tandem (AT)x(T)y repeat, is located approximately 530 bp 5' to the human beta-globin gene (HBB). There is accumulating evidence that BP1 binds to the (AT)9(T)5 allele more strongly than to other alleles, thereby reducing the expression of HBB. In this study, we investigated polymorphisms in the (AT)x(T)y repeat in 57 individuals living in Thailand, including three homozygotes for the hemoglobin E variant (HbE; beta26Glu-->Lys), 22 heterozygotes, and 32 normal homozygotes. We found that (AT)9(T)5 and (AT)7(T)7 alleles were predominant in the studied population and that the HbE variant is in strong linkage disequilibrium with the (AT)9(T)5 allele, which can explain why the betaE chain is inefficiently synthesized compared to the normal betaA chain. Moreover, the mildness of the HbE disease compared to other hemoglobinopathies in Thai may be due, in part, to the presence of the (AT)9(T)5 repeat on the HbE chromosome. In addition, a novel (AC)n polymorphism adjacent to the (AT)x(T)y repeat (i.e., (AC)3(AT)7(T)5) was found through the variation screening in this study.

Inhibition of β protein 1 expression enhances β-globin promoter activity and β-globin mRNA levels in the human erythroleukemia (K562) cell line

OBJECTIVE

In this paper, we report new observations related to the mechanism of the negative regulation of the important adult beta-globin gene in the erythroid cells at the embryonic-fetal stage of their development. We focused on the role of the silencer II region located upstream of the beta-globin gene, which along with its cognate binding protein BP1, negatively regulates beta-globin transcription.

MATERIALS AND METHODS

We prepared plasmid constructs containing the wild-type silencer II sequence, a mutated silencer II sequence, or a mutated control sequence in the beta-globin promoter 690-bp insert, which in turn was linked to an enhanced green fluorescent protein (EGFP) reporter gene. A human erythroleukemia cell line (K562) with embryonic-fetal phenotype was transfected with these EGFP constructs.

RESULTS

Flow cytometry and fluorescence digital imaging showed about threefold increase in the beta-globin promoter activity of the mutated silencer II construct. Introduction of a small interfering RNA (siRNA) complementary to BP1 into the cells caused a 75% decrease in BP1 expression and a simultaneous approximately 40% elevation of beta-globin promoter activity as well as an increase in beta-globin mRNA levels, as compared with controls. We detected no changes in the mRNA levels of positive regulators of hemoglobin transcription such as EKLF and GATA-1.

CONCLUSION

Our results support the involvement of BP1 in the mechanism of the negative regulation of beta-globin transcription. A better understanding of this mechanism may lay the groundwork for novel gene therapy approaches to inhibit the expression of abnormal structural variants of adult beta globin, such as sickle hemoglobin.

The In Vitro Reconstitution of Nucleosome and its Binding Patterns with HMG1/2 and HMG14/17 Proteins

Using atomic force microscopy (AFM), the dynamic process of the in vitro nucleosome reconstitution followed by slow dilution from high salt to low salt was visualized. Data showed that the histone octamers were dissociated from DNA at 1M NaCl. When the salt concentration was slowly reduced to 650 mM and 300 mM, the core histones bound to the naked DNA gradually. Once the salt concentration was reduced to 50 mM the classic "beads-on-a-string" structure was clearly visualized. Furthermore, using the technique of the in vitro reconstitution of nucleosome, the mono- and di- nucleosomes were assembled in vitro with both HS2core (-10681 to -10970 bp) and NCR2 (-372 to -194 bp) DNA sequences in the 5 flanking sequence of human b-globin gene. Data revealed that HMG 1/2 and HMG14/17 proteins binding to both DNA sequences are changeable following the assembly and disassembly of nucleosomes. We suggest that the changeable binding patterns of HMG 14/17 and HMG1/2 proteins with these regulatory elements may be critical in the process of nucleosome assembly, recruitment of chromatin-modifying activities, and the regulation of human b-globin gene expression.

Role of polymorphic sequences 5' to the G(gamma) gene and 5' to the beta gene on the homozygous beta thalassemic phenotype

Sixty-seven homozygous male and female thalassemic patients with different phenotypes, aged between 8 and 33 years, were divided into three groups, according to the severity of their beta-thalassemia (thal) mutations. We investigated whether some co-inherited genetic factors could influence the phenotype. Patients with milder beta-thal defects, homozygotes or compound heterozygotes for the IVS-I-6 (T-->C) or -87 (C-->G) mutations had a milder disease. In addition, determination of the co-inheritance of the -158 (C-->T) G(gamma) polymorphism and the (AT)9T5 repeat motif in the region -540 to -525, 5' to the beta-globin gene, showed that in some patients with severe or mild/severe beta-thal mutations, linked to haplotype III, there was higher Hb F expression. We conclude that in homozygous beta-thal patients, the severity of the mutations is the most important factor influencing the phenotype, but some polymorphisms such as the -158 (C-->T) G(gamma) and (AT)9T5 repeat motif, increasing the Hb F expression and ameliorate the clinical course of the disease.

Evolutionary conservation and functional synergism of curved DNA at the mouse epsilon- and other globin-gene promoters

Human and mouse globin genes were separated approximately 200 million years ago but still share homology and synergism in many aspects including DNA structure. We first mapped DNA bend sites in the mouse epsilon-globin gene and found that these sites were distributed in a regular manner except in the coding region and their overall average distance was 650.7 bp. The first bend site upstream of the cap site (MepsilonB-1, -334 to -147 bp) was found to contain A + T-rich sequences and features contributing to DNA curvature by computer analysis. Transcription assays using deletion constructs indicated strong promoter activity up to bp -215 in erythriod K562 cells. Therefore, the MepsilonB-1 site was located immediately upstream of the promoter region. A reporter gene assay using a series of constructs containing the promoter region revealed that the MepsilonB-1 site showed repressor activity, and on replacement of the DNA curvature with one from another source the activity was retained. A similar feature was found in the other conserved B-1 sites in the human, bovine, and rabbit beta-like globin genes, with the exception of an unconserved B-1 site in the chicken beta-globin gene. A common feature of these conserved B-1 sites was not the nucleotide sequences but the DNA curvature. Furthermore, a unique nucleosome phase at the MepsilonB-1 site was likely to be directed by DNA curvature. Based on these results, DNA curvature is one of the major features of these promoter regions which might influence transcription through nucleosome positioning.

Developmental functions of theDistal-less/Dlx homeobox genes

Distal-less is the earliest known gene specifically expressed in developing insect limbs; its expression is maintained throughout limb development. The homeodomain transcription factor encoded by Distal-less is required for the elaboration of proximodistal pattern elements in Drosophila limbs and can initiate proximodistal axis formation when expressed ectopically. Distal-less homologs, the Dlx genes, are expressed in developing appendages in at least six phyla, including chordates, consistent with requirements for Dlx function in normal appendage development across the animal kingdom. Recent work implicates the Dlx genes of vertebrates in a variety of other developmental processes ranging from neurogenesis to hematopoiesis. We review what is known about the invertebrate and vertebrate Dll/Dlx genes and their varied roles during development. We propose revising the vertebrate nomenclature to reflect phylogenetic relationships among the Dlx genes.

Foetal haemoglobin in normal healthy adults: relationship with polymorphic sequences cis to the beta globin gene

We evaluated the effects of polymorphic markers within the beta globin gene cluster on HbF expression in two groups. These groups were randomly selected from a survey of HbF distribution in a large population study of unrelated healthy Algerian adults (n=827). The first group contained individuals with normal HbF levels (0.1-0.5%) and the second group contained individuals with raised HbF levels (0.8-2.3%). Of the various polymorphic markers analysed, only the -309 G gamma A-->G, the -158 G gamma C-->T, the G gamma IVS2 TC (TG)(9) AG (TG)(2) (CG)(2) and the -540 beta (AT)(9) T(5) sequence configurations were significantly associated with increased HbF levels. More than 84% of the subjects with elevated HbF levels carried one or several of these four marker configurations, suggesting that the beta globin gene cluster exerts a significant effect on HbF expression in healthy individuals.

BP1, a homeodomain-containing isoform of DLX4, represses the beta-globin gene

In earlier studies we identified a putative repressor of the human beta-globin gene, termed beta protein 1 (BP1), which binds to two silencer DNA sequences upstream of the adult human beta-globin gene and to a negative control region upstream of the adult delta-globin gene. Further studies demonstrated an inverse correlation between the binding affinity of the BP1 protein for the distal beta-globin silencer sequence and the severity of sickle cell anemia, suggesting a possible role for BP1 in determining the production of hemoglobin S. We have now cloned a cDNA expressing the BP1 protein. Sequencing revealed that BP1 is a member of the homeobox gene family and belongs to the subfamily called Distal-less (DLX), genes important in early development. Further analysis showed that BP1 is an isoform of DLX4. BP1 protein has repressor function towards the beta-globin promoter, acting through the two beta-globin DNA silencers, demonstrated in transient transfection assays. Strong BP1 expression is restricted to placenta and kidney tissue, with no expression in 48 other human tissues. BP1 exhibits regulated expression in the human erythroid cell line MB-02, where its expression decreases upon induction of the beta-globin gene. BP1 is thus the first member of the DLX family with known DNA binding sites and a function in globin gene regulation.

Fetal hemoglobin elevation in Hb Lepore heterozygotes and its correlation with beta globin cluster linked determinants

We have analysed, at the hematological and molecular level, 51 Hb lepore heterozygotes and three compound heterozygotes for Hb Lepore and HbS (HbLep/HbS) in 26 unselected Portuguese families. The Lepore Boston variant was present in one family, in association with classical haplotype V. All of the other Lepore alleles present haplotype III in association with XmnI (+)5' of (G)gamma gene, in tight linkage disequilibrium to the major mutation found in the Portuguese population, the Lepore Baltimore variant ( delta(68Leu)-beta(84Thr)). The three compound heterozygotes are the first HbLep/HbS individuals reported in the literature, with the Lepore Baltimore mutation linked to haplotype III. In agreement with other studies, these Lepore Baltimore heterozygotes have higher HbF (1.4-14.1% of total hemoglobin) than published cases of Lepore Boston (0.8-5.4%), which is associated with XmnI(-). Among the Lepore Baltimore heterozygotes, the (AT)xTy repeat region at -540 bp of the beta globin gene in trans to the Lepore chromosome, can account for much of the variability in HbF level. The allele (AT)7T7 is associated with lower HbF, and (AT)9T5 is associated with higher HbF. As we previously reported for beta thalassemic carriers, we observe in Lepore Baltimore carriers an effector in trans, linked to the (AT)xTy sequence, acting as an HPFH (Hereditary Persistence of Fetal Hemoglobin) determinant.

Determinants of Transcription of the Chorionic Gonadotropin /Luteinizing Hormone Receptor Gene in Human Breast Cells

Epidemiological evidence suggests that the earlier in life a woman becomes pregnant, the lower her chances for developing breast cancer later in life. This protective effect appears to be due to pregnancy hormone hCG inducing the nonreversible differentiation of proliferative terminal end buds into secretory type lobules. Perhaps this and other actions of hCG are mediated by newly discovered hCG/LH receptors in human breast cells. Thus the hCG actions in breast are potentially important for breast cancer prevention. Because of this importance, we investigated the cis-acting elements and trans-acting proteins that determine the transcription of human chorionic gonadotropin (hCG)/luteinizing hormone (LH) receptor gene in MCF-7, MDA-MB-231, and normal human breast epithelial HMEC cells. These cells contained major-4.8 and 1.8 kb-and minor-9.0, 6.0, and 1.2 kb-hCG/LH receptor transcripts with significantly higher levels in MCF-7 cells. Nuclear run-on transcription, as well as transfection with a fusion construct of luciferase gene and the -2056 to -1 bp of the 5'-flanking region of hCG/LH receptor gene, revealed that MCF-7 cells were transcriptionally more active than the other breast cells. Sequential deletion of the 5'-flanking region revealed that breast cells contained a promoter at -184 to -1 bp. Electrophoretic gel mobility shift assays demonstrated that breast cell nuclear extracts contained Ap2 and Egr promoter binding proteins. Sp1 was also present, but it could not bind because of competition with Egr for binding to a partially overlapping Egr/Sp1 site. The higher levels of Ap2 and Egr binding proteins may explain higher transcription of hCG/LH receptor gene in MCF-7 cells than in the other breast cells.

Functional role of the four different types of (AT)(x)T(y) motifs 5' to the beta-globin gene and their distribution in the Greek population

The polymorphic sequence (AT)(X)T(Y) motif residing 0.5 kb 5' to the human -globin gene has been shown to be a binding site for a putative repressor protein, BP1, in K562 cells. The (AT)(X)T(Y) sequence is characterized by variable length and several configurations. The precise role of the (AT)(X)T(Y) repeats on the regulation of the -globin gene remains unclear. In the present study, we identified the (AT)(X)T(Y) motifs which prevail in the Greek population, established their frequency, and directly investigated their role on -globin gene expression by comparing the effects of the four identified (AT)(X)T(Y) motifs using transient expression assays. Four different configurations were found in the Greek population: the (AT)7T7 motif was the most abundant (81.8%) representing the reference sequence, the (AT)9T5 motif (16.1%), and the (AT)11T3 motif (2%), while the (AT)8T4 motif was absent from normal A chromosomes and was exclusively found on s chromosomes. To evaluate their different role on transcriptional regulation, the four motifs were subcloned upstream of the luciferase reporter gene. Two expression systems were used; MEL cells were transfected with a pGL-2 basic plasmid containing one of the four (AT)(X)T(Y) repeats, the -globin gene promoter, and the luciferase gene, while HeLa cells were transfected with a similar construct (pGL-2 enhancer) including the SV40 enhancer. After 48 h following transient transfection of the cell lines, the expression level of the reporter gene was estimated using a photoilluminometer. The transfected MEL cells exhibited a clearly reduced expression of the luciferase gene driven by the -globin promoter containing the (AT)9T5 and (AT)11T3 configurations. In contrast, HeLa cells did not exhibit any differences among the four motifs. On the basis of these results, we postulate that the (AT)9T5 and (AT)11T3 variants residing 0.5 kb 5' to the -globin gene do not represent simple polymorphisms and can affect its expression in an erythroid environment.

DNA-dependent adenosine triphosphatase (helicaselike transcription factor) activates beta-globin transcription in K562 cells

Correct developmental regulation of beta-like globin gene expression is achieved by preferential transcription of a gene at a given developmental stage, silencing of other beta-like gene promoters, and competition among these promoters for interaction with the locus control region (LCR). Several evolutionarily conserved DNA elements in the promoters of the beta-like genes and LCR have been studied in detail, and the role of their binding factors has been investigated. However, the beta-globin promoter includes additional evolutionarily conserved sequences of unknown function. The present study examined the properties of a 21-base pair (bp) promoter-conserved sequence (PCS) located at positions -115 to -136 bp relative to the transcription start site of the beta-globin gene. A helicaselike transcription factor (HLTF) belonging to the SWI2/SNF2 family of proteins binds to the PCS and a partly homologous sequence in the enhancer region of the LCR hypersensitive site 2 (HS2). Elevation of the level of HLTF in K562 erythroleukemic cells increases beta-promoter activity in transient transfection experiments, and mutations in the PCS that remove HLTF-binding regions abolish this effect, suggesting that HLTF is an activator of beta-globin transcription. Overexpression of HLTF in K562 cells does not affect the endogenous levels of gamma- and epsilon-globin message, but it markedly activates beta-globin transcription. In conclusion, this study reports a transcription factor belonging to the SWI2/SNF2 family, which preferentially activates chromosomal beta-globin gene transcription and which has not previously been implicated in globin gene regulation.

Distinct functions of two isoforms of a homeobox gene, BP1 and DLX7, in the regulation of the beta-globin gene

Homeotic proteins are transcription factors that regulate the expression of multiple genes involved in development and differentiation. We previously isolated a cDNA encoding such a protein from the human leukemia cell line K562, termed Beta Protein 1 (BP1), which is involved in negative regulation of the human beta-globin gene. Sequence comparison revealed that BP1 is a member of the distal-less (DLX) family of homeobox genes and that it shares its homeodomain and 3' sequences with another DLX cDNA, DLX7. BP1 and DLX7 exhibit unique 5' regions, diverging at nucleotide 565 of BP1. We mapped this new distal-less family member BP1 to chromosome 17q21-22 by FISH and PCR, which is the same locus to which DLX7 has been mapped. These results strongly suggest that BP1 and DLX7 are isoforms (derived from the same gene). Since our previous data demonstrated that BP1 and DLX7 are frequently co-expressed, we determined whether DLX7 is also involved in the negative regulation of the beta-globin gene. Mobility shift assays demonstrated that both BP1 and DLX7 proteins, synthesized in vitro, bind to the same BP1 binding site. However, using transient assays, we showed that although BP1 represses activity of a reporter gene through either of two silencer DNA sequences upstream of the beta-globin gene, DLX7 did not show repressor activity against the beta-globin promoter. Further characterization of these apparent isoforms is of significance since they are jointly expressed in acute myeloid leukemia and in many leukemia cell lines.

Nucleotide variation regulates the level of enhancement by hypersensitive site 2 of the beta-globin locus control region

The beta-globin locus control region hypersensitive site 2 (HS2) enhancer possesses a unique property for stimulating high-level globin gene expression. Although the deletion of cis-acting motifs influences the level of enhancement conferred by HS2, there is controversy on whether polymorphism of the same elements contributes to variation of the fetal hemoglobin (HbF) level among patients with sickle cell anemia. We analyzed reporter gene activity of constructs containing variant HS2 enhancers derived from beta(S) chromosomes to directly test the effect of polymorphism on enhancer activity. Constructs containing four enhancer variants linked to an identical gamma-globin promoter showed markedly different levels of reporter gene activity. Juxtaposition of HS2 derived from the Asian and Senegal chromosomes, which are associated with similarly high levels of HbF, to cognate sequence extending to -1500 of the (G)gamma globin gene showed significantly different levels of reporter gene activity. Our findings indicate that nucleotide variation regulates the level of enhancement conferred by HS2; however, the reporter activities showed no correlation with the level of Hb F associated with the common beta(S) chromosomes.

Specific repression of beta-globin promoter activity by nuclear ferritin

Developmental hemoglobin switching involves sequential globin gene activations and repressions that are incompletely understood. Earlier observations, described herein, led us to hypothesize that nuclear ferritin is a repressor of the adult beta-globin gene in embryonic erythroid cells. Our data show that a ferritin-family protein in K562 cell nuclear extracts binds specifically to a highly conserved CAGTGC motif in the beta-globin promoter at -153 to -148 bp from the cap site, and mutation of the CAGTGC motif reduces binding 20-fold in competition gel-shift assays. Purified human ferritin that is enriched in ferritin-H chains also binds the CAGTGC promoter segment. Expression clones of ferritin-H markedly repress beta-globin promoter-driven reporter gene expression in cotransfected CV-1 cells in which the beta-promoter has been stimulated with the transcription activator erythroid Krüppel-like factor (EKLF). We have constructed chloramphenicol acetyltransferase reporter plasmids containing either a wild-type or mutant beta-globin promoter for the -150 CAGTGC motif and have compared the constructs for susceptibility to repression by ferritin-H in cotransfection assays. We find that stimulation by cotransfected EKLF is retained with the mutant promoter, whereas repression by ferritin-H is lost. Thus, mutation of the -150 CAGTGC motif not only markedly reduces in vitro binding of nuclear ferritin but also abrogates the ability of expressed ferritin-H to repress this promoter in our cell transfection assay, providing a strong link between DNA binding and function, and strong support for our proposal that nuclear ferritin-H is a repressor of the human beta-globin gene. Such a repressor could be helpful in treating sickle cell and other genetic diseases.

Regulation of expression of branched-chain alpha-keto acid dehydrogenase subunits in permanent cell lines

The rat hepatoma cell line H4IIEC3 has demonstrated a response to both insulin and glucocorticoids in its accumulation of BCKAD subunit RNAs. It is amenable to BCKAD promoter minigene transfection analyses, demonstrating positive (glucocorticoids) and negative (insulin) regulatory effects. These cells can therefore be used as a model to identify cis-acting sites responsible for regulation of BCKAD subunit promoter activity.

Molecular studies of beta-thalassemia heterozygotes with raised Hb F levels

Hb F levels in beta-thalassemia heterozygotes are usually less than 2%, but amongst 1,059 patients studied, 73 (7%) had Hb F levels above 2.5% (2.6-14.0%). To investigate factors that may influence the increase of Hb F levels in these heterozygotes, we characterized the beta-thalassemia mutations and their chromosomal background, gamma-globin gene promoter variations, and alpha-globin genotypes. All 73 beta-thalassemia heterozygotes carried beta-thalassemia point mutations previously observed in the Greek population; gene mapping excluded b gene cluster deletions; only two cases had an additional gamma-globin gene (gammagammagamma/gammagamma). Five alpha-globin genes (alphaalphaalpha/alphaalpha) were detected in 17/73 cases (23%) as compared to a carrier rate of 1.76% in the general population. Molecular, hematological, and biosynthetic findings in these compound heterozygotes indicated that the raised Hb F levels were caused by cell selection due to ineffective erythropoiesis. In the remaining 56 simple beta-thalassemia heterozygotes, 11 beta-thalassemia mutations were observed, each on the expected haplotype(s), and analysis of the gamma gene promoters revealed three known polymorphisms (in linkage disequilibrium), with minimal influence on gamma-globin levels. However, the overall distribution of beta-thalassemia mutations in the 56 simple beta-thalassemia heterozygotes was significantly different (P<0.0002) compared to that in 986 simple beta-thalassemia heterozygotes with <2.5% Hb F, implicating an association between beta-thalassemia mutations and moderately increased Hb F levels, most notably codon 39 (C-->T), IVS-II-1 (G-->A), codon 6 (-A), and codon 8 (-AA), which accounted for 41/56 (73%) cases with >2.5% Hb F. In the remaining 15/56 (27%) cases, no common underlying globin genotypes could explain the raised Hb F levels. Overall, this study indicates that the control of Hb F levels in beta-thalassemia heterozygotes is heterogeneous and multi-factorial.

The role of trans-acting factors and DNA-bending in the silencing of human beta-globin gene expression

The molecular mechanisms which govern the develop-mental specificity of human beta-globin gene transcription have been studied in K562 cells, a human eyrthroleukemia line that expresses minimal beta-globin. Protein-binding analysis reveals that the 5' region contains three elements bound by trans-acting factors, beta-protein 1 (BP1) and beta-protein 2 (BP2). In vitro mutagenesis of each individual element in a beta-globin vector containing chloramphenicol acetyl-transferase (pCAT) followed by transient transfection into K562 cells increased levels of CAT activity 5. 5-fold higher than wild-type (wt) betaCAT, consistent with their silencing role. Mutagenesis of all three elements, however, resulted in activity significantly lower than wt betaCAT. BP1 and BP2 motifs have overlapping binding sites for high mobility group proteins (HMG1+2), DNA-bending factors, shown here to extrinsically bend the beta-globin promoter. Theoretically, mutations in all beta-protein binding sites could affect the binding of HMG1+2 sufficiently to impede DNA-protein and/or protein-protein interactions needed to facilitate constitutive gene expression. Placing two turns of DNA between BP1 and BP2 motifs also increased expression 3-fold, indicative of spatial constraints required for optimal silencing. However, insertion of the HMG1+2 DNA-bending motif (also equivalent to two turns) facilitates beta-silencing by re-establishment of BP1-BP2 proximity. Thus a combination of general DNA-bending and specific transcriptional factors appear to be involved in beta-globin silencing in the embryonic/fetal erythroid stage.

Glucocorticoid regulation of branched-chain alpha-ketoacid dehydrogenase E2 subunit gene expression

Regulation of the mammalian branched-chain alpha-ketoacid dehydrogenase complex (BCKAD) occurs under a variety of stressful conditions associated with changes in circulating glucocorticoids. Multiple levels of regulation in hepatocytes, including alteration of the levels of the structural subunits available for assembly (E1, alpha-ketoacid decarboxylase; E2, dihydrolipoamide acyltransferase; and E3, dihydrolipoamide dehydrogenase), as well as BCKAD kinase, which serves to phosphorylate the E1alpha subunit and inactivate complex activity, have been proposed. The direct role of glucocorticoids in regulating the expression of the murine gene encoding the major BCKAD subunit E2, upon which the other BCKAD subunits assemble, was therefore examined. Deletion analysis of the 5' proximal 7.0 kb of the murine E2 promoter sequence, using E2 promoter/luciferase expression minigene plasmids introduced into the hepatic H4IIEC3 cell line, suggested a promoter proximal region responsive to glucocorticoid regulation. Linker-scanning mutagenesis combined with deletion analysis established this functional glucocorticoid-responsive unit (GRU) to be located near the murine E2 proximal promoter site at -140 to -70 bp upstream from the transcription initiation site. The presence of this region in plasmid minigenes, containing varying amounts of the murine genomic sequence 5' upstream from proximal E2 promoter sequences, conferred 2-10 fold increases in luciferase reporter gene expression in H4IIEC3 cells, whether introduced by transient transfection or following co-selection for stable transfectants. The GRU region itself appeared to contain multiple interacting elements that combine to regulate overall E2 promoter activity in response to changing physiological conditions associated with varying concentrations of glucocorticoids and likely other hormonal effectors.

Binding of HMG-I(Y) elicits structural changes in a silencer of the human beta-globin gene

Proteins involved in repression of the human beta-globin gene may be useful in the treatment of sickle cell anemia, in conjunction with therapy to reactivate fetal globin genes. If there is a reciprocal elevation of gamma-globin expression upon repression, this approach could be useful in additional hemoglobinopathies. We previously showed that repression of the beta-globin gene appears to be mediated through two DNA sequences, silencers I and II, and identified a protein termed BP1 which binds to both silencer sequences. In this study, we cloned two cDNAs encoding proteins which bind to an oligonucleotide in silencer I containing a BP1 binding site. These cDNAs correspond to HMG-I and HMG-Y, isoforms regarded as architectural proteins. We demonstrate that binding of HMG-I(Y) to this oligonucleotide causes bending/flexure of the DNA. HMG-I(Y) also binds to a second oligonucleotide containing a BP1 binding site located in a negative control region upstream of the delta-globin gene, suggesting a role for HMG-I(Y) in repression of adult globin genes. Expression studies revealed that HMG-I(Y) is ubiquitously expressed in human tissues that do not express beta-globin, being present in 48 of 50 tissues and six hematopoietic cell lines examined. Furthermore, HMG-I(Y) expression is down-regulated during differentiation of primary erythroid cells. We present a model in which HMG-I(Y) alters DNA conformation to allow binding of repressor proteins, and in which the relative amount of HMG-I(Y) helps to determine the repressive state of the beta-globin gene.

Analysis of the promoter of the luteinizing hormone/human chorionic gonadotropin receptor gene in neuroendocrine cells

We investigated the molecular basis of luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptor gene transcription in immortalized alphaT3 gonadotropes, hypothalamic GT1-7 and hippocampal HN33p neurons. Nuclear run-on transcription, as well as transfection assays with fusion constructs of luciferase and the 5'-flanking region of LH/hCG receptor gene, revealed that GT1-7 neurons transcribe more than the alphaT3 or HN33p cells. Transient transfection of truncated reporter gene constructs and gel mobility shift assays revealed that while all neuroendocrine cells use the same promoter, they contain different levels of promoter binding proteins. Higher levels of these proteins may explain increased transcription of the LH/hCG receptor gene in GT1-7 neurons compared with alphaT3 and HN33p cells.

HbS/beta(del)-thalassemia associated with high levels of hemoglobins A2 and F in a Turkish family

Beta-thalassemia and sickle cell disease (SCD) are common disorders in Turkey. Compound heterozygosity for these two disorders (betaS/beta-thalassemia) is encountered frequently. In this report we present hematological and molecular data of two Turkish siblings with betaS/beta(del)-thalassemia caused by a 290 base pair (bp) deletion and associated with increased levels of hemoglobin A2 (HbA2) and hemoglobin F (HbF). Clinical analysis of the two patients showed a mild course of the disease. Haplotypic factors involved in increasing the levels of HbF were analyzed. The two patients showed no changes from the normal sequences at the XmnI site of Ggamma-globin promoter and the (AT)xTy microsatellite 5' to the beta-globin mRNA cap site. The removal of the region between positions -125 to +78 relative to the beta-globin gene mRNA cap site by the 290 bp deletion is thought to allow the beta-locus control region to interact with the promoters of the delta- and gamma-globin genes, leading to increased HbA2 and HbF levels.

Full Activity From Human β-Globin Locus Control Region Transgenes Requires 5′HS1, Distal β-Globin Promoter, and 3′ β-Globin Sequences

The locus control region (LCR) activates high-level human β-globin transgene expression. LCR cassettes composed of 5′HS2-4 linked to the 815 bp β-globin proximal promoter do not express fully. Here, we show that LCR (5′HS2-4) β-globin transgenes that also contain either 5′HS1 or the distal promoter fail to express fully in single- and low-copy transgenic mice. In contrast, full expression is obtained in the presence of both 5′HS1 and the distal promoter. Nine factor binding sites were identified in 5′HS1, using in vitro DNaseI footprint and gel retardation assays, and these include a strong Sp1/Sp3 site, four GATA-1 sites, and two sites that encompass an ACTAAC motif. LCR (5′HS1-4) β-globin transgene constructs with the distal promoter deleted or replaced by spacer DNA show that specific distal promoter sequences are required for full expression. An LCR (5′HS1-4) transgene construct with truncated downstream β-globin gene sequences indicates that 3′ sequences also play an important role. These results show that full expression of the β-globin gene directed by the LCR requires 5′HS1, the distal β-globin promoter, and 3′ sequences, and has implications for gene therapy construct design and models of LCR activation.

Full Activity From Human β-Globin Locus Control Region Transgenes Requires 5′HS1, Distal β-Globin Promoter, and 3′ β-Globin Sequences

The locus control region (LCR) activates high-level human β-globin transgene expression. LCR cassettes composed of 5′HS2-4 linked to the 815 bp β-globin proximal promoter do not express fully. Here, we show that LCR (5′HS2-4) β-globin transgenes that also contain either 5′HS1 or the distal promoter fail to express fully in single- and low-copy transgenic mice. In contrast, full expression is obtained in the presence of both 5′HS1 and the distal promoter. Nine factor binding sites were identified in 5′HS1, using in vitro DNaseI footprint and gel retardation assays, and these include a strong Sp1/Sp3 site, four GATA-1 sites, and two sites that encompass an ACTAAC motif. LCR (5′HS1-4) β-globin transgene constructs with the distal promoter deleted or replaced by spacer DNA show that specific distal promoter sequences are required for full expression. An LCR (5′HS1-4) transgene construct with truncated downstream β-globin gene sequences indicates that 3′ sequences also play an important role. These results show that full expression of the β-globin gene directed by the LCR requires 5′HS1, the distal β-globin promoter, and 3′ sequences, and has implications for gene therapy construct design and models of LCR activation.

Cellular and molecular effects of a pulse butyrate regimen and new inducers of globin gene expression and hematopoiesis

Cooley's anemia is characterized by a deficiency of beta-globin chains, a relative excess of alpha-globin chains, and consequent accelerated programmed death of developing erythroid cells in the bone marrow. Increasing expression of the gamma-globin genes to adequately balance excess alpha-globin chains can ameliorate this disorder. Butyrates induce gamma-globin experimentally, but can also cause cell growth arrest with prolonged exposure or high concentrations, which in turn can accelerate apoptosis. To determine if these potentially opposing effects can be balanced to enhance therapeutic efficacy, an intermittent "pulsed" regimen of butyrate was evaluated. Following induction of gamma-globin mRNA and protein synthesis, total hemoglobin increased in beta-thalassemia patients by more than 2 g/dl above baseline, and Hb F increased above 20% in 5/8 sickle cell patients from baseline levels of 2% Hb F. Specific regulatory regions were identified in the gamma- and beta-globin gene promoters to which new binding of transcription factors, including alpha CP2 (an activator of gamma globin) occur during therapy solely in the butyrate-responsive patients. Other compounds which induce gamma globin, derivatives of acetic, phenoxyacetic, propionic, and cinnamic acids, and dimethylbutyrate, are under investigation. Some of these newer gamma-globin inducers (designed hemokines) provide better potential as therapeutics by also acting to increase hematopoietic cell viability and proliferation. Pharmacologic induction of expression of the endogenous gamma-globin genes is a realistic approach to therapy of the beta-globin disorders for many patients, with some effective agents available now and new therapeutics, with enhanced activities, under development.

Combined effect of two different polymorphic sequences within the beta globin gene cluster on the level of HbF

Beta thalassemia and Hb Lepore heterozygotes included in this study exhibit fetal hemoglobin levels varying from trace quantities to 14% (1.74 g/dl) of total hemoglobin in the adult. In this work, we have examined the correlation of DNA sequence polymorphisms with the observed HbF level. The analysis of polymorphic markers within the beta globin cluster in 39 individuals heterozygous for beta thalassemia or Hb Lepore confirms the previous findings for homozygous beta thalassemia: the presence of both an (AT)9 T5 sequence configuration at position -540 of the beta globin gene and a (C --> T) variation at -158 of the Ggamma globin gene is associated with elevated expression of HbF. However, at least one defective beta globin gene is required to reveal this association. The best evidence is from the study of individuals heterozygous for Hb Lepore with various levels of HbF. In these individuals it was possible to explore the effect of a single (AT)x Ty motif (the other being absent from the rearranged Lepore chromosome) on HbF expression. The presence of the (AT)9 T5 configuration increases HbF level from a median of 0.515 g/dl observed in (AT)7 T7 subjects, to 1.39 g/dl. We confirm the existence of linkage disequilibrium between the (C --> T) variation at -158 of Ggamma gene and the (TG)13 configuration at the second intervening sequence (IVS-2) of Agamma gene and identify two new polymorphisms in this region: (TG)7 (CG)5 (TG)8 linked to haplotype V and (TG)8 (CG)5 (TG)10 linked to haplotype II. This study suggests that two distinct regions of the beta cluster, whether in cis or in trans to each other, can interact to enhance HbF expression when a beta thalassemic determinant is present in heterozigosity.

Heterozygous beta-thalassemia with thalassemia intermedia phenotype

In this study we investigated the molecular bases of the beta-thalassemia intermedia phenotype in six patients belonging to two unrelated families of Sardinian descent. Sequence analysis of the beta globin gene from these patients detected, as the sole abnormality, the heterozygosity for the codon 39 nonsense mutation. The A gamma and Ggamma promoters as well as the HS2 and HS3 core sequences of the beta globin LCR from these patients, did not show any non-polymorphic nucleotide variation from the consensus sequence. One of the parents was heterozygous for codon 39 nonsense mutation but showed the beta-thalassemia carrier phenotype; the other was hematologically normal and had an entirely normal beta globin gene sequence. In both families, other members showed the typical hematological phenotype, clinically silent, of heterozygous beta thalassemia. To explain the thalassemia intermedia phenotype, we postulated the presence of an unknown molecular defect interacting with the beta globin gene mutation. Haplotype analysis excluded that this postulated defect lies in the beta globin gene cluster.

Trans-acting factors from the human fetal liver binding to the human epsilon-globin gene silencer

The developmental stage-specific silencing of the human epsilon-globin gene during embryonic life is controlled, in part, by the silencer (-392 bp approximately -177 bp) upstream of this gene. In order to elucidate its role, the nuclear extract from the human fetal liver has been prepared and the interactions between trans-acting factors and this silencer element have been examined. By using DNaseI footprinting assay, a major protected region from -278 bp to -235 bp within this silencer element was identified. Furthermore, we found in gel mobility shift assay and Southwestern blotting assay that there were at least four trans-acting factors (MW approximately 32, 28, 26 and 22 kD) in the nuclear extract isolated from the human fetal liver, which could specifically bind to this region. Our results suggested that these trans-acting factors might play an important role in silencing the human embryonic epsilon-globin gene expression at the fetal stage through the interactions with this silencer.

Efficient 5' end labeling of dephosphorylated DNA

Efficient 5'-end labeling of DNA is an important procedure in recombinant DNA technology. Prior to labeling, it is important to inactivate alkaline phosphatase, used in the dephosphorylation of the DNA, by using proteinase K. Removal of proteinase K is usually performed by extracting twice with chloroform:isoamyl alcohol. In this report we show that extracting the sample four times with chloroform results in more efficient removal of sodium dodecyl sulfate (SDS), an important constituent of proteinase K buffer, which allows a 25- to 40-fold increase in labeling efficiency compared with extracting twice or once with chloroform, respectively. Unremoved SDS inhibits efficient labeling, possibly by inhibiting the activity of the kinase.

Sequence polymorphisms of potential functional relevance in the beta-globin gene locus

The purpose of this review is to give a general up-date of the most recent developments concerning polymorphisms within the beta-globin gene cluster. The first polymorphisms to be identified were mostly restriction fragment length polymorphisms. They were important markers both for their use as diagnostic tools and for anthropological investigations. Although they have been associated with specific patterns of globin gene expression in the hemoglobinopathies, none have been demonstrated to have any intrinsic functional significance. More recently, additional single nucleotide variations and microsatellite-like polymorphic simple sequence repeats have been identified which are frequently located in trans-acting protein binding segments and hence might affect regulatory processes.

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.

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.

Recombination of endogenous D2 dopamine receptor gene with a metallothionein promoter in GH4C1 cells confers functional and inducible D2 response

We have previously shown that expression of a functional endogenous D2 short dopamine receptor is obtained in GH4C1 cells following transfection with a plasmid that confers resistance to neomycin (pRSVNeo) (Allard et al. (1993) Biochem. Biophys. Res. Commun. 193, 801-807). In order to better understand the mechanisms responsible for such a phenomenon, we cloned and sequenced the 5' region of the D2 gene present in native GH4C1 cells as well as the cDNA of transfected cells. No homology with the published sequence of the rat D2 dopamine receptor promoter was found; however, this region has perfect homology with the mouse metallothionein promoter. In cells expressing D2 receptor, the promoter is fully functional and can regulate dopaminergic D2 receptor mRNA levels and receptor expression in a dose-dependent manner in the presence of Zn2+ or Cd2+. The receptor level is raised from 500 to 3000 fmol/mg of protein in the presence of 100 microM of Zn2+. These results suggest that in GH4C1 cells, a recombination between the mouse metallothionein promoter and the D2 dopamine receptor took place. This system provides us with a cell line expressing an endogenous dopamine D2 receptor in which the level of expression can be easily modulated.