Nuclear protein-binding sites in a transcriptional control region of the rabbit alpha-globin gene

Changes in DNA methylation of erythroid-specific genes in K562 cells exposed to catechol in long term

Catechol is one of phenolic metabolites of benzene that is a general occupational hazard and a ubiquitous environmental air pollutant. Catechol also occurs naturally in fruits, vegetables and cigarettes. Previous studies have revealed that 72h exposure to catechol improved hemin-induced erythroid differentiation of K562 cells accompanied with elevated methylation in erythroid specific genes. In present study, K562 cells were treated with 0, 10 or 20μM catechol for 1-4weeks, hemin-induced hemoglobin synthesis increased in a concentration- and time-dependent manner and the enhanced hemoglobin synthesis was relatively stable. The mRNA expression of α-, β- and γ-globin genes, erythroid heme synthesis enzymes PBGD and ALAS2, transcription factor GATA-1 and NF-E2 showed a significant increase in K562 cells exposed to 20μM catechol for 3w, and catechol enhanced hemin-induced mRNA expression of these genes. Quantitative MassARRAY methylation analysis also confirmed that the exposure to catechol changed DNA methylation levels at several CpG sites in several erythroid-specific genes and their far upstream of regulatory elements. These results demonstrated that long-term exposure to low concentration of catechol enhanced the hemin-induced erythroid differentiation of K562 cells, in which DNA methylation played a role by up-regulating erythroid specific genes.

Long-term exposure of K562 cells to benzene metabolites inhibited erythroid differentiation and elevated methylation in erythroid specific genes

Benzene is a common occupational hazard and a widespread environmental pollutant. Previous studies have revealed that 72 h exposure to benzene metabolites inhibited hemin-induced erythroid differentiation of K562 cells accompanied with elevated methylation in erythroid specific genes. However, little is known about the effects of long-term and low-dose benzene metabolite exposure. In this study, to elucidate the effects of long-term benzene metabolite exposure on erythroid differentiation, K562 cells were treated with low-concentration phenol, hydroquinone and 1,2,4-benzenetriol for at least 3 weeks. After exposure of K562 cells to benzene metabolites, hemin-induced hemoglobin synthesis declined in a concentration- and time-dependent manner, and the hemin-induced expressions of α-, β- and γ-globin genes and heme synthesis enzyme porphobilinogen deaminase were significantly suppressed. Furthermore, when K562 cells were continuously cultured without benzene metabolites for another 20 days after exposure to benzene metabolites for 4 weeks, the decreased erythroid differentiation capabilities still remained stable in hydroquinone- and 1,2,4-benzenetriol-exposed cells, but showed a slow increase in phenol-exposed K562 cells. In addition, methyltransferase inhibitor 5-aza-2'-deoxycytidine significantly blocked benzene metabolites inhibiting hemoglobin synthesis and expression of erythroid genes. Quantitative MassARRAY methylation analysis also confirmed that the exposure to benzene metabolites increased DNA methylation levels at several CpG sites in several erythroid-specific genes and their far-upstream regulatory elements. These results demonstrated that long-term and low-dose exposure to benzene metabolites inhibited the hemin-induced erythroid differentiation of K562 cells, in which DNA methylation played a role through the suppression of erythroid specific genes.

Molecular and cellular analysis of three novel alpha2-globin gene promoter mutations [HBA2: c.-59C>T], [HBA2: c.-81C>A] and [HBA2: c.-91G>A] reveal varying patterns of transcriptional and translational activities

While point mutations affecting the promoter region of β-globin gene are widely described, there are no well characterised reports of any point mutations currently found in the promoter of the α2-globin (HBA2) gene. We present clinical and experimental data for three novel HBA2 gene core and proximal promoter mutations. Using an in vitro system designed to assess the impact of point mutations, the three novel [HBA2:c.-59C>T], [HBA2:c.-81C>A] and [HBA2:c.-91G>A] promoter mutations identified in three unrelated patients were analysed for HBA2 gene transcriptional and translational activities. Following the generation and transfection of expression vectors carrying each mutation, the HBA2 transcription activity of the promoters from each mutant was analysed with quantitative real time-PCR (qReTi-PCR) technique. Immunofluorochemistry (IFC) was used to analyse HBA2 protein synthesis. The analyses showed that [HBA2:c.-59C>T] and [HBA2:c.-91G>A] mutant constructs caused significant reduction in the HBA2 transcription levels by 53.7% (p = 0.0008) and 36.2% (p = 0.004), respectively, resulting in markedly lower HBA2 protein labelling when compared to the wild type as shown with subsequent IFC analysis. Conversely, the [HBA2:c.-81C>A] construct showed no significant changes in either transcription (p = 0.089) or in protein labelling when compared to the wild type. The equal pAmp transcription levels found in each group confirmed that the observed labelling differences were not due to varying transfection efficiencies. This study emphasises the importance of in vitro studies to establish the impact of base substitutions on the level of gene expression, and the value of these studies in clinicopathological correlation so that appropriate advice can be given in genetic counselling.

Interplay between heme oxygenase-1 and the multifunctional transcription factor yin yang 1 in the inhibition of intimal hyperplasia

RATIONALE

induction of heme oxygenase (HO)-1 protects against experimental atherosclerotic diseases, and certain pharmacological HO-1 inducers, like probucol, inhibit the proliferation of vascular smooth muscle cells and, at the same time, promote the growth of endothelial cells in vivo and in vitro.

OBJECTIVE

because such cell-specific effects are reminiscent of the action of the transcription factor Yin Yang (YY)1, we tested the hypothesis that there is a functional relationship between HO-1 and YY1.

METHODS AND RESULTS

we report that probucol increases the number of YY1(+) cells in rat carotid artery following balloon injury at a time coinciding with increased HO-1 expression. The drug also induces the expression of YY1 mRNA and protein in rat aortic smooth muscle cells (RASMCs) in vitro, as do other known HO-1 inducers (tert-butylhydroquinone and hemin) and overexpression of HO-1 using a human HMOX1 cDNA plasmid. Conversely, overexpression of YY1 induces expression of HO-1 in RASMCs. Induction of YY1 expression is dependent on HO-1 enzyme activity and its reaction product CO, because pharmacological inhibition of heme oxygenase activity or CO scavenging block, whereas exposure of RASMCs to a CO-releasing molecule increases, YY1 expression. Furthermore, RNA interference knockdown of YY1 prevents probucol or adeno-HO-1 from inhibiting RASMC proliferation in vitro and neointimal formation in vivo.

CONCLUSIONS

our findings show, for the first time, that HO-1 functionally interplays with the multifunctional transcription factor YY1 and that this interplay explains some of the protective activities of HO-1.

Comparative expression of homologous proteins. A novel mode of transcriptional regulation by the coding sequence folding compatibility of chimeras

Recombinant acetylcholinesterases (AChE) are produced at systematically different levels, depending on the enzyme species. To identify the cause of this difference, we designed expression vectors that differed only by the central region of the coding sequence, encoding Torpedo, rat, and Bungarus AChEs and two reciprocal rat/Bungarus and Bungarus/rat chimeras. We found that folding is a limiting factor in the case of Torpedo AChE and the chimeras, for which only a limited fraction of the synthesized polypeptides becomes active and is secreted. In contrast, the fact that rat AChE is less well produced than Bungarus AChE reflects the levels of their respective mRNAs, which seem to be controlled by their transcription rates. A similar difference was observed in the coding and noncoding orientations; it seems to depend on multiple cis-elements. Using CAT constructs, we found that a DNA fragment from the Bungarus AChE gene stimulates expression of the reporter protein, whereas a homologous fragment from the rat AChE gene had no influence. This stimulating effect appears different from that of classical enhancers, although its mechanism remains unknown. In any case, the present results demonstrate that the coding region contributes to control the level of gene expression.

Identification and characterization of a novel phorbol ester-responsive DNA sequence in the 5'-flanking region of the human dopamine beta-hydroxylase gene

The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), enhances transcription of many eukaryotic genes, including that for dopamine beta-hydroxylase (DBH). In the present study, we report identification and characterization of a novel sequence motif residing in the 5'-flanking region of the human DBH gene, which mediates transcriptional induction by TPA. Deletional analyses indicated the promoter region between -223 and -187 base pairs to be critical. Whereas this region does not contain any putative regulatory motifs with significant sequence homology to the AP-1 motif, extensive deletional and site-directed mutational analyses indicated that a sequence between -210 and -199 base pairs, 5'-ATCCGCCTGTCT-3', may represent a novel TPA-response element (TRE). In addition, alteration of the YY1-binding site decreased TPA-mediated induction of the DBH promoter activity, suggesting that contiguous cis-regulatory element(s) cooperate with this novel sequence motif. Furthermore, insertional mutation analyses between the YY1-binding site and the cyclic AMP-responsive element indicated that the stereospecificity of these motifs is important for intact transcriptional induction by TPA. Taken together, these data suggest that transcriptional up-regulation of the human DBH gene in response to TPA requires coordination of a novel TRE (human DBH TRE, hDTRE), cyclic AMP-responsive element, and the YY1-binding site.

Characteristics of the intron involvement in the mitogen-induced expression of Zfp-36

Zfp-36, the gene encoding the putative zinc finger protein tristetraprolin (TTP), is rapidly induced in fibroblasts by a variety of growth factors. Recent gene knockout experiments have shown that TTP-deficient mice developed arthritis, cachexia, and autoimmunity, all apparently mediated by an excess of tumor necrosis factor alpha. We recently showed that full serum inducibility of Zfp-36 requires elements in the promoter; in addition, removal of the single intron strikingly inhibited serum-induced TTP expression. We show here that replacement of the intron with unrelated sequences, or removal of 95% of the intron but retention of the splice sites, each resulted in the maintenance of approximately 45 and 19%, respectively, of full serum-induced expression. In addition, deletion of intron sequences base pairs 601-655 decreased the serum-induced expression of TTP by 65%. Sequence base pairs 618-626 bound specifically to the transcription factor Sp1; mutation of this binding motif decreased TTP expression by 70%, suggesting that Sp1 binding to this motif contributes to serum induction of Zfp-36. We conclude that full serum-induced expression of Zfp-36 depends on the activation of conventional promoter elements as well as elements in the single intron, and that the presence per se of the intron in its natural location also contributes significantly to the regulated expression of this gene.

Characterization of functional domains within the multifunctional transcription factor, YY1

YY1 is a multifunctional transcription factor capable of either activation or repression of transcription. Using a series of mutant proteins, we have characterized domains responsible for activation or repression. We found that the YY1 transcriptional activation domain lies near the amino terminus and requires amino acids 16-29 and 80-100 for maximal activity. The region between residues 16 and 29 has the potential to form an acidic amphipathic helix, whereas residues between 80 and 100 are rich in proline and glutamine. The YY1 repression domain lies near the carboxyl terminus and is embedded within the YY1 zinc finger region necessary for binding to DNA. Deletion of YY1 amino acids, which include zinc fingers 3 and 4, abolishes repression. However, site-directed mutagenesis, progressive deletion, and internal deletion mutant analyses indicate that the normal structures of zinc fingers 3 and 4 are not required for repression.

Cyclophilin A and FKBP12 interact with YY1 and alter its transcriptional activity

YY1 is a zinc finger transcription factor with unusual structural and functional features. In a yeast two-hybrid screen, two cellular proteins, cyclophilin A (CyPA) and FK506-binding protein 12 (FKBP12), interacted with YY1. These interactions are specific and also occur in mammalian cells. Cyclosporin A and FK506 efficiently disrupt the YY1-CyPA and YY1-FKBP12 interactions. Overexpression of human CyPA and FKBP12 have different effects on YY1-regulated transcription with these effects being promoter-dependent. These results suggest that immunophilins may be mediators in the functional role of YY1.

Flanking and intragenic sequences regulating the expression of the rabbit alpha-globin gene

Despite their descent from a common ancestral gene and the requirement for coordinated, tissue-specific regulation, the alpha- and beta-globin genes in many mammals are regulated in distinctly different ways. Unlike the beta-globin gene, the rabbit alpha-globin gene is transiently expressed at a high level without an added enhancer in transfected erythroid and non-erythroid cells. By examining a series of alpha/beta fusion genes, we show that internal sequences of the rabbit alpha-globin gene (within the first two exons and introns) are required along with the 5' flank for this enhancer-independent expression. Furthermore, deletion of the introns of the alpha-globin gene, or replacement by introns of the beta-globin gene, results in severely decreased expression of the transfecting genes. Hybrid constructs between segments of the alpha-globin gene and a luciferase gene confirm that internal alpha-globin sequences are needed for high level production of RNA in transfected cells. The flanking and internal sequences implicated in regulation of the rabbit alpha-globin gene coincide with a prominent CpG-rich island and may comprise an extended promoter (including both flanking and intragenic sequences) that is active in transfected cells without an enhancer.

A switch region determines the cell type-specific positive or negative action of YY1 on the activity of the human papillomavirus type 18 promoter

YY1 is a zinc finger transcription factor which acts as either a repressor or an activator dependent on the promoter context. YY1 is a potent activator of the genuine human papillomavirus type 18 (HPV-18) upstream regulatory region (URR) in HeLa cells, which are known for high-level expression of the HPV-18 early genes. The activating activity of YY1 is dependent on the presence of a newly identified switch region located upstream of the YY1 binding site. Deletion of this region causes YY1 to act as a repressor of HPV-18 promoter activity. In vivo footprinting of the HPV-18 URR and an in vitro electrophoretic mobility shift assay identified proteins binding to the switch region. Site-directed mutagenesis of the switch region and YY1 binding sites suggests that these two regions work in concert to yield high-level HPV-18 URR activity in HeLa cells but not in HepG2 cells, where HPV-18 is almost inactive. These data identified a novel mode of cell type-specific regulation of HPV-18 promoter activity by positive or negative action of YY1, determined by the switch region binding factor(s).