CACCC and GATA-1 sequences make the constitutively expressed alpha-globin gene erythroid-responsive in mouse erythroleukemia cells

DNase I hypersensitivity and epsilon-globin transcriptional enhancement are separable in locus control region (LCR) HS1 mutant human beta-globin YAC transgenic mice

Expression of the five beta-like globin genes (epsilon, Ggamma, Agamma, delta, beta) in the human beta-globin locus depends on enhancement by the locus control region, which consists of five DNase I hypersensitive sites (5'HS1 through 5'HS5). We report here a novel enhancer activity in 5'HS1 that appears to be potent in transfected K562 cells. Deletion analyses identified a core activating element that bound to GATA-1, and a two-nucleotide mutation that disrupted GATA-1 binding in vitro abrogated 5'HS1 enhancer activity in transfection experiments. To determine the in vivo role of this GATA site, we generated multiple lines of human beta-globin YAC transgenic mice bearing the same two-nucleotide mutation. In the mutant mice, epsilon-, but not gamma-globin, gene expression in primitive erythroid cells was severely attenuated, while adult beta-globin gene expression in definitive erythroid cells was unaffected. Interestingly, DNaseI hypersensitivity near the 5'HS1 mutant sequence was eliminated in definitive erythroid cells, whereas it was only mildly affected in primitive erythroid cells. We therefore conclude that, although the GATA site in 5'HS1 is critical for efficient epsilon-globin gene expression, hypersensitive site formation per se is independent of 5'HS1 function, if any, in definitive erythroid cells.

The control of expression of the alpha-globin gene cluster

The alpha-globin gene cluster is located at the very tip of the short arm of chromosome 16. It produces the alpha-like globins, which is combined with the beta-like globins to form hemoglobin, and its mutants cause alpha-thalassemia, which is one of the most common genetic diseases. Its expression shows a tissue and developmental stage specificity that is balanced with that of the beta-globin gene cluster. In this article, we summarize the research on the control of expression of the alpha-globin gene cluster, mainly with respect to the alpha-major regulatory element (alpha-MRE): HS-40, the tissue-specific and developmental control of its expression, and its chromosomal environment. In summary, the alpha-globin gene cluster is expressed in an open chromosomal environment; HS-40, the 5'-flanking sequence, the transcribed region, and the 3'-flanking sequence interact to fully regulate its expression.

Chromatin structure and transcriptional regulation of the beta-globin locus

Chromatin structure plays a critical role in eukaryotic gene transcriptional regulation. The beta-globin locus provides an ideal system within which to study the interplay between chromatin structure and transcriptional regulation. The process of beta-globin locus activation is remarkably intricate and involves at least two distinct events: chromatin opening and gene activation. Great progress has been made in recent years in understanding how locus control regions confer high-level expression to linked genes. Current interest focuses on some special events, including formation of locus control region hypersensitivity sites, ATP-dependent chromatin remodeling, localized H3 hyperacetylation, and intergenic transcription, which link chromatin and beta-globin locus regulation. These events, and their possible molecular bases, are summarized together with speculations concerning their connections.

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.

Estrogen receptor diminishes DNA-binding activities of chicken GATA-1 and CACCC-binding proteins

The estrogen receptor (ER) repressed erythroid differentiation and erythroid-specific gene expression. In this study, we investigated the effect of ER alpha (referred to throughout as ER) on DNA-binding activities of transcription factors involved in regulating the expression of erythroid-specific genes, and, in particular, the histone H5 gene. Using electrophoretic mobility shift assays, we found that in the presence of rabbit reticulocyte lysate, human ER reduced the binding activities of chicken immature erythrocyte nuclear extracted proteins to GATA and CACCC sites in the H5 promoter and enhancer. In contrast, the binding activities of NF1 and Sp1 were not affected by ER. Binding of ER to an estrogen response element was enhanced by addition of rabbit reticulocyte lysate. This lysate was also necessary for ER to diminish the DNA-binding activity of GATA-1. These results suggest that additional factor(s) are necessary for full ER function. Both GATA-1 and CACCC-binding proteins are critical for the developmentally regulated expression of erythroid-specific genes. We hypothesize that interference in DNA-binding activities of GATA-1 and CACCC-binding proteins is the mechanism by which the ER inhibits regulation of these genes.

Cloning, characterization, and mapping of a murine promiscuous chemokine receptor gene: homolog of the human Duffy gene

We report here the isolation and genomic organization of the orthologous mouse Duffy gene, named Dfy. It is a single copy gene located in chromosome 1 in a region homologous to the human Duffy gene (FY). Sequence analyses indicate that Dfy consists of two exons: exon 1 of 55 nucleotides, which encodes 7 amino acid residues; and exon 2 of 1038 nucleotides, which encodes 327 residues. The single intron consists of 462 nucleotides. The 5'-end promoter region contains motifs involved in vertebrate development in addition to potential binding sites of factors for globin transcription. The open reading frame (ORF) shows 60% homology with the human Duffy protein. However, mouse erythrocytes are serologically Duffy-negative and mouse erythrocyte membrane proteins do not cross-react with two Duffy-specific rabbit polyclonal antibodies. The deduced protein predicts a M(r) of 36,692 and carries three potential N-glycosylation sites to asparagine residues. Hydropathy analysis predicts an exocellular amino-terminal domain of 57 residues, seven transmembrane alpha-helices, and an endocellular carboxy-terminal domain of 29 residues. In bone marrow and spleen, Dfy expresses a major 1.4-kb and a minor 1.8-kb mRNA. Contrary to humans, Dfy is expressed in liver, synthesizing a 1.4-kb mRNA, and is repressed in kidney. Dfy is highly expressed in mouse brain and produces a major 8.5-kb and a minor 10.2-kb mRNA. The human erythroleukemia K562 cells, transfected with cDNA encoding the mouse Duffy-like protein and mouse erythrocytes, have the same chemokine binding profiles indicating that they contain the same protein.