Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0039730 (thalassemia)
 10,305 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have previously described a family of Northern Sardinian descent in which the propositus was affected by thalassemia major resulting from compound heterozygosity for codon 39 nonsense mutation and the beta +IVS II nt 745 mutation and in which all heterozygotes for the beta +IVS II nt 745 mutation had normal hemoglobin (Hb) A2 levels. To define the reasons for normal HbA2 levels in otherwise typical beta-thalassemia heterozygotes, we cloned and sequenced the delta-thalassemia gene in cis to the beta +IVS II nt 745 mutation. The sequence analysis showed a single nucleotide substitution (G----A) at position 69 nts (delta +69) downstream to the polyA addition site. Dot blot analysis with an oligonucleotide probe complementary to the delta +69 mutation detected this mutation in several heterozygotes for the beta +IVS II nt 745 mutation from the proband's family, but failed to show it either in a group of normal individuals of the same origin or in nonrelated heterozygotes for the beta +IVS II nt 745 mutation of the same or different descent from the proband. The delta +69 (G----A) mutation may be responsible for the low delta-globin output from the beta +IVS II nt 745 chromosome or could be a silent polymorphism not affecting the function of the delta-globin gene. The normal G at position 69 is part of a sequence very similar to the core DNA (A/T)GATA(A/G) motif (GATA box) that is a binding site for the GATA-1 protein. Gel-retardation assay has shown that a DNA fragment containing the GATA motif with the G----A at position +69 has increased binding affinity for erythroid-specific DNA binding protein(s) as compared with the wild-type sequence. These findings may suggest that the delta +69 mutation is responsible for the deficient function of the in cis delta-globin gene.
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PMID:Delta-thalassemia due to a mutation in an erythroid-specific binding protein sequence 3' to the delta-globin gene. 130 71

The Indian delta beta-thalassaemia, with elevated fetal gamma globin gene expression, was previously found to have a large deletion beginning 1 kb 3' of the (A) gamma globin gene at GenBank HUMHBB coordinate 42151, and extending into a new L1 sequence. We have now determined the 3' breakpoint of this deletion, and in doing so we have extended the known beta-globin gene cluster DNA sequence from its end at 73326 to projected GenBank coordinate 79016. These data show that the deletion is 32.6 kb long, terminating 11 kb 3' of the beta-globin gene. This 3' breakpoint is at 74772, within a 3.4 kb partial L1 repeat at 74263-77665; the Black ((A) gamma delta beta)(0)-thalassaemia also terminates in this L1, at 76508. In addition, two Alu sequences were found, at 73692-73816 and 78171-78441. Among the protein-binding DNA sequence motifs 3' to the Indian delta beta-thalassaemia breakpoint, at 76581/76607 there is a TGATAA/ACACCC pair that binds the erythroid-specific GATA-1 and ubiquitous CACCC-box binding proteins. We hypothesize that elevated fetal haemoglobin may be due to an enhancer or enhancers 3' to the deletion breakpoints and may involve the TGATAA/ACACCC pair.
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PMID:The 32.6 kb Indian delta beta-thalassaemia deletion ends in a 3.4 kb L1 element downstream of the beta-globin gene. 141 24

Delta-thalassemia is a complex group of inherited disorders of globin genes characterized by impaired synthesis of the delta-globin chain. The T-C substitution was detected at position -77 of the delta-globin gene isolated from three independent Japanese individuals who were homozygotes for delta-thalassemia. To elucidate the significance of the mutation in delta-globin gene expression, we investigated the genotype of three delta-thalassemia homozygotes and 58 normal individuals using dot blot hybridization of the polymerase chain reaction (PCR)-amplified DNA. The mutation was observed in six alleles of three homozygotes, while no mutation was detected in 116 alleles of normal individuals, thereby indicating the close association of this mutation with the thalassemia phenotype. Since the mutation (TTATCT-TCATCT) is located within the inverted binding motif of GATA-1 (T or A-G-A-T-A-G or A), an erythroid cell-specific transcription factor, we did gel retardation assays using nuclear extracts from the erythroid cells. We found that GATA-1 binds the oligonucleotide spanning positions -61 to -90, but does not bind to the oligonucleotide with the mutation at position -77. Competition gel retardation assays showed that GATA-1 binding can be competed out by the fragment with the GATA-1 motif, but not with the mutant oligonucleotide. Analysis of the transient expression of the CAT gene linked to the delta-globin gene promoter region demonstrated that the construct with the mutant promoter region was expressed about 20-fold less compared with the normal one. Thus, the mutation at position -77 impairs delta-globin gene expression by abolishing GATA-1 binding to the AGATAA sequence of the promoter region of the delta-globin gene. This provides a good example of involvement of tissue-specific transacting factors in the molecular pathogenesis of hereditary diseases.
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PMID:Delta-thalassemia caused by disruption of the site for an erythroid-specific transcription factor, GATA-1, in the delta-globin gene promoter. 151 47

We have previously described a unique type of delta beta-thalassemia in a Chinese family characterized by increased expression of the G gamma and A gamma fetal globin genes in the absence of a large deletion in the beta-globlin gene cluster. Our earlier study of the beta-globin gene on this delta beta-thalassemia chromosome showed a promoter mutation in the TATA box. In this report, we describe the results of our study of the fetal globin domain of this delta beta-thalassemia chromosome. We have cloned a 13-kb DNA fragment that includes the G gamma and the A gamma genes and the 3' A gamma enhancer element of this delta beta-thalassemia chromosome. DNA sequence analysis of the G gamma and A gamma-globin genes including their promoters did not show any mutations, but analysis of the putative enhancer element downstream from the A gamma-globin gene showed a C to T substitution 2,401 nucleotides downstream from the A gamma cap site. We performed DNA linkage analysis to determine if this mutation is unique to this chromosome or represents a common polymorphism. Our linkage analysis showed that this mutation is not a common polymorphism and that it is also not an intrinsic part of the haplotype of the chromosome on which it was found. We also studied the interaction of nuclear proteins from erythroid and nonerythroid cells with the DNA sequences surrounding this mutation. We have shown by in vitro DNase I footprinting that this mutation falls within a region that is occupied by a novel DNA-binding protein that binds to this site in nuclear extracts from erythroid, but not nonerythroid cells. The binding of this nuclear protein to DNA appears to be dependent on GATA-1 binding to an adjacent GATA-1 site. We have also developed a new functional assay to compare the activity of the normal and mutant A gamma enhancer elements in erythroid cells. Analysis of the activity of the mutant enhancer shows that the mutation completely eliminates all enhancer activity in this assay. These findings suggest that this mutation of the A gamma enhancer on a chromosome that carries a partially inactivated beta-globin gene may be responsible for the increased expression of both gamma-globin genes seen in this condition.
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PMID:Increased expression of the G gamma and A gamma globin genes associated with a mutation in the A gamma enhancer. 751 19

Transcription factor GATA-1 is essential for the development of erythroid cells and megakaryocytes. Each of its 2 zinc fingers is critical for normal function. The C-terminal finger is necessary for DNA binding. The N finger mediates interaction with FOG-1, a cofactor for GATA-1, and also modulates DNA-binding affinity, notably at complex or palindromic GATA sites. Residues of the N finger-mediating interaction with FOG-1 lie on the surface of the N finger facing away from DNA. Strong sequence conservation of residues facing DNA suggests that this other surface may also have an important role. We report here that a syndrome of X-linked thrombocytopenia with thalassemia in humans is caused by a missense mutation (Arg216Gln) in the GATA-1 N finger. To investigate the functional consequences of this substitution, we used site-directed mutagenesis to alter the corresponding residue in GATA-1. Compared with wild-type GATA-1, Arg216Gln GATA-1 shows comparable affinity to single GATA sites but decreased affinity to palindromic sites. Arg216Gln GATA-1 interacts with FOG-1 similarly with wild-type GATA-1. Arg216Gln GATA-1 supports erythroid maturation of GATA-1 erythroid cells, albeit at reduced efficiency compared with wild-type GATA-1. Together, these findings suggest that residues of the N finger of GATA-1-facing DNA contribute to GATA-1 function apart from interaction with the cofactor FOG-1. This is also the first example of beta-thalassemia in humans caused by a mutation in an erythroid transcription factor.
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PMID:X-linked thrombocytopenia with thalassemia from a mutation in the amino finger of GATA-1 affecting DNA binding rather than FOG-1 interaction. 1220 Mar 64

Hydroxyurea (HU) has been shown to increase the proportion of fetal haemoglobin (HbF) in most sickle cell patients. A low-dosage regimen increased total haemoglobin (Hb) levels in some thalassaemia intermedia patients by preferentially increasing beta-globin biosynthesis. To further characterize these apparent dose-dependent effects of HU, we examined erythroid cells exposed to HU (5-100 micro mol/l) in two-phase liquid culture. Low doses (from 5 to 25 micro mol/l) increased Hb levels by up to 2.7-fold, and a high dose (100 micro mol/l) increased Hb levels when added at d 3-6 of phase II, with no significant changes in response to HU during the late stage of phase II culture (> or = 9 d). HU exposure during d 0-3 of phase II culture increased the number of erythroid colonies to a maximum of fivefold at 5 micro mol/l HU. GATA-1 mRNA was downregulated at a high dose and GATA-2 was dose dependently upregulated over a lower dosage range. Treatment with 100 micro mol/l HU dramatically upregulated the death receptor DR-5, caspase 3, as determined by cDNA microarray analysis. In contrast, 10 micro mol/l HU modestly upregulated mRNA levels of the early growth response gene. Our results suggest that HU exerts concentration-dependent effects on HbF production and erythropoiesis and that these two effects are mediated by distinct molecular mechanisms.
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PMID:Hydroxyurea exerts bi-modal dose-dependent effects on erythropoiesis in human cultured erythroid cells via distinct pathways. 1247 94

GATA family transcription factors play essential roles in broad developmental settings. GATA-1, one of the hematopoietically expressed members, is required for normal erythroid and megakaryocytic differentiation. Over the past few years, mutations in the gene encoding GATA-1 have been linked to several human hematologic disorders, including X-linked dyserythropoietic anemia and thrombocytopenia, X-linked thrombocytopenia and beta-thalassemia, and Down syndrome acute megakaryoblastic leukemia. This review summarizes the role of GATA-1 during normal hematopoiesis and discusses how disease-associated mutations may affect its function.
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PMID:GATA transcription factors in hematologic disease. 1615 17

Alpha-hemoglobin-stabilizing protein (AHSP) is an erythroid protein that binds and stabilizes alpha-hemoglobin during normal erythropoiesis and in pathological states of alpha-hemoglobin excess. AHSP has been proposed as a candidate gene in some Heinz body hemolytic anemias and as a modifier gene in the beta-thalassemia syndromes. To gain additional insight into the molecular mechanisms controlling the erythroid-specific expression of the AHSP gene and provide the necessary tools for further genetic studies of these disorders, we have initiated identification and characterization of the regulatory elements controlling the human AHSP gene. We mapped the 5'-end of the AHSP erythroid cDNA and cloned the 5'-flanking genomic DNA containing the putative AHSP gene promoter. In vitro studies using transfection of promoter/reporter plasmids in human tissue culture cell lines, DNase I footprinting analyses and gel mobility shift assays, identified an AHSP gene erythroid promoter with functionally important binding sites for GATA-1- and Oct-1-related proteins. In transgenic mice, a reporter gene directed by a minimal human AHSP promoter was expressed in bone marrow, spleen, and reticulocytes, but not in nonerythroid tissues. In vivo studies using chromatin immunoprecipitation assays demonstrated hyperacetylation of the promoter region and occupancy by GATA-1. The AHSP promoter is an excellent candidate region for mutations associated with decreased AHSP gene expression.
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PMID:GATA-1 and Oct-1 are required for expression of the human alpha-hemoglobin-stabilizing protein gene. 1618 25

Alpha hemoglobin stabilizing protein (AHSP) is a small protein of 102 residues induced by GATA-1, Oct-1- and EKLF. It is synthesized at a high level in the red blood cell precursors and acts as a chaperone protecting the alpha hemoglobin (alpha-Hb) chains against precipitation. AHSP and alpha-Hb form a heterodimer complex. In the absence of AHSP, alpha-Hb oxidizes and precipitates within the erythrocyte precursors of the bone marrow leading to apoptosis and defective erythropoiesis. In vitro the binding of AHSP to ferrous alpha-Hb accelerates oxidation of the heme iron in alpha-Hb, but the complex is more resistant to protein unfolding. AHSP could act as a modulating factor in beta-thalassemia. Recent studies showed more severe thalassemic syndromes in patients with decreased levels of AHSP and in one patient who carried a structurally abnormal AHSP. Some alpha-Hb variants with structural abnormality located in the contact area between alpha-Hb and AHSP exhibit an instability and a thalassemic like syndrome. We suggest that this could result from a disturbed interaction between alpha-Hb variants and AHSP. To study this interaction, we constructed the pGEX-alpha-AHSP vector that co-expressed human alpha-Hb and AHSP. Using this approach, we investigated the alpha42 (C7), alpha104 (G11) and alpha119 (H2) sites, where variants with some thalassemic features have been described. Results obtained with recombinant Groene Hart alpha-Hb and Diamant alpha-Hb, in which proline 119 is replaced by a serine and a leucine, respectively, showed clearly an impaired interaction with AHSP. In contrast, the alpha mutants at the sites 42 and 104 exhibit a normal interaction with AHSP. The CO rebinding kinetics of the AHSP/alpha-Hb(42mutant) complexes were similar to those previously obtained with the AHSP/alpha-Hb(WT) complex, which shows a modified rate that is intermediate to the classical Hb allosteric states.
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PMID:Impaired binding of AHSP to alpha chain variants: Hb Groene Hart illustrates a mechanism leading to unstable hemoglobins with alpha thalassemic like syndrome. 1705 27

Alpha haemoglobin stabilising protein (AHSP) binds free alpha-globin chains and plays an important role in the protection of red cells, particularly during beta-thalassaemia. Murine ASHP was discovered as a GATA-1 target gene and human AHSP is directly regulated by GATA-1. More recently, AHSP was rediscovered as a highly erythroid Kruppel-like factor (EKLF) -dependent transcript. We have determined the organisation of the murine AHSP gene and compared it to orthologs. There are two CACC box elements in the proximal promoter. The proximal element is absolutely conserved, but does not bind EKLF as it is not a canonical binding site. In rodents, the distal element contains a 3 bp insertion that disrupts the typical EKLF binding consensus region. Nevertheless, EKLF binds this atypical site by gel mobility shift assay, specifically occupies the AHSP promoter in vivo in a chromatin immunoprecipitation assay, and transactivates AHSP through this CACC site in promoter-reporter assays. Our results suggest EKLF can occupy CACC elements in vivo that are not predictable from the consensus binding site inferred from structural studies. We also propose that absence of AHSP in EKLF-null red cells exacerbates the toxicity of free alpha-globin chains, which exist because of the defect in beta-globin gene activation.
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PMID:Genomic organisation and regulation of murine alpha haemoglobin stabilising protein by erythroid Kruppel-like factor. 1706 80


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