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Nature Genetics Apr 2021BCL11A, the major regulator of fetal hemoglobin (HbF, αγ) level, represses γ-globin expression through direct promoter binding in adult erythroid cells in a switch to...
BCL11A, the major regulator of fetal hemoglobin (HbF, αγ) level, represses γ-globin expression through direct promoter binding in adult erythroid cells in a switch to adult hemoglobin (HbA, αβ). To uncover how BCL11A initiates repression, we used CRISPR-Cas9, dCas9, dCas9-KRAB and dCas9-VP64 screens to dissect the γ-globin promoters and identified an activator element near the BCL11A-binding site. Using CUT&RUN and base editing, we demonstrate that a proximal CCAAT box is occupied by the activator NF-Y. BCL11A competes with NF-Y binding through steric hindrance to initiate repression. Occupancy of NF-Y is rapidly established following BCL11A depletion, and precedes γ-globin derepression and locus control region (LCR)-globin loop formation. Our findings reveal that the switch from fetal to adult globin gene expression within the >50-kb β-globin gene cluster is initiated by competition between a stage-selective repressor and a ubiquitous activating factor within a remarkably discrete region of the γ-globin promoters.
Topics: Base Sequence; Binding Sites; Binding, Competitive; CCAAT-Binding Factor; Erythropoiesis; Fetal Hemoglobin; Gene Editing; Gene Expression Regulation; HEK293 Cells; Hemoglobin A; Humans; Models, Molecular; Primary Cell Culture; Promoter Regions, Genetic; Protein Binding; Protein Conformation, alpha-Helical; Protein Conformation, beta-Strand; Protein Interaction Domains and Motifs; Repressor Proteins; Stem Cells; beta-Globins; gamma-Globins
PubMed: 33649594
DOI: 10.1038/s41588-021-00798-y -
Physiological Reviews Apr 2022Globin proteins exist in every cell type of the vasculature, from erythrocytes to endothelial cells, vascular smooth muscle cells, and peripheral nerve cells. Many... (Review)
Review
Globin proteins exist in every cell type of the vasculature, from erythrocytes to endothelial cells, vascular smooth muscle cells, and peripheral nerve cells. Many globin subtypes are also expressed in muscle tissues (including cardiac and skeletal muscle), in other organ-specific cell types, and in cells of the central nervous system (CNS). The ability of each of these globins to interact with molecular oxygen (O) and nitric oxide (NO) is preserved across these contexts. Endothelial α-globin is an example of extraerythrocytic globin expression. Other globins, including myoglobin, cytoglobin, and neuroglobin, are observed in other vascular tissues. Myoglobin is observed primarily in skeletal muscle and smooth muscle cells surrounding the aorta or other large arteries. Cytoglobin is found in vascular smooth muscle but can also be expressed in nonvascular cell types, especially in oxidative stress conditions after ischemic insult. Neuroglobin was first observed in neuronal cells, and its expression appears to be restricted mainly to the CNS and the peripheral nervous system. Brain and CNS neurons expressing neuroglobin are positioned close to many arteries within the brain parenchyma and can control smooth muscle contraction and thus tissue perfusion and vascular reactivity. Overall, reactions between NO and globin heme iron contribute to vascular homeostasis by regulating vasodilatory NO signals and scavenging reactive species in cells of the mammalian vascular system. Here, we discuss how globin proteins affect vascular physiology, with a focus on NO biology, and offer perspectives for future study of these functions.
Topics: Animals; Cardiovascular Physiological Phenomena; Cytoglobin; Endothelial Cells; Globins; Humans; Myoglobin; Neuroglobin
PubMed: 34486392
DOI: 10.1152/physrev.00037.2020 -
Experimental Hematology 2022The accumulation of unbound α-globin chains in red blood cells is a crucial pathophysiology of β-thalassemia. IOX1 (5-carboxy-8-hydroxyquinoline) is a broad-spectrum...
The accumulation of unbound α-globin chains in red blood cells is a crucial pathophysiology of β-thalassemia. IOX1 (5-carboxy-8-hydroxyquinoline) is a broad-spectrum 2-oxoglutarate (2OG)-dependent oxygenase inhibitor that can reduce α-globin mRNA expression in human cord blood erythroid progenitor cells. Therefore, IOX1 has been proposed as a potential compound for β-thalassemia treatment through the decrease in α-globin chain synthesis. However, there is no empirical evidence regarding the consequences of IOX1 in β-thalassemia. In this study, the therapeutic effects of IOX1 were investigated in β-thalassemia/hemoglobin E (HbE) erythroid progenitor cells during in vitro erythropoiesis. The results indicated that IOX1 had no impact on α-globin gene expression, but it led instead to significant decreases in γ-globin and fetal hemoglobin (HbF, αγ) production without affecting well-known globin regulators: KLF1, BCL11A, LRF, and GATA1. In addition, differential mRNA expression of several genes in the hypoxia response pathway revealed the induction of EGLN1, the PHD2-encoding gene, as a result of IOX1 treatment. These findings suggested that IOX1 fails to lower α-globin gene expression; on the contrary, it mediates γ-globin and HbF silencing in β-thalassemia/HbE erythroid progenitor cells. Because of the negative correlation of EGLN1 and γ-globin gene expression after IOX1 treatment, repurposing IOX1 to study the hypoxia response pathway and γ-globin regulation may provide beneficial information for β-thalassemia.
Topics: Adult; Carrier Proteins; Erythroid Cells; Erythroid Precursor Cells; Fetal Hemoglobin; Hemoglobin E; Humans; Hypoxia; RNA, Messenger; Thalassemia; alpha-Globins; beta-Thalassemia; gamma-Globins
PubMed: 35839944
DOI: 10.1016/j.exphem.2022.07.004 -
Genome Biology and Evolution Jun 2015Globins are small heme proteins that play an important role in oxygen supply, but may also have other functions. Globins offer a unique opportunity to study the...
Globins are small heme proteins that play an important role in oxygen supply, but may also have other functions. Globins offer a unique opportunity to study the functional evolution of genes and proteins. We have characterized the globin repertoire of two different turtle species: the Chinese softshell turtle (Pelodiscus sinensis) and the western painted turtle (Chrysemys picta bellii). In the genomes of both species, we have identified eight distinct globin types: hemoglobin (Hb), myoglobin, neuroglobin, cytoglobin, globin E, globin X, globin Y, and androglobin. Therefore, along with the coelacanth, turtles are so far the only known vertebrates with a full globin repertoire. This fact allows for the first time a comparative analysis of the expression of all eight globins in a single species. Phylogenetic analysis showed an early divergence of neuroglobin and globin X before the radiation of vertebrates. Among the other globins, cytoglobin diverged first, and there is a close relationship between myoglobin and globin E; the position of globin Y is not resolved. The globin E gene was selectively lost in the green anole, and the genes coding for globin X and globin Y were deleted in chicken. Quantitative real-time reverse transcription polymerase chain reaction experiments revealed that myoglobin, neuroglobin, and globin E are highly expressed with tissue-specific patterns, which are in line with their roles in the oxidative metabolism of the striated muscles, the brain, and the retina, respectively. Histochemical analyses showed high levels of globin E in the pigment epithelium of the eye. Globin E probably has a myoglobin-like role in transporting O2 across the pigment epithelium to supply in the metabolically highly active retina.
Topics: Animals; Evolution, Molecular; Globins; Hemoglobins; Multigene Family; Myoglobin; Nerve Tissue Proteins; Neuroglobin; Turtles; Vertebrates
PubMed: 26078264
DOI: 10.1093/gbe/evv114 -
The American Journal of Pathology Dec 1983Hemoglobinopathies are due to changes in the normal amino acid sequence of globin. Thalassemias result from imbalance in the normal coordinated synthesis of the globin... (Review)
Review
Hemoglobinopathies are due to changes in the normal amino acid sequence of globin. Thalassemias result from imbalance in the normal coordinated synthesis of the globin subunits that make up the hemoglobin tetramer. It is now apparent that a single globin gene can have coding region mutations which simultaneously produce a structural defect (hemoglobinopathy) and a biosynthetic defect (thalassemia). It is likely that two distinct mutations within the same gene can occur and produce a hemoglobinopathy with features of thalassemia. In this review the authors discuss such disorders and include the Hb Lepore and Constant Spring variants, hyper-unstable globins, mutations which create alternative sites for mRNA splicing, and amino acid substitutions likely to be associated with an additional thalassemia lesion within the same gene.
Topics: Globins; Hemoglobins, Abnormal; Humans; Mutation; Phenotype; RNA, Messenger; Thalassemia
PubMed: 6359893
DOI: No ID Found -
Blood Apr 2022The benign condition hereditary persistence of fetal hemoglobin (HPFH) is known to ameliorate symptoms of co-inherited β-hemoglobinopathies, such as sickle cell disease...
The benign condition hereditary persistence of fetal hemoglobin (HPFH) is known to ameliorate symptoms of co-inherited β-hemoglobinopathies, such as sickle cell disease and β-thalassemia. The condition is sometimes associated with point mutations in the fetal globin promoters that disrupt the binding of the repressors BCL11A or ZBTB7A/LRF, which have been extensively studied. HPFH is also associated with a range of deletions within the β-globin locus that all reside downstream of the fetal HBG2 gene. These deletional forms of HPFH are poorly understood and are the focus of this study. Numerous different mechanisms have been proposed to explain how downstream deletions can boost the expression of the fetal globin genes, including the deletion of silencer elements, of genes encoding noncoding RNA, and bringing downstream enhancer elements into proximity with the fetal globin gene promoters. Here we systematically analyze the deletions associated with both HPFH and a related condition known as δβ-thalassemia and propose a unifying mechanism. In all cases where fetal globin is upregulated, the proximal adult β-globin (HBB) promoter is deleted. We use clustered regularly interspaced short palindromic repeats-mediated gene editing to delete or disrupt elements within the promoter and find that virtually all mutations that reduce ΗΒΒ promoter activity result in elevated fetal globin expression. These results fit with previous models where the fetal and adult globin genes compete for the distal locus control region and suggest that targeting the ΗΒΒ promoter might be explored to elevate fetal globin and reduce sickle globin expression as a treatment of β-hemoglobinopathies.
Topics: Carrier Proteins; Cell Line, Tumor; DNA-Binding Proteins; Fetal Hemoglobin; Gene Expression; Globins; Humans; Transcription Factors; beta-Globins; beta-Thalassemia
PubMed: 35090172
DOI: 10.1182/blood.2021014205 -
IUBMB Life Mar 2011Globins have been found in glial cells and neurons of invertebrates and vertebrates. The first nerve globin has been recognized in the nerve cord of the polychaete... (Review)
Review
Globins have been found in glial cells and neurons of invertebrates and vertebrates. The first nerve globin has been recognized in the nerve cord of the polychaete annelid Aphrodite aculeata in 1872. In some invertebrates, the nerve globin reaches a millimolar concentration which is likely sufficient to sustain the aerobic metabolism and thus the excitability of the nervous system. In 2000, the first vertebrate nerve globin, named neuroglobin (Ngb), has been identified in neuronal tissues of mice and humans. In contrast to invertebrate nerve globins, the concentration of Ngb, the prototype of vertebrate nerve globins, is low (μM), reaching a maximum of 100 μM in retina cells. Therefore, Ngb appears unlikely to act primarily as an O₂ buffer and to facilitate O₂ diffusion to the mitochondria. Indeed, Ngb has been hypothesized to catalyze the formation/decomposition of reactive nitrogen and/or oxygen species and to be part of intracellular signaling pathways enhancing cell survival. Here, we report that neuronal Ngb levels are strongly induced by the steroid hormone 17β-estradiol. Furthermore, Ngb participates to mechanisms involved in 17β-estradiol-induced protective effects against H₂O₂ -induced neurotoxicity.
Topics: Animals; Apoptosis; Estrogens; Globins; Humans; Mice; Nerve Tissue Proteins; Neuroglobin; Neuroprotective Agents; Up-Regulation
PubMed: 21445843
DOI: 10.1002/iub.426 -
Redox Biology Oct 2020Vertebrate hemoglobin (Hb) and myoglobin (Mb) were among the first proteins whose structures and sequences were determined over 50 years ago. In the subsequent... (Review)
Review
Vertebrate hemoglobin (Hb) and myoglobin (Mb) were among the first proteins whose structures and sequences were determined over 50 years ago. In the subsequent pregenomic period, numerous related proteins came to light in plants, invertebrates and bacteria, that shared the myoglobin fold, a signature sequence motif characteristic of a 3-on-3 α-helical sandwich. Concomitantly, eukaryote and bacterial globins with a truncated 2-on-2 α-helical fold were discovered. Genomic information over the last 20 years has dramatically expanded the list of known globins, demonstrating their existence in a limited number of archaeal genomes, a majority of bacterial genomes and an overwhelming majority of eukaryote genomes. In vertebrates, 6 additional globin types were identified, namely neuroglobin (Ngb), cytoglobin (Cygb), globin E (GbE), globin X (GbX), globin Y (GbY) and androglobin (Adgb). Furthermore, functions beyond the familiar oxygen transport and storage have been discovered within the vertebrate globin family, including NO metabolism, peroxidase activity, scavenging of free radicals, and signaling functions. The extension of the knowledge on globin functions suggests that the original roles of bacterial globins must have been enzymatic, involved in defense against NO toxicity, and perhaps also as sensors of O, regulating taxis away or towards high O concentrations. In this review, we aimed to discuss the evolution and remarkable functional diversity of vertebrate globins with particular focus on the variety of non-canonical expression sites of mammalian globins and their according impressive variability of atypical functions.
Topics: Animals; Cytoglobin; Evolution, Molecular; Genomics; Globins; Neuroglobin; Oxygen; Vertebrates
PubMed: 32863222
DOI: 10.1016/j.redox.2020.101687 -
Current Opinion in Hematology May 2014This review will provide an overview of the translational regulation of globin mRNAs and integrated stress response (ISR) during erythropoiesis by heme-regulated eIF2α... (Review)
Review
PURPOSE OF REVIEW
This review will provide an overview of the translational regulation of globin mRNAs and integrated stress response (ISR) during erythropoiesis by heme-regulated eIF2α kinase (HRI). HRI is an intracellular heme sensor that coordinates heme and globin synthesis in erythropoiesis by inhibiting protein synthesis of globins and heme biosynthetic enzymes during heme deficiency.
RECENT FINDINGS
It has been demonstrated recently that HRI also activates the eIF2αP-activating transcription factor 4 (ATF4) ISR in primary erythroid precursors to combat oxidative stress. During chronic iron/heme deficiency in vivo, this HRI-eIF2αP-ATF4 signaling is necessary both to reduce oxidative stress and to promote erythroid differentiation. Augmenting eIF2αP signaling by the small molecule salubrinal, which inhibits dephosphorylation of eIF2αP, reduces excess α-globin synthesis and enhances translation of ATF4 mRNA in mouse β-thalassemic erythroid precursors. Intriguingly, salubrinal treatment of differentiating human CD34⁺ cells in culture increases fetal hemoglobin production with a concomitant decrease of adult hemoglobin by a posttranscriptional mechanism.
SUMMARY
HRI-eIF2αP-ATF4 stress signaling is important not only to inhibit excess globin synthesis during erythropoiesis, but is also critical for adaptation to oxidative stress and for enhancing effective erythropoiesis. Modulation of this signaling pathway with small chemicals may provide a novel therapy for hemoglobinopathy.
Topics: Animals; Erythropoiesis; Gene Expression Regulation; Globins; Humans; Mice; Oxidative Stress; RNA, Messenger; Signal Transduction; eIF-2 Kinase
PubMed: 24714526
DOI: 10.1097/MOH.0000000000000030 -
Advances in Microbial Physiology 2017The discovery of the globin-coupled sensor (GCS) family of haem proteins has provided new insights into signalling proteins and pathways by which organisms sense and... (Review)
Review
The discovery of the globin-coupled sensor (GCS) family of haem proteins has provided new insights into signalling proteins and pathways by which organisms sense and respond to changing oxygen levels. GCS proteins consist of a sensor globin domain linked to a variety of output domains, suggesting roles in controlling numerous cellular pathways, and behaviours in response to changing oxygen concentration. Members of this family of proteins have been identified in the genomes of numerous organisms and characterization of GCS with output domains, including methyl accepting chemotaxis proteins, kinases, and diguanylate cyclases, have yielded an understanding of the mechanism by which oxygen controls activity of GCS protein output domains, as well as downstream proteins and pathways regulated by GCS signalling. Future studies will expand our understanding of these proteins both in vitro and in vivo, likely demonstrating broad roles for GCS in controlling oxygen-dependent microbial physiology and phenotypes.
Topics: Adenylyl Cyclases; Bordetella pertussis; Escherichia coli; Globins; Oxygen; Pectobacterium carotovorum; Second Messenger Systems; Signal Transduction
PubMed: 28760321
DOI: 10.1016/bs.ampbs.2017.05.003