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Structural basis for human ZBTB7A action at the fetal globin promoter.

ABSTRACT: Elevated levels of fetal globin protect against β-hemoglobinopathies, such as sickle cell disease and β-thalassemia. Two zinc-finger (ZF) repressors, BCL11A and ZBTB7A/LRF, bind directly to the fetal globin promoter elements positioned at -115 and -200, respectively. Here, we describe X-ray structures of the ZBTB7A DNA-binding domain, consisting of four adjacent ZFs, in complex with the -200 sequence element, which contains two copies of four consecutive C:G base pairs. ZF1 and ZF2 recognize the 5' C:G quadruple, and ZF4 contacts the 3' C:G quadruple. Natural non-coding DNA mutations associated with hereditary persistence of fetal hemoglobin (HPFH) impair ZBTB7A DNA binding, with the most severe disruptions resulting from mutations in the base pairs recognized by ZF1 and ZF2. Our results firmly establish ZBTB7A/LRF as a key molecular regulator of fetal globin expression and inform genome-editing strategies that inhibit repressor binding and boost fetal globin expression to treat hemoglobinopathies.

SUBMITTER: Yang Y

PROVIDER: S-EPMC8553545 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Disrupting the adult globin promoter alleviates promoter competition and reactivates fetal globin gene expression.

Project description: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.

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KLF1 directly activates expression of the novel fetal globin repressor, ZBTB7A/LRF, in erythroid cells

Project description:Genes encoding the human β-like hemoglobin proteins undergo a developmental switch from fetal γ-globin to adult β-globin expression at around the time of birth. β-hemoglobinopathies, such as sickle cell disease and β-thalassemia, result from mutations affecting the adult β-globin gene. The only treatment options currently available carry significant side-effects. Analyses of heritable variations in fetal hemoglobin (HbF) levels have provided evidence that reactivation of the silenced fetal γ-globin genes in adult erythroid cells is a promising therapy. The γ-globin repressor BCL11A has become the major focus with several studies investigating its regulation and function as a first step to inhibiting its expression or activity. However, a second repression mechanism has recently been shown to be mediated by the transcription factor ZBTB7A/LRF, suggesting that understanding the regulation of ZBTB7A may also be useful. Here we show that KLF1 directly drives expression of ZBTB7A in erythroid cells by binding to its proximal promoter. We have also uncovered an erythroid-specific regulation mechanism, leading to the upregulation of a novel ZBTB7A transcript in the erythroid compartment. The demonstration that ZBTB7A, like BCL11A, is a KLF1 target gene also fits with the observation that reduced KLF1 expression or activity is associated with HbF derepression.

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Structural insights into the recognition of γ-globin gene promoter by BCL11A.

Project description: Not available

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Genetic variants in the G gamma-globin promoter modulate fetal hemoglobin expression in the Colombian population.

Project description:Fetal hemoglobin (HbF) is a determining factor for the development of sickle cell anemia. High HbF levels lower the intensity of symptoms of this disease. HbF levels can vary in patients with sickle cell anemia and individuals without the disease. The purpose of this study was to identify the genetic variants in the G gamma-globin gene promoter that can modulate HbF expression in patients with sickle cell anemia and healthy individuals from Colombia. In total, 413 bp of the G gamma-globin gene promoter were sequenced in 60 patients with sickle cell anemia and 113 healthy individuals. The allelic and genotype frequencies of the identified variants were compared between individuals with low and high HbF for both patients and healthy individuals. In total, we identified 15 variants in both groups, only three of which were shared between patients and healthy individuals. In healthy individuals, sites -16 and -309 (rs112479156) exhibited differences in allele frequencies. The mutant allele of -16 lowered the production of HbF, whereas the mutant allele of -309 increased its production. These results reveal the presence of different mechanisms of HbF regulation between patients with sickle cell and healthy individuals.

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