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Domain-focused CRISPR-screen identifies HRI as a fetal hemoglobin regulator in human erythroid cells

ABSTRACT: Increasing fetal hemoglobin (HbF) levels in adult red blood cells provides clinical benefit to patients with sickle cell disease and some forms of beta-thalassemia. To identify potentially druggable HbF regulators in adult human erythroid cells, we employed a protein kinase-domain focused CRISPR/Cas9-based genetic screen with a newly optimized sgRNA scaffold. The screen uncovered the heme-regulated inhibitor HRI (also known as EIF2AK1), an erythroid-specific kinase that controls protein translation, as an HbF repressor. HRI depletion markedly increased HbF production in a specific manner and reduced sickling in cultured erythroid cells. Diminished expression of the HbF repressor BCL11A accounted in large part for the effects of HRI depletion. Taken together, these results suggest HRI as a potential therapeutic target for hemoglobinopathies.

ORGANISM(S): Homo sapiens

PROVIDER: GSE115687 | GEO | 2018/07/20

REPOSITORIES: GEO

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HRI depletion cooperates with pharmacologic inducers to elevate fetal hemoglobin and reduce sickle cell formation

Project description:Increasing fetal hemoglobin (HbF) provides clinical benefit in patients with sickle cell disease (SCD). We recently identified heme-regulated inhibitor (HRI, EIF2AK1) as a novel HbF regulator. Since HRI is an erythroid-specific protein kinase it presents a potential target for pharmacologic intervention. We find that maximal HbF induction requires >80-85% HRI depletion. As it remains unclear whether this degree of HRI inhibition can be achieved pharmacologically, we explored whether HRI knockdown can be combined with pharmacologic HbF inducers to achieve greater HbF production and minimize potential adverse effects associated with treatments. Strongly cooperative HbF induction was observed when HRI depletion was combined with exposure to pomalidomide or the EHMT1/2 inhibitor UNC0638, but not hydroxyurea. Mechanistically, reduction in the levels of the HbF repressor BCL11A reflected the cooperativity of HRI loss and pomalidomide treatment, whereas UNC0638 did not modulate BCL11A levels. In conjunction with HRI loss, pomalidomide maintained its HbF inducing activity at 10-fold lower concentrations, at which condition there were minimal observed detrimental effects on erythroid cell maturation and viability as well as fewer alterations in the erythroid transcriptome. In sum, this study provides a foundation for the exploration of combining future small molecule HRI inhibitors with additional pharmacologic HbF inducers to maximize HbF production and preserve erythroid cell functionality for the treatment of SCD and other hemoglobinopathies.

2020-09-21 | GSE150341 | GEO

HRI activates ATF4 to promote BCL11A transcription and fetal hemoglobin silencing [ChIP-seq]

Project description:Through a CRISPR-Cas9 guided loss-of-function screen in human erythroid cells we identified transcription factor ATF4, a known HRI-regulated protein, as a novel γ-globin repressor. ATF4 binds to a BCL11A enhancer to augment promoter contacts, stimulates BCL11A transcription to repress γ-globin expression. Notably, mice deficient for HRI displayed normal Bcl11a levels, suggesting species selective regulation that we explain here by demonstrating that the analogous ATF4 motif at the murine Bcl11a enhancer is largely dispensable. This illustrates potential limits of commonly used murine models of globin gene regulation.

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HRI activates ATF4 to promote BCL11A transcription and fetal hemoglobin silencing [Capture-C]

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The LRF/ZBTB7A transcription factor is a BCL11A-independent repressor of fetal hemoglobin

Project description:Hemoglobinopathies, including sickle cell disease and _-thalassemia, are global public health concerns. Induction of fetal-type hemoglobin (HbF) is a promising means to treat these disorders; however, precisely how HbF expression is silenced in adult erythroid cells is not fully understood. Here, we show that the LRF/ZBTB7A transcription factor is a potent repressor of HbF production. LRF inactivation derepresses embryonic/fetal _-globin expression in mouse and human adult erythroid cells. We employed genome-wide analysis of the transcriptome, chromatin accessibility and LRF occupancy sites, and demonstrate that LRF occupies the _-globin loci and maintains nucleosome density necessary for _-globin silencing. LRF confers its repressive activity through a unique NuRD repressor complex independent of BCL11A. Strikingly, human erythroid lines lacking both LRF and BCL11A exhibited almost a complete switch in expression from adult- to fetal-type globin, suggesting that these two factors cumulatively represent the near entirety of _-globin repressive activity in adult erythroid cells. RNA-seq, LRF ChIP-seq and ATAC-seq assays were used to investigtae LRF binding, effect of LRF depletion on transcription and chromatin landscape in mouse and human cells.

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The LRF/ZBTB7A transcription factor is a BCL11A-independent repressor of fetal hemoglobin

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Project description:The fetal-to-adult hemoglobin switch is regulated in a developmental stage-specific manner and reactivation of fetal hemoglobin (HbF) has therapeutic potential for β-hemoglobinopathies. Although BCL11A and ZBTB7A interact with their coregulators, reportedly mediating most γ-globin transcriptional silencing in erythroid in trans, and in cis, the molecular mechanism underlying the epigenetic dysregulation of the switch remains largely unclear. Here we showed that epigenetic inactivation of an ETS2 repressor factor (ERF) reactivates γ-globin expression during stress erythropoiesis, and ERF depletion elevates γ-globin in erythroid cells and in erythroid progenies from the edited HSPCs engrafted into immunodeficient mice. ERF represses γ-globin by directly binding to two motifs regulating HBG expression, independently of the major HbF repressors BCL11A and ZBTB7A. We further uncovered that an lncRNA, RP11-196G18.23 mediates ERF promoter hypermethylation resulting in reactivation of g-globin. Herein, the epigenetic alterations were identified as novel modulators ameliorating the severity of b-thalassemia, thus providing novel therapeutic targets for β-hemoglobinopathies.

2020-12-27 | GSE160602 | GEO

Epigenetic inactivation of ERF reactivates γ-globin expression in β-thalassemia [RNA-seq]

2020-12-27 | GSE160601 | GEO

Targeted disruption of BCL11A-XL specific zinc finger motif for de-repression of fetal globin expression

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Dimethyl fumarate increases fetal hemoglobin, provides heme detoxification, and corrects anemia in sickle cell disease

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