Project description:Basak A, Munschauer M, Lareau CA, Montbleau KE, Ulirsch JC, Hartigan CR, Schenone M, Lian J, Wang Y, Huang Y, Wu X, Gehrke L, Rice CM, An X, Christou HA, Mohandas N, Carr SA, Orkin SH, Chen JJ, Lander ES, and Sankaran VG.
Increased production of the beta-like gamma-globin genes that form fetal hemoglobin can ameliorate the severity of sickle cell disease and beta-thalassemia, the major hemoglobin disorders. BCL11A is a key repressor of the gamma-globin genes and is expressed in a developmental stage-specific manner to regulate the physiologic fetal-to-adult hemoglobin switch. Despite extensive studies, the upstream mechanisms underlying the developmental expression of BCL11A and hemoglobin switching in humans have remained mysterious. Here we show that BCL11A is regulated at the level of mRNA translation during human hematopoietic development. While BCL11A mRNA is comparably expressed at all developmental stages in erythroid cells, robust protein expression only occurs in adult erythroid cells. Importantly, at the earlier stages of development, the observed reduction in protein expression is attributable to decreased synthesis and not increased degradation of BCL11A. While BCL11A protein is not well synthesized at these earlier stages of development, its mRNA curiously continues to be associated with ribosomes. Through unbiased proteomic analyses in erythroid cells, we demonstrate that the RNA-binding protein LIN28B, which is developmentally expressed in a reciprocal pattern to BCL11A, directly interacts with ribosomes. We show that the observed suppression of BCL11A protein translation is mediated by LIN28B through a direct interaction with BCL11A mRNA and independent of its role in let-7 microRNA biogenesis. Finally, we show that BCL11A is the major functional target in LIN28B-mediated fetal hemoglobin induction. Our results reveal a previously unappreciated regulatory mechanism underlying human hemoglobin switching and illuminate opportunities for developing improved treatments for sickle cell disease and beta-thalassemia.
Project description:The fetal hemoglobin (HBG) regulator BCL11A is repressed by HIC2 to regulate hemoglobin switching. HIC2 itself is under developmental control, highly expressed in fetal tissues and decreased in adult cells, but the mechanism of this developmental regulation is unclear. Here, we demonstrate that HIC2 is developmentally controlled by miRNAs, and loss of global miRNA biogenesis through DICER1 depletion leads to upregulation of HIC2 and HBG. We subsequently identify the adult-expressed let-7 miRNA family as a repressor of HIC2 expression. Ectopic expression of let-7 in fetal-type cells repressed HIC2 levels, while let-7 inhibition in adult erythroblasts upregulated HIC2 levels. Let-7 regulates BCL11A and HBG through induction of HIC2 and reduction of GATA1 binding at the BCL11A erythroid enhancer. Finally, HIC2 depletion rescues BCL11A-mediated repression of fetal hemoglobin in let-7 inhibited cells. Together these data demonstrate a key miRNA-mediated mechanism for developmental regulation of BCL11A expression and fetal hemoglobin repression in adult erythroid cells.
Project description:The fetal hemoglobin (HBG) regulator BCL11A is repressed by HIC2 to regulate hemoglobin switching. HIC2 itself is under developmental control, highly expressed in fetal tissues and decreased in adult cells, but the mechanism of this developmental regulation is unclear. Here, we demonstrate that HIC2 is developmentally controlled by miRNAs, and loss of global miRNA biogenesis through DICER1 depletion leads to upregulation of HIC2 and HBG. We subsequently identify the adult-expressed let-7 miRNA family as a repressor of HIC2 expression. Ectopic expression of let-7 in fetal-type cells repressed HIC2 levels, while let-7 inhibition in adult erythroblasts upregulated HIC2 levels. Let-7 regulates BCL11A and HBG through induction of HIC2 and reduction of GATA1 binding at the BCL11A erythroid enhancer. Finally, HIC2 depletion rescues BCL11A-mediated repression of fetal hemoglobin in let-7 inhibited cells. Together these data demonstrate a key miRNA-mediated mechanism for developmental regulation of BCL11A expression and fetal hemoglobin repression in adult erythroid cells.
Project description:The fetal hemoglobin (HBG) regulator BCL11A is repressed by HIC2 to regulate hemoglobin switching. HIC2 itself is under developmental control, highly expressed in fetal tissues and decreased in adult cells, but the mechanism of this developmental regulation is unclear. Here, we demonstrate that HIC2 is developmentally controlled by miRNAs, and loss of global miRNA biogenesis through DICER1 depletion leads to upregulation of HIC2 and HBG. We subsequently identify the adult-expressed let-7 miRNA family as a repressor of HIC2 expression. Ectopic expression of let-7 in fetal-type cells repressed HIC2 levels, while let-7 inhibition in adult erythroblasts upregulated HIC2 levels. Let-7 regulates BCL11A and HBG through induction of HIC2 and reduction of GATA1 binding at the BCL11A erythroid enhancer. Finally, HIC2 depletion rescues BCL11A-mediated repression of fetal hemoglobin in let-7 inhibited cells. Together these data demonstrate a key miRNA-mediated mechanism for developmental regulation of BCL11A expression and fetal hemoglobin repression in adult erythroid cells.
Project description:The fetal hemoglobin (HBG) regulator BCL11A is repressed by HIC2 to regulate hemoglobin switching. HIC2 itself is under developmental control, highly expressed in fetal tissues and decreased in adult cells, but the mechanism of this developmental regulation is unclear. Here, we demonstrate that HIC2 is developmentally controlled by miRNAs, and loss of global miRNA biogenesis through DICER1 depletion leads to upregulation of HIC2 and HBG. We subsequently identify the adult-expressed let-7 miRNA family as a repressor of HIC2 expression. Ectopic expression of let-7 in fetal-type cells repressed HIC2 levels, while let-7 inhibition in adult erythroblasts upregulated HIC2 levels. Let-7 regulates BCL11A and HBG through induction of HIC2 and reduction of GATA1 binding at the BCL11A erythroid enhancer. Finally, HIC2 depletion rescues BCL11A-mediated repression of fetal hemoglobin in let-7 inhibited cells. Together these data demonstrate a key miRNA-mediated mechanism for developmental regulation of BCL11A expression and fetal hemoglobin repression in adult erythroid cells.
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.
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.
Project description:The switch from fetal to adult hemoglobin production has been studied in great depth in part because of its relevance to the treatment of hemolobinopathies. Transcription factor BCL11A, which is essential for repression of the fetal beta-type globin (γ-globin) genes after birth, is largely controlled at the level of transcription but the mechanism of BCL11A developmental control is unknown. Here, using a CRISPR-Cas9 screen in human erythroblasts, we identify transcription factor HIC2 as a repressor of BCL11A transcription. HIC2 and BCL11A expression are anti-correlated in fetal and adult erythroblasts. Forced expression of HIC2 in adult erythroblasts silences BCL11A transcription and markedly induces γ-globin expression. HIC2 binds selectively to constituent erythroid developmental BCL11A enhancer to reduce chromatin accessibility and impair access by transcription factor GATA1, resulting in loss of enhancer activity and enhancer-promoter contacts. Conversely, loss of HIC2 in fetal erythroblasts increases enhancer accessibility, enables GATA1 binding and induces BCL11A transcription. HIC2 is unveiled as a critical evolutionarily conserved regulator of globin gene switching by imposing developmental control on the BCL11A gene.
Project description:The switch from fetal to adult hemoglobin production has been studied in great depth in part because of its relevance to the treatment of hemolobinopathies. Transcription factor BCL11A, which is essential for repression of the fetal beta-type globin (γ-globin) genes after birth, is largely controlled at the level of transcription but the mechanism of BCL11A developmental control is unknown. Here, using a CRISPR-Cas9 screen in human erythroblasts, we identify transcription factor HIC2 as a repressor of BCL11A transcription. HIC2 and BCL11A expression are anti-correlated in fetal and adult erythroblasts. Forced expression of HIC2 in adult erythroblasts silences BCL11A transcription and markedly induces γ-globin expression. HIC2 binds selectively to constituent erythroid developmental BCL11A enhancer to reduce chromatin accessibility and impair access by transcription factor GATA1, resulting in loss of enhancer activity and enhancer-promoter contacts. Conversely, loss of HIC2 in fetal erythroblasts increases enhancer accessibility, enables GATA1 binding and induces BCL11A transcription. HIC2 is unveiled as a critical evolutionarily conserved regulator of globin gene switching by imposing developmental control on the BCL11A gene.
Project description:The switch from fetal to adult hemoglobin production has been studied in great depth in part because of its relevance to the treatment of hemolobinopathies. Transcription factor BCL11A, which is essential for repression of the fetal beta-type globin (γ-globin) genes after birth, is largely controlled at the level of transcription but the mechanism of BCL11A developmental control is unknown. Here, using a CRISPR-Cas9 screen in human erythroblasts, we identify transcription factor HIC2 as a repressor of BCL11A transcription. HIC2 and BCL11A expression are anti-correlated in fetal and adult erythroblasts. Forced expression of HIC2 in adult erythroblasts silences BCL11A transcription and markedly induces γ-globin expression. HIC2 binds selectively to constituent erythroid developmental BCL11A enhancer to reduce chromatin accessibility and impair access by transcription factor GATA1, resulting in loss of enhancer activity and enhancer-promoter contacts. Conversely, loss of HIC2 in fetal erythroblasts increases enhancer accessibility, enables GATA1 binding and induces BCL11A transcription. HIC2 is unveiled as a critical evolutionarily conserved regulator of globin gene switching by imposing developmental control on the BCL11A gene.