HEXIM1 Overexpression Alters GATA1 Activity and Promotes Fetal Globin Expression
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ABSTRACT: Erythropoiesis is a highly organized process whereby multipotent HSCs become committed to the erythroid linage and mature into enucleate erythrocytes. Recent work from our lab demonstrated that HEXIM1 is essential in the regulation of erythroid proliferation, viability and gene expression, and also promotes the expression of GATA1 target genes. New analyses of HEXIM1 overexpression (OE) in HUDEP2 cells revealed a significant increase of gamma globin production, with a higher proportion of cells expressing fetal hemoglobin. To gain insights into the mechanisms underlying the increased fetal globin expression, we performed CUT&RUN assays for Ser5 phosphorylated and total RNPII in HEXIM1 OE and control cells. Surprisingly, OE of HEXIM1 had only modest impacts on RNPII pausing, but instead lead to changes in the genes occupied by RNPII. Our results support a model where elevated HEXIM1 levels promote the pioneer activity of GATA1, and facilitate the expression of a fetal transcriptional program in adult cells in a pTEFb-dependent manner.
Project description:Naturally occurring mutations in the γ-globin promoters can result in hereditary persistence of fetal hemoglobin (HPFH), a benign condition that ameliorates the severity of β-hemoglobinopathies through increased post-natal fetal hemoglobin (HbF) expression. Mutations in the γ-globin promoters result in loss or de novo recruitment of transcription factors, yet the cis-regulatory elements involved in γ-globin transcription in the context of HPFH are not clearly defined. We demonstrate that the -115 cluster of HPFH mutations require GATA1 binding to at -186 in cooperation with NF-Y at the proximal CCAAT box at -85 for γ-globin expression. We show that multiple HPFH mutations increase HbF in an erythroid cell line and result in GATA1 binding at -186. Mutation of the -186 GATA motif in HPFH erythroid cell lines and erythroid-differentiated CD34+ cells resulted in loss of GATA1 binding and reduction in fetal hemoglobin. NF-Y ChIP-seq in HPFH erythroid cell lines demonstrated binding to the proximal CCAAT box at -85 was also found to be critical for HPFH-mediated γ-globin expression. Together, the -186 GATA motif and -85 proximal CCAAT box function in an additive and independent manner. Our results reveal detailed evidence for common, positive acting cis-regulatory elements that may provide more general mechanisms for erythroid gene expression.
Project description:A highly selective and non-genotoxic G9a inhibitor, RK-701 was discovered, which upregulated the mRNA level of γ-globin but not β-globin both in human erythroid cells and in mice. Using RK-701, we examined the induction of the fetal (γ-) globin protein in human erythroid cells; HUDEP-2 and human CD34+ bone marrow and peripheral blood cells.
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.
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:In this study we identified an essential role of the SEC, a crucial regulator of Pol II dynamics, in repressing differentiation for epidermal progenitor maintenance. This repression of differentiation is specifically mediated by the scaffold protein AFF1, but not AFF4. Mechanistically, we find that AFF1-SEC associates with the HEXIM1-containing inactive-PTEFb to directly repress a group of rapid-response genes, which feature robust Pol II pausing near their promoters in the progenitor state. De-repression of these genes occurs within 3 hours of SEC-PTEFb disruption by the peptidomimetic inhibitors. These rapid-response genes include the transcription factor ATF3. Increased ATF3 level is sufficient to promote the expression of key differentiation activators, such as PRDM1, OVOL1, GRHL3 and ZNF750. Furthermore, we find that the dissociation of inactivate P-TEFb from SEC mediates the earliest events of PKC signaling, in triggering epidermal differentiation.
Project description:Development of red blood cells from progenitors requires profound reshaping of both gene expression and metabolism. How these processes are coupled is unclear. Nprl3, an inhibitor of mTORC1, has remained in synteny with the -globin genes for >500 million years, and harbours most of the -globin enhancers. However, whether Nprl3 itself serves an erythroid role is unknown. While hematopoietic progenitors rely on tonic expression of baseline Nprl3, erythroblasts experience ‘boosted’ Nprl3 expression. Using Nprl3-deficient fetal liver and adult competitive bone marrow - fetal liver chimaeras, we show that NprI3 is required for sufficient erythropoiesis. Loss of Nprl3 elevates mTORC1 signalling, suppresses autophagy and disrupts erythroblast glycolysis. Human NPRL3-knockout erythroid progenitors produce fewer enucleated cells and demonstrate dysregulated mTORC1 signalling in response to nutrient availability and erythropoietin. Thus, Nprl3 is a key regulator of erythroid metabolism. Finally, we show that the alpha-globin enhancers upregulate erythoid NprI3 expression, and that this activity supports optimal erythropoiesis.