A mechanism for Ikaros regulation of human globin gene switching.

Institute for Molecular Bioscience, Queensland Bioscience Precinct, University of Queensland, Queensland, Australia.
British Journal of Haematology (Impact Factor: 4.96). 06/2008; 141(3):398-406. DOI: 10.1111/j.1365-2141.2008.07065.x
Source: PubMed

ABSTRACT The human beta globin locus consists of an upstream LCR and functional genes arranged sequentially in the order of their expression during development: 5'-HBE1, HBG2, HBG1, HBD, HBB-3'. Haemoglobin switching entails the successive recruitment of these genes into an active chromatin hub (ACH). Here we show that the transcription factor Ikaros plays a major role in the formation of the beta-globin ACH, and in haemoglobin switching. In Plastic mice, where the DNA-binding region of Ikaros is disrupted by a point mutation, there is concomitant marked down-regulation of HBB, and up-regulation of HBG expression. We show for the first time Ikaros and its family member Eos, bind to critical cis elements implicated in haemoglobin switching and deletional hereditary persistence of fetal haemoglobin (HPFH). Chromatin conformation capture (3C) data demonstrated that Ikaros facilitates long-distance DNA looping between the LCR and a region upstream of HBD. This study provides new insights into the mechanism of stage-specific assembly of the beta-globin ACH, and HPFH.

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    Genomics 10/2014; 105(2). DOI:10.1016/j.ygeno.2014.09.013 · 2.79 Impact Factor
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    ABSTRACT: Ikaros (Ik) is a critical regulator of hematopoietic gene expression. Here we establish that Ik interaction with GATA transcription factors and cyclin dependent kinase 9 (Cdk9), a component of the Positive Transcription Elongation Factor b (P-TEFb), is required for transcriptional activation of Ik target genes. A detailed dissection of Ik-GATA and Ik-Cdk9 protein interactions indicates that the C-terminal zinc-finger domain of Ik interacts directly with the C-terminal zinc-finger of GATA1, GATA2 and GATA3 whereas the N-terminal zinc-finger domain of Ik is required for interaction with the kinase and T-loop domains of Cdk9. The relevance of these interactions is demonstrated in vivo in COS-7 and primary hematopoietic cells, where Ik facilitates Cdk9 and GATA protein recruitment to gene promoters and transcriptional activation. Moreover, the oncogenic isoform Ik6 does not efficiently interact with Cdk9 or GATA proteins in vivo, perturbs Cdk9/P-TEFb recruitment to Ik-target genes, thereby affecting transcription elongation. Finally, characterization of a novel nuclear Ik isoform reveals that Ik exon 6 is dispensable for interaction with Mi2 and GATA proteins but is essential for Cdk9 interaction. Thus, Ik is central to the Ik-GATA-Cdk9 regulatory network, which is broadly utilized for gene regulation in hematopoietic cells.
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    ABSTRACT: PURPOSE OF REVIEW: Krüppel-like factor 1 (KLF1) regulates most aspects of erythropoiesis. Many years ago, transgenic mouse studies implicated KLF1 in the control of the human γ-globin to β-globin switch. In this review, we will integrate these initial studies with recent developments in human genetics to discuss our present understanding of how KLF1 and its target genes direct the switch. RECENT FINDINGS: Recent studies have shown that human mutations in KLF1 are common and mostly asymptomatic, but lead to significant increases in levels of fetal hemoglobin (HbF) (α2γ2) and adult HbA2 (α2δ2). Genome-wide association studies (GWAS) have demonstrated that three primary loci are associated with increased HbF levels in the population: the β-globin locus itself, the BCL11A locus, and a site between MYB and HBS1L. We discuss evidence that KLF1 directly regulates BCL11A, MYB and other genes, which are involved directly or indirectly in γ-globin silencing, thus providing a link between GWAS and KLF1 in hemoglobin switching. SUMMARY: KLF1 regulates the γ-globin to β-globin genetic switch by many mechanisms. Firstly, it facilitates formation of an active chromatin hub (ACH) at the β-globin gene cluster. Specifically, KLF1 conscripts the adult-stage β-globin gene to replace the γ-globin gene within the ACH in a stage-specific manner. Secondly, KLF1 acts as a direct activator of genes that encode repressors of γ-globin gene expression. Finally, KLF1 is a regulator of many components of the cell cycle machinery. We suggest that dysregulation of these genes leads to cell cycle perturbation and 'erythropoietic stress' leading to indirect upregulation of HbF.
    Current opinion in hematology 03/2013; DOI:10.1097/MOH.0b013e32835f59ba · 4.05 Impact Factor

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