The mediator complex functions as a coactivator for GATA-1 in erythropoiesis via subunit Med1/TRAP220

Self Cite

The Mediator complex forms the bridge between transcriptional activators and the RNA polymerase II. Med1 (also known as PBP or TRAP220) is a key component of Mediator that interacts with nuclear hormone receptors and GATA transcription factors. Here, we show dynamic recruitment of GATA-1, TFIIB, Mediator, and RNA polymerase II to the β-globin locus in induced mouse erythoid leukemia cells and in an erythropoietin-inducible hematopoietic progenitor cell line. Using Med1 conditional knockout mice, we demonstrate a specific block in erythroid development but not in myeloid or lymphoid development, highlighted by the complete absence of β-globin gene expression. Thus, Mediator subunit Med1 plays a pivotal role in erythroid development and in β-globin gene activation.blood | hematopoiesis | erythropoiesis | transcriptional regulation | globin

Section: Discussionmentioning

confidence: 92%

Specific erythroid-lineage defect in mice conditionally deficient for Mediator subunit Med1

Stumpf

Yue

Schmitz

et al. 2010

Self Cite

“…GATA-1 interacts with multiple co-regulators (31), including FOG-1 (14,32), CREB-binding protein (CBP)/p300 (33), MED1 (34), and BRG1 (27,28), and all except MED1 have been shown to occupy the LCR (27,28,35,36). We tested whether ER-GATA-1 occupancy at the LCR and promoter is coupled to co-regulator recruitment at these sites.…”

Section: Progressive Assembly Of a Cell Type-specific Chromatin Loopmentioning

confidence: 99%

BRG1 requirement for long-range interaction of a locus control region with a downstream promoter

Kim

Bultman

Kiefer

et al. 2009

115

109

The dynamic packaging of DNA into chromatin is a fundamental step in the control of diverse nuclear processes. Whereas certain transcription factors and chromosomal components promote the formation of higher-order chromatin loops, the co-regulator machinery mediating loop assembly and disassembly is unknown. Using mice bearing a hypomorphic allele of the BRG1 chromatin remodeler, we demonstrate that the Brg1 mutation abrogated a cell type-specific loop between the ␤-globin locus control region and the downstream ␤major promoter, despite trans-acting factor occupancy at both sites. By contrast, distinct loops were insensitive to the Brg1 mutation. Molecular analysis with a conditional allele of GATA-1, a key regulator of hematopoiesis, in a novel cell-based system provided additional evidence that BRG1 functions early in chromatin domain activation to mediate looping. Although the paradigm in which chromatin remodelers induce nucleosome structural transitions is well established, our results demonstrating an essential role of BRG1 in the genesis of specific chromatin loops expands the repertoire of their functions.chromatin ͉ erythroid ͉ GATA-1 ͉ globin ͉ transcription I ntegral to the developmental emergence of specialized cell types is the establishment of cell type-specific chromatin structures. Early studies developed important concepts regarding the impact of nucleosome positioning on protein-chromatin interactions (1), and more recently, ChIP technology (2) ushered in an explosive increase in information on the distribution of histone modifications and nucleosomes genome-wide (3). However, many questions remain unanswered regarding how higher-order chromatin structures are established and regulated.Nucleosomal filaments assemble into 30-nm fibers, which fold into higher-order loops (4). Chromosome conformation capture (3C) (5) studies have provided evidence for looping in response to trans-acting factor binding to chromatin (6-10). Key regulators of erythropoiesis-GATA-1 (11, 12), erythroid Krüppel-like factor (EKLF) (13), and the GATA-1-coregulator friend of GATA-1 (FOG-1) (14)-induce looping at the ␤-globin locus, in which the proximity of the locus control region (LCR) relative to a distant promoter increases (15, 16). The E-protein-interacting factor NL1/ Ldb1 also occupies the LCR and promotes looping (17). However, the role of chromatin modifying and remodeling co-regulators in looping is largely unexplored.Histone acetylation counteracts higher-order folding of chromatin templates in vitro (18), and broad acetylation characterizes active chromatin domains (19,20). Thus, it seems likely that histone acetylases and deacetylases are components of the looping machinery. As methylation of histone H3 at lysine 9 serves as a ligand that mediates heterochromatin protein 1 binding during heterochromatin assembly (21-23), the relevant methyltransferases might control looping. Although chromatin remodeling complexes, such as switch/sucrose nonfermentable (SWI/SNF), induce nucleosome structural transitions and a...

“…FOG-1 facilitates GATA-1 chromatin occupancy (14,15) and interacts with the nucleosome remodeling and deacetylase (NuRD) chromatin remodeling complex (16) containing the ATPase CHD4 (Mi2β), which is required for development of erythroid and other hematopoietic lineages (17,18). GATA-1 also recruits the chromatin remodeler BRG1 (19,20), the histone acetyltransferase CBP/p300 (21), and the mediator complex component Med1 (22,23). BRG1 promotes expression of adult α-and β-like globin genes in erythroid cells (19,24), CBP/p300 mediates GATA-1 function in at least certain contexts (21), and Med1 amplifies GATA-1 activity at select target genes (22).…”

mentioning

confidence: 99%

Establishing a hematopoietic genetic network through locus-specific integration of chromatin regulators

DeVilbiss

Boyer

Bresnick

2013

The establishment and maintenance of cell type-specific transcriptional programs require an ensemble of broadly expressed chromatin remodeling and modifying enzymes. Many questions remain unanswered regarding the contributions of these enzymes to specialized genetic networks that control critical processes, such as lineage commitment and cellular differentiation. We have been addressing this problem in the context of erythrocyte development driven by the transcription factor GATA-1 and its coregulator Friend of GATA-1 (FOG-1). As certain GATA-1 target genes have little to no FOG-1 requirement for expression, presumably additional coregulators can mediate GATA-1 function. Using a genetic complementation assay and RNA interference in GATA-1-null cells, we demonstrate a vital link between GATA-1 and the histone H4 lysine 20 methyltransferase PR-Set7/SetD8 (SetD8). GATA-1 selectively induced H4 monomethylated lysine 20 at repressed, but not activated, loci, and endogenous SetD8 mediated GATA-1-dependent repression of a cohort of its target genes. GATA-1 used different combinations of SetD8, FOG-1, and the FOG-1-interacting nucleosome remodeling and deacetylase complex component Mi2β to repress distinct target genes. Implicating SetD8 as a context-dependent GATA-1 corepressor expands the repertoire of coregulators mediating establishment/maintenance of the erythroid cell genetic network, and provides a biological framework for dissecting the cell type-specific functions of this important coregulator. We propose a coregulator matrix model in which distinct combinations of chromatin regulators are required at different GATA-1 target genes, and the unique attributes of the target loci mandate these combinations.