Dissecting a Multi-Step Mechanism of Beta-Globin Transcriptional Activation.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1207-1207
Author(s):  
Emery H. Bresnick ◽  
Hogune Im ◽  
Kirby D. Johnson ◽  
Jeffrey A. Grass

Abstract Defining factors and signals that establish and maintain the native nucleoprotein structure of endogenous chromatin domains represents a powerful approach for elucidating transcriptional mechanisms. In adult erythroid cells, the locus control region (LCR) and the adult beta-globin genes of the murine beta-globin locus are highly enriched in acetylated histones H3 and H4 (acH3, acH4) and H3 methylated at lysine 4 (H3-meK4). By contrast, the embryonic beta-globin genes reside in a broad region of reduced acetylation. Histone H3 methylated at lysine 79 (H3-meK79) is highly enriched at the adult beta-globin genes, but not at the LCR. To elucidate the molecular steps in beta-globin transcriptional activation, genetic complementation experiments were conducted in GATA-1-null G1E cells containing an estrogen receptor hormone binding domain-GATA-1 fusion protein (ER-GATA-1). Kinetic analysis of ER-GATA-1 occupancy of chromatin and establishment of the histone modification pattern by chromatin immunoprecipitation (ChIP) revealed that GATA-1 occupies multiple regions within the LCR prior to the beta-major promoter. Chromatin accessibility at the promoter was low until ER-GATA-1 assembled into regulatory complexes at the LCR. Subsequently, ER-GATA-1 accessed the beta-major promoter, induced acH3, RNA polymerase II (Pol II) recruitment, and elevated H3-meK79. Acquisition of transcriptional competence appears to require establishment of H3-meK4, which is GATA-1-independent. Blocking transcriptional elongation did not erase H3-meK79, indicating that maintenance of H3-meK79 does not require ongoing elongation. Analysis of N-terminal GATA-1 deletion mutants that retain Friend of GATA-1 (FOG-1) binding and DNA binding activities revealed that FOG-1 binding and DNA binding activities are insufficient for Pol II recruitment and chromatin modification at the promoter. These results support a model in which ER-GATA-1 binding to the LCR increases acH3 at the promoter as an early event in transcriptional activation, which is tightly coupled to ER-GATA-1 access to the promoter, increased promoter accessibility, and Pol II recruitment. Increased promoter accessibility, which likely permits ER-GATA-1 access to the promoter, precedes maximal induction of H3-meK79, a late event in activation. Given the dynamic regulation of H3-meK79 by GATA-1 and NF-E2 and the modulation of H3-meK79 levels during erythropoiesis, we propose that H3-meK79 is a crucial signal that controls the rate of beta-globin transcription. Studies are underway to test this hypothesis and to dissect mechanisms underlying the requirement of N-terminal sequences of GATA-1 for Pol II recruitment and chromatin modification. Furthermore, having identified individual steps in transcriptional activation of the endogenous beta-globin genes, we are testing whether inducers of human fetal hemoglobin affect these specific steps. GATA-1 has been reported by the Crispino group to be expressed as an N-terminally truncated species in megakaryoblastic leukemia. Defining how the N-terminus functions should therefore lead to a molecular understanding of this disorder. As the N-termini of GATA factors differ considerably, one might expect these divergent sequences to establish GATA factor-specific functions, and this prediction is being tested via detailed analysis of the activities of chimeric GATA factors.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. sci-18-sci-18
Author(s):  
Emery H. Bresnick ◽  
Shin-Il Kim ◽  
Scott J. Bultman ◽  
Sherry Lee ◽  
Meghan E. Boyer ◽  
...  

Abstract Key steps in hematopoiesis and the expression of genes encoding hemoglobin subunits are critically dependent upon specific members of the GATA factor family of transcription factors. Our recent efforts have focused on elucidating how GATA factors select functional sites in chromatin and how they function combinatorially with additional regulatory factors. GATA motifs are often arranged in close proximity to E-boxes, and such composite elements commonly mediate GATA factor- and Scl/TAL1-dependent transcriptional responses. Only a small fraction of these composite elements in chromatin are occupied by GATA factors and Scl/TAL1, and a specific epigenetic signature distinguishes occupied versus unoccupied elements genome-wide. In the context of hemoglobin synthesis, we are using genetic and molecular approaches to dissect the multistep mechanism underlying the control of β-globin transcription. GATA-1-containing complexes assemble at the β-globin Locus Control Region (LCR) prior to the murine adult βmajor promoter. Though the LCR physically interacts with the βmajor promoter, this interaction is not required for the binding of several trans-acting factors to the LCR or the promoter. A hypomorphic mutation of the chromatin remodeler BRG1 limits the extent to which RNA Polymerase II (Pol II) is recruited to the promoter and also abrogates the LCR-promoter interaction. Whereas looping is not required for assembly of the full complement of promoter complex components, looping is linked to the establishment of maximal levels of Pol II at the promoter. Collectively, these results provide insights into the relationship between, and importance of, individual steps in the multi-step activation mechanism. I will discuss progress on unraveling mechanisms underlying GATA-1-mediated activation of the adult β-like globin genes as well as fundamental aspects of GATA factor function, which have broad relevance in diverse systems. promoter. Though the LCR physically interacts with the β promoter, this interaction is not required for the binding of several -acting factors to the LCR or the promoter. A hypomorphic mutation of the chromatin remodeler BRG1 limits the extent to which RNA Polymerase II (Pol II) is recruited to the promoter and also abrogates the LCR-promoter interaction. Whereas looping is not required for assembly of the full complement of promoter complex components, looping is linked to the establishment of maximal levels of Pol II at the promoter. Collectively, these results provide insights into the relationship between, and importance of, individual steps in the multi-step activation mechanism. I will discuss progress on unraveling mechanisms underlying GATA-1-mediated activation of the adult β-like globin genes as well as fundamental aspects of GATA factor function, which have broad relevance in diverse systems.


2007 ◽  
Vol 27 (12) ◽  
pp. 4551-4565 ◽  
Author(s):  
Shin-Il Kim ◽  
Scott J. Bultman ◽  
Huie Jing ◽  
Gerd A. Blobel ◽  
Emery H. Bresnick

ABSTRACT GATA factors orchestrate hematopoiesis via multistep transcriptional mechanisms, but the interrelationships and importance of individual steps are poorly understood. Using complementation analysis with GATA-1-null cells and mice containing a hypomorphic allele of the chromatin remodeler BRG1, we dissected the pathway from GATA-1 binding to cofactor recruitment, chromatin loop formation, and transcriptional activation. Analysis of GATA-1-mediated activation of the β-globin locus, in which GATA-1 assembles dispersed complexes at the promoters and the distal locus control region (LCR), revealed molecular intermediates, including GATA-1-independent and GATA-1-containing LCR subcomplexes, both defective in promoting loop formation. An additional intermediate consisted of an apparently normal LCR complex and a promoter complex with reduced levels of total RNA polymerase II (Pol II) and Pol II phosphorylated at serine 5 of the carboxy-terminal domain. Reduced BRG1 activity solely compromised Pol II and serine 5-phosphorylated Pol II occupancy at the promoter, phenocopying the LCR-deleted mouse. These studies defined a hierarchical order of GATA-1-triggered events at a complex locus and establish a novel mechanism of long-range gene regulation.


Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 647-647
Author(s):  
Wulan Deng ◽  
Philip D Gregory ◽  
Andreas Reik ◽  
Gerd Blobel

Abstract Abstract 647 The mammalian β-globin locus is under the coordinated control of multiple transcription factors to ensure the correct expression of the globin genes during development. The distal β-globin locus control region (LCR) physically interacts with β-like globin promoters to form developmentally dynamic chromatin loops. The hematopoietic transcription factor GATA-1 and its associated cofactor Ldb1 bind to the LCR and the β-globin promoter and are essential for loop formation and β-globin expression. However, the molecular basis of chromatin looping and its cause-effect relationship with transcriptional activation are unclear. Here, we examined whether Ldb1 is an effector of GATA-1 during loop formation. Specifically, we tested whether artificial tethering of Ldb1 to the endogenous β-globin promoter and LCR can substitute for GATA-1 function. Ldb1 was fused to artificial zinc finger proteins (ZFP) designed to bind to the LCR and β-globin promoter. Ldb1-ZFPs were introduced pairwise into murine GATA-1 null erythroid cells in which the β-globin locus is relaxed and transcriptionally silent. In vivo binding of the Ldb1-ZFPs to their targets was verified by ChIP assay. Strikingly, expression of Ldb1-ZFPs but not Ldb1 or ZFPs alone led to substantial activation of β-globin transcription in the absence of GATA-1. Moreover, chromosome conformation capture experiments showed that Ldb1-ZFPs triggered physical association between the LCR and the β-globin promoter. Recruitment of RNA polymerase II (Pol II) and its phosphorylation at serine 5 are critical LCR-dependent regulatory steps in β-globin transcription. We found that Ldb1-ZFP expression facilitated Pol II recruitment at the β-globin promoter and serine 5 phosphorylation to the same level as GATA-1-expressing erythroid cells. This is consistent with an Ldb1-ZFP-induced LCR-β-globin promoter chromatin loop. In concert, these results indicate that Ldb1 is a critical effector for GATA-1 by mediating enhancer-promoter loops. In broader terms, our results suggest that chromatin loop formation can be sufficient for gene activation in the absence of an essential transcription factor. We are currently in the process of examining whether targeting of the LCR to embryonic and fetal globin genes can be used to activate them in adult cells. Targeted chromatin loop formation may provide a method to activate fetal or adult hemoglobin expression in individuals with β-thalassemia or sickle cell anemia. Disclosures: No relevant conflicts of interest to declare.


2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Shu-Hao Liou ◽  
Sameer K. Singh ◽  
Robert H. Singer ◽  
Robert A. Coleman ◽  
Wei-Li Liu

AbstractThe tumor suppressor p53 protein activates expression of a vast gene network in response to stress stimuli for cellular integrity. The molecular mechanism underlying how p53 targets RNA polymerase II (Pol II) to regulate transcription remains unclear. To elucidate the p53/Pol II interaction, we have determined a 4.6 Å resolution structure of the human p53/Pol II assembly via single particle cryo-electron microscopy. Our structure reveals that p53’s DNA binding domain targets the upstream DNA binding site within Pol II. This association introduces conformational changes of the Pol II clamp into a further-closed state. A cavity was identified between p53 and Pol II that could possibly host DNA. The transactivation domain of p53 binds the surface of Pol II’s jaw that contacts downstream DNA. These findings suggest that p53’s functional domains directly regulate DNA binding activity of Pol II to mediate transcription, thereby providing insights into p53-regulated gene expression.


Blood ◽  
1994 ◽  
Vol 84 (4) ◽  
pp. 1074-1084 ◽  
Author(s):  
T Nagai ◽  
H Harigae ◽  
H Ishihara ◽  
H Motohashi ◽  
N Minegishi ◽  
...  

Abstract To understand the functional roles that the GATA factors may play during hematopoietic cell differentiation, we examined the expression of GATA factor mRNAs and protein products in various human cell lines. Blot hybridization analyses demonstrated that GATA-1 and GATA-2 mRNAs are expressed abundantly in a set of cell lines established from human myelogenous leukemia cells, but the expression pattern of each factor is distinct. GATA-2 mRNA is expressed in all cell lines tested that express erythroid markers, and, in addition, the mRNA is also expressed in three CD34+ cell lines and two early myeloid cell lines. In contrast, the expression of GATA-1 mRNA showed tight correlation to that of the erythroid/megakaryocytic lineage markers. We also found that the GATA-2 probe identifies two types of mRNA. Structural analysis of genomic DNA clones encoding human GATA-2 coupled with RNA blot analysis demonstrated that there exists an alternative use of polyadenylation consensus sequences in a single exon and this causes the molecular heterogeneity among GATA-2 mRNAs. Through immunochemical and immunohistochemical analyses using anti-GATA-1- and anti-GATA-2- specific antibodies, GATA-2 protein was clearly shown to be present in the nuclei of leukemia-derived early myeloid and CD34+ cell lines, whereas both GATA-1 and GATA-2 proteins are expressed in erythroid/megakaryocytic cell lines. Thus, the expression profile of GATA-2 is consistent with the hypothesis that GATA-2 plays unique roles for the transcriptional activation of genes in cells at an early stage of hematopoietic differentiation and in developing cells of the erythroid and myeloid lineages.


2020 ◽  
Vol 295 (12) ◽  
pp. 3990-4000 ◽  
Author(s):  
Sandeep Singh ◽  
Karol Szlachta ◽  
Arkadi Manukyan ◽  
Heather M. Raimer ◽  
Manikarna Dinda ◽  
...  

DNA double-stranded breaks (DSBs) are strongly associated with active transcription, and promoter-proximal pausing of RNA polymerase II (Pol II) is a critical step in transcriptional regulation. Mapping the distribution of DSBs along actively expressed genes and identifying the location of DSBs relative to pausing sites can provide mechanistic insights into transcriptional regulation. Using genome-wide DNA break mapping/sequencing techniques at single-nucleotide resolution in human cells, we found that DSBs are preferentially located around transcription start sites of highly transcribed and paused genes and that Pol II promoter-proximal pausing sites are enriched in DSBs. We observed that DSB frequency at pausing sites increases as the strength of pausing increases, regardless of whether the pausing sites are near or far from annotated transcription start sites. Inhibition of topoisomerase I and II by camptothecin and etoposide treatment, respectively, increased DSBs at the pausing sites as the concentrations of drugs increased, demonstrating the involvement of topoisomerases in DSB generation at the pausing sites. DNA breaks generated by topoisomerases are short-lived because of the religation activity of these enzymes, which these drugs inhibit; therefore, the observation of increased DSBs with increasing drug doses at pausing sites indicated active recruitment of topoisomerases to these sites. Furthermore, the enrichment and locations of DSBs at pausing sites were shared among different cell types, suggesting that Pol II promoter-proximal pausing is a common regulatory mechanism. Our findings support a model in which topoisomerases participate in Pol II promoter-proximal pausing and indicated that DSBs at pausing sites contribute to transcriptional activation.


2004 ◽  
Vol 24 (14) ◽  
pp. 6419-6429 ◽  
Author(s):  
Peter Eriksson ◽  
Debabrata Biswas ◽  
Yaxin Yu ◽  
James M. Stewart ◽  
David J. Stillman

ABSTRACT The Saccharomyces cerevisiae Nhp6 protein is related to the high-mobility-group B family of architectural DNA-binding proteins that bind DNA nonspecifically but bend DNA sharply. Nhp6 is involved in transcriptional activation by both RNA polymerase II (Pol II) and Pol III. Our previous genetic studies have implicated Nhp6 in facilitating TATA-binding protein (TBP) binding to some Pol II promoters in vivo, and we have used a novel genetic screen to isolate 32 new mutations in TBP that are viable in wild-type cells but lethal in the absence of Nhp6. The TBP mutations that are lethal in the absence of Nhp6 cluster in three regions: on the upper surface of TBP that may have a regulatory role, near residues that contact Spt3, or near residues known to contact either TFIIA or Brf1 (in TFIIIB). The latter set of mutations suggests that Nhp6 becomes essential when a TBP mutant compromises its ability to interact with either TFIIA or Brf1. Importantly, the synthetic lethality for some of the TBP mutations is suppressed by a multicopy plasmid with SNR6 or by an spt3 mutation. It has been previously shown that nhp6ab mutants are defective in expressing SNR6, a Pol III-transcribed gene encoding the U6 splicing RNA. Chromatin immunoprecipitation experiments show that TBP binding to SNR6 is reduced in an nhp6ab mutant. Nhp6 interacts with Spt16/Pob3, the yeast equivalent of the FACT elongation complex, consistent with nhp6ab cells being extremely sensitive to 6-azauracil (6-AU). However, this 6-AU sensitivity can be suppressed by multicopy SNR6 or BRF1. Additionally, strains with SNR6 promoter mutations are sensitive to 6-AU, suggesting that decreased SNR6 RNA levels contribute to 6-AU sensitivity. These results challenge the widely held belief that 6-AU sensitivity results from a defect in transcriptional elongation.


2001 ◽  
Vol 21 (8) ◽  
pp. 2736-2742 ◽  
Author(s):  
Joseph V. Geisberg ◽  
Frank C. Holstege ◽  
Richard A. Young ◽  
Kevin Struhl

ABSTRACT NC2 (Dr1-Drap1 or Bur6-Ydr1) has been characterized in vitro as a general negative regulator of RNA polymerase II (Pol II) transcription that interacts with TATA-binding protein (TBP) and inhibits its function. Here, we show that NC2 associates with promoters in vivo in a manner that correlates with transcriptional activity and with occupancy by basal transcription factors. NC2 rapidly associates with promoters in response to transcriptional activation, and it remains associated under conditions in which transcription is blocked after assembly of the Pol II preinitiation complex. NC2 positively and negatively affects approximately 17% of Saccharomyces cerevisiaegenes in a pattern that resembles the response to general environmental stress. Relative to TBP, NC2 occupancy is high at promoters where NC2 is positively required for normal levels of transcription. Thus, NC2 is associated with the Pol II preinitiation complex, and it can play a direct and positive role at certain promoters in vivo.


2007 ◽  
Vol 27 (6) ◽  
pp. 2059-2073 ◽  
Author(s):  
Victoria H. Cowling ◽  
Michael D. Cole

ABSTRACT Myc is a transcription factor which is dependent on its DNA binding domain for transcriptional regulation of target genes. Here, we report the surprising finding that Myc mutants devoid of direct DNA binding activity and Myc target gene regulation can rescue a substantial fraction of the growth defect in myc −/− fibroblasts. Expression of the Myc transactivation domain alone induces a transcription-independent elevation of the RNA polymerase II (Pol II) C-terminal domain (CTD) kinases cyclin-dependent kinase 7 (CDK7) and CDK9 and a global increase in CTD phosphorylation. The Myc transactivation domain binds to the transcription initiation sites of these promoters and stimulates TFIIH binding in an MBII-dependent manner. Expression of the Myc transactivation domain increases CDK mRNA cap methylation, polysome loading, and the rate of translation. We find that some traditional Myc transcriptional target genes are also regulated by this Myc-driven translation mechanism. We propose that Myc transactivation domain-driven RNA Pol II CTD phosphorylation has broad effects on both transcription and mRNA metabolism.


2020 ◽  
Author(s):  
Yubo Cheng ◽  
Babita Gollen ◽  
Luke Saville ◽  
Christopher Isaac ◽  
Jogender Mehla ◽  
...  

ABSTRACTMore than 97% of the mammalian genome is non-protein coding, and repetitive elements account for more than 50% of noncoding space. However, the functional importance of many non-coding RNAs generated by these elements and their connection with pathologic processes remains elusive. We have previously shown that B2 RNAs, a class of non-coding RNAs that belong to the B2 family of SINE repeats, mediate the transcriptional activation of stress response genes (SRGs) upon application of a stimulus. Notably, B2 RNAs bind RNA Polymerase II (RNA Pol II) and suppress SRG transcription during pro-stimulation state. Upon application of a stimulus, B2 RNAs are processed into fragments and degraded, which in turn releases RNA Pol II from suppression and upregulates SRGs. Here, we demonstrate a novel role for B2 RNAs in transcriptome response to amyloid beta toxicity and pathology in the mouse hippocampus. In healthy hippocampi, activation of SRGs is followed by a transient upregulation of pro-apoptotic factors, such as p53 and miRNA-34c, which target SRGs creating a negative feedback loop that facilitates transition to the pro-stimulation state. Using an integrative RNA genomics approach, we show that in mouse hippocampi of an amyloid precursor protein knock-in mouse model and in an in vitro cell culture model of amyloid beta toxicity, this regulatory loop is dysfunctional due to increased levels of B2 RNA processing, constitutively elevated SRG expression and high p53 levels. Evidence indicates that Hsf1, a master regulator of stress response, mediates B2 RNA processing in cells, and is upregulated during amyloid toxicity accelerating the processing of SINE RNAs and SRG hyper-activation. Our study reveals that in mouse, SINE RNAs constitute a novel pathway deregulated in amyloid beta pathology, with potential implications for similar cases in the human brain, such as Alzheimer’s disease (AD). This data attributes a role to SINE RNA processing in a pathological process as well as a new function to Hsf1 that is independent of its transcription factor activity.


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