BRD4 loading at the transcription start site mediates pause-release and underlies the disproportionate transcriptional response to BET bromodomain inhibition [GRO-Seq]
Ontology highlight
ABSTRACT: BET bromodomain inhibition (BETi) abrogates cancer cell growth by disrupting oncogenic gene expression. BRD4 loading at enhancers has been suggested to mediate pause-release and underlie the selective transcriptional response to BETi. Here, we utilized GRO-seq coupled with ChIP-seq to assess the association between gene control elements and the transcriptional response to BETi. Genes immediately down-regulated by BETi display a marked pause-release defect with a minimal impact on transcript elongation within the gene body. Surprisingly, we find that BRD4 at super-enhancers does not render its associated genes or enhancer RNAs preferentially sensitive to BETi. In contrast, disproportionate loading of BRD4 at transcription start sites (TSS) correlates with the transcriptional response to BETi. Moreover, BRD4 loading at TSSs, but not enhancers, is associated with enhanced promoter-proximal pausing following BETi. Our findings stress a mechanistic role of promoter-associated BRD4 in pause-release and suggest that BRD4 loading at the TSS drives the selective transcriptional response to BETi.
Project description:BET bromodomain inhibition (BETi) abrogates cancer cell growth by disrupting oncogenic gene expression. BRD4 loading at enhancers has been suggested to mediate pause-release and underlie the selective transcriptional response to BETi. Here, we utilized GRO-seq coupled with ChIP-seq to assess the association between gene control elements and the transcriptional response to BETi. Genes immediately down-regulated by BETi display a marked pause-release defect with a minimal impact on transcript elongation within the gene body. Surprisingly, we find that BRD4 at super-enhancers does not render its associated genes or enhancer RNAs preferentially sensitive to BETi. In contrast, disproportionate loading of BRD4 at transcription start sites (TSS) correlates with the transcriptional response to BETi. Moreover, BRD4 loading at TSSs, but not enhancers, is associated with enhanced promoter-proximal pausing following BETi. Our findings stress a mechanistic role of promoter-associated BRD4 in pause-release and suggest that BRD4 loading at the TSS drives the selective transcriptional response to BETi.
Project description:BET bromodomain inhibition (BETi) abrogates cancer cell growth by disrupting oncogenic gene expression. BRD4 loading at enhancers has been suggested to mediate pause-release and underlie the selective transcriptional response to BETi. Here, we utilized GRO-seq coupled with ChIP-seq to assess the association between gene control elements and the transcriptional response to BETi. Genes immediately down-regulated by BETi display a marked pause-release defect with a minimal impact on transcript elongation within the gene body. Surprisingly, we find that BRD4 at super-enhancers does not render its associated genes or enhancer RNAs preferentially sensitive to BETi. In contrast, disproportionate loading of BRD4 at transcription start sites (TSS) correlates with the transcriptional response to BETi. Moreover, BRD4 loading at TSSs, but not enhancers, is associated with enhanced promoter-proximal pausing following BETi. Our findings stress a mechanistic role of promoter-associated BRD4 in pause-release and suggest that BRD4 loading at the TSS drives the selective transcriptional response to BETi.
Project description:Distal enhancers characterized by H3K4me1 mark play critical roles in developmental and transcriptional programs. However, potential roles of specific distal regulatory elements in regulating RNA Polymerase II (Pol II) promoter-proximal pause release remain poorly investigated. Here we report that a unique cohort of jumonji C domain-containing protein 6 (JMJD6) and bromodomain-containing protein 4 (Brd4) co-bound distal enhancers, termed anti-pause enhancers (A-PEs), regulate promoter-proximal pause release of a large subset of transcription units via long-range interactions. Brd4-dependent JMJD6 recruitment on A-PEs mediates erasure of H4R3me2(s), which is directly read by 7SK snRNA, and decapping/demethylation of 7SK snRNA, ensuring the dismissal of the 7SKsnRNA/HEXIM inhibitory complex. The interactions of both JMJD6 and Brd4 with the P-TEFb complex permit its activation and pause release of regulated coding genes. The functions of JMJD6/ Brd4-associated dual histone and RNA demethylase activity on anti-pause enhancers have intriguing implications for these proteins in development, homeostasis and disease. All Gro-seq(s) were designed to reveal the transcriptional targets of JMJD6 and Brd4, and assess the role of JMJD6 and Brd4 in Pol II promoter-proximal pause release. All ChIP-seq(s) were designed to understand the unique features, associated molecular mechanisms and functions of the anti-pause enhancers (A-PEs) discovered in the current study.
Project description:Distal enhancers characterized by H3K4me1 mark play critical roles in developmental and transcriptional programs. However, potential roles of specific distal regulatory elements in regulating RNA Polymerase II (Pol II) promoter-proximal pause release remain poorly investigated. Here we report that a unique cohort of jumonji C domain-containing protein 6 (JMJD6) and bromodomain-containing protein 4 (Brd4) co-bound distal enhancers, termed anti-pause enhancers (A-PEs), regulate promoter-proximal pause release of a large subset of transcription units via long-range interactions. Brd4-dependent JMJD6 recruitment on A-PEs mediates erasure of H4R3me2(s), which is directly read by 7SK snRNA, and decapping/demethylation of 7SK snRNA, ensuring the dismissal of the 7SKsnRNA/HEXIM inhibitory complex. The interactions of both JMJD6 and Brd4 with the P-TEFb complex permit its activation and pause release of regulated coding genes. The functions of JMJD6/ Brd4-associated dual histone and RNA demethylase activity on anti-pause enhancers have intriguing implications for these proteins in development, homeostasis and disease.
Project description:Diffuse Large B-Cell Lymphoma (DLBCL) is a biologically heterogeneous and clinically aggressive disease. Here, we explore the role of BET bromodomain proteins in DLBCL, using integrative chemical genetics and functional epigenomics. We observe highly asymmetric loading of BRD4 at enhancers, with approximately 33% of all BRD4 localizing to enhancers at 1.6% of occupied genes. These super-enhancers prove particularly sensitive to bromodomain inhibition, explaining the selective effect of BET inhibitors on oncogenic and lineage-specific transcriptional circuits. Functional study of genes marked by super-enhancers identifies DLBCLs dependent on OCA-B and suggests a strategy for discovering unrecognized cancer dependencies. Translational studies performed on a comprehensive panel of DLBCLs establish a therapeutic rationale for evaluating BET inhibitors in this disease. ChIP-Seq for various transcription factors and histone modifications in diffuse large B-cell lymphoma cells
Project description:Reactivation of the pluripotency network during somatic cell reprogramming by exogenous transcription factors involves chromatin remodeling and the recruitment of RNA polymerase II (Pol II) to target loci. Here, we report that Pol II is engaged at pluripotency promoters in reprogramming but remains paused and inefficiently released. We also show that bromodomain-containing protein 4 (BRD4) stimulates productive transcriptional elongation of pluripotency genes by dissociating the pause release factor P-TEFb from an inactive complex containing HEXIM1. Consequently, BRD4 overexpression enhances reprogramming efficiency and HEXIM1 suppresses it, whereas Brd4 and Hexim1 knockdown do the opposite. We further demonstrate that the reprogramming factor KLF4 helps recruit P-TEFb to pluripotency promoters. Our work thus provides a mechanism for explaining the reactivation of pluripotency genes in reprogramming and unveils an unanticipated role for KLF4 in transcriptional pause release. Refer to individual Series
Project description:Reactivation of the pluripotency network during somatic cell reprogramming by exogenous transcription factors involves chromatin remodeling and the recruitment of RNA polymerase II (Pol II) to target loci. Here, we report that Pol II is engaged at pluripotency promoters in reprogramming but remains paused and inefficiently released. We also show that bromodomain-containing protein 4 (BRD4) stimulates productive transcriptional elongation of pluripotency genes by dissociating the pause release factor P-TEFb from an inactive complex containing HEXIM1. Consequently, BRD4 overexpression enhances reprogramming efficiency and HEXIM1 suppresses it, whereas Brd4 and Hexim1 knockdown do the opposite. We further demonstrate that the reprogramming factor KLF4 helps recruit P-TEFb to pluripotency promoters. Our work thus provides a mechanism for explaining the reactivation of pluripotency genes in reprogramming and unveils an unanticipated role for KLF4 in transcriptional pause release. Pol II ChIP-seq for MEFs, ESCs and bulk populations of OSKM reprogramming intermediates at two time points.
Project description:Reactivation of the pluripotency network during somatic cell reprogramming by exogenous transcription factors involves chromatin remodeling and the recruitment of RNA polymerase II (Pol II) to target loci. Here, we report that Pol II is engaged at pluripotency promoters in reprogramming but remains paused and inefficiently released. We also show that bromodomain-containing protein 4 (BRD4) stimulates productive transcriptional elongation of pluripotency genes by dissociating the pause release factor P-TEFb from an inactive complex containing HEXIM1. Consequently, BRD4 overexpression enhances reprogramming efficiency and HEXIM1 suppresses it, whereas Brd4 and Hexim1 knockdown do the opposite. We further demonstrate that the reprogramming factor KLF4 helps recruit P-TEFb to pluripotency promoters. Our work thus provides a mechanism for explaining the reactivation of pluripotency genes in reprogramming and unveils an unanticipated role for KLF4 in transcriptional pause release. Examination of differential gene expression after overexpression of Cdk9-DN at 4 time points of somatic cell reprogramming
Project description:The BET family protein BRD4, which forms the CDK9-containing BRD4-PTEFb complex, is considered to be a master regulator of RNA polymerase II (Pol II) pause release. Because its tandem bromodomains interact with acetylated histone lysine residues, it has long been thought that BRD4 requires these bromodomains for its recruitment to chromatin and transcriptional regulatory function. Here, using rapid depletion and genetic complementation with domain deletion mutants, we demonstrate that BRD4 bromodomains are dispensable for Pol II pause release. A minimal, bromodomain-less C-terminal BRD4 fragment containing the PTEFb-interacting C-terminal motif (CTM) is instead both necessary and sufficient to mediate Pol II pause release in the absence of full-length BRD4. Although BRD4-PTEFb can associate with chromatin through acetyl recognition, our results indicate that a distinct, active BRD4-PTEFb population functions to regulate transcription independently of bromodomain-mediated chromatin association. These findings may enable more effective pharmaceutical modulation of BRD4-PTEFb activity.