PR-DUB safeguards Polycomb repression through restricting H2AK119ub1 [RNA-seq]
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ABSTRACT: Polycomb group (PcG) proteins are critical chromatin regulators for cell fate control. The mono-ubiquitylation on histone H2AK119 (H2AK119ub1) is one of the well-recognized mechanisms for Polycomb Repressive Complex 1 (PRC1)-mediated transcription repression. However, the specific H2AK119 deubiquitylation complex composed by ASX-like proteins (ASXLs) and BAP1 has also been genetically characterized as a Polycomb Repressive complex (PR-DUB). Here we try to provide a rationale for these counterintuitive findings. Through re-examining the genomic distribution of H2AK119ub1, we find that H2AK119ub1 is non-negligibly distributed at non-promoter regions and associated with PRC1 sampling. Upon deletion of Asxl2 in mouse embryonic stem cells (ESCs), H2AK119ub1 is pervasively gained, especially at non-promoter regions, which is associated with increased RING1B occupancy. Meanwhile RING1B is significantly lost from a subset of the target promoters and thereby results in minor derepression in Asxl2-null ESCs. However notably, Asxl2 loss causes aberrant lineage differetiation, similar to PcG mutants. Therefore, our data reconcile seemingly paradoxical roles of PR-DUB on transcription repression and highlight the importance of a balanced H2AK119ub1 dynamics in developmental regulation.
Project description:Polycomb group (PcG) proteins are critical chromatin regulators for cell fate control. The mono-ubiquitylation on histone H2AK119 (H2AK119ub1) is one of the well-recognized mechanisms for Polycomb Repressive Complex 1 (PRC1)-mediated transcription repression. However, the specific H2AK119 deubiquitylation complex composed by ASX-like proteins (ASXLs) and BAP1 has also been genetically characterized as a Polycomb Repressive complex (PR-DUB). Here we try to provide a rationale for these counterintuitive findings. Through re-examining the genomic distribution of H2AK119ub1, we find that H2AK119ub1 is non-negligibly distributed at non-promoter regions and associated with PRC1 sampling. Upon deletion of Asxl2 in mouse embryonic stem cells (ESCs), H2AK119ub1 is pervasively gained, especially at non-promoter regions, which is associated with increased RING1B occupancy. Meanwhile RING1B is significantly lost from a subset of the target promoters and thereby results in minor derepression in Asxl2-null ESCs. However notably, Asxl2 loss causes aberrant lineage differetiation, similar to PcG mutants. Therefore, our data reconcile seemingly paradoxical roles of PR-DUB on transcription repression and highlight the importance of a balanced H2AK119ub1 dynamics in developmental regulation.
Project description:Polycomb repressive complexes-1 and -2 (PRC1 and 2), silence developmental genes in spatiotemporally regulated manner during metazoan embryogenesis. How PcG proteins contribute to down-regulation of target genes upon differentiation, however, remains elusive. Here, by differentiating embryonic stem cells into embryoid bodies, we reveal a crucial role of a PCGF1 (Polycomb group RING finger protein 1)-containing variant PRC1 complex (PCGF1-PRC1) to facilitate induced down-regulation of a group of genes. Binding of PCGF1-PRC1 results in down-regulation of transcriptional activity, followed by Histone H2AK119 mono-ubiquitination (H2AK119ub1) and subsequent recruitment of PRC2, to initiate PcG-repressive domain formation. Based on these findings, we propose that PCGF1-PRC1 mediates establishment of PcG-repressive domains at target genes during differentiation.
Project description:Polycomb repressive complexes-1 and -2 (PRC1 and 2), silence developmental genes in spatiotemporally regulated manner during metazoan embryogenesis. How PcG proteins contribute to down-regulation of target genes upon differentiation, however, remains elusive. Here, by differentiating embryonic stem cells into embryoid bodies, we reveal a crucial role of a PCGF1 (Polycomb group RING finger protein 1)-containing variant PRC1 complex (PCGF1-PRC1) to facilitate induced down-regulation of a group of genes. Binding of PCGF1-PRC1 results in down-regulation of transcriptional activity, followed by Histone H2AK119 mono-ubiquitination (H2AK119ub1) and subsequent recruitment of PRC2, to initiate PcG-repressive domain formation. Based on these findings, we propose that PCGF1-PRC1 mediates establishment of PcG-repressive domains at target genes during differentiation.
Project description:Polycomb repressive complexes-1 and -2 (PRC1 and 2), silence developmental genes in spatiotemporally regulated manner during metazoan embryogenesis. How PcG proteins contribute to down-regulation of target genes upon differentiation, however, remains elusive. Here, by differentiating embryonic stem cells into embryoid bodies, we reveal a crucial role of a PCGF1 (Polycomb group RING finger protein 1)-containing variant PRC1 complex (PCGF1-PRC1) to facilitate induced down-regulation of a group of genes. Binding of PCGF1-PRC1 results in down-regulation of transcriptional activity, followed by Histone H2AK119 mono-ubiquitination (H2AK119ub1) and subsequent recruitment of PRC2, to initiate PcG-repressive domain formation. Based on these findings, we propose that PCGF1-PRC1 mediates establishment of PcG-repressive domains at target genes during differentiation.
Project description:BAP1 is recurrently mutated or deleted in a large number of diverse cancer types, including mesothelioma, uveal melanoma and hepatocellular cholangiocarcinoma. BAP1 is the catalytic subunit of the Polycomb Repressive De-Ubiquitination complex (PR-DUB) which removes PRC1 mediated H2AK119ub1. We and others have shown that H2AK119ub1 is essential for maintaining transcriptional repression and contributes to PRC2 chromatin recruitment. However, the precise relationship between BAP1 and PRC1 remains mechanistically elusive. Using embryonic stem cells, we show that a major function of BAP1 is to restrict H2AK119ub1 deposition to target sites. This increases the stability of PcG complexes with their targets and prevents diffuse accumulation of H2AK119ub1 and H3K27me3 modifications. Loss of BAP1 results in a broad increase in H2AK119ub1 levels that are primarily dependent on PCGF3/5-PRC1 complexes with a mechanism that is reminiscent of X-chromosome inactivation. Increased genome-wide H2AK119ub1 levels titrates away PRC2 from its targets and stimulates diffuse H3K27me3 accumulation across the genome. This decreases the activity of PcG repressive machineries at physiological targets and induces a general compaction of the entire chromatin. Our findings provide evidences for a unifying model that resolves the apparent contradiction between BAP1 catalytic activity and its role in vivo, uncovering molecular vulnerabilities that could be useful for BAP1-related pathologies.
Project description:The major function of Polycomb group proteins (PcG) is to maintain transcriptional repression to preserve cellular identity. This is exerted by two distinct repressive complexes, PRC1 and PRC2, that modify histones by depositing H2AK119ub1 and H3K27me3, respectively. Both complexes are essential for development and are deregulated in several types of human tumors. PRC1 and PRC2 exist in different variants and show a complex regulatory cross-talk. However, the contribution that H2AK119ub1 plays in mediating PcG repressive functions remains largely controversial. Coupling an inducible system with the expression of a fully catalytic inactive RING1B mutant, we demonstrated that H2AK119ub1 deposition is essential to maintain PcG-target genes repressed in ESC. Loss of H2AK119ub1 induced a rapid displacement of PRC2 activity and a loss of H3K27me3 deposition. This affected both PRC2.1 and PRC2.2 variants and further correlated with a strong displacement and destabilization of canonical PRC1. Finally, we find that variant PRC1 forms can sense H2AK119ub1 deposition, which contributes to their stabilization specifically at sites where this modification is highly enriched. Overall our data place H2AK119ub1 deposition as central hub that mount PcG repressive machineries to preserve cell transcriptional identit
Project description:The Polycomb repression machinery in Drosophila comprises PRC1 that monoubiquitinates histone H2A at lysine 118 (H2Aub1) and PR-DUB, a major H2Aub1 deubiquitinase, but how H2Aub1 levels must be balanced for Polycomb repression remains enigmatic. We show that H2Aub1 is enriched at Polycomb target genes in early embryos but depleted from these genes during developmental stages when PRC1 represses their transcription. Accordingly, Polycomb targets remain repressed in H2Aub1-deficient animals. In PR-DUB catalytic mutants, high-level H2Aub1 accumulation at Polycomb targets increases chromatin accessibility, consistent with disruption of chromatin fiber folding by H2Aub1 in vitro. Consequently, PR-DUB mutants show defective Polycomb repression, while general transcription is largely unperturbed by the genome-wide, low-level H2Aub1 increase. Changes in H2Aub1 levels alter H3K27 methylation-kinetics but PRC2 nevertheless generates canonical H3K27me3 domains in PRC1 or PR-DUB catalytic mutants. PR-DUB therefore acts as a rheostat that removes excessive H2Aub1 that, though deposited by PRC1, antagonizes PRC1-mediated chromatin compaction.
Project description:The Polycomb repression machinery in Drosophila comprises PRC1 that monoubiquitinates histone H2A at lysine 118 (H2Aub1) and PR-DUB, a major H2Aub1 deubiquitinase, but how H2Aub1 levels must be balanced for Polycomb repression remains enigmatic. We show that H2Aub1 is enriched at Polycomb target genes in early embryos but depleted from these genes during developmental stages when PRC1 represses their transcription. Accordingly, Polycomb targets remain repressed in H2Aub1-deficient animals. In PR-DUB catalytic mutants, high-level H2Aub1 accumulation at Polycomb targets increases chromatin accessibility, consistent with disruption of chromatin fiber folding by H2Aub1 in vitro. Consequently, PR-DUB mutants show defective Polycomb repression, while general transcription is largely unperturbed by the genome-wide, low-level H2Aub1 increase. Changes in H2Aub1 levels alter H3K27 methylation-kinetics but PRC2 nevertheless generates canonical H3K27me3 domains in PRC1 or PR-DUB catalytic mutants. PR-DUB therefore acts as a rheostat that removes excessive H2Aub1 that, though deposited by PRC1, antagonizes PRC1-mediated chromatin compaction.
Project description:The Polycomb repression machinery in Drosophila comprises PRC1 that monoubiquitinates histone H2A at lysine 118 (H2Aub1) and PR-DUB, a major H2Aub1 deubiquitinase, but how H2Aub1 levels must be balanced for Polycomb repression remains enigmatic. We show that H2Aub1 is enriched at Polycomb target genes in early embryos but depleted from these genes during developmental stages when PRC1 represses their transcription. Accordingly, Polycomb targets remain repressed in H2Aub1-deficient animals. In PR-DUB catalytic mutants, high-level H2Aub1 accumulation at Polycomb targets increases chromatin accessibility, consistent with disruption of chromatin fiber folding by H2Aub1 in vitro. Consequently, PR-DUB mutants show defective Polycomb repression, while general transcription is largely unperturbed by the genome-wide, low-level H2Aub1 increase. Changes in H2Aub1 levels alter H3K27 methylation-kinetics but PRC2 nevertheless generates canonical H3K27me3 domains in PRC1 or PR-DUB catalytic mutants. PR-DUB therefore acts as a rheostat that removes excessive H2Aub1 that, though deposited by PRC1, antagonizes PRC1-mediated chromatin compaction.
Project description:Using ChIP-seq, we profiled several histone marks associated with active transcription (H3K4me3) or with Polycomb-mediated silencing (H2AK119ub1 and H3K27me3) in wild-type HAP1 cells and in cells mutated in BAP1, ASXL1, ASXL2, EZH2 and RING1B.