Project description:In Drosophila, a complex consisting of Calypso and ASX catalyzes H2A deubiquitination and has been reported to act as part of the Polycomb machinery in transcriptional silencing. The mammalian homologs of these proteins (BAP1 and ASXL1/2/3, respectively), are frequently mutated in various cancer types, yet their precise functions remain unclear. Using an integrative approach based on isogenic cell lines generated with CRISPR/Cas9, we uncover an unanticipated role for BAP1 in gene activation. This function requires the assembly of an enzymatically active BAP1-associated core complex (BAP1.com) containing one of the redundant ASXL proteins. We investigate the mechanism underlying BAP1.com-mediated transcriptional regulation and show that it does not participate in Polycomb-mediated silencing. Instead, our results establish that the function of BAP1.com is to safeguard transcriptionally active genes against silencing by the Polycomb Repressive Complex 1.
Project description:Polycomb repressive complex 1 (PRC1) catalyzes H2A monoubiquitination (uH2A) and regulates pluripotency in embryonic stem cells (ESCs). However the mechanisms controlling PRC1 recruitment and activity are largely unknown. Here we show that Fbxl10 interacts with Ring1B and Nspc1, forming a non-canonical PRC1. We demonstrate that Fbxl10-PRC1 is essential for H2A ubiquitination in mouse ESCs. Genome-wide analyses reveal that Fbxl10 preferentially binds to CpG islands and co-localizes with Ring1B on Polycomb target genes. Notably, Fbxl10 depletion causes modest dissociation of Ring1B but a major loss of uH2A on target genes. Furthermore rescue experiments for Fbxl10 reveal that its DNA binding capability and integration into PRC1 are required for proper H2A ubiquitination. ES cells lacking Fbxl10, like previously characterized Polycomb mutants, show a severely compromised capacity for successful differentiation. Our results shed light on a novel mechanism how CpG islands regulate chromatin function by affecting polycomb recruitment and activity. All ChIP-seq reactions were performed in either untransfected cells, cells expressing scrambled shRNA or Fbxl10 shRNA, Ring1b-/- or Suz12-/- mouse ES cells
Project description:Polycomb repressive complex 1 (PRC1) catalyzes H2A monoubiquitination (uH2A) and regulates pluripotency in embryonic stem cells (ESCs). However the mechanisms controlling PRC1 recruitment and activity are largely unknown. Here we show that Fbxl10 interacts with Ring1B and Nspc1, forming a non-canonical PRC1. We demonstrate that Fbxl10-PRC1 is essential for H2A ubiquitination in mouse ESCs. Genome-wide analyses reveal that Fbxl10 preferentially binds to CpG islands and co-localizes with Ring1B on Polycomb target genes. Notably, Fbxl10 depletion causes modest dissociation of Ring1B but a major loss of uH2A on target genes. Furthermore rescue experiments for Fbxl10 reveal that its DNA binding capability and integration into PRC1 are required for proper H2A ubiquitination. ES cells lacking Fbxl10, like previously characterized Polycomb mutants, show a severely compromised capacity for successful differentiation. Our results shed light on a novel mechanism how CpG islands regulate chromatin function by affecting polycomb recruitment and activity.
Project description:Transcription regulation involves enzyme-mediated changes in chromatin structure. Here, we describe a novel mode of histone crosstalk during gene silencing, in which histone H2A monoubiquitylation is coupled to the removal of histone H3 Lys 36 dimethylation (H3K36me2). This pathway was uncovered through the identification of dRING-associated factors (dRAF), a novel Polycomb group (PcG) silencing complex harboring the histone H2A ubiquitin ligase dRING, PSC and the F-box protein, and demethylase dKDM2. In vivo, dKDM2 shares many transcriptional targets with Polycomb and counteracts the histone methyltransferases TRX and ASH1. Importantly, cellular depletion and in vitro reconstitution assays revealed that dKDM2 not only mediates H3K36me2 demethylation but is also required for efficient H2A ubiquitylation by dRING/PSC. Thus, dRAF removes an active mark from histone H3 and adds a repressive one to H2A. These findings reveal coordinate trans-histone regulation by a PcG complex to mediate gene repression. Microarray analysis of dKDM2, dRING, PC, PH and PSC target genes in Drosophila S2 cells Expression profiles of Drosophila S2 cells RNAi depleted (KD) for dKDM2, dRING, PC, PH or PSC were compared with expression profile of untreated S2 cells (Mock)
Project description:Malignancies arising from mutation of tumor suppressor genes display an unexplained tissue proclivity. For example, tumor suppressor BAP1 encodes a ubiquitously expressed deubiquitinase for histone H2A but germline mutations predominantly cause uveal melanomas and mesotheliomas. We show that BAP1 inactivation causes apoptosis in mouse embryonic stem cells, fibroblasts, liver and pancreas, whereas melanocytes and mesothelial cells remain viable. E3 ligase RNF2, which silences genes by monoubiquitinating H2A, promoted apoptosis in BAP1-deficient cells by suppressing the pro-survival genes Bcl-2 and Mcl-1. Our data argue that BAP1 modulates gene expression by countering H2A ubiquitination, but its loss only promotes tumorigenesis in cells that do not engage an RNF2-dependent apoptotic program. We propose that intolerance of BAP1 loss, and perhaps the loss of other tumor suppressors, restricts the mutant tumor spectrum.
Project description:Transcription regulation involves enzyme-mediated changes in chromatin structure. Here, we describe a novel mode of histone crosstalk during gene silencing, in which histone H2A monoubiquitylation is coupled to the removal of histone H3 Lys 36 dimethylation (H3K36me2). This pathway was uncovered through the identification of dRING-associated factors (dRAF), a novel Polycomb group (PcG) silencing complex harboring the histone H2A ubiquitin ligase dRING, PSC and the F-box protein, and demethylase dKDM2. In vivo, dKDM2 shares many transcriptional targets with Polycomb and counteracts the histone methyltransferases TRX and ASH1. Importantly, cellular depletion and in vitro reconstitution assays revealed that dKDM2 not only mediates H3K36me2 demethylation but is also required for efficient H2A ubiquitylation by dRING/PSC. Thus, dRAF removes an active mark from histone H3 and adds a repressive one to H2A. These findings reveal coordinate trans-histone regulation by a PcG complex to mediate gene repression. Microarray analysis of dKDM2, dRING, PC, PH and PSC target genes in Drosophila S2 cells
Project description:Malignancies arising from mutation of tumor suppressor genes display an unexplained tissue proclivity. For example, tumor suppressor BAP1 encodes a ubiquitously expressed deubiquitinase for histone H2A but germline mutations predominantly cause uveal melanomas and mesotheliomas. We show that BAP1 inactivation causes apoptosis in mouse embryonic stem cells, fibroblasts, liver and pancreas, whereas melanocytes and mesothelial cells remain viable. E3 ligase RNF2, which silences genes by monoubiquitinating H2A, promoted apoptosis in BAP1-deficient cells by suppressing the pro-survival genes Bcl-2 and Mcl-1. Our data argue that BAP1 modulates gene expression by countering H2A ubiquitination, but its loss only promotes tumorigenesis in cells that do not engage an RNF2-dependent apoptotic program. We propose that intolerance of BAP1 loss, and perhaps the loss of other tumor suppressors, restricts the mutant tumor spectrum.