Project description:Canonical targeting of Polycomb Repressive Complex 1 (PRC1) to repress developmental genes is mediated by cell type-specific, paralogous chromobox (CBX) proteins (CBX2, 4, 6, 7 and 8). Based on their central role in silencing and their dysregulation associated with human disease including cancer, CBX proteins are attractive targets for small molecule chemical probe development. Here, we have used a quantitative and target-specific cellular assay to discover a potent positive allosteric modulator (PAM) of CBX8. The PAM activity of UNC7040 antagonizes H3K27me3 binding by CBX8 while increasing interactions with nucleic acids. We show that treatment with UNC7040 leads to efficient and selective eviction of CBX8-containing PRC1 from chromatin, loss of silencing and reduced proliferation across different cancer cell lines. Our discovery and characterization of UNC7040 not only reveals the most cellularly potent CBX8-specific chemical probe to date, but also corroborates a mechanism of Polycomb regulation by non-specific CBX nucleotide binding activity.
Project description:Polycomb-directed repression of gene expression is frequently misregulated in human diseases. A quantitative and target-specific cellular assay was utilized to discover the first potent positive allosteric modulator (PAM) peptidomimetic, UNC4976, of nucleic acid binding by CBX7, a chromodomain methyl-lysine reader of Polycomb repressive complex 1. The PAM activity of UNC4976 resulted in enhanced efficacy across three orthogonal cellular assays by simultaneously antagonizing H3K27me3-specific recruitment of CBX7 to target genes while increasing non-specific binding to DNA and RNA. PAM activity thereby reequilibrates PRC1 away from H3K27me3 target regions. Together, our discovery and characterization of UNC4976 not only revealed the most cellularly potent PRC1-specific chemical probe to date, but also uncovers a potential mechanism of Polycomb regulation with implications for non-histone lysine methylated interaction partners.
Project description:The polycomb group protein, CBX8, is a neuron-specific component of Polycomb repressive complex 1 (PRC1) in the adult olfactory epithelium. We performed ChIP-seq to identify genes occupied by CBX8-PRC1.
Project description:Polycomb proteins play an essential role in maintaining the repression of developmental genes in self-renewing embryonic stem cells. The exact mechanism allowing the derepression of polycomb target genes during cell differentiation remains unclear. Here, we show that several differentiation genes transiently recruit a Cbx8-containing Polycomb repressive complex (PRC) 1 during their early activation. Depletion of Cbx8 partially impairs the transcriptional activation of these genes. This correlates with a reduction in low but detectable levels of histone H3 lysine 27 acetylation. Prolonged gene activation results in eviction of PRC1 despite persisting H3K27me3. The composition of PRC1 is highly modular and changes when ES cells commit to differentiation. We further demonstrate that the exchange of Cbx7 for Cbx8 is required for the effective activation of differentiation genes. Taken together our results establish a function for a Cbx8-containing complex in facilitating the transition from a Polycomb-repressed chromatin state to an active state. As this affects several key regulatory differentiation genes this mechanism is likely to contribute to the robust execution of differentiation programs. Examination of cbx8 in ES E14 mouse cells in 2 condition before and after 72h stimulation with retinoic acid compared with IgG
Project description:Polycomb proteins play an essential role in maintaining the repression of developmental genes in self-renewing embryonic stem cells. The exact mechanism allowing the derepression of polycomb target genes during cell differentiation remains unclear. Here, we show that several differentiation genes transiently recruit a Cbx8-containing Polycomb repressive complex (PRC) 1 during their early activation. Depletion of Cbx8 partially impairs the transcriptional activation of these genes. This correlates with a reduction in low but detectable levels of histone H3 lysine 27 acetylation. Prolonged gene activation results in eviction of PRC1 despite persisting H3K27me3. The composition of PRC1 is highly modular and changes when ES cells commit to differentiation. We further demonstrate that the exchange of Cbx7 for Cbx8 is required for the effective activation of differentiation genes. Taken together our results establish a function for a Cbx8-containing complex in facilitating the transition from a Polycomb-repressed chromatin state to an active state. As this affects several key regulatory differentiation genes this mechanism is likely to contribute to the robust execution of differentiation programs.
Project description:Polycomb proteins play an essential role in maintaining the repression of developmental genes in self-renewing embryonic stem cells. The exact mechanism allowing the derepression of polycomb target genes during cell differentiation remains unclear. Here, we show that several differentiation genes transiently recruit a Cbx8-containing Polycomb repressive complex (PRC) 1 during their early activation. Depletion of Cbx8 partially impairs the transcriptional activation of these genes. This correlates with a reduction in low but detectable levels of histone H3 lysine 27 acetylation. Prolonged gene activation results in eviction of PRC1 despite persisting H3K27me3. The composition of PRC1 is highly modular and changes when ES cells commit to differentiation. We further demonstrate that the exchange of Cbx7 for Cbx8 is required for the effective activation of differentiation genes. Taken together our results establish a function for a Cbx8-containing complex in facilitating the transition from a Polycomb-repressed chromatin state to an active state. As this affects several key regulatory differentiation genes this mechanism is likely to contribute to the robust execution of differentiation programs.
Project description:Polycomb proteins play an essential role in maintaining the repression of developmental genes in self-renewing embryonic stem cells. The exact mechanism allowing the derepression of polycomb target genes during cell differentiation remains unclear. Here, we show that several differentiation genes transiently recruit a Cbx8-containing Polycomb repressive complex (PRC) 1 during their early activation. Depletion of Cbx8 partially impairs the transcriptional activation of these genes. This correlates with a reduction in low but detectable levels of histone H3 lysine 27 acetylation. Prolonged gene activation results in eviction of PRC1 despite persisting H3K27me3. The composition of PRC1 is highly modular and changes when ES cells commit to differentiation. We further demonstrate that the exchange of Cbx7 for Cbx8 is required for the effective activation of differentiation genes. Taken together our results establish a function for a Cbx8-containing complex in facilitating the transition from a Polycomb-repressed chromatin state to an active state. As this affects several key regulatory differentiation genes this mechanism is likely to contribute to the robust execution of differentiation programs. Four biological replicates were used for each condition (untreated and after 72h of retinoic acid stimulation) and samples were prepared and hybridized to SurePrint G3 Gene Expression Microarrays (Agilent technologies) following the supplier's instructions. Analyses were essentially performed as described (Uribesalgo et al. 2011) selecting differentially expressed probes with a FDR of 0.05 and fold change of > 1.5.