Allosteric activation dictates PRC2 activity independent of its recruitment to chromatin

Abstract

SUMMARYPRC2 is a therapeutic target for several types of cancers currently undergoing clinical trials. Its activity is regulated by a positive feedback loop whereby its terminal enzymatic product, H3K27me3, is specifically recognized and bound by an aromatic cage present in its EED subunit. The ensuing allosteric activation of the complex stimulates H3K27me3 deposition on chromatin. Here, we report a step-wise feedback mechanism entailing key residues within distinctive interfacing motifs of EZH2 or EED that are found mutated in cancers and/or Weaver syndrome. PRC2 harboring these EZH2 or EED mutants manifest little activity in vivo but, unexpectedly, exhibited similar chromatin association as wild-type PRC2, indicating an uncoupling of PRC2 activity and recruitment. With genetic and chemical tools, we further demonstrated that targeting allosteric activation overrode the gain-of-function effect of EZH2 Y646X oncogenic mutations. These results revealed critical implications to the regulation and biology of PRC2 and a novel vulnerability in tackling PRC2-addicted cancers.All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.

Histone H2AK119 Mono-Ubiquitination Is Essential for Polycomb-Mediated Transcriptional Repression

“…This could be an indirect consequence of reduced deposition of H3K27me3 levels together with a reduced affinity of PRC2.1 for target genes that is consistent with the mild impairment of MTF2 chromatin occupancy observed in Jarid2 KO ESCs (Healy et al, 2019). Low H3K27me3 levels could reduce EED affinity for its target sites, compromising spreading and establishment of PcG domains (Lee et al, 2018;Oksuz et al, 2018). Reduced H3K27me3 deposition further correlated with specific cPRC1 displacement from all repressed target loci (represented by PCGF2 and CBX7 ChIP-seq), in agreement with cPRC1 being dependent on the deposition of this modification through the specific activity of CBX proteins (Bernstein et al, 2006;Cao et al, 2002).…”

“…At the same time, H3K27me3 can also serve as an affinity site for both PRC2.1 and PRC2.2 by EED recognition (Margueron et al, 2009). H3K27me3 binding by the WD40 repeats of EED stimulates PRC2 enzymatic activity allosterically inducing H3K27me3 spreading (Lee et al, 2018;Margueron et al, 2009). To shed light into this complex regulatory system, we tested whether loss of H2AK119ub1 deposition preferentially affected PRC2.1 and PRC2.2 target gene association by ChIPseq analyses for MTF2 and JARID2, respectively.…”

Domain Model Explains Propagation Dynamics and Stability of Histone H3K27 and H3K36 Methylation Landscapes

“…It assumes that histones in certain domains can only be methylated up to a defined final state ( Figure 2B). Domains may form due to constraints in the availability and activity of enzymes, reflecting that they are recruited and activated at specific regions of the genome (Ferrari et al, 2014;Lee et al, 2018) and lead to inhomogeneous distributions of enzymes in the nucleus. The domain to which a histone belongs dictates the final methylation state, i.e., whether it can be further methylated or not.…”

Automethylation of PRC2 promotes H3K27 methylation and is impaired in H3K27M pediatric glioma

“…This "write and read" mechanism constitutes the molecular basis by which PRC2 forms extensive chromatin domains comprising H3K27me2/me3 that foster gene repression upon each cycle of cell division (Hansen et al 2008;Oksuz et al 2018;Reinberg and Vales 2018). Disruption of this feedback loop by point mutations in the key regions of EZH2 and EED results in a global loss of H3K27me2/me3 and notably, these mutations were found in human pathological conditions including developmental diseases and cancer (Imagawa et al 2017;Lee et al 2018b).…”