Structural basis for the inhibition of PRC2 by active transcription histone posttranslational modifications

Abstract

Polycomb repressive complex 2 (PRC2) is an epigenetic regulator essential for embryonic development and maintenance of cell identity that trimethylates histone H3 at lysine 27 (H3K27me3) leading to gene silencing. PRC2 is regulated by association with protein cofactors and crosstalk with histone posttranslational modifications. Trimethylated histone H3 K4 (H3K4me3) and K36 (H3K36me3) localize to sites of active transcription where H3K27me3 is absent and inhibit PRC2 activity through unknown mechanisms. Using cryo-electron microscopy we reveal that histone H3 tails modified with H3K36me3 engage poorly with the PRC2 active site and preclude its effective interaction with chromatin, while the H3K4me3 modification binds to the allosteric site in the EED subunit, acting as an antagonist that competes with allosteric activators required for the spreading of the H3K27me3 repressive mark. Thus, the location along the H3 tail of the H3K4me3 and H3K36me3 modifications allow them to target two essential requirements for efficient trimethylation of histone H3K27. We further show that the JARID2 cofactor modulates PRC2 activity in the presence of these histone modifications.

Dual roles of histone H3 lysine-4 in antagonizing Polycomb group function and promoting target gene expression

“…It is possible that the arginine side chain in H3.2K4R histones causes similar steric interference, resulting in reduced catalytic activity of PRC2. H3K4me3 has also been proposed to interact with the allosteric site on the PRC2 subunit EED (Cookis et al 2024). Therefore, it is also possible that H3.2K4R similarly disrupts allosteric activation of PRC2.…”