The trithorax group proteins Kismet and ASH1 promote H3K36 dimethylation to counteract Polycomb group repression inDrosophila

Abstract

SUMMARYMembers of the Polycomb group of repressors and trithorax group of activators maintain heritable states of transcription by modifying nucleosomal histones or remodeling chromatin. Although tremendous progress has been made toward defining the biochemical activities of Polycomb and trithorax group proteins, much remains to be learned about how they interact with each other and the general transcription machinery to maintain on or off states of gene expression. The trithorax group protein Kismet (KIS) is related to the SWI/SNF and CHD families of chromatin remodeling factors. KIS promotes transcription elongation, facilitates the binding of the trithorax group histone methyltransferases ASH1 and TRX to active genes, and counteracts repressive methylation of histone H3 on lysine 27 (H3K27) by Polycomb group proteins. Here, we sought to clarify the mechanism of action of KIS and how it interacts with ASH1 to antagonize H3K27 methylation in Drosophila. We present evidence that KIS promotes transcription elongation and counteracts Polycomb group repression via distinct mechanisms. A chemical inhibitor of transcription elongation, DRB, had no effect on ASH1 recruitment or H3K27 methylation. Conversely, loss of ASH1 function had no effect on transcription elongation. Mutations in kis cause a global reduction in the di-and tri-methylation of histone H3 on lysine 36 (H3K36) -modifications that antagonize H3K27 methylation in vitro. Furthermore, loss of ASH1 significantly decreases H3K36 dimethylation, providing further evidence that ASH1 is an H3K36 dimethylase in vivo. These and other findings suggest that KIS antagonizes Polycomb group repression by facilitating ASH1-dependent H3K36 dimethylation.

H3K36 Methyltransferases as Cancer Drug Targets: Rationale and Perspectives for Inhibitor Development

“…Interestingly, SETMAR does not methylate recombinant nucleosomes in vitro [35], suggesting that SETMAR may indirectly produce H3K36me2 after DNA damage. [36]. In human HeLa cells, H3K36 methylation and H3K27 methylation are rarely found together on the same histone peptide.…”

“…(2016) 8(13) future science group Review Rogawski, Grembecka & Cierpicki repressive complex 2 (PRC2). For example, in Drosophila the H3K36-specific KMTase Ash1 activates Hox genes during development by functioning as an antirepressor and antagonizing repressive H3K27 methylation installed by PRC2 [36]. In human HeLa cells, H3K36 methylation and H3K27 methylation are rarely found together on the same histone peptide.…”

Trithorax and Polycomb group-dependent regulation: a tale of opposing activities

“…The molecular mechanisms behind this TrxG-dependent antagonism of PcG silencing are now starting to take shape (Schmitges et al, 2011;Yuan et al, 2011). The TrxG component Ash1 (mammalian homolog ASH1L) has emerged as a particularly vital player, and reports from the last half of the decade provide compelling evidence that the anti-repressive activity of Ash1 resides in its ability to catalyze H3K36 methylation Dorighi and Tamkun, 2013;Miyazaki et al, 2013;Yuan et al, 2011). Additionally, recent evidence physically and functionally links Trx with CBP, suggesting that the histone-modifying activities of TrxG proteins might be coupled to counteract PcG silencing (Tie et al, 2014).…”

“…But K36 is located outside the p55-Su(z)12 binding site (Schmitges et al, 2011) so how does it inhibit PRC2? Although the exact inhibitory effect of H3K36 methylation on PRC2 biochemical activity remains to be determined, connections between this histone modification and Ash1, which has long been described as an 'antirepressor', bolster its role in counteracting silencing (Dorighi and Tamkun, 2013;Klymenko and Müller, 2004;Kockmann et al, 2013;Miyazaki et al, 2013;Papp and Müller, 2006;Tanaka et al, 2007;Yuan et al, 2011).…”

Drosophila O-GlcNAcase Deletion Globally Perturbs Chromatin O-GlcNAcylation

“…The trimethylation of histone 3 lysine 27 (H3K27me3) by Polycomb repressive complex 2 (PRC2) member Enhancer of zeste (E(z)) is a repressive transcription mark (1)(2)(3). In contrast, histone 3 lysine 4 monomethylation (H3K4me) performed by TRX, histone 3 lysine 36 dimethylation (H3K36me2) by ASH1, and histone 3 lysine 4 trimethylation (H3K4me3) by Compass member SET1 are activating modifications in Drosophila (4,5). Pc group member super sex combs (ogt/sxc) encodes the Drosophila O-GlcNAc transferase (OGT), which regulates Pc-mediated repression by post translationally O-GlcNAcylating and stabilizing Polyhomeotic (Ph), a member of PRC1 in Drosophila (6 -8).…”