Modulation of lysine methylation in myocyte enhancer factor 2 during skeletal muscle cell differentiation

Abstract

Myocyte enhancer factor 2 (MEF2) is a family of transcription factors that regulates many processes, including muscle differentiation. Due to its many target genes, MEF2D requires tight regulation of transcription activity over time and by location. Epigenetic modifiers have been suggested to regulate MEF2-dependent transcription via modifications to histones and MEF2. However, the modulation of MEF2 activity by lysine methylation, an important posttranslational modification that alters the activities of transcription factors, has not been studied. We report the reversible lysine methylation of MEF2D by G9a and LSD1 as a regulatory mechanism of MEF2D activity and skeletal muscle differentiation. G9a methylates lysine-267 of MEF2D and represses its transcriptional activity, but LSD1 counteracts it. This residue is highly conserved between MEF2 members in mammals. During myogenic differentiation of C2C12 mouse skeletal muscle cells, the methylation of MEF2D by G9a decreased, on which MEF2D-dependent myogenic genes were upregulated. We have also identified lysine-267 as a methylation/demethylation site and demonstrate that the lysine methylation state of MEF2D regulates its transcriptional activity and skeletal muscle cell differentiation.

A KAP1 phosphorylation switch controls MyoD function during skeletal muscle differentiation

“…Conversely, corresponding lysine residues are acetylated upon differentiation where MyoD and Mef2D serve as transcriptional activators. In the case of Mef2D, the conversion from the methylated to the acetylated state is facilitated by LSD1-mediated demethylation of K 267 meMef2D, promoting transcriptional activation of muscle genes (Choi et al 2014). Our data suggest a regulatory mechanism by which G9a mediates methylation of Mef2D and MyoD to reinforce the transcriptionally repressive state at muscle genes in proliferating myoblasts.…”

“…Taken together, these results suggest that the MyoD/Mef2/KAP1 complex bound at muscle CRMs likely mediates multiple independent interactions with a set of coregulatory molecules, likely to maximize the specificity and efficiency of this recruitment at highly selected genomic loci. In this context, it is interesting to note that the corepressor G9a has previously been demonstrated to reduce the transcriptional activity of both MyoD (Ling et al 2012) and Mef2D (Choi et al 2014) through methylation of specific lysine residues within these transcription factors. Conversely, corresponding lysine residues are acetylated upon differentiation where MyoD and Mef2D serve as transcriptional activators.…”

“…In growing myoblasts, both MyoD and Mef2D are functionally inactivated by G9a-mediated methylation (Ling et al 2012;Choi et al 2014). Upon differentiation, these factors are demethylated, which allows them to activate muscle gene expression.…”

“…Upon differentiation, these factors are demethylated, which allows them to activate muscle gene expression. For Mef2D, LSD1 was identified as the demethylase responsible for removing methyl residues deposited by G9a at Lys267 (Choi et al 2014). Therefore, we examined the influence of KAP1 on this process (Fig.…”

“…Some of this paradox may stem from the methylation and hence inactivation of MyoD (Ling et al 2012) and Mef2 (Choi et al 2014) by the histone methyltransferase G9a in these cells. MyoD and Mef2 are indeed able to interact with either activators, such as the histone acetyltransferase p300 (Sartorelli et al 1997) and the histone demethylase LSD1 (Choi et al 2010), or repressors, such as G9a (Ling et al 2012;Choi et al 2014). Nevertheless, how the differential recruitment of these cofactors is regulated and hence how MyoD and Mef2D switch from repressors of muscle differentiation genes in proliferating myoblasts to activators of their expression in myotubes remain enigmatic.…”