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 of 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. The methylation status of MEF2D modulates chromatin binding affinity. During myogenic differentiation of C2C12 mouse skeletal muscle cells, the G9a-mediated methylation of MEF2D decreased. Concordantly, MEF2D-dependent myogenic genes were upregulated. The methylation defective mutant of MEF2D readily activated myogenin gene transcription. Thus, we have 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.