Disease relevance of Myef2

• To test whether MEF2 export from the nucleus was causally related to the inhibitory action of TGF-beta, we transfected C2C12 myoblasts with MEF2C containing the nuclear localization signal of simian virus 40 large T antigen (nlsSV40) [1].
• Transcriptional activation of the myogenin gene by MEF2-mediated recruitment of myf5 is inhibited by adenovirus E1A protein [2].
• Centronuclear myopathy in mice lacking a novel muscle-specific protein kinase transcriptionally regulated by MEF2 [3].
• Here we demonstrate that MEF2 transcription factors induced dilated cardiomyopathy and lengthening of myocytes [4].
• MEF2 is upregulated during cardiac hypertrophy and is required for normal post-natal growth of the myocardium [5].

High impact information on Myef2

• The heart responds to stress signals by hypertrophic growth, which is accompanied by activation of the MEF2 transcription factor and reprogramming of cardiac gene expression [6].
• Using fibre-type-specific promoters, we show in cultured muscle cells that PGC-1 alpha activates transcription in cooperation with Mef2 proteins and serves as a target for calcineurin signalling, which has been implicated in slow fibre gene expression [7].
• Paradoxically, MEF2 transcriptional activity, revealed by the expression of a MEF2-dependent transgene, was enhanced in the hearts of Mef2a-mutant mice, reflecting the transcriptional activation of residual MEF2D [8].
• We generated mice deficient in MEF2A, the predominant Mef2 gene product expressed in post-natal cardiac muscle [8].
• Ectopically expressed mouse Twist (Mtwist) was shown to inhibit myogenesis by blocking DNA binding by MyoD, by titrating E proteins, and by inhibiting trans-activation by MEF2 [9].

Chemical compound and disease context of Myef2

• Consistent with their involvement in activation of neuronal gene expression, members of the MEF2 family are expressed in P19 embryonal carcinoma cells that have been induced to form neurons following treatment with retinoic acid [10].

Biological context of Myef2

• In this report, we describe the molecular cloning and characterization of myelin gene expression factor-2 (Myef-2), a protein isolated from mouse brain that binds specifically to single-stranded DNA derived from the MB1 element and represses transcription of the MBP gene in transient transfection assay [11].
• The myogenic basic helix-loop-helix (bHLH) and MEF2 transcription factors are expressed in the myotome of developing somites and cooperatively activate skeletal muscle gene expression [9].
• Recent studies have revealed multiple signaling systems that stimulate and inhibit myogenesis by altering MEF2 phosphorylation and its association with other transcriptional cofactors [12].
• Activation of muscle-specific genes by members of the myocyte enhancer factor 2 (MEF2) and MyoD families of transcription factors is coupled to histone acetylation and is inhibited by class II histone deacetylases (HDACs) 4 and 5, which interact with MEF2 [13].
• Dominant-interfering forms of MEF2 generated by caspase cleavage contribute to NMDA-induced neuronal apoptosis [14].

Anatomical context of Myef2

• Calcineurin initiates skeletal muscle differentiation by activating MEF2 and MyoD [15].
• Members of the MyoD and MEF2 families of transcription factors associate combinatorially to control myoblast specification, differentiation and proliferation [12].
• By using immune electron microscopy and Western blot analysis on subcellular fractions, MEF2 was shown to be tightly associated with cytoskeleton membrane components [1].
• A single MEF-2 site is a major positive regulatory element required for transcription of the muscle-specific subunit of the human phosphoglycerate mutase gene in skeletal and cardiac muscle cells [16].
• In particular, MEF-2 binding activity was up-regulated in 10T1/2 cells stably transfected with a MyoD expression vector only after these cells fused and differentiated into skeletal myotubes [17].

Associations of Myef2 with chemical compounds

• The ability of HDAC4 and -5 to inhibit MEF2 is blocked by phosphorylation of these HDACs at two conserved serine residues, which creates docking sites for the intracellular chaperone protein 14-3-3 [13].
• During muscle regeneration, the enhancer activity was markedly inhibited by cancellation of the binding sites of MEF2, MyoD, or thyroid hormone receptors [18].
• Chromatin immunoprecipitation demonstrated the in vivo recruitment of MEF2 and CARM1 to the endogenous muscle creatine kinase promoter in a differentiation-dependent manner [19].
• Glutathione S-transferase pulldown and immunoprecipitation demonstrate that the repression mechanism involves direct interactions between MEF2 proteins and HDAC7 and is associated with the ability of MEF2 to interact with the N-terminal 121 amino acids of HDAC7 that encode repression domain 1 [20].
• In the presence of cycloheximide, AVP up-regulates the expression of MEF2, but not of myogenin, indicating that the synthesis of a protein intermediate is not necessary for MEF2 induction [21].

Physical interactions of Myef2

• These results support a model of transcriptional activation and stabilization of myogenin expression in which DNA-bound MEF2 recruits myogenic bHLH factors into an active but E1A-sensitive transcription factor complex [2].
• During muscle differentiation, repression of gene transcription by MEF-2/HDAC complexes is relieved due to calcium/calmodulin-dependent (CaM) kinase-induced translocation of HDAC4 and HDAC5 to the cytoplasm [22].

Regulatory relationships of Myef2

• Thus, the MRF4 promoter is regulated by the MEF2 and basic helix-loop-helix MRF protein family through a cross-regulatory circuitry [23].
• We also observed that abrogation of p38 MAPK signaling blocks MEF2 activation using a MEF2 transgenic 'sensor' mouse [24].
• Co-transfection of Gtx prevented the serum-induced activation of the MEF-2-containing reporter genes [25].
• Furthermore, BMP-2 stimulated specific protein.DNA complex formation when an MEF-2 DNA recognition element was used as probe [26].

Other interactions of Myef2

• Myef-2 mRNA is developmentally regulated in mouse brain; its peak expression occurs at postnatal day 7, prior to the onset of MBP expression [11].
• The myogenin promoter contains two essential elements; an E-box and an A/T rich element that bind MRF and MEF2 transcription factors, respectively [15].
• We propose a mechanism in which the inhibition of myogenesis by TGF-beta is mediated through MEF2 localization to the cytoplasm, thus preventing it from participating in an active transcriptional complex [1].
• Located within the proximal promoter are a single MEF2 site and E box that are required for maximum MRF4 expression [23].
• Enhancement by PC4 of MyoD-dependent activation of muscle gene promoters occurs selectively through MEF2 binding sites [27].

Analytical, diagnostic and therapeutic context of Myef2

• Electrophoretic mobility shift assays demonstrated changes in the patterns of MEF-2, CACCC, and MEF-3 DNA binding activities following the conversion of 10T1/2 cells into myoblasts and myotubes by stable transfection with a MyoD expression vector [17].
• Sequence analysis of 976 bp 5' flanking region revealed several potential cis-acting elements: 1) Three E boxes (MyoD binding sites), namely, E1, E2 and E3, located at -79, -832 and -936, respectively; 2) one MEF2 binding site at -864; 3) a region with homology to M-CAT motif at -587; 4) several GC boxes [28].
• Biochemical and cell culture studies have characterized the myocyte enhancer factor 2 (MEF2) transcriptional regulatory proteins as obligatory partners for the myogenic regulatory factors (MRFs) in the differentiation of myogenic cells in culture [24].
• To begin to determine the role of MEF2 factors in CNS development, we used in situ hybridization with gene-specific cRNA probes to define the expression patterns of each of the four Mef2 mRNAs in the developing and mature mouse CNS [29].
• The polymerase chain reaction was used to perform substitution mutagenesis of the MEF-2 binding site, and lack of MEF-2 binding was confirmed by gel retardation assays [30].

References