title: TGF-beta-activated Smad3 represses MEF2-dependent transcription in myogenic differentiation.
abstract: Transforming growth factor beta (TGF-beta) inhibits myogenesis and associated gene expression. We previously reported that the TGF-beta signaling effector Smad3 mediates this inhibition, by interfering with the assembly of myogenic bHLH transcription factor heterodimers on E-box sequences in the regulatory regions of muscle-specific genes. We now show that TGF-beta-activated Smad3 suppresses the function of MEF2, a second class of essential myogenic factors. TGF-beta signaling through Smad3 represses myogenin expression independently of E-boxes, and prevents a tethered MyoD-E47 dimer to activate transcription indirectly through MEF2-binding sites. In addition, Smad3 interacts with MEF2C, which requires its MADS domain, and disrupts its association with the SRC-family coactivator GRIP-1, thus diminishing the transcription activity of MEF2C. Consistent with this physical displacement, TGF-beta signaling blocks the GRIP-1-induced redistribution of MEF2C to discrete nuclear subdomains in 10T1/2 cells, and the recruitment of GRIP-1 to the myogenin promoter in differentiating myoblasts. These findings indicate that the TGF-beta/Smad3 pathway targets two critical components of the myogenic transcription machinery to inhibit terminal differentiation.
authors.affiliation: Departments of Growth and Development and Anatomy, Programs in Cell Biology and Developmental Biology, University of California, San Francisco, CA, USA.
authors.forename: Dong
authors.initials: D
authors.lastname: Liu
authors.forename: Jong Seok
authors.initials: JS
authors.lastname: Kang
authors.forename: Rik
authors.initials: R
authors.lastname: Derynck
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D064326:MEF2 Transcription Factors; D032342:Muscle Cells / Q000166:cytology / Q000502:physiology*; D018006:Myogenic Regulatory Factors; D051958:Nuclear Receptor Coactivator 2; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D051900:Smad3 Protein; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D064326:MEF2 Transcription Factors; D018006:Myogenic Regulatory Factors; D051958:Nuclear Receptor Coactivator 2; D011993:Recombinant Fusion Proteins; D051900:Smad3 Protein; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta