title: Phosphorylation of MRF4 transactivation domain by p38 mediates repression of specific myogenic genes.
abstract: Skeletal myogenesis is associated with the activation of four muscle regulatory factors (MRFs): Myf5, MyoD, Myogenin and MRF4. Here we report that p38 mitogen-activated protein kinase represses the transcriptional activity of MRF4 (involved in late stages of myogenesis), resulting in downregulation of specific muscle genes. MRF4 is phosphorylated in vitro and in vivo by p38 on two serines (Ser31 and Ser42) located in the N-terminal transactivation domain, resulting in reduced MRF4-mediated transcriptional activity. In contrast, nonphosphorylatable MRF4 mutants display increased transcriptional activity and are able to advance both myoblast fusion and differentiation. We also show that expression of desmin and alpha-actin, but not muscle creatin kinase, decreased at late stages of muscle differentiation, correlating with the induction of MRF4 and p38 activation. Accordingly, inhibition of p38 during late myogenesis results in the upregulation of both desmin and alpha-actin. We propose that repression of MRF4 activity by p38 phosphorylation may represent a new mechanism for the silencing of specific muscle genes at the terminal stages of muscle differentiation.
authors.affiliation: Centre de Regulació Genòmica (CRG), Programa de Diferenciació i Cancer, Barcelona, Spain.
authors.forename: Mònica
authors.initials: M
authors.lastname: Suelves
authors.forename: Frederic
authors.initials: F
authors.lastname: Lluís
authors.forename: Vanessa
authors.initials: V
authors.lastname: Ruiz
authors.forename: Angel R
authors.initials: AR
authors.lastname: Nebreda
authors.forename: Pura
authors.initials: P
authors.lastname: Muñoz-Cánoves
mesh_terms: D000199:Actins / Q000096:biosynthesis; D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D003893:Desmin / Q000096:biosynthesis; D015536:Down-Regulation; D020868:Gene Silencing; D048669:MAP Kinase Kinase 6; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D009154:Mutation; D017570:MyoD Protein / Q000378:metabolism; D032448:Myoblasts, Skeletal / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D018006:Myogenic Regulatory Factors / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D012694:Serine / Q000378:metabolism; D015533:Transcriptional Activation; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D000199:Actins; D003893:Desmin; D017570:MyoD Protein; D018006:Myogenic Regulatory Factors; C063403:myogenic factor 6; D012694:Serine; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048669:MAP Kinase Kinase 6