title: Protein kinase A represses skeletal myogenesis by targeting myocyte enhancer factor 2D.
abstract: Activation of protein kinase A (PKA) by elevation of the intracellular cyclic AMP (cAMP) level inhibits skeletal myogenesis. Previously, an indirect modulation of the myogenic regulatory factors (MRFs) was implicated as the mechanism. Because myocyte enhancer factor 2 (MEF2) proteins are key regulators of myogenesis and obligatory partners for the MRFs, here we assessed whether these proteins could be involved in PKA-mediated myogenic repression. Initially, in silico analysis revealed several consensus PKA phosphoacceptor sites on MEF2, and subsequent analysis by in vitro kinase assays indicated that PKA directly and efficiently phosphorylates MEF2D. Using mass spectrometric determination of phosphorylated residues, we document that MEF2D serine 121 and serine 190 are targeted by PKA. Transcriptional reporter gene assays to assess MEF2D function revealed that PKA potently represses the transactivation properties of MEF2D. Furthermore, engineered mutation of MEF2D PKA phosphoacceptor sites (serines 121 and 190 to alanine) rendered a PKA-resistant MEF2D protein, which efficiently rescues myogenesis from PKA-mediated repression. Concomitantly, increased intracellular cAMP-mediated PKA activation also resulted in an enhanced nuclear accumulation of histone deacetylase 4 (HDAC4) and a subsequent increase in the MEF2D-HDAC4 repressor complex. Collectively, these data identify MEF2D as a primary target of PKA signaling in myoblasts that leads to inhibition of the skeletal muscle differentiation program.
authors.affiliation: Department of Biology, York University, 4700 Keele Street, Toronto M3J 1P3, Ontario, Canada.
authors.forename: Min
authors.initials: M
authors.lastname: Du
authors.forename: Robert L S
authors.initials: RL
authors.lastname: Perry
authors.forename: Nathaniel B
authors.initials: NB
authors.lastname: Nowacki
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Gordon
authors.forename: Jahan
authors.initials: J
authors.lastname: Salma
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Zhao
authors.forename: Arif
authors.initials: A
authors.lastname: Aziz
authors.forename: Joseph
authors.initials: J
authors.lastname: Chan
authors.forename: K W Michael
authors.initials: KW
authors.lastname: Siu
authors.forename: John C
authors.initials: JC
authors.lastname: McDermott
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D006655:Histone Deacetylases / Q000502:physiology; D064326:MEF2 Transcription Factors; D051379:Mice; D008969:Molecular Sequence Data; D032342:Muscle Cells / Q000166:cytology* / Q000502:physiology; D024510:Muscle Development / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D018006:Myogenic Regulatory Factors / Q000502:physiology*; D010766:Phosphorylation; D011485:Protein Binding; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D064326:MEF2 Transcription Factors; C578044:Mef2d protein, mouse; D018006:Myogenic Regulatory Factors; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; C498618:Hdac5 protein, mouse; D006655:Histone Deacetylases