title: MyoD targets chromatin remodeling complexes to the myogenin locus prior to forming a stable DNA-bound complex.
abstract: The activation of muscle-specific gene expression requires the coordinated action of muscle regulatory proteins and chromatin-remodeling enzymes. Microarray analysis performed in the presence or absence of a dominant-negative BRG1 ATPase demonstrated that approximately one-third of MyoD-induced genes were highly dependent on SWI/SNF enzymes. To understand the mechanism of activation, we performed chromatin immunoprecipitations analyzing the myogenin promoter. We found that H4 hyperacetylation preceded Brg1 binding in a MyoD-dependent manner but that MyoD binding occurred subsequent to H4 modification and Brg1 interaction. In the absence of functional SWI/SNF enzymes, muscle regulatory proteins did not bind to the myogenin promoter, thereby providing evidence for SWI/SNF-dependent activator binding. We observed that the homeodomain factor Pbx1, which cooperates with MyoD to stimulate myogenin expression, is constitutively bound to the myogenin promoter in a SWI/SNF-independent manner, suggesting a two-step mechanism in which MyoD initially interacts indirectly with the myogenin promoter and attracts chromatin-remodeling enzymes, which then facilitate direct binding by MyoD and other regulatory proteins.
authors.affiliation: University of Massachusetts Medical School, Department of Cell Biology, 55 Lake Avenue North, Worcester, MA 01655, USA.
authors.forename: Ivana L
authors.initials: IL
authors.lastname: de la Serna
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Ohkawa
authors.forename: Charlotte A
authors.initials: CA
authors.lastname: Berkes
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bergstrom
authors.forename: Caroline S
authors.initials: CS
authors.lastname: Dacwag
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Tapscott
authors.forename: Anthony N
authors.initials: AN
authors.lastname: Imbalzano
mesh_terms: D000107:Acetylation; D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D002843:Chromatin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D042002:Chromatin Assembly and Disassembly; D047369:Chromatin Immunoprecipitation; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D064326:MEF2 Transcription Factors; D051379:Mice; D008957:Models, Genetic; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism*; D009132:Muscles / Q000166:cytology / Q000378:metabolism; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism*; D018006:Myogenic Regulatory Factors; D018008:Myogenin / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011401:Promoter Regions, Genetic / Q000235:genetics; D012261:Ribonucleoproteins; D000068103:Serine-Arginine Splicing Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D018797:Cell Cycle Proteins; D002843:Chromatin; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; D006657:Histones; D018398:Homeodomain Proteins; D064326:MEF2 Transcription Factors; C503799:MYOG protein, human; D046912:Multiprotein Complexes; D017570:MyoD Protein; C503801:Myog protein, mouse; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; C481797:Pbx1 protein, mouse; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D012261:Ribonucleoproteins; C499372:SRSF2 protein, mouse; D014157:Transcription Factors; D000068103:Serine-Arginine Splicing Factors; D004247:DNA; C084108:SMARCA4 protein, human; C513194:Smarca4 protein, mouse; D004265:DNA Helicases