Cellular & Molecular Physiology
Department of Cell Biology
Medical Subject Headings
Acetylation; Animals; Cell Cycle Proteins; *Cell Differentiation; Cell Line; Chromatin; *Chromatin Assembly and Disassembly; Chromatin Immunoprecipitation; Cyclin-Dependent Kinase Inhibitor p21; DNA; DNA Helicases; DNA-Binding Proteins; Histones; Homeodomain Proteins; Humans; Kinetics; Mice; Models, Genetic; Multiprotein Complexes; Muscles; MyoD Protein; Myogenic Regulatory Factors; Myogenin; Nerve Tissue Proteins; Nuclear Proteins; Oligonucleotide Array Sequence Analysis; Promoter Regions (Genetics); Ribonucleoproteins; Transcription Factors
Cell Biology | Life Sciences | Medicine and Health Sciences
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.
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Citation: Mol Cell Biol. 2005 May;25(10):3997-4009. Link to article on publisher's site