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Alpha7 integrin expression is negatively regulated by deltaEF1 during skeletal myogenesis
Poonam Jethanandani1, Randall H Kramer
1Department of Cell and Tissue Biology, University of California, San Francisco, California 94143-0640, USA.
The Journal of Biological Chemistry
|September 1, 2005
Summary
DeltaEF1 represses alpha7 integrin expression during myoblast differentiation by binding to regulatory elements and competing with MYOD and the p300/CBP coactivator.
Area of Science:
- Muscle biology
- Molecular regulation of gene expression
- Integrin signaling
Background:
- Alpha7 integrin expression is upregulated during myoblast differentiation into myotubes.
- A negative regulatory element in the alpha7 integrin promoter contains potential binding sites for deltaEF1.
- The role of deltaEF1 in controlling alpha7 integrin expression during muscle development requires elucidation.
Purpose of the Study:
- To investigate the function of deltaEF1 in regulating alpha7 integrin gene transcription.
- To identify the specific mechanisms by which deltaEF1 influences alpha7 integrin expression.
- To explore the interplay between deltaEF1, MYOD, and coactivators in muscle differentiation.
Main Methods:
- Overexpression of deltaEF1 in C2C12 myoblasts.
- Reporter gene assays using the alpha7 integrin promoter.
- Site-directed mutagenesis of putative deltaEF1 binding sites.
- Gel shift assays to assess protein-DNA interactions.
- Chromatin immunoprecipitation to determine in vivo binding.
- Analysis of deltaEF1 interactions with p300/CBP coactivator.
Main Results:
- Overexpression of deltaEF1 significantly down-regulates alpha7 integrin protein and transcriptional activity.
- Two E-box-like sites in the negative regulatory region are critical for deltaEF1-mediated repression.
- Mutation of these sites enhances alpha7 promoter activity.
- deltaEF1 and MYOD binding to the regulatory element is reciprocal and stage-dependent.
- deltaEF1 represses transcription via its N-terminal region, which interacts with p300/CBP.
- p300/CBP can overcome deltaEF1-mediated repression, suggesting titration of the coactivator.
Conclusions:
- deltaEF1 acts as a transcriptional repressor of alpha7 integrin during myoblast differentiation.
- deltaEF1 suppresses alpha7 integrin expression by competing with the activator MYOD and sequestering the p300/CBP coactivator.
- These findings reveal a novel regulatory mechanism controlling integrin expression in developing muscle cells.