Résumé :
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Communication n° 180. We have been interested in the mechanisms by which cytoskeletal proteins serve as sensory elements that assess the functional status of the contractile machinery and influence its assembly and maintenance via communication with factors that control gene expression in muscle cells. Actinin-associated LIM protein (ALP) is a PDZ-LIM protein, which displays up-regulation during muscle differentiation and enhances a-actinin's capacity to crosslink actin filaments. Here, we report that upon induction of differentiation ALP accumulates within cell nuclei of myogenic C2C12 cells before being directed to the Z-discs of C2C12 myotubes. An antisense RNA strategy has allowed us to show that disruption of ALP expression severely affects the expression of the muscle transcription factors myogenin and MyoD, resulting in the inhibition of muscle differentiation. Introduction of a MyoD expression construct into ALP-antisense cells is sufficient to restore the capacity of the cells to differentiate, illustrating that ALP function occurs upstream of MyoD. It is known that MyoD is under the control of SRF, a transcriptional regulator whose activity is modulated by actin dynamics. A dramatic reduction of actin filament bundles is observed in ALP-antisense cells and treatment of these cells with the actin-stabilizing drug jasplakinolide restores the capacity of the cells to differentiate, suggesting that ALP could impact SRF-dependent muscle gene transcription by virtue of its ability to stabilize F-actin. Collectively, these results suggest a critical role of ALP in MyoD regulation, likely via cytoskeletal regulation of SRF.
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