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Inhibition of protein phosphatases blocks myogenesis by first altering MyoD binding activity
S J Kim1, K Y Kim, S J Tapscott
1Laboratory of Chemoprevention, National Cancer Institute, Bethesda, Maryland 20892.
Abstract:
To examine the role of protein phosphatases in skeletal muscle differentiation, C2C12 myoblasts were treated with okadaic acid, a potent in vitro inhibitor of protein phosphatases 1 and 2A which regulate various cellular events in intact cells. We now show that okadaic acid treatment of the mouse myoblast C2C12 cell line reversibly altered the morphology of the cells and blocked differentiation. At a molecular level, it extinguished expression of the myogenic determination genes, MyoD1 and myogenin, but induced the expression of an inhibitor of differentiation, Id. Analysis of the MyoD1 promoter showed that inhibition of MyoD1 expression by okadaic acid occurs at the transcriptional level. These changes occur 10-20 h after okadaic acid treatment. However, within 1 h of treatment the ability of muscle extracts to support a specific MyoD-dependent gel mobility shift using a MyoD DNA binding site is lost. These data suggest that protein phosphatases play an important role during myogenic differentiation.
Insights
Protein phosphatases are crucial for skeletal muscle differentiation. Inhibiting these enzymes with okadaic acid blocked myoblast differentiation and altered gene expression, highlighting their essential role.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biology
Background:
- Skeletal muscle differentiation is a complex process involving precise regulation of gene expression.
- Protein phosphatases (PPs) are key regulators of cellular signaling pathways.
- The specific role of PPs in skeletal muscle differentiation remains to be fully elucidated.
Purpose of the Study:
- To investigate the role of protein phosphatases 1 and 2A in the differentiation of C2C12 myoblasts.
- To determine the molecular mechanisms by which protein phosphatase inhibition affects skeletal muscle differentiation.
Main Methods:
- C2C12 myoblasts were treated with okadaic acid, a specific inhibitor of PPs 1 and 2A.
- Cell morphology and differentiation were assessed.
- Expression levels of myogenic determination genes (MyoD1, myogenin) and differentiation inhibitors (Id) were analyzed using molecular techniques.
- MyoD1 promoter activity was examined to determine the level of regulation.
Main Results:
- Okadaic acid treatment reversibly altered C2C12 myoblast morphology and blocked differentiation.
- Expression of MyoD1 and myogenin was extinguished, while Id expression was induced.
- Inhibition of MyoD1 expression occurred at the transcriptional level.
- A rapid loss (within 1 hour) of MyoD DNA binding activity was observed.
Conclusions:
- Protein phosphatases play a critical role in regulating skeletal muscle differentiation.
- Inhibition of protein phosphatases disrupts the expression of key myogenic regulatory factors and impairs differentiation.
- These findings provide novel insights into the molecular mechanisms governing skeletal muscle development.