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MyoD-dependent induction during myoblast differentiation of p204, a protein also inducible by interferon
1Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA.
Abstract:
p204, an interferon-inducible p200 family protein, inhibits rRNA synthesis in fibroblasts by blocking the binding of the upstream binding factor transcription factor to DNA. Here we report that among 10 adult mouse tissues tested, the level of p204 was highest in heart and skeletal muscles. In cultured C2C12 skeletal muscle myoblasts, p204 was nucleoplasmic and its level was low. During myoblast fusion this level strongly increased, p204 became phosphorylated, and the bulk of p204 appeared in the cytoplasm of the myotubes. Leptomycin B, an inhibitor of nuclear export that blocked myoblast fusion, inhibited the nuclear export signal-dependent translocation of p204 to the cytoplasm. The increase in the p204 level during myoblast fusion was a consequence of MyoD transcription factor binding to several MyoD-specific sequences in the gene encoding p204, followed by transcription. Overexpression of p204 (in C2C12 myoblasts carrying an inducible p204 expression plasmid) accelerated the fusion of myoblasts to myotubes in differentiation medium and induced the fusion even in growth medium. The level of p204 in mouse heart muscle strongly increased during differentiation; it was barely detectable in 10. 5-day-old embryos, reached the peak level in 16.5-day-old embryos, and remained high thereafter. p204 is the second p200 family protein (after p202a) found to be involved in muscle differentiation. (p202a was formerly designated p202. The new designation is due to the identification of a highly similar protein-p202b [H. Wang, G. Chatterjee, J. J. Meyer, C. J. Liu, N. A. Manjunath, P. Bray-Ward, and P. Lengyel, Genomics 60:281-294, 1999].) These results reveal that p204 and p202a function in both muscle differentiation and interferon action.
Insights
The p204 protein, crucial for muscle differentiation, increases during myoblast fusion and is abundant in adult heart and skeletal muscles. Its elevated levels accelerate myotube formation, highlighting its role in muscle development.
Area of Science:
- Molecular Biology
- Cell Biology
- Developmental Biology
Background:
- p204 is an interferon-inducible protein belonging to the p200 family.
- It is known to inhibit rRNA synthesis by interfering with transcription factor binding.
- Previous studies identified p202a (a related protein) as involved in muscle differentiation.
Purpose of the Study:
- To investigate the role and expression of p204 in mouse tissues, particularly during muscle development.
- To elucidate the mechanisms regulating p204 expression and localization during myogenesis.
- To determine the functional impact of p204 on myoblast fusion and differentiation.
Main Methods:
- Analysis of p204 expression levels in adult mouse tissues and during embryonic development.
- Studies using cultured C2C12 skeletal muscle myoblasts to examine p204 localization and phosphorylation during differentiation.
- Investigation of p204's role in myoblast fusion using Leptomycin B and overexpression studies.
- Analysis of MyoD transcription factor binding to the p204 gene promoter.
Main Results:
- p204 expression is highest in adult heart and skeletal muscles.
- During C2C12 myoblast differentiation, p204 levels increase, it becomes phosphorylated, and translocates to the cytoplasm.
- MyoD transcription factor binding to the p204 gene drives its increased expression during myoblast fusion.
- Overexpression of p204 accelerates myoblast fusion and can induce fusion even in growth conditions.
- p204 levels in heart muscle increase significantly during differentiation, peaking in late-stage embryos.
Conclusions:
- p204 plays a significant role in muscle differentiation, promoting myoblast fusion.
- Its expression is regulated by MyoD during myogenesis.
- p204 exhibits dynamic localization changes during myoblast differentiation, involving nuclear export.
- Both p204 and p202a are implicated in muscle differentiation and interferon responses.