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Multiple change in E2F function and regulation occur upon muscle differentiation
1Department of Biochemistry, Tufts University School of Medicine, Boston, Massachusetts 02111.
Abstract:
We have examined regulation of the E2F transcription factor during differentiation of muscle cells. E2F regulates many genes involved in growth control and is also the target of regulation by diverse cellular signals, including the RB family of growth suppressors (e.g., the retinoblastoma protein [RB], p107, and p130). The following aspects of E2F function and regulation during muscle differentiation were investigated: (i) protein-protein interactions, (ii) protein levels, (iii) phosphorylation of the E2F protein, and (iv) transcriptional activity. A distinct E2F complex was present in differentiated cells but not in undifferentiated cells. The p130 protein was a prominent component of the E2F complex associated with differentiation. In contrast, in undifferentiated cells, the p107 protein was the prominent component in one of three E2F complexes. In addition, use of a differentiation-defective muscle line provided genetic and biochemical evidence that quiescence and differentiation are separable events. Exclusive formation of the E2F-p130 complex did not occur in this differentiation-defective line; however, E2F complexes diagnostic of quiescence were readily apparent. Thus, sole formation of the E2F-p130 complex is a necessary event in terminal differentiation. Other changes in E2F function and regulation upon differentiation include decreased phosphorylation and increased repression by E2F. These observations suggest that the regulation of E2F function during terminal differentiation may proceed through differential interaction within the RB family and/or phosphorylation.
Insights
Muscle cell differentiation involves specific E2F transcription factor complexes. The E2F-p130 complex is crucial for terminal differentiation, separable from quiescence.
Area of Science:
- Molecular Biology
- Cellular Biology
- Biochemistry
Background:
- E2F transcription factors regulate genes controlling cell growth.
- E2F activity is modulated by the retinoblastoma (RB) protein family, including RB, p107, and p130.
- Understanding E2F regulation is key to comprehending muscle cell differentiation.
Purpose of the Study:
- To investigate the regulation of the E2F transcription factor during muscle cell differentiation.
- To analyze E2F protein-protein interactions, levels, phosphorylation, and transcriptional activity in differentiating muscle cells.
- To determine the role of specific RB family members in E2F-mediated muscle differentiation.
Main Methods:
- Analysis of E2F protein-protein interactions using co-immunoprecipitation.
- Assessment of E2F protein levels and phosphorylation status via Western blotting.
- Examination of E2F transcriptional activity.
- Utilizing a differentiation-defective muscle cell line for genetic and biochemical studies.
Main Results:
- A unique E2F complex, prominently featuring p130, characterizes differentiated muscle cells.
- In undifferentiated cells, p107 is a key component of certain E2F complexes.
- Genetic and biochemical data show that quiescence and differentiation are distinct processes.
- The E2F-p130 complex formation is essential for terminal differentiation, and its absence in a defective cell line confirms this.
- Differentiation leads to decreased E2F phosphorylation and increased repression by E2F.
Conclusions:
- The formation of the E2F-p130 complex is a necessary event for terminal muscle cell differentiation.
- Regulation of E2F during differentiation may involve differential interactions with RB family proteins and altered phosphorylation.
- Quiescence and terminal differentiation are separable events in muscle cells, with distinct E2F complex requirements.