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Published on: March 27, 2014
Degradation of proto-oncoprotein c-Rel by the ubiquitin-proteasome pathway
E Chen1, R Hrdlickova, J Nehyba
1Intramural Research Support Program, SAIC Frederick, NCI-Frederick Cancer Research and Development Center, Frederick, Maryland 21702, USA.
Abstract:
The c-rel proto-oncogene product, c-Rel, belongs to the Rel/NF-kappaB transcription factor family, which regulates a large variety of cellular functions. The activation of NF-kappaB involves the degradation of the inhibitor, IkappaB, through the ubiquitin-proteasome (Ub-Pr)-mediated pathway. Here we report that the turnover of c-Rel is also regulated by the Ub-Pr pathway, thus adding another level of complexity to the regulation of NF-kappaB. High molecular weight ubiquitinated c-Rel conjugates are detected in cells and accumulate in cells treated with proteasome inhibitors. In a cell-free in vitro degradation assay, c-Rel is degraded specifically through the Ub-Pr pathway. N-terminally truncated c-Rel is readily degraded, implying the dispensability of N-terminal sequence; in contrast, a series of deletion mutants missing C-terminal sequences display a reduced susceptibility to the degradation. Interestingly, the sequence between residues 118 and 171 of c-Rel, i.e. the region immediately following the c-Rel/v-Rel homology domain, appears to play an important role in mediating ubiquitin conjugation and the subsequent degradation. Together with our previous study showing an elevated tumorigenic potential for C-terminally truncated mutants, our data suggest that the C-terminal domain of c-Rel plays an important role in mediating c-Rel degradation and growth control.
Insights
The ubiquitin-proteasome pathway degrades c-Rel, a transcription factor regulating cellular functions. Its C-terminal domain is crucial for this degradation and controlling cell growth.
Area of Science:
- Molecular Biology
- Cellular Biology
- Oncogenesis
Background:
- c-Rel is a proto-oncogene product and member of the Rel/NF-kappaB transcription factor family.
- NF-kappaB activation involves IkappaB degradation via the ubiquitin-proteasome (Ub-Pr) pathway.
- Regulation of NF-kappaB transcription factors is critical for numerous cellular processes.
Purpose of the Study:
- To investigate the role of the ubiquitin-proteasome pathway in c-Rel turnover.
- To identify regions of c-Rel involved in its degradation.
- To understand the implications of c-Rel degradation in growth control.
Main Methods:
- Detection of ubiquitinated c-Rel conjugates in cells.
- Assessment of c-Rel degradation in cells treated with proteasome inhibitors.
- In vitro degradation assays using cell-free systems.
- Analysis of degradation kinetics for various c-Rel deletion mutants.
Main Results:
- Ubiquitinated c-Rel conjugates were detected and accumulated upon proteasome inhibition.
- c-Rel undergoes degradation via the Ub-Pr pathway in vitro.
- N-terminally truncated c-Rel was rapidly degraded, while C-terminal deletions reduced degradation.
- Residues 118-171 of c-Rel are important for ubiquitination and degradation.
Conclusions:
- c-Rel protein turnover is regulated by the ubiquitin-proteasome pathway.
- The C-terminal domain of c-Rel is essential for its degradation and plays a role in growth control.
- Dysregulation of c-Rel degradation may contribute to tumorigenesis.
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