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Detection of Protein Ubiquitination
Published on: August 19, 2009
COP1 functions as a FoxO1 ubiquitin E3 ligase to regulate FoxO1-mediated gene expression
Satomi Kato1, Jixin Ding, Evan Pisck
1Molecular Oncology Research Institute, Tufts-New England Medical Center, Boston, Massachusetts 02111, USA.
The Journal of Biological Chemistry
|September 26, 2008
Summary
Constitutive photomorphogenic 1 (COP1), an E3 ubiquitin ligase, targets the FoxO1 protein for degradation. This COP1-mediated degradation of FoxO1 impacts hepatic glucose production and gluconeogenesis.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Constitutive photomorphogenic 1 (COP1) is a Ring-Finger E3 ubiquitin ligase with known roles in plant development and mammalian cell processes.
- Insulin enhances COP1 expression, suggesting a link between insulin signaling and COP1 activity.
Purpose of the Study:
- To investigate the role of COP1 in regulating the stability and function of FoxO1 protein.
- To elucidate the mechanism by which COP1 affects FoxO1 and its downstream targets.
Main Methods:
- Utilized ectopic expression and knockdown of COP1 in Fao hepatoma cells.
- Performed co-immunoprecipitation to assess COP1-FoxO1 binding.
- Analyzed ubiquitination levels and protein degradation via the ubiquitin-proteasome pathway.
- Measured reporter gene and target gene expression (glucose-6-phosphatase, phosphoenolpyruvate carboxykinase).
Main Results:
- COP1 expression inversely correlated with endogenous FoxO1 protein levels.
- COP1 directly binds to FoxO1, promoting its ubiquitination and proteasomal degradation.
- COP1 suppressed FoxO1-mediated transcription of gluconeogenic genes, including glucose-6-phosphatase and phosphoenolpyruvate carboxykinase.
- COP1 activity led to decreased hepatic glucose production in Fao cells.
Conclusions:
- COP1 functions as an E3 ligase for FoxO1, targeting it for degradation.
- COP1 plays a significant role in regulating hepatic glucose metabolism by controlling FoxO1 stability and activity.
- The COP1-FoxO1 axis represents a potential target for managing metabolic disorders related to gluconeogenesis.
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