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Published on: November 15, 2013
Ku proteins function as corepressors to regulate farnesoid X receptor-mediated gene expression
Masae Ohno1, Masaaki Kunimoto, Makoto Nishizuka
1Department of Molecular Biology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Aichi 467-8603, Japan.
Biochemical and Biophysical Research Communications
|October 17, 2009
Summary
The Ku proteins (Ku70 and Ku80) interact with the farnesoid X receptor (FXR) and act as corepressors, inhibiting bile acid metabolism gene expression. This discovery reveals a novel regulatory mechanism for FXR.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- The farnesoid X receptor (FXR) is a nuclear receptor crucial for regulating bile acid metabolism and enterohepatic circulation.
- FXR's function is modulated by various cofactors, but the specific roles of DNA repair proteins in FXR regulation remain largely unexplored.
Purpose of the Study:
- To identify novel cofactors interacting with FXR.
- To elucidate the functional role of identified cofactors in FXR-mediated gene regulation, particularly concerning bile acid metabolism.
Main Methods:
- Pull-down assays using GST-fused FXR regions (A/B and C) with HeLa cell nuclear extracts.
- Identification of interacting proteins via pull-down assays.
- Chromatin immunoprecipitation (ChIP) assays to assess protein-DNA interactions on the Bile Salt Export Pump (BSEP) promoter.
- Reporter gene assays to evaluate the effect of Ku proteins on FXR-mediated BSEP promoter activity.
Main Results:
- DNA-dependent protein kinase catalytic subunit (DNA-PKcs), Ku70, and Ku80 were identified as FXR-associated factors.
- Ku70 and Ku80 interacted with the C and D regions of FXR, while DNA-PKcs interacted with the A/B region.
- Ku proteins were found to associate with the BSEP promoter in conjunction with FXR.
- Ectopic expression of Ku proteins suppressed FXR-mediated BSEP promoter activity and gene expression.
Conclusions:
- Ku70 and Ku80 function as corepressors for FXR.
- These findings reveal a novel role for DNA repair proteins, Ku70 and Ku80, in the regulation of bile acid metabolism via FXR signaling.
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