Abstract
Farnesoid X receptor (FXR) regulates redox homeostasis and elicits a cytoprotective effect. CCAAT/enhancer binding protein-β (C/EBPβ) plays a role in regulating the expression of hepatocyte-specific genes and contributes to hepatocyte protection and liver regeneration. In view of the role of FXR in xenobiotic metabolism and hepatocyte survival, this study investigated the potential of FXR to activate C/EBPβ for the induction of detoxifying enzymes and the responsible regulatory pathway. Chenodeoxycholic acid (CDCA), a major component in bile acids, activates FXR. In HepG2 cells, CDCA treatment activated C/EBPβ, as shown by increases in its phosphorylation, nuclear accumulation, and expression. 3-(2,6-Dichlorophenyl)-4-(3′-carboxy-2-chlorostilben-4-yl-)oxymethyl-5-isopropyl-isoxazole (GW4064), a synthetic FXR ligand, had similar effects. In addition, CDCA enhanced luciferase gene transcription from the construct containing −1.65-kb GSTA2 promoter, which contained C/EBP response element (pGL-1651). Moreover, CDCA treatment activated AMP-activated protein kinase (AMPK), which led to extracellular signal-regulated kinase 1/2 (ERK1/2) activation, as evidenced by the results of experiments using a dominant-negative mutant of AMPKα and chemical inhibitor. The activation of ERK1/2 was responsible for the activating phosphorylation of C/EBPβ. FXR knockdown attenuated the ability of CDCA to activate AMPK and ERK1/2 and phosphorylate C/EBPβ. Consistently, enforced expression of FXR promoted the phosphorylation of AMPKα, ERK1/2, and C/EBPβ, verifying that C/EBPβ phosphorylation elicited by CDCA results from the activation of AMPK and ERK1/2 by FXR. In mice, CDCA treatment activated C/EBPβ with the induction of detoxifying enzymes in the liver. Our results demonstrate that CDCA induces antioxidant and xenobiotic-metabolizing enzymes by activating C/EBPβ through AMPK-dependent ERK1/2 pathway downstream of FXR.
Footnotes
This work was supported by the National Research Foundation of Korea [Grant Ministry of Education, Science and Technology No. 2011-0001204] funded by the government of Korea.
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.111.038414.
↵ The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material.
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ABBREVIATIONS:
- FXR
- farnesoid X receptor
- CDCA
- chenodeoxycholic acid
- C/EBP
- CCAAT/enhancer binding proteins
- GCS
- γ-glutamylcysteine synthetase
- MnSOD
- manganese superoxide dismutase
- UGT
- UDP-glucuronosyl transferase
- Mrp2
- multidrug resistance protein 2
- GST
- glutathione S-transferase
- AMPK
- AMP-activated protein kinase
- ERK1/2
- extracellular signal-regulated kinase 1/2
- phospho
- phosphorylated
- ACC
- acetyl-CoA carboxylase
- HO-1
- heme oxygenase-1
- AICAR
- 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside
- U0126
- 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene
- siRNA
- small interfering RNA
- GW4064
- 3-(2,6-dichlorophenyl)-4-(3′-carboxy-2-chlorostilben-4-yl-)oxymethyl-5-isopropyl-isoxazole
- PBS
- phosphate-buffered saline
- DN-AMPKα
- dominant-negative mutant form of AMPKα
- DN-MKK1
- dominant-negative mutant of mitogen-activated protein kinase kinase 1
- PCR
- polymerase chain reaction
- LAP
- liver-enriched activator protein
- LIP
- liver-enriched inhibitory protein
- C/EBP-RE
- CCAAT/enhancer binding protein response element
- p90RSK
- p90 ribosomal S6 kinase
- MEK
- mitogen-activated protein kinase/extracellular signal-regulated kinase kinase
- JNK
- c-jun amino-terminal-kinase
- SB203580
- 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole
- SP600125
- 1,9-pyrazoloanthrone
- Nrf2
- nuclear factor erythroid-2-related factor 2.
- Received January 26, 2011.
- Accepted May 19, 2011.
- Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics
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