Abstract
Our previous studies have suggested a role for AMP-activated protein kinase (AMPK) in the induction of CYP2B6 by phenobarbital (PB) in hepatoma-derived cells (Rencurel et al., 2005). In this study, we showed in primary human hepatocytes that: 1) 5′-phosphoribosyl-5-aminoimidazol-4-carboxamide 1-β-d-ribofuranoside and the biguanide metformin, known activators of AMPK, dose-dependently increase the expression of CYP2B6 and CYP3A4 to an extent similar to that of PB. 2) PB, but not the human nuclear receptor constitutive active/androstane receptor (CAR) ligand 6-(4-chlorophenyl)imidazol[2,1-6][1,3]thiazole-5-carbaldehyde, dose-dependently increase AMPK activity. 3) Pharmacological inhibition of AMPK activity with compound C or dominant-negative forms of AMPK blunt the inductive response to phenobarbital. Furthermore, in transgenic mice with a liver-specific deletion of both the α1 and α2 AMPK catalytic subunits, basal levels of Cyp2b10 and Cyp3a11 mRNA were increased but not in primary culture of mouse hepatocytes. However, phenobarbital or 1,4 bis[2-(3,5-dichloropyridyloxy)]benzene, a mouse CAR ligand, failed to induce the expression of these genes in the liver or cultured hepatocytes from mice lacking hepatic expression of the α1 and α2 subunits of AMPK. The distribution of CAR between the nucleus and cytosol was not altered in hepatocytes from mice lacking both AMPK catalytic subunits. These data highlight the essential role of AMPK in the CAR-mediated signal transduction pathway.
Footnotes
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This work was supported by the Swiss National Science Foundation (to F.R.) and by programme grants from the Wellcome Trust (to G.A.R.) and the Medical Research Council, a Postdoctoral Fellowship from the Juvenile Diabetes Research Fund International (to G.d.S.X.), and a Wellcome Trust Advanced Fellowship (to I.L.), a Wellcome Trust Research Leave Fellowships (to G.A.R.). M.F. was supported by a postdoctoral fellowship from the European Commission (grant LSHM-CT-2004-005272/exgenesis). B.V. and F.R. were supported by an exchange program from EGIDE association (PAI Germaine de Staël).
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ABBREVIATIONS: PB, phenobarbital; CAR, constitutive active/androstane receptor; CCRP, cytoplasmic CAR retaining protein; AMPK, AMP-activated protein kinase; AICAR, 5′-phosphoribosyl-5-aminoimidazol-4-carboxamide 1-β-d-ribofuranoside; PCR, polymerase chain reaction; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; PBS, phosphate-buffered saline; GFP, green fluorescent protein; CITCO, 6-(4-chlorophenyl)imidazol[2,1-6][1,3]thiazole-5-carbaldehyde; Rif, rifampicin; RT, reverse transcription; PCR, polymerase chain reaction; TCPOBOP,1,4 bis[2-(3,5-dichloropyridyloxy)]benzene; PGC1α, peroxisome proliferator-activated receptor γ coactivator-1α.
- Received July 31, 2006.
- Revision received September 19, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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