Abstract
The role of the microtubule network in the constitutive androstane receptor (CAR)-mediated transactivation of CYP2B induced by phenobarbital (PB) in rat primary hepatocytes was investigated using the microtubule-disrupting agent nocodazole (NCZ). In human hepatocytes, it was reported that CAR mRNA expression was decreased by a microtubule-disrupting agent through the inhibition of glucocorticoid receptor (GR)-mediated transactivation. However, in the present study, we show that the rat CAR gene was unaffected by the GR-mediated pathway in rat primary hepatocytes treated with NCZ. The PB-induced expression of CYP2B mRNA was repressed in the presence of NCZ for 2 h before and during 4 h of PB treatment, whereas the CAR mRNA and protein expression levels were not affected. Furthermore, the transactivation of the PB-responsive enhancer module-luciferase reporter gene and the nuclear transport of CAR induced by PB were also repressed in the presence of NCZ. Based on these findings, microtubular integrity might be required for PB-induced nuclear translocation of CAR in rat primary hepatocytes. In the same procedures, except that NCZ was replaced with radicicol, the CYP2B mRNA expression induced by PB was also repressed. Taking these into consideration, PB-mediated nuclear translocation of rCAR might be dependent on the 90-kDa heat shock protein as well as the microtubule network.
Footnotes
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↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
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This work was partially supported by the Ministry of Education, Science, Sports, and Culture, Grant-in-Aid for Young Scientists; and by the “Open Research Center” Project.
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.109.060434
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ABBREVIATIONS:
- CAR
- constitutive androstane receptor
- PB
- phenobarbital
- NCZ
- nocodazole
- COL
- colchicine
- RAD
- radicicol
- GR
- glucocorticoid receptor
- Hsp
- heat shock protein
- TCPOBOP
- 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene
- Dex
- dexamethasone
- GFP
- green fluorescent protein
- NLS
- nuclear localization signal
- PBREM
- phenobarbital-responsive enhancer module
- GA
- geldanamycin
- PCR
- polymerase chain reaction
- RT-PCR
- reverse transcription polymerase chain reaction
- DMSO
- dimethyl sulfoxide
- PBS
- phosphate-buffered saline
- PAGE
- polyacrylamide gel electrophoresis
- FK506
- tacrolimus
- SV40
- simian virus 40.
- Received August 20, 2009.
- Accepted November 16, 2009.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
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