Abstract
Dehydroepiandrosterone (DHEA) is a steroid produced by the human adrenal gland. Administration of pharmacological doses of DHEA to rats changes expression of many genes, including the cytochrome P450 family members CYP4A1 and CYP3A23. It is known that induction of CYP4A expression by DHEA requires the peroxisome proliferator-activated receptor α (PPARα). In the current study, PPARα-null mice were used to examine the role of PPARα in expression of CYP3A. In wild-type mice, 150 mg/kg DHEA-sulfate induced Cyp4a and Cyp3a11 mRNAs by 5- and 2-fold, respectively. Induction of Cyp4a expression by DHEA-sulfate was not observed in PPARα-null mice, whereas induction of Cyp3a11 expression by DHEA-sulfate was similar between genotypes. This suggests that PPARα is not involved in induction of Cyp3a11 expression by DHEA. Because expression of CYP3A family members can be induced by activation of another member of the nuclear receptor superfamily, the pregnane X receptor (PXR), we examined the ability of DHEA to activate PXR. In transient transfection assays, DHEA and its metabolites androst-5-ene-3β,17β-diol (ADIOL), androst-5-ene-3,17-dione, and androst-4-ene-3,17-dione were activators of PXR. Maximal induction of a PXR-responsive reporter gene of approximately 3-fold was observed at concentrations of 50 to 100 μM, indicating that these steroids are relatively weak activators of PXR. Human and murine PXR exhibited different specificities for DHEA and its metabolites. ADIOL activated reporter gene expression in the presence of murine but not human PXR. Results of these studies suggest that the induction of rodent CYP3A expression upon treatment with high doses of DHEA occurs through activation of PXR.
Footnotes
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↵1 Present address: Department of Pharmacology, University of Washington School of Medicine, 1959 NE Pacific St., Box 356560, Seattle, WA 98195.
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This study was supported by U.S. Public Health Service Grants DK54774 (to R.A.P.) and CA 89607 (to J.M.P.), National Research Service Award Fellowship F32 ES05927 (to S.L.R.), and Jewish Hospital Foundation Grant 9511-02 (to J.L.F.).
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↵3 The major peroxisome proliferator-responsiveCYP4A form in the rat liver is CYP4A1. The mouse also expresses a hepatic Cyp4a form that is inducible by peroxisome proliferators and cross-reacts in Northern blot analysis with a cDNA probe to rat CYP4A1. In this article, this mouse gene will be designated Cyp4a, the rat gene will be referred to as CYP4A1, and when referring to both rat and mouse genes, CYP4A will be used. Similarly, the major glucocorticoid-inducibleCYP3A forms in rats and mice have different designations, CYP3A23 and Cyp3a11, respectively. However, when referring to both the rat and mouse genes, the more generic CYP3A is used.
- Abbreviations used are::
- DHEA
- dehydroepiandrosterone (3β-hydroxy-androst-5-en-17-one)
- DHEA-S
- dehydroepiandrosterone 3β-sulfate
- PPARα
- peroxisome proliferator-activated receptor α
- PXR
- pregnane X receptor
- ADIOL
- androst-5-ene-3β,17β-diol
- ADIONE
- androst-4-ene-3,17-dione
- 11β-hydroxy-DHEA
- 3β,11β-dihydroxy-androst-5-en-17-one
- 16α-hydroxy-DHEA
- 3β,16α-dihydroxy-androst-5-en-17-one
- 7-oxo-DHEA
- 3β-hydroxy-androst-5-ene-7,17-dione
- 7α-hydroxy-DHEA
- 3β,7α-dihydroxy-androst-5-en-17-one
- DMSO
- dimethyl sulfoxide
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- mPXR
- murine pregnane X receptor
- hPXR
- human pregnane X receptor
- PXRE
- pregnane X receptor responsive element
- LUC
- luciferase
- Received June 26, 2001.
- Accepted February 5, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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