Abstract
The CYP3As are broad-spectrum drug-metabolizing enzymes that are collectively responsible for more than 50% of xenobiotic metabolism. Unlike other CYP3As, murine CYP3A44 is expressed predominantly in the female liver, with much lower levels in male livers and no detectable expression in brain or kidney in either gender. In this study, we examined the role of nuclear hormone receptors in the regulation of Cyp3a44 gene expression. Interestingly, we observed differential effects of pregnane X receptor (PXR) and constitutive androstane receptor (CAR) -mediated activation of Cyp3a44 gene expression, which was gender-specific. For example, activation of PXR by pregnenolone-16α-carbonitrile (PCN) and dexamethasone (DEX) induced CYP3A44 mRNA levels in a PXR-dependent fashion in male mice, whereas no induction was detected in female mice. In contrast, PCN and DEX down-regulated CYP3A44 expression in female PXR null animals. Similar to PXR, CAR activation also showed a male-specific induction with no effect on CYP3A44 levels in females. When PXR knockout mice were challenged with the CAR activator phenobarbital, a significant up-regulation of male CYP3A44 levels was observed, whereas levels in females remained unchanged. We conclude that gender has a critical impact on PXR- and CAR-mediated effects of CYP3A44 expression.
Footnotes
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This work was supported by Grant MH58297 from the National Institute of Mental Health, Department of Health and Human Services.
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The data presented here form part of the dissertation of Sayeepriyadarshini Anakk submitted to the faculty of the University of Texas Houston, Graduate School of Biomedical Sciences in partial fulfillment of the requirements for the Doctor in Philosophy degree.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.106.011270.
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ABBREVIATIONS: PXR, pregnane X receptor; CAR, constitute androstane receptor; PB, phenobarbital; PCN, pregnenolone-16α-carbonitrile; DEX, dexamethasone; TCPOBOP, 1,4-bis[2-(3,5-dichlorpyridyloxy)]benzene; RT-PCR, reverse transcription-polymerase chain reaction.
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↵1 Current affiliation: Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas.
- Received June 1, 2006.
- Accepted September 29, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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