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  • Title: The aldo-keto reductase Akr1b7 gene is a common transcriptional target of xenobiotic receptors pregnane X receptor and constitutive androstane receptor.
    Author: Liu MJ, Takahashi Y, Wada T, He J, Gao J, Tian Y, Li S, Xie W.
    Journal: Mol Pharmacol; 2009 Sep; 76(3):604-11. PubMed ID: 19542321.
    Abstract:
    Aldo-keto reductase (AKR) family 1, member 7 (AKR1B7), a member of the AKR superfamily, has been suggested to play an important role in the detoxification of lipid peroxidation by-products. The nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are xenosensors postulated to alleviate xeno- and endobiotic chemical insults. In this study, we show that the mouse Akr1b7 is a shared transcriptional target of PXR and CAR in the liver and intestine. Treatment of wild-type mice with the PXR agonist pregnenolone-16alpha-carbonitrile (PCN) activated Akr1b7 gene expression, whereas the effect was abrogated in PXR(-/-) mice. Similarly, the activation of Akr1b7 gene expression by the CAR agonist 1,4-bis[2-(3,5-dichlorpyridyloxyl)]-benzene, seen in wild-type mice, was abolished in CAR(-/-) mice. The promoter of Akr1b7 gene was activated by PXR and CAR, and this activation was achieved through the binding of PXR-retinoid X receptor (RXR) or CAR-RXR heterodimers to direct repeat-4 type nuclear receptor-binding sites found in the Akr1b7 gene promoter. At the functional level, treatment with PCN in wild-type mice, but not PXR(-/-) mice, led to a decreased intestinal accumulation of malondialdehyde, a biomarker of lipid peroxidation. The regulation of Akr1b7 by PXR was independent of the liver X receptor (LXR), another nuclear receptor known to regulate this AKR isoform. Because a major function of Akr1b7 is to detoxify lipid peroxidation, the PXR-, CAR-, and LXR-controlled regulatory network of Akr1b7 may have contributed to alleviate toxicity associated with lipid peroxidation.
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