The Nrf2 Activator Oltipraz Also Activates the Constitutive Androstane Receptor

Matthew D. Merrell; Jonathan P. Jackson; Lisa M. Augustine; Craig D. Fisher; Angela L. Slitt; Jonathan M. Maher; Wendong Huang; David D. Moore; Youcai Zhang; Curtis D. Klaassen; Nathan J. Cherrington

doi:10.1124/dmd.108.020867

Abstract

Oltipraz (OPZ) is a well known inducer of NAD(P)H:quinone oxidoreductase (NQO1) along with other enzymes that comprise the nuclear factor E2–related factor 2 (Nrf2) battery of detoxification genes. However, OPZ treatment also induces expression of CYP2B, a gene regulated by the constitutive androstane receptor (CAR). Therefore, this study was designed to determine whether OPZ induces gene expression in the mouse liver through activation of CAR in addition to Nrf2. OPZ increased the mRNA expression of both Cyp2b10 and Nqo1 in C57BL/6 mouse livers. As expected, in livers from Nrf2^-/- mice, OPZ induction of Nqo1 was reduced, indicating Nqo1 induction is dependent on Nrf2 activation, whereas Cyp2b10 induction was unchanged. The robust induction of Cyp2b10 by OPZ in wild-type mice was completely absent in CAR^-/- mice, revealing a CAR-dependent induction by OPZ. OPZ also induced transcription of the human CYP2B6 promoter-reporter containing the phenobarbital (PB) responsive element in mouse liver using an in vivo transcription assay. Additionally, OPZ induced in vivo nuclear accumulation of CAR at 3 h but, as with PB, was unable to reverse androstanol repression of mouse CAR constitutive activity in transiently transfected HepG2 cells. In summary, OPZ induces expression of Cyp2b10 and Nqo1 via the activation of CAR and Nrf2, respectively.

Footnotes

This work was supported by National Institutes of Health Grants ES011646 and ES006694 (to N.J.C.), ES09716 and ES09649 (to C.D.K.), and DK46546 (to D.D.M.).
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.108.020867.
ABBREVIATIONS: OPZ, oltipraz; GST, glutathione-S-transferase; NQO1, NAD(P)H:quinone oxidoreductase; Nrf2, nuclear factor E2-related factor 2; ARE/EpRE, antioxidant response element/electrophile response element; Keap1, Kelch-like ECH-associated protein 1; CAR, constitutive androstane receptor; TCPOBOP, 1,4-bis-[2-(3, 5-dichloropyridyloxy)] benzene; CITCO, 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime; PB, phenobarbital; RXR, retinoid X receptor; bDNA, branched DNA; mCAR, mouse constitutive androstane receptor; PBREM, phenobarbital responsive element; DMSO, dimethyl sulfoxide; ERK, extracellular signal-regulated kinase.
- Received February 7, 2008.
- Accepted May 7, 2008.