Peroxisome proliferator-activated receptor alpha (PPARalpha) agonists induce constitutive androstane receptor (CAR) and cytochrome P450 2B in rat primary hepatocytes.
The constitutive androstane receptor (CAR; NR1I3) is a key transcriptional factor that regulates genes encoding drug-metabolizing enzymes and drug transporters. However, studies on regulation of CAR target genes via up- or down-regulation of CAR are limited. In this study, we examined the effects of PPARalpha agonists (ciprofibrate, bezafibrate, fenofibrate and WY14643) on the expression of CAR and its target gene CYP2B1/2 in rat primary hepatocytes. Results from real-time PCR analysis showed that CAR and CYP2B1/2 mRNAs exhibit increases in response to all PPARalpha agonists studied (5 to 10-folds of control). Pretreatment of cells with cycloheximide, an inhibitor of protein synthesis, completely suppressed increase in CYP2B1/2 mRNA in response to ciprofibrate, suggesting that protein synthesis is required in this process. In addition, the induction of CAR by ciprofibrate on the protein level was observed with nuclear extracts as well as total cell lysates. These results indicate that CYP2B1/2 mRNAs are induced by PPARalpha agonists and that this effect is accompanied by increase in the expression of CAR gene at both mRNA and nuclear protein levels. Activated PPARalpha may increase functional CAR protein, which can induce the expression of CAR target genes such as CYP2B.
Saito
Kosuke
K
Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Chiba University, Chiba 260-8675, Japan.
Kobayashi
Kaoru
K
Mizuno
Yuki
Y
Fukuchi
Yukina
Y
Furihata
Tomomi
T
Chiba
Kan
K
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis* / Q000235:genetics; D018929:Cell Culture Techniques; D002995:Clofibric Acid / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000090702:Constitutive Androstane Receptor; D003513:Cycloheximide / Q000494:pharmacology; D019362:Cytochrome P-450 CYP2B1 / Q000096:biosynthesis* / Q000235:genetics; D004347:Drug Interactions; D004790:Enzyme Induction / Q000187:drug effects / Q000235:genetics; D058607:Fibric Acids; D015971:Gene Expression Regulation, Enzymologic; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D008297:Male; D047493:PPAR alpha / Q000819:agonists*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis* / Q000235:genetics; D013250:Steroid Hydroxylases / Q000096:biosynthesis* / Q000235:genetics
D000090702:Constitutive Androstane Receptor; D058607:Fibric Acids; C000716329:Nr1i3 protein, rat; D047493:PPAR alpha; D018160:Receptors, Cytoplasmic and Nuclear; D002995:Clofibric Acid; D003513:Cycloheximide; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; D019362:Cytochrome P-450 CYP2B1; C025619:steroid 16-beta-hydroxylase; C019304:ciprofibrate