Characterization of peroxisome proliferator-activated receptor alpha--independent effects of PPARalpha activators in the rodent liver: di-(2-ethylhexyl) phthalate also activates the constitutive-activated receptor.
Peroxisome proliferator chemicals (PPC) are thought to mediate their effects in rodents on hepatocyte growth and liver cancer through the nuclear receptor peroxisome proliferator-activated receptor (PPAR) alpha. Recent studies indicate that the plasticizer di-(2-ethylhexyl) phthalate (DEHP) increased the incidence of liver tumors in PPARalpha-null mice. We hypothesized that some PPC, including DEHP, induce transcriptional changes independent of PPARalpha but dependent on other nuclear receptors, including the constitutive-activated receptor (CAR) that mediates phenobarbital (PB) effects on hepatocyte growth and liver tumor induction. To determine the potential role of CAR in mediating effects of PPC, a meta-analysis was performed on transcript profiles from published studies in which rats and mice were exposed to PPC and compared the profiles to those produced by exposure to PB. Valproic acid, clofibrate, and DEHP in rat liver and DEHP in mouse liver induced genes, including Cyp2b family members that are known to be regulated by CAR. Examination of transcript changes by Affymetrix ST 1.0 arrays and reverse transcription-PCR in the livers of DEHP-treated wild-type, PPARalpha-null, and CAR-null mice demonstrated that (1) most (approximately 94%) of the transcriptional changes induced by DEHP were PPARalpha-dependent, (2) many PPARalpha-independent genes overlapped with those regulated by PB, (3) induction of genes Cyp2b10, Cyp3a11, and metallothionine-1 by DEHP was CAR dependent but PPARalpha-independent, and (4) induction of a number of genes (Cyp8b1, Gstm4, and Gstm7) was independent of both CAR and PPARalpha. Our results indicate that exposure to PPARalpha activators including DEHP leads to activation of multiple nuclear receptors in the rodent liver.
National Health and Environmental Effects Research Lab Toxicogenomics Core, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, USA.
Hongzu
H
Ren
Lauren M
LM
Aleksunes
Carmen
C
Wood
Beena
B
Vallanat
Michael H
MH
George
Curtis D
CD
Klaassen
J Christopher
JC
Corton
D000818:Animals; D002994:Clofibrate / Q000633:toxicity; D000090702:Constitutive Androstane Receptor; D004051:Diethylhexyl Phthalate / Q000633:toxicity*; D020869:Gene Expression Profiling / Q000379:methods; D005786:Gene Expression Regulation / Q000187:drug effects; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020411:Oligonucleotide Array Sequence Analysis; D047493:PPAR alpha / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D020025:Peroxisome Proliferators / Q000633:toxicity*; D010634:Phenobarbital / Q000633:toxicity; D010968:Plasticizers / Q000633:toxicity*; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D011987:Receptors, Steroid / Q000819:agonists; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000187:drug effects; D014635:Valproic Acid / Q000633:toxicity
D000090702:Constitutive Androstane Receptor; D047493:PPAR alpha; D020025:Peroxisome Proliferators; D010968:Plasticizers; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D014635:Valproic Acid; D004051:Diethylhexyl Phthalate; D002994:Clofibrate; D010634:Phenobarbital