Transcriptional activation of PPARalpha by phenobarbital in the absence of CAR and PXR.
The nuclear receptors CAR (constitutive androstane receptor) and PXR (pregnane X receptor) mediate the effects of phenobarbital on gene transcription. To investigate the relative contribution of these nuclear receptors to the expression of specific genes we studied the effect of phenobarbital in livers of wild type, CAR(-/-), PXR(-/-) and CAR/PXR(-/-) knockout mice. Spotted Steroltalk v1 cDNA arrays were applied containing probes for genes involved in drug metabolism, sterol biosynthesis, steroid synthesis/transport and heme synthesis. In the absence of CAR and PXR, phenobarbital unexpectedly induced mRNAs of several nuclear receptors, including PPARalpha and its target genes Cyp4a10 and Cyp4a14. Interestingly, in primary cultures of hepatocytes isolated from CAR/PXR(-/-) knockout mice, phenobarbital increased HNF-4alpha levels. In further experiments in these hepatocyte cultures we provide evidence that phenobarbital directly induces transcription of the PPARalpha gene via its HNF-4alpha response element, and indirectly by lack of inhibitory crosstalk of AMPK, CAR and PXR with HNF-4alpha. Our results provide further insight into CAR and PXR-independent effects of phenobarbital and the crosstalk between different nuclear receptor signaling pathways.
Tamasi
Viola
V
Genome Scale Biology, Biozentrum, University of Basel, Basel, Switzerland. vtamasi@mac.com
Juvan
Peter
P
Beer
Markus
M
Rozman
Damjana
D
Meyer
Urs A
UA
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002478:Cells, Cultured; D000090702:Constitutive Androstane Receptor; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D000072470:Cytochrome P450 Family 4; D004247:DNA / Q000235:genetics / Q000378:metabolism; D051557:Hepatocyte Nuclear Factor 4 / Q000235:genetics; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008954:Models, Biological; D047493:PPAR alpha / Q000235:genetics*; D010634:Phenobarbital / Q000494:pharmacology*; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020239:Receptor Cross-Talk; D018160:Receptors, Cytoplasmic and Nuclear / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D011987:Receptors, Steroid / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D015533:Transcriptional Activation / Q000187:drug effects*
D000090702:Constitutive Androstane Receptor; C512110:Cyp4a10 protein, mouse; C436963:Cyp4a14 protein, mouse; D051557:Hepatocyte Nuclear Factor 4; C496593:Hnf4a protein, mouse; D047493:PPAR alpha; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D000072470:Cytochrome P450 Family 4; D010634:Phenobarbital