Ligand-activated pregnane X receptor interferes with HNF-4 signaling by targeting a common coactivator PGC-1alpha. Functional implications in hepatic cholesterol and glucose metabolism.
Previous studies show that feedback inhibition of bile acid production by bile acids is mediated by multiple mechanisms, including activation of pregnane X receptor (PXR). Consistent with these studies, the antibiotic rifampicin, a ligand for human PXR, reduces hepatic bile acid levels in cholestasis patients. To delineate the mechanisms underlying PXR-mediated suppression of bile acid biosynthesis, we examined the functional cross-talk between human PXR and HNF-4, a key hepatic activator of genes involved in bile acid biosynthesis including the cholesterol 7-alpha hydroxylase (CYP7A1) and sterol 12-alpha hydroxylase (CYP8B1) genes. Treatment with rifampicin resulted in repression of endogenous human CYP7A1 expression in HepG2 cells that was reversed by PXR small interfering RNA. The coactivator PGC-1 enhanced transcriptional activity of HNF-4, and this enhancement was suppressed by rifampicin-activated PXR. Endogenous PGC-1 from mouse liver extracts bound to PXR, and recombinant PGC-1 directly interacted with both PXR and HNF-4 in vitro. Rifampicin-dependent interaction of PXR with PGC-1 was shown in cells by coimmunoprecipitation, and intranuclear localization studies using confocal microscopy provided further evidence for this interaction. In chromatin immunoprecipitation studies, rifampicin treatment did not inhibit HNF-4 binding to the native promoters of CYP7A1 and CYP8B1 but resulted in dissociation of PGC-1 and concomitant gene repression. Most interestingly, these rifampicin effects were also observed in the phosphoenolpyruvate carboxykinase gene that contains a functional HNF-4-binding site and is central to hepatic gluconeogenesis. Our study suggests that ligand-activated PXR interferes with HNF-4 signaling by targeting the common coactivator PGC-1, which underlies physiologically relevant inhibitory cross-talk between drug metabolism and cholesterol/glucose metabolism.
Department of Molecular and Integrative Physiology, University of Illinois, Urbana-Champaign, Illinois 61801, USA.
Sonali
S
Bhalla
Cengiz
C
Ozalp
Sungsoon
S
Fang
Lingjin
L
Xiang
Jongsook Kim
JK
Kemper
D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism; D001665:Binding Sites; D015153:Blotting, Western; D019556:COS Cells; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D002790:Cholesterol 7-alpha-Hydroxylase / Q000378:metabolism; D002843:Chromatin / Q000737:chemistry / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D005822:Genetic Vectors; D005947:Glucose / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000737:chemistry; D006360:Heat-Shock Proteins; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D047468:Immunoprecipitation; D008024:Ligands; D008099:Liver / Q000378:metabolism*; D051379:Mice; D009841:Oligonucleotides / Q000737:chemistry; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry* / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D000077297:Pregnane X Receptor; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000378:metabolism; D011987:Receptors, Steroid / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012293:Rifampin / Q000494:pharmacology; D012685:Sepharose / Q000737:chemistry; D015398:Signal Transduction; D013253:Steroid 12-alpha-Hydroxylase / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
D001647:Bile Acids and Salts; D002843:Chromatin; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D006360:Heat-Shock Proteins; D051557:Hepatocyte Nuclear Factor 4; D008024:Ligands; D009841:Oligonucleotides; C486497:PPARGC1A protein, human; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D010750:Phosphoproteins; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D011994:Recombinant Proteins; D014157:Transcription Factors; C099713:nuclear receptor subfamily 0, group B, member 2; D049452:Green Fluorescent Proteins; D012685:Sepharose; D003577:Cytochrome P-450 Enzyme System; D002784:Cholesterol; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; D002790:Cholesterol 7-alpha-Hydroxylase; D013253:Steroid 12-alpha-Hydroxylase; D005982:Glutathione Transferase; D010729:Phosphoenolpyruvate Carboxykinase (GTP); D005978:Glutathione; D005947:Glucose; D012293:Rifampin