Pregnane X receptor (PXR) is a major transcriptional regulator of xenobiotic metabolism and transport pathways in the liver and intestines, which are critical for protecting organisms against potentially harmful xenobiotic and endobiotic compounds. Inadvertent activation of drug metabolism pathways through PXR is known to contribute to drug resistance, adverse drug-drug interactions, and drug toxicity in humans. In both humans and rodents, PXR has been implicated in non-alcoholic fatty liver disease, diabetes, obesity, inflammatory bowel disease, and cancer. Because of PXR's important functions, it has been a therapeutic target of interest for a long time. More recent mechanistic studies have shown that PXR is modulated by multiple PTMs. Herein we provide the first investigation of the role of acetylation in modulating PXR activity. Through LC-MS/MS analysis, we identified lysine 109 (K109) in the hinge as PXR's major acetylation site. Using various biochemical and cell-based assays, we show that PXR's acetylation status and transcriptional activity are modulated by E1A binding protein (p300) and sirtuin 1 (SIRT1). Based on analysis of acetylation site mutants, we found that acetylation at K109 represses PXR transcriptional activity. The mechanism involves loss of RXRα dimerization and reduced binding to cognate DNA response elements. This mechanism may represent a promising therapeutic target using modulators of PXR acetylation levels. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

• Keywords
• Acetylation, Drug metabolism, E1A binding protein p300 (p300), Nuclear receptor, Post-translational modification (PTM), Pregnane X receptor (PXR), Transcription regulation,
• MeSH
• Acetylation MeSH
• Transcriptional Activation * MeSH
• Hep G2 Cells MeSH
• DNA chemistry   metabolism   MeSH
• Escherichia coli genetics   metabolism   MeSH
• HEK293 Cells MeSH
• HeLa Cells MeSH
• Cloning, Molecular MeSH
• Humans MeSH
• Luciferases genetics   metabolism   MeSH
• Lysine chemistry   metabolism   MeSH
• Models, Molecular MeSH
• Protein Multimerization MeSH
• Mutagenesis, Site-Directed MeSH
• Protein Processing, Post-Translational * MeSH
• Pregnane X Receptor MeSH
• Recombinant Proteins chemistry   genetics   metabolism   MeSH
• Genes, Reporter MeSH
• Response Elements MeSH
• Protein Structure, Secondary MeSH
• Sirtuin 1 genetics   metabolism   MeSH
• Receptors, Steroid chemistry   genetics   metabolism   MeSH
• Structural Homology, Protein MeSH
• p300-CBP Transcription Factors genetics   metabolism   MeSH
• Structure-Activity Relationship MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• DNA MeSH
• Luciferases MeSH
• Lysine MeSH
• p300-CBP-associated factor MeSH Browser
• Pregnane X Receptor MeSH
• Recombinant Proteins MeSH
• SIRT1 protein, human MeSH Browser
• Sirtuin 1 MeSH
• Receptors, Steroid MeSH
• p300-CBP Transcription Factors MeSH

Atorvastatin, fluvastatin and rosuvastatin are drugs used for treatment of hypercholesterolemia. They cause numerous drug-drug interactions by inhibiting and inducing drug-metabolizing cytochromes P450. These three statins exist in four optical forms, but they are currently used as enantiopure drugs, i.e., only one single enantiomer. There are numerous evidences that efficacy, adverse effects and toxicity of drugs may be enantiospecific. Therefore, we investigated the effects of optical isomers of atorvastatin, fluvastatin and rosuvastatin on the expression of drug-metabolizing P450s in primary human hepatocytes, using western blots and RT-PCR for measurement of proteins and mRNAs, respectively. The activity of P450 transcriptional regulators, including pregnane X receptor (PXR), aryl hydrocarbon receptor (AhR) and glucocorticoid receptor (GR), was assessed by gene reporter assays and EMSA. Transcriptional activity of AhR was not influenced by any statin tested. Basal transcriptional activity of GR was not affected by tested statins, but dexamethasone-inducible activity of GR was dose-dependently and enantioselectively inhibited by fluvastatin. Basal and ligand-inducible transcriptional activity of PXR was dose-dependently influenced by all tested statins, and the potency and efficacy between individual optical isomers varied depending on statin and optical isomer. The expression of CYP1A1 and CYP1A2 in human hepatocytes was not influenced by tested statins. All statins induced CYP2A6, CYP2B6 and CYP3A4, and the effects on CYP2C9 were rather modulatory. The effects varied between statins and enantiomers and induction potency decreased in order: atorvastatin (RR>RS = SR>SS) > fluvastatin (SR>RS = SS>RR) >> rosuvastatin (only RS active). The data presented here might be of toxicological and clinical importance.

• MeSH
• Atorvastatin pharmacology   MeSH
• Cytochrome P-450 CYP3A biosynthesis   MeSH
• Cytochrome P-450 CYP2A6 biosynthesis   MeSH
• Cytochrome P-450 CYP2B6 biosynthesis   MeSH
• Adult MeSH
• Enzyme Induction drug effects   MeSH
• Fluvastatin MeSH
• Hepatocytes cytology   enzymology   MeSH
• Indoles pharmacology   MeSH
• Cytochrome P-450 CYP2B6 Inducers pharmacology   MeSH
• Cytochrome P-450 CYP3A Inducers pharmacology   MeSH
• Fatty Acids, Monounsaturated pharmacology   MeSH
• Middle Aged MeSH
• Humans MeSH
• Cell Line, Tumor MeSH
• Pregnane X Receptor MeSH
• Rosuvastatin Calcium pharmacology   MeSH
• Aged MeSH
• Stereoisomerism MeSH
• Receptors, Steroid biosynthesis   MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Atorvastatin MeSH
• CYP2A6 protein, human MeSH Browser
• CYP2B6 protein, human MeSH Browser
• CYP3A4 protein, human MeSH Browser
• Cytochrome P-450 CYP3A MeSH
• Cytochrome P-450 CYP2A6 MeSH
• Cytochrome P-450 CYP2B6 MeSH
• Fluvastatin MeSH
• Indoles MeSH
• Cytochrome P-450 CYP2B6 Inducers MeSH
• Cytochrome P-450 CYP3A Inducers MeSH
• Fatty Acids, Monounsaturated MeSH
• Pregnane X Receptor MeSH
• Rosuvastatin Calcium MeSH
• Receptors, Steroid MeSH