St. John's Wort alleviates dextran sodium sulfate-induced colitis through pregnane X receptor-dependent NFκB antagonism.

St. John's wort (SJW), from traditional herbs, activates the pregnane X receptor (PXR), a potential drug target for treating inflammatory bowel disease (IBD). However, how SJW alleviates dextran sodium sulfate (DSS)-induced experimental IBD by activating PXR is unknown. To test this, PXR-humanized, wild-type (WT) and Pxr-null mice, primary intestinal organoids cultures, and the luciferase reporter gene assays were employed. In vivo, a diet supplemented with SJW was found to activate intestinal PXR both in WT and PXR-humanized mice, but not in Pxr-null mice. SJW prevented DSS-induced IBD in PXR-humanized and WT mice, but not in Pxr-null mice. In vitro, hyperforin, a major component of SJW, activated PXR and suppressed tumor necrosis factor (TNF)α-induced nuclear factor (NF) κB translocation in primary intestinal organoids from PXR-humanized mice, but not Pxr-null mice. Luciferase reporter gene assays showed that hyperforin dose-dependently alleviated TNFα-induced NFκB transactivation by activating human PXR in Caco2 cells. Furthermore, SJW therapeutically attenuated DSS-induced IBD in PXR-humanized mice. These data indicate the therapeutic potential of SJW in alleviating DSS-induced IBD in vivo, and TNFα-induced NFκB activation in vitro, dependent on PXR activation, which may have clinical implications for using SJW as a herbal drug anti-IBD treatment.

Regulation of CAR and PXR Expression in Health and Disease.

Pregnane X receptor (PXR, NR1I2) and constitutive androstane receptor (CAR, NR1I3) are members of the nuclear receptor superfamily that mainly act as ligand-activated transcription factors. Their functions have long been associated with the regulation of drug metabolism and disposition, and it is now well established that they are implicated in physiological and pathological conditions. Considerable efforts have been made to understand the regulation of their activity by their cognate ligand; however, additional regulatory mechanisms, among which the regulation of their expression, modulate their pleiotropic effects. This review summarizes the current knowledge on CAR and PXR expression during development and adult life; tissue distribution; spatial, temporal, and metabolic regulations; as well as in pathological situations, including chronic diseases and cancers. The expression of CAR and PXR is modulated by complex regulatory mechanisms that involve the interplay of transcription factors and also post-transcriptional and epigenetic modifications. Moreover, many environmental stimuli affect CAR and PXR expression through mechanisms that have not been elucidated.

Associations between Pregnane X Receptor and Breast Cancer Growth and Progression.

Pregnane X receptor (PXR, NR1I2) is a member of the ligand-activated nuclear receptor superfamily. This receptor is promiscuous in its activation profile and is responsive to a broad array of both endobiotic and xenobiotic ligands. PXR is involved in pivotal cellular detoxification processes to include the regulation of genes that encode key drug-metabolizing cytochrome-P450 enzymes, oxidative stress response, as well as enzymes that drive steroid and bile acid metabolism. While PXR clearly has important regulatory roles in the liver and gastrointestinal tract, this nuclear receptor also has biological functions in breast tissue. In this review, we highlight current knowledge of PXR's role in mammary tumor carcinogenesis. The elevated level of PXR expression in cancerous breast tissue suggests a likely interface between aberrant cell division and xeno-protection in cancer cells. Moreover, PXR itself exerts positive effect on the cell cycle, thereby predisposing tumor cells to unchecked proliferation. Activation of PXR also plays a key role in regulating apoptosis, as well as in acquired resistance to chemotherapeutic agents. The repressive role of PXR in regulating inflammatory mediators along with the existence of genetic polymorphisms within the sequence of the PXR gene may predispose individuals to developing breast cancer. Further investigations into the role that PXR plays in driving tumorigenesis are needed.

Glucocorticoids Increase Renal Excretion of Urate in Mice by Downregulating Urate Transporter 1.

Both nonsteroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids have been widely used for the treatment of gout, a disease promoted by an excess body burden of uric acid (UA); however, their effects on the homeostasis of UA remain poorly understood. The present study showed that 1-week treatments with three NSAIDs (ibuprofen, diclofenac, and indomethacin) had little effect on UA homeostasis in mice, whereas 1-week low doses (1 and 5 mg/kg) of dexamethasone (DEX) significantly decreased serum UA by about 15%. Additionally, low doses of DEX also resulted in increases in hepatic UA concentration and urinary UA excretion, which were associated with an induction of xanthine oxidoreductase (XOR) in the liver and a downregulation of urate transporter 1 (URAT1) in the kidney, respectively. Neither 75 mg/kg DEX nor 100 mg/kg pregnenolone-16α-carbonitrile altered UA concentrations in serum and livers of mice, suggesting that the effect of DEX on UA homeostasis was not due to the pregnane X receptor pathway. Further in vitro studies demonstrated that glucocorticoid receptor (GR) was involved in DEX-mediated downregulation of URAT1. Knockdown of both p65 and c-Jun completely blocked the effect of DEX on URAT1, suggesting that GR regulates URAT1 via its interaction with both nuclear factor κB and activator protein 1 signaling pathways. To conclude, the present study identifies, for the first time, a critical role of glucocorticoids in regulating UA homeostasis and elucidates the mechanism for GR-mediated regulation of URAT1 in mice. SIGNIFICANCE STATEMENT: This study demonstrates, for the first time, a critical role of glucocorticoid receptor in regulating urate transporter 1 in mouse kidney.

Effect of panaxytriol on cytochrome P450 3A4 via the pregnane X receptor regulatory pathway.

Panaxytriol (PXT) is one of the major effective components of red ginseng and Shenmai injection. The present study aimed to explore the effect of PXT on cytochrome P450 3A4 (CYP3A4) based on the pregnane X receptor (PXR)-CYP3A4 regulatory pathway in HepG2 cells and hPXR-overexpressing HepG2 cells treated with PXT for different time periods using quantitative polymerase chain reaction, Western blot, and dual-luciferase reporter gene assays. PXT could upregulate the levels of PXR and CYP3A4 mRNA in HepG2 cells treated with PXT for 1 hr, with no impact on the expression of their protein levels. The expression levels of both PXR and CYP3A4 mRNA and protein in HepG2 cells treated with PXT for 24 hr increased in a concentration-dependent manner. The effects of PXT on the expression of PXR and CYP3A4 mRNA and protein in hPXR-overexpressing HepG2 cells were similar to those in HepG2 cells. Moreover, the influence trend of PXT on CYP3A4 was consistent with that of PXR in HepG2 cells and hPXR-overexpressing HepG2 cells. The dual-luciferase reporter gene assay in HepG2 cells further demonstrated that PXT treatment for specific time periods could significantly induce the expression of CYP3A4 mediated by the PXR regulatory pathway.

Porcine interleukin-6 enhances the expression of CYP2C33 through a constitutive androstane receptor/retinoid X receptor-mediated pathway.

Cytochrome P450, which is expressed in humans and other animals, is a superfamily of drug-metabolizing enzymes that play important roles in the metabolism of endogenous and xenobiotic substrates via oxidation, peroxidation and reduction. Of endogenous substrates, interleukin (IL)-6 is a crucial cytokine involved in inflammation in the liver. The present study aims to elucidate the mechanisms through which IL-6 modulates cytochrome P450 expression. CYP2C33 expression was found to be increased in HepLi cells and primary porcine hepatocytes treated with IL-6 in a concentration-dependent manner. IL-6 treatment also increased the expression of the transcriptional regulators, constitutive androstane receptor (CAR) and pregnane X receptor. Overexpression of CAR promoted CYP2C33 expression at the mRNA and protein levels, whereas knockdown of CAR by small interfering RNA reduced CYP2C33 expression. Luciferase assays showed that IL-6 treatment of HepLi cells and primary porcine hepatocytes increased CYP2C33 promoter activity. Co-immunoprecipitation and western blotting demonstrated that CAR and RXR could form heterodimers. IL-6 affects CYP2C33 expression through CAR/retinoid X receptor (RXR) heterodimers.

ETS-1 induces Sorafenib-resistance in hepatocellular carcinoma cells via regulating transcription factor activity of PXR.

Transcription factor E26 transformation specific sequence 1 (ETS-1) is a primary regulator in the metastasis of human cancer cells, especially hepatocellular carcinoma (HCC) cells; and it would affect the prognosis of HCC patients who received chemotherapies. However, the regulatory role of ETS-1 in the resistance of HCC cells to molecular-targeting agent remains poorly understood. In the present work, we demonstrate that high ETS-1 expression correlates with poor prognosis of advanced HCC patients received Sorafenib treatment. Mechanistically, ETS-1 binds to nuclear Pregnane X receptor (PXR) directly and enhances PXR's transcription factor activity, which further leads to the induction of the PXR's downstream multi-drug resistance related genes. Overexpression of ETS-1 accelerates the metabolic clearance of Sorafenib in HCC cells and leads to the better survival and faster migration of those cells. The therapeutic studies show that ETS-1 promotes the Sorafenib-resistance of HCC tumor models and ETS-1 blockade enhances the anti-tumor capacity of Sorafenib by decreasing PXR activation. Thus, our study suggests that ETS-1 could enhance the activation of PXR and be a potential therapeutic target for overcoming Sorafenib resistance in HCC treatment.