Pregnane X receptor as a therapeutic target to inhibit androgen activity

Single Nucleotide Polymorphisms Associated with Prostate Cancer Progression: A Systematic Review

BACKGROUND

New biomarkers of progression in patients with prostate cancer (PCa) are needed to improve their classification and clinical management. This systematic review investigated the relationship between single nucleotide polymorphisms (SNPs) and PCa progression.

METHODS

A keyword search was performed in Pubmed, EMBASE, Scopus, Web of Science, and Cochrane for publications between 2007 and 2022. We included articles with adjusted and significant associations, a median follow-up greater than or equal to 24 months, patients taken to radical prostatectomy (RP) as a first therapeutic option, and results presented based on biochemical recurrence (BCR).

RESULTS

In the 27 articles selected, 73 SNPs were identified in 39 genes, organized in seven functional groups. Of these, 50 and 23 SNPs were significantly associated with a higher and lower risk of PCa progression, respectively. Likewise, four haplotypes were found to have a significant association with PCa progression.

CONCLUSION

This article highlights the importance of SNPs as potential markers of PCa progression and their possible functional relationship with some genes relevant to its development and progression. However, most variants were identified only in cohorts from two countries; no additional studies reproduce these findings.

Tris(1,3-dichloro-2-propyl) phosphate is a metabolism-disrupting chemical in male mice

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) is an organophosphate flame retardant. The primary TDCPP metabolite, bis(1,3-dichloro-2-propyl) phosphate (BDCPP), is detectable in the urine of over 90 % of Americans. Epidemiological studies show sex-specific associations between urinary BDCPP levels and metabolic syndrome, which is an established risk factor for type 2 diabetes, heart disease, and stroke. We used a mouse model to determine whether TDCPP exposure disrupts glucose homeostasis. Six-week old male and female C57BL/6J mice were given ad libitum access to diets containing vehicle (0.1 % DMSO) and TDCPP resulting in the following treatment groups: 0 mg/kg/day, 0.02 mg/kg/day, 1 mg/kg/day, or 100 mg/kg/day. After being on the experimental diet for five weeks without interruption, body composition was analyzed, glucose and insulin tolerance tests were performed, and fasting glucose and insulin levels were quantified. TDCPP at 100 mg/kg/day caused male sex-specific adiposity, fasting hyperglycemia, and insulin resistance. TDCPP-induced modulation of nuclear receptor activation was investigated using an in vitro screen to identify potential mechanisms of metabolic disruption. TDCPP activated farnesoid X receptor (FXR) and pregnane X receptor (PXR), and inhibited the androgen receptor (AR). PXR target genes, but not FXR target genes, were upregulated in livers from mice exposed to 100 mg TDCPP/kg/day. Interestingly, PXR target genes were differentially expressed in livers from both males and females. It remains to be determined whether TDCPP-induced metabolic disruption occurs via modulation of nuclear receptor activity. Taken together, these studies build upon the association of TDCPP exposure and metabolic syndrome in humans by identifying sex-specific effects of TDCPP on glucose homeostasis in mice.

Orphan receptors in prostate cancer

BACKGROUND

The identification of new cellular receptors has been increasing rapidly. A receptor is called "orphan" if an endogenous ligand has not been identified yet.

METHODS

Here we review receptors that contribute to prostate cancer and are considered orphan or partially orphan. This means that the full spectrum of their endogenous ligands remains unknown.

RESULTS

The orphan receptors are divided into two major families. The first group includes G protein-coupled receptors. Most are orphan olfactory receptors. OR51E1 inhibits cell proliferation and induces senescence in prostate cancer. OR51E2 inhibits prostate cancer growth, but promotes invasiveness and metastasis. GPR158, GPR110, and GPCR-X play significant roles in prostate cancer development and progression. However, GPR160 induces cell cycle arrest and apoptosis. The other major subset of orphan receptors are nuclear receptors. Receptor-related orphan receptor α (RORα) inhibits tumor growth, but RORγ stimulates androgen receptor signaling. PXR contributes to metabolic deactivation of androgens and inhibits cell proliferation. TLX has protumorigenic effects in prostate cancer, while its knockdown triggers cellular senescence and growth arrest. Estrogen-related receptor ERRγ can inhibit tumor growth but ERRα is protumorigenic. Dax1 and short heterodimeric partner are also inhibitory in prostate cancer.

CONCLUSION

There is a "zoo" of relatively underappreciated orphan receptors that play key roles in prostate cancer.

The role of pregnane X receptor (PXR) in substance metabolism

As a member of the nuclear receptor (NR) superfamily, pregnane X receptor (PXR; NR1I2) is a ligand-activated transcription factor that plays a crucial role in the metabolism of xenobiotics and endobiotics in mammals. The tissue distribution of PXR is parallel to its function with high expression in the liver and small intestine and moderate expression in the kidney, stomach, skin, and blood-brain barrier, which are organs and tissues in frequent contact with xenobiotics. PXR was first recognized as an exogenous substance receptor regulating metabolizing enzymes and transporters and functioning in detoxification and drug metabolism in the liver. However, further research revealed that PXR acts as an equally important endogenous substance receptor in the metabolism and homeostasis of endogenous substances. In this review, we summarized the functions of PXR in metabolism of different substances such as glucose, lipid, bile acid, vitamin, minerals, and endocrines, and also included insights of the application of PXR ligands (drugs) in specific diseases.

Aging, hormones and receptors

Ageing is accompanied by deterioration in physical condition and a number of physiological processes and thus a higher risk of a range of diseases and disorders. In particular, we focused on the changes associated with aging, especially the role of small molecules, their role in physiological and pathophysiological processes and potential treatment options. Our previously published results and data from other authors lead to the conclusion that these unwanted changes are mainly linked to the hypothalamic-pituitary-adrenal axis can be slowed down, stopped, or in some cases even reversed by an appropriate treatment, but especially by a life-management adjustment.

PXR Modulates the Prostate Cancer Cell Response to Afatinib by Regulating the Expression of the Monocarboxylate Transporter SLC16A1

Simple Summary

Many kinase inhibitors have been tested as potential alternatives for the treatment of castration-resistant prostate cancers. However, none of these clinical trials led to drug approval despite interesting responses. Our study reveals that genes involved in drug metabolism and their master regulator PXR (Pregnane X Receptor) could be responsible, at least in part, for these disappointing results as they can modulate tumor cell response to specific kinase inhibitors. We found that stable expression of PXR sensitized prostate cancer cells to erlotinib, dabrafenib, and afatinib, while it rendered cells resistant to dasatinib and had no effect for other inhibitors tested. We also report for the first time that sensitization to afatinib is due to an alteration in drug transport that involves the SLC16A1 monocarboxylate transporter. Together, our results further indicate that PXR might be considered as a biomarker of response to kinase inhibitors in castration-resistant prostate cancers.

Abstract

Resistance to castration is a crucial issue in the treatment of metastatic prostate cancer. Kinase inhibitors (KIs) have been tested as potential alternatives, but none of them are approved yet. KIs are subject of extensive metabolism at both the hepatic and the tumor level. Here, we studied the role of PXR (Pregnane X Receptor), a master regulator of metabolism, in the resistance to KIs in a prostate cancer setting. We confirmed that PXR is expressed in prostate tumors and is more frequently detected in advanced forms of the disease. We showed that stable expression of PXR in 22Rv1 prostate cancer cells conferred a resistance to dasatinib and a higher sensitivity to erlotinib, dabrafenib, and afatinib. Higher sensitivity to afatinib was due to a ~ 2-fold increase in its intracellular accumulation and involved the SLC16A1 transporter as its pharmacological inhibition by BAY-8002 suppressed sensitization of 22Rv1 cells to afatinib and was accompanied with reduced intracellular concentration of the drug. We found that PXR could bind to the SLC16A1 promoter and induced its transcription in the presence of PXR agonists. Together, our results suggest that PXR could be a biomarker of response to kinase inhibitors in castration-resistant prostate cancers.

The pregnane X receptor drives sexually dimorphic hepatic changes in lipid and xenobiotic metabolism in response to gut microbiota in mice

BACKGROUND

The gut microbiota-intestine-liver relationship is emerging as an important factor in multiple hepatic pathologies, but the hepatic sensors and effectors of microbial signals are not well defined.

RESULTS

By comparing publicly available liver transcriptomics data from conventional vs. germ-free mice, we identified pregnane X receptor (PXR, NR1I2) transcriptional activity as strongly affected by the absence of gut microbes. Microbiota depletion using antibiotics in Pxr^+/+ vs Pxr^-/- C57BL/6J littermate mice followed by hepatic transcriptomics revealed that most microbiota-sensitive genes were PXR-dependent in the liver in males, but not in females. Pathway enrichment analysis suggested that microbiota-PXR interaction controlled fatty acid and xenobiotic metabolism. We confirmed that antibiotic treatment reduced liver triglyceride content and hampered xenobiotic metabolism in the liver from Pxr^+/+ but not Pxr^-/- male mice.

CONCLUSIONS

These findings identify PXR as a hepatic effector of microbiota-derived signals that regulate the host's sexually dimorphic lipid and xenobiotic metabolisms in the liver. Thus, our results reveal a potential new mechanism for unexpected drug-drug or food-drug interactions. Video abstract.

Gut Microbiome Alters the Activity of Liver Cytochromes P450 in Mice With Sex-Dependent Differences

Sexual differences and the composition/function of the gut microbiome are not considered the most important players in the drug metabolism field; however, from the recent data it is obvious that they may significantly affect the response of the patient to therapy. Here, we evaluated the effect of microbial colonization and sex differences on mRNA expression and the enzymatic activity of hepatic cytochromes P450 (CYPs) in germ-free (GF) mice, lacking the intestinal flora, and control specific-pathogen-free (SPF) mice. We observed a significant increase in the expression of Cyp3a11 in female SPF mice compared to the male group. However, the sex differences were erased in GF mice, and the expression of Cyp3a11 was about the same in both sexes. We have also found higher Cyp2c38 gene expression in female mice compared to male mice in both the SPF and GF groups. Moreover, these changes were confirmed at the level of enzymatic activity, where the female mice exhibit higher levels of functional CYP2C than males in both groups. Interestingly, we observed the same trend as with CYP3A enzymes: a diminished difference between the sexes in GF mice. The presented data indicate that the mouse gut microbiome plays an important role in sustaining sexual dimorphism in terms of hepatic gene expression and metabolism.

Inhibition of LXR signaling by SULT2B1b promotes liver regeneration after partial hepatectomy in mouse models of nonalcoholic fatty liver disease

Hydroxysteroid sulfotransferase 2B1b (SULT2B1b) plays a critical role in hepatic energy homeostasis. Liver X receptors (LXRs) are implicated in multiple physiological functions, including the inhibition of hepatocyte proliferation and regulation of fatty acid and cholesterol metabolism. We have previously reported that SULT2B1b promotes hepatocyte proliferation by inactivating LXR signaling in vivo and in vitro, leading to our hypothesis that SULT2B1b promotes fatty liver regeneration. In the present study, female C57BL/6 and S129 mice were fed a high-fat diet for 8 wk to establish a nonalcoholic fatty liver disease (NAFLD) mouse model. 70% partial hepatectomy (PH) was performed to induce liver regeneration. Our experiments revealed that the SULT2B1b overexpression significantly promotes the regeneration of hepatocytes in NAFLD C57BL/6 mice after PH, increasing liver regrowth by 11% within 1 day, and then by 21%, 33%, and 24% by 2, 3, and 5 days post-PH, respectively. Compared with the wild-type NAFLD S129 mice, SULT2B1 deletion NAFLD S129 mice presented reduced hepatocyte regeneration at postoperative day 2, as verified by decreased liver regrowth (37.4% vs. 46.1%, P < 0.05) and the results of immunohistochemical staining, quantitative real-time polymerase chain reaction, and Western blot analysis. Moreover, LXRα signaling and SULT2B1b expression are highly correlated in the regeneration of NAFLD mouse liver; SULT2B1b overexpression suppresses LXRα signaling, while the LXRα-signaling agonist T0901317 blocks SULT2B1b-induced hepatocyte regeneration in NAFLD mouse liver. Thus, the upregulation of SULT2B1b may promote hepatocyte regeneration via the suppression of LXRα activation in NAFLD mice, providing a potential strategy for improving hepatic-steatosis-related liver regeneration disorders.NEW & NOTEWORTHY This study demonstrates for the first time that hydroxysteroid sulfotransferase 2B1b (SULT2B1b) overexpression promotes the regeneration of fatty liver after partial hepatectomy in mice with nonalcoholic fatty liver disease, while reducing triglyceride accumulation in the regenerative fatty liver. Liver X receptor signaling may be crucial in the SULT2B1b-mediated regeneration of fatty liver. Thus, SULT2B1b may be a potential target for treating hepatic steatosis-related liver regeneration disorders.

Genetic Analysis Reveals a Significant Contribution of CES1 to Prostate Cancer Progression in Taiwanese Men

The genes that influence prostate cancer progression remain largely unknown. Since the carboxylesterase gene family plays a crucial role in xenobiotic metabolism and lipid/cholesterol homeostasis, we hypothesize that genetic variants in carboxylesterase genes may influence clinical outcomes for prostate cancer patients. A total of 478 (36 genotyped and 442 imputed) single nucleotide polymorphisms (SNPs) in five genes of the carboxylesterase family were assessed in terms of their associations with biochemical recurrence (BCR)-free survival in 643 Taiwanese patients with prostate cancer who underwent radical prostatectomy. The strongest association signal was shown in CES1 (P = 9.64×10^-4 for genotyped SNP rs8192935 and P = 8.96 × 10^-5 for imputed SNP rs8192950). After multiple test correction and adjustment for clinical covariates, CES1 rs8192935 (P = 9.67 × 10^-4) and rs8192950 (P = 9.34 × 10^-5) remained significant. These SNPs were correlated with CES1 expression levels, which in turn were associated with prostate cancer aggressiveness. Furthermore, our meta-analysis, including eight studies, indicated that a high CES1 expression predicted better outcomes among prostate cancer patients (hazard ratio 0.82, 95% confidence interval 0.70-0.97, P = 0.02). In conclusion, our findings suggest that CES1 rs8192935 and rs8192950 are associated with BCR and that CES1 plays a tumor suppressive role in prostate cancer.

Activation of Adrenal Steroidogenesis and an Improvement of Mood Balance in Postmenopausal Females after Spa Treatment Based on Physical Activity

Spa treatment can effectively reestablish mood balance in patients with psychiatric disorders. In light of the adrenal gland’s role as a crossroad of psychosomatic medicine, this study evaluated changes in 88 circulating steroids and their relationships with a consolidation of somatic, psychosomatic and psychiatric components from a modified N-5 neurotic questionnaire in 46 postmenopausal 50+ women with anxiety-depressive complaints. The patients underwent a standardized one-month intervention therapy with physical activity and an optimized daily regimen in a spa in the Czech Republic. All participants were on medication with selective serotonin reuptake inhibitors. An increase of adrenal steroidogenesis after intervention indicated a reinstatement of the hypothalamic-pituitary-adrenal axis. The increases of many of these steroids were likely beneficial to patients, including immunoprotective adrenal androgens and their metabolites, neuroactive steroids that stimulate mental activity but protect from excitotoxicity, steroids that suppress pain perception and fear, steroids that consolidate insulin secretion, and steroids that improve xenobiotic clearance. The positive associations between the initial values of neurotic symptoms and their declines after the intervention, as well as between initial adrenal activity and the decline of neurotic symptoms, indicate that neurotic impairment may be alleviated by such therapy provided that the initial adrenal activity is not seriously disrupted.

KLF15 regulates endobiotic and xenobiotic metabolism

Hepatic metabolism and elimination of endobiotics (for example, steroids, bile acids) and xenobiotics (for example, drugs, toxins) is essential for health. While the enzymatic (termed phase I-II) and transport machinery (termed phase III) controlling endobiotic and xenobiotic metabolism (EXM) is known, understanding of molecular nodal points that coordinate EXM function in physiology and disease remains incomplete. Here we show that the transcription factor Kruppel-like factor 15 (KLF15) regulates all three phases of the EXM system by direct and indirect pathways. Unbiased transcriptomic analyses coupled with validation studies in cells, human tissues, and animals, support direct transcriptional control of the EXM machinery by KLF15. Liver-specific deficiency of KLF15 (Li-KO) results in altered expression of numerous phase I-III targets, and renders animals resistant to the pathologic effects of bile acid and acetaminophen toxicity. Furthermore, Li-KO mice demonstrate enhanced degradation and elimination of endogenous steroid hormones, such as testosterone and glucocorticoid, resulting in reduced male fertility and blood glucose levels, respectively. Viral reconstitution of hepatic KLF15 expression in Li-KO mice reverses these phenotypes. Our observations identify a previously unappreciated transcriptional pathway regulating metabolism and elimination of endobiotics and xenobiotics.

The Mouse Microbiome Is Required for Sex-Specific Diurnal Rhythms of Gene Expression and Metabolism

The circadian clock and associated feeding rhythms have a profound impact on metabolism and the gut microbiome. To what extent microbiota reciprocally affect daily rhythms of physiology in the host remains elusive. Here, we analyzed transcriptome and metabolome profiles of male and female germ-free mice. While mRNA expression of circadian clock genes revealed subtle changes in liver, intestine, and white adipose tissue, germ-free mice showed considerably altered expression of genes associated with rhythmic physiology. Strikingly, the absence of the microbiome attenuated liver sexual dimorphism and sex-specific rhythmicity. The resulting feminization of male and masculinization of female germ-free animals is likely caused by altered sexual development and growth hormone secretion, associated with differential activation of xenobiotic receptors. This defines a novel mechanism by which the microbiome regulates host metabolism.

Profiling of bisphenol A and eight its analogues on transcriptional activity via human nuclear receptors

Several bisphenol A (BPA) analogues have been detected in environmental samples, foodstuffs, and/or human biological samples, and there is concern regarding their potential endocrine-disrupting effects. In this study, we characterized the agonistic and/or antagonistic activities of BPA and eight its analogues against human estrogen receptors (ERα/β), androgen receptor (AR), glucocorticoid receptor (GR), pregnane X receptor (PXR), and constitutive androstane receptor (CAR). All the test compounds, except for bisphenol P (BPP), showed both ERα and ERβ agonistic activities, with bisphenol AF (BPAF) being the most potent. On the other hand, BPAF and BPP showed ERα and ERβ antagonistic activities. Interestingly, their ER activities demonstrated a preference toward ERβ. All the test compounds, except for bisphenol S, showed AR antagonistic activities, with bisphenol E being the most potent. Weak GR antagonistic activities were also found in BPA and five its analogues. PXR agonistic activity was observed in the six compounds, with bisphenol Z being the most potent. Results of the CAR assay revealed that BPA and five its analogues acted as CAR inverse agonists. Taken together, these results suggested that BPA analogues demonstrate multiple effects via human nuclear receptors in a similar manner to BPA, and several analogues might have more potent endocrine-disrupting activity than does BPA.

Estrogen and Androgen Blockade for Advanced Prostate Cancer in the Era of Precision Medicine

Androgen deprivation therapy (ADT) has been widely prescribed for patients with advanced prostate cancer (PC) to control key signaling pathways via androgen receptor (AR) and AR-collaborative transcriptional factors; however, PC gradually acquires a lethal phenotype and results in castration-resistant PC (CRPC) during ADT. Therefore, new therapeutic strategies are required in clinical practice. In addition, ARs; estrogen receptors (ERs; ERα and ERβ); and estrogen-related receptors (ERRs; ERRα, ERRβ, and ERRγ) have been reported to be involved in the development or regulation of PC. Recent investigations have revealed the role of associated molecules, such as KLF5, FOXO1, PDGFA, VEGF-A, WNT5A, TGFβ1, and micro-RNA 135a of PC, via ERs and ERRs. Selective ER modulators (SERMs) have been developed. Recently, estrogen and androgen blockade (EAB) using a combination of toremifene and ADT has been demonstrated to improve biochemical recurrence rate in treatment-naïve bone metastatic PC. In the future, the suitability of ADT alone or EAB for individuals may be evaluated by making clinical decisions on the basis of information obtained from RT-PCR, gene-panel, or liquid biopsy to create a “personalized medicine” or “precision medicine”. In this review, we summarize ER and ERR signaling pathways, molecular diagnosis, and SERMs as candidates for advanced PC treatment.

Cyp3a deficiency enhances androgen receptor activity and cholesterol synthesis in the mouse prostate

Testosterone regulates cellular functions in the prostate through activation of the androgen receptor (AR), which may enhance expression levels of cholesterogenic enzymes through activation of sterol regulatory element-binding protein2 (SREBP2). Because testosterone is inactivated to 6β-hydroxytestosterone by cytochrome P450 3A (CYP3A), we examined the effects of Cyp3a deficiency on circulating testosterone levels and its effects on activation of the AR and expression levels of cholesterogenic enzymes in the prostate using Cyp3a-knockout (Cyp3a(-/-)) mice. The results showed that Cyp3a(-/-) mice had remarkably increased free testosterone levels in plasma along with suppressed testosterone 6β-hydroxylation activities in liver microsomes, suggesting that Cyp3a is a major determinant of systemic levels of testosterone in mice. The results also showed that mRNA expression levels of the AR target genes were increased significantly, and that AR bindings to the promoter region of the AR target genes were more abundant in the prostates of Cyp3a(-/-) mice. These findings suggest that AR activation was stimulated in the prostate of Cyp3a(-/-) mice. In addition, the protein expression levels of SREBP cleavage-activating protein (SCAP), mRNA expression levels of SREBP2 target genes and total cholesterol contents were increased in the prostates of Cyp3a(-/-) mice. The findings suggest that Cyp3a deficiency stimulated the expression of Scap via activation of the AR, which elevated cholesterogenic gene expression levels through activation of SREBP2 and increased total cholesterol contents in the prostate.

Pregnane X Receptor and Cancer: Context-Specificity is Key

Pregnane X receptor (PXR) is an adopted orphan nuclear receptor that is activated by a wide-range of endobiotics and xenobiotics, including chemotherapy drugs. PXR plays a major role in the metabolism and clearance of xenobiotics and endobiotics in liver and intestine via induction of drug-metabolizing enzymes and drug-transporting proteins. However, PXR is expressed in several cancer tissues and the accumulating evidence strongly points to the differential role of PXR in cancer growth and progression as well as in chemotherapy outcome. In cancer cells, besides regulating the gene expression of enzymes and proteins involved in drug metabolism and transport, PXR also regulates other genes involved in proliferation, metastasis, apoptosis, anti-apoptosis, inflammation, and oxidative stress. In this review, we focus on the differential role of PXR in a variety of cancers, including prostate, breast, ovarian, endometrial, and colon. We also discuss the future directions to further understand the differential role of PXR in cancer, and conclude with the need to identify novel selective PXR modulators to target PXR in PXR-expressing cancers.

Transcriptional regulation of human hydroxysteroid sulfotransferase SULT2A1 by LXRα

The nuclear receptor liver X receptor (LXR) plays an important role in the metabolism and homeostasis of cholesterol, lipids, bile acids, and steroid hormones. In this study, we uncovered a function of LXRα (NR1H3) in regulating the human hydroxysteroid sulfotransferase SULT2A1, a phase II conjugating enzyme known to sulfonate bile acids, hydroxysteroid dehydroepiandrosterone, and related androgens. We showed that activation of LXR induced the expression of SULT2A1 at mRNA, protein, and enzymatic levels. A combination of promoter reporter gene and chromatin immunoprecipitation assays showed that LXRα transactivated the SULT2A1 gene promoter through its specific binding to the -500- to -258-base pair region of the SULT2A1 gene promoter. LXR small interfering RNA knockdown experiments suggested that LXRα, but not LXRβ, played a dominant role in regulating SULT2A1. In primary human hepatocytes, we found a positive correlation between the expression of SULT2A1 and LXRα, which further supported the regulation of SULT2A1 by LXRα. In summary, our results established human SULT2A1 as a novel LXRα target gene. The expression of LXRα is a potential predictor for the expression of SULT2A1 in human liver.

Biology of PXR: role in drug-hormone interactions

Hormonal homeostasis is essential for a variety of physiological and pathological processes. Elimination and detoxification of xenobiotics, such as drugs introduced into the human body, could disrupt the balance of hormones due to the induction of drug metabolizing enzymes (DMEs) and transporters. Pregnane X receptor (PXR, NR1I2) functions as a master xenobiotic receptor involved in drug metabolism and drug-drug interactions by its coordinated transcriptional regulation of phase I and phase II DMEs and transporters. Recently, increasing evidences indicate that PXR can also mediate the endocrine disruptor function and thus impact the integrity of the endocrine system. This review focuses primarily on the recent advances in our understanding of the function of PXR in glucocorticoid, mineralocorticoid, androgen and estrogen homeostasis. The elucidation of PXR-mediated drug-hormone interactions might have important therapeutic implications in dealing with hormone-dependent diseases and safety assessment of drugs.

The tumor suppressor TERE1 (UBIAD1) prenyltransferase regulates the elevated cholesterol phenotype in castration resistant prostate cancer by controlling a program of ligand dependent SXR target genes

Castrate-Resistant Prostate Cancer (CRPC) is characterized by persistent androgen receptor-driven tumor growth in the apparent absence of systemic androgens. Current evidence suggests that CRPC cells can produce their own androgens from endogenous sterol precursors that act in an intracrine manner to stimulate tumor growth. The mechanisms by which CRPC cells become steroidogenic during tumor progression are not well defined. Herein we describe a novel link between the elevated cholesterol phenotype of CRPC and the TERE1 tumor suppressor protein, a prenyltransferase that synthesizes vitamin K-2, which is a potent endogenous ligand for the SXR nuclear hormone receptor. We show that 50% of primary and metastatic prostate cancer specimens exhibit a loss of TERE1 expression and we establish a correlation between TERE1 expression and cholesterol in the LnCaP-C81 steroidogenic cell model of the CRPC. LnCaP-C81 cells also lack TERE1 protein, and show elevated cholesterol synthetic rates, higher steady state levels of cholesterol, and increased expression of enzymes in the de novo cholesterol biosynthetic pathways than the non-steroidogenic prostate cancer cells. C81 cells also show decreased expression of the SXR nuclear hormone receptor and a panel of directly regulated SXR target genes that govern cholesterol efflux and steroid catabolism. Thus, a combination of increased synthesis, along with decreased efflux and catabolism likely underlies the CRPC phenotype: SXR might coordinately regulate this phenotype. Moreover, TERE1 controls synthesis of vitamin K-2, which is a potent endogenous ligand for SXR activation, strongly suggesting a link between TERE1 levels, K-2 synthesis and SXR target gene regulation. We demonstrate that following ectopic TERE1 expression or induction of endogenous TERE1, the elevated cholesterol levels in C81 cells are reduced. Moreover, reconstitution of TERE1 expression in C81 cells reactivates SXR and switches on a suite of SXR target genes that coordinately promote both cholesterol efflux and androgen catabolism. Thus, loss of TERE1 during tumor progression reduces K-2 levels resulting in reduced transcription of SXR target genes. We propose that TERE1 controls the CPRC phenotype by regulating the endogenous levels of Vitamin K-2 and hence the transcriptional control of a suite of steroidogenic genes via the SXR receptor. These data implicate the TERE1 protein as a previously unrecognized link affecting cholesterol and androgen accumulation that could govern acquisition of the CRPC phenotype.

Cholesterol sulfate and cholesterol sulfotransferase inhibit gluconeogenesis by targeting hepatocyte nuclear factor 4α

Sulfotransferase (SULT)-mediated sulfation represents a critical mechanism in regulating the chemical and functional homeostasis of endogenous and exogenous molecules. The cholesterol sulfotransferase SULT2B1b catalyzes the sulfoconjugation of cholesterol to synthesize cholesterol sulfate (CS). In this study, we showed that the expression of SULT2B1b in the liver was induced in obese mice and during the transition from the fasted to the fed state, suggesting that the regulation of SULT2B1b is physiologically relevant. CS and SULT2B1b inhibited gluconeogenesis by targeting the gluconeogenic factor hepatocyte nuclear factor 4α (HNF4α) in both cell cultures and transgenic mice. Treatment of mice with CS or transgenic overexpression of the CS-generating enzyme SULT2B1b in the liver inhibited hepatic gluconeogenesis and alleviated metabolic abnormalities both in mice with diet-induced obesity (DIO) and in leptin-deficient (ob/ob) mice. Mechanistically, CS and SULT2B1b inhibited gluconeogenesis by suppressing the expression of acetyl coenzyme A (acetyl-CoA) synthetase (Acss), leading to decreased acetylation and nuclear exclusion of HNF4α. Our results also suggested that leptin is a potential effector of SULT2B1b in improving metabolic function. We conclude that SULT2B1b and its enzymatic by-product CS are important metabolic regulators that control glucose metabolism, suggesting CS as a potential therapeutic agent and SULT2B1b as a potential therapeutic target for metabolic disorders.

Sulfotransferase genes: regulation by nuclear receptors in response to xeno/endo-biotics

Pregnane X receptor (PXR) and constitutive active/androstane receptor (CAR), members of the nuclear receptor superfamily, are two major xeno-sensing transcription factors. They can be activated by a broad range of lipophilic xenobiotics including therapeutics drugs. In addition to xenobiotics, endogenous compounds such as steroid hormones and bile acids can also activate PXR and/or CAR. These nuclear receptors regulate genes that encode enzymes and transporters that metabolize and excrete both xenobiotics and endobiotics. Sulfotransferases (SULTs) are a group of these enzymes and sulfate xenobiotics for detoxification. In general, inactivation by sulfation constitutes the mechanism to maintain homeostasis of endobiotics. Thus, deciphering the molecular mechanism by which PXR and CAR regulate SULT genes is critical for understanding the roles of SULTs in the alterations of physiological and pathophysiological processes caused by drug treatment or environmental exposures.

PXR antagonists and implication in drug metabolism

Adopted orphan nuclear receptor (NR), pregnane X receptor (PXR), plays a central role in the regulation of xeno- and endobiotic metabolism. Since the discovery of the functional role of PXR in 1998, there is evolving evidence for the role of PXR agonists in abrogating metabolic pathophysiology (e.g., cholestasis, hypercholesterolemia, and inflammation). However, more recently, it is clear that PXR is also an important mediator of adverse xeno- (e.g., enhances acetaminophen toxicity) and endobiotic (e.g., hepatic steatosis) metabolic phenotypes. Moreover, in cancer therapeutics, PXR activation can induce drug resistance, and there is growing evidence for tissue-specific enhancement of the malignant phenotype. Thus, in these instances, there may be a role for PXR antagonists. However, as opposed to the discovery efforts for PXR agonists, there are only a few antagonists described. The mode of action of these antagonists (e.g., sulforaphane) remains less clear. Our laboratory efforts have focused on this question. Since the original discovery of azoles analogs as PXR antagonists, we have preliminarily defined an important PXR antagonist pharmacophore and developed less-toxic PXR antagonists. In this review, we describe our published and unpublished findings on recent structure-function studies involving the azole chemical scaffold. Further work in the future is needed to fully define potent, more-selective PXR antagonists that may be useful in clinical application.

Activation of human stearoyl-coenzyme A desaturase 1 contributes to the lipogenic effect of PXR in HepG2 cells

The pregnane X receptor (PXR) was previously known as a xenobiotic receptor. Several recent studies suggested that PXR also played an important role in lipid homeostasis but the underlying mechanism remains to be clearly defined. In this study, we found that rifampicin, an agonist of human PXR, induced lipid accumulation in HepG2 cells. Lipid analysis showed the total cholesterol level increased. However, the free cholesterol and triglyceride levels were not changed. Treatment of HepG2 cells with rifampicin induced the expression of the free fatty acid transporter CD36 and ABCG1, as well as several lipogenic enzymes, including stearoyl-CoA desaturase-1 (SCD1), long chain free fatty acid elongase (FAE), and lecithin-cholesterol acyltransferase (LCAT), while the expression of acyl:cholesterol acetyltransferase(ACAT1) was not affected. Moreover, in PXR over-expressing HepG2 cells (HepG2-PXR), the SCD1 expression was significantly higher than in HepG2-Vector cells, even in the absence of rifampicin. Down-regulation of PXR by shRNA abolished the rifampicin-induced SCD1 gene expression in HepG2 cells. Promoter analysis showed that the human SCD1 gene promoter is activated by PXR and a novel DR-7 type PXR response element (PXRE) response element was located at -338 bp of the SCD1 gene promoter. Taken together, these results indicated that PXR activation promoted lipid synthesis in HepG2 cells and SCD1 is a novel PXR target gene.

Expression of the PXR gene in various types of cancer and drug resistance

Pregnane X receptor (PXR) is a member of the nuclear receptor superfamily of ligand-regulated transcription factors. PXR is a key xenobiotic receptor that regulates the expression of genes implicated in drug metabolism, detoxification and clearance, including drug metabolizing enzymes and transporters, suggesting that it is significant in the drug resistance of cancer cells. PXR is expressed in a wide range of tissues in the human body. Studies have demonstrated that PXR is expressed in a variety of tumor types, correlating not only with drug resistance but also with the cell proliferation, apoptosis and prognosis of cancer. The purpose of the present review is to provide a comprehensive review of PXR and its potential roles in multidrug resistance and the biological characteristics of PXR-positive tumors.

Regulation of the human hydroxysteroid sulfotransferase (SULT2A1) by RORα and RORγ and its potential relevance to human liver diseases

The retinoid-related orphan receptors (RORs) were postulated to have functions in tissue development and circadian rhythm. In this study, we revealed a novel function of RORα (NR1F1) and RORγ (NR1F3) in regulating the human hydroxysteroid sulfotransferase (SULT2A1), a phase II conjugating enzyme known to sulfonate bile acids, hydroxysteroid dehydroepiandrosterone, and related androgens. A combination of promoter reporter gene assay and EMSA and chromatin immunoprecipitation (ChIP) assays showed that both RORα and RORγ transactivated the SULT2A1 gene promoter through their binding to a ROR response element found in the SULT2A1 gene promoter. Interestingly, this ROR response element overlaps with a previously reported constitutive androstane receptor response element on the same promoter. Down-regulation of RORα and/or RORγ by small interfering RNA inhibited the expression of endogenous SULT2A1. In primary human hepatocytes and human livers, we found a positive correlation between the expression of SULT2A1 and RORs, which further supported the regulation of SULT2A1 by RORs. We also found that the expression of RORα and RORγ was impaired in several liver disease conditions, such as steatosis/steatohepatitis, fibrosis, and hepatocellular carcinoma. The positive regulation of human SULT2A1 by RORs is opposite to the negative regulation of Sult2a1 by RORs in rodents. In summary, our results established SULT2A1 as a novel ROR target gene. The expression of RORs is a potential predictor for the expression of SULT2A1 as well as disease conditions.

Regulation of CYP3A4 and CYP3A5 expression and modulation of "intracrine" metabolism of androgens in prostate cells by liganded vitamin D receptor

We investigated the capacity for vitamin D receptor (VDR) to modulate the expression of CYP3A4 and other genes that may facilitate the oxidative inactivation of androgens such as testosterone and androstanediol within prostate cells. We report that exposure to the active hormonal form of vitamin D markedly increased gene expression of CYP3A4 and CYP3A5 and ultimately achieved levels of intracellular CYP3A enzyme activity within LNCaP prostate cancer cells that were comparable to that observed for Caco2 cells, an established model of CYP3A induction, and resulted in the increased turnover of testosterone to its inactive 6β-OH metabolite. We demonstrate that VDR directs CYP3A4 and CYP3A5 expression through binding to distinct regulatory motifs located within the 5' promoter regions of both genes. The current data highlight the potential application of VDR-based treatment regimes as a means to limit the bioavailability of growth-promoting androgens within the tumor microenvironment.

Pregnane xenobiotic receptor in cancer pathogenesis and therapeutic response

Pregnane xenobiotic receptor (PXR) is an orphan nuclear receptor that regulates the metabolism of endobiotics and xenobiotics. PXR is promiscuous and unique in that it is activated by a diverse group of xenochemicals, including therapeutic anticancer drugs and naturally-occurring endocrine disruptors. PXR has been predominantly studied to understand its regulatory role in xenobiotic clearance in liver and intestine via induction of drug metabolizing enzymes and drug transporters. PXR, however, is widely expressed and has functional implications in other normal and malignant tissues, including breast, prostate, ovary, endometrium and bone. The differential expression of PXR and its target genes in cancer tissues has been suggested to determine the prognosis of chemotherapeutic outcome. In addition, the emerging evidence points to the implications of PXR in regulating apoptotic and antiapoptotic as well as growth factor signaling that promote tumor proliferation and metastasis. In this review, we highlight the recent progress made in understanding the role of PXR in cancer, discuss the future directions to further understand the mechanistic role of PXR in cancer, and conclude with the need to identify novel selective PXR modulators.

Cytosolic sulfotransferase 2B1b promotes hepatocyte proliferation gene expression in vivo and in vitro

Cytosolic sulfotransferase 2B1b (SULT2B1b) catalyzes the sulfation of 3β-hydroxysteroids and functions as a selective cholesterol and oxysterol sulfotransferase. Activation of liver X receptors (LXRs) by oxysterols has been known to be an antiproliferative factor. Overexpression of SULT2B1b impairs LXR's response to oxysterols, by which it regulates lipid metabolism. The aim of this study was to investigate in vivo and in vitro effects of SULT2B1b on liver proliferation and the underlying mechanisms. Primary rat hepatocytes and C57BL/6 mice were infected with adenovirus encoding SULT2B1b. Liver proliferation was determined by measuring the proliferating cell nuclear antigen (PCNA) immunostaining labeling index. The correlation between SULT2B1b and PCNA expression in mouse liver tissues was determined by double immunofluorescence. Gene expressions were evaluated by quantitative real-time PCR and Western blot analysis. SULT2B1b overexpression in mouse liver tissues increased PCNA-positive cells in a dose- and time-dependent manner. The increased expression of PCNA in mouse liver tissues was only observed in the SULT2B1b transgenic cells. Small interference RNA SULT2B1b significantly inhibited cell cycle regulatory gene expressions in primary rat hepatocytes. LXR activation by T0901317 effectively suppressed SULT2B1b-induced gene expression in vivo and in vitro. SULT2B1b may promote hepatocyte proliferation by inactivating oxysterol/LXR signaling.

Lxrα regulates the androgen response in prostate epithelium

Benign prostatic hyperplasia is a nonmalignant enlargement of the prostate that commonly occurs in older men. We show that liver X receptor (Lxr)-α knockout mice (lxrα(-/-)) develop ventral prostate hypertrophy, correlating with an overaccumulation of secreted proteins in prostatic ducts and an alteration of vesicular trafficking in epithelial cells. In the fluid of the lxrα(-/-) prostates, spermine binding protein is highly accumulated and shows a 3000-fold increase of its mRNA. This overexpression is mediated by androgen hypersensitivity in lxrα(-/-) mice, restricted to the ventral prostate. Generation of chimeric recombinant prostates demonstrates that Lxrα is involved in the establishment of the epithelial-mesenchymal interactions in the mouse prostate. Altogether these results point out the crucial role of Lxrα in the homeostasis of the ventral prostate and suggest lxrα(-/-) mice may be a good model to investigate the molecular mechanisms of benign prostatic hyperplasia.

A mixture of an environmentally realistic concentration of a phthalate and herbicide reduces testosterone in male fathead minnow (Pimephales promelas) through a novel mechanism of action

Several chemicals that are used by humans, such as pesticides and plastics, are released into the aquatic environment through wastewater and runoff and have been shown to be potent disruptors of androgen synthesis at high concentrations. Although many of these chemicals have been studied in isolation, a large amount of uncertainty remains over how fish respond to low concentrations of anti-androgenic mixtures, which more accurately reflects how such chemicals are present in the aquatic environment. In this study male fathead minnows (FHM) (Pimephales promelas) were exposed to environmentally relevant concentrations of two anti-androgens, the herbicide linuron, and the plasticizer di(2-ethylhexyl) phthalate (DEHP) individually and as part of a mixture of the two for a 28-day period. At the end of this period there was a reduction in plasma testosterone (T) concentrations in male FHM exposed to the mixture, but not in FHM exposed individually to linuron or DEHP or the control FHM. There was also a significant reduction in 17β-estradiol (E2) in the DEHP-only and mixture exposed groups as compared to the control. Contrary to what has been previously published for these two chemicals in mammals, the lower plasma T concentrations in male FHM exposed to the mixture was not a result of the inhibition of genes involved in steroidogenesis; nor due to an increase in the expression of genes associated with peroxisome proliferation. Rather, an increase in relative transcript abundance for CYP3A4 in the liver and androgen- and estrogen-specific SULT2A1 and SULT1st2 in the testes provides evidence that the decrease in plasma T and E2 may be linked to increased steroid catabolism. Feedback from the pituitary is not repressed as the relative expression of follicle stimulating hormone β-subunit mRNA transcript levels in the brain was significantly higher in both DEHP and mixture exposed FHM. In addition, luteinizing hormone β-subunit mRNA transcript levels increased but were not significant in the mixture as compared to the control. Hormone receptor mRNA transcript levels in the liver and testes were not significantly different across all four exposure groups. This study highlights the importance of assessing environmentally relevant concentrations of mixtures when determining risk to aquatic organisms.

Activation of liver X receptor increases acetaminophen clearance and prevents its toxicity in mice

Overdose of acetaminophen (APAP), the active ingredient of Tylenol, is the leading cause of drug-induced acute liver failure in the United States. As such, it is necessary to develop novel strategies to prevent or manage APAP toxicity. In this report, we reveal a novel function of the liver X receptor (LXR) in preventing APAP-induced hepatotoxicity. Activation of LXR in transgenic (Tg) mice or by an LXR agonist conferred resistance to the hepatotoxicity of APAP, whereas the effect of LXR agonist on APAP toxicity was abolished in LXR-deficient mice. The increased APAP resistance in LXR Tg mice was associated with increased APAP clearance, increased APAP sulfation, and decreased formation of toxic APAP metabolites. The hepatoprotective effect of LXR may have resulted from the induction of antitoxic phase II conjugating enzymes, such as Gst and Sult2a1, as well as the suppression of protoxic phase I P450 enzymes, such as Cyp3a11 and Cyp2e1. Promoter analysis suggested the mouse Gst isoforms as novel transcriptional targets of LXR. The suppression of Cyp3a11 may be accounted for by the inhibitory effect of LXR on the PXR-responsive transactivation of Cyp3a11. The protective effect of LXR in preventing APAP toxicity is opposite to the sensitizing effect of pregnane X receptor, constitutive androstane receptor, and retinoid X receptor alpha.

CONCLUSION

We conclude that LXR represents a potential therapeutic target for the prevention and treatment of Tylenol toxicity.

Clinical significance of steroid and xenobiotic receptor and its targeted gene CYP3A4 in human prostate cancer

The steroid and xenobiotic receptor (SXR) regulates cytochrome P450 (CYP) enzymes, which are key inactivators of testosterone in the liver and prostate. In the present study, we investigated SXR expression in human prostate tissues. We determined SXR immunoreactivity using an anti-SXR antibody in benign (n = 78) and cancerous (n = 106) tissues obtained by radical prostatectomy. Stained slides were evaluated for the proportion and staining intensity of immunoreactive cells. Total immunoreactivity (IR) scores (range: 0-8) were calculated as the sum of the proportion and intensity scores. Associations between the clinicopathological features of the patients, SXR status, and CYP3A4 immunoreactivity were analyzed. Western blot analyses validated the specificity of the anti-SXR antibody in 293T cells transfected with pcDNA-FLAG-SXR. Positive (IR score: ≥ 2) nuclear SXR staining was observed in 91% (71/78) of benign foci and 47% (50/106) of cancerous lesions. Immunoreactivity scores were significantly lower in the cancerous lesions than in the benign foci (P < 0.0001). Clinicopathological analyses showed that cancer-specific survival in patients with high SXR IR scores (≥ 4) was significantly increased (P = 0.046). Combined data of present and previous studies showed that high IR scores for both the SXR and CYP3A4 correlated with significantly better cancer-specific survival rates in multivariate regression analyses (hazard ratio: 2.15, 95% confidence interval: 1.25-3.55, P = 0.007). We showed differential SXR expression in human prostate tissues. The high expression of the SXR and CYP3A4 is a strong prognostic indicator of favorable outcomes in prostate cancer, and could be a therapeutic target.

Nuclear receptor PXR, transcriptional circuits and metabolic relevance

The pregnane X receptor (PXR, NR1I2) is a ligand activated transcription factor that belongs to the nuclear hormone receptor (NR) superfamily. PXR is highly expressed in the liver and intestine, but low levels of expression have also been found in many other tissues. PXR plays an integral role in xenobiotic and endobiotic metabolism by regulating the expression of drug-metabolizing enzymes and transporters, as well as genes implicated in the metabolism of endobiotics. PXR exerts its transcriptional regulation by binding to its DNA response elements as a heterodimer with the retinoid X receptor (RXR) and recruitment of a host of coactivators. The biological and physiological implications of PXR activation are broad, ranging from drug metabolism and drug-drug interactions to the homeostasis of numerous endobiotics, such as glucose, lipids, steroids, bile acids, bilirubin, retinoic acid, and bone minerals. The purpose of this article is to provide an overview on the transcriptional circuits and metabolic relevance controlled by PXR. This article is part of a Special Issue entitled: Translating Nuclear Receptors from Health to Disease.