Member Of Nuclear Receptor Superfamily Research Articles

Exploring Flexibility of Progesterone Receptor Ligand Binding Domain Using Molecular Dynamics.

Progesterone receptor (PR), a member of nuclear receptor (NR) superfamily, plays a vital role for female reproductive tissue development, differentiation and maintenance. PR ligand, such as progesterone, induces conformation changes in PR ligand binding domain (LBD), thus mediates subsequent gene regulation cascades. PR LBD may adopt different conformations upon an agonist or an antagonist binding. These different conformations would trigger distinct transcription events. Therefore, the dynamics of PR LBD would be of general interest to biologists for a deep understanding of its structure-function relationship. However, no apo-form (non-ligand bound) of PR LBD model has been proposed either by experiments or computational methods so far. In this study, we explored the structural dynamics of PR LBD using molecular dynamics simulations and advanced sampling tools in both ligand-bound and the apo-forms. Resolved by the simulation study, helix 11, helix 12 and loop 895–908 (the loop between these two helices) are quite flexible in antagonistic conformation. Several residues, such as Arg899 and Glu723, could form salt-bridging interaction between helix 11 and helix 3, and are important for the PR LBD dynamics. And we also propose that helix 12 in apo-form PR LBD, not like other NR LBDs, such as human estrogen receptor α (ERα) LBD, may not adopt a totally extended conformation. With the aid of umbrella sampling and metadynamics simulations, several stable conformations of apo-form PR LBD have been sampled, which may work as critical structural models for further large scale virtual screening study to discover novel PR ligands for therapeutic application.

Nuclear receptor retinoid-related orphan receptor α deficiency exacerbates high-fat diet-induced cardiac dysfunction despite improving metabolic abnormality

Retinoid-related orphan receptor α (RORα), a member of the metabolic nuclear receptor superfamily, plays a vital regulatory role in circadian rhythm and metabolism. Here, we investigated the role of RORα in high-fat diet (HFD)-induced cardiac impairments and the underlying mechanisms involved. RORα-deficient stagger mice (sg/sg) and wild type (WT) littermates were fed with either standard diet or HFD. At 20weeks after HFD treatment, RORα deficiency resulted in significantly decreased body weight gain, improved dyslipidemia and ameliorated insulin resistance (evaluated by blood biochemical and glucose/insulin tolerance tests) compared with WT control. However, compared with HFD-treated WT mice, HFD-treated sg/sg mice exhibited significantly augmented myocardial hypertrophy, cardiac fibrosis (wheat germ agglutinin, masson trichrome and sirius red staining) and cardiac dysfunction (echocardiography and hemodynamics). Mechanistically, RORα deficiency impaired mitochondrial biogenesis and function. Additionally, RORα deficiency resulted in inhibition of the AMPK-PGC1α signaling pathway. In contrast, cardiomyocyte-specific RORα overexpression ameliorated myocardial hypertrophy, fibrosis and dysfunction by restoring AMPK-PGC1α signaling, and subsequently normalizing mitochondrial biogenesis. These findings demonstrated for the first time that nuclear receptor RORα deficiency aggravated HFD-induced myocardial dysfunction at least in part by impairing mitochondrial biogenesis in association with disrupting AMPK-PGC1α signaling. This article is part of a Special Issue entitled: Genetic and epigenetic control of heart failure - edited by Jun Ren and Megan Yingmei Zhang.

Peroxisome proliferator-activated receptor Pro12Ala polymorphism and the risks of gestational diabetes mellitus: An updated meta-analysis of 12 studies.

Background:Peroxisome proliferator-activated receptors-λ (PPAR-λ) is a member of nuclear receptor superfamily and acts as a ligand-dependent transcription factor often found in the adrenal gland, the spleen, and adipose tissue. The Pro12Ala polymorphism of PPAR-λ has been associated with the risks of gestational diabetes mellitus (GDM); however, association studies have provided conflicting results. The aim of this Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) compliant meta-analysis is to reach a more up-to-date and accurate estimation of the relationship between Pro12Ala genetic polymorphisms and the risks of GDM.Methods:Eligible studies were retrieved by searching PubMed, EMBASE, Web of Science, Ovid, WanFang, and Chinese National Knowledge Databases and selected according to a pre-defined inclusion criterion. The risk of bias was assessed using the Newcastle-Ottawa quality assessment scale. The per-allele odds ratio (OR) of risk allele proline (Pro) was compared between cases and controls in each study to describe the association between the Pro allele and an individual's risk of GDM. The ORs were pooled using both the random-effects model (the DerSimonian and Laird method) and the fixed effects model (the Mantel-Haenszel method) and the 95% confidence interval (95% CI) was calculated using Woolf method.Results:The final meta-analysis included a total of 11 articles of 12 data sets consisting of 7054 controls and 2980 GDM cases. Our results demonstrate that the Pro allele is not associated with GDM [OR: across multiple populations, 95% CI: 0.98–1.24; P(Z) = 0.01; P(Q) = 0.003]. In the stratified analysis by ethnicity, significantly increased risks were found for the Chinese (OR = 2.36; 95% CI: 1.47–3.78) and Korean (OR = 1.39; 95% CI: 1.00–1.93) populations.Conclusion:These data suggest the potential role of Pro allele in the pathogenesis of GDM in Asian populations. Although the funnel plot of included studies showed assymetry, the results using the “trim and fill” method did not alter the conclusion of this study.

Peroxisome proliferator-activated receptors in cardiacenergy metabolism and cardiovascular disease.

Cardiomyocytes mainly depend on energy produced from the oxidation of fatty acids and mitochondrial oxidative phosphorylation. Shortage of energy or excessive fat accumulation can lead to cardiac disorders. High saturated fat intake and a sedentary life style have a major influence in the development of cardiovascular disease (CVD). Peroxisome proliferator-activated receptors (PPARs), one of the nuclear receptor super family members, play criticalrolein the metabolism of lipids by regulating their oxidation and storage. Furthermore, they are involved in glucose homeostasis as well. PPARs, mainly alpha (α) and beta/delta (β/δ), have a significant effect on the lipid metabolism and anti-inflammation in endothelial cells (ECs), vascular smooth muscle cells, and also in cardiomyocytes. Pro-inflammatory cytokines, mainly tumour necrosis factor-α, released at the site of inflammation in the sub-ECs of coronary arteries can inactivate the PPARs which can eventually lead to decreased energy production in the myocardium. Various synthetic ligands of PPAR-α and β/δ have many favourable effects in modulating the vascular diseases and heart failure. Despite the adverse effects from therapy using PPAR- gamma ligands, several laboratories are now focused on synthesizing partial activators which may combine their beneficial effects with lowering of undesirable side effects. This review discusses the role of isoforms of PPAR in the cardiomyocytes energy balance and CVD. The knowledge will help in the synthesis of ligands for their partial activation in order to render energy balance and protection from CVD.

Peroxisome Proliferator-Activated Receptor γ Activity is Required for Appropriate Cardiomyocyte Differentiation.

Peroxisome proliferator-activated receptor γ (PPARγ) is a member of the PPAR nuclear receptor superfamily. Although PPARγ acts as a master transcription factor in adipocyte differentiation, it is also associated with a variety of cell functions including carbohydrate and lipid metabolism, glucose homeostasis, cell proliferation and cell differentiation. This study aimed to assess the expression level of PPARγ in order to address its role in cardiac cell differentiation of mouse embryonic stem cells (mESCs). In this an intervening study, mESCs were subjected to cardiac differentiation. Total RNA was extracted from the cells and quantitative real time polymerase chain reaction (qPCR) was carried out to estimate level of gene expression. Furthermore, the requirement of PPARγ in cardiac differentiation of mESCs, during cardiac progenitor cells (CPCs) formation, was examined by applying the respective agonist and antagonist. The obtained data revealed an elevation in the expression level of PPARγ during spontaneous formation of CPCs and cardiomyocytes. Our results indicated that during CPC formation, PPARγ inactivation via treatment with GW9662 (GW) reduced expression of CPC and cardiac markers. We conclude that PPARγ modulation has an effective role on cardiac differentiation of mESCs at the early stage of cardiomyogenesis.

Furocoumarins from Cnidium monnieri Act as Peroxisome Proliferatoractivated R........ .and Farnesoid X Receptor Agonists

The fruit of Cnidium monnieri (L) Cusson is an important traditional medicine employed in Taiwan and China as the treatments of impotence, sterilization, renal disease, dermatosis, colpitis, inflammation and gynecological disease. Peroxisome Proliferator-activated Receptor γ (PPARγ) and Farnesoid X receptor (FXR) are the members of nuclear receptor superfamily that have been targeted for developing treatments for chronic liver diseases. In this study, the furocoumarins isolated from the fruit of Cnidium monnieri (L) Cusson were evaluated for their PPARγ and FXR agonism. Indeed, in transient transfection reporter assays, these furocoumarins transactivated PPARγ and FXR to respectively modulate promoter action including ABCA1 and SHP promoters in dose-dependent manner. Through the molecular modeling docking studies these furocoumarins were shown to bind to PPARγ or FXR ligand binding pocket fairly well. All these results indicate that Cnidium monnieri (L) Cusson might possess therapeutic effects through the activation of PPARγ and FXR pathways. Keywords: Farnesoid X receptor (FXR), furocoumarin, nuclear receptors, PEPCK, peroxisome proliferator-activated receptor γ (PPARγ), transient transfection receptor assays.

PPARα agonist, fenofibrate, ameliorates age-related renal injury

The kidney ages quickly compared with other organs. Expression of senescence markers reflects changes in the energy metabolism in the kidney. Two important issues in aging are mitochondrial dysfunction and oxidative stress. Peroxisome proliferator-activated receptor α (PPARα) is a member of the ligand-activated nuclear receptor superfamily. PPARα plays a major role as a transcription factor that regulates the expression of genes involved in various processes. In this study, 18-month-old male C57BL/6 mice were divided into two groups, the control group (n=7) and the fenofibrate-treated group (n=7) was fed the normal chow plus fenofibrate for 6months. The PPARα agonist, fenofibrate, improved renal function, proteinuria, histological change (glomerulosclerosis and tubular interstitial fibrosis), inflammation, and apoptosis in aging mice. This protective effect against age-related renal injury occurred through the activation of AMPK and SIRT1 signaling. The activation of AMPK and SIRT1 allowed for the concurrent deacetylation and phosphorylation of their target molecules and decreased the kidney's susceptibility to age-related changes. Activation of the AMPK-FOXO3a and AMPK-PGC-1α signaling pathways ameliorated oxidative stress and mitochondrial dysfunction. Our results suggest that activation of PPARα and AMPK-SIRT1 signaling may have protective effects against age-related renal injury. Pharmacological targeting of PPARα and AMPK-SIRT1 signaling molecules may prevent or attenuate age-related pathological changes in the kidney.

Constitutive expression of PPARγ inhibits proliferation and migration of gastric cancer cells and down-regulates Wnt/β-Catenin signaling pathway downstream target genes TERT and ENAH

BackgroundPeroxisome proliferator-activated receptor γ (PPARγ) is a member of the PPAR nuclear hormone receptor superfamily, which plays a crucial role in carcinogenesis. Wnt/β-Catenin signaling pathway has been well certified to contribute to the progression of gastric malignancies. β-Catenin mediates transcriptional regulation by forming a complex with LEF/TCF transcription factors, resulting in activation of downstream target genes such as TERT, ENAH. In this study, we aimed at detecting the effect of PPARγ on TERT, ENAH and explaining the further mechanisms of PPARγ on tumor suppression. MethodsThe pEGFP-N1-PPARγ recombinant plasmid has already been constructed by researchers in our laboratory. We stably transfected it into three gastric cancer (GC) cell lines (MKN-28, SGC-7901 and BGC-823). CCK-8 and transwell assay were employed to analyze the capability of cell proliferation and metastasis. The mRNA and protein levels were evaluated by real-time PCR and western blot analysis. ResultsAfter transfected with PPARγ overexpression plasmid, the ability of cell proliferation and migration declined significantly (p<0.05). The expression of PPARγ increased (p<0.05) and β-Catenin was inhibited obviously (p<0.05) in the group of pEGFP-N1-PPARγ plasmid transfection. Meanwhile, the mRNA or protein levels of TERT and ENAH were suppressed (p<0.05) in pEGFP-N1-PPARγ plasmid transfection group compared with control groups. ConclusionPPARγ might inhibit the proliferation and migration of GC cell lines through suppressing the expression of TERT and ENAH. PPARγ played an important role as a physiological regulator and might be a target for the treatment of GC.

PPARγ and Its Ligands: Potential Antitumor Agents in the Digestive System.

Peroxisome proliferator-activated receptor γ (PPARγ) is a versatile member of the ligand-activated nuclear hormone receptor superfamily of transcription factors, with expression in several different cell lines, especially in the digestive system. After being activated by its ligand, PPARγ can suppress the growth of oral, esophageal, gastric, colorectal, liver, biliary, and pancreatic tumor cells, suggesting that PPARγ ligand is a potential anticancer agent in PPARγ-expressing tumors. This review highlights key advances in understanding the effects of PPARγ ligands in the treatment of tumors in the digestive system.

A SUMO-acetyl switch in PXR biology

Post-translational modification (PTM) of nuclear receptor superfamily members regulates various aspects of their biology to include sub-cellular localization, the repertoire of protein-binding partners, as well as their stability and mode of degradation. The nuclear receptor pregnane X receptor (PXR, NR1I2) is a master-regulator of the drug-inducible gene expression in liver and intestine. The PXR-mediated gene activation program is primarily recognized to increase drug metabolism, drug transport, and drug efflux pathways in these tissues. The activation of PXR also has important implications in significant human diseases including inflammatory bowel disease and cancer. Our recent investigations reveal that PXR is modified by multiple PTMs to include phosphorylation, SUMOylation, and ubiquitination. Using both primary cultures of hepatocytes and cell-based assays, we show here that PXR is modified through acetylation on lysine residues. Further, we show that increased acetylation of PXR stimulates its increased SUMO-modification to support active transcriptional suppression. Pharmacologic inhibition of lysine de-acetylation using trichostatin A (TSA) alters the sub-cellular localization of PXR in cultured hepatocytes, and also has a profound impact upon PXR transactivation capacity. Both the acetylation and SUMOylation status of the PXR protein is affected by its ability to associate with the lysine de-acetylating enzyme histone de-acetylase (HDAC)3 in a complex with silencing mediator of retinoic acid and thyroid hormone receptor (SMRT). Taken together, our data support a model in which a SUMO-acetyl ‘switch’ occurs such that acetylation of PXR likely stimulates SUMO-modification of PXR to promote the active repression of PXR-target gene expression. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

Prognostic Methylation Markers for Survival in Cytogenetically Normal AML Patients Treated on SWOG Trials

Purpose: Although abnormal DNA methylation is not limited to promoter CpG islands, studies to date have focused on identifying prognostic methylation markers in gene promoters. The current study aimed at identifying methylation markers for newly-diagnosed AML with normal cytogenetics (AML-NK) using a genome-wide approach.Patients and Methods: Pretreatment samples were from patients treated on SWOG studies S8600, S9333, S9031, S9500, S9918, S0106, and S0112 from 1986 to 2009. We combined comprehensive high-throughput array-based relative methylation analysis (CHARM) with the Cox proportional hazard model controlling for known AML prognostic factors, to identify 654 survival associated methylation regions (SAMRs) in a phase I discovery cohort (n=72). Top ranking SAMRs were then tested using quantitative bisulfite pyro-sequencing and, if validated, studied further in two additional cohorts: a phase II model building cohort (n=65) and a phase III validation cohort (n=65). In addition, an external cohort from the TCGA AML study (LAML) was used for further validation (n=93).Results: Two SAMRs, located in promoter CpG island shore of LZTS2 and NR6A1, respectively, were identified. Multivariate analyses considering age, performance status, white blood count, and platelet count, showed independent prognostic significance of LZTS2 in the phase II model building cohort (P = 0.0073) and a trend of significance in the phase III validation cohort (P = 0.076), with hypomethylation associated with shorter survival. When FLT3 -ITD status was considered in addition to the above factors, hypomethylation of NR6A1 was shown as an independent marker of shorter survival in both the 2nd and 3rd cohorts (P = 0.02 and 0.03, respectively). Kaplan-Meier analyses of SWOG patients from all three phases further demonstrated that hypomethylation of either LZTS2 or NR6A1 was associated with worse overall survival of AML-NK patients (P < 0.001). The prognosis was verified in AML-NK patients from the TCGA acute myeloid leukemia (LAML) cohort. Multivariate analysis showed that methylation values below median at both markers predicted significantly worse overall survival for both cohorts (SWOG cohort, HR 1.89, P <0.001; TCGA-LAML, HR 2.08, P = 0.006). The impact of the methylation was independent of the FLT3 -ITD status, with C-statistics of 0.71 for both studies. Both LZTS2 and NR6A1 function have been associated with cancer biology. LZTS2 encodes the leucine zipper putative tumor suppressor 2 protein. The over-expression of LZTS2 protein was shown to inhibit cancer cell growth in vitro. The NR6A1 gene encodes a nuclear receptor superfamily member. Increased NR6A1 expression was reported to associate with disease progression and aggressiveness in prostate cancer. The significance of NR6A1 in hematological malignancies has not been described.Conclusion: We identified two DNA methylation markers that are prognostic for overall survival of AML-NK patients. They warrant further validation in prospective clinical trials.This study was supported by HOPE Foundation Development Fund and by NIH/NCI National Clinical Trials Network (NCTN) grants CA180888 and CA180819. [Display omitted] [Display omitted] DisclosuresYan:EpigenDx, Inc.: Employment. Erba:Sunesis;Pfizer; Daiichi Sankyo; Ariad: Consultancy; Millennium/Takeda; Celator; Astellas: Research Funding; Seattle Genetics; Amgen: Consultancy, Research Funding; Novartis; Incyte; Celgene: Consultancy, Patents & Royalties; GlycoMimetics; Janssen: Other: Data Safety & Monitoring Committees. Fang:Affymetrix: Research Funding.

Identification and interplay of sequence specific DNA binding proteins involved in regulation of human Pregnane and Xenobiotic Receptor gene

Pregnane and Xenobiotic Receptor (PXR), a member of nuclear receptor superfamily, acts as a ‘xenosensor’ in our body and modulates a network of genes involved in xenobiotic metabolism and elimination. Expression levels of PXR in certain metabolic disorders including cancer are reported to be altered and its induced expression is associated with the development of resistance towards chemotherapy and adverse drug–drug interactions. Though the transcriptional regulation of PXR target genes have been elucidated in significant details, the structure and functional control of PXR promoter itself remains inadequately explored. In this work, we identify a Composite Element (CE) located within the proximal PXR promoter region that consists of multiple overlapping cis-elements and demonstrated that CE interacts specifically with some critical nuclear proteins. Subsequent DNA-protein interaction studies revealed mutually exclusive interactions on CE occurring between Sp1 and two unidentified DNA binding proteins with molecular masses of 50 and 54kDa. Here, we report the identification of 54kDa CE binding protein as a heterogeneous nuclear ribonucleoprotein K (hnRNPK) and demonstrate the effect of hnRNP K and Sp1 on PXR promoter transcriptional activity. Overall, the study indicates that PXR gene is tightly regulated to maintain a low receptor level.

Farnesoid-X-receptor expression in monocrotaline-induced pulmonary arterial hypertension and right heart failure

ObjectiveThe farnesoid-X-receptor (FXR) is a metabolic nuclear receptor superfamily member that is highly expressed in enterohepatic tissue and is also expressed in the cardiovascular system. Multiple nuclear receptors, including FXR, play a pivotal role in cardiovascular disease (CVD). Pulmonary arterial hypertension (PAH) is an untreatable cardiovascular system disease that leads to right heart failure (RHF). However, the potential physiological/pathological roles of FXR in PAH and RHF are unknown. We therefore compared FXR expression in the cardiovascular system in PAH, RHF and a control. Methods and resultsHemodynamic parameters and morphology were assessed in blank solution-exposed control, monocrotaline (MCT)-exposed PAH (4 weeks) and RHF (7 weeks) Sprague–Dawley rats. Real-time reverse transcription polymerase chain reaction (real-time RT-PCR), Western blot (WB), immunohistochemistry (IHC) analysis and immunofluorescence (IF) analysis were performed to assess FXR levels in the lung and heart tissues of MCT-induced PAH and RHF rats. In normal rats, low FXR levels were detected in the heart, and nearly no FXR was expressed in rat lungs. However, FXR expression was significantly elevated in PAH and RHF rat lungs but reduced in PAH and RHF rat right ventricular (RV) tissues. FXR expression was reduced only in RHF rat left ventricular (LV) tissues. ConclusionsThe differential expression of FXR in MCT-induced PAH lungs and heart tissues in parallel with PAH pathophysiological processes suggests that FXR contributes to PAH.

Estrogen-Related Receptor γ Plays a Key Role in Vascular Calcification Through the Upregulation of BMP2 Expression.

Vascular calcification which refers to ectopic mineralization in vascular cells is associated with several conditions, such as chronic kidney disease, atherosclerosis, and diabetes mellitus. Estrogen-related receptor (ERR)γ is a member of the orphan nuclear receptor superfamily, which plays diverse roles in regulating homeostatic and metabolic processes. However, the role of ERRγ in vascular calcification has not been investigated to date. The aim of the present study was to examine the role of ERRγ in vascular calcification. Vascular calcification was induced by treating rat aortic vascular smooth muscle cells with calcification medium. ERRγ expression in vascular smooth muscle cells was induced during calcification medium-induced vascular calcification. Adenovirus-mediated overexpression of ERRγ in vascular smooth muscle cells resulted in the upregulation of the expression of osteogenic genes, including runt-related transcription factor 2, osteopontin, and Msx2, and the downregulation of α-smooth muscle actin. Adenovirus-mediated overexpression of ERRγ induced bone morphogenetic protein 2 (BMP2) expression, leading to increased phosphorylation of the intracellular BMP2 effector proteins SMAD1/5/8. Collectively, these data suggested that ERRγ promotes dedifferentiation of vascular smooth muscle cells to an osteogenic phenotype during the vascular calcification process. Inhibition of endogenous ERRγ expression or activity using a specific siRNA or the selective inverse agonist GSK5182 attenuated vascular calcification and osteogenic gene expression in vitro and in vivo. The present results indicate that ERRγ plays a key role in vascular calcification by upregulating the BMP2 signaling pathway, suggesting that inhibition of ERRγ is a potential therapeutic strategy for the prevention of vascular calcification.

Identification and Characterization of the Androgen Receptor From the American Alligator, Alligator mississippiensis.

Androgens are essential for the development, reproduction, and health throughout the life span of vertebrates, particularly during the initiation and maintenance of male sexual characteristics. Androgen signaling is mediated by the androgen receptor (AR), a member of the steroid nuclear receptor superfamily. Mounting evidence suggests that environmental factors, such as exogenous hormones or contaminants that mimic hormones, can disrupt endocrine signaling and function. The American alligator (Alligator mississippiensis), a unique model for ecological research in that it exhibits environment-dependent sex determination, is oviparous and long lived. Alligators from a contaminated environment exhibit low reproductive success and morphological disorders of the testis and phallus in neonates and juveniles, both associated with androgen signaling; thus, the alterations are hypothesized to be related to disrupted androgen signaling. However, this line of research has been limited because of a lack of information on the alligator AR gene. Here, we isolated A mississippiensis AR homologs (AmAR) and evaluated receptor-hormone/chemical interactions using a transactivation assay. We showed that AmAR responded to all natural androgens and their effects were inhibited by cotreatment with antiandrogens, such as flutamide, p,p'-dichlorodiphenyldichloroethylene, and vinclozolin. Intriguingly, we found a spliced form of the AR from alligator cDNA, which lacks seven amino acids within the ligand-binding domain that shows no response to androgens. Finally, we have initial data on a possible dominant-negative function of the spliced form of the AR against androgen-induced AmAR.

Bone and Nutrition. The vitamin D functions in osteoblasts and osteocytes

The active form of vitamin D, 1α,25-dihydroxyvitamin D(3) (1α,25 (OH) (2)D(3)), plays a key role in mineral and bone homeostasis. 1α,25 (OH) (2)D(3), through binding to the vitamin D receptor (VDR), a member of the nuclear receptor superfamily, regulates the expression of many genes in osteoblasts and osteocytes. The VDR functions in a largely 1α,25 (OH) (2)D(3)-controlled manner by interacting directly with vitamin D response elements located within regulatory regions that are linked to cell-specific target genes. However, the mechanism of VDR action on these bone cell types remains largely unknown. While the direct actions of 1α,25 (OH) (2)D(3) on bone cells are complex and include both cell autonomous and paracrine mechanisms. In this review, we discuss how the VDR affects the transcriptional response of these cells and contribute to bone homeostasis.

SUMOylation and Ubiquitylation Circuitry Controls Pregnane X Receptor Biology in Hepatocytes.

Several nuclear receptor (NR) superfamily members are known to be the molecular target of either the small ubiquitin-related modifier (SUMO) or ubiquitin-signaling pathways. However, little is currently known regarding how these two post-translational modifications interact to control NR biology. We show that SUMO and ubiquitin circuitry coordinately modifies the pregnane X receptor (PXR, NR1I2) to play a key role in regulating PXR protein stability, transactivation capacity, and transcriptional repression. The SUMOylation and ubiquitylation of PXR is increased in a ligand- and tumor necrosis factor alpha -: dependent manner in hepatocytes. The SUMO-E3 ligase enzymes protein inhibitor of activated signal transducer and activator of transcription-1 (STAT1) STAT-1 (PIAS1) and protein inhibitor of activated STAT Y (PIASy) drive high levels of PXR SUMOylation. Expression of protein inhibitor of activated stat 1 selectively increases SUMO(3)ylation as well as PXR-mediated induction of cytochrome P450, family 3, subfamily A and the xenobiotic response. The PIASy-mediated SUMO(1)ylation imparts a transcriptionally repressive function by ameliorating interaction of PXR with coactivator protein peroxisome proliferator-activated receptor gamma coactivator-1-alpha. The SUMO modification of PXR is effectively antagonized by the SUMO protease sentrin protease (SENP) 2, whereas SENP3 and SENP6 proteases are highly active in the removal of SUMO2/3 chains. The PIASy-mediated SUMO(1)ylation of PXR inhibits ubiquitin-mediated degradation of this important liver-enriched NR by the 26S proteasome. Our data reveal a working model that delineates the interactive role that these two post-translational modifications play in reconciling PXR-mediated gene activation of the xenobiotic response versus transcriptional repression of the proinflammatory response in hepatocytes. Taken together, our data reveal that the SUMOylation and ubiquitylation of the PXR interface in a fundamental manner directs its biologic function in the liver in response to xenobiotic or inflammatory stress.

Two homoisoflavonoids act as peroxisome proliferator-activated receptor agonists

Polygonatum odoratum (Mill.) Druce is a well-known traditional Chinese medicine exerting multi-biological functions like removing dryness, promoting secretion of fluid, and quenching thirst, but its molecular mechanism is not fully understood. Peroxisome proliferator-activated receptor (PPAR) γ is a member of nuclear receptor superfamily, and its agonists are prescribed as anti-hyperglycemic drugs. In this study, homoisoflavonoids isolated from P. odoratum were evaluated for their activity against PPARγ by the fluorescence polarization competitive binding assay and transient transfection reporter assays. Primarily, the fluorescence polarization competitive binding assay results showed that 5,7-dihydroxy-6, 8-dimethyl-3-(4′-hydroxybenzyl)chroman-4-one (IC50 = 7 μM) and 5,7-dihydroxy-6-methyl-8-methoxy-3-(4′-hydroxybenzyl)chroman-4-one (IC50 = 12 μM) bound to PPARγ ligand-binding domain with fair binding affinity. Moreover, both homoisoflavonoids transactivated PPARγ-dependent promoters including PPRE (PPARγ response element), SHP, and ABCA1 gene promoters in dose-dependent manner. Further molecular modeling studies demonstrated that they interacted with PPARγ ligand-binding pocket in a similar manner as indeglitazar, a novel PPARγ agonist. All these results highly indicated that 5,7-dihydroxy-6, 8-dimethyl-3-(4′-hydroxybenzyl)chroman-4-one and 5,7-dihydroxy-6-methyl-8-methoxy-3-(4′-hydroxybenzyl)chroman-4-one are the active constituents of P. odoratum and act as PPARγ agonists.

Lepidozenolide from the liverwort Lepidozia fauriana acts as a farnesoid X receptor agonist

Lepidozenolide is a sesquiterpenoid isolated from the liverwort Lepidozia fauriana and its possible bioactivity is unclear. The farnesoid X receptor (FXR) is a member of nuclear receptor superfamily that has been widely targeted for developing treatments for chronic liver disease and hyperglycemia. In this study, whether lepidozenolide may act as a FXR agonist was determined. Indeed, in mammalian one-hybrid and transient transfection reporter assays, lepidozenolide transactivated FXR to modulate promoter action including GAL4, CYP7A1, and PLTP promoters in a dose-dependent manner, while it exhibited slightly less agonistic activity than chenodeoxycholic acid, an endogenous FXR agonist. Through the molecular modeling docking studies lepidozenolide was shown to bind to FXR ligand binding pocket fairly well. All these results indicate that lepidozenolide acts as a FXR agonist.

Xenobiotic Pregnane X Receptor (PXR) Regulates Innate Immunity via Activation of NLRP3 Inflammasome in Vascular Endothelial Cells

Pregnane X receptor (PXR) is a member of nuclear receptor superfamily and responsible for the detoxification of xenobiotics. Our previously study demonstrated that PXR is expressed in endothelial cells (ECs) and acts as a master regulator of detoxification genes to protect ECs against xenobiotics. Vascular endothelial cells are key sentinel cells to sense the pathogens and xenobiotics. In this study, we examined the potential function of PXR in the regulation of innate immunity in vasculatures. Treatments with PXR agonists or overexpression of a constitutively active PXR in cultured ECs increased gene expression of the key pattern recognition receptors, including Toll-like receptors (TLR-2, -4, -9) and NOD-like receptors (NOD-1 and -2 and NLRP3). In particular, PXR agonism triggered the activation of NLRP3 inflammasome and the ensuing cleavage and maturation of caspase-1 and interleukin-1β (IL-1β). Conversely, selective antagonism or gene silencing of PXR abrogated NLRP3 inflammasome activation. In addition, we identified NLRP3 as a transcriptional target of PXR by using the promoter-reporter and ChIP assays. In summary, our findings revealed a novel regulatory mechanism of innate immune by PXR, which may act as a master transcription factor controlling the convergence between the detoxification of xenobiotics and the innate immunity against them.