t0901317 and 22-hydroxycholesterol

Topics: Angiogenic Proteins; ATP Binding Cassette Transporter 1; Benzoates; Benzylamines; Blood Platelets; Cell-Derived Microparticles; Dendritic Cells; Endothelial Cells; Gene Expression Regulation; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Imidazoles; Immunity, Innate; Liver X Receptors; NF-kappa B; Oligodeoxyribonucleotides; Phenylenediamines; Primary Cell Culture; Receptors, G-Protein-Coupled; Signal Transduction; Sterol Regulatory Element Binding Protein 1; Sulfonamides; Toll-Like Receptor 7; Tumor Necrosis Factor-alpha

Liver X receptors (LXRs) play an important role in the regulation of cholesterol by regulating several transporters. In this study, we investigated the role of LXRs in the regulation of human organic anion transporter 1 (hOAT1), a major transporter localized in the basolateral membrane of the renal proximal tubule. Exposure of renal S2 cells expressing hOAT1 to LXR agonists (TO901317 and GW3965) and their endogenous ligand [22(R)-hydroxycholesterol] led to the inhibition of hOAT1-mediated [(14)C]PAH uptake. This inhibition was abolished by coincubation of the above agonists with 22(S)-hydroxycholesterol, an LXR antagonist. Moreover, it was found that the effect of LXR agonists was not mediated by changes in intracellular cholesterol levels. Interestingly, the inhibitory effect of LXRs was enhanced in the presence of 9-cis retinoic acid, a retinoic X receptor agonist. Kinetic analysis revealed that LXR activation decreased the maximum rate of PAH transport (J(max)) but had no effect on the affinity of the transporter (K(t)). This result correlated well with data from Western blot analysis, which showed the decrease in hOAT1 expression following LXR activation. Similarly, TO901317 inhibited [(14)C]PAH uptake by the renal cortical slices as well as decreasing mOAT1 protein expression in mouse kidney. Our findings indicated for the first time that hOAT1 was downregulated by LXR activation in the renal proximal tubule.

Topics: Animals; Benzoates; Benzylamines; Cell Line; Cells, Cultured; Down-Regulation; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Kidney Tubules, Proximal; Liver X Receptors; Mice; Organic Anion Transport Protein 1; Orphan Nuclear Receptors; Sulfonamides

Liver X receptor (LXR) plays a key role in reverse cholesterol transport by inducing the expression of the ATP-binding cassette (ABC) transporters, implicated in cholesterol efflux. Recent data showed that LXR agonists inhibit the proliferation of multiple types of human cancer cells. However, whether these effects are related to cholesterol efflux has not yet been elucidated.. Effects of two LXR agonists (TO901317 and 22(R)-hydroxycholesterol [22(R)-HC]) on proliferation, apoptosis and cholesterol efflux were examined in MCF-7 breast cancer cells.. Treatment with LXR agonists (TO901317 at 20 μM and 22(R)-HC at 2 μg/ml) inhibited proliferation and induced apoptosis of MCF-7 cells. Furthermore, LXR activation resulted in an increase in gene and protein levels of ABCG1 transporters and in cholesterol efflux to isolated high-density lipoprotein (HDL), without affecting the ABCA1/APOA-I mediated efflux. Under these conditions, a remarkable reduction of intracellular and membrane-associated cholesterol levels was observed.. LXR activation in MCF-7 cells could deprive cells of cholesterol, required for their growth, by stimulating its efflux, resulting in the inhibition of cell proliferation and in stimulation of apoptosis.

Topics: Apoptosis; ATP Binding Cassette Transporter, Subfamily G, Member 1; ATP-Binding Cassette Transporters; Breast Neoplasms; Cell Growth Processes; Cell Line, Tumor; Cholesterol; Female; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Lipoproteins, HDL; Liver X Receptors; Orphan Nuclear Receptors; Sulfonamides

Liver X receptors (LXRs) are nuclear receptors that regulate cholesterol, fatty acid, and glucose metabolism in various tissues. However, the renal action of LXRs is not well understood. Here we investigated the effects of LXR-activating ligands on modulation of epithelial sodium channel (ENaC)-mediated sodium transport in collecting duct cells. Exposure of the M1 cells to the synthetic LXR agonists T0901317 and GW3965 or the natural ligand 22R-hydroxycholesterol for 24 h decreased amiloride-sensitive sodium transport, corresponding with an increase of transepithelial resistance. The inhibition of amiloride-sensitive sodium transport after incubation with T0901317 or GW3965 was not mediated by a reduction of Na(+)/K(+)-ATPase-mediated basolateral sodium transport. On the other hand, T0901317 and GW3965 decreased mRNA abundance and membrane expression of ENaC. Preincubation the monolayer with GW3965 attenuated aldosterone-induced stimulation sodium transport. In primary cultures of collecting duct cells, T0901317 and GW3965 similarly inhibited ENaC transport function as in M1 cells. This is the first evidence showing LXR-activating ligands modulate ENaC-mediated sodium transport in collecting duct cells. These results suggest that LXRs may represent a novel therapeutic target for treatment of conditions with dysregulation of ENaC such as hypertension.

Topics: Animals; Anticholesteremic Agents; Benzoates; Benzylamines; Biological Transport; Cells, Cultured; Epithelial Sodium Channels; Hydrocarbons, Fluorinated; Hydroxycholesterols; Kidney Tubules, Collecting; Ligands; Liver X Receptors; Mice; Orphan Nuclear Receptors; Sodium; Sodium-Potassium-Exchanging ATPase; Sulfonamides

Ischemia in the placenta is considered the base of the pathogenesis of preeclampsia, a pregnancy-specific syndrome in which soluble endoglin (sEng) is a prognostic marker and plays a pathogenic role. Here, we investigated the effects of hypoxia and the downstream pathways in the release of sEng.. Under hypoxic conditions, the trophoblast-like cell line JAR showed an increase in sEng parallel to an elevated formation of reactive oxygen species. Because reactive oxygen species are related to the formation of oxysterols, we assessed the effect of 22-(R)-hydroxycholesterol, a natural ligand of the liver X receptor (LXR), and the LXR synthetic agonist T0901317. Treatment of JAR cells or human placental explants with 22-(R)-hydroxycholesterol or T0901317 resulted in a clear increase in sEng that was dependent on LXR. These LXR agonists induced an increased matrix metalloproteinase-14 expression and activity and a significant reduction of its endogenous inhibitor, tissue inhibitor of metalloproteinase-3. In addition, mice treated with LXR agonists underwent an increase in the plasma sEng levels, concomitant with an increase in arterial pressure. Moreover, transgenic mice overexpressing sEng displayed high blood pressure. Finally, administration of an endoglin peptide containing the consensus matrix metalloproteinase-14 cleavage site G-L prevented the oxysterol-dependent increase in arterial pressure and sEng levels in mice.. These studies provide a clue to the involvement of the LXR pathway in sEng release and its pathogenic role in vascular disorders such as preeclampsia.

Topics: Animals; Anticholesteremic Agents; Antigens, CD; Blood Pressure; Cell Line, Tumor; Choriocarcinoma; Endoglin; Female; Human Umbilical Vein Endothelial Cells; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Intracellular Signaling Peptides and Proteins; Ischemia; Liver X Receptors; Male; Matrix Metalloproteinase 14; Mice; Mice, Inbred C57BL; Mice, Transgenic; Orphan Nuclear Receptors; Placenta Diseases; Pre-Eclampsia; Pregnancy; Receptors, Cell Surface; Sulfonamides; Tissue Inhibitor of Metalloproteinase-3; Uterine Neoplasms

Oxygenated cholesterol metabolites known as oxysterols display potent biological activities ranging from regulation of lipid homeostasis to cytotoxicity. Oxysterols have previously been shown to inhibit the invasion of first trimester trophoblasts, an effect which involves activation of the nuclear liver X receptors (LXRs). In the present study, we investigated the effects of several oxysterols on syncytialisation (differentiation and fusion) in term placental trophoblasts. Treatment of cultured term primary trophoblast cells with oxysterols [25-hydroxycholesterol, 7-ketocholesterol, 22(R)-hydroxycholesterol] and the synthetic LXR agonist T0901317 at non-toxic doses decreased expression of GCM-1 and HERV-W mRNA and reduced hCG secretion and placental alkaline phosphatase activity, indicative of diminished trophoblast differentiation. Furthermore, treatment with these compounds also decreased cell fusion measured by E-cadherin immunostaining and quantification of syncytialised nuclei. Treatment with an LXR antagonist (geranylgeranyl diphosphate) abrogated the inhibitory effects of oxysterols and T0901317 on trophoblast syncytialisation indicating that these effects are mediated by LXR. These findings suggest that oxysterols impair differentiation and fusion of term trophoblast cells via an LXR-dependent mechanism.

Topics: Alkaline Phosphatase; Cell Differentiation; Cell Fusion; Chorionic Gonadotropin; DNA-Binding Proteins; Female; Gene Products, env; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Ketocholesterols; Liver X Receptors; Nuclear Proteins; Orphan Nuclear Receptors; Placenta; Pregnancy; Pregnancy Proteins; RNA, Messenger; Sulfonamides; Transcription Factors; Trophoblasts

Previously, we and other groups reported that liver X receptor (LXR) agonists T0901317, 22(R)-hydroxycholesterol, and 24(S)-hydroxycholesterol suppressed the proliferation of prostate and breast cancer cells. In this study, we report that T0901317 and 22(R)-hydroxycholesterol treatment inhibited the proliferation of different progression stages of LNCaP human prostate cancer cells, as well as different commonly used human cancer cell lines. Cancer cell lines with higher LXRα mRNA expression were more sensitive to 22(R)-hydroxycholesterol-induced inhibition. T0901317 treatment decreased the percentage of the cell population in S-phase and caused G(1) cell cycle arrest. Overexpression of S-phase kinase-associated protein 2 (Skp2) partially blocked the suppressive effect of T0901317 treatment. Modulating LXR signaling is therefore a potential adjuvant therapy for advanced prostate cancer and other types of cancer.

Topics: Antineoplastic Agents; Blotting, Western; Cell Line, Tumor; Cell Proliferation; Cell Separation; Flow Cytometry; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Liver X Receptors; Male; Orphan Nuclear Receptors; Sulfonamides

Liver X receptors alpha and beta (LXRalpha, LXRbeta) are key regulators of cholesterol homeostasis. The effects of LXR ligands on endothelial cells are largely unknown. While oxysterol LXR agonists can increase the endothelial-leukocyte interaction, synthetic LXR agonists are anti-atherogenic and anti-inflammatory. Mechanistic differences may underlie such findings.. LXRalpha and LXRbeta were found to be expressed in human endothelial cells. While synthetic LXR agonists could blunt the LPS-induced up-regulation of adhesion molecules (ICAM-1, VCAM-1, E-Selectin), 22-hydroxycholesterol and 24,25-epoxycholesterol enhanced such response. Microarray profiling further showed that the endothelial gene expression fingerprints of 22-hydroxycholesterol and T0901317 largely differed and unexpectedly shared only a restricted number of genes. Indeed, 22-hydroxycholesterol down-regulated eNOS and up-regulated a vast cohort of inflammatory mediators such as adhesion molecules, cytokines, enzymes and transcription factors. Other LXR-activating oxysterols such as 24,25-epoxycholesterol, 25-hydroxycholesterol and 27-hydroxycholesterol could also stimulate the endothelial expression of inflammatory markers, although significant differences were observed. These effects persisted in LXR-silenced cells, confirming the mechanistic dissociation of oxysterol and LXR pathways. Furthermore, the oxysterol-induced expression of inflammatory markers was not secondary to cell apoptosis and may relate to oxidative stress.. LXR-activating oxysterols comprehensively activate the expression of endothelial inflammation markers independently from LXRs. At proper dosage, synthetic LXR agonists are safe on endothelial cells and may even transrepress inflammatory reactions.

Topics: Anticholesteremic Agents; Benzoates; Benzylamines; Cells, Cultured; Chemokines; Cholesterol; E-Selectin; Endothelial Cells; Gene Expression Profiling; Gene Expression Regulation; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Inflammation Mediators; Intercellular Adhesion Molecule-1; Lipopolysaccharides; Liver X Receptors; Orphan Nuclear Receptors; RNA Interference; RNA, Messenger; Signal Transduction; Sulfonamides; Transcription Factors; Transfection; Tumor Necrosis Factor-alpha; Vascular Cell Adhesion Molecule-1

Peroxisome proliferator-activated receptor-gamma (PPARgamma) and liver X receptor-alpha (LXRalpha) are nuclear ligand-activated transcription factors, which regulate lipid metabolism and inflammation. Murine J774.2 macrophages were stimulated with Escherichia coli lipopolysaccharide (concentration, 10 microg/mL) with or without the PPARgamma ligand, 15-deoxy-Delta prostaglandin J2 (15d-PGJ2), or the LXRalpha ligands, 22(R)-hydroxycholesterol and T0901317 (concentration range, 0.01-10 micromol/L), alone or in combination. Nitric oxide (NO) metabolites and tumor necrosis factor alpha production, inducible NO synthase expression, and mitochondrial respiration were measured. When added to the cells as single agents, 15d-PGJ2, 22(R)-hydroxycholesterol, or T0901317 reduced the lipopolysaccharide-induced NO and tumor necrosis factor alpha production and the inducible NO synthase expression, and partially maintained mitochondrial respiration in a concentration-dependent manner. When added to the cells in combination at suboptimal concentrations, 15d-PGJ2 with 22(R)-hydroxycholesterol, or 15d-PGJ2 with T0901317, exerted anti-inflammatory effects similar to much higher concentrations (10,000-fold to 100,000-fold) of each ligand alone. The anti-inflammatory effects of these ligands, alone or in combination, were associated with reduction of nuclear factor-kappaB activation and with enhancement of PPARgamma DNA binding. LXRalpha expression was upregulated in response to 15d-PGJ2 and to the LXRalpha ligands when added alone or in combination. Immunoprecipitation experiments revealed that PPARgamma interacted with LXRalpha. Our data demonstrate that the PPARgamma ligand, 15d-PGJ2, and the LXRalpha ligands, 22(R)-hydroxycholesterol and T0901317, although binding to different nuclear receptors (i.e., PPARgamma and LXRalpha, respectively), affect mediator production through common cell signaling events and exert a synergistic potentiation in a combined treatment at suboptimal concentrations. Thus, our data suggest that PPARgamma and LXRalpha may interact in controlling the inflammatory response in macrophages.

Topics: Animals; Anti-Inflammatory Agents; Cells, Cultured; DNA-Binding Proteins; Drug Synergism; Hydrocarbons, Fluorinated; Hydroxycholesterols; Inflammation; Ligands; Lipopolysaccharides; Liver X Receptors; Macrophages; Mice; NF-kappa B; Nitric Oxide; Nitric Oxide Synthase Type II; Orphan Nuclear Receptors; PPAR gamma; Prostaglandin D2; Receptors, Cytoplasmic and Nuclear; Signal Transduction; Sulfonamides; Tumor Necrosis Factor-alpha

The nuclear liver X receptors (LXRalpha and beta) are regulators of lipid and cholesterol metabolism. Oxysterols are known LXR ligands, but the functional role of hydroxycholesterols is at present unknown. In human myotubes, chronic exposure to the LXR ligand T0901317 promoted formation of diacylglycerol (DAG) and triacylglycerol (TAG), 22-R-hydroxycholesterol (22-R-HC) had no effect, and 22-S-hydroxycholesterol (22-S-HC) reduced the formation. In accordance with this, 22-HC and T0901317 regulated the expression of fatty acid transporter CD36, stearoyl-CoA desaturase-1, acyl-CoA synthetase long chain family member 1 and fatty acid synthase (FAS) differently; all genes were increased by T0901317, 22-R-HC did not change their expression level, while 22-S-HC reduced it. Transfection studies confirmed that the FAS promoter was activated by T0901317 and repressed by 22-S-HC through an LXR response element in the promoter. Both 22-R-HC and T0901317 increased gene expression of LXRalpha, sterol regulatory element-binding protein 1c and ATP-binding cassette transporter A1, while 22-S-HC had little effect. In summary, 22-R-HC regulated lipid metabolism and mRNA expression of some LXR target genes in human myotubes differently than T0901317. Moreover, 22-S-HC did not behave like an inactive ligand; it reduced synthesis of complex lipids and repressed certain genes involved in lipogenesis and lipid handling.

Topics: Animals; Cells, Cultured; DNA-Binding Proteins; fas Receptor; Gene Expression; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Ligands; Lipid Metabolism; Liver X Receptors; Muscle Fibers, Skeletal; Orphan Nuclear Receptors; Promoter Regions, Genetic; Rats; Receptors, Cytoplasmic and Nuclear; RNA, Messenger; Sulfonamides; Transfection; Triglycerides

The cooperation of liver X receptors (LXRs) alpha and beta, and retinoic X receptor (RXR) modulate the expression of several genes involved in lipid metabolism in hepatocyte and macrophages. Using cDNA microarray technology, we have shown previously that several of these genes are also expressed in endothelial cells. In the present study, we investigated whether the activation of LXR and RXR affects the expression of genes involved in lipid metabolism in human endothelial cells. Relative expression of ABCA-1, CETP, SR-B1, EL, LPL, PLTP, ApoE and LDLR was investigated in HUVECs, human fibroblasts (hFB) and HepG2 cells by quantitative real-time PCR. For CETP and EL mRNA expression, the results were HUVECs > hFB > HEPG2; for PLTP, LDLR and LPL: hFB > HUVECs > HEPG2; for SR-B1 and ApoE: HEPG2 > HUVECs > hFB; and for ABCA-1 HEPG2: > hFB > HUVECs. Incubation of HUVECs with LXR agonists as 22-(R)-hydroxycholesterol (22-(R)-HC) or T0901317-induced ABCA1 (20.1- and 17.8-fold), LPL (3.46- and 7.03-fold) and CETP (6.34- and 3.98-fold) expression; EL, LDLR and SR-B1 expression was induced only upon incubation with T0901317 (2.40-, 2.83- and 2.19-fold, respectively) while 22-(R)-HC had no effect on EL and SR-B1 expression (0.8- and 0.9-fold) and decreased LDLR expression (0.4-fold). No effect of either 22-(R)-HC or T0901317 on PLTP and ApoE expression was observed. The RXR agonist, 9-cis retinoic acid (9CRA) alone induced the expression of CETP, LPL and SR-B1 (2.8-, 8.2- and 2.4-fold). No effect of 9CRA on ABCA-1, EL, PLTP, ApoE, and LDLR expression was observed. Association of 9CRA with 22-(R)-HC or T0901317 increased the expression of CETP and LPL while no effect on ABCA-1 or LDLR was observed. Activation of LXRs and RXRs in endothelial cells represents a new target of LXR and RXR agonist in the arterial wall. Modulation of gene expression in the endothelium should be taken into account when studying the effects of LXR and RXR agonists on lipid metabolism in the arterial wall.

Topics: Alitretinoin; ATP Binding Cassette Transporter 1; ATP-Binding Cassette Transporters; Blotting, Western; Carrier Proteins; Cell Line; Cell Line, Tumor; Cells, Cultured; Cholesterol Ester Transfer Proteins; DNA-Binding Proteins; Endothelial Cells; Gene Expression; Glycoproteins; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Lipid Metabolism; Lipoprotein Lipase; Liver X Receptors; Orphan Nuclear Receptors; Receptors, Cytoplasmic and Nuclear; Retinoid X Receptors; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Scavenger Receptors, Class B; Sulfonamides; Tretinoin

Liver X receptors (LXR) alpha and beta are important regulators of lipid homeostasis in liver, adipose and other tissues. However, no such information is available for the human placenta. We determined expression of both LXR alpha and beta in placental trophoblast cell lines, BeWo and JAR. Exposure of BeWo cells to a synthetic LXR agonist, T0901317, resulted in an increase in the amount of mRNA of LXR target genes, sterol regulatory element-binding protein-1 and fatty acid synthase. T0901317 also increased the synthesis of lipids. Moreover, T0901317 resulted in a reduced secretion of hCG during differentiation of these cells. Our data for the first time demonstrate a new role for LXRs in the human placenta.

Topics: Blotting, Northern; Cell Differentiation; Cell Line, Tumor; Chorionic Gonadotropin; DNA-Binding Proteins; Enzyme-Linked Immunosorbent Assay; Fatty Acid Synthases; Female; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Lipids; Liver X Receptors; Orphan Nuclear Receptors; Pregnancy; Receptors, Cytoplasmic and Nuclear; RNA; Sterol Regulatory Element Binding Protein 1; Sulfonamides; Transfection; Trophoblasts

In rodent liver, transcription of the gene encoding cholesterol 7alpha-hydroxylase (CYP7A1), which catalyzes the rate-limiting step in the classic bile acid synthetic pathway, is stimulated by the liver X receptor alpha (LXRalpha), a nuclear receptor for oxysterol metabolites of cholesterol. This feed-forward regulatory loop provides a mechanism for the elimination of excess cholesterol from the body. In this report, we demonstrate that in primary cultures of human hepatocytes, activation of LXRalpha has the opposite effect, repressing CYP7A1 expression. This repression is mediated, at least in part, through induction of the orphan nuclear receptor, short heterodimer partner (SHP), which is also induced by bile acids. We demonstrate that SHP is regulated directly by LXRalpha through a DNA response element that overlaps with the previously characterized bile acid response element. Our data reveal a fundamental difference in the regulation of CYP7A1 in rodent and human hepatocytes and provide evidence that different species employ distinct molecular strategies to regulate cholesterol homeostasis.

Topics: Animals; Anticholesteremic Agents; Blotting, Northern; Cholesterol; Cholesterol 7-alpha-Hydroxylase; DNA-Binding Proteins; Electrophoretic Mobility Shift Assay; Gene Expression Regulation, Enzymologic; Hepatocytes; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Liver X Receptors; Orphan Nuclear Receptors; Promoter Regions, Genetic; Rats; Receptors, Cytoplasmic and Nuclear; Sulfonamides; Transcriptional Activation; Transfection

Fatty acid metabolism is transcriptionally regulated by two reciprocal systems: peroxisome proliferator-activated receptor (PPAR) alpha controls fatty acid degradation, whereas sterol regulatory element-binding protein-1c activated by liver X receptor (LXR) regulates fatty acid synthesis. To explore potential interactions between LXR and PPAR, the effect of LXR activation on PPARalpha signaling was investigated. In luciferase reporter gene assays, overexpression of LXRalpha or beta suppressed PPARalpha-induced peroxisome proliferator response element-luciferase activity in a dose-dependent manner. LXR agonists, T0901317 and 22(R)-hydroxycholesterol, dose dependently enhanced the suppressive effects of LXRs. Gel shift assays demonstrated that LXR reduced binding of PPARalpha/retinoid X receptor (RXR) alpha to peroxisome proliferator response element. Addition of increasing amounts of RXRalpha restored these inhibitory effects in both luciferase and gel shift assays, suggesting the presence of RXRalpha competition. In vitro protein binding assays demonstrated that activation of LXR by an LXR agonist promoted formation of LXR/RXRalpha and, more importantly, LXR/PPARalpha heterodimers, leading to a reduction of PPARalpha/RXRalpha formation. Supportively, in vivo administration of the LXR ligand to mice and rat primary hepatocytes substantially decreased hepatic mRNA levels of PPARalpha-targeted genes in both basal and PPARalpha agonist-induced conditions. The amount of nuclear PPARalpha/RXR heterodimers in the mouse livers was induced by treatment with PPARalpha ligand, and was suppressed by superimposed LXR ligand. Taken together with data from the accompanying paper (Yoshikawa, T., T. Ide, H. Shimano, N. Yahagi, M. Amemiya-Kudo, T. Matsuzaka, S. Yatoh, T. Kitamine, H. Okazaki, Y. Tamura, M. Sekiya, A. Takahashi, A. H. Hasty, R. Sato, H. Sone, J. Osuga, S. Ishibashi, and N. Yamada, Endocrinology 144:1240-1254) describing PPARalpha suppression of the LXR-sterol regulatory element-binding protein-1c pathway, we propose the presence of an intricate network of nutritional transcription factors with mutual interactions, resulting in efficient reciprocal regulation of lipid degradation and lipogenesis.

Topics: Animals; Anticholesteremic Agents; ATP Binding Cassette Transporter 1; ATP-Binding Cassette Transporters; CCAAT-Enhancer-Binding Proteins; Cells, Cultured; DNA-Binding Proteins; Fatty Acids; Gene Expression Regulation; Hepatocytes; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Lipid Metabolism; Liver; Liver X Receptors; Male; Mice; Mice, Inbred C57BL; Nutritional Physiological Phenomena; Orphan Nuclear Receptors; Promoter Regions, Genetic; Rats; Rats, Sprague-Dawley; Receptors, Cytoplasmic and Nuclear; Receptors, Retinoic Acid; Retinoid X Receptors; Signal Transduction; Sterol Regulatory Element Binding Protein 1; Sulfonamides; Transcription Factors; Transcriptional Activation

The nuclear receptors liver X receptor (LXR) alpha and LXRbeta serve as oxysterol receptors and regulate the expression of genes involved in lipid metabolism. LXR activation induces the expression of ATP-binding cassette (ABC) transporters, such as ABCG5 and ABCG8, which inhibit intestinal absorption of cholesterol and phytosterols. Although several synthetic LXR agonists have been generated, these compounds have limited clinical application, because they cause hypertriglycemia by inducing the expression of lipogenic genes in the liver. We synthesized derivatives of phytosterols and found some of them to act as LXR agonists. Among them, YT-32 [(22E)-ergost-22-ene-1alpha,3beta-diol], which is related to ergosterol and brassicasterol, is the most potent LXR agonist. YT-32 directly bound to LXRalpha and LXRbeta and induced the interaction of LXRalpha with cofactors, such as steroid receptor coactivator-1, as effectively as the natural ligands, 22(R)-hydroxycholesterol and 24(S),25-epoxycholesterol. Although the nonsteroidal synthetic LXR agonist T0901317 induced the expression of intestinal ABC transporters and liver lipogenic genes, oral administration of YT-32 selectively activated intestinal ABC transporters in mice. Unlike T0901317 treatment, YT-32 inhibited intestinal cholesterol absorption without increasing plasma triglyceride levels. The phytosterol-derived LXR agonist YT-32 might selectively modulate intestinal cholesterol metabolism.

Topics: Animals; Anticholesteremic Agents; ATP-Binding Cassette Transporters; Biological Transport; Cell Line; Cell Nucleus; Cholesterol; DNA-Binding Proteins; Dose-Response Relationship, Drug; Ergosterol; Genes, Reporter; Glutathione Transferase; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Intestinal Mucosa; Ligands; Liver; Liver X Receptors; Mice; Models, Chemical; Orphan Nuclear Receptors; Phytosterols; Protein Binding; Receptors, Cytoplasmic and Nuclear; Reverse Transcriptase Polymerase Chain Reaction; Sulfonamides; Time Factors; Transfection

Apolipoprotein E (apoE) secreted by macrophages in the artery wall exerts an important protective effect against the development of atherosclerosis, presumably through its ability to promote lipid efflux. Previous studies have shown that increases in cellular free cholesterol levels stimulate apoE transcription in macrophages and adipocytes; however, the molecular basis for this regulation is unknown. Recently, Taylor and colleagues [Shih, S. J., Allan, C., Grehan, S., Tse, E., Moran, C. & Taylor, J. M. (2000) J. Biol. Chem. 275, 31567-31572] identified two enhancers from the human apoE gene, termed multienhancer 1 (ME.1) and multienhancer 2 (ME.2), that direct macrophage- and adipose-specific expression in transgenic mice. We demonstrate here that the nuclear receptors LXRalpha and LXRbeta and their oxysterol ligands are key regulators of apoE expression in both macrophages and adipose tissue. We show that LXR/RXR heterodimers regulate apoE transcription directly, through interaction with a conserved LXR response element present in both ME.1 and ME.2. Moreover, we demonstrate that the ability of oxysterols and synthetic ligands to regulate apoE expression in adipose tissue and peritoneal macrophages is reduced in Lxralpha-/- or Lxrbeta-/- mice and abolished in double knockouts. Basal expression of apoE is not compromised in Lxr null mice, however, indicating that LXRs mediate lipid-inducible rather than tissue-specific expression of this gene. Together with our previous work, these findings support a central role for LXR signaling pathways in the control of macrophage cholesterol efflux through the coordinate regulation of apoE, ABCA1, and ABCG1 expression.

Topics: 3T3 Cells; Adipocytes; Animals; Anticholesteremic Agents; Apolipoproteins E; Arteriosclerosis; ATP Binding Cassette Transporter 1; ATP Binding Cassette Transporter, Subfamily G, Member 1; ATP-Binding Cassette Transporters; Carcinoma, Hepatocellular; Cell Differentiation; Cells, Cultured; Cholesterol; Diet, Atherogenic; Dimerization; DNA-Binding Proteins; Enhancer Elements, Genetic; Gene Expression Regulation; Humans; Hydrocarbons, Fluorinated; Hydroxycholesterols; Ligands; Lipids; Liver Neoplasms; Liver X Receptors; Lovastatin; Macrophages, Peritoneal; Male; Mevalonic Acid; Mice; Mice, Knockout; Organic Chemicals; Orphan Nuclear Receptors; Receptors, Cytoplasmic and Nuclear; Receptors, Retinoic Acid; Recombinant Fusion Proteins; Retinoid X Receptors; RNA, Messenger; Sulfonamides; Tetradecanoylphorbol Acetate; Transcription Factors; Tumor Cells, Cultured