Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Liver X receptors (LXRs) and peroxisome proliferator-activated receptors (PPARs) are members of nuclear receptors that form obligate heterodimers with retinoid X receptors (RXRs). These nuclear receptors play crucial roles in the regulation of fatty acid metabolism: LXRs activate expression of sterol regulatory element-binding protein 1c (SREBP-1c), a dominant lipogenic gene regulator, whereas PPARalpha promotes fatty acid beta-oxidation genes. In the current study, effects of PPARs on the LXR-SREBP-1c pathway were investigated. Luciferase assays in human embryonic kidney 293 cells showed that overexpression of PPARalpha and gamma dose-dependently inhibited SREBP-1c promoter activity induced by LXR. Deletion and mutation studies demonstrated that the two LXR response elements (LXREs) in the SREBP-1c promoter region are responsible for this inhibitory effect of PPARs. Gel shift assays indicated that PPARs reduce binding of LXR/RXR to LXRE. PPARalpha-selective agonist enhanced these inhibitory effects. Supplementation with RXR attenuated these inhibitions by PPARs in luciferase and gel shift assays, implicating receptor interaction among LXR, PPAR, and RXR as a plausible mechanism. Competition of PPARalpha ligand with LXR ligand was observed in LXR/RXR binding to LXRE in gel shift assay, in LXR/RXR formation in nuclear extracts by coimmunoprecipitation, and in gene expression of SREBP-1c by Northern blot analysis of rat primary hepatocytes and mouse liver RNA. These data suggest that PPARalpha activation can suppress LXR-SREBP-1c pathway through reduction of LXR/RXR formation, proposing a novel transcription factor cross-talk between LXR and PPARalpha in hepatic lipid homeostasis.
Mol Endocrinol 2003 Jul
PMID:Cross-talk between peroxisome proliferator-activated receptor (PPAR) alpha and liver X receptor (LXR) in nutritional regulation of fatty acid metabolism. I. PPARs suppress sterol regulatory element binding protein-1c promoter through inhibition of LXR signaling. 1273 Mar 32

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.
Mol Endocrinol 2003 Jul
PMID:Cross-talk between peroxisome proliferator-activated receptor (PPAR) alpha and liver X receptor (LXR) in nutritional regulation of fatty acid metabolism. II. LXRs suppress lipid degradation gene promoters through inhibition of PPAR signaling. 1273 Mar 31

Cyclooxygenase-2 (COX-2) expression and peroxisome proliferator-activated receptor-gamma (PPARgamma) inactivation are linked to increased risk of human breast cancer. This study examines the effect of simultaneous targeting of COX-2 and PPARgamma on the proliferation of human breast cancer cells and on the expression of Bcl-2, BAX, and caspases-3 and -9, modulators of apoptotic cell death. Treatment of MDA-MB-231 breast cancer cells with NS-398 (a COX-2 inhibitor) or ciglitazone (CGZ, a PPARgamma-ligand) significantly inhibited cell proliferation and markedly increased apoptotic rates. These effects were accompanied by upregulation of BAX and caspases-3 and -9 mRNA expression and downregulation of Bcl-2. Compared to the influence of separate treatments, simultaneous treatment with NS-398 and CGZ synergistically inhibited cell proliferation and induced apoptotic cell death. In conclusion, combinational targeting of COX-2 and PPARgamma can inhibit the growth of human breast cancer cells and induce apoptosis to an extent more suprior to that produced by targeting each molecule alone. COX-2 and PPARgamma can be promising molecular targets for combinational chemoprevention or treatment of breast cancer.
Int J Mol Med 2003 Jun
PMID:Inhibition of cyclooxygenase-2 and activation of peroxisome proliferator-activated receptor-gamma synergistically induces apoptosis and inhibits growth of human breast cancer cells. 1273 14

Serum lipid responses to dietary modification are partly determined by genetic factors. The objective of the present study was to investigate the influence of the Pro12Ala polymorphism of the peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2) gene on serum lipid and lipoprotein responses to n-3 fatty acid supplementation. A total of 76 men and 74 women (age 49+/-8 years, body mass index 26.5+/-3.0 kg/m(2)) participated in a controlled multi-center study. Subjects were randomly assigned to consume either fish oil supplements (3.6g n-3 fatty acids/day containing 2.4 g of EPA and DHA) or placebo capsules containing olive oil for 3 months. At baseline, the Pro12Ala polymorphism was not associated with serum total and lipoprotein lipid concentrations or lipoprotein lipase activity in the fasting state. After the 3-month study period, carriers of the Ala12 allele presented a greater decrease in serum triacylglycerol concentration in response to n-3 fatty acid supplementation than did subjects with the Pro12Pro genotype when the total dietary fat intake was below 37 E% (p=0.003) or the intake of saturated fatty acids was below 10 E% (p=0.006). Changes in serum total cholesterol, serum LDL cholesterol and HDL cholesterol concentrations were similar among the genotypes in the n-3 fatty acid supplementation group and in the placebo group. In conclusion, the Pro12Ala polymorphism of the PPAR-gamma2 gene may modify the inter-individual variability in serum triacylglycerol response to n-3 fatty acid supplementation.
Mol Genet Metab 2003 May
PMID:Impact of the Pro12Ala polymorphism of the PPAR-gamma2 gene on serum triacylglycerol response to n-3 fatty acid supplementation. 1276 46

Fenofibrate, a peroxisome proliferator-activated receptor (PPAR)-alpha activator, used as a normolipidemic agent, is thought to offer additional beneficial effects in atherosclerosis. Since angiogenesis is involved in plaque progression, hemorrhage, and instability, the main causes of ischemic events, this study was designed to evaluate the action of fenofibrate on angiogenesis. Our results show that fenofibrate (i) inhibits endothelial cell proliferation induced by angiogenic factors, followed at high concentrations by an increase in apoptosis, (ii) inhibits endothelial cell migration in a healing wound model, (iii) inhibits capillary tube formation in vitro, and (iv) inhibits angiogenesis in vivo. Concerning the mechanism of action, the inhibition of endothelial cell migration by fenofibrate can be explained by a disorganization of the actin cytoskeleton. At the molecular level, fenofibrate markedly decreased basic fibroblast growth factor-induced Akt activation and cyclooxygenase 2 gene expression. This inhibition of angiogenesis could participate in the beneficial effect of fenofibrate in atherosclerosis.
Cell Mol Life Sci 2003 Apr
PMID:Fenofibrate inhibits angiogenesis in vitro and in vivo. 1278 28

The ligand-binding domain (LBD) of apo-nuclear receptors in solution is thought to be a very dynamic structure with many possible conformations. Upon ligand binding, the structure is stabilized to a more rigid conformation. The dynamic stabilization assay is a LBD reassembly assay that takes advantage of the high specificity of the intramolecular interactions that comprise the ligand-bound LBD. Here, we demonstrate dynamic stabilization for the nuclear receptors peroxisome proliferator-activated receptor (PPAR)gamma and nerve growth factor inducible (NGFIB)beta and identify residues important for stabilization of the intramolecular interactions induced by PPARgamma ligands. Site-directed mutagenesis studies identified residues in helices 1 and 8 required for LBD reassembly. Further, disrupting the helix 1/8 interaction in the context of the holo-LBD alters the response of the receptor in a compound-specific manner, suggesting that residues far from the ligand-binding pocket can influence the stability of the ligand-bound receptor. Thus, these results support and extend models of the apo-LBD of PPARgamma as a dynamic structure.
Mol Endocrinol 2003 Sep
PMID:Helix 1/8 interactions influence the activity of nuclear receptor ligand-binding domains. 1281 79

Atherosclerotic lesions occur as a result of excess lipid deposition within the vascular tissues. The peroxisome proliferator-activated receptors (PPARs) present in adipose and hepatic tissues have been shown to promote fatty acid oxidation and lipid storage. An immunohistochemical assessment of PPARalpha and PPARgamma revealed both proteins were also present in the medial and intimal layers of human arteries, predominately in regions containing smooth muscle cells. In agreement with this observation, smooth muscle cells isolated from these vessels were found by RT-PCR to express both PPARalpha and PPARgamma1. The functionality of these receptors was tested with selective PPAR agonists. Mitogenic stimulation of smooth muscle cell proliferation was blocked by 15d-PGJ2, a PPARgamma agonist, as well as by WY14643, a PPARalpha agonist. These data indicate PPAR activation by selective agonists could influence lesion progression directly, as well as indirectly through reductions in serum lipoprotein and triglyceride levels.
Mol Cell Biochem 2003 Apr
PMID:Activation of peroxisome proliferator-activated receptors alpha and gamma1 inhibits human smooth muscle cell proliferation. 1284 50

Initially identified and further developed as inhibitors of cyclooxygenases, nonsteroidal antiinflammatory drugs (NSAIDs) have been more recently shown to bind to and act as agonists of the peroxisome proliferator-activated receptor family of transcription factors. Here we summarize the current knowledge on the functions of the principal targets of NSAIDs and review their role in T and B lymphocytes, with a focus on the molecular mechanisms underlying the effects of NSAIDs on lymphocyte development, activation, differentiation and death.
Cell Mol Life Sci 2003 Jun
PMID:Molecular mechanisms underlying suppression of lymphocyte responses by nonsteroidal antiinflammatory drugs. 1286 76

The nuclear receptor peroxisome proliferator-activated receptor (PPAR) is activated by a diverse group of acidic ligands, including many peroxisome proliferator chemicals present in the environment. Janus tyrosine kinase-signal transducer and activator of transcription (JAK-STAT) signaling is activated by multiple cytokines and hormones and leads to the translocation of dimerized STAT proteins to the nucleus where they activate transcription of target genes. Previous studies have shown that growth hormone (GH)-activated STAT5b can inhibit PPAR-regulated transcription. Here, we show that this inhibitory cross-talk is mutual, and that GH-induced, STAT5b-dependent beta-casein promoter-luciferase reporter gene transcription can be inhibited up to approximately 80% by ligand-activated PPARalpha or PPARgamma. Dose-response experiments showed a direct relationship between the extent of PPAR activation and the degree of inhibition of STAT5-regulated transcription. PPAR did not block STAT5b tyrosine phosphorylation or inhibit DNA-binding activity. Both PPARs inhibited the transcriptional activity of a constitutively active STAT5b mutant, indicating that inhibition occurs downstream of the GH-stimulated STAT5 activation step. Transcriptionally inactive, dominant-negative PPAR mutants did not block STAT5b inhibition by wild-type PPAR, indicating that PPAR target gene transcription is not required. PPARalpha retained its STAT5b inhibitory activity in the presence of the histone deacetylase inhibitor trichostatin, indicating that enhanced histone deacetylase recruitment does not contribute to STAT5b inhibition. PPARalpha lacking the ligand-independent AF-1 trans-activation domain failed to inhibit STAT5b, highlighting the importance of the AF-1 region in STAT5-PPAR inhibitory cross-talk. These findings demonstrate the bidirectionality of cross-talk between the PPAR and STAT pathways and provide a mechanism whereby exposure to environmental chemical activators of PPAR can suppress expression of GH target genes.
Mol Pharmacol 2003 Aug
PMID:Down-regulation of STAT5b transcriptional activity by ligand-activated peroxisome proliferator-activated receptor (PPAR) alpha and PPARgamma. 1286 40

The aim of this study was to examine the expression and regulation of peroxisome proliferator-activated receptor (PPAR) PPARdelta gene in mouse uterus during early pregnancy by in situ hybridization and immunohistochemistry. PPARdelta expression under pseudopregnancy, delayed implantation, hormonal treatment, and artificial decidualization was also investigated. There was a very low level of PPARdelta expression on days 1-4 of pregnancy. On day 5 when embryo implanted, PPARdelta expression was exclusively observed in the subluminal stroma surrounding the implanting blastocyst. No corresponding signals were seen in the uterus on day 5 of pregnancy. There was no detectable PPARdelta signal under delayed implantation. Once delayed implantation was terminated by estrogen treatment and embryo implanted, a strong level of PPARdelta expression was induced in the subluminal stroma surrounding the implanting blastocyst. Estrogen treatment induced a moderate level of PPARdelta expression in the glandular epithelium, while progesterone treatment had no effects in the ovariectomized mice. A strong level of PPARdelta expression was seen in the decidua on days 6-8 of pregnancy. PPARdelta expression was also induced under artificial decidualization. These data suggest that PPARdelta expression at implantation sites require the presence of an active blastocyst and may play an essential role for blastocyst implantation.
Mol Reprod Dev 2003 Nov
PMID:Peroxisome proliferator-activated receptor delta expression and regulation in mouse uterus during embryo implantation and decidualization. 1450


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