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Nekrasova EV, Larionova EE, Danko K, Kuzmina DO, Shavva VS, Kudriavtsev IV, Orlov SV. Regulation of Apolipoprotein A-I Gene Expression in Human Macrophages by Oxidized Low-Density Lipoprotein. BIOCHEMISTRY. BIOKHIMIIA 2021; 86:1201-1213. [PMID: 34903152 DOI: 10.1134/s0006297921100047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Revised: 07/18/2021] [Accepted: 07/23/2021] [Indexed: 06/14/2023]
Abstract
Apolipoprotein A-I (ApoA-I) is a key component of reverse cholesterol transport in humans. In the previous studies, we demonstrated expression of the apoA-I gene in human monocytes and macrophages; however, little is known on the regulation of the apoA-I expression in macrophages during the uptake of modified low-density lipoprotein (LDL), which is one of the key processes in the early stages of atherogenesis leading to formation of foam cells. Here, we demonstrate a complex nature of the apoA-I regulation in human macrophages during the uptake of oxidized LDL (oxLDL). Incubation of macrophages with oxLDL induced expression of the apoA-I gene within the first 24 hours, but suppressed it after 48 h. Both effects depended on the interaction of oxLDL with the TLR4 receptor, rather than on the oxLDL uptake by the macrophages. The oxLDL-mediated downregulation of the apoA-I gene depended on the ERK1/2 and JNK cascades, as well as on the NF-κB cascade.
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Affiliation(s)
| | | | - Katerina Danko
- St. Petersburg State University, St. Petersburg, 199034, Russia
| | - Darya O Kuzmina
- St. Petersburg State University, St. Petersburg, 199034, Russia
| | | | | | - Sergey V Orlov
- Institute of Experimental Medicine, St. Petersburg, 197376, Russia.
- St. Petersburg State University, St. Petersburg, 199034, Russia
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Li B, Cai SY, Boyer JL. The role of the retinoid receptor, RAR/RXR heterodimer, in liver physiology. Biochim Biophys Acta Mol Basis Dis 2021; 1867:166085. [PMID: 33497820 PMCID: PMC11152086 DOI: 10.1016/j.bbadis.2021.166085] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 01/09/2021] [Accepted: 01/12/2021] [Indexed: 12/31/2022]
Abstract
Activated by retinoids, metabolites of vitamin A, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs) play important roles in a wide variety of biological processes, including embryo development, homeostasis, cell proliferation, differentiation and death. In this review, we summarized the functional roles of nuclear receptor RAR/RXR heterodimers in liver physiology. Specifically, RAR/RXR modulate the synthesis and metabolism of lipids and bile acids in hepatocytes, regulate cholesterol transport in macrophages, and repress fibrogenesis in hepatic stellate cells. We have also listed the specific genes that carry these functions and how RAR/RXR regulate their expression in liver cells, providing a mechanistic view of their roles in liver physiology. Meanwhile, we pointed out many questions regarding the detailed signaling of RAR/RXR in regulating the expression of liver genes, and hope future studies will address these issues.
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Affiliation(s)
- Baixue Li
- Liver Center, Yale University School of Medicine, New Haven, CT 06520, United States; College of Basic Medical Sciences, Chengdu University of Traditional Chinese Medicine, Chengdu 610075, China.
| | - Shi-Ying Cai
- Liver Center, Yale University School of Medicine, New Haven, CT 06520, United States.
| | - James L Boyer
- Liver Center, Yale University School of Medicine, New Haven, CT 06520, United States.
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3H-Imidazo[4,5-b]pyridine-6-carboxylic acid derivatives as rexinoids with reduced teratogenicity. Bioorg Med Chem Lett 2019; 29:1891-1894. [PMID: 31160175 DOI: 10.1016/j.bmcl.2019.05.050] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Revised: 05/24/2019] [Accepted: 05/27/2019] [Indexed: 01/08/2023]
Abstract
Several retinoid X receptor (RXR) ligands (rexinoids), such as bexarotene (1), exhibit teratogenicity, which is a serious impediment to their clinical application. We considered that rexinoids with a lower level of maximal RXR transcription activation (i.e., partial agonists) and lower lipid solubility might show weaker adverse side effects. Based on this idea, we modified our previously reported pentamethyltetralin-type RXR partial agonists 5 and 6 to reduce their lipophilicity. Here, we report a new RXR partial agonist, 3-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl)-2-(trifluoromethyl)-3H-imidazo[4,5-b]pyridine-6-carboxylic acid (8, CATF-PMN), which showed greatly reduced teratogenicity in zebrafish embryos.
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Tumor necrosis factor α stimulates endogenous apolipoprotein A-I expression and secretion by human monocytes and macrophages: role of MAP-kinases, NF-κB, and nuclear receptors PPARα and LXRs. Mol Cell Biochem 2018; 448:211-223. [PMID: 29442267 DOI: 10.1007/s11010-018-3327-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Accepted: 02/07/2018] [Indexed: 02/07/2023]
Abstract
Apolipoprotein A-I (ApoA-I) is the main structural and functional protein component of high-density lipoprotein. ApoA-I has been shown to regulate lipid metabolism and inflammation in macrophages. Recently, we found the moderate expression of endogenous apoA-I in human monocytes and macrophages and showed that pro-inflammatory cytokine tumor necrosis factor α (TNFα) increases apoA-I mRNA and stimulates ApoA-I protein secretion by human monocytes and macrophages. Here, we present data about molecular mechanisms responsible for the TNFα-mediated activation of apoA-I gene in human monocytes and macrophages. This activation depends on JNK and MEK1/2 signaling pathways in human monocytes, whereas inhibition of NFκB, JNK, or p38 blocks an increase of apoA-I gene expression in the macrophages treated with TNFα. Nuclear receptor PPARα is a ligand-dependent regulator of apoA-I gene, whereas LXRs stimulate apoA-I mRNA transcription and ApoA-I protein synthesis and secretion by macrophages. Treatment of human macrophages with PPARα or LXR synthetic ligands as well as knock-down of LXRα, and LXRβ by siRNAs interfered with the TNFα-mediated activation of apoA-I gene in human monocytes and macrophages. At the same time, TNFα differently regulated the levels of PPARα, LXRα, and LXRβ binding to the apoA-I gene promoter in THP-1 cells. Obtained results suggest a novel tissue-specific mechanism of the TNFα-mediated regulation of apoA-I gene in monocytes and macrophages and show that endogenous ApoA-I might be positively regulated in macrophage during inflammation.
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Liu J, Hernandez-Ono A, Graham MJ, Galton VA, Ginsberg HN. Type 1 Deiodinase Regulates ApoA-I Gene Expression and ApoA-I Synthesis Independent of Thyroid Hormone Signaling. Arterioscler Thromb Vasc Biol 2016; 36:1356-66. [PMID: 27150392 DOI: 10.1161/atvbaha.116.307330] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Accepted: 04/20/2016] [Indexed: 01/10/2023]
Abstract
OBJECTIVE Plasma levels of high-density lipoprotein cholesterol (HDL-C) and apolipoprotein A-I (ApoA-I) are reduced in individuals with defective insulin signaling. Initial studies using liver-specific insulin receptor (InsR) knockout mice identified reduced expression of type 1 deiodinase (Dio1) as a potentially novel link between defective hepatic insulin signaling and reduced expression of the ApoA-I gene. Our objective was to examine the regulation of ApoA-I expression by Dio1. APPROACH AND RESULTS Acute inactivation of InsR by adenoviral delivery of Cre recombinase to InsR floxed mice reduced HDL-C and expression of both ApoA-I and Dio1. Overexpression of Dio1 in InsR knockout mice restored HDL-C and ApoA-I levels and increased the expression of ApoA-I. Dio1 knockout mice had low expression of ApoA-I and reduced serum levels of HDL-C and ApoA-I. Treatment of C57BL/6J mice with antisense to Dio1 reduced ApoA-I mRNA, HDL-C, and serum ApoA-I. Hepatic 3,5,3'-triiodothyronine content was normal or elevated in InsR knockout mice or Dio1 knockout mice. Knockdown of either InsR or Dio1 by siRNA in HepG2 cells decreased the expression of ApoA-I and ApoA-I synthesis and secretion. siRNA knockdown of InsR or Dio1 decreased activity of a region of the ApoA-I promoter lacking thyroid hormone response elements (region B). Electrophoretic mobility shift assay demonstrated that reduced Dio1 expression decreased the binding of nuclear proteins to region B. CONCLUSIONS Reductions in Dio1 expression reduce the expression of ApoA-I in a 3,5,3'-triiodothyronine-/thyroid hormone response element-independent manner.
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Affiliation(s)
- Jing Liu
- From the Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY (J.L., A.H.-O., H.N.G.); Ionis Pharmaceuticals, Inc, Carlsbad, CA (M.J.G.); and Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, NH (V.A.G.).
| | - Antonio Hernandez-Ono
- From the Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY (J.L., A.H.-O., H.N.G.); Ionis Pharmaceuticals, Inc, Carlsbad, CA (M.J.G.); and Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, NH (V.A.G.)
| | - Mark J Graham
- From the Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY (J.L., A.H.-O., H.N.G.); Ionis Pharmaceuticals, Inc, Carlsbad, CA (M.J.G.); and Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, NH (V.A.G.)
| | - Valerie Anne Galton
- From the Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY (J.L., A.H.-O., H.N.G.); Ionis Pharmaceuticals, Inc, Carlsbad, CA (M.J.G.); and Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, NH (V.A.G.)
| | - Henry N Ginsberg
- From the Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY (J.L., A.H.-O., H.N.G.); Ionis Pharmaceuticals, Inc, Carlsbad, CA (M.J.G.); and Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, NH (V.A.G.).
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Shavva VS, Mogilenko DA, Bogomolova AM, Nikitin AA, Dizhe EB, Efremov AM, Oleinikova GN, Perevozchikov AP, Orlov SV. PPARγ Represses Apolipoprotein A-I Gene but Impedes TNFα-Mediated ApoA-I Downregulation in HepG2 Cells. J Cell Biochem 2016; 117:2010-22. [DOI: 10.1002/jcb.25498] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 01/25/2016] [Indexed: 11/06/2022]
Affiliation(s)
- Vladimir S. Shavva
- Department of Biochemistry; Institute of Experimental Medicine; Russian Academy of Medical Sciences; St. Petersburg Russia
- Department of Embryology; St. Petersburg State University; St. Petersburg Russia
| | - Denis A. Mogilenko
- Department of Biochemistry; Institute of Experimental Medicine; Russian Academy of Medical Sciences; St. Petersburg Russia
- Department of Embryology; St. Petersburg State University; St. Petersburg Russia
| | | | - Artemy A. Nikitin
- Department of Biochemistry; Institute of Experimental Medicine; Russian Academy of Medical Sciences; St. Petersburg Russia
- Department of Biochemistry; St. Petersburg State University; St. Petersburg Russia
| | - Ella B. Dizhe
- Department of Biochemistry; Institute of Experimental Medicine; Russian Academy of Medical Sciences; St. Petersburg Russia
| | - Alexander M. Efremov
- Department of Biochemistry; Institute of Experimental Medicine; Russian Academy of Medical Sciences; St. Petersburg Russia
- Department of Embryology; St. Petersburg State University; St. Petersburg Russia
| | - Galina N. Oleinikova
- Department of Biochemistry; Institute of Experimental Medicine; Russian Academy of Medical Sciences; St. Petersburg Russia
| | - Andrej P. Perevozchikov
- Department of Biochemistry; Institute of Experimental Medicine; Russian Academy of Medical Sciences; St. Petersburg Russia
- Department of Embryology; St. Petersburg State University; St. Petersburg Russia
| | - Sergey V. Orlov
- Department of Biochemistry; Institute of Experimental Medicine; Russian Academy of Medical Sciences; St. Petersburg Russia
- Department of Embryology; St. Petersburg State University; St. Petersburg Russia
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Abstract
It has long been established that the transcriptional activity of retinoic acid (RA) is mediated by members of the nuclear receptor family of ligand-activated transcription factors termed RA receptors (RARs). More recent observations have established that RA also activates an additional nuclear receptor, PPARβ/δ. Partitioning RA between RARs and PPARβ/δ is governed by different intracellular lipid-binding proteins: cellular RA binding protein 2 (CRABP2) delivers RA to nuclear RARs and a fatty acid binding protein (FABP5) delivers the hormone from the cytosol to nuclear PPARβ/δ. Consequently, RA signals through RARs in CRABP2-expressing cells, but activates PPARβ/δ in cells that express a high level of FABP5. RA elicits different and sometimes opposing responses in cells that express different FABP5/CRABP2 ratios because PPARβ/δ and RARs regulate the expression of distinct sets of genes. An overview of the observations that led to the discovery of this non-classical activity of RA are presented here, along with a discussion of evidence demonstrating the involvement of the dual transcriptional activities of RA in regulating energy homeostasis, insulin responses, and adipocyte and neuron differentiation.
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Kardassis D, Gafencu A, Zannis VI, Davalos A. Regulation of HDL genes: transcriptional, posttranscriptional, and posttranslational. Handb Exp Pharmacol 2015; 224:113-179. [PMID: 25522987 DOI: 10.1007/978-3-319-09665-0_3] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
HDL regulation is exerted at multiple levels including regulation at the level of transcription initiation by transcription factors and signal transduction cascades; regulation at the posttranscriptional level by microRNAs and other noncoding RNAs which bind to the coding or noncoding regions of HDL genes regulating mRNA stability and translation; as well as regulation at the posttranslational level by protein modifications, intracellular trafficking, and degradation. The above mechanisms have drastic effects on several HDL-mediated processes including HDL biogenesis, remodeling, cholesterol efflux and uptake, as well as atheroprotective functions on the cells of the arterial wall. The emphasis is on mechanisms that operate in physiologically relevant tissues such as the liver (which accounts for 80% of the total HDL-C levels in the plasma), the macrophages, the adrenals, and the endothelium. Transcription factors that have a significant impact on HDL regulation such as hormone nuclear receptors and hepatocyte nuclear factors are extensively discussed both in terms of gene promoter recognition and regulation but also in terms of their impact on plasma HDL levels as was revealed by knockout studies. Understanding the different modes of regulation of this complex lipoprotein may provide useful insights for the development of novel HDL-raising therapies that could be used to fight against atherosclerosis which is the underlying cause of coronary heart disease.
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Affiliation(s)
- Dimitris Kardassis
- Department of Biochemistry, University of Crete Medical School and Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology of Hellas, Heraklion, Crete, 71110, Greece,
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Alfano C, Magrinelli E, Harb K, Studer M. The nuclear receptors COUP-TF: a long-lasting experience in forebrain assembly. Cell Mol Life Sci 2014; 71:43-62. [PMID: 23525662 PMCID: PMC11114017 DOI: 10.1007/s00018-013-1320-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2012] [Revised: 02/14/2013] [Accepted: 03/04/2013] [Indexed: 12/16/2022]
Abstract
Chicken ovalbumin upstream promoter transcription factors (COUP-TFs) are nuclear receptors belonging to the superfamily of the steroid/thyroid hormone receptors. Members of this family are internalized to the nucleus both in a ligand-dependent or -independent manner and act as strong transcriptional regulators by binding to the DNA of their target genes. COUP-TFs are defined as orphan receptors, since ligands regulating their activity have not so far been identified. From the very beginning of metazoan evolution, these molecules have been involved in various key events during embryonic development and organogenesis. In this review, we will mainly focus on their function during development and maturation of the central nervous system, which has been well characterized in various animal classes ranging from ctenophores to mammals. We will start by introducing the current knowledge on COUP-TF mechanisms of action and then focus our discussion on the crucial processes underlying forebrain ontogenesis, with special emphasis on mammalian development. Finally, the conserved roles of COUP-TFs along phylogenesis will be highlighted, and some hypotheses, worth exploring in future years to gain more insight into the mechanisms controlled by these factors, will be proposed.
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Affiliation(s)
- Christian Alfano
- Institute of Biology Valrose, iBV, UMR INSERM1091/CNRS7277/UNS, 06108 Nice, France
- University of Nice-Sophia Antipolis, UFR Sciences, 06108 Nice, France
| | - Elia Magrinelli
- Institute of Biology Valrose, iBV, UMR INSERM1091/CNRS7277/UNS, 06108 Nice, France
- University of Nice-Sophia Antipolis, UFR Sciences, 06108 Nice, France
| | - Kawssar Harb
- Institute of Biology Valrose, iBV, UMR INSERM1091/CNRS7277/UNS, 06108 Nice, France
- University of Nice-Sophia Antipolis, UFR Sciences, 06108 Nice, France
| | - Michèle Studer
- Institute of Biology Valrose, iBV, UMR INSERM1091/CNRS7277/UNS, 06108 Nice, France
- University of Nice-Sophia Antipolis, UFR Sciences, 06108 Nice, France
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Oleaga C, Ciudad CJ, Izquierdo-Pulido M, Noé V. Cocoa flavanol metabolites activate HNF-3β, Sp1, and NFY-mediated transcription of apolipoprotein AI in human cells. Mol Nutr Food Res 2013; 57:986-95. [PMID: 23293065 DOI: 10.1002/mnfr.201200507] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2012] [Revised: 10/23/2012] [Accepted: 11/04/2012] [Indexed: 12/28/2022]
Abstract
SCOPE To identify the mechanisms by which cocoa induces HDL levels and since apolipoprotein AI (ApoAI) is the major protein in HDLs, we analyzed, upon incubation with cocoa metabolites, ApoAI mRNA levels, its transcriptional regulation, and the levels of the transcription factors involved in this process. METHODS AND RESULTS Epicatechin and cocoa metabolites caused an increase in ApoAI expression in HepG2 cells. Electrophoretic mobility shift assays revealed the involvement of Sites A and B of the ApoAI promoter in the induction of ApoAI mRNA upon incubation with cocoa metabolites. Using supershift assays, we demonstrated the binding of HNF-3β, HNF-4, ER-α, and RXR-α to Site A and the binding of HNF-3β, NFY, and Sp1 to Site B. Luciferase assays performed with a construct containing Site B confirmed its role in the upregulation of ApoAI by cocoa metabolites. Incubation with 3-methyl-epicatechin led to an increase in HNF-3β mRNA, HNF-3β, ER-α, Sp1, and NFY protein levels and the activation of ApoAI transcription mediated by NFY, Sp1, and ER-α. CONCLUSION The activation of ApoAI transcription through Site B by cocoa flavanol metabolites is mainly mediated by an increase in HNF-3β, with a significant contribution of Sp1 and NFY, as a mechanism for the protective role of these compounds in cardiovascular diseases.
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Affiliation(s)
- Carlota Oleaga
- Department of Biochemistry and Molecular Biology, School of Pharmacy, University of Barcelona, Barcelona, Spain
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Citelli M, Bittencourt LL, da Silva SV, Pierucci APT, Pedrosa C. Vitamin A modulates the expression of genes involved in iron bioavailability. Biol Trace Elem Res 2012; 149:64-70. [PMID: 22528770 DOI: 10.1007/s12011-012-9397-6] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2011] [Accepted: 03/22/2012] [Indexed: 01/25/2023]
Abstract
Iron bioavailability seems to be regulated by vitamin A (VA) but the molecular events involved in this mechanism are not well understood. It is also known that retinoids mediate most of their function via interaction with retinoid receptors, which act as ligand-activated transcription factors controlling the expression of a number of target genes. Here, we evaluated the VA effects on the modulation of the levels of mRNA encoding proteins involved in the iron bioavailability, whether in the intestinal absorption process or in the liver iron metabolism. The expression of genes involved in iron intestinal absorption (divalent metal transporter 1, duodenal cytochrome B, ferroportin 1 FPN1, and ferritin) were evaluated in vitro by treating Caco-2 cells with retinoic acid or in vivo by observing the effects of vitamin A deficiency (VAD) in BALB/C mice. Liver hepcidin and ferritin mRNA levels were upregulated by VAD; however, this condition did not promote any change on the expression of those genes that participate in the iron absorption. Moreover, data from the in vitro analysis showed that VA induced FPN1 gene expression by a hepcidin-independent manner. Therefore, the in vivo results support the idea that VAD may not affect iron absorption but would rather affect iron mobilization mechanisms. On the other hand, our results using Caco-2 cells raises the possibility that VA addition to intestinal epithelium may improve iron absorption through the induction of FPN1 gene expression.
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Affiliation(s)
- Marta Citelli
- Instituto de Nutrição, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, RJ, 20551-030, Brazil.
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12
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Kuang YL, Paulson KE, Lichtenstein AH, Matthan NR, Lamon-Fava S. Docosahexaenoic acid suppresses apolipoprotein A-I gene expression through hepatocyte nuclear factor-3β. Am J Clin Nutr 2011; 94:594-600. [PMID: 21653803 DOI: 10.3945/ajcn.111.012526] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND Dietary fish-oil supplementation has been shown in human kinetic studies to lower the production rate of apolipoprotein (apo) A-I, the major protein component of HDL. The underlying mechanism responsible for this effect is not fully understood. OBJECTIVE We investigated the effect and the mechanism of action of the very-long-chain n-3 (omega-3) polyunsaturated fatty acid docosahexaenoic acid (DHA), relative to the saturated fatty acid palmitic acid (PA), on the hepatic expression of apo A-I in HepG2 cells. DESIGN HepG2 cells were treated with different doses of DHA and PA (0-200 μmol/L). mRNA expression levels of apo A-I were assessed by real-time polymerase chain reaction, and apo A-I protein concentrations were measured by immunoassay. DHA dose-dependently suppressed apo A-I mRNA levels and also lowered apo A-I protein concentrations in the media, with maximum effects at 200 μmol/L. This concentration of fatty acids was used in all subsequent experiments. RESULTS To elucidate the mechanism mediating the reduction in apo A-I expression by DHA, transfection experiments were conducted with plasmid constructs containing serial deletions of the apo A-I promoter. The DHA-responsive region was mapped to the -185 to -148 nucleotide region of the apo A-I promoter, which binds the hepatocyte nuclear factor (HNF)-3β. Nuclear extracts from cells treated with DHA or PA had a similar nuclear abundance of HNF-3β. However, electrophoresis mobility shift assays showed less binding of HNF-3β to the -180 to -140 sequence of the apo A-I promoter than did PA-treated cells. As shown by chromatin immunoprecipitation analysis, less HNF-3β was recruited to the apo A-I promoter in DHA-treated cells than in PA-treated cells, which supports the concept of an interference of DHA with the binding of HNF-3β to the apo A-I promoter. CONCLUSION These findings suggest that, in human hepatoma HepG2 cells, DHA inhibits the binding of HNF-3β to the apo A-I promoter, resulting in the repression of apo A-I promoter transactivity and thus a reduction in apo A-I expression.
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Affiliation(s)
- Yu-Lin Kuang
- Lipid Metabolism Laboratory, Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA, USA
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13
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Orlov SV, Mogilenko DA, Shavva VS, Dizhe EB, Ignatovich IA, Perevozchikov AP. Effect of TNFα on activities of different promoters of human apolipoprotein A-I gene. Biochem Biophys Res Commun 2010; 398:224-30. [DOI: 10.1016/j.bbrc.2010.06.064] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2010] [Accepted: 06/15/2010] [Indexed: 11/26/2022]
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14
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von Eynatten M, Humpert PM. Retinol-binding protein-4 in experimental and clinical metabolic disease. Expert Rev Mol Diagn 2008; 8:289-99. [PMID: 18598108 DOI: 10.1586/14737159.8.3.289] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Retinol-binding protein-4 (RBP4), a 21-kDa protein synthesized in the liver and adipose tissue, has recently been described as a murine adipokine involved in the development of insulin resistance. The expression of the gene encoding RBP4 was increased in the adipose tissue, but not in the liver, of insulin-resistant adipose GLUT4(-/-) mice and five other mouse models of obesity and insulin resistance. In addition, intraperitoneal injection or transgenic overexpression of RBP4 in mice induced insulin resistance. While experimental clinical approaches (mostly applying clamp techniques) in humans confirmed correlations of RBP4 with insulin resistance, studies in larger groups out of clinical routine failed to demonstrate a connection with alternative measures of insulin sensitivity. Yet, significant associations of RBP4 with atherogenic lipids were found and a focus of future studies should be the influence on atherosclerosis and related complications. Based on current data, the function of RBP4 as an adipokine exerting metabolic effects in glucose metabolism in humans remains uncertain and might be restricted to rodent models.
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Ramlau R, Zatloukal P, Jassem J, Schwarzenberger P, Orlov SV, Gottfried M, Pereira JR, Temperley G, Negro-Vilar R, Rahal S, Zhang JK, Negro-Vilar A, Dziewanowska ZE. Randomized phase III trial comparing bexarotene (L1069-49)/cisplatin/vinorelbine with cisplatin/vinorelbine in chemotherapy-naive patients with advanced or metastatic non-small-cell lung cancer: SPIRIT I. J Clin Oncol 2008; 26:1886-92. [PMID: 18398154 DOI: 10.1200/jco.2007.12.2614] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PURPOSE This study evaluated whether the combination of the synthetic rexinoid bexarotene with first-line cisplatin/vinorelbine therapy provides additional survival benefit in patients with advanced non-small-cell lung cancer (NSCLC). PATIENTS AND METHODS Patients with stage IIIB with pleural effusion or stage IV NSCLC and Eastern Cooperative Oncology Group performance status 0 to 1 were randomly assigned to open-label bexarotene 400 mg/m(2)/d with cisplatin/vinorelbine or to cisplatin/vinorelbine alone. Antilipid agents were initiated on or before day 1 in the bexarotene arm. Primary efficacy end point was overall survival. Primary, secondary and supportive efficacy analyses were conducted. RESULTS A total of 623 patients (312 control, 311 bexarotene) were enrolled. Overall, no significant difference in survival occurred between the two treatment groups. However, an unplanned retrospective analysis showed that a subpopulation of bexarotene patients (n = 98 of 306) who experienced National Cancer Institute grade 3/4 hypertriglyceridemia had longer median survival compared with control patients (12.3 v 9.9 months; log-rank P = .08). Within that subgroup, those who benefited the most included males, smokers, those with stage IV disease, and those with a 6-month prior weight loss of 5% or more. Incidence, type and severity of grade 3/4 adverse events were comparable between arms, except for leukopenia (higher in chemotherapy arm) and hyperlipemia, hypothyroidism, dyspnea, and headache (higher in chemotherapy/bexarotene arm). CONCLUSION The addition of bexarotene to first-line chemotherapy did not increase survival in patients with advanced NSCLC. However, a subgroup (32%) of bexarotene-treated patients developing high-grade hypertriglyceridemia appeared to have better survival (12.3 months) than controls; thus triglyceride response may be a biomarker of survival benefit with bexarotene.
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Affiliation(s)
- Rodryg Ramlau
- Lung Disease Centre, Oncology Department, ul.Szamarzewskiego, Poznań, Poland.
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Grenier E, Maupas FS, Beaulieu JF, Seidman E, Delvin E, Sane A, Tremblay E, Garofalo C, Levy E. Effect of retinoic acid on cell proliferation and differentiation as well as on lipid synthesis, lipoprotein secretion, and apolipoprotein biogenesis. Am J Physiol Gastrointest Liver Physiol 2007; 293:G1178-89. [PMID: 17916647 DOI: 10.1152/ajpgi.00295.2007] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Dietary vitamin A and its active metabolites are essential nutrients for many functions as well as potent regulators of gene transcription and growth. Although the epithelium of the small intestine is characterized by rapid and constant renewal and enterocytes play a central role in the absorption and metabolism of alimentary retinol, very little is known about the function of retinoids in the human gastrointestinal epithelium and mechanisms by which programs engage the cell cycle are poorly understood. We have assessed the effects of 10 microM 9- and 13-cis-retinoic acid (RA) on proliferation and differentiation processes, lipid esterification, apolipoprotein (apo) biogenesis and lipoprotein secretion along with nuclear factor gene transcription. Treatment of Caco-2 cells with RA at different concentrations and incubation periods revealed the reduction of thymidine incorporation in 60% preconfluent or 100% confluent cells. Concomitantly, RA 1) modulated D-type cyclins by reducing the mitogen-sensitive cyclin D1 and upregulating cyclin D3 expressions and 2) caused a trend of increase in p38 MAPK, which triggers CDX2, a central protein in cell differentiation. RA remained without effect on lipoprotein output and apo synthesis, even for apo A-I that possesses RARE in its promoter. RA, in combination with 22-hydroxycholesterol, could induce apo A-I gene expression without any impact on apo A-I mass. Only the gene expression of peroxisome proliferator-activated receptor (PPAR)beta, retinoic receptor (RAR)beta, and RARgamma was augmented and no alteration was noted in PPARalpha, PPARgamma, liver X receptor (LXR)alpha, LXRbeta, and retinoid X receptors. Taken together, these data highlight RA-induced cell differentiation via specific signaling without a significant impact on apo A-I synthesis.
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Affiliation(s)
- Emilie Grenier
- Department of Nutrition, Université de Montréal, Montréal, Québec, Canada.
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17
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Wehmeier K, Beers A, Haas MJ, Wong NCW, Steinmeyer A, Zugel U, Mooradian AD. Inhibition of apolipoprotein AI gene expression by 1, 25-dihydroxyvitamin D3. Biochim Biophys Acta Mol Cell Biol Lipids 2005; 1737:16-26. [PMID: 16236546 DOI: 10.1016/j.bbalip.2005.09.004] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2005] [Revised: 07/28/2005] [Accepted: 09/09/2005] [Indexed: 11/29/2022]
Abstract
Members of the steroid receptor superfamily are known to alter the transcription of apolipoprotein AI (apo AI), the major apoprotein of high-density lipoprotein (HDL). To assess the role of vitamin D receptor (VDR) in apo AI gene expression, we investigated the effect of 1alpha, 25-dihydroxycholecalciferol (1, 25-(OH)2 D3) as well as the vitamin D antagonist ZK-191784 (ZK), on apo AI gene expression and promoter activity in the human hepatoma cell line HepG2. Apo AI secretion and mRNA levels were both suppressed in a dose-dependent manner in HepG2 cells treated 1, 25-(OH)2 D3. This was accompanied by a similar decrease in apo AI promoter activity. Mapping of the vitamin D response element showed that suppression required a region of the apo AI gene promoter identified previously to contain site A. However, vitamin D treatment had no effect on nuclear factor binding to site A of the apo AI promoter. Treatment with vitamin D receptor antagonist ZK inhibited the ability of 1, 25-(OH)2 D3 to repress apo AI promoter activity, while higher doses of ZK increased apo AI promoter activity. ZK did not alter estradiol stimulated apo AI promoter activity. The VDR antisense ODN had no effect on apo AI promoter activity in control cells, however, it reversed the repression normally seen in cells treated with 1, 25-(OH)2D3. It is concluded that 1, 25-(OH)2 D3 suppresses apo A1 gene expression at the transcriptional level, possibly by altering coactivators or corepressors. This effect requires the VDR as well as a vitamin D response element in the apo AI promoter.
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Affiliation(s)
- Kent Wehmeier
- Division of Endocrinology, Diabetes and Metabolism, Department of Internal Medicine, Saint Louis University School of Medicine, 1402 S. Grand Blvd., St. Louis, MO 63104, USA
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18
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Abstract
PURPOSE OF REVIEW APOA1/C3/A4/A5 are key components modulating lipoprotein metabolism and cardiovascular disease risk. This review examines the evidence regarding linkage disequilibrium and haplotype structure within the A1/C3/A4/A5 cluster, and assesses its association with plasma lipids and cardiovascular disease risk. In addition, we use genomic information from several species to draw inferences about the location of functional variants within this cluster. RECENT FINDINGS The close physical distance of these genes and the interrelated functions of these apolipoproteins have encumbered attempts to determine the role of individual variants on lipid metabolism. Therefore, current research aims to define linkage disequilibrium and haplotype structure within this cluster. Functional variants in regulatory regions are most interesting as they are potentially amenable to therapy. Comparative genomics can contribute to the identification of such functional variants. SUMMARY Genetic variability at the APOA1/C3/A4/A5 cluster has been examined in relation to lipid metabolism and cardiovascular disease risk. However, the findings are inconsistent. This is partly due to the classic approach of studying single and mostly nonfunctional polymorphisms. Moreover, allelic expression may depend on the concurrent presence of environmental factors. Association studies using haplotypes should increase the power to detect true associations and interactions. We hypothesize that phenotypes observed in association with transcriptional regulatory variants can be readily modified by environmental factors. Therefore, studies focusing on regulatory variants may be more fruitful to locate/define future therapeutic targets.
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Affiliation(s)
- Chao-Qiang Lai
- Nutrition and Genomics Laboratory, Jean Mayer--US Department of Agriculture, Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts 02111, USA.
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Mouthiers A, Mejdoubi N, Baillet A, Amélie PA, Porquet D. Retinoids increase alpha-1 acid glycoprotein expression at the transcriptional level through two distinct DR1 retinoic acid responsive elements. ACTA ACUST UNITED AC 2004; 1678:135-44. [PMID: 15157739 DOI: 10.1016/j.bbaexp.2004.03.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2004] [Revised: 03/12/2004] [Accepted: 03/15/2004] [Indexed: 11/26/2022]
Abstract
In the present study, we analyzed the influence of retinoic acids on the expression of alpha-1 acid glycoprotein (AGP). We show that in rat primary hepatocytes, 9-cis retinoic acid and all-trans retinoic acid increase AGP gene expression at the transcriptional level. Transient transfections of rat primary hepatocytes with a reporter construct driven by the rat AGP gene promoter indicated that retinoids regulate AGP gene expression via the -763/-138 region of the AGP promoter. Furthermore, cotransfection experiments with retinoic acid receptor alpha (RARalpha) and retinoid X receptor alpha (RXRalpha) expression vectors in NIH3T3 cells demonstrated that both RXRalpha/RXRalpha homodimer and RXRalpha/RARalpha heterodimer are competent for ligand-induced transactivation of the AGP promoter. Unilateral deletion and site-directed mutagenesis identified two retinoic-acid responsive elements (RARE), RARE-I and RARE-II, which interestingly correspond to a direct repeat of two TGACCT-related hexanucleotides separated by a single bp only (DR1-type response element). Cotransfection assays showed that RXRalpha and RARalpha activate AGP gene transcription through these two elements either as a homodimer (RXRalpha/RXRalpha) or as a heterodimer (RXRalpha/RARalpha). The RXRalpha/RXRalpha homodimer acts most efficiently through the RARE-I response element to promote AGP transactivation, whereas the RXRalpha/RARalpha heterodimer mediates transactivation better via the RARE-II responsive element.
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Affiliation(s)
- Audrey Mouthiers
- Laboratoire de Biochimie et de Biologie Cellulaire, EAD 1595, Tour D4 1(er) étage, Faculté de Pharmacie, Université Paris XI, 5, rue J.B. Clément, 92296 Châtenay-Malabry Cedex, France
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Haas MJ, Horani M, Mreyoud A, Plummer B, Wong NCW, Mooradian AD. Suppression of apolipoprotein AI gene expression in HepG2 cells by TNF alpha and IL-1beta. Biochim Biophys Acta Gen Subj 2003; 1623:120-8. [PMID: 14572909 DOI: 10.1016/j.bbagen.2003.08.004] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Plasma inflammatory cytokines are elevated in obese subjects as well as in those with type 2 diabetes. This presumably results in systemic insulin resistance, characterized by a pro-atherogenic plasma lipid profile and reduced apolipoprotein AI (apoAI) protein levels. To determine how cytokine-mediated insulin resistance suppresses apoAI gene expression, we investigated the effect of tumor necrosis factor alpha (TNF alpha) and interleukin-1beta (IL-1beta) on apoAI protein, mRNA, and transcriptional activity in the human hepatoma cell line HepG2. ApoAI secretion was suppressed in a dose-dependent manner in HepG2 cells treated with both cytokines. ApoAI protein levels were 2892+/-22.0, 2263+/-117, 2458+/-25.0, 3401+/-152, 2333+/-248, 1520+/-41.5 and 956.0+/-11.0 arbitrary units (AU) in cells treated with 0, 0.3, 1.0, 3.0, 10, 30, and 100 ng/ml TNF alpha, achieving statistical significance in the 30 and 100 ng/ml range (P<0.0009). ApoAI protein levels were 4055+/-360, 3697+/-101, 3347+/-327, 1561+/-33.0, 1581+/-182, 810.0+/-59.5, and 1766+/-717 AU in cells treated with similar doses of IL-1beta, achieving statistical significance within the range of 3-100 ng/ml (P<0.02). ApoAI mRNA levels were suppressed 50.8% in HepG2 cells treated with 30 ng/ml TNF alpha for 24 h (P<0.05), and remained suppressed for up to 96 h. Similarly, treatment of cells with 30 ng/ml IL-1beta for 24 h, resulted in 42.9% reduction in apoAI mRNA levels (P<0.05) and remained suppressed for up to 96 h. In order to determine if the effect of TNF alpha and IL-1beta occurs at the transcriptional level, HepG2 cells were transfected with a chloramphenicol acetyltransferase (CAT) reporter gene plasmid containing the full-length apoAI promoter, and after 24 h, treated with TNF alpha (30 ng/ml), IL-1beta (30 ng/ml), or both cytokines. CAT activity was suppressed by both cytokines (24.0+/-1.9% acetylation in control cells vs. 5.6+/-1.2% (P<0.0004), 10.2+/-1.5% (P<0.0006), and 3.9+/-0.9% acetylation (P<0.0002) in cells treated with TNF alpha, IL-1beta, and the combination of both cytokines, respectively) suggesting that cytokine-mediated suppression occurs at the transcriptional level. Using a series of apoAI deletion constructs, the cytokine response element was mapped between nucleotides -325 and -186 (relative to the transcriptional start site). This region contains a previously identified and characterized cis-element, site A, which binds several different transcription factors. Finally, electrophoretic mobility shift assays (EMSA) showed that TNF alpha treatment of HepG2 cells is associated with reduced nuclear factor binding to site A. These studies suggest that inflammatory cytokines down-regulate apoAI expression at least partly through inhibition of binding of the nuclear factors to site A of the apoAI promoter.
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Affiliation(s)
- Michael J Haas
- Department of Internal Medicine, School of Medicine, St. Louis University, Health Sciences Center, 1402 S. Grand Boulevard, St. Louis, MO 63104, USA
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21
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Barbier O, Torra IP, Sirvent A, Claudel T, Blanquart C, Duran-Sandoval D, Kuipers F, Kosykh V, Fruchart JC, Staels B. FXR induces the UGT2B4 enzyme in hepatocytes: a potential mechanism of negative feedback control of FXR activity. Gastroenterology 2003; 124:1926-40. [PMID: 12806625 DOI: 10.1016/s0016-5085(03)00388-3] [Citation(s) in RCA: 145] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
BACKGROUND & AIMS Bile acids are essential for bile formation and intestinal absorption of lipids and fat-soluble vitamins. However, the intrinsic toxicity of hydrophobic bile acids demands a tight control of their intracellular concentrations. Bile acids are ligands for the farnesoid X receptor (FXR) that regulates the expression of genes controlling bile acid synthesis and transport. The human uridine 5'-diphosphate-glucuronosyltransferase 2B4 (UGT2B4) converts hydrophobic bile acids into more hydrophilic glucuronide derivatives. In this study, we identify UGT2B4 as an FXR target gene. METHODS Human hepatocytes or hepatoblastoma HepG2 cells were treated with chenodeoxycholic acid or the synthetic FXR agonist GW4064, and the levels of UGT2B4 messenger RNA, protein, and activity were determined by using real-time polymerase chain reaction, Western blot, and glucuronidation assays. RESULTS Treatment of hepatocytes and HepG2 cells with FXR agonists resulted in an increase of UGT2B4 messenger RNA, protein, and activity. A bile acid response element in the UGT2B4 promoter (B4-BARE) to which FXR, but not retinoid X receptor, binds, was identified by site-directed mutagenesis, electromobility shift, and chromatin immunoprecipitation assays. Retinoid X receptor activation abolished the induction of UGT2B4 expression and inhibited binding of FXR to the B4-BARE, suggesting that retinoid X receptor modulates FXR target gene activation. Overexpression of UGT2B4 in HepG2 cells resulted in the attenuation of bile acid induction of the FXR target gene small heterodimeric partner. CONCLUSIONS These data suggest that UGT2B4 gene induction by bile acids contributes to a feed-forward reduction of bile acid toxicity and a decrease of the activity of these biological FXR activators.
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Affiliation(s)
- Olivier Barbier
- U545 INSERM, Department of Atherosclerosis, Faculty of Pharmacy, Lille Pasteur Institute and University of Lille II, 1 Rue du Pr Calmette, BP 245, 59019 Lille, France
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22
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Uscátegui Peñuela RM, Alvarez Uribe MC, Laguado Salinas I, Soler Terranova W, Martínez Maluendas L, Arias Arteaga R, Duque Jaramillo B, Pérez Giraldo J, Camacho Pérez JA. [Cardiovascular risk factors in children and teenagers aged 6-18 years old from Medellin (Colombia)]. An Pediatr (Barc) 2003; 58:411-7. [PMID: 12724072 DOI: 10.1016/s1695-4033(03)78086-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
OBJECTIVE To evaluate exposure to the major risk factors for cardiovascular disease in children from Medellín according to age, sex, type of school, and socioeconomic status. METHOD We performed a descriptive study in 2611 children aged 6-18 years old from the city of Medellín in Colombia. Lipid profile, blood pressure, body mass index, diet, exercise, alcohol intake, and smoking were evaluated. RESULTS Forty-six percent of the children drank alcohol, 8.7 % smoked and 50 % were physically inactive. Fat and carbohydrate intake was high in 48 % and 47 %, respectively. A total of 9.3 % of the children were overweight and 4.6 % were obese. Systolic and diastolic blood pressure were high in 1.3 % and 3.9 %, respectively. Mean high-density lipoprotein cholesterol (HDL-C) values were lower than in other populations, while triglyceride values were higher. Differences in serum lipid concentrations were found according to age and sex. The prevalence of risk factors according to the National Cholesterol Education Program criteria were: 19.1 % for HDL-C, 17.1 % for triglycerides, 17.0 % for low-density lipoprotein cholesterol (LDL-C), 13.5 % for total cholesterol (TC) and 22.9 % for TC/HDL-C. CONCLUSIONS In children from the city of Medellín, the most prevalent cardiovascular risk factors were related to lifestyle. Mean plasma lipid concentrations varied according to age and sex. The prevalence of overweight was higher than in other populations in Colombia but was lower than that reported for other countries.
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23
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Cui L, Schoene NW, Zhu L, Fanzo JC, Alshatwi A, Lei KY. Zinc depletion reduced Egr-1 and HNF-3beta expression and apolipoprotein A-I promoter activity in Hep G2 cells. Am J Physiol Cell Physiol 2002; 283:C623-30. [PMID: 12107072 DOI: 10.1152/ajpcell.00308.2001] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We examined the influence of zinc status on expression of certain transcription factors involved in regulation of apolipoprotein A-I (apoAI) expression in human hepatoblastoma Hep G2 cells. A low zinc basal medium (zinc deficient, ZD) consisting of DMEM and 10% Chelex100-treated fetal bovine serum was used to deplete cellular zinc over one passage. Cells were also cultured for one passage in medium supplemented with 0.4 (ZD0.4), 4.0 (zinc normal, ZN), 16.0 (zinc adequate, ZA), or 32.0 microM zinc (zinc supplemented, ZS). Compared with ZN cells, cellular zinc levels were 43 and 31% lower in ZD and ZD0.4 cells but 70 and 146% higher in ZA and ZS cells, respectively. Supplementation of 0.4 microM zinc significantly increased DNA contents per plate, from 65% in ZD cells to 83% in ZD0.4 cells compared with ZN cells. Addition of >4 microM zinc in medium did not further increase DNA contents. The proportion of cells in G(1)/S and S phase was about fourfold higher and threefold lower, respectively, in ZD cells compared with ZN and other groups. Nuclear Egr-1 protein was markedly decreased in ZD and ZD0.4 cells. Moreover, hepatocyte nuclear factor (HNF)-3beta was severely degraded in ZD and ZD0.4 cells. In contrast, HNF-4alpha remained stable in all groups and was not significantly lower in ZD and ZD0.4 cells. Furthermore, downregulation of trans-acting factor Egr-1 and cleavage of HNF-3beta were associated with reduction of apoAI promoter activity in zinc-deficient Hep G2 cells. Thus zinc is critical in transcriptional regulation of apoAI gene expression in hepatocytes.
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Affiliation(s)
- Libin Cui
- Department of Nutrition and Food Science, University of Maryland, College Park 20742, USA
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24
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Shi Q, Gross KW, Sigmund CD. Retinoic acid-mediated activation of the mouse renin enhancer. J Biol Chem 2001; 276:3597-603. [PMID: 11058598 DOI: 10.1074/jbc.m008361200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies demonstrate that the mouse renin gene is regulated by a complex enhancer of transcription located 2.6 kilobases upstream of the transcription start site which is under both positive and negative influence. We demonstrate herein that a positive regulatory element (Eb) is repeated 10 bp upstream (Ec), and both are required for baseline activity of the enhancer. The Eb and Ec core sequences are identical to the consensus sequence for the nuclear hormone receptor superfamily of transcription factors, and transcriptional activity of constructs containing the enhancer is increased after treatment with retinoic acid. Maximal induction requires both Eb and Ec. Expression of endogenous renin and a renin-promoter controlled transgene in As4.1 cells, and kidney renin mRNA in C57BL/6J mice was induced after retinoid treatment. Gel mobility supershift analysis revealed the binding of RARalpha and RXRalpha to oligonucleotides containing both Eb and Ec. Reverse transcriptase-polymerase chain reaction analysis revealed that As4.1 cells express both receptor isoforms, along with RARgamma, but do not express RARbeta, RXRbeta, or RXRgamma. Co-transfection of an expression vector encoding wild-type RARalpha increased enhancer activity, whereas a dominant negative mutant of RARalpha significantly attenuated retinoic acid-induced activity of the enhancer. These results demonstrate the importance of the Eb and Ec motifs in controlling baseline activity of the renin enhancer, and suggest the potential importance of retinoids in regulating renin expression.
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Affiliation(s)
- Q Shi
- Department of Internal Medicine, The University of Iowa College of Medicine, Iowa City, Iowa 52242, USA
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25
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Battle TE, Roberson MS, Zhang T, Varvayanis S, Yen A. Retinoic acid-induced blr1 expression requires RARalpha, RXR, and MAPK activation and uses ERK2 but not JNK/SAPK to accelerate cell differentiation. Eur J Cell Biol 2001; 80:59-67. [PMID: 11211936 DOI: 10.1078/0171-9335-00141] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Upstream signaling requirements of retinoic acid (RA)-induced blr1 expression and downstream signaling consequences of blr1 over-expression in a human myeloid leukemia cell line demonstrate that mitogen-activated protein kinase (MAPK) signaling complexes are involved in both avenues. RA-induced myeloid differentiation and G1/G0 growth arrest of HL-60 cells is known to require the activation of the RARalpha and RXR retinoid receptors, as well as activation of the MAPK, ERK2. Transcriptional activation of the Burkitt's lymphoma receptor 1 (blr1) gene occurs early during RA-induced differentiation of HL-60 cells and requires these same three activating processes. The use of retinoid ligands that activate either the RARalpha or the RXR retinoid receptors revealed that blr1 mRNA induction was detectable only when both RARalpha and RXR were activated. Neither the RARalpha nor RXR selective ligands alone induced expression of blr1, but the combination of the two ligands induced the expression of blr1 to the same extent as RA. The MAPKK (MEK) inhibitor, PD98059, was used to determine whether extracellular signal-regulated kinase (ERK2) activation was necessary for induction of blr1 mRNA. PD98059 inhibited induced blr1 mRNA expression, due to RA or activated RARalpha plus RXR ligands, indicating that ERK2 activation is necessary for blr1 mRNA expression. Previous studies showed that ectopic expression of blr1 also caused increased MAPK activation, in particular ERK2, and subsequently accelerated RA-induced differentiation and G1/G0 growth arrest. Inhibition of ERK2 activation inhibited differentiation of blr1 transfectants, suggesting that the accelerated differentiation reflected blr1-enhanced ERK2 activation. The present data also demonstrate that ectopic expression of blr1 increased JNK/SAPK activity, but JNK/ SAPK activation was not needed for accelerated RA-induced differentiation and growth arrest. The results show that the signals known to be required for HL-60 differentiation, activated RARalpha, RXR, and ERK2, are necessary for blr1 mRNA expression. Downstream consequences of blr1 overexpression include enhanced MAPK signaling.
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Affiliation(s)
- T E Battle
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA. traci
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26
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Apolipoprotein A-I gene expression is upregulated by polychlorinated biphenyls in rat liver. J Nutr Biochem 2000; 11:568-573. [PMID: 11137894 DOI: 10.1016/s0955-2863(00)00121-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Xenobiotics such as polychlorinated biphenyls (PCB) increase serum cholesterol level (especially high density lipoprotein cholesterol) and apolipoprotein A-I (apo A-I) level in rats. The effect of PCB on serum apo A-I and hepatic apo A-I gene expression and the relationship between apo A-I and drug-metabolizing enzymes in rats were investigated. Serum levels of cholesterol and apo A-I were increased by dietary addition of PCB in a dose-dependent manner (0-500 mg/kg diet). Hepatic apo A-I mRNA level was also elevated by PCB in a similar fashion. Serum level of cholesterol gradually increased during feeding period of PCB (200 mg/kg diet, 105 days) and reached a two-fold higher level in PCB group than in controls. The levels of serum apo A-I and hepatic apo A-I mRNA linearly elevated during feeding period of PCB and were increased 3- or 4-fold, respectively, compared to controls. Although acute administration (16 hr) of PCB, 3-methylcholanthrene, and phenobarbital induced cytochrome P-450 gene expression in the liver, hepatic apo A-I gene expression was not increased by these xenobiotics. These results indicated that the serum levels of cholesterol and apo A-I had positive correlation with hepatic level of apo A-I mRNA in rats fed PCB, and that hepatic apo A-I gene expression was dependent upon intake of PCB but was not directly related to the induction of drug-metabolizing enzymes. This study demonstrated that xenobiotic-induced hyper-alpha-cholesterolemia would be caused by the increased apo A-I gene expression and cholesterol synthesis in the liver, coordinately.
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Lamon-Fava S. Genistein activates apolipoprotein A-I gene expression in the human hepatoma cell line Hep G2. J Nutr 2000; 130:2489-92. [PMID: 11015478 DOI: 10.1093/jn/130.10.2489] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Soy phytoestrogens have been shown to increase plasma levels of HDL cholesterol and apolipoprotein (apo) A-I, its major protein component, in animal studies and in some human studies. The human hepatoma cell line Hep G2 was used to study the effect of the phytoestrogens genistein and daidzein on apo A-I secretion and gene expression in liver cells. Both genistein and daidzein increased apo A-I secretion in a dose-dependent fashion. Apo A-I concentration in the media of treated cells was increased approximately fivefold by 10 micromol/L genistein (P: < 0.001) and approximately onefold by 10 micromol/L daidzein (P: < 0.001) compared with control cells. The effect of genistein on apo A-I secretion was similar to that observed with 17-beta-estradiol. Treatment of cells with genistein for 24 h increased the transcriptional activity of the apo A-I gene as measured by nuclear run-on assay. Transfection experiments with plasmids containing regulatory regions of the apo A-I gene cloned in front of the luciferase reporter gene indicated that the 5' region of the apo A-I gene contained between nucleotides -256 and -41 is responsible for the increased expression of this gene by genistein.
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Affiliation(s)
- S Lamon-Fava
- Lipid Metabolism Laboratory, Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA, USA
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Kan HY, Georgopoulos S, Zannis V. A hormone response element in the human apolipoprotein CIII (ApoCIII) enhancer is essential for intestinal expression of the ApoA-I and ApoCIII genes and contributes to the hepatic expression of the two linked genes in transgenic mice. J Biol Chem 2000; 275:30423-31. [PMID: 10893424 DOI: 10.1074/jbc.m005641200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have generated transgenic mice carrying wild-type promoters of the human apolipoprotein A-I (apoA-I)-apoCIII gene cluster or promoters mutated in their hormone response elements. The wild-type cluster directed high levels of apoA-I gene expression in liver and intestine, moderate expression in kidney, and low to minimal expression in other tissues. It also directed high levels of chloramphenicol acetyltransferase (CAT) expression (used as a reporter for the apoCIII gene) in liver, low levels in intestine and kidney, and no expression in other tissues. Mutations in the apoCIII promoter and enhancer abolished the intestinal and renal expression of the apoA-I gene, reduced hepatic apoA-I expression by 80%, and abolished CAT expression in all tissues. A similar pattern of expression was obtained by mutations in the apoCIII enhancer alone. Mutations in the proximal apoA-I promoter reduced by 85% hepatic and intestinal apoA-I expression and did not affect CAT expression. The findings suggest that a hormone response element within the apoCIII enhancer is essential for intestinal and renal expression of apoA-I and apoCIII genes and also enhances hepatic expression. The hormone response elements of the proximal apoA-I promoter or the apoCIII enhancer can promote independently low levels of hepatic and intestinal expression of the apoA-I gene in vivo.
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Affiliation(s)
- H Y Kan
- Section of Molecular Genetics, Whitaker Cardiovascular Institute of the Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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Abstract
The key role of vitamin A in embryonal development is reviewed. Special emphasis is given to the physiological action of retinoids, as evident from the retinoid ligand knockout models. Retinoid metabolism in embryonic tissues and teratogenic consequences of retinoid administration at high doses are presented. Physiological and pharmacological actions of retinoids are outlined and explained on the basis of their interactions as ligands of the nuclear retinoid receptors. Immediate target genes and the retinoid response elements of their promoters are summarized. The fundamental role of homeobox genes in embryonal development and the actions of retinoids on their expression are discussed. The similarity of the effects of retinoid ligand knockouts to effects of compound retinoid receptor knockouts on embryogenesis is presented. Although much remains to be clarified, the emerging landscape offers exciting views for future research.
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Affiliation(s)
- S A Ross
- Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Nutritional Products, Labeling, and Dietary Supplements, Washington, DC, USA
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Cyclopropane Derivatives and their Diverse Biological Activities. SMALL RING COMPOUNDS IN ORGANIC SYNTHESIS VI 2000. [DOI: 10.1007/3-540-48255-5_1] [Citation(s) in RCA: 290] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Alvarez R, Checa M, Brun S, Viñas O, Mampel T, Iglesias R, Giralt M, Villarroya F. Both retinoic-acid-receptor- and retinoid-X-receptor-dependent signalling pathways mediate the induction of the brown-adipose-tissue-uncoupling-protein-1 gene by retinoids. Biochem J 2000; 345 Pt 1:91-7. [PMID: 10600643 PMCID: PMC1220734] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/14/2023]
Abstract
The intracellular pathways and receptors mediating the effects of retinoic acid (RA) on the brown-fat-uncoupling-protein-1 gene (ucp-1) have been analysed. RA activates transcription of ucp-1 and the RA receptor (RAR) is known to be involved in this effect. However, co-transfection of an expression vector for retinoid-X receptor (RXR) increases the action of 9-cis RA but not the effects of all-trans RA on the ucp-1 promoter in brown adipocytes. Either RAR-specific ¿p-[(E)-2-(5,6,7,8,-tetrahydro-5,5,8, 8-tetramethyl-2-naphthalenyl)-1-propenyl]benzoic acid¿ or RXR-specific [isopropyl-(E,E)-(R,S)-11-methoxy-3,7, 11-trimethyldodeca-2,4-dienoate, or methoprene] synthetic compounds increase the expression of UCP-1 mRNA and the activity of chloramphenicol acetyltransferase expression vectors driven by the ucp-1 promoter. The RXR-mediated action of 9-cis RA requires the upstream enhancer region at -2469/-2318 in ucp-1. During brown-adipocyte differentiation RXRalpha and RXRgamma mRNA expression is induced in parallel with UCP-1 mRNA, whereas the mRNA for the three RAR subtypes, alpha, beta and gamma, decreases. Co-transfection of murine expression vectors for the different RAR and RXR subtypes indicates that RARalpha and RARbeta as well as RXRalpha are the major retinoid-receptor subtypes capable of mediating the responsiveness of ucp-1 to retinoids. It is concluded that the effects of retinoids on ucp-1 transcription involve both RAR- and RXR-dependent signalling pathways. The responsiveness of brown adipose tissue to retinoids in vivo relies on a complex combination of the capacity of RAR and RXR subtypes to mediate ucp-1 induction and their distinct expression in the differentiated brown adipocyte.
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Affiliation(s)
- R Alvarez
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal 645, 08028-Barcelona, Spain
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Lamon-Fava S, Ordovas JM, Schaefer EJ. Estrogen increases apolipoprotein (apo) A-I secretion in hep G2 cells by modulating transcription of the apo A-I gene promoter. Arterioscler Thromb Vasc Biol 1999; 19:2960-5. [PMID: 10591676 DOI: 10.1161/01.atv.19.12.2960] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Estrogen administration to postmenopausal women has been shown to increase plasma levels of apolipoprotein (apo) A-I. A human hepatoma cell line, Hep G2, was used to test the hypothesis that estrogen increases the hepatic production of apo A-I by modulating gene expression. When Hep G2 cells were treated for 24 hours with E(2), the apo A-I content in the medium increased 4.3+/-1.0-fold at 10 micromol/L E(2) and 1.8+/-0.4-fold at 1 micromol/L E(2) compared with untreated cells. A time-course experiment indicated that there was no E(2)-dependent (10 micromol/L) increase in apo A-I medium content at 1 hour and 2 hours and that apo A-I was 165% of controls at 6 hours and 440% at 24 hours. Hep G2 cells were transfected, by the cationic lipid method, with constructs containing serial deletions of the 5' region of the apo A-I gene (-41/+397, -256/+397, and -2500/+397) cloned in front of the luciferase gene and with or without a 7-kb region spanning the apo C-III/A-IV intergenic region, which has been shown to contain regulatory elements for the expression of the apo A-I gene. With the exception of the construct containing only the basal promoter (-41/+397), the expression of all constructs was 2- to 3-fold greater in the presence of E(2). The smallest construct that maintained E(2) responsiveness, the -256/+397 construct, does not contain a typical estrogen-responsive element. In the same transfection experiments, the 4-fold increase in apo A-I in the culture medium was preserved. However, when the same set of transfections was performed by the calcium phosphate precipitation method, the E(2) effect on the apo A-I content in the culture medium and on transcription activation was nearly abolished. This effect was probably mediated by Ca(2+), because incubation of cells with 20 mmol/L CaCl(2) abolished the E(2) response. In conclusion, E(2) increases apo A-I production in hepatic cells by increasing the transcription of the apo A-I gene.
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Affiliation(s)
- S Lamon-Fava
- Lipid Metabolism Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA.
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Ishaq M, Zhang YM, Natarajan V. Activation-induced down-regulation of retinoid receptor RXRalpha expression in human T lymphocytes. Role of cell cycle regulation. J Biol Chem 1998; 273:21210-6. [PMID: 9694878 DOI: 10.1074/jbc.273.33.21210] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A 5.4-kilobase mRNA, the expression of which is down-regulated after treatment of human peripheral blood mononuclear cells (PBMCs) with various T cell-activating agents, was isolated using an mRNA differential display method. Nucleotide sequence analysis identified the 5' end of this RNA as human retinoid receptor RXRalpha mRNA. Here, we report the nucleotide sequence of 3.6 kilobases of this RNA, which represents the 3' end of RXRalpha mRNA, the sequence of which has not been previously described. Activated PBMCs also expressed lower levels of RXRalpha protein, and a DNA binding assay showed that the activation-induced loss of RXRalpha mRNA and protein expression correlated with the loss of DNA binding activity of this protein. We present evidence that the transition from G0/G1 to S phase of the cell cycle results in the down-regulation of RXRalpha expression and that cell cycle inhibitors, which block the cells in G1 phase, prevent this down-regulation. The decrease in the levels of RXRalpha mRNA was found to be regulated at the post-transcriptional level and involved new protein synthesis. These observations indicate that the levels of RXRalpha expression in T lymphocytes are coupled to cell cycle progression, and there is tight regulatory control of RXRalpha expression during the transition from G0/G1 to S phase of the cell cycle.
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Affiliation(s)
- M Ishaq
- Laboratory of Molecular Cell Biology, SAIC-Frederick, National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, Maryland 21702-1201, USA
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Berthou L, Langouët S, Grudé P, Denèfle P, Branellec D, Guillouzo A. Negative regulation of Apo A-I gene expression by retinoic acid in rat hepatocytes maintained in a coculture system. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1391:329-36. [PMID: 9555083 DOI: 10.1016/s0005-2760(98)00004-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Rat hepatocytes cocultured with rat liver epithelial cells (RLEC) were used to investigate the influence of all-trans retinoic acid (RA) on the regulation of apolipoproteins (Apo) A-I and A-II gene expression, the major protein constituent of high-density lipoproteins. In contrast to rat hepatocytes in conventional primary culture, Apo A-I and Apo A-II gene expression remained high and stable for several days in parenchymal cells in coculture. Treatment of cocultured rat hepatocytes with RA resulted in a specific decrease in Apo A-I mRNA levels whereas no marked difference in Apo A-II mRNA levels was observed. Such a negative effect of RA was already detected as early as 2 days of treatment and was effective for the entire experimental period (6 days). As controls, RARbeta mRNA levels increased whereas those of GAPDH mRNA were not affected by the RA treatment. The decrease in Apo A-I mRNA levels was associated with lower amounts of Apo A-I secreted in the culture medium within day 1 of treatment. This effect required active transcription and protein synthesis. These results show that, contrary to primary pure hepatocyte cultures and hepatoma cell lines, cocultures of rat hepatocytes reproduce the in vivo results suggesting that only well differentiated hepatocytes may correctly respond to RA. Furthermore, they demonstrate that RA can directly act on hepatocytes and differently affect Apo A-I and Apo A-II gene expression.
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Affiliation(s)
- L Berthou
- Department of Biotechnology, CRVA Rhône-Poulenc Rorer Gencell, Vitry-sur-Seine, France
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35
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Harnish DC, Evans MJ, Scicchitano MS, Bhat RA, Karathanasis SK. Estrogen regulation of the apolipoprotein AI gene promoter through transcription cofactor sharing. J Biol Chem 1998; 273:9270-8. [PMID: 9535920 DOI: 10.1074/jbc.273.15.9270] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Estrogen replacement therapy increases plasma concentrations of high density lipoprotein and its major protein constituent, apolipoprotein AI (apoAI). Studies with animal model systems, however, suggest opposite effects. In HepG2 cells stably expressing estrogen receptor alpha (ERalpha), 17beta-estradiol (E2) potently inhibited apoAI mRNA steady state levels. ApoAI promoter deletion mapping experiments indicated that ERalpha plus E2 inhibited apoAI activity through the liver-specific enhancer. Although the ERalpha DNA binding domain was essential but not sufficient for apoAI enhancer inhibition, ERalpha binding to the apoAI enhancer could not be detected by electrophoretic mobility shift assays. Western blotting and cotransfection assays showed that ERalpha plus E2 did not influence the abundance or the activity of the hepatocyte-enriched factors HNF-3beta and HNF-4, two transcription factors essential for apoAI enhancer function. Expression of the ERalpha coactivator RIP140 dramatically repressed apoAI enhancer function in cotransfection experiments, suggesting that RIP140 may also function as a coactivator on the apoAI enhancer. Moreover, estrogen regulation of apoAI enhancer activity was dependent upon the balance between ERalpha and RIP140 levels. At low ratios of RIP140 to ERalpha, E2 repressed apoAI enhancer activity, whereas at high ratios this repression was reversed. Regulation of the apoAI gene by estrogen may thus vary in direction and magnitude depending not only on the presence of ERalpha and E2 but also upon the intracellular balance of ERalpha and coactivators utilized by ERalpha and the apoAI enhancer.
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MESH Headings
- Adaptor Proteins, Signal Transducing
- Apolipoprotein A-I/biosynthesis
- Apolipoprotein A-I/genetics
- Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
- Binding Sites
- Carcinoma, Hepatocellular
- DNA-Binding Proteins/metabolism
- Enhancer Elements, Genetic
- Estradiol/pharmacology
- Gene Expression Regulation, Neoplastic/drug effects
- Hepatocyte Nuclear Factor 3-beta
- Hepatocyte Nuclear Factor 4
- Humans
- Kinetics
- Liver Neoplasms
- Luciferases/biosynthesis
- Nuclear Proteins/metabolism
- Nuclear Receptor Interacting Protein 1
- Phosphoproteins/metabolism
- Promoter Regions, Genetic/drug effects
- RNA, Messenger/biosynthesis
- Receptors, Estrogen/biosynthesis
- Receptors, Estrogen/metabolism
- Recombinant Fusion Proteins/biosynthesis
- Recombinant Fusion Proteins/metabolism
- Transcription Factors/metabolism
- Transcription, Genetic/drug effects
- Transfection
- Tumor Cells, Cultured
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Affiliation(s)
- D C Harnish
- Department of Nuclear Receptors, Wyeth-Ayerst Research, Radnor, Pennsylvania 19087, USA
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Kilbourne EJ, Evans MJ, Karathanasis SK. E1A represses apolipoprotein AI enhancer activity in liver cells through a pRb- and CBP-independent pathway. Nucleic Acids Res 1998; 26:1761-8. [PMID: 9512550 PMCID: PMC147459 DOI: 10.1093/nar/26.7.1761] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The apolipoprotein AI (apoAI) promoter/enhancer contains multiple cis -acting elements on which a variety of hepatocyte-enriched and ubiquitous transcription factors function synergistically to regulate liver-specific transcription. Adenovirus E1A proteins repress tissue-specific gene expression and disrupt the differentiated state in a variety of cell types. In this study expression of E1A 12Sor 13S in hepatoblastoma HepG2 cells repressed apoAI enhancer activity 8-fold. Deletion mapping analysis showed that inhibition by E1A was mediated by the apoAI promoter site B. E1A selectively inhibited the ability of HNF3beta and HNF3alpha to transactivate reporter genes controlled by the apoAI site B and the HNF3 binding site from the transthyretin promoter. The E1A-mediated repression of HNF3 activity was not reversed by overexpression of HNF3beta nor did E1A alter nuclear HNF3beta protein levels or inhibit HNF3 binding to DNA in mobility shift assays. Overexpression of two cofactors known to interact with E1A, pRb and CBP failed to overcome inhibition of HNF3 activity. Similarly, mutations in E1A that disrupt its interaction with pRb or CBP did not compromise its ability to repress HNF3beta transcriptional activity. These data suggest that E1A inhibits HNF3 activity by inactivating a limiting cofactor(s) distinct from pRb or CBP.
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Affiliation(s)
- E J Kilbourne
- Department of Nuclear Receptors, Wyeth-Ayerst Research, 145 King of Prussia Road, Radnor, PA 19087, USA
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37
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Mohan WS, Chen ZQ, Zhang X, Khalili K, Honjo T, Deeley RG, Tam SP. Human S mu binding protein-2 binds to the drug response element and transactivates the human apoA-I promoter: role of gemfibrozil. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)33887-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Lo HW, Ali-Osman F. Genomic cloning of hGSTP1*C, an allelic human Pi class glutathione S-transferase gene variant and functional characterization of its retinoic acid response elements. J Biol Chem 1997; 272:32743-9. [PMID: 9407047 DOI: 10.1074/jbc.272.52.32743] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The complete hGSTP1*C, consisting of 7 exons and 6 introns contained in 3116 base pairs, was isolated from a cosmid genomic library of a glioblastoma multiforme cell line. Although the promoter of hGSTP1*C was identical to that of the previously reported GST-Pi gene, several of its structural features had not been previously described. These include several nucleotide transitions and transversions. Transitions of A --> G at +1404 and C --> T at +2294 in exons 5 and 6, respectively, changed codons Ile104 to Val104 and Ala113 to Val113. The gene also contained a guanine insertion at +51 in the insulin response element in intron 1 and six tandem repeats and one palindromic retinoic acid response element (RARE) consensus half-sites, A(G)GG(T)TC(G)A in intron 5. Retinoic acid (RA) treatment increased GST-Pi gene expression significantly in MGR3 cells. GST-Pi gene constructs with and without RARE deletion were used to show the RARE requirement for GST-Pi gene induction by RA. The isolation of the hGSTP1*C gene and the evidence that it contains functional RAREs should contribute to a better understanding of the molecular regulation of the GST-Pi gene in human cells.
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Affiliation(s)
- H W Lo
- Section of Molecular Therapeutics, Department of Experimental Pediatrics, University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA
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39
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Kyakumoto S, Nemoto T, Sato N, Ota M. Expression of retinoid X receptors and COUP-TFI in a human salivary gland adenocarcinoma cell line. Biochem Cell Biol 1997. [DOI: 10.1139/o97-080] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The growth of the adenocarcinoma cell line derived from human salivary gland (HSG) is regulated by all-trans-retinoic acid (t-RA), which binds to its specific receptor, retinoic acid receptors (RARs), located in the nucleus, and thereby transactivates target genes. In this study, we examined the binding characteristics of the nuclear extract of HSG cells to the retinoic acid response element (RARE) compared with those of in vitro translated RAR alpha and retinoid X receptor alpha (RXR alpha ), a heterodimeric partner of RAR alpha . Gel shift analysis using anti-RAR alpha and anti-RXR alpha antibodies revealed that the translated RAR alpha bound to RARE as a heterodimer with RXR alpha . In contrast, the binding of the nuclear extract of HSG cells to RARE showed a heterogenous pattern, suggesting the existence of several species of RXRs as well as RARs in the nuclei of HSG cells. We therefore tried to clone these putative RXRs by the polymerase chain reaction using degenerated oligonucleotide primers conserved across the RXR family. The DNA sequencing of the recombinant clones revealed the expression of RXR alpha and RXR beta . In addition, chicken ovalbumin upstream promoter-transcription factor I (COUP-TFI), which is also an RXR family member, was cloned. To evaluate the transcriptional activity of RARs and RXRs endogenously expressed in HSG cells, we performed a transient transfection analysis. When HSG cells were transfected with a luciferase reporter plasmid containing two repeats of either the RARE of the RAR beta gene or that of cellular retinol-binding protein II gene, positioned upstream of a thymidine kinase promoter fused to the luciferase sequence, a 2-3-fold induction of luciferase activity was observed in both cases. These results suggest that RARs and RXRs endogenously expressed in HSG cells were transcriptionally active in vivo. Thus, our findings showed that RXR alpha , RXR beta , and COUP-TFI are expressed in HSG cells and suggest that these molecules function as heterodimeric partners of RARs and (or) competitive repressors for RAREs and are involved in cellular responses mediated by retinoids. Key words: retinoid X receptor, retinoic acid receptor, retinoic acid response element, COUP-transcription factor (COUP-TF).
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40
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Kersten S, Reczek PR, Noy N. The tetramerization region of the retinoid X receptor is important for transcriptional activation by the receptor. J Biol Chem 1997; 272:29759-68. [PMID: 9368046 DOI: 10.1074/jbc.272.47.29759] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The retinoid X receptor (RXR), a member of the superfamily of hormone nuclear receptors, is a ligand-inducible transcription factor that is activated by the vitamin A derivative 9-cis-retinoic acid. We previously showed that RXR self-associates into tetramers with a high affinity and that ligand binding induces rapid dissociation of receptor tetramers to smaller species. Here, the RXR region that is responsible for mediating tetramer formation is identified. It is shown that this interface, which we term the "tetramerization domain," critically contains two consecutive phenylalanine residues located at the C-terminal region of the receptor. Mutation of these residues is sufficient to disrupt RXR tetramers without affecting the overall fold of the protein or interfering with ligand binding, dimer formation, or DNA binding by the receptor. Nevertheless, the tetramer-impaired mutant was found to be transcriptionally defective. The newly characterized tetramerization domain and the previously identified main dimerization interface of RXR act autonomously to affect separate intersubunit interactions that, overall, lead to formation of tetramers. Protein-protein interactions mediated by the tetramerization domain, but not those that involve the dimerization interface, are disrupted following ligand binding by RXR. Overall, these data attest to the specificity of the interaction and implicate the tetramerization interface in playing a direct role in regulating transcriptional activation by RXR.
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Affiliation(s)
- S Kersten
- Cornell University, Division of Nutritional Sciences, Savage Hall, Ithaca, New York 14853-6301, USA
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Kaptein A, Neele DM, Twisk J, Hendriks HF, Kooistra T, Princen HM. Mechanism of the slow induction of apolipoprotein A-I synthesis by retinoids in cynomolgus hepatocytes: involvement of retinoic acid and retinoid X receptors. J Lipid Res 1997. [DOI: 10.1016/s0022-2275(20)34941-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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42
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Wu JY, Zhang JJ, Wang Y, Reaves SK, Wang YR, Lei PP, Lei KY. Regulation of apolipoprotein A-I gene expression in Hep G2 cells depleted of Cu by cupruretic tetramine. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C1362-70. [PMID: 9357782 DOI: 10.1152/ajpcell.1997.273.4.c1362] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Studies were designed to examine the regulation of apolipoprotein (apo) A-I gene expression in Cu-depleted Hep G2 cells. The cupruretic chelator N,N'-bis(2-aminoethyl)-1,3-propanediamine 4 HCl (2,3,2-tetramine or TETA) was used to maintain a 77% reduction in cellular Cu in Hep G2 cells. After two passages of TETA treatment, the relative abundance of apoA-I mRNA was elevated 52%. In TETA-treated cells, the rate of apoA-I mRNA decay measured by an actinomycin D chase study was accelerated 108%, and the synthesis of apoA-I mRNA determined by a nuclear runoff assay was enhanced 2.5-fold in TETA-treated cells. All of those changes could be reverted toward the control values with Cu supplementation for only 2 days. In transient transfection assays, a 26.7% increase in chloramphenicol O-acetyltransferase (CAT) activity for the reporter construct -256AI-CAT was observed in the treated cells. However, the ability of apoA-I regulatory protein 1 (ARP-1) to repress the CAT activity was not affected by the depressed Cu status. In addition, gel retardation experiments demonstrated that Cu depletion enhanced the binding of hepatocyte nuclear factor 4 (HNF-4) and other undefined nuclear factors to oligonucleotides containing site A, one of three regulatory sites of the apoA-I gene promoter. Moreover, the relative abundance of HNF-4 mRNA was increased 58% in the Cu-depleted cells. Thus the observed increase in apoA-I gene transcription may be mediated mostly by an elevated level of the regulatory factor, HNF-4. In summary, the present findings established the mechanism by which a depressed cellular Cu status can enhance apoA-I mRNA production and subsequently increase apoA-I synthesis.
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Affiliation(s)
- J Y Wu
- Department of Nutritional Sciences, University of Arizona, Tucson 85721, USA
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Choi HS, Chung M, Tzameli I, Simha D, Lee YK, Seol W, Moore DD. Differential transactivation by two isoforms of the orphan nuclear hormone receptor CAR. J Biol Chem 1997; 272:23565-71. [PMID: 9295294 DOI: 10.1074/jbc.272.38.23565] [Citation(s) in RCA: 227] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We have identified a new murine orphan member of the nuclear hormone receptor superfamily, termed mCAR, that is closely related to the previously described human orphan MB67, referred to here as hCAR. Like hCAR, mCAR expression is highest in liver. In addition to the most abundant mCAR1 isoform, the mCAR gene expresses a truncated mCAR2 variant that is missing the C-terminal portion of the ligand binding/dimerization domain. The mCAR gene has 8 introns, and this mCAR2 variant is generated by a splicing event that skips the 8th exon. mCAR1, like hCAR, binds as a heterodimer with the retinoid X receptor to the retinoic acid response element from the promoter of the retinoic acid receptor beta2 isoform. Consistent with its lack of a critical heterodimerization interface, the mCAR2 variant does not bind this site. Both mCAR1 and hCAR are apparently constitutive transcriptional activators. This activity is dependent on the presence of the conserved C-terminal AF-2 transcriptional activation motif. As expected from its inability to bind DNA, the mCAR2 variant neither transactivates by itself nor inhibits transactivation by hCAR or mCAR1.
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Affiliation(s)
- H S Choi
- Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
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Ramharack R, Spahr MA, Sekerke CS. Retinoids inhibit primary cynomolgus monkey hepatocyte lipoprotein(a) levels. Biochem Biophys Res Commun 1997; 238:48-52. [PMID: 9299449 DOI: 10.1006/bbrc.1997.7240] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Elevated plasma lipoprotein(a) [Lp(a)] independently contributes to a variety of vascular diseases; consequentially, factors that modulate its levels are of interest. Since Lp(a) is produced by a disulfide linkage between apolipoprotein(a) [apo(a)] and apolipoproteinB-100 (apoB-100) of low density lipoprotein (LDL) on the hepatocyte surface, modulation of either particle may be useful in lowering Lp(a). Using primary cynomolgus monkey hepatocyte cultures that endogenously express apo(a) and apoB-100, we showed that all-trans (retinol, retinal, retinoic acid) and 9-cis (retinal, retinoic acid) retinoids lower Lp(a) accumulation in the cell media, with the 9-cis derivatives being > 10-fold more potent than the all-trans stereoisomers. Lp(a) Towering was related to decreases in apo(a) and its cognate transcript, but not to apoB-100. These results demonstrate that retinoids lower Lp(a) levels by decreasing apo(a) through its cognate mRNA.
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Affiliation(s)
- R Ramharack
- Department of Vascular and Cardiac Diseases, Parke-Davis Pharmaceutical Research, Ann Arbor, Michigan 48105, USA.
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46
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Jones HE, Eaton CL, Barrow D, Dutkowski C, Griffiths K. Response of cell growth and retinoic acid receptor expression to retinoic acid in neoplastic and non-neoplastic prostate cell lines. Prostate 1997; 30:174-82. [PMID: 9122042 DOI: 10.1002/(sici)1097-0045(19970215)30:3<174::aid-pros5>3.0.co;2-m] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND Retinoic acid (RA) is recognized as an inhibitor of tumorigenesis, but conversely, has also been shown to act as a tumor enhancer, therefore its role in prostate tumor cell growth was investigated. METHODS The response of two human prostate tumor cell lines (PC-3 and DU-145), and cell lines derived from a well-differentiated canine prostate adenocarcinoma (CPA) and normal canine prostate epithelium (CAPE) to all-trans RA was determined using growth curve analysis. Additionally, the constitutive expression and RA-challenged expression of retinoic acid receptors (RARs) -alpha, -beta, and -gamma mRNA was examined using Northern blotting techniques. RESULTS In response to all-trans RA, the PC-3 and DU-145 cell lines showed considerable growth promotion, while CAPE and CPA cell growth was dramatically inhibited. Each cell line expressed RAR alpha and RAR gamma, with either negligible or no RAR beta transcripts being detected. RAR alpha and -gamma mRNAs detected in the four cell lines were variably regulated in response to RA, and no distinct patterns of RAR regulation that could be related to cell growth responses were observed. CONCLUSIONS The data indicates that no simple association exists between the expression or regulation of RAR subtype mRNAs and the divergent growth responses to RA displayed by the prostate cell lines.
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Affiliation(s)
- H E Jones
- Tenovus Cancer Research Centre, University of Wales College of Medicine, Cardiff, Wales, United Kingdom
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Barger PM, Kelly DP. Identification of a retinoid/chicken ovalbumin upstream promoter transcription factor response element in the human retinoid X receptor gamma2 gene promoter. J Biol Chem 1997; 272:2722-8. [PMID: 9006910 DOI: 10.1074/jbc.272.5.2722] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
To investigate the mechanisms involved in the transcriptional control of retinoid X receptor (RXR) gene expression, the 5'-flanking region of the human RXRgamma2 isoform was characterized. An imperfect hexamer repeat (gamma retinoid X response element; gammaRXRE) with a single nucleotide spacer (GGTTGAaAGGTCA) was identified immediately upstream of the RXRgamma2 gene transcription start site. Cotransfection studies in CV-1 cells with expression vectors for the retinoid receptors RXRalpha and retinoic acid receptor beta (RARbeta) demonstrated that the gammaRXRE confers retinoid-mediated transcriptional activation with preferential activation by RXR in the presence of its cognate ligand, 9-cis-retinoic acid (RA). Electrophoretic mobility shift assays demonstrated that RXR homodimer binding to gammaRXRE is markedly enhanced by 9-cis-RA, whereas RAR.RXR heterodimer binding is ligand-independent. DNA binding studies and cell cotransfection experiments also demonstrated that the nuclear receptor, chicken ovalbumin upstream promoter transcription factor (COUP-TF), repressed transcription via the gammaRXRE. Cotransfection experiments revealed that COUP-TF and RXRalpha compete at the gammaRXRE to modulate transcription bidirectionally over a wide range. These results demonstrate that the human RXRgamma2 gene promoter contains a novel imperfect repeat element capable of mediating RXR-dependent transcriptional autoactivation and COUP-TF-dependent repression.
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Affiliation(s)
- P M Barger
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Levin MS, Davis AE. Retinoic acid increases cellular retinol binding protein II mRNA and retinol uptake in the human intestinal Caco-2 cell line. J Nutr 1997; 127:13-7. [PMID: 9040537 DOI: 10.1093/jn/127.1.13] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Cellular retinol binding protein II (CRBPII) is an abundant small intestinal protein that facilitates vitamin A trafficking and metabolism. The magnitude of retinol uptake and metabolism correlate to CRBPII levels in the human intestinal Caco-2 cell line. To investigate the importance of retinoic acid receptor response elements in the promoter of the CRBPII gene, retinoic acid regulation of CRBPII expression and vitamin A absorption was studied in differentiated Caco-2 cells. All-trans- or 9-cis-retinoic acid increased CRBPII mRNA levels two- to threefold. This was associated with a 50% increase in retinol absorption. Retinoic acid receptor beta and apolipoprotein A1 regulatory protein-1, two nuclear receptors that bind to the CRBPII promoter, were also induced, whereas other retinoid and orphan receptors were not. Thus, retinoic acid may regulate CRBPII expression directly or by selectively changing levels of nuclear receptors or other factors. These studies are the first to demonstrate that retinoic acid can modulate endogenous CRBPII mRNA levels and retinol absorption in Caco-2 cells and suggest that human intestinal vitamin A absorption may be regulated by retinoids.
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Affiliation(s)
- M S Levin
- Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA
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Lala DS, Mukherjee R, Schulman IG, Koch SS, Dardashti LJ, Nadzan AM, Croston GE, Evans RM, Heyman RA. Activation of specific RXR heterodimers by an antagonist of RXR homodimers. Nature 1996; 383:450-3. [PMID: 8837780 DOI: 10.1038/383450a0] [Citation(s) in RCA: 137] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Retinoid X receptor (RXR) plays a central role in the regulation of many intracellular receptor signalling pathways and can mediate ligand-dependent transcription, acting as a homodimer or as a heterodimer. Here we identify an antagonist towards RXR homodimers which also functions as an agonist when RXR is paired as a heterodimer to specific partners, including peroxisome proliferator-activated receptor and retinoic acid receptor. This dimer-selective ligand confers differential interactions on the transcription machinery: the antagonist promotes association with TAF110 (TATA-binding protein (TBP)-associated factor 110) and the co-repressor SMRT, but not with TBP, and these properties are distinct from pure RXR agonists. This unique class of RXR ligands will provide a means to control distinct target genes at the level of transcription and allow the development of retinoids with a new pharmacological action.
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Affiliation(s)
- D S Lala
- Department of Retinoid Research, New Leads Ligand Pharmaceuticals, San Diego, California 92121, USA
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Harnish DC, Malik S, Kilbourne E, Costa R, Karathanasis SK. Control of apolipoprotein AI gene expression through synergistic interactions between hepatocyte nuclear factors 3 and 4. J Biol Chem 1996; 271:13621-8. [PMID: 8662915 DOI: 10.1074/jbc.271.23.13621] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Apolipoprotein AI (apoAI) gene expression in liver depends on synergistic interactions between transcription factors bound to three distinct sites (A, B, and C) within a hepatocyte-specific enhancer in the 5'-flanking region of the gene. In this study, we showed that a segment spanning sites A and B retains substantial levels of enhancer activity in hepatoblastoma HepG2 cells and that sites A and B are occupied by the liver-enriched hepatocyte nuclear factors (HNFs) 4 and 3, respectively, in these cells. In non-hepatic CV-1 cells, HNF-4 and HNF-3beta activated this minimal enhancer synergistically. This synergy was dependent upon simultaneous binding of these factors to their cognate sites, but it was not due to cooperativity in DNA binding. Separation of these sites by varying helical turns of DNA did not affect simultaneous binding of HNF-3beta and HNF-4 nor did it influence their functional synergy. The synergy was, however, dependent upon the cell type used for functional analysis. In addition, this synergy was further potentiated by estrogen treatment of cells cotransfected with the estrogen receptor. These data indicate that a cell type-restricted intermediary factor jointly recruited by HNF-4 and HNF-3 participates in activation of the apoAI enhancer in liver cells and suggest that the activity of this factor is regulated by estrogen.
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Affiliation(s)
- D C Harnish
- Department of Cardiovascular Molecular Biology, Lederle Laboratories, Pearl River, New York 10965, USA
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