1
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CREBH Regulates Systemic Glucose and Lipid Metabolism. Int J Mol Sci 2018; 19:ijms19051396. [PMID: 29738435 PMCID: PMC5983805 DOI: 10.3390/ijms19051396] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2018] [Revised: 04/30/2018] [Accepted: 05/06/2018] [Indexed: 12/23/2022] Open
Abstract
The cyclic adenosine monophosphate (cAMP)-responsive element-binding protein H (CREBH, encoded by CREB3L3) is a membrane-bound transcriptional factor that primarily localizes in the liver and small intestine. CREBH governs triglyceride metabolism in the liver, which mediates the changes in gene expression governing fatty acid oxidation, ketogenesis, and apolipoproteins related to lipoprotein lipase (LPL) activation. CREBH in the small intestine reduces cholesterol transporter gene Npc1l1 and suppresses cholesterol absorption from diet. A deficiency of CREBH in mice leads to severe hypertriglyceridemia, fatty liver, and atherosclerosis. CREBH, in synergy with peroxisome proliferator-activated receptor α (PPARα), has a crucial role in upregulating Fgf21 expression, which is implicated in metabolic homeostasis including glucose and lipid metabolism. CREBH binds to and functions as a co-activator for both PPARα and liver X receptor alpha (LXRα) in regulating gene expression of lipid metabolism. Therefore, CREBH has a crucial role in glucose and lipid metabolism in the liver and small intestine.
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2
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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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3
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Cao X, Li Y. β 3-Adrenergic receptor regulates hepatic apolipoprotein A-I gene expression. J Clin Lipidol 2017; 11:1168-1176. [PMID: 28802864 DOI: 10.1016/j.jacl.2017.07.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Revised: 07/19/2017] [Accepted: 07/21/2017] [Indexed: 11/28/2022]
Abstract
BACKGROUND β3-adrenergic receptor (β3-AR) was shown to upregulate hepatic apolipoprotein A-I (apoA-I) expression and reverse atherosclerotic plaques in vivo experiments. However, the effect of β3-AR on apoA-I expression in vitro is unknown. The specific mechanism underlying β3-AR prevention of atherosclerosis is unclear. OBJECTIVE The present study was designed to investigate the molecular mechanism of β3-AR-mediated regulation of hepatic apoA-I gene expression. METHODS HepG2 cells were preincubated with/without a selective protein kinase A inhibitor (H-89) and then treated with a selective β3-AR agonist (BRL37344) or antagonist (SR59230A). The hepatic apoA-I expression was detected by reverse transcription real-time quantitative polymerase chain reaction and Western blot analysis. Enzyme-linked immunosorbent assay was used to evaluate the secretion of apoA-I. A recombinant plasmid containing the apoA-I promoter was constructed and transiently transfected into HepG2 cells, and dual-luciferase reporter assays were used to examine the activity of the apoA-I promoter. A chromatin immunoprecipitation polymerase chain reaction assay was used to evaluate binding activities of hepatocyte nuclear factor-4 (HNF-4), HNF-3, and early growth response protein-1. RESULTS β3-AR activation significantly upregulated apoA-I expression, promoted apoA-I secretion, and enhanced the activities of the apoA-I promoter, HNF-4, and HNF-3 in hepatocytes, whereas early growth response protein-1 was not affected. Moreover, protein kinase A inhibition partially suppressed the activation of the apoA-I promoter, HNF-4, and HNF-3 and almost completely blocked the upregulation of apoA-I expression induced by β3-AR. CONCLUSION β3-AR activation increased the activities of the apoA-I promoter, HNF-4, and HNF-3, which might account for the mechanism of β3-AR-mediated upregulation of hepatic apoA-I expression. β3-AR might exert an anti-atherosclerotic effect by upregulating hepatic apoA-I expression and promoting the cholesterol reverse transport process.
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Affiliation(s)
- Xiaojing Cao
- Emergency Department, Beijing Anzhen Hospital, Capital Medical University, ChaoYang District, Beijing, China
| | - Yanfang Li
- Emergency Department, Beijing Anzhen Hospital, Capital Medical University, ChaoYang District, Beijing, China.
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4
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Shavva VS, Bogomolova AM, Nikitin AA, Dizhe EB, Oleinikova GN, Lapikov IA, Tanyanskiy DA, Perevozchikov AP, Orlov SV. FOXO1 and LXRα downregulate the apolipoprotein A-I gene expression during hydrogen peroxide-induced oxidative stress in HepG2 cells. Cell Stress Chaperones 2017; 22:123-134. [PMID: 27896567 PMCID: PMC5225066 DOI: 10.1007/s12192-016-0749-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2016] [Revised: 11/14/2016] [Accepted: 11/15/2016] [Indexed: 12/17/2022] Open
Abstract
Reactive oxygen species damage various cell components including DNA, proteins, and lipids, and these impairments could be a reason for severe human diseases including atherosclerosis. Forkhead box O1 (FOXO1), an important metabolic transcription factor, upregulates antioxidant and proapoptotic genes during oxidative stress. Apolipoprotein A-I (ApoA-I) forms high density lipoprotein (HDL) particles that are responsible for cholesterol transfer from peripheral tissues to liver for removal in bile in vertebrates. The main sources for plasma ApoA-I in mammals are liver and jejunum. Hepatic apoA-I transcription depends on a multitude of metabolic transcription factors. We demonstrate that ApoA-I synthesis and secretion are decreased during H2O2-induced oxidative stress in human hepatoma cell line HepG2. Here, we first show that FOXO1 binds to site B of apoA-I hepatic enhancer and downregulates apoA-I gene activity in HepG2 cells. Moreover, FOXO1 and LXRα transcription factors participate in H2O2-triggered downregulation of apoA-I gene together with Src, JNK, p38, and AMPK kinase cascades. Mutations of sites B or C as well as the administration of siRNAs against FOXO1 or LXRα to HepG2 cells abolished the hydrogen peroxide-mediated suppression of apoA-I gene.
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Affiliation(s)
- Vladimir S Shavva
- Department of Biochemistry, Institute of Experimental Medicine, Russian Academy of Medical Sciences, Acad. Pavlov St., 12, St. Petersburg, 197376, 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, Acad. Pavlov St., 12, St. Petersburg, 197376, 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, Acad. Pavlov St., 12, St. Petersburg, 197376, Russia
| | - Galina N Oleinikova
- Department of Biochemistry, Institute of Experimental Medicine, Russian Academy of Medical Sciences, Acad. Pavlov St., 12, St. Petersburg, 197376, Russia
| | - Ivan A Lapikov
- Department of Embryology, St. Petersburg State University, St. Petersburg, Russia
| | - Dmitry A Tanyanskiy
- Department of Biochemistry, Institute of Experimental Medicine, Russian Academy of Medical Sciences, Acad. Pavlov St., 12, St. Petersburg, 197376, Russia
- Department of Fundamental Medicine and Medical Technologies, St. Petersburg State University, St. Petersburg, Russia
| | - Andrej P Perevozchikov
- Department of Biochemistry, Institute of Experimental Medicine, Russian Academy of Medical Sciences, Acad. Pavlov St., 12, St. Petersburg, 197376, 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, Acad. Pavlov St., 12, St. Petersburg, 197376, Russia.
- Department of Embryology, St. Petersburg State University, St. Petersburg, Russia.
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5
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van der Krieken SE, Popeijus HE, Konings M, Dullens SP, Mensink RP, Plat J. C/EBP-β Is Differentially Affected by PPARα Agonists Fenofibric Acid and GW7647, But Does Not Change Apolipoprotein A-I Production During ER-Stress and Inflammation. J Cell Biochem 2016; 118:754-763. [DOI: 10.1002/jcb.25731] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Accepted: 09/09/2016] [Indexed: 12/14/2022]
Affiliation(s)
- Sophie E. van der Krieken
- Department of Human Biology; NUTRIM School of Nutrition and Translational Research in Metabolism; Maastricht University; P.O. Box 616; Maastricht 6200 MD The Netherlands
| | - Herman E. Popeijus
- Department of Human Biology; NUTRIM School of Nutrition and Translational Research in Metabolism; Maastricht University; P.O. Box 616; Maastricht 6200 MD The Netherlands
| | - Maurice Konings
- Department of Human Biology; NUTRIM School of Nutrition and Translational Research in Metabolism; Maastricht University; P.O. Box 616; Maastricht 6200 MD The Netherlands
| | - Stefan P.J. Dullens
- Department of Human Biology; NUTRIM School of Nutrition and Translational Research in Metabolism; Maastricht University; P.O. Box 616; Maastricht 6200 MD The Netherlands
| | - Ronald P. Mensink
- Department of Human Biology; NUTRIM School of Nutrition and Translational Research in Metabolism; Maastricht University; P.O. Box 616; Maastricht 6200 MD The Netherlands
| | - Jogchum Plat
- Department of Human Biology; NUTRIM School of Nutrition and Translational Research in Metabolism; Maastricht University; P.O. Box 616; Maastricht 6200 MD The Netherlands
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6
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Shavva VS, Bogomolova AM, Nikitin AA, Dizhe EB, Tanyanskiy DA, Efremov AM, Oleinikova GN, Perevozchikov AP, Orlov SV. Insulin-Mediated Downregulation of Apolipoprotein A-I Gene in Human Hepatoma Cell Line HepG2: The Role of Interaction Between FOXO1 and LXRβ Transcription Factors. J Cell Biochem 2016; 118:382-396. [PMID: 27404023 DOI: 10.1002/jcb.25651] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2016] [Accepted: 07/11/2016] [Indexed: 12/22/2022]
Abstract
Apolipoprotein A-I (ApoA-I) is a key component of high density lipoproteins which possess anti-atherosclerotic and anti-inflammatory properties. Insulin is a crucial mediator of the glucose and lipid metabolism that has been implicated in atherosclerotic and inflammatory processes. Important mediators of insulin signaling such as Liver X Receptors (LXRs) and Forkhead Box A2 (FOXA2) are known to regulate apoA-I expression in liver. Forkhead Box O1 (FOXO1) is a well-known target of insulin signaling and a key mediator of oxidative stress response. Low doses of insulin were shown to activate apoA-I expression in human hepatoma HepG2 cells. However, the detailed mechanisms for these processes are still unknown. We studied the possible involvement of FOXO1, FOXA2, LXRα, and LXRβ transcription factors in the insulin-mediated regulation of apoA-I expression. Treatment of HepG2 cells with high doses of insulin (48 h, 100 nM) suppresses apoA-I gene expression. siRNAs against FOXO1, FOXA2, LXRβ, or LXRα abrogated this effect. FOXO1 forms a complex with LXRβ and insulin treatment impairs FOXO1/LXRβ complex binding to hepatic enhancer and triggers its nuclear export. Insulin as well as LXR ligand TO901317 enhance the interaction between FOXA2, LXRα, and hepatic enhancer. These data suggest that high doses of insulin downregulate apoA-I gene expression in HepG2 cells through redistribution of FOXO1/LXRβ complex, FOXA2, and LXRα on hepatic enhancer of apoA-I gene. J. Cell. Biochem. 118: 382-396, 2017. © 2016 Wiley Periodicals, Inc.
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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
| | | | - 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
| | - Dmitry A Tanyanskiy
- Department of Biochemistry, Institute of Experimental Medicine, Russian Academy of Medical Sciences, St. Petersburg, Russia.,Department of Fundamental Medicine and Medical Technologies, St. Petersburg State University, 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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7
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Park JG, Xu X, Cho S, Lee AH. Loss of Transcription Factor CREBH Accelerates Diet-Induced Atherosclerosis in Ldlr-/- Mice. Arterioscler Thromb Vasc Biol 2016; 36:1772-81. [PMID: 27417587 DOI: 10.1161/atvbaha.116.307790] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 06/30/2016] [Indexed: 12/14/2022]
Abstract
OBJECTIVE Liver-enriched transcription factor cAMP-responsive element-binding protein H (CREBH) regulates plasma triglyceride clearance by inducing lipoprotein lipase cofactors, such as apolipoprotein A-IV (apoA-IV), apoA-V, and apoC-II. CREBH also regulates apoA-I transcription. This study aims to determine whether CREBH has a role in lipoprotein metabolism and development of atherosclerosis. APPROACH AND RESULTS CREBH-deficient Creb3l3(-/-) mice were bred with Ldlr(-/-) mice creating Ldlr(-/-) Creb3l3(-/-) double knockout mice. Mice were fed on a high-fat and high-sucrose Western diet for 20 weeks. We showed that CREBH deletion in Ldlr(-/-) mice increased very low-density lipoprotein-associated triglyceride and cholesterol levels, consistent with the impairment of lipoprotein lipase-mediated triglyceride clearance in these mice. In contrast, high-density lipoprotein cholesterol levels were decreased in CREBH-deficient mice, which was associated with decreased production of apoA-I from the liver. The results indicate that CREBH directly activated Apoa1 gene transcription. Accompanied by the worsened atherogenic lipid profile, Ldlr(-/-) Creb3l3(-/-) mice developed significantly more atherosclerotic lesions in the aortas than Ldlr(-/-) mice. CONCLUSIONS We identified CREBH as an important regulator of lipoprotein metabolism and suggest that increasing hepatic CREBH activity may be a novel strategy for prevention and treatment of atherosclerosis.
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Affiliation(s)
- Jong-Gil Park
- From the Department of Pathology and Laboratory Medicine, Weill Cornell Medical College, New York, NY
| | - Xu Xu
- From the Department of Pathology and Laboratory Medicine, Weill Cornell Medical College, New York, NY
| | - Sungyun Cho
- From the Department of Pathology and Laboratory Medicine, Weill Cornell Medical College, New York, NY
| | - Ann-Hwee Lee
- From the Department of Pathology and Laboratory Medicine, Weill Cornell Medical College, New York, NY.
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8
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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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9
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Fraczek J, Bolleyn J, Vanhaecke T, Rogiers V, Vinken M. Primary hepatocyte cultures for pharmaco-toxicological studies: at the busy crossroad of various anti-dedifferentiation strategies. Arch Toxicol 2012; 87:577-610. [PMID: 23242478 DOI: 10.1007/s00204-012-0983-3] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Accepted: 11/19/2012] [Indexed: 01/24/2023]
Abstract
Continuously increasing understanding of the molecular triggers responsible for the onset of diseases, paralleled by an equally dynamic evolution of chemical synthesis and screening methods, offers an abundance of pharmacological agents with a potential to become new successful drugs. However, before patients can benefit of newly developed pharmaceuticals, stringent safety filters need to be applied to weed out unfavourable drug candidates. Cost effectiveness and the need to identify compound liabilities, without exposing humans to unnecessary risks, has stimulated the shift of the safety studies to the earliest stages of drug discovery and development. In this regard, in vivo relevant organotypic in vitro models have high potential to revolutionize the preclinical safety testing. They can enable automation of the process, to match the requirements of high-throughput screening approaches, while satisfying ethical considerations. Cultures of primary hepatocytes became already an inherent part of the preclinical pharmaco-toxicological testing battery, yet their routine use, particularly for long-term assays, is limited by the progressive deterioration of liver-specific features. The availability of suitable hepatic and other organ-specific in vitro models is, however, of paramount importance in the light of changing European legal regulations in the field of chemical compounds of different origin, which gradually restrict the use of animal studies for safety assessment, as currently witnessed in cosmetic industry. Fortunately, research groups worldwide spare no effort to establish hepatic in vitro systems. In the present review, both classical and innovative methodologies to stabilize the in vivo-like hepatocyte phenotype in culture of primary hepatocytes are presented and discussed.
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Affiliation(s)
- J Fraczek
- Department of Toxicology, Faculty of Medicine and Pharmacy, Centre for Pharmaceutical Research, Vrije Universiteit Brussel, Belgium.
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10
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Auer S, Hahne P, Soyal SM, Felder T, Miller K, Paulmichl M, Krempler F, Oberkofler H, Patsch W. Potential Role of Upstream Stimulatory Factor 1 Gene Variant in Familial Combined Hyperlipidemia and Related Disorders. Arterioscler Thromb Vasc Biol 2012; 32:1535-44. [DOI: 10.1161/atvbaha.112.245639] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Objective—
Genetic studies implicated upstream stimulatory factor 1 (USF1) in familial combined hyperlipidemia because the rs2073658 minor allele was associated with reduced risk of familial combined hyperlipidemia and related disorders. The molecular mechanisms whereby rs2073658 influences trait expression have remained elusive.
Methods and Results—
Plasma lipids, rs2073658 genotypes (N=372), and hepatic transcript levels (N=96) of
USF1
and genes involved in hepatic lipoprotein production were determined in obese subjects. The rs2073658 minor allele was associated with reduced plasma triglycerides (TGs) (
P
<0.001), hepatic
USF1
(
P
<0.01), and microsomal TG transfer protein transcript levels (
P
<0.05). Functional studies in human hepatocellular carcinoma cells showed that rs2073658 is located in a forkhead box A2 (FOXA2) binding site and that major allele constructs displayed higher transcriptional activity than minor allele constructs. Knockdown of FOXA2 reduced the activity of major, but not minor allele constructs. Furthermore, an interaction between hepatic FOXA2 transcript levels and rs2073658 minor allele carrier status on hepatic
USF1
transcript levels was observed in vivo (
P
<0.05).
USF1
activated the transcription of FOXA2 and FOXA2 strongly activated the transcription of microsomal TG transfer protein.
Conclusion—
A feed-forward loop comprising activation of
USF1
transcription by FOXA2 and activation of FOXA2 transcription by
USF1
, driving microsomal TG transfer protein expression, is modulated by rs2073658. Hence, rs2073658 likely influences hepatic TG secretion.
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Affiliation(s)
- Simon Auer
- From the Department of Laboratory Medicine (S.A., P.H., S.M.S., T.F., H.O., W.P.) and Institute of Pharmacology (M.P., W.P.), Paracelsus Medical University, Salzburg, Austria; Departments of Surgery (K.M.) and Internal Medicine (F.K.), Krankenhaus Hallein, Salzburg, Austria
| | - Penelope Hahne
- From the Department of Laboratory Medicine (S.A., P.H., S.M.S., T.F., H.O., W.P.) and Institute of Pharmacology (M.P., W.P.), Paracelsus Medical University, Salzburg, Austria; Departments of Surgery (K.M.) and Internal Medicine (F.K.), Krankenhaus Hallein, Salzburg, Austria
| | - Selma M. Soyal
- From the Department of Laboratory Medicine (S.A., P.H., S.M.S., T.F., H.O., W.P.) and Institute of Pharmacology (M.P., W.P.), Paracelsus Medical University, Salzburg, Austria; Departments of Surgery (K.M.) and Internal Medicine (F.K.), Krankenhaus Hallein, Salzburg, Austria
| | - Thomas Felder
- From the Department of Laboratory Medicine (S.A., P.H., S.M.S., T.F., H.O., W.P.) and Institute of Pharmacology (M.P., W.P.), Paracelsus Medical University, Salzburg, Austria; Departments of Surgery (K.M.) and Internal Medicine (F.K.), Krankenhaus Hallein, Salzburg, Austria
| | - Karl Miller
- From the Department of Laboratory Medicine (S.A., P.H., S.M.S., T.F., H.O., W.P.) and Institute of Pharmacology (M.P., W.P.), Paracelsus Medical University, Salzburg, Austria; Departments of Surgery (K.M.) and Internal Medicine (F.K.), Krankenhaus Hallein, Salzburg, Austria
| | - Markus Paulmichl
- From the Department of Laboratory Medicine (S.A., P.H., S.M.S., T.F., H.O., W.P.) and Institute of Pharmacology (M.P., W.P.), Paracelsus Medical University, Salzburg, Austria; Departments of Surgery (K.M.) and Internal Medicine (F.K.), Krankenhaus Hallein, Salzburg, Austria
| | - Franz Krempler
- From the Department of Laboratory Medicine (S.A., P.H., S.M.S., T.F., H.O., W.P.) and Institute of Pharmacology (M.P., W.P.), Paracelsus Medical University, Salzburg, Austria; Departments of Surgery (K.M.) and Internal Medicine (F.K.), Krankenhaus Hallein, Salzburg, Austria
| | - Hannes Oberkofler
- From the Department of Laboratory Medicine (S.A., P.H., S.M.S., T.F., H.O., W.P.) and Institute of Pharmacology (M.P., W.P.), Paracelsus Medical University, Salzburg, Austria; Departments of Surgery (K.M.) and Internal Medicine (F.K.), Krankenhaus Hallein, Salzburg, Austria
| | - Wolfgang Patsch
- From the Department of Laboratory Medicine (S.A., P.H., S.M.S., T.F., H.O., W.P.) and Institute of Pharmacology (M.P., W.P.), Paracelsus Medical University, Salzburg, Austria; Departments of Surgery (K.M.) and Internal Medicine (F.K.), Krankenhaus Hallein, Salzburg, Austria
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11
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Wang K, Holterman AX. Pathophysiologic role of hepatocyte nuclear factor 6. Cell Signal 2011; 24:9-16. [PMID: 21893194 DOI: 10.1016/j.cellsig.2011.08.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2011] [Accepted: 08/20/2011] [Indexed: 01/03/2023]
Abstract
Hepatocyte nuclear factor 6 (HNF6) is one of liver-enriched transcription factors. HNF6 utilizes the bipartite onecut-homeodomain sequence to localize the HNF6 protein to the nuclear compartment and binds to specific DNA sequences of numerous target gene promoters. HNF6 regulates an intricate network and mediates complex biological processes that are best known in the liver and pancreas. The function of HNF6 is correlated to cell proliferation, cell cycle regulation, cell differentiation and organogenesis, cell migration and cell-matrix adhesion, glucose metabolism, bile homeostasis, inflammation and so on. HNF6 controls the transcription of its target genes in different ways. The details of the regulatory pathways and their mechanisms are still under investigation. Future study will explore HNF6 novel functions associated with apoptosis, oncogenesis, and modulation of the inflammatory response. This review highlights recent progression pertaining to the pathophysiologic role of HNF6 and summarizes the potential mechanisms in preclinical animal models. HNF6-mediated pathways represent attractive therapeutic targets for the treatment of the relative diseases such as cholestasis.
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Affiliation(s)
- Kewei Wang
- Department of Pediatrics and Surgery/Section of Pediatric Surgery, Rush University Medical Center, Chicago, IL 60612, United States.
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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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Nock A, Ascano JM, Jones T, Barrero MJ, Sugiyama N, Tomita M, Ishihama Y, Malik S. Identification of DNA-dependent protein kinase as a cofactor for the forkhead transcription factor FoxA2. J Biol Chem 2009; 284:19915-26. [PMID: 19478084 PMCID: PMC2740417 DOI: 10.1074/jbc.m109.016295] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2009] [Indexed: 11/06/2022] Open
Abstract
Forkhead factors are important regulators of animal development and homeostasis. They are among the earliest to bind quiescent genes, which they activate in conjunction with other transcription factors. Many liver-specific genes are under the control of FoxA2, a liver-enriched forkhead protein. Here we confirmed by chromatin immunoprecipitation that FoxA2 is one of the factors bound to the promoter-proximal enhancer of the gene encoding apolipoprotein AI (a component of high density lipoprotein) and that it functions in synergy with the nuclear receptor hepatocyte nuclear factor-4alpha. Furthermore, toward identifying additional cofactors that could potentially regulate FoxA2 activity, we identified DNA-dependent protein kinase (DNA-PK) as a FoxA2-associated factor upon affinity purification of epitope-tagged FoxA2. We show that FoxA2, found to be a phosphoprotein in vivo, is also an efficient substrate for DNA-PK, which targets serine 283. This residue is contained within a conserved serine-glutamine phosphorylation signal for DNA-PK, located within the C-terminal third of the polypeptide, just distal to its winged-helix DNA binding domain. We establish that this residue is critical for FoxA2 function because FoxA2 bearing a mutation at this site is severely compromised in its ability to activate a reporter gene under the control of its cognate DNA-binding site (apoAI site B). Complementary experiments rule out that this mutation compromises the ability of FoxA2 to either translocate to the nucleus or to bind site B. We therefore conclude that DNA-PK-dependent phosphorylation of FoxA2 plays a critical role in its transcriptional activation function per se.
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Affiliation(s)
- Adam Nock
- From the Laboratory of Biochemistry and Molecular Biology, Rockefeller University, New York, New York 10065
| | - Janice M. Ascano
- From the Laboratory of Biochemistry and Molecular Biology, Rockefeller University, New York, New York 10065
| | - Tara Jones
- From the Laboratory of Biochemistry and Molecular Biology, Rockefeller University, New York, New York 10065
| | - Maria J. Barrero
- From the Laboratory of Biochemistry and Molecular Biology, Rockefeller University, New York, New York 10065
| | - Naoyuki Sugiyama
- the Institute for Advanced Biosciences, Keio University, 403-1 Daihoji, Tsuruoka, Yamagata 997-0017, Japan, and
| | - Masaru Tomita
- the Institute for Advanced Biosciences, Keio University, 403-1 Daihoji, Tsuruoka, Yamagata 997-0017, Japan, and
| | - Yasushi Ishihama
- the Institute for Advanced Biosciences, Keio University, 403-1 Daihoji, Tsuruoka, Yamagata 997-0017, Japan, and
- PRESTO, Japan Science and Technology Agency, Sanbancho Building, 5-Sanbancho, Chiyodaku, Tokyo 102-0075, Japan
| | - Sohail Malik
- From the Laboratory of Biochemistry and Molecular Biology, Rockefeller University, New York, New York 10065
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15
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Masson D, Qatanani M, Sberna AL, Xiao R, Pais de Barros JP, Grober J, Deckert V, Athias A, Gambert P, Lagrost L, Moore DD, Assem M. Activation of the constitutive androstane receptor decreases HDL in wild-type and human apoA-I transgenic mice. J Lipid Res 2008; 49:1682-91. [DOI: 10.1194/jlr.m700374-jlr200] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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16
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Genistein and daidzein induced apoA-1 transactivation in hepG2 cells expressing oestrogen receptor-α. Br J Nutr 2008; 99:1007-12. [DOI: 10.1017/s0007114507853426] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Studies have shown that soya consumption has been associated with low incidence of CVD. Because the chemical structures of soya isoflavones are similar to oestrogen, the beneficial outcome may be attributed to the oestrogenicity of these compounds. In this study, effect of the soya isoflavone genistein on the mRNA expression of apoA-1 in the human hepatoma HepG2 cell was investigated. Without oestrogen receptor (ER) α transfection, soya isoflavones in the physiological range had no effect on the apoA-1 transcription. Once ERα was ectopically expressed in these cells, soya isoflavone dramatically increased the apoA-1 mRNA abundance quantified by real-time PCR.ApoA-1-reporter assays with plasmid constructed from the 5′-flanking segment upstream to the coding region revealed that the transactivation of theapoA-1promoter was induced by the soya isoflavone in HepG2 cells expressing ERα. This induction was reduced by the anti-oestrogen ICI 182780, but not the inhibitors of protein kinase (PK) C, PKA, or mitogen-activated PK. Based on the previously identified response elements on the promoter, a series of truncated promoter reporter plasmids were then constructed. An induction profile of genistein was built and insulin response core element at − 411 to − 404 appeared to be a potential site of interaction. This study illustrated that soya isoflavones at physiological concentrations could up regulate apoA-1 mRNA expression in ERα-transfected HepG2 cells.
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17
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Dullens SPJ, Plat J, Mensink RP. Increasing apoA-I production as a target for CHD risk reduction. Nutr Metab Cardiovasc Dis 2007; 17:616-628. [PMID: 17703927 DOI: 10.1016/j.numecd.2007.05.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/09/2007] [Revised: 05/08/2007] [Accepted: 05/30/2007] [Indexed: 12/28/2022]
Abstract
Dyslipidemia leading to coronary heart diseases (CHD) enables venues to prevent or treat CHD by other strategies than only lowering serum LDL cholesterol (LDL-C) concentrations, which is currently the most frequently targeted change. Unlike LDL-C, elevated high-density lipoprotein cholesterol (HDL-C) concentrations may protect against the development of CHD as demonstrated in numerous large-scale epidemiological studies. In this review we describe that besides elevating serum HDL-C concentrations by increasing alpha-HDL particles, approaches to elevate HDL-C concentrations by increasing pre-beta HDL particle concentrations seems more attractive. Besides infusion of apoA-I(Milano), using apoA-I mimetics, or delipidation of alpha-HDL particles, elevating de novo apoA-I production may be a suitable target to functionally increase pre-beta HDL particle concentrations. Therefore, a detailed description of the molecular pathways underlying apoA-I synthesis and secretion, completed with an overview of known effects of pharmacological and nutritional compounds on apoA-I synthesis will be presented. This knowledge may ultimately be applied in developing dietary intervention strategies to elevate apoA-I production and serum HDL-C concentrations and consequently lower CHD risk.
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Affiliation(s)
- Stefan P J Dullens
- Department of Human Biology, Maastricht University, Universiteitssingel 50, Maastricht, The Netherlands
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18
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Chan MY, Wai Man G, Chen ZY, Wang J, Leung LK. Oestrogen receptor α is required for biochanin A-induced apolipoprotein A-1 mRNA expression in HepG2 cells. Br J Nutr 2007; 98:534-9. [PMID: 17532863 DOI: 10.1017/s0007114507750857] [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: 11/06/2022]
Abstract
Epidemiological studies have indicated that soya consumption may produce a better plasma lipid profile. The effect may be attributed to the phyto-oestrogens in soya. The red clover (Trifolium pratense) isoflavone biochanin A has a chemical structure similar to those phyto-oestrogens found in soya beans, and is marketed as a nutraceutical for alleviating postmenopausal symptoms. In the present study we investigated the effect of biochanin A on the mRNA expression of ApoA-1 in the hepatic cell line HepG2. Real-time PCR revealed that biochanin A increased ApoA-1 mRNA abundance in cells expressing oestrogen receptor (ER) α. Without ERα transfection, biochanin A had no effect on mRNA abundance. In order to study the transcriptional control, a fragment of the 5′-flanking region of theApoA-1gene was amplified and inserted in a firefly luciferase reporter plasmid. The reporter assay indicated that the transactivation of theApoA-1promoter was induced by biochanin A in HepG2 cells transfected with the ERα expression plasmid. This induction was reduced by the anti-oestrogen ICI 182,780, whereas the inhibitors of protein kinase (PK) C, PKA, or mitogen-activated kinase (ERK) had no suppressive effect. The present study illustrated that biochanin A might up regulate hepatic apoA-1 mRNA expression through an ER-dependent pathway.
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Affiliation(s)
- Ming Yan Chan
- Department of Biochemistry, Faculty of Medicine, The Chinese University of Hong Kong, Room 507C, MMW Bldg, Shatin NT, Hong Kong
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19
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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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20
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Lamon-Fava S, Micherone D. Regulation of apoA-I gene expression: mechanism of action of estrogen and genistein. J Lipid Res 2003; 45:106-12. [PMID: 14563824 DOI: 10.1194/jlr.m300179-jlr200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
We have previously shown that 17-beta-estradiol (E2) and genistein increase the expression of apolipoprotein A-I (apoA-I), the major protein component of HDL, in Hep G2 cells. To elucidate the mechanism mediating the increase in apoA-I gene expression by these compounds, plasmid constructs containing serial deletions of the apoA-I promoter region were generated. The smallest region maintaining response to E2 and genistein spanned the -220 to -148 sequence, and the estrogen antagonist ICI182,780 completely inhibited the E2 and genistein effect. Nuclear extracts from cells treated with E2 and genistein showed increased binding to site B oligonucleotide (-169 to -146), and nuclear extracts from genistein-treated cells showed increased binding to an early growth response factor 1 (Egr-1) oligonucleotide compared to control cells. An increase in the concentrations of Egr-1 and hepatocyte nuclear factor-3beta was observed in nuclear extracts of cells treated with both compounds compared to control cells. Treatment with a specific inhibitor of mitogen-activated protein (MAP) kinase, but not with other inhibitors, abolished the stimulation of apoA-I gene expression by E2 and genistein. These results indicate that the MAP kinase pathway is involved in the regulation of apoA-I gene expression by genistein and E2, possibly through downstream regulation of transcription factors binding to the promoter region.
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Affiliation(s)
- Stefania 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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21
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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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22
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Wang JC, Waltner-Law M, Yamada K, Osawa H, Stifani S, Granner DK. Transducin-like enhancer of split proteins, the human homologs of Drosophila groucho, interact with hepatic nuclear factor 3beta. J Biol Chem 2000; 275:18418-23. [PMID: 10748198 DOI: 10.1074/jbc.m910211199] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Members of the hepatic nuclear factor 3 (HNF3) family, including HNF3alpha, HNF3beta, and HNF3gamma, play important roles in embryonic development, the establishment of tissue-specific gene expression, and the regulation of gene expression in differentiated tissues. We found, using the glutathione S-transferase pull-down method, that the transducin-like Enhancer of split (TLE) proteins, which are the human homologs of Drosophila Groucho, directly associate with HNF3beta. Conserved region II of HNF3beta (amino acids 361-388) is responsible for the interaction with TLE1. A mammalian two-hybrid assay was used to confirm that this interaction occurs in vivo. Overexpression of TLE1 in HepG2 and HeLa cells decreases transactivation mediated through the C-terminal domain of HNF3beta, and Grg5, a naturally occurring dominant negative form of Groucho/TLE, also increases the transcriptional activity of this region of HNF3. These results lead us to suggest that TLE proteins could influence the expression of mammalian genes regulated by HNF3.
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Affiliation(s)
- J C Wang
- Department of Molecular Physiology & Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0615, USA
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23
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Li J, Ning G, Duncan SA. Mammalian hepatocyte differentiation requires the transcription factor HNF-4α. Genes Dev 2000. [DOI: 10.1101/gad.14.4.464] [Citation(s) in RCA: 225] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
HNF-4α is a transcription factor of the nuclear hormone receptor family that is expressed in the hepatic diverticulum at the onset of liver development. Mouse embryos lacking HNF-4α fail to complete gastrulation due to dysfunction of the visceral endoderm. This early embryonic lethality has so far prevented any analyses of the contribution of HNF-4α toward liver development and hepatocyte differentiation. However, we have shown that complementation ofHNF-4 α−/−embryos with a tetraploid embryo-derived wild-type visceral endoderm rescues this early developmental arrest and allowsHNF-4 α−/−embryos to proceed normally through midgestation stages of development. Examination of these rescued embryos revealed that HNF-4α was dispensable for specification and early development of the liver. However,HNF-4α−/− fetal livers failed to express a large array of genes whose expression in differentiated hepatocytes is essential for a functional hepatic parenchyma, including genes encoding several apolipoproteins, metabolic proteins, and serum factors. In addition, we have demonstrated that HNF-4α is essential for expression of the transcription factors HNF-1α and PXR within the fetal liver. We therefore conclude that HNF-4α is both essential for hepatocyte differentiation during mammalian liver development and also crucial for metabolic regulation and liver function.
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Marten NW, Hsiang CH, Yu L, Stollenwerk NS, Straus DS. Functional activity of hepatocyte nuclear factor-1 is specifically decreased in amino acid-limited hepatoma cells. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1447:160-74. [PMID: 10542313 DOI: 10.1016/s0167-4781(99)00165-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Limitation of cultured rat hepatoma cells for an essential amino acid results in a specific decrease in expression of several genes that are preferentially expressed in the liver, including the serum albumin and transthyretin genes. In the work presented here, we examined whether the coordinate repression of these genes is caused by decreased activity of one or more of the liver-enriched transcription factors, hepatocyte nuclear factor-1 (HNF-1), HNF-3, HNF-4 or C/EBP. To address this question, HepG2 human hepatoma cells were transiently transfected with luciferase reporter constructs containing multiple copies of individual transcription factor binding sites. Limitation for an essential amino acid resulted in specific repression of a construct in which luciferase expression was directed by HNF-1. A single HNF-1 binding site located adjacent to the TATA box plays a major role in transcription directed by the serum albumin promoter in transient transfection assays. Amino acid limitation of cells transfected with an albumin promoter/luciferase reporter construct resulted in specific repression of promoter activity. In addition, bacterial methylation or site-directed mutagenesis of the HNF-1 binding site in the albumin proximal promoter region eliminated the regulation of an albumin promoter-luciferase reporter construct under conditions of amino acid limitation. These results demonstrated that the HNF-1 binding site played a major role in regulation of the albumin promoter by amino acid availability. Deletion analysis of the albumin promoter confirmed regulation through the HNF-1 binding site and also identified a second amino acid regulatory element in the upstream region of the albumin promoter, which has been shown previously to contain a functional binding site for HNF-3. The repression of albumin promoter and HNF-1 reporter constructs in amino acid-limited cells occurred without a change in the DNA binding activity of HNF-1. Moreover, HNF-3 DNA binding activity was also not decreased in amino acid-limited cells. These results suggest that the regulation of transcription by amino acids occurs at the level of transcriptional activation by HNF-1 and HNF-3, rather than by alteration of the DNA binding activity of either factor.
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Affiliation(s)
- N W Marten
- Biomedical Sciences Division and Biology Department, University of California, Riverside, CA 92521-0121, USA
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Nakamura T, Fox-Robichaud A, Kikkawa R, Kashiwagi A, Kojima H, Fujimiya M, Wong NC. Transcription factors and age-related decline in apolipoprotein A-I expression. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)33418-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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26
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Transcriptional elongation of the rat apolipoprotein A-I gene: identification and mapping of two arrest sites and their signals. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)33485-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Cui Y, Narayanan CS, Zhou J, Kumar A. Exon-I is involved in positive as well as negative regulation of human angiotensinogen gene expression. Gene X 1998; 224:97-107. [PMID: 9931457 DOI: 10.1016/s0378-1119(98)00512-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
Abstract
Angiotensinogen is the glycoprotein precursor of one of the most potent vasoactive hormones, angiotensin-II. Angiotensinogen gene is primarily expressed in the liver, and this gene locus is linked with human essential hypertension. We show here that a mutation in exon-I reduces the basal expression of the human angiotensinogen gene in liver cells. We also show that a nucleotide sequence in exon-I binds to liver-enriched transcription factor HNF-3 and a ubiquitous factor AP4. Our studies also show that transient transfection of an expression vector containing AP4 coding sequence downregulates the expression of reporter constructs containing human angiotensinogen gene promoter. By contrast, co-transfection of an expression vector containing HNF-3beta coding sequence increases the expression of these reporter constructs. The human angiotensinogen gene has a C/A polymorphism located at -20, and we have shown that estrogen receptor-alpha binds to this sequence when nucleoside A is present at this site. We show here that co-transfection of an expression vector containing AP4 coding sequence reduces estrogen-induced promoter activity of reporter constructs containing human angiotensinogen gene promoter (with nucleoside A at -20) attached to the CAT gene. These studies partly explain the molecular mechanisms involved in tissue-specific expression of the human angiotensinogen gene.
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Affiliation(s)
- Y Cui
- Department of Pathology, New York Medical College, Valhalla, NY 10595, USA
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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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30
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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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31
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Cooper AD, Chen J, Botelho-Yetkinler MJ, Cao Y, Taniguchi T, Levy-Wilson B. Characterization of Hepatic-specific Regulatory Elements in the Promoter Region of the Human Cholesterol 7α-Hydroxylase Gene. J Biol Chem 1997. [DOI: 10.1074/jbc.272.6.3444] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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32
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Taylor AH, Raymond J, Dionne JM, Romney J, Chan J, Lawless DE, Wanke IE, Wong NC. Glucocorticoid increases rat apolipoprotein A-I promoter activity. J Lipid Res 1996. [DOI: 10.1016/s0022-2275(20)37304-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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33
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Saladin R, Vu-Dac N, Fruchart JC, Auwerx J, Staels B. Transcriptional induction of rat liver apolipoprotein A-I gene expression by glucocorticoids requires the glucocorticoid receptor and a labile cell-specific protein. EUROPEAN JOURNAL OF BIOCHEMISTRY 1996; 239:451-9. [PMID: 8706754 DOI: 10.1111/j.1432-1033.1996.0451u.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Treatment with glucocorticoids increases the concentration of plasma high-density lipoprotein (HDL), which is inversely correlated to the development of atherosclerosis. Previously, we demonstrated that repeated administration of glucocorticoids increases apolipoprotein (apo) A-I gene expression and decreases apoA-II gene expression in rat liver. In the present study, the mechanism of glucocorticoid action on hepatic apoA-I and apoA-II expression was studied. A single injection of rats with dexamethasone increased hepatic apoA-I mRNA levels within 6 h and further increases were observed after 12 h and 24 h. In contrast, liver apoA-II mRNA levels gradually decreased after dexamethasone treatment to less than 25% control levels after 24 h. In rat primary hepatocytes and McARH8994 hepatoma cells, addition of dexamethasone increased apoA-I mRNA levels in a time-dependent and dose-dependent manner, whereas apoA-II mRNA levels were unchanged. Simultaneous addition of the glucocorticoid antagonist RU486 prevented the increase in apoA-I mRNA levels after dexamethasone treatment, which suggests that the effects of dexamethasone are mediated through the glucocorticoid receptor. Inhibition of transcription by actinomycin D and nuclear-run-on experiments in McARH8994 cells and primary hepatocytes showed that dexamethasone induced apoA-I, but not apoA-II, gene transcription. Transient-transfection assays in McARH8994 cells with a chloramphenicol acetyl transferase vector driven by the rat-apoA-I-gene promoter demonstrated that the proximal apoA-I promoter could be induced by dexamethasone, and this effect could be abolished by simultaneous treatment with RU486. However, in COS-1 cells, apoA-I promoter transcription was not induced by dexamethasone or cotransfected glucocorticoid receptor. In addition, the induction of apoA-I gene transcription by dexamethasone was blocked by the protein-synthesis inhibitor cycloheximide, which suggests the presence of a labile protein involved in apoA-I gene activation by dexamethasone. In conclusion, our results demonstrate that dexamethasone regulates rat apoA-I, but not apoA-II, gene expression through direct action on the hepatocyte. The induction of apoA-I gene transcription by dexamethasone requires the glucocorticoid receptor and a labile cell-specific protein.
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Affiliation(s)
- R Saladin
- U325 INSERM, Département d'Athérosclérose, Institut Pasteur, Lille, France
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34
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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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35
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Kardassis D, Laccotripe M, Talianidis I, Zannis V. Transcriptional regulation of the genes involved in lipoprotein transport. The role of proximal promoters and long-range regulatory elements and factors in apolipoprotein gene regulation. Hypertension 1996; 27:980-1008. [PMID: 8613278 DOI: 10.1161/01.hyp.27.4.980] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- D Kardassis
- Section of Molecular Genetics, Boston University MedicalCenter, MA 02118-2394, USA
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36
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Chowdhury S, Gotoh T, Mori M, Takiguchi M. CCAAT/enhancer-binding protein beta (C/EBP beta) binds and activates while hepatocyte nuclear factor-4 (HNF-4) does not bind but represses the liver-type arginase promoter. EUROPEAN JOURNAL OF BIOCHEMISTRY 1996; 236:500-9. [PMID: 8612622 DOI: 10.1111/j.1432-1033.1996.00500.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In an attempt to elucidate the mechanism governing liver-specific transcription of the arginase gene, we previously detected two protein-binding sites designated footprint areas A and B at positions around--90 and --55 bp, respectively, relative to the transcription start site of the rat arginase gene. Based on the finding that area A was bound by a liver-selective factor(s) related to CCAAT/enhancer-binding protein (C/EBP), we performed cotransfection assay and showed that C/EBP family members and a related factor, albumin D-element-binding protein (DBP) stimulate transcription from the arginase promoter. In addition to area A, a recombinant C/EBP beta protein bound to area B, which appeared to be primarily responsible for activation by C/EBPs. We unexpectedly found that the arginase promoter activity stimulated by C/EBPs and DBP was repressed by another liver-enriched transcription factor, hepatocyte nuclear factor-4 (HNF-4). Analysis of chimeras formed between the arginase promoter and the herpes simplex virus thymidine kinase promoter allowed us to delimit the negative HNF-4-responsive element into the region overlapping with footprint area B. However, no apparent binding of HNF-4 was observed in this negative element. We speculate that HNF-4 is involved in fine regulation of the arginase gene in the liver or shutdown of the gene in nonhepatic tissues without direct binding to the promoter region.
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Affiliation(s)
- S Chowdhury
- Department of Molecular Genetics, Kumamoto University School of Medicine, Japan
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37
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Ström A, Westin S, Eguchi H, Gustafsson JA, Mode A. Characterization of orphan nuclear receptor binding elements in sex-differentiated members of the CYP2C gene family expressed in rat liver. J Biol Chem 1995; 270:11276-81. [PMID: 7744763 DOI: 10.1074/jbc.270.19.11276] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The HepG2-specific P450 2C factor motif (HPF1-motif) is conserved in many hepatic cytochrome P450 genes (CYP). Its functional importance for rabbit CYP2C genes has led to the proposal that the HPF1 motif acts as a common regulator for the liver-specific expression of CYP2 genes with hepatic nuclear factor (HNF)-4 being the corresponding trans-activator. The HPF1-like elements in the rat CYP2C genes 2C7, 2C11, 2C12, and 2C13 have been studied with regard to functional importance and binding of the orphan receptors HNF-4, apoAI regulatory protein-1 (ARP-1), and v-erbA-related receptors (EAR) 3 and 2. Binding activity in rat liver nuclear extracts includes these orphan receptors as judged from electromobility supershift experiments and from results obtained with expressed receptors, although the element in CYP2C11 did not bind HNF-4. Mutations of the HPF1-like elements in the CYP2C7, CYP2C11, and CYP2C12 promoters had marginal effects on the expression of luciferase reporter gene constructs transiently transfected into HepG2 cells, whereas for CYP2C13 the activity was reduced to 60% of the wild type construct. Coexpression of HNF-4 in COS-7 cells had limited effect on the luciferase activity generated from the 2C promoters, maximally 3-fold. Our data indicate that the HPF1 elements in the rat CYP2C genes have limited functional importance and that HNF-4 is not a major trans-activator for any of these genes.
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Affiliation(s)
- A Ström
- Department of Medical Nutrition, Karolinska Institute, Huddinge University Hospital, Sweden
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38
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Kilbourne EJ, Widom R, Harnish DC, Malik S, Karathanasis SK. Involvement of early growth response factor Egr-1 in apolipoprotein AI gene transcription. J Biol Chem 1995; 270:7004-10. [PMID: 7896852 DOI: 10.1074/jbc.270.12.7004] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Liver-specific expression of the apolipoprotein AI (apoAI) gene is mediated by transcription factors bound to three sites (A, B, and C) in the apoAI enhancer. Sites A and C bind various members of the nuclear receptor superfamily, including the orphan nuclear receptor apolipoprotein regulatory protein-1 (ARP-1); site B binds the liver-enriched factor hepatic nuclear factor-3. The immediate early growth response factor (Egr-1), which is transiently expressed in various pathophysiologic states of the liver, activates the apoAI enhancer and overcomes ARP-1-mediated repression of the enhancer in hepatoblastoma HepG2 cells. Deletion mapping analysis revealed two Egr-1 binding sites, E1 and E2, flanking site A. Erg-1 bound efficiently to both E1 and E2. Sp1 in HepG2 nuclear extracts bound to E2 but not E1. In HepG2 cells, E1 functioned as an Egr-1 response element, whereas E2 had high basal activity and was not further induced by Egr-1. Mutations that prevent Egr-1 binding to the apoAI enhancer abolished its responsiveness to Erg-1, while they had only minor effects on its constitutive activity. These mutations also diminished the ability of Egr-1 to overcome ARP-1-mediated repression. Elimination of transcription factor binding to sites A, B, or C reduced enhancer activity without affecting Egr-1-dependent activation. We argue that Egr-1 is recruited to the apoAI enhancer complex under unusual circumstances, such as those prevailing during liver regeneration, to maintain apoAI transcription levels by overriding prior transcriptional controls.
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Affiliation(s)
- E J Kilbourne
- Department of Cardiovascular Molecular Biology, Lederle Laboratories, Pearl River, New York 10965
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