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Zhang L, Cao Z, Hong Y, He H, Chen L, Yu Z, Gao Y. Squalene Epoxidase: Its Regulations and Links with Cancers. Int J Mol Sci 2024; 25:3874. [PMID: 38612682 PMCID: PMC11011400 DOI: 10.3390/ijms25073874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2024] [Revised: 03/09/2024] [Accepted: 03/19/2024] [Indexed: 04/14/2024] Open
Abstract
Squalene epoxidase (SQLE) is a key enzyme in the mevalonate-cholesterol pathway that plays a critical role in cellular physiological processes. It converts squalene to 2,3-epoxysqualene and catalyzes the first oxygenation step in the pathway. Recently, intensive efforts have been made to extend the current knowledge of SQLE in cancers through functional and mechanistic studies. However, the underlying mechanisms and the role of SQLE in cancers have not been fully elucidated yet. In this review, we retrospected current knowledge of SQLE as a rate-limiting enzyme in the mevalonate-cholesterol pathway, while shedding light on its potential as a diagnostic and prognostic marker, and revealed its therapeutic values in cancers. We showed that SQLE is regulated at different levels and is involved in the crosstalk with iron-dependent cell death. Particularly, we systemically reviewed the research findings on the role of SQLE in different cancers. Finally, we discussed the therapeutic implications of SQLE inhibitors and summarized their potential clinical values. Overall, this review discussed the multifaceted mechanisms that involve SQLE to present a vivid panorama of SQLE in cancers.
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Affiliation(s)
- Lin Zhang
- Department of Thoracic Surgery, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen 518116, China
| | - Zheng Cao
- Department of Pathology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China
| | - Yuheng Hong
- Department of Thoracic Surgery, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China
| | - Haihua He
- Department of Thoracic Surgery, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China
- Department of Oncology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Leifeng Chen
- Department of Thoracic Surgery, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China
- Department of Oncology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Zhentao Yu
- Department of Thoracic Surgery, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen 518116, China
| | - Yibo Gao
- Central Laboratory & Shenzhen Key Laboratory of Epigenetics and Precision Medicine for Cancers, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen 518116, China
- State Key Laboratory of Molecular Oncology, National Cancer Center, National Clinical Research Center for Cancer, Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China
- Laboratory of Translational Medicine, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China
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Peters F, Grimm C. Regulation of ABCA1 by miR-33 and miR-34a in the Aging Eye. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1415:55-59. [PMID: 37440014 DOI: 10.1007/978-3-031-27681-1_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/14/2023]
Abstract
Many age-related diseases, including age-related macular degeneration (AMD), go along with local lipid accumulation and dysregulated lipid metabolism. Several genes involved in lipid metabolism, including ATP-binding cassette transporter A1 (ABCA1), were associated with AMD through genome-wide association studies. Recent studies have shown that loss of ABCA1 in the retinal pigment epithelium (RPE) leads to lipid accumulation and RPE atrophy, a hallmark of AMD, and that antagonizing ABCA1-targeting microRNAs (miRNAs) attenuated pathological changes to the RPE or to macrophages. Here, we focus on two lipid metabolism-modulating miRNAs, miR-33 and miR-34a, which show increased expression in aging RPE cells, and on their potential to regulate ABCA1 levels, cholesterol efflux, and lipid accumulation in AMD pathogenesis.
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Affiliation(s)
- Florian Peters
- Laboratory for Retinal Cell Biology, Department of Ophthalmology, University Hospital Zurich, University of Zurich, Schlieren, Switzerland.
| | - Christian Grimm
- Laboratory for Retinal Cell Biology, Department of Ophthalmology, University Hospital Zurich, University of Zurich, Schlieren, Switzerland
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3
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Tumour microenvironment and metabolic plasticity in cancer and cancer stem cells: Perspectives on metabolic and immune regulatory signatures in chemoresistant ovarian cancer stem cells. Semin Cancer Biol 2018; 53:265-281. [DOI: 10.1016/j.semcancer.2018.10.002] [Citation(s) in RCA: 87] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 10/05/2018] [Accepted: 10/08/2018] [Indexed: 02/06/2023]
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4
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González-Peña D, Dudzik D, Colina-Coca C, de Ancos B, García A, Barbas C, Sánchez-Moreno C. Evaluation of onion as a functional ingredient in the prevention of metabolic impairments associated to diet-induced hypercholesterolaemia using a multiplatform approach based on LC-MS, CE-MS and GC-MS. J Funct Foods 2015. [DOI: 10.1016/j.jff.2015.09.033] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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Plée-Gautier E, Antoun J, Goulitquer S, Le Jossic-Corcos C, Simon B, Amet Y, Salaün JP, Corcos L. Statins increase cytochrome P450 4F3-mediated eicosanoids production in human liver cells: A PXR dependent mechanism. Biochem Pharmacol 2012; 84:571-9. [DOI: 10.1016/j.bcp.2012.05.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Revised: 05/15/2012] [Accepted: 05/15/2012] [Indexed: 11/24/2022]
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6
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Kim EJ, Lee HI, Chung KJ, Noh YH, Ro Y, Koo JH. The ginsenoside-Rb2 lowers cholesterol and triacylglycerol levels in 3T3-L1 adipocytes cultured under high cholesterol or fatty acids conditions. BMB Rep 2009; 42:194-9. [PMID: 19403041 DOI: 10.5483/bmbrep.2009.42.4.194] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The effects of the ginsenoside Rb2 (Rb2) on lipid metabolism were characterized in 3T3-L1 adipocytes to evaluate their utility for treating obesity. While the amounts of total cholesterol and triacylglycerol (TAG) were markedly increased in the adipocytes treated with high amounts of cholesterol and fetal bovine serum (FBS), the test groups treated with Rb2 showed levels that were close to normal. The effect of Rb2 on these cells was comparable to that of lovastatin. Rb2 enhanced the expression of the sterol regulated element binding protein (SREBP) mRNA whereas treatment with cholesterol and FBS led to a reduction in the abundance of this transcript. The activity of fatty acid synthetase (FAS) was lower in the cholesterol group compared to the Rb2 treatment group suggesting that the observed decrease in cholesterol levels and activated SREBP was mediated by Rb2. Treatment with Rb2 also resulted in a decrease in TAG levels in adipocytes cultured under high fatty acid conditions. This effect was mediated by stimulating the expression of SREBP and Leptin mRNA, suggesting that Rb2 might be a valuable component capable of lowering the levels of lipids.
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Affiliation(s)
- Eun Ju Kim
- Department of Biochemistry, School of Medicine, Konkuk University, Seoul 143-701, Korea
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7
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Risé P, Camera M, Caruso D, Ghezzi S, Visioli F, Galli C. Synthesis of long-chain polyunsaturated fatty acids is inhibited in vivo in hypercholesterolemic rabbits and in vitro by oxysterols. Prostaglandins Leukot Essent Fatty Acids 2004; 71:79-86. [PMID: 15207522 DOI: 10.1016/j.plefa.2003.12.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/22/2003] [Accepted: 12/12/2003] [Indexed: 10/26/2022]
Abstract
Plasma total lipids, total cholesterol (cholesterol esters and free cholesterol) and oxysterol (mainly 7 beta-hydroxycholesterol (7 beta OH)) concentrations were significantly elevated in New Zealand rabbits fed a 2% cholesterol-containing diet with respect to controls fed the same diet without cholesterol. In addition, linoleic (18:2 n-6) and alpha-linolenic acid (18:3 n-3) plasma concentrations were significantly elevated in hypercholesterolemic rabbits, while concentrations of long-chain n-6 and n-3 derivatives were reduced. Studies in monocytic cell line THP-1 revealed that 7 beta OH markedly inhibited the conversion of 18:2 to 20:4 n-6 and of 18:3 to 22:6 n-3, indicating depression of the desaturation steps; in particular the inhibition was greater for the Delta 5 desaturation step. Furthermore, experiments of Real-Time PCR showed that 5-10 microM 7 beta OH decreased the Delta 5 gene expression. In conclusion, atherogenic oxysterols interfere with the production of long-chain polyunsaturated fatty acids from their precursors both in hypercholesterolemic rabbits and in cultured cells.
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Affiliation(s)
- P Risé
- Department of Pharmacological Sciences, University of Milan, via Balzaretti 9, 20133 Milan, Italy.
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Nagai M, Sakakibara J, Nakamura Y, Gejyo F, Ono T. SREBP-2 and NF-Y are involved in the transcriptional regulation of squalene epoxidase. Biochem Biophys Res Commun 2002; 295:74-80. [PMID: 12083769 DOI: 10.1016/s0006-291x(02)00623-x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The expression of squalene epoxidase (SE) is highly regulated transcriptionally by cholesterol. To elucidate these molecular mechanisms, we isolated the human and rat genomic clones. The entire human SE gene was about 24 kb long and organized into 11 exons with 10 introns. Unidirectional deletion analysis of the human 5(')-flanking region indicated that the sequence between -264 and -230 bp conferred cholesterol sensitivity on a reporter gene. This region contained a potential copy of consensus sterol regulatory element (SRE) sequence (CCACGCAAC) previously identified in the promoter of cholesterogenic and its related genes. The transcriptional activation observed under overexpression of sterol regulatory element binding protein-2 (SREBP-2) supported the functional role of the SRE sequence. Another deletion analysis showed that the sequence -207 to -192 bp was also active and it contained nuclear factor Y (NF-Y) binding site. Both sites might play critical roles in sterol mediated regulation of SE gene.
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Affiliation(s)
- Masaaki Nagai
- Department of Biochemistry and Internal Medicine, Niigata University School of Medicine, 1-757 Asahimachidori, Niigata 951-8510, Japan.
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9
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Wolf SS, Roder K, Schweizer M. Role of Sp1 and Sp3 in the Transcriptional Regulation of the Rat Fatty Acid Synthase Gene. Arch Biochem Biophys 2001; 385:259-66. [PMID: 11368006 DOI: 10.1006/abbi.2000.2153] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Inspection of the 5' region of the sequence of the rat fatty acid synthase (FAS) gene revealed a high GC content between -900 and +500, implying several binding sites for members of the Sp1 family of transcription factors. Using SL2 and H4IIE cells in conjunction with FAS promoter/luciferase constructs either successively deleted or containing defined deletions we characterized six GC boxes--GC-I to GC-VI--located between -557 and -83 and discovered a seventh, GC-VII, in the first intron. In vitro DNAse I-footprinting, electrophoretic mobility shift assays, and the yeast one-hybrid system indicated that Sp1 as well as Sp3 interacts with GC-I to GC-VII. Each of the GC boxes conferred Sp1-dependent transcription on the FAS-Mini promoter and in the case of GC-I, Sp1, and Sp3 exert an additive effect on FAS promoter activity.
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Affiliation(s)
- S S Wolf
- Department of Biological Sciences, Heriot-Watt University, Edinburgh, United Kingdom
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10
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Abstract
Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.
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Affiliation(s)
- G J Schroepfer
- Departments of Biochemistry, Rice University, Houston, Texas, USA.
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11
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Kawabe Y, Suzuki T, Hayashi M, Hamakubo T, Sato R, Kodama T. The physiological role of sterol regulatory element-binding protein-2 in cultured human cells. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1436:307-18. [PMID: 9989262 DOI: 10.1016/s0005-2760(98)00119-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To clarify the role of the sterol regulatory element-binding protein-2 (SREBP-2), we established cell lines in which human SREBP-2(1-481) could be induced by isopropyl-beta-D-thiogalactopyranoside (IPTG). The range of IPTG-induced changes in SREBP-2(1-481) levels in '23-11' cells, one of these cell lines, was almost the same as that of sterol-induced changes in the levels of mature SREBP-2, indicating that IPTG was able to regulate the expression of SREBP-2(1-481) within the normal physiological range in this cell line. Sterols regulate the expression of the LDL receptor, HMG-CoA reductase, squalene synthase and fatty acid synthase in 23-11 cells as they also do in the parental cell line HeLa S3. IPTG increased mRNA levels of the LDL receptor and HMG-CoA reductase but not squalene synthase both in the presence or absence of excess sterols. Fatty acid synthase mRNA was increased 2 h after the IPTG addition in the absence of excess sterol (10% FBS), but was slightly increased 6 h after the IPTG addition in the presence of excess sterols. In the absence of excess sterols, both SREBP-2(1-481) and endogenous mature SREBP-2 exist in the nucleus. This suggests that an increased amount of SREBP-2 over the normal physiological range is required for the regulation of fatty acid synthase. IPTG increased both the surface binding of 125I-LDL and cholesterol biosynthesis from [14C]acetate significantly in a similar time course. In contrast, fatty acid biosynthesis from [14C]acetate was almost unchanged by IPTG during the same incubation period. These results suggest that physiological amounts of SREBP-2 play a key role in the regulation of cholesterol but not fatty acid metabolism.
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Affiliation(s)
- Y Kawabe
- Fuji-Gotemba Research Laboratories, Chugai Pharmaceutical Co., Ltd., Shizuoka, Japan.
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12
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Chouinard RA, Luo Y, Osborne TF, Walsh A, Tall AR. Sterol regulatory element binding protein-1 activates the cholesteryl ester transfer protein gene in vivo but is not required for sterol up-regulation of gene expression. J Biol Chem 1998; 273:22409-14. [PMID: 9712863 DOI: 10.1074/jbc.273.35.22409] [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: 11/06/2022] Open
Abstract
The plasma cholesteryl ester transfer protein (CETP) plays a central role in high density lipoprotein metabolism and reverse cholesterol transport. Plasma CETP levels are increased in response to dietary or endogenous hypercholesterolemia as a result of increased gene transcription in liver and periphery. Deletional analysis in human CETP transgenic mice localized this response to a region of the proximal promoter which contains a tandem repeat of the sterol regulatory element (SRE) of the 3-hydroxy-3-methylglutaryl-CoA reductase gene. The purpose of the present study was to evaluate the role of the SRE-like element in CETP promoter activity. Gel shift assays using CETP promoter fragments containing these elements showed binding of the transcription factors, sterol regulatory element-binding protein-1 (SREBP-1) and Yin Yang-1 (YY-1). Point mutations in the SRE-like element, designated MUT1 and MUT2, resulted in decreased binding of SREBP-1 (MUT1) or SREBP-1 and YY-1 (MUT2). To determine the in vivo significance of this binding activity, CETP transgenic mice were prepared containing these promoter point mutations. MUT1 and MUT2 transgenic mice expressed CETP activity and mass in plasma. In response to high fat, high cholesterol diets, both MUT1-CETP and MUT2-CETP transgenic mice displayed induction of plasma CETP activity similar to that observed in natural flanking region (NFR) CETP transgenic mice. Moreover, in stably transfected adipocyte cell lines, MUT1 and MUT2 CETP promoter-reporter genes showed significant induction of reporter activity in response to sterols. To evaluate transactivation by SREBP-1, NFR- and MUT1-CETP transgenic mice were crossed with SREBP-1 transgenic mice. Induction of the SREBP transgene in the liver with a low carbohydrate diet resulted in a 3-fold increase in plasma CETP activity in NFR-CETP/SREBP transgenic mice, but there was no significant change in activity in MUT1-CETP/SREBP transgenic mice. Thus, SREBP-1 transactivates the NFR-CETP transgene in vivo, as a result of interaction with the CETP promoter SREs. However, this interaction is not required for positive sterol induction of CETP gene transcription. The results suggest independent regulation of the CETP gene by SREBP-1 and a distinct positive sterol response factor.
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Affiliation(s)
- R A Chouinard
- Division of Molecular Medicine, Department of Medicine, Columbia University, New York, New York 10032, USA
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13
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Swinnen JV, Alen P, Heyns W, Verhoeven G. Identification of diazepam-binding Inhibitor/Acyl-CoA-binding protein as a sterol regulatory element-binding protein-responsive gene. J Biol Chem 1998; 273:19938-44. [PMID: 9685328 DOI: 10.1074/jbc.273.32.19938] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Diazepam-binding inhibitor/acyl-CoA-binding protein (DBI/ACBP), a highly conserved 10-kDa polypeptide, has been implicated in various physiological processes including gamma-aminobutyric acid type A receptor binding, acyl-CoA binding and transport, steroidogenesis, and peptide hormone release. Both in LNCaP prostate cancer cells and 3T3-L1 preadipocytes, the expression of DBI/ACBP is stimulated under conditions that promote lipogenesis (treatment with androgens and insulin, respectively) and that involve the activation of sterol regulatory element-binding proteins (SREBPs). Accordingly, we investigated whether DBI/ACBP expression is under the direct control of SREBPs. Analysis of the human and rat DBI/ACBP promoter revealed the presence of a conserved sterol regulatory element (SRE)-like sequence. Gel shift analysis confirmed that this sequence is able to bind SREBPs. In support of the functionality of SREBP binding, coexpression of SREBP-1a with a DBI/ACBP promoter-reporter gene resulted in a 50-fold increase in transcriptional activity in LNCaP cells. Disruption of the SRE decreased basal expression and abolished SREBP-1a-induced transcriptional activation. In agreement with the requirement of a co-regulator for SREBP function, transcriptional activation by SREBP-1a overexpression was severely diminished when a neighboring NF-Y site was mutated. Cholesterol depletion or androgen treatment, conditions that activate SREBP function in LNCaP cells, led to an increase in DBI/ACBP mRNA expression and SRE-dependent transcriptional activation. These findings indicate that the promoter for DBI/ACBP contains a functional SRE that allows DBI/ACBP to be coregulated with other genes involved in lipid metabolism.
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Affiliation(s)
- J V Swinnen
- Laboratory for Experimental Medicine and Endocrinology, Faculty of Medicine, Onderwijs en Navorsing, Gasthuisberg, Catholic University of Leuven, B-3000 Leuven, Belgium.
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14
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Guan G, Dai P, Shechter I. Differential transcriptional regulation of the human squalene synthase gene by sterol regulatory element-binding proteins (SREBP) 1a and 2 and involvement of 5' DNA sequence elements in the regulation. J Biol Chem 1998; 273:12526-35. [PMID: 9575211 DOI: 10.1074/jbc.273.20.12526] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Transcription of the human squalene synthase (HSS) gene is regulated by variations in the level of cellular cholesterol. Three regulatory elements in the HSS promoter region are known to be involved in the regulation: 1) a modified sterol regulatory element (SRE) 1 (HSS-SRE-1), 2) an inverted SRE-3 (Inv-SRE-3), 3) an inverted Y box (Inv-Y-Box). We report here the regulatory role of distinct cis-elements in the HSS promoter by using mutants of an HSS-luciferase promoter reporter. The activity of a wild-type promoter reporter transiently transfected into HepG-2 cells is increased by sterol depletion of the cells or by coexpression of mature forms of the SRE-binding proteins (SREBP) 1a and SREBP-2. Differential activation by SREBP-1a and SREBP-2 of the reporter gene mutated at various regions of the promoter is observed. Mutation of either the HSS-SRE-1 or the Inv-SRE-3 sequence diminished the activation by SREBP-1a and by sterol depletion but did not affect the activation by SREBP-2. Simultaneous mutations of both of these sequences almost completely abolished activation of the promoter by SREBP-1a or by sterol depletion, but activation by SREBP-2 was retained at 70%. Mutation of the Inv-Y-Box sequence element decreased the activity of the promoter by 50% or more, and if mutated together with both SREs, the activation was almost completely abolished. Mutation of any single GC box of the two located at -40 to -57 did not affect activity, whereas simultaneous mutation of the two decreased activation by SREBP-2 by 60%, by lipid depletion by 20%, and had no effect on the activation by SREBP-1a. A Y box motif at -159 to -166 and an SRE-like sequence element (SRE-1(8/10)) at position -101 to -108 are also involved in the sterol regulation. These results indicate that the complex sterol-mediated transcriptional regulation of the HSS gene is due to the presence of multiple copies of diverse cis elements in the HSS promoter. The differential activation of the HSS promoter may point to specific role of the SREBPs in cholesterogenesis.
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Affiliation(s)
- G Guan
- Department of Biochemistry and Molecular Biology, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799, USA
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15
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Noel-Suberville C, Pallet V, Audouin-Chevallier I, Higueret P, Bonilla S, Martinez AJ, Zulet MA, Portillo MP, Garcin H. Expression of retinoic acid, triiodothyronine, and glucocorticoid hormone nuclear receptors is decreased in the liver of rats fed a hypercholesterolemia-inducing diet. Metabolism 1998; 47:301-8. [PMID: 9500567 DOI: 10.1016/s0026-0495(98)90261-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Several studies have shown that dietary factors modulate cell signaling pathways. The aim of this study was to determine whether a hypercholesterolemia-inducing diet rich in saturated fat and cholesterol modifies rat liver expression of the nuclear receptors of retinoic acid (RAR), triiodothyronine (TR), and glucocorticoid hormone (GR), which are transcriptional factors. The experimental diet contained coconut oil 25 g/100 g as a source of lipids, cholesterol 1 g/100 g, and cholic acid 0.5 g/100 g, and the control diet contained olive oil 5 g/100 g. After 26 days of feeding the hypercholesterolemia-inducing diet, a lower binding capacity of the nuclear receptors and a smaller amount of their mRNA were observed. Moreover, the activities of malic enzyme (ME) and tyrosine aminotransferase (TAT), whose gene promotors contain a response element to TR and GR, respectively, were significantly decreased. These changes occurred in a cellular environment characterized by a high level of cholesterol and free fatty acids (FFAs). Thus, two nonexclusive hypotheses can be proposed to explain this decreased expression of nuclear receptors, one emphasizing the effect of lipidic components on the cellular amount of receptor ligands (retinoic acid [RA] and triiodothyronine [T3]), the other emphasizing a modification of the balance between nuclear receptors that could impede the upregulation of TR and RAR.
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Abstract
Hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or "statins," have been extremely efficacious in decreasing low-density lipoprotein (LDL) cholesterol levels in patients with hypercholesterolemia and in treating patients with dysbetalipoproteinemia, a relatively rare form of hyperlipidemia. Clinical trials have indicated that statins can significantly lower very-low-density lipoprotein (VLDL) triglyceride levels, although the central mechanism of action of statins-i.e., increasing the number of LDL receptors-would appear to suggest that they would have no significant effect on VLDL levels. Through a review of published data from animal and human studies, this article addresses the important clinical question of how drugs that inhibit the rate-limiting enzyme for cholesterol can affect triglyceride metabolism.
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Affiliation(s)
- H N Ginsberg
- Division of Preventive Medicine and Nutrition, Columbia University College of Physicians and Surgeons, New York, New York, USA
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17
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Abstract
Adipose tissue has long been known to house the largest energy reserves in the animal body. Recent research indicates that in addition to this role, the adipocyte functions as a global regulator of energy metabolism. Adipose tissue is exquisitely sensitive to a variety of endocrine and paracrine signals, e.g. insulin, glucagon, glucocorticoids, and tumor necrosis factor (TNF), that combine to control both the secretion of other regulatory factors and the recruitment and differentiation of new adipocytes. The process of adipocyte differentiation is controlled by a cascade of transcription factors, most notably those of the C/EBP and PPAR families, which combine to regulate each other and to control the expression of adipocyte-specific genes. One such gene, i.e. the obese gene, was recently identified and found to encode a hormone, referred to as leptin, that plays a major role in the regulation of energy intake and expenditure. The hormonal and transcriptional control of adipocyte differentiation is discussed, as is the role of leptin and other factors secreted by the adipocyte that participate in the regulation of adipose homeostasis.
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Affiliation(s)
- C S Hwang
- Department of Biological Chemistry, Johns Hopkins University Medical School, Baltimore, Maryland 21205, USA
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18
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Abstract
Current evidence indicates that much of the regulation of adipocyte differentiation serves to modulate a common adipogenic transcriptional control pathway, comprising members of the C/EBP and PPAR families. Hormonal regulators have been found to control expression of these factors and to alter their activity through ligand binding, post-transcriptional modification, and protein-protein interactions.
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Affiliation(s)
- T M Loftus
- Department of Biological Chemistry, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205, USA.
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Fujioka T, Tsujita Y, Shimotsu H. Induction of fatty acid synthesis by pravastatin sodium in rat liver and primary hepatocytes. Eur J Pharmacol 1997; 328:235-9. [PMID: 9218706 DOI: 10.1016/s0014-2999(97)83050-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We examined the effect of pravastatin sodium (pravastatin), a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on fatty acid synthesis in rat liver. The repeated administration of pravastatin to rats at 250 mg/kg for 7 days led to a 2.8-fold increase in fatty acid synthesis in the liver. The diurnal change of fatty acid synthesis was not affected by the treatment. Hepatic fatty acid synthase activity was increased 3.2-fold, while acetyl-CoA carboxylase activity was not changed by the repeated administration of pravastatin. In rat hepatocytes, the incubation with 2 microg/ml pravastatin for 24 h increased fatty acid synthase activity 1.5-fold, as well as HMG-CoA reductase activity 2.8-fold. These results suggest that HMG-CoA reductase inhibitors might increase fatty acid synthesis in vivo through the induction of hepatic fatty acid synthase.
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Affiliation(s)
- T Fujioka
- Pharmacology and Molecular Biology Research Laboratories, Sankyo Co., Ltd., Shinagawa-ku, Tokyo, Japan.
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Guan G, Dai PH, Osborne TF, Kim JB, Shechter I. Multiple sequence elements are involved in the transcriptional regulation of the human squalene synthase gene. J Biol Chem 1997; 272:10295-302. [PMID: 9092581 DOI: 10.1074/jbc.272.15.10295] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The expression of human squalene synthase (HSS) gene is transcriptionally regulated in HepG-2 cells, up to 10-fold, by variations in cellular cholesterol homeostasis. An earlier deletion analysis of the 5'-flanking region of the HSS gene demonstrated that most of the HSS promoter activity is detected within a 69-base pair sequence located between nucleotides -131 and -200. ADD1/SREBP-1c, a rat homologue of sterol regulatory element-binding protein (SREBP)-1c binds to sterol regulatory element (SRE)-1-like sequence (HSS-SRE-1) present in this region (Guan, G., Jiang, G., Koch, R. L. and Shechter, I. (1995) J. Biol. Chem. 270, 21958-21965). In our present study, we demonstrate that mutation of this HSS-SRE-1 element significantly reduced, but did not abolish, the response of HSS promoter to change in sterol concentration. Mutation scanning indicates that two additional DNA promoter sequences are involved in sterol-mediated regulation. The first sequence contains an inverted SRE-3 element (Inv-SRE-3) and the second contains an inverted Y-box (Inv-Y-box) sequence. A single mutation in any of these sequences reduced, but did not completely remove, the response to sterols. Combination mutation studies showed that the HSS promoter activity was abolished only when all three elements were mutated simultaneously. Co-expression of SRE-1- or SRE-2-binding proteins (SREBP-1 or SREBP-2) with HSS promoter-luciferase reporter resulted in a dramatic increase of HSS promoter activity. Gel mobility shift studies indicate differential binding of the SREBPs to regulatory sequences in the HSS promoter. These results indicate that the transcription of the HSS gene is regulated by multiple regulatory elements in the promoter.
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Affiliation(s)
- G Guan
- Department of Biochemistry, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA
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Sato R, Inoue J, Kawabe Y, Kodama T, Takano T, Maeda M. Sterol-dependent transcriptional regulation of sterol regulatory element-binding protein-2. J Biol Chem 1996; 271:26461-4. [PMID: 8900111 DOI: 10.1074/jbc.271.43.26461] [Citation(s) in RCA: 220] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
We show in this manuscript that expression of the mRNA for sterol regulatory element-binding protein-2 (SREBP-2) is regulated by the cellular sterol level in cultured HeLa cells. We have cloned the 5'-flanking region of the gene encoding human SREBP-2. Characterization of this region shows the minimum 50-base pair segment, which contains a 10-base pair sterol regulatory element 1 (SRE-1) identical to the one in the human LDL receptor promoter, confers sterol responsiveness when fused to the luciferase reporter gene. Enforced expression of the truncated SREBP-2 protein (amino acid residues 1-481) also shows that this upstream segment contains the information required for transcriptional activation. The luciferase assays using mutant versions of the reporter genes reveal that the sterol-dependent transcriptional regulation is mediated by two nearby motifs, the SRE-1 and the NF-Y binding site (the inverted CCAAT box, ATTGGC); the latter is reported to play a critical role in sterol-dependent regulation of 3-hydroxy-3-methylglutaryl-coenzyme A synthase and farnesyl diphosphate synthase genes (Jackson, S. M., Ericsson, J., Osborne, T. F., and Edwards, P. A. (1995) J. Biol. Chem. 270, 21445-21448). Gel mobility shift assays demonstrate that the transcription factor NF-Y truly binds to the ATTGGC sequence. These findings suggest that the activity of SREBP-2 is controlled not only post-translationally by proteolytic activation of the precursor protein but also transcriptionally by itself together with NF-Y.
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Affiliation(s)
- R Sato
- Laboratory of Biochemistry, Faculty of Pharmaceutical Sciences, Osaka University, Suita, Osaka 565
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