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Rodrigue‐Way A, Caron V, Bilodeau S, Keil S, Hassan M, Lévy E, Mitchell GA, Tremblay A. Scavenger receptor CD36 mediates inhibition of cholesterol synthesis viaactivation of the PPARγ/PGC‐1α pathway and Insig1/2 expression in hepatocytes. FASEB J 2014; 28:1910-1923. [DOI: 10.1096/fj.13-240168] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/30/2023]
Affiliation(s)
- Amélie Rodrigue‐Way
- Research CenterSainte‐Justine HospitalMontréalQuébecCanada
- Department of Biochemistry and Molecular MedicineUniversity of MontrealMontréalQuébecCanada
| | | | - Stéphanie Bilodeau
- Research CenterSainte‐Justine HospitalMontréalQuébecCanada
- Department of Biochemistry and Molecular MedicineUniversity of MontrealMontréalQuébecCanada
| | - Sarah Keil
- Research CenterSainte‐Justine HospitalMontréalQuébecCanada
- Department of Biochemistry and Molecular MedicineUniversity of MontrealMontréalQuébecCanada
| | - Meryl Hassan
- Research CenterSainte‐Justine HospitalMontréalQuébecCanada
| | - Emile Lévy
- Research CenterSainte‐Justine HospitalMontréalQuébecCanada
| | - Grant A. Mitchell
- Research CenterSainte‐Justine HospitalMontréalQuébecCanada
- Department of Biochemistry and Molecular MedicineUniversity of MontrealMontréalQuébecCanada
- Department of PediatricsUniversity of MontrealMontréalQuébecCanada
| | - André Tremblay
- Research CenterSainte‐Justine HospitalMontréalQuébecCanada
- Department of Biochemistry and Molecular MedicineUniversity of MontrealMontréalQuébecCanada
- Department of Obstetrics and Gynecology, Faculty of MedicineUniversity of MontrealMontréalQuébecCanada
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102
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Pinto JT, Cooper AJL. From cholesterogenesis to steroidogenesis: role of riboflavin and flavoenzymes in the biosynthesis of vitamin D. Adv Nutr 2014; 5:144-63. [PMID: 24618756 PMCID: PMC3951797 DOI: 10.3945/an.113.005181] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Flavin-dependent monooxygenases and oxidoreductases are located at critical branch points in the biosynthesis and metabolism of cholesterol and vitamin D. These flavoproteins function as obligatory intermediates that accept 2 electrons from NAD(P)H with subsequent 1-electron transfers to a variety of cytochrome P450 (CYP) heme proteins within the mitochondria matrix (type I) and the (microsomal) endoplasmic reticulum (type II). The mode of electron transfer in these systems differs slightly in the number and form of the flavin prosthetic moiety. In the type I mitochondrial system, FAD-adrenodoxin reductase interfaces with adrenodoxin before electron transfer to CYP heme proteins. In the microsomal type II system, a diflavin (FAD/FMN)-dependent cytochrome P450 oxidoreductase [NAD(P)H-cytochrome P450 reductase (CPR)] donates electrons to a multitude of heme oxygenases. Both flavoenzyme complexes exhibit a commonality of function with all CYP enzymes and are crucial for maintaining a balance of cholesterol and vitamin D metabolites. Deficits in riboflavin availability, imbalances in the intracellular ratio of FAD to FMN, and mutations that affect flavin binding domains and/or interactions with client proteins result in marked structural alterations within the skeletal and central nervous systems similar to those of disorders (inborn errors) in the biosynthetic pathways that lead to cholesterol, steroid hormones, and vitamin D and their metabolites. Studies of riboflavin deficiency during embryonic development demonstrate congenital malformations similar to those associated with genetic alterations of the flavoenzymes in these pathways. Overall, a deeper understanding of the role of riboflavin in these pathways may prove essential to targeted therapeutic designs aimed at cholesterol and vitamin D metabolism.
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103
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Zhu J, Jiang X, Chehab FF. FoxO4 interacts with the sterol regulatory factor SREBP2 and the hypoxia inducible factor HIF2α at the CYP51 promoter. J Lipid Res 2013; 55:431-42. [PMID: 24353279 DOI: 10.1194/jlr.m043521] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The late steps of cholesterol biosynthesis are oxygen demanding, requiring eleven oxygen molecules per synthesized cholesterol molecule. A key enzymatic reaction, which occurs at the top of the Bloch and Kandutsch-Russell pathways, is the demethylation of lanosterol and dihydrolanosterol (DHL). This reaction is catalyzed by lanosterol 14α demethylase (CYP51) and requires three oxygen molecules. Thus, it is the first step in the distal pathway to be susceptible to oxygen deprivation. Having previously identified that the forkhead transcription factor 4 (FoxO4) represses CYP51 expression, we aimed to characterize its role at the CYP51 promoter. Hypoxia-treated 3T3L1 cells showed decreased cholesterol biosynthesis, accumulation of lanosterol/DHL, and stimulation of FoxO4 expression and its cytoplasmic translocation to the nucleus. Transfection assays with a CYP51 promoter reporter gene revealed that FoxO4 and sterol regulatory element binding protein (SREBP)2 exert a stimulatory effect, whereas FoxO4 and the hypoxia inducible factor (HIF)2α repress CYP51 promoter activity. Electromobility shift, chromatin immunoprecipitation, pull-down, and coimmunoprecipitation assays show that FoxO4 interacts with SREBP2 and HIF2α to modulate CYP51 promoter activity. We also show an inverse correlation between FoxO4 and CYP51 in adipose tissue of ob/ob mice and mouse fetal cortical neurons exposed to hypoxia. Overall, these studies demonstrate a role for FoxO4 in the regulation of CYP51 expression.
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Affiliation(s)
- Jun Zhu
- Departments of Laboratory Medicine University of California, San Francisco, CA 94143
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104
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Fernandes NV, Yeganehjoo H, Katuru R, DeBose-Boyd RA, Morris LL, Michon R, Yu ZL, Mo H. Geranylgeraniol suppresses the viability of human DU145 prostate carcinoma cells and the level of HMG CoA reductase. Exp Biol Med (Maywood) 2013; 238:1265-74. [PMID: 24006306 DOI: 10.1177/1535370213492693] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The rate-limiting enzyme of the mevalonate pathway, 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, provides essential intermediates for the prenylation of nuclear lamins and Ras and dolichol-mediated glycosylation of growth factor receptors. The diterpene geranylgeraniol downregulates the level of HMG CoA reductase and suppresses the growth of human liver, lung, ovary, pancreas, colon, stomach, and blood tumors. We evaluated the growth-suppressive activity of geranylgeraniol in human prostate carcinoma cells. Geranylgeraniol induced dose-dependent suppression of the viability of human DU145 prostate carcinoma cells (IC50=80±18 µmol/L, n=5) following 72-h incubations in 96-well plates. Cell cycle was arrested at the G1 phase with a concomitant decrease in cyclin D1 protein. Geranylgeraniol-induced apoptosis was detected by flow cytometric analysis, fluorescence microscopy following acridine orange and ethidium bromide dual staining, and caspase-3 activation. Geranylgeraniol-induced viability suppression was accompanied by concentration-dependent decrease in the level of HMG CoA reductase protein. As a nonsterol molecule that downregulates HMG CoA reductase in the presence of sterols, geranylgeraniol may have potential in the chemoprevention and/or therapy of human prostate cancer.
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Affiliation(s)
- Nicolle V Fernandes
- Department of Nutrition and Food Sciences, Texas Woman's University, Denton, TX 76204, USA
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105
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Foresti O, Ruggiano A, Hannibal-Bach HK, Ejsing CS, Carvalho P. Sterol homeostasis requires regulated degradation of squalene monooxygenase by the ubiquitin ligase Doa10/Teb4. eLife 2013; 2:e00953. [PMID: 23898401 PMCID: PMC3721249 DOI: 10.7554/elife.00953] [Citation(s) in RCA: 147] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Accepted: 06/18/2013] [Indexed: 01/10/2023] Open
Abstract
Sterol homeostasis is essential for the function of cellular membranes and requires feedback inhibition of HMGR, a rate-limiting enzyme of the mevalonate pathway. As HMGR acts at the beginning of the pathway, its regulation affects the synthesis of sterols and of other essential mevalonate-derived metabolites, such as ubiquinone or dolichol. Here, we describe a novel, evolutionarily conserved feedback system operating at a sterol-specific step of the mevalonate pathway. This involves the sterol-dependent degradation of squalene monooxygenase mediated by the yeast Doa10 or mammalian Teb4, a ubiquitin ligase implicated in a branch of the endoplasmic reticulum (ER)-associated protein degradation (ERAD) pathway. Since the other branch of ERAD is required for HMGR regulation, our results reveal a fundamental role for ERAD in sterol homeostasis, with the two branches of this pathway acting together to control sterol biosynthesis at different levels and thereby allowing independent regulation of multiple products of the mevalonate pathway. DOI:http://dx.doi.org/10.7554/eLife.00953.001.
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Affiliation(s)
- Ombretta Foresti
- Cell and Developmental Biology Programme, Center for Genomic Regulation (CRG), Barcelona, Spain
- Universitat Pompeu Fabra, Barcelona, Spain
| | - Annamaria Ruggiano
- Cell and Developmental Biology Programme, Center for Genomic Regulation (CRG), Barcelona, Spain
- Universitat Pompeu Fabra, Barcelona, Spain
| | - Hans K Hannibal-Bach
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Christer S Ejsing
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Pedro Carvalho
- Cell and Developmental Biology Programme, Center for Genomic Regulation (CRG), Barcelona, Spain
- Universitat Pompeu Fabra, Barcelona, Spain
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106
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Sharpe LJ, Brown AJ. Controlling cholesterol synthesis beyond 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR). J Biol Chem 2013; 288:18707-15. [PMID: 23696639 DOI: 10.1074/jbc.r113.479808] [Citation(s) in RCA: 258] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
3-Hydroxy-3-methylglutaryl-CoA reductase (HMGCR) is the target of the statins, important drugs that lower blood cholesterol levels and treat cardiovascular disease. Consequently, the regulation of HMGCR has been investigated in detail. However, this enzyme acts very early in the cholesterol synthesis pathway, with ∼20 subsequent enzymes needed to produce cholesterol. How they are regulated is largely unexplored territory, but there is growing evidence that enzymes beyond HMGCR serve as flux-controlling points. Here, we introduce some of the known regulatory mechanisms affecting enzymes beyond HMGCR and highlight the need to further investigate their control.
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Affiliation(s)
- Laura J Sharpe
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, New South Wales 2052, Australia
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107
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Pannu PS, Allahverdian S, Francis GA. Oxysterol generation and liver X receptor-dependent reverse cholesterol transport: not all roads lead to Rome. Mol Cell Endocrinol 2013; 368:99-107. [PMID: 22884520 DOI: 10.1016/j.mce.2012.07.013] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 06/30/2012] [Accepted: 07/27/2012] [Indexed: 12/31/2022]
Abstract
Cell cholesterol metabolism is a tightly regulated process, dependent in part on activation of nuclear liver X receptors (LXRs) to increase expression of genes mediating removal of excess cholesterol from cells in the reverse cholesterol transport pathway. LXRs are thought to be activated predominantly by oxysterols generated enzymatically from cholesterol in different cell organelles. Defects resulting in slowed release of cholesterol from late endosomes and lysosomes or reduction in sterol-27-hydroxylase activity lead to specific blocks in oxysterol production and impaired LXR-dependent gene activation. This block does not appear to be compensated by oxysterol production in other cell compartments. The purpose of this review is to summarize current knowledge about oxysterol-dependent activation by LXR of genes involved in reverse cholesterol transport, and what these defects of cell cholesterol homeostasis can teach us about the critical pathways of oxysterol generation for expression of LXR-dependent genes.
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Affiliation(s)
- Parveer S Pannu
- Department of Medicine, UBC James Hogg Research Centre, Institute of Heart and Lung Health at St. Paul's Hospital, Vancouver, BC, Canada V6Z 1Y6.
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108
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Ačimovič J, Rozman D. Steroidal triterpenes of cholesterol synthesis. Molecules 2013; 18:4002-17. [PMID: 23558541 PMCID: PMC6269928 DOI: 10.3390/molecules18044002] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Revised: 03/19/2013] [Accepted: 03/27/2013] [Indexed: 11/21/2022] Open
Abstract
Cholesterol synthesis is a ubiquitous and housekeeping metabolic pathway that leads to cholesterol, an essential structural component of mammalian cell membranes, required for proper membrane permeability and fluidity. The last part of the pathway involves steroidal triterpenes with cholestane ring structures. It starts by conversion of acyclic squalene into lanosterol, the first sterol intermediate of the pathway, followed by production of 20 structurally very similar steroidal triterpene molecules in over 11 complex enzyme reactions. Due to the structural similarities of sterol intermediates and the broad substrate specificity of the enzymes involved (especially sterol-Δ24-reductase; DHCR24) the exact sequence of the reactions between lanosterol and cholesterol remains undefined. This article reviews all hitherto known structures of post-squalene steroidal triterpenes of cholesterol synthesis, their biological roles and the enzymes responsible for their synthesis. Furthermore, it summarises kinetic parameters of enzymes (Vmax and Km) and sterol intermediate concentrations from various tissues. Due to the complexity of the post-squalene cholesterol synthesis pathway, future studies will require a comprehensive meta-analysis of the pathway to elucidate the exact reaction sequence in different tissues, physiological or disease conditions. A major reason for the standstill of detailed late cholesterol synthesis research was the lack of several steroidal triterpene standards. We aid to this efforts by summarizing commercial and laboratory standards, referring also to chemical syntheses of meiosis-activating sterols.
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Affiliation(s)
- Jure Ačimovič
- Centre for Functional Genomics and Bio-Chips, Faculty of Medicine, Institute of Biochemistry, University of Ljubljana, Zaloška 4, Ljubljana SI-1000, Slovenia.
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109
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Blanc M, Hsieh W, Robertson K, Kropp K, Forster T, Shui G, Lacaze P, Watterson S, Griffiths S, Spann N, Meljon A, Talbot S, Krishnan K, Covey D, Wenk M, Craigon M, Ruzsics Z, Haas J, Angulo A, Griffiths W, Glass C, Wang Y, Ghazal P. The transcription factor STAT-1 couples macrophage synthesis of 25-hydroxycholesterol to the interferon antiviral response. Immunity 2013; 38:106-18. [PMID: 23273843 PMCID: PMC3556782 DOI: 10.1016/j.immuni.2012.11.004] [Citation(s) in RCA: 302] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2012] [Accepted: 11/06/2012] [Indexed: 12/18/2022]
Abstract
Recent studies suggest that the sterol metabolic network participates in the interferon (IFN) antiviral response. However, the molecular mechanisms linking IFN with the sterol network and the identity of sterol mediators remain unknown. Here we report a cellular antiviral role for macrophage production of 25-hydroxycholesterol (cholest-5-en-3β,25-diol, 25HC) as a component of the sterol metabolic network linked to the IFN response via Stat1. By utilizing quantitative metabolome profiling of all naturally occurring oxysterols upon infection or IFN-stimulation, we reveal 25HC as the only macrophage-synthesized and -secreted oxysterol. We show that 25HC can act at multiple levels as a potent paracrine inhibitor of viral infection for a broad range of viruses. We also demonstrate, using transcriptional regulatory-network analyses, genetic interventions and chromatin immunoprecipitation experiments that Stat1 directly coupled Ch25h regulation to IFN in macrophages. Our studies describe a physiological role for 25HC as a sterol-lipid effector of an innate immune pathway.
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Affiliation(s)
- Mathieu Blanc
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
| | - Wei Yuan Hsieh
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
| | - Kevin A. Robertson
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
- SynthSys (Synthetic and Systems Biology), University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JD, UK
| | - Kai A. Kropp
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
| | - Thorsten Forster
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
| | - Guanghou Shui
- Departments of Biochemistry and Biological Sciences, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597
| | - Paul Lacaze
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
| | - Steven Watterson
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
- SynthSys (Synthetic and Systems Biology), University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JD, UK
| | - Samantha J. Griffiths
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
| | - Nathanael J. Spann
- Department of Molecular Biology, University of California, San Diego, La Jolla, CA 92093, USA
| | - Anna Meljon
- Institute of Mass Spectrometry, College of Medicine, Grove Building, Swansea University, Singleton Park, Swansea SA2 8PP, UK
| | - Simon Talbot
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
| | - Kathiresan Krishnan
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63011, USA
| | - Douglas F. Covey
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63011, USA
| | - Markus R. Wenk
- Departments of Biochemistry and Biological Sciences, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597
| | - Marie Craigon
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
| | - Zsolts Ruzsics
- Max von Pettenkofer-Institut, Ludwig-Maximilians-Universität München, Genzentrum, Feodor Lynen Str. 25, 81377 Munich, Germany
| | - Jürgen Haas
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
| | - Ana Angulo
- Facultad de Medicina, Institut d’Investigacions Biomèdiques August Pi i Sunyer, Rosselló 149-153, Barcelona 08036, Spain
| | - William J. Griffiths
- Institute of Mass Spectrometry, College of Medicine, Grove Building, Swansea University, Singleton Park, Swansea SA2 8PP, UK
| | - Christopher K. Glass
- Department of Molecular Biology, University of California, San Diego, La Jolla, CA 92093, USA
| | - Yuqin Wang
- Institute of Mass Spectrometry, College of Medicine, Grove Building, Swansea University, Singleton Park, Swansea SA2 8PP, UK
| | - Peter Ghazal
- Division of Pathway Medicine and Edinburgh Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK
- SynthSys (Synthetic and Systems Biology), University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JD, UK
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110
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Theesfeld CL, Hampton RY. Insulin-induced gene protein (INSIG)-dependent sterol regulation of Hmg2 endoplasmic reticulum-associated degradation (ERAD) in yeast. J Biol Chem 2013; 288:8519-8530. [PMID: 23306196 DOI: 10.1074/jbc.m112.404517] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin-induced gene proteins (INSIGs) function in control of cellular cholesterol. Mammalian INSIGs exert control by directly interacting with proteins containing sterol-sensing domains (SSDs) when sterol levels are elevated. Mammalian 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase (HMGR) undergoes sterol-dependent, endoplasmic-reticulum (ER)-associated degradation (ERAD) that is mediated by INSIG interaction with the HMGR SSD. The yeast HMGR isozyme Hmg2 also undergoes feedback-regulated ERAD in response to the early pathway-derived isoprene gernanylgeranyl pyrophosphate (GGPP). Hmg2 has an SSD, and its degradation is controlled by the INSIG homologue Nsg1. However, yeast Nsg1 promotes Hmg2 stabilization by inhibiting GGPP-stimulated ERAD. We have proposed that the seemingly disparate INSIG functions can be unified by viewing INSIGs as sterol-dependent chaperones of SSD clients. Accordingly, we tested the role of sterols in the Nsg1 regulation of Hmg2. We found that both Nsg1-mediated stabilization of Hmg2 and the Nsg1-Hmg2 interaction required the early sterol lanosterol. Lowering lanosterol in the cell allowed GGPP-stimulated Hmg2 ERAD. Thus, Hmg2-regulated degradation is controlled by a two-signal logic; GGPP promotes degradation, and lanosterol inhibits degradation. These data reveal that the sterol dependence of INSIG-client interaction has been preserved for over 1 billion years. We propose that the INSIGs are a class of sterol-dependent chaperones that bind to SSD clients, thus harnessing ER quality control in the homeostasis of sterols.
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Affiliation(s)
- Chandra L Theesfeld
- Section of Cell and Developmental Biology, Division of Biological Sciences, University of California San Diego, La Jolla, California 92093
| | - Randolph Y Hampton
- Section of Cell and Developmental Biology, Division of Biological Sciences, University of California San Diego, La Jolla, California 92093.
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111
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Dong XY, Tang SQ, Chen JD. Dual functions of Insig proteins in cholesterol homeostasis. Lipids Health Dis 2012; 11:173. [PMID: 23249523 PMCID: PMC3564778 DOI: 10.1186/1476-511x-11-173] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Accepted: 12/05/2012] [Indexed: 01/29/2023] Open
Abstract
The molecular mechanism of how cells maintain cholesterol homeostasis has become clearer for the understanding of complicated association between sterol regulatory element-binding proteins (SREBPs), SREBP cleavage-activating protein (SCAP), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) and Insuin induced-genes (Insigs). The pioneering researches suggested that SREBP activated the transcription of genes encoding HMG-CoA reductase and all of the other enzymes involved in the synthesis of cholesterol and lipids. However, SREBPs can not exert their activities alone, they must form a complex with another protein, SCAP in the endoplasmic reticulum (ER) and translocate to Golgi. Insigs are sensors and mediators that regulate cholesterol homeostasis through binding to SCAP and HMG-CoA reductase in diverse tissues such as adipose tissue and liver, as well as the cultured cells. In this article, we aim to review on the dual functions of Insig protein family in cholesterol homeostasis.
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Affiliation(s)
- Xiao-Ying Dong
- College of Veterinary Medicine, South China Agricultural University, No,483 Wu Shan Road, Tian He District, Guangzhou, 510642, China.
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112
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Jo Y, Hartman IZ, DeBose-Boyd RA. Ancient ubiquitous protein-1 mediates sterol-induced ubiquitination of 3-hydroxy-3-methylglutaryl CoA reductase in lipid droplet-associated endoplasmic reticulum membranes. Mol Biol Cell 2012; 24:169-83. [PMID: 23223569 PMCID: PMC3564538 DOI: 10.1091/mbc.e12-07-0564] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Sterol-induced binding to Insigs in endoplasmic reticulum (ER) membranes triggers ubiquitination of the cholesterol biosynthetic enzyme 3-hydroxy-3-methylglutaryl CoA reductase. This ubiquitination, which is mediated by Insig-associated ubiquitin ligases gp78 and Trc8, is obligatory for extraction of reductase from lipid droplet-associated ER membranes into the cytosol for proteasome-mediated, ER-associated degradation (ERAD). In this study, we identify lipid droplet-associated, ancient, ubiquitous protein-1 (Aup1) as one of several proteins that copurify with gp78. RNA interference (RNAi) studies show that Aup1 recruits the ubiquitin-conjugating enzyme Ubc7 to lipid droplets and facilitates its binding to both gp78 and Trc8. The functional significance of these interactions is revealed by the observation that RNAi-mediated knockdown of Aup1 blunts sterol-accelerated ubiquitination of reductase, which appears to occur in lipid droplet-associated membranes and subsequent ERAD of the enzyme. In addition, Aup1 knockdown inhibits ERAD of Insig-1, another substrate for gp78, as well as that of membrane-bound precursor forms of sterol-regulatory, element-binding protein-1 and -2, transcription factors that modulate expression of genes encoding enzymes required for cholesterol synthesis. Considered together, these findings not only implicate a role for Aup1 in maintenance of intracellular cholesterol homeostasis, but they also highlight the close connections among ERAD, lipid droplets, and lipid droplet-associated proteins.
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Affiliation(s)
- Youngah Jo
- Howard Hughes Medical Institute and Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046, USA
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113
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Ablation of gp78 in liver improves hyperlipidemia and insulin resistance by inhibiting SREBP to decrease lipid biosynthesis. Cell Metab 2012; 16:213-25. [PMID: 22863805 DOI: 10.1016/j.cmet.2012.06.014] [Citation(s) in RCA: 101] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/01/2012] [Revised: 04/30/2012] [Accepted: 06/26/2012] [Indexed: 12/28/2022]
Abstract
gp78 is a membrane-anchored ubiquitin ligase mediating the degradation of HMG-CoA reductase (HMGCR) and Insig-1. As a rate-limiting enzyme in cholesterol biosynthesis, HMGCR undergoes rapid sterol-promoted degradation. In contrast, destruction of Insig-1 releases its inhibition on SREBP and stimulates the expression of lipogenic genes. Thus, gp78 has opposite effects on lipid biosynthesis. We here generated liver-specific gp78 knockout (L-gp78(-/-)) mice and showed that although the degradation of HMGCR was blunted, SREBP was suppressed due to the elevation of Insig-1/-2, and therefore the lipid biosynthesis was decreased. The L-gp78(-/-) mice were protected from diet-/age-induced obesity and glucose intolerance. The livers of L-gp78(-/-) mice produced more FGF21, which activated thermogenesis in brown adipocytes and enhanced energy expenditure. Together, the major function of gp78 in liver is regulating lipid biosynthesis through SREBP pathway. Ablation of gp78 decreases the lipid levels and increases FGF21, and is beneficial to patients with metabolic diseases.
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114
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Kristiana I, Luu W, Stevenson J, Cartland S, Jessup W, Belani JD, Rychnovsky SD, Brown AJ. Cholesterol through the looking glass: ability of its enantiomer also to elicit homeostatic responses. J Biol Chem 2012; 287:33897-904. [PMID: 22869373 DOI: 10.1074/jbc.m112.360537] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
How cholesterol is sensed to maintain homeostasis has been explained by direct binding to a specific protein, Scap, or through altering the physical properties of the membrane. The enantiomer of cholesterol (ent-cholesterol) is a valuable tool in distinguishing between these two models because it shares nonspecific membrane effects with native cholesterol (nat-cholesterol), but not specific binding interactions. This is the first study to compare ent- and nat-cholesterol directly on major molecular parameters of cholesterol homeostasis. We found that ent-cholesterol suppressed activation of the master transcriptional regulator of cholesterol metabolism, SREBP-2, almost as effectively as nat-cholesterol. Importantly, ent-cholesterol induced a conformational change in the cholesterol-sensing protein Scap in isolated membranes in vitro, even when steps were taken to eliminate potential confounding effects from endogenous cholesterol. Ent-cholesterol also accelerated proteasomal degradation of the key cholesterol biosynthetic enzyme, squalene monooxygenase. Together, these findings provide compelling evidence that cholesterol maintains its own homeostasis not only via direct protein interactions, but also by altering membrane properties.
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Affiliation(s)
- Ika Kristiana
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, New South Wales 2052, Australia
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115
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Clark PJ, Thompson AJ, Vock DM, Kratz LE, Tolun AA, Muir AJ, McHutchison JG, Subramanian M, Millington DM, Kelley RI, Patel K. Hepatitis C virus selectively perturbs the distal cholesterol synthesis pathway in a genotype-specific manner. Hepatology 2012; 56:49-56. [PMID: 22318926 DOI: 10.1002/hep.25631] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Accepted: 01/23/2012] [Indexed: 12/16/2022]
Abstract
UNLABELLED Hepatitis C virus (HCV) subverts host cholesterol metabolism for key processes in its lifecycle. How this interference results in the frequently observed, genotype-dependent clinical sequelae of hypocholesterolemia, hepatic steatosis, and insulin resistance (IR) remains incompletely understood. Hypocholesterolemia typically resolves after sustained viral response (SVR), implicating viral interference in host lipid metabolism. Using a targeted cholesterol metabolomic platform we evaluated paired HCV genotype 2 (G2) and G3 patient sera for changes in in vivo HCV sterol pathway metabolites. We compared HCV genotypic differences in baseline metabolites and following antiviral treatment to assess whether sterol perturbation resolved after HCV eradication. We linked these metabolites to IR and urine oxidative stress markers. In paired sera from HCV G2 (n = 13) and G3 (n = 20) patients, baseline sterol levels were lower in G3 than G2 for distal metabolites (7-dehyrocholesterol (7DHC) 0.017 versus 0.023 mg/dL; P(adj) = 0.0524, cholesterol 140.9 versus 178.7 mg/dL; P(adj) = 0.0242) but not the proximal metabolite lanosterol. In HCV G3, SVR resulted in increased levels of distal metabolites (cholesterol [Δ55.2 mg/dL; P(adj) = 0.0015], 7DHC [Δ0.0075 mg/dL; P(adj) = 0.0026], lathosterol [Δ0.0430 mg/dL P(adj) = 0.0405]). In contrast, lanosterol was unchanged after SVR (P = 0.9515). CONCLUSION HCV G3, but not G2, selectively interferes with the late cholesterol synthesis pathway, evidenced by lower distal sterol metabolites and preserved lanosterol levels. This distal interference resolves with SVR. Normal lanosterol levels provide a signal for the continued proteolysis of 3-hydroxyl-3-methylglutaryl coenzyme A reductase, which may undermine other host responses to increase cholesterol synthesis. These data may provide a hypothesis to explain why hypocholesterolemia persists in chronic HCV infection, particularly in HCV G3, and is not overcome by host cholesterol compensatory mechanisms.
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Affiliation(s)
- Paul J Clark
- Duke Clinical Research Institute and Department of Gastroenterology, Duke University Medical Center, Durham, NC 27715, USA
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116
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Brown AJ. Cholesterol versus other sterols: How do they compare as physiological regulators of cholesterol homeostasis? EUR J LIPID SCI TECH 2012. [DOI: 10.1002/ejlt.201100295] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Andrew J. Brown
- BABS, School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, Australia
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117
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Fakheri RJ, Javitt NB. 27-Hydroxycholesterol, does it exist? On the nomenclature and stereochemistry of 26-hydroxylated sterols. Steroids 2012; 77:575-7. [PMID: 22366074 DOI: 10.1016/j.steroids.2012.02.006] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2011] [Revised: 02/05/2012] [Accepted: 02/06/2012] [Indexed: 11/15/2022]
Abstract
Significant ambiguity exists in the scientific community with regard to the nomenclature of 26-hydroxylated oxysterols. Oxysterols constitute an important class of compounds that have biological roles in the regulation of cholesterol synthesis and as endogenous selective estrogen receptor modulators (SERMs). The ambiguity is attributable to deviations from clearly stated IUPAC rules and is likely to increase as more biologically active oxysterols are identified. This review provides a uniform approach to the naming of 26-hydroxylated sterols for those of current interest and for those on the horizon such as oxysterols of lanosterol that retain the unsaturation at C-24 and C-25 such as (E)-26-hydroxylanosterol. Using this molecule as a starting point, this review hopes to establish a common language to keep all investigators on the same page.
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118
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New insights into the role of cytochrome P450 reductase (POR) in microsomal redox biology. Acta Pharm Sin B 2012. [DOI: 10.1016/j.apsb.2012.02.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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119
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Bielska AA, Schlesinger P, Covey DF, Ory DS. Oxysterols as non-genomic regulators of cholesterol homeostasis. Trends Endocrinol Metab 2012; 23:99-106. [PMID: 22244444 PMCID: PMC3294026 DOI: 10.1016/j.tem.2011.12.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2011] [Revised: 11/21/2011] [Accepted: 12/05/2011] [Indexed: 12/31/2022]
Abstract
Tight regulation of cellular and plasma cholesterol is crucial to proper cellular functioning because excess free cholesterol is toxic to cells and is associated with atherosclerosis and heart disease. Cellular cholesterol homeostasis is regulated by enzymatically formed oxygenated cholesterol derivatives termed oxysterols. Although the effects of oxysterols on transcriptional pathways are well described, the non-transcriptional mechanisms through which oxysterols acutely modulate cellular cholesterol levels are less well understood. We present emerging evidence suggesting that the membrane biophysical properties of oxysterols underlie their acute cholesterol-regulatory functions and discuss the relevance of these acute effects to cholesterol overload in physiological and pathophysiological states.
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Affiliation(s)
- Agata A Bielska
- Diabetic Cardiovascular Disease Center, Washington University School of Medicine, St Louis, MO 63110, USA
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120
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Goedeke L, Fernández-Hernando C. Regulation of cholesterol homeostasis. Cell Mol Life Sci 2012; 69:915-30. [PMID: 22009455 PMCID: PMC11114919 DOI: 10.1007/s00018-011-0857-5] [Citation(s) in RCA: 130] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Revised: 09/29/2011] [Accepted: 09/29/2011] [Indexed: 01/24/2023]
Abstract
Cholesterol homeostasis is among the most intensely regulated processes in biology. Since its isolation from gallstones at the time of the French Revolution, cholesterol has been extensively studied. Insufficient or excessive cellular cholesterol results in pathological processes including atherosclerosis and metabolic syndrome. Mammalian cells obtain cholesterol from the circulation in the form of plasma lipoproteins or intracellularly, through the synthesis of cholesterol from acetyl coenzyme A (acetyl-CoA). This process is tightly regulated at multiple levels. In this review, we provide an overview of the multiple mechanisms by which cellular cholesterol metabolism is regulated. We also discuss the recent advances in the post-transcriptional regulation of cholesterol homeostasis, including the role of small non-coding RNAs (microRNAs). These novel findings may open new avenues for the treatment of dyslipidemias and cardiovascular diseases.
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Affiliation(s)
- Leigh Goedeke
- Departments of Medicine and Cell Biology, Leon H. Charney Division of Cardiology, New York University School of Medicine, 522 First Avenue, Smilow 703, New York, NY 10016 USA
| | - Carlos Fernández-Hernando
- Departments of Medicine and Cell Biology, Leon H. Charney Division of Cardiology, New York University School of Medicine, 522 First Avenue, Smilow 703, New York, NY 10016 USA
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121
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Cook CC, Kim A, Terao S, Gotoh A, Higuchi M. Consumption of oxygen: a mitochondrial-generated progression signal of advanced cancer. Cell Death Dis 2012; 3:e258. [PMID: 22258408 PMCID: PMC3270275 DOI: 10.1038/cddis.2011.141] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Revised: 11/15/2011] [Accepted: 11/21/2011] [Indexed: 11/29/2022]
Abstract
Changes in mitochondrial genome such as mutation, deletion and depletion are common in cancer and can determine advanced phenotype of cancer; however, detailed mechanisms have not been elucidated. We observed that loss of mitochondrial genome reversibly induced overexpression and activation of proto-oncogenic Ras, especially K-Ras 4A, responsible for the activation of AKT and ERK leading to advanced phenotype of prostate and breast cancer. Ras activation was induced by the overexpression of 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR), the rate-limiting enzyme of the mevalonate pathway. Hypoxia is known to induce proteasomal degradation of HMGR. Well differentiated prostate and breast cancer cells with high mitochondrial DNA content consumed a large amount of oxygen and induced hypoxia. Loss of mitochondrial genome reduced oxygen consumption and increased in oxygen concentration in the cells. The hypoxic-to-normoxic shift led to the overexpression of HMGR through inhibiting proteasomal degradation. Therefore, reduction of mitochondrial genome content induced overexpression of HMGR through hypoxic to normoxic shift and subsequently the endogenous induction of the mevalonate pathway activated Ras that mediates advanced phenotype. Reduction of mitochondrial genome content was associated with the aggressive phenotype of prostate cancer in vitro cell line model and tissue specimens in vivo. Our results elucidate a coherent mechanism that directly links the mitochondrial genome with the advanced progression of the disease.
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Affiliation(s)
- C C Cook
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, USA
| | - A Kim
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, USA
| | - S Terao
- Laboratory of Cell and Gene Therapy, Institute for Advanced Medical Sciences, Hyogo College of Medicine, Nishinomiya, Japan
- Advanced Medicinal Research Center, Hyogo University of Health Science, Kobe, Japan
| | - A Gotoh
- Laboratory of Cell and Gene Therapy, Institute for Advanced Medical Sciences, Hyogo College of Medicine, Nishinomiya, Japan
- Advanced Medicinal Research Center, Hyogo University of Health Science, Kobe, Japan
| | - M Higuchi
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, USA
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122
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Higuchi M. Roles of Mitochondrial DNA Changes on Cancer Initiation and Progression. ACTA ACUST UNITED AC 2012; 1. [PMID: 24319697 DOI: 10.4172/2324-9293.1000e109] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Masahiro Higuchi
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock Arkansas, USA
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123
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Zerenturk EJ, Kristiana I, Gill S, Brown AJ. The endogenous regulator 24(S),25-epoxycholesterol inhibits cholesterol synthesis at DHCR24 (Seladin-1). Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:1269-77. [PMID: 22178193 DOI: 10.1016/j.bbalip.2011.11.009] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Revised: 10/25/2011] [Accepted: 11/22/2011] [Indexed: 11/16/2022]
Abstract
The oxysterol 24(S),25-epoxycholesterol (24,25EC) can affect cholesterol metabolism at multiple points. Previously, we proposed that 24,25EC has an especially significant role in fine-tuning cholesterol synthesis, since it parallels cholesterol production, and without it, acute cholesterol synthesis is exaggerated. 24,25EC is structurally similar to desmosterol, a substrate for the enzyme 3β-hydroxysterol ∆(24)-reductase (DHCR24, also called Seladin-1) which catalyzes a final step in cholesterol synthesis. In this study, we reveal a novel mode by which 24,25EC can regulate cholesterol synthesis, by interfering with DHCR24, resulting in the rapid accumulation of the substrate desmosterol, at the expense of cholesterol. This effect was independent of DHCR24 protein levels, and was observed in multiple mammalian cell-lines, including those of hepatic and neuronal origin. Conversely, overexpression of DHCR24 blunted the inhibition by 24,25EC. We also determined that the specificity of this effect was restricted to certain side-chain oxysterols, notably those oxygenated at C-25. Importantly, endogenous levels of 24,25EC, manipulated by genetic and pharmacological methods, were sufficient to reduce DHCR24 activity. Together, our work introduces a novel role for 24,25EC in cholesterol homeostasis, through its rapid inhibition of cholesterol synthesis at DHCR24. Also, our work provides new insights into a little studied area, the post-transcriptional regulation of DHCR24, an important enzyme in human health and disease.
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Affiliation(s)
- Eser J Zerenturk
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, Australia
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124
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Zou L, Li L, Porter TD. 7-Dehydrocholesterol reductase activity is independent of cytochrome P450 reductase. J Steroid Biochem Mol Biol 2011; 127:435-8. [PMID: 21762780 PMCID: PMC3207014 DOI: 10.1016/j.jsbmb.2011.06.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2011] [Revised: 06/24/2011] [Accepted: 06/25/2011] [Indexed: 11/25/2022]
Abstract
7-Dehydrocholesterol reductase (DHCR7) catalyzes the final step in cholesterol synthesis. The enzyme utilizes NADPH as a source of electrons and has been reported to require NADPH-cytochrome P450 reductase (POR) as its redox partner. To test this hypothesis, microsomes were prepared from the livers of mice in which hepatic cytochrome P450 reductase expression was extinguished during maturation. These microsomes contained negligible levels of POR but had 2.5-fold greater DHCR7 activity than did microsomes from wild-type mice. Consistent with this greater activity, immunoblot analysis of DHCR7 expression indicated that DHCR7 protein levels were elevated 2-fold in POR-null microsomes. Addition of POR to these microsomes provided no stimulation of DHCR7 activity, confirming the lack of a role for POR in DHCR7 activity. Because the original observation that POR was necessary for DHCR7 activity was based, in part, on antibody inhibition studies with POR antibody, the ability of an antibody to the full-length POR protein to inhibit DHCR7 activity and cytochrome c reductase activity was tested; the antibody had no effect on DHCR7 activity but decreased cytochrome c reductase activity (a POR-catalyzed reaction) by 50%. Immunoblot analysis further demonstrated no cross-reactivity between POR and DHCR7 with antibodies to either protein. We conclude that cytochrome P450 reductase is not involved in 7-dehydrocholesterol reductase activity.
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Affiliation(s)
- Ling Zou
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, KY 40536-0596, United States
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125
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Liu WM, Zhang J, Lu LZ, Shi FX, Niu D, Wang DL, Yu B, Tao ZR, Shen JD, Wang DQ, Tian Y. Effects of perilla extract on productive performance, serum values and hepatic expression of lipid-related genes in Shaoxing ducks. Br Poult Sci 2011; 52:381-7. [PMID: 21732885 DOI: 10.1080/00071668.2011.577053] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
1. The aim of this study was to identify the effect of perilla extract, a source of polyunsaturated fatty acids, on lipid metabolism and expression of lipid-related genes in livers of Shaoxing ducks. 2. Two hundred and forty 28-week-old laying ducks received a commercial diet with perilla extract added at 0 (control) or 200 mg/kg of feed. 3. Ducks fed on a diet with perilla extract had increased laying rates compared with control ducks. 4. Serum concentrations of triglycerides were reduced by perilla extract, while high-density lipoprotein cholesterol and total serum cholesterol increased. 5. The expression of genes involved in hepatic lipogenesis, sterol regulatory element-binding protein-1, acetyl CoA carboxylase, stearoyl CoA desaturase, fatty acid synthase, apolipoprotein B, and apolipoprotein very low density lipoprotein, were decreased in the perilla group. 6. The mRNA expression of peroxisome proliferators-activated receptor alpha and acyl-coenzyme A oxidase was enhanced following treatment with perilla extract, and a similar tendency was observed in the expression of liver fatty acid-binding protein. 7. The results show that a diet with 200 mg/kg perilla extract regulated fat metabolism of Shaoxing ducks by improving egg laying, altering serum lipid profiles, stimulating lipid catabolic gene expression and inhibiting lipogenic gene expression in the liver.
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Affiliation(s)
- W M Liu
- College of Animal Science & Technology, Nanjing Agricultural University, Nanjing, China
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126
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Cho SY, Jun HJ, Lee JH, Jia Y, Kim KH, Lee SJ. Linalool reduces the expression of 3-hydroxy-3-methylglutaryl CoA reductase via sterol regulatory element binding protein-2- and ubiquitin-dependent mechanisms. FEBS Lett 2011; 585:3289-96. [PMID: 21944868 DOI: 10.1016/j.febslet.2011.09.012] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Revised: 09/09/2011] [Accepted: 09/09/2011] [Indexed: 11/15/2022]
Abstract
We investigated hypocholesterolemic mechanisms of linalool, an aromatic anti-oxidative monoterpene, which is abundant in teas and essential oils. Oral administration of linalool to mice for 6 weeks significantly lowered total and low-density lipoprotein cholesterol concentrations, and HMG-CoA reductase protein expression (-46%; P<0.05) by both transcriptional and posttranscriptional mechanisms. Linalool suppressed the gene expression of HMG-CoA reductase by reducing the binding of SREBP-2 to its promoter, as assessed by qPCR and chromatin immunoprecipitation, and by inducing ubiquitin-dependent proteolysis of the HMG-CoA reductase. These findings suggest that food molecules with a pleasant scent could exert beneficial metabolic effects through multiple mechanisms.
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Affiliation(s)
- Sung-Yun Cho
- Department of Biotechnology, The Graduate School of Biotechnology, Korea University, Seoul, Republic of Korea
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127
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Leichner GS, Avner R, Harats D, Roitelman J. Metabolically regulated endoplasmic reticulum-associated degradation of 3-hydroxy-3-methylglutaryl-CoA reductase: evidence for requirement of a geranylgeranylated protein. J Biol Chem 2011; 286:32150-61. [PMID: 21778231 PMCID: PMC3173168 DOI: 10.1074/jbc.m111.278036] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 07/18/2011] [Indexed: 11/06/2022] Open
Abstract
In mammalian cells, the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), which catalyzes the rate-limiting step in the mevalonate pathway, is ubiquitylated and degraded by the 26 S proteasome when mevalonate-derived metabolites accumulate, representing a case of metabolically regulated endoplasmic reticulum-associated degradation (ERAD). Here, we studied which mevalonate-derived metabolites signal for HMGR degradation and the ERAD step(s) in which these metabolites are required. In HMGR-deficient UT-2 cells that stably express HMGal, a chimeric protein between β-galactosidase and the membrane region of HMGR, which is necessary and sufficient for the regulated ERAD, we tested inhibitors specific to different steps in the mevalonate pathway. We found that metabolites downstream of farnesyl pyrophosphate but upstream to lanosterol were highly effective in initiating ubiquitylation, dislocation, and degradation of HMGal. Similar results were observed for endogenous HMGR in cells that express this protein. Ubiquitylation, dislocation, and proteasomal degradation of HMGal were severely hampered when production of geranylgeranyl pyrophosphate was inhibited. Importantly, inhibition of protein geranylgeranylation markedly attenuated ubiquitylation and dislocation, implicating for the first time a geranylgeranylated protein(s) in the metabolically regulated ERAD of HMGR.
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Affiliation(s)
- Gil S. Leichner
- From the Department of Human Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69978 and
- the Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer 52621, Israel
| | - Rachel Avner
- the Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer 52621, Israel
| | - Dror Harats
- the Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer 52621, Israel
| | - Joseph Roitelman
- From the Department of Human Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69978 and
- the Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer 52621, Israel
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128
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Spanova M, Daum G. Squalene - biochemistry, molecular biology, process biotechnology, and applications. EUR J LIPID SCI TECH 2011. [DOI: 10.1002/ejlt.201100203] [Citation(s) in RCA: 155] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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129
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Abstract
Cholesterol is an essential molecule for the life cycle of the hepatitis C virus (HCV). This review focuses on the roles of cholesterol in HCV infection and introduces HCV events related to cholesterol metabolism and applications for cholesterol metabolism as a therapeutic target. HCV appears to alter host lipid metabolism into its preferable state, which is clinically recognized as steatosis and hypocholesterolemia. While hepatic fatty acid and triglyceride syntheses are upregulated in chronic hepatitis C patients, no direct evidence of increased hepatic de novo cholesterol biosynthesis has been obtained. Impaired VLDL secretion from hepatocytes is suggested to increase intracellular cholesterol concentrations, which may lead to hypocholesterolemia. Clinically, lower serum cholesterol levels are associated with lower rates of sustained virological responses (SVR) to pegylated-interferon plus ribavirin therapy, but the reason remains unclear. Clinical trials targeting HMG-CoA reductase, the rate-limiting enzyme in the cholesterol biosynthetic pathway, are being conducted using statins. Anti-HCV actions by statins appear to be caused by the inhibition of geranylgeranyl pyrophosphate synthesis rather than their cholesterol lowering effects. Other compounds that block various steps of cholesterol metabolic pathways have also been studied to develop new strategies for the complete eradication of this virus.
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Affiliation(s)
- Akira Honda
- Department of Gastroenterology, Tokyo Medical University Ibaraki Medical Center, Ibaraki, Japan
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130
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Tarling EJ, Edwards PA. Dancing with the sterols: critical roles for ABCG1, ABCA1, miRNAs, and nuclear and cell surface receptors in controlling cellular sterol homeostasis. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:386-95. [PMID: 21824529 DOI: 10.1016/j.bbalip.2011.07.011] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2011] [Revised: 07/13/2011] [Accepted: 07/15/2011] [Indexed: 12/29/2022]
Abstract
ATP binding cassette (ABC) transporters represent a large and diverse family of proteins that transport specific substrates across a membrane. The importance of these transporters is illustrated by the finding that inactivating mutations within 17 different family members are known to lead to specific human diseases. Clinical data from humans and/or studies with mice lacking functional transporters indicate that ABCA1, ABCG1, ABCG4, ABCG5 and ABCG8 are involved in cholesterol and/or phospholipid transport. This review discusses the multiple mechanisms that control cellular sterol homeostasis, including the roles of microRNAs, nuclear and cell surface receptors and ABC transporters, with particular emphasis on recent findings that have provided insights into the role(s) of ABCG1. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).
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Affiliation(s)
- Elizabeth J Tarling
- Department of Biological Chemistry, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA
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131
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Holstein SA, Kuder CH, Tong H, Hohl RJ. Pleiotropic effects of a schweinfurthin on isoprenoid homeostasis. Lipids 2011; 46:907-21. [PMID: 21633866 DOI: 10.1007/s11745-011-3572-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Accepted: 05/12/2011] [Indexed: 11/28/2022]
Abstract
The schweinfurthins, a family of natural products derived from the isoprenoid biosynthetic pathway (IBP), have marked growth inhibitory activity. However, the biochemical basis for the schweinfurthins cellular effects has remained ill-defined. Here, the effects of the synthetic schweinfurthin, 3-deoxyschweinfurthin (3dSB) on multiple aspects of isoprenoid homeostasis are explored. Cytotoxicity assays demonstrate a synergistic interaction between 3dSB and the HMG-CoA reductase inhibitor lovastatin but not with other IBP inhibitors in a variety of human cancer cell lines. The cytotoxic effects of 3dSB were enhanced in cells incubated in lipid-depleted serum. 3dSB was found to enhance the lovastatin-induced decrease in protein prenylation. In addition, 3dSB decreases intracellular farnesyl pyrophosphate and geranylgeranyl pyrophosphate levels in both established cell lines and primary cells. To determine whether 3dSB alters the regulation of expression of genes involved in isoprenoid homeostasis, real-time PCR studies were performed in human cell lines cultured in either lipid-replete or -deplete conditions. These studies demonstrate that 3dSB abrogates lovastatin-induced upregulation of sterol regulatory element-containing genes and lovastatin-induced downregulation of ABCA1. In aggregate, these studies are the first to demonstrate that a schweinfurthin exerts pleiotropic effects on isoprenoid homeostasis.
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Affiliation(s)
- Sarah A Holstein
- Department of Internal Medicine, University of Iowa, Iowa City, IA 52242, USA
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132
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Theesfeld CL, Pourmand D, Davis T, Garza RM, Hampton RY. The sterol-sensing domain (SSD) directly mediates signal-regulated endoplasmic reticulum-associated degradation (ERAD) of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase isozyme Hmg2. J Biol Chem 2011; 286:26298-307. [PMID: 21628456 DOI: 10.1074/jbc.m111.244798] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The sterol-sensing domain (SSD) is a conserved motif in membrane proteins responsible for sterol regulation. Mammalian proteins SREBP cleavage-activating protein (SCAP) and HMG-CoA reductase (HMGR) both possess SSDs required for feedback regulation of sterol-related genes and sterol synthetic rate. Although these two SSD proteins clearly sense sterols, the range of signals detected by this eukaryotic motif is not clear. The yeast HMG-CoA reductase isozyme Hmg2, like its mammalian counterpart, undergoes endoplasmic reticulum (ER)-associated degradation that is subject to feedback control by the sterol pathway. The primary degradation signal for yeast Hmg2 degradation is the 20-carbon isoprene geranylgeranyl pyrophosphate, rather than a sterol. Nevertheless, the Hmg2 protein possesses an SSD, leading us to test its role in feedback control of Hmg2 stability. We mutated highly conserved SSD residues of Hmg2 and evaluated regulated degradation. Our results indicated that the SSD was required for sterol pathway signals to stimulate Hmg2 ER-associated degradation and was employed for detection of both geranylgeranyl pyrophosphate and a secondary oxysterol signal. Our data further indicate that the SSD allows a signal-dependent structural change in Hmg2 that promotes entry into the ER degradation pathway. Thus, the eukaryotic SSD is capable of significant plasticity in signal recognition or response. We propose that the harnessing of cellular quality control pathways to bring about feedback regulation of normal proteins is a unifying theme for the action of all SSDs.
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Affiliation(s)
- Chandra L Theesfeld
- Section of Cell and Developmental Biology, Division of Biological Sciences, University of California San Diego, La Jolla, California 92093, USA
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133
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Xu L, Korade Z, Rosado JDA, Liu W, Lamberson CR, Porter NA. An oxysterol biomarker for 7-dehydrocholesterol oxidation in cell/mouse models for Smith-Lemli-Opitz syndrome. J Lipid Res 2011; 52:1222-1233. [PMID: 21402677 DOI: 10.1194/jlr.m014498] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The level of 7-dehydrocholesterol (7-DHC) is elevated in tissues and fluids of Smith-Lemli-Opitz syndrome (SLOS) patients due to defective 7-DHC reductase. Although over a dozen oxysterols have been identified from 7-DHC free radical oxidation in solution, oxysterol profiles in SLOS cells and tissues have never been studied. We report here the identification and complete characterization of a novel oxysterol, 3β,5α-dihydroxycholest-7-en-6-one (DHCEO), as a biomarker for 7-DHC oxidation in fibroblasts from SLOS patients and brain tissue from a SLOS mouse model. Deuterated (d₇)-standards of 7-DHC and DHCEO were synthesized from d₇-cholesterol. The presence of DHCEO in SLOS samples was supported by chemical derivatization in the presence of d₇-DHCEO standard followed by HPLC-MS or GC-MS analysis. Quantification of cholesterol, 7-DHC, and DHCEO was carried out by isotope dilution MS with the d₇-standards. The level of DHCEO was high and correlated well with the level of 7-DHC in all samples examined (R = 0.9851). Based on our in vitro studies in two different cell lines, the mechanism of formation of DHCEO that involves 5α,6α-epoxycholest-7-en-3β-ol, a primary free radical oxidation product of 7-DHC, and 7-cholesten-3β,5α,6β-triol is proposed. In a preliminary test, a pyrimidinol antioxidant was found to effectively suppress the formation of DHCEO in SLOS fibroblasts.
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Affiliation(s)
- Libin Xu
- Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN 37235
| | - Zeljka Korade
- Department of Psychiatry and Vanderbilt Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37235
| | - Jr Dale A Rosado
- Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN 37235
| | - Wei Liu
- Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN 37235
| | - Connor R Lamberson
- Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN 37235
| | - Ned A Porter
- Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN 37235.
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134
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Gill S, Stevenson J, Kristiana I, Brown AJ. Cholesterol-dependent degradation of squalene monooxygenase, a control point in cholesterol synthesis beyond HMG-CoA reductase. Cell Metab 2011; 13:260-73. [PMID: 21356516 DOI: 10.1016/j.cmet.2011.01.015] [Citation(s) in RCA: 211] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/24/2010] [Revised: 10/22/2010] [Accepted: 01/20/2011] [Indexed: 10/18/2022]
Abstract
Exquisite control of cholesterol synthesis is crucial for maintaining homeostasis of this vital yet potentially toxic lipid. Squalene monooxygenase (SM) catalyzes the first oxygenation step in cholesterol synthesis, acting on squalene before cyclization into the basic steroid structure. Using model cell systems, we found that cholesterol caused the accumulation of the substrate squalene, suggesting that SM may serve as a flux-controlling enzyme beyond 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR, considered as rate limiting). Cholesterol accelerated the proteasomal degradation of SM which required the N-terminal domain, partially conserved in vertebrates but not in lower organisms. Unlike HMGR, SM degradation is not mediated by Insig, 24,25-dihydrolanosterol, or side-chain oxysterols, but rather by cholesterol itself. Importantly, SM's N-terminal domain conferred cholesterol-regulated turnover on heterologous fusion proteins. Furthermore, proteasomal inhibition almost totally eliminated squalene accumulation, highlighting the importance of this degradation mechanism for the control of SM and suggesting this as a possible control point in cholesterol synthesis.
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Affiliation(s)
- Saloni Gill
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney NSW 2052, Australia
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135
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Fakheri RJ, Javitt NB. Autoregulation of cholesterol synthesis: physiologic and pathophysiologic consequences. Steroids 2011; 76:211-5. [PMID: 20951718 DOI: 10.1016/j.steroids.2010.10.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/03/2010] [Revised: 10/06/2010] [Accepted: 10/07/2010] [Indexed: 10/18/2022]
Abstract
Autoregulation of cholesterol synthesis focuses on the 19 metabolic steps from lanosterol to cholesterol. Although synchronization of their rates of synthesis in all tissues was the paradigm, a known exception occurs in the ovary where a local increase in a sterol intermediate, FF-MAS (follicular fluid meiosis activating sterol), activates meiosis during oocyte maturation. Mutations in the genes that govern synchronization cause an increase in sterol intermediates that follow an alternate, oxysterol, pathway of metabolism. Experimental models in animals imply that oxysterol metabolites are determinants of the dysmorphism that occurs during fetal development in these genetic diseases. These few examples may portend a much broader role for sterol intermediates and their novel oxysterol metabolites in physiologic and pathophysiologic processes.
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Affiliation(s)
- Robert J Fakheri
- Department of Medicine, NYU School of Medicine, New York, NY 10016, United States
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136
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Neil H, Ceglarek U, Thiery J, Paul S, Farmer A, Holman R. Impact of atorvastatin and omega-3 ethyl esters 90 on plasma plant sterol concentrations and cholesterol synthesis in type 2 diabetes: A randomised placebo controlled factorial trial. Atherosclerosis 2010; 213:512-7. [DOI: 10.1016/j.atherosclerosis.2010.09.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2010] [Revised: 09/02/2010] [Accepted: 09/10/2010] [Indexed: 11/24/2022]
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137
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Jo Y, Debose-Boyd RA. Control of cholesterol synthesis through regulated ER-associated degradation of HMG CoA reductase. Crit Rev Biochem Mol Biol 2010; 45:185-98. [PMID: 20482385 DOI: 10.3109/10409238.2010.485605] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Multiple mechanisms for feedback control of cholesterol synthesis converge on the rate-limiting enzyme in the pathway, 3-hydroxy-3-methylglutaryl coenzyme A reductase. This complex feedback regulatory system is mediated by sterol and nonsterol metabolites of mevalonate, the immediate product of reductase activity. One mechanism for feedback control of reductase involves rapid degradation of the enzyme from membranes of the endoplasmic reticulum (ER). This degradation results from the accumulation of sterols in ER membranes, which triggers binding of reductase to ER membrane proteins called Insig-1 and Insig-2. Insig binding leads to the recruitment of a membrane-associated ubiquitin ligase called gp78 that initiates ubiquitination of reductase. Ubiquitinated reductase then becomes extracted from ER membranes and is delivered to cytosolic 26S proteasomes through an unknown mechanism that is mediated by the gp78-associated ATPase Valosin-containing protein/p97 and appears to be augmented by nonsterol isoprenoids. Here, we will highlight several advances that have led to the current view of mechanisms for sterol-accelerated, ER-associated degradation of reductase. In addition, we will discuss potential mechanisms for other aspects of the pathway such as selection of reductase for gp78-mediated ubiquitination, extraction of the ubiquitinated enzyme from ER membranes, and the contribution of Insig-mediated degradation to overall regulation of reductase in whole animals.
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Affiliation(s)
- Youngah Jo
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA
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138
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Chang TY, Chang CCY, Bryleva E, Rogers MA, Murphy SR. Neuronal cholesterol esterification by ACAT1 in Alzheimer's disease. IUBMB Life 2010; 62:261-7. [PMID: 20101629 DOI: 10.1002/iub.305] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Cholesterol has been implicated in various neurodegenerative diseases. Here we review the connection between cholesterol and Alzheimer's disease (AD), focusing on a recent study that links neuronal cholesterol esterification with biosynthesis of 24(S)-hydroxycholesterol and the fate of human amyloid precursor protein in a mouse model of AD. We also briefly evaluate the potential of ACAT1 as a drug target for AD.
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Affiliation(s)
- Ta-Yuan Chang
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA.
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139
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Interplay between cholesterol and drug metabolism. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1814:146-60. [PMID: 20570756 DOI: 10.1016/j.bbapap.2010.05.014] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Revised: 05/17/2010] [Accepted: 05/24/2010] [Indexed: 12/14/2022]
Abstract
Cholesterol biosynthetic and metabolic pathways contain several branching points towards physiologically active molecules, such as coenzyme Q, vitamin D, glucocorticoid and steroid hormones, oxysterols, or bile acids. Sophisticated regulatory mechanisms are involved in maintenance of the homeostasis of not only cholesterol but also other cholesterogenic molecules. In addition to endogenous cues, cholesterol homeostasis needs to accommodate also to exogenous cues that are imported into the body, such as chemicals and medications. Steroid and nuclear receptors together with sterol regulatory element-binding protein (SREBP) mediate the fine tuning of biosynthetic and metabolic routes as well as transports of cholesterol and its derivatives. Similarly, drug/xenobiotic metabolism is the subject to the feedback regulation of cytochrome P450 enzymes and transporters. The regulatory mechanisms that maintain the homeostasis of cholesterogenic molecules and are involved in drug metabolism share similarities. Cholesterol and cholesterogenic compounds (bile acids, glucocorticoids, vitamin D, etc.) regulate the xenosensor signaling in drug-mediated induction of the major drug-metabolizing cytochrome P450 enzymes. The key cellular receptors, pregnane X receptor (PXR), constitutive androstane receptor (CAR), vitamin D receptor (VDR), and glucocorticoid receptor (GR) provide a functional cross-talk between the pathways maintaining cholesterol homeostasis and controlling the expression of drug-metabolizing enzymes. These receptors serve as metabolic sensors, resulting in a coordinate regulation of cholesterogenic compounds metabolism and of the defense against xenobiotic and endobiotic toxicity. Herein we present a comprehensive review of functional interactions between cholesterol homeostasis and drug metabolism involving the main nuclear and steroid receptors.
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140
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Interaction of two oxysterols, 7-ketocholesterol and 25-hydroxycholesterol, with phosphatidylcholine and sphingomyelin in model membranes. Chem Phys Lipids 2010; 163:586-93. [DOI: 10.1016/j.chemphyslip.2010.05.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Revised: 04/07/2010] [Accepted: 05/04/2010] [Indexed: 02/03/2023]
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141
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Quality and quantity control at the endoplasmic reticulum. Curr Opin Cell Biol 2010; 22:437-46. [PMID: 20570125 DOI: 10.1016/j.ceb.2010.05.005] [Citation(s) in RCA: 132] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 04/29/2010] [Accepted: 05/03/2010] [Indexed: 11/20/2022]
Abstract
The endoplasmic reticulum (ER) is the site of maturation for secretory and membrane proteins that together make up about one third of the cellular proteome. Cells carefully control the synthetic output of this organelle to regulate both quality and quantity of proteins that emerge. Here, we synthesize current concepts underlying the pathways that mediate protein degradation from the ER and their deployment under physiologic and pathologic conditions.
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142
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Miao H, Jiang W, Ge L, Li B, Song B. Tetra-glutamic acid residues adjacent to Lys248 in HMG-CoA reductase are critical for the ubiquitination mediated by gp78 and UBE2G2. Acta Biochim Biophys Sin (Shanghai) 2010; 42:303-10. [PMID: 20458442 DOI: 10.1093/abbs/gmq022] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Sterol-regulated degradation of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) is a rapid feedback regulatory mechanism by which cells employ to control the cholesterol biosynthesis. This process is initiated by the sterol-induced interaction between HMGCR and Insig-1/ gp78, a membrane-bound ubiquitin ligase complex. There are two Lys residues (Lys89 and Lys248) facing cytosol in the membrane domain of HMGCR, and Lys248 is the major ubiquitination site. In this study, we investigated the mechanism of ubiquitination site selection in HMGCR. We find that the distance of Lys248 to membrane is dispensable for its ubiquitination. However, the conserved tetra-glutamic acid residues adjacent to Lys248 in HMGCR are essential. Replacement of these negatively charged residues with tetraarginine causes the resistance of HMGCR to sterol-induced ubiquitination and degradation, albeit this mutant HMGCR can still binds to Insig-1. We further find that the tetra-glutamic acid residues are necessary but not sufficient for the modification on their adjacent Lys, since they are not functional on Lys89 of HMGCR or in SCAP. UBE2G2, a previously known E2 of gp78, is demonstrated to be involved in the sterol-regulated ubiquitination and degradation of HMGCR. In summary, these results identify the tetraglutamic acid residues as a critical motif in HMGCR for the ubiquitination reaction mediated by gp78 and UBE2G2.
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Affiliation(s)
- Honghua Miao
- The State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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143
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Tang J, Kobayashi K, Suzuki M, Matsumoto S, Muranaka T. The mitochondrial PPR protein LOVASTATIN INSENSITIVE 1 plays regulatory roles in cytosolic and plastidial isoprenoid biosynthesis through RNA editing. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2010; 61:456-66. [PMID: 19929879 DOI: 10.1111/j.1365-313x.2009.04082.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Unlike animals, plants synthesize isoprenoids via two pathways, the cytosolic mevalonate (MVA) pathway and the plastidial 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway. Little information is known about the mechanisms that regulate these complex biosynthetic networks over multiple organelles. To understand such regulatory mechanisms of the biosynthesis of isoprenoids in plants, we previously characterized the Arabidopsis mutant, lovastatin insensitive 1 (loi1), which is resistant to lovastatin and clomazone, specific inhibitors of the MVA and MEP pathways, respectively. LOI1 encodes a pentatricopeptide repeat (PPR) protein localized in mitochondria that is thought to have RNA binding ability and function in post-transcriptional regulation of mitochondrial gene expression. LOI1 belongs to the DYW subclass of PPR proteins, which is hypothesized to be correlated with RNA editing. As a result of analysis of RNA editing of mitochondrial genes in loi1, a defect in RNA editing of three genes, nad4, ccb203 and cox3, was identified in loi1. These genes are related to the respiratory chain. Wild type (WT) treated with some respiration inhibitors mimicked the loi1 phenotype. Interestingly, HMG-CoA reductase activity of WT treated with lovastatin combined with antimycin A, an inhibitor of complex III in the respiratory chain, was higher than that of WT treated with only lovastatin, despite the lack of alteration of transcript or protein levels of HMGR. These results suggest that HMGR enzyme activity is regulated through the respiratory cytochrome pathway. Although various mechanisms exist for isoprenoid biosynthesis, our studies demonstrate the novel possibility that mitochondrial respiration plays potentially regulatory roles in isoprenoid biosynthesis.
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Affiliation(s)
- Jianwei Tang
- RIKEN Plant Science Center, 1-7-22, Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan
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144
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ACAT1 gene ablation increases 24(S)-hydroxycholesterol content in the brain and ameliorates amyloid pathology in mice with AD. Proc Natl Acad Sci U S A 2010; 107:3081-6. [PMID: 20133765 DOI: 10.1073/pnas.0913828107] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cholesterol metabolism has been implicated in the pathogenesis of several neurodegenerative diseases, including the abnormal accumulation of amyloid-beta, one of the pathological hallmarks of Alzheimer disease (AD). Acyl-CoA:cholesterol acyltransferases (ACAT1 and ACAT2) are two enzymes that convert free cholesterol to cholesteryl esters. ACAT inhibitors have recently emerged as promising drug candidates for AD therapy. However, how ACAT inhibitors act in the brain has so far remained unclear. Here we show that ACAT1 is the major functional isoenzyme in the mouse brain. ACAT1 gene ablation (A1-) in triple transgenic (i.e., 3XTg-AD) mice leads to more than 60% reduction in full-length human APPswe as well as its proteolytic fragments, and ameliorates cognitive deficits. At 4 months of age, A1- causes a 32% content increase in 24-hydroxycholesterol (24SOH), the major oxysterol in the brain. It also causes a 65% protein content decrease in HMG-CoA reductase (HMGR) and a 28% decrease in sterol synthesis rate in AD mouse brains. In hippocampal neurons, A1- causes an increase in the 24SOH synthesis rate; treating hippocampal neuronal cells with 24SOH causes rapid declines in hAPP and in HMGR protein levels. A model is provided to explain our findings: in neurons, A1- causes increases in cholesterol and 24SOH contents in the endoplasmic reticulum, which cause reductions in hAPP and HMGR protein contents and lead to amelioration of amyloid pathology. Our study supports the potential of ACAT1 as a therapeutic target for treating certain forms of AD.
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145
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Abstract
Bilayer synthesis during membrane biogenesis involves the concerted assembly of multiple lipid species, requiring coordination of the level of lipid synthesis, uptake, turnover, and subcellular distribution. In this review, we discuss some of the salient conclusions regarding the coordination of lipid synthesis that have emerged from work in mammalian and yeast cells. The principal instruments of global control are a small number of transcription factors that target a wide range of genes encoding enzymes that operate in a given metabolic pathway. Critical in mammalian cells are sterol regulatory element binding proteins (SREBPs) that stimulate expression of genes for the uptake and synthesis of cholesterol and fatty acids. From work with Saccharomyces cerevisiae, much has been learned about glycerophospholipid and ergosterol regulation through Ino2p/Ino4p and Upc2p transcription factors, respectively. Lipid supply is fine-tuned through a multitude of negative feedback circuits initiated by both end products and intermediates of lipid synthesis pathways. Moreover, there is evidence that the diversity of membrane lipids is maintained through cross-regulatory effects, whereby classes of lipids activate the activity of enzymes operating in another metabolic branch.
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Affiliation(s)
- Axel Nohturfft
- Molecular and Metabolic Signalling Centre, Division of Basic Medical Sciences, St. George's University of London, London, SW17 0RE United Kingdom.
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146
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Abstract
Cholesterol and other cholesterol related metabolites, oxysterols, and bile acids, establish specific interactions with enzymes and other proteins involved in cholesterol and bile acid homeostasis, triggering a variety of biological responses. The substrate-enzyme binding represents the best-characterized type of complementary interaction between proteins and small molecules. Key enzymes in the pathway that converts cholesterol to bile acids belong to the cytochrome P450 superfamily. In contrast to the majority of P450 enzymes, those acting on cholesterol and related metabolites exhibit higher stringency with respect to substrate molecules. This stringency, coupled with the specificity of the reactions, dictates the chemical features of intermediate metabolites (oxysterols) and end products (bile acids). Both oxysterols and bile acids have emerged in recent years as new signalling molecules due to their ability to interact and activate nuclear receptors, and consequently to regulate the transcription of genes involved in cholesterol and bile acid homeostasis and metabolism, but also in glucose and fatty acid metabolism. Interestingly, other proteins function as bile acid or sterol receptors. New findings indicate that bile acids also interact with a membrane G protein-coupled receptor, triggering a signalling cascade that ultimately promote energy expenditure. On the other end, cholesterol and side chain oxysterols establish specific interactions with different proteins residing in the endoplasmic reticulum that result in controlled protein degradation and/or trafficking to the Golgi and the nucleus. These regulatory pathways converge and contribute to adapt cholesterol uptake and synthesis to the cellular needs.
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147
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Zhu J, Mounzih K, Chehab EF, Mitro N, Saez E, Chehab FF. Effects of FoxO4 overexpression on cholesterol biosynthesis, triacylglycerol accumulation, and glucose uptake. J Lipid Res 2009; 51:1312-24. [PMID: 20037138 DOI: 10.1194/jlr.m001586] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Forkhead transcription factors FoxO1, FoxO3a, and FoxO4 play a prominent role in regulating cell survival and cell cycle. Whereas FOXO1 was shown to mediate insulin sensitivity and adipocyte differentiation, the role of the transcription factor FoxO4 in metabolism remains ill defined. To uncover the effects of FoxO4, we generated a cellular model of stable FoxO4 overexpression and subjected it to microarray-based gene expression profiling. While pathway analysis revealed a disruption of cholesterol biosynthesis gene expression, biochemical studies revealed an inhibition of cholesterol biosynthesis, which was coupled with decreased mRNA levels of lanosterol 14alpha demethylase (CYP51). FoxO4-mediated repression of CYP51 led to the accumulation of 24,25 dihydrolano-sterol (DHL), which independently and unlike lanosterol inhibited cholesterol biosynthesis. Furthermore, FoxO4-overexpressing cells accumulated lipid droplets and triacylglycerols and had an increase in basal glucose uptake. Recapitulation of these effects was obtained following treatment with CYP51 inhibitors, which also induce DHL buildup. Moreover, DHL but not lanosterol strongly stimulated liver X receptor alpha (LXRalpha) activity, suggesting that DHL and LXRalpha mediate the downstream effects initiated by FoxO4. Together, these studies suggest that FoxO4 acts on CYP51 to regulate the late steps of cholesterol biosynthesis.
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Affiliation(s)
- Jun Zhu
- Department of Laboratory Medicine, University of California, San Francisco, CA, USA
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148
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Garza RM, Tran PN, Hampton RY. Geranylgeranyl pyrophosphate is a potent regulator of HRD-dependent 3-Hydroxy-3-methylglutaryl-CoA reductase degradation in yeast. J Biol Chem 2009; 284:35368-80. [PMID: 19776008 PMCID: PMC2790966 DOI: 10.1074/jbc.m109.023994] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2009] [Revised: 09/18/2009] [Indexed: 11/06/2022] Open
Abstract
3-Hydroxy-3-methylglutaryl (HMG)-CoA reductase (HMGR), the rate-limiting enzymes of sterol synthesis, undergoes feedback-regulated endoplasmic reticulum degradation in both mammals and yeast. The yeast Hmg2p isozyme is subject to ubiquitin-mediated endoplasmic reticulum degradation by the HRD pathway. We had previously shown that alterations in cellular levels of the 15-carbon sterol pathway intermediate farnesyl pyrophosphate (FPP) cause increased Hmg2p ubiquitination and degradation. We now present evidence that the FPP-derived, 20-carbon molecule geranylgeranyl pyrophosphate (GGPP) is a potent endogenous regulator of Hmg2p degradation. This work was launched by the unexpected observation that GGPP addition directly to living yeast cultures caused high potency and specific stimulation of Hmg2p degradation. This effect of GGPP was not recapitulated by FPP, GGOH, or related isoprenoids. GGPP-caused Hmg2p degradation met all the criteria for the previously characterized endogenous signal. The action of added GGPP did not require production of endogenous sterol molecules, indicating that it did not act by causing the build-up of an endogenous pathway signal. Manipulation of endogenous GGPP by several means showed that naturally made GGPP controls Hmg2p stability. Analysis of the action of GGPP indicated that the molecule works upstream of retrotranslocation and can directly alter the structure of Hmg2p. We propose that GGPP is the FPP-derived regulator of Hmg2p ubiquitination. Intriguingly, the sterol-dependent degradation of mammalian HMGR is similarly stimulated by the addition of GGOH to intact cells, implying that a dependence on 20-carbon geranylgeranyl signals may be a common conserved feature of HMGR regulation that may lead to highly specific therapeutic approaches for modulation of HMGR.
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Affiliation(s)
- Renee M. Garza
- From the Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California 92093-0347
| | - Peter N. Tran
- From the Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California 92093-0347
| | - Randolph Y. Hampton
- From the Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California 92093-0347
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149
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Carroll SM, Hampton RY. Usa1p is required for optimal function and regulation of the Hrd1p endoplasmic reticulum-associated degradation ubiquitin ligase. J Biol Chem 2009; 285:5146-56. [PMID: 19940128 DOI: 10.1074/jbc.m109.067876] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Usa1p is a recently discovered member of the HRD ubiquitin ligase complex. The HRD pathway is a conserved route of ubiquitin-dependent, endoplasmic reticulum (ER)-associated degradation (ERAD) of numerous lumenal (ERAD-L) and membrane-anchored (ERAD-M) substrates. We have investigated Usa1p to understand its importance in HRD complex action. Usa1p was required for the optimal function of the Hrd1p E3 ubiquitin ligase; its loss caused deficient degradation of both membrane-associated and lumenal proteins. Furthermore, Usa1p functioned in regulation of Hrd1p by two mechanisms. First, Hrd1p self-degradation, which serves to limit the levels of uncomplexed E3, is absolutely dependent on Usa1p and the ubiquitin-like (Ubl) domain of Usa1p. We found that Usa1p allows Hrd1p degradation by promoting trans interactions between Hrd1p molecules. The Ubl domain of Usa1p was required specifically for Hrd1p self-ubiquitination but not for degradation of either ERAD-L or ERAD-M substrates. In addition, Usa1p was able to attenuate the activity-dependent toxicity of Hrd1p without compromising substrate degradation, indicating a separate role in ligase regulation that operates in parallel to stability control. Many of the described actions of Usa1p are distinct from those of Der1p, which is recruited to the HRD complex by Usa1p. Thus, this novel, conserved factor is broadly involved in the function and regulation of the HRD pathway of ERAD.
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Affiliation(s)
- Sarah M Carroll
- Section of Cell and Developmental Biology, Division of Biological Sciences, University of California San Diego, La Jolla, California 92093, USA
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150
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25-Hydroxycholesterol secreted by macrophages in response to Toll-like receptor activation suppresses immunoglobulin A production. Proc Natl Acad Sci U S A 2009; 106:16764-9. [PMID: 19805370 DOI: 10.1073/pnas.0909142106] [Citation(s) in RCA: 261] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
25-Hydroxycholesterol is produced in mammalian tissues. The function of this oxysterol is unknown. Here we describe a central role for 25-hydroxycholesterol in regulating the immune system. In initial experiments, we found that stimulation of macrophage Toll-like receptors (TLR) induced expression of cholesterol 25-hydroxylase and the synthesis of 25-hydroxycholesterol. Treatment of naïve B cells with nanomolar concentrations of 25-hydroxycholesterol suppressed IL-2-mediated stimulation of B cell proliferation, repressed activation-induced cytidine deaminase (AID) expression, and blocked class switch recombination, leading to markedly decreased IgA production. Consistent with these findings, deletion of the mouse cholesterol 25-hydroxylase gene caused an increase in serum IgA. Conversely, inactivation of the CYP7B1 oxysterol 7alpha-hydroxylase, which degrades 25-hydroxycholesterol, decreased serum IgA. The suppression of IgA class switching in B cells by a macrophage-derived sterol in response to TLR activation provides a mechanism for local and systemic negative regulation of the adaptive immune response by the innate immune system.
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