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Musselman LP, Truong HG, DiAngelo JR. Transcriptional Control of Lipid Metabolism. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2024. [PMID: 38782870 DOI: 10.1007/5584_2024_808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2024]
Abstract
Transcriptional control of lipid metabolism uses a framework that parallels the control of lipid metabolism at the protein or enzyme level, via feedback and feed-forward mechanisms. Increasing the substrates for an enzyme often increases enzyme gene expression, for example. A paucity of product can likewise potentiate transcription or stability of the mRNA encoding the enzyme or enzymes needed to produce it. In addition, changes in second messengers or cellular energy charge can act as on/off switches for transcriptional regulators to control transcript (and protein) abundance. Insects use a wide range of DNA-binding transcription factors (TFs) that sense changes in the cell and its environment to produce the appropriate change in transcription at gene promoters. These TFs work together with histones, spliceosomes, and additional RNA processing factors to ultimately regulate lipid metabolism. In this chapter, we will first focus on the important TFs that control lipid metabolism in insects. Next, we will describe non-TF regulators of insect lipid metabolism such as enzymes that modify acetylation and methylation status, transcriptional coactivators, splicing factors, and microRNAs. To conclude, we consider future goals for studying the mechanisms underlying the control of lipid metabolism in insects.
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Affiliation(s)
- Laura Palanker Musselman
- Department of Biological Sciences, Binghamton University, State University of New York, Binghamton, NY, USA
| | - Huy G Truong
- Division of Science, Pennsylvania State University, Berks Campus, Reading, PA, USA
| | - Justin R DiAngelo
- Division of Science, Pennsylvania State University, Berks Campus, Reading, PA, USA.
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Shu L, Li L, Jiang YQ, Yan J. Advances in membrane-tethered NAC transcription factors in plants. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2024; 342:112034. [PMID: 38365003 DOI: 10.1016/j.plantsci.2024.112034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 02/08/2024] [Accepted: 02/11/2024] [Indexed: 02/18/2024]
Abstract
Transcription factors are central components in cell signal transduction networks and are critical regulators for gene expression. It is estimated that approximately 10% of all transcription factors are membrane-tethered. MTFs (membrane-bound transcription factors) are latent transcription factors that are inherently anchored in the cellular membrane in a dormant form. When plants encounter environmental stimuli, they will be released from the membrane by intramembrane proteases or by the ubiquitin proteasome pathway and then were translocated to the nucleus. The capacity to instantly activate dormant transcription factors is a critical strategy for modulating diverse cellular functions in response to external or internal signals, which provides an important transcriptional regulatory network in response to sudden stimulus and improves plant survival. NTLs (NTM1-like) are a small subset of NAC (NAM, ATAF1/2, CUC2) transcription factors, which contain a conserved NAC domain at the N-terminus and a transmembrane domain at the C-terminus. In the past two decades, several NTLs have been identified from several species, and most of them are involved in both development and stress response. In this review, we review the reports and findings on NTLs in plants and highlight the mechanism of their nuclear import as well as their functions in regulating plant growth and stress response.
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Affiliation(s)
- Lin Shu
- College of Plant Protection, Henan Agricultural University, Zhengzhou, Henan province 450002, China
| | - Longhui Li
- College of Plant Protection, Henan Agricultural University, Zhengzhou, Henan province 450002, China
| | - Yuan-Qing Jiang
- State Key Laboratory of Crop Stress Biology for Arid Areas and, College of Life Sciences, Northwest A & F University, Yangling, Shaanxi province 712100, China
| | - Jingli Yan
- College of Plant Protection, Henan Agricultural University, Zhengzhou, Henan province 450002, China.
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Song H, Chen D, Bai R, Feng Y, Wu S, Wang T, Xia X, Li J, Miao YL, Zuo B, Li F. BCL2-associated athanogene 6 exon24 contributes to testosterone synthesis and male fertility in mammals. Cell Prolif 2022; 55:e13281. [PMID: 35688694 PMCID: PMC9251057 DOI: 10.1111/cpr.13281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2022] [Revised: 05/10/2022] [Accepted: 05/24/2022] [Indexed: 11/28/2022] Open
Abstract
Objectives BCL2‐associated athanogene 6 (BAG6) plays critical roles in spermatogenesis by maintaining testicular cell survival. Our previous data showed porcine BAG6 exon24‐skipped transcript is highly expressed in immature testes compared with mature testes. The objective of this study is to reveal the functional significance of BAG6 exon24 in mammalian spermatogenesis. Materials and Methods CRISPR/Cas9 system was used to generate Bag6 exon24 knockout mice. Testes and cauda epididymal sperm were collected from mice. TMT proteomics analysis was used to discover the protein differences induced by Bag6 exon24 deletion. Testosterone enanthate was injected into mice to generate a high‐testosterone mice model. H&E staining, qRT‐PCR, western blotting, vector/siRNA transfection, immunofluorescence, immunoprecipitation, transmission electron microscopy, TUNEL and ELISA were performed to investigate the phenotypes and molecular basis. Results Bag6 exon24 knockout mice show sub‐fertility along with partially impaired blood‐testis barrier, increased apoptotic testicular cell rate and abnormal sperm morphology. Endoplasmic reticulum stress occurs in Bag6 exon24‐deficient testes and sterol regulatory element‐binding transcription factor 2 is activated; as a result, cytochrome P450 family 51 subfamily A member 1 expression is up‐regulated, which causes a high serum testosterone level. Additionally, serine/arginine‐rich splicing factor 1 down‐regulates BAG6 exon24‐skipped transcripts in porcine Sertoli cells by binding to 35–51 nt on BAG6 exon24 via its N‐terminal RNA‐recognition domain. Conclusions Our findings reveal the critical roles of BAG6 exon24 in testosterone biosynthesis and male fertility, which provides new insights into the regulation of spermatogenesis and pathogenesis of subfertility in mammals.
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Affiliation(s)
- Huibin Song
- Key Laboratory of Pig Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, People's Republic of China
| | - Dake Chen
- Key Laboratory of Pig Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, People's Republic of China
| | - Rong Bai
- Key Laboratory of Pig Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, People's Republic of China
| | - Yue Feng
- Key Laboratory of Pig Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, People's Republic of China
| | - Shang Wu
- Key Laboratory of Pig Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, People's Republic of China
| | - Tiansu Wang
- Key Laboratory of Pig Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, People's Republic of China
| | - Xuanyan Xia
- College of Informatics, Huazhong Agricultural University, Wuhan, People's Republic of China
| | - Jialian Li
- Key Laboratory of Pig Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, People's Republic of China
| | - Yi-Liang Miao
- Key Laboratory of Pig Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, People's Republic of China
| | - Bo Zuo
- Key Laboratory of Pig Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, People's Republic of China.,The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, People's Republic of China
| | - Fenge Li
- Key Laboratory of Pig Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, People's Republic of China.,The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, People's Republic of China
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Sánchez-Álvarez M, del Pozo MÁ, Bosch M, Pol A. Insights Into the Biogenesis and Emerging Functions of Lipid Droplets From Unbiased Molecular Profiling Approaches. Front Cell Dev Biol 2022; 10:901321. [PMID: 35756995 PMCID: PMC9213792 DOI: 10.3389/fcell.2022.901321] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Accepted: 05/17/2022] [Indexed: 11/30/2022] Open
Abstract
Lipid droplets (LDs) are spherical, single sheet phospholipid-bound organelles that store neutral lipids in all eukaryotes and some prokaryotes. Initially conceived as relatively inert depots for energy and lipid precursors, these highly dynamic structures play active roles in homeostatic functions beyond metabolism, such as proteostasis and protein turnover, innate immunity and defense. A major share of the knowledge behind this paradigm shift has been enabled by the use of systematic molecular profiling approaches, capable of revealing and describing these non-intuitive systems-level relationships. Here, we discuss these advances and some of the challenges they entail, and highlight standing questions in the field.
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Affiliation(s)
- Miguel Sánchez-Álvarez
- Cell and Developmental Biology Area, Centro Nacional de Investigaciones Cardiovasculares (CNIC), Madrid, Spain
| | - Miguel Ángel del Pozo
- Cell and Developmental Biology Area, Centro Nacional de Investigaciones Cardiovasculares (CNIC), Madrid, Spain
| | - Marta Bosch
- Lipid Trafficking and Disease Group, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
- Department of Biomedical Sciences, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain
| | - Albert Pol
- Lipid Trafficking and Disease Group, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
- Department of Biomedical Sciences, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
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Abstract
The molecular mechanisms of cellular insulin action have been the focus of much investigation since the discovery of the hormone 100 years ago. Insulin action is impaired in metabolic syndrome, a condition known as insulin resistance. The actions of the hormone are initiated by binding to its receptor on the surface of target cells. The receptor is an α2β2 heterodimer that binds to insulin with high affinity, resulting in the activation of its tyrosine kinase activity. Once activated, the receptor can phosphorylate a number of intracellular substrates that initiate discrete signaling pathways. The tyrosine phosphorylation of some substrates activates phosphatidylinositol-3-kinase (PI3K), which produces polyphosphoinositides that interact with protein kinases, leading to activation of the kinase Akt. Phosphorylation of Shc leads to activation of the Ras/MAP kinase pathway. Phosphorylation of SH2B2 and of Cbl initiates activation of G proteins such as TC10. Activation of Akt and other protein kinases produces phosphorylation of a variety of substrates, including transcription factors, GTPase-activating proteins, and other kinases that control key metabolic events. Among the cellular processes controlled by insulin are vesicle trafficking, activities of metabolic enzymes, transcriptional factors, and degradation of insulin itself. Together these complex processes are coordinated to ensure glucose homeostasis.
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Menon B, Guo X, Garcia N, Gulappa T, Menon KMJ. miR-122 Regulates LHR Expression in Rat Granulosa Cells by Targeting Insig1 mRNA. Endocrinology 2018; 159:2075-2082. [PMID: 29579170 PMCID: PMC5905391 DOI: 10.1210/en.2017-03270] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Accepted: 03/13/2018] [Indexed: 11/19/2022]
Abstract
Luteinizing hormone/chorionic gonadotropin receptor (LHR) expression in the ovary is regulated by a messenger RNA (mRNA) binding protein, which specifically binds to the coding region of LHR mRNA. We have shown that miR-122, a short noncoding RNA, mediates LHR mRNA levels by modulating the expression of LHR mRNA-binding protein (LRBP) through the regulation of sterol regulatory element binding protein (SREBP) activation. The present results show that miR-122 regulates LRBP levels by increasing the processing of SREBP through the degradation of Insig1, the anchoring protein of SREBP. We present evidence showing that mRNA and protein levels of Insig1 undergo a time-dependent increase following the treatment of rat granulosa cells with follicle-stimulating hormone (FSH), which leads to a decrease in LRBP levels. Furthermore, overexpression of miR-122 using an adenoviral vector (AdmiR-122) abolished FSH-induced increases in Insig1 mRNA and protein. We further confirmed the role of Insig1 by showing that inhibition of Insig1 using a specific small interfering RNA prior to FSH treatment resulted in the abrogation of LHR upregulation. Silencing of Insig1 also reversed FSH-mediated decreases in SREBP and LRBP activation. These results show that decreased levels of miR-122 increase Insig1 and suppress SREBP processing in response to FSH stimulation of rat granulosa cells.
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Affiliation(s)
- Bindu Menon
- Department of Obstetrics/Gynecology, University of Michigan Medical School, Ann Arbor, Michigan
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan
- Correspondence: K. M. J. Menon, PhD, 6428 Medical Science Building I, 1150 West Medical Center Drive, University of Michigan Medical School, Ann Arbor, Michigan 48109. E-mail: ; or Bindu Menon, PhD, 6436 Medical Sciences Building 1, 1150 West Medical Center Drive, University of Michigan Medical School, Ann Arbor, Michigan 48109. E-mail:
| | - Xingzi Guo
- Department of Obstetrics/Gynecology, University of Michigan Medical School, Ann Arbor, Michigan
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan
| | - Natalia Garcia
- Department of Obstetrics/Gynecology, University of Michigan Medical School, Ann Arbor, Michigan
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan
| | - Thippeswamy Gulappa
- Department of Obstetrics/Gynecology, University of Michigan Medical School, Ann Arbor, Michigan
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan
| | - K M J Menon
- Department of Obstetrics/Gynecology, University of Michigan Medical School, Ann Arbor, Michigan
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan
- Correspondence: K. M. J. Menon, PhD, 6428 Medical Science Building I, 1150 West Medical Center Drive, University of Michigan Medical School, Ann Arbor, Michigan 48109. E-mail: ; or Bindu Menon, PhD, 6436 Medical Sciences Building 1, 1150 West Medical Center Drive, University of Michigan Medical School, Ann Arbor, Michigan 48109. E-mail:
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Brown MS, Radhakrishnan A, Goldstein JL. Retrospective on Cholesterol Homeostasis: The Central Role of Scap. Annu Rev Biochem 2017; 87:783-807. [PMID: 28841344 DOI: 10.1146/annurev-biochem-062917-011852] [Citation(s) in RCA: 302] [Impact Index Per Article: 43.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Scap is a polytopic membrane protein that functions as a molecular machine to control the cholesterol content of membranes in mammalian cells. In the 21 years since our laboratory discovered Scap, we have learned how it binds sterol regulatory element-binding proteins (SREBPs) and transports them from the endoplasmic reticulum (ER) to the Golgi for proteolytic processing. Proteolysis releases the SREBP transcription factor domains, which enter the nucleus to promote cholesterol synthesis and uptake. When cholesterol in ER membranes exceeds a threshold, the sterol binds to Scap, triggering several conformational changes that prevent the Scap-SREBP complex from leaving the ER. As a result, SREBPs are no longer processed, cholesterol synthesis and uptake are repressed, and cholesterol homeostasis is restored. This review focuses on the four domains of Scap that undergo concerted conformational changes in response to cholesterol binding. The data provide a molecular mechanism for the control of lipids in cell membranes.
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Affiliation(s)
- Michael S Brown
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA; ;
| | - Arun Radhakrishnan
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA; ;
| | - Joseph L Goldstein
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA; ;
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Adaikalakoteswari A, Finer S, Voyias PD, McCarthy CM, Vatish M, Moore J, Smart-Halajko M, Bawazeer N, Al-Daghri NM, McTernan PG, Kumar S, Hitman GA, Saravanan P, Tripathi G. Vitamin B12 insufficiency induces cholesterol biosynthesis by limiting s-adenosylmethionine and modulating the methylation of SREBF1 and LDLR genes. Clin Epigenetics 2015; 7:14. [PMID: 25763114 PMCID: PMC4356060 DOI: 10.1186/s13148-015-0046-8] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Accepted: 01/14/2015] [Indexed: 12/23/2022] Open
Abstract
Background The dietary supply of methyl donors such as folate, vitamin B12, betaine, methionine, and choline is essential for normal growth, development, and physiological functions through the life course. Both human and animal studies have shown that vitamin B12 deficiency is associated with altered lipid profile and play an important role in the prediction of metabolic risk, however, as of yet, no direct mechanism has been investigated to confirm this. Results Three independent clinical studies of women (i) non-pregnant at child-bearing age, (ii) in early pregnancy, and (iii) at delivery showed that low vitamin B12 status was associated with higher total cholesterol, LDL cholesterol, and cholesterol-to-HDL ratio. These results guided the investigation into the cellular mechanisms of induced cholesterol biosynthesis due to vitamin B12 deficiency, using human adipocytes as a model system. Adipocytes cultured in low or no vitamin B12 conditions had increased cholesterol and homocysteine levels compared to control. The induction of cholesterol biosynthesis was associated with reduced s-adenosylmethionine (AdoMet)-to-s-adenosylhomocysteine (AdoHcy) ratio, also known as methylation potential (MP). We therefore studied whether reduced MP could lead to hypomethylation of genes involved in the regulation of cholesterol biosynthesis. Genome-wide and targeted DNA methylation analysis identified that the promoter regions of SREBF1 and LDLR, two key regulators of cholesterol biosynthesis, were hypomethylated under vitamin B12-deficient conditions, and as a result, their expressions and cholesterol biosynthesis were also significantly increased. This finding was further confirmed by the addition of the methylation inhibitor, 5-aza-2′-deoxycytidine, which resulted in increased SREBF1 and LDLR expressions and cholesterol accumulation in vitamin B12-sufficient conditions. Finally, we observed that the expression of SREBF1, LDLR, and cholesterol biosynthesis genes were increased in adipose tissue of vitamin B12 deficient mothers compared to control group. Conclusions Clinical data suggests that vitamin B12 deficiency is an important metabolic risk factor. Regulation of AdoMet-to-AdoHcy levels by vitamin B12 could be an important mechanism by which it can influence cholesterol biosynthesis pathway in human adipocytes. Electronic supplementary material The online version of this article (doi:10.1186/s13148-015-0046-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Antonysunil Adaikalakoteswari
- Division of Metabolic and Vascular Health, Clinical Sciences Research Laboratories, Warwick Medical School, University Hospital Coventry and Warwickshire, University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX UK
| | - Sarah Finer
- Centre for Diabetes, Blizard Institute, Queen Mary University of London, 4 Newark Street, London, E1 2AT UK ; Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Level 4, University of Cambridge, Addenbrooke's Hospital, Box 289, Cambridge, CB2 0QQ UK
| | - Philip D Voyias
- Division of Metabolic and Vascular Health, Clinical Sciences Research Laboratories, Warwick Medical School, University Hospital Coventry and Warwickshire, University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX UK
| | - Ciara M McCarthy
- Division of Metabolic and Vascular Health, Clinical Sciences Research Laboratories, Warwick Medical School, University Hospital Coventry and Warwickshire, University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX UK
| | - Manu Vatish
- Nuffield Department of Obstetrics and Gynaecology University of Oxford Level 3, John Radcliffe Hospital, Oxford, University of Oxford, Oxford, OX3 9DU UK
| | - Jonathan Moore
- Warwick Systems Biology, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL UK
| | - Melissa Smart-Halajko
- Centre for Diabetes, Blizard Institute, Queen Mary University of London, 4 Newark Street, London, E1 2AT UK
| | - Nahla Bawazeer
- Division of Metabolic and Vascular Health, Clinical Sciences Research Laboratories, Warwick Medical School, University Hospital Coventry and Warwickshire, University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX UK
| | - Nasser M Al-Daghri
- Biochemistry Department, College of Science, King Saud University, Riyadh, 11451 Saudi Arabia
| | - Philip G McTernan
- Division of Metabolic and Vascular Health, Clinical Sciences Research Laboratories, Warwick Medical School, University Hospital Coventry and Warwickshire, University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX UK
| | - Sudhesh Kumar
- Division of Metabolic and Vascular Health, Clinical Sciences Research Laboratories, Warwick Medical School, University Hospital Coventry and Warwickshire, University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX UK
| | - Graham A Hitman
- Centre for Diabetes, Blizard Institute, Queen Mary University of London, 4 Newark Street, London, E1 2AT UK
| | - Ponnusamy Saravanan
- Division of Metabolic and Vascular Health, Clinical Sciences Research Laboratories, Warwick Medical School, University Hospital Coventry and Warwickshire, University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX UK ; iDEA Centre, George Eliot Hospital, Nuneton, CV10 7DJ UK
| | - Gyanendra Tripathi
- Division of Metabolic and Vascular Health, Clinical Sciences Research Laboratories, Warwick Medical School, University Hospital Coventry and Warwickshire, University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX UK
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Faulkner RA, Nguyen AD, Jo Y, DeBose-Boyd RA. Lipid-regulated degradation of HMG-CoA reductase and Insig-1 through distinct mechanisms in insect cells. J Lipid Res 2013; 54:1011-22. [PMID: 23403031 PMCID: PMC3653402 DOI: 10.1194/jlr.m033639] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In mammalian cells, levels of the integral membrane proteins 3-hydroxy-3-methylglutaryl-CoA reductase and Insig-1 are controlled by lipid-regulated endoplasmic reticulum-associated degradation (ERAD). The ERAD of reductase slows a rate-limiting step in cholesterol synthesis and results from sterol-induced binding of its membrane domain to Insig-1 and the highly related Insig-2 protein. Insig binding bridges reductase to ubiquitin ligases that facilitate its ubiquitination, thereby marking the protein for cytosolic dislocation and proteasomal degradation. In contrast to reductase, Insig-1 is subjected to ERAD in lipid-deprived cells. Sterols block this ERAD by inhibiting Insig-1 ubiquitination, whereas unsaturated fatty acids block the reaction by preventing the protein's cytosolic dislocation. In previous studies, we found that the membrane domain of mammalian reductase was subjected to ERAD in Drosophila S2 cells. This ERAD was appropriately accelerated by sterols and required the action of Insigs, which bridged reductase to a Drosophila ubiquitin ligase. We now report reconstitution of mammalian Insig-1 ERAD in S2 cells. The ERAD of Insig-1 in S2 cells mimics the reaction that occurs in mammalian cells with regard to its inhibition by either sterols or unsaturated fatty acids. Genetic and pharmacologic manipulations coupled with subcellular fractionation indicate that Insig-1 and reductase are degraded through distinct mechanisms that are mediated by different ubiquitin ligase complexes. Together, these results establish Drosophila S2 cells as a model system to elucidate mechanisms through which lipid constituents of cell membranes (i.e., sterols and fatty acids) modulate the ERAD of Insig-1 and reductase.
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Affiliation(s)
- Rebecca A Faulkner
- Howard Hughes Medical Institute, Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046, USA
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Honma T, Kitano Y, Kijima R, Jibu Y, Kawakami Y, Tsuduki T, Nakagawa K, Miyazawa T. Comparison of the Health Benefits of Different Eras of Japanese Foods : Lipid and Carbohydrate Metabolism Focused Research. J JPN SOC FOOD SCI 2013. [DOI: 10.3136/nskkk.60.541] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Lim HY, Bodmer R. Phospholipid homeostasis and lipotoxic cardiomyopathy: a matter of balance. Fly (Austin) 2011; 5:234-6. [PMID: 21494094 DOI: 10.4161/fly.5.3.15708] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Obesity has reached pandemic proportions globally and is often associated with lipotoxic heart diseases. In the obese state, caloric surplus is accommodated in the adipocytes as triglycerides. As the storage capacity of adipocytes is exceeded or malfunctioning, lipids begin to infiltrate and accumulate in non-adipose tissues, including the myocardium of the heart, leading to organ dysfunction. While the disruption of caloric homeostasis has been widely viewed as a principal mechanism in contributing to peripheral tissue steatosis and lipotoxicity, our recent studies in Drosophila have led to the novel finding that deregulation of phospholipid homeostasis may also significantly contribute to the pathogenesis of lipotoxic cardiomyopathy. Fly mutants that bear perturbations in phosphatidylethanolamine (PE) biosynthesis, such as the easily-shocked (eas) mutants defective in ethanolamine kinase, incurred aberrant activation of the sterol regulatory element binding protein (SREBP) pathway, thereby causing chronic lipogenesis and cardiac steatosis that culminates in the development of lipotoxic cardiomyopathy. Here, we describe the potential relationship between SREBP and other eas-associated phenotypes, such as neuronal excitability defects. We will further discuss the additional implications presented by our work toward the effects of altered lipid metabolism on cellular growth and/or proliferation in response to defective phospholipid homeostasis.
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Affiliation(s)
- Hui-Ying Lim
- Development and Aging Program, Neuroscience, Aging and Stem Cell Research Center, Sanford-Burnham Medical Research Institute, La Jolla, CA, USA
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Activation of sterol regulatory element binding proteins in the absence of Scap in Drosophila melanogaster. Genetics 2010; 185:189-98. [PMID: 20176975 DOI: 10.1534/genetics.110.114975] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The escort factor Scap is essential in mammalian cells for regulated activation of sterol regulatory element binding proteins (SREBPs). SREBPs are membrane-bound transcription factors. Cells lacking Scap cannot activate SREBP. They are therefore deficient in the transcription of numerous genes involved in lipid synthesis and uptake; they cannot survive in the absence of exogenous lipid. Here we report that, in contrast to mammalian cells, Drosophila completely lacking dscap are viable. Flies lacking dscap emerge at approximately 70% of the expected rate and readily survive as homozygous stocks. These animals continue to cleave dSREBP in some tissues. Transcription of dSREBP target genes in dscap mutant larvae is reduced compared to wild type. It is greater than in mutants lacking dSREBP and remains responsive to dietary lipids in dscap mutants. Flies lacking dscap do not require the caspase Drice to activate dSREBP. This contrasts with ds2p mutants. ds2p encodes a protease that releases the transcription factor domain of dSREBP from the membrane. Larvae doubly mutant for dscap and ds2p exhibit phenotypes similar to those of ds2p single mutants. Thus, dScap and dS2P, essential components of the SREBP activation machinery in mammalian cells, are dispensable in Drosophila owing to different compensatory mechanisms.
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Shmueli A, Tsai YC, Yang M, Braun MA, Weissman AM. Targeting of gp78 for ubiquitin-mediated proteasomal degradation by Hrd1: cross-talk between E3s in the endoplasmic reticulum. Biochem Biophys Res Commun 2009; 390:758-62. [PMID: 19835843 DOI: 10.1016/j.bbrc.2009.10.045] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Accepted: 10/09/2009] [Indexed: 10/20/2022]
Abstract
There are an increasing number of ubiquitin ligases (E3s) implicated in endoplasmic reticulum (ER)-associated degradation (ERAD) in mammals. The two for which the greatest amount of information exists are the RING finger proteins gp78 and Hrd1, which are the structural orthologs of the yeast ERAD E3 Hrd1p. We now report that Hrd1, also known as synoviolin, targets gp78 for proteasomal degradation independent of the ubiquitin ligase activity of gp78, without evidence of a reciprocal effect. This degradation is observed in mouse embryonic fibroblasts lacking Hrd1, as well as with acute manipulation of Hrd1. The significance of this is underscored by the diminished level of a gp78-specific substrate, Insig-1, when Hrd1 expression is decreased and gp78 levels are consequently increased. These finding demonstrate a previously unappreciated level of complexity of the ubiquitin system in ERAD and have potentially important ramifications for processes where gp78 is implicated including regulation of lipid metabolism, metastasis, cystic fibrosis and neurodegenerative disorders.
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Affiliation(s)
- Ayelet Shmueli
- Laboratory of Protein Dynamics and Signaling, Center for Cancer Research, National Cancer Institute, NCI, Frederick 21702, USA.
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14
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Nguyen AD, Lee SH, DeBose-Boyd RA. Insig-mediated, sterol-accelerated degradation of the membrane domain of hamster 3-hydroxy-3-methylglutaryl-coenzyme A reductase in insect cells. J Biol Chem 2009; 284:26778-88. [PMID: 19638338 DOI: 10.1074/jbc.m109.032342] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sterol-accelerated degradation of the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase is one of several mechanisms through which cholesterol synthesis is controlled in mammalian cells. This degradation results from sterol-induced binding of the membrane domain of reductase to endoplasmic reticulum membrane proteins called Insig-1 and Insig-2, which are carriers of a ubiquitin ligase called gp78. The ensuing gp78-mediated ubiquitination of reductase is a prerequisite for its rapid, 26 S proteasome-mediated degradation from endoplasmic reticulum membranes, a reaction that slows a rate-limiting step in cholesterol synthesis. Here, we report that the membrane domain of hamster reductase is subject to sterol-accelerated degradation in Drosophila S2 cells, but only when mammalian Insig-1 or Insig-2 are co-expressed. This degradation mimics the reaction that occurs in mammalian cells with regard to its absolute requirement for the action of Insigs, sensitivity to proteasome inhibition, augmentation by nonsterol isoprenoids, and sterol specificity. RNA interference studies reveal that this degradation requires the Drosophila Hrd1 ubiquitin ligase and several other proteins, including a putative substrate selector, which associate with the enzyme in yeast and mammalian systems. These studies define Insigs as the minimal requirement for sterol-accelerated degradation of the membrane domain of reductase in Drosophila S2 cells.
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Affiliation(s)
- Andrew D Nguyen
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046, USA
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15
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Brown MS, Goldstein JL. Cholesterol feedback: from Schoenheimer's bottle to Scap's MELADL. J Lipid Res 2009; 50 Suppl:S15-27. [PMID: 18974038 PMCID: PMC2674699 DOI: 10.1194/jlr.r800054-jlr200] [Citation(s) in RCA: 365] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2008] [Revised: 10/29/2008] [Indexed: 01/12/2023] Open
Abstract
Cholesterol biosynthesis is among the most intensely regulated processes in biology. Synthetic rates vary over hundreds of fold depending on the availability of an external source of cholesterol. Studies of this feedback regulatory process have a rich history. The field began 75 years ago when Rudolf Schoenheimer measured cholesterol balance in mice in a bottle. He found that cholesterol feeding led to decreased cholesterol synthesis, thereby introducing the general phenomenon by which end products of biosynthetic pathways inhibit their own synthesis. Recently, cholesterol feedback has been explained at a molecular level with the discovery of membrane-bound transcription factors called sterol regulatory element-binding proteins (SREBPs), and an appreciation of the sterol-sensing role of their partner, an escort protein called Scap. The key element in Scap is a hexapeptide sequence designated MELADL (rhymes with bottle). Thus, over 75 years, Schoenheimer's bottle led to Scap's MELADL. In addition to their basic importance in membrane biology, these studies have implications for the regulation of plasma cholesterol levels and consequently for the development of atherosclerotic plaques, myocardial infarctions, and strokes. In this article we review the major milestones in the cholesterol feedback story.
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Affiliation(s)
- Michael S. Brown
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Joseph L. Goldstein
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
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16
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Babin PJ, Gibbons GF. The evolution of plasma cholesterol: direct utility or a "spandrel" of hepatic lipid metabolism? Prog Lipid Res 2008; 48:73-91. [PMID: 19049814 DOI: 10.1016/j.plipres.2008.11.002] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2008] [Revised: 11/06/2008] [Accepted: 11/07/2008] [Indexed: 02/07/2023]
Abstract
Fats provide a concentrated source of energy for multicellular organisms. The efficient transport of fats through aqueous biological environments raises issues concerning effective delivery to target tissues. Furthermore, the utilization of fatty acids presents a high risk of cytotoxicity. Improving the efficiency of fat transport while simultaneously minimizing the cytotoxic risk confers distinct selective advantages. In humans, most of the plasma cholesterol is associated with low-density lipoprotein (LDL), a metabolic by-product of very-low-density lipoprotein (VLDL), which originates in the liver. However, the functions of VLDL are not clear. This paper reviews the evidence that LDL arose as a by-product during the natural selection of VLDL. The latter, in turn, evolved as a means of improving the efficiency of diet-derived fatty acid storage and utilization, as well as neutralizing the potential cytotoxicity of fatty acids while conserving their advantages as a concentrated energy source. The evolutionary biology of lipid transport processes has provided a fascinating insight into how and why these VLDL functions emerged during animal evolution. As causes of historical origin must be separated from current utilities, our spandrel-LDL theory proposes that LDL is a spandrel of VLDL selection, which appeared non-adaptively and may later have become crucial for vertebrate fitness.
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Affiliation(s)
- Patrick J Babin
- Université Bordeaux 1, Génomique et Physiologie des Poissons, UMR NuAGe, 33405 Talence, France
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17
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Seo PJ, Kim SG, Park CM. Membrane-bound transcription factors in plants. TRENDS IN PLANT SCIENCE 2008; 13:550-6. [PMID: 18722803 DOI: 10.1016/j.tplants.2008.06.008] [Citation(s) in RCA: 145] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Revised: 06/19/2008] [Accepted: 06/20/2008] [Indexed: 05/03/2023]
Abstract
The ability to activate dormant transcription factors is an important molecular feature of the transcriptional regulatory networks that govern diverse cellular functions. An intriguing example is the controlled proteolytic activation of membrane-bound transcription factors (MTFs). Most MTFs are activated either by intramembrane proteases or by the ubiquitin-proteasome pathway. Recent studies have shown that several members of the bZIP and NAC families in Arabidopsis are membrane-associated and are activated by membrane-associated proteases during stress responses in the endoplasmic reticulum and when the plants experience environmental stresses. A genome-scale analysis shows that over 10% of all transcription factors are membrane bound, indicating that activation of MTFs occurs at the genomic level, allowing transcription to be regulated rapidly under stressful conditions.
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Affiliation(s)
- Pil Joon Seo
- Molecular Signaling Laboratory, Department of Chemistry, Seoul National University, Seoul 151-742, Korea
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18
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Abstract
Cholesterol is an essential component of mammalian cell membranes and is required for proper membrane permeability, fluidity, organelle identity, and protein function. Cells maintain sterol homeostasis by multiple feedback controls that act through transcriptional and posttranscriptional mechanisms. The membrane-bound transcription factor sterol regulatory element binding protein (SREBP) is the principal regulator of both sterol synthesis and uptake. In mammalian cells, the ER membrane protein Insig has emerged as a key component of homeostatic regulation by controlling both the activity of SREBP and the sterol-dependent degradation of the biosynthetic enzyme HMG-CoA reductase. In this review, we focus on recent advances in our understanding of the molecular mechanisms of the regulation of sterol synthesis. A comparative analysis of SREBP and HMG-CoA reductase regulation in mammals, yeast, and flies points toward an equilibrium model for how lipid signals regulate the activity of sterol-sensing proteins and their downstream effectors.
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Affiliation(s)
- Peter J Espenshade
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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19
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Statistical determination of optimal baculovirus infection condition for recombinant protein production in Drosophila S2 cells. Appl Biochem Biotechnol 2007; 142:243-52. [PMID: 18025585 DOI: 10.1007/s12010-007-0016-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2006] [Revised: 08/25/2006] [Accepted: 08/29/2006] [Indexed: 10/23/2022]
Abstract
Insect Drosophila melanogaster S2 cell was developed as plasmid-based and, therefore, a nonlytic expression system for functional foreign proteins. To achieve multiple protein expressions, it was suggested that baculovirus be used on S2 cell system because baculovirus can infect S2 cells but cannot replicate inside the cells. Therefore, establishment of baculovirus infection conditions is the first important step and this should be properly optimized for production yield. We used statistical methodology to optimize the baculovirus infection conditions using green fluorescent protein (GFP) as a reporter protein. Consequently, we arrived at optimal infection conditions through a statistical regression method. The secreted GFP yield from vMT-GFP baculovirus-infected wild-type S2 cells under optimal infection conditions was >15-fold higher than that under nonoptimal conditions and comparable to that from stably transfected recombinant S2 cells.
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20
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Kim KR, Kim YK, Cha HJ. Recombinant baculovirus-based multiple protein expression platform for Drosophila S2 cell culture. J Biotechnol 2007; 133:116-22. [PMID: 17963934 DOI: 10.1016/j.jbiotec.2007.09.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2007] [Revised: 08/11/2007] [Accepted: 09/14/2007] [Indexed: 10/22/2022]
Abstract
A platform for selective and controllable expression of multiple foreign protein types was developed in insect cell culture. Based on the fact that baculovirus cannot replicate in nonpermissive Drosophila melanogaster Schneider line 2 (S2) cells, S2 cells that stably express human erythropoietin (hEPO) under the control of the S2-derived inducible metallothionein (MT) promoter were infected with three types of recombinant baculoviruses, each of which expressed a different fluorescent protein gene under the control of MT promoter. Addition of copper sulfate as an inducer to infected, stably transfected S2 cells resulted in simultaneous expression of hEPO and three fluorescent proteins. Expression profiles and levels of the three induced fluorescent proteins were similar in all single infected cells. Importantly, expression profiles and levels of hEPO were similar in both non-infected and infected cells, indicating that baculovirus expressed recombinant proteins do not adversely affect expression of host cell recombinant proteins. Expressions of the three fluorescent proteins were able to be selectively regulated by altering combination ratios of the three types of recombinant baculoviruses. Collectively, these data indicate that the baculovirus/stably transfected S2 cell system can be successfully used to express multiple foreign proteins in a controlled and selective manner without the burden of additional selection markers. Such a system would be expected to be attractive as a multiple protein expression platform for engineering metabolic or glycosylation pathways.
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Affiliation(s)
- Kyoung Ro Kim
- Department of Chemical Engineering, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
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21
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Radhakrishnan A, Ikeda Y, Kwon HJ, Brown MS, Goldstein JL. Sterol-regulated transport of SREBPs from endoplasmic reticulum to Golgi: oxysterols block transport by binding to Insig. Proc Natl Acad Sci U S A 2007; 104:6511-8. [PMID: 17428920 PMCID: PMC1851665 DOI: 10.1073/pnas.0700899104] [Citation(s) in RCA: 445] [Impact Index Per Article: 26.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cholesterol synthesis in animals is controlled by the regulated transport of sterol regulatory element-binding proteins (SREBPs) from the endoplasmic reticulum to the Golgi, where the transcription factors are processed proteolytically to release active fragments. Transport is inhibited by either cholesterol or oxysterols, blocking cholesterol synthesis. Cholesterol acts by binding to the SREBP-escort protein Scap, thereby causing Scap to bind to anchor proteins called Insigs. Here, we show that oxysterols act by binding to Insigs, causing Insigs to bind to Scap. Mutational analysis of the six transmembrane helices of Insigs reveals that the third and fourth are important for Insig's binding to oxysterols and to Scap. These studies define Insigs as oxysterol-binding proteins, explaining the long-known ability of oxysterols to inhibit cholesterol synthesis in animal cells.
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Affiliation(s)
| | | | - Hyock Joo Kwon
- Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Michael S. Brown
- Departments of *Molecular Genetics and
- To whom correspondence may be addressed. E-mail: or
| | - Joseph L. Goldstein
- Departments of *Molecular Genetics and
- To whom correspondence may be addressed. E-mail: or
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22
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Liu HP, Wu CC, Chang YS. PRA1 promotes the intracellular trafficking and NF-kappaB signaling of EBV latent membrane protein 1. EMBO J 2006; 25:4120-30. [PMID: 16917502 PMCID: PMC1560356 DOI: 10.1038/sj.emboj.7601282] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2006] [Accepted: 07/24/2006] [Indexed: 11/09/2022] Open
Abstract
Latent membrane protein 1 (LMP1), which is an Epstein-Barr virus (EBV)-encoded oncoprotein, induces nuclear factor-kappa B (NF-kappaB) signaling by mimicking the tumor necrosis factor receptor (TNFR). LMP1 signals primarily from intracellular compartments in a ligand-independent manner. Here, we identify a new LMP1-interacting molecule, prenylated Rab acceptor 1 (PRA1), which interacts with LMP1 for the first time through LMP1's transmembrane domain, and show that PRA1 is involved in intracellular LMP1 trafficking and LMP1-induced NF-kappaB activity. Immunofluorescence and biochemical analyses revealed that LMP1 physically interacted with PRA1 at the Golgi apparatus, and the colocalization of LMP1 and PRA1 to the Golgi was sensitive to nocodazole and brefeldin A. Coexpression of a PRA1 export mutant or knockdown of PRA1 led to redistribution of LMP1 and its associated signaling molecules to the endoplasmic reticulum and subsequent impairment of LMP1-induced NF-kappaB activation, but had no effect on CD40- and TNFR1-mediated signaling or the functional integrity of the Golgi apparatus. These novel findings provide important new insights into LMP1, and identify an unexpected new role for PRA1 in cellular signaling.
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Affiliation(s)
- Hao-Ping Liu
- Institute of Microbiology and Immunology, National Yang Ming University, Shih-Pai, Taipei, Taiwan, Republic of China
| | - Chih-Ching Wu
- Proteomics Core Laboratory of Chang Gung Molecular Medicine Research Center, Chang Gung University, Kwei-Shan, Taoyuan, Taiwan, Republic of China
| | - Yu-Sun Chang
- Proteomics Core Laboratory of Chang Gung Molecular Medicine Research Center, Chang Gung University, Kwei-Shan, Taoyuan, Taiwan, Republic of China
- Graduate Institute of Basic Medical Sciences, Chang Gung University, Kwei-Shan, Taoyuan, Taiwan, Republic of China
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23
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Kotzka J, Müller-Wieland D. Sterol regulatory element-binding protein (SREBP)-1: gene regulatory target for insulin resistance? Expert Opin Ther Targets 2006; 8:141-9. [PMID: 15102555 DOI: 10.1517/14728222.8.2.141] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The combined appearance of different cardiovascular risk factors seems to be more prevalent in individuals with decreased insulin sensitivity and increased visceral obesity, thereby being components of the so-called metabolic syndrome. Alterations in transcription factors result in complex dysregulation of gene expression, which might be the key to understanding insulin resistance-associated clinical clustering of coronary risk factors at the cellular or gene regulatory level. Recent examples are peroxisome proliferator-activated receptors and sterol regulatory element-binding proteins (SREBPs), which also appear to be novel drug targets. The authors have recently shown that SREBPs are substrates of mitogen-activated protein kinases, and propose that SREBP-1 might play a role in the development of cellular features belonging to lipotoxicity and, possibly, syndrome X.
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Affiliation(s)
- Jorg Kotzka
- Klinische Biochemie und Pathobiochemie, Deutsches Diabetes-Forschungsinstitut, Leibniz-Institut an der Heinrich-Heine-Universität Düsseldorf, Germany
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24
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Robertson KM, Schuster GU, Steffensen KR, Hovatta O, Meaney S, Hultenby K, Johansson LC, Svechnikov K, Söder O, Gustafsson JA. The liver X receptor-{beta} is essential for maintaining cholesterol homeostasis in the testis. Endocrinology 2005; 146:2519-30. [PMID: 15761042 DOI: 10.1210/en.2004-1413] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The liver X receptor (LXR)alpha and -beta has been found to play a central role in maintaining cellular cholesterol homeostasis. In this study we comprehensively investigated the effect of deleting LXRalpha and -beta on testicular morphology and function. In the absence of LXRbeta, excessive cholesterol accumulated in the Sertoli cells from 2.5 months, resulting in severe cellular disruption and dysregulation of spermatogenesis by 10 months of age. This correlated with gene expression analyses that clearly indicated that LXRbeta was the dominant transcript in the testis Although the LXRalpha(-/-) testis was normal, the LXRalpha(-/-)beta(-/-) testis presented with a more severe phenotype than the LXRbeta(-/-) mice, and males were infertile by 4 months of age, indicating LXRalpha may partially rescue the testicular phenotype. Although Leydig cells did not accumulate excessive cholesterol, declining serum and intratesticular androgen levels with age suggested that these cells were in fact less functional. Treatment of a Sertoli cell line with the LXR agonist T0901317 led to increased expression of known LXR target genes like ATP binding cassette-G1 and sterol regulatory binding protein-1c; similar results were observed in wild-type testis after in vivo administration, suggesting the LXR is functioning in the same way as in other tissues. Ordinarily increased levels of cholesterol activate intracellular sensors to decrease these levels; however, the increasing amount of cholesterol in the Sertoli cells indicates improper control of cholesterol metabolism when LXRbeta is absent. Although the precise molecular mechanism at this time remains unclear, our study highlights the crucial role for LXRbeta in retaining cholesterol homeostasis in Sertoli cells.
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Affiliation(s)
- Kirsten M Robertson
- Karolinska Institutet, Department of Biosciences at Novum, Huddinge 14157, Sweden.
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25
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Abstract
Lipids were long considered to be passive passengers of carrier vesicles with the single role of sealing the transport container. We now know that specific phospholipids are required for efficient fusion, while others facilitate budding and fission. Moreover, the various polyphosphoinositides assist in the recruitment from the cytosol of proteins of the transport machinery. Finally, the segregation of membrane lipids into different fluid phases appears to serve as a 'lipid raft' mechanism for protein sorting at various stages of the secretory and endocytic pathways. The current challenge is to understand how proteins control the metabolism and subcellular localization, and thereby the activity, of the various lipids.
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Affiliation(s)
- Gerrit van Meer
- Department of Membrane Enzymology, Centre for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
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26
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Cho HS, Kim YK, Cha HJ. Expression of double foreign protein types following recombinant baculovirus infection of stably transfected Drosophila S2 cells. Enzyme Microb Technol 2004. [DOI: 10.1016/j.enzmictec.2004.08.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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27
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McPherson R, Gauthier A. Molecular regulation of SREBP function: the Insig-SCAP connection and isoform-specific modulation of lipid synthesis. Biochem Cell Biol 2004; 82:201-11. [PMID: 15052338 DOI: 10.1139/o03-090] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Sterol regulatory element binding proteins (SREBPs) are a family of membrane-bound transcription factors that play a unique and fundamental role in both cholesterol and fatty acid metabolism, relevant to human disease. There are three SREBPs that regulate the expression of over 30 genes. SREBPs are subject to regulation at three levels: proteolytic cleavage, rapid degradation by the ubiquitin-proteasome pathway, and sumoylation. Recently, there have been exciting advances in our understanding of the molecular mechanism of SREBP trafficking and processing with new information on the role of insulin-induced genes and the differential role and regulation of SREBP-1c and -2, which may ultimately lead to novel strategies for the treatment of dyslipidemia and insulin resistance.
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Affiliation(s)
- Ruth McPherson
- Lipoprotein and Atherosclerosis Group, University of Ottawa Heart Institute, ON, Canada.
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28
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Abstract
Cholesterol homeostasis is established by a complex of three proteins, one of which contains a hydrophobic domain previously termed a sterol-sensing domain. New biochemical studies of this domain demonstrate direct high-affinity binding of the sterol-sensing domain to sterol.
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Affiliation(s)
- Tim Levine
- Division of Cell Biology, Institute of Ophthalmology, Bath Street, London EC1V 9EL, United Kingdom
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29
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Engelking LJ, Kuriyama H, Hammer RE, Horton JD, Brown MS, Goldstein JL, Liang G. Overexpression of Insig-1 in the livers of transgenic mice inhibits SREBP processing and reduces insulin-stimulated lipogenesis. J Clin Invest 2004; 113:1168-75. [PMID: 15085196 PMCID: PMC385408 DOI: 10.1172/jci20978] [Citation(s) in RCA: 213] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2004] [Accepted: 01/28/2004] [Indexed: 12/25/2022] Open
Abstract
In the current studies we generated transgenic mice that overexpress human Insig-1 in the liver under a constitutive promoter. In cultured cells Insig-1 and Insig-2 have been shown to block lipid synthesis in a cholesterol-dependent fashion by inhibiting proteolytic processing of sterol regulatory element-binding proteins (SREBPs), membrane-bound transcription factors that activate lipid synthesis. Insig's exert this action in the ER by binding SREBP cleavage-activating protein (SCAP) and preventing it from escorting SREBPs to the Golgi apparatus where the SREBPs are processed to their active forms. In the livers of Insig-1 transgenic mice, the content of all nuclear SREBPs (nSREBPs) was reduced and declined further upon feeding of dietary cholesterol. The nuclear content of the insulin-induced SREBP isoform, SREBP-1c, failed to increase to a normal extent upon refeeding on a high-carbohydrate diet. The nSREBP deficiency produced a marked reduction in the levels of mRNAs encoding enzymes required for synthesis of cholesterol, fatty acids, and triglycerides. Plasma cholesterol levels were strongly reduced, and plasma triglycerides did not exhibit their normal rise after refeeding. These results provide in vivo support for the hypothesis that nSREBPs are essential for high levels of lipid synthesis in the liver and indicate that Insig's modulate nSREBP levels by binding and retaining SCAP in the ER.
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Affiliation(s)
- Luke J Engelking
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, 75390, USA
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