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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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2
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Brandt A, Petrovsky R, Kriebel M, Großhans J. Use of Farnesyl Transferase Inhibitors in an Ageing Model in Drosophila. J Dev Biol 2023; 11:40. [PMID: 37987370 PMCID: PMC10660854 DOI: 10.3390/jdb11040040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 10/24/2023] [Accepted: 10/26/2023] [Indexed: 11/22/2023] Open
Abstract
The presence of farnesylated proteins at the inner nuclear membrane (INM), such as the Lamins or Kugelkern in Drosophila, leads to specific changes in the nuclear morphology and accelerated ageing on the organismal level reminiscent of the Hutchinson-Gilford progeria syndrome (HGPS). Farnesyl transferase inhibitors (FTIs) can suppress the phenotypes of the nuclear morphology in cultured fibroblasts from HGPS patients and cultured cells overexpressing farnesylated INM proteins. Similarly, FTIs have been reported to suppress the shortened lifespan in model organisms. Here, we report an experimental system combining cell culture and Drosophila flies for testing the activity of substances on the HGPS-like nuclear morphology and lifespan, with FTIs as an experimental example. Consistent with previous reports, we show that FTIs were able to ameliorate the nuclear phenotypes induced by the farnesylated nuclear proteins Progerin, Kugelkern, or truncated Lamin B in cultured cells. The subsequent validation in Drosophila lifespan assays demonstrated the applicability of the experimental system: treating adult Drosophila with the FTI ABT-100 reversed the nuclear phenotypes and extended the lifespan of experimentally induced short-lived flies. Since kugelkern-expressing flies have a significantly shorter average lifespan, half the time is needed for testing substances in the lifespan assay.
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Affiliation(s)
| | - Roman Petrovsky
- Department of Biology, Philipps University, Karl-von-Frisch-Straße 8, 35043 Marburg, Germany
| | - Maria Kriebel
- Department of Biology, Philipps University, Karl-von-Frisch-Straße 8, 35043 Marburg, Germany
| | - Jörg Großhans
- Department of Biology, Philipps University, Karl-von-Frisch-Straße 8, 35043 Marburg, Germany
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3
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Li X, Zhang M, Liu M, Liu TH, Hemba-Waduge RUS, Ji JY. Cdk8 attenuates lipogenesis by inhibiting SREBP-dependent transcription in Drosophila. Dis Model Mech 2022; 15:dmm049650. [PMID: 36305265 PMCID: PMC9702540 DOI: 10.1242/dmm.049650] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Accepted: 10/14/2022] [Indexed: 10/10/2023] Open
Abstract
Fine-tuning of lipogenic gene expression is important for the maintenance of long-term homeostasis of intracellular lipids. The SREBP family of transcription factors are master regulators that control the transcription of lipogenic and cholesterogenic genes, but the mechanisms modulating SREBP-dependent transcription are still not fully understood. We previously reported that CDK8, a subunit of the transcription co-factor Mediator complex, phosphorylates SREBP at a conserved threonine residue. Here, using Drosophila as a model system, we observed that the phosphodeficient SREBP proteins (SREBP-Thr390Ala) were more stable and more potent in stimulating the expression of lipogenic genes and promoting lipogenesis in vivo than wild-type SREBP. In addition, starvation blocked the effects of wild-type SREBP-induced lipogenic gene transcription, whereas phosphodeficient SREBP was resistant to this effect. Furthermore, our biochemical analyses identified six highly conserved amino acid residues in the N-terminus disordered region of SREBP that are required for its interactions with both Cdk8 and the MED15 subunit of the small Mediator complex. These results support that the concerted actions of Cdk8 and MED15 are essential for the tight regulation of SREBP-dependent transcription. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Xiao Li
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M University Health Science Center, College Station, TX 77843, USA
| | - Meng Zhang
- Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, Louisiana Cancer Research Center, 1700 Tulane Avenue, New Orleans, LA 70112, USA
| | - Mengmeng Liu
- Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, Louisiana Cancer Research Center, 1700 Tulane Avenue, New Orleans, LA 70112, USA
| | - Tzu-Hao Liu
- Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, Louisiana Cancer Research Center, 1700 Tulane Avenue, New Orleans, LA 70112, USA
| | - Rajitha-Udakara-Sampath Hemba-Waduge
- Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, Louisiana Cancer Research Center, 1700 Tulane Avenue, New Orleans, LA 70112, USA
| | - Jun-Yuan Ji
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M University Health Science Center, College Station, TX 77843, USA
- Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, Louisiana Cancer Research Center, 1700 Tulane Avenue, New Orleans, LA 70112, USA
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4
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Jaramillo-Madrid AC, Ashworth J, Fabris M, Ralph PJ. Phytosterol biosynthesis and production by diatoms (Bacillariophyceae). PHYTOCHEMISTRY 2019; 163:46-57. [PMID: 31005802 DOI: 10.1016/j.phytochem.2019.03.018] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Revised: 03/22/2019] [Accepted: 03/22/2019] [Indexed: 06/09/2023]
Abstract
Diatoms are abundant unicellular marine photosynthetic algae that have genetically diversified their physiology and metabolism while adapting to numerous environments. The metabolic repertoire of diatoms presents opportunities to characterise the biosynthesis and production of new and potentially valuable microalgal compounds, including sterols. Sterols of plant origin, known as phytosterols, have been studied for health benefits including demonstrated cholesterol-lowering properties. In this review we summarise sterol diversity, the unique metabolic features of sterol biosynthesis in diatoms, and prospects for the extraction of diatom phytosterols in comparison to existing sources. We also review biotechnological efforts to manipulate diatom biosynthesis, including culture conditions and avenues for the rational engineering of metabolism and cellular regulation.
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Affiliation(s)
| | - Justin Ashworth
- Climate Change Cluster, University of Technology Sydney, Sydney, Australia.
| | - Michele Fabris
- Climate Change Cluster, University of Technology Sydney, Sydney, Australia; CSIRO Synthetic Biology Future Science Platform, PO Box 2583, Brisbane, QLD, 4001, Australia
| | - Peter J Ralph
- Climate Change Cluster, University of Technology Sydney, Sydney, Australia.
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5
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Individual co-variation between viral RNA load and gene expression reveals novel host factors during early dengue virus infection of the Aedes aegypti midgut. PLoS Negl Trop Dis 2017; 11:e0006152. [PMID: 29261661 PMCID: PMC5752042 DOI: 10.1371/journal.pntd.0006152] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 01/03/2018] [Accepted: 12/04/2017] [Indexed: 12/16/2022] Open
Abstract
Dengue virus (DENV) causes more human infections than any other mosquito-borne virus. The current lack of antiviral strategies has prompted genome-wide screens for host genes that are required for DENV infectivity. Earlier transcriptomic studies that identified DENV host factors in the primary vector Aedes aegypti used inbred laboratory colonies and/or pools of mosquitoes that erase individual variation. Here, we performed transcriptome sequencing on individual midguts in a field-derived Ae. aegypti population to identify new candidate host factors modulating DENV replication. We analyzed the transcriptomic data using an approach that accounts for individual co-variation between viral RNA load and gene expression. This approach generates a prediction about the agonist or antagonist effect of candidate genes on DENV replication based on the sign of the correlation between gene expression and viral RNA load. Using this method, we identified 39 candidate genes that went undetected by conventional pairwise comparison of gene expression levels between DENV-infected midguts and uninfected controls. Only four candidate genes were detected by both methods, emphasizing their complementarity. We demonstrated the value of our approach by functional validation of a candidate agonist gene encoding a sterol regulatory element-binding protein (SREBP), which was identified by correlation analysis but not by pairwise comparison. We confirmed that SREBP promotes DENV infection in the midgut by RNAi-mediated gene knockdown in vivo. We suggest that our approach for transcriptomic analysis can empower genome-wide screens for potential agonist or antagonist factors by leveraging inter-individual variation in gene expression. More generally, this method is applicable to a wide range of phenotypic traits displaying inter-individual variation.
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Rong S, McDonald JG, Engelking LJ. Cholesterol auxotrophy and intolerance to ezetimibe in mice with SREBP-2 deficiency in the intestine. J Lipid Res 2017. [PMID: 28630260 DOI: 10.1194/jlr.m077610] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
SREBP-2 activates transcription of all genes needed for cholesterol biosynthesis. To study SREBP-2 function in the intestine, we generated a mouse model (Vil-BP2-/- ) in which Cre recombinase ablates SREBP-2 in intestinal epithelia. Intestines of Vil-BP2-/- mice had reduced expression of genes required for sterol synthesis, in vivo sterol synthesis rates, and epithelial cholesterol contents. On a cholesterol-free diet, the mice displayed chronic enteropathy with histological abnormalities of both villi and crypts, growth restriction, and reduced survival that was prevented by supplementation of cholesterol in the diet. Likewise, SREBP-2-deficient enteroids required exogenous cholesterol for growth. Blockade of luminal cholesterol uptake into enterocytes with ezetimibe precipitated acutely lethal intestinal damage in Vil-BP2-/- mice, highlighting the critical interplay in the small intestine of sterol absorption via NPC1L1 and sterol synthesis via SREBP-2 in sustaining the intestinal mucosa. These data show that the small intestine requires SREBP-2 to drive cholesterol synthesis that sustains the intestinal epithelia when uptake of cholesterol from the gut lumen is not available, and provide a unique example of cholesterol auxotrophy expressed in an intact, adult mammal.
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Affiliation(s)
- Shunxing Rong
- Departments of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Jeffrey G McDonald
- Departments of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046.,Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Luke J Engelking
- Departments of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046 .,Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
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Lim HY, Wang W, Wessells RJ, Ocorr K, Bodmer R. Phospholipid homeostasis regulates lipid metabolism and cardiac function through SREBP signaling in Drosophila. Genes Dev 2011; 25:189-200. [PMID: 21245170 DOI: 10.1101/gad.1992411] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The epidemic of obesity and diabetes is causing an increased incidence of dyslipidemia-related heart failure. While the primary etiology of lipotoxic cardiomyopathy is an elevation of lipid levels resulting from an imbalance in energy availability and expenditure, increasing evidence suggests a relationship between dysregulation of membrane phospholipid homeostasis and lipid-induced cardiomyopathy. In the present study, we report that the Drosophila easily shocked (eas) mutants that harbor a disturbance in phosphatidylethanolamine (PE) synthesis display tachycardia and defects in cardiac relaxation and are prone to developing cardiac arrest and fibrillation under stress. The eas mutant hearts exhibit elevated concentrations of triglycerides, suggestive of a metabolic, diabetic-like heart phenotype. Moreover, the low PE levels in eas flies mimic the effects of cholesterol deficiency in vertebrates by stimulating the Drosophila sterol regulatory element-binding protein (dSREBP) pathway. Significantly, cardiac-specific elevation of dSREBP signaling adversely affects heart function, reflecting the cardiac eas phenotype, whereas suppressing dSREBP or lipogenic target gene function in eas hearts rescues the cardiac hyperlipidemia and heart function disorders. These findings suggest that dysregulated phospholipid signaling that alters SREBP activity contributes to the progression of impaired heart function in flies and identifies a potential link to lipotoxic cardiac diseases in humans.
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Affiliation(s)
- Hui-Ying Lim
- Development and Aging Program, NASCR (Neuroscience, Aging, and Stem Cell Research) Center, Sanford-Burnham Medical Research Institute, La Jolla, California 92037, USA
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Osborne TF, Espenshade PJ. Evolutionary conservation and adaptation in the mechanism that regulates SREBP action: what a long, strange tRIP it's been. Genes Dev 2009; 23:2578-91. [PMID: 19933148 DOI: 10.1101/gad.1854309] [Citation(s) in RCA: 197] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Sterol regulatory element-binding proteins (SREBPs) are a subfamily of basic helix-loop-helix leucine zipper (bHLH-LZ) transcription factors that are conserved from fungi to humans and are defined by two key features: a signature tyrosine residue in the DNA-binding domain, and a membrane-tethering domain that is a target for regulated proteolysis. Recent studies including genome-wide and model organism approaches indicate SREBPs coordinate cellular lipid metabolism with other cellular physiologic processes. These functions are broadly related as cellular adaptation to environmental changes ranging from nutrient fluctuations to toxin exposure. This review integrates classic features of the SREBP pathway with newer information regarding the regulation and sensing mechanisms that serve to assimilate different cellular physiologic processes for optimal function and growth.
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Affiliation(s)
- Timothy F Osborne
- Department of Molecular Biology and Biochemistry, University of California at Irvine, Irvine, California 92697, USA.
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Seo YK, Zhu B, Jeon TI, Osborne TF. Regulation of steroid 5-alpha reductase type 2 (Srd5a2) by sterol regulatory element binding proteins and statin. Exp Cell Res 2009; 315:3133-9. [PMID: 19500568 DOI: 10.1016/j.yexcr.2009.05.025] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2009] [Revised: 05/09/2009] [Accepted: 05/29/2009] [Indexed: 10/20/2022]
Abstract
In this study, we show that sterol regulatory element binding proteins (SREBPs) regulate expression of Srd5a2, an enzyme that catalyzes the irreversible conversion of testosterone to dihydroxytestosterone in the male reproductive tract and is highly expressed in androgen-sensitive tissues such as the prostate and skin. We show that Srd5a2 is induced in livers and prostate from mice fed a chow diet supplemented with lovastatin plus ezitimibe (L/E), which increases the activity of nuclear SREBP-2. The three fold increase in Srd5a2 mRNA mediated by L/E treatment was accompanied by the induction of SREBP-2 binding to the Srd5a2 promoter detected by a ChIP-chip assay in liver. We identified a SREBP-2 responsive region within the first 300 upstream bases of the mouse Srd5a2 promoter by co-transfection assays which contain a site that bound SREBP-2 in vitro by an EMSA. Srd5a2 protein was also induced in cells over-expressing SREBP-2 in culture. The induction of Srd5a2 through SREBP-2 provides a mechanistic explanation for why even though statin therapy is effective in reducing cholesterol levels in treating hypercholesterolemia it does not compromise androgen production in clinical studies.
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Affiliation(s)
- Young-Kyo Seo
- Department of Molecular Biology and Biochemistry, 3244 McGaugh Hall, University of California, UC Irvine, Irvine, CA 92697-3900, USA
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10
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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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11
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Jeon TI, Zhu B, Larson JL, Osborne TF. SREBP-2 regulates gut peptide secretion through intestinal bitter taste receptor signaling in mice. J Clin Invest 2008; 118:3693-700. [PMID: 18846256 DOI: 10.1172/jci36461] [Citation(s) in RCA: 128] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2008] [Accepted: 08/13/2008] [Indexed: 11/17/2022] Open
Abstract
Bitter taste-sensing G protein-coupled receptors (type 2 taste receptors [T2Rs]) are expressed in taste receptor cells of the tongue, where they play an important role in limiting ingestion of bitter-tasting, potentially toxic compounds. T2Rs are also expressed in gut-derived enteroendocrine cells, where they have also been hypothesized to play a role in limiting toxin absorption. In this study, we have shown that T2R gene expression in both cultured mouse enteroendocrine cells and mouse intestine is regulated by the cholesterol-sensitive SREBP-2. In addition, T2R stimulation of cholecystokinin (CCK) secretion was enhanced directly by SREBP-2 in cultured cells and in mice fed chow supplemented with lovastatin and ezetimibe (L/E) to decrease dietary sterol absorption and increase nuclear activity of SREBP-2. Low-cholesterol diets are naturally composed of high amounts of plant matter that is likely to contain dietary toxins, and CCK is known to improve dietary absorption of fats, slow gastric emptying, and decrease food intake. Thus, these studies suggest that SREBP-2 activation of bitter signaling receptors in the intestine may sensitize the gut to a low-fat diet and to potential accompanying food-borne toxins that make it past the initial aversive response in the mouth.
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Affiliation(s)
- Tae-Il Jeon
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, USA
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Vinci G, Xia X, Veitia RA. Preservation of genes involved in sterol metabolism in cholesterol auxotrophs: facts and hypotheses. PLoS One 2008; 3:e2883. [PMID: 18682733 PMCID: PMC2478713 DOI: 10.1371/journal.pone.0002883] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2008] [Accepted: 07/11/2008] [Indexed: 12/02/2022] Open
Abstract
Background It is known that primary sequences of enzymes involved in sterol biosynthesis are well conserved in organisms that produce sterols de novo. However, we provide evidence for a preservation of the corresponding genes in two animals unable to synthesize cholesterol (auxotrophs): Drosophila melanogaster and Caenorhabditis elegans. Principal Findings We have been able to detect bona fide orthologs of several ERG genes in both organisms using a series of complementary approaches. We have detected strong sequence divergence between the orthologs of the nematode and of the fruitfly; they are also very divergent with respect to the orthologs in organisms able to synthesize sterols de novo (prototrophs). Interestingly, the orthologs in both the nematode and the fruitfly are still under selective pressure. It is possible that these genes, which are not involved in cholesterol synthesis anymore, have been recruited to perform different new functions. We propose a more parsimonious way to explain their accelerated evolution and subsequent stabilization. The products of ERG genes in prototrophs might be involved in several biological roles, in addition to sterol synthesis. In the case of the nematode and the fruitfly, the relevant genes would have lost their ancestral function in cholesterogenesis but would have retained the other function(s), which keep them under pressure. Conclusions By exploiting microarray data we have noticed a strong expressional correlation between the orthologs of ERG24 and ERG25 in D. melanogaster and genes encoding factors involved in intracellular protein trafficking and folding and with Start1 involved in ecdysteroid synthesis. These potential functional connections are worth being explored not only in Drosophila, but also in Caenorhabditis as well as in sterol prototrophs.
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Affiliation(s)
- Giovanna Vinci
- Institut Cochin, Département de Génétique et Développement. Inserm, U567, CNRS, UMR 8104, Université Paris 5, Faculté de Médecine Paris Descartes, UM 3, Paris, France
| | - Xuhua Xia
- CAREG and Biology Department, University of Ottawa, Ottawa, Ontario, Canada
| | - Reiner A. Veitia
- Institut Cochin, Département de Génétique et Développement. Inserm, U567, CNRS, UMR 8104, Université Paris 5, Faculté de Médecine Paris Descartes, UM 3, Paris, France
- Université Denis Diderot/Paris VII, Paris, France
- * E-mail:
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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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14
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Griffin MJ, Wong RHF, Pandya N, Sul HS. Direct interaction between USF and SREBP-1c mediates synergistic activation of the fatty-acid synthase promoter. J Biol Chem 2006; 282:5453-67. [PMID: 17197698 DOI: 10.1074/jbc.m610566200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
To understand the molecular mechanisms underlying transcriptional activation of fatty-acid synthase (FAS), we examined the relationship between upstream stimulatory factor (USF) and SREBP-1c, two transcription factors that we have shown previously to be critical for FAS induction by feeding/insulin. Here, by using a combination of tandem affinity purification and coimmunoprecipitation, we demonstrate, for the first time, that USF and SREBP-1 interact in vitro and in vivo. Glutathione S-transferase pulldown experiments with various USF and sterol regulatory element-binding protein (SREBP) deletion constructs indicate that the basic helix-loop-helix domain of USF interacts directly with the basic helix-loop-helix and an N-terminal region of SREBP-1c. Furthermore, cotransfection of USF and SREBP-1c with an FAS promoter-luciferase reporter construct in Drosophila SL2 cells results in highly synergistic activation of the FAS promoter. We also show similar cooperative activation of the mitochondrial glycerol-3-phosphate acyltransferase promoter by USF and SREBP-1c. Chromatin immunoprecipitation analysis of mouse liver demonstrates that USF binds constitutively to the mitochondrial glycerol 3-phosphate acyltransferase promoter during fasting/refeeding in vivo, whereas binding of SREBP-1 is observed only during refeeding, in a manner identical to that of the FAS promoter. In addition, we show that the synergy we have observed depends on the activation domains of both proteins and that mutated USF or SREBP lacking the N-terminal activation domain could inhibit the transactivation of the other. Closely positioned E-boxes and sterol regulatory elements found in the promoters of several lipogenic genes suggest a common mechanism of induction by feeding/insulin.
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Affiliation(s)
- Michael J Griffin
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720, USA
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15
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Dorner S, Lum L, Kim M, Paro R, Beachy PA, Green R. A genomewide screen for components of the RNAi pathway in Drosophila cultured cells. Proc Natl Acad Sci U S A 2006; 103:11880-5. [PMID: 16882716 PMCID: PMC1525048 DOI: 10.1073/pnas.0605210103] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Posttranscriptional silencing by RNAi is initiated by dsRNAs that are processed into siRNAs that ultimately target homologous mRNAs for degradation. We used luciferase reporter constructs and a cultured cell-based assay to perform a genomewide screen for components of the RNAi pathway in Drosophila melanogaster. The screen identified seven genes that affect the RNAi response, five with previously described function (AGO2, Tis11, Hsc70-3, Hsc70-4, and hdc) and two annotated genes (CG17265 and CG10883).
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Affiliation(s)
- Silke Dorner
- *Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205; and
| | - Lawrence Lum
- *Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205; and
| | - Michelle Kim
- *Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205; and
| | - Renato Paro
- Zentrum für Molekulare Biologie der Universität Heidelberg, D-69120 Heidelberg, Germany
| | - Philip A. Beachy
- *Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205; and
- To whom correspondence may be addressed. E-mail:
or
| | - Rachel Green
- *Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205; and
- To whom correspondence may be addressed. E-mail:
or
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Suh JM, Gao X, McKay J, McKay R, Salo Z, Graff JM. Hedgehog signaling plays a conserved role in inhibiting fat formation. Cell Metab 2006; 3:25-34. [PMID: 16399502 DOI: 10.1016/j.cmet.2005.11.012] [Citation(s) in RCA: 206] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2005] [Revised: 10/10/2005] [Accepted: 11/17/2005] [Indexed: 11/15/2022]
Abstract
Hedgehog (Hh) signals regulate invertebrate and vertebrate development, yet the role of the cascade in adipose development was undefined. To analyze a potential function, we turned to Drosophila and mammalian models. Fat-body-specific transgenic activation of Hh signaling inhibits fly fat formation. Conversely, fat-body-specific Hh blockade stimulated fly fat formation. In mammalian models, sufficiency and necessity tests showed that Hh signaling also inhibits mammalian adipogenesis. Hh signals elicit this function early in adipogenesis, upstream of PPARgamma, potentially diverting preadipocytes as well as multipotent mesenchymal prescursors away from adipogenesis and toward osteogenesis. Hh may elicit these effects by inducing the expression of antiadipogenic transcription factors such as Gata2. These data support the notion that Hh signaling plays a conserved role, from invertebrates to vertebrates, in inhibiting fat formation and highlighting the potential of the Hh pathway as a therapeutic target for osteoporosis, lipodystrophy, diabetes, and obesity.
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Affiliation(s)
- Jae Myoung Suh
- Center for Developmental Biology, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, NB5 118, Dallas, Texas 75390, USA
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17
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Datta S, Wang L, Moore DD, Osborne TF. Regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase promoter by nuclear receptors liver receptor homologue-1 and small heterodimer partner: a mechanism for differential regulation of cholesterol synthesis and uptake. J Biol Chem 2005; 281:807-12. [PMID: 16282330 DOI: 10.1074/jbc.m511050200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cholesterol homeostasis in mammals involves pathways for biosynthesis, cellular uptake, and hepatic conversion to bile acids. Key genes for all three pathways are regulated by negative feedback control. Uptake and biosynthesis are directly regulated by cholesterol through its inhibition of the proteolytic activation of the sterol regulatory element binding proteins. The conversion of cholesterol into bile acids in the liver is regulated through the bile acid-dependent induction of the negatively acting small heterodimer partner nuclear receptor. In this report, we have shown that the small heterodimer partner also directly regulates cholesterol biosynthesis through inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase but has no effect on low density lipoprotein receptor expression. This has significant metabolic significance, as it provides both a mechanism to independently regulate cholesterol synthesis from uptake (an essential regulatory feature known to occur in vivo) and a pathway for direct regulation of cholesterol biosynthesis by bile acids. This latter feature ensures that the early phase of bile acid synthesis (pre-cholesterol) is in metabolic communication with the later stages of the pathway to properly regulate whole pathway flux. This highlights an important regulatory feature that is shared with other key branched, multienzyme pathways, such as glycolysis, where pathway outflow through pyruvate kinase is regulated by the concentration of a key early intermediate, fructose 1,6-bisphosphate.
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Affiliation(s)
- Shrimati Datta
- Department of Molecular Biology and Biochemistry, University of California, Irvine, 92697-3900, USA
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18
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Toth JI, Datta S, Athanikar JN, Freedman LP, Osborne TF. Selective coactivator interactions in gene activation by SREBP-1a and -1c. Mol Cell Biol 2004; 24:8288-300. [PMID: 15340088 PMCID: PMC515064 DOI: 10.1128/mcb.24.18.8288-8300.2004] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Requisite levels of intracellular cholesterol and fatty acids are maintained in part by the sterol regulatory element binding proteins (SREBPs). Three major SREBP isoforms exist; SREBP-1a and SREBP-1c are expressed from overlapping mRNAs, whereas SREBP-2 is encoded by a separate gene. The active forms of SREBP-1a and SREBP-1c differ only at their extreme N termini; SREBP-1c lacks 28 aa present in SREBP-1a and instead contains 4 unique aa of its own. While the SREBP-1a and -1c isoforms differentially activate transcription, the molecular basis of this difference is unknown. Here we define the differences between these proteins that confer the enhanced activity of SREBP-1a and demonstrate that this enhancement is a direct result of its avid binding to the coactivator CREB binding protein (CBP) and the mammalian mediator complex. While previous work determined that the C/H1 zinc finger and KIX domains of CBP bind to SREBP-1a, we provide evidence that the interaction with C/H1 is important for gene activation. We further show that the association between the activation domain of SREBP-1 and mediator is through aa 500 to 824 of DRIP150. Finally, we demonstrate the recruitment of mediator to an SREBP-responsive promoter in a sterol-dependent manner.
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Affiliation(s)
- Julia I Toth
- Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA 92612-3900, USA
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19
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Horn C, Offen N, Nystedt S, Häcker U, Wimmer EA. piggyBac-based insertional mutagenesis and enhancer detection as a tool for functional insect genomics. Genetics 2003; 163:647-61. [PMID: 12618403 PMCID: PMC1462455 DOI: 10.1093/genetics/163.2.647] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Transposon mutagenesis provides a fundamental tool for functional genomics. Here we present a non-species-specific, combined enhancer detection and binary expression system based on the transposable element piggyBac: For the different components of this insertional mutagenesis system, we used widely applicable transposons and distinguishable broad-range transformation markers, which should enable this system to be operational in nonmodel arthropods. In a pilot screen in Drosophila melanogaster, piggyBac mutator elements on the X chromosome were mobilized in males by a Hermes-based jumpstarter element providing piggyBac transposase activity under control of the alpha1-tubulin promoter. As primary reporters in the piggyBac mutator elements, we employed the heterologous transactivators GAL4delta or tTA. To identify larval and adult enhancer detectors, strains carrying UASp-EYFP or TRE-EYFP as secondary reporter elements were used. Tissue-specific enhancer activities were readily observed in the GAL4delta/UASp-based systems, but only rarely in the tTA/TRE system. Novel autosomal insertions were recovered with an average jumping rate of 80%. Of these novel insertions, 3.8% showed homozygous lethality, which was reversible by piggyBac excision. Insertions were found in both coding and noncoding regions of characterized genes and also in noncharacterized and non-P-targeted CG-number genes. This indicates that piggyBac will greatly facilitate the intended saturation mutagenesis in Drosophila.
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Affiliation(s)
- Carsten Horn
- Lehrstuhl für Genetik, Universität Bayreuth, 95447 Bayreuth, Germany
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20
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Tittiger C, Barkawi LS, Bengoa CS, Blomquist GJ, Seybold SJ. Structure and juvenile hormone-mediated regulation of the HMG-CoA reductase gene from the Jeffrey pine beetle, Dendroctonus jeffreyi. Mol Cell Endocrinol 2003; 199:11-21. [PMID: 12581875 DOI: 10.1016/s0303-7207(02)00358-1] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In several pine bark beetle species, juvenile hormone (JH) III regulated 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-R) gene expression has an important role in monoterpenoid pheromone production in males. We investigated the structure and regulated expression of the HMG-R gene (HMG-R) in the Jeffrey pine beetle, Dendroctonus jeffreyi. cDNA and genomic sequences were recovered using a combination of library screening and PCR. The transcribed portion of the gene spans 9.8 kb and is interrupted by 13 introns. When compared to vertebrate HMG-Rs, the distribution of intron sites suggests a functional role for those in the 5' untranslated region and membrane anchor domains. Northern blots show that topically applied JH III stimulates HMG-R expression up to 30-fold in male D. jeffreyi, compared to untreated insects, in both a dose- and time-dependent manner. There was no increase in expression levels in similarly treated female insects. The expression pattern is consistent with the production of monoterpenoid pheromone components in male D. jeffreyi, and suggests the utility of the system as a new tool for studying the mechanism of JH action.
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Affiliation(s)
- Claus Tittiger
- Department of Biochemistry, Mail Stop 330, University of Nevada, Reno 89557, USA.
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21
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Seegmiller AC, Dobrosotskaya I, Goldstein JL, Ho YK, Brown MS, Rawson RB. The SREBP pathway in Drosophila: regulation by palmitate, not sterols. Dev Cell 2002; 2:229-38. [PMID: 11832248 DOI: 10.1016/s1534-5807(01)00119-8] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
In mammals, synthesis of cholesterol and unsaturated fatty acids is controlled by SREBPs, a family of membrane-bound transcription factors. Here, we show that the Drosophila genome encodes all components of the SREBP pathway, including a single SREBP (dSREBP), SREBP cleavage-activating protein (dSCAP), and the two proteases that process SREBP at sites 1 and 2 to release the nuclear fragment. In cultured Drosophila S2 cells, dSREBP is processed at sites 1 and 2, and the liberated fragment increases mRNAs encoding enzymes of fatty acid biosynthesis, but not sterol or isoprenoid biosynthesis. Processing requires dSCAP, but is not inhibited by sterols as in mammals. Instead, dSREBP processing is blocked by palmitic acid. These findings suggest that the ancestral SREBP pathway functions to maintain membrane integrity rather than to control cholesterol homeostasis.
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Affiliation(s)
- Adam C Seegmiller
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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22
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Edwards PA, Ericsson J. Sterols and isoprenoids: signaling molecules derived from the cholesterol biosynthetic pathway. Annu Rev Biochem 2000; 68:157-85. [PMID: 10872447 DOI: 10.1146/annurev.biochem.68.1.157] [Citation(s) in RCA: 341] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Compounds derived from the isoprenoid/cholesterol biosynthetic pathway have recently been shown to have novel biological activities. These compounds include certain sterols, oxysterols, farnesol, and geranylgeraniol, as well as the diphosphate derivatives of isopentenyl, geranyl, farnesyl, geranylgeranyl, and presqualene. They regulate transcriptional and post-transcriptional events that in turn affect lipid synthesis, meiosis, apoptosis, developmental patterning, protein cleavage, and protein degradation.
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Affiliation(s)
- P A Edwards
- Department of Biological Chemistry, University of California Los Angeles 90095, USA.
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23
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Abstract
Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.
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Affiliation(s)
- G J Schroepfer
- Departments of Biochemistry, Rice University, Houston, Texas, USA.
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24
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Nagoshi E, Imamoto N, Sato R, Yoneda Y. Nuclear import of sterol regulatory element-binding protein-2, a basic helix-loop-helix-leucine zipper (bHLH-Zip)-containing transcription factor, occurs through the direct interaction of importin beta with HLH-Zip. Mol Biol Cell 1999; 10:2221-33. [PMID: 10397761 PMCID: PMC25438 DOI: 10.1091/mbc.10.7.2221] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The sterol regulatory element-binding protein-2 (SREBP-2) is produced as a large precursor molecule attached to the endoplasmic reticulum membrane. In response to the sterol depletion, the N-terminal segment of the precursor, which contains a basic helix-loop-helix-leucine zipper domain, is released by two sequential cleavages and is translocated to the nucleus, where it activates the transcription of target genes. The data herein show that released SREBP-2 uses a distinct nuclear transport pathway, which is mediated by importin beta. The mature form of SREBP-2 is actively transported into the nucleus when injected into the cell cytoplasm. SREBP-2 binds directly to importin beta in the absence of importin alpha. Ran-GTP but not Ran-GDP causes the dissociation of the SREBP-2-importin beta complex. G19VRan-GTP inhibits the nuclear import of SREBP-2 in living cells. In the permeabilized cell in vitro transport system, nuclear import of SREBP-2 is reconstituted only by importin beta in conjunction with Ran and its interacting protein p10/NTF2. We further demonstrate that the helix-loop-helix-leucine zipper motif of SREBP-2 contains a novel type of nuclear localization signal, which binds directly to importin beta.
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Affiliation(s)
- E Nagoshi
- Department of Anatomy and Cell Biology, Osaka University Medical School, Osaka 565-0871, Japan
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25
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Pai JT, Guryev O, Brown MS, Goldstein JL. Differential stimulation of cholesterol and unsaturated fatty acid biosynthesis in cells expressing individual nuclear sterol regulatory element-binding proteins. J Biol Chem 1998; 273:26138-48. [PMID: 9748295 DOI: 10.1074/jbc.273.40.26138] [Citation(s) in RCA: 170] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Three sterol regulatory element-binding proteins (SREBP-1a, -1c, and -2) stimulate transcription of genes involved in synthesis and receptor-mediated uptake of cholesterol and fatty acids. Here, we explore the individual roles of each SREBP by preparing lines of Chinese hamster ovary (CHO) cells that express graded amounts of nuclear forms of each SREBP (designated nSREBPs) under control of a muristerone-inducible nuclear receptor system. The parental hamster cell line (M19 cells) lacks its own nSREBPs, owing to a deletion in the gene encoding the Site-2 protease, which releases nSREBPs from cell membranes. By varying the concentration of muristerone, we obtained graded expression of individual nSREBPs in the range that restored lipid synthesis to near physiologic levels. The results show that nSREBP-2 produces a higher ratio of synthesis of cholesterol over fatty acids than does nSREBP-1a. This is due in part to a selective ability of low levels of nSREBP-2, but not nSREBP-1a, to activate the promoter for squalene synthase. nSREBP-1a and -2 both activate transcription of the genes encoding stearoyl-CoA desaturase-1 and -2, thereby markedly enhancing the production of monounsaturated fatty acids. nSREBP-1c was inactive in stimulating any transcription at the concentrations achieved in these studies. The current data support the emerging view that the nSREBPs act in complementary ways to modulate the lipid composition of cell membranes.
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Affiliation(s)
- J T Pai
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA
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