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Girik V, Feng S, Hariri H, Henne WM, Riezman H. Vacuole-Specific Lipid Release for Tracking Intracellular Lipid Metabolism and Transport in Saccharomyces cerevisiae. ACS Chem Biol 2022; 17:1485-1494. [PMID: 35667650 PMCID: PMC9207805 DOI: 10.1021/acschembio.2c00120] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Lipid metabolism is spatiotemporally regulated within cells, yet intervention into lipid functions at subcellular resolution remains difficult. Here, we report a method that enables site-specific release of sphingolipids and cholesterol inside the vacuole in Saccharomyces cerevisiae. Using this approach, we monitored real-time sphingolipid metabolic flux out of the vacuole by mass spectrometry and found that the endoplasmic reticulum-vacuole-tethering protein Mdm1 facilitated the metabolism of sphingoid bases into ceramides. In addition, we showed that cholesterol, once delivered into yeast using our method, could restore cell proliferation induced by ergosterol deprivation, overcoming the previously described sterol-uptake barrier under aerobic conditions. Together, these data define a new way to study intracellular lipid metabolism and transport from the vacuole in yeast.
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Affiliation(s)
- Vladimir Girik
- Department of Biochemistry, University of Geneva, Geneva 1205, Switzerland
| | - Suihan Feng
- Department of Biochemistry, University of Geneva, Geneva 1205, Switzerland.,National Centre of Competence in Research (NCCR) in Chemical Biology, University of Geneva, Geneva 1205, Switzerland
| | - Hanaa Hariri
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, Texas 75390-9039 United States
| | - W Mike Henne
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, Texas 75390-9039 United States
| | - Howard Riezman
- Department of Biochemistry, University of Geneva, Geneva 1205, Switzerland
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2
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Lieu MH, Vallejos MJ, Michael E, Tsunoda S. Mechanisms underlying stage-1 TRPL channel translocation in Drosophila photoreceptors. PLoS One 2012; 7:e31622. [PMID: 22363689 PMCID: PMC3282777 DOI: 10.1371/journal.pone.0031622] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2010] [Accepted: 01/16/2012] [Indexed: 11/22/2022] Open
Abstract
BACKGROUND TRP channels function as key mediators of sensory transduction and other cellular signaling pathways. In Drosophila, TRP and TRPL are the light-activated channels in photoreceptors. While TRP is statically localized in the signaling compartment of the cell (the rhabdomere), TRPL localization is regulated by light. TRPL channels translocate out of the rhabdomere in two distinct stages, returning to the rhabdomere with dark-incubation. Translocation of TRPL channels regulates their availability, and thereby the gain of the signal. Little, however, is known about the mechanisms underlying this trafficking of TRPL channels. METHODOLOGY/PRINCIPAL FINDINGS We first examine the involvement of de novo protein synthesis in TRPL translocation. We feed flies cycloheximide, verify inhibition of protein synthesis, and test for TRPL translocation in photoreceptors. We find that protein synthesis is not involved in either stage of TRPL translocation out of the rhabdomere, but that re-localization to the rhabdomere from stage-1, but not stage-2, depends on protein synthesis. We also characterize an ex vivo eye preparation that is amenable to biochemical and genetic manipulation. We use this preparation to examine mechanisms of stage-1 TRPL translocation. We find that stage-1 translocation is: induced with ATP depletion, unaltered with perturbation of the actin cytoskeleton or inhibition of endocytosis, and slowed with increased membrane sterol content. CONCLUSIONS/SIGNIFICANCE Our results indicate that translocation of TRPL out of the rhabdomere is likely due to protein transport, and not degradation/re-synthesis. Re-localization from each stage to the rhabdomere likely involves different strategies. Since TRPL channels can translocate to stage-1 in the absence of ATP, with no major requirement of the cytoskeleton, we suggest that stage-1 translocation involves simple diffusion through the apical membrane, which may be regulated by release of a light-dependent anchor in the rhabdomere.
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Affiliation(s)
- Minh-Ha Lieu
- Department of Biology, Boston University, Boston, Massachusetts, United States of America
| | - Maximiliano J. Vallejos
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Emily Michael
- Department of Biology, Boston University, Boston, Massachusetts, United States of America
| | - Susan Tsunoda
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
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Georgiev AG, Sullivan DP, Kersting MC, Dittman JS, Beh CT, Menon AK. Osh proteins regulate membrane sterol organization but are not required for sterol movement between the ER and PM. Traffic 2011; 12:1341-55. [PMID: 21689253 DOI: 10.1111/j.1600-0854.2011.01234.x] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Sterol transport between the endoplasmic reticulum (ER) and plasma membrane (PM) occurs by an ATP-dependent, non-vesicular mechanism that is presumed to require sterol transport proteins (STPs). In Saccharomyces cerevisiae, homologs of the mammalian oxysterol-binding protein (Osh1-7) have been proposed to function as STPs. To evaluate this proposal we took two approaches. First we used dehydroergosterol (DHE) to visualize sterol movement in living cells by fluorescence microscopy. DHE was introduced into the PM under hypoxic conditions and observed to redistribute to lipid droplets on growing the cells aerobically. Redistribution required ATP and the sterol acyltransferase Are2, but did not require PM-derived transport vesicles. DHE redistribution occurred robustly in a conditional yeast mutant (oshΔ osh4-1(ts)) that lacks all functional Osh proteins at 37°C. In a second approach we used a pulse-chase protocol to analyze the movement of metabolically radiolabeled ergosterol from the ER to the PM. Arrival of radiolabeled ergosterol at the PM was assessed in isolated PM-enriched fractions as well as by extracting sterols from intact cells with methyl-β-cyclodextrin. These experiments revealed that whereas ergosterol is transported effectively from the ER to the PM in Osh-deficient cells, the rate at which it moves within the PM to equilibrate with the methyl-β-cyclodextrin extractable sterol pool is slowed. We conclude (i) that the role of Osh proteins in non-vesicular sterol transport between the PM, ER and lipid droplets is either minimal, or subsumed by other mechanisms and (ii) that Osh proteins regulate the organization of sterols at the PM.
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Sanxaridis PD, Cronin MA, Rawat SS, Waro G, Acharya U, Tsunoda S. Light-induced recruitment of INAD-signaling complexes to detergent-resistant lipid rafts in Drosophila photoreceptors. Mol Cell Neurosci 2007; 36:36-46. [PMID: 17689976 PMCID: PMC2034437 DOI: 10.1016/j.mcn.2007.05.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2006] [Revised: 05/19/2007] [Accepted: 05/31/2007] [Indexed: 12/01/2022] Open
Abstract
Here, we reveal a novel feature of the dynamic organization of signaling components in Drosophila photoreceptors. We show that the multi-PDZ protein INAD and its target proteins undergo light-induced recruitment to detergent-resistant membrane (DRM) rafts. Reduction of ergosterol, considered to be a key component of lipid rafts in Drosophila, resulted in a loss of INAD-signaling complexes associated with DRM fractions. Genetic analysis demonstrated that translocation of INAD-signaling complexes to DRM rafts requires activation of the entire phototransduction cascade, while constitutive activation of the light-activated channels resulted in recruitment of complexes to DRM rafts in the dark. Mutations affecting INAD and TRP showed that PDZ4 and PDZ5 domains of INAD, as well as the INAD-TRP interaction, are required for translocation of components to DRM rafts. Finally, selective recruitment of phosphorylated, and therefore activatable, eye-PKC to DRM rafts suggests that DRM domains are likely to function in signaling, rather than trafficking.
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Affiliation(s)
| | - Michelle A. Cronin
- Department of Biology, Boston University, 5 Cummington Street, Boston, MA
| | - Satinder S. Rawat
- Program is Gene Function and Expression, University of Massachusetts Medical School, Worcester, MA
| | - Girma Waro
- Department of Biology, Boston University, 5 Cummington Street, Boston, MA
| | - Usha Acharya
- Program is Gene Function and Expression, University of Massachusetts Medical School, Worcester, MA
| | - Susan Tsunoda
- Department of Biology, Boston University, 5 Cummington Street, Boston, MA
- *Address correspondence to: Susan Tsunoda, Department of Biology, Boston University, 5 Cummington Street, Boston, MA 02215, Telephone: 617-358-1756, FAX: 617-353-8484,
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Gyetvai A, Emri T, Takács K, Dergez T, Fekete A, Pesti M, Pócsi I, Lenkey B. Lovastatin possesses a fungistatic effect against Candida albicans, but does not trigger apoptosis in this opportunistic human pathogen. FEMS Yeast Res 2007; 6:1140-8. [PMID: 17156011 DOI: 10.1111/j.1567-1364.2006.00097.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Lovastatin inhibited the growth of Candida albicans in a fungistatic way. Although it triggers apoptosis in a great variety of eukaryotic cells, including many tumour cell lines, lovastatin failed to provoke apoptotic events in this human pathogen. The fungistatic behaviour of this statin might arise from its negative influence on membrane fluidity. Because yeast-->pseudomycelium and hyphae morphogenetic transitions took place under exposure to lovastatin morphogenetic switch and apoptotic cell death must be regulated independently in C. albicans.
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Affiliation(s)
- Agnes Gyetvai
- Department of Microbiology and Biotechnology, Faculty of Science, University of Debrecen, Debrecen, Hungary
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Souza CM, Pichler H. Lipid requirements for endocytosis in yeast. Biochim Biophys Acta Mol Cell Biol Lipids 2007; 1771:442-54. [PMID: 16997624 DOI: 10.1016/j.bbalip.2006.08.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2006] [Revised: 08/10/2006] [Accepted: 08/10/2006] [Indexed: 01/19/2023]
Abstract
Endocytosis is, besides secretion, the most prominent membrane transport pathway in eukaryotic cells. In membrane transport, defined areas of the donor membranes engulf solutes of the compartment they are bordering and bud off with the aid of coat proteins to form vesicles. These transport vehicles are guided along cytoskeletal paths, often matured and, finally, fuse to the acceptor membrane they are targeted to. Lipids and proteins are equally important components in membrane transport pathways. Not only are they the structural units of membranes and vesicles, but both classes of molecules also participate actively in membrane transport processes. Whereas proteins form the cytoskeleton and vesicle coats, confer signals and constitute attachment points for membrane-membrane interaction, lipids modulate the flexibility of bilayers, carry protein recognition sites and confer signals themselves. Over the last decade it has been realized that all classes of bilayer lipids, glycerophospholipids, sphingolipids and sterols, actively contribute to functional membrane transport, in particular to endocytosis. Thus, abnormal bilayer lipid metabolism leads to endocytic defects of different severity. Interestingly, there seems to be a great deal of interdependence and interaction among lipid classes. It will be a challenge to characterize this plenitude of interactions and find out about their impact on cellular processes.
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Czabany T, Athenstaedt K, Daum G. Synthesis, storage and degradation of neutral lipids in yeast. Biochim Biophys Acta Mol Cell Biol Lipids 2007; 1771:299-309. [PMID: 16916618 DOI: 10.1016/j.bbalip.2006.07.001] [Citation(s) in RCA: 166] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2006] [Revised: 07/05/2006] [Accepted: 07/05/2006] [Indexed: 11/30/2022]
Abstract
The single cell eukaryote Saccharomyces cerevisiae is an attractive model to study the complex process of neutral lipid (triacylglycerol and steryl ester) synthesis, storage and turnover. In mammals, defects in the metabolism of these lipids are associated with a number of severe diseases such as atherosclerosis, obesity and type II diabetes. Since the yeast harbors many counterparts of mammalian enzymes involved in these pathways, conclusions drawn from research with the microorganism can be readily applied to the higher eukaryotic system. Here, we summarize our current knowledge of yeast neutral lipid metabolism, report about pathways and enzymes contributing to formation and degradation of triacylglycerols and steryl esters, and describe storage of these components in lipid particles. The interplay of different subcellular compartments in neutral lipid metabolism, regulatory aspects of this process and cell biological consequences of dysfunctions will be discussed.
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Affiliation(s)
- Tibor Czabany
- Institute of Biochemistry, Graz University of Technology, Petersgasse 12/2, A-8010 Graz, Austria
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Lucas ME, Ma Q, Cunningham D, Peters J, Cattanach B, Bard M, Elmore BK, Herman GE. Identification of two novel mutations in the murine Nsdhl sterol dehydrogenase gene and development of a functional complementation assay in yeast. Mol Genet Metab 2003; 80:227-33. [PMID: 14567972 DOI: 10.1016/s1096-7192(03)00137-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Nsdhl is a 3beta-hydroxysterol dehydrogenase that is involved in the removal of C-4 methyl groups in the cholesterol biosynthetic pathway. Mutations in this gene are associated with the X-linked male lethal mouse mutations bare patches (Bpa) and striated (Str) and human CHILD syndrome. We have now detected the missense mutations V53D and A94T in conserved amino acids in two additional Bpa alleles. The latter alters the same amino acid as a missense mutation found in two unrelated CHILD patients, strongly suggesting that differences in the phenotype between Bpa mice and females with CHILD syndrome are unlikely to be explained by different types or sites of mutations. We have also demonstrated that the mouse NSDHL protein can rescue the lethality of erg26 deficient cells of Saccharomyces cerevisiae that lack the yeast ortholog, substantiating the role of NSDHL as a C-3 sterol dehydrogenase. Using this in vivo assay, we have demonstrated that two Str alleles function as hypomorphs, while three Bpa and one Str allele provide no complementation or rescue.
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Affiliation(s)
- Marsha E Lucas
- Department of Pediatrics, Center for Molecular and Human Genetics, Columbus Children's Research Institute, 700 Children's Dr Rm W403, Columbus, OH 43205, USA
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Heese-Peck A, Pichler H, Zanolari B, Watanabe R, Daum G, Riezman H. Multiple functions of sterols in yeast endocytosis. Mol Biol Cell 2002; 13:2664-80. [PMID: 12181337 PMCID: PMC117933 DOI: 10.1091/mbc.e02-04-0186] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Sterols are essential factors for endocytosis in animals and yeast. To investigate the sterol structural requirements for yeast endocytosis, we created a variety of ergDelta mutants, each accumulating a distinct set of sterols different from ergosterol. Mutant erg2Deltaerg6Delta and erg3Deltaerg6Delta cells exhibit a strong internalization defect of the alpha-factor receptor (Ste2p). Specific sterol structures are necessary for pheromone-dependent receptor hyperphosphorylation, a prerequisite for internalization. The lack of phosphorylation is not due to a defect in Ste2p localization or in ligand-receptor interaction. Contrary to most known endocytic factors, sterols seem to function in internalization independently of actin. Furthermore, sterol structures are required at a postinternalization step of endocytosis. ergDelta cells were able to take up the membrane marker FM4-64, but exhibited defects in FM4-64 movement through endosomal compartments to the vacuole. Therefore, there are at least two roles for sterols in endocytosis. Based on sterol analysis, the sterol structural requirements for these two processes were different, suggesting that sterols may have distinct functions at different places in the endocytic pathway. Interestingly, sterol structures unable to support endocytosis allowed transport of the glycosylphosphatidylinositol-anchored protein Gas1p from the endoplasmic reticulum to Golgi compartment.
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11
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Valachovic M, Klobucníková V, Griac P, Hapala I. Heme-regulated expression of two yeast acyl-CoA:sterol acyltransferases is involved in the specific response of sterol esterification to anaerobiosis. FEMS Microbiol Lett 2002; 206:121-5. [PMID: 11786267 DOI: 10.1111/j.1574-6968.2002.tb10996.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Sterol esterification in Saccharomyces cerevisiae is catalyzed by two acyl-CoA:sterol acyltransferases encoded by the genes ARE1 and ARE2. Using double mutants in the HEM1 gene and individual ARE genes we demonstrated that the relative contribution of these two enzymes to sterol esterification was dependent on cellular heme status. Observed changes in sterol esterification could be explained by a different effect of heme on the transcription of both genes: while the ARE1 transcript level was elevated in heme-deficient and anaerobic cells, the ARE2 gene transcript was more abundant in aerobic cells competent for heme synthesis. Our results indicate that transcriptional regulation of ARE genes by heme and specific substrate preferences of Are1p and Are2p may be involved in the adaptation of yeast sterol metabolism to hypoxia.
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Affiliation(s)
- Martin Valachovic
- Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, 900 28, Ivanka pri Dunaji, Slovak Republic
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12
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Jensen-Pergakes K, Guo Z, Giattina M, Sturley SL, Bard M. Transcriptional regulation of the two sterol esterification genes in the yeast Saccharomyces cerevisiae. J Bacteriol 2001; 183:4950-7. [PMID: 11489845 PMCID: PMC95368 DOI: 10.1128/jb.183.17.4950-4957.2001] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Saccharomyces cerevisiae transcribes two genes, ARE1 and ARE2, that contribute disproportionately to the esterification of sterols. Are2p is the major enzyme isoform in a wild-type cell growing aerobically. This likely results from a combination of differential transcription initiation and transcript stability. By using ARE1 and ARE2 promoter fusions to lacZ reporters, we demonstrated that transcriptional initiation from the ARE1 promoter is significantly reduced compared to that from the ARE2 promoter. Furthermore, the half-life of the ARE2 mRNA is approximately 12 times as long as that of the ARE1 transcript. We present evidence that the primary role of the minor sterol esterification isoform encoded by ARE1 is to esterify sterol intermediates, whereas the role of the ARE2 enzyme is to esterify ergosterol, the end product of the pathway. Accordingly, the ARE1 promoter is upregulated in strains that accumulate ergosterol precursors. Furthermore, ARE1 and ARE2 are oppositely regulated by heme. Under heme-deficient growth conditions, ARE1 was upregulated fivefold while ARE2 was down-regulated. ARE2 requires the HAP1 transcription factor for optimal expression, and both ARE genes are derepressed in a rox1 (repressor of oxygen) mutant genetic background. We further report that the ARE genes are not subject to end product inhibition; neither ARE1 nor ARE2 transcription is altered in an are mutant background, nor does overexpression of either ARE gene alter the response of the ARE-lacZ reporter constructs. Our observations are consistent with an important physiological role for Are1p during anaerobic growth when heme is limiting and sterol precursors may accumulate. Conversely, Are2p is optimally required during aerobiosis when ergosterol is plentiful.
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Affiliation(s)
- K Jensen-Pergakes
- Department of Biology, Indiana University-Purdue University at Indianapolis, Indianapolis, Indiana 46202, USA
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13
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Munn AL, Heese-Peck A, Stevenson BJ, Pichler H, Riezman H. Specific sterols required for the internalization step of endocytosis in yeast. Mol Biol Cell 1999; 10:3943-57. [PMID: 10564282 PMCID: PMC25690 DOI: 10.1091/mbc.10.11.3943] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Sterols are major components of the plasma membrane, but their functions in this membrane are not well understood. We isolated a mutant defective in the internalization step of endocytosis in a gene (ERG2) encoding a C-8 sterol isomerase that acts in the late part of the ergosterol biosynthetic pathway. In the absence of Erg2p, yeast cells accumulate sterols structurally different from ergosterol, which is the major sterol in wild-type yeast. To investigate the structural requirements of ergosterol for endocytosis in more detail, several erg mutants (erg2Delta, erg6Delta, and erg2Deltaerg6Delta) were made. Analysis of fluid phase and receptor-mediated endocytosis indicates that changes in the sterol composition lead to a defect in the internalization step. Vesicle formation and fusion along the secretory pathway were not strongly affected in the ergDelta mutants. The severity of the endocytic defect correlates with changes in sterol structure and with the abundance of specific sterols in the ergDelta mutants. Desaturation of the B ring of the sterol molecules is important for the internalization step. A single desaturation at C-8,9 was not sufficient to support internalization at 37 degrees C whereas two double bonds, either at C-5,6 and C-7,8 or at C-5,6 and C-8,9, allowed internalization.
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Affiliation(s)
- A L Munn
- Biozentrum of the University of Basel, CH-4056 Basel, Switzerland
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14
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Leak FW, Tove S, Parks LW. In yeast, upc2-1 confers a decrease in tolerance to LiCl and NaCl, which can be suppressed by the P-type ATPase encoded by ENA2. DNA Cell Biol 1999; 18:133-9. [PMID: 10073572 DOI: 10.1089/104454999315510] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Wild-type yeast cells are unable to take up sterols from their growth media under aerobic conditions and are relatively resistant to monovalent cations. A yeast mutant (upc2-1) with a defect in the aerobic exclusion of sterols was found to have increased sensitivity to LiCl and NaCl. Although cation sensitivity has been reported for mutants that synthesize altered sterols, the mutant with upc2-1 continues to produce the normal sterol, ergosterol. The ENA2 gene was cloned on the basis of remediating the hypersensitivity to the monovalent cations.
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Affiliation(s)
- F W Leak
- Department of Microbiology, North Carolina State University, Raleigh 27695-7615, USA
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15
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Crowley JH, Leak FW, Shianna KV, Tove S, Parks LW. A mutation in a purported regulatory gene affects control of sterol uptake in Saccharomyces cerevisiae. J Bacteriol 1998; 180:4177-83. [PMID: 9696767 PMCID: PMC107415 DOI: 10.1128/jb.180.16.4177-4183.1998] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/1998] [Accepted: 06/14/1998] [Indexed: 11/20/2022] Open
Abstract
Aerobically growing wild-type strains of Saccharomyces cerevisiae are unable to take exogenously supplied sterols from media. This aerobic sterol exclusion is vitiated under anaerobic conditions, in heme-deficient strains, and under some conditions of impaired sterol synthesis. Mutants which can take up sterols aerobically in heme-competent cells have been selected. One of these mutations, designated upc2-1, gives a pleiotropic phenotype in characteristics as diverse as aerobic accumulation of sterols, total lipid storage, sensitivity to metabolic inhibitors, response to altered sterol structures, and cation requirements. During experiments designed to ascertain the effects of various cations on yeast with sterol alterations, it was observed that upc2-1 was hypersensitive to Ca2+. Using resistance to Ca2+ as a screening vehicle, we cloned UPC2 and showed that it is YDR213W, an open reading frame on chromosome IV. This belongs to a fungal regulatory family containing the Zn(II)2Cys6 binuclear cluster DNA binding domain. The single guanine-to-adenine transition in upc2-1 gives a predicted amino acid change from glycine to aspartic acid. The regulatory defect explains the semidominance and pleiotropic effects of upc2-1.
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Affiliation(s)
- J H Crowley
- Department of Microbiology, North Carolina State University, Raleigh, North Carolina 27695-7615, USA
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16
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Sertil O, Cohen BD, Davies KJ, Lowry CV. The DAN1 gene of S. cerevisiae is regulated in parallel with the hypoxic genes, but by a different mechanism. Gene 1997; 192:199-205. [PMID: 9224891 DOI: 10.1016/s0378-1119(97)00028-0] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The DAN1 gene is expressed under anaerobic conditions in yeast and completely repressed during aerobic growth. The function of the gene is unknown, and genetic disruption had no effect on fitness which could be detected, even upon prolonged anaerobic growth. Expression of DAN1 was constitutive in a heme-deficient strain, indicating that heme participates in repression. Expression was blocked by heme in anaerobic medium, suggesting that heme acts as a negative co-effector rather than through its metabolic functions, i.e., in the production of a co-effector. Expression of DAN1 was regulated in parallel with the hypoxic gene ANB1, showing identical kinetics of induction and dose response to heme. However, unlike ANB1, DAN1 is not regulated by the repressor of the hypoxic regulon, ROX1, as shown by observation of normal aerobic repression of DAN1 in a strain carrying a deletion of ROX1. These results indicate the existence of a parallel regulatory system which produces an identical response to oxygen by a different mechanism than that controlling the hypoxic regulon.
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Affiliation(s)
- O Sertil
- Department of Biochemistry and Molecular Biology, Albany Medical College, NY 12208, USA
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17
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Yu C, Kennedy NJ, Chang CC, Rothblatt JA. Molecular cloning and characterization of two isoforms of Saccharomyces cerevisiae acyl-CoA:sterol acyltransferase. J Biol Chem 1996; 271:24157-63. [PMID: 8798656 DOI: 10.1074/jbc.271.39.24157] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Esterification of cholesterol by acyl-CoA:cholesterol acyltransferase (ACAT) is a key element in maintaining cholesterol homeostasis in cells of higher animals. In the budding yeast, Saccharomyces cerevisiae, accumulation of ergosteryl esters accompanies entry into stationary phase and sporulation. We have determined that two genes in yeast, SAT1 and SAT2, encode isozymes of acyl-CoA:sterol acyltransferase (ASAT) which are functionally related to ACAT. The SAT1 isozyme is the major catalytic isoform, accounting for at least 65-75% of total ASAT activity. Targeted deletions of one or both genes do not compromise mitotic cell growth or spore germination. However, diploids that are homozygous for a SAT1 null mutation exhibit significantly reduced sporulation efficiency. Furthermore, a larger fraction of the sporulating diploids arrest after the first meiotic division. Human ACAT expressed in sat1 sat2 mutant cells can catalyze esterification of cholesterol and, to a lesser extent, ergosterol in vitro, but restores ergosteryl oleate formation in vivo to only approximately 8% of that catalyzed by yeast ASAT in wild-type cells.
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Affiliation(s)
- C Yu
- Department of Biological Sciences, Dartmouth College, Dartmouth Medical School, Hanover, New Hampshire 03755, USA
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18
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