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Regulation of the inositol transporter Itr1p by hydrogen peroxide in Saccharomyces cerevisiae. Arch Microbiol 2018; 201:123-134. [PMID: 30283989 DOI: 10.1007/s00203-018-1584-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2018] [Revised: 09/25/2018] [Accepted: 09/28/2018] [Indexed: 10/28/2022]
Abstract
Myo-inositol is a precursor of several membrane phospholipids and sphingolipids and plays a key role in gene regulation in Saccharomyces cerevisiae (S. cerevisiae). Here, we tested whether H2O2 was affecting the levels of the inositol transporters and thus inositol uptake. In S. cerevisiae cells adapted to H2O2 Itr1-GFPp accumulated in the plasma membrane until 20 min, concomitantly with an inhibition of its internalization. Exposure to H2O2 did not alter Itr2-GFPp cellular levels and induced only an 8% decrease at 10 min in the plasma membrane. Therefore, decreased inositol intracellular levels are not caused by decreased levels of inositol transporters in the plasma membrane. However, results show that H2O2 adaptation affects Itr1p turnover and, consequently, H2O2-adapted yeast cells display an inositol transporter phenotype comparable to cells grown in the absence of inositol in growth medium, i.e. accumulation in the plasma membrane and decreased degradation.
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2
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Chen N, Wang J, Zhao Y, Deng Y. Metabolic engineering of Saccharomyces cerevisiae for efficient production of glucaric acid at high titer. Microb Cell Fact 2018; 17:67. [PMID: 29729665 PMCID: PMC5935971 DOI: 10.1186/s12934-018-0914-y] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2018] [Accepted: 04/24/2018] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND Glucaric acid is a high-value-added chemical that can be used in various fields. Because chemical oxidation of glucose to produce glucaric acid is not environmentally friendly, microbial production has attracted increasing interest recently. Biological pathways to synthesize glucaric acid from glucose in both Escherichia coli and Saccharomyces cerevisiae by co-expression of genes encoding myo-inositol-1-phosphate synthase (Ino1), myo-inositol oxygenase (MIOX), and uronate dehydrogenase (Udh) have been constructed. However, low activity and instability of MIOX from Mus musculus was proved to be the bottleneck in this pathway. RESULTS A more stable miox4 from Arabidopsis thaliana was chosen in the present study. In addition, high copy delta-sequence integration of miox4 into the S. cerevisiae genome was performed to increase its expression level further. Enzymatic assay and quantitative real-time PCR analysis revealed that delta-sequence-based integrative expression increased MIOX4 activity and stability, thus increasing glucaric acid titer about eight times over that of episomal expression. By fed-batch fermentation supplemented with 60 mM (10.8 g/L) inositol, the multi-copy integrative expression S. cerevisiae strain produced 6 g/L (28.6 mM) glucaric acid from myo-inositol, the highest titer that had been ever reported in S. cerevisiae. CONCLUSIONS In this study, glucaric acid titer was increased to 6 g/L in S. cerevisiae by integrating the miox4 gene from A. thaliana and the udh gene from Pseudomonas syringae into the delta sequence of genomes. Delta-sequence-based integrative expression increased both the number of target gene copies and their stabilities. This approach could be used for a wide range of metabolic pathway engineering applications with S. cerevisiae.
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Affiliation(s)
- Na Chen
- National Engineering Laboratory for Cereal Fermentation Technology (NELCF), Jiangnan University, 1800 Lihu Road, Wuxi, 214122 Jiangsu China
- School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122 Jiangsu China
| | - Jingya Wang
- National Engineering Laboratory for Cereal Fermentation Technology (NELCF), Jiangnan University, 1800 Lihu Road, Wuxi, 214122 Jiangsu China
- School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122 Jiangsu China
| | - Yunying Zhao
- National Engineering Laboratory for Cereal Fermentation Technology (NELCF), Jiangnan University, 1800 Lihu Road, Wuxi, 214122 Jiangsu China
- School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122 Jiangsu China
| | - Yu Deng
- National Engineering Laboratory for Cereal Fermentation Technology (NELCF), Jiangnan University, 1800 Lihu Road, Wuxi, 214122 Jiangsu China
- School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122 Jiangsu China
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3
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Lauretta R, Lanzolla G, Vici P, Mariani L, Moretti C, Appetecchia M. Insulin-Sensitizers, Polycystic Ovary Syndrome and Gynaecological Cancer Risk. Int J Endocrinol 2016; 2016:8671762. [PMID: 27725832 PMCID: PMC5048026 DOI: 10.1155/2016/8671762] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Revised: 07/12/2016] [Accepted: 08/08/2016] [Indexed: 12/28/2022] Open
Abstract
Preclinical, early phase clinical trials and epidemiological evidence support the potential role of insulin-sensitizers in cancer prevention and treatment. Insulin-sensitizers improve the metabolic and hormonal profile in PCOS patients and may also act as anticancer agents, especially in cancers associated with hyperinsulinemia and oestrogen dependent cancers. Several lines of evidence support the protection against cancer exerted by dietary inositol, in particular inositol hexaphosphate. Metformin, thiazolidinediones, and myoinositol postreceptor signaling may exhibit direct inhibitory effects on cancer cell growth. AMPK, the main molecular target of metformin, is emerging as a target for cancer prevention and treatment. PCOS may be correlated to an increased risk for developing ovarian and endometrial cancer (up to threefold). Several studies have demonstrated an increase in mortality rate from ovarian cancer among overweight/obese PCOS women compared with normal weight women. Long-term use of metformin has been associated with lower rates of ovarian cancer. Considering the evidence supporting a higher risk of gynaecological cancer in PCOS women, we discuss the potential use of insulin-sensitizers as a potential tool for chemoprevention, hypothesizing a possible rationale through which insulin-sensitizers may inhibit tumourigenesis.
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Affiliation(s)
- Rosa Lauretta
- Unit of Endocrinology, Regina Elena National Cancer Institute, Rome, Italy
| | - Giulia Lanzolla
- Unit of Endocrinology, Department of Systems' Medicine, University of Rome Tor Vergata, Section of Reproductive Endocrinology, Fatebenefratelli Hospital “San Giovanni Calibita” Rome, Italy
| | - Patrizia Vici
- Division of Medical Oncology B, Regina Elena National Cancer Institute, Rome, Italy
| | - Luciano Mariani
- Department of Gynaecologic Oncology, HPV-Unit, Regina Elena National Cancer Institute, Rome, Italy
| | - Costanzo Moretti
- Unit of Endocrinology, Department of Systems' Medicine, University of Rome Tor Vergata, Section of Reproductive Endocrinology, Fatebenefratelli Hospital “San Giovanni Calibita” Rome, Italy
| | - Marialuisa Appetecchia
- Unit of Endocrinology, Regina Elena National Cancer Institute, Rome, Italy
- *Marialuisa Appetecchia:
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Finding the sweet spot: how human fungal pathogens acquire and turn the sugar inositol against their hosts. mBio 2015; 6:e00109. [PMID: 25736882 PMCID: PMC4358016 DOI: 10.1128/mbio.00109-15] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Inositol is an essential nutrient with important structural and signaling functions in eukaryotes. Its role in microbial pathogenesis has been reported in fungi, protozoans, and eubacteria. In a recent article, Porollo et al. [mBio 5(6):e01834-14, 2014, doi:10.1128/mBio.01834-14] demonstrated the importance of inositol metabolism in the development and viability of Pneumocystis species—obligate fungal pathogens that remain unculturable in vitro. To understand their obligate nature, the authors used innovative comparative genomic approaches and discovered that Pneumocystis spp. are inositol auxotrophs due to the lack of inositol biosynthetic enzymes and that inositol insufficiency is a contributing factor preventing fungal growth in vitro. This work is in accord with other studies suggesting that inositol plays a conserved role in microbial pathogenesis. Inositol uptake and metabolism therefore may represent novel antimicrobial drug targets. Using comparative genomics to analyze metabolic pathways offers a powerful tool to gain new insights into nutrient utilization in microbes, especially obligate pathogens.
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5
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Two major inositol transporters and their role in cryptococcal virulence. EUKARYOTIC CELL 2011; 10:618-28. [PMID: 21398509 DOI: 10.1128/ec.00327-10] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Cryptococcus neoformans is an AIDS-associated human fungal pathogen and the most common cause of fungal meningitis, with a mortality rate over 40% in AIDS patients. Significant advances have been achieved in understanding its disease mechanisms. Yet the underlying mechanism of a high frequency of cryptococcal meningitis remains unclear. The existence of high inositol concentrations in brain and our earlier discovery of a large inositol transporter (ITR) gene family in C. neoformans led us to investigate the potential role of inositol in Cryptococcus-host interactions. In this study, we focus on functional analyses of two major ITR genes to understand their role in virulence of C. neoformans. Our results show that ITR1A and ITR3C are the only two ITR genes among 10 candidates that can complement the growth defect of a Saccharomyces cerevisiae strain lacking inositol transporters. Both S. cerevisiae strains heterologously expressing ITR1A or ITR3C showed high inositol uptake activity, an indication that they are major inositol transporters. Significantly, itr1a itr3c double mutants showed significant virulence attenuation in murine infection models. Mutating both ITR1A and ITR3C in an ino1 mutant background activates the expression of several remaining ITR candidates and does not show more severe virulence attenuation, suggesting that both inositol uptake and biosynthetic pathways are important for inositol acquisition. Overall, our study provides evidence that host inositol and fungal inositol transporters are important for Cryptococcus pathogenicity.
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6
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Role of an expanded inositol transporter repertoire in Cryptococcus neoformans sexual reproduction and virulence. mBio 2010; 1. [PMID: 20689743 PMCID: PMC2912663 DOI: 10.1128/mbio.00084-10] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2010] [Accepted: 03/18/2010] [Indexed: 12/15/2022] Open
Abstract
Cryptococcus neoformans and Cryptococcus gattii are globally distributed human fungal pathogens and the leading causes of fungal meningitis. Recent studies reveal that myo-inositol is an important factor for fungal sexual reproduction. That C. neoformans can utilize myo-inositol as a sole carbon source and the existence of abundant inositol in the human central nervous system suggest that inositol is important for Cryptococcus development and virulence. In accord with this central importance of inositol, an expanded myo-inositol transporter (ITR) gene family has been identified in Cryptococcus. This gene family contains two phylogenetically distinct groups, with a total of 10 or more members in C. neoformans and at least six members in the sibling species C. gattii. These inositol transporter genes are differentially expressed under inositol-inducing conditions based on quantitative real-time PCR analyses. Expression of ITR genes in a Saccharomyces cerevisiae itr1 itr2 mutant lacking inositol transport can complement the slow-growth phenotype of this strain, confirming that ITR genes are bona fide inositol transporters. Gene mutagenesis studies reveal that the Itr1 and Itr1A transporters are important for myo-inositol stimulation of mating and that functional redundancies among the myo-inositol transporters likely exist. Deletion of the inositol 1-phosphate synthase gene INO1 in an itr1 or itr1a mutant background compromised virulence in a murine inhalation model, indicating the importance of inositol sensing and acquisition for fungal infectivity. Our study provides a platform for further understanding the roles of inositol in fungal physiology and virulence. Cryptococcus neoformans is an AIDS-associated human fungal pathogen that causes over 1 million cases of meningitis annually and is the leading cause of fungal meningitis in immunosuppressed patients. The initial cryptococcal infection is caused predominantly via inhalation of sexual spores or desiccated yeast cells from the environment. How this fungus completes its sexual cycle and produces infectious spores in nature and why it frequently infects the central nervous system to cause fatal meningitis are critical questions that remain to be understood. In this study, we demonstrate that inositol acquisition is important not only for fungal sexual reproduction but also for fungal virulence. We identified an expanded inositol transporter gene family that contains over 10 members, important for both fungal sexual reproduction and virulence. Our work contributes to our understanding of how fungi respond to the environmental inositol availability and its impact on sexual reproduction and virulence.
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Ethylbutyrate, a valproate-like compound, exhibits inositol-depleting effects — A potential mood-stabilizing drug. Life Sci 2009; 84:38-44. [DOI: 10.1016/j.lfs.2008.10.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2008] [Revised: 10/19/2008] [Accepted: 10/28/2008] [Indexed: 11/23/2022]
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8
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Alcázar-Román AR, Wente SR. Inositol polyphosphates: a new frontier for regulating gene expression. Chromosoma 2007; 117:1-13. [DOI: 10.1007/s00412-007-0126-4] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2007] [Revised: 09/12/2007] [Accepted: 09/13/2007] [Indexed: 10/22/2022]
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Azab AN, He Q, Ju S, Li G, Greenberg ML. Glycogen synthase kinase‐3 is required for optimalde novosynthesis of inositol. Mol Microbiol 2007; 63:1248-58. [PMID: 17257308 DOI: 10.1111/j.1365-2958.2007.05591.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Studies have shown that the inositol biosynthetic pathway and the enzyme glycogen synthase kinase-3 (GSK-3) are targets of the mood-stabilizing drugs lithium and valproate. However, a relationship between these targets has not been previously described. We hypothesized that GSK-3 may play a role in inositol synthesis, and that loss of GSK-3 may lead to inositol depletion, thus providing a mechanistic link between the two drug targets. Utilizing a yeast Saccharomyces cerevisiae gsk-3Delta quadruple-null mutant, in which all four genes encoding homologues of mammalian GSK-3 are disrupted, we tested the hypothesis that GSK-3 is required for de novo inositol biosynthesis. The gsk-3Delta mutant exhibited multiple features of inositol depletion, including defective growth in inositol-lacking medium, decreased intracellular inositol, increased INO1 and ITR1 expression, and decreased levels of phosphatidylinositol. Treatment of wild-type cells with a highly specific GSK-3 inhibitor led to a significant increase in INO1 expression. Supplementation with inositol alleviated the temperature sensitivity of gsk-3Delta. Activity of myo-inositol-3 phosphate synthase, the rate-limiting enzyme in inositol de novo biosynthesis, was decreased in gsk-3Delta. These results demonstrate for the first time that GSK-3 is required for optimal myo-inositol-3 phosphate synthase activity and de novo inositol biosynthesis, and that loss of GSK-3 activity causes inositol depletion.
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Affiliation(s)
- Abed N Azab
- Department of Biological Sciences, Wayne State University, Detroit, MI 48202, USA
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10
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Schneider S, Schneidereit A, Konrad KR, Hajirezaei MR, Gramann M, Hedrich R, Sauer N. Arabidopsis INOSITOL TRANSPORTER4 mediates high-affinity H+ symport of myoinositol across the plasma membrane. PLANT PHYSIOLOGY 2006; 141:565-77. [PMID: 16603666 PMCID: PMC1475457 DOI: 10.1104/pp.106.077123] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Four genes of the Arabidopsis (Arabidopsis thaliana) monosaccharide transporter-like superfamily share significant homology with transporter genes previously identified in the common ice plant (Mesembryanthemum crystallinum), a model system for studies on salt tolerance of higher plants. These ice plant transporters had been discussed as tonoplast proteins catalyzing the inositol-dependent efflux of Na(+) ions from vacuoles. The subcellular localization and the physiological role of the homologous proteins in the glycophyte Arabidopsis were unclear. Here we describe Arabidopsis INOSITOL TRANSPORTER4 (AtINT4), the first member of this subgroup of Arabidopsis monosaccharide transporter-like transporters. Functional analyses of the protein in yeast (Saccharomyces cerevisiae) and Xenopus laevis oocytes characterize this protein as a highly specific H(+) symporter for myoinositol. These activities and analyses of the subcellular localization of an AtINT4 fusion protein in Arabidopsis and tobacco (Nicotiana tabacum) reveal that AtINT4 is located in the plasma membrane. AtINT4 promoter-reporter gene plants demonstrate that AtINT4 is strongly expressed in Arabidopsis pollen and phloem companion cells. The potential physiological role of AtINT4 is discussed.
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Affiliation(s)
- Sabine Schneider
- Molekulare Pflanzenphysiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany
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11
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Oliveira R, Lucas C. Expression studies of GUP1 and GUP2, genes involved in glycerol active transport in Saccharomyces cerevisiae, using semi-quantitative RT-PCR. Curr Genet 2004; 46:140-6. [PMID: 15278288 DOI: 10.1007/s00294-004-0519-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2004] [Revised: 06/08/2004] [Accepted: 06/21/2004] [Indexed: 10/26/2022]
Abstract
Glycerol active uptake in Saccharomyces cerevisiae, characterised physiologically as a proton symport, was previously described as repressed by glucose, induced by growth on non-fermentable carbon sources and unresponsive to growth under salt stress. GUP1 and GUP2 were identified and characterised as genes involved in glycerol active uptake. Using semi-quantitative RT-PCR, GUP1 and GUP2 transcription was measured. Unlike active transport activity determined previously, this was shown to be constitutive and not affected by either glucose repression or growth under salt stress. Furthermore, transcription of GUP1 and GUP2 was not affected in the gpd1gpd2 mutant strain grown under salt stress in the presence of small amounts of glycerol, in which case a very high Vmax of glycerol uptake was reported. Intracellular compounds were determined. Glycerol, acetate and trehalose were found to be the major compounds accumulated. Surprisingly, the gpd1gpd2 mutant was found to produce significant amounts of glycerol. Yet, the results provide no evidence for a correlation between the amount of each compound and the glycerol transport activity in any of the strains.
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Affiliation(s)
- Rui Oliveira
- Departamento de Biologia Campus de Gualtar, Centro de Biologia da Universidade do Minho (CB-UM), Braga, Portugal
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12
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Miyashita M, Shugyo M, Nikawa JI. Mutational analysis and localization of the inositol transporters of Saccharomyces cerevisiae. J Biosci Bioeng 2003. [DOI: 10.1016/s1389-1723(03)80196-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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13
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Jansen MLA, De Winde JH, Pronk JT. Hxt-carrier-mediated glucose efflux upon exposure of Saccharomyces cerevisiae to excess maltose. Appl Environ Microbiol 2002; 68:4259-65. [PMID: 12200274 PMCID: PMC124116 DOI: 10.1128/aem.68.9.4259-4265.2002] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2002] [Accepted: 06/18/2002] [Indexed: 11/20/2022] Open
Abstract
When wild-type Saccharomyces cerevisiae strains pregrown in maltose-limited chemostat cultures were exposed to excess maltose, release of glucose into the external medium was observed. Control experiments confirmed that glucose release was not caused by cell lysis or extracellular maltose hydrolysis. To test the hypothesis that glucose efflux involved plasma membrane glucose transporters, experiments were performed with an S. cerevisiae strain in which all members of the hexose transporter (HXT) gene family had been eliminated and with an isogenic reference strain. Glucose efflux was virtually eliminated in the hexose-transport-deficient strain. This constitutes experimental proof that Hxt transporters facilitate export of glucose from S. cerevisiae cells. After exposure of the hexose-transport-deficient strain to excess maltose, an increase in the intracellular glucose level was observed, while the concentrations of glucose 6-phosphate and ATP remained relatively low. These results demonstrate that glucose efflux can occur as a result of uncoordinated expression of the initial steps of maltose metabolism and the subsequent reactions in glucose dissimilation. This is a relevant phenomenon for selection of maltose-constitutive strains for baking and brewing.
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Affiliation(s)
- Mickel L A Jansen
- Kluyver Laboratory of Biotechnology, Delft University of Technology, 2628 BC Delft, The Netherlands
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Lucero P, Moreno E, Lagunas R. Catabolite inactivation of the sugar transporters in Saccharomyces cerevisiae is inhibited by the presence of a nitrogen source. FEMS Yeast Res 2002; 1:307-14. [PMID: 12702334 DOI: 10.1111/j.1567-1364.2002.tb00049.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Saccharomyces cerevisiae uses glucose preferentially to any other carbon source and this preferential use is ensured by control mechanisms triggered by glucose. The consensus is that inactivation of sugar transporters other than glucose transporters is one of these mechanisms. This inactivation is called catabolite inactivation because of its apparent analogy with the catabolite inactivation of gluconeogenic enzymes. Recently, doubt has been cast on the role of the inactivation of the sugar transporters in controlling the use of glucose because this inactivation neither is specifically triggered by glucose nor specifically affects non-glucose sugar transporters. Based on the fact that this inactivation has been almost exclusively investigated using nitrogen-starved cells, it has been proposed that it might be due to the stimulation of the protein turnover that follows nitrogen starvation. The results obtained in this work support this possibility since they show that the presence of a nitrogen source in the medium strongly inhibited the inactivation. It is concluded that, in growing yeast cells, the contribution of the inactivation by glucose of the non-glucose sugar transporters to the preferential use of glucose is much lower than generally believed.
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Affiliation(s)
- Pilar Lucero
- Instituto de Investigaciones Biomédicas Alberto Sols, Consejo Superior de Investigaciones Científicas, Arturo Duperier, 4, 28029 Madrid, Spain
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Séron K, Blondel MO, Haguenauer-Tsapis R, Volland C. Uracil-induced down-regulation of the yeast uracil permease. J Bacteriol 1999; 181:1793-800. [PMID: 10074071 PMCID: PMC93577 DOI: 10.1128/jb.181.6.1793-1800.1999] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In Saccharomyces cerevisiae the FUR4-encoded uracil permease catalyzes the first step of the pyrimidine salvage pathway. The availability of uracil has a negative regulatory effect upon its own transport. Uracil causes a decrease in the level of uracil permease, partly by decreasing the FUR4 mRNA level in a promoter-independent fashion, probably by increasing its instability. Uracil entry also triggers more rapid degradation of the existing permease by promoting high efficiency of ubiquitination of the permease that signals its internalization. A direct binding of intracellular uracil to the permease is possibly involved in this feedback regulation, as the behavior of the permease is similar in mutant cells unable to convert intracellular uracil into UMP. We used cells impaired in the ubiquitination step to show that the addition of uracil produces rapid inhibition of uracil transport. This may be the first response prior to the removal of the permease from the plasma membrane. Similar down-regulation of uracil uptake, involving several processes, was observed under adverse conditions mainly corresponding to a decrease in the cellular content of ribosomes. These results suggest that uracil of exogenous or catabolic origin down-regulates the cognate permease to prevent buildup of excess intracellular uracil-derived nucleotides.
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Affiliation(s)
- K Séron
- Institut Jacques Monod, CNRS/Université Paris 7-Denis Diderot 2, 75251 Paris Cedex 05, France
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Nelson, Koukoumanos, Bohnert. Myo-inositol-dependent sodium uptake in ice plant. PLANT PHYSIOLOGY 1999; 119:165-72. [PMID: 9880357 PMCID: PMC32215 DOI: 10.1104/pp.119.1.165] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/1998] [Accepted: 09/08/1998] [Indexed: 05/18/2023]
Abstract
In salt-stressed ice plants (Mesembryanthemum crystallinum), sodium accumulates to high concentrations in vacuoles, and polyols (myo-inositol, D-ononitol, and D-pinitol) accumulate in the cytosol. Polyol synthesis is regulated by NaCl and involves induction and repression of gene expression (D.E. Nelson, B. Shen, and H.J. Bohnert [1998] Plant Cell 10: 753-764). In the study reported here we found increased phloem transport of myo-inositol and reciprocal increased transport of sodium and inositol to leaves under stress. To determine the relationship between increased translocation and sodium uptake, we analyzed the effects of exogenous application of myo-inositol: The NaCl-inducible ice plant myo-inositol 1-phosphate synthase is repressed in roots, and sodium uptake from root to shoot increases without stimulating growth. Sodium uptake and transport through the xylem was coupled to a 10-fold increase of myo-inositol and ononitol in the xylem. Seedlings of the ice plant are not salt-tolerant, and yet the addition of exogenous myo-inositol conferred upon them patterns of gene expression and polyol accumulation observed in mature, salt-tolerant plants. Sodium uptake and transport through the xylem was enhanced in the presence of myo-inositol. The results indicate an interdependence of sodium uptake and alterations in the distribution of myo-inositol. We hypothesize that myo-inositol could serve not only as a substrate for the production of compatible solutes but also as a leaf-to-root signal that promotes sodium uptake.
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Affiliation(s)
- Nelson
- Department of Biochemistry (D.E.N., M.K., H.J.B.)
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17
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Medintz I, Jiang H, Michels CA. The role of ubiquitin conjugation in glucose-induced proteolysis of Saccharomyces maltose permease. J Biol Chem 1998; 273:34454-62. [PMID: 9852113 DOI: 10.1074/jbc.273.51.34454] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In Saccharomyces, the addition of glucose induces a rapid degradation of maltose permease that is dependent on endocytosis and vacuolar proteolysis (Medintz, I., Jiang, H., Han, E. K., Cui, W., and Michels, C. A. (1996) J. Bacteriol. 178, 2245-2254). Here we report on the role of ubiquitin conjugation in this process. Deletion of DOA4, which causes decreased levels of available ubiquitin, severely decreases the rate of glucose-induced proteolysis, and this is suppressed by the overproduction of ubiquitin. Overexpression of ubiquitin in an endocytosis-deficient end3-ts strain results in the glucose-stimulated accumulation of a larger molecular weight species of maltose permease, which we demonstrate is a ubiquitin-modified form of the protein by utilizing two ubiquitin alleles with different molecular weights. The size of this ubiquitinated species of maltose permease is consistent with monoubiquitination. A promoter mutation that reduces expression of RSP5/NPI1, a postulated ubiquitin-protein ligase, dramatically reduces the rate of glucose-induced proteolysis of maltose permease. The role of various ubiquitin-conjugating enzymes was investigated using strains carrying mutant alleles ubc1Delta ubc4Delta, ubc4Delta ubc5Delta, cdc34-ts2/ubc3, and ubc9-ts. Loss of these functions was not shown to effect glucose-induced proteolysis of maltose permease, but loss of Ubc1, -4, and -5 was found to inhibit maltose permease expression at the post-transcriptional level.
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Affiliation(s)
- I Medintz
- Biology Department, Queens College and the Graduate School of the City University of New York, Flushing, New York 11367, USA
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Abstract
The yeast Saccharomyces cerevisiae is a powerful experimental system to study biochemical, cell biological and molecular biological aspects of lipid synthesis. Most but not all genes encoding enzymes involved in fatty acid, phospholipid, sterol or sphingolipid biosynthesis of this unicellular eukaryote have been cloned, and many gene products have been functionally characterized. Less information is available about genes and gene products governing the transport of lipids between organelles and within membranes, turnover and degradation of complex lipids, regulation of lipid biosynthesis, and linkage of lipid metabolism to other cellular processes. Here we summarize current knowledge about lipid biosynthetic pathways in S. cerevisiae and describe the characteristic features of the gene products involved. We focus on recent discoveries in these fields and address questions on the regulation of lipid synthesis, subcellular localization of lipid biosynthetic steps, cross-talk between organelles during lipid synthesis and subcellular distribution of lipids. Finally, we discuss distinct functions of certain key lipids and their possible roles in cellular processes.
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Affiliation(s)
- G Daum
- Institut für Biochemie und Lebensmittelchemie, Technische Universität, Petersgasse, Graz, Austria.
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20
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Henry SA, Patton-Vogt JL. Genetic regulation of phospholipid metabolism: yeast as a model eukaryote. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1998; 61:133-79. [PMID: 9752720 DOI: 10.1016/s0079-6603(08)60826-0] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Baker's yeast, Saccharomyces cerevisiae, is an excellent and an increasingly important model for the study of fundamental questions in eukaryotic cell biology and genetic regulation. The fission yeast, Schizosaccharomyces pombe, although not as intensively studied as S. cerevisiae, also has many advantages as a model system. In this review, we discuss progress over the past several decades in biochemical and molecular genetic studies of the regulation of phospholipid metabolism in these two organisms and higher eukaryotes. In S. cerevisiae, following the recent completion of the yeast genome project, a very high percentage of the gene-enzyme relationships in phospholipid metabolism have been assigned and the remaining assignments are expected to be completed rapidly. Complex transcriptional regulation, sensitive to the availability of phospholipid precusors, as well as growth phase, coordinates the expression of the structural genes encoding these enzymes in S. cerevisiae. In this article, this regulation is described, the mechanism by which the cell senses the ongoing metabolic activity in the pathways for phospholipid biosynthesis is discussed, and a model is presented. Recent information relating to the role of phosphatidylcholine turnover in S. cerevisiae and its relationship to the secretory pathway, as well as to the regulation of phospholipid metabolism, is also presented. Similarities in the role of phospholipase D-mediated phosphatidylcholine turnover in the secretory process in yeast and mammals lend further credence to yeast as a model system.
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Affiliation(s)
- S A Henry
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
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21
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Campbell CL, Thorsness PE. Escape of mitochondrial DNA to the nucleus in yme1 yeast is mediated by vacuolar-dependent turnover of abnormal mitochondrial compartments. J Cell Sci 1998; 111 ( Pt 16):2455-64. [PMID: 9683639 DOI: 10.1242/jcs.111.16.2455] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Inactivation of Yme1p, a mitochondrially-localized ATP-dependent metallo-protease in the yeast Saccharomyces cerevisiae, causes a high rate of DNA escape from mitochondria to the nucleus as well as pleiotropic functional and morphological mitochondrial defects. The evidence presented here suggests that the abnormal mitochondria of a yme1 strain are degraded by the vacuole. First, electron microscopy of Yme1p-deficient strains revealed mitochondria physically associated with the vacuole via electron dense structures. Second, disruption of vacuolar function affected the frequency of mitochondrial DNA escape from yme1 and wild-type strains. Both PEP4 or PRC1 gene disruptions resulted in a lower frequency of mitochondrial DNA escape. Third, an in vivo assay that monitors vacuole-dependent turnover of the mitochondrial compartment demonstrated an increased rate of mitochondrial turnover in yme1 yeast when compared to the rate found in wild-type yeast. In this assay, vacuolar alkaline phosphatase, encoded by PHO8, was targeted to mitochondria in a strain bearing disruption to the genomic PHO8 locus. Maturation of the mitochondrially localized alkaline phosphatase pro-enzyme requires proteinase A, which is localized in the vacuole. Therefore, alkaline phosphatase activity reflects vacuole-dependent turnover of mitochondria. This assay reveals that mitochondria of a yme1 strain are taken up by the vacuole more frequently than mitochondria of an isogenic wild-type strain when these yeast are cultured in medium necessitating respiratory growth. Degradation of abnormal mitochondria is one pathway by which mitochondrial DNA escapes and migrates to the nucleus.
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Affiliation(s)
- C L Campbell
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071-3944, USA
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22
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Cupers P, ter Haar E, Boll W, Kirchhausen T. Parallel dimers and anti-parallel tetramers formed by epidermal growth factor receptor pathway substrate clone 15. J Biol Chem 1997; 272:33430-4. [PMID: 9407139 DOI: 10.1074/jbc.272.52.33430] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The recently discovered localization of epidermal growth factor receptor pathway substrate clone 15 (Eps15) to plasma membrane clathrin-coated pits and its constitutive association with the endocytic clathrin adaptor protein complex, AP-2, strongly suggest that Eps15 has an important role in the pathway of clathrin-dependent endocytic traffic. We report here that Eps15 forms dimers and tetramers of distinct shape. The Eps15 dimer is an elongated molecule, 32 nm in length. There is a globular "head" at one end of the molecule and an extended "stalk" of 25 nm which is kinked at about 17 nm away from the head. In the Eps15 dimer, two subunits are arranged parallel to each other, so that the head corresponds to two side by side copies of the N-terminal region I, which contains the three Eps15 homology domains. The proximal part of the stalk is the coiled-coil central region II containing 20 heptad repeats. The kink is at the boundary between region II and the C-terminal region III, which contains the AP-2 binding site, 15 aspartic-proline-phenylalanine repeats, and proline-rich Src homology domain ligand sites. The Eps15 tetramer has a "dumbbell" shape, approximately 31 nm in length; it is formed by the anti-parallel association of two Eps15 dimers. Formation of these Eps15 tetramers appears to require contacts between regions I of one dimer and regions III of a second apposing dimer. The extended shapes of the Eps15 dimers and tetramers suggest how Eps15 oligomers are located in the clathrin coat. We discuss the implications for accessibility to partners and for proposed functions of Eps15.
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Affiliation(s)
- P Cupers
- Department of Cell Biology, Harvard Medical School and The Center for Blood Research, Boston, Massachusetts 02115, USA
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23
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Di Fiore PP, Pelicci PG, Sorkin A. EH: a novel protein-protein interaction domain potentially involved in intracellular sorting. Trends Biochem Sci 1997; 22:411-3. [PMID: 9397678 DOI: 10.1016/s0968-0004(97)01127-4] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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Tebar F, Confalonieri S, Carter RE, Di Fiore PP, Sorkin A. Eps15 is constitutively oligomerized due to homophilic interaction of its coiled-coil region. J Biol Chem 1997; 272:15413-8. [PMID: 9182572 DOI: 10.1074/jbc.272.24.15413] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Eps15 is a member of an emerging family of proteins containing a novel protein/protein interaction domain, the EH domain, of as yet unknown function. Recent findings of Eps15 association with clathrin adaptor complex AP-2 and its localization in clathrin-coated pits have implicated Eps15 in the regulation of vesicle trafficking. Here we show that Eps15 exists in several multimeric states in vivo. When purified recombinant Eps15 or lysates of NIH 3T3 cells were treated with cross-linking reagents, covalent dimers of Eps15 and larger covalent multimers were detected in high yield. Large Eps15 oligomers co-immunoprecipitated with AP-2 at an efficiency higher than that of Eps15 dimers. Furthermore, cross-linking of the membrane-bound fraction of Eps15 in mildly permeabilized cells was as efficient as that of the cytosolic fraction. Size-exclusion column chromatography of recombinantly produced Eps15 and of total cell lysates was performed to examine the equilibrium ratio of the monomers versus the aggregated forms of Eps15. These experiments showed that essentially all the Eps15 was aggregated, whereas monomers of Eps15 could be obtained only under strong denaturing conditions. To map the region of Eps15 responsible for dimerization, fusion proteins corresponding to the three structural domains of Eps15 were prepared. Cross-linking analysis revealed that the central portion of Eps15, which possesses a coiled-coil region (residues 321-520), serves as the interacting interface. The possibility that hetero-oligomeric complexes of Eps15 dimers and AP-2 function during the recruitment of proteins into coated pits is discussed.
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Affiliation(s)
- F Tebar
- Department of Pharmacology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA
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25
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Abstract
Inositol hexaphosphate (InsP6 or IP6) is ubiquitous. At 10 microM to 1 mM concentrations, IP6 and its lower phosphorylated forms (IP(1-5)) as well as inositol (Ins) are contained in most mammalian cells, wherein they are important in regulating vital cellular functions such as signal transduction, cell proliferation and differentiation. A striking anti-cancer action of IP6 has been demonstrated both in vivo and in vitro, which is based on the hypotheses that exogenously administered IP6 may be internalized, dephosphorylated to IP(1-5), and inhibit cell growth. There is additional evidence that Ins alone may further enhance the anti-cancer effect of IP6. Besides decreasing cellular proliferation, IP6 also causes differentiation of malignant cells often resulting in a reversion to normal phenotype. These data strongly point towards the involvement of signal transduction pathways, cell cycle regulatory genes, differentiation genes, oncogenes and perhaps, tumor suppressor genes in bringing about the observed anti-neoplastic action of IP6.
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Affiliation(s)
- A M Shamsuddin
- University of Maryland School of Medicine, Baltimore 21201-1192, U.S.A
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