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Hamdani EH, Gudbrandsen M, Bjørkmo M, Chaudhry FA. The system N transporter SN2 doubles as a transmitter precursor furnisher and a potential regulator of NMDA receptors. Glia 2012; 60:1671-83. [PMID: 22821889 DOI: 10.1002/glia.22386] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Revised: 06/14/2012] [Accepted: 06/15/2012] [Indexed: 12/28/2022]
Abstract
Activation of NMDA receptor requires two co-agonists, glutamate and glycine. Despite its intrinsic role in brain functions molecular mechanisms involved in glutamate replenishment and identification of the origin of glycine have eluded characterization. We have performed direct measurements of glycine flux by SN2 (Slc38a5; also known as SNAT5), executed extensive electrophysiological characterization as well as implemented ratiometric analyses to show that SN2 transport resembles SN1 in mechanism but differ in functional implications. We report that rat SN2 mediates electroneutral and bidirectional transport of glutamine and glycine at perisynaptic astroglial membranes. Sophisticated coupled and uncoupled movements of H(+) differentially associate with glutamine and glycine transport by SN2 and regulate pH(i) and the release mode of the transporter. Consequently, SN2 doubles as a transmitter precursor furnisher and a potential regulator of NMDA receptors.
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Affiliation(s)
- El Hassan Hamdani
- The Biotechnology Center and Center for Molecular Biology and Neuroscience, University of Oslo, Blindern, Oslo, Norway
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Chaudhry FA, Krizaj D, Larsson P, Reimer RJ, Wreden C, Storm-Mathisen J, Copenhagen D, Kavanaugh M, Edwards RH. Coupled and uncoupled proton movement by amino acid transport system N. EMBO J 2001; 20:7041-51. [PMID: 11742981 PMCID: PMC125789 DOI: 10.1093/emboj/20.24.7041] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The system N transporter SN1 has been proposed to mediate the efflux of glutamine from cells required to sustain the urea cycle and the glutamine-glutamate cycle that regenerates glutamate and gamma-aminobutyric acid (GABA) for synaptic release. We now show that SN1 also mediates an ionic conductance activated by glutamine, and this conductance is selective for H(+). Although SN1 couples amino acid uptake to H(+) exchange, the glutamine-gated H(+) conductance is not stoichiometrically coupled to transport. Protons thus permeate SN1 both coupled to and uncoupled from amino acid flux, providing novel mechanisms to regulate the transfer of glutamine between cells.
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Affiliation(s)
- Farrukh A. Chaudhry
- Departments of
Neurology and Physiology, Graduate Programs in Neuroscience, Cell Biology and Biomedical Sciences, UCSF School of Medicine, 513 Parnassus Avenue, San Francisco, CA 94143-0435, Vollum Institute, Oregon Health Sciences University, OR, USA and Department of Anatomy, University of Oslo, Oslo, Norway Corresponding author e-mail:
| | - David Krizaj
- Departments of
Neurology and Physiology, Graduate Programs in Neuroscience, Cell Biology and Biomedical Sciences, UCSF School of Medicine, 513 Parnassus Avenue, San Francisco, CA 94143-0435, Vollum Institute, Oregon Health Sciences University, OR, USA and Department of Anatomy, University of Oslo, Oslo, Norway Corresponding author e-mail:
| | - Peter Larsson
- Departments of
Neurology and Physiology, Graduate Programs in Neuroscience, Cell Biology and Biomedical Sciences, UCSF School of Medicine, 513 Parnassus Avenue, San Francisco, CA 94143-0435, Vollum Institute, Oregon Health Sciences University, OR, USA and Department of Anatomy, University of Oslo, Oslo, Norway Corresponding author e-mail:
| | - Richard J. Reimer
- Departments of
Neurology and Physiology, Graduate Programs in Neuroscience, Cell Biology and Biomedical Sciences, UCSF School of Medicine, 513 Parnassus Avenue, San Francisco, CA 94143-0435, Vollum Institute, Oregon Health Sciences University, OR, USA and Department of Anatomy, University of Oslo, Oslo, Norway Corresponding author e-mail:
| | - Christopher Wreden
- Departments of
Neurology and Physiology, Graduate Programs in Neuroscience, Cell Biology and Biomedical Sciences, UCSF School of Medicine, 513 Parnassus Avenue, San Francisco, CA 94143-0435, Vollum Institute, Oregon Health Sciences University, OR, USA and Department of Anatomy, University of Oslo, Oslo, Norway Corresponding author e-mail:
| | - Jon Storm-Mathisen
- Departments of
Neurology and Physiology, Graduate Programs in Neuroscience, Cell Biology and Biomedical Sciences, UCSF School of Medicine, 513 Parnassus Avenue, San Francisco, CA 94143-0435, Vollum Institute, Oregon Health Sciences University, OR, USA and Department of Anatomy, University of Oslo, Oslo, Norway Corresponding author e-mail:
| | - David Copenhagen
- Departments of
Neurology and Physiology, Graduate Programs in Neuroscience, Cell Biology and Biomedical Sciences, UCSF School of Medicine, 513 Parnassus Avenue, San Francisco, CA 94143-0435, Vollum Institute, Oregon Health Sciences University, OR, USA and Department of Anatomy, University of Oslo, Oslo, Norway Corresponding author e-mail:
| | - Michael Kavanaugh
- Departments of
Neurology and Physiology, Graduate Programs in Neuroscience, Cell Biology and Biomedical Sciences, UCSF School of Medicine, 513 Parnassus Avenue, San Francisco, CA 94143-0435, Vollum Institute, Oregon Health Sciences University, OR, USA and Department of Anatomy, University of Oslo, Oslo, Norway Corresponding author e-mail:
| | - Robert H. Edwards
- Departments of
Neurology and Physiology, Graduate Programs in Neuroscience, Cell Biology and Biomedical Sciences, UCSF School of Medicine, 513 Parnassus Avenue, San Francisco, CA 94143-0435, Vollum Institute, Oregon Health Sciences University, OR, USA and Department of Anatomy, University of Oslo, Oslo, Norway Corresponding author e-mail:
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Fei YJ, Sugawara M, Nakanishi T, Huang W, Wang H, Prasad PD, Leibach FH, Ganapathy V. Primary structure, genomic organization, and functional and electrogenic characteristics of human system N 1, a Na+- and H+-coupled glutamine transporter. J Biol Chem 2000; 275:23707-17. [PMID: 10823827 DOI: 10.1074/jbc.m002282200] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have cloned the human Na(+)- and H(+)-coupled amino acid transport system N (hSN1) from HepG2 liver cells and investigated its functional characteristics. Human SN1 protein consists of 504 amino acids and shows high homology to rat SN1 and rat brain glutamine transporter (GlnT). When expressed in mammalian cells, the transport function of human SN1 could be demonstrated with glutamine as the substrate in the presence of LiCl (instead of NaCl) and cysteine. The transport activity was saturable, pH-sensitive, and specific for glutamine, histidine, asparagine, and alanine. Analysis of Li(+) activation kinetics showed a Li(+):glutamine stoichiometry of 2:1. When expressed in Xenopus laevis oocytes, the transport of glutamine or asparagine via human SN1 was associated with inward currents under voltage-clamped conditions. The transport function, monitored as glutamine- or asparagine-induced currents, was saturable, Na(+)-dependent, Li(+)-tolerant, and pH-sensitive. The transport cycle was associated with the involvement of more than one Na(+) ion. Uptake of asparagine was directly demonstrable in these oocytes by using radiolabeled substrate, and this uptake was inhibited by membrane depolarization. In addition, simultaneous measurement of asparagine influx and charge influx in the same oocyte yielded an asparagine:charge ratio of 1. These data suggest that SN1 mediates the influx of two Na(+) and one amino acid substrate per transport cycle coupled to the efflux of one H(+), rendering the transport process electrogenic.
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Affiliation(s)
- Y J Fei
- Departments of Biochemistry and Molecular Biology, and Obstetrics and Gynecology, Medical College of Georgia, Augusta, Georgia 30912, USA
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Kadowaki T, Chen S, Hitomi M, Jacobs E, Kumagai C, Liang S, Schneiter R, Singleton D, Wisniewska J, Tartakoff AM. Isolation and characterization of Saccharomyces cerevisiae mRNA transport-defective (mtr) mutants. J Cell Biol 1994; 126:649-59. [PMID: 8045930 PMCID: PMC2120137 DOI: 10.1083/jcb.126.3.649] [Citation(s) in RCA: 139] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
To understand the mechanisms of mRNA transport in eukaryotes, we have isolated Saccharomyces cerevisiae temperature-sensitive (ts) mutants which accumulate poly(A)+ RNA in the nucleus at the restrictive temperature. A total of 21 recessive mutants were isolated and classified into 16 complementation groups. Backcrossed mRNA transport-defective strains from each complementation group have been analyzed. A strain which is ts for heat shock transcription factor was also analyzed since it also shows nuclear accumulation of poly(A)+ RNA at 37 degrees C. At 37 degrees C the mRNA of each mutant is characterized by atypically long polyA tails. Unlike ts pre-mRNA splicing mutants, these strains do not interrupt splicing of pre-mRNA at 37 degrees C; however four strains accumulate oversized RNA polymerase II transcripts. Some show inhibition of rRNA processing and a further subset of these strains is also characterized by inhibition of tRNA maturation. Several strains accumulate nuclear proteins in the cytoplasm when incubated at semipermissive temperature. Remarkably, many strains exhibit nucleolar fragmentation or enlargement at the restrictive temperature. Most strains show dramatic ultrastructural alterations of the nucleoplasm or nuclear membrane. Distinct mutants accumulate poly(A)+ RNA in characteristic patterns in the nucleus.
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Affiliation(s)
- T Kadowaki
- Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106
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McDaniel LD, Schultz RA. Elevation of sister chromatid exchange frequency in transformed human fibroblasts following exposure to widely used aminoglycosides. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 1993; 21:67-72. [PMID: 8419155 DOI: 10.1002/em.2850210109] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Aminoglycosides are a class of antibiotics that interfere with protein translation. Geneticin and hygromycin are two such agents, which have been shown to exhibit highly toxic effects in mammalian cells. Cloned bacterial genes, which inactivate these antibiotics, have facilitated the establishment of dominant selection systems, which are widely used in eukaryotic molecular genetics. We have examined the effect of aminoglycosides on the sister chromatid exchange (SCE) frequency in transformed human fibroblast cell lines. Geneticin and hygromycin were both found to increase SCE frequency in all cell lines examined, including a cell line derived from a patient with Bloom syndrome, a disorder exhibiting an elevated spontaneous SCE frequency. Induction was seen to occur in a dose-responsive manner and was also observed in cells expressing the resistance genes that inactivate the cellular toxicity of these antibiotics. The implications of these findings for somatic cell genetics and for human gene therapy protocols are discussed.
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Affiliation(s)
- L D McDaniel
- Medical Biotechnology Center, University of Maryland, Baltimore 21201
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Flejter WL, McDaniel LD, Askari M, Friedberg EC, Schultz RA. Characterization of a complex chromosomal rearrangement maps the locus for in vitro complementation of xeroderma pigmentosum group D to human chromosome band 19q13. Genes Chromosomes Cancer 1992; 5:335-42. [PMID: 1283322 DOI: 10.1002/gcc.2870050409] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Microcell-mediated chromosome transfer (MMCT) is a powerful genetic technique that permits the transfer of a single chromosome from one mammalian cell to another. The utility of MMCT for gene mapping strategies is critically dependent on the careful characterization of the chromosomes being transferred. We have recently reported the identification of a single rearranged human chromosome, designated Tneo, which corrects the UV sensitivity and excision repair defect of cells of xeroderma pigmentosum genetic complementation group D (XP-D) in culture (Flejter WL et al., Proc Natl Acad Sci USA 89:261-265, 1992). Additionally, those studies demonstrated a role for the excision repair cross-complementing 2 (ERCC2) gene in the observed phenotypic correction. We now report the results of detailed conventional and molecular cytogenetic characterization of the complementing Tneo chromosome. This analysis revealed a complex rearrangement involving material from human chromosomes 16, 17, and 19. Characterization of deletions of Tneo which retained or lost XP-D complementing ability mapped the gene responsible for phenotypic correction to a small region of the terminal q-arm of this chromosome. This region includes the previously described human DNA repair gene cluster located in the region 19q13.2-q13.3, a result consistent with the notion that the in vitro correction of XP-D cells by the Tneo chromosome is rendered by the ERCC2 locus. The data illustrate the potential value of detailed cytogenetic characterization of a human chromosome present in a somatic cell hybrid, even when that material involves complex rearrangements.
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Affiliation(s)
- W L Flejter
- Division of Human Genetics, University of Maryland, Baltimore 21201
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Flejter WL, McDaniel LD, Johns D, Friedberg EC, Schultz RA. Correction of xeroderma pigmentosum complementation group D mutant cell phenotypes by chromosome and gene transfer: involvement of the human ERCC2 DNA repair gene. Proc Natl Acad Sci U S A 1992; 89:261-5. [PMID: 1729695 PMCID: PMC48216 DOI: 10.1073/pnas.89.1.261] [Citation(s) in RCA: 110] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Cultured cells from individuals afflicted with the genetically heterogeneous autosomal recessive disorder xeroderma pigmentosum (XP) exhibit sensitivity to UV radiation and defective nucleotide excision repair. Complementation of these mutant phenotypes after the introduction of single human chromosomes from repair-proficient cells into XP cells has provided a means of mapping the genes involved in this disease. We now report the phenotypic correction of XP cells from genetic complementation group D (XP-D) by a single human chromosome designated Tneo. Detailed molecular characterization of Tneo revealed a rearranged structure involving human chromosomes 16 and 19, including the excision repair cross-complementing 2 (ERCC2) gene from the previously described human DNA repair gene cluster at 19q13.2-q13.3. Direct transfer of a cosmid bearing the ERCC2 gene conferred UV resistance to XP-D cells.
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Affiliation(s)
- W L Flejter
- Division of Human Genetics, University of Maryland, Baltimore 21201
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Pouysségur J, Chambard JC, L'Allemain G, Magnaldo I, Seuwen K. Transmembrane signalling pathways initiating cell growth in fibroblasts. Philos Trans R Soc Lond B Biol Sci 1988; 320:427-36. [PMID: 2906148 DOI: 10.1098/rstb.1988.0086] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The mechanisms of growth factor action were studied in a fibroblastic cell line capable of reversible growth arrest in G0-G1. This cell line, derived from Chinese hamster lung, can be stimulated to divide by a limited set of purified growth factors, including EGF, FGF, PDGF, alpha-thrombin (THR), serotonin (5-HT) and insulin. THR and 5-HT stimulate, via a G-protein (Gp), a polyphosphoinositide-specific phospholipase C (PtdIns(4,5)P2-PLC). In contrast, the mitogens EGF, FGF, PDGF, and insulin do not stimulate PtdIns(4,5)P2-PLC unless this pathway has been preactivated by THR or AlF-4. Finally, from the specific inhibitory action of pertussis toxin on THR- and 5-HT-induced DNA synthesis, and from the exploitation of the 5-HT pharmacological tools, we conclude that: (i) there are at least two distinct G-proteins involved in signalling growth: Gp, coupling receptors to PtdIns(4,5)P2-PLC, and Gi, coupling receptors negatively to adenylyl cyclase and probably to other unknown effector(s); (ii) activation of receptor-tyrosine kinases provides an alternate growth factor signalling pathway, independent of Gp- and Gi-mediated actions; and (iii) tyrosine kinases positively 'cross-communicate' with the inositol-lipid pathway (phosphorylation of Gp, PLC, PtdIns kinases...?).
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