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Gómez-Gálvez Y, Palomo-Garo C, Fernández-Ruiz J, García C. Potential of the cannabinoid CB(2) receptor as a pharmacological target against inflammation in Parkinson's disease. Prog Neuropsychopharmacol Biol Psychiatry 2016; 64:200-8. [PMID: 25863279 DOI: 10.1016/j.pnpbp.2015.03.017] [Citation(s) in RCA: 130] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Revised: 03/31/2015] [Accepted: 03/31/2015] [Indexed: 12/13/2022]
Abstract
Inflammation is an important pathogenic factor in Parkinson's disease (PD), so that it can contribute to kill dopaminergic neurons of the substantia nigra and to enhance the dopaminergic denervation of the striatum. The cannabinoid type-2 (CB2) receptor has been investigated as a potential anti-inflammatory and neuroprotective target in different neurodegenerative disorders, but still limited evidence has been collected in PD. Here, we show for the first time that CB2 receptors are elevated in microglial cells recruited and activated at lesioned sites in the substantia nigra of PD patients compared to control subjects. Parkinsonian inflammation can be reproduced experimentally in rodents by intrastriatal injections of lipopolysaccharide (LPS) which, through an intense activation of glial elements and peripheral infiltration, provokes a rapid deterioration of the striatum that may extend to the substantia nigra too. Using this experimental model, we recently described a much more intense deterioration of tyrosine hydroxylase (TH)-containing nigral neurons in CB2 receptor-deficient mice compared to wild-type animals, supporting a potential neuroprotective role for this receptor. In the present study, we further explored this issue. First, we found elevated levels of the CB2 receptor measured by qRT-PCR in the striatum and substantia nigra of LPS-lesioned mice, as well as an increase in the immunostaining for this receptor in the LPS-lesioned striatum. Second, we found a significant increase in CD68 immunostaining, which serve to identify activated microglia and also infiltrated peripheral macrophages, in these brain structures in response to LPS insult, which was much more intense in CB2 receptor-deficient mice in the case of the substantia nigra. Next, we observed that the activation of CB2 receptors with a selective agonist (HU-308) reversed LPS-induced elevation of CD68 immunostaining in the striatum and the parallel reduction in TH immunostaining. Lastly, we found that LPS elevated the gene expression of different pro-inflammatory mediators in both the striatum and the substantia nigra, whereas the selective activation of CB2 receptors reduced a part of these mediators, e.g. inducible nitric oxide synthase, although exclusively in the striatum. In conclusion, we have provided the first evidence on the up-regulation of CB2 receptors in glial elements in postmortem tissues of PD patients, which has been confirmed in an inflammatory model of this disease. In addition, we have provided evidence on the benefits derived from their activation in relation with the activation of microglial cells, the infiltration of macrophages and also certain capability of these cells to generate proinflammatory factors.
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Affiliation(s)
- Yolanda Gómez-Gálvez
- Instituto Universitario de Investigación en Neuroquímica, Departamento de Bioquímica y Biología Molecular III, Facultad de Medicina, Universidad Complutense, Madrid, Spain; Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Madrid, Spain; Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain
| | - Cristina Palomo-Garo
- Instituto Universitario de Investigación en Neuroquímica, Departamento de Bioquímica y Biología Molecular III, Facultad de Medicina, Universidad Complutense, Madrid, Spain; Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Madrid, Spain; Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain
| | - Javier Fernández-Ruiz
- Instituto Universitario de Investigación en Neuroquímica, Departamento de Bioquímica y Biología Molecular III, Facultad de Medicina, Universidad Complutense, Madrid, Spain; Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Madrid, Spain; Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain.
| | - Concepción García
- Instituto Universitario de Investigación en Neuroquímica, Departamento de Bioquímica y Biología Molecular III, Facultad de Medicina, Universidad Complutense, Madrid, Spain; Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Madrid, Spain; Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain.
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Gaccioli F, Aye ILMH, Roos S, Lager S, Ramirez VI, Kanai Y, Powell TL, Jansson T. Expression and functional characterisation of System L amino acid transporters in the human term placenta. Reprod Biol Endocrinol 2015; 13:57. [PMID: 26050671 PMCID: PMC4462079 DOI: 10.1186/s12958-015-0054-8] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/26/2014] [Accepted: 05/28/2015] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND System L transporters LAT1 (SLC7A5) and LAT2 (SLC7A8) mediate the uptake of large, neutral amino acids in the human placenta. Many System L substrates are essential amino acids, thus representing crucial nutrients for the growing fetus. Both LAT isoforms are expressed in the human placenta, but the relative contribution of LAT1 and LAT2 to placental System L transport and their subcellular localisation are not well established. Moreover, the influence of maternal body mass index (BMI) on placental System L amino acid transport is poorly understood. Therefore the aims of this study were to determine: i) the relative contribution of the LAT isoforms to System L transport activity in primary human trophoblast (PHT) cells isolated from term placenta; ii) the subcellular localisation of LAT transporters in human placenta; and iii) placental expression and activity of System L transporters in response to maternal overweight/obesity. METHODS System L mediated leucine uptake was measured in PHT cells after treatment with si-RNA targeting LAT1 and/or LAT2. The localisation of LAT isoforms was studied in isolated microvillous plasma membranes (MVM) and basal membranes (BM) by Western blot analysis. Results were confirmed by immunohistochemistry in sections of human term placenta. Expression and activity System L transporters was measured in isolated MVM from women with varying pre-pregnancy BMI. RESULTS Both LAT1 and LAT2 isoforms contribute to System L transport activity in primary trophoblast cells from human term placenta. LAT1 and LAT2 transporters are highly expressed in the MVM of the syncytiotrophoblast layer at term. LAT2 is also localised in the basal membrane and in endothelial cells lining the fetal capillaries. Measurements in isolated MVM vesicles indicate that System L transporter expression and activity is not influenced by maternal BMI. CONCLUSIONS LAT1 and LAT2 are present and functional in the syncytiotrophoblast MVM, whereas LAT2 is also expressed in the BM and in the fetal capillary endothelium. In contrast to placental System A and beta amino acid transporters, MVM System L activity is unaffected by maternal overweight/obesity.
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Affiliation(s)
- Francesca Gaccioli
- Department of Obstetrics and Gynaecology, University of Cambridge, Cambridge, UK.
| | - Irving L M H Aye
- Division of Basic Reproductive Sciences, Department of Obstetrics and Gynaecology, University of Colorado Denver Anschutz Medical Campus, Aurora, Denver, CO, USA.
| | - Sara Roos
- Institute of Biomedicine, The Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden.
| | - Susanne Lager
- Department of Obstetrics and Gynaecology, University of Cambridge, Cambridge, UK.
| | - Vanessa I Ramirez
- Center for Pregnancy and Newborn Research, Department of Obstetrics and Gynecology, University of Texas Health Science Center, San Antonio, TX, USA.
| | - Yoshikatsu Kanai
- Division of Bio-System Pharmacology, Department of Pharmacology, Osaka University Graduate School of Medicine, Osaka, Japan.
| | - Theresa L Powell
- Section of Neonatology, Department of Pediatrics, University of Colorado Denver Anschutz Medical Campus, Aurora, Denver, CO, USA.
| | - Thomas Jansson
- Division of Basic Reproductive Sciences, Department of Obstetrics and Gynaecology, University of Colorado Denver Anschutz Medical Campus, Aurora, Denver, CO, USA.
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3
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García MC, Cinquina V, Palomo-Garo C, Rábano A, Fernández-Ruiz J. Identification of CB₂ receptors in human nigral neurons that degenerate in Parkinson's disease. Neurosci Lett 2014; 587:1-4. [PMID: 25481767 DOI: 10.1016/j.neulet.2014.12.003] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Revised: 10/25/2014] [Accepted: 12/01/2014] [Indexed: 12/13/2022]
Abstract
It is well-demonstrated that cannabinoid CB2 receptors located in glial cells are up-regulated in neurodegenerative disorders serving as a target to control glial influences to neurons. Recent evidence indicates that CB2 receptors may be also located in certain neuronal subpopulations and serve as a marker of neuronal losses. We investigated this possibility in the post-mortem substantia nigra of Parkinson's disease (PD) patients and controls. Immunostaining for the CB2 receptor was found in tyrosine hydroxylase-positive neurons in the substantia nigra, a fact confirmed with double-staining analyses. The signal was found in controls but also in PD patients, in which CB2 receptor labelling was significantly lower, in parallel to the losses of these neurons experienced in the disease. These data show for the first time that CB2 receptors are located in tyrosine hydroxylase-containing neurons in the substantia nigra at levels significantly lower in PD patients compared to controls.
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Affiliation(s)
- María Concepción García
- Departamento de Bioquímica y Biología Molecular, Instituto Universitario de Investigación en Neuroquímica, Facultad de Medicina, Universidad Complutense, Madrid, Spain; Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain; Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Spain
| | - Valentina Cinquina
- Departamento de Bioquímica y Biología Molecular, Instituto Universitario de Investigación en Neuroquímica, Facultad de Medicina, Universidad Complutense, Madrid, Spain; Department of Theoretical and Applied Sciences, University of Insubria, Italy
| | - Cristina Palomo-Garo
- Departamento de Bioquímica y Biología Molecular, Instituto Universitario de Investigación en Neuroquímica, Facultad de Medicina, Universidad Complutense, Madrid, Spain; Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain; Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Spain
| | - Alberto Rábano
- Banco de Tejidos, Fundación CIEN (FCIEN-ISCIII), Madrid, Spain
| | - Javier Fernández-Ruiz
- Departamento de Bioquímica y Biología Molecular, Instituto Universitario de Investigación en Neuroquímica, Facultad de Medicina, Universidad Complutense, Madrid, Spain; Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain; Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Spain.
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4
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Shigeta Y, Kanai Y, Chairoungdua A, Ahmed N, Sakamoto S, Matsuo H, Kim DK, Fujimura M, Anzai N, Mizoguchi K, Ueda T, Akakura K, Ichikawa T, Ito H, Endou H. A novel missense mutation of SLC7A9 frequent in Japanese cystinuria cases affecting the C-terminus of the transporter. Kidney Int 2006; 69:1198-206. [PMID: 16609684 DOI: 10.1038/sj.ki.5000241] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Cystinuria is caused by the inherited defect of apical membrane transport systems for cystine and dibasic amino acids in renal proximal tubules. Mutations in either SLC7A9 or SLC3A1 gene result in cystinuria. The mutations of SLC7A9 gene have been identified mainly from Italian, Libyan Jewish, North American, and Spanish patients. In the present study, we have analyzed cystinuria cases from oriental population (mostly Japanese). Mutation analyses of SLC7A9 and SLC3A1 genes were performed on 41 cystinuria patients. The uptake of 14C-labeled cystine in COS-7 cells was measured to determine the functional properties of mutants. The protein expression and localization were examined by Western blot and confocal laser-scanning microscopy. Among 41 patients analyzed, 35 were found to possess mutations in SLC7A9. The most frequent one was a novel missense mutation P482L that affects a residue near the C-terminus end of the protein and causes severe loss of function. In MDCK II and HEK293 cells, we found that P482L protein was expressed and sorted to the plasma membrane as well as wild type. The alteration of Pro482 with amino acids with bulky side chains reduced the transport function of b(0,+)AT/BAT1. Interestingly, the mutations of SLC7A9 for Japanese cystinuria patients are different from those reported for European and American population. The results of the present study contribute toward understanding the distribution and frequency of cystinuria-related mutations of SLC7A9.
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Affiliation(s)
- Y Shigeta
- Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Shinkawa, Mitaka, Tokyo, Japan
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5
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Park SY, Kim JK, Kim IJ, Choi BK, Jung KY, Lee S, Park KJ, Chairoungdua A, Kanai Y, Endou H, Kim DK. Reabsorption of neutral amino acids mediated by amino acid transporter LAT2 and TAT1 in the basolateral membrane of proximal tubule. Arch Pharm Res 2005; 28:421-32. [PMID: 15918515 DOI: 10.1007/bf02977671] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
In order to understand the renal reabsorption mechanism of neutral amino acids via amino acid transporters, we have isolated human L-type amino acid transporter 2 (hLAT2) and human T-type amino acid transporter 1 (hTAT1) in human, then, we have examined and compared the gene structures, the functional characterizations and the localization in human kidney. Northern blot analysis showed that hLAT2 mRNA was expressed at high levels in the heart, brain, placenta, kidney, spleen, prostate, testis, ovary, lymph node and the fetal liver. The hTAT1 mRNA was detected at high levels in the heart, placenta, liver, skeletal muscle, kidney, pancreas, spleen, thymus and prostate. Immunohistochemical analysis on the human kidney revealed that the hLAT2 and hTAT1 proteins coexist in the basolateral membrane of the renal proximal tubules. The hLAT2 transports all neutral amino acids and hTAT1 transports aromatic amino acids. The basolateral location of the hLAT2 and hTAT1 proteins in the renal proximal tubule as well as the amino acid transport activity of hLAT2 and hTAT1 suggests that these transporters contribute to the renal reabsorption of neutral and aromatic amino acids in the basolateral domain of epithelial proximal tubule cells, respectively. Therefore, LAT2 and TAT1 play essential roles in the reabsorption of neutral amino acids from the epithelial cells to the blood stream in the kidney. Because LAT2 and TAT1 are essential to the efficient absorption of neutral amino acids from the kidney, their defects might be involved in the pathogenesis of disorders caused by a disruption in amino acid absorption such as blue diaper syndrome.
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MESH Headings
- Absorption
- Amino Acid Sequence
- Amino Acid Transport System y+/biosynthesis
- Amino Acid Transport System y+/chemistry
- Amino Acid Transport System y+/genetics
- Amino Acid Transport Systems, Neutral/biosynthesis
- Amino Acid Transport Systems, Neutral/chemistry
- Amino Acid Transport Systems, Neutral/genetics
- Amino Acids, Neutral/metabolism
- Animals
- Base Sequence
- Biological Transport
- Blotting, Northern
- Chromosome Mapping
- Chromosomes, Human, Pair 14/genetics
- Cloning, Molecular
- Fusion Regulatory Protein 1, Light Chains/biosynthesis
- Fusion Regulatory Protein 1, Light Chains/chemistry
- Fusion Regulatory Protein 1, Light Chains/genetics
- Humans
- Immunohistochemistry
- In Situ Hybridization, Fluorescence
- In Vitro Techniques
- Kidney Tubules, Proximal/metabolism
- Molecular Sequence Data
- Oocytes/metabolism
- Xenopus laevis
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Affiliation(s)
- Sun Young Park
- Department of Pediatrics, Kwangju Christian Hospital, Gwangju 503-715, Korea
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6
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Fernández E, Torrents D, Zorzano A, Palacín M, Chillarón J. Identification and functional characterization of a novel low affinity aromatic-preferring amino acid transporter (arpAT). One of the few proteins silenced during primate evolution. J Biol Chem 2005; 280:19364-72. [PMID: 15757906 DOI: 10.1074/jbc.m412516200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have identified in silico arpAT, a gene encoding a new member of the LSHAT family, and cloned it from kidney. Co-expression of arpAT with the heavy subunits rBAT or 4F2hc elicited a sodium-independent alanine transport activity in HeLa cells. L-tyrosine, l-3,4-dihydroxyphenylalanine (L-DOPA), L-glutamine, L-serine, L-cystine, and L-arginine were also transported. Kinetic and cis-inhibition studies showed a K(m) = 1.59 +/- 0.24 mM for L-alanine or IC50 in the millimolar range for most amino acids, except L-proline, glycine, anionic and D-amino acids, which were not inhibitory. L-DOPA and L-tyrosine were the most effective competitive inhibitors of L-alanine transport, with IC50 values of 272.2 +/- 57.1 and 716.3 +/- 112.4 microM, respectively. In the small intestine, arpAT mRNA was located at the enterocytes, in a decreasing gradient from the crypts to the tip of the villi. It was also expressed in neurons from different brain areas. Finally, we show that while the arpAT gene is conserved in rat, dog, and chicken, it has become silenced in humans and chimpanzee. Actually, it has been recently reported that it is one of the 33 recently inactivated genes in the human lineage. The evolutionary implications of the silencing process and the roles of arpAT in transport of L-DOPA in the brain and in aromatic amino acid absorption are discussed.
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MESH Headings
- Alanine/chemistry
- Amino Acid Sequence
- Amino Acid Transport Systems
- Amino Acid Transport Systems, Neutral/biosynthesis
- Amino Acid Transport Systems, Neutral/chemistry
- Amino Acid Transport Systems, Neutral/genetics
- Amino Acids/chemistry
- Amino Acids, Aromatic/metabolism
- Animals
- Arginine/chemistry
- Biological Transport
- Blotting, Northern
- Blotting, Western
- Cell Lineage
- Chickens
- Cloning, Molecular
- Cysteine/chemistry
- DNA, Complementary/metabolism
- Dimerization
- Dogs
- Dose-Response Relationship, Drug
- Evolution, Molecular
- Gene Library
- Gene Silencing
- Glutamine/chemistry
- Glycine/chemistry
- HeLa Cells
- Humans
- In Situ Hybridization
- Inhibitory Concentration 50
- Intestine, Small/metabolism
- Kidney/metabolism
- Kinetics
- Levodopa/metabolism
- Levodopa/pharmacology
- Mice
- Molecular Sequence Data
- Open Reading Frames
- Pan troglodytes
- Phylogeny
- Proline/chemistry
- Protein Binding
- RNA, Messenger/metabolism
- Rats
- Reverse Transcriptase Polymerase Chain Reaction
- Serine/chemistry
- Sodium/chemistry
- Transfection
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Affiliation(s)
- Esperanza Fernández
- Department of Biochemistry and Molecular Biology, Faculty of Biology, and Barcelona Science Park, University of Barcelona, E-08028 Barcelona, Spain
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Jutabha P, Kanai Y, Hosoyamada M, Chairoungdua A, Kim DK, Iribe Y, Babu E, Kim JY, Anzai N, Chatsudthipong V, Endou H. Identification of a novel voltage-driven organic anion transporter present at apical membrane of renal proximal tubule. J Biol Chem 2003; 278:27930-8. [PMID: 12740363 DOI: 10.1074/jbc.m303210200] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A novel transport protein with the properties of voltage-driven organic anion transport was isolated from pig kidney cortex by expression cloning in Xenopus laevis oocytes. A cDNA library was constructed from size-fractionated poly(A)+ RNA and screened for p-aminohippurate (PAH) transport in high potassium medium. A 1856-base pair cDNA encoding a 467-amino acid peptide designated as OATV1 (voltage-driven organic anion transporter 1) was isolated. The predicted amino acid sequence of OATV1 exhibited 60-65% identity to those of human, rat, rabbit, and mouse sodium-dependent phosphate cotransporter type 1 (NPT1), although OATV1 did not transport phosphate. The homology of this transporter to known members of the organic anion transporter family (OAT family) was about 25-30%. OATV1-mediated PAH transport was affected by the changes in membrane potential. The transport was Na+-independent and enhanced at high concentrations of extracellular potassium and low concentrations of extracellular chloride. Under the voltage clamp condition, extracellularly applied PAH induced outward currents in oocytes expressing OATV1. The current showed steep voltage dependence, consistent with the voltage-driven transport of PAH by OATV1. The PAH transport was inhibited by various organic anions but not by organic cations, indicating the multispecific nature of OATV1 for anionic compounds. This transport protein is localized at the apical membrane of renal proximal tubule, consistent with the proposed localization of a voltage-driven organic anion transporter. Therefore, it is proposed that OATV1 plays an important role to excrete drugs, xenobiotics, and their metabolites driven by membrane voltage through the apical membrane of the tubular epithelial cells into the urine.
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Affiliation(s)
- Promsuk Jutabha
- Department of Pharmacology and Toxicology, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo, 181-8611, Japan
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8
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Wang H, Tamba M, Kimata M, Sakamoto K, Bannai S, Sato H. Expression of the activity of cystine/glutamate exchange transporter, system x(c)(-), by xCT and rBAT. Biochem Biophys Res Commun 2003; 305:611-8. [PMID: 12763038 DOI: 10.1016/s0006-291x(03)00808-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The expression of the activity of cystine/glutamate exchange transporter, designated system x(c)(-), requires two components, xCT and 4F2 heavy chain (4F2hc) in Xenopus oocytes. rBAT (related to b(0,+) amino acid transporter) has a significant homology to 4F2hc and is known to be located in the apical membrane of epithelial cells. To determine whether xCT can associate with rBAT and express the activity of system x(c)(-), xCT, and rBAT were co-expressed in Xenopus oocytes and in mammalian cultured cells. In the oocytes injected with rBAT cRNA alone, the activities of cystine and arginine transport were induced, indicating that the system b(0,+)-like transporter was expressed by associating the exogenous rBAT with an endogenous b(0,+)AT-like factor as reported previously. In the oocytes injected with xCT and rBAT cRNAs, the activity of cystine transport was further induced. This induced activity of cystine transport was partially inhibited by glutamate or arginine and completely inhibited by adding both amino acids. In these oocytes, the activity of glutamate transport was also induced and it was strongly inhibited by cystine. In NIH3T3 cells transfected with xCT cDNA alone, the activity of cystine transport was significantly increased, and in the cells transfected with both xCT and rBAT cDNAs, the activity of cystine transport was further enhanced. The enhanced activity was Na(+)-independent and was inhibited by glutamate and homocysteate. These results indicate that rBAT can replace 4F2hc in the expression of the activity of system x(c)(-) and suggest that system x(c)(-) activity could be expressed in the apical membrane of epithelial cells.
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Affiliation(s)
- Hongyu Wang
- Department of Biochemistry, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
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9
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Hisano S, Nogami H. Transporters in the neurohypophysial neuroendocrine system, with special reference to vesicular glutamate transporters (BNPI and DNPI): a review. Microsc Res Tech 2002; 56:122-31. [PMID: 11810715 DOI: 10.1002/jemt.10014] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Recent advances in gene technology have helped to identify novel proteins and allowed study of their distribution and functions in the mammalian brain. One class of these proteins is that of transporters, which exist in plasma and organellar membranes of neurons and other cells to move substances selectively across membranes. These transporters can be categorized further into subclasses by their structural property, substrate selectivity, and site of action. Some of them have been identified in the hypothalamus, which is the only brain site where a neural signal is converted to a humoral one, namely, a hormone for a target organ. This unique neural mechanism has long attracted attention as the neuroendocrine system, part of which has been extensively studied as the hypothalamic-neurohypophysial system involved in secretion of vasopressin and oxytocin. However, transporters in this system have been less well studied. A morphological examination of novel transporters would give us cues to a better understanding of the neuronal organization and function of the system. In this review, we first summarize recent findings on expression of transporter gene and immunoreactivity in the hypothalamus. In the second part, we explain our observations on two vesicular glutamate (inorganic phosphate) transporters (BNPI and DNPI) in the supraoptic and paraventricular nuclei and neurohypophysis. Further study of these and other transporters will provide a basis on which to reevaluate the organization and function of the hypothalamic-neurohypophysial system.
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Affiliation(s)
- Setsuji Hisano
- Laboratory of Neuroendocrinology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba 305-8575, Ibaraki, Japan.
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10
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Chairoungdua A, Kanai Y, Matsuo H, Inatomi J, Kim DK, Endou H. Identification and characterization of a novel member of the heterodimeric amino acid transporter family presumed to be associated with an unknown heavy chain. J Biol Chem 2001; 276:49390-9. [PMID: 11591708 DOI: 10.1074/jbc.m107517200] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We identified a novel amino acid transporter designated Asc-2 (for asc-type amino acid transporter 2). Asc-2 exhibited relatively low but significant sequence similarity to the members of the heterodimeric amino acid transporters. The cysteine residue responsible for the disulfide bond formation between transporters (light chains) and heavy chain subunits in the heterodimeric amino acid transporters is conserved for Asc-2. Asc-2 is, however, not colocalized with the already known heavy chains such as 4F2 heavy chain (4F2hc) or related to b(0,+) amino acid transporter (rBAT) in mouse kidney. Because Asc-2 solely expressed or coexpressed with 4F2hc or rBAT did not induce functional activity, we generated fusion proteins in which Asc-2 is connected with 4F2hc or rBAT. The fusion proteins were sorted to the plasma membrane and expressed the function corresponding to the Na(+)-independent small neutral amino acid transport system asc. Distinct from the already identified system asc transporter Asc-1 which is associated with 4F2hc, Asc-2-mediated transport is less stereoselective and did not accept some of the high affinity substrates of Asc-1 such as alpha-aminoisobutyric acid and beta-alanine. Asc-2 message was detected in kidney, placenta, spleen, lung, and skeletal muscle. In kidney, Asc-2 protein was present in the epithelial cells lining collecting ducts. In the Western blot analysis on mouse erythrocytes and kidney, Asc-2 was detected as multiple bands in the nonreducing condition, whereas the bands shifted to a single band at lower molecular weight, suggesting the association of Asc-2 with other protein(s) via a disulfide bond. The finding of Asc-2 would lead to the establishment of a new subgroup of heterodimeric amino acid transporter family which includes transporters associated not with 4F2hc or rBAT but with other unknown heavy chains.
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Affiliation(s)
- A Chairoungdua
- Department of Pharmacology and Toxicology, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan
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11
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Yanagida O, Kanai Y, Chairoungdua A, Kim DK, Segawa H, Nii T, Cha SH, Matsuo H, Fukushima J, Fukasawa Y, Tani Y, Taketani Y, Uchino H, Kim JY, Inatomi J, Okayasu I, Miyamoto K, Takeda E, Goya T, Endou H. Human L-type amino acid transporter 1 (LAT1): characterization of function and expression in tumor cell lines. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1514:291-302. [PMID: 11557028 DOI: 10.1016/s0005-2736(01)00384-4] [Citation(s) in RCA: 570] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
System L is a major nutrient transport system responsible for the transport of large neutral amino acids including several essential amino acids. We previously identified a transporter (L-type amino acid transporter 1: LAT1) subserving system L in C6 rat glioma cells and demonstrated that LAT1 requires 4F2 heavy chain (4F2hc) for its functional expression. Since its oncofetal expression was suggested in the rat liver, it has been proposed that LAT1 plays a critical role in cell growth and proliferation. In the present study, we have examined the function of human LAT1 (hLAT1) and its expression in human tissues and tumor cell lines. When expressed in Xenopus oocytes with human 4F2hc (h4F2hc), hLAT1 transports large neutral amino acids with high affinity (K(m)= approximately 15- approximately 50 microM) and L-glutamine and L-asparagine with low affinity (K(m)= approximately 1.5- approximately 2 mM). hLAT1 also transports D-amino acids such as D-leucine and D-phenylalanine. In addition, we show that hLAT1 accepts an amino acid-related anti-cancer agent melphalan. When loaded intracellularly, L-leucine and L-glutamine but not L-alanine are effluxed by extracellular substrates, confirming that hLAT1 mediates an amino acid exchange. hLAT1 mRNA is highly expressed in the human fetal liver, bone marrow, placenta, testis and brain. We have found that, while all the tumor cell lines examined express hLAT1 messages, the expression of h4F2hc is varied particularly in leukemia cell lines. In Western blot analysis, hLAT1 and h4F2hc have been confirmed to be linked to each other via a disulfide bond in T24 human bladder carcinoma cells. Finally, in in vitro translation, we show that hLAT1 is not a glycosylated protein even though an N-glycosylation site has been predicted in its extracellular loop, consistent with the property of the classical 4F2 light chain. The properties of the hLAT1/h4F2hc complex would support the roles of this transporter in providing cells with essential amino acids for cell growth and cellular responses, and in distributing amino acid-related compounds.
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MESH Headings
- Amino Acid Transport Systems
- Amino Acids, Essential/metabolism
- Animals
- Antigens, CD/biosynthesis
- Antigens, CD/genetics
- Carrier Proteins/biosynthesis
- Carrier Proteins/chemistry
- Carrier Proteins/genetics
- Carrier Proteins/metabolism
- DNA Probes
- DNA, Complementary/genetics
- DNA, Complementary/isolation & purification
- Fetus/metabolism
- Fusion Regulatory Protein-1
- Humans
- Molecular Sequence Data
- Oocytes/metabolism
- Protein Biosynthesis
- RNA, Complementary/genetics
- RNA, Complementary/isolation & purification
- RNA, Messenger/analysis
- RNA, Messenger/biosynthesis
- Substrate Specificity
- Tumor Cells, Cultured
- Xenopus
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Affiliation(s)
- O Yanagida
- Second Department of Surgery, Kyorin University School of Medicine, Mitaka, Tokyo, Japan
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12
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Abstract
The biochemistry and physiology of L-arginine have to be reconsidered in the light of the recent discovery that the amino acid is the only substrate of all isoforms of nitric oxide synthase (NOS). Generation of nitric oxide, NO, a versatile molecule in signaling processes and unspecific immune defense, is intertwined with synthesis, catabolism and transport of arginine which thus ultimately participates in the regulation of a fine-tuned balance between normal and pathophysiological consequences of NO production. The complex composition of the brain at the cellular level is reflected in a complex differential distribution of the enzymes of arginine metabolism. Argininosuccinate synthetase (ASS) and argininosuccinate lyase which together can recycle the NOS coproduct L-citrulline to L-arginine are expressed constitutively in neurons, but hardly colocalize with each other or with NOS in the same neuron. Therefore, trafficking of citrulline and arginine between neurons necessitates transport capacities in these cells which are fulfilled by well-described carriers for cationic and neutral amino acids. The mechanism of intercellular exchange of argininosuccinate, a prerequisite also for its proposed function as a neuromodulator, remains to be elucidated. In cultured astrocytes transcription and protein expression of arginine transport system y(+) and of ASS are upregulated concomittantly with immunostimulant-mediated induction of NOS-2. In vivo ASS-immunoreactivity was found in microglial cells in a rat model of brain inflammation and in neurons and glial cells in the brains of Alzheimer patients. Any attempt to estimate the contributions of arginine transport and synthesis to substrate supply for NOS has to consider competition for arginine between NOS and arginase, the latter enzyme being expressed as mitochondrial isoform II in nervous tissue. Generation of NOS inhibitors agmatine and methylarginines is documented for the nervous system. Suboptimal supply of NOS with arginine leads to production of detrimental peroxynitrite which may result in neuronal cell death. Data have been gathered recently which point to a particular role of astrocytes in neural arginine metabolism. Arginine appears to be accumulated in astroglial cells and can be released after stimulation with a variety of signals. It is proposed that an intercellular citrulline-NO cycle is operating in brain with astrocytes storing arginine for the benefit of neighbouring cells in need of the amino acid for a proper synthesis of NO.
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Affiliation(s)
- H Wiesinger
- Physiologisch-Chemisches Institut der Universität, Hoppe-Seyler-Strasse 4, D-72076, Tübingen, Germany.
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13
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Kim JY, Kanai Y, Chairoungdua A, Cha SH, Matsuo H, Kim DK, Inatomi J, Sawa H, Ida Y, Endou H. Human cystine/glutamate transporter: cDNA cloning and upregulation by oxidative stress in glioma cells. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1512:335-44. [PMID: 11406111 DOI: 10.1016/s0005-2736(01)00338-8] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
A human cDNA for amino acid transport system x(C)(-) was isolated from diethyl maleate-treated human glioma U87 cells. U87 cells expressed two variants of system x(C)(-) transporters hxCTa and hxCTb with altered C-terminus regions probably generated by the alternative splicing at 3'-ends. Both hxCTa and hxCTb messages were also detected in spinal cord, brain and pancreas, although the level of hxCTb expression appears to be lower than that of hxCTa in these tissues. When expressed in Xenopus oocytes, hxCTb required the heavy chain of 4F2 cell surface antigen (4F2hc) and exhibited the Na(+)-independent transport of L-cystine and L-glutamate, consistent with the properties of system x(C)(-). In agreement with this, 137 kDa band was detected by either anti-xCT or anti-4F2hc antibodies in the non-reducing condition in western blots, whereas it shifted to 50 kDa or 90 kDa bands in the reducing condition, indicating the association of two proteins via disulfide bands. We found that the expression of xCT was rapidly induced in U87 cells upon oxidative stress by diethyl maleate treatment, which was accompanied by the increase in the L-cystine uptake by U87 cells. Because of this highly regulated nature, xCT in glial cells would fulfill the task to protect neurons against oxidative stress by providing suitable amount of cystine to produce glutathione.
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Affiliation(s)
- J Y Kim
- Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Mitaka, Tokyo, Japan
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14
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Kim DK, Kanai Y, Chairoungdua A, Matsuo H, Cha SH, Endou H. Expression cloning of a Na+-independent aromatic amino acid transporter with structural similarity to H+/monocarboxylate transporters. J Biol Chem 2001; 276:17221-8. [PMID: 11278508 DOI: 10.1074/jbc.m009462200] [Citation(s) in RCA: 191] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A cDNA was isolated from rat small intestine by expression cloning which encodes a novel Na+-independent transporter for aromatic amino acids. When expressed in Xenopus oocytes, the encoded protein designated as TAT1 (T-type amino acid transporter 1) exhibited Na+-independent and low-affinity transport of aromatic amino acids such as tryptophan, tyrosine, and phenylalanine (Km values: approximately 5 mm), consistent with the properties of classical amino acid transport system T. TAT1 accepted some variations of aromatic side chains because it interacted with amino acid-related compounds such as l-DOPA and 3-O-methyl-DOPA. Because TAT1 accepted N-methyl- and N-acetyl-derivatives of aromatic amino acids but did not accept their methylesters, it is proposed that TAT1 recognizes amino acid substrates as anions. Consistent with this, TAT1 exhibited sequence similarity (approximately 30% identity at the amino acid level) to H+/monocarboxylate transporters. Distinct from H+/monocarboxylate transporters, however, TAT1 was not coupled with the H+ transport but it mediated an electroneutral facilitated diffusion. TAT1 mRNA was strongly expressed in intestine, placenta, and liver. In rat small intestine TAT1 immunoreactivity was detected in the basolateral membrane of the epithelial cells suggesting its role in the transepithelial transport of aromatic amino acids. The identification of the amino acid transporter with distinct structural and functional characteristics will not only facilitate the expansion of amino acid transporter families but also provide new insights into the mechanisms of substrate recognition of organic solute transporters.
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Affiliation(s)
- D K Kim
- Department of Pharmacology and Toxicology, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan
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15
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Abstract
The export of glutamine from astrocytes, and the uptake of glutamine by neurons, are integral steps in the glutamate-glutamine cycle, a major pathway for the replenishment of neuronal glutamate. We review here the functional and molecular identification of the transporters that mediate this transfer. The emerging picture of glutamine transfer in adult brain is of a dominant pathway mediated by system N transport (SN1) in astrocytes and system A transport (SAT/ATA) in neurons. The participating glutamine transporters are functionally and structurally related, sharing the following properties: (a) unlike many neutral amino acid transporters which have proven to be obligate exchangers, these glutamine transporters mediate net substrate transfer energized by coupling to ionic gradients; (b) they are sensitive to small pH changes in the physiological range; (c) they are susceptible to adaptive and humoral regulation; (d) they are related structurally to the AAAP (amino acid and auxin permeases) family of transporters. A key difference between SN1 and the SAT/ATA transporters is the ready reversibility of glutamine fluxes via SN1 under physiological conditions, which allows SN1 both to sustain a glutamine concentration gradient in astrocytes and to mediate the net outward flux of glutamine. It is likely that the ASCT2 transporter, an obligate exchanger of neutral amino acids, displaces the SN1 transporter as the main carrier of glutamine export in proliferating astrocytes.
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Affiliation(s)
- S Bröer
- Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, Australia.
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16
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Mizoguchi K, Cha SH, Chairoungdua A, Kim DK, Shigeta Y, Matsuo H, Fukushima J, Awa Y, Akakura K, Goya T, Ito H, Endou H, Kanai Y. Human cystinuria-related transporter: localization and functional characterization. Kidney Int 2001; 59:1821-33. [PMID: 11318953 DOI: 10.1046/j.1523-1755.2001.0590051821.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Cystinuria has been proposed to be an inherited defect of apical membrane transport systems for cystine and basic amino acids in renal proximal tubules. Although the mutations of the recently identified transporter BAT1/b(0,+)AT have been related to nontype I cystinuria, the function and localization of human BAT1 (hBAT1)/b(0,+)AT have not been well characterized. METHODS The cDNA encoding hBAT1 was isolated from human kidney. Fluorescence in situ hybridization was performed to map the hBAT1 gene on human chromosomes. Tissue distribution and localization of expression were examined by Northern blot and immunohistochemical analyses. hBAT1 cDNA was transfected to COS-7 cells with rBAT cDNA, and the uptake and efflux of 14C-labeled amino acids were measured to determine the functional properties. The roles of protein kinase-dependent phosphorylation were investigated using inhibitors or activators of protein kinases. RESULTS The hBAT1 gene was mapped to 19q12-13.1 on the human chromosome, which is the locus of nontype I cystinuria. hBAT1 message was expressed predominantly in kidney. hBAT1 protein was localized in the apical membrane of proximal tubules in human kidney. When expressed in COS-7 cells with a type II membrane glycoprotein rBAT (related to b(0,+)-amino acid transporter), hBAT1 exhibited the transport activity with the properties of amino acid transport system b(0,+), which transported cystine as well as basic and neutral amino acids presumably via a substrate exchange mechanism. BAT1-mediated transport was reduced by the protein kinase A activator and enhanced by the tyrosine kinase inhibitor. CONCLUSIONS hBAT1 exhibited the properties expected for a transporter subserving the high-affinity cystine transport system in renal proximal tubules. The hBAT1 gene was mapped to the locus of nontype I cystinuria, confirming the involvement of hBAT1 in cystinuria.
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Affiliation(s)
- K Mizoguchi
- Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Mitaka, Tokyo, Japan
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17
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Ishiia H, Sasaki Y, Goshima Y, Kanai Y, Endou H, Ayusawa D, Ono H, Miyamae T, Misu Y. Involvement of rBAT in Na(+)-dependent and -independent transport of the neurotransmitter candidate L-DOPA in Xenopus laevis oocytes injected with rabbit small intestinal epithelium poly A(+) RNA. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1466:61-70. [PMID: 10825431 DOI: 10.1016/s0005-2736(00)00171-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Although L-3,4-dihydroxyphenylalanine (L-DOPA) is claimed to be a neurotransmitter in the central nervous system (CNS), receptor or transporter molecules for L-DOPA have not been determined. In an attempt to identify a transporter for L-DOPA, we examined whether or not an active and high affinity L-DOPA transport system is expressed in Xenopus laevis oocytes injected with poly A(+) RNA prepared from several tissues. Among the poly A(+) RNAs tested, rabbit intestinal epithelium poly A(+) RNA gave the highest transport activity for L-[(14)C]DOPA in the oocytes. The uptake was approximately five times higher than that of water-injected oocytes, and was partially Na(+)-dependent. L-Tyrosine, L-phenylalanine, L-leucine and L-lysine inhibited this transport activity, whereas D-DOPA, dopamine, glutamate and L-DOPA cyclohexylester, an L-DOPA antagonist did not affect this transport. Coinjection of an antisense cRNA, as well as oligonucleotide complementary to rabbit rBAT (NBAT) cDNA almost completely inhibited the uptake of L-[(14)C]DOPA in the oocytes. On the other hand, an antisense cRNA of rabbit 4F2hc barely affected this L-[(14)C]DOPA uptake activity. rBAT was thus responsible for the L-[(14)C]DOPA uptake activity expressed in X. laevis oocytes injected with poly A(+) RNA from rabbit intestinal epithelium. As rBAT is localized at the target regions of L-DOPA in the CNS, rBAT might be one of the components involved in L-DOPAergic neurotransmission.
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Affiliation(s)
- H Ishiia
- Department of Pharmacology, Yokohama City University of Medicine, Yokohama, Japan
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18
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Valverde F, Garc�a C, L�pez-Mascaraque L, De Carlos JA. Development of the mammillothalamic tract in normal andPax-6 mutant mice. J Comp Neurol 2000. [DOI: 10.1002/(sici)1096-9861(20000417)419:4<485::aid-cne6>3.0.co;2-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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19
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He Y, Janssen WG, Rothstein JD, Morrison JH. Differential synaptic localization of the glutamate transporter EAAC1 and glutamate receptor subunit gluR2 in the rat hippocampus. J Comp Neurol 2000. [DOI: 10.1002/(sici)1096-9861(20000313)418:3<255::aid-cne2>3.0.co;2-6] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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20
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Chairoungdua A, Segawa H, Kim JY, Miyamoto K, Haga H, Fukui Y, Mizoguchi K, Ito H, Takeda E, Endou H, Kanai Y. Identification of an amino acid transporter associated with the cystinuria-related type II membrane glycoprotein. J Biol Chem 1999; 274:28845-8. [PMID: 10506124 DOI: 10.1074/jbc.274.41.28845] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We identified an amino acid transporter that is associated with the cystinuria-related type II membrane glycoprotein, rBAT (related to b(0,+) amino acid transporter). The transporter designated BAT1 (b(0, +)-type amino acid transporter 1) from rat kidney was found to be structurally related to recently identified amino acid transporters for system L, system y(+)L, and system x(-)C, which are linked, via a disulfide bond, to the other type II membrane glycoprotein, 4F2hc (4F2 heavy chain). In the nonreducing condition, a 125-kDa band, which seems to correspond to the heterodimeric complex of BAT1 and rBAT, was detected in rat kidney with anti-BAT1 antibody. The band was shifted to 41 kDa in the reducing condition, confirming that BAT1 and rBAT are linked via a disulfide bond. The BAT1 and rBAT proteins were shown to be colocalized in the apical membrane of the renal proximal tubules where massive cystine transport had been proposed. When expressed in COS-7 cells with rBAT, but not with 4F2hc, BAT1 exhibited a Na(+)-independent transport of cystine as well as basic and neutral amino acids with the properties of system b(0,+). The results from the present investigation were used to establish a family of amino acid transporters associated with type II membrane glycoproteins.
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Affiliation(s)
- A Chairoungdua
- Department of Pharmacology, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, USA
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21
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Kawano H, Fukuda T, Kubo K, Horie M, Uyemura K, Takeuchi K, Osumi N, Eto K, Kawamura K. Pax-6 is required for thalamocortical pathway formation in fetal rats. J Comp Neurol 1999; 408:147-60. [PMID: 10333267 DOI: 10.1002/(sici)1096-9861(19990531)408:2<147::aid-cne1>3.0.co;2-l] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Pax-6, a transcription regulatory factor, has been demonstrated to play important roles in eye, nose, and brain development by analyzing mice, rats, and humans with a Pax-6 gene mutation. We examined the role of Pax-6 with special attention to the formation of efferent and afferent pathways of the cerebral cortex by using the rat Small eye (rSey2), which has a mutation in the Pax-6 gene. In rSey2/rSey2 fetuses, cortical efferent axons develop with normal trajectory, at least within the cortical anlage, when examined with immunohistochemistry of the neuronal cell adhesion molecule TAG-1 and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) labeling from the cortical surface. A remarkable disorder was found in the trajectory of dorsal thalamic axons by immunostaining of the neurofilament and the neural cell adhesion molecule L1 and DiI labeling from the dorsal thalamus. In normal rat fetuses, dorsal thalamic axons curved laterally in the ventral thalamus without invading a Pax-6-immunoreactive cell cluster in the ventral part of the ventral thalamus. These axons then coursed up to the cortical anlage, passing just dorsal to another Pax-6-immunoreactive cell cluster in the amygdaloid region. In contrast, in rSey2/rSey2 fetuses, dorsal thalamic axons extended downward to converge in the ventrolateral corner of the ventral thalamus and fanned out in the amygdaloid region without reaching the cortical anlage. These results suggest that Pax-6-expressing cell clusters along the thalamocortical pathway (ventral part of the ventral thalamus and amygdala) are responsible for the determination of the axonal pathfinding of the thalamocortical pathway.
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Affiliation(s)
- H Kawano
- Department of Anatomy, School of Medicine, Keio University, Tokyo, Japan.
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22
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Pickel VM, Pohorille A, Chan J, Tate SS, Nirenberg MJ. Regional and subcellular distribution of a neutral and basic amino acid transporter in forebrain neurons containing nitric oxide synthase. J Comp Neurol 1999; 404:459-72. [PMID: 9987991 DOI: 10.1002/(sici)1096-9861(19990222)404:4<459::aid-cne4>3.0.co;2-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The neutral and basic amino acid transporter (NBAT) facilitates sodium-independent transport of L-amino acids in renal and intestinal epithelial cells and has been postulated to play a similar role in neurons. In previous studies, NBAT has been detected within enteric and brainstem autonomic neurons in a distribution similar to that of constitutive nitric oxide synthase (cNOS). Furthermore, L-arginine, the required precursor for nitric oxide synthesis, is an excellent NBAT substrate. Together, these findings suggest that NBAT may play a role in the regulation of nitric oxide synthesis, through the control of precursor availability. To gain insight into the potential physiological role of NBAT in central neurons, we used an antipeptide antiserum to examine the light and electron microscopic immunocytochemical localization of NBAT in the rat forebrain and to compare this distribution with that of cNOS. Immunolabeling for NBAT was detected within perikarya and dendrite-like processes that were most numerous in the frontal and cingulate cortex, the ventral striatum, the central amygdala, and the bed nucleus of the stria terminalis. Labeled varicose axonal processes were distributed most densely in the agranular insular cortex and the paraventricular nuclei of the thalamus and hypothalamus (PVH). Electron microscopy showed that immunogold labeling for NBAT was distributed along plasmalemmal and vacuolar membranes within somata, dendrites, and axonal profiles. Many of the NBAT-containing somata and dendrites contained detectable cNOS. Our results suggest that expression of NBAT may provide specific populations of cNOS-containing forebrain neurons with a unique mechanism for regulating somatodendritic synthesis of nitric oxide.
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Affiliation(s)
- V M Pickel
- Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021, USA.
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23
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Palacín M, Estévez R, Bertran J, Zorzano A. Molecular biology of mammalian plasma membrane amino acid transporters. Physiol Rev 1998; 78:969-1054. [PMID: 9790568 DOI: 10.1152/physrev.1998.78.4.969] [Citation(s) in RCA: 587] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Molecular biology entered the field of mammalian amino acid transporters in 1990-1991 with the cloning of the first GABA and cationic amino acid transporters. Since then, cDNA have been isolated for more than 20 mammalian amino acid transporters. All of them belong to four protein families. Here we describe the tissue expression, transport characteristics, structure-function relationship, and the putative physiological roles of these transporters. Wherever possible, the ascription of these transporters to known amino acid transport systems is suggested. Significant contributions have been made to the molecular biology of amino acid transport in mammals in the last 3 years, such as the construction of knockouts for the CAT-1 cationic amino acid transporter and the EAAT2 and EAAT3 glutamate transporters, as well as a growing number of studies aimed to elucidate the structure-function relationship of the amino acid transporter. In addition, the first gene (rBAT) responsible for an inherited disease of amino acid transport (cystinuria) has been identified. Identifying the molecular structure of amino acid transport systems of high physiological relevance (e.g., system A, L, N, and x(c)- and of the genes responsible for other aminoacidurias as well as revealing the key molecular mechanisms of the amino acid transporters are the main challenges of the future in this field.
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Affiliation(s)
- M Palacín
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Spain
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24
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Takahashi F, Morita K, Katai K, Segawa H, Fujioka A, Kouda T, Tatsumi S, Nii T, Taketani Y, Haga H, Hisano S, Fukui Y, Miyamoto KI, Takeda E. Effects of dietary Pi on the renal Na+-dependent Pi transporter NaPi-2 in thyroparathyroidectomized rats. Biochem J 1998; 333 ( Pt 1):175-81. [PMID: 9639577 PMCID: PMC1219570 DOI: 10.1042/bj3330175] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Dietary Pi and parathyroid hormone (PTH) are two most important physiological and pathophysiological regulators of Pi re-absorption in the renal proximal tubule. Effects of dietary Pi on Na+/Pi co-transporter NaPi-2 were investigated in thyroparathyroidectomized (TPTX) rats. NaPi-2 protein and mRNA in the kidney cortex of TPTX rats were increased approximately 3.8- and 2.4-fold in amount respectively compared with those in the sham-operated animals. Administration of PTH to the TPTX rats resulted in a decrease in the amount of NaPi-2 protein, but not in the abundance of NaPi-2 mRNA. Deprivation of dietary Pi in the TPTX rats did not affect the amount of NaPi-2 mRNA and protein. In the Pi-deprived TPTX rats, feeding of a high-Pi diet resulted in marked decreases in Pi transport activity and the amount of NaPi-2 protein in the superficial nephrons. Immunohistochemical analysis demonstrated that administration of PTH to TPTX rats resulted in a decrease in NaPi-2 immunoreactivity from both superficial and juxtamedullary nephrons within 4 h. Switching TPTX animals from a low-Pi diet to the high-Pi diet decreased NaPi-2 immunoreactivity from superficial nephrons, but not from juxtamedullary nephrons, within 4 h. These results suggest that dietary Pi could regulate the amount of NaPi-2 protein in the superficial nephrons in a PTH-independent manner.
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Affiliation(s)
- F Takahashi
- Department of Clinical Nutrition, School of Medicine, Tokushima University, Kuramoto-Cho 3, Tokushima 770, Japan
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25
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Morita K, Haga H, Tanaka H, Fujioka A, Segawa H, Katai K, Tatsumi S, Koda T, Taketani Y, Hisano S, Fukui Y, Miyamoto KI, Takeda E. Effect of dietary phosphate on Na+-dependent phosphate cotransporters function and expression in the rat kidney. Clin Exp Nephrol 1998. [DOI: 10.1007/bf02479931] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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26
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Tanaka H, Miyamoto KI, Morita K, Haga H, Segawa H, Shiraga T, Fujioka A, Kouda T, Taketani Y, Hisano S, Fukui Y, Kitagawa K, Takeda E. Regulation of the PepT1 peptide transporter in the rat small intestine in response to 5-fluorouracil-induced injury. Gastroenterology 1998; 114:714-23. [PMID: 9516392 DOI: 10.1016/s0016-5085(98)70585-2] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
BACKGROUND & AIMS The oligopeptide transport system of the small intestine is resistant to mucosal injury. The mechanism of this resistance was investigated by examining the activity level and expression of the peptide transporter PepT1 in the intestine of rats treated with 5-fluorouracil. METHODS The expression and localization of PepT1 were examined by immunoblot analysis of brush border membrane vesicles and immunohistochemical analysis of intestinal sections with PepT1-specific rabbit polyclonal antibodies. Also, Northern blot analysis was used for the expression of PepT1 messenger RNA (mRNA). RESULTS Although the amounts of sucrase and an Na+-dependent glucose transporter protein in intestinal vesicles decreased markedly after 5-fluorouracil treatment, the amount of PepT1 protein remained largely unaffected. Immunohistochemical analysis also showed that the PepT1 immunoreactivity level was preserved in the brush border membrane of the remaining villi of 5-fluorouracil-treated rats. Levels of amino acid, glucose, and phosphate transporter mRNAs were profoundly depressed in 5-fluorouracil-treated animals, whereas the level of PepT1 mRNA conversely increased. CONCLUSIONS The resistance of intestinal peptide transport to tissue injury may be attributable to increased synthesis of PepT1 rather than to a change in the kinetic properties of the residual absorbing cells.
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Affiliation(s)
- H Tanaka
- Department of Clinical Nutrition, School of Medicine, Tokushima University, Tokushima, Japan
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Segawa H, Miyamoto K, Ogura Y, Haga H, Morita K, Katai K, Tatsumi S, Nii T, Taketani Y, Takeda E. Cloning, functional expression and dietary regulation of the mouse neutral and basic amino acid transporter (NBAT). Biochem J 1997; 328 ( Pt 2):657-64. [PMID: 9371728 PMCID: PMC1218968 DOI: 10.1042/bj3280657] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The Na+-independent dibasic and neutral amino acid transporter NBAT is among the least hydrophobic of mammalian amino acid transporters. The transporter contains one to four transmembrane domains and induces amino acid transport activity via a b0,+-like system when expressed in Xenopus oocytes. However, the physiological role of NBAT remains unclear. Complementary DNA clones encoding mouse NBAT have now been isolated. The expression of mouse NBAT in Xenopus oocytes also induced an obligatory amino acid exchange activity similar to that of the b0,+-like system. The amount of NBAT mRNA in mouse kidney increased during postnatal development, consistent with the increase in renal cystine and dibasic transport activity. Dietary aspartate induced a marked increase in cystine transport via the b0,+ system in mouse ileum. A high-aspartate diet also increased the amount of NBAT mRNA in mouse ileum. In the ileum of mice fed on the aspartate diet, the extent of cystine transport was further increased by preloading brush border membrane vesicles with lysine. Hybrid depletion of NBAT mRNA from ileal polyadenylated RNA revealed that the increase in cystine transport activity induced by the high-aspartate diet, as measured in Xenopus oocytes, was attributable to NBAT. These results demonstrate that mouse NBAT has an important role in cystine transport.
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Affiliation(s)
- H Segawa
- Department of Clinical Nutrition, School of Medicine, Tokushima University, Kuramoto-Cho 3, Tokushima 770, Japan
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Hisano S, Haga H, Li Z, Tatsumi S, Miyamoto KI, Takeda E, Fukui Y. Immunohistochemical and RT-PCR detection of Na+-dependent inorganic phosphate cotransporter (NaPi-2) in rat brain. Brain Res 1997; 772:149-55. [PMID: 9406966 DOI: 10.1016/s0006-8993(97)00884-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Expression of a renal Na+-dependent inorganic phosphate (Pi) cotransporter (NaPi-2) was studied in rat forebrain with reverse transcription and polymerase chain reaction (RT-PCR) and immunohistochemistry. RT-PCR analysis for total RNA from whole brain and sequencing of the PCR products showed expression of NaPi-2 mRNA in the brain. Immunohistochemical analysis revealed NaPi-2 staining in many nonpyramidal neurons of all six layers throughout neocortical areas and in neurons of proisocortical and periallocortical areas. NaPi-2-immunoreactive neurons were also detectable in the piriform cortex, hippocampal formation, caudate-putamen, amygdaloid nuclei and lateral geniculate nucleus. Furthermore, NaPi-2 staining was shown in ependymal cells and microvascular endothelial cells. The present results suggest that NaPi-2 is synthesized within the brain and involved in maintaining Pi homeostasis of certain neurons and/or the entire brain.
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Affiliation(s)
- S Hisano
- Department of Anatomy, School of Medicine, University of Tokushima, Japan.
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Miyamoto K, Segawa H, Tatsumi S, Katai K, Yamamoto H, Taketani Y, Haga H, Morita K, Takeda E. Effects of truncation of the COOH-terminal region of a Na+-independent neutral and basic amino acid transporter on amino acid transport in Xenopus oocytes. J Biol Chem 1996; 271:16758-63. [PMID: 8663184 DOI: 10.1074/jbc.271.28.16758] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
To determine the role of a neutral and basic amino acid transporter (NBAT) in amino acid transport, we microinjected several COOH-terminal deletion mutants of NBAT cRNA into Xenopus oocytes and measured transport activity for arginine, leucine, and cystine in the presence and absence of sodium. Wild-type NBAT significantly stimulated the uptake of all three amino acids 10-20-fold compared with controls. On the other hand, no mutant, except a Delta511-685 mutant, stimulated the uptake of these amino acids. The Delta511-685 mutant significantly increased the uptake of arginine. In the presence of sodium, the Delta511-685 mutant also increased the uptake of leucine. The Delta511-685 mutant did not stimulate cystine uptake in the presence or absence of sodium. The stimulation of arginine uptake by the Delta511-685 mutant was inhibited by a 100-fold excess of unlabeled leucine in the presence of sodium. Inhibition of L-arginine uptake by L-homoserine was seen only in the presence of sodium, and an increase in the inhibition of L-arginine uptake by L-histidine was seen when the extracellular pH was decreased. Furthermore, an inward current in oocytes injected with the Delta511-685 mutant was recorded electrophysiologically when basic amino acids were applied. Homoserine was also taken up, but sodium was necessary for their transport. These properties of the Delta511-685 mutant correspond to those of the y+ amino acid transporter. If NBAT is a component of the b0,+-like amino acid transport system, it is unlikely that a mutant protein (Delta511-685) is able to stimulate an endogenous y+-like transport system. These results suggest that NBAT functions as a activator of the amino acid transport system in Xenopus oocytes.
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Affiliation(s)
- K Miyamoto
- Department of Clinical Nutrition, School of Medicine, Tokushima University, Kuramoto-Cho 3, Tokushima 770, Japan
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