Molecular basis of essential amino acid transport from studies of insect nutrient amino acid transporters of the SLC6 family (NAT-SLC6)

ABSTRACT In Saccharomyces cerevisiae, Avt4 exports neutral and basic amino acids from vacuoles. Previous studies have suggested that the GATA transcription factors, Gln3 and Gat1, which are key regulators that adapt cells in response to changes in amino acid status, are involved in the AVT4 transcription. Here, we show that mutations in the putative GATA-binding sites of the AVT4 promoter reduced AVT4 expression. Consistently, a chromatin immunoprecipitation (ChIP) assay revealed that Gat1-Myc13 binds to the AVT4 promoter. Previous microarray results were confirmed that gln3∆gat1∆ cells showed a decrease in expression of AVT1 and AVT7, which also encode vacuolar amino acid transporters. Additionally, ChIP analysis revealed that the AVT6 encoding vacuolar acidic amino acid exporter represents a new direct target of the GATA transcription factor. The broad effect of the GATA transcription factors on the expression of AVT transporters suggests that vacuolar amino acid transport is integrated into cellular amino acid homeostasis.

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Placental amino acid transport

AJP Cell Physiology ◽

10.1152/ajpcell.1995.268.6.c1321 ◽

1995 ◽

Vol 268 (6) ◽

pp. C1321-C1331 ◽

Cited By ~ 85

Author(s):

A. J. Moe

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Human Placenta ◽

Amino Acid Transport ◽

Single Layer ◽

Maternal Blood ◽

Transport Systems ◽

Amino Acid Transporters ◽

Acid Transport ◽

Principal Mechanism

Normal fetal growth and development depend on a continuous supply of amino acids from the mother to the fetus. The placenta is responsible for the transfer of amino acids between the two circulations. The human placenta is hemomonochorial, meaning that the maternal and fetal circulations are separated by a single layer of polarized epithelium called the syncytiotrophoblast, which is in direct contact with maternal blood. Transport proteins located in the microvillous and basal membranes of the syncytiotrophoblast are the principal mechanism for transfer from maternal blood to fetal blood. Knowledge of the function and regulation of syncytiotrophoblast amino acid transporters is of great importance in understanding the mechanism of placental transport and potentially improving fetal and newborn outcomes. The development of methods for the isolation of microvillous and basal membrane vesicles from human placenta over the past two decades has contributed greatly to this understanding. Now a primary cultured trophoblast model is available to study amino acid transport and regulation as the cells differentiate. The types of amino acid transporters and their distribution between the syncytiotrophoblast microvillous and basal membranes are somewhat unique compared with other polarized epithelia. These differences may reflect the unusual circumstance of this epithelium that is exposed to blood on both sides. The current state of knowledge as to the types of transport systems present in syncytiotrophoblast, their regulation, and the effects of maternal consumption of drugs on transport are discussed.

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Correction: Genetic Disruption of the Multifunctional CD98/LAT1 Complex Demonstrates the Key Role of Essential Amino Acid Transport in the Control of mTORC1 and Tumor Growth

Cancer Research ◽

10.1158/0008-5472.can-17-1457 ◽

2017 ◽

Vol 77 (13) ◽

pp. 3721-3721

Keyword(s):

Amino Acid ◽

Tumor Growth ◽

Amino Acid Transport ◽

Essential Amino Acid ◽

Acid Transport

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Expression of solute carrier 7A4 (SLC7A4) in the plasma membrane is not sufficient to mediate amino acid transport activity

Biochemical Journal ◽

10.1042/bj20020084 ◽

2002 ◽

Vol 364 (3) ◽

pp. 767-775 ◽

Cited By ~ 40

Author(s):

Sabine WOLF ◽

Annette JANZEN ◽

Nicole VÉKONY ◽

Ursula MARTINÉ ◽

Dennis STRAND ◽

...

Keyword(s):

Plasma Membrane ◽

Amino Acid ◽

Protein Expression ◽

Amino Acid Transport ◽

Fluorescent Protein ◽

Xenopus Laevis Oocytes ◽

Amino Acid Transporters ◽

Acid Transport ◽

Transport Activity ◽

Solute Carrier

Member 4 of human solute carrier family 7 (SLC7A4) exhibits significant sequence homology with the SLC7 subfamily of human cationic amino acid transporters (hCATs) [Sperandeo, Borsani, Incerti, Zollo, Rossi, Zuffardi, Castaldo, Taglialatela, Andria and Sebastio (1998) Genomics 49, 230–236]. It is therefore often referred to as hCAT-4 even though no convincing transport activity has been shown for this protein. We expressed SLC7A4 in Xenopus laevis oocytes, but could not detect any transport activity for cationic, neutral or anionic amino acids or for the polyamine putrescine. In addition, human glioblastoma cells stably overexpressing a fusion protein between SLC7A4 and the enhanced green fluorescent protein (EGFP) did not exhibit an increased transport activity for l-arginine. The lack of transport activity was not due to a lack of SLC7A4 protein expression in the plasma membrane, as in both cell types SLC7A4-EGFP exhibited a similar subcellular localization and level of protein expression as functional hCAT-EGFP proteins. The expression of SLC7A4 can be induced in NT2 teratocarcinoma cells by treatment with retinoic acid. However, also for this endogenously expressed SLC7A4, we could not detect any transport activity for l-arginine. Our data demonstrate that the expression of SLC7A4 in the plasma membrane is not sufficient to induce an amino acid transport activity in X. laevis oocytes or human cells. Therefore, SLC7A4 is either not an amino acid transporter or it needs additional (protein) factor(s) to be functional.

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Amino-acid-dependent modulation of amino acid transport in Xenopus laevis oocytes.

Journal of Experimental Biology ◽

10.1242/jeb.199.4.923 ◽

1996 ◽

Vol 199 (4) ◽

pp. 923-931 ◽

Cited By ~ 2

Author(s):

P M Taylor ◽

S Kaur ◽

B Mackenzie ◽

G J Peter

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Xenopus Laevis ◽

Amino Acid Transport ◽

Acid Mixture ◽

Xenopus Laevis Oocytes ◽

Amino Acid Transporters ◽

Amino Acid Supplementation ◽

Acid Transport ◽

Acid Supplementation

We have measured rates of uptake of arginine, glutamine, glutamate, serine, phenylalanine and glycine in Xenopus laevis oocytes cultured for periods of up to 24h in saline in the presence or absence of a mixture of 20 amino acids at concentrations approximating those in Xenopus plasma. Amino acid supplementation increased the total intracellular amino acid concentration from 8.2 to 18.4 nmol per oocyte. Specific Na(+)-dependent amino acid transporters (systems B0,+, Xag-) exhibit 'adaptive regulation' (up-regulation during amino acid deprivation and down-regulation during amino acid supplementation). Na(+)-independent transporters of glutamate, glutamine and glycine (including system asc) display an opposite modulation in activity, which may help to combat amino-acid-induced oxidative stress by increasing the supply of glutathione precursors. Single amino acids at physiological plasma concentrations (0.47 mmol l-1 L-alanine, 0.08 mmol l-1 L-glutamate) mimicked at least some effects of the amino acid mixture. The mechanisms of transport modulation do not appear to include trans-amino acid or membrane potential effects and, in the case of Na(+)-independent transport, are independent of protein or mRNA synthesis. Furthermore, activation of protein kinase C by phorbol 12-myristate 13-acetate did not significantly affect endogenous glutamine and glutamate transport. The Xenopus oocyte appears to possess endogenous signalling mechanisms for selectively modulating the activity of amino acid transport proteins expressed in its surface membranes, a factor for consideration when using oocytes as an expression system for structure-function studies of cloned amino acid transporters.

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Molecular cloning of the mouse IMINO system: an Na+- and Cl−-dependent proline transporter

Biochemical Journal ◽

10.1042/bj20050100 ◽

2005 ◽

Vol 386 (3) ◽

pp. 417-422 ◽

Cited By ~ 72

Author(s):

Sonja KOWALCZUK ◽

Angelika BRÖER ◽

Michael MUNZINGER ◽

Nadine TIETZE ◽

Karin KLINGEL ◽

...

Keyword(s):

Small Intestine ◽

Amino Acid ◽

Epithelial Cells ◽

Xenopus Laevis ◽

Molecular Cloning ◽

Amino Acid Transport ◽

Tissue Expression ◽

Xenopus Laevis Oocytes ◽

Acid Transport ◽

Slc6 Family

Neurotransmitter transporters of the SLC6 family play an important role in the removal of neurotransmitters in brain tissue and in amino acid transport in epithelial cells. Here we demonstrate that the mouse homologue of slc6a20 has all properties of the long-sought IMINO system. The mouse has two homologues corresponding to the single human SLC6A20 gene: these have been named XT3 and XT3s1. Expression of mouse XT3s1, but not XT3, in Xenopus laevis oocytes induced an electrogenic Na+-and-Cl−-dependent transporter for proline, hydroxyproline, betaine, N-methylaminoisobutyric acid and pipecolic acid. Expression of XT3s1 was found in brain, kidney, small intestine, thymus, spleen and lung, whereas XT3 prevailed in kidney and lung. Accordingly we suggest that the two homologues be termed ‘XT3s1 IMINOB’ and ‘XT3 IMINOK’ to indicate the tissue expression of the two genes.

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Heteromeric amino acid transporters: biochemistry, genetics, and physiology

AJP Renal Physiology ◽

10.1152/ajprenal.2001.281.6.f995 ◽

2001 ◽

Vol 281 (6) ◽

pp. F995-F1018 ◽

Cited By ~ 120

Author(s):

Josep Chillarón ◽

Ramón Roca ◽

Alfonso Valencia ◽

Antonio Zorzano ◽

Manuel Palacín

Keyword(s):

Amino Acid ◽

Amino Acid Transport ◽

Human Genetics ◽

Disulfide Bridge ◽

Transport Systems ◽

Cell Physiology ◽

Amino Acid Transporters ◽

Acid Transport ◽

Membrane Glycoproteins ◽

Cell Functions

The heteromeric amino acid transporters (HATs) are composed of two polypeptides: a heavy subunit (HSHAT) and a light subunit (LSHAT) linked by a disulfide bridge. HSHATs are N-glycosylated type II membrane glycoproteins, whereas LSHATs are nonglycosylated polytopic membrane proteins. The HSHATs have been known since 1992, and the LSHATs have been described in the last three years. HATs represent several of the classic mammalian amino acid transport systems (e.g., L isoforms, y+L isoforms, asc, x[Formula: see text], and b0,+). Members of the HAT family are the molecular bases of inherited primary aminoacidurias cystinuria and lysinuric protein intolerance. In addition to the role in amino acid transport, one HSHAT [the heavy subunit of the cell-surface antigen 4F2 (also named CD98)] is involved in other cell functions that might be related to integrin activation. This review covers the biochemistry, human genetics, and cell physiology of HATs, including the multifunctional character of CD98.

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Amino Acid Transporters as Disease Modifiers and Drug Targets

SLAS DISCOVERY Advancing Life Sciences ◽

10.1177/2472555218755629 ◽

2018 ◽

Vol 23 (4) ◽

pp. 303-320 ◽

Cited By ~ 12

Author(s):

Stefan Bröer

Keyword(s):

Amino Acid ◽

Amino Acid Transport ◽

Neurological Disorders ◽

Cell Biology ◽

Drug Targets ◽

Therapeutic Strategy ◽

Amino Acid Transporters ◽

Acid Transport ◽

Membrane Protein Expression

Amino acids perform a variety of functions in cells and organisms, particularly in the synthesis of proteins, as energy metabolites, neurotransmitters, and precursors for many other molecules. Amino acid transport plays a key role in all these functions. Inhibition of amino acid transport is pursued as a therapeutic strategy in several areas, such as diabetes and related metabolic disorders, neurological disorders, cancer, and stem cell biology. The role of amino acid transporters in these disorders and processes is well established, but the implementation of amino acid transporters as drug targets is still in its infancy. This is at least in part due to the underdeveloped pharmacology of this group of membrane proteins. Recent advances in structural biology, membrane protein expression, and inhibitor screening methodology will see an increased number of improved and selective inhibitors of amino acid transporters that can serve as tool compounds for further studies.

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Placental amino acid transport may be regulated by maternal vitamin D and vitamin D-binding protein: results from the Southampton Women's Survey

British Journal Of Nutrition ◽

10.1017/s0007114515001178 ◽

2015 ◽

Vol 113 (12) ◽

pp. 1903-1910 ◽

Cited By ~ 24

Author(s):

J. K. Cleal ◽

P. E. Day ◽

C. L. Simner ◽

S. J. Barton ◽

P. A. Mahon ◽

...

Keyword(s):

Gene Expression ◽

Vitamin D ◽

Body Composition ◽

Amino Acid ◽

Amino Acid Transport ◽

Amino Acid Transporter ◽

Amino Acid Transporters ◽

Acid Transport ◽

Vitamin D Binding Protein ◽

Maternal Factors

Both maternal 25-hydroxyvitamin D (25(OH)D) concentrations during pregnancy and placental amino acid transporter gene expression have been associated with development of the offspring in terms of body composition and bone structure. Several amino acid transporter genes have vitamin D response elements in their promoters suggesting the possible linkage of these two mechanisms. We aimed to establish whether maternal 25(OH)D and vitamin D-binding protein (VDBP) levels relate to expression of placental amino acid transporters. RNA was extracted from 102 placental samples collected in the Southampton Women's Survey, and gene expression was analysed using quantitative real-time PCR. Gene expression data were normalised to the geometric mean of three housekeeping genes, and related to maternal factors and childhood body composition. Maternal serum 25(OH)D and VDBP levels were measured by radioimmunoassay. Maternal 25(OH)D and VDBP levels were positively associated with placental expression of specific genes involved in amino acid transport. Maternal 25(OH)D and VDBP concentrations were correlated with the expression of specific placental amino acid transporters, and thus may be involved in the regulation of amino acid transfer to the fetus. The positive correlation of VDBP levels and placental transporter expression suggests that delivery of vitamin D to the placenta may be important. This exploratory study identifies placental amino acid transporters which may be altered in response to modifiable maternal factors and provides a basis for further studies.

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Gene-product designations for amino acid transporters.

Journal of Experimental Biology ◽

10.1242/jeb.196.1.51 ◽

1994 ◽

Vol 196 (1) ◽

pp. 51-57 ◽

Cited By ~ 1

Author(s):

H N Christensen ◽

L M Albritton ◽

D K Kakuda ◽

C L MacLeod

Keyword(s):

Amino Acid ◽

Gene Product ◽

Amino Acid Transport ◽

Full Range ◽

Transport Systems ◽

Amino Acid Transporters ◽

Gene Products ◽

Acid Transport ◽

Good Set ◽

Cloned Gene

The molecular cloning of genes that encode amino acid transporters presents the scientific community with the opportunity to name their gene products using a scheme that could usefully recall the well-defined transport system most similar in properties to the newly identified cloned gene product. To avoid the problem of rising confusion, we propose to take advantage of established designation methods that indicate the types of amino acids transported and the co-substrate ion requirement of their transport. The economy obligated by the necessity to keep the number of symbols in a gene name to a minimum will rarely permit a listing of the full range of substrates, since amino acid transport systems have broad substrate specificities with co-substrate requirements that can differ in a substrate-specific manner. Hence, the use of established systems to codify groups of amino acid transport systems, which allow identification of the substrate range by using 1-3 letters, e.g. A, L or even ASC, could be integrated with a system used to indicate the ion-dependence of transport. The discoverers of transporters are mainly proceeding with commendable reserve and are inviting discussion, a desire which this essay urges be facilitated by more formal arrangements for further planning. These discoverers have also shown, along with an expressed desire for guidance, well-advised spontaneity in making reference to the substrate range, two trends that together suggest that a good set of designations can evolve that will be highly descriptive.(ABSTRACT TRUNCATED AT 250 WORDS)

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