scholarly journals Involvement of the L-Type Amino Acid Transporter Lat2 in the Transport of 3,3′-Diiodothyronine across the Plasma Membrane

2015 ◽  
Vol 4 (Suppl. 1) ◽  
pp. 42-50 ◽  
Author(s):  
Anita Kinne ◽  
Melanie Wittner ◽  
Eva K. Wirth ◽  
Katrin M. Hinz ◽  
Ralf Schülein ◽  
...  
Keyword(s):  
Amino Acid ◽  
Thyroid Hormone ◽  
Thyroid Hormones ◽  
Surface Expression ◽  
Amino Acid Transporter ◽  
Cell System ◽  
Monocarboxylate Transporter ◽  
Cell Surface Expression ◽  
Xenopus Laevis Oocytes ◽  
Acid Transporter

Thyroid hormones are transported across cell membranes by transmembrane transporter proteins, for example by members of the monocarboxylate transporter (MCT) and the L-type amino acid transporter (LAT) families. LATs consist of a light chain (e.g. LAT2) and a heavy chain (CD98), which is essential for their cell surface expression and functionality. The specificity of Lat2 for thyroid hormones and their metabolites and its role in their transport was not fully clear. This fact motivated us to establish a cell system to elucidate the uptake of thyroid hormones and their metabolites by mouse Lat2. The coinjection of cRNA coding for Lat2 and CD98 into Xenopus laevis oocytes resulted in a markedly increased level of 3,3′-diiodo-L-thyronine (3,3′-T2) and to some extent also enhanced T3 transport. To gain insight into properties of thyroid hormones and their metabolites transported by Lat2, we inhibited 3,3′-T2 uptake by various iodothyronine derivatives. T1 and T2 derivatives as well as 2-aminobicyclo-[2,2,1]-heptane-2-carboxylic acid strongly competed with 3,3′-T2 uptake. In addition, we performed T2 uptake measurements with the thyroid hormone-specific transporter MCT8. For both Lat2 and MCT8, Km values in a low micromolar range were calculated. We demonstrated that oocytes are a suitable system for thyroid hormone transport studies mediated by Lat2. Our data indicates that Lat2 compared to other thyroid hormone transporters prefers 3,3′-T2 as the substrate. Thus, Lat2 might contribute to the availability of thyroid hormone by importing and/or exporting 3,3′-T2, which is generated either by T3 inactivation or by rapid deiodinase 1-mediated rT3 degradation.

scholarly journals Neutral amino acid transporter ASCT2 displays substrate-induced Na+ exchange and a substrate-gated anion conductance

2000 ◽  
Vol 346 (3) ◽  
pp. 705-710 ◽  
Author(s):  
Angelika BRÖER ◽  
Carsten WAGNER ◽  
Florian LANG ◽  
Stefan BRÖER
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Anion Channel ◽  
Amino Acid Transporter ◽  
Neutral Amino Acid ◽  
Xenopus Laevis Oocytes ◽  
Anion Conductance ◽  
Neutral Amino Acid Transporter ◽  
Inward Currents ◽  
Acid Transporter

The neutral amino acid transporter ASCT2 mediates electroneutral obligatory antiport but at the same time requires Na+ for its function. To elucidate the mechanism, ASCT2 was expressed in Xenopus laevis oocytes and transport was analysed by flux studies and two-electrode voltage clamp recordings. Flux studies with 22NaCl indicated that the uptake of one molecule of glutamine or alanine is accompanied by the uptake of four to seven Na+ ions. Similarly to the transport of amino acids, the Na+ uptake was mediated by an obligatory Na+ exchange mechanism that depended on the presence of amino acids but was not stoichiometrically coupled to the amino acid transport. Other cations could not replace Na+ in this transport mechanism. When NaCl was replaced by NaSCN in the transport buffer, the superfusion of oocytes with amino acid substrates resulted in large inward currents, indicating the presence of a substrate-gated anion channel in the ASCT2 transporter. The Km for glutamine derived from these experiments is in good agreement with the Km derived from flux studies; it varied between 40 and 90 μM at holding potentials of -60 and -20 mV respectively. The permeability of the substrate-gated anion conductance decreased in the order SCN- NO3- > I- > Cl- and also required the presence of Na+.

Galectin-lattice sustains function of cationic amino acid transporter and insulin secretion of pancreatic β cells

2020 ◽  
Vol 167 (6) ◽  
pp. 587-596 ◽  
Author(s):  
Kento Maeda ◽  
Masayoshi Tasaki ◽  
Yukio Ando ◽  
Kazuaki Ohtsubo
Keyword(s):  
Insulin Secretion ◽  
Amino Acid ◽  
Cell Surface ◽  
Amino Acid Transporter ◽  
Cell Surface Expression ◽  
Cationic Amino Acid Transporter ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Cationic Amino Acid ◽  
Acid Transporter

Abstract Maintenance of cell surface residency and function of glycoproteins by lectins are essential for regulating cellular functions. Galectins are β-galactoside-binding lectins and form a galectin-lattice, which regulates stability, clustering, membrane sub-domain localization and endocytosis of plasmalemmal glycoproteins. We have previously reported that galectin-2 (Gal-2) forms a complex with cationic amino acid transporter 3 (CAT3) in pancreatic β cells, although the biological significance of the molecular interaction between Gal-2 and CAT3 has not been elucidated. In this study, we demonstrated that the structure of N-glycan of CAT3 was either tetra- or tri-antennary branch structure carrying β-galactosides, which works as galectin-ligands. Indeed, CAT3 bound to Gal-2 using β-galactoside epitope. Moreover, the disruption of the glycan-mediated bindings between galectins and CAT3 significantly reduced cell surface expression levels of CAT3. The reduced cell surface residency of CAT3 attenuated the cellular arginine uptake activities and subsequently reduced nitric oxide production, and thus impaired the arginine-stimulated insulin secretion of pancreatic β cells. These results indicate that galectin-lattice stabilizes CAT3 by preventing endocytosis to sustain the arginine-stimulated insulin secretion of pancreatic β cells. This provides a novel cell biological insight into the endocrinological mechanism of nutrition metabolism and homeostasis.

scholarly journals Intestinal peptidases form functional complexes with the neutral amino acid transporter B0AT1

2012 ◽  
Vol 446 (1) ◽  
pp. 135-148 ◽  
Author(s):  
Stephen J. Fairweather ◽  
Angelika Bröer ◽  
Megan L. O'Mara ◽  
Stefan Bröer
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Amino Acid Transporter ◽  
The Body ◽  
Site Directed Mutagenesis ◽  
Substrate Affinity ◽  
Xenopus Laevis Oocytes ◽  
Acid Transporter

The brush-border membrane of the small intestine and kidney proximal tubule are the major sites for the absorption and re-absorption of nutrients in the body respectively. Transport of amino acids is mediated through the action of numerous secondary active transporters. In the mouse, neutral amino acids are transported by B0AT1 [broad neutral (0) amino acid transporter 1; SLC6A19 (solute carrier family 6 member 19)] in the intestine and by B0AT1 and B0AT3 (SLC6A18) in the kidney. Immunoprecipitation and Blue native electrophoresis of intestinal brush-border membrane proteins revealed that B0AT1 forms complexes with two peptidases, APN (aminopeptidase N/CD13) and ACE2 (angiotensin-converting enzyme 2). Physiological characterization of B0AT1 expressed together with these peptidases in Xenopus laevis oocytes revealed that APN increased the substrate affinity of the transporter up to 2.5-fold and also increased its surface expression (Vmax). Peptide competition experiments, in silico modelling and site-directed mutagenesis of APN suggest that the catalytic site of the peptidase is involved in the observed changes of B0AT1 apparent substrate affinity, possibly by increasing the local substrate concentration. These results provide evidence for the existence of B0AT1-containing digestive complexes in the brush-border membrane, interacting differentially with various peptidases, and responding to the dynamic needs of nutrient absorption in the intestine and kidney.

scholarly journals Transport of butyryl-l-carnitine, a potential prodrug, via the carnitine transporter OCTN2 and the amino acid transporter ATB0,+

2007 ◽  
Vol 293 (5) ◽  
pp. G1046-G1053 ◽  
Author(s):  
Sonne R. Srinivas ◽  
Puttur D. Prasad ◽  
Nagavedi S. Umapathy ◽  
Vadivel Ganapathy ◽  
Prem S. Shekhawat
Keyword(s):  
Amino Acid ◽  
Mammalian Cells ◽  
High Capacity ◽  
Amino Acid Transporter ◽  
Xenopus Laevis Oocytes ◽  
Loss Of Function ◽  
Bacterial Fermentation ◽  
Carnitine Transporter ◽  
Inward Currents ◽  
Acid Transporter

l-Carnitine is absorbed in the intestinal tract via the carnitine transporter OCTN2 and the amino acid transporter ATB0,+. Loss-of-function mutations in OCTN2 may be associated with inflammatory bowel disease (IBD), suggesting a role for carnitine in intestinal/colonic health. In contrast, ATB0,+ is upregulated in bowel inflammation. Butyrate, a bacterial fermentation product, is beneficial for prevention/treatment of ulcerative colitis. Butyryl-l-carnitine (BC), a butyrate ester of carnitine, may have potential for treatment of gut inflammation, since BC would supply both butyrate and carnitine. We examined the transport of BC via ATB0,+ to determine if this transporter could serve as a delivery system for BC. We also examined the transport of BC via OCTN2. Studies were done with cloned ATB0,+ and OCTN2 in heterologous expression systems. BC inhibited ATB0,+-mediated glycine transport in mammalian cells (IC50, 4.6 ± 0.7 mM). In Xenopus laevis oocytes expressing human ATB0,+, BC induced Na+-dependent inward currents under voltage-clamp conditions. The currents were saturable with a K0.5 of 1.4 ± 0.1 mM. Na+ activation kinetics of BC-induced currents suggested involvement of two Na+ per transport cycle. BC also inhibited OCTN2-mediated carnitine uptake (IC50, 1.5 ± 0.3 μM). Transport of BC via OCTN2 is electrogenic, as evidenced from BC-induced inward currents. These currents were Na+ dependent and saturable ( K0.5, 0.40 ± 0.02 μM). We conclude that ATB0,+ is a low-affinity/high-capacity transporter for BC, whereas OCTN2 is a high-affinity/low-capacity transporter. ATB0,+ may mediate intestinal absorption of BC when OCTN2 is defective.

Expression of the mammalian Na+-independent L System amino acid transporter in Xenopus laevis oocytes

1989 ◽  
Vol 275 (2) ◽  
pp. 591-596 ◽  
Author(s):  
Suresh S. Tate ◽  
Reiko Urade ◽  
Thomas V. Getchell ◽  
Sidney Udenfriend
Keyword(s):  
Amino Acid ◽  
Xenopus Laevis ◽  
Amino Acid Transporter ◽  
Xenopus Laevis Oocytes ◽  
L System ◽  
Acid Transporter

scholarly journals Aminoaciduria, but normal thyroid hormone levels and signalling, in mice lacking the amino acid and thyroid hormone transporter Slc7a8

2011 ◽  
Vol 439 (2) ◽  
pp. 249-255 ◽  
Author(s):  
Doreen Braun ◽  
Eva K. Wirth ◽  
Franziska Wohlgemuth ◽  
Nathalie Reix ◽  
Marc O. Klein ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Thyroid Hormone ◽  
Thyroid Hormones ◽  
Cell Types ◽  
Monocarboxylate Transporter ◽  
Functional Compensation ◽  
Neutral Amino Acids ◽  
System L ◽  
Neurological Phenotype

LAT2 (system L amino acid transporter 2) is composed of the subunits Slc7a8/Lat2 and Slc3a2/4F2hc. This transporter is highly expressed along the basolateral membranes of absorptive epithelia in kidney and small intestine, but is also abundant in the brain. Lat2 is an energy-independent exchanger of neutral amino acids, and was shown to transport thyroid hormones. We report in the present paper that targeted inactivation of Slc7a8 leads to increased urinary loss of small neutral amino acids. Development and growth of Slc7a8−/− mice appears normal, suggesting functional compensation of neutral amino acid transport by alternative transporters in kidney, intestine and placenta. Movement co-ordination is slightly impaired in mutant mice, although cerebellar development and structure remained inconspicuous. Circulating thyroid hormones, thyrotropin and thyroid hormone-responsive genes remained unchanged in Slc7a8−/− mice, possibly because of functional compensation by the thyroid hormone transporter Mct8 (monocarboxylate transporter 8), which is co-expressed in many cell types. The reason for the mild neurological phenotype remains unresolved.

Sign in / Sign up

Export Citation Format

Share Document