Luminal Heterodimeric Amino Acid Transporter Defective in Cystinuria

Pfeiffer, Rahel; Loffing, Johannes; Rossier, Grégoire; Bauch, Christian; Meier, Christian; Eggermann, Thomas; Loffing‐Cueni, Dominique; Kühn, Lukas C.; Verrey, François

doi:10.1091/mbc.10.12.4135

Cited by 114 publications

(155 citation statements)

References 39 publications

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“…Laser scanning confocal microscopic analyses demonstrated that b 0,ϩ AT and rBAT colocalized on the apical plasma membrane of the b 0,ϩ AT-rBAT transfectants. This distribution reflects the normal localization of these transport proteins in proximal tubular cells in vivo (13)(14)(15). Cotransfection of MDCK II cells with these two subunits resulted in a gain of function, which was evidenced by a 10-fold increase in the V max for the transport of cystine.…”

Section: Discussionmentioning

confidence: 65%

“…transporter is known to transport cystine and is localized to the luminal plasma membrane of the target epithelial cells, i.e., proximal tubular cells (2,(13)(14)(15).…”

Section: Discussionmentioning

confidence: 99%

“…More importantly, this amino acid transporter has a high affinity for cystine (11,12) and, in the kidneys, is localized exclusively in the luminal plasma membrane of the target epithelial cells, i.e., proximal tubular cells (13)(14)(15). On the basis of these characteristics, we hypothesize that system b 0,ϩ is capable of transporting mercuric ions, in the form of Cys-S-Hg-S-Cys, into the intracellular compartment of renal epithelial cells.…”

mentioning

confidence: 99%

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Mercuric Conjugates of Cysteine Are Transported by the Amino Acid Transporter System b0,+

Bridges¹,

Bauch²,

Verrey³

et al. 2004

Journal of the American Society of Nephrology

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Abstract. Humans and other mammals continue to be exposed to various forms of mercury in the environment. The kidneys, specifically the epithelial cells lining the proximal tubules, are the primary targets where mercuric ions accumulate and exert their toxic effects. Although the actual mechanisms involved in the transport of mercuric ions along the proximal tubule have not been defined, current evidence implicates mercuric conjugates of cysteine, primarily 2-amino-3-(2-amino-2-carboxyethylsulfanylmercuricsulfanyl)propionic acid (Cys-S-Hg-S-Cys), as the most likely transportable species of inorganic mercury (Hg 2ϩ ). Because Cys-S-Hg-S-Cys and the amino acid cystine (Cys-S-S-Cys) are structurally similar, it was hypothesized that Cys-S-Hg-S-Cys might act as a molecular mimic of cystine at one or more of the amino acid transporters involved in the luminal absorption of this amino acid. One such candidate is the Na ϩ -independent heterodimeric transporter system b 0,ϩ . Therefore, the transport of Cys-S-Hg-S-Cys and cystine was studied in MDCK II cells that were or were not stably transfected with b 0,ϩ AT-rBAT. Transport of Cys-S-Hg-S-Cys and cystine across the luminal plasma membrane was similar in the transfected cells, indicating that Cys-S-Hg-S-Cys can behave as a molecular mimic of cystine at the site of system b 0,ϩ . Moreover, only the b 0,ϩ AT-rBAT transfectants became selectively intoxicated during exposure to Cys-S-Hg-S-Cys. These findings indicate that system b 0,ϩ likely contributes to the nephropathy induced by Hg 2ϩ in vivo. These data represent the first direct molecular evidence for the participation of a specific transporter in the luminal uptake of a large divalent metal cation in proximal tubular cells.A large body of evidence indicates that the epithelial cells lining the convoluted and straight segments of the proximal tubule are the primary sites where inorganic mercury (Hg 2ϩ ) is taken up and accumulated in vivo (1,2). Although the actual mechanisms by which mercuric ions are taken up by these cells are not well defined, a number of recent in vivo findings indicate that the uptake of Hg 2ϩ at the luminal membrane of proximal tubular cells is dependent on the activities of the brush border enzymes ␥-glutamyltransferase (3-8) and cysteinylglycinase (8). It seems that mercuric conjugates of GSH, while in the lumen of the proximal tubule, are degraded sequentially by these enzymes to yield a cysteine-S-conjugate of mercury, primarily 2-amino-3-(2-amino-2-carboxyethylsulfanylmercuricsulfanyl)propionic acid (Cys-S-Hg-S-Cys) (2). This conjugate is thought to be the principal species of Hg 2ϩ taken up at the luminal plasma membrane of proximal tubular epithelial cells (3-8).Recent studies using brush border membrane vesicles (9) and isolated perfused proximal tubular segments (8,10) indicate that Cys-S-Hg-S-Cys is indeed transported across the luminal membrane of proximal tubular epithelial cells. Moreover, competitive inhibition experiments using isolated perfused proximal tubular segments have i...

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Section: Discussionmentioning

confidence: 65%

“…transporter is known to transport cystine and is localized to the luminal plasma membrane of the target epithelial cells, i.e., proximal tubular cells (2,(13)(14)(15).…”

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Mercuric Conjugates of Cysteine Are Transported by the Amino Acid Transporter System b0,+

Bridges¹,

Bauch²,

Verrey³

et al. 2004

Journal of the American Society of Nephrology

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“…Two heteromeric amino acid transport exchangers (systems b o,ϩ and y ϩ L) have a major role in the reabsorption of cystine and dibasic amino acids (2)(3)(4). First, the heterodimer formed by rBAT and b o,ϩ AT is the amino acid transporter b o,ϩ , which mediates high-affinity uptake of cystine and dibasic amino acids coupled with the efflux of neutral amino acids (5)(6)(7)(8) at the apical membrane of epithelial cells of the proximal tubule (9). Indeed, mutations in the rBAT (SLC3A1) gene cause type I cystinuria, and mutations in the b o,ϩ AT (SLC7A9) gene cause mainly non-type I and also type I cystinuria (recessive inherited aminoacidurias of cystine and dibasic amino acids) (6,10,11).…”

mentioning

confidence: 99%

Basolateral LAT-2 Has a Major Role in the Transepithelial Flux of L-Cystine in the Renal Proximal Tubule Cell Line OK

Fernández¹,

Torrents²,

Chillarón³

et al. 2003

Journal of the American Society of Nephrology

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Abstract. During renal reabsorption, the amino acid transporters b o,ϩ and y ϩ L have a major role in the apical uptake of cystine and dibasic amino acids and in the basolateral efflux of dibasic amino acids, respectively. In contrast, the transporters responsible for the basolateral efflux of the apically transported cystine are unknown. This study shows the expression of system L and y ϩ L transport activities in the basolateral domain of the proximal tubule-derived cell line OK and the cloning of the corresponding LAT-2 and y ϩ LAT-1 cDNAs. Stable transfection with a LAT-2 antisense sequence demonstrated the specific role of LAT-2 in the basolateral system L amino acid exchange activity in OK cells. This partial reduction of LAT-2 expression decreased apical-to-basolateral trans-epithelial flux of cystine and resulted in a twofold to threefold increase in the intracellular content of cysteine. In contrast, the content of serine, threonine, and alanine showed a tendency to decrease, whereas other LAT-2 substrates were not affected. This demonstrates that LAT-2 plays a major specific role in the net basolateral efflux of cysteine and points to LAT-2 as a candidate gene to modulate cystine reabsorption.In the kidney, most glomerulus-filtered amino acids are reabsorbed in the early proximal tubule (1). The amino acids are taken up through the brush border membrane and exit the epithelial cells through the basolateral membrane to the interstitial space. Two heteromeric amino acid transport exchangers (systems b o,ϩ and y ϩ L) have a major role in the reabsorption of cystine and dibasic amino acids (2-4). First, the heterodimer formed by rBAT and b o,ϩ AT is the amino acid transporter b o,ϩ , which mediates high-affinity uptake of cystine and dibasic amino acids coupled with the efflux of neutral amino acids (5-8) at the apical membrane of epithelial cells of the proximal tubule (9). Indeed, mutations in the rBAT (SLC3A1) gene cause type I cystinuria, and mutations in the b o,ϩ AT (SLC7A9) gene cause mainly non-type I and also type I cystinuria (recessive inherited aminoacidurias of cystine and dibasic amino acids) (6,10,11). Second, y ϩ LAT-1 dimerizes with 4F2hc to form the amino acid transporter y ϩ L, which mediates the efflux of cationic amino acids coupled with the influx of neutral amino acids plus sodium (12-14). Mutations in y ϩ LAT-1 (SLC7A7) cause lysinuric protein intolerance (15,16), an inherited aminoaciduria due to defective dibasic amino acid efflux from the basolateral membrane of proximal tubule epithelial cells (17). Thus, systems b o,ϩ and y ϩ L explain the trans-epithelial transport of dibasic amino acids. In contrast, the amino acid transporters that play a major role in the basolateral efflux of the apically taken-up cystine remain to be identified.Polarized OK cells, a proximal tubule-derived cell line from the American opossum, has been extensively used as a model for transport studies in renal epithelial cells. Indeed, OK cells express rBAT-associated system b o,ϩ transport activity in the...

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“…Uptakes-Oocyte preparation and cRNA injection were carried out according to previously described procedures (8,10). Briefly, injected oocytes were incubated for 72 h in ND96 buffer (96 mM NaCl, 2 mM KCl, 1 mM MgCl 2 , 1 mM CaCl 2 , and 10 mM HEPES, pH 7.4, adjusted with KOH) supplemented with tetracycline (50 mg/l).…”

Section: Functional Experiments In Xenopus Laevis Oocytes-mentioning

confidence: 99%

Aromatic Amino Acid Transporter AAT-9 of Caenorhabditis elegans Localizes to Neurons and Muscle Cells

Veljkovic

Bacconi

Steták

et al. 2004

Journal of Biological Chemistry

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The Caenorhabditis elegans genome encodes nine homologues of mammalian glycoprotein-associated amino acid transporters. Two of these C. elegans proteins (AAT-1 and AAT-3) have been shown to function as catalytic subunits (light chains) of heteromeric amino acid transporters. These proteins need to associate with a glycoprotein heavy chain subunit (ATG-2) to reach the cell surface in a manner similar to that of their mammalian homologues. AAT-1 and AAT-3 contain a cysteine residue in the second putative extracellular loop through which a disulfide bridge can form with a heavy chain. In contrast, six C. elegans members of this family (AAT-4 to AAT-9) lack such a cysteine residue. We show here that one of these transporter proteins, AAT-9, reaches the cell surface in Xenopus oocytes without an exogenous heavy chain and that it functions as an exchanger of aromatic amino acids. Two-electrode voltage clamp experiments demonstrate that AAT-9 displays a substrate-activated conductance. Immunofluorescence shows that it is expressed close to the pharyngeal bulbs within C. elegans neurons. The selective expression of an aat-9 promoter-green fluorescent protein construct in several neurons of this region and in wall muscle cells around the mouth supports and extends these localization data. Taken together, the results show that AAT-9 is expressed in excitable cells of the nematode head and pharynx in which it may provide a pathway for aromatic amino acid transport.

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Luminal Heterodimeric Amino Acid Transporter Defective in Cystinuria

Cited by 114 publications

References 39 publications

Mercuric Conjugates of Cysteine Are Transported by the Amino Acid Transporter System b0,+

Mercuric Conjugates of Cysteine Are Transported by the Amino Acid Transporter System b0,+

Basolateral LAT-2 Has a Major Role in the Transepithelial Flux of L-Cystine in the Renal Proximal Tubule Cell Line OK

Aromatic Amino Acid Transporter AAT-9 of Caenorhabditis elegans Localizes to Neurons and Muscle Cells

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