The amino acid transporter asc-1 is not involved in cystinuria

Marta Pineda, Mariona Font, Maria Teresa Bassi, Marta Manzoni, Giuseppe Borsani, Valeria Marigo, Esperanza Fernández, Rafael Martín Del Río, Jesǔs Purroy, Antonio Zorzano, Virginia Nunes, Manuel Palacín

Research output: Contribution to journalArticle

Abstract

Background. The human amino acid transporter asc-1 (SLC7A10) exhibits substrate selectivity for small neutral amino acids, including cysteine, is expressed in kidney, is located close to the cystinuria B gene and presents sequence variants (e.g., E112D) in some cystinuria patients. We have cloned human asc-1, assessed its transport characteristics, localized its expression in kidney, searched for mutations in cystinuria patients, and tested the transport function of variant E112D. Methods. We used an EST-based homology cloning strategy. Transport characteristics of asc-1 were assessed by coexpression with 4F2hc in Xenopus oocytes and HeLa cells. Localization of asc-1 mRNA in kidney was assessed by in situ hybridization. Exons and intron-exon boundaries were polymerase chain reaction (PCR)-amplified from blood cell DNA and mutational screening was performed by single-stranded conformational polymorphism (SSCP). Results. Asc-1 reaches the plasma membrane in HeLa cells, unlike in oocytes, most probably by interaction with endogenous 4F2hc and presents similar transport characteristics to those in oocytes coexpressing asc-1/4F2hc. Asc-1 mediates a substantial efflux of alanine in a facilitated diffusion mode of transport. Expression of asc-1 mRNA localized to Henle's loop, distal tubules, and collecting ducts. Finally, SLC7A10 polymorphisms were identified in cystinuria probands and the SLC7A10 sequence variant E112D showed full transport activity. Conclusion. The lack of expression of asc-1 in the proximal tubule indicates that it plays no role in the bulk of renal reabsorption of amino acids. No mutations causing cystinuria have been found in SLC7A10. The facilitated diffusion mode of transport and the expression in distal nephron suggest a role for asc-1 in osmotic adaptation.

Original languageEnglish
Pages (from-to)1453-1464
Number of pages12
JournalKidney International
Volume66
Issue number4
DOIs
Publication statusPublished - Oct 2004

Keywords

  • Asc-1
  • Cystinuria
  • Heteromeric amino acid transporter
  • SLC7A10

ASJC Scopus subject areas

  • Nephrology

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