System A amino acid transporter SNAT2 shows subtype-specific affinity for betaine and hyperosmotic inducibility in placental trophoblasts

Tomohiro Nishimura, Risa Yagi, Mariko Usuda, Kenji Oda, Mai Yamazaki, Sayaka Suda, Yu Takahashi, Fumiyasu Okazaki, Yoshimichi Sai, Kei Higuchi, Tetsuo Maruyama, Masatoshi Tomi, Emi Nakashima

研究成果: Article

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Betaine uptake is induced by hypertonic stress in a placental trophoblast cell line, and involvement of amino acid transport system A was proposed. Here, we aimed to identify the subtype(s) of system A that mediates hypertonicity-induced betaine uptake. Measurement of [14C]betaine uptake by HEK293 cells transiently transfected with human or rat sodium-coupled neutral amino acid transporters (SNATs), SNAT1, SNAT2 and SNAT4 revealed that only human and rat SNAT2 have betaine uptake activity. The Michaelis constants (Km) of betaine uptake by human and rat SNAT2 were estimated to be 5.3 mM and 4.6 mM, respectively. Betaine exclusively inhibited the uptake activity of SNAT2 among the rat system A subtypes. We found that rat SNAT1, SNAT2 and SNAT4 were expressed at the mRNA level under isotonic conditions, while expression of SNAT2 and SNAT4 was induced by hypertonicity in TR-TBT 18d-1 cells. Western blot analyses revealed that SNAT2 expression on plasma membrane of TR-TBT 18d-1 cells was more potently induced by hypertonicity than that in total cell lysate. Immunocytochemistry confirmed the induction of SNAT2 expression in TR-TBT 18d-1 cells exposed to hypertonic conditions and indicated that SNAT2 was localized on the plasma membrane in these cells. Our results indicate that SNAT2 transports betaine, and that tonicity-sensitive SNAT2 expression may be involved in regulation of betaine concentration in placental trophoblasts.

元の言語English
ページ(範囲)1306-1312
ページ数7
ジャーナルBiochimica et Biophysica Acta - Biomembranes
1838
発行部数5
DOI
出版物ステータスPublished - 2014 5

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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