Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes

Fiona E. Baird, Kevin J. Bett, Catherine MacLean, Andrew R. Tee, Harinder S. Hundal, Peter M. Taylor

    Research output: Contribution to journalArticle

    46 Citations (Scopus)

    Abstract

    Baird FE, Bett KJ, MacLean C, Tee AR, Hundal HS, Taylor PM. Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes. Am J Physiol Endocrinol Metab 297: E822-E829, 2009. First published July 21, 2009; doi:10.1152/ajpendo.00330.2009.-The System L transporter facilitates cellular import of large neutral amino acids (AAs) such as Leu, a potent activator of the intracellular target of rapamycin (TOR) pathway, which signals for cell growth. System L is an AA exchanger, proposed to accumulate certain AAs by coupling to dissipation of concentration gradient(s) of exchange substrates generated by secondary active AA transporters such as System A (SNAT2). We addressed the hypothesis that this type of coupling (termed tertiary active transport) acts as an indirect mechanism to extend the range of AA stimulating TOR to those transported by both Systems A and L (e. g., Gln) through downstream enhancement of Leu accumulation. System A overexpression enabled Xenopus oocytes to accumulate substrate AAs (notably Ser, Gln, Ala, Pro, Met; totaling 2.6 nmol/oocyte) from medium containing a physiological AA mixture at plasma concentrations. Net accumulation of System L (4F2hc-xLAT1) substrates from this medium by System L-overexpressing oocytes was increased by 90% (from 0.7 to 1.35 nmol/oocyte; mainly Leu, Ile) when Systems A and L were coexpressed, coincident with a decline in accumulation of specific System A substrates (Gln, Ser, Met), as expected if the latter were also System L substrates and functional coupling of the transport Systems occurred. AA flux coupling was confirmed as trans-stimulation of Leu influx in System L-expressing oocytes by Gln injection (0.5 nmol/oocyte). The observed changes in Leu accumulation are sufficient to activate the TOR pathway in oocytes, although intracellular AA metabolism limits the potential for AA accumulation by tertiary active transport in this system.

    Original languageEnglish
    Pages (from-to)E822-E829
    Number of pages8
    JournalAmerican Journal of Physiology, Endocrinology and Metabolism
    Volume297
    Issue number3
    DOIs
    Publication statusPublished - Sep 2009

    Keywords

    • nutrient transport
    • target of rapamycin pathway
    • glutamine
    • leucine
    • amino acid exchanger
    • CELL-GROWTH
    • MAMMALIAN TARGET
    • PROTEIN-SYNTHESIS
    • GENE-EXPRESSION
    • LAEVIS OOCYTES
    • MTOR PATHWAY
    • MUSCLE-CELLS
    • GLUTAMINE
    • RAPAMYCIN
    • TRANSINHIBITION

    Cite this

    Baird, Fiona E. ; Bett, Kevin J. ; MacLean, Catherine ; Tee, Andrew R. ; Hundal, Harinder S. ; Taylor, Peter M. / Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes. In: American Journal of Physiology, Endocrinology and Metabolism. 2009 ; Vol. 297, No. 3. pp. E822-E829.
    @article{02dd5c3d8cdf499a85df836d0d9b1827,
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    abstract = "Baird FE, Bett KJ, MacLean C, Tee AR, Hundal HS, Taylor PM. Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes. Am J Physiol Endocrinol Metab 297: E822-E829, 2009. First published July 21, 2009; doi:10.1152/ajpendo.00330.2009.-The System L transporter facilitates cellular import of large neutral amino acids (AAs) such as Leu, a potent activator of the intracellular target of rapamycin (TOR) pathway, which signals for cell growth. System L is an AA exchanger, proposed to accumulate certain AAs by coupling to dissipation of concentration gradient(s) of exchange substrates generated by secondary active AA transporters such as System A (SNAT2). We addressed the hypothesis that this type of coupling (termed tertiary active transport) acts as an indirect mechanism to extend the range of AA stimulating TOR to those transported by both Systems A and L (e. g., Gln) through downstream enhancement of Leu accumulation. System A overexpression enabled Xenopus oocytes to accumulate substrate AAs (notably Ser, Gln, Ala, Pro, Met; totaling 2.6 nmol/oocyte) from medium containing a physiological AA mixture at plasma concentrations. Net accumulation of System L (4F2hc-xLAT1) substrates from this medium by System L-overexpressing oocytes was increased by 90{\%} (from 0.7 to 1.35 nmol/oocyte; mainly Leu, Ile) when Systems A and L were coexpressed, coincident with a decline in accumulation of specific System A substrates (Gln, Ser, Met), as expected if the latter were also System L substrates and functional coupling of the transport Systems occurred. AA flux coupling was confirmed as trans-stimulation of Leu influx in System L-expressing oocytes by Gln injection (0.5 nmol/oocyte). The observed changes in Leu accumulation are sufficient to activate the TOR pathway in oocytes, although intracellular AA metabolism limits the potential for AA accumulation by tertiary active transport in this system.",
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    Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes. / Baird, Fiona E.; Bett, Kevin J.; MacLean, Catherine; Tee, Andrew R.; Hundal, Harinder S.; Taylor, Peter M.

    In: American Journal of Physiology, Endocrinology and Metabolism, Vol. 297, No. 3, 09.2009, p. E822-E829.

    Research output: Contribution to journalArticle

    TY - JOUR

    T1 - Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes

    AU - Baird, Fiona E.

    AU - Bett, Kevin J.

    AU - MacLean, Catherine

    AU - Tee, Andrew R.

    AU - Hundal, Harinder S.

    AU - Taylor, Peter M.

    PY - 2009/9

    Y1 - 2009/9

    N2 - Baird FE, Bett KJ, MacLean C, Tee AR, Hundal HS, Taylor PM. Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes. Am J Physiol Endocrinol Metab 297: E822-E829, 2009. First published July 21, 2009; doi:10.1152/ajpendo.00330.2009.-The System L transporter facilitates cellular import of large neutral amino acids (AAs) such as Leu, a potent activator of the intracellular target of rapamycin (TOR) pathway, which signals for cell growth. System L is an AA exchanger, proposed to accumulate certain AAs by coupling to dissipation of concentration gradient(s) of exchange substrates generated by secondary active AA transporters such as System A (SNAT2). We addressed the hypothesis that this type of coupling (termed tertiary active transport) acts as an indirect mechanism to extend the range of AA stimulating TOR to those transported by both Systems A and L (e. g., Gln) through downstream enhancement of Leu accumulation. System A overexpression enabled Xenopus oocytes to accumulate substrate AAs (notably Ser, Gln, Ala, Pro, Met; totaling 2.6 nmol/oocyte) from medium containing a physiological AA mixture at plasma concentrations. Net accumulation of System L (4F2hc-xLAT1) substrates from this medium by System L-overexpressing oocytes was increased by 90% (from 0.7 to 1.35 nmol/oocyte; mainly Leu, Ile) when Systems A and L were coexpressed, coincident with a decline in accumulation of specific System A substrates (Gln, Ser, Met), as expected if the latter were also System L substrates and functional coupling of the transport Systems occurred. AA flux coupling was confirmed as trans-stimulation of Leu influx in System L-expressing oocytes by Gln injection (0.5 nmol/oocyte). The observed changes in Leu accumulation are sufficient to activate the TOR pathway in oocytes, although intracellular AA metabolism limits the potential for AA accumulation by tertiary active transport in this system.

    AB - Baird FE, Bett KJ, MacLean C, Tee AR, Hundal HS, Taylor PM. Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes. Am J Physiol Endocrinol Metab 297: E822-E829, 2009. First published July 21, 2009; doi:10.1152/ajpendo.00330.2009.-The System L transporter facilitates cellular import of large neutral amino acids (AAs) such as Leu, a potent activator of the intracellular target of rapamycin (TOR) pathway, which signals for cell growth. System L is an AA exchanger, proposed to accumulate certain AAs by coupling to dissipation of concentration gradient(s) of exchange substrates generated by secondary active AA transporters such as System A (SNAT2). We addressed the hypothesis that this type of coupling (termed tertiary active transport) acts as an indirect mechanism to extend the range of AA stimulating TOR to those transported by both Systems A and L (e. g., Gln) through downstream enhancement of Leu accumulation. System A overexpression enabled Xenopus oocytes to accumulate substrate AAs (notably Ser, Gln, Ala, Pro, Met; totaling 2.6 nmol/oocyte) from medium containing a physiological AA mixture at plasma concentrations. Net accumulation of System L (4F2hc-xLAT1) substrates from this medium by System L-overexpressing oocytes was increased by 90% (from 0.7 to 1.35 nmol/oocyte; mainly Leu, Ile) when Systems A and L were coexpressed, coincident with a decline in accumulation of specific System A substrates (Gln, Ser, Met), as expected if the latter were also System L substrates and functional coupling of the transport Systems occurred. AA flux coupling was confirmed as trans-stimulation of Leu influx in System L-expressing oocytes by Gln injection (0.5 nmol/oocyte). The observed changes in Leu accumulation are sufficient to activate the TOR pathway in oocytes, although intracellular AA metabolism limits the potential for AA accumulation by tertiary active transport in this system.

    KW - nutrient transport

    KW - target of rapamycin pathway

    KW - glutamine

    KW - leucine

    KW - amino acid exchanger

    KW - CELL-GROWTH

    KW - MAMMALIAN TARGET

    KW - PROTEIN-SYNTHESIS

    KW - GENE-EXPRESSION

    KW - LAEVIS OOCYTES

    KW - MTOR PATHWAY

    KW - MUSCLE-CELLS

    KW - GLUTAMINE

    KW - RAPAMYCIN

    KW - TRANSINHIBITION

    U2 - 10.1152/ajpendo.00330.2009

    DO - 10.1152/ajpendo.00330.2009

    M3 - Article

    C2 - 19622785

    VL - 297

    SP - E822-E829

    JO - American Journal of Physiology, Endocrinology and Metabolism

    JF - American Journal of Physiology, Endocrinology and Metabolism

    SN - 0193-1849

    IS - 3

    ER -