Proteasomal modulation of cellular SNAT2 (SLC38A2) abundance and function by unsaturated fatty acid availability

Francesca Nardi, Thorsten M. Hoffmann, Clare Stretton, Emma Cwiklinski, Peter M. Taylor, Harinder S. Hundal (Lead / Corresponding author)

    Research output: Contribution to journalArticle

    16 Citations (Scopus)

    Abstract

    Expression and activity of the System A/SNAT2 (SLC38A2) amino acid transporter is up-regulated by amino acid starvation and hypertonicity by a mechanism dependent on both ATF4-mediated transcription of the SLC38A2 gene and enhanced stabilization of SNAT2 itself, which forms part of an integrated cellular stress response to nutrient deprivation and osmotic stress. Here we demonstrate that this adaptive increase in System A function is restrained in cells subjected to prior incubation with linoleic acid (LOA, an unsaturated C18:2 fatty acid) for 24 h. While fatty acid treatment had no detectable effect upon stress-induced SNAT2 or ATF4 gene transcription, the associated increase in SNAT2 protein/membrane transport activity were strongly suppressed in L6 myotubes or HeLa cells preincubated with LOA. Cellular ubiquitination of many proteins was increased by LOA and although the fatty acid-induced loss of SNAT2 could be attenuated by proteasomal inhibition, the functional increase in System A transport activity associated with amino acid starvation/hypertonicity that depends upon processing/maturation and delivery of SNAT2 to the cell surface could not be rescued. LOA up-regulated cellular expression of Nedd4.2, an E3-ligase implicated in SNAT2 ubiquitination, but shRNA-directed Nedd4.2 gene silencing could not curb fatty acid-induced loss of SNAT2 adaptation. However, expression of SNAT2 in which seven putative lysyl-ubiquitination sites in the cytoplasmic N-terminal domain were mutated to alanine protected SNAT2 against LOA-induced proteasomal degradation. Collectively, our findings indicate that increased availability of unsaturated fatty acids can compromise the stress-induced induction/adaptation in SNAT2 expression and function by promoting its degradation via the ubiquitin-proteasome system.

    Original languageEnglish
    Pages (from-to)8173-8184
    Number of pages12
    JournalJournal of Biological Chemistry
    Volume290
    Issue number13
    DOIs
    Publication statusPublished - 27 Mar 2015

    Fingerprint

    Unsaturated Fatty Acids
    Ubiquitination
    Fatty Acids
    Modulation
    Availability
    Genes
    Transcription
    Starvation
    Amino Acid Transport Systems
    Amino Acids
    Curbs
    Degradation
    Ubiquitin-Protein Ligases
    Membrane Transport Proteins
    Skeletal Muscle Fibers
    Osmotic Pressure
    Gene Silencing
    Linoleic Acid
    Proteasome Endopeptidase Complex
    Ubiquitin

    Cite this

    Nardi, Francesca ; Hoffmann, Thorsten M. ; Stretton, Clare ; Cwiklinski, Emma ; Taylor, Peter M. ; Hundal, Harinder S. / Proteasomal modulation of cellular SNAT2 (SLC38A2) abundance and function by unsaturated fatty acid availability. In: Journal of Biological Chemistry. 2015 ; Vol. 290, No. 13. pp. 8173-8184.
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    abstract = "Expression and activity of the System A/SNAT2 (SLC38A2) amino acid transporter is up-regulated by amino acid starvation and hypertonicity by a mechanism dependent on both ATF4-mediated transcription of the SLC38A2 gene and enhanced stabilization of SNAT2 itself, which forms part of an integrated cellular stress response to nutrient deprivation and osmotic stress. Here we demonstrate that this adaptive increase in System A function is restrained in cells subjected to prior incubation with linoleic acid (LOA, an unsaturated C18:2 fatty acid) for 24 h. While fatty acid treatment had no detectable effect upon stress-induced SNAT2 or ATF4 gene transcription, the associated increase in SNAT2 protein/membrane transport activity were strongly suppressed in L6 myotubes or HeLa cells preincubated with LOA. Cellular ubiquitination of many proteins was increased by LOA and although the fatty acid-induced loss of SNAT2 could be attenuated by proteasomal inhibition, the functional increase in System A transport activity associated with amino acid starvation/hypertonicity that depends upon processing/maturation and delivery of SNAT2 to the cell surface could not be rescued. LOA up-regulated cellular expression of Nedd4.2, an E3-ligase implicated in SNAT2 ubiquitination, but shRNA-directed Nedd4.2 gene silencing could not curb fatty acid-induced loss of SNAT2 adaptation. However, expression of SNAT2 in which seven putative lysyl-ubiquitination sites in the cytoplasmic N-terminal domain were mutated to alanine protected SNAT2 against LOA-induced proteasomal degradation. Collectively, our findings indicate that increased availability of unsaturated fatty acids can compromise the stress-induced induction/adaptation in SNAT2 expression and function by promoting its degradation via the ubiquitin-proteasome system.",
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    Proteasomal modulation of cellular SNAT2 (SLC38A2) abundance and function by unsaturated fatty acid availability. / Nardi, Francesca; Hoffmann, Thorsten M.; Stretton, Clare; Cwiklinski, Emma; Taylor, Peter M.; Hundal, Harinder S. (Lead / Corresponding author).

    In: Journal of Biological Chemistry, Vol. 290, No. 13, 27.03.2015, p. 8173-8184.

    Research output: Contribution to journalArticle

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