Regulation of targets of mTOR (mammalian target of rapamycin) signalling by intracellular amino acid availability

Anne Beugnet, Andrew R. Tee, Peter M. Taylor, Christopher G. Proud

    Research output: Contribution to journalArticlepeer-review

    233 Citations (Scopus)

    Abstract

    In mammalian cells, amino acids affect the phosphorylation state and function of several proteins involved in mRNA translation that are regulated via the rapamycin-sensitive mTOR (mammalian target of rapamycin) pathway. These include ribosomal protein S6 kinase, S6K1, and eukaryotic initiation factor 4E-binding protein, 4E-BP1. Amino acids, especially branched-chain amino acids, such as leucine, promote phosphorylation of 4E-BP1 and S6K1, and permit insulin to further increase their phosphorylation. However, it is not clear whether these effects are exerted by extracellular or intracellular amino acids. Inhibition of protein synthesis is expected to increase the intracellular level of amino acids, whereas inhibiting proteolysis has the opposite effect. We show in the present study that inhibition of protein synthesis by any of several protein synthesis inhibitors tested allows insulin to regulate 4E-BP1 or S6K1 in amino-acid-deprived cells, as does the addition of amino acids to the medium. In particular, insulin activates S6K1 and promotes initiation factor complex assembly in amino-acid-deprived cells treated with protein synthesis inhibitors, but cannot do so in the absence of these compounds. Their effects occur at concentrations commensurate with their inhibition of protein synthesis and are not due to activation of stress-activated kinase cascades. Inhibition of protein breakdown (autophagy) impairs the ability of insulin to regulate 4E-BP1 or S6K1 under such conditions. These and other data presented in the current study are consistent with the idea that it is intracellular amino acid levels that regulate mTOR signalling.
    Original languageEnglish
    Pages (from-to)555-566
    Number of pages12
    JournalBiochemical Journal
    Volume372
    Issue number2
    DOIs
    Publication statusPublished - 1 Jun 2003

    Keywords

    • Cycloheximide
    • Initiation factor
    • mRNA translation
    • Phosphorylation
    • S6 kinase

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