Intracellular sensing of amino acids in Xenopus laevis oocytes stimulates p70 S6 kinase in a target of rapamycin-dependent manner.
Amino acids exert modulatory effects on proteins involved in control of mRNA translation in animal cells through the target of rapamycin (TOR) signaling pathway. Here we use oocytes of Xenopus laevis to investigate mechanisms by which amino acids are "sensed" in animal cells. Small ( approximately 48%) but physiologically relevant increases in intracellular but not extracellular total amino acid concentration (or Leu or Trp but not Ala, Glu, or Gln alone) resulted in increased phosphorylation of p70(S6K) and its substrate ribosomal protein S6. This response was inhibited by rapamycin, demonstrating that the effects require the TOR pathway. Alcohols of active amino acids substituted for amino acids with lower efficiency. Oocytes were refractory to changes in external amino acid concentration unless surface permeability of the cell to amino acids was increased by overexpression of the System L amino acid transporter. Amino acid-induced, rapamycin-sensitive activation of p70(S6K) was conferred when System L-expressing oocytes were incubated in extracellular amino acids, supporting intracellular localization of the putative amino acid sensor. In contrast to lower eukaryotes such as yeast, which possess an extracellular amino acid sensor, our findings provide the first direct evidence for an intracellular location for the putative amino acid sensor in animal cells that signals increased amino acid availability to TOR/p70(S6K).
Christie
Graham R
GR
Medical Research Council Nutrient Sensing and Signaling Group, Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, Scotland.
Hajduch
Eric
E
Hundal
Harinder S
HS
Proud
Christopher G
CG
Taylor
Peter M
PM
D000409:Alanine / Q000737:chemistry; D000438:Alcohols / Q000494:pharmacology; D020816:Amino Acid Motifs; D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D015153:Blotting, Western; D004305:Dose-Response Relationship, Drug; D018698:Glutamic Acid / Q000737:chemistry; D005973:Glutamine / Q000737:chemistry; D007930:Leucine / Q000737:chemistry / Q000494:pharmacology; D009865:Oocytes / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology*; D013997:Time Factors; D014364:Tryptophan / Q000737:chemistry; D014982:Xenopus laevis / Q000196:embryology* / Q000378:metabolism*
D000438:Alcohols; D000596:Amino Acids; D005973:Glutamine; D018698:Glutamic Acid; D014364:Tryptophan; D019893:Ribosomal Protein S6 Kinases; D007930:Leucine; D000409:Alanine; D020123:Sirolimus