The mTORC1 Signaling Network Senses Changes in Cellular Purine Nucleotide Levels

• Published in: Cell reports (Cambridge) 2017-10, Vol.21 (5), p.1331-1346
• Main Authors: Hoxhaj, Gerta, Hughes-Hallett, James, Timson, Rebecca C., Ilagan, Erika, Yuan, Min, Asara, John M., Ben-Sahra, Issam, Manning, Brendan D.
• Format: Article
• Language: English
• Subjects: AMPK; ATP; GTP; mTOR; nucleotides; nutrient sensing; purine; Rag GTPases; Rheb; tuberous sclerosis complex
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2017.10.029

Mechanistic (or mammalian) target of rapamycin complex 1 (mTORC1) integrates signals from growth factors and nutrients to control biosynthetic processes, including protein, lipid, and nucleic acid synthesis. We find that the mTORC1 pathway is responsive to changes in purine nucleotides in a manner analogous to its sensing of amino acids. Depletion of cellular purines, but not pyrimidines, inhibits mTORC1, and restoration of intracellular adenine nucleotides via addition of exogenous purine nucleobases or nucleosides acutely reactivates mTORC1. Adenylate sensing by mTORC1 is dependent on the tuberous sclerosis complex (TSC) protein complex and its regulation of Rheb upstream of mTORC1, but independent of energy stress and AMP-activated protein kinase (AMPK). Even though mTORC1 signaling is not acutely sensitive to changes in intracellular guanylates, long-term depletion of guanylates decreases Rheb protein levels. Our findings suggest that nucleotide sensing, like amino acid sensing, enables mTORC1 to tightly coordinate nutrient availability with the synthesis of macromolecules, such as protein and nucleic acids, produced from those nutrients. [Display omitted] •Depletion of purine, but not pyrimidine, nucleotides inhibits mTORC1 signaling•The mTORC1 pathway acutely senses changes in intracellular adenylates•Adenylate sensing is dependent on the TSC complex, but not AMPK or the Rag GTPases•Long-term guanylate depletion decreases Rheb protein levels mTORC1 integrates signals from growth factors and nutrients to coordinately control macromolecular synthesis. Hoxhaj et al. identify intracellular purine nucleotides as an upstream regulatory input into the mTORC1 pathway. Acutely, mTORC1 senses adenylates in a manner dependent on the TSC complex, while prolonged guanylate depletion results in reduced Rheb levels.