But, by chance, the authors discovered that higher ATP concentrations converted mTOR into a robust kinase. Dropping ATP levels in vitro, or adding glycolytic inhibitors in vivo resulted in a drop in mTOR-specific phosphorylations of target proteins.
Apparently mTOR can act as a cellular ATP sensor because it has a weak, millimolar affinity for ATP. When both ATP and amino acids are available, mTOR upregulates translation and ribosome biogenesis, and downregulates autophagy. The remaining question is whether cancer cells that have gained a selective growth advantage by boosting mTOR activity do so through raising intracellular ATP levels. ▪