The mammalian target of rapamycin (mTOR) is an evolutionally conserved kinase which exists in two distinct structural and functional complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Of the two complexes, mTORC1 couples nutrient abundance to cell growth and proliferation by sensing and integrating a variety of inputs arising from amino acids, cellular stresses, energy status, and growth factors. Defects in mTORC1 regulation are implicated in the development of many metabolic diseases, including cancer and diabetes. Over the past decade, significant advances have been made in deciphering the complexity of the signaling processes contributing to mTORC1 regulation and function, but the mechanistic details are still not fully understood. In particular, how amino acid availability is sensed by cells and signals to mTORC1 remains unclear. In this review, we discuss the current understanding of nutrient-dependent control of mTORC1 signaling and will focus on the key components involved in amino acid signaling to mTORC1.

Summary The metabolism of glucose and glutamine, primary carbon-sources utilized by mitochondria to generate energy and macromolecules for cell growth, is directly regulated by mTORC1. We show that glucose and glutamine, by supplying carbons to the TCA cycle to produce ATP, positively feed back to mTORC1 through an AMPK-, TSC1/2-, and Rag-independent mechanism by regulating mTORC1 assembly and its lysosomal localization. We discovered that ATP-dependent TTT-RUVBL1/2 complex was disassembled and repressed by energy depletion, resulting in its decreased interaction with mTOR. The TTT-RUVBL complex was necessary for the interaction between mTORC1 and Rag, and formation of mTORC1 obligate dimers. In cancer tissues, TTT-RUVBL complex mRNAs were elevated, and positively correlated with transcripts encoding proteins of anabolic metabolism and mitochondrial function - all mTORC1-regulated processes. Thus, the TTT-RUVBL1/2 complex responds to the cell’s metabolic state, directly regulating the functional assembly of mTORC1, and indirectly controlling the nutrient signal from Rags to mTORC1.

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