Spatial Compartmentalization of mTORC1 to the Outer Mitochondrial Membrane to Regulate Mitochondrial Metabolism

Abstract

mTOR complex 1 (mTORC1) integrates inputs from multiple pathways, such as PI3K/Akt, AMPK, Ca2+, and cAMP/PKA, and senses diverse signals to regulate cell growth, protein translation, and proliferation. Although the subcellular compartmentalization of signaling pathways can enhance signal specificity and efficiency, the spatial regulation of mTORC1 and its specific functions are still poorly understood. A pool of mTORC1 associated with the outer mitochondrial membrane has previously been identified but the function of mitochondrial mTORC1 is largely unknown. Previous studies have linked mTORC1 inhibition to changes in mitochondrial metabolism through its effect on transcription or translation, but a direct role for mTORC1 at the mitochondria is not yet elucidated. By targeting our FRET‐based mTORC1 activity reporter, TORCAR, to the outer mitochondrial membrane, we found that treating cells with platelet‐derived growth factor leads to a gradual increase in mitochondrial mTORC1 activity, and that this response is abrogated with rapamycin pre‐treatment. In pursuit of identifying the function of mTORC1 at the outer mitochondrial membrane, we have also developed a genetically encodable peptide‐based mTORC1 inhibitor, TerminaTOR, targeted to the outer mitochondrial membrane for specific subcellular inhibition of mTORC1. Using these molecular tools, we set out to examine whether mitochondrial mTORC1 activity is critical for mitochondria‐governed cellular homeostasis. We hypothesize that mitochondrial mTORC1 plays a critical role in altering mitochondrial metabolism upon stimulation with growth factor. We aim to further elucidate the functions of this activity by selectively inhibiting mitochondrial mTORC1 using mitochondria‐targeted TerminaTOR and quantifying changes in mitochondrial metabolism. We will also identify mitochondrial proteins that may interact with mTORC1 to contribute to these metabolic changes. This research will increase our understanding of the role that mTORC1 may play in diseases associated with altered metabolism or mitochondrial dysfunction.