Redox Regulates Mammalian Target of Rapamycin Complex 1 (mTORC1) Activity by Modulating the TSC1/TSC2-Rheb GTPase Pathway

Abstract

Mammalian target of rapamycin (mTOR) is a kinase that plays a key role in a wide array of cellular processes and exists in two distinct functional complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Although mTORC2 is primarily activated by growth factors, mTORC1 is regulated by numerous extracellular and intracellular signals such as nutrients, growth factors, and cellular redox. Previous study has shown that cysteine oxidants sufficiently activate mTORC1 activity under amino acid-depleted conditions and that a reducing agent effectively suppresses amino acid-induced mTORC1 activity, thereby raising the possibility that redox-sensitive mechanisms underlie amino acid-dependent mTORC1 regulation. However, the molecular mechanism by which redox regulates mTORC1 activity is not well understood. In this study, we show that the redox-sensitive regulation of mTORC1 occurs via Rheb but not the Rag small GTPase. Enhancing cellular redox potential with cysteine oxidants significantly increases Rheb GTP levels. Importantly, modulation of the cellular redox potential with a cysteine oxidant or reducing agent failed to alter mTORC1 activity in TSC1 ؊/؊ or TSC2 ؊/؊ mouse embryonic fibroblast cells. Furthermore, a cysteine oxidant has little effect on mTOR localization but sufficiently activates mTORC1 activity in both p18 ؊/؊ and control mouse embryonic fibroblast cells, suggesting that the redox-sensitive regulation of mTORC1 occurs independent of the Ragulator⅐Rag complex. Taken together, our results suggest that the TSC complex plays an important role in redox-sensitive mTORC1 regulation and argues for the activation of mTORC1 in places other than the lysosome upon inhibition of the TSC complex.The mammalian target of rapamycin (mTOR) 2 belongs to the family of phosphatidylinositol 3-kinase (PI3K)-related kinases and shares high sequence similarity to PI3K despite possessing protein kinase activity (1). mTOR is an evolutionarily conserved protein kinase that forms two distinct functional complexes termed mTOR complex 1 and mTOR complex 2 (mTORC1 and mTORC2, respectively) (2-4). mTORC1 is known to be a rapamycin-sensitive complex that regulates a wide array of cellular processes such as cell growth and autophagy, whereas mTORC2 is known to be rapamycin-resistant and involved in the regulation of cell survival as well as cytoskeletal reorganization. Although mTORC2 activation is primarily mediated by growth factors, mTORC1 activation can be achieved by multiple inputs such as amino acids, growth factors, glucose, and oxidative stress (5, 6).Recent studies have shown that two small GTPases, Rheb and Rag, play an essential role in the regulation of mTORC1 activation (7-10). Rheb interacts with and activates mTORC1, whereas Rag small GTPases function as essential spatial regulators of mTORC1 localization (8, 11-13). The Rag small GTPases function as heterodimers formed between RagA/B and RagC/D and bind to the MP1⅐p14⅐p18 complex (Ragulator), which is predominantly expressed on the lysosomal membrane (12,14). Upon ...

Characterization of residue‐dependent differences in the peripheral membrane association of the FATC domain of the kinase ‘target of rapamycin’ by NMR and CD spectroscopy

“…Consistent with this, a redox-sensitive formation of TORC1 and its signaling function was suggested [19][20][21][22]. Analysis of the FATC sequence with the program e-motif (G. Tevzadze personal communication) suggested that the C-terminal end that is rich in aromatic residues (Fig.…”

Evidence that a mitochondrial death spiral underlies antagonistic pleiotropy

“…In addition, PTEN, which removes the 3’ phosphate from PIP 3 and thus opposes PI3K activity, is likewise inhibited by ROS (Lee et al ., 2002; Leslie et al ., 2003; Connor et al ., 2005). Finally, ROS inhibits the Tsc1/Tsc2 complex, thereby relieving Tor from upstream inhibition (Yoshida et al ., 2011). Thus, ROS acts through a variety of targets to activate IIS and Tor.…”

Rheb in neuronal degeneration, regeneration, and connectivity

“…In addition, the lysosomal re-localization of TSC complex is also an important stress response to inhibit mTORC1-mediated growth and the presence of any single stress maintains TSC complex at the lysosomes (Demetriades et al, 2016). Rheb-mTORC1 is also able to sense the cellular redox state (Patel and Tamanoi, 2006;Di Nardo et al, 2009;Yoshida et al, 2011) which occurs independent of the amino acid levels and the Rag-regulator system. In addition to TSC complex, there are other upstream regulators for Rheb.…”