1. Figure 1 mTOR complex biology
Figure 1 | mTOR complex biology. Rapamycin-sensitive mTOR complex 1 (mTORC1) is composed of mTOR in association with regulatory associated protein of mTOR (Raptor) and other proteins not shown here (mammalian lethal with Sec13 protein 8, proline-rich substrate of Akt of 40 kD and DEP domain-containing mTOR-interacting protein). mTORC1 is regulated by environmental cues (nutrients, growth factors and energy) to drive cell growth and metabolism. Many signalling pathways converge on the tumour suppressors tuberous sclerosis complex 1 (TSC1) and TSC2, GTPase activating proteins and major negative regulator of RHEB (Ras homologue enriched in brain), that directly stimulates mTORC1. The two main downstream targets of mTORC1 are p70 ribosomal S6 kinase (S6K) and 4E-binding protein 1 (4EBP1); their phosphorylation by mTORC1 drives ribosome synthesis, cap-dependent translation and cell growth. The transcription factor sterol regulatory element binding protein 1 (SREBP1) is activated by mTORC1 and regulates lipid synthesis. Rapamycin-insensitive mTOR complex 2 (mTORC2) lacks Raptor but includes rapamycin-insensitive companion of mTOR (Rictor) as an essential component. Known substrates of mTORC2 include Akt and the serum and glucocorticoid-induced kinase-1 (SGK1). 3-phosphoinositide-dependent protein kinase-1 (PDK1) enhances Akt activity by phosphorylating the activation loop at Thr308. mTORC2 uniquely stabilizes Akt via phosphorylation of the turn motif at Ser450 (not shown), and further stimulates Akt kinase activity by phosphorylating the hydrophobic motif at Ser473. mTORC2 controls fundamental cellular processes including metabolism, differentiation, cell cycle arrest and DNA repair. Ribosomes have been found to physically associate with mTORC2. Rapamycin and rapalogues form complexes with FK506 binding protein 12 (FKBP12) and acutely inhibit mTORC1 assembly, whereas inhibition of mTORC2 assembly requires chronic exposure and is inconsistent across cell types. AMPK, AMP-activated protein kinase; PGC1-α, peroxisome proliferator-activated receptor-γ coactivator-1α; PI3K, phosphoinositide 3-kinase; PKCα, protein kinase Cα; ULK, UNK-51-like autophagy-activating kinase.
Fantus, D. et al. (2016) Roles of mTOR complexes in the kidney: implications for renal disease and transplantation
Nat. Rev. Nephrol. doi: /nrneph