Active-Site Inhibitors of mTOR Target Rapamycin-Resistant Outputs of mTORC1 and mTORC2

By M. Feldman, Beth Apsel, A. Uotila, R. Loewith, Zachary A. Knight, D. Ruggero, Kevan M. Shokat. PLoS Biology, 2009

1,174 citations recorded by the source corpus.

The mammalian target of rapamycin (mTOR) regulates cell growth and survival by integrating nutrient and hormonal signals. These signaling functions are distributed between at least two distinct mTOR protein complexes: mTORC1 and mTORC2. mTORC1 is sensitive to the selective inhibitor rapamycin and activated by growth factor stimulation via the canonical phosphoinositide 3-kinase (PI3K)→Akt→mTOR pathway. Activated mTORC1 kinase up-regulates protein synthesis by phosphorylating key regulators of mRNA translation. By contrast, mTORC2 is resistant to rapamycin. Genetic studies have suggested that mTORC2 may phosphorylate Akt at S473, one of two phosphorylation sites required for Akt activation; this has been controversial, in part because RNA interference and gene knockouts produce distinct Akt phospho-isoforms. The central role of mTOR in controlling key cellular growth and survival pathways has sparked interest in discovering mTOR inhibitors that bind to the ATP site and therefore target both mTORC2 and mTORC1. We investigated mTOR signaling in cells and animals with two novel and specific mTOR kinase domain inhibitors (TORKinibs). Unlike rapamycin, these TORKinibs (PP242 and PP30) inhibit mTORC2, and we use them to show that pharmacological inhibition of mTOR blocks the phosphorylation of Akt at S473 and prevents its full activation. Furthermore, we show that TORKinibs inhibit proliferation of primary cells more completely than rapamycin. Surprisingly, we find that mTORC2 is not the basis for this enhanced activity, and we show that the TORKinib PP242 is a more effective mTORC1 inhibitor than rapamycin. Importantly, at the molecular level, PP242 inhibits cap-dependent translation under conditions in which rapamycin has no effect. Our findings identify new functional features of mTORC1 that are resistant to rapamycin but are effectively targeted by TORKinibs. These potent new pharmacological agents complement rapamycin in the study of mTOR and its role in normal physiology and human disease.

Subfields: Immunology, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/ee92bfa21fa2fb76b934166dcee07a9d90532633

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Citations in the corpus

mTOR complex 1 regulates lipin 1 localization to control the SREBP pathway. (2011, positive): “…ﬁnding that rapamycin, which allosterically partially inhibits mTOR kinase activity (Brown et al., 1995), does not inhibit 4E-BP1 phosphorylation equally well in all cell contexts despite invariantly promoting S6K1 dephosphorylation (Choo et al., 2008; Feldman et al., 2009; Thoreen et al., 2009).”
Targeting the phosphoinositide 3-kinase (PI3K) pathway in cancer (2009, background): “Recent studies have described torkinibs and torin1 — potent and selective ATP-competitive inhibitors of mTOR that inhibit both mTORC1 and mTORC2 complexes and impair cell growth and proliferation more effectively than rapamyci”
mTOR inhibits autophagy by controlling ULK1 ubiquitylation, self-association and function through AMBRA1 and TRAF6 (2013, methodology): “(d) HEK293 cells were co-transfected with vectors encoding AMBRA1 together with ULK1–Myc FL (full length) or its deletion mutants encoding the kinase and the proline-rich domains (1829–1,051), and the ULK1 carboxy-terminal domain (11-828).”
The LKB1-AMPK pathway: metabolism and growth control in tumor suppression (2009, result): “aspx?CdrID=42555">rapamycin , although recent studies show that rapamycin does not fully suppress mTORC1 activity in many cell type”
mTOR Signaling in Growth, Metabolism, and Disease. (2017, background): “The first came with the realization that, as allosteric inhibitors, the rapalogs block the phosphorylation of some but not all mTORC1 substrates (Fig. 5B, Choo et al., 2008; Feldman et al., 2009; Kang et al., 2013; Thoreen et al., 2009).”
mTOR: from growth signal integration to cancer, diabetes and ageing (2010, background): “Furthermore, rapamycin does not fully inhibit all the functions of mTORC1; of note, rapamycin only affects 4E-BP1 phosphorylation transiently and partiall”
Targeting PI3K signalling in cancer: opportunities, challenges and limitations (2009, background): “Interestingly, two independent studies observed that mTOR catalytic site inhibitors were more potent than rapamycin in their inhibition of mTORC1 and this was likely to account for their increased anti-proliferative activity compared with rapamyci”
mTOR signaling in growth control and disease (2012, positive): “groups have developed small molecules that directly inhibit mTOR kinase activity (Chresta et al., 2010; Feldman et al., 2009; Garcı́a-Martı́nez et al., 2009; Thoreen et al., 2009; Yu et al., 2009).”
In brief (2011, positive): “ThemTOR inhibitor PP242 (Feldman et al., 2009) abolished the in vitro phosphorylation of Ser473 (Figure 5C), confirming that the ribosome-associated Ser473 kinase was mTORC2.”