Leucyl-tRNA synthetase controls TORC1 via the EGO complex

Department of Biology, Division of Biochemistry, University of Fribourg, CH-1700 Fribourg, Switzerland.
Molecular cell (Impact Factor: 14.02). 03/2012; 46(1):105-10. DOI: 10.1016/j.molcel.2012.02.009
Source: PubMed


The target of rapamycin complex 1 (TORC1) is an essential regulator of eukaryotic cell growth that responds to growth factors, energy levels, and amino acids. The mechanisms through which the preeminent amino acid leucine signals to the TORC1-regulatory Rag GTPases, which activate TORC1 within the yeast EGO complex (EGOC) or the structurally related mammalian Rag-Ragulator complex, remain elusive. We find that the leucyl-tRNA synthetase (LeuRS) Cdc60 interacts with the Rag GTPase Gtr1 of the EGOC in a leucine-dependent manner. This interaction is necessary and sufficient to mediate leucine signaling to TORC1 and is disrupted by the engagement of Cdc60 in editing mischarged tRNA(Leu). Thus, the EGOC-TORC1 signaling module samples, via the LeuRS-intrinsic editing domain, the fidelity of tRNA(Leu) aminoacylation as a proxy for leucine availability.

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Available from: Claudio De Virgilio, Sep 10, 2014
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    • "In mammalian cells, these include (1) the pentameric Ragulator complex that tethers Rag heterodimers to the lysosomal membrane and acts as RagA/B GEF (Bar- Peled et al., 2012), (2) the heterotrimeric GATOR1 complex with RagA/B GAP activity (Bar-Peled et al., 2013), and (3) the heterodimeric FNIP-Folliculin complex that functions as RagC/ D GAP (Petit et al., 2013; Tsun et al., 2013). The amino-acidsensitive events upstream of these Rag GTPase regulators are currently poorly understood, but likely involve both lysosomal amino acid sensors, such as the v-ATPase and lysosomal amino acid transporter(s) (Rebsamen et al., 2015; Wang et al., 2015; Zoncu et al., 2011), and cytoplasmic amino acid sensors, such as the leucyl-tRNA synthetase (LeuRS) (Bonfils et al., 2012; Han et al., 2012). Some of the regulatory mechanisms impinging on Rag GTPases have been remarkably conserved throughout evolution . "
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    ABSTRACT: Rag GTPases assemble into heterodimeric complexes consisting of RagA or RagB and RagC or RagD in higher eukaryotes, or Gtr1 and Gtr2 in yeast, to relay amino acid signals toward the growth-regulating target of rapamycin complex 1 (TORC1). The TORC1-stimulating state of Rag GTPase heterodimers, containing GTP- and GDP-loaded RagA/B/Gtr1 and RagC/D/Gtr2, respectively, is maintained in part by the FNIP-Folliculin RagC/D GAP complex in mammalian cells. Here, we report the existence of a similar Lst4-Lst7 complex in yeast that functions as a GAP for Gtr2 and that clusters at the vacuolar membrane in amino acid-starved cells. Refeeding of amino acids, such as glutamine, stimulated the Lst4-Lst7 complex to transiently bind and act on Gtr2, thereby entailing TORC1 activation and Lst4-Lst7 dispersal from the vacuolar membrane. Given the remarkable functional conservation of the RagC/D/Gtr2 GAP complexes, our findings could be relevant for understanding the glutamine addiction of mTORC1-dependent cancers.
    Cell Reports 09/2015; 13(1). DOI:10.1016/j.celrep.2015.08.059 · 8.36 Impact Factor
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    • "Endogenous membranes of the protein secretory pathway have also emerged as important platforms for Tor signaling. First, all components of the TORC1 complex (Tor1, Tor2, Kog1, Lst8, and Tco89) (Cardenas and Heitman 1995; Kunz et al. 2000; Chen and Kaiser 2003; Wedaman et al. 2003; Reinke et al. 2004; Aronova et al. 2007) as well as TORC1 regulators (EGO complex) (Dubouloz et al. 2005; Gao and Kaiser 2006; Kim et al. 2008; Binda et al. 2009; Bonfils et al. 2012) and downstream effectors, such as the Tap42–Sit4 phosphatase complex and the AGC kinase Sch9 (Yan et al. 2006; Urban et al. 2007) localize to the late endosome and vacuole membranes. Moreover, the Golgi Ca 2+ /Mn 2+ ATPase Pmr1 has been described to negatively regulate TORC1 function (Devasahayam et al. 2006). "
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    ABSTRACT: Nitrogen catabolite repression (NCR) is the regulatory pathway through which Saccharomyces cerevisiae responds to the available nitrogen status and selectively utilizes rich nitrogen sources in preference to poor ones. Expression of NCR-sensitive genes is mediated by two transcription activators, Gln3 and Gat1, in response to provision of a poorly used nitrogen source or following treatment with the TORC1 inhibitor, rapamycin. During nitrogen excess, the transcription activators are sequestered in the cytoplasm in a Ure2-dependent fashion. Here, we show that Vps components are required for Gln3 localization and function in response to rapamycin treatment when cells are grown in defined yeast nitrogen base but not in complex yeast peptone dextrose medium. On the other hand, Gat1 function was altered in vps mutants in all conditions tested. A significant fraction of Gat1, like Gln3, is associated with light intracellular membranes. Further, our results are consistent with the possibility that Ure2 might function downstream of the Vps components during the control of GATA factor-mediated gene expression. These observations demonstrate distinct media-dependent requirements of vesicular trafficking components for wild-type responses of GATA factor localization and function. As a result, the current model describing participation of Vps system components in events associated with translocation of Gln3 into the nucleus following rapamycin treatment or growth in nitrogen-poor medium requires modification.
    MicrobiologyOpen 06/2014; 3(3). DOI:10.1002/mbo3.168 · 2.21 Impact Factor
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    • "Given that mTORC1-S6K1 pathway can be activated by nutritional components including amino acids, which occurs through the Leucyl-tRNA synthetase-Rag [26, 27], we hypothesize that chronic L-arginine supplementation may cause endothelial dysfunction and senescence through mTORC1-S6K1 pathway and Arg-II. "
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    ABSTRACT: L-arginine supplementation is proposed to improve health status or as adjunct therapy for diseases including cardiovascular diseases. However, controversial results and even detrimental effects of L-arginine supplementation are reported. We investigate potential mechanisms of L-arginine-induced detrimental effects on vascular endothelial cells. Human endothelial cells were exposed to a physiological (0.1 mmol/L) or pharmacological (0.5 mmol/L) concentration of L-arginine for 30 minutes (acute) or 7 days (chronic). The effects of L-arginine supplementation on endothelial senescence phenotype, i.e., levels of senescence-associated beta-galactosidase, expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1, eNOS-uncoupling, arginase-II expression/activity, and mTORC1-S6K1 activity were analyzed. While acute L-arginine treatment enhances endothelial NO production accompanied with superoxide production and activation of S6K1 but no up-regulation of arginase-II, chronic L-arginine supplementation causes endothelial senescence, up-regulation of the adhesion molecule expression, and eNOS-uncoupling (decreased NO and enhanced superoxide production), which are associated with S6K1 activation and up-regulation of arginase-II. Silencing either S6K1 or arginase-II inhibits up-regulation/activation of each other, prevents endothelial dysfunction, adhesion molecule expression, and senescence under the chronic L-arginine supplementation condition. These results demonstrate that S6K1 and arginase-II form a positive circuit mediating the detrimental effects of chronic L-arginine supplementation on endothelial cells.
    Aging 05/2014; 6(5). · 6.43 Impact Factor
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