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      Where is mTOR and what is it doing there?

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      The Journal of Cell Biology
      The Rockefeller University Press

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          Abstract

          Target of rapamycin (TOR) forms two conserved, structurally distinct kinase complexes termed TOR complex 1 (TORC1) and TORC2. Each complex phosphorylates a different set of substrates to regulate cell growth. In mammals, mTOR is stimulated by nutrients and growth factors and inhibited by stress to ensure that cells grow only during favorable conditions. Studies in different organisms have reported localization of TOR to several distinct subcellular compartments. Notably, the finding that mTORC1 is localized to the lysosome has significantly enhanced our understanding of mTORC1 regulation. Subcellular localization may be a general principle used by TOR to enact precise spatial and temporal control of cell growth.

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          Most cited references110

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          mTOR controls mitochondrial oxidative function through a YY1-PGC-1alpha transcriptional complex.

          Transcriptional complexes that contain peroxisome-proliferator-activated receptor coactivator (PGC)-1alpha control mitochondrial oxidative function to maintain energy homeostasis in response to nutrient and hormonal signals. An important component in the energy and nutrient pathways is mammalian target of rapamycin (mTOR), a kinase that regulates cell growth, size and survival. However, it is unknown whether and how mTOR controls mitochondrial oxidative activities. Here we show that mTOR is necessary for the maintenance of mitochondrial oxidative function. In skeletal muscle tissues and cells, the mTOR inhibitor rapamycin decreased the gene expression of the mitochondrial transcriptional regulators PGC-1alpha, oestrogen-related receptor alpha and nuclear respiratory factors, resulting in a decrease in mitochondrial gene expression and oxygen consumption. Using computational genomics, we identified the transcription factor yin-yang 1 (YY1) as a common target of mTOR and PGC-1alpha. Knockdown of YY1 caused a significant decrease in mitochondrial gene expression and in respiration, and YY1 was required for rapamycin-dependent repression of those genes. Moreover, mTOR and raptor interacted with YY1, and inhibition of mTOR resulted in a failure of YY1 to interact with and be coactivated by PGC-1alpha. We have therefore identified a mechanism by which a nutrient sensor (mTOR) balances energy metabolism by means of the transcriptional control of mitochondrial oxidative function. These results have important implications for our understanding of how these pathways might be altered in metabolic diseases and cancer.
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            An ER-mitochondria tethering complex revealed by a synthetic biology screen.

            Communication between organelles is an important feature of all eukaryotic cells. To uncover components involved in mitochondria/endoplasmic reticulum (ER) junctions, we screened for mutants that could be complemented by a synthetic protein designed to artificially tether the two organelles. We identified the Mmm1/Mdm10/Mdm12/Mdm34 complex as a molecular tether between ER and mitochondria. The tethering complex was composed of proteins resident of both ER and mitochondria. With the use of genome-wide mapping of genetic interactions, we showed that the components of the tethering complex were functionally connected to phospholipid biosynthesis and calcium-signaling genes. In mutant cells, phospholipid biosynthesis was impaired. The tethering complex localized to discrete foci, suggesting that discrete sites of close apposition between ER and mitochondria facilitate interorganelle calcium and phospholipid exchange.
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              Rapamycin passes the torch: a new generation of mTOR inhibitors.

              Mammalian target of rapamycin (mTOR) is an atypical protein kinase that controls growth and metabolism in response to nutrients, growth factors and cellular energy levels, and it is frequently dysregulated in cancer and metabolic disorders. Rapamycin is an allosteric inhibitor of mTOR, and was approved as an immuno-suppressant in 1999. In recent years, interest has focused on its potential as an anticancer drug. However, the performance of rapamycin and its analogues (rapalogues) has been undistinguished despite isolated successes in subsets of cancer, suggesting that the full therapeutic potential of targeting mTOR has yet to be exploited. A new generation of ATP-competitive inhibitors that directly target the mTOR catalytic site display potent and comprehensive mTOR inhibition and are in early clinical trials.
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                Author and article information

                Journal
                J Cell Biol
                J. Cell Biol
                jcb
                The Journal of Cell Biology
                The Rockefeller University Press
                0021-9525
                1540-8140
                25 November 2013
                : 203
                : 4
                : 563-574
                Affiliations
                Biozentrum, University of Basel, CH-4056 Basel, Switzerland
                Author notes
                Correspondence to Michael N. Hall: M.Hall@ 123456unibas.ch
                Article
                201306041
                10.1083/jcb.201306041
                3840941
                24385483
                140f542e-29f6-404d-abe8-59c99f764379
                © 2013 Betz and Hall

                This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

                History
                : 7 June 2013
                : 24 October 2013
                Categories
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                Cell biology
                Cell biology

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