Cell-Type-Dependent Regulation of mTORC1 by REDD1 and the Tumor Suppressors TSC1/TSC2 and LKB1 in Response to Hypoxia

ABSTRACT mTORC1 is a critical regulator of cell growth that integrates multiple signals and is deregulated in cancer. We previously reported that mTORC1 regulation by hypoxia involves Redd1 and the Tsc1/Tsc2 complex. Here we show that Redd1 induction by hypoxia is tissue dependent and that hypoxia signals are relayed to mTORC1 through different pathways in a tissue-specific manner. In the liver, Redd1 induction is restricted to the centrilobular area, and in primary hepatocytes, mTORC1 inhibition by hypoxia is independent of Redd1. Furthermore, Tsc1/Tsc2 and Arnt (Hif-1β) are similarly dispensable. Hypoxia signaling in hepatocytes involves Lkb1, AMP-activated protein kinase (AMPK), and raptor. Differences in signal relay extend beyond hypoxia and involve AMPK signaling. AMPK activation (using 5-aminoimidazole-4-carboxamide riboside [AICAR]) induces raptor phosphorylation and inhibits mTORC1 in both mouse embryo fibroblasts (MEFs) and hepatocytes, but whereas mTORC1 inhibition is Tsc1/Tsc2 dependent in MEFs, it is independent in hepatocytes. In liver cells, raptor phosphorylation is essential for both AMPK and hypoxia signaling. Thus, context-specific signals are required for raptor phosphorylation-induced mTORC1 inhibition. Our data illustrate a heretofore unappreciated topological complexity in mTORC1 regulation. Interestingly, topological differences in mTORC1 regulation by the tumor suppressor proteins Lkb1 and Tsc1/Tsc2 may underlie their tissue specificity of tumor suppressor action.

[1]  M. Ernstoff.  mTOR Pathway and mTOR Inhibitors in Cancer Therapy , 2011 .

[2]  J. Brugarolas,et al.  Uncoupling hypoxia signaling from oxygen sensing in the liver results in hypoketotic hypoglycemic death , 2011, Oncogene.

[3]  B. Viollet,et al.  Metformin, independent of AMPK, inhibits mTORC1 in a rag GTPase-dependent manner. , 2010, Cell metabolism.

[4]  N. Grishin,et al.  Structural analysis and functional implications of the negative mTORC1 regulator REDD1. , 2010, Biochemistry.

[5]  S. Lowe,et al.  miR-221 overexpression contributes to liver tumorigenesis , 2009, Proceedings of the National Academy of Sciences.

[6]  Maria Deak,et al.  Structure of the LKB1-STRAD-MO25 Complex Reveals an Allosteric Mechanism of Kinase Activation , 2009, Science.

[7]  J. Blenis,et al.  Molecular mechanisms of mTOR-mediated translational control , 2009, Nature Reviews Molecular Cell Biology.

[8]  D. Sabatini,et al.  DEPTOR Is an mTOR Inhibitor Frequently Overexpressed in Multiple Myeloma Cells and Required for Their Survival , 2009, Cell.

[9]  J. Avruch,et al.  Amino acid regulation of TOR complex 1. , 2009, American journal of physiology. Endocrinology and metabolism.

[10]  A. Hinnebusch,et al.  Regulation of Translation Initiation in Eukaryotes: Mechanisms and Biological Targets , 2009, Cell.

[11]  J. Mateo,et al.  Silibinin inhibits hypoxia-inducible factor-1α and mTOR/p70S6K/4E-BP1 signalling pathway in human cervical and hepatoma cancer cells: implications for anticancer therapy , 2009, Oncogene.

[12]  J. Pouysségur,et al.  Activation of HIF‐1α in exponentially growing cells via hypoxic stimulation is independent of the Akt/mTOR pathway , 2009, Journal of cellular physiology.

[13]  J. Brugarolas.  mTORC1 Signaling and Hypoxia , 2009 .

[14]  J. Gutkind,et al.  Hypoxia-induced energy stress inhibits the mTOR pathway by activating an AMPK/REDD1 signaling axis in head and neck squamous cell carcinoma. , 2008, Neoplasia.

[15]  P. O’Farrell,et al.  An RNA interference screen identifies a novel regulator of target of rapamycin that mediates hypoxia suppression of translation in Drosophila S2 cells. , 2008, Molecular biology of the cell.

[16]  B. Turk,et al.  AMPK phosphorylation of raptor mediates a metabolic checkpoint. , 2008, Molecular cell.

[17]  J. Moss,et al.  Mesenchymal–epithelial interactions involving epiregulin in tuberous sclerosis complex hamartomas , 2008, Proceedings of the National Academy of Sciences.

[18]  P. Lambin,et al.  The mTOR target 4E‐BP1 contributes to differential protein expression during normoxia and hypoxia through changes in mRNA translation efficiency , 2008, Proteomics.

[19]  D. Sgroi,et al.  Hypoxia regulates TSC1/2-mTOR signaling and tumor suppression through REDD1-mediated 14-3-3 shuttling. , 2008, Genes & development.

[20]  R. Abraham,et al.  Mammalian target of rapamycin as a therapeutic target in oncology. , 2008, Expert opinion on therapeutic targets.

[21]  P. Cohen,et al.  The selectivity of protein kinase inhibitors: a further update. , 2007, The Biochemical journal.

[22]  Adiel Cohen,et al.  PRAS40 and PRR5-Like Protein Are New mTOR Interactors that Regulate Apoptosis , 2007, PloS one.

[23]  D. Hardie,et al.  AMP-activated/SNF1 protein kinases: conserved guardians of cellular energy , 2007, Nature Reviews Molecular Cell Biology.

[24]  C. Proud,et al.  PRAS40 Is a Target for Mammalian Target of Rapamycin Complex 1 and Is Required for Signaling Downstream of This Complex* , 2007, Journal of Biological Chemistry.

[25]  A. Nakashima,et al.  The Proline-rich Akt Substrate of 40 kDa (PRAS40) Is a Physiological Substrate of Mammalian Target of Rapamycin Complex 1* , 2007, Journal of Biological Chemistry.

[26]  R. Roth,et al.  PRAS40 Regulates mTORC1 Kinase Activity by Functioning as a Direct Inhibitor of Substrate Binding* , 2007, Journal of Biological Chemistry.

[27]  C. Rhee,et al.  Hypoxic condition- and high cell density-induced expression of Redd1 is regulated by activation of hypoxia-inducible factor-1alpha and Sp1 through the phosphatidylinositol 3-kinase/Akt signaling pathway. , 2007, Cellular signalling.

[28]  H Phillip Koeffler,et al.  RTP801 is a novel retinoic acid-responsive gene associated with myeloid differentiation. , 2007, Experimental hematology.

[29]  S. Carr,et al.  PRAS40 is an insulin-regulated inhibitor of the mTORC1 protein kinase. , 2007, Molecular cell.

[30]  Timothy J. Griffin,et al.  Insulin signalling to mTOR mediated by the Akt/PKB substrate PRAS40 , 2007, Nature Cell Biology.

[31]  Ming You,et al.  TSC2 Integrates Wnt and Energy Signals via a Coordinated Phosphorylation by AMPK and GSK3 to Regulate Cell Growth , 2006, Cell.

[32]  Robert J. Schneider,et al.  Hypoxia Inhibits Protein Synthesis through a 4E-BP1 and Elongation Factor 2 Kinase Pathway Controlled by mTOR and Uncoupled in Breast Cancer Cells , 2006, Molecular and Cellular Biology.

[33]  C. Walker,et al.  Activity of TSC2 is inhibited by AKT-mediated phosphorylation and membrane partitioning , 2006, The Journal of cell biology.

[34]  Russell G. Jones,et al.  Hypoxia-induced energy stress regulates mRNA translation and cell growth. , 2006, Molecular cell.

[35]  F. Kaper,et al.  Mutations in the PI3K/PTEN/TSC2 pathway contribute to mammalian target of rapamycin activity and increased translation under hypoxic conditions. , 2006, Cancer research.

[36]  C. Johannessen,et al.  Regulation of mTOR and Cell Growth in Response to Energy Stress by REDD1 , 2005, Molecular and Cellular Biology.

[37]  K. Inoki,et al.  The Stress-inducted Proteins RTP801 and RTP801L Are Negative Regulators of the Mammalian Target of Rapamycin Pathway* , 2005, Journal of Biological Chemistry.

[38]  Wolfgang Arnold,et al.  REDD1 integrates hypoxia-mediated survival signaling downstream of phosphatidylinositol 3-kinase , 2005, Oncogene.

[39]  E. Hafen,et al.  Regulation of mTOR function in response to hypoxia by REDD1 and the TSC1/TSC2 tumor suppressor complex. , 2004, Genes & development.

[40]  E. Hafen,et al.  The hypoxia-induced paralogs Scylla and Charybdis inhibit growth by down-regulating S6K activity upstream of TSC in Drosophila. , 2004, Genes & development.

[41]  P. Einat,et al.  Inhibition of oxygen-induced retinopathy in RTP801-deficient mice. , 2004, Investigative ophthalmology & visual science.

[42]  R. DePinho,et al.  The LKB1 tumor suppressor negatively regulates mTOR signaling. , 2004, Cancer cell.

[43]  J. Brugarolas,et al.  Dysregulation of HIF and VEGF is a unifying feature of the familial hamartoma syndromes. , 2004, Cancer cell.

[44]  H. S. Kim,et al.  Genetic analysis of the LKB1/STK11 gene in hepatocellular carcinomas. , 2004, European journal of cancer.

[45]  K. Inoki,et al.  TSC2 Mediates Cellular Energy Response to Control Cell Growth and Survival , 2003, Cell.

[46]  Jérôme Boudeau,et al.  Complexes between the LKB1 tumor suppressor, STRADα/β and MO25α/β are upstream kinases in the AMP-activated protein kinase cascade , 2003, Journal of biology.

[47]  J. Howell,et al.  A Novel Hypoxia-inducible Factor-independent Hypoxic Response Regulating Mammalian Target of Rapamycin and Its Targets* , 2003, Journal of Biological Chemistry.

[48]  Paul Tempst,et al.  GbetaL, a positive regulator of the rapamycin-sensitive pathway required for the nutrient-sensitive interaction between raptor and mTOR. , 2003, Molecular cell.

[49]  J. Goldstein,et al.  Liver-specific mRNA for Insig-2 down-regulated by insulin: Implications for fatty acid synthesis , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[50]  Y. Xiong,et al.  14-3-3β Binds to and Negatively Regulates the Tuberous Sclerosis Complex 2 (TSC2) Tumor Suppressor Gene Product, Tuberin* , 2003, The Journal of Biological Chemistry.

[51]  J. Crespo,et al.  Two TOR complexes, only one of which is rapamycin sensitive, have distinct roles in cell growth control. , 2002, Molecular cell.

[52]  M. Seldin,et al.  Hepatocellular carcinoma caused by loss of heterozygosity in Lkb1 gene knockout mice. , 2002, Cancer research.

[53]  J. Avruch,et al.  Raptor, a Binding Partner of Target of Rapamycin (TOR), Mediates TOR Action , 2002, Cell.

[54]  D. Sabatini,et al.  mTOR Interacts with Raptor to Form a Nutrient-Sensitive Complex that Signals to the Cell Growth Machinery , 2002, Cell.

[55]  David Sidransky,et al.  Inactivation of LKB1/STK11 is a common event in adenocarcinomas of the lung. , 2002, Cancer research.

[56]  Dena Leshkowitz,et al.  Identification of a Novel Hypoxia-Inducible Factor 1-Responsive Gene, RTP801, Involved in Apoptosis , 2002, Molecular and Cellular Biology.

[57]  Robert A. Weinberg,et al.  Enumeration of the Simian Virus 40 Early Region Elements Necessary for Human Cell Transformation , 2002, Molecular and Cellular Biology.

[58]  Hongbing Zhang,et al.  A mouse model of TSC1 reveals sex-dependent lethality from liver hemangiomas, and up-regulation of p70S6 kinase activity in Tsc1 null cells. , 2002, Human molecular genetics.

[59]  M. Gassmann,et al.  HIF‐1 is expressed in normoxic tissue and displays an organ‐specific regulation under systemic hypoxia , 2001, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[60]  G. Thomas,et al.  Ribosomal S6 kinase signaling and the control of translation. , 1999, Experimental cell research.

[61]  T. Mäkelä,et al.  Growth suppression by Lkb1 is mediated by a G(1) cell cycle arrest. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[62]  M. Brown,et al.  Disruption of LDL receptor gene in transgenic SREBP-1a mice unmasks hyperlipidemia resulting from production of lipid-rich VLDL. , 1999, The Journal of clinical investigation.

[63]  P. Buc-Calderon,et al.  Hypoxia increases the association of 4E‐binding protein 1 with the initiation factor 4E in isolated rat hepatocytes , 1999, FEBS letters.

[64]  Philippe Soriano.  Generalized lacZ expression with the ROSA26 Cre reporter strain , 1999, Nature Genetics.

[65]  M Aguet,et al.  Inducible gene targeting in mice , 1995, Science.

[66]  P. Fisher,et al.  Cell cycle arrest. , 1995, Science.

[67]  D. Kwiatkowski,et al.  Tuberous sclerosis. , 1994, Archives of dermatology.

[68]  T. S. P. S.,et al.  GROWTH , 1924, Nature.