Regulation of mTORC1 by amino acids

doi:10.1016/j.tcb.2014.03.003

Trends in Cell Biology

Volume 24, Issue 7, July 2014, Pages 400-406

https://doi.org/10.1016/j.tcb.2014.03.003 Get rights and content

Highlights

•
Cellular amino acid levels tightly control the activity of the master growth regulator mTORC1.
•
The emergence of molecular details on how the mTORC1 pathway senses amino acids is an important advance in the field.
•
The amino acid sensing pathway is composed of several multicomponent complexes that act in concert to convey changes in amino acid levels to mTORC1.

The mechanistic target of rapamycin complex I (mTORC1) is a central regulator of cellular and organismal growth, and hyperactivation of this pathway is implicated in the pathogenesis of many human diseases including cancer and diabetes. mTORC1 promotes growth in response to the availability of nutrients, such as amino acids, which drive mTORC1 to the lysosomal surface, its site of activation. How amino acid levels are communicated to mTORC1 is only recently coming to light by the discovery of a lysosome-based signaling system composed of Rags (Ras-related GTPases) and Ragulator v-ATPase, GATOR (GAP activity towards Rags), and folliculin (FLCN) complexes. Increased understanding of this pathway will not only provide insight into growth control but also into the human pathologies triggered by its deregulation.

Section snippets

Overview of mTORC1 signaling

Growth is a fundamental biological process that is highly influenced by an organism's environment. For multicellular eukaryotes, including mammals, nutrient availability within the local environment is a major determinant of growth and is sensed through central signaling pathways that engage anabolic programs necessary to increase cell and body size. By coupling nutrient-sensing to long-range growth factor and hormonal signaling networks, animals are able to readily adjust their growth and

Amino acid signaling and mTORC1 localization

Early investigations revealed that amino acids are necessary to stimulate protein synthesis in rat skeletal muscles [28], a process now known to be under the control of mTORC1. Subsequent studies in cultured mammalian cells confirmed that a mixture of all 20 amino acids activated mTORC1 and that the combination of amino acid and growth factor signaling was necessary for the phosphorylation of canonical mTORC1 substrates 29, 30. Whether all amino acids, one particular amino acid, or an amino

The lysosome: key site of amino acid sensing

Extracellular amino acids must cross the plasma membrane to reactivate mTORC1 after their depletion from cell culture media [31]. Nevertheless, treating cells with cycloheximide, a protein synthesis inhibitor, preserves sufficient intracellular pools of amino acids to rescue mTORC1 signaling even in the absence of extracellular amino acids. This finding argues that the sensing mechanism must occur within the cell and not at its periphery [34]. The use of a cell-free reconstitution assay

The Rag GTPases mediate the amino acid signal to mTORC1

For a long time it was believed that the amino acid signal impinged on the TSC complex–Rheb axis; however, the development of TSC2^−/− mice suggested otherwise. mTORC1 signaling remained sensitive to a change in amino acid levels in mouse embryonic fibroblasts (MEFs) obtained from these animals 40, 41, implicating an alternative route for sensing. This alternative pathway, identified by biochemical and genetic screens 34, 42, centers around the Rag GTPases which lay the molecular foundation for

Regulation of the Rag GTPases

The Rags are critical for proper amino acid sensing because their tight coordination with amino acid levels prevents deregulation of mTORC1 signaling. This coordination depends on Rag GTPase activators and inhibitors which modulate their nucleotide-bound state. The recent identification of some of these regulators highlights a complex signaling network upstream of the Rag GTPases (Figure 1).

Spatial regulation of the TSC complex

A new rigorous study shows that that, like mTORC1, the TSC complex translocates to and from the lysosomal surface in response to insulin signaling but not to amino acid levels [73]. Akt-dependent phosphorylation of TSC2, presumed by many to inhibit TSC complex GAP activity, is responsible for driving the TSC complex off the lysosomal surface, allowing mTORC1 activation by removing TSC from Rheb, the target of its GAP activity [73]. Given the number of signals upstream of mTORC1 that converge on

Concluding remarks

This is an exciting time to study how amino acids are sensed by mTORC1. With the discovery of so many new pathway components there remain many more questions than answers. Clearly, understanding the interplay between positive and negative regulators, and the existence of additional human pathologies associated with these factors are of high interest (Box 3). With the use of a combination of bioinformatic and systems-biology approaches together with more traditional discovery platforms, the

Acknowledgments

We thank Lynne Chantranupong and Shuyu Wang for helpful suggestions and Tom DeCesare for figure design. This work was supported by grants from the National Institutes of Health (CA103866 and AI47389) and Department of Defense (W81XWH-07-0448) to D.M.S. L.B.P is the Lallage Feazel Wall Fellow of the Damon Runyon Cancer Research Foundation (DRG-2178-14). D.M.S. is an investigator of the Howard Hughes Medical Institute.

References (86)

M. Laplante et al.
mTOR signaling in growth control and disease
Cell
(2012)
C.K. Yip
Structure of the human mTOR complex I and its implications for rapamycin inhibition
Mol. Cell
(2010)
D.H. Kim
mTOR interacts with raptor to form a nutrient-sensitive complex that signals to the cell growth machinery
Cell
(2002)
K. Hara
Raptor, a binding partner of target of rapamycin (TOR), mediates TOR action
Cell
(2002)
T.R. Peterson
DEPTOR is an mTOR inhibitor frequently overexpressed in multiple myeloma cells and required for their survival
Cell
(2009)
Y. Sancak
PRAS40 is an insulin-regulated inhibitor of the mTORC1 protein kinase
Mol. Cell
(2007)
D.H. Kim
GbetaL, a positive regulator of the rapamycin-sensitive pathway required for the nutrient-sensitive interaction between raptor and mTOR
Mol. Cell
(2003)
C.C. Dibble
TBC1D7 is a third subunit of the TSC1–TSC2 complex upstream of mTORC1
Mol. Cell
(2012)
L. Ma
Phosphorylation and functional inactivation of TSC2 by Erk implications for tuberous sclerosis and cancer pathogenesis
Cell
(2005)
B.D. Manning
Identification of the tuberous sclerosis complex-2 tumor suppressor gene product tuberin as a target of the phosphoinositide 3-kinase/akt pathway
Mol. Cell
(2002)

H.C. Dan

Phosphatidylinositol 3-kinase/Akt pathway regulates tuberous sclerosis tumor suppressor complex by phosphorylation of tuberin

J. Biol. Chem.

(2002)

K. Inoki

TSC2 mediates cellular energy response to control cell growth and survival

Cell

(2003)

A.V. Budanov et al.

p53 target genes sestrin1 and sestrin2 connect genotoxic stress and mTOR signaling

Cell

(2008)

K. Hara

Amino acid sufficiency and mTOR regulate p70 S6 kinase and eIF-4E BP1 through a common effector mechanism

J. Biol. Chem.

(1998)

P. Nicklin

Bidirectional transport of amino acids regulates mTOR and autophagy

Cell

(2009)

A. Efeyan

Amino acids and mTORC1: from lysosomes to disease

Trends Mol. Med.

(2012)

Y. Sancak

Ragulator–Rag complex targets mTORC1 to the lysosomal surface and is necessary for its activation by amino acids

Cell

(2010)

M. Binda

The Vam6 GEF controls TORC1 by activating the EGO Complex

Mol. Cell

(2009)

E.M. Smith

The tuberous sclerosis protein TSC2 is not required for the regulation of the mammalian target of rapamycin by amino acids and certain cellular stresses

J. Biol. Chem.

(2005)

T. Sekiguchi

Novel G proteins, Rag C and Rag D, interact with GTP-binding proteins, Rag A and Rag B

J. Biol. Chem.

(2001)

A. Schurmann

Cloning of a novel family of mammalian GTP-binding proteins (RagA, RagBs, RagB1) with remote similarity to the Ras-related GTPases

J. Biol. Chem.

(1995)

L. Bar-Peled

Ragulator is a GEF for the Rag GTPases that signal amino acid to mTORC1

Cell

(2012)

F. Dubouloz

The TOR and EGO protein complexes orchestrate microautophagy in yeast

Mol. Cell

(2005)

T. Zhang

Ego3 functions as a homodimer to mediate the interaction between Gtr1–Gtr2 and Ego1 in the ego complex to activate TORC1

Structure

(2012)

K. Kogan

Structural conservation of components in the amino acid sensing branch of the TOR pathway in yeast and mammals

J. Mol. Biol.

(2010)

J.L. Bos

GEFs and GAPs: critical elements in the control of small G proteins

Cell

(2007)

Y. Cai

The structural basis for activation of the Rab Ypt1p by the TRAPP membrane-tethering complexes

Cell

(2008)

Z.Y. Tsun

The folliculin tumor suppressor is a GAP for the RagC/D GTPases that signal amino acid levels to mTORC1

Mol. Cell

(2013)

M. Nordmann

The Mon1–Ccz1 complex is the GEF of the late endosomal Rab7 homolog Ypt7

Curr. Biol.

(2010)

J.M. Han

Leucyl-tRNA synthetase is an intracellular leucine sensor for the mTORC1-signaling pathway

Cell

(2012)

G. Bonfils

Leucyl-tRNA synthetase controls TORC1 via the EGO complex

Mol. Cell

(2012)

Y.M. Kim

SH3BP4 is a negative regulator of amino acid-Rag GTPase-mTORC1 signaling

Mol. Cell

(2012)

S. Menon

Spatial control of the TSC complex integrates insulin and nutrient regulation of mTORC1 at the lysosome

Cell

(2014)

I. Garcia-Saez

Structural characterization of HBXIP: the protein that interacts with the anti-apoptotic protein survivin and the oncogenic viral protein HBx

J. Mol. Biol.

(2011)

E.V. Koonin et al.

Dynein light chains of the Roadblock/LC7 group belong to an ancient protein superfamily implicated in NTPase regulation

Curr. Biol.

(2000)

J.H. Jeong

Crystal structure of the Gtr1p(GTP)–Gtr2p(GDP) protein complex reveals large structural rearrangements triggered by GTP-to-GDP conversion

J. Biol. Chem.

(2012)

P.P. Hsu

The mTOR-regulated phosphoproteome reveals a mechanism of mTORC1-mediated inhibition of growth factor signaling

Science

(2011)

Y. Yu

Phosphoproteomic analysis identifies Grb10 as an mTORC1 substrate that negatively regulates insulin signaling

Science

(2011)

X.M. Ma et al.

Molecular mechanisms of mTOR-mediated translational control

Nat. Rev. Mol. Cell Biol.

(2009)

J.D. Rabinowitz et al.

Autophagy and metabolism

Science

(2010)

L.J. Saucedo

Rheb promotes cell growth as a component of the insulin/TOR signalling network

Nat. Cell Biol.

(2003)

H. Stocker

Rheb is an essential regulator of S6K in controlling cell growth in Drosophila

Nat. Cell Biol.

(2003)

K. Inoki

Rheb GTPase is a direct target of TSC2 GAP activity and regulates mTOR signaling

Genes Dev.

(2003)

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Trends in Cell Biology

ReviewRegulation of mTORC1 by amino acids

Highlights

Section snippets

Overview of mTORC1 signaling

Amino acid signaling and mTORC1 localization

The lysosome: key site of amino acid sensing

The Rag GTPases mediate the amino acid signal to mTORC1

Regulation of the Rag GTPases

Spatial regulation of the TSC complex

Concluding remarks

Acknowledgments

Cell

Mol. Cell

Cell

Cell

Cell

Mol. Cell

Mol. Cell

Mol. Cell

Cell

Mol. Cell

J. Biol. Chem.

Cell

Cell

J. Biol. Chem.

Cell

Trends Mol. Med.

Cell

Mol. Cell

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

Cell

Mol. Cell

Structure

J. Mol. Biol.

Cell

Cell

Mol. Cell

Curr. Biol.

Cell

Mol. Cell

Mol. Cell

Cell

J. Mol. Biol.

Curr. Biol.

J. Biol. Chem.

The mTOR-regulated phosphoproteome reveals a mechanism of mTORC1-mediated inhibition of growth factor signaling

Science

Phosphoproteomic analysis identifies Grb10 as an mTORC1 substrate that negatively regulates insulin signaling

Science

Molecular mechanisms of mTOR-mediated translational control

Nat. Rev. Mol. Cell Biol.

Autophagy and metabolism

Science

Rheb promotes cell growth as a component of the insulin/TOR signalling network

Nat. Cell Biol.

Rheb is an essential regulator of S6K in controlling cell growth in Drosophila

Nat. Cell Biol.

Rheb GTPase is a direct target of TSC2 GAP activity and regulates mTOR signaling

Genes Dev.

Review
Regulation of mTORC1 by amino acids