Cell Metab. 2019 Jan 8;29(1):192-201.e7. doi: 10.1016/j.cmet.2018.08.013. Epub 2018 Sep 6.

Leucine Signals to mTORC1 via Its Metabolite Acetyl-Coenzyme A.

Son SM¹, Park SJ², Lee H², Siddiqi F², Lee JE³, Menzies FM², Rubinsztein DC⁴.

Author information

1: Department of Medical Genetics, Cambridge Institute for Medical Research (CIMR), University of Cambridge, Cambridge, UK; UK Dementia Research Institute, Cambridge Institute for Medical Research (CIMR), University of Cambridge, Cambridge, UK.
2: Department of Medical Genetics, Cambridge Institute for Medical Research (CIMR), University of Cambridge, Cambridge, UK.
3: Department of Anatomy, Bk21 Plus Project for Medical Sciences and Brain Research Institute, Yonsei University College of Medicine, Seoul 03722, Republic of Korea.
4: Department of Medical Genetics, Cambridge Institute for Medical Research (CIMR), University of Cambridge, Cambridge, UK; UK Dementia Research Institute, Cambridge Institute for Medical Research (CIMR), University of Cambridge, Cambridge, UK. Electronic address: dcr1000@cam.ac.uk.

Abstract

The mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) is a master regulator of cell growth and metabolism. Leucine (Leu) activates mTORC1 and many have tried to identify the mechanisms whereby cells sense Leu in this context. Here we describe that the Leu metabolite acetyl-coenzyme A (AcCoA) positively regulates mTORC1 activity by EP300-mediated acetylation of the mTORC1 regulator, Raptor, at K1097. Leu metabolism and consequent mTORC1 activity are regulated by intermediary enzymes. As AcCoA is a Leu metabolite, this process directly correlates with Leu abundance, and does not require Leu sensing via intermediary proteins, as has been described previously. Importantly, we describe that this pathway regulates mTORC1 in a cell-type-specific manner. Finally, we observed decreased acetylated Raptor, and inhibited mTORC1 and EP300 activity in fasted mice tissues. These results provide a direct mechanism for mTORC1 regulation by Leu metabolism.

KEYWORDS:

Raptor; acetyl-CoA; amino acid sensing; autophagy; leucine; mTOR; starvation

PMID:: 30197302
PMCID:: PMC6331339
DOI:: 10.1016/j.cmet.2018.08.013

Free PMC Article

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Figure 1

MCCC1, Which Regulates Leu Metabolism, Modifies mTORC1 Signaling in HeLa Cells
(A) Leu metabolic pathway. Blue box shows MCCC1 protein.
(B) Control and MCCC1 knockdown (transfected with pool or four deconvoluted oligos) HeLa cells were used to determine whether MCCC1 can regulate mTORC1 signal. Blots are representative of at least three independent experiments (N = 3). P- indicates phosphorylated protein. Note that oligo no. 2 has not knocked down MCCC1. p-S6K1 (Thr389), p-S6 (Ser235/236), p-4E-BP1 (Thr37/46).
(C) Re-introduction to MCCC1 knockdown HeLa cells with MCCC1 cDNA. Blots are representative of at least three independent experiments (N = 3).
(D) Control and MCCC1 knockdown HeLa cells were either left untreated, AA starved for 2 hr, or AA starved and then Leu was added for 0.5 hr, then immunostained with mTOR and LAMP1 antibodies as shown. Co-localization panels show an overlap between mTOR and LAMP1 signals. The fraction of mTOR-positive lysosomes were determined using Volocity software. Values are mean ± SEM. n = ∼50 cells. ^∗p < 0.05, ^∗∗p < 0.01 versus control cells; ^##p < 0.01 versus AA-starved cells (two-tailed t test); ns, not significant. Scale bars, 5 μm and 1 μm (enlarged images). The experiment was repeated an additional two times (N = 3). NC, normal control.
(E) Immunoblots of control and MCCC1-knockdown HeLa cells with or without Leu or alpha-ketoisocaproate (KIC) under AA-starved conditions. Blots are representative of at least three independent experiments (N = 3). ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001 versus control cells; ^#p < 0.05, ^##p < 0.01 versus AA-starved cells; ^&&p < 0.01 versus MCCC1 knockdown cells. p-ULK1 (Ser757).
(F) Immunoblots of control and MCCC1-knockdown HeLa cells with or without 3-hydroxy-3-methylglutaryl-coenzyme A (HCoA) or AcCoA. ^∗p < 0.05, ^∗∗p < 0.01 versus control cells; ^#p < 0.05, ^##p < 0.01 versus AA-starved cells. N = 3.

Leucine Signals to mTORC1 via Its Metabolite Acetyl-Coenzyme A

Cell Metab. 2019 Jan 8;29(1):192-201.e7.

Figure 2

AcCoA, the Metabolite of Leu Metabolism, Is Important for mTORC1 Regulation in Some Cell Types
(A) Measurement of total and cytosolic AcCoA levels in control and MCCC1 knockdown HeLa cells. ^∗∗p < 0.01 versus control cells. N = 3.
(B) Measurement of total and cytosolic AcCoA levels on HeLa cells with or without Leu or DCA under AA-starved conditions. ^∗∗p < 0.01 versus control cells; ^#p < 0.05, ^##p < 0.01 versus AA-starved cells. N = 4.
(C) mTORC1 regulation under AA-starved conditions with or without Leu, KIC, HCoA, or DCA in HeLa cells. Blots are representative of at least three independent experiments (N = 3).
(D) mTORC1 distribution to lysosomal membranes under AA starvation with or without Leu, KIC, DCA, or AcCoA in HeLa cells. Scale bars, 5 μm and 1 μm (enlarged images).
(E) Quantification of (D). Values are mean ± SEM. n = about 60 cells. ^∗∗p < 0.01 versus control cells; ^##p < 0.01, ^###p < 0.001 versus AA-starved cells (two-tailed t test).
(F) Measurement of total and cytosolic AcCoA levels in control and ACLY knockdown HeLa cells. ^∗∗p < 0.01 versus control cells. N = 3.
(G) Immunoblots of control and ACLY knockdown HeLa cells with or without Leu or DCA under AA-starved conditions. Blots are representative of at least three independent experiments. N = 3.
(H) mTORC1 regulation under AA-starved conditions with or without Leu or DCA in SH-SY5Y cells. ^∗∗p < 0.01, ^∗∗∗p < 0.001 versus control cells; ^#p < 0.05, ^##p < 0.01 versus AA-starved cells (two-tailed t test). NC, normal control; NEA, non-essential AA mixture; EA, essential AA mixture. N = 4.
(I) The role of DCA in Mccc1 knockdown primary neurons. ^∗∗p < 0.01 versus control small hairpin RNA (shRNA)-infected neurons; ^#p < 0.05 versus Mccc1 shRNA-infected neurons. N = 3.
(J) mTORC1 regulation under starved condition with or without Leu, KIC, HCoA, or DCA on primary neurons. ^∗p < 0.01, ^∗∗p < 0.01 versus control neurons; ^#p < 0.05 versus starved neurons. N = 3.
(K) mTORC1 regulation using phosphorylated S6 (p-S6; Ser235/236) antibody in primary neurons. Values are mean ± SEM. n = about 50 cells. ^∗∗p < 0.01 versus control neurons; ^#p < 0.05 versus starved neurons (two-tailed t test). Scale bar, 10 μm.

Leucine Signals to mTORC1 via Its Metabolite Acetyl-Coenzyme A

Cell Metab. 2019 Jan 8;29(1):192-201.e7.

Figure 3

mTORC1 Is Regulated by AcCoA via EP300 Acetyltransferase
(A) EP300 inhibitors (c646 and spermidine [Sp]) inhibit AcCoA-induced rescue of mTORC1 activity in AA-starved HeLa cells. N = 4.
(B) Effects of EP300 knockdown with replacement with wild-type (EP300 WT) or catalytically inactive EP300 (EP300 Mut) on mTORC1 signaling in response to AA deprivation with or without AcCoA. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001 versus control cells; ^#p < 0.05, ^##p < 0.01, ^###p < 0.001 versus AA-starved cells; ^&p < 0.05 versus EP300 knockdown cells (two-tailed t test); ns, not significant. N = 3.
(C) mTORC1 regulation by AcCoA in control HeLa cells or in EP300, KAT2A, or KAT2B knockdown HeLa cells. Blots are representative of at least three independent experiments (N = 3).
(D) mTORC1 distribution onto lysosomal membranes on control and EP300 knockdown HeLa cells in response to AA deprivation with or without AcCoA. Values are mean ± SEM. n = about 50 cells. ^∗p < 0.05 versus control cells; ^#p < 0.05 versus AA-starved cells (two-tailed t test). Scale bars, 5 μm and 1 μm (enlarged images).
(E) mTORC2 regulation by EP300 activity. ^∗p < 0.05 versus control cells; ^#p < 0.05 versus AA-starved cells (two-tailed t test). N = 3. p-PKCα/β (Thr638/641), p-AKT (Ser473).
(F) Localization of EP300 to the nucleus under AA-starved conditions. N, nuclear; C, cytoplasm. n = about 30 cells. ^∗p < 0.05, ^∗∗p < 0.01 versus control cells. Scale bar, 5 μm.
(G) Nuclear or cytoplasmic EP300 activities under AA-starved condition. ^∗p < 0.05 versus control cells. N = 4.
(H) Change in EP300 localization under AA starvation with or without Leu or AcCoA. ^∗∗p < 0.01 versus control cells; ^#p < 0.05, ^##p < 0.01, ^###p < 0.001 versus AA-starved cells (two-tailed t test). N = 3.
(I) Differential regulation of acetylation of nuclear (H3) and cytoplasmic (ATG7 and Raptor) substrates by EP300 under basal and AA starvation conditions. N = 3.

Leucine Signals to mTORC1 via Its Metabolite Acetyl-Coenzyme A

Cell Metab. 2019 Jan 8;29(1):192-201.e7.

Figure 4

Raptor Acetylation by EP300 Is Important for mTORC1 Regulation
(A) Interaction of EP300 with components of the mTORC1 using GFP-trap or immunoprecipitation (IP) with EP300 antibody. GFP- or YFP-tagged mTORC1 constructs (GFP vector, YFP-mTOR, YFP-Raptor, YFP-proline-rich Akt substrate of 40 kDa [PRAS40], and YFP-DEP domain-containing mTOR-interacting protein [DEPTOR]) were used. Asterisks indicate the predicted position of mTOR, PRAS40, or DEPTOR. HC, heavy immunoglobulin G (IgG) chain; LC, light IgG chain. N = 3.
(B) Decreased acetylation of Raptor under AA-starved conditions independently of interaction with mTOR. Acetylated mTOR level was not altered by AA starvation. ^∗∗p < 0.01 versus control cells. N = 3.
(C) Acetylation of Raptor by EP300, not by KAT2A or KAT2B. ^∗∗∗p < 0.001 versus control cells. N = 3.
(D) Raptor K1097R mutant (KR) is not acetylated. WT, wild-type; KR, K1097R mutant. ^∗∗p < 0.01, ^∗∗∗p < 0.001 versus Raptor WT-expressing control cells. N = 3.
(E) Cells were depleted of Raptor with small interfering RNA (siRNA) and reconstituted with Raptor WT or KR, then analyzed for mTORC1 activity in the presence or absence of AA, the latter with/without AcCoA in HeLa cells. ^∗p < 0.05, ^∗∗p < 0.01 versus Raptor WT-expressing control cells; ^#p < 0.05 versus AA-starved cells; ^&p < 0.05 versus Raptor KR-expressing cells (two-tailed t test); ns, not significant. N = 3.
(F and G) Reduced interaction of Raptor KR mutant with the Rag complex using GFP-trap (F) or IP with Flag antibody (G). N = 3.
(H) mTORC1 distribution onto lysosomal membranes in HeLa cells depleted of Raptor then reconstituted with Raptor WT or Raptor KR. Scale bars, 10 μm and 2 μm (enlarged images). n = about 40 cells. ^∗∗p < 0.01 versus Raptor WT-expressing control cells.
(I and J) Decreased AcCoA levels and acetylation of Raptor in fasted mice brains, livers, and muscles. After 22.5 hr starvation, mice were given free access to food for 1.5 hr followed by a second round of starvation for another 22.5 hr. The tissue samples from fed (n = 5) and fasted mice (n = 6) were analyzed for AcCoA (I) and acetylated Raptor (J) levels. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001 versus fed mice.

Leucine Signals to mTORC1 via Its Metabolite Acetyl-Coenzyme A

Cell Metab. 2019 Jan 8;29(1):192-201.e7.