TMEM55B contributes to lysosomal homeostasis and amino acid-induced mTORC1 activation

SummaryAutophagy is a catabolic process whereby cytoplasmic components are degraded within lysosomes, allowing cells to maintain energy homeostasis during nutrient depletion. Several studies have shown that the CDK inhibitor p27Kip1 promotes starvation-induced autophagy. However, the underlying mechanism remains unknown. Here, we report that in amino acid deprived cells, p27 controls autophagy via an mTORC1-dependent mechanism. During prolonged amino acid starvation, a fraction of p27 is recruited to lysosomes where it interacts with LAMTOR1, a component of the Ragulator complex required for mTORC1 lysosomal localization and activation. p27 binding to LAMTOR1 prevents Ragulator assembly and function and subsequent mTORC1 activation, thereby promoting autophagy. Conversely, upon amino acid withdrawal, p27−/− cells exhibit elevated mTORC1 signaling, impaired lysosomal activity and autophagy, and resistance to apoptosis. This is associated with sequestration of TFEB in the cytoplasm, preventing the induction of lysosomal genes required for lysosomal function. Silencing of LAMTOR1 or mTOR inhibition restores autophagy and induces apoptosis in p27−/− cells. Together, these results reveal a direct, coordinated regulation between the cell cycle and cell growth machineries.

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PAT2 regulates autophagy through vATPase assembly and lysosomal acidification in brown adipocytes

10.1101/2020.01.24.918078 ◽

2020 ◽

Cited By ~ 1

Author(s):

Jiefu Wang ◽

Martin Krueger ◽

Stefanie M. Hauck ◽

Siegfried Ussar

Keyword(s):

Amino Acid ◽

Brown Adipocyte ◽

Amino Acid Transporters ◽

Mitochondrial Uncoupling ◽

Brown Adipocytes ◽

Brown Adipose ◽

Glucose And Lipid Homeostasis ◽

Mtorc1 Activation ◽

Lysosomal Acidification

Brown adipose tissue (BAT) plays a key role in maintaining body temperature as well as glucose and lipid homeostasis by its ability to dissipate energy through mitochondrial uncoupling. To facilitate these tasks BAT needs to adopt its thermogenic activity and substrate utilization to changes in nutrient availability, regulated by a complex network of neuronal, endocrine and nutritional inputs. Amongst this multitude of factors influencing BAT activity changes in the autophagic response of brown adipocytes are an important regulator of its thermogenic capacity and activity. Increasing evidence supports an important role of amino acid transporters in mTORC1 activation and the regulation of autophagy. However, a specific role of amino acid transporters in BAT regulating its function has not been described. Here we show that the brown adipocyte specific proton coupled amino acid transporter PAT2 rapidly translocates from the plasma membrane to the lysosome in response to amino acid withdrawal, where it facilitates the assembly of the lysosomal vATPase. Loss or overexpression of PAT2 therefore impair lysosomal acidification, autophagolysosome formation and starvation induced mTORC1 activation.

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mTORC1 Activation Requires DRAM-1 by Facilitating Lysosomal Amino Acid Efflux

Molecular Cell ◽

10.1016/j.molcel.2019.07.021 ◽

2019 ◽

Vol 76 (1) ◽

pp. 163-176.e8 ◽

Cited By ~ 5

Author(s):

Florian Beaumatin ◽

Jim O’Prey ◽

Valentin J.A. Barthet ◽

Barbara Zunino ◽

Jean-Philippe Parvy ◽

...

Keyword(s):

Amino Acid ◽

Amino Acid Efflux ◽

Mtorc1 Activation

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ATF4-Mediated Upregulation of REDD1 and Sestrin2 Suppresses mTORC1 Activity during Prolonged Leucine Deprivation

Journal of Nutrition ◽

10.1093/jn/nxz309 ◽

2019 ◽

Vol 150 (5) ◽

pp. 1022-1030 ◽

Cited By ~ 5

Author(s):

Dandan Xu ◽

Weiwei Dai ◽

Lydia Kutzler ◽

Holly A Lacko ◽

Leonard S Jefferson ◽

...

Keyword(s):

Amino Acids ◽

Dna Damage ◽

Amino Acid ◽

Protein Kinase ◽

Dna Damage Response ◽

Dependent Manner ◽

Mouse Embryo Fibroblasts ◽

Damage Response ◽

Mtorc1 Activation ◽

In Cells

ABSTRACT Background The protein kinase target of rapamycin (mTOR) in complex 1 (mTORC1) is activated by amino acids and in turn upregulates anabolic processes. Under nutrient-deficient conditions, e.g., amino acid insufficiency, mTORC1 activity is suppressed and autophagy is activated. Intralysosomal amino acids generated by autophagy reactivate mTORC1. However, sustained mTORC1 activation during periods of nutrient insufficiency would likely be detrimental to cellular homeostasis. Thus, mechanisms must exist to prevent amino acids released by autophagy from reactivating the kinase. Objective The objective of the present study was to test whether mTORC1 activity is inhibited during prolonged leucine deprivation through ATF4-dependent upregulation of the mTORC1 suppressors regulated in development and DNA damage response 1 (REDD1) and Sestrin2. Methods Mice (8 wk old; C57Bl/6 × 129SvEV) were food deprived (FD) overnight and one-half were refed the next morning. Mouse embryo fibroblasts (MEFs) deficient in ATF4, REDD1, and/or Sestrin2 were deprived of leucine for 0–16 h. mTORC1 activity and ATF4, REDD1, and Sestrin2 expression were assessed in liver and cell lysates. Results Refeeding FD mice resulted in activation of mTORC1 in association with suppressed expression of both REDD1 and Sestrin2 in the liver. In cells in culture, mTORC1 exhibited a triphasic response to leucine deprivation, with an initial suppression followed by a transient reactivation from 2 to 4 h and a subsequent resuppression after 8 h. Resuppression occurred concomitantly with upregulated expression of ATF4, REDD1, and Sestrin2. However, in cells lacking ATF4, neither REDD1 nor Sestrin2 expression was upregulated by leucine deprivation, and resuppression of mTORC1 was absent. Moreover, in cells lacking either REDD1 or Sestrin2, mTORC1 resuppression was attenuated, and in cells lacking both proteins resuppression was further blunted. Conclusions The results suggest that leucine deprivation upregulates expression of both REDD1 and Sestrin2 in an ATF4-dependent manner, and that upregulated expression of both proteins is involved in resuppression of mTORC1 during prolonged leucine deprivation.

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MAP4K3 inhibits Sirtuin-1 to repress LKB1-AMPK to promote amino acid dependent activation of mTORC1

10.1101/2021.11.08.467702 ◽

2021 ◽

Author(s):

Albert La Spada ◽

Mary Rose Branch ◽

Cynthia Hsu ◽

Kohta Ohnishi ◽

Elian Lee ◽

...

Keyword(s):

Amino Acid ◽

Signaling Pathway ◽

Nutrient Status ◽

Sirtuin 1 ◽

Regulatory Factor ◽

Ampk Pathway ◽

Regulatory Link ◽

Mtorc1 Activation ◽

Established Role ◽

Potent Effector

mTORC1 is the key rheostat controlling cellular metabolic state. Of the various inputs to mTORC1, the most potent effector of intracellular nutrient status is amino acid supply. Despite an established role for MAP4K3 in promoting mTORC1 activation in the presence of amino acids, the signaling pathway by which MAP4K3 controls mTORC1 activation remains unknown. Here we examined the process of MAP4K3 activation of mTORC1 and found that MAP4K3 represses the LKB1-AMPK pathway to prevent TSC1/2 complex inactivation of Rheb. When we sought the regulatory link between MAP4K3 and LKB1 inhibition, we discovered that MAP4K3 physically interacts with the master nutrient regulatory factor Sirtuin-1 and phosphorylates Sirtuin-1 to repress LKB1 activation. Our results reveal the existence of a novel signaling pathway linking amino acid satiety with MAP4K3-dependent suppression of SIRT1 to inactivate the repressive LKB1-AMPK pathway and thereby potently activate the mTORC1 complex to dictate the metabolic disposition of the cell.

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Insights into the Interaction of Lysosomal Amino Acid Transporters SLC38A9 and SLC36A1 Involved in mTORC1 Signaling in C2C12 Cells

Biomolecules ◽

10.3390/biom11091314 ◽

2021 ◽

Vol 11 (9) ◽

pp. 1314

Author(s):

Dan Wang ◽

Xuebin Wan ◽

Xiaoli Du ◽

Zhuxia Zhong ◽

Jian Peng ◽

...

Keyword(s):

Skeletal Muscle ◽

Amino Acid ◽

Skeletal Muscle Mass ◽

Mammalian Target Of Rapamycin ◽

C2c12 Cells ◽

Amino Acid Transporters ◽

Interacting Proteins ◽

Mtorc1 Signaling ◽

Amino Acid Sensing ◽

Mtorc1 Activation

Amino acids are critical for mammalian target of rapamycin complex 1 (mTORC1) activation on the lysosomal surface. Amino acid transporters SLC38A9 and SLC36A1 are the members of the lysosomal amino acid sensing machinery that activates mTORC1. The current study aims to clarify the interaction of SLC38A9 and SLC36A1. Here, we discovered that leucine increased expressions of SLC38A9 and SLC36A1, leading to mTORC1 activation. SLC38A9 interacted with SLC36A1 and they enhanced each other’s expression levels and locations on the lysosomal surface. Additionally, the interacting proteins of SLC38A9 in C2C12 cells were identified to participate in amino acid sensing mechanism, mTORC1 signaling pathway, and protein synthesis, which provided a resource for future investigations of skeletal muscle mass.

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WDR41 supports lysosomal response to changes in amino acid availability

Molecular Biology of the Cell ◽

10.1091/mbc.e17-12-0703 ◽

2018 ◽

Vol 29 (18) ◽

pp. 2213-2227 ◽

Cited By ~ 10

Author(s):

Joseph Amick ◽

Arun Kumar Tharkeshwar ◽

Catherine Amaya, ◽

Shawn M. Ferguson

Keyword(s):

Amino Acid ◽

Protein Complex ◽

Essential Role ◽

Interacting Protein ◽

Amino Acid Availability ◽

Autophagy Induction ◽

Mtorc1 Signaling ◽

Parallel Pattern ◽

Mtorc1 Activation ◽

Lateral Sclerosis

C9orf72 mutations are a major cause of amyotrophic lateral sclerosis and frontotemporal dementia. The C9orf72 protein undergoes regulated recruitment to lysosomes and has been broadly implicated in control of lysosome homeostasis. However, although evidence strongly supports an important function for C9orf72 at lysosomes, little is known about the lysosome recruitment mechanism. In this study, we identify an essential role for WDR41, a prominent C9orf72 interacting protein, in C9orf72 lysosome recruitment. Analysis of human WDR41 knockout cells revealed that WDR41 is required for localization of the protein complex containing C9orf72 and SMCR8 to lysosomes. Such lysosome localization increases in response to amino acid starvation but is not dependent on either mTORC1 inhibition or autophagy induction. Furthermore, WDR41 itself exhibits a parallel pattern of regulated association with lysosomes. This WDR41-dependent recruitment of C9orf72 to lysosomes is critical for the ability of lysosomes to support mTORC1 signaling as constitutive targeting of C9orf72 to lysosomes relieves the requirement for WDR41 in mTORC1 activation. Collectively, this study reveals an essential role for WDR41 in supporting the regulated binding of C9orf72 to lysosomes and solidifies the requirement for a larger C9orf72 containing protein complex in coordinating lysosomal responses to changes in amino acid availability.

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Rheb and Rags come together at the lysosome to activate mTORC1

Biochemical Society Transactions ◽

10.1042/bst20130037 ◽

2013 ◽

Vol 41 (4) ◽

pp. 951-955 ◽

Cited By ~ 48

Author(s):

Marlous J. Groenewoud ◽

Fried J.T. Zwartkruis

Keyword(s):

Amino Acids ◽

Growth Factors ◽

Amino Acid ◽

Cell Growth ◽

Mammalian Target Of Rapamycin ◽

Maturation Process ◽

Phospholipase D1 ◽

Strict Requirement ◽

Mtorc1 Activation ◽

Dependent Interaction

mTORC1 (mammalian target of rampamycin complex 1) is a highly conserved protein complex regulating cell growth and metabolism via its kinase mTOR (mammalian target of rapamycin). The activity of mTOR is under the control of various GTPases, of which Rheb and the Rags play a central role. The presence of amino acids is a strict requirement for mTORC1 activity. The heterodimeric Rag GTPases localize mTORC1 to lysosomes by their amino-acid-dependent interaction with the lysosomal Ragulator complex. Rheb is also thought to reside on lysosomes to activate mTORC1. Rheb is responsive to growth factors, but, in conjunction with PLD1 (phospholipase D1), is also an integral part of the machinery that stimulates mTORC1 in response to amino acids. In the present article, we provide a brief overview of novel mechanisms by which amino acids affect the function of Rags. On the basis of existing literature, we postulate that Rheb is activated at the Golgi from where it will travel to lysosomes. Maturation of endosomes into lysosomes may be required to assure a continuous supply of GTP-bound Rheb for mTORC1 activation, which may help to drive the maturation process.

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