scholarly journals Src regulates amino acid-mediated mTORC1 activation by disrupting GATOR1-Rag GTPase interaction

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Rituraj Pal ◽  
Michela Palmieri ◽  
Arindam Chaudhury ◽  
Tiemo Jürgen Klisch ◽  
Alberto di Ronza ◽  
...  
2020 ◽  
Author(s):  
Ada Nowosad ◽  
Pauline Jeannot ◽  
Caroline Callot ◽  
Justine Creff ◽  
Renaud T. Perchey ◽  
...  

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.


Author(s):  
Jiefu Wang ◽  
Martin Krueger ◽  
Stefanie M. Hauck ◽  
Siegfried Ussar

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.


2019 ◽  
Vol 76 (1) ◽  
pp. 163-176.e8 ◽  
Author(s):  
Florian Beaumatin ◽  
Jim O’Prey ◽  
Valentin J.A. Barthet ◽  
Barbara Zunino ◽  
Jean-Philippe Parvy ◽  
...  

2019 ◽  
Vol 150 (5) ◽  
pp. 1022-1030 ◽  
Author(s):  
Dandan Xu ◽  
Weiwei Dai ◽  
Lydia Kutzler ◽  
Holly A Lacko ◽  
Leonard S Jefferson ◽  
...  

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.


2018 ◽  
Vol 115 (23) ◽  
pp. E5279-E5288 ◽  
Author(s):  
Minji Lee ◽  
Jong Hyun Kim ◽  
Ina Yoon ◽  
Chulho Lee ◽  
Mohammad Fallahi Sichani ◽  
...  

A protein synthesis enzyme, leucyl-tRNA synthetase (LRS), serves as a leucine sensor for the mechanistic target of rapamycin complex 1 (mTORC1), which is a central effector for protein synthesis, metabolism, autophagy, and cell growth. However, its significance in mTORC1 signaling and cancer growth and its functional relationship with other suggested leucine signal mediators are not well-understood. Here we show the kinetics of the Rag GTPase cycle during leucine signaling and that LRS serves as an initiating “ON” switch via GTP hydrolysis of RagD that drives the entire Rag GTPase cycle, whereas Sestrin2 functions as an “OFF” switch by controlling GTP hydrolysis of RagB in the Rag GTPase–mTORC1 axis. The LRS–RagD axis showed a positive correlation with mTORC1 activity in cancer tissues and cells. The GTP–GDP cycle of the RagD–RagB pair, rather than the RagC–RagA pair, is critical for leucine-induced mTORC1 activation. The active RagD–RagB pair can overcome the absence of the RagC–RagA pair, but the opposite is not the case. This work suggests that the GTPase cycle of RagD–RagB coordinated by LRS and Sestrin2 is critical for controlling mTORC1 activation, and thus will extend the current understanding of the amino acid-sensing mechanism.


2018 ◽  
Vol 23 (6) ◽  
pp. 418-434 ◽  
Author(s):  
Yutaka Hashimoto ◽  
Michiko Shirane ◽  
Keiichi I. Nakayama
Keyword(s):  

2021 ◽  
Author(s):  
Albert La Spada ◽  
Mary Rose Branch ◽  
Cynthia Hsu ◽  
Kohta Ohnishi ◽  
Elian Lee ◽  
...  

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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