scholarly journals GADD34 is a modulator of autophagy during starvation

2020 ◽  
Vol 6 (39) ◽  
pp. eabb0205 ◽  
Author(s):  
Gennaro Gambardella ◽  
Leopoldo Staiano ◽  
Maria Nicoletta Moretti ◽  
Rossella De Cegli ◽  
Luca Fagnocchi ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Program Implementation ◽  
Protein Phosphatase ◽  
Protein Translation ◽  
Protein Phosphatase 1 ◽  
Autophagic Flux ◽  
Protein Synthesis Inhibition ◽  
Transcriptional Program ◽  
Mtorc1 Signaling ◽  
Main Regulator

Cells respond to starvation by shutting down protein synthesis and by activating catabolic processes, including autophagy, to recycle nutrients. This two-pronged response is mediated by the integrated stress response (ISR) through phosphorylation of eIF2α, which represses protein translation, and by inhibition of mTORC1 signaling, which promotes autophagy also through a stress-responsive transcriptional program. Implementation of such a program, however, requires protein synthesis, thus conflicting with general repression of translation. How is this mismatch resolved? We found that the main regulator of the starvation-induced transcriptional program, TFEB, counteracts protein synthesis inhibition by directly activating expression of GADD34, a component of the protein phosphatase 1 complex that dephosphorylates eIF2α. We discovered that GADD34 plays an essential role in autophagy by tuning translation during starvation, thus enabling lysosomal biogenesis and a sustained autophagic flux. Hence, the TFEB-GADD34 axis integrates the mTORC1 and ISR pathways in response to starvation.

Leucine and mTORC1: a complex relationship

2012 ◽  
Vol 302 (11) ◽  
pp. E1329-E1342 ◽  
Author(s):  
Kayleigh M. Dodd ◽  
Andrew R. Tee
Keyword(s):  
Signal Transduction ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Protein Turnover ◽  
Muscle Growth ◽  
Protein Translation ◽  
Amino Acid Availability ◽  
Intracellular Amino Acid ◽  
System L ◽  
Mtorc1 Signaling

Amino acid availability is a rate-limiting factor in the regulation of protein synthesis. When amino acid supplies become restricted, mammalian cells employ homeostatic mechanisms to rapidly inhibit processes such as protein synthesis, which demands high levels of amino acids. Muscle cells in particular are subject to high protein turnover rates to maintain amino acid homeostasis. Mammalian target of rapamycin complex 1 (mTORC1) is an evolutionary conserved multiprotein complex that coordinates a network of signaling cascades and functions as a key mediator of protein translation, gene transcription, and autophagy. Signal transduction through mTORC1, which is centrally involved in muscle growth through enhanced protein translation, is governed by intracellular amino acid supply. The branched-chain amino acid leucine is critical for muscle growth and acts in part through activation of mTORC1. Recent research has revealed that mTORC1 signaling is coordinated primarily at the lysosomal membranes. This discovery has sparked a wealth of research in this field, revealing several different signaling molecules involved in transducing the amino acid signal to mTORC1, including the Rag GTPases, MAP4K3, and Vps34/ULK1. This review evaluates the current knowledge regarding cellular mechanisms that control and sense the intracellular amino acid pool. We discuss the role of leucine and mTORC1 in the regulation of amino acid transport via the system L and system A transporters such as LAT1 and SNAT2, as well as protein degradation via autophagic and proteasomal pathways. We also describe the complexities of energy homeostasis via AMPK and cell receptor-mediated growth signals that also converge on mTORC1. Leucine is a particularly potent regulator of protein turnover, to the extent where leucine stimulation alone is sufficient to stimulate mTORC1 signal transduction. The significance of leucine in this context is not yet known; however, recent advancements in this area will also be covered within this review.

scholarly journals Cytoskeletal vimentin regulates cell size and autophagy through mTORC1 signaling

2021 ◽  
Author(s):  
John Elias Eriksson ◽  
Ponnuswamy Mohanasundaram ◽  
Leila S Coelho-Rato ◽  
Mayank Modi ◽  
Marta Urbanska ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Cell Size ◽  
Cancer Progression ◽  
Ribosome Biogenesis ◽  
Mrna Translation ◽  
Autophagic Flux ◽  
Intermediate Filament Protein ◽  
Downstream Target ◽  
Mtorc1 Signaling ◽  
Filament Protein

The nutrient-activated mTORC1 (mechanistic target of rapamycin kinase complex 1) signaling pathway determines cell size by controlling mRNA translation, ribosome biogenesis, protein synthesis, and autophagy. Here we show that vimentin, a cytoskeletal intermediate filament protein that we know to be important for wound healing and cancer progression, determines cell size through mTORC1 signaling, an effect that is also manifested at the organism level in mice. We found that vimentin maintains normal cell size by supporting mTORC1 activation and through inhibition of autophagic flux. This regulation is manifested at all levels of downstream target activation and regulation of protein synthesis. We show that vimentin controls mTORC1 mobility by allowing access to lysosomes. Vimentin inhibits the autophagic flux in normal fibroblasts even under starved conditions, indicating a growth factor-independent inhibition of autophagy at the level of mTORC1. Our findings demonstrate that vimentin couples cell size signaling and autophagy with the biomechanics, sensing, and kinetic functions of the cytoskeleton.

scholarly journals mTORC1 signaling is not essential for the maintenance of muscle mass and function in adult sedentary mice

2019 ◽  
Author(s):  
Alexander S. Ham ◽  
Kathrin Chojnowska ◽  
Lionel A. Tintignac ◽  
Shuo Lin ◽  
Alexander Schmidt ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Muscle Mass ◽  
Ex Vivo ◽  
Morphological Changes ◽  
Muscle Fibers ◽  
Protein Translation ◽  
Muscle Size ◽  
Mtorc1 Signaling ◽  
And Function

AbstractBackgroundThe balance between protein synthesis and degradation (proteostasis) is a determining factor for muscle size and function. Signaling via the mammalian target of rapamycin complex 1 (mTORC1) regulates proteostasis in skeletal muscle by affecting protein synthesis and autophagosomal protein degradation. Indeed, genetic inactivation of mTORC1 in developing and growing muscle causes atrophy resulting in a lethal myopathy. However, systemic dampening of mTORC1 signaling by its allosteric inhibitor rapamycin is beneficial at the organismal level and increases lifespan. Whether the beneficial effect of rapamycin comes at the expense of muscle mass and function is yet to be established.MethodsWe conditionally ablated the gene coding for the mTORC1-essential component raptor in muscle fibers of adult mice (iRAmKO). We performed detailed phenotypic and biochemical analyses of iRAmKO mice and compared them with RAmKO mice, which lack raptor in developing muscle fibers. We also used polysome profiling and proteomics to assess protein translation and associated signaling in skeletal muscle of iRAmKO mice.ResultsAnalysis at different time points reveal that, as in RAmKO mice, the proportion of oxidative fibers decreases, but slow-type fibers increase in iRAmKO mice. Nevertheless, no significant decrease in body and muscle mass, or muscle fiber area was detected up to 5 months post-raptor depletion. Similarly, ex vivo muscle force was not significantly reduced in iRAmKO mice. Despite stable muscle size and function, inducible raptor depletion significantly reduced the expression of key components of the translation machinery and overall translation rates.ConclusionsRaptor depletion and hence complete inhibition of mTORC1 signaling in fully-grown muscle leads to metabolic and morphological changes without inducing muscle atrophy even after 5 months. Together, our data indicate that maintenance of muscle size does not require mTORC1 signaling, suggesting that rapamycin treatment is unlikely to negatively affect muscle mass and function.

scholarly journals Autophagy is essential to support skeletal muscle plasticity in response to endurance exercise

2014 ◽  
Vol 307 (8) ◽  
pp. R956-R969 ◽  
Author(s):  
Anthony M. J. Sanchez ◽  
Henri Bernardi ◽  
Guillaume Py ◽  
Robin B. Candau
Keyword(s):  
Skeletal Muscle ◽  
Nutritional Status ◽  
Endurance Exercise ◽  
Muscle Protein ◽  
Protein Translation ◽  
Autophagic Flux ◽  
Muscle Plasticity ◽  
Mtorc1 Signaling ◽  
Ubiquitin Proteasome ◽  
The Impact

Physical exercise is a stress that can substantially modulate cellular signaling mechanisms to promote morphological and metabolic adaptations. Skeletal muscle protein and organelle turnover is dependent on two major cellular pathways: Forkhead box class O proteins (FOXO) transcription factors that regulate two main proteolytic systems, the ubiquitin-proteasome, and the autophagy-lysosome systems, including mitochondrial autophagy, and the MTORC1 signaling associated with protein translation and autophagy inhibition. In recent years, it has been well documented that both acute and chronic endurance exercise can affect the autophagy pathway. Importantly, substantial efforts have been made to better understand discrepancies in the literature on its modulation during exercise. A single bout of endurance exercise increases autophagic flux when the duration is long enough, and this response is dependent on nutritional status, since autophagic flux markers and mRNA coding for actors involved in mitophagy are more abundant in the fasted state. In contrast, strength and resistance exercises preferentially raise ubiquitin-proteasome system activity and involve several protein synthesis factors, such as the recently characterized DAGK for mechanistic target of rapamycin activation. In this review, we discuss recent progress on the impact of acute and chronic exercise on cell component turnover systems, with particular focus on autophagy, which until now has been relatively overlooked in skeletal muscle. We especially highlight the most recent studies on the factors that can impact its modulation, including the mode of exercise and the nutritional status, and also discuss the current limitations in the literature to encourage further works on this topic.

scholarly journals Active ERK Contributes to Protein Translation by Preventing JNK-Dependent Inhibition of Protein Phosphatase 1

2006 ◽  
Vol 177 (3) ◽  
pp. 1636-1645 ◽  
Author(s):  
Martha M. Monick ◽  
Linda S. Powers ◽  
Thomas J. Gross ◽  
Dawn M. Flaherty ◽  
Christopher W. Barrett ◽  
...  
Keyword(s):  
Protein Phosphatase ◽  
Protein Translation ◽  
Protein Phosphatase 1 ◽  
Dependent Inhibition

scholarly journals Protein Phosphatase 1 Regulates Human Cytomegalovirus Protein Translation by Restraining AMPK Signaling

2021 ◽  
Vol 12 ◽  
Author(s):  
Carmen Stecher ◽  
Sanja Marinkov ◽  
Lucia Mayr-Harting ◽  
Ana Katic ◽  
Marie-Theres Kastner ◽  
...  
Keyword(s):  
Human Cytomegalovirus ◽  
Protein Phosphatase ◽  
Catalytic Domain ◽  
Human Fibroblasts ◽  
Elongation Factor ◽  
Early Time ◽  
Protein Translation ◽  
Protein Phosphatase 1 ◽  
Ampk Signaling ◽  
Protein Protein Interaction

Human cytomegalovirus (HCMV) carries the human protein phosphatase 1 (PP1) and other human proteins important for protein translation in its tegument layer for a rapid supply upon infection. However, the biological relevance behind PP1 incorporation and its role during infection is unclear. Additionally, PP1 is a difficult molecular target due to its promiscuity and similarities between the catalytic domain of multiple phosphatases. In this study, we circumvented these shortcomings by using 1E7-03, a small molecule protein–protein interaction inhibitor, as a molecular tool of noncatalytic PP1 inhibition. 1E7-03 treatment of human fibroblasts severely impaired HCMV replication and viral protein translation. More specifically, PP1 inhibition led to the deregulation of metabolic signaling pathways starting at very early time points post-infection. This effect was at least partly mediated by the prevention of AMP-activated protein kinase dephosphorylation, leading to elongation factor 2 hyperphosphorylation and reduced translation rates. These findings reveal an important mechanism of PP1 for lytic HCMV infection.

scholarly journals Negative regulation of autophagy by UBA6-BIRC6–mediated ubiquitination of LC3

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Rui Jia ◽  
Juan S Bonifacino
Keyword(s):  
Protein Synthesis ◽  
Ubiquitin Ligase ◽  
Neurodegenerative Disorders ◽  
Hippocampal Neurons ◽  
Negative Regulation ◽  
Nutrient Deprivation ◽  
Autophagic Flux ◽  
Whole Genome ◽  
Protein Synthesis Inhibition ◽  
Ubiquitin Conjugating Enzyme

Although the process of autophagy has been extensively studied, the mechanisms that regulate it remain insufficiently understood. To identify novel autophagy regulators, we performed a whole-genome CRISPR/Cas9 knockout screen in H4 human neuroglioma cells expressing endogenous LC3B tagged with a tandem of GFP and mCherry. Using this methodology, we identified the ubiquitin-activating enzyme UBA6 and the hybrid ubiquitin-conjugating enzyme/ubiquitin ligase BIRC6 as autophagy regulators. We found that these enzymes cooperate to monoubiquitinate LC3B, targeting it for proteasomal degradation. Knockout of UBA6 or BIRC6 increased autophagic flux under conditions of nutrient deprivation or protein synthesis inhibition. Moreover, UBA6 or BIRC6 depletion decreased the formation of aggresome-like induced structures in H4 cells, and α-synuclein aggregates in rat hippocampal neurons. These findings demonstrate that UBA6 and BIRC6 negatively regulate autophagy by limiting the availability of LC3B. Inhibition of UBA6/BIRC6 could be used to enhance autophagic clearance of protein aggregates in neurodegenerative disorders.

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