scholarly journals Autoregulation of the Mechanistic Target of Rapamycin (mTOR) Complex 2 Integrity Is Controlled by an ATP-dependent Mechanism

2013 ◽  
Vol 288 (38) ◽  
pp. 27019-27030 ◽  
Author(s):  
Chien-Hung Chen ◽  
Vladimir Kiyan ◽  
Assylbek A. Zhylkibayev ◽  
Dubek Kazyken ◽  
Olga Bulgakova ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Kinase Activity ◽  
Glucose Deprivation ◽  
Nutrient Sensing ◽  
Atp Depletion ◽  
Target Of Rapamycin ◽  
Central Component ◽  
Mechanistic Target Of Rapamycin ◽  
Living Organisms ◽  
In Cells

Nutrients are essential for living organisms because they fuel biological processes in cells. Cells monitor nutrient abundance and coordinate a ratio of anabolic and catabolic reactions. Mechanistic target of rapamycin (mTOR) signaling is the essential nutrient-sensing pathway that controls anabolic processes in cells. The central component of this pathway is mTOR, a highly conserved and essential protein kinase that exists in two distinct functional complexes. The nutrient-sensitive mTOR complex 1 (mTORC1) controls cell growth and cell size by phosphorylation of the regulators of protein synthesis S6K1 and 4EBP1, whereas its second complex, mTORC2, regulates cell proliferation by functioning as the regulatory kinase of Akt and other members of the AGC kinase family. The regulation of mTORC2 remains poorly characterized. Our study shows that the cellular ATP balance controls a basal kinase activity of mTORC2 that maintains the integrity of mTORC2 and phosphorylation of Akt on the turn motif Thr-450 site. We found that mTOR stabilizes SIN1 by phosphorylation of its hydrophobic and conserved Ser-260 site to maintain the integrity of mTORC2. The optimal kinase activity of mTORC2 requires a concentration of ATP above 1.2 mm and makes this kinase complex highly sensitive to ATP depletion. We found that not amino acid but glucose deprivation of cells or acute ATP depletion prevented the mTOR-dependent phosphorylation of SIN1 on Ser-260 and Akt on Thr-450. In a low glucose medium, the cells carrying a substitution of SIN1 with its phosphomimetic mutant show an increased rate of cell proliferation related to a higher abundance of mTORC2 and phosphorylation of Akt. Thus, the homeostatic ATP sensor mTOR controls the integrity of mTORC2 and phosphorylation of Akt on the turn motif site.

scholarly journals Regulation of protein kinase Cδ Nuclear Import and Apoptosis by Mechanistic Target of Rapamycin Complex-1

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Antonio Layoun ◽  
Alexander A. Goldberg ◽  
Ayesha Baig ◽  
Mikaela Eng ◽  
Ortal Attias ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Nuclear Import ◽  
Target Of Rapamycin ◽  
Interferon Β ◽  
Structural Mechanism ◽  
Mechanistic Target Of Rapamycin ◽  
Kinase C ◽  
Nuclear Content ◽  
In Cells

AbstractInactivation of the protein complex ‘mechanistic target of rapamycin complex 1’ (mTORC1) can increase the nuclear content of transcriptional regulators of metabolism and apoptosis. Previous studies established that nuclear import of signal transducer and activator of transcription-1 (STAT1) requires the mTORC1-associated adaptor karyopherin-α1 (KPNA1) when mTORC1 activity is reduced. However, the role of other mTORC1-interacting proteins in the complex, including ‘protein kinase C delta’ (PKCδ), have not been well characterized. In this study, we demonstrate that PKCδ, a STAT1 kinase, contains a functional ‘target of rapamycin signaling’ (TOS) motif that directs its interaction with mTORC1. Depletion of KPNA1 by RNAi prevented the nuclear import of PKCδ in cells exposed to the mTORC1 inhibitor rapamycin or amino acid restriction. Mutation of the TOS motif in PKCδ led to its loss of regulation by mTORC1 or karyopherin-α1, resulting in increased constitutive nuclear content. In cells expressing wild-type PKCδ, STAT1 activity and apoptosis were increased by rapamycin or interferon-β. Those expressing the PKCδ TOS mutant exhibited increased STAT1 activity and apoptosis; further enhancement by rapamycin or interferon-β, however, was lost. Therefore, the TOS motif in PKCδ is a novel structural mechanism by which mTORC1 prevents PKCδ and STAT1 nuclear import, and apoptosis.

scholarly journals Conformational sampling of membranes by Akt controls its activation and inactivation

2018 ◽  
Vol 115 (17) ◽  
pp. E3940-E3949 ◽  
Author(s):  
Iva Lučić ◽  
Manoj K. Rathinaswamy ◽  
Linda Truebestein ◽  
David J. Hamelin ◽  
John E. Burke ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Conformational Changes ◽  
Membrane Binding ◽  
Second Messenger ◽  
Target Of Rapamycin ◽  
Conformational Sampling ◽  
Mechanistic Target Of Rapamycin ◽  
Protein Kinase Akt ◽  
In Cells ◽  
Phosphoinositide Dependent Kinase

The protein kinase Akt controls myriad signaling processes in cells, ranging from growth and proliferation to differentiation and metabolism. Akt is activated by a combination of binding to the lipid second messenger PI(3,4,5)P3 and its subsequent phosphorylation by phosphoinositide-dependent kinase 1 and mechanistic target of rapamycin complex 2. The relative contributions of these mechanisms to Akt activity and signaling have hitherto not been understood. Here, we show that phosphorylation and activation by membrane binding are mutually interdependent. Moreover, the converse is also true: Akt is more rapidly dephosphorylated in the absence of PIP3, an autoinhibitory process driven by the interaction of its PH and kinase domains. We present biophysical evidence for the conformational changes in Akt that accompany its activation on membranes, show that Akt is robustly autoinhibited in the absence of PIP3 irrespective of its phosphorylation, and map the autoinhibitory PH−kinase interface. Finally, we present a model for the activation and inactivation of Akt by an ordered series of membrane binding, phosphorylation, dissociation, and dephosphorylation events.

scholarly journals Mechanistic Target of Rapamycin Inhibitors in Renal Cell Carcinoma: Potential, Limitations, and Perspectives

2021 ◽  
Vol 9 ◽  
Author(s):  
Seraina Faes ◽  
Nicolas Demartines ◽  
Olivier Dormond
Keyword(s):  
Renal Cell Carcinoma ◽  
Cell Proliferation ◽  
Cell Carcinoma ◽  
Renal Cell ◽  
Mtor Inhibitors ◽  
Target Of Rapamycin ◽  
Cancer Cell Proliferation ◽  
Hypoxia Inducible Factors ◽  
Mtor Signaling Pathway ◽  
Mechanistic Target Of Rapamycin

Several elements highlight the importance of the mechanistic target of rapamycin (mTOR) in the biology of renal cell carcinoma (RCC). mTOR signaling pathway is indeed frequently activated in RCC, inducing cancer cell proliferation and survival. In addition, mTOR promotes tumor angiogenesis and regulates the expression of hypoxia-inducible factors that play an important role in a subset of RCC. Despite mTOR protumorigenic effects, mTOR inhibitors have failed to provide long-lasting anticancer benefits in RCC patients, highlighting the need to readdress their role in the treatment of RCC. This review aims to present the rationale and limitations of targeting mTOR in RCC. Future roles of mTOR inhibitors in the treatment of RCC are also discussed, in particular in the context of immunotherapies.

scholarly journals PIP30/FAM192A is a novel regulator of the nuclear proteasome activator PA28γ

2017 ◽  
Author(s):  
Beata Jonik-Nowak ◽  
Thomas Menneteau ◽  
Didier Fesquet ◽  
Véronique Baldin ◽  
Catherine Bonne-Andrea ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Cellular Stress Response ◽  
Cajal Body ◽  
Cajal Bodies ◽  
Central Component ◽  
20S Proteasome ◽  
Independent Manner ◽  
Nuclear Dynamics ◽  
Multiple Functions ◽  
In Cells

ABSTRACTPA28γ is a nuclear activator of the 20S proteasome involved in the regulation of several essential cellular processes, such as cell proliferation, apoptosis, nuclear dynamics and cellular stress response. Unlike the 19S regulator of the proteasome, which specifically recognizes ubiquitylated proteins, PA28γ promotes the degradation of several substrates by the proteasome in an ATP- and ubiquitin-independent manner. However its exact mechanisms of action are unclear and likely to involve additional partners that remain to be identified. Here we report the identification of the first cofactor of PA28γ, PIP30/FAM192A. PIP30 binds directly and specifically via its C-terminal end and in an interaction stabilized by casein kinase 2 phosphorylation to both free and 20S proteasome-associated PA28γ. Its recruitment to proteasome-containing complexes depends on PA28γ and its expression increases the association of PA28γ with the 20S proteasome in cells. Further dissection of its possible roles shows that PIP30 alters PA28γ-dependent activation of peptide degradation by the 20S proteasome in vitro and negatively controls in cells the presence of PA28γ in Cajal Bodies by inhibition of its association with the key Cajal body component coilin. Altogether, our data show that PIP30 deeply affects PA28γ interactions with cellular proteins, including 20S proteasome, demonstrating that it is an important regulator of PA28γ in cells and thus a new player in the control of the multiple functions of the proteasome within the nucleus.Significance StatementThe 20S proteasome is a key actor of the control of protein levels and integrity in cells. To perform its multiple functions, it works with a series of regulators, among which a nuclear complex called PA28γ. In particular, PA28γ participates in the regulation of cell proliferation and nuclear dynamics. We describe here the characterization of a novel protein, PIP30/FAM192A, which binds tightly to PA28γ and favors its interaction with the 20S proteasome while inhibiting its association with coilin, a central component of nuclear Cajal bodies. Thus PIP30/FAM192A critically controls the interactome and consequently the functions of PA28γ, and appears to be a new player in the fine regulation of intracellular proteostasis in the cell nucleus.

scholarly journals Mechanistic target of rapamycin signaling in mouse models of accelerated aging

2019 ◽  
Vol 75 (1) ◽  
pp. 64-72 ◽  
Author(s):  
Jin Young Lee ◽  
Brian K Kennedy ◽  
Chen-Yu Liao
Keyword(s):  
Mouse Models ◽  
Accelerated Aging ◽  
Nutrient Sensing ◽  
Mtor Signaling ◽  
Human Diseases ◽  
Target Of Rapamycin ◽  
Cellular Processes ◽  
Positive Effects ◽  
Mechanistic Target Of Rapamycin ◽  
Age Related

Abstract The mechanistic target of rapamycin (mTOR) is an essential nutrient-sensing kinase that integrates and regulates a number of fundamental cellular processes required for cell growth, cell motility, translation, metabolism, and autophagy. mTOR signaling has been implicated in the progression of many human diseases, and its dysregulation has been reported in several pathological processes, especially in age-related human diseases and mouse models of accelerated aging. In addition, many studies have demonstrated that the regulation of mTOR activity has a beneficial effect on longevity in several mouse models of aging. However, not all mouse models of accelerated aging show positive effects on aging-associated phenotypes in response to targeting mTOR signaling. Here, we review the effects of interventions that modulate mTOR signaling on aging-related phenotypes in different mouse models of accelerated aging and discuss their implications with respect to aging and aging-related disorders.

scholarly journals Differential regulation of mTORC1 activation by leucine and β-hydroxy-β-methylbutyrate in skeletal muscle of neonatal pigs

2020 ◽  
Vol 128 (2) ◽  
pp. 286-295 ◽  
Author(s):  
Agus Suryawan ◽  
Marko Rudar ◽  
Marta L. Fiorotto ◽  
Teresa A. Davis
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Nutrient Sensing ◽  
Target Of Rapamycin ◽  
Neonatal Pigs ◽  
Mechanistic Target Of Rapamycin ◽  
Mtor Phosphorylation ◽  
Dependent Protein ◽  
Mtorc1 Activation ◽  
Mtor Complex 1

Leucine (Leu) and its metabolite β-hydroxy-β-methylbutyrate (HMB) stimulate mechanistic target of rapamycin (mTOR) complex 1 (mTORC1)-dependent protein synthesis in the skeletal muscle of neonatal pigs. This study aimed to determine whether HMB and Leu utilize common nutrient-sensing mechanisms to activate mTORC1. In study 1, neonatal pigs were fed one of five diets for 24 h: low protein (LP), high protein (HP), or LP supplemented with 4 (LP+HMB4), 40 (LP+HMB40), or 80 (LP+HMB80) μmol HMB·kg body wt−1·day−1. In study 2, neonatal pigs were fed for 24 h: LP, LP supplemented with Leu (LP+Leu), or HP diets delivering 9, 18, and 18 mmol Leu·kg body wt−1·day−1, respectively. The upstream signaling molecules that regulate mTORC1 activity were analyzed. mTOR phosphorylation on Ser2448 and Ser2481 was greater in LP+HMB40, LP+HMB80, and LP+Leu than in LP and greater in HP than in HMB-supplemented groups ( P < 0.05), whereas HP and LP+Leu were similar. Rheb-mTOR complex formation was lower in LP than in HP ( P < 0.05), with no enhancement by HMB or Leu supplementation. The Sestrin2-GATOR2 complex was more abundant in LP than in HP and was reduced by Leu ( P < 0.05) but not HMB supplementation. RagA-mTOR and RagC-mTOR complexes were higher in LP+Leu and HP than in LP and HMB groups ( P < 0.05). There were no treatment differences in RagB-SH3BP4, Vps34-LRS, and RagD-LRS complex abundances. Phosphorylation of Erk1/2 and TSC2, but not AMPK, was lower in LP than HP ( P < 0.05) and unaffected by HMB or Leu supplementation. Our results demonstrate that HMB stimulates mTORC1 activation in neonatal muscle independent of the leucine-sensing pathway mediated by Sestrin2 and the Rag proteins. NEW & NOTEWORTHY Dietary supplementation with either leucine or its metabolite β-hydroxy-β-methylbutyrate (HMB) stimulates protein synthesis in skeletal muscle of the neonatal pig. Our results demonstrate that both leucine and HMB stimulate mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) phosphorylation in neonatal muscle. This leucine-stimulated process involves dissociation of the Sestrin2-GATOR2 complex and increased binding of Rag A/C to mTOR. However, HMB’s activation of mTORC1 is independent of this leucine-sensing pathway.

scholarly journals eIF4GI links nutrient sensing by mTOR to cell proliferation and inhibition of autophagy

2008 ◽  
Vol 181 (2) ◽  
pp. 293-307 ◽  
Author(s):  
Francisco Ramírez-Valle ◽  
Steve Braunstein ◽  
Jiri Zavadil ◽  
Silvia C. Formenti ◽  
Robert J. Schneider
Keyword(s):  
Cell Proliferation ◽  
Nutrient Sensing ◽  
Open Reading Frames ◽  
Initiation Factor ◽  
Mitochondrial Activity ◽  
Breast Cancers ◽  
Initiation Factors ◽  
Translation Initiation Factors ◽  
Upstream Open Reading Frames ◽  
In Cells

Translation initiation factors have complex functions in cells that are not yet understood. We show that depletion of initiation factor eIF4GI only modestly reduces overall protein synthesis in cells, but phenocopies nutrient starvation or inhibition of protein kinase mTOR, a key nutrient sensor. eIF4GI depletion impairs cell proliferation, bioenergetics, and mitochondrial activity, thereby promoting autophagy. Translation of mRNAs involved in cell growth, proliferation, and bioenergetics were selectively inhibited by reduction of eIF4GI, as was the mRNA encoding Skp2 that inhibits p27, whereas catabolic pathway factors were increased. Depletion or overexpression of other eIF4G family members did not recapitulate these results. The majority of mRNAs that were translationally impaired with eIF4GI depletion were excluded from polyribosomes due to the presence of multiple upstream open reading frames and low mRNA abundance. These results suggest that the high levels of eIF4GI observed in many breast cancers might act to specifically increase proliferation, prevent autophagy, and release tumor cells from control by nutrient sensing.

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