IndraLab
Statements
sparser
"The lead compound they developed is a dimeric quinacrine (DQ661), which is derived from Lys05, has improved lysosomal targeting capability and impairs the activity of palmitoyl-protein thioesterase (PPT1), which is required for mTOR interaction with Rheb at the lysosome [ xref ]; inhibition of PPT1 also prevents mTORC1 from associating with the lysosomal membrane, causing mTOR inhibition [ xref ]."
sparser
"For example, the TSC1/TSC2 complex inhibits mTOR functions by inactivating Rheb; Rheb binds and activates mTOR only when the former is in its GTP-bound form. xref The phosphoinositide-3-kinase (PI3K)-Akt pathway activates mTOR by Akt-mediated phosphorylation of TSC2, followed by disassembly and inhibition of the TSC1/TSC2 complex. xref , xref The extracellular signal-related kinase (ERK) stimulates mTOR activation by either directly phosphorylating TSC2 or by inducing TSC2 phosphorylation via its two downstream effectors, ribosomal S6 kinase (RSK) and DAPK. xref – xref Finally, AMP-activated protein kinase (AMPK) phosphorylates TSC2 and stabilizes the TSC1/TSC2 complex, thereby inhibiting Rheb-mediated activation of mTOR. xref AMPK can also regulate mTOR function in a TSC-independent manner by directly phosphorylating Raptor, an essential component of mTORC1, to inhibit mTOR activity. xref Notably, TSC1 and 2, PI3K, and Akt are all subject to mutation in human tumors."
reach
"In addition to the interactions between Rheb, Rag GTPases, and mTOR, several protein complexes have been found to act upstream of Rheb and Rag GTPases to control their nucleotide loading status : either by promoting the hydrolysis of GTP and increasing the ratio of GDP/GTP by working as the GAP, or by stimulating the exchange between GDP and GTP by working as the GEF."
sparser
"However, Rag interaction with mTORC1 does not directly activate the mTOR kinase; rather Rag proteins modulate cellular translocation of mTORC1 to the lysosome that facilitates an mTOR and RHEB interaction, which in the presence of elevated AA concentrations, results in RHEB-induced activation of mTORC1."
sparser
"Although it has been proposed that the GTP-bound, active from of RHEB physically binds to mTORC1 and enhances its kinase activity [ xref ], the detailed molecular mechanism of mTORC1 activation by RHEB has been elusive until recently; the cryo-electron microscopy (cryo-EM) structure of the mTORC1-RHEB complex has revealed that RHEB directly binds to mTOR distantly from the kinase catalytic site and causes a conformational change that allosterically realigns the catalytic site, thereby enhancing mTORC1 activity [ xref , xref ]."
sparser
"In view of the fact that the human experimental studies by xref and xref have observed consistent results, there seems to be reason to believe that both aerobic exercise and resistance exercise can downregulate the expression of TSC2, promote the dissociation of TSC2-Rheb, and enhance the lysosomal co-localization of mTOR-Rheb, which subsequently inhibits the conversion of Rheb to inactive state loaded with GDP and promotes the activation of mTORC1."
sparser
"Rheb-GTP binds to mTOR complex 1 (mTORC1) to activate its kinase
activity toward the S6Ks, 4E-BP1, and other substrates, leading to enhancement of
multiple anabolic biosynthetic pathways that enable production of the building
blocks (e.g. nucleotides) and macromolecules (e.g. ribosomes) required for cell size
increase and mitosis ( xref )."
sparser
"Sancak and coworkers had previously suggested that Rheb localizes to late endosomes, and that amino acid-stimulated mTORC1 translocation facilitates mTOR-Rheb interactions. xref We find that in TSC2 −/− cells overexpressing Rab5CA, endogenous Rheb is hyperactivated but still cannot activate mTORC1."
sparser
"We observed that Rheb is associated with LEs in hippocampal neurons and recent structural studies suggest a central position of activated Rheb in the complex associating Rag and mTORC1 to the lysosome surface [24, 31, 32] and show that Rheb binds to mTOR at a site remote from its kinase active site resulting in a conformational change that favors mTOR activity [26] ."
reach
"Using the sensitive advanced imaging technique of time correlated single photon counting coupled with fluorescence lifetime imaging and molecular GFP fusion technology, it was possible for the first time to probe directly the nature of the interaction between Rheb, mTOR and raptor as well as raptor and mTOR whilst providing new insights into their sub-cellular localization."
sparser
"The gene products of TSC1 (called hamartin) and TSC2 (called tuberin) assemble the TSC1/2 complex, which physiologically suppresses mTOR by inhibiting Rheb, an essential activator of the mTORC. xref Patients with TSC present with epilepsy early in life and have the characteristic presence of “tubers,” tumorlike focal lesions all over the body including in brains. xref Children with TSC can present with sleep abnormalities such as increased incidences of night waking, parasomnias, severe difficult waking up early in the morning, and daytime sleepiness. xref These abnormalities were not significantly different between epileptic and nonepileptic subgroups, representing inherent sleep and circadian disruptions in TSC patients. xref In a polysomnography study on children with TSC, sleep architecture was found to be severely disrupted, with sleep fragmentation, a shorter total sleep time, reduced sleep efficiency, and decreased rapid eye movement sleep. xref Interestingly, in this study, nocturnal seizures were recorded in some patients and associated with a more severe sleep fragmentation. xref In an adult cohort of TSC patients, similar sleep abnormalities were found, namely insomnia and excessive daytime sleepiness, which, unlike in the pediatric group, was positively correlated with their seizure history and antiseizure drug use. xref To illustrate the scale of sleep abnormalities in TSC, a large natural history study of more than 2000 patients with TSC reported sleep abnormalities as the second most reported behavioral problem in about 40% of the patients. xref Thus, it is clear that patients with TSC present with chronic sleep abnormalities, regardless of their seizure history, which indicates an intrinsic circadian dysfunction."
reach
"Intracellularly, schweinfurthins and their analogs arrested trans-Golgi-network trafficking, likely by binding to oxysterol-binding proteins, leading to an effective inhibition of mTOR/AKT signaling through inducing endoplasmic reticulum stress and suppressing both lipid raft-mediated PI3K activation and mTOR/RheB complex formation."
sparser
"We found that TET can enhance the interaction of SQSTM1 with MAP1LC3-II and ubiquitinated proteins due to NRF2-mediated SQSTM1 transcription and Rheb-mTOR signaling activation, thus dramatically inducing SQSTM1-selective autophagy and directly leading to Col-I degradation in lysosome ( xref )."
sparser
"In response to amino acids, Raptor interacts with the lysosomal Ras-related guanosine 5’-triphosphate (GTP)-binding protein (Rag small GTPase protein complex tethering mTORC1 to the lysosomal membrane, where it encounters another small GTPase, Ras homolog enriched in brain (Rheb) that directly interacts with the mTOR kinase and stimulates the activity of mTORC1 [ xref , xref ]."
sparser
"It can be argued that the very weak affinity of Rheb for MTOR results in a loss of the Rheb-MTOR interaction upon cell extraction; however, this returns to the question of how the Rheb activation mechanism demonstrated by Yang et al . xref relates to the mechanism operative in the cell and whether a continuing association of Rheb with MTOR is required for the maintenance of MTORC1 activity in the cell."
reach
"However, Rag interaction with mTORC1 does not directly activate the mTOR kinase; rather Rag proteins modulate cellular translocation of mTORC1 to the lysosome that facilitates an mTOR and RHEB interaction, which in the presence of elevated AA concentrations, results in RHEB induced activation of mTORC1."
sparser
"Previous studies demonstrated that the interaction between Rheb and mTOR was independent of Rheb’s GTP/GDP-loading status in vivo ( xref ; xref ), and the GDP-bound Rheb D60I mutant displayed a higher binding affinity to mTOR compared to wild-type or GTP-bound Rheb mutants in vivo ."
sparser
"Consequently, we demonstrated that RHEB binds to the whole mTOR both in the presence or absence of GTPγS, with five-fold weaker affinity in the presence of GTPγS. In addition, RHEB bound to the truncated mTOR fragments of N-heat domain (∆N, aa 60-167) or M-heat domain (∆M, aa 967-1023) with the same affinity in the absence of GTP."
reach
"We observed that Rheb is associated with LEs in hippocampal neurons and recent structural studies suggest a central position of activated Rheb in the complex associating Rag and mTORC1 to the lysosome surface [24, 31, 32] and show that Rheb binds to mTOR at a site remote from its kinase active site resulting in a conformational change that favors mTOR activity [26]."
sparser
"The site of Rheb-MTOR interaction identified by cryo-EM, accompanied by extensive biochemical verification of Rheb-GTP activation of MTORC1, invalidates the earlier conclusion that Rheb binds to the MTOR catalytic domain, which was based on the use of Rheb co-expression with MTOR fragments xref ."
sparser
"Consequently, we demonstrated that RHEB binds to the whole mTOR both in the presence or absence of GTPγS, with five-fold weaker affinity in the presence of GTPγS. In addition, RHEB bound to the truncated mTOR fragments of N-heat domain (∆N, aa 60–167) or M-heat domain (∆M, aa 967–1023) with the same affinity in the absence of GTP."
| PMC
sparser
"Fluorescence lifetime imaging of overexpressed Rheb, MTOR, and Raptor, each fused to fluorescent proteins, did detect the presence of a Rheb-MTOR complex in both the cytoplasm and the nucleus (the latter devoid of Raptor) xref ; as yet, however, the presence of endogenous Rheb in the nucleus and its localization therein await confirmation."
reach
"Mechanistically, schweinfurthins and their analogs arrested trans-Golgi-network trafficking, an intracellular vesicular trafficking system, resulting in the induction of endoplasmic reticulum stress and the suppression of both lipid raft mediated PI3K activation and mTOR and RheB complex formation, which collectively led to an effective inhibition of mTOR and AKT signaling."
sparser
"Proximity ligation assays (PLAs) in WT PPT1 and KO PPT1 cells established a significant loss of physical interaction between the LAMTOR1/p18 subunit of Ragulator and the ATP6V1A subunit of the vacuolar-type H+-ATPase (v-ATPase), which is critical for and results in the loss of mTOR-Rheb physical interactions ( xref ) ( xref , xref )."
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"However, in terms of leucine stimulation, the latest report by Suryawan et al. found that neonatal pigs fed with a low protein diet supplemented with leucine or its metabolite beta-hydroxy-beta-methylbutyrate (HMbeta) failed to promote the Rheb and mTOR complex formation, but this effect was not observed in pigs fed a high protein diet combined with leucine supplementation."
reach
"The results illustrate the power of GFP-technology combined with FRET-FLIM imaging in the study of the interaction of signalling components in living cells, here providing evidence for a direct physical interaction between mTOR and Rheb and between mTOR and raptor in living cells for the first time."
sparser
"However, in terms of leucine stimulation, the latest report by Suryawan et al. found that neonatal pigs fed with a low-protein diet supplemented with leucine or its metabolite β-hydroxy-β-methylbutyrate (HMβ) failed to promote the Rheb–mTOR complex formation, but this effect was not observed in pigs fed a high-protein diet combined with leucine supplementation ( xref )."
reach
"Quenching in the lifetime of the donor (EGFP-mTOR) from 2400 +/- 100 ps to 2000 +/- 100 ps in the nuclear regions indicates that EGFP-mTOR and DsRed-Rheb interact (due to excited state energy transfer) differently (i.e. they are closer) in the cell nucleus than in the cytoplasm, likely brought about by a different conformation of the mTOR and Rheb complex."
sparser
"The results illustrate the power of GFP-technology combined with FRET-FLIM imaging in the study of the interaction of signalling components in living cells, here providing evidence for a direct physical interaction between mTOR and Rheb and between mTOR and raptor in living cells for the first time."
sparser
"Song and coworkers have also confirmed that resistance exercise in the human skeletal muscle resulted in the rapid translocation of mTOR toward the lysosome, with the concurrent dissociation of TSC2 from Rheb, which would facilitate the interaction of mTOR and GTP‐Rheb (Song et al., xref )."
sparser
"A number of studies have looked at the involvement of Rheb in the cellular response to amino acids (Garami et al , xref ; Inoki et al , xref ; Tee et al , xref ; Zhang et al , xref ; Long et al , xref ; Smith et al , xref ; Roccio et al , xref ; Bai et al , xref ; Sancak et al , xref ), with some disagreement on whether amino acids affect Rheb GTP‐loading or Rheb‐mTOR binding."
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"Hence the dynamic aspects of the interaction between mTOR, Rheb and raptor in living cells requires new approaches for the detection of interaction, such as provided by the fluorescence resonance energy transfer - fluorescence lifetime imaging (FRET-FLIM) technique for observation of appropriately labelled materials in an active environment [XREF_BIBR - XREF_BIBR]."
sparser
"For instance, similar to Rheb binding to mTOR, binding of DNA/Ku70/80 to DNA-PKcs (which together form the DNA-PK complex) has been proposed to stimulate DNA-PKcs activity via an allosteric mechanism that involves the movement of the N-HEAT towards the FAT domain, leading to conformational changes in the KD [ xref ]."