Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P42345 (mTOR)
 26,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Autophagy is a vital response to nutrient starvation. Here, we screened a kinase-specific siRNA library using an autophagy assay in human embryonic kidney 293 cells that measures lipidation of the marker protein GFP-LC3 following amino acid starvation. This screen identified ULK1 in addition to other novel candidates that could be confirmed with multiple siRNAs. Knockdown of ULK1, but not the related kinase ULK2, inhibited the autophagic response. Also, ULK1 knockdown inhibited rapamycin-induced autophagy consistent with a role downstream of mTOR. Overexpression of ULK1 inhibited autophagy and this inhibition was independent of its kinase activity. Deletion of the PDZ domain-binding Val-Tyr-Ala motif at the ULK1 C terminus generated a more potent dominant-negative protein. Further deletions revealed that the minimal ULK1 dominant-negative region could be mapped to residues 1-351. Full-length ULK1 localized to cytoplasmic structures, some of which were GFP-LC3-positive, and this localization required the conserved C-terminal domain. In contrast, ULK1-(1-351) was diffuse in the cytoplasm. These experiments reveal at least two domains in ULK1 which likely function via unique sets of effectors to regulate autophagy.
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PMID:siRNA screening of the kinome identifies ULK1 as a multidomain modulator of autophagy. 1759 59

Autophagy is an intracellular degradation system, by which cytoplasmic contents are degraded in lysosomes. Autophagy is dynamically induced by nutrient depletion to provide necessary amino acids within cells, thus helping them adapt to starvation. Although it has been suggested that mTOR is a major negative regulator of autophagy, how it controls autophagy has not yet been determined. Here, we report a novel mammalian autophagy factor, Atg13, which forms a stable approximately 3-MDa protein complex with ULK1 and FIP200. Atg13 localizes on the autophagic isolation membrane and is essential for autophagosome formation. In contrast to yeast counterparts, formation of the ULK1-Atg13-FIP200 complex is not altered by nutrient conditions. Importantly, mTORC1 is incorporated into the ULK1-Atg13-FIP200 complex through ULK1 in a nutrient-dependent manner and mTOR phosphorylates ULK1 and Atg13. ULK1 is dephosphorylated by rapamycin treatment or starvation. These data suggest that mTORC1 suppresses autophagy through direct regulation of the approximately 3-MDa ULK1-Atg13-FIP200 complex.
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PMID:Nutrient-dependent mTORC1 association with the ULK1-Atg13-FIP200 complex required for autophagy. 1921 35

Autophagy, the starvation-induced degradation of bulky cytosolic components, is up-regulated in mammalian cells when nutrient supplies are limited. Although mammalian target of rapamycin (mTOR) is known as the key regulator of autophagy induction, the mechanism by which mTOR regulates autophagy has remained elusive. Here, we identify that mTOR phosphorylates a mammalian homologue of Atg13 and the mammalian Atg1 homologues ULK1 and ULK2. The mammalian Atg13 binds both ULK1 and ULK2 and mediates the interaction of the ULK proteins with FIP200. The binding of Atg13 stabilizes and activates ULK and facilitates the phosphorylation of FIP200 by ULK, whereas knockdown of Atg13 inhibits autophagosome formation. Inhibition of mTOR by rapamycin or leucine deprivation, the conditions that induce autophagy, leads to dephosphorylation of ULK1, ULK2, and Atg13 and activates ULK to phosphorylate FIP200. These findings demonstrate that the ULK-Atg13-FIP200 complexes are direct targets of mTOR and important regulators of autophagy in response to mTOR signaling.
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PMID:ULK-Atg13-FIP200 complexes mediate mTOR signaling to the autophagy machinery. 1922 51

Autophagy is a degradative process that recycles long-lived and faulty cellular components. It is linked to many diseases and is required for normal development. ULK1, a mammalian serine/threonine protein kinase, plays a key role in the initial stages of autophagy, though the exact molecular mechanism is unknown. Here we report identification of a novel protein complex containing ULK1 and two additional protein factors, FIP200 and ATG13, all of which are essential for starvation-induced autophagy. Both FIP200 and ATG13 are critical for correct localization of ULK1 to the pre-autophagosome and stability of ULK1 protein. Additionally, we demonstrate by using both cellular experiments and a de novo in vitro reconstituted reaction that FIP200 and ATG13 can enhance ULK1 kinase activity individually but both are required for maximal stimulation. Further, we show that ATG13 and ULK1 are phosphorylated by the mTOR pathway in a nutrient starvation-regulated manner, indicating that the ULK1.ATG13.FIP200 complex acts as a node for integrating incoming autophagy signals into autophagosome biogenesis.
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PMID:ULK1.ATG13.FIP200 complex mediates mTOR signaling and is essential for autophagy. 1925 18

High nutrient availability stimulates the mammalian target of rapamycin complex 1 (mTORC1) to coordinately activate anabolic processes, such as protein synthesis, while inhibiting the cellular catabolism of autophagy. Positive regulation of protein synthesis through the mTORC1 substrates p70 ribosomal S6 kinase (p70S6K) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1) has been well characterized. The complementary inhibitory mechanism in which mTORC1 phosphorylates the autophagy regulatory complex containing unc-51-like kinase 1 (ULK1), the mammalian Atg13 protein, and focal adhesion kinase interacting protein of 200 kD (FIP200) has also been elucidated.
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PMID:mTORC1 phosphorylates the ULK1-mAtg13-FIP200 autophagy regulatory complex. 1969 Mar 28

Autophagy, a catabolic process responsible for the degradation of cytosolic components, is upregulated when nutrient supplies are limited. A critical step in autophagy induction comprises the inactivation of a key negative regulator of the process, the Ser/Thr kinase mammalian target of rapamycin (mTOR). Thus far, only a few substrates of mTOR that control autophagy have been identified, including ULK1 and Atg13, both of which function as positive mediators. Here we identify death-associated protein 1 (DAP1) as a novel substrate of mTOR that negatively regulates autophagy. The link of DAP1 to autophagy was first apparent in that its knockdown enhanced autophagic flux and in that it displayed a rapid decline in its phosphorylation in response to amino acid starvation. Mapping of the phosphorylation sites and analysis of phosphorylation mutants indicated that DAP1 is functionally silenced in growing cells through mTOR-dependent phosphorylations on Ser3 and Ser51. Inactivation of mTOR during starvation caused a rapid reduction in these phosphorylation sites and converted the protein into an active suppressor of autophagy. These results are consistent with a "Gas and Brake" model in which mTOR inhibition also controls a buffering mechanism that counterbalances the autophagic flux and prevents its overactivation under nutrient deprivation.
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PMID:DAP1, a novel substrate of mTOR, negatively regulates autophagy. 2053 36

Essential amino acids (EAA) stimulate skeletal muscle protein synthesis (MPS) in humans. Leucine may have a greater stimulatory effect on MPS than other EAA and/or decrease muscle protein breakdown (MPB). To determine the effect of 2 different leucine concentrations on muscle protein turnover and associated signaling, young men (n = 6) and women (n = 8) ingested 10 g EAA in 1 of 2 groups: composition typical of high quality proteins (CTRL; 1.8 g leucine) or increased leucine concentration (LEU; 3.5 g leucine). Participants were studied for 180 min postingestion. Fractional synthetic rate and leg phenylalanine and leucine kinetics were assessed on muscle biopsies using stable isotopic techniques. Signaling was determined by immunoblotting. Arterial leucine concentration and delivery to the leg increased in both groups and was significantly higher in LEU than in CTRL; however, transport into the muscle and intracellular availability did not differ between groups. MPS increased similarly in both groups 60 min postingestion. MPB decreased at 60 min only in LEU, but net muscle protein balance improved similarly. Components of mammalian target of rapamycin (mTOR) signaling were improved in LEU, but no changes were observed in ubiquitin-proteasome system signaling. Changes in light chain 3 and mTOR association with Unc-51-like kinase 1 indicate autophagy decreased more in LEU. We conclude that in 10 g of EAA, the leucine content typical of high quality proteins (~1.8 g) is sufficient to induce a maximal skeletal muscle protein anabolic response in young adults, but leucine may play a role in autophagy regulation.
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PMID:Excess leucine intake enhances muscle anabolic signaling but not net protein anabolism in young men and women. 2084 86

Autophagy is a highly orchestrated intracellular bulk degradation process that is activated by various environmental stresses. The serine/threonine kinase ULK1, like its yeast homologue Atg1, is a key initiator of autophagy that is negatively regulated by the mTOR kinase. However, the molecular mechanism that controls the inhibitory effect of mTOR on ULK1-mediated autophagy is not fully understood. Here we identified AMPK, a central energy sensor, as a new ULK1-binding partner. We found that AMPK binds to the PS domain of ULK1 and this interaction is required for ULK1-mediated autophagy. Interestingly, activation of AMPK by AICAR induces 14-3-3 binding to the AMPK-ULK1-mTORC1 complex, which coincides with raptor Ser792 phosphorylation and mTOR inactivation. Consistently, AICAR induces autophagy in TSC2-deficient cells expressing wild-type raptor but not the mutant raptor that lacks the AMPK phosphorylation sites (Ser722 and Ser792). Taken together, these results suggest that AMPK association with ULK1 plays an important role in autophagy induction, at least in part, by phosphorylation of raptor to lift the inhibitory effect of mTOR on the ULK1 autophagic complex.
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PMID:The association of AMPK with ULK1 regulates autophagy. 2107 12

Autophagy is a process by which components of the cell are degraded to maintain essential activity and viability in response to nutrient limitation. Extensive genetic studies have shown that the yeast ATG1 kinase has an essential role in autophagy induction. Furthermore, autophagy is promoted by AMP activated protein kinase (AMPK), which is a key energy sensor and regulates cellular metabolism to maintain energy homeostasis. Conversely, autophagy is inhibited by the mammalian target of rapamycin (mTOR), a central cell-growth regulator that integrates growth factor and nutrient signals. Here we demonstrate a molecular mechanism for regulation of the mammalian autophagy-initiating kinase Ulk1, a homologue of yeast ATG1. Under glucose starvation, AMPK promotes autophagy by directly activating Ulk1 through phosphorylation of Ser 317 and Ser 777. Under nutrient sufficiency, high mTOR activity prevents Ulk1 activation by phosphorylating Ulk1 Ser 757 and disrupting the interaction between Ulk1 and AMPK. This coordinated phosphorylation is important for Ulk1 in autophagy induction. Our study has revealed a signalling mechanism for Ulk1 regulation and autophagy induction in response to nutrient signalling.
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PMID:AMPK and mTOR regulate autophagy through direct phosphorylation of Ulk1. 2140 67

Protein synthesis and autophagy work as two opposing processes to control cell growth in response to nutrient supply. The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) pathway, which acts as a master regulator to control protein synthesis, has recently been shown to inhibit autophagy by phosphorylating and inactivating ULK1, an autophagy regulatory protein. ULK1 also inhibits phosphorylation of a mTORC1 substrate, S6K1, indicating that a complex signaling interplay exists between mTORC1 and ULK1. Here, we demonstrate that ULK1 induces multisite phosphorylation of Raptor in vivo and in vitro. Using phospho-specific antibodies we identify Ser855 and Ser859 as being strongly phosphorylated by ULK1, with moderate phosphorylation of Ser792 also observed. Interestingly, ULK1 overexpression also increases phosphorylation of Raptor Ser863 and the mTOR autophosphorylation site, Ser2481 in a mTORC1-dependent manner. Despite this evidence for heightened mTORC1 kinase activity following ULK1 overexpresssion, mTORC1-mediated phosphorylation of S6K1 and 4E-BP1 is significantly inhibited. ULK1 expression has no effect on protein-protein interactions between the components of mTORC1, but does reduce the ability of Raptor to bind to the substrate 4E-BP1. Furthermore, shRNA knockdown of ULK1 leads to increased phosphorylation of mTORC1 substrates and decreased phosphorylation of Raptor at Ser859 and Ser792. We propose a new mechanism whereby ULK1 contributes to mTORC1 inhibition through hindrance of substrate docking to Raptor. This is a novel negative feedback loop that occurs upon activation of autophagy to maintain mTORC1 inhibition when nutrient supplies are limiting.
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PMID:ULK1 inhibits mTORC1 signaling, promotes multisite Raptor phosphorylation and hinders substrate binding. 2146 Jun 30


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