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Target of Rapamycin (TOR) Regulates Growth in Response to Nutritional Signals.
Weisman, R
Microbiology spectrum. 2016;(5)
Abstract
All organisms can respond to the availability of nutrients by regulating their metabolism, growth, and cell division. Central to the regulation of growth in response to nutrient availability is the target of rapamycin (TOR) signaling that is composed of two structurally distinct complexes: TOR complex 1 (TORC1) and TOR complex 2 (TORC2). The TOR genes were first identified in yeast as target of rapamycin, a natural product of a soil bacterium, which proved beneficial as an immunosuppressive and anticancer drug and is currently being tested for a handful of other pathological conditions including diabetes, neurodegeneration, and age-related diseases. Studies of the TOR pathway unraveled a complex growth-regulating network. TOR regulates nutrient uptake, transcription, protein synthesis and degradation, as well as metabolic pathways, in a coordinated manner that ensures that cells grow or cease growth in response to nutrient availability. The identification of specific signals and mechanisms that stimulate TOR signaling is an active and exciting field of research that has already identified nitrogen and amino acids as key regulators of TORC1 activity. The signals, as well as the cellular functions of TORC2, are far less well understood. Additional open questions in the field concern the relationships between TORC1 and TORC2, as well as the links with other nutrient-responsive pathways. Here I review the main features of TORC1 and TORC2, with a particular focus on yeasts as model organisms.
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mTORC1- and mTORC2-interacting proteins keep their multifunctional partners focused.
Bracho-Valdés, I, Moreno-Alvarez, P, Valencia-Martínez, I, Robles-Molina, E, Chávez-Vargas, L, Vázquez-Prado, J
IUBMB life. 2011;(10):896-914
Abstract
The mammalian target of rapamycin, best known as mTOR, is a phylogenetically conserved serine/threonine kinase that controls life-defining cellular processes such as growth, metabolism, survival, and migration under the influence of multiple interacting proteins. Historically, the cellular activities blocked by rapamycin in mammalian cells were considered the only events controlled by mTOR. However, this paradigm changed with the discovery of two signaling complexes differentially sensitive to rapamycin, whose catalytic component is mTOR. The one sensitive to rapamycin, known as mTORC1, promotes protein synthesis in response to growth factors and nutrients via the phosphorylation of p70S6K and 4EBP1; while the other, known as mTORC2, promotes cell migration and survival via the activation of Rho GTPases and the phosphorylation of AKT, respectively. Although mTORC2 kinase activity is not inhibited by rapamycin, hours of incubation with this antibiotic can impede the assembly of this signaling complex. The direct mechanism by which mTORC2 leads to cell migration depends on its interaction with P-Rex1, a Rac-specific guanine nucleotide exchange factor, while additional indirect pathways involve the intervention of PKC or AKT, multifunctional ubiquitous serine/threonine kinases that activate effectors of cell migration upon being phosphorylated by mTORC2 in response to chemotactic signals. These mTORC2 effectors are altered in metastatic cancer. Numerous clinical trials are testing mTOR inhibitors as potential antineoplasic drugs. Here, we briefly review the actions of mTOR with emphasis on the controlling role of mTORC1 and mTORC2-interacting proteins and highlight the mechanisms linked to cell migration.
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Leucine-enriched nutrients and the regulation of mammalian target of rapamycin signalling and human skeletal muscle protein synthesis.
Drummond, MJ, Rasmussen, BB
Current opinion in clinical nutrition and metabolic care. 2008;(3):222-6
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Abstract
PURPOSE OF REVIEW To highlight recent studies that have examined the cell-signalling mechanisms responsible for the amino acid (primarily leucine and the essential amino acids) stimulation of human skeletal muscle protein synthesis. RECENT FINDINGS Ingestion of a leucine-enriched essential amino acid nutrient solution rapidly and potently activates the mammalian target of rapamycin signalling pathway and protein synthesis in human skeletal muscle. Further, mTOR signalling and muscle protein synthesis are enhanced when leucine-enriched nutrients are ingested following resistance exercise. The addition of leucine to regular meals may improve the ability of feeding to stimulate protein synthesis in old human muscle. SUMMARY Leucine and essential amino acids appear to stimulate human muscle protein synthesis primarily by activating the mammalian target of rapamycin signalling pathway. How human muscle cells sense an increase in leucine and/or essential amino acids to activate mammalian target of rapamycin signalling is currently unknown. Recent work, however, suggests that the kinases hVps34 and MAP43K may be involved. Leucine-enriched essential amino acid ingestion, in combination with resistance exercise in some cases, may be a useful intervention to promote mTOR signalling and protein synthesis in an effort to counteract a variety of muscle wasting conditions (e.g. sarcopenia, cachexia, AIDS, inactivity/bed rest, sepsis, kidney failure, and trauma).
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Drug coated stents for carotid intervention.
Tepe, G, Schmehl, J, Claussen, CD, Ernemann, U, Pereira, P, Duda, SH
The Journal of cardiovascular surgery. 2005;(3):249-59
Abstract
Carotid endarterectomy has demonstrated its superiority over medical treatment of symptomatic as well as asymptomatic stenosis of the extracranial carotid artery. Although minimally invasive methods initially failed to produce similar results, stent implantation is becoming an alternative technique for stroke prophylaxis with technical advances, cerebral protection and careful patient selection. Even though restenosis does not seem to be a major limitation compared to coronary interventions, in-stent restenosis might occur more frequently with an increasing number of procedures performed and longer follow-up periods. Drug eluting stents have shown to attenuate this complication. Currently, no clinical data on drug eluting stents in carotid arteries are available. This article discusses the current literature on carotid artery stenting and the potential role of drug eluting stents in this field.
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Drug-eluting stents: from randomized trials to the real world.
Saia, F, Degertekin, M, Lemos, PA, Serruys, PW
Minerva cardioangiologica. 2004;(5):349-63
Abstract
Drug-eluting stents have been developed to prevent in-stent restenosis following percutaneous coronary revascularization. In a number of randomized trials, polymer-coated sirolimus- and paclitaxel-eluting stents have been proven to markedly reduce the incidence of angiographic restenosis and repeat revascularization when compared to bare metal stents. Effectiveness of sirolimus-eluting stents in the prevention of restenosis has been confirmed in many subsets of patients and lesions not included in randomized trials, such as in-stent restenosis, chronic total occlusion, acute myocardial infarction, and others. Very promising data in the real world are emerging for utilization of paclitaxel-eluting stents as well. Other drug-eluting stents gave less brilliant results or even true failures, whilst a number of new drugs and stent platforms are under clinical or preclinical evaluation. In this review we describe the main clinical trials on drug-eluting stents, and the most recent informations derived from observational studies and registries. Moreover, preliminary results on new drug-eluting stents are summarized.