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Activation of the Mechanistic Target of Rapamycin in SLE: Explosion of Evidence in the Last Five Years.
Oaks, Z, Winans, T, Huang, N, Banki, K, Perl, A
Current rheumatology reports. 2016;(12):73
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Abstract
The mechanistic target of rapamycin (mTOR) is a central regulator in cell growth, activation, proliferation, and survival. Activation of the mTOR pathway underlies the pathogenesis of systemic lupus erythematosus (SLE). While mTOR activation and its therapeutic reversal were originally discovered in T cells, recent investigations have also uncovered roles in other cell subsets including B cells, macrophages, and "non-immune" organs such as the liver and the kidney. Activation of mTOR complex 1 (mTORC1) precedes the onset of SLE and associated co-morbidities, such as anti-phospholipid syndrome (APS), and may act as an early marker of disease pathogenesis. Six case reports have now been published that document the development of SLE in patients with genetic activation of mTORC1. Targeting mTORC1 over-activation with N-acetylcysteine, rapamycin, and rapalogs provides an opportunity to supplant current therapies with severe side effect profiles such as prednisone or cyclophosphamide. In the present review, we will discuss the recent explosion of findings in support for a central role for mTOR activation in SLE.
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Healthy CD4+ T lymphocytes are not affected by targeted therapies against the PI3K/Akt/mTOR pathway in T-cell acute lymphoblastic leukemia.
Alameen, AA, Simioni, C, Martelli, AM, Zauli, G, Ultimo, S, McCubrey, JA, Gonelli, A, Marisi, G, Ulivi, P, Capitani, S, et al
Oncotarget. 2016;(34):55690-55703
Abstract
An attractive molecular target for novel anti-cancer therapies is the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway which is commonly deregulated in many types of cancer. Nevertheless, the effects of PI3K/Akt/mTOR inhibitors on T lymphocytes, a key component of immune responses, have been seldom explored. In this study we investigated the effects on human CD4+ T-cells of a panel of PI3K/Akt/mTOR inhibitors: BGT226, Torin-2, MK-2206, and ZSTK474. We also assessed their efficacy against two acute leukemia T cell lines. T lymphocytes were stimulated with phytohemagglutinin. Inhibitor effects on cell cycle and apoptosis were analyzed by flow cytometry, while cytotoxicity was assessed by MTT assays. In addition, the activation status of the pathway as well as induction of autophagy were analyzed by Western blotting. Quiescent healthy T lymphocytes were unaffected by the drugs whereas mitogen-stimulated lymphocytes as well as leukemic cell lines displayed a cell cycle block, caspase-dependent apoptosis, and dephosphorylation of key components of the signaling pathway. Autophagy was also induced in proliferating lymphocytes and in JURKAT and MOLT-4 cell lines. When autophagy was inhibited by 3-methyladenine or Bafilomycin A1, drug cytotoxicity was increased, indicating that autophagy is a protective mechanism. Therefore, our findings suggest that PI3K/Akt/mTOR inhibitors preserve lymphocyte viability. This is a valuable result to be taken into account when selecting drugs for targeted cancer therapy in order to minimize detrimental effects on immune function.
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Growing knowledge of the mTOR signaling network.
Huang, K, Fingar, DC
Seminars in cell & developmental biology. 2014;:79-90
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Free full text
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Abstract
The kinase mTOR (mechanistic target of rapamycin) integrates diverse environmental signals and translates these cues into appropriate cellular responses. mTOR forms the catalytic core of at least two functionally distinct signaling complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). mTORC1 promotes anabolic cellular metabolism in response to growth factors, nutrients, and energy and functions as a master controller of cell growth. While significantly less well understood than mTORC1, mTORC2 responds to growth factors and controls cell metabolism, cell survival, and the organization of the actin cytoskeleton. mTOR plays critical roles in cellular processes related to tumorigenesis, metabolism, immune function, and aging. Consequently, aberrant mTOR signaling contributes to myriad disease states, and physicians employ mTORC1 inhibitors (rapamycin and analogs) for several pathological conditions. The clinical utility of mTOR inhibition underscores the important role of mTOR in organismal physiology. Here we review our growing knowledge of cellular mTOR regulation by diverse upstream signals (e.g. growth factors; amino acids; energy) and how mTORC1 integrates these signals to effect appropriate downstream signaling, with a greater emphasis on mTORC1 over mTORC2. We highlight dynamic subcellular localization of mTORC1 and associated factors as an important mechanism for control of mTORC1 activity and function. We will cover major cellular functions controlled by mTORC1 broadly. While significant advances have been made in the last decade regarding the regulation and function of mTOR within complex cell signaling networks, many important findings remain to be discovered.
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Helicobacter pylori promotes eukaryotic protein translation by activating phosphatidylinositol 3 kinase/mTOR.
Sokolova, O, Vieth, M, Gnad, T, Bozko, PM, Naumann, M
The international journal of biochemistry & cell biology. 2014;:157-63
Abstract
The innate immune response elicited by Helicobacter pylori in the human gastric mucosa involves a range of cellular signalling pathways, including those implicated in metabolism regulation. In this study, we analysed H. pylori-induced PI3K/Akt/mTOR signalling, which regulates glycolysis and protein synthesis and associates thereby with cellular energy- and nutrients-consuming processes such as growth and proliferation. The immunohistochemical analysis demonstrated that Akt kinase phosphorylation is abundant in gastric biopsies obtained from gastritis, gastric adenoma and adenocarcinoma patients. Infection with H. pylori led to the phosphorylation of Akt effectors mTOR and S6 in a type 4 secretion system (T4SS)-independent manner in AGS cells. We observed that the activation of these molecules was dependent on PI3K and the Src family tyrosine kinases. Furthermore, H. pylori induced the phosphorylation of 4E-BP1 and eIF4E and suppressed the phosphorylation of eEF2, which are important regulators of protein synthesis. Inhibition of PI3K and Akt kinase prevented the phosphorylation of 4E-BP1, suggesting that PI3K signalling is involved in the regulation of translation initiation during H. pylori infection. Metabolic labelling showed that infected cells had higher rates of [(35)S]methionine/cysteine incorporation, and this effect could be prevented using LY294002, an PI3K inhibitor. Thus, H. pylori activates PI3K/Akt signalling, mTOR, eIFs and protein translation, which might impact H. pylori-related gastric pathophysiology.
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Combined therapeutic application of mTOR inhibitor and vitamin D(3) for inflammatory bone destruction of rheumatoid arthritis.
Kim, TH, Choi, SJ, Lee, YH, Song, GG, Ji, JD
Medical hypotheses. 2012;(6):757-60
Abstract
Inflammatory bone destruction is a prominent feature and a cause of substantial morbidity in several inflammatory diseases, including rheumatoid arthritis (RA), periodontitis, and peri-prosthetic loosening. Osteoclasts are unique, multinucleated giant cells that effectively resorb bone and thus are directly responsible for bone destruction in several inflammatory diseases. PI3K/Akt/mTOR pathway has been well known to play important roles in regulating adaptive and innate immune cell function. In addition to play roles in immune responses, several lines of evidence demonstrate that PI3K/Akt/mTOR pathway is critical for osteoclast differentiation and survival. These results suggest that inhibition of PI3K/Akt/mTOR pathway could protect against bone destruction in inflammatory diseases, including RA. However, the clinical use of mTOR inhibitors may be hampered due to limited clinical efficacy and frequent toxic side effects. In the treatment of RA, combination therapy with various disease-modifying antirheumatic drugs (DMARDs) has been suggested to improve the therapeutic efficacy and limit the side effects. In this report, we show several experimental evidences that vitamin D(3) modulates mTOR pathway, and present a hypothesis that the combination of mTOR inhibitor and vitamin D(3) can effectively inhibit osteoclast differentiation and function in chronic inflammatory condition such as RA, therefore this combination will be a powerful therapeutic regimen in preventing the inflammation-induced bone destruction in RA.