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

Prostate cancer cells require high rates of de novo fatty acid synthesis and protein synthesis for their rapid growth. We report here that the growth of these cells is markedly diminished by incubation with activators of AMP-activated protein kinase (AMPK), a fuel-sensing enzyme that has been shown to diminish both of these processes in intact tissues. Inhibition of cell growth was observed when AMPK was activated by either 5-aminoimidazole-4-carboxamide riboside (AICAR) or the thiazolidinedione rosiglitazone. Thus, a 90% inhibition of the growth of androgen-independent (DU145, PC3) and androgen-sensitive (LNCaP) cells was achieved after 4 days of exposure to one or both of these agents. Where studied, this was associated with a decrease in the concentration of malonyl CoA, an intermediate of de novo fatty acid synthesis, and an increase in expression of the cell cycle inhibitor p21. In addition, AICAR inhibited two key enzymes involved in protein synthesis, mTOR and p70S6K, and blocked the ability of the androgen R1881 to increase cell growth and the expression of two enzymes for de novo fatty acid synthesis, acetyl CoA carboxylase and fatty acid synthase, in the LNCaP cells. The results suggest that AMPK is a potential target for the treatment of prostate cancer.
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PMID:AMP-activated protein kinase activators can inhibit the growth of prostate cancer cells by multiple mechanisms. 1535 29

Although most cells in the embryonic mouse cortex express the serine-threonine kinase Akt-1, a small population of progenitors expresses Akt-1 protein at a higher level. To determine the functional significance of this difference, we used a retrovirus to increase Akt-1 expression in cortical progenitors. Increased Akt expression enhanced Akt activation after growth factor stimulation of progenitors. In vivo, it promoted retention in progenitor layers, the ventricular zone and subventricular zone. In vitro, it enhanced proliferation and survival, but did not impair migration. Moreover, it increased the proportion of stem cells, defined by a self-renewal assay. These effects did not depend on the Akt substrate p21(Cip1). In contrast, rapamycin, an inhibitor of mTOR (mammalian target of rapamycin), altered effects of elevated Akt-1 selectively: it eliminated the increase in stem cells and reduced the proliferative response, but had no effect on survival. The ability of elevated Akt-1 to increase the self-renewing population therefore depends on a rapamycin-sensitive mechanism (presumably inhibition of mTOR activity) but not on p21(Cip1), and can be distinguished from its effects on the proliferation and survival of other types of progenitors. Our findings suggest that expression of a high level of Akt-1 by a subpopulation of cortical progenitors biases their responses to extrinsic signals to increase their survival, proliferation, and/or self-renewal. Heterogeneity in Akt-1 level among progenitors could therefore allow cells that share a microenvironment to respond differently to the same extrinsic signals.
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PMID:Akt-1 expression level regulates CNS precursors. 1545 27

Although DNA damaging agents have revolutionized chemotherapy against solid tumors, a narrow therapeutic window combined with severe side effects has limited their broader use. Here we show that RAD001 (everolimus), a rapamycin derivative, dramatically enhances cisplatin-induced apoptosis in wild-type p53, but not mutant p53 tumor cells. The use of isogenic tumor cell lines expressing either wild-type mTOR cDNA or a mutant that does not bind RAD001 demonstrates that the effects of RAD001 are through inhibition of mTOR function. We further show that RAD001 sensitizes cells to cisplatin by inhibiting p53-induced p21 expression. Unexpectedly, this effect is attributed to a small but significant inhibition of p21 translation combined with its short half-life. These findings provide the molecular rationale for combining DNA damaging agents with RAD001, showing that a general effect on a major anabolic process may dramatically enhance the efficacy of an established drug protocol in the treatment of cancer patients with solid tumors.
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PMID:The mTOR inhibitor RAD001 sensitizes tumor cells to DNA-damaged induced apoptosis through inhibition of p21 translation. 1579 77

Most bone marrow (BM) malignancies develop in association with an angiogenic phenotype and increased numbers of endothelial cells. The molecular mechanisms involved in the modulation and recruitment of BM endothelium are largely unknown and may provide novel therapeutic targets for neoplastic diseases. We observed that angiogenic stimulation of BM endothelial cells activates mTOR and engages its downstream pathways 4E-BP1 and S6K1, which are inhibited by the mTOR-specific blockers rapamycin and CCI-779. Both mTOR blockers significantly inhibit growth factor- and leukemia-induced proliferation of BM endothelium by inducing G0/G1 cell-cycle arrest. This effect is associated with down-regulation of cyclin D1 and cdk2 phosphorylation, and up-regulation of the cdk inhibitors p27(kip1) and p21(cip1). Under conditions that reproduce the biomechanical fluidic environment of the BM, CCI-779 is equally effective in inhibiting BM endothelial-cell proliferation. Finally, simultaneous blockade of mTOR and NF-kappaB pathways synergize to significantly inhibit or abrogate the proliferative responses of BM endothelial cells to mitogenic stimuli. This study identifies mTOR as an important pathway for the proangiogenic stimulation of BM endothelium. Modulation of this pathway may serve as a valid therapeutic intervention in BM malignancies evolving in association with an angiogenic phenotype.
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PMID:Proangiogenic stimulation of bone marrow endothelium engages mTOR and is inhibited by simultaneous blockade of mTOR and NF-kappaB. 1614 50

The PI3K/PTEN/Akt signaling pathway has emerged in recent years as a main player in human cancers, increasing proliferation and decreasing apoptosis of transformed cells, and thus becoming a potential target for therapeutic intervention. Our previous data have demonstrated that Akt-mediated signaling is of a key relevance in the mouse skin carcinogenesis system, one of the best-known models of experimental carcinogenesis. Here, we investigated the involvement of several pathways as mediators of Akt-induced increased proliferation and tumorigenesis in keratinocytes. Tumors produced by subcutaneous injection of Akt-transformed keratinocytes showed increased Foxo3a phosphorylation, but no major alterations in p21(Cip1/WAF1), p27(Kip1) or mdm2 expression and/or localization. In contrast, we found increased expression and nuclear localization of DeltaNp63, beta-catenin and Lef1. Concomitantly, we also found increased expression of c-myc and CycD1, targets of the beta-catenin/Tcf pathway. Such increase is associated with increased phosphorylation and stabilization of c-myc protein as well as increased translation of c-myc and CycD1 due to mTOR activation. Using immunohistochemistry approaches in samples of oral dysplasias and human head and neck squamous cell carcinomas, we confirmed that increased Akt activation significantly correlates with increased DeltaNp63 and CycD expression, c-myc phosphorylation and nuclear accumulation of beta-catenin. Collectively, these results demonstrate that Akt is able to transform keratinocytes by specific mechanisms involving transcriptional and post-transcriptional processes.
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PMID:Molecular determinants of Akt-induced keratinocyte transformation. 1624 57

A major determinant in platelet production is the megakaryocyte (MK) size that is regulated both by ploidization and the increase in cytoplasmic volume at the end of maturation. Here we investigated the involvement of the mammalian target of rapamycin (mTOR) pathway in the regulation of megakaryopoiesis. We show that phosphorylation of mTOR, p70S6K1, and 4E-BP1 was diminished in thrombopoietin-cultured human MKs after rapamycin treatment. Rapamycin induced an inhibition in the G1/S transition and a decrease in the mean MK ploidy via a diminution of p21 and cyclin D3 occurring at a transcriptional level. Both cycling (2N/4N) and polyploid (8N/16N) MKs were reduced in size, with a size reduction slightly more pronounced in mature polyploid MKs than in immature ones. Rapamycin also induced a delay in the expression of MK markers and prevented the generation of proplatelet MKs. Additional experiments performed in vitro with MKs from mutant mice showed that the decrease in mean ploidy level and the delay in MK differentiation in the presence of rapamycin were less pronounced in CdknIa (p21)-/- MKs than in CdknIa (p21)+/+ MKs. These findings indicate that the mTOR pathway plays an important role during megakaryopoiesis by regulating ploidy, cell size, and maturation, in part by regulating p21 and cyclin D3.
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PMID:Mammalian target of rapamycin (mTOR) regulates both proliferation of megakaryocyte progenitors and late stages of megakaryocyte differentiation. 1628 43

Early diabetic nephropathy is characterized by renal hypertrophy that is mainly due to proximal tubular hypertrophy. Mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase, and its signaling has been reported to regulate protein synthesis and cellular growth, specifically, hypertrophy. Therefore, we examined the effect of mTOR signaling on diabetic renal hypertrophy by using the specific inhibitor for mTOR, rapamycin. Ten days after streptozotocin-induced diabetes, mice showed kidney hypertrophy with increases in the phosphorylation of p70S6kinase and the expression of cyclin kinase inhibitors, p21(Cip1) and p27(Kip1), in the kidneys. The intraperitoneal injection of rapamycin (2 mg/kg/day) markedly attenuated the enhanced phosphorylation of p70S6kinase, the increment of cyclin-dependent kinase inhibitors, and renal enlargement without any changes of clinical parameters, including blood glucose, blood pressure, and food intake. Overexpression of a constitutive active form of p70S6kinase resulted in increased cell size of cultured mouse proximal tubule cells; thus, activation of p70S6kinase causes hypertrophy of proximal tubular cells. Our findings suggest that activation of mTOR signaling causes renal hypertrophy at the early stage of diabetes.
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PMID:Inhibition of mTOR signaling with rapamycin attenuates renal hypertrophy in the early diabetic mice. 1636 54

PTEN deficiency predisposes to a subset of human cancers, but the mechanism that underlies such selectivity is unknown. We have generated a mouse line that conditionally deletes Pten in urogenital epithelium. These mice develop carcinomas at high frequency in the prostate but at relatively low frequency in the bladder, despite early and complete penetrance of hyperplasia in both organs. Cell proliferation is initially high in the bladder of newborn Pten-deficient mice but within days is inhibited by p21 induction. In contrast, proliferation remains elevated in Pten-deficient prostate, where p21 is never induced, suggesting that p21 induction is a bladder-specific compensatory mechanism to inhibit proliferation caused by Pten deletion. Furthermore, the AKT/mammalian target of rapamycin growth pathway, which is highly activated in Pten-deficient prostate, is not activated in bladder epithelium. Our results reveal alternative downstream signaling pathways activated by Pten deficiency that lead to tissue-specific susceptibilities to tumorigenesis.
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PMID:Pten deficiency activates distinct downstream signaling pathways in a tissue-specific manner. 1648 91

AMPK is a serine/threonine protein kinase, which serves as an energy sensor in all eukaryotic cell types. Published studies indicate that AMPK activation strongly suppresses cell proliferation in non-malignant cells as well as in tumour cells. These actions of AMPK appear to be mediated through multiple mechanisms including regulation of the cell cycle and inhibition of protein synthesis, de novo fatty acid synthesis, specifically the generation of mevalonate as well as other products downstream of mevalonate in the cholesterol synthesis pathway. Cell cycle regulation by AMPK is mediated by up-regulation of the p53-p21 axis as well as regulation of TSC2-mTOR (mammalian target of rapamycin) pathway. The AMPK signalling network contains a number of tumour suppressor genes including LKB1, p53, TSC1 and TSC2, and overcomes growth factor signalling from a variety of stimuli (via growth factors and by abnormal regulation of cellular proto-oncogenes including PI3K, Akt and ERK). These observations suggest that AMPK activation is a logical therapeutic target for diseases rooted in cellular proliferation, including atherosclerosis and cancer. In this review, we discuss about exciting recent advances indicating that AMPK functions as a suppressor of cell proliferation by controlling a variety of cellular events in normal cells as well as in tumour cells.
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PMID:AMPK and cell proliferation--AMPK as a therapeutic target for atherosclerosis and cancer. 1661 76

Anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL) frequently carries the t(2;5)(p23;q35) resulting in aberrant expression of chimeric nucleophosmin-ALK. Previously, nucleophosmin-ALK has been shown to activate phosphatidylinositol 3-kinase (PI3K) and its downstream effector, the serine/threonine kinase AKT. In this study, we hypothesized that the mammalian target of rapamycin (mTOR) pathway, which functions downstream of AKT, mediates the oncogenic effects of activated PI3K/AKT in ALK+ ALCL. Here, we provide evidence that mTOR signaling phosphoproteins, including mTOR, eukaryotic initiation factor 4E-binding protein-1, p70S6K, and ribosomal protein S6, are highly phosphorylated in ALK+ ALCL cell lines and tumors. We also show that AKT activation contributes to mTOR phosphorylation, at least in part, as forced expression of constitutively active AKT by myristoylated AKT adenovirus results in increased phosphorylation of mTOR and its downstream effectors. Conversely, inhibition of AKT expression or activity results in decreased mTOR phosphorylation. In addition, pharmacologic inhibition of PI3K/AKT down-regulates the activation of the mTOR signaling pathway. We also show that inhibition of mTOR with rapamycin, as well as silencing mTOR gene product expression using mTOR-specific small interfering RNA, decreased phosphorylation of mTOR signaling proteins and induced cell cycle arrest and apoptosis in ALK+ ALCL cells. Cell cycle arrest was associated with modulation of G(1)-S-phase regulators, including the cyclin-dependent kinase inhibitors p21(waf1) and p27(kip1). Apoptosis following inhibition of mTOR expression or function was associated with down-regulation of antiapoptotic proteins, including c-FLIP, MCL-1, and BCL-2. These findings suggest that the mTOR pathway contributes to nucleophosmin-ALK/PI3K/AKT-mediated tumorigenesis and that inhibition of mTOR represents a potential therapeutic strategy in ALK+ ALCL.
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PMID:Activation of mammalian target of rapamycin signaling pathway contributes to tumor cell survival in anaplastic lymphoma kinase-positive anaplastic large cell lymphoma. 1681 31


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