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)

The mechanisms of cell transformation mediated by the nucleophosmin (NPM)/anaplastic lymphoma kinase (ALK) tyrosine kinase are only partially understood. Here, we report that cell lines and native tissues derived from the NPM/ALK-expressing T-cell lymphoma display persistent activation of mammalian target of rapamycin (mTOR) as determined by phosphorylation of mTOR targets S6rp and 4E-binding protein 1 (4E-BP1). The mTOR activation is serum growth factor-independent but nutrient-dependent. It is also dependent on the expression and enzymatic activity of NPM/ALK as demonstrated by cell transfection with wild-type and functionally deficient NPM/ALK, small interfering RNA (siRNA)-mediated NPM/ALK depletion and kinase activity suppression using the inhibitor WHI-P154. The NPM/ALK-induced mTOR activation is transduced through the mitogen-induced extracellular kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathway and, to a much lesser degree, through the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway. Accordingly, whereas the low-dose PI3K inhibitor wortmannin and Akt inhibitor III profoundly inhibited Akt phosphorylation, they had a very modest effect on S6rp and 4E-BP1 phosphorylation. In turn, MEK inhibitors U0126 and PD98059 and siRNA-mediated depletion of either ERK1 or ERK2 inhibited S6rp phosphorylation much more effectively. Finally, the mTOR inhibitor rapamycin markedly decreased proliferation and increased the apoptotic rate of ALK+TCL cells. These findings identify mTOR as a novel key target of NPM/ALK and suggest that mTOR inhibitors may prove effective in therapy of ALK-induced malignancies.
 ...
PMID:Oncogenic tyrosine kinase NPM/ALK induces activation of the rapamycin-sensitive mTOR signaling pathway. 1841 91

Converging signals from the mammalian target of rapamycin (mTOR) and phosphoinositide 3-kinase (PI3K) pathways are well established to modulate translation initiation. Less is known regarding the molecular basis of protein synthesis regulated by other inputs, such as agonists of the Ras/extracellular signal-regulated kinase (ERK) signaling cascade. Ribosomal protein (rp) S6 is a component of the 40S ribosomal subunit that becomes phosphorylated at several serine residues upon mitogen stimulation, but the exact molecular mechanisms regulating its phosphorylation and the function of phosphorylated rpS6 is poorly understood. Here, we provide evidence that activation of the p90 ribosomal S6 kinases (RSKs) by serum, growth factors, tumor promoting phorbol esters, and oncogenic Ras is required for rpS6 phosphorylation downstream of the Ras/ERK signaling cascade. We demonstrate that while ribosomal S6 kinase 1 (S6K1) phosphorylates rpS6 at all sites, RSK exclusively phosphorylates rpS6 at Ser(235/236) in vitro and in vivo using an mTOR-independent mechanism. Mutation of rpS6 at Ser(235/236) reveals that phosphorylation of these sites promotes its recruitment to the 7-methylguanosine cap complex, suggesting that Ras/ERK signaling regulates assembly of the translation preinitiation complex. These data demonstrate that RSK provides an mTOR-independent pathway linking the Ras/ERK signaling cascade to the translational machinery.
 ...
PMID:RAS/ERK signaling promotes site-specific ribosomal protein S6 phosphorylation via RSK and stimulates cap-dependent translation. 1736 Jul 4

Ornithine decarboxylase (ODC) is the first and generally rate-limiting enzyme in polyamine biosynthesis. Deregulation of ODC is critical for oncogenic growth, and ODC is a target of Ras. These experiments examine translational regulation of ODC in RIE-1 cells, comparing untransformed cells with those transformed by an activated Ras12V mutant. Analysis of the ODC 5' untranslated region (5'UTR) revealed four splice variants with the presence or absence of two intronic sequences. All four 5'UTR species were found in both cell lines; however, variants containing intronic sequences were more abundant in Ras-transformed cells. All splice variants support internal ribosome entry site (IRES)-mediated translation, and IRES activity is markedly elevated in cells transformed by Ras. Inhibition of Ras effector targets indicated that the ODC IRES element is regulated by the phosphorylation status of the translation factor eIF4E. Dephosphorylation of eIF4E by inhibition of mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase (MEK) or the eIF4E kinase Mnk1/2 increases ODC IRES activity in both cell lines. When both the Raf/MEK/ERK and phosphatidylinositol 3-kinase/mammalian target of rapamycin pathways are inhibited in normal cells, ODC IRES activity is very low and cells arrest in G(1). When these pathways are inhibited in Ras-transformed cells, cell cycle arrest does not occur and ODC IRES activity increases, helping to maintain high ODC activity.
 ...
PMID:Ras transformation of RIE-1 cells activates cap-independent translation of ornithine decarboxylase: regulation by the Raf/MEK/ERK and phosphatidylinositol 3-kinase pathways. 1751 Apr 13

Lung cancer is the leading cause of cancer-related mortality in the world, with more than 1 million deaths per year. Over the past years, lung cancer treatment has been based on cytotoxic agents and an improvement in the outcome and quality of life for patients has been observed. However, it has become clear that additional therapeutic strategies are urgently required in order to provide an improved survival benefit for patients. Two major intracellular signaling pathways, the Ras/Raf/extracellular signal-regulated kinase (Erk) and the phosphoinositide 3-kinase (PI3K)/Akt pathways have been extensively studied in neoplasia, including lung cancer. Furthermore, the study of constitutively activated receptor tyrosine kinases (RTKs) and their downstream signaling mediators has opened a promising new field of investigation for lung cancer treatment. Since both the Ras/Raf/Erk and the PI3K/Akt pathways are downstream of a plethora of activated RTKs, they have been extensively studied for the development of novel anti-tumor agents. Moreover, the mammalian target of rapamycin (mTOR) has been identified as a downstream target of the PI3K/Akt pathway. Rapamycin and its derivatives are highly selective and very potent inhibitors of mTOR and initial pre-clinical and clinical studies have reported encouraging results for different tumor types. Nevertheless for lung cancer, this approach has not been successful yet. Here we will review the molecular basis of PI3K/Akt/mTOR signaling in lung cancer and further discuss the therapeutic potential of multi-targeted strategies involving mTOR inhibitors.
 ...
PMID:Targeting mTOR signaling in lung cancer. 1754 May 77

Fibroblast growth factor-2 (FGF-2) has been shown to induce both angiogenesis and lymphangiogenesis in the mouse corneum; however, the signalling mechanism underlying FGF-2-induced lymphangiogenesis remains unknown. Here we investigated the effect of FGF-2 on newly developed temperature-sensitive rat lymphatic endothelial (TR-LE) cells. The supernatant of PC-3 prostate cancer cells facilitated tube-like formation in TR-LE cells, and formation was inhibited by neutralising antibodies against FGF-2. The addition of FGF-2 stimulated tube-like formation as well as proliferation and chemotactic migration of TR-LE cells. Blockade of the Akt signalling pathway by LY294002 abolished the elongation of tubes induced by FGF-2, whereas inhibition of the extracellular signal-regulated kinase (ERK) signalling pathway had no effect. Rapamycin abrogated the phosphorylation of p70S6kinase and consistently inhibited the formation of tubes induced by FGF-2. Furthermore, tube-like formation induced by the supernatant of PC-3 cells was inhibited by LY294002 or rapamycin. These data suggest that FGF-2 exerts lymphangiogenic effects by activating the Akt/mammalian target of rapamycin (mTOR)/p70S6kinase pathway in lymphatic endothelial cells, and that the pathway provides a potent target for tumour lymphangiogenesis.
 ...
PMID:Tumour-derived fibroblast growth factor-2 exerts lymphangiogenic effects through Akt/mTOR/p70S6kinase pathway in rat lymphatic endothelial cells. 1757 Jun 54

The mechanisms by which tobacco promotes lung cancer remain incompletely understood. Herein, we report that nicotine, a major component of tobacco, promotes the proliferation of cultured non-small cell lung carcinoma (NSCLC) cells; this effect was most noticeable at 5 days. However, nicotine had no effect on apoptosis of NSCLC cells. In experiments designed to unveil the mechanisms for this effect, we found that nicotine also stimulated mRNA and protein expression of fibronectin. Fibronectin is a matrix glycoprotein that regulates important cellular processes (e.g., adhesion, proliferation, and differentiation) and is highly expressed in tobacco-related lung disorders. Of note, reagents against the integrin alpha5beta1 (antibodies, RGD peptides, alpha5 shRNA) blocked the mitogenic effects of nicotine. Thus, nicotine stimulated NSCLC cell proliferation indirectly via fibronectin induction. We then focused on the mechanisms responsible for nicotine-induced fibronectin expression in NSCLC cells and found that nicotine stimulated the surface expression of alpha7 nicotinic acetylcholine receptor (alpha7 nAChR), and that alpha-bungarotoxin, an inhibitor of alpha7 nAChR, abolished the nicotine-induced fibronectin response. The fibronectin-inducing effects of nicotine were associated with activation of extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3-K)/mammalian target of rapamycin (mTOR) signaling pathways, and were abrogated by inhibitors of ERK (PD98059), PI3-K (LY294002), and mTOR (rapamycin), but not by inhibitors of protein kinase (PK)C (calphostin C) and PKA (H89). These observations suggest that nicotine stimulates NSCLC proliferation through induction of fibronectin, and that these events are mediated through nAChR-mediated signals that include ERK and PI3-K/mTOR pathways. This work highlights the role of fibronectin and alpha5beta1 integrins as potential targets for anti-lung cancer therapies.
 ...
PMID:Nicotine stimulates human lung cancer cell growth by inducing fibronectin expression. 1760 Mar 15

The multidrug resistance gene 1 (MDR1) product, P-glycoprotein (P-gp), pumps out a variety of anticancer agents from the cell, including anthracyclines, Vinca alkaloids, and taxanes. The expression of P-gp therefore confers resistance to these anticancer agents. In our present study, we found that FTI-277 (a farnesyltransferase inhibitor), U0126 [an inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)], and 17-allylamino-17-demethoxygeldanamycin (an inhibitor of heat shock protein 90) reduced the endogenous expression levels of P-gp in the human colorectal cancer cells, HCT-15 and SW620-14. In contrast, inhibitors of phosphatidylinositol 3-OH kinase, mammalian target of rapamycin, p38 mitogen-activated protein kinase, and c-Jun NH(2)-terminal kinase did not affect P-gp expression in these cells. We further found that U0126 down-regulated exogenous P-gp expression in the MDR1-transduced human breast cancer cells, MCF-7/MDR and MDA-MB-231/MDR. However, the MDR1 mRNA levels in these cells were unaffected by this treatment. PD98059 (a MEK inhibitor), ERK small interfering RNA, and p90 ribosomal S6 kinase (RSK) small interfering RNA also suppressed P-gp expression. Conversely, epidermal growth factor and basic fibroblast growth factor enhanced P-gp expression, but the MDR1 mRNA levels were unchanged in epidermal growth factor-stimulated cells. Pulse-chase analysis revealed that U0126 promoted P-gp degradation but did not affect the biosynthesis of this gene product. The pretreatment of cells with U0126 enhanced the paclitaxel-induced cleavage of poly(ADP-ribose) polymerase and paclitaxel sensitivity. Furthermore, U0126-treated cells showed high levels of rhodamine123 uptake. Hence, our present data show that inhibition of the MEK-ERK-RSK pathway down-regulates P-gp expression levels and diminishes the cellular multidrug resistance.
 ...
PMID:Inhibition of the mitogen-activated protein kinase pathway results in the down-regulation of P-glycoprotein. 1762 Apr 38

Tuberous sclerosis (TS) is an autosomal dominant disease associated with the formation of usually benign tumors or hamartomas. The disease is connected with upregulation of mammalian target of rapamycin, central regulator of protein translation, which is usually regarded to be activated by Akt kinase. Here, we show for the first time that in all four brain lesions and one angiomyolipoma from TS patients both extracellular signal-regulated kinase (Erk) and p90 ribosomal S6 kinase 1 activation as well as Erk-dependent phosphorylation of p70 ribosomal S6 kinase 1 are markedly elevated whereas Akt, participating in the classical pathway of mammalian target of rapamycin activation is not always activated. Erk activation is also present in TS-derived cell lines. Importantly, Erk inhibition leads to the decrease of proliferation potential of such lines. These results show that Erk is specifically implicated in the pathogenesis of hamartomas.
 ...
PMID:Brain tumor formation in tuberous sclerosis depends on Erk activation. 1762 32

The role of adenosine monophosphate activated protein kinase (AMPK) in regulating multiple myeloma (MM) cell growth is not yet clear. In this study, we show that the AMPK activators 5-aminoimidazole-4-carboxamide riboside (AICAr) and D942 inhibit cell growth in MM cell lines. AICAr also induced an S-phase cell cycle arrest in all four tested cell lines and led to phosphorylation and thus activation of AMPK. Furthermore, the inhibition of a nucleoside transporter by nitrobenzyl-thio-9-beta-d-ribofuranosylpurine (NBTI), inhibition of the adenosine kinase by iodotubericidine and inhibition of AMPK by AMPKI Compound C reversed AICAr effects, indicating that the cellular effects of AICAr were mediated by AMPK. Activation of AMPK inhibited basal extracellular signal-regulated kinase (ERK), mammalian target of rapamycin (mTOR) and P70S6 kinase (P70S6K) as well as AKT phosphorylation, and blocked IL-6, IGF-1, and HS-5 stromal cell conditioned medium-induced increase of cell growth. Troglitazone, which has previously been shown to activate AMPK, similarly inhibited MM cell growth, activated AMPK, and decreased ERK and P70S6K phosphorylation. Our results suggest that activation of AMPK inhibits MM cell growth despite stimulation with IL-6, IGF-1, or HS-5 stromal cell conditioned medium and represents a potential new target in the therapy of MM.
 ...
PMID:Activation of adenosine monophosphate activated protein kinase inhibits growth of multiple myeloma cells. 1766 98

Interferon (IFN)alpha induces apoptosis via Bak and Bax and the mitochondrial pathway. Here, we investigated the role of known IFNalpha-induced signaling cascades upstream of Bak activation. By pharmacological and genetic inhibition of the kinases protein kinase C (PKC)delta, extracellular signal-regulated kinase (ERK), and c-Jun NH(2)-terminal kinase (JNK) in U266-1984 and RHEK-1 cells, we could demonstrate that all three enzymes are critical for the apoptosis-associated mitochondrial events and apoptotic cell death induced by IFNalpha, at a step downstream of phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR). Furthermore, the activation of JNK was found to occur in a PKCdelta/ERK-dependent manner. Inhibition of these kinases did not affect the canonical IFNalpha-stimulated Janus tyrosine kinase-signal transducer and activator of transcription signaling or expression of IFN-responsive genes. Therefore, enucleated cells (cytoplasts) were examined for IFNalpha-induced apoptosis, to test directly whether this process depends on gene transcription. Cytoplasts were found to undergo apoptosis after IFNalpha treatment, as analyzed by several apoptosis markers by using flow cytometry, live cell imaging, and biochemical analysis of flow-sorted cytoplasts. Furthermore, inhibition of mTOR, ERK, and JNK blocked IFNalpha-induced apoptosis in cytoplasts. In conclusion, IFNalpha-induced apoptosis requires activation of ERK1/2, PKCdelta, and JNK downstream of PI3K and mTOR, and it can occur in a nucleus-independent manner, thus demonstrating for the first time that IFNalpha induces apoptosis in the absence of de novo transcription.
 ...
PMID:Interferon alpha induces nucleus-independent apoptosis by activating extracellular signal-regulated kinase 1/2 and c-Jun NH2-terminal kinase downstream of phosphatidylinositol 3-kinase and mammalian target of rapamycin. 1794 3


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>