651
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Meikle L, Talos DM, Onda H, Pollizzi K, Rotenberg A, Sahin M, Jensen FE, Kwiatkowski DJ. A mouse model of tuberous sclerosis: neuronal loss of Tsc1 causes dysplastic and ectopic neurons, reduced myelination, seizure activity, and limited survival. J Neurosci 2007; 27:5546-58. [PMID: 17522300 PMCID: PMC6672762 DOI: 10.1523/jneurosci.5540-06.2007] [Citation(s) in RCA: 339] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Tuberous sclerosis (TSC) is a hamartoma syndrome caused by mutations in TSC1 or TSC2 in which cerebral cortical tubers and seizures are major clinical issues. We have engineered mice in which most cortical neurons lose Tsc1 expression during embryonic development. These Tsc1 mutant mice display several neurological abnormalities beginning at postnatal day 5 with subsequent failure to thrive and median survival of 35 d. The mice also display clinical and electrographic seizures both spontaneously and with physical stimulation, and some seizures end in a fatal tonic phase. Many cortical and hippocampal neurons are enlarged and/or dysplastic in the Tsc1 mutant mice, strongly express phospho-S6, and are ectopic in multiple sites in the cortex and hippocampus. There is a striking delay in myelination in the mutant mice, which appears to be caused by an inductive neuronal defect. This new TSC brain model replicates several features of human TSC brain lesions and implicates an important function of Tsc1/Tsc2 in neuronal development.
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Affiliation(s)
- Lynsey Meikle
- Division of Translational Medicine, Department of Medicine, Brigham and Women's Hospital and
| | - Delia M. Talos
- Department of Neurology, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - Hiroaki Onda
- Division of Translational Medicine, Department of Medicine, Brigham and Women's Hospital and
| | - Kristen Pollizzi
- Division of Translational Medicine, Department of Medicine, Brigham and Women's Hospital and
| | - Alexander Rotenberg
- Department of Neurology, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - Mustafa Sahin
- Department of Neurology, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - Frances E. Jensen
- Department of Neurology, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - David J. Kwiatkowski
- Division of Translational Medicine, Department of Medicine, Brigham and Women's Hospital and
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652
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Krymskaya VP. Targeting the phosphatidylinositol 3-kinase pathway in airway smooth muscle: rationale and promise. BioDrugs 2007; 21:85-95. [PMID: 17402792 DOI: 10.2165/00063030-200721020-00003] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The phosphatidylinositol 3-kinase (PI3K) signaling pathway plays a critical role in regulating cell growth, proliferation, survival, and motility. Structural alterations, e.g. airway remodeling, in asthma and chronic obstructive pulmonary disease (COPD) are associated with increased airway smooth muscle (ASM) cell growth and proliferation due to the frequent stimulation of ASM by inflammatory mediators, contractile agonists, and growth factors. The critical role of the PI3K signaling pathway in regulating ASM cell growth and proliferation is well established. However, recent discovery of the tumor suppressor proteins tuberous sclerosis complex 1 (TSC1) and TSC2, also known as hamartin and tuberin, as downstream effectors of PI3K and upstream regulators of the mammalian target of rapamycin (mTOR) and S6 kinase 1(S6K1) shed a new light on the PI3K signaling cascade in regulating cell growth and proliferation. The activity of TSC1/TSC2 is regulated by growth factors, nutrients, and energy; thus, TSC1/TSC2 serves as a signaling module for protein translational regulation, cell cycle progression, and cell size, which are key events controlling cell growth and proliferation. This article highlights the potential contribution of the PI3K-TSC1/TSC2-mTOR/S6K1 pathway in smooth muscle remodeling. Pharmacologic manipulation of this signaling pathway could have a major impact on treatment of asthma and COPD.
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Affiliation(s)
- Vera P Krymskaya
- Pulmonary, Allergy and Critical Care Division, Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104-3403, USA.
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653
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Zhang Y, Guo K, LeBlanc RE, Loh D, Schwartz GJ, Yu YH. Increasing dietary leucine intake reduces diet-induced obesity and improves glucose and cholesterol metabolism in mice via multimechanisms. Diabetes 2007; 56:1647-54. [PMID: 17360978 DOI: 10.2337/db07-0123] [Citation(s) in RCA: 400] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Leucine, as an essential amino acid and activator of mTOR (mammalian target of rapamycin), promotes protein synthesis and suppresses protein catabolism. However, the effect of leucine on overall glucose and energy metabolism remains unclear, and whether leucine has beneficial effects as a long-term dietary supplement has not been examined. In the present study, we doubled dietary leucine intake via leucine-containing drinking water in mice with free excess to either a rodent chow or a high-fat diet (HFD). While it produced no major metabolic effects in chow-fed mice, increasing leucine intake resulted in up to 32% reduction of weight gain (P < 0.05) and a 25% decrease in adiposity (P < 0.01) in HFD-fed mice. The reduction of adiposity resulted from increased resting energy expenditure associated with increased expression of uncoupling protein 3 in brown and white adipose tissues and in skeletal muscle, while food intake was not decreased. Increasing leucine intake also prevented HFD-induced hyperglycemia, which was associated with improved insulin sensitivity, decreased plasma concentrations of glucagon and glucogenic amino acids, and downregulation of hepatic glucose-6-phosphatase. Additionally, plasma levels of total and LDL cholesterol were decreased by 27% (P < 0.001) and 53% (P < 0.001), respectively, in leucine supplemented HFD-fed mice compared with the control mice fed the same diet. The reduction in cholesterol levels was largely independent of leucine-induced changes in adiposity. In conclusion, increases in dietary leucine intake substantially decrease diet-induced obesity, hyperglycemia, and hypercholesterolemia in mice with ad libitum consumption of HFD likely via multiple mechanisms.
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Affiliation(s)
- Yiying Zhang
- Department of Pediatrics, Division of Molecular Genetics, Columbia University, New York, NY 10032, USA.
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654
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Kenerson H, Folpe AL, Takayama TK, Yeung RS. Activation of the mTOR pathway in sporadic angiomyolipomas and other perivascular epithelioid cell neoplasms. Hum Pathol 2007; 38:1361-71. [PMID: 17521703 PMCID: PMC2722219 DOI: 10.1016/j.humpath.2007.01.028] [Citation(s) in RCA: 157] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2006] [Revised: 01/29/2007] [Accepted: 01/30/2007] [Indexed: 02/07/2023]
Abstract
Angiomyolipoma (AML) belong to a family of tumors known as perivascular epithelioid cell tumors (PEComas) that share a common immunophenotypic profile of muscle and melanocytic differentiation. These tumors are clonal in nature and have a strong association with tuberous sclerosis. Genetic analyses have reported allelic imbalance at the TSC2 locus on 16p13. In the context of non-tuberous sclerosis complex (TSC), non-lymphangioleiomyomatosis-associated AMLs, and non-renal PEComas, the functional status of the TSC2 signaling pathway has not been reported. Studies over the last several years have uncovered a critical role of the TSC1/2 genes in negatively regulating the Rheb/mTOR/p70S6K cascade. Here, we examined the activity of this pathway in sporadic AMLs and PEComas using immunohistochemical and biochemical analyses. We found increased levels of phospho-p70S6K, a marker of mTOR activity, in 15 of 15 non-TSC AMLs. This was accompanied by reduced phospho-AKT expression, a pattern that is consistent with the disruption of TSC1/2 function. Western blot analysis confirmed mTOR activation concurrent with the loss of TSC2 and not TSC1 in sporadic AMLs. Similarly, elevated phospho-p70S6K and reduced phospho-AKT expression was detected in 14 of 15 cases of extrarenal PEComas. These observations provide the first functional evidence that mTOR activation is common to sporadic, non-TSC-related AMLs and PEComas. This suggests the possibility that mTOR inhibitors such as rapamycin may be therapeutic for this class of disease.
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Affiliation(s)
- Heidi Kenerson
- Department of Pathology, Surgery, University of Washington, Seattle, WA
| | | | | | - Raymond S. Yeung
- Department of Pathology, Surgery, University of Washington, Seattle, WA
- To whom correspondence and reprints should be addressed: Department of Surgery, Box 356410, University of Washington, 1959 NE Pacific, Seattle, WA 98195. Tel: 206-616-6405; Fax: 206-616-6406; e-mail:
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655
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Mirouse V, Swick LL, Kazgan N, St Johnston D, Brenman JE. LKB1 and AMPK maintain epithelial cell polarity under energetic stress. ACTA ACUST UNITED AC 2007; 177:387-92. [PMID: 17470638 PMCID: PMC2064817 DOI: 10.1083/jcb.200702053] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
LKB1 is mutated in both familial and spontaneous tumors, and acts as a master kinase that activates the PAR-1 polarity kinase and the adenosine 5′monophosphate–activated kinase (AMPK). This has led to the hypothesis that LKB1 acts as a tumor suppressor because it is required to maintain cell polarity and growth control through PAR-1 and AMPK, respectively. However, the genetic analysis of LKB1–AMPK signaling in vertebrates has been complicated by the existence of multiple redundant AMPK subunits. We describe the identification of mutations in the single Drosophila melanogaster AMPK catalytic subunit AMPKα. Surprisingly, ampkα mutant epithelial cells lose their polarity and overproliferate under energetic stress. LKB1 is required in vivo for AMPK activation, and lkb1 mutations cause similar energetic stress–dependent phenotypes to ampkα mutations. Furthermore, lkb1 phenotypes are rescued by a phosphomimetic version of AMPKα. Thus, LKB1 signals through AMPK to coordinate epithelial polarity and proliferation with cellular energy status, and this might underlie the tumor suppressor function of LKB1.
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Affiliation(s)
- Vincent Mirouse
- The Gurdon Institute, Department of Genetics, University of Cambridge, Cambridge, England, UK
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656
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Tzatsos A, Tsichlis PN. Energy depletion inhibits phosphatidylinositol 3-kinase/Akt signaling and induces apoptosis via AMP-activated protein kinase-dependent phosphorylation of IRS-1 at Ser-794. J Biol Chem 2007; 282:18069-18082. [PMID: 17459875 DOI: 10.1074/jbc.m610101200] [Citation(s) in RCA: 122] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Energy depletion activates AMP-activated protein kinase (AMPK) and inhibits cell growth via TSC2-dependent suppression of mTORC1 signaling. Long term energy depletion also induces apoptosis by mechanisms that are not well understood to date. Here we show that AMPK, activated by energy depletion, inhibited cell survival by binding to and phosphorylating IRS-1 at Ser-794. Phosphorylation of IRS-1 at this site inhibited phosphatidylinositol 3-kinase/Akt signaling, suppressed the mitochondrial membrane potential, and promoted apoptosis. Of the treatments promoting energy depletion, glucose deprivation, hypoxia, and inhibition of ATP synthesis in the mitochondria stimulated phosphorylation of IRS-1 at Ser-794 via an LKB1/AMPK-dependent manner, whereas oxidative stress and 2-deoxyglucose stimulated phosphorylation at this site via a Ca2+/calmodulin-dependent protein kinase kinase beta/AMPK axis. These data define a novel pathway that cooperates with other adaptive mechanisms to formulate the cellular response to energy depletion.
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Affiliation(s)
- Alexandros Tzatsos
- Molecular Oncology Research Institute, Tufts-New England Medical Center, Boston, Massachusetts 02111
| | - Philip N Tsichlis
- Molecular Oncology Research Institute, Tufts-New England Medical Center, Boston, Massachusetts 02111.
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657
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Knox S, Ge H, Dimitroff BD, Ren Y, Howe KA, Arsham AM, Easterday MC, Neufeld TP, O'Connor MB, Selleck SB. Mechanisms of TSC-mediated control of synapse assembly and axon guidance. PLoS One 2007; 2:e375. [PMID: 17440611 PMCID: PMC1847706 DOI: 10.1371/journal.pone.0000375] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2006] [Accepted: 03/19/2007] [Indexed: 01/13/2023] Open
Abstract
Tuberous sclerosis complex is a dominant genetic disorder produced by mutations in either of two tumor suppressor genes, TSC1 and TSC2; it is characterized by hamartomatous tumors, and is associated with severe neurological and behavioral disturbances. Mutations in TSC1 or TSC2 deregulate a conserved growth control pathway that includes Ras homolog enriched in brain (Rheb) and Target of Rapamycin (TOR). To understand the function of this pathway in neural development, we have examined the contributions of multiple components of this pathway in both neuromuscular junction assembly and photoreceptor axon guidance in Drosophila. Expression of Rheb in the motoneuron, but not the muscle of the larval neuromuscular junction produced synaptic overgrowth and enhanced synaptic function, while reductions in Rheb function compromised synapse development. Synapse growth produced by Rheb is insensitive to rapamycin, an inhibitor of Tor complex 1, and requires wishful thinking, a bone morphogenetic protein receptor critical for functional synapse expansion. In the visual system, loss of Tsc1 in the developing retina disrupted axon guidance independently of cellular growth. Inhibiting Tor complex 1 with rapamycin or eliminating the Tor complex 1 effector, S6 kinase (S6k), did not rescue axon guidance abnormalities of Tsc1 mosaics, while reductions in Tor function suppressed those phenotypes. These findings show that Tsc-mediated control of axon guidance and synapse assembly occurs via growth-independent signaling mechanisms, and suggest that Tor complex 2, a regulator of actin organization, is critical in these aspects of neuronal development.
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Affiliation(s)
- Sarah Knox
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Hong Ge
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Brian D. Dimitroff
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Yi Ren
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Katie A. Howe
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Andrew M. Arsham
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Mathew C. Easterday
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Thomas P. Neufeld
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Michael B. O'Connor
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Scott B. Selleck
- The Developmental Biology Center, Department of Pediatrics, The University of Minnesota, Minneapolis, Minnesota, United States of America
- The Developmental Biology Center, Department of Genetics, Cell Biology and Development, The University of Minnesota, Minneapolis, Minnesota, United States of America
- * To whom correspondence should be addressed. E-mail:
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658
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Gery S, Park DJ, Vuong PT, Virk RK, Muller CI, Hofmann WK, Koeffler HP. RTP801 is a novel retinoic acid–responsive gene associated with myeloid differentiation. Exp Hematol 2007; 35:572-8. [PMID: 17379067 PMCID: PMC1922386 DOI: 10.1016/j.exphem.2007.01.049] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2006] [Revised: 01/20/2007] [Accepted: 01/22/2007] [Indexed: 10/23/2022]
Abstract
OBJECTIVE Retinoids are crucial in the regulation of fundamental cellular processes including terminal differentiation of both normal and malignant myeloid progenitors. The aim of this study was to identify and characterize retinoic acid (RA) target genes. METHODS AND RESULTS RTP801 is a recently cloned stress response gene that acts as a negative regulator of the mTOR pathway. Here we identified RTP801 as a novel early RA target gene in myeloid cells. RTP801 mRNA levels are induced in acute myeloid leukemia (AML) cell lines during RA-dependent differentiation and are differentially expressed during maturation of normal CD34(+) cells. The myeloid-specific, differentiation-related transcription factor C/EBPepsilon also induces RTP801 expression. Overexpression of RTP801 in the U937 leukemic cells leads to growth inhibition and apoptosis. Conversely, silencing of endogenous RTP801 by shRNA reduces RA-induced differentiation of the U937 cells. Downregulation of RTP801 also abrogates hypoxia-induced inhibition of mTOR in those cells. CONCLUSION Taken together, our data suggest that RTP801 is an important RA-regulated gene involved in myeloid differentiation, which could represent a therapeutic target in leukemia.
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Affiliation(s)
- Sigal Gery
- Division of Hematology/Oncology, UCLA School of Medicine, Cedars-Sinai Medical Center, 8700 Beverly Boulevard, Los Angeles, CA 90048, USA.
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659
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Abstract
Phosphatase and tensin homolog (Pten) phosphatase opposes intracellular phosphoinositide 3-kinase (PI3K)/Akt signaling and is a potent tumor suppressor, while Golgi beta1,6 N-acetylglucosaminyltransferase V (Mgat5) is positively associated with cancer progression and metastasis. beta1,6GlcNAc-branched N-glycans on receptor glycoproteins promote their surface residency and sensitizes cells to growth factor signaling. Here we demonstrate that the Pten heterozygosity in mouse embryonic fibroblasts enhances cell adhesion-dependent PI3K/Akt signaling, cell spreading, and proliferation, while Pten/Mgat5 double mutant cells are normalized. However, planar asymmetry typical of fibroblasts and invasive carcinomas is not fully rescued, suggesting that Mgat5 and Pten function together to regulate the membrane dynamics of PI3K/Akt signaling typical of motile cells. Pten heterozygosity was associated with increased surface beta1,6GlcNAc-branched N-glycans, suggesting positive feedback from PI3K signaling to N-glycan branching. In vivo, Mgat5(-/-) Pten(+/-) and Mgat5(+/-)Pten(+/-)mutant mice showed a small but significant increase in longevity compared with Pten(+/-) mice. Taken together, our results reveal that Mgat5 and Pten interact in an opposing manner to regulate cellular sensitivities to extracelluar growth cues.
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Affiliation(s)
- Pam Cheung
- Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Avenue, R988 Toronto, Ontario, Canada M5G 1X5
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660
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Proud CG. Signalling to translation: how signal transduction pathways control the protein synthetic machinery. Biochem J 2007; 403:217-34. [PMID: 17376031 DOI: 10.1042/bj20070024] [Citation(s) in RCA: 380] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Recent advances in our understanding of both the regulation of components of the translational machinery and the upstream signalling pathways that modulate them have provided important new insights into the mechanisms by which hormones, growth factors, nutrients and cellular energy status control protein synthesis in mammalian cells. The importance of proper control of mRNA translation is strikingly illustrated by the fact that defects in this process or its control are implicated in a number of disease states, such as cancer, tissue hypertrophy and neurodegeneration. Signalling pathways such as those involving mTOR (mammalian target of rapamycin) and mitogen-activated protein kinases modulate the phosphorylation of translation factors, the activities of the protein kinases that act upon them and the association of RNA-binding proteins with specific mRNAs. These effects contribute both to the overall control of protein synthesis (which is linked to cell growth) and to the modulation of the translation or stability of specific mRNAs. However, important questions remain about both the contributions of individual regulatory events to the control of general protein synthesis and the mechanisms by which the translation of specific mRNAs is controlled.
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Affiliation(s)
- Christopher G Proud
- Department of Biochemistry and Molecular Biology, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, Canada V6T 1Z3.
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661
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Abstract
Tuberous sclerosis complex (TSC) is a congenital syndrome characterized by the widespread development of benign tumors in multiple organs, caused by mutations in one of the tumor suppressor genes, TSC1 or TSC2. About 80% of affected patients have a new mutation, and the remaining 20% have inherited a TSC gene mutation from a parent. The disorder affects approximately 1 in 6000 individuals. Cortical tubers are the neuropathological hallmark of TSC. The most common neurological manifestations of TSC are epilepsy, mental retardation, and autistic behavior. Epilepsy occurs in up to 80-90% of patients and is often intractable, with a poor response to anticonvulsant medications. While the molecular basis of TSC is well established, far less is known about the mechanisms of epilepsy in this disorder. In this article, we first summarize known clinical aspects of TSC with emphasis on its neurological features. Then, based on the molecular, pathological, immunohistochemical, neurochemical, and physiological properties of tubers in patients with TSC and in animal models, we discuss possible mechanisms of seizures and epileptogenesis in TSC. Finally, we provide an updated literature review and a consensus statement from the Tuberous Sclerosis Complex Working Group for future research into the mechanisms of epilepsy in TSC.
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Affiliation(s)
- Gregory L Holmes
- Neuroscience Center at Dartmouth, Section of Neurology, Dartmouth Medical School, Hanover, New Hampshire, USA.
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662
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Moerke NJ, Aktas H, Chen H, Cantel S, Reibarkh MY, Fahmy A, Gross JD, Degterev A, Yuan J, Chorev M, Halperin JA, Wagner G. Small-molecule inhibition of the interaction between the translation initiation factors eIF4E and eIF4G. Cell 2007; 128:257-67. [PMID: 17254965 DOI: 10.1016/j.cell.2006.11.046] [Citation(s) in RCA: 424] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2006] [Revised: 09/15/2006] [Accepted: 11/23/2006] [Indexed: 12/21/2022]
Abstract
Assembly of the eIF4E/eIF4G complex has a central role in the regulation of gene expression at the level of translation initiation. This complex is regulated by the 4E-BPs, which compete with eIF4G for binding to eIF4E and which have tumor-suppressor activity. To pharmacologically mimic 4E-BP function we developed a high-throughput screening assay for identifying small-molecule inhibitors of the eIF4E/eIF4G interaction. The most potent compound identified, 4EGI-1, binds eIF4E, disrupts eIF4E/eIF4G association, and inhibits cap-dependent translation but not initiation factor-independent translation. While 4EGI-1 displaces eIF4G from eIF4E, it effectively enhances 4E-BP1 association both in vitro and in cells. 4EGI-1 inhibits cellular expression of oncogenic proteins encoded by weak mRNAs, exhibits activity against multiple cancer cell lines, and appears to have a preferential effect on transformed versus nontransformed cells. The identification of this compound provides a new tool for studying translational control and establishes a possible new strategy for cancer therapy.
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MESH Headings
- Animals
- Antineoplastic Agents/chemistry
- Antineoplastic Agents/isolation & purification
- Antineoplastic Agents/pharmacology
- Cell Line, Transformed
- Cell Line, Tumor
- Cell Transformation, Neoplastic/drug effects
- Cell Transformation, Neoplastic/genetics
- Cell Transformation, Neoplastic/metabolism
- Drug Evaluation, Preclinical/methods
- Eukaryotic Initiation Factor-4E/drug effects
- Eukaryotic Initiation Factor-4E/genetics
- Eukaryotic Initiation Factor-4E/metabolism
- Eukaryotic Initiation Factor-4G/drug effects
- Eukaryotic Initiation Factor-4G/genetics
- Eukaryotic Initiation Factor-4G/metabolism
- Feedback, Physiological/drug effects
- Feedback, Physiological/physiology
- Fluorescence Polarization Immunoassay/methods
- Gene Expression Regulation, Neoplastic/drug effects
- Gene Expression Regulation, Neoplastic/genetics
- Humans
- Hydrazones
- Jurkat Cells
- Mice
- Models, Molecular
- Nitro Compounds/chemistry
- Nitro Compounds/isolation & purification
- Nitro Compounds/pharmacology
- Oncogenes/drug effects
- Oncogenes/genetics
- Peptide Fragments/genetics
- Peptide Fragments/metabolism
- Peptide Fragments/pharmacology
- Protein Binding/drug effects
- Protein Binding/genetics
- Protein Biosynthesis/drug effects
- Protein Biosynthesis/genetics
- RNA, Messenger/drug effects
- RNA, Messenger/genetics
- Thiazoles/chemistry
- Thiazoles/isolation & purification
- Thiazoles/pharmacology
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Affiliation(s)
- Nathan J Moerke
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
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663
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Komatsu M, Ueno T, Waguri S, Uchiyama Y, Kominami E, Tanaka K. Constitutive autophagy: vital role in clearance of unfavorable proteins in neurons. Cell Death Differ 2007; 14:887-94. [PMID: 17332773 DOI: 10.1038/sj.cdd.4402120] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Investigations pursued during the last decade on neurodegenerative diseases have revealed a common mechanism underlying the development of such diseases: conformational disorder of certain proteins leads to the formation of misfolded protein oligomers, which subsequently develop into large protein aggregates. These aggregates entangle other denatured proteins and lipids to form disease-specific inclusion bodies. The failure of the ubiquitin-proteasome system to shred the protein aggregates has led investigators to focus their attention to autophagy, a bulk degradative system coupled with lysosomes, which is involved in non-selective shredding of large amounts of cytoplasmic components. Research in this field has demonstrated the accumulation of autophagic vacuoles and intracytoplasmic protein aggregates in patients with various neurodegenerative diseases. Although autophagy fails to degrade large protein aggregates once they are formed in the cytoplasm, drug-induced activation of autophagy is effective in preventing aggregate deposition, indicating that autophagy significantly contributes to the clearance of aggregate-prone proteins. The pivotal role of autophagy in the clearance of aggregate-prone proteins has been confirmed by a deductive approach using a brain-specific autophagy-ablated mouse model. In this review, we discuss the consequences of autophagy deficiency in neurons.
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Affiliation(s)
- M Komatsu
- Department of Biochemistry, Juntendo University School of Medicine, Tokyo, Japan
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664
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Abstract
Steady laminar flow in the straight parts of the arterial tree is atheroprotective, whereas disturbed flow with oscillation in branch points and the aortic root are athero-prone, in part, because of the distinct roles of the flow patterns in regulating the cell cycle of vascular endothelial cells (ECs). To elucidate the molecular basis underlying the endothelial cell cycle regulated by distinct flow patterns, we conducted flow-channel experiments to investigate the effects of laminar versus oscillatory flows on activation of AMP-activated protein kinase (AMPK) and Akt in ECs. Laminar flow caused a transient activation of both AMPK and Akt, but oscillatory flow activated only Akt, with AMPK being maintained at its basal level. Constitutively active and dominant-negative mutants of AMPK and Akt were used to elucidate further the positive effect of Akt and negative role of AMPK in mediating mTOR (mammalian target of rapamycin) and its target p70S6 kinase (S6K) in response to laminar and oscillatory flows. Measurements of phosphorylation of mTOR Ser2448 and S6K Thr389 showed that AMPK, by counteracting Akt under laminar flow, resulted in a transient activation of S6K. Under oscillatory flow, because of the lack of AMPK activation to effect negative regulation, S6K was activated in a sustained manner. As a functional consequence, AMPK activation attenuated cell cycle progression in response to both laminar and oscillatory flows. In contrast, AMPK inhibition promoted EC cycle progression by decreasing the cell population in the G(0)/G(1) phase and increasing it in the S+G(2)/M phase. In vivo, phosphorylation of the promitotic S6K in mouse thoracic aorta was much less than that in mouse aortic root. In contrast, AMPK phosphorylation was higher in the thoracic aorta. These results provide a molecular mechanism by which laminar versus oscillatory flow regulates the endothelial cell cycle.
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Affiliation(s)
- Deliang Guo
- Division of Biomedical Sciences, University of California, Riverside, CA 92521-0121, USA
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665
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Moumen A, Patané S, Porras A, Dono R, Maina F. Met acts on Mdm2 via mTOR to signal cell survival during development. Development 2007; 134:1443-51. [PMID: 17329361 DOI: 10.1242/dev.02820] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Coordination of cell death and survival is crucial during embryogenesis and adulthood, and alteration of this balance can result in degeneration or cancer. Growth factor receptors such as Met can activate phosphatidyl-inositol-3' kinase (PI3K), a major intracellular mediator of growth and survival. PI3K can then antagonize p53-triggered cell death, but the underlying mechanisms are not fully understood. We used genetic and pharmacological approaches to uncover Met-triggered signaling pathways that regulate hepatocyte survival during embryogenesis. Here, we show that PI3K acts via mTOR (Frap1) to regulate p53 activity both in vitro and in vivo. mTOR inhibits p53 by promoting the translation of Mdm2, a negative regulator of p53. We also demonstrate that the PI3K effector Akt is required for Met-triggered Mdm2 upregulation, in addition to being necessary for the nuclear translocation of Mdm2. Inhibition of either mTOR or Mdm2 is sufficient to block cell survival induced by Hgf-Met in vitro. Moreover, in vivo inhibition of mTOR downregulates Mdm2 protein levels and induces p53-dependent apoptosis. Our studies identify a novel mechanism for Met-triggered cell survival during embryogenesis, involving translational regulation of Mdm2 by mTOR. Moreover, they reinforce mTOR as a potential drug target in cancer.
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Affiliation(s)
- Anice Moumen
- Developmental Biology Institute of Marseille-Luminy (IBDML CNRS-INSERM-Université de la Méditerrannée, Campus de Luminy-Case 907, 13288 Marseille Cedex 09, France
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666
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Urano J, Sato T, Matsuo T, Otsubo Y, Yamamoto M, Tamanoi F. Point mutations in TOR confer Rheb-independent growth in fission yeast and nutrient-independent mammalian TOR signaling in mammalian cells. Proc Natl Acad Sci U S A 2007; 104:3514-9. [PMID: 17360675 PMCID: PMC1805553 DOI: 10.1073/pnas.0608510104] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2006] [Indexed: 12/19/2022] Open
Abstract
Rheb is a unique member of the Ras superfamily GTP-binding proteins. We as well as others previously have shown that Rheb is a critical component of the TSC/TOR signaling pathway. In fission yeast, Rheb is encoded by the rhb1 gene. Rhb1p is essential for growth and directly interacts with Tor2p. In this article, we report identification of 22 single amino acid changes in the Tor2 protein that enable growth in the absence of Rhb1p. These mutants also exhibit decreased mating efficiency. Interestingly, the mutations are located in the C-terminal half of the Tor2 protein, clustering mainly within the FAT and kinase domains. We noted some differences in the effect of a mutation in the FAT domain (L1310P) and in the kinase domain (E2221K) on growth and mating. Although the Tor2p mutations bypass Rhb1p's requirement for growth, they are incapable of suppressing Rhb1p's requirement for resistance to stress and toxic amino acids, pointing to multiple functions of Rhb1p. In mammalian systems, we find that mammalian target of rapamycin (mTOR) carrying analogous mutations (L1460P or E2419K), although sensitive to rapamycin, exhibits constitutive activation even when the cells are starved for nutrients. These mutations do not show significant difference in their ability to form complexes with Raptor, Rictor, or mLST8. Furthermore, we present evidence that mutant mTOR can complex with wild-type mTOR and that this heterodimer is active in nutrient-starved cells.
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Affiliation(s)
- Jun Urano
- *Department of Microbiology, Immunology, and Molecular Genetics, Jonsson Comprehensive Cancer Center, Molecular Biology Institute, University of California, Los Angeles, CA 90095; and
| | - Tatsuhiro Sato
- *Department of Microbiology, Immunology, and Molecular Genetics, Jonsson Comprehensive Cancer Center, Molecular Biology Institute, University of California, Los Angeles, CA 90095; and
| | - Tomohiko Matsuo
- Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
| | - Yoko Otsubo
- Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
| | - Masayuki Yamamoto
- Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
| | - Fuyuhiko Tamanoi
- *Department of Microbiology, Immunology, and Molecular Genetics, Jonsson Comprehensive Cancer Center, Molecular Biology Institute, University of California, Los Angeles, CA 90095; and
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667
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Visigalli R, Barilli A, Bussolati O, Sala R, Gazzola GC, Parolari A, Tremoli E, Simon A, Closs EI, Dall'Asta V. Rapamycin stimulates arginine influx through CAT2 transporters in human endothelial cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:1479-87. [PMID: 17397797 DOI: 10.1016/j.bbamem.2007.02.016] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2006] [Revised: 01/25/2007] [Accepted: 02/15/2007] [Indexed: 01/03/2023]
Abstract
In endothelial cells Tumor Necrosis Factor-alpha (TNFalpha) stimulates arginine transport through the increased expression of SLC7A2/CAT2 transcripts. Here we show that also rapamycin, an inhibitor of mTOR kinase, stimulates system y(+)-mediated arginine uptake in human endothelial cells derived from either saphenous (HSVECs) or umbilical veins (HUVECs). When used together with TNFalpha, rapamycin produces an additive stimulation of arginine transport in both cell models. These effects are observed also upon incubation with AICAR, a stimulator of Adenosine-Monophosphate-dependent-Protein Kinase (AMPK) that produces a rapamycin-independent inhibition of the mTOR pathway. Rapamycin increases the V(max) of high affinity arginine transport and causes the appearance of a low affinity component that is particularly evident if the treatment is carried out in the presence of TNFalpha. RT-qPCR studies have demonstrated that these kinetic changes correspond to the induction of both the high affinity transporter CAT2B and the low affinity isoform CAT2A. Western blot and immunocytochemical analyses indicate that, consistently, the expression of CAT2 proteins is also stimulated under the same conditions. These changes are associated with an increase of the intracellular arginine concentration but with a decrease of NO production. Thus, our data suggest that mTOR activity is associated with the repression of CAT2 expression at mRNA and protein level.
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Affiliation(s)
- Rossana Visigalli
- Department of Experimental Medicine, Unit of General and Clinical Pathology, University of Parma, via Volturno 39, 43100 Parma, Italy
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668
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Yoon P, Giafis N, Smith J, Mears H, Katsoulidis E, Sassano A, Altman J, Redig AJ, Tallman MS, Platanias LC. Activation of mammalian target of rapamycin and the p70 S6 kinase by arsenic trioxide in BCR-ABL-expressing cells. Mol Cancer Ther 2007; 5:2815-23. [PMID: 17121928 DOI: 10.1158/1535-7163.mct-06-0263] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Arsenic trioxide (As(2)O(3)) exhibits important antitumor activities in vitro and in vivo, but the precise mechanisms by which it induces its effects are not known. We provide evidence that during treatment of BCR-ABL-expressing cells with As(2)O(3), there is activation of a cellular pathway involving the p70 S6 kinase (p70S6K). Our data show that p70S6K is rapidly phosphorylated on Thr(421) and Ser(424) and is activated in an As(2)O(3)-inducible manner. The mammalian target of rapamycin (mTOR) is also phosphorylated/activated in an As(2)O(3)-inducible manner, and its activity is required for downstream engagement of p70S6K. p70S6K subsequently phosphorylates the S6 ribosomal protein on Ser(235)/Ser(236) and Ser(240)/Ser(244) to promote initiation of mRNA translation. Treatment of chronic myelogenous leukemia-derived cell lines with As(2)O(3) also results in phosphorylation of the 4E-BP1 repressor of mRNA translation on Thr(37)/Thr(46) and Thr(70), sites required for its deactivation and its dissociation from the eukaryotic initiation factor 4E complex to allow cap-dependent mRNA translation. In studies to determine the functional relevance of this pathway, we found that inhibition of mTOR and downstream cascades enhances induction of apoptosis by As(2)O(3). Consistent with this, the mTOR inhibitor rapamycin strongly potentiated As(2)O(3)-mediated suppression of primitive leukemic progenitors from the bone marrow of chronic myelogenous leukemia patients. Altogether, our data show that the mTOR/p70S6K pathway is activated in a negative feedback regulatory manner in response to As(2)O(3) in BCR-ABL-transformed cells and plays a key regulatory role in the induction of anti-leukemic responses.
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MESH Headings
- Antineoplastic Agents/pharmacology
- Arsenic Trioxide
- Arsenicals/pharmacology
- Dose-Response Relationship, Drug
- Fusion Proteins, bcr-abl
- Humans
- K562 Cells
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/drug therapy
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/metabolism
- Oxides/pharmacology
- Phosphorylation/drug effects
- Protein Kinases/metabolism
- Protein-Tyrosine Kinases/metabolism
- Ribosomal Protein S6 Kinases, 70-kDa/metabolism
- Signal Transduction/drug effects
- TOR Serine-Threonine Kinases
- Tumor Cells, Cultured
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Affiliation(s)
- Patrick Yoon
- Robert H. Lurie Comprehensive Cancer Center, 303 East Superior Street, Lurie 3-107, Chicago, IL 60611, USA
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669
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Pelletier CL, Maggi LB, Brady SN, Scheidenhelm DK, Gutmann DH, Weber JD. TSC1 sets the rate of ribosome export and protein synthesis through nucleophosmin translation. Cancer Res 2007; 67:1609-17. [PMID: 17308101 PMCID: PMC2859708 DOI: 10.1158/0008-5472.can-06-2875] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Nucleophosmin (B23) is a nucleolar phosphoprotein that has been implicated in numerous cellular processes. In particular, nucleophosmin interacts with nucleolar components of newly synthesized ribosomes to promote ribosome nuclear export. Nucleophosmin is a classic mitogen-induced protein, with changes in its expression correlating with growth factor stimulation. In this study, we examined the underlying mechanism of nucleophosmin induction and showed that hyperproliferative signals emanating from oncogenic H-Ras(V12) cause tremendous increases in nucleophosmin protein expression. Nucleophosmin protein accumulation was dependent on mammalian target of rapamycin (mTOR) activation, as rapamycin completely prevented nucleophosmin induction. Consistent with this finding, genetic ablation of Tsc1, a major upstream inhibitor of mTOR, resulted in nucleophosmin protein induction through increased translation of existing nucleophosmin mRNAs. Increases in nucleophosmin protein accumulation were suppressed by reintroduction of TSC1. Induction of nucleophosmin through Tsc1 loss resulted in a greater pool of actively translating ribosomes in the cytoplasm, higher overall rates of protein synthesis, and increased cell proliferation, all of which were dependent on efficient nucleophosmin nuclear export. Nucleophosmin protein accumulation in the absence of Tsc1 promoted the nuclear export of maturing ribosome subunits, providing a mechanistic link between TSC1/mTOR signaling, nucleophosmin-mediated nuclear export of ribosome subunits, protein synthesis levels, and cell growth.
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Affiliation(s)
- Corey L. Pelletier
- Division of Molecular Oncology, Department of Internal Medicine, Siteman Cancer Center, Washington University School of Medicine, St. Louis, Missouri
| | - Leonard B. Maggi
- Division of Molecular Oncology, Department of Internal Medicine, Siteman Cancer Center, Washington University School of Medicine, St. Louis, Missouri
| | - Suzanne N. Brady
- Division of Molecular Oncology, Department of Internal Medicine, Siteman Cancer Center, Washington University School of Medicine, St. Louis, Missouri
| | | | - David H. Gutmann
- Department of Neurology, Washington University School of Medicine, St. Louis, Missouri
| | - Jason D. Weber
- Division of Molecular Oncology, Department of Internal Medicine, Siteman Cancer Center, Washington University School of Medicine, St. Louis, Missouri
- Department of Cell Biology, Washington University School of Medicine, St. Louis, Missouri
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670
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Shindo S, Numazawa S, Yoshida T. A physiological role of AMP-activated protein kinase in phenobarbital-mediated constitutive androstane receptor activation and CYP2B induction. Biochem J 2007; 401:735-41. [PMID: 17032173 PMCID: PMC1770843 DOI: 10.1042/bj20061238] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
CAR (constitutive androstane receptor) is a nuclear receptor that regulates the transcription of target genes, including CYP (cytochrome P450) 2B and 3A. The transactivation by CAR is regulated by its subcellular localization; however, the mechanism that governs nuclear translocation has yet to be clarified. It has been reported recently that AMPK (AMP-activated protein kinase) is involved in phenobarbital-mediated CYP2B induction in a particular culture system. We therefore investigated in vivo whether AMPK is involved in the activation of CAR-dependent gene expression. Immunoblot analysis using an antibody which recognizes Thr-172-phosphorylated AMPKalpha1/2 revealed phenobarbital-induced AMPK activation in rat and mouse livers as well. Phenobarbital, however, failed to increase the liver phospho-AMPK level of tumour-bearing rats in which CAR nuclear translocation had been impaired. In in vivo reporter gene assays employing PBREM (phenobarbital-responsive enhancer module) from CYP2B1, an AMPK inhibitor 8-bromo-AMP abolished phenobarbital-induced transactivation. In addition, Cyp2b10 gene expression was attenuated by 8-bromo-AMP. Forced expression of a dominant-negative mutant and the wild-type of AMPKalpha2 in the mouse liver suppressed and further enhanced phenobarbital-induced PBREM-reporter activity respectively. Moreover, the AMPK activator AICAR (5-amino-4-imidazolecarboxamide riboside) induced PBREM transactivation and an accumulation of CAR in the nuclear fraction of the mouse liver. However, AICAR and metformin, another AMPK activator, failed to induce hepatic CYP2B in mice and rats. These observations suggest that AMPK is at least partly involved in phenobarbital-originated signalling, but the kinase activation by itself is not sufficient for CYP2B induction in vivo.
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Affiliation(s)
- Sawako Shindo
- Department of Biochemical Toxicology, School of Pharmaceutical Sciences, Showa University, 1-5-8 Hatanodai, Shinagawa, Tokyo 142-8555, Japan
| | - Satoshi Numazawa
- Department of Biochemical Toxicology, School of Pharmaceutical Sciences, Showa University, 1-5-8 Hatanodai, Shinagawa, Tokyo 142-8555, Japan
- To whom correspondence should be addressed (email )
| | - Takemi Yoshida
- Department of Biochemical Toxicology, School of Pharmaceutical Sciences, Showa University, 1-5-8 Hatanodai, Shinagawa, Tokyo 142-8555, Japan
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671
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Abstract
This review focuses on remarkable recent findings concerning the mechanism by which the LKB1 protein kinase that is mutated in Peutz-Jeghers cancer syndrome operates as a tumor suppressor. We discuss evidence that the cellular localization and activity of LKB1 is controlled through its interaction with a catalytically inactive protein resembling a protein kinase, termed STRAD, and an armadillo repeat-containing protein, named mouse protein 25 (MO25). The data suggest that LKB1 functions as a tumor suppressor by not only inhibiting proliferation, but also by exerting profound effects on cell polarity and, most unexpectedly, on the ability of a cell to detect and respond to low cellular energy levels. Genetic and biochemical findings indicate that LKB1 exerts its effects by phosphorylating and activating 14 protein kinases, all related to the AMP-activated protein kinase. The work described in this review shows how a study of an obscure cancer syndrome can uncover new and important regulatory pathways, relevant to the understanding of multiple human diseases.
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Affiliation(s)
- Dario R Alessi
- Medical Research Council, Protein Phosphorylation Unit, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland.
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672
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Patel PH, Tamanoi F. Increased Rheb-TOR signaling enhances sensitivity of the whole organism to oxidative stress. J Cell Sci 2007; 119:4285-92. [PMID: 17038544 DOI: 10.1242/jcs.03199] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The accumulation of free radical damage to an organism over its lifespan can cause premature aging and disease including cancer, atherosclerosis and neurodegenerative disorders. The well-conserved Rheb-Target-of-rapamycin (TOR)-S6-kinase (S6K) signaling pathway regulates several cellular processes and has been shown to influence lifespan and diseases such as cancer and neurodegenerative disorders. Using adult Drosophila, we describe for the first time in metazoans that TOR activity can influence the stress response. We find that mildly increasing systemic Rheb-TOR-S6K signaling sensitizes the whole organism to oxidative stress and promotes senescence of locomotor activity with age. Furthermore, we find that S6K is required for increased Rheb-TOR signaling to sensitize the whole organism to oxidative stress and promote the senescence of locomotor activity. Interestingly, we also find that increasing Rheb-TOR signaling in muscle can increase the sensitivity of adults to oxidative stress. These data imply that pathological situations that increase TOR activity might perturb the ability of the whole organism to cope with stress causing disease progression and aging.
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Affiliation(s)
- Parthive H Patel
- Molecular Biology Institute, Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, CA 90095-1489, USA
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673
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Torres-Arzayus MI, Yuan J, DellaGatta JL, Lane H, Kung AL, Brown M. Targeting the AIB1 oncogene through mammalian target of rapamycin inhibition in the mammary gland. Cancer Res 2007; 66:11381-8. [PMID: 17145884 DOI: 10.1158/0008-5472.can-06-2316] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Amplified in breast cancer 1 (AIB1), an estrogen receptor (ER) coactivator, is frequently amplified or overexpressed in human breast cancer. We previously developed a transgenic mouse model in which AIB1 can act as an oncogene, giving rise to a premalignant hyperplastic mammary phenotype as well as to a high incidence of mammary tumors that are primarily ER(+). In this model, the AIB1 transgene is responsible for continued activation of the insulin-like growth factor-I receptor, suggesting a role for the activation of the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (mTOR) pathway in the premalignant phenotype and tumor development. Here we show that treatment of AIB1 transgenic mice with the mTOR inhibitor RAD001 reverts the premalignant phenotype. Furthermore, treatment of cell lines derived from AIB1-dependent mammary tumors with RAD001 in culture leads to a G(1) cell cycle arrest. Lastly, tumor growth after injection of ER(+) AIB1 tumor cell lines into wild-type animals is inhibited by RAD001 treatment. In this ER(+) model, inhibition of tumor growth by RAD001 was significantly better than inhibition by the antiestrogen 4-hydroxytamoxifen alone, whereas a combination of both RAD001 and 4-hydroxytamoxifen was most effective. Based on these results, we propose that the combination of mTOR inhibition and ER-targeted endocrine therapy may improve the outcome of the subset of ER(+) breast cancers overexpressing AIB1. These studies provide preclinical support for the clinical development of RAD001 and suggest that AIB1 may be a predictive factor of RAD001 response.
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MESH Headings
- Animals
- Blotting, Western
- Cell Proliferation/drug effects
- Cell Survival/drug effects
- Cell Survival/genetics
- Cell Survival/physiology
- Dose-Response Relationship, Drug
- Endometrial Hyperplasia/chemically induced
- Endometrial Hyperplasia/prevention & control
- Estrogen Receptor alpha/agonists
- Estrogen Receptor alpha/genetics
- Estrogen Receptor alpha/metabolism
- Everolimus
- Female
- G1 Phase/drug effects
- G1 Phase/genetics
- G1 Phase/physiology
- Histone Acetyltransferases/genetics
- Histone Acetyltransferases/physiology
- Immunohistochemistry
- Immunosuppressive Agents/pharmacology
- Immunosuppressive Agents/therapeutic use
- Mammary Neoplasms, Experimental/genetics
- Mammary Neoplasms, Experimental/pathology
- Mammary Neoplasms, Experimental/prevention & control
- Mice
- Mice, Transgenic
- Nuclear Receptor Coactivator 3
- Oncogenes/genetics
- Oncogenes/physiology
- Precancerous Conditions/genetics
- Precancerous Conditions/pathology
- Precancerous Conditions/prevention & control
- Protein Kinases/physiology
- Receptors, Estrogen/agonists
- Receptors, Estrogen/genetics
- Receptors, Estrogen/metabolism
- Sirolimus/analogs & derivatives
- Sirolimus/pharmacology
- Sirolimus/therapeutic use
- TOR Serine-Threonine Kinases
- Tamoxifen/adverse effects
- Tamoxifen/analogs & derivatives
- Tamoxifen/pharmacology
- Tamoxifen/therapeutic use
- Trans-Activators/genetics
- Trans-Activators/physiology
- Tumor Cells, Cultured
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Affiliation(s)
- Maria I Torres-Arzayus
- Division of Molecular and Cellular Oncology, Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA
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674
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Kaur S, Lal L, Sassano A, Majchrzak-Kita B, Srikanth M, Baker DP, Petroulakis E, Hay N, Sonenberg N, Fish EN, Platanias LC. Regulatory Effects of Mammalian Target of Rapamycin-activated Pathways in Type I and II Interferon Signaling. J Biol Chem 2007; 282:1757-68. [PMID: 17114181 DOI: 10.1074/jbc.m607365200] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The mechanisms regulating initiation of mRNA translation for the generation of protein products that mediate interferon (IFN) responses are largely unknown. We have previously shown that both Type I and II IFNs engage the mammalian target of rapamycin (mTOR), resulting in downstream phosphorylation and deactivation of the translational repressor 4E-BP1 (eIF4E-binding protein 1). In the current study, we provide direct evidence that such regulation of 4E-BP1 by IFNalpha or IFNgamma results in sequential dissociation of 4E-BP1 from eukaryotic initiation factor-4E and subsequent formation of a functional complex between eukaryotic initiation factor-4E and eukaryotic initiation factor-4G, to allow initiation of mRNA translation. We also demonstrate that the induction of key IFNalpha- or IFNgamma-inducible proteins (ISG15 (interferon-stimulated gene 15) and CXCL10) that mediate IFN responses are enhanced in 4E-BP1 (4E-BP1(-/-)) knockout MEFs, as compared with wild-type 4E-BP1(+/+) MEFs. On the other hand, IFN-dependent transcriptional regulation of the Isg15 and Cxcl10 genes is intact in the absence of 4E-BP1, as determined by real time reverse transcriptase-PCR assays and promoter assays for ISRE and GAS, establishing that 4E-BP1 plays a selective negative regulatory role in IFN-induced mRNA translation. Interestingly, the induction of expression of ISG15 and CXCL10 proteins by IFNs was also strongly enhanced in cells lacking expression of the tuberin (TSC2(-/-)) or hamartin (TSC1(-/-)) genes, consistent with the known negative regulatory effect of the TSC1-TSC2 complex on mTOR activation. In other work, we demonstrate that the induction of an IFN-dependent antiviral response is strongly enhanced in cells lacking expression of 4E-BP1 and TSC2, demonstrating that these elements of the IFN-activated mTOR pathway exhibit important regulatory effects in the generation of IFN responses. Taken altogether, our data suggest an important role for mTOR-dependent pathways in IFN signaling and identify 4E-BP1 and TSC1-TSC2 as key components in the generation of IFN-dependent biological responses.
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Affiliation(s)
- Surinder Kaur
- Robert H. Lurie Comprehensive Cancer Center and Division of Hematology-Oncology, Northwestern University Medical School and Lakeside Veterans Affairs Medical Center, Chicago, Illinois 60611, USA
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675
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Gan B, Yoo Y, Guan JL. Association of Focal Adhesion Kinase with Tuberous Sclerosis Complex 2 in the Regulation of S6 Kinase Activation and Cell Growth. J Biol Chem 2006; 281:37321-9. [PMID: 17043358 DOI: 10.1074/jbc.m605241200] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tuberous sclerosis complex 1 (TSC1) and TSC2 tumor suppressor proteins have been shown to negatively regulate cell growth through inhibition of the mammalian target of rapamycin (mTOR) pathway. Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that plays a critical role in integrin signaling. Here we identify a novel interaction between FAK and TSC2 and show that TSC2 is phosphorylated by FAK. Furthermore, we show that overexpression of FAK kinase dead mutant inhibits the phosphorylation of ribosomal S6 kinase (S6K) and eukaryotic initiation factor 4E-binding protein-1, two key mTOR (mammalian target of rapamycin) downstream targets, and negatively regulates the cell size and that FAK regulation of S6K phosphorylation is through TSC2. Finally, we provide data that FAK plays a positive role in cell adhesion-induced S6K phosphorylation, whereas TSC2 is required for cell suspension-induced S6K inactivation. Together, these results suggest that FAK might regulate S6K activation and cell size through its interaction with and phosphorylation of TSC2 and also provide a previously unappreciated role of TSC2 in the regulation of mTOR signaling by cell adhesion.
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Affiliation(s)
- Boyi Gan
- Department of Molecular Medicine, Cornell University, Ithaca, New York 14853, USA
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676
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Makky K, Tekiela J, Mayer AN. Target of rapamycin (TOR) signaling controls epithelial morphogenesis in the vertebrate intestine. Dev Biol 2006; 303:501-13. [PMID: 17222402 PMCID: PMC2715143 DOI: 10.1016/j.ydbio.2006.11.030] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2006] [Revised: 11/16/2006] [Accepted: 11/17/2006] [Indexed: 10/23/2022]
Abstract
The target of rapamycin (TOR) signaling pathway regulates cell growth and proliferation, however the extent to which TOR signaling mediates particular organogenesis programs remains to be determined. Here we report an examination of TOR signaling during zebrafish development, using a combination of small molecule treatment and morpholino-mediated gene knockdown. First, we amplified and sequenced the full-length cDNA for the zebrafish TOR ortholog (ztor). By in situ hybridization, we found that ztor is expressed ubiquitously in the early embryo, but displays a dynamic pattern in the gut between 48 and 72 h post-fertilization (hpf). Treatment of zebrafish embryos with rapamycin induced only a mild general developmental delay up to 72 hpf, but digestive tract development became arrested at the primitive gut tube stage. Rapamycin inhibited intestinal epithelial growth, morphogenesis and differentiation. Using morpholino-mediated gene knockdown of TOR pathway components, we show that this effect is mediated specifically by the rapamycin-sensitive TOR complex 1 (TORC1). Thus, in addition to regulating cell growth and proliferation, TOR signaling controls the developmental program guiding epithelial morphogenesis in the vertebrate intestine.
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Affiliation(s)
| | | | - Alan N. Mayer
- *Author for correspondence, phone: 414-456-5894, fax: 414-456-6632,
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677
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Pallet N, Beaune P, Thervet E, Legendre C, Anglicheau D. Inhibiteurs de mTOR : Des antiprolifératifs pléiotropiques. Med Sci (Paris) 2006; 22:947-52. [PMID: 17101096 DOI: 10.1051/medsci/20062211947] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Studies of rapamycin properties in yeast led to the discovery of TOR (target of rapamycin) and its mammalian analogue, mTOR. mTOR is a central regulator of cell growth and proliferation in response to environmental stimuli such as growth factors and nutrients. mTOR regulates several pathways, particularly translation process by controlling the activity of two proteins in response to a broad range of mitogenic stimuli, S6K1 and 4E-BP1. Inhibition of cell growth by rapamycine and analogues have been demonstrated in numerous cell types, explaining the broad development of these drugs in clinical practice. Rapamycine is a potent immunosuppressive drug used in solid organ transplantation for the prevention of allograft rejection. In oncology, mTOR inhibitors are currently evaluated in several types of cancers. They are now widely used for coating stents to reduce post-stenting restenosis after coronary angioplasty. Finally, rapamycine is now evaluated in various diseases characterized by cell growth disorders such as phacomatosis and autosomal dominant polycystic kidney disease.
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Affiliation(s)
- Nicolas Pallet
- Service de Transplantation Rénale, Hôpital Necker, AP-HP, Université Paris V-René Descartes, 149, Rue de Sèvres, 75015 Paris, France.
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678
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Juvet SC, McCormack FX, Kwiatkowski DJ, Downey GP. Molecular pathogenesis of lymphangioleiomyomatosis: lessons learned from orphans. Am J Respir Cell Mol Biol 2006; 36:398-408. [PMID: 17099139 PMCID: PMC2176113 DOI: 10.1165/rcmb.2006-0372tr] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Lymphangioleiomyomatosis (LAM) is a rare progressive cystic lung disease affecting young women. The pivotal observation that LAM occurs both spontaneously and as part of the tuberous sclerosis complex (TSC) led to the hypothesis that these disorders share common genetic and pathogenetic mechanisms. In this review we describe the evolution of our understanding of the molecular and cellular basis of LAM and TSC, beginning with the discovery of the TSC1 and TSC2 genes and the demonstration of their involvement in sporadic (non-TSC) LAM. This was followed by rapid delineation of the signaling pathways in Drosophila melanogaster with confirmation in mice and humans. This knowledge served as the foundation for novel therapeutic approaches that are currently being used in human clinical trials.
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Affiliation(s)
- Stephen C Juvet
- National Jewish Medical and Research Center, 1400 Jackson Street, Denver, CO 80206, USA
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679
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Tehrani AM, Hwang SK, Kim TH, Cho CS, Hua J, Nah WS, Kwon JT, Kim JS, Chang SH, Yu KN, Park SJ, Bhandari DR, Lee KH, An GH, Beck GR, Cho MH. Aerosol delivery of Akt controls protein translation in the lungs of dual luciferase reporter mice. Gene Ther 2006; 14:451-8. [PMID: 17051249 DOI: 10.1038/sj.gt.3302879] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Lung cancer has emerged as a leading cause of cancer death in the world; however, most of the current conventional therapies are not sufficiently effective in altering the progression of disease. Therefore, development of novel treatment approaches is needed. Although several genes and methods have been used for cancer gene therapy, a number of problems such as specificity, efficacy and toxicity reduce their application. This has led to re-emergence of aerosol gene delivery as a noninvasive method for lung cancer treatment. In this study, nano-sized glucosylated polyethyleneimine (GPEI) was used as a gene delivery carrier to investigate the effects of Akt wild type (WT) and kinase deficient (KD) on Akt-related signaling pathways and protein translation in the lungs of CMV- LucR-cMyc-IRES-LucF dual reporter mice. These mice are a powerful tool for the discrimination between cap-dependent/-independent protein translation. Aerosols containing self-assembled nano-sized GPEI/Akt WT or GPEI/Akt KD were delivered into the lungs of reporter mice through nose-only-inhalation-chamber with the aid of nebulizer. Aerosol delivery of Akt WT caused the increase of protein expression levels of Akt-related signals, whereas aerosol delivery of Akt KD did not. Furthermore, dual luciferase activity assay showed that aerosol delivery of Akt WT enhanced cap-dependent protein translation, whereas a reduction in cap-dependent protein translation by Akt KD was observed. Our results clearly showed that targeting Akt may be a good strategy for prevention as well as treatment of lung cancer. These studies suggest that our aerosol delivery is compatible for in vivo gene delivery which could be used as a noninvasive gene therapy in the future.
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Affiliation(s)
- A M Tehrani
- Laboratory of Toxicology, College of Veterinary Medicine and BK21 Program for Veterinary Science, Seoul, Korea
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680
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Raab-Graham KF, Haddick PCG, Jan YN, Jan LY. Activity- and mTOR-dependent suppression of Kv1.1 channel mRNA translation in dendrites. Science 2006; 314:144-8. [PMID: 17023663 DOI: 10.1126/science.1131693] [Citation(s) in RCA: 214] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Mammalian target of rapamycin (mTOR) is implicated in synaptic plasticity and local translation in dendrites. We found that the mTOR inhibitor, rapamycin, increased the Kv1.1 voltage-gated potassium channel protein in hippocampal neurons and promoted Kv1.1 surface expression on dendrites without altering its axonal expression. Moreover, endogenous Kv1.1 mRNA was detected in dendrites. Using Kv1.1 fused to the photoconvertible fluorescence protein Kaede as a reporter for local synthesis, we observed Kv1.1 synthesis in dendrites upon inhibition of mTOR or the N-methyl-d-aspartate (NMDA) glutamate receptor. Thus, synaptic excitation may cause local suppression of dendritic Kv1 channels by reducing their local synthesis.
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Affiliation(s)
- Kimberly F Raab-Graham
- Howard Hughes Medical Institute, Departments of Physiology and Biochemistry, University of California, San Francisco, CA 94158, USA
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681
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Abstract
The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that controls many aspects of cellular physiology, including transcription, translation, cell size, cytoskeletal organization and autophagy. Recent advances in the mTOR signaling field have found that mTOR exists in two heteromeric complexes, mTORC1 and mTORC2. The activity of mTORC1 is regulated by the integration of many signals, including growth factors, insulin, nutrients, energy availability and cellular stressors such as hypoxia, osmotic stress, reactive oxygen species and viral infection. In this review we highlight recent advances in the mTOR signaling field that relate to how the two mTOR complexes are regulated, and we discuss stress conditions linked to the mTOR signaling network that have not been extensively covered in other reviews. Given the diversity of signals that have been shown to impinge on mTOR, we also speculate on other signal-transduction pathways that may be linked to mTOR in the future.
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Affiliation(s)
- M N Corradetti
- Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA.
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682
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Baba M, Hong SB, Sharma N, Warren MB, Nickerson ML, Iwamatsu A, Esposito D, Gillette WK, Hopkins RF, Hartley JL, Furihata M, Oishi S, Zhen W, Burke TR, Linehan WM, Schmidt LS, Zbar B. Folliculin encoded by the BHD gene interacts with a binding protein, FNIP1, and AMPK, and is involved in AMPK and mTOR signaling. Proc Natl Acad Sci U S A 2006; 103:15552-7. [PMID: 17028174 PMCID: PMC1592464 DOI: 10.1073/pnas.0603781103] [Citation(s) in RCA: 353] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Birt-Hogg-Dubé syndrome, a hamartoma disorder characterized by benign tumors of the hair follicle, lung cysts, and renal neoplasia, is caused by germ-line mutations in the BHD(FLCN) gene, which encodes a tumor-suppressor protein, folliculin (FLCN), with unknown function. The tumor-suppressor proteins encoded by genes responsible for several other hamartoma syndromes, LKB1, TSC1/2, and PTEN, have been shown to be involved in the mammalian target of rapamycin (mTOR) signaling pathway. Here, we report the identification of the FLCN-interacting protein, FNIP1, and demonstrate its interaction with 5' AMP-activated protein kinase (AMPK), a key molecule for energy sensing that negatively regulates mTOR activity. FNIP1 was phosphorylated by AMPK, and its phosphorylation was reduced by AMPK inhibitors, which resulted in reduced FNIP1 expression. AMPK inhibitors also reduced FLCN phosphorylation. Moreover, FLCN phosphorylation was diminished by rapamycin and amino acid starvation and facilitated by FNIP1 overexpression, suggesting that FLCN may be regulated by mTOR and AMPK signaling. Our data suggest that FLCN, mutated in Birt-Hogg-Dubé syndrome, and its interacting partner FNIP1 may be involved in energy and/or nutrient sensing through the AMPK and mTOR signaling pathways.
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Affiliation(s)
- Masaya Baba
- Laboratories of *Immunobiology and
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20894
| | - Seung-Beom Hong
- Laboratories of *Immunobiology and
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20894
| | | | - Michelle B. Warren
- Laboratories of *Immunobiology and
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20894
| | | | - Akihiro Iwamatsu
- Department of Pathology, Kochi Medical School, Kochi University, Kochi 783-8505, Japan
| | | | | | | | | | - Mutsuo Furihata
- Department of Pathology, Kochi Medical School, Kochi University, Kochi 783-8505, Japan
| | - Shinya Oishi
- **Medicinal Chemistry, Center for Cancer Research, National Cancer Institute–Frederick, Frederick, MD 21702
| | - Wei Zhen
- Laboratories of *Immunobiology and
| | - Terrence R. Burke
- **Medicinal Chemistry, Center for Cancer Research, National Cancer Institute–Frederick, Frederick, MD 21702
| | - W. Marston Linehan
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20894
| | - Laura S. Schmidt
- Laboratories of *Immunobiology and
- Basic Research Program, SAIC–Frederick, Inc., National Cancer Institute–Frederick, Frederick, MD 21702
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20894
- To whom correspondence should be addressed at:
National Cancer Institute–Frederick, Building 560, Room 12-69, Frederick, MD 21702. E-mail:
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683
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Abstract
It has become clear in recent years that autophagy not only serves to produce amino acids for ongoing protein synthesis and to produce substrates for energy production when cells become starved but autophagy is also able to eliminate defective cell structures and for this reason the process may be implicated in several diseased states. Autophagy is controlled by complex signalling pathways, including that used by insulin. In these pathways, phosphatidylinositol 3-kinases and the protein kinase mTOR play important roles.
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Affiliation(s)
- Alfred J Meijer
- Department of Medical Biochemistry, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
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684
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King A, Selak MA, Gottlieb E. Succinate dehydrogenase and fumarate hydratase: linking mitochondrial dysfunction and cancer. Oncogene 2006; 25:4675-82. [PMID: 16892081 DOI: 10.1038/sj.onc.1209594] [Citation(s) in RCA: 502] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The phenomenon of enhanced glycolysis in tumours has been acknowledged for decades, but biochemical evidence to explain it is only just beginning to emerge. A significant hint as to the triggers and advantages of enhanced glycolysis in tumours was supplied by the recent discovery that succinate dehydrogenase (SDH) and fumarate hydratase (FH) are tumour suppressors and which associated, for the first time, mitochondrial enzymes and their dysfunction with tumorigenesis. Further steps forward showed that the substrates of SDH and FH, succinate and fumarate, respectively, can mediate a 'metabolic signalling' pathway. Succinate or fumarate, which accumulate in mitochondria owing to the inactivation of SDH or FH, leak out to the cytosol, where they inhibit a family of prolyl hydroxylase enzymes (PHDs). Depending on the PHD inhibited, two newly recognized pathways that support tumour maintenance may ensue: affected cells become resistant to certain apoptotic signals and/or activate a pseudohypoxic response that enhances glycolysis and is conveyed by hypoxia-inducible factor.
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Affiliation(s)
- A King
- Cancer Research UK, The Beatson Institute for Cancer Research, Glasgow, UK
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685
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Guertin DA, Guntur KVP, Bell GW, Thoreen CC, Sabatini DM. Functional genomics identifies TOR-regulated genes that control growth and division. Curr Biol 2006; 16:958-70. [PMID: 16713952 DOI: 10.1016/j.cub.2006.03.084] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2005] [Revised: 03/09/2006] [Accepted: 03/22/2006] [Indexed: 01/08/2023]
Abstract
BACKGROUND The TOR (target of rapamycin) ser/thr protein kinase is the central component of a eukaryotic signaling pathway that regulates growth and is the direct target of the clinically useful drug rapamycin. Recent efforts have identified at least two multiprotein complexes that contain TOR, but little is known in higher eukaryotes about the genes downstream of TOR that control growth. RESULTS By combining the use of a small molecule inhibitor (rapamycin), transcriptional profiling, and RNA interference in Drosophila tissue culture cells, we identified genes whose expression responds to Drosophila TOR (dTOR) inhibition and that regulate cell size. Several of the dTOR-regulated genes that function in cell size control have additional roles in cell division. Most of these genes are conserved in mammals and several are linked to human disease. This set of genes is highly enriched for regulators of ribosome biogenesis, which emphasizes the importance of TOR-dependent transcription in building the protein synthesis machinery in higher eukaryotes. In addition, we identify two dTOR-regulated genes, CG3071 and CG6677, whose human orthologs, SAW and ASH2L, are also under TOR-dependent transcriptional control and encode proteins with conserved functional roles in growth. CONCLUSIONS We conclude that combining RNA interference with genomic analysis approaches, such as transcriptional profiling, is an effective way to identify genes functioning in a particular biological process. Moreover, this strategy, if applied in model systems with simpler genomes, can identify genes with conserved functions in mammals.
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Affiliation(s)
- David A Guertin
- Whitehead Institute for Biomedical Research and Massachusetts Institute of Technology, Nine Cambridge Center, Cambridge, Massachusetts 02142, USA
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686
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Mavrakis M, Lippincott-Schwartz J, Stratakis CA, Bossis I. Depletion of type IA regulatory subunit (RIalpha) of protein kinase A (PKA) in mammalian cells and tissues activates mTOR and causes autophagic deficiency. Hum Mol Genet 2006; 15:2962-71. [PMID: 16963469 DOI: 10.1093/hmg/ddl239] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The human PRKAR1A gene encodes the regulatory subunit 1-alpha (RIalpha) of the cAMP-dependent protein kinase A (PKA) holoenzyme. Regulation of the catalytic activity of PKA is the only well-studied function of RIalpha. Inactivating PRKAR1A mutations cause primary pigmented nodular adrenocortical disease (PPNAD) or Carney complex (CNC), an inherited syndrome associated with abnormal skin pigmentation and multiple neoplasias, including PPNAD. Histochemistry of tissues from CNC patients is indicative of autophagic deficiency and this led us to investigate the relationship between RIalpha and mammalian autophagy. We found that fluorescently tagged RIalpha associates with late endosomes and autophagosomes in cultured cells. The number of autophagosomes in prkar1a-/- mouse embryonic fibroblasts (MEFs) was reduced compared with wild-type MEFs. RIalpha co-immunoprecipitated with mTOR kinase, a major regulator of autophagy. Phosphorylated-mTOR levels and mTOR activity were dramatically increased in prkar1a-/- mouse cells, and in HEK 293 cells with RIalpha levels reduced by siRNA. Finally, phosphorylated-mTOR levels and mTOR activity were increased in CNC cells and in PPNAD tissues. These data suggest that RIalpha deficiency decreases autophagy by the activation of mTOR, providing a molecular basis to autophagic deficiency in PPNAD.
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Affiliation(s)
- Manos Mavrakis
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
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687
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Dash PK, Orsi SA, Moore AN. Spatial memory formation and memory-enhancing effect of glucose involves activation of the tuberous sclerosis complex-Mammalian target of rapamycin pathway. J Neurosci 2006; 26:8048-56. [PMID: 16885218 PMCID: PMC6673778 DOI: 10.1523/jneurosci.0671-06.2006] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The tuberous sclerosis complex-mammalian target of rapamycin (TSC-mTOR) cascade integrates growth factor and nutritional signals to regulate the synthesis of specific proteins. Because both growth factor signaling and glucose have been implicated in memory formation, we questioned whether mTOR activity is required for long-term spatial memory formation and whether this cascade is involved in the memory-augmenting effect of centrally applied glucose. To test our hypothesis, we directly administered rapamycin (an inhibitor of mTOR), glucose, 5-aminoimidazole-4-carboxamide-1beta-4-ribonucleoside (AICAR; an activator of AMP kinase), or glucose plus rapamycin into the dorsal hippocampus after we trained rats in the Morris water maze task. The results from these studies indicate that glucose enhances, whereas AICAR and rapamycin both impair, long-term spatial memory. Furthermore, the memory-impairing effect of targeted rapamycin administration could not be overcome by coadministration of glucose. Consistent with these behavioral results, biochemical analysis revealed that glucose and AICAR had opposing influences on the activation of the TSC-mTOR cascade, as indicated by the phosphorylation of ribosomal S6 kinase (S6K) and 4E binding protein 1 (4EBP1), targets of mTOR. Together, these findings suggest that memory formation requires the mTOR cascade and that the memory-enhancing effect of glucose involves its ability to activate this pathway.
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Affiliation(s)
- Pramod K Dash
- The Vivian L. Smith Center for Neurologic Research and Department of Neurobiology and Anatomy, The University of Texas Medical School, Houston, Texas 77225, USA.
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688
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Abstract
Most human cancers derive from a single cell targeted by genetic and epigenetic alterations that initiate malignant transformation. Progressively, these early cancer cells give rise to different generations of daughter cells that accumulate additional mutations, acting in concert to drive the full neoplastic phenotype. As we have currently deciphered many of the gene pathways disrupted in cancer, our knowledge about the nature of the normal cells susceptible to transformation upon mutation has remained more elusive. Adult stem cells are those that show long-term replicative potential, together with the capacities of self-renewal and multi-lineage differentiation. These stem cell properties are tightly regulated in normal development, yet their alteration may be a critical issue for tumorigenesis. This concept has arisen from the striking degree of similarity noted between somatic stem cells and cancer cells, including the fundamental abilities to self-renew and differentiate. Given these shared attributes, it has been proposed that cancers are caused by transforming mutations occurring in tissue-specific stem cells. This hypothesis has been functionally supported by the observation that among all cancer cells within a particular tumor, only a minute cell fraction has the exclusive potential to regenerate the entire tumor cell population; these cells with stem-like properties have been termed cancer stem cells. Cancer stem cells can originate from mutation in normal somatic stem cells that deregulate their physiological programs. Alternatively, mutations may target more committed progenitor cells or even mature cells, which become reprogrammed to acquire stem-like functions. In any case, mutated genes should promote expansion of stem/progenitor cells, thus increasing their predisposition to cancer development by expanding self-renewal and pluripotency over their normal tendency towards relative quiescency and proper differentiation.
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Affiliation(s)
- José A Martínez-Climent
- Division of Oncology, Center for Applied Medical Research University of Navarra, Pamplona, Spain.
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689
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Abstract
Polycystic kidneys are caused by an amazingly broad array of genetic mutations and manipulations. The ciliary hypothesis has evolved as the unifying concept of cystogenesis: cilia, bend by fluid flow, initiate a calcium influx that prevents cyst formation. The integrity of ciliary functions has been linked to the polycystic kidney disease gene products localizing to the cilium or the basal body/centrosome. Until recently, the signals and cellular programs located downstream of the ciliary-mediated calcium flux have remained elusive. Now, several reports point towards a role of the cilium or the basal body/centrosome complex in planar cell polarity, a pathway that orients cell in the plane of a tissue layer. First, Inversin, a protein mutated in nephronophthisis type II was found to act as a switch between the canonical and the noncanonical Wnt cascade, suggesting that beta-catenin/TCF-dependent gene transcription has to be curtailed to allow normal tubular differentiation. Second, heterozygote deletions of Bardet-Biedl syndrome proteins affect neural tube closure and disrupt the cochlear sterociliary bundles, two typical planar cell polarity defects. Third, tubular epithelial cells undergo oriented cell division during tubular elongation, along the axis of the anterior-posterior axis of the nephron. Thus, the cilium or the basal body/centrosome complex may provide the spatial cues to position the centrosome and the mitotic spindle before the next cell division. Failure to communicate this spatial information may condemn the tubular epithelial cells to proliferate and to form cysts.
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Affiliation(s)
- M Simons
- Renal Division, University Hospital Freiburg, Freiburg, Germany.
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690
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Pallet N, Thervet E, Legendre C, Anglicheau D. Néphrotoxicité du sirolimus : données cliniques et expérimentales. Nephrol Ther 2006; 2:183-90. [PMID: 16966063 DOI: 10.1016/j.nephro.2006.04.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2005] [Revised: 03/14/2006] [Accepted: 04/12/2006] [Indexed: 01/29/2023]
Abstract
Sirolimus (SRL, rapamycin) is a potent immunosuppressive drug that binds to and inhibits mammalian Target Of Rapamycine (mTOR) kinase activity, a central controller of cell growth. In response to amino acids, hormones and growth factors, mTOR activates the translational machinery. By inhibiting mTOR, SRL reduces the translational process and T-cell proliferation in the mid-to-late G1 phase of the cell cycle. The antiproliferative effects of SRL are not limited to activated T cells. SRL has also been shown to block the cell cycle in various cell types such as epithelial renal cells, and many types of tumor cell lines. Since the approval by the US Food and Drug Administration and by the European agency, SRL has provoked great interest, as evidenced by the exponential increase in clinical studies. However, whereas preclinical studies failed to show any nephrotoxic effect on animal models, many clinical trials raised the possibility that SRL might be associated with renal adverse events. The evidence for SRL-associated early graft nephrotoxicity emerged from these results, and subsequent experimental data gave some explanations about the involved mechanisms. The aim of this review is to summarize the various renal adverse events reported in clinical studies and to present the experimental evidence for putative mechanisms of action for this SRL-induced nephrotoxicity.
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Affiliation(s)
- Nicolas Pallet
- Service de transplantation rénale et de soins intensifs, hôpital Necker-Enfants-Malades, APHP et université Paris-V, René-Descartes, 149, rue de Sèvres, 75743 cedex 15 Paris, France
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691
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Faivre S, Kroemer G, Raymond E. Current development of mTOR inhibitors as anticancer agents. Nat Rev Drug Discov 2006; 5:671-88. [PMID: 16883305 DOI: 10.1038/nrd2062] [Citation(s) in RCA: 734] [Impact Index Per Article: 40.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Mammalian target of rapamycin (mTOR) is a kinase that functions as a master switch between catabolic and anabolic metabolism and as such is a target for the design of anticancer agents. The most established mTOR inhibitors--rapamycin and its derivatives--showed long-lasting objective tumour responses in clinical trials, with CCI-779 being a first-in-class mTOR inhibitor that improved the survival of patients with advanced renal cell carcinoma. This heralded the beginning of extensive clinical programmes to further evaluate mTOR inhibitors in several tumour types. Here we review the clinical development of this drug class and look at future prospects for incorporating these agents into multitarget or multimodality strategies against cancer.
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Affiliation(s)
- Sandrine Faivre
- Service Inter Hospitalier de Cancrologie, Beaujon University Hospital, 100 Boulevard du General Leclerc, 92118 Clichy Cedex, France
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692
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Pinkston JM, Garigan D, Hansen M, Kenyon C. Mutations that increase the life span of C. elegans inhibit tumor growth. Science 2006; 313:971-5. [PMID: 16917064 DOI: 10.1126/science.1121908] [Citation(s) in RCA: 171] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Mutations in gld-1 cause lethal germline tumors in the nematode Caenorhabditis elegans. We find that a wide variety of mutations that extend C. elegans' life span confer resistance to these tumors. The long life spans of daf-2/insulin-receptor mutants were not shortened at all by gld-1 mutations; we attribute this finding to decreased cell division and increased DAF-16/p53-dependent apoptosis within the tumors. Mutations that increase life span by restricting food intake or inhibiting respiration did not affect apoptosis but reduced tumor cell division. Unexpectedly, none of these longevity mutations affected mitosis in normal germlines; this finding suggests that cellular changes that lead to longevity preferentially antagonize tumor cell growth.
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Affiliation(s)
- Julie M Pinkston
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158, USA
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693
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Inoue T, Yoshida T, Shimizu Y, Kobayashi T, Yamasaki T, Toda Y, Segawa T, Kamoto T, Nakamura E, Ogawa O. Requirement of androgen-dependent activation of protein kinase Czeta for androgen-dependent cell proliferation in LNCaP Cells and its roles in transition to androgen-independent cells. Mol Endocrinol 2006; 20:3053-69. [PMID: 16931574 DOI: 10.1210/me.2006-0033] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
A cell line that we designed, AILNCaP, proliferated in androgen-depleted medium after emerging from long-term androgen-depleted cultures of an androgen-sensitive prostate cancer cell line, LNCaP. Using this cell line as a model of progression to androgen independence, we demonstrated that the activity of the mammalian target of rapamycin/p70 S6 kinase transduction pathway is down-regulated after androgen depletion in LNCaP, whereas its activation is related to transition of this cell line to androgen-independent proliferation. Kinase activity of protein kinase Czeta is regulated by androgen stimulation in LNCaP cells, whereas it is activated constitutively in AILNCaP cells under androgen-depleted conditions. Treatment with a protein kinase Czeta pseudosubstrate inhibitor reduced p70 S6 kinase activity and cell proliferation in both cell lines. We identified that both protein kinase Czeta and p70 S6 kinase were associated in LNCaP cells and this association was enhanced by the androgen stimulation. We examined the expression of phospho-protein kinase Czeta and phospho-p70 S6 kinase in hormone-naive prostate cancer specimens and found that the expression of both kinases was correlated with each other in those specimens. Significant correlation was observed between the expression of both kinases and Ki67 expression. Most of the prostate cancer cells that survived after prior hormonal treatment also expressed both kinases. This is the first report that shows the significance of this pathway for both androgen-dependent and -independent cell proliferation in prostate cancer. Our data suggest that protein kinase Czeta/mammalian target of rapamycin/S6 kinase pathway plays an important role for the transition of androgen-dependent to androgen-independent prostate cancer cells.
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Affiliation(s)
- Takahiro Inoue
- Department of Urology, Kyoto University Graduate School of Medicine, 54 Kawaharacho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan
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694
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Cho DH, Choi YJ, Jo SA, Ryou J, Kim JY, Chung J, Jo I. Troglitazone acutely inhibits protein synthesis in endothelial cells via a novel mechanism involving protein phosphatase 2A-dependent p70 S6 kinase inhibition. Am J Physiol Cell Physiol 2006; 291:C317-26. [PMID: 16825603 DOI: 10.1152/ajpcell.00491.2005] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Thiazolidinediones (TZDs), synthetic peroxisome proliferator-activated receptor gamma (PPARgamma) ligands, have been implicated in the inhibition of protein synthesis in a variety of cells, but the underlying mechanisms remain obscure. We report that troglitazone, the first TZD drug, acutely inhibited protein synthesis by decreasing p70 S6 kinase (p70S6K) activity in bovine aortic endothelial cells (BAEC). This inhibition was not accompanied by decreased phosphorylation status or in vitro kinase activity of mammalian target of rapamycin (mTOR). Furthermore, cotreatment with rapamycin, a specific mTOR inhibitor, and troglitazone additively inhibited both p70S6K activity and protein synthesis, suggesting that the inhibitory effects of troglitazone are not mediated by mTOR. Overexpression of the wild-type p70S6K gene significantly reversed the troglitazone-induced inhibition of protein synthesis, indicating an important role of p70S6K. Okadaic acid, a protein phosphatase 2A (PP2A) inhibitor, partially reversed the troglitazone-induced inhibition of p70S6K activity and protein synthesis. Although troglitazone did not alter total cellular PP2A activity, it increased the physical association between p70S6K and PP2A, suggesting an underlying molecular mechanism. GW9662, a PPARgamma antagonist, did not alter any of the observed inhibitory effects. Finally, we also found that the mTOR-independent inhibitory mechanism of troglitazone holds for the TZDs ciglitazone, pioglitazone, and rosiglitazone, in BAEC and other types of endothelial cells tested. In conclusion, our data demonstrate for the first time that troglitazone (and perhaps other TZDs) acutely decreases p70S6K activity through a PP2A-dependent mechanism that is independent of mTOR and PPARgamma, leading to the inhibition of protein synthesis in endothelial cells.
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Affiliation(s)
- Du-Hyong Cho
- Dept. of Biomedical Sciences, National Institute of Health, 5 Nokbun-dong, Eunpyunggu, Seoul 122-701, Korea
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695
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Lau CK, Yang ZF, Lam CT, Tam KH, Poon RTP, Fan ST. Suppression of hypoxia inducible factor-1alpha (HIF-1alpha) by YC-1 is dependent on murine double minute 2 (Mdm2). Biochem Biophys Res Commun 2006; 348:1443-8. [PMID: 16919599 DOI: 10.1016/j.bbrc.2006.08.015] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2006] [Accepted: 08/04/2006] [Indexed: 11/24/2022]
Abstract
Inhibition of HIF-1alpha activity provides an important strategy for the treatment of cancer. Recently, 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) has been identified as an anti-HIF-1alpha drug in cancer therapy with unclear molecular mechanism. In the present study, we aimed to investigate the effect and mechanism of YC-1 on HIF-1alpha in a hepatocellular carcinoma cell line under hypoxic condition, which was generated by incubating cells with 0.1% O(2). The phenotypic and molecular changes of cells were determined by cell proliferation assay, apoptosis assay, luciferase promoter assay, and Western blot analysis. YC-1 arrested tumor cell growth in a dose-dependent manner, whereas it did not induce cell apoptosis. Hypoxia-induced upregulation of HIF-1alpha was suppressed by YC-1 administration. YC-1 inhibited HIF-1alpha protein synthesis under normoxia and affected protein stability under hypoxia. YC-1 suppressed the expression of total and phosphorylated forms of murine double minute 2 (Mdm2), whereas this inhibitory effect was blocked by overexpression of Mdm2. In conclusion, YC-1 suppressed both protein synthesis and stability of HIF-1alpha in HCC cells, and its inhibitory effects on HIF-1alpha were dependent on Mdm2.
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Affiliation(s)
- Chi Keung Lau
- Center for the Study of Liver Disease and Department of Surgery, The University of Hong Kong, Pokfulam, Hong Kong, China
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696
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Eto I. "Nutritional and chemopreventive anti-cancer agents up-regulate expression of p27Kip1, a cyclin-dependent kinase inhibitor, in mouse JB6 epidermal and human MCF7, MDA-MB-321 and AU565 breast cancer cells". Cancer Cell Int 2006; 6:20. [PMID: 16899133 PMCID: PMC1559648 DOI: 10.1186/1475-2867-6-20] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2006] [Accepted: 08/09/2006] [Indexed: 12/23/2022] Open
Abstract
Background p27(Kip1) is a cyclin-dependent kinase inhibitor. When up-regulated, p27 inhibits G1-to-S phase transition of the cell cycle. This report addresses the question of whether various nutritional and chemopreventive anti-cancer agents up-regulate the expression of p27 in preneoplastic and neoplastic cells. Results Experimental evidence presented in the first half of this report shows that these agents fairly faithfully up-regulate expression of p27 in mouse epidermal (JB6) and human breast cancer (MCF7, MDA-MB-321, and AU565) cells. Up-regulation appears to be specific to p27 because expression of cyclin D1, E, and A, and p21Cip1/Waf1 was not modulated by these agents. Up-regulation of the expression of p27 is likely due to the activation of translation rather than transcription of p27 because (a) up-regulation is mediated by the 5'-untranslated region (-575) of the p27 gene and (b) the antibiotic actinomycin D, an inhibitor of transcription, did not attenuate the up-regulation of p27. This latter finding is likely to preclude the existence of cryptic transcription factor binding site(s) in the 5'-untranslated region of p27 gene. The experimental evidence, presented in the second half of this report, was obtained using the 5'-untranslated region (-575) of p27 gene. The evidence suggests that cancer preventive agents up-regulate expression of p27 by at least four different molecular signaling pathways: (a) Caloric restriction is likely to up-regulate p27 expression via 5'-AMP-activated protein kinase (AMPK; a metabolic energy sensor or cellular fuel gauge), tuberous sclerosis complex (TSC), and mammalian target of rapamycin (mTOR). Amino acid deficiencies also up-regulate the expression of p27 using some components of this pathway. (b) 4-Hydroxytamoxifen (but not tamoxifen), genistein (but not genistin), daidzein, and probably other nutritional and chemopreventive anti-cancer agents could up-regulate expression of p27 via receptor protein tyrosine kinases (RPTKs), phosphoinositide 3-kinase (PI3K), phosphoinosite-dependent kinase (PDK), Akt/PKB and mTOR. (c) Expression of p27 could also be up-regulated via RPTKs followed by MAPKs – MEK, ERK and p38MAPK – and probably MNK. Finally, (d) global hypomethylation of 5'-m7G cap of mRNAs could also up-regulate expression of p27. Conclusion Based on these findings, we conclude that various nutritional and chemopreventive anti-cancer agents up-regulate expression of p27 in (pre)neoplastic cells.
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Affiliation(s)
- Isao Eto
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, Alabama, USA.
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697
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Marshall S. Role of insulin, adipocyte hormones, and nutrient-sensing pathways in regulating fuel metabolism and energy homeostasis: a nutritional perspective of diabetes, obesity, and cancer. ACTA ACUST UNITED AC 2006; 2006:re7. [PMID: 16885148 DOI: 10.1126/stke.3462006re7] [Citation(s) in RCA: 144] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Traditionally, nutrients such as glucose and amino acids have been viewed as substrates for the generation of high-energy molecules and as precursors for the biosynthesis of macromolecules. However, it is now apparent that nutrients also function as signaling molecules in functionally diverse signal transduction pathways. Glucose and amino acids trigger signaling cascades that regulate various aspects of fuel and energy metabolism and control the growth, proliferation, and survival of cells. Here, we provide a functional and regulatory overview of three well-established nutrient signaling pathways-the hexosamine signaling pathway, the mTOR (mammalian target of rapamycin) signaling pathway, and the adenosine monophosphate-activated protein kinase (AMPK) signaling pathway. Nutrient signaling pathways are interconnected, coupled to insulin signaling, and linked to the release of metabolic hormones from adipose tissue. Thus, nutrient signaling pathways do not function in isolation. Rather, they appear to serve as components of a larger "metabolic regulatory network" that controls fuel and energy metabolism (at the cell, tissue, and whole-body levels) and links nutrient availability with cell growth and proliferation. Understanding the diverse roles of nutrients and delineating nutrient signaling pathways should facilitate drug discovery research and the search for novel therapeutic compounds to prevent and treat various human diseases such as diabetes, obesity, and cancer.
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698
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Charest A, Wilker EW, McLaughlin ME, Lane K, Gowda R, Coven S, McMahon K, Kovach S, Feng Y, Yaffe MB, Jacks T, Housman D. ROS fusion tyrosine kinase activates a SH2 domain-containing phosphatase-2/phosphatidylinositol 3-kinase/mammalian target of rapamycin signaling axis to form glioblastoma in mice. Cancer Res 2006; 66:7473-81. [PMID: 16885344 DOI: 10.1158/0008-5472.can-06-1193] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Glioblastoma multiforme is the most common and lethal form of primary brain cancer. Diagnosis of this advanced glioma has a poor prognosis due to the ineffectiveness of current therapies. Aberrant expression of receptor tyrosine kinases (RTK) in glioblastoma multiformes is suggestive of their role in initiation and maintenance of these tumors of the central nervous system. In fact, ectopic expression of the orphan RTK ROS is a frequent event in human brain cancers, yet the pathologic significance of this expression remains undetermined. Here, we show that a glioblastoma-associated, ligand-independent rearrangement product of ROS (FIG-ROS) cooperates with loss of the tumor suppressor gene locus Ink4a;Arf to produce glioblastomas in the mouse. We show that this FIG-ROS-mediated tumor formation in vivo parallels the activation of the tyrosine phosphatase SH2 domain-containing phosphatase-2 (SHP-2) and a phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin signaling axis in tumors and tumor-derived cell lines. We have established a fully penetrant preclinical model for adult onset of glioblastoma multiforme in keeping with major genetic events observed in the human disease. These findings provide novel and important insights into the role of ROS and SHP-2 function in solid tumor biology and set the stage for preclinical testing of targeted therapeutic approaches.
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Affiliation(s)
- Al Charest
- Department of Biology and Center for Cancer Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
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699
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Sodhi A, Chaisuparat R, Hu J, Ramsdell AK, Manning BD, Sausville EA, Sawai ET, Molinolo A, Gutkind JS, Montaner S. The TSC2/mTOR pathway drives endothelial cell transformation induced by the Kaposi's sarcoma-associated herpesvirus G protein-coupled receptor. Cancer Cell 2006; 10:133-43. [PMID: 16904612 DOI: 10.1016/j.ccr.2006.05.026] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2005] [Revised: 03/08/2006] [Accepted: 05/10/2006] [Indexed: 12/22/2022]
Abstract
The Kaposi's sarcoma-associated herpesvirus (KSHV), the infectious causative agent of Kaposi's sarcoma (KS), encodes a G protein-coupled receptor (vGPCR) implicated in the initiation of KS. Here we demonstrate that Kaposi's sarcomagenesis involves stimulation of tuberin (TSC2) phosphorylation by vGPCR, promoting the activation of mTOR through both direct and paracrine mechanisms. Pharmacologic inhibition of mTOR with rapamycin prevented vGPCR sarcomagenesis, while overactivation of this pathway was sufficient to render endothelial cells oncogenic. Moreover, mice haploinsufficient for TSC2 are predisposed to vascular sarcomas remarkably similar to KS. Collectively, these results implicate mTOR in KS initiation and suggest that the sarcomagenic potential of KSHV may be a direct consequence of the profound sensitivity of endothelial cells to vGPCR dysregulation of the TSC2/mTOR pathway.
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Affiliation(s)
- Akrit Sodhi
- Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892, USA
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700
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Abstract
Tuberous sclerosis is a serious inherited disease which poses major challenges for affected families and those caring for them. Identification of the genes causing the condition and study of their protein products has shed light on the pathogenesis of the disease and provided valuable new information about signalling pathways regulating protein synthesis and cell growth. There is now the exciting possibility of drug therapy for some of the manifestations of the disease.
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Affiliation(s)
- John R W Yates
- Department of Medical Genetics, University of Cambridge, Cambridge, UK.
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