201
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Crino PB, Miyata H, Vinters HV. Neurodevelopmental disorders as a cause of seizures: neuropathologic, genetic, and mechanistic considerations. Brain Pathol 2006; 12:212-33. [PMID: 11958376 PMCID: PMC8095994 DOI: 10.1111/j.1750-3639.2002.tb00437.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
This review will consider patterns of developmental neuropathologic abnormalities-malformations of cortical development (MCD)--encountered in infants (often with infantile spasms), children, and adults with intractable epilepsy. Treatment of epilepsy associated with some MCD, such as focal cortical dysplasia and tubers of tuberous sclerosis, may include cortical resection performed to remove the "dysplastic" region of cortex. In extreme situations (eg, hemimegalencephaly), hemispherectomy may be carried out on selected patients. Neuropathologic (including immunohistochemical) findings within these lesions will be considered. Other conditions that cause intractable epilepsy and often mental retardation, yet are not necessarily amenable to surgical treatment (eg, lissencephaly, periventricular nodular heterotopia, double cortex syndrome) will be discussed. Over the past 10 years there has been an explosion of information on the genetics of MCD. The genes responsible for many MCD (eg, TSC1, TSC2, LIS-1, DCX, FLN1) have been cloned and permit important mechanistic studies to be carried out with the purpose of understanding how mutations within these genes result in abnormal cortical cytoarchitecture and anomalous neuroglial differentiation. Finally, novel techniques allowing for analysis of patterns of gene expression within single cells, including neurons, is likely to provide answers to the most vexing and important question about these lesions: Why are they epileptogenic?
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Affiliation(s)
- Peter B Crino
- PENN Epilepsy Center, Department of Neurology, University of Pennsylvania, Philadelphia 19104, USA.
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202
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Abstract
Tuberous sclerosis complex (TSC) is a multiorgan genetic disease caused by inactivation of either the TSC1 or TSC2 genes. The disorder typically has profound neurologic involvement and often presents early in life with epilepsy, developmental delay, mental retardation, and autism. These features are generally accepted to result from structural brain abnormalities that are found in patients with TSC. Although much progress has recently been made in discerning the function(s) of the TSC genes, many questions remain as to the role of these genes in brain development and homeostasis. This review will summarize recent progress and suggest future avenues of basic science research.
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Affiliation(s)
- Kevin C Ess
- Departments of Neurology and Pediatrics, Washington University School of Medicine, St Louis, MO, USA.
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203
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Zacharek SJ, Xiong Y, Shumway SD. Negative regulation of TSC1-TSC2 by mammalian D-type cyclins. Cancer Res 2006; 65:11354-60. [PMID: 16357142 DOI: 10.1158/0008-5472.can-05-2236] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The metazoan cell cycle is driven by the timely and composite activities of cyclin-dependent kinases (CDKs). Among these, cyclin D- and cyclin E-dependent kinases phosphorylate the pRb family proteins during G(1) phase of the cell cycle and thereby advance cells beyond the restriction point. Increasing evidence suggests that cyclin D-dependent kinases might affect events other than Rb pathway-mediated entry into S phase, such as accumulation of cell mass. However, little is known about cyclin D activity toward Rb-independent pathway(s) or non-pRb substrates. In this article, we show that the tumor suppressor TSC2 is a cyclin D binding protein. Coexpression of cyclin D1-CDK4/6 in cultured cells leads to increased phosphorylation and decreased detection of both TSC2 and TSC1, and promotes the phosphorylation of the mTOR substrates, 4E-BP1 and S6K1, two key effectors of cell growth that are negatively regulated by the TSC1-TSC2 complex. At the cellular level, ectopic expression of cyclin D1 restores the cell size decrease caused by TSC1-TSC2 expression. Intriguingly, down-regulation of TSC proteins was also observed by the expression of a mutant cyclin D1 that is unable to bind to CDK4/6, or by the coexpression of cyclin D1 with either an INK4 inhibitor or with catalytically inactive CDK6, indicating that cyclin D may regulate TSC1-TSC2 independently of CDK4/6. Together, these observations suggest that mammalian D-type cyclins participate in cell growth control through negative regulation of TSC1-TSC2 function.
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Affiliation(s)
- Sima J Zacharek
- Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, 27599, USA
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204
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Kimball SR, Jefferson LS. New functions for amino acids: effects on gene transcription and translation. Am J Clin Nutr 2006; 83:500S-507S. [PMID: 16470021 DOI: 10.1093/ajcn/83.2.500s] [Citation(s) in RCA: 166] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Amino acids act to regulate multiple processes related to gene expression, including modulation of the function of the proteins that mediate messenger RNA (mRNA) translation. By modulating the function of translation initiation and elongation factors, amino acids regulate the translation of mRNA on a global scale and also act to cause preferential changes in the translation of mRNAs encoding particular proteins or families of proteins. However, amino acids do not directly regulate the function of translation initiation and elongation factors, but instead modulate signaling through pathways traditionally considered to be solely involved in mediating the action of hormones. The best-characterized example of amino acid-induced regulation of a signal transduction pathway is one involving a protein kinase referred to as the mammalian target of rapamycin (mTOR), through which the branched-chain amino acids, particularly leucine, act to modulate the function of proteins engaged in both global mRNA translation and the selection of specific mRNAs for translation. Less understood at this point in time is evidence suggesting that amino acids also act to regulate mRNA translation through mTOR-independent mechanisms. The goal of the present review is to briefly summarize studies, primarily those performed in the laboratories of the authors, that focus on the role of the branched-chain amino acids in the regulation of mRNA translation in skeletal muscle.
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Affiliation(s)
- Scot R Kimball
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033-0850, USA
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205
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Lin HJ, Hsieh FC, Song H, Lin J. Elevated phosphorylation and activation of PDK-1/AKT pathway in human breast cancer. Br J Cancer 2006; 93:1372-81. [PMID: 16288304 PMCID: PMC2361529 DOI: 10.1038/sj.bjc.6602862] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Activation of kinases signalling pathways contributes to various malignant phenotypes in human cancers, including breast tumour. To examine the possible activation of these signalling molecules, we examined the phosphorylation status in 12 protein kinases and transcription factors in normal primary human mammary epithelial cells, telomerase-immortalised human breast epithelial cell line, and two breast cancer lines, MDA-MB-468 and MCF-7, using Kinexus phosphorylated protein screening assays. The phosphorylation of FAK, mTOR, p70S6K, and PDK-1 were elevated in both breast cancer cell lines, whereas the phosphorylation of AKT, EGFR, ErbB2/Her2, PDGFR, Shc, and Stat3 were elevated in only one breast cancer line compared to normal primary mammary epithelial cells and telomerase-immortalised breast epithelial cells. The same findings were confirmed by Western blotting and by kinase assays. We further substantiated the phosphorylation status of these molecules in tissue microarray slides containing 89 invasive breast cancer tissues as well as six normal mammary tissues with immunohistochemistry staining using phospho-specific antibodies. Consistent findings were obtained as greater than 70% of invasive breast carcinomas expressed moderate to high levels of phosphorylated PDK-1, AKT, p70S6K, and EGFR. In sharp contrast, phosphorylation of the same proteins was nearly undetectable or was at low levels in normal mammary tissues under the same assay. Elevated phosphorylation of PDK-1, AKT, mTOR, p70S6K, S6, EGFR, and Stat3 were highly associated with invasive breast tumours (P<0.05). Taken together, our results suggest that activation of these kinase pathways by phosphorylation may in part account for molecular pathogenesis of human breast carcinoma. Particularly, moderate to high level of PDK-1 phosphorylation was found in 86% of high-grade metastasised breast tumours. This is the first report demonstrating phosphorylation of PDK-1 is frequently elevated in breast cancer with concomitantly increased phosphorylation of downstream kinases, including AKT, mTOR, p70S6K, S6, and Stat3. This finding thus suggested PDK-1 may promote oncogenesis in part through the activation of AKT and p70S6K and rationalised that PDK-1 as well as downstream components of PDK-1 signalling pathway may be promising therapeutic targets to treat breast cancer.
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Affiliation(s)
- H-J Lin
- Division of Medical Technology, School of Allied Medical Professions, College of Medicine and Public Health, The Ohio State University, Suite 535A, Atwell Hall, 453 West 10th Street, Columbus, OH 43210, USA.
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206
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Giordano A, Avellino R, Ferraro P, Romano S, Corcione N, Romano MF. Rapamycin antagonizes NF-kappaB nuclear translocation activated by TNF-alpha in primary vascular smooth muscle cells and enhances apoptosis. Am J Physiol Heart Circ Physiol 2006; 290:H2459-65. [PMID: 16428340 DOI: 10.1152/ajpheart.00750.2005] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Several lines of evidence support the view that rapamycin inhibits NF-kappaB. TNF-alpha, a potent inducer of NF-kappaB, is released after artery injury (e.g., balloon angioplasty) and plays an important role in inflammation and restenosis. We investigated the effect of rapamycin on NF-kappaB activation and apoptosis in vascular smooth muscle cells (VSMCs) stimulated with TNF-alpha. Using EMSA, we found that TNF-alpha caused NF-kappaB nuclear translocation in VSMCs after 1 h of incubation. Rapamycin inhibited IkappaBalpha degradation, thereby preventing nuclear translocation. Activation of NF-kappaB was accompanied by an increase of Bcl-xL and Bfl-1/A1 proteins, detected by Western blot assay, whereas rapamycin prevented the TNF-alpha-induced enhancement of these antiapoptotic proteins. The extent of apoptosis of VSMCs exposed to TNF-alpha was significantly enhanced by rapamycin. The effect of rapamycin appeared to be independent of the phosphatidylinositol 3-kinase/Akt-protein kinase B survival pathway, because the phosphatidylinositol 3-kinase inhibitor wortmannin neither prevented IkappaBalpha degradation nor increased apoptosis of cells incubated with TNF-alpha. Finally, we demonstrate that the large immunophilin FK-506 binding protein FKBP51 is essential for TNF-alpha-induced NF-kappaB activation in VSMCs. Our findings show that rapamycin inhibits NF-kappaB activation and acts in concert with TNF-alpha in induction of VSMC apoptosis.
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Affiliation(s)
- Arturo Giordano
- Department of Biochemistry and Medical Biotechnology, University of Naples Federico II, via S. Pansini 5, 80131 Naples, Italy
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207
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McCormack FX. Lymphangioleiomyomatosis. MEDGENMED : MEDSCAPE GENERAL MEDICINE 2006; 8:15. [PMID: 16915145 PMCID: PMC1682009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Affiliation(s)
- Francis X McCormack
- Division of Pulmonary and Critical Care, The University of Cincinnati School of Medicine, Cincinnati, Ohio, USA
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208
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Piedimonte LR, Wailes IK, Weiner HL. Tuberous sclerosis complex: molecular pathogenesis and animal models. Neurosurg Focus 2006; 20:E4. [PMID: 16459994 DOI: 10.3171/foc.2006.20.1.5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Mutations in one of two genes, TSC1 and TSC2, result in a similar disease phenotype by disrupting the normal interaction of their protein products, hamartin and tuberin, which form a functional signaling complex. Disruption of these genes in the brain results in abnormal cellular differentiation, migration, and proliferation, giving rise to the characteristic brain lesions of tuberous sclerosis complex (TSC) called cortical tubers. The most devastating complications of TSC affect the central nervous system and include epilepsy, mental retardation, autism, and glial tumors. Relevant animal models, including conventional and conditional knockout mice, are valuable tools for studying the normal functions of tuberin and hamartin and the way in which disruption of their expression gives rise to the variety of clinical features that characterize TSC. In the future, these animals will be invaluable preclinical models for the development of highly specific and efficacious treatments for children affected with TSC.
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Affiliation(s)
- Leandro R Piedimonte
- Division of Pediatric Neurosurgery, Department of Neurosurgery, New York University School of Medicine, New York, New York 10016, USA
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209
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Patel PH, Tamanoi F. Using Drosophila and yeast genetics to investigate a role for the Rheb GTPase in cell growth. Methods Enzymol 2006; 407:443-54. [PMID: 16757344 DOI: 10.1016/s0076-6879(05)07036-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The small, Ras-like GTPase Rheb plays an important role in the regulation of cell growth by the insulin/PI3K and nutrient/TOR pathways in eukaryotic systems. Studies in genetically tractable organisms such as Drosophila melanogaster and fission yeast (S. pombe) were critical for establishing the significance of Rheb in cell growth. In Drosophila, we find that overexpression of Drosophila Rheb (dRheb) in S2 cells causes their accumulation in S phase and an increase in cell size. In contrast, treatment of S2 cells with double-stranded RNA (RNAi) toward dRheb results in G1 arrest and a reduction in cell size. These altered cell size phenotypes observed in culture are also recapitulated in vivo. Overexpression of dRheb results in increased cell and tissue size without an increase in cell number; reduction of dRheb function results in reduced cell and tissue size. In S. pombe, inhibition of Rheb (SpRheb) expression also results in small, rounded cells that arrest in G0/G1. We will discuss here how we use Drosophila and S. pombe to explain a mechanism by which Rheb promotes cell growth.
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Affiliation(s)
- Parthive H Patel
- Molecular Biology Institute, University of California Los Angeles, Los Angeles, California, USA
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210
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Astrinidis A, Henske EP. Tuberous sclerosis complex: linking growth and energy signaling pathways with human disease. Oncogene 2005; 24:7475-81. [PMID: 16288294 DOI: 10.1038/sj.onc.1209090] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The most exciting advances in the tuberous sclerosis complex (TSC) field occurred in 1993 and 1997 with the cloning of the TSC2 and TSC1 genes, respectively, and in 2003 with the identification of Rheb as the target of tuberin's (TSC2) GTPase activating protein (GAP) domain. Rheb has a dual role: it activates mTOR and inactivates B-Raf. Activation of mTOR leads to increased protein synthesis through phosphorylation of p70S6K and 4E-BP1. Upon insulin or growth factor stimulation, tuberin is phosphorylated by several kinases, including AKT/PKB, thereby suppressing its GAP activity and activating mTOR. Phosphorylation of hamartin (TSC1) by CDK1 also negatively regulates the activity of the hamartin/tuberin complex. Despite these biochemical advances, exactly how mutations in TSC1 or TSC2 lead to the clinical manifestations of TSC is far from being understood. Two of the most unusual phenotypes in TSC are the apparent metastasis of benign cells carrying TSC1 and TSC2 mutations, resulting in pulmonary lymphangiomyomatosis, and the ability of cells with TSC1 or TSC2 mutations to differentiate into the separate components of renal angiomyolipomas (vessels, smooth muscle and fat). We will discuss how the TSC signaling pathways are affected by mutations in TSC1 or TSC2, focusing on how these mutations may lead to the renal and pulmonary manifestations of TSC.
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211
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Kaur S, Uddin S, Platanias LC. The PI3' kinase pathway in interferon signaling. J Interferon Cytokine Res 2005; 25:780-787. [PMID: 16375606 DOI: 10.1089/jir.2005.25.780] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Interferons (IFNs) are pleiotropic cytokines with important immunomodulatory, antitumor, antiviral, and growth inhibitory properties. Consistent with the multiplicity of their effects, the IFNs activate several cellular cascades after they bind to their receptors. Although the Jak-Stat pathway is the most studied pathway, it appears that additional signaling cascades play roles in IFN signaling. The phosphatidylinositol 3'-kinase (PI3'K) pathway has emerged as one of the critical players in IFN signal transduction and is the focus of this review. This pathway is activated distinctively from the Stat pathway but plays important roles in the regulation of IFN-dependent gene transcription and initiation of mRNA translation.
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Affiliation(s)
- Surinder Kaur
- Robert H. Lurie Comprehensive Cancer Center and Division of Hematology-Oncology, Northwestern University Medical School, 303 East Superior Street, Chicago, IL 60611, USA
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212
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Abstract
The oncogene AKT (also called protein kinase B (PKB)) signals to the translational machinery, and activation of protein synthesis by Akt is associated with cancer formation. Akt directly stimulates the activity of translation initiation factors and upregulates ribosome biogenesis. Activation of protein synthesis by Akt is phylogenetically conserved from Drosophila to humans, and is important for regulating cell growth, proliferation and cell survival. Consequently, translation defects due to aberrant Akt activation may be a crucial mechanism leading to tumorigenesis. However, few in vivo studies have established a causative role for aberrant protein synthesis control in cancer. A major challenge in the future will be to identify the specific mRNAs regulated at the level of translation control directly relevant for cellular transformation. In this review, we highlight and discuss the emerging molecular and genetic evidence that support a model by which deregulation of specific or global protein synthesis contributes to cancer.
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Affiliation(s)
- Davide Ruggero
- Human Genetics Program, Fox Chase Cancer Center, PA 19111, USA.
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213
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Dekanty A, Lavista-Llanos S, Irisarri M, Oldham S, Wappner P. The insulin-PI3K/TOR pathway induces a HIF-dependent transcriptional response in Drosophila by promoting nuclear localization of HIF-alpha/Sima. J Cell Sci 2005; 118:5431-41. [PMID: 16278294 DOI: 10.1242/jcs.02648] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The hypoxia-inducible factor (HIF) is a heterodimeric transcription factor composed of a constitutively expressed HIF-beta subunit and an oxygen-regulated HIF-alpha subunit. We have previously defined a hypoxia-inducible transcriptional response in Drosophila melanogaster that is homologous to the mammalian HIF-dependent response. In Drosophila, the bHLH-PAS proteins Similar (Sima) and Tango (Tgo) are the functional homologues of the mammalian HIF-alpha and HIF-beta subunits, respectively. HIF-alpha/Sima is regulated by oxygen at several different levels that include protein stability and subcellular localization. We show here for the first time that insulin can activate HIF-dependent transcription, both in Drosophila S2 cells and in living Drosophila embryos. Using a pharmacological approach as well as RNA interference, we determined that the effect of insulin on HIF-dependent transcriptional induction is mediated by PI3K-AKT and TOR pathways. We demonstrate that stimulation of the transcriptional response involves upregulation of Sima protein but not sima mRNA. Finally, we have analyzed in vivo the effect of the activation of the PI3K-AKT pathway on the subcellular localization of Sima protein. Overexpression of dAKT and dPDK1 in normoxic embryos provoked a major increase in Sima nuclear localization, mimicking the effect of a hypoxic treatment. A similar increase in Sima nuclear localization was observed in dPTEN homozygous mutant embryos, confirming that activation of the PI3K-AKT pathway promotes nuclear accumulation of Sima protein. We conclude that regulation of HIF-alpha/Sima by the PI3K-AKT-TOR pathway is a major conserved mode of regulation of the HIF-dependent transcriptional response in Drosophila.
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Affiliation(s)
- Andrés Dekanty
- Instituto Leloir and IIB, FCEyN-Universidad de Buenos Aires, CONICET, Patricias Argentinas 435, Buenos Aires (1405), Argentina
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214
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Tavazoie SF, Alvarez VA, Ridenour DA, Kwiatkowski DJ, Sabatini BL. Regulation of neuronal morphology and function by the tumor suppressors Tsc1 and Tsc2. Nat Neurosci 2005; 8:1727-34. [PMID: 16286931 DOI: 10.1038/nn1566] [Citation(s) in RCA: 376] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2005] [Accepted: 09/15/2005] [Indexed: 12/31/2022]
Abstract
Mutations in the TSC1 or TSC2 tumor suppressor genes lead to tuberous sclerosis complex (TSC), a dominant hamartomatous disorder that often presents with mental retardation, epilepsy and autism. The etiology of these neurological symptoms is unclear and the function of the TSC pathway in neurons is unknown. We found that in post-mitotic, hippocampal pyramidal neurons of mice and rats, loss of Tsc1 or Tsc2 triggered enlargement of somas and dendritic spines and altered the properties of glutamatergic synapses. Furthermore, loss of a single copy of the Tsc1 gene was sufficient to perturb dendritic spine structure. Morphological changes required regulation of the actin-depolymerization factor cofilin at a conserved LIM-kinase phosphorylation site, the phosphorylation of which was increased by loss of Tsc2. Thus, the TSC pathway regulates growth and synapse function in neurons, and perturbations of neuronal structure and function are likely to contribute to the pathogenesis of the neurological symptoms of TSC.
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Affiliation(s)
- Sohail F Tavazoie
- Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, Massachusetts 02115, USA
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215
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Partridge L, Piper MDW, Mair W. Dietary restriction in Drosophila. Mech Ageing Dev 2005; 126:938-50. [PMID: 15935441 DOI: 10.1016/j.mad.2005.03.023] [Citation(s) in RCA: 249] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 03/10/2005] [Accepted: 03/15/2005] [Indexed: 11/27/2022]
Abstract
The fruit fly Drosophila is a useful organism for the investigation of the mechanisms by which dietary restriction (DR) extends lifespan. Its relatively short generation time, well-characterised molecular biology, genetics and physiology and ease of handling for demographic analysis are all major strengths. Lifespan has been extended by DR applied to adult Drosophila, by restriction of the availability of live yeast or by co-ordinate dilution of the whole food medium. Lifespan increases to a maximum through DR with a progressive dilution of the food and then decreases through starvation as the food is diluted further. Daily and lifetime fecundities of females are reduced by food dilution throughout the DR and starvation range. Standard Drosophila food ingredients differ greatly between laboratories and fly stocks can differ in their responses to food dilution, and a full range of food concentrations should therefore be investigated when examining the response to DR. Flies do not alter the time that they spend feeding in response to DR. Both mean and maximum lifespan are extended by DR. The nutrients critical for the response to DR in Drosophila require definition. The extension of lifespan in response to DR is very much greater in females than in males. Two nutrient-sensing pathways, the insulin/IGF-like and TOR pathways, have been implicated in mediating this response of lifespan to DR in Drosophila, as have two protein deacetylases, dSir2 and Rpd3, although the precise nature of this interaction remain to be characterised. Although female fecundity is reduced by DR, the response of lifespan to DR appears normal in sterile females, possibly implying that reduced fecundity is not necessary for extension of lifespan by DR. There is no reduction in metabolic rate or in the rate of generation of superoxide and hydrogen peroxide from isolated mitochondria in response to DR. DR acts acutely and rapidly (within 48 h) to reduce the mortality of flies that are fully fed to the level found in animals exposed to DR throughout life. This rapid mortality rate recovery provides a powerful framework within which to further investigate the mechanisms by which DR extends lifespan.
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Affiliation(s)
- Linda Partridge
- UCL Centre for Research on Ageing, Department of Biology, University College London, London WC1E 6BT, UK.
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216
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Kwiatkowski DJ, Manning BD. Tuberous sclerosis: a GAP at the crossroads of multiple signaling pathways. Hum Mol Genet 2005; 14 Spec No. 2:R251-8. [PMID: 16244323 DOI: 10.1093/hmg/ddi260] [Citation(s) in RCA: 314] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Tuberous sclerosis complex (TSC) is an autosomal dominant disorder that is characterized by benign tumors (hamartomas and hamartias) involving multiple organ systems, due to inactivating mutations in TSC1 or TSC2. Here, we review recent advances in our understanding of the growth and signaling functions of the TSC1 and TSC2 proteins. Led by seminal studies in Drosophila, the TSC1/TSC2 complex has been positioned in an ancestrally conserved signaling pathway that regulates cell growth. TSC1/TSC2 receives inputs from at least three major signaling pathways in the form of kinase-mediated phosphorylation events that regulate its function as a GTPase activating protein (GAP): the PI3K-Akt pathway, the ERK1/2-RSK1 pathway and the LKB1-AMPK pathway. TSC1/TSC2 functions as a GAP towards Rheb, which is a major regulator of the mammalian target of rapamycin (mTOR). In the absence of either TSC1 or TSC2, high levels of Rheb-GTP lead to constitutive activation of mTOR-raptor signaling, thereby leading to enhanced and deregulated protein synthesis and cell growth. As a specific inhibitor of mTOR, rapamycin has therapeutic potential for the treatment of TSC hamartomas.
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Affiliation(s)
- David J Kwiatkowski
- Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, One Blackfan Circle, 6th Floor, Room 216, Boston, MA 02115, USA.
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217
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Wei JJ, Chiriboga L, Arslan AA, Melamed J, Yee H, Mittal K. Ethnic differences in expression of the dysregulated proteins in uterine leiomyomata. Hum Reprod 2005; 21:57-67. [PMID: 16172143 DOI: 10.1093/humrep/dei309] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Black ethnicity is one of the risk factors for uterine leiomyomata (ULM). Little is known about the ethnic differences in leiomyoma-associated gene products in women with uterine leiomyomata. METHODS A total of 120 hysterectomies with ULM were collected from black, Asian, Hispanic and white women (30 cases from each group). Twenty-two gene products were selected for the study. The expressions of the selected dysregulated gene products were measured by the semiquantification and the immunoscores were normalized by matched myometrium. RESULTS The relative expressions of progesterone receptor A (PR-A) (up-regulation), retinoid acid receptor alpha (down-regulation), and retinoid X receptor alpha (RXRalpha) (no change) in leiomyomata compared to normal myometrium in black women were significantly different compared to other ethnic groups (P < 0.05). About one-third of ULM from black women subclustered together in association with a group of up-regulated gene products. Many other gene products, including local growth factors, insulin-like growth factor (IGF)-signalling proteins, and cell proliferation markers, were dysregulated in ULM but showed non-significant differences between the ethnic groups. CONCLUSIONS There are substantial differences of the sex steroid receptors and other nuclear receptors between black women and other ethnic groups. Based on tissue microarray data, there are at least two broad groups of leiomyomata presented by the dysregulation of different groups of gene products. One is dominated by up-regulation of amplified in breast cancer 1, CD24, hamartin, human mobility group gene 2, IGF2, PR-A and RXR, and the other is characterized by up-regulation of epithelial growth factor receptor, down-regulation of hamartin, PR-A and tuberin.
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Affiliation(s)
- Jian-Jun Wei
- Department of Pathology, New York University School of Medicine, bellevue Hospital, 560 First Avenue, New York, NY 10016, USA.
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218
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Sofer A, Lei K, Johannessen CM, Ellisen LW. Regulation of mTOR and cell growth in response to energy stress by REDD1. Mol Cell Biol 2005; 25:5834-45. [PMID: 15988001 PMCID: PMC1168803 DOI: 10.1128/mcb.25.14.5834-5845.2005] [Citation(s) in RCA: 358] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The tuberous sclerosis tumor suppressors TSC1 and TSC2 regulate the mTOR pathway to control translation and cell growth in response to nutrient and growth factor stimuli. We have recently identified the stress response REDD1 gene as a mediator of tuberous sclerosis complex (TSC)-dependent mTOR regulation by hypoxia. Here, we demonstrate that REDD1 inhibits mTOR function to control cell growth in response to energy stress. Endogenous REDD1 is induced following energy stress, and REDD1-/- cells are highly defective in dephosphorylation of the key mTOR substrates S6K and 4E-BP1 following either ATP depletion or direct activation of the AMP-activated protein kinase (AMPK). REDD1 likely acts on the TSC1/2 complex, as regulation of mTOR substrate phosphorylation by REDD1 requires TSC2 and is blocked by overexpression of the TSC1/2 downstream target Rheb but is not blocked by inhibition of AMPK. Tetracycline-inducible expression of REDD1 triggers rapid dephosphorylation of S6K and 4E-BP1 and significantly decreases cellular size. Conversely, inhibition of endogenous REDD1 by short interfering RNA increases cell size in a rapamycin-sensitive manner, and REDD1-/- cells are defective in cell growth regulation following ATP depletion. These results define REDD1 as a critical transducer of the cellular response to energy depletion through the TSC-mTOR pathway.
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Affiliation(s)
- Avi Sofer
- Massachusetts General Hospital Cancer Center and Harvard Medical School, GRJ-904, 55 Fruit Street, Boston, Massachusetts 02114, USA
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219
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Teleman AA, Chen YW, Cohen SM. Drosophila Melted Modulates FOXO and TOR Activity. Dev Cell 2005; 9:271-81. [PMID: 16054033 DOI: 10.1016/j.devcel.2005.07.004] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2005] [Revised: 05/18/2005] [Accepted: 07/13/2005] [Indexed: 12/31/2022]
Abstract
The insulin/PI3K signaling pathway controls both tissue growth and metabolism. Here, we identify Melted as a new modulator of this pathway in Drosophila. Melted interacts with both Tsc1 and FOXO and can recruit these proteins to the cell membrane. We provide evidence that in the melted mutant, TOR activity is reduced and FOXO is activated. The melted mutant condition mimics the effects of nutrient deprivation in a normal animal, producing an animal with 40% less fat than normal.
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220
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Coelho CMA, Kolevski B, Walker CD, Lavagi I, Shaw T, Ebert A, Leevers SJ, Marygold SJ. A genetic screen for dominant modifiers of a small-wing phenotype in Drosophila melanogaster identifies proteins involved in splicing and translation. Genetics 2005; 171:597-614. [PMID: 15998720 PMCID: PMC1456774 DOI: 10.1534/genetics.105.045021] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Studies in the fly, Drosophila melanogaster, have revealed that several signaling pathways are important for the regulation of growth. Among these, the insulin receptor/phosphoinositide 3-kinase (PI3K) pathway is remarkable in that it affects growth and final size without disturbing pattern formation. We have used a small-wing phenotype, generated by misexpression of kinase-dead PI3K, to screen for novel mutations that specifically disrupt organ growth in vivo. We identified several complementation groups that dominantly enhance this small-wing phenotype. Meiotic recombination in conjunction with visible markers and single-nucleotide polymorphisms (SNPs) was used to map five enhancers to single genes. Two of these, nucampholin and prp8, encode pre-mRNA splicing factors. The three other enhancers encode factors required for mRNA translation: pixie encodes the Drosophila ortholog of yeast RLI1, and RpL5 and RpL38 encode proteins of the large ribosomal subunit. Interestingly, mutations in several other ribosomal protein-encoding genes also enhance the small-wing phenotype used in the original screen. Our work has therefore identified mutations in five previously uncharacterized Drosophila genes and provides in vivo evidence that normal organ growth requires optimal regulation of both pre-mRNA splicing and mRNA translation.
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Affiliation(s)
- Carmen M A Coelho
- Growth Regulation Laboratory, Cancer Research UK London Research Institute
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221
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Wislez M, Spencer ML, Izzo JG, Juroske DM, Balhara K, Cody DD, Price RE, Hittelman WN, Wistuba II, Kurie JM. Inhibition of mammalian target of rapamycin reverses alveolar epithelial neoplasia induced by oncogenic K-ras. Cancer Res 2005; 65:3226-35. [PMID: 15833854 DOI: 10.1158/0008-5472.can-04-4420] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The serine/threonine kinase AKT and its downstream mediator mammalian target of rapamycin (mTOR) are activated in lung adenocarcinoma, and clinical trials are under way to test whether inhibition of mTOR is useful in treating lung cancer. Here, we report that mTOR inhibition blocked malignant progression in K-ras(LA1) mice, which undergo somatic activation of the K-ras oncogene and display morphologic changes in alveolar epithelial cells that recapitulate those of precursors of human lung adenocarcinoma. Levels of phospho-S6(Ser236/235), a downstream mediator of mTOR, increased with malignant progression (normal alveolar epithelial cells to adenocarcinoma) in K-ras(LA1) mice and in patients with lung adenocarcinoma. Atypical alveolar hyperplasia, an early neoplastic change, was prominently associated with macrophages and expressed high levels of phospho-S6(Ser236/235). mTOR inhibition in K-ras(LA1) mice by treatment with the rapamycin analogue CCI-779 reduced the size and number of early epithelial neoplastic lesions (atypical alveolar hyperplasia and adenomas) and induced apoptosis of intraepithelial macrophages. LKR-13, a lung adenocarcinoma cell line derived from K-ras(LA1) mice, was resistant to treatment with CCI-779 in vitro. However, LKR-13 cells grown as syngeneic tumors recruited macrophages, and those tumors regressed in response to treatment with CCI-779. Lastly, conditioned medium from primary cultures of alveolar macrophages stimulated the proliferation of LKR-13 cells. These findings provide evidence that the expansion of lung adenocarcinoma precursors induced by oncogenic K-ras requires mTOR-dependent signaling and that host factors derived from macrophages play a critical role in adenocarcinoma progression.
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Affiliation(s)
- Marie Wislez
- Department of Thoracic/Head and Neck Medical Oncology, University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA
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222
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Findlay GM, Harrington LS, Lamb RF. TSC1-2 tumour suppressor and regulation of mTOR signalling: linking cell growth and proliferation? Curr Opin Genet Dev 2005; 15:69-76. [PMID: 15661536 DOI: 10.1016/j.gde.2004.11.002] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Understanding the relationship between growth and proliferation in multicellular organisms requires identification of the key regulators of growth control, and an understanding of how they regulate growth and how growth is linked to cell proliferation. Recent progress in understanding the mechanisms of growth control indicates that the tuberous sclerosis complex tumour-suppressor TSC1-2 serves as a point of integration between growth-stimulatory and growth-suppressive signalling upstream of a small GTPase, Rheb. However, Rheb-induced growth might not explain the additional effects of TSC1-2 upon cell proliferation.
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Affiliation(s)
- Greg M Findlay
- Cancer Research UK Centre for Cell and Molecular Biology, The Institute of Cancer Research, London, SW3 6JB, UK
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223
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Lee L, Sudentas P, Donohue B, Asrican K, Worku A, Walker V, Sun Y, Schmidt K, Albert MS, El-Hashemite N, Lader AS, Onda H, Zhang H, Kwiatkowski DJ, Dabora SL. Efficacy of a rapamycin analog (CCI-779) and IFN-gamma in tuberous sclerosis mouse models. Genes Chromosomes Cancer 2005; 42:213-27. [PMID: 15578690 DOI: 10.1002/gcc.20118] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Tuberous sclerosis complex (TSC) is a familial tumor disorder for which there is no effective medical therapy. Disease-causing mutations in the TSC1 or TSC2 gene lead to increased mammalian target of rapamycin (mTOR) kinase activity in the conserved mTOR signaling pathway, which regulates nutrient uptake, cell growth, and protein translation. The normal function of TSC1 and TSC2 gene products is to form a complex that reduces mTOR kinase activity. Thus, mTOR kinase inhibition may be a useful targeted therapeutic approach. Elevated interferon-gamma (IFN-gamma) expression is associated with decreased severity of kidney tumors in TSC patients and mouse models; therefore, IFN-gamma also has therapeutic potential. We studied cohorts of Tsc2+/- mice and a novel mouse model of Tsc2-null tumors in order to evaluate the efficacy of targeted therapy for TSC. We found that treatment with either an mTOR kinase inhibitor (CCI-779, a rapamycin analog) or with IFN-gamma reduced the severity of TSC-related disease without significant toxicity. These results constitute definitive preclinical data that justify proceeding with clinical trials using these agents in selected patients with TSC and related disorders.
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Affiliation(s)
- Laifong Lee
- Division of Hematology, Brigham and Women's Hospital, Boston, MA 02115, USA
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224
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Holz MK, Blenis J. Identification of S6 kinase 1 as a novel mammalian target of rapamycin (mTOR)-phosphorylating kinase. J Biol Chem 2005; 280:26089-93. [PMID: 15905173 DOI: 10.1074/jbc.m504045200] [Citation(s) in RCA: 281] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Here we demonstrate that mammalian target of rapamycin (mTOR) is phosphorylated in a rapamycin-sensitive manner. We show that S6 kinase 1 (S6K1), but not Akt, directly phosphorylates mTOR in cell-free in vitro system and in cells. Expression of a constitutively active, rapamycin- and wortmannin-resistant S6K1 leads to constitutive phosphorylation of mTOR, whereas knock-down of S6K1 using small inhibitory RNA greatly reduces mTOR phosphorylation despite elevated Akt activity. Importantly, phosphorylation of mTOR by S6K1 occurs at threonine 2446/serine 2448. This region has been shown previously to be part of a regulatory repressor domain. These sites are also constitutively phosphorylated in the breast cancer cell line MCF7 carrying an amplification of the S6K1 gene, but not in a less tumorigenic cell line, MCF10a. Many models for Akt signaling to mTOR have been presented, suggesting direct phosphorylation by Akt. These models must be reconsidered in light of the present findings.
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Affiliation(s)
- Marina K Holz
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
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225
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Avellino R, Romano S, Parasole R, Bisogni R, Lamberti A, Poggi V, Venuta S, Romano MF. Rapamycin stimulates apoptosis of childhood acute lymphoblastic leukemia cells. Blood 2005; 106:1400-6. [PMID: 15878982 DOI: 10.1182/blood-2005-03-0929] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The phosphatidyl-inositol 3 kinase (PI3k)/Akt pathway has been implicated in childhood acute lymphoblastic leukemia (ALL). Because rapamycin suppresses the oncogenic processes sustained by PI3k/Akt, we investigated whether rapamycin affects blast survival. We found that rapamycin induces apoptosis of blasts in 56% of the bone marrow samples analyzed. Using the PI3k inhibitor wortmannin, we show that the PI3k/Akt pathway is involved in blast survival. Moreover, rapamycin increased doxorubicin-induced apoptosis even in nonresponder samples. Anthracyclines activate nuclear factor kappaB (NF-kappaB), and disruption of this signaling pathway increases the efficacy of apoptogenic stimuli. Rapamycin inhibited doxorubicin-induced NF-kappaB in ALL samples. Using a short interfering (si) RNA approach, we demonstrate that FKBP51, a large immunophilin inhibited by rapamycin, is essential for drug-induced NF-kappaB activation in human leukemia. Furthermore, rapamycin did not increase doxorubicin-induced apoptosis when NF-kappaB was overexpressed. In conclusion, rapamycin targets 2 pathways that are crucial for cell survival and chemoresistance of malignant lymphoblasts--PI3k/Akt through the mammalian target of rapamycin and NF-kappaB through FKBP51--suggesting that the drug could be beneficial in the treatment of childhood ALL.
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Affiliation(s)
- Raffaella Avellino
- Department of Biochemistry and Medical Biotechnologies, Federico II University, Via S. Pansini 5, 80131 Naples, Italy
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226
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Goberdhan DCI, Meredith D, Boyd CAR, Wilson C. PAT-related amino acid transporters regulate growth via a novel mechanism that does not require bulk transport of amino acids. Development 2005; 132:2365-75. [PMID: 15843412 DOI: 10.1242/dev.01821] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Growth in normal and tumour cells is regulated by evolutionarily conserved extracellular inputs from the endocrine insulin receptor (InR) signalling pathway and by local nutrients. Both signals modulate activity of the intracellular TOR kinase, with nutrients at least partly acting through changes in intracellular amino acid levels mediated by amino acid transporters. We show that in Drosophila, two molecules related to mammalian proton-assisted SLC36 amino acid transporters (PATs), CG3424 and CG1139, are potent mediators of growth. These transporters genetically interact with TOR and other InR signalling components, indicating that they control growth by directly or indirectly modulating the effects of TOR signalling. A mutation in the CG3424 gene, which we have named pathetic (path), reduces growth in the fly. In a heterologous Xenopus oocyte system, PATH also activates the TOR target S6 kinase in an amino acid-dependent way. However, functional analysis reveals that PATH has an extremely low capacity and an exceptionally high affinity compared with characterised human PATs and the CG1139 transporter. PATH and potentially other PAT-related transporters must therefore control growth via a mechanism that does not require bulk transport of amino acids into the cell. As PATH is likely to be saturated in vivo, we propose that one specialised function of high-affinity PAT-related molecules is to maintain growth as local nutrient levels fluctuate during development.
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Affiliation(s)
- Deborah C I Goberdhan
- Department of Human Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, UK.
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227
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Abstract
Cell growth (increase in cell mass or size) is tightly coupled to nutrient availability, growth factors and the energy status of the cell. The target of rapamycin (TOR) integrates all three inputs to control cell growth. The discovery of upstream regulators of TOR (AMPK, the TSC1-TSC2 complex and Rheb) has provided new insights into the mechanism by which TOR integrates its various inputs. A recent finding in flies reveals that TOR controls not only growth of the cell in which it resides (cell-autonomous growth) but also the growth of distant cells, thereby determining organ and organism size in addition to the size of isolated cells. In yeast and mammals, the identification of two structurally and functionally distinct multiprotein TOR complexes (TORC1 and TORC2) has provided a molecular basis for the complexity of TOR signaling. Furthermore, TOR has emerged as a regulator of growth-related processes such as development, aging and the response to hypoxia. Thus, TOR is part of an intra- and inter-cellular signaling network with a remarkably broad role in eukaryotic biology.
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Affiliation(s)
- Dietmar E Martin
- Division of Biochemistry, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
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228
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Inoki K, Ouyang H, Li Y, Guan KL. Signaling by target of rapamycin proteins in cell growth control. Microbiol Mol Biol Rev 2005; 69:79-100. [PMID: 15755954 PMCID: PMC1082789 DOI: 10.1128/mmbr.69.1.79-100.2005] [Citation(s) in RCA: 259] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Target of rapamycin (TOR) proteins are members of the phosphatidylinositol kinase-related kinase (PIKK) family and are highly conserved from yeast to mammals. TOR proteins integrate signals from growth factors, nutrients, stress, and cellular energy levels to control cell growth. The ribosomal S6 kinase 1 (S6K) and eukaryotic initiation factor 4E binding protein 1(4EBP1) are two cellular targets of TOR kinase activity and are known to mediate TOR function in translational control in mammalian cells. However, the precise molecular mechanism of TOR regulation is not completely understood. One of the recent breakthrough studies in TOR signaling resulted in the identification of the tuberous sclerosis complex gene products, TSC1 and TSC2, as negative regulators for TOR signaling. Furthermore, the discovery that the small GTPase Rheb is a direct downstream target of TSC1-TSC2 and a positive regulator of the TOR function has significantly advanced our understanding of the molecular mechanism of TOR activation. Here we review the current understanding of the regulation of TOR signaling and discuss its function as a signaling nexus to control cell growth during normal development and tumorigenesis.
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Affiliation(s)
- Ken Inoki
- Life Science Institute, University of Michigan Medical School, 5450 Medical Science I Bldg., Ann Arbor, MI 48109-0606, USA
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229
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Wei J, Chiriboga L, Mizuguchi M, Yee H, Mittal K. Expression profile of tuberin and some potential tumorigenic factors in 60 patients with uterine leiomyomata. Mod Pathol 2005; 18:179-88. [PMID: 15467714 DOI: 10.1038/modpathol.3800283] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Human uterine leiomyomata are the most common tumors in women of reproductive age. The pathogenesis of leiomyomata remains unknown. An animal model of Eker rats with deleted tuberous sclerosis complex gene 2 (tuberin) shows increased incidence of leiomyomata. The role of tuberin in human leiomyomata is unknown. In this study, we designed a tissue microarray with tissue cores of leiomyomata and the matched myometrium from 60 hysterectomy specimens. We examined the expression of tuberin and tuberous sclerosis complex gene 1 product hamartin, proteins of the insulin-signaling pathway, steroid receptors and some of their cofactors, and human mobility group gene A2 by immunohistochemistry. We found that nearly half of the cases displayed either reduction or loss of tuberin in leiomyomata compared with matched normal myometrium. No change of hamartin was noted. Furthermore, a significant reduction of glucocorticoid receptor was found in leiomyomata with reduced tuberin. The proteins insulin like growth factor 1, insulin-like growth factor receptor beta, AKT kinase, and phosphatidylinositol 3-kinase were upregulated. Nearly half of leiomyomata show upregulation of human mobility group gene A2, along with the steroid receptor cofactors. Our findings suggest that there are two broad groups of uterine leiomyomata. One group is associated with an alteration of tuberin and glucocorticoid receptor. The other group is associated with upregulation of human mobility group gene A2 and steroid receptor cofactors.
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Affiliation(s)
- Jianjun Wei
- Department of Pathology, New York University School of Medicine, New York, NY 10016, USA
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230
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Abstract
Drosophila melanogaster is emerging as one of the most effective tools for analyzing the function of human disease genes, including those responsible for developmental and neurological disorders, cancer, cardiovascular disease, metabolic and storage diseases, and genes required for the function of the visual, auditory and immune systems. Flies have several experimental advantages, including their rapid life cycle and the large numbers of individuals that can be generated, which make them ideal for sophisticated genetic screens, and in future should aid the analysis of complex multigenic disorders. The general principles by which D. melanogaster can be used to understand human disease, together with several specific examples, are considered in this review.
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Affiliation(s)
- Ethan Bier
- Section of Cell and Developmental Biology, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92039, USA.
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231
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Takahashi DK, Dinday MT, Barbaro NM, Baraban SC. Abnormal cortical cells and astrocytomas in the Eker rat model of tuberous sclerosis complex. Epilepsia 2005; 45:1525-30. [PMID: 15571510 DOI: 10.1111/j.0013-9580.2004.23004.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
PURPOSE In patients with tuberous sclerosis complex (TSC), a wide range of neurologic abnormalities develop, including mental retardation and seizures. Brains from TSC patients are characterized by the presence of cortical tubers, large dysmorphic neurons, and abnormal cytomegalic cells. Although analysis of human TSC brain samples led to the identification of these abnormal cell types, very little is known about how these cells function. In an effort to model TSC-associated CNS abnormalities (and ultimately to analyze the electrophysiologic properties of abnormal cells), we examined Eker rats carrying a Tsc2 mutation. Anatomic studies, including standard histologic stains and immunocytochemistry, were performed on young Eker rats exposed to a carcinogen in utero or aged untreated Eker rats (18-24 months old). METHODS Pregnant TSC2+/- females were injected once a day with hydroquinone (HQ), and offspring were killed at postnatal day P14 or P28. Coronal tissue sections throughout the CNS were prepared and stained for cresyl violet. In separate studies, brains of old untreated Eker rats were sectioned for anatomic analysis by using standard immunohistochemical techniques. RESULTS Tissue sections stained with cresyl violet did not reveal any gross differences between HQ-treated Eker (Tsc2Ek/+) rats and siblings (Tsc2+/+). However, two classes of abnormal giant cells were observed in brain sections from untreated aged Eker rats: (a) large dysmorphic pyramid-like cells immunoreactive for NeuN, tuberin, and EAAC-1 in layers IV-VI; and (b) abnormal cytomegalic cells immunoreactive for glial fibrillary acidic protein (GFAP), vimentin, and nestin in deep cortical layers or along the white matter. In addition, large subependymal astrocytomas were observed in four animals. CONCLUSIONS Our data suggest that cortical tuber formation in Eker rats is a rare event and that prenatal exposure to a nongenotoxic carcinogen such as HQ is not sufficient to induce tuber formation. However, with advanced age, an increased likelihood of astrocytoma formation and the emergence of dysmorphic neurons and cytomegalic cells in the Eker rat brain might exist; each of these abnormalities mimics those seen clinically and could contribute to neurologic problems associated with TSC. Further analysis of this rodent model may be warranted.
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Affiliation(s)
- D Koji Takahashi
- Epilepsy Research Laboratory, Department of Neurological Surgery, University of California, San Francisco, San Francisco, California, USA
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232
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Avruch J, Lin Y, Long X, Murthy S, Ortiz-Vega S. Recent advances in the regulation of the TOR pathway by insulin and nutrients. Curr Opin Clin Nutr Metab Care 2005; 8:67-72. [PMID: 15586002 DOI: 10.1097/00075197-200501000-00010] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
PURPOSE OF REVIEW The aim of this article is to summarize recent advances in the understanding of the regulation of the target of rapamycin (TOR), a protein kinase that is regulated independently by insulin, amino acids and energy sufficiency and which participates in the control of the component of protein synthesis responsible for cell growth. RECENT FINDINGS These have been found in two major areas: genetic studies in Drosophila followed by studies in mammalian systems have identified the components of the Tuberous Sclerosis protein complex, a heterodimer of the proteins Hamartin and Tuberin, as inhibitors of TOR signaling, and as the major targets by which the insulin/IGF-1 signal transduction pathway, through the protein kinase PKB, and the energy status of the cell, through the AMP-activated protein kinase, regulate the TOR signaling. In turn, the inhibitory action of the tuberous sclerosis protein complex has been shown to be mediated by its ability to deactivate the small, ras-like GTPase Rheb. A second advance has been achieved by the identification of the TOR-associated protein raptor, as an indispensable substrate binding sub-unit of the TOR complex, and as the site at which the inhibitory effects on TOR signaling of rapamycin and amino acid deficiency converge. SUMMARY These findings bring us closer to the understanding of how nutrients and insulin coordinate protein synthesis to regulate anabolic cell growth.
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Affiliation(s)
- Joseph Avruch
- Diabetes Unit and Medical Services and Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts, USA.
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233
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Inoki K, Corradetti MN, Guan KL. Dysregulation of the TSC-mTOR pathway in human disease. Nat Genet 2005; 37:19-24. [PMID: 15624019 DOI: 10.1038/ng1494] [Citation(s) in RCA: 764] [Impact Index Per Article: 38.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2004] [Accepted: 11/23/2004] [Indexed: 12/15/2022]
Abstract
The mammalian target of rapamycin (mTOR) has a central role in the regulation of cell growth. mTOR receives input from multiple signaling pathways, including growth factors and nutrients, to stimulate protein synthesis by phosphorylating key translation regulators such as ribosomal S6 kinase and eukaryote initiation factor 4E binding protein 1. High levels of dysregulated mTOR activity are associated with several hamartoma syndromes, including tuberous sclerosis complex, the PTEN-related hamartoma syndromes and Peutz-Jeghers syndrome. These disorders are all caused by mutations in tumor-suppressor genes that negatively regulate mTOR. Here we discuss the emerging evidence for a functional relationship between the mTOR signaling pathway and several genetic diseases, and we present evidence supporting a model in which dysregulation of mTOR may be a common molecular basis, not only for hamartoma syndromes, but also for other cellular hypertrophic disorders.
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Affiliation(s)
- Ken Inoki
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109, USA
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234
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Abstract
Many human diseases occur when the precise regulation of cell growth (cell mass/size) and proliferation (rates of cell division) is compromised. This review highlights those human disorders that occur as a result of inappropriate cellular signal transduction through the mammalian target of rapamycin (mTOR), a major pathway that coordinates proper cell growth and proliferation by regulating ribosomal biogenesis and protein translation. Recent studies reveal that the tuberous sclerosis complex (TSC)-1/2, PTEN, and LKB1 tumor suppressor proteins tightly control mTOR. Loss of these tumor suppressors leads to an array of hamartoma syndromes as a result of heightened mTOR signaling. Since mTOR plays a pivotal role in maintaining proper cell size and growth, dysregulation of mTOR signaling results in these benign tumor syndromes and an array of other human disorders.
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Affiliation(s)
- Andrew R Tee
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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235
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Brugarolas J, Lei K, Hurley RL, Manning BD, Reiling JH, Hafen E, Witters LA, Ellisen LW, Kaelin WG. Regulation of mTOR function in response to hypoxia by REDD1 and the TSC1/TSC2 tumor suppressor complex. Genes Dev 2004; 18:2893-904. [PMID: 15545625 PMCID: PMC534650 DOI: 10.1101/gad.1256804] [Citation(s) in RCA: 1065] [Impact Index Per Article: 50.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Mammalian target of rapamycin (mTOR) is a central regulator of protein synthesis whose activity is modulated by a variety of signals. Energy depletion and hypoxia result in mTOR inhibition. While energy depletion inhibits mTOR through a process involving the activation of AMP-activated protein kinase (AMPK) by LKB1 and subsequent phosphorylation of TSC2, the mechanism of mTOR inhibition by hypoxia is not known. Here we show that mTOR inhibition by hypoxia requires the TSC1/TSC2 tumor suppressor complex and the hypoxia-inducible gene REDD1/RTP801. Disruption of the TSC1/TSC2 complex through loss of TSC1 or TSC2 blocks the effects of hypoxia on mTOR, as measured by changes in the mTOR targets S6K and 4E-BP1, and results in abnormal accumulation of Hypoxia-inducible factor (HIF). In contrast to energy depletion, mTOR inhibition by hypoxia does not require AMPK or LKB1. Down-regulation of mTOR activity by hypoxia requires de novo mRNA synthesis and correlates with increased expression of the hypoxia-inducible REDD1 gene. Disruption of REDD1 abrogates the hypoxia-induced inhibition of mTOR, and REDD1 overexpression is sufficient to down-regulate S6K phosphorylation in a TSC1/TSC2-dependent manner. Inhibition of mTOR function by hypoxia is likely to be important for tumor suppression as TSC2-deficient cells maintain abnormally high levels of cell proliferation under hypoxia.
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Affiliation(s)
- James Brugarolas
- Dana-Farber Cancer Institute and Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA
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236
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Reiling JH, Hafen E. The hypoxia-induced paralogs Scylla and Charybdis inhibit growth by down-regulating S6K activity upstream of TSC in Drosophila. Genes Dev 2004; 18:2879-92. [PMID: 15545626 PMCID: PMC534649 DOI: 10.1101/gad.322704] [Citation(s) in RCA: 246] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Diverse extrinsic and intrinsic cues must be integrated within a developing organism to ensure appropriate growth at the cellular and organismal level. In Drosophila, the insulin receptor/TOR/S6K signaling network plays a fundamental role in the control of metabolism and cell growth. Here we show that scylla and charybdis, two homologous genes identified as growth suppressors in an EP (enhancer/promoter) overexpression screen, act as negative regulators of growth. The simultaneous loss of both genes generates flies that are more susceptible to reduced oxygen concentrations (hypoxia) and that show mild overgrowth phenotypes. Conversely, scylla or charybdis overactivation reduces growth. Growth inhibition is associated with a reduction in S6K but not PKB/Akt activity. Together, genetic and biochemical analysis places Scylla/Charybdis downstream of PKB and upstream of TSC. Furthermore, we show that scylla and charybdis are induced under hypoxic conditions and that scylla is a target of Drosophila HIF-1 (hypoxia-inducible factor-1) like its mammalian counterpart RTP801/REDD1, thus establishing a potential cross-talk between growth and oxygen sensing.
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Affiliation(s)
- Jan H Reiling
- Zoologisches Institut, Universität Zürich, CH-8057 Zürich, Switzerland
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237
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Kim SE, Cho JY, Kim KS, Lee SJ, Lee KH, Choi KY. Drosophila PI3 kinase and Akt involved in insulin-stimulated proliferation and ERK pathway activation in Schneider cells. Cell Signal 2004; 16:1309-17. [PMID: 15337530 DOI: 10.1016/j.cellsig.2004.04.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2004] [Revised: 04/03/2004] [Accepted: 04/03/2004] [Indexed: 12/26/2022]
Abstract
We have characterized the role of Drosophila PI3K and AKT in ERK pathway activation involving insulin-induced proliferation using Drosophila Schneider cells. After insulin treatment, dPI3K and dAKT activities were both increased along with activation of the dERK pathway components dMEK and dERK. The insulin-induced activations of dERK and dAKT were blocked by LY294002, dPTEN, and by an AKT inhibitor, indicating involvement of dPI3K and dAKT in the insulin-induced dERK and dAKT activations. Proliferation and the G1 to S phase cell cycle progression due to insulin were also blocked by PI3K and AKT inhibitors, indicating that the Drosophila PI3K-AKT pathway involves insulin-mediated cell proliferation. The insulin-stimulated size increase was blocked by both LY294002 and AKT inhibitor, not by U0126, indicating that insulin-mediated size control by dPI3K and dAKT occurs independently of the ERK pathway. This study indicates that dPI3K and dAKT are involved in insulin-induced ERK pathway activation leading to proliferation in Drosophila Schneider cells.
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Affiliation(s)
- Sung-Eun Kim
- Department of Biotechnology, Division of Cellular and Molecular Biology, Yonsei University, 132 Shinchon-Dong, Seodemun-Gu, Seoul 120-752, South Korea
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238
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Abstract
Regulation of growth and proliferation in higher eukaryotic cells results from an integration of nutritional, energy, and mitogenic signals. Biochemical processes underlying cell growth and proliferation are governed by the phosphatidylinositol 3-kinase (PI3K) and target of rapamycin (TOR) signaling pathways. The importance of the interplay between these two pathways is underscored by the discovery that the TOR inhibitor rapamycin is effective against tumors caused by misregulation of the PI3K pathway. We review here recent data concerning the convergence of the PI3K and TOR pathways, the role of these pathways in cell growth and proliferation, and the regulation of growth by downstream TOR targets.
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239
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Bateman JM, McNeill H. Temporal Control of Differentiation by the Insulin Receptor/Tor Pathway in Drosophila. Cell 2004; 119:87-96. [PMID: 15454083 DOI: 10.1016/j.cell.2004.08.028] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2004] [Revised: 08/12/2004] [Accepted: 08/16/2004] [Indexed: 11/17/2022]
Abstract
Multicellular organisms must integrate growth and differentiation precisely to pattern complex tissues. Despite great progress in understanding how different cell fates are induced, it is poorly understood how differentiation decisions are temporally regulated. In a screen for patterning mutants, we isolated alleles of tsc1, a component of the insulin receptor (InR) growth control pathway. We find that loss of tsc1 disrupts patterning due to a loss of temporal control of differentiation. tsc1 controls the timing of differentiation downstream or in parallel to the RAS/MAPK pathway. Examination of InR, PI3K, PTEN, Tor, Rheb, and S6 kinase mutants demonstrates that increased InR signaling leads to precocious differentiation while decreased signaling leads to delays in differentiation. Importantly, cell fates are unchanged, but tissue organization is lost upon loss of developmental timing controls. These data suggest that intricate developmental decisions are coordinated with nutritional status and tissue growth by the InR signaling pathway.
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Affiliation(s)
- Joseph M Bateman
- Cancer Research UK, 44 Lincoln's Inn Fields, London, WC2A 3PX, England
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240
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Abstract
The study of hereditary tumor syndromes has laid a solid foundation toward understanding the genetic basis of cancer. One of the latest examples comes from the study of tuberous sclerosis complex (TSC). As a member of the phakomatoses, TSC is characterized by the appearance of benign tumors, most notably in the central nervous system, kidney, heart, lung, and skin. While classically described as "hamartomas," the pathology of the lesions has features suggestive of abnormal cellular proliferation, size, differentiation, and migration. Occasionally, tumors progress to become malignant (i.e., renal cell carcinoma). The genetic basis of this disease has been attributed to mutations in one of two unlinked genes, TSC1 and TSC2. Cells undergo bi-allelic inactivation of either gene to give rise to tumors in a classic tumor suppressor "two-hit" paradigm. The functions of the TSC1 and TSC2 gene products, hamartin and tuberin, respectively, have remained ill defined until recently. Genetic, biochemical, and biologic analyses have highlighted their role as negative regulators of the mTOR signaling pathway. Tuberin, serving as a substrate of AKT and AMPK, mediates mTOR activity by coordinating inputs from growth factors and energy availability in the control of cell growth, proliferation, and survival. Emerging evidence also suggests that the TSC 1/2 complex may play a role in modulating the activity of beta-catenin and TGFbeta. These findings provide novel functional links between the TSC genes and other tumor suppressors responsible for Cowden's disease (PTEN), Peutz-Jeghers syndrome (LKB1), and familial polyposis (APC). Common sporadic cancers such as prostate, lung, colon, endometrium, and breast have ties to these genes, highlighting the potential role of the TSC proteins in human cancers. Rapamycin, a specific mTOR inhibitor, has potent antitumoral activities in preclinical models of TSC and is currently undergoing phase I/II clinical studies.
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Affiliation(s)
- Baldwin C Mak
- Department of Surgery, University of Washington, Seattle, Washington 98195, USA
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241
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Abstract
The evolutionarily conserved checkpoint protein kinase, TOR (target of rapamycin), has emerged as a major effector of cell growth and proliferation via the regulation of protein synthesis. Work in the last decade clearly demonstrates that TOR controls protein synthesis through a stunning number of downstream targets. Some of the targets are phosphorylated directly by TOR, but many are phosphorylated indirectly. In this review, we summarize some recent developments in this fast-evolving field. We describe both the upstream components of the signaling pathway(s) that activates mammalian TOR (mTOR) and the downstream targets that affect protein synthesis. We also summarize the roles of mTOR in the control of cell growth and proliferation, as well as its relevance to cancer and synaptic plasticity.
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Affiliation(s)
- Nissim Hay
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 60607, USA.
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242
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Abstract
Recent studies point to an emerging role for the TOR (target of rapamycin) pathway in the regulation of life span. In this Perspective, we discuss the possibility that this pathway is an important modulator of nutrient-dependent changes in life span. Additionally, we discuss the interactions between the TOR and insulin-like signaling pathways as well as the key downstream processes that TOR regulates.
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Affiliation(s)
- Pankaj Kapahi
- Buck Institute for Age Research, Novato, CA 94945, USA.
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243
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Abstract
Tuberous sclerosis complex results from mutations in the TSC1 (hamartin) and TSC2 (tuberin) genes. Tubers are cortical developmental malformations in patients with tuberous sclerosis complex that are associated with intractable epilepsy and are composed of histologically distinct cell types, including giant cells and dysplastic neurons. We recently showed that tubers can be dynamic lesions characterized by populations of cells undergoing proliferation, migration, and death. We demonstrate that there is cell-specific activation of the mammalian target of rapamycin (mTOR)/p70S6 kinase/ribosomal S6 cascade in tubers and that giant cells express activated (phosphorylated) p70S6 kinase and ribosomal S6 protein. These findings support impaired hamartin- and tuberin-mediated mTOR pathway regulation. Tubers likely form by constitutive activation of the mTOR cascade during brain development as a consequence of impaired hamartin or tuberin function.
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Affiliation(s)
- Peter B Crino
- PENN Epilepsy Center and Department of Neurology, University of Pennsylvania Medical Center, Philadelphia, PA 19104, USA.
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244
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Au KS, Williams AT, Gambello MJ, Northrup H. Molecular genetic basis of tuberous sclerosis complex: from bench to bedside. J Child Neurol 2004; 19:699-709. [PMID: 15563017 DOI: 10.1177/08830738040190091101] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Tuberous sclerosis complex is an autosomal dominant disease of benign tumors occurring in multiple organ systems of the body. Either of two genes, TSC1 or TSC2, can be mutated, resulting in the tuberous sclerosis complex phenotype. The protein products of the tuberous sclerosis complex genes, hamartin (TSC1) and tuberin (TSC2), have been discovered to play important roles in several cell-signaling pathways. Knowledge regarding the function of the tuberin-hamartin complex has led to therapeutic intervention trials. Numerous pathogenic mutations have been elucidated in individuals affected with tuberous sclerosis complex. Information on the type and distribution of nearly 1000 mutations in the two genes is discussed. Mosaicism for tuberous sclerosis complex mutations has been documented, complicating provision of genetic counseling to families. Emerging genotype-phenotype correlations should provide guidance for better medical care of individuals with tuberous sclerosis complex.
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Affiliation(s)
- Kit-Sing Au
- Department of Pediatrics, Division of Medical Genetics, The University of Texas Medical School at Houston, Houston, TX 77030, USA
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245
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Abstract
The most devastating complications of tuberous sclerosis complex affect the central nervous system and include epilepsy, mental retardation, autism, and glial tumors. Mutations in one of two genes, TSC1 and TSC2, result in a similar disease phenotype by disrupting the normal interaction of their protein products, hamartin and tuberin, which form a functional signaling complex. Disruption of these genes in the brain results in abnormal cellular differentiation, migration, and proliferation, giving rise to characteristic brain lesions called cortical tubers. Relevant animal models, including conventional and conditional knockout mice, are valuable tools for studying the normal functions of tuberin and hamartin and how disruption of their expression gives rise to the variety of clinical features that characterize tuberous sclerosis complex. In the future, these animals will be invaluable preclinical models for the development of highly specific and efficacious treatments for children affected with tuberous sclerosis complex.
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246
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Crino PB. Malformations of cortical development: molecular pathogenesis and experimental strategies. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2004; 548:175-91. [PMID: 15250594 DOI: 10.1007/978-1-4757-6376-8_13] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
Abstract
Malformations of cortical development (MCD) are developmental brain lesions characterized by abnormal formation of the cerebral cortex and a high clinical association with epilepsy in infants, children, and adults. Despite multiple anti-epileptic drugs (AEDs), treatment of epilepsy associated with MCD may require cortical resection performed to remove the cytoarchitecturally abnormal region of cortex. Single genes responsible for distinct MCD including lissencephaly, subcortical band heterotopia, and tuberous sclerosis, have been identified and permit important mechanistic insights into how gene mutations result in abnormal cortical cytoarchitecture. The pathogenesis of MCD such as focal cortical dysplasia, hemimegalencephaly, and polymicrogyria, remains unknown. A variety of new techniques including cDNA array analysis now allow for analysis of gene expression within MCD.
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Affiliation(s)
- Peter B Crino
- Penn Epilespsy Center, Department of Neurology, University of Pennsylvania Medical Center, Philadelphia, USA
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247
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Kimball SR, Jefferson LS. Amino acids as regulators of gene expression. Nutr Metab (Lond) 2004; 1:3. [PMID: 15507151 PMCID: PMC524028 DOI: 10.1186/1743-7075-1-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2004] [Accepted: 08/17/2004] [Indexed: 02/04/2023] Open
Abstract
The role of amino acids as substrates for protein synthesis is well documented. However, a function for amino acids in modulating the signal transduction pathways that regulate mRNA translation has only recently been described. Interesting, some of the signaling pathways regulated by amino acids overlap with those classically associated with the cellular response to hormones such as insulin and insulin-like growth factors. The focus of this review is on the signaling pathways regulated by amino acids, with a particular emphasis on the branched-chain amino acid leucine, and the steps in mRNA translation controlled by the signaling pathways.
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Affiliation(s)
- Scot R Kimball
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Leonard S Jefferson
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
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248
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Lu Z, Hu X, Li Y, Zheng L, Zhou Y, Jiang H, Ning T, Basang Z, Zhang C, Ke Y. Human Papillomavirus 16 E6 Oncoprotein Interferences with Insulin Signaling Pathway by Binding to Tuberin. J Biol Chem 2004; 279:35664-70. [PMID: 15175323 DOI: 10.1074/jbc.m403385200] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Tuberous sclerosis complex (TSC) is a genetic disorder caused by mutations in either TSC1 or TSC2 tumor suppressor gene. TSC1 and TSC2 products, Harmatin and Tuberin, form the functional complex to serve as the negative regulator for insulin-induced phosphorylation of S6 kinase and elF4E-binding protein 1. High-risk human papillomavirus (HPV) infection is the necessary cause for cervical cancer. E6 oncoprotein encoded by HPV plays a pivotal role in carcinogenesis by interference with the host intracellular protein functions. In this study, we show that HPV16 E6 interacts with tumor suppressor gene TSC2 product, Tuberin, and results in the phosphorylation of S6 kinase and S6 even in the absence of insulin. The overexpression of Tuberin overcomes the effect of E6 on S6 kinase phosphorylation. Binding with HPV16 E6 causes the proteasome-mediated degradation of Tuberin. A DILG motif and an ELVG motif located in the carboxyl-terminal of Tuberin are required for E6 binding. In addition, the Tuberin interaction region in E6 has been mapped in the amino-terminal portion of HPV16 E6, which is different from the binding domain with p53. These results provide a possible link between E6-induced oncogenesis and the insulin-stimulated cell proliferation signaling pathway.
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Affiliation(s)
- Zheming Lu
- Department of Genetics, Beijing Institute for Cancer Research, School of Oncology, Peking University, 1 Da Hong Luo Chang Street, West District, Beijing 100034, People's Republic of China
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249
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Abstract
Growth of organisms and their constituent parts responds to both intrinsic and extrinsic cues during development: organisms of a given species generally grow at a predictable rate and to a specific body size, but individuals can modify this program during development in response to environmental conditions. Recent experiments, using gene knockouts and targeted overexpression, have revealed the central role of a signaling network controlled by the PI3K and TOR kinases in this regulation. These signaling molecules control growth by coordinately regulating a large number of cell biological processes. This review focuses on the cellular activities regulated by PI3K and TOR during development, and discusses how changes in different aspects of cellular metabolism may interact to regulate growth.
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Affiliation(s)
- Thomas P Neufeld
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA.
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250
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Kapahi P, Zid BM, Harper T, Koslover D, Sapin V, Benzer S. Regulation of lifespan in Drosophila by modulation of genes in the TOR signaling pathway. Curr Biol 2004; 14:885-90. [PMID: 15186745 PMCID: PMC2754830 DOI: 10.1016/j.cub.2004.03.059] [Citation(s) in RCA: 1003] [Impact Index Per Article: 47.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2004] [Revised: 03/22/2004] [Accepted: 03/22/2004] [Indexed: 11/27/2022]
Abstract
In many species, reducing nutrient intake without causing malnutrition extends lifespan. Like DR (dietary restriction), modulation of genes in the insulin-signaling pathway, known to alter nutrient sensing, has been shown to extend lifespan in various species. In Drosophila, the target of rapamycin (TOR) and the insulin pathways have emerged as major regulators of growth and size. Hence we examined the role of TOR pathway genes in regulating lifespan by using Drosophila. We show that inhibition of TOR signaling pathway by alteration of the expression of genes in this nutrient-sensing pathway, which is conserved from yeast to human, extends lifespan in a manner that may overlap with known effects of dietary restriction on longevity. In Drosophila, TSC1 and TSC2 (tuberous sclerosis complex genes 1 and 2) act together to inhibit TOR (target of rapamycin), which mediates a signaling pathway that couples amino acid availability to S6 kinase, translation initiation, and growth. We find that overexpression of dTsc1, dTsc2, or dominant-negative forms of dTOR or dS6K all cause lifespan extension. Modulation of expression in the fat is sufficient for the lifespan-extension effects. The lifespan extensions are dependent on nutritional condition, suggesting a possible link between the TOR pathway and dietary restriction.
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