401
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Kuo M, Zilberfarb V, Gangneux N, Christeff N, Issad T. O-glycosylation of FoxO1 increases its transcriptional activity towards the glucose 6-phosphatase gene. FEBS Lett 2008; 582:829-34. [PMID: 18280254 DOI: 10.1016/j.febslet.2008.02.010] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2007] [Revised: 01/31/2008] [Accepted: 02/07/2008] [Indexed: 10/22/2022]
Abstract
Mono-O-glycosylations post-translationally regulate the activity of nucleocytoplasmic proteins. We showed that glucosamine and an inhibitor of deglycosylation (PUGNAc) induced O-glycosylation of FoxO1, resulting in increased expression of a glucose-6-phosphatase reporter gene. This effect was independent of FoxO1 re-localisation, since it was also observed with constitutively nuclear FoxO1-AAA mutant. Moreover, in HepG2 cells, glucosamine and PUGNAc have a synergistic effect on the glucose-6-phosphatase reporter gene, and this effect was inhibited by FoxO1 siRNAs. Since glucose-6-phosphatase plays a key role in hepatic glucose production, our observation may be of importance with regard to glucotoxicity associated with chronic hyperglycaemia in diabetes.
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Affiliation(s)
- Meishiue Kuo
- Institut Cochin, Université Paris Descartes, 22 Rue Méchain, CNRS (UMR 8104), Paris, France
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402
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Zhang Y, Xu J, Puscau C, Kim Y, Wang X, Alam H, Hu PJ. Caenorhabditis elegans EAK-3 inhibits dauer arrest via nonautonomous regulation of nuclear DAF-16/FoxO activity. Dev Biol 2008; 315:290-302. [PMID: 18241854 DOI: 10.1016/j.ydbio.2007.12.032] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2007] [Accepted: 12/11/2007] [Indexed: 11/30/2022]
Abstract
Insulin regulates development, metabolism, and lifespan via a conserved PI3K/Akt pathway that promotes cytoplasmic sequestration of FoxO transcription factors. The regulation of nuclear FoxO is poorly understood. In the nematode Caenorhabditis elegans, insulin-like signaling functions in larvae to inhibit dauer arrest and acts during adulthood to regulate lifespan. In a screen for genes that modulate C. elegans insulin-like signaling, we identified eak-3, which encodes a novel protein that is specifically expressed in the two endocrine XXX cells. The dauer arrest phenotype of eak-3 mutants is fully suppressed by mutations in daf-16/FoxO, which encodes the major target of C. elegans insulin-like signaling, and daf-12, which encodes a nuclear receptor regulated by steroid hormones known as dafachronic acids. eak-3 mutation does not affect DAF-16/FoxO subcellular localization but enhances expression of the direct DAF-16/FoxO target sod-3 in a daf-16/FoxO- and daf-12-dependent manner. eak-3 mutants have normal lifespans, suggesting that EAK-3 decouples insulin-like regulation of development and longevity. We propose that EAK-3 activity in the XXX cells promotes the synthesis and/or secretion of a hormone that acts in parallel to AKT-1 to inhibit the expression of DAF-16/FoxO target genes. Similar hormonal pathways may regulate FoxO target gene expression in mammals.
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Affiliation(s)
- Yanmei Zhang
- Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA
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403
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FoxO transcription factors activate Akt and attenuate insulin signaling in heart by inhibiting protein phosphatases. Proc Natl Acad Sci U S A 2007; 104:20517-22. [PMID: 18077353 DOI: 10.1073/pnas.0610290104] [Citation(s) in RCA: 184] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Insulin resistance and metabolic syndrome are rapidly expanding public health problems. Acting through the PI3K/Akt pathway, insulin and insulin-like growth factor-1 (IGF-1) inactivate FoxO transcription factors, a class of highly conserved proteins important in numerous physiological functions. However, even as FoxO is a downstream target of insulin, FoxO factors also control upstream signaling elements governing insulin sensitivity and glucose metabolism. Here, we report that sustained activation of either FoxO1 or FoxO3 in cardiac myocytes increases basal levels of Akt phosphorylation and kinase activity. FoxO-activated Akt directly interacts with and phosphorylates FoxO, providing feedback inhibition. We reported previously that FoxO factors attenuate cardiomyocyte calcineurin (PP2B) activity. We now show that calcineurin forms a complex with Akt and inhibition of calcineurin enhances Akt phosphorylation. In addition, FoxO activity suppresses protein phosphatase 2A (PP2A) and disrupts Akt-PP2A and Akt-calcineurin interactions. Repression of Akt-PP2A/B interactions and phosphatase activities contributes, at least in part, to FoxO-dependent increases in Akt phosphorylation and kinase activity. Resveratrol, an activator of Sirt1, increases the transcriptional activity of FoxO1 and triggers Akt phosphorylation in heart. Importantly, FoxO-mediated increases in Akt activity diminish insulin signaling, as manifested by reduced Akt phosphorylation, reduced membrane translocation of Glut4, and decreased insulin-triggered glucose uptake. Also, inactivation of the gene coding for FoxO3 enhances insulin-dependent Akt phosphorylation. Taken together, this study demonstrates that changes in FoxO activity have a dose-responsive repressive effect on insulin signaling in cardiomyocytes through inhibition of protein phosphatases, which leads to altered Akt activation, reduced insulin sensitivity, and impaired glucose metabolism.
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404
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Zhao J, Brault JJ, Schild A, Cao P, Sandri M, Schiaffino S, Lecker SH, Goldberg AL. FoxO3 coordinately activates protein degradation by the autophagic/lysosomal and proteasomal pathways in atrophying muscle cells. Cell Metab 2007; 6:472-83. [PMID: 18054316 DOI: 10.1016/j.cmet.2007.11.004] [Citation(s) in RCA: 1135] [Impact Index Per Article: 66.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/10/2007] [Revised: 09/30/2007] [Accepted: 11/06/2007] [Indexed: 01/18/2023]
Abstract
Muscle atrophy occurs in many pathological states and results primarily from accelerated protein degradation and activation of the ubiquitin-proteasome pathway. However, the importance of lysosomes in muscle atrophy has received little attention. Activation of FoxO transcription factors is essential for the atrophy induced by denervation or fasting, and activated FoxO3 by itself causes marked atrophy of muscles and myotubes. Here, we report that FoxO3 does so by stimulating overall protein degradation and coordinately activating both lysosomal and proteasomal pathways. Surprisingly, in C2C12 myotubes, most of this increased proteolysis is mediated by lysosomes. Activated FoxO3 stimulates lysosomal proteolysis in muscle (and other cell types) by activating autophagy. FoxO3 also induces the expression of many autophagy-related genes, which are induced similarly in mouse muscles atrophying due to denervation or fasting. These studies indicate that decreased IGF-1-PI3K-Akt signaling activates autophagy not only through mTOR but also more slowly by a transcription-dependent mechanism involving FoxO3.
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Affiliation(s)
- Jinghui Zhao
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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405
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Hatta M, Cirillo LA. Chromatin Opening and Stable Perturbation of Core Histone:DNA Contacts by FoxO1. J Biol Chem 2007; 282:35583-93. [DOI: 10.1074/jbc.m704735200] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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406
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Hsu HJ, LaFever L, Drummond-Barbosa D. Diet controls normal and tumorous germline stem cells via insulin-dependent and -independent mechanisms in Drosophila. Dev Biol 2007; 313:700-12. [PMID: 18068153 DOI: 10.1016/j.ydbio.2007.11.006] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Revised: 10/31/2007] [Accepted: 11/02/2007] [Indexed: 01/08/2023]
Abstract
The external environment influences stem cells, but this process is poorly understood. Our previous work showed that germline stem cells (GSCs) respond to diet via neural insulin-like peptides (DILPs) that act directly on the germ line to upregulate stem cell division and cyst growth under a protein-rich diet in Drosophila. Here, we report that DILPs specifically control the G2 phase of the GSC cell cycle via phosphoinositide-3 kinase (PI3K) and dFOXO, and that a separate diet mediator regulates the G1 phase. Furthermore, GSC tumors, which escape the normal stem cell regulatory microenvironment, or niche, still respond to diet via both mechanisms, indicating that niche signals are not required for GSCs to sense or respond to diet. Our results document the effects of diet and insulin-like signals on the cell cycle of stem cells within an intact organism and demonstrate that the response to diet requires multiple signals. Moreover, the retained ability of GSC tumors to respond to diet parallels the long known connections between diet, insulin signaling, and cancer risk in humans.
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Affiliation(s)
- Hwei-Jan Hsu
- Department of Cell and Developmental Biology, 4120B Medical Research Building III, Vanderbilt University Medical Center, 465 21st Avenue South, Nashville, TN 37232-8240, USA
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407
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Walter PL, Steinbrenner H, Barthel A, Klotz LO. Stimulation of selenoprotein P promoter activity in hepatoma cells by FoxO1a transcription factor. Biochem Biophys Res Commun 2007; 365:316-21. [PMID: 17986386 DOI: 10.1016/j.bbrc.2007.10.171] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2007] [Accepted: 10/28/2007] [Indexed: 02/02/2023]
Abstract
Selenoprotein P (SeP) is the major selenoprotein in human plasma, acting as an antioxidant and serving the transport of selenium from the liver to extrahepatic tissues. We here demonstrate that the human SeP promoter responds to overexpression of FoxO1a as well as of a constitutively active form of FoxO1a. Two FoxO-responsive elements were identified and characterized by generation of point mutation and deletion constructs. Similarly, SeP mRNA was upregulated in response to activation of FoxO1a in rat hepatoma cells stably transfected with a hydroxytamoxifen-regulatable form of FoxO1a. Insulin, stimulating the phosphorylation and inactivation of FoxO1a via phosphoinositide 3-kinase (PI3K) and Akt, suppressed SeP promoter activity and mRNA synthesis. This suppressive effect of insulin on SeP expression was attenuated by inhibitors of PI3K. In conclusion, the selenoprotein P promoter is a target of the Akt/FoxO signal transduction cascade and SeP expression is regulated at the level of transcription by the forkhead box protein FoxO1a in human and rat hepatoma cells.
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Affiliation(s)
- Philippe L Walter
- Institut für Biochemie und Molekularbiologie I, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany
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408
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Abstract
Forkhead box (Fox) proteins are a superfamily of evolutionarily conserved transcriptional regulators, which control a wide spectrum of biological processes. As a consequence, a loss or gain of Fox function can alter cell fate and promote tumorigenesis as well as cancer progression. Here we discuss the evidence that the deregulation of Fox family transcription factors has a crucial role in the development and progression of cancer, and evaluate the emerging role of Fox proteins as direct and indirect targets for therapeutic intervention, as well as biomarkers for predicting and monitoring treatment responses.
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Affiliation(s)
- Stephen S Myatt
- Cancer Research UK laboratories, Department of Oncology, MRC Cyclotron Building, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK
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409
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Elghazi L, Rachdi L, Weiss AJ, Cras-Méneur C, Bernal-Mizrachi E. Regulation of beta-cell mass and function by the Akt/protein kinase B signalling pathway. Diabetes Obes Metab 2007; 9 Suppl 2:147-57. [PMID: 17919189 DOI: 10.1111/j.1463-1326.2007.00783.x] [Citation(s) in RCA: 63] [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: 12/31/2022]
Abstract
The insulin receptor substrate-2/phosphoinositide 3-kinase (PI3K) pathway plays a critical role in the regulation of beta-cell mass and function, demonstrated both in vitro and in vivo. The serine threonine kinase Akt is one of the promising downstream molecules of this pathway that has been identified as a potential target to regulate function and induce proliferation and survival of beta cells. Here we summarize some of the molecular mechanisms, downstream signalling pathways and critical components involved in the regulation of beta-cell mass and function by Akt.
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Affiliation(s)
- L Elghazi
- Department of Internal Medicine, Division of Endocrinology, Washington University School of Medicine, Metabolism & Lipid Research, St Louis, MO 63110, USA
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410
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Tsai KL, Sun YJ, Huang CY, Yang JY, Hung MC, Hsiao CD. Crystal structure of the human FOXO3a-DBD/DNA complex suggests the effects of post-translational modification. Nucleic Acids Res 2007; 35:6984-94. [PMID: 17940099 PMCID: PMC2175300 DOI: 10.1093/nar/gkm703] [Citation(s) in RCA: 157] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2007] [Revised: 08/17/2007] [Accepted: 08/23/2007] [Indexed: 01/02/2023] Open
Abstract
FOXO3a is a transcription factor of the FOXO family. The FOXO proteins participate in multiple signaling pathways, and their transcriptional activity is regulated by several post-translational mechanisms, including phosphorylation, acetylation and ubiquitination. Because these post-translational modification sites are located within the C-terminal basic region of the FOXO DNA-binding domain (FOXO-DBD), it is possible that these post-translational modifications could alter the DNA-binding characteristics. To understand how FOXO mediate transcriptional activity, we report here the 2.7 A crystal structure of the DNA-binding domain of FOXO3a (FOXO3a-DBD) bound to a 13-bp DNA duplex containing a FOXO consensus binding sequence (GTAAACA). Based on a unique structural feature in the C-terminal region and results from biochemical and mutational studies, our studies may explain how FOXO-DBD C-terminal phosphorylation by protein kinase B (PKB) or acetylation by cAMP-response element binding protein (CBP) can attenuate the DNA-binding activity and thereby reduce transcriptional activity of FOXO proteins. In addition, we demonstrate that the methyl groups of specific thymine bases within the consensus sequence are important for FOXO3a-DBD recognition of the consensus binding site.
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Affiliation(s)
- Kuang-Lei Tsai
- Institute of Molecular Biology, Academia Sinica, Taipei, 115, Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 30043, Taiwan, Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA, and Center for Molecular Medicine, China Medical University Hospital, Taichung, 404, Taiwan
| | - Yuh-Ju Sun
- Institute of Molecular Biology, Academia Sinica, Taipei, 115, Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 30043, Taiwan, Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA, and Center for Molecular Medicine, China Medical University Hospital, Taichung, 404, Taiwan
| | - Cheng-Yang Huang
- Institute of Molecular Biology, Academia Sinica, Taipei, 115, Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 30043, Taiwan, Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA, and Center for Molecular Medicine, China Medical University Hospital, Taichung, 404, Taiwan
| | - Jer-Yen Yang
- Institute of Molecular Biology, Academia Sinica, Taipei, 115, Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 30043, Taiwan, Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA, and Center for Molecular Medicine, China Medical University Hospital, Taichung, 404, Taiwan
| | - Mien-Chie Hung
- Institute of Molecular Biology, Academia Sinica, Taipei, 115, Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 30043, Taiwan, Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA, and Center for Molecular Medicine, China Medical University Hospital, Taichung, 404, Taiwan
| | - Chwan-Deng Hsiao
- Institute of Molecular Biology, Academia Sinica, Taipei, 115, Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 30043, Taiwan, Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA, and Center for Molecular Medicine, China Medical University Hospital, Taichung, 404, Taiwan
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411
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Korsheninnikova E, Voshol PJ, Baan B, van der Zon GCM, Havekes LM, Romijn JA, Maassen JA, Ouwens DM. Dynamics of insulin signalling in liver during hyperinsulinemic euglycaemic clamp conditions in vivo and the effects of high-fat feeding in male mice. Arch Physiol Biochem 2007; 113:173-85. [PMID: 18158643 DOI: 10.1080/13813450701669084] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Insulin is an important regulator of hepatic carbohydrate, lipid, and protein metabolism, and the regulation of these processes by insulin is disturbed under conditions of insulin resistance and type 2 diabetes. Despite these alterations, the impact of insulin resistance on insulin signalling in the liver is not well defined. Variations in time and dose of insulin stimulation as well as plasma glucose levels may underlie this. The present study aimed at determining the dynamics of activation of hepatic insulin signalling in vivo at insulin concentrations resembling those achieved after a meal, and addressing the effects of high-fat feeding. An unexpected finding of this study was the biphasic activation pattern of the IRS-PI3K-PKB/Akt pathway. Our findings indicate that the first burst of activation contributes to regulation of glucose metabolism. The physiological function of the second peak is still unknown, but may involve regulation of protein synthesis. Finally, high-fat feeding caused hepatic insulin resistance, as illustrated by a reduced suppression of hepatic glucose production. A sustained increased phosphorylation of the serine/threonine kinases p70S6kinase and Jun N-terminal kinase in the absence of insulin may underlie the abrogated phosphorylation of the IRS proteins and their downstream targets.
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Affiliation(s)
- E Korsheninnikova
- Departments of Molecular Cell Biology, Leiden University Medical Centre, Leiden, The Netherlands
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412
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Zheng X, Yang Z, Yue Z, Alvarez JD, Sehgal A. FOXO and insulin signaling regulate sensitivity of the circadian clock to oxidative stress. Proc Natl Acad Sci U S A 2007; 104:15899-904. [PMID: 17895391 PMCID: PMC2000406 DOI: 10.1073/pnas.0701599104] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Circadian rhythms can be regulated by many environmental and endogenous factors. We show here a sensitivity of circadian clock function to oxidative stress that is revealed in flies lacking the foxo gene product. When exposed to oxidative stress, wild-type flies showed attenuated clock gene cycling in peripheral tissues, whereas foxo mutants also lost behavioral rhythms driven by the central clock. FOXO is expressed predominantly in the fat body, and transgenic expression in this tissue rescued the mutant behavioral phenotype, suggesting that foxo has non-cell-autonomous effects on central circadian clock function. Overexpression of signaling molecules that affect FOXO activity, such as the insulin receptor or Akt, in the fat body also increased susceptibility of the central clock to oxidative stress. Finally, foxo mutants showed a rapid decline in rest:activity rhythms with age, supporting the idea that the increase of oxidative stress contributes to age-associated degeneration of behavioral rhythms and indicating the importance of FOXO in mitigating this deterioration. Together these data demonstrate that metabolism affects central clock function and provide a link among insulin signaling, oxidative stress, aging, and circadian rhythms.
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Affiliation(s)
- Xiangzhong Zheng
- Howard Hughes Medical Institute and Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Zhaohai Yang
- Howard Hughes Medical Institute and Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Zhifeng Yue
- Howard Hughes Medical Institute and Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - John D. Alvarez
- Howard Hughes Medical Institute and Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Amita Sehgal
- Howard Hughes Medical Institute and Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
- *To whom correspondence should be addressed at
Howard Hughes Medical Institute and Department of Neuroscience, University of Pennsylvania School of Medicine, 232 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104. E-mail:
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413
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Lunetta KL, D'Agostino RB, Karasik D, Benjamin EJ, Guo CY, Govindaraju R, Kiel DP, Kelly-Hayes M, Massaro JM, Pencina MJ, Seshadri S, Murabito JM. Genetic correlates of longevity and selected age-related phenotypes: a genome-wide association study in the Framingham Study. BMC MEDICAL GENETICS 2007; 8 Suppl 1:S13. [PMID: 17903295 PMCID: PMC1995604 DOI: 10.1186/1471-2350-8-s1-s13] [Citation(s) in RCA: 159] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
BACKGROUND Family studies and heritability estimates provide evidence for a genetic contribution to variation in the human life span. METHODS We conducted a genome wide association study (Affymetrix 100K SNP GeneChip) for longevity-related traits in a community-based sample. We report on 5 longevity and aging traits in up to 1345 Framingham Study participants from 330 families. Multivariable-adjusted residuals were computed using appropriate models (Cox proportional hazards, logistic, or linear regression) and the residuals from these models were used to test for association with qualifying SNPs (70, 987 autosomal SNPs with genotypic call rate > or =80%, minor allele frequency > or =10%, Hardy-Weinberg test p > or = 0.001). RESULTS In family-based association test (FBAT) models, 8 SNPs in two regions approximately 500 kb apart on chromosome 1 (physical positions 73,091,610 and 73, 527,652) were associated with age at death (p-value < 10(-5)). The two sets of SNPs were in high linkage disequilibrium (minimum r2 = 0.58). The top 30 SNPs for generalized estimating equation (GEE) tests of association with age at death included rs10507486 (p = 0.0001) and rs4943794 (p = 0.0002), SNPs intronic to FOXO1A, a gene implicated in lifespan extension in animal models. FBAT models identified 7 SNPs and GEE models identified 9 SNPs associated with both age at death and morbidity-free survival at age 65 including rs2374983 near PON1. In the analysis of selected candidate genes, SNP associations (FBAT or GEE p-value < 0.01) were identified for age at death in or near the following genes: FOXO1A, GAPDH, KL, LEPR, PON1, PSEN1, SOD2, and WRN. Top ranked SNP associations in the GEE model for age at natural menopause included rs6910534 (p = 0.00003) near FOXO3a and rs3751591 (p = 0.00006) in CYP19A1. Results of all longevity phenotype-genotype associations for all autosomal SNPs are web posted at http://www.ncbi.nlm.nih.gov/projects/gap/cgi-bin/study.cgi?id=phs000007 webcite. CONCLUSION Longevity and aging traits are associated with SNPs on the Affymetrix 100K GeneChip. None of the associations achieved genome-wide significance. These data generate hypotheses and serve as a resource for replication as more genes and biologic pathways are proposed as contributing to longevity and healthy aging.
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Affiliation(s)
- Kathryn L Lunetta
- The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA
- Department of Biostatistics, Boston University School of Public Health, Boston, MA, USA
| | - Ralph B D'Agostino
- The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA
- Statistics and Consulting Unit, Department of Mathematics, Boston University, Boston, MA, USA
| | - David Karasik
- Hebrew Senior Life Institute for Aging Research and Harvard Medical School, Boston, MA, USA
| | - Emelia J Benjamin
- The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA
- Section of General Internal Medicine and the Departments of Neurology, Cardiology, and Preventive Medicine, Boston University School of Medicine, Boston, MA, USA
| | - Chao-Yu Guo
- The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA
- Section of General Internal Medicine and the Departments of Neurology, Cardiology, and Preventive Medicine, Boston University School of Medicine, Boston, MA, USA
| | - Raju Govindaraju
- The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA
- Section of General Internal Medicine and the Departments of Neurology, Cardiology, and Preventive Medicine, Boston University School of Medicine, Boston, MA, USA
| | - Douglas P Kiel
- Hebrew Senior Life Institute for Aging Research and Harvard Medical School, Boston, MA, USA
| | - Margaret Kelly-Hayes
- The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA
- Section of General Internal Medicine and the Departments of Neurology, Cardiology, and Preventive Medicine, Boston University School of Medicine, Boston, MA, USA
| | - Joseph M Massaro
- The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA
- Statistics and Consulting Unit, Department of Mathematics, Boston University, Boston, MA, USA
| | - Michael J Pencina
- The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA
- Statistics and Consulting Unit, Department of Mathematics, Boston University, Boston, MA, USA
| | - Sudha Seshadri
- The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA
- Section of General Internal Medicine and the Departments of Neurology, Cardiology, and Preventive Medicine, Boston University School of Medicine, Boston, MA, USA
| | - Joanne M Murabito
- The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA
- Section of General Internal Medicine and the Departments of Neurology, Cardiology, and Preventive Medicine, Boston University School of Medicine, Boston, MA, USA
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414
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Gilardi F, Mitro N, Godio C, Scotti E, Caruso D, Crestani M, De Fabiani E. The pharmacological exploitation of cholesterol 7alpha-hydroxylase, the key enzyme in bile acid synthesis: from binding resins to chromatin remodelling to reduce plasma cholesterol. Pharmacol Ther 2007; 116:449-72. [PMID: 17959250 DOI: 10.1016/j.pharmthera.2007.08.003] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2007] [Accepted: 08/16/2007] [Indexed: 01/25/2023]
Abstract
Mammals dispose of cholesterol mainly through 7alpha-hydroxylated bile acids, and the enzyme catalyzing the 7alpha-hydroxylation, cholesterol 7alpha-hydroxylase (CYP7A1), has a deep impact on cholesterol homeostasis. In this review, we present the study of regulation of CYP7A1 as a good exemplification of the extraordinary contribution of molecular biology to the advancement of our understanding of metabolic pathways that has taken place in the last 2 decades. Since the cloning of the gene from different species, experimental evidence has accumulated, indicating that the enzyme is mainly regulated at the transcriptional level and that bile acids are the most important physiological inhibitors of CYP7A1 transcription. Multiple mechanisms are involved in the control of CYP7A1 transcription and a variety of transcription factors and nuclear receptors participate in sophisticated regulatory networks. A higher order of transcriptional regulation, stemming from the so-called histone code, also applies to CYP7A1, and recent findings clearly indicate that chromatin remodelling events have profound effects on its expression. CYP7A1 also acts as a sensor of signals coming from the gut, thus representing another line of defence against the toxic effects of bile acids and a downstream target of agents acting at the intestinal level. From the pharmacological point of view, bile acid binding resins were the first primitive approach targeting the negative feed-back regulation of CYP7A1 to reduce plasma cholesterol. In recent years, new drugs have been designed based on recent discoveries of the regulatory network, thus confirming the position of CYP7A1 as a focus for innovative pharmacological intervention.
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Affiliation(s)
- Federica Gilardi
- Dipartimento di Scienze Farmacologiche, Università degli Studi di Milano, Milan, Italy
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415
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Kitazawa M, Ohizumi Y, Oike Y, Hishinuma T, Hashimoto S. Angiopoietin-related growth factor suppresses gluconeogenesis through the Akt/forkhead box class O1-dependent pathway in hepatocytes. J Pharmacol Exp Ther 2007; 323:787-93. [PMID: 17804676 DOI: 10.1124/jpet.107.127530] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Angiopoietin-related growth factor (AGF; or Angptl6) is a liver-derived, circulating factor and is considered to be a regulator of metabolic homeostasis. AGF is capable of counteracting both obesity and obesity-related insulin resistance. However, the target tissues and the molecular mechanisms underlying the antiobesity and antidiabetic actions of AGF have not been completely defined. Using rat hepatoma H4IIEc3 cells or primary hepatocytes, we demonstrate that AGF suppresses glucose production in a concentration-dependent manner through reduced expression of a key gluconeogenic enzyme, glucose-6-phosphatase (G6Pase), at both transcriptional and translational levels. The action of AGF on glucose production was inhibited by pretreatment of the cells with LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one], a phosphoinositide 3-kinase (PI3K) inhibitor, and Akt (protein kinase B) inhibitors. AGF increased the phosphorylation of Akt and its substrates, glycogen synthase kinase 3beta and forkhead box class O1 (FoxO1), a key transcription factor for G6Pase expression. Furthermore, an immunohistochemical approach with anti-FoxO1 antibody demonstrated that AGF stimulation promoted translocation of FoxO1 from the nucleus to the cytoplasm in the cells. These results suggest that in hepatocytes, AGF suppresses gluconeogenesis via reduced transcriptional activity of FoxO1 resulting from the activation of PI3K/Akt signaling cascades.
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Affiliation(s)
- Masashi Kitazawa
- Molecular Medicine Research Laboratories, Drug Discovery Research, Astellas Pharma, Inc., 21 Miyukigaoka, Tsukuba, Ibaraki 305-8585, Japan.
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416
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Li L, Naples M, Song H, Yuan R, Ye F, Shafi S, Adeli K, Ng DS. LCAT-null mice develop improved hepatic insulin sensitivity through altered regulation of transcription factors and suppressors of cytokine signaling. Am J Physiol Endocrinol Metab 2007; 293:E587-94. [PMID: 17551001 DOI: 10.1152/ajpendo.00278.2007] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We previously reported that LCAT-deficient mice develop not only low HDL-cholesterol but also hypertriglyceridemia, hepatic triglyceride (TG) overproduction, and, unexpectedly, improved hepatic insulin sensitivity and reduced hepatic TG content. Here, we examined the mechanistic links underlying this apparent paradox. The LDL receptor-deficient (Ldlr)(-/-)xLcat(-/-) mouse model and age- and sex-matched Ldlr(-/-)xLcat(+/+) littermates, both in C57Bl/6 background, were employed. Studies of hepatic insulin signal transduction showed an upregulation of hepatic Irs2 mRNA level (5.3-fold, P = 0.02), IRS-2 protein mass level (1.5-fold, P = 0.009) and pIRS-2 (1.8-fold. P = 0.02) in the Ldlr(-/-)xLcat(-/-) mice. There was a 1.2-fold increase in pAkt (P = 0.03) with a nonsignificant change in total Akt. We observed a significant shift in its downstream transcription factor FoxO-1 to the cytosolic compartment (2.3-fold increase in cytosolic/nuclear ratio, P = 0.04). We also observed a significant 3.1-fold increase in nuclear abundance of FoxA-2 mass (P = 0.017) and a 1.5-fold upregulation of its coactivator PGC-1beta (P = 0.002), the coordinated actions of which promotes hepatic TG production and beta-oxidation. Increased hepatic insulin signaling in the Ldlr(-/-)xLcat(-/-) mice was associated with an upregulation of the Tcfe3 gene (1.7-fold, P = 0.024), a selective downregulation of the Socs-1 gene by 60% (P = 0.01), and no change in PTP-1B protein mass. These data suggest that LCAT deficiency induces complex alterations in hepatic signal transduction cascades, which explain, at least in part, the observed enhanced insulin signaling in association with hepatic TG overproduction and reduced hepatic TG content.
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Affiliation(s)
- Lixin Li
- Department of Medicine, St. Michael's Hospital, Toronto, Ontario, Canada
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417
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Abstract
Forkhead box O (FoxO) transcription factors FoxO1, FoxO3a, FoxO4 and FoxO6, the mammalian orthologs of Caenorhabditis elegans DAF-16, are emerging as an important family of proteins that modulate the expression of genes involved in apoptosis, the cell cycle, DNA damage repair, oxidative stress, cell differentiation, glucose metabolism and other cellular functions. FoxO proteins are regulated by multiple mechanisms. They undergo inhibitory phosphorylation by protein kinases such as Akt, SGK, IKK and CDK2 in response to external and internal stimuli. By contrast, they are activated by upstream regulators such as JNK and MST1 under stress conditions. Their activities are counterbalanced by the acetylases CBP and p300 and the deacetylase SIRT1. Also, whereas polyubiquitylation of FoxO1 and FoxO3a leads to their degradation by the proteasome, monoubiquitylation of FoxO4 facilitates its nuclear localization and augments its transcriptional activity. Thus, the potent functions of FoxO proteins are tightly controlled by complex signaling pathways under physiological conditions; dysregulation of these proteins may ultimately lead to disease such as cancer.
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Affiliation(s)
- Haojie Huang
- Cancer Center and Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55455, USA.
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418
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Jing E, Gesta S, Kahn CR. SIRT2 regulates adipocyte differentiation through FoxO1 acetylation/deacetylation. Cell Metab 2007; 6:105-14. [PMID: 17681146 PMCID: PMC2083635 DOI: 10.1016/j.cmet.2007.07.003] [Citation(s) in RCA: 356] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2006] [Revised: 04/26/2007] [Accepted: 07/16/2007] [Indexed: 01/08/2023]
Abstract
The family of mammalian Sirtuin proteins comprises seven members homologous to yeast Sir2. Here we show that SIRT2, a cytoplasmic sirtuin, is the most abundant sirtuin in adipocytes. Sirt2 expression is downregulated during preadipocyte differentiation in 3T3-L1 cells. Overexpression of SIRT2 inhibits differentiation, whereas reducing SIRT2 expression promotes adipogenesis. Both effects are accompanied by corresponding changes in the expression of PPARgamma, C/EBPalpha, and genes marking terminal adipocyte differentiation, including Glut4, aP2, and fatty acid synthase. The mechanism underlying the effects of reduced SIRT2 in 3T3-L1 adipocytes includes increased acetylation of FOXO1, with direct interaction between SIRT2 and FOXO1. This interaction enhances insulin-stimulated phosphorylation of FOXO1, which in turn regulates FOXO1 nuclear and cytosolic localization. Thus, Sirt2 acts as an important regulator of adipocyte differentiation through modulation of FOXO1 acetylation/phosphorylation and activity and may play a role in controlling adipose tissue mass and function.
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Affiliation(s)
- Enxuan Jing
- Department of Cellular and Molecular Physiology, Joslin Diabetes Center, Harvard Medical School, Boston, MA 02215, USA
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419
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Li X, Monks B, Ge Q, Birnbaum MJ. Akt/PKB regulates hepatic metabolism by directly inhibiting PGC-1alpha transcription coactivator. Nature 2007; 447:1012-6. [PMID: 17554339 DOI: 10.1038/nature05861] [Citation(s) in RCA: 374] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Accepted: 04/16/2007] [Indexed: 01/16/2023]
Abstract
Type 2 diabetes mellitus, a disease with significant effects on the health and economy of Western societies, involves disturbances in both lipid and carbohydrate metabolism. In the insulin-resistant or diabetic state, the liver is unresponsive to the actions of insulin with regard to the suppression of glucose output but continues to produce large amounts of lipid, the latter mimicking the fed, insulin-replete condition. The disordered distribution of lipids contributes to the cardiovascular disease that is the greatest cause of mortality of type 2 diabetes mellitus. Yet the precise signal transduction pathways by which insulin regulates hepatic lipid synthesis and degradation remain largely unknown. Here we describe a mechanism by which insulin, through the intermediary protein kinase Akt2/protein kinase B (PKB)-beta, elicits the phosphorylation and inhibition of the transcriptional coactivator peroxisome proliferator-activated receptor-coactivator 1alpha (PGC-1alpha), a global regulator of hepatic metabolism during fasting. Phosphorylation prevents the recruitment of PGC-1alpha to the cognate promoters, impairing its ability to promote gluconeogenesis and fatty acid oxidation. These results define a mechanism by which insulin controls lipid catabolism in the liver and suggest a novel site for therapy in type 2 diabetes mellitus.
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Affiliation(s)
- Xinghai Li
- Institute for Diabetes, Obesity and Metabolism, Cox Institute, University of Pennsylvania School of Medicine and the Howard Hughes Medical Institute, Philadelphia, Pennsylvania 19104, USA
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420
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Ono M, Chia DJ, Merino-Martinez R, Flores-Morales A, Unterman TG, Rotwein P. Signal Transducer and Activator of Transcription (Stat) 5b-Mediated Inhibition of Insulin-Like Growth Factor Binding Protein-1 Gene Transcription: A Mechanism for Repression of Gene Expression by Growth Hormone. Mol Endocrinol 2007; 21:1443-57. [PMID: 17426286 DOI: 10.1210/me.2006-0543] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Abstract
GH plays a central role in controlling somatic growth, tissue regeneration, and intermediary metabolism in most vertebrate species through mechanisms dependent on the regulation of gene expression. Recent studies using transcript profiling have identified large cohorts of genes whose expression is induced by GH. Other results have demonstrated that signal transducer and activator of transcription (Stat) 5b, a latent transcription factor activated by the GH receptor-associated protein kinase, Jak2, is a key agent in the GH-stimulated gene activation that leads to somatic growth. By contrast, little is known about the steps through which GH-initiated signaling pathways reduce gene expression. Here we show that Stat5b plays a critical role in the GH-regulated inhibition of IGF binding protein-1 gene transcription by impairing the actions of the FoxO1 transcription factor on the IGF binding protein-1 promoter. Additional observations using transcript profiling in the liver indicate that Stat5b may be a general mediator of GH-initiated gene repression. Our results provide a model for understanding how GH may simultaneously stimulate and inhibit the expression of different cohorts of genes via the same transcription factor, potentially explaining how GH action leads to integrated biological responses in the whole organism.
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Affiliation(s)
- Mitsuru Ono
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, 3181 Southwest Sam Jackson Road, Portland, Oregon 97239, USA
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421
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Southgate RJ, Neill B, Prelovsek O, El-Osta A, Kamei Y, Miura S, Ezaki O, McLoughlin TJ, Zhang W, Unterman TG, Febbraio MA. FOXO1 regulates the expression of 4E-BP1 and inhibits mTOR signaling in mammalian skeletal muscle. J Biol Chem 2007; 282:21176-86. [PMID: 17510058 DOI: 10.1074/jbc.m702039200] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mammalian target of rapamycin (mTOR) is regulated by growth factors to promote protein synthesis. In mammalian skeletal muscle, the Forkhead-O1 transcription factor (FOXO1) promotes catabolism by activating ubiquitin-protein ligases. Using C2C12 mouse myoblasts that stably express inducible FOXO1-ER fusion proteins and transgenic mice that specifically overexpress constitutively active FOXO1 in skeletal muscle (FOXO(++/+)), we show that FOXO1 inhibits mTOR signaling and protein synthesis. Activation of constitutively active FOXO1 induced the expression of eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) mRNA via binding to the promoter. This resulted in an increased total 4E-BP1 abundance and a reduced 4E-BP1 (Thr-37/46) phosphorylation. The reduction in 4E-BP1 phosphorylation was associated with a reduction in the abundance of Raptor and mTOR proteins, Raptor-associated mTOR, reduced phosphorylation of the downstream protein p70S6 kinase, and attenuated incorporation of [(14)C]phenylalanine into protein. The FOXO(++/+) mice, characterized by severe skeletal muscle atrophy, displayed similar patterns of mRNA expression and protein abundance to those observed in the constitutively active FOXO1 C2C12 myotubes. These data suggest that FOXO1 may be an important therapeutic target for human diseases where anabolism is impaired.
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Affiliation(s)
- Robert J Southgate
- Cellular & Molecular Metabolism Laboratory, The Baker Heart Research Institute, Commercial Road, Melbourne 3004, Victoria, Australia
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422
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Barthel A, Ostrakhovitch EA, Walter PL, Kampkötter A, Klotz LO. Stimulation of phosphoinositide 3-kinase/Akt signaling by copper and zinc ions: mechanisms and consequences. Arch Biochem Biophys 2007; 463:175-82. [PMID: 17509519 DOI: 10.1016/j.abb.2007.04.015] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2007] [Accepted: 04/12/2007] [Indexed: 12/01/2022]
Abstract
The phosphoinositide 3'-kinase (PI3K)/Akt signaling cascade controls cellular processes such as apoptosis and proliferation. Moreover, it is a mediator of insulin effects on target cells and as such is a major regulator of fuel metabolism. The PI3K/Akt cascade was demonstrated to be activated by stressful stimuli, including heat shock and reactive oxygen species (ROS). This minireview focuses on activation of the pathway by exposure of cells to heavy metal ions, Cu2+ and Zn2+. It is hypothesized that stimulation of PI3K/Akt is the molecular mechanism underlying the known insulin-mimetic effects of copper and zinc ions. Following a brief summary of PI3K/Akt signaling and of activation of the cascade by Cu2+ and Zn2+, mechanisms of metal-induced PI3K/Akt activation are discussed with a focus on the role of ROS and of cellular thiols (glutathione, thioredoxin) and protein tyrosine phosphatases in Cu2+ and Zn2+ signaling. Finally, consequences of metal-induced PI3K/Akt activation are discussed, focusing on the modulation of FoxO-family transcription factors by Cu2+ and Zn2+.
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Affiliation(s)
- Andreas Barthel
- Medizinische Klinik I, BG Kliniken Bergmannsheil, Ruhr-Universität, Bochum, Germany
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423
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Kino T, Chrousos GP. Virus-mediated modulation of the host endocrine signaling systems: clinical implications. Trends Endocrinol Metab 2007; 18:159-66. [PMID: 17400471 PMCID: PMC7128651 DOI: 10.1016/j.tem.2007.03.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/08/2006] [Revised: 02/27/2007] [Accepted: 03/16/2007] [Indexed: 12/30/2022]
Abstract
Viruses, which are among the simplest infective pathogens, can produce characteristic endocrine manifestations in infected patients. In addition to the classic modification of the host endocrine system by either direct or indirect destruction of the endocrine organs and/or effects exerted by systemic production of inflammatory and/or stress mediators, recent progress in molecular virology and endocrinology has revealed that virus-encoded molecules might alter the host endocrine-signaling systems by affecting extracellular and/or intracellular signal transduction and hormone sensitivity of host target tissues. Here, we provide a brief overview of such viral-mediated modulation of host endocrine signaling systems. We propose that virus-encoded molecules and the signaling systems they influence are potential therapeutic targets for the treatment of disorders that are associated with some viral infections.
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Affiliation(s)
- Tomoshige Kino
- Pediatric Endocrinology Section, Reproductive Biology and Medicine Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-1109, USA.
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424
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Heikkinen S, Auwerx J, Argmann CA. PPARgamma in human and mouse physiology. Biochim Biophys Acta Mol Cell Biol Lipids 2007; 1771:999-1013. [PMID: 17475546 PMCID: PMC2020525 DOI: 10.1016/j.bbalip.2007.03.006] [Citation(s) in RCA: 168] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2006] [Revised: 03/14/2007] [Accepted: 03/19/2007] [Indexed: 11/23/2022]
Abstract
The peroxisome proliferator activated receptor gamma (PPARgamma) is a member in the nuclear receptor superfamily which mediates part of the regulatory effects of dietary fatty acids on gene expression. As PPARgamma also coordinates adipocyte differentiation, it is an important component in storing the excess nutritional energy as fat. Our genes have evolved into maximizing energy storage, and PPARgamma has a central role in the mismatch between our genes and our affluent western society which results in a broad range of metabolic disturbances, collectively known as the metabolic syndrome. A flurry of human and mouse studies has shed new light on the mechanisms how the commonly used insulin sensitizer drugs and PPARgamma activators, thiazolidinediones, act, and which of their physiological effects are dependent of PPARgamma. It is now evident that the full activation of PPARgamma is less advantageous than targeted modulation of its activity. Furthermore, new roles for PPARgamma signaling have been discovered in inflammation, bone morphogenesis, endothelial function, cancer, longevity, and atherosclerosis, to mention a few. Here we draw together and discuss these recent advances in the research into PPARgamma biology.
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Affiliation(s)
- Sami Heikkinen
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/Université Louis Pasteur, 67404 Illkirch, France
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425
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Mounier C, Posner BI. Transcriptional regulation by insulin: from the receptor to the gene. Can J Physiol Pharmacol 2007; 84:713-24. [PMID: 16998535 DOI: 10.1139/y05-152] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Insulin, after binding to its receptor, regulates many cellular processes and the expression of several genes. For a subset of genes, insulin exerts a negative effect on transcription; for others, the effect is positive. Insulin controls gene transcription by modifying the binding of transcription factors on insulin-response elements or by regulating their transcriptional activities. Different insulin-signaling cascades have been characterized as mediating the insulin effect on gene transcription. In this review, we analyze recent data on the molecular mechanisms, mostly in the liver, through which insulin exerts its effect. We first focus on the key transcription factors (viz. Foxo, sterol-response-element-binding protein family (SREBP), and Sp1) involved in the regulation of gene transcription by insulin. We then present current information on the way insulin downregulates and upregulates gene transcription, using as examples of downregulation phosphoenolpyruvate carboxykinase (PEPCK) and insulin-like growth factor binding protein 1 (IGFBP-1) genes and of upregulation the fatty acid synthase and malic enzyme genes. The last part of the paper focuses on the signaling cascades activated by insulin in the liver, leading to the modulation of gene transcription.
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Affiliation(s)
- Catherine Mounier
- BioMed, Department of Biological Science, University of Quebec in Montreal, 141 President Kennedy, Montreal, QC H2X 3Y7, Canada
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426
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Shiojima I, Walsh K. Regulation of cardiac growth and coronary angiogenesis by the Akt/PKB signaling pathway. Genes Dev 2007; 20:3347-65. [PMID: 17182864 DOI: 10.1101/gad.1492806] [Citation(s) in RCA: 285] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Postnatal growth of the heart is primarily achieved through hypertrophy of individual myocytes. Cardiac growth observed in athletes represents adaptive or physiological hypertrophy, whereas cardiac growth observed in patients with hypertension or valvular heart diseases is called maladaptive or pathological hypertrophy. These two types of hypertrophy are morphologically, functionally, and molecularly distinct from each other. The serine/threonine protein kinase Akt is activated by various extracellular stimuli in a phosphatidylinositol-3 kinase-dependent manner and regulates multiple aspects of cellular functions including survival, growth and metabolism. In this review we will discuss the role of the Akt signaling pathway in the heart, focusing on the regulation of cardiac growth, contractile function, and coronary angiogenesis. How this signaling pathway contributes to the development of physiological/pathological hypertrophy and heart failure will also be discussed.
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Affiliation(s)
- Ichiro Shiojima
- Molecular Cardiology, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
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427
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Kuningas M, Mägi R, Westendorp RGJ, Slagboom PE, Remm M, van Heemst D. Haplotypes in the human Foxo1a and Foxo3a genes; impact on disease and mortality at old age. Eur J Hum Genet 2007; 15:294-301. [PMID: 17245409 DOI: 10.1038/sj.ejhg.5201766] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Recently, the Daf-16 gene has been shown to regulate the lifespan of nematodes and flies. In mammals, the Daf-16 homologues are forkhead (FOXO) transcription factors, of which specific functions have been identified for Foxo1a and Foxo3a. Despite that, their influence on human age-related trajectories and lifespan is unknown. Here, we analysed the effect of genetic variance in Foxo1a and Foxo3a on metabolic profile, age-related diseases, fertility, fecundity and mortality. This study was carried out in the prospective population-based Leiden 85-plus Study, which includes 1245 participants, aged 85 years or more. The mean follow-up time was 4.4 years. Haplotype analyses of Foxo1a revealed that carriers of haplotype 3 'TCA' have higher HbA1c levels (P=0.025) and a 1.14-fold higher all-cause mortality risk (P=0.021). This increase in mortality was attributable to death from diabetes, for which a 2.43-fold increase was observed (P=0.025). The analyses with Foxo3a haplotypes revealed no differences in metabolic profile, fertility or fecundity. However, increased risks of stroke were observed for Foxo3a block-A haplotype 2 'GAGC' (P=0.007) and haplotype 4 'AAAT' (P=0.014) carriers. In addition, the haplotype 2 'GAGC' carriers had a 1.13-fold increased risk for all-cause mortality (P=0.036) and 1.19-fold increased risk for cardiovascular mortality (P=0.052). In conclusion, this study shows that genetic variation in evolutionarily conserved Foxo1a and Foxo3a genes influences lifespan in our study population.
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Affiliation(s)
- Maris Kuningas
- Department of Gerontology and Geriatrics, Leiden University Medical Center, Leiden, The Netherlands.
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428
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Zhang Y, Ma K, Sadana P, Chowdhury F, Gaillard S, Wang F, McDonnell DP, Unterman TG, Elam MB, Park EA. Estrogen-related receptors stimulate pyruvate dehydrogenase kinase isoform 4 gene expression. J Biol Chem 2006; 281:39897-906. [PMID: 17079227 DOI: 10.1074/jbc.m608657200] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The pyruvate dehydrogenase complex (PDC) catalyzes the conversion of pyruvate to acetyl-CoA in mitochondria and is a key regulatory enzyme in the oxidation of glucose to acetyl-CoA. Phosphorylation of PDC by the pyruvate dehydrogenase kinases (PDK2 and PDK4) inhibits PDC activity. Expression of the PDK genes is elevated in diabetes, leading to the decreased oxidation of pyruvate to acetyl-CoA. In these studies we have investigated the transcriptional regulation of the PDK4 gene by the estrogen-related receptors (ERRalpha and ERRgamma). The ERRs are orphan nuclear receptors whose physiological roles include the induction of fatty acid oxidation in heart and muscle. Previously, we found that the peroxisome proliferator-activated receptor gamma coactivator (PGC-1alpha) stimulates the expression of PDK4. Here we report that ERRalpha and ERRgamma stimulate the PDK4 gene in hepatoma cells, suggesting a novel role for ERRs in controlling pyruvate metabolism. In addition, both ERR isoforms recruit PGC-1alpha to the PDK4 promoter. Insulin, which decreases the expression of the PDK4 gene, inhibits the induction of PDK4 by ERRalpha and ERRgamma. The forkhead transcription factor (FoxO1) binds the PDK4 gene and contributes to the induction of PDK4 by ERRs and PGC-1alpha. Insulin suppresses PDK4 expression in part through the dissociation of FoxO1 and PGC-1alpha from the PDK4 promoter. Our data demonstrate a key role for the ERRs in the induction of hepatic PDK4 gene expression.
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Affiliation(s)
- Yi Zhang
- Department of Pharmacology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
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429
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Meng ZX, Sun JX, Ling JJ, Lv JH, Zhu DY, Chen Q, Sun YJ, Han X. Prostaglandin E2 regulates Foxo activity via the Akt pathway: implications for pancreatic islet beta cell dysfunction. Diabetologia 2006; 49:2959-68. [PMID: 17033838 DOI: 10.1007/s00125-006-0447-5] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/28/2006] [Accepted: 07/25/2006] [Indexed: 11/24/2022]
Abstract
AIMS/HYPOTHESIS Prostaglandin E(2) (PGE(2)) is a well-recognised inhibitor of glucose-stimulated insulin secretion (GSIS). The aim of this study was to investigate the signalling pathway of PGE(2) in beta cell function regulation in HIT-T15 cells and isolated rat islets. MATERIALS AND METHODS mRNA levels of the prostaglandin E receptor 3 (Ptger3) were measured by real-time PCR. Western blot analysis was used to detect changes in the levels of PTGER3, phosphorylated and total Akt, phosphorylated and total forkhead box 'Other' (Foxo). Transient transfection and reporter assays were used to measure Foxo transcriptional activity. The biological significance of PGE(2) in beta cell function was analysed using MTT, flow cytometry and GSIS assays. RESULTS We found that treating HIT-T15 cells with exogenous PGE(2) stimulated Ptger3 gene expression specifically, and diminished cAMP generation. These were accompanied by the downregulation of Akt and Foxo phosphorylation in HIT-T15 cells and isolated rat islets. Moreover, PGE(2) upregulated basal and partially reversed constitutively active Akt-inactivated Foxo transcriptional activity. Furthermore, GSIS was impaired in PGE(2)-treated HIT-T15 cells and isolated islets. However, the dosage used in the above experiments did not affect beta cell viability and apoptosis. In addition, insulin-like growth factor 1 (IGF-1) pretreatment reversed the effects of PGE(2), and wortmannin treatment abolished the preventive effects of IGF-1. CONCLUSIONS/INTERPRETATION Our observations strongly suggest that PGE(2) can induce pancreatic beta cell dysfunction through the induction of Ptger3 gene expression and inhibition of Akt/Foxo phosphorylation without impacting beta cell viability. These results shed light on the mechanisms of PGE(2) actions in pancreatic beta cell dysfunction.
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Affiliation(s)
- Z X Meng
- Key Laboratory of Human Functional Genomics of Jiangsu Province, School of Basic Medical Science, Nanjing Medical University, Nanjing, PR China
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430
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den Boer MAM, Voshol PJ, Kuipers F, Romijn JA, Havekes LM. Hepatic glucose production is more sensitive to insulin-mediated inhibition than hepatic VLDL-triglyceride production. Am J Physiol Endocrinol Metab 2006; 291:E1360-4. [PMID: 16849628 DOI: 10.1152/ajpendo.00188.2006] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Insulin is an important inhibitor of both hepatic glucose output and hepatic VLDL-triglyceride (VLDL-TG) production. We investigated whether both processes are equally sensitive to insulin-mediated inhibition. To test this, we used euglycemic clamp studies with four increasing plasma concentrations of insulin in wild-type C57Bl/6 mice. By extrapolation, we estimated that half-maximal inhibition of hepatic glucose output and hepatic VLDL-TG production by insulin were obtained at plasma insulin levels of approximately 3.6 and approximately 6.8 ng/ml, respectively. In the same experiments, we measured that half-maximal decrease of plasma free fatty acid levels and half-maximal stimulation of peripheral glucose uptake were reached at plasma insulin levels of approximately 3.0 and approximately 6.0 ng/ml, respectively. We conclude that, compared with insulin sensitivity of hepatic glucose output, peripheral glucose uptake and hepatic VLDL-TG production are less sensitive to insulin.
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Affiliation(s)
- Marion A M den Boer
- Dept. of Endocrinology and Metabolism, Leiden University Medical Center, 2333 ZA, Leiden, The Netherlands.
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431
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Yang JY, Xia W, Hu MCT. Ionizing radiation activates expression of FOXO3a, Fas ligand, and Bim, and induces cell apoptosis. Int J Oncol 2006. [PMID: 16865280 DOI: 10.3892/ijo.29.3.643] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Genotoxic stress such as ionizing radiation can induce DNA damage and promote cell-cycle arrest or apoptosis through either a p53-dependent or -independent pathway. Recently, members of the FOXO Forkhead transcription factor family have been implicated in playing a role in both DNA repair and apoptosis in mammalian cells that promoted us to examine the role of FOXO transcription factors in ionizing radiation-induced apoptosis. Here, we show that ionizing radiation can promote FOXO3a (FKHRL1) transcriptional activity and protein expression level, and induce nuclear translocation of FOXO3a in Saos2, a p53-null osteosarcoma cell line. Ionizing radiation stimulates expression of apoptosis-inducing proteins such as Fas ligand and the Bcl-2 interacting mediator of cell death (Bim) leading to cellular apoptosis. The observed upregulation of proapoptotic genes and apoptosis in cells without p53 in response to ionizing radiation suggests a novel p53-independent mechanism underlying ionizing radiation-induced apoptosis in cancer cells.
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Affiliation(s)
- Jer-Yen Yang
- Department of Molecular and Cellular Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, 77030, USA
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432
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Walter PL, Kampkötter A, Eckers A, Barthel A, Schmoll D, Sies H, Klotz LO. Modulation of FoxO signaling in human hepatoma cells by exposure to copper or zinc ions. Arch Biochem Biophys 2006; 454:107-13. [PMID: 16973122 DOI: 10.1016/j.abb.2006.08.016] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2006] [Revised: 08/11/2006] [Accepted: 08/11/2006] [Indexed: 11/15/2022]
Abstract
Cells respond to heavy metal stress by activating signaling cascades regulating cellular proliferation and survival. We here demonstrate that the anti-apoptotic kinase Akt is activated in HepG2 human hepatoma cells exposed to copper or zinc ions. Cu2+- and Zn2+-induced phosphorylation of Akt was blocked by phosphoinositide 3-kinase (PI3K) inhibitors, wortmannin and LY294002. Moreover, several endogenous Akt substrates were phosphorylated, including glycogen synthase kinase-3 and transcription factors of the FoxO family, FoxO1a and FoxO4. Exposure to Cu2+ or Zn2+ elicited the subcellular redistribution of an overexpressed FoxO1a-EGFP fusion protein from nucleus to cytoplasm, which was not seen with a mutant FoxO1a form devoid of Akt phosphorylation sites. Both FoxO phosphorylation and nuclear exclusion were blocked by wortmannin. Likewise, the subcellular translocation from nucleus to cytoplasm of the Caenorhabditis elegans FoxO ortholog, DAF-16, was caused in starved worms exposed to copper ions. Activity of the promoter of the human glucose 6-phosphatase gene, known to be regulated by insulin and FoxO1a, was demonstrated in reporter gene assays to be attenuated in hepatoma cells exposed to Cu2+. However, this suppression of glucose 6-phosphatase promoter activity was independent of modulation of the PI3K/Akt pathway. In summary, the PI3K/Akt pathway is activated in human hepatoma cells exposed to Cu2+ or Zn2+, resulting in the phosphorylation and subcellular relocalisation of transcription factor FoxO1a. Furthermore, copper is demonstrated to exert an insulin-mimetic effect also independently of the PI3K/Akt/FoxO pathway.
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Affiliation(s)
- Philippe L Walter
- Institut für Biochemie und Molekularbiologie I, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany
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433
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Wang P, Keijer J, Bunschoten A, Bouwman F, Renes J, Mariman E. Insulin modulates the secretion of proteins from mature 3T3-L1 adipocytes: a role for transcriptional regulation of processing. Diabetologia 2006; 49:2453-62. [PMID: 16896944 DOI: 10.1007/s00125-006-0321-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/01/2006] [Accepted: 04/19/2006] [Indexed: 01/31/2023]
Abstract
AIMS/HYPOTHESIS Under conditions of insulin resistance and type 2 diabetes, fat cells are subjected to increased levels of insulin, which may have a major impact on the secretion of adipokines. MATERIALS AND METHODS Using transcriptomics and proteomics, we investigated how insulin affects the transcription and protein secretion profile of mature 3T3-L1 adipocytes. RESULTS We found that insulin has a significant impact on protein secretion of 3T3-L1 adipocytes. However, transcription is not the major regulation point for these secreted proteins. For extracellular matrix components, our data suggest that the mRNA level of processing enzymes, but not of target proteins, is the regulating point at which insulin stimulates secretion and function of the relevant proteins. Among these enzymes, we report a novel finding, namely that sulfatase 2 gene is regulated by insulin, which may induce a functional change in cultured adipocytes. CONCLUSIONS/INTERPRETATION We propose that enhancement of protein processing and secretion rather than transcription of the secreted protein genes is part of the strategic role of insulin in the induction of cellular responses.
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Affiliation(s)
- P Wang
- Functional Genomics Group, Research Institute NUTRIM, Department of Human Biology, Maastricht University, Maastricht, The Netherlands
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434
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Abid MR, Shih SC, Otu HH, Spokes KC, Okada Y, Curiel DT, Minami T, Aird WC. A novel class of vascular endothelial growth factor-responsive genes that require forkhead activity for expression. J Biol Chem 2006; 281:35544-53. [PMID: 16980307 DOI: 10.1074/jbc.m608620200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recently, we have shown that transient phosphorylation and inhibition of the pro-apoptotic transcription factor, forkhead, by vascular endothelial growth factor (VEGF) is essential for endothelial cell (EC) survival and proliferation. The goal of the present study was to determine whether forkhead (FKHR) also plays a positive role in agonist-mediated gene induction. Human coronary artery ECs were transduced with adenovirus overexpressing constitutively active phosphorylation-resistant triple mutant FKHR or transfected with small interference RNA (siRNA) against FKHR. The cells were then treated in the absence or presence of VEGF and assayed for gene expression using quantitative real-time PCR and Northern blots analyses. The data revealed a novel set of VEGF-responsive genes that require FKHR activity for optimal expression in ECs, including bone morphogenic protein 2, cbp/p300-interacting transactivator 2, decay accelerating factor (DAF), vascular cell adhesion molecule-1 (VCAM-1), manganese superoxide dismutase, endothelial-specific molecule-1, RING1 and YY1-binding protein, and matrix metalloproteinase-10. Consistent with a positive role for FKHR in mediating VEGF induction of DAF and VCAM-1 mRNA, siRNA against FKHR attenuated the effect of VEGF on complement-mediated EC lysis and monocyte adhesion, respectively. VEGF induction of the forkhead-dependent genes was down-regulated by the NF-kappaB inhibitor, constitutively active Ad-IkappaB, and in some cases by the nuclear factor of activated T-cells (NF-AT) inhibitor, cyclosporin. Together, these findings suggest that the VEGF-forkhead signaling axis plays an important functional role in ECs beyond the regulation of cell survival/apoptosis and cell cycle.
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Affiliation(s)
- Md Ruhul Abid
- Center for Vascular Biology Research, Department of Medicine, the Division of Molecular, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
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435
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Jacinto E, Facchinetti V, Liu D, Soto N, Wei S, Jung SY, Huang Q, Qin J, Su B. SIN1/MIP1 maintains rictor-mTOR complex integrity and regulates Akt phosphorylation and substrate specificity. Cell 2006; 127:125-37. [PMID: 16962653 DOI: 10.1016/j.cell.2006.08.033] [Citation(s) in RCA: 1082] [Impact Index Per Article: 60.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2006] [Revised: 07/23/2006] [Accepted: 08/29/2006] [Indexed: 12/15/2022]
Abstract
Mammalian target of rapamycin (mTOR) controls cell growth and proliferation via the raptor-mTOR (TORC1) and rictor-mTOR (TORC2) protein complexes. Recent biochemical studies suggested that TORC2 is the elusive PDK2 for Akt/PKB Ser473 phosphorylation in the hydrophobic motif. Phosphorylation at Ser473, along with Thr308 of its activation loop, is deemed necessary for Akt function, although the regulatory mechanisms and physiological importance of each phosphorylation site remain to be fully understood. Here, we report that SIN1/MIP1 is an essential TORC2/PDK2 subunit. Genetic ablation of sin1 abolished Akt-Ser473 phosphorylation and disrupted rictor-mTOR interaction but maintained Thr308 phosphorylation. Surprisingly, defective Ser473 phosphorylation affected only a subset of Akt targets in vivo, including FoxO1/3a, while other Akt targets, TSC2 and GSK3, and the TORC1 effectors, S6K and 4E-BP1, were unaffected. Our findings reveal that the SIN1-rictor-mTOR function in Akt-Ser473 phosphorylation is required for TORC2 function in cell survival but is dispensable for TORC1 function.
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Affiliation(s)
- Estela Jacinto
- Department of Physiology and Biophysics, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
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436
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Engelman JA, Luo J, Cantley LC. The evolution of phosphatidylinositol 3-kinases as regulators of growth and metabolism. Nat Rev Genet 2006; 7:606-19. [PMID: 16847462 DOI: 10.1038/nrg1879] [Citation(s) in RCA: 2453] [Impact Index Per Article: 136.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Phosphatidylinositol 3-kinases (PI3Ks) evolved from a single enzyme that regulates vesicle trafficking in unicellular eukaryotes into a family of enzymes that regulate cellular metabolism and growth in multicellular organisms. In this review, we examine how the PI3K pathway has evolved to control these fundamental processes, and how this pathway is in turn regulated by intricate feedback and crosstalk mechanisms. In light of the recent advances in our understanding of the function of PI3Ks in the pathogenesis of diabetes and cancer, we discuss the exciting therapeutic opportunities for targeting this pathway to treat these diseases.
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Affiliation(s)
- Jeffrey A Engelman
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
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437
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Luong N, Davies CR, Wessells RJ, Graham SM, King MT, Veech R, Bodmer R, Oldham SM. Activated FOXO-mediated insulin resistance is blocked by reduction of TOR activity. Cell Metab 2006; 4:133-42. [PMID: 16890541 DOI: 10.1016/j.cmet.2006.05.013] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/03/2005] [Revised: 04/07/2006] [Accepted: 05/19/2006] [Indexed: 11/21/2022]
Abstract
Reducing insulin/IGF signaling allows for organismal survival during periods of inhospitable conditions by regulating the diapause state, whereby the organism stockpiles lipids, reduces fertility, increases stress resistance, and has an increased lifespan. The Target of Rapamycin (TOR) responds to changes in growth factors, amino acids, oxygen tension, and energy status; however, it is unclear how TOR contributes to physiological homeostasis and disease conditions. Here, we show that reducing the function of Drosophila TOR results in decreased lipid stores and glucose levels. Importantly, this reduction of dTOR activity blocks the insulin resistance and metabolic syndrome phenotypes associated with increased activity of the insulin responsive transcription factor, dFOXO. Reduction in dTOR function also protects against age-dependent decline in heart function and increases longevity. Thus, the regulation of dTOR activity may be an ancient "systems biological" means of regulating metabolism and senescence, that has important evolutionary, physiological, and clinical implications.
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Affiliation(s)
- Nancy Luong
- The Burnham Institute for Medical Research, Cancer Research Center, Neuroscience and Aging Center, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
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438
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Abstract
The forkhead box O1A (FOXO1A) has been identified as one gene that is up-regulated early in the decidualization process. To further investigate the role of FOXO1A during this process, six genes, IGFBP1, PRL, TIMP3, LAMB1, CNR1, and DCN, shown to be up-regulated during decidualization, were chosen as potential targets of FOXO1A action. Treatment of human endometrial stromal cells with hormones (estradiol and medroxyprogesterone acetate) plus dibutyryl cAMP (H+dbcAMP) for 48 h increased expression of IGFBP1, PRL, TIMP3, CNR1, and DCN but not LAMB1, as measured by real-time PCR. Silencing of FOXO1A using small interfering RNA oligonucleotides decreased IGFBP1 and DCN levels and increased CNR1, TIMP3, and PRL levels. LAMB1 was not affected. When FOXO1A was overexpressed in human endometrial stromal cells, expression of IGFBP1, DCN, and PRL increased, whereas levels of TIMP3 and CNR1 decreased. Addition of H+dbcAMP caused an increased expression of IGFBP1, PRL, and DCN beyond that of FOXO1A alone. TIMP3 and CNR1 levels decreased even further in response to H+dbcAMP compared with FOXO1A alone. LAMB1, which was unresponsive to FOXO1A, decreased when H+dbcAMP was added. Overexpressing FOXO1A also caused a change in cell shape, in that the stromal fibroblasts acquired a rounded, epithelioid appearance. Finally, reporter studies showed that cotransfection of FOXO1A significantly increased PRL promoter activity but not TIMP3 promoter activity. Addition of H+dbcAMP resulted in a significant increase in PRL promoter activity and a significant decrease in TIMP3 promoter activity. In summary, this study demonstrates the versatile nature of FOXO1A in the regulation of a number of decidualization-specific genes.
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Affiliation(s)
- Oscar L Buzzio
- Department of Obstetrics and Gynecology, Northwestern University, Chicago, Illinois 60611, USA
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439
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Wijchers PJEC, Burbach JPH, Smidt MP. In control of biology: of mice, men and Foxes. Biochem J 2006; 397:233-46. [PMID: 16792526 PMCID: PMC1513289 DOI: 10.1042/bj20060387] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2006] [Revised: 05/04/2006] [Accepted: 05/05/2006] [Indexed: 12/11/2022]
Abstract
Forkhead proteins comprise a highly conserved family of transcription factors, named after the original forkhead gene in Drosophila. To date, over 100 forkhead genes have been identified in a large variety of species, all sharing the evolutionary conserved 'forkhead' DNA-binding domain, and the cloning and characterization of forkhead genes have continued in recent years. Forkhead transcription factors regulate the expression of countless genes downstream of important signalling pathways in most, if not all, tissues and cell types. Recent work has provided novel insights into the mechanisms that contribute to their functional diversity, including functional protein domains and interactions of forkheads with other transcription factors. Studies using loss- and gain-of-function models have elucidated the role of forkhead factors in developmental biology and cellular functions such as metabolism, cell division and cell survival. The importance of forkhead transcription factors is underlined by the developmental defects observed in mutant model organisms, and multiple human disorders and cancers which can be attributed to mutations within members of the forkhead gene family. This review provides a comprehensive overview of current knowledge on forkhead transcription factors, from structural organization and regulatory mechanisms to cellular and developmental functions in mice and humans. Finally, we will discuss how novel insights gained from involvement of 'Foxes' in the mechanisms underlying human pathology may create new opportunities for treatment strategies.
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Key Words
- cell cycle
- development
- forkhead
- fox
- immunoregulation
- transcription factor
- cbp, creb (camp-response-element-binding protein)-binding protein
- ccnb, cyclin b
- cdk, cyclin-dependent kinase
- cki, cdk inhibitor
- dyrk1a, dual-specificity tyrosine-phosphorylated and -regulated kinase 1a
- er, oestrogen receptor
- fha, forkhead-associated domain
- fm, foxh1 motif
- fox, forkhead box
- gadd45a, growth arrest and dna-damage-inducible protein 45α
- hdac, histone deacetylase
- iκb, inhibitory κb
- ikkβ, iκb kinase β
- mh domain, mothers against decapentaplegic homology domain
- nf-κb, nuclear factor κb
- nls, nuclear localization signal
- pkb, protein kinase b
- plk-1, polo-like kinase 1
- scf, skp2/cullin/f-box
- sgk, serum- and glucocorticoid-induced protein kinase
- smad, similar to mothers against decapentaplegic
- sid, smad-interaction domain
- sim, smad-interaction motif
- tgfβ, transforming growth factor β
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Affiliation(s)
- Patrick J E C Wijchers
- Rudolf Magnus Institute of Neuroscience, Department of Pharmacology and Anatomy, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands.
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440
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Onuma H, Vander Kooi BT, Boustead JN, Oeser JK, O'Brien RM. Correlation between FOXO1a (FKHR) and FOXO3a (FKHRL1) binding and the inhibition of basal glucose-6-phosphatase catalytic subunit gene transcription by insulin. Mol Endocrinol 2006; 20:2831-47. [PMID: 16840535 DOI: 10.1210/me.2006-0085] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Insulin inhibits transcription of the genes encoding the glucose-6-phosphatase catalytic subunit (G6Pase), phosphoenolpyruvate carboxykinase, and IGF binding protein-1 through insulin response sequences (IRSs) that share the same core sequence, T(G/A)TTTT(G/T). The transcription factors FOXO1a and FOXO3a have been shown to bind these elements, but there are conflicting reports as to whether this binding correlates with the action of insulin on gene transcription. Some researchers concluded, from overexpression experiments using FOXO1a, that binding correlated with the insulin response, whereas others concluded, mainly from gel retardation competition experiments using FOXO3a, that it did not. We show here that, although these factors can differentially activate gene transcription in a context-dependent manner, these conflicting data are not explained by a difference in FOXO1a and FOXO3a binding specificity. Instead, we find that gel retardation competition and binding experiments give different results; the latter reveal a correlation between FOXO1a/3a binding and the inhibition of basal G6Pase gene transcription by insulin. In addition, these data show that the binding of FOXO1a/3a to two adjacent IRSs in the G6Pase promoter is cooperative and that promoter context alters the specific IRS base requirements for FOXO1a-stimulated fusion gene expression. Surprisingly, an analysis of insulin action mediated through the G6Pase and IGF binding protein-1 IRSs in the context of a heterologous thymidine kinase promoter reveals that signaling through the latter does not support the accepted model for insulin-stimulated FOXO nuclear exclusion.
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Affiliation(s)
- Hiroshi Onuma
- Department of Molecular Physiology and Biophysics, 761 Preston Research Building, Vanderbilt University Medical School, Nashville, Tennessee 37232-0615, USA
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441
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Arden KC. Multiple roles of FOXO transcription factors in mammalian cells point to multiple roles in cancer. Exp Gerontol 2006; 41:709-17. [PMID: 16806782 DOI: 10.1016/j.exger.2006.05.015] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2006] [Revised: 05/13/2006] [Accepted: 05/16/2006] [Indexed: 12/13/2022]
Abstract
The FOXO family of transcription factors has been implicated in several cellular processes including cell cycle arrest, cell death and protection from stress stimuli. FOXO function is influenced by multiple signaling pathways. Many of these pathways are known to be misregulated in cancer. Perturbation of FOXO function leads to uncontrolled cell proliferation and accumulation of DNA damage. It is becoming clear that active FOXO proteins play an important role in keeping cells in check and inactivation of FOXO proteins is associated with characteristics of cancer cells. FOXO proteins may represent new therapeutic targets for a broad spectrum of cancers.
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Affiliation(s)
- Karen C Arden
- Ludwig Institute for Cancer Research, Departments of Medicine and Cancer Center, University of California at San Diego School of Medicine, 9500 Gilman Drive, La Jolla, CA 92093-0669, USA.
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442
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Cho CY, Koo SH, Wang Y, Callaway S, Hedrick S, Mak PA, Orth AP, Peters EC, Saez E, Montminy M, Schultz PG, Chanda SK. Identification of the tyrosine phosphatase PTP-MEG2 as an antagonist of hepatic insulin signaling. Cell Metab 2006; 3:367-78. [PMID: 16679294 DOI: 10.1016/j.cmet.2006.03.006] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/18/2005] [Revised: 12/01/2005] [Accepted: 03/09/2006] [Indexed: 10/24/2022]
Abstract
Insulin resistance is a primary defect in type 2 diabetes characterized by impaired peripheral glucose uptake and insufficient suppression of hepatic glucose output. Insulin signaling inhibits liver glucose production by inducing nuclear exclusion of the gluconeogenic transcription factor FOXO1 in an Akt-dependent manner. Through the concomitant application of genome-scale functional screening and quantitative image analysis, we have identified PTP-MEG2 as a modulator of insulin-dependent FOXO1 subcellular localization. Ectopic expression of PTP-MEG2 in cells inhibited insulin-induced phosphorylation of the insulin receptor, while RNAi-mediated reduction of PTP-MEG2 transcript levels enhanced insulin action. Additionally, adenoviral-mediated depletion of PTP-MEG2 in livers of diabetic (db/db) mice resulted in insulin sensitization and normalization of hyperglycemia. These data implicate PTP-MEG2 as a mediator of blood glucose homeostasis through antagonism of insulin signaling, and suggest that modulation of PTP-MEG2 activity may be an effective strategy in the treatment of type 2 diabetes.
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Affiliation(s)
- Charles Y Cho
- Genomics Institute of the Novartis Research Foundation, 10675 John Jay Hopkins Drive, San Diego, CA 92121, USA
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443
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Luo J, Sobkiw CL, Hirshman MF, Logsdon MN, Li TQ, Goodyear LJ, Cantley LC. Loss of class IA PI3K signaling in muscle leads to impaired muscle growth, insulin response, and hyperlipidemia. Cell Metab 2006; 3:355-66. [PMID: 16679293 DOI: 10.1016/j.cmet.2006.04.003] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2005] [Revised: 03/12/2006] [Accepted: 04/13/2006] [Indexed: 11/27/2022]
Abstract
The evolutionarily conserved phosphoinositide 3-kinase (PI3K) signaling pathway mediates both the metabolic effects of insulin and the growth-promoting effects of insulin-like growth factor-1 (IGF-1). We have generated mice deficient in both the p85alpha/p55alpha/p50alpha and the p85beta regulatory subunits of class I(A) PI3K in skeletal muscles. PI3K signaling in the muscle of these animals is severely impaired, leading to a significant reduction in muscle weight and fiber size. These mice also exhibit muscle insulin resistance and whole-body glucose intolerance. Despite their ability to maintain normal fasting and fed blood glucose levels, these mice show increased body fat content and elevated serum free fatty acid and triglyceride levels. These results demonstrate that in vivo p85 is a critical mediator of class I(A) PI3K signaling in the regulation of muscle growth and metabolism. Our finding also indicates that compromised muscle PI3K signaling could contribute to symptoms of hyperlipidemia associated with human type 2 diabetes.
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MESH Headings
- Animals
- Blood Glucose/metabolism
- Body Composition
- Diabetes Mellitus, Type 2/blood
- Diabetes Mellitus, Type 2/enzymology
- Diabetes Mellitus, Type 2/pathology
- Fatty Acids, Nonesterified/blood
- Glucose/metabolism
- Glucose Intolerance
- Hyperlipidemias/blood
- Hyperlipidemias/enzymology
- Hyperlipidemias/pathology
- Hypoglycemic Agents/pharmacology
- Insulin/pharmacology
- Insulin Resistance
- Insulin-Like Growth Factor I/pharmacology
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Muscle, Skeletal/drug effects
- Muscle, Skeletal/enzymology
- Muscle, Skeletal/growth & development
- Muscle, Skeletal/pathology
- Muscular Atrophy/blood
- Muscular Atrophy/enzymology
- Muscular Atrophy/pathology
- Phosphatidylinositol 3-Kinases/deficiency
- Phosphatidylinositol 3-Kinases/genetics
- Phosphatidylinositol 3-Kinases/metabolism
- Signal Transduction
- Triglycerides/blood
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Affiliation(s)
- Ji Luo
- Department of Systems Biology, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02115, USA
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444
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Zhang W, Patil S, Chauhan B, Guo S, Powell DR, Le J, Klotsas A, Matika R, Xiao X, Franks R, Heidenreich KA, Sajan MP, Farese RV, Stolz DB, Tso P, Koo SH, Montminy M, Unterman TG. FoxO1 regulates multiple metabolic pathways in the liver: effects on gluconeogenic, glycolytic, and lipogenic gene expression. J Biol Chem 2006; 281:10105-17. [PMID: 16492665 DOI: 10.1074/jbc.m600272200] [Citation(s) in RCA: 378] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
FoxO transcription factors are important targets of insulin action. To better understand the role of FoxO proteins in the liver, we created transgenic mice expressing constitutively active FoxO1 in the liver using the alpha1-antitrypsin promoter. Fasting glucose levels are increased, and glucose tolerance is impaired in transgenic (TGN) versus wild type (WT) mice. Interestingly, fasting triglyceride and cholesterol levels are reduced despite hyperinsulinemia, and post-prandial changes in triglyceride levels are markedly suppressed in TGN versus WT mice. Activation of pro-lipogenic signaling pathways (atypical protein kinase C and protein kinase B) and the ability to suppress beta-hydroxybutyrate levels are not impaired in TGN. In contrast, de novo lipogenesis measured with (3)H(2)O is suppressed by approximately 70% in the liver of TGN versus WT mice after refeeding. Gene-array studies reveal that the expression of genes involved in gluconeogenesis, glycerol transport, and amino acid catabolism is increased, whereas genes involved in glucose utilization by glycolysis, the pentose phosphate shunt, lipogenesis, and sterol synthesis pathways are suppressed in TGN versus WT. Studies with adenoviral vectors in isolated hepatocytes confirm that FoxO1 stimulates expression of gluconeogenic genes and suppresses expression of genes involved in glycolysis, the shunt pathway, and lipogenesis, including glucokinase and SREBP-1c. Together, these results indicate that FoxO proteins promote hepatic glucose production through multiple mechanisms and contribute to the regulation of other metabolic pathways important in the adaptation to fasting and feeding in the liver, including glycolysis, the pentose phosphate shunt, and lipogenic and sterol synthetic pathways.
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Affiliation(s)
- Wenwei Zhang
- Departments of Medicine and Physiology and Biophysics, University of Illinois College of Medicine, Chicago, IL 60612, USA
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445
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Stuart JA, Brown MF. Energy, quiescence and the cellular basis of animal life spans. Comp Biochem Physiol A Mol Integr Physiol 2006; 143:12-23. [PMID: 16377223 DOI: 10.1016/j.cbpa.2005.11.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2005] [Revised: 11/02/2005] [Accepted: 11/03/2005] [Indexed: 01/11/2023]
Abstract
Animals are routinely faced with harsh environmental conditions in which insufficient energy is available to grow and reproduce. Many animals adapt to this challenge by entering a dormant, or quiescent state. In some animals, such as the nematode Caenorhabditis elegans, quiescence is coincident with increased stress resistance and longevity. Here we review evidence that the rules of life span extension established in C. elegans may be generally true of most animals. That is, that the rate of animal aging correlates inversely with cellular resistance to physiological stress, particularly oxidative stress, and that stress resistance is co-regulated with the quiescence adaptation (where the latter occurs). We discuss evidence for highly conserved intracellular signalling pathways involved in energy sensing that are sensitive to aspects of mitochondrial energy transduction and can be modulated in response to energetic flux. We provide a broad overview of the current knowledge of the relationships between energy, metabolism and life span.
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Affiliation(s)
- Jeffrey A Stuart
- Department of Biological Sciences, Brock University, St. Catharines, Ontario, Canada L2S 3A1.
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446
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Greer EL, Brunet A. FOXO transcription factors at the interface between longevity and tumor suppression. Oncogene 2005; 24:7410-25. [PMID: 16288288 DOI: 10.1038/sj.onc.1209086] [Citation(s) in RCA: 984] [Impact Index Per Article: 51.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A wide range of human diseases, including cancer, has a striking age-dependent onset. However, the molecular mechanisms that connect aging and cancer are just beginning to be unraveled. FOXO transcription factors are promising candidates to serve as molecular links between longevity and tumor suppression. These factors are major substrates of the protein kinase Akt. In the presence of insulin and growth factors, FOXO proteins are relocalized from the nucleus to the cytoplasm and degraded via the ubiquitin-proteasome pathway. In the absence of growth factors, FOXO proteins translocate to the nucleus and upregulate a series of target genes, thereby promoting cell cycle arrest, stress resistance, or apoptosis. Stress stimuli also trigger the relocalization of FOXO factors into the nucleus, thus allowing an adaptive response to stress stimuli. Consistent with the notion that stress resistance is highly coupled with lifespan extension, activation of FOXO transcription factors in worms and flies increases longevity. Emerging evidence also suggests that FOXO factors play a tumor suppressor role in a variety of cancers. Thus, FOXO proteins translate environmental stimuli into changes in gene expression programs that may coordinate organismal longevity and tumor suppression.
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Affiliation(s)
- Eric L Greer
- Department of Genetics, Stanford University, CA 94305, USA
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447
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Gan L, Han Y, Bastianetto S, Dumont Y, Unterman TG, Quirion R. FoxO-dependent and -independent mechanisms mediate SirT1 effects on IGFBP-1 gene expression. Biochem Biophys Res Commun 2005; 337:1092-6. [PMID: 16236254 DOI: 10.1016/j.bbrc.2005.09.169] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2005] [Accepted: 09/28/2005] [Indexed: 11/26/2022]
Abstract
Sirtuin 1 (SirT1), an NAD-dependent deacetylase that is important for promoting longevity during caloric restriction, can deacetylate and enhance the function of forkhead box transcription factors, O subfamily (FoxO). We examined the effect of SirT1 on the regulation of insulin-like growth factor-binding protein 1 (IGFBP-1), a known target of FoxO proteins that is increased in fasting. Co-transfection with a SirT1 expression vector dose-dependently stimulated IGFBP-1 promoter activity and a heterologous reporter gene construct containing three FoxO-binding sites linked to a minimal promoter. This effect is mimicked by 20muM resveratrol, a potent SirT1 activator, and immunoprecipitation and Western blotting confirm that SirT1 and FoxO1 interact in cells. Interestingly, mutation of FoxO-binding sites in the IGFBP-1 promoter reduces, but does not completely disrupt, the stimulatory effect of SirT1 on promoter activity. We found that overexpression of SirT1 is accompanied by enhanced mitogen-activated protein kinase (MAPK) activation. Treatment of SirT1-cotransfected cells with PD98059, which inhibits MAPK activation, decreased IGFBP-1 promoter activity by approximately 50%, in a FoxO-binding site-independent manner, and disrupts the residual effect of SirT1. These results indicate that SirT1 stimulates IGFBP-1 promoter activity through FoxO-dependent and -independent mechanisms, and provides the first evidence that activation of MAPK contributes to effects of SirT1 on gene expression.
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Affiliation(s)
- Lixia Gan
- Douglas Hospital Research Center, Department of Psychiatry, McGill University, Montreal, Que., Canada H4H 1R3
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448
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Abstract
Transducer of regulated CREB activity (TORC) proteins promote transactivation by the cAMP response element binding protein (CREB) and mediate effects of cAMP agonists on gene expression. Koo et al. now report that TORC phosphorylation and nuclear/cytoplasmic shuttling play a key role in the regulation of gluconeogenesis by cAMP. Control of TORC phosphorylation and function may integrate the effects of multiple factors involved in metabolic control, including cAMP agonists, insulin, and AMP kinases. TORCs, and kinases affecting TORC function, are promising new therapeutic targets for the treatment of diabetes mellitus.
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Affiliation(s)
- Sandip Patil
- Department of Medicine and Physiology, University of Illinois at Chicago College of Medicine, Medical Research Service, USA
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449
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Matsuzaki H, Daitoku H, Hatta M, Aoyama H, Yoshimochi K, Fukamizu A. Acetylation of Foxo1 alters its DNA-binding ability and sensitivity to phosphorylation. Proc Natl Acad Sci U S A 2005; 102:11278-83. [PMID: 16076959 PMCID: PMC1183558 DOI: 10.1073/pnas.0502738102] [Citation(s) in RCA: 366] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The FOXO family of forkhead transcription factors plays a key role in a variety of biological processes, including metabolism, cell proliferation, and oxidative stress response. We previously reported that Foxo1, a member of the FOXO family, is regulated through reversible acetylation catalyzed by histone acetyltransferase cAMP-response element-binding protein (CREB)-binding protein (CBP) and NAD-dependent histone deacetylase silent information regulator 2, and that the acetylation at Lys-242, Lys-245, and Lys-262 of Foxo1 attenuates its transcriptional activity. However, the molecular mechanism by which acetylation modulates Foxo1 activity remains unknown. Here, we show that the positive charge of these lysines in Foxo1 contributes to its DNA-binding, and acetylation at these residues by CBP attenuates its ability to bind cognate DNA sequence. Remarkably, we also show that acetylation of Foxo1 increases the levels of its phosphorylation at Ser-253 through the phosphatidylinositol 3-kinase-protein kinase B signaling pathway, and this effect was overridden on the acetylation-deficient Foxo1 mutant. Furthermore, in in vitro kinase reactions, the association of wild-type Foxo1 and its target DNA sequence inhibits the protein kinase B-dependent phosphorylation of Foxo1, whereas mutated Foxo1 proteins, which mimic constitutively acetylated states, are efficiently phosphorylated even in the presence of the DNA. These results suggest that acetylation regulates the function of Foxo1 through altering the affinity with the target DNA and the sensitivity for phosphorylation.
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Affiliation(s)
- Hitomi Matsuzaki
- Center for Tsukuba Advanced Research Alliance, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
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