101
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Velichkova M, Juan J, Kadandale P, Jean S, Ribeiro I, Raman V, Stefan C, Kiger AA. Drosophila Mtm and class II PI3K coregulate a PI(3)P pool with cortical and endolysosomal functions. ACTA ACUST UNITED AC 2010; 190:407-25. [PMID: 20696708 PMCID: PMC2922644 DOI: 10.1083/jcb.200911020] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Turnover of endosomal PI(3)P by mtm maintains endolysosomal homeostasis and cortical remodeling in Drosophila hemocytes during migration. Reversible phosphoinositide phosphorylation provides a dynamic membrane code that balances opposing cell functions. However, in vivo regulatory relationships between specific kinases, phosphatases, and phosphoinositide subpools are not clear. We identified myotubularin (mtm), a Drosophila melanogaster MTM1/MTMR2 phosphoinositide phosphatase, as necessary and sufficient for immune cell protrusion formation and recruitment to wounds. Mtm-mediated turnover of endosomal phosphatidylinositol 3-phosphate (PI(3)P) pools generated by both class II and III phosphatidylinositol 3-kinases (Pi3K68D and Vps34, respectively) is needed to down-regulate membrane influx, promote efflux, and maintain endolysosomal homeostasis. Endocytosis, but not endolysosomal size, contributes to cortical remodeling by mtm function. We propose that Mtm-dependent regulation of an endosomal PI(3)P pool has separable consequences for endolysosomal homeostasis and cortical remodeling. Pi3K68D depletion (but not Vps34) rescues protrusion and distribution defects in mtm-deficient immune cells and restores functions in other tissues essential for viability. The broad interactions between mtm and class II Pi3K68D suggest a novel strategy for rebalancing PI(3)P-mediated cell functions in MTM-related human disease.
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Affiliation(s)
- Michaella Velichkova
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA 92093, USA
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102
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Leibiger IB, Brismar K, Berggren PO. Novel aspects on pancreatic beta-cell signal-transduction. Biochem Biophys Res Commun 2010; 396:111-5. [DOI: 10.1016/j.bbrc.2010.02.174] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2010] [Accepted: 02/28/2010] [Indexed: 10/19/2022]
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103
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Abstract
Phosphoinositide 3-kinases (PI3Ks) function early in intracellular signal transduction pathways and affect many biological functions. A further level of complexity derives from the existence of eight PI3K isoforms, which are divided into class I, class II and class III PI3Ks. PI3K signalling has been implicated in metabolic control, immunity, angiogenesis and cardiovascular homeostasis, and is one of the most frequently deregulated pathways in cancer. PI3K inhibitors have recently entered clinical trials in oncology. A better understanding of how the different PI3K isoforms are regulated and control signalling could uncover their roles in pathology and reveal in which disease contexts their blockade could be most beneficial.
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104
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Burchfield JG, Lopez JA, Mele K, Vallotton P, Hughes WE. Exocytotic vesicle behaviour assessed by total internal reflection fluorescence microscopy. Traffic 2010; 11:429-39. [PMID: 20070611 DOI: 10.1111/j.1600-0854.2010.01039.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The regulated trafficking or exocytosis of cargo-containing vesicles to the cell surface is fundamental to all cells. By coupling the technology of fluorescently tagged fusion proteins with total internal reflection fluorescence microscopy (TIRFM), it is possible to achieve the high spatio-temporal resolution required to study the dynamics of sub-plasma membrane vesicle trafficking and exocytosis. TIRFM has been used in a number of cell types to visualize and dissect the various steps of exocytosis revealing how molecules identified via genetic and/or biochemical approaches are involved in the regulation of this process. Here, we summarize the contribution of TIRFM to our understanding of the mechanism of exocytosis and discuss the novel methods of analysis that are required to exploit the large volumes of data that can be produced using this technique.
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Affiliation(s)
- James G Burchfield
- The Garvan Institute of Medical Research, 384 Victoria Street, Sydney, New South Wales 2010, Australia
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105
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Leibiger B, Moede T, Uhles S, Barker CJ, Creveaux M, Domin J, Berggren PO, Leibiger IB. Insulin-feedback via PI3K-C2alpha activated PKBalpha/Akt1 is required for glucose-stimulated insulin secretion. FASEB J 2010; 24:1824-37. [PMID: 20061534 DOI: 10.1096/fj.09-148072] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Phosphatidylinositide 3-kinases (PI3Ks) play central roles in insulin signal transduction. While the contribution of class Ia PI3K members has been extensively studied, the role of class II members remains poorly understood. The diverse actions of class II PI3K-C2alpha have been attributed to its lipid product PI(3)P. By applying pharmacological inhibitors, transient overexpression and small-interfering RNA-based knockdown of PI3K and PKB/Akt isoforms, together with PI-lipid profiling and live-cell confocal and total internal reflection fluorescence microscopy, we now demonstrate that in response to insulin, PI3K-C2alpha generates PI(3,4)P(2), which allows the selective activation of PKBalpha/Akt1. Knockdown of PI3K-C2alpha expression and subsequent reduction of PKBalpha/Akt1 activity in the pancreatic beta-cell impaired glucose-stimulated insulin release, at least in part, due to reduced glucokinase expression and increased AS160 activity. Hence, our results identify signal transduction via PI3K-C2alpha as a novel pathway whereby insulin activates PKB/Akt and thus discloses PI3K-C2alpha as a potential drugable target in type 2 diabetes. The high degree of codistribution of PI3K-C2alpha and PKBalpha/Akt1 with insulin receptor B type, but not A type, in the same plasma membrane microdomains lends further support to the concept that selectivity in insulin signaling is achieved by the spatial segregation of signaling events.
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Affiliation(s)
- Barbara Leibiger
- Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Stockholm, Sweden
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106
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Marwick JA, Chung KF, Adcock IM. Phosphatidylinositol 3-kinase isoforms as targets in respiratory disease. Ther Adv Respir Dis 2010; 4:19-34. [PMID: 20051446 DOI: 10.1177/1753465809352792] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Respiratory diseases such as chronic obstructive pulmonary disease [COPD], severe asthma, cystic fibrosis [CF] and idiopathic pulmonary fibrosis [IPF] are inadequately controlled by current therapies. The underlying molecular mechanisms and pathogenesis of these diseases remain unclear, making identification and validation of potential new therapeutic targets difficult. However, recent studies have identified the central signalling mediator PI3K as playing an integral role in the immune system including initiation and maintenance of inflammatory responses. Specifically, the relatively leukocyte-specific PI3Kgamma and PI3Kdelta isoforms are central to leukocyte function and can be targeted pharmacologically. Early to man studies using selective PI3K isoform inhibitors are required to determine whether they have a future in treating respiratory disease, particularly in controlling both innate and adaptive inflammatory responses as well as restoring glucocorticoid function and reducing tumorigenesis.
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Affiliation(s)
- John A Marwick
- Section of Airways Disease, National Heart and Lung Institute, Imperial College London, London, UK.
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107
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108
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Falasca M, Maffucci T. Rethinking phosphatidylinositol 3-monophosphate. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1793:1795-803. [PMID: 19852987 DOI: 10.1016/j.bbamcr.2009.10.003] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 06/13/2009] [Revised: 10/06/2009] [Accepted: 10/13/2009] [Indexed: 11/27/2022]
Abstract
A generally accepted view considers phosphatidylinositol 3-monophosphate (PtdIns3P) as a lipid confined to the endosomal compartment where it regulates trafficking pathways and is produced constitutively and exclusively by class III phosphoinositide 3-kinase (PI3K). Recent evidence suggests that this phosphoinositide has a more complex role as a second messenger involved in different physiological and pathological events and that specific intracellular localization of kinases and/or phosphatases is critical for PtdIns3P synthesis and PtdIns3P-dependent intracellular functions. Here, we review the current knowledge of the regulation and function of PtdIns3P and discuss how the view of PtdIns3P changed in the last few years.
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Affiliation(s)
- Marco Falasca
- Queen Mary University of London, Barts and The London School of Medicine and Dentistry, Blizard Institute of Cell and Molecular Science, Centre for Diabetes, Inositide Signalling Group, 4 Newark Street, London E1 2AT, UK.
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109
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Abstract
PI3Ks (phosphoinositide 3-kinases) have important roles in a variety of cellular activities, including survival, proliferation, growth, shape, migration and intracellular sorting. Consistent with their function in cell survival and growth, the gene for the class Iα PI3K catalytic subunit is a common site of gain-of-function mutations in cancers. Ongoing structural studies of these enzymes and the complexes they make with their regulatory subunits have helped to clarify the mechanistic basis of this role in tumour development. The broad spectrum of biological activities associated with various isotypes of class I PI3Ks has led to an intense search for isotype-specific inhibitors as tools in mammalian cell biology and for therapeutic application. Structural studies of the class I PI3Ks suggest that flexibility may be a component of the catalytic cycle of the enzymes.
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110
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Lopez JA, Burchfield JG, Blair DH, Mele K, Ng Y, Vallotton P, James DE, Hughes WE. Identification of a distal GLUT4 trafficking event controlled by actin polymerization. Mol Biol Cell 2009; 20:3918-29. [PMID: 19605560 DOI: 10.1091/mbc.e09-03-0187] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The insulin-stimulated trafficking of GLUT4 to the plasma membrane in muscle and fat tissue constitutes a central process in blood glucose homeostasis. The tethering, docking, and fusion of GLUT4 vesicles with the plasma membrane (PM) represent the most distal steps in this pathway and have been recently shown to be key targets of insulin action. However, it remains unclear how insulin influences these processes to promote the insertion of the glucose transporter into the PM. In this study we have identified a previously uncharacterized role for cortical actin in the distal trafficking of GLUT4. Using high-frequency total internal reflection fluorescence microscopy (TIRFM) imaging, we show that insulin increases actin polymerization near the PM and that disruption of this process inhibited GLUT4 exocytosis. Using TIRFM in combination with probes that could distinguish between vesicle transport and fusion, we found that defective actin remodeling was accompanied by normal insulin-regulated accumulation of GLUT4 vesicles close to the PM, but the final exocytotic fusion step was impaired. These data clearly resolve multiple steps of the final stages of GLUT4 trafficking, demonstrating a crucial role for actin in the final stage of this process.
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Affiliation(s)
- Jamie A Lopez
- Diabetes and Obesity Research Program, The Garvan Institute of Medical Research, Sydney, NSW 2010, Australia
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111
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Ng SKL, Neo SY, Yap YW, Karuturi RKM, Loh ESL, Liau KH, Ren EC. Ablation of phosphoinositide-3-kinase class II alpha suppresses hepatoma cell proliferation. Biochem Biophys Res Commun 2009; 387:310-5. [PMID: 19591801 DOI: 10.1016/j.bbrc.2009.07.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2009] [Accepted: 07/02/2009] [Indexed: 02/07/2023]
Abstract
Cancer such as hepatocellular carcinoma (HCC) is characterized by complex perturbations in multiple signaling pathways, including the phosphoinositide-3-kinase (PI3K/AKT) pathways. Herein we investigated the role of PI3K catalytic isoforms, particularly class II isoforms in HCC proliferation. Among the siRNAs tested against the eight known catalytic PI3K isoforms, specific ablation of class II PI3K alpha (PIK3C2alpha) was the most effective in impairing cell growth and this was accompanied by concomitant decrease in PIK3C2alpha mRNA and protein levels. Colony formation ability of cells deficient for PIK3C2alpha was markedly reduced and growth arrest was associated with increased caspase 3 levels. A small but significant difference in gene dosage and expression levels was detected between tumor and non-tumor tissues in a cohort of 19 HCC patients. Taken together, these data suggest for the first time that in addition to class I PI3Ks in cancer, class II PIK3C2alpha can modulate HCC cell growth.
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112
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Srivastava S, Di L, Zhdanova O, Li Z, Vardhana S, Wan Q, Yan Y, Varma R, Backer J, Wulff H, Dustin ML, Skolnik EY. The class II phosphatidylinositol 3 kinase C2beta is required for the activation of the K+ channel KCa3.1 and CD4 T-cells. Mol Biol Cell 2009; 20:3783-91. [PMID: 19587117 DOI: 10.1091/mbc.e09-05-0390] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Ca(2+)-activated K(+) channel KCa3.1 is required for Ca(2+) influx and the subsequent activation of T-cells. We previously showed that nucleoside diphosphate kinase beta (NDPK-B), a mammalian histidine kinase, directly phosphorylates and activates KCa3.1 and is required for the activation of human CD4 T lymphocytes. We now show that the class II phosphatidylinositol 3 kinase C2beta (PI3K-C2beta) is activated by the T-cell receptor (TCR) and functions upstream of NDPK-B to activate KCa3.1 channel activity. Decreased expression of PI3K-C2beta by siRNA in human CD4 T-cells resulted in inhibition of KCa3.1 channel activity. The inhibition was due to decreased phosphatidylinositol 3-phosphate [PI(3)P] because dialyzing PI3K-C2beta siRNA-treated T-cells with PI(3)P rescued KCa3.1 channel activity. Moreover, overexpression of PI3K-C2beta in KCa3.1-transfected Jurkat T-cells led to increased TCR-stimulated activation of KCa3.1 and Ca(2+) influx, whereas silencing of PI3K-C2beta inhibited both responses. Using total internal reflection fluorescence microscopy and planar lipid bilayers, we found that PI3K-C2beta colocalized with Zap70 and the TCR in peripheral microclusters in the immunological synapse. This is the first demonstration that a class II PI3K plays a critical role in T-cell activation.
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Affiliation(s)
- Shekhar Srivastava
- Division of Nephrology, Department of Pharmacology, The Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute for Biomolecular Medicine, New York University Langone Medical Center, New York, NY 10016
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113
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Sasaki T, Takasuga S, Sasaki J, Kofuji S, Eguchi S, Yamazaki M, Suzuki A. Mammalian phosphoinositide kinases and phosphatases. Prog Lipid Res 2009; 48:307-43. [PMID: 19580826 DOI: 10.1016/j.plipres.2009.06.001] [Citation(s) in RCA: 190] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Phosphoinositides are lipids that are present in the cytoplasmic leaflet of a cell's plasma and internal membranes and play pivotal roles in the regulation of a wide variety of cellular processes. Phosphoinositides are molecularly diverse due to variable phosphorylation of the hydroxyl groups of their inositol rings. The rapid and reversible configuration of the seven known phosphoinositide species is controlled by a battery of phosphoinositide kinases and phosphoinositide phosphatases, which are thus critical for phosphoinositide isomer-specific localization and functions. Significantly, a given phosphoinositide generated by different isozymes of these phosphoinositide kinases and phosphatases can have different biological effects. In mammals, close to 50 genes encode the phosphoinositide kinases and phosphoinositide phosphatases that regulate phosphoinositide metabolism and thus allow cells to respond rapidly and effectively to ever-changing environmental cues. Understanding the distinct and overlapping functions of these phosphoinositide-metabolizing enzymes is important for our knowledge of both normal human physiology and the growing list of human diseases whose etiologies involve these proteins. This review summarizes the structural and biological properties of all the known mammalian phosphoinositide kinases and phosphoinositide phosphatases, as well as their associations with human disorders.
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Affiliation(s)
- Takehiko Sasaki
- Department of Pathology and Immunology, Akita University, Graduate School of Medicine, Akita 010-8543, Japan.
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114
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Braccini L, Ciraolo E, Morello F, Lu X, Hirsch E. PI3K signaling: a crossroads of metabolic regulation. Expert Rev Endocrinol Metab 2009; 4:349-357. [PMID: 30781275 DOI: 10.1586/eem.09.19] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Insulin exerts a fundamental role in glucose metabolism. Several lines of evidence have established PI3Ks as crucial signaling crossroads of metabolic regulation. These kinases play a key role in glucose homeostasis through the generation of lipid secondary messengers upon membrane receptor activation, thus regulating liver gluconeogenesis and glycogen synthesis. While class IA Pl3Kα historically appeared as the major PI3K isoform involved in insulin-mediated glucose metabolism, emerging evidence has demonstrated the contribution of other PI3K isoforms. In this review, we focus on the prototypical insulin receptor-PI3K pathway and on the effects of its impairment on metabolism, insulin sensitivity and the molecular pathophysiology of diabetes mellitus.
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Affiliation(s)
- Laura Braccini
- a Molecular Biotechnology Center, Via Nizza 52, 10126 Turin, Italy.
| | - Elisa Ciraolo
- b Molecular Biotechnology Center, Via Nizza 52, 10126 Turin, Italy.
| | - Fulvio Morello
- c Molecular Biotechnology Center, Via Nizza 52, 10126 Turin, Italy.
| | - Xiaoyun Lu
- d Molecular Biotechnology Center, Via Nizza 52, 10126 Turin, Italy.
| | - Emilio Hirsch
- e Professor, Molecular Biotechnology Center, Via Nizza 52, 10126 Turin, Italy.
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115
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Alterations of insulin signaling in type 2 diabetes: A review of the current evidence from humans. Biochim Biophys Acta Mol Basis Dis 2009; 1792:83-92. [DOI: 10.1016/j.bbadis.2008.10.019] [Citation(s) in RCA: 153] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2008] [Revised: 10/21/2008] [Accepted: 10/21/2008] [Indexed: 01/03/2023]
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116
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Dail MB, Shack LA, Chambers JE, Burgess SC. Global liver proteomics of rats exposed for 5 days to phenobarbital identifies changes associated with cancer and with CYP metabolism. Toxicol Sci 2008; 106:556-69. [PMID: 18796496 PMCID: PMC2581678 DOI: 10.1093/toxsci/kfn198] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Accepted: 09/10/2008] [Indexed: 12/14/2022] Open
Abstract
A global proteomics approach was applied to model the hepatic response elicited by the toxicologically well-characterized xenobiotic phenobarbital (PB), a prototypical inducer of hepatic xenobiotic metabolizing enzymes and a well-known nongenotoxic liver carcinogen in rats. Differential detergent fractionation two-dimensional liquid chromatography electrospray ionization tandem mass spectrometry and systems biology modeling were used to identify alterations in toxicologically relevant hepatic molecular functions and biological processes in the livers of rats following a 5-day exposure to PB at 80 mg/kg/day or a vehicle control. Of the 3342 proteins identified, expression of 121 (3.6% of the total proteins) was significantly increased and 127 (3.8%) significantly decreased in the PB group compared to controls. The greatest increase was seen for cytochrome P450 (CYP) 2B2 (167-fold). All proteins with statistically significant differences from control were then analyzed using both Gene Ontology (GO) and Ingenuity Pathways Analysis (IPA, 5.0 IPA-Tox) for cellular location, function, network connectivity, and possible disease processes, especially as they relate to CYP-mediated metabolism and nongenotoxic carcinogenesis mechanisms. The GO results suggested that PB's mechanism of nongenotoxic carcinogenesis involves both increased xenobiotic metabolism, especially induction of the 2B subfamily of CYP enzymes, and increased cell cycle activity. Apoptosis, however, also increased, perhaps, as an attempt to counter the rising cancer threat. Of the IPA-mapped proteins, 41 have functions which are procarcinogenic and 14 anticarcinogenic according to the hypothesized nongenotoxic mechanism of imbalance between apoptosis and cellular proliferation. Twenty-two additional IPA nodes can be classified as procarcinogenic by the competing theory of increased metabolism resulting in the formation of reactive oxygen species. Since the systems biology modeling corresponded well to PB effects previously elucidated via more traditional methods, the global proteomic approach is proposed as a new screening methodology that can be incorporated into future toxicological studies.
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Affiliation(s)
- Mary B. Dail
- Center for Environmental Health Sciences, College of Veterinary Medicine
- Department of Basic Sciences, College of Veterinary Medicine
| | - L. Allen Shack
- Department of Basic Sciences, College of Veterinary Medicine
| | - Janice E. Chambers
- Center for Environmental Health Sciences, College of Veterinary Medicine
- Department of Basic Sciences, College of Veterinary Medicine
| | - Shane C. Burgess
- Department of Basic Sciences, College of Veterinary Medicine
- Mississippi Agriculture and Forestry Experiment Station
- Institute for Digital Biology
- Life Sciences and Biotechnology Institute, Mississippi State University, Mississippi State, Mississippi 39762
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117
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Wen PJ, Osborne SL, Morrow IC, Parton RG, Domin J, Meunier FA. Ca2+-regulated pool of phosphatidylinositol-3-phosphate produced by phosphatidylinositol 3-kinase C2alpha on neurosecretory vesicles. Mol Biol Cell 2008; 19:5593-603. [PMID: 18843041 DOI: 10.1091/mbc.e08-06-0595] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Phosphatidylinositol-3-phosphate [PtdIns(3)P] is a key player in early endosomal trafficking and is mainly produced by class III phosphatidylinositol 3-kinase (PI3K). In neurosecretory cells, class II PI3K-C2alpha and its lipid product PtdIns(3)P have recently been shown to play a critical role during neuroexocytosis, suggesting that two distinct pools of PtdIns(3)P might coexist in these cells. However, the precise characterization of this additional pool of PtdIns(3)P remains to be established. Using a selective PtdIns(3)P probe, we have identified a novel PtdIns(3)P-positive pool localized on secretory vesicles, sensitive to PI3K-C2alpha knockdown and relatively resistant to wortmannin treatment. In neurosecretory cells, stimulation of exocytosis promoted a transient albeit large increase in PtdIns(3)P production localized on secretory vesicles sensitive to PI3K-C2alpha knockdown and expression of PI3K-C2alpha catalytically inactive mutant. Using purified chromaffin granules, we found that PtdIns(3)P production is controlled by Ca(2+). We confirmed that PtdIns(3)P production from recombinantly expressed PI3K-C2alpha is indeed regulated by Ca(2+). We provide evidence that a dynamic pool of PtdIns(3)P synthesized by PI3K-C2alpha occurs on secretory vesicles in neurosecretory cells, demonstrating that the activity of a member of the PI3K family is regulated by Ca(2+) in vitro and in living neurosecretory cells.
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Affiliation(s)
- Peter J Wen
- Molecular Dynamics of Synaptic Function Laboratory, Queensland Brain Institute and School of Biomedical Sciences, The University of Queensland, St. Lucia, 4072 Queensland, Australia
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118
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Mallo GV, Espina M, Smith AC, Terebiznik MR, Alemán A, Finlay BB, Rameh LE, Grinstein S, Brumell JH. SopB promotes phosphatidylinositol 3-phosphate formation on Salmonella vacuoles by recruiting Rab5 and Vps34. ACTA ACUST UNITED AC 2008; 182:741-52. [PMID: 18725540 PMCID: PMC2518712 DOI: 10.1083/jcb.200804131] [Citation(s) in RCA: 215] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Salmonella colonizes a vacuolar niche in host cells during infection. Maturation of the Salmonella-containing vacuole (SCV) involves the formation of phosphatidylinositol 3-phosphate (PI(3)P) on its outer leaflet. SopB, a bacterial virulence factor with phosphoinositide phosphatase activity, was proposed to generate PI(3)P by dephosphorylating PI(3,4)P2, PI(3,5)P2, and PI(3,4,5)P3. Here, we examine the mechanism of PI(3)P formation during Salmonella infection. SopB is required to form PI(3,4)P2/PI(3,4,5)P3 at invasion ruffles and PI(3)P on nascent SCVs. However, we uncouple these events experimentally and reveal that SopB does not dephosphorylate PI(3,4)P2/PI(3,4,5)P3 to produce PI(3)P. Instead, the phosphatase activity of SopB is required for Rab5 recruitment to the SCV. Vps34, a PI3-kinase that associates with active Rab5, is responsible for PI(3)P formation on SCVs. Therefore, SopB mediates PI(3)P production on the SCV indirectly through recruitment of Rab5 and its effector Vps34. These findings reveal a link between phosphoinositide phosphatase activity and the recruitment of Rab5 to phagosomes.
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Affiliation(s)
- Gustavo V Mallo
- Cell Biology Program, Hospital for Sick Children, Toronto, Ontario, Canada
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119
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Function and dysfunction of the PI system in membrane trafficking. EMBO J 2008; 27:2457-70. [PMID: 18784754 PMCID: PMC2536629 DOI: 10.1038/emboj.2008.169] [Citation(s) in RCA: 167] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2008] [Accepted: 08/05/2008] [Indexed: 02/01/2023] Open
Abstract
The phosphoinositides (PIs) function as efficient and finely tuned switches that control the assembly–disassembly cycles of complex molecular machineries with key roles in membrane trafficking. This important role of the PIs is mainly due to their versatile nature, which is in turn determined by their fast metabolic interconversions. PIs can be tightly regulated both spatially and temporally through the many PI kinases (PIKs) and phosphatases that are distributed throughout the different intracellular compartments. In spite of the enormous progress made in the past 20 years towards the definition of the molecular details of PI–protein interactions and of the regulatory mechanisms of the individual PIKs and phosphatases, important issues concerning the general principles of the organisation of the PI system and the coordination of the different PI-metabolising enzymes remain to be addressed. The answers should come from applying a systems biology approach to the study of the PI system, through the integration of analyses of the protein interaction data of the PI enzymes and the PI targets with those of the ‘phenomes' of the genetic diseases that involve these PI-metabolising enzymes.
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120
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Abstract
Accumulated evidence over the last several years indicates that insulin regulates multiple steps in the overall translocation of GLUT4 vesicles to the fat/muscle cell surface, including formation of an intracellular storage pool of GLUT4 vesicles, its movement to the proximity of the cell surface, and the subsequent docking/fusion with the plasma membrane. Insulin-stimulated formation of phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P(3); and in some cases, of its catabolite PtdIns(3,4)P(2)] plays a pivotal role in this process. PtdIns(3,4,5)P(3) is synthesized by the activated wortmannin-sensitive class IA phosphoinositide (PI) 3-kinase and controls the rate-limiting cell surface terminal stages of the GLUT4 journey. However, recent research is consistent with the conclusion that signals by each of the remaining five PIs, i.e., PtdIns(3)P, PtdIns(4)P, PtdIns(5)P, PtdIns(3,5)P(2), and PtdIns(4,5)P(2), may act in concert with that of PtdIns(3,4,5)P(3) in integrating the insulin receptor-issued signals with GLUT4 surface translocation and glucose transport activation. This review summarizes the experimental evidence supporting the complementary function of these PIs in insulin responsiveness of fat and muscle cells, with particular reference to mechanistic insights and functional significance in the regulation of overall GLUT4 vesicle dynamics.
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Affiliation(s)
- Assia Shisheva
- Wayne State University School of Medicine, Detroit, MI 48201, USA.
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Talior-Volodarsky I, Randhawa VK, Zaid H, Klip A. Alpha-actinin-4 is selectively required for insulin-induced GLUT4 translocation. J Biol Chem 2008; 283:25115-25123. [PMID: 18617516 DOI: 10.1074/jbc.m801750200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Insulin induces GLUT4 translocation to the muscle cell surface. Using differential amino acid labeling and mass spectrometry, we observed insulin-dependent co-precipitation of actinin-4 (ACTN4) with GLUT4 (Foster, L. J., Rudich, A., Talior, I., Patel, N., Huang, X., Furtado, L. M., Bilan, P. J., Mann, M., and Klip, A. (2006) J. Proteome Res. 5, 64-75). ACTN4 links F-actin to membrane proteins, and actin dynamics are essential for GLUT4 translocation. We hypothesized that ACTN4 may contribute to insulin-regulated GLUT4 traffic. In L6 muscle cells insulin, but not platelet-derived growth factor, increased co-precipitation of ACTN4 with GLUT4. Small interfering RNA-mediated ACTN4 knockdown abolished the gain in surface-exposed GLUT4 elicited by insulin but not by platelet-derived growth factor, membrane depolarization, or mitochondrial uncoupling. In contrast, knockdown of alpha-actinin-1 (ACTN1) did not prevent GLUT4 translocation by insulin. GLUT4 colocalized with ACTN4 along the insulin-induced cortical actin mesh and ACTN4 knockdown prevented GLUT4-actin colocalization without impeding actin remodeling or Akt phosphorylation, maintaining GLUT4 in a tight perinuclear location. We propose that ACTN4 contributes to GLUT4 traffic, likely by tethering GLUT4 vesicles to the cortical actin cytoskeleton.
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Affiliation(s)
| | - Varinder K Randhawa
- Program in Cell Biology, Hospital for Sick Children, Toronto, Ontario M5G 1X8; Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Hilal Zaid
- Program in Cell Biology, Hospital for Sick Children, Toronto, Ontario M5G 1X8
| | - Amira Klip
- Program in Cell Biology, Hospital for Sick Children, Toronto, Ontario M5G 1X8; Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
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Insulin action on glucose transporters through molecular switches, tracks and tethers. Biochem J 2008; 413:201-15. [DOI: 10.1042/bj20080723] [Citation(s) in RCA: 214] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Glucose entry into muscle cells is precisely regulated by insulin, through recruitment of GLUT4 (glucose transporter-4) to the membrane of muscle and fat cells. Work done over more than two decades has contributed to mapping the insulin signalling and GLUT4 vesicle trafficking events underpinning this response. In spite of this intensive scientific research, there are outstanding questions that continue to challenge us today. The present review summarizes the knowledge in the field, with emphasis on the latest breakthroughs in insulin signalling at the level of AS160 (Akt substrate of 160 kDa), TBC1D1 (tre-2/USP6, BUB2, cdc16 domain family member 1) and their target Rab proteins; in vesicle trafficking at the level of vesicle mobilization, tethering, docking and fusion with the membrane; and in the participation of the cytoskeleton to achieve optimal temporal and spatial location of insulin-derived signals and GLUT4 vesicles.
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Lodhi IJ, Bridges D, Chiang SH, Zhang Y, Cheng A, Geletka LM, Weisman LS, Saltiel AR. Insulin stimulates phosphatidylinositol 3-phosphate production via the activation of Rab5. Mol Biol Cell 2008; 19:2718-28. [PMID: 18434594 DOI: 10.1091/mbc.e08-01-0105] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Phosphatidylinositol 3-phosphate (PI(3)P) plays an important role in insulin-stimulated glucose uptake. Insulin promotes the production of PI(3)P at the plasma membrane by a process dependent on TC10 activation. Here, we report that insulin-stimulated PI(3)P production requires the activation of Rab5, a small GTPase that plays a critical role in phosphoinositide synthesis and turnover. This activation occurs at the plasma membrane and is downstream of TC10. TC10 stimulates Rab5 activity via the recruitment of GAPEX-5, a VPS9 domain-containing guanyl nucleotide exchange factor that forms a complex with TC10. Although overexpression of plasma membrane-localized GAPEX-5 or constitutively active Rab5 promotes PI(3)P formation, knockdown of GAPEX-5 or overexpression of a dominant negative Rab5 mutant blocks the effects of insulin or TC10 on this process. Concomitant with its effect on PI(3)P levels, the knockdown of GAPEX-5 blocks insulin-stimulated Glut4 translocation and glucose uptake. Together, these studies suggest that the TC10/GAPEX-5/Rab5 axis mediates insulin-stimulated production of PI(3)P, which regulates trafficking of Glut4 vesicles.
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Affiliation(s)
- Irfan J Lodhi
- Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA
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Abstract
The Class III PI3K (phosphoinositide 3-kinase), Vps34 (vacuolar protein sorting 34), was first described as a component of the vacuolar sorting system in Saccharomyces cerevisiae and is the sole PI3K in yeast. The homologue in mammalian cells, hVps34, has been studied extensively in the context of endocytic sorting. However, hVps34 also plays an important role in the ability of cells to respond to changes in nutrient conditions. Recent studies have shown that mammalian hVps34 is required for the activation of the mTOR (mammalian target of rapamycin)/S6K1 (S6 kinase 1) pathway, which regulates protein synthesis in response to nutrient availability. In both yeast and mammalian cells, Class III PI3Ks are also required for the induction of autophagy during nutrient deprivation. Finally, mammalian hVps34 is itself regulated by nutrients. Thus Class III PI3Ks are implicated in the regulation of both autophagy and, through the mTOR pathway, protein synthesis, and thus contribute to the integration of cellular responses to changing nutritional status.
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Parkinson GN, Vines D, Driscoll PC, Djordjevic S. Crystal structures of PI3K-C2alpha PX domain indicate conformational change associated with ligand binding. BMC STRUCTURAL BIOLOGY 2008; 8:13. [PMID: 18312637 PMCID: PMC2292188 DOI: 10.1186/1472-6807-8-13] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Accepted: 02/29/2008] [Indexed: 11/15/2022]
Abstract
Background PX domains have specialized protein structures involved in binding of phosphoinositides (PIs). Through binding to the various PIs PX domains provide site-specific membrane signals to modulate the intracellular localisation and biological activity of effector proteins. Several crystal structures of these domains are now available from a variety of proteins. All PX domains contain a canonical core structure with main differences exhibited within the loop regions forming the phosphoinositide binding pockets. It is within these areas that the molecular basis for ligand specificity originates. Results We now report two new structures of PI3K-C2α PX domain that crystallised in a P3121 space group. The two structures, refined to 2.1 Å and 2.5 Å, exhibit significantly different conformations of the phosphoinositide-binding loops. Unexpectedly, in one of the structures, we have detected a putative-ligand trapped in the binding site during the process of protein purification and crystallisation. Conclusion The two structures reported here provide a more complete description of the phosphoinositide binding region compared to the previously reported 2.6 Å crystal structure of human PI3K-C2α PX where this region was highly disordered. The structures enabled us to further analyse PI specificity and to postulate that the observed conformational change could be related to ligand-binding.
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Affiliation(s)
- Gary N Parkinson
- Cancer Research UK Biomolecular Structure Group, The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1AX, UK.
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