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Pena E, San Martin-Salamanca R, El Alam S, Flores K, Arriaza K. Tau Protein Alterations Induced by Hypobaric Hypoxia Exposure. Int J Mol Sci 2024; 25:889. [PMID: 38255962 PMCID: PMC10815386 DOI: 10.3390/ijms25020889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 12/21/2023] [Accepted: 01/05/2024] [Indexed: 01/24/2024] Open
Abstract
Tauopathies are a group of neurodegenerative diseases whose central feature is dysfunction of the microtubule-associated protein tau (MAPT). Although the exact etiology of tauopathies is still unknown, it has been hypothesized that their onset may occur up to twenty years before the clear emergence of symptoms, which has led to questions about whether the prognosis of these diseases can be improved by, for instance, targeting the factors that influence tauopathy development. One such factor is hypoxia, which is strongly linked to Alzheimer's disease because of its association with obstructive sleep apnea and has been reported to affect molecular pathways related to the dysfunction and aggregation of tau proteins and other biomarkers of neurological damage. In particular, hypobaric hypoxia exposure increases the activation of several kinases related to the hyperphosphorylation of tau in neuronal cells, such as ERK, GSK3β, and CDK5. In addition, hypoxia also increases the levels of inflammatory molecules (IL-β1, IL-6, and TNF-α), which are also associated with neurodegeneration. This review discusses the many remaining questions regarding the influence of hypoxia on tauopathies and the contribution of high-altitude exposure to the development of these diseases.
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Affiliation(s)
| | | | - Samia El Alam
- High Altitude Medicine Research Center (CEIMA), Arturo Prat University, Iquique 1110939, Chile; (E.P.); (R.S.M.-S.); (K.F.); (K.A.)
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2
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Grandizoli Saletti P, Casillas-Espinosa PM, Panagiotis Lisgaras C, Bi Mowrey W, Li Q, Liu W, Brady RD, Ali I, Silva J, Yamakawa G, Hudson M, Li C, Braine EL, Coles L, Cloyd JC, Jones NC, Shultz SR, Moshé SL, O'Brien TJ, Galanopoulou AS. Tau Phosphorylation Patterns in the Rat Cerebral Cortex After Traumatic Brain Injury and Sodium Selenate Effects: An Epibios4rx Project 2 Study. J Neurotrauma 2024; 41:222-243. [PMID: 36950806 PMCID: PMC11079442 DOI: 10.1089/neu.2022.0219] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/24/2023] Open
Abstract
Sodium selenate (SS) activates protein phosphatase 2 (PP2A) and reduces phosphorylated tau (pTAU) and late post-traumatic seizures after lateral fluid percussion injury (LFPI). In EpiBioS4Rx Project 2, a multi-center international study for post-traumatic targets, biomarkers, and treatments, we tested the target relevance and modification by SS of pTAU forms and PP2A and in the LFPI model, at two sites: Einstein and Melbourne. In Experiment 1, adult male rats were assigned to LFPI and sham (both sites) and naïve controls (Einstein). Motor function was monitored by neuroscores. Brains were studied with immunohistochemistry (IHC), Western blots (WBs), or PP2A activity assay, from 2 days to 8 weeks post-operatively. In Experiment 2, LFPI rats received SS for 7 days (SS0.33: 0.33 mg/kg/day; SS1: 1 mg/kg/day, subcutaneously) or vehicle (Veh) post-LFPI and pTAU, PR55 expression, or PP2A activity were studied at 2 days and 1 week (on treatment), or 2 weeks (1 week off treatment). Plasma selenium and SS levels were measured. In Experiment 1 IHC, LFPI rats had higher cortical pTAU-Ser202/Thr205-immunoreactivity (AT8-ir) and pTAU-Ser199/202-ir at 2 days, and pTAU-Thr231-ir (AT180-ir) at 2 days, 2 weeks, and 8 weeks, ipsilaterally to LFPI, than controls. LFPI-2d rats also had higher AT8/total-TAU5-ir in cortical extracts ipsilateral to the lesion (WB). PP2A (PR55-ir) showed time- and region-dependent changes in IHC, but not in WB. PP2A activity was lower in LFPI-1wk than in sham rats. In Experiment 2, SS did not affect neuroscores or cellular AT8-ir, AT180-ir, or PR55-ir in IHC. In WB, total cortical AT8/total-TAU-ir was lower in SS0.33 and SS1 LFPI rats than in Veh rats (2 days, 1 week); total cortical PR55-ir (WB) and PP2A activity were higher in SS1 than Veh rats (2 days). SS dose dependently increased plasma selenium and SS levels. Concordant across-sites data confirm time and pTAU form-specific cortical increases ipsilateral to LFPI. The discordant SS effects may either suggest SS-induced reduction in the numbers of cells with increased pTAU-ir, need for longer treatment, or the involvement of other mechanisms of action.
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Affiliation(s)
- Patricia Grandizoli Saletti
- Saul R. Korey Department of Neurology, Laboratory of Developmental Epilepsy, Albert Einstein College of Medicine, Bronx New York, USA
| | - Pablo M. Casillas-Espinosa
- Department of Neuroscience, Monash University, Melbourne, Australia
- Department of Medicine, The University of Melbourne, Parkville, Australia
- Department of Neurology, Alfred Health, Melbourne, Australia
| | - Christos Panagiotis Lisgaras
- Saul R. Korey Department of Neurology, Laboratory of Developmental Epilepsy, Albert Einstein College of Medicine, Bronx New York, USA
| | - Wenzhu Bi Mowrey
- Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx New York, USA
| | - Qianyun Li
- Saul R. Korey Department of Neurology, Laboratory of Developmental Epilepsy, Albert Einstein College of Medicine, Bronx New York, USA
| | - Wei Liu
- Saul R. Korey Department of Neurology, Laboratory of Developmental Epilepsy, Albert Einstein College of Medicine, Bronx New York, USA
| | - Rhys D. Brady
- Department of Neuroscience, Monash University, Melbourne, Australia
- Department of Medicine, The University of Melbourne, Parkville, Australia
| | - Idrish Ali
- Department of Neuroscience, Monash University, Melbourne, Australia
- Department of Medicine, The University of Melbourne, Parkville, Australia
| | - Juliana Silva
- Department of Neuroscience, Monash University, Melbourne, Australia
| | - Glenn Yamakawa
- Department of Medicine, The University of Melbourne, Parkville, Australia
| | - Matt Hudson
- Department of Neuroscience, Monash University, Melbourne, Australia
- Department of Medicine, The University of Melbourne, Parkville, Australia
| | - Crystal Li
- Department of Neuroscience, Monash University, Melbourne, Australia
| | - Emma L. Braine
- Department of Neuroscience, Monash University, Melbourne, Australia
- Department of Medicine, The University of Melbourne, Parkville, Australia
| | - Lisa Coles
- University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
| | - James C. Cloyd
- University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
| | - Nigel C. Jones
- Department of Neuroscience, Monash University, Melbourne, Australia
- Department of Medicine, The University of Melbourne, Parkville, Australia
- Department of Neurology, Alfred Health, Melbourne, Australia
| | - Sandy R. Shultz
- Department of Neuroscience, Monash University, Melbourne, Australia
- Department of Medicine, The University of Melbourne, Parkville, Australia
- Department of Neurology, Alfred Health, Melbourne, Australia
| | - Solomon L. Moshé
- Saul R. Korey Department of Neurology, Laboratory of Developmental Epilepsy, Albert Einstein College of Medicine, Bronx New York, USA
- Isabelle Rapin Division of Child Neurology, Albert Einstein College of Medicine, Bronx New York, USA
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx New York, USA
- Department of Pediatrics, Albert Einstein College of Medicine, Bronx New York, USA
| | - Terence J. O'Brien
- Department of Neuroscience, Monash University, Melbourne, Australia
- Department of Medicine, The University of Melbourne, Parkville, Australia
- Department of Neurology, Alfred Health, Melbourne, Australia
| | - Aristea S. Galanopoulou
- Saul R. Korey Department of Neurology, Laboratory of Developmental Epilepsy, Albert Einstein College of Medicine, Bronx New York, USA
- Isabelle Rapin Division of Child Neurology, Albert Einstein College of Medicine, Bronx New York, USA
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx New York, USA
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3
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Burakov A, Vorobjev I, Semenova I, Cowan A, Carson J, Wu Y, Rodionov V. Persistent growth of microtubules at low density. Mol Biol Cell 2021; 32:435-445. [PMID: 33439670 PMCID: PMC8098851 DOI: 10.1091/mbc.e20-08-0546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Microtubules (MTs) often form a polarized array with minus ends anchored at the centrosome and plus ends extended toward the cell margins. Plus ends display behavior known as dynamic instability—transitions between rapid shortening and slow growth. It is known that dynamic instability is regulated locally to ensure entry of MTs into nascent areas of the cytoplasm, but details of this regulation remain largely unknown. Here, we test an alternative hypothesis for the local regulation of MT behavior. We used microsurgery to isolate a portion of peripheral cytoplasm from MTs growing from the centrosome, creating cytoplasmic areas locally depleted of MTs. We found that in sparsely populated areas MT plus ends persistently grew or paused but never shortened. In contrast, plus ends that entered regions of cytoplasm densely populated with MTs frequently transitioned to shortening. Persistent growth of MTs in sparsely populated areas could not be explained by a local increase in concentration of free tubulin subunits or elevation of Rac1 activity proposed to enhance MT growth at the cell leading edge during locomotion. These observations suggest the existence of a MT density–dependent mechanism regulating MT dynamics that determines dynamic instability of MTs in densely populated areas of the cytoplasm and persistent growth in sparsely populated areas.
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Affiliation(s)
- Anton Burakov
- R.D. Berlin Center for Cell Analysis and Modeling and Department of Cell Biology, UConn Health, Farmington, CT 06030.,A.N. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119992, Russia
| | - Ivan Vorobjev
- R.D. Berlin Center for Cell Analysis and Modeling and Department of Cell Biology, UConn Health, Farmington, CT 06030.,A.N. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119992, Russia.,Department of Biology, School of Sciences and Humanities and National Laboratory Astana, Nazarbayev University, 010000 Nur-Sultan, Kazakhstan
| | - Irina Semenova
- R.D. Berlin Center for Cell Analysis and Modeling and Department of Cell Biology, UConn Health, Farmington, CT 06030
| | - Ann Cowan
- R.D. Berlin Center for Cell Analysis and Modeling and Department of Cell Biology, UConn Health, Farmington, CT 06030
| | - John Carson
- R.D. Berlin Center for Cell Analysis and Modeling and Department of Cell Biology, UConn Health, Farmington, CT 06030
| | - Yi Wu
- R.D. Berlin Center for Cell Analysis and Modeling and Department of Cell Biology, UConn Health, Farmington, CT 06030
| | - Vladimir Rodionov
- R.D. Berlin Center for Cell Analysis and Modeling and Department of Cell Biology, UConn Health, Farmington, CT 06030
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Schreidah CM, Ratnayake K, Senarath K, Karunarathne A. Microcystins: Biogenesis, Toxicity, Analysis, and Control. Chem Res Toxicol 2020; 33:2225-2246. [PMID: 32614166 DOI: 10.1021/acs.chemrestox.0c00164] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Microcystins are cyclic peptide toxins formed by cyanobacteria. These toxins are recognized for their association with algal blooms, posing a significant threat to ecosystems and drinking water quality. Due to the growing environmental concerns they raise, a comprehensive review on microcystins' genesis, toxicity, and analytical methods for their quantitative determination is outlined. Genes, including the mcyABC cluster, regulate microcystin biogenesis. Bioanalytical experiments have identified key environmental factors, such as temperature and nitrogen availability, that promote microcystin production. Microcystin toxicity is explored based on its modulatory effects on protein phosphatases 1 and 2A in specific tissues and organs. Additionally, biochemical mechanisms of chelation, transportation, resultant oxidative stress, and tumor promotion abilities of microcystins are also discussed. Various analytical methods to separate, detect, and quantify microcystins, including the quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, nuclear magnetic resonance spectroscopy, and chromatographic platforms-linked tandem mass spectrometry (LC-MS) for unequivocal structural identification, are also reviewed. Since control of microcystins in water is of great necessity, both water treatment and mechanisms of abiotic transformation and microbial degradation are also discussed.
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Affiliation(s)
- Celine M Schreidah
- Vagelos College of Physicians and Surgeons, Columbia University, New York, New York 10032, United States
- Department of Chemistry and Biochemistry, University of Toledo, Toledo, Ohio 43606, United States
| | - Kasun Ratnayake
- Department of Chemistry and Biochemistry, University of Toledo, Toledo, Ohio 43606, United States
| | - Kanishka Senarath
- Department of Chemistry and Biochemistry, University of Toledo, Toledo, Ohio 43606, United States
- Department of Chemistry, University of Colombo, Colombo 00300, Sri Lanka
| | - Ajith Karunarathne
- Department of Chemistry and Biochemistry, University of Toledo, Toledo, Ohio 43606, United States
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5
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Liu B, Lin L, Riazuddin S, Zubair A, Wang L, Di LJ, Li R, Dong TT, Deng CX, Tong WM. RETRACTED: PP2ACα deficiency impairs early cortical development through inducing DNA damage in neuroprojenitor cells. Int J Biochem Cell Biol 2019; 109:40-58. [PMID: 30710753 DOI: 10.1016/j.biocel.2019.01.021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Revised: 01/25/2019] [Accepted: 01/29/2019] [Indexed: 01/09/2023]
Abstract
This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor in Chief due to objections raised by persons identified as co-authors of corresponding author Bo Liu. The University of Macau states that Bo Liu is not affiliated with the University of Macau. The purported co-authors who are only affiliated with University of Macau report their names have been misappropriated for use on this paper without notice or prior permission. These co-authors deny any involvement in the study, preparation or submission of the manuscript, or review of any supporting data. The purported co-authors who are affiliated with the University of Maryland, Baltimore report their names and credentials have been misappropriated for use on this paper without notice or permission. These co-authors deny any involvement in the study, preparation or submission of the manuscript, or review of any supporting data. The National Institute of Health also states that none of the co-authors are affiliated with the institution. The University of Maryland, Baltimore states that Bo Liu is not affiliated with the university. Bo Liu has been non-responsive to approaches from the Publisher. Rui Li and Ting-Ting Dong were not reachable by the Publisher. Lin Lin confirmed the affiliation with The University of California Riverside; Chu-Xia Deng confirmed the affiliation with the University of Macau; Wei-Min Tong confirmed the affiliation with the Chinese Academy of Medical Sciences.
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Affiliation(s)
- Bo Liu
- Department of Otorhinolaryngology Head&Neck Surgery, University of Maryland School of Medicine, Baltimore, USA; University of Macau, Macau, China.
| | - Lin Lin
- University of Macau, Macau, China; Department of Pathology, Institute of Basic Medical Sciences, Chinese Academy of Sciences. Beijing, China
| | - Saima Riazuddin
- Department of Otorhinolaryngology Head&Neck Surgery, University of Maryland School of Medicine, Baltimore, USA
| | - Ahmed Zubair
- Department of Otorhinolaryngology Head&Neck Surgery, University of Maryland School of Medicine, Baltimore, USA
| | - Li Wang
- Branch of Cancer Research, Jones Hopkins University, Baltimore, USA
| | - Li-Jun Di
- Branch of Cancer Research, Jones Hopkins University, Baltimore, USA
| | - Rui Li
- Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; Department of Pathology, Institute of Basic Medical Sciences, Chinese Academy of Sciences. Beijing, China.
| | - Ting-Ting Dong
- Department of Pathology, Institute of Basic Medical Sciences, Chinese Academy of Sciences. Beijing, China; China Agricultural University, Beijing, China
| | - Chu-Xia Deng
- National Institute of Neurological Disorders and Stroke, National Institute of Heath, Bethesda, USA.
| | - Wei-Min Tong
- National Institute of Neurological Disorders and Stroke, National Institute of Heath, Bethesda, USA.
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6
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Schuhmacher D, Sontag JM, Sontag E. Protein Phosphatase 2A: More Than a Passenger in the Regulation of Epithelial Cell-Cell Junctions. Front Cell Dev Biol 2019; 7:30. [PMID: 30895176 PMCID: PMC6414416 DOI: 10.3389/fcell.2019.00030] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 02/22/2019] [Indexed: 12/17/2022] Open
Abstract
Cell–cell adhesion plays a key role in the maintenance of the epithelial barrier and apicobasal cell polarity, which is crucial for homeostasis. Disruption of cell–cell adhesion is a hallmark of numerous pathological conditions, including invasive carcinomas. Adhesion between apposing cells is primarily regulated by three types of junctional structures: desmosomes, adherens junctions, and tight junctions. Cell junctional structures are highly regulated multiprotein complexes that also serve as signaling platforms to control epithelial cell function. The biogenesis, integrity, and stability of cell junctions is controlled by complex regulatory interactions with cytoskeletal and polarity proteins, as well as modulation of key component proteins by phosphorylation/dephosphorylation processes. Not surprisingly, many essential signaling molecules, including protein Ser/Thr phosphatase 2A (PP2A) are associated with intercellular junctions. Here, we examine how major PP2A enzymes regulate epithelial cell–cell junctions, either directly by associating with and dephosphorylating component proteins, or indirectly by affecting signaling pathways that control junctional integrity and cytoskeletal dynamics. PP2A deregulation has severe consequences on the stability and functionality of these structures, and disruption of cell–cell adhesion and cell polarity likely contribute to the link between PP2A dysfunction and human carcinomas.
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Affiliation(s)
- Diana Schuhmacher
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, University of Newcastle, Callaghan, NSW, Australia
| | - Jean-Marie Sontag
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, University of Newcastle, Callaghan, NSW, Australia.,Hunter Medical Research Institute, New Lambton Heights, NSW, Australia
| | - Estelle Sontag
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, University of Newcastle, Callaghan, NSW, Australia.,Hunter Medical Research Institute, New Lambton Heights, NSW, Australia
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7
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Li D, Musante V, Zhou W, Picciotto MR, Nairn AC. Striatin-1 is a B subunit of protein phosphatase PP2A that regulates dendritic arborization and spine development in striatal neurons. J Biol Chem 2018; 293:11179-11194. [PMID: 29802198 DOI: 10.1074/jbc.ra117.001519] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 05/06/2018] [Indexed: 01/09/2023] Open
Abstract
Striatin-1, a subunit of the serine/threonine phosphatase PP2A, is preferentially expressed in neurons in the striatum. As a member of the striatin family of B subunits, striatin-1 is a core component together with PP2A of a multiprotein complex called STRIPAK, the striatin-interacting phosphatase and kinase complex. Little is known about the function of striatin-1 or the STRIPAK complex in the mammalian striatum. Here, we identify a selective role for striatin-1 in striatal neuron maturation. Using a small hairpin RNA (shRNA) knockdown approach in primary striatal neuronal cultures, we determined that reduced expression of striatin-1 results in increased dendritic complexity and an increased density of dendritic spines, classified as stubby spines. The dendritic phenotype was rescued by co-expression of a striatin-1 mutant construct insensitive to the knockdown shRNA but was not rescued by co-expression of PP2A- or Mob3-binding deficient striatin-1 constructs. Reduction of striatin-1 did not result in deficits in neuronal connectivity in this knockdown model, as we observed no abnormalities in synapse formation or in spontaneous excitatory postsynaptic currents. Thus, this study suggests that striatin-1 is a regulator of neuronal development in striatal neurons.
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Affiliation(s)
- Daniel Li
- From the Department of Psychiatry, Yale University, New Haven, Connecticut 06520
| | - Veronica Musante
- From the Department of Psychiatry, Yale University, New Haven, Connecticut 06520
| | - Wenliang Zhou
- From the Department of Psychiatry, Yale University, New Haven, Connecticut 06520
| | - Marina R Picciotto
- From the Department of Psychiatry, Yale University, New Haven, Connecticut 06520
| | - Angus C Nairn
- From the Department of Psychiatry, Yale University, New Haven, Connecticut 06520
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8
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Protein phosphatase 2ACα gene knock-out results in cortical atrophy through activating hippo cascade in neuronal progenitor cells. Int J Biochem Cell Biol 2018; 95:53-62. [DOI: 10.1016/j.biocel.2017.12.015] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2017] [Revised: 12/02/2017] [Accepted: 12/19/2017] [Indexed: 12/12/2022]
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9
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Cui G, Li Y, Ding K, Hao S, Wang J, Zhang Z. Attribution of Bax and mitochondrial permeability transition pore on cantharidin-induced apoptosis of Sf9 cells. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2017; 142:91-101. [PMID: 29107253 DOI: 10.1016/j.pestbp.2017.01.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Revised: 01/11/2017] [Accepted: 01/14/2017] [Indexed: 06/07/2023]
Abstract
To investigate the insecticidal mechanism of cantharidin, a promising biological pesticide substance from blister beetle, on Sf9 cells, a cultured cell line derived from fall armyworm, Spodoptera frugiperda, we preliminary studied the attribution of Bax channel and mitochondrial permeability transition pore on cantharidin-induced mitochondrial apoptosis signal pathway. Changes in cell morphology, activity of mitochondrial dehydrogenases, release of cytochrome C and mitochondrial transmembrane potential were detected when the two channels were blocked by specific inhibitors, Bax channel blocker and cyclosporin A. Results showed that cantharidin-induced apoptotic features, including changes in the cell morphology, release of cytochrome C and decrease in mitochondrial transmembrane potential could be significantly inhibited by Bax channel blocker, while cyclosporin A accelerated the downward trend of mitochondrial dehydrogenases activity and caused a decrease of Ca2+ in mitochondria. In summary, Bax might be necessary but not exclusively for the apoptosis induced by cantharidin and the attribution of these channels seems to be more complexity.
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Affiliation(s)
- Gaofeng Cui
- College of Plant Science and Technology, Beijing University of Agriculture, Beijing 102206, China
| | - Yuansheng Li
- College of Plant Science and Technology, Beijing University of Agriculture, Beijing 102206, China
| | - Kai Ding
- College of Plant Science and Technology, Beijing University of Agriculture, Beijing 102206, China
| | - Shaodong Hao
- College of Plant Science and Technology, Beijing University of Agriculture, Beijing 102206, China
| | - Jinzhong Wang
- College of Plant Science and Technology, Beijing University of Agriculture, Beijing 102206, China
| | - Zhiyong Zhang
- College of Plant Science and Technology, Beijing University of Agriculture, Beijing 102206, China.
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10
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Hyodo T, Ito S, Asano-Inami E, Chen D, Senga T. A regulatory subunit of protein phosphatase 2A, PPP2R5E, regulates the abundance of microtubule crosslinking factor 1. FEBS J 2017; 283:3662-3671. [PMID: 27521566 DOI: 10.1111/febs.13835] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Revised: 07/24/2016] [Accepted: 08/12/2016] [Indexed: 12/22/2022]
Abstract
Dynamic changes in microtubule organization are regulated by numerous microtubule-associating proteins and their post-translational modification. Microtubule crosslinking factor 1 (MTCL1) is a recently identified protein that regulates microtubule organization. To obtain further insight into its functions, we searched for proteins that associate with it using mass spectrometry analysis. We found that PPP2R5E, a regulatory subunit of protein phosphatase 2A, interacted with MTCL1. Depletion of PPP2R5E reduced the abundance of MTCL1 abundance, whereas exogenous expression of PPP2R5E increased endogenous MTCL1. Furthermore, inhibition of phosphatase activity by okadaic acid reduced MTCL1, which was restored by the addition of the protease inhibitor MG132. Finally, we show that cells depleted of PPP2R5E and MTCL1 exhibited defects in microtubule organization. Our results suggest that the PPP2R5E phosphatase may contribute to microtubule organization by stabilizing MTCL1.
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Affiliation(s)
- Toshinori Hyodo
- Division of Cancer Biology, Nagoya University Graduate School of Medicine, Japan
| | - Satoko Ito
- Division of Cancer Biology, Nagoya University Graduate School of Medicine, Japan
| | - Eri Asano-Inami
- Division of Cancer Biology, Nagoya University Graduate School of Medicine, Japan.,Department of Obstetrics and Gynecology Collaborative Research, Bell Research Center, Nagoya University Graduate School of Medicine, Japan
| | - Dan Chen
- Division of Cancer Biology, Nagoya University Graduate School of Medicine, Japan
| | - Takeshi Senga
- Division of Cancer Biology, Nagoya University Graduate School of Medicine, Japan.
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11
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Hoffman A, Taleski G, Sontag E. The protein serine/threonine phosphatases PP2A, PP1 and calcineurin: A triple threat in the regulation of the neuronal cytoskeleton. Mol Cell Neurosci 2017; 84:119-131. [PMID: 28126489 DOI: 10.1016/j.mcn.2017.01.005] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Revised: 01/16/2017] [Accepted: 01/21/2017] [Indexed: 01/08/2023] Open
Abstract
The microtubule, F-actin and neurofilament networks play a critical role in neuronal cell morphogenesis, polarity and synaptic plasticity. Significantly, the assembly/disassembly and stability of these cytoskeletal networks is crucially modulated by protein phosphorylation and dephosphorylation events. Herein, we aim to more closely examine the role played by three major neuronal Ser/Thr protein phosphatases, PP2A, PP1 and calcineurin, in the homeostasis of the neuronal cytoskeleton. There is strong evidence that these enzymes interact with and dephosphorylate a variety of cytoskeletal proteins, resulting in major regulation of neuronal cytoskeletal dynamics. Conversely, we also discuss how multi-protein cytoskeletal scaffolds can also influence the regulation of these phosphatases, with important implications for neuronal signalling and homeostasis. Not surprisingly, deregulation of these cytoskeletal scaffolds and phosphatase dysfunction are associated with many neurological diseases.
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Affiliation(s)
- Alexander Hoffman
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, and Hunter Medical Research Institute, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Goce Taleski
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, and Hunter Medical Research Institute, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Estelle Sontag
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, and Hunter Medical Research Institute, University of Newcastle, Callaghan, NSW 2308, Australia.
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12
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Abstract
Abundant neurofibrillary lesions in certain brain regions constitute one of the defining neuropathological characteristics of Alzheimer's disease, where their presence correlates with the degree of dementia. An understanding of the mechanisms that lead to the neurofibrillary pathology is critical for elucidating the pathogenesis of Alzheimer's disease and for developing effective therapeutic strategies. Neurofibrillary lesions consist of neurofibrillary tangles, neuropil threads, and abnormal neurites. Ultrastructurally, each of these lesions consists of abnormal paired helical and straight filaments. These filaments are made of the six brain isoforms of microtubule-associated protein tau in a hyperphosphorylated and an abnormally phosphorylated state. Several candidate protein kinases and protein phosphatases for the hyperphos phorylation of tau have been identified. Moreover, recent results suggest that an interaction between tau protein and sulfated glycosaminoglycans may play an important role in inducing both the hyperphosphor ylation of tau and the formation of paired helical and straight filaments. NEUROSCIENTIST 3:131-141, 1997
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Affiliation(s)
- Michel Goedert
- Medical Research Council Laboratory of Molecular Biology Cambridge
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13
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Koss DJ, Robinson L, Mietelska-Porowska A, Gasiorowska A, Sepčić K, Turk T, Jaspars M, Niewiadomska G, Scott RH, Platt B, Riedel G. Polymeric alkylpyridinium salts permit intracellular delivery of human Tau in rat hippocampal neurons: requirement of Tau phosphorylation for functional deficits. Cell Mol Life Sci 2015; 72:4613-32. [PMID: 26070304 PMCID: PMC11113860 DOI: 10.1007/s00018-015-1949-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Revised: 05/13/2015] [Accepted: 06/03/2015] [Indexed: 11/27/2022]
Abstract
Patients suffering from tauopathies including frontotemporal dementia (FTD) and Alzheimer's disease (AD) present with intra-neuronal aggregation of microtubule-associated protein Tau. During the disease process, Tau undergoes excessive phosphorylation, dissociates from microtubules and aggregates into insoluble neurofibrillary tangles (NFTs), accumulating in the soma. While many aspects of the disease pathology have been replicated in transgenic mouse models, a region-specific non-transgenic expression model is missing. Complementing existing models, we here report a novel region-specific approach to modelling Tau pathology. Local co-administration of the pore-former polymeric 1,3-alkylpyridinium salts (Poly-APS) extracted from marine sponges, and synthetic full-length 4R recombinant human Tau (hTau) was performed in vitro and in vivo. At low doses, Poly-APS was non-toxic and cultured cells exposed to Poly-APS (0.5 µg/ml) and hTau (1 µg/ml; ~22 µM) had normal input resistance, resting-state membrane potentials and Ca(2+) transients induced either by glutamate or KCl, as did cells exposed to a low concentration of the phosphatase inhibitor Okadaic acid (OA; 1 nM, 24 h). Combined hTau loading and phosphatase inhibition resulted in a collapse of the membrane potential, suppressed excitation and diminished glutamate and KCl-stimulated Ca(2+) transients. Stereotaxic infusions of Poly-APS (0.005 µg/ml) and hTau (1 µg/ml) bilaterally into the dorsal hippocampus at multiple sites resulted in hTau loading of neurons in rats. A separate cohort received an additional 7-day minipump infusion of OA (1.2 nM) intrahippocampally. When tested 2 weeks after surgery, rats treated with Poly-APS+hTau+OA presented with subtle learning deficits, but were also impaired in cognitive flexibility and recall. Hippocampal plasticity recorded from slices ex vivo was diminished in Poly-APS+hTau+OA subjects, but not in other treatment groups. Histological sections confirmed the intracellular accumulation of hTau in CA1 pyramidal cells and along their processes; phosphorylated Tau was present only within somata. This study demonstrates that cognitive, physiological and pathological symptoms reminiscent of tauopathies can be induced following non-mutant hTau delivery into CA1 in rats, but functional consequences hinge on increased Tau phosphorylation. Collectively, these data validate a novel model of locally infused recombinant hTau protein as an inducer of Tau pathology in the hippocampus of normal rats; future studies will provide insights into the pathological spread and maturation of Tau pathology.
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Affiliation(s)
- Dave J Koss
- School of Medical Sciences, University of Aberdeen, Foresterhill, AB25 2ZD, Aberdeen, UK
| | - Lianne Robinson
- School of Medical Sciences, University of Aberdeen, Foresterhill, AB25 2ZD, Aberdeen, UK
- Behavioural Neuroscience Core Facility, Division of Neuroscience, University of Dundee, Dundee, UK
| | | | - Anna Gasiorowska
- Department of Neurophysiology, Nencki Institute of Experimental Biology, Warsaw, Poland
- Mossakowski Medical Research Centre, Warsaw, Poland
| | - Kristina Sepčić
- Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia
| | - Tom Turk
- Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia
| | - Marcel Jaspars
- Department of Chemistry, Marine Biodiscovery Centre, University of Aberdeen, Aberdeen, UK
| | - Grazyna Niewiadomska
- Department of Neurophysiology, Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Roderick H Scott
- School of Medical Sciences, University of Aberdeen, Foresterhill, AB25 2ZD, Aberdeen, UK
| | - Bettina Platt
- School of Medical Sciences, University of Aberdeen, Foresterhill, AB25 2ZD, Aberdeen, UK
| | - Gernot Riedel
- School of Medical Sciences, University of Aberdeen, Foresterhill, AB25 2ZD, Aberdeen, UK.
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Woodruff JB, Wueseke O, Hyman AA. Pericentriolar material structure and dynamics. Philos Trans R Soc Lond B Biol Sci 2015; 369:rstb.2013.0459. [PMID: 25047613 PMCID: PMC4113103 DOI: 10.1098/rstb.2013.0459] [Citation(s) in RCA: 205] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A centrosome consists of two barrel-shaped centrioles embedded in a matrix of proteins known as the pericentriolar material (PCM). The PCM serves as a platform for protein complexes that regulate organelle trafficking, protein degradation and spindle assembly. Perhaps most important for cell division, the PCM concentrates tubulin and serves as the primary organizing centre for microtubules in metazoan somatic cells. Thus, similar to other well-described organelles, such as the nucleus and mitochondria, the cell has compartmentalized a multitude of vital biochemical reactions in the PCM. However, unlike these other organelles, the PCM is not membrane bound, but rather a dynamic collection of protein complexes and nucleic acids that constitute the organelle's interior and determine its boundary. How is the complex biochemical machinery necessary for the myriad centrosome functions concentrated and maintained in the PCM? Recent advances in proteomics and RNAi screening have unveiled most of the key PCM components and hinted at their molecular interactions (
table 1). Now we must understand how the interactions between these molecules contribute to the mesoscale organization and the assembly of the centrosome. Among outstanding questions are the intrinsic mechanisms that determine PCM shape and size, and how it functions as a biochemical reaction hub.
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Affiliation(s)
- Jeffrey B Woodruff
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany
| | - Oliver Wueseke
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany
| | - Anthony A Hyman
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany
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15
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Ali Y, Ruan K, Grace Zhai R. Drosophila Models of Tauopathy. Mov Disord 2015. [DOI: 10.1016/b978-0-12-405195-9.00054-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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16
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Sun Y, Zheng Q, Sun YT, Huang P, Guo ZL, Xu LH. Microcystin-LR induces protein phosphatase 2A alteration in a human liver cell line. ENVIRONMENTAL TOXICOLOGY 2014; 29:1236-1244. [PMID: 23436320 DOI: 10.1002/tox.21854] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Revised: 01/09/2013] [Accepted: 01/17/2013] [Indexed: 06/01/2023]
Abstract
Microcystin-LR (MC-LR) is a potent inhibitor of protein phosphatases 1 and 2A, and has potent hepatotoxicity and tumor promotion activity. Numerous studies on MC-LR toxicity have been conducted in rat hepatocytes, but few studies of the effects of microcystins on human hepatocytes have been done. In this study, HL7702 cells (a human normal liver cell line) were incubated in MC-LR for 24 h. The existence of MC-LR in HL7702 cells was confirmed. Furthermore, PP2A activity and the alteration of PP2A subunits were assessed. The results show that PP2A activity decreased from the concentration of 1 μM MC-LR, showing a concentration-dependent decline, to about 34% at 10 μM MC-LR. This activity undergone opposite change with alternations of phosphorylated Y307-PP2A/C and PP2A/C subunit but showed same change with the alteration of the ratio of methylated L309-PP2A/C to PP2A/C. B55α, a regulatory subunit of PP2A, was slightly increases in cells treated with the highest concentration of MC-LR (10 μM), and colocalized increasedly with rearranged-microtubules after 1 μM MC-LR exposure. However, the proportion of early apoptotic cells did not show any change at various concentration of MC-LR for 24 h. To our knowledge, this is the first report showing MC-LR-induced alteration of PP2A phosphatase in human cultured hepatocytes, and the mechanism of action seems to be similar as described before in vitro. The alteration of PP2A and microtubule seems to be the early event induced by MC-LR exposure.
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Affiliation(s)
- Yu Sun
- Department of Biochemistry and Molecular Biology, School of Medicine, Zhejiang University, 310058 Hangzhou, China
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17
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Sontag JM, Sontag E. Protein phosphatase 2A dysfunction in Alzheimer's disease. Front Mol Neurosci 2014; 7:16. [PMID: 24653673 PMCID: PMC3949405 DOI: 10.3389/fnmol.2014.00016] [Citation(s) in RCA: 222] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2014] [Accepted: 02/22/2014] [Indexed: 01/26/2023] Open
Abstract
Protein phosphatase 2A (PP2A) is a large family of enzymes that account for the majority of brain Ser/Thr phosphatase activity. While PP2A enzymes collectively modulate most cellular processes, sophisticated regulatory mechanisms are ultimately responsible for ensuring isoform-specific substrate specificity. Of particular interest to the Alzheimer’s disease (AD) field, alterations in PP2A regulators and PP2A catalytic activity, subunit expression, methylation and/or phosphorylation, have been reported in AD-affected brain regions. “PP2A” dysfunction has been linked to tau hyperphosphorylation, amyloidogenesis and synaptic deficits that are pathological hallmarks of this neurodegenerative disorder. Deregulation of PP2A enzymes also affects the activity of many Ser/Thr protein kinases implicated in AD. This review will more specifically discuss the role of the PP2A/Bα holoenzyme and PP2A methylation in AD pathogenesis. The PP2A/Bα isoform binds to tau and is the primary tau phosphatase. Its deregulation correlates with increased tau phosphorylation in vivo and in AD. Disruption of PP2A/Bα-tau protein interactions likely contribute to tau deregulation in AD. Significantly, alterations in one-carbon metabolism that impair PP2A methylation are associated with increased risk for sporadic AD, and enhanced AD-like pathology in animal models. Experimental studies have linked deregulation of PP2A methylation with down-regulation of PP2A/Bα, enhanced phosphorylation of tau and amyloid precursor protein, tau mislocalization, microtubule destabilization and neuritic defects. While it remains unclear what are the primary events that underlie “PP2A” dysfunction in AD, deregulation of PP2A enzymes definitely affects key players in the pathogenic process. As such, there is growing interest in developing PP2A-centric therapies for AD, but this may be a daunting task without a better understanding of the regulation and function of specific PP2A enzymes.
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Affiliation(s)
- Jean-Marie Sontag
- Faculty of Health and Medicine, School of Biomedical Sciences and Pharmacy, The University of Newcastle Callaghan, NSW, Australia
| | - Estelle Sontag
- Faculty of Health and Medicine, School of Biomedical Sciences and Pharmacy, The University of Newcastle Callaghan, NSW, Australia
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18
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Kadioglu O, Kermani NS, Kelter G, Schumacher U, Fiebig HH, Greten HJ, Efferth T. Pharmacogenomics of cantharidin in tumor cells. Biochem Pharmacol 2014; 87:399-409. [DOI: 10.1016/j.bcp.2013.10.025] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Revised: 10/28/2013] [Accepted: 10/29/2013] [Indexed: 12/29/2022]
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Abstract
Cell cycle progression is largely controlled by reversible protein phosphorylation mediated by cyclically activated kinases and phosphatases. It has long been known that cyclin B-Cdk1 activation triggers mitotic entry, and the enzymatic network controlling its activation and inactivation has been well characterized. Much more recently protein phosphatase 2A (PP2A) together with its B55 regulatory subunit has been recognized as the major activity dephosphorylating Cdk1 targets. Moreover, PP2A-B55 activity is high in late M phase and interphase, but low at mitotic entry. A series of discoveries in the fly and frog model systems have uncovered the molecular mechanism mediating this regulation. The Greatwall (Gwl) kinase activates endosulfines, which become specific inhibitors of PP2A-B55. Cdk1-dependent activation of Gwl at mitotic entry leads to PP2A-B55 downregulation, which synergizes with Cdk1 activation to promote the phosphorylated states of several mitotic substrates. Much less is known on the mechanisms inactivating Gwl and endosulfines at mitotic exit. Recent reports show the importance of spatiotemporal regulation of Gwl, endosulfines, and PP2A-B55 for cell cycle progression. The various systems and cell types differ in their dependence on the Gwl-PP2A axis for cell cycle progression. Moreover, this pathway also regulates gene expression in yeast, and this function could be conserved in metazoans.
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Affiliation(s)
- Peng Wang
- Department of Biochemistry, Institut de recherche en immunologie et en cancérologie, Université de Montréal, Édouard-Montpetit Blvd., Montréal, QC, Canada, H3T 1J4
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20
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Long JB, Van Vactor D. Embryonic and larval neural connectivity: progressive changes in synapse form and function at the neuromuscular junction mediated by cytoskeletal regulation. WILEY INTERDISCIPLINARY REVIEWS. DEVELOPMENTAL BIOLOGY 2013; 2:747-65. [PMID: 24123935 DOI: 10.1002/wdev.114] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
During development, precise formation of millions of synaptic connections is critical for the formation of a functional nervous system. Synaptogenesis is a complex multistep process in which axons follow gradients of secreted and cell surface guidance cues to reach their target area, at which point they must accurately distinguish their specific target. Upon target recognition, the axonal growth cone undergoes rapid growth and morphological changes, ultimately forming a functional synapse that continues to remodel during activity-dependent plasticity. Significant evidence suggests that the underlying actin and microtubule (MT) cytoskeletons are key effectors throughout synaptogenesis downstream of numerous receptors and signaling pathways. An increasing number of cytoskeletal-associated proteins have been shown to influence actin and MT stability and dynamics and many of these regulators have been implicated during synaptic morphogenesis using both mammalian and invertebrate model systems. In this review, we present an overview of the role cytoskeletal regulators play during the formation of the Drosophila neuromuscular junction.
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Affiliation(s)
- Jennifer B Long
- Department of Cell Biology and Program in Neuroscience, Harvard Medical School, Boston, MA, USA
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21
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Lin H, Miller ML, Granas DM, Dutcher SK. Whole genome sequencing identifies a deletion in protein phosphatase 2A that affects its stability and localization in Chlamydomonas reinhardtii. PLoS Genet 2013; 9:e1003841. [PMID: 24086163 PMCID: PMC3784568 DOI: 10.1371/journal.pgen.1003841] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 08/13/2013] [Indexed: 11/19/2022] Open
Abstract
Whole genome sequencing is a powerful tool in the discovery of single nucleotide polymorphisms (SNPs) and small insertions/deletions (indels) among mutant strains, which simplifies forward genetics approaches. However, identification of the causative mutation among a large number of non-causative SNPs in a mutant strain remains a big challenge. In the unicellular biflagellate green alga Chlamydomonas reinhardtii, we generated a SNP/indel library that contains over 2 million polymorphisms from four wild-type strains, one highly polymorphic strain that is frequently used in meiotic mapping, ten mutant strains that have flagellar assembly or motility defects, and one mutant strain, imp3, which has a mating defect. A comparison of polymorphisms in the imp3 strain and the other 15 strains allowed us to identify a deletion of the last three amino acids, Y313F314L315, in a protein phosphatase 2A catalytic subunit (PP2A3) in the imp3 strain. Introduction of a wild-type HA-tagged PP2A3 rescues the mutant phenotype, but mutant HA-PP2A3 at Y313 or L315 fail to rescue. Our immunoprecipitation results indicate that the Y313, L315, or YFLΔ mutations do not affect the binding of PP2A3 to the scaffold subunit, PP2A-2r. In contrast, the Y313, L315, or YFLΔ mutations affect both the stability and the localization of PP2A3. The PP2A3 protein is less abundant in these mutants and fails to accumulate in the basal body area as observed in transformants with either wild-type HA-PP2A3 or a HA-PP2A3 with a V310T change. The accumulation of HA-PP2A3 in the basal body region disappears in mated dikaryons, which suggests that the localization of PP2A3 may be essential to the mating process. Overall, our results demonstrate that the terminal YFL tail of PP2A3 is important in the regulation on Chlamydomonas mating.
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Affiliation(s)
- Huawen Lin
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Michelle L. Miller
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - David M. Granas
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Center for Genomic Sciences and System Biology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Susan K. Dutcher
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
- * E-mail:
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22
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Li YH, Kang H, Xu YN, Heo YT, Cui XS, Kim NH, Oh JS. Greatwall Kinase Is Required for Meiotic Maturation in Porcine Oocytes1. Biol Reprod 2013; 89:53. [DOI: 10.1095/biolreprod.113.109850] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
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23
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Martin M, Geudens I, Bruyr J, Potente M, Bleuart A, Lebrun M, Simonis N, Deroanne C, Twizere JC, Soubeyran P, Peixoto P, Mottet D, Janssens V, Hofmann WK, Claes F, Carmeliet P, Kettmann R, Gerhardt H, Dequiedt F. PP2A regulatory subunit Bα controls endothelial contractility and vessel lumen integrity via regulation of HDAC7. EMBO J 2013; 32:2491-503. [PMID: 23955003 DOI: 10.1038/emboj.2013.187] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Accepted: 07/19/2013] [Indexed: 01/04/2023] Open
Abstract
To supply tissues with nutrients and oxygen, the cardiovascular system forms a seamless, hierarchically branched, network of lumenized tubes. Here, we show that maintenance of patent vessel lumens requires the Bα regulatory subunit of protein phosphatase 2A (PP2A). Deficiency of Bα in zebrafish precludes vascular lumen stabilization resulting in perfusion defects. Similarly, inactivation of PP2A-Bα in cultured ECs induces tubulogenesis failure due to alteration of cytoskeleton dynamics, actomyosin contractility and maturation of cell-extracellular matrix (ECM) contacts. Mechanistically, we show that PP2A-Bα controls the activity of HDAC7, an essential transcriptional regulator of vascular stability. In the absence of PP2A-Bα, transcriptional repression by HDAC7 is abrogated leading to enhanced expression of the cytoskeleton adaptor protein ArgBP2. ArgBP2 hyperactivates RhoA causing inadequate rearrangements of the EC actomyosin cytoskeleton. This study unravels the first specific role for a PP2A holoenzyme in development: the PP2A-Bα/HDAC7/ArgBP2 axis maintains vascular lumens by balancing endothelial cytoskeletal dynamics and cell-matrix adhesion.
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Affiliation(s)
- Maud Martin
- Laboratory of Protein Signaling and Interactions, Interdisciplinary Cluster for Applied Genoproteomics (GIGA-R), University of Liège, Sart-Tilman, Belgium
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24
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Duncan JE, Lytle NK, Zuniga A, Goldstein LSB. The Microtubule Regulatory Protein Stathmin Is Required to Maintain the Integrity of Axonal Microtubules in Drosophila. PLoS One 2013; 8:e68324. [PMID: 23840848 PMCID: PMC3694009 DOI: 10.1371/journal.pone.0068324] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2012] [Accepted: 05/22/2013] [Indexed: 12/25/2022] Open
Abstract
Axonal transport, a form of long-distance, bi-directional intracellular transport that occurs between the cell body and synaptic terminal, is critical in maintaining the function and viability of neurons. We have identified a requirement for the stathmin (stai) gene in the maintenance of axonal microtubules and regulation of axonal transport in Drosophila. The stai gene encodes a cytosolic phosphoprotein that regulates microtubule dynamics by partitioning tubulin dimers between pools of soluble tubulin and polymerized microtubules, and by directly binding to microtubules and promoting depolymerization. Analysis of stai function in Drosophila, which has a single stai gene, circumvents potential complications with studies performed in vertebrate systems in which mutant phenotypes may be compensated by genetic redundancy of other members of the stai gene family. This has allowed us to identify an essential function for stai in the maintenance of the integrity of axonal microtubules. In addition to the severe disruption in the abundance and architecture of microtubules in the axons of stai mutant Drosophila, we also observe additional neurological phenotypes associated with loss of stai function including a posterior paralysis and tail-flip phenotype in third instar larvae, aberrant accumulation of transported membranous organelles in stai deficient axons, a progressive bang-sensitive response to mechanical stimulation reminiscent of the class of Drosophila mutants used to model human epileptic seizures, and a reduced adult lifespan. Reductions in the levels of Kinesin-1, the primary anterograde motor in axonal transport, enhance these phenotypes. Collectively, our results indicate that stai has an important role in neuronal function, likely through the maintenance of microtubule integrity in the axons of nerves of the peripheral nervous system necessary to support and sustain long-distance axonal transport.
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Affiliation(s)
- Jason E. Duncan
- Department of Biology, Willamette University, Salem, Oregon, United States of America
- * E-mail:
| | - Nikki K. Lytle
- Department of Biology, Willamette University, Salem, Oregon, United States of America
| | - Alfredo Zuniga
- Department of Biology, Willamette University, Salem, Oregon, United States of America
| | - Lawrence S. B. Goldstein
- Howard Hughes Medical Institute, Department of Cellular and Molecular Medicine, School of Medicine, University of California San Diego, La Jolla, California, United States of America
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Haeseleer F, Sokal I, Gregory FD, Lee A. Protein phosphatase 2A dephosphorylates CaBP4 and regulates CaBP4 function. Invest Ophthalmol Vis Sci 2013; 54:1214-26. [PMID: 23341017 DOI: 10.1167/iovs.12-11319] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE CaBP4 is a neuronal Ca(2+)-binding protein that is expressed in the retina and in the cochlea, and is essential for normal photoreceptor synaptic function. CaBP4 is phosphorylated by protein kinase C zeta (PKCζ) in the retina at serine 37, which affects its interaction with and modulation of voltage-gated Ca(v)1 Ca(2+) channels. In this study, we investigated the potential role and functional significance of protein phosphatase 2A (PP2A) in CaBP4 dephosphorylation. METHODS The effect of protein phosphatase inhibitors, light, and overexpression of PP2A subunits on CaBP4 dephosphorylation was measured in in vitro assays. Pull-down experiments using retinal or transfected HEK293 cell lysates were used to investigate the association between CaBP4 and PP2A subunits. Electrophysiologic recordings of cotransfected HEK293 cells were performed to analyze the effect of CaBP4 dephosphorylation in modulating Ca(v)1.3 currents. RESULTS PP2A inhibitors, okadaic acid (OA), and fostriecin, but not PP1 selective inhibitors, NIPP-1, and inhibitor 2, block CaBP4 dephosphorylation in retinal lysates. Increased phosphatase activity in light-dependent conditions reverses phosphorylation of CaBP4 by PKCζ. In HEK293 cells, overexpression of PP2A enhances the rate of dephosphorylation of CaBP4. In addition, inhibition of protein phosphatase activity by OA increases CaBP4 phosphorylation and potentiates the modulatory effect of CaBP4 on Ca(v)1.3 Ca(2+) channels in HEK293T cells. CONCLUSIONS This study provides evidence that CaBP4 is dephosphorylated by PP2A in the retina. Our findings reveal a novel role for protein phosphatases in regulating CaBP4 function in the retina, which may fine tune presynaptic Ca(2+) signals at the photoreceptor synapse.
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Affiliation(s)
- Françoise Haeseleer
- Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195, USA.
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26
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Liu Y, He P, Zhang M, Shi L, Zhu H, Wang Y, Zhao J. Silencing of the human SET gene in vitro with lentivirus-mediated RNA interference. Mol Med Rep 2013; 7:843-7. [PMID: 23338687 DOI: 10.3892/mmr.2013.1275] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2012] [Accepted: 12/19/2012] [Indexed: 11/06/2022] Open
Abstract
In our previous study, SET was identified as one of the differentially expressed proteins that was associated with tetra-arsenic tetra-sulfide (As4S4)-induced NB4-R1 [retinoic acid-resistant acute promyelocytic leukemia (APL) cell line] apoptosis. However, the mechanism through which SET regulates pathways during this process remains unclear. The aim of this study was to construct lentivirus-mediated short hairpin RNA (shRNA) against SET and investigate the effect of SET on As4S4-induced retinoic acid-resistant APL cell apoptosis. In the present study, 4 different oligonucleotides targeting the human SET gene were synthesized and cloned into the eukaryotic expression plasmid pGCSIL-GFP. The recombinant vectors were introduced into NB4-R1 cells. The silencing efficiency was measured by real-time quantitative PCR (RT-qPCR) and western blotting. Our results showed that the 4 recombinant RNA interference (RNAi) vectors were constructed successfully. Fluorescence microscopy demonstrated that infection efficiency ranged from 70 to 90%. Infection with the 4 different RNAi vectors significantly knocked down the expression of SET by 52.8, 69.1, 48.9 and 90.3% at the mRNA level, and 92.5, 96.3, 91.7 and 98.4% at the protein level, respectively. We attempt to clarify the mechanism of As4S4 treatment on retinoic acid-resistant APL.
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Affiliation(s)
- Yanfeng Liu
- Department of Hematology, The First Affiliated Hospital, School of Medicine, Xi'an Jiaotong University, Xi'an 710061, PR China
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Hashiguchi M, Hashiguchi T. Kinase–Kinase Interaction and Modulation of Tau Phosphorylation. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 300:121-60. [DOI: 10.1016/b978-0-12-405210-9.00004-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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28
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Abstract
Protein phosphatases of the type 2A family (PP2A) represent a major fraction of cellular Ser/Thr phosphatase activity in any given human tissue. In this review, we describe how the holoenzymic nature of PP2A and the existence of several distinct PP2A composing subunits allow for the generation of multiple structurally and functionally different PP2A complexes, explaining why PP2A is involved in the regulation of so many diverse cell biological and physiological processes. Moreover, in human disease, most notably in several cancers and Alzheimer's Disease, PP2A expression and/or activity have been found significantly decreased, underscoring its important functions as a major tumor suppressor and tau phosphatase. Hence, several recent preclinical studies have demonstrated that pharmacological restoration of PP2A activity, as well as pharmacological PP2A inhibition, under certain conditions, may be of significant future therapeutic value.
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29
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Iketani M, Iizuka A, Sengoku K, Kurihara Y, Nakamura F, Sasaki Y, Sato Y, Yamane M, Matsushita M, Nairn AC, Takamatsu K, Goshima Y, Takei K. Regulation of neurite outgrowth mediated by localized phosphorylation of protein translational factor eEF2 in growth cones. Dev Neurobiol 2012; 73:230-46. [PMID: 23008267 DOI: 10.1002/dneu.22058] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Revised: 09/12/2012] [Accepted: 09/15/2012] [Indexed: 11/10/2022]
Abstract
Nerve growth cones contain mRNA and its translational machinery and thereby synthesize protein locally. The regulatory mechanisms in the growth cone, however, remain largely unknown. We previously found that the calcium entry-induced increase of phosphorylation of eukaryotic elongation factor-2 (eEF2), a key component of mRNA translation, within growth cones showed growth arrest of neurites. Because dephosphorylated eEF2 and phosphorylated eEF2 are known to promote and inhibit mRNA translation, respectively, the data led to the hypothesis that eEF2-mediating mRNA translation may regulate neurite outgrowth. Here, we validated the hypothesis by using a chromophore-assisted light inactivation (CALI) technique to examine the roles of localized eEF2 and eEF2 kinase (EF2K), a specific calcium calmodulin-dependent enzyme for eEF2 phosphorylation, in advancing growth cones of cultured chick dorsal root ganglion (DRG) neurons. The phosphorylated eEF2 was weakly distributed in advancing growth cones, whereas eEF2 phosphorylation was increased by extracellular adenosine triphosphate (ATP)-evoked calcium transient through P2 purinoceptors in growth cones and resulted in growth arrest of neurites. The increase of eEF2 phosphorylation within growth cones by inhibition of protein phosphatase 2A known to dephosphorylate eEF2 also showed growth arrest of neurites. CALI of eEF2 within growth cones resulted in retardation of neurite outgrowth, whereas CALI of EF2K enhanced neurite outgrowth temporally. Moreover, CALI of EF2K abolished the ATP-induced retardation of neurite outgrowth. These findings suggest that an eEF2 phosphorylation state localized to the growth cone regulates neurite outgrowth.
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Affiliation(s)
- Masumi Iketani
- Division of Medical Life Sciences, Yokohama City University School of Medicine, Yokohama 236-0004, Japan
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Acute administration of L-DOPA induces changes in methylation metabolites, reduced protein phosphatase 2A methylation, and hyperphosphorylation of Tau protein in mouse brain. J Neurosci 2012; 32:9173-81. [PMID: 22764226 DOI: 10.1523/jneurosci.0125-12.2012] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Folate deficiency and hypomethylation have been implicated in a number of age-related neurodegenerative disorders including dementia and Parkinson's disease (PD). Levodopa (L-dopa) therapy in PD patients has been shown to cause an increase in plasma total homocysteine as well as depleting cellular concentrations of the methyl donor, S-adenosylmethionine (SAM), and increasing the demethylated product S-adenosylhomocysteine (SAH). Modulation of the cellular SAM/SAH ratio can influence activity of methyltransferase enzymes, including leucine carboxyl methyltransferase that specifically methylates Ser/Thr protein phosphatase 2A (PP2A), a major Tau phosphatase. Here we show in human SH-SY5Y cells, in dopaminergic neurons, and in wild-type mice that l-dopa results in a reduced SAM/SAH ratio that is associated with hypomethylation of PP2A and increased phosphorylation of Tau (p-Tau) at the Alzheimer's disease-like PHF-1 phospho-epitope. The effect of L-dopa on PP2A and p-Tau was exacerbated in cells exposed to folate deficiency. In the folate-deficient mouse model, L-dopa resulted in a marked depletion of SAM and an increase in SAH in various brain regions with parallel downregulation of PP2A methylation and increased Tau phosphorylation. L-Dopa also enhanced demethylated PP2A amounts in the liver. These findings reveal a novel mechanism involving methylation-dependent pathways in L-dopa induces PP2A hypomethylation and increases Tau phosphorylation, which may be potentially detrimental to neuronal cells.
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31
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Sontag JM, Nunbhakdi-Craig V, White CL, Halpain S, Sontag E. The protein phosphatase PP2A/Bα binds to the microtubule-associated proteins Tau and MAP2 at a motif also recognized by the kinase Fyn: implications for tauopathies. J Biol Chem 2012; 287:14984-93. [PMID: 22403409 DOI: 10.1074/jbc.m111.338681] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The predominant brain microtubule-associated proteins MAP2 and tau play a critical role in microtubule cytoskeletal organization and function. We have previously reported that PP2A/Bα, a major protein phosphatase 2A (PP2A) holoenzyme, binds to and dephosphorylates tau, and regulates microtubule stability. Here, we provide evidence that MAP2 co-purifies with and is dephosphorylated by endogenous PP2A/Bα in bovine gray matter. It co-localizes with PP2A/Bα in immature and mature human neuronal cell bodies. PP2A co-immunoprecipitates with and directly interacts with MAP2. Using in vitro binding assays, we show that PP2A/Bα binds to MAP2c isoforms through a region encompassing the microtubule-binding domain and upstream proline-rich region. Tau and MAP2 compete for binding to and dephosphorylation by PP2A/Bα. Remarkably, the protein-tyrosine kinase Fyn, which binds to the proline-rich RTPPKSP motif conserved in both MAP2 and tau, inhibits the interaction of PP2A/Bα with either tau or MAP2c. The corresponding synthetic RTPPKSP peptide, but not the phosphorylated RpTPPKSP version, competes with Tau and MAP2c for binding to PP2A/Bα. Significantly, down-regulation of PP2A/Bα and deregulation of Fyn-Tau protein interactions have been linked to enhanced tau phosphorylation in Alzheimer disease. Together, our results suggest that PP2A/Bα is part of segregated MAP2 and tau signaling scaffolds that can coordinate the action of key kinases and phosphatases involved in modulating neuronal plasticity. Deregulation of these compartmentalized multifunctional protein complexes is likely to contribute to tau deregulation, microtubule disruption, and altered signaling in tauopathies.
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Affiliation(s)
- Jean-Marie Sontag
- School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, New South Wales 2308, Australia
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32
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Pitre A, Davis N, Paul M, Orr AW, Skalli O. Synemin promotes AKT-dependent glioblastoma cell proliferation by antagonizing PP2A. Mol Biol Cell 2012; 23:1243-53. [PMID: 22337773 PMCID: PMC3315805 DOI: 10.1091/mbc.e11-08-0685] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Synemin is an intermediate filament protein present in glioblastomas (GBMs) but not in normal brain. In GBM cells synemin interacts with and antagonizes PP2A, which is the phosphatase dephosphorylating Akt. This maintains the phosphorylation status of Akt sites that are substrates for PDPK1 and mTORc2, thereby fostering proliferation. The intermediate filament protein synemin is present in astrocyte progenitors and glioblastoma cells but not in mature astrocytes. Here we demonstrate a role for synemin in enhancing glioblastoma cell proliferation and clonogenic survival, as synemin RNA interference decreased both behaviors by inducing G1 arrest along with Rb hypophosphorylation and increased protein levels of the G1/S inhibitors p21Cip1 and p27Kip1. Akt involvement was demonstrated by decreased phosphorylation of its substrate, p21Cip1, and reduced Akt catalytic activity and phosphorylation at essential activation sites. Synemin silencing, however, did not affect the activities of PDPK1 and mTOR complex 2, which directly phosphorylate Akt activation sites, but instead enhanced the activity of the major regulator of Akt dephosphorylation, protein phosphatase type 2A (PP2A). This was accompanied by changes in PP2A subcellular distribution resulting in increased physical interactions between PP2A and Akt, as shown by proximity ligation assays (PLAs). PLAs and immunoprecipitation experiments further revealed that synemin and PP2A form a protein complex. In addition, treatment of synemin-silenced cells with the PP2A inhibitor cantharidic acid resulted in proliferation and pAkt and pRb levels similar to those of controls. Collectively these results indicate that synemin positively regulates glioblastoma cell proliferation by helping sequester PP2A away from Akt, thereby favoring Akt activation.
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Affiliation(s)
- Aaron Pitre
- Department of Cellular Biology and Anatomy, Louisiana State University Health Sciences Center, Shreveport, LA 71130, USA
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33
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Wu J, Lou H, Alerte TNM, Stachowski EK, Chen J, Singleton AB, Hamilton RL, Perez RG. Lewy-like aggregation of α-synuclein reduces protein phosphatase 2A activity in vitro and in vivo. Neuroscience 2012; 207:288-97. [PMID: 22326202 DOI: 10.1016/j.neuroscience.2012.01.028] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2011] [Revised: 12/07/2011] [Accepted: 01/14/2012] [Indexed: 10/14/2022]
Abstract
α-synuclein (α-Syn) is a chaperone-like protein that is highly implicated in Parkinson's disease (PD) as well as in dementia with Lewy bodies (DLB). Rare forms of PD occur in individuals with mutations of α-Syn or triplication of wild type α-Syn, and in both PD and DLB the intraneuronal inclusions known as Lewy bodies contain aggregated α-Syn that is highly phosphorylated on serine 129. In neuronal cells and in the brains of α-Syn overexpressing transgenic mice, soluble α-Syn stimulates the activity of protein phosphatase 2A (PP2A), a major serine/threonine phosphatase. Serine 129 phosphorylation of α-Syn attenuates its stimulatory effects on PP2A and also accelerates α-Syn aggregation; however, it is unknown if aggregation of α-Syn into Lewy bodies impairs PP2A activity. To assess for this, we measured the impact of α-Syn aggregation on PP2A activity in vitro and in vivo. In cell-free assays, aggregated α-Syn had ∼50% less PP2A stimulatory effects than soluble recombinant α-Syn. Similarly in DLB and α-Syn triplication brains, which contain robust α-Syn aggregation with high levels of serine 129 phosphorylation, PP2A activity was also ∼50% attenuated. As α-Syn normally stimulates PP2A activity, our data suggest that overexpression of α-Syn or sequestration of α-Syn into Lewy bodies has the potential to alter the phosphorylation state of key PP2A substrates; raising the possibility that all forms of synucleinopathy will benefit from treatments aimed at optimizing PP2A activity.
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Affiliation(s)
- J Wu
- Department of Neurology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
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34
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Low expression of PP2A regulatory subunit B55α is associated with T308 phosphorylation of AKT and shorter complete remission duration in acute myeloid leukemia patients. Leukemia 2011; 25:1711-7. [PMID: 21660042 PMCID: PMC3191228 DOI: 10.1038/leu.2011.146] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The regulation of Protein Kinase B (AKT) is a dynamic process that depends on the balance between phosphorylation by upstream kinases for activation and inactivation by dephosphorylation by protein phosphatases. Phosphorylated AKT is commonly found in acute myeloid leukemia (AML) and confers an unfavorable prognosis. Understanding the relative importance of upstream kinases and AKT phosphatase in the activation of AKT is relevant for the therapeutic targeting of this signaling axis in AML. The B55α subunit of Protein Phosphatase 2A (PP2A) has been implicated in AKT dephosphorylation but its role in regulating AKT in AML is unknown. We examined B55α protein expression in blast cells derived from 511 AML patients using Reverse Phase Protein Analysis (RPPA). B55α protein expression was lower in AML cells compared to normal CD34+ cells. B55α protein levels negatively correlated with T308 phosphorylation levels. Low levels of B55α were associated with shorter complete remission duration demonstrating that decreased expression is an adverse prognostic factor in AML. These findings suggest that decreased B55α expression in AML is at least partially responsible for increased AKT signaling in AML and suggests that therapeutic targeting of PP2A could counteract this.
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35
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Gharbi-Ayachi A, Labbé JC, Burgess A, Vigneron S, Strub JM, Brioudes E, Van-Dorsselaer A, Castro A, Lorca T. The substrate of Greatwall kinase, Arpp19, controls mitosis by inhibiting protein phosphatase 2A. Science 2010; 330:1673-1677. [PMID: 21164014 DOI: 10.1016/b978-0-12-374145-5.00168-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Initiation and maintenance of mitosis require the activation of protein kinase cyclin B-Cdc2 and the inhibition of protein phosphatase 2A (PP2A), which, respectively, phosphorylate and dephosphorylate mitotic substrates. The protein kinase Greatwall (Gwl) is required to maintain mitosis through PP2A inhibition. We describe how Gwl activation results in PP2A inhibition. We identified cyclic adenosine monophosphate-regulated phosphoprotein 19 (Arpp19) and α-Endosulfine as two substrates of Gwl that, when phosphorylated by this kinase, associate with and inhibit PP2A, thus promoting mitotic entry. Conversely, in the absence of Gwl activity, Arpp19 and α-Endosulfine are dephosphorylated and lose their capacity to bind and inhibit PP2A. Although both proteins can inhibit PP2A, endogenous Arpp19, but not α-Endosulfine, is responsible for PP2A inhibition at mitotic entry in Xenopus egg extracts.
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Affiliation(s)
- Aicha Gharbi-Ayachi
- Universités Montpellier 2 et 1, Centre de Recherche de Biochimie Macromoléculaire, CNRS UMR 5237, IFR 122, 1919 Route de Mende, 34293 Montpellier cedex 5, France
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36
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Foley TD, Melideo SL, Healey AE, Lucas EJ, Koval JA. Phenylarsine oxide binding reveals redox-active and potential regulatory vicinal thiols on the catalytic subunit of protein phosphatase 2A. Neurochem Res 2010; 36:232-40. [PMID: 21080067 DOI: 10.1007/s11064-010-0310-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/28/2010] [Indexed: 11/24/2022]
Abstract
Our earlier finding that the activity of protein phosphatase 2A from rat brain is inhibited by micromolar concentrations of the dithiol cross-linking reagent phenylarsine oxide (PAO) has encouraged the hypothesis that the catalytic subunit (PP2Ac) of PP2A contains one or more pairs of closely-spaced (vicinal) thiol pairs that may contribute to regulation of the enzyme. The results of the present study demonstrate using immobilized PAO-affinity chromatography that PP2Ac from rat brain formed stable DTT-sensitive adducts with PAO with or without associated regulatory subunits. In addition, a subset of the PAO-binding vicinal thiols of PP2Ac was readily oxidized to disulfide bonds in vitro. Importantly, a small fraction of PP2Ac was still found to contain disulfide bonds after applying stringent conditions designed to prevent protein disulfide bond formation during homogenization and fractionation of the brains. These findings establish the presence of potentially regulatory and redox-active PAO-binding vicinal thiols on the catalytic subunit of PP2A and suggest that a population of PP2Ac may contain disulfide bonds in vivo.
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Affiliation(s)
- Timothy D Foley
- Department of Chemistry, University of Scranton, Scranton, PA 18510, USA.
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37
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Sontag JM, Nunbhakdi-Craig V, Mitterhuber M, Ogris E, Sontag E. Regulation of protein phosphatase 2A methylation by LCMT1 and PME-1 plays a critical role in differentiation of neuroblastoma cells. J Neurochem 2010; 115:1455-65. [PMID: 21044074 DOI: 10.1111/j.1471-4159.2010.07049.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Neuritic alterations are a major feature of many neurodegenerative disorders. Methylation of protein phosphatase 2A (PP2A) catalytic C subunit by the leucine carboxyl methyltransferase (LCMT1), and demethylation by the protein phosphatase methylesterase 1, is a critical PP2A regulatory mechanism. It modulates the formation of PP2A holoenzymes containing the Bα subunit, which dephosphorylate key neuronal cytoskeletal proteins, including tau. Significantly, we have reported that LCMT1, methylated C and Bα expression levels are down-regulated in Alzheimer disease-affected brain regions. In this study, we show that enhanced expression of LCMT1 in cultured N2a neuroblastoma cells, which increases endogenous methylated C and Bα levels, induces changes in F-actin organization. It promotes serum-independent neuritogenesis and development of extended tau-positive processes upon N2a cell differentiation. These stimulatory effects can be abrogated by LCMT1 knockdown and S-adenosylhomocysteine, an inhibitor of methylation reactions. Expression of protein phosphatase methylesterase 1 and the methylation-site L309Δ C subunit mutant, which decrease intracellular methylated C and Bα levels, block N2a cell differentiation and LCMT1-mediated neurite formation. Lastly, inducible and non-inducible knockdown of Bα in N2a cells inhibit process outgrowth. Altogether, our results establish a novel mechanistic link between PP2A methylation and development of neurite-like processes.
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Affiliation(s)
- Jean-Marie Sontag
- School of Biomedical Sciences and Pharmacy, Faculty of Health, The University of Newcastle, Callaghan, NSW, Australia.
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38
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Bai Q, Burton EA. Zebrafish models of Tauopathy. Biochim Biophys Acta Mol Basis Dis 2010; 1812:353-63. [PMID: 20849952 DOI: 10.1016/j.bbadis.2010.09.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2010] [Accepted: 09/08/2010] [Indexed: 01/06/2023]
Abstract
Tauopathies are a group of incurable neurodegenerative diseases, in which loss of neurons is accompanied by intracellular deposition of fibrillar material composed of hyperphosphorylated forms of the microtubule-associated protein Tau. A zebrafish model of Tauopathy could complement existing murine models by providing a platform for genetic and chemical screens, in order to identify novel therapeutic targets and compounds with disease-modifying potential. In addition, Tauopathy zebrafish would be useful for hypothesis-driven experiments, especially those exploiting the potential to deploy in vivo imaging modalities. Several considerations, including conservation of specialized neuronal and other cellular populations, and biochemical pathways implicated in disease pathogenesis, suggest that the zebrafish brain is an appropriate setting in which to model these complex disorders. Novel transgenic zebrafish lines expressing wild-type and mutant forms of human Tau in CNS neurons have recently been reported. These studies show evidence that human Tau undergoes disease-relevant changes in zebrafish neurons, including somato-dendritic relocalization, hyperphosphorylation and aggregation. In addition, preliminary evidence suggests that Tau transgene expression can precipitate neuronal dysfunction and death. These initial studies are encouraging that the zebrafish holds considerable promise as a model in which to study Tauopathies. Further studies are necessary to clarify the phenotypes of transgenic lines and to develop assays and models suitable for unbiased high-throughput screening approaches. This article is part of a Special Issue entitled Zebrafish Models of Neurological Diseases.
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Affiliation(s)
- Qing Bai
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, PA, USA
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39
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Flegg CP, Sharma M, Medina-Palazon C, Jamieson C, Galea M, Brocardo MG, Mills K, Henderson BR. Nuclear export and centrosome targeting of the protein phosphatase 2A subunit B56alpha: role of B56alpha in nuclear export of the catalytic subunit. J Biol Chem 2010; 285:18144-54. [PMID: 20378546 DOI: 10.1074/jbc.m109.093294] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Protein phosphatase (PP) 2A is a heterotrimeric enzyme regulated by specific subunits. The B56 (or B'/PR61/PPP2R5) class of B-subunits direct PP2A or its substrates to different cellular locations, and the B56alpha, -beta, and -epsilon isoforms are known to localize primarily in the cytoplasm. Here we studied the pathways that regulate B56alpha subcellular localization. We detected B56alpha in the cytoplasm and nucleus, and at the nuclear envelope and centrosomes, and show that cytoplasmic localization is dependent on CRM1-mediated nuclear export. The inactivation of CRM1 by leptomycin B or by siRNA knockdown caused nuclear accumulation of ectopic and endogenous B56alpha. Conversely, CRM1 overexpression shifted B56alpha to the cytoplasm. We identified a functional nuclear export signal at the C terminus (NES; amino acids 451-469), and site-directed mutagenesis of the NES (L461A) caused nuclear retention of full-length B56alpha. Active NESs were identified at similar positions in the cytoplasmic B56-beta and epsilon isoforms, but not in the nuclear-localized B56-delta or gamma isoforms. The transient expression of B56alpha induced nuclear export of the PP2A catalytic (C) subunit, and this was blocked by the L461A NES mutation. In addition, B56alpha co-located with the PP2A active (A) subunit at centrosomes, and its centrosome targeting involved sequences that bind to the A-subunit. Fluorescence Recovery after Photobleaching (FRAP) assays revealed dynamic and immobile pools of B56alpha-GFP, which was rapidly exported from the nucleus and subject to retention at centrosomes. We propose that B56alpha can act as a PP2A C-subunit chaperone and regulates PP2A activity at diverse subcellular locations.
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Affiliation(s)
- Cameron P Flegg
- From the Westmead Institute for Cancer Research, Westmead Millennium Institute at Westmead Hospital, University of Sydney, Westmead New South Wales 2145, Australia
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40
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Antony R, Lukiw WJ, Bazan NG. Neuroprotectin D1 induces dephosphorylation of Bcl-xL in a PP2A-dependent manner during oxidative stress and promotes retinal pigment epithelial cell survival. J Biol Chem 2010; 285:18301-8. [PMID: 20363734 DOI: 10.1074/jbc.m109.095232] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Retinal pigment epithelial (RPE) cell integrity is critical for the survival of photoreceptor cells. Bcl-x(L) is a major anti-apoptotic Bcl-2 protein required for RPE cell survival, and phosphorylation of Bcl-x(L) at residue Ser-62 renders this protein pro-apoptotic. In this study, we identify serine/threonine protein phosphatase 2A (PP2A) as a key regulator of Bcl-x(L) phosphorylation at residue Ser-62 in ARPE-19 cells, a spontaneously arising RPE cell line in which Bcl-x(L) is highly expressed. We found that either PP2A inhibitor okadaic acid or depletion of catalytic subunit alpha of PP2A (PP2A/Calpha) by small interfering RNA enhanced Bcl-x(L) phosphorylation when activated with hydrogen peroxide and tumor necrosis factor alpha-induced oxidative stress. Disruption of PP2A/Calpha exacerbated oxidative stress-induced apoptosis. PP2A/Calpha colocalized and interacted with S62Bcl-x(L) in cells stressed with H(2)O(2)/tumor necrosis factor alpha. By contrast, the omega-3 fatty acid docosahexaenoic acid derivative, neuroprotectin D1 (NPD1), a potent activator of survival signaling, down-regulated oxidative stress-induced phosphorylation of Bcl-x(L) by increasing protein phosphatase activity. NPD1 also attenuated the oxidative stress-induced apoptosis by knockdown of PP2A/Calpha and increased the association of PP2A/Calpha with S62Bcl-x(L) as well as total Bcl-x(L). NPD1 also enhanced the heterodimerization of Bcl-x(L) with its counterpart, pro-apoptotic protein Bax. Thus, NPD1 modulates the activation of this Bcl-2 family protein by dephosphorylating in a PP2A-dependent manner, suggesting a coordinated, NPD1-mediated regulation of cell survival in response to oxidative stress.
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Affiliation(s)
- Rajee Antony
- Neuroscience Center of Excellence, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA
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41
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Torres JZ, Ban KH, Jackson PK. A specific form of phospho protein phosphatase 2 regulates anaphase-promoting complex/cyclosome association with spindle poles. Mol Biol Cell 2010; 21:897-904. [PMID: 20089842 PMCID: PMC2836970 DOI: 10.1091/mbc.e09-07-0598] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2009] [Revised: 12/28/2009] [Accepted: 01/08/2010] [Indexed: 11/11/2022] Open
Abstract
In early mitosis, the END (Emi1/NuMA/Dynein-dynactin) network anchors the anaphase-promoting complex/cyclosome (APC/C) to the mitotic spindle and poles. Spindle anchoring restricts APC/C activity, thereby limiting the destruction of spindle-associated cyclin B and ensuring maintenance of spindle integrity. Emi1 binds directly to hypophosphorylated APC/C, linking the APC/C to the spindle via NuMA. However, whether the phosphorylation state of the APC/C is important for its association with the spindle and what kinases and phosphatases are necessary for regulating this event remain unknown. Here, we describe the regulation of APC/C-mitotic spindle pole association by phosphorylation. We find that only hypophosphorylated APC/C associates with microtubule asters, suggesting that phosphatases are important. Indeed, a specific form of PPP2 (CA/R1A/R2B) binds APC/C, and PPP2 activity is necessary for Cdc27 dephosphorylation. Screening by RNA interference, we find that inactivation of CA, R1A, or R2B leads to delocalization of APC/C from spindle poles, early mitotic spindle defects, a failure to congress chromosomes, and decreased levels of cyclin B on the spindle. Consistently, inhibition of cyclin B/Cdk1 activity increased APC/C binding to microtubules. Thus, cyclin B/Cdk1 and PPP2 regulate the dynamic association of APC/C with spindle poles in early mitosis, a step necessary for proper spindle formation.
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Affiliation(s)
- Jorge Z. Torres
- *Department of Pathology and
- Department of Cell Regulation, Genentech Inc., South San Francisco, CA 94080
| | - Kenneth H. Ban
- *Department of Pathology and
- Program in Cancer Biology, Stanford University School of Medicine, Stanford, CA 94305; and
| | - Peter K. Jackson
- *Department of Pathology and
- Department of Cell Regulation, Genentech Inc., South San Francisco, CA 94080
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A nonhomologous end-joining pathway is required for protein phosphatase 2A promotion of DNA double-strand break repair. Neoplasia 2010; 11:1012-21. [PMID: 19794960 DOI: 10.1593/neo.09720] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2009] [Revised: 06/25/2009] [Accepted: 06/25/2009] [Indexed: 12/31/2022] Open
Abstract
Protein phosphatase 2A (PP2A) functions as a potent tumor suppressor, but its mechanism(s) remains enigmatic. Specific disruption of PP2A by either expression of SV40 small tumor antigen or depletion of endogenous PP2A/C by RNA interference inhibits Ku DNA binding and DNA-PK activities, which results in suppression of DNA double-strand break (DSB) repair and DNA end-joining in association with increased genetic instability (i.e., chromosomal and chromatid breaks). Overexpression of the PP2A catalytic subunit (PP2A/C) enhances Ku and DNA-PK activities with accelerated DSB repair. Camptothecin-induced DSBs promote PP2A to associate with Ku 70 and Ku 86. PP2A directly dephosphorylates Ku as well as the DNA-PK catalytic subunit (DNA-PKcs) in vitro and in vivo, which enhances the formation of a functional Ku/DNA-PKcs complex. Intriguingly, PP2A promotes DSB repair in wild type mouse embryonic fibroblast (MEF) cells but has no such effect in Ku-deficient MEF cells, suggesting that the Ku 70/86 heterodimer is required for PP2A promotion of DSB repair. Thus, PP2A promotion of DSB repair may occur in a novel mechanism by activating the nonhomologous end-joining pathway through direct dephosphorylation of Ku and DNA-PKcs, which may contribute to maintenance of genetic stability.
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43
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Palidwor GA, Shcherbinin S, Huska MR, Rasko T, Stelzl U, Arumughan A, Foulle R, Porras P, Sanchez-Pulido L, Wanker EE, Andrade-Navarro MA. Detection of alpha-rod protein repeats using a neural network and application to huntingtin. PLoS Comput Biol 2009; 5:e1000304. [PMID: 19282972 PMCID: PMC2647740 DOI: 10.1371/journal.pcbi.1000304] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2008] [Accepted: 01/27/2009] [Indexed: 01/10/2023] Open
Abstract
A growing number of solved protein structures display an elongated structural
domain, denoted here as alpha-rod, composed of stacked pairs of anti-parallel
alpha-helices. Alpha-rods are flexible and expose a large surface, which makes
them suitable for protein interaction. Although most likely originating by
tandem duplication of a two-helix unit, their detection using sequence
similarity between repeats is poor. Here, we show that alpha-rod repeats can be
detected using a neural network. The network detects more repeats than are
identified by domain databases using multiple profiles, with a low level of
false positives (<10%). We identify alpha-rod repeats in
approximately 0.4% of proteins in eukaryotic genomes. We then
investigate the results for all human proteins, identifying alpha-rod repeats
for the first time in six protein families, including proteins STAG1-3, SERAC1,
and PSMD1-2 & 5. We also characterize a short version of these repeats
in eight protein families of Archaeal, Bacterial, and Fungal species. Finally,
we demonstrate the utility of these predictions in directing experimental work
to demarcate three alpha-rods in huntingtin, a protein mutated in
Huntington's disease. Using yeast two hybrid analysis and an
immunoprecipitation technique, we show that the huntingtin fragments containing
alpha-rods associate with each other. This is the first definition of domains in
huntingtin and the first validation of predicted interactions between fragments
of huntingtin, which sets up directions toward functional characterization of
this protein. An implementation of the repeat detection algorithm is available
as a Web server with a simple graphical output: http://www.ogic.ca/projects/ard. This can be further visualized
using BiasViz, a graphic tool for representation of multiple sequence
alignments. Many proteins have an elongated structural domain formed by a stack of alpha
helices (alpha-rod), often found to interact with other proteins. The
identification of an alpha-rod in a protein can therefore tell something about
both the function and the structure of that protein. Though alpha-rods can be
readily identified from the structure of proteins, for the vast majority of
known proteins this is unavailable, and we have to use their amino acid
sequence. Because alpha-rods have highly variable sequences, commonly used
methods of domain identification by sequence similarity have difficulty
detecting them. However, alpha-rods do have specific patterns of amino acid
properties along their sequences, so we used a computational method based on a
neural network to learn these patterns. We illustrate how this method finds
novel instances of the domain in proteins from a wide range of organisms. We
performed detailed analysis of huntingtin, the protein mutated in
Huntington's chorea, a neurodegenerative disease. The function of
huntingtin remains a mystery partially due to the lack of knowledge about its
structure. Therefore, we defined three alpha-rods in this protein and
experimentally verified how they interact with each other, a novel result that
opens new avenues for huntingtin research.
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Deng X, Gao F, May WS. Protein phosphatase 2A inactivates Bcl2's antiapoptotic function by dephosphorylation and up-regulation of Bcl2-p53 binding. Blood 2009; 113:422-8. [PMID: 18845789 PMCID: PMC2615654 DOI: 10.1182/blood-2008-06-165134] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Accepted: 09/16/2008] [Indexed: 11/20/2022] Open
Abstract
Bcl2 is associated with chemoresistance and poor prognosis in patients with various hematologic malignancies. DNA damage-induced p53/Bcl2 interaction at the outer mitochondrial membrane results in a Bcl2 conformational change with loss of its antiapoptotic activity in interleukin-3-dependent myeloid H7 cells. Here we find that specific disruption of protein phosphatase 2A (PP2A) activity by either expression of small t antigen or depletion of PP2A/C by RNA interference enhances Bcl2 phosphorylation and suppresses cisplatin-stimulated p53/Bcl2 binding in association with prolonged cell survival. By contrast, treatment of cells with C2-ceramide (a potent PP2A activator) or expression of the PP2A catalytic subunit (PP2A/C) inhibits Bcl2 phosphorylation, leading to increased p53/Bcl2 binding and apoptotic cell death. Mechanistically, PP2A-mediated dephosphorylation of Bcl2 in vitro promotes its direct interaction with p53 as well as a conformational change in Bcl2. PP2A directly interacts with the BH4 domain of Bcl2 as a docking site to potentially "bridge" PP2A to Bcl2's flexible loop domain containing the target serine 70 phosphorylation site. Thus, PP2A may provide a dual inhibitory effect on Bcl2's survival function by both dephosphorylating Bcl2 and enhancing p53-Bcl2 binding. Activating PP2A to dephosphorylate Bcl2 and/or increase Bcl2/p53 binding may represent an efficient and novel approach for treatment of hematologic malignancies.
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Affiliation(s)
- Xingming Deng
- Department of Medicine, Division of Hematology/Oncology, University of Florida Shands Cancer Center, Gainesville, FL 32610-3633, USA
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Kotadia S, Kao LR, Comerford SA, Jones RT, Hammer RE, Megraw TL. PP2A-dependent disruption of centrosome replication and cytoskeleton organization in Drosophila by SV40 small tumor antigen. Oncogene 2008; 27:6334-46. [PMID: 18663356 DOI: 10.1038/onc.2008.254] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Viruses of the DNA tumor virus family share the ability to transform vertebrate cells through the action of virus-encoded tumor antigens that interfere with normal cell physiology. They accomplish this very efficiently by inhibiting endogenous tumor suppressor proteins that control cell proliferation and apoptosis. Simian virus 40 (SV40) encodes two oncoproteins, large tumor antigen, which directly inhibits the tumor suppressors p53 and Rb, and small tumor antigen (ST), which interferes with serine/threonine protein phosphatase 2A (PP2A). We have constructed a Drosophila model for SV40 ST expression and show that ST induces supernumerary centrosomes, an activity we also demonstrate in human cells. In early Drosophila embryos, ST also caused increased microtubule stability, chromosome segregation errors, defective assembly of actin into cleavage furrows, cleavage failure, a rise in cyclin E levels and embryonic lethality. Using ST mutants and genetic interaction experiments between ST and PP2A subunit mutations, we show that all of these phenotypes are dependent on ST's interaction with PP2A. These analyses demonstrate the validity and utility of Drosophila as a model for viral oncoprotein function in vivo.
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Affiliation(s)
- S Kotadia
- Department of Pharmacology, The Cecil and Ida Green Center for Reproductive Biology Sciences, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390-9051, USA
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Targeted disruption of the PME-1 gene causes loss of demethylated PP2A and perinatal lethality in mice. PLoS One 2008; 3:e2486. [PMID: 18596935 PMCID: PMC2438471 DOI: 10.1371/journal.pone.0002486] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2008] [Accepted: 05/13/2008] [Indexed: 11/29/2022] Open
Abstract
Background Phosphoprotein phosphatase 2A (PP2A), a major serine-threonine protein phosphatase in eukaryotes, is an oligomeric protein comprised of structural (A) and catalytic (C) subunits to which a variable regulatory subunit (B) can associate. The C subunit contains a methyl ester post-translational modification on its C-terminal leucine residue, which is removed by a specific methylesterase (PME-1). Methylesterification is thought to control the binding of different B subunits to AC dimers, but little is known about its physiological significance in vivo. Methodology/Principal Findings Here, we show that targeted disruption of the PME-1 gene causes perinatal lethality in mice, a phenotype that correlates with a virtually complete loss of the demethylated form of PP2A in the nervous system and peripheral tissues. Interestingly, PP2A catalytic activity over a peptide substrate was dramatically reduced in PME-1(−/−) tissues, which also displayed alterations in phosphoproteome content. Conclusions These findings suggest a role for the demethylated form of PP2A in maintenance of enzyme function and phosphorylation networks in vivo.
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KAM E, NIRUNSUKSIRI W, HAGER B, FLECKMAN P, DALE B. Protein phosphatase activity in human keratinocytes cultured from normal epidermis and epidermis from patients with harlequin ichthyosis. Br J Dermatol 2008. [DOI: 10.1046/j.1365-2133.1997.19802086.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Binker MG, Zhao DY, Pang SJY, Harrison RE. Cytoplasmic linker protein-170 enhances spreading and phagocytosis in activated macrophages by stabilizing microtubules. THE JOURNAL OF IMMUNOLOGY 2007; 179:3780-91. [PMID: 17785815 DOI: 10.4049/jimmunol.179.6.3780] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Activation of macrophages causes increased cell spreading, increased secretion of cytokines and matrix metalloproteinases, and enhanced phagocytosis. The intracellular mechanisms driving the up-regulation of these activities have not been completely clarified. We observe that classical activation of murine resident peritoneal or RAW 264.7 macrophages with a combination of IFN-gamma and LPS induces an increase in stabilized cytoplasmic microtubules (MTs), measured with an anti-acetylated alpha-tubulin Ab. We examined the mechanism of this MT stabilization and find that macrophage activation causes redistribution of the MT plus-end tracking protein, cytoplasmic linker protein-170 (CLIP-170). CLIP-170 is localized at the distal plus-ends of MTs in resting macrophages, but accumulates along the length of MTs in IFN-gamma/LPS-activated cells. A direct involvement of CLIP-170 in MT stabilization has not been thoroughly established. In this study, we show that expression of a mutant CLIP-170 chimeric protein (dominant-negative CLIP-170-GFP), lacking the MT-binding domain, prevents MT stabilization in activated RAW 264.7 macrophages. Furthermore, we find enhanced CLIP-170 association with MTs and MT stabilization by treating resting macrophages with okadaic acid, implicating the protein phosphatase 2A in CLIP-170 binding and MT stabilization in RAW 264.7 cells. Finally, we observed enhanced cell spreading and phagocytosis in both IFN-gamma/LPS-activated and okadaic acid-treated resting RAW 264.7 cells, which are markedly reduced in activated cells expressing dominant-negative CLIP-170-GFP. These results identify CLIP-170 as a key regulator of MT stabilization and establish a prominent role for stabilized MTs in cell spreading and phagocytosis in activated macrophages.
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Affiliation(s)
- Marcelo G Binker
- Department of Biological Sciences, University of Toronto at Scarborough, Toronto, Ontario, Canada
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Boudreau RTM, Conrad DM, Hoskin DW. Differential involvement of reactive oxygen species in apoptosis caused by the inhibition of protein phosphatase 2A in Jurkat and CCRF-CEM human T-leukemia cells. Exp Mol Pathol 2007; 83:347-56. [PMID: 17936751 DOI: 10.1016/j.yexmp.2007.09.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2007] [Accepted: 09/14/2007] [Indexed: 12/16/2022]
Abstract
A better understanding of dysregulated signaling pathways in cancer cells may suggest novel strategies to prevent tumor development and/or progression. Here we show that Jurkat and CCRF-CEM human T-leukemia cell lines were more sensitive than normal human T cells to the cytotoxic effect of inhibiting protein phosphatase 2A (PP2A). Inhibition of PP2A by okadaic acid (OA) caused T-leukemia cells to die by apoptosis, as indicated by DNA fragmentation, caspase-3 activation, loss of mitochondrial membrane potential (DeltaPsi(m)), and changes in nuclear morphology that were consistent with apoptosis. PP2A might therefore be a useful intracellular target for the treatment of T cell-derived leukemias. We also observed that reactive oxygen species (ROS) were generated in response to PP2A inhibition in T-leukemia cells. However, loss of DeltaPsi(m) that resulted from PP2A inhibition was not prevented by exogenous antioxidants (glutathione and N-acetyl-cysteine), indicating that OA-induced changes in mitochondrial membrane permeability were not a consequence of ROS production. Moreover, exogenous antioxidants protected CCRF-CEM T-leukemia cells from apoptosis caused by PP2A inhibition but failed to prevent OA-induced apoptosis in Jurkat T-leukemia cells, indicating a differential role for ROS in apoptosis caused by PP2A inhibition in two different human T-leukemia cell lines.
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Affiliation(s)
- Robert T M Boudreau
- Department of Microbiology and Immunology, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada B3H 1X5
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Csortos C, Kolosova I, Verin AD. Regulation of vascular endothelial cell barrier function and cytoskeleton structure by protein phosphatases of the PPP family. Am J Physiol Lung Cell Mol Physiol 2007; 293:L843-54. [PMID: 17693486 DOI: 10.1152/ajplung.00120.2007] [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: 12/29/2022] Open
Abstract
Reversible phosphorylation of cytoskeletal and cytoskeleton-associated proteins is a significant element of endothelial barrier function regulation. Therefore, understanding the mechanisms of phosphorylation/dephosphorylation of endothelial cell cytoskeletal proteins is vital to the treatment of severe lung disorders such as high permeability pulmonary edema. In vivo, there is a controlled balance between the activities of protein kinases and phosphatases. Due to various external or internal signals, this balance may be shifted. The actual balances at a given time alter the phosphorylation level of certain proteins with appropriate physiological consequences. The latest information about the structure and regulation of different types of Ser/Thr protein phosphatases participating in the regulation of endothelial cytoskeletal organization and barrier function will be reviewed here.
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Affiliation(s)
- Csilla Csortos
- Department of Medicine, Division of Biological Sciences, The University of Chicago, Chicago, Illinois, USA
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