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Human cancer-associated mutations in the Aα subunit of protein phosphatase 2A increase lung cancer incidence in Aα knock-in and knockout mice. Mol Cell Biol 2011; 31:3832-44. [PMID: 21791616 DOI: 10.1128/mcb.05744-11] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Strong evidence has indicated that protein phosphatase 2A (PP2A) is a tumor suppressor, but a mouse model for testing the tumor suppressor activity was missing. The most abundant forms of trimeric PP2A holoenzyme consist of the scaffolding Aα subunit, one of several regulatory B subunits, and the catalytic Cα subunit. Aα mutations were discovered in a variety of human carcinomas. All carcinoma-associated mutant Aα subunits are defective in binding the B or B and C subunits. Here we describe two knock-in mice expressing cancer-associated Aα point mutants defective in binding B' subunits, one knockout mouse expressing truncated Aα defective in B and C subunit binding, and a floxed mouse for generating conditional Aα knockouts. We found that the cancer-associated Aα mutations increased the incidence of cancer by 50 to 60% in lungs of FVB mice treated with benzopyrene, demonstrating that PP2A acts as a tumor suppressor. We show that the effect of Aα mutation on cancer incidence is dependent on the tumor suppressor p53. The finding that the Aα mutation E64D, which was detected in a human lung carcinoma, increases the lung cancer incidence in mice suggests that this mutation also played a role in the development of the carcinoma in which it was discovered.
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252
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Abstract
A recently identified novel role for PPTR-1, the regulatory subunit of phosphatase 2A, in P granule segregation challenges the belief that P granules are responsible for determining the germline in Caenorhabditis elegans.
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Affiliation(s)
- Matthew R Marcello
- Department of Molecular Genetics, Microbiology and Immunology, UMDNJ-Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
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253
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Wurzenberger C, Gerlich DW. Phosphatases: providing safe passage through mitotic exit. Nat Rev Mol Cell Biol 2011; 12:469-82. [PMID: 21750572 DOI: 10.1038/nrm3149] [Citation(s) in RCA: 236] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The mitosis-to-interphase transition involves dramatic cellular reorganization from a state that supports chromosome segregation to a state that complies with all functions of an interphase cell. This process, termed mitotic exit, depends on the removal of mitotic phosphorylations from a broad range of substrates. Mitotic exit regulation involves inactivation of mitotic kinases and activation of counteracting protein phosphatases. The key mitotic exit phosphatase in budding yeast, Cdc14, is now well understood. By contrast, in animal cells, it is now emerging that mitotic exit relies on distinct regulatory networks, including the protein phosphatases PP1 and PP2A.
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Affiliation(s)
- Claudia Wurzenberger
- Institute of Biochemistry, Department of Biology, Swiss Federal Institute of Technology Zürich (ETHZ), HPM D11.3, Schafmattstrasse 18, 8093 Zürich, Switzerland
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254
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Induction of PP2A Bβ, a regulator of IL-2 deprivation-induced T-cell apoptosis, is deficient in systemic lupus erythematosus. Proc Natl Acad Sci U S A 2011; 108:12443-8. [PMID: 21746932 DOI: 10.1073/pnas.1103915108] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The activity and substrate specificity of the ubiquitously expressed phosphatase PP2A is determined by the type of regulatory (B) subunit that couples to the catalytic/scaffold core of the enzyme. We determined that the Bβ subunit (PPP2R2B) is expressed in resting T cells, its transcription is down-regulated during T-cell activation, and up-regulated in conditions of low IL-2. Specifically, high levels of PP2A Bβ were produced during IL-2 deprivation-induced apoptosis, whereas Fas ligation had no effect. Forced expression of the Bβ subunit in primary human T cells was sufficient to induce apoptosis, whereas silencing using siRNA protected activated T cells from IL-2 withdrawal-induced cell death. Because T-cell apoptosis is known to be altered in T cells from patients with systemic lupus erythematosus, we analyzed the regulation of PP2A Bβ in this autoimmune disease. We found that levels of PP2A Bβ did not increase upon IL-2 deprivation in 50% of the patients. Remarkably, this defect was accompanied by resistance to apoptosis. Importantly, kinetics of cell death were normal in cells of patients that up-regulated PP2A Bβ in a normal manner. We have identified a unique role for the phosphatase PP2A, particularly the holoenzyme formed by PP2A Bβ. Bβ appears to trigger apoptosis of T cells in the absence of IL-2 and probably contributes to the termination of a no-longer-needed immune response. We propose that defective production of PP2A Bβ upon IL-2 deprivation results in apoptosis resistance and longer survival of autoreactive T cells, in a subset of SLE patients.
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255
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Slupe AM, Merrill RA, Strack S. Determinants for Substrate Specificity of Protein Phosphatase 2A. Enzyme Res 2011; 2011:398751. [PMID: 21755039 PMCID: PMC3132988 DOI: 10.4061/2011/398751] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Accepted: 04/28/2011] [Indexed: 12/22/2022] Open
Abstract
Protein phosphatase 2A- (PP2A-) catalyzed dephosphorylation of target substrate proteins is widespread and critical for cellular function. PP2A is predominantly found as a heterotrimeric complex of a catalytic subunit (C), a scaffolding subunit (A), and one member of 4 families of regulatory subunits (B). Substrate specificity of the holoenzyme complex is determined by the subcellular locale the complex is confined to, selective incorporation of the B subunit, interactions with endogenous inhibitory proteins, and specific intermolecular interactions between PP2A and target substrates. Here, we discuss recent studies that have advanced our understanding of the molecular determinants for PP2A substrate specificity.
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Affiliation(s)
- Andrew M Slupe
- Department of Pharmacology, University of Iowa, 2-432 BSB, Iowa City, IA 52242, USA
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256
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Elam CA, Wirschell M, Yamamoto R, Fox LA, York K, Kamiya R, Dutcher SK, Sale WS. An axonemal PP2A B-subunit is required for PP2A localization and flagellar motility. Cytoskeleton (Hoboken) 2011; 68:363-72. [PMID: 21692192 DOI: 10.1002/cm.20519] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Revised: 05/26/2011] [Accepted: 06/03/2011] [Indexed: 11/10/2022]
Abstract
Analysis of Chlamydomonas axonemes revealed that the protein phosphatase, PP2A, is localized to the outer doublet microtubules and is implicated in regulation of dynein-driven motility. We tested the hypothesis that PP2A is localized to the axoneme by a specialized, highly conserved 55-kDa B-type subunit identified in the Chlamydomonas flagellar proteome. The B-subunit gene is defective in the motility mutant pf4. Consistent with our hypothesis, both the B- and C- subunits of PP2A fail to assemble in pf4 axonemes, while the dyneins and other axonemal structures are fully assembled in pf4 axonemes. Two pf4 intragenic revertants were recovered that restore PP2A to the axonemes and re-establish nearly wild-type motility. The revertants confirmed that the slow-swimming Pf4 phenotype is a result of the defective PP2A B-subunit. These results demonstrate that the axonemal B-subunit is, in part, an anchor protein required for PP2A localization and that PP2A is required for normal ciliary motility.
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Affiliation(s)
- Candice A Elam
- Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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257
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Landrieu I, Smet-Nocca C, Amniai L, Louis JV, Wieruszeski JM, Goris J, Janssens V, Lippens G. Molecular implication of PP2A and Pin1 in the Alzheimer's disease specific hyperphosphorylation of Tau. PLoS One 2011; 6:e21521. [PMID: 21731772 PMCID: PMC3121875 DOI: 10.1371/journal.pone.0021521] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Accepted: 05/30/2011] [Indexed: 02/06/2023] Open
Abstract
Background Tau phosphorylation and dephosphorylation regulate in a poorly understood manner its physiological role of microtubule stabilization, and equally its integration in Alzheimer disease (AD) related fibrils. A specific phospho-pattern will result from the balance between kinases and phosphatases. The heterotrimeric Protein Phosphatase type 2A encompassing regulatory subunit PR55/Bα (PP2AT55α) is a major Tau phosphatase in vivo, which contributes to its final phosphorylation state. We use NMR spectroscopy to determine the dephosphorylation rates of phospho-Tau by this major brain phosphatase, and present site-specific and kinetic data for the individual sites including the pS202/pT205 AT8 and pT231 AT180 phospho-epitopes. Methodology/Principal Findings We demonstrate the importance of the PR55/Bα regulatory subunit of PP2A within this enzymatic process, and show that, unexpectedly, phosphorylation at the pT231 AT180 site negatively interferes with the dephosphorylation of the pS202/pT205 AT8 site. This inhibitory effect can be released by the phosphorylation dependent prolyl cis/trans isomerase Pin1. Because the stimulatory effect is lost with the dimeric PP2A core enzyme (PP2AD) or with a phospho-Tau T231A mutant, we propose that Pin1 regulates the interaction between the PR55/Bα subunit and the AT180 phospho-epitope on Tau. Conclusions/Significance Our results show that phosphorylation of T231 (AT180) can negatively influence the dephosphorylation of the pS202/pT205 AT8 epitope, even without an altered PP2A pool. Thus, a priming dephosphorylation of pT231 AT180 is required for efficient PP2AT55α-mediated dephosphorylation of pS202/pT205 AT8. The sophisticated interplay between priming mechanisms reported for certain Tau kinases and the one described here for Tau phosphatase PP2AT55α may contribute to the hyperphosphorylation of Tau observed in AD neurons.
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Affiliation(s)
- Isabelle Landrieu
- CNRS-UMR 8576, Federative Research Institute IFR 147, University of Lille-North of France, Villeneuve d'Ascq, France.
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258
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Kubiak JZ, El Dika M. Canonical and Alternative Pathways in Cyclin-Dependent Kinase 1/Cyclin B Inactivation upon M-Phase Exit in Xenopus laevis Cell-Free Extracts. Enzyme Res 2011; 2011:523420. [PMID: 21755042 PMCID: PMC3132491 DOI: 10.4061/2011/523420] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Revised: 04/01/2011] [Accepted: 04/18/2011] [Indexed: 11/20/2022] Open
Abstract
Cyclin-Dependent Kinase 1 (CDK1) is the major M-phase kinase known also as the M-phase Promoting Factor or MPF. Studies performed during the last decade have shown many details of how CDK1 is regulated and also how it regulates the cell cycle progression. Xenopus laevis cell-free extracts were widely used to elucidate the details and to obtain a global view of the role of CDK1 in M-phase control. CDK1 inactivation upon M-phase exit is a primordial process leading to the M-phase/interphase transition during the cell cycle. Here we discuss two closely related aspects of CDK1 regulation in Xenopus laevis cell-free extracts: firstly, how CDK1 becomes inactivated and secondly, how other actors, like kinases and phosphatases network and/or specific inhibitors, cooperate with CDK1 inactivation to assure timely exit from the M-phase.
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Affiliation(s)
- Jacek Z Kubiak
- Cell Cycle Group, Institute of Genetics & Development, University of Rennes 1, CNRS-UMR 6061, Faculty of Medicine, 2 Avenue Prof. Léon Bernard, CS 34317, 35043 Rennes Cedex, France
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259
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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: 61] [Impact Index Per Article: 4.7] [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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260
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Ye H, Li L, Yin Y. Recent advances in the regulation of brassinosteroid signaling and biosynthesis pathways. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2011; 53:455-68. [PMID: 21554539 DOI: 10.1111/j.1744-7909.2011.01046.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Brassinosteroids (BRs) play important roles in plant growth, development and responses to environmental cues. BRs signal through plasma membrane receptor BRI1 and co-receptor BAK1, and several positive (BSK1, BSU1, PP2A) and negative (BKI1, BIN2 and 14-3-3) regulators to control the activities of BES1 and BZR1 family transcription factors, which regulate the expression of hundreds to thousands of genes for various BR responses. Recent studies identified novel signaling components in the BR pathways and started to establish the detailed mechanisms on the regulation of BR signaling. In addition, the molecular mechanism and transcriptional network through which BES1 and BZR1 control gene expression and various BR responses are beginning to be revealed. BES1 recruits histone demethylases ELF6 and REF6 as well as a transcription elongation factor IWS1 to regulate target gene expression. Identification of BES1 and BZR1 target genes established a transcriptional network for BR response and crosstalk with other signaling pathways. Recent studies also revealed regulatory mechanisms of BRs in many developmental processes and regulation of BR biosynthesis. Here we provide an overview and discuss some of the most recent progress in the regulation of BR signaling and biosynthesis pathways.
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Affiliation(s)
- Huaxun Ye
- Department of Genetics, Development and Cell Biology, Iowa State University, Ames, USA
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261
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Wu G, Wang X, Li X, Kamiya Y, Otegui MS, Chory J. Methylation of a phosphatase specifies dephosphorylation and degradation of activated brassinosteroid receptors. Sci Signal 2011; 4:ra29. [PMID: 21558554 PMCID: PMC4854194 DOI: 10.1126/scisignal.2001258] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Internalization of cell surface receptors, followed by either recycling back to the plasma membrane or degradation, is crucial for receptor homeostasis and signaling. The plant brassinosteroid (BR) receptor, BRASSINOSTEROID INSENSITIVE 1 (BRI1), undergoes constitutive cycling between the plasma membrane and the internal membranes. We show that protein phosphatase 2A (PP2A) dephosphorylated BRI1 and that Arabidopsis thaliana rcn1, a mutant for a PP2A subunit, caused an increase in BRI1 abundance and BR signaling. We report the identification, in A. thaliana, of a suppressor of bri1, sbi1, which caused selective accumulation of BR-activated BRI1, but not the BR co-receptor BAK1 (BRI1-ASSOCIATED KINASE 1), in the membranous compartment. SBI1 mRNA was induced by BRs, and SBI1 encodes a leucine carboxylmethyltransferase (LCMT) that methylated PP2A and controlled its membrane-associated subcellular localization. We propose that BRs increase production of SBI1, which methylates PP2A, thus facilitating its association with activated BRI1. This leads to receptor dephosphorylation and degradation, and thus to the termination of BR signaling.
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Affiliation(s)
- Guang Wu
- Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
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262
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Brestovitsky A, Sharf R, Mittelman K, Kleinberger T. The adenovirus E4orf4 protein targets PP2A to the ACF chromatin-remodeling factor and induces cell death through regulation of SNF2h-containing complexes. Nucleic Acids Res 2011; 39:6414-27. [PMID: 21546548 PMCID: PMC3159439 DOI: 10.1093/nar/gkr231] [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: 12/29/2022] Open
Abstract
The adenovirus E4 open-reading-frame 4 (E4orf4) protein regulates the progression of viral infection and when expressed individually it induces non-classical apoptosis in transformed cells. Here we show that E4orf4 associates with the ATP-dependent chromatin-remodeling factor ACF that consists of a sucrose non fermenting-2h (SNF2h) ATPase and an Acf1 regulatory subunit. Furthermore, E4orf4 targets protein phosphatase 2A (PP2A) to this complex and to chromatin. Obstruction of SNF2h activity inhibits E4orf4-induced cell death, whereas knockdown of Acf1 results in enhanced E4orf4-induced toxicity in both mammalian and yeast cells, and Acf1 overexpression inhibits E4orf4′s ability to downregulate early adenovirus gene expression in the context of viral infection. Knockdown of the Acf1 homolog, WSTF, inhibits E4orf4-induced cell death. Based on these results we suggest that the E4orf4–PP2A complex inhibits ACF and facilitates enhanced chromatin-remodeling activities of other SNF2h-containing complexes, such as WSTF–SNF2h. The resulting switch in chromatin remodeling determines life versus death decisions and contributes to E4orf4 functions during adenovirus infection.
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Affiliation(s)
- Anna Brestovitsky
- Department of Molecular Microbiology, Faculty of Medicine, Technion - Israel Institute of Technology, Bat Galim, Haifa 31096, Israel
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263
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Heidari B, Matre P, Nemie-Feyissa D, Meyer C, Rognli OA, Møller SG, Lillo C. Protein phosphatase 2A B55 and A regulatory subunits interact with nitrate reductase and are essential for nitrate reductase activation. PLANT PHYSIOLOGY 2011; 156:165-72. [PMID: 21436382 PMCID: PMC3091043 DOI: 10.1104/pp.111.172734] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Posttranslational activation of nitrate reductase (NR) in Arabidopsis (Arabidopsis thaliana) and other higher plants is mediated by dephosphorylation at a specific Ser residue in the hinge between the molybdenum cofactor and heme-binding domains. The activation of NR in green leaves takes place after dark/light shifts, and is dependent on photosynthesis. Previous studies using various inhibitors pointed to protein phosphatases sensitive to okadaic acid, including protein phosphatase 2A (PP2A), as candidates for activation of NR. PP2As are heterotrimeric enzymes consisting of a catalytic (C), structural (A), and regulatory (B) subunit. In Arabidopsis there are five, three, and 18 of these subunits, respectively. By using inducible artificial microRNA to simultaneously knock down the three structural subunits we show that PP2A is necessary for NR activation. The structural subunits revealed overlapping functions in the activation process of NR. Bimolecular fluorescence complementation was used to identify PP2A regulatory subunits interacting with NR, and the two B55 subunits were positive. Interactions of NR and B55 were further confirmed by the yeast two-hybrid assay. In Arabidopsis the B55 group consists of the close homologs B55α and B55β. Interestingly, the homozygous double mutant (b55α × b55β) appeared to be lethal, which shows that the B55 group has essential functions that cannot be replaced by other regulatory subunits. Mutants homozygous for mutation in Bβ and heterozygous for mutation in Bα revealed a slower activation rate for NR than wild-type plants, pointing to these subunits as part of a PP2A complex responsible for NR dephosphorylation.
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264
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Mice lacking phosphatase PP2A subunit PR61/B'delta (Ppp2r5d) develop spatially restricted tauopathy by deregulation of CDK5 and GSK3beta. Proc Natl Acad Sci U S A 2011; 108:6957-62. [PMID: 21482799 DOI: 10.1073/pnas.1018777108] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Functional diversity of protein phosphatase 2A (PP2A) enzymes mainly results from their association with distinct regulatory subunits. To analyze the functions of one such holoenzyme in vivo, we generated mice lacking PR61/B'δ (B56δ), a subunit highly expressed in neural tissues. In PR61/B'δ-null mice the microtubule-associated protein tau becomes progressively phosphorylated at pathological epitopes in restricted brain areas, with marked immunoreactivity for the misfolded MC1-conformation but without neurofibrillary tangle formation. Behavioral tests indicated impaired sensorimotor but normal cognitive functions. These phenotypical characteristics were further underscored in PR61/B'δ-null mice mildly overexpressing human tau. PR61/B'δ-containing PP2A (PP2A(T61δ)) poorly dephosphorylates tau in vitro, arguing against a direct dephosphorylation defect. Rather, the activity of glycogen synthase kinase-3β, a major tau kinase, was found increased, with decreased phosphorylation of Ser-9, a putative cyclin-dependent kinase 5 (CDK5) target. Accordingly, CDK5 activity is decreased, and its cellular activator p35, strikingly absent in the affected brain areas. As opposed to tau, p35 is an excellent PP2A(T61δ) substrate. Our data imply a nonredundant function for PR61/B'δ in phospho-tau homeostasis via an unexpected spatially restricted mechanism preventing p35 hyperphosphorylation and its subsequent degradation.
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265
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Shouse GP, Nobumori Y, Panowicz MJ, Liu X. ATM-mediated phosphorylation activates the tumor-suppressive function of B56γ-PP2A. Oncogene 2011; 30:3755-65. [PMID: 21460856 DOI: 10.1038/onc.2011.95] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Protein phosphatase 2A (PP2A) is a family of heterotrimeric protein phosphatases that has a multitude of functions inside the cell, acting through various substrate targets in cell-signaling pathways. Recent evidence suggests that a subset of PP2A holoenzymes function as tumor suppressors and one particular family of B subunits, B56, are implicated in this function. However, the regulatory mechanisms that govern activation of B56-PP2A tumor-suppressive function have not been elucidated. In the present study, we demonstrate that ataxia-telangiectasia mutated (ATM) directly phosphorylates and specifically regulates B56γ3, B56γ2 and B56δ, after DNA damage. We further show that phosphorylation of B56γ3 at Ser510 leads to an increase in B56γ3-PP2A complexes, and direction of PP2A phosphatase activity toward the substrate p53, activating its tumor-suppressive functions. In addition, we found that under cell growth conditions B56γ3 is kept at low levels through the actions of the E3 ubiquitin ligase MDM2, and, importantly, phosphorylation of B56γ3 by ATM leads to upregulation of the protein by blocking MDM2-mediated B56γ3 ubiquitination. Finally, we show that Ser510 phosphorylation significantly enhances the ability of B56γ3 to inhibit cell proliferation and anchorage-independent growth. These results provide mechanistic insight into the regulation of PP2A tumor-suppressive function, and suggest a model for parallel regulation of p53 and B56γ3.
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Affiliation(s)
- G P Shouse
- Department of Biochemistry, University of California, Riverside, USA
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266
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Smet-Nocca C, Broncel M, Wieruszeski JM, Tokarski C, Hanoulle X, Leroy A, Landrieu I, Rolando C, Lippens G, Hackenberger CPR. Identification of O-GlcNAc sites within peptides of the Tau protein and their impact on phosphorylation. MOLECULAR BIOSYSTEMS 2011; 7:1420-9. [PMID: 21327254 DOI: 10.1039/c0mb00337a] [Citation(s) in RCA: 97] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Phosphorylation of the microtubule-associated Tau protein plays a major role in the regulation of its activity of tubulin polymerization and/or stabilization of microtubule assembly. A dysregulation of the phosphorylation/dephosphorylation balance leading to the hyperphosphorylation of Tau proteins in neurons is thought to favor their aggregation into insoluble filaments. This in turn might underlie neuronal death as encountered in many neurodegenerative disorders, including Alzheimer's disease. Another post-translational modification, the O-linked β-N-acetylglucosaminylation (O-GlcNAcylation), controls the phosphorylation state of Tau, although the precise mechanism is not known. Moreover, analytical difficulties have hampered the precise localization of the O-GlcNAc sites on Tau, except for the S400 site that was very recently identified on the basis of ETD-FT-MS. Here, we identify three O-GlcNAc sites by screening a library of small peptides sampling the proline-rich, the microtubule-associated repeats and the carboxy-terminal domains of Tau as potential substrates for the O-β-N-acetylglucosaminyltransferase (OGT). The in vitro activity of the nucleocytoplasmic OGT was assessed by tandem mass spectrometry and NMR spectroscopy. Using phosphorylated peptides, we establish the relationship between phosphate and O-GlcNAc incorporation at these sites. Phosphorylation of neighboring residues S396 and S404 was found to decrease significantly S400 O-GlcNAcylation. Reciprocally, S400 O-GlcNAcylation reduces S404 phosphorylation by the CDK2/cyclinA3 kinase and interrupts the GSK3β-mediated sequential phosphorylation process.
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Affiliation(s)
- Caroline Smet-Nocca
- Unité de Glycobiologie Structurale et Fonctionnelle, CNRS UMR8576, IFR 147, Université de Lille1, 59655 Villeneuve d'Ascq Cedex, France.
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267
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Abstract
Transcription factors are the common convergence points of signal transduction pathways to affect gene transcription. Signal transduction activity results in posttranslational modification (PTM) of transcription factors and the sum of these modifications at any given time point will determine the action of the transcription factor. It has been suggested that these PTMs provide a transcription factor code analogous to the histone code. However, the number and variety of these modifications and the lack of knowledge in general of their dynamics precludes at present a concise view of how combinations of PTMs affect transcription factor function. Also, a single type of PTM such as phosphorylation can have opposing effects on transcription factor activity. Transcription factors of the Forkhead box O (FOXO) class are predominantly regulated through signaling, by phosphoinositide 3-kinase/protein kinase B (also known as AKT) pathway and a reactive oxygen species/c-Jun N-terminal kinase pathway. Both pathways result in increased FOXO phosphorylation yet with opposing result. Whereas PKB-mediated phosphorylation inactivates FOXO, c-Jun N-terminal kinase-mediated phosphorylation results in activation of FOXO. Here we discuss regulation of FOXO transcription factors by phosphorylation as an example for understanding integration of signal transduction at the level of transcription activity.
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268
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Greco TM, Yu F, Guise AJ, Cristea IM. Nuclear import of histone deacetylase 5 by requisite nuclear localization signal phosphorylation. Mol Cell Proteomics 2011; 10:M110.004317. [PMID: 21081666 PMCID: PMC3033682 DOI: 10.1074/mcp.m110.004317] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Histone deacetylase 5 (HDAC5), a class IIa deacetylase, is a prominent regulator of cellular and epigenetic processes that underlie the progression of human disease, ranging from cardiac hypertrophy to cancer. Although it is established that phosphorylation mediates 14-3-3 protein binding and provides the essential link between HDAC5 nucleo-cytoplasmic shuttling and transcriptional repression, thus far only four phospho-acceptor sites have been functionally characterized. Here, using a combinatorial proteomics approach and phosphomutant screening, we present the first evidence that HDAC5 has at least 17 in vivo phosphorylation sites within functional domains, including Ser278 and Ser279 within the nuclear localization signal (NLS), Ser1108 within the nuclear export signal, and Ser755 in deacetylase domain. Global and targeted MS/MS analyses of NLS peptides demonstrated the presence of single (Ser278 and Ser279) and double (Ser278/Ser279) phosphorylations. The double S278/279A mutation showed reduced association with HDAC3, slightly decreased deacetylation activity, and significantly increased cytoplasmic localization compared with wild type HDAC5, whereas the S278A and S1108A phosphomutants were not altered. Live cell imaging revealed a deficiency in nuclear import of S278/279A HDAC5. Phosphomutant stable cell lines confirmed the cellular redistribution of NLS mutants and revealed a more pronounced cytoplasmic localization for the single S279A mutant. Proteomic analysis of immunoisolated S278/279A, S279A, and S259/498A mutants linked altered cellular localization to changes in protein interactions. S278/279A and S279A HDAC5 showed reduced association with the NCoR-HDAC3 nuclear corepressor complex as well as protein kinase D enzymes, which were potentiated in the S259/498A mutant. These results provide the first link between phosphorylation outside the known 14-3-3 sites and downstream changes in protein interactions. Together these studies identify Ser279 as a critical phosphorylation within the NLS involved in the nuclear import of HDAC5, providing a regulatory point in nucleo-cytoplasmic shuttling that may be conserved in other class IIa HDACs-HDAC4 and HDAC9.
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Affiliation(s)
| | | | - Amanda J. Guise
- From the ‡Department of Molecular Biology, Princeton University, Princeton, New Jersey, U.S.A
| | - Ileana M. Cristea
- From the ‡Department of Molecular Biology, Princeton University, Princeton, New Jersey, U.S.A
- § To whom correspondence should be addressed: 210 Lewis Thomas Laboratory, Department of Molecular Biology, Princeton University, Princeton, NJ 08544. Tel.: 6092589417; Fax: 6092584575; E-mail:
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269
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PP2A activates brassinosteroid-responsive gene expression and plant growth by dephosphorylating BZR1. Nat Cell Biol 2011; 13:124-31. [PMID: 21258370 PMCID: PMC3077550 DOI: 10.1038/ncb2151] [Citation(s) in RCA: 338] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2010] [Accepted: 11/17/2010] [Indexed: 11/24/2022]
Abstract
When brassinosteroid (BR) levels are low, the GSK3-like kinase BIN2 phosphorylates and inactivates the BZR1 transcription factor to inhibit growth in plants. BR promotes growth by inducing dephosphorylation of BZR1, but the phosphatase that dephosphorylates BZR1 has remained unknown. Here we identified protein phosphatase 2A (PP2A) as BZR1-interacting proteins using tandem affinity purification. Genetic analyses demonstrated a positive role of PP2A in BR signalling and BZR1 dephosphorylation. Members of the B'regulatory subunits of PP2A directly interact with BZR1's putative PEST domain containing the site of the bzr1-1D mutation. Interaction with and dephosphorylation by PP2A are enhanced by the bzr1-1D mutation, reduced by two intragenic bzr1-1D suppressor mutations, and abolished by deletion of the PEST domain. This study reveals a crucial function of PP2A in dephosphorylating and activating BZR1 and completes the set of core components of the BR-signalling cascade from cell surface receptor kinase to gene regulation in the nucleus.
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270
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Haccard O, Jessus C. Greatwall kinase, ARPP-19 and protein phosphatase 2A: shifting the mitosis paradigm. Results Probl Cell Differ 2011; 53:219-234. [PMID: 21630148 DOI: 10.1007/978-3-642-19065-0_11] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Control of entry into mitosis has long been seen in terms of an explosive activation of cyclin-dependent kinase 1, the mitotic driver ensuring the phosphorylation of hundreds of proteins required for cell division. However, if these phosphorylations are maintained during M-phase, they must be removed when cells exit mitosis. It has been surmised that an "antimitotic" phosphatase must be inhibited to allow mitosis entry and activated for returning to interphase. This chapter discusses a series of recent works conducted on Xenopus egg extracts that provide the answers regarding the identity and the regulation of such a phosphatase. PP2A-B55δ is the major phosphatase controlling exit from mitosis; it is negatively regulated by the kinase Greatwall that phosphorylates the small protein ARPP-19 and converts it into a potent PP2A inhibitor. These findings provide a new element of paramount importance in the control of mitosis.
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Affiliation(s)
- Olivier Haccard
- UMR-CNRS 7622 Biologie du Développement, Université Paris 6, 9 quai Saint-Bernard, 75005 Paris, France
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271
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Yang NY, Fernandez C, Richter M, Xiao Z, Valencia F, Tice DA, Pasquale EB. Crosstalk of the EphA2 receptor with a serine/threonine phosphatase suppresses the Akt-mTORC1 pathway in cancer cells. Cell Signal 2011; 23:201-12. [PMID: 20837138 PMCID: PMC2972709 DOI: 10.1016/j.cellsig.2010.09.004] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Accepted: 09/05/2010] [Indexed: 12/31/2022]
Abstract
Receptor tyrosine kinases of the Eph family play multiple roles in the physiological regulation of tissue homeostasis and in the pathogenesis of various diseases, including cancer. The EphA2 receptor is highly expressed in most cancer cell types, where it has disparate activities that are not well understood. It has been reported that interplay of EphA2 with oncogenic signaling pathways promotes cancer cell malignancy independently of ephrin ligand binding and receptor kinase activity. In contrast, stimulation of EphA2 signaling with ephrin-A ligands can suppress malignancy by inhibiting the Ras-MAP kinase pathway, integrin-mediated adhesion, and epithelial to mesenchymal transition. Here we show that ephrin-A1 ligand-dependent activation of EphA2 decreases the growth of PC3 prostate cancer cells and profoundly inhibits the Akt-mTORC1 pathway, which is hyperactivated due to loss of the PTEN tumor suppressor. Our results do not implicate changes in the activity of Akt upstream regulators (such as Ras family GTPases, PI3 kinase, integrins, or the Ship2 lipid phosphatase) in the observed loss of Akt T308 and S473 phosphorylation downstream of EphA2. Indeed, EphA2 can inhibit Akt phosphorylation induced by oncogenic mutations of not only PTEN but also PI3 kinase. Furthermore, it can decrease the hyperphosphorylation induced by constitutive membrane-targeting of Akt. Our data suggest a novel signaling mechanism whereby EphA2 inactivates the Akt-mTORC1 oncogenic pathway through Akt dephosphorylation mediated by a serine/threonine phosphatase. Ephrin-A1-induced Akt dephosphorylation was observed not only in PC3 prostate cancer cells but also in other cancer cell types. Thus, activation of EphA2 signaling represents a possible new avenue for anti-cancer therapies that exploit the remarkable ability of this receptor to counteract multiple oncogenic signaling pathways.
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Affiliation(s)
- Nai-Ying Yang
- Sanford-Burnham Medical Research Institute, La Jolla, CA, USA
| | | | - Melanie Richter
- Sanford-Burnham Medical Research Institute, La Jolla, CA, USA
| | | | - Fatima Valencia
- Sanford-Burnham Medical Research Institute, La Jolla, CA, USA
| | | | - Elena B. Pasquale
- Sanford-Burnham Medical Research Institute, La Jolla, CA, USA
- University of California San Diego, La Jolla, CA, USA
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272
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Yasutis K, Vignali M, Ryder M, Tameire F, Dighe SA, Fields S, Kozminski KG. Zds2p regulates Swe1p-dependent polarized cell growth in Saccharomyces cerevisiae via a novel Cdc55p interaction domain. Mol Biol Cell 2010; 21:4373-86. [PMID: 20980617 PMCID: PMC3002390 DOI: 10.1091/mbc.e10-04-0326] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 08/20/2010] [Accepted: 10/19/2010] [Indexed: 11/18/2022] Open
Abstract
Deletion of the paralogs ZDS1 and ZDS2 in the budding yeast Saccharomyces cerevisiae causes a mis-regulation of polarized cell growth. Here we show a function for these genes as regulators of the Swe1p (Wee1p) kinase-dependent G2/M checkpoint. We identified a conserved domain in the C-terminus of Zds2p consisting of amino acids 813-912 (hereafter referred to as ZH4 for Zds homology 4) that is required for regulation of Swe1p-dependent polarized bud growth. ZH4 is shown by protein affinity assays to be necessary and sufficient for interaction with Cdc55p, a regulatory subunit of protein phosphatase 2A (PP2A). We hypothesized that the Zds proteins are in a pathway that negatively regulates the Swe1p-dependent G2/M checkpoint via Cdc55p. Supporting this model, deletion of CDC55 rescues the aberrant bud morphology of a zds1Δzds2Δ strain. We also show that expression of ZDS1 or ZDS2 from a strong galactose-inducible promoter can induce mitosis even when the Swe1p-dependent G2/M checkpoint is activated by mis-organization of the actin cytoskeleton. This negative regulation requires the CDC55 gene. Together these data indicate that the Cdc55p/Zds2p module has a function in the regulation of the Swe1p-dependent G2/M checkpoint.
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Affiliation(s)
- Kimberly Yasutis
- *Departments of Biology and
- Cell and Developmental Biology Program, University of Virginia, Charlottesville, VA 22904; and
| | | | | | | | | | - Stanley Fields
- Departments of Genome Sciences and Medicine and
- Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195
| | - Keith G. Kozminski
- *Departments of Biology and
- Cell Biology and
- Cell and Developmental Biology Program, University of Virginia, Charlottesville, VA 22904; and
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273
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Pitman MR, Barr RK, Gliddon BL, Magarey AM, Moretti PAB, Pitson SM. A critical role for the protein phosphatase 2A B'α regulatory subunit in dephosphorylation of sphingosine kinase 1. Int J Biochem Cell Biol 2010; 43:342-7. [PMID: 21075214 DOI: 10.1016/j.biocel.2010.11.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2010] [Revised: 10/20/2010] [Accepted: 11/05/2010] [Indexed: 12/15/2022]
Abstract
Sphingosine kinase 1 (SK1) is an important regulator of cellular signalling that has gained recent attention as a potential target for anti-cancer therapies. SK1 activity, subcellular localization and oncogenic function are regulated by phosphorylation and dephosphorylation at Ser225. ERK1/2 have been identified as the protein kinases responsible for phosphorylation and activation of SK1. Conversely, dephosphorylation and deactivation of SK1 occurs by protein phosphatase 2A (PP2A). Active PP2A, however, is a heterotrimer, composed of tightly associated catalytic and structural subunits that can interact with an array of regulatory subunits, which are critical for determining holoenzyme substrate specificity and subcellular localization. Thus, PP2A represents a large family of holoenzyme complexes with different activities and diverse substrate specificities. To date the regulatory subunit essential for targeting PP2A to SK1 has remained undefined. Here, we demonstrate a critical role for the B'α (B56α/PR61α/PPP2R5A) regulatory subunit of PP2A in SK1 dephosphorylation. B'α was found to interact with the c-terminus of SK1, and reduce SK1 phosphorylation when overexpressed, while having no effect on upstream ERK1/2 activation. siRNA-mediated knockdown of B'α increased SK1 phosphorylation, activity and membrane localization of endogenous SK1. Furthermore, overexpression of B'α blocked agonist-induced translocation of SK1 to the plasma membrane and abrogated SK1-induced neoplastic transformation of NIH3T3 fibroblasts. Thus, the PP2A-B'α holoenzyme appears to function as an important endogenous regulator of SK1.
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Affiliation(s)
- Melissa R Pitman
- Molecular Signalling Laboratory, Centre for Cancer Biology, SA Pathology, Frome Road, Adelaide, South Australia 5000, Australia
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274
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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: 49] [Impact Index Per Article: 3.5] [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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275
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Saha S, Kaur P, Ewing RM. The bait compatibility index: computational bait selection for interaction proteomics experiments. J Proteome Res 2010; 9:4972-81. [PMID: 20731387 DOI: 10.1021/pr100267t] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Protein interaction network maps have been generated for multiple species, making use of large-scale methods such as yeast two-hybrid (Y2H) and affinity purification mass spectrometry (AP-MS). These methods take fundamentally different approaches toward characterizing protein networks, and the resulting data sets provide complementary views of the protein interactome. The specific determinants of the outcome of Y2H and AP-MS experiments, in terms of detection of interacting proteins are, however, poorly understood. Here we show that a statistical model built using sequence- and annotation-based features of bait proteins is able to identify bait features that are significant determinants of the outcome of interaction proteomics experiments. We show that bait features are able to explain in part the disparities observed between Y2H and AP-MS constructed networks and can be used to derive the "bait compatibility index", a numeric score that assesses the compatibility of bait proteins with each technology. Aside from understanding the bias and limitations of interaction proteomics, our approach provides a rational, data-driven method for prioritization of baits for interaction proteomics experiments, an essential requirement for future proteome-wide applications of these technologies.
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Affiliation(s)
- Sudipto Saha
- Center for Proteomics and Bioinformatics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
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276
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Yang J, Phiel C. Functions of B56-containing PP2As in major developmental and cancer signaling pathways. Life Sci 2010; 87:659-66. [PMID: 20934435 DOI: 10.1016/j.lfs.2010.10.003] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Revised: 09/08/2010] [Accepted: 09/23/2010] [Indexed: 12/20/2022]
Abstract
Members of the B'/B56/PR61 family regulatory subunits of PP2A determine the subcellular localization, substrate specificity, and catalytic activity of PP2A in a wide range of biological processes. Here, we summarize the structure and intracellular localization of B56-containing PP2As and review functions of B56-containing PP2As in several major developmental/cancer signaling pathways.
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Affiliation(s)
- Jing Yang
- The Research Institute at Nationwide Children's Hospital, Department of Pediatrics, the Ohio State University, 700 Children's Dr., Columbus, OH, 43205, United States.
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277
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Schmitz MHA, Held M, Janssens V, Hutchins JRA, Hudecz O, Ivanova E, Goris J, Trinkle-Mulcahy L, Lamond AI, Poser I, Hyman AA, Mechtler K, Peters JM, Gerlich DW. Live-cell imaging RNAi screen identifies PP2A-B55alpha and importin-beta1 as key mitotic exit regulators in human cells. Nat Cell Biol 2010; 12:886-93. [PMID: 20711181 PMCID: PMC3839080 DOI: 10.1038/ncb2092] [Citation(s) in RCA: 265] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2010] [Accepted: 07/02/2010] [Indexed: 01/20/2023]
Abstract
When vertebrate cells exit mitosis various cellular structures are re-organized to build functional interphase cells. This depends on Cdk1 (cyclin dependent kinase 1) inactivation and subsequent dephosphorylation of its substrates. Members of the protein phosphatase 1 and 2A (PP1 and PP2A) families can dephosphorylate Cdk1 substrates in biochemical extracts during mitotic exit, but how this relates to postmitotic reassembly of interphase structures in intact cells is not known. Here, we use a live-cell imaging assay and RNAi knockdown to screen a genome-wide library of protein phosphatases for mitotic exit functions in human cells. We identify a trimeric PP2A-B55alpha complex as a key factor in mitotic spindle breakdown and postmitotic reassembly of the nuclear envelope, Golgi apparatus and decondensed chromatin. Using a chemically induced mitotic exit assay, we find that PP2A-B55alpha functions downstream of Cdk1 inactivation. PP2A-B55alpha isolated from mitotic cells had reduced phosphatase activity towards the Cdk1 substrate, histone H1, and was hyper-phosphorylated on all subunits. Mitotic PP2A complexes co-purified with the nuclear transport factor importin-beta1, and RNAi depletion of importin-beta1 delayed mitotic exit synergistically with PP2A-B55alpha. This demonstrates that PP2A-B55alpha and importin-beta1 cooperate in the regulation of postmitotic assembly mechanisms in human cells.
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Affiliation(s)
- Michael H. A. Schmitz
- Institute of Biochemistry, Swiss Federal Institute of Technology Zurich (ETHZ), Schafmattstrasse 18, CH-8093 Zurich, Switzerland
- Marine Biological Laboratory, Woods Hole, MA 02543, USA
| | - Michael Held
- Institute of Biochemistry, Swiss Federal Institute of Technology Zurich (ETHZ), Schafmattstrasse 18, CH-8093 Zurich, Switzerland
- Marine Biological Laboratory, Woods Hole, MA 02543, USA
| | - Veerle Janssens
- Laboratory of Protein Phosphorylation and Proteomics, Department of Molecular Cell Biology, Faculty of Medicine, KU Leuven, Gasthuisberg O&N1, Herestraat 49 Box 901, B-3000 Leuven, Belgium
| | | | - Otto Hudecz
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Elitsa Ivanova
- Laboratory of Protein Phosphorylation and Proteomics, Department of Molecular Cell Biology, Faculty of Medicine, KU Leuven, Gasthuisberg O&N1, Herestraat 49 Box 901, B-3000 Leuven, Belgium
| | - Jozef Goris
- Laboratory of Protein Phosphorylation and Proteomics, Department of Molecular Cell Biology, Faculty of Medicine, KU Leuven, Gasthuisberg O&N1, Herestraat 49 Box 901, B-3000 Leuven, Belgium
| | - Laura Trinkle-Mulcahy
- Department of Cellular & Molecular Medicine and the Ottawa Institute of Systems Biology, University of Ottawa, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada
| | - Angus I. Lamond
- Wellcome Trust Centre for Gene Regulation & Expression, MSI/WTB/JBC Complex, University of Dundee, Dundee, DD1 5EH, UK
| | - Ina Poser
- Max-Planck-Institute for Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany
| | - Anthony A. Hyman
- Max-Planck-Institute for Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany
| | - Karl Mechtler
- Institute of Molecular Pathology, Dr. Bohr-Gasse 7, 1030 Vienna, Austria
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Jan-Michael Peters
- Institute of Molecular Pathology, Dr. Bohr-Gasse 7, 1030 Vienna, Austria
| | - Daniel W. Gerlich
- Institute of Biochemistry, Swiss Federal Institute of Technology Zurich (ETHZ), Schafmattstrasse 18, CH-8093 Zurich, Switzerland
- Marine Biological Laboratory, Woods Hole, MA 02543, USA
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278
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Oleinik NV, Krupenko NI, Krupenko SA. ALDH1L1 inhibits cell motility via dephosphorylation of cofilin by PP1 and PP2A. Oncogene 2010; 29:6233-44. [PMID: 20729910 PMCID: PMC2992098 DOI: 10.1038/onc.2010.356] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Here we report that ALDH1L1 (FDH, a folate enzyme with tumor suppressor-like properties) inhibits cell motility. The underlying mechanism involves F-actin stabilization, re-distribution of cytoplasmic actin towards strong preponderance of filamentous actin, and formation of actin stress fibers. A549 cells expressing FDH demonstrated a much slower recovery of GFP-actin fluorescence in a FRAP assay, as well as an increase in G-actin polymerization and a decrease in F-actin depolymerization rates in pyren-actin fluorescence assays indicating the inhibition of actin dynamics. These effects were associated with robust dephosphorylation of the actin depolymerizing factor cofilin by PP1 and PP2A serine/threonine protein phosphatases but not the cofilin-specific phosphatases slingshot and chronophin. In fact, the PP1/PP2A inhibitor calyculin prevented cofilin dephosphorylation and restored motility. Inhibition of FDH-induced apoptosis by the JNK inhibitor SP600125 or the pan-caspase inhibitor zVAD-fmk did not restore motility or levels of phospho-cofilin, indicating that the observed effects are independent from FDH function in apoptosis. Interestingly, cofilin siRNA or expression of phosphorylation-deficient S3A cofilin mutant resulted in a decrease of G-actin and the actin stress fiber formation, the effects seen upon FDH expression. In contrast, the expression of S3D mutant, mimicking constitutive phosphorylation, prevented these effects further supporting the cofilin-dependent mechanism. Dephosphorylation of cofilin and inhibition of motility in response to FDH can be also prevented by the increased folate in media. Furthermore, folate depletion itself, in the absence of FDH, resulted in cofilin dephosphorylation and inhibition of motility in several cell lines. Our experiments showed that these effects were folate-specific and not a general response to nutrient starvation. Overall, this study demonstrates the presence of distinct intracellular signaling pathways regulating motility in response to folate status and points toward mechanisms involving folates in promoting a malignant phenotype.
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Affiliation(s)
- N V Oleinik
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA
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279
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Structural basis for the glucan phosphatase activity of Starch Excess4. Proc Natl Acad Sci U S A 2010; 107:15379-84. [PMID: 20679247 DOI: 10.1073/pnas.1009386107] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Living organisms utilize carbohydrates as essential energy storage molecules. Starch is the predominant carbohydrate storage molecule in plants while glycogen is utilized in animals. Starch is a water-insoluble polymer that requires the concerted activity of kinases and phosphatases to solubilize the outer surface of the glucan and mediate starch catabolism. All known plant genomes encode the glucan phosphatase Starch Excess4 (SEX4). SEX4 can dephosphorylate both the starch granule surface and soluble phosphoglucans and is necessary for processive starch metabolism. The physical basis for the function of SEX4 as a glucan phosphatase is currently unclear. Herein, we report the crystal structure of SEX4, containing phosphatase, carbohydrate-binding, and C-terminal domains. The three domains of SEX4 fold into a compact structure with extensive interdomain interactions. The C-terminal domain of SEX4 integrally folds into the core of the phosphatase domain and is essential for its stability. The phosphatase and carbohydrate-binding domains directly interact and position the phosphatase active site toward the carbohydrate-binding site in a single continuous pocket. Mutagenesis of the phosphatase domain residue F167, which forms the base of this pocket and bridges the two domains, selectively affects the ability of SEX4 to function as a glucan phosphatase. Together, these results reveal the unique tertiary architecture of SEX4 that provides the physical basis for its function as a glucan phosphatase.
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280
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Yu UY, Ahn JH. Phosphorylation on the PPP2R5D B regulatory subunit modulates the biochemical properties of protein phosphatase 2A. BMB Rep 2010; 43:263-7. [PMID: 20423611 DOI: 10.5483/bmbrep.2010.43.4.263] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
To characterize the biochemical properties of the PP2A regulatory B subunit, PPP2R5D, we analyzed its phosphorylation sites, stoichiometry and effect on holoenzyme activity. PPP2R5D was phosphorylated on Ser-53, Ser-68, Ser-81, and Ser-566 by protein kinase A, and mutations at all four of these sites abolished any significant phosphorylation in vitro. In HEK293 cells, however, the Ser-566 was the major phosphorylation site after PKA activation by forskolin, with marginal phosphorylation on Ser-81. Inhibitory tyrosine phosphorylation on Tyr-307 of the PP2A catalytic C subunit was decreased after forskolin treatment. Kinetic analysis showed that overall PP2A activity was increased with phosphorylation by PPP2R5D phosphorylation. The apparent Km was reduced from 11.25 microM to 1.175 microM with PPP2R5D phosphorylation, resulting in an increase in catalytic activity. These data suggest that PKAmediated activation of PP2A is enabled by PPP2R5D phosphorylation, which modulates the affinity of the PP2A holoenzyme to its physiological substrates.
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Affiliation(s)
- Un Young Yu
- Department of Biochemistry, Ewha Womans University School of Medicine, Seoul 158-710, Korea
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281
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Charest PG, Shen Z, Lakoduk A, Sasaki AT, Briggs SP, Firtel RA. A Ras signaling complex controls the RasC-TORC2 pathway and directed cell migration. Dev Cell 2010; 18:737-49. [PMID: 20493808 DOI: 10.1016/j.devcel.2010.03.017] [Citation(s) in RCA: 120] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Revised: 01/25/2010] [Accepted: 03/03/2010] [Indexed: 11/17/2022]
Abstract
Ras was found to regulate Dictyostelium chemotaxis, but the mechanisms that spatially and temporally control Ras activity during chemotaxis remain largely unknown. We report the discovery of a Ras signaling complex that includes the Ras guanine exchange factor (RasGEF) Aimless, RasGEFH, protein phosphatase 2A (PP2A), and a scaffold designated Sca1. The Sca1/RasGEF/PP2A complex is recruited to the plasma membrane in a chemoattractant- and F-actin-dependent manner and is enriched at the leading edge of chemotaxing cells where it regulates F-actin dynamics and signal relay by controlling the activation of RasC and the downstream target of rapamycin complex 2 (TORC2)-Akt/protein kinase B (PKB) pathway. In addition, PKB and PKB-related PKBR1 phosphorylate Sca1 and regulate the membrane localization of the Sca1/RasGEF/PP2A complex, and thereby RasC activity, in a negative feedback fashion. Thus, our study uncovered a molecular mechanism whereby RasC activity and the spatiotemporal activation of TORC2 are tightly controlled at the leading edge of chemotaxing cells.
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Affiliation(s)
- Pascale G Charest
- Section of Cell and Developmental Biology, Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0380, USA
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282
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Solano-Parada J, Gonzalez-Gonzalez G, Torró LMDP, dos Santos MFB, Espino AM, Burgos M, Osuna A. Effectiveness of intranasal vaccination against Angiostrongylus costaricensis using a serine/threonine phosphatase 2 A synthetic peptide and recombinant antigens. Vaccine 2010; 28:5185-96. [PMID: 20558243 DOI: 10.1016/j.vaccine.2010.05.072] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2009] [Revised: 05/20/2010] [Accepted: 05/28/2010] [Indexed: 01/26/2023]
Abstract
Intranasal immunization was assayed in C57BL/6 mice against Angiostrongylus costaricensis using a synthetic and a recombinant peptide belonging to the catalytic region of the serine/threonine phosphatase 2 A (PP2A) of the parasite. Immunization was carried out with the synthetic peptide (SP) polymerized either with itself or with the beta fraction of the cholera toxin (CTB) and then enclosed in nanocapsules of phosphatidyl choline, cholesterol and Quil A (ISCOM). Another group of mice was immunized with recombinant peptide. Immunization consisted of two intranasal inoculations at two-week intervals, and the challenge with L3 larvae was made one month after the last vaccination. The effectiveness of immunization was evaluated 30 days after infection by analysis of the number of parasites in the arteries of the immunized mice, as well as by measuring spleen sizes in the experimental groups. The response induced was determined by identifying the isotypes of IgG as well as the IgE and IgA specific antigen response. The interleukins produced by the splenocyte culture of the different groups were assessed after exposing them to the peptide used in the immunization. From our results, 60%, 80%, and 100% protection against the A. costaricensis challenge was achieved in mice immunized with polymerized synthetic peptide in ISCOM, synthetic peptide polymerized with the CTB in ISCOM and inclusion bodies respectively. Splenomegaly was found to be less evident in the immunized mice than in the controls. A significant increase in IFN gamma and IL-17 levels was observed in the group with 100% protection. The results showed that vaccination through the nasal mucosa may constitute a useful method of immunization and result in a protective immune response against A. costaricensis.
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Affiliation(s)
- J Solano-Parada
- Institute of Biotechnology, Biochemistry and Molecular Parasitology Group, University of Granada, Edif Mecenas, Campus Fuentenueva, 18071 Granada, Spain
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283
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Roberts KG, Smith AM, McDougall F, Carpenter H, Horan M, Neviani P, Powell JA, Thomas D, Guthridge MA, Perrotti D, Sim ATR, Ashman LK, Verrills NM. Essential requirement for PP2A inhibition by the oncogenic receptor c-KIT suggests PP2A reactivation as a strategy to treat c-KIT+ cancers. Cancer Res 2010; 70:5438-47. [PMID: 20551067 DOI: 10.1158/0008-5472.can-09-2544] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Oncogenic mutations of the receptor tyrosine kinase c-KIT play an important role in the pathogenesis of gastrointestinal stromal tumors, systemic mastocytosis, and some acute myeloid leukemias (AML). Although juxtamembrane mutations commonly detected in gastrointestinal stromal tumor are sensitive to tyrosine kinase inhibitors, the kinase domain mutations frequently encountered in systemic mastocytosis and AML confer resistance and are largely unresponsive to targeted inhibition by the existing agent imatinib. In this study, we show that myeloid cells expressing activated c-KIT mutants that are imatinib sensitive (V560G) or imatinib resistant (D816V) can inhibit the tumor suppressor activity of protein phosphatase 2A (PP2A). This effect was associated with the reduced expression of PP2A structural (A) and regulatory subunits (B55alpha, B56alpha, B56gamma, and B56delta). Overexpression of PP2A-Aalpha in D816V c-KIT cells induced apoptosis and inhibited proliferation. In addition, pharmacologic activation of PP2A by FTY720 reduced proliferation, inhibited clonogenic potential, and induced apoptosis of mutant c-KIT(+) cells, while having no effect on wild-type c-KIT cells or empty vector controls. FTY720 treatment caused the dephosphorylation of the D816V c-KIT receptor and its downstream signaling targets pAkt, pSTAT5, and pERK1/2. Additionally, in vivo administration of FTY720 delayed the growth of V560G and D816V c-KIT tumors, inhibited splenic and bone marrow infiltration, and prolonged survival. Our findings show that PP2A inhibition is essential for c-KIT-mediated tumorigenesis, and that reactivating PP2A may offer an attractive strategy to treat drug-resistant c-KIT(+) cancers.
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Affiliation(s)
- Kathryn G Roberts
- School of Biomedical Sciences, University of Newcastle, Callaghan, New South Wales, Australia
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284
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Yan Y, Cao PT, Greer PM, Nagengast ES, Kolb RH, Mumby MC, Cowan KH. Protein phosphatase 2A has an essential role in the activation of gamma-irradiation-induced G2/M checkpoint response. Oncogene 2010; 29:4317-29. [PMID: 20498628 DOI: 10.1038/onc.2010.187] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
G2/M checkpoint activation after DNA damage results in G2/M cell cycle arrest that allows time for DNA repair before the entry of cells into mitosis. Activation of G2/M checkpoint involves a series of signaling events, which include activation of ataxia telangiectecia-mutated and Rad3-related (ATR) and Chk1 kinases and inhibition of Cdc2/Cyclin B activity. Studies presented in this report show that serine (Ser)/threonine (Thr) protein phosphatase 2A (PP2A) has an important role in G2/M checkpoint activation in response to gamma-irradiation (IR) exposure. Using PP2A inhibitors, as well as siRNA targeting various forms of Ser/Thr protein phosphatases, results presented in this report show that specific PP2A inhibition abrogates IR-induced activation of ATR and Chk1 kinases, as well as phosphorylation of Cdc2-Tyr15, and attenuates IR-induced G2/M arrest. These results suggest an important regulation of PP2A on IR-induced G2/M checkpoint signaling response.
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Affiliation(s)
- Y Yan
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE, USA
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285
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Bollen M, Peti W, Ragusa MJ, Beullens M. The extended PP1 toolkit: designed to create specificity. Trends Biochem Sci 2010; 35:450-8. [PMID: 20399103 DOI: 10.1016/j.tibs.2010.03.002] [Citation(s) in RCA: 381] [Impact Index Per Article: 27.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2010] [Revised: 03/03/2010] [Accepted: 03/04/2010] [Indexed: 01/03/2023]
Abstract
Protein Ser/Thr phosphatase-1 (PP1) catalyzes the majority of eukaryotic protein dephosphorylation reactions in a highly regulated and selective manner. Recent studies have identified an unusually diversified PP1 interactome with the properties of a regulatory toolkit. PP1-interacting proteins (PIPs) function as targeting subunits, substrates and/or inhibitors. As targeting subunits, PIPs contribute to substrate selection by bringing PP1 into the vicinity of specific substrates and by modulating substrate specificity via additional substrate docking sites or blocking substrate-binding channels. Many of the nearly 200 established mammalian PIPs are predicted to be intrinsically disordered, a property that facilitates their binding to a large surface area of PP1 via multiple docking motifs. These novel insights offer perspectives for the therapeutic targeting of PP1 by interfering with the binding of PIPs or substrates.
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Affiliation(s)
- Mathieu Bollen
- Laboratory of Biosignaling & Therapeutics, Department of Molecular Cell Biology, University of Leuven, B-3000 Leuven, Belgium.
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286
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Ogura KI, Okada T, Mitani S, Gengyo-Ando K, Baillie DL, Kohara Y, Goshima Y. Protein phosphatase 2A cooperates with the autophagy-related kinase UNC-51 to regulate axon guidance in Caenorhabditis elegans. Development 2010; 137:1657-67. [PMID: 20392746 DOI: 10.1242/dev.050708] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
UNC-51 is a serine/threonine protein kinase conserved from yeast to humans. The yeast homolog Atg1 regulates autophagy (catabolic membrane trafficking) required for surviving starvation. In C. elegans, UNC-51 regulates the axon guidance of many neurons by a different mechanism than it and its homologs use for autophagy. UNC-51 regulates the subcellular localization (trafficking) of UNC-5, a receptor for the axon guidance molecule UNC-6/Netrin; however, the molecular details of the role for UNC-51 are largely unknown. Here, we report that UNC-51 physically interacts with LET-92, the catalytic subunit of serine/threonine protein phosphatase 2A (PP2A-C), which plays important roles in many cellular functions. A low allelic dose of LET-92 partially suppressed axon guidance defects of weak, but not severe, unc-51 mutants, and a low allelic dose of PP2A regulatory subunits A (PAA-1/PP2A-A) and B (SUR-6/PP2A-B) partially enhanced the weak unc-51 mutants. We also found that LET-92 can work cell-non-autonomously on axon guidance in neurons, and that LET-92 colocalized with UNC-51 in neurons. In addition, PP2A dephosphorylated phosphoproteins that had been phosphorylated by UNC-51. These results suggest that, by forming a complex, PP2A cooperates with UNC-51 to regulate axon guidance by regulating phosphorylation. This is the first report of a serine/threonine protein phosphatase functioning in axon guidance in vivo.
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Affiliation(s)
- Ken-ichi Ogura
- Department of Molecular Pharmacology and Neurobiology, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
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287
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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: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [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, Stanford University School of Medicine, Stanford, CA 94305, USA.
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288
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Saraf A, Oberg EA, Strack S. Molecular determinants for PP2A substrate specificity: charged residues mediate dephosphorylation of tyrosine hydroxylase by the PP2A/B' regulatory subunit. Biochemistry 2010; 49:986-95. [PMID: 20017541 DOI: 10.1021/bi902160t] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Together with protein phosphatase 1, protein phosphatase 2A (PP2A) contributes the bulk of Ser/Thr phosphatase activity in most cell types. The predominant form of PP2A is a heterotrimer of catalytic (C), scaffolding (A), and diverse regulatory subunits (B, B', and B''). We have previously shown that N-terminal phosphorylation sites in tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis, are specifically dephosphorylated by PP2A holoenzymes containing the B'beta regulatory subunit. Here, we identify a Glu residue conserved in B' regulatory subunits that is critical for dephosphorylation and inactivation of tyrosine hydroxylase in vitro and in PC12 cells. According to the PP2A heterotrimer crystal structure, Glu153 (B'beta numbering) abuts the catalytic site on the C subunit, and we demonstrate that Glu153 substitution inhibits multisite TH dephosphorylation without compromising PP2A/B'beta holoenzyme assembly or in vitro dephosphorylation of model substrates. Apart from its role in modulating TH activity, Glu153 is also necessary for PP2A/B'beta-mediated enhancement of nerve growth factor signaling. Furthermore, global phosphoproteome analysis suggests that Glu153 mediates dephosphorylation of most B'beta substrates in PC12 cells. With regard to selectivity determinants in the substrate, we show that B'beta Glu153 recognizes Arg37 and Arg38 in TH to direct dephosphorylation of both upstream (Ser31) and downstream (Ser40) sites. These results provide evidence of a subunit-spanning substrate docking site on the PP2A/B' holoenzyme, in which negatively charged side chains in the regulatory subunit interact with positive charges proximal to phosphorylated residues to mediate site-specific dephosphorylation.
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Affiliation(s)
- Amit Saraf
- Department of Pharmacology, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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289
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Bobulescu IA, Quiñones H, Gisler SM, Di Sole F, Hu MC, Shi M, Zhang J, Fuster DG, Wright N, Mumby M, Moe OW. Acute regulation of renal Na+/H+ exchanger NHE3 by dopamine: role of protein phosphatase 2A. Am J Physiol Renal Physiol 2010; 298:F1205-13. [PMID: 20181665 DOI: 10.1152/ajprenal.00708.2009] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Nephrogenic dopamine is a potent natriuretic paracrine/autocrine hormone that is central for mammalian sodium homeostasis. In the renal proximal tubule, dopamine induces natriuresis partly via inhibition of the sodium/proton exchanger NHE3. The signal transduction pathways and mechanisms by which dopamine inhibits NHE3 are complex and incompletely understood. This manuscript describes the role of the serine/threonine protein phosphatase 2A (PP2A) in the regulation of NHE3 by dopamine. The PP2A regulatory subunit B56δ (coded by the Ppp2r5d gene) directly associates with more than one region of the carboxy-terminal hydrophilic putative cytoplasmic domain of NHE3 (NHE3-cyto), as demonstrated by yeast-two-hybrid, coimmunoprecipitation, blot overlay, and in vitro pull-down assays. Phosphorylated NHE3-cyto is a substrate for purified PP2A in an in vitro dephosphorylation reaction. In cultured renal cells, inhibition of PP2A by either okadaic acid or by overexpression of the simian virus 40 (SV40) small T antigen blocks the ability of dopamine to inhibit NHE3 activity and to reduce surface NHE3 protein. Dopamine-induced NHE3 redistribution is also blocked by okadaic acid ex vivo in rat kidney cortical slices. These studies demonstrate that PP2A is an integral and critical participant in the signal transduction pathway between dopamine receptor activation and NHE3 inhibition.
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Affiliation(s)
- I Alexandru Bobulescu
- Dept. of Internal Medicine, Div. of Nephrology, Univ. of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-8856, USA
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290
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Adenovirus protein E4orf4 induces premature APCCdc20 activation in Saccharomyces cerevisiae by a protein phosphatase 2A-dependent mechanism. J Virol 2010; 84:4798-809. [PMID: 20164229 DOI: 10.1128/jvi.02434-09] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Protein phosphatase 2A (PP2A) has been implicated in cell cycle progression and mitosis; however, the complexity of PP2A regulation via multiple B subunits makes its functional characterization a significant challenge. The human adenovirus protein E4orf4 has been found to induce both high Cdk1 activity and the accumulation of cells in G(2)/M in both mammalian and yeast cells, effects which are largely dependent on the B55/Cdc55 regulatory subunit of PP2A. Thus, E4orf4 represents a unique means by which the function of a specific form of PP2A can be delineated in vivo. In Saccharomyces cerevisiae, only two PP2A regulatory subunits exist, Cdc55 and Rts1. Here, we show that E4orf4-induced toxicity depends on a functional interaction with Cdc55. E4orf4 expression correlates with the inappropriate reduction of Pds1 and Scc1 in S-phase-arrested cells. The unscheduled loss of these proteins suggests the involvement of PP2A(Cdc55) in the regulation of the Cdc20 form of the anaphase-promoting complex (APC). Contrastingly, activity of the Hct1 form of the APC is not induced by E4orf4, as demonstrated by the observed stability of its substrates. We propose that E4orf4, being a Cdc55-specific inhibitor of PP2A, demonstrates the role of PP2A(Cdc55) in regulating APC(Cdc20) activity.
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291
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A PP4 phosphatase complex dephosphorylates RPA2 to facilitate DNA repair via homologous recombination. Nat Struct Mol Biol 2010; 17:365-72. [PMID: 20154705 DOI: 10.1038/nsmb.1769] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2009] [Accepted: 11/25/2009] [Indexed: 12/29/2022]
Abstract
Double-stranded DNA breaks (DSBs) induce a phosphorylation-mediated signaling cascade, but the role of phosphatases in this pathway remains unclear. Here we show that human protein phosphatase 4 (PP4) dephosphorylates replication protein A (RPA) subunit RPA2, regulating its role in the DSB response. PP4R2, a regulatory subunit of PP4, mediates the DNA damage-dependent association between RPA2 and the PP4C catalytic subunit. PP4 efficiently dephosphorylates phospho-RPA2 in vitro, and silencing PP4R2 in cells alters the kinetics and pattern of RPA2 phosphorylation. Depletion of PP4R2 impedes homologous recombination (HR) via inefficient loading of the essential HR factor RAD51, causing an extended G2-M checkpoint and hypersensitivity to DNA damage. Cells expressing phosphomimetic RPA2 mutants have a comparable phenotype, suggesting that PP4-mediated dephosphorylation of RPA2 is necessary for an efficient DNA-damage response. These observations provide new insight into the role and regulation of RPA phosphorylation in HR-mediated repair.
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292
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Narasimhan SD, Mukhopadhyay A, Tissenbaum HA. InAKTivation of insulin/IGF-1 signaling by dephosphorylation. Cell Cycle 2010; 8:3878-84. [PMID: 19901535 DOI: 10.4161/cc.8.23.10072] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Signal transduction pathways are tightly regulated by phosphorylation-dephosphorylation cycles and yet the mammalian genome contains far more genes that encode for protein kinases than protein phosphatases. Therefore, to target specific substrates, many phosphatases associate with distinct regulatory subunits and thereby modulate multiple cellular processes. One such example is the C. elegans PP2A regulatory subunit PPTR-1 that negatively regulates the insulin/insulin-like growth factor signaling pathway to modulate longevity, dauer diapause, fat metabolism and stress resistance. PPTR-1, as well as its mammalian homolog B56beta, specifically target the PP2A enzyme to AKT and mediate the dephosphorylation of this important kinase at a conserved threonine residue. In C. elegans, the major consequence of this modulation is activation of the FOXO transcription factor homolog DAF-16, which in turn regulates transcription of its many target genes involved in longevity and stress resistance. Understanding the function of B56 subunits may have important consequences in diseases such as Type 2 diabetes and cancer where the balance of Akt phosphorylation is deregulated.
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Affiliation(s)
- Sri Devi Narasimhan
- Program in Gene Function and Expression, University of Massachusetts Medical School, Worcester, MA, USA
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293
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Tseng TS, Briggs WR. The Arabidopsis rcn1-1 mutation impairs dephosphorylation of Phot2, resulting in enhanced blue light responses. THE PLANT CELL 2010; 22:392-402. [PMID: 20139163 PMCID: PMC2845423 DOI: 10.1105/tpc.109.066423] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2009] [Revised: 01/09/2010] [Accepted: 01/21/2010] [Indexed: 05/20/2023]
Abstract
Phototropins (phot) sense blue light through the two N-terminal chromophore binding LOV domains and activate the C-terminal kinase domain. The resulting phototropin autophosphorylation is essential for biological activity. We identified the A1 subunit of Ser/Thr protein phosphatase 2A (PP2A) as interacting with full-length phot2 in yeast and also interacting with phot2 in an in vitro protein binding assay. Phenotypic characterizations of a phot1-5 rcn1-1 (for root curling in n-naphthylphthalamic acid1) double mutant, in which phot2 is the only functional phototropin and PP2A activity is reduced, showed enhanced phototropic sensitivity and enhanced blue light-induced stomatal opening, suggesting that PP2A activity is involved in regulating phot2 function. When treated with cantharidin, a chemical inhibitor of PP2A, the phot1-5 mutant exhibited enhanced phot2-mediated phototropic responses like those of the phot1-5 rcn1-1 double mutant. Immunoblot analysis to examine phot2 endogenous phosphorylation levels and in vitro phosphorylation assays of phot2 extracted from plants during dark recovery from blue light exposure confirmed that phot2 is more slowly dephosphorylated in the reduced PP2A activity background than in the wild-type PP2A background, suggesting that phosphorylated phot2 is a substrate of PP2A activity. While reduced PP2A activity enhanced the activity of phot2, it did not enhance either phot1 dephosphorylation or the activity of phot1 in mediating phototropism or stomatal opening.
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294
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PR65, the HEAT-repeat scaffold of phosphatase PP2A, is an elastic connector that links force and catalysis. Proc Natl Acad Sci U S A 2010; 107:2467-72. [PMID: 20133745 DOI: 10.1073/pnas.0914073107] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
PR65 is the two-layered (alpha-alpha solenoid) HEAT-repeat (Huntingtin, elongation factor 3, a subunit of protein phosphatase 2A, PI3 kinase target of rapamycin 1) scaffold of protein phosphatase PP2A. Molecular dynamics simulations predict that, at forces expected in living systems, PR65 undergoes (visco-)elastic deformations in response to pulling/pushing on its ends. At lower forces, smooth global flexural and torsional changes occur via even redistribution of stress along the hydrophobic core of the molecule. At intermediate forces, helix-helix separation along one layer ("fracturing") leads to global relaxation plus loss of contact in the other layer to unstack the affected units. Fracture sites are determined by unusual sequences in contiguous interhelix turns. Normal mode analysis of the heterotrimeric PP2A enzyme reveals that its ambient conformational fluctuations are dominated by elastic deformations of PR65, which introduce a mechanical linkage between the separately bound regulatory and catalytic subunits. PR65-dominated fluctuations of PP2A have the effect of opening and closing the enzyme's substrate binding/catalysis interface, as well as altering the positions of certain catalytic residues. These results suggest that substrate binding/catalysis are sensitive to mechanical force. Force could be imposed from the outside (e.g., in PP2A's response to spindle tension) or arise spontaneously (e.g., in PP2A's interaction with unstructured proteins such as Tau, a microtubule-associated Alzheimer's-implicated protein). The presented example supports the view that conformation and function of protein complexes can be modulated by mechanical energy inputs, as well as by chemical energy inputs from ligand binding. Given that helical-repeat proteins are involved in many cellular processes, the findings also encourage the view that mechanical forces may be of widespread importance.
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295
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Kasten KR, Goetzman HS, Reid MR, Rasper AM, Adediran SG, Robinson CT, Cave CM, Solomkin JS, Lentsch AB, Johannigman JA, Caldwell CC. Divergent adaptive and innate immunological responses are observed in humans following blunt trauma. BMC Immunol 2010; 11:4. [PMID: 20100328 PMCID: PMC2823662 DOI: 10.1186/1471-2172-11-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2009] [Accepted: 01/25/2010] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND The immune response to trauma has traditionally been modeled to consist of the systemic inflammatory response syndrome (SIRS) followed by the compensatory anti-inflammatory response syndrome (CARS). We investigated these responses in a homogenous cohort of male, severe blunt trauma patients admitted to a University Hospital surgical intensive care unit (SICU). After obtaining consent, peripheral blood was drawn up to 96 hours following injury. The enumeration and functionality of both myeloid and lymphocyte cell populations were determined. RESULTS Neutrophil numbers were observed to be elevated in trauma patients as compared to healthy controls. Further, neutrophils isolated from trauma patients had increased raft formation and phospho-Akt. Consistent with this, the neutrophils had increased oxidative burst compared to healthy controls. In direct contrast, blood from trauma patients contained decreased naïve T cell numbers. Upon activation with a T cell specific mitogen, trauma patient T cells produced less IFN-gamma as compared to those from healthy controls. Consistent with these results, upon activation, trauma patient T cells were observed to have decreased T cell receptor mediated signaling. CONCLUSIONS These results suggest that following trauma, there are concurrent and divergent immunological responses. These consist of a hyper-inflammatory response by the innate arm of the immune system concurrent with a hypo-inflammatory response by the adaptive arm.
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Affiliation(s)
- Kevin R Kasten
- Division of Research, Department of Surgery, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0558, USA
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296
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Protein phosphatase 6 interacts with the DNA-dependent protein kinase catalytic subunit and dephosphorylates gamma-H2AX. Mol Cell Biol 2010; 30:1368-81. [PMID: 20065038 DOI: 10.1128/mcb.00741-09] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs) plays a major role in the repair of DNA double-strand breaks (DSBs) by nonhomologous end joining (NHEJ). We have previously shown that DNA-PKcs is autophosphorylated in response to ionizing radiation (IR) and that dephosphorylation by a protein phosphatase 2A (PP2A)-like protein phosphatase (PP2A, PP4, or PP6) regulates the protein kinase activity of DNA-PKcs. Here we report that DNA-PKcs interacts with the catalytic subunits of PP6 (PP6c) and PP2A (PP2Ac), as well as with the PP6 regulatory subunits PP6R1, PP6R2, and PP6R3. Consistent with a role in the DNA damage response, silencing of PP6c by small interfering RNA (siRNA) induced sensitivity to IR and delayed release from the G(2)/M checkpoint. Furthermore, siRNA silencing of either PP6c or PP6R1 led to sustained phosphorylation of histone H2AX on serine 139 (gamma-H2AX) after IR. In contrast, silencing of PP6c did not affect the autophosphorylation of DNA-PKcs on serine 2056 or that of the ataxia-telangiectasia mutated (ATM) protein on serine 1981. We propose that a novel function of DNA-PKcs is to recruit PP6 to sites of DNA damage and that PP6 contributes to the dephosphorylation of gamma-H2AX, the dissolution of IR-induced foci, and release from the G(2)/M checkpoint in vivo.
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297
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Abstract
Bacterial chemotaxis is mediated by two reversible protein modification chemistries: phosphorylation and carboxyl methylation. Attractants bind to membrane chemoreceptors that control the activity of a protein kinase which acts in turn to control flagellar motor activity. Coordinate changes in receptor carboxyl methylation provide a negative feedback mechanism that serves a memory function. Protein carboxyl methylation might play an analogous role in the nervous system. Two protein carboxyl methyltransferases serve to regulate signal transduction pathways in eukaryotic cells. One is highly expressed in the Purkinje layer of the cerebellum where it methyl esterifies prenylated cysteine residues at the carboxyl-termini of Ras-related and heterotrimeric G-proteins. The other is abundant throughout the brain where it methylates the carboxyl-terminus of protein phosphatase 2A. The phosphatase methyltransferase and the protein methylesterase that reverses phosphatase methylation are structurally related to the corresponding bacterial chemotaxis methylating and demethylating enzymes. Recent results indicate that deficiencies in phosphatase methylation play an important role in the etiology of Alzheimer's disease.
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Affiliation(s)
- Zhu Li
- Signum Biosciences, Inc., Monmouth Junction, NJ 08852, USA
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298
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Abstract
The reversible phosphorylation of proteins is accomplished by opposing activities of kinases and phosphatases. Relatively few protein serine/threonine phosphatases (PSPs) control the specific dephosphorylation of thousands of phosphoprotein substrates. Many PSPs, exemplified by protein phosphatase 1 (PP1) and PP2A, achieve substrate specificity and regulation through combinatorial interactions between conserved catalytic subunits and a large number of regulatory subunits. Other PSPs, represented by PP2C and FCP/SCP, contain both catalytic and regulatory domains within the same polypeptide chain. Here, we discuss biochemical and structural investigations that advance the mechanistic understanding of the three major classes of PSPs, with a focus on PP2A.
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Affiliation(s)
- Yigong Shi
- Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
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299
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Matre P, Meyer C, Lillo C. Diversity in subcellular targeting of the PP2A B'eta subfamily members. PLANTA 2009; 230:935-45. [PMID: 19672620 DOI: 10.1007/s00425-009-0998-z] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2009] [Accepted: 07/22/2009] [Indexed: 05/20/2023]
Abstract
Protein phosphatase 2A (PP2A) is a serine/threonine-specific phosphatase comprising a catalytic subunit (C), a scaffolding subunit (A), and a regulatory subunit (B). The B subunits are believed to be responsible for substrate specificity and localization of the PP2A complex. In plants, three families of B subunits exist, i.e. B (B55), B', and B''. Here, we report differential subcellular targeting within the Arabidopsis B'eta subfamily, which consists of the close homologs B'eta, B'theta, B'gamma and B'zeta. Phenotypes of corresponding knockouts were observed, and particularly revealed delayed flowering for the B'eta knockout. The B' subunits were linked to fluorescent tags and transiently expressed in various tissues of onion, tobacco and Arabidopsis. B'eta and B'gamma targeted the cytosol and nucleus. B'zeta localized to the cytoplasm and partly co-localized with mitochondrial markers when the N-terminus was free. Provided its C-terminus was free, the B'theta subunit targeted peroxisomes. The importance of the C-terminal end for peroxisomal targeting was further confirmed by truncation of the C-terminus. The results revealed that the closely related B' subunits are targeting different organelles in plants, and exemplify the usage of the peptide serine-serine-leucine as a PTS1 peroxisomal signaling peptide.
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Affiliation(s)
- Polina Matre
- Faculty of Science and Technology, University of Stavanger, Centre for Organelle Research, 4036 Stavanger, Norway
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300
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Castilho PV, Williams BC, Mochida S, Zhao Y, Goldberg ML. The M phase kinase Greatwall (Gwl) promotes inactivation of PP2A/B55delta, a phosphatase directed against CDK phosphosites. Mol Biol Cell 2009; 20:4777-89. [PMID: 19793917 DOI: 10.1091/mbc.e09-07-0643] [Citation(s) in RCA: 153] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
We have previously shown that Greatwall kinase (Gwl) is required for M phase entry and maintenance in Xenopus egg extracts. Here, we demonstrate that Gwl plays a crucial role in a novel biochemical pathway that inactivates, specifically during M phase, "antimitotic" phosphatases directed against phosphorylations catalyzed by cyclin-dependent kinases (CDKs). A major component of this phosphatase activity is heterotrimeric PP2A containing the B55delta regulatory subunit. Gwl is activated during M phase by Cdk1/cyclin B (MPF), but once activated, Gwl promotes PP2A/B55delta inhibition with no further requirement for MPF. In the absence of Gwl, PP2A/B55delta remains active even when MPF levels are high. The removal of PP2A/B55delta corrects the inability of Gwl-depleted extracts to enter M phase. These findings support the hypothesis that M phase requires not only high levels of MPF function, but also the suppression, through a Gwl-dependent mechanism, of phosphatase(s) that would otherwise remove MPF-driven phosphorylations.
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Affiliation(s)
- Priscila V Castilho
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
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