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Peris I, Romero-Murillo S, Vicente C, Narla G, Odero MD. Regulation and role of the PP2A-B56 holoenzyme family in cancer. Biochim Biophys Acta Rev Cancer 2023; 1878:188953. [PMID: 37437699 DOI: 10.1016/j.bbcan.2023.188953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2023] [Revised: 07/07/2023] [Accepted: 07/08/2023] [Indexed: 07/14/2023]
Abstract
Protein phosphatase 2A (PP2A) inactivation is common in cancer, leading to sustained activation of pro-survival and growth-promoting pathways. PP2A consists of a scaffolding A-subunit, a catalytic C-subunit, and a regulatory B-subunit. The functional complexity of PP2A holoenzymes arises mainly through the vast repertoire of regulatory B-subunits, which determine both their substrate specificity and their subcellular localization. Therefore, a major challenge for developing more effective therapeutic strategies for cancer is to identify the specific PP2A complexes to be targeted. Of note, the development of small molecules specifically directed at PP2A-B56α has opened new therapeutic avenues in both solid and hematological tumors. Here, we focus on the B56/PR61 family of PP2A regulatory subunits, which have a central role in directing PP2A tumor suppressor activity. We provide an overview of the mechanisms controlling the formation and regulation of these complexes, the pathways they control, and the mechanisms underlying their deregulation in cancer.
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Affiliation(s)
- Irene Peris
- Department of Biochemistry and Genetics, University of Navarra, Pamplona, Spain; Centro de Investigación Médica Aplicada (CIMA), University of Navarra, Pamplona, Spain; Instituto de Investigación Sanitaria de Navarra (IdiSNA), Pamplona, Spain.
| | - Silvia Romero-Murillo
- Department of Biochemistry and Genetics, University of Navarra, Pamplona, Spain; Centro de Investigación Médica Aplicada (CIMA), University of Navarra, Pamplona, Spain
| | - Carmen Vicente
- Centro de Investigación Médica Aplicada (CIMA), University of Navarra, Pamplona, Spain; Instituto de Investigación Sanitaria de Navarra (IdiSNA), Pamplona, Spain
| | - Goutham Narla
- Division of Genetic Medicine, Department of Internal Medicine, The University of Michigan Medical School, Ann Arbor, MI, USA
| | - Maria D Odero
- Department of Biochemistry and Genetics, University of Navarra, Pamplona, Spain; Centro de Investigación Médica Aplicada (CIMA), University of Navarra, Pamplona, Spain; Instituto de Investigación Sanitaria de Navarra (IdiSNA), Pamplona, Spain; CIBERONC, Instituto de Salud Carlos III, Madrid, Spain.
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Yu H, Zaveri S, Sattar Z, Schaible M, Perez Gandara B, Uddin A, McGarvey LR, Ohlmeyer M, Geraghty P. Protein Phosphatase 2A as a Therapeutic Target in Pulmonary Diseases. MEDICINA (KAUNAS, LITHUANIA) 2023; 59:1552. [PMID: 37763671 PMCID: PMC10535831 DOI: 10.3390/medicina59091552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 08/22/2023] [Accepted: 08/24/2023] [Indexed: 09/29/2023]
Abstract
New disease targets and medicinal chemistry approaches are urgently needed to develop novel therapeutic strategies for treating pulmonary diseases. Emerging evidence suggests that reduced activity of protein phosphatase 2A (PP2A), a complex heterotrimeric enzyme that regulates dephosphorylation of serine and threonine residues from many proteins, is observed in multiple pulmonary diseases, including lung cancer, smoke-induced chronic obstructive pulmonary disease, alpha-1 antitrypsin deficiency, asthma, and idiopathic pulmonary fibrosis. Loss of PP2A responses is linked to many mechanisms associated with disease progressions, such as senescence, proliferation, inflammation, corticosteroid resistance, enhanced protease responses, and mRNA stability. Therefore, chemical restoration of PP2A may represent a novel treatment for these diseases. This review outlines the potential impact of reduced PP2A activity in pulmonary diseases, endogenous and exogenous inhibitors of PP2A, details the possible PP2A-dependent mechanisms observed in these conditions, and outlines potential therapeutic strategies for treatment. Substantial medicinal chemistry efforts are underway to develop therapeutics targeting PP2A activity. The development of specific activators of PP2A that selectively target PP2A holoenzymes could improve our understanding of the function of PP2A in pulmonary diseases. This may lead to the development of therapeutics for restoring normal PP2A responses within the lung.
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Affiliation(s)
- Howard Yu
- Department of Medicine, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203, USA; (H.Y.); (S.Z.); (Z.S.); (M.S.); (B.P.G.); (A.U.); (L.R.M.)
| | - Sahil Zaveri
- Department of Medicine, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203, USA; (H.Y.); (S.Z.); (Z.S.); (M.S.); (B.P.G.); (A.U.); (L.R.M.)
| | - Zeeshan Sattar
- Department of Medicine, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203, USA; (H.Y.); (S.Z.); (Z.S.); (M.S.); (B.P.G.); (A.U.); (L.R.M.)
| | - Michael Schaible
- Department of Medicine, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203, USA; (H.Y.); (S.Z.); (Z.S.); (M.S.); (B.P.G.); (A.U.); (L.R.M.)
| | - Brais Perez Gandara
- Department of Medicine, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203, USA; (H.Y.); (S.Z.); (Z.S.); (M.S.); (B.P.G.); (A.U.); (L.R.M.)
| | - Anwar Uddin
- Department of Medicine, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203, USA; (H.Y.); (S.Z.); (Z.S.); (M.S.); (B.P.G.); (A.U.); (L.R.M.)
| | - Lucas R. McGarvey
- Department of Medicine, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203, USA; (H.Y.); (S.Z.); (Z.S.); (M.S.); (B.P.G.); (A.U.); (L.R.M.)
| | | | - Patrick Geraghty
- Department of Medicine, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203, USA; (H.Y.); (S.Z.); (Z.S.); (M.S.); (B.P.G.); (A.U.); (L.R.M.)
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Domènech Omella J, Cortesi EE, Verbinnen I, Remmerie M, Wu H, Cubero FJ, Roskams T, Janssens V. A Novel Mouse Model of Combined Hepatocellular-Cholangiocarcinoma Induced by Diethylnitrosamine and Loss of Ppp2r5d. Cancers (Basel) 2023; 15:4193. [PMID: 37627221 PMCID: PMC10453342 DOI: 10.3390/cancers15164193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Revised: 08/11/2023] [Accepted: 08/17/2023] [Indexed: 08/27/2023] Open
Abstract
Primary liver cancer (PLC) can be classified in hepatocellular (HCC), cholangiocarcinoma (CCA), and combined hepatocellular-cholangiocarcinoma (cHCC-CCA). The molecular mechanisms involved in PLC development and phenotype decision are still not well understood. Complete deletion of Ppp2r5d, encoding the B56δ subunit of Protein Phosphatase 2A (PP2A), results in spontaneous HCC development in mice via a c-MYC-dependent mechanism. In the present study, we aimed to examine the role of Ppp2r5d in an independent mouse model of diethylnitrosamine (DEN)-induced hepatocarcinogenesis. Ppp2r5d deletion (heterozygous and homozygous) accelerated HCC development, corroborating its tumor-suppressive function in liver and suggesting Ppp2r5d may be haploinsufficient. Ppp2r5d-deficient HCCs stained positively for c-MYC, consistent with increased AKT activation in pre-malignant and tumor tissues of Ppp2r5d-deficient mice. We also found increased YAP activation in Ppp2r5d-deficient tumors. Remarkably, in older mice, Ppp2r5d deletion resulted in cHCC-CCA development in this model, with the CCA component showing increased expression of progenitor markers (SOX9 and EpCAM). Finally, we observed an upregulation of Ppp2r5d in tumors from wildtype and heterozygous mice, revealing a tumor-specific control mechanism of Ppp2r5d expression, and suggestive of the involvement of Ppp2r5d in a negative feedback regulation restricting tumor growth. Our study highlights the tumor-suppressive role of mouse PP2A-B56δ in both HCC and cHCC-CCA, which may have important implications for human PLC development and targeted treatment.
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Affiliation(s)
- Judit Domènech Omella
- Laboratory of Protein Phosphorylation & Proteomics, Department of Cellular & Molecular Medicine, University of Leuven (KU Leuven), 3000 Leuven, Belgium; (J.D.O.); (I.V.); (M.R.)
| | - Emanuela E. Cortesi
- Translational Cell & Tissue Research, University of Leuven (KU Leuven), 3000 Leuven, Belgium; (E.E.C.); (T.R.)
| | - Iris Verbinnen
- Laboratory of Protein Phosphorylation & Proteomics, Department of Cellular & Molecular Medicine, University of Leuven (KU Leuven), 3000 Leuven, Belgium; (J.D.O.); (I.V.); (M.R.)
| | - Michiel Remmerie
- Laboratory of Protein Phosphorylation & Proteomics, Department of Cellular & Molecular Medicine, University of Leuven (KU Leuven), 3000 Leuven, Belgium; (J.D.O.); (I.V.); (M.R.)
| | - Hanghang Wu
- Department of Immunology, Ophthalmology & ENT, Complutense University School of Medicine, 28040 Madrid, Spain; (H.W.); (F.J.C.)
| | - Francisco J. Cubero
- Department of Immunology, Ophthalmology & ENT, Complutense University School of Medicine, 28040 Madrid, Spain; (H.W.); (F.J.C.)
- Health Research Institute Gregorio Marañón (IiSGM), 28007 Madrid, Spain
- Centre for Biomedical Research, Network on Liver and Digestive Diseases (CIBEREHD), 28029 Madrid, Spain
| | - Tania Roskams
- Translational Cell & Tissue Research, University of Leuven (KU Leuven), 3000 Leuven, Belgium; (E.E.C.); (T.R.)
- Department of Pathology, University Hospitals Leuven (UZ Leuven), 3000 Leuven, Belgium
| | - Veerle Janssens
- Laboratory of Protein Phosphorylation & Proteomics, Department of Cellular & Molecular Medicine, University of Leuven (KU Leuven), 3000 Leuven, Belgium; (J.D.O.); (I.V.); (M.R.)
- KU Leuven Cancer Institute (LKI), 3000 Leuven, Belgium
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Dzinovic I, Winkelmann J, Zech M. Genetic intersection between dystonia and neurodevelopmental disorders: Insights from genomic sequencing. Parkinsonism Relat Disord 2022; 102:131-140. [DOI: 10.1016/j.parkreldis.2022.08.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Revised: 08/12/2022] [Accepted: 08/18/2022] [Indexed: 10/15/2022]
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Dyson JJ, Abbasi F, Varadkar P, McCright B. Growth arrest of PPP2R5C and PPP2R5D double knockout mice indicates a genetic interaction and conserved function for these PP2A B subunits. FASEB Bioadv 2021; 4:273-282. [PMID: 35415460 PMCID: PMC8984082 DOI: 10.1096/fba.2021-00130] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Revised: 12/01/2021] [Accepted: 12/07/2021] [Indexed: 12/03/2022] Open
Abstract
Protein phosphatase 2A (PP2A) is a heterotrimeric phosphatase that controls a wide range of cellular functions. The catalytic activity and intracellular location of PP2A are modulated by its association with regulatory B subunits, including B56 proteins, which are encoded by five separate genes in humans and mice. The specific effects of each B56 protein on PP2A activity and function are largely unknown. As part of an effort to identify specific PP2A–B56 functions, we created knockout strains of B56β, B56δ, and B56ε using CRISPR/Cas9n. We found that none of the individual B56 genes are essential for mouse survival. However, mice that have both B56δ and B56γ inactivated (B56δγ−), arrest fetal development around Day E12. The hearts of B56δγ‐ mice have a single outflow vessel rather than having both an aorta and a pulmonary artery. Thus, there appears to be strong genetic interaction between B56δ and B56γ, and together they are necessary for heart development. Of note, both these proteins have been shown to localize to the nucleus and have the most related peptide sequences of the B56 family members. Our results suggest there are B56 subfamilies, which work in conjunction to regulate specific PP2A functions.
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Affiliation(s)
- Jade J. Dyson
- FDA Center for Biologics Evaluation and Research Silver Spring Maryland USA
| | - Fatima Abbasi
- FDA Center for Biologics Evaluation and Research Silver Spring Maryland USA
| | - Prajakta Varadkar
- FDA Center for Biologics Evaluation and Research Silver Spring Maryland USA
| | - Brent McCright
- FDA Center for Biologics Evaluation and Research Silver Spring Maryland USA
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Protein Phosphatase 2A (PP2A) mutations in brain function, development, and neurologic disease. Biochem Soc Trans 2021; 49:1567-1588. [PMID: 34241636 DOI: 10.1042/bst20201313] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 06/09/2021] [Accepted: 06/11/2021] [Indexed: 12/15/2022]
Abstract
By removing Ser/Thr-specific phosphorylations in a multitude of protein substrates in diverse tissues, Protein Phosphatase type 2A (PP2A) enzymes play essential regulatory roles in cellular signalling and physiology, including in brain function and development. Here, we review current knowledge on PP2A gene mutations causally involved in neurodevelopmental disorders and intellectual disability, focusing on PPP2CA, PPP2R1A and PPP2R5D. We provide insights into the impact of these mutations on PP2A structure, substrate specificity and potential function in neurobiology and brain development.
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Lambrecht C, Ferreira GB, Omella JD, Libbrecht L, DE Vos R, Derua R, Mathieu C, Overbergh L, Waelkens E, Janssens V. Differential Proteomic Analysis of Hepatocellular Carcinomas from Ppp2r5d Knockout Mice and Normal (Knockout) Livers. Cancer Genomics Proteomics 2021; 17:669-685. [PMID: 33099469 DOI: 10.21873/cgp.20222] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 09/13/2020] [Accepted: 09/14/2020] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Hepatocellular carcinoma (HCC) is the major type of primary liver cancer. Mice lacking the tumor-suppressive protein phosphatase 2A subunit B56δ (Ppp2r5d) spontaneously develop HCC, correlating with increased c-MYC oncogenicity. MATERIALS AND METHODS We used two-dimensional difference gel electrophoresis-coupled matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to identify differential proteomes of livers from wild-type, non-cancerous and HCC-affected B56δ knockout mice. RESULTS A total of 23 proteins were differentially expressed/regulated in liver between wild-type and non-cancerous knockout mice, and 119 between non-cancerous and HCC knockout mice ('cancer proteins'). Overlap with our reported differential transcriptome data was poor. Overall, 56% of cancer proteins were reported before in HCC proteomics studies; 44% were novel. Gene Ontology analysis revealed cancer proteins mainly associated with liver metabolism (18%) and mitochondria (15%). Ingenuity Pathway Analysis identified 'cancer' and 'gastrointestinal disease' as top hits. CONCLUSION We identified several proteins for further exploration as novel potential HCC biomarkers, and independently underscored the relevance of Ppp2r5d knockout mice as a valuable hepatocarcinogenesis model.
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Affiliation(s)
- Caroline Lambrecht
- Laboratory of Protein Phosphorylation and Proteomics, Department Cellular and Molecular Medicine, University of Leuven (KU Leuven), Leuven, Belgium
| | - Gabriela Bomfim Ferreira
- Clinical and Experimental Endocrinology, Department Clinical and Experimental Medicine, University of Leuven (KU Leuven), Leuven, Belgium
| | - Judit DomÈnech Omella
- Laboratory of Protein Phosphorylation and Proteomics, Department Cellular and Molecular Medicine, University of Leuven (KU Leuven), Leuven, Belgium
| | - Louis Libbrecht
- Department of Pathology, Université Catholique de Louvain (UCL), Brussels, Belgium
| | - Rita DE Vos
- Translational Cell and Tissue Research, Department Imaging and Pathology, University of Leuven (KU Leuven), Leuven, Belgium
| | - Rita Derua
- Laboratory of Protein Phosphorylation and Proteomics, Department Cellular and Molecular Medicine, University of Leuven (KU Leuven), Leuven, Belgium
| | - Chantal Mathieu
- Clinical and Experimental Endocrinology, Department Clinical and Experimental Medicine, University of Leuven (KU Leuven), Leuven, Belgium
| | - Lut Overbergh
- Clinical and Experimental Endocrinology, Department Clinical and Experimental Medicine, University of Leuven (KU Leuven), Leuven, Belgium
| | - Etienne Waelkens
- Laboratory of Protein Phosphorylation and Proteomics, Department Cellular and Molecular Medicine, University of Leuven (KU Leuven), Leuven, Belgium
| | - Veerle Janssens
- Laboratory of Protein Phosphorylation and Proteomics, Department Cellular and Molecular Medicine, University of Leuven (KU Leuven), Leuven, Belgium .,LKI, KU Leuven Cancer Institute, Leuven, Belgium
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Gao RL, Liu LK, Guo LM, Wang KJ, Liu HP. CqPP2A inhibits white spot syndrome virus infection by up-regulating antimicrobial substances expression in red claw crayfish Cherax quadricarinatus. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2021; 116:103913. [PMID: 33137394 DOI: 10.1016/j.dci.2020.103913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Revised: 10/27/2020] [Accepted: 10/27/2020] [Indexed: 06/11/2023]
Abstract
Protein phosphatase 2A (PP2A) is an important serine/threonine phosphatase, a highly conserved enzyme widely expressed in eukaryotic cells, which accounts for a majority of the serine/threonine phosphatase activity in cells implicated in regulation of immune signaling pathways and antiviral response. However, most of studies about PP2A have been conducted in mammals but few in crustaceans. In this study, two subunits of PP2A (named as CqPP2Ab and CqPP2Ac) were characterized to be involved in white spot syndrome virus (WSSV) infection in the haematopoietic tissue (Hpt) cells from red claw crayfish Cherax quadricarinatus. The open reading frame (ORF) of CqPP2Ab was 1341 bp encoding 446 amino acids with seven WD40 domains, and the ORF of CqPP2Ac was 930 bp encoding 309 amino acids with a PP2Ac domain. Tissue distribution analysis showed that the mRNA transcript of CqPP2Ab and CqPP2Ac were both widely expressed in all the tested tissues with the highest expression in hemocyte, followed by high expression in Hpt. The gene expressions of CqPP2Ab and CqPP2Ac were both significantly down-regulated at 6 h post WSSV infection (6 hpi) in Hpt cells. Importantly, the expression of viral immediate early gene IE1 and late viral gene envelope protein VP28 were both significantly increased post WSSV infection after gene silencing of CqPP2Ab or CqPP2Ac in Hpt cells, suggesting that CqPP2Ab and CqPP2Ac could inhibit WSSV infection in Hpt cells, probably by increasing the antimicrobial substances expression in consideration to the significantly reduced expression of anti-lipopolysaccharide factor, crustin, and lysozyme after gene silencing of CqPP2Ab or CqPP2Ac, respectively. These findings provide a new light on the mechanism of WSSV infection and the antiviral response in crustaceans.
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Affiliation(s)
- Rui-Lin Gao
- State Key Laboratory of Marine Environmental Science, State-Province Joint Engineering Laboratory of Marine Bioproducts and Technology, College of Ocean and Earth Sciences, Xiamen University, Xiamen, 361102, Fujian, China
| | - Ling-Ke Liu
- State Key Laboratory of Marine Environmental Science, State-Province Joint Engineering Laboratory of Marine Bioproducts and Technology, College of Ocean and Earth Sciences, Xiamen University, Xiamen, 361102, Fujian, China
| | - Li-Mei Guo
- State Key Laboratory of Marine Environmental Science, State-Province Joint Engineering Laboratory of Marine Bioproducts and Technology, College of Ocean and Earth Sciences, Xiamen University, Xiamen, 361102, Fujian, China
| | - Ke-Jian Wang
- State Key Laboratory of Marine Environmental Science, State-Province Joint Engineering Laboratory of Marine Bioproducts and Technology, College of Ocean and Earth Sciences, Xiamen University, Xiamen, 361102, Fujian, China
| | - Hai-Peng Liu
- State Key Laboratory of Marine Environmental Science, State-Province Joint Engineering Laboratory of Marine Bioproducts and Technology, College of Ocean and Earth Sciences, Xiamen University, Xiamen, 361102, Fujian, China; Laboratory for Marine Biology and Biotechnology, Pilot National Laboratory for Marine Science and Technology, Qingdao, China.
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Song J, Merrill RA, Usachev AY, Strack S. The X-linked intellectual disability gene product and E3 ubiquitin ligase KLHL15 degrades doublecortin proteins to constrain neuronal dendritogenesis. J Biol Chem 2020; 296:100082. [PMID: 33199366 PMCID: PMC7948412 DOI: 10.1074/jbc.ra120.016210] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 10/27/2020] [Accepted: 11/16/2020] [Indexed: 11/13/2022] Open
Abstract
Proper brain development and function requires finely controlled mechanisms for protein turnover, and disruption of genes involved in proteostasis is a common cause of neurodevelopmental disorders. Kelch-like 15 (KLHL15) is a substrate adaptor for cullin3-containing E3 ubiquitin ligases, and KLHL15 gene mutations were recently described as a cause of severe X-linked intellectual disability. Here, we used a bioinformatics approach to identify a family of neuronal microtubule-associated proteins as KLHL15 substrates, which are themselves critical for early brain development. We biochemically validated doublecortin (DCX), also an X-linked disease protein, and doublecortin-like kinase 1 and 2 as bona fide KLHL15 interactors and mapped KLHL15 interaction regions to their tandem DCX domains. Shared with two previously identified KLHL15 substrates, a FRY tripeptide at the C-terminal edge of the second DCX domain is necessary for KLHL15-mediated ubiquitination of DCX and doublecortin-like kinase 1 and 2 and subsequent proteasomal degradation. Conversely, silencing endogenous KLHL15 markedly stabilizes these DCX domain-containing proteins and prolongs their half-life. Functionally, overexpression of KLHL15 in the presence of WT DCX reduces dendritic complexity of cultured hippocampal neurons, whereas neurons expressing FRY-mutant DCX are resistant to KLHL15. Collectively, our findings highlight the critical importance of the E3 ubiquitin ligase adaptor KLHL15 in proteostasis of neuronal microtubule-associated proteins and identify a regulatory network important for development of the mammalian nervous system.
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Affiliation(s)
- Jianing Song
- Department of Neuroscience and Pharmacology and the Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa, USA
| | - Ronald A Merrill
- Department of Neuroscience and Pharmacology and the Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa, USA
| | - Andrew Y Usachev
- Department of Neuroscience and Pharmacology and the Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa, USA
| | - Stefan Strack
- Department of Neuroscience and Pharmacology and the Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa, USA.
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The Role of MYC and PP2A in the Initiation and Progression of Myeloid Leukemias. Cells 2020; 9:cells9030544. [PMID: 32110991 PMCID: PMC7140463 DOI: 10.3390/cells9030544] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Revised: 02/23/2020] [Accepted: 02/24/2020] [Indexed: 12/18/2022] Open
Abstract
The MYC transcription factor is one of the best characterized PP2A substrates. Deregulation of the MYC oncogene, along with inactivation of PP2A, are two frequent events in cancer. Both proteins are essential regulators of cell proliferation, apoptosis, and differentiation, and they, directly and indirectly, regulate each other’s activity. Studies in cancer suggest that targeting the MYC/PP2A network is an achievable strategy for the clinic. Here, we focus on and discuss the role of MYC and PP2A in myeloid leukemias.
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Biswas D, Cary W, Nolta JA. PPP2R5D-Related Intellectual Disability and Neurodevelopmental Delay: A Review of the Current Understanding of the Genetics and Biochemical Basis of the Disorder. Int J Mol Sci 2020; 21:ijms21041286. [PMID: 32074998 PMCID: PMC7072873 DOI: 10.3390/ijms21041286] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Revised: 02/03/2020] [Accepted: 02/10/2020] [Indexed: 12/14/2022] Open
Abstract
Protein Phosphatase 2 Regulatory Subunit B′ Delta (PPP2R5D)-related intellectual disability (ID) and neurodevelopmental delay results from germline de novo mutations in the PPP2R5D gene. This gene encodes the protein PPP2R5D (also known as the B56 delta subunit), which is an isoform of the subunit family B56 of the enzyme serine/threonine-protein phosphatase 2A (PP2A). Clinical signs include intellectual disability (ID); autism spectrum disorder (ASD); epilepsy; speech problems; behavioral challenges; and ophthalmologic, skeletal, endocrine, cardiac, and genital malformations. The association of defective PP2A activity in the brain with a wide range of severity of ID, along with its role in ASD, Alzheimer’s disease, and Parkinson’s-like symptoms, have recently generated the impetus for further research into mutations within this gene. PP2A, together with protein phosphatase 1 (PP1), accounts for more than 90% of all phospho-serine/threonine dephosphorylations in different tissues. The specificity for a wide variety of substrates is determined through nearly 100 different PP2A holoenzymes that are formed by at least 23 types of regulatory B subunits, and two isoforms each of the catalytic subunit C and the structural subunit A. In the mammalian brain, PP2A-mediated protein dephosphorylation plays an important role in learning and memory. The PPP2R5D subunit is highly expressed in the brain and the PPP2A–PPP2R5D holoenzyme plays an important role in maintaining neurons and regulating neuronal signaling. From 2015 to 2017, 25 individuals with PPP2R5D-related developmental disorder were diagnosed. Since then, Whole-Exome Sequencing (WES) has helped to identify more unrelated individuals clinically diagnosed with a neurodevelopmental disorder with pathological variants of PPP2R5D. In this review, we discuss the current understanding of the clinical and genetic aspects of the disorder in the context of the known functions of the PP2A–PPP2R5D holoenzyme in the brain, as well as the pathogenic mutations in PPP2R5D that lead to deficient PP2A–PPP2R5D dephosphorylation and their implications during development and in the etiology of autism, Parkinson’s disease, Alzheimer’s disease, and so forth. In the future, tools such as transgenic animals carrying pathogenic PPP2R5D mutations, and patient-derived induced pluripotent stem cell lines need to be developed in order to fully understand the effects of these mutations on different neural cell types.
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Affiliation(s)
- Dayita Biswas
- SPARK Program Scholar, Institute for Regenerative Cures, University of California, Sacramento, CA 95817, USA;
| | - Whitney Cary
- Stem Cell Program, UC Davis School of Medicine. The University of California, Sacramento, CA 95817, USA
- UC Davis Gene Therapy Program, University of California, Sacramento, CA 95817, USA
- Correspondence: (W.C.); (J.A.N.)
| | - Jan A. Nolta
- SPARK Program Scholar, Institute for Regenerative Cures, University of California, Sacramento, CA 95817, USA;
- Stem Cell Program, UC Davis School of Medicine. The University of California, Sacramento, CA 95817, USA
- UC Davis Gene Therapy Program, University of California, Sacramento, CA 95817, USA
- Correspondence: (W.C.); (J.A.N.)
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Elgenaidi IS, Spiers JP. Regulation of the phosphoprotein phosphatase 2A system and its modulation during oxidative stress: A potential therapeutic target? Pharmacol Ther 2019; 198:68-89. [PMID: 30797822 DOI: 10.1016/j.pharmthera.2019.02.011] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Accepted: 02/15/2019] [Indexed: 02/06/2023]
Abstract
Phosphoprotein phosphatases are of growing interest in the pathophysiology of many diseases and are often the neglected partner of protein kinases. One family member, PP2A, accounts for dephosphorylation of ~55-70% of all serine/threonine phosphosites. Interestingly, dysregulation of kinase signalling is a hallmark of many diseases in which an increase in oxidative stress is also noted. With this in mind, we assess the evidence to support oxidative stress-mediated regulation of the PP2A system In this article, we first present an overview of the PP2A system before providing an analysis of the regulation of PP2A by endogenous inhibitors, post translational modification, and miRNA. Next, a detailed critique of data implicating reactive oxygen species, ischaemia, ischaemia-reperfusion, and hypoxia in regulating the PP2A holoenzyme and associated regulators is presented. Finally, the pharmacological targeting of PP2A, its endogenous inhibitors, and enzymes responsible for its post-translational modification are covered. There is extensive evidence that oxidative stress modulates multiple components of the PP2A system, however, most of the data pertains to the catalytic subunit of PP2A. Irrespective of the underlying aetiology, free radical-mediated attenuation of PP2A activity is an emerging theme. However, in many instances, a dichotomy exists, which requires clarification and mechanistic insight. Nevertheless, this raises the possibility that pharmacological activation of PP2A, either through small molecule activators of PP2A or CIP2A/SET antagonists may be beneficial in modulating the cellular response to oxidative stress. A better understanding of which, will have wide ranging implications for cancer, heart disease and inflammatory conditions.
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Affiliation(s)
- I S Elgenaidi
- Department of Pharmacology and Therapeutics, Trinity College Dublin, Ireland
| | - J P Spiers
- Department of Pharmacology and Therapeutics, Trinity College Dublin, Ireland.
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13
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Physiologic functions of PP2A: Lessons from genetically modified mice. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2019; 1866:31-50. [DOI: 10.1016/j.bbamcr.2018.07.010] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Revised: 07/11/2018] [Accepted: 07/14/2018] [Indexed: 01/03/2023]
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14
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Lambrecht C, Libbrecht L, Sagaert X, Pauwels P, Hoorne Y, Crowther J, Louis JV, Sents W, Sablina A, Janssens V. Loss of protein phosphatase 2A regulatory subunit B56δ promotes spontaneous tumorigenesis in vivo. Oncogene 2017; 37:544-552. [DOI: 10.1038/onc.2017.350] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 06/08/2017] [Accepted: 07/03/2017] [Indexed: 12/19/2022]
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15
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Hyodo T, Ito S, Asano-Inami E, Chen D, Senga T. A regulatory subunit of protein phosphatase 2A, PPP2R5E, regulates the abundance of microtubule crosslinking factor 1. FEBS J 2017; 283:3662-3671. [PMID: 27521566 DOI: 10.1111/febs.13835] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Revised: 07/24/2016] [Accepted: 08/12/2016] [Indexed: 12/22/2022]
Abstract
Dynamic changes in microtubule organization are regulated by numerous microtubule-associating proteins and their post-translational modification. Microtubule crosslinking factor 1 (MTCL1) is a recently identified protein that regulates microtubule organization. To obtain further insight into its functions, we searched for proteins that associate with it using mass spectrometry analysis. We found that PPP2R5E, a regulatory subunit of protein phosphatase 2A, interacted with MTCL1. Depletion of PPP2R5E reduced the abundance of MTCL1 abundance, whereas exogenous expression of PPP2R5E increased endogenous MTCL1. Furthermore, inhibition of phosphatase activity by okadaic acid reduced MTCL1, which was restored by the addition of the protease inhibitor MG132. Finally, we show that cells depleted of PPP2R5E and MTCL1 exhibited defects in microtubule organization. Our results suggest that the PPP2R5E phosphatase may contribute to microtubule organization by stabilizing MTCL1.
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Affiliation(s)
- Toshinori Hyodo
- Division of Cancer Biology, Nagoya University Graduate School of Medicine, Japan
| | - Satoko Ito
- Division of Cancer Biology, Nagoya University Graduate School of Medicine, Japan
| | - Eri Asano-Inami
- Division of Cancer Biology, Nagoya University Graduate School of Medicine, Japan.,Department of Obstetrics and Gynecology Collaborative Research, Bell Research Center, Nagoya University Graduate School of Medicine, Japan
| | - Dan Chen
- Division of Cancer Biology, Nagoya University Graduate School of Medicine, Japan
| | - Takeshi Senga
- Division of Cancer Biology, Nagoya University Graduate School of Medicine, Japan.
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16
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Rima M, Daghsni M, De Waard S, Gaborit N, Fajloun Z, Ronjat M, Mori Y, Brusés JL, De Waard M. The β 4 subunit of the voltage-gated calcium channel (Cacnb4) regulates the rate of cell proliferation in Chinese Hamster Ovary cells. Int J Biochem Cell Biol 2017; 89:57-70. [PMID: 28587927 DOI: 10.1016/j.biocel.2017.05.032] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Revised: 05/20/2017] [Accepted: 05/30/2017] [Indexed: 01/03/2023]
Abstract
The β subunits of Voltage-Gated Calcium Channel (VGCC) are cytosolic proteins that interact with the VGCC pore -forming subunit and participate in the trafficking of the channel to the cell membrane and in ion influx regulation. β subunits also exert functions independently of their binding to VGCC by translocation to the cell nucleus including the control of gene expression. Mutations of the neuronal Cacnb4 (β4) subunit are linked to human neuropsychiatric disorders including epilepsy and intellectual disabilities. It is believed that the pathogenic phenotype induced by these mutations is associated with channel-independent functions of the β4 subunit. In this report, we investigated the role of β4 subunit in cell proliferation and cell cycle progression and examined whether these functions could be altered by a pathogenic mutation. To this end, stably transfected Chinese Hamster Ovary (CHO-K1) cells expressing either rat full-length β4 or the rat C-terminally truncated epileptic mutant variant β1-481 were generated. The subcellular localization of both proteins differed significantly. Full-length β4 localizes almost exclusively in the cell nucleus and concentrates into the nucleolar compartment, while the C-terminal-truncated β1-481 subunit was less concentrated within the nucleus and absent from the nucleoli. Cell proliferation was found to be reduced by the expression of β4, while it was unaffected by the epileptic mutant. Also, full-length β4 interfered with cell cycle progression by presumably preventing cells from entering the S-phase via a mechanism that partially involves endogenous B56δ, a regulatory subunit of the phosphatase 2A (PP2A) that binds β4 but not β1-481. Analysis of β4 subcellular distribution during the cell cycle revealed that the protein is highly expressed in the nucleus at the G1/S transition phase and that it is translocated out of the nucleus during chromatin condensation and cell division. These results suggest that nuclear accumulation of β4 at the G1/S transition phase affects the progression into S-phase resulting in a decrease in the rate of cell proliferation. Regulation of the cell cycle exit is a critical step in determining the number of neuronal precursors and neuronal differentiation suggesting that mutations of the β4 subunit could affect neural development and formation of the mature central nervous system.
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Affiliation(s)
- Mohamad Rima
- INSERM UMR1087, LabEx Ion Channels Science and Therapeutics, Institut du Thorax, Nantes, F-44000 France; CNRS, UMR6291, Nantes, F-44000 France; Azm Center for Research in Biotechnology and its Application, Lebanese University, 1300, Tripoli, Lebanon
| | - Marwa Daghsni
- INSERM UMR1087, LabEx Ion Channels Science and Therapeutics, Institut du Thorax, Nantes, F-44000 France; CNRS, UMR6291, Nantes, F-44000 France; Université de Tunis El Manar, Faculté de Médecine de Tunis, LR99ES10 Laboratoire de Génétique Humaine, 1007, Tunis, Tunisia
| | - Stephan De Waard
- INSERM UMR1087, LabEx Ion Channels Science and Therapeutics, Institut du Thorax, Nantes, F-44000 France; CNRS, UMR6291, Nantes, F-44000 France; Université de Nantes, Nantes, F-44000 France
| | - Nathalie Gaborit
- INSERM UMR1087, LabEx Ion Channels Science and Therapeutics, Institut du Thorax, Nantes, F-44000 France; CNRS, UMR6291, Nantes, F-44000 France; Université de Nantes, Nantes, F-44000 France
| | - Ziad Fajloun
- Azm Center for Research in Biotechnology and its Application, Lebanese University, 1300, Tripoli, Lebanon; Faculty of Sciences III, Lebanese University, 1300, Tripoli, Lebanon
| | - Michel Ronjat
- INSERM UMR1087, LabEx Ion Channels Science and Therapeutics, Institut du Thorax, Nantes, F-44000 France; CNRS, UMR6291, Nantes, F-44000 France; Université de Nantes, Nantes, F-44000 France
| | - Yasuo Mori
- Laboratory of Molecular Biology, Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan
| | - Juan L Brusés
- Department of Natural Sciences, Mercy College, Dobbs Ferry, NY 10522, USA
| | - Michel De Waard
- INSERM UMR1087, LabEx Ion Channels Science and Therapeutics, Institut du Thorax, Nantes, F-44000 France; CNRS, UMR6291, Nantes, F-44000 France; Université de Nantes, Nantes, F-44000 France.
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17
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Shen Y, Dong LF, Zhou RM, Yao J, Song YC, Yang H, Jiang Q, Yan B. Role of long non-coding RNA MIAT in proliferation, apoptosis and migration of lens epithelial cells: a clinical and in vitro study. J Cell Mol Med 2016; 20:537-48. [PMID: 26818536 PMCID: PMC4759467 DOI: 10.1111/jcmm.12755] [Citation(s) in RCA: 96] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2015] [Accepted: 11/06/2015] [Indexed: 12/18/2022] Open
Abstract
Age‐related cataract is among the most common chronic disorders of ageing and is the world's leading blinding disorder. Long non‐coding RNAs play important roles in several biological processes and complicated diseases. However, the role of lncRNAs in the setting of cataract is still unknown. Here, we extracted total RNAs from the transparent and age‐matched cataractous human lenses, and determined lncRNA expression profiles using microarray analysis. We found that 38 lncRNAs were differentially expressed between transparent and cataractous lenses. 17 of 20 differentially expressed lncRNAs were further verified by quantitative RT‐PCRs. One top abundant lncRNA, MIAT, was specifically up‐regulated both in the plasma fraction of whole blood and aqueous humor of cataract patients. MIAT knockdown could affect the proliferation, apoptosis and migration of Human lens epithelial cells (HLECs) upon oxidative stress. Posterior capsule opacification (PCO) is a common complication of cataract surgery, which is associated with abnormal production of inflammatory factors. MIAT knockdown could repress tumour necrosis factor‐α‐induced abnormal proliferation and migration of HLECs, suggesting a potential role of MIAT in PCO‐related pathological process. Moreover, we found that MIAT acted as a ceRNA, and formed a feedback loop with Akt and miR‐150‐5p to regulate HLEC function. Collectively, this study provides a novel insight into the pathogenesis of age‐related cataract.
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Affiliation(s)
- Yi Shen
- Eye Hospital, Nanjing Medical University, Nanjing, China
| | - Ling-Feng Dong
- Eye Hospital, Nanjing Medical University, Nanjing, China.,The Fourth School of Clinical Medicine, Nanjing Medical University, Nanjing, China
| | - Rong-Mei Zhou
- Eye Hospital, Nanjing Medical University, Nanjing, China.,The Fourth School of Clinical Medicine, Nanjing Medical University, Nanjing, China
| | - Jin Yao
- Eye Hospital, Nanjing Medical University, Nanjing, China.,The Fourth School of Clinical Medicine, Nanjing Medical University, Nanjing, China
| | - Yu-Chen Song
- The Fourth School of Clinical Medicine, Nanjing Medical University, Nanjing, China
| | - Hong Yang
- The Fourth School of Clinical Medicine, Nanjing Medical University, Nanjing, China
| | - Qin Jiang
- Eye Hospital, Nanjing Medical University, Nanjing, China.,The Fourth School of Clinical Medicine, Nanjing Medical University, Nanjing, China
| | - Biao Yan
- The Fourth School of Clinical Medicine, Nanjing Medical University, Nanjing, China
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18
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Shang L, Henderson LB, Cho MT, Petrey DS, Fong CT, Haude KM, Shur N, Lundberg J, Hauser N, Carmichael J, Innis J, Schuette J, Wu YW, Asaikar S, Pearson M, Folk L, Retterer K, Monaghan KG, Chung WK. De novo missense variants in PPP2R5D are associated with intellectual disability, macrocephaly, hypotonia, and autism. Neurogenetics 2015; 17:43-9. [PMID: 26576547 DOI: 10.1007/s10048-015-0466-9] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 10/22/2015] [Indexed: 12/19/2022]
Abstract
Protein phosphatase 2A (PP2A) is a heterotrimeric protein serine/threonine phosphatase and is involved in a broad range of cellular processes. PPP2R5D is a regulatory B subunit of PP2A and plays an important role in regulating key neuronal and developmental regulation processes such as PI3K/AKT and glycogen synthase kinase 3 beta (GSK3β)-mediated cell growth, chromatin remodeling, and gene transcriptional regulation. Using whole-exome sequencing (WES), we identified four de novo variants in PPP2R5D in a total of seven unrelated individuals with intellectual disability (ID) and other shared clinical characteristics, including autism spectrum disorder, macrocephaly, hypotonia, seizures, and dysmorphic features. Among the four variants, two have been previously reported and two are novel. All four amino acids are highly conserved among the PP2A subunit family, and all change a negatively charged acidic glutamic acid (E) to a positively charged basic lysine (K) and are predicted to disrupt the PP2A subunit binding and impair the dephosphorylation capacity. Our data provides further support for PPP2R5D as a genetic cause of ID.
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Affiliation(s)
- Linshan Shang
- Department of Pediatrics, Columbia University Medical Center, New York, NY, USA
| | | | | | - Donald S Petrey
- Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, New York, NY, USA
| | - Chin-To Fong
- University of Rochester Medical Center, Rochester, NY, USA
| | | | | | | | | | | | - Jeffrey Innis
- Division of Pediatric Genetics, University of Michigan Health System, Ann Arbor, MI, USA
- Department of Human Genetics, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Jane Schuette
- Division of Pediatric Genetics, University of Michigan Health System, Ann Arbor, MI, USA
- Department of Human Genetics, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Yvonne W Wu
- Departments of Neurology and Pediatrics, University of California San Francisco, San Francisco, CA, USA
| | | | | | | | | | | | - Wendy K Chung
- Department of Pediatrics, Columbia University Medical Center, New York, NY, USA.
- Department of Medicine, Columbia University Medical Center, New York, NY, USA.
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19
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Chu D, Tan J, Xie S, Jin N, Yin X, Gong CX, Iqbal K, Liu F. GSK-3β is Dephosphorylated by PP2A in a Leu309 Methylation-Independent Manner. J Alzheimers Dis 2015; 49:365-75. [DOI: 10.3233/jad-150497] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Dandan Chu
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Co-innovation Center of Neuroregeneration, Nantong, PR China
| | - Jianxin Tan
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Co-innovation Center of Neuroregeneration, Nantong, PR China
| | - Shutao Xie
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Co-innovation Center of Neuroregeneration, Nantong, PR China
- Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Nana Jin
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Co-innovation Center of Neuroregeneration, Nantong, PR China
- Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Xiaomin Yin
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Co-innovation Center of Neuroregeneration, Nantong, PR China
| | - Cheng-Xin Gong
- Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Khalid Iqbal
- Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Fei Liu
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Co-innovation Center of Neuroregeneration, Nantong, PR China
- Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
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20
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Houge G, Haesen D, Vissers LELM, Mehta S, Parker MJ, Wright M, Vogt J, McKee S, Tolmie JL, Cordeiro N, Kleefstra T, Willemsen MH, Reijnders MRF, Berland S, Hayman E, Lahat E, Brilstra EH, van Gassen KLI, Zonneveld-Huijssoon E, de Bie CI, Hoischen A, Eichler EE, Holdhus R, Steen VM, Døskeland SO, Hurles ME, FitzPatrick DR, Janssens V. B56δ-related protein phosphatase 2A dysfunction identified in patients with intellectual disability. J Clin Invest 2015; 125:3051-62. [PMID: 26168268 DOI: 10.1172/jci79860] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Accepted: 05/27/2015] [Indexed: 12/17/2022] Open
Abstract
Here we report inherited dysregulation of protein phosphatase activity as a cause of intellectual disability (ID). De novo missense mutations in 2 subunits of serine/threonine (Ser/Thr) protein phosphatase 2A (PP2A) were identified in 16 individuals with mild to severe ID, long-lasting hypotonia, epileptic susceptibility, frontal bossing, mild hypertelorism, and downslanting palpebral fissures. PP2A comprises catalytic (C), scaffolding (A), and regulatory (B) subunits that determine subcellular anchoring, substrate specificity, and physiological function. Ten patients had mutations within a highly conserved acidic loop of the PPP2R5D-encoded B56δ regulatory subunit, with the same E198K mutation present in 6 individuals. Five patients had mutations in the PPP2R1A-encoded scaffolding Aα subunit, with the same R182W mutation in 3 individuals. Some Aα cases presented with large ventricles, causing macrocephaly and hydrocephalus suspicion, and all cases exhibited partial or complete corpus callosum agenesis. Functional evaluation revealed that mutant A and B subunits were stable and uncoupled from phosphatase activity. Mutant B56δ was A and C binding-deficient, while mutant Aα subunits bound B56δ well but were unable to bind C or bound a catalytically impaired C, suggesting a dominant-negative effect where mutant subunits hinder dephosphorylation of B56δ-anchored substrates. Moreover, mutant subunit overexpression resulted in hyperphosphorylation of GSK3β, a B56δ-regulated substrate. This effect was in line with clinical observations, supporting a correlation between the ID degree and biochemical disturbance.
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21
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Restricted protein phosphatase 2A targeting by Merkel cell polyomavirus small T antigen. J Virol 2015; 89:4191-200. [PMID: 25631078 DOI: 10.1128/jvi.00157-15] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
UNLABELLED Merkel cell polyomavirus (MCV) is a newly discovered human cancer virus encoding a small T (sT) oncoprotein. We performed MCV sT FLAG-affinity purification followed by mass spectroscopy (MS) analysis, which identified several protein phosphatases (PP), including PP2A A and C subunits and PP4C, as potential cellular interacting proteins. PP2A targeting is critical for the transforming properties of nonhuman polyomaviruses, such as simian virus 40 (SV40), but is not required for MCV sT-induced rodent cell transformation. We compared similarities and differences in PP2A binding between MCV and SV40 sT. While SV40 sT coimmunopurified with subunits PP2A Aα and PP2A C, MCV sT coimmunopurified with PP2A Aα, PP2A Aβ, and PP2A C. Scanning alanine mutagenesis at 29 sites across the MCV sT protein revealed that PP2A-binding domains lie on the opposite molecular surface from a previously described large T stabilization domain (LSD) loop that binds E3 ligases, such as Fbw7. MCV sT-PP2A interactions can be functionally distinguished by mutagenesis from MCV sT LSD-dependent 4E-BP1 hyperphosphorylation and viral DNA replication enhancement. MCV sT has a restricted range for PP2A B subunit substitution, inhibiting only the assembly of B56α into the phosphatase holoenzyme. In contrast, SV40 sT inhibits the assembly of B55α, B56α and B56ε into PP2A. We conclude that MCV sT is required for Merkel cell carcinoma growth, but its in vitro transforming activity depends on LSD interactions rather than PP2A targeting. IMPORTANCE Merkel cell polyomavirus is a newly discovered human cancer virus that promotes cancer, in part, through expression of its small T (sT) oncoprotein. Animal polyomavirus sT oncoproteins have been found to cause experimental tumors by blocking the activities of a group of phosphatases called protein phosphatase 2A (PP2A). Our structural analysis reveals that MCV sT also displaces the B subunit of PP2A to inhibit PP2A activity. MCV sT, however, only displaces a restricted subset of PP2A B subunits, which is insufficient to cause tumor cell formation in vitro. MCV sT instead transforms tumor cells through another region called the large T stabilization domain. The PP2A targeting and transforming activities lie on opposite faces of the MCV sT molecule and can be genetically separated from each other.
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22
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Liu X, Liu Q, Fan Y, Wang S, Liu X, Zhu L, Liu M, Tang H. Downregulation of PPP2R5E expression by miR-23a suppresses apoptosis to facilitate the growth of gastric cancer cells. FEBS Lett 2014; 588:3160-9. [DOI: 10.1016/j.febslet.2014.05.068] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Revised: 05/22/2014] [Accepted: 05/22/2014] [Indexed: 01/29/2023]
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23
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Varadkar P, Despres D, Kraman M, Lozier J, Phadke A, Nagaraju K, Mccright B. The protein phosphatase 2A B56γ regulatory subunit is required for heart development. Dev Dyn 2014; 243:778-90. [PMID: 24425002 DOI: 10.1002/dvdy.24111] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2013] [Revised: 12/16/2013] [Accepted: 12/19/2013] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Protein Phosphatase 2A (PP2A) function is controlled by regulatory subunits that modulate the activity of the catalytic subunit and direct the PP2A complex to specific intracellular locations. To study PP2A's role in signal transduction pathways that control growth and differentiation in vivo, a transgenic mouse lacking the B56γ regulatory subunit of PP2A was made. RESULTS Lack of PP2A activity specific to the PP2A-B56γ holoenzyme, resulted in the formation of an incomplete ventricular septum and a decrease in the number of ventricular cardiomyocytes. During cardiac development, B56γ is expressed in the nucleus of α-actinin-positive cardiomyocytes that contain Z-bands. The pattern of B56γ expression correlated with the cardiomyocyte apoptosis we observed in B56γ-deficient mice during mid to late gestation. In addition to the cardiac phenotypes, mice lacking B56γ have a decrease in locomotive coordination and gripping strength, indicating that B56γ has a role in controlling PP2A activity required for efficient neuromuscular function. CONCLUSIONS PP2A-B56γ activity is required for efficient cardiomyocyte maturation and survival. The PP2A B56γ regulatory subunit controls PP2A substrate specificity in vivo in a manner that cannot be fully compensated for by other B56 subunits.
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Affiliation(s)
- Prajakta Varadkar
- Division of Cellular and Gene Therapies, Center for Biologics Evaluation and Research, FDA, Bethesda, Maryland
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24
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Abstract
Protein phosphatases of the type 2A family (PP2A) represent a major fraction of cellular Ser/Thr phosphatase activity in any given human tissue. In this review, we describe how the holoenzymic nature of PP2A and the existence of several distinct PP2A composing subunits allow for the generation of multiple structurally and functionally different PP2A complexes, explaining why PP2A is involved in the regulation of so many diverse cell biological and physiological processes. Moreover, in human disease, most notably in several cancers and Alzheimer's Disease, PP2A expression and/or activity have been found significantly decreased, underscoring its important functions as a major tumor suppressor and tau phosphatase. Hence, several recent preclinical studies have demonstrated that pharmacological restoration of PP2A activity, as well as pharmacological PP2A inhibition, under certain conditions, may be of significant future therapeutic value.
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25
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Tadmouri A, Kiyonaka S, Barbado M, Rousset M, Fablet K, Sawamura S, Bahembera E, Pernet-Gallay K, Arnoult C, Miki T, Sadoul K, Gory-Faure S, Lambrecht C, Lesage F, Akiyama S, Khochbin S, Baulande S, Janssens V, Andrieux A, Dolmetsch R, Ronjat M, Mori Y, De Waard M. Cacnb4 directly couples electrical activity to gene expression, a process defective in juvenile epilepsy. EMBO J 2012; 31:3730-44. [PMID: 22892567 DOI: 10.1038/emboj.2012.226] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Accepted: 07/17/2012] [Indexed: 12/11/2022] Open
Abstract
Calcium current through voltage-gated calcium channels (VGCC) controls gene expression. Here, we describe a novel signalling pathway in which the VGCC Cacnb4 subunit directly couples neuronal excitability to transcription. Electrical activity induces Cacnb4 association to Ppp2r5d, a regulatory subunit of PP2A phosphatase, followed by (i) nuclear translocation of Cacnb4/Ppp2r5d/PP2A, (ii) association with the tyrosine hydroxylase (TH) gene promoter through the nuclear transcription factor thyroid hormone receptor alpha (TRα), and (iii) histone binding through association of Cacnb4 with HP1γ concomitantly with Ser(10) histone H3 dephosphorylation by PP2A. This signalling cascade leads to TH gene repression by Cacnb4 and is controlled by the state of interaction between the SH3 and guanylate kinase (GK) modules of Cacnb4. The human R482X CACNB4 mutation, responsible for a form of juvenile myoclonic epilepsy, prevents association with Ppp2r5 and nuclear targeting of the complex by altering Cacnb4 conformation. These findings demonstrate that an intact VGCC subunit acts as a repressor recruiting platform to control neuronal gene expression.
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Affiliation(s)
- Abir Tadmouri
- Unité Inserm U, Grenoble Institute of Neuroscience, Université Joseph Fourier, La Tronche, France
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26
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Sents W, Ivanova E, Lambrecht C, Haesen D, Janssens V. The biogenesis of active protein phosphatase 2A holoenzymes: a tightly regulated process creating phosphatase specificity. FEBS J 2012; 280:644-61. [PMID: 22443683 DOI: 10.1111/j.1742-4658.2012.08579.x] [Citation(s) in RCA: 157] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Protein phosphatase type 2A (PP2A) enzymes constitute a large family of Ser/Thr phosphatases with multiple functions in cellular signaling and physiology. The composition of heterotrimeric PP2A holoenzymes, resulting from the combinatorial assembly of a catalytic C subunit, a structural A subunit, and regulatory B-type subunit, provides the essential determinants for substrate specificity, subcellular targeting, and fine-tuning of phosphatase activity, largely explaining why PP2A is functionally involved in so many diverse physiological processes, sometimes in seemingly opposing ways. In this review, we highlight how PP2A holoenzyme biogenesis and enzymatic activity are controlled by a sophisticatedly coordinated network of five PP2A modulators, consisting of α4, phosphatase 2A phosphatase activator (PTPA), leucine carboxyl methyl transferase 1 (LCMT1), PP2A methyl esterase 1 (PME-1) and, potentially, target of rapamycin signaling pathway regulator-like 1 (TIPRL1), which serve to prevent promiscuous phosphatase activity until the holoenzyme is completely assembled. Likewise, these modulators may come into play when PP2A holoenzymes are disassembled following particular cellular stresses. Malfunctioning of these cellular control mechanisms contributes to human disease. The potential therapeutic benefits or pitfalls of interfering with these regulatory mechanisms will be briefly discussed.
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Affiliation(s)
- Ward Sents
- Laboratory of Protein Phosphorylation & Proteomics, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
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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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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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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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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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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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Götz J, Gladbach A, Pennanen L, van Eersel J, Schild A, David D, Ittner LM. Animal models reveal role for tau phosphorylation in human disease. Biochim Biophys Acta Mol Basis Dis 2010; 1802:860-71. [DOI: 10.1016/j.bbadis.2009.09.008] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2009] [Revised: 09/03/2009] [Accepted: 09/07/2009] [Indexed: 12/18/2022]
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Grochola LF, Vazquez A, Bond EE, Würl P, Taubert H, Müller TH, Levine AJ, Bond GL. Recent natural selection identifies a genetic variant in a regulatory subunit of protein phosphatase 2A that associates with altered cancer risk and survival. Clin Cancer Res 2009; 15:6301-8. [PMID: 19773383 DOI: 10.1158/1078-0432.ccr-09-0797] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE A regulated p53-dependent stress response is crucial in suppressing tumor formation and mediating the response to commonly used cancer therapeutics. However, little is known about the human, inherited genetics of this important signaling pathway. EXPERIMENTAL DESIGN Studies of human genetic variants in the p53 tumor suppressor gene and MDM2 oncogene have shown that single nucleotide polymorphisms (SNP) can affect p53 signaling, confer cancer risk, and alter outcome, and also suggest that the pathway is under evolutionary selective pressure. Here, we attempt to accelerate the identification of functional p53 pathway SNPs by incorporating these characteristics into an analysis of 142 genes that are known to affect p53 signaling. RESULTS We report that a genomic scan for recent natural selection denotes that of the 142 genes studied, the PPP2R5E gene that encodes a regulatory subunit of the tumor suppressing protein phosphatase 2A resides in a naturally selected genomic region. We go on to show that a selected SNP in PPP2R5E (epsilon-SNP2) associates with significant allelic differences in the onset (up to 19.2 years; P = 0.0002) and risk (odds ratio, up to 8.1; P = 0.0009) of soft tissue sarcoma development, as well as overall survival (relative risk, up to 3.04; P = 0.026). CONCLUSIONS The PPP2R5E gene is identified as harboring genetic variants that can affect human cancer and are possibly under evolutionary selection pressure.
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Affiliation(s)
- Lukasz F Grochola
- Ludwig Institute for Cancer Research, University of Oxford, Oxford, United Kingdom
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Zwaenepoel K, Louis JV, Goris J, Janssens V. Diversity in genomic organisation, developmental regulation and distribution of the murine PR72/B" subunits of protein phosphatase 2A. BMC Genomics 2008; 9:393. [PMID: 18715506 PMCID: PMC2529318 DOI: 10.1186/1471-2164-9-393] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2008] [Accepted: 08/20/2008] [Indexed: 01/03/2023] Open
Abstract
Background Protein phosphatase 2A (PP2A) is a serine/threonine-specific phosphatase displaying vital functions in growth and development through its role in various signalling pathways. PP2A holoenzymes comprise a core dimer composed of a catalytic C and a structural A subunit, which can associate with a variable B-type subunit. The importance of the B-type subunits for PP2A regulation cannot be overestimated as they determine holoenzyme localisation, activity and substrate specificity. Three B-type subunit families have been identified: PR55/B, PR61/B' and PR72/B", of which the latter is currently the least characterised. Results We deduced the sequences and genomic organisation of the different murine PR72/B" isoforms: three genes encode nine isoforms, five of which are abundantly expressed and give rise to genuine PP2A subunits. Thereby, one novel subunit was identified. Using Northern blotting, we examined the tissue-specific and developmental expression of these subunits. All subunits are highly expressed in heart, suggesting an important cardiac function. Immunohistochemical analysis revealed a striated expression pattern of PR72 and PR130 in heart and skeletal muscle, but not in bladder smooth muscle. The subcellular localisation and cell cycle regulatory ability of several PR72/B" isoforms were determined, demonstrating differences as well as similarities. Conclusion In contrast to PR55/B and PR61/B', the PR72/B" family seems evolutionary more divergent, as only two of the murine genes have a human orthologue. We have integrated these results in a more consistent nomenclature of both human and murine PR72/B" genes and their transcripts/proteins. Our results provide a platform for the future generation of PR72/B" knockout mice.
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Affiliation(s)
- Karen Zwaenepoel
- Protein Phosphorylation and Proteomics Group, Dept, Molecular Cell Biology, Faculty of Medicine, K,U, Leuven, Gasthuisberg O&N1, Herestraat 49 box 901, B-3000 Leuven, Belgium.
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Arnold HK, Sears RC. A tumor suppressor role for PP2A-B56alpha through negative regulation of c-Myc and other key oncoproteins. Cancer Metastasis Rev 2008; 27:147-58. [PMID: 18246411 DOI: 10.1007/s10555-008-9128-9] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Loss or inhibition of the serine/threonine protein phosphatase 2A (PP2A) has revealed a critical tumor suppressor function for PP2A. However, PP2A has also been shown to have important roles in cell cycle progression and survival. Therefore, PP2A is not a typical tumor suppressor. This is most likely due to the fact that PP2A represents a large number of different holoenzymes. Further understanding of PP2A function(s), and especially its tumor suppressor activity, will depend largely on our ability to determine specific targets for these different PP2A holoenzymes and to gain an understanding of how these targets confer tumor suppressor activity or contribute to cell cycle progression and cell survival. Recent work has identified c-Myc as a target of the PP2A holoenzyme, PP2A-B56alpha. This holoenzyme also negatively regulates beta-catenin expression and modulates the anti-apoptotic activity of Bcl2, thus characterizing PP2A-B56alpha as a tumor suppressor PP2A holoenzyme. This review will focus on the role of PP2A-B56alpha in regulating c-Myc and will place this tumor suppressor activity of PP2A within the context of its other tumor suppressor functions. Finally, the mechanism(s) through which PP2A-B56alpha tumor suppressor activity may be lost in cancer will be discussed.
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Affiliation(s)
- Hugh K Arnold
- Department of Molecular and Medical Genetics, Oregon Health & Sciences University, Portland, OR 97239, USA
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Janssens V, Longin S, Goris J. PP2A holoenzyme assembly: in cauda venenum (the sting is in the tail). Trends Biochem Sci 2008; 33:113-21. [PMID: 18291659 DOI: 10.1016/j.tibs.2007.12.004] [Citation(s) in RCA: 307] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Revised: 12/20/2007] [Accepted: 12/21/2007] [Indexed: 01/22/2023]
Abstract
Protein phosphatase 2A (PP2A), a major phospho-serine/threonine phosphatase, is conserved throughout eukaryotes. It dephosphorylates a plethora of cellular proteins, including kinases and other signaling molecules involved in cell division, gene regulation, protein synthesis and cytoskeleton organization. PP2A enzymes typically exist as heterotrimers comprising catalytic C-, structural A- and regulatory B-type subunits. The B-type subunits function as targeting and substrate-specificity factors; hence, holoenzyme assembly with the appropriate B-type subunit is crucial for PP2A specificity and regulation. Recently, several biochemical and structural determinants have been described that affect PP2A holoenzyme assembly. Moreover, the effects of specific post-translational modifications of the C-terminal tail of the catalytic subunit indicate that a 'code' might regulate dynamic exchange of regulatory B-type subunits, thus affecting the specificity of PP2A.
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Affiliation(s)
- Veerle Janssens
- Protein Phosphorylation and Proteomics Laboratory, Department of Molecular Cell Biology, Faculty of Medicine, K.U. Leuven, Leuven, Belgium
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37
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Expression of nucleostemin in prostate cancer and its effect on the proliferation of PC-3 cells. Chin Med J (Engl) 2008. [DOI: 10.1097/00029330-200802020-00004] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
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Control of mitotic exit by PP2A regulation of Cdc25C and Cdk1. Proc Natl Acad Sci U S A 2007; 104:19867-72. [PMID: 18056802 DOI: 10.1073/pnas.0709879104] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Inactivation of maturation-promoting factor [(MPF) Cdk1/Cyclin B] is a key event in the exit from mitosis. Although degradation of Cyclin B is important for MPF inactivation, recent studies indicate that Cdk1 phosphorylation and inactivation occur before Cyclin B degradation and, therefore, also may be important steps in the exit from mitosis. Cdk1 activity is controlled by the Cdc25C phosphatase, which is turned on at the G(2)/M transition to catalyze Cdk1 activation. PP2A:B56delta is a negative regulator of Cdc25C during interphase. We show here that PP2A:B56delta also regulates Cdc25C at mitosis. Failure of PP2A:B56delta to dephosphorylate Cdc25C at mitosis results in prolonged hyperphosphorylation and activation of Cdc25C, causing persistent dephosphorylation and, hence, activation of Cdk1. This constitutive activation of Cdc25C and Cdk1 leads to a delayed exit from mitosis. Consistent with Cdk1 as a major biological target of B56delta, stable knockdown and germ-line mouse KO of B56delta leads to compensatory transcriptional up-regulation of Wee1 kinase to oppose the Cdc25C activity and permit cell survival. These observations place PP2A:B56delta as a key upstream regulator of Cdk1 activity upon exit from mitosis.
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Longin S, Zwaenepoel K, Louis JV, Dilworth S, Goris J, Janssens V. Selection of protein phosphatase 2A regulatory subunits is mediated by the C terminus of the catalytic Subunit. J Biol Chem 2007; 282:26971-26980. [PMID: 17635907 DOI: 10.1074/jbc.m704059200] [Citation(s) in RCA: 137] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein phosphatase 2A (PP2A) is a family of multifunctional serine/threonine phosphatases all composed of a catalytic C, a structural A, and a regulatory B subunit. Assembly of the complex with the appropriate B subunit forms the key to the functional specificity and regulation of PP2A. Emerging evidence suggests a crucial role for methylation and phosphorylation of the PP2A C subunit in this process. In this study, we show that PP2A C subunit methylation was not absolutely required for binding the PR61/B' and PR72/B'' subunit families, whereas binding of the PR55/B subunit family was determined by methylation and the nature of the C-terminal amino acid side chain. Moreover mutation of the phosphorylatable Tyr(307) or Thr(304) residues differentially affected binding of distinct B subunit family members. Down-regulation of the PP2A methyltransferase LCMT1 by RNA interference gradually reduced the cellular amount of methylated C subunit and induced a dynamic redistribution of the remaining methylated PP2A(C) between different PP2A trimers consistent with their methylation requirements. Persistent knockdown of LCMT1 eventually resulted in specific degradation of the PR55/B subunit and apoptotic cell death. Together these results establish a crucial foundation for understanding PP2A regulatory subunit selection.
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Affiliation(s)
- Sari Longin
- Protein Phosphorylation and Proteomics Laboratory, Department of Molecular Cell Biology, Faculty of Medicine, KULeuven, Herestraat 49 bus 901, B-3000 Leuven, Belgium
| | - Karen Zwaenepoel
- Protein Phosphorylation and Proteomics Laboratory, Department of Molecular Cell Biology, Faculty of Medicine, KULeuven, Herestraat 49 bus 901, B-3000 Leuven, Belgium
| | - Justin V Louis
- Protein Phosphorylation and Proteomics Laboratory, Department of Molecular Cell Biology, Faculty of Medicine, KULeuven, Herestraat 49 bus 901, B-3000 Leuven, Belgium
| | - Stephen Dilworth
- Department of Metabolic Medicine, Imperial College Faculty of Medicine, Hammersmith Hospital, London W12 0NN, United Kingdom
| | - Jozef Goris
- Protein Phosphorylation and Proteomics Laboratory, Department of Molecular Cell Biology, Faculty of Medicine, KULeuven, Herestraat 49 bus 901, B-3000 Leuven, Belgium
| | - Veerle Janssens
- Protein Phosphorylation and Proteomics Laboratory, Department of Molecular Cell Biology, Faculty of Medicine, KULeuven, Herestraat 49 bus 901, B-3000 Leuven, Belgium.
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Saraf A, Virshup DM, Strack S. Differential expression of the B'beta regulatory subunit of protein phosphatase 2A modulates tyrosine hydroxylase phosphorylation and catecholamine synthesis. J Biol Chem 2006; 282:573-80. [PMID: 17085438 DOI: 10.1074/jbc.m607407200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis, is stimulated by N-terminal phosphorylation by several kinases and inhibited by protein serine/threonine phosphatase 2A (PP2A). PP2A is a family of heterotrimeric holoenzymes containing one of more than a dozen different regulatory subunits. In comparison with rat forebrain extracts, adrenal gland extracts exhibited TH hyperphosphorylation at Ser(19), Ser(31), and Ser(40), as well as reduced phosphatase activity selectively toward phosphorylated TH. Because the B'beta regulatory subunit of PP2A is expressed in brain but not in adrenal glands, we tested the hypothesis that PP2A/B'beta is a specific TH phosphatase. In catecholamine-secreting PC12 cells, inducible expression of B'beta decreased both N-terminal Ser phosphorylation and in situ TH activity, whereas inducible silencing of endogenous B'beta had the opposite effect. Furthermore, PP2A/B'beta directly dephosphorylated TH in vitro. As to specificity, other PP2A regulatory subunits had negligible effects on TH activity and phosphorylation in situ and in vitro. Whereas B'beta was highly expressed in dopaminergic cell bodies in the substantia nigra, the PP2A regulatory subunit was excluded from TH-positive terminal fields in the striatum and failed to colocalize with presynaptic markers in general. Consistent with a model in which B'beta enrichment in neuronal cell bodies helps confine catecholamine synthesis to axon terminals, TH phosphorylation was higher in processes than in somata of dopaminergic neurons. In summary, we show that B'beta recruits PP2A to modulate TH activity in a tissue- and cell compartment specific fashion.
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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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Schild A, Schmidt K, Lim YA, Ke Y, Ittner LM, Hemmings BA, Götz J. Altered levels of PP2A regulatory B/PR55 isoforms indicate role in neuronal differentiation. Int J Dev Neurosci 2006; 24:437-43. [PMID: 17045446 DOI: 10.1016/j.ijdevneu.2006.08.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2006] [Revised: 08/22/2006] [Accepted: 08/22/2006] [Indexed: 11/23/2022] Open
Abstract
The ubiquitously expressed serine/threonine-specific protein phosphatase 2A (PP2A) is prominent in brain where it serves a wide range of functions under both physiological and pathological conditions. PP2A holoenzymes are composed of a catalytic subunit and a tightly complexed scaffolding subunit. This core enzyme associates with regulatory subunits of the B/PR55, B'/PR56/PR61, B''/PR72 and B'''/PR93/PR110 families. We previously determined distribution and expression levels of the four members of the B/PR55 family in brain, as dysregulation of this subunit family has been specifically implicated in neurodegenerative disorders including Alzheimer's disease. In the present study, we used cell lines widely used in neuroscience research to determine levels of the four PR55 isoforms by qRT-PCR under different experimental conditions. We show that PR55alpha mRNA levels are highest in both HEK293 cells and SH-SY5Y neuroblastoma cells whereas PR55beta levels are lowest. Stepwise neuronal differentiation of SH-SY5Y cells causes the selective upregulation of PR55beta, and to some extent PR55gamma and PR55delta, but not PR55alpha mRNAs. In agreement with the qRT-PCR analysis, neuronal differentiation does not alter PR55alpha protein levels, whereas interestingly, PR55beta and PR55gamma protein levels are reduced when compared to undifferentiated cells. Our data point at specific roles for distinct regulatory B/PR55 subunits of PP2A in neuron-like cells with PR55alpha being the major isoform.
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Affiliation(s)
- Andreas Schild
- Division of Psychiatry Research, University of Zurich, August Forel Strasse 1, 8008 Zurich, Switzerland
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Viquez NM, Li CR, Wairkar YP, DiAntonio A. The B' protein phosphatase 2A regulatory subunit well-rounded regulates synaptic growth and cytoskeletal stability at the Drosophila neuromuscular junction. J Neurosci 2006; 26:9293-303. [PMID: 16957085 PMCID: PMC6674517 DOI: 10.1523/jneurosci.1740-06.2006] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Synaptic growth is essential for the development and plasticity of neural circuits. To identify molecular mechanisms regulating synaptic growth, we performed a gain-of-function screen for synapse morphology mutants at the Drosophila neuromuscular junction (NMJ). We isolated a B' regulatory subunit of protein phosphatase 2A (PP2A) that we have named well-rounded (wrd). Neuronal overexpression of wrd leads to overgrowth of the synaptic terminal. Endogenous Wrd protein is present in the larval nervous system and muscle and is enriched at central and neuromuscular synapses. wrd is required for normal synaptic development; in its absence, there are fewer synaptic boutons and there is a decrease in synaptic strength. wrd functions presynaptically to promote normal synaptic growth and postsynaptically to maintain normal levels of evoked transmitter release. In the absence of wrd, the presynaptic cytoskeleton is abnormal, with an increased proportion of unbundled microtubules. Reducing PP2A enzymatic activity also leads to an increase in unbundled microtubules, an effect enhanced by reducing wrd levels. Hence, wrd promotes the function of PP2A and is required for normal cytoskeletal organization, synaptic growth, and synaptic function at the Drosophila NMJ.
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Affiliation(s)
- Natasha M. Viquez
- Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Caroline R. Li
- Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Yogesh P. Wairkar
- Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Aaron DiAntonio
- Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110
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Perrotti D, Neviani P. ReSETting PP2A tumour suppressor activity in blast crisis and imatinib-resistant chronic myelogenous leukaemia. Br J Cancer 2006; 95:775-81. [PMID: 16953242 PMCID: PMC2360538 DOI: 10.1038/sj.bjc.6603317] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The deregulated kinase activity of p210-BCR/ABL oncoproteins, hallmark of chronic myelogenous leukaemia (CML), induces and sustains the leukaemic phenotype, and contributes to disease progression. Imatinib mesylate, a BCR/ABL kinase inhibitor, is effective in most of chronic phase CML patients. However, a significant percentage of CML patients develop resistance to imatinib and/or still progresses to blast crisis, a disease stage that is often refractory to imatinib therapy. Furthermore, there is compelling evidence indicating that the CML leukaemia stem cell is also resistant to imatinib. Thus, there is still a need for new drugs that, if combined with imatinib, will decrease the rate of relapse, fully overcome imatinib resistance and prevent blastic transformation of CML. We recently reported that the activity of the tumour suppressor protein phosphatase 2A (PP2A) is markedly inhibited in blast crisis CML patient cells and that molecular or pharmacologic re-activation of PP2A phosphatase led to growth suppression, enhanced apoptosis, impaired clonogenic potential and decreased in vivo leukaemogenesis of imatinib-sensitive and -resistant (T315I included) CML-BC patient cells and/or BCR/ABL+ myeloid progenitor cell lines. Thus, the combination of PP2A phosphatase-activating and BCR/ABL kinase-inhibiting drugs may represent a powerful therapeutic strategy for blast crisis CML patients.
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Affiliation(s)
- D Perrotti
- Human Cancer Genetics Program, Department of Molecular Virology, Immunology and Medical Genetics, and The Comprehensive Cancer Center, The Ohio State University, Columbus, OH 43210, USA.
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Arnold HK, Sears RC. Protein phosphatase 2A regulatory subunit B56alpha associates with c-myc and negatively regulates c-myc accumulation. Mol Cell Biol 2006; 26:2832-44. [PMID: 16537924 PMCID: PMC1430332 DOI: 10.1128/mcb.26.7.2832-2844.2006] [Citation(s) in RCA: 204] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2005] [Revised: 10/07/2005] [Accepted: 01/10/2006] [Indexed: 01/05/2023] Open
Abstract
Protein phosphatase 2A (PP2A) plays a prominent role in controlling accumulation of the proto-oncoprotein c-Myc. PP2A mediates its effects on c-Myc by dephosphorylating a conserved residue that normally stabilizes c-Myc, and in this way, PP2A enhances c-Myc ubiquitin-mediated degradation. Stringent regulation of c-Myc levels is essential for normal cell function, as c-Myc overexpression can lead to cell transformation. Conversely, PP2A has tumor suppressor activity. Uncovering relevant PP2A holoenzymes for a particular target has been limited by the fact that cellular PP2A represents a large heterogeneous population of trimeric holoenzymes, composed of a conserved catalytic subunit and a structural subunit along with a variable regulatory subunit which directs the holoenzyme to a specific target. We now report the identification of a specific PP2A regulatory subunit, B56alpha, that selectively associates with the N terminus of c-Myc. B56alpha directs intact PP2A holoenzymes to c-Myc, resulting in a dramatic reduction in c-Myc levels. Inhibition of PP2A-B56alpha holoenzymes, using small hairpin RNA to knock down B56alpha, results in c-Myc overexpression, elevated levels of c-Myc serine 62 phosphorylation, and increased c-Myc function. These results uncover a new protein involved in regulating c-Myc expression and reveal a critical interconnection between a potent oncoprotein, c-Myc, and a well-documented tumor suppressor, PP2A.
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Affiliation(s)
- Hugh K Arnold
- Department of Molecular and Medical Genetics, Oregon Health & Sciences University, 3181 S.W. Sam Jackson Park Rd., L103A, Portland, Oregon 97239, USA
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Schild A, Isenmann S, Tanimoto N, Tonagel F, Seeliger MW, Ittner LM, Kretz A, Ogris E, Götz J. Impaired development of the Harderian gland in mutant protein phosphatase 2A transgenic mice. Mech Dev 2006; 123:362-71. [PMID: 16679006 DOI: 10.1016/j.mod.2006.03.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2005] [Revised: 02/22/2006] [Accepted: 03/07/2006] [Indexed: 10/24/2022]
Abstract
Although Harderian glands are especially large in rodents, many features of this retroocular gland, including its development and function, are not well established. Protein phosphatase 2A (PP2A) is a family of heterotrimeric enzymes expressed in this gland. PP2A substrate specificity is determined by regulatory subunits with leucine 309 of the catalytic subunit playing a crucial role in the recruitment of regulatory subunits into the complex in vitro. Here we expressed an L309A mutant catalytic subunit in Harderian gland of transgenic mice. We found a delayed postnatal development and hypoplasia of the gland, causing enophthalmos. To determine why expression of the L309A mutant caused this phenotype, we determined the PP2A subunit composition. We found an altered subunit composition in the transgenic gland that was accompanied by pronounced changes of proteins regulating cell adhesion. Specifically, cadherin and beta-catenin were dramatically reduced and shifted to the cytosol. Furthermore, we found an inactivating phosphorylation of the cadherin-directed glycogen synthase kinase-3beta. In conclusion, the carboxy-terminal leucine L309 of the PP2A catalytic subunit determines PP2A heterotrimer composition in vivo. Moreover, our data demonstrate that PP2A subunit composition plays a crucial role in regulating cell adhesion and as a consequence in the development of the Harderian gland.
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Affiliation(s)
- Andreas Schild
- Division of Psychiatry Research, University of Zurich, 8008 Zurich, Switzerland
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Schild A, Ittner LM, Götz J. Altered phosphorylation of cytoskeletal proteins in mutant protein phosphatase 2A transgenic mice. Biochem Biophys Res Commun 2006; 343:1171-8. [PMID: 16580638 DOI: 10.1016/j.bbrc.2006.03.066] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2006] [Accepted: 03/09/2006] [Indexed: 12/30/2022]
Abstract
Protein phosphatase 2A (PP2A) is a family of heterotrimeric enzymes with diverse functions under physiologic and pathologic conditions such as Alzheimer's disease. All PP2A holoenzymes have in common a catalytic subunit C and a structural scaffolding subunit A. These core subunits assemble with various regulatory B subunits to form heterotrimers with distinct functions in the cell. Substrate specificity of PP2A in vitro is determined by regulatory subunits with leucine 309 of the catalytic subunit C playing a crucial role in the recruitment of regulatory subunits into the complex. Here we expressed a mutant form of Calpha, L309A, in brain and Harderian (lacrimal) gland of transgenic mice. We found an altered recruitment of regulatory subunits into the complex, demonstrating a role for the carboxyterminal leucine of Calpha in regulating holoenzyme assembly in vivo. This was associated with an increased phosphorylation of tau in brain and an impaired dephosphorylation of vimentin demonstrating that both cytoskeletal proteins are in vivo substrates of distinct PP2A holoenzyme complexes.
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Affiliation(s)
- Andreas Schild
- Division of Psychiatry Research, University of Zürich, 8008 Zürich, Switzerland
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Abstract
Although the small DNA tumor virus SV40 (simian virus 40) fails to replicate in human cells, understanding how SV40 transforms human and murine cells has and continues to provide important insights into cancer initiation and maintenance. The early region of SV40 encodes two oncoproteins: the large T (LT) and small t (ST) antigens. SV40 LT contributes to murine and human cell transformation in part by inactivating the p53 and retinoblastoma protein tumor suppressor proteins. SV40 ST inhibits the activity of the protein phosphatase 2A (PP2A) family of serine-threonine phosphatases, and this interaction is required for SV40-mediated transformation of human cells. PP2A regulates multiple signaling pathways, suggesting many possible targets important for viral replication and cell transformation. Genetic manipulation of particular PP2A subunits has confirmed a role for specific complexes in transformation, and recent work implicates the perturbation of the phosphatidylinositol 3-kinase/Akt pathway and c-Myc stability in transformation by ST and PP2A. Mutations in PP2A subunits occur at low frequency in human tumors, suggesting that alterations of PP2A signaling play a role in both experimentally induced and spontaneously arising cancers. Unraveling the complexity of PP2A signaling will not only provide further insights into cancer development but may identify novel targets with promise for therapeutic manipulation.
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Affiliation(s)
- Jason D Arroyo
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA
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Chen W, Arroyo JD, Timmons JC, Possemato R, Hahn WC. Cancer-associated PP2A Aalpha subunits induce functional haploinsufficiency and tumorigenicity. Cancer Res 2005; 65:8183-92. [PMID: 16166293 DOI: 10.1158/0008-5472.can-05-1103] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The introduction of SV40 small t antigen or the suppression of PP2A B56gamma subunit expression contributes to the experimental transformation of human cells. To investigate the role of cancer-associated PP2A Aalpha subunit mutants in transformation, we introduced several PP2A Aalpha mutants into immortalized but nontumorigenic human cells. These PP2A Aalpha mutants exhibited defects in binding to other PP2A subunits and impaired phosphatase activity. Although overexpression of these mutants failed to render immortalized cells tumorigenic, partial suppression of endogenous PP2A Aalpha expression activated the AKT pathway and permitted cells to form tumors in immunodeficient mice. These findings suggest that cancer-associated Aalpha mutations contribute to cancer development by inducing functional haploinsufficiency, disturbing PP2A holoenzyme composition, and altering the enzymatic activity of PP2A.
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Affiliation(s)
- Wen Chen
- Department of Medical Oncology, Dana-Farber Cancer Institute and Brigham and Women's Hospital, Boston, Massachusetts 02115, USA
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Yang HX, Jin GL, Meng L, Zhang JZ, Liu WB, Shou CC. Screening and identification of proteins interacting with nucleostemin. World J Gastroenterol 2005; 11:4812-4. [PMID: 16097049 PMCID: PMC4398727 DOI: 10.3748/wjg.v11.i31.4812] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To identify the proteins interacting with nucleostemin (NS), thereby gaining an insight into the function of NS.
METHODS: Yeast two-hybrid assay was performed to screen a human placenta cDNA library with the full length of NS as a bait. X-Gal assay and β-galactosidase filter assay were subsequently conducted to check the positive clones and the gene was identified by DNA sequencing. To further confirm the interaction of two proteins, the DNA fragment coding NS and the DNA fragment isolated from the positive clone were inserted into the mammalian expression vector pcDNA3 and pcDNA3-myc, respectively. Then, two plasmids were cotransfected into the COS-7 cells by DEAE-dextron. The total protein from the cotransfected cells was extracted and coimmunoprecipitation and Western blot were performed with suitable antibodies sequentially.
RESULTS: Two positive clones that interacted with NS were obtained from human placenta cDNA library. One was an alpha isoform of human protein phosphatase 2 regulatory subunit B (B56) (PPP2R5A) and the other was a novel gene being highly homologous to the gene associated with spondylo paralysis. The co-immunoprecipitation also showed that NS specifically interacted with PPP2R5A.
CONCLUSION: NS and PPP2R5A interact in yeast and mammalian cells, respectively, which is helpful for addressing the function of NS in cancer development and progression.
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Affiliation(s)
- Hai-Xia Yang
- Department of Biochemistry and Molecular Biology, Peking University School of Oncology and Beijing Institute for Cancer Research, Beijing 100034, China
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