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Reza MI, Kumar A, Pabelick CM, Britt RD, Prakash YS, Sathish V. Downregulation of protein phosphatase 2Aα in asthmatic airway smooth muscle. Am J Physiol Lung Cell Mol Physiol 2024; 326:L651-L659. [PMID: 38529552 DOI: 10.1152/ajplung.00050.2024] [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: 02/14/2024] [Revised: 03/18/2024] [Accepted: 03/21/2024] [Indexed: 03/27/2024] Open
Abstract
Airway smooth muscle cell (ASM) is renowned for its involvement in airway hyperresponsiveness through impaired ASM relaxation and bronchoconstriction in asthma, which poses a significant challenge in the field. Recent studies have explored different targets in ASM to alleviate airway hyperresponsiveness, however, a sizeable portion of patients with asthma still experience poor control. In our study, we explored protein phosphatase 2 A (PP2A) in ASM as it has been reported to regulate cellular contractility by controlling intracellular calcium ([Ca2+]i), ion channels, and respective regulatory proteins. We obtained human ASM cells and lung tissues from healthy and patients with asthma and evaluated PP2A expression using RNA-Seq data, immunofluorescence, and immunoblotting. We further investigated the functional importance of PP2A by determining its role in bronchoconstriction using mouse bronchus and human ASM cell [Ca2+]i regulation. We found robust expression of PP2A isoforms in human ASM cells with PP2Aα being highly expressed. Interestingly, PP2Aα was significantly downregulated in asthmatic tissue and human ASM cells exposed to proinflammatory cytokines. Functionally, FTY720 (PP2A agonist) inhibited acetylcholine- or methacholine-induced bronchial contraction in mouse bronchus and further potentiated isoproterenol-induced bronchial relaxation. Mechanistically, FTY720 inhibited histamine-evoked [Ca2+]i response and myosin light chain (MLC) phosphorylation in the presence of interleukin-13 (IL-13) in human ASM cells. To conclude, we for the first time established PP2A signaling in ASM, which can be further explored to develop novel therapeutics to alleviate airway hyperresponsiveness in asthma.NEW & NOTEWORTHY This novel study deciphered the expression and function of protein phosphatase 2Aα (PP2Aα) in airway smooth muscle (ASM) during asthma and/or inflammation. We showed robust expression of PP2Aα in human ASM while its downregulation in asthmatic ASM. Similarly, we demonstrated reduced PP2Aα expression in ASM exposed to proinflammatory cytokines. PP2Aα activation inhibited bronchoconstriction of isolated mouse bronchi. In addition, we unveiled that PP2Aα activation inhibits the intracellular calcium release and myosin light chain phosphorylation in human ASM.
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Affiliation(s)
- Mohammad Irshad Reza
- Department of Pharmaceutical Sciences, North Dakota State University, Fargo, North Dakota, United States
| | - Ashish Kumar
- Department of Pharmaceutical Sciences, North Dakota State University, Fargo, North Dakota, United States
| | - Christina M Pabelick
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, United States
| | - Rodney D Britt
- Center for Perinatal Research, Abigail Wexner Research Institute at Nationwide Children's Hospital, Columbus, Ohio, United States
- Department of Pediatrics, The Ohio State University, Columbus, Ohio, United States
| | - Y S Prakash
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, United States
| | - Venkatachalem Sathish
- Department of Pharmaceutical Sciences, North Dakota State University, Fargo, North Dakota, United States
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Ji N, Chen Z, Wang Z, Sun W, Yuan Q, Zhang X, Jia X, Wu J, Jiang J, Song M, Xu T, Liu Y, Ma Q, Sun Z, Bao Y, Zhang M, Huang M. LincR-PPP2R5C Promotes Th2 Cell Differentiation Through PPP2R5C/PP2A by Forming an RNA-DNA Triplex in Allergic Asthma. ALLERGY, ASTHMA & IMMUNOLOGY RESEARCH 2024; 16:71-90. [PMID: 38262392 PMCID: PMC10823138 DOI: 10.4168/aair.2024.16.1.71] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2023] [Revised: 08/13/2023] [Accepted: 08/22/2023] [Indexed: 01/25/2024]
Abstract
PURPOSE The roles and mechanisms of long noncoding RNAs (lncRNAs) in T helper 2 (Th2) differentiation from allergic asthma are poorly understood. We aimed to explore a novel lncRNA, LincR-protein phosphatase 2 regulatory subunit B' gamma (PPP2R5C), in Th2 differentiation in a mouse model of asthma. METHODS LincR-PPP2R5C from RNA-seq data of CD4+ T cells of asthma-like mice were validated and confirmed by quantitative reverse transcription polymerase chain reaction, northern blotting, nuclear and cytoplasmic separation, and fluorescence in situ hybridization (FISH). Lentiviruses encoding LincR-PPP2R5C or shRNA were used to overexpress or silence LincR-PPP2R5C in CD4+ T cells. The interactions between LincR-PPP2R5C and PPP2R5C were explored with western blotting, chromatin isolation by RNA purification assay, and fluorescence resonance energy transfer. An ovalbumin-induced acute asthma model in knockout (KO) mice (LincR-PPP2R5C KO, CD4 conditional LincR-PPP2R5C KO) was established to explore the roles of LincR-PPP2R5C in Th2 differentiation. RESULTS LncR-PPP2R5C was significantly higher in CD4+ T cells from asthmatic mice ex vivo and Th2 cells in vitro. The lentivirus encoding LincR-PPP2R5C suppressed Th1 differentiation; in contrast, the short hairpin RNA (shRNA) lentivirus decreased LincR-PPP2R5C and Th2 differentiation. Mechanistically, LincR-PPP2R5C deficiency suppressed the phosphatase activity of the protein phosphatase 2A (PP2A) holocomplex, resulting in a decline in Th2 differentiation. The formation of an RNA-DNA triplex between LincR-PPP2R5C and the PPP2R5C promoter enhanced PPP2R5C expression and activated PP2A. LincR-PPP2R5C KO and CD4 conditional KO decreased Th2 differentiation, airway hyperresponsiveness and inflammatory responses. CONCLUSIONS LincR-PPP2R5C regulated PPP2R5C expression and PP2A activity by forming an RNA-DNA triplex with the PPP2R5C promoter, leading to Th2 polarization in a mouse model of acute asthma. Our data presented the first definitive evidence of lncRNAs in the regulation of Th2 cells in asthma.
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Affiliation(s)
- Ningfei Ji
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Zhongqi Chen
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Zhengxia Wang
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Wei Sun
- Department of Respiratory and Critical Care Medicine, Xishan People's Hospital of Wuxi City, Wuxi Branch of Zhongda Hospital Affiliate to Southeast University, Wuxi, China
| | - Qi Yuan
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Xijie Zhang
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Xinyu Jia
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Jingjing Wu
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Jingxian Jiang
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Meijuan Song
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Tingting Xu
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Yanan Liu
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Qiyun Ma
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Zhixiao Sun
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Yanmin Bao
- Department of Respiratory Medicine, Shenzhen Children's Hospital, Shenzhen, China
| | - Mingshun Zhang
- Jiangsu Province Engineering Research Center of Antibody Drugs, NHC Key Laboratory of Antibody Technique, Department of Immunology, Nanjing Medical University, Nanjing, China.
| | - Mao Huang
- Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China.
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Corzo G, Seeling-Branscomb CE, Seeling JM. Differential Synonymous Codon Selection in the B56 Gene Family of PP2A Regulatory Subunits. Int J Mol Sci 2023; 25:392. [PMID: 38203563 PMCID: PMC10778929 DOI: 10.3390/ijms25010392] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Revised: 12/18/2023] [Accepted: 12/23/2023] [Indexed: 01/12/2024] Open
Abstract
Protein phosphatase 2A (PP2A) functions as a tumor suppressor and consists of a scaffolding, catalytic, and regulatory subunit. The B56 gene family of regulatory subunits impart distinct functions onto PP2A. Codon usage bias (CUB) involves the selection of synonymous codons, which can affect gene expression by modulating processes such as transcription and translation. CUB can vary along the length of a gene, and differential use of synonymous codons can be important in the divergence of gene families. The N-termini of the gene product encoded by B56α possessed high CUB, high GC content at the third codon position (GC3), and high rare codon content. In addition, differential CUB was found in the sequence encoding two B56γ N-terminal splice forms. The sequence encoding the N-termini of B56γ/γ, relative to B56δ/γ, displayed CUB, utilized more frequent codons, and had higher GC3 content. B56α mRNA had stronger than predicted secondary structure at their 5' end, and the B56δ/γ splice variants had long regions of weaker than predicted secondary structure at their 5' end. The data suggest that B56α is expressed at relatively low levels as compared to the other B56 isoforms and that the B56δ/γ splice variant is expressed more highly than B56γ/γ.
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Affiliation(s)
- Gabriel Corzo
- Department of Biology, Hofstra University, Hempstead, NY 11549, USA;
| | | | - Joni M. Seeling
- Department of Biology, Hofstra University, Hempstead, NY 11549, USA;
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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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Zhao M, Yang Y, Shi Y, Chen X, Yang Y, Pan L, Du Z, Sun H, Yao C, Ma G, Du A. PP2Acα-B'/PR61 Holoenzyme of Toxoplasma gondii Is Required for the Amylopectin Metabolism and Proliferation of Tachyzoites. Microbiol Spectr 2023; 11:e0010423. [PMID: 37199633 PMCID: PMC10269777 DOI: 10.1128/spectrum.00104-23] [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: 01/08/2023] [Accepted: 04/26/2023] [Indexed: 05/19/2023] Open
Abstract
Here, we report that the inhibition of the PP2A subfamily by okadaic acid results in an accumulation of polysaccharides in the acute infection stage (tachyzoites) of Toxoplasma gondii, which is a protozoan of global zoonotic importance and a model for the apicomplexan parasites. The loss of the catalytic subunit α of PP2A (ΔPP2Acα) in RHΔku80 leads to the polysaccharide accumulation phenotype in the base of tachyzoites as well as residual bodies and significantly compromises the intracellular growth in vitro and the virulence in vivo. A metabolomic analysis revealed that the accumulated polysaccharides in ΔPP2Acα are derived from interrupted glucose metabolism, which affects the production of ATP and energy homeostasis in the T. gondii knockout. The assembly of the PP2Acα holoenzyme complex involved in the amylopectin metabolism in tachyzoites is possibly not regulated by LCMT1 or PME1, and this finding contributes to the identification of the regulatory B subunit (B'/PR61). The loss of B'/PR61 results in the accumulation of polysaccharide granules in the tachyzoites as well as reduced plaque formation ability, exactly the same as ΔPP2Acα. Taken together, we have identified a PP2Acα-B'/PR61 holoenzyme complex that plays a crucial role in the carbohydrate metabolism and viability in T. gondii, and its deficiency in function remarkably suppresses the growth and virulence of this important zoonotic parasite both in vitro and in vivo. Hence, rendering the PP2Acα-B'/PR61 holoenzyme functionless should be a promising strategy for the intervention of Toxoplasma acute infection and toxoplasmosis. IMPORTANCE Toxoplasma gondii switches back and forth between acute and chronic infections, mainly in response to host immunologic status, which is characterized by flexible but specific energy metabolism. Polysaccharide granules are accumulated in the acute infection stage of T. gondii that have been exposed to a chemical inhibitor of the PP2A subfamily. The genetic depletion of the catalytic subunit α of PP2A leads to this phenotype and significantly affects the cell metabolism, energy production, and viability. Further, a regulatory B subunit PR61 is necessary for the PP2A holoenzyme to function in glucose metabolism and in the intracellular growth of T. gondii tachyzoites. A deficiency of this PP2A holoenzyme complex (PP2Acα-B'/PR61) in T. gondii knockouts results in the abnormal accumulation of polysaccharides and the disruption of energy metabolism, suppressing their growth and virulence. These findings provide novel insights into cell metabolism and identify a potential target for an intervention against a T. gondii acute infection.
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Affiliation(s)
- Mingxiu Zhao
- Institute of Preventive Veterinary Medicine, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, College of Animal Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Yi Yang
- Institute of Preventive Veterinary Medicine, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, College of Animal Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Yue Shi
- Institute of Preventive Veterinary Medicine, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, College of Animal Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
- Hainan Institute, Zhejiang University, Yazhou Bay Sci-Tech City, Sanya, China
| | - Xueqiu Chen
- Institute of Preventive Veterinary Medicine, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, College of Animal Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Yimin Yang
- Institute of Preventive Veterinary Medicine, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, College of Animal Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Lingtao Pan
- Institute of Preventive Veterinary Medicine, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, College of Animal Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Zhendong Du
- Institute of Preventive Veterinary Medicine, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, College of Animal Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Hongchao Sun
- Department of Animal Parasitology, Institute of Animal Husbandry and Veterinary Medicine, Zhejiang Academy of Agricultural Science, Hangzhou, Zhejiang Province, China
| | - Chaoqun Yao
- Department of Biomedical Sciences and One Health Center for Zoonoses and Tropical Veterinary Medicine, Ross University School of Veterinary Medicine, Basseterre, St. Kitts and Nevis
| | - Guangxu Ma
- Institute of Preventive Veterinary Medicine, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, College of Animal Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
- Department of Veterinary Biosciences, Melbourne Veterinary School, The University of Melbourne, Parkville, Victoria, Australia
| | - Aifang Du
- Institute of Preventive Veterinary Medicine, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, College of Animal Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
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Dai J, Xie R, Sun ZN, Kou XL, Zhang JQ, Qi C, Liu R, Gao X, Wang J, Gao J. Protein phosphatase 2A deficiency in hippocampal CA1 inhibits priming effect of morphine on conditioned place preference in mice. Cereb Cortex 2023:6982733. [PMID: 36627245 DOI: 10.1093/cercor/bhac527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 12/12/2022] [Accepted: 12/13/2022] [Indexed: 01/12/2023] Open
Abstract
Studies have shown that protein phosphorylation plays an important role in morphine abuse. However, the neurobiological mechanism of protein phosphatase 2A (PP2A) underlying the morphine-priming process is still unclear. Here we constructed T29-2-Cre; PP2Afl/fl conditional knockout mice (KO) and investigated the role of hippocampal PP2A in morphine priming. We observed that the deficit of PP2A inhibited the priming behavior of morphine and blocked the priming-induced long-term potentiation (LTP) in the hippocampus of KO mice. Moreover, the expression levels of Rack1 and the membrane GluN2B were significantly reduced in the nucleus accumbens of KO mice compared with those in the control mice, which may be attributed to the decreased HDAC4 in the hippocampus of KO mice. Consistent with it, the similar inhibited priming effects were also observed in the wild-type mice treated with sodium butyrate (NaB)-a nonspecific inhibitor of histone deacetylases-3 h after morphine administration. Taken together, our results suggest that hippocampal PP2A may be involved in morphine priming through the PP2A/HDAC4/Rack1 pathway.
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Affiliation(s)
- Jing Dai
- Department of Neurobiology, School of Basic Medical Science, Nanjing Medical University, Longmian Road 101, Jiangning District, Nanjing 211166, China
| | - Ran Xie
- Department of Neurobiology, School of Basic Medical Science, Nanjing Medical University, Longmian Road 101, Jiangning District, Nanjing 211166, China
| | - Zhou-Na Sun
- Department of Neurobiology, School of Basic Medical Science, Nanjing Medical University, Longmian Road 101, Jiangning District, Nanjing 211166, China
| | - Xiao-Lin Kou
- Department of Neurobiology, School of Basic Medical Science, Nanjing Medical University, Longmian Road 101, Jiangning District, Nanjing 211166, China
| | - Jia-Qi Zhang
- Department of Neurobiology, School of Basic Medical Science, Nanjing Medical University, Longmian Road 101, Jiangning District, Nanjing 211166, China
| | - Cui Qi
- Department of Neurobiology, School of Basic Medical Science, Nanjing Medical University, Longmian Road 101, Jiangning District, Nanjing 211166, China
| | - Rui Liu
- Department of Neurobiology, School of Basic Medical Science, Nanjing Medical University, Longmian Road 101, Jiangning District, Nanjing 211166, China
| | - Xiang Gao
- SKL of Pharmaceutical Biotechnology and Model Animal Research Center, Collaborative Innovation Center for Genetics and Development, Nanjing Biomedical Research Institute, Nanjing University, Xianlin Avenue 163, Qixia District, Nanjing 210061, China
| | - Jing Wang
- Department of Neurobiology, School of Basic Medical Science, Nanjing Medical University, Longmian Road 101, Jiangning District, Nanjing 211166, China
| | - Jun Gao
- Department of Neurobiology, School of Basic Medical Science, Nanjing Medical University, Longmian Road 101, Jiangning District, Nanjing 211166, China.,Department of Rehabilitation Medicine, The Affiliated Jiangsu Shengze Hospital to Nanjing Medical University, Shichang West Road 1399, Wujiang District, Suzhou 215228, China
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Li C, Wen L, Dong J, Li L, Huang J, Yang J, Liang T, Li T, Xia Z, Chen C. Alterations in cellular metabolisms after TKI therapy for Philadelphia chromosome-positive leukemia in children: A review. Front Oncol 2022; 12:1072806. [PMID: 36561525 PMCID: PMC9766352 DOI: 10.3389/fonc.2022.1072806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Accepted: 11/23/2022] [Indexed: 12/12/2022] Open
Abstract
Incidence rates of chronic myeloid leukemia (CML) and Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) are lower but more aggressive in children than in adults due to different biological and host factors. After the clinical application of tyrosine kinase inhibitor (TKI) blocking BCR/ABL kinase activity, the prognosis of children with CML and Ph+ ALL has improved dramatically. Yet, off-target effects and drug tolerance will occur during the TKI treatments, contributing to treatment failure. In addition, compared to adults, children may need a longer course of TKIs therapy, causing detrimental effects on growth and development. In recent years, accumulating evidence indicates that drug resistance and side effects during TKI treatment may result from the cellular metabolism alterations. In this review, we provide a detailed summary of the current knowledge on alterations in metabolic pathways including glucose metabolism, lipid metabolism, amino acid metabolism, and other metabolic processes. In order to obtain better TKI treatment outcomes and avoid side effects, it is essential to understand how the TKIs affect cellular metabolism. Hence, we also discuss the relevance of cellular metabolism in TKIs therapy to provide ideas for better use of TKIs in clinical practice.
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Affiliation(s)
- Chunmou Li
- Department of Pediatrics, the Seventh Affiliated Hospital of Sun Yat-Sen University, Shenzhen, Guangdong, China
| | - Luping Wen
- Department of Pharmacy, The Seventh Affiliated Hospital of Sun Yat-Sen University, Shenzhen, Guangdong, China
| | - Junchao Dong
- Key Laboratory of Tropical Disease Control, Ministry of Education, Sun Yat-sen University, Shenzhen, Guangdong, China
| | - Lindi Li
- Department of Pediatrics, the Seventh Affiliated Hospital of Sun Yat-Sen University, Shenzhen, Guangdong, China
| | - Junbin Huang
- Department of Pediatrics, the Seventh Affiliated Hospital of Sun Yat-Sen University, Shenzhen, Guangdong, China
| | - Jing Yang
- Department of Pediatrics, the Seventh Affiliated Hospital of Sun Yat-Sen University, Shenzhen, Guangdong, China
| | - Tianqi Liang
- Department of Pediatrics, the Seventh Affiliated Hospital of Sun Yat-Sen University, Shenzhen, Guangdong, China
| | - Tianwen Li
- Department of Pediatrics, the Seventh Affiliated Hospital of Sun Yat-Sen University, Shenzhen, Guangdong, China
| | - Zhigang Xia
- Department of Pediatrics, the Seventh Affiliated Hospital of Sun Yat-Sen University, Shenzhen, Guangdong, China
| | - Chun Chen
- Department of Pediatrics, the Seventh Affiliated Hospital of Sun Yat-Sen University, Shenzhen, Guangdong, China,*Correspondence: Chun Chen,
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Wang P, Li W, Liu Z, He X, Lan R, Liu Y, Chu M. Analysis of the Association of Two SNPs in the Promoter Regions of the PPP2R5C and SLC39A5 Genes with Litter Size in Yunshang Black Goats. Animals (Basel) 2022; 12:ani12202801. [PMID: 36290187 PMCID: PMC9597746 DOI: 10.3390/ani12202801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Revised: 10/08/2022] [Accepted: 10/13/2022] [Indexed: 11/16/2022] Open
Abstract
Screening for candidate genes and genetic variants associated with litter size is important for goat breeding. The aim of this study was to analyze the relationship between single nucleotide polymorphisms (SNPs) in PPP2R5C and SLC39A5 and litter size in Yunshang black goats. KASP genotyping was used to detect the SNP genetic markers in the PPP2R5C and SLC39A5 in a population of 569 Yunshang black goats. The results show that there were two SNPs in the PPP2R5C and SLC39A5 promoter regions. Association analysis revealed that the polymorphisms PPP2R5C g.65977743C>T and SLC39A5 g.50676693T>C were significantly associated with the litter size of the third parity of Yunshang black goats (p < 0.05). To further explore the regulatory mechanism of the two genes, the expression of different genotypes of PPP2R5C and SLC39A5 was validated by RT-qPCR and Western blotting. The expression of PPP2R5C was significantly higher in individuals with the TT genotype than in those with the TC and CC genotypes (p < 0.05). The expression of SLC39A5 was also significantly higher in individuals with the TT genotype than in TC and CC genotypes (p < 0.05). Dual luciferase reporter analysis showed that the luciferase activity of PPP2R5C-C variant was significantly higher than that of PPP2R5C-T variant (p < 0.05). The luciferase activity of SLC39A5-T variant was significantly higher than that of SLC39A5-C variant (p < 0.05). Software was used to predict the binding of transcription factors to the polymorphic sites, and the results show that SOX18, ZNF418, and ZNF667 and NKX2-4 and TBX6 might bind to PPP2R5C g.65977743C>T and SLC39A5 g.50676693T>C, respectively. These results provide new insights into the identification of candidate genes for marker-assisted selection (MAS) in goats.
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Affiliation(s)
- Peng Wang
- Key Laboratory of Animal Genetics, Breeding and Reproduction of Ministry of Agriculture and Rural Affairs, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Wentao Li
- Key Laboratory of Animal Genetics, Breeding and Reproduction of Ministry of Agriculture and Rural Affairs, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Ziyi Liu
- Key Laboratory of Animal Genetics, Breeding and Reproduction of Ministry of Agriculture and Rural Affairs, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Xiaoyun He
- Key Laboratory of Animal Genetics, Breeding and Reproduction of Ministry of Agriculture and Rural Affairs, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Rong Lan
- Yunnan Animal Science and Veterinary Institute, Kunming 650224, China
| | - Yufang Liu
- Key Laboratory of Animal Genetics, Breeding and Reproduction of Ministry of Agriculture and Rural Affairs, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China
- Correspondence: (Y.L.); (M.C.); Tel.: +86-10-62819850 (Y.L. & M.C.)
| | - Mingxing Chu
- Key Laboratory of Animal Genetics, Breeding and Reproduction of Ministry of Agriculture and Rural Affairs, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China
- Correspondence: (Y.L.); (M.C.); Tel.: +86-10-62819850 (Y.L. & M.C.)
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Sarmasti Emami S, Zhang D, Yang X. Interaction of the Hippo Pathway and Phosphatases in Tumorigenesis. Cancers (Basel) 2020; 12:E2438. [PMID: 32867200 PMCID: PMC7564220 DOI: 10.3390/cancers12092438] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 08/21/2020] [Accepted: 08/25/2020] [Indexed: 01/05/2023] Open
Abstract
The Hippo pathway is an emerging tumor suppressor signaling pathway involved in a wide range of cellular processes. Dysregulation of different components of the Hippo signaling pathway is associated with a number of diseases including cancer. Therefore, identification of the Hippo pathway regulators and the underlying mechanism of its regulation may be useful to uncover new therapeutics for cancer therapy. The Hippo signaling pathway includes a set of kinases that phosphorylate different proteins in order to phosphorylate and inactivate its main downstream effectors, YAP and TAZ. Thus, modulating phosphorylation and dephosphorylation of the Hippo components by kinases and phosphatases play critical roles in the regulation of the signaling pathway. While information regarding kinase regulation of the Hippo pathway is abundant, the role of phosphatases in regulating this pathway is just beginning to be understood. In this review, we summarize the most recent reports on the interaction of phosphatases and the Hippo pathway in tumorigenesis. We have also introduced challenges in clarifying the role of phosphatases in the Hippo pathway and future direction of crosstalk between phosphatases and the Hippo pathway.
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Affiliation(s)
| | | | - Xiaolong Yang
- Department of Pathology and Molecular Medicine, Queen’s University, Kingston, ON K7L 3N6, Canada; (S.S.E.); (D.Z.)
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10
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Marelli S, Williamson JC, Protasio AV, Naamati A, Greenwood EJD, Deane JE, Lehner PJ, Matheson NJ. Antagonism of PP2A is an independent and conserved function of HIV-1 Vif and causes cell cycle arrest. eLife 2020; 9:e53036. [PMID: 32292164 PMCID: PMC7920553 DOI: 10.7554/elife.53036] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Accepted: 03/17/2020] [Indexed: 01/01/2023] Open
Abstract
The seminal description of the cellular restriction factor APOBEC3G and its antagonism by HIV-1 Vif has underpinned two decades of research on the host-virus interaction. We recently reported that HIV-1 Vif is also able to degrade the PPP2R5 family of regulatory subunits of key cellular phosphatase PP2A (PPP2R5A-E; Greenwood et al., 2016; Naamati et al., 2019). We now identify amino acid polymorphisms at positions 31 and 128 of HIV-1 Vif which selectively regulate the degradation of PPP2R5 family proteins. These residues covary across HIV-1 viruses in vivo, favouring depletion of PPP2R5A-E. Through analysis of point mutants and naturally occurring Vif variants, we further show that degradation of PPP2R5 family subunits is both necessary and sufficient for Vif-dependent G2/M cell cycle arrest. Antagonism of PP2A by HIV-1 Vif is therefore independent of APOBEC3 family proteins, and regulates cell cycle progression in HIV-infected cells.
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Affiliation(s)
- Sara Marelli
- Department of Medicine, University of CambridgeCambridgeUnited Kingdom
- Cambridge Institute of Therapeutic Immunology and Infectious Disease (CITIID), University of CambridgeCambridgeUnited Kingdom
| | - James C Williamson
- Department of Medicine, University of CambridgeCambridgeUnited Kingdom
- Cambridge Institute of Therapeutic Immunology and Infectious Disease (CITIID), University of CambridgeCambridgeUnited Kingdom
| | - Anna V Protasio
- Department of Medicine, University of CambridgeCambridgeUnited Kingdom
- Cambridge Institute of Therapeutic Immunology and Infectious Disease (CITIID), University of CambridgeCambridgeUnited Kingdom
| | - Adi Naamati
- Department of Medicine, University of CambridgeCambridgeUnited Kingdom
- Cambridge Institute of Therapeutic Immunology and Infectious Disease (CITIID), University of CambridgeCambridgeUnited Kingdom
| | - Edward JD Greenwood
- Department of Medicine, University of CambridgeCambridgeUnited Kingdom
- Cambridge Institute of Therapeutic Immunology and Infectious Disease (CITIID), University of CambridgeCambridgeUnited Kingdom
| | - Janet E Deane
- Department of Clinical Neuroscience, University of CambridgeCambridgeUnited Kingdom
- Cambridge Institute for Medical Research (CIMR), University of CambridgeCambridgeUnited Kingdom
| | - Paul J Lehner
- Department of Medicine, University of CambridgeCambridgeUnited Kingdom
- Cambridge Institute of Therapeutic Immunology and Infectious Disease (CITIID), University of CambridgeCambridgeUnited Kingdom
| | - Nicholas J Matheson
- Department of Medicine, University of CambridgeCambridgeUnited Kingdom
- Cambridge Institute of Therapeutic Immunology and Infectious Disease (CITIID), University of CambridgeCambridgeUnited Kingdom
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11
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Huang C, Liu T, Wang Q, Hou W, Zhou C, Song Z, Shi YS, Gao X, Chen G, Yin Z, Hu Y. Loss of PP2A Disrupts the Retention of Radial Glial Progenitors in the Telencephalic Niche to Impair the Generation for Late-Born Neurons During Cortical Development†. Cereb Cortex 2020; 30:4183-4196. [PMID: 32186707 DOI: 10.1093/cercor/bhaa042] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Telencephalic radial glial progenitors (RGPs) are retained in the ventricular zone (VZ), the niche for neural stem cells during cortical development. However, the underlying mechanism is not well understood. To study whether protein phosphatase 2A (PP2A) may regulate the above process, we generate Ppp2cα conditional knockout (cKO) mice, in which PP2A catalytic subunit α (PP2Acα) is inactivated in neural progenitor cells in the dorsal telencephalon. We show that RGPs are ectopically distributed in cortical areas outside of the VZ in Ppp2cα cKO embryos. Whereas deletion of PP2Acα does not affect the proliferation of RGPs, it significantly impairs the generation of late-born neurons. We find complete loss of apical adherens junctions (AJs) in the ventricular membrane in Ppp2cα cKO cortices. We observe abundant colocalization for N-cadherin and PP2Acα in control AJs. Moreover, in vitro analysis reveals direct interactions of N-cadherin to PP2Acα and to β-catenin. Overall, this study not only uncovers a novel function of PP2Acα in retaining RGPs into the VZ but also demonstrates the impact of PP2A-dependent retention of RGPs on the generation for late-born neurons.
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Affiliation(s)
- Chaoli Huang
- State Key Laboratory of Pharmaceutical Biotechnology, MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Institute for Brain Sciences, Nanjing University, Nanjing 210061, China
| | - Tingting Liu
- State Key Laboratory of Pharmaceutical Biotechnology, MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Institute for Brain Sciences, Nanjing University, Nanjing 210061, China
| | - Qihui Wang
- State Key Laboratory of Pharmaceutical Biotechnology, MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Institute for Brain Sciences, Nanjing University, Nanjing 210061, China
| | - Weikang Hou
- State Key Laboratory of Pharmaceutical Biotechnology, MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Institute for Brain Sciences, Nanjing University, Nanjing 210061, China
| | - Cuihua Zhou
- Department of Anesthesiology, The Second Affiliated Changzhou People's Hospital of Nanjing Medical University, Changzhou 213000, China
| | - Zeyuan Song
- Department of Anesthesiology, The Second Affiliated Changzhou People's Hospital of Nanjing Medical University, Changzhou 213000, China
| | - Yun Stone Shi
- State Key Laboratory of Pharmaceutical Biotechnology, MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Institute for Brain Sciences, Nanjing University, Nanjing 210061, China
| | - Xiang Gao
- State Key Laboratory of Pharmaceutical Biotechnology, MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Institute for Brain Sciences, Nanjing University, Nanjing 210061, China
| | - Guiquan Chen
- State Key Laboratory of Pharmaceutical Biotechnology, MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Institute for Brain Sciences, Nanjing University, Nanjing 210061, China
| | - Zhenyu Yin
- Department of Geriatric, Nanjing Drum Tower Hospital, Nanjing University Medical School, Nanjing 210008, China
| | - Yimin Hu
- Department of Anesthesiology, The Second Affiliated Changzhou People's Hospital of Nanjing Medical University, Changzhou 213000, China
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12
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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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13
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Aouida M, Eshrif A, Ramotar D. Yeast Lacking the PP2A Phosphatase Regulatory Subunit Rts1 Sensitizes rad51 Mutants to Specific DNA Damaging Agents. Front Genet 2019; 10:1117. [PMID: 31781172 PMCID: PMC6857479 DOI: 10.3389/fgene.2019.01117] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Accepted: 10/16/2019] [Indexed: 11/13/2022] Open
Abstract
Rts1 is a regulatory subunit of the trimeric protein phosphatase 2A phosphatase and it participates in many biological processes by modulating the phosphorylation status of proteins. Consistent with its role, mutants lacking Rts1 display multiple phenotypes. We have previously performed a high throughput screen to search for yeast haploid mutants with altered sensitivity to the anticancer drug bleomycin, which acts by damaging the DNA to produce single and double strand breaks. RTS1 was among the genes that when singly deleted cause sensitivity to bleomycin. We investigate whether Rts1 plays a role in the repair of bleomycin-induced DNA lesions. We show that deletion of the RTS1 gene in the rad51 null background, lacking Rad51 known to be involved in the repair of bleomycin-induced DNA lesions, resulted in double mutants that were sensitized to bleomycin and not to other DNA damaging agents that creates DNA adducts. We further show that Rts1 has the ability to bind to DNA and in its absence cells displayed an increase in the frequency of both spontaneous and bleomycin-induced mutations compared to the parent. This is the first report implicating Rts1 with a role in DNA damage and repair, perhaps regulating the phosphorylation status of one or more proteins involved in the repair of DNA strand breaks.
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Affiliation(s)
- Mustapha Aouida
- College of Health and Life Sciences, Hamad Bin Khalifa University, Education City, Qatar Foundation, Doha, Qatar
| | - Abdelmoez Eshrif
- Maisonneuve-Rosemont Hospital, Research Center, Department of Medicine, Université de Montréal, Montréal, QC, Canada
| | - Dindial Ramotar
- College of Health and Life Sciences, Hamad Bin Khalifa University, Education City, Qatar Foundation, Doha, Qatar.,Maisonneuve-Rosemont Hospital, Research Center, Department of Medicine, Université de Montréal, Montréal, QC, Canada
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14
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Hein AL, Brandquist ND, Ouellette CY, Seshacharyulu P, Enke CA, Ouellette MM, Batra SK, Yan Y. PR55α regulatory subunit of PP2A inhibits the MOB1/LATS cascade and activates YAP in pancreatic cancer cells. Oncogenesis 2019; 8:63. [PMID: 31659153 PMCID: PMC6817822 DOI: 10.1038/s41389-019-0172-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2019] [Revised: 10/02/2019] [Accepted: 10/04/2019] [Indexed: 12/11/2022] Open
Abstract
PP2A holoenzyme complexes are responsible for the majority of Ser/Thr phosphatase activities in human cells. Each PP2A consists of a catalytic subunit (C), a scaffold subunit (A), and a regulatory subunit (B). While the A and C subunits each exists only in two highly conserved isoforms, a large number of B subunits share no homology, which determines PP2A substrate specificity and cellular localization. It is anticipated that different PP2A holoenzymes play distinct roles in cellular signaling networks, whereas PP2A has only generally been defined as a putative tumor suppressor, which is mostly based on the loss-of-function studies using pharmacological or biological inhibitors for the highly conserved A or C subunit of PP2A. Recent studies of specific pathways indicate that some PP2A complexes also possess tumor-promoting functions. We have previously reported an essential role of PR55α, a PP2A regulatory subunit, in the support of oncogenic phenotypes, including in vivo tumorigenicity/metastasis of pancreatic cancer cells. In this report, we have elucidated a novel role of PR55α-regulated PP2A in the activation of YAP oncoprotein, whose function is required for anchorage-independent growth during oncogenesis of solid tumors. Our data show two lines of YAP regulation by PR55α: (1) PR55α inhibits the MOB1-triggered autoactivation of LATS1/2 kinases, the core member of the Hippo pathway that inhibits YAP by inducing its proteasomal degradation and cytoplasmic retention and (2) PR55α directly interacts with and regulates YAP itself. Accordingly, PR55α is essential for YAP-promoted gene transcriptions, as well as for anchorage-independent growth, in which YAP plays a key role. In summary, current findings demonstrate a novel YAP activation mechanism based on the PR55α-regulated PP2A phosphatase.
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Affiliation(s)
- Ashley L Hein
- Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, NE, USA
| | - Nichole D Brandquist
- Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, NE, USA
| | - Caroline Y Ouellette
- Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, NE, USA
| | | | - Charles A Enke
- Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, NE, USA
| | - Michel M Ouellette
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, USA.,Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, USA
| | - Surinder K Batra
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, USA.
| | - Ying Yan
- Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, NE, USA. .,Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, USA.
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15
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El Taweel M, Gawdat RM, Abdelfattah R. Prognostic Impact of PPP2R5C Gene Expression in Adult Acute Myeloid Leukemia Patients with Normal Cytogenetics. Indian J Hematol Blood Transfus 2019; 36:37-46. [PMID: 32158086 DOI: 10.1007/s12288-019-01142-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Accepted: 05/28/2019] [Indexed: 10/26/2022] Open
Abstract
Protein Phosphatase 2A (PP2A) is a crucial regulator of the cellular signalling pathways, proliferation, cell cycle checkpoints and apoptosis. The PPP2R5C gene encodes PP2A regulatory B56γ subunit. Malignant transformation may occur, if mRNA of PPP2R5C is functionally deregulated, structurally altered, decreased or overexpressed. Therefore, the purpose of the study was to examine PPP2R5C mRNA expression, evaluate its association with the different clinical and haematological parameters and determine its prognostic impact in Egyptian adult acute myeloid leukaemia patients with normal cytogenetics (CN-AML). Peripheral blood samples of 50 de novo CN-AML patients and 20 age- and gender-matched healthy controls were examined for PPP2R5C expression by Quantitative Real Time-Polymerase Chain Reaction. The expression levels of PPP2R5C mRNA were significantly higher in the CN-AML samples than in the control samples (P ≤ 0.001). There was a statistical significant difference between the low and high expression levels of PPP2R5C with regard to age (P = 0.005, r = - 0.447, P = 0.001). The patients with an unfavourable response to induction chemotherapy had significant higher PPP2R5C expression levels than those with a favourable response (P = 0.002). There was a significant influence of high PPP2R5C expression levels on the overall survival and progression free survival (P = 0.03, 0.026), respectively. PPP2R5C overexpression is an adverse prognostic factor which affects leukaemogenesis in the CN-AML, it may predict the disease progression and overall survival during the follow-up of the patients.
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Affiliation(s)
- Maha El Taweel
- 1Clinical Pathology Department, National Cancer Institute, Cairo University, Cairo, Egypt
| | - Rania M Gawdat
- 2Clinical and Chemical Pathology Department, Faculty of Medicine, Beni-Suef Teaching Hospital, Beni-Suef University, Beni- Suef, Egypt
| | - Rafaat Abdelfattah
- 3Department of Medical Oncology, National Cancer Institute, Cairo University, Cairo, Egypt
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16
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Fowle H, Zhao Z, Graña X. PP2A holoenzymes, substrate specificity driving cellular functions and deregulation in cancer. Adv Cancer Res 2019; 144:55-93. [PMID: 31349904 PMCID: PMC9994639 DOI: 10.1016/bs.acr.2019.03.009] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
PP2A is a highly conserved eukaryotic serine/threonine protein phosphatase of the PPP family of phosphatases with fundamental cellular functions. In cells, PP2A targets specific subcellular locations and substrates by forming heterotrimeric holoenzymes, where a core dimer consisting of scaffold (A) and catalytic (C) subunits complexes with one of many B regulatory subunits. PP2A plays a key role in positively and negatively regulating a myriad of cellular processes, as it targets a very sizable fraction of the cellular substrates phosphorylated on Ser/Thr residues. This review focuses on insights made toward the understanding on how the subunit composition and structure of PP2A holoenzymes mediates substrate specificity, the role of substrate modulation in the signaling of cellular division, growth, and differentiation, and its deregulation in cancer.
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Affiliation(s)
- Holly Fowle
- Fels Institute for Cancer Research and Molecular Biology and Temple University Lewis Katz School of Medicine, Philadelphia, PA, United States
| | - Ziran Zhao
- Fels Institute for Cancer Research and Molecular Biology and Temple University Lewis Katz School of Medicine, Philadelphia, PA, United States
| | - Xavier Graña
- Fels Institute for Cancer Research and Molecular Biology and Temple University Lewis Katz School of Medicine, Philadelphia, PA, United States.
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17
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Fan L, Liu MH, Guo M, Hu CX, Yan ZW, Chen J, Chen GQ, Huang Y. FAM122A, a new endogenous inhibitor of protein phosphatase 2A. Oncotarget 2018; 7:63887-63900. [PMID: 27588481 PMCID: PMC5325411 DOI: 10.18632/oncotarget.11698] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Accepted: 08/24/2016] [Indexed: 01/19/2023] Open
Abstract
The regulation of the ubiquitously expressed protein phosphatase 2A (PP2A) is essential for various cellular functions such as cell proliferation, transformation, and fate determination. In this study, we demonstrate that the highly conserved protein in mammals, designated FAM122A, directly interacts with PP2A-Aα and B55α rather than B56α subunits, and inhibits the phosphatase activity of PP2A-Aα/B55α/Cα complex. Further, FAM122A potentiates the degradation of catalytic subunit PP2A-Cα with the increased poly-ubiquitination. In agreement, FAM122A silencing inhibits while its overexpression enhances cell growth and colony-forming ability. Collectively, we identify FAM122A as a new endogenous PP2A inhibitor and its physiological and pathophysiological significances warrant to be further investigated.
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Affiliation(s)
- Li Fan
- Department of Pathophysiology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Rui-Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Man-Hua Liu
- Department of Pathophysiology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Rui-Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Meng Guo
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences of Chinese Academy of Sciences and Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Chuan-Xi Hu
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences of Chinese Academy of Sciences and Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Zhao-Wen Yan
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences of Chinese Academy of Sciences and Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Jing Chen
- Department of Pathophysiology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Rui-Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Guo-Qiang Chen
- Department of Pathophysiology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Rui-Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.,Institute of Health Sciences, Shanghai Institutes for Biological Sciences of Chinese Academy of Sciences and Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Ying Huang
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences of Chinese Academy of Sciences and Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
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18
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Sumner RP, Thorne LG, Fink DL, Khan H, Milne RS, Towers GJ. Are Evolution and the Intracellular Innate Immune System Key Determinants in HIV Transmission? Front Immunol 2017; 8:1246. [PMID: 29056936 PMCID: PMC5635324 DOI: 10.3389/fimmu.2017.01246] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Accepted: 09/19/2017] [Indexed: 01/05/2023] Open
Abstract
HIV-1 is the single most important sexually transmitted disease in humans from a global health perspective. Among human lentiviruses, HIV-1 M group has uniquely achieved pandemic levels of human-to-human transmission. The requirement to transmit between hosts likely provides the strongest selective forces on a virus, as without transmission, there can be no new infections within a host population. Our perspective is that evolution of all of the virus-host interactions, which are inherited and perpetuated from host-to-host, must be consistent with transmission. For example, CXCR4 use, which often evolves late in infection, does not favor transmission and is therefore lost when a virus transmits to a new host. Thus, transmission inevitably influences all aspects of virus biology, including interactions with the innate immune system, and dictates the biological niche in which the virus exists in the host. A viable viral niche typically does not select features that disfavor transmission. The innate immune response represents a significant selective pressure during the transmission process. In fact, all viruses must antagonize and/or evade the mechanisms of the host innate and adaptive immune systems that they encounter. We believe that viewing host-virus interactions from a transmission perspective helps us understand the mechanistic details of antiviral immunity and viral escape. This is particularly true for the innate immune system, which typically acts from the very earliest stages of the host-virus interaction, and must be bypassed to achieve successful infection. With this in mind, here we review the innate sensing of HIV, the consequent downstream signaling cascades and the viral restriction that results. The centrality of these mechanisms to host defense is illustrated by the array of countermeasures that HIV deploys to escape them, despite the coding constraint of a 10 kb genome. We consider evasion strategies in detail, in particular the role of the HIV capsid and the viral accessory proteins highlighting important unanswered questions and discussing future perspectives.
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Affiliation(s)
- Rebecca P. Sumner
- Division of Infection and Immunity, University College London, London, United Kingdom
| | - Lucy G. Thorne
- Division of Infection and Immunity, University College London, London, United Kingdom
| | - Doug L. Fink
- Division of Infection and Immunity, University College London, London, United Kingdom
| | - Hataf Khan
- Division of Infection and Immunity, University College London, London, United Kingdom
| | - Richard S. Milne
- Division of Infection and Immunity, University College London, London, United Kingdom
| | - Greg J. Towers
- Division of Infection and Immunity, University College London, London, United Kingdom
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19
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Zhao L, Wang L, Chi C, Lan W, Su Y. The emerging roles of phosphatases in Hedgehog pathway. Cell Commun Signal 2017; 15:35. [PMID: 28931407 PMCID: PMC5607574 DOI: 10.1186/s12964-017-0191-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Accepted: 09/14/2017] [Indexed: 01/12/2023] Open
Abstract
Hedgehog signaling is evolutionarily conserved and plays a pivotal role in cell fate determination, embryonic development, and tissue renewal. As aberrant Hedgehog signaling is tightly associated with a broad range of human diseases, its activities must be precisely controlled. It has been known that several core components of Hedgehog pathway undergo reversible phosphorylations mediated by protein kinases and phosphatases, which acts as an effective regulatory mechanism to modulate Hedgehog signal activities. In contrast to kinases that have been extensively studied in these phosphorylation events, phosphatases were thought to function in an unspecific manner, thus obtained much less emphasis in the past. However, in recent years, increasing evidence has implicated that phosphatases play crucial and specific roles in the context of developmental signaling, including Hedgehog signaling. In this review, we present a summary of current progress on phosphatase studies in Hedgehog pathway, emphasizing the multiple employments of protein serine/threonine phosphatases during the transduction of morphogenic Hedgehog signal in both Drosophila and vertebrate systems, all of which provide insights into the importance of phosphatases in the specific regulation of Hedgehog signaling.
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Affiliation(s)
- Long Zhao
- Cardiovascular Research Center, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, 02129, USA
| | - Liguo Wang
- Institute of Evolution & Marine Biodiversity, College of Marine Life Sciences, Ocean University of China, Qingdao, 266003, China
| | - Chunli Chi
- Institute of Evolution & Marine Biodiversity, College of Marine Life Sciences, Ocean University of China, Qingdao, 266003, China
| | - Wenwen Lan
- Institute of Evolution & Marine Biodiversity, College of Marine Life Sciences, Ocean University of China, Qingdao, 266003, China
| | - Ying Su
- Institute of Evolution & Marine Biodiversity, College of Marine Life Sciences, Ocean University of China, Qingdao, 266003, China.
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20
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Greenwood EJD, Matheson NJ, Wals K, van den Boomen DJH, Antrobus R, Williamson JC, Lehner PJ. Temporal proteomic analysis of HIV infection reveals remodelling of the host phosphoproteome by lentiviral Vif variants. eLife 2016; 5:e18296. [PMID: 27690223 PMCID: PMC5085607 DOI: 10.7554/elife.18296] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Accepted: 09/28/2016] [Indexed: 12/20/2022] Open
Abstract
Viruses manipulate host factors to enhance their replication and evade cellular restriction. We used multiplex tandem mass tag (TMT)-based whole cell proteomics to perform a comprehensive time course analysis of >6500 viral and cellular proteins during HIV infection. To enable specific functional predictions, we categorized cellular proteins regulated by HIV according to their patterns of temporal expression. We focussed on proteins depleted with similar kinetics to APOBEC3C, and found the viral accessory protein Vif to be necessary and sufficient for CUL5-dependent proteasomal degradation of all members of the B56 family of regulatory subunits of the key cellular phosphatase PP2A (PPP2R5A-E). Quantitative phosphoproteomic analysis of HIV-infected cells confirmed Vif-dependent hyperphosphorylation of >200 cellular proteins, particularly substrates of the aurora kinases. The ability of Vif to target PPP2R5 subunits is found in primate and non-primate lentiviral lineages, and remodeling of the cellular phosphoproteome is therefore a second ancient and conserved Vif function.
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Affiliation(s)
- Edward JD Greenwood
- Cambridge Institute for Medical Research, Department of Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Nicholas J Matheson
- Cambridge Institute for Medical Research, Department of Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Kim Wals
- Cambridge Institute for Medical Research, Department of Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Dick JH van den Boomen
- Cambridge Institute for Medical Research, Department of Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Robin Antrobus
- Cambridge Institute for Medical Research, Department of Medicine, University of Cambridge, Cambridge, United Kingdom
| | - James C Williamson
- Cambridge Institute for Medical Research, Department of Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Paul J Lehner
- Cambridge Institute for Medical Research, Department of Medicine, University of Cambridge, Cambridge, United Kingdom
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Metformin inhibits JAK2V617F activity in MPN cells by activating AMPK and PP2A complexes containing the B56α subunit. Exp Hematol 2016; 44:1156-1165.e4. [PMID: 27576133 DOI: 10.1016/j.exphem.2016.08.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2016] [Revised: 08/16/2016] [Accepted: 08/18/2016] [Indexed: 12/18/2022]
Abstract
Metformin suppresses the growth of a variety of malignant hematologic cells. It is widely accepted that metformin inhibits the growth of malignant cells primarily by suppressing the mTOR pathway or regulating autophagy. In contrast, we found another possible mechanism that inhibits the growth of malignant cells, suppression of the activity of the oncogenic kinase JAK2V617F. We identified at least two distinct mechanisms involved in metformin-induced JAK2V617F inhibition. First, metformin increases reactive oxygen species levels in these cells, leading to the inhibition of SHP-2, a positive regulator of JAK2V617F. These effects of metformin require AMPK. Second, metformin activates protein tyrosine phosphatase PP2A, a negative regulator of JAK2V617F. Furthermore, we determined that among the numerous PP2A subfamily members, the PP2A complex containing the B56α subunit is responsible for the inhibition of JAK2V617F. In contrast, the B56α-containing PP2A complex functions as a positive regulator of JAK2V617F by inhibiting AMPK. Finally, we determined that metformin enhances the antileukemic action of ruxolitinib in HEL and SET-2 cells. Our present observations suggest that the combination of metformin with ruxolitinib might be a new therapeutic option for treating JAK2V617F-induced myeloproliferative neoplasms. In addition, activators specific for PP2A complexes containing the B56α subunit may be useful for the treatment of JAK2V617F-induced myeloproliferative neoplasms.
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Promotion of Cell Viability and Histone Gene Expression by the Acetyltransferase Gcn5 and the Protein Phosphatase PP2A in Saccharomyces cerevisiae. Genetics 2016; 203:1693-707. [PMID: 27317677 DOI: 10.1534/genetics.116.189506] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 05/27/2016] [Indexed: 01/23/2023] Open
Abstract
Histone modifications direct chromatin-templated events in the genome and regulate access to DNA sequence information. There are multiple types of modifications, and a common feature is their dynamic nature. An essential step for understanding their regulation, therefore, lies in characterizing the enzymes responsible for adding and removing histone modifications. Starting with a dosage-suppressor screen in Saccharomyces cerevisiae, we have discovered a functional interaction between the acetyltransferase Gcn5 and the protein phosphatase 2A (PP2A) complex, two factors that regulate post-translational modifications. We find that RTS1, one of two genes encoding PP2A regulatory subunits, is a robust and specific high-copy suppressor of temperature sensitivity of gcn5∆ and a subset of other gcn5∆ phenotypes. Conversely, loss of both PP2A(Rts1) and Gcn5 function in the SAGA and SLIK/SALSA complexes is lethal. RTS1 does not restore global transcriptional defects in gcn5∆; however, histone gene expression is restored, suggesting that the mechanism of RTS1 rescue includes restoration of specific cell cycle transcripts. Pointing to new mechanisms of acetylation-phosphorylation cross-talk, RTS1 high-copy rescue of gcn5∆ growth requires two residues of H2B that are phosphorylated in human cells. These data highlight the potential significance of dynamic phosphorylation and dephosphorylation of these deeply conserved histone residues for cell viability.
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23
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Pusey M, Bail S, Xu Y, Buiakova O, Nestor M, Yang JJ, Rice LM. Inhibition of protein methylesterase 1 decreased cancerous phenotypes in endometrial adenocarcinoma cell lines and xenograft tumor models. Tumour Biol 2016; 37:11835-11842. [PMID: 27048286 DOI: 10.1007/s13277-016-5036-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Accepted: 03/28/2016] [Indexed: 12/15/2022] Open
Abstract
Protein methylesterase 1 (PME-1) promotes cancerous phenotypes through the demethylation and inactivation of protein phosphatase 2A. We previously demonstrated that PME-1 overexpression promotes Akt, ERK, and may promote Wnt signaling and increases tumor burden in a xenograft model of endometrial cancer. Here, we show that covalent PME-1 inhibitors decrease cell proliferation and invasive growth in vitro but have no effect in vivo at the concentrations tested; however, depletion of PME-1 with shRNA in an endometrial cancer xenograft model significantly reduced tumor growth. Thus, discovery of more potent PME-1 inhibitors may be beneficial for the treatment of endometrial cancer.
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Affiliation(s)
- Michelle Pusey
- Oncoveda, Cancer Signaling and Cell Cycle Team, Medical Diagnostic Laboratories, LLC, 1000 Waterview Drive, Room 345, Hamilton, NJ, 08691, USA
| | - Sophie Bail
- Oncoveda, Cancer Signaling and Cell Cycle Team, Medical Diagnostic Laboratories, LLC, 1000 Waterview Drive, Room 345, Hamilton, NJ, 08691, USA
| | - Yan Xu
- Invivotek, LLC, 16 Black Forest Road, Hamilton, NJ, 08691, USA
| | - Olesia Buiakova
- Invivotek, LLC, 16 Black Forest Road, Hamilton, NJ, 08691, USA
| | - Mariya Nestor
- Pathology Department, Members of Genesis Biotechnology Group, LLC, Medical Diagnostic Laboratories LLC, 2439 Kuser Road, Hamilton, NJ, 08690, USA
| | - Jing-Jing Yang
- Pathology Department, Members of Genesis Biotechnology Group, LLC, Medical Diagnostic Laboratories LLC, 2439 Kuser Road, Hamilton, NJ, 08690, USA
| | - Lyndi M Rice
- Oncoveda, Cancer Signaling and Cell Cycle Team, Medical Diagnostic Laboratories, LLC, 1000 Waterview Drive, Room 345, Hamilton, NJ, 08691, USA.
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24
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Qureshi O, Cho H, Choudhary M, Seeling JM. A Nonsynonymous/Synonymous Substitution Analysis of the B56 Gene Family Aids in Understanding B56 Isoform Diversity. PLoS One 2015; 10:e0145529. [PMID: 26692027 PMCID: PMC4687035 DOI: 10.1371/journal.pone.0145529] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Accepted: 12/04/2015] [Indexed: 11/18/2022] Open
Abstract
Gene duplication leads to the formation of gene families, wherein purifying or neutral selection maintains the original gene function, while diversifying selection confers new functions onto duplicated genes. The B56 gene family is highly conserved; it is encoded by one gene in protists and fungi, and five genes in vertebrates. B56 regulates protein phosphatase 2A (PP2A), an abundant heterotrimeric serine/threonine phosphatase that functions as a tumor suppressor and consists of a scaffolding “A” and catalytic “C” subunit heterodimer bound to a regulatory “B” subunit. Individual regulatory B56 subunits confer disparate functions onto PP2A in various cell-cell signaling pathways. B56 proteins share a conserved central core domain, but have divergent N- and C-termini which play a role in isoform specificity. We carried out a nonsynonymous/synonymous substitution analysis to better understand the divergence of vertebrate B56 genes. When five B56 paralogs from ten vertebrate species were analyzed, the gene family displayed purifying selection; stronger purifying selection was revealed when individual B56 isoforms were analyzed separately. The B56 core experienced stronger purifying selection than the N- and C-termini, which correlates with the presence of several contacts between the core and the AC heterodimer. Indeed, the majority of the contact points that we analyzed between B56 and the AC heterodimer experienced strong purifying selection. B56 subfamilies showed distinct patterns of selection in their N- and C-termini. The C-terminus of the B56-1 subfamily and the N-terminus of the B56-2 subfamily exhibited strong purifying selection, suggesting that these termini carry out subfamily-specific functions, while the opposite termini exhibited diversifying selection and likely carry out isoform-specific functions. We also found reduced synonymous substitutions at the N- and C-termini when grouping B56 genes by species but not by isoform, suggesting species-specific codon bias may have a role in regulating B56 gene expression.
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Affiliation(s)
- Osama Qureshi
- Department of Biological Sciences, Sam Houston State University, Huntsville, TX, United States of America
| | - Hyuk Cho
- Department of Computer Science, Sam Houston State University, Huntsville, TX, United States of America
| | - Madhusudan Choudhary
- Department of Biological Sciences, Sam Houston State University, Huntsville, TX, United States of America
| | - Joni M Seeling
- Department of Biological Sciences, Sam Houston State University, Huntsville, TX, United States of America
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Maertens GN. B'-protein phosphatase 2A is a functional binding partner of delta-retroviral integrase. Nucleic Acids Res 2015; 44:364-76. [PMID: 26657642 PMCID: PMC4705670 DOI: 10.1093/nar/gkv1347] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 11/19/2015] [Indexed: 12/31/2022] Open
Abstract
To establish infection, a retrovirus must insert a DNA copy of its RNA genome into host chromatin. This reaction is catalysed by the virally encoded enzyme integrase (IN) and is facilitated by viral genus-specific host factors. Herein, cellular serine/threonine protein phosphatase 2A (PP2A) is identified as a functional IN binding partner exclusive to δ-retroviruses, including human T cell lymphotropic virus type 1 and 2 (HTLV-1 and HTLV-2) and bovine leukaemia virus (BLV). PP2A is a heterotrimer composed of a scaffold, catalytic and one of any of four families of regulatory subunits, and the interaction is specific to the B' family of the regulatory subunits. B'-PP2A and HTLV-1 IN display nuclear co-localization, and the B' subunit stimulates concerted strand transfer activity of δ-retroviral INs in vitro. The protein-protein interaction interface maps to a patch of highly conserved residues on B', which when mutated render B' incapable of binding to and stimulating HTLV-1 and -2 IN strand transfer activity.
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Affiliation(s)
- Goedele N Maertens
- Division of Infectious Diseases, St. Mary's campus, Imperial College London, Norfolk Place, London, W2 1PG, UK
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26
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Kurimchak A, Graña X. PP2A: more than a reset switch to activate pRB proteins during the cell cycle and in response to signaling cues. Cell Cycle 2015; 14:18-30. [PMID: 25483052 PMCID: PMC4612414 DOI: 10.4161/15384101.2014.985069] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
In their active hypophosphorylated state, members of the retinoblastoma family of pocket proteins negatively regulate cell cycle progression at least in part by repressing expression of E2F-dependent genes. Mitogen-dependent activation of G1 and G1/S Cyclin Dependent Kinases (CDKs) results in coordinated hyperphosphorylation and inactivation of these proteins, which no longer bind and repress E2Fs. S and G2/M CDKs maintain pocket protein hyperphosphorylated through the end of mitosis. The inactivating action of inducible CDKs is opposed by the Ser/Thr protein phosphatases PP2A and PP1. Various trimeric PP2A holoenzymes have been implicated in dephosphorylation of pocket proteins in response to specific cellular signals and stresses or as part of an equilibrium with CDKs throughout the cell cycle. PP1 has specifically been implicated in dephosphorylation of pRB in late mitosis and early G1. This review is particularly focused on the emerging role of PP2A as a major hub for integration of growth suppressor signals that require rapid inactivation of pocket proteins. Of note, activation of particular PP2A holoenzymes triggers differential activation of pocket proteins in the presence of active CDKs.
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Affiliation(s)
- Alison Kurimchak
- a Fels Institute for Cancer Research and Molecular Biology and Department of Biochemistry; Temple University School of Medicine ; Philadelphia , PA USA
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27
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Sun D, Buttitta L. Protein phosphatase 2A promotes the transition to G0 during terminal differentiation in Drosophila. Development 2015; 142:3033-45. [PMID: 26253406 DOI: 10.1242/dev.120824] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2014] [Accepted: 07/28/2015] [Indexed: 12/22/2022]
Abstract
Protein phosphatase type 2A complex (PP2A) has been known as a tumor suppressor for over two decades, but it remains unclear exactly how it suppresses tumor growth. Here, we provide data indicating a novel role for PP2A in promoting the transition to quiescence upon terminal differentiation in vivo. Using Drosophila eyes and wings as a model, we find that compromising PP2A activity during the final cell cycle prior to a developmentally controlled cell cycle exit leads to extra cell divisions and delays entry into quiescence. By systematically testing the regulatory subunits of Drosophila PP2A, we find that the B56 family member widerborst (wdb) is required for the role of PP2A in promoting the transition to quiescence. Cells in differentiating tissues with compromised PP2A retain high Cdk2 activity when they should be quiescent, and genetic epistasis tests demonstrate that ectopic Cyclin E/Cdk2 activity is responsible for the extra cell cycles caused by PP2A inhibition. The loss of wdb/PP2A function cooperates with aberrantly high Cyclin E protein levels, allowing cells to bypass a robust G0 late in development. This provides an example of how loss of PP2A can cooperate with oncogenic mutations in cancer. We propose that the PP2A complex plays a novel role in differentiating tissues to promote developmentally controlled quiescence through the regulation of Cyclin E/Cdk2 activity.
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Affiliation(s)
- Dan Sun
- University of Michigan, Department of Molecular, Cellular and Developmental Biology, Ann Arbor, MI 48109, USA
| | - Laura Buttitta
- University of Michigan, Department of Molecular, Cellular and Developmental Biology, Ann Arbor, MI 48109, USA
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28
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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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29
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Ohno S, Naito Y, Mukai S, Yabuta N, Nojima H. ELAS1-mediated inhibition of the cyclin G1-B'γ interaction promotes cancer cell apoptosis via stabilization and activation of p53. Oncogene 2015; 34:5983-96. [PMID: 25915850 DOI: 10.1038/onc.2015.47] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Revised: 01/09/2015] [Accepted: 01/27/2015] [Indexed: 12/16/2022]
Abstract
Radiation therapy (RT) is useful for selectively killing cancer cells. However, because high levels of ionizing radiation (IR) are toxic to normal cells, RT cannot be applied repeatedly to cancer patients. Therefore, novel chemicals that enhance the efficacy of chemoradiotherapy (CRT) would be valuable. Here, we report that ELAS1, a peptide corresponding to the protein phosphatase 2A (PP2A) association domain of cyclin G1 (CycG1), can enhance the efficacy of CRT. ELAS1 interacts with the PP2A B'γ-subunit and competitively inhibits association with CycG1, thereby preventing the PP2A holoenzyme from dephosphorylating target proteins, Mdm2 (pT218) and p53 (pS46), following DNA double-strand break (DSB) insults. Doxycycline (Dox)-induced overexpression of Myc-ELAS1 caused γ-irradiation to induce apoptosis in human osteosarcoma (U2OS) cells, at 1/10th the effective dosage of γ-irradiation required for apoptosis in Myc-vector-expressing cells; ELAS1 peptide incorporation into U2OS cells also showed similar apoptotic effects. Moreover, administration of DSB-inducing chemicals, camptothecin (CPT) or irinotecan, to Myc-ELAS1-expressing U2OS cells also induced efficient apoptosis with only 1/100th (CPT) or 1/5th (irinotecan) of the amounts of drugs required for this effect in Myc-vector-expressing cells. Taken together, ELAS1 may be important for the design of ELAS1-mimetic compounds to improve CRT efficacy.
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Affiliation(s)
- S Ohno
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - Y Naito
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - S Mukai
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - N Yabuta
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
| | - H Nojima
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
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30
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Kiely M, Kiely PA. PP2A: The Wolf in Sheep's Clothing? Cancers (Basel) 2015; 7:648-69. [PMID: 25867001 PMCID: PMC4491676 DOI: 10.3390/cancers7020648] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Revised: 03/16/2015] [Accepted: 03/23/2015] [Indexed: 12/21/2022] Open
Abstract
Protein Phosphatase 2A (PP2A) is a major serine/threonine phosphatase in cells. It consists of a catalytic subunit (C), a structural subunit (A), and a regulatory/variable B-type subunit. PP2A has a critical role to play in homeostasis where its predominant function is as a phosphatase that regulates the major cell signaling pathways in cells. Changes in the assembly, activity and substrate specificity of the PP2A holoenzyme have a direct role in disease and are a major contributor to the maintenance of the transformed phenotype in cancer. We have learned a lot about how PP2A functions from specific mutations that disrupt the core assembly of PP2A and from viral proteins that target PP2A and inhibit its effect as a phosphatase. This prompted various studies revealing that restoration of PP2A activity benefits some cancer patients. However, our understanding of the mechanism of action of this is limited because of the complex nature of PP2A holoenzyme assembly and because it acts through a wide variety of signaling pathways. Information on PP2A is also conflicting as there are situations whereby inactivation of PP2A induces apoptosis in many cancer cells. In this review we discuss this relationship and we also address many of the pertinent and topical questions that relate to novel therapeutic strategies aimed at altering PP2A activity.
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Affiliation(s)
- Maeve Kiely
- Department of Life Sciences, and Materials and Surface Science Institute, University of Limerick, Limerick 78666, Ireland.
| | - Patrick A Kiely
- Department of Life Sciences, and Materials and Surface Science Institute, University of Limerick, Limerick 78666, Ireland.
- Stokes Institute, University of Limerick 78666, Limerick, Ireland.
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31
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Jin Z, Chung JW, Mei W, Strack S, He C, Lau GW, Yang J. Regulation of nuclear-cytoplasmic shuttling and function of Family with sequence similarity 13, member A (Fam13a), by B56-containing PP2As and Akt. Mol Biol Cell 2015; 26:1160-73. [PMID: 25609086 PMCID: PMC4357514 DOI: 10.1091/mbc.e14-08-1276] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Recent genome-wide association studies reveal that the FAM13A gene is associated with human lung function and a variety of lung diseases, including chronic obstructive pulmonary disease, asthma, lung cancer, and pulmonary fibrosis. The biological functions of Fam13a, however, have not been studied. In an effort to identify novel substrates of B56-containing PP2As, we found that B56-containing PP2As and Akt act antagonistically to control reversible phosphorylation of Fam13a on Ser-322. We show that Ser-322 phosphorylation acts as a molecular switch to control the subcellular distribution of Fam13a. Fam13a shuttles between the nucleus and cytoplasm. When Ser-322 is phosphorylated by Akt, the binding between Fam13a and 14-3-3 is enhanced, leading to cytoplasmic sequestration of Fam13a. B56-containing PP2As dephosphorylate phospho-Ser-322 and promote nuclear localization of Fam13a. We generated Fam13a-knockout mice. Fam13a-mutant mice are viable and healthy, indicating that Fam13a is dispensable for embryonic development and physiological functions in adult animals. Intriguingly, Fam13a has the ability to activate the Wnt pathway. Although Wnt signaling remains largely normal in Fam13a-knockout lungs, depletion of Fam13a in human lung cancer cells causes an obvious reduction in Wnt signaling activity. Our work provides important clues to elucidating the mechanism by which Fam13a may contribute to human lung diseases.
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Affiliation(s)
- Zhigang Jin
- Department of Comparative Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61802
| | - Jin Wei Chung
- Department of Comparative Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61802
| | - Wenyan Mei
- Department of Comparative Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61802
| | - Stefan Strack
- Department of Pharmacology, University of Iowa Carver College of Medicine, Iowa City, IA 52242
| | - Chunyan He
- Department of Epidemiology, Richard M. Fairbanks School of Public Health, Indiana University, Indianapolis, IN 46202
| | - Gee W Lau
- Department of Pathobiology, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61802
| | - Jing Yang
- Department of Comparative Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61802
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32
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Park M, Choi YA, Lee HG, Kim KI, Lim JS, Lee MS, Oh KS, Yang Y. Dephosphorylation of CCAAT/enhancer-binding protein β by protein phosphatase 2A containing B56δ is required at the early time of adipogenesis. Biochim Biophys Acta Mol Cell Biol Lipids 2014; 1841:1608-18. [PMID: 25152162 DOI: 10.1016/j.bbalip.2014.08.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Revised: 07/26/2014] [Accepted: 08/12/2014] [Indexed: 12/11/2022]
Abstract
It is known that protein phosphatase 2A (PP2A) expression is increased in high-fat diet (HFD)-induced obese mice, but the role of PP2A in adipogenesis as well as obesity remains to be addressed. In this study, the role of PP2A in adipogenesis was explored. Preadipocytes were treated with okadaic acid (OA) during adipogenesis and the degree of adipogenesis was determined. The OA treatment blocked adipogenesis at the early time of adipogenesis, but not at the late time. In the early time of adipogenesis, CCAAT/enhancer-binding protein β (C/EBPβ) activation is preceded by the expression of key adipogenic transcription factors including PPARγ and C/EBPα, which function at the late time of adipogenesis, and then C/EBPβ is degraded. However, the inhibition of PP2A by OA treatment sustained phosphorylation of C/EBPβ and delayed its degradation. In turn, PPARγ and C/EBPα activation was altered. Among the various regulatory B56 subunits consisting of PP2A holoenzyme, B56δ was directly bound to C/EBPβ and was responsible for the dephosphorylation of C/EBPβ by PP2A. Taken together, these findings suggest that the phosphorylation of C/EBPβ after hormonal induction has to be inactivated by PP2A containing B56δ at the early time of adipogenesis to allow the completion of adipogenesis.
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Affiliation(s)
- Miyoung Park
- Department of Life Science, Sookmyung Women's University, Seoul 140-742, Republic of Korea
| | - Yeon A Choi
- Department of Life Science, Sookmyung Women's University, Seoul 140-742, Republic of Korea
| | - Hee Gu Lee
- Korea Research Institute of Bioscience and Biotechnology, Daejon 305-333, Republic of Korea
| | - Keun Il Kim
- Department of Life Science, Sookmyung Women's University, Seoul 140-742, Republic of Korea
| | - Jong-Seok Lim
- Department of Life Science, Sookmyung Women's University, Seoul 140-742, Republic of Korea
| | - Myeong-Sok Lee
- Department of Life Science, Sookmyung Women's University, Seoul 140-742, Republic of Korea
| | - Ki-Sook Oh
- Department of Life Science, Sookmyung Women's University, Seoul 140-742, Republic of Korea
| | - Young Yang
- Department of Life Science, Sookmyung Women's University, Seoul 140-742, Republic of Korea.
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Bernal M, Zhurinsky J, Iglesias-Romero AB, Sanchez-Romero MA, Flor-Parra I, Tomas-Gallardo L, Perez-Pulido AJ, Jimenez J, Daga RR. Proteome-wide search for PP2A substrates in fission yeast. Proteomics 2014; 14:1367-80. [PMID: 24634168 DOI: 10.1002/pmic.201300136] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Revised: 02/19/2014] [Accepted: 03/07/2014] [Indexed: 11/10/2022]
Abstract
PP2A (protein phosphatase 2A) is a major phosphatase in eukaryotic cells that plays an essential role in many processes. PP2A mutations in Schizosaccharomyces pombe result in defects of cell cycle control, cytokinesis and morphogenesis. Which PP2A substrates are responsible for these changes is not known. In this work, we searched for PP2A substrates in S. pombe using two approaches, 2D-DIGE analysis of PP2A complex mutants and identification of PP2A interacting proteins. In both cases, we used MS to identify proteins of interest. In the DIGE experiment, we compared proteomes of wild-type S. pombe, deletion of pta2, the phosphoactivator of the PP2A catalytic subunit, and pab1-4, a mutant of B-type PP2A regulatory subunit. A total of 1742 protein spots were reproducibly resolved by 2D-DIGE and 51 spots demonstrated significant changes between PP2A mutants and the wild-type control. MS analysis of these spots identified 27 proteins that include key regulators of glycerol synthesis, carbon metabolism, amino acid biosyntesis, vitamin production, and protein folding. Importantly, we independently identified a subset of these proteins as PP2A binding partners by affinity precipitation, suggesting they may be direct targets of PP2A. We have validated our approach by demonstrating that phosphorylation of Gpd1, a key enzyme in glycerol biogenesis, is regulated by PP2A and that ability of cells to respond to osmotic stress by synthesizing glycerol is compromised in the PP2A mutants. Our work contributes to a better understanding of PP2A function and identifies potential PP2A substrates.
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Affiliation(s)
- Manuel Bernal
- Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide-Consejo Superior de Investigaciones Científicas, Junta de Andalucía, Sevilla, Spain
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Backendorf C, Noteborn MHM. Apoptin Towards Safe and Efficient Anticancer Therapies. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 818:39-59. [DOI: 10.1007/978-1-4471-6458-6_3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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Chen Y, Liu S, Shen Q, Zha X, Zheng H, Yang L, Chen S, Wu X, Li B, Li Y. Differential gene expression profiles of PPP2R5C-siRNA-treated malignant T cells. DNA Cell Biol 2013; 32:573-81. [PMID: 23941244 DOI: 10.1089/dna.2013.2138] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Recently, alterations in the expression pattern of PPP2R5C associated with malignant transformation have been characterized, and PPP2R5C overexpression was demonstrated in leukemias. To confirm the role of PPP2R5C in proliferation and its molecular mechanism, three PPP2R5C-siRNAs and a scrambled nonsilencing siRNA control were used to treat Molt-4 and Jurkat T cells. After nucleofection, PPP2R5C expression and biological consequences based on a highly efficient and specific PPP2R5C-siRNA were demonstrated by qRT-PCR, CCK-8 assay, Annexin V/PI, and flow cytometry. The global gene expression profile of PPP2R5C-siRNA-treated Jurkat T cells was established. A significant reduction in the PPP2R5C mRNA level was observed at 24 to 72 h in Molt-4 and Jurkat T cells with all of the PPP2R5C-siRNAs. The proliferation rate of Molt-4 and Jurkat T cells transfected with different PPP2R5C-siRNAs was significantly decreased at 72 h compared with the control (p<0.05). However, the transfected cells did not show a significant increase in Annexin V/PI-positive cells (apoptosis). The highly efficient PPP2R5C-siRNA2 was used to treat Jurkat T cells for gene expression profile analysis. In total, 439 genes were upregulated, and 524 genes were downregulated at least twofold in PPP2R5C-siRNA-treated Jurkat T cells. Changes in signaling pathway genes closely related to the TCR, Wnt, calcium, MAPK, and p53 signaling pathways were observed. In conclusion, the suppression of PPP2R5C by RNA interference could effectively inhibit the proliferation of leukemic T cells, the PPP2R5C-siRNA treatment altered gene expression profiles, and the differential expression of the glycogen synthase kinase 3 beta (GSK-3β), ataxia telangiectasia mutated (ATM), and Mdm2 p53 binding protein homolog (MDM2) genes may play an important role in the effects of PPP2R5C knockdown in Jurkat T cells.
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Affiliation(s)
- Yu Chen
- 1 Key Laboratory for Regenerative Medicine of Ministry of Education, Jinan University , Guangzhou, China
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MacKay KB, Tu Y, Young SG, Clarke SG. Circumventing embryonic lethality with Lcmt1 deficiency: generation of hypomorphic Lcmt1 mice with reduced protein phosphatase 2A methyltransferase expression and defects in insulin signaling. PLoS One 2013; 8:e65967. [PMID: 23840384 PMCID: PMC3688711 DOI: 10.1371/journal.pone.0065967] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Accepted: 05/03/2013] [Indexed: 11/18/2022] Open
Abstract
Protein phosphatase 2A (PP2A), the major serine/threonine phosphatase in eukaryotic cells, is a heterotrimeric protein composed of structural, catalytic, and targeting subunits. PP2A assembly is governed by a variety of mechanisms, one of which is carboxyl-terminal methylation of the catalytic subunit by the leucine carboxyl methyltransferase LCMT1. PP2A is nearly stoichiometrically methylated in the cytosol, and although some PP2A targeting subunits bind independently of methylation, this modification is required for the binding of others. To examine the role of this methylation reaction in mammalian tissues, we generated a mouse harboring a gene-trap cassette within intron 1 of Lcmt1. Due to splicing around the insertion, Lcmt1 transcript and LCMT1 protein levels were reduced but not eliminated. LCMT1 activity and methylation of PP2A were reduced in a coordinate fashion, suggesting that LCMT1 is the only PP2A methyltransferase. These mice exhibited an insulin-resistance phenotype, indicating a role for this methyltransferase in signaling in insulin-sensitive tissues. Tissues from these animals will be vital for the in vivo identification of methylation-sensitive substrates of PP2A and how they respond to differing physiological conditions.
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Affiliation(s)
- Kennen B. MacKay
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California, United States of America
- Molecular Biology Institute, University of California Los Angeles, Los Angeles, California, United States of America
| | - Yiping Tu
- Department of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
| | - Stephen G. Young
- Molecular Biology Institute, University of California Los Angeles, Los Angeles, California, United States of America
- Department of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
- Department of Human Genetics, University of California Los Angeles, Los Angeles, California, United States of America
| | - Steven G. Clarke
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California, United States of America
- Molecular Biology Institute, University of California Los Angeles, Los Angeles, California, United States of America
- * E-mail:
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Naito Y, Yabuta N, Sato J, Ohno S, Sakata M, Kasama T, Ikawa M, Nojima H. Recruitment of cyclin G2 to promyelocytic leukemia nuclear bodies promotes dephosphorylation of γH2AX following treatment with ionizing radiation. Cell Cycle 2013; 12:1773-84. [PMID: 23656780 DOI: 10.4161/cc.24878] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Cyclin G2 (CycG2) and Cyclin G1 (CycG1), two members of the Cyclin G subfamily, share high amino acid homology in their Cyclin G boxes. Functionally, they play a common role as association partners of the B'γ subunit of protein phosphatase 2A (PP2A) and regulate PP2A function, and their expression is increased following DNA damage. However, whether or not CycG1 and CycG2 have distinct roles during the cellular DNA damage response has remained unclear. Here, we report that CycG2, but not CycG1, co-localized with promyelocytic leukemia (PML) and γH2AX, forming foci following ionizing radiation (IR), suggesting that CycG2 is recruited to sites of DNA repair and that CycG1 and CycG2 have distinct functions. PML failed to localize to nuclear foci when CycG2 was depleted, and vice versa. This suggests that PML and CycG2 mutually influence each other's functions following IR. Furthermore, we generated CycG2-knockout (Ccng2 (-/-) ) mice to investigate the functions of CycG2. These mice were born healthy and developed normally. However, CycG2-deficient mouse embryonic fibroblasts displayed an abnormal response to IR. Dephosphorylation of γH2AX and checkpoint kinase 2 following IR was delayed in Ccng2 (-/-) cells, suggesting that DNA damage repair may be perturbed in the absence of CycG2. Although knockdown of B'γ in wild-type cells also delayed dephosphorylation of γH2AX, knockdown of B'γ in Ccng2 (-/-) cells prolonged this delay, suggesting that CycG2 cooperates with B'γ to dephosphorylate γH2AX. Taken together, we conclude that CycG2 is localized at DNA repair foci following DNA damage, and that CycG2 regulates the dephosphorylation of several factors necessary for DNA repair.
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Affiliation(s)
- Yoko Naito
- Department of Molecular Genetics, Research Institute for Microbial Diseases, Osaka University, Suita City, Osaka, Japan
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Impaired expression of protein phosphatase 2A subunits enhances metastatic potential of human prostate cancer cells through activation of AKT pathway. Br J Cancer 2013; 108:2590-600. [PMID: 23598299 PMCID: PMC3694226 DOI: 10.1038/bjc.2013.160] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Background: Protein phosphatase 2A (PP2A) is a dephosphorylating enzyme, loss of which can contribute to prostate cancer (PCa) pathogenesis. The aim of this study was to analyse the transcriptional and translational expression patterns of individual subunits of the PP2A holoenzyme during PCa progression. Methods: Immunohistochemistry (IHC), western blot, and real-time PCR was performed on androgen-dependent (AD) and androgen-independent (AI) PCa cells, and benign and malignant prostate tissues for all the three PP2A (scaffold, regulatory, and catalytic) subunits. Mechanistic and functional studies were performed using various biochemical and cellular techniques. Results: Through immunohistochemical analysis we observed significantly reduced levels of PP2A-A and -B′γ subunits (P<0.001 and P=0.0002) in PCa specimens compared with benign prostate. Contemporarily, there was no significant difference in PP2A-C subunit expression between benign and malignant tissues. Similar to the expression pattern observed in tissues, the endogenous levels of PP2A-A and B′γ subunits were abrogated from the low metastatic to high metastatic and AD to AI cell line models, without any change in the catalytic subunit expression. Furthermore, using in vitro studies we demonstrated that PP2A-Aα scaffold subunit has a role in dampening AKT, β-catenin, and FAK (focal adhesion kinase) signalling. Conclusion: We conclude that loss of expression of scaffold and regulatory subunits of PP2A is responsible for its altered function during PCa pathogenesis.
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Sakowicz-Burkiewicz M, Kitowska A, Grden M, Maciejewska I, Szutowicz A, Pawelczyk T. Differential effect of adenosine receptors on growth of human colon cancer HCT 116 and HT-29 cell lines. Arch Biochem Biophys 2013; 533:47-54. [PMID: 23454010 DOI: 10.1016/j.abb.2013.02.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Revised: 02/01/2013] [Accepted: 02/18/2013] [Indexed: 11/27/2022]
Abstract
The study aimed to evaluate the impact of adenosine receptors (ARs) on human colon tumor cells (HCT 116, HT-29) growth and sensitivity to 5-Fluorouracil (5-FU) an anticancer chemotherapeutic drug. The exposure of cancer cells to a selective A(3)-AR agonist (IB-MECA) resulted in an increase in HT-29 cells number, whereas the number of HCT 116 cells decreased significantly. In the presence of IB-MECA (1 μM) the percentage of apoptotic HT-29 cells significantly decreased, whereas the number of apoptotic and necrotic HCT 116 cells increased by 3- and 2,5-fold, respectively. The application of a selective A(2A)-AR agonist resulted in the increased survival of HCT 116 cells, but not HT-29 cells. The blockade of A(2A)-AR with ZM 241385 (0.1 μM) significantly increased the cytotoxicity of 5-FU (1 μM) in HCT 116 cells but not in HT-29 cells. The suppression of A(3)-AR with MRS 1523 (1 μM) increased the sensitivity of HT-29 cells to 5-FU while response of HCT 116 cells to 5-FU decreased. The growth promoting effect of IB-MECA in HT-29 cells was associated with the decreased intracellular cAMP level, whereas IB-MECA growth inhibitory effect in HCT 116 cells was abolished by okadaic acid (2 nM) indicating the involvement of protein phosphatase PP2A.
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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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Oberg EA, Nifoussi SK, Gingras AC, Strack S. Selective proteasomal degradation of the B'β subunit of protein phosphatase 2A by the E3 ubiquitin ligase adaptor Kelch-like 15. J Biol Chem 2012; 287:43378-89. [PMID: 23135275 DOI: 10.1074/jbc.m112.420281] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Protein phosphatase 2A (PP2A), a ubiquitous and pleiotropic regulator of intracellular signaling, is composed of a core dimer (AC) bound to a variable (B) regulatory subunit. PP2A is an enzyme family of dozens of heterotrimers with different subcellular locations and cellular substrates dictated by the B subunit. B'β is a brain-specific PP2A regulatory subunit that mediates dephosphorylation of Ca(2+)/calmodulin-dependent protein kinase II and tyrosine hydroxylase. Unbiased proteomic screens for B'β interactors identified Cullin3 (Cul3), a scaffolding component of E3 ubiquitin ligase complexes, and the previously uncharacterized Kelch-like 15 (KLHL15). KLHL15 is one of ∼40 Kelch-like proteins, many of which have been identified as adaptors for the recruitment of substrates to Cul3-based E3 ubiquitin ligases. Here, we report that KLHL15-Cul3 specifically targets B'β to promote turnover of the PP2A subunit by ubiquitylation and proteasomal degradation. Comparison of KLHL15 and B'β tissue expression profiles suggests that the E3 ligase adaptor contributes to selective expression of the PP2A/B'β holoenzyme in the brain. We mapped KLHL15 residues critical for homodimerization as well as interaction with Cul3 and B'β. Explaining PP2A subunit selectivity, the divergent N terminus of B'β was found necessary and sufficient for KLHL15-mediated degradation, with Tyr-52 having an obligatory role. Although KLHL15 can interact with the PP2A/B'β heterotrimer, it only degrades B'β, thus promoting exchange with other regulatory subunits. E3 ligase adaptor-mediated control of PP2A holoenzyme composition thereby adds another layer of regulation to cellular dephosphorylation events.
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Affiliation(s)
- Elizabeth A Oberg
- Department of Pharmacology, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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Abstract
Directed protein phosphorylation is indisputably critical for a multitude of cellular processes. A growing body of research demonstrates A kinase anchoring proteins (AKAPs) to mediate a significant number of phosphorylation events in the heart. By acting as molecular tethers for the regulatory subunit of protein kinase A, AKAPs focus kinase activity onto specific substrate. In the time since their discovery, the AKAP model has evolved in appreciation of the broader role these scaffolds play in coordinating multiple signaling enzymes to efficiently regulate dynamic cellular processes. The focus of this review is on the emerging role of AKAPs in regulating the 3 main cardiac phosphatases: Protein Phosphatase 1 by AKAP18 and Yotiao, and Protein Phosphatases 2A and 2B by muscle specific A-kinase anchoring protein.
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Kumar A, Pandurangan AK, Lu F, Fyrst H, Zhang M, Byun HS, Bittman R, Saba JD. Chemopreventive sphingadienes downregulate Wnt signaling via a PP2A/Akt/GSK3β pathway in colon cancer. Carcinogenesis 2012; 33:1726-35. [PMID: 22581840 DOI: 10.1093/carcin/bgs174] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Sphingadienes (SDs) derived from soy and other natural sphingolipids are cytotoxic to colon cancer cells via an Akt-dependent mechanism and reduce adenoma formation in Apc(Min/+) mice. Wnt signaling is fundamental to colon carcinogenesis and is the basis for spontaneous tumorigenesis in Apc(Min/+) mice and patients with familial adenomatous polyposis. In the present study, we investigated the impact of SDs on Wnt signaling. Oral SD administration reduced levels of active β-catenin and Wnt targets c-Myc and cyclin D1 in Apc(Min/+) mouse intestinal tissues. Colon cancer cells treated with SDs exhibited reduced Wnt transcriptional activity, as well as reduced nuclear β-catenin localization and subsequent reduction in active-β-catenin levels. Further, we observed a decrease in phosphorylated (inactive) GSK3β in SD-treated mice and colon cancer cells. Expression of constitutively active myristoylated-Akt or inactivation of GSK3β using LiCl attenuated SD-mediated inhibition of Wnt transcriptional activity and active-β-catenin levels. SDs exhibited additive effects with inhibitors of the phosphatidylinositol-3-kinase/Akt/mTOR pathway to induce cytotoxicity. Further, a combination regime of SDs and low-dose rapamycin decreased visible polyps in Apc(Min/+) mice and reduced the levels of Wnt target gene expression and mTOR target activation. SD-mediated inhibition of Akt and Wnt pathways and cytotoxicity in colon cancer cells was dependent upon the activity of protein phosphatase 2A, as shown by reversal of these effects by pretreatment with okadaic acid or calyculin A. Our cumulative findings indicate that SDs inhibit Wnt signaling through a protein phosphatase 2A/Akt/GSK3β-dependent mechanism that may contribute to their chemopreventive effects in intestinal tumorigenesis.
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Affiliation(s)
- Ashok Kumar
- Center for Cancer Research, Children's Hospital Oakland Research Institute, Oakland, CA 94609, USA
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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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Abstract
Alterations in the functional levels of cyclin-dependent kinase-8 (CDK8) or its partner, cyclin C, have been clearly associated with cancers, including colon cancer, melanoma, and osteosarcoma. Walleye dermal sarcoma virus encodes a retroviral cyclin (RV-cyclin) that localizes to interchromatin granule clusters and binds CDK8. It also binds to the Aα subunit (PR65) of protein phosphatase 2A (PP2A). Binding to the Aα subunit excludes the regulatory B subunit, but not the catalytic C subunit, in a manner similar to that of T antigens of the small DNA tumor viruses. The expression of the RV-cyclin enhances the activity of immune affinity-purified CDK8 in vitro for RNA polymerase II carboxy-terminal domain (CTD) and histone H3 substrates. PP2A also enhances CDK8 kinase activity in vitro for the CTD but not for histone H3. The PP2A enhancement of CDK8 is independent of RV-cyclin expression and likely plays a role in the normal regulation of CDK8. The manipulation of endogenous PP2A activity by inhibition, amendment, or depletion confirmed its role in CDK8 activation by triggering CDK8 autophosphorylation. Although RV-cyclin and PP2A both enhance CDK8 activity, their actions are uncoupled and additive in kinase reactions. PP2A may be recruited to CDK8 in the Mediator complex by a specific PP2A B subunit or additionally by the RV-cyclin in infected cells, but the RV-cyclin appears to activate CDK8 directly and in a manner independent of its physical association with PP2A.
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Bononi A, Agnoletto C, De Marchi E, Marchi S, Patergnani S, Bonora M, Giorgi C, Missiroli S, Poletti F, Rimessi A, Pinton P. Protein kinases and phosphatases in the control of cell fate. Enzyme Res 2011; 2011:329098. [PMID: 21904669 PMCID: PMC3166778 DOI: 10.4061/2011/329098] [Citation(s) in RCA: 209] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2011] [Revised: 05/06/2011] [Accepted: 06/08/2011] [Indexed: 12/19/2022] Open
Abstract
Protein phosphorylation controls many aspects of cell fate and is often deregulated in pathological conditions. Several recent findings have provided an intriguing insight into the spatial regulation of protein phosphorylation across different subcellular compartments and how this can be finely orchestrated by specific kinases and phosphatases. In this review, the focus will be placed on (i) the phosphoinositide 3-kinase (PI3K) pathway, specifically on the kinases Akt and mTOR and on the phosphatases PP2a and PTEN, and on (ii) the PKC family of serine/threonine kinases. We will look at general aspects of cell physiology controlled by these kinases and phosphatases, highlighting the signalling pathways that drive cell division, proliferation, and apoptosis.
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Affiliation(s)
- Angela Bononi
- Section of General Pathology, Department of Experimental and Diagnostic Medicine, Interdisciplinary Center for the Study of Inflammation (ICSI) and LTTA Center, University of Ferrara, 44100 Ferrara, Italy
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Jin Z, Mei W, Strack S, Jia J, Yang J. The antagonistic action of B56-containing protein phosphatase 2As and casein kinase 2 controls the phosphorylation and Gli turnover function of Daz interacting protein 1. J Biol Chem 2011; 286:36171-9. [PMID: 21878643 DOI: 10.1074/jbc.m111.274761] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The Hedgehog (Hh) pathway is evolutionarily conserved and plays critical roles during embryonic development and adult tissue homeostasis. Defective Hh signaling has been linked to a wide range of birth defects and cancers. Hh family proteins regulate the expression of their downstream target genes through the control of proteolytic processing and the transcriptional activation function of Gli transcription factors. Although Hh-dependent regulation of Gli has been studied extensively, other Gli regulatory mechanisms remain relatively unappreciated. Here we report our identification of a novel signaling cascade that controls the stability of Gli proteins. This cascade consists of Daz interacting protein 1 (Dzip1), casein kinase 2 (CK2), and B56 containing protein phosphatase 2As (PP2As). We provide evidence that Dzip1 is involved in a novel Gli turnover pathway. We show that CK2 directly phosphorylates Dzip1 at four serine residues, Ser-664/665/706/714. B56-containing PP2As, through binding to a domain located between amino acid residue 474 and 550 of Dzip1, dephosphorylate Dzip1 on these CK2 sites. Our mutagenesis analysis further demonstrates that the unphosphorylatable form of Dzip1 is more potent in promoting Gli turnover. Consistently, we found that the stability of Gli proteins was decreased upon CK2 inhibition and increased by inhibition of B56-containing PP2As. Thus, reversible phosphorylation of Dzip1, which is controlled by the antagonistic action of CK2 and B56-containing PP2As, has an important impact on the stability of Gli transcription factors and Hh signaling.
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Affiliation(s)
- Zhigang Jin
- The Research Institute at Nationwide Children's Hospital, Department of Pediatrics, the Ohio State University, Columbus, Ohio 43205, USA
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Abstract
It is clear that mTORC1 (mammalian target of rapamycin complex 1) is regulated by the presence of ambient amino acid nutrients. However, the mechanism by which amino acids regulate mTORC1 is still open to question, despite extensive efforts. Our recent work has revealed that PR61ϵ, a B56 family regulatory subunit of PP2A (protein phosphatase 2A), associates with and regulates the activity of MAP4K3 (mitogen-activated protein kinase kinase kinase kinase 3), a protein kinase regulated by amino acid sufficiency that acts upstream of mTORC1. In searching for a physiological process regulated by amino acids, we have demonstrated recently that arginine plays a role in the activation of LPS (lipopolysaccharide)-induced MEK [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase]/ERK signalling in macrophages. PP2A similarly associates with the upstream regulator of MEK in this signalling pathway, TPL-2 (tumour progression locus-2), in response to arginine availability. Thus PP2A is a negative regulator of both MAP4K3 and TPL-2 in both mTORC1 and MEK/ERK signalling pathways.
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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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