1
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Yun QS, Bao YX, Jiang JB, Guo Q. Mechanisms of norcantharidin against renal tubulointerstitial fibrosis. Pharmacol Rep 2024; 76:263-272. [PMID: 38472637 DOI: 10.1007/s43440-024-00578-5] [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: 09/02/2023] [Revised: 02/15/2024] [Accepted: 02/16/2024] [Indexed: 03/14/2024]
Abstract
Renal tubulointerstitial fibrosis (RTIF) is a common feature and inevitable consequence of all progressive chronic kidney diseases, leading to end-stage renal failure regardless of the initial cause. Although research over the past few decades has greatly improved our understanding of the pathophysiology of RTIF, until now there has been no specific treatment available that can halt the progression of RTIF. Norcantharidin (NCTD) is a demethylated analogue of cantharidin, a natural compound isolated from 1500 species of medicinal insect, the blister beetle (Mylabris phalerata Pallas), traditionally used for medicinal purposes. Many studies have found that NCTD can attenuate RTIF and has the potential to be an anti-RTIF drug. This article reviews the recent progress of NCTD in the treatment of RTIF, with emphasis on the pharmacological mechanism of NCTD against RTIF.
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Affiliation(s)
- Qin-Su Yun
- Department of Pharmacy, The First People's Hospital of Changzhou and the 3rd Affiliated Hospital of Soochow University, 185 Juqian Street, Changzhou, 213003, Jiangsu, China
| | - Yu-Xin Bao
- Research Center for Medicine and Biology, Zunyi Medical University, 6 West Xuefu Road, Zunyi, 563000, Guizhou, China.
| | - Jie-Bing Jiang
- Department of Pharmacology, Naval Medical University, Shanghai, 200433, China
| | - Qian Guo
- Institute of Geriatrics (Shanghai University), Affiliated Nantong Hospital of Shanghai University (The Sixth People's Hospital of Nantong), School of Medicine, Shanghai University, 881 Yonghe Road, Nantong, 226001 , Jiangsu, China.
- Shanghai Engineering Research Center of Organ Repair, School of Medicine, Shanghai University, 99 Shangda Road, Shanghai, 200444, China.
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2
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Dow LF, Case AM, Paustian MP, Pinkerton BR, Simeon P, Trippier PC. The evolution of small molecule enzyme activators. RSC Med Chem 2023; 14:2206-2230. [PMID: 37974956 PMCID: PMC10650962 DOI: 10.1039/d3md00399j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Accepted: 09/20/2023] [Indexed: 11/19/2023] Open
Abstract
There is a myriad of enzymes within the body responsible for maintaining homeostasis by providing the means to convert substrates to products as and when required. Physiological enzymes are tightly controlled by many signaling pathways and their products subsequently control other pathways. Traditionally, most drug discovery efforts focus on identifying enzyme inhibitors, due to upregulation being prevalent in many diseases and the existence of endogenous substrates that can be modified to afford inhibitor compounds. As enzyme downregulation and reduction of endogenous activators are observed in multiple diseases, the identification of small molecules with the ability to activate enzymes has recently entered the medicinal chemistry toolbox to afford chemical probes and potential therapeutics as an alternative means to intervene in diseases. In this review we highlight the progress made in the identification and advancement of non-kinase enzyme activators and their potential in treating various disease states.
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Affiliation(s)
- Louise F Dow
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center Omaha NE 68106 USA
| | - Alfie M Case
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center Omaha NE 68106 USA
| | - Megan P Paustian
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center Omaha NE 68106 USA
| | - Braeden R Pinkerton
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center Omaha NE 68106 USA
| | - Princess Simeon
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center Omaha NE 68106 USA
| | - Paul C Trippier
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center Omaha NE 68106 USA
- Fred & Pamela Buffett Cancer Center, University of Nebraska Medical Center Omaha NE 68106 USA
- UNMC Center for Drug Discovery, University of Nebraska Medical Center Omaha NE 68106 USA
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3
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Shao L, Ma Y, Fang Q, Huang Z, Wan S, Wang J, Yang L. Role of protein phosphatase 2A in kidney disease (Review). Exp Ther Med 2021; 22:1236. [PMID: 34539832 PMCID: PMC8438693 DOI: 10.3892/etm.2021.10671] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Accepted: 01/06/2021] [Indexed: 12/12/2022] Open
Abstract
Kidney disease affects millions of people worldwide and is a financial burden on the healthcare system. Protein phosphatase 2A (PP2A), which is involved in renal development and the function of ion-transport proteins, aquaporin-2 and podocytes, is likely to serve an important role in renal processes. PP2A is associated with the pathogenesis of a variety of different kidney diseases including podocyte injury, inflammation, tumors and chronic kidney disease. The current review aimed to discuss the structure and function of PP2A subunits in the context of kidney diseases. How dysregulation of PP2A in the kidneys causes podocyte death and the inactivation of PP2A in renal carcinoma tissues is discussed. Inhibition of PP2A activity prevents epithelial-mesenchymal transition and attenuates renal fibrosis, creating a favorable inflammatory microenvironment and promoting the initiation and progression of tumor pathogenesis. The current review also indicates that PP2A serves an important role in protection against renal inflammation. Understanding the detailed mechanisms of PP2A provides information that can be utilized in the design and application of novel therapeutics for the treatment and prevention of renal diseases.
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Affiliation(s)
- Lishi Shao
- Department of Radiology, Kunming Medical University and The Second Affiliated Hospital, Kunming, Yunnan 650500, P.R. China
| | - Yiqun Ma
- Department of Radiology, Kunming Medical University and The Second Affiliated Hospital, Kunming, Yunnan 650500, P.R. China
| | - Qixiang Fang
- Department of Urology, The First Affiliated Hospital of the Medical College of Xi'an Jiaotong University, Xi'an, Shaanxi 710049, P.R. China
| | - Ziye Huang
- Department of Urology, Kunming Medical University and The Second Affiliated Hospital, Kunming, Yunnan 650500, P.R. China
| | - Shanshan Wan
- Department of Radiology, Yunnan Kun-Gang Hospital, Anning, Yunnan 650300, P.R. China
| | - Jiaping Wang
- Department of Radiology, Kunming Medical University and The Second Affiliated Hospital, Kunming, Yunnan 650500, P.R. China
| | - Li Yang
- Department of Anatomy, Histology and Embryology, Kunming Medical University, Kunming, Yunnan 650500, P.R. China
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4
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PP2Acα promotes macrophage accumulation and activation to exacerbate tubular cell death and kidney fibrosis through activating Rap1 and TNFα production. Cell Death Differ 2021; 28:2728-2744. [PMID: 33934104 PMCID: PMC8408198 DOI: 10.1038/s41418-021-00780-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 04/02/2021] [Accepted: 04/07/2021] [Indexed: 02/01/2023] Open
Abstract
Macrophage accumulation and activation play an essential role in kidney fibrosis; however, the underlying mechanisms remain to be explored. By analyzing the kidney tissues from patients and animal models with kidney fibrosis, we found a large induction of PP2Acα in macrophages. We then generated a mouse model with inducible macrophage ablation of PP2Acα. The knockouts developed less renal fibrosis, macrophage accumulation, or tubular cell death after unilateral ureter obstruction or ischemic reperfusion injury compared to control littermates. In cultured macrophages, PP2Acα deficiency resulted in decreased cell motility by inhibiting Rap1 activity. Moreover, co-culture of PP2Acα-/- macrophages with tubular cells resulted in less tubular cell death attributed to downregulated Stat6-mediated tumor necrosis factor α (TNFα) production in macrophages. Together, this study demonstrates that PP2Acα promotes macrophage accumulation and activation, hence accelerates tubular cell death and kidney fibrosis through regulating Rap1 activation and TNFα production.
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5
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AMOTL2 inhibits JUN Thr239 dephosphorylation by binding PPP2R2A to suppress the proliferation in non-small cell lung cancer cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2020; 1868:118858. [PMID: 32950569 DOI: 10.1016/j.bbamcr.2020.118858] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 08/22/2020] [Accepted: 09/13/2020] [Indexed: 12/16/2022]
Abstract
Protein phosphatase 2A (PP2A) complex comprises an extended family of intracellular protein serine/threonine phosphatases, that participate in different signaling transduction pathways. Different functions of PP2As are determined by the variety of regulatory subunits. In this study, CRISPR/Cas9-mediated loss-of-function screen revealed that PPP2R2A downregulation suppressed cell growth in NSCLC cells. AMOTL2 was identified and confirmed as a novel binding partner of PPP2R2A in NSCLC cells by mass spectrometry, CO-IP, GST pull-down and immunofluorescence. Upregulation of AMOTL2 also led to cell proliferation delay in human and mouse lung tumor cells. The proto-oncogene JUN is a key subunit of activator protein-1 (AP-1) transcription factor which plays crucial role in regulating tumorigenesis and its activity is negatively regulated by the phosphorylation at T239. Our results showed that either AMOTL2 upregulation or PPP2R2A downregulation led to great increase in JUN T239 phosphorylation. AMOTL2 bound PPP2R2A in cytoplasm, which reduced nuclear localization of PPP2R2A. In conclusion, AMOTL2 and PPP2R2A act respectively as negative and positive regulator of cell growth in NSCLC cells and function in the AMOTL2-PPP2R2A-JUN axis, in which AMOTL2 inhibits the entry of PPP2R2A into the nucleus to dephosphorylate JUN at T239.
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Chen H, Xu J, Wang P, Shu Q, Huang L, Guo J, Zhang X, Zhang H, Wang Y, Shen Z, Chen X, Zhang Q. Protein phosphatase 2 regulatory subunit B''Alpha silencing inhibits tumor cell proliferation in liver cancer. Cancer Med 2019; 8:7741-7753. [PMID: 31647192 PMCID: PMC6912040 DOI: 10.1002/cam4.2620] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2019] [Revised: 09/29/2019] [Accepted: 10/06/2019] [Indexed: 12/24/2022] Open
Abstract
Aim To explore the effects of protein phosphatase 2 regulatory subunit B''Alpha (PPP2R3A) on the proliferation and migration of liver cancer cells. Methods Expression of PPP2R3A in tumor tissues of hepatocellular carcinoma (HCC) patients was detected by immunohistochemistry and western blotting. In two liver cancer cell lines (HepG2 and HuH7), PPP2R3A expression was silenced and then overexpression with PPP2R3A lentiviral vectors, and the effects of PPP2R3A knockdown or overexpression on the proliferation, cell cycle, migration, and invasion of HCC cells were determined in vitro. In a xenograft cancer model in nude mice, the in vivo effects of PPP2R3A knockdown on tumor growth and cancer cell proliferation were evaluated. Results PPP2R3A expression was found in tumor foci in six of eight HCC samples, at a level higher than that in the adjacent para‐tumor tissues. PPP2R3A expression was observed primarily in the cytoplasm of the cancer cells. Knockdown of PPP2R3A resulted in significant inhibition of hepatoma cell proliferation (P < .05), migration (P < .01), and invasion (P < .01) as well as a significant delay in the G1/S transition in both liver cancer lines (P < .05) and increased p53 expression. Conversely, overexpression of PPP2R3A promoted the proliferation (P < .05) and altered cell cycle progression (P < .05) of both liver cancer cell lines. In vivo, PPP2R3A knockdown in liver cancer cells led to significant reductions in the tumor volume (P < .001) and the expression of Ki‐67 in tumor tissues (P < .05). Conclusion PPP2R3A may play a role in liver cancer via the regulation of tumor cell proliferation and invasion.
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Affiliation(s)
- Huijuan Chen
- Department of Liver Transplantation, The Third Medical Centre, Chinese PLA (People's Liberation Army) General Hospital, Beijing, China.,Graduate School, Anhui Medical University, Hefei, China
| | - Jing Xu
- National Translational Science Center for Molecular Medicine & Department of Cell Biology, State Key Laboratory of Cancer Biology, Fourth Military Medical University, Xi'an, China
| | - Peixiao Wang
- Department of Gastroenterology, Henan Children's Hospital, Zhengzhou, China
| | - Qingming Shu
- Pathology Department, The Third Medical Centre, Chinese PLA (People's Liberation Army) General Hospital, Beijing, China
| | - Lihong Huang
- Medical Department, The Third Medical Centre, Chinese PLA (People's Liberation Army) General Hospital, Beijing, China
| | - Jing Guo
- Medical Department, The Third Medical Centre, Chinese PLA (People's Liberation Army) General Hospital, Beijing, China
| | - Xuyi Zhang
- Medical Department, The Third Medical Centre, Chinese PLA (People's Liberation Army) General Hospital, Beijing, China
| | - Hongying Zhang
- Medical Department, The Third Medical Centre, Chinese PLA (People's Liberation Army) General Hospital, Beijing, China
| | - Ying Wang
- Department of Liver Transplantation, The Third Medical Centre, Chinese PLA (People's Liberation Army) General Hospital, Beijing, China
| | - Zhongyang Shen
- Department of Liver Transplantation, The Third Medical Centre, Chinese PLA (People's Liberation Army) General Hospital, Beijing, China.,Department of Transplantation Surgery, Tianjin First Central Hospital, Tianjin, China
| | - Xinguo Chen
- Department of Liver Transplantation, The Third Medical Centre, Chinese PLA (People's Liberation Army) General Hospital, Beijing, China
| | - Qing Zhang
- Department of Liver Transplantation, The Third Medical Centre, Chinese PLA (People's Liberation Army) General Hospital, Beijing, China
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7
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Uchida E, Suwa S, Yoshimoto R, Watanabe K, Kasama T, Miura O, Fukuda T. TOPK is regulated by PP2A and BCR/ABL in leukemia and enhances cell proliferation. Int J Oncol 2019; 54:1785-1796. [PMID: 30864683 DOI: 10.3892/ijo.2019.4740] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2018] [Accepted: 01/21/2019] [Indexed: 11/06/2022] Open
Abstract
Although treatment of chronic myeloid leukemia (CML) has improved with the development of tyrosine kinase inhibitors (TKIs), patients develop fatal blast crisis (BC) whilst receiving TKI treatment. Alternative treatments for cases resistant to TKIs are required. A serine/threonine protein kinase, T‑lymphokine‑activated killer cell‑originated protein kinase (TOPK), is highly expressed in various malignant tumors. Binding of peptides to human leukocyte antigen was assessed via mass spectrometry in K562 CML cells. TOPK expression was assessed in various CML cell lines and in clinical samples obtained from patients with CML using reverse transcription‑quantitative polymerase chain reaction and western blot assays. It was observed that TOPK was expressed abundantly in BCR/ABL‑positive cell lines and at significantly higher levels in CML clinical samples compared with healthy donor samples. Overexpression of BCR/ABL or the presence of its inhibitor imatinib upregulated and downregulated TOPK expression, respectively, indicating that TOPK may be a target of BCR/ABL. TOPK inhibitor OTS514 suppressed proliferation of BCR/ABL‑positive cell lines and colony formation of CD34‑positive cells from patients with CML compared with lymphoma patients without bone marrow involvement. Furthermore, phosphorylation of TOPK was increased by protein phosphatase 2A (PP2A) inhibitor okadaic acid and was decreased in the presence of PP2A activator FTY720 compared with untreated samples. As constitutive BCR/ABL activity and inhibition of PP2A are key mechanisms of CML development, TOPK may be a crucial signaling molecule for this disease. Inhibition of TOPK may control disease status of CML, even in cases resistant to TKIs.
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Affiliation(s)
- Emi Uchida
- Department of Hematology, Tokyo Medical and Dental University, Tokyo 113‑8519, Japan
| | - Shihoko Suwa
- Department of Hematology, Tokyo Medical and Dental University, Tokyo 113‑8519, Japan
| | - Ryoto Yoshimoto
- Department of Hematology, Tokyo Medical and Dental University, Tokyo 113‑8519, Japan
| | - Ken Watanabe
- Department of Hematology, Tokyo Medical and Dental University, Tokyo 113‑8519, Japan
| | - Takeshi Kasama
- Research Center for Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo 113‑8519, Japan
| | - Osamu Miura
- Department of Hematology, Tokyo Medical and Dental University, Tokyo 113‑8519, Japan
| | - Tetsuya Fukuda
- Department of Hematology, Tokyo Medical and Dental University, Tokyo 113‑8519, Japan
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8
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Zhang Y, Jiang X, Qin C, Cuevas S, Jose PA, Armando I. Dopamine D2 receptors' effects on renal inflammation are mediated by regulation of PP2A function. Am J Physiol Renal Physiol 2016; 310:F128-34. [PMID: 26290374 PMCID: PMC4719046 DOI: 10.1152/ajprenal.00453.2014] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Accepted: 06/15/2015] [Indexed: 01/11/2023] Open
Abstract
Lack or downregulation of the dopamine D2 receptor (D2R) results in increased renal expression of injury markers and proinflammatory factors that is independent of a blood pressure increase. This study aimed to determine the mechanisms involved in the regulation of renal inflammation by D2Rs. Silencing D2Rs in mouse renal proximal tubule cells increased the expression of the proinflammatory TNF-α, monocyte chemoattractant protein-1 (MCP-1), and IL-6. D2R downregulation also increased Akt phosphorylation and activity, and glycogen synthase kinase-3β (GSK3β) phosphorylation and cyclin D1 expression, downstream targets of Akt; however. phosphatidylinositol 3-kinase (PI3K) activity was not affected. Conversely, D2R stimulation decreased Akt and GSK3β phosphorylation and cyclin D1 expression. Increased phospho-Akt, in the absence of increased PI3K activity, may result from decreased Akt dephosphorylation. Inhibition of protein phosphatase 2A (PP2A) with okadaic acid reproduced the effects of D2R downregulation on Akt, GSK3β, and cyclin D1. The PP2A catalytic subunit and regulatory subunit PPP2R2C coimmunoprecipitated with the D2R. Basal phosphatase activity and the expression of PPP2R2C were decreased by D2R silencing that also blunted the increase in phosphatase activity induced by D2R stimulation. Similarly, silencing PPP2R2C also increased the phosphorylation of Akt and GSK3β. Moreover, downregulation of PPP2R2C resulted in increased expression of TNF-α, MCP-1, and IL-6, indicating that decreased phosphatase activity may be responsible for the D2R effect on inflammatory factors. Indeed, the increase in NF-κB reporter activity induced by D2R silencing was blunted by increasing PP2A activity with protamine. Our results show that D2R controls renal inflammation, at least in part, by modulation of the Akt pathway through effects on PP2A activity/expression.
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Affiliation(s)
- Yanrong Zhang
- Division of Nephrology, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland; Institute of Laboratory Animal Science, Chinese Academy of Medical Sciences (CAMS) and Comparative Medicine Centre, Peking Union Medical Collage (PUMC), Beijing, P. R. China; and
| | - Xiaoliang Jiang
- Division of Nephrology, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland; Institute of Laboratory Animal Science, Chinese Academy of Medical Sciences (CAMS) and Comparative Medicine Centre, Peking Union Medical Collage (PUMC), Beijing, P. R. China; and
| | - Chuan Qin
- Division of Nephrology, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland; Institute of Laboratory Animal Science, Chinese Academy of Medical Sciences (CAMS) and Comparative Medicine Centre, Peking Union Medical Collage (PUMC), Beijing, P. R. China; and
| | - Santiago Cuevas
- Division of Nephrology, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland
| | - Pedro A Jose
- Division of Nephrology, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland; Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland
| | - Ines Armando
- Division of Nephrology, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland
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9
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O'Hearn EE, Hwang HS, Holmes SE, Rudnicki DD, Chung DW, Seixas AI, Cohen RL, Ross CA, Trojanowski JQ, Pletnikova O, Troncoso JC, Margolis RL. Neuropathology and Cellular Pathogenesis of Spinocerebellar Ataxia Type 12. Mov Disord 2015; 30:1813-1824. [PMID: 26340331 DOI: 10.1002/mds.26348] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Revised: 06/16/2015] [Accepted: 06/24/2015] [Indexed: 11/07/2022] Open
Abstract
OBJECTIVE SCA12 is a progressive autosomal-dominant disorder, caused by a CAG/CTG repeat expansion in PPP2R2B on chromosome 5q32, and characterized by tremor, gait ataxia, hyperreflexia, dysmetria, abnormal eye movements, anxiety, depression, and sometimes cognitive impairment. Neuroimaging has demonstrated cerebellar and cortical atrophy. We now present the neuropathology of the first autopsied SCA12 brain and utilize cell models to characterize potential mechanisms of SCA12 neurodegeneration. METHODS A fixed SCA12 brain was examined using gross, microscopic, and immunohistochemical methods. The effect of the repeat expansion on PPP2R2B Bβ1 expression was examined in multiple cell types by transient transfection of constructs containing the PPP2R2B Bβ1 promoter region attached to a luciferase reporter. The neurotoxic effect of PPP2R2B overexpression was examined in transfected rat primary neurons. RESULTS Neuropathological investigation revealed enlarged ventricles, marked cerebral cortical atrophy and Purkinje cell loss, less-prominent cerebellar and pontine atrophy, and neuronal intranuclear ubiquitin-positive inclusions, consistent with Marinesco bodies, which did not stain for long polyglutamine tracts, alpha-synuclein, tau, or transactive response DNA-binding protein 43. Reporter assays demonstrated that the region of PPP2R2B containing the repeat functions as a promoter, and that promoter activity increases with longer repeat length and is dependent on cell type, repeat sequence, and sequence flanking the repeat. Overexpression of PPP2R2B in primary cortical neurons disrupted normal morphology. CONCLUSIONS SCA12 involves extensive, but selective, neurodegeneration distinct from Alzheimer's disease, synucleinopathies, tauopathies, and glutamine expansion diseases. SCA12 neuropathology may arise from the neurotoxic effect of repeat-expansion-induced overexpression of PPP2R2B.
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Affiliation(s)
- Elizabeth E O'Hearn
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Laboratory of Genetic Neurobiology, Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Hyon S Hwang
- Laboratory of Genetic Neurobiology, Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Susan E Holmes
- Laboratory of Genetic Neurobiology, Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Dobrila D Rudnicki
- Laboratory of Genetic Neurobiology, Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Daniel W Chung
- Laboratory of Genetic Neurobiology, Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Ana I Seixas
- Laboratory of Genetic Neurobiology, Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Instituto de Biologia Molecular e Celular, Universidade do Porto, Oporto, Portugal
| | - Rachael L Cohen
- Laboratory of Genetic Neurobiology, Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Christopher A Ross
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Laboratory of Genetic Neurobiology, Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Departments of Neuroscience and Pharmacology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - John Q Trojanowski
- Institute on Aging, Alzheimer's Disease Core Center, Udall Parkinson's Research Center, Center for Neurodegenerative Disease, Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA
| | - Olga Pletnikova
- Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Juan C Troncoso
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Russell L Margolis
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Laboratory of Genetic Neurobiology, Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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10
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Wong PM, Feng Y, Wang J, Shi R, Jiang X. Regulation of autophagy by coordinated action of mTORC1 and protein phosphatase 2A. Nat Commun 2015; 6:8048. [PMID: 26310906 PMCID: PMC4552084 DOI: 10.1038/ncomms9048] [Citation(s) in RCA: 176] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Accepted: 07/11/2015] [Indexed: 12/19/2022] Open
Abstract
Autophagy is a cellular catabolic process critical for cell viability and homoeostasis. Inhibition of mammalian target of rapamycin (mTOR) complex-1 (mTORC1) activates autophagy. A puzzling observation is that amino acid starvation triggers more rapid autophagy than pharmacological inhibition of mTORC1, although they both block mTORC1 activity with similar kinetics. Here we find that in addition to mTORC1 inactivation, starvation also causes an increase in phosphatase activity towards ULK1, an mTORC1 substrate whose dephosphorylation is required for autophagy induction. We identify the starvation-stimulated phosphatase for ULK1 as the PP2A–B55α complex. Treatment of cells with starvation but not mTORC1 inhibitors triggers dissociation of PP2A from its inhibitor Alpha4. Furthermore, pancreatic ductal adenocarcinoma cells, whose growth depends on high basal autophagy, possess stronger basal phosphatase activity towards ULK1 and require ULK1 for sustained anchorage-independent growth. Taken together, concurrent mTORC1 inactivation and PP2A–B55α stimulation fuel ULK1-dependent autophagy. Starvation rapidly triggers autophagy by inactivating mTORC1 signalling, however mTORC1 inhibition does not fully recapitulate this rapid induction. Wong et al. identify a parallel starvation-senstive pathway regulating autophagy, mediated by protein phosphatase 2A-dependent dephosphorylation of ULK1.
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Affiliation(s)
- Pui-Mun Wong
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA
| | - Yan Feng
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA
| | - Junru Wang
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA
| | - Rong Shi
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA.,Xiangya School of Medicine, Central South University, Hunan 410008, China
| | - Xuejun Jiang
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA
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11
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Beca F, Pereira M, Cameselle-Teijeiro JF, Martins D, Schmitt F. Altered PPP2R2A and Cyclin D1 expression defines a subgroup of aggressive luminal-like breast cancer. BMC Cancer 2015; 15:285. [PMID: 25879784 PMCID: PMC4409761 DOI: 10.1186/s12885-015-1266-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Accepted: 03/25/2015] [Indexed: 11/30/2022] Open
Abstract
Background PPP2R2A deletions were recently linked to a subgroup of luminal breast carcinoma (BC) that exhibits poor survival. This subgroup also exhibited amplification of a chromosome region containing the Cyclin D1 coding gene, CCND1. Therefore, we aimed to investigate whether a combination of PPP2R2A (B55α) and Cyclin D1 expression statuses evaluated by immunohistochemistry (IHC) could define a subgroup of luminal BC that exhibits poor survival. Methods First we conducted a retrospective cohort study using sequencing data from The Cancer Genome Atlas initiative to correlate PPP2R2A copy number alteration (CNA) status with its expression level and the corresponding overall survival (OS). Next, also using a retrospective cohort study design, we evaluated the PPP2R2A (B55α) expression levels by IHC in a total of 807 BC patients from two independent cohorts (discovery cohort n = 349 and validation cohort n = 458). Cyclin D1 expression was also evaluated, and the PPP2R2A (B55α)-/low/Cyclin D1high phenotype was evaluated as a predictor of disease-free survival (DFS) and OS in luminal-like BC patients. Results Deletions in the PPP2R2A gene strongly correlate with lower mRNA expression and poorer OS. PPP2R2A (B55α)-/low carcinomas have significantly shorter DFS and OS. Furthermore, in univariate analysis, the PPP2R2A (B55α)-/low/Cyclin D1high phenotype is significantly associated with poorer DFS and OS. In a multivariate analysis, the PPP2R2A (B55α)-/low/Cyclin D1high phenotype is significantly associated with poor DFS, thus defining a group of luminal-like BC with higher risk of relapse. Conclusion We demonstrate that BCs harboring PPP2R2A deletions are associated with worse OS. Moreover, this is the first study to demonstrate that the combination of altered PPP2R2A (B55α) and high Cyclin D1 expression by IHC defines a subgroup of luminal-like BC patients with a high risk of relapse and death. Electronic supplementary material The online version of this article (doi:10.1186/s12885-015-1266-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Francisco Beca
- IPATIMUP - Institute of Molecular Pathology and Immunology of the University of Porto, Rua Dr, Roberto Frias, s/n, 4200-465 Porto, Porto, Portugal. .,Department of Medical Oncology, Dana-Farber Cancer Institute, 450 Brookline Ave., Boston, MA, 02215-5450, USA.
| | - Miguel Pereira
- Division of Surgical Oncology, Department of Surgery, Massachusetts General Hospital Cancer Center, 55 Fruit St, Boston, MA, 02114, USA.
| | | | - Diana Martins
- IBMC - Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180, Porto, Portugal.
| | - Fernando Schmitt
- Department of Pathology and Medicine, Laboratorie National de Sante 1, Rue Louis Reche, L-3555, Dudelange, Luxembourg.
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12
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The Ser/Thr phosphatase PP2A regulatory subunit widerborst inhibits notch signaling. PLoS One 2014; 9:e101884. [PMID: 25006677 PMCID: PMC4090204 DOI: 10.1371/journal.pone.0101884] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Accepted: 06/12/2014] [Indexed: 01/23/2023] Open
Abstract
Drosophila Enhancer of split M8, an effector of Notch signaling, is regulated by protein kinase CK2. The phosphatase PP2A is thought to play an opposing (inhibitory) role, but the identity of the regulatory subunit was unknown. The studies described here reveal a role for the PP2A regulatory subunit widerborst (wdb) in three developmental contexts; the bristle, wing and the R8 photoreceptors of the eye. wdb overexpression elicits bristle and wing defects akin to reduced Notch signaling, whereas hypomorphic mutations in this PP2A subunit elicit opposite effects. We have also evaluated wdb functions using mutations in Notch and E(spl) that affect the eye. We find that the eye and R8 defects of the well-known Nspl mutation are enhanced by a hypomorphic allele of wdb, whereas they are strongly rescued by wdb overexpression. Similarly, ectopic wdb rescues the eye and R8 defects of the E(spl)D mutation, which affects the m8 gene. In addition, wdb overexpression also rescues the bristle defects of ectopically expressed M8, or the eye and R8 defects of its CK2 phosphomimetic variant M8-S159D. The latter finding suggests that PP2A may target M8 at highly conserved residues in the vicinity of the CK2 site, whose phosphorylation controls repression of Atonal and the R8 fate. Together, the studies identify PP2A-Wdb as a participant in Notch signaling, and suggest that M8 activity is controlled by phosphorylation and dephosphorylation. The conservation of the phosphorylation sites between Drosophila E(spl) and the HES/HER proteins from mammals, reptiles, amphibians, birds and fish raises the prospect that this mode of regulation is widespread.
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13
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Galbo T, Perry RJ, Nishimura E, Samuel VT, Quistorff B, Shulman GI. PP2A inhibition results in hepatic insulin resistance despite Akt2 activation. Aging (Albany NY) 2014; 5:770-81. [PMID: 24150286 PMCID: PMC3838779 DOI: 10.18632/aging.100611] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
In the liver, insulin suppresses hepatic gluconeogenesis by activating Akt, which inactivates the key gluconeogenic transcription factor FoxO1 (Forkhead Box O1). Recent studies have implicated hyperactivity of the Akt phosphatase Protein Phosphatase 2A (PP2A) and impaired Akt signaling as a molecular defect underlying insulin resistance. We therefore hypothesized that PP2A inhibition would enhance insulin-stimulated Akt activity and decrease glucose production. PP2A inhibitors increased hepatic Akt phosphorylation and inhibited FoxO1 in vitro and in vivo, and suppressed gluconeogenesis in hepatocytes. Paradoxically, PP2A inhibition exacerbated insulin resistance in vivo. This was explained by phosphorylation of both hepatic glycogen synthase (GS) (inactivation) and phosphorylase (activation) resulting in impairment of glycogen storage. Our findings underline the significance of GS and Phosphorylase as hepatic PP2A substrates and importance of glycogen metabolism in acute plasma glucose regulation.
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Affiliation(s)
- Thomas Galbo
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06510, USA
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14
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Bai XL, Zhang Q, Ye LY, Hu QD, Fu QH, Zhi X, Su W, Su RG, Ma T, Chen W, Xie SZ, Chen CL, Liang TB. Inhibition of protein phosphatase 2A enhances cytotoxicity and accessibility of chemotherapeutic drugs to hepatocellular carcinomas. Mol Cancer Ther 2014; 13:2062-72. [PMID: 24867249 DOI: 10.1158/1535-7163.mct-13-0800] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Hepatocellular carcinoma (HCC) is one of the most common and therapeutically challenging malignancies worldwide. For patients ineligible for "curative resection" or liver transplantation, chemotherapy is an important minimally effective option. Strategies for chemosensitization are urgently needed. Here, we report that LB-100, a serine/threonine protein phosphatase 2A (PP2A) inhibitor, enhances the cytotoxicity of chemotherapy for HCC in vitro and in vivo. We found that LB-100 significantly enhanced inhibition of HCC by doxorubicin and cisplatin in vitro and in vivo in a PP2A-dependent way, while having little inhibitory activity when used alone. LB-100 promoted vascular endothelial growth factor secretion and vasculogenic mimicry, associated with increased microvessel density and blood perfusion of tumor cell xenografts. LB-100 also enhanced paracellular endothelial permeability to Evans Blue dye and doxorubicin in vivo and in vitro, presumably by altering vascular endothelial-cadherin contact between cells. Changes in permeability and perfusion were accompanied by increased accumulation of doxorubicin in HCC xenografts but not in normal liver tissue. In conclusion, LB-100 enhances chemotherapy by interfering with DNA damage-induced defense mechanisms and by increasing angiogenesis and drug penetration into tumor cells. The induction of angiogenesis and vascular permeability of tumor xenografts by inhibition of PP2A may be a novel approach for enhancing the cytotoxic treatment of HCC and potentially other cancers.
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MESH Headings
- Animals
- Antineoplastic Combined Chemotherapy Protocols/pharmacology
- Antineoplastic Combined Chemotherapy Protocols/therapeutic use
- Bridged Bicyclo Compounds, Heterocyclic/administration & dosage
- Capillary Permeability/drug effects
- Carcinoma, Hepatocellular/blood supply
- Carcinoma, Hepatocellular/drug therapy
- Carcinoma, Hepatocellular/pathology
- Cell Line, Tumor
- Cell Membrane Permeability
- Cisplatin/administration & dosage
- Doxorubicin/administration & dosage
- Drug Synergism
- Human Umbilical Vein Endothelial Cells/drug effects
- Human Umbilical Vein Endothelial Cells/metabolism
- Humans
- Inhibitory Concentration 50
- Liver Neoplasms, Experimental/blood supply
- Liver Neoplasms, Experimental/drug therapy
- Liver Neoplasms, Experimental/pathology
- Mice, Inbred BALB C
- Mice, Nude
- Neovascularization, Pathologic/pathology
- Piperazines/administration & dosage
- Protein Phosphatase 2/antagonists & inhibitors
- Protein Phosphatase 2/metabolism
- Tumor Burden/drug effects
- Xenograft Model Antitumor Assays
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Affiliation(s)
- Xue-Li Bai
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Qi Zhang
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Long-Yun Ye
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Qi-Da Hu
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Qi-Han Fu
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Xiao Zhi
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Wei Su
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Ri-Ga Su
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Tao Ma
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Wei Chen
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Shang-Zhi Xie
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Cong-Lin Chen
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Ting-Bo Liang
- Department of Hepatobiliary and Pancreatic Surgery, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
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15
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Kirchhefer U, Heinick A, König S, Kristensen T, Müller FU, Seidl MD, Boknik P. Protein phosphatase 2A is regulated by protein kinase Cα (PKCα)-dependent phosphorylation of its targeting subunit B56α at Ser41. J Biol Chem 2013; 289:163-76. [PMID: 24225947 DOI: 10.1074/jbc.m113.507996] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Protein phosphatase 2A (PP2A) is a family of multifunctional serine/threonine phosphatases consisting of a catalytic C, a structural A, and a regulatory B subunit. The substrate and therefore the functional specificity of PP2A are determined by the assembly of the enzyme complex with the appropriate regulatory B subunit families, namely B55, B56, PR72, or PR93/PR110. It has been suggested that additional levels of regulating PP2A function may result from the phosphorylation of B56 isoforms. In this study, we identified a novel phosphorylation site at Ser(41) of B56α. This phosphoamino acid residue was efficiently phosphorylated in vitro by PKCα. We detected a 7-fold higher phosphorylation of B56α in failing human hearts compared with nonfailing hearts. Purified PP2A dimeric holoenzyme (subunits C and A) was able to dephosphorylate PKCα-phosphorylated B56α. The potency of B56α for PP2A inhibition was markedly increased by PKCα phosphorylation. PP2A activity was also reduced in HEK293 cells transfected with a B56α mutant, where serine 41 was replaced by aspartic acid, which mimics phosphorylation. More evidence for a functional role of PKCα-dependent phosphorylation of B56α was derived from Fluo-4 fluorescence measurements in phenylephrine-stimulated Flp293 cells. The endoplasmic reticulum Ca(2+) release was increased by 23% by expression of the pseudophosphorylated form compared with wild-type B56α. Taken together, our results suggest that PKCα can modify PP2A activity by phosphorylation of B56α at Ser(41). This interplay between PKCα and PP2A represents a new mechanism to regulate important cellular functions like cellular Ca(2+) homeostasis.
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Affiliation(s)
- Uwe Kirchhefer
- From the Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, 48149 Münster, Germany
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16
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Yang R, Yang L, Qiu F, Zhang L, Wang H, Yang X, Deng J, Fang W, Zhou Y, Lu J. Functional genetic polymorphisms in PP2A subunit genes confer increased risks of lung cancer in southern and eastern Chinese. PLoS One 2013; 8:e77285. [PMID: 24204789 PMCID: PMC3812212 DOI: 10.1371/journal.pone.0077285] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2013] [Accepted: 09/02/2013] [Indexed: 12/28/2022] Open
Abstract
Protein phosphatase-2A (PP2A) is one of the major cellular serine-threonine phosphatases and functions as a tumor suppressor that negatively regulates the activity of some oncogenic kinases. Recent studies have reported that PP2A expression was suppressed during lung carcinogenesis, we there hypothesized that the single nucleotide polymorphisms (SNPs) in PP2A subunit genes may affect PP2A function and thus contribute to lung cancer susceptibility. In a two-stage case-control study with a total of 1559 lung cancer patients and 1679 controls, we genotyped eight putative functional SNPs and one identified functional SNP (i.e., rs11453459) in seven major PP2A subunits (i.e., PPP2R1A, PPP2R1B, PPP2CA, PPP2R2A, PPP2R2B, PPP2R5C, PPP2R5E) in southern and eastern Chinese. We found that rs11453459G (-G/GG) variant genotypes of PPP2R1A and the rs1255722AA variant genotype of PPP2R5E conferred increased risks of lung cancer (rs11453459, -G/GG vs. –: OR = 1.31, 95% CI = 1.13–1.51; rs1255722, AA vs. AG/GG: OR = 1.27, 95% CI = 1.07–1.51). After combined the two variants, the number of the adverse genotypes was positively associated with lung cancer risk in a dose-response manner (Ptrend = 5.63×10−6). Further functional assay showed that lung cancer tissues carrying rs1255722AA variant genotype had a significantly lower mRNA level of PPP2R5E compared with tissues carrying GG/GA genotypes. However, such effect was not observed for the other SNPs and other combinations. Our findings suggested that the two functional variants in PPP2R1A and PPP2R5E and their combination are associated with lung cancer risk in Chinese, which may be valuable biomarkers to predict risk of lung cancer.
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Affiliation(s)
- Rongrong Yang
- The Institute for Chemical Carcinogenesis, The State Key Lab of Respiratory Disease, Guangzhou Medical University, Guangzhou, China
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17
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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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18
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Ballesteros I, Domínguez T, Sauer M, Paredes P, Duprat A, Rojo E, Sanmartín M, Sánchez-Serrano JJ. Specialized functions of the PP2A subfamily II catalytic subunits PP2A-C3 and PP2A-C4 in the distribution of auxin fluxes and development in Arabidopsis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2013; 73:862-72. [PMID: 23167545 DOI: 10.1111/tpj.12078] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Revised: 11/12/2012] [Accepted: 11/16/2012] [Indexed: 05/09/2023]
Abstract
Protein phosphorylation is a key molecular switch used to transmit information in biological signalling networks. The output of these signalling circuits is governed by the counteracting activities of protein kinases and phosphatases that determine the direction of the switch. Whereas many kinases have been functionally characterized, it has been difficult to ascribe precise cellular roles to plant phosphatases, which are encoded by enlarged gene families that may provide a high degree of genetic redundancy. In this work we have analysed the role in planta of catalytic subunits of protein phosphatase 2A (PP2A), a family encoded by five genes in Arabidopsis. Our results indicate that the two members of subfamily II, PP2A-C3 and PP2A-C4, have redundant functions in controlling embryo patterning and root development, processes that depend on auxin fluxes. Moreover, polarity of the auxin efflux carrier PIN1 and auxin distribution, determined with the DR5(pro) :GFP proxy, are affected by mutations in PP2A-C3 and PP2A-C4. Previous characterization of mutants in putative PP2A regulatory subunits had established a link between this class of phosphatases and PIN dephosphorylation and subcellular distribution. Building on those findings, the results presented here suggest that PP2A-C3 and PP2A-C4 catalyse this reaction and contribute critically to the establishment of auxin gradients for proper plant development.
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Affiliation(s)
- Isabel Ballesteros
- Departamento de Genética Molecular de Plantas, Centro Nacional de Biotecnología CSIC, Campus Universidad Autónoma de Madrid, Cta. Colmenar Viejo km. 15,500, 28049 Madrid, Spain
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19
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Walter G, Ruediger R. Mouse model for probing tumor suppressor activity of protein phosphatase 2A in diverse signaling pathways. Cell Cycle 2012; 11:451-9. [PMID: 22262169 DOI: 10.4161/cc.11.3.19057] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Evidence that protein phosphatase 2A (PP2A) is a tumor suppressor in humans came from the discovery of mutations in the genes encoding the Aα and Aβ subunits of the PP2A trimeric holoenzymes, Aα-B-C and Aβ-B-C. One point mutation, Aα-E64D, was found in a human lung carcinoma. It renders Aα specifically defective in binding regulatory B' subunits. Recently, we reported a knock-in mouse expressing Aα-E64D and an Aα knockout mouse. The mutant mice showed a 50-60% increase in the incidence of lung cancer induced by benzopyrene. Importantly, PP2A's tumor suppressor activity depended on p53. These data provide the first direct evidence that PP2A is a tumor suppressor in mice. In addition, they suggest that PP2A is a tumor suppressor in humans. Here, we report that PP2A functions as a tumor suppressor in mice that develop lung cancer triggered by oncogenic K-ras. We discuss whether PP2A may function as a tumor suppressor in diverse tissues, with emphasis on endometrial and ovarian carcinomas, in which Aα mutations were detected at a high frequency. We propose suitable mouse models for examining whether PP2A functions as tumor suppressor in major growth-stimulatory signaling pathways, and we discuss the prospect of using the PP2A activator FTY720 as a drug against malignancies that are driven by these pathways.
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Affiliation(s)
- Gernot Walter
- Department of Pathology, University of California, San Diego, La Jolla, CA, USA.
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20
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Ahn JH, Kim Y, Kim HS, Greengard P, Nairn AC. Protein kinase C-dependent dephosphorylation of tyrosine hydroxylase requires the B56δ heterotrimeric form of protein phosphatase 2A. PLoS One 2011; 6:e26292. [PMID: 22046270 PMCID: PMC3198769 DOI: 10.1371/journal.pone.0026292] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Accepted: 09/24/2011] [Indexed: 11/19/2022] Open
Abstract
Tyrosine hydroxylase, which plays a critical role in regulation of dopamine synthesis, is known to be controlled by phosphorylation at several critical sites. One of these sites, Ser40, is phosphorylated by a number of protein kinases, including protein kinase A. The major protein phosphatase that dephosphorylates Ser40 is protein phosphatase-2A (PP2A). A recent study has also linked protein kinase C to the dephosphorylation of Ser40 [1], but the mechanism is unclear. PP2A isoforms are comprised of catalytic, scaffold, and regulatory subunits, the regulatory B subunits being able to influence cellular localization and substrate selection. In the current study, we find that protein kinase C is able to phosphorylate a key regulatory site in the B56δ subunit leading to activation of PP2A. In turn, activation of the B56δ-containing heterotrimeric form of PP2A is responsible for enhanced dephosphorylation of Ser40 of tyrosine hydroylase in response to stimulation of PKC. In support of this mechanism, down-regulation of B56δ expression in N27 cells using RNAi was found to increase dopamine synthesis. Together these studies reveal molecular details of how protein kinase C is linked to reduced tyrosine hydroxylase activity via control of PP2A, and also add to the complexity of protein kinase/protein phosphatase interactions.
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Affiliation(s)
- Jung-Hyuck Ahn
- Department of Biochemistry, Ewha Womans University School of Medicine, Seoul, Korea
- * E-mail: (JHA); (ACN)
| | - Yong Kim
- Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, New York, United States of America
| | - Hee-Sun Kim
- Department of Molecular Medicine and Tissue Injury Defense Research Center, Ewha Womans University, School of Medicine, Seoul, Korea
| | - Paul Greengard
- Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, New York, United States of America
| | - Angus C. Nairn
- Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, New York, United States of America
- Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut, United States of America
- * E-mail: (JHA); (ACN)
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21
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Nagendra DC, Burke J, Maxwell GL, Risinger JI. PPP2R1A mutations are common in the serous type of endometrial cancer. Mol Carcinog 2011; 51:826-31. [PMID: 21882256 DOI: 10.1002/mc.20850] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2011] [Revised: 07/28/2011] [Accepted: 08/04/2011] [Indexed: 01/02/2023]
Abstract
Recently unbiased sequencing efforts identified PPP2R1A mutations in clear cell ovarian cancers (OCC). Similar mutations were also noted with high frequency in uterine serous carcinoma. Because the endometrium develops from the same developmental precursors we further examined the hypothesis that PPP2R1A mutations might also occur in diverse histologic subtypes of uterine cancer. We sequenced the PPP2R1A in 22 cell line models of uterine cancer and 10 primary cancers. We found no mutations in the cell lines originally derived from endometrioid (n = 13), undifferentiated (n = 3), clear cell (n = 1), and carcinosarcoma (n = 3) cancers. However, we found a CCC (Pro) to CGC (Arg) codon 179 mutation in the ACI-158 serous carcinoma cell line, a CCC (Pro) to CTC (Leu) in a primary serous carcinoma as well as a CGC (Arg) to CAC (His) codon 258 mutation in a poorly differentiated endometrioid cancer. We sequenced a large panel of endometrial malignancies (n = 181) and found 12 mutants. Importantly, we confirmed a high frequency of mutation in 8 of 25 (32%) serous carcinomas a subtype with well-recognized poor prognosis. Mutations were infrequent in endometrioid cancer and absent in clear cell and carcinosarcoma subtypes. The PPP2R1A mutation regions are conserved among species and known to interact with the regulatory subunits of the PP2A enzyme. PPP2R1A mutant endometrial cancers may represent good candidates for personalized drug therapies particularly for women with the lethal serous histologic variant of uterine cancer.
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Affiliation(s)
- Deepak C Nagendra
- Department of Obstetrics, Gynecology and Reproductive Biology, Michigan State University College of Human Medicine, Grand Rapids, Michigan 49503, USA
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22
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Human cancer-associated mutations in the Aα subunit of protein phosphatase 2A increase lung cancer incidence in Aα knock-in and knockout mice. Mol Cell Biol 2011; 31:3832-44. [PMID: 21791616 DOI: 10.1128/mcb.05744-11] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Strong evidence has indicated that protein phosphatase 2A (PP2A) is a tumor suppressor, but a mouse model for testing the tumor suppressor activity was missing. The most abundant forms of trimeric PP2A holoenzyme consist of the scaffolding Aα subunit, one of several regulatory B subunits, and the catalytic Cα subunit. Aα mutations were discovered in a variety of human carcinomas. All carcinoma-associated mutant Aα subunits are defective in binding the B or B and C subunits. Here we describe two knock-in mice expressing cancer-associated Aα point mutants defective in binding B' subunits, one knockout mouse expressing truncated Aα defective in B and C subunit binding, and a floxed mouse for generating conditional Aα knockouts. We found that the cancer-associated Aα mutations increased the incidence of cancer by 50 to 60% in lungs of FVB mice treated with benzopyrene, demonstrating that PP2A acts as a tumor suppressor. We show that the effect of Aα mutation on cancer incidence is dependent on the tumor suppressor p53. The finding that the Aα mutation E64D, which was detected in a human lung carcinoma, increases the lung cancer incidence in mice suggests that this mutation also played a role in the development of the carcinoma in which it was discovered.
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Elam CA, Wirschell M, Yamamoto R, Fox LA, York K, Kamiya R, Dutcher SK, Sale WS. An axonemal PP2A B-subunit is required for PP2A localization and flagellar motility. Cytoskeleton (Hoboken) 2011; 68:363-72. [PMID: 21692192 DOI: 10.1002/cm.20519] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Revised: 05/26/2011] [Accepted: 06/03/2011] [Indexed: 11/10/2022]
Abstract
Analysis of Chlamydomonas axonemes revealed that the protein phosphatase, PP2A, is localized to the outer doublet microtubules and is implicated in regulation of dynein-driven motility. We tested the hypothesis that PP2A is localized to the axoneme by a specialized, highly conserved 55-kDa B-type subunit identified in the Chlamydomonas flagellar proteome. The B-subunit gene is defective in the motility mutant pf4. Consistent with our hypothesis, both the B- and C- subunits of PP2A fail to assemble in pf4 axonemes, while the dyneins and other axonemal structures are fully assembled in pf4 axonemes. Two pf4 intragenic revertants were recovered that restore PP2A to the axonemes and re-establish nearly wild-type motility. The revertants confirmed that the slow-swimming Pf4 phenotype is a result of the defective PP2A B-subunit. These results demonstrate that the axonemal B-subunit is, in part, an anchor protein required for PP2A localization and that PP2A is required for normal ciliary motility.
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Affiliation(s)
- Candice A Elam
- Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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Samofalova DA, Karpov PA, Nuporko AY, Blume YB. Reconstruction of the spatial structure of plant phosphatases types 1 and 2A in complexes with okadaic acid. CYTOL GENET+ 2011. [DOI: 10.3103/s0095452711030108] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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PP2A activates brassinosteroid-responsive gene expression and plant growth by dephosphorylating BZR1. Nat Cell Biol 2011; 13:124-31. [PMID: 21258370 PMCID: PMC3077550 DOI: 10.1038/ncb2151] [Citation(s) in RCA: 338] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2010] [Accepted: 11/17/2010] [Indexed: 11/24/2022]
Abstract
When brassinosteroid (BR) levels are low, the GSK3-like kinase BIN2 phosphorylates and inactivates the BZR1 transcription factor to inhibit growth in plants. BR promotes growth by inducing dephosphorylation of BZR1, but the phosphatase that dephosphorylates BZR1 has remained unknown. Here we identified protein phosphatase 2A (PP2A) as BZR1-interacting proteins using tandem affinity purification. Genetic analyses demonstrated a positive role of PP2A in BR signalling and BZR1 dephosphorylation. Members of the B'regulatory subunits of PP2A directly interact with BZR1's putative PEST domain containing the site of the bzr1-1D mutation. Interaction with and dephosphorylation by PP2A are enhanced by the bzr1-1D mutation, reduced by two intragenic bzr1-1D suppressor mutations, and abolished by deletion of the PEST domain. This study reveals a crucial function of PP2A in dephosphorylating and activating BZR1 and completes the set of core components of the BR-signalling cascade from cell surface receptor kinase to gene regulation in the nucleus.
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Sablina AA, Hector M, Colpaert N, Hahn WC. Identification of PP2A complexes and pathways involved in cell transformation. Cancer Res 2011; 70:10474-84. [PMID: 21159657 DOI: 10.1158/0008-5472.can-10-2855] [Citation(s) in RCA: 132] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The simian virus 40 small t (SV40ST) oncoprotein interacts with protein phosphatase 2A (PP2A), an abundantly expressed family of serine-threonine phosphatases. This interaction is essential for the transformation of human cells by SV40, and several PP2A subunits have been implicated as tumor suppressor genes. However, the pathways controlled by specific PP2A complexes involved in cell transformation remain incompletely understood. Using a comprehensive loss-of-function approach, we identified 4 PP2A regulatory subunits [B56α, B56γ, PR72/PR130, and PTPA (protein phosphatase 2A activator)], which when suppressed replaced the expression of SV40ST in human cell transformation. We found that manipulation of complexes containing PP2A B56α, B56γ, and PR72/PR130 activates the pathways regulated by c-Myc, Wnt, and PI3K (phosphoinositide 3-kinase)/Akt in a manner that depends on their specific phosphatase activity. In contrast, suppression of PTPA disrupts the assembly of PP2A heterotrimeric complexes, which leads to the activation of these same oncogenic pathways. These observations delineate the PP2A family members and pathways perturbed by SV40ST during human cell transformation.
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Affiliation(s)
- Anna A Sablina
- Department of Medical Oncology, Dana-Farber Cancer Institute, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA.
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Foley TD, Melideo SL, Healey AE, Lucas EJ, Koval JA. Phenylarsine oxide binding reveals redox-active and potential regulatory vicinal thiols on the catalytic subunit of protein phosphatase 2A. Neurochem Res 2010; 36:232-40. [PMID: 21080067 DOI: 10.1007/s11064-010-0310-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/28/2010] [Indexed: 11/24/2022]
Abstract
Our earlier finding that the activity of protein phosphatase 2A from rat brain is inhibited by micromolar concentrations of the dithiol cross-linking reagent phenylarsine oxide (PAO) has encouraged the hypothesis that the catalytic subunit (PP2Ac) of PP2A contains one or more pairs of closely-spaced (vicinal) thiol pairs that may contribute to regulation of the enzyme. The results of the present study demonstrate using immobilized PAO-affinity chromatography that PP2Ac from rat brain formed stable DTT-sensitive adducts with PAO with or without associated regulatory subunits. In addition, a subset of the PAO-binding vicinal thiols of PP2Ac was readily oxidized to disulfide bonds in vitro. Importantly, a small fraction of PP2Ac was still found to contain disulfide bonds after applying stringent conditions designed to prevent protein disulfide bond formation during homogenization and fractionation of the brains. These findings establish the presence of potentially regulatory and redox-active PAO-binding vicinal thiols on the catalytic subunit of PP2A and suggest that a population of PP2Ac may contain disulfide bonds in vivo.
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Affiliation(s)
- Timothy D Foley
- Department of Chemistry, University of Scranton, Scranton, PA 18510, USA.
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Abstract
It has been a long journey since tautomycin (TTM) was isolated in 1987 and the discovery that it inhibited protein phosphatase 1 (PP1) more strongly than PP2A until finally the cocrystal structure of TTM and PP1 was presented early in 2009. The fact that TTM shows preference to inhibit PP1 over PP2A makes this compound unique among the known PP1 and PP2A inhibitors. A number of groups were involved in work aiming to unravel TTM's interactions with PP1 and by doing so hoping to disentangle the secrets as to why TTM is a better inhibitor of PP1 than PP2A. This Focus Review looks back at the work conducted with TTM in order to establish its point of interaction with PP1 prior to X-ray structure. Finally the conclusions before the X-ray structure are compared with the real situation.
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Affiliation(s)
- Magne O Sydnes
- Laboratory of Organic Chemistry, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8601, Japan
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Yoon BS, Jun EK, Park G, Jun Yoo S, Moon JH, Soon Baik C, Kim A, Kim H, Kim JH, Young Koh G, Taek Lee H, You S. Optimal Suppression of Protein Phosphatase 2A Activity Is Critical for Maintenance of Human Embryonic Stem Cell Self-Renewal. Stem Cells 2010; 28:874-884. [DOI: 10.1002/stem.412] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/30/2023]
Abstract
Abstract
The self-renewal of embryonic stem cells involves a balance between processes governed by crosstalk between intrinsic and extrinsic factors. We hypothesized that protein serine/threonine phosphatase 2A (PP2A) may play a central role in the signaling pathways that regulate human embryonic stem cell (hESC) self-renewal. Biochemical analyses revealed that PP2A activity gradually increases over the course of hESC differentiation; PP2A/C and PP2A/A levels also increased. The overexpression of PP2A/C or the addition of PP2A activator C2-ceramide promoted hESC differentiation. Accordingly, the addition of PP2A inactivator okadaic acid (OA) maintained hESC self-renewal in the absence of basic fibroblast growth factor (bFGF). The hESCs maintained with OA expressed pluripotency markers and exhibited substantial telomerase activity with normal karyotypes. The hESCs were able to differentiate into derivatives of the three germ layers, both in vitro and in vivo. Furthermore, the addition of OA and bFGF enabled the maintenance of hESC self-renewal without feeder cells, even in chemically defined xeno-free media. These findings shed a light on the role of PP2A in hESC differentiation and provide a novel strategy for maintaining the self-renewal capability of hESC in bFGF-free, feeder cell-free, and xeno-free media through the optimal suppression of PP2A activity using OA.
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Affiliation(s)
- Byung Sun Yoon
- Laboratories of Cell Function Regulation, Korea University, Seoul, Korea
- Institute of Life Science and Natural Resources, Korea University, Seoul, Korea
| | - Eun Kyoung Jun
- Laboratories of Cell Function Regulation, Korea University, Seoul, Korea
| | - Gyuman Park
- Research Institute for Skin Image, Korea University Guro Hospital, Seoul, Korea
| | - Seung Jun Yoo
- Laboratories of Cell Function Regulation, Korea University, Seoul, Korea
| | - Jai-Hee Moon
- Laboratories of Cell Function Regulation, Korea University, Seoul, Korea
| | | | - Aeree Kim
- Department of Pathology, College of Medicine, Korea University Guro Hospital, Seoul, Korea
| | - Hyunggee Kim
- Laboratories of Cell Function Regulation, Korea University, Seoul, Korea
| | - Jong-Hoon Kim
- Stem Cell Biology, College of Life Sciences and Biotechnology, Korea University, Seoul, Korea
| | - Gou Young Koh
- National Research Laboratory of Vascular Biology, Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Korea
| | - Hoon Taek Lee
- Department of Animal Biotechnology, Bio-Organ Research Center/Animal Resources Research Center, Konkuk University, Seoul, Korea
| | - Seungkwon You
- Laboratories of Cell Function Regulation, Korea University, Seoul, Korea
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Dupont WD, Breyer JP, Bradley KM, Schuyler PA, Plummer WD, Sanders ME, Page DL, Smith JR. Protein phosphatase 2A subunit gene haplotypes and proliferative breast disease modify breast cancer risk. Cancer 2010; 116:8-19. [PMID: 19890961 DOI: 10.1002/cncr.24702] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND Protein phosphatase 2A (PP2A) is a major cellular phosphatase and plays key regulatory roles in growth, differentiation, and apoptosis. Women who are diagnosed with benign proliferative breast disease are at increased risk for the subsequent development of breast cancer. METHODS The authors evaluated genetic variation of PP2A holoenzyme subunits for their potential contribution to breast cancer risk. A nested case-control investigation was performed on a cohort of women who had a history of benign breast disease. The women were followed for an average of 18 years, and DNA prepared from the original archival benign breast biopsy (1954-1995) was available for 450 women who were diagnosed with breast cancer on follow-up and for 890 of 900 women in a control group who were matched on race, age, and year of entry biopsy. RESULTS Single allele-based and haplotype-based tests of association were conducted with assessment of significance by permutation testing. Significant risk and protective haplotypes of the PP2A structural/regulatory subunit A alpha isoform (PPP2R1A) were identified and had odds ratios of 1.63 (95% confidence interval [CI], 1.3-2.1) and 0.55 (95% CI, 0.41-0.76), respectively. These odds ratios remained significant after the analysis was adjusted for multiple comparisons. Women who had both the PPP2R1A risk haplotype and a history of proliferative breast disease had an odds ratio of 2.44 (95% CI, 1.7-3.5) for the subsequent development of breast cancer. The effects of haplotypes for 2 PP2A regulatory subunit genes, PP2 regulatory subunit B alpha isoform (PPP2R2A) and PP2A regulatory subunit B' epsilon isoform (PPP2R5E) on breast cancer risk were nominally significant but did not remain significant after the analysis was adjusted for multiple comparisons. CONCLUSIONS The current findings supported the previously hypothesized role of PP2A as a tumor suppressor gene in breast cancer.
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Affiliation(s)
- William D Dupont
- Department of Biostatistics, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN 37232-2158, USA.
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Kunttas-Tatli E, Bose A, Kahali B, Bishop CP, Bidwai AP. Functional dissection of Timekeeper (Tik) implicates opposite roles for CK2 and PP2A during Drosophila neurogenesis. Genesis 2010; 47:647-58. [PMID: 19536808 DOI: 10.1002/dvg.20543] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Repression by E(spl)M8 during inhibitory Notch (N) signaling (lateral inhibition) is regulated, in part, by protein kinase CK2, but the involvement of a phosphatase has been unclear. The studies we report here employ Tik, a unique dominant-negative (DN) mutation in the catalytic subunit of CK2, in a Gal4-UAS based assay for impaired lateral inhibition. Specifically, overexpression of Tik elicits ectopic bristles in N(+) flies and suppresses the retinal defects of the gain-of-function allele N(spl). Functional dissection of the two substitutions in Tik (M(161)K and E(165)D), suggests that both mutations contribute to its DN effects. While the former replacement compromises CK2 activity by impairing ATP-binding, the latter affects a conserved motif implicated in binding the phosphatase PP2A. Accordingly, overexpression of microtubule star (mts), the PP2A catalytic subunit closely mimics the phenotypic effects of loss of CK2 functions in N(+) or N(spl) flies, and elicits notched wings, a characteristic of N mutations. Our findings suggest antagonistic roles for CK2 and PP2A during inhibitory N signaling.
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Affiliation(s)
- Ezgi Kunttas-Tatli
- Department of Biology, West Virginia University, Morgantown, West Virginia, USA
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Sydnes MO, Miyazaki A, Isobe M, Ohinata H, Miyazu M, Takai A. Development of a new protein labeling strategy, oxidation labeling. part 1: Preliminary evaluation and synthesis of tautomycin containing a metal coordinating unit. Tetrahedron 2010. [DOI: 10.1016/j.tet.2009.12.036] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Abstract
Bacterial chemotaxis is mediated by two reversible protein modification chemistries: phosphorylation and carboxyl methylation. Attractants bind to membrane chemoreceptors that control the activity of a protein kinase which acts in turn to control flagellar motor activity. Coordinate changes in receptor carboxyl methylation provide a negative feedback mechanism that serves a memory function. Protein carboxyl methylation might play an analogous role in the nervous system. Two protein carboxyl methyltransferases serve to regulate signal transduction pathways in eukaryotic cells. One is highly expressed in the Purkinje layer of the cerebellum where it methyl esterifies prenylated cysteine residues at the carboxyl-termini of Ras-related and heterotrimeric G-proteins. The other is abundant throughout the brain where it methylates the carboxyl-terminus of protein phosphatase 2A. The phosphatase methyltransferase and the protein methylesterase that reverses phosphatase methylation are structurally related to the corresponding bacterial chemotaxis methylating and demethylating enzymes. Recent results indicate that deficiencies in phosphatase methylation play an important role in the etiology of Alzheimer's disease.
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Affiliation(s)
- Zhu Li
- Signum Biosciences, Inc., Monmouth Junction, NJ 08852, USA
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34
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The Structure of Protein Phosphatase 2A and Its Inhibition of Tumorigenesis. PROG BIOCHEM BIOPHYS 2009. [DOI: 10.3724/sp.j.1206.2008.00420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Mochida S, Ikeo S, Gannon J, Hunt T. Regulated activity of PP2A-B55 delta is crucial for controlling entry into and exit from mitosis in Xenopus egg extracts. EMBO J 2009; 28:2777-85. [PMID: 19696736 DOI: 10.1038/emboj.2009.238] [Citation(s) in RCA: 224] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2009] [Accepted: 07/15/2009] [Indexed: 11/09/2022] Open
Abstract
Entry into mitosis depends on the activity of cyclin-dependent kinases (CDKs). Conversely, exit from mitosis occurs when mitotic cyclins are degraded, thereby extinguishing CDK activity. Exit from mitosis must also require mitotic phosphoproteins to revert to their interphase hypophosphorylated forms, but there is a controversy about which phosphatase(s) is/are responsible for dephosphorylating the CDK substrates. We find that PP2A associated with a B55 delta subunit is relatively specific for a model mitotic CDK substrate in Xenopus egg extracts. The phosphatase activity measured by this substrate is regulated during the cell cycle--high in interphase and suppressed during mitosis. Depletion of PP2A-B55 delta (in interphase) from 'cycling' frog egg extracts accelerated their entry into mitosis and kept them indefinitely in mitosis. When PP2A-B55 delta was depleted from mitotic extracts, however, exit from mitosis was hardly delayed, showing that other phosphatase(s) are also required for mitotic exit. Increasing the concentration of PP2A-B55 delta in extracts by adding recombinant enzyme inhibited the entry into mitosis. This form of PP2A seems to be a key regulator of entry into and exit from mitosis.
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Affiliation(s)
- Satoru Mochida
- Cancer Research UK, London Research Institute, Clare Hall Laboratories, South Mimms, Herts, UK
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Affiliation(s)
- Brett M Collins
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia.
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Ruvolo VR, Kurinna SM, Karanjeet KB, Schuster TF, Martelli AM, McCubrey JA, Ruvolo PP. PKR regulates B56(alpha)-mediated BCL2 phosphatase activity in acute lymphoblastic leukemia-derived REH cells. J Biol Chem 2008; 283:35474-85. [PMID: 18957415 DOI: 10.1074/jbc.m800951200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Protein phosphatase 2A (PP2A) is a heterotrimer comprising catalytic, scaffold, and regulatory (B) subunits. There are at least 21 B subunit family members. Thus PP2A is actually a family of enzymes defined by which B subunit is used. The B56 family member B56alpha is a phosphoprotein that regulates dephosphorylation of BCL2. The stress kinase PKR has been shown to phosphorylate B56alpha at serine 28 in vitro, but it has been unclear how PKR might regulate the BCL2 phosphatase. In the present study, PKR regulation of B56alpha in REH cells was examined, because these cells exhibit robust BCL2 phosphatase activity. PKR was found to be basally active in REH cells as would be predicted if the kinase supports B56alpha-mediated dephosphorylation of BCL2. Suppression of PKR promoted BCL2 phosphorylation with concomitant loss of B56alpha phosphorylation at serine 28 and inhibition of mitochondrial PP2A activity. PKR supports stress signaling in REH cells, as suppression of PKR promoted chemoresistance to etoposide. Suppression of PKR promoted B56alpha proteolysis, which could be blocked by a proteasome inhibitor. However, the mechanism by which PKR supports B56alpha protein does not involve PKR-mediated phosphorylation of the B subunit at serine 28 but may involve eIF2alpha activation of AKT. Phosphorylation of serine 28 by PKR promotes mitochondrial localization of B56alpha, because wild-type but not mutant S28A B56alpha promoted mitochondrial PP2A activity. Cells expressing wild-type B56alpha but not S28A B56alpha were sensitized to etoposide. These results suggest that PKR regulates B56alpha-mediated PP2A signaling in REH cells.
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Affiliation(s)
- Vivian R Ruvolo
- Section of Signal Transduction and Apoptosis, University of Minnesota Hormel Institute, Austin, Minnesota 55912, USA
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Rodríguez AD, Lear MJ, La Clair JJ. Identification of the Binding of Sceptrin to MreB via a Bidirectional Affinity Protocol. J Am Chem Soc 2008; 130:7256-8. [DOI: 10.1021/ja7114019] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Abimael D. Rodríguez
- Department of Chemistry, University of Puerto Rico, P.O. Box 23346, UPR Station, San Juan, Puerto Rico 00931-3346, Department of Chemistry and Medicinal Chemistry Program, National University of Singapore, 3 Science Drive 3, Singapore 117543, and Xenobe Research Institute, 3371 Adams Avenue, San Diego, California 92116
| | - Martin J. Lear
- Department of Chemistry, University of Puerto Rico, P.O. Box 23346, UPR Station, San Juan, Puerto Rico 00931-3346, Department of Chemistry and Medicinal Chemistry Program, National University of Singapore, 3 Science Drive 3, Singapore 117543, and Xenobe Research Institute, 3371 Adams Avenue, San Diego, California 92116
| | - James J. La Clair
- Department of Chemistry, University of Puerto Rico, P.O. Box 23346, UPR Station, San Juan, Puerto Rico 00931-3346, Department of Chemistry and Medicinal Chemistry Program, National University of Singapore, 3 Science Drive 3, Singapore 117543, and Xenobe Research Institute, 3371 Adams Avenue, San Diego, California 92116
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Ishida A, Sueyoshi N, Shigeri Y, Kameshita I. Negative regulation of multifunctional Ca2+/calmodulin-dependent protein kinases: physiological and pharmacological significance of protein phosphatases. Br J Pharmacol 2008; 154:729-40. [PMID: 18454172 DOI: 10.1038/bjp.2008.127] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Multifunctional Ca2+/calmodulin-dependent protein kinases (CaMKs) play pivotal roles in intracellular Ca2+ signaling pathways. There is growing evidence that CaMKs are involved in the pathogenic mechanisms underlying various human diseases. In this review, we begin by briefly summarizing our knowledge of the involvement of CaMKs in the pathogenesis of various diseases suggested to be caused by the dysfunction/dysregulation or aberrant expression of CaMKs. It is widely known that the activities of CaMKs are strictly regulated by protein phosphorylation/dephosphorylation of specific phosphorylation sites. Since phosphorylation status is balanced by protein kinases and protein phosphatases, the mechanism of dephosphorylation/deactivation of CaMKs, corresponding to their 'switching off', is extremely important, as is the mechanism of phosphorylation/activation corresponding to their 'switching on'. Therefore, we focus on the regulation of multifunctional CaMKs by protein phosphatases. We summarize the current understanding of negative regulation of CaMKs by protein phosphatases. We also discuss the biochemical properties and physiological significance of a protein phosphatase that we designated as Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP), and those of its homologue CaMKP-N. Pharmacological applications of CaMKP inhibitors are also discussed. These compounds may be useful not only for exploring the physiological functions of CaMKP/CaMKP-N, but also as novel chemotherapies for various diseases.
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Affiliation(s)
- A Ishida
- Laboratory of Molecular Brain Science, Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Japan.
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Wang PY, Weng J, Lee S, Anderson RG. The N Terminus Controls Sterol Binding while the C Terminus Regulates the Scaffolding Function of OSBP. J Biol Chem 2008; 283:8034-45. [DOI: 10.1074/jbc.m707631200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Sydnes MO, Kuse M, Kurono M, Shimomura A, Ohinata H, Takai A, Isobe M. Protein phosphatase inhibitory activity of tautomycin photoaffinity probes evaluated at femto-molar level. Bioorg Med Chem 2008; 16:1747-55. [DOI: 10.1016/j.bmc.2007.11.034] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2007] [Revised: 11/06/2007] [Accepted: 11/06/2007] [Indexed: 10/22/2022]
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Yan L, Lavin VA, Moser LR, Cui Q, Kanies C, Yang E. PP2A regulates the pro-apoptotic activity of FOXO1. J Biol Chem 2008; 283:7411-20. [PMID: 18211894 DOI: 10.1074/jbc.m708083200] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
FOXO1, a member of the evolutionarily conserved forkhead family of transcription factors, regulates expression of a number of genes that play critical roles in cell cycle and apoptosis. A pivotal regulatory mechanism of FOXO is reversible phosphorylation, catalyzed by kinases and phosphatases. Phosphorylation of FOXO1 is associated with 14-3-3 binding and cytosolic localization, whereas dephosphorylated FOXO1 translocates to the nucleus and is transcriptionally active. Experiments were performed to identify the serine/threonine phosphatase that dephosphorylates FOXO1. PP2A inhibitors, okadaic acid and fostriecin, increased FOXO1 phosphorylation in vitro and in cells. Microcystin-agarose pull-downs suggested that a phosphatase binds to FOXO1, and PP2A catalytic subunit was identified in endogenous FOXO1 immunocomplexes, indicating that PP2A is a FOXO1 phosphatase. Purified PP2A interacted directly with FOXO1 and dephosphorylated FOXO1 in vitro. Silencing of PP2A protected FOXO1 from dephosphorylation and delayed FOXO1 nuclear translocation, confirming the physiologic role of PP2A in the regulation of FOXO1 function. Furthermore, inhibition of PP2A phosphatases rescued FOXO1-mediated cell death by regulating the level of the pro-apoptotic protein BIM. We conclude that PP2A is a physiologic phosphatase of FOXO1.
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Affiliation(s)
- Ling Yan
- Department of Pediatrics, Cancer Biology, , The Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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Abstract
Reversible phosphorylation, catalyzed by kinases and phosphatases, regulates many apoptosis molecules. Phosphorylation inactivates, whereas dephosphorylation activates, the pro-apoptotic functions of select apoptotic regulators, including the BCL2 family, such as BAD, and transcription factors such as FOXOs. The apoptotic function of the BH3 molecule BAD is exquisitely regulated by phosphorylation. Although phosphorylated BAD is sequestered in the cytosol, dephosphorylated BAD translocates to the mitochondria and inactivates BCL-xL and BCL2. Analogously, Akt-phosphorylated FOXO1 is cytosolic and inactive as a transcription factor, but dephosphorylated FOXO1 translocates to the nucleus, where it regulates the expression of pro-apoptotic Bim and cell cycle inhibitors. By use of inhibitor experiments and a combination of immunoprecipitations and tagged pull-downs in interaction studies, we identified PP2A enzymes as BAD and FOXO1 phosphatases. PP2A dephosphorylation of BAD is regulated by competitive interaction of 14-3-3, PP2A, and BAD. On survival factor deprivation, PP2A dephosphorylation of pSer112 plays the gatekeeper role for subsequent dephosphorylation at pSer136 and pSer155 by multiple phosphatases. In contrast, PP2A and 14-3-3 can interact with FOXO1 concomitantly, but PP2A dephosphorylates the pThr24 and pSer256 only once 14-3-3 dissociates. Functional assays of cell death, Bim upregulation by FOXO1, and FOXO1 nuclear translocation in the presence of phosphatase inhibitors and phosphatase siRNAs revealed the physiologic significance of PP2A activity on BAD and FOXO1. Demonstrating the role of PP2A in regulating the function of two very different cell death molecules, a BH3 protein and a transcription factor, suggests that activation of pro-apoptotic factors by protein phosphatases may be a general regulatory mechanism in apoptosis.
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Affiliation(s)
- Chi-Wu Chiang
- Institute of Molecular Medicine and Center for Gene Regulation and Signal Transduction Research, National Cheng Kung University, Tainan, Taiwan
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Abstract
Human cytomegalovirus (HCMV) induces cellular stress responses during infection due to nutrient depletion, energy depletion, hypoxia and synthetic stress, e.g., endoplasmic reticulum (ER) stress. Cellular stress responses initiate processes that allow the cell to survive the stress; some of these may be beneficial to HCMV replication while others are not. Several studies show that HCMV manipulates stress response signaling in order to maintain beneficial effects while inhibiting detrimental effects. The inhibition of translation is the most common effect of stress responses that would be detrimental to HCMV infection. This chapter will focus on the mechanisms by which cap-dependent translation is maintained during HCMV infection through alterations of the phosphatidylinositol-3' kinase (PI3K)-Akt-tuberous sclerosis complex (TSC)-mammalian target of rapamycin (mTOR) signaling pathway. The emerging picture is that HCMV affects this pathway in multiple ways, thus ensuring that cap-dependent translation is maintained despite the induction of stress responses that would normally inhibit it. Such dramatic alterations of this pathway lead to questions of what other beneficial effects the virus might gain from these changes and how these changes may contribute to HCMV pathogenesis.
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47
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Yang J, Roe SM, Prickett TD, Brautigan DL, Barford D. The structure of Tap42/alpha4 reveals a tetratricopeptide repeat-like fold and provides insights into PP2A regulation. Biochemistry 2007; 46:8807-15. [PMID: 17616149 DOI: 10.1021/bi7007118] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Physiological functions of protein phosphatase 2A (PP2A) are determined via the association of its catalytic subunit (PP2Ac) with diverse regulatory subunits. The predominant form of PP2Ac assembles into a heterotrimer comprising the scaffolding PR65/A subunit together with a variable regulatory B subunit. A distinct population of PP2Ac associates with the Tap42/alpha4 subunit, an interaction mutually exclusive with that of PR65/A. Tap42/alpha4 is also an interacting subunit of the PP2Ac-related phosphatases, PP4 and PP6. Tap42/alpha4, an essential protein in yeast and suppressor of apoptosis in mammals, contributes to critical cellular functions including the Tor signaling pathway. Here, we describe the crystal structure of the PP2Ac-interaction domain of Saccharomyces cerevisiae Tap42. The structure reveals an all alpha-helical protein with striking similarity to 14-3-3 and tetratricopeptide repeat (TPR) proteins. Mutational analyses of structurally conserved regions of Tap42/alpha4 identified a positively charged region critical for its interactions with PP2Ac. We propose a scaffolding function for Tap42/alpha4 whereby the interaction of PP2Ac at its N-terminus promotes the dephosphorylation of substrates recruited to the C-terminal region of the molecule.
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Affiliation(s)
- Jing Yang
- Section of Structural Biology, Chester Beatty Laboratories, Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK
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48
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Sheehan KA, Ke Y, Solaro RJ. p21-Activated kinase-1 and its role in integrated regulation of cardiac contractility. Am J Physiol Regul Integr Comp Physiol 2007; 293:R963-73. [PMID: 17609315 DOI: 10.1152/ajpregu.00253.2007] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We review here a novel concept in the regulation of cardiac contractility involving variations in the activity of the multifunctional enzyme, p21-activated kinase 1 (Pak1), a member of a family of proteins in the small G protein-signaling pathway that is activated by Cdc42 and Rac1. There is a large body of evidence from studies in noncardiac tissue that Pak1 activity is key in regulation of a number of cellular functions, including cytoskeletal dynamics, cell motility, growth, and proliferation. Although of significant potential impact, the role of Pak1 in regulation of the heart has been investigated in only a few laboratories. In this review, we discuss the structure of Pak1 and its sites of posttranslational modification and molecular interactions. We assemble an overview of the current data on Pak1 signaling in noncardiac tissues relative to similar signaling pathways in the heart, and we identify potential roles of Pak1 in cardiac regulation. Finally, we discuss the current state of Pak1 research in the heart in regard to regulation of contractility through functional myofilament and Ca(2+)-flux modification. An important aspect of this regulation is the modulation of kinase and phosphatase activity. We have focused on Pak1 regulation of protein phosphatase 2A (PP2A), which is abundant in cardiac muscle, thereby mediating dephosphorylation of sarcomeric proteins and sensitizing the myofilaments to Ca(2+). We present a model for Pak1 signaling that provides a mechanism for specifically affecting cardiac cellular processes in which regulation of protein phosphorylation states by PP2A dephosphorylation predominates.
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Affiliation(s)
- Katherine A Sheehan
- Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, 835 S. Wolcott Ave., Chicago, IL 60612-7342, USA.
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49
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Foley TD, Petro LA, Stredny CM, Coppa TM. Oxidative inhibition of protein phosphatase 2A activity: role of catalytic subunit disulfides. Neurochem Res 2007; 32:1957-64. [PMID: 17562162 DOI: 10.1007/s11064-007-9394-x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2007] [Accepted: 05/21/2007] [Indexed: 10/23/2022]
Abstract
A molecular basis for the inhibition of brain protein phosphatase 2A (PP2A) activity by oxidative stress was examined in a high-speed supernatant (HSS) fraction from rat cerebral cortex. PP2A activity was subject to substantial disulfide reducing agent-reversible inhibition in the HSS fraction. Results of gel electrophoresis support the conclusions that inhibition of PP2A activity was associated with the both the disulfide cross-linking of the catalytic subunit (PP2A(C)) of the enzyme to other brain proteins and with the formation of an apparent novel intramolecular disulfide bond in PP2A(C). Additional findings that the vicinal dithiol cross-linking reagent phenylarsine oxide (PAO) produced a potent dithiothreitol-reversible inhibition of PP2A activity suggest that the cross-linking of PP2A(C) vicinal thiols to form an intramolecular disulfide bond may be sufficient to inhibit PP2A activity under oxidative stress. We propose that the dithiol-disulfide equilibrium of a vicinal thiol pair of PP2A(C) may confer redox sensitivity on cellular PP2A.
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Affiliation(s)
- Timothy D Foley
- Department of Chemistry, University of Scranton, 800 Linden St., Scranton, PA 18510, USA.
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50
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Ahn JH, Sung JY, McAvoy T, Nishi A, Janssens V, Goris J, Greengard P, Nairn AC. The B''/PR72 subunit mediates Ca2+-dependent dephosphorylation of DARPP-32 by protein phosphatase 2A. Proc Natl Acad Sci U S A 2007; 104:9876-81. [PMID: 17535922 PMCID: PMC1887582 DOI: 10.1073/pnas.0703589104] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2007] [Indexed: 12/18/2022] Open
Abstract
In dopaminoceptive neurons, dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) plays a central role in integrating the effects of dopamine and other neurotransmitters. Phosphorylation of DARPP-32 at Thr-34 by protein kinase A results in inhibition of protein phosphatase 1 (PP1), and phosphorylation at Thr-75 by Cdk5 (cyclin-dependent kinase 5) results in inhibition of protein kinase A. Dephosphorylation at Thr-34 involves primarily the Ca(2+)-dependent protein phosphatase, PP2B (calcineurin), whereas dephosphorylation of Thr-75 involves primarily PP2A, the latter being subject to control by both cAMP- and Ca(2+)-dependent regulatory mechanisms. In the present study, we have investigated the mechanism of Ca(2+)-dependent regulation of Thr-75 by PP2A. We show that the PR72 (or B'' or PPP2R3A) regulatory subunit of PP2A is highly expressed in striatum. Through the use of overexpression and down-regulation by using RNAi, we show that PP2A, in a heterotrimeric complex with the PR72 subunit, mediates Ca(2+)-dependent dephosphorylation at Thr-75 of DARPP-32. The PR72 subunit contains two Ca(2+) binding sites formed by E and F helices (EF-hands 1 and 2), and we show that the former is necessary for the ability of PP2A activity to be regulated by Ca(2+), both in vitro and in vivo. Our studies also indicate that the PR72-containing form of PP2A is necessary for the ability of glutamate acting at alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and NMDA receptors to regulate Thr-75 dephosphorylation. These studies further our understanding of the complex signal transduction pathways that regulate DARPP-32. In addition, our studies reveal an alternative intracellular mechanism whereby Ca(2+) can activate serine/threonine phosphatase activity.
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Affiliation(s)
- Jung-Hyuck Ahn
- *Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY 10021
| | - Jee Young Sung
- *Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY 10021
| | - Thomas McAvoy
- *Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY 10021
| | - Akinori Nishi
- Department of Pharmacology, Kurume University School of Medicine, 67 Asahi-machi, Kurume, Fukuoka 830-0011, Japan
| | - Veerle Janssens
- Division of Biochemistry, Katholieke Universitet Leuven, Herestraat 49, B-3000 Leuven, Belgium; and
| | - Jozef Goris
- Division of Biochemistry, Katholieke Universitet Leuven, Herestraat 49, B-3000 Leuven, Belgium; and
| | - Paul Greengard
- *Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY 10021
| | - Angus C. Nairn
- *Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY 10021
- Department of Psychiatry, Yale University School of Medicine, New Haven, CT 06508
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