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Peris I, Romero-Murillo S, Vicente C, Narla G, Odero MD. Regulation and role of the PP2A-B56 holoenzyme family in cancer. Biochim Biophys Acta Rev Cancer 2023; 1878:188953. [PMID: 37437699 DOI: 10.1016/j.bbcan.2023.188953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2023] [Revised: 07/07/2023] [Accepted: 07/08/2023] [Indexed: 07/14/2023]
Abstract
Protein phosphatase 2A (PP2A) inactivation is common in cancer, leading to sustained activation of pro-survival and growth-promoting pathways. PP2A consists of a scaffolding A-subunit, a catalytic C-subunit, and a regulatory B-subunit. The functional complexity of PP2A holoenzymes arises mainly through the vast repertoire of regulatory B-subunits, which determine both their substrate specificity and their subcellular localization. Therefore, a major challenge for developing more effective therapeutic strategies for cancer is to identify the specific PP2A complexes to be targeted. Of note, the development of small molecules specifically directed at PP2A-B56α has opened new therapeutic avenues in both solid and hematological tumors. Here, we focus on the B56/PR61 family of PP2A regulatory subunits, which have a central role in directing PP2A tumor suppressor activity. We provide an overview of the mechanisms controlling the formation and regulation of these complexes, the pathways they control, and the mechanisms underlying their deregulation in cancer.
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Affiliation(s)
- Irene Peris
- Department of Biochemistry and Genetics, University of Navarra, Pamplona, Spain; Centro de Investigación Médica Aplicada (CIMA), University of Navarra, Pamplona, Spain; Instituto de Investigación Sanitaria de Navarra (IdiSNA), Pamplona, Spain.
| | - Silvia Romero-Murillo
- Department of Biochemistry and Genetics, University of Navarra, Pamplona, Spain; Centro de Investigación Médica Aplicada (CIMA), University of Navarra, Pamplona, Spain
| | - Carmen Vicente
- Centro de Investigación Médica Aplicada (CIMA), University of Navarra, Pamplona, Spain; Instituto de Investigación Sanitaria de Navarra (IdiSNA), Pamplona, Spain
| | - Goutham Narla
- Division of Genetic Medicine, Department of Internal Medicine, The University of Michigan Medical School, Ann Arbor, MI, USA
| | - Maria D Odero
- Department of Biochemistry and Genetics, University of Navarra, Pamplona, Spain; Centro de Investigación Médica Aplicada (CIMA), University of Navarra, Pamplona, Spain; Instituto de Investigación Sanitaria de Navarra (IdiSNA), Pamplona, Spain; CIBERONC, Instituto de Salud Carlos III, Madrid, Spain.
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2
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Ferreira AF, Santiago J, Silva JV, Oliveira PF, Fardilha M. PP1, PP2A and PP2B Interplay in the Regulation of Sperm Motility: Lessons from Protein Phosphatase Inhibitors. Int J Mol Sci 2022; 23:ijms232315235. [PMID: 36499559 PMCID: PMC9737803 DOI: 10.3390/ijms232315235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Revised: 11/30/2022] [Accepted: 12/01/2022] [Indexed: 12/11/2022] Open
Abstract
Male fertility relies on the ability of spermatozoa to fertilize the egg in the female reproductive tract (FRT). Spermatozoa acquire activated motility during epididymal maturation; however, to be capable of fertilization, they must achieve hyperactivated motility in the FRT. Extensive research found that three protein phosphatases (PPs) are crucial to sperm motility regulation, the sperm-specific protein phosphatase type 1 (PP1) isoform gamma 2 (PP1γ2), protein phosphatase type 2A (PP2A) and protein phosphatase type 2B (PP2B). Studies have reported that PP activity decreases during epididymal maturation, whereas protein kinase activity increases, which appears to be a requirement for motility acquisition. An interplay between these PPs has been extensively investigated; however, many specific interactions and some inconsistencies remain to be elucidated. The study of PPs significantly advanced following the identification of naturally occurring toxins, including calyculin A, okadaic acid, cyclosporin, endothall and deltamethrin, which are powerful and specific PP inhibitors. This review aims to overview the protein phosphorylation-dependent biochemical pathways underlying sperm motility acquisition and hyperactivation, followed by a discussion of the PP inhibitors that allowed advances in the current knowledge of these pathways. Since male infertility cases still attain alarming numbers, additional research on the topic is required, particularly using other PP inhibitors.
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Affiliation(s)
- Ana F. Ferreira
- Laboratory of Signal Transduction, Institute for Biomedicine-iBiMED, Medical Sciences Department, University of Aveiro, 3810-193 Aveiro, Portugal
| | - Joana Santiago
- Laboratory of Signal Transduction, Institute for Biomedicine-iBiMED, Medical Sciences Department, University of Aveiro, 3810-193 Aveiro, Portugal
| | - Joana V. Silva
- Laboratory of Signal Transduction, Institute for Biomedicine-iBiMED, Medical Sciences Department, University of Aveiro, 3810-193 Aveiro, Portugal
| | - Pedro F. Oliveira
- QOPNA & LAQV, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
| | - Margarida Fardilha
- Laboratory of Signal Transduction, Institute for Biomedicine-iBiMED, Medical Sciences Department, University of Aveiro, 3810-193 Aveiro, Portugal
- Correspondence: ; Tel.: +351-918-143-947
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Pan L, Chen J, He X, Zhan T, Shen H. Aqueous photodegradation of okadaic acid and dinophysistoxin-1: Persistence, kinetics, photoproducts, pathways, and toxicity evaluation. THE SCIENCE OF THE TOTAL ENVIRONMENT 2020; 743:140593. [PMID: 32673911 DOI: 10.1016/j.scitotenv.2020.140593] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Revised: 06/26/2020] [Accepted: 06/26/2020] [Indexed: 06/11/2023]
Abstract
Diarrhetic shellfish poisoning (DSP) toxins are a class of natural organic contaminants that pose a serious threat not only to marine ecosystems and fisheries but also to human health. They are widely distributed in coastal and offshore waters around the world. However, the persistence and photochemical degradation characteristics of DSP in an aqueous environment are still unclear. This study aimed to elucidate the photochemical fate of two representative DSP toxins, namely, okadaic acid (OA) and dinophysistoxin-1 (DTX1). Results showed that photo-mediated chemical reactions play a crucial role in eliminating DSP toxins in seawater. However, the degradation of OA and DTX1 was relatively slow under natural solar radiation, with a removal efficiency of 90.0% after exposure for more than 20 days. When the reaction solutions of OA and DTX1 were exposed to Hg lamp radiation, their degradation followed pseudo-first-order kinetics, and was remarkably influenced by seawater pH and metal-ion concentration. A total of 24 tentative transformation products (TPs) of OA and DTX1 were identified via liquid chromatography high-resolution mass spectrometry. C12 (C43H66O11) and C24 (C44H68O11) were the main TPs. The following possible photodegradation pathways were proposed: decarboxylation, photoinduced hydrolysis, chain scission, and photo-oxidation. Toxicity assays via protein phosphatase 2A inhibition proved that photochemical processes could significantly reduce the DSP toxicity of irradiated solutions by approximately 88%. This work provides an enhanced understanding of the fate of DSP toxins in the aqueous environment, allowing for an improved assessment of their environmental impacts.
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Affiliation(s)
- Lei Pan
- Marine Bioresource and Environment Research Center, Key Laboratory of Marine Eco-Environmental Science and Technology, The First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China; College of Chemistry and Molecular Engineering, Qingdao Technology University of Shandong, Qingdao 266042, China
| | - Junhui Chen
- Marine Bioresource and Environment Research Center, Key Laboratory of Marine Eco-Environmental Science and Technology, The First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China; Laboratory for Marine Ecology and Environmental Science, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266071, China.
| | - Xiuping He
- Marine Bioresource and Environment Research Center, Key Laboratory of Marine Eco-Environmental Science and Technology, The First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China; Laboratory for Marine Ecology and Environmental Science, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266071, China
| | - Tianrong Zhan
- College of Chemistry and Molecular Engineering, Qingdao Technology University of Shandong, Qingdao 266042, China
| | - Huihui Shen
- Marine Bioresource and Environment Research Center, Key Laboratory of Marine Eco-Environmental Science and Technology, The First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China; Laboratory for Marine Ecology and Environmental Science, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266071, China
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Araki S, Osuka K, Takata T, Tsuchiya Y, Watanabe Y. Coordination between Calcium/Calmodulin-Dependent Protein Kinase II and Neuronal Nitric Oxide Synthase in Neurons. Int J Mol Sci 2020; 21:ijms21217997. [PMID: 33121174 PMCID: PMC7662388 DOI: 10.3390/ijms21217997] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Revised: 10/21/2020] [Accepted: 10/22/2020] [Indexed: 12/15/2022] Open
Abstract
Ca2+/calmodulin (CaM)-dependent protein kinase II (CaMKII) is highly abundant in the brain and exhibits broad substrate specificity, thereby it is thought to participate in the regulation of neuronal death and survival. Nitric oxide (NO), produced by neuronal NO synthase (nNOS), is an important neurotransmitter and plays a role in neuronal activity including learning and memory processes. However, high levels of NO can contribute to excitotoxicity following a stroke and neurodegenerative disease. Aside from NO, nNOS also generates superoxide which is involved in both cell injury and signaling. CaMKII is known to activate and translocate from the cytoplasm to the post-synaptic density in response to neuronal activation where nNOS is predominantly located. Phosphorylation of nNOS at Ser847 by CaMKII decreases NO generation and increases superoxide generation. Conversely, NO-induced S-nitrosylation of CaMKII at Cys6 is a prominent determinant of the CaMKII inhibition in ATP competitive fashion. Thus, the "cross-talk" between CaMKII and NO/superoxide may represent important signal transduction pathways in brain. In this review, we introduce the molecular mechanism of and pathophysiological role of mutual regulation between CaMKII and nNOS in neurons.
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Affiliation(s)
- Shoma Araki
- Department of Pharmacology, Showa Pharmaceutical University, Machida, Tokyo 194-8543, Japan; (S.A.); (T.T.); (Y.T.)
| | - Koji Osuka
- Department of Neurological Surgery, Aichi Medical University, Aichi 480-1195, Japan;
| | - Tsuyoshi Takata
- Department of Pharmacology, Showa Pharmaceutical University, Machida, Tokyo 194-8543, Japan; (S.A.); (T.T.); (Y.T.)
- Department of Environmental Health Sciences and Molecular Toxicology, Graduate School of Medicine, Tohoku University, Miyagi 980-8575, Japan
| | - Yukihiro Tsuchiya
- Department of Pharmacology, Showa Pharmaceutical University, Machida, Tokyo 194-8543, Japan; (S.A.); (T.T.); (Y.T.)
| | - Yasuo Watanabe
- Department of Pharmacology, Showa Pharmaceutical University, Machida, Tokyo 194-8543, Japan; (S.A.); (T.T.); (Y.T.)
- Correspondence:
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Naraki Y, Watanabe M, Takeya K. Inhibitory effects of rubratoxin A, a potent inhibitor of protein phosphatase 2, on the Ca 2+-dependent contraction of skinned carotid artery from guinea pig. J Smooth Muscle Res 2020; 55:14-22. [PMID: 31006724 PMCID: PMC6473161 DOI: 10.1540/jsmr.55.14] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Rubratoxin A, a potent inhibitor of PP2A, is known to suppress smooth muscle contraction.
The inhibitory role of PP2A in smooth muscle contraction is still unclear. In order to
clarify the regulatory mechanisms of PP2A on vascular smooth muscle contractility, we
examined the effects of rubratoxin A on the Ca2+-induced contraction of β-escin
skinned carotid artery preparations from guinea pigs. Rubratoxin A at 1 µM and 10 µM
significantly inhibited skinned carotid artery contraction at any Ca2+
concentration. The data fitting to the Hill equation in [Ca2+]-contraction
relationship indicated that rubratoxin A decreased Fmax-Ca2+ and increased
[Ca2+]50, indices of Ca2+ sensitivity for the force and
myosin-actin interaction, respectively. These results suggest that PP2A inhibition causes
downregulation of the myosin light chain phosphorylation and direct interference with
myosin-actin interaction.
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Affiliation(s)
- Yasuyuki Naraki
- Department of Frontier Health Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashiogu, Arakawa-ku, Tokyo 116-8551, Japan
| | - Masaru Watanabe
- Department of Frontier Health Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashiogu, Arakawa-ku, Tokyo 116-8551, Japan
| | - Kosuke Takeya
- Department of Veterinary Biochemistry, Faculty of Veterinary Medicine, Okayama University of Science, Imabari-shi, Ehime 794-8555, Japan
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Duhart JC, Raftery LA. Mob Family Proteins: Regulatory Partners in Hippo and Hippo-Like Intracellular Signaling Pathways. Front Cell Dev Biol 2020; 8:161. [PMID: 32266255 DOI: 10.3389/fcell.2020.00161/full] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2019] [Accepted: 02/28/2020] [Indexed: 05/26/2023] Open
Abstract
Studies in yeast first delineated the function of Mob proteins in kinase pathways that regulate cell division and shape; in multicellular eukaryotes Mobs regulate tissue growth and morphogenesis. In animals, Mobs are adaptors in Hippo signaling, an intracellular signal-transduction pathway that restricts growth, impacting the development and homeostasis of animal organs. Central to Hippo signaling are the Nuclear Dbf2-Related (NDR) kinases, Warts and LATS1 and LATS2, in flies and mammals, respectively. A second Hippo-like signaling pathway has been uncovered in animals, which regulates cell and tissue morphogenesis. Central to this emergent pathway are the NDR kinases, Tricornered, STK38, and STK38L. In Hippo signaling, NDR kinase activation is controlled by three activating interactions with a conserved set of proteins. This review focuses on one co-activator family, the highly conserved, non-catalytic Mps1-binder-related (Mob) proteins. In this context, Mobs are allosteric activators of NDR kinases and adaptors that contribute to assembly of multiprotein NDR kinase activation complexes. In multicellular eukaryotes, the Mob family has expanded relative to model unicellular yeasts; accumulating evidence points to Mob functional diversification. A striking example comes from the most sequence-divergent class of Mobs, which are components of the highly conserved Striatin Interacting Phosphatase and Kinase (STRIPAK) complex, that antagonizes Hippo signaling. Mobs stand out for their potential to modulate the output from Hippo and Hippo-like kinases, through their roles both in activating NDR kinases and in antagonizing upstream Hippo or Hippo-like kinase activity. These opposing Mob functions suggest that they coordinate the relative activities of the Tricornered/STK38/STK38L and Warts/LATS kinases, and thus have potential to assemble nodes for pathway signaling output. We survey the different facets of Mob-dependent regulation of Hippo and Hippo-like signaling and highlight open questions that hinge on unresolved aspects of Mob functions.
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Affiliation(s)
- Juan Carlos Duhart
- School of Life Sciences, University of Nevada, Las Vegas, Las Vegas, NV, United States
| | - Laurel A Raftery
- School of Life Sciences, University of Nevada, Las Vegas, Las Vegas, NV, United States
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7
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Duhart JC, Raftery LA. Mob Family Proteins: Regulatory Partners in Hippo and Hippo-Like Intracellular Signaling Pathways. Front Cell Dev Biol 2020; 8:161. [PMID: 32266255 PMCID: PMC7096357 DOI: 10.3389/fcell.2020.00161] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2019] [Accepted: 02/28/2020] [Indexed: 12/16/2022] Open
Abstract
Studies in yeast first delineated the function of Mob proteins in kinase pathways that regulate cell division and shape; in multicellular eukaryotes Mobs regulate tissue growth and morphogenesis. In animals, Mobs are adaptors in Hippo signaling, an intracellular signal-transduction pathway that restricts growth, impacting the development and homeostasis of animal organs. Central to Hippo signaling are the Nuclear Dbf2-Related (NDR) kinases, Warts and LATS1 and LATS2, in flies and mammals, respectively. A second Hippo-like signaling pathway has been uncovered in animals, which regulates cell and tissue morphogenesis. Central to this emergent pathway are the NDR kinases, Tricornered, STK38, and STK38L. In Hippo signaling, NDR kinase activation is controlled by three activating interactions with a conserved set of proteins. This review focuses on one co-activator family, the highly conserved, non-catalytic Mps1-binder-related (Mob) proteins. In this context, Mobs are allosteric activators of NDR kinases and adaptors that contribute to assembly of multiprotein NDR kinase activation complexes. In multicellular eukaryotes, the Mob family has expanded relative to model unicellular yeasts; accumulating evidence points to Mob functional diversification. A striking example comes from the most sequence-divergent class of Mobs, which are components of the highly conserved Striatin Interacting Phosphatase and Kinase (STRIPAK) complex, that antagonizes Hippo signaling. Mobs stand out for their potential to modulate the output from Hippo and Hippo-like kinases, through their roles both in activating NDR kinases and in antagonizing upstream Hippo or Hippo-like kinase activity. These opposing Mob functions suggest that they coordinate the relative activities of the Tricornered/STK38/STK38L and Warts/LATS kinases, and thus have potential to assemble nodes for pathway signaling output. We survey the different facets of Mob-dependent regulation of Hippo and Hippo-like signaling and highlight open questions that hinge on unresolved aspects of Mob functions.
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Affiliation(s)
| | - Laurel A. Raftery
- School of Life Sciences, University of Nevada, Las Vegas, Las Vegas, NV, United States
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8
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Lin FY, Lin YF, Lin YS, Yang CM, Wang CC, Hsiao YH. Relative D3 vitamin deficiency and consequent cognitive impairment in an animal model of Alzheimer's disease: Potential involvement of collapsin response mediator protein-2. Neuropharmacology 2019; 164:107910. [PMID: 31838171 DOI: 10.1016/j.neuropharm.2019.107910] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Revised: 12/06/2019] [Accepted: 12/09/2019] [Indexed: 12/17/2022]
Abstract
Alzheimer's disease (AD) starts with memory impairments that can be observed before the appearance of significant neuropathology; thus, identifying mechanisms to stop AD progression is an urgent priority. Epidemiological and clinical data show that the consequences of vitamin D deficiency are relevant to disease risk and can be observed in the progression of many diseases, especially AD, whereas higher serum levels of vitamin D are associated with better cognitive test performance. However, the potential therapeutic strategy and underlying mechanisms of vitamin D supplementation against AD still need to be further investigated. In the present study, we found that 3xTg-AD mice with vitamin D supplementation exhibited an increase in serum vitamin D concentrations and improved cognition. We measured serum vitamin D binding protein (VDBP) concentrations and found that serum VDBP levels were increased in 3xTg-AD mice compared to B6129S control mice, but there was no significant difference between control- and vitamin D-treated 3xTg-AD groups. The vitamin D-mediated memory improvement may be accompanied by the suppression of increased hippocampal collapsin response mediator protein-2 (CRMP2) phosphorylation, and the restoration of CRMP2 phosphorylation by okadaic acid (OA) could abolish the beneficial effects of vitamin D. In addition, we found that CRMP2 was associated with NR2B and PSD-95 in 3xTg-AD mice with vitamin D supplementation. This CRMP2-NR2B interaction could be disrupted by a TAT-CBD3 peptide or OA, leading to attenuated memory protection in vitamin D-treated 3xTg-AD mice. Therefore, CRMP2 may be involved in vitamin D-mediated memory improvement in AD.
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Affiliation(s)
- Fang-Yu Lin
- Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan, Taiwan
| | - Yu-Fen Lin
- Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan, Taiwan
| | - Yung-Shuen Lin
- Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan, Taiwan
| | - Chun-Ming Yang
- Department of Neurology, Chi Mei Medical Center, Tainan, Taiwan; Clinical Competency Center, Chi Mei Medical Center, Tainan, Taiwan
| | - Che-Chuan Wang
- Department of Neurosurgery, Chi-Mei Medical Center, Tainan, Taiwan; Center for General Education, Southern Taiwan University of Science and Technology, Tainan, Taiwan
| | - Ya-Hsin Hsiao
- Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan, Taiwan; Institute of Basic Medical Sciences, College of Medicine, National Cheng Kung University, Tainan, Taiwan; Institute of Behavioral Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
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9
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Novel Insights on the Toxicity of Phycotoxins on the Gut through the Targeting of Enteric Glial Cells. Mar Drugs 2019; 17:md17070429. [PMID: 31340532 PMCID: PMC6669610 DOI: 10.3390/md17070429] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2019] [Revised: 07/15/2019] [Accepted: 07/19/2019] [Indexed: 02/08/2023] Open
Abstract
In vitro and in vivo studies have shown that phycotoxins can impact intestinal epithelial cells and can cross the intestinal barrier to some extent. Therefore, phycotoxins can reach cells underlying the epithelium, such as enteric glial cells (EGCs), which are involved in gut homeostasis, motility, and barrier integrity. This study compared the toxicological effects of pectenotoxin-2 (PTX2), yessotoxin (YTX), okadaic acid (OA), azaspiracid-1 (AZA1), 13-desmethyl-spirolide C (SPX), and palytoxin (PlTX) on the rat EGC cell line CRL2690. Cell viability, morphology, oxidative stress, inflammation, cell cycle, and specific glial markers were evaluated using RT-qPCR and high content analysis (HCA) approaches. PTX2, YTX, OA, AZA1, and PlTX induced neurite alterations, oxidative stress, cell cycle disturbance, and increase of specific EGC markers. An inflammatory response for YTX, OA, and AZA1 was suggested by the nuclear translocation of NF-κB. Caspase-3-dependent apoptosis and induction of DNA double strand breaks (γH2AX) were also observed with PTX2, YTX, OA, and AZA1. These findings suggest that PTX2, YTX, OA, AZA1, and PlTX may affect intestinal barrier integrity through alterations of the human enteric glial system. Our results provide novel insight into the toxicological effects of phycotoxins on the gut.
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Tramentozzi E, Ferraro P, Hossain M, Stillman B, Bianchi V, Pontarin G. The dNTP triphosphohydrolase activity of SAMHD1 persists during S-phase when the enzyme is phosphorylated at T592. Cell Cycle 2018; 17:1102-1114. [PMID: 30039733 PMCID: PMC6110608 DOI: 10.1080/15384101.2018.1480216] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2017] [Revised: 06/01/2018] [Accepted: 05/16/2018] [Indexed: 01/31/2023] Open
Abstract
SAMHD1 is the major catabolic enzyme regulating the intracellular concentrations of DNA precursors (dNTPs). The S-phase kinase CDK2-cyclinA phosphorylates SAMHD1 at Thr-592. How this modification affects SAMHD1 function is highly debated. We investigated the role of endogenous SAMHD1 phosphorylation during the cell cycle. Thr-592 phosphorylation occurs first at the G1/S border and is removed during mitotic exit parallel with Thr-phosphorylations of most CDK1 targets. Differential sensitivity to the phosphatase inhibitor okadaic acid suggested different involvement of the PP1 and PP2 families dependent upon the time of the cell cycle. SAMHD1 turn-over indicates that Thr-592 phosphorylation does not cause rapid protein degradation. Furthermore, SAMHD1 influenced the size of the four dNTP pools independently of its phosphorylation. Our findings reveal that SAMHD1 is active during the entire cell cycle and performs an important regulatory role during S-phase by contributing with ribonucleotide reductase to maintain dNTP pool balance for proper DNA replication.
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Affiliation(s)
| | - Paola Ferraro
- Department of Biology, University of Padova, Padova, Italy
| | - Manzar Hossain
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA
| | - Bruce Stillman
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA
| | - Vera Bianchi
- Department of Biology, University of Padova, Padova, Italy
| | - Giovanna Pontarin
- Department of Biology, University of Padova, Padova, Italy
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA
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11
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Protein phosphatases 1 and 2A and their naturally occurring inhibitors: current topics in smooth muscle physiology and chemical biology. J Physiol Sci 2017; 68:1-17. [PMID: 28681362 PMCID: PMC5754374 DOI: 10.1007/s12576-017-0556-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Accepted: 06/27/2017] [Indexed: 12/26/2022]
Abstract
Protein phosphatases 1 and 2A (PP1 and PP2A) are the most ubiquitous and abundant serine/threonine phosphatases in eukaryotic cells. They play fundamental roles in the regulation of various cellular functions. This review focuses on recent advances in the functional studies of these enzymes in the field of smooth muscle physiology. Many naturally occurring protein phosphatase inhibitors with different relative PP1/PP2A affinities have been discovered and are widely used as powerful research tools. Current topics in the chemical biology of PP1/PP2A inhibitors are introduced and discussed, highlighting the identification of the gene cluster responsible for the biosynthesis of calyculin A in a symbiont microorganism of a marine sponge.
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12
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Filter JJ, Williams BC, Eto M, Shalloway D, Goldberg ML. Unfair competition governs the interaction of pCPI-17 with myosin phosphatase (PP1-MYPT1). eLife 2017; 6. [PMID: 28387646 PMCID: PMC5441869 DOI: 10.7554/elife.24665] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2016] [Accepted: 03/31/2017] [Indexed: 11/30/2022] Open
Abstract
The small phosphoprotein pCPI-17 inhibits myosin light-chain phosphatase (MLCP). Current models postulate that during muscle relaxation, phosphatases other than MLCP dephosphorylate and inactivate pCPI-17 to restore MLCP activity. We show here that such hypotheses are insufficient to account for the observed rapidity of pCPI-17 inactivation in mammalian smooth muscles. Instead, MLCP itself is the critical enzyme for pCPI-17 dephosphorylation. We call the mutual sequestration mechanism through which pCPI-17 and MLCP interact inhibition by unfair competition: MLCP protects pCPI-17 from other phosphatases, while pCPI-17 blocks other substrates from MLCP’s active site. MLCP dephosphorylates pCPI-17 at a slow rate that is, nonetheless, both sufficient and necessary to explain the speed of pCPI-17 dephosphorylation and the consequent MLCP activation during muscle relaxation. DOI:http://dx.doi.org/10.7554/eLife.24665.001
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Affiliation(s)
- Joshua J Filter
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States
| | - Byron C Williams
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States
| | - Masumi Eto
- Department of Molecular Physiology and Biophysics, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, United States
| | - David Shalloway
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States
| | - Michael L Goldberg
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States
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13
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Bastan R, Eskandari N, J Ardakani H, T Peachell P. Effects of fostriecin on β2-adrenoceptor-driven responses in human mast cells. J Immunotoxicol 2017; 14:60-65. [PMID: 28090813 DOI: 10.1080/1547691x.2016.1259277] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
As part of the intracellular processes leading to mast cell and basophil activation, phosphorylation of key substrates is likely to be important. These processes, mediated by phosphatases, are responsible for regulating phosphorylation. The aim of the present study was to determine effects fostriecin - a selective inhibitor of PP2A (protein phosphatase-2) - on β2-adrenoceptor-driven responses in human mast cells. Here, the effects of fostriecin (PP inhibitors) on the inhibition of histamine release from HLMC, on β-adrenoceptor-driven responses in mast cells and on desensitization were investigated. Long-term incubation (24 h) of mast cells with fostriecin (10-6 M) resulted in a significant (p < 0.001) reduction in the maximal response (from 41.2 [± 3.0] to 29.9 [± 4.2] %) to salbutamol following fostriecin treatment. The results showed that fostriecin pretreatment significantly attenuated the inhibitory effects of salbutamol. Overall, the present study suggested that PP2A has an important role in regulating mast cell β2-adrenoceptors.
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Affiliation(s)
- Reza Bastan
- a Department of Human Vaccines , Razi Serum and Vaccine Research Institute , Karaj , Iran
| | - Nahid Eskandari
- b Department of Immunology , Applied Physiology Research Center, Isfahan University of Medical Sciences , Isfahan , Iran
| | - Hamidrez J Ardakani
- b Department of Immunology , Applied Physiology Research Center, Isfahan University of Medical Sciences , Isfahan , Iran
| | - Peter T Peachell
- c Academic Unit of Respiratory Medicine , Medical School, University of Sheffield , Sheffield , UK
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14
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Moore CE, Juan J, Lin Y, Gaskill CL, Puschner B. Comparison of Protein Phosphatase Inhibition Assay with LC-MS/MS for Diagnosis of Microcystin Toxicosis in Veterinary Cases. Mar Drugs 2016; 14:E54. [PMID: 27005635 PMCID: PMC4820308 DOI: 10.3390/md14030054] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Revised: 02/29/2016] [Accepted: 03/03/2016] [Indexed: 11/16/2022] Open
Abstract
Microcystins are acute hepatotoxins of increasing global concern in drinking and recreational waters and are a major health risk to humans and animals. Produced by cyanobacteria, microcystins inhibit serine/threonine protein phosphatase 1 (PP1). A cost-effective PP1 assay using p-nitrophenyl phosphate was developed to quickly assess water and rumen content samples. Significant inhibition was determined via a linear model, which compared increasing volumes of sample to the log-transformed ratio of the exposed rate over the control rate of PP1 activity. To test the usefulness of this model in diagnostic case investigations, samples from two veterinary cases were tested. In August 2013 fifteen cattle died around two ponds in Kentucky. While one pond and three tested rumen contents had significant PP1 inhibition and detectable levels of microcystin-LR, the other pond did not. In August 2013, a dog became fatally ill after swimming in Clear Lake, California. Lake water samples collected one and four weeks after the dog presented with clinical signs inhibited PP1 activity. Subsequent analysis using liquid chromatography-mass spectrometry (LC-MS/MS) detected microcystin congeners -LR, -LA, -RR and -LF but not -YR. These diagnostic investigations illustrate the advantages of using functional assays in combination with LC-MS/MS.
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Affiliation(s)
- Caroline E Moore
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California at Davis, 1089 Veterinary Medicine Drive, 2225 VM3B, Davis, CA 95616, USA.
| | - Jeanette Juan
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California at Davis, 1089 Veterinary Medicine Drive, 2225 VM3B, Davis, CA 95616, USA.
| | - Yanping Lin
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California at Davis, 1089 Veterinary Medicine Drive, 2225 VM3B, Davis, CA 95616, USA.
| | - Cynthia L Gaskill
- Veterinary Diagnostic Laboratory, University of Kentucky, Lexington, KY 40511, USA.
| | - Birgit Puschner
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California at Davis, 1089 Veterinary Medicine Drive, 2225 VM3B, Davis, CA 95616, USA.
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15
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Ishida M, Takeya K, Miyazu M, Yoshida A, Takai A. Force-inhibiting effect of Ser/Thr protein phosphatase 2A inhibitors on bovine ciliary muscle. J Smooth Muscle Res 2015; 51:10-21. [PMID: 26004377 PMCID: PMC5137268 DOI: 10.1540/jsmr.51.10] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Ciliary muscle is a smooth muscle characterized by a rapid response to muscarinic receptor stimulation and sustained contraction. Although it is evident that these contractions are Ca(2+)-dependent, detailed molecular mechanisms are still unknown. In order to elucidate the role of Ser/Thr protein phosphatase 2A (PP2A) in ciliary muscle contraction, we examined the effects of okadaic acid and other PP2A inhibitors on contractions induced by carbachol (CCh) and ionomycin in bovine ciliary muscle strips (BCM). Okadaic acid inhibited ionomycin-induced contraction, while it did not cause significant changes in CCh-induced contraction. Fostriecin showed similar inhibitory effects on the contraction of BCM. On the other hand, rubratoxin A inhibited both ionomycin- and CCh-induced contractions. These results indicated that PP2A was involved at least in ionomycin-induced Ca(2+)-dependent contraction, and that BCM had a unique regulatory mechanism in CCh-induced contraction.
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Affiliation(s)
- Minori Ishida
- Department of Physiology, Asahikawa Medical University, Hokkaido, Japan
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16
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Dedinszki D, Sipos A, Kiss A, Bátori R, Kónya Z, Virág L, Erdődi F, Lontay B. Protein phosphatase-1 is involved in the maintenance of normal homeostasis and in UVA irradiation-induced pathological alterations in HaCaT cells and in mouse skin. Biochim Biophys Acta Mol Basis Dis 2014; 1852:22-33. [PMID: 25446992 DOI: 10.1016/j.bbadis.2014.11.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Revised: 10/27/2014] [Accepted: 11/04/2014] [Indexed: 12/23/2022]
Abstract
The number of ultraviolet (UV) radiation-induced skin diseases such as melanomas is on the rise. The altered behavior of keratinocytes is often coupled with signaling events in which Ser/Thr specific protein kinases and phosphatases regulate various cellular functions. In the present study the role of protein phosphatase-1 (PP1) was investigated in the response of human keratinocyte (HaCaT) cells and mouse skin to UV radiation. PP1 catalytic subunit (PP1c) isoforms, PP1cα/γ and PP1cδ, are all localized to the cytoskeleton and cytosol of keratinocytes, but PP1cδ was found to be dominant over PP1α/γ in the nucleus. PP1c-silencing in HaCaT cells decreased the phosphatase activity and suppressed the viability of the cells. Exposure to a 10 J/cm(2) UVA dose induced HaCaT cell death and resulted in a 30% decrease of phosphatase activity. PP1c-silencing and UVA irradiation altered the gene expression profile of HaCaT cells and suggested that the expression of 19 genes was regulated by the combined treatments with many of these genes being involved in malignant transformation. Microarray analysis detected altered expression levels of genes coding for melanoma-associated proteins such as keratin 1/10, calcium binding protein S100A8 and histone 1b. Treatment of Balb/c mice with the PP1-specific inhibitor tautomycin (TM) exhibited increased levels of keratin 1/10 and S100A8, and a decreased level of histone 1b proteins following UVA irradiation. Moreover, TM treatment increased pigmentation of the skin which was even more apparent when TM was followed by UVA irradiation. Our data identify PP1 as a regulator of the normal homeostasis of keratinocytes and the UV-response.
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Affiliation(s)
- Dóra Dedinszki
- Department of Medical Chemistry, University of Debrecen, Debrecen H-4032, Hungary
| | - Adrienn Sipos
- Department of Medical Chemistry, University of Debrecen, Debrecen H-4032, Hungary
| | - Andrea Kiss
- Department of Medical Chemistry, University of Debrecen, Debrecen H-4032, Hungary
| | - Róbert Bátori
- Department of Medical Chemistry, University of Debrecen, Debrecen H-4032, Hungary
| | - Zoltán Kónya
- Department of Medical Chemistry, University of Debrecen, Debrecen H-4032, Hungary
| | - László Virág
- Department of Medical Chemistry, University of Debrecen, Debrecen H-4032, Hungary; MTA-DE Cell Biology and Signaling Research Group, University of Debrecen, Debrecen H-4032, Hungary
| | - Ferenc Erdődi
- Department of Medical Chemistry, University of Debrecen, Debrecen H-4032, Hungary; MTA-DE Cell Biology and Signaling Research Group, University of Debrecen, Debrecen H-4032, Hungary
| | - Beáta Lontay
- Department of Medical Chemistry, University of Debrecen, Debrecen H-4032, Hungary.
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17
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Microcystins alter chemotactic behavior in Caenorhabditis elegans by selectively targeting the AWA sensory neuron. Toxins (Basel) 2014; 6:1813-36. [PMID: 24918360 PMCID: PMC4073131 DOI: 10.3390/toxins6061813] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Revised: 05/17/2014] [Accepted: 05/28/2014] [Indexed: 11/16/2022] Open
Abstract
Harmful algal blooms expose humans and animals to microcystins (MCs) through contaminated drinking water. While hepatotoxicity following acute exposure to MCs is well documented, neurotoxicity after sub-lethal exposure is poorly understood. We developed a novel statistical approach using a generalized linear model and the quasibinomial family to analyze neurotoxic effects in adult Caenorhabditis elegans exposed to MC-LR or MC-LF for 24 h. Selective effects of toxin exposure on AWA versus AWC sensory neuron function were determined using a chemotaxis assay. With a non-monotonic response MCs altered AWA but not AWC function, and MC-LF was more potent than MC-LR. To probe a potential role for protein phosphatases (PPs) in MC neurotoxicity, we evaluated the chemotactic response in worms exposed to the PP1 inhibitor tautomycin or the PP2A inhibitor okadaic acid for 24 h. Okadaic acid impaired both AWA and AWC function, while tautomycin had no effect on function of either neuronal cell type at the concentrations tested. These findings suggest that MCs alter the AWA neuron at concentrations that do not cause AWC toxicity via mechanisms other than PP inhibition.
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18
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Protein phosphatase 1 dephosphorylates Orc2. Biochem Biophys Res Commun 2014; 447:437-40. [DOI: 10.1016/j.bbrc.2014.04.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Accepted: 04/04/2014] [Indexed: 11/23/2022]
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19
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Williams BC, Filter JJ, Blake-Hodek KA, Wadzinski BE, Fuda NJ, Shalloway D, Goldberg ML. Greatwall-phosphorylated Endosulfine is both an inhibitor and a substrate of PP2A-B55 heterotrimers. eLife 2014; 3:e01695. [PMID: 24618897 PMCID: PMC3949306 DOI: 10.7554/elife.01695] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Accepted: 01/30/2014] [Indexed: 11/13/2022] Open
Abstract
During M phase, Endosulfine (Endos) family proteins are phosphorylated by Greatwall kinase (Gwl), and the resultant pEndos inhibits the phosphatase PP2A-B55, which would otherwise prematurely reverse many CDK-driven phosphorylations. We show here that PP2A-B55 is the enzyme responsible for dephosphorylating pEndos during M phase exit. The kinetic parameters for PP2A-B55's action on pEndos are orders of magnitude lower than those for CDK-phosphorylated substrates, suggesting a simple model for PP2A-B55 regulation that we call inhibition by unfair competition. As the name suggests, during M phase PP2A-B55's attention is diverted to pEndos, which binds much more avidly and is dephosphorylated more slowly than other substrates. When Gwl is inactivated during the M phase-to-interphase transition, the dynamic balance changes: pEndos dephosphorylated by PP2A-B55 cannot be replaced, so the phosphatase can refocus its attention on CDK-phosphorylated substrates. This mechanism explains simultaneously how PP2A-B55 and Gwl together regulate pEndos, and how pEndos controls PP2A-B55. DOI: http://dx.doi.org/10.7554/eLife.01695.001.
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Affiliation(s)
- Byron C Williams
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States
| | - Joshua J Filter
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States
| | | | - Brian E Wadzinski
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, United States
| | - Nicholas J Fuda
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States
| | - David Shalloway
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States
| | - Michael L Goldberg
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States
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20
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Arvanitoyannis IS, Kotsanopoulos KV, Papadopoulou A. Rapid Detection of Chemical Hazards (Toxins, Dioxins, and PCBs) in Seafood. Crit Rev Food Sci Nutr 2014; 54:1473-528. [DOI: 10.1080/10408398.2011.641132] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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21
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Lin H, Miller ML, Granas DM, Dutcher SK. Whole genome sequencing identifies a deletion in protein phosphatase 2A that affects its stability and localization in Chlamydomonas reinhardtii. PLoS Genet 2013; 9:e1003841. [PMID: 24086163 PMCID: PMC3784568 DOI: 10.1371/journal.pgen.1003841] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 08/13/2013] [Indexed: 11/19/2022] Open
Abstract
Whole genome sequencing is a powerful tool in the discovery of single nucleotide polymorphisms (SNPs) and small insertions/deletions (indels) among mutant strains, which simplifies forward genetics approaches. However, identification of the causative mutation among a large number of non-causative SNPs in a mutant strain remains a big challenge. In the unicellular biflagellate green alga Chlamydomonas reinhardtii, we generated a SNP/indel library that contains over 2 million polymorphisms from four wild-type strains, one highly polymorphic strain that is frequently used in meiotic mapping, ten mutant strains that have flagellar assembly or motility defects, and one mutant strain, imp3, which has a mating defect. A comparison of polymorphisms in the imp3 strain and the other 15 strains allowed us to identify a deletion of the last three amino acids, Y313F314L315, in a protein phosphatase 2A catalytic subunit (PP2A3) in the imp3 strain. Introduction of a wild-type HA-tagged PP2A3 rescues the mutant phenotype, but mutant HA-PP2A3 at Y313 or L315 fail to rescue. Our immunoprecipitation results indicate that the Y313, L315, or YFLΔ mutations do not affect the binding of PP2A3 to the scaffold subunit, PP2A-2r. In contrast, the Y313, L315, or YFLΔ mutations affect both the stability and the localization of PP2A3. The PP2A3 protein is less abundant in these mutants and fails to accumulate in the basal body area as observed in transformants with either wild-type HA-PP2A3 or a HA-PP2A3 with a V310T change. The accumulation of HA-PP2A3 in the basal body region disappears in mated dikaryons, which suggests that the localization of PP2A3 may be essential to the mating process. Overall, our results demonstrate that the terminal YFL tail of PP2A3 is important in the regulation on Chlamydomonas mating.
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Affiliation(s)
- Huawen Lin
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Michelle L. Miller
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - David M. Granas
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Center for Genomic Sciences and System Biology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Susan K. Dutcher
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
- * E-mail:
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22
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Gao N, Huang J, He W, Zhu M, Kamm KE, Stull JT. Signaling through myosin light chain kinase in smooth muscles. J Biol Chem 2013; 288:7596-7605. [PMID: 23362260 DOI: 10.1074/jbc.m112.427112] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK) phosphorylates smooth muscle myosin regulatory light chain (RLC) to initiate contraction. We used a tamoxifen-activated, smooth muscle-specific inactivation of MLCK expression in adult mice to determine whether MLCK was differentially limiting in distinct smooth muscles. A 50% decrease in MLCK in urinary bladder smooth muscle had no effect on RLC phosphorylation or on contractile responses, whereas an 80% decrease resulted in only a 20% decrease in RLC phosphorylation and contractile responses to the muscarinic agonist carbachol. Phosphorylation of the myosin light chain phosphatase regulatory subunit MYPT1 at Thr-696 and Thr-853 and the inhibitor protein CPI-17 were also stimulated with carbachol. These results are consistent with the previous findings that activation of a small fraction of MLCK by limiting amounts of free Ca(2+)/calmodulin combined with myosin light chain phosphatase inhibition is sufficient for robust RLC phosphorylation and contractile responses in bladder smooth muscle. In contrast, a 50% decrease in MLCK in aortic smooth muscle resulted in 40% inhibition of RLC phosphorylation and aorta contractile responses, whereas a 90% decrease profoundly inhibited both responses. Thus, MLCK content is limiting for contraction in aortic smooth muscle. Phosphorylation of CPI-17 and MYPT1 at Thr-696 and Thr-853 were also stimulated with phenylephrine but significantly less than in bladder tissue. These results indicate differential contributions of MLCK to signaling. Limiting MLCK activity combined with modest Ca(2+) sensitization responses provide insights into how haploinsufficiency of MLCK may result in contractile dysfunction in vivo, leading to dissections of human thoracic aorta.
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Affiliation(s)
- Ning Gao
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390
| | - Jian Huang
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390
| | - Weiqi He
- Model Animal Research Center and Ministry of Education Key Laboratory of Model Animal for Disease Study, Nanjing University, 210061 Nanjing, China
| | - Minsheng Zhu
- Model Animal Research Center and Ministry of Education Key Laboratory of Model Animal for Disease Study, Nanjing University, 210061 Nanjing, China
| | - Kristine E Kamm
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390
| | - James T Stull
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390.
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23
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Zeller P, Quenault H, Huguet A, Blanchard Y, Fessard V. Transcriptomic comparison of cyanotoxin variants in a human intestinal model revealed major differences in oxidative stress response: effects of MC-RR and MC-LR on Caco-2 cells. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2012; 82:13-21. [PMID: 22721844 DOI: 10.1016/j.ecoenv.2012.05.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Revised: 04/30/2012] [Accepted: 05/03/2012] [Indexed: 06/01/2023]
Abstract
Microcystins (MCs) are cyclic hepatotoxins produced by various species of cyanobacteria. Their structure includes two variable amino acids (AA) giving rise to more than 90 MC variants, however most of the studies to date have focused on the most toxic variant: microcystin LR (MC-LR). Ingestion is the major route of human exposure to MCs and several in vivo studies have demonstrated macroscopic effects on the gastro-intestinal tract. However, little information exists concerning the pathways affected by MC variants on intestinal cells. In the current study, we have investigated the effects of MC-RR and MC-LR on the human intestinal cell line Caco-2 using a non-selective method and compared their response at the pangenomic scale. The cells were incubated for 4h or 24h with a range of non-toxic concentrations of MC-RR or MC-LR. Minimal effects were observed after short term exposures (4h) to either MC variant. In contrast, dose dependent modulations of gene transcription levels were observed with MC-RR and MC-LR after 24h. The transcriptomic profiles induced by MC-RR were quite similar to those induced by MC-LR, suggestive of a largely common mechanism of toxicity. However, changes in total gene expression were more pronounced following exposure to MC-LR compared to MC-RR, as revealed by functional annotation. MC-LR affected two principal pathways, the oxidative stress response and cell cycle regulation, which did not elicit significant alteration following MC-RR exposure. This work is the first comparative description of the effects of MC-LR and MC-RR in a human intestinal cell model at the pangenomic scale. It has allowed us to propose differences in the mechanism of toxicity for MC-RR and MC-LR. These results illustrate that taking into account the toxicity of MC variants remains a key point for risk assessment.
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Affiliation(s)
- Perrine Zeller
- Anses, Fougères laboratory, Contaminant Toxicology Unit, La Haute Marche, BP 90203, 35302 Fougères Cedex, France
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24
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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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25
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Yan Y, Cao PT, Greer PM, Nagengast ES, Kolb RH, Mumby MC, Cowan KH. Protein phosphatase 2A has an essential role in the activation of gamma-irradiation-induced G2/M checkpoint response. Oncogene 2010; 29:4317-29. [PMID: 20498628 DOI: 10.1038/onc.2010.187] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
G2/M checkpoint activation after DNA damage results in G2/M cell cycle arrest that allows time for DNA repair before the entry of cells into mitosis. Activation of G2/M checkpoint involves a series of signaling events, which include activation of ataxia telangiectecia-mutated and Rad3-related (ATR) and Chk1 kinases and inhibition of Cdc2/Cyclin B activity. Studies presented in this report show that serine (Ser)/threonine (Thr) protein phosphatase 2A (PP2A) has an important role in G2/M checkpoint activation in response to gamma-irradiation (IR) exposure. Using PP2A inhibitors, as well as siRNA targeting various forms of Ser/Thr protein phosphatases, results presented in this report show that specific PP2A inhibition abrogates IR-induced activation of ATR and Chk1 kinases, as well as phosphorylation of Cdc2-Tyr15, and attenuates IR-induced G2/M arrest. These results suggest an important regulation of PP2A on IR-induced G2/M checkpoint signaling response.
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Affiliation(s)
- Y Yan
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE, USA
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26
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Fagerholm AE, Habrant D, Koskinen AMP. Calyculins and related marine natural products as serine-threonine protein phosphatase PP1 and PP2A inhibitors and total syntheses of calyculin A, B, and C. Mar Drugs 2010; 8:122-72. [PMID: 20161975 PMCID: PMC2817927 DOI: 10.3390/md80100122] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2009] [Revised: 01/12/2010] [Accepted: 01/13/2010] [Indexed: 11/22/2022] Open
Abstract
Calyculins, highly cytotoxic polyketides, originally isolated from the marine sponge Discodermia calyx by Fusetani and co-workers, belong to the lithistid sponges group. These molecules have become interesting targets for cell biologists and synthetic organic chemists. The serine/threonine protein phosphatases play an essential role in the cellular signalling, metabolism, and cell cycle control. Calyculins express potent protein phosphatase 1 and 2A inhibitory activity, and have therefore become valuable tools for cellular biologists studying intracellular processes and their control by reversible phosphorylation. Calyculins might also play an important role in the development of several diseases such as cancer, neurodegenerative diseases, and type 2-diabetes mellitus. The fascinating structures of calyculins have inspired various groups of synthetic organic chemists to develop total syntheses of the most abundant calyculins A and C. However, with fifteen chiral centres, a cyano-capped tetraene unit, a phosphate-bearing spiroketal, an anti, anti, anti dipropionate segment, an alpha-chiral oxazole, and a trihydroxylated gamma-amino acid, calyculins reach versatility that only few natural products can surpass, and truly challenge modern chemists' asymmetric synthesis skills.
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Affiliation(s)
- Annika E. Fagerholm
- Laboratory of Organic Chemistry, Helsinki University of Technology, PO Box 6100, FIN-02015 HUT, Finland; E-Mails:
(A.E.F.);
(D.H.)
| | - Damien Habrant
- Laboratory of Organic Chemistry, Helsinki University of Technology, PO Box 6100, FIN-02015 HUT, Finland; E-Mails:
(A.E.F.);
(D.H.)
| | - Ari M. P. Koskinen
- Laboratory of Organic Chemistry, Helsinki University of Technology, PO Box 6100, FIN-02015 HUT, Finland; E-Mails:
(A.E.F.);
(D.H.)
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27
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Li W, Luo Y, Ju J, Rajski SR, Osada H, Shen B. Characterization of the tautomycetin biosynthetic gene cluster from Streptomyces griseochromogenes provides new insight into dialkylmaleic anhydride biosynthesis. JOURNAL OF NATURAL PRODUCTS 2009; 72:450-459. [PMID: 19191560 PMCID: PMC2967020 DOI: 10.1021/np8007478] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Tautomycetin (TTN) is a highly potent and specific protein phosphatase inhibitor isolated from Streptomyces griseochromogenes. The biological activity of TTN makes it an important lead for drug discovery, whereas its rare dialkylmaleic anhydride moiety and structural similarity to tautomycin (TTM), another potent phosphatase inhibitor with tremendous medicinal potential, draws attention to novel biosynthetic chemistries responsible for its production. To elucidate the biosynthetic machinery associated with TTN production, the ttn biosynthetic gene cluster from S. griseochromogenes was isolated and characterized, and its involvement in TTN biosynthesis confirmed by gene inactivation and complementation experiments. The ttn cluster was localized to a 79 kb DNA region, consisting of 19 open reading frames that encode two modular type I polyketide synthases (TtnAB), one type II thioesterase (TtnH), eight proteins for dialkylmaleic anhydride biosynthesis (TtnKLMNOPRS), four tailoring enzymes (TtnCDFI), two regulatory proteins (TtnGQ), and one resistance protein (TtnJ). A model for TTN biosynthesis is proposed on the basis of functional assignments from sequence analysis, which agrees well with previous feeding experiments, has been supported by in vivo gene inactivation experiments, and is supported by analogy to the recently reported ttm cluster. These findings set the stage to fully investigate TTN biosynthesis and to biosynthetically engineer new TTN analogues.
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Affiliation(s)
| | | | | | | | | | - Ben Shen
- To whom correspondence should be addressed. Tel: (608) 263-2673. Fax: (608) 262-5345.
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Yazid S, Solito E, Christian H, McArthur S, Goulding N, Flower R. Cromoglycate drugs suppress eicosanoid generation in U937 cells by promoting the release of Anx-A1. Biochem Pharmacol 2009; 77:1814-26. [PMID: 19428336 PMCID: PMC2888050 DOI: 10.1016/j.bcp.2009.03.010] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2009] [Revised: 03/09/2009] [Accepted: 03/10/2009] [Indexed: 12/15/2022]
Abstract
Using biochemical, epifluorescence and electron microscopic techniques in a U937 model system, we investigated the effect of anti-allergic drugs di-sodium cromoglycate and sodium nedocromil on the trafficking and release of the anti-inflammatory protein Annexin-A1 (Anx-A1) when this was triggered by glucocorticoid (GC) treatment. GCs alone produced a rapid (within 5 min) concentration-dependent activation of PKCα/β (Protein Kinase C; EC 2.7.11.13) and phosphorylation of Anx-A1 on Ser27. Both phosphoproteins accumulated at the plasma membrane and Anx-A1 was subsequently externalised thereby inhibiting thromboxane (Tx) B2 generation. When administered alone, cromoglycate or nedocromil had little effect on this pathway however, in the presence of a fixed sub-maximal concentration of GCs, increasing amounts of the cromoglycate-like drugs caused a striking concentration-dependent enhancement of Anx-A1 and PKCα/β phosphorylation, membrane recruitment and Anx-A1 release from cells resulting in greatly enhanced inhibition of TxB2 generation. GCs also stimulated phosphatase accumulation at the plasma membrane of U937 cells. Both cromoglycate and nedocromil inhibited this enzymatic activity as well as that of a highly purified PP2A phosphatase preparation. We conclude that stimulation by the cromoglycate-like drugs of intracellular Anx-A1 trafficking and release (hence inhibition of eicosanoid release) is secondary to inhibition of a phosphatase PP2A (phosphoprotein phosphatase; EC 3.1.3.16), which probably forms part of a control loop to limit Anx-A1 release. These experiments provide a basis for a novel mechanism of action for the cromolyns, a group of drugs that have long puzzled investigators.
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Affiliation(s)
- Samia Yazid
- Biochemical Pharmacology, William Harvey Research Institute, Bart's and the London School of Medicine and Dentistry, London, UK
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29
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Mi J, Bolesta E, Brautigan DL, Larner JM. PP2A regulates ionizing radiation-induced apoptosis through Ser46 phosphorylation of p53. Mol Cancer Ther 2009; 8:135-40. [PMID: 19139122 DOI: 10.1158/1535-7163.mct-08-0457] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In response to ionizing radiation, p53 plays a critical role in regulating DNA repair and apoptosis. Among multiple phosphorylation sites, evidence suggests that Ser46 promotes apoptotic cell death through mitochondrial outer membrane permeabilization (MOMP) and subsequent activation of the caspase 7-PARP pathway. Therefore, we investigated which phosphatase regulates Ser46 after ionizing radiation, reasoning that the responsible phosphatase should be a target for radiosensitization. We determined that both inhibition of PP2A by the cell-permeable inhibitor calyculin A and knockdown of PP2A by RNAi (a) enhanced Ser46 phosphorylation in p53 and (b) induced coincident caspase 7 and PARP cleavage in response to ionizing radiation. Furthermore, mutation of p53 Ser46 to Ala attenuated ionizing radiation-induced apoptotic signaling. Consequently, we concluded that PP2A regulates ionizing radiation-induced apoptotic signaling through dephosphorylation of p53 Ser46.
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Affiliation(s)
- Jun Mi
- Department of Radiation Oncology, Center for Cell Signaling, University of Virginia Health System, Box 800383 Charlottesville, VA, USA
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30
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Wang W, Brautigan DL. Phosphatase inhibitor 2 promotes acetylation of tubulin in the primary cilium of human retinal epithelial cells. BMC Cell Biol 2008; 9:62. [PMID: 19036150 PMCID: PMC2630314 DOI: 10.1186/1471-2121-9-62] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2008] [Accepted: 11/26/2008] [Indexed: 01/23/2023] Open
Abstract
BACKGROUND Primary cilia are flagella-like projections from the centriole of mammalian cells that have a key role in cell signaling. Human diseases are linked to defects in primary cilia. Microtubules make up the axoneme of cilia and are selectively acetylated and this is thought to contribute to the stability of the structure. However, mechanisms to regulate tubulin acetylation in cilia are poorly understood. RESULTS Endogenous phosphatase inhibitor-2 (I-2) was found concentrated in cilia of human epithelial cells, and was localized to cilia early in the process of formation, prior to the full acetylation of microtubules. Knockdown of I-2 by siRNA significantly reduced the acetylation of microtubules in cilia, without a net decrease in whole cell tubulin acetylation. There was a reduction in the percentage of I-2 knockdown cells with a primary cilium, but no apparent alteration in the cilium length, suggesting no change in microtubule-based transport processes. Inhibition of either histone deacetylases with trichostatin A, or protein phosphatase-1 with calyculin A in I-2 knockdown cells partially rescued the acetylation of microtubules in cilia and the percentage of cells with a primary cilium. CONCLUSION The regulatory protein I-2 localizes to the primary cilium where it affects both Ser/Thr phosphorylation and is required for full tubulin acetylation. Rescue of tubulin acetylation in I-2 knockdown cells by different chemical inhibitors shows that deacetylases and phosphatases are functionally interconnected to regulate microtubules. As a multifunctional protein, I-2 may link cell cycle progression to structure and stability of the primary cilium.
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Affiliation(s)
- Weiping Wang
- Center for Cell Signaling, University of Virginia, School of Medicine, Charlottesville, Virginia, 22908, USA
- Department of Microbiology, University of Virginia, School of Medicine, Charlottesville, Virginia, 22908, USA
| | - David L Brautigan
- Center for Cell Signaling, University of Virginia, School of Medicine, Charlottesville, Virginia, 22908, USA
- Department of Microbiology, University of Virginia, School of Medicine, Charlottesville, Virginia, 22908, USA
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Obara K, Ito Y, Shimada H, Nakayama K. The relaxant effect of okadaic acid on canine basilar artery involves activation of PKCalpha and phosphorylation of the myosin light chain at Thr-9. Eur J Pharmacol 2008; 598:87-93. [PMID: 18835557 DOI: 10.1016/j.ejphar.2008.09.023] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2007] [Revised: 09/04/2008] [Accepted: 09/18/2008] [Indexed: 11/29/2022]
Abstract
Vasodilator responses induced by okadaic acid were investigated in canine basilar artery precontracted with 80 mM KCl. Okadaic acid (1 microM) relaxed the artery and this relaxant effect was partially inhibited by Gö6976, a conventional protein kinase C inhibitor, and calphostin C, an inhibitor of conventional and novel PKCs. Rottlerin, a specific inhibitor of PKCdelta, did not influence okadaic acid's effect. KCl increased phosphorylation of 20,000-Dalton myosin light chain (MLC(20)) at Ser-19. Okadaic acid additionally increased MLC(20) phosphorylation at Thr-18 and Thr-9, resulting in triphosphorylation of MLC(20). This phosphorylation was inhibited by Gö6976. Okadaic acid stimulated phosphorylation of PKCalpha and 17,000-Dalton PKC-potentiated inhibitory phosphoprotein (CPI-17), and Gö6976 inhibited these phosphorylations. These results suggest that okadaic acid's relaxant effect involves MLC(20) triphosphorylation through a direct phosphorylation by PKCalpha and an indirect phosphorylation by inhibition of myosin light chain phosphatase through PKCalpha-mediated CPI-17 phosphorylation.
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Affiliation(s)
- Kazuo Obara
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka-City, Shizuoka 422-8526, Japan.
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Allum LL, Mountfort DO, Gooneratne R, Pasco N, Goussain G, Hall EAH. Assessment of protein phosphatase in a re-usable rapid assay format in detecting microcystins and okadaic acid as a precursor to biosensor development. Toxicon 2008; 52:745-53. [PMID: 18812183 DOI: 10.1016/j.toxicon.2008.08.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2008] [Accepted: 08/20/2008] [Indexed: 11/19/2022]
Abstract
The feasibility of developing an immobilised protein phosphatase (PP) biosensor was tested by immobilising PP onto CNBr-activated Sepharose beads placed in Millipore microfilter plate wells. Under optimised immobilised enzyme assay conditions, okadaic acid (OA) and microcystin LR (MC-LR) inhibited Upstate Biotechnology PP (PP-2A), with IC50 values of 12.5 and 11nM respectively. Similarly, immobilised recombinant PP type 1 (rec PP-1) was inhibited by MC-LR and OA, with IC50 values of 150 and >1000nM respectively. The IC50 values for free PP-2A against OA and MC-LR were 2.5 and 3.5nM, and 0.7nM and 200nM for rec PP-1 against the same substrates respectively. For free and immobilised Neptunea arthritic PP (PP-2Ana) against OA the IC50 values were 0.45 and >1000nM respectively. Of the three immobilised enzyme systems, PP-2A showed greatest sensitivity to OA and MC-LR followed by rec PP-1 and PP-2Ana. In assessments for re-usability (determined by removal of > or =70% OA or MC-LR inhibition of PP-2A by washing), <50% of the original activity remained after 20 washings. Including 1M NaCl in the wash buffer did not increase enzyme activity with wash frequency, but rather "salted in" the inhibitor. The LoD of immobilised PP-2A to MC-LR meets the WHO guideline of 1microgl(-1) for drinking water, and the sensitivity to OA (3.5microgl(-1)) would allow detection of DSP during the peak of some phytoplankton blooms.
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Affiliation(s)
- L L Allum
- Agricultural and Life Sciences Division, PO Box 84, Lincoln University, Canterbury, New Zealand
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33
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Cole AR, Soutar MPM, Rembutsu M, van Aalten L, Hastie CJ, McLauchlan H, Peggie M, Balastik M, Lu KP, Sutherland C. Relative resistance of Cdk5-phosphorylated CRMP2 to dephosphorylation. J Biol Chem 2008; 283:18227-37. [PMID: 18460467 DOI: 10.1074/jbc.m801645200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Collapsin response mediator protein 2 (CRMP2) binds to microtubules and regulates axon outgrowth in neurons. This action is regulated by sequential phosphorylation by the kinases cyclin-dependent kinase 5 (Cdk5) and glycogen synthase kinase 3 (GSK3) at sites that are hyperphosphorylated in Alzheimer disease. The increased phosphorylation in Alzheimer disease could be due to increases in Cdk5 and/or GSK3 activity or, alternatively, through decreased activity of a CRMP phosphatase. Here we establish that dephosphorylation of CRMP2 at the residues targeted by GSK3 (Ser-518/Thr-514/Thr-509) is carried out by a protein phosphatase 1 family member in vitro, in neuroblastoma cells, and primary cortical neurons. Inhibition of GSK3 activity using insulin-like growth factor-1 or the highly selective inhibitor CT99021 causes rapid dephosphorylation of CRMP2 at these sites. In contrast, pharmacological inhibition of Cdk5 using purvalanol results in only a gradual and incomplete dephosphorylation of CRMP2 at the site targeted by Cdk5 (Ser-522), suggesting a distinct phosphatase targets this residue. A direct comparison of dephosphorylation at the Cdk5 versus GSK3 sites in vitro shows that the Cdk5 site is comparatively resistant to phosphatase treatment. The presence of the peptidyl-prolyl isomerase enzyme, Pin1, does not affect dephosphorylation of Ser-522 in vitro, in cells, or in Pin1 transgenic mice. Instead, the relatively high resistance of this site to phosphatase treatment is at least in part due to the presence of basic residues located nearby. Similar sequences in Tau are also highly resistant to phosphatase treatment. We propose that relative resistance to phosphatases might be a common feature of Cdk5 substrates and could contribute to the hyperphosphorylation of CRMP2 and Tau observed in Alzheimer disease.
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Affiliation(s)
- Adam R Cole
- Neurosciences Institute, Division of Pathology and Neuroscience, University of Dundee, Ninewells Hospital, Dundee, Scotland, UK
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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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35
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Tachi M, Imanishi SY, Harada KI. Phosphoprotein analysis for investigation of in vivo relationship between protein phosphatase inhibitory activities and acute hepatotoxicity of microcystin-LR. ENVIRONMENTAL TOXICOLOGY 2007; 22:620-629. [PMID: 18000846 DOI: 10.1002/tox.20294] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Microcystin-LR (MCLR) produced by freshwater cyanobacteria is a potent hepatotoxin and inhibits protein serine/threonine phosphatases 1 and 2A (PP1 and PP2A). Okadaic acid (OA) is a similar phosphatase inhibitor, which has less affinity to PP1 than PP2A. MCLR and OA behave similarly with primary culture hepatocytes with the induction of phosphorylation of the cytokeratins, morphological changes, and apoptosis. The purpose of this study was to investigate the in vivo relationship between the protein phosphatase inhibitory activities and the acute hepatotoxicity of MCLR compared to OA. MCLR and OA were intraperitoneally administrated to mice at approximately 220 microg/kg. After 30 min, the liver of only the MCLR-treated mouse was dark-colored and heavier than that of the control mouse. Subsequently, the phosphoproteins of the mouse liver were chemically modified with reversible biotinylation reagent and selectively analyzed by LC/MS/MS. Consequently, the phosphorylated Ser 354 of formyltetrahydrofolate dehydrogenase, which is an abundant enzyme in the liver cytoplasm, was observed in the MCLR- and the OA-treated mice 9.5 and 5.3 times more intensely than in the control mouse respectively, suggesting that MCLR and OA inhibited PP2A and induced the resulting phosphorylation. These results supported the hypothesis that the acute hepatotoxicity is possibly caused by the PP1 inhibition, and not by the PP2A inhibition.
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Affiliation(s)
- Masahiko Tachi
- Graduate School of Environmental and Human Sciences, Meijo University, 150 Yagotoyama, Tempaku, Nagoya 468-8503, Japan.
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36
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Chassin C, Hornef MW, Bens M, Lotz M, Goujon JM, Vimont S, Arlet G, Hertig A, Rondeau E, Vandewalle A. Hormonal control of the renal immune response and antibacterial host defense by arginine vasopressin. ACTA ACUST UNITED AC 2007; 204:2837-52. [PMID: 17967904 PMCID: PMC2118508 DOI: 10.1084/jem.20071032] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Ascending urinary tract infection (UTI) and pyelonephritis caused by uropathogenic Escherichia coli (UPEC) are very common infections that can cause severe kidney damage. Collecting duct cells, the site of hormonally regulated ion transport and water absorption controlled by vasopressin, are the preferential intrarenal site of bacterial adhesion and initiation of inflammatory response. We investigated the effect of the potent V2 receptor (V2R) agonist deamino-8-D-arginine vasopressin (dDAVP) on the activation of the innate immune response using established and primary cultured collecting duct cells and an experimental model of ascending UTI. dDAVP inhibited Toll-like receptor 4–mediated nuclear factor κB activation and chemokine secretion in a V2R-specific manner. The dDAVP-mediated suppression involved activation of protein phosphatase 2A and required an intact cystic fibrosis transmembrane conductance regulator Cl− channel. In vivo infusion of dDAVP induced a marked fall in proinflammatory mediators and neutrophil recruitment, and a dramatic rise in the renal bacterial burden in mice inoculated with UPECs. Conversely, administration of the V2R antagonist SR121463B to UPEC-infected mice stimulated both the local innate response and the antibacterial host defense. These findings evidenced a novel hormonal regulation of innate immune cellular activation and demonstrate that dDAVP is a potent modulator of microbial-induced inflammation in the kidney.
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Affiliation(s)
- Cécilia Chassin
- Institut National de la Santé et de la Recherche Médicale, U773, Centre de Recherche Biomédicale Bichat-Beaujon, BP 416, 75018 Paris, France
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37
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Sugiyama N, Konoki K, Tachibana K. Isolation and characterization of okadaic acid binding proteins from the marine sponge Halichondria okadai. Biochemistry 2007; 46:11410-20. [PMID: 17867706 DOI: 10.1021/bi700490n] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Okadaic acid, first isolated from the marine sponge Halichondria okadai, is a potent inhibitor of protein phosphatases 1 and 2A (PP1 and PP2A, respectively). Photoaffinity labeling experiments previously performed with biotinylated photoreactive okadaic acid revealed the presence of okadaic acid binding protein (OABP) in the crude extract of H. okadai. In this article, OABP1 and OABP2 were purified from H. okadai as guided by the binding affinity of [27-3H]okadaic acid. OABP1 has an approximate molecular mass of 37 kDa in SDS-PAGE analysis. Edman degradation followed by molecular cloning and sequencing identified OABP1 as being 88% identical to the rabbit PP2Abeta catalytic subunit. On the other hand, HPLC analysis revealed that OABP2 consists of three 22 kDa proteins (OABP2.1, OABP2.2, and OABP2.3). Electrospray ionization mass spectrometry indicated that OABP2.1 and OABP2.2 form a complex with okadaic acid. The complete amino acid sequence of OABP2, determined by Edman degradation and molecular cloning, showed that OABP2.1 is 96% identical to OABP2.2 and 66% identical to OABP2.3, while being very slightly homologous to any protein phosphatases known to date. OABP2 did not exhibit phosphatase activity, though it bound to okadaic acid with a Kd of 0.97 nM. Furthermore, OABP2 was not detected in the sponge Halichondria japonica or the dinoflagellate Prorocentrum lima. We thus speculated that OABP2 might be involved in detoxifying okadaic acid.
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Affiliation(s)
- Naoyuki Sugiyama
- Department of Chemistry, School of Science, The University of Tokyo, Japan
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38
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Humphries KM, Pennypacker JK, Taylor SS. Redox regulation of cAMP-dependent protein kinase signaling: kinase versus phosphatase inactivation. J Biol Chem 2007; 282:22072-9. [PMID: 17548350 DOI: 10.1074/jbc.m702582200] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Many components of cellular signaling pathways are sensitive to regulation by oxidation and reduction. Previously, we described the inactivation of cAMP-dependent protein kinase (PKA) by direct oxidation of a reactive cysteine in the activation loop of the kinase. In the present study, we demonstrate that in HeLa cells PKA activity follows a biphasic response to thiol oxidation. Under mild oxidizing conditions, or short exposure to oxidants, forskolin-stimulated PKA activity is enhanced. This enhancement was blocked by sulfhydryl reducing agents, demonstrating a reversible mode of activation. In contrast, forskolin-stimulated PKA activity is inhibited by more severe oxidizing conditions. Mild oxidation enhanced PKA activity stimulated by forskolin, isoproterenol, or the cell-permeable analog, 8-bromo-cAMP. When cells were lysed in the presence of serine/threonine phosphatase inhibitor, NaF, the PKA-enhancing effect of oxidation was blunted. These results suggest oxidation of a PKA-counteracting phosphatase may be inhibited, thus enhancing the apparent kinase activity. Using an in vivo PKA activity reporter, we demonstrated that mild oxidation does indeed prolong the PKA signal induced by isoproterenol by inhibiting counteracting phosphatase activity. The results of this study demonstrate in live cells a unique synergistic mechanism whereby the PKA signaling pathway is enhanced in an apparent biphasic manner.
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Affiliation(s)
- Kenneth M Humphries
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0654, USA
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Bielinski VA, Mumby MC. Functional analysis of the PP2A subfamily of protein phosphatases in regulating Drosophila S6 kinase. Exp Cell Res 2007; 313:3117-26. [PMID: 17570358 PMCID: PMC1991331 DOI: 10.1016/j.yexcr.2007.05.008] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2007] [Revised: 05/04/2007] [Accepted: 05/08/2007] [Indexed: 12/23/2022]
Abstract
Phosphorylation and activation of ribosomal S6 protein kinase is an important link in the regulation of cell size by the target of rapamycin (TOR) protein kinase. A combination of selective inhibition and RNA interference were used to test the roles of members of the PP2A subfamily of protein phosphatases in dephosphorylation of Drosophila S6 kinase (dS6K). Treatment of Drosophila Schneider 2 cells with calyculin A, a selective inhibitor of PP2A-like phosphatases, resulted in a 7-fold increase in the basal level of dS6K phosphorylation at the TOR phosphorylation site (Thr398) and blocked dephosphorylation following inactivation of TOR by amino acid starvation or rapamycin treatment. Knockdown of the PP2A catalytic subunit increased basal dS6K phosphorylation and inhibited dephosphorylation induced by amino acid withdrawal. In contrast, depletion of the catalytic subunits of the other two members of the subfamily did not enhance dS6K phosphorylation. Knockdown of PP4 caused a 20% decrease in dS6K phosphorylation and knockdown of PP6 had no effect. Knockdown of the Drosophila B56-2 subunit resulted in enhanced dephosphorylation of dS6K following removal of amino acids. In contrast, knockdown of the homologs of the other PP2A regulatory subunits had no effects. Knockdown of the Drosophila homolog of the PP2A/PP4/PP6 interaction protein alpha4/Tap42 did not affect S6K phosphorylation, but did induce apoptosis. These results indicate that PP2A, but not other members of this subfamily, is likely to be a major S6K phosphatase in intact cells and is consistent with an important role for this phosphatase in the TOR pathway.
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Affiliation(s)
- Vincent A Bielinski
- Department of Pharmacology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9041, USA
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40
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Chen X, Zheng Y, Shen Y. Natural Products with Maleic Anhydride Structure: Nonadrides, Tautomycin, Chaetomellic Anhydride, and Other Compounds. Chem Rev 2007; 107:1777-830. [PMID: 17439289 DOI: 10.1021/cr050029r] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Xiaolong Chen
- Institute of Bioengineering, Zhejiang University of Technology, Hangzhou 310032, P. R. China
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41
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Li HH, Cai X, Shouse GP, Piluso LG, Liu X. A specific PP2A regulatory subunit, B56gamma, mediates DNA damage-induced dephosphorylation of p53 at Thr55. EMBO J 2007; 26:402-11. [PMID: 17245430 PMCID: PMC1783465 DOI: 10.1038/sj.emboj.7601519] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2006] [Accepted: 11/29/2006] [Indexed: 11/09/2022] Open
Abstract
Protein phosphatase 2A (PP2A) has been implicated to exert its tumor suppressive function via a small subset of regulatory subunits. In this study, we reported that the specific B regulatory subunits of PP2A B56gamma1 and B56gamma3 mediate dephosphorylation of p53 at Thr55. Ablation of the B56gamma protein by RNAi, which abolishes the Thr55 dephosphorylation in response to DNA damage, reduces p53 stabilization, Bax expression and cell apoptosis. To investigate the molecular mechanisms, we have shown that the endogenous B56gamma protein level and association with p53 increase after DNA damage. Finally, we demonstrate that Thr55 dephosphorylation is required for B56gamma3-mediated inhibition of cell proliferation and cell transformation. These results suggest a molecular mechanism for B56gamma-mediated tumor suppression and provide a potential route for regulation of B56gamma-specific PP2A complex function.
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Affiliation(s)
- Heng-Hong Li
- Department of Biochemistry, University of California, Riverside, CA, USA
| | - Xin Cai
- Department of Biochemistry, University of California, Riverside, CA, USA
| | - Geoffrey P Shouse
- Department of Biochemistry, University of California, Riverside, CA, USA
| | - Landon G Piluso
- Department of Biochemistry, University of California, Riverside, CA, USA
| | - Xuan Liu
- Department of Biochemistry, University of California, Riverside, CA, USA
- Department of Biochemistry, University of California, 900 University Ave, Riverside, CA 92521, USA. Tel.: +1 951 827 4350; Fax: +1 951 827 4434; E-mail:
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Isobe M, Kurono M, Tsuboi K, Takai A. Synthesis of [18,19,21,22-13C4]-Labeled Tautomycin as an NMR Probe of Protein Phosphatase Inhibitor. Chem Asian J 2007; 2:377-85. [PMID: 17441173 DOI: 10.1002/asia.200600387] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We have accomplished the synthesis of 13C-labeled tautomycin at the C18, C19, C21, and C22 positions starting from 100% [13C]triethylphosphonoacetate for the purpose of elucidating the dynamics and conformation of the C17-C26 moiety. NMR spectroscopy of 13C-labeled tautomycin revealed strong binding with protein phosphatase type 1 and new features in the 13C NMR spectrum, such as the very small three-bond coupling constants (2J).
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Affiliation(s)
- Minoru Isobe
- Laboratory of Organic Chemistry, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
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44
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Shiraishi M, Tanabe A, Saito N, Sasaki Y. Unphosphorylated MARCKS is involved in neurite initiation induced by insulin-like growth factor-I in SH-SY5Y cells. J Cell Physiol 2007; 209:1029-38. [PMID: 16941482 DOI: 10.1002/jcp.20814] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Myristoylated alanine-rich C kinase substrate (MARCKS) has been suggested to be involved in various aspects of neuronal cell differentiation, including neurite outgrowth. However, the precise mechanisms by which MARCKS phosphorylation is regulated, and how MARCKS contributes to neurite outgrowth, are poorly understood. Here, we found that treatment of SH-SY5Y cells with insulin-like growth factor-I (IGF-I) induced a rapid and transient decrease in the level of phosphorylated MARCKS (P-MARCKS) to below the basal level. The decrease in P-MARCKS induced by IGF-I was blocked by pretreatment of cells with phosphoinositide 3-kinase (PI3K) inhibitors, LY294002 and wortmannin. A decrease in P-MARCKS was also observed in cells treated with a Rho-dependent kinase (ROCK) inhibitor, Y27632. Furthermore, IGF-I induced transient inactivation of RhoA, an upstream effector of ROCK. We showed that MARCKS was translocated to the membrane and colocalized with F-actin at the lamellipodia and the tips of neurites in the cells stimulated with IGF-I. Finally, overexpression of wild-type MARCKS or an unphosphorylatable mutant of MARCKS enhanced the number of neurite-bearing cells relative to vector-transfected cells. Taken together, these findings suggest that unphosphorylated MARCKS is involved in neurite initiation, and highlight the important role played by MARCKS in organization of the actin cytoskeleton.
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Affiliation(s)
- Mitsuya Shiraishi
- Laboratory of Pharmacology, School of Pharmaceutical Science, Kitasato University, Shirokane 5-9-1, Minato-ku, Tokyo 108-8641, Japan.
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Li W, Ju J, Osada H, Shen B. Utilization of the methoxymalonyl-acyl carrier protein biosynthesis locus for cloning of the tautomycin biosynthetic gene cluster from Streptomyces spiroverticillatus. J Bacteriol 2006; 188:4148-52. [PMID: 16707708 PMCID: PMC1482887 DOI: 10.1128/jb.00172-06] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Tautomycin (TTM), a potent protein phosphatase inhibitor, consists of a polyketide chain containing a spiroketal moiety and an acyl chain bearing a dialkylmaleic anhydride structure. PCR using degenerate primers was used to clone genes from Streptomyces spiroverticillatus for formation of the methoxymalonyl-acyl carrier protein. This locus was found to contain five genes (ttmC, ttmA, ttmD, ttmB, and ttmE), one of which was used as a probe to clone the 110-kb TTM biosynthetic gene cluster. The involvement of the ttmA gene in TTM biosynthesis was confirmed by gene inactivation and mutation complementation experiments.
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Affiliation(s)
- Wenli Li
- Division of Pharmaceutical Sciences, School of Pharmacy, University of Wisconsin-Madison, 777 Highland Ave., Madison, WI 53705, USA
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Mounier C, Dumas V, Posner BI. Regulation of hepatic insulin-like growth factor-binding protein-1 gene expression by insulin: central role for mammalian target of rapamycin independent of forkhead box O proteins. Endocrinology 2006; 147:2383-91. [PMID: 16455781 DOI: 10.1210/en.2005-0902] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The expression of IGF-binding protein-1 (IGFBP-1) is induced in rat liver by dexamethasone and glucagon and is completely inhibited by 100 nM insulin. Various studies have implicated phosphatidylinositol 3-kinase, protein kinase B (Akt), phosphorylation of the transcription factors forkhead in rhabdomyosarcoma 1 (Foxo1)/Foxo3, and the mammalian target of rapamycin (mTOR) in insulin's effect. In this study we examined insulin regulation of IGFBP-1 in both subconfluent and confluent hepatocytes. In subconfluent hepatocytes, insulin inhibition of IGFBP-1 mRNA levels was blocked by inhibiting PI3 kinase activation, and there was a corresponding inhibition of Foxo1/Foxo3 phosphorylation. In these same cells, inhibition of the insulin effect by rapamycin occurred in the presence of insulin-induced Foxo1/Foxo3 phosphorylation. In confluent hepatocytes, insulin could not activate the phosphatidylinositol 3-kinase (PI3 kinase)-Akt-Foxo1/Foxo3 pathway, but still inhibited IGFBP-1 gene expression in an mTOR-dependent manner. In subconfluent hepatocytes, the serine/threonine phosphatase inhibitor okadaic acid (100 nM) partially inhibited IGFBP-1 gene expression by 40%, but did not produce phosphorylation of either Akt or Foxo proteins. In contrast, 1 nm insulin inhibited the IGFBP-1 mRNA level by 40% and correspondingly activated Akt and Foxo1/Foxo3 phosphorylation to a level comparable to that observed with 100 nM insulin. These results suggest a potential role for a serine/threonine phosphatase(s) in the regulation of IGFBP-1 gene transcription, which is not downstream of mTOR and is independent of Akt. In conclusion, we have found that in rat liver, insulin inhibition of IGFBP-1 mRNA levels can occur in the absence of the phosphorylation of Foxo1/Foxo3, whereas activation of the mTOR pathway is both necessary and sufficient.
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Affiliation(s)
- Catherine Mounier
- Polypeptide Hormone Laboratory, Faculty of Medicine, McGill University, Montréal, Quebéc, Canada
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Nishikata M, Yoshimura Y, Deyama Y, Suzuki K. Continuous assay of protein tyrosine phosphatases based on fluorescence resonance energy transfer. Biochimie 2006; 88:879-86. [PMID: 16540231 DOI: 10.1016/j.biochi.2006.02.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2005] [Accepted: 02/04/2006] [Indexed: 11/22/2022]
Abstract
An assay method that continuously measures the protein tyrosine phosphatase (PTP)-catalyzed dephosphorylation reaction based on fluorescence resonance energy transfer (FRET) was developed as an improvement of our previously reported discontinuous version [M. Nishikata, K. Suzuki, Y. Yoshimura, Y. Deyama, A. Matsumoto, Biochem. J. 343 (1999) 385-391]. The assay uses oligopeptide substrates that contain (7-methoxycoumarin-4-yl)acetyl (Mca) group as a fluorescence donor and 2,4-dinitrophenyl (DNP) group as a fluorescence acceptor, in addition to a phosphotyrosine residue located between these two groups. In the assay, a PTP solution is added to a buffer solution containing a FRET substrate and chymotrypsin. The PTP-catalyzed dephosphorylation of the substrate and subsequent chymotryptic cleavage of the dephosphorylated substrate results in a disruption of FRET, thereby increasing Mca fluorescence. In this study, we used FRET substrates that are much more susceptible to chymotryptic cleavage after dephosphorylation than the substrate used in our discontinuous assay, thus enabling the continuous assay without significant PTP inactivation by chymotrypsin. The rate of fluorescence increase strictly reflected the rate of dephosphorylation at appropriate chymotrypsin concentrations. Since the continuous assay allows the measurement of initial rate of dephosphorylation reaction, kinetic parameters for the dephosphorylation reactions of FRET substrates by Yersinia, T-cell and LAR PTPs were determined. The continuous assay was compatible with the measurement of very low PTP activity in a crude enzyme preparation and was comparable in sensitivity to assays that use radiolabeled substrates.
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Affiliation(s)
- M Nishikata
- Central Research Division, Hokkaido University Graduate School of Dental Medicine, Kita-ku, Kita-13 Nishi-7, 060-8586 Sapporo, Hokkaido, Japan.
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Song T, Hatano N, Kume K, Sugimoto K, Yamaguchi F, Tokuda M, Watanabe Y. Inhibition of neuronal nitric-oxide synthase by phosphorylation at Threonine1296 in NG108-15 neuronal cells. FEBS Lett 2005; 579:5658-62. [PMID: 16214135 DOI: 10.1016/j.febslet.2005.09.037] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2005] [Revised: 09/09/2005] [Accepted: 09/09/2005] [Indexed: 11/20/2022]
Abstract
We demonstrate that neuronal nitric-oxide synthase (nNOS) is directly inhibited through the phosphorylation of Thr(1296) in NG108-15 neuronal cells. Treatment of NG108-15 cells expressing nNOS with calyculin A, an inhibitor of protein phosphatase 1 and 2A, revealed a dose-dependent inhibition of nNOS enzyme activity with concomitant phosphorylation of Thr(1296) residue. Cells expressing a phosphorylation-deficient mutant in which Thr(1296) was changed to Ala proved resistant to phosphorylation and suppression of NOS activity. Mimicking phosphorylation mutant of nNOS in which Thr(1296) is changed to Asp showed a significant decrease in nNOS enzyme activity, being competitive with NADPH, relative to the wild-type enzyme. These data suggest that phosphorylation of nNOS at Thr(1296) may involve the attenuation of nitric oxide production in neuronal cells through the decrease of NADPH-binding to the enzyme.
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Affiliation(s)
- Tao Song
- Department of Cell Physiology, Kagawa University, Faculty of Medicine, Miki-cho, Kida-gun, Japan
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To KKW, Wang X, Yu CW, Ho YP, Au-Yeung SCF. Protein phosphatase 2A inhibition and circumvention of cisplatin cross-resistance by novel TCM-platinum anticancer agents containing demethylcantharidin. Bioorg Med Chem 2004; 12:4565-73. [PMID: 15358284 DOI: 10.1016/j.bmc.2004.07.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2004] [Revised: 07/05/2004] [Accepted: 07/06/2004] [Indexed: 11/23/2022]
Abstract
Novel TCM-platinum compounds [Pt(C(8)H(8)O(5))(NH(2)R)(2)] 1-5, derived from integrating demethylcantharidin, a modified component from a traditional Chinese medicine (TCM) with a platinum moiety, possess anticancer and protein phosphatase 2A inhibition properties. The compounds are able to circumvent cisplatin resistance by apparently targeting the DNA repair mechanism. Novel isosteric analogues [Pt(C(9)H(10)O(4))(NH(2)R)(2)] A and B, devoid of PP2A-inhibitory activity, were found to suffer from an enhanced DNA repair and were cross-resistant to cisplatin. The results advocate a well-defined structure-activity requirement associating the PP2A-inhibiting demethylcantharidin with the circumvention of cisplatin cross-resistance demonstrated by TCM-Pt compounds 1-5.
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Affiliation(s)
- Kenneth K W To
- School of Pharmacy, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong Special Administrative Region, Hong Kong
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Kim N, Cao W, Song IS, Kim CY, Harnett KM, Cheng L, Walsh MP, Biancani P. Distinct kinases are involved in contraction of cat esophageal and lower esophageal sphincter smooth muscles. Am J Physiol Cell Physiol 2004; 287:C384-94. [PMID: 15128504 DOI: 10.1152/ajpcell.00390.2003] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Contraction of smooth muscle depends on the balance of myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP) activities. Because MLCK activation depends on the activation of calmodulin, which requires a high Ca2+concentration, phosphatase inhibition has been invoked to explain contraction at low cytosolic Ca2+levels. The link between activation of the Ca2+-independent protein kinase Cε (PKCε) and MLC phosphorylation observed in the esophagus (ESO) (Sohn UD, Cao W, Tang DC, Stull JT, Haeberle JR, Wang CLA, Harnett KM, Behar J, and Biancani P. Am J Physiol Gastrointest Liver Physiol 281: G467–G478, 2001), however, has not been elucidated. We used phosphatase and kinase inhibitors and antibodies to signaling enzymes in combination with intact and saponin-permeabilized isolated smooth muscle cells from ESO and lower esophageal sphincter (LES) to examine PKCε-dependent, Ca2+-independent signaling in ESO. The phosphatase inhibitors okadaic acid and microcystin-LR, as well as an antibody to the catalytic subunit of type 1 protein serine/threonine phosphatase, elicited similar contractions in ESO and LES. MLCK inhibitors (ML-7, ML-9, and SM-1) and antibodies to MLCK inhibited contraction induced by phosphatase inhibition in LES but not in ESO. The PKC inhibitor chelerythrine and antibodies to PKCε, but not antibodies to PKCβII, inhibited contraction of ESO but not of LES. In ESO, okadaic acid triggered translocation of PKCε from cytosolic to particulate fraction and increased activity of integrin-linked kinase (ILK). Antibodies to the mitogen-activated protein (MAP) kinases ERK1/ERK2 and to ILK, and the MAP kinase kinase (MEK) inhibitor PD-98059, inhibited okadaic acid-induced ILK activity and contraction of ESO. We conclude that phosphatase inhibition potentiates the effects of MLCK in LES but not in ESO. Contraction of ESO is mediated by activation of PKCε, MEK, ERK1/2, and ILK.
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Affiliation(s)
- Nayoung Kim
- Department of Medicine, Seoul National University, Bundang Hospital, Seoungnam, Gyeronggi-Do 463-707, Korea
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