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An Interaction Network of the Human SEPT9 Established by Quantitative Mass Spectrometry. G3-GENES GENOMES GENETICS 2019; 9:1869-1880. [PMID: 30975701 PMCID: PMC6553528 DOI: 10.1534/g3.119.400197] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Septins regulate the organization of the actin cytoskeleton, vesicle transport and fusion, chromosome alignment and segregation, and cytokinesis in mammalian cells. SEPT9 is part of the core septin hetero-octamer in human cells which is composed of SEPT2, SEPT6, SEPT7, and SEPT9. SEPT9 has been linked to a variety of intracellular functions as well as to diseases and diverse types of cancer. A targeted high-throughput approach to systematically identify the interaction partners of SEPT9 has not yet been performed. We applied a quantitative proteomics approach to establish an interactome of SEPT9 in human fibroblast cells. Among the newly identified interaction partners were members of the myosin family and LIM domain containing proteins. Fluorescence microscopy of SEPT9 and its interaction partners provides additional evidence that SEPT9 might participate in vesicle transport from and to the plasma membrane as well as in the attachment of actin stress fibers to cellular adhesions.
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Ankyrin domain of myosin 16 influences motor function and decreases protein phosphatase catalytic activity. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2015; 44:207-18. [PMID: 25775934 DOI: 10.1007/s00249-015-1015-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Revised: 02/17/2015] [Accepted: 02/24/2015] [Indexed: 01/11/2023]
Abstract
The unconventional myosin 16 (Myo16), which may have a role in regulation of cell cycle and cell proliferation, can be found in both the nucleus and the cytoplasm. It has a unique, eight ankyrin repeat containing pre-motor domain, the so-called ankyrin domain (My16Ank). Ankyrin repeats are present in several other proteins, e.g., in the regulatory subunit (MYPT1) of the myosin phosphatase holoenzyme, which binds to the protein phosphatase-1 catalytic subunit (PP1c). My16Ank shows sequence similarity to MYPT1. In this work, the interactions of recombinant and isolated My16Ank were examined in vitro. To test the effects of My16Ank on myosin motor function, we used skeletal muscle myosin or nonmuscle myosin 2B. The results showed that My16Ank bound to skeletal muscle myosin (K D ≈ 2.4 µM) and the actin-activated ATPase activity of heavy meromyosin (HMM) was increased in the presence of My16Ank, suggesting that the ankyrin domain can modulate myosin motor activity. My16Ank showed no direct interaction with either globular or filamentous actin. We found, using a surface plasmon resonance-based binding technique, that My16Ank bound to PP1cα (K D ≈ 540 nM) and also to PP1cδ (K D ≈ 600 nM) and decreased its phosphatase activity towards the phosphorylated myosin regulatory light chain. Our results suggest that one function of the ankyrin domain is probably to regulate the function of Myo16. It may influence the motor activity, and in complex with the PP1c isoforms, it can play an important role in the targeted dephosphorylation of certain, as yet unidentified, intracellular proteins.
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Korrodi-Gregório L, Esteves SLC, Fardilha M. Protein phosphatase 1 catalytic isoforms: specificity toward interacting proteins. Transl Res 2014; 164:366-91. [PMID: 25090308 DOI: 10.1016/j.trsl.2014.07.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 06/26/2014] [Accepted: 07/01/2014] [Indexed: 01/21/2023]
Abstract
The coordinated and reciprocal action of serine-threonine protein kinases and protein phosphatases produces transitory phosphorylation, a fundamental regulatory mechanism for many biological processes. Phosphoprotein phosphatase 1 (PPP1), a major serine-threonine phosphatase, in particular, is ubiquitously distributed and regulates a broad range of cellular functions, including glycogen metabolism, cell cycle progression, and muscle relaxation. PPP1 has evolved effective catalytic machinery but in vitro lacks substrate specificity. In vivo, its specificity is achieved not only by the existence of different PPP1 catalytic isoforms, but also by binding of the catalytic moiety to a large number of regulatory or targeting subunits. Here, we will address exhaustively the existence of diverse PPP1 catalytic isoforms and the relevance of their specific partners and consequent functions.
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Affiliation(s)
- Luís Korrodi-Gregório
- Laboratório de Transdução de Sinais, Departamento de Biologia, Secção Autónoma de Ciências de Saúde, Centro de Biologia Celular, Universidade de Aveiro, Aveiro, Portugal
| | - Sara L C Esteves
- Laboratório de Transdução de Sinais, Departamento de Biologia, Secção Autónoma de Ciências de Saúde, Centro de Biologia Celular, Universidade de Aveiro, Aveiro, Portugal
| | - Margarida Fardilha
- Laboratório de Transdução de Sinais, Departamento de Biologia, Secção Autónoma de Ciências de Saúde, Centro de Biologia Celular, Universidade de Aveiro, Aveiro, Portugal.
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Arf guanine nucleotide-exchange factors BIG1 and BIG2 regulate nonmuscle myosin IIA activity by anchoring myosin phosphatase complex. Proc Natl Acad Sci U S A 2013; 110:E3162-70. [PMID: 23918382 DOI: 10.1073/pnas.1312531110] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Brefeldin A-inhibited guanine nucleotide-exchange factors BIG1 and BIG2 activate, through their Sec7 domains, ADP ribosylation factors (Arfs) by accelerating the replacement of Arf-bound GDP with GTP for initiation of vesicular transport or activation of specific enzymes that modify important phospholipids. They are also implicated in regulation of cell polarization and actin dynamics for directed migration. Reciprocal coimmunoprecipitation of endogenous HeLa cell BIG1 and BIG2 with myosin IIA was demonstrably independent of Arf guanine nucleotide-exchange factor activity, because effects of BIG1 and BIG2 depletion were reversed by overexpression of the cognate BIG molecule C-terminal sequence that follows the Arf activation site. Selective depletion of BIG1 or BIG2 enhanced specific phosphorylation of myosin regulatory light chain (T18/S19) and F-actin content, which impaired cell migration in Transwell assays. Our data are clear evidence of these newly recognized functions for BIG1 and BIG2 in transduction or integration of mechanical signals from integrin adhesions and myosin IIA-dependent actin dynamics. Thus, by anchoring or scaffolding the assembly, organization, and efficient operation of multimolecular myosin phosphatase complexes that include myosin IIA, protein phosphatase 1δ, and myosin phosphatase-targeting subunit 1, BIG1 and BIG2 serve to integrate diverse biophysical and biochemical events in cells.
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Eto M, Kirkbride JA, Chugh R, Karikari NK, Kim JI. Nuclear localization of CPI-17, a protein phosphatase-1 inhibitor protein, affects histone H3 phosphorylation and corresponds to proliferation of cancer and smooth muscle cells. Biochem Biophys Res Commun 2013; 434:137-42. [PMID: 23541585 DOI: 10.1016/j.bbrc.2013.03.055] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 03/17/2013] [Indexed: 01/23/2023]
Abstract
CPI-17 (C-kinase-activated protein phosphatase-1 (PP1) inhibitor, 17kDa) is a cytoplasmic protein predominantly expressed in mature smooth muscle (SM) that regulates the myosin-associated PP1 holoenzyme (MLCP). Here, we show CPI-17 expression in proliferating cells, such as pancreatic cancer and hyperplastic SM cells. Immunofluorescence showed that CPI-17 was concentrated in nuclei of human pancreatic cancer (Panc1) cells. Nuclear accumulation of CPI-17 was also detected in the proliferating vascular SM cell culture and cells at neointima of rat vascular injury model. The N-terminal 21-residue tail domain of CPI-17 was necessary for the nuclear localization. Phospho-mimetic Asp-substitution of CPI-17 at Ser12 attenuated the nuclear import. CPI-17 phosphorylated at Ser12 was not localized at nuclei, suggesting a suppressive role of Ser12 phosphorylation in the nuclear import. Activated CPI-17 bound to all three isoforms of PP1 catalytic subunit in Panc1 nuclear extracts. CPI-17 knockdown in Panc1 resulted in dephosphorylation of histone H3 at Thr3, Ser10 and Thr11, whereas it had no effects on the phosphorylation of myosin light chain and merlin, the known targets of MLCP. In parallel, CPI-17 knockdown suppressed Panc1 proliferation. We propose that CPI-17 accumulated in the nucleus through the N-terminal tail targets multiple PP1 signaling pathways regulating cell proliferation.
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Affiliation(s)
- Masumi Eto
- Department of Molecular Physiology and Biophysics, and Kimmel Cancer Center, Thomas Jefferson University, 1020 Locust Street, PA 19107, USA.
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Butler T, Paul J, Europe-Finner N, Smith R, Chan EC. Role of serine-threonine phosphoprotein phosphatases in smooth muscle contractility. Am J Physiol Cell Physiol 2013; 304:C485-504. [PMID: 23325405 DOI: 10.1152/ajpcell.00161.2012] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The degree of phosphorylation of myosin light chain 20 (MLC20) is a major determinant of force generation in smooth muscle. Myosin phosphatases (MPs) contain protein phosphatase (PP) 1 as catalytic subunits and are the major enzymes that dephosphorylate MLC20. MP regulatory targeting subunit 1 (MYPT1), the main regulatory subunit of MP in all smooth muscles, is a key convergence point of contractile and relaxatory pathways. Combinations of regulatory mechanisms, including isoform splicing, multiple phosphorylation sites, and scaffolding proteins, modulate MYPT1 activity with tissue and agonist specificities to affect contraction and relaxation. Other members of the PP1 family that do not target myosin, as well as PP2A and PP2B, dephosphorylate a range of proteins that affect smooth muscle contraction. This review discusses the role of phosphatases in smooth muscle contractility with a focus on MYPT1 in uterine smooth muscle. Myometrium shares characteristics of vascular and other visceral smooth muscles yet, during healthy pregnancy, undergoes hypertrophy, hyperplasia, quiescence, and labor as physiological processes. Myometrium presents an accessible model for the study of normal and pathological smooth muscle function, and a better understanding of myometrial physiology may allow the development of novel therapeutics for the many disorders of myometrial physiology from preterm labor to dysmenorrhea.
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Affiliation(s)
- Trent Butler
- Mothers and Babies Research Centre, Faculty of Health, University of Newcastle, Callaghan, NSW 2308, Australia
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Park CY, Tambe D, Alencar AM, Trepat X, Zhou EH, Millet E, Butler JP, Fredberg JJ. Mapping the cytoskeletal prestress. Am J Physiol Cell Physiol 2010; 298:C1245-52. [PMID: 20164383 DOI: 10.1152/ajpcell.00417.2009] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Cell mechanical properties on a whole cell basis have been widely studied, whereas local intracellular variations have been less well characterized and are poorly understood. To fill this gap, here we provide detailed intracellular maps of regional cytoskeleton (CSK) stiffness, loss tangent, and rate of structural rearrangements, as well as their relationships to the underlying regional F-actin density and the local cytoskeletal prestress. In the human airway smooth muscle cell, we used micropatterning to minimize geometric variation. We measured the local cell stiffness and loss tangent with optical magnetic twisting cytometry and the local rate of CSK remodeling with spontaneous displacements of a CSK-bound bead. We also measured traction distributions with traction microscopy and cell geometry with atomic force microscopy. On the basis of these experimental observations, we used finite element methods to map for the first time the regional distribution of intracellular prestress. Compared with the cell center or edges, cell corners were systematically stiffer and more fluidlike and supported higher traction forces, and at the same time had slower remodeling dynamics. Local remodeling dynamics had a close inverse relationship with local cell stiffness. The principal finding, however, is that systematic regional variations of CSK stiffness correlated only poorly with regional F-actin density but strongly and linearly with the regional prestress. Taken together, these findings in the intact cell comprise the most comprehensive characterization to date of regional variations of cytoskeletal mechanical properties and their determinants.
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Affiliation(s)
- Chan Young Park
- Dept. of Environmental Health, Harvard School of Public Health, Boston, MA 02115, USA
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Kiss A, Lontay B, Bécsi B, Márkász L, Oláh E, Gergely P, Erdodi F. Myosin phosphatase interacts with and dephosphorylates the retinoblastoma protein in THP-1 leukemic cells: its inhibition is involved in the attenuation of daunorubicin-induced cell death by calyculin-A. Cell Signal 2008; 20:2059-70. [PMID: 18755268 DOI: 10.1016/j.cellsig.2008.07.018] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2008] [Revised: 07/18/2008] [Accepted: 07/18/2008] [Indexed: 10/21/2022]
Abstract
Reversible phosphorylation of the retinoblastoma protein (pRb) is an important regulatory mechanism in cell cycle progression. The role of protein phosphatases is less understood in this process, especially concerning the regulatory/targeting subunits involved. It is shown that pretreatment of THP-1 leukemic cells with calyculin-A (CL-A), a cell-permeable phosphatase inhibitor, attenuated daunorubicin (DNR)-induced cell death and resulted in increased pRb phosphorylation and protection against proteolytic degradation. Protein phosphatase-1 catalytic subunits (PP1c) dephosphorylated the phosphorylated C-terminal fragment of pRb (pRb-C) slightly, whereas when PP1c was complexed to myosin phosphatase target subunit-1 (MYPT1) in myosin phosphatase (MP) holoenzyme dephosphorylation was stimulated. The pRb-C phosphatase activity of MP was partially inhibited by anti-MYPT1(1-296) implicating MYPT1 in targeting PP1c to pRb. MYPT1 became phosphorylated on both inhibitory sites (Thr695 and Thr850) upon CL-A treatment of THP-1 cells resulting in the inhibition of MP activity. MYPT1 and pRb coprecipitated from cell lysates by immunoprecipitation with either anti-MYPT1 or anti-pRb antibodies implying that pRb-MYPT1 interaction occurred at cellular levels. Surface plasmon resonance-based experiments confirmed binding of pRb-C to both PP1c and MYPT1. In control and DNR-treated cells, MYPT1 and pRb were predominantly localized in the nucleus exhibiting partial colocalization as revealed by immunofluorescence using confocal microscopy. Upon CL-A treatment, nucleo-cytoplasmic shuttling of both MYPT1 and pRb, but not PP1c, was observed. The above data imply that MP, with the targeting role of MYPT1, may regulate the phosphorylation level of pRb, thereby it may be involved in the control of cell cycle progression and in the mediation of chemoresistance of leukemic cells.
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Affiliation(s)
- Andrea Kiss
- Department of Medical Chemistry, University of Debrecen Medical and Health Science Center, Debrecen, Nagyerdei krt. 98, Hungary
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Eto M, Kirkbride JA, Brautigan DL. Assembly of MYPT1 with protein phosphatase-1 in fibroblasts redirects localization and reorganizes the actin cytoskeleton. ACTA ACUST UNITED AC 2008; 62:100-9. [PMID: 16106448 DOI: 10.1002/cm.20088] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Dephosphorylation of actin-binding proteins by a specialized form of protein Ser/Thr phosphatase type-1 (PP1) regulates smooth muscle contraction and morphology and motility of nonmuscle cells. This myosin and ezrin/radixin/moesin (ERM)-targeted phosphatase comprises the delta isoform PP1 catalytic subunit plus a primary regulatory subunit called myosin phosphatase targeting (MYPT1). We reconstructed myosin/ERM phosphatase in living rat embryo fibroblasts (REF52 cells) by transient expression of epitope-tagged MYPT1 (myc-MYPT1) plus HA-tagged PP1. Unexpectedly, wild-type myc-MYPT1 expressed alone accumulated predominantly in the nucleus, as visualized by immunofluorescent microscopy, whereas if coexpressed with HA-PP1, it was localized in the cytosol and deposited on cytoskeleton myofilaments. The F38A mutation of MYPT1 that eliminates PP1 binding gave nuclear localization of myc-MYPT1, even when coexpressed with HA-PP1. Thus, expression of both subunits was necessary to form myosin/ERM phosphatase in situ and mediate myofilament localization. The results indicate there is little endogenous PP1 available for interaction or interchange with ectopic regulatory subunits in living cells. We concluded that myosin binding by the C-terminal domain of MYPT1 is not sufficient to override nuclear import in fibroblasts, but the binding of PP1 to myc-MYPT1 neutralizes nuclear import. Full-length myc-MYPT1 plus HA-PP1 induced only subtle changes in organization of the actin cytoskeleton, however coexpression of myc-MYPT1(1-300) with HA-PP1 dispersed stress fibers without major alteration in morphology and myc-MYPT1(1-498) disrupted the cytoskeleton and produced radically extended cells that appeared like neurons. Based on these responses, we conclude that the MYPT1 C-terminus functions as an auto-inhibitory domain, and a central domain in MYPT1 can mediate extensive reorganization of the actin cytoskeleton.
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Affiliation(s)
- Masumi Eto
- Department of Molecular Physiology and Biological Physics, Center for Cell Signaling, University of Virginia School of Medicine, Charlottesville, Virginia 22908, USA
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Thermodynamic evidence of non-muscle myosin II–lipid-membrane interaction. Biochem Biophys Res Commun 2008; 366:500-5. [DOI: 10.1016/j.bbrc.2007.11.170] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2007] [Accepted: 11/29/2007] [Indexed: 11/19/2022]
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Matsumura F, Hartshorne DJ. Myosin phosphatase target subunit: Many roles in cell function. Biochem Biophys Res Commun 2007; 369:149-56. [PMID: 18155661 DOI: 10.1016/j.bbrc.2007.12.090] [Citation(s) in RCA: 153] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2007] [Accepted: 12/11/2007] [Indexed: 12/12/2022]
Abstract
Phosphorylation of myosin II is important in many aspects of cell function and involves a myosin kinase, e.g. myosin light chain kinase, and a myosin phosphatase (MP). MP is regulated by the myosin phosphatase target subunit (MYPT1). The domain structure, properties, and genetic analyses of MYPT1 and its isoforms are outlined. MYPT1 binds the catalytic subunit of type 1 phosphatase, delta isoform, and also acts as an interactive platform for many other proteins. A key reaction for MP is with phosphorylated myosin II and the first process shown to be regulated by MP was contractile activity of smooth muscle. In cell division and cell migration myosin II phosphorylation also plays a critical role and these are discussed. However, based on the wide range of partners for MYPT1 it is likely that MP is implicated with substrates other than myosin II. Open questions are whether the diverse functions of MP reflect different cellular locations and/or specific roles for the MYPT1 isoforms.
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Affiliation(s)
- Fumio Matsumura
- Department of Molecular Biology and Biochemistry, Rutgers University, 604, Allison Road, Piscataway, NJ 08855, USA
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Koga Y, Ikebe M. A novel regulatory mechanism of myosin light chain phosphorylation via binding of 14-3-3 to myosin phosphatase. Mol Biol Cell 2007; 19:1062-71. [PMID: 18094049 DOI: 10.1091/mbc.e07-07-0668] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Myosin II phosphorylation-dependent cell motile events are regulated by myosin light-chain (MLC) kinase and MLC phosphatase (MLCP). Recent studies have revealed myosin phosphatase targeting subunit (MYPT1), a myosin-binding subunit of MLCP, plays a critical role in MLCP regulation. Here we report the new regulatory mechanism of MLCP via the interaction between 14-3-3 and MYPT1. The binding of 14-3-3beta to MYPT1 diminished the direct binding between MYPT1 and myosin II, and 14-3-3beta overexpression abolished MYPT1 localization at stress fiber. Furthermore, 14-3-3beta inhibited MLCP holoenzyme activity via the interaction with MYPT1. Consistently, 14-3-3beta overexpression increased myosin II phosphorylation in cells. We found that MYPT1 phosphorylation at Ser472 was critical for the binding to 14-3-3. Epidermal growth factor (EGF) stimulation increased both Ser472 phosphorylation and the binding of MYPT1-14-3-3. Rho-kinase inhibitor inhibited the EGF-induced Ser472 phosphorylation and the binding of MYPT1-14-3-3. Rho-kinase specific siRNA also decreased EGF-induced Ser472 phosphorylation correlated with the decrease in MLC phosphorylation. The present study revealed a new RhoA/Rho-kinase-dependent regulatory mechanism of myosin II phosphorylation by 14-3-3 that dissociates MLCP from myosin II and attenuates MLCP activity.
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Affiliation(s)
- Yasuhiko Koga
- Department of Physiology, University of Massachusetts Medical School, Worcester, MA 01655, USA
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Villa-Moruzzi E. Targeting of FAK Ser910 by ERK5 and PP1delta in non-stimulated and phorbol ester-stimulated cells. Biochem J 2007; 408:7-18. [PMID: 17692050 PMCID: PMC2049076 DOI: 10.1042/bj20070058] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Ser910 of FAK (focal adhesion kinase) was phosphorylated in fibroblasts treated with the phorbol ester PMA and dephosphorylated by PP1d (protein phosphatase 1d), as indicated by shRNA (small-hairpin RNA) gene silencing. Ser910 of FAK was reported previously to be an ERK (extracellular-signal-regulated kinase) 1/2 target in cells treated with phorbol esters. In contrast, various approaches, including the use of the MEK (mitogen-activated protein kinase/ERK kinase) inhibitors UO126 and CI-1040 to inhibit ERK1/2 pointed to the involvement of ERK5. This hypothesis was confirmed by: (i) shRNA ERK5 gene silencing, which resulted in complete pSer910 loss in non-stimulated and PMA-stimulated cells; (ii) direct phosphorylation of recombinant FAK by ERK5; and (iii) ERK5 activation by PMA. PMA stimulation and ERK5 silencing in MDA-MB 231 and MDA-MB 361 breast cancer cells indicated Ser910 targeting by ERK5 also in these cells. Given the proximity of Ser910 to the FAT (focal adhesion targeting) regulatory domain of FAK, cell proliferation and morphology were investigated in FAK-/- cells expressing S910A mutant FAK. The cell growth rate decreased and exposure to PMA induced peculiar morphological changes in cells expressing S910A, with respect to wild-type FAK, suggesting a role for Ser910 in these processes. The present study indicates, for the first time, the phosphorylation of Ser910 of FAK by ERK5 and its dephosphorylation by PP1d, and suggested a role for Ser910 in the control of cell shape and proliferation.
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Affiliation(s)
- Emma Villa-Moruzzi
- Dipartimento di Patologia Sperimentale, Sezione Patologia Generale, via Roma 55, 56126 Pisa, Italy.
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Gao C, Furge K, Koeman J, Dykema K, Su Y, Cutler ML, Werts A, Haak P, Vande Woude GF. Chromosome instability, chromosome transcriptome, and clonal evolution of tumor cell populations. Proc Natl Acad Sci U S A 2007; 104:8995-9000. [PMID: 17517657 PMCID: PMC1885616 DOI: 10.1073/pnas.0700631104] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Chromosome instability and aneuploidy are hallmarks of cancer, but it is not clear how changes in the chromosomal content of a cell contribute to the malignant phenotype. Previously we have shown that we can readily isolate highly proliferative tumor cells and their revertants from highly invasive tumor cell populations, indicating how phenotypic shifting can contribute to malignant progression. Here we show that chromosome instability and changes in chromosome content occur with phenotypic switching. Further, we show that changes in the copy number of each chromosome quantitatively impose a proportional change in the chromosome transcriptome ratio. This correlation also applies to subchromosomal regions of derivative chromosomes. Importantly, we show that the changes in chromosome content and the transcriptome favor the expression of a large number of genes appropriate for the specific tumor phenotype. We conclude that chromosome instability generates the necessary chromosome diversity in the tumor cell populations and, therefore, the transcriptome diversity to allow for environment-facilitated clonal expansion and clonal evolution of tumor cell populations.
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Affiliation(s)
| | | | | | | | - Yanli Su
- Laboratories of *Molecular Oncology
| | - Mary Lou Cutler
- University Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814
| | | | - Pete Haak
- Microarray Technology, Van Andel Research Institute, 333 Bostwick Avenue, N.E., Grand Rapids, MI 49503; and
| | - George F. Vande Woude
- Laboratories of *Molecular Oncology
- To whom correspondence should be addressed. E-mail:
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Eto M, Kirkbride J, Elliott E, Lo SH, Brautigan DL. Association of the tensin N-terminal protein-tyrosine phosphatase domain with the alpha isoform of protein phosphatase-1 in focal adhesions. J Biol Chem 2007; 282:17806-15. [PMID: 17435217 DOI: 10.1074/jbc.m700944200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Focal adhesions attach cultured cells to the extracellular matrix, and we found endogenous protein phosphatase-1alpha isoform (PP1alpha) localized in adhesions across the entire area of adherent fibroblasts. However, in fibroblasts migrating into a scrape wound or spreading after replating PP1alpha did not appear in adhesions near the leading edge but was recruited into other adhesions coincident in time and space with incorporation of tensin. Endogenous tensin and PP1alpha co-precipitated from cell lysates with isoform-specific PP1 antibodies. Chemical cross-linking of focal adhesion preparations with Lomant's reagent demonstrated molecular proximity of endogenous PP1alpha and tensin, whereas neither focal adhesion kinase nor vinculin was cross-linked and co-precipitated with PP1alpha, suggesting distinct spatial subdomains within adhesions. Transient expression of truncated tensin showed the N-terminal 360 residues, which comprise a protein-tyrosine phosphatase domain, alone were sufficient for isoform-selective co-precipitation of co-expressed PP1alpha. Human prostate cancer PC3 cells are deficient in tensin relative to fibroblasts and have fewer, mostly peripheral adhesions. Transient expression of green fluorescent protein tensin in these cancer cells induced formation of adhesions and recruited endogenous PP1alpha into those adhesions. Thus, the protein-tyrosine phosphatase domain of tensin exhibits isoform-specific association with PP1alpha in a restricted spatial region of adhesions that are formed during cell migration.
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Affiliation(s)
- Masumi Eto
- Center for Cell Signaling, University of Virginia School of Medicine, Charlottesville, Virginia 22908, USA
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Takamoto N, Komatsu S, Komaba S, Niiro N, Ikebe M. Novel ZIP kinase isoform lacks leucine zipper. Arch Biochem Biophys 2006; 456:194-203. [PMID: 17126281 PMCID: PMC2758612 DOI: 10.1016/j.abb.2006.09.026] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2006] [Revised: 09/26/2006] [Accepted: 09/26/2006] [Indexed: 12/26/2022]
Abstract
Zipper-interacting protein kinase (ZIP kinase) has been thought to be involved in apoptosis and the C-terminal leucine zipper motif is important for its function. Recent studies have revealed that ZIP kinase also plays a role in regulating myosin phosphorylation. Here, we found novel ZIP kinase isoform in which the C-terminal non-kinase domain containing a leucine zipper is eliminated (hZIPK-S). hZIPK-S binds to myosin phosphatase targeting subunit 1(MYPT1) similar to the long isoform (hZIPK-L). In addition, we found that hZIPK-S as well as hZIPK-L bind to myosin. These results indicate that a leucine zipper is not critical for the binding of ZIP kinase to MYPT1 and myosin. Consistently, hZIPK-S localized with stress-fibers where they co-localized with myosin. The residues 278-311, the C-terminal side of the kinase domain common to the both isoforms, is involved in the binding to MYPT1, while the myosin binding domain is within the kinase domain. These results suggest that the newly found hZIPK-S as well as the long isoform play an important role in the regulation of myosin phosphorylation.
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Affiliation(s)
| | | | | | | | - Mitsuo Ikebe
- Correspondence addressed to Mitsuo Ikebe, FAX: 508-856-4600, e-mail:
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Bianchi M, De Lucchini S, Marin O, Turner D, Hanks S, Villa-Moruzzi E. Regulation of FAK Ser-722 phosphorylation and kinase activity by GSK3 and PP1 during cell spreading and migration. Biochem J 2006; 391:359-70. [PMID: 15975092 PMCID: PMC1276935 DOI: 10.1042/bj20050282] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In addition to tyrosine sites, FAK (focal adhesion kinase) is phosphorylated on multiple serine residues. In the present study, the regulation of two of these sites, Ser-722 (S1) and Ser-911 (S4), was investigated. Phosphorylation of S1 (but not S4) decreased in resuspended cells, and recovered during spreading on fibronectin, indicating adhesion-dependent regulation. GSK3 (glycogen synthase kinase 3) inhibitors decreased S1 phosphorylation, and siRNA (short interfering RNA) silencing indicated further the involvement of GSK3beta. Furthermore, GSK3beta was found to become activated during cell spreading on fibronectin, and to physically associate with FAK. S1 phosphorylation was observed to decrease in wounded cell monolayers, while GSK3beta underwent inactivation and later was observed to increase to the original level within 24 h. Direct phosphorylation of S1, requiring pre-phosphorylation of Ser-726 in the +4 position, was demonstrated using purified GSK3 and a synthetic peptide containing FAK residues 714-730. An inhibitory role for S1 phosphorylation in FAK signalling was indicated by findings that both alanine substitution for S1 and dephosphorylation of S1 by PP1 (serine/threonine protein phosphatase type-1) resulted in an increase in FAK kinase activity; likewise, this role was also shown by cell treatment with the GSK3 inhibitor LiCl. The inhibitory role was confirmed by the finding that cells expressing FAK with alanine substitution for S1 displayed improved cell spreading and faster migration in wound-healing and trans-well assays. Finally, the finding that S1 phosphorylation increased in cells treated with the PP1 inhibitor okadaic acid indicated targeting of this site by PP1. These results indicate an additional mechanism for regulation of FAK activity during cell spreading and migration, involving Ser-722 phosphorylation modulated through the competing actions of GSK3beta and PP1.
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Affiliation(s)
- Mariarita Bianchi
- *Department of Experimental Pathology, University of Pisa, 56126 Pisa, Italy
| | - Stefania De Lucchini
- †Cell and Developmental Biology Laboratories, Department of Physiology and Biochemistry, University of Pisa, 56010 Pisa, Italy
- ‡Scuola Normale Superiore of Pisa, 56126 Pisa, Italy
| | - Oriano Marin
- §Department of Biological Chemistry, University of Padova, 35121 Padova, Italy
| | - David L. Turner
- ∥Department of Biological Chemistry and Mental Health Research Institute, University of Michigan, Ann Arbor, MI 48109, U.S.A
| | - Steven K. Hanks
- ¶Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, U.S.A
| | - Emma Villa-Moruzzi
- *Department of Experimental Pathology, University of Pisa, 56126 Pisa, Italy
- To whom correspondence should be addressed (email )
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19
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Haystead TAJ. ZIP kinase, a key regulator of myosin protein phosphatase 1. Cell Signal 2005; 17:1313-22. [PMID: 16005610 DOI: 10.1016/j.cellsig.2005.05.008] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2005] [Accepted: 05/06/2005] [Indexed: 10/25/2022]
Abstract
Two major physiological roles have been defined for zipper interacting protein kinase (ZIPK), regulation of apoptosis in non-muscle cells and regulation of Ca(2+) sensitization in smooth muscle. Although much attention has focused on the role of ZIPK in the regulation of apoptotic events, its roles in smooth muscle are likely to have equal if not greater physiological relevance. We first identified ZIPK as a major protein kinase controlling the phosphorylation of myosin phosphatase (SMPP-1M) and the inhibitor protein CPI17 in smooth muscle. Phosphorylation of SMPP-1M and CPI17 by ZIPK inhibits phosphatase activity towards myosin and causes profound Ca(2+) sensitization and contraction in smooth muscle. ZIPK will also directly phosphorylate both muscle and non-muscle myosin. The highly selective actions of ZIPK in the control of myosin phosphorylation potentially make the enzyme an ideal candidate for the development of novel therapeutics to treat smooth muscle related disorders such as hypertension or asthma.
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Affiliation(s)
- Timothy A J Haystead
- Department of Pharmacology and Cancer Biology, Duke University, Durham, NC 27710, USA.
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20
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Surks HK, Riddick N, Ohtani KI. M-RIP targets myosin phosphatase to stress fibers to regulate myosin light chain phosphorylation in vascular smooth muscle cells. J Biol Chem 2005; 280:42543-51. [PMID: 16257966 DOI: 10.1074/jbc.m506863200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Vascular smooth muscle cell contraction and relaxation are directly related to the phosphorylation state of the regulatory myosin light chain. Myosin light chains are dephosphorylated by myosin phosphatase, leading to vascular smooth muscle relaxation. Myosin phosphatase is localized not only at actin-myosin stress fibers where it dephosphorylates myosin light chains, but also in the cytoplasm and at the cell membrane. The mechanisms by which myosin phosphatase is targeted to these loci are incompletely understood. We recently identified myosin phosphatase-Rho interacting protein as a member of the myosin phosphatase complex that directly binds both the myosin binding subunit of myosin phosphatase and RhoA and is localized to actin-myosin stress fibers. We hypothesized that myosin phosphatase-Rho interacting protein targets myosin phosphatase to the contractile apparatus to dephosphorylate myosin light chains. We used RNA interference to silence the expression of myosin phosphatase-Rho interacting protein in human vascular smooth muscle cells. Myosin phosphatase-Rho interacting protein silencing reduced the localization of the myosin binding subunit to stress fibers. This reduction in stress fiber myosin phosphatase-Rho interacting protein and myosin binding subunit increased basal and lysophosphatidic acid-stimulated myosin light chain phosphorylation. Neither cellular myosin phosphatase, myosin light chain kinase, nor RhoA activities were changed by myosin phosphatase-Rho interacting protein silencing. Furthermore, myosin phosphatase-Rho interacting protein silencing resulted in marked phenotypic changes in vascular smooth muscle cells, including increased numbers of stress fibers, increased cell area, and reduced stress fiber inhibition in response to a Rho-kinase inhibitor. These data support the importance of myosin phosphatase-Rho interacting protein-dependent targeting of myosin phosphatase to stress fibers for regulating myosin light chain phosphorylation state and morphology in human vascular smooth muscle cells.
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Affiliation(s)
- Howard K Surks
- Molecular Cardiology Research Institute and Department of Medicine, Division of Cardiology, Tufts-New England Medical Center, Boston, Massachusetts 02111, USA.
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21
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Wu Y, Murányi A, Erdodi F, Hartshorne DJ. Localization of myosin phosphatase target subunit and its mutants. J Muscle Res Cell Motil 2005; 26:123-34. [PMID: 15999227 DOI: 10.1007/s10974-005-2579-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2004] [Accepted: 02/21/2005] [Indexed: 11/28/2022]
Abstract
Transient transfection of NIH3T3 cells with various constructs of myosin phosphatase target subunit (MYPT1) and GFP showed distinct cellular localizations. Constructs containing the N-terminal nuclear localization signals (NLS), i.e. full-length MYPT1 and N-terminal MYPT1 fragments, were concentrated in the nucleus. Full-length chicken and human MYPT1-GFP showed discrete nuclear foci. Deletion of the N-terminal NLS or use of central or C-terminal MYPT1 fragments did not show unique nuclear distributions (C-terminal NLS are present). Transient transfection of NIH3T3 cells (in the presence of serum) with full-length MYPT1-GFP caused a marked decrease in number of attached cells, an apparent block in the cell cycle prior to M phase and signs of increased apoptosis. Under conditions of serum starvation the unique nuclear localization of MYPT1-GFP was not found and there was no marked decrease in the number of attached cells (after 48 h). Stable transfection of HEK 293 cells with GFP-MYPT1 was obtained. MYPT1 and its N-terminal mutants bound to retinoblastoma protein (Rb), raising the possibility that Rb is implicated in the effects caused by overexpression of MYPT1.
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Affiliation(s)
- Yue Wu
- Muscle Biology Group, University of Arizona, Tucson, AZ 85721, USA
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22
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Lontay B, Kiss A, Gergely P, Hartshorne DJ, Erdodi F. Okadaic acid induces phosphorylation and translocation of myosin phosphatase target subunit 1 influencing myosin phosphorylation, stress fiber assembly and cell migration in HepG2 cells. Cell Signal 2005; 17:1265-75. [PMID: 16038801 DOI: 10.1016/j.cellsig.2005.01.008] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2004] [Revised: 01/14/2005] [Accepted: 01/14/2005] [Indexed: 10/25/2022]
Abstract
It was determined that the myosin phosphatase (MP) activity and content of myosin phosphatase target subunit 1 (MYPT1) were correlated in subcellular fractions of human hepatocarcinoma (HepG2) cells. In control cells MYPT1 was localized in the cytoplasm and in the nucleus, as determined by confocal microscopy. Treatment of HepG2 cells with 50 nM okadaic acid (OA), a cell-permeable phosphatase inhibitor, induced several changes: 1) a marked redistribution of MYPT1 to the plasma membrane associated with an increased level of phosphorylation of MYPT1 at Thr695. Both effects showed only a slight influence with the Rho-kinase inhibitor, Y-27632; 2) an increase in phosphorylation of MYPT1 at Thr850 associated with its accumulation in the perinuclear region and nucleus. These effects were markedly reduced by Y-27632; 3) an increased phosphorylation of the 20 kDa myosin II light chain at Ser19 associated with an increased location of myosin II at the cell center. These effects were partially counteracted by Y-27632; 4) an increase in stress fiber formation and a decrease in cell migration, both OA-induced effects were blocked by Y-27632. In HepG2 lysates, OA (5-100 nM) did not affect MP activity but inhibited PP2A activity. These results indicate that OA induces differential phosphorylation and translocation of MYPT1, dependent on PP2A and, to varying extents, on ROK. These changes are associated with an increased level of myosin II phosphorylation and attenuation of hepatic cell migration.
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Affiliation(s)
- Beáta Lontay
- Department of Medical Chemistry, Research Center for Molecular Medicine, Medical and Health Science Center, University of Debrecen, H-4026 Debrecen, Bem tér 18/B, Hungary
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23
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Lontay B, Serfozo Z, Gergely P, Ito M, Hartshorne DJ, Erdodi F. Localization of myosin phosphatase target subunit 1 in rat brain and in primary cultures of neuronal cells. J Comp Neurol 2004; 478:72-87. [PMID: 15334650 DOI: 10.1002/cne.20273] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Myosin phosphatase (PP1M) is composed of the delta isoform of the PP1 catalytic subunit (PP1cdelta), the myosin phosphatase target subunit (MYPT), and a 20 kDa subunit. Western blots detected higher amounts of the MYPT1 isoform compared to MYPT2 in whole brain extracts. The localization of MYPT1 was studied in rat brain and in primary cell cultures of neurons using specific antibodies. Analysis of lysates of brain regions for MYPT1 and PP1M by Western blots using anti-MYPT1 antibodies and by phosphatase assays with myosin as substrate suggested a ubiquitous distribution. Immunohistochemistry of tissue sections revealed that MYPT1 was distributed in all areas of the brain, with staining observed in many different cell types. Depending on the method used for fixation, the MYPT1 appeared with varying intensity in nuclei, in nucleoli, and in the cytoplasm. In primary hippocampal cultures, MYPT1 was identified by confocal microscopy in the cytoplasm and in the nucleus, whereas a predominantly cytoplasmic localization was found in cochlear nucleus cells. In cultured cells, MYPT1 and PP1cdelta colocalized with synaptophysin. PP1M activity was high in synaptosomes isolated from the cerebral cortex, but was relatively low in the postsynaptic densities. The interaction of MYPT1 with synaptophysin and with known partners (Rho-kinase, PP1cdelta) in brain extracts was shown by immunoprecipitation with anti-MYPT1. Pull-down assays from synaptosomes, using GST-MYPT1, also confirmed these interactions. In conclusion, the widespread cellular and subcellular localization of MYPT1 implies that PP1M may play an important role in the dephosphorylation of key regulatory proteins in neuronal cells.
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Affiliation(s)
- Beáta Lontay
- Department of Medical Chemistry, Research Center for Molecular Medicine, Medical and Health Science Center, University of Debrecen, H-4012 Debrecen, Bem tér 18/B, Hungary
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24
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Eto M, Kitazawa T, Brautigan DL. Phosphoprotein inhibitor CPI-17 specificity depends on allosteric regulation of protein phosphatase-1 by regulatory subunits. Proc Natl Acad Sci U S A 2004; 101:8888-93. [PMID: 15184667 PMCID: PMC428442 DOI: 10.1073/pnas.0307812101] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2003] [Indexed: 11/18/2022] Open
Abstract
Inhibition of myosin phosphatase is critical for agonist-induced contractility of vascular smooth muscle. The protein CPI-17 is a phosphorylation-dependent inhibitor of myosin phosphatase and, in response to agonists, Thr-38 is phosphorylated by protein kinase C, producing a >1,000-fold increase in inhibitory potency. Here, we addressed how CPI-17 could selectively inhibit myosin phosphatase among other protein phosphatase-1 (PP1) holoenzymes. PP1 in cell lysates was separated by sequential affinity chromatography into at least two fractions, one bound specifically to thiophospho-CPI-17, and another bound specifically to inhibitor-2. The MYPT1 regulatory subunit of myosin phosphatase was concentrated only in the fraction bound to thiophospho-CPI-17. This binding was eliminated by addition of excess microcystin-LR to the lysate, showing that binding at the active site of PP1 is required. Phospho-CPI-17 failed to inhibit glycogen-bound PP1 from skeletal muscle, composed primarily of PP1 with the striated muscle glycogen-targeting subunit (G(M)) regulatory subunit. Phospho-CPI-17 was dephosphorylated during assay of glycogen-bound PP1, not MYPT1-associated PP1, even though these two holoenzymes have the same PP1 catalytic subunit. Phosphorylation of CPI-17 in rabbit arteries was enhanced by calyculin A but not okadaic acid or fostriecin, consistent with PP1-mediated dephosphorylation. We propose that CPI-17 binds at the PP1 active site where it is dephosphorylated, but association of MYPT1 with PP1C allosterically retards this hydrolysis, resulting in formation of a complex of MYPT1.PP1C.P-CPI-17, leading to an increase in smooth muscle contraction.
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Affiliation(s)
- Masumi Eto
- Center for Cell Signaling, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
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25
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Suyama E, Kawasaki H, Nakajima M, Taira K. Identification of genes involved in cell invasion by using a library of randomized hybrid ribozymes. Proc Natl Acad Sci U S A 2003; 100:5616-21. [PMID: 12719525 PMCID: PMC156250 DOI: 10.1073/pnas.1035850100] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Libraries of RNA helicase-coupled randomized ribozymes are a powerful tool for the identification of functional genes. We have demonstrated the usefulness of this functional gene-discovery system by identifying genes involved in tumor invasion, a process that is an essential feature of tumor metastasis: the spread of cancer cells from the original tumor to other sites in the body that imposes serious problems in the prognosis and treatment of cancer. Using a filter-based invasion assay in vitro, we isolated ribozymes that enhanced the invasive properties of NIH 3T3 fibroblasts. Sequence analysis of selected clones and a database search revealed that genes such as the gene for Gem GTPase and uncharacterized genes that resemble genes for myosin phosphatase and protein-tyrosine-phosphatase are involved in cell invasion. Our system for gene identification by using ribozymes and the functional analysis of target genes should help to clarify the complex mechanisms of invasion and metastasis and might provide information that is relevant to cancer therapy.
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Affiliation(s)
- Eigo Suyama
- Department of Chemistry and Biotechnology, School of Engineering, University of Tokyo, Hongo, Tokyo 113-8656, Japan
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26
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Takizawa N, Schmidt DJ, Mabuchi K, Villa-Moruzzi E, Tuft RA, Ikebe M. M20, the small subunit of PP1M, binds to microtubules. Am J Physiol Cell Physiol 2003; 284:C250-62. [PMID: 12388116 DOI: 10.1152/ajpcell.00153.2002] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Myosin light chain phosphatase (PP1M) is composed of three subunits, i.e., M20, MBS, and a catalytic subunit. Whereas MBS is assigned as a myosin binding subunit, the function of M20 is unknown. In the present study, we found that M20 binds to microtubules. The binding activity was revealed by cosedimentation of M20 with microtubules and binding of tubulin to M20 affinity resin. Green fluorescent protein (GFP)-tagged M20 (M20-GFP) was expressed in chicken primary smooth muscle cells and COS-7 cells and was used as a probe for studying the association between M20 and microtubules in living cells. M20-GFP was localized on filamentous structures in both cell types. Colocalization analysis revealed that M20-GFP colocalized with tubulin. Treatment with nocodazole, but not cytochalasin B, abolished the filamentous structure of M20-GFP. These results indicate that M20-GFP associates with microtubules in cells. Microinjection of rhodamine-tubulin into the M20-expressing cells revealed that incorporation of rhodamine-tubulin into microtubules was significantly facilitated by microtubule-associated M20. Consistent with this result, M20 enhanced the rate of tubulin polymerization in vitro and produced elongated microtubules. These results suggest that M20 has a microtubule binding activity and plays a role in regulating microtubule dynamics.
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Affiliation(s)
- Norio Takizawa
- Department of Physiology and Biomedical Imaging Group, University of Massachusetts Medical School, Worcester 01655, USA
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27
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Deng JT, Sutherland C, Brautigan DL, Eto M, Walsh MP. Phosphorylation of the myosin phosphatase inhibitors, CPI-17 and PHI-1, by integrin-linked kinase. Biochem J 2002; 367:517-24. [PMID: 12144526 PMCID: PMC1222907 DOI: 10.1042/bj20020522] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2002] [Revised: 06/24/2002] [Accepted: 07/29/2002] [Indexed: 11/17/2022]
Abstract
Integrin-linked kinase (ILK) has been implicated in Ca(2+)- independent contraction of smooth muscle via its ability to phosphorylate myosin. We investigated the possibility that this kinase might also phosphorylate and regulate the myosin light-chain phosphatase inhibitor proteins CPI-17 [protein kinase C (PKC)-dependent phosphatase inhibitor of 17 kDa] and PHI-1 (phosphatase holoenzyme inhibitor-1), known substrates of PKC. Both phosphatase inhibitors were phosphorylated by ILK in an in-gel kinase assay and in solution. A Thr-->Ala mutation at Thr(38) of CPI-17 and Thr(57) of PHI-1 eliminated phosphorylation by ILK. Phosphopeptide mapping, phospho amino acid analysis and immunoblotting using phospho-specific antibodies indicated that ILK predominantly phosphorylated the site critical for potent inhibition, i.e. Thr(38) of CPI-17 or Thr(57) of PHI-1. CPI-17 and PHI-1 thiophosphorylated by ILK at Thr(38) or Thr(57) respectively inhibited myosin light-chain phosphatase (MLCP) activity bound to myosin, whereas the site-specific mutants CPI-17-Thr(38)Ala and PHI-1-Thr(57)Ala, treated with ILK under identical conditions, like the untreated wild-type proteins had no effect on the phosphatase. Consistent with these effects, both thiophospho-CPI-17 and -PHI-1 induced Ca(2+) sensitization of contraction of Triton X-100-demembranated rat-tail arterial smooth muscle, whereas CPI-17-Thr(38)Ala and PHI-1-Thr(57)Ala treated with ILK in the presence of adenosine 5'-[gamma-thio]triphosphate failed to evoke a contractile response. We conclude that ILK may activate smooth-muscle contraction both directly, via phosphorylation of myosin, and indirectly, via phosphorylation and activation of CPI-17 and PHI-1, leading to inhibition of MLCP.
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Affiliation(s)
- Jing Ti Deng
- Smooth Muscle Research Group and Canadian Institutes of Health Research Group in Regulation of Vascular Contractility, University of Calgary Faculty of Medicine, 3330 Hospital Drive N.W., Calgary, Alberta T2N 4N1, Canada
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28
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Murányi A, MacDonald JA, Deng JT, Wilson DP, Haystead TAJ, Walsh MP, Erdodi F, Kiss E, Wu Y, Hartshorne DJ. Phosphorylation of the myosin phosphatase target subunit by integrin-linked kinase. Biochem J 2002; 366:211-6. [PMID: 12030846 PMCID: PMC1222775 DOI: 10.1042/bj20020401] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2002] [Revised: 05/15/2002] [Accepted: 05/27/2002] [Indexed: 11/17/2022]
Abstract
A mechanism proposed for regulation of myosin phosphatase (MP) activity is phosphorylation of the myosin phosphatase target subunit (MYPT1). Integrin-linked kinase (ILK) is associated with the contractile machinery and can phosphorylate myosin at the myosin light-chain kinase sites. The possibility that ILK may also phosphorylate and regulate MP was investigated. ILK was associated with the MP holoenzyme, shown by Western blots and in-gel kinase assays. MYPT1 was phosphorylated by ILK and phosphorylation sites in the N- and C-terminal fragments of MYPT1 were detected. From sequence analyses, three sites were identified: a primary site at Thr(709), and two other sites at Thr(695) and Thr(495). One of the sites for cAMP-dependent protein kinase (PKA) was Ser(694). Assays with the catalytic subunit of type 1 phosphatase indicated that only the C-terminal fragment of MYPT1 phosphorylated by zipper-interacting protein kinase, and ILK inhibited activity. The phosphorylated N-terminal fragment activated phosphatase activity and phosphorylation by PKA was without effect. Using full-length MYPT1 constructs phosphorylated by various kinases it was shown that Rho kinase gave marked inhibition; ILK produced an intermediate level of inhibition, which was considerably reduced for the Thr(695)-->Ala mutant; and PKA had no effect. In summary, phosphorylation of the various sites indicated that Thr(695) was the major inhibitory site, Thr(709) had only a slight inhibitory effect and Ser(694) had no effect. The findings that ILK phosphorylated both MYPT1 and myosin and the association of ILK with MP suggest that ILK may influence cytoskeletal structure or function.
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Affiliation(s)
- Andrea Murányi
- Muscle Biology Group, University of Arizona, Tucson, AZ 85721-0038, U.S.A
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29
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Shin HM, Je HD, Gallant C, Tao TC, Hartshorne DJ, Ito M, Morgan KG. Differential association and localization of myosin phosphatase subunits during agonist-induced signal transduction in smooth muscle. Circ Res 2002; 90:546-53. [PMID: 11909818 DOI: 10.1161/01.res.0000012822.23273.ec] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
It has been known for some time that agonist-induced contractions of vascular smooth muscle are often associated with a sensitization of the contractile apparatus to intracellular Ca2+. One mechanism that has been suggested to explain Ca2+ sensitization is inhibition of myosin phosphatase activity. In the present study, we tested the hypothesis that differential localization of the phosphatase might be associated with its inhibition. Quantitative confocal microscopy of freshly dissociated, fully contractile smooth muscle cells was used in parallel with measurements of myosin light chain and myosin phosphatase phosphorylation. The results indicate that, in the smooth muscle cells, the catalytic and targeting subunits of the phosphatase are dissociated from each other in an agonist-specific manner and that the dissociation is accompanied by a slower rate of myosin phosphorylation. Targeting of myosin phosphatase to the cell membrane precedes the dissociation of subunits and is associated with phosphorylation of the targeting subunit at a Rho-associated kinase (ROK) phosphorylation site. The phosphorylation and membrane translocation of the targeting subunit are inhibited by a ROK inhibitor. This dissociation of subunits may provide a mechanism for the decreased phosphatase activity of phosphorylated myosin phosphatase.
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Affiliation(s)
- Heung-Mook Shin
- Boston Biomedical Research Institute, Watertown, Mass 02472, USA
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30
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Fresu M, Bianchi M, Parsons JT, Villa-Moruzzi E. Cell-cycle-dependent association of protein phosphatase 1 and focal adhesion kinase. Biochem J 2001; 358:407-14. [PMID: 11513739 PMCID: PMC1222073 DOI: 10.1042/0264-6021:3580407] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Immunofluorescence studies with protein phosphatase-1 (PP1) isoforms-specific antibodies detected PP1delta, but not alpha or gamma1, at focal adhesions. PP1delta also co-immunoprecipitated with the focal adhesion kinase (FAK) and the alphav-integrin. In the present study glutathione S-transferase (GST)-PP1delta pulled-down FAK from fibroblasts extract and the interaction domain localized between residues 159 and 295 of delta. The association was confirmed by the ability to GST-FAK-related non-kinase (FRNK) to pull-down PP1delta from fibroblasts extract. GST-FRNK also pulled-down purified muscle PP1 catalytic subunit, thus indicating direct interaction between FAK and PP1. FAK displays consensus sequences for phosphorylation by cell division cycle kinase-2-cyclin B, and might be a PP1 substrate. In fact, FAK immunoprecipitated from metabolically-labelled mitotic HeLa cells without tyrosine phosphatase inhibitors was phosphorylated on Ser only and was dephosphorylated in vitro by purified muscle PP1, with loss of phospho-Ser. No PP1 was associated with FAK immunoprecipitated from mitotic HeLa cells. However, progressively more PP1 activity was assayed in FAK-immunoprecipitates obtained from cells released from mitosis. The associated activity was maximal at 2 h from the mitotic release (when 85-90% of the cells remained round) and decreased to basal level by 8 h (when cells were all polygonal). At the same time FAK underwent dephosphorylation, which was completed by 4 h. FAK obtained from cells at 1.5 h was Ser-phosphorylated, and underwent dephosphorylation during in vitro incubation, with loss of phospho-Ser, indicating the presence of active FAK-bound phosphatase. The only FAK-associated PP1 isoform between 1 and 8 h was PP1delta. The results suggest that FAK dephosphorylation by PP1delta occurs in cells released from mitosis, and confirmed the specific association of PP1delta, as detected previously in adherent cells.
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Affiliation(s)
- M Fresu
- Department of Experimental Pathology, University of Pisa, Via Roma 55 56126 Pisa, Italy
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31
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Katoh K, Kano Y, Amano M, Onishi H, Kaibuchi K, Fujiwara K. Rho-kinase--mediated contraction of isolated stress fibers. J Cell Biol 2001; 153:569-84. [PMID: 11331307 PMCID: PMC2190572 DOI: 10.1083/jcb.153.3.569] [Citation(s) in RCA: 251] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
It is widely accepted that actin filaments and the conventional double-headed myosin interact to generate force for many types of nonmuscle cell motility, and that this interaction occurs when the myosin regulatory light chain (MLC) is phosphorylated by MLC kinase (MLCK) together with calmodulin and Ca(2+). However, recent studies indicate that Rho-kinase is also involved in regulating the smooth muscle and nonmuscle cell contractility. We have recently isolated reactivatable stress fibers from cultured cells and established them as a model system for actomyosin-based contraction in nonmuscle cells. Here, using isolated stress fibers, we show that Rho-kinase mediates MLC phosphorylation and their contraction in the absence of Ca(2+). More rapid and extensive stress fiber contraction was induced by MLCK than was by Rho-kinase. When the activity of Rho-kinase but not MLCK was inhibited, cells not only lost their stress fibers and focal adhesions but also appeared to lose cytoplasmic tension. Our study suggests that actomyosin-based nonmuscle contractility is regulated by two kinase systems: the Ca(2+)-dependent MLCK and the Rho-kinase systems. We propose that Ca(2+) is used to generate rapid contraction, whereas Rho-kinase plays a major role in maintaining sustained contraction in cells.
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Affiliation(s)
- K Katoh
- Department of Structural Analysis, National Cardiovascular Center Research Institute, Suita, Osaka 565-8565, Japan.
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32
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Bianchi M, Villa-Moruzzi E. Binding of phosphatase-1 delta to the retinoblastoma protein pRb involves domains that include substrate recognition residues and a pRB binding motif. Biochem Biophys Res Commun 2001; 280:1-3. [PMID: 11162467 DOI: 10.1006/bbrc.2000.4067] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Protein Ser/Thr phosphatase-1 (PP1) controls the retinoblastoma protein (pRb) function, including its dephosphorylation at mitotic exit. Since PP1delta was found to coimmunoprecipitate with pRb from mitotic and early G1 cells, we further investigated the PP1delta-pRb association using GST-full length and GST-deletion mutants of delta. GST-delta pulled-down pRb from G2, mitotic and G1 HeLa cells, thus confirming the coimmunoprecipitation results. Among the delta deletion mutants tested, pRb was pulled down by mutant 159-295, which reproduces the C-terminal domain of delta without the C-terminus, whereas the C-terminus alone did not pull-down pRb. Further fragmentation of the 159-295 mutant indicated that pRb was pulled down by fragment 195-260, which includes several residues involved in substrate binding, and by fragment 159-212, which contains the putative pRb-binding motif LxSxE. Altogether the results supported the hypothesis that PP1delta may contribute to the dephosphorylation of pRb at mitotic exit and that the PP1delta-pRb interaction may be at multiple sites.
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Affiliation(s)
- M Bianchi
- Department of Experimental Pathology, University of Pisa, via Roma 55, 56126 Pisa, Italy
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Ma A, Richardson A, Schaefer EM, Parsons JT. Serine phosphorylation of focal adhesion kinase in interphase and mitosis: a possible role in modulating binding to p130(Cas). Mol Biol Cell 2001; 12:1-12. [PMID: 11160818 PMCID: PMC30563 DOI: 10.1091/mbc.12.1.1] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Focal adhesion kinase (FAK) is an important regulator of integrin signaling in adherent cells and accordingly its activity is significantly modulated during mitosis when cells detach from the extracellular matrix. During mitosis, FAK becomes heavily phosphorylated on serine residues concomitant with its inactivation and dephosphorylation on tyrosine. Little is known about the regulation of FAK activity by serine phosphorylation. In this report, we characterize two novel sites of serine phosphorylation within the C-terminal domain of FAK. Phosphorylation-specific antibodies directed to these sites and against two previously characterized sites of serine phosphorylation were used to study the regulated phosphorylation of FAK in unsynchronized and mitotic cells. Among the four major phosphorylation sites, designated pS1-pS4, phosphorylation of pS1 (Ser722) is unchanged in unsynchronized and mitotic cells. In contrast, pS3 and pS4 (Ser843 and Ser910) exhibit increased phosphorylation during mitosis. In vitro peptide binding experiments provide evidence that phosphorylation of pS1 (Ser722) may play a role in modulating FAK binding to the SH3 domain of the adapter protein p130(Cas).
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Affiliation(s)
- A Ma
- Department of Microbiology, Health Sciences Center, University of Virginia, Charlottesville, Virginia 22908, USA
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Tóth A, Kiss E, Gergely P, Walsh MP, Hartshorne DJ, Erdödi F. Phosphorylation of MYPT1 by protein kinase C attenuates interaction with PP1 catalytic subunit and the 20 kDa light chain of myosin. FEBS Lett 2000; 484:113-7. [PMID: 11068043 DOI: 10.1016/s0014-5793(00)02138-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The effect of phosphorylation in the N-terminal region of myosin phosphatase target subunit 1 (MYPT1) on the interactions with protein phosphatase 1 catalytic subunit (PP1c) and with phosphorylated 20 kDa myosin light chain (P-MLC20) was studied. Protein kinase C (PKC) phosphorylated threonine-34 (1 mol/mol), the residue preceding the consensus PP1c-binding motif ((35)KVKF(38)) in MYPT1(1-38), but this did not affect binding of the peptide to PP1c. PKC incorporated 2 mol P(i) into MYPT1(1-296) suggesting a second site of phosphorylation within the ankyrin repeats (residues 40-296). This phosphorylation diminished the stimulatory effect of MYPT1(1-296) on the P-MLC20 phosphatase activity of PP1c. Binding of PP1c or P-MLC20 to phosphorylated MYPT1(1-296) was also attenuated. It is concluded that phosphorylation of MYPT1 by PKC may therefore result in altered dephosphorylation of myosin.
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Affiliation(s)
- A Tóth
- Department of Medical Chemistry, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary
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35
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Eto M, Wong L, Yazawa M, Brautigan DL. Inhibition of myosin/moesin phosphatase by expression of the phosphoinhibitor protein CPI-17 alters microfilament organization and retards cell spreading. CELL MOTILITY AND THE CYTOSKELETON 2000; 46:222-34. [PMID: 10913968 DOI: 10.1002/1097-0169(200007)46:3<222::aid-cm6>3.0.co;2-b] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Cell migration and cytokinesis require reorganization of the cytoskeleton, involving phosphorylation and dephosphorylation of proteins such as myosin II and moesin. Myosin and moesin bind directly to a regulatory subunit of myosin/moesin phosphatase (MMP) that contains a protein type-1 phosphatase (PP1) catalytic subunit. Here we examined the role of MMP in cytoskeletal dynamics using a phosphorylation-dependent inhibitor protein specific for MMP, called CPI-17. Fibroblasts do not express CPI-17, making them a null background to study effects of expression. Wild type CPI-17 in rat embryo fibroblasts caused (1) abnormal accumulation of cortical F-actin fibers, distinct from the stress fibers induced by expression of active RhoA; (2) progressive contraction of cell area, leaving behind filamentous extensions that stained for F-actin and moesin, but not myosin; and (3) significantly retarded spreading of fibroblasts on fibronectin with elevated myosin II light chain phosphorylation. A phosphorylation site mutant CPI-17(T38A) and inhibitor-2 (Inh2), another PP1-specific inhibitor protein, served as controls and did not elicit these same responses when expressed at the same level as CPI-17. Inhibition of myosin light chain kinase by ML-9 prevented the abnormal accumulation of cortical microfilaments by CPI-17, but did not reverse shrinkage in area, whereas kinase inhibitors HA1077 and H7 prevented CPI-17-induced changes in microfilament distribution and cell contraction. These results highlight the physiological importance of myosin/moesin phosphatase regulation to dynamic remodeling of the cytoskeleton.
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Affiliation(s)
- M Eto
- Center for Cell Signaling, University of Virginia School of Medicine, Charlottesville 22908, USA
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36
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Abstract
Reversible protein phosphorylation is a major regulatory mechanism of intracellular signal transduction. Protein phosphatase 1 (PP1) is one of four major types of serine-threonine phosphatases mediating signaling pathways, but the means by which its activity is modulated has only recently begun to come into focus.
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Affiliation(s)
- J B Aggen
- Department of Chemistry, University of California, Advanced Medicine, Inc., Irvine, South San Francisco, CA 92697, USA
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37
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Verin AD, Csortos C, Durbin SD, Aydanyan A, Wang P, Patterson CE, Garcia JG. Characterization of the protein phosphatase 1 catalytic subunit in endothelium: Involvement in contractile responses. J Cell Biochem 2000. [DOI: 10.1002/1097-4644(2000)79:1<113::aid-jcb110>3.0.co;2-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Puntoni F, Villa-Moruzzi E. Protein phosphatase-1 activation and association with the retinoblastoma protein in colcemid-induced apoptosis. Biochem Biophys Res Commun 1999; 266:279-83. [PMID: 10581203 DOI: 10.1006/bbrc.1999.1800] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Protein phosphatase-1 (PP1) is cell cycle regulated and potentially related to apoptosis. We studied PP1 in HeLa cells exposed to colcemid, which leads first to mitotic block, then to cell death within 72 h. The soluble PP1 activity, which was low at 14 h (mitosis), was then reversibly activated (maximally around 48 h), with parallel changes in the protein levels of the alpha, gamma1 and delta PP1 isoforms. PP1 activation suggested its involvement in dephosphorylating proteins relevant to apoptosis. Among these, we examined the retinoblastoma protein (pRb). This was found hyperphosphorylated at 14 h. Hypophosphorylated pRb appeared at 24 h, increased at 48 h, and was the only form left at 72 h. PP1 was found to associate with immunoprecipitated pRb, as indicated by PP1 activity assays on the pRb-immunocomplexes. The pRb-associated PP1 activity was low at 14 h, maximal at 24 h, low again by 72 h and was due to PP1delta. The presence of active PP1 suggests its involvement in pRb dephosphorylation.
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Affiliation(s)
- F Puntoni
- Department of Experimental Pathology, University of Pisa, Pisa, 56126, Italy
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40
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Kawano Y, Fukata Y, Oshiro N, Amano M, Nakamura T, Ito M, Matsumura F, Inagaki M, Kaibuchi K. Phosphorylation of myosin-binding subunit (MBS) of myosin phosphatase by Rho-kinase in vivo. J Cell Biol 1999; 147:1023-38. [PMID: 10579722 PMCID: PMC2169354 DOI: 10.1083/jcb.147.5.1023] [Citation(s) in RCA: 451] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Rho-associated kinase (Rho-kinase), which is activated by the small GTPase Rho, phosphorylates myosin-binding subunit (MBS) of myosin phosphatase and thereby inactivates the phosphatase activity in vitro. Rho-kinase is thought to regulate the phosphorylation state of the substrates including myosin light chain (MLC), ERM (ezrin/radixin/moesin) family proteins and adducin by their direct phosphorylation and by the inactivation of myosin phosphatase. Here we identified the sites of phosphorylation of MBS by Rho-kinase as Thr-697, Ser-854 and several residues, and prepared antibody that specifically recognized MBS phosphorylated at Ser-854. We found by use of this antibody that the stimulation of MDCK epithelial cells with tetradecanoylphorbol-13-acetate (TPA) or hepatocyte growth factor (HGF) induced the phosphorylation of MBS at Ser-854 under the conditions in which membrane ruffling and cell migration were induced. Pretreatment of the cells with Botulinum C3 ADP-ribosyltransferase (C3), which is thought to interfere with Rho functions, or Rho-kinase inhibitors inhibited the TPA- or HGF-induced MBS phosphorylation. The TPA stimulation enhanced the immunoreactivity of phosphorylated MBS in the cytoplasm and membrane ruffling area of MDCK cells. In migrating MDCK cells, phosphorylated MBS as well as phosphorylated MLC at Ser-19 were localized in the leading edge and posterior region. Phosphorylated MBS was localized on actin stress fibers in REF52 fibroblasts. The microinjection of C3 or dominant negative Rho-kinase disrupted stress fibers and weakened the accumulation of phosphorylated MBS in REF52 cells. During cytokinesis, phosphorylated MBS, MLC and ERM family proteins accumulated at the cleavage furrow, and the phosphorylation level of MBS at Ser-854 was increased. Taken together, these results indicate that MBS is phosphorylated by Rho-kinase downstream of Rho in vivo, and suggest that myosin phosphatase and Rho-kinase spatiotemporally regulate the phosphorylation state of Rho-kinase substrates including MLC and ERM family proteins in vivo in a cooperative manner.
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Affiliation(s)
- Yoji Kawano
- Division of Signal Transduction, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan
| | - Yuko Fukata
- Division of Signal Transduction, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan
| | - Noriko Oshiro
- Division of Signal Transduction, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan
| | - Mutsuki Amano
- Division of Signal Transduction, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan
| | - Toshikazu Nakamura
- Division of Biochemistry, Osaka University Medical School, Suita, Osaka 565-0871, Japan
| | - Masaaki Ito
- The First Department of Internal Medicine, Mie University School of Medicine, Edobashi, Tsu, Mie 514-8507, Japan
| | - Fumio Matsumura
- Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08855
| | - Masaki Inagaki
- Laboratory of Biochemistry, Aichi Cancer Center Research Institute, Chikusa-ku, Nagoya 464-0021, Japan
| | - Kozo Kaibuchi
- Division of Signal Transduction, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan
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Abstract
Cancer progression to the invasive and metastatic stage represents the most formidable barrier to successful treatment. To develop rational therapies, we must determine the molecular bases of these transitions. Cell motility is one of the defining characteristics of invasive tumors, enabling tumors to migrate into adjacent tissues or transmigrate limiting basement membranes and extracellular matrices. Invasive tumor cells have been demonstrated to present dysregulated cell motility in response to extracellular signals from growth factors and cytokines. Recent findings suggest that this growth factor receptor-mediated motility is one of the most common aberrations in tumor cells leading to invasiveness and represents a cellular behavior distinct from-adhesion-related haptokinetic and haptotactic migration. This review focuses on the emerging understanding of the biochemical and biophysical foundations of growth factor-induced cell motility and tumor cell invasiveness, and the implications for development of targeted agents, with particular emphasis on signaling from the epidermal growth factor (EGF) and hepatocyte growth factor (HGF) receptors, as these have most often been associated with tumor invasion. The nascent models highlight the roles of various intracellular signaling pathways including phospholipase C-gamma (PLC gamma), phosphatidylinositol (PI)3'-kinase, mitogen-activated protein (MAP) kinase, and actin cytoskeleton-related events. Development of novel agents against tumor invasion will require not only a detailed appreciation of the biochemical regulatory elements of motility but also a paradigm shift in our approach to and assessment of cancer therapy.
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Affiliation(s)
- A Wells
- Department of Pathology, University of Alabama at Birmingham, USA
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42
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Totsukawa G, Yamakita Y, Yamashiro S, Hosoya H, Hartshorne DJ, Matsumura F. Activation of myosin phosphatase targeting subunit by mitosis-specific phosphorylation. J Cell Biol 1999; 144:735-44. [PMID: 10037794 PMCID: PMC2132942 DOI: 10.1083/jcb.144.4.735] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
It has been demonstrated previously that during mitosis the sites of myosin phosphorylation are switched between the inhibitory sites, Ser 1/2, and the activation sites, Ser 19/Thr 18 (Yamakita, Y., S. Yamashiro, and F. Matsumura. 1994. J. Cell Biol. 124:129- 137; Satterwhite, L.L., M.J. Lohka, K.L. Wilson, T.Y. Scherson, L.J. Cisek, J.L. Corden, and T.D. Pollard. 1992. J. Cell Biol. 118:595-605), suggesting a regulatory role of myosin phosphorylation in cell division. To explore the function of myosin phosphatase in cell division, the possibility that myosin phosphatase activity may be altered during cell division was examined. We have found that the myosin phosphatase targeting subunit (MYPT) undergoes mitosis-specific phosphorylation and that the phosphorylation is reversed during cytokinesis. MYPT phosphorylated either in vivo or in vitro in the mitosis-specific way showed higher binding to myosin II (two- to threefold) compared to MYPT from cells in interphase. Furthermore, the activity of myosin phosphatase was increased more than twice and it is suggested this reflected the increased affinity of myosin binding. These results indicate the presence of a unique positive regulatory mechanism for myosin phosphatase in cell division. The activation of myosin phosphatase during mitosis would enhance dephosphorylation of the myosin regulatory light chain, thereby leading to the disassembly of stress fibers during prophase. The mitosis-specific effect of phosphorylation is lost on exit from mitosis, and the resultant increase in myosin phosphorylation may act as a signal to activate cytokinesis.
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Affiliation(s)
- G Totsukawa
- Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08855, USA
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43
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Hirano M, Niiro N, Hirano K, Nishimura J, Hartshorne DJ, Kanaide H. Expression, subcellular localization, and cloning of the 130-kDa regulatory subunit of myosin phosphatase in porcine aortic endothelial cells. Biochem Biophys Res Commun 1999; 254:490-6. [PMID: 9918866 DOI: 10.1006/bbrc.1998.9973] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In endothelial cells in situ and in primary culture, immunoblot analysis revealed an expression of the 130-kDa subunit of myosin phosphatase, similar to the myosin phosphatase targeting subunit (MYPT) of smooth muscle. Screening of an endothelial cell cDNA library yielded a clone encoding an NH2-terminal fragment of 89.6 kDa, closely related to smooth muscle MYPT1. Two isoforms differing by a central insert of 56 residues were detected. In growing cells, MYPT1 was localized on stress fiber, but at confluence the localization pattern changed and MYPT1 was distributed close to the cell membrane and at cell-cell contacts. The membrane localization of MYPT1 suggested a target other than myosin and raised the possibility that MYPT1 may be involved in dephosphorylation of alternative substrate(s). These distinct mechanisms would also be dependent on the growth state of the endothelial cells, i.e., regulation of actin-myosin interactions in growing cells and an unknown function in cells at confluence.
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Affiliation(s)
- M Hirano
- Research Institute of Angiocardiology, Kyushu University, Fukuoka, 812-8582, Japan
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44
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Gunning P, Weinberger R, Jeffrey P, Hardeman E. Isoform sorting and the creation of intracellular compartments. Annu Rev Cell Dev Biol 1999; 14:339-72. [PMID: 9891787 DOI: 10.1146/annurev.cellbio.14.1.339] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The generation of isoforms via gene duplication and alternative splicing has been a valuable evolutionary tool for the creation of biological diversity. In addition to the formation of molecules with related but different functional characteristics, it is now apparent that isoforms can be segregated into different intracellular sites within the same cell. Sorting has been observed in a wide range of genes, including those encoding structural molecules, receptors, channels, enzymes, and signaling molecules. This results in the creation of intracellular compartments that (a) can be independently controlled and (b) have different functional properties. The sorting mechanisms are likely to operate at the level of both proteins and mRNAs. Isoform sorting may be an important consequence of the evolution of isoforms and is likely to have contributed to the diversity of functional properties within groups of isoforms.
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Affiliation(s)
- P Gunning
- Oncology Research Unit, New Children's Hospital, Parramatta, NSW, Australia.
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45
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Abstract
Myosin phosphorylation is an important mechanism in regulating contractile activity of smooth muscle. The level of myosin phosphorylation depends on the balance of two enzymes, myosin light chain kinase and myosin phosphatase. Recently it has been discovered that myosin phosphatase can be regulated and this renewed interest in characterization of the phosphatase. It is suggested that the myosin phosphatase is composed of three subunits: a catalytic subunit of type 1 phosphatase (delta isoform; PP1c delta); and two non-catalytic subunits, large and small (M20). The large subunit is thought to be a targeting subunit and is termed myosin phosphatase target subunit (MYPT). There are several isoforms of MYPT and two genes have been identified on human chromosomes 1 and 12. A dominant feature of MYPT is a series of ankyrin repeats at the N-terminal end of the molecule and these may be involved in binding to the catalytic subunit and to substrate, phosphorylated myosin. In addition, at the N-terminal fringe of the ankyrin motifs is a consensus PP1c binding motif. The function of the M20 subunit is not established but is known to bind to the C-terminal end of MYPT. Various interactions between subunits that might be relevant for the regulation of phosphatase activity are discussed.
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Affiliation(s)
- D J Hartshorne
- Muscle Biology Group, University of Arizona, Tucson 85721-0038, USA
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46
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Abstract
Cell motility is induced by many growth factors acting through cognate receptors with intrinsic tyrosine kinase activity (RPTK). However, most of the links between receptor activation and the biophysical processes of cell motility remain undeciphered. We have focused on the mechanisms by which the EGF receptor (EGFR) actuates fibroblast cell motility in an attempt to define this integrated process in one system. Our working model is that divergent, but interconnected pathways lead to the biophysical processes necessary for cell motility: cytoskeleton reorganization, membrane extension, formation of new adhesions to substratum, cell contraction, and release of adhesions at the rear. We postulate that for any given growth factor some of the pathways/processes will be actively signaled and rate-limiting, while others will be permissive due to background low-level activation. Certain couplings have been defined, such as PLCgamma and actin modifying proteins being involved in cytoskeletal reorganization and lamellipod extension and MEK being implicated in detachment from substratum. Others are suggested by complementary investigations in integrin-mediated motility, including rac in membrane protrusion, rho in new adhesions, myosin II motors in contraction, and calpain in detachment, but have yet to be placed in growth factor-induced motility. Our model postulates that many biochemical pathways will be shared between chemokinetic and haptokinetic motility but that select pathways will be activated only during RPTK-enhanced motility.
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Affiliation(s)
- A Wells
- Department of Pathology, University of Alabama at Birmingham, and Birmingham VA Medical Center, 35294-0007, USA.
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47
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Pettit EJ, Fay FS. Cytosolic free calcium and the cytoskeleton in the control of leukocyte chemotaxis. Physiol Rev 1998; 78:949-67. [PMID: 9790567 DOI: 10.1152/physrev.1998.78.4.949] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
In response to a chemotactic gradient, leukocytes extravasate and chemotax toward the site of pathogen invasion. Although fundamental in the control of many leukocyte functions, the role of cytosolic free Ca2+ in chemotaxis is unclear and has been the subject of debate. Before becoming motile, the cell assumes a polarized morphology, as a result of modulation of the cytoskeleton by G protein and kinase activation. This morphology may be reinforced during chemotaxis by the intracellular redistribution of Ca2+ stores, cytoskeletal constituents, and chemoattractant receptors. Restricted subcellular distributions of signaling molecules, such as Ca2+, Ca2+/calmodulin, diacylglycerol, and protein kinase C, may also play a role in some types of leukocyte. Chemotaxis is an essential function of most cells at some stage during their development, and a deeper understanding of the molecular signaling and structural components involved will enable rational design of therapeutic strategies in a wide variety of diseases.
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Affiliation(s)
- E J Pettit
- Biomedical Imaging Group, University of Massachusetts Medical Center, Worcester, USA
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48
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Kotani H, Ito M, Hamaguchi T, Ichikawa K, Nakano T, Shima H, Nagao M, Ohta N, Furuichi Y, Takahashi T, Umekawa H. The delta isoform of protein phosphatase type 1 is localized in nucleolus and dephosphorylates nucleolar phosphoproteins. Biochem Biophys Res Commun 1998; 249:292-6. [PMID: 9705875 DOI: 10.1006/bbrc.1998.9126] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The immunolocalization and substrates of protein phosphatases present in nucleolus were investigated using Swiss 3T3 cells and Novikoff hepatoma ascites cells. The protein phosphatase activity was detected in the extract of the isolated nucleoli and its activity was inhibited by okadaic acid with IC50 value of 160 nM. Immunoblotting assay indicated that PP1c delta but not PP1c alpha, PP1c gamma 1, and PP2Ac was localized in the isolated nucleoli. Confocal microscopy showed that PP1c delta was localized in nucleoli, nuclei, and cytosol, though the intensity of fluorescence at the nucleoli was stronger than that of the cytosol or nuclei. PP1c delta was co-localized with the major nucleolar phosphoprotein B23 at nucleoli. The phosphatase was capable of dephosphorylating several proteins in the nucleolus, including B23. The Km of PP1 for the recombinant B23.1, phosphorylated by endogenous kinase(s), was 3.5 microM. These results indicate that PP1c delta is the major serine/threonine phosphatase present in nucleolus and it dephosphorylates nucleolar phosphoproteins, including B23.
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Affiliation(s)
- H Kotani
- First Department of Internal Medicine, Mie University School of Medicine, Japan
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49
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Abstract
In muscle protein phosphatase 1 (PP1) is involved in growth factor signal transduction and metabolic regulations. Three isoforms of the catalytic subunit are found in mammalian cells (PP1alpha, PP1gamma1 and PP1delta), with potentially different functions. We investigated the changes in the PP1 isoforms in differentiating C2C12 myoblasts. Few hours after differentiation induction the soluble PP1 activity was reversibly increased, displaying a peak at 6h. This was due to activation mainly of PP1alpha, with no change in the immunodetected protein. A further indication of PP1alpha involvement came from the observation that electroporation of inactive PP1alpha into myoblasts induced a differentiation delay of at least 24h. Subsequently, starting from 9-12 h, the activities and protein levels of all the three soluble PP1 isoforms decreased, reaching a minimum around 48 h. By this time the cells had undergone morphological changes and myosin became immunodetectable. We conclude that PP1 may be involved in myoblast differentiation, based on: 1) its higher activity in myoblasts than in myocytes, 2) the reversible activation of soluble PP1alpha during the first 6h from differentiation induction, 3) the delay in differentiation onset following electroporation of inactive PP1alpha into myoblasts.
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Affiliation(s)
- M Tognarini
- Department of Biomedicine, University of Pisa, Italy
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50
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Villa-Moruzzi E, Tognarini M, Cecchini G, Marchisio PC. Protein phosphatase 1 delta is associated with focal adhesions. CELL ADHESION AND COMMUNICATION 1998; 5:297-305. [PMID: 9762470 DOI: 10.3109/15419069809040299] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
In all mammalian cells protein phosphatase-1 (PP1) exists in three isoforms, defined as alpha, gamma 1 and delta. Immunofluorescence studies with isoform-specific antibodies indicated that delta, but not alpha or gamma 1, is enriched at focal adhesions in HeLa cells, fibroblasts, endothelial cells and keratinocytes. This was confirmed also by interference reflection microscopy, which indicated that PP1 delta was in areas of tight adhesion of the membrane to the extracellular matrix at sites where the microfilament cytoskeleton is organized. In all the cell types so far considered the PP1 delta in focal adhesions represented only a small aliquot of the total PP1 delta, which was predominantly localized to the nucleus. The association of PP1 delta to focal adhesions was confirmed by the co-immunoprecipitation of PP1 delta with the focal adhesion kinase pp125FAK and with the alpha v integrin. Comparison between the amount of PP1 delta associated with focal adhesion proteins and that of PP1 delta recovered in an anti-PP1 delta immunoprecipitate confirmed that only a minor amount of the enzyme was associated with the focal adhesions. Since some focal adhesion proteins are phosphorylated on Ser/Thr, it is likely that PP1 delta may be involved in the regulation of focal adhesion functions and particularly in the signaling pathway generated by cell-substratum adhesion.
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