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Cho E, Lou HJ, Kuruvilla L, Calderwood DA, Turk BE. PPP6C negatively regulates oncogenic ERK signaling through dephosphorylation of MEK. Cell Rep 2021; 34:108928. [PMID: 33789117 PMCID: PMC8068315 DOI: 10.1016/j.celrep.2021.108928] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Revised: 01/26/2021] [Accepted: 03/10/2021] [Indexed: 12/21/2022] Open
Abstract
Flux through the RAF-MEK-ERK protein kinase cascade is shaped by phosphatases acting on the core components of the pathway. Despite being an established drug target and a hub for crosstalk regulation, little is known about dephosphorylation of MEK, the central kinase within the cascade. Here, we identify PPP6C, a phosphatase frequently mutated or downregulated in melanoma, as a major MEK phosphatase in cells exhibiting oncogenic ERK pathway activation. Recruitment of MEK to PPP6C occurs through an interaction with its associated regulatory subunits. Loss of PPP6C causes hyperphosphorylation of MEK at activating and crosstalk phosphorylation sites, promoting signaling through the ERK pathway and decreasing sensitivity to MEK inhibitors. Recurrent melanoma-associated PPP6C mutations cause MEK hyperphosphorylation, suggesting that they promote disease at least in part by activating the core oncogenic pathway driving melanoma. Collectively, our studies identify a key negative regulator of ERK signaling that may influence susceptibility to targeted cancer therapies. Through an shRNA screen, Cho et al. identify PPP6C as a phosphatase that inactivates the kinase MEK, sensitizing tumor cells to clinical MEK inhibitors. This study suggests that cancer-associated loss-of-function PPP6C mutations prevalent in melanoma serve to activate the core oncogenic RAF-MEK-ERK pathway that drives the disease.
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Affiliation(s)
- Eunice Cho
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06520, USA
| | - Hua Jane Lou
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06520, USA
| | - Leena Kuruvilla
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06520, USA
| | - David A Calderwood
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06520, USA; Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520, USA
| | - Benjamin E Turk
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06520, USA.
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2
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Ramos-Miguel A, Sánchez-Blázquez P, García-Sevilla JA. Effects of Gαi 2 and Gαz protein knockdown on alpha 2A-adrenergic and cannabinoid CB 1 receptor regulation of MEK-ERK and FADD pathways in mouse cerebral cortex. Pharmacol Rep 2021; 73:1122-1135. [PMID: 33641090 DOI: 10.1007/s43440-021-00240-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2020] [Revised: 02/05/2021] [Accepted: 02/18/2021] [Indexed: 11/29/2022]
Abstract
BACKGROUND Alpha2A-adrenergic (α2A-AR) and cannabinoid CB1 (CB1-R) receptors exert their functions modulating multiple signaling pathways, including MEK-ERK (extracellular signal-regulated kinases) and FADD (Fas-associated protein with death domain) cascades. These molecules are relevant in finding biased agonists with fewer side effects, but the mechanisms involving their modulations by α2A-AR- and CB1-R in vivo are unclear. This study investigated the roles of Gαi2 and Gαz proteins in mediating α2A-AR- and CB1-R-induced alterations of MEK-ERK and FADD phosphorylation (p-) in mouse brain cortex. METHODS Gαi2 or Gαz protein knockdown was induced in mice with selective antisense oligodeoxinucleotides (ODNs; 3 nmol/day, 5 days) prior to UK-14,304 (UK or brimonidine; 1 mg/kg) or WIN55212-2 (WIN; 8 mg/kg) acute treatments. Inactivated (p-T286) MEK1, activated (p-S217/221) MEK1/2, activated (p-T202/Y204) ERK1/2, p-S191 FADD, and the corresponding total forms of these proteins were quantified by immunoblotting. RESULTS Increased (+ 88%) p-T286 MEK1 cortical density, with a concomitant reduction (-43%) of activated ERK was observed in UK-treated mice. Both effects were attenuated by Gαi2 or Gαz antisense ODNs. Contrastingly, WIN induced Gαi2- and Gαz-independent upregulations of p-T286 MEK1 (+ 63%), p-S217/221 MEK1/2 (+ 86%), and activated ERK (+ 111%) in brain. Pro-apoptotic FADD was downregulated (- 34 to 39%) following UK and WIN administration, whereas the neuroprotective p-S191 FADD was increased (+ 74%) in WIN-treated mice only. None of these latter effects required from Gαi2 or Gαz protein integrity. CONCLUSION The results indicate that α2A-AR (UK), but not CB1-R (WIN), agonists use Gαi2 and Gαz proteins to modulate MEK-ERK, but not FADD, pathway in mouse brain cortex.
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Affiliation(s)
- Alfredo Ramos-Miguel
- Department of Pharmacology, University of the Basque Country (EHU/UPV), Barrio Sarriena s/n, ES48940, Leioa, Biscay, Spain. .,Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Madrid, Spain. .,Department of Psychiatry, University of British Columbia, Vancouver, BC, Canada.
| | | | - Jesús A García-Sevilla
- Laboratori de Neurofarmacologia, Institut Universitari d'Investigació en Ciències de la Salut (IUNICS), Universitat de les Illes Balears, Palma de Mallorca, Spain
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3
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Invergo BM, Petursson B, Akhtar N, Bradley D, Giudice G, Hijazi M, Cutillas P, Petsalaki E, Beltrao P. Prediction of Signed Protein Kinase Regulatory Circuits. Cell Syst 2020; 10:384-396.e9. [DOI: 10.1016/j.cels.2020.04.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 01/24/2020] [Accepted: 04/20/2020] [Indexed: 01/18/2023]
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4
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Zou J, Lei T, Guo P, Yu J, Xu Q, Luo Y, Ke R, Huang D. Mechanisms shaping the role of ERK1/2 in cellular senescence (Review). Mol Med Rep 2018; 19:759-770. [PMID: 30535440 PMCID: PMC6323238 DOI: 10.3892/mmr.2018.9712] [Citation(s) in RCA: 56] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2018] [Accepted: 10/10/2018] [Indexed: 01/19/2023] Open
Abstract
Senescence is a result of cellular stress and is a potential mechanism for regulating cancer. As a member of the mitogen-activated protein kinase family, ERK1/2 (extracellular signal-regulated protein kinase) has an important role in delivering extracellular signals to the nucleus, and these signals regulate the cell cycle, cell proliferation and cell development. Previous studies demonstrated that ERK1/2 is closely associated with cell aging; however other previous studies suggested that ERK1/2 exerts an opposite effect on aging models and target proteins, even within the same cell model. Recent studies demonstrated that the effect of ERK1/2 on aging is likely associated with its target proteins and regulators, negative feedback loops, phosphorylated ERK1/2 factors and ERK1/2 translocation from the cytoplasm to the nucleus. The present review aims to examine the mechanism of ERK1/2 and discuss its role in cellular outcomes and novel drug development.
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Affiliation(s)
- Junrong Zou
- Research Institute of Digestive Diseases, Department of Gastroenterology, The First Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Tingting Lei
- Research Institute of Digestive Diseases, Department of Gastroenterology, The First Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Pei Guo
- Department of Pathology, Shenzhen Hospital of Southern Medical University, Shenzhen, Guangdong 518110, P.R. China
| | - Jason Yu
- Department of Pharmacology, Boston University School of Medicine, Boston, MA 02118, USA
| | - Qichao Xu
- Department of Pharmacology, The People's Hospital of Xinyu City, Xinyu, Jiangxi 338025, P.R. China
| | - Yunfei Luo
- Jiangxi Provincial Key Laboratory of Tumor Pathogenesis and Molecular Pathology, Department of Pathophysiology, School of Basic Medical Sciences, Medical College of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Rong Ke
- Department of Surgery, University of Illinois at Chicago College of Medicine, Chicago, IL 60612, USA
| | - Deqiang Huang
- Research Institute of Digestive Diseases, Department of Gastroenterology, The First Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
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5
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Kubin T, Cetinkaya A, Schönburg M, Beiras-Fernandez A, Walther T, Richter M. The MEK1 inhibitors UO126 and PD98059 block PDGF-AB induced phosphorylation of threonine 292 in porcine smooth muscle cells. Cytokine 2017; 95:51-54. [PMID: 28235676 DOI: 10.1016/j.cyto.2017.02.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2016] [Revised: 01/22/2017] [Accepted: 02/06/2017] [Indexed: 11/30/2022]
Abstract
PDGF-AB and FGF-2 (GFs) induce smooth muscle cell (SMC) proliferation which is indispensible for arteriogenesis. While there is common agreement that GFs stimulate SMC proliferation through phosphorylation (P-) of MEK1/2 at Ser218/222, we previously demonstrated that the MEK inhibitors PD98059 and UO126 did not inhibit P-Ser218/222 as originally proposed but caused strong hyperphosphorylation. Here, we demonstrate that GFs increased phosphorylation of MEK1 at Thr292 while UO126 and PD98059 blocked this phosphorylation. This was again surprising since phosphorylation of Thr292 is regarded as a negative feedback loop. Our findings suggest that inhibition of Thr292 phosphorylation in combination with hyperphosphorylation of Ser218/222 serves as an "off" switch of SMC proliferation and potentially of arteriogenesis.
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Affiliation(s)
- Thomas Kubin
- Department of Cardiac Surgery, Kerckhoff-Clinic, Benekestrasse 2-8, Bad Nauheim 61231, Germany; Res Group Vascular Genomics, Kerckhoff Clinic, Benekestrasse 2-8, Bad Nauheim 61231, Germany.
| | - Ayse Cetinkaya
- Department of Cardiac Surgery, Kerckhoff-Clinic, Benekestrasse 2-8, Bad Nauheim 61231, Germany
| | - Markus Schönburg
- Department of Cardiac Surgery, Kerckhoff-Clinic, Benekestrasse 2-8, Bad Nauheim 61231, Germany
| | - Andres Beiras-Fernandez
- Department of Thoracic and Cardiovascular Surgery, Johann-Wolfgang-Goethe University Hospital, Theodor-Stem-Kai 7, 60590 Frankfurt/Main, Germany
| | - Thomas Walther
- Department of Cardiac Surgery, Kerckhoff-Clinic, Benekestrasse 2-8, Bad Nauheim 61231, Germany
| | - Manfred Richter
- Department of Cardiac Surgery, Kerckhoff-Clinic, Benekestrasse 2-8, Bad Nauheim 61231, Germany.
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6
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Lake D, Corrêa SAL, Müller J. Negative feedback regulation of the ERK1/2 MAPK pathway. Cell Mol Life Sci 2016; 73:4397-4413. [PMID: 27342992 PMCID: PMC5075022 DOI: 10.1007/s00018-016-2297-8] [Citation(s) in RCA: 351] [Impact Index Per Article: 43.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Revised: 06/16/2016] [Accepted: 06/17/2016] [Indexed: 01/04/2023]
Abstract
The extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinase (MAPK) signalling pathway regulates many cellular functions, including proliferation, differentiation, and transformation. To reliably convert external stimuli into specific cellular responses and to adapt to environmental circumstances, the pathway must be integrated into the overall signalling activity of the cell. Multiple mechanisms have evolved to perform this role. In this review, we will focus on negative feedback mechanisms and examine how they shape ERK1/2 MAPK signalling. We will first discuss the extensive number of negative feedback loops targeting the different components of the ERK1/2 MAPK cascade, specifically the direct posttranslational modification of pathway components by downstream protein kinases and the induction of de novo gene synthesis of specific pathway inhibitors. We will then evaluate how negative feedback modulates the spatiotemporal signalling dynamics of the ERK1/2 pathway regarding signalling amplitude and duration as well as subcellular localisation. Aberrant ERK1/2 activation results in deregulated proliferation and malignant transformation in model systems and is commonly observed in human tumours. Inhibition of the ERK1/2 pathway thus represents an attractive target for the treatment of malignant tumours with increased ERK1/2 activity. We will, therefore, discuss the effect of ERK1/2 MAPK feedback regulation on cancer treatment and how it contributes to reduced clinical efficacy of therapeutic agents and the development of drug resistance.
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Affiliation(s)
- David Lake
- Warwick Medical School, University of Warwick, Coventry, UK
| | - Sonia A L Corrêa
- School of Life Sciences, University of Warwick, Coventry, UK
- Faculty of Life Sciences, University of Bradford, Bradford, UK
| | - Jürgen Müller
- Warwick Medical School, University of Warwick, Coventry, UK.
- Aston Medical Research Institute, Aston Medical School, Aston University, Birmingham, B4 7ET, UK.
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7
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Sharma SB, Ruppert JM. MicroRNA-Based Therapeutic Strategies for Targeting Mutant and Wild Type RAS in Cancer. Drug Dev Res 2015; 76:328-42. [PMID: 26284568 DOI: 10.1002/ddr.21270] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
MicroRNAs (miRs) have been causally implicated in the progression and development of a wide variety of cancers. miRs modulate the activity of key cell signaling networks by regulating the translation of pathway component proteins. Thus, the pharmacological targeting of miRs that regulate cancer cell signaling networks, either by promoting (using miR-supplementation) or by suppressing (using antisense oligonucleotide-based strategies) miR activity is an area of intense research. The RAS-extracellular signal regulated kinase (ERK) pathway represents a major miR-regulated signaling network that endows cells with some of the classical hallmarks of cancer, and is often inappropriately activated in malignancies by somatic genetic alteration through point mutation or alteration of gene copy number. In addition, recent progress indicates that many tumors may be deficient in GTPase activating proteins (GAPs) due to the collaborative action of oncogenic miRs. Recent studies also suggest that in tumors harboring a mutant RAS allele there is a critical role for wild type RAS proteins in determining overall RAS-ERK pathway activity. Together, these two advances comprise a new opportunity for therapeutic intervention. In this review, we evaluate miR-based therapeutic strategies for modulating RAS-ERK signaling in cancers; in particular for more direct modulation of RAS-GTP levels, with the potential to complement current strategies to yield more durable treatment responses. To this end, we discuss the potential for miR-based therapies focused on three prominent miRs including the pan-RAS regulator let-7 and the GAP regulator comprised of miR-206 and miR-21 (miR-206/21).
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Affiliation(s)
- Sriganesh B Sharma
- Department of Biochemistry, West Virginia University, Morgantown, WV, 26506, USA.,Program in Cancer Cell Biology, West Virginia University, Morgantown, WV, 26506, USA
| | - John Michael Ruppert
- Department of Biochemistry, West Virginia University, Morgantown, WV, 26506, USA.,The Mary Babb Randolph Cancer Center, West Virginia University, Morgantown, WV, 26506, USA
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8
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Pike T, Widberg C, Goodall A, Payne E, Giles N, Hancock J, Gabrielli B. Truncated MEK1 is required for transient activation of MAPK signalling in G2 phase cells. Cell Signal 2013; 25:1423-8. [DOI: 10.1016/j.cellsig.2013.03.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Accepted: 03/16/2013] [Indexed: 02/08/2023]
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9
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Bromberg-White JL, Andersen NJ, Duesbery NS. MEK genomics in development and disease. Brief Funct Genomics 2012; 11:300-10. [PMID: 22753777 PMCID: PMC3398258 DOI: 10.1093/bfgp/els022] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The mitogen-activated protein kinase kinases (the MAPK/ERK kinases; MKKs or MEKs) and their downstream substrates, the extracellular-regulated kinases have been intensively studied for their roles in development and disease. Until recently, it had been assumed any mutation affecting their function would have lethal consequences. However, the identification of MEK1 and MEK2 mutations in developmental syndromes as well as chemotherapy-resistant tumors, and the discovery of genomic variants in MEK1 and MEK2 have led to the realization the extent of genomic variation associated with MEKs is much greater than had been appreciated. In this review, we will discuss these recent advances, relating them to what is currently understood about the structure and function of MEKs, and describe how they change our understanding of the role of MEKs in development and disease.
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Affiliation(s)
- Jennifer L Bromberg-White
- Laboratory of Cancer and Developmental Cell Biology, Van Andel Research Institute, 333 Bostwick Avenue NE, Grand Rapids, MI 49503, USA
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10
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Crosstalk between cdk5 and MEK-ERK signalling upon opioid receptor stimulation leads to upregulation of activator p25 and MEK1 inhibition in rat brain. Neuroscience 2012; 215:17-30. [PMID: 22537847 DOI: 10.1016/j.neuroscience.2012.04.035] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 04/03/2012] [Accepted: 04/16/2012] [Indexed: 11/21/2022]
Abstract
Cyclin-dependent kinase 5 (cdk5) participates in opioid receptor signalling through complex molecular mechanisms. The acute effects of selective μ-(fentanyl) and δ-(SNC-80) opioid receptor agonists, as well as the chronic effects of morphine (the prototypic opiate agonist mainly acting at μ-receptors), modulating cdk5 and activators p35/p25 and their interactions with neurotoxic/apoptotic factors, dopamine- and cAMP-regulated phosphoprotein of 32kDa (DARPP-32) and extracellular signal-regulated kinase (ERK) were quantified (Western Blot analyses) in the rat corpus striatum and/or cerebral cortex. To assess the involved mechanisms, MDL28170 was used to inhibit calpain activity and SL327 to disrupt MEK (ERK kinase)-ERK activation. Acute fentanyl (0.1mg/kg) and SNC-80 (10mg/kg) induced rapid (7-60 min) 2- to 4-fold increases of p25 content, without induction of cdk5/p25 pro-apoptotic c-Jun NH(2)-terminal protein kinase or aberrant cleavage of poly(ADP-ribose)-polymerase-1, a hallmark of apoptosis. In contrast, fentanyl and SNC-80 stimulated cdk5-mediated p-Thr75 DARPP-32 (+116-166%; PKA inhibition) and p-Thr286 MEK1 (+21-82%; MEK inactivation), and this latter effect resulted in uncoupling of MEK to ERK signals. Calpain inhibition with MDL28170 (cleavage of p35 to p25) attenuated fentanyl-induced p25 accumulation (-57%), but not the stimulation of p-Thr286 MEK1 or p-Thr75 DARPP-32. MEK-ERK inhibition with SL327 fully prevented fentanyl-induced p25 upregulation. Notably, chronic morphine treatment (10-100mg/kg for 6 days) also increased p25 content and p25/p35 ratio (and activated/inactivated MEK1) in rat brain cortex, which indicated that p25 upregulation persisted under the sustained stimulation of μ-opioid receptors. The results demonstrate that the acute stimulation of opioid receptors leads to upregulation of p25 activator through a MEK-ERK and calpain-dependent pathway, and to disruption of MEK-ERK signalling by a cdk5/p35-induced MEK1 inhibition. Moreover, the effects induced by the sustained stimulation of μ-receptors with morphine suggest the participation of cdk5/p25 complex in opiate-induced long-term neuroplasticity.
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11
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MEK1/2 dual-specificity protein kinases: Structure and regulation. Biochem Biophys Res Commun 2012; 417:5-10. [DOI: 10.1016/j.bbrc.2011.11.145] [Citation(s) in RCA: 178] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2011] [Accepted: 11/30/2011] [Indexed: 11/17/2022]
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12
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Sicard A, Semblat JP, Doerig C, Hamelin R, Moniatte M, Dorin-Semblat D, Spicer JA, Srivastava A, Retzlaff S, Heussler V, Waters AP, Doerig C. Activation of a PAK-MEK signalling pathway in malaria parasite-infected erythrocytes. Cell Microbiol 2011; 13:836-45. [PMID: 21371233 PMCID: PMC3123749 DOI: 10.1111/j.1462-5822.2011.01582.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Merozoites of malaria parasites invade red blood cells (RBCs), where they multiply by schizogony, undergoing development through ring, trophozoite and schizont stages that are responsible for malaria pathogenesis. Here, we report that a protein kinase-mediated signalling pathway involving host RBC PAK1 and MEK1, which do not have orthologues in the Plasmodium kinome, is selectively stimulated in Plasmodium falciparum-infected (versus uninfected) RBCs, as determined by the use of phospho-specific antibodies directed against the activated forms of these enzymes. Pharmacological interference with host MEK and PAK function using highly specific allosteric inhibitors in their known cellular IC50 ranges results in parasite death. Furthermore, MEK inhibitors have parasiticidal effects in vitro on hepatocyte and erythrocyte stages of the rodent malaria parasite Plasmodium berghei, indicating conservation of this subversive strategy in malaria parasites. These findings have profound implications for the development of novel strategies for antimalarial chemotherapy.
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Affiliation(s)
- Audrey Sicard
- INSERM U609/Inserm-EPFL Joint Laboratory,Global Health Institute, Lausanne, Switzerland
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Keshet Y, Seger R. The MAP kinase signaling cascades: a system of hundreds of components regulates a diverse array of physiological functions. Methods Mol Biol 2010; 661:3-38. [PMID: 20811974 DOI: 10.1007/978-1-60761-795-2_1] [Citation(s) in RCA: 426] [Impact Index Per Article: 30.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Sequential activation of kinases within the mitogen-activated protein (MAP) kinase (MAPK) cascades is a common, and evolutionary-conserved mechanism of signal transduction. Four MAPK cascades have been identified in the last 20 years and those are usually named according to the MAPK components that are the central building blocks of each of the cascades. These are the extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-Terminal kinase (JNK), p38, and ERK5 cascades. Each of these cascades consists of a core module of three tiers of protein kinases termed MAPK, MAPKK, and MAP3K, and often two additional tiers, the upstream MAP4K and the downstream MAPKAPK, which can complete five tiers of each cascade in certain cell lines or stimulations. The transmission of the signal via each cascade is mediated by sequential phosphorylation and activation of the components in the sequential tiers. These cascades cooperate in transmitting various extracellular signals and thus control a large number of distinct and even opposing cellular processes such as proliferation, differentiation, survival, development, stress response, and apoptosis. One way by which the specificity of each cascade is regulated is through the existence of several distinct components in each tier of the different cascades. About 70 genes, which are each translated to several alternatively spliced isoforms, encode the entire MAPK system, and allow the wide array of cascade's functions. These components, their regulation, as well as their involvement together with other mechanisms in the determination of signaling specificity by the MAPK cascade is described in this review. Mis-regulation of the MAPKs signals usually leads to diseases such as cancer and diabetes; therefore, studying the mechanisms of specificity-determination may lead to better understanding of these signaling-related diseases.
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Affiliation(s)
- Yonat Keshet
- Department of Biological Regulation, The Weizmann Institute of Science, Rehovot, Israel
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14
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A Mek1–Mek2 heterodimer determines the strength and duration of the Erk signal. Nat Struct Mol Biol 2009; 16:294-303. [DOI: 10.1038/nsmb.1564] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2008] [Accepted: 01/23/2009] [Indexed: 01/07/2023]
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15
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Zhang HY, Zhang X, Chen X, Thomas D, Hormi-Carver K, Elder F, Spechler SJ, Souza RF. Differences in activity and phosphorylation of MAPK enzymes in esophageal squamous cells of GERD patients with and without Barrett's esophagus. Am J Physiol Gastrointest Liver Physiol 2008; 295:G470-8. [PMID: 18617556 PMCID: PMC2536777 DOI: 10.1152/ajpgi.90262.2008] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We hypothesized that, in esophageal squamous epithelial cells, there are differences among individuals in the signal transduction pathways activated by acid reflux that might underlie the development of Barrett's esophagus. To explore that hypothesis, we immortalized nonneoplastic, esophageal squamous cells from patients with gastroesophageal reflux disease (GERD) with (NES-B3T) and without (NES-G2T) Barrett's esophagus and used those cells to study acid effects on MAPK proteins. During endoscopy in patients with GERD with and without Barrett's esophagus, we took biopsy specimens from the distal squamous esophagus to study MAPK proteins before and after esophageal perfusion with 0.1 N HCl. We used immunoblotting and Western blotting to study MEK1/2 phosphorylation at two activating sites (serines 217/221), MEK1 phosphorylation at an inhibitory site (threonine 286), and MEK1/2 activity. After acid exposure, both cell lines exhibited increased MEK1/2 phosphorylation at the activating sites; the NES-B3T cells had higher levels of MEK1 phosphorylation at the inhibitory site, however, and only the NES-G2T cells showed an acid-induced increase in MEK1/2 activity. Similarly, in the squamous epithelium of patients with GERD with and without Barrett's esophagus, acid perfusion increased MEK1/2 phosphorylation at the activating sites in both patient groups; the Barrett's patients had higher levels of MEK1 phosphorylation at the inhibitory site, however, and only the patients without Barrett's demonstrated an acid-induced increase in ERK1/2 phosphorylation. In esophageal squamous cell lines and biopsies from patients with GERD with and without Barrett's esophagus, we have found differences in MAPK pathways activated by acid exposure. We speculate that these differences might underlie the development of Barrett's metaplasia.
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Affiliation(s)
- Hui Ying Zhang
- Departments of Medicine and Pathology, Veterans Affairs North Texas Health Care System and the University of Texas Southwestern Medical School; and Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
| | - Xi Zhang
- Departments of Medicine and Pathology, Veterans Affairs North Texas Health Care System and the University of Texas Southwestern Medical School; and Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
| | - Xi Chen
- Departments of Medicine and Pathology, Veterans Affairs North Texas Health Care System and the University of Texas Southwestern Medical School; and Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
| | - Deena Thomas
- Departments of Medicine and Pathology, Veterans Affairs North Texas Health Care System and the University of Texas Southwestern Medical School; and Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
| | - Kathy Hormi-Carver
- Departments of Medicine and Pathology, Veterans Affairs North Texas Health Care System and the University of Texas Southwestern Medical School; and Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
| | - Frederick Elder
- Departments of Medicine and Pathology, Veterans Affairs North Texas Health Care System and the University of Texas Southwestern Medical School; and Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
| | - Stuart J. Spechler
- Departments of Medicine and Pathology, Veterans Affairs North Texas Health Care System and the University of Texas Southwestern Medical School; and Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
| | - Rhonda F. Souza
- Departments of Medicine and Pathology, Veterans Affairs North Texas Health Care System and the University of Texas Southwestern Medical School; and Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
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16
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Sturgill TW. MAP kinase: it's been longer than fifteen minutes. Biochem Biophys Res Commun 2008; 371:1-4. [PMID: 18406346 DOI: 10.1016/j.bbrc.2008.04.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2008] [Accepted: 04/02/2008] [Indexed: 10/22/2022]
Abstract
The review highlights evidence for different functions in the cell cycle of the two MAP kinase kinases, MEK1 and MEK2, and the two MAP kinases, ERK1 and ERK2. Functional differences may explain why instances of cell cycle arrest can be MEK1 or MEK2 dependent.
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Affiliation(s)
- Thomas W Sturgill
- Department of Pharmacology, University of Virginia, 1300 Jefferson Park Avenue, Charlottesville, VA 22908, USA.
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17
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De Boer L, Oakes V, Beamish H, Giles N, Stevens F, Somodevilla-Torres M, Desouza C, Gabrielli B. Cyclin A/cdk2 coordinates centrosomal and nuclear mitotic events. Oncogene 2008; 27:4261-8. [PMID: 18372919 DOI: 10.1038/onc.2008.74] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Cyclin A/cdk2 has a role in progression through S phase, and a large pool is also activated in G2 phase. Here we report that this G2 phase pool regulates the timing of progression into mitosis. Knock down of cyclin A by siRNA or addition of a specific cdk2 small molecule inhibitor delayed entry into mitosis by delaying cells in G2 phase. The G2 phase-delayed cells contained elevated levels of inactive cyclin B/cdk1. However, increased microtubule nucleation at the centrosomes was observed, and the centrosomes stained for markers of cyclin B/cdk1 activity. Both microtubule nucleation at the centrosomes and the phosphoprotein markers were lost with short-term treatment of the cdk1/2 inhibitor roscovitine but not the Mek1/2 inhibitor U0126. Cyclin A/cdk2 localized at the centrosomes in late G2 phase after separation of the centrosomes but before the start of prophase. Thus G2 phase cyclin A/cdk2 controls the timing of entry into mitosis by controlling the subsequent activation of cyclin B/cdk1, but also has an unexpected role in coordinating the activation of cyclin B/cdk1 at the centrosome and in the nucleus.
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Affiliation(s)
- L De Boer
- Cancer Biology Program, Diamantina Institute for Cancer, Immunology and Metabolic Medicine, University of Queensland, Princess Alexandra Hospital, Brisbane, Queensland, Australia
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18
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Shaul YD, Seger R. The MEK/ERK cascade: from signaling specificity to diverse functions. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1773:1213-26. [PMID: 17112607 DOI: 10.1016/j.bbamcr.2006.10.005] [Citation(s) in RCA: 671] [Impact Index Per Article: 37.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Received: 08/09/2006] [Revised: 10/10/2006] [Accepted: 10/13/2006] [Indexed: 11/19/2022]
Abstract
The ERK signaling cascade is a central MAPK pathway that plays a role in the regulation of various cellular processes such as proliferation, differentiation, development, learning, survival and, under some conditions, also apoptosis. The ability of this cascade to regulate so many distinct, and even opposing, cellular processes, raises the question of signaling specificity determination by this cascade. Here we describe mechanisms that cooperate to direct MEK-ERK signals to their appropriate downstream destinations. These include duration and strength of the signals, interaction with specific scaffolds, changes in subcellular localization, crosstalk with other signaling pathways, and presence of multiple components with distinct functions in each tier of the cascade. Since many of the mechanisms do not function properly in cancer cells, understanding them may shed light not only on the regulation of normal cell proliferation, but also on mechanisms of oncogenic transformation.
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Affiliation(s)
- Yoav D Shaul
- Department of Biological Regulation, The Weizmann Institute of Science, 76100 Rehovot, Israel
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19
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Marchetti S, Gimond C, Roux D, Gothié E, Pouysségur J, Pagès G. Inducible expression of a MAP kinase phosphatase-3-GFP chimera specifically blunts fibroblast growth and ras-dependent tumor formation in nude mice. J Cell Physiol 2004; 199:441-50. [PMID: 15095291 DOI: 10.1002/jcp.10465] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The p42/p44 mitogen activated protein kinase (MAPK) pathway participates in a wide range of cellular programs including proliferation, migration, differentiation, and survival. Specific pharmacological inhibitors, like PD98059 and U0126, are often used to inhibit p42/p44 MAPK signaling. However, these inhibitors are not appropriate to study the function of these kinases in whole organisms. We thus developed an inducible system designed to inhibit p42/p44 MAPK activity through the expression of a phosphatase specific for these two kinases, the MAPK phosphatase 3 (MKP-3). A fibroblast cell line was established in which MKP-3 expression is controlled by tetracycline. Tetracycline-induced MKP-3 resulted in partial de-phosphorylation of p42/p44 MAPKs in serum-stimulated cells. However, we could improve MKP-3 stability and thereby the rate of MAPK de-phosphorylation, when the C-terminal end of MKP-3 was fused to the green fluorescent protein (GFP). Importantly, the fusion of GFP to MKP-3 did not alter the specificity of the phosphatase towards its MAPK substrates. We further show that conditional expression of MKP-3-GFP in this fibroblast cell line results in the inhibition of: (a) the phosphorylation of the p42/p44 MAPK substrates Elk1 and HIF-1alpha, (b) vascular endothelial growth factor (VEGF), cyclin D1, and c-fos gene transcription in response to MAPK pathway activation, and (c) cell proliferation. Finally, the MKP-3-GFP inducible cell line was transformed by Ha-ras and injected into nude mice. Treatment of mice with the tetracycline analog doxycycline resulted in a large delay in tumor emergence and growth as compared to the untreated control group, indicating that MKP-3-GFP activity is maintained in vivo. Altogether, these results show that inducible expression of MKP-3-GFP constitutes a valuable tool to study the role of p42/p44 MAPKs in various cellular responses in both cultured cell and animal models, a tool that may also be used to block unwanted cell growth in pathological conditions.
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Affiliation(s)
- S Marchetti
- Institute of Signaling, Developmental Biology and Cancer Research, Nice, France
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20
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Harding A, Giles N, Burgess A, Hancock JF, Gabrielli BG. Mechanism of mitosis-specific activation of MEK1. J Biol Chem 2003; 278:16747-54. [PMID: 12609978 DOI: 10.1074/jbc.m301015200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Activation of cyclin B-Cdc2 is an absolute requirement for entry into mitosis, but other protein kinase pathways that also have mitotic functions are activated during G(2)/M progression. The MAPK cascade has well established roles in entry and exit from mitosis in Xenopus, but relatively little is known about the regulation and function of this pathway in mammalian mitosis. Here we report a detailed analysis of the activity of all components of the Ras/Raf/MEK/ERK pathway in HeLa cells during normal G(2)/M. The focus of this pathway is the dramatic activation of an endomembrane-associated MEK1 without the corresponding activation of the MEK substrate ERK. This is because of the uncoupling of MEK1 activation from ERK activation. The mechanism of this uncoupling involves the cyclin B-Cdc2-dependent proteolytic cleavage of the N-terminal ERK-binding domain of MEK1 and the phosphorylation of Thr(286). These results demonstrate that cyclin B-Cdc2 activity regulates signaling through the MAPK pathway in mitosis.
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Affiliation(s)
- Angus Harding
- Cancer Biology Program, Centre for Immunology and Cancer Research, University of Queensland, Queensland 4102, Australia
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21
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Gopalbhai K, Jansen G, Beauregard G, Whiteway M, Dumas F, Wu C, Meloche S. Negative regulation of MAPKK by phosphorylation of a conserved serine residue equivalent to Ser212 of MEK1. J Biol Chem 2003; 278:8118-25. [PMID: 12506122 DOI: 10.1074/jbc.m211870200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The MAPKKs MEK1 and MEK2 are activated by phosphorylation, but little is known about how these enzymes are inactivated. Here, we show that MEK1 is phosphorylated in vivo at Ser(212), a residue conserved among all MAPKK family members. Mutation of Ser(212) to alanine enhanced the basal activity of MEK1, whereas the phosphomimetic aspartate mutation completely suppressed the activation of both wild-type MEK1 and the constitutively activated MEK1(S218D/S222D) mutant. Phosphorylation of Ser(212) did not interfere with activating phosphorylation of MEK1 at Ser(218)/Ser(222) or with binding to ERK2 substrate. Importantly, mimicking phosphorylation of the equivalent Ser(212) residue of the yeast MAPKKs Pbs2p and Ste7p similarly abrogated their biological function. Our findings suggest that Ser(212) phosphorylation represents an evolutionarily conserved mechanism involved in the negative regulation of MAPKKs.
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Affiliation(s)
- Kailesh Gopalbhai
- Institut de Recherches Cliniques de Montréal and the Department of Pharmacology, Université de Montréal, Quebec H2W 1R7, Canada
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22
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Shapiro P. Ras-MAP kinase signaling pathways and control of cell proliferation: relevance to cancer therapy. Crit Rev Clin Lab Sci 2002; 39:285-330. [PMID: 12385501 DOI: 10.1080/10408360290795538] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The mitogen-activated protein (MAP) kinase pathways represent several families of signal transduction cascades that mediate information provided by extracellular stimuli. MAP kinase pathways regulate a wide range of physiological responses, including cell proliferation, apoptosis, cell differentiation, and tissue development. Constitutive activation of MAP kinase proteins in experimental models has been shown to cause cell transformation and is implicated in tumorigenesis. Of clinical importance, MAP kinase pathways are regulated by Ras G-proteins, which are found to be mutated and constitutively active in approximately 30% of all human cancers. Thus, a major goal in the treatment of cancer is the development of specific compounds that target Ras and critical downstream signaling proteins responsible for uncontrolled cell growth. A variety of biochemical, molecular, and structural approaches have been used to develop drug compounds that target signaling proteins important for MAP kinase pathway activation. These compounds have been useful tools for identifying the mechanisms of MAP kinase pathway signaling and hold promise for clinical use. This review will present an overview of the major proteins involved in Ras and MAP kinase signaling pathways and their function in regulating cell cycle events and proliferation. In addition, some of the relevant compounds that have been developed to inhibit the activities of these proteins and MAP kinase signaling are discussed.
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Affiliation(s)
- Paul Shapiro
- Department of Pharmaceutical Sciences, University of Maryland-School of Pharmacy, Baltimore 21201, USA
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23
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Milanini-Mongiat J, Pouysségur J, Pagès G. Identification of two Sp1 phosphorylation sites for p42/p44 mitogen-activated protein kinases: their implication in vascular endothelial growth factor gene transcription. J Biol Chem 2002; 277:20631-9. [PMID: 11904305 DOI: 10.1074/jbc.m201753200] [Citation(s) in RCA: 248] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Sp1 regulates activation of many genes implicated in tumor growth and cell cycle progression. We have previously demonstrated its implication in the up-regulation of vascular endothelial growth factor (VEGF) gene transcription following growth factor stimulation of quiescent cells, a situation where p42/p44 mitogen-activate protein kinase (MAPK) activity is dramatically increased. Here we show that p42/p44 MAPK directly phosphorylates Sp1 on threonines 453 and 739 both in vitro and in vivo. Mutation of these sites to alanines decreases by half the MAPK-dependent transcriptional activity of Sp1, in the context of the VEGF promoter, in SL2 Drosophila cells devoid of the endogenous Sp1 protein. Moreover, inducible overexpression of the (T453A,T739A) Sp1 double mutant compromises MAPK-driven VEGF mRNA transcription in fibroblasts. These results highlight Sp1 as a key molecular link between elevated activation of the Ras >> p42/p44MAPK signaling pathway and increased VEGF expression, two major steps deregulated in tumor cells.
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Affiliation(s)
- Julie Milanini-Mongiat
- Institute of Signalling, Developmental Biology and Cancer Research, Centre Antoine Lacassagne, 33 avenue de Valombrose, 06189 Nice cedex 2, France
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24
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Coles LC, Shaw PE. PAK1 primes MEK1 for phosphorylation by Raf-1 kinase during cross-cascade activation of the ERK pathway. Oncogene 2002; 21:2236-44. [PMID: 11948406 DOI: 10.1038/sj.onc.1205302] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2001] [Revised: 01/02/2002] [Accepted: 01/08/2002] [Indexed: 11/08/2022]
Abstract
The serine/threonine kinase Raf-1 acts downstream of Ras in the MAPK pathway leading to ERK activation in response to mitogens. Raf-1 has oncogenic potential, but is normally controlled by a complex interplay of inhibitory and activating mechanisms. Although Raf-1 is phosphorylated in unstimulated cells, mitogens cause its membrane recruitment by Ras and subsequent phosphorylation on additional sites. Some of these events modulate Raf-1 kinase activity while others determine interactions with other proteins. These changes regulate the ability of Raf-1 to phosphorylate its downstream targets MEK1 and MEK2. Rho family small G proteins act synergistically with Raf-1 to stimulate the ERK pathway by a cross-cascade mechanism that enhances MEK phosphorylation by Raf-1. Here we show that both Raf-1 and MEK1 are phosphorylated by PAK1 and that mutations at PAK1 phosphorylation sites in either protein prevent cross-cascade activation. In contrast, MEK1 activation by constitutively-active Raf-1 is refractory to mutations at PAK1 phosphorylation sites. Phosphorylation of MEK1 on serine 298 does not appear to regulate the interaction between Raf-1 and MEK1, but rather the ability of Raf-1 to phosphorylate MEK1 with which it is complexed in vivo. Our findings indicate that PAK1 primes MEK1 for activation by Raf-1 and imply another level of regulation in the ERK cascade.
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Affiliation(s)
- Lucy C Coles
- School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham NG7 2UH, UK
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25
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Sharma P, Sharma M, Amin ND, Sihag RK, Grant P, Ahn N, Kulkarni AB, Pant HC. Phosphorylation of MEK1 by cdk5/p35 down-regulates the mitogen-activated protein kinase pathway. J Biol Chem 2002; 277:528-34. [PMID: 11684694 DOI: 10.1074/jbc.m109324200] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cyclin-dependent protein kinase 5 (cdk5), a member of the cdk family, is active mainly in postmitotic cells and plays important roles in neuronal development and migration, neurite outgrowth, and synaptic transmission. In this study we investigated the relationship between cdk5 activity and regulation of the mitogen-activated protein (MAP) kinase pathway. We report that cdk5 phosphorylates the MAP kinase kinase-1 (MEK1) in vivo as well as the Ras-activated MEK1 in vitro. The phosphorylation of MEK1 by cdk5 resulted in inhibition of MEK1 catalytic activity and the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2. In p35 (cdk5 activator) -/- mice, which lack appreciable cdk5 activity, we observed an increase in the phosphorylation of NF-M subunit of neurofilament proteins that correlated with an up-regulation of MEK1 and ERK1/2 activity. The activity of a constitutively active MEK1 with threonine 286 mutated to alanine (within a TPXK cdk5 phosphorylation motif in the proline-rich domain) was not affected by cdk5 phosphorylation, suggesting that Thr286 might be the cdk5/p35 phosphorylation-dependent regulatory site. These findings support the hypothesis that cdk5 and the MAP kinase pathway cross-talk in the regulation of neuronal functions. Moreover, these data and the recent studies of Harada et al. (Harada, T., Morooka, T., Ogawa, S., and Nishida, E. (2001) Nat. Cell Biol. 3, 453-459) have prompted us to propose a model for feedback down-regulation of the MAP kinase signal cascade by cdk5 inactivation of MEK1.
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Affiliation(s)
- Pushkar Sharma
- Laboratory of Neurochemistry, NINDS, National Institutes of Health, Bethesda, Maryland 20892, USA
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26
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Cha H, Lee EK, Shapiro P. Identification of a C-terminal region that regulates mitogen-activated protein kinase kinase-1 cytoplasmic localization and ERK activation. J Biol Chem 2001; 276:48494-501. [PMID: 11604401 DOI: 10.1074/jbc.m107601200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The C-terminal region of mitogen-activated protein kinase kinase-1 and 2 (MKK1 and MKK2) may function in regulating interactions with upstream kinases or the magnitude and duration of ERK mitogen-activated protein kinase activity. The MKK C-terminal region contains a proline-rich region that reportedly functions in regulating interactions with the Raf-1 kinase and ERK activity. In addition, phosphorylation sites in the C terminus of MKK1 have been suggested to either sustain or attenuate MKK1 activity. To further understand how phosphorylation at the C terminus of MKK1 and protein interactions regulate MKK1 function, we have generated several MKK1 C-terminal deletion mutants and examined their function in regulating MKK1 localization, ERK protein activation, and cell growth. A deletion of C-terminal amino acids encompassing two putative alpha-helices between residues 330 and 379 caused a re-distribution of mutant MKK1 proteins to membrane compartments. Immunofluorescence analysis of MKK1 mutants revealed a loss of homogenous cytosolic distribution that is typically observed with MKK1 wild type, suggesting this region regulates MKK1 cellular localization. In contrast, MKK1 C-terminal deletion mutants localized to various sized punctate regions that overlapped with lysosome compartments. ERK activation in response to constitutively active Raf-1 or growth factor stimulus was attenuated in cells expressing MKK1 C-terminal deletion mutants. This could be partly explained by the inability of Raf-1 to phosphorylate MKK1 C-terminal deletion mutants even though the phosphorylation sites were intact in these mutants. Finally, we show that cells expressing MKK1 C-terminal deletion mutants displayed characteristic patterns of apoptotic cell death and reduced cell proliferation. These findings identify a novel C-terminal region between amino acid residues 330 and 379 on MKK1 that is necessary for regulating the cytoplasmic distribution and subsequent ERK protein activation necessary for cell survival and viability.
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Affiliation(s)
- H Cha
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland 21201, USA
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27
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Barry OP, Mullan B, Sheehan D, Kazanietz MG, Shanahan F, Collins JK, O'Sullivan GC. Constitutive ERK1/2 activation in esophagogastric rib bone marrow micrometastatic cells is MEK-independent. J Biol Chem 2001; 276:15537-46. [PMID: 11297525 DOI: 10.1074/jbc.m010847200] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this study, we examined the mitogen-activated protein kinase (MAPK) cascade in micrometastatic cell lines generated from rib bone marrow (RBM) of patients undergoing resection of esophagogastric malignancies. The molecular mechanism(s) involved in esophagogastric MAPK activation have not previously been investigated. Constitutive activation of both ERK1 and -2 isoforms was evident in each of the five RBM cell lines. Elk-1, a transcription factor activated by the ERK1/2 pathway was also found to be constitutively activated. Cell lines generated from metastases of involved lymph nodes (OC2) and ascites (OC1) of patients with esophageal cancer do not display, however, hyperphosphorylation of ERK1/2. Constitutive RBM ERK1/2 activation is protein kinase C and phosphatidylinositol 3-kinase dependent. Surprisingly, constitutive ERK1/2 activation is MEK-independent. Pharmacological inhibition of MEK with two specific inhibitors, PD 98059 and U0126, were both ineffective in blocking ERK activation. Similarly, the use of a dominant negative MEK mutant was without effect. Interestingly, experiments overexpressing two different dominant negative Pak1 mutants significantly reduced RBM ERK1/2 activation, albeit not to the same extent for all cell lines. We also examined the role of three different phosphatases, PAC1, MKP-1, and -2. While RBM ERK1/2 activation was found to be PAC1- and MKP-2-independent, surprisingly, MKP-1 was down-regulated in all five RBM cell lines. In conclusion, we provide evidence for the first time for a MEK-independent constitutive ERK1/2 activation pathway in esophagogastric RBM cell lines. These findings have important implications for drug treatment strategies which currently target MEK in other forms of cancer.
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Affiliation(s)
- O P Barry
- Cork Cancer Research Center, National University of Ireland, Cork, Ireland
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28
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Pearson G, Robinson F, Beers Gibson T, Xu BE, Karandikar M, Berman K, Cobb MH. Mitogen-activated protein (MAP) kinase pathways: regulation and physiological functions. Endocr Rev 2001; 22:153-83. [PMID: 11294822 DOI: 10.1210/edrv.22.2.0428] [Citation(s) in RCA: 1318] [Impact Index Per Article: 57.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Mitogen-activated protein (MAP) kinases comprise a family of ubiquitous proline-directed, protein-serine/threonine kinases, which participate in signal transduction pathways that control intracellular events including acute responses to hormones and major developmental changes in organisms. MAP kinases lie in protein kinase cascades. This review discusses the regulation and functions of mammalian MAP kinases. Nonenzymatic mechanisms that impact MAP kinase functions and findings from gene disruption studies are highlighted. Particular emphasis is on ERK1/2.
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Affiliation(s)
- G Pearson
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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29
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Affiliation(s)
- J E Ferrell
- Department of Molecular Pharmacology, Stanford University School of Medicine, California 94305-5332, USA
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30
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Ligterink W, Hirt H. Mitogen-activated protein [MAP] kinase pathways in plants: versatile signaling tools. INTERNATIONAL REVIEW OF CYTOLOGY 2001; 201:209-75. [PMID: 11057833 DOI: 10.1016/s0074-7696(01)01004-x] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Mitogen-activated protein kinases (MAPKs) are important signaling tools in all eukaryotes, and function in mediating an enormous variety of external signals to appropriate cellular responses. MAPK pathways have been studied extensively in yeast and mammalian cells, and a large body of knowledge on their functioning has accumulated, which is summarized briefly. Plant MAPK pathways have attracted increasing interest, resulting in the isolation of a large number of different components of MAPK cascades. Studies on the functions of these components have revealed that MAPKs play important roles in the response to a broad variety of stresses, as well as in the signaling of most plant hormones and in developmental processes. Finally, the involvement of various plant phosphatases in the inactivation of MAPKs is discussed.
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Affiliation(s)
- W Ligterink
- Institute of Microbiology and Genetics, Vienna Biocenter, University of Vienna, Austria
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31
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Hayne C, Tzivion G, Luo Z. Raf-1/MEK/MAPK pathway is necessary for the G2/M transition induced by nocodazole. J Biol Chem 2000; 275:31876-82. [PMID: 10884385 DOI: 10.1074/jbc.m002766200] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The dynamic balance between polymerization and depolymerization of microtubules is critical for cells to enter and exit mitosis, and drugs that disrupt this balance, such as taxol, colchicine, and nocodazole, arrest the cell cycle in mitosis. Although the Raf/MEK/MAPK pathway can be activated by these drugs, its role in mitosis has not been addressed. Here, we characterize activation of Raf/MEK/MAPK by nocodazole when mitosis is induced. We find that at early time points (up to 3 h) in nocodazole induction, Raf/MEK/MAPK is activated, and inhibition of MAPK activation by a MEK inhibitor, PD98059 or U0126, reduces the number of cells entering mitosis by creating a block at G(2). At later time points and in mitosis, activation of MEK/MAPK is severely inhibited, even though Raf-1 activity remains high and can be further increased by growth factor. This inhibition is reversed when cells are released from metaphase and enter G(0)/G(1) phase. In addition, we find that binding of Raf-1 to 14-3-3 is progressively induced by nocodazole, reaching a maximum in mitosis, and that this binding is necessary to maintain mitotic Raf-1 activity. Our present study indicates that activation of the Raf/MEK/MAPK pathway is necessary for the G(2)/M progression.
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Affiliation(s)
- C Hayne
- Diabetes and Metabolism Research Unit, Section of Endocrinology, Evans Department of Medicine and the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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32
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Colanzi A, Deerinck TJ, Ellisman MH, Malhotra V. A specific activation of the mitogen-activated protein kinase kinase 1 (MEK1) is required for Golgi fragmentation during mitosis. J Cell Biol 2000; 149:331-9. [PMID: 10769026 PMCID: PMC2175149 DOI: 10.1083/jcb.149.2.331] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/1999] [Accepted: 02/07/2000] [Indexed: 11/22/2022] Open
Abstract
Incubation of permeabilized cells with mitotic extracts results in extensive fragmentation of the pericentriolarly organized stacks of cisternae. The fragmented Golgi membranes are subsequently dispersed from the pericentriolar region. We have shown previously that this process requires the cytosolic protein mitogen-activated protein kinase kinase 1 (MEK1). Extracellular signal-regulated kinase (ERK) 1 and ERK2, the known downstream targets of MEK1, are not required for this fragmentation (Acharya et al. 1998). We now provide evidence that MEK1 is specifically phosphorylated during mitosis. The mitotically phosphorylated MEK1, upon partial proteolysis with trypsin, generates a different peptide population compared with interphase MEK1. MEK1 cleaved with the lethal factor of the anthrax toxin can still be activated by its upstream mitotic kinases, and this form is fully active in the Golgi fragmentation process. We believe that the mitotic phosphorylation induces a change in the conformation of MEK1 and that this form of MEK1 recognizes Golgi membranes as a target compartment. Immunoelectron microscopy analysis reveals that treatment of permeabilized normal rat kidney (NRK) cells with mitotic extracts, treated with or without lethal factor, converts stacks of pericentriolar Golgi membranes into smaller fragments composed predominantly of tubuloreticular elements. These fragments are similar in distribution, morphology, and size to the fragments observed in the prometaphase/metaphase stage of the cell cycle in vivo.
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Affiliation(s)
- Antonino Colanzi
- Department of Biology, Department of Neurosciences, University of California San Diego, La Jolla, California 92093-0347
| | - Thomas J. Deerinck
- National Center for Microscopy and Imaging Research, Department of Neurosciences, University of California San Diego, La Jolla, California 92093-0347
| | - Mark H. Ellisman
- National Center for Microscopy and Imaging Research, Department of Neurosciences, University of California San Diego, La Jolla, California 92093-0347
| | - Vivek Malhotra
- Department of Biology, Department of Neurosciences, University of California San Diego, La Jolla, California 92093-0347
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33
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Abstract
We have used site-directed mutagenesis to explore the mechanisms underlying Raf-1 activation in mitosis, and we have excluded most previously characterized activating interactions. Our results indicate that the primary locus of activation lies in the carboxyl-half of the molecule, although the extent of activation can be influenced by the amino-proximal region, particularly by the Raf-1 zinc finger. We also found that Raf-1 is hyperphosphorylated in mitosis at multiple sites within residues 283-302 and that these hyperphosphorylations are not required for activation. In addition, neither Mek1 nor Mek2 are stably activated in coordination with Raf-1 in nocodazole-arrested cells. Overall, the data suggest that the mechanism(s) responsible for activating Raf-1 during mitosis, and the subsequent downstream effects, are distinct from those involved in growth factor stimulation.
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Affiliation(s)
- A D Laird
- Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853, USA
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34
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Lowe M, Rabouille C, Nakamura N, Watson R, Jackman M, Jämsä E, Rahman D, Pappin DJ, Warren G. Cdc2 kinase directly phosphorylates the cis-Golgi matrix protein GM130 and is required for Golgi fragmentation in mitosis. Cell 1998; 94:783-93. [PMID: 9753325 DOI: 10.1016/s0092-8674(00)81737-7] [Citation(s) in RCA: 250] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Mitotic fragmentation of the Golgi apparatus can be largely explained by disruption of the interaction between GM130 and the vesicle-docking protein p115. Here we identify a single serine (Ser-25) in GM130 as the key phosphorylated target and Cdc2 as the responsible kinase. MEK1, a component of the MAP kinase signaling pathway recently implicated in mitotic Golgi fragmentation, was not required for GM130 phosphorylation or mitotic fragmentation either in vitro or in vivo. We propose that Cdc2 is directly involved in mitotic Golgi fragmentation and that signaling via MEK1 is not required for this process.
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Affiliation(s)
- M Lowe
- Cell Biology Laboratory, Imperial Cancer Research Fund, London, United Kingdom
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35
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Dang A, Frost JA, Cobb MH. The MEK1 proline-rich insert is required for efficient activation of the mitogen-activated protein kinases ERK1 and ERK2 in mammalian cells. J Biol Chem 1998; 273:19909-13. [PMID: 9677429 DOI: 10.1074/jbc.273.31.19909] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
MEK1 and MEK2 contain a proline-rich insert not present in any other known MEK (MAP (mitogen-activated protein)/ERK (extracellular signal-regulated kinase) kinase) family members. We examined the effect of removing the MEK1 polyproline insert on MEK activity, its binding to Raf, and its ability to activate ERKs in cells. Deletion of the insert had no effect on either the activity of MEK1 or on its ability to bind to Raf-1. Both wild type and constitutively active MEK1 coimmunoprecipitated with Raf-1 whether or not the insert was present. Deletion of the insert did not reduce activation of MEK1 by EGF or activated Raf in cells. The proline-rich insert enhanced the ability of an otherwise equally active MEK1 protein to regulate endogenous ERKs in mammalian cells. Overexpression of either constitutively active MEK1 lacking the insert or ERK2 compensates for the weaker in vivo activity of the MEK1 deletion mutant. Expression of the insert in cells reduced activation of ERKs by EGF. We conclude that the proline-rich insert is not the site of the MEK-Raf interaction and that the polyproline insert is required for its efficient activation of downstream ERKs in cells.
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Affiliation(s)
- A Dang
- University of Texas Southwestern Medical Center, Department of Pharmacology, Dallas, Texas 75235-9041, USA
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36
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Pahan K, Sheikh FG, Namboodiri AM, Singh I. Inhibitors of protein phosphatase 1 and 2A differentially regulate the expression of inducible nitric-oxide synthase in rat astrocytes and macrophages. J Biol Chem 1998; 273:12219-26. [PMID: 9575170 DOI: 10.1074/jbc.273.20.12219] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nitric oxide produced by inducible nitric-oxide synthase (iNOS) in different cells including brain cells in response to proinflammatory cytokines plays an important role in the pathophysiology of stroke and other neurodegenerative diseases. The present study underlines the importance of protein phosphatase (PP) 1 and 2A in the regulation of the differential expression of iNOS in rat primary astrocytes and macrophages. Compounds (calyculin A, microcystin, okadaic acid, and cantharidin) that inhibit PP 1 and 2A were found to stimulate the lipopolysaccharide (LPS)- and cytokine-mediated expression of iNOS and production of NO in rat primary astrocytes and C6 glial cells. However, these inhibitors inhibited the LPS- and cytokine-mediated expression of iNOS and production of NO in rat resident macrophages and RAW 264.7 cells. Similarly, okadaic acid, an inhibitor of PP 1/2A, stimulated the iNOS promoter-derived chloramphenicol acetyltransferase activity in astrocytes and inhibited the iNOS promoter-derived chloramphenicol acetyltransferase activity in macrophages, indicating that okadaic acid also differentially regulates the transcription of the iNOS gene in astrocytes and macrophages. The observed stimulation of the expression of iNOS in astrocytes and the inhibition of the expression of iNOS in macrophages with the inhibition of PP 1/2A activity clearly delineate a novel role of PP 1/2A in the differential regulation of iNOS in rat astrocytes and macrophages. Because the activation of NF-kappaB is necessary for the induction of iNOS and the expression of tumor necrosis factor (TNF)-alpha also depends on the activation of NF-kappaB, we examined the effect of okadaic acid on the LPS-mediated activation of NF-kappaB and production of TNF-alpha in rat primary astrocytes and macrophages. Interestingly, in both cell types, okadaic acid stimulated the LPS-mediated DNA binding as well as transcriptional activity of NF-kappaB and production of TNF-alpha. This study suggests that the stimulation of iNOS expression in astrocytes by inhibitors of PP 1/2A is possibly due to the stimulation of NF-kappaB activation; however, activation of NF-kappaB is not sufficient for the induction of iNOS in macrophages and that apart from NF-kappaB some other signaling pathway(s) sensitive to PP 1 and/or PP 2A is/are possibly involved in the regulation of iNOS in macrophages. This differential induction of iNOS as compared with similar activation of NF-kappaB by inhibitors of PP 1/2A indicates the involvement of different intracellular signaling events for the induction of iNOS in two cell types of the same animal species.
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Affiliation(s)
- K Pahan
- Department of Pediatrics, Medical University of South Carolina, Charleston, South Carolina 29425, USA
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37
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Affiliation(s)
- T S Lewis
- Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Colorado, Boulder 80309, USA
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38
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Wang J, Vantus T, Merlevede W, Vandenheede JR. Identification and characterization of an auto-activating MEK kinase from bovine brain: phosphorylation of serine-298 in the proline-rich domain of the mammalian MEKs. Int J Biochem Cell Biol 1997; 29:1071-83. [PMID: 9416003 DOI: 10.1016/s1357-2725(97)00054-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Mitogen-activated protein kinase kinases (MKKs or MEKs) are dual specificity tyrosine/threonine protein kinases that are activated by phosphorylation at two closely spaced serine residues (serines-218 and -222) by the c-mos and raf proto-oncogenes. This double phosphorylation is both necessary and sufficient for MEKs to activate the MAP kinase enzymes in vitro. The specificity or regulation of in vivo signaling to the mammalian MEKs (MEK1 and MEK2) was recently reported also to involve the differential phosphorylation of a proline-rich peptide located between the MEK kinase-subdomains IX and X. Here we report the purification and characterization of an auto-activating protein kinase from bovine brain that phosphorylates serine-298 of the MEK1 and MEK2 proline-rich insert peptides. The auto-activation of the MEK-S298 peptide kinase is the result of an intermolecular phosphorylation event that can be prevented by the peptide substrates. The inactive kinase migrates on gel filtration as a 90 kDa protein, and after activation as a 43 kDa phosphoprotein. Incorporation of 32P[phosphate] into 40-42 kDa proteins on SDS-PAGE parallels the activation of the enzyme, and dephosphorylation by protein phosphatase 2Ac reverses the activation. SDS-PAGE renaturation assays show that the 40 kDa protein has the capacity to autophosphorylate, and exhibits kinase activity towards myelin basic protein after activation. Phosphorylation of purified bovine brain MEK or recombinant MEK1 by the auto-activated kinase does not activate the enzyme, and does not interfere with the in vitro raf-mediated MEK activation. We conclude that still unknown kinases may control the MAP kinase pathway by targeting MEK.
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Affiliation(s)
- J Wang
- Afdeling Biochemie, Faculteit Geneeskunde, Katholieke Universiteit Leuven, Belgium
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39
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Abstract
Studies of the roles of oncoproteins in cell cycle progression have concentrated on G1 because transformation is frequently associated with loss of G1 checkpoint control. However, it has become evident that G2 and mitotic checkpoints are often compromised in transformed cells and that many tumour suppressor proteins and oncoprotein kinases regulate and/or are activated in G2 and M. Disruption of p53 and ATM tumour suppressor protein functions can eliminate G2 and M checkpoints. The Src family kinases are activated in mitosis and collectively play an indispensable role in progression through G2/M. In addition, evidence suggests that Mos and elements of the Ras/Raf/MAPK cascade are also active in mitosis and appear likely to regulate G2 and/or M. Potential targets of these kinases include likely regulators of gene expression and microtubule dynamics such as Sam68 and Oncoprotein 18/stathmin. The ability of some oncoproteins to perturb orderly progression through both G1 and/or S and G2 and/or M is probably important for transformation.
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Affiliation(s)
- A D Laird
- Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, NY 14853, USA
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40
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Abstract
Nearly all cell surface receptors utilize one or more of the mitogen-activated protein kinase cascades in their repertoire of signal transduction mechanisms. Recent advances in the study of such cascades include the cloning of genes encoding novel members of the cascades, further definition of the roles of the cascades in responses to extracellular signals, and examination of cross-talk between different cascades.
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Affiliation(s)
- M J Robinson
- University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75235-904,1 USA.
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41
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Downey GP, Butler JR, Brumell J, Borregaard N, Kjeldsen L, Sue-A-Quan AK, Grinstein S. Chemotactic peptide-induced activation of MEK-2, the predominant isoform in human neutrophils. Inhibition by wortmannin. J Biol Chem 1996; 271:21005-1011. [PMID: 8702863 DOI: 10.1074/jbc.271.35.21005] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Exposure of neutrophils to a variety of agonists including chemoattractant peptides and cytokines induces degranulation and activation of the oxidative burst which are required for bacterial killing. The signaling pathways regulating these important functions are incompletely characterized. Mitogen-activated protein (MAP) kinases, which include the extracellular signal-regulated kinases (ERKs), are activated rapidly in neutrophils, suggesting that they may regulate cell activation. We found that neutrophils express two isoforms of MAP/ERK kinase (MEK), mixed-function kinases that are responsible for phosphorylation and activation of ERK. Like MEK-1, MEK-2 was found to reside in the cytosol both before and after stimulation. Studies were undertaken to define the relative abundance and functional contribution of MEK-1 and MEK-2 in neutrophils and to characterize the signaling pathways leading to their activation. Although the abundance of the two isoforms was similar, the activity of MEK-2 was at least 3-fold greater than that of MEK-1. A rise in cytosolic [Ca2+] was insufficient for MEK stimulation, and blunting the [Ca2+] change with intracellular chelators failed to prevent receptor-mediated activation of either isoform, implying that cytosolic Ca2+ transients are not necessary. In contrast, both MEK-1 and MEK-2 were activated by exposure of cells to protein kinase C (PKC) agonists. Conversely, PKC antagonists inhibited the chemotactic stimulation of both isoforms, suggesting that PKC was required for their activation. Despite these similarities, clear differences were also found in the pathways leading to activation of the MEK isoforms. In particular, MEK-2 was considerably more sensitive than MEK-1 to the phosphatidylinositol 3-kinase inhibitor wortmannin. Phosphorylation and activation of ERK-1 and ERK-2 were also reduced by this inhibitor. In summary, MEK-2 is stimulated in formyl-methionyl-leucyl-phenylalanine-treated neutrophils, where it appears to be functionally the predominant isoform. The time course and inhibitor sensitivity of MEK-2 activation parallel those of several components of the microbicidal response, suggesting a signaling role of the MEK-ERK pathway.
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Affiliation(s)
- G P Downey
- Department of Medicine, Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada
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42
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43
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Cobb MH, Xu S, Cheng M, Ebert D, Robbins D, Goldsmith E, Robinson M. Structural analysis of the MAP kinase ERK2 and studies of MAP kinase regulatory pathways. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 1996; 36:49-65. [PMID: 8783554 DOI: 10.1016/s1054-3589(08)60576-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- M H Cobb
- The University of Texas Southwestern Medical Center, Department of Pharmacology, Dallas 75235, USA
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44
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Moriguchi T, Gotoh Y, Nishida E. Activation of two isoforms of mitogen-activated protein kinase kinase in response to epidermal growth factor and nerve growth factor. EUROPEAN JOURNAL OF BIOCHEMISTRY 1995; 234:32-8. [PMID: 8529659 DOI: 10.1111/j.1432-1033.1995.032_c.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Mitogen-activated protein kinase kinase (MAPKK) is a dual-specificity protein kinase which phosphorylates and activates mitogen-activated protein kinase (MAPK). cDNAs encoding two isoforms of MAPKK, MAPKK1 and MAPKK2 (also known as MEK1 and MEK2), have been cloned in mammalian cells. To analyze the characteristics of MAPKK1 and MAPKK2 individually, we have produced specific anti-MAPKK serum against each isoform. MAPKK1 and MAPKK2 have apparent molecular masses of 45 kDa and 47 kDa, respectively, on SDS/polyacrylamide gel electrophoresis. In mouse tissues, MAPKK1 was highly enriched in brain, while MAPKK2 was present relatively evenly. In rat fibroblastic 3Y1 cells, epidermal growth factor (EGF) treatment induced activation of both MAPKK1 and MAPKK2. Immunoprecipitation experiments have shown that the time courses of activation and deactivation of both isoforms of MAPKK were superimposed. In PC12 cells, both MAPKK1 and MAPKK2 were activated in response to nerve growth factor (NGF) as well as EGF, and the time courses of activation and deactivation of both isoforms were indistinguishable from each other in the NGF-stimulated cells and also in the EGF-stimulated cells. Furthermore, localization of both MAPKK1 and MAPKK2 in the cytoplasm was unchanged in response to EGF and NGF. Thus, the same or quite similar mechanisms may operate in the regulation of the activation and deactivation of two isoforms of MAPKK, and both kinases might have redundant functions when expressed in the same cell.
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Affiliation(s)
- T Moriguchi
- Department of Genetics and Molecular Biology, Kyoto University, Japan
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45
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Bosc DG, Slominski E, Sichler C, Litchfield DW. Phosphorylation of casein kinase II by p34cdc2. Identification of phosphorylation sites using phosphorylation site mutants in vitro. J Biol Chem 1995; 270:25872-8. [PMID: 7592773 DOI: 10.1074/jbc.270.43.25872] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The alpha and beta subunits of casein kinase II are dramatically phosphorylated in cells that are arrested in mitosis (Litchfield, D. W., Lüscher, B., Lozeman, F. J., Eisenman, R. N., and Krebs, E.G. (1992) J. Biol. Chem. 267, 13943-13951). Comparative phosphopeptide mapping experiments indicated that the mitotic phosphorylation sites on the alpha subunit of casein kinase II can be phosphorylated in vitro by p34cdc2. In the present study, we have demonstrated that a glutathione S-transferase fusion protein encoding the C-terminal 126 amino acids of the alpha subunit is phosphorylated by p34cdc2 at the same sites as intact casein kinase II, indicating that the mitotic phosphorylation sites are localized within the C-terminal domain of alpha. Four residues within this domain, Thr-344, Thr-360, Ser-362, and Ser-370, conform to the minimal consensus sequence for p34cdc2 phosphorylation. Synthetic peptides corresponding to regions of alpha that contain each of these residues are phosphorylated by p34cdc2 at these sites. Furthermore, alterations in the phosphorylation of the glutathione S-transferase proteins encoding the C-terminal domain of alpha are observed when any of the four residues are mutated to alanine. When all four residues are mutated to alanine, the fusion protein is no longer phosphorylated by p34cdc2 at any of the sites that are phosphorylated in mitotic cells. These results indicate that Thr-344, Thr-360, Ser-362, and Ser-370 are the sites on the alpha subunit of casein kinase II that are phosphorylated in mitotic cells.
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Affiliation(s)
- D G Bosc
- Manitoba Institute of Cell Biology, Manitoba Cancer Treatment and Research Foundation, Winnipeg, Canada
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46
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Affiliation(s)
- J D Graves
- Department of Pharmacology, University of Washington, Seattle 98195-7280, USA
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47
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Zhou G, Bao ZQ, Dixon JE. Components of a new human protein kinase signal transduction pathway. J Biol Chem 1995; 270:12665-9. [PMID: 7759517 DOI: 10.1074/jbc.270.21.12665] [Citation(s) in RCA: 516] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We have identified two components of a new protein kinase signaling cascade, MAPK/ERK kinase 5 (MEK5) and extracellular signal-regulated kinase 5 (ERK5). The MEK5 cDNA was isolated by degenerate PCR and encodes a 444-amino acid protein, which has approximately 40% identity to known MEKs. ERK5 was identified by a specific interaction with the MEK5 mutants S311A/T315A and K195M in the yeast two-hybrid system. The proteins were found to interact in an in vitro binding assay as well. ERK5 did not interact with MEK1 or MEK2. ERK5 is predicted to contain 815 amino acids and is approximately twice the size of all known ERKs. The C terminus of ERK5 has sequences which suggest that it may be targeted to the cytoskeleton. Sequences located in the N terminus of MEK5 may be important in coupling GTPase signaling molecules to the MEK5 protein kinase cascade. Both MEK5 and ERK5 are expressed in many adult tissue and are abundant in heart and skeletal muscle. A recombinant GST-ERK5 kinase domain displays autophosphorylation on Ser/Thr and Tyr residues.
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Affiliation(s)
- G Zhou
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor 48109-0606, USA
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48
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Pelech SL. Networking with proline-directed protein kinases implicated in tau phosphorylation. Neurobiol Aging 1995; 16:247-56; discussion 257-61. [PMID: 7566335 DOI: 10.1016/0197-4580(94)00187-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Proline-directed kinases such as the mitogen-activated protein (MAP) kinases, cyclin-dependent protein kinase 5 (CDK5) and glycogen synthase 3 (GSK3) have been implicated in the hyperphosphorylation of the tau protein associated with Alzheimer's disease. Such aberrant phosphorylation of tau appears to compromise on its ability to bind to and stabilize microtubules, and this may contribute to Alzheimer's disease pathology. In this review, the architecture of the intracellular signal transduction pathways that regulate proline-directed kinases is described. The MAP kinases serve as major intersection points in the flow of information from a plethora of extracellular stimuli and affect diverse cellular processes that are often important for cell proliferation. Although brain contains terminally differentiated neurons, many of the known components of MAP kinase-dependent lines of communication are highly expressed in the nervous system. Similar signalling pathways may also regulate CDK5 and GSK3. In mitotic cells, abnormal activation of the protein kinase network at multiple points can contribute to oncogenic transformation. It is proposed that Alzheimer's disease may also result from accumulated defects in the kinase network that governs the proline-directed kinases such that their inappropriate activation is sustained in the affected neurons. A detailed understanding of proline-directed kinase-dependent pathways may permit the identification of rational targets for the therapeutic intervention of Alzheimer's disease and other neurological disorders.
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Affiliation(s)
- S L Pelech
- Biomedical Research Centre, University of British Columbia, Vancouver, Canada
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49
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Denton RM, Tavaré JM. Does mitogen-activated-protein kinase have a role in insulin action? The cases for and against. EUROPEAN JOURNAL OF BIOCHEMISTRY 1995; 227:597-611. [PMID: 7867619 DOI: 10.1111/j.1432-1033.1995.tb20179.x] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The discovery of the mitogen-activated protein (MAP) kinase family of protein kinases has sparked off an intensive effort to elucidate their role in the regulation of many cellular processes. These protein kinases were originally identified based on their rapid activation by insulin. In this review we concentrate on examining the evidence for and against a role for the MAP kinases Erk-1 and Erk-2 in mediating the effects of insulin. While there is good evidence in favour of a direct role for MAP kinase in the growth-promoting effects of insulin and the regulation of Glut-1 and c-fos expression, and AP-1 transcriptional complex activity, this is by no means conclusive. MAP kinase may also play a role in the control of mRNA translation by insulin. On the other hand, the evidence suggests that MAP kinase is not sufficient for the acute regulation of glucose transport (Glut-4 translocation), glycogen synthesis, acetyl-CoA carboxylase or pyruvate dehydrogenase activity. The findings suggest that insulin may utilise at least three distinct signalling pathways which do not involve MAP kinase.
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Affiliation(s)
- R M Denton
- Department of Biochemistry, School of Medical Sciences, University of Bristol, England
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50
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Shannon JD, Fox JW. Identification of phosphorylation sites by Edman degradation. ACTA ACUST UNITED AC 1995. [DOI: 10.1016/s1080-8914(06)80017-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/29/2023]
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