1
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Ngo VA. Insight into molecular basis and dynamics of full-length CRaf kinase in cellular signaling mechanisms. Biophys J 2024:S0006-3495(24)00438-7. [PMID: 38946141 DOI: 10.1016/j.bpj.2024.06.028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Revised: 05/15/2024] [Accepted: 06/28/2024] [Indexed: 07/02/2024] Open
Abstract
Raf kinases play key roles in signal transduction in cells for regulating proliferation, differentiation, and survival. Despite decades of research into functions and dynamics of Raf kinases with respect to other cytosolic proteins, understanding Raf kinases is limited by the lack of their full-length structures at the atomic resolution. Here, we present the first model of the full-length CRaf kinase obtained from artificial intelligence/machine learning algorithms with a converging ensemble of structures simulated by large-scale temperature replica exchange simulations. Our model is validated by comparing simulated structures with the latest cryo-EM structure detailing close contacts among three key domains and regions of the CRaf. Our simulations identify potentially new epitopes of intramolecule interactions within the CRaf and reveal a dynamical nature of CRaf kinases, in which the three domains can move back and forth relative to each other for regulatory dynamics. The dynamic conformations are then used in a docking algorithm to shed insight into the paradoxical effect caused by vemurafenib in comparison with a paradox breaker PLX7904. We propose a model of Raf-heterodimer/KRas-dimer as a signalosome based on the dynamics of the full-length CRaf.
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Affiliation(s)
- Van A Ngo
- Advanced Computing for Life Sciences and Engineering, Science Engagement Section, Computing and Computational Sciences, National Center for Computational Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee.
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2
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Chessel A, De Crozé N, Molina MD, Taberner L, Dru P, Martin L, Lepage T. RAS-independent ERK activation by constitutively active KSR3 in non-chordate metazoa. Nat Commun 2023; 14:3970. [PMID: 37407549 DOI: 10.1038/s41467-023-39606-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Accepted: 06/21/2023] [Indexed: 07/07/2023] Open
Abstract
During early development of the sea urchin embryo, activation of ERK signalling in mesodermal precursors is not triggered by extracellular RTK ligands but by a cell-autonomous, RAS-independent mechanism that was not understood. We discovered that in these cells, ERK signalling is activated through the transcriptional activation of a gene encoding a protein related to Kinase Suppressor of Ras, that we named KSR3. KSR3 belongs to a family of catalytically inactive allosteric activators of RAF. Phylogenetic analysis revealed that genes encoding kinase defective KSR3 proteins are present in most non-chordate metazoa but have been lost in flies and nematodes. We show that the structure of KSR3 factors resembles that of several oncogenic human RAF mutants and that KSR3 from echinoderms, cnidarians and hemichordates activate ERK signalling independently of RAS when overexpressed in cultured cells. Finally, we used the sequence of KSR3 factors to identify activating mutations of human B-RAF. These findings reveal key functions for this family of factors as activators of RAF in RAS-independent ERK signalling in invertebrates. They have implications on the evolution of the ERK signalling pathway and suggest a mechanism for its co-option in the course of evolution.
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Affiliation(s)
- Aline Chessel
- Institut de Biologie Valrose CNRS, Université Côte d'Azur, Nice, France
| | - Noémie De Crozé
- Institut de Biologie Valrose CNRS, Université Côte d'Azur, Nice, France
| | - Maria Dolores Molina
- Department of Genetics, Microbiology and Statistics, Faculty of Biology, University of Barcelona, Barcelona, Catalonia, Spain
| | - Laura Taberner
- Institut de Biologie Valrose CNRS, Université Côte d'Azur, Nice, France
| | - Philippe Dru
- CNRS, Laboratoire de Biologie du Développement de Villefranche-sur-Mer (LBDV), Institut de la Mer de Villefranche, 181 Chemin du Lazaret, 06230, Villefranche-sur-Mer, France
| | - Luc Martin
- Institut de Biologie Valrose CNRS, Université Côte d'Azur, Nice, France
| | - Thierry Lepage
- Institut de Biologie Valrose CNRS, Université Côte d'Azur, Nice, France.
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3
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Kondo Y, Paul JW, Subramaniam S, Kuriyan J. New insights into Raf regulation from structural analyses. Curr Opin Struct Biol 2021; 71:223-231. [PMID: 34454301 DOI: 10.1016/j.sbi.2021.07.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Revised: 07/06/2021] [Accepted: 07/10/2021] [Indexed: 01/07/2023]
Abstract
BRAF is a highly regulated protein kinase that controls cell fate in animal cells. Recent structural analyses have revealed how active and inactive forms of BRAF bind to dimers of the scaffold protein 14-3-3. Inactive BRAF binds to 14-3-3 as a monomer and is held in an inactive conformation by interactions with ATP and the substrate kinase MEK, a striking example of enzyme inhibition by substrate binding. A change in the phosphorylation state of BRAF shifts the stoichiometry of the BRAF:14-3-3 complex from 1:2 to 2:2, resulting in stabilization of the active dimeric form of the kinase. These new findings uncover unexpected features of the regulatory mechanisms underlying Raf biology and help explain the paradoxical activation of Raf by small-molecule inhibitors.
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Affiliation(s)
- Yasushi Kondo
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, CA, 94720, USA
| | - Joseph W Paul
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, CA, 94720, USA
| | | | - John Kuriyan
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, CA, 94720, USA; Howard Hughes Medical Institute, University of California, Berkeley, CA, 94720, USA; Department of Chemistry, University of California, Berkeley, CA, 94720, USA; Division of Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
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4
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The 14-3-3 Proteins as Important Allosteric Regulators of Protein Kinases. Int J Mol Sci 2020; 21:ijms21228824. [PMID: 33233473 PMCID: PMC7700312 DOI: 10.3390/ijms21228824] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Revised: 11/20/2020] [Accepted: 11/20/2020] [Indexed: 12/14/2022] Open
Abstract
Phosphorylation by kinases governs many key cellular and extracellular processes, such as transcription, cell cycle progression, differentiation, secretion and apoptosis. Unsurprisingly, tight and precise kinase regulation is a prerequisite for normal cell functioning, whereas kinase dysregulation often leads to disease. Moreover, the functions of many kinases are regulated through protein–protein interactions, which in turn are mediated by phosphorylated motifs and often involve associations with the scaffolding and chaperon protein 14-3-3. Therefore, the aim of this review article is to provide an overview of the state of the art on 14-3-3-mediated kinase regulation, focusing on the most recent mechanistic insights into these important protein–protein interactions and discussing in detail both their structural aspects and functional consequences.
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Sluchanko NN, Bustos DM. Intrinsic disorder associated with 14-3-3 proteins and their partners. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2019; 166:19-61. [PMID: 31521232 DOI: 10.1016/bs.pmbts.2019.03.007] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Protein-protein interactions (PPIs) mediate a variety of cellular processes and form complex networks, where connectivity is achieved owing to the "hub" proteins whose interaction with multiple protein partners is facilitated by the intrinsically disordered protein regions (IDPRs) and posttranslational modifications (PTMs). Universal regulatory proteins of the eukaryotic 14-3-3 family nicely exemplify these concepts and are the focus of this chapter. The extremely wide interactome of 14-3-3 proteins is characterized by high levels of intrinsic disorder (ID) enabling protein phosphorylation and consequent specific binding to the well-structured 14-3-3 dimers, one of the first phosphoserine/phosphothreonine binding modules discovered. However, high ID enrichment also challenges structural studies, thereby limiting the progress in the development of small molecule modulators of the key 14-3-3 PPIs of increased medical importance. Besides the well-known structural flexibility of their variable C-terminal tails, recent studies revealed the strong and conserved ID propensity hidden in the N-terminal segment of 14-3-3 proteins (~40 residues), normally forming the α-helical dimerization region, that may have a potential role for the dimer/monomer dynamics and recently reported moonlighting chaperone-like activity of these proteins. We review the role of ID in the 14-3-3 structure, their interactome, and also in selected 14-3-3 complexes. In addition, we discuss approaches that, in the future, may help minimize the disproportion between the large amount of known 14-3-3 partners and the small number of 14-3-3 complexes characterized with atomic precision, to unleash the whole potential of 14-3-3 PPIs as drug targets.
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Affiliation(s)
- Nikolai N Sluchanko
- A.N. Bach Institute of Biochemistry, Federal Research Center of Biotechnology of the Russian Academy of Sciences, Moscow, Russian Federation; Department of Biophysics, Faculty of Biology, M.V. Lomonosov Moscow State University, Moscow, Russian Federation.
| | - Diego M Bustos
- Instituto de Histología y Embriología (IHEM) - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), CC56, Universidad Nacional de Cuyo (UNCuyo), Mendoza, Argentina; Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo (UNCuyo), Mendoza, Argentina
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6
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Harvey BJ, Thomas W. Aldosterone-induced protein kinase signalling and the control of electrolyte balance. Steroids 2018; 133:67-74. [PMID: 29079406 DOI: 10.1016/j.steroids.2017.10.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Revised: 10/18/2017] [Accepted: 10/21/2017] [Indexed: 01/20/2023]
Abstract
Aldosterone acts through the mineralocorticoid receptor (MR) to modulate gene expression in target tissues. In the kidney, the principal action of aldosterone is to promote sodium conservation in the distal nephron and so indirectly enhance water conservation under conditions of hypotension. Over the last twenty years the rapid activation of protein kinase signalling cascades by aldosterone has been described in various tissues. This review describes the integration of rapid protein kinase D signalling responses with the non-genomic actions of aldosterone and transcriptional effects of MR activation.
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Affiliation(s)
- Brian J Harvey
- Molecular Medicine Laboratories, Royal College of Surgeons in Ireland, Education Centre, Beaumont Hospital, Dublin, Ireland
| | - Warren Thomas
- Molecular Medicine Laboratories, Royal College of Surgeons in Ireland, Education Centre, Beaumont Hospital, Dublin, Ireland; Perdana University - Royal College of Surgeons in Ireland School of Medicine, Serdang, Selangor, Malaysia.
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7
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Jansen JM, Wartchow C, Jahnke W, Fong S, Tsang T, Pfister K, Zavorotinskaya T, Bussiere D, Cheng JM, Crawford K, Dai Y, Dove J, Fang E, Feng Y, Florent JM, Fuller J, Gossert AD, Hekmat-Nejad M, Henry C, Klopp J, Lenahan WP, Lingel A, Ma S, Meyer A, Mishina Y, Narberes J, Pardee G, Ramurthy S, Rieffel S, Stuart D, Subramanian S, Tandeske L, Widger S, Widmer A, Winterhalter A, Zaror I, Hardy S. Inhibition of prenylated KRAS in a lipid environment. PLoS One 2017; 12:e0174706. [PMID: 28384226 PMCID: PMC5383040 DOI: 10.1371/journal.pone.0174706] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Accepted: 03/14/2017] [Indexed: 12/30/2022] Open
Abstract
RAS mutations lead to a constitutively active oncogenic protein that signals through multiple effector pathways. In this chemical biology study, we describe a novel coupled biochemical assay that measures activation of the effector BRAF by prenylated KRASG12V in a lipid-dependent manner. Using this assay, we discovered compounds that block biochemical and cellular functions of KRASG12V with low single-digit micromolar potency. We characterized the structural basis for inhibition using NMR methods and showed that the compounds stabilized the inactive conformation of KRASG12V. Determination of the biophysical affinity of binding using biolayer interferometry demonstrated that the potency of inhibition matches the affinity of binding only when KRAS is in its native state, namely post-translationally modified and in a lipid environment. The assays we describe here provide a first-time alignment across biochemical, biophysical, and cellular KRAS assays through incorporation of key physiological factors regulating RAS biology, namely a negatively charged lipid environment and prenylation, into the in vitro assays. These assays and the ligands we discovered are valuable tools for further study of KRAS inhibition and drug discovery.
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Affiliation(s)
- Johanna M. Jansen
- Department of Global Discovery Chemistry, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
- * E-mail:
| | - Charles Wartchow
- Department of Global Discovery Chemistry, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Wolfgang Jahnke
- Center for Proteomic Chemistry, Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Susan Fong
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Tiffany Tsang
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Keith Pfister
- Department of Global Discovery Chemistry, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Tatiana Zavorotinskaya
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Dirksen Bussiere
- Department of Global Discovery Chemistry, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Jan Marie Cheng
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Kenneth Crawford
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Yumin Dai
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Jeffrey Dove
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Eric Fang
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Yun Feng
- Department of Oncology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts, United States of America
| | - Jean-Michel Florent
- Center for Proteomic Chemistry, Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - John Fuller
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Alvar D. Gossert
- Center for Proteomic Chemistry, Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Mohammad Hekmat-Nejad
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Chrystèle Henry
- Center for Proteomic Chemistry, Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Julia Klopp
- Center for Proteomic Chemistry, Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - William P. Lenahan
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Andreas Lingel
- Department of Global Discovery Chemistry, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Sylvia Ma
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Arndt Meyer
- Department of Global Discovery Chemistry, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Yuji Mishina
- Department of Oncology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts, United States of America
| | - Jamie Narberes
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Gwynn Pardee
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Savithri Ramurthy
- Department of Global Discovery Chemistry, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Sebastien Rieffel
- Center for Proteomic Chemistry, Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Darrin Stuart
- Department of Oncology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts, United States of America
| | - Sharadha Subramanian
- Department of Global Discovery Chemistry, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Laura Tandeske
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Stephania Widger
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Armin Widmer
- Center for Proteomic Chemistry, Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Aurelie Winterhalter
- Center for Proteomic Chemistry, Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Isabel Zaror
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
| | - Stephen Hardy
- Department of Oncology, Novartis Institutes for BioMedical Research, Emeryville, California, United States of America
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8
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Kumar R. An account of fungal 14-3-3 proteins. Eur J Cell Biol 2017; 96:206-217. [PMID: 28258766 DOI: 10.1016/j.ejcb.2017.02.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2017] [Revised: 02/21/2017] [Accepted: 02/21/2017] [Indexed: 01/09/2023] Open
Abstract
14-3-3s are a group of relatively low molecular weight, acidic, dimeric, protein(s) conserved from single-celled yeast to multicellular vertebrates including humans. Despite lacking catalytic activity, these proteins have been shown to be involved in multiple cellular processes. Apart from their role in normal cellular physiology, recently these proteins have been implicated in various medical consequences. In this present review, fungal 14-3-3 protein localization, interactions, transcription, regulation, their role in the diverse cellular process including DNA duplication, cell cycle, protein trafficking or secretion, apoptosis, autophagy, cell viability under stress, gene expression, spindle positioning, role in carbon metabolism have been discussed. In the end, I also highlighted various roles of yeasts 14-3-3 proteins in tabular form. Thus this review with primary emphasis on yeast will help in appreciating the significance of 14-3-3 proteins in cell physiology.
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Affiliation(s)
- Ravinder Kumar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, Maharashtra, India.
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9
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Seo SB, Lee JJ, Yun HH, Im CN, Kim YS, Ko JH, Lee JH. 14-3-3β Depletion Drives a Senescence Program in Glioblastoma Cells Through the ERK/SKP2/p27 Pathway. Mol Neurobiol 2017; 55:1259-1270. [PMID: 28116547 DOI: 10.1007/s12035-017-0407-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 01/12/2017] [Indexed: 12/12/2022]
Abstract
The induction of senescence in cancer cells has recently been implicated as a mechanism of tumor regression in response to various modes of stress. 14-3-3 proteins are conserved scaffolding molecules that are involved in various cellular functions. Among the seven isoforms, 14-3-3β is specifically expressed in astrocytoma in correlation with the malignancy grade. We investigated the possible role of 14-3-3β in the regulation of senescence induction in A172 glioblastoma cells. The knockdown of 14-3-3β by specific small interfering RNA resulted in a significant change in cellular phenotypes and an increase in cells staining positive for senescence-associated β-galactosidase. Western blotting of the 14-3-3β-depleted A172 cells revealed increased p27 expression and decreased SKP2 expression, while the expression of p53 and p21 was not altered. Subsequently, we demonstrated that ERK is a key modulator of SKP2/p27 axis activity in 14-3-3β-mediated senescence based on the following: (1) 14-3-3β knockdown decreased p-ERK levels; (2) treatment with U0126, an MEK inhibitor, completely reproduced the senescence morphology as well as the expression profiles of p27 and SKP2; and (3) the senescence phenotypes induced by 14-3-3β depletion were considerably recovered by constitutively active ERK expression. Our results indicate that 14-3-3β negatively regulates senescence in glioblastoma cells via the ERK/SKP2/p27 pathway. Furthermore, 14-3-3β depletion also resulted in senescence phenotypes in U87 glioblastoma cells, suggesting that 14-3-3β could be targeted to induce premature senescence as a therapeutic strategy against glioblastoma progression.
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Affiliation(s)
- Sung Bin Seo
- Department of Biochemistry, College of Medicine, The Catholic University of Korea, 222, Banpo-daero, Seocho-gu, Seoul, 06591, Republic of Korea.,The Institute for Aging and Metabolic Diseases, College of Medicine, The Catholic University of Korea, Seoul, 06591, Republic of Korea
| | - Je-Jung Lee
- Tunneling Nanotube Research Center, Korea University, Seoul, 02841, Republic of Korea
| | - Hye Hyeon Yun
- Department of Biochemistry, College of Medicine, The Catholic University of Korea, 222, Banpo-daero, Seocho-gu, Seoul, 06591, Republic of Korea.,The Institute for Aging and Metabolic Diseases, College of Medicine, The Catholic University of Korea, Seoul, 06591, Republic of Korea
| | - Chang-Nim Im
- Department of Biochemistry, College of Medicine, The Catholic University of Korea, 222, Banpo-daero, Seocho-gu, Seoul, 06591, Republic of Korea.,The Institute for Aging and Metabolic Diseases, College of Medicine, The Catholic University of Korea, Seoul, 06591, Republic of Korea
| | - Yong-Sam Kim
- Genome Editing Research Center, KRIBB, Daejeon, 34141, Republic of Korea
| | - Jeong-Heon Ko
- Genome Editing Research Center, KRIBB, Daejeon, 34141, Republic of Korea
| | - Jeong-Hwa Lee
- Department of Biochemistry, College of Medicine, The Catholic University of Korea, 222, Banpo-daero, Seocho-gu, Seoul, 06591, Republic of Korea. .,The Institute for Aging and Metabolic Diseases, College of Medicine, The Catholic University of Korea, Seoul, 06591, Republic of Korea.
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10
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Abstract
Cells respond to changes in their environment, to developmental cues, and to pathogen aggression through the action of a complex network of proteins. These networks can be decomposed into a multitude of signaling pathways that relay signals from the microenvironment to the cellular components involved in eliciting a specific response. Perturbations in these signaling processes are at the root of multiple pathologies, the most notable of these being cancer. The study of receptor tyrosine kinase (RTK) signaling led to the first description of a mechanism whereby an extracellular signal is transmitted to the nucleus to induce a transcriptional response. Genetic studies conducted in drosophila and nematodes have provided key elements to this puzzle. Here, we briefly discuss the somewhat lesser known contribution of these multicellular organisms to our understanding of what has come to be known as the prototype of signaling pathways. We also discuss the ostensibly much larger network of regulators that has emerged from recent functional genomic investigations of RTK/RAS/ERK signaling.
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Affiliation(s)
- Dariel Ashton-Beaucage
- Institute for Research in Immunology and Cancer, Laboratory of Intracellular Signaling, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montreal, QC, Canada, H3C 3J7
| | - Marc Therrien
- Institute for Research in Immunology and Cancer, Laboratory of Intracellular Signaling, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montreal, QC, Canada, H3C 3J7.
- Département de Pathologie et de Biologie Cellulaire, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montreal, QC, Canada, H3C 3J7.
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11
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Sacristán-Reviriego A, Molina M, Martín H. Methods to Study Protein Tyrosine Phosphatases Acting on Yeast MAPKs. Methods Mol Biol 2016; 1447:385-398. [PMID: 27514817 DOI: 10.1007/978-1-4939-3746-2_21] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Mitogen activated protein kinases (MAPK) pathways play a key role in orchestrating the eukaryotic cellular response to different stimuli. In this process, phosphorylation of both conserved threonine and tyrosine residues of MAPKs is essential for their activation. Identification of tyrosine and dual specificity protein phosphatases capable of dephosphorylating these phosphosites is thus critical to gain insight into their regulation. Due to the conservation of pivotal elements in eukaryotic signaling, yeast has turned into a valuable tool to increase the knowledge of MAPK signaling in other cell types. Here we describe an in vivo method to evaluate the capacity of a protein, from yeast or other origin, to act as a MAPK phosphatase. It relies on the ability of the phosphatase to reduce, when overexpressed, both the amount of activated MAPK and the transcription from a specific promoter regulated by the corresponding pathway. To this end, the pathway has to be previously activated, preferentially through overexpression of a hyperactive allele of an upstream component within the MAPK module. Additionally, the ability of an overexpressed "trapping" inactive phosphatase version to modify these readouts is also analyzed. Western blotting analysis with specific anti-phospho MAPK antibodies and flow cytometry-based determination of fluorescence produced by GFP whose expression is driven by MAPK-regulated promoters are the selected techniques for monitoring these readouts.
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Affiliation(s)
- Almudena Sacristán-Reviriego
- Departamento de Microbiología II, Facultad de Farmacia, Instituto Ramón y Cajal de Investigaciones Sanitarias (IRYCIS), Universidad Complutense de Madrid, Plaza de Ramón y Cajal s/n, 28040, Madrid, Spain
| | - María Molina
- Departamento de Microbiología II, Facultad de Farmacia, Instituto Ramón y Cajal de Investigaciones Sanitarias (IRYCIS), Universidad Complutense de Madrid, Plaza de Ramón y Cajal s/n, 28040, Madrid, Spain
| | - Humberto Martín
- Departamento de Microbiología II, Facultad de Farmacia, Instituto Ramón y Cajal de Investigaciones Sanitarias (IRYCIS), Universidad Complutense de Madrid, Plaza de Ramón y Cajal s/n, 28040, Madrid, Spain.
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12
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Abstract
RAF family kinases were among the first oncoproteins to be described more than 30 years ago. They primarily act as signalling relays downstream of RAS, and their close ties to cancer have fuelled a large number of studies. However, we still lack a systems-level understanding of their regulation and mode of action. The recent discovery that the catalytic activity of RAF depends on an allosteric mechanism driven by kinase domain dimerization is providing a vital new piece of information towards a comprehensive model of RAF function. The fact that current RAF inhibitors unexpectedly induce ERK signalling by stimulating RAF dimerization also calls for a deeper structural characterization of this family of kinases.
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13
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PASTUHOV SI, HISAMOTO N, MATSUMOTO K. MAP kinase cascades regulating axon regeneration in C. elegans. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2015; 91:63-75. [PMID: 25792136 PMCID: PMC4410086 DOI: 10.2183/pjab.91.63] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Accepted: 01/13/2015] [Indexed: 06/04/2023]
Abstract
Mitogen-activated protein kinase (MAPK) signaling cascades are activated by diverse stimuli such as growth factors, cytokines, neurotransmitters and various types of cellular stress. Our evolving understanding of these signal cascades has been facilitated by genetic analyses and physiological characterization in model organisms such as the nematode Caenorhabditis elegans. Genetic and biochemical studies in C. elegans have shed light on the physiological roles of MAPK cascades in the control of cell fate decision, neuronal function and immunity. Recently it was demonstrated that MAPK signaling is also important for axon regeneration in C. elegans, and the use of C. elegans as a model system has significantly advanced our understanding of the largely conserved molecular mechanisms underlying axon regeneration. This review summarizes our current understanding of the role and regulation of MAPK signaling in C. elegans axon regeneration.
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Affiliation(s)
- Strahil Iv. PASTUHOV
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, Japan
| | - Naoki HISAMOTO
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, Japan
| | - Kunihiro MATSUMOTO
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, Japan
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Azoulay-Alfaguter I, Strazza M, Mor A. Chaperone-mediated specificity in Ras and Rap signaling. Crit Rev Biochem Mol Biol 2014; 50:194-202. [PMID: 25488471 DOI: 10.3109/10409238.2014.989308] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Ras and Rap proteins are closely related small guanosine triphosphatase (GTPases) that share similar effector-binding domains but operate in a very different signaling networks; Ras has a dominant role in cell proliferation, while Rap mediates cell adhesion. Ras and Rap proteins are regulated by several shared processes such as post-translational modification, phosphorylation, activation by guanine exchange factors and inhibition by GTPase-activating proteins. Sub-cellular localization and trafficking of these proteins to and from the plasma membrane are additional important regulatory features that impact small GTPases function. Despite its importance, the trafficking mechanisms of Ras and Rap proteins are not completely understood. Chaperone proteins play a critical role in trafficking of GTPases and will be the focus of the discussion in this work. We will review several aspects of chaperone biology focusing on specificity toward particular members of the small GTPase family. Understanding this specificity should provide key insights into drug development targeting individual small GTPases.
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15
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An S, Yang Y, Ward R, Liu Y, Guo XX, Xu TR. Raf-interactome in tuning the complexity and diversity of Raf function. FEBS J 2014; 282:32-53. [PMID: 25333451 DOI: 10.1111/febs.13113] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2014] [Revised: 10/06/2014] [Accepted: 10/14/2014] [Indexed: 12/23/2022]
Abstract
Raf kinases have been intensely studied subsequent to their discovery 30 years ago. The Ras-Raf-mitogen-activated protein kinase/extracellular signal-regulated kinase kinase-extracellular signal-regulated kinase/mitogen-activated protein kinase (Ras-Raf-MEK-ERK/MAPK) signaling pathway is at the heart of the signaling networks that control many fundamental cellular processes and Raf kinases takes centre stage in the MAPK pathway, which is now appreciated to be one of the most common sources of the oncogenic mutations in cancer. The dependency of tumors on this pathway has been clearly demonstrated by targeting its key nodes; however, blockade of the central components of the MAPK pathway may have some unexpected side effects. Over recent years, the Raf-interactome or Raf-interacting proteins have emerged as promising targets for protein-directed cancer therapy. This review focuses on the diversity of Raf-interacting proteins and discusses the mechanisms by which these proteins regulate Raf function, as well as the implications of targeting Raf-interacting proteins in the treatment of human cancer.
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Affiliation(s)
- Su An
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Yunnan, China
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Nussinov R, Jang H. Dynamic multiprotein assemblies shape the spatial structure of cell signaling. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2014; 116:158-64. [PMID: 25046855 PMCID: PMC4250281 DOI: 10.1016/j.pbiomolbio.2014.07.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 07/07/2014] [Indexed: 11/25/2022]
Abstract
Cell signaling underlies critical cellular decisions. Coordination, efficiency as well as fail-safe mechanisms are key elements. How the cell ensures that these hallmarks are at play are important questions. Cell signaling is often viewed as taking place through discrete and cross-talking pathways; oftentimes these are modularized to emphasize distinct functions. While simple, convenient and clear, such models largely neglect the spatial structure of cell signaling; they also convey inter-modular (or inter-protein) spatial separation that may not exist. Here our thesis is that cell signaling is shaped by a network of multiprotein assemblies. While pre-organized, the assemblies and network are loose and dynamic. They contain transiently-associated multiprotein complexes which are often mediated by scaffolding proteins. They are also typically anchored in the membrane, and their continuum may span the cell. IQGAP1 scaffolding protein which binds proteins including Raf, calmodulin, Mek, Erk, actin, and tens more, with actin shaping B-cell (and likely other) membrane-anchored nanoclusters and allosterically polymerizing in dynamic cytoskeleton formation, and Raf anchoring in the membrane along with Ras, provides a striking example. The multivalent network of dynamic proteins and lipids, with specific interactions forming and breaking, can be viewed as endowing gel-like properties. Collectively, this reasons that efficient, productive and reliable cell signaling takes place primarily through transient, preorganized and cooperative protein-protein interactions spanning the cell rather than stochastic, diffusion-controlled processes.
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Affiliation(s)
- Ruth Nussinov
- Cancer and Inflammation Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, National Cancer Institute, Frederick, MD 21702, USA; Sackler Inst. of Molecular Medicine, Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
| | - Hyunbum Jang
- Cancer and Inflammation Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, National Cancer Institute, Frederick, MD 21702, USA
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Zhang Y, Kweon HK, Shively C, Kumar A, Andrews PC. Towards systematic discovery of signaling networks in budding yeast filamentous growth stress response using interventional phosphorylation data. PLoS Comput Biol 2013; 9:e1003077. [PMID: 23825934 PMCID: PMC3694812 DOI: 10.1371/journal.pcbi.1003077] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Accepted: 04/17/2013] [Indexed: 11/19/2022] Open
Abstract
Reversible phosphorylation is one of the major mechanisms of signal transduction, and signaling networks are critical regulators of cell growth and development. However, few of these networks have been delineated completely. Towards this end, quantitative phosphoproteomics is emerging as a useful tool enabling large-scale determination of relative phosphorylation levels. However, phosphoproteomics differs from classical proteomics by a more extensive sampling limitation due to the limited number of detectable sites per protein. Here, we propose a comprehensive quantitative analysis pipeline customized for phosphoproteome data from interventional experiments for identifying key proteins in specific pathways, discovering the protein-protein interactions and inferring the signaling network. We also made an effort to partially compensate for the missing value problem, a chronic issue for proteomics studies. The dataset used for this study was generated using SILAC (Stable Isotope Labeling with Amino acids in Cell culture) technique with interventional experiments (kinase-dead mutations). The major components of the pipeline include phosphopeptide meta-analysis, correlation network analysis and causal relationship discovery. We have successfully applied our pipeline to interventional experiments identifying phosphorylation events underlying the transition to a filamentous growth form in Saccharomyces cerevisiae. We identified 5 high-confidence proteins from meta-analysis, and 19 hub proteins from correlation analysis (Pbi2p and Hsp42p were identified by both analyses). All these proteins are involved in stress responses. Nine of them have direct or indirect evidence of involvement in filamentous growth. In addition, we tested four of our predicted proteins, Nth1p, Pbi2p, Pdr12p and Rcn2p, by interventional phenotypic experiments and all of them present differential invasive growth, providing prospective validation of our approach. This comprehensive pipeline presents a systematic way for discovering signaling networks using interventional phosphoproteome data and can suggest candidate proteins for further investigation. We anticipate the methodology to be applicable as well to other interventional studies via different experimental platforms.
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Affiliation(s)
- Yan Zhang
- Department of Computational Medicine and Bioinformatics, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Hye Kyong Kweon
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Christian Shively
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Anuj Kumar
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Philip C. Andrews
- Department of Computational Medicine and Bioinformatics, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
- * E-mail:
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Integrated analyses of genome-wide DNA occupancy and expression profiling identify key genes and pathways involved in cellular transformation by a Marek's disease virus oncoprotein, Meq. J Virol 2013; 87:9016-29. [PMID: 23740999 DOI: 10.1128/jvi.01163-13] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Marek's disease (MD) is an economically significant disease in chickens that is caused by the highly oncogenic Marek's disease virus (MDV). A major unanswered question is the mechanism of MDV-induced tumor formation. Meq, a bZIP transcription factor discovered in the 1990s, is critically involved in viral oncogenicity, but only a few of its host target genes have been described, impeding our understanding of MDV-induced tumorigenesis. Using chromatin immunoprecipitation-sequencing (ChIP-seq) and microarray analysis, a high-confidence list of Meq binding sites in the chicken genome and a global transcriptome of Meq-responsive genes were generated. Meq binding sites were found to be enriched in the promoter regions of upregulated genes but not in those of downregulated genes. ChIP-seq was also performed for c-Jun, a known heterodimeric partner of Meq. The close location of binding sites of Meq and c-Jun was noted, suggesting cooperativity between these two factors in modulating transcription. Pathway analysis indicated that Meq transcriptionally regulates many genes that are part of several signaling pathways including the extracellular signal-regulated kinase /mitogen-activated protein kinase (ERK/MAPK), Jak-STAT, and ErbB pathways, which are critical for oncogenesis and/or include signaling mediators involved in apoptosis. Meq activates oncogenic signaling cascades by transcriptionally activating major kinases in the ERK/MAPK pathway and simultaneously repressing phosphatases, as verified using inhibitors of MEK and ERK1/2 in a cell proliferation assay. This study provides significant insights into the mechanistic basis of Meq-dependent cell transformation.
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Huang XY, Ke AW, Shi GM, Zhang X, Zhang C, Shi YH, Wang XY, Ding ZB, Xiao YS, Yan J, Qiu SJ, Fan J, Zhou J. αB-crystallin complexes with 14-3-3ζ to induce epithelial-mesenchymal transition and resistance to sorafenib in hepatocellular carcinoma. Hepatology 2013; 57:2235-47. [PMID: 23316005 DOI: 10.1002/hep.26255] [Citation(s) in RCA: 127] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Accepted: 12/13/2012] [Indexed: 12/11/2022]
Abstract
UNLABELLED The overall survival of patients with hepatocellular carcinoma (HCC) remains poor, and the molecular pathogenesis remains incompletely defined in HCC. Here we report that increased expression of αB-Crystallin in human HCC predicts poor survival and disease recurrence after surgery. Multivariate analysis identifies αB-Crystallin expression as an independent predictor for postoperative recurrence and overall survival. We show that elevated expression of αB-Crystallin promotes HCC progression in vivo and in vitro. We demonstrate that αB-Crystallin overexpression fosters HCC progression by inducing epithelial-mesenchymal transition (EMT) in HCC cells through activation of the extracellular-regulated protein kinase (ERK) cascade, which can counteract the effect of sorafenib. αB-Crystallin complexes with and elevates 14-3-3ζ protein, leading to up-regulation of ERK1/2 activity. Moreover, overexpression of αB-Crystallin in HCC cells induces EMT progression through an ERK1/2/Fra-1/slug signaling pathway. Clinically, our data reveal that overexpression of both αB-Crystallin and 14-3-3ζ correlates with the HCC poorest survival outcomes, and sorafenib response is impaired in patients with αB-Crystallin overexpression. CONCLUSION These data suggest that the αB-Crystallin-14-3-3ζ complex acts synergistically to promote HCC progression by constitutively activating ERK signaling. This study reveals αB-Crystallin as a potential therapeutic target for HCC and a biomarker for predicting sorafenib treatment response. (HEPATOLOGY 2013).
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Affiliation(s)
- Xiao-Yong Huang
- Liver Cancer Institute, Zhongshan Hospital, Fudan University; Key Laboratory of Carcinogenesis and Cancer Invasion (Fudan University), Ministry of Education, Shanghai, PR China
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Fernandez-Piñar P, Alemán A, Sondek J, Dohlman HG, Molina M, Martín H. The Salmonella Typhimurium effector SteC inhibits Cdc42-mediated signaling through binding to the exchange factor Cdc24 in Saccharomyces cerevisiae. Mol Biol Cell 2012; 23:4430-43. [PMID: 23015760 PMCID: PMC3496616 DOI: 10.1091/mbc.e12-03-0243] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Expression of the Salmonella effector SteC in yeast leads to down-regulation of the mating and HOG pathways by Cdc42 inhibition. This is mediated by the SteC N-terminal domain through binding to the GEF Cdc24. SteC alters Cdc24 localization and also interacts with human GEF Vav1, suggesting that SteC could target Cdc42 function in host cells. Intracellular survival of Salmonella relies on the activity of proteins translocated into the host cell by type III secretion systems (T3SS). The protein kinase activity of the T3SS effector SteC is required for F-actin remodeling in host cells, although no SteC target has been identified so far. Here we show that expression of the N-terminal non-kinase domain of SteC down-regulates the mating and HOG pathways in Saccharomyces cerevisiae. Epistasis analyses using constitutively active components of these pathways indicate that SteC inhibits signaling at the level of the GTPase Cdc42. We demonstrate that SteC interacts through its N-terminal domain with the catalytic domain of Cdc24, the sole S. cerevisiae Cdc42 guanine nucleotide exchange factor (GEF). SteC also binds to the human Cdc24-like GEF protein Vav1. Moreover, expression of human Cdc42 suppresses growth inhibition caused by SteC. Of interest, the N-terminal SteC domain alters Cdc24 cellular localization, preventing its nuclear accumulation. These data reveal a novel functional domain within SteC, raising the possibility that this effector could also target GTPase function in mammalian cells. Our results also highlight the key role of the Cdc42 switch in yeast mating and HOG pathways and provide a new tool to study the functional consequences of Cdc24 localization.
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Affiliation(s)
- Pablo Fernandez-Piñar
- Departamento de Microbiología II, Facultad de Farmacia, Universidad Complutense de Madrid, and Instituto Ramón y Cajal de Investigaciones Sanitarias, 28040 Madrid, Spain
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21
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Targeting Raf/MEK/ERK pathway in pituitary adenomas. Eur J Cancer 2012; 48:389-95. [DOI: 10.1016/j.ejca.2011.11.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Revised: 10/01/2011] [Accepted: 11/02/2011] [Indexed: 12/11/2022]
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22
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Bruscoli S, Velardi E, Di Sante M, Bereshchenko O, Venanzi A, Coppo M, Berno V, Mameli MG, Colella R, Cavaliere A, Riccardi C. Long glucocorticoid-induced leucine zipper (L-GILZ) protein interacts with ras protein pathway and contributes to spermatogenesis control. J Biol Chem 2011; 287:1242-51. [PMID: 22110132 DOI: 10.1074/jbc.m111.316372] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Correct function of spermatogonia is critical for the maintenance of spermatogenesis throughout life, but the cellular pathways regulating undifferentiated spermatogonia proliferation, differentiation, and survival are only partially known. We show here that long glucocorticoid-induced leucine zipper (L-GILZ) is highly expressed in spermatogonia and primary spermatocytes and controls spermatogenesis. Gilz deficiency in knock-out (gilz KO) mice leads to a complete loss of germ cell lineage within first cycles of spermatogenesis, resulting in male sterility. Spermatogenesis failure is intrinsic to germ cells and is associated with increased proliferation and aberrant differentiation of undifferentiated spermatogonia and with hyperactivity of Ras signaling pathway as indicated by an increase of ERK and Akt phosphorylation. Spermatogonia differentiation does not proceed beyond the prophase of the first meiotic division due to massive apoptosis associated with accumulation of unrepaired chromosomal damage. These results identify L-GILZ as a novel important factor for undifferentiated spermatogonia function and spermatogenesis.
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Affiliation(s)
- Stefano Bruscoli
- Department of Clinical and Experimental Medicine, Section of Pharmacology, Toxicology, and Chemotherapy, Medical School, University of Perugia, Via del Giochetto, 06122 Perugia, Italy
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23
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Discovery and structural characterization of a small molecule 14-3-3 protein-protein interaction inhibitor. Proc Natl Acad Sci U S A 2011; 108:16212-6. [PMID: 21908710 DOI: 10.1073/pnas.1100012108] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The 14-3-3 family of phosphoserine/threonine-recognition proteins engage multiple nodes in signaling networks that control diverse physiological and pathophysiological functions and have emerged as promising therapeutic targets for such diseases as cancer and neurodegenerative disorders. Thus, small molecule modulators of 14-3-3 are much needed agents for chemical biology investigations and therapeutic development. To analyze 14-3-3 function and modulate its activity, we conducted a chemical screen and identified 4-[(2Z)-2-[4-formyl-6-methyl-5-oxo-3-(phosphonatooxymethyl)pyridin-2-ylidene]hydrazinyl]benzoate as a 14-3-3 inhibitor, which we termed FOBISIN (FOurteen-three-three BInding Small molecule INhibitor) 101. FOBISIN101 effectively blocked the binding of 14-3-3 with Raf-1 and proline-rich AKT substrate, 40 kD(a) and neutralized the ability of 14-3-3 to activate exoenzyme S ADP-ribosyltransferase. To provide a mechanistic basis for 14-3-3 inhibition, the crystal structure of 14-3-3ζ in complex with FOBISIN101 was solved. Unexpectedly, the double bond linking the pyridoxal-phosphate and benzoate moieties was reduced by X-rays to create a covalent linkage of the pyridoxal-phosphate moiety to lysine 120 in the binding groove of 14-3-3, leading to persistent 14-3-3 inactivation. We suggest that FOBISIN101-like molecules could be developed as an entirely unique class of 14-3-3 inhibitors, which may serve as radiation-triggered therapeutic agents for the treatment of 14-3-3-mediated diseases, such as cancer.
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Inoue M, Yasuda K, Uemura H, Yasaka N, Inoue H, Sei Y, Horikoshi N, Fukuma T. Phosphorylation-dependent protein interaction with Trypanosoma brucei 14-3-3 proteins that display atypical target recognition. PLoS One 2010; 5:e15566. [PMID: 21203569 PMCID: PMC3006207 DOI: 10.1371/journal.pone.0015566] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Accepted: 11/12/2010] [Indexed: 11/19/2022] Open
Abstract
Background The 14-3-3 proteins are structurally conserved throughout eukaryotes and participate in protein kinase signaling. All 14-3-3 proteins are known to bind to evolutionally conserved phosphoserine-containing motifs (modes 1 and/or 2) with high affinity. In Trypanosoma brucei, 14-3-3I and II play pivotal roles in motility, cytokinesis and the cell cycle. However, none of the T. brucei 14-3-3 binding proteins have previously been documented. Methodology/Principal Findings Initially we showed that T. brucei 14-3-3 proteins exhibit far lower affinity to those peptides containing RSxpSxP (mode 1) and RxY/FxpSxP (mode 2) (where x is any amino acid residue and pS is phosphoserine) than human 14-3-3 proteins, demonstrating the atypical target recognition by T. brucei 14-3-3 proteins. We found that the putative T. brucei protein phosphatase 2C (PP2c) binds to T. brucei 14-3-3 proteins utilizing its mode 3 motif (–pS/pTx1-2-COOH, where x is not Pro). We constructed eight chimeric PP2c proteins replacing its authentic mode 3 motif with potential mode 3 sequences found in Trypanosoma brucei genome database, and tested their binding. As a result, T. brucei 14-3-3 proteins interacted with three out of eight chimeric proteins including two with high affinity. Importantly, T. brucei 14-3-3 proteins co-immunoprecipitated with an uncharacterized full-length protein containing identified high-affinity mode 3 motif, suggesting that both proteins form a complex in vivo. In addition, a synthetic peptide derived from this mode 3 motif binds to T. brucei 14-3-3 proteins with high affinity. Conclusion/Significance Because of the atypical target recognition of T. brucei 14-3-3 proteins, no 14-3-3-binding proteins have been successfully identified in T. brucei until now whereas over 200 human 14-3-3-binding proteins have been identified. This report describes the first discovery of the T. brucei 14-3-3-binding proteins and their binding motifs. The high-affinity phosphopeptide will be a powerful tool to identify novel T. brucei 14-3-3-binding proteins.
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Affiliation(s)
- Masahiro Inoue
- Division of Eukaryotic Microbiology, Department of Infectious Medicine, Kurume University School of Medicine, Kurume, Japan.
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25
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Panni S, Montecchi-Palazzi L, Kiemer L, Cabibbo A, Paoluzi S, Santonico E, Landgraf C, Volkmer-Engert R, Bachi A, Castagnoli L, Cesareni G. Combining peptide recognition specificity and context information for the prediction of the 14-3-3-mediated interactome in S. cerevisiae
and H. sapiens. Proteomics 2010; 11:128-43. [DOI: 10.1002/pmic.201000030] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2010] [Revised: 09/24/2010] [Accepted: 10/09/2010] [Indexed: 11/08/2022]
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26
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Urano-Tashiro Y, Sasaki H, Sugawara-Kawasaki M, Yamada T, Sugiyama A, Akiyama H, Kawasaki Y, Tashiro F. Implication of Akt-dependent Prp19 alpha/14-3-3beta/Cdc5L complex formation in neuronal differentiation. J Neurosci Res 2010; 88:2787-97. [PMID: 20629186 DOI: 10.1002/jnr.22455] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
PRP19alpha and CDC5L are major components of the active spliceosome. However, their association process is still unknown. Here, we demonstrated that PRP19 alpha/14-3-3beta/CDC5L complex formation is regulated by Akt during nerve growth factor (NGF)-induced neuronal differentiation of PC12 cells. Analysis of PRP19 alpha mutants revealed that the phosphorylation of PRP19 alpha at Thr 193 by Akt was critical for its binding with 14-3-3beta to translocate into the nuclei and for PRP19 alpha/14-3-3beta/CDC5L complex formation in neuronal differentiation. Forced expression of either sense PRP19 alpha or sense 14-3-3beta RNAs promoted NGF-induced neuronal differentiation, whereas down-regulation of these mRNAs showed a suppressive effect. The nonphosphorylation mutant PRP19 alpha T193A lost its binding ability with 14-3-3beta and acted as a dominant-negative mutant in neuronal differentiation. These results imply that Akt-dependent phosphorylation of PRP19 alpha at Thr193 triggers PRP19 alpha/14-3-3beta/CDC5L complex formation in the nuclei, likely to assemble the active spliceosome against neurogenic pre-mRNAs.
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Affiliation(s)
- Yumiko Urano-Tashiro
- Department of Biological Science and Technology, Faculty of Industrial Science and Technology, Tokyo University of Science, Chiba, Japan
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27
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Affiliation(s)
- P Lenormand
- Centre de Biochimie-CNRS UMR 134, Université de Nice, Parc Valrose, 06108 Nice Cedex 2, France
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28
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Lee M. Overexpression of human Raf-1 enhances radiosensitivity in fission yeast, Schizosaccharomyces pombe. Cell Biochem Funct 2009; 26:125-31. [PMID: 17614099 DOI: 10.1002/cbf.1428] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Recently we isolated Rad24, a 14-3-3 homologue, which is essential for DNA damage checkpoint, as a Raf-1 interacting protein by screening a Schizosaccharomyces pombe (S. pombe) cDNA library. Raf-1 was also found to recognize Cdc25 that is sequestered and inactivated by Rad24. In the present study, experiments were performed to determine the effect of overexpression of Raf-1 proteins on asynchronously growing S. pombe cells. The overexpression of Rad24 induced elongated cell morphology and reduction in growth rate, resulting in cell cycle arrest while the overexpression of catalytically active Raf-1 led to a decrease in cell size at division in S. pombe. However, the active Raf-1 failed to rescue the growth arrest induced by Rad24 overexpression. In addition, the cells carrying catalytically active Raf-1 were significantly more radiosensitive than those from a normal control as assessed by ultraviolet sensitivity assay, suggesting that constitutive overproduction of Raf-1 kinase can revert DNA replication checkpoint arrest caused by UV irradiation. Taken together, these data suggest that Raf-1 may interfere with the role of Rad24 by competing with Rad24 for binding to Cdc25 in DNA repair, bypassing the checkpoint pathway through Cdc25 activation.
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Affiliation(s)
- Michael Lee
- Department of Biology, College of Natural Sciences, University of Incheon, Incheon, Korea.
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Sun XJ, Liu F. Phosphorylation of IRS proteins Yin-Yang regulation of insulin signaling. VITAMINS AND HORMONES 2009; 80:351-87. [PMID: 19251044 DOI: 10.1016/s0083-6729(08)00613-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Growing evidence reveals that insulin signal pathway is not static, but is rather a dynamic, flexible, and fed in by negative (Yin) and positive (Yang) regulation in response to environmental changes. Normal insulin response reflects the balance between Yin and Yang regulation acting upon insulin signaling pathway. Conceivably, imbalance between the Yin and Yang results in abnormal insulin sensitivity such as insulin resistance. IRS-proteins are insulin receptor substrates that mediate insulin signaling via multiple tyrosyl phosphorylations. However, they are also substrates for many serine/threonine kinases downstream of other signaling network and become serine phosphorylated in response to various conditions such as inflammation, stress and over nutrients. The serine phosphorylation of IRS-proteins alters the capacities of IRS-proteins to be phosphorylated on tyrosyl, therefore, able to mediate insulin signaling. The unique structure of IRS-proteins render them idea molecules to fulfill the task to sense the environmental cues and integrate them into insulin sensitivity through serine/threonine phosphorylation. This review intends to summarize the role of IRS-proteins in insulin signaling with focuses on the role of Yin and Yang regulation of insulin signaling pathway. Understanding the dynamic of these complicated regulation net work not only provide us a complete picture of what happens in the normal conditions, but also pathaphysiological conditions such as obesity and insulin resistance.
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Affiliation(s)
- Xiao Jian Sun
- Department of Medicine, The University of Chicago, Chicago, Illinois 60637, USA
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30
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Ustilago maydis Rho1 and 14-3-3 homologues participate in pathways controlling cell separation and cell polarity. EUKARYOTIC CELL 2009; 8:977-89. [PMID: 19411618 DOI: 10.1128/ec.00009-09] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Proteins of the 14-3-3 and Rho-GTPase families are functionally conserved eukaryotic proteins that participate in many important cellular processes such as signal transduction, cell cycle regulation, malignant transformation, stress response, and apoptosis. However, the exact role(s) of these proteins in these processes is not entirely understood. Using the fungal maize pathogen, Ustilago maydis, we were able to demonstrate a functional connection between Pdc1 and Rho1, the U. maydis homologues of 14-3-3epsilon and Rho1, respectively. Our experiments suggest that Pdc1 regulates viability, cytokinesis, chromosome condensation, and vacuole formation. Similarly, U. maydis Rho1 is also involved in these three essential processes and exerts an additional function during mating and filamentation. Intriguingly, yeast two-hybrid and epistasis experiments suggest that both Pdc1 and Rho1 could be constituents of the same regulatory cascade(s) controlling cell growth and filamentation in U. maydis. Overexpression of rho1 ameliorated the defects of cells depleted for Pdc1. Furthermore, we found that another small G protein, Rac1, was a suppressor of lethality for both Pdc1 and Rho1. In addition, deletion of cla4, encoding a Rac1 effector kinase, could also rescue cells with Pdc1 depleted. Inferring from these data, we propose a model for Rho1 and Pdc1 functions in U. maydis.
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Deakin NO, Bass MD, Warwood S, Schoelermann J, Mostafavi-Pour Z, Knight D, Ballestrem C, Humphries MJ. An integrin-alpha4-14-3-3zeta-paxillin ternary complex mediates localised Cdc42 activity and accelerates cell migration. J Cell Sci 2009; 122:1654-64. [PMID: 19401330 DOI: 10.1242/jcs.049130] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Alpha4 integrins are used by leukocytes and neural crest derivatives for adhesion and migration during embryogenesis, immune responses and tumour invasion. The pro-migratory activity of alpha4 integrin is mediated in part through the direct binding of the cytoplasmic domain to paxillin. Here, using intermolecular FRET and biochemical analyses, we report a novel interaction of the alpha4 integrin cytoplasmic domain with 14-3-3zeta. This interaction depends on serine phosphorylation of alpha4 integrin at a site (S978) distinct from that which regulates paxillin binding (S988). Using a combination of metabolic labelling and targeted mass spectrometry by multiple reaction monitoring we demonstrate the low stoichiometry phosphorylation of S978. The interaction between alpha4 integrin and 14-3-3zeta is enhanced by the direct association between 14-3-3zeta and paxillin, resulting in the formation of a ternary complex that stabilises the recruitment of each component. Although pair-wise interaction between alpha4 integrin and paxillin is sufficient for normal Rac1 regulation, the integrity of the ternary complex is essential for focused Cdc42 activity at the lamellipodial leading edge and directed cell movement. Taken together, these data identify a key signalling nexus mediating alpha4 integrin-dependent migration.
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Affiliation(s)
- Nicholas O Deakin
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK
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Nekhoroshkova E, Albert S, Becker M, Rapp UR. A-RAF kinase functions in ARF6 regulated endocytic membrane traffic. PLoS One 2009; 4:e4647. [PMID: 19247477 PMCID: PMC2645234 DOI: 10.1371/journal.pone.0004647] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2008] [Accepted: 01/13/2009] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND RAF kinases direct ERK MAPK signaling to distinct subcellular compartments in response to growth factor stimulation. METHODOLOGY/PRINCIPAL FINDINGS Of the three mammalian isoforms A-RAF is special in that one of its two lipid binding domains mediates a unique pattern of membrane localization. Specific membrane binding is retained by an N-terminal fragment (AR149) that corresponds to a naturally occurring splice variant termed DA-RAF2. AR149 colocalizes with ARF6 on tubular endosomes and has a dominant negative effect on endocytic trafficking. Moreover actin polymerization of yeast and mammalian cells is abolished. AR149/DA-RAF2 does not affect the internalization step of endocytosis, but trafficking to the recycling compartment. CONCLUSIONS/SIGNIFICANCE A-RAF induced ERK activation is required for this step by activating ARF6, as A-RAF depletion or inhibition of the A-RAF controlled MEK-ERK cascade blocks recycling. These data led to a new model for A-RAF function in endocytic trafficking.
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Affiliation(s)
- Elena Nekhoroshkova
- Institut für Medizinische Strahlenkunde und Zellforschung (MSZ), University of Würzburg, Würzburg, Germany
| | - Stefan Albert
- Institut für Medizinische Strahlenkunde und Zellforschung (MSZ), University of Würzburg, Würzburg, Germany
| | - Matthias Becker
- Institut für Medizinische Strahlenkunde und Zellforschung (MSZ), University of Würzburg, Würzburg, Germany
| | - Ulf R. Rapp
- Institut für Medizinische Strahlenkunde und Zellforschung (MSZ), University of Würzburg, Würzburg, Germany
- * E-mail:
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Down-regulation of 14-3-3zeta suppresses anchorage-independent growth of lung cancer cells through anoikis activation. Proc Natl Acad Sci U S A 2007; 105:162-7. [PMID: 18162532 DOI: 10.1073/pnas.0710905105] [Citation(s) in RCA: 129] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The family of 14-3-3 proteins has emerged as critical regulators of diverse cellular responses under both physiological and pathological conditions. Here, we report an important role of 14-3-3zeta in tumorigenesis through a mechanism that involves anoikis resistance. 14-3-3zeta is up-regulated in a number of cancer types, including lung cancer. Through an RNAi approach using human lung adenocarcinoma-derived A549 cells as a model system, we have found that knockdown of a single zeta isoform of 14-3-3 is sufficient to restore the sensitivity of cancer cells to anoikis and impair their anchorage-independent growth. Enhanced anoikis appears to be mediated in part by up-regulated BH3-only proteins, Bad and Bim, coupled with decreased Mcl-1, resulting in the subsequent activation of Bax. This study suggests a model in which anchorage-independent growth of lung cancer cells requires the presence of 14-3-3zeta. This work not only reveals a critical role of 14-3-3zeta in anoikis suppression in lung cancer cells, but also identifies and validates 14-3-3zeta as a potential molecular target for anticancer therapeutic development.
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Lee M, Yoo HS. Human Raf-1 proteins associate with Rad24 and Cdc25 in cell-cycle checkpoint pathway of fission yeast, Schizosaccharomyces pombe. J Cell Biochem 2007; 101:488-97. [PMID: 17243098 DOI: 10.1002/jcb.21199] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Raf-1 is a serine/threonine protein kinase that connects cell surface receptor signals to nuclear transcription factors. By screening Schizosaccharomyces pombe (S. pombe) cDNA library, we isolated Rad24, which is a 14-3-3 homolog that is important in the DNA damage checkpoint in S. pombe, as a Raf-1 interacting protein. The interaction found in yeast was confirmed by co-immunoprecipitation. Furthermore, Cdc25, which has been known to bind to Rad24, also associated with Raf-1 and was phosphorylated in vitro by catalytically active Raf-1. However, in the presence of Raf-1, an interaction between Rad24 and Cdc25 was inhibited in triple hybrid assay, indicating that Raf-1 inhibits the interaction between Rad24 and Cdc25. An in vitro competition assay showed that the binding of Cdc25 and of Rad24 to Raf-1 is mutually exclusive. Western blots of whole cell lysates probed with polyclonal antibodies specific for tyrosine-15-phosphorylated Cdc2 showed that overproduction of Rad24 led to the dephosphorylation of tyrosine residue on Cdc2, which is known to be activated through dephosphorylation by Cdc25 phosphatase. Unexpectedly, overexpression of catalytically inactive mutant protein of Raf-1, S624A, also caused tyrosine dephosphorylation of Cdc2. Thus, these data suggest that Raf-1 may interfere with the role of Rad24 by competing with Rad24 for binding to Cdc25 or a direct phosphorylation of Cdc25, bypassing the checkpoint pathway in DNA repair through Cdc25 activation.
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Affiliation(s)
- Michael Lee
- Department of Biology, College of Natural Sciences, University of Incheon, Incheon, Korea.
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35
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Ayroldi E, Zollo O, Bastianelli A, Marchetti C, Agostini M, Di Virgilio R, Riccardi C. GILZ mediates the antiproliferative activity of glucocorticoids by negative regulation of Ras signaling. J Clin Invest 2007; 117:1605-15. [PMID: 17492054 PMCID: PMC1865030 DOI: 10.1172/jci30724] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2006] [Accepted: 03/13/2007] [Indexed: 12/30/2022] Open
Abstract
Tsc22d3 coding for glucocorticoid-induced leucine zipper (GILZ) was initially identified as a dexamethasone-responsive gene involved in the control of T lymphocyte activation and apoptosis. However, the physiological role of this molecule and its function in the biological activity of glucocorticoids (GCs) has not been clarified. Here, we demonstrate that GILZ interacts directly with Ras in vitro and in vivo as shown by GILZ and Ras coimmunoprecipitation and colocalization upon PMA activation in primary mouse spleen T lymphocytes and thymus cells. The analysis of GILZ mutants showed that they bound Ras through the tuberous sclerosis complex box (TSC) and, depending on the Ras activation level, formed a trimeric complex with Ras and Raf, which we previously identified as a GILZ binder. As a consequence of these interactions, GILZ diminished the activation of Ras and Raf downstream targets including ERK1/2, AKT/PKB serine/threonine kinase, and retinoblastoma (Rb) phosphorylation and cyclin D1 expression, leading to inhibition of Ras- and Raf-dependent cell proliferation and Ras-induced NIH-3T3 transformation. GILZ silencing resulted in an increase in concanavalin A-induced T cell proliferation and, most notably, inhibition of dexamethasone antiproliferative effects. Together, these findings indicate that GILZ serves as a negative regulator of Ras- and Raf-induced proliferation and is an important mediator of the antiproliferative effect of GCs.
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Affiliation(s)
- Emira Ayroldi
- Department of Clinical and Experimental Medicine, Section of Pharmacology, University of Perugia, Perugia, Italy
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36
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Lundquist JJ, Dudek SM. Differential activation of extracellular signal-regulated kinase 1 and a related complex in neuronal nuclei. BRAIN CELL BIOLOGY 2006; 35:267-81. [PMID: 18392730 PMCID: PMC3755592 DOI: 10.1007/s11068-008-9018-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2007] [Revised: 10/30/2007] [Accepted: 01/28/2008] [Indexed: 10/22/2022]
Abstract
The extracellular signal-regulated kinases 1 and 2 (ERKs 1/2) are known to participate in regulating transcription in response to moderate depolarization, such as synaptic stimulation, but how the same active enzyme can differentially regulate distinct transcriptional programs induced with abnormal depolarization (high potassium) is unknown. We hypothesized that ERK1 or 2 accomplishes this differential nuclear response through close association with other proteins in stable complexes. In support of this hypothesis, we have found that immunoreactivity for an apparent high molecular weight complex containing phospho-ERK1 increased in response to synaptic stimulation, but decreased in response to high potassium; p-ERK immunoreactivity at 44/42 kDa increased in both cases. Evidence supporting the conclusion that the band of interest contained ERK1 in a complex, as opposed to it being an unrelated protein crossreacting with antibodies against p-ERK, is that ERK1 (p44 MAPK) and 14-3-3 protein were electroeluted from the 160-kDa band cut from a gel. We also found the nuclear complexes to be exceptionally durable, suggesting a role for the crosslinking enzyme, transglutaminase, in its stabilization. In addition, we found other components of the ERK pathway, including MEK, ERK2, p90RSK, and Elk-1, migrating at higher-than-expected weights in brain nuclei. These results describe a novel stable complex of ERK1 in neuronal nuclei that responds differentially to synaptic and depolarizing stimulation, and thus may be capable of mediating gene transcription in a way distinct from the monomeric protein.
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Affiliation(s)
- Joseph J Lundquist
- National Institute of Environmental Health Sciences, National Institutes of Health, MD F2-04, PO Box 12233, Research Triangle Park, NC 27709, USA
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37
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Lau JMC, Wu C, Muslin AJ. Differential role of 14-3-3 family members in Xenopus development. Dev Dyn 2006; 235:1761-76. [PMID: 16607644 DOI: 10.1002/dvdy.20816] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The 14-3-3 proteins are intracellular dimeric phosphoserine/threonine binding molecules that participate in signal transduction, checkpoint control, nutrient sensing, and cell survival pathways. Previous work established that 14-3-3 proteins are required in early Xenopus laevis development by modulating fibroblast growth factor signaling. Although this general requirement for 14-3-3 proteins in Xenopus early embryogenesis is established, there is no information about the specific role of individual 14-3-3 genes. Botanical studies previously demonstrated functional specificity among 14-3-3 genes during plant development. In this study, an antisense morpholino oligo microinjection approach was used to characterize the requirement for six specific 14-3-3 family members in Xenopus embryogenesis. Microinjection experiments followed by Western blot analysis showed that morpholinos reduced specific 14-3-3 protein levels. Embryos lacking specific 14-3-3 isoforms displayed unique phenotypic defects. In particular, reduction of 14-3-3 tau (tau) protein, and to a lesser extent, 14-3-3 epsilon (epsilon), resulted in embryos with prominent gastrulation and axial patterning defects and reduced mesodermal marker gene expression. In contrast, reduction of 14-3-3 zeta (zeta) protein caused no obvious phenotypic abnormalities. Reduction of 14-3-3 gamma (gamma) protein resulted in eye defects without gastrulation abnormalities. Therefore, individual 14-3-3 genes have separable functions in vertebrate embryonic development.
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Affiliation(s)
- Jeffrey M C Lau
- Center for Cardiovascular Research, Department of Medicine, and Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Li J, Tewari M, Vidal M, Lee SS. The 14-3-3 protein FTT-2 regulates DAF-16 in Caenorhabditis elegans. Dev Biol 2006; 301:82-91. [PMID: 17098225 PMCID: PMC1963419 DOI: 10.1016/j.ydbio.2006.10.013] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2006] [Revised: 10/09/2006] [Accepted: 10/10/2006] [Indexed: 10/24/2022]
Abstract
The Caenorhabditis elegans daf-2/insulin-like signaling pathway is critical for regulating development, longevity, metabolism and stress resistance. We identified the 14-3-3 protein FTT-2 to be a new regulatory component of this pathway. We found that RNAi knock down of ftt-2 specifically enhanced the daf-2-mediated dauer formation phenotype. Furthermore, ftt-2 knock down caused the nuclear accumulation of DAF-16/FOXO, the forkhead transcription factor that is the major downstream effecter of daf-2/insulin-like signaling, and enhanced the transcriptional activities of DAF-16. In contrast to ftt-2, RNAi knock down of par-5/ftt-1, the only other gene predicted to encode a 14-3-3 protein in C. elegans, did not show any notable effect on dauer formation, DAF-16 localization, or DAF-16 downstream gene transcription, underscoring the functional specification of FTT-2 and PAR-5 despite their high sequence homology. Using co-immunoprecipitation, we revealed that FTT-2 formed a complex with GFP-fused DAF-16 in C. elegans. Our results indicate that FTT-2 binds to DAF-16 in C. elegans and regulates DAF-16 by sequestering it in the cytoplasm. A similar mechanism of regulation of FOXO by 14-3-3zeta has been reported in mammalian cells, highlighting the high degree of conservation of the daf-2/insulin-like signaling pathway.
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Affiliation(s)
- Ji Li
- Department of Molecular Biology, Cornell University, Ithaca, NY 14850
| | - Muneesh Tewari
- Center for Cancer Systems Biology (CCSB) and Department of Cancer Biology, Dana-Farber Cancer Institute, and Department of Genetics, Harvard Medical School, Boston, MA 02115
- Fred Hutchinson Cancer Research Center, Human Biology Division, Seattle, WA, 98109
| | - Marc Vidal
- Center for Cancer Systems Biology (CCSB) and Department of Cancer Biology, Dana-Farber Cancer Institute, and Department of Genetics, Harvard Medical School, Boston, MA 02115
| | - Siu Sylvia Lee
- Department of Molecular Biology, Cornell University, Ithaca, NY 14850
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Abramow-Newerly M, Ming H, Chidiac P. Modulation of subfamily B/R4 RGS protein function by 14-3-3 proteins. Cell Signal 2006; 18:2209-22. [PMID: 16839744 DOI: 10.1016/j.cellsig.2006.05.011] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2006] [Accepted: 05/09/2006] [Indexed: 12/01/2022]
Abstract
Regulator of G protein signalling (RGS) proteins are primarily known for their ability to act as GTPase activating proteins (GAPs) and thus attenuate G protein function within G protein-coupled receptor (GPCR) signalling pathways. However, RGS proteins have been found to interact with additional binding partners, and this has introduced more complexity to our understanding of their potential role in vivo. Here, we identify a novel interaction between RGS proteins (RGS4, RGS5, RGS16) and the multifunctional protein 14-3-3. Two isoforms, 14-3-3beta and 14-3-3epsilon, directly interact with all three purified RGS proteins and data from in vitro steady state GTP hydrolysis assays show that 14-3-3 inhibits the GTPase activity of RGS4 and RGS16, but has limited effects on RGS5 under comparable conditions. Moreover in a competitive pull-down experiment, 14-3-3epsilon competes with Galphao for RGS4, but not for RGS5. This mechanism is further reinforced in living cells, where 14-3-3epsilon sequesters RGS4 in the cytoplasm and impedes its recruitment to the plasma membrane by Galpha protein. Thus, 14-3-3 might act as a molecular chelator, preventing RGS proteins from interacting with Galpha, and ultimately prolonging the signal transduction pathway. In conclusion, our findings suggest that 14-3-3 proteins may indirectly promote GPCR signalling via their inhibitory effects on RGS GAP function.
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Affiliation(s)
- Maria Abramow-Newerly
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada N6A 5C1
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Rodriguez LG, Guan JL. 14-3-3 regulation of cell spreading and migration requires a functional amphipathic groove. J Cell Physiol 2005; 202:285-94. [PMID: 15389601 DOI: 10.1002/jcp.20122] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The 14-3-3 proteins associate with many cellular proteins that participate in the regulation of various cellular events including apoptosis, the cell cycle, spreading, and migration. We have previously described that 14-3-3beta binds the beta1-integrin and overexpression of 14-3-3beta promoted increased cell spreading and migration (Han et al. [2001] Oncogene 20: 346-357). In this study, we find that mutation of Ser 60 of 14-3-3beta, outside of the amphipathic groove which is involved in 14-3-3 protein interactions with other ligands, abolished its interaction with integrin. Surprisingly, this mutant retained its ability to promote cell spreading, suggesting that 14-3-3beta interaction with the beta1-integrin is not required for its regulation of cell adhesion. We next showed that mutations of several critical residues in the amphipathic groove did not affect 14-3-3beta interaction with the beta1-integrin. As expected, these mutants disrupted their association with the phosphoserine dependent ligands Raf and Cas. Analysis of the groove mutant LF (mutation of Arg129Tyr130 to Leu and Phe) indicated that, unlike wild type 14-3-3beta, it could not stimulate cell spreading or migration, suggesting that a functional amphipathic groove is required for 14-3-3 regulation of cell adhesion and migration. Consistent with this, cells expressing the LF mutant exhibited a delay in F-actin organization compared to cells expressing wild type or the S60A mutant (Ser 60 to Ala mutation) upon cell adhesion to fibronectin (FN). Taken together, these studies identified a novel binding site on 14-3-3 for integrin beta1 and showed that a functional amphipathic groove, rather than its interaction with integrin beta1, is required for 14-3-3 regulation of cell spreading and migration.
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Affiliation(s)
- Luis G Rodriguez
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
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Darling DL, Yingling J, Wynshaw-Boris A. Role of 14–3–3 Proteins in Eukaryotic Signaling and Development. Curr Top Dev Biol 2005; 68:281-315. [PMID: 16125003 DOI: 10.1016/s0070-2153(05)68010-6] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
14-3-3 genes encode a ubiquitous family of highly conserved eukaryotic proteins from fungi to humans and plants with several molecular and cellular functions. Most notably, 14-3-3 proteins bind to phosphoserine/phosphothreonine motifs in a sequence-specific manner. More than 100 14-3-3 binding partners involved in signal transduction, cell cycle regulation, apoptosis, stress responses, and malignant transformation have been identified. The 14-3-3 proteins form homodimers and heterodimers, and there is redundancy of the binding specificity and function of different 14-3-3 proteins because of their highly similar amino acid sequence and tertiary structure. 14-3-3 proteins can regulate target protein function by several mechanisms. Although the molecular and cellular functions of 14-3-3 proteins have been well studied, there have been fewer studies addressing the in vivo role of 14-3-3s. Here we review what is known about 14-3-3 proteins during eukaryotic development.
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Affiliation(s)
- Dawn L Darling
- Department of Pediatrics, University of California, San Diego, La Jolla, California 92093, USA
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Wilker E, Yaffe MB. 14-3-3 Proteins—a focus on cancer and human disease. J Mol Cell Cardiol 2004; 37:633-42. [PMID: 15350836 DOI: 10.1016/j.yjmcc.2004.04.015] [Citation(s) in RCA: 171] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2004] [Revised: 03/10/2004] [Accepted: 04/23/2004] [Indexed: 12/17/2022]
Abstract
14-3-3 Proteins are a ubiquitous family of molecules that participate in protein kinase signaling pathways within all eukaryotic cells. Functioning as phosphoserine/phosphothreonine-binding modules, 14-3-3 proteins participate in phosphorylation-dependent protein-protein interactions that control progression through the cell cycle, initiation and maintenance of DNA damage checkpoints, activation of MAP kinases, prevention of apoptosis, and coordination of integrin signaling and cytoskeletal dynamics. In this review, we discuss the regulation of 14-3-3 structure and ligand binding, with a focus on the role of 14-3-3 proteins in human disease, particularly cancer. We discuss the latest data on the role of different 14-3-3 isotypes, the interaction of 14-3-3 proteins with Raf, Cdc25, and various integrin family members, and the likelihood that 14-3-3 proteins could be useful therapeutic targets in the treatment of human disease.
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Affiliation(s)
- Erik Wilker
- Center for Cancer Research, Massachusetts Institute of Technology, E18-580, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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Voigt J, Stevanovic S, Schirle M, Fausel M, Maier J, Adam KH, Marquardt O. A 14-3-3 protein of Chlamydomonas reinhardtii associated with the endoplasmic reticulum: nucleotide sequence of the cDNA and the corresponding gene and derived amino acid sequence. ACTA ACUST UNITED AC 2004; 1679:180-94. [PMID: 15344298 DOI: 10.1016/j.bbaexp.2004.06.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Two major 14-3-3 proteins of the unicellular green alga Chlamydomonas reinhardtii were purified and partially sequenced. The obtained data show that the 30-kDa isoform predominant in the cytosol is encoded by a previously cloned and sequenced 14-3-3 cDNA whereas the 27-kDa isoform represents a new 14-3-3 protein which is largely associated with the endoplasmic reticulum (ER). Therefore, the corresponding cDNA was cloned and sequenced. The nucleotide sequence of this new cDNA species and the derived amino acid sequence differ considerably from the previously cloned Chlamydomonas 14-3-3 cDNA. The conclusion that the divergent evolution of the corresponding genes must have started rather early as compared to the 14-3-3 genes of other organisms was corroborated by their different genomic organization. The amino acid sequences of both 14-3-3 isoforms were comparatively analysed to find differences which might be responsible for their differential binding to the ER.
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Affiliation(s)
- Jürgen Voigt
- Physiologisch-chemisches Institut, Eberhard-Karls-Universität Tübingen, Germany.
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Abstract
Growth and differentiation of the budding yeast Saccharomyces cerevisiae is regulated by six functionally distinct but structurally similar MAP kinase cascades. Three of the protein kinases in the cascade that regulates G1-phase arrest and mating have recently been shown to form a multikinase complex with a LIM-domain-containing protein called Ste5. These studies implicate Ste5 as a tethering protein that physically links protein kinases operating sequentially in a cascade. The significance of this complex for the regulation and specificity of signal transduction is explored in this review.
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Affiliation(s)
- E A Elion
- Dept of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
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Hekman M, Wiese S, Metz R, Albert S, Troppmair J, Nickel J, Sendtner M, Rapp UR. Dynamic changes in C-Raf phosphorylation and 14-3-3 protein binding in response to growth factor stimulation: differential roles of 14-3-3 protein binding sites. J Biol Chem 2003; 279:14074-86. [PMID: 14688280 DOI: 10.1074/jbc.m309620200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Phosphorylation events play a crucial role in Raf activation. Phosphorylation of serines 259 and 621 in C-Raf and serines 364 and 728 in B-Raf has been suggested to be critical for association with 14-3-3 proteins. To study the functional consequences of Raf phosphorylations at these positions, we developed and characterized phosphospecific antibodies directed against 14-3-3 binding epitopes: a monoclonal phosphospecific antibody (6B4) directed against pS621 and a polyclonal antibody specific for B-Raf-pS364 epitope. Although 6B4 detected both C- and B-Raf in Western blots, it specifically recognizes the native form of C-Raf but not B-Raf. Contrary to B-Raf, a kinase-dead mutant of C-Raf was found to be only poorly phosphorylated in the Ser-621 position. Moreover, serine 259 to alanine mutation prevented the Ser-621 phosphorylation suggesting an interdependence between these two 14-3-3 binding domains. Direct C-Raf.14-3-3 binding studies with purified proteins combined with competition assays revealed that the 14-3-3 binding domain surrounding pS621 represents the high affinity binding site, whereas the pS259 epitope mediates lower affinity binding. Raf isozymes differ in their 14-3-3 association rates. The time course of endogenous C-Raf activation in mammalian cells by nerve growth factor (NGF) has been examined using both phosphospecific antibodies directed against 14-3-3 binding sites (6B4 and anti-pS259) as well as phosphospecific antibodies directed against the activation domain (anti-pS338 and anti-pY340/pY341). Time course of Ser-621 phosphorylation, in contrast to Ser-259 phosphorylation, exhibited unexpected pattern reaching maximal phosphorylation within 30 s of NGF stimulation. Phosphorylation of tyrosine 340/341 reached maximal levels subsequent to Ser-621 phosphorylation and was coincident with emergence of kinase activity. Taken together, we found substantial differences between C-Raf.14-3-3 binding epitopes pS259 and pS621 and visualized for the first time the sequence of the essential C-Raf phosphorylation events in mammalian cells in response to growth factor stimulation.
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Affiliation(s)
- Mirko Hekman
- Institute for Medical Radiation and Cell Research, University of Wuerzburg, 97078 Wuerzburg
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Kinoshita T, Emi T, Tominaga M, Sakamoto K, Shigenaga A, Doi M, Shimazaki KI. Blue-light- and phosphorylation-dependent binding of a 14-3-3 protein to phototropins in stomatal guard cells of broad bean. PLANT PHYSIOLOGY 2003; 133:1453-63. [PMID: 14605223 PMCID: PMC300702 DOI: 10.1104/pp.103.029629] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Phototropins are blue-light (BL) receptor serine (Ser)/threonine kinases, and contain two light, oxygen, and voltage (LOV) domains, and are members of the PAS domain superfamily. They mediate phototropism, chloroplast movement, leaf expansion, and stomatal opening of higher plants in response to BL. In stomatal guard cells, genetic analysis has revealed that phototropins mediate activation of the plasma membrane H+-ATPase by phosphorylation and drive stomatal opening. However, biochemical evidence for the involvement of phototropins in the BL response of stomata is lacking. Using guard cell protoplasts, we showed that broad bean (Vicia faba) phototropins (Vfphots) were phosphorylated by BL, and that this phosphorylation of Vfphots reached to the maximum level earlier than that of the H+-ATPase. Phosphorylation of both Vfphots and H+-ATPase showed similar sensitivity to BL and were similarly suppressed by protein kinase and flavoprotein inhibitors. We found that a 14-3-3 protein was bound to Vfphots upon phosphorylation, and this binding occurred earlier than the H+-ATPase phosphorylation. Vfphots (Vfphot1a and Vfphot1b) were expressed in Escherichia coli, and phosphorylation sites were determined to be Ser-358 for Vfphot1a and Ser-344 for Vfphot1b, which are localized between LOV1 and LOV2. We conclude that Vfphots act as BL receptors in guard cells and that phosphorylation of a Ser residue between LOV1 and LOV2 and subsequent 14-3-3 protein binding are likely to be key steps of BL response in stomata. The binding of a 14-3-3 protein to Vfphot was found in etiolated seedlings and leaves in response to BL, suggesting that this event was common to phototropin-mediated responses.
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Affiliation(s)
- Toshinori Kinoshita
- Department of Biology, Faculty of Science, Kyushu University, Ropponmatsu, Fukuoka, Japan 810-8560
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Affiliation(s)
- Daniela Berg
- Institute for Human Genetics, Department of Medical Genetics, University of Tübingen, Calwerstrasse 7, 72076 Tübingen, Germany.
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Chang F, Steelman LS, Lee JT, Shelton JG, Navolanic PM, Blalock WL, Franklin RA, McCubrey JA. Signal transduction mediated by the Ras/Raf/MEK/ERK pathway from cytokine receptors to transcription factors: potential targeting for therapeutic intervention. Leukemia 2003; 17:1263-93. [PMID: 12835716 DOI: 10.1038/sj.leu.2402945] [Citation(s) in RCA: 513] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The Ras/Raf/Mitogen-activated protein kinase/ERK kinase (MEK)/extracellular-signal-regulated kinase (ERK) cascade couples signals from cell surface receptors to transcription factors, which regulate gene expression. Depending upon the stimulus and cell type, this pathway can transmit signals, which result in the prevention or induction of apoptosis or cell cycle progression. Thus, it is an appropriate pathway to target for therapeutic intervention. This pathway becomes more complex daily, as there are multiple members of the kinase and transcription factor families, which can be activated or inactivated by protein phosphorylation. The diversity of signals transduced by this pathway is increased, as different family members heterodimerize to transmit different signals. Furthermore, additional signal transduction pathways interact with the Raf/MEK/ERK pathway to regulate positively or negatively its activity, or to alter the phosphorylation status of downstream targets. Abnormal activation of this pathway occurs in leukemia because of mutations at Ras as well as genes in other pathways (eg PI3K, PTEN, Akt), which serve to regulate its activity. Dysregulation of this pathway can result in autocrine transformation of hematopoietic cells since cytokine genes such as interleukin-3 and granulocyte/macrophage colony-stimulating factor contain the transacting binding sites for the transcription factors regulated by this pathway. Inhibitors of Ras, Raf, MEK and some downstream targets have been developed and many are currently in clinical trials. This review will summarize our current understanding of the Ras/Raf/MEK/ERK signal transduction pathway and the downstream transcription factors. The prospects of targeting this pathway for therapeutic intervention in leukemia and other cancers will be evaluated.
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Affiliation(s)
- F Chang
- Department of Microbiology and Immunology, Brody School of Medicine at East Carolina University, Greenville, NC 27858, USA
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Chen XQ, Chen JG, Zhang Y, Hsiao WWL, Yu ACH. 14-3-3gamma is upregulated by in vitro ischemia and binds to protein kinase Raf in primary cultures of astrocytes. Glia 2003; 42:315-24. [PMID: 12730952 DOI: 10.1002/glia.10185] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The 14-3-3 protein family comprises critical regulatory molecules involved in signaling during cell division, proliferation, and apoptosis. Despite extensive study, the functions of the 14-3-3 proteins in brain remain unclear. 14-3-3gamma, a subtype of the 14-3-3 family of proteins, was thought to be brain- and neuron-specific. Using RNA arbitrarily primed PCR, we identified an upregulated cDNA fragment of the 14-3-3gamma gene in primary cultures of astrocytes. Using Northern blot analysis, we confirmed this fragment was brain-specific. In cultures of astrocytes, 14-3-3gamma genes and proteins were differentially expressed at different ages and the proteins were distributed only in the cytoplasm. These results indicated that 14-3-3gamma was not neuron-specific but also expressed in astrocytes. The function of this protein in brain is unclear. Northern and Western blot analyses demonstrated that 14-3-3gamma mRNA and protein were upregulated in cultured astrocytes in an anaerobic chamber-induced ischemia model. The induction of 14-3-3gamma proteins was neither suppressed by an MAP kinase inhibitor (U0126) nor a PI-3 kinase inhibitor (LY294002). These data indicated that induction of 14-3-3gamma might not involve PI-3 and MAP kinase-dependent pathways. Using coimmunoprecipitation, we demonstrated that endogenous 14-3-3gamma bound to c-Raf-1 and p-Raf 259. As Raf is one of the critical serine/threonine kinases controlling cell growth, differentiation, and death, the binding of 14-3-3gamma to Raf indicates the critical role of this protein in ischemia-induced apoptosis and the changes in signal transduction in astrocytes in culture.
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Affiliation(s)
- Xiao Qian Chen
- Neuroscience Research Institute, Peking University and Department of Neurobiology, Peking University Health Science Center, Beijing, China
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50
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Chen HK, Fernandez-Funez P, Acevedo SF, Lam YC, Kaytor MD, Fernandez MH, Aitken A, Skoulakis EMC, Orr HT, Botas J, Zoghbi HY. Interaction of Akt-phosphorylated ataxin-1 with 14-3-3 mediates neurodegeneration in spinocerebellar ataxia type 1. Cell 2003; 113:457-68. [PMID: 12757707 DOI: 10.1016/s0092-8674(03)00349-0] [Citation(s) in RCA: 308] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Spinocerebellar ataxia type 1 (SCA1) is one of several neurological disorders caused by a CAG repeat expansion. In SCA1, this expansion produces an abnormally long polyglutamine tract in the protein ataxin-1. Mutant polyglutamine proteins accumulate in neurons, inducing neurodegeneration, but the mechanism underlying this accumulation has been unclear. We have discovered that the 14-3-3 protein, a multifunctional regulatory molecule, mediates the neurotoxicity of ataxin-1 by binding to and stabilizing ataxin-1, thereby slowing its normal degradation. The association of ataxin-1 with 14-3-3 is regulated by Akt phosphorylation, and in a Drosophila model of SCA1, both 14-3-3 and Akt modulate neurodegeneration. Our finding that phosphatidylinositol 3-kinase/Akt signaling and 14-3-3 cooperate to modulate the neurotoxicity of ataxin-1 provides insight into SCA1 pathogenesis and identifies potential targets for therapeutic intervention.
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Affiliation(s)
- Hung-Kai Chen
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
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