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Ricketts MD, Emptage RP, Blobel GA, Marmorstein R. The Heme-Regulated Inhibitor Kinase Requires Dimerization for Heme- Sensing Activity. J Biol Chem 2022; 298:102451. [PMID: 36063997 PMCID: PMC9520036 DOI: 10.1016/j.jbc.2022.102451] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 08/17/2022] [Accepted: 08/19/2022] [Indexed: 11/24/2022] Open
Abstract
The heme-regulated inhibitor (HRI) is a heme-sensing kinase that regulates mRNA translation in erythroid cells. In heme deficiency, HRI is activated to phosphorylate eukaryotic initiation factor 2α and halt production of globins, thus avoiding accumulation of heme-free globin chains. HRI is inhibited by heme via binding to one or two heme-binding domains within the HRI N-terminal and kinase domains. HRI has recently been found to inhibit fetal hemoglobin (HbF) production in adult erythroid cells. Depletion of HRI increases HbF production, presenting a therapeutically exploitable target for the treatment of patients with sickle cell disease or thalassemia, which benefit from elevated HbF levels. HRI is known to be an oligomeric enzyme that is activated through autophosphorylation, although the exact nature of the HRI oligomer, its relation to autophosphorylation, and its mode of heme regulation remain unclear. Here, we employ biochemical and biophysical studies to demonstrate that HRI forms a dimeric species that is not dependent on autophosphorylation, the C-terminal coiled-coil domain in HRI is essential for dimer formation, and dimer formation facilitates efficient autophosphorylation and activation of HRI. We also employ kinetic studies to demonstrate that the primary avenue by which heme inhibits HRI is through the heme-binding site within the kinase domain, and that this inhibition is relatively independent of binding of ATP and eukaryotic initiation factor 2α substrates. Together, these studies highlight the mode of heme inhibition and the importance of dimerization in human HRI heme-sensing activity.
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Affiliation(s)
- M Daniel Ricketts
- Department of Biochemistry and Biophysics and the Abramson Family Cancer Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Ryan P Emptage
- Department of Biochemistry and Biophysics and the Abramson Family Cancer Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Gerd A Blobel
- Division of Hematology, Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Ronen Marmorstein
- Department of Biochemistry and Biophysics and the Abramson Family Cancer Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
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2
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Cytoplasmic proteotoxicity regulates HRI-dependent phosphorylation of eIF2α via the Hsp70-Bag3 module. iScience 2022; 25:104282. [PMID: 35573186 PMCID: PMC9097715 DOI: 10.1016/j.isci.2022.104282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Revised: 02/27/2022] [Accepted: 04/19/2022] [Indexed: 11/30/2022] Open
Abstract
The major heat shock protein Hsp70 forms a complex with a scaffold protein Bag3 that links it to components of signaling pathways. Via these interactions, the Hsp70-Bag3 module functions as a proteotoxicity sensor that controls cell signaling. Here, to search for pathways regulated by the complex, we utilized JG-98, an allosteric inhibitor of Hsp70 that blocks its interaction with Bag3. RNAseq followed by the pathway analysis indicated that several signaling pathways including UPR were activated by JG-98. Surprisingly, only the eIF2α-associated branch of the UPR was activated, while other UPR branches were not induced, suggesting that the response was unrelated to the ER proteotoxicity and ER-associated kinase PERK1. Indeed, induction of the UPR genes under these conditions was driven by a distinct eIF2α kinase HRI. Hsp70-Bag3 directly interacted with HRI and regulated eIF2α phosphorylation upon cytoplasmic proteotoxicity. Therefore, cytosolic proteotoxicity can activate certain UPR genes via Hsp70-Bag3-HRI-eIF2α axis. Disruption of Hsp70-Bag3 module activates the unfolded protein response (UPR) This induction of UPR genes is mediated by HRI-dependent phosphorylation of eIF2α Hsp70-Bag3 “monitors” cytoplasmic proteotoxicity to activate the HRI-eIF2α axis eIF2α integrates proteotoxicity signals from ER and cytoplasm
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3
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Mathangasinghe Y, Fauvet B, Jane SM, Goloubinoff P, Nillegoda NB. The Hsp70 chaperone system: distinct roles in erythrocyte formation and maintenance. Haematologica 2021; 106:1519-1534. [PMID: 33832207 PMCID: PMC8168490 DOI: 10.3324/haematol.2019.233056] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Indexed: 01/14/2023] Open
Abstract
Erythropoiesis is a tightly regulated cell differentiation process in which specialized oxygen- and carbon dioxide-carrying red blood cells are generated in vertebrates. Extensive reorganization and depletion of the erythroblast proteome leading to the deterioration of general cellular protein quality control pathways and rapid hemoglobin biogenesis rates could generate misfolded/aggregated proteins and trigger proteotoxic stresses during erythropoiesis. Such cytotoxic conditions could prevent proper cell differentiation resulting in premature apoptosis of erythroblasts (ineffective erythropoiesis). The heat shock protein 70 (Hsp70) molecular chaperone system supports a plethora of functions that help maintain cellular protein homeostasis (proteostasis) and promote red blood cell differentiation and survival. Recent findings show that abnormalities in the expression, localization and function of the members of this chaperone system are linked to ineffective erythropoiesis in multiple hematological diseases in humans. In this review, we present latest advances in our understanding of the distinct functions of this chaperone system in differentiating erythroblasts and terminally differentiated mature erythrocytes. We present new insights into the protein repair-only function(s) of the Hsp70 system, perhaps to minimize protein degradation in mature erythrocytes to warrant their optimal function and survival in the vasculature under healthy conditions. The work also discusses the modulatory roles of this chaperone system in a wide range of hematological diseases and the therapeutic gain of targeting Hsp70.
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Affiliation(s)
| | - Bruno Fauvet
- Department of Plant Molecular Biology, Lausanne University, Lausanne
| | - Stephen M Jane
- Central Clinical School, Monash University, Prahran, Victoria, Australia; Department of Hematology, Alfred Hospital, Monash University, Prahran, Victoria
| | | | - Nadinath B Nillegoda
- Australian Regenerative Medicine Institute, Monash University, Clayton, Victoria.
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4
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Koncha RR, Ramachandran G, Sepuri NBV, Ramaiah KVA. CCCP-induced mitochondrial dysfunction - characterization and analysis of integrated stress response to cellular signaling and homeostasis. FEBS J 2021; 288:5737-5754. [PMID: 33837631 DOI: 10.1111/febs.15868] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 02/26/2021] [Accepted: 04/07/2021] [Indexed: 12/11/2022]
Abstract
Mitochondrial dysfunction mediated by CCCP (carbonyl cyanide m-chlorophenyl hydrazone), an inhibitor of mitochondrial oxidative phosphorylation, evokes the integrated stress response (ISR), which is analyzed here by eIF2α phosphorylation and expression profiles of ATF4 and CHOP proteins. Our findings suggest that the CCCP-induced ISR pathway is mediated by activation of HRI kinase, but not by GCN2, PERK, or PKR. Also, CCCP activates AMPK, a cellular energy sensor, and AKT, a regulator implicated in cell survival, and suppresses phosphorylation of mTORC1 substrates eIF4E-BP1 and S6K. CCCP also downregulates translation and promotes autophagy, leading to noncaspase-mediated cell death in HepG2 cells. All these events are neutralized by NAC, an anti-ROS, suggesting that CCCP-induced mitochondrial dysfunction promotes oxidative stress. ISRIB, an inhibitor of the ISR pathway, mitigates CCCP-induced expression of ATF4 and CHOP, activation of AKT, and autophagy, similar to NAC. However, it fails to reverse CCCP-induced AMPK activation, suggesting that CCCP-induced autophagy is dependent on ISR and independent of AMPK activation. ISRIB restores partly, inhibition in eIF4E-BP1 phosphorylation, promotes eIF2α phosphorylation, albeit slowly, and mitigates suppression of translation accordingly, in CCCP-treated cells. These findings are consistent with the idea that CCCP-induced oxidative stress leading to eIF2α phosphorylation and ATF4 expression, which is known to stimulate genes involved in autophagy, play a pro-survival role together with AKT activation and regulate mTOR-mediated eIF4E-BP1 phosphorylation.
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Affiliation(s)
| | - Gayatri Ramachandran
- Department of Biochemistry, School of Life Sciences, University of Hyderabad, India
| | - Naresh Babu V Sepuri
- Department of Biochemistry, School of Life Sciences, University of Hyderabad, India
| | - Kolluru V A Ramaiah
- Department of Biochemistry, School of Life Sciences, University of Hyderabad, India
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Abdel-Nour M, Carneiro LAM, Downey J, Tsalikis J, Outlioua A, Prescott D, Costa LSD, Hovingh ES, Farahvash A, Gaudet RG, Molinaro R, van Dalen R, Lau CCY, Azimi FC, Escalante NK, Trotman-Grant A, Lee JE, Gray-Owen SD, Divangahi M, Chen JJ, Philpott DJ, Arnoult D, Girardin SE. The heme-regulated inhibitor is a cytosolic sensor of protein misfolding that controls innate immune signaling. Science 2019; 365:eaaw4144. [PMID: 31273097 PMCID: PMC10433729 DOI: 10.1126/science.aaw4144] [Citation(s) in RCA: 75] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Revised: 04/16/2019] [Accepted: 06/07/2019] [Indexed: 12/13/2022]
Abstract
Multiple cytosolic innate sensors form large signalosomes after activation, but this assembly needs to be tightly regulated to avoid accumulation of misfolded aggregates. We found that the eIF2α kinase heme-regulated inhibitor (HRI) controls NOD1 signalosome folding and activation through a process requiring eukaryotic initiation factor 2α (eIF2α), the transcription factor ATF4, and the heat shock protein HSPB8. The HRI/eIF2α signaling axis was also essential for signaling downstream of the innate immune mediators NOD2, MAVS, and TRIF but dispensable for pathways dependent on MyD88 or STING. Moreover, filament-forming α-synuclein activated HRI-dependent responses, which suggests that the HRI pathway may restrict toxic oligomer formation. We propose that HRI, eIF2α, and HSPB8 define a novel cytosolic unfolded protein response (cUPR) essential for optimal innate immune signaling by large molecular platforms, functionally homologous to the PERK/eIF2α/HSPA5 axis of the endoplasmic reticulum UPR.
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Affiliation(s)
- Mena Abdel-Nour
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
| | - Leticia A. M. Carneiro
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
| | - Jeffrey Downey
- Department of Microbiology and Immunology, McGill University, Montreal, QC, Canada
| | - Jessica Tsalikis
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
| | - Ahmed Outlioua
- INSERM U1197, Hôpital Paul Brousse, Bâtiment Lavoisier, 94807 Villejuif Cedex, France
- Molecular Genetics and Immunophysiopathology Research Team, Health and Environment Laboratory, Aïn Chock Faculty of Sciences, Hassan II University of Casablanca, Casablanca, Morocco
| | - Dave Prescott
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
- Department of Immunology, University of Toronto, Toronto, ON, Canada
| | | | - Elise S. Hovingh
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
| | - Armin Farahvash
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
| | - Ryan G. Gaudet
- Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Raphael Molinaro
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
| | - Rob van Dalen
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
| | - Charles C. Y. Lau
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
- Department of Immunology, University of Toronto, Toronto, ON, Canada
| | - Farshad C. Azimi
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
| | | | | | - Jeffrey E. Lee
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
| | - Scott D. Gray-Owen
- Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Maziar Divangahi
- Department of Microbiology and Immunology, McGill University, Montreal, QC, Canada
| | - Jane-Jane Chen
- Institute of Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Dana J. Philpott
- Department of Immunology, University of Toronto, Toronto, ON, Canada
| | - Damien Arnoult
- INSERM U1197, Hôpital Paul Brousse, Bâtiment Lavoisier, 94807 Villejuif Cedex, France
| | - Stephen E. Girardin
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
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6
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Mimura J, Inose-Maruyama A, Taniuchi S, Kosaka K, Yoshida H, Yamazaki H, Kasai S, Harada N, Kaufman RJ, Oyadomari S, Itoh K. Concomitant Nrf2- and ATF4-activation by Carnosic Acid Cooperatively Induces Expression of Cytoprotective Genes. Int J Mol Sci 2019; 20:ijms20071706. [PMID: 30959808 PMCID: PMC6480217 DOI: 10.3390/ijms20071706] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Revised: 03/29/2019] [Accepted: 03/30/2019] [Indexed: 12/12/2022] Open
Abstract
Carnosic acid (CA) is a phytochemical found in some dietary herbs, such as Rosmarinus officinalis L., and possesses antioxidative and anti-microbial properties. We previously demonstrated that CA functions as an activator of nuclear factor, erythroid 2 (NF-E2)-related factor 2 (Nrf2), an oxidative stress-responsive transcription factor in human and rodent cells. CA enhances the expression of nerve growth factor (NGF) and antioxidant genes, such as HO-1 in an Nrf2-dependent manner in U373MG human astrocytoma cells. However, CA also induces NGF gene expression in an Nrf2-independent manner, since 50 μM of CA administration showed striking NGF gene induction compared with the classical Nrf2 inducer tert-butylhydroquinone (tBHQ) in U373MG cells. By comparative transcriptome analysis, we found that CA activates activating transcription factor 4 (ATF4) in addition to Nrf2 at high doses. CA activated ATF4 in phospho-eIF2α- and heme-regulated inhibitor kinase (HRI)-dependent manners, indicating that CA activates ATF4 through the integrated stress response (ISR) pathway. Furthermore, CA activated Nrf2 and ATF4 cooperatively enhanced the expression of NGF and many antioxidant genes while acting independently to certain client genes. Taken together, these results represent a novel mechanism of CA-mediated gene regulation evoked by Nrf2 and ATF4 cooperation.
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Affiliation(s)
- Junsei Mimura
- Department of Stress Response Science, Center for Advanced Medical Research, Hirosaki University Graduate School of Medicine, Hirosaki 036-8562, Japan.
| | - Atsushi Inose-Maruyama
- Department of Stress Response Science, Center for Advanced Medical Research, Hirosaki University Graduate School of Medicine, Hirosaki 036-8562, Japan.
- Department of Microbiology, Tohoku Medical and Pharmaceutical University, Sendai 981-8558, Japan.
| | - Shusuke Taniuchi
- Division of Molecular Biology, Institute of Advanced Medical Sciences, The University of Tokushima, Tokushima 770-8503, Japan.
| | - Kunio Kosaka
- Research and Development Center, Nagase & Co. Ltd., Kobe 651-2241, Japan.
| | - Hidemi Yoshida
- Department of Vascular Biology, Institute of Brain Science, Hirosaki University Graduate School of Medicine, Hirosaki 036-8562, Japan.
| | - Hiromi Yamazaki
- Department of Stress Response Science, Center for Advanced Medical Research, Hirosaki University Graduate School of Medicine, Hirosaki 036-8562, Japan.
| | - Shuya Kasai
- Department of Stress Response Science, Center for Advanced Medical Research, Hirosaki University Graduate School of Medicine, Hirosaki 036-8562, Japan.
| | - Nobuhiko Harada
- Department of Stress Response Science, Center for Advanced Medical Research, Hirosaki University Graduate School of Medicine, Hirosaki 036-8562, Japan.
- Institute for Animal Experimentation, Tohoku University Graduate School of Medicine, Sendai 980-8575, Japan.
| | - Randal J Kaufman
- Degenerative Diseases Research Program, Sanford Burnham Prebys Medical Discovery Research Institute, La Jolla, CA 92037, USA.
| | - Seiichi Oyadomari
- Division of Molecular Biology, Institute of Advanced Medical Sciences, The University of Tokushima, Tokushima 770-8503, Japan.
| | - Ken Itoh
- Department of Stress Response Science, Center for Advanced Medical Research, Hirosaki University Graduate School of Medicine, Hirosaki 036-8562, Japan.
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Comprehensive review on the HSC70 functions, interactions with related molecules and involvement in clinical diseases and therapeutic potential. Pharmacol Ther 2012; 136:354-74. [PMID: 22960394 DOI: 10.1016/j.pharmthera.2012.08.014] [Citation(s) in RCA: 195] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Accepted: 08/14/2012] [Indexed: 12/28/2022]
Abstract
Heat shock cognate protein 70 (HSC70) is a constitutively expressed molecular chaperone which belongs to the heat shock protein 70 (HSP70) family. HSC70 shares some of the structural and functional similarity with HSP70. HSC70 also has different properties compared with HSP70 and other heat shock family members. HSC70 performs its full functions by the cooperation of co-chaperones. It interacts with many other molecules as well and regulates various cellular functions. It is also involved in various diseases and may become a biomarker for diagnosis and potential therapeutic targets for design, discovery, and development of novel drugs to treat various diseases. In this article, we provide a comprehensive review on HSC70 from the literatures including the basic general information such as classification, structure and cellular location, genetics and function, as well as its protein association and interaction with other proteins. In addition, we also discussed the relationship of HSC70 and related clinical diseases such as cancer, cardiovascular, neurological, hepatic and many other diseases and possible therapeutic potential and highlight the progress and prospects of research in this field. Understanding the functions of HSC70 and its interaction with other molecules will help us to reveal other novel properties of this protein. Scientists may be able to utilize this protein as a biomarker and therapeutic target to make significant advancement in scientific research and clinical setting in the future.
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9
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Abstract
Multisubunit complexes containing molecular chaperones regulate protein production, stability, and degradation in virtually every cell type. We are beginning to recognize how generalized and tissue-specific chaperones regulate specialized aspects of erythropoiesis. For example, chaperones intersect with erythropoietin signaling pathways to protect erythroid precursors against apoptosis. Molecular chaperones also participate in hemoglobin synthesis, both directly and indirectly. Current knowledge in these areas only scratches the surface of what is to be learned. Improved understanding of how molecular chaperones regulate erythropoietic development and hemoglobin homeostasis should identify biochemical pathways amenable to pharmacologic manipulation in a variety of red blood cell disorders including thalassemia and other anemias associated with hemoglobin instability.
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Ramya TNC, Karmodiya K, Surolia A, Surolia N. 15-Deoxyspergualin Primarily Targets the Trafficking of Apicoplast Proteins in Plasmodium falciparum. J Biol Chem 2007; 282:6388-97. [PMID: 17194705 DOI: 10.1074/jbc.m610251200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
15-Deoxyspergualin, an immunosuppressant with tumoricidal and antimalarial properties, has been implicated in the inhibition of a diverse array of cellular processes including polyamine synthesis and protein synthesis. Endeavoring to identify the mechanism of antimalarial action of this molecule, we examined its effect on Plasmodium falciparum protein synthesis, polyamine biosynthesis, and transport. 15-Deoxyspergualin stalled protein synthesis in P. falciparum through Hsp70 sequestration and subsequent phosphorylation of the eukaryotic initiation factor eIF2alpha. However, protein synthesis inhibition as well as polyamine depletion were invoked only by high micromolar concentrations of 15-deoxyspergualin, in contrast to the submicromolar concentrations sufficient to inhibit parasite growth. Further investigations demonstrated that 15-deoxyspergualin in the malaria parasite primarily targets the hitherto underexplored process of trafficking of nucleus-encoded proteins to the apicoplast. Our finding that 15-deoxyspergualin kills the malaria parasite by interfering with targeting of nucleus-encoded proteins to the apicoplast not only exposes a chink in the armor of the malaria parasite, but also reveals new realms in our endeavors to study this intriguing biological process.
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Affiliation(s)
- T N C Ramya
- Indian Institute of Science, Bangalore 560012, India
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Galam L, Hadden MK, Ma Z, Ye Q, Yun BG, Blagg BSJ, Matts RL. High-throughput assay for the identification of Hsp90 inhibitors based on Hsp90-dependent refolding of firefly luciferase. Bioorg Med Chem 2007; 15:1939-46. [PMID: 17223347 PMCID: PMC1906718 DOI: 10.1016/j.bmc.2007.01.004] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2006] [Revised: 12/20/2006] [Accepted: 01/01/2007] [Indexed: 10/23/2022]
Abstract
Previously, we have demonstrated that the renaturation of heat denatured firefly luciferase is dependent upon the activity of Hsp90 in rabbit reticulocyte lysate. Here, we demonstrate that this assay may identify inhibitors that obstruct the chaperone activity of Hsp90 either by direct binding to its N-terminal or C-terminal nucleotide binding sites or by interference with the ability of the chaperone to switch conformations. The assay was adapted and optimized for high-throughput screening. Greater than 20,000 compounds were screened to demonstrate the feasibility of using this assay on a large scale. The assay was reproducible (av Z-factor=0.62) and identified 120 compounds that inhibited luciferase renaturation by greater than 70% at a concentration of 12.5 microg/mL. IC50 values for twenty compounds with varying structures were determined for inhibition of luciferase refolding and in cell-based assays for Hsp90 inhibition. Several compounds had IC50 values <10 microM and represent a number of new lead structures with the potential for further development and optimization as potent Hsp90 inhibitors.
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Affiliation(s)
- Lakshmi Galam
- Department of Biochemistry and Molecular Biology, NRC 246, Oklahoma State University, Stillwater, Oklahoma, U.S.A. 74078
| | - M. Kyle Hadden
- Department of Medicinal Chemistry, 1251 Wescoe Hall Drive, Malott 4070, The University of Kansas, Lawrence, Kansas, U.S.A. 66045-7563
| | - Zeqiang Ma
- High-Throughput Screening Laboratory, The University of Kansas, 1501 Wakarusa Drive, Lawrence, Kansas, U.S.A. 66047
| | - Qi–Zhuang Ye
- High-Throughput Screening Laboratory, The University of Kansas, 1501 Wakarusa Drive, Lawrence, Kansas, U.S.A. 66047
| | - Bo-Geon Yun
- Department of Biochemistry and Molecular Biology, NRC 246, Oklahoma State University, Stillwater, Oklahoma, U.S.A. 74078
| | - Brian S. J. Blagg
- Department of Medicinal Chemistry, 1251 Wescoe Hall Drive, Malott 4070, The University of Kansas, Lawrence, Kansas, U.S.A. 66045-7563
| | - Robert L. Matts
- Department of Biochemistry and Molecular Biology, NRC 246, Oklahoma State University, Stillwater, Oklahoma, U.S.A. 74078
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Hussain SG, Ramaiah KVA. Reduced eIF2alpha phosphorylation and increased proapoptotic proteins in aging. Biochem Biophys Res Commun 2007; 355:365-70. [PMID: 17300747 DOI: 10.1016/j.bbrc.2007.01.156] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2007] [Accepted: 01/26/2007] [Indexed: 12/26/2022]
Abstract
A decline in relative levels and phosphorylation of many of the eukaryotic initiation factors (eIFs) including S6, the 40S ribosomal subunit protein in many of the rat tissues during chronological aging is accompanied by elevated levels of eIF2alpha kinases, such as PKR and PERK, but not their activity. Concomitant with increased eIF2alpha phosphorylation, young tissues displayed a higher level of eIF2B to tolerate the toxic effect of eIF2alpha phosphorylation on translation, ATF4, a b-zip transcriptional factor that is produced as part of the gene expression programme in response to eIF2alpha phosphorylation, and BiP, an endoplasmic reticulum (ER) molecular chaperone and regulator of ER stress sensors. Decline in eIF2alpha phosphorylation in aged tissues is associated with a higher level of GADD34, a subunit of eIF2alpha phosphatase, and proapoptotic proteins like CHOP/GADD153 and phospho JNK, suggesting that young tissues possess an efficient ER stress adaptive mechanism that declines with aging.
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Affiliation(s)
- Syed G Hussain
- Department of Biochemistry, University of Hyderabad, Hyderabad 500 046, AP, India
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13
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Ramya T, Surolia N, Surolia A. 15-deoxyspergualin inhibits eukaryotic protein synthesis through eIF2alpha phosphorylation. Biochem J 2007; 401:411-20. [PMID: 16952278 PMCID: PMC1820809 DOI: 10.1042/bj20060879] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
DSG (15-deoxyspergualin), an immunosuppressant with tumoricidal properties, binds potently to the regulatory C-terminal 'EEVD' motif of Hsps (heat-shock proteins). In the present study we demonstrate that DSG inhibits eukaryotic protein synthesis by sequestering Hsp70 which is required for maintaining HRI (haem-regulated inhibitor), a kinase of the eIF2alpha (eukaryotic initiation factor 2alpha), inactive. DSG stalled initiation of protein synthesis through phosphorylation of HRI and eIF2alpha. Addition of a recombinant eIF2alpha (S51A) protein, which lacks the phosphorylation site, lowered the inhibitory potential of DSG in reticulocyte lysate. The inhibitory effect of DSG was also attenuated in HRI knockdown cells. Moreover, exogenous addition of Hsp70 or the peptide 'EEVD' reversed the inhibitory effect of DSG. Interestingly, the inhibitory effect of DSG in different mammalian cancer cells was found to negatively correlate with the amount of Hsp70 expressed in the cells, emphasizing the link with Hsp70 in DSG inhibition of eukaryotic translation.
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Affiliation(s)
- T. N. C. Ramya
- *Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
| | - Namita Surolia
- †Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064, India
- Correspondence may be addressed to either N. Surolia (email ) or A. Surolia (email )
| | - Avadhesha Surolia
- *Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
- ‡National Institute of Immunology, New Delhi 110067, India
- Correspondence may be addressed to either N. Surolia (email ) or A. Surolia (email )
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14
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Suragani RNVS, Ghosh S, Ehtesham NZ, Ramaiah KVA. Expression and purification of the subunits of human translational initiation factor 2 (eIF2): phosphorylation of eIF2 alpha and beta. Protein Expr Purif 2005; 47:225-33. [PMID: 16289913 DOI: 10.1016/j.pep.2005.10.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2005] [Revised: 10/01/2005] [Accepted: 10/03/2005] [Indexed: 11/22/2022]
Abstract
Eukaryotic initiation factor 2 (eIF2) is a GDP-binding protein with three subunits: alpha, beta, and gamma. It delivers initiator tRNA (Met-tRNAi) to 40S ribosomes in a GTP-dependent manner. The factor regulates the translation of messenger RNAs through the phosphorylation of serine 51 residue in the small or alpha-subunit of eIF2 (eIF2alpha) and modulation of its interaction with a rate-limiting heteropentameric protein eIF2B. To understand the structural, functional, and regulatory roles of each of these subunits in the various activities of phosphorylated and unphosphorylated eIF2, such, as its ability to interact with GTP, Met-tRNAi, 40S ribosomes and with various proteins, we have for the first time over expressed all the three subunits of human eIF2 independently, and, also together in Sf9 cells using pFast Bac HT vector of baculovirus expression system. The expression of all subunits increased with increase in infection time up to 72 h. We have also over expressed three mutant forms of eIF2alpha viz, S51A, S51D, and S48A in which the serine at 51 or 48 position is replaced by an alanine or aspartic acid with 6x histidine tag at the N-terminus. Further, any of the two subunits or all the three subunits of eIF2 were coexpressed by multiple infection of cells with recombinant viruses. Purified alpha (wt and mutants) and beta subunits were found suitable to serve as substrates for different kinases. The recombinant subunits of eIF2alpha and beta-subunits were also phosphorylated in cultured insect cells. Phosphorylation of eIF2alpha in vitro was not significantly different in the presence and absence of the other subunits.
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15
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Abstract
The is a double-stranded RNA-activated protein kinase (PKR) has been largely investigated for its key role in viral host defense. Although best characterized by its function in mediating the antiviral and antiproliferative effects of interferon (IFN), PKR is also implicated in transcriptional regulation, cell differentiation, signal transduction, and tumor suppression. However, recent findings identifying PKR as an important effector of apoptosis have led to an increased interest in PKR modulation as an antitumor strategy. PKR can either be up-regulated through direct induction by the transcription factor E2F-1, or it can be activated through direct protein-protein interactions with the melanoma differentiation-associated gene-7 (MDA7, IL-24). Additionally, the intracellular formation of double-stranded RNA by transfection with antisense RNA complementary to tumor-specific RNA sequences can induce PKR activation and apoptosis selective to these tumor cells. The growing application of viral vector-based gene therapies and oncolytic, replicating viruses that must elude viral defense in order to be effective, has also drawn attention to PKR. Oncolytic viruses, like the attenuated herpes simplex virus R3616, the vesicular stomatitis virus, or reovirus, specifically replicate in tumor cells only because the viral host defense in the permissive cells is suppressed. In this article we review the role of PKR as an effector of apoptosis and a target for tumor treatment strategies and discuss the potential of PKR-modifying agents to treat patients with cancer. Targeted gene therapy against cancer can be approached by activation of PKR with the down-regulation of protein synthesis and induction of apoptosis, or by suppression of PKR with the propagation of oncolytic virus. Since the PKR pathway can be modified by many routes, antitumor therapies combining oncolytic virus, gene therapies, and chemotherapy with PKR modifiers are likely to emerge in the near future as therapeutic options in the treatment of patients with cancer.
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Affiliation(s)
- Stephan A Vorburger
- Department of Surgical Oncology, The University of Texas M D Anderson Cancer Center, Houston, Texas 77030, USA
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16
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Pang Q, Christianson TA, Keeble W, Koretsky T, Bagby GC. The anti-apoptotic function of Hsp70 in the interferon-inducible double-stranded RNA-dependent protein kinase-mediated death signaling pathway requires the Fanconi anemia protein, FANCC. J Biol Chem 2002; 277:49638-43. [PMID: 12397061 DOI: 10.1074/jbc.m209386200] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proteins encoded by five of the six known Fanconi anemia (FA) genes form a heteromeric complex that facilitates repair of DNA damage induced by cross-linking agents. A certain number of these proteins, notably FANCC, also function independently to modulate apoptotic signaling, at least in part, by suppressing ground state activation of the pro-apoptotic interferon-inducible double-stranded RNA-dependent protein kinase (PKR). Because certain FANCC mutations interdict its anti-apoptotic function without interfering with the capacity of FANCC to participate functionally in the FA multimeric complex, we suspected that FANCC enhances cell survival independent of its participation in the complex. By investigating this function in both mammalian cells and in yeast, an organism with no FA orthologs, we show that FANCC inhibited the kinase activity of PKR both in vivo and in vitro, and this effect depended upon a physical interaction between FANCC and Hsp70 but not on interactions of FANCC with other Fanconi proteins. Hsp70, FANCC, and PKR form a ternary complex in lymphoblasts and in yeast expressing PKR. We conclude that Hsp70 requires the cooperation of FANCC to suppress PKR activity and support survival of hematopoietic cells and that FANCC does not require the multimeric FA complex to exert this function.
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Affiliation(s)
- Qishen Pang
- OHSU Cancer Institute, Department of Medicine and Molecular and Medical Genetics, Oregon Health and Science University, Portland, OR 97201, USA
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17
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Zhan K, Vattem KM, Bauer BN, Dever TE, Chen JJ, Wek RC. Phosphorylation of eukaryotic initiation factor 2 by heme-regulated inhibitor kinase-related protein kinases in Schizosaccharomyces pombe is important for fesistance to environmental stresses. Mol Cell Biol 2002; 22:7134-46. [PMID: 12242291 PMCID: PMC139816 DOI: 10.1128/mcb.22.20.7134-7146.2002] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Protein synthesis is regulated by the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha) in response to different environmental stresses. One member of the eIF2alpha kinase family, heme-regulated inhibitor kinase (HRI), is activated under heme-deficient conditions and blocks protein synthesis, principally globin, in mammalian erythroid cells. We identified two HRI-related kinases from Schizosaccharomyces pombe which have full-length homology with mammalian HRI. The two HRI-related kinases, named Hri1p and Hri2p, exhibit autokinase and kinase activity specific for Ser-51 of eIF2alpha, and both activities were inhibited in vitro by hemin, as previously described for mammalian HRI. Overexpression of Hri1p, Hri2p, or the human eIF2alpha kinase, double-stranded-RNA-dependent protein kinase (PKR), impeded growth of S. pombe due to elevated phosphorylation of eIF2alpha. Cells from strains with deletions of the hri1(+) and hri2(+) genes, individually or in combination, exhibited a reduced growth rate when exposed to heat shock or to arsenic compounds. Measurements of in vivo phosphorylation of eIF2alpha suggest that Hri1p and Hri2p differentially phosphorylate eIF2alpha in response to these stress conditions. These results demonstrate that HRI-related enzymes are not unique to vertebrates and suggest that these eIF2alpha kinases are important participants in diverse stress response pathways in some lower eukaryotes.
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Affiliation(s)
- Ke Zhan
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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18
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Ma K, Vattem KM, Wek RC. Dimerization and release of molecular chaperone inhibition facilitate activation of eukaryotic initiation factor-2 kinase in response to endoplasmic reticulum stress. J Biol Chem 2002; 277:18728-35. [PMID: 11907036 DOI: 10.1074/jbc.m200903200] [Citation(s) in RCA: 190] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphorylation of eukaryotic initiation factor-2 (eIF2) by pancreatic eIF2 kinase (PEK), induces a program of translational expression in response to accumulation of malfolded protein in the endoplasmic reticulum (ER). This study addresses the mechanisms activating PEK, also designated PERK or EIF2AK3. We describe the characterization of two regions in the ER luminal portion of the transmembrane PEK that carry out distinct functions in the regulation of this eIF2 kinase. The first region mediates oligomerization between PEK polypeptides, and deletion of this portion of PEK blocked induction of eIF2 kinase activity. The second characterized region of PEK facilitates interaction with ER chaperones. In the absence of stress, PEK associates with ER chaperones GRP78 (BiP) and GRP94, and this binding is released in response to ER stress. ER luminal sequences flanking the transmembrane domain are required for GRP78 interaction, and deletion of this portion of PEK led to its activation even in the absence of ER stress. These results suggest that this ER chaperone serves as a repressor of PEK activity, and release of ER chaperones from PEK when misfolded proteins accumulate in the ER induces gene expression required to enhance the protein folding capacity of the ER.
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Affiliation(s)
- Kun Ma
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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19
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Yan W, Gale MJ, Tan SL, Katze MG. Inactivation of the PKR protein kinase and stimulation of mRNA translation by the cellular co-chaperone P58(IPK) does not require J domain function. Biochemistry 2002; 41:4938-45. [PMID: 11939789 DOI: 10.1021/bi0121499] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
P58(IPK) was discovered as an inhibitor of the interferon-induced, protein kinase, PKR. Upon virus infection, PKR can, as part of the host defense system, inhibit mRNA translation by phosphorylating the alpha subunit of protein synthesis eukaryotic initiation factor 2 (eIF-2alpha). We previously found that influenza virus recruits the cellular P58(IPK) co-chaperone to inhibit PKR activity and thus facilitate viral protein synthesis. P58(IPK) contains nine tetratricopeptide repeat (TPR) motifs in addition to the highly conserved J domain found in all DnaJ chaperone family members. To define the role of molecular chaperones in regulating cell growth in addition to PKR regulation, we performed a detailed analysis of the P58(IPK) J domain. Using growth rescue assays, we found that the P58(IPK) J domain substituted for the J domains of other DnaJ proteins, including DnaJ in Escherichia coli and Ydj1 in Saccharomyces cerevisiae. This is the first time a cellular J domain from a mammalian DnaJ family member was shown to be functional in both prokaryotic DnaJ and eukaryotic Ydj1 constructs. Furthermore, point mutations within the conserved HPD residue cluster of the P58(IPK) J domain disrupted P58(IPK) J function including stimulation of ATPase activity of Hsp70. However, the P58(IPK) HPD mutants still inhibited PKR activity and thus supported cell growth in a yeast rescue assay. Overexpression of the HPD mutants of P58(IPK), similar to their wild-type counterpart, also stimulated mRNA translation in a mammalian cell system. Taken together, our data necessitate a model of P58(IPK) inhibition of PKR kinase activity and stimulation of mRNA translation, which does not require classical J domain function found in the DnaJ molecular chaperone family.
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Affiliation(s)
- Wei Yan
- Department of Microbiology and Washington Regional Primate Research Center, University of Washington, Seattle, Washington 98195, USA
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20
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Thulasiraman V, Yun BG, Uma S, Gu Y, Scroggins BT, Matts RL. Differential inhibition of Hsc70 activities by two Hsc70-binding peptides. Biochemistry 2002; 41:3742-53. [PMID: 11888292 DOI: 10.1021/bi012137n] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The ability of two high-affinity Hsc70-binding peptides [FYQLALT (peptide-Phi) and NIVRKKK (peptide-K)] to differentially inhibit Hsc70-dependent processes in rabbit reticulocyte lysate (RRL) was examined. Both peptide-Phi and peptide-K inhibited chaperone-dependent renaturation of luciferase in RRL. Peptide-Phi, but not peptide-K, blocked Hsp90/Hsc70-dependent transformation of the heme-regulated eIF2 alpha kinase (HRI) into an active, heme-regulatable kinase. In contrast, peptide-K, but not peptide-Phi, inhibited Hsc70-mediated suppression of the activation of mature-transformed HRI. Furthermore, HDJ2 (Human DnaJ homologue 2), but not HDJ1, potentiated the ability of Hsc70 to suppress the activation of HRI in RRL. Mechanistically, peptide-K inhibited, while peptide-Phi enhanced, HDJ2-induced stimulation of Hsc70 ATPase activity in vitro. The data presented support the hypotheses that peptide-Phi acts to inhibit Hsc70 function by binding to the hydrophobic peptide-binding cleft of Hsc70, while peptide-K acts through binding to a site that modulates the interaction of Hsc70 with DnaJ homologues. Overall, the data indicate that peptide-Phi and peptide-K have differential effects on Hsc70 functions under quasi-physiological conditions in RRL, and suggest that therapeutically valuable peptide mimetics can be designed to inhibit specific functions of Hsc70.
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Affiliation(s)
- Vanitha Thulasiraman
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078-3035, USA
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21
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Hon T, Lee HC, Hach A, Johnson JL, Craig EA, Erdjument-Bromage H, Tempst P, Zhang L. The Hsp70-Ydj1 molecular chaperone represses the activity of the heme activator protein Hap1 in the absence of heme. Mol Cell Biol 2001; 21:7923-32. [PMID: 11689685 PMCID: PMC99961 DOI: 10.1128/mcb.21.23.7923-7932.2001] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In Saccharomyces cerevisiae, heme directly mediates the effects of oxygen on transcription through the heme activator protein Hap1. In the absence of heme, Hap1 is bound by at least four cellular proteins, including Hsp90 and Ydj1, forming a higher-order complex, termed HMC, and its activity is repressed. Here we purified the HMC and showed by mass spectrometry that two previously unidentified major components of the HMC are the Ssa-type Hsp70 molecular chaperone and Sro9 proteins. In vivo functional analysis, combined with biochemical analysis, strongly suggests that Ssa proteins are critical for Hap1 repression in the absence of heme. Ssa may repress the activities of both Hap1 DNA-binding and activation domains. The Ssa cochaperones Ydj1 and Sro9 appear to assist Ssa in Hap1 repression, and only Ydj1 residues 1 to 172 containing the J domain are required for Hap1 repression. Our results suggest that Ssa-Ydj1 and Sro9 act together to mediate Hap1 repression in the absence of heme and that molecular chaperones promote heme regulation of Hap1 by a mechanism distinct from the mechanism of steroid signaling.
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Affiliation(s)
- T Hon
- Department of Biochemistry, NYU School of Medicine, New York, New York 10016, USA
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22
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Uma S, Yun BG, Matts RL. The heme-regulated eukaryotic initiation factor 2alpha kinase. A potential regulatory target for control of protein synthesis by diffusible gases. J Biol Chem 2001; 276:14875-83. [PMID: 11278914 DOI: 10.1074/jbc.m011476200] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Nitric oxide (NO) has been reported to inhibit protein synthesis in eukaryotic cells by increasing the phosphorylation of the alpha-subunit of eukaryotic initiation factor (eIF) 2. However, the mechanism through which this increase occurs has not been characterized. In this report, we examined the effect of the diffusible gases nitric oxide (NO) and carbon monoxide (CO) on the activation of the heme-regulated eIF2alpha kinase (HRI) in rabbit reticulocyte lysate. Spectral analysis indicated that both NO and CO bind to the N-terminal heme-binding domain of HRI. Although NO was a very potent activator of HRI, CO markedly suppressed NO-induced HRI activation. The NO-induced activation of HRI was transduced through the interaction of NO with the N-terminal heme-binding domain of HRI and not through S-nitrosylation of HRI. We postulate that the regulation of HRI activity by diffusible gases may be of wider physiological significance, as we further demonstrate that NO generators increase eIF2alpha phosphorylation levels in NT2 neuroepithelial and C2C12 myoblast cells and activate HRI immunoadsorbed from extracts of these non-erythroid cell lines.
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Affiliation(s)
- S Uma
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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23
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Shao J, Grammatikakis N, Scroggins BT, Uma S, Huang W, Chen JJ, Hartson SD, Matts RL. Hsp90 regulates p50(cdc37) function during the biogenesis of the activeconformation of the heme-regulated eIF2 alpha kinase. J Biol Chem 2001; 276:206-14. [PMID: 11036079 DOI: 10.1074/jbc.m007583200] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recent studies indicate that p50(cdc37) facilitates Hsp90-mediated biogenesis of certain protein kinases. In this report, we examined whether p50(cdc37) is required for the biogenesis of the heme-regulated eIF2 alpha kinase (HRI) in reticulocyte lysate. p50(cdc37) interacted with nascent HRI co-translationally and this interaction persisted during the maturation and activation of HRI. p50(cdc37) stimulated HRI's activation in response to heme deficiency, but did not activate HRI per se. p50(cdc37) function was specific to immature and inactive forms of the kinase. Analysis of mutant Cdc37 gene products indicated that the N-terminal portion of p50(cdc37) interacted with immature HRI, but not with Hsp90, while the C-terminal portion of p50(cdc37) interacted with Hsp90. The Hsp90-specific inhibitor geldanamycin disrupted the ability of both Hsp90 and p50(cdc37) to bind HRI and promote its activation, but did not disrupt the native association of p50(cdc37) with Hsp90. A C-terminal truncated mutant of p50(cdc37) inhibited HRI's activation, prevented the interaction of Hsp90 with HRI, and bound to HRI irrespective of geldanamycin treatment. Additionally, native complexes of HRI with p50(cdc37) were detected in cultured K562 erythroleukemia cells. These results suggest that p50(cdc37) provides an activity essential to HRI biogenesis via a process regulated by nucleotide-mediated conformational switching of its partner Hsp90.
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Affiliation(s)
- J Shao
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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24
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Scheper GC, Van Wijk R, Thomas AAM. Regulation of the Activity of Eukaryotic Initiation Factors in Stressed Cells. SIGNALING PATHWAYS FOR TRANSLATION 2001. [DOI: 10.1007/978-3-662-09889-9_2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
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25
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Dastoor Z, Dreyer J. Nuclear translocation and aggregate formation of heat shock cognate protein 70 (Hsc70) in oxidative stress and apoptosis. J Cell Sci 2000; 113 ( Pt 16):2845-54. [PMID: 10910769 DOI: 10.1242/jcs.113.16.2845] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recent evidence has shown a role for the heat shock cognate protein Hsc70 in the response to oxidative stress. We have investigated the subcellular distribution of Hsc70 by means of laser scanning confocal microscopy in neuroblastoma NB41A3 cells, in fibroblasts R6 cells and in R6-Bcl-2, an apoptosis-resistant cell line, and its function in oxidative stress and in apoptosis has been evaluated. Endogenous Hsc70 is localised predominantly in the cytoplasm in unstressed cells, whereas oxidative stress but not apoptosis induces its translocation into the nucleus. In transfected cells overexpressing Hsc70 increased nuclear translocation and aggregation of Hsc70 in intracellular speckles is observed after oxidative stress and, to a lesser degree, after exposure to apoptotic agents. Bcl-2 did not influence the movement of Hsc70 nor the formation of Hsc70-containing speckles. Nuclear translocation of Hsc70 can be modulated by the expression of components from a previously described plasma membrane oxidoreductase involved in the cellular response against oxidative stress. Our data may suggest a correlation between differential translocation of Hsc70 with specific functions in apoptosis and a potential role in the protection against reactive oxygen species.
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Affiliation(s)
- Z Dastoor
- Institute of Biochemistry, University of Fribourg, CH-1700 Fribourg, Switzerland
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26
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Uma S, Matts RL, Guo Y, White S, Chen JJ. The N-terminal region of the heme-regulated eIF2alpha kinase is an autonomous heme binding domain. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:498-506. [PMID: 10632719 DOI: 10.1046/j.1432-1327.2000.01021.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The N-terminal domain (NTD) of the heme-regulated eukaryotic initiation factor (eIF)2alpha kinase (HRI) was aligned to sequences in the NCBI data base using ENTREZ and a PAM250 matrix. Significant similarity was found between amino acids 11-118 in the NTD of rabbit HRI and amino acids 16-120 in mammalian alpha-globins. Several conserved amino acid residues present in globins are conserved in the NTD of HRI. His83 of HRI was predicted to be equivalent to the proximal heme ligand (HisF8) that is conserved in all globins. Molecular modeling of the NTD indicated that its amino acid sequence was compatible with the globin fold. Recombinant NTD (residues 1-159) was expressed in Escherichia coli. Spectral analysis of affinity purified recombinant NTD indicated that the NTD contained stably bound hemin. Mutational analysis indicated that His83 played a critical structural role in the stable binding of heme to the NTD, and was required to stabilize full length HRI synthesized de novo in the rabbit reticulocyte lysate. These results indicate that the NTD of HRI is an autonomous heme-binding domain, with His83 possibly serving as the proximal heme binding ligand.
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Affiliation(s)
- S Uma
- Department of Biochemistry, Oklahoma State University, Stillwater, USA
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27
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Latour I, De Ros E, Denef JF, Buc Calderon P. Protein S-thiolation can mediate the inhibition of protein synthesis induced by tert-butyl hydroperoxide in isolated rat hepatocytes. Toxicol Appl Pharmacol 1999; 160:1-9. [PMID: 10502497 DOI: 10.1006/taap.1999.8757] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A rapid inhibition of protein synthesis is observed when isolated rat hepatocytes are incubated in the presence of 0.25-0.5 mM of tert-butyl hydroperoxide (tBOOH). Such an inhibition occurs in the absence of a cytolytic effect by tBOOH. Iron chelators (o-phenanthroline and desferrioxiamine), protected against oxidative cell death, but they did not modify the inhibition of protein synthesis caused by tBOOH (0.5 mM), suggesting that free radicals are less implicated in such an impairment. Electron micrographs of hepatocytes under oxidative stress show disaggregation of polyribosomes but not oxidative alterations, such as blebs or mitochondrial swelling. Protein synthesis inhibition is accompanied by a decrease in reduced glutathione (GSH) and an increase in glutathione disulfide (GSSG) and the level of protein S-thiolation (protein mixed disulfides formation). Such an increase of GSSG appears as a critical event since diethylmaleate (DEM) at 0.2 mM reduced GSH content by more than 50% but did not affect either GSSG content or protein synthesis. The addition of exogenous GSH and N-acetylcysteine (NAC) to tBOOH-treated hepatocytes significantly reduced the formation of protein mixed disulfides and restored the depressed protein synthesis either completely or partially. We suggest that S-thiolation of some key proteins may be involved in protein synthesis inhibition by tBOOH.
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Affiliation(s)
- I Latour
- Métabolisme, Université Catholique de Louvain, Bruxelles, 1200, Belgium
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28
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Uma S, Thulasiraman V, Matts RL. Dual role for Hsc70 in the biogenesis and regulation of the heme-regulated kinase of the alpha subunit of eukaryotic translation initiation factor 2. Mol Cell Biol 1999; 19:5861-71. [PMID: 10454533 PMCID: PMC84435 DOI: 10.1128/mcb.19.9.5861] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The heme-regulated kinase of the alpha subunit of eukaryotic initiation factor 2 (HRI) is activated in rabbit reticulocyte lysate (RRL) in response to a number of environmental conditions, including heme deficiency, heat shock, and oxidative stress. Activation of HRI causes an arrest of initiation of protein synthesis. Recently, we have demonstrated that the heat shock cognate protein Hsc70 negatively modulates the activation of HRI in RRL in response to these environmental conditions. Hsc70 is also known to be a critical component of the Hsp90 chaperone machinery in RRL, which plays an obligatory role for HRI to acquire and maintain a conformation that is competent to activate. Using de novo-synthesized HRI in synchronized pulse-chase translations, we have examined the role of Hsc70 in the regulation of HRI biogenesis and activation. Like Hsp90, Hsc70 interacted with nascent HRI and HRI that was matured to a state which was competent to undergo stimulus-induced activation (mature-competent HRI). Interaction of HRI with Hsc70 was required for the transformation of HRI, as the Hsc70 antagonist clofibric acid inhibited the folding of HRI into a mature-competent conformation. Unlike Hsp90, Hsc70 also interacted with transformed HRI. Clofibric acid disrupted the interaction of Hsc70 with transformed HRI that had been matured and transformed in the absence of the drug. Disruption of Hsc70 interaction with transformed HRI in heme-deficient RRL resulted in its hyperactivation. Furthermore, activation of HRI in response to heat shock or denatured proteins also resulted in a similar blockage of Hsc70 interaction with transformed HRI. These results indicate that Hsc70 is required for the folding and transformation of HRI into an active kinase but is subsequently required to negatively attenuate the activation of transformed HRI.
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Affiliation(s)
- S Uma
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078-3035, USA
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