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Activation of SsoPK4, an Archaeal eIF2α Kinase Homolog, by Oxidized CoA. Proteomes 2015; 3:89-116. [PMID: 28248264 PMCID: PMC5217372 DOI: 10.3390/proteomes3020089] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Revised: 04/30/2015] [Accepted: 05/05/2015] [Indexed: 01/08/2023] Open
Abstract
The eukaryotic protein kinase (ePK) paradigm provides integral components for signal transduction cascades throughout nature. However, while so-called typical ePKs permeate the Eucarya and Bacteria, atypical ePKs dominate the kinomes of the Archaea. Intriguingly, the catalytic domains of the handful of deduced typical ePKs from the archaeon Sulfolobus solfataricus P2 exhibit significant resemblance to the protein kinases that phosphorylate translation initiation factor 2α (eIF2α) in response to cellular stresses. We cloned and expressed one of these archaeal eIF2α protein kinases, SsoPK4. SsoPK4 exhibited protein-serine/threonine kinase activity toward several proteins, including the S. solfataricus homolog of eIF2α, aIF2α. The activity of SsoPK4 was inhibited in vitro by 3ʹ,5ʹ-cyclic AMP (Ki of ~23 µM) and was activated by oxidized Coenzyme A, an indicator of oxidative stress in the Archaea. Activation enhanced the apparent affinity for protein substrates, Km, but had little effect on Vmax. Autophosphorylation activated SsoPK4 and rendered it insensitive to oxidized Coenzyme A.
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Sano R, Reed JC. ER stress-induced cell death mechanisms. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:3460-3470. [PMID: 23850759 DOI: 10.1016/j.bbamcr.2013.06.028] [Citation(s) in RCA: 1426] [Impact Index Per Article: 129.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Revised: 06/24/2013] [Accepted: 06/26/2013] [Indexed: 02/07/2023]
Abstract
The endoplasmic-reticulum (ER) stress response constitutes a cellular process that is triggered by a variety of conditions that disturb folding of proteins in the ER. Eukaryotic cells have developed an evolutionarily conserved adaptive mechanism, the unfolded protein response (UPR), which aims to clear unfolded proteins and restore ER homeostasis. In cases where ER stress cannot be reversed, cellular functions deteriorate, often leading to cell death. Accumulating evidence implicates ER stress-induced cellular dysfunction and cell death as major contributors to many diseases, making modulators of ER stress pathways potentially attractive targets for therapeutics discovery. Here, we summarize recent advances in understanding the diversity of molecular mechanisms that govern ER stress signaling in health and disease. This article is part of a Special Section entitled: Cell Death Pathways.
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Affiliation(s)
- Renata Sano
- Sanford-Burnham Medical Research Institute, La Jolla, CA, 92037, USA
| | - John C Reed
- Sanford-Burnham Medical Research Institute, La Jolla, CA, 92037, USA.
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Laing KG, Elia A, Jeffrey I, Matys V, Tilleray VJ, Souberbielle B, Clemens MJ. In vivo effects of the Epstein-Barr virus small RNA EBER-1 on protein synthesis and cell growth regulation. Virology 2002; 297:253-69. [PMID: 12083824 DOI: 10.1006/viro.2002.1354] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recent studies have suggested a role for the Epstein-Barr virus-encoded RNA EBER-1 in malignant transformation. EBER-1 inhibits the activity of the protein kinase PKR, an inhibitor of protein synthesis with tumour suppressor properties. In human 293 cells and murine embryonic fibroblasts, transient expression of EBER-1 promoted total protein synthesis and enhanced the expression of cotransfected reporter genes. However reporter gene expression was stimulated equally well in cells from control and PKR knockout mice. NIH 3T3 cells stably expressing EBER-1 exhibited a greatly increased frequency of colony formation in soft agar, and protein synthesis in these cells was relatively resistant to inhibition by the calcium ionophore A23187. Nevertheless clones containing a high concentration of EBER-1 were not invariably tumourigenic. We conclude that EBER-1 can enhance protein synthesis by a PKR-independent mechanism and that, although this RNA may contribute to the oncogenic potential of Epstein-Barr virus, its expression is not always sufficient for malignant transformation.
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Affiliation(s)
- Kenneth G Laing
- Department of Biochemistry and Immunology, St. George's Hospital Medical School, Cranmer Terrace, London, United Kingdom
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Kawagishi-Kobayashi M, Silverman JB, Ung TL, Dever TE. Regulation of the protein kinase PKR by the vaccinia virus pseudosubstrate inhibitor K3L is dependent on residues conserved between the K3L protein and the PKR substrate eIF2alpha. Mol Cell Biol 1997; 17:4146-58. [PMID: 9199350 PMCID: PMC232268 DOI: 10.1128/mcb.17.7.4146] [Citation(s) in RCA: 105] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The mammalian double-stranded RNA-activated protein kinase PKR is a component of the cellular antiviral defense mechanism and phosphorylates Ser-51 on the alpha subunit of the translation factor eIF2 to inhibit protein synthesis. To identify the molecular determinants that specify substrate recognition by PKR, we performed a mutational analysis on the vaccinia virus K3L protein, a pseudosubstrate inhibitor of PKR. High-level expression of PKR is lethal in the yeast Saccharomyces cerevisiae because PKR phosphorylates eIF2alpha and inhibits protein synthesis. We show that coexpression of vaccinia virus K3L can suppress the growth-inhibitory effects of PKR in yeast, and using this system, we identified both loss-of-function and hyperactivating mutations in K3L. Truncation of, or point mutations within, the C-terminal portion of the K3L protein, homologous to residues 79 to 83 in eIF2alpha, abolished PKR inhibitory activity, whereas the hyperactivating mutation, K3L-H47R, increased the homology between the K3L protein and eIF2alpha adjacent to the phosphorylation site at Ser-51. Biochemical and yeast two-hybrid analyses revealed that the suppressor phenotype of the K3L mutations correlated with the affinity of the K3L protein for PKR and was inversely related to the level of eIF2alpha phosphorylation in the cell. These results support the idea that residues conserved between the pseudosubstrate K3L protein and the authentic substrate eIF2alpha play an important role in substrate recognition, and they suggest that PKR utilizes sequences both near and over 30 residues from the site of phosphorylation for substrate recognition. Finally, by reconstituting part of the mammalian antiviral defense mechanism in yeast, we have established a genetically useful system to study viral regulators of PKR.
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Affiliation(s)
- M Kawagishi-Kobayashi
- Laboratory of Eukaryotic Gene Regulation, National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA
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Pinna LA, Ruzzene M. How do protein kinases recognize their substrates? BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1314:191-225. [PMID: 8982275 DOI: 10.1016/s0167-4889(96)00083-3] [Citation(s) in RCA: 342] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- L A Pinna
- Dipartimento di Chimica Biologica, Università di Padova, Italy.
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Taylor DR, Lee SB, Romano PR, Marshak DR, Hinnebusch AG, Esteban M, Mathews MB. Autophosphorylation sites participate in the activation of the double-stranded-RNA-activated protein kinase PKR. Mol Cell Biol 1996; 16:6295-302. [PMID: 8887659 PMCID: PMC231632 DOI: 10.1128/mcb.16.11.6295] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The interferon-induced RNA-dependent protein kinase PKR is found in cells in a latent state. In response to the binding of double-stranded RNA, the enzyme becomes activated and autophosphorylated on several serine and threonine residues. Consequently, it has been postulated that autophosphorylation is a prerequisite for activation of the kinase. We report the identification of PKR sites that are autophosphorylated in vitro concomitantly with activation and examine their roles in the activation of PKR. Mutation of one site, threonine 258, results in a kinase that is less efficient in autophosphorylation and in phosphorylating its substrate, the initiation factor eIF2, in vitro. The mutant kinase is also impaired in vivo, displaying reduced ability to inhibit protein synthesis in yeast and mammalian cells and to induce a slow-growth phenotype in Saccharomyces cerevisiae. Mutations at two neighboring sites, serine 242 and threonine 255, exacerbated the effect. Taken together with earlier results (S. B. Lee, S. R. Green, M. B. Mathews, and M. Esteban, Proc. Natl. Acad. Sci. USA 91:10551-10555, 1994), these data suggest that the central part of the PKR molecule, lying between its RNA-binding and catalytic domains, regulates kinase activity via autophosphorylation.
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Affiliation(s)
- D R Taylor
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
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Qian W, Zhu S, Sobolev AY, Wek RC. Expression of vaccinia virus K3L protein in yeast inhibits eukaryotic initiation factor-2 kinase GCN2 and the general amino acid control pathway. J Biol Chem 1996; 271:13202-7. [PMID: 8662715 DOI: 10.1074/jbc.271.22.13202] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Phosphorylation of the alpha subunit of eukaryotic initiation factor-2 (eIF-2) is a well characterized mechanism regulating protein synthesis. Viral and cellular proteins have been identified that regulate the activity of the eIF-2alpha kinases. The regulatory protein, K3L, from vaccinia virus is homologous to the amino terminus of eIF-2alpha and is thought to inhibit the activity of the double-stranded RNA-dependent kinase suppressing the antiviral mechanism mediated by this kinase. We investigated whether K3L can inhibit the activity of the yeast eIF-2alpha kinase GCN2. Expression of K3L protein in yeast reduced the level of eIF-2alpha phosphorylation by GCN2 and blocked the stimulation of the general amino acid control pathway in response to starvation conditions. Accompanying in vitro studies showed that recombinant K3L protein reduced GCN2 autophosphorylation and phosphorylation eIF-2alpha. In agreement with the hypothesis that K3L inhibits eIF-2alpha kinases by functioning as a pseudosubstrate, we observed that K3L directly interacted with the kinase catalytic domain of GCN2. Together, these results indicate that K3L is a specific inhibitor of eIF-2alpha kinases from mammals and yeast and suggest that the kinases contain common structural features important for recognition of their substrate eIF-2alpha.
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Affiliation(s)
- W Qian
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5122, USA
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Oh BH, Ames GF, Kim SH. Structural basis for multiple ligand specificity of the periplasmic lysine-, arginine-, ornithine-binding protein. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)47196-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Sharp TV, Schwemmle M, Jeffrey I, Laing K, Mellor H, Proud CG, Hilse K, Clemens MJ. Comparative analysis of the regulation of the interferon-inducible protein kinase PKR by Epstein-Barr virus RNAs EBER-1 and EBER-2 and adenovirus VAI RNA. Nucleic Acids Res 1993; 21:4483-90. [PMID: 7901835 PMCID: PMC311179 DOI: 10.1093/nar/21.19.4483] [Citation(s) in RCA: 149] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The interferon-inducible protein kinase PKR interacts with a number of small viral RNA species, including adenovirus VAI RNA and the Epstein-Barr virus-encoded RNA EBER-1. These RNAs bind to PKR and protect protein synthesis from inhibition by double-stranded RNA in the reticulocyte lysate system. Using a peptide phosphorylation assay we show here that EBER-1, like VAI, directly inhibits the activation of purified PKR. A second Epstein-Barr virus RNA, EBER-2, also regulates PKR. EBER-1, EBER-2 and VAI RNA exhibit mutually competitive binding to the native or recombinant enzyme, as assessed by U.V. crosslinking experiments and filter binding assays. The affinities of all three RNAs for PKR in vitro are similar (Kd = ca. 0.3 nM). Since this protein kinase has been proposed to exert a tumour suppressor function in vivo, the ability of EBER-1 to inhibit its activation suggests a role for this small RNA in cell transformation by Epstein-Barr virus.
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Affiliation(s)
- T V Sharp
- Department of Cellular and Molecular Sciences, St George's Hospital Medical School, London, UK
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The eIF-2 alpha protein kinases, regulators of translation in eukaryotes from yeasts to humans. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)52994-x] [Citation(s) in RCA: 297] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Mellor H, Price NT, Oldfield S, Sarre TF, Proud CG. Purification and characterisation of an initiation-factor-2 kinase from uninduced mouse erythroleukaemia cells. EUROPEAN JOURNAL OF BIOCHEMISTRY 1993; 211:529-38. [PMID: 8094668 DOI: 10.1111/j.1432-1033.1993.tb17579.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Mouse erythroleukaemia (MEL) cells, which have not been induced into erythroid development, contain a protein kinase (MKu) which phosphorylates the alpha subunit of protein-synthesis-initiation factor 2 (eIF-2 alpha). In this paper, we show that this kinase phosphorylates both eIF-2 alpha and a synthetic peptide based on the phosphorylation site in eIF-2 alpha at Ser51, the target residue for other eIF-2 alpha kinases. Consistent with this, prior treatment of eIF-2 with MKu impaired the exchange of bound GDP for GTP which is catalysed by the exchange factor eIF-2B. Using a modified cell-free translation system, we have shown that MKu inhibits translation, consistent with the above observations concerning the site of phosphorylation and the effect of phosphorylation on eIF-2B-mediated guanine-nucleotide exchange. MKu has been purified and its properties have been compared with those of the haem-controlled repressor eIF-2 alpha kinase (HCR) from rabbit reticulocytes. Its behaviour on gel filtration is similar to that of HCR, while its behaviour on anion exchange resembles that of certain phosphorylated species of HCR. Highly purified preparations of MKu contain a protein with an apparent molecular mass of 98 kDa which comigrates with HCR on SDS/PAGE. This protein undergoes phosphorylation when incubated in the presence of Mg(2+)-ATP, and both this apparent autophosphorylation and the activity of the kinase against eIF-2 alpha are inhibited by the same, low, (10 microM) concentrations of haemin. Phosphorylation of the 98-kDa components present in the MEL-cell kinase preparation and in purified rabbit reticulocyte HCR occurs on serine and threonine residues. Analysis of these phosphoproteins by peptide mapping reveals significant differences in their structures, indicating that they may be closely related, but are certainly not identical.
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Affiliation(s)
- H Mellor
- Department of Biochemistry, School of Medical Sciences, University of Bristol, England
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Affiliation(s)
- M J Clemens
- Department of Cellular and Molecular Sciences, St George's Hospital Medical School, London, U.K
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Affiliation(s)
- C G Proud
- Department of Biochemistry, School of Medical Sciences, University of Bristol, England
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Abstract
A peptide P(45-56) corresponding to residues 45-56 (sequence: ILLSELSRRRIR) of eIF-2 alpha was synthesised. It was phosphorylated by both of the well characterised eIF-2 alpha kinases viz.; the heme-controlled repressor (HCR) and the double stranded RNA-dependent inhibitor (dsI). Of four other protein kinases tested only protein kinase C (PKC) phosphorylated P(45-56), with complete dependence on phosphatidylserine. Only the residue corresponding to serine-51 in eIF-2 alpha was phosphorylated by HCR, dsI or PKC. The phosphorylation of the peptide by dsI and the phosphorylation of eIF-2 alpha by dsI or HCR showed sigmoidal kinetics with respect to substrate concentration.
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Affiliation(s)
- H Mellor
- Department of Biochemistry, School of Medical Sciences, University of Bristol, U.K
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