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Bhattacharjee P, Wang D, Anderson D, Buckler JN, de Geus E, Yan F, Polekhina G, Schittenhelm R, Creek DJ, Harris LD, Sadler AJ. The immune response to RNA suppresses nucleic acid synthesis by limiting ribose 5-phosphate. EMBO J 2024; 43:2636-2660. [PMID: 38778156 PMCID: PMC11217295 DOI: 10.1038/s44318-024-00100-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 02/29/2024] [Accepted: 03/19/2024] [Indexed: 05/25/2024] Open
Abstract
During infection viruses hijack host cell metabolism to promote their replication. Here, analysis of metabolite alterations in macrophages exposed to poly I:C recognises that the antiviral effector Protein Kinase RNA-activated (PKR) suppresses glucose breakdown within the pentose phosphate pathway (PPP). This pathway runs parallel to central glycolysis and is critical to producing NADPH and pentose precursors for nucleotides. Changes in metabolite levels between wild-type and PKR-ablated macrophages show that PKR controls the generation of ribose 5-phosphate, in a manner distinct from its established function in gene expression but dependent on its kinase activity. PKR phosphorylates and inhibits the Ribose 5-Phosphate Isomerase A (RPIA), thereby preventing interconversion of ribulose- to ribose 5-phosphate. This activity preserves redox control but decreases production of ribose 5-phosphate for nucleotide biosynthesis. Accordingly, the PKR-mediated immune response to RNA suppresses nucleic acid production. In line, pharmacological targeting of the PPP during infection decreases the replication of the Herpes simplex virus. These results identify an immune response-mediated control of host cell metabolism and suggest targeting the RPIA as a potential innovative antiviral treatment.
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Affiliation(s)
- Pushpak Bhattacharjee
- Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research and Department of Molecular and Translational Sciences, Monash University, Clayton, VIC, 3168, Australia
| | - Die Wang
- Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research and Department of Molecular and Translational Sciences, Monash University, Clayton, VIC, 3168, Australia
| | - Dovile Anderson
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Joshua N Buckler
- Ferrier Research Institute, Victoria University of Wellington, Lower Hutt, 5010, New Zealand
| | - Eveline de Geus
- Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research and Department of Molecular and Translational Sciences, Monash University, Clayton, VIC, 3168, Australia
| | - Feng Yan
- Australian Centre for Blood Diseases, Department of Clinical Hematology, Monash University, Clayton, VIC, 3004, Australia
| | - Galina Polekhina
- Department of Epidemiology & Preventive Medicine, Monash University, Melbourne, VIC, 3004, Australia
| | - Ralf Schittenhelm
- Monash Proteomics & Metabolomics Facility, Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, VIC, 3800, Australia
| | - Darren J Creek
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Lawrence D Harris
- Ferrier Research Institute, Victoria University of Wellington, Lower Hutt, 5010, New Zealand
| | - Anthony J Sadler
- Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research and Department of Molecular and Translational Sciences, Monash University, Clayton, VIC, 3168, Australia.
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Auto-phosphorylation Represses Protein Kinase R Activity. Sci Rep 2017; 7:44340. [PMID: 28281686 PMCID: PMC5345052 DOI: 10.1038/srep44340] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Accepted: 02/07/2017] [Indexed: 12/11/2022] Open
Abstract
The central role of protein kinases in controlling disease processes has spurred efforts to develop pharmaceutical regulators of their activity. A rational strategy to achieve this end is to determine intrinsic auto-regulatory processes, then selectively target these different states of kinases to repress their activation. Here we investigate auto-regulation of the innate immune effector protein kinase R, which phosphorylates the eukaryotic initiation factor 2α to inhibit global protein translation. We demonstrate that protein kinase R activity is controlled by auto-inhibition via an intra-molecular interaction. Part of this mechanism of control had previously been reported, but was then controverted. We account for the discrepancy and extend our understanding of the auto-inhibitory mechanism by identifying that auto-inhibition is paradoxically instigated by incipient auto-phosphorylation. Phosphor-residues at the amino-terminus instigate an intra-molecular interaction that enlists both of the N-terminal RNA-binding motifs of the protein with separate surfaces of the C-terminal kinase domain, to co-operatively inhibit kinase activation. These findings identify an innovative mechanism to control kinase activity, providing insight for strategies to better regulate kinase activity.
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Anderson E, Quartararo C, Brown RS, Shi Y, Yao X, Cole JL. Analysis of monomeric and dimeric phosphorylated forms of protein kinase R. Biochemistry 2010; 49:1217-25. [PMID: 20088595 DOI: 10.1021/bi901873p] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
PKR (protein kinase R) is induced by interferon and is a key component of the innate immunity antiviral pathway. Upon binding double-stranded RNA (dsRNA) or dimerization in the absence of dsRNA, PKR undergoes autophosphorylation at multiple serines and threonines that activate the kinase. Although it has previously been demonstrated that phosphorylation enhances PKR dimerization, gel filtration analysis reveals a second monomeric phosphorylated form. These forms are termed phosphorylated dimeric PKR (pPKRd) and phosphorylated monomeric PKR (pPKRm). These two forms do not reversibly interconvert. Sedimentation equilibrium measurements reveal that pPKRm dimerizes weakly with a K(d) similar to that of unphosphorylated PKR. Isoelectric focusing and mass spectrometry demonstrate that both pPKRm and pPKRd are heterogeneous in their phosphorylation states, with an average of 9 or 10 phosphates. Equilibrium chemical denaturation analysis indicates that phosphorylation destabilizes the kinase domain by approximately 1.5 kcal/mol in the dimeric form but not in the monomeric form. Limited proteolysis also reveals that phosphorylation induces a conformational change in pPKRd that is not detected in pPKRm. pPKRm binds dsRNA with an affinity similar to that of unphosphorylated PKR, whereas binding cannot be detected with pPKRd. Despite these substantial differences in biophysical properties, both pPKRm and pPKRd are catalytically competent and are activated to phosphorylate the PKR substrate eIF2alpha in the absence of dsRNA. Thus, both monomeric and dimeric forms of phosphorylated PKR may participate in the interferon antiviral pathway.
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Affiliation(s)
- Eric Anderson
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, USA
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Gabel F, Wang D, Madern D, Sadler A, Dayie K, Daryoush MZ, Schwahn D, Zaccai G, Lee X, Williams BRG. Dynamic flexibility of double-stranded RNA activated PKR in solution. J Mol Biol 2006; 359:610-23. [PMID: 16650856 DOI: 10.1016/j.jmb.2006.03.049] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2006] [Revised: 03/21/2006] [Accepted: 03/22/2006] [Indexed: 12/31/2022]
Abstract
PKR, an interferon-induced double-stranded RNA activated serine-threonine kinase, is a component of signal transduction pathways mediating cell growth control and responses to stress and viral infection. Analysis of separate PKR functional domains by NMR and X-ray crystallography has revealed details of PKR RNA binding domains and kinase domain, respectively. Here, we report the structural characteristics, calculated from biochemical and neutron scattering data, of a native PKR fraction with a high level of autophosphorylation and constitutive kinase activity. The experiments reveal association of the protein monomer into dimers and tetramers, in the absence of double-stranded RNA or other activators. Low-resolution structures of the association states were obtained from the large angle neutron scattering data and reveal the relative orientation of all protein domains in the activated kinase dimer. Low-resolution structures were also obtained for a PKR tetramer-monoclonal antibody complex. Taken together, this information leads to a new model for the structure of the functioning unit of the enzyme, highlights the flexibility of PKR and sheds light on the mechanism of PKR activation. The results of this study emphasize the usefulness of low-resolution structural studies in solution on large flexible multiple domain proteins.
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Affiliation(s)
- Frank Gabel
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
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Nguyen QN, Chavli RV, Marques JT, Conrad PG, Wang D, He W, Belisle BE, Zhang A, Pastor LM, Witney FR, Morris M, Heitz F, Divita G, Williams BRG, McMaster GK. Light controllable siRNAs regulate gene suppression and phenotypes in cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1758:394-403. [PMID: 16497269 DOI: 10.1016/j.bbamem.2006.01.003] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2005] [Revised: 01/06/2006] [Accepted: 01/09/2006] [Indexed: 10/25/2022]
Abstract
Small interfering RNA (siRNA) is widely recognized as a powerful tool for targeted gene silencing. However, siRNA gene silencing occurs during transfection, limiting its use is in kinetic studies, deciphering toxic and off-target effects and phenotypic assays requiring temporal, and/or spatial regulation. We developed a novel controllable siRNA (csiRNA) that is activated by light. A single photo removable group is coupled during oligonucleotide synthesis to the 5' end of the antisense strand of the siRNA, which blocks the siRNA's activity. A low dose of light activates the siRNA, independent of transfection resulting in knock down of specific target mRNAs and proteins (GAPDH, p53, survivin, hNuf2) without stimulating non-specific effects such as regulated protein kinase PKR and induction of the interferon response. We demonstrate survivin and hNuf2 csiRNAs temporally knockdown their mRNAs causing multinucleation and cell death by mitotic arrest, respectively. Furthermore, we demonstrate a dose-dependent light regulation of hNuf2 csiRNA activity and resulting phenotype. The light controllable siRNAs are introduced into cells using commercially available reagents including the MPG peptide based delivery system. The csiRNAs are comparable to standard siRNAs in their transfection efficiency and potency of gene silencing. This technology should be of interest for phenotypic assays such as cell survival, cell cycle regulation, and cell development.
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Affiliation(s)
- Quan N Nguyen
- Genospectra, Inc., 6519 Dumbarton Circle, Fremont, CA 94555, USA
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Lemaire PA, Lary J, Cole JL. Mechanism of PKR activation: dimerization and kinase activation in the absence of double-stranded RNA. J Mol Biol 2005; 345:81-90. [PMID: 15567412 DOI: 10.1016/j.jmb.2004.10.031] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2004] [Revised: 10/07/2004] [Accepted: 10/08/2004] [Indexed: 11/16/2022]
Abstract
The kinase PKR is a central component of the interferon antiviral pathway. PKR is activated upon binding double-stranded (ds) RNA to undergo autophosphorylation. Although PKR is known to dimerize, the relationship between dimerization and activation remains unclear. Here, we directly characterize dimerization of PKR in free solution using analytical ultracentrifugation and correlate self-association with autophosphorylation activity. Latent, unphosphorylated PKR exists predominantly as a monomer at protein concentrations below 2 mg/ml. A monomer sedimentation coefficient of s(20,w)(0)=3.58 S and a frictional ratio of f/f(0)=1.62 indicate an asymmetric shape. Sedimentation equilibrium measurements indicate that PKR undergoes a weak, reversible monomer-dimer equilibrium with K(d)=450 microM. This dimerization reaction serves to initiate a previously unrecognized dsRNA-independent autophosphorylation reaction. The resulting activated enzyme is phosphorylated on the two critical threonine residues present in the activation loop and is competent to phosphorylate the physiological substrate, eIF2alpha. Dimer stability is enhanced by approximately 500-fold upon autophosphorylation. We propose a chain reaction model for PKR dsRNA-independent activation where dimerization of latent enzyme followed by intermolecular phosphorylation serves as the initiation step. Subsequent propagation steps likely involve phosphorylation of latent PKR monomers by activated enzyme within high-affinity heterodimers. Our results support a model whereby dsRNA functions by bringing PKR monomers into close proximity in a manner that is analogous to the dimerization of free PKR.
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Affiliation(s)
- Peter A Lemaire
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA
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