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Guillemin A, Kumar A, Wencker M, Ricci EP. Shaping the Innate Immune Response Through Post-Transcriptional Regulation of Gene Expression Mediated by RNA-Binding Proteins. Front Immunol 2022; 12:796012. [PMID: 35087521 PMCID: PMC8787094 DOI: 10.3389/fimmu.2021.796012] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Accepted: 12/13/2021] [Indexed: 12/20/2022] Open
Abstract
Innate immunity is the frontline of defense against infections and tissue damage. It is a fast and semi-specific response involving a myriad of processes essential for protecting the organism. These reactions promote the clearance of danger by activating, among others, an inflammatory response, the complement cascade and by recruiting the adaptive immunity. Any disequilibrium in this functional balance can lead to either inflammation-mediated tissue damage or defense inefficiency. A dynamic and coordinated gene expression program lies at the heart of the innate immune response. This expression program varies depending on the cell-type and the specific danger signal encountered by the cell and involves multiple layers of regulation. While these are achieved mainly via transcriptional control of gene expression, numerous post-transcriptional regulatory pathways involving RNA-binding proteins (RBPs) and other effectors play a critical role in its fine-tuning. Alternative splicing, translational control and mRNA stability have been shown to be tightly regulated during the innate immune response and participate in modulating gene expression in a global or gene specific manner. More recently, microRNAs assisting RBPs and post-transcriptional modification of RNA bases are also emerging as essential players of the innate immune process. In this review, we highlight the numerous roles played by specific RNA-binding effectors in mediating post-transcriptional control of gene expression to shape innate immunity.
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Affiliation(s)
- Anissa Guillemin
- LBMC, Laboratoire de Biologie et Modelisation de la Cellule, Université de Lyon, ENS de Lyon, Universite Claude Bernard Lyon 1, CNRS, UMR 5239, INSERM, U1293, Lyon, France
| | - Anuj Kumar
- CRCL, Centre de Recherche en Cancérologie de Lyon, INSERM U1052, CNRS UMR 5286, Lyon, France
| | - Mélanie Wencker
- LBMC, Laboratoire de Biologie et Modelisation de la Cellule, Université de Lyon, ENS de Lyon, Universite Claude Bernard Lyon 1, CNRS, UMR 5239, INSERM, U1293, Lyon, France
- CIRI, Centre International de Recherche en Infectiologie, Université de Lyon, ENS de Lyon, CNRS, UMR 5308, INSERM, Lyon, France
| | - Emiliano P. Ricci
- LBMC, Laboratoire de Biologie et Modelisation de la Cellule, Université de Lyon, ENS de Lyon, Universite Claude Bernard Lyon 1, CNRS, UMR 5239, INSERM, U1293, Lyon, France
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2
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Lee HC, Fu CY, Lin CY, Hu JR, Huang TY, Lo KY, Tsai HY, Sheu JC, Tsai HJ. Poly(U)-specific endoribonuclease ENDOU promotes translation of human CHOP mRNA by releasing uORF element-mediated inhibition. EMBO J 2021; 40:e104123. [PMID: 33511665 PMCID: PMC8167367 DOI: 10.15252/embj.2019104123] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 11/18/2020] [Accepted: 11/30/2020] [Indexed: 12/24/2022] Open
Abstract
Upstream open reading frames (uORFs) are known to negatively affect translation of the downstream ORF. The regulatory proteins involved in relieving this inhibition are however poorly characterized. In response to cellular stress, eIF2α phosphorylation leads to an inhibition of global protein synthesis, while translation of specific factors such as CHOP is induced. We analyzed a 105‐nt inhibitory uORF in the transcript of human CHOP (huORFchop) and found that overexpression of the zebrafish or human ENDOU poly(U)‐endoribonuclease (Endouc or ENDOU‐1, respectively) increases CHOP mRNA translation also in the absence of stress. We also found that Endouc/ENDOU‐1 binds and cleaves the huORFchop transcript at position 80G‐81U, which induces CHOP translation independently of phosphorylated eIF2α. However, both ENDOU and phospho‐eIF2α are nonetheless required for maximal translation of CHOP mRNA. Increased levels of ENDOU shift a huORFchop reporter as well as endogenous CHOP transcripts from the monosome to polysome fraction, indicating an increase in translation. Furthermore, we found that the uncapped truncated huORFchop‐69‐105‐nt transcript contains an internal ribosome entry site (IRES), facilitating translation of the cleaved transcript. Therefore, we propose a model where ENDOU‐mediated transcript cleavage positively regulates CHOP translation resulting in increased CHOP protein levels upon stress. Specifically, CHOP transcript cleavage changes the configuration of huORFchop thereby releasing its inhibition and allowing the stalled ribosomes to resume translation of the downstream ORF.
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Affiliation(s)
- Hung-Chieh Lee
- Institute of Biomedical Sciences, Mackay Medical College, New Taipei City, Taiwan
| | - Chuan-Yang Fu
- Institute of Biomedical Sciences, Mackay Medical College, New Taipei City, Taiwan
| | - Cheng-Yung Lin
- Institute of Biomedical Sciences, Mackay Medical College, New Taipei City, Taiwan
| | - Jia-Rung Hu
- Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan
| | - Ting-Ying Huang
- Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan
| | - Kai-Yin Lo
- Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan
| | - Hsin-Yue Tsai
- Institute of Molecular Medicine, School of Medicine, National Taiwan University, Taipei, Taiwan
| | - Jin-Chuan Sheu
- Liver Disease Prevention and Treatment Research Foundation, Taipei, Taiwan
| | - Huai-Jen Tsai
- Institute of Biomedical Sciences, Mackay Medical College, New Taipei City, Taiwan.,Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan.,Department of Life Science, Fu Jen Catholic University, New Taipei, Taiwan
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3
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Markiewicz L, Drazkowska K, Sikorski PJ. Tricks and threats of RNA viruses - towards understanding the fate of viral RNA. RNA Biol 2021; 18:669-687. [PMID: 33618611 PMCID: PMC8078519 DOI: 10.1080/15476286.2021.1875680] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 12/22/2020] [Accepted: 01/09/2021] [Indexed: 12/24/2022] Open
Abstract
Human innate cellular defence pathways have evolved to sense and eliminate pathogens, of which, viruses are considered one of the most dangerous. Their relatively simple structure makes the identification of viral invasion a difficult task for cells. In the course of evolution, viral nucleic acids have become one of the strongest and most reliable early identifiers of infection. When considering RNA virus recognition, RNA sensing is the central mechanism in human innate immunity, and effectiveness of this sensing is crucial for triggering an appropriate antiviral response. Although human cells are armed with a variety of highly specialized receptors designed to respond only to pathogenic viral RNA, RNA viruses have developed an array of mechanisms to avoid being recognized by human interferon-mediated cellular defence systems. The repertoire of viral evasion strategies is extremely wide, ranging from masking pathogenic RNA through end modification, to utilizing sophisticated techniques to deceive host cellular RNA degrading enzymes, and hijacking the most basic metabolic pathways in host cells. In this review, we aim to dissect human RNA sensing mechanisms crucial for antiviral immune defences, as well as the strategies adopted by RNA viruses to avoid detection and degradation by host cells. We believe that understanding the fate of viral RNA upon infection, and detailing the molecular mechanisms behind virus-host interactions, may be helpful for developing more effective antiviral strategies; which are urgently needed to prevent the far-reaching consequences of widespread, highly pathogenic viral infections.
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4
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Wang H, Song Y, Wu Y, Kumar V, Mahato RI, Su Q. Activation of dsRNA-Dependent Protein Kinase R by miR-378 Sustains Metabolic Inflammation in Hepatic Insulin Resistance. Diabetes 2021; 70:710-719. [PMID: 33419758 PMCID: PMC7897349 DOI: 10.2337/db20-0181] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Accepted: 12/24/2020] [Indexed: 12/12/2022]
Abstract
MicroRNAs (miRNAs) are noncoding small RNAs that regulate various pathophysiological cellular processes. Here, we report that expression of the miR-378 family was significantly induced by metabolic inflammatory inducers, a high-fructose diet, and inflammatory cytokine tumor necrosis factor-α. Hepatic miRNA profiling revealed that expression of miR-378a was highly upregulated, which, in turn, targeted the 3'-untranslated region of PPARα mRNA, impaired mitochondrial fatty acid β-oxidation, and induced mitochondrial and endoplasmic reticulum stress. More importantly, the upregulated miR-378a can directly bind to and activate the double-strand RNA (dsRNA)-dependent protein kinase R (PKR) to sustain the metabolic stress. In vivo, genetic depletion of miR-378a prevented PKR activation and ameliorated inflammatory stress and insulin resistance. Counterbalancing the upregulated miR-378a using nanoparticles encapsulated with an anti-miR-378a oligonucleotide restored PPARα activity, inhibited PKR activation and ER stress, and improved insulin sensitivity in fructose-fed mice. Our study delineated a novel mechanism of miR-378a in the pathogenesis of metabolic inflammation and insulin resistance through targeting metabolic signaling at both mRNA (e.g., PPARα) and protein (e.g., PKR) molecules. This novel finding of functional interaction between miRNAs (e.g., miR-378a) and cellular RNA binding proteins (e.g., PKR) is biologically significant because it greatly broadens the potential targets of miRNAs in cellular pathophysiological processes.
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Affiliation(s)
- Hao Wang
- Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast, Belfast, U.K
| | - Yongyan Song
- Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE
| | - Yuxin Wu
- Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast, Belfast, U.K
| | - Virender Kumar
- Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, NE
| | - Ram I Mahato
- Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, NE
| | - Qiaozhu Su
- Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast, Belfast, U.K.
- Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE
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5
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Sadeq S, Al-Hashimi S, Cusack CM, Werner A. Endogenous Double-Stranded RNA. Noncoding RNA 2021; 7:15. [PMID: 33669629 PMCID: PMC7930956 DOI: 10.3390/ncrna7010015] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Revised: 02/15/2021] [Accepted: 02/17/2021] [Indexed: 02/07/2023] Open
Abstract
The birth of long non-coding RNAs (lncRNAs) is closely associated with the presence and activation of repetitive elements in the genome. The transcription of endogenous retroviruses as well as long and short interspersed elements is not only essential for evolving lncRNAs but is also a significant source of double-stranded RNA (dsRNA). From an lncRNA-centric point of view, the latter is a minor source of bother in the context of the entire cell; however, dsRNA is an essential threat. A viral infection is associated with cytoplasmic dsRNA, and endogenous RNA hybrids only differ from viral dsRNA by the 5' cap structure. Hence, a multi-layered defense network is in place to protect cells from viral infections but tolerates endogenous dsRNA structures. A first line of defense is established with compartmentalization; whereas endogenous dsRNA is found predominantly confined to the nucleus and the mitochondria, exogenous dsRNA reaches the cytoplasm. Here, various sensor proteins recognize features of dsRNA including the 5' phosphate group of viral RNAs or hybrids with a particular length but not specific nucleotide sequences. The sensors trigger cellular stress pathways and innate immunity via interferon signaling but also induce apoptosis via caspase activation. Because of its central role in viral recognition and immune activation, dsRNA sensing is implicated in autoimmune diseases and used to treat cancer.
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Affiliation(s)
| | | | | | - Andreas Werner
- Biosciences Institute, Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK; (S.S.); (S.A.-H.); (C.M.C.)
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6
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Roca Suarez AA, Testoni B, Baumert TF, Lupberger J. Nucleic Acid-Induced Signaling in Chronic Viral Liver Disease. Front Immunol 2021; 11:624034. [PMID: 33613561 PMCID: PMC7892431 DOI: 10.3389/fimmu.2020.624034] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 12/21/2020] [Indexed: 12/12/2022] Open
Abstract
A hallmark for the development and progression of chronic liver diseases is the persistent dysregulation of signaling pathways related to inflammatory responses, which eventually promotes the development of hepatic fibrosis, cirrhosis and hepatocellular carcinoma (HCC). The two major etiological agents associated with these complications in immunocompetent patients are hepatitis B virus (HBV) and hepatitis C virus (HCV), accounting for almost 1.4 million liver disease-associated deaths worldwide. Although both differ significantly from the point of their genomes and viral life cycles, they exert not only individual but also common strategies to divert innate antiviral defenses. Multiple virus-modulated pathways implicated in stress and inflammation illustrate how chronic viral hepatitis persistently tweaks host signaling processes with important consequences for liver pathogenesis. The following review aims to summarize the molecular events implicated in the sensing of viral nucleic acids, the mechanisms employed by HBV and HCV to counter these measures and how the dysregulation of these cellular pathways drives the development of chronic liver disease and the progression toward HCC.
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Affiliation(s)
- Armando Andres Roca Suarez
- INSERM, U1110, Institut de Recherche sur les Maladies Virales et Hépatiques, Strasbourg, France.,Université de Strasbourg, Strasbourg, France.,INSERM U1052, CNRS UMR-5286, Cancer Research Center of Lyon (CRCL), Lyon, France.,University of Lyon, Université Claude-Bernard (UCBL), Lyon, France
| | - Barbara Testoni
- INSERM U1052, CNRS UMR-5286, Cancer Research Center of Lyon (CRCL), Lyon, France.,University of Lyon, Université Claude-Bernard (UCBL), Lyon, France
| | - Thomas F Baumert
- INSERM, U1110, Institut de Recherche sur les Maladies Virales et Hépatiques, Strasbourg, France.,Université de Strasbourg, Strasbourg, France.,Institut Hospitalo-Universitaire, Pôle Hépato-digestif, Nouvel Hôpital Civil, Strasbourg, France.,Institut Universitaire de France (IUF), Paris, France
| | - Joachim Lupberger
- INSERM, U1110, Institut de Recherche sur les Maladies Virales et Hépatiques, Strasbourg, France.,Université de Strasbourg, Strasbourg, France
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7
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Asthana V, Stern BS, Tang Y, Bugga P, Li A, Ferguson A, Asthana A, Bao G, Drezek RA. Development of a Novel Class of Self-Assembling dsRNA Cancer Therapeutics: A Proof-of-Concept Investigation. MOLECULAR THERAPY-ONCOLYTICS 2020; 18:419-431. [PMID: 32913891 PMCID: PMC7452102 DOI: 10.1016/j.omto.2020.07.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/01/2020] [Accepted: 07/28/2020] [Indexed: 10/26/2022]
Abstract
Cancer has proven to be an extremely difficult challenge to treat. Several fundamental issues currently underlie cancer treatment, including differentiating self from nonself, functional coupling of the recognition and therapeutic components of various therapies, and the propensity of cancerous cells to develop resistance to common treatment modalities via evolutionary pressure. Given these limitations, there is an increasing need to develop an all-encompassing therapeutic that can uniquely target malignant cells, decouple recognition from treatment, and overcome evolutionarily driven cancer resistance. We describe herein a new class of programmable self-assembling double-stranded RNA (dsRNA)-based cancer therapeutics that uniquely targets aberrant genetic sequences and in a functionally decoupled manner, undergoes oncogenic RNA-activated displacement (ORAD), initiating a therapeutic cascade that induces apoptosis and immune activation. As a proof of concept, we show that RNA strands targeting the EWS/Fli1 fusion gene in Ewing sarcoma cells that are end blocked with phosphorothioate bonds and additionally sealed with a 2'-deoxyuridine (2'-U)-modified DNA protector can be used to induce specific and potent killing of cells containing the target oncogenic sequence but not wild type.
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Affiliation(s)
| | - Brett S Stern
- Department of Bioengineering, Rice University, Houston, TX 77030, USA
| | - Yuqi Tang
- Department of Bioengineering, Rice University, Houston, TX 77030, USA
| | - Pallavi Bugga
- Department of Bioengineering, Rice University, Houston, TX 77030, USA
| | - Ang Li
- Department of Bioengineering, Rice University, Houston, TX 77030, USA
| | - Adam Ferguson
- Department of Bioengineering, Rice University, Houston, TX 77030, USA
| | - Anantratn Asthana
- Department of Bioengineering, Rice University, Houston, TX 77030, USA
| | - Gang Bao
- Department of Bioengineering, Rice University, Houston, TX 77030, USA
| | - Rebekah A Drezek
- Department of Bioengineering, Rice University, Houston, TX 77030, USA
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8
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RNA Signaling in Pulmonary Arterial Hypertension-A Double-Stranded Sword. Int J Mol Sci 2020; 21:ijms21093124. [PMID: 32354189 PMCID: PMC7247700 DOI: 10.3390/ijms21093124] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 04/26/2020] [Accepted: 04/27/2020] [Indexed: 12/17/2022] Open
Abstract
Recognition of and response to pathogens and tissue injury is driven by the innate immune system via activation of pattern recognition receptors. One of the many patterns recognized is RNA and, while several receptors bind RNA, Toll-like receptor 3 (TLR3) is well placed for initial recognition of RNA molecules due to its localization within the endosome. There is a growing body of work describing a role for TLR3 in maintenance of vascular homeostasis. For example, TLR3 deficiency has been shown to play repair and remodeling roles in the systemic vasculature and in lung parenchyma. A hallmark of pulmonary arterial hypertension (PAH) is pulmonary vascular remodeling, yet drivers and triggers of this remodeling remain incompletely understood. Based on its role in the systemic vasculature, our group discovered reduced endothelial TLR3 expression in PAH and revealed a protective role for a TLR3 agonist in rodent models of pulmonary hypertension. This review will provide an overview of RNA signaling in the vasculature and how it relates to PAH pathobiology, including whether targeting double-stranded RNA signaling is a potential treatment option for PAH.
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9
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Nguyen TA, Bieging-Rolett KT, Putoczki TL, Wicks IP, Attardi LD, Pang KC. SIDT2 RNA Transporter Promotes Lung and Gastrointestinal Tumor Development. iScience 2019; 20:14-24. [PMID: 31546103 PMCID: PMC6817685 DOI: 10.1016/j.isci.2019.09.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2018] [Revised: 08/20/2019] [Accepted: 09/05/2019] [Indexed: 02/07/2023] Open
Abstract
RNautophagy is a newly described type of selective autophagy whereby cellular RNAs are transported into lysosomes for degradation. This process involves the transmembrane protein SIDT2, which transports double-stranded RNA (dsRNA) across the endolysosomal membrane. We previously demonstrated that SIDT2 is a transcriptional target of p53, but its role in tumorigenesis, if any, is unclear. Unexpectedly, we show here that Sidt2−/− mice with concurrent oncogenic KrasG12D activation develop significantly fewer tumors than littermate controls in a mouse model of lung adenocarcinoma. Consistent with this observation, loss of SIDT2 also leads to enhanced survival and delayed tumor development in an Apcmin/+ mouse model of intestinal cancer. Within the intestine, Apcmin/+;Sidt2−/− mice display accumulation of dsRNA in association with increased phosphorylation of eIF2α and JNK as well as elevated rates of apoptosis. Taken together, our data demonstrate a role for SIDT2, and by extension RNautophagy, in promoting tumor development. Loss of the SIDT2 double-stranded RNA (dsRNA) transporter leads to accumulation of dsRNA in tissues is associated with increased apoptosis reduces tumor burden in mouse models of lung adenocarcinoma and intestinal cancer
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Affiliation(s)
- Tan A Nguyen
- The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Department of Medical Biology, University of Melbourne, Parkville, VIC, Australia
| | - Kathryn T Bieging-Rolett
- Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, USA; Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA
| | - Tracy L Putoczki
- The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Department of Medical Biology, University of Melbourne, Parkville, VIC, Australia
| | - Ian P Wicks
- The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Department of Medical Biology, University of Melbourne, Parkville, VIC, Australia
| | - Laura D Attardi
- Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, USA; Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA
| | - Ken C Pang
- The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Murdoch Children's Research Institute, Parkville, VIC, Australia; Department of Paediatrics, University of Melbourne, Parkville, VIC, Australia; Department of Psychiatry, University of Melbourne, Parkville, VIC, Australia.
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10
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Mayo CB, Erlandsen H, Mouser DJ, Feinstein AG, Robinson VL, May ER, Cole JL. Structural Basis of Protein Kinase R Autophosphorylation. Biochemistry 2019; 58:2967-2977. [PMID: 31246429 DOI: 10.1021/acs.biochem.9b00161] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The RNA-activated protein kinase, PKR, is a key mediator of the innate immunity response to viral infection. Viral double-stranded RNAs induce PKR dimerization and autophosphorylation. The PKR kinase domain forms a back-to-back dimer. However, intermolecular ( trans) autophosphorylation is not feasible in this arrangement. We have obtained PKR kinase structures that resolves this dilemma. The kinase protomers interact via the known back-to-back interface as well as a front-to-front interface that is formed by exchange of activation segments. Mutational analysis of the front-to-front interface support a functional role in PKR activation. Molecular dynamics simulations reveal that the activation segment is highly dynamic in the front-to-front dimer and can adopt conformations conducive to phosphoryl transfer. We propose a mechanism where back-to-back dimerization induces a conformational change that activates PKR to phosphorylate a "substrate" kinase docked in a front-to-front geometry. This mechanism may be relevant to related kinases that phosphorylate the eukaryotic initiation factor eIF2α.
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11
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Kaempfer R, Ilan L, Cohen-Chalamish S, Turgeman O, Namer LS, Osman F. Control of mRNA Splicing by Intragenic RNA Activators of Stress Signaling: Potential Implications for Human Disease. Front Genet 2019; 10:464. [PMID: 31139209 PMCID: PMC6527590 DOI: 10.3389/fgene.2019.00464] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Accepted: 04/30/2019] [Indexed: 11/13/2022] Open
Abstract
A critical step in the cellular stress response is transient activation of the RNA-dependent protein kinase PKR by double-helical RNA, resulting in down-regulation of protein synthesis through phosphorylation of the α chain of translation initiation factor eIF2, a major PKR substrate. However, intragenic elements of 100–200 nucleotides in length within primary transcripts of cellular genes, exemplified by the tumor necrosis factor (TNF)-α gene and fetal and adult globin genes, are capable of forming RNA structures that potently activate PKR and thereby strongly enhance mRNA splicing efficiency. By inducing nuclear eIF2α phosphorylation, these PKR activator elements enable highly efficient early spliceosome assembly yet do not impair translation of the mature spliced mRNA. The TNF-α RNA activator of PKR folds into a compact pseudoknot that is highly conserved within the phylogeny. Upon excision of β-globin first intron, the RNA activator of PKR, located in exon 1, is silenced through strand displacement by a short sequence within exon 2, restricting thereby the ability to activate PKR to the splicing process without impeding subsequent synthesis of β-globin essential for survival. This activator/silencer mechanism likewise controls splicing of α-globin pre-mRNA, but the exonic locations of PKR activator and silencer sequences are reversed, demonstrating evolutionary flexibility. Impaired splicing efficiency may underlie numerous human β-thalassemia mutations that map to the β-globin RNA activator of PKR or its silencer. Even where such mutations change the encoded amino acid sequence during subsequent translation, they carry the potential of first impairing PKR-dependent mRNA splicing or shutoff of PKR activation needed for optimal translation.
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Affiliation(s)
- Raymond Kaempfer
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Lena Ilan
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Smadar Cohen-Chalamish
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Orli Turgeman
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Lise Sarah Namer
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Farhat Osman
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
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12
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Kakiyama S, Tabara M, Nishibori Y, Moriyama H, Fukuhara T. Long DCL4-substrate dsRNAs efficiently induce RNA interference in plant cells. Sci Rep 2019; 9:6920. [PMID: 31061468 PMCID: PMC6502814 DOI: 10.1038/s41598-019-43443-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 02/26/2019] [Indexed: 12/29/2022] Open
Abstract
RNA interference (RNAi) is induced by the direct transfer of double-stranded RNAs (dsRNAs) into protoplasts prepared from Arabidopsis thaliana seedlings. In this protoplast RNAi system, we compared the efficacies of various-sized dsRNAs (between 21 and 139 nucleotides [nt]) for inducing RNAi and assessed the dsRNA-cleaving activities of Dicer-like 3 (DCL3) and 4 (DCL4). After the direct transfer of dsRNAs into protoplasts, cleaved RNA products of 21 nt were detected from long 130- or 500-nt dsRNAs by DCL4 but not from 37-nt dsRNAs. These results indicate that DCL4 preferentially cleaves long dsRNAs in protoplasts, consistent with our previous biochemical data regarding the substrate specificity of DCL4. Direct transfer of long dsRNAs of approximately 130 nt into protoplasts induces RNAi much more effectively (by approximately 60- to 400-fold) than direct transfer of short 37-nt dsRNAs. Although transfer of 21-nt dsRNAs into protoplasts induced RNAi without DCL4 activity, the induction of RNAi was less effective (by approximately 0.01-fold) compared with long dsRNAs. These results indicate that cleavage of long dsRNAs exceeding 100 nt by DCL4 into 21-nt dsRNAs is essential for efficient induction of RNAi in plant cells.
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Affiliation(s)
- Sayaka Kakiyama
- Department of Applied Biological Sciences, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu, Tokyo, 183-8509, Japan
| | - Midori Tabara
- Department of Applied Biological Sciences, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu, Tokyo, 183-8509, Japan
| | - Yuki Nishibori
- Department of Applied Biological Sciences, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu, Tokyo, 183-8509, Japan
| | - Hiromitsu Moriyama
- Department of Applied Biological Sciences, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu, Tokyo, 183-8509, Japan
| | - Toshiyuki Fukuhara
- Department of Applied Biological Sciences, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu, Tokyo, 183-8509, Japan. .,Institute of Global Innovation Research, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu, Tokyo, 183-8509, Japan.
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13
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Schwartz SL, Conn GL. RNA regulation of the antiviral protein 2'-5'-oligoadenylate synthetase. WILEY INTERDISCIPLINARY REVIEWS-RNA 2019; 10:e1534. [PMID: 30989826 DOI: 10.1002/wrna.1534] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Revised: 03/12/2019] [Accepted: 03/14/2019] [Indexed: 12/25/2022]
Abstract
The innate immune system is a broad collection of critical intra- and extra-cellular processes that limit the infectivity of diverse pathogens. The 2'-5'-oligoadenylate synthetase (OAS) family of enzymes are important sensors of cytosolic double-stranded RNA (dsRNA) that play a critical role in limiting viral infection by activating the latent ribonuclease (RNase L) to halt viral replication and establish an antiviral state. Attesting to the importance of the OAS/RNase L pathway, diverse viruses have developed numerous distinct strategies to evade the effects of OAS activation. How OAS proteins are regulated by viral or cellular RNAs is not fully understood but several recent studies have provided important new insights into the molecular mechanisms of OAS activation by dsRNA. Other studies have revealed unanticipated features of RNA sequence and structure that strongly enhance activation of at least one OAS family member. While these discoveries represent important advances, they also underscore the fact that much remains to be learned about RNA-mediated regulation of the OAS/RNase L pathway. In particular, defining the full complement of RNA molecular signatures that activate OAS is essential to our understanding of how these proteins maximize their protective role against pathogens while still accurately discriminating host molecules to avoid inadvertent activation by cellular RNAs. A more complete knowledge of OAS regulation may also serve as a foundation for the development of novel antiviral therapeutic strategies and lead the way to a deeper understanding of currently unappreciated cellular functions of the OAS/RNase L pathway in the absence of infection. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications Translation > Translation Regulation.
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Affiliation(s)
- Samantha L Schwartz
- Department of Biochemistry, Emory University School of Medicine and Graduate Program in Biochemistry, Cell and Developmental Biology (BCDB), Atlanta, Georgia
| | - Graeme L Conn
- Department of Biochemistry, Emory University School of Medicine and Graduate Program in Biochemistry, Cell and Developmental Biology (BCDB), Atlanta, Georgia
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14
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Raja MAG, Katas H, Amjad MW. Design, mechanism, delivery and therapeutics of canonical and Dicer-substrate siRNA. Asian J Pharm Sci 2019; 14:497-510. [PMID: 32104477 PMCID: PMC7032099 DOI: 10.1016/j.ajps.2018.12.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 12/07/2018] [Accepted: 12/24/2018] [Indexed: 12/12/2022] Open
Abstract
Upon the discovery of RNA interference (RNAi), canonical small interfering RNA (siRNA) has been recognized to trigger sequence-specific gene silencing. Despite the benefits of siRNAs as potential new drugs, there are obstacles still to be overcome, including off-target effects and immune stimulation. More recently, Dicer substrate siRNA (DsiRNA) has been introduced as an alternative to siRNA. Similarly, it also is proving to be potent and target-specific, while rendering less immune stimulation. DsiRNA is 25–30 nucleotides in length, and is further cleaved and processed by the Dicer enzyme. As with siRNA, it is crucial to design and develop a stable, safe, and efficient system for the delivery of DsiRNA into the cytoplasm of targeted cells. Several polymeric nanoparticle systems have been well established to load DsiRNA for in vitro and in vivo delivery, thereby overcoming a major hurdle in the therapeutic uses of DsiRNA. The present review focuses on a comparison of siRNA and DsiRNA on the basis of their design, mechanism, in vitro and in vivo delivery, and therapeutics.
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Affiliation(s)
- Maria Abdul Ghafoor Raja
- Department of Pharmaceutics, Faculty of Pharmacy, Northern Border University, Rafha 73211, Saudi Arabia
| | - Haliza Katas
- Centre for Drug Delivery Research, Faculty of Pharmacy, Universiti Kebangsaan Malaysia, Kuala Lumpur 50300, Malaysia
| | - Muhammad Wahab Amjad
- Department of Pharmaceutics, Faculty of Pharmacy, Northern Border University, Rafha 73211, Saudi Arabia
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15
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Okamoto K, Rausch JW, Wakashin H, Fu Y, Chung JY, Dummer PD, Shin MK, Chandra P, Suzuki K, Shrivastav S, Rosenberg AZ, Hewitt SM, Ray PE, Noiri E, Le Grice SFJ, Hoek M, Han Z, Winkler CA, Kopp JB. APOL1 risk allele RNA contributes to renal toxicity by activating protein kinase R. Commun Biol 2018; 1:188. [PMID: 30417125 PMCID: PMC6220249 DOI: 10.1038/s42003-018-0188-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Accepted: 10/03/2018] [Indexed: 01/09/2023] Open
Abstract
APOL1 risk alleles associate with chronic kidney disease in African Americans, but the mechanisms remain to be fully understood. We show that APOL1 risk alleles activate protein kinase R (PKR) in cultured cells and transgenic mice. This effect is preserved when a premature stop codon is introduced to APOL1 risk alleles, suggesting that APOL1 RNA but not protein is required for the effect. Podocyte expression of APOL1 risk allele RNA, but not protein, in transgenic mice induces glomerular injury and proteinuria. Structural analysis of the APOL1 RNA shows that the risk variants possess secondary structure serving as a scaffold for tandem PKR binding and activation. These findings provide a mechanism by which APOL1 variants damage podocytes and suggest novel therapeutic strategies.
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Affiliation(s)
- Koji Okamoto
- Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD, 20892, USA
- Division of Nephrology, Endocrinology and Vascular Medicine, Department of Medicine, Tohoku University Hospital, 1-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi, 980-8574, Japan
- Department of Nephrology, Endocrinology, Hemodialysis & Apheresis, University Hospital, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 133-8655, Japan
| | - Jason W Rausch
- Reverse Transcriptase Biochemistry Section, Basic Research Program, Frederick National Laboratory for Cancer Research, 1050 Boyle Street, Frederick, MD, 21702, USA
| | - Hidefumi Wakashin
- Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD, 20892, USA
| | - Yulong Fu
- Children's National Health System, 111 Michigan Ave NW, Washington, DC, 20010, USA
| | - Joon-Yong Chung
- Experimental Pathology Lab, Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD, 20892, USA
| | - Patrick D Dummer
- Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD, 20892, USA
| | - Myung K Shin
- Merck Research Laboratories, Merck and Co., Inc., 2000 Galloping Hill Rd, Kenilworth, NJ, 07033, USA
| | - Preeti Chandra
- Division of Nephrology, Department of Medicine, University of Maryland School of Medicine, 655 W. Baltimore Street, Baltimore, MD, 21201, USA
| | - Kosuke Suzuki
- Division of Nephrology, Endocrinology and Vascular Medicine, Department of Medicine, Tohoku University Hospital, 1-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi, 980-8574, Japan
| | - Shashi Shrivastav
- Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD, 20892, USA
| | - Avi Z Rosenberg
- Department of Pathology, Johns Hopkins Medical Institutions, 720 Rutland Avenue, Baltimore, MD, 21287, USA
| | - Stephen M Hewitt
- Experimental Pathology Lab, Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD, 20892, USA
| | - Patricio E Ray
- Children's National Health System, 111 Michigan Ave NW, Washington, DC, 20010, USA
| | - Eisei Noiri
- Department of Nephrology, Endocrinology, Hemodialysis & Apheresis, University Hospital, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 133-8655, Japan
| | - Stuart F J Le Grice
- Reverse Transcriptase Biochemistry Section, Basic Research Program, Frederick National Laboratory for Cancer Research, 1050 Boyle Street, Frederick, MD, 21702, USA
| | - Maarten Hoek
- Merck Research Laboratories, Merck and Co., Inc., 2000 Galloping Hill Rd, Kenilworth, NJ, 07033, USA
| | - Zhe Han
- Children's National Health System, 111 Michigan Ave NW, Washington, DC, 20010, USA
| | - Cheryl A Winkler
- Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, Leidos Biomedical Research, Frederick National Laboratory, 8560 Progress Dr., Frederick, MD, 21702, USA
| | - Jeffrey B Kopp
- Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD, 20892, USA.
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16
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Defining the Role of Stress Granules in Innate Immune Suppression by the Herpes Simplex Virus 1 Endoribonuclease VHS. J Virol 2018; 92:JVI.00829-18. [PMID: 29793959 DOI: 10.1128/jvi.00829-18] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Accepted: 05/16/2018] [Indexed: 12/20/2022] Open
Abstract
In response to virus-induced shutoff host protein synthesis, dynamic aggregates containing mRNA, RNA-binding proteins and translation factors termed stress granules (SGs) often accumulate within the cytoplasm. SGs typically form following phosphorylation and inactivation of the eukaryotic translation initiation factor 2α (eIF2α), a substrate of the double-stranded RNA (dsRNA)-activated kinase protein kinase R (PKR). The detection of innate immune sensors and effectors like PKR at SGs suggests a role in pathogen nucleic acid sensing. However, the functional importance of SGs in host innate responses is unclear and has primarily been examined in response to infection with select RNA viruses. During infection with the DNA virus herpes simplex virus 1 (HSV-1), the virus-encoded virion host shutoff (VHS) endoribonuclease is required to restrict interferon production, PKR activation, and SG formation, although the relationship between these activities remains incompletely understood. Here, we show that in cells infected with a VHS-deficient HSV-1 (ΔVHS) dsRNA accumulated and localized to SGs. Surprisingly, formation of dsRNA and its concentration at SGs was not required for beta interferon mRNA induction, indicating that suppression of type I interferon induction by VHS does not stem from its control of dsRNA accumulation. Instead, STING signaling downstream of cGMP-AMP synthase (cGAS)-dependent DNA sensing is required for beta interferon induction. In contrast, significantly less PKR activation is observed when SG assembly is disrupted by ISRIB, an inhibitor of phosphorylated eIF2α-mediated translation repression, or depleting SG scaffolding proteins G3BP1 or TIA1. This demonstrates that PKR activation is intimately linked to SG formation and that SGs form important hubs to potentiate PKR activation during infection.IMPORTANCE Formation of cytoplasmic stress granules that are enriched for innate immune sensors and effectors is suppressed during many viral infections. It is unclear, however, to what extent this is a side effect of viral efforts to maintain protein synthesis or intentional disruption of a hub for innate immune sensing. In this study, we utilize a herpes simplex virus 1 mutant lacking the RNA nuclease VHS which upon infection induces SGs, PKR activation, and beta interferon to address this question. We show that dsRNA is localized to SGs and that SGs can function to promote PKR activation in the context of a DNA virus infection, but we find no evidence to support their importance for interferon induction during HSV-1 infection.
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17
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Takahashi H, Kozhuharova A, Sharma H, Hirose M, Ohyama T, Fasolo F, Yamazaki T, Cotella D, Santoro C, Zucchelli S, Gustincich S, Carninci P. Identification of functional features of synthetic SINEUPs, antisense lncRNAs that specifically enhance protein translation. PLoS One 2018; 13:e0183229. [PMID: 29414979 PMCID: PMC5802440 DOI: 10.1371/journal.pone.0183229] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 08/01/2017] [Indexed: 12/26/2022] Open
Abstract
SINEUPs are antisense long noncoding RNAs, in which an embedded SINE B2 element UP-regulates translation of partially overlapping target sense mRNAs. SINEUPs contain two functional domains. First, the binding domain (BD) is located in the region antisense to the target, providing specific targeting to the overlapping mRNA. Second, the inverted SINE B2 represents the effector domain (ED) and enhances translation. To adapt SINEUP technology to a broader number of targets, we took advantage of a high-throughput, semi-automated imaging system to optimize synthetic SINEUP BD and ED design in HEK293T cell lines. Using SINEUP-GFP as a model SINEUP, we extensively screened variants of the BD to map features needed for optimal design. We found that most active SINEUPs overlap an AUG-Kozak sequence. Moreover, we report our screening of the inverted SINE B2 sequence to identify active sub-domains and map the length of the minimal active ED. Our synthetic SINEUP-GFP screening of both BDs and EDs constitutes a broad test with flexible applications to any target gene of interest.
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Affiliation(s)
- Hazuki Takahashi
- RIKEN Center for Life Science Technologies, Division of Genomic Technologies, Yokohama, Kanagawa, Japan
| | - Ana Kozhuharova
- RIKEN Center for Life Science Technologies, Division of Genomic Technologies, Yokohama, Kanagawa, Japan
| | - Harshita Sharma
- RIKEN Center for Life Science Technologies, Division of Genomic Technologies, Yokohama, Kanagawa, Japan
| | - Masakazu Hirose
- RIKEN Center for Life Science Technologies, Division of Genomic Technologies, Yokohama, Kanagawa, Japan
| | - Takako Ohyama
- RIKEN Center for Life Science Technologies, Division of Structural and Synthetic Biology, Yokohama, Kanagawa, Japan
| | - Francesca Fasolo
- Area of Neuroscience, Scuola Internazionale Superiore di Studi Avanzati, Trieste, Italy
| | - Toshio Yamazaki
- RIKEN Center for Life Science Technologies, Division of Structural and Synthetic Biology, Yokohama, Kanagawa, Japan
| | - Diego Cotella
- Department of Health Sciences, Università del Piemonte Orientale, Novara, Italy
| | - Claudio Santoro
- Department of Health Sciences & IRCAD, Università del Piemonte Orientale, Novara, Italy
| | - Silvia Zucchelli
- Area of Neuroscience, Scuola Internazionale Superiore di Studi Avanzati, Trieste, Italy
- Department of Health Sciences, Università del Piemonte Orientale, Novara, Italy
| | - Stefano Gustincich
- Area of Neuroscience, Scuola Internazionale Superiore di Studi Avanzati, Trieste, Italy
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, Genova, Italy
| | - Piero Carninci
- RIKEN Center for Life Science Technologies, Division of Genomic Technologies, Yokohama, Kanagawa, Japan
- TransSINE Technologies, Yokohama, Kanagawa, Japan
- * E-mail:
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18
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Abstract
Although the antiviral kinase PKR was originally characterized as a double-stranded RNA activated enzyme it can be stimulated by RNAs containing limited secondary structure. Single-stranded regions in such RNAs contribute to binding and activation but the mechanism is not understood. Here, we demonstrate that single-stranded RNAs bind to PKR with micromolar dissociation constants and can induce activation. Addition of a 5'-triphosphate slightly enhances binding affinity. Single-stranded RNAs also activate PKR constructs lacking the double-stranded RNA binding domain and bind to a basic region adjacent to the N-terminus of the kinase. However, the isolated kinase is not activated by and does not bind single-stranded RNA. Photocrosslinking measurements demonstrate that that the basic region interacts with RNA in the context of full length PKR. We propose that bivalent interactions with the double stranded RNA binding domain and the basic region underlie the ability of RNAs containing limited structure to activate PKR by enhancing binding affinity and thereby increasing the population of productive complexes containing two PKRs bound to a single RNA.
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19
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Ghatak S, Hascall VC, Markwald RR, Feghali-Bostwick C, Artlett CM, Gooz M, Bogatkevich GS, Atanelishvili I, Silver RM, Wood J, Thannickal VJ, Misra S. Transforming growth factor β1 (TGFβ1)-induced CD44V6-NOX4 signaling in pathogenesis of idiopathic pulmonary fibrosis. J Biol Chem 2017; 292:10490-10519. [PMID: 28389561 DOI: 10.1074/jbc.m116.752469] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2016] [Revised: 04/06/2017] [Indexed: 01/06/2023] Open
Abstract
Idiopathic pulmonary fibrosis (IPF) is a progressive clinical syndrome of fatal outcome. The lack of information about the signaling pathways that sustain fibrosis and the myofibroblast phenotype has prevented the development of targeted therapies for IPF. Our previous study showed that isolated fibrogenic lung fibroblasts have high endogenous levels of the hyaluronan receptor, CD44V6 (CD44 variant containing exon 6), which enhances the TGFβ1 autocrine signaling and induces fibroblasts to transdifferentiate into myofibroblasts. NADPH oxidase 4 (NOX4) enzyme, which catalyzes the reduction of O2 to hydrogen peroxide (H2O2), has been implicated in the cardiac and lung myofibroblast phenotype. However, whether CD44V6 regulates NOX4 to mediate tissue repair and fibrogenesis is not well-defined. The present study assessed the mechanism of how TGF-β-1-induced CD44V6 regulates the NOX4/reactive oxygen species (ROS) signaling that mediates the myofibroblast differentiation. Specifically, we found that NOX4/ROS regulates hyaluronan synthesis and the transcription of CD44V6 via an effect upon AP-1 activity. Further, CD44V6 is part of a positive-feedback loop with TGFβ1/TGFβRI signaling that acts to increase NOX4/ROS production, which is required for myofibroblast differentiation, myofibroblast differentiation, myofibroblast extracellular matrix production, myofibroblast invasion, and myofibroblast contractility. Both NOX4 and CD44v6 are up-regulated in the lungs of mice subjected to experimental lung injury and in cases of human IPF. Genetic (CD44v6 shRNA) or a small molecule inhibitor (CD44v6 peptide) targeting of CD44v6 abrogates fibrogenesis in murine models of lung injury. These studies support a function for CD44V6 in lung fibrosis and offer proof of concept for therapeutic targeting of CD44V6 in lung fibrosis disorders.
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Affiliation(s)
- Shibnath Ghatak
- From the Department of Regenerative Medicine and Cell Biology,
| | - Vincent C Hascall
- the Department of Biomedical Engineering/ND20, Cleveland Clinic, Cleveland, Ohio 44195
| | | | | | - Carol M Artlett
- the Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
| | - Monika Gooz
- the College of Pharmacy/Pharmaceutical Biomedical Science, Medical University of South Carolina, Charleston, South Carolina 29425
| | | | - Ilia Atanelishvili
- the Division of Rheumatology and Immunology, Department of Medicine, and
| | - Richard M Silver
- the Division of Rheumatology and Immunology, Department of Medicine, and
| | - Jeanette Wood
- Genkyotex, 16 Chemin des Aulx, CH-1228 Plan-les-Ouates Geneva, Switzerland, and
| | - Victor J Thannickal
- the Division of Pulmonary, Allergy, and Critical Care Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294-0006
| | - Suniti Misra
- From the Department of Regenerative Medicine and Cell Biology,
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20
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Ghatak S, Markwald RR, Hascall VC, Dowling W, Lottes RG, Baatz JE, Beeson G, Beeson CC, Perrella MA, Thannickal VJ, Misra S. Transforming growth factor β1 (TGFβ1) regulates CD44V6 expression and activity through extracellular signal-regulated kinase (ERK)-induced EGR1 in pulmonary fibrogenic fibroblasts. J Biol Chem 2017; 292:10465-10489. [PMID: 28389562 DOI: 10.1074/jbc.m116.752451] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2016] [Revised: 04/06/2017] [Indexed: 01/06/2023] Open
Abstract
The appearance of myofibroblasts is generally thought to be the underlying cause of the fibrotic changes that underlie idiopathic pulmonary fibrosis. However, the cellular/molecular mechanisms that account for the fibroblast-myofibroblast differentiation/activation in idiopathic pulmonary fibrosis remain poorly understood. We investigated the functional role of hyaluronan receptor CD44V6 (CD44 containing variable exon 6 (v6)) for differentiation of lung fibroblast to myofibroblast phenotype. Increased hyaluronan synthesis and CD44 expression have been detected in numerous fibrotic organs. Previously, we found that the TGFβ1/CD44V6 pathway is important in lung myofibroblast collagen-1 and α-smooth-muscle actin synthesis. Because increased EGR1 (early growth response-1) expression has been shown to appear very early and nearly coincident with the expression of CD44V6 found after TGFβ1 treatment, we investigated the mechanism(s) of regulation of CD44V6 expression in lung fibroblasts by TGFβ1. TGFβ1-mediated CD44V6 up-regulation was initiated through EGR1 via ERK-regulated transcriptional activation. We showed that TGFβ1-induced CD44V6 expression is through EGR1-mediated AP-1 (activator protein-1) activity and that the EGR1- and AP-1-binding sites in the CD44v6 promoter account for its responsiveness to TGFβ1 in lung fibroblasts. We also identified a positive-feedback loop in which ERK/EGR1 signaling promotes CD44V6 splicing and found that CD44V6 then sustains ERK signaling, which is important for AP-1 activity in lung fibroblasts. Furthermore, we identified that HAS2-produced hyaluronan is required for CD44V6 and TGFβRI co-localization and subsequent CD44V6/ERK1/EGR1 signaling. These results demonstrate a novel positive-feedback loop that links the myofibroblast phenotype to TGFβ1-stimulated CD44V6/ERK/EGR1 signaling.
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Affiliation(s)
- Shibnath Ghatak
- From the Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, South Carolina 29425,
| | - Roger R Markwald
- From the Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, South Carolina 29425
| | - Vincent C Hascall
- the Department of Biomedical Engineering, Cleveland Clinic, Cleveland, Ohio 44195
| | - William Dowling
- From the Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, South Carolina 29425.,the College of Charleston, Charleston, South Carolina 29424
| | | | | | - Gyada Beeson
- Drug Discovery and Biomedical sciences, Medical University of South Carolina, Charleston, South Carolina 29425
| | - Craig C Beeson
- Drug Discovery and Biomedical sciences, Medical University of South Carolina, Charleston, South Carolina 29425
| | - Mark A Perrella
- the Division of Pulmonary and Critical Care Medicine, Department of Medicine, and the Department of Pediatric Newborn Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, and
| | - Victor J Thannickal
- the Division of Pulmonary, Allergy, and Critical Care Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294-0006
| | - Suniti Misra
- From the Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, South Carolina 29425,
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21
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PKR activation and eIF2α phosphorylation mediate human globin mRNA splicing at spliceosome assembly. Cell Res 2017; 27:688-704. [PMID: 28374749 DOI: 10.1038/cr.2017.39] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Revised: 11/20/2016] [Accepted: 12/30/2016] [Indexed: 02/01/2023] Open
Abstract
Short elements in mammalian mRNA can control gene expression by activating the RNA-dependent protein kinase PKR that attenuates translation by phosphorylating cytoplasmic eukaryotic initiation factor 2α (eIF2α). We demonstrate a novel, positive role for PKR activation and eIF2α phosphorylation in human globin mRNA splicing. PKR localizes in splicing complexes and associates with splicing factor SC35. Splicing and early-stage spliceosome assembly on β-globin pre-mRNA depend strictly on activation of PKR by a codon-containing RNA fragment within exon 1 and on phosphorylation of nuclear eIF2α on Serine 51. Nonphosphorylatable mutant eIF2αS51A blocked β-globin mRNA splicing in cells and nuclear extract. Mutations of the β-globin RNA activator abrogated PKR activation and profoundly affected mRNA splicing efficiency. PKR depletion abrogated splicing and spliceosome assembly; recombinant PKR effectively restored splicing. Excision of the first intron of β-globin induces strand displacement within the RNA activator of PKR by a sequence from exon 2, a structural rearrangement that silences the ability of spliced β-globin mRNA to activate PKR. Thus, the ability to activate PKR is transient, serving solely to enable splicing. α-Globin pre-mRNA splicing is controlled likewise but positions of PKR activator and silencer are reversed, demonstrating evolutionary flexibility in how PKR activation regulates globin mRNA splicing through eIF2α phosphorylation.
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22
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Yuen KC. Measurement of RNA-induced PKR Activation in vitro. Bio Protoc 2017; 7:e2178. [PMID: 34458488 DOI: 10.21769/bioprotoc.2178] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 01/31/2017] [Accepted: 02/22/2017] [Indexed: 11/02/2022] Open
Abstract
Protein kinase R (PKR) is one of the key RNA-activated sensors for innate immunity. PKR is activated by pathogenic or aberrant RNAs such as short double-stranded RNAs or those with imperfect secondary structures, as well as a reduction in the amount and number of RNA modifications. Activation of PKR may be an underlying mechanism for the pathogenesis of human diseases. In this protocol, I describe a method for studying levels of RNA-induced PKR activation in vitro.
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Affiliation(s)
- Kobe C Yuen
- Stowers Institute for Medical Research, Kansas City, MO, USA.,Present address: 1 DNA Way, South San Francisco, USA
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23
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Weng Y, Shi Y, Xia X, Zhou W, Wang H, Wang C. A multi-shRNA vector enhances the silencing efficiency of exogenous and endogenous genes in human cells. Oncol Lett 2017; 13:1553-1562. [PMID: 28454290 PMCID: PMC5403481 DOI: 10.3892/ol.2017.5672] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Accepted: 09/27/2016] [Indexed: 01/10/2023] Open
Abstract
RNA interference (RNAi) is a powerful technology for suppressing gene function. In most studies, small interfering RNAs (siRNAs) consist of one short hairpin RNA (shRNA) and, therefore, are often unable to achieve loss-of-function of their target genes. In the current study, an RNAi vector containing three shRNAs under the control of three RNA polymerase III U6 promoters was constructed. RNAi vectors containing one or two shRNAs were generated for comparisons. A pilot study targeting exogenously expressed DsRed in the HEK293 cell line revealed promising effects and a high selectivity for the multi-shRNA RNAi vector. Akt2 is constitutively expressed in cultured SKOV3 human ovarian cancer cells, and the multi-shRNA RNAi vector showed a strong efficiency for downregulating the expression of Akt2 in these cells, with no apparent interferon response. In addition, the Akt2-3shRNA vector, containing three shRNAs targeting Akt2, showed the best effect of all the shRNA vectors in reversing paclitaxel-induced resistance in SKOV3 cells. This study developed a widely applicable resource for enhancing the efficiency of gene silencing and a novel technique for performing complex loss-of-function screens in mammalian cells.
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Affiliation(s)
- Yanjie Weng
- Cancer Biology Research Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, P.R. China
| | - Ying Shi
- Cancer Biology Research Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, P.R. China
| | - Xi Xia
- Cancer Biology Research Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, P.R. China.,Department of Gynecology and Obstetrics, Affiliated Shenzhen Nanshan Hospital, Guangdong Medical College, Shenzhen, Guangdong 518052, P.R. China
| | - Wenjuan Zhou
- Cancer Biology Research Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, P.R. China
| | - Hongyan Wang
- Cancer Biology Research Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, P.R. China
| | - Changyu Wang
- Cancer Biology Research Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, P.R. China
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Masuda T, Wan J, Yerrabelli A, Berlinicke C, Kallman A, Qian J, Zack DJ. Off Target, but Sequence-Specific, shRNA-Associated Trans-Activation of Promoter Reporters in Transient Transfection Assays. PLoS One 2016; 11:e0167867. [PMID: 27977714 PMCID: PMC5158200 DOI: 10.1371/journal.pone.0167867] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2016] [Accepted: 11/21/2016] [Indexed: 11/23/2022] Open
Abstract
Transient transfection promoter reporter assays are commonly used in the study of transcriptional regulation, and can be used to define and characterize both cis-acting regulatory sequences and trans-acting factors. In the process of using a variety of reporter assays designed to study regulation of the rhodopsin (rho) promoter, we discovered that rhodopsin promoter-driven reporter expression could be activated by certain species of shRNA in a gene-target-independent but shRNA sequence-specific manner, suggesting involvement of a specific shRNA associated pathway. Interestingly, the shRNA-mediated increase of rhodopsin promoter activity was synergistically enhanced by the rhodopsin transcriptional regulators CRX and NRL. Additionally, the effect was cell line-dependent, suggesting that this pathway requires the expression of cell-type specific factors. Since microRNA (miRNA) and interferon response-mediated processes have been implicated in RNAi off-target phenomena, we performed miRNA and gene expression profiling on cells transfected with shRNAs that do target a specific gene but have varied effects on rho reporter expression in order to identify transcripts whose expression levels are associated with shRNA induced rhodopsin promoter reporter activity. We identified a total of 50 miRNA species, and by microarray analysis, 320 protein-coding genes, some of which were predicted targets of the identified differentially expressed miRNAs, whose expression was altered in the presence of shRNAs that stimulated rhodopsin-promoter activity in a non-gene-targeting manner. Consistent with earlier studies on shRNA off-target effects, a number of interferon response genes were among those identified to be upregulated. Taken together, our results confirm the importance of considering off-target effects when interpreting data from RNAi experiments and extend prior results by focusing on the importance of including multiple and carefully designed controls in the design and analysis of the effects of shRNA on transient transfection-based transcriptional assays.
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Affiliation(s)
- Tomohiro Masuda
- Department of Ophthalmology, Wilmer Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Jun Wan
- Department of Ophthalmology, Wilmer Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Anitha Yerrabelli
- Department of Ophthalmology, Wilmer Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Cindy Berlinicke
- Department of Ophthalmology, Wilmer Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Alyssa Kallman
- Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Jiang Qian
- Department of Ophthalmology, Wilmer Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Donald J. Zack
- Department of Ophthalmology, Wilmer Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
- Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
- Institut de la Vision, University Pierre and Marie Curie, Paris, France
- * E-mail:
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25
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Parlea L, Puri A, Kasprzak W, Bindewald E, Zakrevsky P, Satterwhite E, Joseph K, Afonin KA, Shapiro BA. Cellular Delivery of RNA Nanoparticles. ACS COMBINATORIAL SCIENCE 2016; 18:527-47. [PMID: 27509068 PMCID: PMC6345529 DOI: 10.1021/acscombsci.6b00073] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
RNA nanostructures can be programmed to exhibit defined sizes, shapes and stoichiometries from naturally occurring or de novo designed RNA motifs. These constructs can be used as scaffolds to attach functional moieties, such as ligand binding motifs or gene expression regulators, for nanobiology applications. This review is focused on four areas of importance to RNA nanotechnology: the types of RNAs of particular interest for nanobiology, the assembly of RNA nanoconstructs, the challenges of cellular delivery of RNAs in vivo, and the delivery carriers that aid in the matter. The available strategies for the design of nucleic acid nanostructures, as well as for formulation of their carriers, make RNA nanotechnology an important tool in both basic research and applied biomedical science.
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Affiliation(s)
- Lorena Parlea
- Gene Regulation and Chromosome Biology Laboratory, National Cancer Institute, Frederick, Maryland 21702, United States
| | - Anu Puri
- Gene Regulation and Chromosome Biology Laboratory, National Cancer Institute, Frederick, Maryland 21702, United States
| | - Wojciech Kasprzak
- Basic Science Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, Maryland 21702, United States
| | - Eckart Bindewald
- Basic Science Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, Maryland 21702, United States
| | - Paul Zakrevsky
- Gene Regulation and Chromosome Biology Laboratory, National Cancer Institute, Frederick, Maryland 21702, United States
| | - Emily Satterwhite
- Department of Chemistry, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, United States
| | - Kenya Joseph
- Department of Chemistry, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, United States
| | - Kirill A. Afonin
- Department of Chemistry, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, United States
- Nanoscale Science Program, University of North Carolina at Charlotte, Charlotte North Carolina 28223, United States
- The Center for Biomedical Engineering and Science, University of North Carolina at Charlotte, Charlotte North Carolina 28223, United States
| | - Bruce A. Shapiro
- Gene Regulation and Chromosome Biology Laboratory, National Cancer Institute, Frederick, Maryland 21702, United States
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Abstract
The ability to distinguish between self and nonself is the fundamental basis of the immune system in all organisms. The conceptual distinction between self and nonself, however, breaks down when it comes to endogenous retroviruses and other retroelements. While some retroelements retain the virus-like features including the capacity to replicate and reinvade the host genome, most have become inactive through mutations or host epigenetic silencing. And yet, accumulating evidence suggests that endogenous retroelements, both active and inactive, play important roles not only in pathogenesis of immune disorders, but also in proper functioning of the immune system. This review discusses the recent development in our understanding of the interaction between retroelements and the host innate immune system. In particular, it focuses on the impact of retroelement transcripts on the viral RNA sensors such as Toll-like receptors, RIG-I-like receptors, protein kinase R, and the inflammasomes.
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Affiliation(s)
- X Mu
- Harvard Medical School, Boston, MA, United States; Boston Children's Hospital, Boston, MA, United States
| | - S Ahmad
- Harvard Medical School, Boston, MA, United States; Boston Children's Hospital, Boston, MA, United States
| | - S Hur
- Harvard Medical School, Boston, MA, United States; Boston Children's Hospital, Boston, MA, United States.
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27
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Abstract
Immune sensing of foreign nucleic acids among abundant self nucleic acids is a hallmark of virus detection and antiviral defence. Efficient antiviral defence requires a balanced process of sensing foreign nucleic acids and ignoring self nucleic acids. This balance is accomplished by a multilevel, fail-safe system which combines immune sensing of pathogen-specific nucleic acid structures with specific labelling of self nucleic acids and nuclease-mediated degradation. Cellular localization of nucleic acids, nucleic acid secondary structure, nucleic acid sequence and chemical modification all contribute to selective recognition of foreign nucleic acids. Nucleic acid sensing occurs in immune cells and non-immune cells and results in antiviral responses that include the induction of antiviral effector proteins, the secretion of cytokines alarming neighbouring cells, the secretion of chemokines, which attract immune cells, and the induction of cell death. Vertebrate cells cannot completely avoid the occurrence of endogenous self nucleic acid structures with immunostimulatory properties. Therefore, additional mechanisms involving self-nucleic acid modification and nuclease-mediated degradation are necessary to diminish uncontrolled immune activation. Viruses have established sophisticated mechanisms to exploit and adopt endogenous tolerance mechanisms or to avoid the presentation of characteristic molecular features recognized by nucleic acid sensing receptors.
The detection of viruses by the immune system is mediated predominantly by the sensing of nucleic acids. Here, the authors review our current understanding of how this complex immune sensory system discriminates self from non-self nucleic acids to reliably detect pathogenic viruses, and discuss the future perspectives and implications for human disease. Innate immunity against pathogens relies on an array of immune receptors to detect molecular patterns that are characteristic of the pathogens, including receptors that are specialized in the detection of foreign nucleic acids. In vertebrates, nucleic acid sensing is the dominant antiviral defence pathway. Stimulation of nucleic acid receptors results in antiviral immune responses with the production of type I interferon (IFN), as well as the expression of IFN-stimulated genes, which encode molecules such as cell-autonomous antiviral effector proteins. This Review summarizes the tremendous progress that has been made in understanding how this sophisticated immune sensory system discriminates self from non-self nucleic acids in order to reliably detect pathogenic viruses.
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Affiliation(s)
- Martin Schlee
- Institute of Clinical Chemistry and Clinical Pharmacology, University Hospital, University of Bonn, Sigmund-Freud-Strasse 25, D-53127 Bonn, Germany
| | - Gunther Hartmann
- Institute of Clinical Chemistry and Clinical Pharmacology, University Hospital, University of Bonn, Sigmund-Freud-Strasse 25, D-53127 Bonn, Germany
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28
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Gamil AAA, Xu C, Mutoloki S, Evensen Ø. PKR Activation Favors Infectious Pancreatic Necrosis Virus Replication in Infected Cells. Viruses 2016; 8:v8060173. [PMID: 27338445 PMCID: PMC4926193 DOI: 10.3390/v8060173] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Revised: 05/31/2016] [Accepted: 06/03/2016] [Indexed: 01/17/2023] Open
Abstract
The double-stranded RNA-activated protein kinase R (PKR) is a Type I interferon (IFN) stimulated gene that has important biological and immunological functions. In viral infections, in general, PKR inhibits or promotes viral replication, but PKR-IPNV interaction has not been previously studied. We investigated the involvement of PKR during infectious pancreatic necrosis virus (IPNV) infection using a custom-made rabbit antiserum and the PKR inhibitor C16. Reactivity of the antiserum to PKR in CHSE-214 cells was confirmed after IFNα treatment giving an increased protein level. IPNV infection alone did not give increased PKR levels by Western blot, while pre-treatment with PKR inhibitor before IPNV infection gave decreased eukaryotic initiation factor 2-alpha (eIF2α) phosphorylation. This suggests that PKR, despite not being upregulated, is involved in eIF2α phosphorylation during IPNV infection. PKR inhibitor pre-treatment resulted in decreased virus titers, extra- and intracellularly, concomitant with reduction of cells with compromised membranes in IPNV-permissive cell lines. These findings suggest that IPNV uses PKR activation to promote virus replication in infected cells.
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Affiliation(s)
- Amr A A Gamil
- Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, P.O. Box 8146 Dep., 0033 Oslo, Norway.
| | - Cheng Xu
- Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, P.O. Box 8146 Dep., 0033 Oslo, Norway.
| | - Stephen Mutoloki
- Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, P.O. Box 8146 Dep., 0033 Oslo, Norway.
| | - Øystein Evensen
- Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, P.O. Box 8146 Dep., 0033 Oslo, Norway.
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29
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Hull CM, Bevilacqua PC. Discriminating Self and Non-Self by RNA: Roles for RNA Structure, Misfolding, and Modification in Regulating the Innate Immune Sensor PKR. Acc Chem Res 2016; 49:1242-9. [PMID: 27269119 DOI: 10.1021/acs.accounts.6b00151] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Pathogens are recognized by the innate immune system in part via their unique and complex RNA signatures. A key sensor in human innate immunity is the RNA-activated protein kinase, protein kinase R (PKR), which has two double-stranded RNA (dsRNA) binding motifs (dsRBMs) at its N-terminus. Early studies described PKR as being activated potently by long stretches of perfect dsRNA, a signature typical of viruses. More recently, we and others have found that PKR is also activated by RNAs having structural defects such as bulges and internal loops. This Account describes advances in our understanding of the ability of PKR to detect diverse foreign RNAs and how that recognition plays significant roles in discriminating self from non-self. The experiments discussed employ a wide range of techniques including activation assays, native polyacrylamide gel electrophoresis (PAGE), protein footprinting, and small-angle X-ray scattering (SAXS). We discuss how misfolding and dimerization of RNA lead to activation of PKR. We also present recent findings on the activation of PKR by varied bacterial functional RNAs including ribozymes and riboswitches, which are among the few structured RNAs known to interact with PKR in a site-specific manner. Molecular models for how these structured RNAs activate PKR are provided. Studies by SAXS revealed that PKR straightens bent RNAs. Most external and internal RNA cellular modifications introduced in vitro and found naturally, such as the m7G cap and m6A group, abrogate activation of PKR, but other modifications, such as 5'-ppp and 2'-fluoro groups, are immunostimulatory and potential anticancer agents. Genome-wide studies of RNA folding in vitro and in vivo have provided fresh insights into general differences in RNA structure among bacteria, viruses, and human. These studies suggest that in vivo, cellular human RNAs are less folded than once thought, unwound by helicases, destabilized by m6A modifications, and often bound up with proteins, all conditions known to abrogate activation of PKR. It thus appears that non-self RNAs are detected as unmodified, naked RNAs with appreciable secondary and tertiary structure. Observation that PKR is activated by structured but otherwise diverse RNAs is consistent both with the broad-spectrum nature of innate immunity and the nonspecific recognition of RNA by the dsRBM family. These findings provide a possible explanation for the apparent absence of protein-free structured human RNAs, such as ribozymes and riboswitches.
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Affiliation(s)
- Chelsea M. Hull
- Department of Chemistry and Center for RNA Molecular
Biology and ‡Department of
Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Philip C. Bevilacqua
- Department of Chemistry and Center for RNA Molecular
Biology and ‡Department of
Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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30
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Fros JJ, Pijlman GP. Alphavirus Infection: Host Cell Shut-Off and Inhibition of Antiviral Responses. Viruses 2016; 8:v8060166. [PMID: 27294951 PMCID: PMC4926186 DOI: 10.3390/v8060166] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2016] [Revised: 06/01/2016] [Accepted: 06/07/2016] [Indexed: 12/18/2022] Open
Abstract
Alphaviruses cause debilitating disease in humans and animals and are transmitted by blood-feeding arthropods, typically mosquitoes. With a traditional focus on two models, Sindbis virus and Semliki Forest virus, alphavirus research has significantly intensified in the last decade partly due to the re-emergence and dramatic expansion of chikungunya virus in Asia, Europe, and the Americas. As a consequence, alphavirus–host interactions are now understood in much more molecular detail, and important novel mechanisms have been elucidated. It has become clear that alphaviruses not only cause a general host shut-off in infected vertebrate cells, but also specifically suppress different host antiviral pathways using their viral nonstructural proteins, nsP2 and nsP3. Here we review the current state of the art of alphavirus host cell shut-off of viral transcription and translation, and describe recent insights in viral subversion of interferon induction and signaling, the unfolded protein response, and stress granule assembly.
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Affiliation(s)
- Jelke J Fros
- Nuffield Department of Medicine, Peter Medawar Building for Pathogen Research, University of Oxford, Oxford OX1 3SY, England, UK.
- Laboratory of Virology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen 6700 AB, The Netherlands.
| | - Gorben P Pijlman
- Laboratory of Virology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen 6700 AB, The Netherlands.
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31
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Hull CM, Anmangandla A, Bevilacqua PC. Bacterial Riboswitches and Ribozymes Potently Activate the Human Innate Immune Sensor PKR. ACS Chem Biol 2016; 11:1118-27. [PMID: 27011290 DOI: 10.1021/acschembio.6b00081] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The innate immune system provides the first line of defense against pathogens through the recognition of nonspecific patterns in RNA to protect the cell in a generalized way. The human RNA-activated protein kinase, PKR, is a dsRNA binding protein and an essential sensor in the innate immune response, which recognizes viral and bacterial pathogens through their RNAs. Upon activation via RNA-dependent autophosphorylation, PKR phosphorylates the eukaryotic initiation factor eIF2α, leading to termination of translation. PKR has a well-characterized role in recognizing viral RNA, where it binds long stretches of double-stranded RNA nonsequence specifically to promote activation; however, the mechanism by which bacterial RNA activates PKR and the mode by which self RNA avoids activating PKR are unknown. We characterized activation of PKR by three functional bacterial RNAs with pseudoknots and extensive tertiary structure: the cyclic di-GMP riboswitch, the glmS riboswitch-ribozyme, and the twister ribozyme, two of which are ligand-activated. These RNAs were found to activate PKR with comparable potency to long dsRNA. Enzymatic structure mapping in the absence and presence of PKR reveals a clear PKR footprint and provides a structural basis for how these bacterial RNAs activate PKR. In the case of the cyclic di-GMP riboswitch and the glmS riboswitch-ribozyme, PKR appears to dimerize on the peripheral double-stranded regions of the native RNA tertiary structure. Overall, these results provide new insights into how PKR acts as an innate immune signaling protein for the presence of bacteria and suggest a reason for the apparent absence of protein-free riboswitches and ribozymes in the human genome.
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Affiliation(s)
- Chelsea M. Hull
- Department
of Chemistry, Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Ananya Anmangandla
- Department
of Chemistry, Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Philip C. Bevilacqua
- Department
of Chemistry, Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Department
of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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32
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Husain B, Mayo C, Cole JL. Role of the Interdomain Linker in RNA-Activated Protein Kinase Activation. Biochemistry 2015; 55:253-61. [PMID: 26678943 DOI: 10.1021/acs.biochem.5b01171] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
RNA-activated protein kinase (PKR) is a key component of the interferon-induced antiviral pathway in higher eukaryotes. Upon recognition of viral dsRNA, PKR is activated via dimerization and autophosphorylation. PKR contains two N-terminal dsRNA binding domains (dsRBD) and a C-terminal kinase domain. The dsRBDs and the kinase are separated by a long, unstructured ∼80-amino acid linker in the human enzyme. The length of the N-terminal portion of the linker varies among PKR sequences, and it is completely absent in one ortholog. Here, we characterize the effects of deleting the variable region from the human enzyme to produce PKRΔV. The linker deletion results in quantitative but not qualitative changes in catalytic activity, RNA binding, and conformation. PKRΔV is somewhat more active and exhibits more cooperative RNA binding. As we previously observed for the full-length enzyme, PKRΔV is flexible in solution and adopts a range of compact and extended conformations. The conformational ensemble is biased toward compact states that might be related to weak interactions between the dsRBD and kinase domains. PKR retains RNA-induced autophosphorylation upon complete removal of the linker, indicating that the C-terminal, basic region is also not required for activity.
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Affiliation(s)
- Bushra Husain
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
| | - Christopher Mayo
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
| | - James L Cole
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
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33
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Husain B, Hesler S, Cole JL. Regulation of PKR by RNA: formation of active and inactive dimers. Biochemistry 2015; 54:6663-72. [PMID: 26488609 DOI: 10.1021/acs.biochem.5b01046] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
PKR is a member of the eIF2α family of protein kinases that inhibit translational initiation in response to stress stimuli and functions as a key mediator of the interferon-induced antiviral response. PKR contains a dsRNA binding domain that binds to duplex regions present in viral RNAs, resulting in kinase activation and autophosphorylation. An emerging theme in the regulation of protein kinases is the allosteric linkage of dimerization and activation. The PKR kinase domain forms a back-to-back parallel dimer that is implicated in activation. We have developed a sensitive homo-Förster resonance energy transfer assay for kinase domain dimerization to directly probe the relationship among RNA binding, activation, and dimerization. In the case of perfect duplex RNAs, dimerization is correlated with activation and dsRNAs containing 30 bp or more efficiently induce kinase domain dimerization and activation. However, more complex duplex RNAs containing a 10-15 bp 2'-O-methyl RNA barrier produce kinase dimers but do not activate. Similarly, inactivating mutations within the PKR dimer interface that disrupt key electrostatic and hydrogen binding interactions fail to abolish dimerization. Our data support a model in which activating RNAs induce formation of a back-to-back parallel PKR kinase dimer whereas nonactivating RNAs either fail to induce dimerization or produce an alternative, inactive dimer configuration, providing an additional mechanism for distinguishing between host and pathogen RNA.
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Affiliation(s)
- Bushra Husain
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
| | - Stephen Hesler
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
| | - James L Cole
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
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34
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Launer-Felty K, Wong CJ, Cole JL. Structural analysis of adenovirus VAI RNA defines the mechanism of inhibition of PKR. Biophys J 2015; 108:748-57. [PMID: 25650941 DOI: 10.1016/j.bpj.2014.12.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 12/01/2014] [Accepted: 12/08/2014] [Indexed: 01/24/2023] Open
Abstract
Protein kinase R (PKR) is activated by dsRNA produced during virus replication and plays a major role in the innate immunity response to virus infection. In response, viruses have evolved multiple strategies to evade PKR. Adenovirus virus-associated RNA-I (VAI) is a short, noncoding transcript that functions as an RNA decoy to sequester PKR in an inactive state. VAI consists of an apical stem-loop, a highly structured central domain, and a terminal stem. Chemical probing and mutagenesis demonstrate that the central domain is stabilized by a pseudoknot. A structural model of VAI was obtained from constraints derived from chemical probing and small angle x-ray scattering (SAXS) measurements. VAI adopts a flat, extended conformation with the apical and terminal stems emanating from a protuberance in the center. This model reveals how the apical stem and central domain assemble to produce an extended duplex that is precisely tuned to bind a single PKR monomer with high affinity, thereby inhibiting activation of PKR by viral dsRNA.
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Affiliation(s)
- Katherine Launer-Felty
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut
| | - C Jason Wong
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut
| | - James L Cole
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut; Department of Chemistry, University of Connecticut, Storrs, Connecticut.
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35
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Wang X, Vukovic L, Koh HR, Schulten K, Myong S. Dynamic profiling of double-stranded RNA binding proteins. Nucleic Acids Res 2015; 43:7566-76. [PMID: 26184879 PMCID: PMC4551942 DOI: 10.1093/nar/gkv726] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2015] [Accepted: 07/03/2015] [Indexed: 01/13/2023] Open
Abstract
Double-stranded (ds) RNA is a key player in numerous biological activities in cells, including RNA interference, anti-viral immunity and mRNA transport. The class of proteins responsible for recognizing dsRNA is termed double-stranded RNA binding proteins (dsRBP). However, little is known about the molecular mechanisms underlying the interaction between dsRBPs and dsRNA. Here we examined four human dsRBPs, ADAD2, TRBP, Staufen 1 and ADAR1 on six dsRNA substrates that vary in length and secondary structure. We combined single molecule pull-down (SiMPull), single molecule protein-induced fluorescence enhancement (smPIFE) and molecular dynamics (MD) simulations to investigate the dsRNA-dsRBP interactions. Our results demonstrate that despite the highly conserved dsRNA binding domains, the dsRBPs exhibit diverse substrate specificities and dynamic properties when in contact with different RNA substrates. While TRBP and ADAR1 have a preference for binding simple duplex RNA, ADAD2 and Staufen1 display higher affinity to highly structured RNA substrates. Upon interaction with RNA substrates, TRBP and Staufen1 exhibit dynamic sliding whereas two deaminases ADAR1 and ADAD2 mostly remain immobile when bound. MD simulations provide a detailed atomic interaction map that is largely consistent with the affinity differences observed experimentally. Collectively, our study highlights the diverse nature of substrate specificity and mobility exhibited by dsRBPs that may be critical for their cellular function.
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Affiliation(s)
- Xinlei Wang
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Institute for Genomic Biology, University of Illinois, 1206 W. Gregory St,. Urbana, IL 61801, USA
| | - Lela Vukovic
- Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Hye Ran Koh
- Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Institute for Genomic Biology, University of Illinois, 1206 W. Gregory St,. Urbana, IL 61801, USA Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Klaus Schulten
- Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Biophysics and Computational Biology, University of Illinois, 1110 W. Green St., Urbana, IL 61801, USA
| | - Sua Myong
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Institute for Genomic Biology, University of Illinois, 1206 W. Gregory St,. Urbana, IL 61801, USA Biophysics and Computational Biology, University of Illinois, 1110 W. Green St., Urbana, IL 61801, USA
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36
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Ballarín-González B, Thomsen TB, Howard KA. Clinical translation of RNAi-based treatments for respiratory diseases. Drug Deliv Transl Res 2015; 3:84-99. [PMID: 25787868 PMCID: PMC7097609 DOI: 10.1007/s13346-012-0098-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The ability to harness the RNA interference (RNAi) mechanism as a potential potent therapeutic has attracted great interest from academia and industry. Numerous preclinical and recent clinical trials have demonstrated the effectiveness of RNAi triggers such as synthetic small interfering RNA (siRNA). Chemical modification and delivery technologies can be utilized to avoid immune stimulation and improve the bioactivity and pharmacokinetics. Local application to the respiratory epithelia allows direct access to the site of respiratory pathogens that include influenza and respiratory syncytial virus (RSV). This review outlines the essential steps required for the clinical translation of RNAi-based respiratory therapies including disease and RNA target selection, siRNA design, respiratory barriers, and delivery solutions. Attention is given to antiviral therapies and preclinical evaluation with focus on the current status of anti-RSV clinical trials.
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Affiliation(s)
- Borja Ballarín-González
- Interdisciplinary Nanoscience Center (iNANO), Department of Molecular Biology and Genetics, University of Aarhus, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark
| | - Troels Bo Thomsen
- Interdisciplinary Nanoscience Center (iNANO), Department of Molecular Biology and Genetics, University of Aarhus, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark
| | - Kenneth Alan Howard
- Interdisciplinary Nanoscience Center (iNANO), Department of Molecular Biology and Genetics, University of Aarhus, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark
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Zhou HR, He K, Landgraf J, Pan X, Pestka JJ. Direct activation of ribosome-associated double-stranded RNA-dependent protein kinase (PKR) by deoxynivalenol, anisomycin and ricin: a new model for ribotoxic stress response induction. Toxins (Basel) 2014; 6:3406-25. [PMID: 25521494 PMCID: PMC4280541 DOI: 10.3390/toxins6123406] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Revised: 11/29/2014] [Accepted: 12/08/2014] [Indexed: 01/04/2023] Open
Abstract
Double-stranded RNA (dsRNA)-activated protein kinase (PKR) is a critical upstream mediator of the ribotoxic stress response (RSR) to the trichothecene deoxynivalenol (DON) and other translational inhibitors. Here, we employed HeLa cell lysates to: (1) characterize PKR’s interactions with the ribosome and ribosomal RNA (rRNA); (2) demonstrate cell-free activation of ribosomal-associated PKR and (3) integrate these findings in a unified model for RSR. Robust PKR-dependent RSR was initially confirmed in intact cells. PKR basally associated with 40S, 60S, 80S and polysome fractions at molar ratios of 7, 2, 23 and 3, respectively. Treatment of ATP-containing HeLa lysates with DON or the ribotoxins anisomycin and ricin concentration-dependently elicited phosphorylation of PKR and its substrate eIF2α. These phosphorylations could be blocked by PKR inhibitors. rRNA immunoprecipitation (RNA-IP) of HeLa lysates with PKR-specific antibody and sequencing revealed that in the presence of DON or not, the kinase associated with numerous discrete sites on both the 18S and 28S rRNA molecules, a number of which contained double-stranded hairpins. These findings are consistent with a sentinel model whereby multiple PKR molecules basally associate with the ribosome positioning them to respond to ribotoxin-induced alterations in rRNA structure by dimerizing, autoactivating and, ultimately, evoking RSR.
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Affiliation(s)
- Hui-Ren Zhou
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824, USA.
| | - Kaiyu He
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA.
| | - Jeff Landgraf
- Research Technology Support Facility, Michigan State University, East Lansing, MI 48824, USA.
| | - Xiao Pan
- Center for Integrative Toxicology, Michigan State University, East Lansing, MI 48824, USA.
| | - James J Pestka
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824, USA.
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Launer-Felty K, Cole JL. Domain interactions in adenovirus VAI RNA mediate high-affinity PKR binding. J Mol Biol 2014; 426:1285-95. [PMID: 24394721 DOI: 10.1016/j.jmb.2013.12.019] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Revised: 12/16/2013] [Accepted: 12/17/2013] [Indexed: 10/25/2022]
Abstract
Protein kinase R (PKR) is a component of the innate immunity antiviral pathway. PKR is activated upon binding to double-stranded RNA (dsRNA) to undergo dimerization and autophosphorylation. Adenovirus-associated RNA I (VAI) is a short, non-coding transcript whose major function is to inhibit the activity of PKR. VAI contains three domains: an apical stem-loop, a highly structured central domain, and a terminal stem. Previous studies have localized PKR binding to the apical stem and to the central domain. However, the molecular mechanism for inhibition of PKR is not known. We have characterized the stoichiometry and affinity of PKR binding to VAI and several domain constructs using analytical ultracentrifugation and correlated VAI binding and PKR inhibition. Although PKR binding to simple dsRNAs is not regulated by divalent ion, analysis of the interaction of the isolated dsRNA binding domain with VAI reveals that the binding affinity is enhanced by divalent ion. Dissection of VAI into its constituent domains indicates that none of the isolated domains retains the PKR binding affinity or inhibitory potency of the full-length RNA. PKR is capable of binding the isolated terminal stem, but deletion of this domain from VAI does not affect PKR binding or inhibition. These results indicate that both the apical stem and the central domain are required to form a high-affinity PKR binding site. Our data support a model whereby VAI functions as a PKR inhibitor because it binds a monomer tightly but does not facilitate dimerization.
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Affiliation(s)
- Katherine Launer-Felty
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA
| | - James L Cole
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA; Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA.
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39
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Angart P, Vocelle D, Chan C, Walton SP. Design of siRNA Therapeutics from the Molecular Scale. Pharmaceuticals (Basel) 2013; 6:440-68. [PMID: 23976875 PMCID: PMC3749788 DOI: 10.3390/ph6040440] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
While protein-based therapeutics is well-established in the market, development of nucleic acid therapeutics has lagged. Short interfering RNAs (siRNAs) represent an exciting new direction for the pharmaceutical industry. These small, chemically synthesized RNAs can knock down the expression of target genes through the use of a native eukaryotic pathway called RNA interference (RNAi). Though siRNAs are routinely used in research studies of eukaryotic biological processes, transitioning the technology to the clinic has proven challenging. Early efforts to design an siRNA therapeutic have demonstrated the difficulties in generating a highly-active siRNA with good specificity and a delivery vehicle that can protect the siRNA as it is transported to a specific tissue. In this review article, we discuss design considerations for siRNA therapeutics, identifying criteria for choosing therapeutic targets, producing highly-active siRNA sequences, and designing an optimized delivery vehicle. Taken together, these design considerations provide logical guidelines for generating novel siRNA therapeutics.
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Affiliation(s)
- Phillip Angart
- Department of Chemical Engineering and Materials Science, Michigan State University, 428 S. Shaw Lane, Room 2527, East Lansing, MI 48824, USA; (P.A.); (D.V.); (C.C.)
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40
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Elbarbary RA, Li W, Tian B, Maquat LE. STAU1 binding 3' UTR IRAlus complements nuclear retention to protect cells from PKR-mediated translational shutdown. Genes Dev 2013; 27:1495-510. [PMID: 23824540 PMCID: PMC3713430 DOI: 10.1101/gad.220962.113] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2013] [Accepted: 05/29/2013] [Indexed: 11/24/2022]
Abstract
For a number of human genes that encode transcripts containing inverted repeat Alu elements (IRAlus) within their 3' untranslated region (UTR), product mRNA is efficiently exported to the cytoplasm when the IRAlus, which mediate nuclear retention, are removed by alternative polyadenylation. Here we report a new mechanism that promotes gene expression by targeting mRNAs that maintain their 3' UTR IRAlus: Binding of the dsRNA-binding protein Staufen1 (STAU1) to 3' UTR IRAlus inhibits nuclear retention so as to augment the nuclear export of 3' UTR IRAlus-containing mRNAs (IRAlus mRNAs). Moreover, we found that 3' UTR IRAlus-bound STAU1 enhances 3' UTR IRAlus mRNA translation by precluding protein kinase R (PKR) binding, which obviates PKR activation, eukaryotic translation initiation factor 2α (eIF2α) phosphorylation, and repression of global cell translation. Thus, STAU1 binding to 3' UTR IRAlus functions along with 3' UTR IRAlus-mediated nuclear retention to suppress the shutdown of cellular translation triggered by PKR binding to endogenous cytoplasmic dsRNAs. We also show that a changing STAU1/PKR ratio contributes to myogenesis via effects on the 3' UTR IRAlus of mRNA encoding the microRNA-binding protein LIN28.
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Affiliation(s)
- Reyad A. Elbarbary
- Department of Biochemistry and Biophysics, School of Medicine and Dentistry
- Center for RNA Biology, University of Rochester, Rochester, New York 14642, USA
| | - Wencheng Li
- Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey–New Jersey Medical School, Newark, New Jersey 07101, USA
| | - Bin Tian
- Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey–New Jersey Medical School, Newark, New Jersey 07101, USA
| | - Lynne E. Maquat
- Department of Biochemistry and Biophysics, School of Medicine and Dentistry
- Center for RNA Biology, University of Rochester, Rochester, New York 14642, USA
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Bierle CJ, Semmens KM, Geballe AP. Double-stranded RNA binding by the human cytomegalovirus PKR antagonist TRS1. Virology 2013; 442:28-37. [PMID: 23601785 DOI: 10.1016/j.virol.2013.03.024] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Revised: 02/15/2013] [Accepted: 03/25/2013] [Indexed: 02/02/2023]
Abstract
Protein Kinase R (PKR) inhibits translation initiation following double-stranded RNA (dsRNA) binding and thereby represses viral replication. Human cytomegalovirus (HCMV) encodes two noncanonical dsRNA binding proteins, IRS1 and TRS1, and the expression of at least one of these PKR antagonists is essential for HCMV replication. In this study, we investigated the role of dsRNA binding by TRS1 in PKR inhibition. We found that purified TRS1 binds specifically to dsRNA with an affinity lower than that of PKR. Point mutants in the TRS1 dsRNA binding domain that were deficient in rescuing the replication of vaccinia virus lacking its PKR antagonist E3L were unable to bind to dsRNA but retained the ability bind to PKR. Thus TRS1 binding to dsRNA and to PKR are separable. Overall, our results are most consistent with a model in which TRS1 binds simultaneously to both dsRNA and PKR to inhibit PKR activation.
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Affiliation(s)
- Craig J Bierle
- Program in Molecular and Cellular Biology, University of Washington, Seattle, WA 98115, United States.
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Nallagatla SR, Jones CN, Ghosh SKB, Sharma SD, Cameron CE, Spremulli LL, Bevilacqua PC. Native tertiary structure and nucleoside modifications suppress tRNA's intrinsic ability to activate the innate immune sensor PKR. PLoS One 2013; 8:e57905. [PMID: 23483938 PMCID: PMC3587421 DOI: 10.1371/journal.pone.0057905] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 01/28/2013] [Indexed: 11/17/2022] Open
Abstract
Interferon inducible protein kinase PKR is an essential component of innate immunity. It is activated by long stretches of dsRNA and provides the first line of host defense against pathogens by inhibiting translation initiation in the infected cell. Many cellular and viral transcripts contain nucleoside modifications and/or tertiary structure that could affect PKR activation. We have previously demonstrated that a 5'-end triphosphate-a signature of certain viral and bacterial transcripts-confers the ability of relatively unstructured model RNA transcripts to activate PKR to inhibit translation, and that this activation is abrogated by certain modifications present in cellular RNAs. In order to understand the biological implications of native RNA tertiary structure and nucleoside modifications on PKR activation, we study here the heavily modified cellular tRNAs and the unmodified or the lightly modified mitochondrial tRNAs (mt-tRNA). We find that both a T7 transcript of yeast tRNA(Phe) and natively extracted total bovine liver mt-tRNA activate PKR in vitro, whereas native E. coli, bovine liver, yeast, and wheat tRNA(Phe) do not, nor do a variety of base- or sugar-modified T7 transcripts. These results are further supported by activation of PKR by a natively folded T7 transcript of tRNA(Phe)in vivo supporting the importance of tRNA modification in suppressing PKR activation in cells. We also examine PKR activation by a T7 transcript of the A14G pathogenic mutant of mt-tRNA(Leu), which is known to dimerize, and find that the misfolded dimeric form activates PKR in vitro while the monomeric form does not. Overall, the in vitro and in vivo findings herein indicate that tRNAs have an intrinsic ability to activate PKR and that nucleoside modifications and native RNA tertiary folding may function, at least in part, to suppress such activation, thus serving to distinguish self and non-self tRNA in innate immunity.
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Affiliation(s)
- Subba Rao Nallagatla
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, PA, USA
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43
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Abstract
The ability to regulate gene activity in a spatiotemporally controllable manner is vital for biological discovery that will impact disease diagnosis and treatment. While conditional gene silencing is possible in other genetic model organisms, this technology is largely unavailable in zebrafish, an important vertebrate model organism for functional gene discovery. Here, using short hairpin RNAs (shRNAs) designed in the microRNA-30 backbone, which have been shown to mimic natural microRNA primary transcripts and be more effective than simple shRNAs, we report stable RNA interference-mediated gene silencing in zebrafish employing the yeast Gal4-UAS system. Using this approach, we reveal at single-cell resolution the role of atypical protein kinase Cλ (aPKCλ) in regulating neural progenitor/stem cell division. We also show effective silencing of the one-eyed-pinhead and no-tail/brachyury genes. Furthermore, we demonstrate stable integration and germ-line transmission of the UAS-miR-shRNAs for aPKCλ, the expressivity of which is controllable by the strength and expression of Gal4. This technology shall significantly advance the utility of zebrafish for understanding fundamental vertebrate biology and for the identification and evaluation of important therapeutic targets.
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Abstract
The proteins harboring double-stranded RNA binding domains (dsRBDs) play diverse functional roles such as RNA localization, splicing, editing, export, and translation, yet mechanistic basis and functional significance of dsRBDs remain unclear. To unravel this enigma, we investigated transactivation response RNA binding protein (TRBP) consisting of three dsRBDs, which functions in HIV replication, protein kinase R(PKR)-mediated immune response, and RNA silencing. Here we report an ATP-independent diffusion activity of TRBP exclusively on dsRNA in a length-dependent manner. The first two dsRBDs of TRBP are essential for diffusion, whereas the third dsRBD is dispensable. Two homologs of TRBP, PKR activator and R3D1-L, displayed the same diffusion, implying a universality of the diffusion activity among this protein family. Furthermore, a Dicer-TRBP complex on dsRNA exhibited dynamic diffusion, which was correlated with Dicer's catalytic activity. These results implicate the dsRNA-specific diffusion activity of TRBP that contributes to enhancing siRNA and miRNA processing by Dicer.
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Patel S, Blose JM, Sokoloski JE, Pollack L, Bevilacqua PC. Specificity of the double-stranded RNA-binding domain from the RNA-activated protein kinase PKR for double-stranded RNA: insights from thermodynamics and small-angle X-ray scattering. Biochemistry 2012; 51:9312-22. [PMID: 23140277 DOI: 10.1021/bi300935p] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The interferon-inducible, double-stranded (ds) RNA-activated protein kinase (PKR) contains a dsRNA-binding domain (dsRBD) and plays key roles in viral pathogenesis and innate immunity. Activation of PKR is typically mediated by long dsRNA, and regulation of PKR is disfavored by most RNA imperfections, including bulges and internal loops. Herein, we combine isothermal titration calorimetry (ITC), electrophoretic mobility shift assays, and small-angle X-ray scattering (SAXS) to dissect the thermodynamic basis for the specificity of the dsRBD termed "p20" for various RNAs and to detect any RNA conformational changes induced upon protein binding. We monitor binding of p20 to chimeric duplexes containing terminal RNA-DNA hybrid segments and a central dsRNA segment, which was either unbulged ("perfect") or bulged. The ITC data reveal strong binding of p20 to the perfect duplex (K(d) ~ 30 nM) and weaker binding to the bulged duplex (K(d) ~ 2-5 μM). SAXS reconstructions and p(r) distance distribution functions further uncover that p20 induces no significant conformational change in perfect dsRNA but largely straightens bulged dsRNA. Together, these observations support the dsRBD's ability to tightly bind to only A-form RNA and suggest that in a noninfected cell, PKR may be buffered via weak interactions with various bulged and looped RNAs, which it may straighten. This work suggests that PKR-regulating RNAs with complex secondary and tertiary structures likely mimic dsRNA and/or engage portions of PKR outside of the dsRBD.
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Affiliation(s)
- Sunita Patel
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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46
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Kinetic mechanism for viral dsRNA length discrimination by MDA5 filaments. Proc Natl Acad Sci U S A 2012; 109:E3340-9. [PMID: 23129641 DOI: 10.1073/pnas.1208618109] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The viral sensor MDA5 distinguishes between cellular and viral dsRNAs by length-dependent recognition in the range of ~0.5-7 kb. The ability to discriminate dsRNA length at this scale sets MDA5 apart from other dsRNA receptors of the immune system. We have shown previously that MDA5 forms filaments along dsRNA that disassemble upon ATP hydrolysis. Here, we demonstrate that filament formation alone is insufficient to explain its length specificity, because the intrinsic affinity of MDA5 for dsRNA depends only moderately on dsRNA length. Instead, MDA5 uses a combination of end disassembly and slow nucleation kinetics to "discard" short dsRNA rapidly and to suppress rebinding. In contrast, filaments on long dsRNA cycle between partial end disassembly and elongation, bypassing nucleation steps. MDA5 further uses this repetitive cycle of assembly and disassembly processes to repair filament discontinuities, which often are present because of multiple, internal nucleation events, and to generate longer, continuous filaments that more accurately reflect the length of the underlying dsRNA scaffold. Because the length of the continuous filament determines the stability of the MDA5-dsRNA interaction, the mechanism proposed here provides an explanation for how MDA5 uses filament assembly and disassembly dynamics to discriminate between self vs. nonself dsRNA.
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47
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Abstract
The double-stranded RNA-dependent protein kinase PKR plays multiple roles in cells, in response to different stress situations. As a member of the interferon (IFN)‑Stimulated Genes, PKR was initially recognized as an actor in the antiviral action of IFN, due to its ability to control translation, through phosphorylation, of the alpha subunit of eukaryotic initiation factor 2 (eIF2α). As such, PKR participates in the generation of stress granules, or autophagy and a number of viruses have designed strategies to inhibit its action. However, PKR deficient mice resist most viral infections, indicating that PKR may play other roles in the cell other than just acting as an antiviral agent. Indeed, PKR regulates several signaling pathways, either as an adapter protein and/or using its kinase activity. Here we review the role of PKR as an eIF2α kinase, its participation in the regulation of the NF-κB, p38MAPK and insulin pathways, and we focus on its role during infection with the hepatitis C virus (HCV). PKR binds the HCV IRES RNA, cooperates with some functions of the HCV core protein and may represent a target for NS5A or E2. Novel data points out for a role of PKR as a pro-HCV agent, both as an adapter protein and as an eIF2α-kinase, and in cooperation with the di-ubiquitin-like protein ISG15. Developing pharmaceutical inhibitors of PKR may help in resolving some viral infections as well as stress-related damages.
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Affiliation(s)
- Stéphanie Dabo
- Unit Hepacivirus and Innate Immunity, Department Virology, Institut Pasteur, 28 rue du Dr Roux, 75724 Paris Cedex 15, France.
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Husain B, Mukerji I, Cole JL. Analysis of high-affinity binding of protein kinase R to double-stranded RNA. Biochemistry 2012; 51:8764-70. [PMID: 23062027 DOI: 10.1021/bi301226h] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Protein kinase R (PKR) is an interferon-induced kinase that plays a pivotal role in the innate immunity response to viral infection. PKR is activated upon binding to double-stranded RNA (dsRNA). Our previous analysis of binding of PKR to dsRNAs ranging from 20 to 40 bp supports a dimerization model for activation in which 30 bp represents the minimal length required to bind two PKR monomers and activate PKR via autophosphorylation. These studies were complicated by the formation of protein-RNA aggregates, particularly at low salt concentrations using longer dsRNAs. Here, we have taken advantage of the enhanced sensitivity afforded using fluorescence-detected analytical ultracentrifugation to reduce the RNA concentrations from micromolar to nanomolar. Under these conditions, we are able to characterize high-affinity binding of PKR to longer dsRNAs in 75 mM NaCl. The PKR binding stoichiometries are increased at lower salt concentrations but remain lower than those previously obtained for the dsRNA binding domain. The dependence of the limiting PKR binding stoichiometries on dsRNA length does not conform to standard models for nonspecific binding and suggests that binding to longer sequences occurs via a different binding mode with a larger site size. Although dimerization plays a key role in the PKR activation mechanism, the ability of shorter dsRNAs to bind two PKR monomers is not sufficient to induce autophosphorylation. We propose that activation of PKR by longer RNAs is correlated with an alternative binding mode in which both of the dsRNA binding motifs contact the RNA, inducing PKR to dimerize via a direct interaction of the kinase domains.
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Affiliation(s)
- Bushra Husain
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, United States
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McAllister CS, Taghavi N, Samuel CE. Protein kinase PKR amplification of interferon β induction occurs through initiation factor eIF-2α-mediated translational control. J Biol Chem 2012; 287:36384-92. [PMID: 22948139 PMCID: PMC3476304 DOI: 10.1074/jbc.m112.390039] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Revised: 08/31/2012] [Indexed: 12/24/2022] Open
Abstract
The protein kinase PKR is activated by RNA with double-stranded (ds) structure and subsequently impairs translation through phosphorylation of protein synthesis initiation factor eIF-2α. PKR also mediates activation of signal transduction pathways leading to interferon beta (IFN-β) gene induction following virus-infection or RNA transfection. We previously demonstrated in measles virus-infected cells that PKR is required for the maximal induction of IFN-β gene expression by the interferon promoter stimulator gene 1 (IPS-1) adaptor-dependent cytosolic RNA sensor pathway. While both IPS-1 and PKR are important mediators of IFN-β induction, with PKR contributing to an enhanced NF-κB activation, the mechanism by which PKR enhances NF-κB activity and amplifies IFN-β induction is unresolved. Herein we tested the possibility that PKR could activate signal transduction pathways indirectly through translational control responses. Following transfection with synthetic or natural dsRNAs or infection with measles virus, we observed increased mRNA but decreased protein levels for the inhibitor of NF-κB signaling, IκB-α, that correlated with PKR activation and eIF-2α phosphorylation. Importantly, knockdown of PKR increased IκB-α protein levels and impaired IFN-β induction. Additionally, inhibition of translation by cycloheximide treatment rescued IFN-β induction following PKR knockdown but not IPS-1 knockdown. Mutation of eIF-2α to prevent phosphorylation also impaired IFN-β induction in PKR-sufficient virus-infected cells. These results suggest that an eIF-2α-dependent translation inhibition mechanism is sufficient to explain the PKR-mediated amplification of IPS-1-dependent IFN-β induction by foreign RNA.
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Affiliation(s)
- Christopher S. McAllister
- From the Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, California 93106
| | - Nora Taghavi
- From the Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, California 93106
| | - Charles E. Samuel
- From the Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, California 93106
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50
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Multi-level regulation of cellular recognition of viral dsRNA. Cell Mol Life Sci 2012; 70:1949-63. [PMID: 22960755 PMCID: PMC7079809 DOI: 10.1007/s00018-012-1149-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Revised: 08/20/2012] [Accepted: 08/23/2012] [Indexed: 12/13/2022]
Abstract
Effective antiviral immunity depends on accurate recognition of viral RNAs by the innate immune system. Double-stranded RNA (dsRNA) often accumulates in virally infected cells and was initially considered a unique viral signature that was sufficient to initiate antiviral response through dsRNA receptors and dsRNA-dependent effectors such as Toll-like receptor 3, retinoic acid inducible gene-1, protein kinase RNA-activated and oligoadenylate synthetase. However, dsRNA is also present in many cellular RNAs, raising a question of how these receptors and effectors discriminate between viral and cellular dsRNAs. Accumulating evidence suggests that innate immune sensors detect not only dsRNA structure but also other and often multiple features of RNA such as length, sequence, cellular location, post-transcriptional processing and modification, which are divergent between viral and cellular RNAs. This review summarizes recent findings on the substrate specificities of a few selected dsRNA-dependent effectors and receptors, which have revealed more complex mechanisms involved in cellular discrimination between self and non-self RNA.
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