ADAR1
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ADAR1 edits adenosines to inosines in cellular double-stranded (ds)RNA, thereby preventing aberrant activation of antiviral dsRNA sensors, as well as interferon (IFN) induction in Aicardi-Goutières syndrome (AGS) encephalopathy. Recently, Nakahama et al., Tang et al., Maurano et al., and de Reuver et al. demonstrated that Adar1 Zα domain-mutant mice show aberrant MDA5 and PKR activation, developing encephalopathies; short Z-RNA patches within cellular dsRNA are unexpectedly crucial in causing aberrant antiviral responses.
- MeSH
- adenosindeaminasa * genetika metabolismus MeSH
- antivirové látky MeSH
- autoimunitní nemoci nervového systému * genetika MeSH
- dvouvláknová RNA MeSH
- editace RNA MeSH
- lidé MeSH
- myši MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
In recent years, numerous evidence has been accumulated about the extent of A-to-I editing in human RNAs and the key role ADAR1 plays in the cellular editing machinery. It has been shown that A-to-I editing occurrence and frequency are tissue-specific and essential for some tissue development, such as the liver. To study the effect of ADAR1 function in hepatocytes, we have created Huh7.5 ADAR1 KO cell lines. Upon IFN treatment, the Huh7.5 ADAR1 KO cells show rapid arrest of growth and translation, from which they do not recover. We analyzed translatome changes by using a method based on sequencing of separate polysome profile RNA fractions. We found significant changes in the transcriptome and translatome of the Huh7.5 ADAR1 KO cells. The most prominent changes include negatively affected transcription by RNA polymerase III and the deregulation of snoRNA and Y RNA levels. Furthermore, we observed that ADAR1 KO polysomes are enriched in mRNAs coding for proteins pivotal in a wide range of biological processes such as RNA localization and RNA processing, whereas the unbound fraction is enriched mainly in mRNAs coding for ribosomal proteins and translational factors. This indicates that ADAR1 plays a more relevant role in small RNA metabolism and ribosome biogenesis.
- MeSH
- adenosindeaminasa * genetika metabolismus MeSH
- buněčné linie MeSH
- editace RNA * MeSH
- genový knockout MeSH
- hepatocyty * metabolismus MeSH
- lidé MeSH
- messenger RNA genetika metabolismus MeSH
- polyribozomy metabolismus genetika MeSH
- proteiny vázající RNA * genetika metabolismus MeSH
- proteosyntéza MeSH
- transkriptom MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
Adar null mutant mouse embryos die with aberrant double-stranded RNA (dsRNA)-driven interferon induction, and Adar Mavs double mutants, in which interferon induction is prevented, die soon after birth. Protein kinase R (Pkr) is aberrantly activated in Adar Mavs mouse pup intestines before death, intestinal crypt cells die, and intestinal villi are lost. Adar Mavs Eifak2 (Pkr) triple mutant mice rescue all defects and have long-term survival. Adenosine deaminase acting on RNA 1 (ADAR1) and PKR co-immunoprecipitate from cells, suggesting PKR inhibition by direct interaction. AlphaFold studies on an inhibitory PKR dsRNA binding domain (dsRBD)-kinase domain interaction before dsRNA binding and on an inhibitory ADAR1 dsRBD3-PKR kinase domain interaction on dsRNA provide a testable model of the inhibition. Wild-type or editing-inactive human ADAR1 expressed in A549 cells inhibits activation of endogenous PKR. ADAR1 dsRNA binding is required for, but is not sufficient for, PKR inhibition. Mutating the ADAR1 dsRBD3-PKR contact prevents co-immunoprecipitation, ADAR1 inhibition of PKR activity, and co-localization of ADAR1 and PKR in cells.
- MeSH
- adenosindeaminasa * metabolismus genetika MeSH
- aktivace enzymů MeSH
- buňky A549 MeSH
- dvouvláknová RNA * metabolismus MeSH
- kinasa eIF-2 * metabolismus MeSH
- lidé MeSH
- myši MeSH
- proteinové domény MeSH
- proteiny vázající RNA * metabolismus genetika MeSH
- vazba proteinů MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
The RNA editing enzyme adenosine deaminase acting on RNA 1 (ADAR1) is essential for correct functioning of innate immune responses. The ADAR1p110 isoform is mainly nuclear and ADAR1p150, which is interferon (IFN) inducible, is predominately cytoplasmic. Using three different methods - co-immunoprecipitation (co-IP) of endogenous ADAR1, Strep-tag co-IP and BioID with individual ADAR1 isoforms - a comprehensive interactome was generated during both homeostasis and the IFN response. Both known and novel interactors as well as editing regulators were identified. Nuclear proteins were detected as stable interactors with both ADAR1 isoforms. In contrast, BioID identified distinct protein networks for each ADAR1 isoform, with nuclear components observed with ADAR1p110 and components of cytoplasmic cellular condensates with ADAR1p150. RNase A digestion distinguished between distal and proximal interactors, as did a double-stranded RNA (dsRNA)-binding mutant of ADAR1 which demonstrated the importance of dsRNA binding for ADAR1 interactions. IFN treatment did not affect the core ADAR1 interactomes but resulted in novel interactions, the majority of which are proximal interactions retained after RNase A treatment. Short treatment with high molecular weight poly(I:C) during the IFN response resulted in dsRNA-binding-dependent changes in the proximal protein network of ADAR1p110 and association of the ADAR1p150 proximal protein network with some components of antiviral stress granules.
- MeSH
- adenosindeaminasa * metabolismus genetika MeSH
- buněčné jádro * metabolismus MeSH
- cytoplazma * metabolismus MeSH
- dvouvláknová RNA metabolismus genetika MeSH
- editace RNA MeSH
- HEK293 buňky MeSH
- HeLa buňky MeSH
- interferony metabolismus genetika MeSH
- lidé MeSH
- mapy interakcí proteinů MeSH
- poly I-C farmakologie MeSH
- protein - isoformy * metabolismus genetika MeSH
- proteiny vázající RNA * metabolismus genetika MeSH
- vazba proteinů MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
Adenosine deaminase acting on RNA 1 (ADAR1) is the principal enzyme for the adenosine-to-inosine RNA editing that prevents the aberrant activation of cytosolic nucleic acid sensors by endogenous double stranded RNAs and the activation of interferon-stimulated genes. In mice, the conditional neural crest deletion of Adar1 reduces the survival of melanocytes and alters the differentiation of Schwann cells that fail to myelinate nerve fibers in the peripheral nervous system. These myelination defects are partially rescued upon the concomitant removal of the Mda5 antiviral dsRNA sensor in vitro, suggesting implication of the Mda5/Mavs pathway and downstream effectors in the genesis of Adar1 mutant phenotypes. By analyzing RNA-Seq data from the sciatic nerves of mouse pups after conditional neural crest deletion of Adar1 (Adar1cKO), we here identified the transcription factors deregulated in Adar1cKO mutants compared to the controls. Through Adar1;Mavs and Adar1cKO;Egr1 double-mutant mouse rescue analyses, we then highlighted that the aberrant activation of the Mavs adapter protein and overexpression of the early growth response 1 (EGR1) transcription factor contribute to the Adar1 deletion associated defects in Schwann cell development in vivo. In silico and in vitro gene regulation studies additionally suggested that EGR1 might mediate this inhibitory effect through the aberrant regulation of EGR2-regulated myelin genes. We thus demonstrate the role of the Mda5/Mavs pathway, but also that of the Schwann cell transcription factors in Adar1-associated peripheral myelination defects.
- MeSH
- adenosindeaminasa * genetika metabolismus MeSH
- buněčná diferenciace * genetika MeSH
- crista neuralis * metabolismus MeSH
- IFIH1 genetika metabolismus MeSH
- myelinová pochva metabolismus MeSH
- myši knockoutované * MeSH
- myši MeSH
- Schwannovy buňky * metabolismus patologie MeSH
- zvířata MeSH
- Check Tag
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
Adenosine deaminases acting on RNA (ADARs) convert adenosine to inosine in dsRNA. ADAR editing in pre-mRNAs recodes open reading frames and alters splicing, mRNA structure and interactions with miRNAs. Here, we review ADAR gene expression, splice forms, posttranslational modifications, subcellular localizations and functions of ADAR protein isoforms. ADAR1 edits cellular dsRNA to prevent aberrant activation of cytoplasmic antiviral dsRNA sensors; ADAR1 mutations lead to aberrant expression of interferon in Aicardi Goutières syndrome (AGS), a human congenital encephalopathy. We review related studies on mouse Adar1 mutant phenotypes, their rescues by preventing signaling from the antiviral RIG-I-like Sensors (RLRs), as well as Adar1 mechanisms in innate immune suppression and other roles of Adar1, including editing-independent effects. ADAR2, expressed primarily in CNS, edits glutamate receptor transcripts; regulation of ADAR2 activity in response to neuronal activity mediates homeostatic synaptic plasticity of vertebrate AMPA and kainite receptors. In Drosophila, synapses and synaptic proteins show dramatic decreases at night during sleep; Drosophila Adar, an orthologue of ADAR2, edits hundreds of mRNAs; the most conserved editing events occur in transcripts encoding synapse-associated proteins. Adar mutant flies exhibit locomotion defects associated with very increased sleep pressure resulting from a failure of homeostatic synaptic processes. A study on Adar2 mutant mice identifies a new role in circadian rhythms, acting indirectly through miRNAs such as let-7 to modulate levels of let-7 target mRNAs; ADAR1 also regulates let-7 miRNA processing. Drosophila ADAR, an orthologue of vertebrate ADAR2, also regulates let-7 miRNA levels and Adar mutant flies have a circadian mutant phenotype.
- MeSH
- adenosindeaminasa genetika metabolismus MeSH
- cirkadiánní hodiny * MeSH
- editace RNA * MeSH
- lidé MeSH
- přirozená imunita * MeSH
- spánek * MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
We review the structures and functions of ADARs and their involvements in human diseases. ADAR1 is widely expressed, particularly in the myeloid component of the blood system, and plays a prominent role in promiscuous editing of long dsRNA. Missense mutations that change ADAR1 residues and reduce RNA editing activity cause Aicardi-Goutières Syndrome, a childhood encephalitis and interferonopathy that mimics viral infection and resembles an extreme form of Systemic Lupus Erythmatosus (SLE). In Adar1 mouse mutant models aberrant interferon expression is prevented by eliminating interferon activation signaling from cytoplasmic dsRNA sensors, indicating that unedited cytoplasmic dsRNA drives the immune induction. On the other hand, upregulation of ADAR1 with widespread promiscuous RNA editing is a prominent feature of many cancers and particular site-specific RNA editing events are also affected. ADAR2 is most highly expressed in brain and is primarily required for site-specific editing of CNS transcripts; recent findings indicate that ADAR2 editing is regulated by neuronal excitation for synaptic scaling of glutamate receptors. ADAR2 is also linked to the circadian clock and to sleep. Mutations in ADAR2 could contribute to excitability syndromes such as epilepsy, to seizures, to diseases involving neuronal plasticity defects, such as autism and Fragile-X Syndrome, to neurodegenerations such as ALS, or to astrocytomas or glioblastomas in which reduced ADAR2 activity is required for oncogenic cell behavior. The range of human disease associated with ADAR1 mutations may extend further to include other inflammatory conditions while ADAR2 mutations may affect psychiatric conditions.
- MeSH
- adenosindeaminasa * genetika metabolismus MeSH
- duševní poruchy * genetika metabolismus MeSH
- dvouvláknová RNA * genetika metabolismus MeSH
- editace RNA genetika MeSH
- lidé MeSH
- mutace * MeSH
- mutantní kmeny myší MeSH
- myši MeSH
- nemoci nervového systému * genetika metabolismus MeSH
- proteiny vázající RNA * genetika metabolismus MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
The human cytomegalovirus (HCMV) is extremely prevalent in the human population. Infection by HCMV is life threatening in immune compromised individuals and in immune competent individuals it can cause severe birth defects, developmental retardation and is even associated with tumor development. While numerous mechanisms were developed by HCMV to interfere with immune cell activity, much less is known about cellular mechanisms that operate in response to HCMV infection. Here we demonstrate that in response to HCMV infection, the expression of the short form of the RNA editing enzyme ADAR1 (ADAR1-p110) is induced. We identified the specific promoter region responsible for this induction and we show that ADAR1-p110 can edit miR-376a. Accordingly, we demonstrate that the levels of the edited-miR-376a (miR-376a(e)) increase during HCMV infection. Importantly, we show that miR-376a(e) downregulates the immune modulating molecule HLA-E and that this consequently renders HCMV infected cells susceptible to elimination by NK cells.
- MeSH
- adenosindeaminasa genetika MeSH
- buňky NK imunologie MeSH
- cytomegalovirové infekce genetika imunologie MeSH
- Cytomegalovirus MeSH
- editace RNA genetika MeSH
- lidé MeSH
- mikro RNA genetika MeSH
- proteiny vázající RNA MeSH
- western blotting MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
ADAR RNA editing enzymes are high-affinity dsRNA-binding proteins that deaminate adenosines to inosines in pre-mRNA hairpins and also exert editing-independent effects. We generated a Drosophila AdarE374A mutant strain encoding a catalytically inactive Adar with CRISPR/Cas9. We demonstrate that Adar adenosine deamination activity is necessary for normal locomotion and prevents age-dependent neurodegeneration. The catalytically inactive protein, when expressed at a higher than physiological level, can rescue neurodegeneration in Adar mutants, suggesting also editing-independent effects. Furthermore, loss of Adar RNA editing activity leads to innate immune induction, indicating that Drosophila Adar, despite being the homolog of mammalian ADAR2, also has functions similar to mammalian ADAR1. The innate immune induction in fly Adar mutants is suppressed by silencing of Dicer-2, which has a RNA helicase domain similar to MDA5 that senses unedited dsRNAs in mammalian Adar1 mutants. Our work demonstrates that the single Adar enzyme in Drosophila unexpectedly has dual functions.
- MeSH
- adenosindeaminasa chemie genetika MeSH
- adenosinmonofosfát metabolismus MeSH
- bodová mutace genetika MeSH
- degenerace nervu patologie MeSH
- Drosophila melanogaster genetika imunologie MeSH
- editace RNA genetika MeSH
- katalýza MeSH
- lokomoce MeSH
- messenger RNA genetika metabolismus MeSH
- mozek metabolismus MeSH
- přirozená imunita genetika MeSH
- proteinové domény MeSH
- proteiny Drosophily chemie genetika metabolismus MeSH
- regulace genové exprese MeSH
- ribonukleasa III metabolismus MeSH
- RNA-helikasy metabolismus MeSH
- stárnutí patologie MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, N.I.H., Extramural MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
Modified bases act as marks on cellular RNAs so that they can be distinguished from foreign RNAs, reducing innate immune responses to endogenous RNA. In humans, mutations giving reduced levels of one base modification, adenosine-to-inosine deamination, cause a viral infection mimic syndrome, a congenital encephalitis with aberrant interferon induction. These Aicardi-Goutières syndrome 6 mutations affect adenosine deaminase acting on RNA 1 (ADAR1), which generates inosines in endogenous double-stranded (ds)RNA. The inosine base alters dsRNA structure to prevent aberrant activation of antiviral cytosolic helicase RIG-I-like receptors. We review how effects of inosines, ADARs, and other modified bases have been shown to be important in innate immunity and cancer.
