Leveraging genetics to understand ADAR1-mediated RNA editing in health and disease.

Endogenous, long double-stranded RNA (dsRNA) can resemble viral dsRNA and be recognized by cytosolic dsRNA sensors, triggering autoimmunity. Genetic studies of rare, inherited human diseases and experiments using mouse models have established the importance of adenosine-to-inosine RNA editing by the enzyme adenosine deaminase acting on RNA 1 (ADAR1) as a critical safeguard against autoinflammatory responses to cellular dsRNA. More recently, human genetic studies have revealed that dsRNA editing and sensing mechanisms are involved in common inflammatory diseases, emphasizing the broader role of dsRNA in modulating immune responses and disease pathogenesis.

GGNBP2 regulates MDA5 sensing triggered by self double-stranded RNA following loss of ADAR1 editing.

Adenosine-to-inosine (A-to-I) editing of double-stranded RNA (dsRNA) by ADAR1 is an essential modifier of the immunogenicity of cellular dsRNA. The role of MDA5 in sensing unedited cellular dsRNA and the downstream activation of type I interferon (IFN) signaling are well established. However, we have an incomplete understanding of pathways that modify the response to unedited dsRNA.

A highly conserved A-to-I RNA editing event within the glutamate-gated chloride channel GluClα is necessary for olfactory-based behaviors in .

A-to-I RNA editing is a cellular mechanism that generates transcriptomic and proteomic diversity, which is essential for neuronal and immune functions. It involves the conversion of specific adenosines in RNA molecules to inosines, which are recognized as guanosines by cellular machinery. Despite the vast number of editing sites observed across the animal kingdom, pinpointing critical sites and understanding their in vivo functions remains challenging.

An improved SNAP-ADAR tool enables efficient RNA base editing to interfere with post-translational protein modification.

RNA base editing relies on the introduction of adenosine-to-inosine changes into target RNAs in a highly programmable manner in order to repair disease-causing mutations. Here, we propose that RNA base editing could be broadly applied to perturb protein function by removal of regulatory phosphorylation and acetylation sites. We demonstrate the feasibility on more than 70 sites in various signaling proteins and identify key determinants for high editing efficiency and potent down-stream effects.

Smooth muscle expression of RNA editing enzyme controls activation of RNA sensor MDA5 in atherosclerosis.

Unlabelled: Mapping the genomic architecture of complex disease has been predicated on the understanding that genetic variants influence disease risk through modifying gene expression. However, recent discoveries have revealed that a significant burden of disease heritability in common autoinflammatory disorders and coronary artery disease (CAD) is mediated through genetic variation modifying post-transcriptional modification of RNA through adenosine-to-inosine (A-to-I) RNA editing. This common RNA modification is catalyzed by ADAR enzymes, where ADAR1 edits specific immunogenic double stranded RNA (dsRNA) to prevent activation of the double strand RNA (dsRNA) sensor MDA5 ( ) and stimulation of an interferon stimulated gene (ISG) response.

Multifaceted roles of RNA editing enzyme ADAR1 in innate immunity.

Innate immunity must be tightly regulated to enable sensitive pathogen detection while averting autoimmunity triggered by pathogen-like host molecules. A hallmark of viral infection, double-stranded RNAs (dsRNAs) are also abundantly encoded in mammalian genomes, necessitating surveillance mechanisms to distinguish "self" from "nonself." ADAR1, an RNA editing enzyme, has emerged as an essential safeguard against dsRNA-induced autoimmunity.

Voices: Challenges and opportunities in RNA biology.

In the first of many thematic issues marking the 30 anniversary of Cell Chemical Biology, we highlight the contribution of chemical biology to RNA biology in a special issue on RNA modulation. We asked several leaders in the field to share their opinions on the current challenges and opportunities in RNA biology.

ADAR1p150 prevents MDA5 and PKR activation via distinct mechanisms to avert fatal autoinflammation.

Effective immunity requires the innate immune system to distinguish foreign nucleic acids from cellular ones. Cellular double-stranded RNAs (dsRNAs) are edited by the RNA-editing enzyme ADAR1 to evade being recognized as viral dsRNA by cytoplasmic dsRNA sensors, including MDA5 and PKR. The loss of ADAR1-mediated RNA editing of cellular dsRNA activates MDA5.

A-to-I RNA editing by ADAR and its therapeutic applications: From viral infections to cancer immunotherapy.

ADAR deaminases catalyze adenosine-to-inosine (A-to-I) editing on double-stranded RNA (dsRNA) substrates that regulate an umbrella of biological processes. One of the two catalytically active ADAR enzymes, ADAR1, plays a major role in innate immune responses by suppression of RNA sensing pathways which are orchestrated through the ADAR1-dsRNA-MDA5 axis. Unedited immunogenic dsRNA substrates are potent ligands for the cellular sensor MDA5.

ADAR1p150 Prevents MDA5 and PKR Activation via Distinct Mechanisms to Avert Fatal Autoinflammation.

Effective immunity requires the innate immune system to distinguish foreign (non-self) nucleic acids from cellular (self) nucleic acids. Cellular double-stranded RNAs (dsRNAs) are edited by the RNA editing enzyme ADAR1 to prevent their dsRNA structure pattern being recognized as viral dsRNA by cytoplasmic dsRNA sensors including MDA5, PKR and ZBP1. A loss of ADAR1-mediated RNA editing of cellular dsRNA activates MDA5.

Ablation of Adar1 in myeloid cells imprints a global antiviral state in the lung and heightens early immunity against SARS-CoV-2.

Under normal homeostatic conditions, self-double-stranded RNA (self-dsRNA) is modified by adenosine deaminase acting on RNA 1 (ADAR1) to prevent the induction of a type I interferon-mediated inflammatory cascade. Antigen-presenting cells (APCs) sense pathogen-associated molecular patterns, such as dsRNA, to activate the immune response. The impact of ADAR1 on the function of APCs and the consequences to immunity are poorly understood.

CLUSTER guide RNAs enable precise and efficient RNA editing with endogenous ADAR enzymes in vivo.

RNA base editing represents a promising alternative to genome editing. Recent approaches harness the endogenous RNA-editing enzyme adenosine deaminase acting on RNA (ADAR) to circumvent problems caused by ectopic expression of engineered editing enzymes, but suffer from sequence restriction, lack of efficiency and bystander editing. Here we present in silico-optimized CLUSTER guide RNAs that bind their target messenger RNAs in a multivalent fashion, achieve editing with high precision and efficiency and enable targeting of sequences that were not accessible using previous gRNA designs.

RNA editing restricts hyperactive ciliary kinases.

Protein kinase activity must be precisely regulated, but how a cell governs hyperactive kinases remains unclear. In this study, we generated a constitutively active mitogen-activated protein kinase DYF-5 (DYF-5CA) in that disrupted sensory cilia. Genetic suppressor screens identified that mutations of ADR-2, an RNA adenosine deaminase, rescued ciliary phenotypes of We found that animals abnormally transcribed antisense RNAs that pair with messenger RNA (mRNA) to form double-stranded RNA, recruiting ADR-2 to edit the region ectopically.

Learning cis-regulatory principles of ADAR-based RNA editing from CRISPR-mediated mutagenesis.

Adenosine-to-inosine (A-to-I) RNA editing catalyzed by ADAR enzymes occurs in double-stranded RNAs. Despite a compelling need towards predictive understanding of natural and engineered editing events, how the RNA sequence and structure determine the editing efficiency and specificity (i.e.

Unbiased Identification of trans Regulators of ADAR and A-to-I RNA Editing.

Adenosine-to-inosine RNA editing is catalyzed by adenosine deaminase acting on RNA (ADAR) enzymes that deaminate adenosine to inosine. Although many RNA editing sites are known, few trans regulators have been identified. We perform BioID followed by mass spectrometry to identify trans regulators of ADAR1 and ADAR2 in HeLa and M17 neuroblastoma cells.

Zinc Finger RNA-Binding Protein Zn72D Regulates ADAR-Mediated RNA Editing in Neurons.

Adenosine-to-inosine RNA editing, catalyzed by adenosine deaminase acting on RNA (ADAR) enzymes, alters RNA sequences from those encoded by DNA. These editing events are dynamically regulated, but few trans regulators of ADARs are known in vivo. Here, we screen RNA-binding proteins for roles in editing regulation with knockdown experiments in the Drosophila brain.

Adar RNA editing-dependent and -independent effects are required for brain and innate immune functions in Drosophila.

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 Adar 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.

Global landscape and genetic regulation of RNA editing in cortical samples from individuals with schizophrenia.

RNA editing critically regulates neurodevelopment and normal neuronal function. The global landscape of RNA editing was surveyed across 364 schizophrenia cases and 383 control postmortem brain samples from the CommonMind Consortium, comprising two regions: dorsolateral prefrontal cortex and anterior cingulate cortex. In schizophrenia, RNA editing sites in genes encoding AMPA-type glutamate receptors and postsynaptic density proteins were less edited, whereas those encoding translation initiation machinery were edited more.

ADAR1: A New Target for Immuno-oncology Therapy.

Three recent studies by Ishizuka et al. (2019), Liu et al. (2019), and Gannon et al.

Precise RNA editing by recruiting endogenous ADARs with antisense oligonucleotides.

Site-directed RNA editing might provide a safer or more effective alternative to genome editing in certain clinical scenarios. Until now, RNA editing has relied on overexpression of exogenous RNA editing enzymes or of endogenous human ADAR (adenosine deaminase acting on RNA) enzymes. Here we describe the engineering of chemically optimized antisense oligonucleotides that recruit endogenous human ADARs to edit endogenous transcripts in a simple and programmable way, an approach we call RESTORE (recruiting endogenous ADAR to specific transcripts for oligonucleotide-mediated RNA editing).

Illuminating spatial A-to-I RNA editing signatures within the brain.

Adenosine-to-inosine (A-to-I) RNA editing, catalyzed by ADAR enzymes, is a ubiquitous mechanism that generates transcriptomic diversity. This process is particularly important for proper neuronal function; however, little is known about how RNA editing is dynamically regulated between the many functionally distinct neuronal populations of the brain. Here, we present a spatial RNA editing map in the brain and show that different neuronal populations possess distinct RNA editing signatures.