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Adenosine-to-inosine (A-to-I) RNA editing, catalyzed by ADAR enzymes, is a prevalent and conserved RNA modification. While A-to-I RNA editing is essential in mammals, in Caenorhabditis elegans, it is not, making them invaluable for RNA editing research. In C. elegans, ADR-2 is the sole catalytic A-to-I editing enzyme, and ADR-1 is an RNA editing regulator. ADAR localization is well-studied in humans but not well-established in C. elegans. In this study, we examine the cellular and tissue-specific localization of ADR-2. We show that while ADR-2 is present in most cells in the embryo, at later developmental stages, its expression is both tissue- and cell-type-specific. Additionally, both ADARs are mainly in the nucleus. ADR-2 is adjacent to the chromosomes during the cell cycle. We show that the nuclear localization of endogenous ADR-2 depends on ADBP-1, not ADR-1. In adbp-1 mutant worms, ADR-2 is mislocalized, while ADR-1 is not, leading to decreased editing levels and de-novo editing, mostly in exons, suggesting that ADR-2 is also functional in the cytoplasm. Besides, mutated ADBP-1 affects gene expression. Furthermore, we show that ADR-2 targets adenosines with different surrounding nucleotides in exons and introns. Our findings indicate that ADR-2 cellular localization is highly regulated and affects its function., (© The Author(s) 2024. Published by Oxford University Press on behalf of Nucleic Acids Research.)

A-to-I RNA editing, catalyzed by ADAR proteins, is widespread in eukaryotic transcriptomes. Studies showed that, in C. elegans, ADR-2 can actively deaminate dsRNA, whereas ADR-1 cannot. Therefore, we set out to study the effect of each of the ADAR genes on the RNA editing process. We performed comprehensive phenotypic, transcriptomics, proteomics, and RNA binding screens on worms mutated in a single ADAR gene. We found that ADR-1 mutants exhibit more-severe phenotypes than ADR-2, and some of them are a result of non-editing functions of ADR-1. We also show that ADR-1 significantly binds edited genes and regulates mRNA expression, whereas the effect on protein levels is minor. In addition, ADR-1 primarily promotes editing by ADR-2 at the L4 stage of development. Our results suggest that ADR-1 has a significant role in the RNA editing process and in altering editing levels that affect RNA expression; loss of ADR-1 results in severe phenotypes., (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)

In recent years, A-to-I RNA modifications performed by the Adenosine Deaminase Acting on RNA (ADAR) protein family were found to be expressed at altered levels in multiple human malignancies. A-to-I RNA editing changes adenosine to inosine on double stranded RNA, thereby changing transcript sequence and structure. Although A-to-I RNA editing have the potential to change essential mRNA transcripts, affecting their corresponding protein structures, most of the human editing sites identified to date reside in non-coding repetitive transcripts such as Alu elements. Therefore, the impact of the hypo- or hyper-editing found in specific cancers remains unknown. Moreover, it is yet unclear whether or not changes in RNA editing and ADAR expression levels facilitate or even drive cancer progression or are just a byproduct of other affected pathways. In both cases, however, the levels of RNA editing and ADAR enzymes can possibly be used as specific biomarkers, as their levels change differently in specific malignancies. More significantly, recent studies suggest that ADAR enzymes can be used to reverse the oncogenic process, suggesting a potential for gene therapies. This review focuses on new findings that suggest that RNA editing by ADARs can affect cancer progression and even formation. We also discuss new possibilities of using ADAR enzymes and RNA editing as cancer biomarkers, indicators of chemotherapeutic drug sensitivity, and even to be themselves potential therapeutic tools., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A-to-I RNA editing is a conserved widespread phenomenon in which adenosine (A) is converted to inosine (I) by adenosine deaminases (ADARs) in double-stranded RNA regions, mainly noncoding. Mutations in ADAR enzymes in Caenorhabditis elegans cause defects in normal development but are not lethal as in human and mouse. Previous studies in C. elegans indicated competition between RNA interference (RNAi) and RNA editing mechanisms, based on the observation that worms that lack both mechanisms do not exhibit defects, in contrast to the developmental defects observed when only RNA editing is absent. To study the effects of RNA editing on gene expression and function, we established a novel screen that enabled us to identify thousands of RNA editing sites in nonrepetitive regions in the genome. These include dozens of genes that are edited at their 3' UTR region. We found that these genes are mainly germline and neuronal genes, and that they are down-regulated in the absence of ADAR enzymes. Moreover, we discovered that almost half of these genes are edited in a developmental-specific manner, indicating that RNA editing is a highly regulated process. We found that many pseudogenes and other lncRNAs are also extensively down-regulated in the absence of ADARs in the embryo but not in the fourth larval (L4) stage. This down-regulation is not observed upon additional knockout of RNAi. Furthermore, levels of siRNAs aligned to pseudogenes in ADAR mutants are enhanced. Taken together, our results suggest a role for RNA editing in normal growth and development by regulating silencing via RNAi., (© 2017 Goldstein et al.; Published by Cold Spring Harbor Laboratory Press.)

Adenosine deaminases that act on RNAs (ADARs) interact with double-stranded RNAs, deaminating adenosines to inosines. Previous studies of Caenorhabditis elegans indicated an antagonistic interaction between ADAR and RNAi machineries, with ADAR defects suppressed upon additional knockout of RNAi. This suggests a pool of common RNA substrates capable of engaging both pathways. To define and characterize such substrates, we examined small RNA and mRNA populations of ADAR mutants and identified a distinct set of loci from which RNAi-dependent short RNAs are markedly upregulated. At these same loci, we observed populations of multiply edited transcripts, supporting a specific role for ADARs in preventing access to the RNAi pathway for an extensive population of dsRNAs. Characterization of these loci revealed a substantial overlap with noncoding and intergenic regions, suggesting that the landscape of ADAR targets may extend beyond previously annotated classes of transcripts.

Adenosine to inosine (A-to-I) RNA editing is a highly conserved regulatory process carried out by adenosine-deaminases (ADARs) on double-stranded RNA (dsRNAs). Although a considerable fraction of the transcriptome is edited, the function of most editing sites is unknown. Previous studies indicate changes in A-to-I RNA editing frequencies following exposure to several stress types. However, the overall effect of stress on the expression of ADAR targets is not fully understood. Here, we performed high-throughput RNA sequencing of wild-type and ADAR mutant Caenorhabditis elegans worms after heat-shock to analyze the effect of heat-shock stress on the expression pattern of genes. We found that ADAR regulation following heat-shock does not directly involve heat-shock related genes. Our analysis also revealed that long non-coding RNAs (lncRNAs) and pseudogenes, which have a tendency for secondary RNA structures, are enriched among upregulated genes following heat-shock in ADAR mutant worms. The same group of genes is downregulated in ADAR mutant worms under permissive conditions, which is likely, considering that A-to-I editing protects endogenous dsRNA from RNA-interference (RNAi). Therefore, temperature increases may destabilize dsRNA structures and protect them from RNAi degradation, despite the lack of ADAR function. These findings shed new light on the dynamics of gene expression under heat-shock in relation to ADAR function. [ABSTRACT FROM AUTHOR]