A computational screen for site selective A-to-I editing detects novel sites in neuron specific Hu proteins

Background  

Several bioinformatic approaches have previously been used to find novel sites of ADAR mediated A-to-I RNA editing in human. These studies have discovered thousands of genes that are hyper-edited in their non-coding intronic regions, especially in alu retrotransposable elements, but very few substrates that are site-selectively edited in coding regions. Known RNA edited substrates suggest, however, that site selective A-to-I editing is particularly important for normal brain development in mammals.     

Substrate-dependent contribution of double-stranded RNA-binding motifs to ADAR2 function

ADAR2 is a double-stranded RNA-specific adenosine deaminase involved in the editing of mammalian RNAs by the site-specific conversion of adenosine to inosine (A-to-I). ADAR2 contains two tandem double-stranded RNA-binding motifs (dsRBMs) that are not only important for efficient editing of RNA substrates but also necessary for localizing ADAR2 to nucleoli. The sequence and structural similarity of these motifs have raised questions regarding the role(s) that each dsRBM plays in ADAR2 function. Here, we demonstrate that the dsRBMs of ADAR2 differ in both their ability to modulate subnuclear localization as well as to promote site-selective A-to-I conversion. Surprisingly, dsRBM1 contributes to editing activity in a substrate-dependent manner, indicating that dsRBMs recognize distinct structural determinants in each RNA substrate. Although dsRBM2 is essential for the editing of all substrates examined, a point mutation in this motif affects editing for only a subset of RNAs, suggesting that dsRBM2 uses unique sets of amino acid(s) for functional interactions with different RNA targets. The dsRBMs of ADAR2 are interchangeable for subnuclear targeting, yet such motif alterations do not support site-selective editing, indicating that the unique binding preferences of each dsRBM differentially contribute to their pleiotropic function.     

ADAR1介导的RNA编辑在血液肿瘤中的调控作用

RNA编辑是发生于双链RNA（dsRNA）上的一类重要转录后反应,可通过碱基插入、缺失或替换的方式改变RNA的核苷酸序列从而丰富转录组和蛋白质组水平的多样性。哺乳动物中最常见的RNA编辑是ADAR家族介导的腺嘌呤-次黄嘌呤编辑（A-to-I）,其在碱基配对过程中被识别为鸟嘌呤。人类转录组中已报道了数百万个A-to-I编辑位点,而ADAR1是最主要的催化酶。在血液肿瘤中,ADAR1的失调将直接影响基因编码区、非编码区和miRNA前体的A-to-I编辑状态,从而导致一系列分子事件改变,如蛋白质编码序列改变、内含子滞留、选择性剪接和miRNA生物发生受抑制。近年来研究发现,异常的RNA编辑导致分子调控网络的紊乱,促进细胞增殖、凋亡受阻和细胞耐药,是白血病干细胞（LSCs）生成和干性维持的重要因素。目前,以RNA编辑为靶点的新药（如rebecsinib）已经在动物实验中取得良好疗效。有别于传统抗肿瘤药,表观遗传抗肿瘤药有望克服血液肿瘤的耐药、复发难题,为患者提供全新治疗选择。本综述总结了ADAR1介导的RNA编辑在血液肿瘤中的作用机制及其生物学功能研究的进展,并探讨了其在药物研发和临床应用中的价值。     

Reduced levels of protein recoding by A-to-I RNA editing in Alzheimer's disease

Adenosine to inosine (A-to-I) RNA editing, catalyzed by the ADAR enzyme family, acts on dsRNA structures within pre-mRNA molecules. Editing of the coding part of the mRNA may lead to recoding, amino acid substitution in the resulting protein, possibly modifying its biochemical and biophysical properties. Altered RNA editing patterns have been observed in various neurological pathologies. Here, we present a comprehensive study of recoding by RNA editing in Alzheimer''s disease (AD), the most common cause of irreversible dementia. We have used a targeted resequencing approach supplemented by a microfluidic-based high-throughput PCR coupled with next-generation sequencing to accurately quantify A-to-I RNA editing levels in a preselected set of target sites, mostly located within the coding sequence of synaptic genes. Overall, editing levels decreased in AD patients’ brain tissues, mainly in the hippocampus and to a lesser degree in the temporal and frontal lobes. Differential RNA editing levels were observed in 35 target sites within 22 genes. These results may shed light on a possible association between the neurodegenerative processes typical for AD and deficient RNA editing.     

The RNA editing enzymes ADARs: mechanism of action and human disease

A-to-I RNA editing is a ubiquitous and crucial molecular mechanism able to convert adenosines into inosines (then read as guanosines by several intracellular proteins/enzymes) within RNA molecules, changing the genomic information. The A-to-I deaminase enzymes (ADARs), which modify the adenosine, can alter the splicing and translation machineries, the double-stranded RNA structures and the binding affinity between RNA and RNA-binding proteins. ADAR activity is an essential mechanism in mammals and altered editing has been associated with several human diseases. Many efforts are now being concentrated on modifying ADAR activity in vivo in an attempt to correct RNA editing dysfunction. Concomitantly, ongoing studies aim to show the way that the ADAR deaminase domain can be used as a possible new tool, an intracellular Trojan horse, for the correction of heritage diseases not related to RNA editing events.