King's College London, Department of Clinical Neuroscience, Institute of Psychiatry, PO51, De Crespigny Park Denmark Hill, London SE58AF, United Kingdom.
Neurosci Lett. 2011 Jun 22;497(2):139-43. doi: 10.1016/j.neulet.2011.04.047. Epub 2011 May 5.
The astroglial EAAT2 glutamate transporter is essential for clearing glutamate in the central nervous system and protecting against excitotoxicity. It is implicated in amyotrophic lateral sclerosis (ALS, the most common type of motor neurone disease) where less EAAT2 is found, possibly involving aberrant intron 7 retention transcripts. We report adenine/inosine RNA editing at a novel site in intron 7 of EAAT2 pre-mRNA that appears to activate a cryptic alternative polyadenylation site, generating intron 7 retention transcripts. This polyadenylation site includes two overlapping polyadenylation signals opposite the editing site in a strong stem-loop, which is highly conserved in primates. In pre-mRNA, we observed variable editing levels at this site, which were significantly higher in spinal cord (p=0.001) and motor cortex (p=0.005) from ALS patients, but not in cerebellum, demonstrating specificity for clinically relevant regions. By contrast, incomplete mRNA molecules polyadenylated in intron 7 are always completely edited. Cell culture experiments confirm this strong correlation between editing and polyadenylation in intron 7, strongly suggesting activation of the alternative polyadenylation site by editing. Prediction of inosine base-pairing from published data suggests that RNA editing releases the polyadenylation signals from the stem-loop, providing a plausible mechanism. To the best of our knowledge, this is the first report of RNA editing activating an alternative polyadenylation signal.
星形胶质细胞 EAAT2 谷氨酸转运体对于清除中枢神经系统中的谷氨酸并防止兴奋毒性至关重要。它与肌萎缩侧索硬化症（ALS，最常见的运动神经元疾病类型）有关，在 ALS 中发现的 EAAT2 较少，可能涉及异常的内含子 7 保留转录本。我们报告了 EAAT2 前体 mRNA 内含子 7 中新位点的腺嘌呤/肌苷 RNA 编辑，该编辑似乎激活了一个隐藏的可变多聚腺苷酸化位点，产生内含子 7 保留转录本。该多聚腺苷酸化位点包括编辑位点对面强茎环中两个重叠的多聚腺苷酸化信号，该茎环在灵长类动物中高度保守。在前体 mRNA 中，我们观察到该位点的编辑水平存在可变性，在 ALS 患者的脊髓（p=0.001）和运动皮层（p=0.005）中显著升高，但在小脑不升高，表明该编辑具有针对临床相关区域的特异性。相比之下，多聚腺苷酸化在内含子 7 中的不完全 mRNA 分子总是完全编辑。细胞培养实验证实了内含子 7 中编辑和多聚腺苷酸化之间的这种强烈相关性，强烈表明编辑激活了替代的多聚腺苷酸化位点。根据已发表的数据预测肌苷碱基配对表明，RNA 编辑将多聚腺苷酸化信号从茎环中释放出来，提供了一种合理的机制。据我们所知，这是首次报道 RNA 编辑激活替代多聚腺苷酸化信号的报告。
