BACKGROUND Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving loss of motor neurons and having no known cure and uncertain etiology. Several studies have drawn connections between altered retrotransposon expression and ALS. Certain features of the LINE-1 (L1) retrotransposon-encoded ORF1 protein (ORF1p) are analogous to those of neurodegeneration-associated RNA-binding proteins, including formation of cytoplasmic aggregates. In this study we explore these features and consider possible links between L1 expression and ALS. RESULTS We first considered factors that modulate aggregation and subcellular distribution of LINE-1 ORF1p, including nuclear localization. Changes to some ORF1p amino acid residues alter both retrotransposition efficiency and protein aggregation dynamics, and we found that one such polymorphism is present in endogenous L1s abundant in the human genome. We failed, however, to identify CRM1-mediated nuclear export signals in ORF1p nor strict involvement of cell cycle in endogenous ORF1p nuclear localization in human 2102Ep germline teratocarcinoma cells. Some proteins linked with ALS bind and colocalize with L1 ORF1p ribonucleoprotein particles in cytoplasmic RNA granules. Increased expression of several ALS-associated proteins, including TAR DNA Binding Protein (TDP-43), strongly limits cell culture retrotransposition, while some disease-related mutations modify these effects. Using quantitative reverse transcription PCR (RT-qPCR) of ALS tissues and reanalysis of publicly available RNA-Seq datasets, we asked if changes in expression of retrotransposons are associated with ALS. We found minimal altered expression in sporadic ALS tissues but confirmed a previous report of differential expression of many repeat subfamilies in C9orf72 gene-mutated ALS patients. CONCLUSIONS Here we extended understanding of the subcellular localization dynamics of the aggregation-prone LINE-1 ORF1p RNA-binding protein. However, we failed to find compelling evidence for misregulation of LINE-1 retrotransposons in sporadic ALS nor a clear effect of ALS-associated TDP-43 protein on L1 expression. In sum, our study reveals that the interplay of active retrotransposons and the molecular features of ALS are more complex than anticipated. Thus, the potential consequences of altered retrotransposon activity for ALS and other neurodegenerative disorders are worthy of continued investigation.

中文翻译：

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肌萎缩侧索硬化症背景下 LINE-1 蛋白的特性和重复元件表达。


背景肌萎缩侧索硬化症（ALS）是一种致命的神经退行性疾病，涉及运动神经元的丧失，并且没有已知的治愈方法和不确定的病因。一些研究已经发现逆转录转座子表达改变与 ALS 之间存在联系。 LINE-1 (L1) 逆转录转座子编码的 ORF1 蛋白 (ORF1p) 的某些特征与神经退行性变相关的 RNA 结合蛋白的特征类似，包括细胞质聚集体的形成。在本研究中，我们探索这些特征并考虑 L1 表达与 ALS 之间可能的联系。结果我们首先考虑了调节 LINE-1 ORF1p 聚集和亚细胞分布的因素，包括核定位。一些 ORF1p 氨基酸残基的变化会改变逆转录转座效率和蛋白质聚集动力学，我们发现人类基因组中丰富的内源性 L1 中存在一种这样的多态性。然而，我们未能鉴定出 ORF1p 中 CRM1 介导的核输出信号，也未能鉴定出人 2102Ep 种系畸胎癌细胞中内源性 ORF1p 核定位中细胞周期的严格参与。一些与 ALS 连接的蛋白质与细胞质 RNA 颗粒中的 L1 ORF1p 核糖核蛋白颗粒结合并共定位。包括 TAR DNA 结合蛋白 (TDP-43) 在内的多种 ALS 相关蛋白的表达增加，强烈限制细胞培养物逆转座，而一些与疾病相关的突变会改变这些影响。使用 ALS 组织的定量逆转录 PCR (RT-qPCR) 并对公开的 RNA-Seq 数据集进行重新分析，我们询问逆转录转座子表达的变化是否与 ALS 相关。 我们在散发性 ALS 组织中发现了最小的表达改变，但证实了之前关于 C9orf72 基因突变的 ALS 患者中许多重复亚家族差异表达的报告。结论在这里，我们扩展了对易于聚集的 LINE-1 ORF1p RNA 结合蛋白的亚细胞定位动力学的理解。然而，我们未能找到令人信服的证据证明散发性 ALS 中 LINE-1 逆转录转座子的错误调节，也未能找到 ALS 相关 TDP-43 蛋白对 L1 表达的明显影响。总之，我们的研究表明，活性逆转录转座子与 ALS 分子特征之间的相互作用比预期的更为复杂。因此，逆转录转座子活性改变对 ALS 和其他神经退行性疾病的潜在后果值得继续研究。