Nonsense-mediated messenger RNA decay of survival motor neuron 1 causes spinal muscular atrophy
Nonsense-mediated messenger RNA decay of survival motor neuron 1 causes spinal muscular atrophy
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DOI：
10.1007/s00439-007-0455-7
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发表时间：
2008-03-01
期刊：
影响因子：
5.3
通讯作者：
Wirth, Brunhilde
中科院分区：
文献类型：
--
作者：
Brichta, Lars;Garbes, Lutz;Wirth, Brunhilde
常染色体隐性遗传性近端脊髓性肌萎缩症 (SMA) 是一种因存活运动神经元 1 (SMN1) 功能丧失而导致的神经退行性疾病。由于缺失或基因转换导致 SMN1 纯合性缺失约占 SMA 病例的 96%。在剩下的 4% 中，通常会发现细微的 SMN1 突变。在这里，我们描述了三个 I 型 SMA 个体中的两个新的基因内 SMN1 突变：外显子 3 中的点突变 (c.469C > T) 和内含子 4 中的替换 (c.628-140A > G)。体内剪接测定表明，内含子替换创建了一个新的剪接供体位点，最终导致异常剪接并在 SMN1 转录物的外显子 4 和 5 之间插入来自内含子 4 的 65 bp (c.627_628ins65)。这两种突变都使得 SMN1 转录物容易受到无义介导的 mRNA 衰减 (NMD) 的影响，从而导致 mRNA 降解、SMN 蛋白水平不足以及 SMA 表型的形成。用翻译抑制剂嘌呤霉素和依米丁治疗患者细胞系显着增加了突变型 SMN1 转录物的水平。在 siRNA 介导的 UPF1（NMD 必需因子）敲低后观察到类似的效果。这项研究提供了第一个证据，证明 SMN1 转录本的 NMD 是 SMA 患者亚群疾病的分子基础。
Autosomal recessive proximal spinal muscular atrophy (SMA) is a neurodegenerative disorder resulting from functional loss of survival motor neuron 1 (SMN1). Homozygous absence of SMN1 due to deletion or gene conversion accounts for about 96% of SMA cases. In the remaining 4%, subtle SMN1 mutations are commonly identified. Here, we describe two novel intragenic SMN1 mutations in three type I SMA individuals: a point mutation in exon 3 (c.469C > T) and a substitution in intron 4 (c.628-140A > G). In-vivo splicing assays demonstrated that the intronic substitution creates a novel splice donor site, culminating in aberrant splicing and insertion of 65 bp from intron 4 between exons 4 and 5 in SMN1 transcripts (c.627_628ins65). Both mutations render SMN1 transcripts susceptible to nonsense-mediated mRNA decay (NMD), resulting in mRNA degradation, insufficient SMN protein levels and development of an SMA phenotype. Treatment of patient cell lines with the translation inhibitors puromycin and emetine markedly increased the levels of mutant SMN1 transcripts. A similar effect was observed after siRNA-mediated knockdown of UPF1, a factor essential for NMD. This study provides first evidence that NMD of SMN1 transcripts is responsible for the molecular basis of disease in a subset of SMA patients.