Mattis Virginia B, Bowerman Melissa, Kothary Rashmi, Lorson Christian L
Department of Veterinary Pathobiology, Life Sciences Center, Room 404, University of Missouri, Columbia, MO 65211, United States.
Neurosci Lett. 2008 Sep 5;442(1):54-8. doi: 10.1016/j.neulet.2008.06.059. Epub 2008 Jun 26.
Spinal muscular atrophy (SMA) affects about 1 in every 6000 children born and is the leading genetic cause of infant death. SMA is a recessive disorder caused by the mutation or deletion of Survival Motor Neuron-1 (SMN1). SMN2, a nearly identical copy gene, has the potential to encode the same protein as SMN1 and is retained in all SMA patients. The majority of SMN2-derived transcripts are alternatively spliced and therefore encode a truncated isoform lacking exon 7 (SMNDelta7), which is a defective protein because it is unstable, has a reduced ability to self-associate and is unable to efficiently function in SMN cellular activities. However, we have shown that the SMN C-terminus functions non-specifically, since heterologous sequences can compensate for the exon 7 sequence. Several classes of compounds identified in SMN-inducing high throughput screens have been proposed to function through a read-through mechanism; however, a functional analysis of the SMNDelta7 read-through product has not been performed. In this report, the SMNDelta7 read-through product is characterized and compared to the SMNDelta7 protein. In a series of in vitro and cell based assays, SMNDelta7 read-through product is shown to increase protein stability, promote neurite outgrowths in SMN deficient neurons, and significantly elevate SMN-dependent UsnRNP assembly in extracts from SMA patient fibroblasts. Collectively, these results demonstrate that SMNDelta7 read-through product is more active than the SMNDelta7 protein and suggest that SMA therapeutics that specifically induce SMNDelta7 read-through may provide an alternative platform for drug discovery.
脊髓性肌萎缩症（SMA）影响每6000名出生儿童中的约1名，是婴儿死亡的主要遗传原因。SMA是一种由生存运动神经元1（SMN1）突变或缺失引起的隐性疾病。SMN2是一个几乎相同的拷贝基因，有可能编码与SMN1相同的蛋白质，并且在所有SMA患者中都存在。大多数源自SMN2的转录本会发生可变剪接，因此编码一种缺少外显子7的截短异构体（SMNDelta7），这是一种有缺陷的蛋白质，因为它不稳定，自我缔合能力降低，并且无法在SMN细胞活动中有效发挥作用。然而，我们已经表明SMN的C末端具有非特异性功能，因为异源序列可以补偿外显子7序列。在诱导SMN的高通量筛选中鉴定出的几类化合物被认为是通过通读机制发挥作用的；然而，尚未对SMNDelta7通读产物进行功能分析。在本报告中，对SMNDelta7通读产物进行了表征并与SMNDelta7蛋白进行了比较。在一系列体外和基于细胞的试验中，SMNDelta7通读产物显示出可提高蛋白质稳定性，促进SMN缺陷神经元中的神经突生长，并显著提高SMA患者成纤维细胞提取物中SMN依赖性UsnRNP组装。总体而言，这些结果表明SMNDelta7通读产物比SMNDelta7蛋白更具活性，并表明特异性诱导SMNDelta7通读的SMA治疗方法可能为药物发现提供一个替代平台。
