SMN post-translational modification in Spinal Muscular Atrophy

总结 脊髓性肌萎缩症（SMA）是一种神经退行性疾病，其特征是运动神经元丢失， 骨骼肌萎缩SMA是婴儿期最常见的遗传性死亡原因，但尚无有效的治疗方法 目前可用。运动神经元存活（SMN）蛋白水平降低导致SMA。虽然 SMN复合物是一种多功能机器，参与RNA代谢的几个方面，其最好的分子 定义的功能是在装配小核核糖核蛋白（snRNP），这是必不可少的， 转录后RNA调控，包括前mRNA剪接和组蛋白mRNA的3 '端加工。 最近，我们证明了SMN依赖性剪接事件对体内运动神经元功能至关重要 并将具有基本神经元功能的基因的缺陷剪接与表型 SMA动物模型中SMN缺乏的后果。这些发现揭示了SMN的破坏 在snRNP组装中起作用，作为SMA病理学的分子机制。的识别 调节SMN功能的信号通路不仅对于揭示后运动的基本方面至关重要， 转录基因调控以及SMA治疗策略。然而，很少有人知道后- 控制SMN生物学的翻译修饰。 在初步研究中，我们发现SMN被SUMO（小泛素样修饰物）修饰， SUMO化的抑制改变了SMN的亚细胞分布。类小泛素化是一种可逆的翻译后修饰， 涉及多种细胞过程的修饰。重要的是，类小泛素化参与了 肌萎缩侧索硬化症、亨廷顿病和阿尔茨海默病的发病机制。该项目将 研究我们的假设，即SMN复合物的sumoylation是一种调控机制， snRNP生物合成和其他RNA过程在SMA中被破坏。 在具体目标1中，我们将使用细胞模型系统来确定细胞的sumoylation需求。 SMN复合物的表达、稳定性、定位和功能。在具体目标2中，我们将研究 SMN类小泛素化与SMA病理学之间的联系。为了实现这一点，我们将研究野生型 在SMA小鼠模型中使用AAV介导的表达来测定非类小泛素化的SMN突变体的表达， SMN类小泛素化是否是关键的体内功能所必需的，其破坏有助于SMA 病理 该项目的成功完成将揭示SUMO化在SMN生物学调节中的作用。在 除了解开控制基本RNA依赖性的新的调控网络的相关性外， 细胞过程，该项目有可能将sumoylation与SMA病理联系起来，并为 该途径作为这种毁灭性人类疾病的候选治疗靶点的未来研究。

SUMMARY Spinal muscular atrophy (SMA) is a neurodegenerative disease characterized by motor neuron loss and skeletal muscle atrophy. SMA is the most common genetic cause of death in infancy, but no effective treatment is currently available. Reduced levels of the survival motor neuron (SMN) protein cause SMA. Although the SMN complex is a multifunctional machine involved in several aspects of RNA metabolism, its best molecularly defined function is in the assembly of the small nuclear ribonucleoproteins (snRNPs) that are essential for post-transcriptional RNA regulation, including pre-mRNA splicing and 3'-end processing of histone mRNAs. Recently, we demonstrated that SMN-dependent splicing events are essential for motor neuron function in vivo and directly linked defective splicing of a gene with essential neuronal functions to the phenotypic consequences of SMN deficiency in animal models of SMA. These findings revealed disruption of SMN function in snRNP assembly as the molecular mechanism underlying SMA pathology. The identification of signaling pathways that regulate SMN function is critical not only for revealing fundamental aspects of post- transcriptional gene regulation but also strategies for SMA therapy. However, little is known of post- translational modifications that control SMN biology. In preliminary studies, we have found that SMN is modified by SUMO (Small Ubiquitin-like Modifier) and that inhibition of sumoylation alters SMN subcellular distribution. Sumoylation is a reversible post-translational modification involved in a variety of cellular processes. Importantly, sumoylation has been implicated in the pathogenesis of amyotrophic lateral sclerosis, Huntington's and Alzheimer's diseases. This project will investigate our hypothesis that sumoylation of the SMN complex is a regulatory mechanism for the control of snRNP biogenesis and other RNA processes that are disrupted in SMA. In Specific Aim 1, we will use cell model systems to determine the requirement of sumoylation for the expression, stability, localization and function of the SMN complex. In Specific Aim 2, we will investigate the link between sumoylation of SMN and SMA pathology. To achieve this, we will study the function of wild-type and non-sumoylatable SMN mutants using AAV-mediated expression in a mouse model of SMA to determine whether SMN sumoylation is required for the critical in vivo function whose disruption contributes to SMA pathology. Successful completion of this project will reveal the role of sumoylation in the regulation of SMN biology. In addition to the relevance for unraveling novel regulatory networks that control fundamental RNA-dependent cellular processes, this project has the potential to link sumoylation to SMA pathology and open the way for future studies of this pathway as a candidate therapeutic target for this devastating human disease.