Regulation of SMN and Identification of its Downstream Target

标题： SMN稳定性的调控及其下游靶标的确定 摘要 脊髓性肌萎缩症(SMA)是一种由存活运动神经元1(SMN1)基因突变引起的疾病， 是导致婴儿死亡的最常见的遗传原因。人类有两个SMN基因的拷贝，端粒 SMN1，编码全长形式(FL-SMN)，以及着丝粒SMN2，主要编码 快速降级的截断形式(SMN7)以及全长形式。在最严重的情况下，1型 SMA，有1到2个拷贝的SMN2基因，患者在2岁内死于呼吸道 失败了。然而，SMN2基因拷贝较多的患者表现出不太严重的SMA(III型 SMA)。SMA的发生是由于脊髓运动神经元FL-SMN蛋白含量减少所致。因此，大部分 对SMA进行治疗干预的努力主要集中在提高FL-SMN蛋白产品的水平。 我们的初步结果表明，SMN存在于含有E3泛素连接酶的复合体中。 促进复合体(APC)和RNA结合蛋白HUD。APC将蛋白质靶向蛋白酶体，用于 降解，而HUD稳定mRNAs。此外，有证据表明APC在神经细胞中的作用。 存活、轴突生长和突触功能，而HUD参与了神经元的成熟和维持 神经元。我们还从以前的研究中了解到，SMN可能是运输、稳定和/或 轴突中某些mRNAs的翻译。这些数据一起促使我们制定了一个工作模型 其中：1)APC的泛素化调节SMN或SMN的其他成员的稳定性和/或功能 2)轴突中可能与HUD-SMN相关的mRNAs对于生长和生存是重要的 运动神经元。在这项建议的第一部分，我们将调查APC在监管SMN方面的作用 稳定性和功能性。我们将首先描述APC和SMN在神经元中的相互作用。那么，我们会 探讨抑制APC-SMN相互作用对SMN功能、稳定性和定位的影响 蛋白。在第二部分中，我们将重点研究一个可能在轴突中发挥作用的轴突smn靶基因。 外延生长。由于FL-SMN的数量与疾病的严重程度密切相关， 了解APC和SMN之间的相互作用并阐明SMN的下游靶点 将为SMA的生物学提供重要的见解，并有可能产生新的治疗方案 治疗这种疾病。

TITLE: Regulation of SMN stability and identification of its downstream targets SUMMARY Spinal Muscular Atrophy (SMA), a disease caused by the mutations of Survival Motor Neuron 1 (SMN1) gene, is the most common genetic cause of infant mortality. Humans have two copies of the SMN gene, the telomeric SMN1, which encodes for a full-length form (FL-SMN), and the centromeric SMN2, which encodes primarily for a rapidly-degraded truncated form (SMN7) as well as the full-length form. In the most severe form, Type 1 SMA, there are 1 or 2 copies of the SMN2 gene, and patients die within 2 years of age due to respiratory failure. Patients with more copies of the SMN2 gene, however, manifest a less severe form of SMA (Type III SMA). SMA occurs due to decreased amount of FL-SMN protein in spinal motor neurons. Therefore, much of the effort for therapeutic interventions in SMA has focused on increasing the level of FL-SMN protein products. Our preliminary results show that SMN is found in a complex containing an E3 ubiquitin ligase the Anaphase- Promoting Complex (APC) and HuD, a RNA binding protein. The APC targets proteins to the proteasome for degradation whereas HuD stabilizes mRNAs. Furthermore, evidence indicates a role for APC in neuronal survival, axonal growth, and synaptic function, and HuD is involved in the maturation and maintenance of neurons. We also know from previous studies that SMN may be necessary for the transport, stability and/or translation of certain mRNAs in neurites. These data together prompted us to formulate a working model in which: 1) ubiquitination by APC regulates the stability and/or function of SMN or other members of the SMN complex and 2) the putative HuD-SMN-associated mRNAs in axons are important for the growth and survival of motor neurons. In the first part of this proposal, we will investigate the role of APC in regulation of SMN stability and function. We will first characterize the interaction between APC and SMN in neurons. Then, we will investigate the effect of inhibiting the APC-SMN interaction on the function, stability, localization, of SMN protein. In the second part, we will focus on one axonal SMN target mRNA which is likely to play a role in axon outgrowth. Since there is a tight correlation between the amount of FL-SMN and the severity of disease, understanding the interaction between APC and SMN as well as elucidating the downstream targets of SMN will provide important insights into the biology of SMA and has the potential to generate new treatment options for this disease.