Regulation of SMN and Identification of its Downstream Target

标题： SMN稳定性的调节及其下游靶标的鉴定 总结 脊髓性肌萎缩症（SMA）是由运动神经元生存基因1（SMN 1）突变引起的一种疾病， 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 SMN 1编码全长形式（FL-SMN），而着丝粒SMN 2主要编码 一种快速降解的截短型（SMN7)以及全长形式。在最严重的形式，1型 SMA，有1或2个SMN 2基因拷贝，患者在2岁内因呼吸道疾病死亡。 失败然而，具有更多SMN 2基因拷贝的患者表现出较不严重的SMA形式（III型 SMA）。SMA的发生是由于脊髓运动神经元中FL-SMN蛋白的量减少。因此，许多 SMA治疗干预措施的重点是提高FL-SMN蛋白产物的水平。 我们的初步结果表明，SMN存在于含有E3遍在蛋白连接酶后期的复合物中- 促进复合物（APC）和HuD，一种RNA结合蛋白。APC将蛋白质靶向蛋白酶体， 而HuD稳定mRNA。此外，有证据表明APC在神经元中的作用。 存活、轴突生长和突触功能，而HuD参与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、稳定性和/或 神经突中某些mRNA的翻译。这些数据共同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的其它成员的稳定性和/或功能 复合物和2）轴突中假定的HuD-SMN相关mRNA对生长和存活很重要 运动神经元。在这个建议的第一部分，我们将探讨APC在SMN调节中的作用 稳定性和功能。我们将首先描述APC和SMN在神经元中的相互作用。那就 研究抑制APC与SMN相互作用对SMN功能、稳定性、定位的影响 蛋白在第二部分中，我们将重点关注一种可能在轴突中起作用的轴突SMN靶mRNA， 结果由于FL-SMN的量与疾病的严重程度之间存在紧密的相关性， 了解APC和SMN之间的相互作用以及阐明SMN的下游靶点 将为SMA生物学提供重要见解，并有可能产生新的治疗选择 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.