Myotonic Dystrophy Type 2

描述(申请人提供)：强直性肌营养不良症2(DM2)是一种常见的肌肉疾病，临床上与强直性肌营养不良症1(DM1)有关。DM2是由位于染色体3Q上的锌指因子编码基因ZNF9内含子1的CCTG重复序列扩大引起的。虽然DM1和DM2患者的一些症状相似，但其他症状只针对一种疾病。DM2的特殊特征包括没有先天性疾病，没有发育的大脑异常，没有发育迟缓，骨骼肌症状明显减轻。我实验室的主要研究重点是DM1和DM2的分子碱基的研究。在对DM1的研究过程中，我们发现DMPK基因中CTG三联体重复序列的扩增通过未翻译的RNA CUG重复序列导致DM1的病理改变。Cug重复序列的扩展影响两种RNA结合蛋白，CUGBP1和MNBL。DM2也是由未翻译的CCTG重复序列的扩展引起的，这表明DM1和DM2的RNA依赖机制相似。然而，DM2表型的特殊特征表明，DM2的分子机制与DM1的不同。我们发现DM2中的RNA CCUG重复序列与不同的RNA结合蛋白相互作用，并与大型蛋白质-蛋白质复合体相互作用，称为Mega蛋白质-蛋白质复合体(MPPC)。这些复合体与CCUG重复序列特异结合，但不与CUG重复序列结合。DM2细胞胞浆和胞核均可见MPPC。DM2患者成肌细胞胞浆MPPC含量增加，而胞核MPPC含量降低。这一应用的主要假设是CCUG重复通过改变大的蛋白质-蛋白质复合体的生物学功能而导致DM2病理。为了检验这一假说，我们设计了三个具体目标。我们发现胞质MPPC含有9种蛋白，包括CUGBP1、EJF-2a和eIF-2p，这三种蛋白都参与了mRNAs的翻译调控。特定目的1将鉴定细胞质MPPC的其他蛋白质成分，并研究细胞质MPPC在mRNA翻译中的作用。特定目的2将确定核MPPC内蛋白质的身份，检查该复合体是否在剪接中发挥作用，并调查核MPPC的变化是否导致DM2的异常剪接。具体目标3将研究CCUG重复扩增增加DM2细胞胞浆中MPPC数量和减少细胞核中MPPC数量的机制。

DESCRIPTION (provided by applicant): Myotonic Dystrophy 2 (DM2) is a common muscular disease clinically related to Myotonic Dystrophy 1 (DM1). DM2 is caused by expansion of CCTG repeats in intron 1 of the zinc finger factor encoding gene, ZNF9, located on chromosome 3q. While some symptoms in the patients with DM1 and DM2 are similar, others are specific just for one type of disease. DM2 specific features include a lack of congenital form of disease, lack of developmental brain abnormalities, lack of retardation and significantly milder symptoms in skeletal muscle. The main focus of research in my laboratory is the investigation of molecular bases for DM1 and DM2. In the course of our studies on DM1, we found that expansion of CTG triplet repeats in DMPK gene causes DM1 pathology through un-translated RNA CUG repeats. CUG repeat expansion affects two RNA-binding proteins, CUGBP1 and MNBL. DM2 is also caused by expansion of untranslated CCTG repeats suggesting similar RNA-dependent mechanisms for DM1 and DM2. However, specific features of DM2 phenotype suggest that molecular mechanisms of DM2 are not identical to those of DM1. We found that RNA CCUG repeats in DM2 interact with distinct RNA-binding proteins and with large protein-protein complexes, designated as Mega Protein-Protein Complexes (MPPC). These complexes bind specifically to CCUG repeats but not to CUG repeats. MPPC are observed in cytoplasm and in nuclei of DM2 cells. The amounts of cytoplasmic MPPC are increased in DM2 myoblasts, while the levels of nuclear MPPC are reduced in DM2 patients. The major hypothesis of this application is that CCUG repeats cause DM2 pathology via changes of biological functions of large protein-protein complexes. Three Specific Aims are designed to test this hypothesis. We have found that cytoplasmic MPPC contains 9 proteins including CUGBP1, eJF-2a and eIF-2p, all three proteins are involved in the regulation of translation of mRNAs. Specific Aim 1 will identify other protein components of cytoplasmic MPPC and examine the role of cytoplasmic MPPC in mRNA translation. Specific Aim 2 will determine identity of proteins within nuclear MPPC, examine if this complex plays a role in splicing and investigate if the alterations in nuclear MPPC cause abnormal splicing in DM2. Specific Aim 3 will study the mechanisms by which expansion of CCUG repeats increases amounts of MPPC in cytoplasm of DM2 cells and reduces amounts of MPPC in nuclei.