Molecular Mechanisms of Ataxin-1 Action

描述（由申请人提供）：Ataxin-1 （Atx1）是一种神经退行性疾病蛋白，其扩展的谷氨酰胺重复形式导致人类脊髓小脑性共济失调1型（SCA1），并在小鼠和果蝇中发挥细胞毒性。虽然Atx1和SCA1之间的联系已经建立了十多年，但Atx1的确切特性及其与SCA1发病机制的联系尚不清楚。长期以来，人们一直认为Atx1中扩大的谷氨酰胺重复序列是导致毒性作用的罪魁祸首，但越来越多的证据表明，该蛋白的固有特性在SCA1病理中也起着重要作用。在我们的研究中，我们最近在体外和体内都发现Atx1直接与一类保守的转录共抑制因子结合，包括脊椎动物的SMRT（类视黄醇和甲状腺激素受体的沉默介质）及其果蝇同源的SMRTER。因此，我们假设AtxVs特性的一个关键方面涉及转录调控，并且保守的SMRT/ smrter依赖的调控途径的干扰是其在脊椎动物和无脊椎动物中的细胞毒性的部分原因。由于SMRT和SMRTER都是核受体共抑制因子，本研究探讨了atx1介导的细胞毒性是否涉及SMRT/SMRTER及其相关的核受体。在Specific Aim 1中，我们提出了各种分子生物学方法，包括染色质免疫沉淀法，来研究Atx1是否通过其与SMRT的相互作用参与脊椎动物甲状腺激素受体（TR）信号传导。在Specific Aim 2中，我们将使用遗传学方法来阐明果蝇中Atx1、SMRTER和蜕皮激素受体（TR的功能等效物）之间的关系。最后，在Specific Aim 3中，基于我们最近发现的Atx1的两个功能域，SMRT/SMRTER相互作用的AXH （Atx1和HMG-box蛋白）结构域和自关联的NBA （Boat和Atx1的n端区域）结构域，我们将研究这两个结构域可能对Atxl的细胞毒性产生的具体后果。将Atx1的功能与核激素受体信号传导联系起来将具有重大意义，因为它表明可以利用激素或影响核激素受体运作的化合物进行干预，以开发治疗SCA1的药物。

DESCRIPTION (provided by applicant): Ataxin-1 (Atx1) is a neurodegenerative disorder protein whose expanded glutamine-repeat form causes spinocerebellar ataxia type 1 (SCA1) in humans and which exerts cytotoxicity in mice and in Drosophila. Although the linkage between Atx1 and SCA1 has been established for more than a decade, the exact properties of Atx1 and their connection to the pathogenesis of SCA1 remain unclear. It was long thought that the expanded glutamine-repeat in Atx1 is the main culprit that brings about toxic effects, yet growing evidence indicates that the protein's inherent properties also play an important role in SCA1 pathology. In our research, we recently established that Atx1 binds directly to a class of conserved transcriptional co- repressors, including vertebrate SMRT (Silencing Mediator of Retinoid and Thyroid hormone receptors) and its Drosophila cognate SMRTER, both in vitro and in vivo. Consequently, we hypothesize that one key aspect of AtxVs properties involves transcriptional regulation, and that perturbation of conserved SMRT/SMRTER-dependent regulatory pathways is partly responsible for its cytotoxicity in both vertebrates and invertebrates. Because both SMRT and SMRTER are nuclear receptor co-repressors, this proposal probes whether Atx1-mediated cytotoxicity involves SMRT/SMRTER and their associating nuclear receptors. In Specific Aim 1, we propose various molecular biology approaches, including the chromatin immunoprecipitation method, to investigate whether Atx1, by means of its interaction with SMRT, is involved in thyroid hormone receptor (TR) signaling in vertebrates. In Specific Aim 2, we will use genetic approaches to elucidate the relationships among Atx1, SMRTER, and ecdysone receptor (the functional equivalent of TR) in Drosophila. Finally, in Specific Aim 3, building on our recent discovery of two functional domains of Atx1, the SMRT/SMRTER interacting AXH (Atx1 and HMG-box protein) domain and a self-association NBA (N-terminal region of Boat and Atx1) domain, we will investigate the specific consequences that these two domains may have for Atxl's cytotoxicity. Connecting the functions of Atx1 to nuclear hormone receptor signaling will have major implications, since it suggests that intervention with hormones or with chemical compounds that affect the operation of nuclear hormone receptors can be exploited to develop therapeutic agents for treating SCA1.