Ubiquitin and regulation of prion induction by a short-lived protein

描述(申请人提供)：Prion是传染性蛋白质亚型，在哺乳动物中会导致致命的和不可治愈的神经退行性疾病，并在酵母中传播可遗传的特征。大多数Prion形成高度有序的纤维聚合物(淀粉样蛋白)，类似于其他淀粉样变性和神经包涵体疾病所涉及的聚集体，如阿尔茨海默病、帕金森病或亨廷顿病。因此，Prion可以被认为是一种淀粉样蛋白，可以招募相同序列的蛋白质分子，将它们转化为淀粉样蛋白状态，并将其传递给其他细胞。现在越来越清楚的是，除了在疾病中的作用外，一些普里恩和其他淀粉样蛋白或淀粉样聚集体还具有重要的生物学功能：存储肽激素；微生物细胞彼此或与底物连接；控制表观遗传开关；适应应激环境条件；以及与记忆相关的长期突触变化。虽然许多蛋白质在体外形成淀粉样蛋白，但对体内形成淀粉样蛋白或蛋白的机制知之甚少。可能有基本途径和诱导途径都有一些共同的特征。蛋白质在同质多聚体和/或异质多聚体复合体中的初始结合可能导致Prion“种子”的形成。当淀粉样蛋白在细胞和/或局部隔室中以高浓度积累时，发生这种事件的可能性就会增加。事实上，通过Pron蛋白的过度表达和/或其他聚集的富含qN的蛋白的存在，促进了酵母Pron的从头形成。已知的影响蛋白质水平和动态平衡的过程，如某些生理应激、泛素蛋白酶体系统(UPS)功能受损或未折叠蛋白反应(UPR)缺陷，也会增加Prion的形成。相反，肌动蛋白细胞骨架的缺陷降低了普恩形成的速度，这表明与细胞骨架的结合对于参与普恩成核的某个步骤是重要的(S)。因此，导致Prion蛋白或异源Priongen蛋白积累并控制其定位的生理应激可能对Prion的形成产生深远的影响。Lsb2是一种酵母蛋白，在酵母翻译终止因子Sup35过表达的情况下，它的过度表达会刺激蛋白的形成(指定为[PSI])。与其在启动子发生中的作用一致，Lsb2在胁迫下被诱导，在K80泛素化，以蛋白酶体依赖的方式降解，并定位于肌动蛋白斑块。这项研究的总体目标是揭示异源蛋白稳态参与真核细胞中Pron形成的分子机制。我们将定义Lsb2在应力诱导的[PSI]Prion形成中的作用。我们将询问是否需要Lsb2的特定细胞定位才能诱导普恩病毒的能力，UPS和Lsb2的共价修饰在触发普恩形成中发挥了什么作用，以及与生理和应激相关的Lsb2水平的变化是否参与了普恩诱导。

DESCRIPTION (provided by applicant): Prions are infectious protein isoforms that cause fatal and incurable neurodegenerative diseases in mammals and transmit heritable traits in yeast. Most prions form highly ordered fibrous polymers (amyloids), resembling the aggregates involved in other amyloidoses and neural inclusion diseases, such as Alzheimer, Parkinson, or Huntington diseases. Thus, a prion can be thought of as an amyloid that can recruit protein molecules of the same sequence, convert them into an amyloid state, and be transmitted to other cells. It is now becoming clear that in addition to their role in disease, some prions and other amyloids or amyloid-like aggregates perform important biological functions: storage of peptide hormones; attachment of microbial cells to each other or to substrates; control of epigenetic switches; adaptation to stressful environmental conditions; and long-term synaptic changes associated with memory. While many proteins form amyloids in vitro, little is known about the mechanisms of amyloid or prion formation in vivo. There are likely both basal and induced pathways that share some common features. An initial association of proteins in homomultimeric and/or heteromultimeric complexes may lead to formation of the prion "seed". The probability of such an event is increased when the amyloidogenic protein is accumulated at high concentrations in the cell and/or in a local compartment. Indeed, de novo formation of a yeast prion is promoted by overexpression of the prion protein and/or the presence of other aggregated QN-rich proteins. Processes known to affect protein levels and homeostasis, such as some physiological stresses, impairment of ubiquitin proteasome system (UPS) function, or defects in the unfolded protein response (UPR), also increase prion formation. Conversely, defects in the actin cytoskeleton diminish the rate of prion formation, suggesting that binding to cytoskeleton is important for some step(s) involved in prion nucleation. Thus, physiological stresses that cause the accumulation of prion proteins or heterologous prionogenic proteins, and that control their localization may have profound effects on the formation of prions. Lsb2 is a yeast protein whose overexpression stimulates the formation of a prion (designated [PSI+]) in the presence of overexpression of the yeast translational termination factor Sup35. Consistent with its role in prionogenesis, Lsb2 is induced by stress, ubiquitinated at K80, degraded in a proteasome-dependent fashion, and localized to actin patches. The overall goal of this research is to uncover the molecular mechanisms by which heterologous protein homeostasis participates in prion formation in eukaryotic cells. We will define the role of Lsb2 in the stress-induced formation of the [PSI+] prion. We will ask if a specific cellular localization of Lsb2 is required for prion-inducing ability, what role UPS and covalent modifications of Lsb2 play in triggering the formation of prions, and if physiological and stress- related variations in Lsb2 levels are involved in prion induction.