FUNCTION OF ALZHEIMER DISEASE PRESENILIN 2

阿尔茨海默病(AD)是一种破坏性的神经退行性疾病，导致记忆、认知和异常行为的丧失。据估计，目前美国阿尔茨海默病的发病率约为400万，但由于预期寿命的延长，预计到2020年将增至1400万。导致阿尔茨海默病的机制尚不清楚，也没有已知的治疗方法。三个基因的突变已被证明与AD的发生有关；β淀粉样前体蛋白，以及两个高度相关的基因，早老素1和早老素2(PS2)。这三个基因在神经元中的功能以及这些基因突变导致阿尔茨海默病的机制都不清楚。有趣的是，大多数与AD相关的突变发生在普遍表达的早老素的基因中。有证据表明，早老素在发育过程中发挥作用，也可能参与调节细胞程序性死亡(细胞凋亡)。我们和其他人已经证明，PS2在分裂细胞和非分裂细胞中的过度表达都会诱导细胞凋亡。此外，我们还发现PS2在分裂细胞中的过度表达导致细胞停滞在细胞周期的G1期。有趣的是，这种细胞周期停滞被FAD PS2(N141I)突变增强。我们建议详细研究PS2过表达导致细胞周期停滞的机制及其与细胞凋亡和AD的关系。在一项配套工作中，我们使用酵母2-杂交系统来识别与PS2相互作用的蛋白质。发现许多可能的相互作用分子结合了PS2的亲水环和C-末端序列。其中包括一种新的结合PS2环序列的钙结合肉豆蔻酰化蛋白(我们称之为CALMYRIN)，以及一种包含泛素样基和泛素结合基序的新蛋白，它既能与早老素的C端序列又能与环序列结合。有趣的是，Calmyrin并不像我们所知的那样与PS1的相应环序列强烈结合，并且是第一个被发现优先结合一种早老素而不是另一种的蛋白质。Calmyrin在过度表达时会导致细胞死亡，并与PS2协同作用，因此双重过度表达导致的死亡水平是单独表达每种蛋白质的两倍。为了更全面地了解早老素及其相互作用的蛋白质，我们建议对这些假定的相互作用因子进行研究和表征。最终，我们希望这些研究将有助于更好地理解早老素在正常细胞和阿尔茨海默病中的作用。

Alzheimer's Disease (AD) is a devastating neurodegenerative disorder that results in loss of memory, cognition, and aberrant behavior. The incidence of AD in the USA is estimated to be approximately 4 million today, but is expected to rise to 14 million by the year 2020 due to an anticipated increase in life expectancy. The mechanisms that cause AD are not known and there is no known cure. Mutations in three genes have been shown to be associated with development of AD; the beta amyloid precursor protein, and two highly related genes, presenilin 1 and presenilin 2 (PS2). Neither the functions of these three genes in neurons nor the mechanisms by which mutations in these genes cause AD are known. Interestingly most AD-associated mutations occur in the genes for the presenilins which are ubiquitously expressed. Evidence indicates presenilins function in development and may also be involved in the regulation of programmed cell death (apoptosis). We and others have shown that overexpression of PS2 in both dividing and non dividing cells induces apoptosis. Furthermore, we have found that overexpression of PS2 in dividing cells leads to the arrest of cells in the G1 phase of the cell cycle. Interestingly, this cell cycle arrest is potentiated by the FAD PS2(N141I) mutation. We propose to study in detail the mechanisms by which PS2 overexpression leads to cell cycle arrest and the relationship to apoptosis and AD. In a companion effort we used the yeast 2-hybrid system to identify proteins that interact with PS2. A number of putative interactors were found to bind the hydrophilic loop and C- terminal sequences of PS2. These include a novel calcium-binding myristoylated protein (which we have termed CALMYRIN) which binds PS2 loop sequences, and a novel protein which contains ubiquitin- like and ubiquitin-association motifs which binds to both the C- terminal and loop sequences of presenilins. Interestingly, calmyrin does not bind as avidly to the corresponding loop sequences of PS1 and to our knowledge is the first protein that has been found to preferentially bind one presenilin and not the other. Calmyrin causes cell death when overexpressed, and acts synergistically with PS2 so that dual overexpression results in twice the level of death compared to expression of each protein individually. In order to build a more global understanding of presenilins and the proteins with which they interact we propose to study and characterize these putative interactors. Eventually we hope these studies will contribute to a better understanding of how presenilins function in normal cells and in AD.