Citron M, Eckman C B, Diehl T S, Corcoran C, Ostaszewski B L, Xia W, Levesque G, St George Hyslop P, Younkin S G, Selkoe D J
Center for Neurologic Diseases, Harvard Institutes of Medicine, Boston, Massachusetts 02115, USA.
Neurobiol Dis. 1998 Aug;5(2):107-16. doi: 10.1006/nbdi.1998.0183.
Humans harboring missense mutations in the presenilin 1 (PS1) gene undergo progressive cerebral deposition of the 42-residue amyloid beta-protein (A beta 42) at an early age and develop severe Alzheimer's disease. A beta 42 is selectively elevated in the conditioned media of cells expressing mutant but not wild-type PS1, indicating that presenilin mutations alter APP processing. Here we analyze the effects of various PS1 mutant constructs on the cellular production of A beta 42. A construct expressing only the PS1 N-terminal endoproteolytic fragment with the mutation Y115H causes no significant increase in A beta 42, whereas a full-length PS1 construct with the same mutation does. This result suggests that the pathogenic effect of mutant presenilins is produced by the full-length molecule even though only a minor proportion of total PS1 occurs as holoprotein in tissues and cell lines. We demonstrate that the effects of two different PS1 mutations are additive when engineered into the same PS1 molecule. Therefore, two mutations alter gamma-secretase processing of APP more than one and the PS1 mutations described to date do not cause the maximum possible PS1-mediated rise in A beta 42. When a PS1 mutation was expressed in cells carrying the APPV717I mutation, A beta 42 rose dramatically to become the predominant secreted A beta species, an observation of interest for transgenic modeling of AD. Our results are consistent with the hypothesis that presenilin is a major regulator of the proteolytic processing of APP by gamma-secretases.
携带早老素1（PS1）基因错义突变的人在早年就会出现42个氨基酸残基的β淀粉样蛋白（Aβ42）在大脑中进行性沉积，并发展为严重的阿尔茨海默病。在表达突变型而非野生型PS1的细胞的条件培养基中，Aβ42选择性升高，这表明早老素突变会改变APP的加工过程。在此，我们分析了各种PS1突变体构建体对Aβ42细胞产生的影响。仅表达带有Y115H突变的PS1 N端内蛋白水解片段的构建体不会导致Aβ42显著增加，而具有相同突变的全长PS1构建体则会导致Aβ42增加。这一结果表明，尽管在组织和细胞系中，全长分子形式的PS1仅占总PS1的一小部分，但突变型早老素的致病作用是由全长分子产生的。我们证明，当将两种不同的PS1突变引入同一PS1分子时，它们的作用是相加性的。因此，两种突变对APP的γ-分泌酶加工的改变比一种突变更大，并且迄今为止描述的PS1突变不会导致PS1介导的Aβ42升高达到最大可能程度。当在携带APPV717I突变的细胞中表达PS1突变时，Aβ42急剧上升，成为主要的分泌型Aβ种类，这一观察结果对于AD的转基因建模具有重要意义。我们的结果与早老素是γ-分泌酶对APP进行蛋白水解加工的主要调节因子这一假设一致。
