Pitsi Didier, Kienlen-Campard Pascal, Octave Jean-Noël
Laboratoire de pharmacologie expérimentale, Université catholique de Louvain, Brussels, Belgium.
J Neurochem. 2002 Oct;83(2):390-9. doi: 10.1046/j.1471-4159.2002.01138.x.
Aggregates of beta-amyloid peptide (Abeta) are the major component of the amyloid core of the senile plaques observed in Alzheimer's disease (AD). Abeta results from the amyloidogenic processing of its precursor, the amyloid precursor protein (APP), by beta- and gamma-secretase activities. If beta-secretase has recently been identified and termed BACE, the identity of gamma-secretase is still obscure. Studies with knock-out mice showed that presenilin 1 (PS1), of which mutations are known to be the first cause of inherited AD, is mandatory for the gamma-secretase activity. However, the proteolytic activity of PS1 remains a matter of debate. Here we used transfected Sf9 insect cells, a cellular model lacking endogenous beta- and/or gamma-secretase activities, to characterize the role of BACE and PS1 in the amyloidogenic processing of human APP. We show that, in Sf9 cells, BACE performs the expected beta-secretase cleavage of APP, generating C99. We also show that C99, which is a substrate of gamma-secretase, tightly binds to the human PS1. Despite this interaction, Sf9 cells still do not produce Abeta. This strongly argues against a direct proteolytic activity of PS1 in APP processing, and points toward an implication of PS1 in trafficking/presenting its substrate to the gamma-secretase.
β-淀粉样肽（Aβ）聚集体是阿尔茨海默病（AD）中观察到的老年斑淀粉样核心的主要成分。Aβ是其前体淀粉样前体蛋白（APP）经β-和γ-分泌酶活性进行淀粉样生成加工的产物。虽然β-分泌酶最近已被鉴定并命名为BACE，但γ-分泌酶的身份仍不清楚。对基因敲除小鼠的研究表明，早老素1（PS1）是γ-分泌酶活性所必需的，已知其突变是遗传性AD的首要病因。然而，PS1的蛋白水解活性仍是一个有争议的问题。在这里，我们使用转染的Sf9昆虫细胞（一种缺乏内源性β-和/或γ-分泌酶活性的细胞模型）来表征BACE和PS1在人APP淀粉样生成加工中的作用。我们表明，在Sf9细胞中，BACE对APP进行预期的β-分泌酶切割，产生C99。我们还表明，作为γ-分泌酶底物的C99与人PS1紧密结合。尽管存在这种相互作用，Sf9细胞仍然不产生Aβ。这有力地反驳了PS1在APP加工中具有直接蛋白水解活性的观点，并表明PS1在将其底物运输/呈递给γ-分泌酶方面发挥作用。
