Presenilin 1 Stabilizes the C-terminal Fragment of the Amyloid Precursor Protein Independently of γ-Secretase Activity*
Presenilin 1 Stabilizes the C-terminal Fragment of the Amyloid Precursor Protein Independently of γ-Secretase Activity*
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早老素 1 可稳定淀粉样前体蛋白的 C 末端片段，与 γ 分泌酶活性无关*
DOI：
10.1074/jbc.m312710200
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发表时间：
2004
影响因子：
4.8
通讯作者：
J. Octave
中科院分区：
文献类型：
--
作者：
D. Pitsi;J. Octave
β-分泌酶对跨膜淀粉样前体蛋白(APP)的切割使APP的C末端片段C99锚定在质膜上。C99随后被γ-分泌酶处理，这是一种不寻常的天冬氨酸蛋白酶活性，在很大程度上依赖于早老素(PS)，产生积累在阿尔茨海默病患者大脑中的淀粉样蛋白β-肽(Aβ)。有人认为PS蛋白是这种蛋白分解活性的催化核心，但也发现了一些其他蛋白质对γ-分泌酶的切割是必需的。PS在γ分泌酶活性中的确切作用仍然存在争议，因为缺乏PS的细胞仍然会产生某些形式的Aβ。在这里，我们使用表达C99的昆虫细胞来证明，与C99结合的早老素1的表达不仅增加了这些细胞产生Aβ，而且同样程度地增加了细胞内C99的水平。通过脉冲追逐实验，我们确定这是由于表达PS1的细胞中C99的半衰期增加所致。在从全长人APP产生C99的中国仓鼠卵巢细胞中，也观察到了类似的结果。最后，我们证明了γ分泌酶的功能性抑制剂不会改变pS1增加细胞内C99水平的能力。这一发现表明，PS1与C99的结合并不一定导致其立即被γ分泌酶切割，这可能是一种时空调节或诱导的事件，并为PS1上存在底物对接位点提供了生化证据。
The cleavage of the transmembrane amyloid precursor protein (APP) by β-secretase leaves the C-terminal fragment of APP, C99, anchored in the plasma membrane. C99 is subsequently processed by γ-secretase, an unusual aspartyl protease activity largely dependent on presenilin (PS), generating the amyloid β-peptide (Aβ) that accumulates in the brain of patients with Alzheimer's disease. It has been suggested that PS proteins are the catalytic core of this proteolytic activity, but a number of other proteins mandatory for γ-secretase cleavage have also been discovered. The exact role of PS in the γ-secretase activity remains a matter of debate, because cells devoid of PS still produce some forms of Aβ. Here, we used insect cells expressing C99 to demonstrate that the expression of presenilin 1 (PS1), which binds C99, not only increases the production of Aβ by these cells but also increases the intracellular levels of C99 to the same extent. Using pulse-chase experiments, we established that this results from an increased half-life of C99 in cells expressing PS1. In Chinese hamster ovary cells producing C99 from full-length human APP, similar results were observed. Finally, we show that a functional inhibitor of γ-secretase does not alter the ability of PS1 to increase the intracellular levels of C99. This finding suggests that the binding of PS1 to C99 does not necessarily lead to its immediate cleavage by γ-secretase, which could be a spatio-temporally regulated or an induced event, and provides biochemical evidence for the existence of a substrate-docking site on PS1.