The Alternatively Spliced Kunitz Protease Inhibitor Domain Alters Amyloid β Protein Precursor Processing and Amyloid β Protein Production in Cultured Cells
The insoluble amyloid deposited extracellularly in the brains of patients with Alzheimer's disease (AD) is composed of amyloid β protein, a â¼4-kDa secreted protein that is derived from a set of large proteins collectively referred to as the amyloid β protein precursor (βAPP). During normal...
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Veröffentlicht in: | The Journal of biological chemistry 1996-11, Vol.271 (48), p.30929 |
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Zusammenfassung: | The insoluble amyloid deposited extracellularly in the brains of patients with Alzheimer's disease (AD) is composed of amyloid
β protein, a â¼4-kDa secreted protein that is derived from a set of large proteins collectively referred to as the amyloid
β protein precursor (βAPP). During normal processing the βAPP is cleaved by β secretase, producing a large NH 2 -terminal secreted derivative (sAPPβ) and a COOH-terminal fragment beginning at Aβ1, which is subsequently cleaved by γ secretase
releasing secreted Aβ. Most secreted Aβ is Aβ1-40, but â¼10% of secreted Aβ is Aβ1-42. Alternative βAPP cleavage by α secretase
produces a slightly longer NH 2 -terminal secreted derivative (sAPPα) and a COOH-terminal fragment beginning at Aβ17, which is subsequently cleaved by γ secretase
releasing a â¼3-kDa secreted form of Aβ (P3). Several of the βAPP isoforms that are produced by alternative splicing contain
a 56-amino acid Kunitz protease inhibitor (KPI) domain known to inhibit proteases such as trypsin and chymotrypsin. To determine
whether the KPI domain influences the proteolytic cleavages that generate Aβ, we compared Aβ production in transfected cells
expressing human KPI-containing βAPP751 or KPI-free βAPP695. We focused on Aβs ending at Aβ42 because these forms appear to
be most relevant to AD. Using specific sandwich enzyme-linked immunosorbent assays, we analyzed full-length Aβ1-42 and total
Aβ ending at Aβ42 (Aβ1-42 + P3(42)). In addition, we analyzed the large secreted derivatives produced by α secretase (sAPPα)
and β secretase (sAPPβ). In mouse teratocarcinoma (P19) cells expressing βAPP695 or βAPP751, expression of the KPI-containing
βAPP751 resulted in the secretion of a lower percentage of P3(42) and sAPPα and a correspondingly higher percentage of Aβ1-42
and sAPPβ. Similar results were obtained in human embryonic kidney (293) cells. These results indicate that expression of
the KPI domain reduces α secretase cleavage so that less P3 and relatively more full-length Aβ are produced. Thus, in human
brain and in animal models of AD, the amount of KPI-containing βAPP produced may be an important factor influencing Aβ deposition. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1074/jbc.271.48.30929 |