Dual Role of α-Secretase Cleavage in the Regulation of γ-Secretase Activity for Amyloid Production

Yuan Tian,Christina J. Crump,Yue-Ming Li

doi:10.1074/jbc.m110.128439

Yuan Tian, Christina J. Crump + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m110.128439

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Abstract

Processing of the amyloid precursor protein (APP) by β- and γ-secretases generates pathogenic β-amyloid (Aβ) peptides associated with Alzheimer disease (AD), whereas cleavage of APP by α-secretases precludes Aβ formation. Little is known about the role of α-secretase cleavage in γ-secretase regulation. Here, we show that α-secretase-cleaved APP C-terminal product (αCTF) functions as an inhibitor of γ-secretase. We demonstrate that the substrate inhibitory domain (ASID) within αCTF, which is bisected by the α-secretase cleavage site, contributes to this negative regulation because deleting or masking this domain turns αCTF into a better substrate for γ-secretase. Moreover, α-secretase cleavage can potentiate the inhibitory effect of ASID. Inhibition of γ-secretase activity by αCTF is observed in both in vitro and cellular systems. This work reveals an unforeseen role for α-secretase in generating an endogenous γ-secretase inhibitor that down-regulates the production of Aβ. Deregulation of this feedback mechanism may contribute to the pathogenesis of AD.

Highlights

Second intramembrane cleavage is dependent on the first cleavage, such as in Notch and sterol regulatory element binding proteins signaling
A distinctive feature of amyloid precursor protein (APP) processing compared with other regulated intramembrane proteolysis (RIP) is the existence of two proteases (␤- and ␣-secretase) that are both capable of executing the first cleavage
It has been reported that Alzheimer disease (AD) patients have reduced levels of ␣-secretase activity relative to that of healthy controls, but there was no difference in the level of sAPP␤ [15, 16], which results from ␤-secretase cleavage

Summary

EXPERIMENTAL PROCEDURES

Expression of Biotinylated Recombinant Proteins—AviTag, a specific peptide sequence that can be biotinylated with biotin ligase, was cloned into a pIAD16 vector [18] to generate a pIAD16Avi plasmid. APP fragments with FLAG tag were inserted into the pIAD16Avi vector. For expression of biotinylated protein, pIAD16Avi-APP and pACYC164, which encodes biotin ligase, were co-transformed in BL21 (DE3) cells

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RESULTS

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DISCUSSION