APPε, the ε-secretase-derived N-terminal product of the β-amyloid precursor protein, behaves as a type I protein and undergoes α-, β-, and γ-secretase cleavages

beta-Amyloid peptide accumulates in the brain of patients affected by sporadic or familial forms of Alzheimer's disease. It derives from the proteolytic attacks of the beta-amyloid precursor protein (beta APP) by beta- and gamma-secretase activities. An additional epsilon cleavage taking place a few residues C-terminal to the gamma-site has been reported, leading to the formation of an intracellular fragment referred to as APP intracellular domain C50. This epsilon cleavage received particular attention because it resembles the S3 Notch cleavage generating Notch intracellular domain. Indeed, APP intracellular domain, like its Notch counterpart, appears to mediate important physiological functions. gamma and epsilon cleavages on beta APP appear spatio-temporally linked but pharmacologically distinct and discriminable by mutagenesis approaches. As these cleavages could be seen as either deleterious (gamma-site) or beneficial (epsilon-site), it appears of most interest to set up models aimed at studying these activities separately, particularly to design specific and bioavailable inhibitors. On the other hand, it is important to respect the topology of the substrates in order to examine physiologically relevant cleavages. Here we describe the obtention of cells overexpressing APP epsilon, the epsilon-secretase-derived N-terminal fragment of beta APP. Interestingly, this N-terminal fragment of beta APP was shown by biochemical and immunohistochemical approaches to behave as a genuine membrane-bound protein. APP epsilon undergoes constitutive and protein kinase C-regulated alpha-secretase cleavages. Furthermore, APP epsilon is targeted by the beta-secretase beta-site APP-cleaving enzyme and is subsequently cleaved by gamma-secretase. The resulting beta-amyloid peptide production is fully prevented by various gamma-secretase inhibitors. Altogether, our study shows that APP epsilon is a relevant beta APP derivative to study gamma-secretase activities and to design specific inhibitors without facing any rate-limiting effect of epsilon-secretase-derived cleavage.