Pharmacological analysis of Drosophila melanogaster gamma-secretase with respect to differential proteolysis of Notch and APP

The gamma-secretase aspartyl protease is responsible for the cleavage of numerous type I integral membrane proteins, including amyloid precursor protein (APP) and Notch. APP cleavage contributes to the generation of toxic amyloid beta Peptides in Alzheimer's disease, whereas cleavage of the Notch receptor is required for normal physiological signaling between differentiating cells. Mutagenesis studies as well as in vivo analyses of Notch and APP activity in the presence of pharmacological inhibitors indicate that these substrates can be differentially modulated by inhibition of mammalian gamma-secretase, although some biochemical studies instead show nearly identical dose-response inhibitor effects on Notch and APP cleavages. Here, we examine the dose-response effects of several inhibitors on Notch and APP in Drosophila melanogaster cells, which possess a homogeneous form of gamma-secretase. Four different inhibitors that target different domains of gamma-secretase exhibit similar dose-response effects for both substrates, including rank order of inhibitor potencies and effective concentration ranges. For two inhibitors, modest differences in inhibitor dose responses toward Notch and APP were detected, suggesting that inhibitors might be identified that possess some discrimination in their ability to target alternative gamma-secretase substrates. These findings also indicate that despite an overall conservation in inhibitor potencies toward different gamma-secretase substrates, quantitative differences might exist that could be relevant for the development of therapeutically valuable substrate-specific inhibitors.