Racl changes the substrate specificity of γ-secretase between amyloid precursor protein and Notchl

Beta amyloid peptide is generated from amyloid precursor protein (APP) by proteolytic cleavage of beta- and gamma-secretases, and plays a critical role in the pathogenesis of Alzheimer's disease. Since gamma-secretase cleaves several proteins including APP and Notch in a number of cell types, it is important to understand the conditions determining gamma-secretase substrate specificity. In the present study, inhibition of Racl attenuated gamma-secretase activity for APP, resulting in decreased production of the APP intracellular domain but accumulated C-terminal fragments (APP-CTF). In contrast, Racl inhibitor, NSC23766 increased production of the Notchl intracellular domain but slightly decreased the ectodomain-shed form of Notchl (Notch Delta E). To elucidate the mechanism underlying these observations, we performed co-immunoprecipitation experiments to analyze the interaction between Racl and presenilin1 (PSI), a component of the gamma-secretase complex. Inhibition of Racl enhanced its interaction with PSI. Under the same condition, PSI interacted more strongly with Notch Delta E than with APP-CTF. Our results suggested that PSI determines the referred substrate for gamma-secretase between APP and Notchl, depending on the activation status of Racl. (c) 2008 Elsevier Inc. All rights reserved.