The transcriptionally active amyloid precursor protein (APP) intracellular domain is preferentially produced from the 695 isoform of APP in a β-secretase-dependent pathway

Amyloidogenic processing of the amyloid precursor protein (APP) by β- and γ-secretases generates several biologically active products, including amyloid-β (Aβ) and the APP intracellular domain (AICD). AICD regulates transcription of several neuronal genes, especially the Aβ-degrading enzyme, neprilysin (NEP). APP exists in several alternatively spliced isoforms, APP695, APP751, and APP770. We have examined whether each isoform can contribute to AICD generation and hence up-regulation of NEP expression. Using SH-SY5Y neuronal cells stably expressing each of the APP isoforms, we observed that only APP695 up-regulated nuclear AICD levels (9-fold) and NEP expression (6-fold). Increased NEP expression was abolished by a β- or γ-secretase inhibitor but not an α-secretase inhibitor. This correlated with a marked increase in both Aβ1-40 and Aβ1-42 in APP695 cells as compared with APP751 or APP770 cells. Similar phenomena were observed in Neuro2a but not HEK293 cells. SH-SY5Y cells expressing the Swedish mutant of APP695 also showed an increase in Aβ levels and NEP expression as compared with wild-type APP695 cells. Chromatin immunoprecipitation revealed that AICD was associated with the NEP promoter in APP695, Neuro2a, and APPSwe cells but not APP751 nor APP770 cells where AICD was replaced by histone deacetylase 1 (HDAC1). AICD occupancy of the NEP promoter was replaced by HDAC1 after treatment of the APP695 cells with a β- but not an α-secretase inhibitor. The increased AICD and NEP levels were significantly reduced in cholesterol-depleted APP695 cells. In conclusion, Aβ and functional AICD appear to be preferentially synthesized through β-secretase action on APP695. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.