RNA interference silencing of the adaptor molecules ShcC and Fe65 differentially affect amyloid precursor protein processing and Aβ generation

The amyloid precursor protein (APP) and its pathogenic by-product amyloid-beta protein (A beta) play central roles in Alzheimer disease (AD) neuropathogenesis. APP can be cleaved by beta-secretase (BACE) and alpha-secretase to produce APP-C99 and APP-C83. These C-terminal fragments can then be cleaved by gamma-secretase to produce A beta and p3, respectively. p3 has been reported to promote apoptosis, and A beta is the key component of senile plaques in AD brain. APP adaptor proteins with phosphotyrosine-binding domains, including ShcA (SHC1), ShcC (SHC3), and Fe65 (APBB1), can bind to and interact with the conserved YENPTY motif in the APP-C terminus. Here we have described for the first time the effects of RNA interference (RNAi) silencing of ShcA, ShcC, and Fe65 expression on APP processing and A beta production. RNAi silencing of ShcC led to reductions in the levels of APP-C-terminal fragments (APP-CTFs) and A beta in H4 human neuroglioma cells stably overexpressing full-length APP (H4-FL-APP cells) but not in those expressing APP-C99 (H4-APP-C99 cells). RNAi silencing of ShcC also led to reductions in BACE levels in H4-FL-APP cells. In contrast, RNAi silencing of the homologue ShcA had no effect on APP processing or A beta levels. RNAi silencing of Fe65 increased APP-CTF levels, although also decreasing A beta levels in H4-FL-APP cells. These findings suggest that pharmacologically blocking interaction of APP with ShcC and Fe65 may provide novel therapeutic strategies against AD.