Nicastrin Is Required for Assembly of Presenilin/ -Secretase Complexes to Mediate Notch Signaling and for Processing and Trafficking of -Amyloid Precursor Protein in Mammals

Recent studies indicate that nicastrin (NCT) and presenilins form functional components of a multimeric -secretase complex required for the regulated intramembraneous proteolysis of Notch and -amyloid (A ) precursor protein (APP). To determine whether nicastrin is required for proteolytic processing of Notch and APP in mammals and the role of nicastrin in presenilin/ -secretase complex assembly, we generated nicastrin-deficient (NCT / ) mice and derived fibroblasts from NCT / embryos. Nicastrin-null embryos died by embryonic day 10.5 and exhibited several patterning defects, including abnormal somite segmentation, phenotypes that are reminiscent of embryos lacking Notch1 or both presenilins. Importantly, secretion of A peptides is abolished in NCT / fibroblasts, whereas it is reduced by 50% in NCT / cells; the failure to generate A peptides in NCT / cells is accompanied by destabilization of the presenilin/ -secretase complex and accumulation of APP–C-terminal fragments. Moreover, APP trafficking analysis in NCT / fibroblasts revealed a significant delay in the rate of APP reinternalization compared with that of control cells. Together, these results establish that nicastrin is an essential component of the multimeric -secretase complex in mammals required for both -secretase activity and APP trafficking and suggest that nicastrin may be a valuable therapeutic target for Alzheimer’s disease.