Subcellular Compartment and Molecular Subdomain of β-Amyloid Precursor Protein Relevant to the Aβ42-promoting Effects of Alzheimer Mutant Presenilin 2

Abstract

Increased production of amyloid β peptides ending at position 42 (Aβ42) is one of the pathogenic phenotypes caused by mutant forms of presenilins (PS) linked to familial Alzheimer's disease. To identify the subcellular compartment(s) in which familial Alzheimer's disease mutant PS2 (mt PS2) affects the γ-cleavage of βAPP to increase Aβ42, we co-expressed the C-terminal 99-amino acid fragment of βAPP (C100) tagged with sorting signals to the endoplasmic reticulum (C100/ER) or to the trans-Golgi network (C100/TGN) together with mt PS2 in N2a cells. C100/TGN co-transfected with mt PS2 increased levels or ratios of intracellular as well as secreted Aβ42 at similar levels to those with C100 without signals (C100/WT), whereas C100/ER yielded a negligible level of Aβ, which was not affected by co-transfection of mt PS2. To identify the molecular subdomain of βAPP required for the effects of mt PS2, we next co-expressed C100 variously truncated at the C-terminal cytoplasmic domain together with mt PS2. All types of C-terminally truncated C100 variants including that lacking the entire cytoplasmic domain yielded the secreted form of Aβ3 at levels comparable with those from C100/WT, and co-transfection of mt PS2 increased the secretion of Aβ42. These results suggest that (i) late intracellular compartments including TGN are the major sites in which Aβ42 is produced and up-regulated by mt PS2 and that (ii) the anterior half of C100 lacking the entire cytoplasmic domain is sufficient for the overproduction of Aβ42 caused by mt PS2.