Enhanced production and oligomerization of the 42-residue amyloid beta-protein by Chinese hamster ovary cells stably expressing mutant presenilins

Mutations in the presenilin 1 (PS1) and presenilin 2 (PS2) genes cause the most common and aggressive form of early onset familial Alzheimer's disease, To elucidate their pathogenic mechanism, wild-type (wt) or mutant (M146L, C410Y) PS1 and wt or mutant (M239V) PS2 genes were stably transfected into Chinese hamster ovary cells that overexpress the beta-amyloid precursor protein (APP), The identity of the 43-45-kDa PS1 holoproteins was confirmed by N-terminal padiosequencing. PS1 was rapidly processed (t(1/2) = 40 min) in the endoplasmic reticulum into stable fragments, Wild-type and mutant PS2 holoproteins exhibited similar halflives (1.5 h); however, their endoproteolytic fragments showed both mutation-specific and cell type specific differences, Mutant PS1 or PS2 consistently induced a 1.4-2.5-fold increase (p < 0.001) in the relative production of the highly amyloidogenic 42-residue form of amyloid beta-protein (A beta(42)) as determined by quantitative immunoprecipitation and by enzyme-linked immunosorbent assay, In mutant PS1 and PS2 cell lines with high increases in A beta(42)/A beta(total) ratios, spontaneous formation of low molecular weight oligomers of A beta(42) was observed in media, suggesting enhanced A beta aggregation from the elevation of A beta(42). We conclude that mutant PS1 and PS2 proteins enhance the proteolysis of beta-amyloid precursor protein by the gamma-secretase cleaving at A beta residue 42, thereby promoting amyloidogenesis.