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 sta bly transfected into Chinese hamster ovary cells that overexpress the beta-amyloid precursor protein (APP), The identity of the 43-45-kDa PS 1 holoproteins was confirmed by N-terminal padiosequencing. PS1 was ra pidly processed (t(1/2) = 40 min) in the endoplasmic reticulum into st able fragments, Wild-type and mutant PS2 holoproteins exhibited simila r halflives (1.5 h); however, their endoproteolytic fragments showed b oth mutation-specific and cell type specific differences, Mutant PS1 o r 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 amy loid beta-protein (A beta(42)) as determined by quantitative immunopre cipitation 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 t he elevation of A beta(42). We conclude that mutant PS1 and PS2 protei ns enhance the proteolysis of beta-amyloid precursor protein by the ga mma-secretase cleaving at A beta residue 42, thereby promoting amyloid ogenesis.