Inhibiting amyloid precursor protein C-terminal cleavage promotes an interaction with presenilin 1

Presenilin 1 (PS1) plays a pivotal role in the production of the amyloid-be ta protein, which is central to the pathogenesis of Alzheimer's disease. It has been demonstrated that PS1 regulates the gamma-secretase proteolysis o f the amyloid precursor protein (APP) C-terminal fragment (APP-C100), which is the final step in amyloid-beta protein production. The mechanism and de tailed pathway of this PS1 activity has yet to be fully resolved, but it ma y be due to a presenilin-controlled trafficking of the APP fragment or poss ibly an inherent PS1 proteolytic activity. We have investigated the possibi lity of a direct interaction of PS1 and the APP-C100 within the high molecu lar mass presenilin complex. However, the APP-C100 is rapidly degraded, and if it forms, then any PS1-APP complex is likely to be very transitory. To circumvent this problem, we have utilized the protease inhibitor N-acetyl-l eucyl-norleucinal (LLnL) and the lysosomotropic agent NH4Cl, which inhibits the turnover of the APP-C100, Under these conditions, levels of the fragme nt increased appreciably, and as shown by glycerol gradient analysis, the A PP-C100 shifted to a higher molecular mass complex that overlapped with PS1 . Immunoprecipitation studies demonstrated that a significant population of the APP-C100 co-precipitated with PS1. These findings suggest that PSI may mediate the shuttling of APP fragments and/or facilitate their presentatio n for gamma-secretase cleavage through a direct interaction.