Presenilin-1 affects trafficking and processing of βAPP and is targeted in a complex with nicastrin to the plasma membrane

A myloid beta-peptide (Abeta) is generated by the consecutive cleavages of beta- and gamma-secretase. The intramembraneous gamma-secretase cleavage critically depends on the activity of presenilins (PS1 and PS2). Although there is evidence that PSs are aspartyl proteases with gamma-secretase activity, it remains controversial whether their subcellular localization overlaps with the cellular sites of Abeta production. We now demonstrate that biologically active GFP-tagged PSI as well as endogenous PS1 are targeted to the plasma membrane (PM) of living cells. On the way to the PM, PS1 binds to nicastrin (Nct), an essential component of the gamma-secretase complex. This complex is targeted through the secretory pathway where PS1-bound Nct becomes endoglycosidase H resistant. Moreover, surface-biotinylated Nct can be coimmunoprecipitated with PS1 antibodies, demonstrating that this complex is located to cellular sites with gamma-secretase activity. Inactivating PS1 or PS2 function by mutagenesis of one of the critical aspartate residues or by gamma-secretase inhibitors results in delayed reinternalization of the beta-amyloid precursor protein and its accumulation at the cell surface. Our data suggest that PS is targeted as a biologically active complex with Nct through the secretory pathway to the cell surface and suggest a dual function of PS in gamma-secretase processing and in trafficking.