AbstractWe recently demonstrated that the presenilin‐dependent γ‐secretase complex regulates the expression and activity of neprilysin, one of the main enzymes that degrade the amyloid β‐peptide (Aβ) which accumulates in Alzheimer's disease. Here, we examined the influence of endogenous nicastrin (NCT), a member of the γ‐secretase complex, on neprilysin physiology. We show that nicastrin deficiency drastically lowers neprilysin expression, membrane‐bound activity and mRNA levels, but it did not modulate the expression of two other putative Aβ‐cleaving enzymes, endothelin‐converting enzyme and insulin‐degrading enzyme. Furthermore, we show that nicastrin restores neprilysin activity and expression in nicastrin‐deficient, but not presenilin‐deficient fibroblasts, indicating that the control of neprilysin necessitates the complete γ‐secretase complex harbouring its four reported components. Finally, we show that NCT expression peaked 24 h after NCT cDNA transfection of wild‐type and NCT–/– fibroblasts, while neprilysin expression drastically increased only after 36 h and was maximal at 48 h. This delayed effect on neprilysin expression correlates well with our demonstration of an indirect γ‐secretase‐dependent modulation of neprilysin at its transcriptional level.