Untersuchungen zur intrazellulären Lokalisation der γ-Sekretase

Alzheimer´s disease is characterized by brain deposition of
extracellular amyloid β-peptide containing plaques. The cellular
site of γ-secretase activity, which releases amyloid β-peptide and
the corresponding APP intracellular domain (AICD) remains
controversial. Proposed cleavage sites range from the endoplasmic
reticulum, the Golgi apparatus, the cell surface to endosomal
compartments. We now used C99-GFP, a fluorescent reporter substrate
for γ-secretase activity and monitored AICD production in living
cells. C99-GFP is efficiently cleaved by γ-secretase and AICD-GFP
is released into the cytosol. Inhibiting γ-secretase results in
accumulation of C99-GFP in early endosomes. By blocking selective
transport steps along the secretory pathway we demonstrate that
γ-secretase does not cleave its substrates in the endoplasmic
reticulum, the Golgi/trans-Golgi network or in secretory vesicles.
In contrast, inhibition of endocytosis did not inhibit cleavage of
C99-GFP. Similar results were obtained for another γ-secretase
substrate, NotchΔE. Our results suggest that intracellular domains
are generated by γ-secretase at the plasma membrane and/or early
endosomes.