The Role of Presenilin-1 in the γ-Secretase Cleavage of the Amyloid Precursor Protein of Alzheimer's Disease

Rachid Essalmani,Christian Czech,Jean Menager,Luc Mercken,Bernadette Tasiaux,Jean-Noël Octave

doi:10.1074/jbc.275.3.1525

Abstract

Presenilin-1 (PS1) is required for the release of the intracellular domain of Notch from the plasma membrane as well as for the cleavage of the amyloid precursor protein (APP) at the gamma-secretase cleavage site. It remains to be demonstrated whether PS1 acts by facilitating the activity of the protease concerned or is the protease itself. PS1 could have a gamma-secretase activity by itself or could traffic APP and Notch to the appropriate cellular compartment for processing. Human APP 695 and PS1 were coexpressed in Sf9 insect cells, in which endogenous gamma-secretase activity is not detected. In baculovirus-infected Sf9 cells, PS1 undergoes endoproteolysis and interacts with APP. However, PS1 does not cleave APP in Sf9 cells. In CHO cells, endocytosis of APP is required for Abeta secretion. Deletion of the cytoplasmic sequence of APP (APPDeltaC) inhibits both APP endocytosis and Abeta production. When APPDeltaC and PS1 are coexpressed in CHO cells, Abeta is secreted without endocytosis of APP. Taken together, these results conclusively show that, although PS1 does not cleave APP in Sf9 cells, PS1 allows the secretion of Abeta without endocytosis of APP by CHO cells.

Highlights

Presenilin-1 (PS1) is required for the release of the intracellular domain of Notch from the plasma membrane as well as for the cleavage of the amyloid precursor protein (APP) at the ␥-secretase cleavage site
These results conclusively show that, PS1 does not cleave APP in Sf9 cells, PS1 allows the secretion of A␤ without endocytosis of APP by CHO cells
When PS1 was produced in CHO cells expressing APP⌬C, a significant A␤ secretion was measured (Fig. 4, c and d). This A␤ production did not result from APP⌬C internalization, because PS1 did not induce endocytosis of APP⌬C (Fig. 2a). This extracellular A␤ production was lower than that measured in CHO cells expressing the full-length APP, these results clearly demonstrate that PS1 allows secretion of A␤ without endocytosis of APP by CHO cells

Summary

The abbreviations used are

A␤, amyloid peptide; APP, amyloid precursor protein; APP⌬C, APP without the cytoplasmic sequence; PS, presenilin; PAGE, polyacrylamide gel electrophoresis; CHO, Chinese hamster ovary cell. Uble N-terminal domain of APP containing the first 17 amino acids of A␤ Another fraction of newly synthesized APP appears at the plasma membrane. Following endocytosis of this transmembrane APP, the cleavage by ␤-secretase at the N terminus of A␤ generates a C-terminal fragment of APP that contains the entire A␤ sequence. The recent demonstration that PS1 deficiency reduces the proteolytic release of the Notch intracellular domain indicates that PS1 regulates both APP processing and Notch signaling by influencing protein cleavage events (8 –11). Human APP expressed by insect cells is cleaved by an ␣-secretase activity generating a C-terminal fragment of APP identical to that produced in mammalian cells [14]. In CHO cells, PS1 allows the secretion of A␤ without endocytosis of APP

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION