The discrepancy between presenilin subcellular localization and gamma-secretase processing of amyloid precursor protein.
We investigated the relationship between PS1 and gamma-secretase processing of amyloid precursor protein (APP) in primary cultures of neurons. Increasing the amount of APP at the cell surface or towards endosomes did not significantly affect PS1-dependent gamma-secretase cleavage, although little PS1 is present in those subcellular compartments. In contrast, almost no gamma-secretase processing was observed when holo-APP or APP-C99, a direct substrate for gamma-secretase, were specifically retained in the endoplasmic reticulum (ER) by a double lysine retention motif. Nevertheless, APP-C99-dilysine (KK) colocalized with PS1 in the ER. In contrast, APP-C99 did not colocalize with PS1, but was efficiently processed by PS1-dependent gamma-secretase. APP-C99 resides in a compartment that is negative for ER, intermediate compartment, and Golgi marker proteins. We conclude that gamma-secretase cleavage of APP-C99 occurs in a specialized subcellular compartment where little or no PS1 is detected. This suggests that at least one other factor than PS1, located downstream of the ER, is required for the gamma-cleavage of APP-C99. In agreement, we found that intracellular gamma-secretase processing of APP-C99-KK both at the gamma40 and the gamma42 site could be restored partially after brefeldin A treatment. Our data confirm the "spatial paradox" and raise several questions regarding the PS1 is gamma-secretase hypothesis.
Cupers
P
P
Center for Human Genetics, Neuronal Cell Biology Group, Flanders Interuniversity Institute for Biotechnology and Catholic University of Leuven, B-3000 Leuven, Belgium.
Bentahir
M
M
Craessaerts
K
K
Orlans
I
I
Vanderstichele
H
H
Saftig
P
P
De Strooper
B
B
Annaert
W
W
D053829:Amyloid Precursor Protein Secretases; D016564:Amyloid beta-Protein Precursor / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D016282:Aspartic Acid Endopeptidases; D002451:Cell Compartmentation; D002478:Cells, Cultured; D010450:Endopeptidases / Q000302:isolation & purification / Q000378:metabolism*; D004721:Endoplasmic Reticulum; D006056:Golgi Apparatus; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D009474:Neurons / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D053764:Presenilin-1; D011499:Protein Processing, Post-Translational; D021381:Protein Transport / Q000235:genetics
D016564:Amyloid beta-Protein Precursor; D008565:Membrane Proteins; D053764:Presenilin-1; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509282:Bace1 protein, mouse