Nicastrin is critical for stability and trafficking but not association of other presenilin/gamma-secretase components.
gamma-Secretase, which is responsible for the intramembranous cleavage of Alzheimer beta-amyloid precursor protein and the signaling receptor Notch, is a multiprotein complex consisting of at least four components: presenilin (PS); nicastrin (Nct); APH-1 (anterior pharynx-defective-1); and presenilin enhancer-2 (PEN-2). Presenilin 1 (PS1) is known to be essential for the stability, interaction, and trafficking of the other PS1/gamma-secretase components. However, the precise functions of the other components remain elusive. Here, we investigated the functions of Nct within the PS1/gamma-secretase complex. We demonstrated that the loss of Nct expression in the embryonic fibroblast cells (Nct KO cells) results in dramatically decreased levels of APH-1, PEN-2, and PS1 fragments accompanied by a significant accumulation of full-length PS1. In the absence of Nct, PEN-2 and full-length PS1 are subjected to proteasome-mediated degradation, whereas the degradation of APH-1 is mediated by both proteasomal and lysosomal pathways. Unlike the case of wild type cells in which the gamma-secretase complex mainly locates in the trans-Golgi network, the majority of residual PEN-2, APH-1, and the uncleaved full-length PS1 in Nct KO cells reside in the endoplasmic reticulum, which remain associated with each other in the absence of Nct. Interestingly, significant amounts of full-length PS1 and PEN-2, but not APH-1, are detected on the plasma membrane in Nct KO cells, suggesting the Nct-independent cell surface delivery of the PEN-2.PS1. Finally, the diminished PEN-2 protein level in Nct-deficient cells can be partially restored by overexpression of exogenous PS1, APH-1, or PEN-2 individually or collectively, indicating a dispensable role for Nct in controlling PEN-2 level. Taken together, our study demonstrates a critical role of Nct in the stability and proper intracellular trafficking of other components of the PS1/ gamma-secretase complex but not in maintaining the association of PEN-2, APH-1, and full-length PS1.
Zhang
Yun-wu
YW
Center for Neuroscience and Aging, The Burnham Institute, La Jolla, California 92037, USA.
Luo
Wen-jie
WJ
Wang
Hong
H
Lin
Ping
P
Vetrivel
Kulandaivelu S
KS
Liao
Fang
F
Li
Feng
F
Wong
Philip C
PC
Farquhar
Marilyn G
MG
Thinakaran
Gopal
G
Xu
Huaxi
H
D053829:Amyloid Precursor Protein Secretases; D000818:Animals; D016282:Aspartic Acid Endopeptidases; D019921:Biotinylation; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D010450:Endopeptidases / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D047468:Immunoprecipitation; D007700:Kinetics; D008247:Lysosomes / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000502:physiology*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D053764:Presenilin-1; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D034622:RNA Interference; D051880:Receptors, Notch; D021601:trans-Golgi Network / Q000378:metabolism
D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C508853:PSEN1 protein, human; C469349:PSENEN protein, human; D053764:Presenilin-1; D051880:Receptors, Notch; C413604:nicastrin protein; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; C509282:Bace1 protein, mouse; D046988:Proteasome Endopeptidase Complex