gamma-Secretase activity requires the presenilin-dependent trafficking of nicastrin through the Golgi apparatus but not its complex glycosylation.
Nicastrin and presenilin are two major components of the gamma-secretase complex, which executes the intramembrane proteolysis of type I integral membrane proteins such as the amyloid precursor protein (APP) and Notch. Nicastrin is synthesized in fibroblasts and neurons as an endoglycosidase-H-sensitive glycosylated precursor protein (immature nicastrin) and is then modified by complex glycosylation in the Golgi apparatus and by sialylation in the trans-Golgi network (mature nicastrin). These modifications are not observed with exogenously overexpressed nicastrin. Under normal cell culture conditions, only mature nicastrin is expressed at the cell surface and binds to the presenilin heterodimers. Mature nicastrin has a half-life of more than 24 hours. In the absence of presenilin 1 and 2, nicastrin remains entirely endoglycosidase H sensitive, is retained in the endoplasmic reticulum and is slowly degraded. Single presenilin 1 or presenilin 2 deficiency affects glycosylation of nicastrin to a lesser extent than the combined presenilin deficiencies, suggesting a correlation between either the transport of nicastrin out of the endoplasmic reticulum or the concomitant complex glycosylation of nicastrin, and gamma-secretase activity. However, when complex glycosylation of nicastrin was inhibited using mannosidase I inhibitors, gamma-secretase cleavage of APP or Notch was not inhibited and the immature nicastrin still associates with presenilin and appears at the cell surface. Complex glycosylation of nicastrin is therefore not needed for gamma-secretase activity. Because the trafficking of nicastrin to the Golgi apparatus is dependent on presenilins, our data point to a central role of presenilin in nicastrin maturation/localization, which could help to partially resolve the 'spatial paradox'.
Herreman
An
A
Laboratory for Neuronal Cell Biology, Center for Human Genetics, Gasthuisberg/KULeuven and Flanders Interuniversity Institute for Biotechnology (VIB), Herestraat 49, 3000 Leuven, Belgium.
Van Gassen
Geert
G
Bentahir
Mustapha
M
Nyabi
Omar
O
Craessaerts
Katleen
K
Mueller
Ulrike
U
Annaert
Wim
W
De Strooper
Bart
B
D000544:Alzheimer Disease / Q000378:metabolism; D053829:Amyloid Precursor Protein Secretases; D000818:Animals; D016282:Aspartic Acid Endopeptidases; D002478:Cells, Cultured; D010450:Endopeptidases / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology; D015870:Gene Expression; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000166:cytology; D008358:Mannose / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D009474:Neurons / Q000166:cytology / Q000201:enzymology*; D009844:Oligosaccharides / Q000378:metabolism; D053764:Presenilin-1; D053766:Presenilin-2
D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009844:Oligosaccharides; C508853:PSEN1 protein, human; C508861:PSEN2 protein, human; D053764:Presenilin-1; D053766:Presenilin-2; C413604:nicastrin protein; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; C509282:Bace1 protein, mouse; D008358:Mannose