title: Different cofactor activities in gamma-secretase assembly: evidence for a nicastrin-Aph-1 subcomplex.
abstract: The gamma-secretase complex is required for intramembrane cleavage of several integral membrane proteins, including the Notch receptor, where it generates an active signaling fragment. Four putative gamma-secretase components have been identified-presenilin (Psn), nicastrin (Nct), Aph-1, and Pen-2. Here, we use a stepwise coexpression approach to investigate the role of each new component in gamma-secretase assembly and activation. Coexpression of all four proteins leads to high level accumulation of mature Psn and increased proteolysis of Notch. Aph-1 and Nct may form a subcomplex that stabilizes the Psn holoprotein at an early step in gamma-secretase assembly. Subcomplex levels of Aph-1 are down-regulated by stepwise addition of Psn, suggesting that Aph-1 might not enter the mature complex. In contrast, Pen-2 accumulates proportionally with Psn, and is associated with Psn endoproteolysis during gamma-secretase assembly. These results demonstrate that Aph-1 and Pen-2 are essential cofactors for Psn, but that they play different roles in gamma-secretase assembly and activation.
authors.affiliation: University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
authors.forename: Yue
authors.initials: Y
authors.lastname: Hu
authors.forename: Mark E
authors.initials: ME
authors.lastname: Fortini
mesh_terms: D053829:Amyloid Precursor Protein Secretases; D000818:Animals; D029742:Caenorhabditis elegans Proteins; D029721:Drosophila Proteins / Q000378:metabolism; D004331:Drosophila melanogaster / Q000166:cytology / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D009154:Mutation; D053764:Presenilin-1; D051880:Receptors, Notch; D015398:Signal Transduction
chemical_list: C405066:APH-1 protein, C elegans; D029742:Caenorhabditis elegans Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C497759:N protein, Drosophila; C473290:Pen-2 protein, Drosophila; D053764:Presenilin-1; D051880:Receptors, Notch; C413604:nicastrin protein; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases