title: Aph-1 contributes to the stabilization and trafficking of the gamma-secretase complex through mechanisms involving intermolecular and intramolecular interactions.
abstract: Gamma-secretase cleaves type I transmembrane proteins, including beta-amyloid precursor protein and Notch, and requires the formation of a protein complex comprised of presenilin, nicastrin, Aph-1, and Pen-2 for its activity. Aph-1 is implicated in the stabilization of this complex, although its precise mechanistic role remains unknown. Substitution of the first glycine within the transmembrane GXXXG motif of Aph-1 causes a loss-of-function phenotype in Caenorhabditis elegans. Here, using an untranslated region-targeted RNA interference/rescue strategy in Drosophila Schneider 2 cells, we show that Aph-1 contributes to the assembly of the gamma-secretase complex by multiple mechanisms involving intermolecular and intramolecular interactions depending on or independent of the conserved glycines. Aph-1 binds to nicastrin forming an early subcomplex independent of the conserved glycines within the endoplasmic reticulum. Certain mutations in the conserved GXXXG motif affect the interaction of the Aph-1.nicastrin subcomplex with presenilin that mediates trafficking of the presenilin.Aph-1.nicastrin tripartite complex to the Golgi. The same mutations decrease the stability of Aph-1 polypeptides themselves, possibly by affecting intramolecular associations through the transmembrane domains. Our data suggest that the proper assembly of the Aph-1.nicastrin subcomplex with presenilin is the prerequisite for the trafficking as well as the enzymatic activity of the gamma-secretase complex and that Aph-1 functions as a stabilizing scaffold in the assembly of this complex.
authors.affiliation: Department of Neuropathology and Neuroscience, Graduate School of Pharmaceutical Sciences, University of Tokyo, Japan.
authors.forename: Manabu
authors.initials: M
authors.lastname: Niimura
authors.forename: Noriko
authors.initials: N
authors.lastname: Isoo
authors.forename: Nobumasa
authors.initials: N
authors.lastname: Takasugi
authors.forename: Makiko
authors.initials: M
authors.lastname: Tsuruoka
authors.forename: Kumiko
authors.initials: K
authors.lastname: Ui-Tei
authors.forename: Kaoru
authors.initials: K
authors.lastname: Saigo
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Morohashi
authors.forename: Taisuke
authors.initials: T
authors.lastname: Tomita
authors.forename: Takeshi
authors.initials: T
authors.lastname: Iwatsubo
mesh_terms: D020413:3' Untranslated Regions; D020816:Amino Acid Motifs; D053829:Amyloid Precursor Protein Secretases; D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D029721:Drosophila Proteins / Q000096:biosynthesis / Q000502:physiology*; D004331:Drosophila melanogaster / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005816:Genetic Complementation Test; D005998:Glycine / Q000737:chemistry; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism / Q000502:physiology*; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000096:biosynthesis / Q000502:physiology*; D008954:Models, Biological; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034622:RNA Interference
chemical_list: D020413:3' Untranslated Regions; C405066:APH-1 protein, C elegans; C500358:Aph-1 protein, Drosophila; D029742:Caenorhabditis elegans Proteins; D018076:DNA, Complementary; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D008565:Membrane Proteins; D010455:Peptides; D049452:Green Fluorescent Proteins; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D005998:Glycine