title: Pen-2 is sequestered in the endoplasmic reticulum and subjected to ubiquitylation and proteasome-mediated degradation in the absence of presenilin.
abstract: The gamma-secretase complex catalyzes intramembrane proteolysis of a number of transmembrane proteins, including amyloid precursor protein, Notch, ErbB4, and E-cadherin. gamma-Secretase is known to contain four major protein constituents: presenilin (PS), nicastrin, Aph-1, and Pen-2, all of which are integral membrane proteins. There is increasing evidence that the formation of the complex and the stability of the individual components are tightly controlled in the cell, assuring correct composition of functional complexes. In this report, we investigate the topology, localization, and mechanism for destabilization of Pen-2 in relation to PS function. We show that PS1 regulates the subcellular localization of Pen-2: in the absence of PS, Pen-2 is sequestered in the endoplasmic reticulum (ER) and not transported to post-ER compartments, where the mature gamma-secretase complexes reside. PS deficiency also leads to destabilization of Pen-2, which is alleviated by proteasome inhibitors. In keeping with this, we show that Pen-2, which adopts a hairpin structure with the N and C termini facing the luminal space, is ubiquitylated prior to degradation and presumably retrotranslocated from the ER to the cytoplasm. Collectively, our data suggest that failure to become incorporated into the gamma-secretase complex leads to degradation of Pen-2 through the ER-associated degradation-proteasome pathway.
authors.affiliation: Department of Neurotec, Karolinska Institutet, Section for Experimental Geriatrics, Novum, SE-141 86 Huddinge, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Bergman
authors.forename: Emil M
authors.initials: EM
authors.lastname: Hansson
authors.forename: Sharon E
authors.initials: SE
authors.lastname: Pursglove
authors.forename: Mark R
authors.initials: MR
authors.lastname: Farmery
authors.forename: Lars
authors.initials: L
authors.lastname: Lannfelt
authors.forename: Urban
authors.initials: U
authors.lastname: Lendahl
authors.forename: Johan
authors.initials: J
authors.lastname: Lundkvist
authors.forename: Jan
authors.initials: J
authors.lastname: Näslund
mesh_terms: D053829:Amyloid Precursor Protein Secretases; D000818:Animals; D016282:Aspartic Acid Endopeptidases; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D021381:Protein Transport; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D009097:Multienzyme Complexes; C469349:PSENEN protein, human; D014452:Ubiquitins; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; D046988:Proteasome Endopeptidase Complex