title: Turnover of C99 is controlled by a crosstalk between ERAD and ubiquitin-independent lysosomal degradation in human neuroglioma cells.
abstract: Alzheimer's disease (AD) is characterized by the buildup of amyloid-β peptides (Aβ) aggregates derived from proteolytic processing of the β-amyloid precursor protein (APP). Amyloidogenic cleavage of APP by β-secretase/BACE1 generates the C-terminal fragment C99/CTFβ that can be subsequently cleaved by γ-secretase to produce Aβ. Growing evidence indicates that high levels of C99/CTFβ are determinant for AD. Although it has been postulated that γ-secretase-independent pathways must control C99/CTFβ levels, the contribution of organelles with degradative functions, such as the endoplasmic reticulum (ER) or lysosomes, is unclear. In this report, we investigated the turnover and amyloidogenic processing of C99/CTFβ in human H4 neuroglioma cells, and found that C99/CTFβ is localized at the Golgi apparatus in contrast to APP, which is mostly found in endosomes. Conditions that localized C99/CTFβ to the ER resulted in its degradation in a proteasome-dependent manner that first required polyubiquitination, consistent with an active role of the ER associated degradation (ERAD) in this process. Furthermore, when proteasomal activity was inhibited C99/CTFβ was degraded in a chloroquine (CQ)-sensitive compartment, implicating lysosomes as alternative sites for its degradation. Our results highlight a crosstalk between degradation pathways within the ER and lysosomes to avoid protein accumulation and toxicity.
authors.affiliation: Department of Physiology, School of Medicine and Centro de Investigación Sur-Austral en Enfermedades del Sistema Nervioso, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Hianara A
authors.initials: HA
authors.lastname: Bustamante
authors.affiliation: Department of Physiology, School of Medicine and Centro de Investigación Sur-Austral en Enfermedades del Sistema Nervioso, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Andrés
authors.initials: A
authors.lastname: Rivera-Dictter
authors.affiliation: Department of Physiology, School of Medicine and Centro de Investigación Sur-Austral en Enfermedades del Sistema Nervioso, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Viviana A
authors.initials: VA
authors.lastname: Cavieres
authors.affiliation: Department of Physiology, School of Medicine and Centro de Investigación Sur-Austral en Enfermedades del Sistema Nervioso, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Vanessa C
authors.initials: VC
authors.lastname: Muñoz
authors.affiliation: Department of Physiology, School of Medicine and Centro de Investigación Sur-Austral en Enfermedades del Sistema Nervioso, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Alexis
authors.initials: A
authors.lastname: González
authors.affiliation: Department of Physiology, School of Medicine and Centro de Investigación Sur-Austral en Enfermedades del Sistema Nervioso, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Yimo
authors.initials: Y
authors.lastname: Lin
authors.affiliation: Department of Physiology, School of Medicine and Centro de Investigación Sur-Austral en Enfermedades del Sistema Nervioso, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Gonzalo A
authors.initials: GA
authors.lastname: Mardones
authors.affiliation: Department of Physiology, School of Medicine and Centro de Investigación Sur-Austral en Enfermedades del Sistema Nervioso, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Patricia V
authors.initials: PV
authors.lastname: Burgos
mesh_terms: D000595:Amino Acid Sequence; D053829:Amyloid Precursor Protein Secretases / Q000235:genetics / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D016282:Aspartic Acid Endopeptidases / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002738:Chloroquine / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism*; D008969:Molecular Sequence Data; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism; D061988:Proteasome Inhibitors / Q000494:pharmacology; D059748:Proteolysis / Q000187:drug effects*; D015398:Signal Transduction; D054875:Ubiquitination
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D010446:Peptide Fragments; D061988:Proteasome Inhibitors; C543304:amyloid beta-protein precursor C-terminal fragment beta, human; D002738:Chloroquine; D053829:Amyloid Precursor Protein Secretases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; D046988:Proteasome Endopeptidase Complex