title: Serum Starvation Induces BACE1 Processing and Secretion.
abstract: β-secretase (BACE1) is a type 1 transmembrane protein implicated in Alzheimer's Disease (AD) pathogenesis. Cleavage of Amyloid Precursor Protein (APP), initiated by BACE1 and followed by γ-secretase, leads to the formation of toxic Aβ peptides. Increased levels of BACE1 have been detected in the CSF of AD patients compared to age-matched healthy controls indicating that neurodegenerative conditions induce shedding of BACE1.
  
  
  
  To mimic such conditions, we examined whether serum deprivation stimulates proteolysis-dependent secretion of BACE1.
  
  
  
  Detection of BACE1 secretion in BACE1 overexpressing cells or ADAM10/ADAM17 knockout fibroblasts cultured under serum deprivation conditions, using western blot analysis.
  
  
  
  We found that serum deprivation of U251 neuroblastoma or HEK293T cells overexpressing BACE1 stimulated secretion of BACE1. Using ADAM10/ADAM17 knockout fibroblasts and inhibitors of both ADAM10 and ADAM17, we obtained data indicating that these proteases are involved in serum-starvation induced shedding of BACE1. This is unexpected since BACE1 is localized mainly in lipid rafts while ADAM10 is localized mainly in nonlipid raft domains. We hypothesized that serum deprivation results in alterations in the lipid composition of the membrane which can alter the localization of ADAM10 and BACE1. In support, we obtained results indicating that extraction of membrane cholesterol following incubation with methyl β cyclodextrin potentiated the effect of serum deprivation. Secreted BACE1 was also found to be enzymatically active towards immunoprecipiated full length APP.
  
  
  
  Serum starvation induces ADAM10-mediated BACE1 secretion.
authors: Division of Human and Animal Physiology, Department of Biology, National and Kapodistrian University of Athens, Athens, Greece.
authors: A V
authors: AV
authors: Stavropoulou
authors: Division of Human and Animal Physiology, Department of Biology, National and Kapodistrian University of Athens, Athens, Greece.
authors: O
authors: O
authors: Mavrofrydi
authors: Biochemical Institute, University Kiel, Kiel, Germany.
authors: P
authors: P
authors: Saftig
authors: Division of Animal and Human Physiology, Department of Biology, National & Kapodistrian University of Athens, Panepistimiopolis, 157 84 Ilisia, Greece.
authors: S
authors: S
authors: Efthimiopoulos
mesh_terms: D000072197:ADAM10 Protein / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics; D000072198:ADAM17 Protein / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics; D053829:Amyloid Precursor Protein Secretases / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism; D016282:Aspartic Acid Endopeptidases / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002784:Cholesterol / Q000378:metabolism; D016895:Culture Media, Serum-Free; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D021962:Membrane Microdomains / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics; D044967:Serum / Q000378:metabolism*; D013312:Stress, Physiological / Q000187:drug effects / Q000502:physiology*; D013501:Surface-Active Agents / Q000494:pharmacology; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: C545487:APP protein, human; D016564:Amyloid beta-Protein Precursor; D016895:Culture Media, Serum-Free; D008565:Membrane Proteins; D013501:Surface-Active Agents; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol; D053829:Amyloid Precursor Protein Secretases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; D000072197:ADAM10 Protein; C491236:ADAM10 protein, human; D000072198:ADAM17 Protein; C000606462:ADAM17 protein, human
keywords: ADAM10; ADAM17; Alzheimer's disease; BACE1; cholesterol; proteolysis; secretion; serum starvation.; shedding