Background: 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.
Objective: To mimic such conditions, we examined whether serum deprivation stimulates proteolysis-dependent
secretion of BACE1.
Method: Detection of BACE1 secretion in BACE1 overexpressing cells or ADAM10/ADAM17 knockout fibroblasts
cultured under serum deprivation conditions, using western blot analysis.
Results: 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
Conclusion: Serum starvation induces ADAM10-mediated BACE1 secretion.