The endosomal-associated deubiquitinating enzyme USP8 regulates BACE1 ubiquitination and degradation.
β-site amyloid precursor protein cleaving enzyme (BACE1) is the rate-limiting
enzyme in the production of amyloid beta (Aβ), the toxic peptide that accumulates
in the brain of subjects affected by Alzheimer's disease. Previous studies have shown
that BACE1 is degraded via the lysosomal pathway, BACE1 is ubiquitinated at lysine 501
and that blocking ubiquitination at lysine 501 resul... read morets in BACE1 stabilization. Ubiquitin
conjugation is a reversible process mediated by deubiquitinating enzymes (DUBs). The
ubiquitin specific peptidase 8 (USP8), an endosomal-associated deubiquitinating enzyme,
regulates the ubiquitination, trafficking and lysosomal degradation of several plasma
membrane proteins. Thus, we hypothesized that USP8 regulates BACE1 ubiquitination,
trafficking and lysosomal degradation. Here we report that USP8 directly deubiquitinates
BACE1. In H4 human neuroglioma cells, RNAi-mediated depletion of USP8 increases BACE1
ubiquitination, promotes BACE1 accumulation in the early endosomes and late
endosomes/lysosomes, and decreases BACE1 levels in the recycling endosomes. Furthermore,
USP8 depletion reduces levels of both ectopically expressed and endogenous BACE1.
Decreases in BACE1 are accompanied by the decreased formation of amyloid precursor
protein C-terminal fragments (APP-CTFs) C99 and C89, products of BACE1 cleavage of APP.
Moreover, Aβ levels are decreased. While USP8 depletion does not affect the levels
of APP-CTFs in a manner independent of BACE1, USP8 depletion decreases the stability of
the amyloid precursor protein intracellular domain (AICD) and reduces its cellular
levels. Our findings demonstrate that USP8 plays a key role in the trafficking and
degradation of BACE1 by deubiquitinating lysine 501. These studies suggest that
therapies able to accelerate BACE1 degradation (e.g. by increasing BACE1 ubiquitination)
may represent a potential treatment for AD.
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Neuroscience.
Advisor: Giuseppina Tesco.
Committee: Peter Juo, Grace Gill, Yongjie Yang, and Doo Yeon Kim.
Keyword: Neurosciences.read less