The trans-Golgi network is a major site for ?-secretase processing of amyloid precursor protein in primary neurons.

ABSTRACT: Amyloid precursor protein (APP) is processed along the amyloidogenic pathway by the ?-secretase, BACE1, generating ?-amyloid (A?), or along the nonamyloidogenic pathway by ?-secretase, precluding A? production. The plasma membrane is considered the major site for ?-secretase-mediated APP cleavage, but other cellular locations have not been rigorously investigated. Here, we report that APP is processed by endogenous ?-secretase at the trans-Golgi network (TGN) of both transfected HeLa cells and mouse primary neurons. We have previously shown the adaptor protein complex, AP-4, and small G protein ADP-ribosylation factor-like GTPase 5b (Arl5b) are required for efficient post-Golgi transport of APP to endosomes. We found here that AP-4 or Arl5b depletion results in Golgi accumulation of APP and increased secretion of the soluble ?-secretase cleavage product sAPP?. Moreover, inhibition of ?-secretase following APP accumulation in the TGN increases the levels of the membrane-bound C-terminal fragments of APP from both ?-secretase cleavage (?-CTF, named C83 according to its band size) and BACE1 cleavage (?-CTF/C99). The level of C83 was ?4 times higher than that of C99, indicating that ?-secretase processing is the major pathway and that BACE1 processing is the minor pathway in the TGN. AP-4 silencing in mouse primary neurons also resulted in the accumulation of endogenous APP in the TGN and enhanced ?-secretase processing. These findings identify the TGN as a major site for ?-secretase processing in HeLa cells and primary neurons and indicate that both APP processing pathways can occur within the TGN compartment along the secretory pathway.

SUBMITTER: Tan JZA 

PROVIDER: S-EPMC6364769 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature