ADP ribosylation factor 6 (ARF6) controls amyloid precursor protein (APP) processing by mediating the endosomal sorting of BACE1.

Amyloid β (Aβ) peptides, the primary constituents of senile plaques and a hallmark in Alzheimer's disease pathology, are generated through the sequential cleavage of amyloid precursor protein (APP) by β-site APP cleaving enzyme 1 (BACE1) and γ-secretase. The early endosome is thought to represent a major compartment for APP processing; however, the mechanisms of how BACE1 encounters APP are largely unknown. In contrast to APP internalization, which is clathrin-dependent, we demonstrate that BACE1 is sorted to early endosomes via a route controlled by the small GTPase ADP ribosylation factor 6 (ARF6). Altering ARF6 levels or its activity affects endosomal sorting of BACE1, and consequently results in altered APP processing and Aβ production. Furthermore, sorting of newly internalized BACE1 from ARF6-positive towards RAB GTPase 5 (RAB5)-positive early endosomes depends on its carboxyterminal short acidic cluster-dileucine motif. This ARF6-mediated sorting of BACE1 is confined to the somatodendritic compartment of polarized neurons in agreement with Aβ peptides being primarily secreted from here. These results demonstrate a spatial separation between APP and BACE1 during surface-to-endosome transport, suggesting subcellular trafficking as a regulatory mechanism for this proteolytic processing step. It thereby provides a novel avenue to interfere with Aβ production through a selective modulation of the distinct endosomal transport routes used by BACE1 or APP.