Intracellular Amyloid Precursor Protein Sorting and Amyloid-β Secretion Are Regulated by Src-Mediated Phosphorylation of Mint2

Mint adaptor proteins bind to the membrane-bound amyloid precursor protein (APP) and affect the production of pathogenic amyloid-beta (A beta) peptides related to Alzheimer's disease (AD). Previous studies have shown that loss of each of the three Mint proteins delays the age-dependent production of amyloid plaques in transgenic mouse models of AD. However, the cellular and molecular mechanisms underlying Mints effect on amyloid production are unclear. Because A beta generation involves the internalization of membrane-bound APP via endosomes and Mints bind directly to the endocytic motif of APP, we proposed that Mints are involved in APP intracellular trafficking, which in turn, affects A beta generation. Here, we show that APP endocytosis was attenuated in Mint knock-out neurons, revealing a role for Mints in APP trafficking. We also show that the endocytic APP sorting processes are regulated by Src-mediated phosphorylation of Mint2 and that internalized APP is differentially sorted between autophagic and recycling trafficking pathways. A Mint2 phosphomimetic mutant favored endocytosis of APP along the autophagic sorting pathway leading to increased intracellular A beta accumulation. Conversely, the Mint2 phospho-resistant mutant increased APP localization to the recycling pathway and back to the cell surface thereby enhancing A beta 42 secretion. These results demonstrate that Src-mediated phosphorylation of Mint2 regulates the APP endocytic sorting pathway, providing a mechanism for regulating A beta secretion.