Overexpression of SNX3 Decreases Amyloid-β Peptide Production by Reducing Internalization of Amyloid Precursor Protein

Background: Sorting nexins (SNXs) have diverse functions in protein sorting and membrane trafficking. Recently, single-nucleotide polymorphisms in SNX3 were found to be associated with Alzheimer disease. However, it remains unknown whether SNX3 participates in amyloid (A)beta peptide production. Objective: To examine the role of SNX3 in A beta production and APP processing. Methods: The effect of increased expression of SNX3 was studied in HEK293T cells. A beta peptides were measured by immunoassay. Protein-protein association was analyzed by a bimolecular fluorescence complementation (BiFC) assay. APP uptake was measured with an alpha-bungarotoxin-binding assay, and flow cytometry was used to measure cell surface APP levels. Results: We found that overexpression of SNX3 in HEK293T cells decreases the levels of secreted A beta and soluble N-terminal APP fragments (sAPP beta). The reduction correlated with a decreased association of APP with BACE1, as revealed by BiFC. This effect may, in part, be explained by a reduced internalization of APP; SNX3 overexpression reduced APP internalization as determined by an alpha-bungarotoxin-binding assay, and caused increased APP levels on the cell surface, as shown by flow cytometry. In addition, SNX3 overexpression increased the cellular levels of full-length APP. Conclusion: These results provide evidence that SNX3 regulates A beta production by influencing the internalization of APP. (c) 2018 S. Karger AG, Basel