The Amyloid Precursor Protein of Alzheimer's Disease Clusters at the Organelle/Microtubule Interface on Organelles that Bind Microtubules in an ATP Dependent Manner: e0147808

• Published in: PloS one 2016-01, Vol.11 (1)
• Main Authors: Stevenson, James W, Conaty, Eliza A, Walsh, Rylie B, Poidomani, Paul J, Samoriski, Colin M, Scollins, Brianne J, DeGiorgis, Joseph A
• Format: Article
• Language: English
• ISSN: 1932-6203
• DOI: 10.1371/journal.pone.0147808

The amyloid precursor protein (APP) is a causal agent in the pathogenesis of Alzheimer's disease and is a transmembrane protein that associates with membrane-limited organelles. APP has been shown to co-purify through immunoprecipitation with a kinesin light chain suggesting that APP may act as a trailer hitch linking kinesin to its intercellular cargo, however this hypothesis has been challenged. Previously, we identified an mRNA transcript that encodes a squid homolog of human APP770. The human and squid isoforms share 60% sequence identity and 76% sequence similarity within the cytoplasmic domain and share 15 of the final 19 amino acids at the C-terminus establishing this highly conserved domain as a functionally import segment of the APP molecule. Here, we study the distribution of squid APP in extruded axoplasm as well as in a well-characterized reconstituted organelle/microtubule preparation from the squid giant axon in which organelles bind microtubules and move towards the microtubule plus-ends. We find that APP associates with microtubules by confocal microscopy and co-purifies with KI-washed axoplasmic organelles by sucrose density gradient fractionation. By electron microscopy, APP clusters at a single focal point on the surfaces of organelles and localizes to the organelle/microtubule interface. In addition, the association of APP-organelles with microtubules is an ATP dependent process suggesting that the APP-organelles contain a microtubule-based motor protein. Although a direct kinesin/APP association remains controversial, the distribution of APP at the organelle/microtubule interface strongly suggests that APP-organelles have an orientation and that APP like the Alzheimer's protein tau has a microtubule-based function.