Intraneuronal compartments of the amyloid precursor protein.

The amyloid precursor protein (APP) is the parent molecule from which beta-amyloid protein is cleaved and deposits as amyloid fibrils in the senile plaques of Alzheimer's disease. Its primary structure resembles a receptor; however, no ligand has been identified. In growing hippocampal neurons APP is localized to growth cones. APP immunoreactivity was highly enriched in the axons of mature cultured neurons, where it appears as a specialization of the axonal membrane. Its anterograde translocation occurs via a kinesin-based motor. Following cytosolic acidification, APP colocalizes with late endosomes that get redistributed from the neuronal cell body to the processes. APP colocalizes in cultured hippocampal neurons to clathrin-immunoreactive clusters of vesicular-like structures. The finding lends additional credence to the possibility that APP could function as a receptor.