THE BETA-AMYLOID DOMAIN IS ESSENTIAL FOR AXONAL SORTING OF AMYLOID PRECURSOR PROTEIN

We have analysed the axonal sorting signals of amyloid precursor prote in (APP). Wild-type and mutant versions of human APP were expressed in hippocampal neurons using the Semliki forest virus system. We show th at wild-type APP and mutations implicated in Alzheimer's disease and a nother brain beta-amyloidosis are sorted to the axon, By analysis of d eletion mutants we found that the membrane-inserted. APP ectodomain bu t not the cytoplasmic tail is required for axonal sorting, Systematic deletions of the APP ectodomain identified two regions required for ax onal delivery: one encoded by exons 11-15 in the carbohydrate domain, the other encoded by exons 16-17 in the juxtamembraneous beta-amyloid domain. Treatment of the cells with the N-glycosylation inhibitor tuni camycin induced missorting of wild-type APP, supporting the importance of glycosylation in axonal sorting of APP. The data revealed a hierar chy of sorting signals on APP: the beta-amyloid-dependent membrane pro ximal signal was the major contributor to axonal sorting, ,chile N-gly cosylation had a weaker effect. Furthermore, recessive somatodendritic signals, most likely in the cytoplasmic tail, directed the protein to the dendrites when the ectodomain nas deleted, Analysis of detergent solubility of APP and another axonally delivered protein, hemagglutini n. demonstrated that only hemagglutinin formed CHAPS-insoluble complex es, suggesting distinct mechanisms of axonal sorting for these two pro teins, This study is the first delineation of sorting requirements of an axonally targeted protein in polarized neurons and indicates that t he beta-amyloid domain plays a major role in axonal delivery of APP.