The principal component of Alzheimer's amyloid plaques, A␤, derives from proteolytic processing of the Alzheimer's amyloid protein precursor (APP). FE65 is a brain-enriched protein that binds to APP. Although several laboratories have characterized the APP-FE65 interaction in vitro, the possible relevance of this interaction to Alzheimer's disease has remained unclear. We demonstrate here that APP and FE65 co-localize in the endoplasmic reticulum/Golgi and possibly in endosomes. Moreover, FE65 increases translocation of APP to the cell surface, as well as both ␣APP s and A␤ secretion. The dramatic (4-fold) FE65-dependent increase in A␤ secretion suggests that agents which inhibit the interaction of FE65 with APP might reduce A␤ secretion in the brain and therefore be useful for preventing or slowing amyloid plaque formation.Amyloid plaques are one of the major hallmarks of Alzheimer's disease (AD) 1 pathology. The plaque core is largely composed of an approximately 4-kDa peptide referred to as A␤ (1, 2). Because mutations linked to AD have been shown to increase secretion of A␤ (3), secreted A␤ is believed to play a causative role in AD etiology. The precursor to A␤ is the Alzheimer's amyloid protein precursor (APP) (4,5). APP is a type I integral membrane protein, the majority of which is found in the ER/Golgi (6). A fraction of APP is transported to the plasma membrane, then routed through the endosomal/lysosomal system (6 -12).At least three unidentified proteases, known as the ␣-, ␤-, and ␥-secretases, process APP (7,(13)(14)(15)(16). The combination of ␤ and ␥ cleavages generates A␤. ␣-Secretase cleaves APP within the A␤ domain, releasing ␣APP s , the large extracellular domain. While ␣APP s is generated primarily at or en route to the plasma membrane (17), A␤ is formed in both the secretory and endocytic pathways (8). It has been suggested that the majority of secreted A␤ is made in the endocytic pathway (8).Several studies have shown that the cytoplasmic tail of APP is important for the regulation of APP metabolism and localization. The carboxyl terminus of APP contains the sequence YENPTY. NPXY is a consensus sequence for endocytosis of low density lipoprotein receptors (18). Deletion of portions of APP that contain the YENPTY sequence results in increased secretion of APP s and decreased secretion of A␤ (8, 19 -22). The effects of these deletions are thought to be the result of increased APP at the cell surface. Mutation of the second tyrosine in the YENPTY sequence to alanine also increases APP s secretion but has no effect on A␤ secretion (23). These observations suggest that secretion of A␤ and APP s may be regulated independently by signals in the cytoplasmic tail of APP.FE65 is a brain-enriched protein of unknown function (24) that binds to the cytoplasmic domain of APP. FE65 contains two types of protein-protein interaction domains: a WW domain in the amino terminus and tandem phosphotyrosine interaction domains (PIDs) in the carboxyl terminus. WW domains recognize poly-proline sequences (25), whe...

FE65 binds to the Alzheimer amyloid precursor protein (APP), but the function of this interaction has not been identified. Here, we report that APP and FE65 are involved in regulation of cell movement. APP and FE65 colocalize with actin and Mena, an Abl-associated signaling protein thought to regulate actin dynamics, in lamellipodia. APP and FE65 specifically concentrate with β1-integrin in dynamic adhesion sites known as focal complexes, but not in more static adhesion sites known as focal adhesions. Overexpression of APP accelerates cell migration in an MDCK cell wound–healing assay. Coexpression of APP and FE65 dramatically enhances the effect of APP on cell movement, probably by regulating the amount of APP at the cell surface. These data are consistent with a role for FE65 and APP, possibly in a Mena-containing macromolecular complex, in regulation of actin-based motility.

What determines where synapses will form along an axon or how proteins are deposited at nascent synapses remains unknown. Here, we show that the initial formation of presynaptic terminals occurs preferentially at predefined sites within the axons of cortical neurons. Time-lapse imaging of synaptic vesicle protein transport vesicles (STVs) indicates that STVs pause repeatedly at these sites, even in the absence of neuronal or glial contact. Contact with a neuroligin-expressing non-neuronal cell induces formation of presynaptic terminals specifically at these STV pause sites. Remarkably, formation of stable contacts with dendritic filopodia also occurs selectively at STV pause sites. Although it is not yet known which molecules comprise the predefined sites, STV pausing is regulated by cues that affect synaptogenesis. Overall, these data are consistent with the hypothesis that regulation of STV pausing might be an important mechanism for accumulation of presynaptic proteins at nascent synapses and support a new model in which many en passant synapses form specifically at predefined sites in young axons.

Although the Alzheimer amyloid protein precursor (APP) has been studied intensely for more than a decade, its function in neurons is unresolved. Much less is known about its binding partner FE65. We have shown recently that APP and FE65 synergistically regulate the movement of transfected cells. It remained to be shown whether endogenous APP and FE65 could play a similar role in vivo. Here, we show that FE65, like APP, is expressed at high levels in neurons. Using a combination of immunofluorescence, live imaging, and subcellular fractionation, we find that FE65 and APP localize in vitro and in vivo to the most motile regions of neurons, the growth cones. Within growth cones, APP and FE65 concentrate in actin-rich lamellipodia. Finally, APP and FE65 interact in nerve terminals, where they associate with Rab5-containing synaptic organelles but not with synaptic vesicles. Our data are consistent with a role for the APP/FE65 complex in regulation of actin-based membrane motility in neurons, which could be important for highly dynamic processes such as neurite growth and synapse modification.