Understanding the intracellular transport of the ␤-amyloid precursor protein (APP) is a major key to elucidate the regulation of APP processing and thus ␤-amyloid peptide generation in Alzheimer disease pathogenesis. APP and its two paralogues, APLP1 and APLP2 (APLPs), are processed in a very similar manner by the same protease activities. A putative candidate involved in APP transport is protein interacting with APP tail 1 (PAT1), which was reported to interact with the APP intracellular domain. We show that PAT1a, which is 99.0% identical to PAT1, binds to APP, APLP1, and APLP2 in vivo and describe their co-localization in trans-Golgi network vesicles or endosomes in primary neurons. We further demonstrate a direct interaction of PAT1a with the basolateral sorting signal of APP/APLPs. Moreover, we provide evidence for a direct role of PAT1a in APP/APLP transport as overexpression or RNA interference-mediated knockdown of PAT1a modulates APP/APLPs levels at the cell surface. Finally, we show that PAT1a promotes APP/APLPs processing, resulting in increased secretion of ␤-amyloid peptide. Taken together, our data establish PAT1a as a functional link between APP/APLPs transport and their processing.Amyloid plaques, the major hallmark of Alzheimer disease, are mainly composed of the ␤-amyloid peptide (A␤), 6 which is proteolytically derived from the ␤-amyloid precursor protein (APP) (1). APP belongs to a protein family with two mammalian paralogues, the ␤-amyloid precursor-like proteins (APLP) 1 and 2 (2-5). APP/APLPs share highly conserved protein domain organization (6), form homo-and heterotypic interactions (7), and are proteolytically processed in a similar manner (8). The extracellular domain of APP/APLPs can be cleaved by ␣-secretases or, alternatively, by the ␤-secretase ␤-site APP cleaving enzyme 1 (BACE 1) (8 -12). The resulting membraneretained C-terminal fragments (CTFs) are subsequently processed by cleavage within the transmembrane domain by the ␥-secretase complex (13,14). Consecutive ␤-and ␥-cleavage of APP/APLPs results in the release of A␤/A␤-like peptides, whereas ␣-and ␥-cleavage generate p3/p3-like fragments, respectively. Concomitantly, both processing pathways liberate the corresponding intracellular domains (ICDs) (8,15,16). A function in nuclear signaling was proposed for the APP/APLP ICDs (16 -18), suggesting that processing of APP/APLPs is a crucial step in the pathology of Alzheimer disease and central to the physiological function of APP/APLPs.For APP, a number of intracellular interaction partners, such as Fe65 (19), Fe65L1 (20), or X11␣ and X11␤ (21), are known to affect its processing. All of these proteins interact with the NPTY motif in the intracellular domain of APP, APLP1, and APLP2 via their phosphotyrosine binding (PTB) domain (22). Protein interacting with APP tail 1 (PAT1) binds to the basolateral sorting sequence (BaSS) of APP and is associated with microtubules. Further, an influence on APP cleavage at the cell surface has been proposed (23). Therefore, a kinesin light cha...

SummarySeveral studies suggest that the generation of Ab is highly dependent on the levels of cholesterol within membranes' detergentresistant microdomains (DRM). Indeed, the b-amyloid precursor protein (APP) cleaving machinery, namely b-and c-secretases, has been shown to be present in DRM and its activity depends on membrane cholesterol levels. Counterintuitive to the localization of the cleavage machinery, the substrate, APP, localizes to membranes' detergent-soluble microdomains enriched in phospholipids (PL), indicating that Ab generation is highly dependent on the capacity of enzyme and substrate to diffuse along the lateral plane of the membrane and therefore on the internal equilibrium of the different lipids of DRM and non-DRM domains. Here, we studied to which extent changes in the content of a main non-DRM lipid might affect the proteolytic processing of APP. As phosphatidylethanolamine (PE) accounts for the majority of PL, we focused on its impact on the regulation of APP proteolysis. In mammalian cells, siRNA-mediated knock-down of PE synthesis resulted in decreased Ab owing to a dual effect: promoted a-secretase cleavage and decreased c-secretase processing of APP. In vivo, in Drosophila melanogaster, genetic reduction in PL synthesis results in decreased c-secretase-dependent cleavage of APP. These results suggest that modulation of the membrane-soluble domains could be a valuable alternative to reduce excessive Ab generation.

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