Functions as a cell surface receptor and performs physiological functions on the surface of neurons relevant to neurite growth, neuronal adhesion and axonogenesis. Interaction between APP molecules on neighboring cells promotes synaptogenesis. Involved in cell mobility and transcription regulation through protein-protein interactions (By similarity). Can promote transcription activation through binding to APBB1-KAT5 and inhibit Notch signaling through interaction with Numb (By similarity). Couples to apoptosis-inducing pathways such as those mediated by G(o) and JIP. Inhibits G(o)-alpha ATPase activity. Acts as a kinesin I membrane receptor, mediating the axonal transport of beta-secretase and presenilin 1 (By similarity). By acting as a kinesin I membrane receptor, plays a role in axonal anterograde transport of cargo towards synapes in axons (By similarity). May be involved in copper homeostasis/oxidative stress through copper ion reduction. Can regulate neurite outgrowth through binding to components of the extracellular matrix such as heparin and collagen I and IV (By similarity). The splice isoforms that contain the BPTI domain possess protease inhibitor activity. Induces a AGER-dependent pathway that involves activation of p38 MAPK, resulting in internalization of amyloid-beta peptide and leading to mitochondrial dysfunction in cultured mitochondrial dysfunction in cultured cortical neurons. Provides Cu(2+) ions for GPC1 which are required for release of nitric oxide (NO) and subsequent degradation of the heparan sulfate chains on GPC1 (By similarity). Amyloid-beta peptides are lipophilic metal chelators with metal-reducing activity. Binds transient metals such as copper, zinc and iron. Rat and mouse amyloid-beta peptides bind only weakly transient metals and have little reducing activity due to substitutions of transient metal chelating residues. Amyloid-beta protein 42 may activate mononuclear phagocytes in the brain and elicits inflammatory responses. Promotes both tau aggregation and TPK II-mediated phosphorylation. Also binds GPC1 in lipid rafts (By similarity). Appicans elicit adhesion of neural cells to the extracellular matrix and may regulate neurite outgrowth in the brain. The gamma-CTF peptides as well as the caspase-cleaved peptides, including C31, are potent enhancers of neuronal apoptosis. N-APP binds TNFRSF21 triggering caspase activation and degeneration of both neuronal cell bodies (via caspase-3) and axons (via caspase-6). Binds, via its C-terminus, to the PID domain of several cytoplasmic proteins, including APBB family members, the APBA family, MAPK8IP1, SHC1 and NUMB and DAB1 (By similarity). Binding to DAB1 inhibits its serine phosphorylation (By similarity). Interacts (via NPXY motif) with DAB2 (via PID domain); the interaction is impaired by tyrosine phosphorylation of the NPXY motif. Also interacts with GPCR-like protein BPP, APPBP1, IB1, KNS2 (via its TPR domains), APPBP2 (via BaSS) and DDB1. In vitro, it binds MAPT via the MT-binding domains (By similarity). Associates with microtubules in the presence of ATP and in a kinesin-dependent manner (By similarity). Interacts, through a C-terminal domain, with GNAO1. Amyloid-beta protein 42 binds CHRNA7 in hippocampal neurons (By similarity). Amyloid-beta associates with HADH2 (By similarity). Interacts with CPEB1, ANKS1B, TNFRSF21 and AGER (By similarity). Interacts with ITM2B. Interacts with ITM2C. Interacts with IDE. Can form homodimers; dimerization is enhanced in the presence of Cu(2+) ions. Can form homodimers; this is promoted by heparin binding (By similarity). Amyloid-beta protein 40 interacts with S100A9 (By similarity). CTF-alpha product of APP interacts with GSAP (By similarity). Isoform APP695 interacts with SORL1 (via N-terminal ectodomain); this interaction retains APP in the trans-Golgi network and reduces processing into soluble APP-alpha and amyloid-beta peptides (By similarity). The C99 fragment also interacts with SORL1 (By similarity). Isoform APP751 interacts with SORL1 (By similarity). Isoform APP770 interacts with SORL1 (By similarity). Interacts with PLD3 (By similarity). Interacts with VDAC1 (By similarity). Interacts with NSG1; could regulate APP processing (By similarity). Amyloid-beta protein 42 interacts with FPR2 (By similarity). Interacts with SYT7 (By similarity). Interacts (via transmembrane region) with PSEN1; the interaction is direct (By similarity). Interacts with LRRK2 (By similarity). Interacts (via cytoplasmic domain) with KIF5B (PubMed:23011729). Interacts (via C-terminus) with APBB2/FE65L1 (via C-terminus) (By similarity). Interacts (via intracellular domain) with APBB3 (By similarity). Cell surface protein that rapidly becomes internalized via clathrin-coated pits. Only a minor proportion is present at the cell membrane; most of the protein is present in intracellular vesicles. During maturation, the immature APP (N-glycosylated in the endoplasmic reticulum) moves to the Golgi complex where complete maturation occurs (O-glycosylated and sulfated). After alpha-secretase cleavage, soluble APP is released into the extracellular space and the C-terminal is internalized to endosomes and lysosomes. Some APP accumulates in secretory transport vesicles leaving the late Golgi compartment and returns to the cell surface. APP sorts to the basolateral surface in epithelial cells (By similarity). During neuronal differentiation, the Thr-742 phosphorylated form is located mainly in growth cones, moderately in neurites and sparingly in the cell body (PubMed:10341243). Casein kinase phosphorylation can occur either at the cell surface or within a post-Golgi compartment. Associates with GPC1 in perinuclear compartments. Colocalizes with SORL1 in a vesicular pattern in cytoplasm and perinuclear regions (By similarity). Associates with FPR2 at the cell surface and the complex is then rapidly internalized. Located to both the cytoplasm and nuclei of neurons. It can be translocated to the nucleus through association with APBB1 (Fe65) (By similarity). In dopaminergic neurons, the phosphorylated Thr-743 form is localized to the nucleus (By similarity). Expressed in the brain (PubMed:23011729). In the brain, non-L-APP isoforms are expressed in neurons, isoform APP695 being the predominant form. In astrocytes and microglial cells, almost 50% is L-isoform (appican). From 6 days to 7 months, levels of KPI-containing isoforms increase in the brain cortex and hippocampus. Levels of L-APP increase in all brain regions during the same period, but levels are low compared to non-L-APP isoforms. Phosphorylation of mature, glycosylated APP occurs 48-72 hours after treatment of neuronal cells with nerve growth factor which correlates with the timing of neurite outgrowth. The transmembrane helix undergoes a conformation change and unravels partially when bound to PSEN1, facilitating cleavage by PSEN1. The basolateral sorting signal (BaSS) is required for sorting of membrane proteins to the basolateral surface of epithelial cells. The GFLD subdomain binds Cu(2+) ions; this promotes homodimerization. The NPXY sequence motif found in many tyrosine-phosphorylated proteins is required for the specific binding of the PID domain. However, additional amino acids either N- or C-terminal to the NPXY motif are often required for complete interaction. The PID domain-containing proteins which bind APP require the YENPTY motif for full interaction. These interactions are independent of phosphorylation on the terminal tyrosine residue. The YENPXY site is also involved in clathrin-mediated endocytosis. The C-terminal region can bind zinc ions; this favors dimerization and formation of higher oligomers. The OX-2 motif shows some similarity to a region in the N-terminus of CD200/MOX2. Proteolytically processed under normal cellular conditions. Cleavage either by alpha-secretase, beta-secretase or theta-secretase leads to generation and extracellular release of soluble APP peptides, S-APP-alpha and S-APP-beta, and the retention of corresponding membrane-anchored C-terminal fragments, C80, C83 and C99. Subsequent processing of C80 and C83 by gamma-secretase yields P3 peptides. This is the major secretory pathway and is non-amyloidogenic. Alternatively, presenilin/nicastrin-mediated gamma-secretase processing of C99 releases the amyloid-beta proteins, amyloid-beta protein 40 and amyloid-beta protein 42, major components of amyloid plaques, and the cytotoxic C-terminal fragments, gamma-CTF(50), gamma-CTF(57) and gamma-CTF(59). PSEN1 cleavage is more efficient with C83 than with C99 as substrate (in vitro). Amyloid-beta protein 40 and Amyloid-beta protein 42 are cleaved by ACE. Many other minor amyloid-beta peptides, amyloid-beta 1-X peptides, are found in cerebral spinal fluid (CSF) including the amyloid-beta X-15 peptides, produced from the cleavage by alpha-secretase. Proteolytically cleaved by caspases during neuronal apoptosis. Cleavage at Asp-739 by either caspase-3, -8 or -9 results in the production of the neurotoxic C31 peptide and the increased production of amyloid-beta peptides. N-glycosylated. O-glycosylated. O-linkage of chondroitin sulfate to the L-APP isoforms produces the APP proteoglycan core proteins, the appicans. The chondroitin sulfate chain of appicans contains 4-O-sulfated galactose in the linkage region and chondroitin sulfate E in the repeated disaccharide region. Phosphorylation in the C-terminal on tyrosine, threonine and serine residues is neuron-specific (PubMed:9085254, PubMed:10329382, PubMed:10341243). Phosphorylation can affect APP processing, neuronal differentiation and interaction with other proteins (PubMed:10341243). Phosphorylated on Thr-743 in neuronal cells by Cdc5 kinase and Mapk10, in dividing cells by Cdc2 kinase in a cell-cycle dependent manner with maximal levels at the G2/M phase and, in vitro, by GSK-3-beta (PubMed:10936190). The Thr-743 phosphorylated form causes a conformational change which reduces binding of Fe65 family members (By similarity). In dopaminergic (DA) neurons, phosphorylation on Thr-743 by LRKK2 promotes the production and the nuclear translocation of the APP intracellular domain (AICD) which induces DA neuron apoptosis (By similarity). Phosphorylation on Tyr-757 is required for SHC binding. Phosphorylated in the extracellular domain by casein kinases on both soluble and membrane-bound APP (By similarity). This phosphorylation is inhibited by heparin (By similarity). Extracellular binding and reduction of copper, results in a corresponding oxidation of Cys-144 and Cys-158, and the formation of a disulfide bond. Trophic-factor deprivation triggers the cleavage of surface APP by beta-secretase to release sAPP-beta which is further cleaved to release an N-terminal fragment of APP (N-APP). Amyloid-beta peptides are degraded by IDE. Sulfated on tyrosine residues. Chelation of metal ions, notably copper, iron and zinc, can induce histidine-bridging between amyloid-beta molecules resulting in amyloid-beta-metal aggregates. Rat and mouse amyloid-beta peptides have an arginine residue substituted for the bridging histidine residue and are thus less capable of forming amyloid aggregates. Extracellular zinc-binding increases binding of heparin to APP and inhibits collagen-binding (By similarity). L-isoforms are referred to as appicans. L-isoforms are referred to as appicans. L-isoforms are referred to as appicans. L-isoforms are referred to as appicans. Belongs to the APP family.