Disease relevance of APP

• To test whether overexpression of APP generates abnormally processed derivatives that affect the viability of neurons, we stably transfected full-length human APP complementary DNA into murine embryonal carcinoma P19 cells [1].
• We examined the effects of apoE isoforms on the processing of amyloid precursor protein (APP) and on Abeta production in rat neuroblastoma B103 cells stably transfected with human wild-type APP695 (B103-APP) [2].
• Regional levels of APP and APP-beta were nearly constant at all ages, while A beta levels dramatically and predictably increased in brain regions undergoing histochemically confirmed amyloidosis, most notably in the cortex and hippocampus [3].
• We also tested for the APP codon 693 mutation associated with hereditary cerebral hemorrhage with amyloidosis-Dutch type, for PRIP gene missense mutations at codons 102, 117, and 200, and for the PRIP insertion mutations which are associated with Creutzfeld-Jakob disease and Gerstmann-Straussler Scheinker syndrome [4].
• These effects were observed with APP695 and APP751 expressed in stably transfected CHO cells, as well as with endogenous APP in human glioma (Hs 683) cells [5].

Psychiatry related information on APP

• Familial Alzheimer's disease (FAD) is a genetically heterogeneous disorder that includes a rare early-onset form linked to mutations in the amyloid b protein precursor (APP) gene [6].
• We report a mutation at a novel site in APP in a three-generation Iowa family with autosomal dominant dementia beginning in the sixth or seventh decade of life [7].
• We previously showed that mice over-expressing a human mutated form of APP (APP(V717F)) display age-dependent recognition memory deficits associated with the progression of amyloid deposition [8].
• The protease inhibitor-containing APP751/770 isoforms represented an average of 10.5% of total APP in CSF of patients with Alzheimer's disease (AD, n = 22), multi-infarct dementia (MID, n = 5) and normal controls (n = 10) [9].

High impact information on APP

• Duplication of the APP locus, resulting in accumulation of amyloid-beta peptides, causes ADEOAD with CAA [10].
• We report duplication of the APP locus on chromosome 21 in five families with autosomal dominant early-onset Alzheimer disease (ADEOAD) and cerebral amyloid angiopathy (CAA) [10].
• The amyloid-beta precursor protein (APP) is directly and efficiently cleaved by caspases during apoptosis, resulting in elevated amyloid-beta (A beta) peptide formation [11].
• The predominant site of caspase-mediated proteolysis is within the cytoplasmic tail of APP, and cleavage at this site occurs in hippocampal neurons in vivo following acute excitotoxic or ischemic brain injury [11].
• An earlier age at onset has also been demonstrated in familial AD patients with mutations in the amyloid precursor protein (APP) gene (APP717 and APP670/671)13 carrying the APOE epsilon-4 allele compared to those who do not, but not in familial AD patients with APP692 or 693 mutations, or in chromosome 14-linked familial AD patients [12].

Chemical compound and disease context of APP

• Mutations in PS1 have been shown to cause early-onset inherited forms of Alzheimer's disease (AD) by a gain-of-function mechanism that alters proteolytic processing of the amyloid precursor protein (APP) resulting in increased production of neurotoxic forms of amyloid beta-peptide [13].
• The amyloid beta protein (beta/A4) that is deposited in senile plaques and in cerebral vessels in Alzheimer's disease (AD) is derived from a larger membrane-associated glycoprotein, the amyloid beta protein precursor (APP) [14].
• The central hypothesis guiding this review is that nicotine may play an important role in APP secretion and protection against toxicity induced by APP metabolic fragments (beta-amyloid [Abeta], carboxyl terminal [CT]) [15].
• These data suggest a dual role in cell signaling for APP and its CTFs in neuroblastoma cells, in a manner similar to that previously reported for other tyrosine kinase receptor, through a tightly regulated coupling with alternative intracellular adaptors to control the signaling of the cell [16].
• We have previously shown that all members of the APP protein family are up-regulated upon retinoic acid (RA)-induced neuronal differentiation of SH-SY5Y neuroblastoma cells [17].

Biological context of APP

• We show that the low density lipoprotein (LDL) receptor-related protein (LRP) is responsible for the endocytosis of secreted APP [18].
• Clues to the function of APP derive from the recent finding that it is a member of a highly conserved protein family that includes the mammalian amyloid precursor-like protein (APLP1) gene which maps to the same general region of human chromosome 19 linked to late-onset FAD [6].
• We report here that overexpression of this APP transgene in neurons is sufficient to produce extracellular dense-core amyloid plaques, neurofibrillary tangles and neuronal degeneration similar to that in the AD brain [19].
• We have now screened complementary DNA libraries constructed from peripheral tissues to determine whether the messenger RNA encoding APP in these tissues is identical to that expressed in brain, and we identify a second APP mRNA that encodes an additional internal domain with a sequence characteristic of a Kunitz-type serine protease inhibitor [20].
• Platelet PN-II/APP was localized in platelet alpha-granules and was secreted upon platelet activation [21].

Anatomical context of APP

• The A4 protein (or beta-protein) is a 42- or 43-amino-acid peptide present in the extracellular neuritic plaques in Alzheimer's disease and is derived from a membrane-bound amyloid protein precursor (APP) [22].
• In cultured cells, the decrease in Abeta42 secretion was accompanied by an increase in the Abeta(1-38) isoform, indicating that NSAIDs subtly alter gamma-secretase activity without significantly perturbing other APP processing pathways or Notch cleavage [23].
• This non-covalent association was specific for the APP family of proteins and restricted to immature forms, occurring probably during transit through the endoplasmic reticulum [24].
• These results indicate that the phosphorylation of APP regulates the formation of a pAPP-JIP-1 complex that accumulates in neurites independent of nonphosphorylated APP [25].
• Upon overexpression of the APP-family members, transformations of cell fates during the development of the peripheral nervous system were observed [26].

Associations of APP with chemical compounds

• Furthermore, short-term administration of ibuprofen to mice that produce mutant beta-amyloid precursor protein (APP) lowered their brain levels of Abeta42 [23].
• G(o) protein treated with GTP-gamma S lost the ability to associate with APP [27].
• We show that control of cholesterol and SM metabolism involves APP processing [28].
• We show that HS and heparin interact directly with BACE1 and inhibit in vitro processing of peptide and APP substrates [29].
• Treatment of cells with brefeldin A or incubation at 20 degrees C did not block complex formation, suggesting that the association between APP and PS occurs in part in the endoplasmic reticulum [30].

Physical interactions of APP

• In vitro, apolipoprotein E in cerebrospinal fluid binds to synthetic beta A4 peptide (the primary constituent of the senile plaque) with high avidity [31].
• A2M has been implicated biochemically in binding and degradation of the amyloid beta (Abeta) protein which accumulates in SP [32].
• In baculovirus-infected Sf9 cells, PS1 undergoes endoproteolysis and interacts with APP [33].
• The molecular mechanisms that link the gamma-secretase multicomponent amyloid precursor protein (APP) processing complex to biochemical properties of BACE generating the N terminus of the amyloid beta-peptide have not, as yet, been identified [34].
• Our previous data demonstrate that the apoE receptor ApoEr2 co-precipitated with APP and suggest that there are extracellular and intracellular interactions between these two transmembrane proteins [35].

Enzymatic interactions of APP

• Antisense inhibition of endogenous BACE messenger RNA decreased the amount of beta-secretase cleavage products, and purified BACE protein cleaved APP-derived substrates with the same sequence specificity as beta-secretase [36].
• It was hypothesized that PS1 might directly cleave APP [37].
• We propose that the Alcs and APP are coordinately metabolized in neurons and that their cleaved cytoplasmic fragments are reciprocally involved in the regulation of FE65-dependent gene transactivation [38].
• Purified BACE2 cleaves human amyloid precursor protein (APP) sequences at the beta-secretase site, and near the alpha-secretase site, mainly at A beta-Phe(20)--Ala(21) and also at A beta-Phe(19)--Phe(20) [39].
• The tumor necrosis factor (TNF)-alpha converting enzyme (TACE) can cleave the cell-surface ectodomain of the amyloid-beta precursor protein (APP), thus decreasing the generation of amyloid-beta (Abeta) by cultured non-neuronal cells [40].

Co-localisations of APP

• We also found that hBH interacted and colocalized with APP as determined by subcellular fractionation, in vitro binding assay, and confocal immunolocalization [41].
• Human BACE forms dimers and colocalizes with APP [34].
• Asp1 colocalizes with APP in the Golgi/endoplasmic reticulum compartments of cultured cells [42].
• In affected regions of AD brain, ACT and APOE colocalize with Abeta deposits and reactive microglia and astrocytes [43].
• In addition, it is well-known that acetylcholinesterase (AChE) colocalizes with Abeta deposits of brains in AD patients and accelerates assembly of Abeta peptides through the peripheral site of the enzyme (Inestrosa et al., 1996) [44].

Regulatory relationships of APP

• Our findings identify HS as a natural regulator of BACE1 and suggest a novel mechanism for control of APP processing [29].
• We now report that expression of the human PS-1 L286V mutation in PC12 cells increases their susceptibility to apoptosis induced by trophic factor withdrawal and Abeta [45].
• All the PS1 and PS2 mutations assessed in this series led to enhanced deposition of total Abeta and Abeta(x-42/43) but not Abeta(x-40) senile plaques in the superior temporal sulcus when compared with brains from sporadic Alzheimer's disease patients [46].
• In human embryonic kidney 293 cells expression of APLP1 strongly activated APP shedding by alpha-secretase and slightly reduced beta-secretase cleavage [47].
• These results demonstrate that CTCF activates transcription from the APP promoter and that the activation domain is located on the N-terminal side of the zinc finger domain [48].

Other interactions of APP

• Immunocytochemical studies of brain tissue from 26 patients with Down's syndrome showed that the deposition of A4 protein amyloid began in these patients approximately 50 years earlier than it began in 127 normal aging subjects studied previously, although the rate of deposition was the same [49].
• Presenilin mutations produce increases in beta-amyloid (Abeta) formation and apoptosis in many experimental systems [50].
• Analysis of PS2 immunoprecipitates revealed that a fraction of APP was associated with the PS2 immunocomplexes [24].
• Our results indicate that the proteinase inhibitor domain of APP and gelatinase A may be involved in the formation of beta-AP [51].
• Thus, calsenilin may mediate the effects of wild-type and mutant presenilins on apoptosis and on Abeta formation [50].

Analytical, diagnostic and therapeutic context of APP

• By immunoprecipitation/Western blot analysis, APP was consistently found to coimmunoprecipitate with PS1 or PS2 proteins [30].
• Among the secreted N-terminal APP fragments, APPbeta levels were significantly reduced by PMA treatment, whereas APPalpha levels were unchanged, in contrast to most cell culture studies [52].
• APP expression was detectable in resting PBMC by northern blot analysis, immunoblotting studies, and immunohistochemistry [53].
• Full-length FE65 increased co-immunoprecipitation of ApoEr2 and APP [35].
• In addition we showed by S1 nuclease protection and polymerase chain reaction analysis of reverse transcribed RNA (RT-PCR) that T-lymphocytes, macrophages, and microglial cells expressed a new APP isoform by selection of a novel alternative splice site and exclusion of exon 15 of the APP gene [54].

References