Endoproteolytic Cleavage of FE65 Converts the Adaptor Protein to a Potent Suppressor of the sAPPα Pathway in Primates

Abstract

Adaptor protein FE65 (APBB1) specifically binds to the intracellular tail of the type I transmembrane protein, ␤-amyloid precursor protein (APP). The formation of this complex may be important for modulation of the processing and function of APP. APP is proteolytically cleaved at multiple sites. The cleavages and their regulation are of central importance in the pathogenesis of dementias of the Alzheimer type. In cell cultures and perhaps in vivo, secretion of the ␣-cleaved APP ectodomain (sAPP␣) is the major pathway in the most cells. Regulation of the process may require extracellular/intracellular cues. Neither extracellular ligands nor intracellular mediators have been identified, however. Here, we show novel evidence that the major isoform of FE65 (97-kDa FE65, p97FE65) can be converted to a 65-kDa N-terminally truncated C-terminal fragment (p65FE65) via endoproteolysis. The cleavage region locates immediately after an acidic residue cluster but before the three major protein-protein binding domains. The cleavage activity is particularly high in human and non-human primate cells and low in rodent cells; the activity appears to be triggered/enhanced by high cell density, presumably via cell-cell/cell-substrate contact cues. As a result, p65FE65 exhibits extraordinarily high affinity for APP (up to 40-fold higher than p97FE65) and potent suppression (up to 90%) of secretion of sAPP␣. Strong p65FE65-APP binding is required for the suppression. The results suggest that p65FE65 may be an intracellular mediator in a signaling cascade regulating ␣-secretion of APP, particularly in primates.FE65 is a multimodular adaptor protein, consisting of three major protein-protein interaction domains, a WW domain and two phosphotyrosine interaction domains (PID) 1 (1, 2) ( Fig. 2A). The interaction between FE65 and APP mainly takes place between the C-terminal PID (PID2) and the APP intracellular domain (AICD), although other regions may also potentially contribute to the action. The physiological effects of FE65-〈PP complexes are not well understood. Genetic evidence suggests that strong FE65-〈PP binding was favored by natural selection during animal evolution toward human lineage (3). 〈PP is a widely studied protein because of its role in the pathogenesis of dementias of the Alzheimer type (DAT). FE65 is predominantly expressed in central nervous system neurons, and its expression is regulated during development and aging, with high levels corresponding to the timing of neural tissue formation and high neuronal activity (4 -8). Selective knockout of the p97FE65 isoform results in modest impairments in learning but severe deficits in relearning spatial tasks (8). These phenotypes reflect reduced synaptic plasticity. Thus, the APP-FE65 pathway may play roles in normal and abnormal cognitive functions. In addition to binding to AICD, FE65 can also interact, at least in vitro, with several other proteins through its WW and PID1 domains (1, 2). FE65 is able to translocate between the nucleus and cytoplasm, consistent with the d...

Fe65 Stimulates Proteolytic Liberation of the β-Amyloid Precursor Protein Intracellular Domain

“…7B, bottom blot). The size of the observed protein matches the p65Fe65 endoproteolytic protein product reported previously (18). Interestingly, this proteolytic cleavage maps to the amino-terminal portion of Fe65.…”

“…Various studies have concluded that Fe65 either inhibits or promotes secretion of APP s␣ (10,12,18). The results of our analysis of AICD production indicate that Fe65 promotes cleavage of APP by ␣-secretase, a conclusion that implies that Fe65 should increase rather than decrease production of APP s␣ .…”

“…Truncation of Fe65 amino-terminal to the recently identified acidic residue cluster (ARC) domain (18) enhances Fe65 stimulation of APP proteolysis (Fig. 4).…”

“…The Myc epitope-tagged Fe65 vectors were generously provided by Dr. Qubai Hu and Dr. George Martin. The generation of the pcDNA3.1-Fe65myc vectors has been reported previously (14,18), whereby the human neuronal, non-neuronal, and non-neuronal a2 sequence is cloned into pcDNA3.1/Myc-His(ϩ)B at the BamHI and NotI sites (Invitrogen). Untagged versions of these vectors were also generated by leaving the stop codon intact following the subcloning of the cDNA.…”

Amyloid-β and lysozyme proteotoxicity in Drosophila : Beneficial effects of lysozyme and serum amyloid P component in models of Alzheimer’s disease and lysozyme amyloidosis

“…Around 20 proteins have been demonstrated to interact with AICD, one of them being Fe65 (Bórquez and González-Billault, 2012). Fe65 is able to bind AβPP and it acts as a potent modulator controlling the balance between the non-amyloidogenic and amyloidogenic pathways (Hu et al, 2005). AICD also functions as a transcription factor and regulates a number of cellular processes, one being a negative feedback loop, decreasing AβPP trafficking to the cell surface by binding to the promotor site for Wiskott-Aldrich syndrome protein (WASP)-family verprolin homologous protein 1, WAVE1 (Ceglia et al, 2015).…”