Amyloid precursor‐like protein 1 (APLP1) exhibits stronger zinc‐dependent neuronal adhesion than amyloid precursor protein and APLP2

Abstract

The amyloid precursor protein (APP) and its paralogs, amyloid precursor-like protein 1 (APLP1) and APLP2, are metalloproteins with a putative role both in synaptogenesis and in maintaining synapse structure. Here, we studied the effect of zinc on membrane localization, adhesion, and secretase cleavage of APP, APLP1, and APLP2 in cell culture and rat neurons. For this, we employed live-cell microscopy techniques, a microcontact printing adhesion assay and ELISA for protein detection in cell culture supernatants. We report that zinc induces the multimerization of proteins of the amyloid precursor protein family and enriches them at cellular adhesion sites. Thus, zinc facilitates the formation of de novo APP and APLP1 containing adhesion complexes, whereas it does not have such influence on APLP2. Furthermore, zinc-binding prevented cleavage of APP and APLPs by extracellular secretases. In conclusion, the complexation of zinc modulates neuronal functions of APP and APLPs by (i) regulating formation of adhesion complexes, most prominently for APLP1, and (ii) by reducing the concentrations of neurotrophic soluble APP/APLP ectodomains. Keywords: amyloid precursor protein, amyloid precursor-like protein, neuronal adhesion, number and brightness, zinc. Abbreviations used: AD, Alzheimer's disease; ADAM, a disintegrin and metalloproteinase; APLP, amyloid precursor-like protein; APP, amyloid precursor protein; Ab, b-amyloid peptide; BMGY, buffered glycerol-complex medium; BMMY, buffered methanol-complex medium; cLSM, confocal laser scanning microscopy; HBS, HEPES-buffered saline; N&B, number and brightness; PDL, poly-D-lysine; PDMS, polydimethylsiloxane; PM, plasma membrane; RIP, regulated intramembrane proteolysis; sAPP/APLP, soluble APP/APLP; YFP, yellow fluorescent protein. 266

Novel Insights into the Physiological Function of the APP (Gene) Family and Its Proteolytic Fragments in Synaptic Plasticity

“…Under steady state conditions, the majority of full-length APP is located in the Golgi apparatus and in the trans-Golgi network (Thinakaran and Koo, 2008). When present at the plasma membrane APP and APLPs were shown to form homo- and heterotypic cis interactions and have been proposed to mediate cell–cell interactions in trans (Soba et al, 2005; Kaden et al, 2009; Baumkötter et al, 2012; Mayer et al, 2016). Synaptic adhesion by APP might not only be crucial to build and maintain synaptic contacts, but also to regulate synaptic plasticity (see Figure 2).…”

“…Highest expression levels at the membrane were observed for APLP1 suggesting that it might be the family member with the upmost potential to mediate cell contacts (Kaden et al, 2009). Recently, the study of Mayer et al (2016) identified APP and APLP2 to exhibit basal adhesive properties while APLP1 mediated neuronal adhesion is dynamic and regulated by zinc. Copper was instead shown to induce cis - and trans -dimerization of APP at its E1 domain (Baumkötter et al, 2014).…”

“…Copper was instead shown to induce cis - and trans -dimerization of APP at its E1 domain (Baumkötter et al, 2014). Importantly enhanced trans or cis interaction of APPs or APLPs is accompanied by a reduction of ectodomain shedding of the proteins (Stahl et al, 2014; Mayer et al, 2016) and might therefore interfere with the ability to modulate synaptic function.…”

“…In that study, Lassek and colleagues further show that APP deletion disturbs Ca 2+ homeostasis, due to a misregulation of calmodulin and neuromodulin but not of the expression of CaMKII or Ca 2+ channels. APLP1 is also localized at the presynaptic active zone (Laßek et al, 2016), but beside the function as mediator of neuronal adhesion (Kaden et al, 2009; Mayer et al, 2016) and its potential involvement in GABAergic neurotransmission (Vnencak et al, 2015) no other role or interaction partners have been attributed so far.…”

Phosphatidylserine Lateral Organization Influences the Interaction of Influenza Virus Matrix Protein 1 with Lipid Membranes

“…A plasmid expressing a lactadherin fragment fused to mRFP (mRFP-Lact-C2) (Addgene, Cambridge, MA) was a gift from Sergio Grinstein (46). A plasmid expressing a myristoylatedpalmitoylated yellow fluorescent protein (YFP) (61,62) was modified to obtain a myristoylatedpalmitoylated mRFP (myr-palm mRFP) plasmid. The mRFP-Lact-C2 and myristoylated-palmitoylated YFP plasmids were incubated with the restriction enzymes AgeI and BsrgI (Thermo Fisher Scientific, Darmstadt, Germany); the two products were then ligated overnight with the T4 DNA ligase enzyme (Thermo Fisher Scientific, Darmstadt, Germany), and ligation success was confirmed by sequencing.…”