| Abstract No.: | A-C1107 |
| Country: | Canada |
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| Title: | PRESENILIN 1/ NPRAP INTERACTION IN ALZHEIMER'S DISEASE |
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| Authors/Affiliations: | 1 Carolina Koutras*; 1 Chantal Godin; 1 Georges Lévesque;
1 Université Laval, Québec, QC, Canada
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| Content: | Objectives: Independently of its role in amyloïd production, presenilin1 also participates in other pathways within the cell, among those is the putative neural plakophilin-related armadillo protein (NPRAP or delta catenin). NPRAP is a brain specific protein, interacts with presenilin 1 and cadherins and maps to chromosome 5q15.2 near Cri-du-Chat deletion locus, a syndrome associated with severe mental retardation. Interestingly, it was reported that deletion of delta-catenin/NPRAP, leads to severe cognitive and synaptic dysfunction, which are both characteristics of Alzheimer’s disease (AD). The aim of this project is to elucidate the molecular mechanisms underlying the PS1/NPRAP interaction in normal and pathological conditions.
Materials and Methods: We use human neuroblastoma SH SY5Y cells transiently or stably overexpressing NPRAP and presenilins to characterize the functional PS1/NPRAP interaction. A variety of cellular and molecular techniques, such as, confocal microscopy, transfection, RT-PCR, immunoprecipitation and immunoblotting, cDNA microarray, cholinesterase and luciferase assays, yeast two hybrid system, cloning strategies (NPRAPΔNLS) and ChIP-cloning experiments were used to assess the NPRAP pathway.
Results: We observed that overexpressed presenilin 1 C-terminal fragment, which interacts with NPRAP, diminish NPRAP protein levels in a dose dependent manner. Further analysis revealed no decrease in NPRAP mRNA suggesting a role for PS1-CTF in NPRAP protein level modulation, but not gene expression. However, inhibition of protein degradation pathways failed to restore NPRAP protein levels. These results observed in pre-cleared lysates correlate with aggregation of NPRAP into a concentric, single, perinuclear structure, which also contains PS1-CTF. We also found changes in synaptophysin protein expression in the presence of mutant presenilin and NPRAP. Microarray analysis failed to identify the modulation of synaptophysin. However, it shows that NPRAP expression downregulates the level of butyrylcholinesterase, a enzyme linked to AD. This observation was confirmed by RT-PCR and enzymatic activity.
Conclusion: Here we show that wild type PS1-CTF, which harbored mutations responsible for early onset Alzheimer's disease, can change cytoplasmic distribution of NPRAP, from periphery where the later binds to cadherins, to a concentrical structure adjacent to the nucleus. This PS1-CTF/NPRAP phenomenon shows that, in some way, presenilins are involved with intracellular NPRAP mobility. We also demonstrate evidence of butyrylcholinesterase gene repression by NPRAP, leaving open the possibility of a novel function for this protein. These new results will help to understand the mechanism by which mutant presenilin can actually affect NPRAP induced gene regulation, thus extending our findings to the comprehension of Alzheimer’s disease.* Altogether, our data suggest that PS1 via its interaction with NPRAP may has physiological roles linked to AD but independent of its role in A production.
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