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gamma-cleavage-independent functions of presenilin, nicastrin, and Aph-1 regulate cell-junction organization and prevent tau toxicity in vivo.

Research paper by Laura E LE Doglio, Ritu R Kanwar, George R GR Jackson, Mar M Perez, Jesús J Avila, Colin C Dingwall, Carlos G CG Dotti, Mark E ME Fortini, Fabián F Feiguin

Indexed on: 06 May '06Published on: 06 May '06Published in: Neuron



Abstract

Genetic analysis of familial Alzheimer's disease has revealed that mutations in the gamma-secretase enzyme presenilin promote toxic Abeta secretion; however, presenilin mutations might also influence tau hyperphosphorylation and neurodegeneration through gamma-secretase-independent mechanisms. To address this possibility and determine whether other components of the gamma-secretase complex possess similar regulatory functions, we analyzed the roles of presenilin, nicastrin, and aph-1 in a Drosophila model for tau-induced neurodegeneration. Here, we show that presenilin and nicastrin prevent tau toxicity by modulating the PI3K/Akt/GSK3beta phosphorylation pathway, whereas aph-1 regulates aPKC/PAR-1 activities. Moreover, we found that these transmembrane proteins differentially regulate the intracellular localization of GSK3beta and aPKC at cell junctions. Inhibition of gamma-secretase activity neither interfered with these kinase pathways nor induced aberrant tau phosphorylation. These results establish new in vivo molecular functions for the three components of the gamma-secretase complex and reveal a different mechanism that might contribute to neuronal degeneration in Alzheimer's disease.