Pen2 and Presenilin-1 Modulate the Dynamic Equilibrium of Presenilin-1 and Presenilin-2 γ-Secretase Complexes

Lisa Placanica,Leonid Tarassishin,Guangli Yang,Erica Peethumnongsin,Seong-Hun Kim,Hui Zheng,Sangram S Sisodia,Yue-Ming Li

doi:10.1074/jbc.m807269200

Abstract

gamma-Secretase is known to play a pivotal role in the pathogenesis of Alzheimer disease through production of amyloidogenic Abeta42 peptides. Early onset familial Alzheimer disease mutations in presenilin (PS), the catalytic core of gamma-secretase, invariably increase the Abeta42:Abeta40 ratio. However, the mechanism by which these mutations affect gamma-secretase complex formation and cleavage specificity is poorly understood. We show that our in vitro assay system recapitulates the effect of PS1 mutations on the Abeta42:Abeta40 ratio observed in cell and animal models. We have developed a series of small molecule affinity probes that allow us to characterize active gamma-secretase complexes. Furthermore we reveal that the equilibrium of PS1- and PS2-containing active complexes is dynamic and altered by overexpression of Pen2 or PS1 mutants and that formation of PS2 complexes is positively correlated with increased Abeta42:Abeta40 ratios. These data suggest that perturbations to gamma-secretase complex equilibrium can have a profound effect on enzyme activity and that increased PS2 complexes along with mutated PS1 complexes contribute to an increased Abeta42:Abeta40 ratio.

Highlights

␤-Amyloid (A␤)5 peptides are believed to play a causative role in Alzheimer disease (AD)
Using newly developed biotinylated small molecular probes and activity assays, we revealed that expression of presenilin enhancer 2 (Pen2) or PS1 familial early onset AD (FAD) mutants markedly shifts the equilibrium of PS1containing active complexes to that of PS2-containing complexes and results in an overall increase in the A␤42:A␤40 ratio in both stable cell lines and animal models
This is consistent with earlier reports that showed that the C terminus of Pen2 is critical for complex formation [34] and that expression of a C-terminally tagged Pen2 (Pen2-Myc-His6) resulted in destabilization of the PS1 heterodimer and mature Nct [8]

Summary

Introduction

␤-Amyloid (A␤)5 peptides are believed to play a causative role in Alzheimer disease (AD). Using newly developed biotinylated small molecular probes and activity assays, we revealed that expression of Pen2 or PS1 FAD mutants markedly shifts the equilibrium of PS1containing active complexes to that of PS2-containing complexes and results in an overall increase in the A␤42:A␤40 ratio in both stable cell lines and animal models.

Results

Conclusion