Microtubular interactions of presenilin direct kinesis of Abeta peptide and its precursors.

In our previous study we demonstrated that presenilin 1 (PS1) interacts with cytoplasmic linker protein 170/Restin (CLIP-170/Restin). Herein we show that disruption of the interaction of these proteins within neuronal cell-lines (SY5Y and N2a) can be accomplished by the transfection of vectors that drive the expression of peptide fragments corresponding to their binding domains (BDPs). Interestingly, the disruption of the PS1/CLIP-170 complex is associated with both decreased secretion of endogenous Abeta and decreased uptake of exogenous Abeta from the medium. BDP-expressing cells were also more resistant to surges of Abeta secretion induced by thapsigargin and ionomycin (that elevate intracellular calcium concentrations) and mutations in PS1 linked to familial Alzheimer's disease. Uptake of Abeta by SY5Y cells was amplified when preincubated with ApoE and was mediated through lipoprotein receptor-related protein (LRP). BDP-expressing cells or cells treated with PS1 anti-sense oligonucleotides were less capable of taking up Abeta from the medium compared with controls, indicating that the PS1/CLIP-170 interaction is involved and that PS1 cannot be substituted. In this study, we also mapped the minimum binding domains (mBDPs) of PS1 and CLIP-70 to regions corresponding to the N-terminal end of the large cytoplasmic loop of PS1 and the metal binding motif-containing C-terminal end of CLIP-170. Further, our data obtained from experiments involving in vitro taxol-polymerization of tubulin and confocal immunofluorescence suggest that PS1, via CLIP-170, may serve as an anchor to the microtubules for specific subcellular fractions containing amyloidogenic fragments. Interestingly, Notch is absent from this population of microtubule binding subcellular fractions and its cleavage was unaffected in cells transfected with the PS1-based BDP. This raises the possibility that the interaction of PS1 with CLIP-170 could provide the conceptual basis for anti-amyloidogenic therapeutic strategies with improved specificity. However, this approach may be hampered by a low efficiency, because it may also block Abeta clearance from the interstitial space of the CNS.