Cyclic cis-Locked Phospho-Dipeptides Reduce Entry of A?PP into Amyloidogenic Processing Pathway.

ABSTRACT: The cis/trans isomerization of X-Pro peptide bonds in proteins in some instances acts as a molecular switch in biological pathways. Our prior work suggests that the cis isomer of the phospho-Thr668-Pro669 motif, located in the cytoplasmic domain of the amyloid-? protein precursor (A?PP), is correlated with an increase in amyloidogenic processing of A?PP and production of amyloid-beta (A?), the neurotoxic peptide fragment in Alzheimer's disease (AD). We designed a 100% cis-locked cyclic dipeptide composed of cyclized phospho-Thr-Pro (pCDP) as a mimic for this putative pathological conformation, and three phosphate-blocked derivatives (pCDP-diBzl, pCDP-Bzl, and pCDP-diPOM). Two H4 neuroglioma cell lines were established as AD cell models for use in testing these compounds: H4-A?PP695 for stable overexpression of wild-type A?PP695, and H4-BACE1 for stable overexpression of ?-site A?PP cleaving enzyme-1 (BACE1). The level of the secreted A?PP fragment resulting from BACE1 activity, sA?PP?, served as a key proxy for amyloidogenic processing, since cleavage of A?PP by BACE1 is a requisite first step in A? production. Of the compounds tested, pCDP-diBzl decreased sA?PP? levels in both cell lines, while pCDP-diPOM decreased sA?PP? levels in only H4-BACE1 cells, all with similar dose-dependences and patterns of proteolytic A?PP fragments. Enzymatic assays showed that none of the pCDP derivatives directly inhibit BACE1 catalytic activity. These results suggest a model in which pCDP-diBzl and pCDP-diPOM act at a common point to inhibit entry of A?PP into the amyloidogenic A?PP processing pathway but through different targets, and provide important insights for the development of novel AD therapeutics.

SUBMITTER: Fisher CL 

PROVIDER: S-EPMC5096988 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature