Dilysine retrieval signal-containing p24 proteins collaborate in inhibiting gamma-cleavage of amyloid precursor protein.

摘要

gamma-Secretase mediates intramembranous gamma-cleavage and epsilon-cleavage of beta-amyloid precursor protein (APP) to liberate beta-amyloid peptide (Abeta) and APP intracellular domain respectively from the membrane. Although the regulatory mechanism of gamma-secretase cleavage remains unresolved, a member of the p24 cargo protein family, named p24delta(1) or TMP21, has been identified as an activity-modulating component. The p24 family proteins are divided into four subfamilies (p24alpha, beta, delta and gamma). In contrast to p24delta(1), p24beta(1) has reportedly no effect on gamma-cleavage. In this study, we determined whether p24alpha(2), p24gamma(3) or p24gamma(4) modulates APP processing. Knockdown of cellular p24alpha(2) induced a significant increase in Abeta generation but not in APP intracellular domain production in cell-based and cell-free assays, whereas p24alpha(2) over-expression suppressed Abeta secretion. By contrast, Abeta secretion was not altered by p24gamma(3) or p24gamma(4) knockdown. Endogenous p24alpha(2) co-immunoprecipitated with core components of the gamma-secretase complex, and the anti-p24alpha(2) immunoprecipitate exhibited gamma-secretase activity. Mutational disruption of the conserved dilysine ER-retrieval motifs of p24alpha(2) and p24delta(1) perturbed inhibition of gamma-cleavage. Simultaneous knockdown, or co-over-expression, of these proteins had no additive or synergistic effect on Abeta generation. Our findings suggest that dilysine ER-retrieval signal-containing p24 proteins, p24alpha(2) and p24delta(1), bind with gamma-secretase complexes and collaborate in attenuating gamma-cleavage of APP.