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  • Title: Novel alpha-secretase cleavage of Alzheimer's amyloid beta precursor protein in the endoplasmic reticulum of COS7 cells.
    Author: Shin RW, Saido TC, Maeda M, Kitamoto T.
    Journal: Neurosci Lett; 2005 Mar 07; 376(1):14-9. PubMed ID: 15694266.
    Abstract:
    In the processing of APP, alpha- and beta-secretase pathways compete with each other for cleaving APP. Therefore, physiologically these two secretases are likely to colocalize in the same subcellular compartments. Previously beta-secretase cleavage of APP was found in the endoplasmic reticulum (ER). We herein tested whether alpha-secretase cleavage is also detected in the ER. We used experimental system of COS7 cells transfected with cDNA encoding human APP695, and the cell lysates and media were examined for its proteolytic products. When APP expression is concentrated in the ER by BFA-mediated transport inhibition or by using mutant APP harboring an ER-retrieval motif, alpha-secretase product sAPPalpha was accumulated in the cells. Immunofluorescence microscopy revealed that the ER-targeted APP produced intracellular accumulation of sAPPalpha, colocalizing with an ER marker. These results indicate that alpha-secretase cleavage of APP occurs in the ER. Further we examined the effects of phorbol ester PDBu, a direct activator of PKC, on the alpha-secretase and beta-secretase cleavages of APP occurring in the ER. Treatment with PDBu of COS7 cells transfected with the ER-targeted APP increased production of sAPPalpha and conversely decreased production of beta-secretase product sAPPbeta. Thus, in the ER, alpha-secretase competes with beta-secretase for cleaving APP and such competitive correlation might modulate the production of Abeta42 found in this compartment.
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