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J Biol Chem. 2010 May 14;285(20):14920-31. doi: 10.1074/jbc.M109.038760. Epub 2010 Mar 18.

Human CRB2 inhibits gamma-secretase cleavage of amyloid precursor protein by binding to the presenilin complex.

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Molecular Neuroscience Research Center, Shiga University of Medical Science, Shiga 520-2192, Japan.


Drosophila Crumbs has been reported to attenuate Notch signaling by inhibition of gamma-secretase cleavage at the wing margins. gamma-Secretase is an intramembrane protease that is responsible for the generation of amyloid-beta (Abeta) peptides from the beta-amyloid precursor protein (APP). Here, we re-examined gamma-secretase inhibition by human CRB2, which is the most abundant Crumbs ortholog in the brain. Transfected CRB2 inhibited proteolytic production of Abeta and APP intracellular domains from APP C-terminal fragments in HEK293 and SH-SY5Y cells. Conversely, knockdown of endogenous CRB2 increased gamma-secretase cleavage products in SH-SY5Y cells. CRB2 inhibition of gamma-cleavage was also detected in cell-free assays. CRB2 interacted with the gamma-secretase complex, but was not a competitive substrate for gamma-cleavage. The transmembrane domain of CRB2 was indispensable for inhibition of Abeta generation and mediated CRB2 binding with the gamma-secretase complex. In addition, the cytoplasmic domain appeared to play a supportive role in gamma-secretase inhibition, whereas mutational disruption of the two protein-binding motifs involved in the formation of cell adhesion complexes did not affect gamma-secretase inhibition. Co-overexpression of presenilin-1 or APH-1 abrogated gamma-secretase inhibition probably through prevention of the incorporation of CRB2 into the gamma-secretase complex. Our results suggest that CRB2 functions as an inhibitory binding protein that is involved in the formation of a mature but inactive pool of the gamma-secretase complex.

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