Neutralization of the γ-secretase activity by monoclonal antibody against extracellular domain of nicastrin.

Several lines of evidence suggest that aberrant Notch signaling contributes to the development of several types of cancer. Activation of Notch receptor is executed through intramembrane proteolysis by γ-secretase, which is a multimeric membrane-embedded protease comprised of presenilin, nicastrin (NCT), anterior pharynx defective 1 and PEN-2. In this study, we report the neutralization of the γ-secretase activity by a novel monoclonal antibody A5226A against the extracellular domain of NCT, generated by using a recombinant budded baculovirus as an immunogen. This antibody recognized fully glycosylated mature NCT in the active γ-secretase complex on the cell surface, and inhibited the γ-secretase activity by competing with the substrate binding in vitro. Moreover, A5226A abolished the γ-secretase activity-dependent growth of cancer cells in a xenograft model. Our data provide compelling evidence that NCT is a molecular target for the mechanism-based inhibition of γ-secretase, and that targeting NCT might be a novel therapeutic strategy against cancer caused by aberrant γ-secretase activity and Notch signaling.