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 gamma-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 gamma-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 gamma-secretase complex on the cell surface, and inhibited the gamma-secretase activity by competing with the substrate binding in vitro. Moreover, A5226A abolished the gamma-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 gamma-secretase, and that targeting NCT might be a novel therapeutic strategy against cancer caused by aberrant gamma-secretase activity and Notch signaling. Oncogene (2012) 31, 787-798; doi:10.1038/onc.2011.265; published online 4 July 2011