Probable catalytic subunit of the gamma-secretase complex; an endoprotease complex that catalyzes the intramembrane cleavage of integral membrane proteins such as Notch receptors and APP (beta-amyloid precursor protein). Requires the other members of the gamma-secretase complex to have a protease activity. May play a role in intracellular signaling and gene expression or in linking chromatin to the nuclear membrane. Stimulates cell-cell adhesion though its association with the E-cadherin/catenin complex. Under conditions of apoptosis or calcium influx; cleaves E-cadherin promoting the disassembly of the E-cadherin/catenin complex and increasing the pool of cytoplasmic beta-catenin; thus negatively regulating Wnt signaling. May also play a role in hematopoiesis. {ECO:0000269|PubMed:10206644; ECO:0000269|PubMed:10545183; ECO:0000269|PubMed:10593990; ECO:0000269|PubMed:10811883; ECO:0000269|PubMed:10899933; ECO:0000269|PubMed:11226248; ECO:0000269|PubMed:15341515; ECO:0000269|PubMed:16305624}.