et al., 2007). These studies suggest that PS1/γ-secretase plays a role of tumor suppressor in fibroblasts. In that regard, PS1 is implicated as a negative regulator of the Wnt/β-catenin signaling pathway (Xia et al., 2001). Following its cleavage, PS1CTF/NTF forms a complex with GSK3 and β-catenin (Tesco and Tanzi, 2000). Kang and colleagues suggest that PS1 functions as a scaffold that rapidly couples β-catenin phosphorylation through sequential kinase activities independent of the Wnt-regulated Axin/CK1α complex (Kang et al., 2002).
