Requirement for presenilin 1 in facilitating lagged 2-mediated endoproteolysis and signaling of notch 1

Presenilin 1 (PS1), a polytopic membrane protein, is required for endoprote olytic processing at gamma -secretase site within the transmembrane domain of amyloid precursor proteins (APP). In addition, PS1 and its orthologues f acilitate signaling of Notch family members, cell-surface receptors that sp ecify cell fates during development. To clarify the mechanism(s) by which P S facilitates Notch signaling, we examined human Jagged-2-dependent metabol ism and activity of a chimeric full-length Notch1-GFP molecule expressed in fibroblasts with heterozygous, or homozygous deletions of PS1. We demonstr ate that PS1 is required for facilitating lagged 2-mediated proteolysis and that translocation and accumulation of NICD in the nucleus correlates with signaling activity. Moreover, in a ligand-independent, Ca2+-depletion para digm, we demonstrate that PS1 facilitates endoproteolysis of a plasma-membr ane-associated, Notch1-GFP derivative. Finally, we report that NICD product ion is inhibited by L-685,458, a potent and selective inhibitor that blocks solubilized gamma -secretase activity and A beta production in cultured ce lls. These findings strongly suggest that intramembranous processing of APP and Notch 1 are mediated by similar, if not identical, proteases that requ ire PS1 for their activation.