Effect of PS1 deficiency and an APP gamma-secretase inhibitor on Notch1 signaling in primary mammalian neurons

Presenilin 1 (PSI) has been implicated in normal Notch1 processing and sign aling in several experimental systems. In the present study, the relationsh ip between PS1 and Notch1 in mammalian neurons is studied by analyzing Notc h1 cleavage and C-terminal nuclear translocation as well as Notch I signali ng via the transactivation of a CBFI-luciferase reporter construct. We show that full-length Notch1 [NI(FL)I transfected into wild type (WT) primary n eurons is cleaved in the presence of its biological ligand Delta (DI) and t ranslocated to the nucleus within 1-3 min of ligand addition. PS1 deficient neurons show normal Notch1 insertion into the cellular membrane, yet lack Notch1 activation resulting in markedly inhibited nuclear translocation of the C-terminal Notch fragment (NICD). PSI deficient neurons also have impai red Notch 1 signaling which can be restored fully or partially to levels se en in WT littermates by transfection with WT or familial Alzheimer's diseas e-associated M146L mutant PS1, respectively. We also show that pharmacologi cal inhibition of PS1-associated gamma -secretase activity parallels the ef fects of genetic PS1 deficiency in these assays. These results support the hypothesis that PS1 deficiency blocks neuronal Notch1 processing and signal ing. (C) 2001 Elsevier Science B.V. All rights reserved.