Evidence for a physical interaction between presenilin and Notch

Genetic analyses in Caenorhabditis elegans demonstrate that sel-12 and hop- 1, homologues of the Alzheimer's disease-associated presenilin genes, modif y signaling through LIN-12 and GLP-1, homologues of the Notch cell surface receptor. To gain insight into the biochemical basis of this genetic intera ction, we tested the possibility that presenilin-1 (PS1) physically associa tes with the Notch1 receptor in mammalian cells. Notch1 and PSI coimmunopre cipitated from transiently transfected human embryonic kidney 293 cell lysa tes in a detergent-sensitive manner, consistent with a noncovalent physical association between the two proteins. The interaction predominantly occurr ed early in the secretory pathway prior to Notch cleavage in the Golgi, bec ause PS1 immunoprecipitation preferentially recovered the full-length Notch 1 precursor. When PS1 was immunoprecipitated from 293 cells that had been m etabolically labeled with [S-35]methionine and [35S]cysteine, Notch1 was th e primary protein detected in PS1 immunoprecipitates, suggesting that this interaction is specific. Furthermore, endogenous Notch and presenilin coimm unoprecipitated from cultured Drosophila cells, indicating that physical in teraction can occur at physiological expression levels. These results sugge st that the genetic relationship between presenilins and the Notch signalin g pathway derives from a direct physical association between these proteins in the secretory pathway.