Evidence for a physical interaction between presenilin and Notch

Area of Science:

• Molecular Biology
• Cell Biology
• Neuroscience

Background:

• Genetic studies in C. elegans revealed that sel-12 and hop-1, homologs of Alzheimer's disease-associated presenilin genes, influence signaling via LIN-12 and GLP-1, homologs of the Notch receptor.
• Understanding the biochemical basis of this genetic interaction is crucial for elucidating the role of presenilins in cellular signaling.

Purpose of the Study:

• To investigate the potential physical association between presenilin-1 (PS1) and the Notch1 receptor in mammalian cells.
• To determine the nature and location of the interaction between PS1 and Notch1 within the cell.

Main Methods:

• Coimmunoprecipitation assays using human embryonic kidney 293 cells transiently transfected with Notch1 and PS1.
• Metabolic labeling of cells with [35S]methionine and [35S]cysteine followed by immunoprecipitation.
• Coimmunoprecipitation from cultured Drosophila cells to assess interaction at physiological expression levels.

Main Results:

• Notch1 and PS1 were found to coimmunoprecipitate from cell lysates in a detergent-sensitive manner, indicating a noncovalent physical association.
• The interaction primarily occurred in the early secretory pathway, before Notch cleavage, with PS1 immunoprecipitation recovering full-length Notch1 precursor.
• Notch1 was the predominant protein detected in PS1 immunoprecipitates, suggesting specificity, and endogenous Notch and presenilin also coimmunoprecipitated in Drosophila cells.

Conclusions:

• Presenilins directly physically associate with the Notch receptor.
• This physical interaction occurs within the secretory pathway.
• The findings suggest that the genetic link between presenilins and Notch signaling is mediated by this direct physical association.