Schematic of the Notch
signaling pathway. (1) The Notch receptor
processing takes place in the ER, by the enzyme O-fut (O-fucosyltransferase) that adds fucose to
the Notch precursor. (2) In the trans-Golgi network, furin-like convertase
cleaves full-length Notch (S1 cleavage) generating a heterodimer molecule,
which is then glycosylated by Fringe proteins (3). (4) The heterodimer
Notch receptors are then trafficked to the cell membrane. (5) Activation
of Notch receptor takes place when a Delta/Serrate family of ligands
binds to the extracellular receptor of Notch. (6) Upon ligand binding,
S2 cleavage occurs by the ADAM protease (also known as TACE). (7)
The ligand bound to the Notch extracellular domain (NECD) gets internalized
by the signal sending cell and (8) gets degraded inside the lysosomes.
(9) S3 cleavage occurs by the γ-secretase enzyme, which results
in the release of the Notch intracellular domain (NICD) that gets
internalized into the nucleus (10) and (11) binds to the DNA binding
domain, CSL, thereby replacing the corepressors with the coactivators
and facilitating the transcription of Notch targeted genes. (12) In
the absence of NICD, the DNA binding domain, CSL, is bound to the
corepressor complex, which inhibits the transcription of Notch targeted
genes.