NOTCH1 functions as a receptor for membrane-bound ligands Jagged1, Jagged2 and Delta1 to regulate cell-fate determination. Upon ligand activation through the released notch intracellular domain (NICD) it forms a transcriptional activator complex with RBP-J kappa and activates genes of the enhancer of split locus. This protein effects the implementation of differentiation, proliferation and apoptotic programs, and may be important for normal lymphocyte function. In altered form, it may contribute to transformation or progression in some T-cell neoplasms. In fetal tissues it is most abundant in spleen, brain stem and lung. NOTCH1 is also present in most adult tissues where it is found mainly in lymphoid tissues. NOTCH1 is synthesized in the endoplasmic reticulum as an inactive form which is proteolytically cleaved by a furin-like convertase in the trans-Golgi network before it reaches the plasma membrane to yield an active, ligand-accessible form. Cleavage results in a C-terminal fragment N(TM) and a N-terminal fragment N(EC). Following ligand binding, it is cleaved by TNF-alpha converting enzyme (TACE) to yield a membrane-associated intermediate fragment called notch extracellular truncation (NEXT). This fragment is then cleaved by presenilin dependent gamma-secretase to release a notch-derived peptide containing the intracellular domain (NICD) from the membrane NOTCH1 truncation is associated with T-cell acute lymphoblastic leukemia. NOTCH1 contains a putative 5 ANK repeats and 36 EGF-like domains.
