Pre-NOTCH Expression and Processing

The cleavage of NOTCH results in formation of mature NOTCH heterodimers that consist of NOTCH extracellular domain (NEC i.e. NECD) and NOTCH transmembrane and intracellular domain (NTM i.e. NTMICD). NOTCH heterodimers translocate to the cell surface where they function in cell to cell signaling.


Pre-NOTCH Expression and Processing ↗
Stable identifier: R-HSA-1912422 Compartments: nucleoplasm, cytosol, endoplasmic reticulum membrane, endoplasmic reticulum lumen, Golgi membrane, Golgi lumen, plasma membrane In humans and other mammals the NOTCH gene family has four members, NOTCH1, NOTCH2, NOTCH3 and NOTCH4, encoded on four different chromosomes. Their transcription is developmentally regulated and tissue specific, but very little information exists on molecular mechanisms of transcriptional regulation. Translation of NOTCH mRNAs is negatively regulated by a number of recently discovered microR-NAs (Li et al. 2009, Pang et al.2010, Ji et al. 2009, Kong et al. 2010, Marcet et al. 2011, Ghisi et al. 2011, Song et al. 2009, Hashimoto et al. 2010, Costa et al. 2009).
The nascent forms of NOTCH precursors, Pre-NOTCH1, Pre-NOTCH2, Pre-NOTCH3 and Pre-NOTCH4, undergo extensive posttranslational modifications in the endoplasmic reticulum and Golgi apparatus to become functional. In the endoplasmic reticulum, conserved serine and threonine residues in the EGF repeats of NOTCH extracellular domain are fucosylated and glucosylated by POFUT1 and POGLUT1, respectively (Yao et al. 2011, Stahl et al. 2008, Wang et al. 2001, Shao et al. 2003, Acar et al. 2008, Fernandez Valdivia et al. 2011).
In the Golgi apparatus, fucose groups attached to NOTCH EGF repeats can be elongated by additional glycosylation steps initiated by fringe enzymes (Bruckner et al. 2000, Cohen et al. 1997, Johnston et al. 1997, Chen et al. 2001. Fringe-mediated modification modulates NOTCH signaling but is not an obligatory step in Pre-NOTCH processing. Typically, processing of Pre-NOTCH in the Golgi involves cleavage by FURIN convertase (Blaumueller et al. 1997, Logeat et al. 1998, Gordon et al. 2009, Rand et al. 2000, Chan et al. 1998

Stable identifier: R-HSA-1912399
Compartments: endoplasmic reticulum membrane, endoplasmic reticulum lumen In the endoplasmic reticulum, glycosyl transferases modify NOTCH precursors by glycosylating conserved serine and threonine residues in EGF repeats of NOTCH.
O-fucosyl transferase POFUT1 fucosylates NOTCH serine and threonine residues that conform to the consensus sequence C2-X(4-5)-S/T-C3, where C2 and C3 are the second and third cysteine residue within the EGF repeat, and X(4-5) is four to five amino acid residues of any type (Yao et al. 2011, Stahl et al. 2008, Wang et al. 2001, Shao et al. 2003.
O-glucosyl transferase POGLUT1, mammalian homolog of the Drosophila enzyme Rumi, adds a glucosyl group to conserved serine residues within the EGF repeats of NOTCH. The consensus sequence for PO-GLUT1-mediated glucosylation is C1-X-S-X-P-C2, where C1 and C2 are the first and second cysteine residue in the EGF repeat, respectively, while X represents any amino acid (Acar et al. 2008, Fernandez-Valdivia et al. 2011. Both fucosylation and glucosylation of NOTCH receptor precursors are essential for functionality.

Literature references
Lopez, M., Fernandez-Valdivia, R., Takeuchi, H., Leonardi, J., Haltiwanger, RS., Jafar-Nejad, H. et al. (2011). Regulation of mammalian Notch signaling and embryonic development by the protein O-glucosyltransferase Rumi. Development, 138, 1925-34 Compartments: Golgi membrane, Golgi lumen, plasma membrane, endoplasmic reticulum membrane NOTCH undergoes final posttranslational processing in the Golgi apparatus (Lardelli et al. 1994, Blaumueller et al. 1997, Weinmaster et al. 1991, Weinmaster et al. 1992, Uyttendaele et al. 1996. Movement of NOTCH precursors from the endoplasmic reticulum to Golgi is controlled by SEL1L protein, a homolog of C. elegans sel-1. SEL1L localizes to the endoplasmic reticulum membrane and prevents translocation of misfolded proteins, therefore serving as a quality control check (Li et al. 2010, Sundaram et al. 1993, Francisco et al. 2010. Similarly, C. elegans sel-9 and its mammalian homolog TMED2 are Golgi membrane proteins that participate in quality control of proteins transported from Golgi to the plasma membrane. Translocation of a mutant C. elegans NOTCH homolog lin-12 from the Golgi to the plasma membrane is negatively regulated by sel-9 (Wen et al. 1999). A GTPase RAB6 positively controls NOTCH trafficking through Golgi (Purcell et al. 1999).
Processing of mammalian NOTCH precursors in the Golgi typically involves the cleavage by FURIN convertase. Pre-NOTCH is a ~300 kDa protein, and cleavage by FURIN produces two fragments with approximate sizes of 110 kDa and 180 kDa. The 110 kDa fragment contains the transmembrane and intracellular domains of NOTCH and is known as NTM or NTMICD. The 189 kDa fragment contains NOTCH extracellular sequence and is known as NEC or NECD. The NTM and NEC fragments heterodimerize (Blaumueller et al. 1997, Logeat et al. 1998, Chan et al. 1998) and are held together by disulfide bonds and calcium ions (Rand et al. 2000, Gordon et al. 2009).
An optional step in Pre-NOTCH processing in the Golgi is modification by fringe enzymes. Fringe enzymes are glycosyl transferases that initiate elongation of O-linked fucose on fucosylated peptides by addition of a beta 1,3 N-acetylglucosaminyl group, resulting in formation of disaccharide chains on NOTCH