PathwayStep5509 PathwayStep5510 PathwayStep5511 PathwayStep5512 PathwayStep5513 PathwayStep5514 PathwayStep5515 PathwayStep5516 Transport of NOTCH precursor to Golgi Sialylation of Pre-NOTCH Fringe-modified Pre-NOTCH is cleaved by FURIN Mature NOTCH heterodimer traffics to the plasma membrane Transport of fringe-modified NOTCH to plasma membrane NOTCH precursor cleaved to form mature NOTCH Glycosylation of Pre-NOTCH by FRINGE Galactosylation of Pre-NOTCH Pre-NOTCH Processing in Golgi Authored: Jassal, B, 2004-12-15 13:08:03 Edited: D'Eustachio, P, 2012-02-06 Edited: Orlic-Milacic, M, 2012-02-10 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). <br><br> <br>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). <br> <br> <br>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 EGF repeats (GlcNAc-bet1,3-fucitol). Three fringe enzymes are known in mammals: LFNG (lunatic fringe), MFNG (manic fringe) and RFNG (radical fringe). LFNG shows the highest catalytic activity in modifying NOTCH (Bruckner et al. 2000, Moloney et al. 2000). Fringe-created disaccharide chains on NOTCH EGF repeats are further extended by B4GALT1 (beta-1,4-galactosyltransferase 1), which adds galactose to the N-acetylglucosaminyl group, resulting in formation of trisaccharide Gal-beta1,4-GlcNAc-beta1,3-fucitol chains (Moloney et al. 2000, Chen et al. 2001). Formation of trisaccharide chains is the minimum requirement for fringe-mediated modulation of NOTCH signaling, although fringe-modified NOTCH expressed on the cell surface predominantly contains tetrasaccharide chains on EGF repeats. The tetrasaccharide chains are formed by sialyltransferase(s) that add sialic acid to galactose, resulting in formation of Sia-alpha2,3-Gal-beta1,4-GlcNAc-beta1,3-fucitol (Moloney et al. 2000). Three known Golgi membrane sialyltransferases could be performing this function: ST3GAL3, ST3GAL4 and ST3GAL6 (Harduin-Lepers et al. 2001). The modification of NOTCH by fringe enzymes modulates NOTCH-signaling by increasing the affinity of NOTCH receptors for delta-like ligands, DLL1 and DLL4, while decreasing affinity for jagged ligands, JAG1 and JAG2. Pubmed10366590 Pubmed10459009 Pubmed10669757 Pubmed10935626 Pubmed10935637 Pubmed11135303 Pubmed11707585 Pubmed1295745 Pubmed1764995 Pubmed19701457 Pubmed20170518 Pubmed20197277 Pubmed7918097 Pubmed8293978 Pubmed8681805 Pubmed9187150 Pubmed9244302 Pubmed9653148 Pubmed9727485 Reactome Database ID Release 431912420 Reactome, http://www.reactome.org ReactomeREACT_118798 Reviewed: Haw, R, 2012-02-06 Reviewed: Joutel, A, 2004-12-15