Regulation of Notch Signaling by O-Linked Fucose

Abstract

Notch and its ligands are modified by a protein O-fucosyltransferase (OFUT1) that attaches fucose to a Serine or Threonine within EGF domains. By using RNAi to decrease Ofut1 expression in Drosophila, we demonstrate that O-linked fucose is positively required for Notch signaling, including both Fringe-dependent and Fringe-independent processes. The requirement for Ofut1 is cell autonomous, in the signal-receiving cell, and upstream of Notch activation. The transcription of Ofut1 is developmentally regulated, and surprisingly, overexpression of Ofut1 inhibits Notch signaling. Together, these results indicate that OFUT1 is a core component of the Notch pathway, which is required for the activation of Notch by its ligands, and whose regulation may contribute to the pattern of Notch activation during development.

Protein O -fucosyltransferase 1 is an essential component of Notch signaling pathways

“…Furthermore, it seems likely that O-fucose is required on the extracellular domain of all mammalian Notch receptors for Notch signaling to occur. Whereas O-FucT-1 is predicted to act on Notch ligands (6), the phenotype of Pofut1 Ϫ/Ϫ embryos suggests a cell-autonomous function for O-FucT-1 in the Notch-expressing cell, as was also found in Drosophila (17). However, it is also possible that ligand phenotypes are masked or precluded by the early death of Pofut1 Ϫ/Ϫ embryos.…”

“…The Notch signaling defects in Pofut1 Ϫ/Ϫ mouse embryos and the results of down-regulation of O-FucT-1 by RNA interference in Drosophila (17) show that O-fucose on Notch clearly does not function solely as the substrate of Fringe. The somitogenic phenotype of Pofut1 Ϫ/Ϫ mouse embryos is consistent with inactivation of Notch1, Notch2, and Notch4 in PSM (22,27); the vasculogenic and cardiogenic phenotypes are consistent with inactivation of Notch1 and Notch4 during development (22); and the neurogenic phenotype is consistent with inactivation of Notch1 and Notch3 in neuroepithelium (47).…”

“…If decreased Notch signaling is due to reduced O-fucose on Notch, inactivation of protein O-fucosyltransferase 1 (O-FucT-1) should give a Notch receptor mutant phenotype. Consistent with this prediction, RNA interference (RNAi) of Drosophila OFUT1 was recently shown to cause both Fringe-dependent and Fringeindependent developmental defects typical of Notch receptor inactivation (17). Mammals have four Notch receptors, with the Notch1 receptor being most similar to Drosophila Notch.…”

Physiology and pathology of notch signalling system

“…Another explanation could be that all mutations really cause altered receptor activity by the classic RBP/JK system, but in some cases the anomalies of the signalling system are not in vitro detectable. Notch signalling activity is, in fact, highly dependent on cell context (Okajima and Irvine, 2002) and it is regulated by signal activity modulators (Justice and Jan, 2002) not always detectable in vitro.…”

The Amadori Rearrangement for Carbohydrate Conjugation: Scope and Limitations

“…They serve as a source of energy and as structural material in plants, and they also play a key role in cell–cell recognition and communication,1 cellular differentiation,2 and immune response,3 both in healthy and disease states of living organisms.…”