The divergent DSL ligand Dll3 does not activate Notch signaling but cell autonomously attenuates signaling induced by other DSL ligands

Abstract

Mutations in the DSL (Delta, Serrate, Lag2) Notch (N) ligand Delta-like (Dll) 3 cause skeletal abnormalities in spondylocostal dysostosis, which is consistent with a critical role for N signaling during somitogenesis. Understanding how Dll3 functions is complicated by reports that DSL ligands both activate and inhibit N signaling. In contrast to other DSL ligands, we show that Dll3 does not activate N signaling in multiple assays. Consistent with these findings, Dll3 does not bind to cells expressing any of the four N receptors, and N1 does not bind Dll3-expressing cells. However, in a cell-autonomous manner, Dll3 suppressed N signaling, as was found for other DSL ligands. Therefore, Dll3 functions not as an activator as previously reported but rather as a dedicated inhibitor of N signaling. As an N antagonist, Dll3 promoted Xenopus laevis neurogenesis and inhibited glial differentiation of mouse neural progenitors. Finally, together with the modulator lunatic fringe, Dll3 altered N signaling levels that were induced by other DSL ligands.

Regulation of Notch signaling by glycosylation

“…In general, the binding of soluble Delta1 ECD to Notch1 or Notch2 assayed by flow cytometry or immunofluorescence microscopy has conformed to predictions [19,21]. By contrast, Delta3 does not bind to Notch1 nor activate Notch signaling [22]. In addition, Jagged1 binding is not significantly altered by overexpression of Lfng, Mfng or Rfng, despite the fact that Jagged1-induced Notch1 signaling is affected by each Fringe in signaling assays [19].…”

Proteolytic Processing of Delta-like 1 by ADAM Proteases

“…QT6 or mouse L fibroblasts were employed to present Notch ligands to Notch-expressing cells (21,32). One of the reasons of a modest increase in Notch activity in our system may be that co-culture with control CHO.Vec cells had already stimulated Notch 4 -5-fold when compared with the conditions without CHO.Vec cells (results are not shown).…”

Sphingosine-1-phosphate promotes expansion of cancer stem cells via S1PR3 by a ligand-independent Notch activation

“…Notch is generally activated by binding of Notch ligands to Notch and then cleaved by ADAM17 and g-secretase 25 . Among Notch ligands (Jagged1, 2 and Delta-like ligand (Dll) 1, 3 and 4), Dll3 is not capable to activate Notch signalling in adjacent cells 26 .…”