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Evidence of non-canonical NOTCH signaling: Delta-like 1 homolog (DLK1) directly interacts with the NOTCH1 receptor in mammals

2016; Elsevier BV; Volume: 28; Issue: 4 Linguagem: Inglês

10.1016/j.cellsig.2016.01.003

1873-3913

Gunnhildur Ásta Traustadóttir, Charlotte Harken Jensen, Mads Thomassen, Hans Christian Beck, Sussi Bagge Mortensen, Jorge Laborda, Victoriano Baladrón, Søren P. Sheikh, Ditte Caroline Andersen,

Cerebrovascular and genetic disorders

Canonical NOTCH signaling, known to be essential for tissue development, requires the Delta-Serrate-LAG2 (DSL) domain for NOTCH to interact with its ligand. However, despite lacking DSL, Delta-like 1 homolog (DLK1), a protein that plays a significant role in mammalian development, has been suggested to interact with NOTCH1 and act as an antagonist. This non-canonical interaction is, however controversial, and evidence for a direct interaction, still lacking in mammals. In this study, we elucidated the putative DLK1-NOTCH1 interaction in a mammalian context. Taking a global approach and using Dlk1+/+ and Dlk1−/− mouse tissues at E16.5, we demonstrated that several NOTCH signaling pathways indeed are affected by DLK1 during tissue development, and this was supported by a lower activation of NOTCH1 protein in Dlk1+/+ embryos. Likewise, but using a distinct Dlk1-manipulated (siRNA) setup in a mammalian cell line, NOTCH signaling was substantially inhibited by DLK1. Using a mammalian two-hybrid system, we firmly established that the effect of DLK1 on NOTCH signaling was due to a direct interaction between DLK1 and NOTCH1. By careful dissection of this mechanism, we found this interaction to occur between EGF domains 5 and 6 of DLK1 and EGF domains 10–15 of NOTCH1. Thus, our data provide the first evidence for a direct interaction between DLK1 and NOTCH1 in mammals, and substantiate that non-canonical NOTCH ligands exist, adding to the complexity of NOTCH signaling.