The non-canonical NOTCH1 ligand Delta-like 1 homolog (DLK1) self interacts in mammals

In the present study, we employed the mammalian two-hybrid (MTH) system, a genetic in vivo protein-protein interaction system, to show robust DLK1-DLK1, DLK1-FnI (Fibronectin) and DLK1-CFR (cysteine-rich FGF receptor) interactions, whereas the proposed DLK1-IGFBP1 interaction was not supported by MTH. Very little has previously been described on the DLK1 self-interaction. Herein, we showed by immunoprecipitation as well as Sulfo-SBED label transfer that the DLK1-DLK1 interaction likely is part of Dlk1's function in preadipocytes. Furthermore our data suggest that DLK1 interacts with itself through EGF domain 4 and 5, which is distinct from the recently described NOTCH1-DLK1 interaction, which occurs between EGF domain 5 and 6. This opens up the possibility that Notch independent mechanisms like the DLK1-DLK1 interaction may modulate the non-canonical NOTCH1-DLK1 interaction further complexing this system.