Abstract
Delta1 acts as a membrane-bound ligand that interacts with the Notch receptor and plays a critical role in cell fate specification. By using peptide affinity chromatography followed by mass spectrometry, we have identified Dlg1 as a partner of the Delta1 C-terminal region. Dlg1 is a human homolog of the Drosophila Discs large tumor suppressor, a member of the membrane-associated guanylate kinase family of molecular scaffolds. We confirmed this interaction by co-immunoprecipitation experiments between endogenous Dlg1 and transduced Delta1 in a 3T3 cell line stably expressing Delta1. Moreover, we showed that deletion of a canonical C-terminal PDZ-binding motif (ATEV) in Delta1 abrogated this interaction. Delta4 also interacted with Dlg1, whereas Jagged1, another Notch ligand, did not. In HeLa cells, transfected Delta1 triggered the accumulation of endogenous Dlg1 at sites of cell-cell contact. Expression of Delta1 also reduced the motility of 3T3 cells. Finally, deletion of the ATEV motif totally abolished these effects but did not interfere with the ability of Delta1 to induce Notch signaling and T cell differentiation in co-culture experiments. These results point to a new, probably cell-autonomous function of Delta1, which is independent of its activity as a Notch ligand.
Highlights
Notch receptors and their ligands are essential in many binary cell fate decisions in various tissues from worm to vertebrates
The Notch receptor undergoes two proteolytic cleavages [10, 11], which release the intracellular region of the receptor that translocates into the nucleus, where it participates in transcriptional activation of target genes together with CSL and Mastermind [12,13,14,15]
The Notch ligands are well known as activators of the Notch cascade by an intercellular mechanism, but some results suggest that they might exhibit an intrinsic function in the signaling cell [8, 22, 34]
Summary
Notch receptors and their ligands are essential in many binary cell fate decisions in various tissues from worm to vertebrates. Deletion of the four C-terminal residues encompassing the Delta1 PDZ-binding motif abolished the Delta1/Dlg1 interaction but did not affect Notch activation in a T cell differentiation assay.
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