title: The EGF-like proteins DLK1 and DLK2 function as inhibitory non-canonical ligands of NOTCH1 receptor that modulate each other's activities.
abstract: The protein DLK2, highly homologous to DLK1, belongs to the EGF-like family of membrane proteins, which includes NOTCH receptors and their DSL-ligands. The molecular mechanisms by which DLK proteins regulate cell differentiation and proliferation processes are not fully established yet. In previous reports, we demonstrated that DLK1 interacts with itself and with specific EGF-like repeats of the NOTCH1 extracellular region involved in the binding to NOTCH1 canonical ligands. Moreover, the interaction of DLK1 with NOTCH1 caused an inhibition of basal NOTCH signaling in preadipocytes and mesenchymal multipotent cells. In this work, we demonstrate, for the first time, that DLK2 interacts with itself, with DLK1, and with the same NOTCH1 receptor region as DLK1 does. We demonstrate also that the interaction of DLK2 with NOTCH1 similarly results in an inhibition of NOTCH signaling in preadipocytes and Mouse Embryo fibloblasts. In addition, we demonstrate that a membrane DLK1 variant, lacking the sequence recognized by the protease TACE, also inhibits NOTCH signaling. Furthermore, both DLK1 and DLK2 are able to decrease NOTCH activity also when triggered by specific NOTCH ligands. However, the decrease in NOTCH signaling induced by overexpression of Dlk2 is reversed by the overexpression of Dlk1, and viceversa. We conclude that DLK1 and DLK2 act as inhibitory non-canonical protein ligands for the NOTCH1 receptor that modulate NOTCH signaling.
authors.affiliation: Department of Inorganic and Organic Chemistry and Biochemistry, University of Castilla-La Mancha, Albacete, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Sánchez-Solana
authors.forename: María Luisa
authors.initials: ML
authors.lastname: Nueda
authors.forename: María Desamparados
authors.initials: MD
authors.lastname: Ruvira
authors.forename: María José
authors.initials: MJ
authors.lastname: Ruiz-Hidalgo
authors.forename: Eva María
authors.initials: EM
authors.lastname: Monsalve
authors.forename: Samuel
authors.initials: S
authors.lastname: Rivero
authors.forename: José Javier
authors.initials: JJ
authors.lastname: García-Ramírez
authors.forename: María José M
authors.initials: MJ
authors.lastname: Díaz-Guerra
authors.forename: Victoriano
authors.initials: V
authors.lastname: Baladrón
authors.forename: Jorge
authors.initials: J
authors.lastname: Laborda
mesh_terms: D016475:3T3 Cells; D041721:3T3-L1 Cells; D048868:Adaptor Proteins, Signal Transducing; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000166:cytology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D047468:Immunoprecipitation; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D011485:Protein Binding; D051881:Receptor, Notch1 / Q000235:genetics / Q000378:metabolism*; D000072099:Serrate-Jagged Proteins; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002135:Calcium-Binding Proteins; C519665:DLL4 protein, mouse; C512925:Dlk1 protein, mouse; C559657:Dlk2 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D051881:Receptor, Notch1; D000072099:Serrate-Jagged Proteins