Microfibrillar proteins MAGP-1 and MAGP-2 induce Notch1 extracellular domain dissociation and receptor activation.
Unlike most receptors, Notch serves as both the receiver and direct transducer of signaling events. Activation can be mediated by one of five membrane-bound ligands of either the Delta-like (-1, -2, -4) or Jagged/Serrate (-1, -2) families. Alternatively, dissociation of the Notch heterodimer with consequent activation can also be mediated experimentally by calcium chelators or by mutations that destabilize the Notch1 heterodimer, such as in the human disease T cell acute lymphoblastic leukemia. Here we show that MAGP-2, a protein present on microfibrils, can also interact with the EGF-like repeats of Notch1. Co-expression of MAGP-2 with Notch1 leads to both cell surface release of the Notch1 extracellular domain and subsequent activation of Notch signaling. Moreover, we demonstrate that the C-terminal domain of MAGP-2 is required for binding and activation of Notch1. Based on the high level of homology, we predicted and further showed that MAGP-1 can also bind to Notch1, cause the release of the extracellular domain, and activate signaling. Notch1 extracellular domain release induced by MAGP-2 is dependent on formation of the Notch1 heterodimer by a furin-like cleavage, but does not require the subsequent ADAM metalloprotease cleavage necessary for production of the Notch signaling fragment. Together these results demonstrate for the first time that the microfibrillar proteins MAGP-1 and MAGP-2 can function outside of their role in elastic fibers to activate a cellular signaling pathway.
Department of Biological Chemistry, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA.
Alison
A
Miyamoto
Rhiana
R
Lau
Patrick W
PW
Hein
J Michael
JM
Shipley
Gerry
G
Weinmaster
D000818:Animals; D019921:Biotinylation; D015153:Blotting, Western; D019556:COS Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D003285:Contractile Proteins / Q000502:physiology*; D004247:DNA / Q000737:chemistry; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D016326:Extracellular Matrix Proteins / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D006023:Glycoproteins / Q000502:physiology*; D006801:Humans; D047468:Immunoprecipitation; D036341:Intercellular Signaling Peptides and Proteins; D008024:Ligands; D008957:Models, Genetic; D009154:Mutation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D000072260:RNA Splicing Factors; D051881:Receptor, Notch1 / Q000737:chemistry* / Q000378:metabolism; D051880:Receptors, Notch / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D020798:Two-Hybrid System Techniques
D003285:Contractile Proteins; D016326:Extracellular Matrix Proteins; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D008024:Ligands; C115627:MFAP5 protein, human; D000072260:RNA Splicing Factors; D051881:Receptor, Notch1; D051880:Receptors, Notch; C016598:microfibrillar protein; D004247:DNA