Dual roles of Cripto as a ligand and coreceptor in the nodal signaling pathway.
The EGF-CFC gene Cripto encodes an extracellular protein that has been implicated in the signaling pathway for the transforming growth factor beta (TGF beta) ligand Nodal. Although recent findings in frog and fish embryos have suggested that EGF-CFC proteins function as coreceptors for Nodal, studies in cell culture have implicated Cripto as a growth factor-like signaling molecule. Here we reconcile these apparently disparate models of Cripto function by using a mammalian cell culture assay to investigate the signaling activities of Nodal and EGF-CFC proteins. Using a luciferase reporter assay, we found that Cripto has activities consistent with its being a coreceptor for Nodal. However, Cripto can also function as a secreted signaling factor in cell coculture assays, suggesting that it may also act as a coligand for Nodal. Furthermore, we found that the ability of Cripto to bind to Nodal and mediate Nodal signaling requires the addition of an O-linked fucose monosaccharide to a conserved site within EGF-CFC proteins. We propose a model in which Cripto has dual roles as a coreceptor as well as a coligand for Nodal and that this signaling interaction with Nodal is regulated by an unusual form of glycosylation. Our findings highlight the significance of extracellular modulation of ligand activity as an important means of regulating TGF beta signaling pathways during vertebrate development.
Yan
Yu-Ting
YT
Center for Advanced Biotechnology and Medicine and Department of Pediatric, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
Liu
Jan-Jan
JJ
Luo
Yi
Y
E
Chaosu
C
Haltiwanger
Robert S
RS
Abate-Shen
Cory
C
Shen
Michael M
MM
D030201:Activin Receptors, Type I / Q000737:chemistry / Q000378:metabolism; D020816:Amino Acid Motifs; D002478:Cells, Cultured; D003432:Cross-Linking Reagents / Q000737:chemistry; D004815:Epidermal Growth Factor; D058851:GPI-Linked Proteins; D006031:Glycosylation; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008562:Membrane Glycoproteins; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D055457:Nodal Protein; D011506:Proteins; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*
D003432:Cross-Linking Reagents; D058851:GPI-Linked Proteins; D036341:Intercellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; C526007:NODAL protein, human; D009363:Neoplasm Proteins; D055457:Nodal Protein; D011506:Proteins; D011994:Recombinant Proteins; C070636:TDGF1 protein, human; D016212:Transforming Growth Factor beta; D004815:Epidermal Growth Factor; D008156:Luciferases; C425423:ACVR1 protein, human; D030201:Activin Receptors, Type I