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Dual roles of Cripto as a ligand and coreceptor in the nodal signaling pathway
Yu-Ting Yan1, Jan-Jan Liu, Yi Luo
1Center 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.
Abstract:
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.
Insights
Cripto acts as both a coreceptor and coligand for Nodal signaling, a dual role regulated by O-linked fucosylation. This finding clarifies Cripto
Area of Science:
- Developmental Biology
- Molecular Signaling
- Glycobiology
Background:
- The EGF-CFC gene Cripto encodes an extracellular protein involved in transforming growth factor beta (TGF-β) signaling, specifically with the Nodal ligand.
- Previous studies proposed divergent roles for EGF-CFC proteins: coreceptors for Nodal in embryonic contexts and growth factor-like signaling molecules in cell culture.
Purpose of the Study:
- To reconcile the differing models of Cripto function by investigating its signaling activities with Nodal in mammalian cell culture.
- To elucidate the precise molecular mechanisms underlying Cripto's interaction with Nodal and its role in TGF-β signaling pathways.
Main Methods:
- Utilized a luciferase reporter assay in mammalian cell culture to assess Nodal and EGF-CFC protein signaling.
- Employed cell coculture assays to evaluate Cripto's function as a secreted signaling factor.
- Investigated the requirement of O-linked fucose glycosylation for Cripto-Nodal binding and signaling.
Main Results:
- Confirmed Cripto's activity as a coreceptor for Nodal in mammalian cell culture.
- Demonstrated Cripto's capacity to function as a secreted signaling factor, suggesting a coligand role.
- Identified that O-linked fucosylation of a conserved site in EGF-CFC proteins is essential for Cripto to bind Nodal and mediate its signaling.
Conclusions:
- Proposed a model where Cripto exhibits dual functions as both a coreceptor and a coligand for Nodal.
- Highlighted that this Nodal-Cripto signaling interaction is regulated by an atypical O-linked glycosylation mechanism.
- Emphasized the importance of extracellular modulation of ligand activity in regulating TGF-β signaling during vertebrate development.